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Sample records for amorphous silicon carbide

  1. Simulation in Amorphous Silicon and Amorphous Silicon Carbide Pin Diodes

    OpenAIRE

    Gonçalves, Dora; Fernandes, Miguel; Louro, Paula; Fantoni, Alessandro; Vieira, Manuela

    2014-01-01

    Part 21: Electronics: Devices International audience Photodiodes are devices used as image sensors, reactive to polychromatic light and subsequently color detecting, and they are also used in optical communication applications. To improve these devices performance it is essential to study and control their characteristics, in fact their capacitance and spectral and transient responses. This study considers two types of diodes, an amorphous silicon pin and an amorphous silicon carbide pi...

  2. Structural relaxation of amorphous silicon carbide

    International Nuclear Information System (INIS)

    We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions

  3. Structural relaxation of amorphous silicon carbide.

    Science.gov (United States)

    Ishimaru, Manabu; Bae, In-Tae; Hirotsu, Yoshihiko; Matsumura, Syo; Sickafus, Kurt E

    2002-07-29

    We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions. PMID:12144449

  4. Neutron irradiation induced amorphization of silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Snead, L.L.; Hay, J.C. [Oak Ridge National Lab., TN (United States)

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  5. Neutron irradiation induced amorphization of silicon carbide

    International Nuclear Information System (INIS)

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 x 1025 n/m2. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density (-10.8%), elastic modulus as measured using a nanoindentation technique (-45%), hardness as measured by nanoindentation (-45%), and standard Vickers hardness (-24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C

  6. Structural relaxation in amorphous silicon carbide

    International Nuclear Information System (INIS)

    High purity single crystal and chemically vapor deposited (CVD) silicon carbide have been amorphized under fast neutron irradiation. The gradual transition in physical properties from the as-amorphized state to a more relaxed amorphous state prior to crystallization is studied. For the three bulk properties studied: density, electrical resistivity, and thermal conductivity, large property changes occur upon annealing between the amorphization temperature and the point of crystallization. These physical property changes occur in the absence of crystallization and are attributed to short and perhaps medium range ordering during annealing. It is demonstrated that the physical properties of amorphous SiC (a-SiC) can vary greatly and are likely a function of the irradiation state producing the amorphization. The initiation of crystallization as measured using bulk density and in situ TEM is found to be ∼875 deg. C, though the kinetics of crystallization above this point are seen to depend on the technique used. It is speculated that in situ TEM and other thin-film approaches to study crystallization of amorphous SiC are flawed due to thin-film effects

  7. Tunable plasticity in amorphous silicon carbide films.

    Science.gov (United States)

    Matsuda, Yusuke; Kim, Namjun; King, Sean W; Bielefeld, Jeff; Stebbins, Jonathan F; Dauskardt, Reinhold H

    2013-08-28

    Plasticity plays a crucial role in the mechanical behavior of engineering materials. For instance, energy dissipation during plastic deformation is vital to the sufficient fracture resistance of engineering materials. Thus, the lack of plasticity in brittle hybrid organic-inorganic glasses (hybrid glasses) often results in a low fracture resistance and has been a significant challenge for their integration and applications. Here, we demonstrate that hydrogenated amorphous silicon carbide films, a class of hybrid glasses, can exhibit a plasticity that is even tunable by controlling their molecular structure and thereby leads to an increased and adjustable fracture resistance in the films. We decouple the plasticity contribution from the fracture resistance of the films by estimating the "work-of-fracture" using a mean-field approach, which provides some insight into a potential connection between the onset of plasticity in the films and the well-known rigidity percolation threshold. PMID:23876200

  8. Amorphous silicon carbide films prepared using vaporized silicon ink

    Science.gov (United States)

    Masuda, Takashi; Shen, Zhongrong; Takagishi, Hideyuki; Ohdaira, Keisuke; Shimoda, Tatsuya

    2014-03-01

    The deposition of wide-band-gap silicon films using nonvacuum processes rather than conventional vacuum processes is of substantial interest because it may reduce cost. Herein, we present the optical and electrical properties of p-type hydrogenated amorphous silicon carbide (a-SiC:H) films prepared using a nonvacuum process in a simple chamber with a vaporized silicon ink consisting of cyclopentasilane, cyclohexene, and decaborane. The incorporation of carbon into the silicon network induced by the addition of cyclohexene to the silicon ink resulted in an increase in the optical band gap (Eg) of films from 1.56 to 2.11 eV. The conductivity of films with Eg 1.9 eV show lower conductivity than expected because of the incorporation of excess carbon without the formation of Si-C bonds.

  9. Optical contrast in ion-implanted amorphous silicon carbide nanostructures

    International Nuclear Information System (INIS)

    Topographic and optical contrasts formed by Ga+ ion irradiation of thin films of amorphous silicon carbide have been investigated with scanning near-field optical microscopy. The influence of ion-irradiation dose has been studied in a pattern of sub-micrometre stripes. While the film thickness decreases monotonically with ion dose, the optical contrast rapidly increases to a maximum value and then decreases gradually. The results are discussed in terms of the competition between the effects of ion implantation and surface milling by the ion beam. The observed effects are important for uses of amorphous silicon carbide thin films as permanent archives in optical data storage applications

  10. Ion beam irradiation of relaxed amorphous silicon carbide

    International Nuclear Information System (INIS)

    In-situ transmittance measurements at λ=633 nm are used during ion irradiation to probe the defect generation in relaxed amorphous silicon carbide (SiC). The optical constants of amorphous SiC are strongly correlated to the thermal history of the material and the transmittance of ion implanted amorphous SiC (unrelaxed amorphous) increases after annealing in the temperature range 100-700 deg. C. The transmittance of annealed amorphous SiC (relaxed) during subsequent implantation decreases and saturates to the value of unrelaxed amorphous. In-situ transmittance measurements allow to follow directly the defect generation and to measure the fluence at which the transmittance saturates (derelaxation fluence). The effect of different ions (He and Ar) on these phenomena is explored. The obtained results are compared and discussed with similar measurements performed on amorphous silicon

  11. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    OpenAIRE

    Dong Chen; Fei Gao; Bo Liu

    2015-01-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C in...

  12. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    International Nuclear Information System (INIS)

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer

  13. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Boccard, Mathieu; Holman, Zachary C. [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States)

    2015-08-14

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  14. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    Science.gov (United States)

    Boccard, Mathieu; Holman, Zachary C.

    2015-08-01

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  15. Amorphous silicon carbide coatings for extreme ultraviolet optics

    Science.gov (United States)

    Kortright, J. B.; Windt, David L.

    1988-01-01

    Amorphous silicon carbide films formed by sputtering techniques are shown to have high reflectance in the extreme ultraviolet spectral region. X-ray scattering verifies that the atomic arrangements in these films are amorphous, while Auger electron spectroscopy and Rutherford backscattering spectroscopy show that the films have composition close to stoichiometric SiC, although slightly C-rich, with low impurity levels. Reflectance vs incidence angle measurements from 24 to 1216 A were used to derive optical constants of this material, which are presented here. Additionally, the measured extreme ultraviolet efficiency of a diffraction grating overcoated with sputtered amorphous silicon carbide is presented, demonstrating the feasibility of using these films as coatings for EUV optics.

  16. Amorphous Silicon Carbide for Photovoltaic Applications

    OpenAIRE

    JANZ, Stefan

    2006-01-01

    Within this work amorphous SiC is investigated for its applicability in photovoltaic devices. The temperature stability and dopability of SiC makes this material very attractive for applications in this area. Physical basics of amorphous SiC networks and plasma processes are discussed and first measurements with FTIR of the different layer types show the complexity of the network. The special features of the plasma reactor such as high temperature deposition and two-source excitation are also...

  17. Nanoindentation-induced amorphization in silicon carbide

    Science.gov (United States)

    Szlufarska, Izabela; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2004-07-01

    The nanoindentation-induced amorphization in SiC is studied using molecular dynamics simulations. The load-displacement response shows an elastic shoulder followed by a plastic regime consisting of a series of load drops. Analyses of bond angles, local pressure, and shear stress, and shortest-path rings show that these drops are related to dislocation activities under the indenter. We show that amorphization is driven by coalescence of dislocation loops and that there is a strong correlation between load-displacement response and ring distribution.

  18. Room temperature visible photoluminescence of silicon nanocrystallites embedded in amorphous silicon carbide matrix

    International Nuclear Information System (INIS)

    The nanocrystalline silicon embedded in amorphous silicon carbide matrix was prepared by varying rf power in high vacuum plasma enhanced chemical vapor deposition system using silane methane gas mixture highly diluted in hydrogen. In this paper, we have studied the evolution of the structural, optical, and electrical properties of this material as a function of rf power. We have observed visible photoluminescence at room temperature and also have discussed the role played by the Si nanocrystallites and the amorphous silicon carbide matrix. The decrease of the nanocrystalline size, responsible for quantum confinement effect, facilitated by the amorphous silicon carbide matrix, is shown to be the primary cause for the increase in the PL intensity, blueshift of the PL peak position, decrease of the PL width (full width at half maximum) as well as the increase of the optical band gap and the decrease of the dark conductivity

  19. Silicon nanocrystals on amorphous silicon carbide alloy thin films: Control of film properties and nanocrystals growth

    International Nuclear Information System (INIS)

    The present study demonstrates the growth of silicon nanocrystals on amorphous silicon carbide alloy thin films. Amorphous silicon carbide films [a-Si1−xCx:H (with x 1−xCx:H layer. The effect of short-time annealing at 700 °C on the composition and properties of the layer was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was observed that the silicon-to-carbon ratio in the layer remains unchanged after short-time annealing, but the reorganization of the film due to a large dehydrogenation leads to a higher density of SiC bonds. Moreover, the film remains amorphous after the performed short-time annealing. In a second part, it was shown that a high density (1 × 1012 cm−2) of silicon nanocrystals can be grown by low pressure chemical vapor deposition on a-Si0.8C0.2 surfaces at 700 °C, from silane diluted in hydrogen. The influence of growth time and silane partial pressure on nanocrystals size and density was studied. It was also found that amorphous silicon carbide surfaces enhance silicon nanocrystal nucleation with respect to SiO2, due to the differences in surface chemical properties. - Highlights: ► Silicon nanocrystals (Si-NC) growth on amorphous silicon carbide alloy thin films ► Plasma deposited amorphous silicon carbide films with well-controlled properties ► Study on the thermal effect of 700 °C short-time annealing on the layer properties ► Low pressure chemical vapor deposition (LPCVD) of Si-NC ► High density (1 × 1012 cm−2) of Si-NC was achieved on a-Si0.8C0.2 surfaces by LPCVD.

  20. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    Science.gov (United States)

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-11-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized.

  1. Ion-beam-induced amorphous structures in silicon carbide

    International Nuclear Information System (INIS)

    Atomistic structure of ion-beam-induced amorphous silicon carbide (a-SiC) has been investigated by cross-sectional transmission electron microscopy. The electron intensities of halo patterns recorded on imaging plates were digitized quantitatively to extract reduced interference functions. We demonstrated the relationship between maximum scattering vector (Qmax) measured in scattering experiments and the resolution of the corresponding pair-distribution function by changing Qmax values from 160 to 230 nm-1. The results revealed that the C-C peak becomes broadened and eventually a shoulder as the Qmax value becomes shorter, indicating that Qmax values of -1 measured in previous studies are not enough to detect C-C homonuclear bonds in a-SiC. We are the first to reveal the existence of C-C and Si-Si homonuclear bonds in a-SiC using a diffraction technique

  2. Solid phase epitaxy of amorphous silicon carbide: Ion fluence dependence

    International Nuclear Information System (INIS)

    We have investigated the effect of radiation damage and impurity concentration on solid phase epitaxial growth of amorphous silicon carbide (SiC) as well as microstructures of recrystallized layer using transmission electron microscopy. Single crystals of 6H-SiC with (0001) orientation were irradiated with 150 keV Xe ions to fluences of 1015 and 1016/cm2, followed by annealing at 890 deg. C. Full epitaxial recrystallization took place in a specimen implanted with 1015 Xe ions, while retardation of recrystallization was observed in a specimen implanted with 1016/cm2 Xe ions. Atomic pair-distribution function analyses and energy dispersive x-ray spectroscopy results suggested that the retardation of recrystallization of the 1016 Xe/cm2 implanted sample is attributed to the difference in amorphous structures between the 1015 and 1016 Xe/cm2 implanted samples, i.e., more chemically disordered atomistic structure and higher Xe impurity concentration in the 1016 Xe/cm2 implanted sample

  3. Growth and Characterization of Hydrogenated Amorphous Silicon and Hydrogenated Amorphous Silicon Carbide with Liquid Organometallic Sources.

    Science.gov (United States)

    Gaughan, Kevin David

    The growth and characterization of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon -carbon (rm a-rm Si _{1-X}C_{X}: H) alloys employing liquid organometallic sources are described. N -type a-Si:H films were grown using a mixture of silane and tertiarybutylphosphine (TBP-rm C_4H _9P_2) vapor in a plasma enhanced chemical vapor deposition system. Impurity levels from parts per million to about 5 at. % phosphorus have been incorporated into the film with this method. Tertiarybutylphosphine is less toxic and less pyrophoric than phosphine which is usually used in n-type doping of a-Si:H films. Optical and electronic properties were characterized by room temperature as well as temperature dependent dark conductivity, photothermal deflection spectroscopy, infrared vibrational spectroscopy, electron spin resonance, and electron microprobe analysis. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine. The experimental results are compared with the predictions of several models that describe the chemical equilibrium between active dopants and deep defects. A pronounced decrease in the effects of doping, such as an increase in the activation energy of electrical conductivity and an decrease in the conductivity of the sample, were seen in heavily doped films (TBP/SiH _4> 0.5%), perhaps influenced by the increased carbon and/or phosphorus concentrations. Amorphous silicon-carbide alloys have been grown by the plasma decomposition of ditertiarybutylsilane ( rm DTBS-rm SiH_2(C _4H_9)_2). The optical bandgaps, which varied from 2.2 to 3.3 eV, are strongly dependent upon the deposition conditions. The carbon concentrations in these films varied from 60 to 95 at. %. The optical band-edge is very broad compared to that which is found in a-Si:H and this breadth is essentially independent of the deposition conditions. The plasma decomposition of admixtures of DTBS and silane has produced rm a- rm Si_{1-X

  4. Electronic properties of intrinsic and doped amorphous silicon carbide films

    Energy Technology Data Exchange (ETDEWEB)

    Vetter, M. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain)]. E-mail: mvetter@eel.upc.edu; Voz, C. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain); Ferre, R. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain); Martin, I. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain); Orpella, A. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain); Puigdollers, J. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain); Andreu, J. [Departament de Fisica Aplicada i Optica, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona (Spain); Alcubilla, R. [Departament d' Enginyeria Electronica, Universitat Politecnica de Catalunya, Gran Capita s/n, Modul C4, E-08034 Barcelona (Spain)

    2006-07-26

    Hydrogenated amorphous silicon carbide (a-SiC{sub x} : H) films have shown excellent surface passivation of crystalline silicon. With the aim of large area deposition of these films the influence of the rf plasma power was investigated. It is found that homogenous deposition with effective surface recombination velocity lower than 100 cms{sup -1} is possible up to 6'' diameter in a simple parallel plate reactor by optimizing deposition parameters. For application in solar cell processes the conductivity of these a-SiC{sub x} : H films might become of importance since good surface passivation results from field-effect passivation which needs an insulating dielectric layer. Therefore, the temperature dependence of the dark dc conductivity of these films was investigated in the temperature range from - 20 to 260 deg. C. Two transition temperatures, T {sub s}{approx}80 deg. C and T {sub s}{approx}170 deg. C, were found where conductivity increases, resp. decreases over-exponential. From Arrhenius plots activation energy (E {sub a}) and conductivity pre-factor ({sigma} {sub 0}) were calculated for a large number of samples with different composition. A correlation between E {sub a} and {sigma} {sub 0} was found giving a Meyer-Neldel relation with a slope of 59 mV, corresponding to a material characteristic temperature T {sub m} = 400 deg. C, and an intercept at {sigma} {sub 00} = 0.1 {omega}{sup -1}cm{sup -1}.

  5. Electronic properties of intrinsic and doped amorphous silicon carbide films

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon carbide (a-SiCx : H) films have shown excellent surface passivation of crystalline silicon. With the aim of large area deposition of these films the influence of the rf plasma power was investigated. It is found that homogenous deposition with effective surface recombination velocity lower than 100 cms-1 is possible up to 6'' diameter in a simple parallel plate reactor by optimizing deposition parameters. For application in solar cell processes the conductivity of these a-SiCx : H films might become of importance since good surface passivation results from field-effect passivation which needs an insulating dielectric layer. Therefore, the temperature dependence of the dark dc conductivity of these films was investigated in the temperature range from - 20 to 260 deg. C. Two transition temperatures, T s∼80 deg. C and T s∼170 deg. C, were found where conductivity increases, resp. decreases over-exponential. From Arrhenius plots activation energy (E a) and conductivity pre-factor (σ 0) were calculated for a large number of samples with different composition. A correlation between E a and σ 0 was found giving a Meyer-Neldel relation with a slope of 59 mV, corresponding to a material characteristic temperature T m = 400 deg. C, and an intercept at σ 00 = 0.1 Ω-1cm-1

  6. Silicon nanocrystals on amorphous silicon carbide alloy thin films: Control of film properties and nanocrystals growth

    Energy Technology Data Exchange (ETDEWEB)

    Barbe, Jeremy, E-mail: jeremy.barbe@hotmail.com [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, 31062 Toulouse (France); Xie, Ling; Leifer, Klaus [Department of Engineering Sciences, Uppsala University, Box 534, S-751 21 Uppsala (Sweden); Faucherand, Pascal; Morin, Christine; Rapisarda, Dario; De Vito, Eric [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Makasheva, Kremena; Despax, Bernard [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, 31062 Toulouse (France); CNRS, LAPLACE, F-31062 Toulouse (France); Perraud, Simon [CEA, Liten, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)

    2012-11-01

    The present study demonstrates the growth of silicon nanocrystals on amorphous silicon carbide alloy thin films. Amorphous silicon carbide films [a-Si{sub 1-x}C{sub x}:H (with x < 0.3)] were obtained by plasma enhanced chemical vapor deposition from a mixture of silane and methane diluted in hydrogen. The effect of varying the precursor gas-flow ratio on the film properties was investigated. In particular, a wide optical band gap (2.3 eV) was reached by using a high methane-to-silane flow ratio during the deposition of the a-Si{sub 1-x}C{sub x}:H layer. The effect of short-time annealing at 700 Degree-Sign C on the composition and properties of the layer was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was observed that the silicon-to-carbon ratio in the layer remains unchanged after short-time annealing, but the reorganization of the film due to a large dehydrogenation leads to a higher density of SiC bonds. Moreover, the film remains amorphous after the performed short-time annealing. In a second part, it was shown that a high density (1 Multiplication-Sign 10{sup 12} cm{sup -2}) of silicon nanocrystals can be grown by low pressure chemical vapor deposition on a-Si{sub 0.8}C{sub 0.2} surfaces at 700 Degree-Sign C, from silane diluted in hydrogen. The influence of growth time and silane partial pressure on nanocrystals size and density was studied. It was also found that amorphous silicon carbide surfaces enhance silicon nanocrystal nucleation with respect to SiO{sub 2}, due to the differences in surface chemical properties. - Highlights: Black-Right-Pointing-Pointer Silicon nanocrystals (Si-NC) growth on amorphous silicon carbide alloy thin films Black-Right-Pointing-Pointer Plasma deposited amorphous silicon carbide films with well-controlled properties Black-Right-Pointing-Pointer Study on the thermal effect of 700 Degree-Sign C short-time annealing on the layer properties Black-Right-Pointing-Pointer Low pressure

  7. Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide.

    Science.gov (United States)

    Chang, Geng-rong; Ma, Fei; Ma, Da-yan; Xu, Ke-wei

    2010-11-19

    Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells. PMID:20975214

  8. Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide

    International Nuclear Information System (INIS)

    Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells.

  9. Fracture properties of hydrogenated amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic–inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m−2) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited Si-O-Si suboxide bond formation that occurs in the films.

  10. Effect of amorphous silicon carbide layer thickness on the passivation quality of crystalline silicon surface

    OpenAIRE

    Ferré Tomas, Rafel; Martín García, Isidro; Vetter, Michael; Garin Escriva, Moises; Alcubilla González, Ramón

    2005-01-01

    Surface passivation of p-type crystalline silicon wafers by means of phosphorus-doped hydrogenated amorphous silicon carbide films [a-SiCx(n):H] has been investigated. Particularly, we focused on the effects of layer thickness on the c-Si surface passivation quality resulting in the determination of the fixed charge density, Qf, within the a-SiCx(n):H film and the fundamental recombination of holes, Sp0. The main result is that surface recombination velocity decreases with film...

  11. Electrical and optical properties of amorphous silicon carbide, silicon nitride and germanium carbide prepared by the glow discharge technique

    International Nuclear Information System (INIS)

    Amorphous specimens of silicon carbide, silicon nitride and germanium carbide have been prepared by decomposition of suitable gaseous mixtures in a r.f. glow discharge. Substrates were held at a temperature Tsub(d) between 400 and 800 K during deposition. In all three of the above materials the results of optical absorption and of d.c. conductivity measurements show a systematic variation with Tsub(d) and with the volume ratio of the gases used. Electron microprobe results on silicon carbide specimens indicate that a wide range of film compositions can be prepared. The optical gap has a pronounced maximum at the composition Sisub(0.32)Csub(0.68) where it is 2.8 eV for a sample deposited at Tsub(d) = 500 K, but shifts to lower energies with increasing Tsub(d). The conductivity above about 400 K has a single activation energy approximately equal to half the optical gap and extended state conduction predominates if the silicon content exceeds 32%. If the latter is reduced, hopping transport takes over and it is suggested that the excess carbon in the network tends to bond in three-fold graphic coordination. Absence of any obvious feature in the electronic properties at the stoichiometric composition SiC implies that there is little tendency towards compound formation in the glow discharge films. The present results are discussed in relation to measurements on specimens prepared by different methods. (author)

  12. On electronic structure of polymer-derived amorphous silicon carbide ceramics

    Science.gov (United States)

    Wang, Kewei; Li, Xuqin; Ma, Baisheng; Wang, Yiguang; Zhang, Ligong; An, Linan

    2014-06-01

    The electronic structure of polymer-derived amorphous silicon carbide ceramics was studied by combining measurements of temperature-dependent conductivity and optical absorption. By comparing the experimental results to theoretical models, electronic structure was constructed for a carbon-rich amorphous silicon carbide, which revealed several unique features, such as deep defect energy level, wide band-tail band, and overlap between the band-tail band and defect level. These unique features were discussed in terms of the microstructure of the material and used to explain the electric behavior.

  13. Evidence for cascade overlap and grain boundary enhanced amorphization in silicon carbide irradiated with Kr ions

    International Nuclear Information System (INIS)

    Evolution of amorphous domains in silicon carbide with 1 MeV Kr2+ irradiation is investigated using high-resolution transmission electron microscopy and simulations. An unusual morphology of highly curved crystalline/amorphous boundaries is observed in the images, which is identified as a result of cascade overlap and reproduced by a coarse-grained model informed by atomistic simulations. Comparison of local amorphization fractions near grain boundaries and within grain interiors provides experimental evidence for the interstitial starvation mechanism in SiC for the first time. As a competing effect to defect sinks, interstitial starvation increases the rate of local amorphization near grain boundaries and reduces the radiation resistance of nanocrystalline silicon carbide

  14. Controlled growth of nanocrystalline silicon within amorphous silicon carbide thin films

    Science.gov (United States)

    Kole, Arindam; Chaudhuri, Partha

    2014-04-01

    Controlled formation of nanocrystalline silicon (nc-Si) within hydrogenated amorphous silicon carbide (a-SiC:H) thin films has been demonstrated by a rf (13.56 MHz) plasma chemical vapour deposition (PECVD) method at a low deposition temperature of 200°C by regulating the deposition pressure (Pr) between 26.7 Pa and 133.3 Pa. Evolution of the size and the crystalline silicon volume fraction within the a-SiC:H matrix has been studied by XRD, Raman and HRTEM. The study reveals that at Pr of 26.7 Pa there are mostly isolated grains of nc-Si within the a-SiC:H matrix with average size of 4.5 nm. With increase of Pr the isolated nc-Si grains coalesce more and more giving rise to larger size connected nc-Si islands which appear as microcrystalline silicon in the Raman spectra. As a result net isolated nc-Si volume fraction decreases while the total crystalline silicon volume fraction increases.

  15. Toughening thin-film structures with ceramic-like amorphous silicon carbide films.

    Science.gov (United States)

    Matsuda, Yusuke; Ryu, Ill; King, Sean W; Bielefeld, Jeff; Dauskardt, Reinhold H

    2014-01-29

    A significant improvement of adhesion in thin-film structures is demonstrated using embedded ceramic-like amorphous silicon carbide films (a-SiC:H films). a-SiC:H films exhibit plasticity at the nanoscale and outstanding chemical and thermal stability unlike most materials. The multi-functionality and the ease of processing of the films have potential to offer a new toughening strategy for reliability of nanoscale device structures. PMID:23894055

  16. Atomistic modeling of amorphous silicon carbide: An approximate first-principles study in constrained solution space

    OpenAIRE

    Atta-Fynn, Raymond; Biswas, Parthapratim

    2009-01-01

    Localized basis ab initio molecular dynamics simulation within the density functional framework has been used to generate realistic configurations of amorphous silicon carbide (a-SiC). Our approach consists of constructing a set of smart initial configurations that conform essential geometrical and structural aspects of the materials obtained from experimental data, which is subsequently driven via first-principles force-field to obtain the best solution in a reduced solution space. A combina...

  17. Applications of microcrystalline hydrogenated cubic silicon carbide for amorphous silicon thin film solar cells

    International Nuclear Information System (INIS)

    We demonstrated the fabrication of n-i-p type amorphous silicon (a-Si:H) thin film solar cells using phosphorus doped microcrystalline cubic silicon carbide (μc-3C-SiC:H) films as a window layer. The Hot-wire CVD method and a covering technique of titanium dioxide TiO2 on TCO was utilized for the cell fabrication. The cell configuration is TCO/TiO2/n-type μc-3C-SiC:H/intrinsic a-Si:H/p-type μc- SiCx (a-SiCx:H including μc-Si:H phase)/Al. Approximately 4.5% efficiency with a Voc of 0.953 V was obtained for AM-1.5 light irradiation. We also prepared a cell with the undoped a-Si1-xCx:H film as a buffer layer to improve the n/i interface. A maximum Voc of 0.966 V was obtained

  18. Direct observations of thermally induced structural changes in amorphous silicon carbide

    International Nuclear Information System (INIS)

    Thermally induced structural relaxation in amorphous silicon carbide (SiC) has been examined by means of in situ transmission electron microscopy (TEM). The amorphous SiC was prepared by high-energy ion beam irradiation into a single crystalline 4H-SiC substrate. Cross-sectional TEM observations and electron energy-loss spectroscopy measurements revealed that thermal annealing induces a remarkable volume reduction, so-called densification, of amorphous SiC. From radial distribution function analyses using electron diffraction, notable changes associated with structural relaxation were observed in chemical short-range order. It was confirmed that the structural changes observed by the in situ TEM study agree qualitatively with those of the bulk material. On the basis of the alteration of chemical short-range order, we discuss the origin of thermally induced densification in amorphous SiC

  19. Amorphous silicon carbide heterojunction solar cells on p-type substrates

    International Nuclear Information System (INIS)

    The performance of silicon heterojunction (SHJ) solar cells is discussed in this paper in regard to their dependence on the applied amorphous silicon layers, their thicknesses and surface morphology. The emitter system investigated in this work consists of an n-doped, hydrogenized, amorphous silicon carbide a-SiC:H(n) layer with or without a pure, hydrogenized, intrinsic, amorphous silicon a-Si:H(i) intermediate layer. All solar cells were fabricated on p-type FZ-silicon and feature a high-efficiency backside consisting of a SiO2 passivation layer and a diffused local boron back surface field, allowing us to focus only on the effects of the front side emitter system. The highest solar cell efficiency achieved within this work is 18.5%, which is one of the highest values for SHJ-solar cells using p-type substrates. A dependence of the passivation quality on the surface morphology was only observed for solar cells including an a-Si:H(i) layer. It could be shown that the fill factor suffers from a reduction due to a reduced pseudo fill factor for emitter thicknesses below 11 nm due to a lower passivation quality and/or a higher potential for shunting thorough the a-Si emitter to the crystalline wafer with the conductive indium tin oxide layer. Furthermore, the influence of a variation of the doping gas flow (PH3) during the plasma enhanced chemical vapor deposition of the doped amorphous silicon carbide a-SiC:H(n) on the solar cell current-voltage characteristic-parameter has been investigated. We could demonstrate that a-SiC:H(n) shows in principle the same dependence on PH3-flow as pure a-Si:H(n).

  20. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix.

    Science.gov (United States)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching. PMID:24521208

  1. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    OpenAIRE

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; KONAGAI, MAKOTO

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by ...

  2. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    Science.gov (United States)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-02-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching.

  3. Growth and Physical Structure of Amorphous Boron Carbide Deposited by Magnetron Sputtering on a Silicon Substrate with a Titanium Interlayer

    OpenAIRE

    Roberto Caniello; Espedito Vassallo; Anna Cremona; Giovanni Grosso; David Dellasega; Maurizio Canetti; Enrico Miorin

    2013-01-01

    Multilayer amorphous boron carbide coatings were produced by radiofrequency magnetron sputtering on silicon substrates. To improve the adhesion, titanium interlayers with different thickness were interposed between the substrate and the coating. Above three hundreds nanometer, the enhanced roughness of the titanium led to the growth of an amorphous boron carbide with a dense and continuing columnar structure, and no delamination effect was observed. Correspondingly, the adhesion of the coatin...

  4. 2H-SiC Dendritic Nanocrystals In Situ Formation from Amorphous Silicon Carbide under Electron Beam Irradiation

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Under electron beam irradiation, the in-situ formation of 2H-SiC dentritic nanocrystals from amorphous silicon carbide at room temperature was observed. The homogenous transition mainly occurs at the thin edge and on the surface of specimen where the energy obtained from electron beam irradiation is high enough to cause the amorphous crystallizing into 2H-SiC.

  5. Atomistic modeling of amorphous silicon carbide using a bond-order potential

    International Nuclear Information System (INIS)

    Molecular dynamics simulations were performed with a Brenner-type bond-order potential to study the melting of silicon carbide (SiC), the structure of amorphous SiC produced by quenching from the melt, and the evolution of the amorphous state after isochronal annealing at elevated temperatures. The simulations reveal that SiC melts above 3700 K with an enthalpy of fusion of about 0.6 eV/atom. The density of the quenched liquid is about 2820 kg/m3, in excellent agreement with the experimental value for SiC amorphized by neutron irradiation. In addition to the loss of long-range order, the quenched liquid shows short-range disorder as measured by the C homonuclear bond ratio. Upon annealing, there is partial recovery of short-range order

  6. Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

    International Nuclear Information System (INIS)

    The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiCx) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiCx/SiO2/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiCx, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiCx can promote the application of Si QDs in low-power consumption semiconductor memory devices

  7. Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Xixing; Zeng, Xiangbin, E-mail: eexbzeng@163.com; Zheng, Wenjun; Liao, Wugang [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Feng, Feng [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Shenzhen Institute of Huazhong University of Science and Technology, Shenzhen 518000 (China)

    2015-01-14

    The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiC{sub x}) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiC{sub x}/SiO{sub 2}/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiC{sub x}, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiC{sub x} can promote the application of Si QDs in low-power consumption semiconductor memory devices.

  8. Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

    Science.gov (United States)

    Wen, Xixing; Zeng, Xiangbin; Zheng, Wenjun; Liao, Wugang; Feng, Feng

    2015-01-01

    The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiCx) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiCx/SiO2/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiCx, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiCx can promote the application of Si QDs in low-power consumption semiconductor memory devices.

  9. Evidence of chemical ordering in amorphous hydrogenated silicon carbide

    International Nuclear Information System (INIS)

    Amorphous Si/sub 0.68/C/sub 0.32/:H prepared by radio frequency glow discharge from a mixture of methane and silane was studied by means of the complementary techniques of electron energy-loss spectroscopy and electron diffraction. The experimental results are consistent with Si and C forming a tetrahedral network with nearest neighbor distances similar to those in crystalline Si and crystalline SiC. There is evidence that the C atoms tend to be surrounded by four Si atoms rather than a random distribution of C and Si on the tetrahedral network

  10. In situ ultraviolet treatment in an Ar ambient upon p-type hydrogenated amorphous silicon-carbide windows of hydrogenated amorphous silicon based solar cells

    International Nuclear Information System (INIS)

    We proposed an in situ postdeposition ultraviolet treatment in an Ar ambient (UTA) to improve the p/i interface of amorphous silicon based solar cell. We have increased the conversion efficiency by ∼16% by improving the built-in potential and reducing recombination at the p/i interface. Through spectroscopic ellipsometry and Fourier-transform infrared measurements, it is concluded that the UTA process induces structural modification of the p-type hydrogenated amorphous silicon-carbide (p-a-SiC:H) window layer. An ultrathin p-a-SiC:H contamination layer formed during the UTA process acts as a buffer layer at the interface

  11. Direct Transformation of Amorphous Silicon Carbide into Graphene under Low Temperature and Ambient Pressure

    OpenAIRE

    Tao Peng; Haifeng Lv; Daping He; Mu Pan; Shichun Mu

    2013-01-01

    A large-scale availability of the graphene is critical to the successful application of graphene-based electronic devices. The growth of epitaxial graphene (EG) on insulating silicon carbide (SiC) surfaces has opened a new promising route for large-scale high-quality graphene production. However, two key obstacles to epitaxial growth are extremely high requirements for almost perfectly ordered crystal SiC and harsh process conditions. Here, we report that the amorphous SiC (a-Si1−xCx) nano-sh...

  12. Dangling bond electron spin-lattice relaxation in rf-sputtered hydrogenated amorphous silicon and silicon carbide

    International Nuclear Information System (INIS)

    Electron spin resonance methods have been used to measure the temperature dependence of the spin-lattice relaxation time T1 of dangling bond electrons in hydrogenated amorphous silicon and silicon carbide samples prepared by radio frequency sputtering. The T1 measurements were made by a combination of continuous-wave absorption mode saturation and periodic adiabatic passage methods over the temperature range 100--400 K, yielding T/sup -1/1proportionalT2 behavior consistent with relaxation by two-level systems

  13. Deuterium permeation and thermal behaviors of amorphous silicon carbide coatings on steels

    International Nuclear Information System (INIS)

    In this study, deuterium permeation measurements for SS316 and F82H steels coated with amorphous silicon carbide films by radio frequency magnetron sputtering are performed. The driving deuterium pressure dependence of the coated sample shows a large surface contribution. Deuterium trapping in the amorphous structure is suggested by the temporal change in the permeation flux. Permeation reduction factors of 103 are achieved with 1.5-μm-thick coated F82H at 723-823 K; however, the coating degraded at 873 K. Cracks are generated in the coating because of the tensile stress derived from a large difference in the thermal expansion between the coating and the steel.

  14. Amorphous Silicon Carbide Passivating Layers to Enable Higher Processing Temperature in Crystalline Silicon Heterojunction Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Boccard, Mathieu [Arizona State Univ., Mesa, AZ (United States); Holman, Zachary [Arizona State Univ., Mesa, AZ (United States)

    2015-04-06

    "Very efficient crystalline silicon (c-Si) solar cells have been demonstrated when thin layers of intrinsic and doped hydrogenated amorphous silicon (a-Si:H) are used for passivation and carrier selectivity in a heterojunction device. One limitation of this device structure is the (parasitic) absorption in the front passivation/collection a-Si:H layers; another is the degradation of the a-Si:H-based passivation upon temperature, limiting the post-processes to approximately 200°C thus restricting the contacting possibilities and potential tandem device fabrication. To alleviate these two limitations, we explore the potential of amorphous silicon carbide (a-SiC:H), a widely studied material in use in standard a-Si:H thin-film solar cells, which is known for its wider bandgap, increased hydrogen content and stronger hydrogen bonding compared to a-Si:H. We study the surface passivation of solar-grade textured n-type c-Si wafers for symmetrical stacks of 10-nm-thick intrinsic a-SiC:H with various carbon content followed by either p-doped or n-doped a-Si:H (referred to as i/p or i/n stacks). For both doping types, passivation (assessed through carrier lifetime measurements) is degraded by increasing the carbon content in the intrinsic a-SiC:H layer. Yet, this hierarchy is reversed after annealing at 350°C or more due to drastic passivation improvements upon annealing when an a-SiC:H layer is used. After annealing at 350°C, lifetimes of 0.4 ms and 2.0 ms are reported for i/p and i/n stacks, respectively, when using an intrinsic a-SiC:H layer with approximately 10% of carbon (initial lifetimes of 0.3 ms and 0.1 ms, respectively, corresponding to a 30% and 20-fold increase, respectively). For stacks of pure a-Si:H material the lifetimes degrade from 1.2 ms and 2.0 ms for i/p and i/n stacks, respectively, to less than 0.1 ms and 1.1 ms (12-fold and 2-fold decrease, respectively). For complete solar cells using pure a-Si:H i/p and i/n stacks, the open-circuit voltage (Voc

  15. Nanostructural properties of amorphous silicon carbide by GISAXS and optical spectroscopy

    International Nuclear Information System (INIS)

    The nano-structural properties of non-stehiometric hydrogenated amorphous silicon carbide thin films, deposited by magnetron sputtering in wide range of carbon concentration (5-50 at.%) and high hydrogen content (17-45 at.%), were analysed by GISAXS (Grazing Incidence Small Angle X-ray Scattering). The film composition and density were estimated by combining vibrational spectroscopy, RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). It was found that by increasing carbon and hydrogen concentration, the film density decreases, indicating the increase of voids contribution. The GISAXS was performed on ELETTRA synchrotron radiation source, Trieste (Italy). The obtained results show the presence of 'particles' with variation in mean dimensions between 1.7 and 2.5 nm and broad size distribution. The size of 'particles', most probably large voids or voids agglomerates, increases with carbon to silicon ratio and decreases with hydrogen concentration

  16. Plasma deposition of amorphous silicon carbide thin films irradiated with neutrons

    Science.gov (United States)

    Huran, J.; Bohacek, P.; Kucera, M.; Kleinova, A.; Sasinkova, V.; IEE SAS, Bratislava, Slovakia Team; Polymer Institute, SAS, Bratislava, Slovakia Team; Institute of Chemistry, SAS, Bratislava, Slovakia Team

    2015-09-01

    Amorphous silicon carbide and N-doped silicon carbide thin films were deposited on P-type Si(100) wafer by plasma enhanced chemical vapor deposition (PECVD) technology using silane, methane, ammonium and argon gases. The concentration of elements in the films was determined by RBS and ERDA method. Chemical compositions were analyzed by FTIR spectroscopy. Photoluminescence properties were studied by photoluminescence spectroscopy (PL). Irradiation of samples with various neutron fluencies was performed at room temperature. The films contain silicon, carbon, hydrogen, nitrogen and small amount of oxygen. From the IR spectra, the films contained Si-C, Si-H, C-H, Si-N, N-H and Si-O bonds. No significance effect on the IR spectra after neutron irradiation was observed. PL spectroscopy results of films showed decreasing PL intensity after neutron irradiation and PL intensity decreased with increased neutron fluencies. The measured current of the prepared structures increased after irradiation with neutrons and rise up with neutron fluencies.

  17. Effect of the formation conditions on the local density of electronic states of amorphous films of silicon carbide

    International Nuclear Information System (INIS)

    The method of ultrafine x-ray emission spectroscopy was used to examine the effect of the formation conditions (power of the rf discharge and substrate temperature) on the nature of energy distribution of the valency states of silicon in amorphous films of silicon carbide produced by rf sputtering a target made of polycrystalline carbide. The results show the existence of optimum conditions under which the coordination of silicon atoms is closest to their coordination in the crystal. Under these conditions, the density of occupied localised states is minimum. (author)

  18. Crystallization mechanism of silicon quantum dots upon thermal annealing of hydrogenated amorphous Si-rich silicon carbide films

    International Nuclear Information System (INIS)

    We have investigated the crystallization process of silicon quantum dots (QDs) imbedded in hydrogenated amorphous Si-rich silicon carbide (a-SiC:H) films. Analysis reveals that crystallization of silicon QDs upon thermal annealing of the samples can be explained in terms of bonding configuration and evolution of microstructure. The precursor gases were dissociated via electron impact reactions in the plasma-enhanced chemical vapor deposition, where the hydrogenated silicon radicals and reactive SiHn species lead to the formation of primary Si nuclei. With increasing annealing temperature, the breaking of SiHn bonds and decomposition of Si-rich SiC were progressively enhanced, allowing the formation of crystalline silicon QDs inside the a-SiC:H matrix. The results help clarify a probable mechanism for the growth of silicon QDs and provide the possibility to optimize the microstructure of silicon QDs in a-SiC:H films. - Highlights: • Si-rich SiC samples are grown by plasma-enhanced chemical vapor deposition. • Silicon radicals and reactive SiHn (n = 1,2,3) exist in the as-grown samples. • Annealing temperature induces the growth of crystalline silicon quantum dots. • Carbon atoms are incorporated in the formation of Si-C and C-H bonds in the matrix

  19. Amorphous structures of silicon carbonitride formed by high-dose nitrogen ion implantation into silicon carbide

    International Nuclear Information System (INIS)

    Short-range order in amorphous silicon carbonitride (a-SiCxNy) has been examined using transmission electron microscopy. Single crystals of 6H-SiC with [0 0 0 1] orientation were implanted with 180 keV nitrogen ions at ambient temperature to a fluence of 5 x 1017 N+/cm2, followed by thermally annealing at 1500 deg. C for 30 min. A fully amorphous layer was formed at the topmost layer in the as-implanted sample. A part of the amorphous phase transformed into crystalline SiC after annealing. Radial distribution functions extracted via nano-beam electron diffraction patterns clearly showed that atomistic structures of the ion-beam-induced amorphous phase are different from those of the remaining amorphous phase in the annealed sample: a-SiCxNy possesses an intermediate bond length between Si-C and Si-N, while Si-N and Si-C bonds become more pronounced in the amorphous layer of the annealed specimen

  20. Focused ion beam writing of optical patterns in amorphous silicon carbide

    International Nuclear Information System (INIS)

    In the present work we investigate the use of ion beam techniques for properties modification and optimisation of wide-bandgap materials with view of their uses in sub-micron lithography and high-density data storage for archival purposes. We propose scanning near-field optical microscopy as a novel technique for characterizing the ion-implanted patterns fabricated in amorphous silicon carbide (a-SiC:H). Different patterns have been fabricated in a-SiC:H films with a focused Ga+-ion beam system and examined with scanning near-field optical microscopy and atomic force microscopy. Although a considerable thickness change (thinning tendency) has been observed in the ion-irradiated areas, the near-field measurements confirm increases of optical absorption in these areas. The observed values of the optical contrast modulation are sufficient to justify the efficiency of the method for optical data recording using focused ion beams. (author)

  1. Charge transport and activation energy of amorphous silicon carbide thin film on quartz at elevated temperature

    Science.gov (United States)

    Dinh, Toan; Viet Dao, Dzung; Phan, Hoang-Phuong; Wang, Li; Qamar, Afzaal; Nguyen, Nam-Trung; Tanner, Philip; Rybachuk, Maksym

    2015-06-01

    We report on the temperature dependence of the charge transport and activation energy of amorphous silicon carbide (a-SiC) thin films grown on quartz by low-pressure chemical vapor deposition. The electrical conductivity as characterized by the Arrhenius rule was found to vary distinctly under two activation energy thresholds of 150 and 205 meV, corresponding to temperature ranges of 300 to 450 K and 450 to 580 K, respectively. The a-SiC/quartz system displayed a high temperature coefficient of resistance ranging from -4,000 to -16,000 ppm/K, demonstrating a strong feasibility of using this material for highly sensitive thermal sensing applications.

  2. Direct visualization of photoinduced glassy dynamics on the amorphous silicon carbide surface by STM movies

    Science.gov (United States)

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

    2015-03-01

    Glassy dynamics can be controlled by light irradiation. Sub- and above-bandgap irradiation cause numerous phenomena in glasses including photorelaxation, photoexpansion, photodarkening and pohtoinduced fluidity. We used scanning tunneling microscopy to study surface glassy dynamics of amorphous silicon carbide irradiated with above- bandgap 532 nm light. Surface clusters of ~ 4-5 glass forming unit in diameter hop mostly in a two-state fashion, both without and with irradiation. Upon irradiation, the average surface hopping activity increases by a factor of 3. A very long (~1 day) movie of individual clusters with varying laser power density provides direct evidence for photoinduced enhanced hopping on the glass surfaces. We propose two mechanisms: heating and electronic for the photoenhanced surface dynamics.

  3. Synthesis of amorphous silicon carbide nanoparticles in a low temperature low pressure plasma reactor.

    Science.gov (United States)

    Lin, Hongfei; Gerbec, Jeffrey A; Sushchikh, Michael; McFarland, Eric W

    2008-08-13

    Commercial scale production of silicon carbide (SiC) nanoparticles smaller than 10 nm remains a significant challenge. In this paper, a microwave plasma reactor and appropriate reaction conditions have been developed for the synthesis of amorphous SiC nanoparticles. This continuous gas phase process is amenable to large scale production use and utilizes the decomposition of tetramethylsilane (TMS) for both the silicon and the carbon source. The influence of synthesis parameters on the product characteristics was investigated. The as-prepared SiC particles with sizes between 4 and 6 nm were obtained from the TMS precursor in a plasma operated at low temperature and low precursor partial pressure (0.001-0.02 Torr) using argon as the carrier gas (3 Torr). The carbon:silicon ratio was tuned by the addition of hydrogen and characterized by x-ray photoelectron spectroscopy. The reaction mechanism of SiC nanoparticle formation in the microwave plasma was investigated by mass spectroscopy of the gaseous products. PMID:21828814

  4. Synthesis of amorphous silicon carbide nanoparticles in a low temperature low pressure plasma reactor

    International Nuclear Information System (INIS)

    Commercial scale production of silicon carbide (SiC) nanoparticles smaller than 10 nm remains a significant challenge. In this paper, a microwave plasma reactor and appropriate reaction conditions have been developed for the synthesis of amorphous SiC nanoparticles. This continuous gas phase process is amenable to large scale production use and utilizes the decomposition of tetramethylsilane (TMS) for both the silicon and the carbon source. The influence of synthesis parameters on the product characteristics was investigated. The as-prepared SiC particles with sizes between 4 and 6 nm were obtained from the TMS precursor in a plasma operated at low temperature and low precursor partial pressure (0.001-0.02 Torr) using argon as the carrier gas (3 Torr). The carbon:silicon ratio was tuned by the addition of hydrogen and characterized by x-ray photoelectron spectroscopy. The reaction mechanism of SiC nanoparticle formation in the microwave plasma was investigated by mass spectroscopy of the gaseous products

  5. Characterization of LPCVD amorphous silicon carbide (a-SiC) as material for electron transparent windows

    International Nuclear Information System (INIS)

    We investigate on the physical and chemical properties of non-stoichiometric amorphous silicon carbide (a-SiCx) thin layers deposited by low-pressure chemical vapor deposition (LPCVD). Characterizations are specifically tailored to understand the suitability of a-SiCx as electron transparent window material. The structure, composition, continuity, intrinsic stress, etch-rates and roughness of the layers are determined. The a-SiCx layers are highly uniform and continuous, showing tensile intrinsic stress and high chemical inertness. The layer with the lowest roughness (0.22 nm) and intrinsic stress (0.7 GPa) is employed to fabricate electron transparent windows of 16 nm for use in a Transmission Electron Microscope (TEM). The resulting windows are highly transparent, enabling the acquisition of TEM images down to the resolution limit of the microscope (0.12 nm). Moreover, the a-SiCx windows show a resistance to electron beam damage which is up to 9 times higher than that of the commonly employed low-stress LPCVD silicon nitride (SiNx). Therefore, the proposed a-SiCx is particularly suited for TEM experiments where high chemical inertness and/or long exposures to the TEM electron beam are required. In addition, the a-SiCx layer could advantageously be employed in the design of microelectromechanical systems (MEMS), especially those operating in harsh environments. - Highlights: ► Very thin non-stoichiometric amorphous SiC (a-SiCx) layers are deposited by LPCVD. ► Layers of 20 nm are continuous, show tensile stress and high chemical inertness. ► Electron transparent windows made of a-SiCx are fabricated. ► a-SiCx windows are highly transparent allowing TEM images with 0.12 nm resolution. ► a-SiCx windows show high resistance to TEM electron beam

  6. Growth and Physical Structure of Amorphous Boron Carbide Deposited by Magnetron Sputtering on a Silicon Substrate with a Titanium Interlayer

    Directory of Open Access Journals (Sweden)

    Roberto Caniello

    2013-01-01

    Full Text Available Multilayer amorphous boron carbide coatings were produced by radiofrequency magnetron sputtering on silicon substrates. To improve the adhesion, titanium interlayers with different thickness were interposed between the substrate and the coating. Above three hundreds nanometer, the enhanced roughness of the titanium led to the growth of an amorphous boron carbide with a dense and continuing columnar structure, and no delamination effect was observed. Correspondingly, the adhesion of the coating became three time stronger than in the case of a bare silicon substrate. Physical structure and microstructural proprieties of the coatings were investigated by means of a scan electron microscopy, atomic force microscopy and X-ray diffraction. The adhesion of the films was measured by a scratch tester.

  7. Experimental and ab initio study of enhanced resistance to amorphization of nanocrystalline silicon carbide under electron irradiation

    Science.gov (United States)

    Jamison, Laura; Zheng, Ming-Jie; Shannon, Steve; Allen, Todd; Morgan, Dane; Szlufarska, Izabela

    2014-02-01

    The crystalline-to-amorphous transition in nanocrystalline silicon carbide (ncSiC) has been studied using 1.25 MeV electron irradiation. When compared to literature values for single crystal silicon carbide under electron irradiation, an increase in the dose to amorphization (DTA) was observed, indicative of an increase in radiation resistance. Factors that contribute to this improvement are grain refinement, grain texture, and a high density of stacking faults (SFs) in this sample of ncSiC. To test the effect of SFs on the DTA, density functional theory simulations were conducted. It was found that SFs reduced the energy barriers for both Si interstitial migration and the rate-limiting defect recovery reaction, which may explain the increased DTA.

  8. Tailoring the Mechanical Properties of High-Aspect-Ratio Carbon Nanotube Arrays using Amorphous Silicon Carbide Coatings

    OpenAIRE

    Poelma, R.H.; Morana, B.; Vollebregt, S.; Schlangen, H.E.J.G.; Van Zeijl, H.W.; Fan, X.; Zhang, G. Q.

    2014-01-01

    The porous nature of carbon nanotube (CNT) arrays allows for the unique opportunity to tailor their mechanical response by the infiltration and deposition of nanoscale conformal coatings. Here, we fabricate novel photo-lithographically defined CNT pillars that are conformally coated with amorphous silicon carbide (a-SiC) to strengthen the interlocking of individual CNTs at junctions using low pressure chemical vapor deposition (LPCVD). We further quantify the mechanical response by performing...

  9. Performance of microdot (MDOT) detectors with conductive coating of doped amorphous silicon carbide (a-Si:C:H)

    International Nuclear Information System (INIS)

    A conductive coating of doped amorphous silicon carbide (a-Si:C:H) has been used in the fabrication of microdot (MDOT) detectors, to minimize the defocusing, away from the anodes, of the drifting primary electrons. This defocusing is caused by the existence of the readout line passing below the insulating layer. The defocusing effect and other effects of the conductive coating on the performance of these detectors fabricated in this way have been investigated

  10. Surface plasmon enhanced photoluminescence in amorphous silicon carbide films by adjusting Ag island film sizes

    International Nuclear Information System (INIS)

    Ag island films with different sizes are deposited on hydrogenated amorphous silicon carbide (α-SiC:H) films, and the influences of Ag island films on the optical properties of the α-SiC:H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increases with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence (PL) enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of α-SiC:H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  11. Optical contrast formation in amorphous silicon carbide with high-energy focused ion beams

    International Nuclear Information System (INIS)

    Thin films (d ∼ 1 μm) of hydrogenated amorphous silicon carbide (a-Si1-xCx:H), deposited by RF reactive magnetron sputtering with different carbon content x, have been implanted with high fluences (Φ = 1016-1017 cm-2) of high-energy (E = 0.2-1 MeV) He+ ions as the implant species. The induced structural modification of the implanted material results in a considerable change of its optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from photo-thermal-deflection spectroscopy (PDS) data. This shift is accompanied by a remarkable increase of the absorption coefficient over one order of magnitude (photo-darkening effect) in the measured photon energy range (0.6-3.8 eV), depending on the ion fluence, energy and carbon content of the films. These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by Raman spectroscopy and infra-red (IR) optical transmission measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused high-energy He+ ion beams.

  12. Fabrication of Amorphous Silicon Carbide Films from Decomposition of Tetramethylsilane using ECR plasma of Ar

    International Nuclear Information System (INIS)

    Mechanically-hard hydrogenated amorphous silicon carbide (a-SiCx:H) films were formed from the decomposition of Si(CH3)4 using the electron-cyclotron resonance plasma flow of Ar. An external radio-frequency (RF) voltage was applied to the substrate with the negative self-bias voltage (−VRF) of 0–100 V. Compositional analysis was made with a combination of Rutherford backscattering and elastic recoil detection analysis. The C/Si ratios of films were 2.2–2.7. Film hardness was measured with a nano-indentation testing equipment. Chemical bonding was analyzed using carbon-K near edge X-ray absorption fine structure (C-K NEXAFS) spectroscopy using an accelerator NewSUBARU. The peak-fitting analysis of the C-K NEXAFS spectra yielded the sp2/(sp2+sp3) ratios, being fully correlated with film hardness. With supported by the IR and Raman spectroscopic measurements, the change of the chemical structure induced by −VRF was discussed.

  13. Degradation mechanism of amorphous silicon carbide fiber due to air-exposure at high temperatures

    International Nuclear Information System (INIS)

    The degradation mechanism of the amorphous silicon carbide fiber, Tyranno-ZMI, exposed in air at 1173-1873 K for 20 ks were studied. The average strength of the bare fiber, which was prepared by etching away the oxidation layer on the fiber surface, decreased with increasing exposure temperature, especially when exposed at the temperature higher than 1673 K. The measurement of the crystallite size of β-SiC in the fiber with Sherrer method revealed that coarsening of the crystalline occurred in the fiber exposed at the temperatures higher than 1773 K. The scanning electron microscope observation of the fiber surface showed that the many defects formed on the fiber surface. By introducing an artificial notch directly into the fiber specimens using a focused-ion(Ga+)-beam, the fracture toughness values of the as-supplied fiber and of the fiber exposed at 1673 and 1773 K were determined to be 1.8±0.3, 1.9±0.4 and 1.3±0.4 MPa √m, respectively. Based on these results, the reason for the degradation of the fiber was attributed to the extension of the surface defect which was enhanced by the reduction in fracture toughness due to coarsening of the β-SiC crystalline. (author)

  14. Atomistic modeling of amorphous silicon carbide: an approximate first-principles study in constrained solution space.

    Science.gov (United States)

    Atta-Fynn, Raymond; Biswas, Parthapratim

    2009-07-01

    Localized basis ab initio molecular dynamics simulation within the density functional framework has been used to generate realistic configurations of amorphous silicon carbide (a-SiC). Our approach consists of constructing a set of smart initial configurations that conform to essential geometrical and structural aspects of the materials obtained from experimental data, which is subsequently driven via a first-principles force field to obtain the best solution in a reduced solution space. A combination of a priori information (primarily structural and topological) along with the ab initio optimization of the total energy makes it possible to model a large system size (1000 atoms) without compromising the quantum mechanical accuracy of the force field to describe the complex bonding chemistry of Si and C. The structural, electronic and vibrational properties of the models have been studied and compared to existing theoretical models and available data from experiments. We demonstrate that the approach is capable of producing large, realistic configurations of a-SiC from first-principles simulation that display its excellent structural and electronic properties. Our study reveals the presence of predominant short range order in the material originating from heteronuclear Si-C bonds with a coordination defect concentration as small as 5% and a chemical disorder parameter of about 8%. PMID:21828477

  15. Ion beam effects on the hydrogenated bonds of amorphous silicon carbide

    International Nuclear Information System (INIS)

    Ion irradiation of amorphous hydrogenated silicon carbide films introduces additional disorder into the films and leads to chemical modifications. These effects were monitored using Infrared, UV-visible optical and Raman spectroscopies. Samples were prepared by plasma enhanced chemical vapour deposition (PECVD), then irradiated with 300 keV Ar+ to fluences ranging from 5x1013 to 1x1015 cm-2. The hydrogen concentration was determined by elastic recoil detection analysis using 2.0 MeV He+ beam. After ion irradiation, the absorption coefficient in the UV-visible energy range was observed to increase by an order of magnitude, while the optical energy gap decreases from 3.2 eV to 2.0 eV. These changes are due to the formation of carbon clusters, as evidenced by the carbon yield in Raman measurements. Infrared spectra indicate that this excess of carbon atoms results from the breaking of CHn bonds in the as-grown film and by a concomitant decrease in the hydrogen concentration. In addition, defects created by ion bombardment change the oscillator strength of the Si-H vibrational modes

  16. Atomistic modeling of amorphous silicon carbide: an approximate first-principles study in constrained solution space

    International Nuclear Information System (INIS)

    Localized basis ab initio molecular dynamics simulation within the density functional framework has been used to generate realistic configurations of amorphous silicon carbide (a-SiC). Our approach consists of constructing a set of smart initial configurations that conform to essential geometrical and structural aspects of the materials obtained from experimental data, which is subsequently driven via a first-principles force field to obtain the best solution in a reduced solution space. A combination of a priori information (primarily structural and topological) along with the ab initio optimization of the total energy makes it possible to model a large system size (1000 atoms) without compromising the quantum mechanical accuracy of the force field to describe the complex bonding chemistry of Si and C. The structural, electronic and vibrational properties of the models have been studied and compared to existing theoretical models and available data from experiments. We demonstrate that the approach is capable of producing large, realistic configurations of a-SiC from first-principles simulation that display its excellent structural and electronic properties. Our study reveals the presence of predominant short range order in the material originating from heteronuclear Si-C bonds with a coordination defect concentration as small as 5% and a chemical disorder parameter of about 8%.

  17. Direct transformation of amorphous silicon carbide into graphene under low temperature and ambient pressure.

    Science.gov (United States)

    Peng, Tao; Lv, Haifeng; He, Daping; Pan, Mu; Mu, Shichun

    2013-01-01

    A large-scale availability of the graphene is critical to the successful application of graphene-based electronic devices. The growth of epitaxial graphene (EG) on insulating silicon carbide (SiC) surfaces has opened a new promising route for large-scale high-quality graphene production. However, two key obstacles to epitaxial growth are extremely high requirements for almost perfectly ordered crystal SiC and harsh process conditions. Here, we report that the amorphous SiC (a-Si(1-x)C(x)) nano-shell (nano-film) can be directly transformed into graphene by using chlorination method under very mild reaction conditions of relative low temperature (800°C) and the ambient pressure in chlorine (Cl(2)) atmosphere. Therefore, our finding, the direct transformation of a-Si(1-x)C(x) into graphene under much milder condition, will open a door to apply this new method to the large-scale production of graphene at low costs. PMID:23359349

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2014-04-01

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

  20. Structure-Property Relationships in Polymer Derived Amorphous/Nano-Crystalline Silicon Carbide for Nuclear Applications

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) is a promising candidate for several applications in nuclear reactors owing to its high thermal conductivity, high melting temperature, good chemical stability, and resistance to swelling under heavy ion bombardment. However, fabricating SiC by traditional powder processing route generally requires very high temperatures for pressureless sintering. Polymer derived ceramic materials offer unique advantages such as ability to fabricate net shaped components, incorporate reinforcements and relatively low processing temperatures. Furthermore, for SiC based ceramics fabricated using polymer infiltration process (PIP), the microstructure can be tailored by controlling the processing parameters, to get an amorphous, nanocrystalline or crystalline SiC. In this work, fabrication of polymer derived amorphous and nano-grained SiC is presented and its application as an in-core material is explored. Monolithic SiC samples are fabricated by controlled pyrolysis of allyl-hydrido-poly-carbo-silane (AHPCS) under inert atmosphere. Chemical changes, phase transformations and microstructural changes occurring during the pyrolysis process are studied as a function of the processing temperature. Polymer cross-linking and polymer to ceramic conversion is studied using infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are performed to monitor the mass loss and phase change as a function of temperature. X-ray diffraction studies are done to study the intermediate phases and microstructural changes. Variation in density is carefully monitored as a function of processing temperature. Owing to shrinkage and gas evolution during pyrolysis, precursor derived ceramics are inherently porous and composite fabrication typically involves repeated cycles of polymer re-infiltration and pyrolysis. However, there is a limit to the densification that can be achieved by this method and porosity in the final materials presents

  1. Tailored amorphous silicon carbide barrier dielectrics by nitrogen and oxygen doping

    International Nuclear Information System (INIS)

    The effects of N or O doping into hydrogenated amorphous silicon carbide (a-SiC:H) films on molecular structure and resulting material properties with particular attention to elastic constant, cohesive fracture energy, and moisture-assisted cracking were investigated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy characterizations demonstrated that doped N primarily formed Si-N and N-H bonds, and doped O formed Si-O suboxide bonds. The elastic constant of both N-doped a-SiC:H (a-SiCN:H) and O-doped a-SiC:H (a-SiCO:H) films increased with increasing N and O atomic concentrations (at.%). The cohesive fracture energy, Gc, of the a-SiCN:H and a-SiCO:H films also increased with increasing N and O at.%. These increases in the mechanical properties of the films were attributed to film densification with increasing N and O at.%. The a-SiCN:H films exhibited a greater increase in Gc than the a-SiCO:H films, which was due to the moisture-insensitivity of the a-SiCN:H films as opposed to the a-SiCO:H films. The a-SiCN:H films exhibited no moisture-assisted fracture behavior, which was attributed to moisture-insensitivity of Si-N bonds due to their less polar nature. - Highlights: ► N and O doping were used to enhance the mechanical properties of a-SiC:H films. ► N and O doping significantly improved the elastic and fracture properties. ► N doping made the films insensitive to moisture-assisted cracking. ► Changes in the mechanical properties were related to the molecular structure

  2. Photoelectron yield spectroscopy and inverse photoemission spectroscopy evaluations of p-type amorphous silicon carbide films prepared using liquid materials

    Directory of Open Access Journals (Sweden)

    Tatsuya Murakami

    2016-05-01

    Full Text Available Phosphorus-doped amorphous silicon carbide films were prepared using a polymeric precursor solution. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross-linkage, providing semiconducting properties in the films. The valence and conduction states of resultant films were determined directly through the combination of inverse photoemission spectroscopy and photoelectron yield spectroscopy. The incorporated carbon widened energy gap and optical gap comparably in the films with lower carbon concentrations. In contrast, a large deviation between the energy gap and the optical gap was observed at higher carbon contents because of exponential widening of the band tail.

  3. A Study of The Evolution of The Silicon Nanocrystallites in The Amorphous Silicon Carbide Under Argon Dilution of the Source Gases

    OpenAIRE

    Kole, A.; Chaudhuri, P.

    2011-01-01

    Structural evolution of the hydrogenated amorphous silicon carbide (a-SiC:H) films deposited by rf-PECVD from a mixture of SiH4 and CH4 diluted in Ar shows that a smooth transition from amorphous to nanocrystalline phase occurs in the material by increasing the Ar dilution. The optical band gap (Eg) decreases from 1.99 eV to 1.91 eV and the H-content (CH) decreases from 14.32 at% to 5.29 at% by increasing the dilution from 94 % to 98 %. at 98 % Ar dilution, the material contains irregular sha...

  4. Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

    International Nuclear Information System (INIS)

    Silicon carbide thin films are deposited on Si (100) substrates by ablating a SiC polycrystalline target in vacuum using a focused high power Kr F excimer laser. The effect of deposition temperature and laser intensity on the microstructure of the films is studied. Grazing Incidence X-ray Diffraction (GIXRD) is utilized to investigate the crystallographic phase and growth orientation of the deposited films. Their chemical bonding and structural ordering are deduced by Fourier Transform Infrared Spectroscopy (FTIR). Atomic Force Microscopy (AFM) was used to determine their surface roughness and morphology while paramagnetic defects were analyzed by the Electron Paramagnetic Resonance (EPR). It was found that the substrate temperature Td significantly affects the microstructure of the films. Indeed, (111) oriented 3C-SiC crystals are detected at Td greater than 800 degree C. But FTIR spectroscopy results show that the substrate temperature 625 degree C is a critical temperature at which structural changes occur in such a way that bonding is enhanced leading to a more ordered microstructure at higher temperatures. Si-C below 800 degree C, the films have a smooth surface morphology, whereas a sharp increase in roughness and diameter and particle height is detected above 800 degree C. These results agree with those obtained by GIXRD thus confirming that the onset of crystallinity in the layers takes place above 800 degree C. The EPR measurements indicate that the paramagnetic defects are typical of clustered carbon atoms whose arrangement are modified by varying Td. Temperature dependent EPR measurement confirm that a densification of the films take place around 625 degree C while a large scale crystallization occurs at 800 C. Increasing the laser energy E, from 200 to 400 mJ, has little effect on the microstructure of the SiC films but leads to the formation of larger grains. This work greatly contributes to understand the microstructural transition from the amorphous

  5. Nuclear reaction analysis of hydrogen in amorphous silicon and silicon carbide films

    International Nuclear Information System (INIS)

    The 1H(11B, α)αα nuclear reaction is used to determine the H content and the density of amorphous semiconductor Si1-sub(x)Csub(x)H2 and SiHsub(z) thin films. Rutherford backscattering is used to determine the x values and infrared transmission to study the hydrogen bonds. We have observed a transfer or/and a release of hydrogen under bombardment by various ions and we show that this last effect must be taken into account for a correct determination of the hydrogen content. An attempt is made to correlate the hydrogen release with electronic and nuclear energy losses. (orig.)

  6. Silicon carbide bodies

    International Nuclear Information System (INIS)

    A self-bonded silicon carbide body produced by siliconising a preformed mixture of particles (shaped by means other than slip-casting) of carbon and silicon carbide in the beta form has a mean grain size in the range of 0.1 to 5 microns. Such a body may be produced using silicon carbide particles having a mean surface area in the range 0.5 to 20 square metres per gram. The silicon carbide particles may be produced by heating a mixture of silica and silicon to generate silicon monoxide vapour and passing the vapour through a bed of particulate carbon. (author)

  7. Effect of deposition temperature on the properties of amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    Silicon carbide films were deposited on n-type Si substrates (111) of resistivity 2-7 Ω cm in a high-frequency parallel-plate plasma reactor. The deposition temperatures were 250, 350 and 450 deg. C, respectively. The RBS results showed that the concentrations of Si and C in the films depend a little on the deposition temperature. The films contain a small amount of oxygen and nitrogen. IR results showed the presence of Si-C, Si-H, C-H, Si-O, Si-N specific bonds. The AFM micrographs revealed that the film surface is rather smooth and compact

  8. The Synthesis and Structural Properties of Crystalline Silicon Quantum Dots upon Thermal Annealing of Hydrogenated Amorphous Si-Rich Silicon Carbide Films

    Science.gov (United States)

    Wen, Guozhi; Zeng, Xiangbin; Li, Xianghu

    2016-08-01

    Silicon quantum dots (QDs) embedded in non-stoichiometric hydrogenated silicon carbide (SiC:H) thin films have been successfully synthesized by plasma-enhanced chemical vapor deposition and post-annealing. The chemical composition analyses have been carried out by x-ray photoelectron spectroscopy (XPS). The bonding configurations have been deduced from Fourier transform infrared absorption measurements (FTIR). The evolution of microstructure with temperature has been characterized by glancing incident x-ray diffraction (XRD) and Raman diffraction spectroscopy. XPS and FTIR show that it is in Si-rich feature and there are a few hydrogenated silicon clusters in the as-grown sample. XRD and Raman diffraction spectroscopy show that it is in amorphous for the as-grown sample, while crystalline silicon QDs have been synthesized in the 900°C annealed sample. Silicon atoms precipitation from the SiC matrix or silicon phase transition from amorphous SiC is enhanced with annealing temperature increase. The average sizes of silicon QDs are about 5.1 nm and 5.6 nm, the number densities are as high as 1.7 × 1012 cm-2 and 3.2 × 1012 cm-2, and the crystalline volume fractions are about 58.3% and 61.3% for the 900°C and 1050°C annealed samples, respectively. These structural properties analyses provide an understanding about the synthesis of silicon QDs upon thermal annealing for applications in next generation optoelectronic and photovoltaic devices.

  9. Amorphous Silicon Carbide Photoelectrode for Hydrogen Production from Water using Sunlight

    OpenAIRE

    Zhu, Feng; Hu, Jian; Matulionis, Ilvydas; Deutsch, Todd; Gaillard, Nicolas; Miller, Eric; Madan, Arun

    2010-01-01

    State-of-the-art a-SiC:H films have been prepared using RF-PECVD deposition technique. Incorporation of carbon in amorphous silicon network increases the bandgap to >2.0eV and adding H2 during fabrication has led to a material with low defects. A-SiC:H with Eg=2.0eV used as the active layer in single junction solar cell led to an efficiency of ~7%, which also indicated that a-SiC:H is high-quality and that it has potential to be used as photoelectrode. Immersing in pH2 sulphamic acid electrol...

  10. Performance of microstrip gas chambers with conductive surface coating of doped amorphous silicon carbide (a-Si:C:H)

    International Nuclear Information System (INIS)

    A new technique involves the use of doped amorphous silicon carbide (a-Si:C:H) as a conductive surface coating in the fabrication of microstrip gas chambers, to eliminate the effect of charge accumulation on the substrate surface. The performance of these detectors made in this way has been tested, measuring gas gains with respect to several operating parameters such as time, anode voltage (Va), backplane voltage (Vb), and drift voltage (Vd). Doped a-Si:C:H film is a conductive surface coating that works well, and is an attractive alternative to other surface treatments of the substrate, because its resistivity can be easily controlled over a wide range by doping, it has a naturally good radiation hardness, and large areas can be coated at relatively low cost. (orig.)

  11. Fabrication of hydrogenated amorphous silicon carbide films by decomposition of hexamethyldisilane with microwave discharge flow of Ar

    Science.gov (United States)

    Ito, Haruhiko; Kumakura, Motoki; Suzuki, Tsuneo; Niibe, Masahito; Kanda, Kazuhiro; Saitoh, Hidetoshi

    2016-06-01

    Hydrogenated amorphous silicon carbide films have been fabricated by the decomposition of hexamethyldisilane with a microwave discharge flow of Ar. Mechanically hard films were obtained by applying radio-frequency (RF) bias voltages to the substrate. The atomic compositions of the films were analyzed by a combination of Rutherford backscattering and elastic recoil detection, X-ray photoelectron spectroscopy (XPS), and glow discharge optical emission spectroscopy. The chemical structure was analyzed by carbon-K near-edge X-ray absorption fine structure spectroscopy, high-resolution XPS, and Fourier transform infrared absorption spectroscopy. The structural changes upon the application of RF bias were investigated, and the concentration of O atoms near the film surface was found to play a key role in the mechanical hardness of the present films.

  12. The effect of relatively low hydrogen dilution on the properties of carbon-rich hydrogenated amorphous silicon carbide films

    International Nuclear Information System (INIS)

    Carbon-rich hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) using silane, ethylene and hydrogen as gas sources. The effect of relatively low hydrogen dilution on the properties of as-deposited samples was investigated. A variety of techniques including Scanning Electron Microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Raman scattering (RS), UV-VIS spectrophotometer and photoluminescence (PL) spectroscopy were used to characterize the grown films. The deposition rate decreases with hydrogen dilution. The silicon to carbon ratio increases slightly with the addition of hydrogen. The phenomenon can be attributed to the dissipation of power density caused by hydrogen dilution. Raman G peak position shifting to a lower wave number indicates that hydrogen dilution reduces the size and concentration of sp2 carbon clusters, which is caused by the etching effect by atomic hydrogen. The optical band gap, which is controlled by the sp2 carbon clusters and Si/C ratio, changes unmonotonously. The as-deposited samples exhibited a blue-green room-temperature (RT) PL well visible to the naked eye with UV excitation. The PL band can be attributed to the radiative recombination of electron-hole pairs within small sp2 clusters containing C=C and C-H units in a sp3 amorphous matrix.

  13. The influence of radio frequency power on the characteristics of carbon-rich hydrogenated amorphous silicon carbide films

    International Nuclear Information System (INIS)

    A series of carbon-rich hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were prepared at different radio frequency (RF) powers from silane-ethylene-hydrogen plasma. The effect of the RF power on the bonding configurations and microstructures has been investigated. The grown films were characterized by a collection of techniques including Scanning Electron Microscope, Fourier transform infrared(FTIR) spectroscopy, Raman scattering and photoluminescence spectroscopy. The deposition rate increases upon RF power due to the enhancement of chemical reactivity of plasma. The carbon to silicon ratio increases, for more C2H4 molecules decompose with the enhancement of RF power and more carbon atoms are bonded into the films. Raman G peak position shifts to a higher wavenumber, which indicates that the size and concentration of sp2 carbon clusters increase as the RF power becomes stronger. Blue-green photoluminescence is detected at room temperature. The PL band can be attributed to the existence of the amorphous carbon clusters in films with high carbon concentrations.

  14. Nanocrystalline silicon and silicon quantum dots formation within amorphous silicon carbide by plasma enhanced chemical vapour deposition method controlling the Argon dilution of the process gases

    International Nuclear Information System (INIS)

    Structural and optical properties of the amorphous silicon carbide (a-SiC:H) thin films deposited by radio frequency plasma enhanced chemical vapour deposition method from a mixture of silane (SiH4) and methane (CH4) diluted in argon (Ar) have been studied with variation of Ar dilution from 94% to 98.4%. It is observed that nanocrystalline silicon starts to form within the a-SiC:H matrix by increasing the dilution to 96%. With further increase in Ar dilution to 98% formation of the silicon nanocrystals (nc-Si) with variable size is enhanced. The optical band gap (Eg) of the a-SiC:H film decreases from 2.0 eV to 1.9 eV with increase in Ar dilution from 96% to 98% as the a-SiC:H films gradually become Si rich. On increasing the Ar dilution further to 98.4% leads to the appearance of crystalline silicon quantum dots (c-Si q-dots) of nearly uniform size of 3.5 nm. The quantum confinement effect is apparent from the sharp increase in the Eg value to 2.6 eV. The phase transformation phenomenon from nc-Si within the a-SiC:H films to Si q-dot were further studied by high resolution transmission electron microscopy and the grazing angle X-ray diffraction spectra. A relaxation in the lattice strain has been observed with the formation of Si q-dots.

  15. An environment-dependent interatomic potential for silicon carbide: calculation of bulk properties, high-pressure phases, point and extended defects, and amorphous structures

    International Nuclear Information System (INIS)

    An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542). The functional form of the original EDIP has been generalized and two sets of parameters have been proposed. Tests with these two potentials have been performed for many properties of SiC, including bulk properties, high-pressure phases, point and extended defects, and amorphous structures. One parameter set allows us to keep the original EDIP formulation for silicon, and is shown to be well suited for modelling irradiation-induced effects in silicon carbide, with a very good description of point defects and of the disordered phase. The other set, including a new parametrization for silicon, has been shown to be efficient for modelling point and extended defects, as well as high-pressure phases.

  16. An environment-dependent interatomic potential for silicon carbide: calculation of bulk properties, high-pressure phases, point and extended defects, and amorphous structures.

    Science.gov (United States)

    Lucas, G; Bertolus, M; Pizzagalli, L

    2010-01-27

    An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542). The functional form of the original EDIP has been generalized and two sets of parameters have been proposed. Tests with these two potentials have been performed for many properties of SiC, including bulk properties, high-pressure phases, point and extended defects, and amorphous structures. One parameter set allows us to keep the original EDIP formulation for silicon, and is shown to be well suited for modelling irradiation-induced effects in silicon carbide, with a very good description of point defects and of the disordered phase. The other set, including a new parametrization for silicon, has been shown to be efficient for modelling point and extended defects, as well as high-pressure phases. PMID:21386297

  17. Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching

    International Nuclear Information System (INIS)

    In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K2S2O8 solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K2S2O8 solution has been proposed.

  18. Structural and optical properties of hydrogenated amorphous silicon carbide films by helicon wave plasma-enhanced chemical vapour deposition

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon carbide (a-Si1-xCx : H) films with different carbon concentrations have been deposited using the helicon wave plasma-enhanced chemical vapour deposition technique under the condition of strong hydrogen dilution. The a-Si1-xCx:H films with carbon content x up to 0.64 have been deposited. Their structural and optical properties are investigated using Fourier transform infrared spectroscopy, Raman scattering, ultraviolet-visible transmittance spectroscopy and x-ray photoelectron spectroscopy. The deposition rate, optical band gap and B factor related to structural disorder are found to monotonically change in the investigated range with methane-silane gas flow ratios. It is found that the deposited films exist with the structure of Si-like clusters and Si-C networks when silicon content is high, while they consist mainly of C-like clusters and Si-C networks for carbon-rich samples. A large optical band gap is obtained in high carbon concentration samples, which is attributed to the high density characteristic of helicon wave plasmas and the strong hydrogen dilution condition

  19. Microstructures of the silicon carbide nanowires obtained by annealing the mechanically-alloyed amorphous powders

    International Nuclear Information System (INIS)

    Silicon, graphite and boron nitride powders were mechanically alloyed for 40 h in argon. The as-milled powders were annealed at 1700 °C in nitrogen for 30 min. The annealed powders are covered by a thick layer of gray–green SiC nanowires, which are 300 nm to 1000 nm in diameter and several hundred microns in length. Trace iron in the raw powders acts as a catalyst, promoting the V–L–S process. It follows that the actual substances contributing to the growth of the SiC nanowires may be silicon, graphite and the metal impurities in the raw powders. The results from HRTEM and XRD reveal that the products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. It is interestingly found that 6H–SiC coexists with 3C–SiC in one nodular nanowire. This novel structure may introduce periodic potential field along the longitudinal direction of the nanowires, and may find applications in the highly integrated optoelectronic devices. - Graphical abstract: Display Omitted - Highlights: • SiC nanowires were prepared by annealing the mechanically alloyed amorphous powders. • SiC nanowires are 300 nm to 1000 nm in diameter and several hundred microns in length. • The products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. • Trace Fe in the raw powders acts as a catalyst, promoting the V–L–S process. • 6H–SiC coexists with 3C–SiC in one nodular SiC nanowire

  20. Microstructures of the silicon carbide nanowires obtained by annealing the mechanically-alloyed amorphous powders

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Pengfei, E-mail: zhangpengfei1984@163.com; Li, Xinli

    2015-07-15

    Silicon, graphite and boron nitride powders were mechanically alloyed for 40 h in argon. The as-milled powders were annealed at 1700 °C in nitrogen for 30 min. The annealed powders are covered by a thick layer of gray–green SiC nanowires, which are 300 nm to 1000 nm in diameter and several hundred microns in length. Trace iron in the raw powders acts as a catalyst, promoting the V–L–S process. It follows that the actual substances contributing to the growth of the SiC nanowires may be silicon, graphite and the metal impurities in the raw powders. The results from HRTEM and XRD reveal that the products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. It is interestingly found that 6H–SiC coexists with 3C–SiC in one nodular nanowire. This novel structure may introduce periodic potential field along the longitudinal direction of the nanowires, and may find applications in the highly integrated optoelectronic devices. - Graphical abstract: Display Omitted - Highlights: • SiC nanowires were prepared by annealing the mechanically alloyed amorphous powders. • SiC nanowires are 300 nm to 1000 nm in diameter and several hundred microns in length. • The products contain both straight α/β-SiC nanowires and nodular α/β-SiC nanochains. • Trace Fe in the raw powders acts as a catalyst, promoting the V–L–S process. • 6H–SiC coexists with 3C–SiC in one nodular SiC nanowire.

  1. Neutron-irradiation effect on the electrical characteristics of amorphous silicon carbide and nitrogen-doped silicon carbide films prepared by PECVDtechnology

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) and nitrogen-doped silicon carbide (SiC(N)) films were deposited on p-type Si(100) substrates at various deposition conditions by means of plasma-enhanced chemical vapor deposition (PECVD) technology using silane (SiH4), methane (CH4), and ammonia (NH3) gas as precursors. The concentration of elements in the films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical composition was analyzed by Fourier transform infrared spectroscopy (FT-IR). The films contain a small amount of oxygen. IR results showed the presence of Si-C, Si-N, Si-H, C-H, C-N, N-H, and Si-O bonds. The current-voltage (I-V) characteristics of samples before and after neutron irradiation were measured. The measured current increases after irradiation with neutrons. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Physical and bonding characteristics of N-doped hydrogenated amorphous silicon carbide films grown by PECVD and annealed by pulsed electron beam

    International Nuclear Information System (INIS)

    Nitrogen-doped amorphous silicon carbide films were grown by a plasma enhanced chemical vapour deposition (PE CVD) technique. The actual amount of nitrogen in the SiC films is determined by Rutherford backscattering spectrometry (RBS). For irradiation experiments we use electron beams with a kinetic energy 200 keV, a pulse duration of 300 ns, and a beam current of 150 A/cm2. It is found that with increased nitrogen doping and following activation of dopants the resistivity of the amorphous SiC films is substantially reduced

  3. Mechanisms of amorphization-induced swelling in silicon carbide: the molecular dynamics answer

    International Nuclear Information System (INIS)

    We present here the continuation of an investigation of the irradiation-induced swelling of SiC using classical molecular dynamics (CMD) simulations. Heavy ion irradiation has been assumed to affect the material in two successive steps (a) creation of local atomic disorder, modeled by the introduction of extended amorphous areas with various sizes and shapes in a crystalline SiC sample at constant volume (b) induced swelling, determined through relaxation using Molecular Dynamics at constant pressure. This swelling has been computed as a function of the amorphous fraction introduced. Two different definitions of the amorphous fraction were introduced to enable meaningful comparisons of our calculations with experiments and elastic modeling. One definition based on the displacements relative to the ideal lattice positions was used to compare the CMD results with data from experiments combining ion implantations and channeled Rutherford Backscattering analyses. A second definition based on atomic coordination was used to compare the CMD results to those yielded by a simplified elastic model. The results obtained are as follows. On the one hand, comparison of the swelling obtained as a function of the lattice amorphous fraction with the experimental results shows that the melting-quench amorphization simulates the best the irradiation-induced amorphization observed experimentally. This is consistent with the thermal spike phenomenon taking place during ion implantation. On the other hand, disorder analysis at the atomic scale confirms the elastic behavior of the amorphization-induced swelling, in agreement with the comparison with the results of an elastic model. First, no major structural reconstruction occurs during relaxation or annealing. Second, the systems with the most disordered and constrained amorphous area undergo the largest swelling. This means that the disorder and the constraints of the bulk amorphous area are the driving forces for the swelling

  4. Chemical Analysis Methods for Silicon Carbide

    Institute of Scientific and Technical Information of China (English)

    Shen Keyin

    2006-01-01

    @@ 1 General and Scope This Standard specifies the determination method of silicon dioxide, free silicon, free carbon, total carbon, silicon carbide, ferric sesquioxide in silicon carbide abrasive material.

  5. Room temperature photoluminescence spectrum modeling of hydrogenated amorphous silicon carbide thin films by a joint density of tail states approach and its application to plasma deposited hydrogenated amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    Room temperature photoluminescence (PL) spectrum of hydrogenated amorphous silicon carbide (a-SiCx:H) thin films was modeled by a joint density of tail states approach. In the frame of these analyses, the density of tail states was defined in terms of empirical Gaussian functions for conduction and valance bands. The PL spectrum was represented in terms of an integral of joint density of states functions and Fermi distribution function. The analyses were performed for various values of energy band gap, Fermi energy and disorder parameter, which is a parameter that represents the width of the energy band tails. Finally, the model was applied to the measured room temperature PL spectra of a-SiCx:H thin films deposited by plasma enhanced chemical vapor deposition system, with various carbon contents, which were determined by X-ray photoelectron spectroscopy measurements. The energy band gap and disorder parameters of the conduction and valance band tails were determined and compared with the optical energies and Urbach energies, obtained by UV–Visible transmittance measurements. As a result of the analyses, it was observed that the proposed model sufficiently represents the room temperature PL spectra of a-SiCx:H thin films. - Highlights: ► Photoluminescence spectra (PL) of the films were modeled. ► In the model, joint density of tail states and Fermi distribution function are used. ► Various values of energy band gap, Fermi energy and disorder parameter are applied. ► The model was applied to the measured PL of the films. ► The proposed model represented the room temperature PL spectrum of the films.

  6. Stabilization of boron carbide via silicon doping.

    Science.gov (United States)

    Proctor, J E; Bhakhri, V; Hao, R; Prior, T J; Scheler, T; Gregoryanz, E; Chhowalla, M; Giulani, F

    2015-01-14

    Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping. PMID:25427850

  7. Stabilization of boron carbide via silicon doping

    Science.gov (United States)

    Proctor, J. E.; Bhakhri, V.; Hao, R.; Prior, T. J.; Scheler, T.; Gregoryanz, E.; Chhowalla, M.; Giulani, F.

    2015-01-01

    Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.

  8. Structural evolutions in polymer-derived carbon-rich amorphous silicon carbide.

    Science.gov (United States)

    Wang, Kewei; Ma, Baisheng; Li, Xuqin; Wang, Yiguang; An, Linan

    2015-01-29

    The detailed structural evolutions in polycarbosilane-derived carbon-rich amorphous SiC were investigated semiquantitatively by combining experimental and analytical methods. It is revealed that the material is comprised of a Si-containing matrix phase and a free-carbon phase. The matrix phase is amorphous, comprised of SiC4 tetrahedra, SiCxOx-4 tetrahedra, and Si-C-C-Si/Si-C-H defects. With increasing pyrolysis temperature, the amorphous matrix becomes more ordered, accompanied by a transition from SiC2O2 to SiCO3. The transition was completed at 1250 °C, where the matrix phase started to crystallize by forming a small amount of β-SiC. The free-carbon phase was comprised of carbon nanoclusters and C-dangling bonds. Increasing pyrolysis temperature led to the transition of the free carbon from amorphous carbon to nanocrystalline graphite. The size of the carbon clusters decreased first and then increased, while the C-dangling bond content decreased continuously. The growth of carbon clusters was attributed to Ostwald ripening and described using a two-dimensional grain growth model. The calculated activation energy suggested that the decrease in C-dangling bonds is directly related to the lateral growth of the carbon clusters. PMID:25490064

  9. n-type emitter surface passivation in c-Si solar cells by means of antireflective amorphous silicon carbide layers

    OpenAIRE

    Ferré Tomas, Rafel; Martín García, Isidro; Ortega Villasclaras, Pablo Rafael; Vetter, Michael; Torres, I.; Alcubilla González, Ramón

    2006-01-01

    Emitter saturation current densities (JOe) of phosphorus-diffused planar c-Si solar cell emitters passivated by silicon carbide (SiCx) layers have been determined in a wide sheet resistance range (20-500 Ω/sp). Phosphorus diffusions were performed using solid planar diffusion sources without employing any drive-in step. Stacks of two SiCx layers were deposited by plasma enhanced chemical vapor deposition: first a thin silicon rich layer with excellent passivating properties and th...

  10. Silicon carbide thyristor

    Science.gov (United States)

    Edmond, John A. (Inventor); Palmour, John W. (Inventor)

    1996-01-01

    The SiC thyristor has a substrate, an anode, a drift region, a gate, and a cathode. The substrate, the anode, the drift region, the gate, and the cathode are each preferably formed of silicon carbide. The substrate is formed of silicon carbide having one conductivity type and the anode or the cathode, depending on the embodiment, is formed adjacent the substrate and has the same conductivity type as the substrate. A drift region of silicon carbide is formed adjacent the anode or cathode and has an opposite conductivity type as the anode or cathode. A gate is formed adjacent the drift region or the cathode, also depending on the embodiment, and has an opposite conductivity type as the drift region or the cathode. An anode or cathode, again depending on the embodiment, is formed adjacent the gate or drift region and has an opposite conductivity type than the gate.

  11. Structural relaxation of amorphous silicon carbide thin films in thermal annealing

    International Nuclear Information System (INIS)

    Amorphous Si0.4C0.6 thin films were deposited by radio frequency magnetron sputtering onto non-heated single crystal Si substrates, followed by annealing at 800 deg. C or 1100 deg. C in the vacuum chamber. The chemical bond properties and atomic local ordering as a function of the annealing temperature were characterized by Auger electron spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Infrared absorption spectroscopy, X-ray diffraction, and Raman spectroscopy measurements. We have examined the evolution of microstructure in annealing-induced relaxation process, and investigated the initial stages of thermal crystallization of amorphous Si0.4C0.6. Meanwhile, the structure of excess C in the films also has been studied

  12. Amorphization and recrystallization processes in monocrystalline beta silicon carbide thin films

    International Nuclear Information System (INIS)

    Individual, as well as multiple doses of 27Al+, 31P+, 28Si+, and 28Si+ and 12C+, were implanted into (100) oriented monocrystalline β-SiC films. The critical energy of approx. =16 eV/atom required for the amorphization of β-SiC via implantation of 27Al+ and 31P+ was determined using the TRIM84 computer program for calculation of the damage-energy profiles coupled with the results of RBS/ion channeling analyses. In order to recrystallize amorphized layers created by the individual implantation of all four ion species, thermal annealing at 1600, 1700, or 18000C was employed. Characterization of the recrystallized layers was performed using XTEM. Examples of SPE regrown layers containing precipitates and dislocation loops, highly faulted-microtwinned regions, and random crystallites were observed

  13. Excimer laser crystallization of amorphous silicon carbide produced by ion implantation

    International Nuclear Information System (INIS)

    4H-SiC was implanted with 100-250 keV Ge+ and Xe+ ions and doses of 1x1014 to 1x1016 cm-2 at room temperature in order to produce 40-200 nm thick amorphous surface layers. The samples were irradiated with 1-50,000 pulses of a KrF excimer laser (248 nm wavelength, 30 ns pulse duration) using fluences of 150-900 mJ/cm2 to investigate the crystallization process as a function of the laser parameters. Crystallization as well as redistribution of the impurity atoms were analyzed by Rutherford backscattering spectrometry and infrared reflection measurements. Phase transitions occurring during the irradiation were studied by means of time-resolved reflectivity measurements. In order to explain the observed phase transitions numerical analysis was performed by solving the inhomogeneous heat flow equation using the parameters of the corresponding phases. In this work, we give a consistent description of the experimental results by the numerical simulations for the given laser setup. Depending on the amorphous layer thickness, melting, solidification, and crystallization of the amorphous phase can be effectively controlled by both the laser fluence and the number of laser pulses

  14. A Study of The Evolution of The Silicon Nanocrystallites in The Amorphous Silicon Carbide Under Argon Dilution of the Source Gases

    Directory of Open Access Journals (Sweden)

    A. Kole

    2011-01-01

    Full Text Available Structural evolution of the hydrogenated amorphous silicon carbide (a-SiC:H films deposited by rf-PECVD from a mixture of SiH4 and CH4 diluted in Ar shows that a smooth transition from amorphous to nanocrystalline phase occurs in the material by increasing the Ar dilution. The optical band gap (Eg decreases from 1.99 eV to 1.91 eV and the H-content (CH decreases from 14.32 at% to 5.29 at% by increasing the dilution from 94 % to 98 %. at 98 % Ar dilution, the material contains irregular shape Si nanocrystallites with sizes over 10 nm. Increasing the Ar dilution further to 98.4 % leads to a reduction of the size of the Si nanocrystals to regular shape Si quantum dots of size about 5 nm. The quantum confinement effect is apparent from the increase in the Eg value to 2.6 eV at 98.4 % Ar dilution. Formation of Si quantum dots may be explained by the etching of the nanocrystallites of Si by the energetic ion bombardment from the plasma.

  15. Effect of radio-frequency bias voltage on the optical and structural properties of hydrogenated amorphous silicon carbide

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films have been deposited using the electron cyclotron resonance chemical vapor deposition process under varying negative rf-bias voltage at the substrate. The optical and structural properties of these films are characterized using Rutherford backscattering spectroscopy, transmittance/reflectance spectrophotometry, photothermal deflection spectroscopy, Fourier transform infrared absorption, Raman scattering, and room temperature photoluminescence (PL). These films deposited using a gas mixture of silane, methane, and hydrogen at a constant gas flow ratio showed a slight increase in the carbon fraction x, but very obvious structural transformation, at increasing rf induced bias voltage from -20 to -120 V. Near stoichiometric a-Si1-xCx:H films with a carbon fraction x of almost 0.5 are achieved at low bias voltage range from -20 to -60 V. Visible PL with relatively low efficiency can be observed from such films at room temperature. For larger bias voltages from -80 to -120 V, slightly C-rich a-Si1-xCx:H films (x>0.5) with larger optical gaps are obtained. These films have relatively higher PL efficiency, and the relative quantum efficiency was also found to depend strongly on the optical gap. Structurally, it was found that there is an increase in the hydrogen content and carbon sp2 bonding in the films at larger bias voltages. The latter leads to an increase in the disorder in the films. The linear relationship observed between the Urbach energy E0 and B factor in the Tauc equation suggests that the local defects related to microstructural disorder resulting from alloying with carbon dominate the overall defect structure of the films. Substrate biasing is noted to be crucial for the formation of Si - C bonds, as deduced from the Raman scattering results. [copyright] 2001 American Institute of Physics

  16. Spectroscopy and structural properties of amorphous and nanocrystalline silicon carbide thin films

    OpenAIRE

    Halindintwali, Sylvain; Knoesen, D.; B.A. Julies; Arendse, C.J.; Muller, T; Gengler, Régis Y N; Rudolf, P.; van Loosdrecht, P.H.M.

    2011-01-01

    Amorphous SiC:H thin films were grown by hot wire chemical vapour deposition from a SiH4/CH4/H2 mixture at a substrate temperature below 400 °C. Thermal annealing in an argon environment up to 900 °C shows that the films crystallize as μc-Si:H and SiC with a porous microstructure that favours an oxidation process. By a combination of spectroscopic tools comprising Fourier transform infrared, Raman scattering and X-rays photoelectron spectroscopy we show that the films evolve from the amorphou...

  17. Ion-beam induced defects and nanoscale amorphous clusters in silicon carbide

    International Nuclear Information System (INIS)

    Atomic-level simulations have been employed to study the defects and nanoscale disordering induced in 3C-SiC by C, Si and Au ions with energies up to 50 keV. Energetic C and Si ions primarily produce interstitials, vacancies, antisite defects and small defect clusters directly in collision cascades. The overlap of Si cascades produces nanoscale defect clusters. In the case of energetic Au ions, nanoscale amorphous domains are produced directly within the Au cascades along with point defects and smaller clusters. In about 25% of the Au cascades, one or more subcascades contain nanoscale clusters that exhibit a structure that is consistent with an amorphous state. Structural image simulations of the subcascade structures produced by energetic Si and Au recoils are consistent with experimental high-resolution transmission electron microscopy images. Simulations of close-pair production and recombination in SiC indicate that the activation energies for recombination of most close pairs range from 0.24 to 0.38 eV

  18. Ion-Beam Induced Defects and Nanoscale Amorphous Clusters in Silicon Carbide

    International Nuclear Information System (INIS)

    Atomic-level simulations have been employed to study the defects and nanoscale disordering induced in 3C-SiC by C, Si, and Au ions with energies up to 50 keV. Energetic C and Si ions primarily produce interstitials, vacancies, antisite defects, and small defect clusters directly during the collision cascade. The overlap of Si cascades produces nanoscale defect clusters. In the case of energetic Au ions, nanoscale amorphous domains are produced directly within the Au cascade along with point defects and smaller clusters. In about 25% of the 50 keV Au cascades, one or more of the subcascades contain nanoscale clusters that exhibit a structure that is consistent with an amorphous state. Structural image simulations of the subcascade structures produced by energetic Si and Au recoils are consistent with experimental high-resolution transmission electron microscopy images. Simulations on close-pair production and recombination in SiC indicate that the activation energies for recombination of most close pairs range from 0.24 to 0.38 eV

  19. Far-infrared absorption measurements of graphite, amorphous carbon, and silicon carbide

    Science.gov (United States)

    Tanabe, T.; Nakada, Y.; Kamijo, F.; Sakata, A.

    The mass absorption coefficients of graphite (G), amorphous-carbon (AC), and SiC grains at 25-250 microns are determined experimentally at room temperature and applied to the interpretation of published IR observations of IRC+10216. Absorption measurements are obtained using a single-beam grating spectrometer with a Goley-cell detector by a polyethylene-powder-tablet technique. The results are presented in a table and graphs. The mass absorption constants (in sq cm/g) are calculated as 642 for G, 281 for AC produced in Ar, 93.9 for AC produced in H2, and 19.6 for SiC; power-law relationships to wavelength, with indices of -2.18, 0.60, -0.59, and -1.37 (respectively) are established. AC is found to be the most likely constituent of the IRC+10216 dust cloud, permitting the dust mass to be estimated as 0.0001 solar mass.

  20. Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

    International Nuclear Information System (INIS)

    SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 deg. C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 deg. C produces layers with increasingly uniform environment of the Si-C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 deg. C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp2 carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 deg. C, post-deposition annealing at 1100 deg. C reduces the spin density as a result of a more uniform Si-C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes

  1. Sintered silicon carbide

    International Nuclear Information System (INIS)

    A sintered silicon carbide body having a predominantly equiaxed microstructure consists of 91 to 99.85% by weight of silicon carbide at least 95% of which is the alpha phase, up to 5.0% by weight carbonized organic material, 0.15 to 3.0% of boron, and up to 1.0% by weight additional carbon. A mixture of 91 to 99.85 parts by weight silicon carbide having a surface area of 1 to 100 m2/g, 0.67 to 20 parts of a carbonizable organic binder with a carbon content of at least 33% by weight, 0.15 to 5 parts of a boron source containing 0.15 to 3.0 parts by weight boron and up to 15 parts by weight of a temporary binder is mixed with a solvent, the mixture is then dried, shaped to give a body with a density of at least 1.60 g/cc and fired at 1900 to 22500C to obtain an equiaxed microstructure. (author)

  2. Comparison of silicon oxide and silicon carbide absorber materials in silicon thin-film solar cells

    Directory of Open Access Journals (Sweden)

    Walder Cordula

    2015-01-01

    Full Text Available Since solar energy conversion by photovoltaics is most efficient for photon energies at the bandgap of the absorbing material the idea of combining absorber layers with different bandgaps in a multijunction cell has become popular. In silicon thin-film photovoltaics a multijunction stack with more than two subcells requires a high bandgap amorphous silicon alloy top cell absorber to achieve an optimal bandgap combination. We address the question whether amorphous silicon carbide (a-SiC:H or amorphous silicon oxide (a-SiO:H is more suited for this type of top cell absorber. Our single cell results show a better performance of amorphous silicon carbide with respect to fill factor and especially open circuit voltage at equivalent Tauc bandgaps. The microstructure factor of single layers indicates less void structure in amorphous silicon carbide than in amorphous silicon oxide. Yet photoconductivity of silicon oxide films seems to be higher which could be explained by the material being not truly intrinsic. On the other hand better cell performance of amorphous silicon carbide absorber layers might be connected to better hole transport in the cell.

  3. Comparison of silicon oxide and silicon carbide absorber materials in silicon thin-film solar cells

    Science.gov (United States)

    Walder, Cordula; Kellermann, Martin; Wendler, Elke; Rensberg, Jura; von Maydell, Karsten; Agert, Carsten

    2015-02-01

    Since solar energy conversion by photovoltaics is most efficient for photon energies at the bandgap of the absorbing material the idea of combining absorber layers with different bandgaps in a multijunction cell has become popular. In silicon thin-film photovoltaics a multijunction stack with more than two subcells requires a high bandgap amorphous silicon alloy top cell absorber to achieve an optimal bandgap combination. We address the question whether amorphous silicon carbide (a-SiC:H) or amorphous silicon oxide (a-SiO:H) is more suited for this type of top cell absorber. Our single cell results show a better performance of amorphous silicon carbide with respect to fill factor and especially open circuit voltage at equivalent Tauc bandgaps. The microstructure factor of single layers indicates less void structure in amorphous silicon carbide than in amorphous silicon oxide. Yet photoconductivity of silicon oxide films seems to be higher which could be explained by the material being not truly intrinsic. On the other hand better cell performance of amorphous silicon carbide absorber layers might be connected to better hole transport in the cell.

  4. Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

    NARCIS (Netherlands)

    Khan, R.U.A.; Silva, S.R.P.; Van Swaaij, R.A.C.M.M.

    2003-01-01

    Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p

  5. Analysis on the interfacial properties of transparent conducting oxide and hydrogenated p-type amorphous silicon carbide layers in p–i–n amorphous silicon thin film solar cell structure

    International Nuclear Information System (INIS)

    Quantitative estimation of the specific contact resistivity and energy barrier at the interface between transparent conducting oxide (TCO) and hydrogenated p-type amorphous silicon carbide (a-Si1−xCx:H(p)) was carried out by inserting an interfacial buffer layer of hydrogenated p-type microcrystalline silicon (μc-Si:H(p)) or hydrogenated p-type amorphous silicon (a-Si:H(p)). In addition, superstrate configuration p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated by plasma enhanced chemical vapor deposition to investigate the effect of the inserted buffer layer on the solar cell device. Ultraviolet photoelectron spectroscopy was employed to measure the work functions of the TCO and a-Si1−xCx:H(p) layers and to allow direct calculations of the energy barriers at the interfaces. Especially interface structures were compared with/without a buffer which is either highly doped μc-Si:H(p) layer or low doped a-Si:H(p) layer, to improve the contact properties of aluminum-doped zinc oxide and a-Si1−xCx:H(p). Out of the two buffers, the superior contact properties of μc-Si:H(p) buffer could be expected due to its higher conductivity and slightly lower specific contact resistivity. However, the overall solar cell conversion efficiencies were almost the same for both of the buffered structures and the resultant similar efficiencies were attributed to the difference between the fill factors of the solar cells. The effects of the energy barrier heights of the two buffered structures and their influence on solar cell device performances were intensively investigated and discussed with comparisons. - Highlights: ► Decrease of fill factor due to high contact resistance of Al:ZnO/a-SiC:H(p) interface. ► Insertion of buffer layer (μc-Si or a-Si) between Al:ZnO and p-layer for comparison. ► μc-Si:H(p) buffer with high conductivity has better fill factor but higher barrier. ► a-Si:H(p) buffer with low conductivity forms lower barrier and

  6. Amorphous silicon thermometer

    International Nuclear Information System (INIS)

    The carbon glass resistance thermometers (CGRT) shows an unstable drift by heat cycles. Since we were looking for a more stable element of thermometer for cryogenic and high magnetic field environments, we selected amorphous silicon as a substitute for CGRT. The resistance of many amorphous samples were measured at 4K, at 77K, and 300K. We eventually found an amorphous silicon (Si-H) alloy whose the sensitivity below 77K was comparable to that of the germanium resistance thermometer with little magnetic field influence. (author)

  7. Comparison of silicon oxide and silicon carbide absorber materials in silicon thin-film solar cells

    OpenAIRE

    Walder Cordula; Kellermann Martin; Wendler Elke; Rensberg Jura; von Maydell Karsten; Agert Carsten

    2015-01-01

    Since solar energy conversion by photovoltaics is most efficient for photon energies at the bandgap of the absorbing material the idea of combining absorber layers with different bandgaps in a multijunction cell has become popular. In silicon thin-film photovoltaics a multijunction stack with more than two subcells requires a high bandgap amorphous silicon alloy top cell absorber to achieve an optimal bandgap combination. We address the question whether amorphous silicon carbide (a-SiC:H) or ...

  8. High-rate, low-temperature synthesis of composition controlled hydrogenated amorphous silicon carbide films in low-frequency inductively coupled plasmas

    International Nuclear Information System (INIS)

    It is commonly believed that in order to synthesize high-quality hydrogenated amorphous silicon carbide (a-Si1-xCx : H) films at competitive deposition rates it is necessary to operate plasma discharges at high power regimes and with heavy hydrogen dilution. Here we report on the fabrication of hydrogenated amorphous silicon carbide films with different carbon contents x (ranging from 0.09 to 0.71) at high deposition rates using inductively coupled plasma (ICP) chemical vapour deposition with no hydrogen dilution and at relatively low power densities (∼0.025 W cm-3) as compared with existing reports. The film growth rate Rd peaks at x = 0.09 and x = 0.71, and equals 18 nm min-1 and 17 nm min-1, respectively, which is higher than other existing reports on the fabrication of a-Si1-xCx : H films. The extra carbon atoms for carbon-rich a-Si1-xCx : H samples are incorporated via diamond-like sp3 C-C bonding as deduced by Fourier transform infrared absorption and Raman spectroscopy analyses. The specimens feature a large optical band gap, with the maximum of 3.74 eV obtained at x = 0.71. All the a-Si1-xCx : H samples exhibit low-temperature (77 K) photoluminescence (PL), whereas only the carbon-rich a-Si1-xCx : H samples (x ≥ 0.55) exhibit room-temperature (300 K) PL. Such behaviour is explained by the static disorder model. High film quality in our work can be attributed to the high efficiency of the custom-designed ICP reactor to create reactive radical species required for the film growth. This technique can be used for a broader range of material systems where precise compositional control is required

  9. Electronic properties of disordered silicon carbides

    International Nuclear Information System (INIS)

    The disorder effects on the electronic properties of silicon carbide were studied at the atomic or micro-structural scale. We have investigated a great variety of materials: silicon carbide fibers, carbonated amorphous silicon films, single crystals and amorphous or crystalline SiC powders. The DC and AC conductivity measurements on the SiC fibers point out the major role of their micro-structure at the nanometric scale, which leads to large dielectric constants. Hopping of polaronic carriers is the dominant conduction mechanism. An electrons spin resonance study of all the materials was performed: sp2 hybridized carbon is always present, in diluted form in the amorphous systems or as free carbon in the crystalline one. Some irradiation defects of SiC were identified: silicon or carbon vacancy and carbon complexes with sp2 hybridization. Such a carbon is responsible of the low paramagnetic stability of the silicon dangling bonds. It is believed to induce the polaronic behavior of the localized carriers. (Author). refs., figs., tabs

  10. The growth of cubic silicon carbide on a compliant substrate

    Science.gov (United States)

    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

  11. Investigations on silicon/amorphous-carbon and silicon/nanocrystalline palladium/ amorphous-carbon interfaces.

    Science.gov (United States)

    Roy, M; Sengupta, P; Tyagi, A K; Kale, G B

    2008-08-01

    Our previous work revealed that significant enhancement in sp3-carbon content of amorphous carbon films could be achieved when grown on nanocrystalline palladium interlayer as compared to those grown on bare silicon substrates. To find out why, the nature of interface formed in both the cases has been investigated using Electron Probe Micro Analysis (EPMA) technique. It has been found that a reactive interface in the form of silicon carbide and/silicon oxy-carbide is formed at the interface of silicon/amorphous-carbon films, while palladium remains primarily in its native form at the interface of nanocrystalline palladium/amorphous-carbon films. However, there can be traces of dissolved oxygen within the metallic layer as well. The study has been corroborated further from X-ray photoelectron spectroscopic studies. PMID:19049221

  12. High-Q silicon carbide photonic-crystal cavities

    Science.gov (United States)

    Lee, Jonathan Y.; Lu, Xiyuan; Lin, Qiang

    2015-01-01

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 104 with mode volume ˜ 0.60 ( λ / n ) 3 at wavelength 1.5 μm. A corresponding Purcell factor value of ˜104 is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

  13. Palladium interaction with silicon carbide

    International Nuclear Information System (INIS)

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC–5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd3Si and SiO2 phases, while the second peak and the third peak are correlated with the formation of Pd2Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO2 phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiCxOy phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation

  14. Palladium interaction with silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Gentile, M., E-mail: Marialuisa.Gentile@manchester.ac.uk [Centre for Nuclear Energy Technology (C-NET), School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom); Xiao, P. [Materials Science Centre, School of Materials, The University of Manchester, Manchester M13 9PL (United Kingdom); Abram, T. [Centre for Nuclear Energy Technology (C-NET), School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom)

    2015-07-15

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC–5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd{sub 3}Si and SiO{sub 2} phases, while the second peak and the third peak are correlated with the formation of Pd{sub 2}Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO{sub 2} phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiC{sub x}O{sub y} phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

  15. Palladium interaction with silicon carbide

    Science.gov (United States)

    Gentile, M.; Xiao, P.; Abram, T.

    2015-07-01

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC-5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd3Si and SiO2 phases, while the second peak and the third peak are correlated with the formation of Pd2Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO2 phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiCxOy phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

  16. Compressive creep of hot pressed silicon carbide

    International Nuclear Information System (INIS)

    Silicon carbide has a good match of chemical, mechanical and thermal properties and therefore is considered an excellent structural ceramic for high temperature applications. The aim of the present work is compressive creep evaluation of liquid phase sintered silicon carbide with aluminum and rare earth oxide as sintering aids. Rare earth oxides are possible additives considering their highly refractory remnant grain-boundary phase and lower synthesis costs compared to high purity rare earth. Samples were prepared with silicon carbide powder (90 wt%) and aluminum oxide (5 wt%) plus rare earth oxide (5 wt%) additions. Powders were mixed, milled and hot pressed at 1800 deg. C in argon atmosphere. Compressive creep tests were carried out under stress from 150 to 300 MPa and temperatures from 1300 to 1400 deg. C. At lower creep test temperatures, the obtained stress exponent values were correlated to mechanisms based on diffusion. At intermediate temperatures, grain-boundary sliding becomes operative, accommodated by diffusion. At higher temperatures cavities are discernible. Oxidation reactions and ionic diffusion result on surface oxidized layer, grain-boundary amorphous and intergranular crystalline Al6Si2O13, δ-Y2Si2O7 and YAG phases. In this case cavitation and amorphous phases redistribution enhance grain-boundary sliding, not accommodated by diffusion. Coalescence occurs at triple point and multigrain-junctions, with subsequent strain rate acceleration and cavitational creep.

  17. Free electron laser annealing of silicon carbide

    International Nuclear Information System (INIS)

    We have studied the application of FEL for the semiconductor processing on the practical device fabrication. FEL annealing at a variety of wavelengths (10.0-13.0 μm) have been performed under room temperature for amorphous silicon carbide (a-SiC) and Nitrogen implanted cubic silicon carbide (3C-SiC) films. Infrared absorption spectroscopy indicated that the annealing at 12.6 μm, corresponding to the absorption peak of Si-C stretch mode, was effective for recrystallization. On the other hand, Hall effect measurements showed the increase of carrier density for N-implanted 3C-SiC films at around 10.4 μm, whereas the absorption was weak at this wavelength. The present results demonstrated that the direct excitation of the lattice vibration with FEL can induce the reconstruction of disordered atoms and activating dopants even at room temperature. (author)

  18. Porous silicon carbide (SIC) semiconductor device

    Science.gov (United States)

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

    1996-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  19. In situ-grown hexagonal silicon nanocrystals in silicon carbide-based films

    OpenAIRE

    Kim, Tae-Youb; Huh, Chul; Park, Nae-Man; Choi, Cheol-Jong; Suemitsu, Maki

    2012-01-01

    Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by ...

  20. Ion bombardment effects in plasma deposition of hydrogenated amorphous silicon carbide films: a comparative study of d.c. and r.f. discharges

    International Nuclear Information System (INIS)

    The structure and the properties of hydrogenated amorphous silicon carbide films produced at room temperature by d.c. and r.f. glow discharge decomposition of silane and ethylene were studied with a systematic control of the ion flux at the surface of the growing film. The composition and structure of the films were monitored by measuring their IR absorption, their refractive index and their optical gap. The ion fluxes were determined from the saturation current of a small grid probe located in the substrate holder. It was found that d.c. cathodic and r.f. films show an inorganic structure with a dispersed carbon phase while d.c. anodic films exhibit mainly hydrogenated carbon clusters. These structural changes are thought to result from differences in the energies of the bombarding ions. The versatility of the r.f. and d.c. proximity discharges in comparison with d.c. discharges (anodic and cathodic films) is also emphasized. (Auth.)

  1. Silicon carbide as platform for energy applications

    DEFF Research Database (Denmark)

    Syväjärvi, Mikael; Jokubavicius, Valdas; Sun, Jianwu;

    Silicon carbide is emerging as a novel material for a range of energy and environmental technologies. Previously, silicon carbide was considered as a material mainly for transistor applications. We have initiated the use of silicon carbide material towards optoelectronics in general lighting and...

  2. Palladium interaction with silicon carbide

    OpenAIRE

    M. Gentile, P. Xiao, T. Abram

    2015-01-01

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide...

  3. Amorphous silicon based particle detectors

    OpenAIRE

    Wyrsch, N; Franco, A; Riesen, Y.; Despeisse, M; S. Dunand; Powolny, F; Jarron, P.; Ballif, C.

    2012-01-01

    Radiation hard monolithic particle sensors can be fabricated by a vertical integration of amorphous silicon particle sensors on top of CMOS readout chip. Two types of such particle sensors are presented here using either thick diodes or microchannel plates. The first type based on amorphous silicon diodes exhibits high spatial resolution due to the short lateral carrier collection. Combination of an amorphous silicon thick diode with microstrip detector geometries permits to achieve micromete...

  4. Highly conductive microcrystalline silicon carbide films deposited by the hot wire cell method and its application to amorphous silicon solar cells

    International Nuclear Information System (INIS)

    Microcrystalline silicon carbide (μc-Si1-xCx) films were successfully deposited by the hot wire cell method using a gas mixture of SiH4, H2 and C2H2. It was confirmed by Fourier transform infrared and X-ray diffraction analyses that the films consisted of μc-Si grains embedded in a-Si1-xCx tissue. The p-type μc-Si1-xCx films were deposited using B2H6 as a doping gas. A dark conductivity of 0.2 S/cm and an activation energy of 0.067 eV were obtained. The p-type μc-Si1-xCx was used as a window layer of a-Si solar cells, in which the intrinsic layer was deposited by photo-chemical vapor deposition, and an initial conversion efficiency of 10.2% was obtained

  5. Microstructural characterisation of silicon nitride-bonded silicon carbide

    International Nuclear Information System (INIS)

    The microstructure of a commercial silicon nitride-bonded silicon carbide ceramic composite, formed via the nitridation of Si powder-SiC preforms, has been characterised by transmission electron microscopy. A mechanism combining reaction bonding and liquid-phase sintering is proposed to describe the development and observed morphology of the microstructure of the bonding matrix, which comprises predominantly phases based on Si2N2O and β-Si3N4 and an amorphous phase. Qualitative microanalysis of amorphous matrix regions has revealed significant concentrations of oxygen, aluminium and calcium, with Al also being detected in both of the surrounding cyrstalline phases. It is thus suggested that the principal constituents of the matrix are in fact O' and β' sialons. (orig.)

  6. Ultrasonic characterization of microwave joined silicon carbide/silicon carbide

    International Nuclear Information System (INIS)

    High frequency (50--150 MHz), ultrasonic immersion testing has been used to characterize the surface and interfacial joint conditions of microwave bonded, monolithic silicon carbide (SiC) materials. The high resolution ultrasonic C-scan images point to damage accumulation after thermal cycling. Image processing was used to study the effects of the thermal cycling on waveform shape, amplitude and distribution. Such information is useful for concurrently engineering material fabrication processes and suitable nondestructive test procedures

  7. Methods for producing silicon carbide fibers

    Energy Technology Data Exchange (ETDEWEB)

    Garnier, John E.; Griffith, George W.

    2016-03-01

    Methods of producing silicon carbide fibers. The method comprises reacting a continuous carbon fiber material and a silicon-containing gas in a reaction chamber at a temperature ranging from approximately 1500.degree. C. to approximately 2000.degree. C. A partial pressure of oxygen in the reaction chamber is maintained at less than approximately 1.01.times.10.sup.2 Pascal to produce continuous alpha silicon carbide fibers. Continuous alpha silicon carbide fibers and articles formed from the continuous alpha silicon carbide fibers are also disclosed.

  8. Valence band offset and Schottky barrier at amorphous boron and boron carbide interfaces with silicon and copper

    International Nuclear Information System (INIS)

    In order to understand the fundamental charge transport in a-B:H and a-BX:H (X = C, N, P) compound heterostructure devices, X-ray photoelectron spectroscopy has been utilized to determine the valence band offset and Schottky barrier present at amorphous boron compound interfaces formed with (1 0 0) Si and polished poly-crystalline Cu substrates. For interfaces formed by plasma enhanced chemical vapor deposition of a-B4–5C:H on (1 0 0) Si, relatively small valence band offsets of 0.2 ± 0.2 eV were determined. For a-B:H/Cu interfaces, a more significant Schottky barrier of 0.8 ± 0.16 eV was measured. These results are in contrast to those observed for a-BN:H and BP where more significant band discontinuities (>1–2 eV) were observed for interfaces with Si and Cu.

  9. Valence band offset and Schottky barrier at amorphous boron and boron carbide interfaces with silicon and copper

    Energy Technology Data Exchange (ETDEWEB)

    King, Sean W., E-mail: sean.king@intel.com [Logic Technology Development, Intel Corporation, 5200 NE Elam Young Parkway, Hillsboro, OR 97124 (United States); French, Marc; Xu, Guanghai [Logic Technology Development, Intel Corporation, 5200 NE Elam Young Parkway, Hillsboro, OR 97124 (United States); French, Benjamin [Ocotillo Materials Laboratory, Intel Corporation, 4500 S. Dobson Road, Chandler, AZ 85248 (United States); Jaehnig, Milt; Bielefeld, Jeff; Brockman, Justin; Kuhn, Markus [Logic Technology Development, Intel Corporation, 5200 NE Elam Young Parkway, Hillsboro, OR 97124 (United States)

    2013-11-15

    In order to understand the fundamental charge transport in a-B:H and a-BX:H (X = C, N, P) compound heterostructure devices, X-ray photoelectron spectroscopy has been utilized to determine the valence band offset and Schottky barrier present at amorphous boron compound interfaces formed with (1 0 0) Si and polished poly-crystalline Cu substrates. For interfaces formed by plasma enhanced chemical vapor deposition of a-B{sub 4–5}C:H on (1 0 0) Si, relatively small valence band offsets of 0.2 ± 0.2 eV were determined. For a-B:H/Cu interfaces, a more significant Schottky barrier of 0.8 ± 0.16 eV was measured. These results are in contrast to those observed for a-BN:H and BP where more significant band discontinuities (>1–2 eV) were observed for interfaces with Si and Cu.

  10. Laser micromachining of silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Sciti, D.; Bellosi, A. [CNR-IRTEC, Faenza (Italy). Research Inst. for Ceramics Technology

    2002-07-01

    Two different laser processing procedures on silicon carbide are studied: i) surface treatment through a pulsed KrF excimer laser, with the aim of evaluating the surface microstructure modifications and variation the surface roughness in function of the processing parameters. In all the cases, the presence of a thin scale due to melting and solidification, crack formation and surface pores closure were observed. ii) A pulsed CO{sub 2} laser was used to form a micro-holes texture on the surface of silicon carbide. Holes dimensions in the range 80-100 {mu}m were obtained using a laser power of 0.5 kW and pulse duration of 1 ms. The possibility of producing a regular array of microholes was demonstrated. (orig.)

  11. Thermally Sprayed Silicon Carbide Coating

    OpenAIRE

    Mubarok, Fahmi

    2014-01-01

    Thermal spraying of silicon carbide (SiC) material is a challenging task since SiC tends to decompose during elevated temperature atmospheric spraying process. The addition of metal or ceramic binders as a matrix phase is necessary to facilitate the bonding of SiC particles, allowing SiC coatings to be deposited. In the conventional procedure, the matrix phase is added through mechanical mixing or mechanical alloying of the powder constituents, making it difficult to achieve homogeneous distr...

  12. Effect of hydrogen on the microstructure of silicon carbide

    International Nuclear Information System (INIS)

    The effect of hydrogenation on the microstructure of a pressureless sintered silicon carbide was studied. Samples which were annealed in a 40:60 mole % H2:Ar atmosphere at 14000C for 50 hours were microstructurally compared with unannealed samples and samples that had been annealed in a similar manner but using an argon atmosphere. The results were also compared with microstructural results obtained from in situ studies using both hydrogen and argon atmospheres. These results were compared with a thermodynamic model which was constructed using a free energy minimization technique. The observed effects of hydrogenation were surface decarburization and amorphization throughout the silicon carbide material. Other observations include the thermally induced growth of microcrystalline silicon and accelerated amorphization around the silicon microcrystals in samples used in hydrogen in situ studies. An analysis of the microstructure of the reference material was also performed

  13. Silicon carbide as platform for energy applications

    OpenAIRE

    Syväjärvi, Mikael; Jokubavicius, Valdas; Sun, Jianwu; Liu, Xinyu; Løvvik, Ole Martin; Ou, Haiyan; Wellmann, Peter

    2015-01-01

    Silicon carbide is emerging as a novel material for a range of energy and environmental technologies. Previously, silicon carbide was considered as a material mainly for transistor applications. We have initiated the use of silicon carbide material towards optoelectronics in general lighting and solar cells, and further pursue concepts in materials for thermoelectrics, biofuel cells and supercapacitor research proposals. In fact, there are a number of energy applications which can be based on...

  14. Polytype distribution in circumstellar silicon carbide.

    Science.gov (United States)

    Daulton, T L; Bernatowicz, T J; Lewis, R S; Messenger, S; Stadermann, F J; Amari, S

    2002-06-01

    The inferred crystallographic class of circumstellar silicon carbide based on astronomical infrared spectra is controversial. We have directly determined the polytype distribution of circumstellar SiC from transmission electron microscopy of presolar silicon carbide from the Murchison carbonaceous meteorite. Only two polytypes (of a possible several hundred) were observed: cubic 3C and hexagonal 2H silicon carbide and their intergrowths. We conclude that this structural simplicity is a direct consequence of the low pressures in circumstellar outflows and the corresponding low silicon carbide condensation temperatures. PMID:12052956

  15. High-Q silicon carbide photonic-crystal cavities

    International Nuclear Information System (INIS)

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 104 with mode volume ∼0.60(λ/n)3 at wavelength 1.5 μm. A corresponding Purcell factor value of ∼104 is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics

  16. High-Q silicon carbide photonic-crystal cavities

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jonathan Y. [Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627 (United States); Lu, Xiyuan [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); Lin, Qiang, E-mail: qiang.lin@rochester.edu [Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627 (United States); Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

    2015-01-26

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 10{sup 4} with mode volume ∼0.60(λ/n){sup 3} at wavelength 1.5 μm. A corresponding Purcell factor value of ∼10{sup 4} is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

  17. Fabrication of silicon nitride-silicon carbide nanocomposite ceramics

    International Nuclear Information System (INIS)

    Silicon nitride-silicon carbide nanocomposites have so far been fabricated by hot-pressing fine amorphous Si-C-N powder produced by CVD. This composite exhibited excellent strength and fracture toughness and maintained high strength to temperatures above 1200 C. The current work deals with the fabrication of nanocomposites produced using mixtures of Si3N4 and nanosize SiC powders. Conventional processing techniques were used to optimise the dispersion of the SiC particles. Densification was achieved by pressureless sintering, gas pressure sintering and sinter/HIPping. Mechanical properties such as hardness, fracture toughness and strength at room temperature were assessed. The nanocomposites produced were compared with composites produced using alternative starting materials. (orig.)

  18. Silicon carbide nanowires synthesized with phenolic resin and silicon powders

    Science.gov (United States)

    Zhao, Hongsheng; Shi, Limin; Li, Ziqiang; Tang, Chunhe

    2009-02-01

    Large-scale silicon carbide nanowires with the lengths up to several millimeters were synthesized by a coat-mix, moulding, carbonization, and high-temperature sintering process, using silicon powder and phenolic resin as the starting materials. Ordinary SiC nanowires, bamboo-like SiC nanowires, and spindle SiC nanochains are found in the fabricated samples. The ordinary SiC nanowire is a single-crystal SiC phase with a fringe spacing of 0.252 nm along the [1 1 1] growth direction. Both of the bamboo-like SiC nanowires and spindle SiC nanochains exhibit uniform periodic structures. The bamboo-like SiC nanowires consist of amorphous stem and single-crystal knots, while the spindle SiC nanochains consist of uniform spindles which grow uniformly on the entire nanowires.

  19. A study of silicon carbide synthesis from waste serpentine.

    Science.gov (United States)

    Cheng, T W; Hsu, C W

    2006-06-01

    There are 60000 tons of serpentine wastes produced in year 2004 in Taiwan. This is due to the well-developed joints in the serpentine ore body as well as the stringent requirements of the particle size and chemical composition of serpentine by iron making company. The waste also creates considerable environmental problems. The purpose of this study is reutilization of waste serpentine to produce a high value silica powder after acid leaching. These siliceous microstructure products obtained from serpentine would be responsible for high reactivity and characteristic molecular sieving effect. In this study, the amorphous silica powder was then synthesized to silicon carbide with the C/SiO(2) molar ratio of 3. The experiment results show that silicon carbide can be synthesized in 1550 degrees C. The formed silicon carbide was whisker beta type SiC which can be used as raw materials for industry. PMID:16405956

  20. Material properties of silicon and silicon carbide foams

    Science.gov (United States)

    Jacoby, Marc T.; Goodman, William A.

    2005-08-01

    Silicon and silicon carbide foams provide the lightweighting element for Schafer Corporation's silicon and silicon carbide lightweight mirror systems (SLMSTM and SiC-SLMSTM). SLMSTM and SiC-SLMSTM provide the enabling technology for manufacturing lightweight, athermal optical sub-assemblies and instruments. Silicon and silicon carbide foam samples were manufactured and tested under a Schafer-funded Internal Research and Development program in various configurations to obtain mechanical and thermal property data. The results of the mechanical tests that are reported in this paper include Young's modulus, compression strength, tensile strength, Poisson's ratio and vibrational damping. The results of the thermal tests include thermal conductivity and coefficient of thermal expansion.

  1. Plasma Deposition of Amorphous Silicon

    Science.gov (United States)

    Calcote, H. F.

    1982-01-01

    Strongly adhering films of silicon are deposited directly on such materials as Pyrex and Vycor (or equivalent materials) and aluminum by a non-equilibrium plasma jet. Amorphous silicon films are formed by decomposition of silicon tetrachloride or trichlorosilane in the plasma. Plasma-jet technique can also be used to deposit an adherent silicon film on aluminum from silane and to dope such films with phosphorus. Ability to deposit silicon films on such readily available, inexpensive substrates could eventually lead to lower cost photovoltaic cells.

  2. Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

    OpenAIRE

    Khan, R U A; Silva, S. R. P.; Van Swaaij, R.A.C.M.M.

    2003-01-01

    Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p layer had to be reduced from 9 to 2.5 nm in order to ensure sufficient conduction through the PAC film. Although the resulting external parameters suggest a decrease in the device efficiency from 9...

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

    Science.gov (United States)

    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

  4. Amorphous silicon germanium carbide photo sensitive bipolar junction transistor with a base-contact and a continuous tunable high current gain

    Energy Technology Data Exchange (ETDEWEB)

    Bablich, A., E-mail: andreas.bablich@uni-siegen.de [Department of Electrical and Computer Engineering, Institute for Microsystem Technologies, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany); Merfort, C., E-mail: merfort@imt.e-technik.uni-siegen.de [Department of Electrical and Computer Engineering, Institute for Microsystem Technologies, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany); Eliasz, J., E-mail: jacek.eliasz@student.uni-siegen.de [Department of Electrical and Computer Engineering, Institute for Microsystem Technologies, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany); Schäfer-Eberwein, H., E-mail: heiko.schaefer@uni-siegen.de [Department of Electrical and Computer Engineering, Institute of High Frequency and Quantum Electronics, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany); Haring-Bolivar, P., E-mail: peter.haring@uni-siegen.de [Department of Electrical and Computer Engineering, Institute of High Frequency and Quantum Electronics, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany); Boehm, M., E-mail: markus.boehm@uni-siegen.de [Department of Electrical and Computer Engineering, Institute for Microsystem Technologies, University of Siegen, Hoelderlinstrasse 3, 57076 Siegen (Germany)

    2014-05-02

    In this paper, the design, fabrication and characterization of an amorphous silicon germanium carbide (a-SiGeC:H) photo sensitive bipolar junction transistor (PS-BJT) with three terminals are presented. Whereas the current gain of similar transistor devices presented in the past (Wu et al., 1984; Hwang et al., 1993; Nascetti and Caputo, 2002; Chang et al., 1985a,b; Wu et al, 1985; Hong et al., 1990) can only be controlled with photo induced charge generation, the n–i–δp–i–n structure developed features a contacted base to provide the opportunity to adjust the current gain optically and electrically, too. Electron microscope-, current-/voltage- and spectral measurements were performed to study the PS-BJT behavior and calculate the electrical and optical current gain. The spectral response maximum of the base–collector diode has a value of 170 mA/W applying a base–collector voltage of − 1 V and is located at 620 nm. The base–emitter diode reaches a sensitivity of 25.7 mA/W at 530 nm with a base-emitter voltage of − 3 V. The good a-Si:H transport properties are validated in a μτ-product of 4.6 × 10{sup −6} cm{sup 2} V s, which is sufficient to reach a continuous base- and photo-tunable current gain of up to − 126 at a base current of I{sub B} = + 10 nA and a collector–emitter voltage of V{sub CE} = − 3 V. The transistor obtains a maximum collector current of − 65.5 μA (V{sub CE} = − 3 V) and + 56.2 μA (V{sub CE} = + 3 V) at 10,000 lx 5300 K white-light illumination. At 3300 lx, the electrical current gain reaches a value of + 100 (V{sub CE} = + 2 V) at I{sub B} = 10 nA. With a negative base current of I{sub B} = − 10 nA the electrical gain can be adjusted between 87 (V{sub CE} = + 2 V) and − 106 (V{sub CE} = -3 V), respectively. When no base charge is applied, the transistor is “off” for V{sub CE} > − 3 V. Reducing the base current increases the electrical current gain. Operating with a voltage V{sub CE} of just ± 2 V

  5. Amorphous silicon germanium carbide photo sensitive bipolar junction transistor with a base-contact and a continuous tunable high current gain

    International Nuclear Information System (INIS)

    In this paper, the design, fabrication and characterization of an amorphous silicon germanium carbide (a-SiGeC:H) photo sensitive bipolar junction transistor (PS-BJT) with three terminals are presented. Whereas the current gain of similar transistor devices presented in the past (Wu et al., 1984; Hwang et al., 1993; Nascetti and Caputo, 2002; Chang et al., 1985a,b; Wu et al, 1985; Hong et al., 1990) can only be controlled with photo induced charge generation, the n–i–δp–i–n structure developed features a contacted base to provide the opportunity to adjust the current gain optically and electrically, too. Electron microscope-, current-/voltage- and spectral measurements were performed to study the PS-BJT behavior and calculate the electrical and optical current gain. The spectral response maximum of the base–collector diode has a value of 170 mA/W applying a base–collector voltage of − 1 V and is located at 620 nm. The base–emitter diode reaches a sensitivity of 25.7 mA/W at 530 nm with a base-emitter voltage of − 3 V. The good a-Si:H transport properties are validated in a μτ-product of 4.6 × 10−6 cm2 V s, which is sufficient to reach a continuous base- and photo-tunable current gain of up to − 126 at a base current of IB = + 10 nA and a collector–emitter voltage of VCE = − 3 V. The transistor obtains a maximum collector current of − 65.5 μA (VCE = − 3 V) and + 56.2 μA (VCE = + 3 V) at 10,000 lx 5300 K white-light illumination. At 3300 lx, the electrical current gain reaches a value of + 100 (VCE = + 2 V) at IB = 10 nA. With a negative base current of IB = − 10 nA the electrical gain can be adjusted between 87 (VCE = + 2 V) and − 106 (VCE = -3 V), respectively. When no base charge is applied, the transistor is “off” for VCE > − 3 V. Reducing the base current increases the electrical current gain. Operating with a voltage VCE of just ± 2 V, the device presented in this paper obtains no optical gain with an incident

  6. Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

    Science.gov (United States)

    Chang, Geng-Rong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2011-12-01

    Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon. PMID:22409005

  7. TEM and RBS studies of hydrogen implanted silicon and silicon carbide

    International Nuclear Information System (INIS)

    Single crystal silicon and silicon carbide were implanted at temperatures of 960K, 3000K and 8000K with 50 keV to 80 keV H+ ions to fluences of 2 x 10 17 H+/cm2 or 8 x 1017 H+/cm2. Post implantation annealing was conducted at >8000K. Microstructural changes were investigated with cross-sectional TEM and RBS/channeling. Results show that for silicon, a highly hydrogen doped amorphous layer is formed at 960K whereas at 3000K, crystallinity is maintained despite hydrogen trapping. Annealing behavior depends strongly upon the as-implanted microstructure and the stability of the Si-H layer. Silicon carbide develops an amorphous damage layer at temperatures 0K when implanted with 8 x 1017 H+/cm2. (author)

  8. In situ-grown hexagonal silicon nanocrystals in silicon carbide-based films.

    Science.gov (United States)

    Kim, Tae-Youb; Huh, Chul; Park, Nae-Man; Choi, Cheol-Jong; Suemitsu, Maki

    2012-01-01

    Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by adjusting the flow rate of the silane gas. We suggest that this phenomenon is attributed to the quantum confinement effect of hexagonal Si-NCs in silicon carbide-based film with a change in the sizes and emission states of the NCs. PMID:23171576

  9. Synthesis of silicon carbide at room temperature from colloidal suspensions of silicon dioxide and carbon nanotubes

    Science.gov (United States)

    Zhukalin, D. A.; Tuchin, A. V.; Kulikova, T. V.; Bityutskaya, L. A.

    2015-11-01

    Experimental and theoretical approaches were used for the investigation of mechanisms and conditions of self-organized nanostructures formation in the drying drop of the mixture of colloidal suspensions of nanoscale amorphous silicon dioxide and carbon nanotubes. The formation of rodlike structures with diameter 250-300nm and length ∼4pm was revealed. The diffraction analysis of the obtained nanostructures showed the formation of the silicon carbide phase at room temperature.

  10. Characterization of silicon-silicon carbide ceramic derived from carbon-carbon silicon carbide composites

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Vijay K. [Indian Institute of Technology, Varanasi (India). Dept. of Mechanical Engineering; Krenkel, Walter [Univ. of Bayreuth (Germany). Dept. of Ceramic Materials Engineering

    2013-04-15

    The main objective of the present work is to process porous silicon - silicon carbide (Si - SiC) ceramic by the oxidation of carboncarbon silicon carbide (C/C - SiC) composites. Phase studies are performed on the oxidized porous composite to examine the changes due to the high temperature oxidation. Further, various characterization techniques are performed on Si- SiC ceramics in order to study the material's microstructure. The effects of various parameters such as fiber alignment (twill weave and short/chopped fiber) and phenolic resin type (resol and novolak) are characterized.

  11. Production and characterization of nanostructured silicon carbide

    Science.gov (United States)

    Wallis, Kendra Lee

    Nanostructured materials continue to attract attention because of their new and interesting properties, which are very different from their macrostructured equivalents. Since the size of grain and surface differs, a better understanding of the microstructure, the mechanism of formation, and methods of controlling surface properties is necessary. In this study, nanostructured silicon carbide has been produced from the solid-solid reaction of a mixture of silicon nanopowder and carbon multiwalled nanotubes (MWNT) sintered by induction. A study of the reaction rate at different temperatures has yielded a value for the activation energy of 254 +/- 36 kJ/mol, and has led to the conclusion that the reaction is diffusion-controlled. A second method produced pure silicon carbide nanowires using a procedure which kept the solid reactants, silicon powder and MWNT, separated while sintering at a constant temperature of 1200°C. Silicon in the vapor-phase reacted at the surface of the MWNTs followed by diffusion of both precursors through the product phase boundary. The reaction time was varied, and a morphological study has been done describing changes in shape and size as a function of time. The initial reaction produced a layer of SiC providing the outer shell of coaxial structures with carbon nanotubes inside. As Si and C diffused through the product phase to react at the interface, the tube became filled with SiC to form solid SiC nanowires, and the outer diameter of the nanowires grew continuously as reaction time increased. After long sintering times, growth continued in two dimensions, fusing nanowires together into planar structures. In addition, the precursor form of carbon was varied, and nanowires produced by two different types of nanotubes have been studied. The produced SiC nanowires show cubic crystal structure. After a few hours of sintering, stacking faults began to occur inside the wires, and the frequency of occurrence of the stacking faults increased as

  12. Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica.

    Science.gov (United States)

    Luo, Xiaogang; Ma, Wenhui; Zhou, Yang; Liu, Dachun; Yang, Bin; Dai, Yongnian

    2009-01-01

    Silicon carbide nanowires have been synthesized at 1400 degrees C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core-shell structure and grow along direction. The diameter of silicon carbide nanowires is about 50-200 nm and the length from tens to hundreds of micrometers. The vapor-solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core-shell interface. PMID:20651911

  13. Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

    Directory of Open Access Journals (Sweden)

    Luo Xiaogang

    2009-01-01

    Full Text Available Abstract Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core–shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50–200 nm and the length from tens to hundreds of micrometers. The vapor–solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core–shell interface.

  14. Synthesis and Characterization of Amorphous Carbide-based Thin Films

    OpenAIRE

    Folkenant, Matilda

    2015-01-01

    In this thesis, research on synthesis, structure and characterization of amorphous carbide-based thin films is presented. Crystalline and nanocomposite carbide films can exhibit properties such as high electrical conductivity, high hardness and low friction and wear. These properties are in many cases structure-related, and thus, within this thesis a special focus is put on how the amorphous structure influences the material properties. Thin films within the Zr-Si-C and Cr-C-based systems hav...

  15. Adjustable ultraviolet sensitive detectors based on amorphous silicon

    OpenAIRE

    TOPIC, M; Stiebig, H.; Krause, M.; Wagner, H.

    2001-01-01

    Thin-film detectors made of hydrogenated amorphous silicon (LI-Si:H) and amorphous silicon carbide (a-SiC:H) with adjustable sensitivity in the ultraviolet (UV) spectrum were developed. Thin PIN diodes deposited on glass substrates in N-I-P layer sequence with a total thickness of down to 33 nm and a semitransparent Ag front contact were fabricated. The optimized diodes with a 10 nm Ag contact exhibit spectral response values above 80 mA/W in the wavelength range from 295 to 395 nm with a max...

  16. Atomic structure of amorphous shear bands in boron carbide.

    Science.gov (United States)

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses. PMID:24052052

  17. Subsurface damage of single crystalline silicon carbide in nanoindentation tests.

    Science.gov (United States)

    Yan, Jiwang; Gai, Xiaohui; Harada, Hirofumi

    2010-11-01

    The response of single crystalline silicon carbide (SiC) to a Berkovich nanoindenter was investigated by examining the indents using a transmission electron microscope and the selected area electron diffraction technique. It was found that the depth of indentation-induced subsurface damage was far larger than the indentation depth, and the damaging mechanism of SiC was distinctly different from that of single crystalline silicon. For silicon, a broad amorphous region is formed underneath the indenter after unloading; for SiC, however, no amorphous phase was detected. Instead, a polycrystalline structure with a grain size of ten nanometer level was identified directly under the indenter tip. Micro cracks, basal plane dislocations and possible cross slips were also found around the indent. These finding provide useful information for ultraprecision manufacturing of SiC wafers. PMID:21138038

  18. Silicon Carbide Solar Cells Investigated

    Science.gov (United States)

    Bailey, Sheila G.; Raffaelle, Ryne P.

    2001-01-01

    The semiconductor silicon carbide (SiC) has long been known for its outstanding resistance to harsh environments (e.g., thermal stability, radiation resistance, and dielectric strength). However, the ability to produce device-quality material is severely limited by the inherent crystalline defects associated with this material and their associated electronic effects. Much progress has been made recently in the understanding and control of these defects and in the improved processing of this material. Because of this work, it may be possible to produce SiC-based solar cells for environments with high temperatures, light intensities, and radiation, such as those experienced by solar probes. Electronics and sensors based on SiC can operate in hostile environments where conventional silicon-based electronics (limited to 350 C) cannot function. Development of this material will enable large performance enhancements and size reductions for a wide variety of systems--such as high-frequency devices, high-power devices, microwave switching devices, and high-temperature electronics. These applications would supply more energy-efficient public electric power distribution and electric vehicles, more powerful microwave electronics for radar and communications, and better sensors and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines. The 6H-SiC polytype is a promising wide-bandgap (Eg = 3.0 eV) semiconductor for photovoltaic applications in harsh solar environments that involve high-temperature and high-radiation conditions. The advantages of this material for this application lie in its extremely large breakdown field strength, high thermal conductivity, good electron saturation drift velocity, and stable electrical performance at temperatures as high as 600 C. This behavior makes it an attractive photovoltaic solar cell material for devices that can operate within three solar radii of the Sun.

  19. Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor

    Science.gov (United States)

    Barnard, Thomas Duncan (Inventor); Lipowitz, Jonathan (Inventor); Nguyen, Kimmai Thi (Inventor)

    2001-01-01

    A process for producing polycrystalline silicon carbide by heating an amorphous ceramic fiber that contains silicon and carbon in an environment containing boron oxide vapor. The boron oxide vapor is produced in situ by the reaction of a boron containing material such as boron carbide and an oxidizing agent such as carbon dioxide, and the amount of boron oxide vapor can be controlled by varying the amount and rate of addition of the oxidizing agent.

  20. Amorphous silicon crystalline silicon heterojunction solar cells

    CERN Document Server

    Fahrner, Wolfgang Rainer

    2013-01-01

    Amorphous Silicon/Crystalline Silicon Solar Cells deals with some typical properties of heterojunction solar cells, such as their history, the properties and the challenges of the cells, some important measurement tools, some simulation programs and a brief survey of the state of the art, aiming to provide an initial framework in this field and serve as a ready reference for all those interested in the subject. This book helps to ""fill in the blanks"" on heterojunction solar cells. Readers will receive a comprehensive overview of the principles, structures, processing techniques and the curre

  1. Direct plasmadynamic synthesis of ultradisperse silicon carbide

    Science.gov (United States)

    Sivkov, A. A.; Nikitin, D. S.; Pak, A. Ya.; Rakhmatullin, I. A.

    2013-01-01

    Ultradisperse cubic silicon carbide (β-SiC) has been obtained by direct plasmadynamic synthesis in pulsed supersonic carbon-silicon plasma jet incident on a copper obstacle in argon atmosphere. The powdered product has a high content of β-SiC in the form of single crystals with average size of about 100 nm and nearly perfect crystallographic habit.

  2. 13C NMR spectroscopy of amorphous hydrogenated carbon and amorphous hydrogenated boron carbide

    International Nuclear Information System (INIS)

    We report the 13C NMR spectrum of amorphous hydrogenated carbon and boron carbide. The amorphous hydrogenated carbon spectra consist primarily of an sp3 line at 40 ppm and an sp2 line at 140 ppm and are in reasonable agreement with the recent theoretical calculations of Mauri, Pfrommer, and Louie, but there are some notable discrepancies. The amorphous hydrogenated boron carbide spectra are very different from those of amorphous hydrogenated carbon, being dominated by one line at 15 ppm. We interpret this line as due to carbon bound in boron carbide icosahedra, because polycrystalline boron carbide with boron carbide icosahedra as the unit cell gives very similar NMR spectra. copyright 1999 The American Physical Society

  3. Exoelectron analysis of amorphous silicon

    Science.gov (United States)

    Dekhtyar, Yu. D.; Vinyarskaya, Yu. A.

    1994-04-01

    The method based on registration of photothermostimulated exoelectron emission (PTSE) is used in the proposed new field of investigating the structural defects in amorphous silicon (a-Si). This method can be achieved if the sample under investigation is simultaneously heated and illuminated by ultraviolet light. The mechanism of PTSE from a-Si has been studied in the case of a hydrogenized amorphous silicon (a-Si:H) film grown by glow discharge method. The electronic properties and annealing of defects were analyzed in the study. It has been shown from the results that the PTSE from a-Si:H takes place as a prethreshold single-photon external photoeffect. The exoemission spectroscopy of a-Si:H was shown to be capable in the study of thermally and optically stimulated changes in the electronic structure of defects, their annealing, as well as diffusion of atomic particles, such as hydrogen.

  4. Colloidal Photoluminescent Amorphous Porous Silicon, Methods Of Making Colloidal Photoluminescent Amorphous Porous Silicon, And Methods Of Using Colloidal Photoluminescent Amorphous Porous Silicon

    KAUST Repository

    Chaieb, Sahraoui

    2015-04-09

    Embodiments of the present disclosure provide for a colloidal photoluminescent amorphous porous silicon particle suspension, methods of making a colloidal photoluminescent amorphous porous silicon particle suspension, methods of using a colloidal photoluminescent amorphous porous silicon particle suspension, and the like.

  5. Initial results and long-term clinical follow-up of an amorphous hydrogenated silicon-carbide-coated stent in daily practice.

    Science.gov (United States)

    Hanekamp, Clara EE; Bonnier, Hans JRM; Michels, Rolf H; Peels, Kathinka H; Heijmen, Eric PCM; Hagen Ev, Eduard van; Koolen, Jacques J

    1998-01-01

    The hemocompatibility and biocompatibility of a stent are determined by the physical and electrochemical properties of the stent surface. The aim of this study was to determine the feasibility, safety and efficacy of implantation of a stent coated with silicon carbide. Baseline characteristics were collected prospectively. The occurrence of cardiac adverse events and the angina score were assessed at clinical follow-up. A total of 193 Tensum stents were implanted in 174 patients. In hospital, one patient experienced stent thrombosis and in 6% of the patients a creatinine kinase elevation to 240 U/l or more occurred. Long-term follow-up was performed in 172 patients, with a mean follow-up of 454 +/- 181 days. Ninety-seven per cent were still alive, 15% had undergone target-vessel revascularization, and 2% had angiographic restenosis and were treated with medication only. Seventy-one per cent of the patients were free of anginal complaints, and 20% had anginal complaints in Canadian Cardiac Society class I or II. The Tensum coronary stent showed to be a safe and efficacious device in this study, with a high primary success rate and favorable long-term clinical followup. PMID:12623396

  6. Amorphous silicon based betavoltaic devices

    OpenAIRE

    Wyrsch, N; Riesen, Y.; Franco, A; S. Dunand; Kind, H.; Schneider, S.; Ballif, C.

    2013-01-01

    Hydrogenated amorphous silicon betavoltaic devices are studied both by simulation and experimentally. Devices exhibiting a power density of 0.1 μW/cm2 upon Tritium exposure were fabricated. However, a significant degradation of the performance is taking place, especially during the first hours of the exposure. The degradation behavior differs from sample to sample as well as from published results in the literature. Comparisons with degradation from beta particles suggest an effect of tritium...

  7. Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

    Science.gov (United States)

    Tanaka, Hidehiko

    1987-01-01

    A silicon carbide powder of a 5-micron grain size is mixed with 0.15 to 0.60 wt% mixture of a boron compound, i.e., boric acid, boron carbide (B4C), silicon boride (SiB4 or SiB6), aluminum boride, etc., and an aluminum compound, i.e., aluminum, aluminum oxide, aluminum hydroxide, aluminum carbide, etc., or aluminum boride (AlB2) alone, in such a proportion that the boron/aluminum atomic ratio in the sintered body becomes 0.05 to 0.25 wt% and 0.05 to 0.40 wt%, respectively, together with a carbonaceous additive to supply enough carbon to convert oxygen accompanying raw materials and additives into carbon monoxide.

  8. Stoichiometric Defects in Silicon Carbide

    International Nuclear Information System (INIS)

    Defect structures showing odd-membered rings are known features of several tetrahedral semiconductors as well as carbon nano-structures; examples of them are bond defects in crystalline and amorphous silicon, Stone Wales defects in fullerenes and carbon nano-tubes, and the core structure of partial dislocations in some tetrahedral semiconductors. We investigate, using Density Functional Theory, two types of stoichiometry-conserving defects, which we call SCD and anti-SCD and which are metastable structures presenting five- and seven-membered rings, both in the cubic and in the hexagonal 4H-SiC polytypes. We also investigate the annealing properties of the two mentioned variants and find that one of them (SCD) easily disappears, turning back to a normal site, while the other (anti-SCD) transforms to an antisite pair, overcoming a barrier of 0. 21 eV. The very short lifetimes at ambient conditions explain why those defects have not been observed up to now, but they suggest they should be observable at very low temperature, and we provide local vibrational modes to facilitate their identification. (authors)

  9. Method of fabricating porous silicon carbide (SiC)

    Science.gov (United States)

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

    1995-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  10. Amorphous-silicon cell reliability testing

    Science.gov (United States)

    Lathrop, J. W.

    1985-01-01

    The work on reliability testing of solar cells is discussed. Results are given on initial temperature and humidity tests of amorphous silicon devices. Calibration and measurement procedures for amorphous and crystalline cells are given. Temperature stress levels are diagrammed.

  11. Continuous method of producing silicon carbide fibers

    Science.gov (United States)

    Barnard, Thomas Duncan (Inventor); Nguyen, Kimmai Thi (Inventor); Rabe, James Alan (Inventor)

    1999-01-01

    This invention pertains to a method for production of polycrystalline ceramic fibers from silicon oxycarbide (SiCO) ceramic fibers wherein the method comprises heating an amorphous ceramic fiber containing silicon and carbon in an inert environment comprising a boron oxide and carbon monoxide at a temperature sufficient to convert the amorphous ceramic fiber to a polycrystalline ceramic fiber. By having carbon monoxide present during the heating of the ceramic fiber, it is possible to achieve higher production rates on a continuous process.

  12. Silicon carbide, an emerging high temperature semiconductor

    Science.gov (United States)

    Matus, Lawrence G.; Powell, J. Anthony

    In recent years, the aerospace propulsion and space power communities have expressed a growing need for electronic devices that are capable of sustained high temperature operation. Applications for high temperature electronic devices include development instrumentation within engines, engine control, and condition monitoring systems, and power conditioning and control systems for space platforms and satellites. Other earth-based applications include deep-well drilling instrumentation, nuclear reactor instrumentation and control, and automotive sensors. To meet the needs of these applications, the High Temperature Electronics Program at the Lewis Research Center is developing silicon carbide (SiC) as a high temperature semiconductor material. Research is focussed on developing the crystal growth, characterization, and device fabrication technologies necessary to produce a family of silicon carbide electronic devices and integrated sensors. The progress made in developing silicon carbide is presented, and the challenges that lie ahead are discussed.

  13. An improved method of preparing silicon carbide

    International Nuclear Information System (INIS)

    A method of preparing silicon carbide is described which comprises forming a desired shape from a polysilane of the average formula:[(CH3)2Si][CH3Si]. The polysilane contains from 0 to 60 mole percent (CH3)2Si units and from 40 to 100 mole percent CH3Si units. The remaining bonds on the silicon are attached to another silicon atom or to a halogen atom in such manner that the average ratio of halogen to silicon in the polysilane is from 0.3:1 to 1:1. The polysilane has a melt viscosity at 1500C of from 0.005 to 500 Pa.s and an intrinsic viscosity in toluene of from 0.0001 to 0.1. The shaped polysilane is heated in an inert atmosphere or in a vacuum to an elevated temperature until the polysilane is converted to silicon carbide. (author)

  14. Silicon carbide microsystems for harsh environments

    CERN Document Server

    Wijesundara, Muthu B J

    2011-01-01

    Silicon Carbide Microsystems for Harsh Environments reviews state-of-the-art Silicon Carbide (SiC) technologies that, when combined, create microsystems capable of surviving in harsh environments, technological readiness of the system components, key issues when integrating these components into systems, and other hurdles in harsh environment operation. The authors use the SiC technology platform suite the model platform for developing harsh environment microsystems and then detail the current status of the specific individual technologies (electronics, MEMS, packaging). Additionally, methods

  15. Wear and wear transition in silicon carbide ceramics during sliding

    International Nuclear Information System (INIS)

    Wear and wear transition in silicon carbide ceramics during sliding have been investigated. Three different microstructures, i.e., solid-state-sintered silicon carbide, liquid-phase-sintered silicon carbide, and a liquid-phase-sintered SiC-TiB2 composite, were produced by hot pressing. Wear data and examinations of worn surfaces showed that the wear behavior of these silicon carbide ceramics was significantly different. In the solid-state-sintered silicon carbide, the wear occurred by a grooving process. In the liquid-phase-sintered silicon carbide and composite, on the other hand, an abrupt transition in the wear mechanism from an initial grooving process to a grain pullout process occurred during the test. The transition occurred significantly earlier in the composite than in the carbide. The different wear behavior in these silicon carbide ceramics is discussed in relation to the grain or interphase boundary strength

  16. Rapid thermal annealing and crystallization mechanisms study of silicon nanocrystal in silicon carbide matrix

    OpenAIRE

    Wan Zhenyu; Huang Shujuan; Green Martin; Conibeer Gavin

    2011-01-01

    Abstract In this paper, a positive effect of rapid thermal annealing (RTA) technique has been researched and compared with conventional furnace annealing for Si nanocrystalline in silicon carbide (SiC) matrix system. Amorphous Si-rich SiC layer has been deposited by co-sputtering in different Si concentrations (50 to approximately 80 v%). Si nanocrystals (Si-NC) containing different grain sizes have been fabricated within the SiC matrix under two different annealing conditions: furnace anneal...

  17. Amorphous silicon based solar cells

    OpenAIRE

    Al Tarabsheh, Anas

    2007-01-01

    This thesis focuses on the deposition of hydrogenated amorphous silicon (a-Si:H) films bymeans of plasma enhanced chemical vapour deposition (PECVD). This technique allows the growth of device quality a-Si:H at relatively low deposition temperatures, below 140 °C and, therefore, enables the use of low-cost substrates, e.g. plastic foils. The maximum efficiencies of a-Si:H solar cells in this work are η= 6.8 % at a deposition temperature Tdep = 180 °C and η = 4.9 % at a deposition ...

  18. Amorphous silicon based radiation detectors

    International Nuclear Information System (INIS)

    We describe the characteristics of thin(1 μm) and thick (>30μm) hydrogenated amorphous silicon p-i-n diodes which are optimized for detecting and recording the spatial distribution of charged particles, x-rays and γ rays. For x-ray, γ ray, and charged particle detection we can use thin p-i-n photosensitive diode arrays coupled to evaporated layers of suitable scintillators. For direct detection of charged particles with high resistance to radiation damage, we use the thick p-i-n diode arrays. 13 refs., 7 figs

  19. Casimir forces from conductive silicon carbide surfaces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-01-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of fr

  20. Low temperature CVD deposition of silicon carbide

    International Nuclear Information System (INIS)

    The coating of graphite on silicon carbide from the gaseous phase in a hot-well, open flow reactor at 1150degC is described. This study constitutes the first part of an investigation of the process for the coating of nuclear fuel by chemical vapor deposition (CVD)

  1. Micromachining of Silicon Carbide using femtosecond lasers

    Energy Technology Data Exchange (ETDEWEB)

    Farsari, M [Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, PO Box 1527, 71110 Heraklion, Crete (Greece); Filippidis, G [Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, PO Box 1527, 71110 Heraklion, Crete (Greece); Zoppel, S [Vienna University of Technology, Photonics Institute, Gusshausstr. 27-29/387, 1040 Vienna (Austria); Reider, G A [Vienna University of Technology, Photonics Institute, Gusshausstr. 27-29/387, 1040 Vienna (Austria); Fotakis, C [Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, PO Box 1527, 71110 Heraklion, Crete (Greece)

    2007-04-15

    We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

  2. Micromachining of Silicon Carbide using femtosecond lasers

    International Nuclear Information System (INIS)

    We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude

  3. High frequency organ-pipe modes in amorphous boron carbide observed using surface Brillouin scattering

    International Nuclear Information System (INIS)

    Amorphous boron carbide films of 2 micron thickness were deposited at room temperature by a thermal deposition process on single-crystal silicon substrates. The elastic constants of an amorphous B4C film have been successfully measured by surface Brillouin scattering as a function of temperature, in the process, revealing a phase transition at about 350 deg.C. Quantized wave-vector components perpendicular to the film surface associated with organ-pipe modes occurring within the film were used in conjunction with elastodynamic Green's function calculations as well as independent measurement of longitudinal frequency from bulk excitations to extract the elastic constants

  4. An improved method for preparing silicon carbide

    International Nuclear Information System (INIS)

    A desired shape is formed from a polysilane and the shape is heated in an inert atmosphere or under vacuum to 1150 to 16000C until the polysilane is converted to silicon carbide. The polysilane contains from 0 to 60 mole percent of (CH3)2Si units and from 40 to 100 mole percent of CH3Si units. The remaining bonds on silicon are attached to another silicon atom or to a chlorine or bromine atom, such that the polysilane contains from 10 to 43 weight percent of hydrolyzable chlorine or from 21 to 63 weight percent of hydrolyzable bromine. (author)

  5. Reliable Breakdown Obtained in Silicon Carbide Rectifiers

    Science.gov (United States)

    Neudeck, Philip G.

    1997-01-01

    The High Temperature Integrated Electronics and Sensor (HTIES) Program at the NASA Lewis Research Center is currently developing silicon carbide (SiC) for use in harsh conditions where silicon, the semiconductor used in nearly all of today's electronics, cannot function. Silicon carbide's demonstrated ability to function under extreme high-temperature, high-power, and/or high-radiation conditions will enable significant improvements to a far-ranging variety of applications and systems. These range from improved high-voltage switching for energy savings in public electric power distribution and electric vehicles, to more powerful microwave electronics for radar and cellular communications, to sensor and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines.

  6. Coaxial nanocable: silicon carbide and silicon oxide sheathed with boron nitride and carbon

    Science.gov (United States)

    Zhang; Suenaga; Colliex; Iijima

    1998-08-14

    Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a beta-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation. PMID:9703508

  7. Surface chemistry and friction behavior of the silicon carbide (0001) surface at temperatures to 1500 deg C

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1981-01-01

    X-ray photoelectron and Auger electron spectroscopy analyses and friction studies were conducted with a silicon carbide (0001) surface in contact with iron at various temperatures to 1200 or 1500 C in a vacuum of 10 to the minus 8th power Pa. The results indicate that there is a significant temperature influence on both the surface chemistry and friction properties of silicon carbide. The principal contaminant of adsorbed amorphous carbon on the silicon carbide surface in the as received state is removed by simply heating to 400 C. Above 400 C, graphite and carbide type carbine are the primary species on the silicon carbide surface, in addition to silicon. The coefficients of friction of polycrystalline iron sliding against a single crystal silicon carbide (0001) surface were high at temperatures to 800 C. Similar coefficients of friction were obtained at room temperature after the silicon carbide was preheated at various temperatures up 800 C. When the friction experiments were conducted above 800 C or when the specimens were preheated to above 800 C, the coefficients of friction were dramatically lower. At 800 C the silicon and carbide type carbon are at a maximum intensity in the XPS spectra. With increasing temperature above 800 C, the concentration of the graphite increases rapidly on the surface, whereas those of the carbide type carbon and silicon decrease rapidly.

  8. Depressurization amorphization of single-crystal boron carbide.

    Science.gov (United States)

    Yan, X Q; Tang, Z; Zhang, L; Guo, J J; Jin, C Q; Zhang, Y; Goto, T; McCauley, J W; Chen, M W

    2009-02-20

    We report depressurization amorphization of single-crystal boron carbide (B4C) investigated by in situ high-pressure Raman spectroscopy. It was found that localized amorphization of B4C takes place during unloading from high pressures, and nonhydrostatic stresses play a critical role in the high-pressure phase transition. First-principles molecular dynamics simulations reveal that the depressurization amorphization results from pressure-induced irreversible bending of C-B-C atomic chains cross-linking 12 atom icosahedra at the rhombohedral vertices. PMID:19257688

  9. Novel fabrication of silicon carbide based ceramics for nuclear applications

    Science.gov (United States)

    Singh, Abhishek Kumar

    Advances in nuclear reactor technology and the use of gas-cooled fast reactors require the development of new materials that can operate at the higher temperatures expected in these systems. These materials include refractory alloys based on Nb, Zr, Ta, Mo, W, and Re; ceramics and composites such as SiC--SiCf; carbon--carbon composites; and advanced coatings. Besides the ability to handle higher expected temperatures, effective heat transfer between reactor components is necessary for improved efficiency. Improving thermal conductivity of the fuel can lower the center-line temperature and, thereby, enhance power production capabilities and reduce the risk of premature fuel pellet failure. Crystalline silicon carbide has superior characteristics as a structural material from the viewpoint of its thermal and mechanical properties, thermal shock resistance, chemical stability, and low radioactivation. Therefore, there have been many efforts to develop SiC based composites in various forms for use in advanced energy systems. In recent years, with the development of high yield preceramic precursors, the polymer infiltration and pyrolysis (PIP) method has aroused interest for the fabrication of ceramic based materials, for various applications ranging from disc brakes to nuclear reactor fuels. The pyrolysis of preceramic polymers allow new types of ceramic materials to be processed at relatively low temperatures. The raw materials are element-organic polymers whose composition and architecture can be tailored and varied. The primary focus of this study is to use a pyrolysis based process to fabricate a host of novel silicon carbide-metal carbide or oxide composites, and to synthesize new materials based on mixed-metal silicocarbides that cannot be processed using conventional techniques. Allylhydridopolycarbosilane (AHPCS), which is an organometal polymer, was used as the precursor for silicon carbide. Inert gas pyrolysis of AHPCS produces near-stoichiometric amorphous

  10. Investigation of Sb diffusion in amorphous silicon

    OpenAIRE

    Csik, A.; Langer, G A; Erdelyi, G.; Beke, D. L.; Erdelyi, Z.; Vad, K.

    2009-01-01

    Amorphous silicon materials and its alloys become extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry (SNMS). Amorphous Si/Si1-xSbx/Si tri-layer samples with 5 at% antimony concentration were...

  11. Tests Of Amorphous-Silicon Photovoltaic Modules

    Science.gov (United States)

    Ross, Ronald G., Jr.

    1988-01-01

    Progress in identification of strengths and weaknesses of amorphous-silicon technology detailed. Report describes achievements in testing reliability of solar-power modules made of amorphous-silicon photovoltaic cells. Based on investigation of modules made by U.S. manufacturers. Modules subjected to field tests, to accelerated-aging tests in laboratory, and to standard sequence of qualification tests developed for modules of crystalline-silicon cells.

  12. Doping of silicon carbide by ion implantation

    International Nuclear Information System (INIS)

    It appeared that in some fields, as the hostile environments (high temperature or irradiation), the silicon compounds showed limitations resulting from the electrical and mechanical properties. Doping of 4H and 6H silicon carbide by ion implantation is studied from a physicochemical and electrical point of view. It is necessary to obtain n-type and p-type material to realize high power and/or high frequency devices, such as MESFETs and Schottky diodes. First, physical and electrical properties of silicon carbide are presented and the interest of developing a process technology on this material is emphasised. Then, physical characteristics of ion implantation and particularly classical dopant implantation, such as nitrogen, for n-type doping, and aluminium and boron, for p-type doping are described. Results with these dopants are presented and analysed. Optimal conditions are extracted from these experiences so as to obtain a good crystal quality and a surface state allowing device fabrication. Electrical conduction is then described in the 4H and 6H-SiC polytypes. Freezing of free carriers and scattering processes are described. Electrical measurements are carried out using Hall effect on Van der Panw test patterns, and 4 point probe method are used to draw the type of the material, free carrier concentrations, resistivity and mobility of the implanted doped layers. These results are commented and compared to the theoretical analysis. The influence of the technological process on electrical conduction is studied in view of fabricating implanted silicon carbide devices. (author)

  13. Genesis Silicon Carbide Concentrator Target 60003 Preliminary Ellipsometry Mapping Results

    Science.gov (United States)

    Calaway, M. J.; Rodriquez, M. C.; Stansbery, E. K.

    2007-01-01

    The Genesis concentrator was custom designed to focus solar wind ions primarily for terrestrial isotopic analysis of O-17/O-16 and O-18/O-16 to +/-1%, N-15/N-14 to +/-1%, and secondarily to conduct elemental and isotopic analysis of Li, Be, and B. The circular 6.2 cm diameter concentrator target holder was comprised of four quadrants of highly pure semiconductor materials that included one amorphous diamond-like carbon, one C-13 diamond, and two silicon carbide (SiC). The amorphous diamond-like carbon quadrant was fractured upon impact at Utah Test and Training Range (UTTR), but the remaining three quadrants survived fully intact and all four quadrants hold an important collection of solar wind. The quadrants were removed from the target holder at NASA Johnso n Space Center Genesis Curation Laboratory in April 2005, and have been housed in stainless steel containers under continual nitrogen purge since time of disintegration. In preparation for allocation of a silicon carbide target for oxygen isotope analyses at UCLA, the two SiC targets were photographed for preliminary inspection of macro particle contamination from the hard non-nominal landing as well as characterized by spectroscopic ellipsometry to evaluate thin film contamination. This report is focused on Genesis SiC target sample number 60003.

  14. Characterisation of silicon carbide films deposited by plasma-enhanced chemical vapour deposition

    International Nuclear Information System (INIS)

    The paper presents a characterisation of amorphous silicon carbide films deposited in plasma-enhanced chemical vapour deposition (PECVD) reactors for MEMS applications. The main parameter was optimised in order to achieve a low stress and high deposition rate. We noticed that the high frequency mode (13.56 MHz) gives a low stress value which can be tuned from tensile to compressive by selecting the correct power. The low frequency mode (380 kHz) generates high compressive stress (around 500 MPa) due to ion bombardment and, as a result, densification of the layer achieved. Temperature can decrease the compressive value of the stress (due to annealing effect). A low etching rate of the amorphous silicon carbide layer was noticed for wet etching in KOH 30% at 80 oC (around 13 A/min) while in HF 49% the layer is practically inert. A very slow etching rate of amorphous silicon carbide layer in XeF2 -7 A/min- was observed. The paper presents an example of this application: PECVD-amorphous silicon carbide cantilevers fabricated using surface micromachining by dry-released technique in XeF2

  15. Interaction of energetic tritium with silicon carbide

    International Nuclear Information System (INIS)

    In order to investigate the physical and chemical interactions of energetic hydrogen isotope species with silicon carbide, recoil tritium from the 3He(n,p)T reaction has been allowed to react with K-T silicon carbide and silicon carbide powder. The results show that if the silicon carbide has been degassed and annealed at 14000C prior to tritium bombardment, a considerable fraction of the tritium (ca. 40%) is released as HTO from the SiC upon heating to 13500C under vacuum conditions. Most of the remaining tritium is retained in SiC, e.g., the retention of the tritium in the K-T SiC was found to be 62 and 22% upon heating to 600 and 13500C, respectively. This is in direct contrast to graphite samples in which the tritium is not released to any significant extent even when heated to 13500C. Samples which were exposed to H2O and H2 prior to tritium bombardment were heated to 6000C after the irradiation. The results obtained indicate that a total of 38.7 and 2.49% of the tritium is released in the form of HT and CH3T in the case of H2 or H2O exposure, respectively. Treatment of degassed samples after tritium bombardment with H2O and H2 at temperatures up to 10000C leads to the release of up to 44.9% of the tritium as HT and CH3T. 42 references, 2 figures, 2 tables

  16. Magnetism of hydrogen-irradiated silicon carbide

    International Nuclear Information System (INIS)

    Spin-polarized density functional theory is used to study two-hydrogen defect complexes in silicon carbide. We find that the magnetism depends on the distances of the two hydrogen atoms. Magnetism appears when the two hydrogen defects are distant from each other, and magnetism cancels out if they are close to each other. The critical distance between the two hydrogen defects is determined.

  17. Mechanical properties of Silicon Carbide Nanowires

    Science.gov (United States)

    Alkhateeb, Abdullah; Zhang, Daqing; McIlroy, David; Aston, David Eric

    2004-05-01

    Silicon carbide nanowires could be potentially useful for high strength materials which lead to the interest in understanding their mechanical properties. In this report we use the digital pulse force microscopy to analyze the mechanical properties of SiC nanowires .Stiffness and adhesion images of SiC nanowires on silicon grating were obtained and calibrated force-distance curves were plotted along the wire which spans on a 1.5 micron trench. Moreover, spring constant and Young's modules have been calculated from the linear part of the force-distance curves.

  18. Microresonators with Q-factors over a million from highly stressed epitaxial silicon carbide on silicon

    Science.gov (United States)

    Kermany, Atieh R.; Brawley, George; Mishra, Neeraj; Sheridan, Eoin; Bowen, Warwick P.; Iacopi, Francesca

    2014-02-01

    We utilize the excellent mechanical properties of epitaxial silicon carbide (SiC) on silicon plus the capability of tuning its residual stress within a large tensile range to fabricate microstrings with fundamental resonant frequencies (f0) of several hundred kHz and mechanical quality factors (Q) of over a million. The fabrication of the perfect-clamped string structures proceeds through simple silicon surface micromachining processes. The resulting f × Q product in vacuum is equal or higher as compared to state-of-the-art amorphous silicon nitride microresonators. We demonstrate that as the residual epitaxial SiC stress is doubled, the f × Q product for the fundamental mode of the strings shows a four-fold increase.

  19. Silicon carbide for chemical application prepared by SPS method

    Czech Academy of Sciences Publication Activity Database

    Brožek, Vlastimil; Kubatík, Tomáš František; Vilémová, Monika; Mušálek, Radek; Mastný, L.

    Prague: Czech Society of Industrial Chemistry, 2014 - (Kalenda, P.; Lubojacký, J.), s. 129-134 ISBN 978-80-86238-64-7. [Mezinárodní chemicko-technologická konference/2./. Mikulov (CZ), 07.04.2014-09.04.2014] R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61389021 Keywords : silicon carbide * spark plasma sintering * silicon carbide corrosion * impurities in silicon carbide Subject RIV: JG - Metallurgy www.icct.cz

  20. Effect of Heat Treatment on Silicon Carbide Based Joining Materials for Fusion Energy

    Energy Technology Data Exchange (ETDEWEB)

    Lewinsohn, Charles A.; Jones, Russell H.; Nozawa, T.; Kotani, M.; Kishimoto, H.; Katoh, Y.; Kohyama, A.

    2001-10-01

    Two general approaches to obtaining silicon carbide-based joint materials were used. The first method relies on reactions between silicon and carbon to form silicon carbide, or to bond silicon carbide powders together. The second method consists of pyrolysing a polycarbosilane polymer to yield an amorphous, covalently bonded material. In order to assess the long-term durability of the joint materials, various heat treatments were performed and the effects on the mechanical properties of the joints were measured. Although the joints derived from the polycarbosilane polymer were not the strongest, the value of strength measured was not affected by heat treatment. On the other hand, the value of the strength of the reaction-based joints was affected by heat treatment, indicating the presence of residual stresses or unreacted material subsequent to processing. Further investigation of reaction-based joining should consist of detailed microscopic studies; however, continued study of joints derived from polymers is also warranted.

  1. Ion beam synthesis of buried oxide layers in silicon carbide

    International Nuclear Information System (INIS)

    A field emission gun scanning transmission electron microscope equipped with an energy-dispersive X-ray spectrometer (EDX) and an electron energy loss spectrometer (EELS) has been used to characterize the microstructures, elemental distributions, and chemical bonding states of oxygen ion implanted silicon carbide (SiC). 6H-SiC substrates with the (0 0 0 1) orientation were implanted with 180 keV oxygen ions at 650 deg. C to fluences of 0.7x1018 and 1.4x1018 cm-2. A continuous amorphous layer is formed in the as-implanted state under these irradiation conditions. The amorphous layer is uniform in the low-dose sample, while it consists of three layers in the high-dose one. EDX maps of elemental distributions suggest that the layered structure in the latter sample originates from compositional fluctuations of silicon, carbon and oxygen. EELS measurements suggest that the amorphous regions in the high-dose sample consist of well-defined SiO2 layer which is accompanied by sp2-bonded carbon

  2. Raman Amplifier Based on Amorphous Silicon Nanoparticles

    OpenAIRE

    M.A. Ferrara; Rendina, I.; S. N. Basu; Dal Negro, L.; Sirleto, L.

    2012-01-01

    The observation of stimulated Raman scattering in amorphous silicon nanoparticles embedded in Si-rich nitride/silicon superlattice structures (SRN/Si-SLs) is reported. Using a 1427 nm continuous-wavelength pump laser, an amplification of Stokes signal up to 0.9 dB/cm at 1540.6 nm and a significant reduction in threshold power of about 40% with respect to silicon are experimentally demonstrated. Our results indicate that amorphous silicon nanoparticles are a great promise for Si-based Raman la...

  3. Silicon Carbide Corrugated Mirrors for Space Telescopes Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Trex Enterprises Corporation (Trex) proposes technology development to manufacture monolithic, lightweight silicon carbide corrugated mirrors (SCCM) suitable for...

  4. Indentation fatigue in silicon nitride, alumina and silicon carbide ceramics

    Indian Academy of Sciences (India)

    A K Mukhopadhyay

    2001-04-01

    Repeated indentation fatigue (RIF) experiments conducted on the same spot of different structural ceramics viz. a hot pressed silicon nitride (HPSN), sintered alumina of two different grain sizes viz. 1 m and 25 m, and a sintered silicon carbide (SSiC) are reported. The RIF experiments were conducted using a Vicker’s microhardness tester at various loads in the range 1–20 N. Subsequently, the gradual evolution of the damage was characterized using an optical microscope in conjunction with the image analysing technique. The materials were classified in the order of the decreasing resistance against repeated indentation fatigue at the highest applied load of 20 N. It was further shown that there was a strong influence of grain size on the development of resistance against repeated indentation fatigue on the same spot. Finally, the poor performance of the sintered silicon carbide was found out to be linked to its previous thermal history.

  5. Laser annealing of hydrogen implanted amorphous silicon

    International Nuclear Information System (INIS)

    Amorphous silicon, prepared by silicon bombardment at energies of 200 to 250 keV, was implanted with 40 keV H2+ to peak concentrations up to 15 at .% and recrystallized in air by single 20 nsec pulses at 1.06 μm from a Nd:glass laser. Amorphous layer formation and recrystallization were verified using Raman spectroscopy and ion backscattering/channeling analysis

  6. Electron tunnelling into amorphous germanium and silicon.

    Science.gov (United States)

    Smith, C. W.; Clark, A. H.

    1972-01-01

    Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

  7. Challenges in amorphous silicon solar cell technology

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon is nowadays extensively used for a range of devices, amongst others solar cells. Solar cell technology has matured over the last two decades and resulted in conversion efficiencies in excess of 15%. In this paper the operation of amorphous silicon solar cells is briefly described. For tandem solar cell, amorphous silicon germanium is often used as material for the intrinsic layer of the bottom cell. This improves the red response of the cell. In order to optimize the performance of amorphous silicon germanium solar cells, profiling of the germanium concentration near the interfaces is applied. We show in this paper that the performance is strongly dependent on the width of the grading near the interfaces. The best performance is achieved when using a grading width that is as small as possible near the p-i interface and as wide as possible near the i-n interface. High-rate deposition of amorphous silicon is nowadays one of the main issues. Using the Expanding Thermal Plasma deposition method very high deposition rates can be achieved. This method has been applied for the fabrication of an amorphous silicon solar cell with a conversion efficiency of 5,8%. (authors)

  8. Microstructure evolution and energy band alignment at the interface of a Si-rich amorphous silicon carbide/c-Si heterostructure

    Science.gov (United States)

    Wen, Xixing; Zeng, Xiangbin; Liao, Wugang; Wen, Yangyang; Chen, Xiaoxiao

    2015-11-01

    The microstructure evolution of Si-rich amorphous a-SiC:H films obtained under different annealing conditions was investigated by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The influence of its microstructure on the energy band alignment at a Si-rich a-SiC:H/n-type c-Si hetero-interface was analyzed by ultraviolet visible transmission spectroscopy and ultraviolet photoelectron spectroscopy. The results revealed that the as-deposited Si-rich a-SiC:H film was mainly in an amorphous state. After annealing, Si and SiC quantum dots (QDs) formed, and the crystallinity of the QDs and the proportion of SiC QDs increased with increasing the annealing time at the same annealing temperature. It is found that the energy band alignment at the hetero-interface was influenced by the crystallinity of the films, the sizes of the QDs, and the relative proportion of Si to SiC QDs in a-SiC:H films. Moreover, the contact potential at the hetero-interface decreased with the improved crystallinity of the QDs in a-SiC:H film. The determination of energy band alignment at the Si-rich a-SiC:H/c-Si hetero-interface is beneficial to understanding the carrier transport behavior and designing hetero-structure devices.

  9. Evolution of defects in silicon carbide implanted with helium ions

    Science.gov (United States)

    Zhang, Chonghong; Song, Yin; Yang, Yitao; Zhou, Chunlan; Wei, Long; Ma, Hongji

    2014-05-01

    Effects of accumulation of radiation damage in silicon carbide are important concerns for the use of silicon carbide in advanced nuclear energy systems. In the present work lattice damage in silicon carbide crystal (4H type) implanted with 100 keV 4He+ ions was investigated with Rutherford backscattering spectrometry in channeling geometry (RBS/c) and positron beam Doppler broadening spectrometry (PBDB). Helium implantation was performed at the specimen temperature of 510 K to avoid amorphization of the SiC crystal. Fluences of helium ions were selected to be in the range from 1 × 1016 to 3 × 1016 ions cm-2, around the dose threshold for the formation of observable helium bubbles under transmission electron microscopes (TEM). The RBS/c measurements show distinctly different annealing behavior of displaced Si atoms at doses below or above the threshold for helium bubble formation. The RBS/c yield in the peak damage region of the specimen implanted to 3 × 1016 He-ions cm-2 shows an increase on the subsequently thermal annealing above 873 K, which is readily ascribed to the extra displacement of Si atoms due to helium bubble growth. The RBS/c yield in the specimen implanted to a lower ion fluence of 1.5 × 1016 He-ions cm-2 decreases monotonously on annealing from ambient temperatures up to 1273 K. The PBDB measurements supply evidence of clustering of vacancies at temperatures from 510 to 1173 K, and dissociation of vacancy clusters above 1273 K. The similarity of annealing behavior in PBDB profiles for helium implantation to 1 × 1016 and 3 × 1016 ions cm-2 is ascribed to the saturation of trapping of positrons in vacancy type defects in the damaged layers in the specimens helium-implanted to the two dose levels.

  10. Shock-wave strength properties of boron carbide and silicon carbide

    International Nuclear Information System (INIS)

    Time-resolved velocity interferometry measurements have been made on boron carbide and silicon carbide ceramics to assess dynamic equation-of-state and strength properties of these materials. Hugoniot precursor characteristics, and post-yield shock and release wave properties, indicated markedly different dynamic strength and flow behavior for the two carbides. (orig.)

  11. Atomic-scale disproportionation in amorphous silicon monoxide.

    Science.gov (United States)

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material. PMID:27172815

  12. Atomic-scale disproportionation in amorphous silicon monoxide

    Science.gov (United States)

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material. PMID:27172815

  13. Influence of radiation damage on krypton diffusion in silicon carbide

    Science.gov (United States)

    Friedland, E.; Hlatshwayo, T. T.; van der Berg, N. G.; Mabena, M. C.

    2015-07-01

    Diffusion of krypton in poly and single crystalline silicon carbide is investigated and compared with the previously obtained results for xenon, which pointed to a different diffusion mechanism than observed for chemically active elements. For this purpose 360 keV krypton ions were implanted in commercial 6H-SiC and CVD-SiC wafers at room temperature, 350 °C and 600 °C. Width broadening of the implantation profiles and krypton retention during isochronal and isothermal annealing up to temperatures of 1400 °C was determined by RBS-analysis, whilst in the case of 6H-SiC damage profiles were simultaneously obtained by α-particle channeling. Little diffusion and no krypton loss was detected in the initially amorphized and eventually recrystallized surface layer of cold implanted 6H-SiC during annealing up to 1200 °C. Above that temperature thermal etching of the implanted surface became increasingly important. No diffusion or krypton loss is detected in the hot implanted 6H-SiC samples during annealing up to 1400 °C. Radiation damage dependent grain boundary diffusion is observed at 1300 °C in CVD-SiC. The results seem to indicate, that the chemically inert noble gas atoms do not form defect-impurity complexes, which strongly influence the diffusion behavior of other diffusors in silicon carbide.

  14. Influence of radiation damage on krypton diffusion in silicon carbide

    International Nuclear Information System (INIS)

    Diffusion of krypton in poly and single crystalline silicon carbide is investigated and compared with the previously obtained results for xenon, which pointed to a different diffusion mechanism than observed for chemically active elements. For this purpose 360 keV krypton ions were implanted in commercial 6H-SiC and CVD-SiC wafers at room temperature, 350 °C and 600 °C. Width broadening of the implantation profiles and krypton retention during isochronal and isothermal annealing up to temperatures of 1400 °C was determined by RBS-analysis, whilst in the case of 6H-SiC damage profiles were simultaneously obtained by α-particle channeling. Little diffusion and no krypton loss was detected in the initially amorphized and eventually recrystallized surface layer of cold implanted 6H-SiC during annealing up to 1200 °C. Above that temperature thermal etching of the implanted surface became increasingly important. No diffusion or krypton loss is detected in the hot implanted 6H-SiC samples during annealing up to 1400 °C. Radiation damage dependent grain boundary diffusion is observed at 1300 °C in CVD-SiC. The results seem to indicate, that the chemically inert noble gas atoms do not form defect-impurity complexes, which strongly influence the diffusion behavior of other diffusors in silicon carbide

  15. Process for forming silicon carbide films and microcomponents

    Science.gov (United States)

    Hamza, Alex V.; Balooch, Mehdi; Moalem, Mehran

    1999-01-01

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C.sub.60 precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C.sub.60 with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C.sub.60 on silicon dioxide at surface temperatures less than 1250 K.

  16. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    S Mandal; A Seal; S K Dalui; A K Dey; S Ghatak; A K Mukhopadhyay

    2001-04-01

    The present work deals with the sintering of SiC with a low melting additive by microwave technique. The mechanical characteristics of the products were compared with that of conventionally sintered products. The failure stress of the microwave sintered products, in biaxial flexure, was superior to that of the products made by conventional sintering route in ambient condition. In firing of products by conventionally sintered process, SiC grain gets oxidized producing SiO2 (∼ 32 wt%) and deteriorates the quality of the product substantially. Partially sintered silicon carbide by such a method is a useful material for a varieties of applications ranging from kiln furniture to membrane material.

  17. Deep reactive ion etching of silicon carbide

    OpenAIRE

    Tanaka, S.; Rajanna, K.; Abe, T.(High Energy Accelerator Research Organization (KEK), 305-0801, Tsukuba, Japan); Esashi, M

    2001-01-01

    In this article, we describe more than 100-\\mu m-deep reactive ion etching (RIE) of silicon carbide (SiC) in oxygen-added sulfur hexafluoride (SF6) plasma. We used a homemade magnetically enhanced, inductively coupled plasma reactive ion etcher (ME-ICP-RIE) and electroplated nickel masks. First, 5 h etching experiments using etching gases with 0%, 5%, 10% and 20% oxygen were performed by supplying rf power of 150 and 130 W to an ICP antenna and a sample stage, respectively. They demonstrated ...

  18. Critically coupled surface phonon-polariton excitation in silicon carbide.

    Science.gov (United States)

    Neuner, Burton; Korobkin, Dmitriy; Fietz, Chris; Carole, Davy; Ferro, Gabriel; Shvets, Gennady

    2009-09-01

    We observe critical coupling to surface phonon-polaritons in silicon carbide by attenuated total reflection of mid-IR radiation. Reflectance measurements demonstrate critical coupling by a double scan of wavelength and incidence angle. Critical coupling occurs when prism coupling loss is equal to losses in silicon carbide and the substrate, resulting in maximal electric field enhancement. PMID:19724526

  19. Brazed boron-silicon carbide/aluminum structural panels

    Science.gov (United States)

    Arnold, W. E., Jr.; Bales, T. T.; Brooks, T. G.; Lawson, A. G.; Mitchell, P. D.; Royster, D. M.; Wiant, R.

    1978-01-01

    Fluxless brazing process minimizes degradation of mechanical properties composite material of silicon carbide coated boron fibers in an aluminum matrix. Process is being used to fabricate full-scale Boron-Silicon Carbide/Aluminum-Titanium honeycomb core panels for flight testing and ground testing.

  20. Determination of boron and silicon in boron carbide

    International Nuclear Information System (INIS)

    A sodium carbonate fusion technique for the dissolution of boron carbide followed by the determination of boron by alkalimetric titration and silicon impurity by spectrophotometry is described. The elemental boron content in the commercially available boron carbide ranged from 77.2 to 77.60 % and the silicon in the range 1170 to 2500 ppm. (author)

  1. An investigation on gamma attenuation behaviour of titanium diboride reinforced boron carbide-silicon carbide composites

    Science.gov (United States)

    Buyuk, Bulent; Beril Tugrul, A.

    2014-04-01

    In this study, titanium diboride (TiB2) reinforced boron carbide-silicon carbide composites were investigated against Cs-137 and Co-60 gamma radioisotope sources. The composite materials include 70% boron carbide (B4C) and 30% silicon carbide (SiC) by volume. Titanium diboride was reinforced to boron carbide-silicon carbide composites as additive 2% and 4% by volume. Average particle sizes were 3.851 µm and 170 nm for titanium diboride which were reinforced to the boron carbide silicon carbide composites. In the experiments the gamma transmission technique was used to investigate the gamma attenuation properties of the composite materials. Linear and mass attenuation coefficients of the samples were determined. Theoretical mass attenuation coefficients were calculated from XCOM computer code. The experimental results and theoretical results were compared and evaluated with each other. It could be said that increasing the titanium diboride ratio causes higher linear attenuation values against Cs-137 and Co-60 gamma radioisotope sources. In addition decreasing the titanium diboride particle size also increases the linear and mass attenuation properties of the titanium diboride reinforced boron carbide-silicon carbide composites.

  2. Effect of thermal annealing on the structural and mechanical properties of amorphous silicon carbide films prepared by polymer-source chemical vapor deposition

    International Nuclear Information System (INIS)

    We report on the effect of thermal annealing on the structural and mechanical properties of amorphous SiC thin films prepared by means of a polymer-source chemical vapor deposition process. The chemical bondings of the a-SiC:H films were systematically examined by means of Fourier transform infrared spectroscopy (FTIR). The film composition was measured by X-ray photoelectron spectroscopy, while X-ray reflectivity measurements were used to account for the film density variations caused by the post-annealing treatments over the 750-1200 oC range. In addition, their mechanical properties (hardness and Young's modulus) were investigated by using the nano-indentation technique. FTIR measurements revealed that not only the intensity of a-SiC absorption band linearly increases but also its position is found to shift to a higher wave number as a result of annealing. In addition, the bond density of Si-C is found to increase from (101.6-224.5) x 1021 bond.cm-3 accompanied by a decrease of Si-H bond density from (2.58-0.46)x 1021 bond.cm-3 as a result of increasing the annealing temperature (Ta) from 750 to 1200 oC. Annealing-induced film densification is confirmed, as the a-SiC film density is found to increase from 2.36 to ∼ 2.75 g/cm-3 when Ta is raised from 750 to 1200 oC. In addition, as Ta is increased from 750 to 1200 oC, both hardness and Young's modulus are found to increase from 15.5 to 17.6 GPa and 155 to 178 GPa, respectively. Our results confirm the previously established linear correlation between the mechanical properties of the a-SiC films and their bond densities.

  3. Growth Mechanism of Silicon Carbide (SIC) on Clean Silicon Surfaces

    International Nuclear Information System (INIS)

    An understanding of the growth mechanisms of silicon carbide (SiC) on the silicon surfaces is important not only for technological applications but also from the point of view of fundamental research. Due to the great lattice (20%) mismatch as well as to the high reaction temperature (above 1000 degrees for standard thermal techniques), rough silicon carbide surfaces with high density of defects and voids have been generally obtained. The voids are related to the low diffusion coefficient of silicon in SiC, which should enhance the Si diffusion mechanism throughout the silicon layers. Therefore, in order to improve the crystalline quality several types of precursors have been used with the aim to lower the silicon carbide temperature formation. Among the several growth processes investigated, the exposure of a hot silicon substrate to C60, acetylene, ethylene and graphite has been reported to produce cubic SiC films at temperatures in the range between 600 degrees and 900 degrees. Acetylene, in doses between 3600 and 30000 Langmuir (1 L= 1x1O-6 Torr.s), has been found to strongly react with Si(111)7x7 reconstructed substrate kept at temperature ranging between 6000C and 8000C and to form cubic silicon carbide nanostructures. They grow following the heteroepitaxial relationship SiC[111]//Si[111] and are characterized, for the highest acetylene doses, by a good crystalline quality with a rather flat morphology. A scanning tunneling microscopy (STM) study performed on Si(111)7x7 reconstructed surface imaged in real time, during low acetylene exposures (less than 600 L) while keeping the silicon surface at 6000C, has shown that this surface technique allows to image in real space the local modifications of the system and to identify the starting point of the reaction process together with its time evolution. Besides we investigated the role played by the temperature of Si(111)7x7 surface during different acetylene exposures in the morphology modification of the reacted

  4. Distribution and characterization of iron in implanted silicon carbide

    International Nuclear Information System (INIS)

    Analytical electron microscopy (AEM) and Rutherford backscattering spectroscopy-ion channeling (RBS-C) have been used to characterize single crystal α-silicon carbide implanted at room temperature with 160 keV 57Fe ions to fluences of 1, 3, and 6 x 1016 ions/cm2. Best correlations among AEM, RBS, and TRIM calculations were obtained assuming a density of the amorphized implanted regions equal to that of crystalline SiC. No iron-rich precipitates or clusters were detected by AEM. Inspection of the electron energy loss fine structure for iron in the implanted specimens suggests that the iron is not metallically-bonded, supporting conclusions from earlier conversion electron Moessbauer spectroscopy (CEMS) studies. In-situ annealing surprisingly resulted in crystallization at 600 degrees C with some redistribution of the implanted iron

  5. A first principles study of palladium in silicon carbide

    International Nuclear Information System (INIS)

    Full text of publication follows. Silicon carbide has been used in nuclear industry and is still considered as a coating material for nuclear fuel. Its main role should be to retain fission products. It has been observed, however, that some fission products, like palladium and silver, attack the SiC layer and are supposed to be responsible for corrosion of the material, which could facilitate fission products release. We used first principles calculations based on Density Functional Theory (DFT) in order to investigate the energetic, structural, and kinetic properties of Pd impurities inside beta-SiC; we obtained solution and migration energies in pure SiC and discuss some basic thermodynamical issues of the corrosion process. Moreover we consider some possible effects of the disorder, which is known to be induced by irradiation in the form of amorphized regions, on Pd kinetics, and we will mention some issues related to the recombination of intrinsic defects created by irradiation. (author)

  6. Microstructure of molybdenum disilicide-silicon carbide nanocomposite thin films

    International Nuclear Information System (INIS)

    Composite thin films of molybdenum disilicide-silicon carbide (MoSi2-SiC) have been deposited via rf magnetron sputtering onto molybdenum substrates. An intermediate layer was deposited in the presence of nitrogen gas and evaluated as a potential diffusion barrier layer. The composite films have been characterized using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and Auger electron spectroscopy. The as-deposited films were amorphous but crystallized into nanometer-sized grains after annealing under vacuum at 1,000 C for 30 min. There was a significant amount of interdiffusion between the film and substrate, which resulted in the formation of subsilicides such as Mo5Si3 and MoSi3, as well as Mo2C. The films that were deposited via reactive sputtering in a nitrogen ambient were amorphous in both the as-deposited and annealed conditions. Significantly fewer second phases were detected with the presence of the intermediate layer, which suggests the potential use of the nitrided (MoSixNyCz) layer as a high-temperature diffusion barrier layer for the silicon and carbon

  7. Amorphous silicon detectors in positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Conti, M. (Istituto Nazionale di Fisica Nucleare, Pisa (Italy) Lawrence Berkeley Lab., CA (USA)); Perez-Mendez, V. (Lawrence Berkeley Lab., CA (USA))

    1989-12-01

    The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters {epsilon}{sup 2}{tau}'s are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs.

  8. Amorphous silicon detectors in positron emission tomography

    International Nuclear Information System (INIS)

    The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters ε2τ's are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs

  9. Silicon Carbide: The Problem with Laboratory Spectra

    Science.gov (United States)

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

    2000-03-01

    The interpretation of astronomical observations of infrared (IR) silicon carbide (SiC) features in the spectra of carbon stars have revealed discrepancies between the work of astronomers and that of meteoriticists. The silicon carbide observed around carbon stars has been attributed to one type of SiC (α) while meteoritic samples believed to have formed around such stars are of another type of SiC (β). The key to solving this problem has been to understand the sources of laboratory data used by astronomers in order to interpret the IR spectra. Through comparison of thin film IR absorption spectra and spectra taken using finely ground samples dispersed in potassium bromide (KBr) pellets we show that the previously invoked ``KBr matrix-correction'' is unnecessary for powder dispersions obtained from very fine grain sizes of SiC. Comparison of our data and previous measurements show that dust around carbon stars is β-SiC, consistent with laboratory studies of presolar grains in meteorites. The implications of these findings affect twenty years of work. The IR spectroscopic laboratory data used by astronomers to identify dust species in space must be carefully scrutinized to ensure that the KBr correction is not responsible for further misattributions of minerals in astronomical dust features.

  10. Growth and Characterization of Amorphous Silicon Carbides Films%微波等离子体化学气相沉积法生长非晶碳化硅薄膜

    Institute of Scientific and Technical Information of China (English)

    陈修勇; 辛煜

    2012-01-01

    利用SH4(80%Ar稀释)和CH4作为源气体,通过改变源气体流量比、基片温度、沉积气压等参量,使用微波电子回旋共振化学气相沉积法生长非晶碳化硅薄膜.实验结果表明碳化硅薄膜沉积速率随气体流量比R(CH4/(CH4+SiH4))的增加而减小、随基片温度的升高明显减小、随沉积气压的增加先增大后减小.红外结构表明:在较低流量比R下,薄膜主要由硅团簇和非晶碳化硅两相组成,而当R>0.5时,薄膜的结构主要由非晶碳化硅组成,薄膜中键合的H主要是Si和C的封端原子.同时,沉积温度的升高使碳化硅薄膜中Si-H,C-C和C-H键的含量减少,而薄膜中Si-C含量明显增加且峰位发生了红移.薄膜相结构的转变是薄膜光学带隙变化的原因.%The amorphous silicon carbide (a-SiχQ1-χ:H) films were grown by microwave electron cyclotron resonance chemical vapor deposition (MWECR-CVD) with CH^and argon-diluted S1H4 as the precursors.The impacts of the growth conditions on microstructures and stoichiometry of the films were studied. The results show that the ratio of the gas flow rates, R = CH^/I CH4 + SiH() , substrate temperature and pressure strongly affect the deposition rate of the films. For example, the deposition rate markedly decreases with increases of both the gas-flow ratio and the substrate temperature;as the pressure rises up,the deposition rate follows an increase-decrease mode. We found that an increase of the substrate temperature decreased the density of Si-H,C-C and C-H bonds,and resulted in a red-shift of the Si-C absorption peak.

  11. Transverse and longitudinal vibrations in amorphous silicon

    Science.gov (United States)

    Beltukov, Y. M.; Fusco, C.; Tanguy, A.; Parshin, D. A.

    2015-12-01

    We show that harmonic vibrations in amorphous silicon can be decomposed to transverse and longitudinal components in all frequency range even in the absence of the well defined wave vector q. For this purpose we define the transverse component of the eigenvector with given ω as a component, which does not change the volumes of Voronoi cells around atoms. The longitudinal component is the remaining orthogonal component. We have found the longitudinal and transverse components of the vibrational density of states for numerical model of amorphous silicon. The vibrations are mostly transverse below 7 THz and above 15 THz. In the frequency interval in between the vibrations have a longitudinal nature. Just this sudden transformation of vibrations at 7 THz from almost transverse to almost longitudinal ones explains the prominent peak in the diffusivity of the amorphous silicon just above 7 THz.

  12. Atomic-scale disproportionation in amorphous silicon monoxide

    OpenAIRE

    Hirata, Akihiko; Kohara, Shinji; Asada, Toshihiro; Arao, Masazumi; Yogi, Chihiro; Imai, Hideto; Tan, Yongwen; Fujita, Takeshi; Chen, Mingwei

    2016-01-01

    Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphou...

  13. DEFECTS IN AMORPHOUS CHALCOGENIDES AND SILICON

    OpenAIRE

    Adler, D.

    1981-01-01

    Our comprehension of the physical properties of amorphous semiconductors has improved considerably over the past few years, but many puzzles remain. From our present perspective, the major features of chalcogenide glasses appear to be well understood, and some of the fine points which have arisen recently have been explained within the same general model. On the other hand, there are a grear number of unresolved mysteries with regard to amorphous silicon-based alloys. In this paper, the valen...

  14. Inverted amorphous silicon solar cell utilizing cermet layers

    Science.gov (United States)

    Hanak, Joseph J.

    1979-01-01

    An amorphous silicon solar cell incorporating a transparent high work function metal cermet incident to solar radiation and a thick film cermet contacting the amorphous silicon opposite to said incident surface.

  15. NMR INVESTIGATIONS OF HYDROGENATED AMORPHOUS SILICON

    OpenAIRE

    J. Reimer

    1981-01-01

    A review is presented of the N.M.R. (Nuclear Magnetic Resonance) studies to date of hydrogenated amorphous silicon-hydrogen films. Structural features of proton N.M.R. lineshapes, dynamics of hydrogen containing defect sites, and the promise of quantitative determinations of local silicon-hydrogen bonding environments are discussed in detail. Finally, some comments are given on future directions for N.M.R. studies of hydrogenated thin films.

  16. Stable Transistors in Hydrogenated Amorphous Silicon

    OpenAIRE

    J. M. Shannon

    2004-01-01

    Thin-film field-effect transistors in hydrogenated amorphous silicon are notoriously unstable due to the formation of silicon dangling bond trapping states in the accumulated channel region during operation. Here, we show that by using a source-gated transistor a major improvement in stability is obtained. This occurs because the electron quasi-Fermi level is pinned near the center of the band in the active source region of the device and strong accumulation of electrons is prevented. The use...

  17. Exposure to Fibres, Crystalline Silica, Silicon Carbide and Sulphur Dioxide in the Norwegian Silicon Carbide Industry

    OpenAIRE

    Føreland, S.; Bye, E; Bakke, B.; Eduard, W

    2008-01-01

    Objectives: The aim of this study was to assess personal exposure to fibres, crystalline silica, silicon carbide (SiC) and sulphur dioxide in the Norwegian SiC industry. Methods: Approximately 720 fibre samples, 720 respirable dust samples and 1400 total dust samples were collected from randomly chosen workers from the furnace, processing and maintenance departments in all three Norwegian SiC plants. The respirable dust samples were analysed for quartz, cristobalite and non-fibrous SiC conten...

  18. Microwave synthesis of phase-pure, fine silicon carbide powder

    International Nuclear Information System (INIS)

    Fine, monophasic silicon carbide powder has been synthesized by direct solid-state reaction of its constituents namely silicon and carbon in a 2.45 GHz microwave field. Optimum parameters for the silicon carbide phase formation have been determined by varying reaction time and reaction temperature. The powders have been characterized for their particle size, surface area, phase composition (X-ray diffraction) and morphology (scanning electron microscope). Formation of phase-pure silicon carbide can be achieved at 1300 deg. C in less than 5 min of microwave exposure, resulting in sub-micron-sized particles. The free energy values for Si + C → SiC reaction were calculated for different temperatures and by comparing them with the experimental results, it was determined that phase-pure silicon carbide can be achieved at around 1135 deg. C

  19. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Science.gov (United States)

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics. PMID:26394207

  20. Separation of Nuclear Fuel Surrogates from Silicon Carbide Inert Matrix

    International Nuclear Information System (INIS)

    The objective of this project has been to identify a process for separating transuranic species from silicon carbide (SiC). Silicon carbide has become one of the prime candidates for the matrix in inert matrix fuels, (IMF) being designed to reduce plutonium inventories and the long half-lives actinides through transmutation since complete reaction is not practical it become necessary to separate the non-transmuted materials from the silicon carbide matrix for ultimate reprocessing. This work reports a method for that required process

  1. Silver diffusion through silicon carbide in microencapsulated nuclear fuels TRISO

    International Nuclear Information System (INIS)

    The silver diffusion through silicon carbide is a challenge that has persisted in the development of microencapsulated fuels TRISO (Tri structural Isotropic) for more than four decades. The silver is known as a strong emitter of gamma radiation, for what is able to diffuse through the ceramic coatings of pyrolytic coal and silicon carbide and to be deposited in the heat exchangers. In this work we carry out a recount about the art state in the topic of the diffusion of Ag through silicon carbide in microencapsulated fuels and we propose the role that the complexities in the grain limit can have this problem. (Author)

  2. Pressureless sintering of beta silicon carbide nanoparticles

    International Nuclear Information System (INIS)

    This study reports the pressureless sintering of cubic phase silicon carbide nanoparticles (β-SiC). Green blended compounds made of SiC nano-sized powder, a fugitive binder and a sintering agent (boron carbide, B4C), have been prepared. The binder is removed at low temperature (e.g. 800 degrees C) and the pressureless sintering studied between 1900 and 2100 degrees C. The nearly theoretical density (98% relative density) was obtained after 30 min at 2100 degrees C. The structural and microstructural evolutions during the heat treatment were characterised. The high temperatures needed for the sintering result in the β-SiC to α-SiC transformation which is revealed by the change of the composite microstructure. From 1900 degrees C, dense samples are composed of β-SiC grains surrounding α-SiC platelets in a well-defined orientation. TEM investigations and calculation of the activation energy of the sintering provided insight to the densification mechanism. (authors)

  3. Nanoporous Silicon Carbide for Nanoelectromechanical Systems Applications

    Science.gov (United States)

    Hossain, T.; Khan, F.; Adesida, I.; Bohn, P.; Rittenhouse, T.; Lienhard, Michael (Technical Monitor)

    2003-01-01

    A major goal of this project is to produce porous silicon carbide (PSiC) via an electroless process for eventual utilization in nanoscale sensing platforms. Results in the literature have shown a variety of porous morphologies in SiC produced in anodic cells. Therefore, predictability and reproducibility of porous structures are initial concerns. This work has concentrated on producing morphologies of known porosity, with particular attention paid toward producing the extremely high surface areas required for a porous flow sensor. We have conducted a parametric study of electroless etching conditions and characteristics of the resulting physical nanostructure and also investigated the relationship between morphology and materials properties. Further, we have investigated bulk etching of SiC using both photo-electrochemical etching and inductively-coupled-plasma reactive ion etching techniques.

  4. Microwave hybrid synthesis of silicon carbide nanopowders

    International Nuclear Information System (INIS)

    Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 deg. C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm)

  5. Preparation of Silicon Carbide with High Properties

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In order to prepare silicon carbide with high properties, three kinds of SiC powders A, B, and C with different composition and two kinds of additives, which were Y2O3-Al2O3 system and Y2O3-La2O3 system, were used in this experiment. The properties of hot-pressed SiC ceramics were measured. With the same additives, different SiC powder resulted in different properties. On the other hand, with the same SiC powder, increasing the amount of the additive Y2O3-Al2O3 improved properties of SiC ceramics at room temperature, and increasing the amount of the additive Y2O3-La2O3 improved property SiC ceramics at elevated temperature. In addition, the microstructure of SiC ceramics was studied by scanning electron microscopy.

  6. Chemical Mechanical Polishing of Silicon Carbide

    Science.gov (United States)

    Powell, J. Anthony; Pirouz

    1999-01-01

    The High Temperature Integrated Electronics and Sensors (HTIES) team at the NASA Lewis Research Center is developing silicon carbide (SiC) as an enabling electronic technology for many aerospace applications. The Lewis team is focusing on the chemical vapor deposition of the thin, single-crystal SiC films from which devices are fabricated. These films, which are deposited (i.e., epitaxially "grown") on commercial wafers, must consist of a single crystal with very few structural defects so that the derived devices perform satisfactorily and reliably. Working in collaboration (NASA grant) with Professor Pirouz of Case Western Reserve University, we developed a chemical-mechanical polishing (CMP) technique for removing the subsurface polishing damage prior to epitaxial growth of the single-crystal SiC films.

  7. Thermal Oxidation of Silicon Carbide Substrates

    Institute of Scientific and Technical Information of China (English)

    Xiufang Chen; Li'na Ning; Yingmin Wang; Juan Li; Xiangang Xu; Xiaobo Hu; Minhua Jiang

    2009-01-01

    Thermal oxidation was used to remove the subsurface damage of silicon carbide (SiC) surfaces. The anisotrow of oxidation and the composition of oxide layers on Si and C faces were analyzed. Regular pits were observed on the surface after the removal of the oxide layers, which were detrimental to the growth of high quality epitaxial layers. The thickness and composition of the oxide layers were characterized by Rutherford backscat-tering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS), respectively. Epitaxial growth was performed in a metal organic chemical vapor deposition (MOCVD) system. The substrate surface morphol-ogy after removing the oxide layer and gallium nitride (GaN) epilayer surface were observed by atomic force microscopy (AFM). The results showed that the GaN epilayer grown on the oxidized substrates was superior to that on the unoxidized substrates.

  8. Impurities in silicon carbide ceramics and their role during high temperature creep

    OpenAIRE

    Backhaus-Ricoult, M.; Mozdzierz, N.; Eveno, P.

    1993-01-01

    The high-temperature compressive creep behaviour of hot-pressed silicon carbide ceramics with different additive packages (boron and carbon or no additive) is investigated as a function of several parameters: the microstructure, the nature of the additives and that of the impurities. Additional carbon is present in all the materials investigated, as graphite precipitates of various size and amount. In materials densified with addition of boron, large precipitates of B25C and small amorphous s...

  9. Noise and degradation of amorphous silicon devices

    NARCIS (Netherlands)

    Bakker, J.P.R.

    2003-01-01

    Electrical noise measurements are reported on two devices of the disordered semiconductor hydrogenated amorphous silicon (a-Si:H). The material is applied in sandwich structures and in thin-film transistors (TFTs). In a sandwich configuration of an intrinsic layer and two thin doped layers, the obse

  10. Film adhesion in amorphous silicon solar cells

    Indian Academy of Sciences (India)

    A R M Yusoff; M N Syahrul; K Henkel

    2007-08-01

    A major issue encountered during fabrication of triple junction -Si solar cells on polyimide substrates is the adhesion of the solar cell thin films to the substrates. Here, we present our study of film adhesion in amorphous silicon solar cells made on different polyimide substrates (Kapton VN, Upilex-S and Gouldflex), and the effect of tie coats on film adhesion.

  11. Preparation of hydrogenated amorphous silicon tin alloys

    OpenAIRE

    Vergnat, M.; Marchal, G.; Piecuch, M.

    1987-01-01

    This paper describes a new method to obtain hydrogenated amorphous semiconductor alloys. The method is reactive co-evaporation. Silicon tin hydrogenated alloys are prepared under atomic hydrogen atmosphere. We discuss the influence of various parameters of preparation (hydrogen pressure, tungsten tube temperature, substrate temperature, annealing...) on electrical properties of samples.

  12. A review of oxide, silicon nitride, and silicon carbide brazing

    International Nuclear Information System (INIS)

    There is growing interest in using ceramics for structural applications, many of which require the fabrication of components with complicated shapes. Normal ceramic processing methods restrict the shapes into which these materials can be produced, but ceramic joining technology can be used to overcome many of these limitations, and also offers the possibility for improving the reliability of ceramic components. One method of joining ceramics is by brazing. The metallic alloys used for bonding must wet and adhere to the ceramic surfaces without excessive reaction. Alumina, partially stabilized zirconia, and silicon nitride have high ionic character to their chemical bonds and are difficult to wet. Alloys for brazing these materials must be formulated to overcome this problem. Silicon carbide, which has some metallic characteristics, reacts excessively with many alloys, and forms joints of low mechanical strength. The brazing characteristics of these three types of ceramics, and residual stresses in ceramic-to-metal joints are briefly discussed

  13. Effect of Ion Beam Irradiation on Silicon Carbide with Different Microstructures

    International Nuclear Information System (INIS)

    SiC and SiC/SiC composites are one of promising candidates for structural materials of the next generation energy systems such as the gas-cooled reactors and fusion reactors. This anticipation yields many material issues, and radiation effects of silicon carbide are recognized as an important research subject. Silicon carbide has diverse crystal structures (called polytypes), such as α-SiC (hexagonal structure), β-SiC (cubic structure) and amorphous SiC. Among these polytypes, β-SiC has been studied as matrix material in SiC/SiC composites. Near-stoichiometric β-SiC with high crystallinity and purity is considered as suitable material in the next generation energy system and matrix material in SiC/SiC composites because of its excellent radiation resistance. Highly pure and crystalline β-SiC and SiC/SiC composites could be obtained by the chemical vapor deposition (CVD) and Infiltration (CVI) process using a gas mixture of methyltrichlorosilane (CH3SiCl3, MTS) and purified H2. SiC produced by the CVD method has different grain size and microstructural morphology depended on the process conditions such as temperature, pressure and the input gas ratio. In this work, irradiation effects of silicon carbide were investigated using ion beam irradiation with emphasis on the influence of grain size and grain boundary. MeV ion irradiation at low temperature makes amorphous phase in silicon carbide. The microstructures and mechanical property changes of silicon carbide with different structures were analyzed after ion beam irradiation

  14. Generation of correlated photons in hydrogenated amorphous-silicon waveguides

    OpenAIRE

    Clemmen, S.; Perret, A; Selvaraja, Shankar Kumar; Bogaerts, Wim; Van Thourhout, Dries; Baets, Roel; Emplit, Ph.; Massar, S.

    2011-01-01

    We report the first (to our knowledge) observation of correlated photon emission in hydrogenated amorphous- silicon waveguides. We compare this to photon generation in crystalline silicon waveguides with the same geome- try. In particular, we show that amorphous silicon has a higher nonlinearity and competes with crystalline silicon in spite of higher loss.

  15. Light-induced Voc increase and decrease in high-efficiency amorphous silicon solar cells

    OpenAIRE

    Stuckelberger, Michael; Riesen, Yannick Samuel; Despeisse, Matthieu; Schüttauf, Jan-Willem Alexander; Haug, Franz-Josef; Ballif, Christophe

    2014-01-01

    High-efficiency amorphous silicon (a-Si:H) solar cells were deposited with different thicknesses of the p-type amorphous silicon carbide layer on substrates of varying roughness. We observed a light-induced open-circuit voltage (Voc) increase upon light soaking for thin p-layers, but a decrease for thick p-layers. Further, the Voc increase is enhanced with increasing substrate roughness. After correction of the p-layer thickness for the increased surface area of rough substrates, we can exclu...

  16. ADHERENCE AND PROPERTIES OF SILICON CARBIDE BASED FILMS ON STEEL

    OpenAIRE

    Lelogeais, M.; Ducarroir, M.; Berjoan, R.

    1991-01-01

    Coatings of silicon carbide with various compositions have been obtained in a r.f plasma assisted process using tetramethylsilane and argon as input gases. Some properties against mechanical applications of such deposits on steel have been investigated. Residual stresses and hardness are reported and discussed in relation with plasma parameters and deposit composition. By scratch testing, it was shown that the silicon carbide films on steel denote a good adherence when compared with previous ...

  17. Rapid Wolff–Kishner reductions in a silicon carbide microreactor

    OpenAIRE

    Newman, Stephen G.; Gu, Lei; Lesniak, Christoph; Victor, Georg; Meschke, Frank; Abahmane, Lahbib; Jensen, Klavs F.

    2013-01-01

    Wolff–Kishner reductions are performed in a novel silicon carbide microreactor. Greatly reduced reaction times and safer operation are achieved, giving high yields without requiring a large excess of hydrazine. The corrosion resistance of silicon carbide avoids the problematic reactor compatibility issues that arise when Wolff–Kishner reductions are done in glass or stainless steel reactors. With only nitrogen gas and water as by-products, this opens the possibility of performing selective, l...

  18. Synthesis of nano powder of silicon carbide by means of sol gel method and its structural analysis

    International Nuclear Information System (INIS)

    The results of XRD research of silicon carbide nano powder structure formation during its synthesis by means of sol-gel method are presented. The efficient regime of annealing for its transition from an amorphous phase to the crystalline one depending on annealing temperature and carbon concentration is determined. (author)

  19. Polymeric synthesis of silicon carbide with microwaves.

    Science.gov (United States)

    Aguilar, Juan; Urueta, Luis; Valdez, Zarel

    2007-01-01

    The aim of this work is conducting polymeric synthesis with microwaves for producing beta-SiC. A polymeric precursor was prepared by means of hydrolysis and condensation reactions from pheniltrimethoxysilane, water, methanol, ammonium hydroxide and chloride acid. The precursor was placed into a quartz tube in vacuum; pyrolysis was carried out conventionally in a tube furnace, and by microwaves at 2.45 GHz in a multimode cavity. Conventional tests took place in a scheme where temperature was up to 1500 degrees C for 120 minutes. Microwave heating rate was not controlled and tests lasted 60 and 90 minutes, temperature was around 900 degrees C. Products of the pyrolysis were analyzed by means of x-ray diffraction; in the microwave case the diffraction patterns showed a strong background of either very fine particles or amorphous material, then infrared spectroscopy was also employed for confirming carbon bonds. In both processes beta-SiC was found as the only produced carbide. PMID:17645205

  20. Ion bombardment and disorder in amorphous silicon

    International Nuclear Information System (INIS)

    The effect of ion bombardment during growth on the structural and optical properties of amorphous silicon are presented. Two series of films were deposited under electrically grounded and positively biased substrate conditions. The biased samples displayed lower growth rates and increased hydrogen content relative to grounded counterparts. The film structure was examined using Raman spectroscopy. The transverse optic like phonon band position was used as a parameter to characterize network order. Biased samples displayed an increased order of the amorphous network relative to grounded samples. Furthermore, biased samples exhibited a larger optical gap. These results are correlated and attributed to reduced ion bombardment effects

  1. Synthesis of silicon carbide nanowires by solid phase source chemical vapor deposition

    Institute of Scientific and Technical Information of China (English)

    NI Jie; LI Zhengcao; ZHANG Zhengjun

    2007-01-01

    In this paper,we report a simple approach to synthesize silicon carbide(SiC)nanowires by solid phase source chemical vapor deposition(CVD) at relatively low temperatures.3C-SiC nanowires covered by an amorphous shell were obtained on a thin film which was first deposited on silicon substrates,and the nanowires are 20-80 am in diameter and several μm in length,with a growth direction of[200].The growth of the nanowires agrees well on vapor-liquid-solid (VLS)process and the film deposited on the substrates plays an important role in the formation of nanowires.

  2. The effect of substrate bias on titanium carbide/amorphous carbon nanocomposite films deposited by filtered cathodic vacuum arc

    International Nuclear Information System (INIS)

    The titanium carbide/amorphous carbon nanocomposite films have been deposited on silicon substrate by filtered cathodic vacuum arc (FCVA) technology, the effects of substrate bias on composition, structures and mechanical properties of the films are studied by scanning electron spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy and nano-indentation. The results show that the Ti content, deposition rate and hardness at first increase and then decrease with increasing the substrate bias. Maximum hardness of the titanium carbide/amorphous carbon nanocomposite film is 51 Gpa prepared at −400 V. The hardness enhancement may be attributed to the compressive stress and the fraction of crystalline TiC phase due to ion bombardment

  3. Silicon Carbide Technology for Grid Integrated Photovoltaic Applications: Dynamic Characterization of Silicon Carbide Transistors.

    OpenAIRE

    Tiwari, Subhadra

    2011-01-01

    For the endorsement of the study of potential utilization of the emerging silicon carbide (SiC) devices, three SiC active switches, namely SJEP120R063 (1200V, 63 mohm) SiC JFET manufactured by Semisouth, BT1206AC-P1 (1200V, 125 mohm) SiC BJT by TranSiC and CMF20120 (1200V, 80 mohm, 33A) SiC MOSFET by Cree have been investigated systematically in this thesis work.The four layer PCB board with the smart layouts like the drain and gate traces are either perpendicular to each other or run into di...

  4. Silicon nano-carbide in strengthening and ceramic technologies

    Science.gov (United States)

    Rudneva, V. V.; Galevsky, G. V.; Kozyrev, N. A.

    2015-09-01

    Technological advantages and conditions of new quality assurance of coatings and products, provided by silicon nano-carbide, have been ascertained in the course of composite electrodeposition of coatings, structural ceramics patterning, and surface hardening of steels via electro-explosive alloying. Silicon nano-carbide has been recommended to be used as a component of wear and corrosion resistant chromium carbide electrodeposited coatings, which can be operated at high temperatures and used for strengthening tools and equipment including those with a complex microrelief of functional surfaces. Silicon nano-carbide as a component of composite “silicon carbide - boron - carbon” can be applied to produce ceramic half products via solid phase sintering in argon under pressure of 0.1 MPa and temperature 2273 K. Application of silicon nano-carbide in technology of tool steel surface hardening via electroexplosive alloying ensures obtaining of a high micro-hard, wear and heat resistant shielding layer which is about 20 μm deep.

  5. PHYSICAL PROPERTIES OF AMORPHOUS CVD SILICON

    OpenAIRE

    Hirose, M.

    1981-01-01

    Amorphous silicon produced from the chemical vapor decomposition of silane at ~600 °C offers a pure silicon network containing no bonded-hydrogen and involving native defects of the order of 1 x 1019 cm-3. Doped phosphorus or boron atoms in the CVD a-Si interact with the defects to reduce the gap states and the spin density as well. The mechanism of the defect compensation has been interpreted in terms of complex-defect formation through the reaction between three-fold dopant atoms and divaca...

  6. Self-Diffusion in Amorphous Silicon

    Science.gov (United States)

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-01

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on 29Si/natSi heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and 700 °C with an activation energy of (4.4 ±0.3 ) eV . In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about 700 °C , which can be interpreted as the consequence of a high diffusion entropy.

  7. The Local Structure of Amorphous Silicon

    Science.gov (United States)

    Treacy, M. M. J.; Borisenko, K. B.

    2012-02-01

    It is widely believed that the continuous random network (CRN) model represents the structural topology of amorphous silicon. The key evidence is that the model can reproduce well experimental reduced density functions (RDFs) obtained by diffraction. By using a combination of electron diffraction and fluctuation electron microscopy (FEM) variance data as experimental constraints in a structural relaxation procedure, we show that the CRN is not unique in matching the experimental RDF. We find that inhomogeneous paracrystalline structures containing local cubic ordering at the 10 to 20 angstrom length scale are also fully consistent with the RDF data. Crucially, they also matched the FEM variance data, unlike the CRN model. The paracrystalline model has implications for understanding phase transformation processes in various materials that extend beyond amorphous silicon.

  8. Amorphous metallic films in silicon metallization systems

    Science.gov (United States)

    So, F.; Kolawa, E.; Nicolet, M. A.

    1985-01-01

    Diffusion barrier research was focussed on lowering the chemical reactivity of amorphous thin films on silicon. An additional area of concern is the reaction with metal overlays such as aluminum, silver, and gold. Gold was included to allow for technology transfer to gallium arsenide PV cells. Amorphous tungsten nitride films have shown much promise. Stability to annealing temperatures of 700, 800, and 550 C were achieved for overlays of silver, gold, and aluminum, respectively. The lower results for aluminum were not surprising because there is an eutectic that can form at a lower temperature. It seems that titanium and zirconium will remove the nitrogen from a tungsten nitride amorphous film and render it unstable. Other variables of research interest were substrate bias and base pressure during sputtering.

  9. Amorphous silicon for thin-film transistors

    OpenAIRE

    Schropp, Rudolf Emmanuel Isidore

    1987-01-01

    Hydrogenated amorphous silicon (a-Si:H) has considerable potential as a semiconducting material for large-area photoelectric and photovoltaic applications. Moreover, a-Si:H thin-film transistors (TFT’s) are very well suited as switching devices in addressable liquid crystal display panels and addressable image sensor arrays, due to a new technology of low-cost, Iow-temperature processing overlarge areas. ... Zie: Abstract

  10. Transverse and longitudinal vibrations in amorphous silicon

    OpenAIRE

    Beltukov, Y. M.; De Fusco, C; Tanguy, A.; Parshin, D. A.

    2015-01-01

    We show that harmonic vibrations in amorphous silicon can be decomposed to transverse and longitudinal components in all frequency range even in the absence of the well defined wave vector ${\\bf q}$. For this purpose we define the transverse component of the eigenvector with given $\\omega$ as a component, which does not change the volumes of Voronoi cells around atoms. The longitudinal component is the remaining orthogonal component. We have found the longitudinal and transverse components of...

  11. Optical characterisation of cubic silicon carbide

    International Nuclear Information System (INIS)

    The varied properties of Silicon Carbide (SiC) are helping to launch the material into many new applications, particularly in the field of novel semiconductor devices. In this work, the cubic form of SiC is of interest as a basis for developing integrated optical components. Here, the formation of a suitable SiO2 buried cladding layer has been achieved by high dose oxygen ion implantation. This layer is necessary for the optical confinement of propagating light, and hence optical waveguide fabrication. Results have shown that optical propagation losses of the order of 20 dB/cm are obtainable. Much of this loss can be attributed to mode leakage and volume scattering. Mode leakage is a function of the effective oxide thickness, and volume scattering related to the surface layer damage. These parameters have been shown to be controllable and so suggests that further reduction in the waveguide loss is feasible. Analysis of the layer growth mechanism by RBS, XTEM and XPS proves that SiO2 is formed, and that the extent, of formation depends on implant dose and temperature. The excess carbon generated is believed to exit the oxide layer by a number of varying mechanisms. The result of this appears to be a number of stable Si-C-O intermediaries that, form regions to either depth extreme of the SiO2 layer. Early furnace tests suggest a need to anneal at, temperatures approaching the melting point of the silicon substrate, and that the quality of the virgin material is crucial in controlling the resulting oxide growth. (author)

  12. Bright Single Photon Emitter in Silicon Carbide

    Science.gov (United States)

    Lienhard, Benjamin; Schroeder, Tim; Mouradian, Sara; Dolde, Florian; Trong Tran, Toan; Aharonovich, Igor; Englund, Dirk

    Efficient, on-demand, and robust single photon emitters are of central importance to many areas of quantum information processing. Over the past 10 years, color centers in solids have emerged as excellent single photon emitters. Color centers in diamond are among the most intensively studied single photon emitters, but recently silicon carbide (SiC) has also been demonstrated to be an excellent host material. In contrast to diamond, SiC is a technologically important material that is widely used in optoelectronics, high power electronics, and microelectromechanical systems. It is commercially available in sizes up to 6 inches and processes for device engineering are well developed. We report on a visible-spectrum single photon emitter in 4H-SiC. The emitter is photostable at both room and low temperatures, and it enables 2 million photons/second from unpatterned bulk SiC. We observe two classes of orthogonally polarized emitters, each of which has parallel absorption and emission dipole orientations. Low temperature measurements reveal a narrow zero phonon line with linewidth < 0.1 nm that accounts for more than 30% of the total photoluminescence spectrum. To our knowledge, this SiC color emitter is the brightest stable room-temperature single photon emitter ever observed.

  13. Thermal equation of state of silicon carbide

    Science.gov (United States)

    Wang, Yuejian; Liu, Zhi T. Y.; Khare, Sanjay V.; Collins, Sean Andrew; Zhang, Jianzhong; Wang, Liping; Zhao, Yusheng

    2016-02-01

    A large volume press coupled with in-situ energy-dispersive synchrotron X-ray was used to probe the change of silicon carbide (SiC) under high pressure and temperature (P-T) up to 8.1 GPa and 1100 K. The obtained pressure-volume-temperature data were fitted to a modified high-T Birch-Murnaghan equation of state, yielding values of a series of thermo-elastic parameters, such as the ambient bulk modulus KTo = 237(2) GPa, temperature derivative of the bulk modulus at a constant pressure (∂K/∂T)P = -0.037(4) GPa K-1, volumetric thermal expansivity α(0, T) = a + bT with a = 5.77(1) × 10-6 K-1 and b = 1.36(2) × 10-8 K-2, and pressure derivative of the thermal expansion at a constant temperature (∂α/∂P)T = 6.53 ± 0.64 × 10-7 K-1 GPa-1. Furthermore, we found the temperature derivative of the bulk modulus at a constant volume, (∂KT/∂T)V, equal to -0.028(4) GPa K-1 by using a thermal pressure approach. In addition, the elastic properties of SiC were determined by density functional theory through the calculation of Helmholtz free energy. The computed results generally agree well with the experimentally determined values.

  14. Improved silicon carbide for advanced heat engines

    Science.gov (United States)

    Whalen, Thomas J.

    1989-01-01

    The development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines is studied. Injection molding was the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals were to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in four-point loading. Statistically designed experiments were performed throughout the program and a fluid mixing process employing an attritor mixer was developed. Compositional improvements in the amounts and sources of boron and carbon used and a pressureless sintering cycle were developed which provided samples of about 99 percent of theoretical density. Strengths were found to improve significantly by annealing in air. Strengths in excess of 550 MPa (80 ksi) with Weibull modulus of about 9 were obtained. Further improvements in Weibull modulus to about 16 were realized by proof testing. This is an increase of 86 percent in strength and 100 percent in Weibull modulus over the baseline data generated at the beginning of the program. Molding yields were improved and flaw distributions were observed to follow a Poisson process. Magic angle spinning nuclear magnetic resonance spectra were found to be useful in characterizing the SiC powder and the sintered samples. Turbocharger rotors were molded and examined as an indication of the moldability of the mixes which were developed in this program.

  15. Casimir force measurements from silicon carbide surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-02-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.

  16. Casimir forces from conductive silicon carbide surfaces

    Science.gov (United States)

    Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-05-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.

  17. Palladium Implanted Silicon Carbide for Hydrogen Sensing

    Science.gov (United States)

    Muntele, C. I.; Ila, D.; Zimmerman, R. L.; Muntele, L.; Poker, D. B.; Hensley, D. K.; Larkin, David (Technical Monitor)

    2001-01-01

    Silicon carbide is intended for use in fabrication of high-temperature, efficient hydrogen sensors. Traditionally, when a palladium coating is applied on the exposed surface of SiC, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. We have produced both a palladium coated SiC as well as a palladium, ion implanted SiC sensor. The palladium implantation was done at 500 C into the Si face of 6H, N-type SiC at various energies, and at various fluences. Then, we measured the hydrogen sensitivity response of each fabricated sensor by exposing them to hydrogen while monitoring the current flow across the p-n junction(s), with respect to time. The sensitivity of each sensor was measured at temperatures between 27 and 300 C. The response of the SiC sensors produced by Pd implantation has revealed a completely different behaviour than the SiC sensors produced by Pd deposition. In the Pd-deposited SiC sensors as well as in the ones reported in the literature, the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd-implanted SiC sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100 C. We will present the details and conclusions from the results obtained during this meeting.

  18. Rapid thermal annealing and crystallization mechanisms study of silicon nanocrystal in silicon carbide matrix

    Directory of Open Access Journals (Sweden)

    Wan Zhenyu

    2011-01-01

    Full Text Available Abstract In this paper, a positive effect of rapid thermal annealing (RTA technique has been researched and compared with conventional furnace annealing for Si nanocrystalline in silicon carbide (SiC matrix system. Amorphous Si-rich SiC layer has been deposited by co-sputtering in different Si concentrations (50 to approximately 80 v%. Si nanocrystals (Si-NC containing different grain sizes have been fabricated within the SiC matrix under two different annealing conditions: furnace annealing and RTA both at 1,100°C. HRTEM image clearly reveals both Si and SiC-NC formed in the films. Much better "degree of crystallization" of Si-NC can be achieved in RTA than furnace annealing from the research of GIXRD and Raman analysis, especially in high-Si-concentration situation. Differences from the two annealing procedures and the crystallization mechanism have been discussed based on the experimental results.

  19. Rapid thermal annealing and crystallization mechanisms study of silicon nanocrystal in silicon carbide matrix.

    Science.gov (United States)

    Wan, Zhenyu; Huang, Shujuan; Green, Martin A; Conibeer, Gavin

    2011-01-01

    In this paper, a positive effect of rapid thermal annealing (RTA) technique has been researched and compared with conventional furnace annealing for Si nanocrystalline in silicon carbide (SiC) matrix system. Amorphous Si-rich SiC layer has been deposited by co-sputtering in different Si concentrations (50 to approximately 80 v%). Si nanocrystals (Si-NC) containing different grain sizes have been fabricated within the SiC matrix under two different annealing conditions: furnace annealing and RTA both at 1,100°C. HRTEM image clearly reveals both Si and SiC-NC formed in the films. Much better "degree of crystallization" of Si-NC can be achieved in RTA than furnace annealing from the research of GIXRD and Raman analysis, especially in high-Si-concentration situation. Differences from the two annealing procedures and the crystallization mechanism have been discussed based on the experimental results. PMID:21711625

  20. Temperature-induced phase development in titanium-implanted silicon carbide

    International Nuclear Information System (INIS)

    Silicon carbide has been implated with titanium at three different doses. Transmission electron microscopy and Rutherford back-scattering (RBS) have been used to follow changes resulting from post-implantation heat treatment. The as-implanted layer is amorphous, and after a low temperature anneal a fine, non-equilibrium titanium carbide precipitate appears in the amorphous matrix. At higher temperatures, first the ternary phase Ti3SiC2 and the SiC crystallizes. RBS measurements show that the initial Gaussian titanium concentration profile changes near the ternary phase precipitation temperature, developing side peaks at the area of maximum initial concentration gradient. Thermodynamic and kinetic factors in the observed phase development are discussed, and the need for a metastable phase diagram is considered. (orig.)

  1. The diffusion bonding of silicon carbide and boron carbide using refractory metals

    International Nuclear Information System (INIS)

    Joining is an enabling technology for the application of structural ceramics at high temperatures. Metal foil diffusion bonding is a simple process for joining silicon carbide or boron carbide by solid-state, diffusive conversion of the metal foil into carbide and silicide compounds that produce bonding. Metal diffusion bonding trials were performed using thin foils (5 microm to 100 microm) of refractory metals (niobium, titanium, tungsten, and molybdenum) with plates of silicon carbide (both α-SiC and β-SiC) or boron carbide that were lapped flat prior to bonding. The influence of bonding temperature, bonding pressure, and foil thickness on bond quality was determined from metallographic inspection of the bonds. The microstructure and phases in the joint region of the diffusion bonds were evaluated using SEM, microprobe, and AES analysis. The use of molybdenum foil appeared to result in the highest quality bond of the metal foils evaluated for the diffusion bonding of silicon carbide and boron carbide. Bonding pressure appeared to have little influence on bond quality. The use of a thinner metal foil improved the bond quality. The microstructure of the bond region produced with either the α-SiC and β-SiC polytypes were similar

  2. Nickel-induced crystallization of amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, J A; Arce, R D; Buitrago, R H [INTEC (CONICET-UNL), Gueemes 3450, S3000GLN Santa Fe (Argentina); Budini, N; Rinaldi, P, E-mail: jschmidt@intec.unl.edu.a [FIQ - UNL, Santiago del Estero 2829, S3000AOM Santa Fe (Argentina)

    2009-05-01

    The nickel-induced crystallization of hydrogenated amorphous silicon (a-Si:H) is used to obtain large grained polycrystalline silicon thin films on glass substrates. a-Si:H is deposited by plasma enhanced chemical vapour deposition at 200 deg. C, preparing intrinsic and slightly p-doped samples. Each sample was divided in several pieces, over which increasing Ni concentrations were sputtered. Two crystallization methods are compared, conventional furnace annealing (CFA) and rapid thermal annealing (RTA). The crystallization was followed by optical microscopy and scanning electron microscopy observations, X-ray diffraction, and reflectance measurements in the UV region. The large grain sizes obtained - larger than 100{mu}m for the samples crystallized by CFA - are very encouraging for the preparation of low-cost thin film polycrystalline silicon solar cells.

  3. Low Power Phase Change Memory using Silicon Carbide as a Heater Layer

    Science.gov (United States)

    Aziz, M. S.; Yin, Y.; Hosaka, S.; Mohammed, Z.; Alip, R. I.

    2015-11-01

    The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using two types heating element was investigated. With separate heater structure, simulation was done using COMSOL Multiphysic 5.0. Silicon carbide (SiC) and Titanium Sitride (TiSi3) has been selected as a heater and differences of them have been studied. The voltage boundary is 0.905V and temperature of the memory layer is 463K when using SIC as a heater. While the voltage boundary and temperature of memory layer when using TiSi3 are 1.103 V and 459K respectively. Based on the result of a simulation, the suitable material of heater layer for separate heater structure is Silicon carbide (SiC) compared with Titanium Sitride (TiSi3).

  4. Influence of radiation damage on xenon diffusion in silicon carbide

    Science.gov (United States)

    Friedland, E.; Gärtner, K.; Hlatshwayo, T. T.; van der Berg, N. G.; Thabethe, T. T.

    2014-08-01

    Diffusion of xenon in poly and single crystalline silicon carbide and the possible influence of radiation damage on it are investigated. For this purpose 360 keV xenon ions were implanted in commercial 6H-SiC and CVD-SiC wafers at room temperature, 350 °C and 600 °C. Width broadening of the implantation profiles and xenon retention during isochronal and isothermal annealing up to temperatures of 1500 °C was determined by RBS-analysis, whilst in the case of 6H-SiC damage profiles were simultaneously obtained by α-particle channelling. No diffusion or xenon loss was detected in the initially amorphized and eventually recrystallized surface layer of cold implanted 6H-SiC during annealing up to 1200 °C. Above that temperature serious erosion of the implanted surface occurred, which made any analysis impossible. No diffusion or xenon loss is detected in the hot implanted 6H-SiC samples during annealing up to 1400 °C. Radiation damage dependent grain boundary diffusion is observed at 1300 °C in CVD-SiC.

  5. Gas phase separation of silicon carbide and silicon nitride

    International Nuclear Information System (INIS)

    Pure silicon carbide and silicon nitride in compact, pore-free form have valuable properties which only could never be fully utilized so far. The two compounds cannot be melted or sintered in their pure form, additives are required for hot-pressing or pressureless sintering, and only porous material is obtained by reaction sintering, where only Si and C or Si and N are used. - The new technique of chemical gas phase separation might help to overcome the drawbacks of present techniques. In the new technique SiC is produced e.g., by pyrolysis of CH3SiCl3 and Si3N4, e.g. by reacting SiCl4 with NH3. With this techniques, the pores in SiC and Si3N4 bodies can be filled later (gas phase impregnation), very fine SiC and Si3N4 powders can be produced as well as SiC monofilaments suitable as components for SiC compound bodies. In addition fibre compound bodies can be obtained by gas phase impregnation. (orig.)

  6. Modelling the light induced metastable effects in amorphous silicon

    OpenAIRE

    Munyeme, G.; Chinyama, G.K.; Zeman, M.; R. E. I. Schropp; Weg, W

    2008-01-01

    We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which act as efficient charge trapping and recombination centres. The increase in dangling bond states causes a decrease in the performance of amorphous silicon solar cells. To show this effect, a modelli...

  7. Implanted bottom gate for epitaxial graphene on silicon carbide

    International Nuclear Information System (INIS)

    We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between. (paper)

  8. Optimum Design of Lightweight Silicon Carbide Mirror Assembly

    Institute of Scientific and Technical Information of China (English)

    HAN Yuanyuan; ZHANG Yumin; HAN Jiecai; ZHANG Jianhan; YAO Wang; ZHOU Yufeng

    2008-01-01

    According to the design requirement and on the basis of the principle that the thermal expansion coefficient of the support structure should match with that of the mirror, a lightweight silicon carbide primary mirror assembly was designed. Finite element analysis combined with the parameter-optimized method was used during the design. Lightweight cell and rigid rib structure were used for the mirror assembly. The static, dynamic and thermal properties of the primary mirror assembly were analyzed. It is shown that after optimization, the lightweight ratio of the silicon carbide mirror is 52.5%, and the rigidity of the silicon carbide structure is high enough to support the required mirror. When temperature changes, the deformation of the mirror surface is in proportion to the temperature difference.

  9. Porous-shaped silicon carbide ultraviolet photodetectors on porous silicon substrates

    International Nuclear Information System (INIS)

    Highlights: ► Porous-shaped silicon carbide thin film was deposited on porous silicon substrate. ► Thermal annealing was followed to enhance the physical properties of samples. ► Metal–semiconductor-metal ultraviolet detectors were fabricated on samples. ► The effect of annealing temperature on electrical performance of devices was studied. ► The efficiency of photodetectors was enhanced by annealing at elevated temperatures. -- Abstract: A metal–semiconductor-metal (MSM) ultraviolet photodetector was fabricated based on a porous-shaped structure of silicon carbide (SiC). For increasing the surface roughness of SiC and hence enhancing the light absorption effect in fabricated devices, porous silicon (PS) was chosen as a template; SiC was deposited on PS substrates via radio frequency magnetron sputtering. Therefore, the deposited layers followed the structural pattern of PS skeleton and formed a porous-shaped SiC layer on PS substrate. The structural properties of samples showed that the as-deposited SiC was amorphous. Thus, a post-deposition annealing process with elevated temperatures was required to convert its amorphous phase to crystalline phase. The morphology of the sputtered samples was examined via scanning electron and atomic force microscopies. The grain size and roughness of the deposited layers clearly increased upon an increase in the annealing temperature. The optical properties of sputtered SiC were enhanced due to applying high temperatures. The most intense photoluminescence peak was observed for the sample with 1200 °C of annealing temperature. For the metallization of the SiC substrates to fabricate MSM photodetectors, two interdigitated Schottky contacts of Ni with four fingers for each electrode were deposited onto all the porous substrates. The optoelectronic characteristics of MSM UV photodetectors with porous-shaped SiC substrates were studied in the dark and under UV illumination. The electrical characteristics of fabricated

  10. Three-Terminal Amorphous Silicon Solar Cells

    OpenAIRE

    Cheng-Hung Tai; Chu-Hsuan Lin; Chih-Ming Wang; Chun-Chieh Lin

    2011-01-01

    Many defects exist within amorphous silicon since it is not crystalline. This provides recombination centers, thus reducing the efficiency of a typical a-Si solar cell. A new structure is presented in this paper: a three-terminal a-Si solar cell. The new back-to-back p-i-n/n-i-p structure increased the average electric field in a solar cell. A typical a-Si p-i-n solar cell was also simulated for comparison using the same thickness and material parameters. The 0.28 μm-thick three-terminal a-Si...

  11. Radiation resistance studies of amorphous silicon films

    Science.gov (United States)

    Woodyard, James R.; Payson, J. Scott

    1989-01-01

    Hydrogenated amorphous silicon thin films were irradiated with 2.00 MeV helium ions using fluences ranging from 1E11 to 1E15 cm(-2). The films were characterized using photothermal deflection spectroscopy and photoconductivity measurements. The investigations show that the radiation introduces sub-band-gap states 1.35 eV below the conduction band and the states increase supralinearly with fluence. Photoconductivity measurements suggest the density of states above the Fermi energy is not changing drastically with fluence.

  12. Flaw imaging and ultrasonic techniques for characterizing sintered silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Baaklini, G.Y.; Abel, P.B.

    1987-08-01

    The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

  13. Amorphous silicon oxide window layers for high-efficiency silicon heterojunction solar cells

    OpenAIRE

    Seif, Johannes Peter; Descoeudres, Antoine; Filipic, Miha; Smole, Franc; Topic, Marko; Holman, Zachary Charles; De Wolf, Stefaan; Ballif, Christophe

    2014-01-01

    In amorphous/crystalline silicon heterojunction solar cells, optical losses can be mitigated by replacing the amorphous silicon films by wider bandgap amorphous silicon oxide layers. In this article, we use stacks of intrinsic amorphous silicon and amorphous silicon oxide as front intrinsic buffer layers and show that this increases the short-circuit current density by up to 0.43 mA/cm2 due to less reflection and a higher transparency at short wavelengths. Additionally, high open-circuit volt...

  14. Amorphous silicon-based microchannel plates

    International Nuclear Information System (INIS)

    Microchannel plates (MCP) based on hydrogenated amorphous silicon (a-Si:H) were recently introduced to overcome some of the limitations of crystalline silicon and glass MCP. The typical thickness of a-Si:H based MCPs (AMCP) ranges between 80 and 100 μm and the micromachining of the channels is realized by deep reactive ion etching (DRIE). Advantages and issues regarding the fabrication process are presented and discussed. Electron amplification is demonstrated and analyzed using Electron Beam Induced Current (EBIC) technique. The gain increases as a function of the bias voltage, limited to −340 V on account of high leakage currents across the structure. EBIC maps on 10° tilted samples confirm that the device active area extend to the entire channel opening. AMCP characterization with the electron beam shows gain saturation and signal quenching which depends on the effectiveness of the charge replenishment in the channel walls.

  15. Amorphous silicon-based microchannel plates

    Energy Technology Data Exchange (ETDEWEB)

    Franco, Andrea, E-mail: andrea.franco@epfl.ch [Ecole Polytechnique Federale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and thin-film electronics laboratory, Breguet 2, CH-2000 Neuchatel (Switzerland); Riesen, Yannick; Wyrsch, Nicolas; Dunand, Sylvain [Ecole Polytechnique Federale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and thin-film electronics laboratory, Breguet 2, CH-2000 Neuchatel (Switzerland); Powolny, Francois; Jarron, Pierre [European Organization for Nuclear Research (CERN), CH-1211 Geneva 23 (Switzerland); Ballif, Christophe [Ecole Polytechnique Federale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and thin-film electronics laboratory, Breguet 2, CH-2000 Neuchatel (Switzerland)

    2012-12-11

    Microchannel plates (MCP) based on hydrogenated amorphous silicon (a-Si:H) were recently introduced to overcome some of the limitations of crystalline silicon and glass MCP. The typical thickness of a-Si:H based MCPs (AMCP) ranges between 80 and 100 {mu}m and the micromachining of the channels is realized by deep reactive ion etching (DRIE). Advantages and issues regarding the fabrication process are presented and discussed. Electron amplification is demonstrated and analyzed using Electron Beam Induced Current (EBIC) technique. The gain increases as a function of the bias voltage, limited to -340 V on account of high leakage currents across the structure. EBIC maps on 10 Degree-Sign tilted samples confirm that the device active area extend to the entire channel opening. AMCP characterization with the electron beam shows gain saturation and signal quenching which depends on the effectiveness of the charge replenishment in the channel walls.

  16. Method for the production of a silicon carbide body

    International Nuclear Information System (INIS)

    For an improved method of producing silicon carbide elements of complex shape (gas turbine engines), selected fractions of silicon carbide particles (65 to 75% by weight particle size 40 to 0C to 4550C in an atmosphere with 10 to 30vol.% of oxygen removes the excess carbon at the surface of the body and provides it with an open pore structue. Silication is started by heating to at least 15400C in an oxygen-free atmosphere which consits mostly of nitrogen and 0 to 10vol% hydrogen. The hydrogen is active in removing enough carbon and, possibly, graphite from the body to obtain a sufficiently free volume for the subsequent conversion of the residual carbon into silicon carbide. The nitrogen converts oxidic impurities of the initial material into silicon nitride. After removing the nitrogen-hydrogen atmosphere, the body is kept in a vacuum lower than the steam pressure of silicon at silication temperature, with nitrogen being removed from the silicon nitride and transferred into silicon metal. The thus cleaned formed piece, which is now highly porous, is then silicated at temperatures between 14250C and 17650C in a nitrogen-charged environment. (IHOE)

  17. Characterization of oxide scales thermally formed on single-crystal silicon carbide.

    Science.gov (United States)

    Chayasombat, B; Kato, T; Hirayama, T; Tokunaga, T; Sasaki, K; Kuroda, K

    2010-08-01

    Microstructures of oxide scales thermally formed on single-crystal silicon carbide were investigated using transmission electron microscopy. The oxide scales were formed on the Si-face of 6H-SiC at 1273-1473 K in dry oxygen. Spherical patterns were observed on the surfaces of the oxidized samples by an optical microscope in some regions. In these regions, cross-sectional transmission electron microscopy (TEM) observations show that the oxide scale was divided into two layers; the upper layer (surface side) was composed of crystalline silica, and the lower layer on the silicon carbide substrate was amorphous silica, while the oxide scales in the surroundings of the patterns were composed of only amorphous silica. The oxidation activation energy in the amorphous silica layer of the Si-face of 6H-SiC was found to be 408 kJ/mol by the evolution of thickness directly measured from the cross-sectional scanning electron microscopy and TEM images. PMID:20554755

  18. Endurance Tests Of Amorphous-Silicon Photovoltaic Modules

    Science.gov (United States)

    Ross, Ronald G., Jr.; Sugimura, Russell S.

    1989-01-01

    Failure mechanisms in high-power service studied. Report discusses factors affecting endurance of amorphous-silicon solar cells. Based on field tests and accelerated aging of photovoltaic modules. Concludes that aggressive research needed if amorphous-silicon modules to attain 10-year life - value U.S. Department of Energy established as goal for photovoltaic modules in commercial energy-generating plants.

  19. Modelling the light induced metastable effects in amorphous silicon

    NARCIS (Netherlands)

    Munyeme, G.; Chinyama, G.K.; Zeman, M.; Schropp, R.E.I.; van der Weg, W.

    2008-01-01

    We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which a

  20. Silicon Carbide Technologies for High Temperature Motor Drives

    OpenAIRE

    Snefjellå, Øyvind Holm

    2011-01-01

    Many applications benefit from using converters which can operate at high temperatures among them; down-hole drilling, hybrid vehicles and space craft. The theoretical performance of transistors made of Silicon Carbide (SiC) is investigated in this work. It is shown that their properties at high temperatures are superior compared to Silicon (Si) devices. Two half-bridge converters, using SiC normally-off Junction Field Effect Transistors (JFET) and SiC Bipolar Junction Transistors (BJT), are ...

  1. Refractory ceramics to silicon carbide. 5. tot. rev. ed

    Energy Technology Data Exchange (ETDEWEB)

    Elvers, B. (ed.); Hawkins, S. (ed.); Russey, W. (ed.); Schulz, G. (ed.)

    1993-01-01

    This volume contains 28 contributions to the following topics: Refractory Ceramics, Reinforced Plastics; Release Agents; Resins, Natural; Resins, Synthetic; Resorcinol; Resources of Oil and Gas; Rhenium and Rhenium Compounds; Rodenticides; Rubber (1. Survey, 2. Natural, 3. Synthetic, 4. Chemicals, 5. Technology, 6. Testing); Rubidium and Rubidium Compounds; Salicylic Acid; Saponins; Sealing Materials; Seasonings; Sedatives; Selenium and Selenium Compounds; Semiconductors; Shoe Polishes; Silica; Silicates; Silicon; Silicon Carbide. (orig.)

  2. Processing and mechanical properties of silicon nitride/silicon carbide ceramic nanocomposites derived from polymer precursors

    Science.gov (United States)

    Gasch, Matthew Jeremy

    Creep deformation of silicon nitride and silicon carbide ceramics is dominated by a solution-precipitation process through the glassy interface phase at grain boundary regions, which is formed by the reaction of oxide additives with the silicon oxide surface layer of the ceramic powder particles during liquid phase sintering. The ultimate approach to increase the creep resistance of these materials is to decrease the oxide content at the grain boundaries, rendering the solution-precipitation process non-effective. This research presents a new method of enhancing the creep properties of silicon nitride/silicon carbide composites by forming micro-nano and nano-nano microstructures during sintering. Starting from amorphous Si-C-N powders of micrometric size particles, powders were consolidated in three ways: (1) Consolidation of pyrolyzed powders without additives, (2) Electric Field Assisted Sintering (EFAS) of pyrolyzed powders with and without additives and (3) High pressure sintering. In all three cases, nanocomposites with varied grain size were achieved. High temperature mechanical creep testing was performed on the samples sintered by EFAS. Creep rates ranged from 1 x 10-8/s to 1 x 10-11/s depending on method in which powders were prepared and total oxide additive amount. For samples with high oxide contents the stress exponent was found to be n ˜ 2 with an activation energy of Q ˜ 600kJ/mol*K, indicating the typical solution precipitation process of deformation. But for the nano-nano composites sintered with little to none oxide additive, the stress exponent was found to be n ˜ 1 with and activation energy of Q ˜ 200kJ/mol*K, hinting at a diffusion controlled mechanism of creep deformation. For the nano-nano composites sintered without oxide additives, oxygen was found in the microstructure. However, oxygen contamination was found to distribute at grain boundary regions especially triple junctions. It is suggested that this highly dispersed distribution of

  3. Sintering of nano crystalline silicon carbide by doping with boron carbide

    Indian Academy of Sciences (India)

    M S Datta; A K Bandyopadhyay; B Chaudhuri

    2002-06-01

    Sinterable nano silicon carbide powders of mean particle size (37 nm) were prepared by attrition milling and chemical processing of an acheson type alpha silicon carbide having mean particle size of 0.39 m (390 nm). Pressureless sintering of these powders was achieved by addition of boron carbide of 0.5 wt% together with carbon of 1 wt% at 2050°C at vacuum (3 mbar) for 15 min. Nearly 99% sintered density was obtained. The mechanism of sintering was studied by scanning electron microscopy and transmission electron microscopy. This study shows that the mechanism is a solid-state sintering process. Polytype transformation from 6H to 4H was observed.

  4. Study of sintering temperature on the structure of silicon carbide membrane

    Science.gov (United States)

    Sadighzadeh, A.; Mashayekhan, Sh.; Nedaie, B.; Ghorashi, A. H.

    2014-09-01

    Study of the microstructure of silicon carbide (SiC) membrane as a function of sintering temperature and the percentage amount of additive kaolin is the outcome of the experimental fabrications presented in this paper. The SEM micrographs are used to investigate the impact of above parameters on the porosity of membrane. The experimental results show that the rise in the temperature causes more sintering of powder particles, growing granules, augmentation of the number of pores and consequently increasing the total porosity of membrane. Using XRD analyses, it is found that SiC amorphous phase is highly sensitive to the temperature and its crystallization physically grows with temperature increase.

  5. Optical Kerr nonlinearity in a high-Q silicon carbide microresonator.

    Science.gov (United States)

    Lu, Xiyuan; Lee, Jonathan Y; Rogers, Steven; Lin, Qiang

    2014-12-15

    We demonstrate a high-Q amorphous silicon carbide (a-SiC) microresonator with optical Q as high as 1.3 × 10(5). The high optical quality allows us to characterize the third-order nonlinear susceptibility of a-SiC. The Kerr nonlinearity is measured to be n2 = (5.9 ± 0.7) × 10(−15) cm(2)/W in the telecom band around 1550 nm. The strong Kerr nonlinearity and high optical quality render a-SiC microresonators a promising platform for integrated nonlinear photonics. PMID:25607031

  6. PECVD silicon carbide surface micromachining technology and selected MEMS applications

    NARCIS (Netherlands)

    Rajaraman, V.; Pakula, L.S.; Yang, H.; French, P.J.; Sarro, P.M.

    2011-01-01

    Attractive material properties of plasma enhanced chemical vapour deposited (PECVD) silicon carbide (SiC) when combined with CMOS-compatible low thermal budget processing provides an ideal technology platform for developing various microelectromechanical systems (MEMS) devices and merging them with

  7. Influence of nanometric silicon carbide on phenolic resin composites properties

    Indian Academy of Sciences (India)

    GEORGE PELIN; CRISTINA-ELISABETA PELIN; ADRIANA STEFAN; ION DINC\\u{A}; ANTON FICAI; ECATERINA ANDRONESCU; ROXANA TRUSC\\u{A}

    2016-06-01

    This paper presents a preliminary study on obtaining and characterization of phenolic resin-based composites modified with nanometric silicon carbide. The nanocomposites were prepared by incorporating nanometric silicon carbide (nSiC) into phenolic resin at 0.5, 1 and 2 wt% contents using ultrasonication to ensure uniform dispersion of the nanopowder, followed by heat curing of the phenolic-based materials at controlled temperature profile up to 120$^{\\circ}$C. The obtained nanocomposites were characterized by FTIR spectroscopy and scanning electron microscopy analysis and evaluated in terms of mechanical, tribological and thermal stability under load. The results highlight the positive effect of the nanometric silicon carbide addition in phenolic resin on mechanical, thermo-mechanical and tribological performance, improving their strength, stiffness and abrasive properties. The best results were obtained for 1 wt% nSiC, proving that this value is the optimum nanometric silicon carbide content. The results indicate that these materials could be effectively used to obtain ablative or carbon–carbon composites in future studies.

  8. An infrared and luminescence study of tritiated amorphous silicon

    International Nuclear Information System (INIS)

    Tritium has been incorporated into amorphous silicon. Infrared spectroscopy shows new infrared vibration modes due to silicon-tritium (Si-T) bonds in the amorphous silicon network. Si-T vibration frequencies are related to Si-H vibration frequencies by simple mass relationships. Inelastic collisions of β particles, produced as a result of tritium decay, with the amorphous silicon network results in the generation of electron-hole pairs. Radiative recombination of these carriers is observed. Dangling bonds associated with the tritium decay reduce luminescence efficiency

  9. A STUDY OF TIN IMPURITY ATOMS IN AMORPHOUS SILICON

    OpenAIRE

    Rabchanova, Tatiana

    2013-01-01

    Using the Mössbauer spectroscopy method for the 119 Sn isotope the state of tin impurity atoms in amorphous a-Si silicon is studied. The electrical and optical properties of tin doped films of thermally spray-coated amorphous silicon have been studied. It is shown that in contrast to the crystalline silicon where tin is an electrically inactive substitution impurity, in vacuum deposited amorphous silicon it produces an acceptor band near the valence band and a fraction of the tin atoms become...

  10. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    International Nuclear Information System (INIS)

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes

  11. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    Science.gov (United States)

    Muzha, A.; Fuchs, F.; Tarakina, N. V.; Simin, D.; Trupke, M.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.; Dyakonov, V.; Krueger, A.; Astakhov, G. V.

    2014-12-01

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  12. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    Energy Technology Data Exchange (ETDEWEB)

    Muzha, A. [Institute of Organic Chemistry, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Fuchs, F.; Simin, D.; Astakhov, G. V., E-mail: astakhov@physik.uni-wuerzburg.de [Experimental Physics VI, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Tarakina, N. V. [Wilhelm Conrad Röntgen Research Centre for Complex Material Systems (RCCM), Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Experimental Physics III, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Trupke, M. [Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, 1020 Wien (Austria); Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Dyakonov, V. [Experimental Physics VI, Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Wilhelm Conrad Röntgen Research Centre for Complex Material Systems (RCCM), Julius-Maximilian University of Würzburg, 97074 Würzburg (Germany); Bavarian Center for Applied Energy Research (ZAE Bayern), 97074 Würzburg (Germany); and others

    2014-12-15

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  13. Evidence for a silicon oxycarbide phase in the Nicalon silicon carbide fibre

    Energy Technology Data Exchange (ETDEWEB)

    Porte, L.; Sartre, A.

    1989-01-01

    The Nicalon silicon carbide fibre has been studied by X-ray photoelectron spectroscopy. Elements entering the fiber are carbon, silicon and oxygen. In addition to previously reported chemical entities (silicon carbide, silica and graphitic carbon) evidence is found of the presence of a new supplementary phase which is attributed to an intermediate silicon oxycarbide phase. As this phase is found to participate in very appreciable proportions to the composition of the fiber, some influence on the properties of this fiber can be anticipated. 17 references.

  14. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications Phase 2. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Sundberg, G.J.; Vartabedian, A.M.; Wade, J.A.; White, C.S. [Norton Co., Northboro, MA (United States). Advanced Ceramics Div.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP`ed Si{sub 3}N{sub 4} with 4wt% Y{sub 2}O{sub 3} (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  15. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications, phase 2

    Science.gov (United States)

    Sundberg, G. J.; Vartabedian, A. M.; Wade, J. A.; White, C. S.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP'ed Si3N4 with 4wt% Y2O3 (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  16. Fabrication and properties of silicon carbide nanowires

    Science.gov (United States)

    Shim, Hyun Woo

    2008-12-01

    Silicon carbide (SiC), with excellent electrical, thermal, and mechanical properties, is a promising material candidate for future devices such as high-temperature electronics and super-strong lightweight structures. Combined with superior intrinsic properties, the nanomaterials of SiC show further advantages thanks to nanoscale effects. This thesis reports the growth mechanism, the self-integration, and the friction of SiC nanowires. The study involves nanowires fabrication using thermal evaporation, structure characterization using electron microscopy, friction measurement, and theoretical modeling. The study on nanowire growth mechanism requires understanding of the surfaces and interfaces of nanowire crystal. The catalyzed growth of SiC nanowires involves interfaces between source vapor, catalytic liquid, and nanowire solid. Our experimental observation includes the periodical twinning in a faceted SiC nanowire and three stage structure transitions during the growth. The proposed theoretical model shows that such phenomenon is the result of surface energy minimization process during the catalytic growth. Surface interactions also exist between nanowires, leading to their self-integration. Our parametric growth study reveals novel self-integration of SiC-SiO 2 core-shell nanowires as a result of SiO2 joining. Attraction between nanowires through van der Waals force and enhanced SiO2 diffusion at high temperature transform individual nanowires to the integrated nanojunctions, nanocables, and finally nanowebs. We also show that such joining process becomes effective either during growth or by annealing. The solid friction is a result of the interaction between two solid surfaces, and it depends on the adhesion and the deformation of two contacting solids among other factors. Having strong adhesion as shown from gecko foot-hairs, nanostructured materials should also have strong friction; this study is the first to investigate friction of nanostructures under

  17. Characterization and adsorption modeling of silicon carbide-derived carbons.

    Science.gov (United States)

    Nguyen, T X; Bae, J-S; Bhatia, S K

    2009-02-17

    We present characterization results of silicon carbide-derived carbons (Si-CDCs) prepared from both nano- and micron-sized betaSiC particles by oxidation in pure chlorine atmosphere at various synthesis temperatures (600-1000 degrees C). Subsequently, the adsorption modeling study of simple gases (CH4 and CO2) in these Si-CDC samples for a wide range of pressures and temperatures using our Finite Wall Thickness model [Nguyen, T. X.; Bhatia, S. K. Langmuir 2004, 20, 3532] was also carried out. In general, characterization results showed that the core of Si-CDC particles contains predominantly amorphous material while minor graphitization was also observed on the surface of these particles for all the investigated synthesis temperatures (600-1000 degrees C). Furthermore, postsynthetic heat treatment at 1000 degrees C for 3 days, as well as particle size of precursor (betaSiC) were shown to have slight impact on the graphitization. In spite of the highly disordered nature of Si-CDC samples, the adsorption modeling results revealed that the Finite Wall Thickness model provides reasonably good prediction of experimental adsorption data of CO2 and CH4 in all the investigated Si-CDC samples at the temperatures of 273 K, 313 K, and 333 K for a wide range of pressure up to 200 bar. Furthermore, the impact of the difference in molecular size and geometry between analysis and probing gases on the prediction of the experimental adsorption isotherm in a disordered carbon using the slit-pore model is also found. Finally, the correlation between compressibility of the Si-CDC samples under high pressure adsorption and their synthesis temperature was deduced from the adsorption modeling. PMID:19123908

  18. The addition of silicon carbide to surrogate nuclear fuel kernels made by the internal gelation process

    International Nuclear Information System (INIS)

    The US Department of Energy plans to use the internal gelation process to make tristructural isotropic (TRISO)-coated transuranic (TRU) fuel particles. The focus of this work is to develop TRU fuel kernels with high crush strengths, good ellipticity, and adequately dispersed silicon carbide (SiC). The submicron SiC particles in the TRU kernels are to serve as getters for excess oxygen and to potentially sequester palladium, rhodium, and ruthenium, which could damage the coatings during irradiation. Zirconium oxide microspheres stabilized with yttrium were used as surrogates because zirconium and TRU microspheres from the internal gelation process are amorphous and encounter similar processing problems. The hardness of SiC required modifications to the experimental system that was used to make uranium carbide kernels. Suitable processing conditions and equipment changes were identified so that the SiC could be homogeneously dispersed in gel spheres for subsequent calcination into strong spherical kernels.

  19. Synthesis and processing of beta silicon carbide powder by silicon - carbon reaction

    International Nuclear Information System (INIS)

    SiC is an important structural ceramic and finds applications in nuclear industry. Processing of SiC ceramic components for such applications require sinter-active beta silicon carbide powders. Various novel methods have been reported for the synthesis of beta SiC powder based on silica - carbon and silicon - carbon reactions. In this research, beta-silicon carbide (β-SiC) was synthesized from the reaction of Si and C. In this research, beta-silicon carbide (β-SiC) was synthesized from the reaction of Si and C. Stoichiometric amount of silicon and petroleum coke having agglomerate size ∼ 5-8μ were planetarily wet mixed, dried, granulated and compacted to reaction specimens

  20. Selective-area laser deposition (SALD) Joining of silicon carbide with silicon carbide filler

    Science.gov (United States)

    Harrison, Shay Llewellyn

    Selective Area Laser Deposition (SALD) is a gas-phase, solid freeform fabrication (SFF) process that utilizes a laser-driven, pyrolytic gas reaction to form a desired solid product. This solid product only forms in the heated zone of the laser beam and thus can be selectively deposited by control of the laser position. SALD Joining employs the SALD method to accomplish 'welding' of ceramic structures together. The solid reaction product serves as a filler material to bond the two parts. The challenges involved with ceramic joining center around the lack of a liquid phase, little plastic deformation and diffusivity and poor surface wetting for many ceramic materials. Due to these properties, traditional metal welding procedures cannot be applied to ceramics. Most alternative ceramic welding techniques use some form of a metal addition to overcome these material limitations. However, the metal possesses a lower ultimate use temperature than the ceramic substrate and therefore it decreases the temperature range over which the joined part can be safely used. SALD Joining enjoys several advantages over these ceramic welding procedures. The solid filler material chemistry can be tailored to match the type of ceramic substrate and therefore fabricate monolithic joints. The SALD filler material bonds directly to the substrate and the joined structure is made in a one step process, without any post-processing. The research documented in this dissertation focused on SALD Joining of silicon carbide structures with silicon carbide filler material. A historical progression of gas-phase SFF research and a literature review of the most prominent ceramic joining techniques are provided. A variety of SiC substrates were examined, as were various conditions of gas precursor pressures and mixtures, laser beam scan speed and joint configuration. The SALD material was characterized for composition and structure by x-ray diffraction, transmission electron microscopy and nuclear magnetic

  1. Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures

    Science.gov (United States)

    Pradeepkumar, Aiswarya; Mishra, Neeraj; Kermany, Atieh Ranjbar; Boeckl, John J.; Hellerstedt, Jack; Fuhrer, Michael S.; Iacopi, Francesca

    2016-07-01

    Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications.

  2. SILICON CARBIDE CERAMICS FOR COMPACT HEAT EXCHANGERS

    Energy Technology Data Exchange (ETDEWEB)

    DR. DENNIS NAGLE; DR. DAJIE ZHANG

    2009-03-26

    Silicon carbide (SiC) materials are prime candidates for high temperature heat exchangers for next generation nuclear reactors due to their refractory nature and high thermal conductivity at elevated temperatures. This research has focused on demonstrating the potential of liquid silicon infiltration (LSI) for making SiC to achieve this goal. The major advantage of this method over other ceramic processing techniques is the enhanced capability of making high dense, high purity SiC materials in complex net shapes. For successful formation of net shape SiC using LSI techniques, the carbon preform reactivity and pore structure must be controlled to allow the complete infiltration of the porous carbon structure which allows complete conversion of the carbon to SiC. We have established a procedure for achieving desirable carbon properties by using carbon precursors consisting of two readily available high purity organic materials, crystalline cellulose and phenolic resin. Phenolic resin yields a glassy carbon with low chemical reactivity and porosity while the cellulose carbon is highly reactive and porous. By adjusting the ratio of these two materials in the precursor mixtures, the properties of the carbons produced can be controlled. We have identified the most favorable carbon precursor composition to be a cellulose resin mass ratio of 6:4 for LSI formation of SiC. The optimum reaction conditions are a temperature of 1800 C, a pressure of 0.5 Torr of argon, and a time of 120 minutes. The fully dense net shape SiC material produced has a density of 2.96 g cm{sup -3} (about 92% of pure SiC) and a SiC volume fraction of over 0.82. Kinetics of the LSI SiC formation process was studied by optical microscopy and quantitative digital image analysis. This study identified six reaction stages and provided important understanding of the process. Although the thermal conductivity of pure SiC at elevated temperatures is very high, thermal conductivities of most commercial Si

  3. SILICON CARBIDE CERAMICS FOR COMPACT HEAT EXCHANGERS

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) materials are prime candidates for high temperature heat exchangers for next generation nuclear reactors due to their refractory nature and high thermal conductivity at elevated temperatures. This research has focused on demonstrating the potential of liquid silicon infiltration (LSI) for making SiC to achieve this goal. The major advantage of this method over other ceramic processing techniques is the enhanced capability of making high dense, high purity SiC materials in complex net shapes. For successful formation of net shape SiC using LSI techniques, the carbon preform reactivity and pore structure must be controlled to allow the complete infiltration of the porous carbon structure which allows complete conversion of the carbon to SiC. We have established a procedure for achieving desirable carbon properties by using carbon precursors consisting of two readily available high purity organic materials, crystalline cellulose and phenolic resin. Phenolic resin yields a glassy carbon with low chemical reactivity and porosity while the cellulose carbon is highly reactive and porous. By adjusting the ratio of these two materials in the precursor mixtures, the properties of the carbons produced can be controlled. We have identified the most favorable carbon precursor composition to be a cellulose resin mass ratio of 6:4 for LSI formation of SiC. The optimum reaction conditions are a temperature of 1800 C, a pressure of 0.5 Torr of argon, and a time of 120 minutes. The fully dense net shape SiC material produced has a density of 2.96 g cm-3 (about 92% of pure SiC) and a SiC volume fraction of over 0.82. Kinetics of the LSI SiC formation process was studied by optical microscopy and quantitative digital image analysis. This study identified six reaction stages and provided important understanding of the process. Although the thermal conductivity of pure SiC at elevated temperatures is very high, thermal conductivities of most commercial Si

  4. Dynamics of hydrogen in hydrogenated amorphous silicon

    Indian Academy of Sciences (India)

    Ranber Singh; S Prakash

    2003-07-01

    The problem of hydrogen diffusion in hydrogenated amorphous silicon (a-Si:H) is studied semiclassically. It is found that the local hydrogen concentration fluctuations-induced extra potential wells, if intense enough, lead to the localized electronic states in a-Si:H. These localized states are metastable. The trapping of electrons and holes in these states leads to the electrical degradation of the material. These states also act as recombination centers for photo-generated carriers (electrons and holes) which in turn may excite a hydrogen atom from a nearby Si–H bond and breaks the weak (strained) Si–Si bond thereby apparently enhancing the hydrogen diffusion and increasing the light-induced dangling bonds.

  5. Three-Terminal Amorphous Silicon Solar Cells

    Directory of Open Access Journals (Sweden)

    Cheng-Hung Tai

    2011-01-01

    Full Text Available Many defects exist within amorphous silicon since it is not crystalline. This provides recombination centers, thus reducing the efficiency of a typical a-Si solar cell. A new structure is presented in this paper: a three-terminal a-Si solar cell. The new back-to-back p-i-n/n-i-p structure increased the average electric field in a solar cell. A typical a-Si p-i-n solar cell was also simulated for comparison using the same thickness and material parameters. The 0.28 μm-thick three-terminal a-Si solar cell achieved an efficiency of 11.4%, while the efficiency of a typical a-Si p-i-n solar cell was 9.0%. Furthermore, an efficiency of 11.7% was achieved by thickness optimization of the three-terminal solar cell.

  6. Amorphous Silicon-Carbon Nanostructure Solar Cells

    Science.gov (United States)

    Schriver, Maria; Regan, Will; Loster, Matthias; Zettl, Alex

    2011-03-01

    Taking advantage of the ability to fabricate large area graphene and carbon nanotube networks (buckypaper), we produce Schottky junction solar cells using undoped hydrogenated amorphous silicon thin films and nanostructured carbon films. These films are useful as solar cell materials due their combination of optical transparency and conductance. In our cells, they behave both as a transparent conductor and as an active charge separating layer. We demonstrate a reliable photovoltaic effect in these devices with a high open circuit voltage of 390mV in buckypaper devices. We investigate the unique interface properties which result in an unusual J-V curve shape and optimize fabrication processes for improved solar conversion efficiency. These devices hold promise as a scalable solar cell made from earth abundant materials and without toxic and expensive doping processes.

  7. Short range atomic migration in amorphous silicon

    Science.gov (United States)

    Strauß, F.; Jerliu, B.; Geue, T.; Stahn, J.; Schmidt, H.

    2016-05-01

    Experiments on self-diffusion in amorphous silicon between 400 and 500 °C are presented, which were carried out by neutron reflectometry in combination with 29Si/natSi isotope multilayers. Short range diffusion is detected on a length scale of about 2 nm, while long range diffusion is absent. Diffusivities are in the order of 10-19-10-20 m2/s and decrease with increasing annealing time, reaching an undetectable low value for long annealing times. This behavior is strongly correlated to structural relaxation and can be explained as a result of point defect annihilation. Diffusivities for short annealing times of 60 s follow the Arrhenius law with an activation enthalpy of (0.74 ± 0.21) eV, which is interpreted as the activation enthalpy of Si migration.

  8. Amorphous Silicon Display Backplanes on Plastic Substrates

    Science.gov (United States)

    Striakhilev, Denis; Nathan, Arokia; Vygranenko, Yuri; Servati, Peyman; Lee, Czang-Ho; Sazonov, Andrei

    2006-12-01

    Amorphous silicon (a-Si) thin-film transistor (TFT) backplanes are very promising for active-matrix organic light-emitting diode displays (AMOLEDs) on plastic. The technology benefits from a large manufacturing base, simple fabrication process, and low production cost. The concern lies in the instability of the TFTs threshold voltage (VT) and its low device mobility. Although VT-instability can be compensated by means of advanced multi-transistor pixel circuits, the lifetime of the display is still dependent on the TFT process quality and bias conditions. A-Si TFTs with field-effect mobility of 1.1 cm2/V · s and pixel driver circuits have been fabricated on plastic substrates at 150 °C. The circuits are characterized in terms of current drive capability and long-term stability of operation. The results demonstrate sufficient and stable current delivery and the ability of the backplane on plastic to meet AMOLED requirements.

  9. Surface passivation of crystalline silicon by Cat-CVD amorphous and nanocrystalline thin silicon films

    OpenAIRE

    Voz Sánchez, Cristóbal; Martin, I.; Orpella, A.; Puigdollers i González, Joaquim; Vetter, M.; Alcubilla González, Ramón; Soler Vilamitjana, David; Fonrodona Turon, Marta; Bertomeu i Balagueró, Joan; Andreu i Batallé, Jordi

    2003-01-01

    In this work, we study the electronic surface passivation of crystalline silicon with intrinsic thin silicon films deposited by Catalytic CVD. The contactless method used to determine the effective surface recombination velocity was the quasi-steady-state photoconductance technique. Hydrogenated amorphous and nanocrystalline silicon films were evaluated as passivating layers on n- and p-type float zone silicon wafers. The best results were obtained with amorphous silicon films, which allowed ...

  10. Study on the substrate-induced crystallisation of amorphous SiC-precursor ceramics. TIB/A; Untersuchungen zur substratinduzierten Kristallisation amorpher SiC-Precursorkeramiken

    Energy Technology Data Exchange (ETDEWEB)

    Rau, C.

    2000-12-01

    In the present thesis the crystallization behaviour of amorphous silicon-carbon materials (SiC{sub x}) was studied. The main topic of the experimental studies formed thereby the epitactical crystallization of thin silicon carbide layers on monocrystalline substrates of silicon carbides or silicon. Furthermore by thermolysis of the polymer amorphous SiC{sub x}-powder was obtained.

  11. Photoluminescent properties of silicon carbide and porous silicon carbide after annealing

    International Nuclear Information System (INIS)

    Photoluminescent (PL) p-type 6H porous silicon carbides (PSCs), which showed a strong blue-green photoluminescence band centered at approximately 490 nm, were annealed in Ar and vacuum conditions. The morphological, optical, and chemical states after annealing are reported on electrochemically etched SiC semiconductors. The thermal treatments in the Ar and vacuum environments showed different trends in the PL spectra of the PSC. In particular, in the case of annealing in a vacuum, the PL spectra showed both a weak red PL peak near 630 nm and a relatively intense PL peak at around 430 nm in the violet region. SEM images showed that the etched surface had spherical nanostructures, mesostructures, and islands. With increasing annealing temperature it changes all spherical nanostructures. The average pore size observed at the surface of the PSC before annealing was of the order of approximately 10 nm. In order to investigate the surface of a series of samples in detail, both the detection of a particular chemical species and the electronic environments at the surface are examined using X-ray photoelectron spectroscopy (XPS). The chemical states from each XPS spectrum depend differently before and after annealing the surface at various temperatures. From these results, the PL spectra could be attributed not only to the quantum size effects but also to the oxide state.

  12. STATUS OF HIGH FLUX ISOTOPE REACTOR IRRADIATION OF SILICON CARBIDE/SILICON CARBIDE JOINTS

    Energy Technology Data Exchange (ETDEWEB)

    Katoh, Yutai [ORNL; Koyanagi, Takaaki [ORNL; Kiggans, Jim [ORNL; Cetiner, Nesrin [ORNL; McDuffee, Joel [ORNL

    2014-09-01

    Development of silicon carbide (SiC) joints that retain adequate structural and functional properties in the anticipated service conditions is a critical milestone toward establishment of advanced SiC composite technology for the accident-tolerant light water reactor (LWR) fuels and core structures. Neutron irradiation is among the most critical factors that define the harsh service condition of LWR fuel during the normal operation. The overarching goal of the present joining and irradiation studies is to establish technologies for joining SiC-based materials for use as the LWR fuel cladding. The purpose of this work is to fabricate SiC joint specimens, characterize those joints in an unirradiated condition, and prepare rabbit capsules for neutron irradiation study on the fabricated specimens in the High Flux Isotope Reactor (HFIR). Torsional shear test specimens of chemically vapor-deposited SiC were prepared by seven different joining methods either at Oak Ridge National Laboratory or by industrial partners. The joint test specimens were characterized for shear strength and microstructures in an unirradiated condition. Rabbit irradiation capsules were designed and fabricated for neutron irradiation of these joint specimens at an LWR-relevant temperature. These rabbit capsules, already started irradiation in HFIR, are scheduled to complete irradiation to an LWR-relevant dose level in early 2015.

  13. Analytical and Experimental Evaluation of Joining Silicon Carbide to Silicon Carbide and Silicon Nitride to Silicon Nitride for Advanced Heat Engine Applications Phase II

    Energy Technology Data Exchange (ETDEWEB)

    Sundberg, G.J.

    1994-01-01

    Techniques were developed to produce reliable silicon nitride to silicon nitride (NCX-5101) curved joins which were used to manufacture spin test specimens as a proof of concept to simulate parts such as a simple rotor. Specimens were machined from the curved joins to measure the following properties of the join interlayer: tensile strength, shear strength, 22 C flexure strength and 1370 C flexure strength. In parallel, extensive silicon nitride tensile creep evaluation of planar butt joins provided a sufficient data base to develop models with accurate predictive capability for different geometries. Analytical models applied satisfactorily to the silicon nitride joins were Norton's Law for creep strain, a modified Norton's Law internal variable model and the Monkman-Grant relationship for failure modeling. The Theta Projection method was less successful. Attempts were also made to develop planar butt joins of siliconized silicon carbide (NT230).

  14. Development of a continuous spinning process for producing silicon carbide - silicon nitride precursor fibers

    Science.gov (United States)

    1985-01-01

    An apparatus was designed for the continuous production of silicon carbide - silicon nitride precursor fibers. The precursor polymer can be fiberized, crosslined and pyrolyzed. The product is a metallic black fiber with the composition of the type C sub x Si sub y n sub z. Little, other than the tensile strength and modulus of elasticity, is known of the physical properties.

  15. Novel silicon carbide/polypyrrole composites; preparation and physicochemical properties

    International Nuclear Information System (INIS)

    Novel silicon carbide/polypyrrole (SiC/PPy) conducting composites were prepared using silicon carbide as inorganic substrate. The surface modification of SiC was performed in aqueous solution by oxidative polymerization of pyrrole using ferric chloride as oxidant. Elemental analysis was used to determine the mass loading of polypyrrole in the SiC/PPy composites. Scanning electron microscopy showed the surface modification of SiC by PPy. PPy in composites was confirmed by the presence of PPy bands in the infrared spectra of SiC/PPy containing various amounts of conducting polymer. The conductivity of SiC/PPy composites depends on PPy content on the surface. The composite containing 35 wt.% PPy showed conductivity about 2 S cm-1, which is in the same range as the conductivity of pure polypyrrole powder prepared under the same conditions using the same oxidant. PPy in the composites was clearly detected by X-ray photoelectron spectroscopy (XPS) measurements by its N1s and Cl2p peaks. High resolution scans of the C1s regions distinguished between silicon carbide and polypyrrole carbons. The fraction of polypyrrole at the composite surface was estimated from the silicon and nitrogen levels. The combination of XPS and conductivity measurements suggests that the surface of the SiC/PPy composites is polypyrrole-rich for a conducting polymer mass loading of at least 12.6 wt.%

  16. Revised activation estimates for silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Heinisch, H.L. [Pacific Northwest National Lab., Richland, WA (United States); Cheng, E.T.; Mann, F.M.

    1996-10-01

    Recent progress in nuclear data development for fusion energy systems includes a reevaluation of neutron activation cross sections for silicon and aluminum. Activation calculations using the newly compiled Fusion Evaluated Nuclear Data Library result in calculated levels of {sup 26}Al in irradiated silicon that are about an order of magnitude lower than the earlier calculated values. Thus, according to the latest internationally accepted nuclear data, SiC is much more attractive as a low activation material, even in first wall applications.

  17. Revised activation estimates for silicon carbide

    International Nuclear Information System (INIS)

    Recent progress in nuclear data development for fusion energy systems includes a reevaluation of neutron activation cross sections for silicon and aluminum. Activation calculations using the newly compiled Fusion Evaluated Nuclear Data Library result in calculated levels of 26Al in irradiated silicon that are about an order of magnitude lower than the earlier calculated values. Thus, according to the latest internationally accepted nuclear data, SiC is much more attractive as a low activation material, even in first wall applications

  18. Amorphous silicon-based PINIP structure for color sensor

    International Nuclear Information System (INIS)

    A series of hydrogenated amorphous silicon carbide (a-SiC:H) films was prepared by plasma enhanced chemical vapor deposition (PECVD) technology. The microstructure and photoelectronic properties of the film are investigated by absorption spectra (in the ultraviolet to near-infrared range) and Fourier transform infrared (FTIR) spectra. The results show that good band gap controllability (1.83-3.64 eV) was achieved by adjusting the plasma parameters. In the energy range around 2.1 eV, the a-Si1-xC x:H films exhibit good photosensitivity, opening the possibility to use this wide band gap material for device application, especially when blue color detectors are concerned. A multilayer device with a stack of glass/TCO(ZnO:Ga)/P(a-SiC:H)/I(a-SiC:H)/N(a-Si:H)/I(a-Si:H)/P(a-Si:H)/Al has been prepared. The devices can detect blue and red colors under different bias voltages. The optimization of the device, especially the film thickness and the band gap offset used to achieve better detectivity, is also done in this work

  19. A tough, thermally conductive silicon carbide composite with high strength up to 1600 degreesC in Air

    Science.gov (United States)

    Ishikawa; Kajii; Matsunaga; Hogami; Kohtoku; Nagasawa

    1998-11-13

    A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), fibrous fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC). PMID:9812889

  20. Hydrogen distribution in amorphous silicon and silicon based alloys

    International Nuclear Information System (INIS)

    The results of hydrogen evolution experiments on amorphous silicon alloys prepared by high frequency PECVD of gas mixtures containing SiH4, NH3, PH2, B2H6 are compared. Using a very low heating rate of 5 degree/min it is possible to resolve fine structure on the exodiffusion spectra. Three evolution processes are observed: (a) low temperature effusion due to included gas (b) mid temperature effusion due to 'clustered' hydrogen bonds (c) high temperature effusion due to 'isolated' hydrogen bonds In addition it is possible to oberve very fine structure 'puffing' due to the release of molecular hydrogen at mid to high temperature. Silicon and silicon nitride films have been annealed at low temperatures before the exodiffusion experiments and changes in the evolution spectra are observed, dependent on the annealing process. A scanning electron microscope study of the effect of high temperature heat treatment has also been undertaken. These results are correlated with infra-red absorption measurements and the influence of doping concentration and substrate character discussed. Under certain preparation conditions the films blister on heating and finally burst forming circular craters, and these effects are shown to be dependent on substrate material and intrinsic stress of the as-grown films

  1. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    Science.gov (United States)

    Riesen, Y.; Stuckelberger, M.; Haug, F.-J.; Ballif, C.; Wyrsch, N.

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy

  2. Plasma-enhanced chemical vapor deposited silicon carbide as an implantable dielectric coating.

    Science.gov (United States)

    Cogan, Stuart F; Edell, David J; Guzelian, Andrew A; Ping Liu, Ying; Edell, Robyn

    2003-12-01

    Amorphous silicon carbide (a-SiC) films, deposited by plasma-enhanced chemical vapor deposition (PECVD), have been evaluated as insulating coatings for implantable microelectrodes. The a-SiC was deposited on platinum or iridium wire for measurement of electrical leakage through the coating in phosphate-buffered saline (PBS, pH 7.4). Low leakage currents of silicon nitride formed by low-pressure chemical vapor deposition (LPCVD). Dissolution rates of LPCVD silicon nitride were 2 nm/h and 0.4 nm/day at 90 and 37 degrees C, respectively, while a-SiC had a dissolution rate of 0.1 nm/h at 90 degrees C and no measurable dissolution at 37 degrees C. Biocompatibility was assessed by implanting a-SiC-coated quartz discs in the subcutaneous space of the New Zealand White rabbit. Histological evaluation showed no chronic inflammatory response and capsule thickness was comparable to silicone or uncoated quartz controls. Amorphous SiC-coated microelectrodes were implanted in the parietal cortex for periods up to 150 days and the cortical response evaluated by histological evaluation of neuronal viability at the implant site. The a-SiC was more stable in physiological saline than LPCVD Si(3)N(4) and well tolerated in the cortex. PMID:14613234

  3. Modification of silicon nitride and silicon carbide surfaces for food and biosensor applications

    OpenAIRE

    Rosso, M.

    2009-01-01

    Silicon-rich silicon nitride (SixN4, x > 3) is a robust insulating material widely used for the coating of microdevices: its high chemical and mechanical inertness make it a material of choice for the reinforcement of fragile microstructures (e.g. suspended microcantilevers, micro-fabricated membranes-“microsieves”) or for the coating of the exposed surfaces of sensors (field-effect transistors, waveguide optical detectors). To a more limited extent, silicon carbide (SiC) can find similar ...

  4. Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon.

    Science.gov (United States)

    Ben Slama, Sonia; Hajji, Messaoud; Ezzaouia, Hatem

    2012-01-01

    Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications. PMID:22901341

  5. Proton NMR studies of PECVD hydrogenated amorphous silicon films and HWCVD hydrogenated amorphous silicon films

    Science.gov (United States)

    Herberg, Julie Lynn

    This dissertation discusses a new understanding of the internal structure of hydrogenated amorphous silicon. Recent research in our group has included nuclear spin echo double resonance (SEDOR) measurements on device quality hydrogenated amorphous silicon photovoltaic films. Using the SEDOR pulse sequence with and without the perturbing 29Si pulse, we obtain Fourier transform spectra for film at 80K that allows us to distinguish between molecular hydrogen and hydrogen bonded to silicon. Using such an approach, we have demonstrated that high quality a-Si:H films produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) from SiH 4 contains about ten atomic percent hydrogen, nearly 40% of which is molecular hydrogen, individually trapped in the amorphous equivalent of tetragonal sites (T-sites). The main objective of this dissertation is to examine the difference between a-Si:H made by PECVD techniques and a-Si:H made by Hot Wire Chemical Vapor Deposition (HWCVD) techniques. Proton NMR and 1H- 29Si SEDOR NMR are used to examine the hydrogen structure of HWCVD a-Si:H films prepared at the University of Utrecht and at the National Renewable Energy Laboratory (NREL). Past NMR studies have shown that high quality PECVD a-Si:H films have geometries in which 40% of the contained hydrogen is present as H2 molecules individually trapped in the amorphous equivalent of T-sites. A much smaller H2 fraction sometimes is physisorbed on internal surfaces. In this dissertation, similar NMR methods are used to perform structural studies of the two HWCVD aSi:H samples. The 3kHz resonance line from T-site-trapped H2 molecules shows a hole-burn behavior similar to that found for PECVD a-Si:H films as does the 24kHz FWHM line from clustered hydrogen bonded to silicon. Radio frequency hole-burning is a tool to distinguish between inhomogenous and homogeneous broadening. In the hole-burn experiments, the 3kHz FWHM resonance line from T-site-trapped H2 molecules shows a hole

  6. Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

    Science.gov (United States)

    Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

    2007-01-01

    A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

  7. Effect of alumina on silicon carbide bodies with clay bonding

    International Nuclear Information System (INIS)

    Components made of silicon carbide are very important ceramic products due to their good resistance against thermal shocks. Home made of such products having silicate bonding usually have various defects in their structures. In this research effects of alumina addition on the components made of silicon carbide with clay bonding have been investigated, in order to see its effects on mechanical and structural properties such as blistering. Addition of up to 15 weights %. Al2O3 improved thermal shock resistance and increased bending strength from 25 MPa to 32 MPa due to Al2O3 transformation to mullite. However, when the amounts of alumina exceed 15 weights % mechanical strength as well as resistance to thermal shock reduced due to reman ing of Al2O3 in the components after sintering

  8. Nanowires of silicon carbide and 3D SiC/C nanocomposites with inverse opal structure

    International Nuclear Information System (INIS)

    Synthesis, morphology, structural and optical characteristics of SiC NWs and SiC/C nanocomposites with an inverse opal lattice have been investigated. The samples were prepared by carbothermal reduction of silica (SiC NWs) and by thermo-chemical treatment of opal matrices (SiC/C) filled with carbon compounds which was followed by silicon dioxide dissolution. It was shown that the nucleation of SiC NWs occurs at the surface of carbon fibers felt. It was observed three preferred growth direction of the NWs: [111], [110] and [112]. HRTEM studies revealed the mechanism of the wires growth direction change. SiC/C- HRTEM revealed in the structure of the composites, except for silicon carbide, graphite and amorphous carbon, spherical carbon particles containing concentric graphite shells (onion-like particles).

  9. Laser annealing of amorphous silicon core optical fibers

    OpenAIRE

    Healy, N; Mailis, S.; Day, T. D.; Sazio, P.J.A.; Badding, J. V.; A.C. Peacock

    2012-01-01

    Laser annealing of an optical fiber with an amorphous silicon core is demonstrated. The annealing process produces a fiber that has a highly crystalline core, whilst reducing the optical transmission losses by ~3 orders of magnitude.

  10. Nanocavity Shrinkage and Preferential Amorphization during Irradiation in Silicon

    Institute of Scientific and Technical Information of China (English)

    ZHU Xian-Fang; WANG Zhan-Guo

    2005-01-01

    @@ We model the recent experimental results and demonstrate that the internal shrinkage of nanocavities in silicon is intrinsically associated with preferential amorphization as induced by self-ion irradiation.

  11. Thermal properties of amorphous/crystalline silicon superlattices.

    Science.gov (United States)

    France-Lanord, Arthur; Merabia, Samy; Albaret, Tristan; Lacroix, David; Termentzidis, Konstantinos

    2014-09-01

    Thermal transport properties of crystalline/amorphous silicon superlattices using molecular dynamics are investigated. We show that the cross-plane conductivity of the superlattices is very low and close to the conductivity of bulk amorphous silicon even for amorphous layers as thin as ≃ 6 Å. The cross-plane thermal conductivity weakly increases with temperature which is associated with a decrease of the Kapitza resistance with temperature at the crystalline/amorphous interface. This property is further investigated considering the spatial analysis of the phonon density of states in domains close to the interface. Interestingly, the crystalline/amorphous superlattices are shown to display large thermal anisotropy, according to the characteristic sizes of elaborated structures. These last results suggest that the thermal conductivity of crystalline/amorphous superlattices can be phonon engineered, providing new directions for nanostructured thermoelectrics and anisotropic materials in thermal transport. PMID:25105883

  12. Progress in Studies on Carbon and Silicon Carbide Nanocomposite Materials

    International Nuclear Information System (INIS)

    Silicon carbide nanofiber and carbon nanotubes are introduced. The structure and application of nanotubers (nanofibers) in carbon/carbon composites are emphatically presented. Due to the unique structure of nanotubers (nanofibers), they can modify the microstructure of pyrocarbon and induce the deposition of pyrocarbon with high text in carbon/carbon composites. So the carbon/carbon composites modified by CNT/CNF have more excellent properties.

  13. Rheology of silicon carbide/vinyl ester nanocomposites

    OpenAIRE

    Yong, Virginia; Hahn, H. Thomas

    2006-01-01

    Silicon carbide (SiC) nanoparticles with no surface treatment raise the viscosity of a vinyl ester resin much more intensely than micrometer-size SiC particles. An effective dispersant generally causes a reduction in the resin viscosity attributed to its surface-active properties and thereby increases the maximum fraction of particles that can be introduced. This article assesses the rheological behavior of SiC-nanoparticle-filled vinyl ester resin systems with the Bingham, power-law, Hersche...

  14. Anodic etching of p-type cubic silicon carbide

    Science.gov (United States)

    Harris, G. L.; Fekade, K.; Wongchotigul, K.

    1992-01-01

    p-Type cubic silicon carbide was anodically etched using an electrolyte of HF:HCl:H2O. The etching depth was determined versus time with a fixed current density of 96.4 mA/sq cm. It was found that the etching was very smooth and very uniform. An etch rate of 22.7 nm/s was obtained in a 1:1:50 HF:HCl:H2O electrolyte.

  15. Silicon carbide materials for LWR application: current status and issues

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) is a very attractive engineering ceramic in particular for high-temperature use and nuclear application due to its high-temperature strength, oxygen resistance, chemical stability, low activation, radiation resistance, etc. Silicon carbide composites have pseudo ductile behaviour by de-bonding and sliding at fiber/matrix interphase. Fundamental mechanical properties of highly crystalline nuclear grade SiC composites are stable following neutron irradiation. Silicon carbide composites are promising materials for accident-tolerant fuel. The sophistication of the technology infrastructure for safety has been requested by the Ministry of Economy, Trade and Industry (METI) in Japan. The research and development of fuel such as SiC cladding are expected to be described in a new road map by METI. Silicon carbide is a promising material for LWR application in terms of excellent stability of dimension and strength under neutron irradiation and excellent resistance to high-temperature steam. Fundamental fabrication technique and joining technique have been established. Current SiC/SiC composites have C interphase and environmental coating is required to prevent oxidation. Novel porous SiC/SiC composites do not have C interphase and have excellent oxidation resistance, although hermetic coating is required. The issues of SiC composite development for LWR application are as follows: The SiC/SiC composites have impurities depending on fabrication methods. It is important to understand the effect of impurities on the resistance to high-temperature water under normal operation and the resistance to high-temperature steam in the case of severe accident. The synergetic effect of irradiation and high-temperature water is also important. The reaction with fuel under neutron irradiation needs to be clarified. As for material development, coating, joining technique and large scale fabrication should be considered as important issues. Material cost should be

  16. Progress in Studies on Carbon and Silicon Carbide Nanocomposite Materials

    OpenAIRE

    Peng Xiao; Jie Chen; Xian-feng Xu

    2010-01-01

    Silicon carbide nanofiber and carbon nanotubes are introduced. The structure and application of nanotubers (nanofibers) in carbon/carbon composites are emphatically presented. Due to the unique structure of nanotubers (nanofibers), they can modify the microstructure of pyrocarbon and induce the deposition of pyrocarbon with high text in carbon/carbon composites. So the carbon/carbon composites modified by CNT/CNF have more excellent properties.

  17. The chemical reactivity of REFEL silicon carbide

    International Nuclear Information System (INIS)

    There was no general or localised attack of REFEL SiC during 700 h immersion in up to 80% H2SO4 or HCl solutions at 1000C. In water at =0C and NaOH solutions at =0C the free silicon was leached from the ceramic, being controlled by silica dissolution, whose rate increased with solution pH. Silicon removal also predominated in steam at 5000C, through volatile product formation. Solid-solid interaction was measurable during 100 h contact with representative Ni based alloys at >= 8000C and with Fe and Co based alloys at >= 9000C, with the formation of metallic silicides. Carbon and silicon were picked up by the alloys. (author)

  18. Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon

    OpenAIRE

    Ben Slama, Sonia; Hajji, Messaoud; Ezzaouia, Hatem

    2012-01-01

    Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that...

  19. Structure and Optical Properties of Silicon Nanocrystals Embedded in Amorphous Silicon Thin Films Obtained by PECVD

    OpenAIRE

    Monroy, B. M.; Aduljay Remolina Millán; García-Sánchez, M. F.; Ponce, A.; Picquart, M.; Santana, G.

    2011-01-01

    Silicon nanocrystals embedded in amorphous silicon matrix were obtained by plasma enhanced chemical vapor deposition using dichlorosilane as silicon precursor. The RF power and dichlorosilane to hydrogen flow rate ratio were varied to obtain different crystalline fractions and average sizes of silicon nanocrystals. High-resolution transmission electron microscopy images and RAMAN measurements confirmed the existence of nanocrystals embedded in the amorphous matrix with average sizes between 2...

  20. Reaction kinetics of nanostructured silicon carbide

    Science.gov (United States)

    Wallis, K. L.; Patyk, J. K.; Zerda, T. W.

    2008-08-01

    SiC nanowires were produced from carbon nanotubes and silicon by two different methods at high temperature. X-ray powder diffraction was used to determine SiC concentration. The reaction rate using the Avrami-Erofeev method was determined for samples sintered at temperatures ranging from 1313 to 1823 K. The activation energy was found to be (254 ± 36) kJ mol-1. The limiting factor in SiC formation is diffusion of silicon and carbon atoms through the produced layer of SiC.

  1. Reaction kinetics of nanostructured silicon carbide

    International Nuclear Information System (INIS)

    SiC nanowires were produced from carbon nanotubes and silicon by two different methods at high temperature. X-ray powder diffraction was used to determine SiC concentration. The reaction rate using the Avrami-Erofeev method was determined for samples sintered at temperatures ranging from 1313 to 1823 K. The activation energy was found to be (254 ± 36) kJ mol-1. The limiting factor in SiC formation is diffusion of silicon and carbon atoms through the produced layer of SiC

  2. Interaction of hydrogenated amorphous silicon films with transparent conductive films

    OpenAIRE

    Kitagawa, M.; Mori, K; Ishihara, S.; Ohno, M.; Hirao, T.; Yoshioka, Y.; Kohiki, S

    1983-01-01

    The effects of the deposition temperature on the interaction of the hydrogenated amorphous silicon films with indium-tin-oxide and tin-oxide films have been investigated in the temperature range 150-300 degrees C, using Auger electron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy. It was found that the constituent atoms such as indium and tin are detected in the thin amorphous silicon films deposited. Around the interface between the transparent conductive fi...

  3. PHOTOEMISSION STUDIES OF THE TRANSITION FROM AMORPHOUS TO MICROCRYSTALLINE SILICON

    OpenAIRE

    Richter, H.; Ley, L.

    1981-01-01

    We have studied a series of samples spanning the range from purely amorphous to microcrystalline silicon prepared by chemical transport in a hydrogen plasma or by sputtering in a H2/Ar mixture. The first order Raman spectra show a superposition of amorphous and crystalline contribution, showing some features of wurtzite-silicon. The electronic density of states, as deduced from X-ray photoelectron-spectroscopy, shows a gradual change from microcrystalline structure for samples prepared by che...

  4. Experimentally Constrained Molecular Relaxation: The case of hydrogenated amorphous silicon

    OpenAIRE

    Biswas, Parthapratim; Atta-Fynn, Raymond; Drabold, David A.

    2007-01-01

    We have extended our experimentally constrained molecular relaxation technique (P. Biswas {\\it et al}, Phys. Rev. B {\\bf 71} 54204 (2005)) to hydrogenated amorphous silicon: a 540-atom model with 7.4 % hydrogen and a 611-atom model with 22 % hydrogen were constructed. Starting from a random configuration, using physically relevant constraints, {\\it ab initio} interactions and the experimental static structure factor, we construct realistic models of hydrogenated amorphous silicon. Our models ...

  5. Bonding and Integration Technologies for Silicon Carbide Based Injector Components

    Science.gov (United States)

    Halbig, Michael C.; Singh, Mrityunjay

    2008-01-01

    Advanced ceramic bonding and integration technologies play a critical role in the fabrication and application of silicon carbide based components for a number of aerospace and ground based applications. One such application is a lean direct injector for a turbine engine to achieve low NOx emissions. Ceramic to ceramic diffusion bonding and ceramic to metal brazing technologies are being developed for this injector application. For the diffusion bonding, titanium interlayers (PVD and foils) were used to aid in the joining of silicon carbide (SiC) substrates. The influence of such variables as surface finish, interlayer thickness (10, 20, and 50 microns), processing time and temperature, and cooling rates were investigated. Microprobe analysis was used to identify the phases in the bonded region. For bonds that were not fully reacted an intermediate phase, Ti5Si3Cx, formed that is thermally incompatible in its thermal expansion and caused thermal stresses and cracking during the processing cool-down. Thinner titanium interlayers and/or longer processing times resulted in stable and compatible phases that did not contribute to microcracking and resulted in an optimized microstructure. Tensile tests on the joined materials resulted in strengths of 13-28 MPa depending on the SiC substrate material. Non-destructive evaluation using ultrasonic immersion showed well formed bonds. For the joining technology of brazing Kovar fuel tubes to silicon carbide, preliminary development of the joining approach has begun. Various technical issues and requirements for the injector application are addressed.

  6. The Development of Silicon Carbide Based Hydrogen and Hydrocarbon Sensors

    Science.gov (United States)

    Liu, Chung-Chiun

    1994-01-01

    Silicon carbide is a high temperature electronic material. Its potential for development of chemical sensors in a high temperature environment has not been explored. The objective of this study is to use silicon carbide as the substrate material for the construction of chemical sensors for high temperature applications. Sensors for the detection of hydrogen and hydrocarbon are developed in this program under the auspices of Lewis Research Center, NASA. Metal-semiconductor or metal-insulator-semiconductor structures are used in this development. Specifically, using palladium-silicon carbide Schottky diodes as gas sensors in the temperature range of 100 to 400 C are designed, fabricated and assessed. The effect of heat treatment on the Pd-SiC Schottky diode is examined. Operation of the sensors at 400 C demonstrate sensitivity of the sensor to hydrogen and hydrocarbons. Substantial progress has been made in this study and we believe that the Pd-SiC Schottky diode has potential as a hydrogen and hydrocarbon sensor over a wide range of temperatures. However, the long term stability and operational life of the sensor need to be assessed. This aspect is an important part of our future continuing investigation.

  7. Silicon Carbide Mounts for Fabry-Perot Interferometers

    Science.gov (United States)

    Lindemann, Scott

    2011-01-01

    Etalon mounts for tunable Fabry- Perot interferometers can now be fabricated from reaction-bonded silicon carbide structural components. These mounts are rigid, lightweight, and thermally stable. The fabrication of these mounts involves the exploitation of post-casting capabilities that (1) enable creation of monolithic structures having reduced (in comparison with prior such structures) degrees of material inhomogeneity and (2) reduce the need for fastening hardware and accommodations. Such silicon carbide mounts could be used to make lightweight Fabry-Perot interferometers or could be modified for use as general lightweight optical mounts. Heretofore, tunable Fabry-Perot interferometer structures, including mounting hardware, have been made from the low-thermal-expansion material Invar (a nickel/iron alloy) in order to obtain the thermal stability required for spectroscopic applications for which such interferometers are typically designed. However, the high mass density of Invar structures is disadvantageous in applications in which there are requirements to minimize mass. Silicon carbide etalon mounts have been incorporated into a tunable Fabry-Perot interferometer of a prior design that originally called for Invar structural components. The strength, thermal stability, and survivability of the interferometer as thus modified are similar to those of the interferometer as originally designed, but the mass of the modified interferometer is significantly less than the mass of the original version.

  8. Visible-blind ultraviolet photodetectors on porous silicon carbide substrates

    International Nuclear Information System (INIS)

    Highlights: • Highly reliable UV detectors are fabricated on porous silicon carbide substrates. • The optical properties of samples are enhanced by increasing the current density. • The optimized sample exhibits enhanced sensitivity to the incident UV radiation. - Abstract: Highly reliable visible-blind ultraviolet (UV) photodetectors were successfully fabricated on porous silicon carbide (PSC) substrates. High responsivity and high photoconductive gain were observed in a metal–semiconductor–metal ultraviolet photodetector that was fabricated on an optimized PSC substrate. The PSC samples were prepared via the UV-assisted photo-electrochemical etching of an n-type hexagonal silicon carbide (6H-SiC) substrate using different etching current densities. The optical results showed that the current density is an outstanding etching parameter that controls the porosity and uniformity of PSC substrates. A highly porous substrate was synthesized using a suitable etching current density to enhance its light absorption, thereby improving the sensitivity of UV detector with this substrate. The electrical characteristics of fabricated devices on optimized PSC substrates exhibited enhanced sensitivity and responsivity to the incident radiation

  9. Diode Based on Amorphous SiC

    Directory of Open Access Journals (Sweden)

    V.S. Zakhvalinskii

    2013-12-01

    Full Text Available Diode structure on the basis of amorphous silicon carbide and p-type polycrystalline silicon (Eurosolar were obtained with magnetron RF-nonreactive sputtering method from solid-phase target in argon atmosphere.

  10. Diode Based on Amorphous SiC

    OpenAIRE

    V.S. Zakhvalinskii; L.V. Borisenko; A.J. Aleynikov; E.A. Piljuk; I. Goncharov; S.V. Taran

    2013-01-01

    Diode structure on the basis of amorphous silicon carbide and p-type polycrystalline silicon (Eurosolar) were obtained with magnetron RF-nonreactive sputtering method from solid-phase target in argon atmosphere.

  11. Determination of boron content in boron carbide, boron nitride and amorphous boron

    International Nuclear Information System (INIS)

    In the present article an analyzing method of determination of boron content in boron carbide, boron nitride and amorphous boron described. Examined samples were digested with potassium hydroxide and potassium nitrate in nickel crucible and the boron contents determined subsequently by an alcalimetric titration of boric acid in presence of mannite resp. sorbite. (author)

  12. Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

    OpenAIRE

    Luo Xiaogang; Ma Wenhui; Zhou Yang; Liu Dachun; Yang Bin; Dai Yongnian

    2009-01-01

    Abstract Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core–shell structure and gr...

  13. Extreme-Environment Silicon-Carbide (SiC) Wireless Sensor Suite

    Science.gov (United States)

    Yang, Jie

    2015-01-01

    Phase II objectives: Develop an integrated silicon-carbide wireless sensor suite capable of in situ measurements of critical characteristics of NTP engine; Compose silicon-carbide wireless sensor suite of: Extreme-environment sensors center, Dedicated high-temperature (450 deg C) silicon-carbide electronics that provide power and signal conditioning capabilities as well as radio frequency modulation and wireless data transmission capabilities center, An onboard energy harvesting system as a power source.

  14. Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers

    Science.gov (United States)

    Cunning, Benjamin V.; Ahmed, Mohsin; Mishra, Neeraj; Ranjbar Kermany, Atieh; Wood, Barry; Iacopi, Francesca

    2014-08-01

    Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices.

  15. Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers

    International Nuclear Information System (INIS)

    Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices. (paper)

  16. Amorphous Silicon: Flexible Backplane and Display Application

    Science.gov (United States)

    Sarma, Kalluri R.

    Advances in the science and technology of hydrogenated amorphous silicon (a-Si:H, also referred to as a-Si) and the associated devices including thin-film transistors (TFT) during the past three decades have had a profound impact on the development and commercialization of major applications such as thin-film solar cells, digital image scanners and X-ray imagers and active matrix liquid crystal displays (AMLCDs). Particularly, during approximately the past 15 years, a-Si TFT-based flat panel AMLCDs have been a huge commercial success. a-Si TFT-LCD has enabled the note book PCs, and is now rapidly replacing the venerable CRT in the desktop monitor and home TV applications. a-Si TFT-LCD is now the dominant technology in use for applications ranging from small displays such as in mobile phones to large displays such as in home TV, as well-specialized applications such as industrial and avionics displays.

  17. Mechanical behaviour of silicon carbide submitted to high temperature

    International Nuclear Information System (INIS)

    Ceramics (composite ceramics) are considered materials for manufacturing structure pieces of future nuclear reactor cores. In condition of nominal running, the temperature of these components is estimated at 500-800 C and could reach 1600 C in accidental condition. On account of its refractory properties and of its good compatibility with neutron flux, silicon carbide is retained for such applications, particularly for fuel cladding material (SiC/SiC composite). A study aiming to specify the mechanical behaviour of the monolithic αSiC (hexagonal structure) between 1000 and 1500 C as well as its evolution after ionic irradiation is presented. This study presents particularly the mechanical characterizations of SiC in three points bending obtained until 1450 C and surface characterizations led on SiC irradiated with ions. The rupture tests in three points bending carried out in temperature on specimens pre-cracked by indentation show an increase of 85% of the SiC rupture stress between 1000 and 1300 C. Above 1300 C, the damage of SiC induces a significant decrease of the rupture stress. Aniso-thermal creep tests on polished specimens show that the SiC presents a viscoplastic behaviour from 1200 C. Surface characterizations by Raman spectroscopy, micro and nano-indentation, acoustic microscopy led at ambient temperature on fresh and irradiated to Xe ions (94 MeV) SiC at 400 C are presented too. The formation of a structural disorder and of Si-Si homonuclear bonds disorder, suggesting a SiC amorphization, are revealed by Raman spectroscopy between 3*1014 and 3.6*1015 ions/cm2 of fluence. These microstructural changes lead to a macroscopic swelling quantifiable by measuring the height of the step formed during irradiations between the non irradiated and irradiated areas. Measurements by profilometry show that between 3*1014 and 1.2*1015 ions/cm2 of fluence, the height of the step increases of 47 nm to 83 nm, and then is stabilized with the fluence increase. The

  18. Mechanism for amorphization of boron carbide B4C under uniaxial compression

    Science.gov (United States)

    Aryal, Sitaram; Rulis, Paul; Ching, W. Y.

    2011-11-01

    Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B4C), B11C-CBC, and B12-CCC, where B11C or B12 is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B11C-CBC (B12-CCC) polytype becomes amorphous at a uniaxial strain s = 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B11C and B12 icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (Cij) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.

  19. Anharmonic Decay of Vibrational States in Amorphous Silicon

    OpenAIRE

    Fabian, Jaroslav; Allen, Philip B.

    1996-01-01

    Anharmonic decay rates are calculated for a realistic atomic model of amorphous silicon. The results show that the vibrational states decay on picosecond timescales and follow the two-mode density of states, similar to crystalline silicon, but somewhat faster. Surprisingly little change occurs for localized states. These results disagree with a recent experiment.

  20. Nanoscale engineering of radiation tolerant silicon carbide.

    Science.gov (United States)

    Zhang, Yanwen; Ishimaru, Manabu; Varga, Tamas; Oda, Takuji; Hardiman, Chris; Xue, Haizhou; Katoh, Yutai; Shannon, Steven; Weber, William J

    2012-10-14

    Radiation tolerance is determined by how effectively the microstructure can remove point defects produced by irradiation. Engineered nanocrystalline SiC with a high-density of stacking faults (SFs) has significantly enhanced recombination of interstitials and vacancies, leading to self-healing of irradiation-induced defects. While single crystal SiC readily undergoes an irradiation-induced crystalline to amorphous transformation at room temperature, the nano-engineered SiC with a high-density of SFs exhibits more than an order of magnitude increase in radiation resistance. Molecular dynamics simulations of collision cascades show that the nano-layered SFs lead to enhanced mobility of interstitial Si atoms. The remarkable radiation resistance in the nano-engineered SiC is attributed to the high-density of SFs within nano-sized grain structures that significantly enhance point defect annihilation. PMID:22948711

  1. Preparation and Characterization of Amorphous Silicon Oxide Nanowires

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO).Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that the silicon nanowires are smooth.Selected area electron diffraction (SAED) shows that the silicon nanowires are amorphous and energy-dispersive X-ray spectroscopy (EDS) indicates that the nanowires have the composition of Si and O elements in an atomic ratio of 1:2, their composition approximates that of SiO2.SiO is considered to be used as a Si sources to produce SiNWs.We conclude that the growth mechanism is closely related to the defect structure and silicon monoxide followed by growth through an oxide-assisted vapor-solid reaction.

  2. Electrical characteristics of amorphous iron-tungsten contacts on silicon

    OpenAIRE

    Finetti, M.; Pan, E. T-S.; Suni, I.; Nicolet, M-A.

    1983-01-01

    The electrical characteristics of amorphous Fe-W contacts have been determined on both p-type and n-type silicon. The amorphous films were obtained by cosputtering from a composite target. Contact resistivities, pc=1×10^−7 and pc=2.8×10^−6, were measured on n+ and p+ silicon, respectively. These values remain constant after thermal treatment up to at least 500°C. A barrier height, φBn=0.61 V, was measured on n-type silicon.

  3. Electrical characteristics of amorphous iron-tungsten contacts on silicon

    Science.gov (United States)

    Finetti, M.; Pan, E. T.-S.; Nicolet, M.-A.; Suni, I.

    1983-01-01

    The electrical characteristics of amorphous Fe-W contacts have been determined on both p-type and n-type silicon. The amorphous films were obtained by cosputtering from a composite target. Contact resistivities of 1 x 10 to the -7th and 2.8 x 10 to the -6th were measured on n(+) and p(+) silicon, respectively. These values remain constant after thermal treatment up to at least 500 C. A barrier height of 0.61 V was measured on n-type silicon.

  4. Hydrogenated amorphous silicon deposited by ion-beam sputtering

    Science.gov (United States)

    Lowe, V. E.; Henin, N.; Tu, C.-W.; Tavakolian, H.; Sites, J. R.

    1981-01-01

    Hydrogenated amorphous silicon films 1/2 to 1 micron thick were deposited on metal and glass substrates using ion-beam sputtering techniques. The 800 eV, 2 mA/sq cm beam was a mixture of argon and hydrogen ions. The argon sputtered silicon from a pure (7.6 cm) single crystal wafer, while the hydrogen combined with the sputtered material during the deposition. Hydrogen to argon pressure ratios and substrate temperatures were varied to minimize the defect state density in the amorphous silicon. Characterization was done by electrical resistivity, index of refraction and optical absorption of the films.

  5. Production of technical silicon and silicon carbide from rice-husk

    Directory of Open Access Journals (Sweden)

    A. Z. Issagulov

    2014-10-01

    Full Text Available In the article there are studied physical and chemical properties of silicon-carbonic raw material – rice-husk, thermophysical characteristics of the process of rice-husk pyrolysis in nonreactive and oxidizing environment; structure and phase composition of products of the rice-husk pyrolysis in interval of temperatures 150 – 850 °С and high temperature pyrolysis in interval of temperatures 900 – 1 500 °С. There are defined the silicon-carbon production conditions, which meet the requirements applicable to charging materials at production of technical silicon and silicon carbide.

  6. CURRENT PATH IN AMORPHOUS-SILICON FIELD EFFECT TRANSISTORS

    OpenAIRE

    M. MATSUMURA; Kuno, S.; Uchida, Y.

    1981-01-01

    On-resistance of amorphous-silicon field effect transistors with staggered electrodes was investigated. It was found that dependences of the on-resistance on geometrical parameters were classified into two groups. The origin was attributed to the residual resistance between the n+ electrode and the channel which was formed at the silicon-silicon dioxide interface. The resistance was analyzed by taking space charge effect into account, and we found that it changes in accordance with sample pre...

  7. Silicon Carbide Emitter Turn-Off Thyristor

    Directory of Open Access Journals (Sweden)

    Jun Wang

    2008-01-01

    Full Text Available A novel MOS-controlled SiC thyristor device, the SiC emitter turn-off thyristor (ETO is a promising technology for future high-voltage switching applications because it integrates the excellent current conduction capability of a SiC thyristor with a simple MOS-control interface. Through unity-gain turn-off, the SiC ETO also achieves excellent Safe Operation Area (SOA and faster switching speeds than silicon ETOs. The world's first 4.5-kV SiC ETO prototype shows a forward voltage drop of 4.26 V at 26.5 A/cm2 current density at room and elevated temperatures. Tested in an inductive circuit with a 2.5 kV DC link voltage and a 9.56-A load current, the SiC ETO shows a fast turn-off time of 1.63 microseconds and a low 9.88 mJ turn-off energy. The low switching loss indicates that the SiC ETO could operate at about 4 kHz if 100 W/cm2 conduction and the 100 W/cm2 turn-off losses can be removed by the thermal management system. This frequency capability is about 4 times higher than 4.5-kV-class silicon power devices. The preliminary demonstration shows that the SiC ETO is a promising candidate for high-frequency, high-voltage power conversion applications, and additional developments to optimize the device for higher voltage (>5 kV and higher frequency (10 kHz are needed.

  8. Pressureless sintered silicon carbide tailored with aluminium nitride sintering agent

    International Nuclear Information System (INIS)

    This study reports the influence of aluminium nitride on the pressureless sintering of cubic phase silicon carbide nanoparticles (β-SiC). Pressureless sintering was achieved at 2000 degrees C for 5 min with the additions of boron carbide together with carbon of 1 wt% and 6 wt%, respectively, and a content of aluminium nitride between 0 and 10 wt%. Sintered samples present relative densities higher than 92%. The sintered microstructure was found to be greatly modified by the introduction of aluminium nitride, which reflects the influence of nitrogen on the β-SiC to α-SiC transformation. The toughness of sintered sample was not modified by AlN incorporation and is relatively low (around 2.5 MPa m1/2). Materials exhibited transgranular fracture mode, indicating a strong bonding between SiC grains. (authors)

  9. Optical bandgap of ultra-thin amorphous silicon films deposited on crystalline silicon by PECVD

    OpenAIRE

    Yaser Abdulraheem; Ivan Gordon; Twan Bearda; Hosny Meddeb; Jozef Poortmans

    2014-01-01

    An optical study based on spectroscopic ellipsometry, performed on ultrathin hydrogenated amorphous silicon (a-Si:H) layers, is presented in this work. Ultrathin layers of intrinsic amorphous silicon have been deposited on n-type mono-crystalline silicon (c-Si) wafers by plasma enhanced chemical vapor deposition (PECVD). The layer thicknesses along with their optical properties –including their refractive index and optical loss- were characterized by spectroscopic ellipsometry (SE) in a wavel...

  10. Microstructural analysis of silicon carbide monofilaments.

    Science.gov (United States)

    Shatwell, R. A.; Dyos, K. L.; Prentice, C.; Ward, Y.; Young, R. J.

    2001-02-01

    In the development of monofilaments, a good understanding of the process/property relationships is essential. Transmission electron microscopy (TEM) is a powerful tool but too slow and expensive to be used routinely. Alternative, cheaper techniques have therefore been investigated. The microstructures of three SiC monofilaments (DERA Sigma SM1140+, Textron SCS-6 and Ultra-SCS) and some experimental samples were studied using a combination of TEM, electron microprobe analysis, Raman microprobe analysis, thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found that the Raman technique was complementary to TEM and easily identified the presence of amorphous C and Si. These could not be seen by electron or X-ray diffraction techniques. DSC indicated the presence of free Si in the DERA Sigma SM1140+ monofilament by a distinctive peak at approximately 1400 degrees C. TGA showed the reaction of monofilament components with gaseous species. The Textron SCS-6 and Ultra species lost weight as C was oxidized to gaseous CO. By contrast, the Sigma monofilament gained weight from formation of SiO2 from the free Si. The separations of the transverse optical phonon peaks in the Raman spectra were correlated with the density of stacking faults in the SiC crystallites. This was similar in all monofilaments. Analysis of the polarization of the Raman scattering gave information on the orientation of crystallites. The crystallites in SM1140+ and SCS-6 were orientated predominantly with the parallel to the radius. Preliminary interpretation of the polarized Raman scattering from Ultra-SCS indicated more than one orientation of crystallite. One possibility was a mixture of and directions parallel to the radius. PMID:11207920

  11. Dual hot-wire arrangement for the deposition of silicon and silicon carbide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Tao, E-mail: t.chen@outlook.com; Bangalore Rajeeva, Bharath; Wolff, Johannes; Schmalen, Andreas; Finger, Friedhelm, E-mail: f.finger@fz-juelich.de

    2015-01-30

    A dual hot-wire arrangement has been designed and investigated for the deposition of various thin film materials by the hot-wire chemical vapor deposition (HWCVD) technique. Tantalum and rhenium wires were used for silicon and silicon carbide depositions with hydrogen diluted silane and monomethylsilane, respectively. It is shown that the both types of filaments are mechanically stable after alternate depositions of silicon and silicon carbide with a total deposition time of about 80 h. Good material quality of the deposited films is demonstrated. By taking advantage of this dual hot-wire arrangement, it is possible to deposit both kinds of thin film materials with the individual optimum deposition conditions in a single HWCVD chamber. - Highlights: • A dual hot-wire arrangement consisting of Ta and Re wire sets was developed. • This dual wire arrangement can be mechanically stable with proper treatment on the wire surface. • Silicon and silicon carbide films of good quality were prepared with Ta and Re wires respectively. • The dual wire arrangement provides a solution for the preparation of multiple materials in a single hot-wire chamber.

  12. Dual hot-wire arrangement for the deposition of silicon and silicon carbide thin films

    International Nuclear Information System (INIS)

    A dual hot-wire arrangement has been designed and investigated for the deposition of various thin film materials by the hot-wire chemical vapor deposition (HWCVD) technique. Tantalum and rhenium wires were used for silicon and silicon carbide depositions with hydrogen diluted silane and monomethylsilane, respectively. It is shown that the both types of filaments are mechanically stable after alternate depositions of silicon and silicon carbide with a total deposition time of about 80 h. Good material quality of the deposited films is demonstrated. By taking advantage of this dual hot-wire arrangement, it is possible to deposit both kinds of thin film materials with the individual optimum deposition conditions in a single HWCVD chamber. - Highlights: • A dual hot-wire arrangement consisting of Ta and Re wire sets was developed. • This dual wire arrangement can be mechanically stable with proper treatment on the wire surface. • Silicon and silicon carbide films of good quality were prepared with Ta and Re wires respectively. • The dual wire arrangement provides a solution for the preparation of multiple materials in a single hot-wire chamber

  13. Study of Nitrogen Concentration in Silicon Carbide

    Science.gov (United States)

    Wang, Hui; Yan, Cheng-Feng; Kong, Hai-Kuan; Chen, Jian-Jun; Xin, Jun; Shi, Er-Wei; Yang, Jian-Hua

    2013-06-01

    This work focused on studying the nitrogen concentration ( C N) in SiC. The variations of C N in the synthesis of SiC powder as well as the transport during SiC crystal growth have been investigated for broad ranges of temperature and Ar pressure. Before SiC crystal growth, SiC powders were synthesized from high-purity silicon and carbon powders. The concentrations of nitrogen, free C, and free Si in the as-prepared powders were all measured. C N in the SiC source powder decreased with increasing temperature and decreasing Ar pressure, whereas it did not show a remarkable trend with the molar ratio of free Si to free C. SiC crystal was then grown by the physical vapor transport (PVT) technique using the as-prepared powder. The distribution of C N in the remaining material indirectly indicated the temperature field of crystal growth. In addition, compared with introducing N2 during SiC crystal growth, doping with nitrogen during synthesis of the SiC source powder might be a better method to control C N in SiC crystals.

  14. Light-induced Voc increase and decrease in high-efficiency amorphous silicon solar cells

    Science.gov (United States)

    Stuckelberger, M.; Riesen, Y.; Despeisse, M.; Schüttauf, J.-W.; Haug, F.-J.; Ballif, C.

    2014-09-01

    High-efficiency amorphous silicon (a-Si:H) solar cells were deposited with different thicknesses of the p-type amorphous silicon carbide layer on substrates of varying roughness. We observed a light-induced open-circuit voltage (Voc) increase upon light soaking for thin p-layers, but a decrease for thick p-layers. Further, the Voc increase is enhanced with increasing substrate roughness. After correction of the p-layer thickness for the increased surface area of rough substrates, we can exclude varying the effective p-layer thickness as the cause of the substrate roughness dependence. Instead, we explain the observations by an increase of the dangling-bond density in both the p-layer—causing a Voc increase—and in the intrinsic absorber layer, causing a Voc decrease. We present a mechanism for the light-induced increase and decrease, justified by the investigation of light-induced changes of the p-layer and supported by Advanced Semiconductor Analysis simulation. We conclude that a shift of the electron quasi-Fermi level towards the conduction band is the reason for the observed Voc enhancements, and poor amorphous silicon quality on rough substrates enhances this effect.

  15. Molybdenum isotopic composition of single silicon carbides from supernovae.

    Energy Technology Data Exchange (ETDEWEB)

    Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S.; Pellin, M. J.

    1999-02-03

    Presolar silicon carbide grains form in a variety of types of stars, including asymptotic giant branch red giant stars and supernovae. The dominant mechanisms of heavy element nucleosynthesis, the s-process and r-process, are thought to occur in AGB stars and supernovae, respectively. We have previously reported that mainstream SiC grains have strong enrichments in the s-process isotopes of Sr, Zr and Mo. We report here the first measurements of Mo isotopes in X-type SiC grains, which have previously been identified as having formed from supernova ejecta.

  16. Electronic properties of finite-length silicon carbide nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Alfieri, G. [Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto (Japan); Kimoto, T. [Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto (Japan); Photonics and Electronics Science and Engineering Center (PESEC), Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto (Japan)

    2009-02-15

    The electronic properties of silicon carbide nanotubes (SiCNT) as a function of length, were investigated by means of density functional theory (DFT). We found that the increasing nanotube length yields a higher localization of the lowest unoccupied and highest occupied molecular orbitals (LUMO and HOMO), thus affecting the behavior of the band gap and chemical reactivity of the SiCNTs. It is also found that structural stability increases for longer and larger nanotubes. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Effect of Constituents of Silicon Carbide Composites on Oxidation Behaviour

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) composites consist with SiC fibers, SiC matrix and fiber/matrix interphase. SiC composites and monolithic SiC ceramics which are the reference materials for the SiC composite matrices were exposed in air or steam environment up to 1400°C. Significant degradation was observed for the composites with C interphase after exposure in air or steam. Oxidation behaviour was also affected by impurities in SiC. (author)

  18. Planar carbon defect in the structure of cubic silicon carbide

    International Nuclear Information System (INIS)

    Two phases of silicon carbide characterized by close lattice parameters are distinguished in the solid solution of carbon in β-SiC by high-resolution XRD. They transformed into one phase after high-pressure sintering. 29Si NMR data on the initial SiC-C solid solution powder and that sintered at high pressure confirmed the high-resolution XRD data completely. The inhomogeneous structure of the SiC-C solid solution characterized by the existence of thin diamond layers inside β-SiC crystals is established by transmission electron microscopy

  19. EUV nanosecond laser ablation of silicon carbide, tungsten and molybdenum

    Czech Academy of Sciences Publication Activity Database

    Frolov, Oleksandr; Koláček, Karel; Schmidt, Jiří; Štraus, Jaroslav; Choukourov, A.; Kasuya, K.

    Meieki, Nakamura-ku, Nagoya: Japan Society of Applied Physics, 2015 - (Toyoda, H.; Vukovic, M.), GT1.00124-GT1.00124. (APS Meeting). ISBN 978-4-86348-529-7. [International Conference on Reactive Plasmas, 68th Gaseous Electronics Conference and 33rd Symposium on Plasma Processing/9./. Honolulu, Hawaii (US), 12.10.2015-16.10.2015] R&D Projects: GA MŠk(CZ) LG13029; GA ČR(CZ) GA14-29772S Institutional support: RVO:61389021 Keywords : EUV laser * laser ablation * tungsten * silicon carbide * molybdenum * surface modification * capillary discharge Subject RIV: BL - Plasma and Gas Discharge Physics

  20. Decoding the message from meteoritic stardust silicon carbide grains

    OpenAIRE

    Lewis, Karen M.; Lugaro, Maria; Gibson, Brad K.; Pilkington, Kate

    2013-01-01

    Micron-sized stardust grains that originated in ancient stars are recovered from meteorites and analysed using high-resolution mass spectrometry. The most widely studied type of stardust is silicon carbide (SiC). Thousands of these grains have been analysed with high precision for their Si isotopic composition. Here we show that the distribution of the Si isotopic composition of the vast majority of stardust SiC grains carry the imprints of a spread in the age-metallicity distribution of thei...

  1. Temperature Induced Voltage Offset Drifts in Silicon Carbide Pressure Sensors

    Science.gov (United States)

    Okojie, Robert S.; Lukco, Dorothy; Nguyen, Vu; Savrun, Ender

    2012-01-01

    We report the reduction of transient drifts in the zero pressure offset voltage in silicon carbide (SiC) pressure sensors when operating at 600 C. The previously observed maximum drift of +/- 10 mV of the reference offset voltage at 600 C was reduced to within +/- 5 mV. The offset voltage drifts and bridge resistance changes over time at test temperature are explained in terms of the microstructure and phase changes occurring within the contact metallization, as analyzed by Auger electron spectroscopy and field emission scanning electron microscopy. The results have helped to identify the upper temperature reliable operational limit of this particular metallization scheme to be 605 C.

  2. Characterisation of silicon carbide layers formed during BNCD deposition

    Czech Academy of Sciences Publication Activity Database

    Taylor, Andrew; Ashcheulov, Petr; Čada, Martin; Drahokoupil, Jan; Fekete, Ladislav; Klimša, Ladislav; Olejníček, Jiří; Remeš, Zdeněk; Čtvrtlík, R.; Tomáštík, J.; Janíček, P.; Mistrík, J.; Kopeček, Jaromír; Mortet, Vincent

    Coventry: University of Warwick, 2015. P6.1-P6.3 [De Beers Diamond Conference 2015. 06.07.2015-09.07.2015, Warwick] R&D Projects: GA ČR GA13-31783S; GA MŠk LO1409; GA MŠk(CZ) LM2011029 Grant ostatní: OP VK(XE) CZ.1.07/2.3.00/20.0306 Institutional support: RVO:68378271 Keywords : silicon carbide * nano-crystalline diamond Subject RIV: BM - Solid Matter Physics ; Magnetism

  3. Photoluminescence and Raman spectroscopy characterization of boron- and nitrogen-doped 6H silicon carbide

    DEFF Research Database (Denmark)

    Ou, Yiyu; Jokubavicius, Valdas; Liu, Chuan; Berg, Rolf W.; Linnarsson, Margareta; Kamiyama, Satoshi; Lu, Zhaoyue; Yakimova, Rositza; Syväjärvi, Mikael; Ou, Haiyan

    2011-01-01

    Boron - and nitrogen-doped 6H silicon carbide epilayers grown on low off-axis 6H silicon carbide substrates have been characterized by photoluminescence and Raman spectroscopy. Combined with secondary ion mass spectrometry results, preferable doping type and optimized concentration could be...

  4. Method of enhanced lithiation of doped silicon carbide via high temperature annealing in an inert atmosphere

    Science.gov (United States)

    Hersam, Mark C.; Lipson, Albert L.; Bandyopadhyay, Sudeshna; Karmel, Hunter J; Bedzyk, Michael J

    2014-05-27

    A method for enhancing the lithium-ion capacity of a doped silicon carbide is disclosed. The method utilizes heat treating the silicon carbide in an inert atmosphere. Also disclosed are anodes for lithium-ion batteries prepared by the method.

  5. Fluidized bed dip coated silicon carbide on graphite

    International Nuclear Information System (INIS)

    Silicon carbide (SiC) coatings hold great promise in high temperature applications by virtue of their excellent physical and chemical properties. They are produced by techniques ranging from chemical vapor deposition to reaction bonding by melt infiltration. Reaction bonded SiC finds importance in nuclear applications as high temperature, thermally conducting coatings with good abrasion resistance. Additionally, they also possess the ability to withstand high neutron fluence, and thereby find importance as a protective layer in the graphite fuel tubes used in the compact high temperature reactor. The current work explores the deposition of SiC on graphite cylinders by dip-coating a heated graphite rod in a fluidized bed of silicon. The solid state reaction of silicon and carbon under vacuum/inert atmosphere and elevated temperatures is explored. A novel idea of immersing a heated graphite sample in a bed of fluidized silicon powder is presented. The graphite sample is heated to 1450-1550 deg C prior to dipping in the fluidized bed of silicon. The technique presents advantages of quick heating and lower deposition times, and reasonably uniform coatings. Importantly, the setup does not require effluent treatment nor does it involve the use of corrosive precursors leading to higher operational safety as opposed to other vapor deposition methods. The method is well adapted for three-dimensional surfaces as well. Initial experimental results are presented along with the design details of the perforated distributor plate for the coating unit, and the feasibility of the technique is explored. (author)

  6. Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen concentrations and structures were obtained. The transition from an amorphous to a crystalline material, induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen from the films plays an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced crystallization was obtained on samples deposited at lower substrate temperatures. A correlation between these measurements allows to analyze the evolution of structural properties of the samples. The presence of voids in the material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline silicon thin films.

  7. Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Budini, N., E-mail: nbudini@intec.unl.edu.a [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Rinaldi, P.A. [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Schmidt, J.A.; Arce, R.D.; Buitrago, R.H. [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Facultad de Ingenieria Quimica, UNL, Santiago del Estero 2829, S3000AOM Santa Fe (Argentina)

    2010-07-01

    Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen concentrations and structures were obtained. The transition from an amorphous to a crystalline material, induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen from the films plays an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced crystallization was obtained on samples deposited at lower substrate temperatures. A correlation between these measurements allows to analyze the evolution of structural properties of the samples. The presence of voids in the material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline silicon thin films.

  8. Experimental investigation on material migration phenomena in micro-EDM of reaction-bonded silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Liew, Pay Jun [Department of Mechanical Systems and Design, Tohoku University, Aramaki Aoba 6-6-01, Aoba-ku, Sendai, 980-8579 (Japan); Manufacturing Process Department, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100, Durian Tunggal, Melaka (Malaysia); Yan, Jiwang, E-mail: yan@mech.keio.ac.jp [Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama, 223-8522 (Japan); Kuriyagawa, Tsunemoto [Department of Mechanical Systems and Design, Tohoku University, Aramaki Aoba 6-6-01, Aoba-ku, Sendai, 980-8579 (Japan)

    2013-07-01

    Material migration between tool electrode and workpiece material in micro electrical discharge machining of reaction-bonded silicon carbide was experimentally investigated. The microstructural changes of workpiece and tungsten tool electrode were examined using scanning electron microscopy, cross sectional transmission electron microscopy and energy dispersive X-ray under various voltage, capacitance and carbon nanofibre concentration in the dielectric fluid. Results show that tungsten is deposited intensively inside the discharge-induced craters on the RB-SiC surface as amorphous structure forming micro particles, and on flat surface region as a thin interdiffusion layer of poly-crystalline structure. Deposition of carbon element on tool electrode was detected, indicating possible material migration to the tool electrode from workpiece material, carbon nanofibres and dielectric oil. Material deposition rate was found to be strongly affected by workpiece surface roughness, voltage and capacitance of the electrical discharge circuit. Carbon nanofibre addition in the dielectric at a suitable concentration significantly reduced the material deposition rate.

  9. Silicon carbide absorption features: dust formation in the outflows of extreme carbon stars

    CERN Document Server

    Speck, Angela K; Wakeman, Kristina; Wheeler, Caleb H; Thompson, Grant

    2008-01-01

    Infrared carbon stars without visible counterparts are generally known as extreme carbon stars. We have selected a subset of these stars with absorption features in the 10-13 $\\mu$m range, which has been tentatively attributed to silicon carbide (SiC). We add three new objects meeting these criterion to the seven previously known, bringing our total sample to ten sources. We also present the result of radiative transfer modeling for these stars, comparing these results to those of previous studies. In order to constrain model parameters, we use published mass-loss rates, expansion velocities and theoretical dust condensation models to determine the dust condensation temperature. These show that the inner dust temperatures of the dust shells for these sources are significantly higher than previously assumed. This also implies that the dominant dust species should be graphite instead of amorphous carbon. In combination with the higher condensation temperature we show that this results in a much higher accelerat...

  10. Modeling and simulation of boron-doped nanocrystalline silicon carbide thin film by a field theory.

    Science.gov (United States)

    Xiong, Liming; Chen, Youping; Lee, James D

    2009-02-01

    This paper presents the application of a multiscale field theory in modeling and simulation of boron-doped nanocrystalline silicon carbide (B-SiC). The multiscale field theory was briefly introduced. Based on the field theory, numerical simulations show that intergranular glassy amorphous films (IGFs) and nano-sized pores exist in triple junctions of the grains for nanocrystalline B-SiC. Residual tensile stress in the SiC grains and compressive stress on the grain boundaries (GBs) were observed. Under tensile loading, it has been found that mechanical response of 5 wt% boron-SiC exhibits five characteristic regimes. Deformation mechanism at atomic scale has been revealed. Tensile strength and Young's modulus of nanocrystalline SiC were accurately reproduced. PMID:19441448

  11. Experimental investigation on material migration phenomena in micro-EDM of reaction-bonded silicon carbide

    International Nuclear Information System (INIS)

    Material migration between tool electrode and workpiece material in micro electrical discharge machining of reaction-bonded silicon carbide was experimentally investigated. The microstructural changes of workpiece and tungsten tool electrode were examined using scanning electron microscopy, cross sectional transmission electron microscopy and energy dispersive X-ray under various voltage, capacitance and carbon nanofibre concentration in the dielectric fluid. Results show that tungsten is deposited intensively inside the discharge-induced craters on the RB-SiC surface as amorphous structure forming micro particles, and on flat surface region as a thin interdiffusion layer of poly-crystalline structure. Deposition of carbon element on tool electrode was detected, indicating possible material migration to the tool electrode from workpiece material, carbon nanofibres and dielectric oil. Material deposition rate was found to be strongly affected by workpiece surface roughness, voltage and capacitance of the electrical discharge circuit. Carbon nanofibre addition in the dielectric at a suitable concentration significantly reduced the material deposition rate.

  12. GHz-rate optical parametric amplifier in hydrogenated amorphous silicon

    International Nuclear Information System (INIS)

    We demonstrate optical parametric amplification operating at GHz-rates at telecommunications wavelengths using a hydrogenated amorphous silicon waveguide through the nonlinear optical process of four-wave mixing. We investigate how the parametric amplification scales with repetition rate. The ability to achieve amplification at GHz-repetition rates shows hydrogenated amorphous silicon’s potential for telecommunication applications and a GHz-rate optical parametric oscillator. (paper)

  13. Epitaxy of silicon carbide on silicon: Micromorphological analysis of growth surface evolution

    Science.gov (United States)

    Shikhgasan, Ramazanov; Ştefan, Ţălu; Dinara, Sobola; Sebastian, Stach; Guseyn, Ramazanov

    2015-10-01

    The main purpose of our research was the study of evolution of silicon carbide films on silicon by micromorphological analysis. Surface micromorphologies of Silicon Carbide epilayers with two different thicknesses were compared by means of fractal geometry. Silicon Carbide films were prepared on Si substrates by magnetron sputtering of polycrystalline target SiC in Ar atmosphere (99.999% purity). Synthesis of qualitative SiC/Si templates solves the questions of large diameter SiC single-crystal wafers formation. This technology decreases financial expenditure and provides integration of SiC into silicon technology. These hybrid substrates with buffer layer of high oriented SiC are useful for growth of both wide band gap materials (SiC, AlN, GaN) and graphene. The main problem of SiC heteroepitaxy on Si (1 1 1) is the large difference (∼20%) of the lattice parameters. Fractal analysis of surface morphology of heteroepitaxial films could help to understand the films growth mechanisms. The 3D (three-dimensional) surfaces revealed a fractal structure at the nanometer scale. The fractal dimension (D) provided global quantitative values that characterize the scale properties of surface geometry.

  14. Silicon Carbide Sensors and Electronics for Harsh Environment Applications

    Science.gov (United States)

    Evans, Laura J.

    2007-01-01

    Silicon carbide (SiC) semiconductor has been studied for electronic and sensing applications in extreme environment (high temperature, extreme vibration, harsh chemical media, and high radiation) that is beyond the capability of conventional semiconductors such as silicon. This is due to its near inert chemistry, superior thermomechanical and electronic properties that include high breakdown voltage and wide bandgap. An overview of SiC sensors and electronics work ongoing at NASA Glenn Research Center (NASA GRC) will be presented. The main focus will be two technologies currently being investigated: 1) harsh environment SiC pressure transducers and 2) high temperature SiC electronics. Work highlighted will include the design, fabrication, and application of SiC sensors and electronics, with recent advancements in state-of-the-art discussed as well. These combined technologies are studied for the goal of developing advanced capabilities for measurement and control of aeropropulsion systems, as well as enhancing tools for exploration systems.

  15. Low temperature synthesis and photoluminescence of cubic silicon carbide

    International Nuclear Information System (INIS)

    Cubic silicon carbide (3C-SiC) powder was synthesized at 460 deg. C in the ScCO2-metallic Na system, using cheap industrial FeSiδ alloy (≤500 mesh) and CO2, as silicon and carbon sources, respectively. The products were characterized by x-ray diffraction and Raman spectrum analysis. The results show that increasing the heating-up rate, adding a metallic sodium dose and prolonging the heating time favour the formation of 3C-SiC. A very strong photoluminescence band peaking at 436 nm was observed, showing a blue shift compared with the blue-green luminescence from films of 3C-SiC. A possible mechanism behind the blue shift is discussed

  16. Superconductivity in heavily boron-doped silicon carbide

    Directory of Open Access Journals (Sweden)

    Markus Kriener, Takahiro Muranaka, Junya Kato, Zhi-An Ren, Jun Akimitsu and Yoshiteru Maeno

    2008-01-01

    Full Text Available The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide. The sample used for that study consisted of cubic and hexagonal SiC phase fractions and hence this led to the question which of them participated in the superconductivity. Here we studied a hexagonal SiC sample, free from cubic SiC phase by means of x-ray diffraction, resistivity, and ac susceptibility.

  17. Decoding the message from meteoritic stardust silicon carbide grains

    CERN Document Server

    Lewis, Karen M; Gibson, Brad K; Pilkington, Kate

    2013-01-01

    Micron-sized stardust grains that originated in ancient stars are recovered from meteorites and analysed using high-resolution mass spectrometry. The most widely studied type of stardust is silicon carbide (SiC). Thousands of these grains have been analysed with high precision for their Si isotopic composition. Here we show that the distribution of the Si isotopic composition of the vast majority of stardust SiC grains carry the imprints of a spread in the age-metallicity distribution of their parent stars and of a power-law increase of the relative formation efficiency of SiC dust with the metallicity. This result offers a solution for the long-standing problem of silicon in stardust SiC grains, confirms the necessity of coupling chemistry and dynamics in simulations of the chemical evolution of our Galaxy, and constrains the modelling of dust condensation in stellar winds as function of the metallicity.

  18. Silicon dioxide and aluminium nitride as gate dielectric for high temperature and high power silicon carbide MOSFETs

    OpenAIRE

    Zetterling, Carl-Mikael

    1997-01-01

    Silicon carbide (SIC) is a wide bandgap semiconductor thathas been suggested as a replacement for silicon in applicationsusing high voltages, high frequencies, high temperatures orcombinations thereof. Several basic process steps need to bedeveloped for reliable manufacturing of long-term stableelectronic devices. One important process step is the formationof an insulator on the silicon carbide surface that may be usedas a) a gate dielectric, b) for device isolation or c) forpassivation of th...

  19. Modelling structure and properties of amorphous silicon boron nitride ceramics

    OpenAIRE

    Johann Christian Schön; Alexander Hannemann; Guneet Sethi; Ilya Vladimirovich Pentin; Martin Jansen

    2011-01-01

    Silicon boron nitride is the parent compound of a new class of high-temperature stable amorphous ceramics constituted of silicon, boron, nitrogen, and carbon, featuring a set of properties that is without precedent, and represents a prototypical random network based on chemical bonds of predominantly covalent character. In contrast to many other amorphous materials of technological interest, a-Si3B3N7 is not produced via glass formation, i.e. by quenching from a melt, the reason being that th...

  20. Mechanism of Germanium-Induced Perimeter Crystallization of Amorphous Silicon

    OpenAIRE

    Hakim, M. M. A.; Ashburn, P.

    2007-01-01

    We report a study aimed at highlighting the mechanism of a new amorphous silicon crystallization phenomenon that originates from the perimeter of a germanium layer during low-temperature annealing (500°C). Results are reported on doped and undoped amorphous silicon films, with thicknesses in the range 40–200 nm, annealed at a temperature of 500 or 550°C. A comparison is made of crystallization arising from Ge and SiGe layers and the role of damage from a high-dose fluorine implant is investig...

  1. Potential of amorphous and microcrystalline silicon solar cells

    OpenAIRE

    Meier, Johannes; Spitznagel, J.; Kroll, U.; Bucher, C.; Faÿ Sylvie; Moriarty, T.; Shah, Arvind

    2008-01-01

    Low pressure chemical vapour deposition (LP-CVD) ZnO as front transparent conductive oxide (TCO), developed at IMT, has excellent light-trapping properties for a-Si:H p-i-n single-junction and ‘micromorph’ (amorphous/microcrystalline silicon) tandem solar cells. A stabilized record efficiency of 9.47% has independently been confirmed by NREL for an amorphous silicon single-junction p-i-n cell (~1 cm2) deposited on LP-CVD ZnO coated glass. Micromorph tandem cells with an initial efficiency of ...

  2. Surface orientation effects in crystalline-amorphous silicon interfaces

    OpenAIRE

    Nolan, Michael; Legesse, Merid; Fagas, Giorgos

    2012-01-01

    In this paper we present the results of empirical potential and density functional theory (DFT) studies of models of interfaces between amorphous silicon (a-Si) or hydrogenated amorphous Si (a-Si:H) and crystalline Si (c-Si) on three unreconstructed silicon surfaces, namely (100), (110) and (111). In preparing models of a-Si on c-Si, melting simulations are run with classical molecular dynamics (MD) at 3000 K for 10 ps to melt part of the crystalline surface and the structure is quenched to 3...

  3. Towards new binary compounds: Synthesis of amorphous phosphorus carbide by pulsed laser deposition

    International Nuclear Information System (INIS)

    We have recently undertaken comprehensive computational studies predicting possible crystal structures of the as yet unknown phosphorus carbide as a function of composition. In this work, we report the synthesis of amorphous phosphorus–carbon films by pulsed laser deposition. The local bonding environments of carbon and phosphorus in the synthesised materials have been analysed by x-ray photoelectron spectroscopy; we have found strong evidence for the formation of direct P–C bonding and hence phosphorus carbide. There is a good agreement between the bonding environments found in this phosphorus carbide material and those predicted in the computational work. In particular, the local bonding environments are consistent with those found in the β-InS-like structures that we predict to be low in energy for phosphorus:carbon ratios between 0.25 and 1. Highlights: ► We have synthesised amorphous phosphorus–carbon films by pulsed laser deposition. ► X-ray photoelectron spectroscopy results indicate formation of direct P–C bonds and hence phosphorus carbide. ► Local bonding environments are consistent with those in predicted structures.

  4. Development of the SOFIA silicon carbide secondary mirror

    Science.gov (United States)

    Fruit, Michel; Antoine, Pascal; Varin, Jean-Luc; Bittner, Hermann; Erdmann, Matthias

    2003-02-01

    The SOFIA telescope is ajoint NASA-DLR project for a 2.5 m airborne Stratospheric Observatory for IR Astronomy to be flown in a specially adapted Boeing 747 SP plane, Kayser-Threde being resopinsible for the development of the Telescope Optics. The φ 352 mm Secondary Mirror is mounted ona chopping mechanism to allow avoidance of background noise during IR observations. Stiffness associated to lightness is a major demand for such a mirror to achieve high frequency chopping. This leads to select SIlicon Carbide for the mirror blank. Its development has been run by the ASTRIUM/BOOSTEC joint venture SiCSPACE, taking full benefit of the instrinsic properties of the BOOSTEC SiC-100 sintered material, associated to qualified processes specifically developed for space borne mirrors by ASTRIUM. Achieved performances include a low mass of 1.97 kg, a very high stiffness with a first resonant frequency of 1865 Hz and a measured optical surface accuracy of 39 nm rms, using Ion Beam Figuring. It is proposed here to present the major design features of the SOFIA Secondary Mirror, highlighting the main advantages of using Silicon Carbide, the main steps of its development and the achieved optomechanical performances of the developed mirror.

  5. Fatigue behavior of continuous fiber silicon-carbide-aluminum composites

    Science.gov (United States)

    Johnson, W. S.; Wallis, R. R.

    1984-01-01

    Four lay-ups of continuous fiber silicon carbide (SCS2) fiber/aluminum matrix composites were tested to assess fatigue mechanisms including stiffness loss when cycled below their respective fatigue limits. The lay-ups were 0 (sub 8), 0(sub 2)/ + or - 45 (sub 2s), 0/90 (sub 2s),and 0/ + or 45/90 (subs). The data were compared with predictions from the author's previously published shakedown model which predicts fatigue-induced stiffness loss in metal matrix composites. A fifth lay-up, + or - 45 (sub 2s), was tested to compare shakedown and fatigue limits. The particular batch of silicon-carbide fibers tested in this program had a somewhat lower modulus (340 GPa) than expected and displayed poor bonding to the aluminum matrix. Good agreement was obtained between the stiffness loss model and the test data. The fatigue damage below the fatigue limit was primarily in the form of matrix cracking. The fatigue limit corresponded to the laminate shakedown for the + or - 45 (sub 2s) laminate.

  6. Stress envelope of silicon carbide composites at elevated temperatures

    International Nuclear Information System (INIS)

    To identify a comprehensive stress envelope, i.e., strength anisotropy map, of silicon carbide fiber-reinforced silicon carbide matrix composite (SiC/SiC composite) for practical component design, tensile and compressive tests were conducted using the small specimen test technique specifically tailored for high-temperature use. In-plane shear properties were, however, estimated using the off-axial tensile method and assuming that the mixed mode failure criterion, i.e., Tsai–Wu criterion, is valid for the composites. The preliminary test results indicate no significant degradation to either proportional limit stress (PLS) or fracture strength by tensile loading at temperatures below 1000 °C. A similarly good tolerance of compressive properties was identified at elevated temperatures, except for a slight degradation in PLS. With the high-temperature test data of tensile, compressive and in-plane shear properties, the stress envelopes at elevated temperatures were finally obtained. A slight reduction in the design limit was obvious at elevated temperatures when the compressive mode is dominant, whereas a negligibly small impact on the design is expected by considering the tensile loading case

  7. Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

    International Nuclear Information System (INIS)

    The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of Si-Si bonds are concluded for the pyrolysis temperature Tp = 270 to 360 °C. The appearance of amorphous silicon phonon bands in Raman spectra for films prepared at Tp ≥ 330 °C suggests the construction of a three-dimensional amorphous silicon network. Films prepared at Tp ≥ 360 °C exhibit a hydrogen content near 10 at.% and an optical gap near 1.6 eV similar to device-grade vacuum processed a-Si:H. However, the infrared microstructure factor, the spin density, and the photosensitivity require significant improvements. - Highlights: ► We fabricate hydrogenated amorphous silicon (a-Si:H) films by a solution process. ► The a-Si:H films are prepared by pyrolytic transformation in polysilane solution. ► We investigate basic properties in relation to the pyrolysis temperature. ► Raman spectra, hydrogen content, and optical gap are similar to device-grade a-Si:H. ► Microstructure factor, spin density, and photoconductivity show poor quality.

  8. Development of refractory armored silicon carbide by infrared transient liquid phase processing

    Science.gov (United States)

    Hinoki, Tatsuya; Snead, Lance L.; Blue, Craig A.

    2005-12-01

    Tungsten (W) and molybdenum (Mo) were coated on silicon carbide (SiC) for use as a refractory armor using a high power plasma arc lamp at powers up to 23.5 MW/m 2 in an argon flow environment. Both tungsten powder and molybdenum powder melted and formed coating layers on silicon carbide within a few seconds. The effect of substrate pre-treatment (vapor deposition of titanium (Ti) and tungsten, and annealing) and sample heating conditions on microstructure of the coating and coating/substrate interface were investigated. The microstructure was observed by scanning electron microscopy (SEM) and optical microscopy (OM). The mechanical properties of the coated materials were evaluated by four-point flexural tests. A strong tungsten coating was successfully applied to the silicon carbide substrate. Tungsten vapor deposition and pre-heating at 5.2 MW/m 2 made for a refractory layer containing no cracks propagating into the silicon carbide substrate. The tungsten coating was formed without the thick reaction layer. For this study, small tungsten carbide grains were observed adjacent to the interface in all conditions. In addition, relatively large, widely scattered tungsten carbide grains and a eutectic structure of tungsten and silicon were observed through the thickness in the coatings formed at lower powers and longer heating times. The strength of the silicon carbide substrate was somewhat decreased as a result of the processing. Vapor deposition of tungsten prior to powder coating helped prevent this degradation. In contrast, molybdenum coating was more challenging than tungsten coating due to the larger coefficient of thermal expansion (CTE) mismatch as compared to tungsten and silicon carbide. From this work it is concluded that refractory armoring of silicon carbide by Infrared Transient Liquid Phase Processing is possible. The tungsten armored silicon carbide samples proved uniform, strong, and capable of withstanding thermal fatigue testing.

  9. Development of refractory armored silicon carbide by infrared transient liquid phase processing

    International Nuclear Information System (INIS)

    Tungsten (W) and molybdenum (Mo) were coated on silicon carbide (SiC) for use as a refractory armor using a high power plasma arc lamp at powers up to 23.5 MW/m2 in an argon flow environment. Both tungsten powder and molybdenum powder melted and formed coating layers on silicon carbide within a few seconds. The effect of substrate pre-treatment (vapor deposition of titanium (Ti) and tungsten, and annealing) and sample heating conditions on microstructure of the coating and coating/substrate interface were investigated. The microstructure was observed by scanning electron microscopy (SEM) and optical microscopy (OM). The mechanical properties of the coated materials were evaluated by four-point flexural tests. A strong tungsten coating was successfully applied to the silicon carbide substrate. Tungsten vapor deposition and pre-heating at 5.2 MW/m2 made for a refractory layer containing no cracks propagating into the silicon carbide substrate. The tungsten coating was formed without the thick reaction layer. For this study, small tungsten carbide grains were observed adjacent to the interface in all conditions. In addition, relatively large, widely scattered tungsten carbide grains and a eutectic structure of tungsten and silicon were observed through the thickness in the coatings formed at lower powers and longer heating times. The strength of the silicon carbide substrate was somewhat decreased as a result of the processing. Vapor deposition of tungsten prior to powder coating helped prevent this degradation. In contrast, molybdenum coating was more challenging than tungsten coating due to the larger coefficient of thermal expansion (CTE) mismatch as compared to tungsten and silicon carbide. From this work it is concluded that refractory armoring of silicon carbide by Infrared Transient Liquid Phase Processing is possible. The tungsten armored silicon carbide samples proved uniform, strong, and capable of withstanding thermal fatigue testing

  10. Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

    OpenAIRE

    Masuda, Takashi; Matsuki, Yasuo; Shimoda, Tatsuya

    2012-01-01

    The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of S...

  11. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    OpenAIRE

    Riesen, Y.; Stuckelberger, M.; Haug, F. -J.; Ballif, C.; N. Wyrsch

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with dif...

  12. Meteoritic silicon carbide and its stellar sources - Implications for galactic chemical evolution

    Science.gov (United States)

    Ming, Tang; Anders, Edward; Hoppe, Peter; Zinner, Ernst

    1989-01-01

    Interstellar silicon carbide grains in meteorites provide a novel means for studying the carbon-star population of about 5 x 10 to the 9th years ago. Their C-12/C-13 ratios differ greatly from the solar value but resemble those of present-day csrbon stars, implying little change in the galactic C-13 inventory. Isotope data on nitrogen and silicon suggest that the silicon carbide grains come mainly from red giants, with small contributions from novae.

  13. TEM investigation of aluminium containing precipitates in high aluminium doped silicon carbide

    International Nuclear Information System (INIS)

    Full text: Silicon carbide is a promising semiconductor material for applications in high temperature and high power devices. The successful growth of good quality epilayers in this material has enhanced its potential for device applications. As a novel semiconductor material, there is a need for studying its basic physical properties and the role of dopants in this material. In this study, silicon carbide epilayers were grown on 4H-SiC wafers of (0001) orientation with a miscut angle of 8 deg at a temperature of 1550 deg C. The epilayers contained regions of high aluminium doping well above the solubility of aluminium in silicon carbide. High temperature annealing of this material resulted in the precipitation of aluminium in the wafers. The samples were analysed by secondary ion mass spectrometry and transmission electron microscopy. Selected area diffraction studies show the presence of aluminium carbide and aluminium silicon carbide phases. Copyright (2002) Australian Society for Electron Microscopy Inc

  14. A simple method for the synthesis of silicon carbide nanorods.

    Science.gov (United States)

    Kholmanov, I N; Kharlamov, A; Barborini, E; Lenardi, C; Li Bassi, A; Bottani, C E; Ducati, C; Maffi, S; Kirillova, N V; Milani, P

    2002-10-01

    SiC nanorods were synthesized by a reaction at a temperature of 1200 degrees C, under an argon gas atmosphere, from silicon and amorphous carbon powders mixed by ball milling. The reaction product, which contain SiC nanorods and nanoparticles, has been characterized by high-resolution transmission electron microscopy, X-ray diffraction, and micro-Raman spectroscopy. The synthesized nanorods are more than 1 micron long with a mean diameter of about 10-30 nm. The nanorods possess a well-defined crystalline structure with a thin layer of amorphous SiO2 on the surface. Raman shifts of SiC nanorods and the role of structural defects are discussed. PMID:12908277

  15. [Synergetic effects of silicon carbide and molecular sieve loaded catalyst on microwave assisted catalytic oxidation of toluene].

    Science.gov (United States)

    Wang, Xiao-Hui; Bo, Long-Li; Liu, Hai-Nan; Zhang, Hao; Sun, Jian-Yu; Yang, Li; Cai, Li-Dong

    2013-06-01

    Molecular sieve loaded catalyst was prepared by impregnation method, microwave-absorbing material silicon carbide and the catalyst were investigated for catalytic oxidation of toluene by microwave irradiation. Research work examined effects of silicon carbide and molecular sieve loading Cu-V catalyst's mixture ratio as well as mixed approach changes on degradation of toluene, and characteristics of catalyst were measured through scanning electron microscope, specific surface area test and X-ray diffraction analysis. The result showed that the fixed bed reactor had advantages of both thermal storage property and low-temperature catalytic oxidation when 20% silicon carbide was filled at the bottom of the reactor, and this could effectively improve the utilization of microwave energy as well as catalytic oxidation efficiency of toluene. Under microwave power of 75 W and 47 W, complete-combustion temperatures of molecular sieve loaded Cu-V catalyst and Cu-V-Ce catalyst to toluene were 325 degrees C and 160 degrees C, respectively. Characteristics of the catalysts showed that mixture of rare-earth element Ce increased the dispersion of active components in the surface of catalyst, micropore structure of catalyst effectively guaranteed high adsorption capacity for toluene, while amorphous phase of Cu and V oxides increased the activity of catalyst greatly. PMID:23947020

  16. First-principles study of hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Jarolimek, K.; Groot, R.A. de; Wijs, G.A. de; Zeman, M.

    2009-01-01

    We use a molecular-dynamics simulation within density-functional theory to prepare realistic structures of hydrogenated amorphous silicon. The procedure consists of heating a crystalline structure of Si64H8 to 2370 K, creating a liquid and subsequently cooling it down to room temperature. The effect

  17. Photocurrent images of amorphous-silicon solar-cell modules

    Science.gov (United States)

    Kim, Q.; Shumka, A.; Trask, J.

    1985-01-01

    Results obtained in applying the unique characteristics of the solar cell laser scanner to investigate the defects and quality of amorphous silicon cells are presented. It is concluded that solar cell laser scanners can be effectively used to nondestructively test not only active defects but also the cell quality and integrity of electrical contacts.

  18. Long-term stability of amorphous-silicon modules

    Science.gov (United States)

    Ross, R. G., Jr.

    1986-01-01

    The Jet Propulsion Laboratory (JPL) program of developing qualification tests necessary for amorphous silicon modules, including appropriate accelerated environmental tests reveal degradation due to illumination. Data were given which showed the results of temperature-controlled field tests and accelerated tests in an environmental chamber.

  19. Integral bypass diodes in an amorphous silicon alloy photovoltaic module

    Science.gov (United States)

    Hanak, J. J.; Flaisher, H.

    1991-01-01

    Thin-film, tandem-junction, amorphous silicon (a-Si) photovoltaic modules were constructed in which a part of the a-Si alloy cell material is used to form bypass protection diodes. This integral design circumvents the need for incorporating external, conventional diodes, thus simplifying the manufacturing process and reducing module weight.

  20. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    NARCIS (Netherlands)

    Jarolimek, K.; De Groot, R.A.; De Wijs, G.A.; Zeman, M.

    2010-01-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principle

  1. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    NARCIS (Netherlands)

    Jarolimek, K.; Groot, R.A. de; Wijs, G.A. de; Zeman, M.

    2010-01-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principle

  2. A new tevchnique for production of amorphous silicon solar cells

    International Nuclear Information System (INIS)

    It is presented a new technique for the production of amorphous silicon solar cells based on the development of thin films of a-Si in a reactor in which the decomposition of the sylane, induced by capacitively coupled RF, and the film deposition occur in separate chambers. (M.W.O.)

  3. Ion-assisted recrystallization of amorphous silicon

    Science.gov (United States)

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

    1989-12-01

    Our recent work on ion-beam-assisted epitaxial growth of amorphous Si layers on single crystal substrates is reviewed. The planar motion of the crystal-amorphous interface was monitored in situ, during irradiations, by transient reflectivity measurements. This technique allows the measurement of the ion-induced growth rate with a very high precision. We have observed that this growth rate scales linearly with the number of displacements produced at the crystal-amorphous interface by the impinging ions. Moreover the regrowth onto oriented substrates is a factor of ≈ 4 faster with respect to that on substrates. Impurities dissolved in the amorphous layer influence the kinetics of recrystallization. For instance, dopants such as As, B and P enhance the ion-induced growth rate while oxygen has the opposite effect. The dependence of the rate on impurity concentration is however less strong with respect to pure thermal annealing. For instance, an oxygen concentration of 1 × 1021 / cm3 decreases the ion-induced growth rate by a factor of ≈ 3; this same concentration would have decreased the rate of pure thermal annealing by more than 4 orders of magnitude. The reduced effects of oxygen during ion-beam crystallization allow the regrowth of deposited Si layers despite the presence of a high interfacial oxygen content. The process is investigated in detail and its possible application to the microelectronic technology is discussed.

  4. TRANSFORMATIONS IN NANO-DIAMONDS WITH FORMATION OF NANO-POROUS SILICON CARBIDE AT HIGH PRESSURE

    Directory of Open Access Journals (Sweden)

    V. N. Kovalevsky

    2014-11-01

    Full Text Available The paper contains investigations on regularities of diamond - silicon carbide composite structure formation at impact-wave excitation. It has been determined that while squeezing a porous blank containing Si (SiC nano-diamond by explosive detonation products some processes are taking place such as diamond nano-particles consolidation, reverse diamond transition into graphite, fragments formation from silicon carbide. A method for obtaining high-porous composites with the presence of ultra-disperse diamond particles has been developed. Material with three-dimensional high-porous silicon-carbide structure has been received due to nano-diamond graphitation at impact wave transmission and plastic deformation. The paper reveals nano-diamonds inverse transformation into graphite and its subsequent interaction with the silicon accompanied by formation of silicon-carbide fragments with dimensions of up to 100 nm.

  5. Silicon-Carbide Power MOSFET Performance in High Efficiency Boost Power Processing Unit for Extreme Environments

    Science.gov (United States)

    Ikpe, Stanley A.; Lauenstein, Jean-Marie; Carr, Gregory A.; Hunter, Don; Ludwig, Lawrence L.; Wood, William; Del Castillo, Linda Y.; Fitzpatrick, Fred; Chen, Yuan

    2016-01-01

    Silicon-Carbide device technology has generated much interest in recent years. With superior thermal performance, power ratings and potential switching frequencies over its Silicon counterpart, Silicon-Carbide offers a greater possibility for high powered switching applications in extreme environment. In particular, Silicon-Carbide Metal-Oxide- Semiconductor Field-Effect Transistors' (MOSFETs) maturing process technology has produced a plethora of commercially available power dense, low on-state resistance devices capable of switching at high frequencies. A novel hard-switched power processing unit (PPU) is implemented utilizing Silicon-Carbide power devices. Accelerated life data is captured and assessed in conjunction with a damage accumulation model of gate oxide and drain-source junction lifetime to evaluate potential system performance at high temperature environments.

  6. Raman and ellipsometric characterization of hydrogenated amorphous silicon thin films

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films were deposited by plasma-enhanced vapor deposition (PECVD) at different silane temperatures (Tg) before glow-discharge. The effect of Tg on the amorphous network and optoelectronic properties of the films has been investigated by Raman scattering spectra, ellipsometric transmittance spectra, and dark conductivity measurement, respectively. The results show that the increase in Tg leads to an improved ordering of amorphous network on the short and intermediate scales and an increase of both refractive index and absorption coefficient in a-Si:H thin films. It is indicated that the dark conductivity increases by two orders of magnitude when Tg is raised from room temperature (RT) to 433 K. The continuous ordering of amorphous network of a-Si:H thin films deposited at a higher Tg is the main cause for the increase of dark conductivity.

  7. Raman and ellipsometric characterization of hydrogenated amorphous silicon thin films

    Institute of Scientific and Technical Information of China (English)

    LIAO NaiMan; LI Wei; KUANG YueJun; JIANG YaDong; LI ShiBin; WU ZhiMing; QI KangCheng

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films were deposited by plasma-enhanced vapor depo-sition (PEOVD) at different silane temperatures (Tg) before glow-discharge. The effect of Tg on the amorphous network and optoelectronic properties of the films has been investigated by Raman scat-tering spectra, ellipsometric transmittance spectra, and dark conductivity measurement, respectively. The results show that the increase in Tg leads to an improved ordering of amorphous network on the short and intermediate scales and an increase of both refractive index and absorption coefficient in a-Si:H thin films. It is indicated that the dark conductivity increases by two orders of magnitude when Tg is raised from room temperature (RT) to 433 K. The continuous ordering of amorphous network of a-Si:H thin films deposited at a higher Tg is the main cause for the increase of dark conductivity.

  8. Hydrogen-free amorphous silicon with no tunneling states.

    Science.gov (United States)

    Liu, Xiao; Queen, Daniel R; Metcalf, Thomas H; Karel, Julie E; Hellman, Frances

    2014-07-11

    The ubiquitous low-energy excitations, known as two-level tunneling systems (TLSs), are one of the universal phenomena of amorphous solids. Low temperature elastic measurements show that e-beam amorphous silicon (a-Si) contains a variable density of TLSs which diminishes as the growth temperature reaches 400 °C. Structural analyses show that these a-Si films become denser and more structurally ordered. We conclude that the enhanced surface energetics at a high growth temperature improved the amorphous structural network of e-beam a-Si and removed TLSs. This work obviates the role hydrogen was previously thought to play in removing TLSs in the hydrogenated form of a-Si and suggests it is possible to prepare "perfect" amorphous solids with "crystal-like" properties for applications. PMID:25062205

  9. Characterization of SiC (SCS-6) Fiber Reinforced Reaction-Formed Silicon Carbide Matrix Composites

    Science.gov (United States)

    Singh, Mrityunjay; Dickerson, Robert M.

    1995-01-01

    Silicon carbide (SCS-6) fiber reinforced-reaction formed silicon carbide matrix composites were fabricated using NASA's reaction forming process. Silicon-2 at a percent of niobium alloy was used as an infiltrant instead of pure silicon to reduce the amount of free silicon in the matrix after reaction forming. The matrix primarily consists of silicon carbide with a bi-modal grain size distribution. Minority phases dispersed within the matrix are niobium disilicide (NbSi2), carbon and silicon. Fiber push-out tests on these composites determined a debond stress of approx. 67 MPa and a frictional stress of approx. 60 MPa. A typical four point flexural strength of the composite is 297 MPa (43.1 KSi). This composite shows tough behavior through fiber pull out.

  10. Characterization of SiC Fiber (SCS-6) Reinforced-Reaction-Formed Silicon Carbide Matrix Composites

    Science.gov (United States)

    Singh, M.; Dickerson, R. M.

    1996-01-01

    Silicon carbide fiber (SCS-6) reinforced-reaction-formed silicon carbide matrix composites were fabricated using a reaction-forming process. Silicon-2 at.% niobium alloy was used as an infiltrant instead of pure silicon to reduce the amount of free silicon in the matrix after reaction forming. The matrix primarily consists of silicon carbide with a bimodal grain size distribution. Minority phases dispersed within the matrix are niobium disilicide (NbSi2), carbon, and silicon. Fiber pushout tests on these composites determined a debond stress of approximately 67 MPa and a frictional stress of approximately 60 MPa. A typical four-point flexural strength of the composite is 297 MPa (43.1 KSi). This composite shows tough behavior through fiber pullout.

  11. Low Cost Fabrication of Silicon Carbide Based Ceramics and Fiber Reinforced Composites

    Science.gov (United States)

    Singh, M.; Levine, S. R.

    1995-01-01

    A low cost processing technique called reaction forming for the fabrication of near-net and complex shaped components of silicon carbide based ceramics and composites is presented. This process consists of the production of a microporous carbon preform and subsequent infiltration with liquid silicon or silicon-refractory metal alloys. The microporous preforms are made by the pyrolysis of a polymerized resin mixture with very good control of pore volume and pore size thereby yielding materials with tailorable microstructure and composition. Mechanical properties (elastic modulus, flexural strength, and fracture toughness) of reaction-formed silicon carbide ceramics are presented. This processing approach is suitable for various kinds of reinforcements such as whiskers, particulates, fibers (tows, weaves, and filaments), and 3-D architectures. This approach has also been used to fabricate continuous silicon carbide fiber reinforced ceramic composites (CFCC's) with silicon carbide based matrices. Strong and tough composites with tailorable matrix microstructure and composition have been obtained. Microstructure and thermomechanical properties of a silicon carbide (SCS-6) fiber reinforced reaction-formed silicon carbide matrix composites are discussed.

  12. CARBON REMOVAL FROM METALLIC SILICON BY CARBIDE SETTLING FOR SOLAR GRADE SILICON PRODUCTION

    Directory of Open Access Journals (Sweden)

    Tiago Ramos Ribeiro

    2015-03-01

    Full Text Available The use of solar energy is growing sharply in the past years. The most used material for solar cells is high-purity silicon produced by refining low-purity silicon. With the increasing demand for photovoltaic components, new refining processes have been investigated. Carbon is one of the impurities to be removed and one possible removing technique is based on the settling of silicon carbide particles. Settling tests were carried out at 1,500°C during one and six hours. Results show that differences in settling time do not affect carbon removal significantly and that the carbon contents after settling are still higher than that required by standards for solar grade silicon (43 ppm. Results from this work and from literature show that settling is not a feasible processing step for carbon removal to the level needed for photovoltaic applications.

  13. A Novel Compact and Reliable Hybrid Silicon/Silicon Carbide Device Module for Efficient Power Conversion Project

    Data.gov (United States)

    National Aeronautics and Space Administration — United Silicon Carbide, Inc. proposes to develop a novel compact, efficient and high-temperature power module, based on unique co-packaging approach of normally-off...

  14. Amorphous silicon rich silicon nitride optical waveguides for high density integrated optics

    DEFF Research Database (Denmark)

    Philipp, Hugh T.; Andersen, Karin Nordström; Svendsen, Winnie Edith;

    2004-01-01

    Amorphous silicon rich silicon nitride optical waveguides clad in silica are presented as a high-index contrast platform for high density integrated optics. Performance of different cross-sectional geometries have been measured and are presented with regards to bending loss and insertion loss. A...

  15. Heat-Induced Agglomeration of Amorphous Silicon Nanoparticles Toward the Formation of Silicon Thin Film.

    Science.gov (United States)

    Jang, Bo Yun; Kim, Ja Young; Seo, Gyeongju; Shin, Chae-Ho; Ko, Chang Hyun

    2016-01-01

    The thermal behavior of silicon nanoparticles (Si NPs) was investigated for the preparation of silicon thin film using a solution process. TEM analysis of Si NPs, synthesized by inductively coupled plasma, revealed that the micro-structure of the Si NPs was amorphous and that the Si NPs had melted and merged at a comparatively low temperature (~750 °C) considering bulk melting temperature of silicon (1414 °C). A silicon ink solution was prepared by dispersing amorphous Si NPs in propylene glycol (PG). It was then coated onto a silicon wafer and a quartz plate to form a thin film. These films were annealed in a vacuum or in an N₂ environment to increase their film density. N2 annealing at 800 °C and 1000 °C induced the crystallization of the amorphous thin film. An elemental analysis by the SIMS depth profile showed that N₂annealing at 1000 °C for 180 min drastically reduced the concentrations of carbon and oxygen inside the silicon thin film. These results indicate that silicon ink prepared using amorphous Si NPs in PG can serve as a proper means of preparing silicon thin film via solution process. PMID:27398566

  16. High quality crystalline silicon surface passivation by combined intrinsic and n-type hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Schuttauf, J.A.; van der Werf, C.H.M.; Kielen, I.M.; van Sark, W.G.J.H.M.; Rath, J.K.

    2011-01-01

    We investigate the influence of thermal annealing on the passivation quality of crystalline silicon (c-Si) surfaces by intrinsic and n-type hydrogenated amorphous silicon (a-Si:H) films. For temperatures up to 255 C, we find an increase in surface passivation quality, corresponding to a decreased da

  17. Raman spectra of silicon carbide small particles and nanowires

    Science.gov (United States)

    Wieligor, Monika; Wang, Yuejian; Zerda, T. W.

    2005-04-01

    Two manufacturing protocols of silicon carbide (SiC) nanowires are discussed. The Raman spectra of produced SiC nanowires are compared with spectra of SiC powders of various grain sizes. The temperature and pressure dependence of the Raman spectra for powders is similar to that of bulk crystals, but is different for nanowires. Frequency shifts, band broadenings and the presence of shoulders are discussed in terms of crystal size, character of defects and their population. The concentration of defects in synthesized nanowires depends on the sintering method. Raman intensity enhancement of the LO phonon was observed when the wavelength of the excitation laser was changed from 780 to 514 nm.

  18. High Strength Silicon Carbide Foams and Their Deformation Behavior

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Silicon carbide (SiC) foams with a continuously connected open-cell structure were prepared and characterized for their mechanical performance. The apparent densities of SiC foams were controlled between about 0.4 and 1.3 g/cm3, with corresponding compressive strengths ranging from about 13 to 60 MPa and flexural strengths from about 8 to 30 MPa. Compressive testing of the SiC foams yielded stress-strain curves with only one linear-elastic region, which is different from those reported on ceramic foams in literature. This can possibly be attributed to the existence of filaments with fine, dense and high strength microstructures. The SiC and the filaments respond homogeneously to applied loading.

  19. Preparation of porous silicon carbide by combustion synthesis

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yu-min; ZHANG Jian-han; HAN Jie-cai

    2005-01-01

    Porous silicon carbide ceramics were prepared by combustion synthesis technique. SiC/TiC composite was gained by combustion reaction of Si, C and Ti. Thermodynamics analysis of Si-C-Ti system indicates that the content of TiC in products should be larger than 30%. The experimental results show that the content of Ti+C should be larger than 25% to achieve a complete combustion reaction. The X-ray diffractometry results show that the final products with a relative density of 45%-64% are composed of α-SiC, β-SiC, TiC and a small quantity of Si. The images of scanning electron microscopy show that the structures of grain in SiC based porous ceramics consist of particles with a few microns in size.

  20. Application of silicon carbide to synchrotron-radiation mirrors

    International Nuclear Information System (INIS)

    Damage to conventional mirror materials exposed to the harsh synchrotron radiation (SR) environment has prompted the SR user community to search for more suitable materials. Next-generation insertion devices, with their attendant flux increases, will make the problem of mirror design even more difficult. A parallel effort in searching for better materials has been underway within the laser community for several years. The technology for dealing with high thermal loads is highly developed among laser manufacturers. Performance requirements for laser heat exchangers are remarkably similar to SR mirror requirements. We report on the application of laser heat exchanger technology to the solution of typical SR mirror design problems. The superior performance of silicon carbide for laser applications is illustrated by various material trades studies, and its superior performance for SR applications is illustrated by means of model calculations

  1. High surface area silicon carbide-coated carbon aerogel

    Science.gov (United States)

    Worsley, Marcus A; Kuntz, Joshua D; Baumann, Theodore F; Satcher, Jr, Joe H

    2014-01-14

    A metal oxide-carbon composite includes a carbon aerogel with an oxide overcoat. The metal oxide-carbon composite is made by providing a carbon aerogel, immersing the carbon aerogel in a metal oxide sol under a vacuum, raising the carbon aerogel with the metal oxide sol to atmospheric pressure, curing the carbon aerogel with the metal oxide sol at room temperature, and drying the carbon aerogel with the metal oxide sol to produce the metal oxide-carbon composite. The step of providing a carbon aerogel can provide an activated carbon aerogel or provide a carbon aerogel with carbon nanotubes that make the carbon aerogel mechanically robust. Carbon aerogels can be coated with sol-gel silica and the silica can be converted to silicone carbide, improved the thermal stability of the carbon aerogel.

  2. THz saturable absorption in turbostratic multilayer graphene on silicon carbide.

    Science.gov (United States)

    Bianco, Federica; Miseikis, Vaidotas; Convertino, Domenica; Xu, Ji-Hua; Castellano, Fabrizio; Beere, Harvey E; Ritchie, David A; Vitiello, Miriam S; Tredicucci, Alessandro; Coletti, Camilla

    2015-05-01

    We investigated the room-temperature Terahertz (THz) response as saturable absorber of turbostratic multilayer graphene grown on the carbon-face of silicon carbide. By employing an open-aperture z-scan method and a 2.9 THz quantum cascade laser as source, a 10% enhancement of transparency is observed. The saturation intensity is several W/cm2, mostly attributed to the Pauli blocking effect in the intrinsic graphene layers. A visible increase of the modulation depth as a function of the number of graphene sheets was recorded as consequence of the low nonsaturable losses. The latter in turn revealed that crystalline disorder is the main limitation to larger modulations, demonstrating that the THz nonlinear absorption properties of turbostratic graphene can be engineered via a proper control of the crystalline disorder and the layers number. PMID:25969255

  3. Raman spectra of silicon carbide small particles and nanowires

    International Nuclear Information System (INIS)

    Two manufacturing protocols of silicon carbide (SiC) nanowires are discussed. The Raman spectra of produced SiC nanowires are compared with spectra of SiC powders of various grain sizes. The temperature and pressure dependence of the Raman spectra for powders is similar to that of bulk crystals, but is different for nanowires. Frequency shifts, band broadenings and the presence of shoulders are discussed in terms of crystal size, character of defects and their population. The concentration of defects in synthesized nanowires depends on the sintering method. Raman intensity enhancement of the LO phonon was observed when the wavelength of the excitation laser was changed from 780 to 514 nm

  4. Silicon carbide, a semiconductor for space power electronics

    Science.gov (United States)

    Powell, J. A.; Matus, Lawrence G.

    1991-01-01

    After many years of promise as a high temperature semiconductor, silicon carbide (SiC) is finally emerging as a useful electronic material. Recent significant progress that has led to this emergence has been in the area of crystal growth and device fabrication technology. High quality of single-crystal SiC wafers, up to 25 mm in diameter, can now be produced routinely from boules grown by a high temperature (2700 K) sublimation process. Device fabrication processes, including chemical vapor deposition (CVD), in situ doping during CVD, reactive ion etching, oxidation, metallization, etc. have been used to fabricate p-n junction diodes and MOSFETs. The diode was operated to 870 K and the MOSFET to 770 K.

  5. Role of amorphous silicon domains on Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide film

    Institute of Scientific and Technical Information of China (English)

    陈长勇; 陈维德; 李国华; 宋淑芳; 丁琨; 许振嘉

    2003-01-01

    An investigation on the correlation between amorphous Si (a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carriers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:Hfilms.

  6. Role of amorphous silicon domains of Er3+ emission in the Er—doped hydrogenated amorphous silicon suboxide film

    Institute of Scientific and Technical Information of China (English)

    ChenChang-Yong; ChenWei-De; LeGuo-Hua; SongShu-Fang; DingKun; XuZhen-Jia

    2003-01-01

    An investigation on the correlation between amorphous Si(a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carrlers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:H films.

  7. Interface modification effect between p-type a-SiC:H and ZnO:Al in p-i-n amorphous silicon solar cells

    OpenAIRE

    Baek, Seungsin; Lee, Jeong Chul; Lee, Youn-Jung; Iftiquar, Sk Md; Kim, Youngkuk; Park, Jinjoo; Yi, Junsin

    2012-01-01

    Aluminum-doped zinc oxide (ZnO:Al) [AZO] is a good candidate to be used as a transparent conducting oxide [TCO]. For solar cells having a hydrogenated amorphous silicon carbide [a-SiC:H] or hydrogenated amorphous silicon [a-Si:H] window layer, the use of the AZO as TCO results in a deterioration of fill factor [FF], so fluorine-doped tin oxide (Sn02:F) [FTO] is usually preferred as a TCO. In this study, interface engineering is carried out at the AZO and p-type a-SiC:H interface to obtain a b...

  8. The current understanding on the diamond machining of silicon carbide

    International Nuclear Information System (INIS)

    The Glenn Research Centre of NASA, USA (www.grc.nasa.gov/WWW/SiC/, silicon carbide electronics) is in pursuit of realizing bulk manufacturing of silicon carbide (SiC), specifically by mechanical means. Single point diamond turning (SPDT) technology which employs diamond (the hardest naturally-occurring material realized to date) as a cutting tool to cut a workpiece is a highly productive manufacturing process. However, machining SiC using SPDT is a complex process and, while several experimental and analytical studies presented to date aid in the understanding of several critical processes of machining SiC, the current knowledge on the ductile behaviour of SiC is still sparse. This is due to a number of simultaneously occurring physical phenomena that may take place on multiple length and time scales. For example, nucleation of dislocation can take place at small inclusions that are of a few atoms in size and once nucleated, the interaction of these nucleations can manifest stresses on the micrometre length scales. The understanding of how these stresses manifest during fracture in the brittle range, or dislocations/phase transformations in the ductile range, is crucial to understanding the brittle–ductile transition in SiC. Furthermore, there is a need to incorporate an appropriate simulation-based approach in the manufacturing research on SiC, owing primarily to the number of uncertainties in the current experimental research that includes wear of the cutting tool, poor controllability of the nano-regime machining scale (effective thickness of cut), and coolant effects (interfacial phenomena between the tool, workpiece/chip and coolant), etc. In this review, these two problems are combined together to posit an improved understanding on the current theoretical knowledge on the SPDT of SiC obtained from molecular dynamics simulation. (topical review)

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

    Science.gov (United States)

    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.

  10. Advanced Measurements of Silicon Carbide Ceramic Matrix Composites

    Energy Technology Data Exchange (ETDEWEB)

    Farhad Farzbod; Stephen J. Reese; Zilong Hua; Marat Khafizov; David H. Hurley

    2012-08-01

    Silicon carbide (SiC) is being considered as a fuel cladding material for accident tolerant fuel under the Light Water Reactor Sustainability (LWRS) Program sponsored by the Nuclear Energy Division of the Department of Energy. Silicon carbide has many potential advantages over traditional zirconium based cladding systems. These include high melting point, low susceptibility to corrosion, and low degradation of mechanical properties under neutron irradiation. In addition, ceramic matrix composites (CMCs) made from SiC have high mechanical toughness enabling these materials to withstand thermal and mechanical shock loading. However, many of the fundamental mechanical and thermal properties of SiC CMCs depend strongly on the fabrication process. As a result, extrapolating current materials science databases for these materials to nuclear applications is not possible. The “Advanced Measurements” work package under the LWRS fuels pathway is tasked with the development of measurement techniques that can characterize fundamental thermal and mechanical properties of SiC CMCs. An emphasis is being placed on development of characterization tools that can used for examination of fresh as well as irradiated samples. The work discuss in this report can be divided into two broad categories. The first involves the development of laser ultrasonic techniques to measure the elastic and yield properties and the second involves the development of laser-based techniques to measurement thermal transport properties. Emphasis has been placed on understanding the anisotropic and heterogeneous nature of SiC CMCs in regards to thermal and mechanical properties. The material properties characterized within this work package will be used as validation of advanced materials physics models of SiC CMCs developed under the LWRS fuels pathway. In addition, it is envisioned that similar measurement techniques can be used to provide process control and quality assurance as well as measurement of

  11. Silicon Carbide High-Temperature Power Rectifiers Fabricated and Characterized

    Science.gov (United States)

    1996-01-01

    The High Temperature Integrated Electronics and Sensors (HTIES) team at the NASA Lewis Research Center is developing silicon carbide (SiC) for use in harsh conditions where silicon, the semiconductor used in nearly all of today's electronics, cannot function. Silicon carbide's demonstrated ability to function under extreme high-temperature, high power, and/or high-radiation conditions will enable significant improvements to a far ranging variety of applications and systems. These improvements range from improved high-voltage switching for energy savings in public electric power distribution and electric vehicles, to more powerful microwave electronics for radar and cellular communications, to sensors and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines. In the case of jet engines, uncooled operation of 300 to 600 C SiC power actuator electronics mounted in key high-temperature areas would greatly enhance system performance and reliability. Because silicon cannot function at these elevated temperatures, the semiconductor device circuit components must be made of SiC. Lewis' HTIES group recently fabricated and characterized high-temperature SiC rectifier diodes whose record-breaking characteristics represent significant progress toward the realization of advanced high-temperature actuator control circuits. The first figure illustrates the 600 C probe-testing of a Lewis SiC pn-junction rectifier diode sitting on top of a glowing red-hot heating element. The second figure shows the current-versus voltage rectifying characteristics recorded at 600 C. At this high temperature, the diodes were able to "turn-on" to conduct 4 A of current when forward biased, and yet block the flow of current ($quot;turn-off") when reverse biases as high as 150 V were applied. This device represents a new record for semiconductor device operation, in that no previous semiconductor electronic device has ever simultaneously demonstrated 600 C functionality

  12. Electrical Characterization of Amorphous Silicon Nitride Passivation Layers for Crystalline Silicon Solar Cells

    OpenAIRE

    Helland, Susanne

    2011-01-01

    High quality surface passivation is important for the reduction of recombination losses in solar cells. In this work, the passivation properties of amorphous hydrogenated silicon nitride for crystalline silicon solar cells were investigated, using electrical characterization, lifetime measurements and spectroscopic ellipsometry. Thin films of varying composition were deposited on p-type monocrystalline silicon wafers by plasma enhanced chemical vapor deposition (PECVD). Highest quality surfac...

  13. Kirchhoff?s generalised law applied to amorphous silicon / crystalline silicon heterostructures

    OpenAIRE

    Brüggemann, Rudolf

    2009-01-01

    Abstract The electro- and photoluminescence spectra of amorphous silicon / crystalline silicon heterostructures and solar cells are determined by emission from the crystalline-silicon layer and are computed with Kirchhoff?s generalised law. The interface defect density strongly influences the luminescence yield which may be used to monitor the interface quality. Based on a comparison between numerical and analytically determined spectra, the temperature dependence of experimental e...

  14. The effect of sintering additive on fracture behavior of carbon-whisker-reinforced silicon carbide composites

    International Nuclear Information System (INIS)

    Hot-pressed silicon carbide composites reinforced with carbon fiber were prepared. Aluminum and yttrium oxides served as sintering additives and low-cost α phase SiC was used as starting powder, instead of the more expensive β-SiC. In the sintering process, the SiC-matrix grains grew larger via solution reprecipitation. Reaction of Al2O3/Y2O3 additives with SiO2 on the surface of SiC or its oxidation products caused formation and distribution of a low-eutectic-point phase around the SiC grains and carbon whiskers. Such amorphous films can be found in triple-junctions and boundaries of SiC grains. Excess sintering additives improve the room-temperature flexural strength, but reduce the fracture toughness. Coupled with a higher sintering temperature, they contribute to the diffusion of yttrium ions into carbon fiber, and make the reaction layer thicker. Non-homogeneous amorphous inclusions between grains and whiskers are harmful for mechanical properties. A combination of grain bridging, crack deflection and whisker debonding can improve fracture toughness

  15. Quantitative analysis of the epitaxial recrystallization effect induced by swift heavy ions in silicon carbide

    Science.gov (United States)

    Benyagoub, A.

    2015-12-01

    This paper discusses recent results on the recrystallization effect induced by swift heavy ions (SHI) in pre-damaged silicon carbide. The recrystallization kinetics was followed by using increasing SHI fluences and by starting from different levels of initial damage within the SiC samples. The quantitative analysis of the data shows that the recrystallization rate depends drastically on the local amount of crystalline material: it is nil in fully amorphous regions and becomes more significant with increasing amount of crystalline material. For instance, in samples initially nearly half-disordered, the recrystallization rate per incident ion is found to be 3 orders of magnitude higher than what it is observed with the well-known IBIEC process using low energy ions. This high rate can therefore not be accounted for by the existing IBIEC models. Moreover, decreasing the electronic energy loss leads to a drastic reduction of the recrystallization rate. A comprehensive quantitative analysis of all the experimental results shows that the SHI induced high recrystallization rate can only be explained by a mechanism based on the melting of the amorphous zones through a thermal spike process followed by an epitaxial recrystallization initiated from the neighboring crystalline regions if the size of the latter exceeds a certain critical value. This quantitative analysis also reveals that recent molecular dynamics calculations supposed to reproduce this phenomenon are wrong since they overestimated the recrystallization rate by a factor ∼40.

  16. Effect of laser pulsed radiation on the properties of implanted layers of silicon carbide

    International Nuclear Information System (INIS)

    Results are presented of investigation into pulsed laser radiation effects on the layers of GH polytype silicon carbide converted to amorphous state by implantation of boron and aluminium ions. The implantation doses were selected to be 5x1016 for boron and 5x1015 cm-2 for aluminium, with the ion energies being 60 and 80 keV, respectively. The samples annealed under nanosecond regime are stated to posseys neither photoluminescence (PL) nor cathodoluminescence (CL). At the same time the layers annealed in millisecond regime have a weak PL at 100 K and CL at 300 K. The PL and CL are observed in samples, laser-annealed at radiation energy density above 150-160 J/cm2 in case of boron ion implantation and 100-120 J/cm2 in case of aluminium ion implantation. Increasing the radiation energy density under the nanosecond regime of laser annealing results in the surface evaporation due to superheating of amorphous layers. Increasing the energy density above 220-240 J/cm2 results in destruction of the samples

  17. Oxidation resistant zirconium diboride–silicon carbide coatings for silicon carbide coated graphite materials

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Wang; Wenbo, Han, E-mail: wbhan@hit.edu.cn; Xinxin, Jin; Xinghong, Zhang; Jiaxing, Gao; Shanbao, Zhou

    2015-04-25

    Highlights: • ZrB{sub 2}–SiC/SiC coated graphite specimens were prepared by pack cementation. • Weight loss of ZS50 sample was 2.9% after oxidation and 6.5% after 15 thermal shocks. • Residual silicon is beneficial to oxidation resistance and thermal shock resistance. - Abstract: Four ZrB{sub 2}–SiC/SiC dual-layer coatings were prepared on the surface of graphite matrix by pack cementation to improve the oxidation and thermal shock resistance of graphite. The crystalline structure and morphology as well as the resistance to oxidation and thermal shock of these coatings were investigated. The results indicated that the weight loss of the ZS50 coating sample, whose pack powders contained 52.4 wt.% ZrB{sub 2}, 39.2 wt.% Si and 8.4 wt.% graphite, was only 2.9% after oxidation in air at 1500 °C for 19 h and 6.5% after thermal shocks between 1500 °C and room temperature for 15 cycles. With the increasing silicon in pack powders, some residual silicon appeared in ZS50 coating, which was considered to be beneficial to oxidation resistance and thermal shock resistance because it can improve the density of coating and the SiO{sub 2} formed by oxidation of residual Si can heal the microcracks at high temperature.

  18. Oxidation resistant zirconium diboride–silicon carbide coatings for silicon carbide coated graphite materials

    International Nuclear Information System (INIS)

    Highlights: • ZrB2–SiC/SiC coated graphite specimens were prepared by pack cementation. • Weight loss of ZS50 sample was 2.9% after oxidation and 6.5% after 15 thermal shocks. • Residual silicon is beneficial to oxidation resistance and thermal shock resistance. - Abstract: Four ZrB2–SiC/SiC dual-layer coatings were prepared on the surface of graphite matrix by pack cementation to improve the oxidation and thermal shock resistance of graphite. The crystalline structure and morphology as well as the resistance to oxidation and thermal shock of these coatings were investigated. The results indicated that the weight loss of the ZS50 coating sample, whose pack powders contained 52.4 wt.% ZrB2, 39.2 wt.% Si and 8.4 wt.% graphite, was only 2.9% after oxidation in air at 1500 °C for 19 h and 6.5% after thermal shocks between 1500 °C and room temperature for 15 cycles. With the increasing silicon in pack powders, some residual silicon appeared in ZS50 coating, which was considered to be beneficial to oxidation resistance and thermal shock resistance because it can improve the density of coating and the SiO2 formed by oxidation of residual Si can heal the microcracks at high temperature

  19. Atomically resolved surface structures of vapor deposited amorphous silicon-carbon alloys: An atomic force microscopy and spectroscopic study

    International Nuclear Information System (INIS)

    Silicon carbide alloys are widely used in high-tech applications due to their interesting combination of chemical, mechanical and electronic properties. Growing thin films of this material in a simple and controlled way is a hot topic in modern material's science. In particular, the possibility to tailor the film properties just by tuning the deposition temperature would be an important progress. In the present work amorphous silicon-carbon alloys thin films have been deposited by electron beam sublimation of a poly-crystalline silicon carbide target in vacuum environment. The deposition temperature was varied from Room Temperature to about 1300 K. The resulting films were analyzed by means of Ultra High Vacuum-Atomic Force Microscopy (UHV-AFM) down to even atomic resolution. The observed features agree with literature data, e.g. interatomic bond lengths, as achieved by others methods, and the structural arrangements of silicon and carbon atoms as concluded from IR and Raman spectroscopy measurements carried out on the same samples. The results not only allow a correlation between film properties and deposition temperature but also support the notion of the UHV-AFM images of the amorphous surfaces being atomically resolved.

  20. Plasma Deposition of Doped Amorphous Silicon

    Science.gov (United States)

    Calcote, H. F.

    1985-01-01

    Pair of reports present further experimental details of investigation of plasma deposition of films of phosphorous-doped amosphous silicon. Probe measurements of electrical resistance of deposited films indicated films not uniform. In general, it appeared that resistance decreased with film thickness.