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Sample records for veselbas aprpes si

  1. Single crystalline PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices.

    Science.gov (United States)

    Lin, Yung-Chen; Lu, Kuo-Chang; Wu, Wen-Wei; Bai, Jingwei; Chen, Lih J; Tu, K N; Huang, Yu

    2008-03-01

    We report the formation of PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices from such heterostructures. Scanning electron microscopy studies show that silicon nanowires can be converted into PtSi nanowires through controlled reactions between lithographically defined platinum pads and silicon nanowires. High-resolution transmission electron microscopy studies show that PtSi/Si/PtSi heterostructure has an atomically sharp interface with epitaxial relationships of Si[110]//PtSi[010] and Si(111)//PtSi(101). Electrical measurements show that the pure PtSi nanowires have low resistivities approximately 28.6 microOmega.cm and high breakdown current densities>1x10(8) A/cm2. Furthermore, using single crystal PtSi/Si/PtSi nanowire heterostructures with atomically sharp interfaces, we have fabricated high-performance nanoscale field-effect transistors from intrinsic silicon nanowires, in which the source and drain contacts are defined by the metallic PtSi nanowire regions, and the gate length is defined by the Si nanowire region. Electrical measurements show nearly perfect p-channel enhancement mode transistor behavior with a normalized transconductance of 0.3 mS/microm, field-effect hole mobility of 168 cm2/V.s, and on/off ratio>10(7), demonstrating the best performing device from intrinsic silicon nanowires.

  2. Ordering at Si(111)/o-Si and Si(111)/SiO2 Interfaces

    DEFF Research Database (Denmark)

    Robinson, I. K.; Waskiewicz, W. K.; Tung, R. T.

    1986-01-01

    X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both Si(111)/a-Si and Si(111)/SiO2 examples there are features in the perpendicular-momentum-transfer dependence which are not expec......X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both Si(111)/a-Si and Si(111)/SiO2 examples there are features in the perpendicular-momentum-transfer dependence which...... are not expected from an ideal sharp interface. The diffraction profiles are explained by models with partially ordered layers extending into the amorphous region. In the Si(111)/a-Si case there is clear evidence of stacking faults which are attributed to residual 7×7 reconstruction....

  3. SI - Small Scale Advantages

    OpenAIRE

    Nordström, Marie; Kallin Westin, Lena

    2006-01-01

    Not being part of a larger SI-organisation has both advantages and disadvantages. In this paper we try to illustrate the advantages of doing SI small scale. In a large scale SI-organisation the supervisors are often not teachers themselves and/or not familiar with the practices of a specific course. To have teaching staff supervising a SIproject completely focused on one course is favourable in many ways. The decision to introduce SI was taken by the department of Computing Science to support...

  4. Manufacture and properties of Si-SiC-MoSi sub 2 composites. Herstellung und Eigenschaften von Si-SiC-MoSi sub 2 -Verbundwerkstoffe

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, W.; Wruss, W.; Stroh, R.; Lux, B. (Technische Univ., Vienna (Austria). Inst. fuer Chemische Technologie Anorganischer Stoffe); Ekstroem, T. (SANDVIK Hard Materials AB, Stockholm (Sweden))

    1990-06-01

    This report deals with the manufacture of SiC-Si-MoSi{sub 2} composites, i.e. with modified SiSiC composites. The scope of application of SiSiC is limited by the melting temperature of silicon ({approx equal} 1420deg C) and by the chemical resistance of the silicon binder phase with respect to the surrounding medium. The application temperature can be raised and the corrosion resistance improved by replacing the silicon matrix with refractory silicides, e.g. molybdenum disilicide. The free silicon composite was partially replaced with molybdenum disilicide by infiltrating an SiC-C green compact with the Si-Mo melt. The insertion of the new phase reduces the room-temparture strength from 323 MPa for the unalloyed SiSiC (density: 2.83 g/cm{sup 3}, 42.7 vol.% silicon) to 171 MPa (density: 3.05 g/cm{sup 3}, 5.8 vol.% MoSi{sub 2}, referred to the silicon binder). However, the high-temperature properties of the altered material are expected to be improved via ductilization of MoSi{sub 2} at {approx equal} 1000deg C. (orig.).

  5. Growth of Amorphous and Epitaxial ZnSiP2-Si Alloys on Si

    Energy Technology Data Exchange (ETDEWEB)

    Tamboli, Adele C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Martinez, Aaron [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Link, Elisa M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Norman, Andrew [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schnepf, Rekha [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perkins, Craig [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Stradins, Paul [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Toberer, Eric [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Leick, Noemi [Formerly NREL

    2018-01-03

    ZnSiP2 is a wide band gap material that is lattice matched with Si, offering the potential for Si-based optoelectronic materials and devices, including multijunction photovoltaics. We present a carbon-free chemical vapor deposition process for the growth of both epitaxial and amorphous thin films of ZnSiP2-Si alloys with tunable Si content on Si substrates. Si alloy content is widely tunable across the full composition space in amorphous films. Optical absorption of these films reveals relatively little variation with Si content, despite the fact that ZnSiP2 has a much wider band gap of 2.1 eV. Post-growth crystallization of Si-rich films resulted in epitaxial alignment, as measured by X-ray diffraction and transmission electron microscopy. These films have an optical absorption onset near 1.1 eV, suggesting the possibility of band gap tuning with Si content in crystalline films. The optical absorption is comparably strong to pure ZnSiP2, suggesting a more direct transition than in pure Si.

  6. Si-to-Si wafer bonding using evaporated glass

    DEFF Research Database (Denmark)

    Reus, Roger De; Lindahl, M.

    1997-01-01

    Anodic bonding of Si to Si four inch wafers using evaporated glass was performed in air at temperatures ranging from 300°C to 450°C. Although annealing of Si/glass structures around 340°C for 15 minutes eliminates stress, the bonded wafer pairs exhibit compressive stress. Pull testing revealed...

  7. Admittance of a-Si:H/c-Si Schottky diodes

    Energy Technology Data Exchange (ETDEWEB)

    Gall, S.; Hirschauer, R.; Braeunig, D. [Hahn-Meitner-Inst., Berlin (Germany). Dept. AT; Kolter, M. [Forschungszentrum Juelich (Germany)

    1996-12-31

    Heterojunction devices, based on hydrogenated amorphous silicon (a-Si:H) and single crystalline silicon (c-Si), are likely candidates for high efficiency solar cells. The authors have measured the admittance (conductance and capacitance) of a-Si:H/c-Si heterostructure Schottky diodes as a function of frequency, temperature and voltage in the dark and under spectral illumination (in the wavelength range between {lambda} = 500nm and {lambda} = 1,200nm). Thus, it is possible to observe the activation/deactivation of trapping-detrapping effects within the a-Si:H layer (near the a-SiH/c-Si interface). They have determined the conduction band offset of the a-Si:H/c-Si heterostructure. The spectral behavior of the admittance is dominated by the absorption of light in the c-Si and the valence band offset of the heterojunction. The authors have also developed an equivalent circuit of the a-Si:H/c-Si heterostructure Schottky diode in the dark, which is capable of describing the measured behavior.

  8. Helimagnetic order in bulk MnSi and CoSi/MnSi superlattices

    Science.gov (United States)

    Loh, G. C.; Khoo, K. H.; Gan, C. K.

    2017-01-01

    Skyrmions are nanoscopic whirls of spins that reside in chiral magnets. It is only fairly recent that a plethora of applications for these quasiparticles emerges, especially in data storage. On the other hand, spin spirals are the periodic analogs of skyrmions, and are equally imperative in the course of exploration to enhance our understanding of helimagnetism. In this study, a new infrastructure based on the B20 compound, MnSi is propounded as a hosting material for spin spirals; alternating thin layers of CoSi and MnSi in the superlattice form provides a facile way of varying the properties of the spin spirals across a continuum. Using first-principles calculations based on full-potential linearized augmented plane-wave (FLAPW)-based density functional theory (DFT), the spin order of bulk MnSi, MnSi film, and the CoSi/MnSi superlattice is investigated. Spin dispersion plots as a function of propagation vectors show that the spiral size changes in the presence of CoSi - we find that the size of the spiral is reduced in the superlattice with thin CoSi layers (CoSi:MnSi=1:1 thickness ratio), whilst at a larger CoSi:MnSi=2:1 thickness ratio, the material behaves as a ferromagnet. In a similar fashion, the spin moment and orbital occupancy depend significantly on the thickness of the CoSi layers. However, the exchange interaction between Mn atoms appears to be generally impervious to the presence of CoSi. Succinctly, the CoSi/MnSi superlattice could be an excellent functional material in data storage applications.

  9. Reliability implications of defects in high temperature annealed Si/SiO{sub 2}/Si structures

    Energy Technology Data Exchange (ETDEWEB)

    Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S. [Sandia National Labs., Albuquerque, NM (United States); Devine, R.A.B.; Mathiot, D. [France Telecom/CNET, Meylan (France); Wilson, I.H.; Xu, J.B. [Chinese Univ. of Hong Kong (Hong Kong)

    1994-08-01

    High-temperature post-oxidation annealing of poly-Si/SiO{sub 2}/Si structures such as metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field effect transistors is known to result in enhanced radiation sensitivity, increased 1/f noise, and low field breakdown. The authors have studied the origins of these effects from a spectroscopic standpoint using electron paramagnetic resonance (EPR) and atomic force microscopy. One result of high temperature annealing is the generation of three types of paramagnetic defect centers, two of which are associated with the oxide close to the Si/SiO{sub 2} interface (oxygen-vacancy centers) and the third with the bulk Si substrate (oxygen-related donors). In all three cases, the origin of the defects may be attributed to out-diffusion of O from the SiO{sub 2} network into the Si substrate with associated reduction of the oxide. The authors present a straightforward model for the interfacial region which assumes the driving force for O out-diffusion is the chemical potential difference of the O in the two phases (SiO{sub 2} and the Si substrate). Experimental evidence is provided to show that enhanced hole trapping and interface-trap and border-trap generation in irradiated high-temperature annealed Si/SiO{sub 2}/Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies.

  10. Strained Si/SiGe MOS transistor model

    Directory of Open Access Journals (Sweden)

    Tatjana Pešić-Brđanin

    2009-06-01

    Full Text Available In this paper we describe a new model of surfacechannel strained-Si/SiGe MOSFET based on the extension of non-quasi-static (NQS circuit model previously derived for bulk-Si devices. Basic equations of the NQS model have been modified to account for the new physical parameters of strained-Si and relaxed-SiGe layers. From the comparisons with measurements, it is shown that a modified NQS MOS including steady-state self heating can accurately predict DC characteristics of Strained Silicon MOSFETs.

  11. Brazing SiC/SiC Composites to Metals

    Science.gov (United States)

    Steffier, Wayne S.

    2004-01-01

    Experiments have shown that active brazing alloys (ABAs) can be used to join SiC/SiC composite materials to metals, with bond strengths sufficient for some structural applications. The SiC/SiC composite coupons used in the experiments were made from polymerbased SiC fiber preforms that were chemical-vapor-infiltrated with SiC to form SiC matrices. Some of the metal coupons used in the experiments were made from 304 stainless steel; others were made from oxygen-free, high-conductivity copper. Three ABAs were chosen for the experiments: two were chosen randomly from among a number of ABAs that were on hand at the time; the third ABA was chosen because its titanium content (1.25 percent) is less than those of the other two ABAs (1.75 and 4.5 percent, respectively) and it was desired to evaluate the effect of reducing the titanium content, as described below. The characteristics of ABAs that are considered to be beneficial for the purpose of joining SiC/SiC to metal include wettability, reactivity, and adhesion to SiC-based ceramics. Prior to further development, it was verified that the three chosen ABAs have these characteristics. For each ABA, suitable vacuum brazing process conditions were established empirically by producing a series of (SiC/SiC)/ABA wetting samples. These samples were then sectioned and subjected to scanning electron microscopy (SEM) and energy-dispersive x-ray spectrometry (EDS) for analysis of their microstructures and compositions. Specimens for destructive mechanical tests were fabricated by brazing of lap joints between SiC/SiC coupons 1/8-in. (.3.2- mm) thick and, variously, stainless steel or copper tabs. The results of destructive mechanical tests and the SEM/EDS analysis were used to guide the development of a viable method of brazing the affected materials.

  12. Highly sensitive NIR PtSi/Si-nanostructure detectors

    Science.gov (United States)

    Li, Hua-gao; Guo, Pei; Yuan, An-bo; Long, Fei; Li, Rui-zhi; Li, Ping; Li, Yi

    2016-10-01

    We report a high external quantum efficiency (EQE) photodiode detector with PtSi/Si-nanostructures. Black silicon nanostructures were fabricated by metal-assist chemical etching (MCE), a 2 nm Pt layer was subsequently deposited on black silicon surface by DC magnetron sputtering system, and PtSi/Si-nanostructures were formed in vacuum annealing at 450 oC for 5 min. As the PtSi/Si-nanostructures presented a spiky shape, the absorption of incident light was remarkably enhanced for the repeat reflection and absorption. The breakdown voltage, dark current, threshold voltage and responsivity of the device were investigated to evaluate the performance of the PtSi/Si-nanostructures detector. The threshold voltage and dark currents of the PtSi/Si-nanostructure photodiode tends to be slightly higher than those of the standard diodes. The breakdown voltage remarkably was reduced because of existing avalanche breakdown in PtSi/Si-nanostructures. However, the photodiodes had high response at room temperature in near infrared region. At -5 V reverse bias voltage, the responsivity was 0.72 A/W in 1064 nm wavelength, and the EQE was 83.9%. By increasing the reverse bias voltage, the responsivity increased. At -60 V reverse bias voltage, the responsivity was 3.5 A/W, and the EQE was 407.5%, which means the quantum efficiency of PtSi/Si-nanostructure photodiodes was about 10 times higher than that of a standard diode. Future research includes how to apply this technology to enhance the NIR sensitivity of image sensors, such as Charge Coupled Devices (CCD).

  13. Deformation effects in the 28 Si+ 12 C and 28 Si+ 28 Si reactions

    Indian Academy of Sciences (India)

    Deformation effects in the 28Si + 12C and 28Si + 28Si reactions. C Bhattacharya M Rousseau C Beck V Rauch R M Freeman R Nouicer F Haas O Dorvaux K Eddahbi P Papka O Stezwski S Szilner D Mahboub A Szanto De Toledo A Hachem E Martin S J Sanders. Contributed Papers : Nuclear reactions Volume 57 Issue 1 ...

  14. Creep Investigation of SiCf-SiBC Composites

    Science.gov (United States)

    Farizy, Gaëlle; Chermant, Jean-Louis; Vicens, Jean; Sangleboeuf, Jean-Christophe

    The concept of ceramic matrix composites was proposed in the eighties to be used in the aeronautical and space domains. Classical SiCf-SiC have changed into complex materials, such as SiCf-SiBC investigated in this work: that composite is reinforced with SiC Hi-Nicalon fibers and has a multi-layer and self-sealing matrix. This matrix has been fabricated by means of several chemical vapor infiltrations with different compositions. Prior to the matrix infiltration, a pyrocarbon interphase has been deposited on the fibrous preform. The self-sealing property of this composite is due to the presence of boron in certain matrix layers, which will react with the atmosphere and particularly oxygen, to create a sealant glass, which protects pyrocarbon and SiC fibers.

  15. Synthesis and characterization of laminated Si/SiC composites

    Directory of Open Access Journals (Sweden)

    Salma M. Naga

    2013-01-01

    Full Text Available Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results.

  16. Structure of MnSi on SiC(0001)

    Science.gov (United States)

    Meynell, S. A.; Spitzig, A.; Edwards, B.; Robertson, M. D.; Kalliecharan, D.; Kreplak, L.; Monchesky, T. L.

    2016-11-01

    We report on the growth and magnetoresistance of MnSi films grown on SiC(0001) by molecular beam epitaxy. The growth resulted in a textured MnSi(111) film with a predominantly [1 1 ¯0 ] MnSi (111 )∥[11 2 ¯0 ] SiC(0001) epitaxial relationship, as demonstrated by transmission electron microscopy, reflection high energy electron diffraction, and atomic force microscopy. The 500 ∘C temperature required to crystallize the film leads to a dewetting of the MnSi layer. Although the sign of the lattice mismatch suggested the films would be under compressive stress, the films acquire an in-plane tensile strain likely driven by the difference in thermal expansion coefficients between the film and substrate during annealing. As a result, the magnetoresistive response demonstrates that the films possess a hard-axis out-of-plane magnetocrystalline anisotropy.

  17. SiC/SiC Cladding Materials Properties Handbook

    Energy Technology Data Exchange (ETDEWEB)

    Snead, Mary A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Singh, Gyanender P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-08-01

    When a new class of material is considered for a nuclear core structure, the in-pile performance is usually assessed based on multi-physics modeling in coordination with experiments. This report aims to provide data for the mechanical and physical properties and environmental resistance of silicon carbide (SiC) fiber–reinforced SiC matrix (SiC/SiC) composites for use in modeling for their application as accidenttolerant fuel cladding for light water reactors (LWRs). The properties are specific for tube geometry, although many properties can be predicted from planar specimen data. This report presents various properties, including mechanical properties, thermal properties, chemical stability under normal and offnormal operation conditions, hermeticity, and irradiation resistance. Table S.1 summarizes those properties mainly for nuclear-grade SiC/SiC composites fabricated via chemical vapor infiltration (CVI). While most of the important properties are available, this work found that data for the in-pile hydrothermal corrosion resistance of SiC materials and for thermal properties of tube materials are lacking for evaluation of SiC-based cladding for LWR applications.

  18. Joining of SiC ceramics and SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

    1995-08-01

    This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method has the potential to facilitate the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent efforts have focused on transferring the joining technology to industry. Several industrial partners have been identified and collaborative research projects are in progress. Investigations are focusing on applying the joining method to sintered a-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

  19. Joining of SiC ceramics and SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

    1996-08-01

    This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method will permit the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent emphasis has been given to technology transfer activities, and several collaborative research efforts are in progress. Investigations are focusing on applying the joining method to sintered {alpha}-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

  20. Methods of radiation effects evaluation of SiC/SiC composite and SiC fibers

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    This report covers material presented at the IEA/Jupiter Joint International Workshop on SiC/SiC Composites for Fusion structural Applications held in conjunction with ICFRM-8, Sendai, Japan, Oct. 23--24, 1997. Several methods for radiation effects evaluation of SiC fibers and fiber-reinforced SiC/SiC composite are presented.

  1. Synthesis and structural property of Si nanosheets connected to Si nanowires using MnCl{sub 2}/Si powder source

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Erchao [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Ueki, Akiko [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Meng, Xiang [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Suzuki, Hiroaki [Graduate School of Engineering, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Itahara, Hiroshi [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Tatsuoka, Hirokazu, E-mail: tatsuoka.hirokazu@shizuoka.ac.jp [Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan)

    2016-08-15

    Graphical abstract: Si nanosheets connected to Si nanowires synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst avoid the use of air-sensitive SiH{sub 4} or SiCl{sub 4}. It was evident from these structural features of the nanosheets (leaf blade) with nanowires (petiole) that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes of the Si(111) nanosheets was clearly explained by the interference with the extra diffraction spots that arose due to the reciprocal lattice streaking effect. - Highlights: • New Si nanosheets connected to Si nanowires were synthesized using MnCl{sub 2}/Si powders. • The synthesis method has benefits in terms of avoiding air sensitive SiH{sub 4} or SiCl{sub 4}. • Structural property and electron diffraction of the Si nanosheets were clarified. • Odd lattice fringes of the Si nanosheets observed by HRTEM were clearly explained. - Abstract: Si nanosheets connected to Si nanowires were synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst. The synthesis method has benefits in terms of avoiding conventionally used air-sensitive SiH{sub 4} or SiCl{sub 4}. The existence of the Si nanosheets connected to the Si<111> nanowires, like sprouts or leaves with petioles, was observed, and the surface of the nanosheets was Si{111}. The nanosheets were grown in the growth direction of <211> perpendicular to that of the Si nanowires. It was evident from these structural features of the nanosheets that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes, which do not appear for Si bulk crystals, of the Si(111) nanosheets obtained by high resolution transmission electron microscopy was clearly explained due to the extra diffraction spots that arose by the reciprocal lattice streaking effect.

  2. Si nanoparticle interfaces in Si/SiO solar cell materials

    DEFF Research Database (Denmark)

    Kilpeläinen, S.; Kujala, J.; Tuomisto, F.

    2013-01-01

    Novel solar cell materials consisting of Si nanoparticles embedded in SiO2 layers have been studied using positron annihilation spectroscopy in Doppler broadening mode and photoluminescence. Two positron-trapping interface states are observed after high temperature annealing at 1100 °C. One...

  3. a-Si:H/SiNW shell/core for SiNW solar cell applications

    Science.gov (United States)

    2013-01-01

    Vertically aligned silicon nanowires have been synthesized by the chemical etching of silicon wafers. The influence of a hydrogenated amorphous silicon (a-Si:H) layer (shell) on top of a silicon nanowire (SiNW) solar cell has been investigated. The optical properties of a-Si:H/SiNWs and SiNWs are examined in terms of optical reflection and absorption properties. In the presence of the a-Si:H shell, 5.2% reflection ratio in the spectral range (250 to 1,000 nm) is achieved with a superior absorption property with an average over 87% of the incident light. In addition, the characteristics of the solar cell have been significantly improved, which exhibits higher open-circuit voltage, short-circuit current, and efficiency by more than 15%, 12%, and 37%, respectively, compared with planar SiNW solar cells. Based on the current–voltage measurements and morphology results, we show that the a-Si:H shell can passivate the defects generated by wet etching processes. PMID:24195734

  4. Low dose irradiation performance of SiC interphase SiC/SiC composites

    Science.gov (United States)

    Snead, L. L.; Osborne, M. C.; Lowden, R. A.; Strizak, J.; Shinavski, R. J.; More, K. L.; Eatherly, W. S.; Bailey, J.; Williams, A. M.

    1998-03-01

    Reduced oxygen Hi-Nicalon™ fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either `porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1×10 25 n m -2 ( E>0.1 MeV) in the temperature range of 260 to 1060°C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber.

  5. Improved characterization of Si-SiO2 interfaces

    Science.gov (United States)

    Su, P.

    Silicon is the heart of modern semiconductor devices. The dominance of Si in semiconductor technology depends on the superior quality and properties of thermally grown SiO2 compared with the oxide that can be placed on any other semiconductor. The well established quasistatic and conductance methods used in the study of the Si-SiO2 interface are improved by using an effectively thin composite insulator, low carrier concentration substrates, and most importantly, low level illumination at a wavelength that creates electron hole pairs. The samples investigated had a thermally grown oxide prepared in dry oxygen. They were never exposed to H2 or H2O at an elevated temperature. The composite gate insulator was completed by having an e-gun deposited 250 A layer on LaF3. The resulting interface, subjected to the improved experimental method, yields a wealth of distinctive structure rather than the often reported featureless U-shaped interface-state density.

  6. Total Ionizing Dose Effects of Si Vertical Diffused MOSFET with SiO2 and Si3N4/SiO2 Gate Dielectrics

    Directory of Open Access Journals (Sweden)

    Jiongjiong Mo

    2017-01-01

    Full Text Available The total ionizing dose irradiation effects are investigated in Si vertical diffused MOSFETs (VDMOSs with different gate dielectrics including single SiO2 layer and double Si3N4/SiO2 layer. Radiation-induced holes trapping is greater for single SiO2 layer than for double Si3N4/SiO2 layer. Dielectric oxidation temperature dependent TID effects are also studied. Holes trapping induced negative threshold voltage shift is smaller for SiO2 at lower oxidation temperature. Gate bias during irradiation leads to different VTH shift for different gate dielectrics. Single SiO2 layer shows the worst negative VTH at VG=0 V, while double Si3N4/SiO2 shows negative VTH shift at VG=-5 V, positive VTH shift at VG=10 V, and negligible VTH shift at VG=0 V.

  7. Graphene-Si heterogeneous nanotechnology

    Science.gov (United States)

    Akinwande, Deji; Tao, Li

    2013-05-01

    It is widely envisioned that graphene, an atomic sheet of carbon that has generated very broad interest has the largest prospects for flexible smart systems and for integrated graphene-silicon (G-Si) heterogeneous very large-scale integrated (VLSI) nanoelectronics. In this work, we focus on the latter and elucidate the research progress that has been achieved for integration of graphene with Si-CMOS including: wafer-scale graphene growth by chemical vapor deposition on Cu/SiO2/Si substrates, wafer-scale graphene transfer that afforded the fabrication of over 10,000 devices, wafer-scalable mitigation strategies to restore graphene's device characteristics via fluoropolymer interaction, and demonstrations of graphene integrated with commercial Si- CMOS chips for hybrid nanoelectronics and sensors. Metrology at the wafer-scale has led to the development of custom Raman processing software (GRISP) now available on the nanohub portal. The metrology reveals that graphene grown on 4-in substrates have monolayer quality comparable to exfoliated flakes. At room temperature, the high-performance passivated graphene devices on SiO2/Si can afford average mobilities 3000cm2/V-s and gate modulation that exceeds an order of magnitude. The latest growth research has yielded graphene with high mobilities greater than 10,000cm2/V-s on oxidized silicon. Further progress requires track compatible graphene-Si integration via wafer bonding in order to translate graphene research from basic to applied research in commercial R and D laboratories to ultimately yield a viable nanotechnology.

  8. Studi Tentang Pengaruh Doping Tinggi Terhadap Resistansi Basis Dan Bandgap Narrowing Pada Si/si1-xgex /Si Hbt

    OpenAIRE

    Achmad Fadhol

    2003-01-01

    Study About High Influence Doping to Base Resistance and Bandgap Narrowing at Si/Si1-xGex/Si HeterojunctionBipolar Transistor. Heterojunction is a link formed bedween two semiconductor materials and differend bandgapwhich has thinness under 50nm and grow the mixture of plate SiGe as bases. The link is an abrupt link or graded one.In this research learnt formulation of doping concentration influence to basis resistance and bandgap narrowing throughSi/Si1-xGex/Si Heterojunction Bipolar Transist...

  9. Growth of CNTs on Fe-Si catalyst prepared on Si and Al coated Si substrates.

    Science.gov (United States)

    Teng, F-Y; Ting, Jyh-Ming; Sharma, Sahendra P; Liao, Kun-Hou

    2008-03-05

    In this paper we report the effect of Al interlayers on the growth characteristics of carbon nanotubes (CNTs) using as-deposited and plasma etched Fe-Si catalyst films as the catalysts. Al interlayers having various thicknesses ranging from 2 to 42 nm were deposited on Si substrates prior to the deposition of Fe-Si catalysts. It was found that the Al interlayer diffuses into the Fe-Si catalyst during the plasma etching prior to the CNT growth, leading to the swelling and amorphization of the catalyst. This allows enhanced carbon diffusion in the catalyst and therefore a faster growth rate of the resulting CNTs. It was also found that use of an Al interlayer having a thickness of ∼3 ± 1 nm is most effective. Due to the effectiveness of this, the normally required catalyst etching is no longer needed for the growth of CNTs.

  10. SiC-SiC and C-SiC Honeycomb for Advanced Flight Structures Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The proposed project builds upon the work done in Phase I with the development of a C-SiC CMC honeycomb material that was successfully tested for mechanical...

  11. Improving Thermomechanical Properties of SiC/SiC Composites

    Science.gov (United States)

    DiCarlo, James A.; Bhatt, Ramakrishna T.

    2006-01-01

    Today, a major thrust toward improving the thermomechanical properties of engine components lies in the development of fiber-reinforced silicon carbide matrix composite materials, including SiC-fiber/SiC-matrix composites. These materials are lighter in weight and capable of withstanding higher temperatures, relative to state-of-the-art metallic alloys and oxide-matrix composites for which maximum use temperatures are in the vicinity of 1,100 C. In addition, the toughness or damage tolerance of the SiC-matrix composites is significantly greater than that of unreinforced silicon-based monolithic ceramics. For successful application in advanced engine systems, the SiC-matrix composites should be able to withstand component service stresses and temperatures for the desired component lifetimes. Inasmuch as the high-temperature structural lives of ceramic materials are typically limited by creep-induced growth of flaws, a key property required of such composite materials is high resistance to creep under conditions of use. Also, the thermal conductivity of the materials should be as high as possible so as to minimize component thermal gradients and thermal stresses. A state-of-the-art SiC-matrix composite is typically fabricated in a three-step process: (1) fabrication of a component-shaped architectural preform reinforced by thermally stable high-performance fibers, (2) chemical-vapor infiltration (CVI) of a fiber-coating material such as boron nitride (BN) into the preform, and (3) infiltration of an SiC-based matrix into the remaining porosity in the preform. Generally, the matrices of the highest-performing composites are fabricated by initial use of a CVI SiC matrix component that is typically more thermally stable and denser than matrix components formed by processes other than CVI. As such, the initial SiC matrix component made by CVI provides better environmental protection to the coated fibers embedded within it. Also, the denser CVI SiC imparts to the

  12. Spectral characteristics of a-Si:H/c-Si heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Gall, S.; Hirschauer, R.; Braeunig, D. [Hahn-Meitner-Institut Berlin, Department AT, Berlin (Germany); Kolter, M. [Forschungszentrum Juelich, Department ISI-PV, Juelich (Germany)

    1997-10-21

    We have examined the current-voltage characteristic of i-a-Si:H/n-c-Si heterojunction Schottky solar cells in the dark and under different illumination (spectrum AM1.5) intensities as well as the voltage- and temperature-dependent spectral response of these devices. The photocurrent from the crystalline silicon depends on both voltage and temperature due to their influence on the impact of the band offsets. From our measurements of the spectral response we conclude that there is a small conduction band offset {Delta}E{sub c} and a large valence band offset {Delta}E{sub v} at the i-a-Si:H/n-c-Si heterojunction. The large valence band offset inhibits the collection of photogenerated holes from the crystalline silicon under normal photovoltaic conditions. Thus, the current-voltage characteristic under illumination between V=0 V and V=V{sub oc} is caused only by the photocurrent from the a-Si:H layer

  13. Ionic S(N)i-Si Nucleophilic Substitution in N-Methylaniline-Induced Si-Si Bond Cleavages of Si2Cl6.

    Science.gov (United States)

    Zhang, Jie; Xie, Ju; Lee, Myong Euy; Zhang, Lin; Zuo, Yujing; Feng, Shengyu

    2016-03-24

    N-Methylaniline-induced Si-Si bond cleavage of Si2Cl6 has been theoretically studied. All calculations were performed by using DFT at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) levels. An ionic SN i-Si nucleophilic substitution mechanism, which is a newly found nucleophilic substitution in silicon-containing compounds, is proposed in the N-methylaniline-induced Si-Si bond cleavage in Si2Cl6. Unlike general S(N)i-Si nucleophilic substitutions that go through a pentacoordinated silicon transition state, ionic nucleophilic substitution goes through a tetracoordinated silicon transition state, in which the Si-Si bond is broken and siliconium ions are formed. Special cleavage of the Si-Si bond is presumably due to the good bonding strength between Si and N atoms, which leads to polarization of the Si-Si bond and eventually to heterolytic cleavage. Calculation results show that, in excess N-methylaniline, the final products of the reaction, including (NMePh)(3-n) SiHCl(n) (n=0-2) and (NMePh)(4-n) SiCl(n) (n=2-3), are the Si-Si cleavage products of Si2Cl6 and the corresponding amination products of the former. The ionic S(N)i-Si nucleophilic substitution mechanism can also be employed to describe the amination of chlorosilane by N-methylaniline. The suggested mechanisms are consistent with experimental data. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Quantum wells based on Si/SiO{sub x} stacks for nanostructured absorbers

    Energy Technology Data Exchange (ETDEWEB)

    Berghoff, B.; Suckow, S.; Roelver, R.; Spangenberg, B.; Kurz, H. [Institute of Semiconductor Electronics, RWTH Aachen University, Sommerfeldstr. 24, 52074 Aachen (Germany); Sologubenko, A.; Mayer, J. [Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstr. 55, 52074 Aachen (Germany); Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, 52426 Juelich (Germany)

    2010-11-15

    We report on electrical transport and quantum confinement in thermally annealed Si/SiO{sub x} multiple quantum well (QW) stacks. Results are correlated with the morphology of the stacks. High temperature annealing of Si/SiO{sub x} stacks leads to precipitation of excess Si from the SiO{sub x} layers, which enhances the degree of crystallization and increases the grain sizes in the Si QWs compared to the conventional Si/SiO{sub 2} system. Moreover, the excess Si forms highly conductive pathways between adjacent Si QWs that are separated by ultrathin silicon oxide barriers. This results in an increase of conductivity by up to 10 orders of magnitude compared to the tunneling dominated transport in Si/SiO{sub 2} stacks. The stacks exhibit a distinct quantum confinement as confirmed by photoluminescence measurements. (author)

  15. Modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy

    Energy Technology Data Exchange (ETDEWEB)

    Wu Yuying [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China)], E-mail: wyy532001@163.com; Liu Xiangfa [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China); Shandong Binzhou Bohai Piston Co., Ltd., Binzhou 256602, Shandong (China); Jiang Binggang [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China); Huang Chuanzhen [School of Mechanical Engineering, Shandong University, Jinan 250061 (China)

    2009-05-27

    Modification effect of Ni-38 wt.%Si on the Al-12 wt.%Si alloy has been studied by differential scanning calorimeter, torsional oscillation viscometer and liquid X-ray diffraction experiments. It is found that there is a modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy, i.e. primary Si can precipitate in the microstructure of Al-12 wt.%Si alloy when Ni and Si added in the form of Ni-38 wt.%Si, but not separately. Ni-38 wt.%Si alloy brings 'genetic materials' into the Al-Si melt, which makes the melt to form more ordering structure, promotes the primary Si precipitated. Moreover, the addition of Ni-38 wt.%Si, which decreases the solidification supercooling degree of Al-12 wt.%Si alloy, is identical to the effect of heterogeneous nuclei.

  16. Effect of starting composition on formation of MoSi2–SiC ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 35; Issue 4. Effect of starting ... MoSi2–SiC nanocomposite powders were successfully synthesized by ball milling Mo, Si and graphite elemental powders. Effects of ... Mo5Si3 was formed during annealing as a product of a reaction between MoSi2 and excess graphite.

  17. Current–voltage studies on β-FeSi2/Si heterojunction

    Indian Academy of Sciences (India)

    – characteristics of both -FeSi2/n-Si and -FeSi2/p-Si were studied at room temperature. The junctions were formed by depositing Fe on Si selectively followed by thermal annealing and some samples were later treated by pulsed laser. Temperature of thermal annealing and diode area were also varied. – studies ...

  18. Mo-Si alloy development

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.T.; Heatherly, L.; Wright, J.L. [Oak Ridge National Lab., TN (United States)

    1996-06-01

    The objective of this task is to develop new-generation corrosion-resistant Mo-Si intermetallic alloys as hot components in advanced fossil energy conversion and combustion systems. The initial effort is devoted to Mo{sub 5}-Si{sub 3}-base (MSB) alloys containing boron additions. Three MSB alloys based on Mo-10.5Si-1.1B (wt %), weighing 1500 g were prepared by hot pressing of elemental and alloy powders at temperatures to 1600{degrees}C in vacuum. Microporosities and glassy-phase (probably silicate phases) formations are identified as the major concerns for preparation of MSB alloys by powder metallurgy. Suggestions are made to alleviate the problems of material processing.

  19. Analysis of Si/SiGe Heterostructure Solar Cell

    Directory of Open Access Journals (Sweden)

    Ashish Kumar Singh

    2014-01-01

    Full Text Available Sunlight is the largest source of carbon-neutral energy. Large amount of energy, about 4.3 × 1020 J/hr (Lewis, 2005, is radiated because of nuclear fusion reaction by sun, but it is unfortunate that it is not exploited to its maximum level. Various photovoltaic researches are ongoing to find low cost, and highly efficient solar cell to fulfil looming energy crisis around the globe. Thin film solar cell along with enhanced absorption property will be the best, so combination of SiGe alloy is considered. The paper presented here consists of a numerical model of Si/Si1-xGex heterostructure solar cell. The research has investigated characteristics such as short circuit current density (Jsc, generation rate (G, absorption coefficient (α, and open circuit voltage (Voc with optimal Ge concentration. The addition of Ge content to Si layer will affect the property of material and can be calculated with the use of Vegard’s law. Due to this, short circuit current density increases.

  20. Influence of CrSi2 nanocrystals on the electrical properties of Au/Si - p/CrSi2 NCs/Si(111) - n mesa-diodes

    Science.gov (United States)

    Galkin, Nikolay G.; Dózsa, Laszlo; Chusovitin, Evgenii A.; Dotsenko, Sergey A.; Pécz, Bela; Dobos, Laszlo

    Semiconducting CrSi2 nanocrystals (NCs) with high density (4×1010 cm-2) and narrow size distribution were grown by reactive deposition epitaxy (RDE) of 0.6 nm Cr at 550 °C on Si(111)7 × 7 substrate. Based on DRS, AFM and TEM results silicon cap epitaxy growth procedure on silicon with high density of CrSi2 NCs has been proposed. Monolithic Si(111)/ CrSi2 NCs/Si(111) structures with three layers of buried CrSi2 NCs have been successfully grown by repeating of CrSi2 NCs formation and silicon epitaxial growth. Electrical characterization of Schottky junctions formed on the grown structures has shown that the formation of point defects generated during the growth of the Si cap layer strongly depends on the cap growth conditions and on the Cr deposition rate.

  1. Microwave joining of SiC

    Energy Technology Data Exchange (ETDEWEB)

    Silberglitt, R.; Ahmad, I.; Tian, Y.L. [FM Technologies, Inc., Fairfax, VA (United States)] [and others

    1997-04-01

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

  2. Measurements for Cu and Si diffusivities in Al-Cu-Si alloys by diffusion couples

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Dingfei [College of Materials Science and Engineering, Chongqing University, Chongqing 400045 (China)]. E-mail: zhangdingfei@cqu.edu.cn; Morral, John E. [Department of Materials Science and Engineering, Ohio State University, OH 43210 (United States); Brody, Harold D. [Institute of Materials Science, University of Connecticut, CT 06268 (United States)

    2007-02-25

    This paper deals with diffusivity measurements for Cu and Si atoms in Al-Cu-Si alloys by diffusion couples. With Cu and Si concentration profiles in the diffusion couples treated by different heating temperatures and times, their diffusivities including D {sub CuCu}, D {sub SiSi}, D {sub CuSi} and D {sub SiCu} in Al-Cu-Si ternary alloys could be calculated and their D {sub 0} and Q also could be obtained by their diffusivities under different temperatures.

  3. Using SI Units in Astronomy

    Science.gov (United States)

    Dodd, Richard

    2011-12-01

    1. Introduction; 2. An introduction to SI units; 3. Dimensional analysis; 4. Unit of angular measure (radian); 5. Unit of time (second); 6. Unit of length (metre); 7. Unit of mass (kilogram); 8. Unit of luminous intensity (candela); 9. Unit of thermodynamic temperature (kelvin); 10. Unit of electric current (ampere); 11. Unit of amount of substance (mole); 12. Astronomical taxonomy; Index.

  4. The HFIR 14J irradiation SiC/SiC composite and SiC fiber collaboration

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States); Kohyama, Akira; Katoh, Yutai [Kyoto Univ., Uji, Kyoto (Japan); Hasegawa, Akira [Tohoku Univ., Aramaki, Sendai (Japan); Snead, L. [Oak Ridge National Lab., TN (United States); Scholz, R.

    1998-09-01

    A short introduction with references establishes the current status of research and development of SiC{sub f}/SiC composites for fusion energy systems with respect to several key issues. The SiC fiber and composite specimen types selected for the JUPITER 14J irradiation experiment are presented together with the rationale for their selection.

  5. Proton trapping at the Si/SiO2 interface studied by first-principles method

    Science.gov (United States)

    Zhang, Qiming; Tang, Shaoping; Wallace, R. M.; Archer, L.

    1998-03-01

    The behavior of mobile protons at the Si/SiO2 interface has drawn substantial interests since it was found to play the critical role in a proposed non-volatile memory device based on Si/SiO_2/Si structures(K. Vanheusden et al.), Nature 386, 587 (1997). We have investigated the bonding and diffusion properties of a proton at the interface by first-principles local density cluster total energy approach (DMol). A 73 atom cluster model is used to simulate the Si/SiO2 interface which is constructed from beta-cristobalite SiO2 on Si(001) surface. In agreement with previous calculation of proton in bulk Si, the Si-Si bond center is found to be a stable site for proton on the Si side. On the SiO2 side, proton is found to bond with O atoms. The energy for the proton at corresponding binding sites decreases while the proton penetrate into the oxide, forming an energy well which confines protons in oxide in a Si/SiO_2/Si structure. The diffusion barrier for a proton hopping between the neighboring binding sites is 0.73 eV, in good agreement with the experimental activation energy ( 0.8 eV)^1.

  6. 3C-SiC nanocrystal growth on 10° miscut Si(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Deokar, Geetanjali, E-mail: gitudeo@gmail.com [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); D' Angelo, Marie; Demaille, Dominique [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Cavellin, Catherine Deville [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Faculté des Sciences et Technologie UPEC, 61 av. De Gaulle, Créteil F-94010 (France)

    2014-04-01

    The growth of 3C-SiC nano-crystal (NC) on 10° miscut Si(001) substrate by CO{sub 2} thermal treatment is investigated by scanning and high resolution transmission electron microscopies. The vicinal Si(001) surface was thermally oxidized prior to the annealing at 1100 °C under CO{sub 2} atmosphere. The influence of the atomic steps at the vicinal SiO{sub 2}/Si interface on the SiC NC growth is studied by comparison with the results obtained for fundamental Si(001) substrates in the same conditions. For Si miscut substrate, a substantial enhancement in the density of the SiC NCs and a tendency of preferential alignment of them along the atomic step edges is observed. The SiC/Si interface is abrupt, without any steps and epitaxial growth with full relaxation of 3C-SiC occurs by domain matching epitaxy. The CO{sub 2} pressure and annealing time effect on NC growth is analyzed. The as-prepared SiC NCs can be engineered further for potential application in optoelectronic devices and/or as a seed for homoepitaxial SiC or heteroepitaxial GaN film growth. - Highlights: • Synthesis of 3C-SiC nanocrystals epitaxied on miscut-Si using a simple technique • Evidence of domain matching epitaxy at the SiC/Si interface • SiC growth proceeds along the (001) plane of host Si. • Substantial enhancement of the SiC nanocrystal density due to the miscut • Effect of the process parameters (CO{sub 2} pressure and annealing duration)

  7. The influence of strain on the diffusion of Si dimers on Si(001)

    NARCIS (Netherlands)

    Zoethout, E.; Zoethout, E.; Gurlu, O.; Gürlü, O.; Zandvliet, Henricus J.W.; Poelsema, Bene

    2000-01-01

    The influence of lattice mismatch-induced tensile strain on the diffusion of Si dimers on Si(001) has been studied. The rate of surface diffusion of a Si dimer along the substrate dimer rows is relatively insensitive to tensile strain, whereas the rate of diffusion for a Si dimer across the

  8. A sensitive optical sensor based on DNA-labelled Si@SiO2 core ...

    Indian Academy of Sciences (India)

    2017-10-31

    Oct 31, 2017 ... fluorescent assay based on DNA-labelled Si@SiO2 core–shell nanoparticles for the detection of mercury (II) in environmental samples was investigated. Probe DNA was conjugated on the surface of the Si@SiO2 core–shell nanoparticles via 5 - terminal-SH (thiol group) reaction. The detection protocol was ...

  9. Preparation of Si3N4–SiC composites by microwave route

    Indian Academy of Sciences (India)

    Unknown

    composited the creep resistance has also been reported to improve (Niihara et al 1990; Hirano et al 1996; Rendtel et al 1998; Yamada and Kamiya 1999). Possibilities of making engine components using Si3N4–SiC composites have been discussed in the literature. Si3N4–SiC compo- sites can be designed and sintered ...

  10. Laser cladding of Al-Si/SiC composite coatings : Microstructure and abrasive wear behavior

    NARCIS (Netherlands)

    Anandkumar, R.; Almeida, A.; Vilar, R.; Ocelik, V.; De Hosson, J.Th.M.

    2007-01-01

    Surface coatings of an Al-Si-SiC composite were produced on UNS A03560 cast Al-alloy substrates by laser cladding using a mixture of powders of Al-12 wt.% Si alloy and SiC. The microstructure of the coatings depends considerably on the processing parameters. For a specific energy of 26 MJ/m2 the

  11. Location and Electronic Nature of Phosphorus in the Si Nanocrystal--SiO2 System.

    Science.gov (United States)

    König, Dirk; Gutsch, Sebastian; Gnaser, Hubert; Wahl, Michael; Kopnarski, Michael; Göttlicher, Jörg; Steininger, Ralph; Zacharias, Margit; Hiller, Daniel

    2015-05-22

    Up to now, no consensus exists about the electronic nature of phosphorus (P) as donor for SiO2-embedded silicon nanocrystals (SiNCs). Here, we report on hybrid density functional theory (h-DFT) calculations of P in the SiNC/SiO2 system matching our experimental findings. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated. Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. For the first time, we obtain ionisation states of P atoms in the SiNC/SiO2 system at room temperature using X-ray absorption near edge structure (XANES) spectroscopy, eliminating structural artefacts due to sputtering as occurring in XPS. K energies of P in SiO2 and SiNC/SiO2 superlattices (SLs) were calibrated with non-degenerate P-doped Si wafers. results confirm measured core level energies, connecting and explaining XANES spectra with h-DFT electronic structures. While P can diffuse into SiNCs and predominantly resides on interstitial sites, its ionization probability is extremely low, rendering P unsuitable for introducing electrons into SiNCs embedded in SiO2. Increased sample conductivity and photoluminescence (PL) quenching previously assigned to ionized P donors originate from deep defect levels due to P.

  12. SiO adsorption on a p(2 × 2) reconstructed Si(1 0 0) surface

    NARCIS (Netherlands)

    Violanda, M.|info:eu-repo/dai/nl/304840262; Rudolph, H.|info:eu-repo/dai/nl/304830496

    2009-01-01

    We have investigated the adsorption mechanism of SiO molecule incident on a clean Si(1 0 0) p(2 × 2) reconstructed surface using density functional theory based methods. Stable adsorption geometries of SiO on Si surface, as well as their corresponding activation and adsorption energies are

  13. Growth of Au-catalysed Si nanowires by low pressure chemical vapour deposition on Si(100) and amorphous Si surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Santoni, A; Villacorta, F Jimenez; Rufoloni, A; Mancini, A [ENEA C.R. Frascati, v. E. Fermi 45, I-00044 Frascati (Italy)

    2006-12-06

    Au-mediated Si nanowires (SiNW) have been grown at low temperatures (500-560 {sup 0}C) on crystalline Si(100) and amorphous Si surfaces by means of low pressure chemical vapour deposition from Si{sub 2}H{sub 6} in the 0.05-1.2 mbar range. The influence of the substrates on the nanowire (NW) growth and morphology has been investigated by means of x-ray photoelectron spectroscopy and scanning electron microscopy. No NW growth has been observed on the Au covered amorphous Si surfaces. On both substrates, the NW exhibit inhomogeneous sidewalls and a new morphology showing NW entrenchment which has been explained as a consequence of vapour-liquid-solid growth termination due to Au diffusion on the SiNW sidewalls.

  14. Enhancement of thermoelectric power factor in CrSi2 film via Si:B addition

    Science.gov (United States)

    Hou, Q. R.; Gu, B. F.; Chen, Y. B.

    2015-09-01

    In this paper, we report a large enhancement in the thermoelectric power factor in CrSi2 film via Si:B (1 at.% B content) addition. The Si:B-enriched CrSi2 films are prepared by co-sputtering CrSi2 and heavily B-doped Si targets. Both X-ray diffraction patterns and Raman spectra confirm the formation of the crystalline phase CrSi2. Raman spectra also indicate the crystallization of the added Si:B. With the addition of Si:B, the electrical resistivity (R) decreases especially at low temperatures while the Seebeck coefficient (S) increases above 533 K. As a result, the thermoelectric power factor, PF = S2/R, is greatly enhanced and can reach 716 × 10-6W/m ṡK2 at 583 K, which is much larger than that of the pure CrSi2 film.

  15. Abrupt GaP/Si hetero-interface using bistepped Si buffer

    Energy Technology Data Exchange (ETDEWEB)

    Ping Wang, Y., E-mail: yanping.wang@insa-rennes.fr; Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O. [UMR FOTON, CNRS, INSA Rennes, Rennes F-35708 (France); Stodolna, J.; Ponchet, A. [CEMES-CNRS, Université de Toulouse, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 04 (France); Bahri, M.; Largeau, L.; Patriarche, G. [Laboratoire de Photonique et Nanostructures, CNRS UPR 20, Route de Nozay, Marcoussis 91460 (France); Magen, C. [LMA, INA-ARAID, and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza (Spain)

    2015-11-09

    We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

  16. Misfit dislocation locking and rotation during gallium nitride growth on SiC/Si substrates

    Science.gov (United States)

    Kukushkin, S. A.; Osipov, A. V.; Bessolov, V. N.; Konenkova, E. V.; Panteleev, V. N.

    2017-04-01

    The effect of changing the misfit dislocation propagation direction during GaN layer growth on the AlN/SiC/Si(111) structure surface is detected. The effect is as follows. As the GaN layer growing on AlN/SiC/Si(111) reaches a certain thickness of 300 nm, misfit dislocations initially along the layer growth axis stop and begin to move in the direction perpendicular to the growth axis. A theoretical model of AlN and GaN nucleation on the (111) SiC/Si face, explaining the effect of changing the misfit dislocation motion direction, is constructed. The effect of changing the nucleation mechanism from the island one for AlN on SiC/Si(111) to the layer one for the GaN layer on AlN/SiC/Si is experimentally detected and theoretically explained.

  17. Effect of Si interface surface roughness to the tunneling current of the Si/Si{sub 1-x}Ge{sub x}/Si heterojunction bipolar transistor

    Energy Technology Data Exchange (ETDEWEB)

    Hasanah, Lilik, E-mail: lilikhasanah@upi.edu; Suhendi, Endi; Tayubi, Yuyu Rahmat; Yuwono, Heru [Department of Physics Education, Universitas Pendidikan Indonesia, Jl. Setiabudhi 229 Bandung 40154 (Indonesia); Nandiyanto, Asep Bayu Dani [Department Kimia, Universitas Pendidikan Indonesia, Jl. Setiabudhi 229 Bandung 40154 (Indonesia); Murakami, Hideki [Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8527 (Japan); Khairrurijal [Physics of Electronic Materials Research Division, Institut Teknologi Bandung, Bandung 40132 (Indonesia)

    2016-02-08

    In this work we discuss the surface roughness of Si interface impact to the tunneling current of the Si/Si{sub 1-x}Ge{sub x}/Si heterojunction bipolar transistor. The Si interface surface roughness can be analyzed from electrical characteristics through the transversal electron velocity obtained as fitting parameter factor. The results showed that surface roughness increase as Ge content of virtual substrate increase This model can be used to investigate the effect of Ge content of the virtual substrate to the interface surface condition through current-voltage characteristic.

  18. Formation of Si/SiC multilayers by low-energy ion implantation and thermal annealing

    NARCIS (Netherlands)

    Dobrovolskiy, S.; Yakshin, A.E.; Yakshin, Andrey; Tichelaar, F.D.; Verhoeven, J.; Louis, E.; Louis, Eric; Bijkerk, Frederik

    2010-01-01

    Si/SiC multilayer systems for XUV reflection optics with a periodicity of 10–20 nm were produced by sequential deposition of Si and implantation of 1 keV View the MathML source ions. Only about 3% of the implanted carbon was transferred into the SiC, with a thin, 0.5–1 nm, buried SiC layer being

  19. Si

    African Journals Online (AJOL)

    similar, the prevalence of helminthiasis was high in Dawaro and Guragie ethnic groups which may be due to difference in living habit that needs further investigation. As other studies showed (21), logically as well, those from analphabet mother and low income family should have more intestinal parasitosis because of the.

  20. Cathodoluminescence studies on GaN on Si(211) and Si(311) substrates; Kathodolumineszenzuntersuchungen an GaN auf Si(211)- und Si(311)-Substraten

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Mathias; Dempewolf, Anja; Bertram, Frank; Hempel, Thomas; Christen, Juergen; Ravash, Roghaiyeh; Dadgar, Armin; Krost, Alois [Institut fuer Experimentelle Physik, Otto-von-Guericke-Universitaet Magdeburg (Germany)

    2011-07-01

    Spectrally resolved cathodoluminescence measurements were used to study GaN layers on Si(211) and Si(311 substrates at liquid helium temperatures. Non-c axis oriented GaN growth allows a reduction of polarization fields and thus the quantum confined Stark effect (QCSE) that reduces the efficiency of optoelectronic devices. The authors used appropriated high-indices Si(h11) substrates with a MOVPE grown AlN seed layer and an AlGaN buffer layer, two thick GaN layers with an AlN interlayer. The low-temperature luminescence spectra showed three dominant luminescence channels: the bound exciton D(0),X), donor-acceptor pairs (DAP) and basal plane stacking faults luminescence. The stacking fault luminescence on Si(211) is significantly reduced compared to GaN on Si(311). The results indicate a strong inhomogeneity of Si(311) compared to Si(211).

  1. Preparation of biomorphic SiC ceramics

    Directory of Open Access Journals (Sweden)

    Egelja A.

    2008-01-01

    Full Text Available This paper deals with a new method for producing non-oxide ceramic using wood as a template. SiC with a woodlike microstructure has been prepared by carbothermal reduction reactions of Tilia wood/TEOS composite at 1873K. The porous carbon preform was infiltrated with TEOS (Si(OC2H54, as a source of silica, without pressure at 298K. The morphology of resulting porous SiC ceramics, as well as the conversion mechanism of wood to SiC ceramics, have been investigated by scanning electron microscopy (SEM/EDS and X-ray diffraction analysis (XRD. Obtained SiC ceramics consists of β-SiC with traces of α-SiC.

  2. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays

    Directory of Open Access Journals (Sweden)

    Liu Jian

    2009-01-01

    Full Text Available Abstract Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondary nanostructures of SiO2 nanowires are highly dense grown on the primary Cd4SiS6 core-SiO2 sheath nanowires and formed hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays which stand vertically on silicon substrates. The possible growth mechanism of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays is proposed. The optical properties of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays are investigated using Raman and Photoluminescence spectroscopy.

  3. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays.

    Science.gov (United States)

    Liu, Jian; Wang, Chunrui; Xie, Qingqing; Cai, Junsheng; Zhang, Jing

    2009-10-29

    Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondary nanostructures of SiO2 nanowires are highly dense grown on the primary Cd4SiS6 core-SiO2 sheath nanowires and formed hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays which stand vertically on silicon substrates. The possible growth mechanism of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays is proposed. The optical properties of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays are investigated using Raman and Photoluminescence spectroscopy.

  4. Nucleation and void formation mechanisms in SiC thin film growth on Si by carbonization

    Energy Technology Data Exchange (ETDEWEB)

    Li, J.P.; Steckl, A.J. [Univ. of Cincinnati, OH (United States)

    1995-02-01

    The nucleation mechanisms for SiC thin films on Si were investigated by interrupting the growth at very brief times ({approximately}1 to 10 s) using rapid thermal chemical vapor deposition in conjunction with hydrocarbon carbonization. The resulting SiC nuclei and films on Si have been studied by scanning electron microscopy and atomic force microscopy. The hydrocarbon partial pressure in the gas stream was found to determine the nucleation mode. Low precursor concentration results in initial three-dimensional (island) growth which enables the study or trench and void formation. Voids were observed to initiate when two neighboring nuclei come in contact. Trenches in the Si substrate surround each isolated nucleus, with the trench depth increasing with the diameter of the island. SiC films grown for a nominal reaction time of 1 s indicate that increasing the propane concentration results in decreases in SiC grain size and surface roughness and an increase in the nuclei density. A model is proposed for the nucleation process of SiC growth on Si by carbonization consisting of the following key steps: (1) the initial nucleation density is determined by the precursor concentration; (2) lateral and vertical growth of individual nuclei proceeds by consumption of Si atoms around their periphery, forming trenches in the substrate; (3) Si voids are formed in the Si substrate near the SiC/Si interface when nuclei grow large enough to come in contact and, thus, restrict the supply of Si atoms.

  5. Three-dimensional crossbar arrays of self-rectifying Si/SiO2/Si memristors

    Science.gov (United States)

    Li, Can; Han, Lili; Jiang, Hao; Jang, Moon-Hyung; Lin, Peng; Wu, Qing; Barnell, Mark; Yang, J. Joshua; Xin, Huolin L.; Xia, Qiangfei

    2017-06-01

    Memristors are promising building blocks for the next-generation memory and neuromorphic computing systems. Most memristors use materials that are incompatible with the silicon dominant complementary metal-oxide-semiconductor technology, and require external selectors in order for large memristor arrays to function properly. Here we demonstrate a fully foundry-compatible, all-silicon-based and self-rectifying memristor that negates the need for external selectors in large arrays. With a p-Si/SiO2/n-Si structure, our memristor exhibits repeatable unipolar resistance switching behaviour (105 rectifying ratio, 104 ON/OFF) and excellent retention at 300 °C. We further build three-dimensinal crossbar arrays (up to five layers of 100 nm memristors) using fluid-supported silicon membranes, and experimentally confirm the successful suppression of both intra- and inter-layer sneak path currents through the built-in diodes. The current work opens up opportunities for low-cost mass production of three-dimensional memristor arrays on large silicon and flexible substrates without increasing circuit complexity.

  6. Fiber/matrix interfaces for SiC/SiC composites: Multilayer SiC coatings

    Energy Technology Data Exchange (ETDEWEB)

    Halverson, H.; Curtin, W.A. [Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States)

    1996-08-01

    Tensile tests have been performed on composites of CVI SiC matrix reinforced with 2-d Nicalon fiber cloth, with either pyrolitic carbon or multilayer CVD SiC coatings [Hypertherm High-Temperature Composites Inc., Huntington Beach, CA.] on the fibers. To investigate the role played by the different interfaces, several types of measurements are made on each sample: (i) unload-reload hysteresis loops, and (ii) acoustic emission. The pyrolitic carbon and multilayer SiC coated materials are remarkably similar in overall mechanical responses. These results demonstrate that low-modulus, or compliant, interface coatings are not necessary for good composite performance, and that complex, hierarchical coating structures may possibly yield enhanced high-temperature performance. Analysis of the unload/reload hysteresis loops also indicates that the usual {open_quotes}proportional limit{close_quotes} stress is actually slightly below the stress at which the 0{degrees} load-bearing fibers/matrix interfaces slide and are exposed to atmosphere.

  7. An Isotope Study of Hydrogenation of poly-Si/SiOx Passivated Contacts for Si Solar Cells: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Schnabel, Manuel; Nemeth, William; van de Loo, Bas, W.H.; Macco, Bart; Kessels, Wilhelmus, M.M.; Stradins, Paul; Young, David, L.

    2017-06-26

    For many years, the record Si solar cell efficiency stood at 25.0%. Only recently have several companies and institutes managed to produce more efficient cells, using passivated contacts of made doped poly-Si or a-Si:H and a passivating intrinsic interlayer in all cases. Common to these designs is the need to passivate the layer stack with hydrogen. In this contribution, we perform a systematic study of passivated contact passivation by hydrogen, using poly-Si/SiOx passivated contacts on n-Cz-Si, and ALD Al2O3 followed by a forming gas anneal (FGA) as the hydrogen source. We study p-type and n-type passivated contacts with implied Voc exceeding 690 and 720 mV, respectively, and perform either the ALD step or the FGA with deuterium instead of hydrogen in order to separate the two processes via SIMS. By examining the deuterium concentration at the SiOx in both types of samples, we demonstrate that the FGA supplies negligible hydrogen species to the SiOx, regardless of whether the FGA is hydrogenated or deuterated. Instead, it supplies the thermal energy needed for hydrogen species in the Al2O3 to diffuse there. Furthermore, the concentration of hydrogen species at the SiOx can saturate while implied Voc continues to increase, showing that the energy from the FGA is also required for hydrogen species already at the SiOx to find recombination-active defects to passivate.

  8. Silicon Promotes Exodermal Casparian Band Formation in Si-Accumulating and Si-Excluding Species by Forming Phenol Complexes

    National Research Council Canada - National Science Library

    Fleck, Alexander T; Schulze, Sascha; Hinrichs, Martin; Specht, André; Waßmann, Friedrich; Schreiber, Lukas; Schenk, Manfred K

    2015-01-01

    We studied the effect of Silicon (Si) on Casparian band (CB) development, chemical composition of the exodermal CB and Si deposition across the root in the Si accumulators rice and maize and the Si non-accumulator onion...

  9. Impact Resistance of Uncoated SiC/SiC Composites

    Science.gov (United States)

    Bhatt, Ramakrishna T.; Choi, Sung R.; Cosgriff, Laura M.; Fox, Dennis S.; Lee, Kang N.

    2008-01-01

    Two-dimensional woven SiC/SiC composites fabricated by melt infiltration method were impact tested at room temperature and at 1316 C in air using 1.59-mm diameter steel-ball projectiles at velocities ranging from 115 to 400 m/s. The extent of substrate damage with increasing projectile velocity was imaged and analyzed using optical and scanning electron microscopy, and non-destructive evaluation (NDE) methods such as pulsed thermography, and computed tomography. The impacted specimens were tensile tested at room temperature to determine their residual mechanical properties. Results indicate that at 115 m/s projectile velocity, the composite showed no noticeable surface or internal damage and retained its as-fabricated mechanical properties. As the projectile velocity increased above this value, the internal damage increased and mechanical properties degraded: At velocities >300 m/s, the projectile penetrated through the composite, but the composite retained approx.50% of the ultimate tensile strength of the as-fabricated composite and exhibited non-brittle failure. Predominant internal damages are delamination of fiber plies, fiber fracture and matrix shearing.

  10. Phase transformation in SiOx/SiO₂ multilayers for optoelectronics and microelectronics applications.

    Science.gov (United States)

    Roussel, M; Talbot, E; Pratibha Nalini, R; Gourbilleau, F; Pareige, P

    2013-09-01

    Due to the quantum confinement, silicon nanoclusters (Si-ncs) embedded in a dielectric matrix are of prime interest for new optoelectronics and microelectronics applications. In this context, SiO(x)/SiO₂ multilayers have been prepared by magnetron sputtering and subsequently annealed to induce phase separation and Si clusters growth. The aim of this paper is to study phase separation processes and formation of nanoclusters in SiO(x)/SiO₂ multilayers by atom probe tomography. Influences of the silicon supersaturation, annealing temperature and SiO(x) and SiO₂ layer thicknesses on the final microstructure have been investigated. It is shown that supersaturation directly determines phase separation regime between nucleation/classical growth and spinodal decomposition. Annealing temperature controls size of the particles and interface with the surrounding matrix. Layer thicknesses directly control Si-nc shapes from spherical to spinodal-like structures. Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Formation of high-density Si nanodots by agglomeration of ultra-thin amorphous Si films

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Hiroki [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)], E-mail: hkondo@alice.xtal.nagoya-u.ac.jp; Ueyama, Tomonori [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Ikenaga, Eiji; Kobayashi, Keisuke [Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Sakai, Akira [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Ogawa, Masaki [EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Zaima, Shigeaki [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

    2008-11-03

    High-density and similarly-sized Si nanodots were formed by annealing ultra-thin amorphous Si (a-Si) films deposited on SiO{sub 2}/Si substrates in vacuum. Dependences of density and diameter of the Si nanodots on the a-Si film thickness and, annealing temperature and time were investigated by scanning electron microscopy. It is found that drastic increase (decrease) in the density (diameter) occurred at an a-Si thickness of 1 nm. By agglomeration of sub-nanometer thick a-Si films, a density larger than 10{sup 12} cm{sup -2}, an average diameter smaller than 5 nm, and a dispersion of diameter less than 15% were achieved.

  12. In situ growth of SiC nanowires on RS-SiC substrate(s)

    Science.gov (United States)

    Yang, Wen; Araki, Hiroshi; Hu, Quanli; Ishikawa, Nobuhiro; Suzuki, Hiroshi; Noda, Tetsuji

    2004-03-01

    SiC nanowires over 10 μm in length and 20-100 nm in diameter have been synthesized by a novel in situ chemical vapor growth process on RS-SiC plates. The SiC nanowires were identified as single crystal β-SiC with Si-C chemistry. The growth direction of the nanowires is . The growth mechanism is discussed and a kinetic vapor-solid growth mechanism is proposed. The process demonstrates the possibility to fabricate SiC nanowires in ceramic matrix composites, such as continuous SiC fibers reinforced SiC matrix composites, with the SiC nanowires uniformly dispersed in the matrix.

  13. Formation of nanocrystalline CrSi 2 layers in Si by ion implantation and pulsed annealing

    Science.gov (United States)

    Batalov, R. I.; Bayazitov, R. M.; Valeev, V. F.; Galkin, N. G.; Goroshko, D. L.; Galkin, K. N.; Chusovitin, E. A.; Gaiduk, P. I.; Ivlev, G. D.; Gatskevich, E. I.

    In this work buried nanocrystalline CrSi2 layers were synthesized by ion implantation, pulsed annealing and MBE. The structural, optical and thermoelectrical properties of CrSi2 layers were studied by methods of SEM, TEM, RBS, PL and Seebeck coefficient measurements. The characteristic features of pulsed nanosecond annealing of Cr-implanted Si and epitaxial growth of triple Si/nc-CrSi2/Si heterostructures were established. It is shown that grown Si/nc-CrSi2/Si heterostructures, which preliminary implanted with the high-dose (ϕ = 6 × 1016cm-2) of Cr+ ions, have the noticeable low temperature (T = 10 - 100 K) photoluminescence signal at 1450-1600 nm and the large Seebeck coefficient (-(60-300) μV/K) in the temperature range of T = 340 - 415 K.

  14. Heteroepitaxial growth of SiC on Si by gas source MBE with silacyclobutane

    Energy Technology Data Exchange (ETDEWEB)

    Chen, J.; Steckl, A.J. [Cincinnati Univ., OH (United States). Nanoelectronics Lab.; Loboda, M.J. [Dow Corning Corp., Midland, MI (United States)

    1998-06-01

    3C-SiC films have been grown by MBE on Si(100) and Si(111) from the organosilane precursor silacyclobutane at temperatures of 800 to 1000 C and pressures of 1 to 5 x 10{sup -6} Torr. The chemical composition of the grown films provided by SIMS indicates a Si to C atomic ratio of about 1. The chemical structure of SiC was confirmed by FTIR. The surface morphology and crystallinity of SiC films were studied by SEM and RHEED. X-ray diffraction reveals that SiC films grown on Si(111) with the presence of native oxide exhibit better crystallinity than those grown on Si(111) surfaces from which the oxide is removed in-situ prior to growth. (orig.) 11 refs.

  15. Si doping superlattice structure on 6H-SiC(0001

    Directory of Open Access Journals (Sweden)

    Li Lianbi

    2017-01-01

    Full Text Available Si-DSL structures multilayers are prepared on 6H-SiC(0001 successfully. The energy offsets of the n-Si/n-6H-SiC heterojunction in the conduction band and valance band are 0.21eV and 1.65eV, respectively. TEM characterizations of the p/n-Si DSL confirms the epitaxial growth of the Si films with [1-11] preferred orientation and the misfit dislocations with a Burgers vector of 1/3 at the p-Si/n-Si interface. J-V measurements indicate that the heterostructure has apparent rectifying behavior. Under visible illumination with light intensity of 0.6W/cm2, the heterostructure demonstrates significant photoelectric response, and the photocurrent density is 2.1mA/cm2. Non-UV operation of the SiC-based photoelectric device is realized.

  16. High-performance a -Si/c-Si heterojunction photoelectrodes for photoelectrochemical oxygen and hydrogen evolution

    KAUST Repository

    Wang, Hsin Ping

    2015-05-13

    Amorphous Si (a-Si)/crystalline Si (c-Si) heterojunction (SiHJ) can serve as highly efficient and robust photoelectrodes for solar fuel generation. Low carrier recombination in the photoelectrodes leads to high photocurrents and photovoltages. The SiHJ was designed and fabricated into both photoanode and photocathode with high oxygen and hydrogen evolution efficiency, respectively, by simply coating of a thin layer of catalytic materials. The SiHJ photoanode with sol-gel NiOx as the catalyst shows a current density of 21.48 mA/cm2 at the equilibrium water oxidation potential. The SiHJ photocathode with 2 nm sputter-coated Pt catalyst displays excellent hydrogen evolution performance with an onset potential of 0.640 V and a solar to hydrogen conversion efficiency of 13.26%, which is the highest ever reported for Si-based photocathodes. © 2015 American Chemical Society.

  17. Propagation of misfit dislocations from buffer/Si interface into Si

    Science.gov (United States)

    Liliental-Weber, Zuzanna [El Sobrante, CA; Maltez, Rogerio Luis [Porto Alegre, BR; Morkoc, Hadis [Richmond, VA; Xie, Jinqiao [Raleigh, VA

    2011-08-30

    Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

  18. Grafted SiC nanocrystals

    DEFF Research Database (Denmark)

    Saini, Isha; Sharma, Annu; Dhiman, Rajnish

    2017-01-01

    ), raman spectroscopy and X-ray diffraction (XRD) measurements. UV–Visible absorption spectroscopy was used to study optical properties such as optical energy gap (Eg), Urbach's energy (Eu), refractive index (n), real (ε1) and imaginary (ε2) parts of dielectric constant of PVA as well as PVA......) were determined. Microhardness measurements performed at an applied load of 9.8 mN showed an increase in the Knoop microhardness number (KHN) of PVA containing 0.015 wt% PVA-g-SiC nanocrystals. Detailed analysis of current-voltage data indicates that the conduction mechanism responsible for increase...

  19. Si@SiOx/Graphene Nanosheets Composite: Ball Milling Synthesis and Enhanced Lithium Storage Performance

    Directory of Open Access Journals (Sweden)

    Xiaoyong Tie

    2018-01-01

    Full Text Available Si@SiOx/grapheme nanosheet (Si@SiOx/GNS nanocomposites as high-performance anode materials for lithium-ion batteries are prepared by mechanically blending the mixture of expanded graphite (EG with Si nanoparticles, and characterized by Raman spectrum, X-ray diffraction (XRD, field emission scanning electron microscopy, and transmission electron microscopy. During ball milling process, the size of Si nanoparticles will decrease, and the layer of EG can be peeled off to thin multilayers. Electrochemical tests reveal that the Si@SiOx/GNS nanocomposites show enhanced cycling stability, high reversible capacity, and rate capability, even with high content of active materials of 80% and without electrolyte additives. The retained revisable capacity is 1,055 mAh g−1 after 50 cycles at 0.2 A g−1 and about 63.6% of the initial value. The great electrochemical performance of Si@SiOx/GNS nanocomposites can be ascribed to GNS prepared through heat-treat and ball-milling methods, the decrease in the size of Si nanoparticles and SiOx layer on Si surface, which enhance the interactions between Si and GNS.

  20. Microwave Annealing for NiSiGe Schottky Junction on SiGe P-Channel

    Directory of Open Access Journals (Sweden)

    Yu-Hsien Lin

    2015-11-01

    Full Text Available In this paper, we demonstrated the shallow NiSiGe Schottky junction on the SiGe P-channel by using low-temperature microwave annealing. The NiSiGe/n-Si Schottky junction was formed for the Si-capped/SiGe multi-layer structure on an n-Si substrate (Si/Si0.57Ge0.43/Si through microwave annealing (MWA ranging from 200 to 470 °C for 150 s in N2 ambient. MWA has the advantage of being diffusion-less during activation, having a low-temperature process, have a lower junction leakage current, and having low sheet resistance (Rs and contact resistivity. In our study, a 20 nm NiSiGe Schottky junction was formed by TEM and XRD analysis at MWA 390 °C. The NiSiGe/n-Si Schottky junction exhibits the highest forward/reverse current (ION/IOFF ratio of ~3 × 105. The low temperature MWA is a very promising thermal process technology for NiSiGe Schottky junction manufacturing.

  1. Switching Performance Evaluation of Commercial SiC Power Devices (SiC JFET and SiC MOSFET) in Relation to the Gate Driver Complexity

    DEFF Research Database (Denmark)

    Pittini, Riccardo; Zhang, Zhe; Andersen, Michael A. E.

    2013-01-01

    and JFETs. The recent introduction of SiC MOSFET has proved that it is possible to have highly performing SiC devices with a minimum gate driver complexity; this made SiC power devices even more attractive despite their device cost. This paper presents an analysis based on experimental results...... of the switching losses of various commercially available Si and SiC power devices rated at 1200 V (Si IGBTs, SiC JFETs and SiC MOSFETs). The comparison evaluates the reduction of the switching losses which is achievable with the introduction of SiC power devices; this includes analysis and considerations...

  2. SI PC104 Performance Test Report

    Energy Technology Data Exchange (ETDEWEB)

    Montelongo, S

    2005-12-16

    The Spectral Instruments (SI) PC104 systems associated with the SI-1000 CCD camera exhibited intermittent power problems during setup, test and operations which called for further evaluation and testing. The SI PC104 System is the interface between the SI-1000 CCD camera and its associated Diagnostic Controller (DC). As such, the SI PC104 must be a reliable, robust system capable of providing consistent performance in various configurations and operating conditions. This SI PC104 system consists of a stackable set of modules designed to meet the PC104+ Industry Standard. The SI PC104 System consists of a CPU module, SI Camera card, Media converter card, Video card and a I/O module. The root cause of power problems was identified as failing solder joints at the LEMO power connector attached to the SI Camera Card. The recommended solution was to provide power to the PC104 system via a PC104+ power supply module configured into the PC104 stack instead of thru the LEMO power connector. Test plans (2) were developed to test SI PC104 performance and identify any outstanding issues noted during extended operations. Test Plan 1 included performance and image acquisition tests. Test Plan 2 verified performance after implementing recommendations. Test Plan 2 also included verifying integrity of system files and driver installation after bootup. Each test plan was implemented to fully test against each set of problems noted. Test Plan presentations and Test Plan results are attached as appendices. Anticipated test results will show successful operation and reliable performance of the SI PC104 system receiving its power via a PC104 power supply module. A SI PC104 Usage Recommendation Memo will be sent out to the SI PC104 User Community. Recommendation memo(s) are attached as appendices.

  3. Effect of SiC particle addition on microstructure of Mg2Si/Al composite

    Directory of Open Access Journals (Sweden)

    Zhao Yuguang

    2014-03-01

    Full Text Available In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy (SEM and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fiber-form to a short fiber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no significant change in dendrite arm spacing (DAS was observed in the presence of SiC particles.

  4. Influence of substrate treatment on the growth of advanced core–shell alloys and compounds of FeSi@SiO2 and SiO2 nanowires

    CSIR Research Space (South Africa)

    Thabethe, S

    2014-12-01

    Full Text Available Advanced core–shell FeSi@SiO(subx) nanowires are observed when FeCl(sub3) vapour is made to flow over a SiO(sub2)/Si substrate at 1100 degress C. The thickness of the SiO(subx) sheath (d0) is found to depend inversely as the period of time of HF...

  5. An optically controlled SiC lateral power transistor based on SiC/SiCGe super junction structure

    Energy Technology Data Exchange (ETDEWEB)

    Pu Hongbin; Cao Lin; Ren Jie; Chen Zhiming; Nan Yagong, E-mail: puhongbin@xaut.edu.c [Xi' an University of Technology, Xi' an 710048 (China)

    2010-04-15

    An optically controlled SiC/SiCGe lateral power transistor based on superjunction structure has been proposed, in which n-SiCGe/p-SiC superjunction structure is employed to improve device figure of merit. Performance of the novel optically controlled power transistor was simulated using Silvaco Atlas tools, which has shown that the device has a very good response to the visible light and the near infrared light. The optoelectronic responsivities of the device at 0.5 {mu}m and 0.7 {mu}m are 330 mA/W and 76.2 mA/W at 2 V based voltage, respectively. (semiconductor devices)

  6. Hierarchical Cd4SiS6/SiO2 Heterostructure Nanowire Arrays

    OpenAIRE

    Liu, Jian; Wang, Chunrui; Xie, Qingqing; Cai, Junsheng; Zhang, Jing

    2009-01-01

    Abstract Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondar...

  7. Temperature depopulation of the GeSi/Si quantum dots with non-equilibrium charge carriers

    Science.gov (United States)

    Sofronov, A. N.; Vorobjev, L. E.; Firsov, D. A.; Balagula, R. M.; Tonkikh, A. A.

    2017-07-01

    We study the temperature dependencies of equilibrium and photo-induced infrared absorption in GeSi/Si quantum dots in a wide spectral range. We show that, in spite of the large valence band offset at GeSi/Si interface and strong confinement for holes, the effect of intensive temperature depopulation of the GeSi/Si quantum dots can take place even at the temperatures below 300 K due to the large difference in density of states of the silicon valence band and quantum dot states, when the bipolar diffusion of charge carriers is not restricted.

  8. Catalyzed precipitation in Al-Cu-Si

    Science.gov (United States)

    Mitlin, D.; Morris, J. W.; Radmilovic, V.

    2000-11-01

    The work reported here concerns the effect of Si on the precipitation of θ' phase (metastable Al2Cu) during the isothermal aging of Al-2Cu-1 Si (wt pct). The binary alloys Al-2Cu and Al-1 Si were studied for comparison. Only two precipitate phases were detected: essentially pure Si in Al-1 Si and Al-2Cu-1 Si, and θ' (metastable Al2Cu) in Al-2Cu and Al-2Cu-1Si. On aging the ternary alloy at 225 °C, Si precipitates first and catalyzes the θ' phase. The precipitates in the ternary alloy are smaller, are more densely distributed, have lower aspect ratios, and coarsen more slowly than those in the binary Al-2Cu aged at the same temperature. While the shapes of individual θ' precipitates in binary Al-2Cu are strongly affected by the kinetic problem of nucleating growth ledges, which produces a significant scatter in the aspect ratio for samples of given thickness, the overall evolution of particle shape with size follows the predictions of the Khachaturyan-Hairapetyan (KH) thermoelastic theory, which reduces to κ= L/d ∞ √ L at large sizes. The KH theory provides an estimate for the interfacial tension of the broad Al- θ' interface of 85 to 96 mJ/m2, which is near the values for other low-energy interfaces in Al, such as the twin boundary energy (100 mJ/m2) and the antiphase boundary energy in δ' Al3Li (70 mJ/m2). Si and θ' precipitates in Al-2Cu-1 Si have a strong elastic interaction because of their compensating strain fields. This elastic interaction promotes the nucleation of θ' precipitates on Si, decreases the expected aspect ratio of θ', and inhibits coarsening. Finally, Si precipitation in ternary Al-2Cu-1 Si differs from that in binary Al-1 Si in that the Si precipitates are coarser, more equiaxed, and more extensively twinned. These changes appear to be effects of Cu, which increases the solubility of Si in Al and adsorbs on the Si-Al interface, promoting twinning by a “step-poisoning” effect at the interface.

  9. Epitaxy of Si1- x C x via ultrahigh-vacuum chemical vapor deposition using Si2H6, Si3H8, or Si4H10 as Si precursors

    Science.gov (United States)

    Koo, Sangmo; Jang, Hyunchul; Ko, Dae-Hong

    2017-09-01

    In this study, disilane (Si2H6), trisilane (Si3H8), and tetrasilane (Si4H10) were used as Si precursors for the growth of Si1- x C x epilayers, and the growth properties of the layers were compared. The use of a higher-order silane significantly increased the growth rates of the Si1- x C x epilayers at a processing temperature of 650 °C. In addition, a higher growth rate realized by using a higher-order silane promoted an increase in the substitutional carbon concentration in the Si1- x C x epilayers owing to the additional injection of a C-source gas (SiH3CH3) and the incorporation of C atoms into substitutional sites. The differences in growth properties between Si precursors were explained on the basis of reaction mechanisms.

  10. Optical Properties Of Sputtered Si: H

    Science.gov (United States)

    Martin, P. M.; Pawlewicz, W. T.; Mann, I. B.

    1982-04-01

    Sputtered Si:H is a very promising material for use in thin-film solar cells, solar selective absorbers and optical coatings for the near infrared region. Optical property-composition relationships have been determined for Si:H coatings having wide ranges of H content and Si-H bonding. The dependence of the optical absorption edge, optical band gap and refractive index at 2 μm wavelength on H content and Si-H bonding is described. Microstructural and topographical features of the films that influence their absorption and scattering characteristics are discussed. Composition and bonding diagrams used to select deposition conditions for the desired optical properties are also presented. Finally, multilayer Si:H/Si02 all-dielectric laser mirrors with reflectances greater than 99% at 1.315, 2.7 and 3.8 μm are described to illustrate the application of these coatings.

  11. Synthesis of biomorphaus SiC-ceramics

    Directory of Open Access Journals (Sweden)

    Egelja Adela D.

    2007-01-01

    Full Text Available The carbothermal reduction processing of partially mineralized fir (Abies alba samples was used to obtain highly-porous SiC ceramics with cellular structure. The infiltration of TEOS (tetraetilortosilikat, Si(OC2H54 as a silica source, was conducted in order to carry out the mineralization process. Synthesis of the SiC was achieved with a C/SiO2 replica annealing at 1723 K in Ar atmosphere. The obtained samples were characterized using X-ray photoelectron spectroscopy (XPS, scanning electron microscopy (SEM and energy dispersive spectrometry (EDS. The experimental results revealed that the hierarchical bimorphous wood structure was preserved even after high-temperature treatment. Microstructural characterization of the ceramics revealed the presence of the P-SiC phase and traces of the a-SiC phase.

  12. On the role of heterolayer relaxation in luminescence response of Si/SiGe:Er structures

    Energy Technology Data Exchange (ETDEWEB)

    Krasilnikova, Ludmila; Stepikhova, Margarita; Drozdov, Yurij; Krasilnik, Zakharii [Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod (Russian Federation); Chalkov, Vadim; Shengurov, Vladimir [Physico-Technical Research Institute, Nizhny Novgorod State University, Gagarin Ave. 23, 603950 Nizhny Novgorod (Russian Federation)

    2011-03-15

    In this contribution we discuss the luminescence properties of Si/Si{sub 1-x}Ge{sub x}:Er/Si structures being of interest for a laser realization. The influence of the strain relaxation processes that take place in such kind of structures on their photoluminescence response at 1.54 {mu}m has been analyzed. The studies were performed for Si/Si{sub 1-x}Ge{sub x}:Er/Si structures with the different thickness of Si{sub 1-x}Ge{sub x}:Er layers, and consequently the degree of strain relaxation. It is shown that the structural defects arising in Si/Si{sub 1-x}Ge{sub x}:Er/Si structures due to the relaxation play only negligible role in their photoluminescence response. The contribution of the structural defects in the photoluminescence response at 1.54 {mu}m became apparent only in thin partially relaxed Si/Si{sub 1-x}Ge{sub x}:Er/Si structures, the photoluminescence spectra of which are represented by the broad ''defect related'' lines. Intense photoluminescence related with the optically active Er centers of different types was observed for the strained and completely relaxed Si/Si{sub 1-x}Ge{sub x}:Er/Si structures containing thick (d > 1 {mu}m) Si{sub 1-x}Ge{sub x}:Er layers. The external quantum efficiency of these structures reaches the value of 6.3 x 10{sup -5} at T =77 K. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. The compatibility of SiC/SiC composites with ceramic breeder materials

    Energy Technology Data Exchange (ETDEWEB)

    Sample, T. (Institute for Advanced Materials, Commission of the European Communities, Joint Research Centre, I-21020, Ispra (Vatican City State, Holy See) (Italy)); Fenici, P. (Institute for Advanced Materials, Commission of the European Communities, Joint Research Centre, I-21020, Ispra (Vatican City State, Holy See) (Italy)); Kolbe, H. (Institute for Advanced Materials, Commission of the European Communities, Joint Research Centre, I-21020, Ispra (Vatican City State, Holy See) (Italy)); Orecchia, L. (Institute for Advanced Materials, Commission of the European Communities, Joint Research Centre, I-21020, Ispra (Vatican City State, Holy See) (Italy))

    1994-09-01

    The compatibility of three lithium-containing ceramic breeder materials Li[sub 4]SiO[sub 4], Li[sub 2]ZrO[sub 3] and LiAlO[sub 2] with two industrially available SiC/SiC composites was determined. Simple capsule tests were carried out at 600 and 800 C in closed capsules, dynamic vacuum and flowing helium. All three breeder materials were reactive towards the SiO[sub 2] content of the SiC/SiC composites forming a surface layer of Li[sub 2]SiO[sub 3]. The as-received' Li[sub 4]SiO[sub 4] was found to be much more reactive than Li[sub 2]ZrO[sub 3] or LiAlO[sub 2]. However, the greater reactivity was found to be governed by the Li[sub 2]CO[sub 3] impurity content of the Li[sub 4]SiO[sub 4] granules. Removal of the Li[sub 2]CO[sub 3], through thermal decomposition under vacuum, reduced the extend of Li[sub 2]SiO[sub 3] formation. The reaction of the breeder materials to form Li[sub 2]SiO[sub 3] is briefly discussed in relation to the probable operating conditions for a SiC/SiC composite structural material in a blanket. ((orig.))

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

    Science.gov (United States)

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

    2017-05-25

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

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

    Directory of Open Access Journals (Sweden)

    Lianbi Li

    2017-05-01

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

  16. Microstructure design and control for improvement of thermal conductivity of SiCf/SiC composites

    Science.gov (United States)

    Yoshida, Katsumi; Kajikawa, Satoshi; Yano, Toyohiko

    2013-09-01

    We focused on microstructure design and control of SiCf/SiC composite based on our fabrication process and the simple model of thermal conductivity of the SiCf/SiC composite, and the improvement of their thermal conductivity was investigated. Submicron-sized α-SiC with coarse α-SiC particles addition was used as the starting materials for SiC matrix layers between SiC fiber cloths because it showed higher thermal conductivity. The thermal conductivity of PCS-composite, EPD-composite and Untreated-composite was 18, 45 and 56 W/m K, respectively, and these values were much higher than that of the composites reported in our previous papers. Untreated composite is simply considered as a multilayered composite consisting of the SiC fiber layers with high thermal conductivity and the SiC matrix layers with high thermal conductivity. The experimental thermal conductivity of the Untreated composite well agreed with the theoretical thermal conductivity calculated by series model. Thermal conductivity of EPD-composite was lower than that of Untreated composite. In EPD-composite, the thermal conductivity of SiC fiber layers with the SiC matrix should be lower than that of SiC fibers themselves due to the SiC matrix with slightly lower thermal conductivity in SiC fiber cloths. The SiC matrix formed in SiC fiber cloths in PCS-composite was derived from PCS, and this matrix would show much lower thermal conductivity due to its low crystallinity. PCS-composite is considered as a multilayered composite consisting of the SiC fiber layers with very low thermal conductivity and the SiC matrix layers with high thermal conductivity, and thus the PCS-composite has low thermal conductivity. In this study, higher thermal conductivity of SiCf/SiC composite was successfully achieved by EPD process and using microstructure-controlled SiC matrix and polycrystalline SiC fibers.

  17. Chemical compatibility issues associated with use of SiC/SiC in advanced reactor concepts

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, Dane F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2015-09-01

    Silicon carbide/silicon carbide (SiC/SiC) composites are of interest for components that will experience high radiation fields in the High Temperature Gas Cooled Reactor (HTGR), the Very High Temperature Reactor (VHTR), the Sodium Fast Reactor (SFR), or the Fluoride-cooled High-temperature Reactor (FHR). In all of the reactor systems considered, reactions of SiC/SiC composites with the constituents of the coolant determine suitability of materials of construction. The material of interest is nuclear grade SiC/SiC composites, which consist of a SiC matrix [high-purity, chemical vapor deposition (CVD) SiC or liquid phase-sintered SiC that is crystalline beta-phase SiC containing small amounts of alumina-yttria impurity], a pyrolytic carbon interphase, and somewhat impure yet crystalline beta-phase SiC fibers. The interphase and fiber components may or may not be exposed, at least initially, to the reactor coolant. The chemical compatibility of SiC/SiC composites in the three reactor environments is highly dependent on thermodynamic stability with the pure coolant, and on reactions with impurities present in the environment including any ingress of oxygen and moisture. In general, there is a dearth of information on the performance of SiC in these environments. While there is little to no excess Si present in the new SiC/SiC composites, the reaction of Si with O2 cannot be ignored, especially for the FHR, in which environment the product, SiO2, can be readily removed by the fluoride salt. In all systems, reaction of the carbon interphase layer with oxygen is possible especially under abnormal conditions such as loss of coolant (resulting in increased temperature), and air and/ or steam ingress. A global outline of an approach to resolving SiC/SiC chemical compatibility concerns with the environments of the three reactors is presented along with ideas to quickly determine the baseline compatibility performance of SiC/SiC.

  18. Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

    Science.gov (United States)

    Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

    2017-11-25

    The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

  19. Graphene/Si-nanowire heterostructure molecular sensors.

    Science.gov (United States)

    Kim, Jungkil; Oh, Si Duk; Kim, Ju Hwan; Shin, Dong Hee; Kim, Sung; Choi, Suk-Ho

    2014-06-20

    Wafer-scale graphene/Si-nanowire (Si-NW) array heterostructures for molecular sensing have been fabricated by vertically contacting single-layer graphene with high-density Si NWs. Graphene is grown in large scale by chemical vapour deposition and Si NWs are vertically aligned by metal-assisted chemical etching of Si wafer. Graphene plays a key role in preventing tips of vertical Si NWs from being bundled, thereby making Si NWs stand on Si wafer separately from each other under graphene, a critical structural feature for the uniform Schottky-type junction between Si NWs and graphene. The molecular sensors respond very sensitively to gas molecules by showing 37 and 1280% resistance changes within 3.5/0.15 and 12/0.15 s response/recovery times under O2 and H2 exposures in air, respectively, highest performances ever reported. These results together with the sensor responses in vacuum are discussed based on the surface-transfer doping mechanism.

  20. siRNA and innate immunity.

    Science.gov (United States)

    Robbins, Marjorie; Judge, Adam; MacLachlan, Ian

    2009-06-01

    Canonical small interfering RNA (siRNA) duplexes are potent activators of the mammalian innate immune system. The induction of innate immunity by siRNA is dependent on siRNA structure and sequence, method of delivery, and cell type. Synthetic siRNA in delivery vehicles that facilitate cellular uptake can induce high levels of inflammatory cytokines and interferons after systemic administration in mammals and in primary human blood cell cultures. This activation is predominantly mediated by immune cells, normally via a Toll-like receptor (TLR) pathway. The siRNA sequence dependency of these pathways varies with the type and location of the TLR involved. Alternatively nonimmune cell activation may also occur, typically resulting from siRNA interaction with cytoplasmic RNA sensors such as RIG1. As immune activation by siRNA-based drugs represents an undesirable side effect due to the considerable toxicities associated with excessive cytokine release in humans, understanding and abrogating this activity will be a critical component in the development of safe and effective therapeutics. This review describes the intracellular mechanisms of innate immune activation by siRNA, the design of appropriate sequences and chemical modification approaches, and suitable experimental methods for studying their effects, with a view toward reducing siRNA-mediated off-target effects.

  1. Ge/SiGe for silicon photonics

    Science.gov (United States)

    Ishikawa, Yasuhiko

    2017-01-01

    Near-infrared Ge photonic devices on a Si platform are presented toward low-cost, low-energy and high-capacity optical communications. Using Ge epitaxial layers selectively grown by chemical vapor deposition on Si-on-insulator layers, Ge photodiodes (PDs) of vertical pin structures are integrated with Si optical waveguides. The integrated Ge PDs show high responsivities as large as 0.8 A/W at 1.55 μm with the 3-dB cutoff frequency more than 10 GHz. SiGe/Ge heterostructures have potential applications to higher-performance devices. One application is to low-noise and low-voltage avalanche photodiodes (APDs), where a SiGe layer is inserted at the interface between the optical absorption layer of Ge and the carrier-multiplication layer of Si or Ge. The band discontinuity at the interface enhances the impact ionization for photo-generated carriers injected via SiGe. Fabricated APDs show an enhanced multiplication gain. The other application of SiGe is to a stressor to control the direct bandgap of Ge. As a proof of concept, a tensile-strained Si0.2Ge0.8 overlayer is shown to induce a compressive stress in the underlying Ge mesa stripe, leading to a blue shift in the absorption edge of Ge.

  2. Si isotope homogeneity of the solar nebula

    Energy Technology Data Exchange (ETDEWEB)

    Pringle, Emily A.; Savage, Paul S.; Moynier, Frédéric [Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130 (United States); Jackson, Matthew G. [Department of Earth Science, University of California, Santa Barbara, CA 93109 (United States); Barrat, Jean-Alix, E-mail: eapringle@wustl.edu, E-mail: savage@levee.wustl.edu, E-mail: pringle@ipgp.fr, E-mail: moynier@ipgp.fr, E-mail: jackson@geol.ucsb.edu, E-mail: Jean-Alix.Barrat@univ-brest.fr [Université Européenne de Bretagne, Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, F-29280 Plouzané Cedex (France)

    2013-12-20

    The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in {sup 29}Si/{sup 28}Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of {sup 29}Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium-aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

  3. SiD Letter of Intent

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, H., (Ed.); Burrows, P., (Ed.); Oreglia, M., (Ed.); Berger, E.L.; Guarino, V.; Repond, J.; Weerts, H.; Xia, L.; Zhang, J.; /Argonne, HEP; Zhang, Q.; /Argonne, HEP /Beijing, Inst. High Energy Phys.; Srivastava, A.; /Birla Inst. Tech. Sci.; Butler, J.M.; /Boston U.; Goldstein, Joel; Velthuis, J.; /Bristol U.; Radeka, V.; /Brookhaven; Zhu, R.-Y.; /Caltech.; Lutz, P.; /DAPNIA, Saclay; de Roeck, A.; Elsener, K.; Gaddi, A.; Gerwig, H.; /CERN /Cornell U., LNS /Ewha Women' s U., Seoul /Fermilab /Gent U. /Darmstadt, GSI /Imperial Coll., London /Barcelona, Inst. Microelectron. /KLTE-ATOMKI /Valencia U., IFIC /Cantabria Inst. of Phys. /Louis Pasteur U., Strasbourg I /Durham U., IPPP /Kansas State U. /Kyungpook Natl. U. /Annecy, LAPP /LLNL, Livermore /Louisiana Tech. U. /Paris U., VI-VII /Paris U., VI-VII /Munich, Max Planck Inst. /MIT, LNS /Chicago, CBC /Moscow State U. /Nanjing U. /Northern Illinois U. /Obninsk State Nucl. Eng. U. /Paris U., VI-VII /Strasbourg, IPHC /Prague, Inst. Phys. /Princeton U. /Purdue U. /Rutherford /SLAC /SUNY, Stony Brook /Barcelona U. /Bonn U. /UC, Davis /UC, Santa Cruz /Chicago U. /Colorado U. /Delhi U. /Hawaii U. /Helsinki U. /Indiana U. /Iowa U. /Massachusetts U., Amherst /Melbourne U. /Michigan U. /Minnesota U. /Mississippi U. /Montenegro U. /New Mexico U. /Notre Dame U. /Oregon U. /Oxford U. /Ramon Llull U., Barcelona /Rochester U. /Santiago de Compostela U., IGFAE /Hefei, CUST /Texas U., Arlington /Texas U., Dallas /Tokyo U. /Washington U., Seattle /Wisconsin U., Madison /Wayne State U. /Yale U. /Yonsei U.

    2012-04-11

    This document presents the current status of the Silicon Detector (SiD) effort to develop an optimized design for an experiment at the International Linear Collider. It presents detailed discussions of each of SiD's various subsystems, an overview of the full GEANT4 description of SiD, the status of newly developed tracking and calorimeter reconstruction algorithms, studies of subsystem performance based on these tools, results of physics benchmarking analyses, an estimate of the cost of the detector, and an assessment of the detector R and D needed to provide the technical basis for an optimised SiD.

  4. Strain relaxation in nano-patterned strained-Si/SiGe heterostructure on insulator

    Energy Technology Data Exchange (ETDEWEB)

    Liu Xuyn, E-mail: liuyan@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Graduate University of Chinese Academy of Sciences, Beijing 100080 (China); Liu Weili, E-mail: rabbitlwl@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Ma Xiaobo [State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China); Graduate University of Chinese Academy of Sciences, Beijing 100080 (China); Lv Shilong; Song Zhitang; Lin Chenglu [State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China)

    2010-03-15

    In order to evaluate the strain stability, arrays of strained Si/SiGe nano-stripes and nano-pillars were fabricated by Electron-Beam Lithography (EBL) and Reactive-Ion Etching (RIE). The strain relaxation in the patterned strained Si on SiGe-on-insulator (SGOI) was investigated by high-resolution UV micro-Raman spectroscopy. The Raman measurements before and after patterning indicate that most of the strain in the top strained Si is maintained until scaling down to 300 nm, and relaxation of <15% is observed in pillars with a dimension of 150 nm x 150 nm. In the nano-patterned heterostructure strained Si/SiGe, the observed relaxation is small, which is mainly attributed to the fully relaxed and dislocation-free SiGe virtual substrate fabricated by modified Ge condensation.

  5. Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

    Energy Technology Data Exchange (ETDEWEB)

    Deceglie, Michael G [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Silverman, Timothy J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Subedi, Indra [University of Toledo; Podraza, Nikolas J. [University of Toledo

    2017-10-18

    Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through-the-silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128-2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300-2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measured total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.

  6. Low specific contact resistance of NiSi and PtSi to Si: impact of interface

    NARCIS (Netherlands)

    Tiggelman, N.; Kovalgin, Alexeij Y.; Brennan, R.; Wolters, Robertus A.M.

    2010-01-01

    We recently reported low specific contact resistance values of NiSi and PtSi to silicon. In recent publications, such low values were attributed to dopant segregation. In this work, we tested this hypothesis by spreading resistance probe and secondary ion mass spectroscopy analyses. The observed

  7. Sputtered Gold as an Effective Schottky Gate for Strained Si/SiGe Nanostructures

    Science.gov (United States)

    Scott, Gavin; Xiao, Ming; Croke, Ed; Yablonovitch, Eli; Jiang, Hongwen

    2007-03-01

    Metallization of Schottky surface gates by sputtering Au on strained Si/SiGe heterojunctions enables the depletion of the two dimensional electron gas (2DEG) at a relatively small voltage while maintaining an extremely low level of leakage current. A fabrication process has been developed to enable the formation of sub-micron Au electrodes sputtered onto Si/SiGe without the need of a wetting layer.

  8. Raman scattering in Si/SiGe nanostructures: Revealing chemical composition, strain, intermixing, and heat dissipation

    Energy Technology Data Exchange (ETDEWEB)

    Mala, S. A.; Tsybeskov, L., E-mail: tsybesko@njit.edu [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102 (United States); Lockwood, D. J.; Wu, X.; Baribeau, J.-M. [National Research Council, Ottawa, Ontario K1A 0R6 (Canada)

    2014-07-07

    We present a quantitative analysis of Raman scattering in various Si/Si{sub 1-x}Ge{sub x} multilayered nanostructures with well-defined Ge composition (x) and layer thicknesses. Using Raman and transmission electron microscopy data, we discuss and model Si/SiGe intermixing and strain. By analyzing Stokes and anti-Stokes Raman signals, we calculate temperature and discuss heat dissipation in the samples under intense laser illumination.

  9. Passivation of surface-nanostructured f-SiC and porous SiC

    DEFF Research Database (Denmark)

    Ou, Haiyan; Lu, Weifang; Ou, Yiyu

    The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper.......The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper....

  10. Tunneling magnetoresistance in Si nanowires

    KAUST Repository

    Montes Muñoz, Enrique

    2016-11-09

    We investigate the tunneling magnetoresistance of small diameter semiconducting Si nanowires attached to ferromagnetic Fe electrodes, using first principles density functional theory combined with the non-equilibrium Green\\'s functions method for quantum transport. Silicon nanowires represent an interesting platform for spin devices. They are compatible with mature silicon technology and their intrinsic electronic properties can be controlled by modifying the diameter and length. Here we systematically study the spin transport properties for neutral nanowires and both n and p doping conditions. We find a substantial low bias magnetoresistance for the neutral case, which halves for an applied voltage of about 0.35 V and persists up to 1 V. Doping in general decreases the magnetoresistance, as soon as the conductance is no longer dominated by tunneling.

  11. Addimer diffusions on Si(100)

    CERN Document Server

    Lee, G D; Lu, Z Y; Ho, K M

    1999-01-01

    The diffusion pathways along the trough and between the trough and the dimer row on the Si(100) surface are investigated by tight-binding molecular dynamics calculations using the environment dependent tight-binding silicon potential and by ab initio calculations using the Car-Parrinello method. The studies discover new diffusion pathways consisting of rotation of addimer. The calculated energy barrier are in excellent agreement with experiment. The rotational diffusion pathway between the trough and the dimer row is much more energetically favorable than other diffusion pathways by parallel and perpendicular addimer. The new pathway along the trough is nearly same as the energy barrier of the diffusion pathway by dissociation of the addimer.

  12. Study of indentation induced cracks in MoSi2-reaction bonded SiC ...

    Indian Academy of Sciences (India)

    Unknown

    SiC ceramics. O P CHAKRABARTI*, P K DAS and S MONDAL. Central Glass and Ceramic Research Institute, Kolkata 700 032, India. Abstract. MoSi2–RBSC composite samples were prepared by infiltration of Si–2 at.% Mo melt into a preform of commercial SiC and petroleum coke powder. The infiltrated sample had a ...

  13. Advances in SiC/SiC Composites for Aero-Propulsion

    Science.gov (United States)

    DiCarlo, James A.

    2013-01-01

    In the last decade, considerable progress has been made in the development and application of ceramic matrix composites consisting of silicon carbide (SiC) based matrices reinforced by small-diameter continuous-length SiC-based fibers. For example, these SiC/SiC composites are now in the early stages of implementation into hot-section components of civil aero-propulsion gas turbine engines, where in comparison to current metallic components they offer multiple advantages due to their lighter weight and higher temperature structural capability. For current production-ready SiC/SiC, this temperature capability for long time structural applications is 1250 degC, which is better than 1100 degC for the best metallic superalloys. Foreseeing that even higher structural reliability and temperature capability would continue to increase the advantages of SiC/SiC composites, progress in recent years has also been made at NASA toward improving the properties of SiC/SiC composites by optimizing the various constituent materials and geometries within composite microstructures. The primary objective of this chapter is to detail this latter progress, both fundamentally and practically, with particular emphasis on recent advancements in the materials and processes for the fiber, fiber coating, fiber architecture, and matrix, and in the design methods for incorporating these constituents into SiC/SiC microstructures with improved thermo-structural performance.

  14. Microstructure and abrasive wear studies of laser clad Al-Si/SiC composite coatings

    NARCIS (Netherlands)

    Anandkumar, R.; Colaco, R.; Ocelik, V.; De Hosson, J. Th. M.; Vilar, R.; Gyulai, J; Szabo, PJ

    2007-01-01

    Surface coatings of Al-Si/SiC metal-matrix composites were deposited on Al-7 wt. % Si alloy substrates by laser cladding. The microstructure of the coatings was characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of the coating

  15. Fabrication and characterization of Ti3SiC2–SiC nanocomposite by ...

    Indian Academy of Sciences (India)

    Administrator

    in situ reaction synthesis of TiC/Si/Al powders. BAOYAN LIANG†, MINGZHI WANG*, ... The microstructure and mechanical properties of Ti3SiC2–SiC nanocomposite fabricated by in situ hot pressing (HP) synthesis process were .... 7 mm × 27 mm bars for measuring the three-point bend- ing strength with a span of 20 mm. 3.

  16. siRNAmod: A database of experimentally validated chemically modified siRNAs.

    Science.gov (United States)

    Dar, Showkat Ahmad; Thakur, Anamika; Qureshi, Abid; Kumar, Manoj

    2016-01-28

    Small interfering RNA (siRNA) technology has vast potential for functional genomics and development of therapeutics. However, it faces many obstacles predominantly instability of siRNAs due to nuclease digestion and subsequently biologically short half-life. Chemical modifications in siRNAs provide means to overcome these shortcomings and improve their stability and potency. Despite enormous utility bioinformatics resource of these chemically modified siRNAs (cm-siRNAs) is lacking. Therefore, we have developed siRNAmod, a specialized databank for chemically modified siRNAs. Currently, our repository contains a total of 4894 chemically modified-siRNA sequences, comprising 128 unique chemical modifications on different positions with various permutations and combinations. It incorporates important information on siRNA sequence, chemical modification, their number and respective position, structure, simplified molecular input line entry system canonical (SMILES), efficacy of modified siRNA, target gene, cell line, experimental methods, reference etc. It is developed and hosted using Linux Apache MySQL PHP (LAMP) software bundle. Standard user-friendly browse, search facility and analysis tools are also integrated. It would assist in understanding the effect of chemical modifications and further development of stable and efficacious siRNAs for research as well as therapeutics. siRNAmod is freely available at: http://crdd.osdd.net/servers/sirnamod.

  17. Thermal Stability of siRNA Modulates Aptamer- conjugated siRNA Inhibition

    Directory of Open Access Journals (Sweden)

    Alexey Berezhnoy

    2012-01-01

    Full Text Available Oligonucleotide aptamer-mediated in vivo cell targeting of small interfering RNAs (siRNAs is emerging as a useful approach to enhance the efficacy and reduce the adverse effects resulting from siRNA-mediated genetic interference. A current main impediment in aptamer-mediated siRNA targeting is that the activity of the siRNA is often compromised when conjugated to an aptamer, often requiring labor intensive and time consuming design and testing of multiple configurations to identify a conjugate in which the siRNA activity has not been significantly reduced. Here, we show that the thermal stability of the siRNA is an important parameter of siRNA activity in its conjugated form, and that siRNAs with lower melting temperature (Tm are not or are minimally affected when conjugated to the 3′ end of 2′F-pyrimidine-modified aptamers. In addition, the configuration of the aptamer-siRNA conjugate retains activity comparable with the free siRNA duplex when the passenger strand is co-transcribed with the aptamer and 3′ overhangs on the passenger strand are removed. The approach described in this paper significantly reduces the time and effort necessary to screening siRNA sequences that retain biological activity upon aptamer conjugation, facilitating the process of identifying candidate aptamer-siRNA conjugates suitable for in vivo testing.

  18. Polycrystalline SiC as source material for the growth of fluorescent SiC layers

    DEFF Research Database (Denmark)

    Kaiser, M.; Hupfer, T.; Jokubavicus, V.

    2013-01-01

    Polycrystalline doped SiC act as source for fluorescent SiC. We have studied the growth of individual grains with different polytypes in the source material. We show an evolution and orientation of grains of different polytypes in polycrystalline SiC ingots grown by the Physical Vapor Transport m...

  19. Study of indentation induced cracks in MoSi2-reaction bonded SiC ...

    Indian Academy of Sciences (India)

    The infiltrated sample had a density > 92% of the theoretical density (TD) and microstructurally contained SiC, MoSi2, residual Si and unreacted C. The material was tested for indentation fracture toughness at room temperature with a Vicker's indenter and KIC was found to be 4.42 MPa√m which is around 39% higher than ...

  20. Fabrication and characterization of Ti3SiC2–SiC nanocomposite by ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 34; Issue 7. Fabrication and characterization of Ti3SiC2–SiC nanocomposite by in situ reaction synthesis of TiC/Si/Al powders. Baoyan Liang Mingzhi Wang Xiaopu Li Yunchao Mu. Volume 34 Issue 7 December 2011 pp 1309-1311 ...

  1. SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

    Science.gov (United States)

    Chanadee, Tawat

    2017-11-01

    Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO2, Mg, Mg2SiO4, Mg2Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg2SiO4. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.

  2. On iron contamination in mechanically alloyed Cr-Si powders

    Energy Technology Data Exchange (ETDEWEB)

    Fernandes, Bruno B. [Universidade do Vale do Paraiba, Instituto de Pesquisa e Desenvolvimento, Sao Jose dos, Campos-SP, CEP 12244-000 (Brazil); Rodrigues, Geovani [Faculdade de Engenharia Quimica de Lorena, Departamento de Engenharia de Materiais, Caixa Postal 116, Lorena-SP, CEP 12600-970 (Brazil); Coelho, Gilberto C. [Faculdade de Engenharia Quimica de Lorena, Departamento de Engenharia de Materiais, Caixa Postal 116, Lorena-SP, CEP 12600-970 (Brazil); Ramos, Alfeu S. [Universidade do Vale do Paraiba, Instituto de Pesquisa e Desenvolvimento, Sao Jose dos, Campos-SP, CEP 12244-000 (Brazil)]. E-mail: alfeu@univap.br

    2005-09-25

    The present work reports on iron contamination and phase transformation during high-energy ball milling from high-purity elemental powder Cr-25Si, Cr-37.5Si, Cr-50Si, and Cr-66Si mixtures (at%) and their subsequent heat treatment. Samples were characterized in the as-milled state as well as after heat treatment by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microanalysis via energy dispersive spectrometry (EDS). Only Cr peaks were observed in Cr-25Si and Cr-37.5Si powders after milling for 200 h, suggesting that amorphous phases can be formed. In Cr-50Si and Cr-66Si powders, the CrSi and CrSi{sub 2} phases were formed during ball milling, respectively. In Cr-25Si and Cr-50Si milled powders, heat-treated at 1200 deg. C for 4 h, the formation of the Cr{sub 3}Si and CrSi phases dissolving up to 15 and 16.9 at%Fe, respectively, was noted. In addition, the ternary Cr{sub 9}Fe{sub 9}Si{sub 2} phase was also formed in heat-treated Cr-25Si powders. A small amount of Cr{sub 5}Si{sub 3} and CrSi{sub 2} was formed in heat-treated Cr-37.5Si and Cr-66Si powders, respectively.

  3. Eutrophication alters Si cycling and litter decomposition in wetlands

    NARCIS (Netherlands)

    Emsens, Willem-Jan; Schoelynck, Jonas; Grootjans, Ab P.; Struyf, Eric; van Diggelen, Rudy

    2016-01-01

    Anthropogenic eutrophication of wetlands may have a significant impact on the global biogeochemical silicon (Si) cycle, as Si filtering by wetland vegetation codetermines fluxes of Si towards the oceans. We experimentally investigated how macronutrient (NPK) enrichment alters total Si storage and Si

  4. PROMOTION OF THE SI(100)-O2 REACTION BY SM

    NARCIS (Netherlands)

    ONSGAARD, J; GHIJSEN, J; JOHNSON, RL; CHRISTIANSEN, M; ORSKOV, F; GODOWSKI, PJ

    1991-01-01

    It is demonstrated that ultrathin and thin films of Sm on Si (001) strongly promote the oxidation of Si. Photoemission measurements of the Si 2p core electrons show binding-energy shifts characteristic of Si2O3 and SiO2. The oxygen binding is conditioned by the presence of Sm, which is also

  5. Lateral boron distribution in polycrystalline SiC source materials

    DEFF Research Database (Denmark)

    Linnarsson, M. K.; Kaiser, M.; Liljedahl, R.

    2013-01-01

    Polycrystalline SiC containing boron and nitrogen are used in growth of fluorescent SiC for white LEDs. Two types of doped polycrystalline SiC have been studied in detail with secondary ion mass spectrometry: sintered SiC and poly-SiC prepared by sublimation in a physical vapor transport setup. T...

  6. Liposomal siRNA for ovarian cancer.

    Science.gov (United States)

    Mangala, Lingegowda S; Han, Hee Dong; Lopez-Berestein, Gabriel; Sood, Anil K

    2009-01-01

    Discovery of RNA interference (RNAi) has been one of the most important findings in the last ten years. In recent years, small interfering RNA (siRNA)-mediated gene silencing is beginning to show substantial promise as a new treatment modality in preclinical studies because of its robust gene selective silencing. However, until recently, delivery of siRNA in vivo was a major impediment to its use as a therapeutic modality. We have used a neutral liposome, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), for highly efficient in vivo siRNA delivery. Using siRNA tagged with Alexa-555, incorporated in DOPC liposomes, we have demonstrated efficient intra-tumoral delivery following either intraperitoneal or intravenous injection. Furthermore, EphA2-targeted siRNA in DOPC liposomes showed significant target modulation and anti-tumor efficacy.

  7. DLC-Si protective coatings for polycarbonates

    Directory of Open Access Journals (Sweden)

    Damasceno J.C.

    2003-01-01

    Full Text Available In this work, a-C:H:Si (DLC-Si films were produced onto crystalline silicon and polycarbonate substrates by the rf-PACVD technique from gaseous mixtures of CH4 + SiH4 and C2H2 + SiH4. The effects of self-bias and gas composition upon mechanical and optical properties of the films were investigated. Micro-hardness, residual stress, surface roughness and refractive index measurements were employed for characterization. By incorporating low concentrations of silicon and by exploring the more favorable conditions for the rf-PACVD deposition technique, highly adherent DLC-Si thin films were produced with reduced internal stresses (lower than 1 GPa, high hardness (around 20 GPa and high deposition rates (up to 10 µm/h. Results that show the technological viability of this material for application as protective coatings for polycarbonates are also discussed.

  8. Polarized Raman spectroscopy study of NiSi film grown on Si(001) substrate

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Li; Ren, Yiming; Tang, Bo; Cheng, Xinhong; Zhang, Xuefei; Xu, Dapeng; Luo, Hijun; Huang, Yunmi [Wenzhou University, Department of Physics, Wenzhou (China)

    2009-11-15

    We report on the growth of NiSi film on Si(001) substrate with an orientation of NiSi[200]//Si[001]. Polarized Raman spectroscopy was used to assign the symmetry of the NiSi Raman peaks. Raman peaks at 213 cm{sup -1}, 295 cm{sup -1}, and 367 cm{sup -1} are assigned to be A{sub g} symmetry and peaks at 196 cm{sup -1}, and 254 cm{sup -1} are B{sub 3g} symmetry. (orig.)

  9. Deep inelastic reactions of /sup 28/Si on /sup 28/Si and /sup 27/Al

    Energy Technology Data Exchange (ETDEWEB)

    Manduchi, C.; Manduchi, M.T.R.; Segato, G.F.; Andolfato, F.

    1986-12-01

    The deep inelastic reactions of /sup 28/Si on /sup 28/Si at incident energies of 125 and 138 MeV, and /sup 28/Si on /sup 27/Al at 130 MeV, have been studied by measuring inclusive fragment distributions, and fragment-fragment coincidences. The experiment employed a coincidence spectrometer consisting of two multiparameter ion chambers. Inclusive measurements exhibit behaviour characteristic of strongly damped processes. Two-fragment exclusive measurements in the /sup 28/Si-/sup 28/Si reaction show interesting selective phenomena in both mass and charge spectra of the emitted fragments.

  10. Growth of CrSi2 Nanostructures Using CrCl2 Powder on Si Substrates

    OpenAIRE

    Wen Li; Meng Erchao; Tomoji Matsushita; Shingo Oda; Daisuke Ishikawa; Kaito Nakane; Hirokazu Tatsuoka

    2013-01-01

    Chromium disilicide (CrSi2) nanostructures were grown by the exposure of Si (111) substrates to CrCl2 vapor in an argon gas flow at atmospheric pressure without using any metal catalyst. Dependence of the growth condition on the structural property was investigated. Hexagonal-shaped CrSi2 microrods were grown at 750 °C with 0.05 g of CrCl2. As the quantity of CrCl2 increased to 0.1 g, the bundle of CrSi2 nanowires with microrods and web-liked CrSi2 nanostructure with turning angles were grown...

  11. High Efficiency Hybrid Solar Cells Using Nanocrystalline Si Quantum Dots and Si Nanowires.

    Science.gov (United States)

    Dutta, Mrinal; Thirugnanam, Lavanya; Trinh, Pham Van; Fukata, Naoki

    2015-07-28

    We report on an efficient hybrid Si nanocrystal quantum dot modified radial p-n junction thinner Si solar cell that utilizes the advantages of effective exciton collection by energy transfer from nanocrystal-Si (nc-Si) quantum dots to underlying radial p-n junction Si nanowire arrays with excellent carrier separation and propagation via the built-in electric fields of radial p-n junctions. Minimization of recombination, optical, and spectrum losses in this hybrid structure led to a high cell efficiency of 12.9%.

  12. High Mobility Transport Layer Structures for Rhombohedral Si/Ge/SiGe Devices

    Science.gov (United States)

    Choi, Sang Hyouk (Inventor); Park, Yeonjoon (Inventor); King, Glen C. (Inventor); Kim, Hyun-Jung (Inventor); Lee, Kunik (Inventor)

    2017-01-01

    An electronic device includes a trigonal crystal substrate defining a (0001) C-plane. The substrate may comprise Sapphire or other suitable material. A plurality of rhombohedrally aligned SiGe (111)-oriented crystals are disposed on the (0001) C-plane of the crystal substrate. A first region of material is disposed on the rhombohedrally aligned SiGe layer. The first region comprises an intrinsic or doped Si, Ge, or SiGe layer. The first region can be layered between two secondary regions comprising n+doped SiGe or n+doped Ge, whereby the first region collects electrons from the two secondary regions.

  13. Evaluation of CVI SiC/SiC Composites for High Temperature Applications

    Science.gov (United States)

    Kiser, D.; Almansour, A.; Smith, C.; Gorican, D.; Phillips, R.; Bhatt, R.; McCue, T.

    2017-01-01

    Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites are candidate materials for various high temperature turbine engine applications because of their high specific strength and good creep resistance at temperatures of 1400 C (2552 F) and higher. Chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composites (CMC) incorporating Sylramic-iBN SiC fiber were evaluated via fast fracture tensile tests (acoustic emission damage characterization to assess cracking behavior), tensile creep testing, and microscopy. The results of this testing and observed material behavior degradation mechanisms are reviewed.

  14. Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

    Directory of Open Access Journals (Sweden)

    Yorinobu Kunimune

    2016-04-01

    Full Text Available We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO stack structure using ultraviolet laser-assisted atom probe tomography (APT. The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %. Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA, which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

  15. Boosting light emission from Si-based thin film over Si and SiO(2) nanowires architecture.

    Science.gov (United States)

    Yu, Zhongwei; Qian, Shengyi; Yu, Linwei; Misra, Soumyadeep; Zhang, Pei; Wang, Junzhuan; Shi, Yi; Xu, Ling; Xu, Jun; Chen, Kunji; Roca i Cabarrocas, Pere

    2015-03-09

    Silicon (Si)-based light emitting thin film has been a key ingredient for all-Si-based optoelectronics. Besides material engineering, adopting a novel 3D photonic architecture represents an effective strategy to boost light excitation and extraction from Si-based thin film material. We here explore the use of a nanowires (NW) framework, grown via vapor-liquid-solid mode, to achieve strongly enhanced yellow-green luminescence from SiN(x)O(y)/NW core-shell structure, with an order of magnitude enhancement compared to co-deposited planar references. We found that choosing geometrically-identical but different NW cores (Si or SiO(2)) can lead to profound influence on the overall light emission performance. Combining parametric investigation and theoretical modeling, we have been able to evaluate the key contributions arising from different mechanisms that include near-field enhancement, 3D light trapping and enhanced light extraction. These new findings indicate a new and effective strategy for strong Si-based thin film light emitting source, while being generic enough to be applicable in a wide variety of other thin film materials.

  16. Luminescence of Nanoporous Si and ALD-Deposited ZnO on Nanoporous Si Substrate

    Science.gov (United States)

    Pham, Vuong-Hung; Tam, Phuong Dinh; Dung, Nguyen Huu; Nguyen, Duy-Hung; Huy, Pham Thanh

    2017-08-01

    This paper reports the attempt at synthesizing nanoporous silicon (Si) with a dendritic-like structure and atomic layer deposition (ALD) of ZnO on nanoporous Si to control light emission intensity and emission center by applying an optimum voltage, etching time and thickness of ZnO layer. The dendritic-like structure of nanoporous Si was formed with low etching voltages of 5-10 V. Fourier transform infrared absorption spectra of the nanoporous Si reveals that the intensities of hydride stretching, SiH2 scissor mode and Si-O-Si vibration peak increase with the increasing of etching time. The formation of a thick dendritic-like structure with an increasing SiH2 bond resulted in significant enhancement of luminescence. In addition, the ALD-deposited ZnO layer on nanoporous Si resulted in light emission from both ZnO and nanoporous Si under a single excitation source. These results suggest the potential application of an ALD-deposited ZnO layer on nanoporous Si in designing materials for advanced optoelectronics.

  17. Improving Passivation Process of Si Nanocrystals Embedded in SiO2 Using Metal Ion Implantation

    Directory of Open Access Journals (Sweden)

    Jhovani Bornacelli

    2013-01-01

    Full Text Available We studied the photoluminescence (PL of Si nanocrystals (Si-NCs embedded in SiO2 obtained by ion implantation at MeV energy. The Si-NCs are formed at high depth (1-2 μm inside the SiO2 achieving a robust and better protected system. After metal ion implantation (Ag or Au, and a subsequent thermal annealing at 600°C under hydrogen-containing atmosphere, the PL signal exhibits a noticeable increase. The ion metal implantation was done at energies such that its distribution inside the silica does not overlap with the previously implanted Si ion . Under proper annealing Ag or Au nanoparticles (NPs could be nucleated, and the PL signal from Si-NCs could increase due to plasmonic interactions. However, the ion-metal-implantation-induced damage can enhance the amount of hydrogen, or nitrogen, that diffuses into the SiO2 matrix. As a result, the surface defects on Si-NCs can be better passivated, and consequently, the PL of the system is intensified. We have selected different atmospheres (air, H2/N2 and Ar to study the relevance of these annealing gases on the final PL from Si-NCs after metal ion implantation. Studies of PL and time-resolved PL indicate that passivation process of surface defects on Si-NCs is more effective when it is assisted by ion metal implantation.

  18. Electronic Properties of Si-Hx Vibrational Modes at Si Waveguide Interface.

    Science.gov (United States)

    Bashouti, Muhammad Y; Yousefi, Peyman; Ristein, Jürgen; Christiansen, Silke H

    2015-10-01

    Attenuated total reflectance (ATR) and X-ray photoelectron spectroscopy in suite with Kelvin probe were conjugated to explore the electronic properties of Si-Hx vibrational modes by developing Si waveguide with large dynamic detection range compared with conventional IR. The Si 2p emission and work-function related to the formation and elimination of Si-Hx bonds at Si surfaces are monitored based on the detection of vibrational mode frequencies. A transition between various Si-Hx bonds and thus related vibrational modes is monitored for which effective momentum transfer could be demonstrated. The combination of the aforementioned methods provides for results that permit a model for the kinetics of hydrogen termination of Si surfaces with time and advanced surface characterizing of hybrid-terminated semiconducting solids.

  19. Ge nanocrystals embedded in ultrathin Si3N4 multilayers with SiO2 barriers

    Science.gov (United States)

    Bahariqushchi, R.; Gundogdu, Sinan; Aydinli, A.

    2017-04-01

    Multilayers of germanium nanocrystals (NCs) embedded in thin films of silicon nitride matrix separated with SiO2 barriers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). SiGeN/SiO2 alternating bilayers have been grown on quartz and Si substrates followed by post annealing in Ar ambient from 600 to 900 °C. High resolution transmission electron microscopy (HRTEM) as well as Raman spectroscopy show good crystallinity of Ge confined to SiGeN layers in samples annealed at 900 °C. Strong compressive stress for SiGeN/SiO2 structures were observed through Raman spectroscopy. Size, as well as NC-NC distance were controlled along the growth direction for multilayer samples by varying the thickness of bilayers. Visible photoluminescence (PL) at 2.3 and 3.1 eV with NC size dependent intensity is observed and possible origin of PL is discussed.

  20. Light emissions from LiNbO sub 3 /SiO sub 2 /Si structures

    CERN Document Server

    Wu, X L; Tang, N; Deng, S S; Bao, X M

    2003-01-01

    LiNbO sub 3 (LN) films with a high degree of (006) texture were deposited on Si-based dense SiO sub 2 layers by pulsed laser deposition. After annealing, the LN/SiO sub 2 /Si structures were revealed to have ultraviolet-, green-, and red-emitting properties related to self-trapped excitons and E' defect pairs in the SiO sub 2 surface, which are induced by the photorefractive effect of the LN films. The emission wavelength can be tuned by introducing different dopants into the LN films. Waveguiding properties of the structures were demonstrated. The results obtained indicate that the LN/SiO sub 2 /Si structures could be expected to have important applications in modern optoelectronic integration. (letter to the editor)

  1. Effect of PECVD SiNx/SiOyNx-Si interface property on surface passivation of silicon wafer

    Science.gov (United States)

    Jia, Xiao-Jie; Zhou, Chun-Lan; Zhu, Jun-Jie; Zhou, Su; Wang, Wen-Jing

    2016-12-01

    It is studied in this paper that the electrical characteristics of the interface between SiOyNx/SiNx stack and silicon wafer affect silicon surface passivation. The effects of precursor flow ratio and deposition temperature of the SiOyNx layer on interface parameters, such as interface state density Dit and fixed charge Qf, and the surface passivation quality of silicon are observed. Capacitance-voltage measurements reveal that inserting a thin SiOyNx layer between the SiNx and the silicon wafer can suppress Qf in the film and Dit at the interface. The positive Qf and Dit and a high surface recombination velocity in stacks are observed to increase with the introduced oxygen and minimal hydrogen in the SiOyNx film increasing. Prepared by deposition at a low temperature and a low ratio of N2O/SiH4 flow rate, the SiOyNx/SiNx stacks result in a low effective surface recombination velocity (Seff) of 6 cm/s on a p-type 1 Ω·cm-5 Ω·cm FZ silicon wafer. The positive relationship between Seff and Dit suggests that the saturation of the interface defect is the main passivation mechanism although the field-effect passivation provided by the fixed charges also make a contribution to it. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA050302) and the National Natural Science Foundation of China (Grant No. 61306076).

  2. Experimental and thermodynamic assessments of substitutions in the AlFeSi, FeMnSi, FeSiZr and AlCaFeSi systems (65 wt % Si) - solidification simulation

    Energy Technology Data Exchange (ETDEWEB)

    Gueneau, C. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. des Procedes d`Enrichissement]|[Paris-11 Univ., 91 - Orsay (France)]|[Compagnie de Produits Chimiques et Electrometallurgiques Pechiney, 74 - Passy-Chedde (France). Lab. Graphitation; Servant, C. [Paris-11 Univ., 91 - Orsay (France); Ansara, I. [Ecole Nationale Superieure d`Electrochimie et d`Electrometallurgie, 38 - Grenoble (France)

    1994-12-31

    The substitutions of Al <-> Si, Fe <-> Mn and Fe <-> Zr in some intermetallic compounds of the Al-Fe-Si, Fe-Mn-Si and Fe-Si-Zr systems are modelled in the Si-rich corner using a two sublattice model. The solidification paths of the studied alloys are determined at equilibrium. The ascalculated phase volume fractions of the alloys are compared to the experimental ones. Finally, a solidification simulation using the Gulliver-Scheil`s model is performed in order to explain the formation of some precipitates experimentally observed. (authors). 14 figs., 19 refs.

  3. Compact hybrid Si microring lasers

    Science.gov (United States)

    Liang, Di; Bowers, John E.; Fiorentino, Marco; Beausoleil, Raymond G.

    2010-02-01

    In this paper we review the recent progress in developing compact microring lasers on the hybrid silicon platform. A simplified self-aligned process is used to fabricate devices as small as 15 μm in diameter. The optically-pumped, continuous wave (cw) devices show low threshold carrier density, comparable to the carrier density to reach material transparency. In the electrically-pumped lasers, the short cavity length leads to the minimum laser threshold less than 5 mA in cw operation. The maximum cw lasing temperature is up to 65 °C. Detailed studies in threshold as a function of coupling coefficient and bus waveguide width are presented. Surface recombination at the dry-etched exposed interface is investigated qualitatively by studying the current-voltage characteristics. Ring resonator-based figures of merits including good spectral purity and large side-mode suppression ratio are demonstrated. Thermal impedance data is extracted from temperature-dependent spectral measurement, and buried oxide layer in silicon-on-insulator wafer is identified as the major thermal barrier to cause high thermal impedance for small-size devices. The demonstrated compact hybrid ring lasers have low power consumption, small footprint and dynamic performance. They are promising for Si-based optical interconnects and flip-flop applications.

  4. Gold and silver/Si nanocomposite layers

    Energy Technology Data Exchange (ETDEWEB)

    Kleps, Irina [National Institute for Research and Development in Microtechnologies (IMT-Bucharest), P.O. Box 38-160, Bucharest (Romania)], E-mail: irinak@imt.ro; Danila, Mihai; Angelescu, Anca; Miu, Mihaela; Simion, Monica; Ignat, Teodora; Bragaru, Adina [National Institute for Research and Development in Microtechnologies (IMT-Bucharest), P.O. Box 38-160, Bucharest (Romania); Dumitru, Lucia; Teodosiu, Gabriela [Institute of Biology, 296 Splaiul Independentei, P.O. Box 56-53, Bucharest, 060031 (Romania)], E-mail: biologie@ibiol.ro

    2007-09-15

    Ag and Au nanolayers were realised by physical and chemical deposition methods on porous silicon (PS) nanostructured surfaces for biomedical applications: support for living cells, biodegradable material for the slow release of drugs/minerals, and as a bioactive material for scaffolds. Au nanoparticles on nanocrystalline Si are widely used in increasing substrate biocompatibility properties. It has an electrochemical potential of + 0.332 mV and surface energy around 25 erg/cm{sup 2}, close to those of living tissues. The Au nanocrystallites orientation on nanocrystalline Si substrates is also of great interest for application in biochemistry; the Au (111)/nc-Si surface has a higher density of atoms compared with Au (100); this favours the attachment of a higher number of atoms and bio-molecules on the gold surface. Ag nanoparticles on nanocrystalline Si are important for the latter's anti-microbial properties. In minute concentrations, Ag is highly toxic to germs while relatively non-toxic to human cells. Microbes are unlikely to develop a resistance against silver, as they do against conventional and highly targeted antibiotics. The Au and Ag nanoparticles/silicon nanocomposite layers as-deposited and thermally treated were investigated by optical microscopy, X-ray diffraction, and biological tests using eukaryotic and prokaryotic cell cultures. The experimental results sustain the use of Au/Si and Ag/Si or combined Ag/Au/Si nanocomposite structures as biocompatible and anti-microbial matrix.

  5. Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries.

    Science.gov (United States)

    Ngo, Duc Tung; Le, Hang T T; Pham, Xuan-Manh; Park, Choong-Nyeon; Park, Chan-Jin

    2017-09-27

    Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO2@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO2 and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g(-1) and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g(-1) was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g(-1) at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO2 cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.

  6. Light trapping of crystalline Si solar cells by use of nanocrystalline Si layer plus pyramidal texture

    Energy Technology Data Exchange (ETDEWEB)

    Imamura, Kentaro; Nonaka, Takaaki; Onitsuka, Yuya; Irishika, Daichi; Kobayashi, Hikaru, E-mail: h.kobayashi@sanken.osaka-u.ac.jp

    2017-02-15

    Highlights: • Ultralow reflectivity Si wafers with light trapping effect can be obtained by forming a nanocrystalline Si layer on pyramidal textured Si surfaces. • Surface passivation using phosphosilicate glass improved minority carrier lifetime of the nanocrystalline Si layer/Si structure. • A high photocurrent density of 40.1 mA/cm{sup 2}, and a high conversion efficiency of 18.5% were achieved. - Abstract: The surface structure chemical transfer (SSCT) method has been applied to fabrication of single crystalline Si solar cells with 170 μm thickness. The SSCT method, which simply involves immersion of Si wafers in H{sub 2}O{sub 2} plus HF solutions and contact of Pt catalyst with Si taking only ∼30 s for 6 in. wafers, can decrease the reflectivity to less than 3% by the formation of a nanocrystalline Si layer. However, the reflectivity of the nanocrystalline Si layer/flat Si surface/rear Ag electrode structure in the wavelength region longer than 1000 nm is high because of insufficient absorption of incident light. The reflectivity in the long wavelength region is greatly decreased by the formation of the nanocrystalline Si layer on pyramidal textured Si surfaces due to an increase in the optical path length. Deposition of phosphosilicate glass (PSG) on the nanocrystalline Si layer for formation of pn-junction does not change the ultralow reflectivity because the surface region of the nanocrystalline Si layer possesses a refractive index of 1.4 which is nearly the same as that of PSG of 1.4–1.5. The PSG layer is found to passivate the nanocrystalline Si layer, which is evident from an increase in the minority carrier lifetime from 12 to 44 μs. Hydrogen treatment at 450 °C further increases the minority carrier lifetime approximately to a doubled value. The solar cells with the Si layer/pyramidal Si substrate/boron-diffused back surface field/Ag rear electrode> structure show a high conversion efficiency of 18

  7. Irradiation test of high density Si material

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Man Soon; Choo, Kee Nam; Lee, Chul Yong; Yang, Seong Woo; Shim, Kyue Taek; Park, Sang Jun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-10-15

    The feasibility of irradiation test for the high-density Si material entrusted by Guju Inc. was reviewed. The high density Si material is used for a sealing of the penetration holes of piping at the nuclear power plants. The irradiation test was performed and the density changes between before and after irradiation test were measured. The irradiation tests were performed 2 times for 1 day and 20 days at IP 4 hole of HANARO. The 3 Si specimens irradiated were without flaws and the density changes after irradiation were successfully measured. The result satisfies the requirement of the design specification.

  8. Removal of B from Si by Hf addition during Al–Si solvent refining process

    Science.gov (United States)

    Lei, Yun; Ma, Wenhui; Sun, Luen; Wu, Jijun; Dai, Yongnian; Morita, Kazuki

    2016-01-01

    Abstract A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6 to 8.8 × 10−7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (Hf addition, slower cooling rate, and Al-rich Al–Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al–Si melt was 1173 K and the cooling rate was 4.5–7.6 K min–1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si. PMID:27877853

  9. Removal of B from Si by Hf addition during Al-Si solvent refining process.

    Science.gov (United States)

    Lei, Yun; Ma, Wenhui; Sun, Luen; Wu, Jijun; Dai, Yongnian; Morita, Kazuki

    2016-01-01

    A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al-Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al-Si melt was estimated to range from 4.9 × 10-6 to 8.8 × 10-7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (Hf addition, slower cooling rate, and Al-rich Al-Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al-Si melt was 1173 K and the cooling rate was 4.5-7.6 K min-1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si.

  10. Removal of C and SiC from Si and FeSi during ladle refining and solidification

    Energy Technology Data Exchange (ETDEWEB)

    Klevan, Ole Svein

    1997-12-31

    The utilization of solar energy by means of solar cells requires the Si to be very pure. The purity of Si is important for other applications as well. This thesis mainly studies the total removal of carbon from silicon and ferrosilicon. The decarburization includes removal of SiC particles by stirring and during casting in addition to reduction of dissolved carbon by gas purging. It was found that for three commercial qualities of FeSi75, Refined, Gransil, and Standard lumpy, the refined quality is lowest in carbon, followed by Gransil and Standard. A decarburization model was developed that shows the carbon removal by oxidation of dissolved carbon to be a slow process at atmospheric pressure. Gas stirring experiments have shown that silicon carbide particles are removed by transfer to the ladle wall. The casting method of ferrosilicon has a strong influence on the final total carbon content in the commercial alloy. Shipped refined FeSi contains about 100 ppm total carbon, while the molten alloy contains roughly 200 ppm. The total carbon out of the FeSi-furnace is about 1000 ppm. It is suggested that low values of carbon could be obtained on an industrial scale by injection of silica combined with the use of vacuum. Also, the casting system could be designed to give low carbon in part of the product. 122 refs., 50 figs., 24 tabs.

  11. Half-life of 31Si

    CERN Document Server

    D'Agostino, Giancarlo; Mana, Giovanni; Oddone, Massimo

    2016-01-01

    Half-life values are widely used in nuclear chemistry to model the exponential decay of the quantified radionuclides. The analysis of existing data reveals a general lack of information on the performed experiments and an almost complete absence of uncertainty budgets. This is the situation for 31Si, the radionuclide produced via neutron capture reaction recently used to quantify trace amounts of 30Si in a sample of the silicon material highly enriched in 28Si and used for the determination of the Avogadro constant. In order to improve the quality of the now recommended 157.36(26) min value, we carried out repeated observations of the 31Si decay rate via gamma-ray spectrometry measurements. This paper reports the result we obtained, including details of the experiment and the evaluation of the uncertainty.

  12. Pr5Si3N9

    Directory of Open Access Journals (Sweden)

    Saskia Lupart

    2009-06-01

    Full Text Available Single crystals of Pr5Si3N9, pentapraseodymium trisilicon nonanitride, were obtained by the reaction of elemental praseodymium with silicon diimide in a radio-frequency furnace at 1873 K. The crystal structure consists of a chain-like Si—N substructure of corner-sharing SiN4 tetrahedra. An additional Q1-type [SiN4] unit is attached to every second tetrahedron directed alternately in opposite directions. The resulting branched chains interlock with each other, building up a three-dimensional structure. The central atoms of the Q1-type [SiN4] unit and of its attached tetrahedron are situated on a mirror plane, as are two of the four crystallographically unique Pr3+ ions. The latter are coordinated by six to ten N atoms, with Pr—N distances similar to those of other rare earth nitridosilicates.

  13. High-efficiency si/polymer hybrid solar cells based on synergistic surface texturing of Si nanowires on pyramids.

    Science.gov (United States)

    He, Lining; Lai, Donny; Wang, Hao; Jiang, Changyun; Rusli

    2012-06-11

    An efficient Si/PEDOT:PSS hybrid solar cell using synergistic surface texturing of Si nanowires (SiNWs) on pyramids is demonstrated. A power conversion efficiency (PCE) of 9.9% is achieved from the cells using the SiNW/pyramid binary structure, which is much higher than similar cells based on planar Si, pyramid-textured Si, and SiNWs. The PCE is the highest reported to-date for hybrid cells based on Si nanostructures and PEDOT. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Si/SiC heterojunction optically controlled transistor with charge compensation layer

    Directory of Open Access Journals (Sweden)

    Pu Hongbin

    2016-01-01

    Full Text Available A novel n-SiC/p-Si/n-Si optically controlled transistor with charge compensation layer has been studied in the paper. The performance of the device is simulated using Silvaco Atlas tools, which indicates excellent performances of the device in both blocking state and conducting state. The device also has a good switching characteristic with 0.54μs as rising time and 0.66μs as falling time. With the charge compensation layer, the breakdown voltage and the spectral response intensity of the device are improved by 90V and 33A/W respectively. Compared with optically controlled transistor without charge compensation layer, the n-SiC/p-Si/n-Si optically controlled transistor with charge compensation layer has a better performance.

  15. Structural and Morphological Investigation of Pendeo-Epitaxy 3C-SiC on Si Substrates

    Science.gov (United States)

    Kim, Byeung C.; Capano, Michael A.

    2008-05-01

    Successful pendeo-epitaxy growth of cubic silicon carbide (3C-SiC) on off-axis Si(001) substrates was achieved. The structural and morphological characteristics of pendeo-epitaxy 3C-SiC were strongly affected by underlying stripes and seed layer thickness. Stripes perpendicular to the Si substrate off-axis provide about three times faster lateral growth rate compared with parallel oriented stripes. Root-mean-square (RMS) measurements using atomic force microscope (AFM) indicate that the surface morphology of Pendeo-epitaxy 3C-SiC films remarkably improves with increasing seed layer thickness: from 9.8 nm for 3 μm thickness to 0.5 nm for 10 μm thickness. These effects on pendeo-epitaxy 3C-SiC are discussed with scanning electron microscopy (SEM) and AFM investigation.

  16. Structure and chemistry of passivated SiC/SiO{sub 2} interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Houston Dycus, J.; Xu, Weizong; LeBeau, James M. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907 (United States); Lichtenwalner, Daniel J.; Hull, Brett; Palmour, John W. [Power Devices R& D, Wolfspeed, A Cree Company, Research Triangle Park, North Carolina 27709 (United States)

    2016-05-16

    Here, we report on the chemistry and structure of 4H-SiC/SiO{sub 2} interfaces passivated either by nitric oxide annealing or Ba deposition. Using aberration corrected scanning transmission electron microscopy and spectroscopy, we find that Ba and N remain localized at SiC/SiO{sub 2} interface after processing. Further, we find that the passivating species can introduce significant changes to the near-interface atomic structure of SiC. Specifically, we quantify significant strain for nitric oxide annealed sample where Si dangling bonds are capped by N. In contrast, strain is not observed at the interface of the Ba treated samples. Finally, we place these results in the context of field effect mobility.

  17. The Effect of Si Morphology on Machinability of Al-Si Alloys

    Directory of Open Access Journals (Sweden)

    Muhammet Uludağ

    2015-12-01

    Full Text Available Many of the cast parts require some sort of machining like milling, drilling to be used as a finished product. In order to improve the wear properties of Al alloys, Si is added. The solubility of Si in Al is quite low and it has a crystallite type structure. It behaves as particulate metal matrix composite which makes it an attractive element. Thus, the wear and machinability properties of these type of alloys depend on the morphology of Si in the matrix. In this work, Sr was added to alter the morphology of Si in Al-7Si and Al-12Si. Cylindrical shaped samples were cast and machinability characteristics of Sr addition was studied. The relationship between microstructure and machinability was evaluated.

  18. Brazing of SiC using Cu-Si non reactive alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gasse, A. [C.E.A., CEREM-DEM, Grenoble (France); Chaumat, G. [C.E.A., CEREM-DEM, Grenoble (France); Rado, C. [INPG/LTCM-ENSEEG, Saint Martin d`Heres (France); Eustathopoulos, N. [INPG/LTCM-ENSEEG, Saint Martin d`Heres (France)

    1995-12-31

    SiC was brazed with a Cu 24 at% Si alloy under high vacuum at 1473 K. This alloy well wets SiC without any measurable reactivity and after cooling, leads to an interface which appears to be strong. It was found that the degree of filling of the joint by the alloy depends mainly on the geometry of the ceramic-metal-vapour system. It is shown that geometrical factors influence the kinetics of deoxidation of both alloys and SiC surfaces and, as a consequence, considerably modify the wetting kinetics and filling of the joint. Successful helium-tight tube/plate brazed joints have been obtained. Nevertheless, thermal expansion mismatch remains considerable between the SiC and the Cu-Si alloy. Further work is needed to improve the mechanical behaviour of such junctions to avoid crack formation. (orig./MM)

  19. Silicon Photonics Cloud (SiCloud)

    DEFF Research Database (Denmark)

    DeVore, P. T. S.; Jiang, Y.; Lynch, M.

    2015-01-01

    Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths.......Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths....

  20. RBS using {sup 28}Si beams

    Energy Technology Data Exchange (ETDEWEB)

    Ophel, T.R. [Australian National Univ., Canberra, ACT (Australia); Mitchell, I.V. [University of Western Ontario, London, ON (Canada). Dept. of Physics

    1996-12-31

    Measurements of RBS using {sup 28}Si beams have been made to evaluate the enhancement of sensitivity that should obtain from kinematic suppression of silicon substrate scattering. Two detection methods were tried. Aside from a surface barrier detector, a magnetic spectrometer, instrumented with a multi-electrode gas focal plane detector, was used to indicate the resolution attainable with low energy {sup 28}Si ions. The results confirm that kinematically suppressed RBS does provide greatly improved sensitivity. 5 refs., 2 figs.

  1. Temperature-dependent 29Si incorporation during deposition of highly enriched 28Si films

    Science.gov (United States)

    Dwyer, K. J.; Kim, H. S.; Simons, D. S.; Pomeroy, J. M.

    2017-11-01

    In this study, we examine the mechanisms leading to 29Si incorporation into highly enriched 28Si films deposited by hyperthermal ion beams at elevated temperatures in the dilute presence of natural abundance silane (SiH4) gas. Enriched 28Si is a critical material in the development of quantum information devices because 28Si is free of nuclear spins that cause decoherence in a quantum system. We deposit epitaxial thin films of 28Si enriched in situ beyond 99.999 98% 28Si onto Si(100) using an ion-beam deposition system and seek to develop the ability to systematically vary the enrichment and measure the impact on quantum coherence. We use secondary ion mass spectrometry to measure the residual 29Si isotope fraction in enriched samples deposited from ≈250 ∘C up to 800 °C. The 29Si isotope fraction is found to increase from 4 ×10-6 at around 800 °C. From these data, we estimate the temperature dependence of the incorporation fraction s of SiH4, which increases sharply from about 2.9 ×10-4 at 500 °C to 2.3 ×10-2 at 800 °C. We determine an activation energy of 1.00(8) eV associated with the abrupt increase in incorporation and conclude that below 500 °C, a temperature-independent mechanism such as activation from ion collisions with adsorbed SiH4 molecules is the primary incorporation mechanism. Direct incorporation from the adsorbed state is found to be minimal.

  2. Antioxidant migration resistance of SiOxlayer in SiOx/PLA coated film.

    Science.gov (United States)

    Huang, Chongxing; Zhao, Yuan; Su, Hongxia; Bei, Ronghua

    2018-02-01

    As novel materials for food contact packaging, inorganic silicon oxide (SiO x ) films are high barrier property materials that have been developed rapidly and have attracted the attention of many manufacturers. For the safe use of SiO x films for food packaging it is vital to study the interaction between SiO x layers and food contaminants, as well as the function of a SiO x barrier layer in antioxidant migration resistance. In this study, we deposited a SiO x layer on polylactic acid (PLA)-based films to prepare SiO x /PLA coated films by plasma-enhanced chemical vapour deposition. Additionally, we compared PLA-based films and SiO x /PLA coated films in terms of the migration of different antioxidants (e.g. t-butylhydroquinone [TBHQ], butylated hydroxyanisole [BHA], and butylated hydroxytoluene [BHT]) via specific migration experiments and then investigated the effects of a SiO x layer on antioxidant migration under different conditions. The results indicate that antioxidant migration from SiO x /PLA coated films is similar to that for PLA-based films: with increase of temperature, decrease of food simulant polarity, and increase of single-sided contact time, the antioxidant migration rate and amount in SiO x /PLA coated films increase. The SiO x barrier layer significantly reduced the amount of migration of antioxidants with small and similar molecular weights and similar physical and chemical properties, while the degree of migration blocking was not significantly different among the studied antioxidants. However, the migration was affected by temperature and food simulant. Depending on the food simulants considered, the migration amount in SiO x /PLA coated films was reduced compared with that in PLA-based films by 42-46%, 44-47%, and 44-46% for TBHQ, BHA, and BHT, respectively.

  3. Si nanoparticle-decorated Si nanowire networks for Li-ion battery anodes

    KAUST Repository

    Hu, Liangbing

    2011-01-01

    We designed and fabricated binder-free, 3D porous silicon nanostructures for Li-ion battery anodes, where Si nanoparticles electrically contact current collectors via vertically grown silicon nanowires. When compared with a Si nanowire anode, the areal capacity was increased by a factor of 4 without having to use long, high temperature steps under vacuum that vapour-liquid-solid Si nanowire growth entails. © 2011 The Royal Society of Chemistry.

  4. Stability of Ta-encapsulating Si clusters on Si(111)-(7x7) surfaces

    CERN Document Server

    Uchida, N; Miyazaki, T; Kanayama, T

    2003-01-01

    Tantalum containing Si cluster ions TaSi sub 1 sub 0 sub - sub 1 sub 3 H sub x sup + were synthesized in an ion trap and deposited onto Si(111)-(7x7) surfaces with a kinetic energy of 18 eV. Scanning tunnelling microscope observations revealed that the clusters adsorbed on the surface without decomposition, consistent with ab initio calculation results, that predicted the clusters would have stable Si-cage structures with a Ta atom at the centre. (rapid communication)

  5. Hybrid Integrated Si/SiN Platforms for Wideband Optical Processing

    Science.gov (United States)

    2017-05-08

    this issue, we developed a new techniques for fabrication of the hybrid Si/SiN material platform based on a high-quality wafer bonding process (Figure 4...The main advantage of this new process based on wafer bonding is the possibility of wafer-scale development of Si/SiN material platform that...34 into the die, the trapped air and chemical by-products of bonding can escape the interface, resulting in the void-free fusion of the two dies

  6. SiCGe/SiC heterojunction and its MEDICI simulation of optoelectronic characteristics

    Science.gov (United States)

    Lü, Zheng; Chen, Zhi-Ming; Pu, Hong-Bin

    2005-06-01

    Optoelectronic characteristics of the SiC1-xGex /SiC heterojunction photodiode are simulated using MEDICI after the theoretical investigation of key properties for SiC1-xGex. The calculations show that SiC1-xGex /SiC with x=0.3 may have a small lattice mismatch with 3C-SiC and a good response to the visible light and the near infrared light. The response spectrum of the SiC1-xGex /SiC heterojunction photodiode, which consists of a p-type SiC1-xGex absorption layer with a doping concentration of 1×1015cm-3, a thickness of 1.6μm and x=0.3, has a peak of 250mA/W at 0.52μm and the peak can even reach 102mA/W at 0.7μm.

  7. Specimen size effect considerations for irradiation studies of SiC/SiC

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E.; Henager, C.H. Jr.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-10-01

    For characterization of the irradiation performance of SiC/SiC, limited available irradiation volume generally dictates that tests be conducted on a small number of relatively small specimens. Flexure testing of two groups of bars with different sizes cut from the same SiC/SiC plate suggested the following lower limits for flexure specimen number and size: Six samples at a minimum for each condition and a minimum bar size of 30 x 6.0 x 2.0 mm{sup 3}.

  8. Next Generation, Si-Compatible Materials and Devices in the Si-Ge-Sn System

    Science.gov (United States)

    2015-10-09

    Photoluminescence from Ge1-x-ySixSny, ternaries and LEDs: Synthesis of light emitting Ge1-x-ySixSny, materials with tunable wavelengths over a wide range in the...AFRL-AFOSR-VA-TR-2016-0044 Next generation, Si-compatible materials and devices in the Si-Ge-Sn system John Kouvetakis ARIZONA STATE UNIVERSITY Final...4. TITLE AND SUBTITLE Next generation, Si-compatible materials and devices in the Si-Ge-Sn system 5a. CONTRACT NUMBER FA9550-12-1-0208 5b. GRANT

  9. Electrical Conductivity of SiC/Si Composites Obtained from Wood Preforms

    Science.gov (United States)

    Béjar, Marco Antonio; Mena, Rodrigo; Toro, Juan Esteban

    2011-02-01

    Biomorphic SiC/Si composites were produced from pine and beech wood, and the corresponding electrical conductivity was determined as a function of the temperature. Firstly, wood preforms were pyrolized at 1050 °C in nitrogen. Then, the pyrolized preforms were impregnated with liquid silicon and kept at 1600 °C for 2 h in vacuum. The SiC/Si composites were obtained due to the produced carbothermal reaction. As expected, the resulting electrical conductivity of these composites increased with the temperature and with the silicon content.

  10. siPRED: Predicting siRNA Efficacy Using Various Characteristic Methods

    Science.gov (United States)

    Pan, Wei-Jie; Chen, Chi-Wei; Chu, Yen-Wei

    2011-01-01

    Small interfering RNA (siRNA) has been used widely to induce gene silencing in cells. To predict the efficacy of an siRNA with respect to inhibition of its target mRNA, we developed a two layer system, siPRED, which is based on various characteristic methods in the first layer and fusion mechanisms in the second layer. Characteristic methods were constructed by support vector regression from three categories of characteristics, namely sequence, features, and rules. Fusion mechanisms considered combinations of characteristic methods in different categories and were implemented by support vector regression and neural networks to yield integrated methods. In siPRED, the prediction of siRNA efficacy through integrated methods was better than through any method that utilized only a single method. Moreover, the weighting of each characteristic method in the context of integrated methods was established by genetic algorithms so that the effect of each characteristic method could be revealed. Using a validation dataset, siPRED performed better than other predictive systems that used the scoring method, neural networks, or linear regression. Finally, siPRED can be improved to achieve a correlation coefficient of 0.777 when the threshold of the whole stacking energy is ≥−34.6 kcal/mol. siPRED is freely available on the web at http://predictor.nchu.edu.tw/siPRED. PMID:22102913

  11. Fabrication of Si/SiO2 Superlattice Microwire Array Solar Cells Using Microsphere Lithography

    Directory of Open Access Journals (Sweden)

    Shigeru Yamada

    2016-01-01

    Full Text Available A fabrication process for silicon/silicon dioxide (Si/SiO2 superlattice microwire array solar cells was developed. The Si/SiO2 superlattice microwire array was fabricated using a microsphere lithography process with polystyrene particles. The solar cell shows a photovoltaic effect and an open-circuit voltage of 128 mV was obtained. The limiting factors of the solar cell performance were investigated from the careful observations of the solar cell structures. We also investigated the influence of the microwire array structure on light trapping in the solar cells.

  12. Brazing of SiC using Cu-Si non reactive alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gasse, A.; Chaumat, G. [CEA Centre d`Etudes de Grenoble, 38 (France). Dept. d`Etudes des Materiaux; Rado, C.; Eustathopoulos, N. [Institut National Polytechnique, 38 - Grenoble (France)

    1995-12-31

    Wetting and adherence of filler metals on ceramics used to be achieved with active elements such as titanium. However, sessile drop experiments had already showed that a Cu 24 at % Si alloy has excellent wetting and adherence properties on SiC substrates under high vacuum without any measurable reactivity. Despite this good wetting, incomplete filling of joints was sometimes observed with such alloys in certain brazing experiments. This discrepancy is explained by a detailed analysis of Cu-Si alloy wetting mechanisms on SiC and confirmed by brazing experiments in different geometries. (authors). 8 figs.

  13. Expanding the Repertoire of Molecular Linkages to Silicon: Si-S, Si-Se, and Si-Te Bonds.

    Science.gov (United States)

    Hu, Minjia; Liu, Fenglin; Buriak, Jillian M

    2016-05-04

    Silicon is the foundation of the electronics industry and is now the basis for a myriad of new hybrid electronics applications, including sensing, silicon nanoparticle-based imaging and light emission, photonics, and applications in solar fuels, among others. From interfacing of biological materials to molecular electronics, the nature of the chemical bond plays important roles in electrical transport and can have profound effects on the electronics of the underlying silicon itself, affecting its work function, among other things. This work describes the chemistry to produce ≡Si-E bonds (E = S, Se, and Te) through very fast microwave heating (10-15 s) and direct thermal heating (hot plate, 2 min) through the reaction of hydrogen-terminated silicon surfaces with dialkyl or diaryl dichalcogenides. The chemistry produces surface-bound ≡Si-SR, ≡Si-SeR, and ≡Si-TeR groups. Although the interfacing of molecules through ≡Si-SR and ≡Si-SeR bonds is known, to the best of our knowledge, the heavier chalcogenide variant, ≡Si-TeR, has not been described previously. The identity of the surface groups was determined by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and depth profiling with time-of-flight-secondary ionization mass spectrometry (ToF-SIMS). Possible mechanisms are outlined, and the most likely, based upon parallels with well-established molecular literature, involve surface silyl radicals or dangling bonds that react with either the alkyl or aryl dichalcogenide directly, REER, or its homolysis product, the alkyl or aryl chalcogenyl radical, RE· (where E = S, Se, and Te).

  14. Spheroidization of Si in Al-12.6wt.%Si at eutectic temperature and its tensile properties

    Science.gov (United States)

    Jiaqing, Zhu; Ya, Liu; Haoping, Peng; Jianhua, Wang; Xuping, Su

    2017-10-01

    The morphology of Si affects significantly the mechanical properties of eutectic Al-Si alloy. In this letter, we report a novel method for the spheroidization of Si in eutectic Al-Si alloy. The results show that Si in eutectic Al-Si alloy could be spheroidized after annealing at eutectic temperature for 3 h. Si phase in the alloy exists in the form of ellipsoidal particles without faceted edges. The surface shape factor of Si phase is 0.8 and the average size of Si particles is only 3.3 µm. Compared with cast eutectic Al-Si alloy, the tensile strength and the hardness of the annealed alloy are decreased by 8.2% and 8.6%, respectively, but its elongation is increased by 79.4%. The fracture mode of Al-12.6%Si alloy annealed at 577 °C for 3 h belongs to ductile fracture.

  15. Silicon electrodeposition from chloride-fluoride melts containing K2SiF6 and SiO2

    Directory of Open Access Journals (Sweden)

    Zhuk Sergey I.

    2017-01-01

    Full Text Available Silicon electrodeposition on glassy carbon from the KF-KCl-K2SiF6, KF-KCl-K2SiF6-KOH and KF-KCl-K2SiF6-SiO2 melts was studied by the cyclic voltammetry. Тhe electroreduction of Si(IV to metallic Si was observed as a single 4-electron wave under all considered conditions. The reactions of cathode reduction of silicon from fluoride and oxyfluoride complexes were suggested. It was shown that the process can be controlled by the preliminary transformation of SiO44- to SiF62- and SiOxFyz-. The influence of the current density on structure and morphology of silicon deposits obtained during galvanostatic electrolysis of the KF-KCl-K2SiF6-SiO2 melt was studied.

  16. Evaluation of band offset at amorphous-Si/BaSi{sub 2} interfaces by hard x-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Takabe, Ryota; Takeuchi, Hiroki; Du, Weijie; Toko, Kaoru; Suemasu, Takashi [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Ito, Keita [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Japan Society for the Promotion of Science (JSPS), Chiyoda, Tokyo 102-0083 (Japan); Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan); Ueda, Shigenori [Synchrotron X-Ray Station at SPring-8, National Institute for Materials Science (NIMS), Sayo, Hyogo 679-5148 (Japan); Quantum Beam Unit, NIMS, Tsukuba, Ibaraki 305-0047 (Japan); Kimura, Akio [Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan)

    2016-04-28

    The 730 nm-thick undoped BaSi{sub 2} films capped with 5 nm-thick amorphous Si (a-Si) intended for solar cell applications were grown on Si(111) by molecular beam epitaxy. The valence band (VB) offset at the interface between the BaSi{sub 2} and the a-Si was measured by hard x-ray photoelectron spectroscopy to understand the carrier transport properties by the determination of the band offset at this heterointerface. We performed the depth-analysis by varying the take-off angle of photoelectrons as 15°, 30°, and 90° with respect to the sample surface to obtain the VB spectra of the BaSi{sub 2} and the a-Si separately. It was found that the barrier height of the a-Si for holes in the BaSi{sub 2} is approximately −0.2 eV, whereas the barrier height for electrons is approximately 0.6 eV. This result means that the holes generated in the BaSi{sub 2} layer under solar radiation could be selectively extracted through the a-Si/BaSi{sub 2} interface, promoting the carrier separation in the BaSi{sub 2} layer. We therefore conclude that the a-Si/BaSi{sub 2} interface is beneficial for BaSi{sub 2} solar cells.

  17. Optical properties investigation of [nc-Si:SiO{sub 2}/SiO{sub 2}]{sub 30} periodic multilayer films

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Liang; Zhu, Jiang; Wei, Shenjin; Zhu, Huanfeng; Chen, Kun; Xu, Da [Fudan University, Department of Optical Science and Engineering, Shanghai (China); Li, Jing [Fudan University, Department of Optical Science and Engineering, Shanghai (China); Fudan University, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Shanghai (China)

    2012-11-15

    The optical properties of 30-layer [nc-Si:SiO{sub 2}/SiO{sub 2}]{sub 30} periodic films have been studied. The films were prepared by alternately evaporating SiO and SiO{sub 2} onto Si(100) substrates, followed by annealing at 1100 {sup circle} C. Spectroscopic ellipsometry spectrum analysis was used to determine the optical constants of the samples via the Forouhi-Bloomer model. The optical bandgap of a single periodic film is calculated. The photoluminescence (PL) spectra of three samples with different thicknesses clearly show that there are two physical origins of the PL process. (orig.)

  18. Electrospun a-Si using Liquid Silane/Polymer Inks

    Energy Technology Data Exchange (ETDEWEB)

    D.L. Schulz; J.M. Hoey; J. Smith; J. Lovaasen; C. Braun; X. Dai; K. Anderson; A. Elangovan; X. Wu; S. Payne; K. Pokhodnya; I. Akhatov; L. Pederson; P. Boudjouk

    2010-12-01

    Amorphous silicon nanowires (a-SiNWs) were prepared by electrospinning cyclohexasilane (Si{sub 6}H{sub 12}) admixed with polymethylmethacrylate (PMMA) in toluene. Raman spectroscopy characterization of these wires (d {approx} 50-2000 nm) shows 350 C treatment yields a-SiNWs. Porous a-SiNWs are obtained using a volatile polymer.

  19. A porous Si-emitter crystalline-Si solar cell with 18.97% efficiency

    Science.gov (United States)

    Wang, Liang-Xing; Zhou, Zhi-Quan; Hao, Hong-Chen; Lu, Ming

    2016-10-01

    A p-n junction was made on p-type Si wafer (15 × 15 × 0.2 mm3 in size) via phosphorous diffusion at 900 °C. Porous Si (PSi) with ultralow reflectivity (ultraviolet and visible regimes) was achieved by etching a Ag-coated n+ Si emitter in a solution of HF, H2O2 and H2O. The PSi was found to mainly consist of Si nanocrystallites with bandgap widths larger than that of bulk Si. Compared to other micro- or nanostructured Si-based crystalline-Si solar cells found in the literature, this PSi one possessed the feature of a graded band gap, which helped to suppress the surface recombination. In addition, the preparation method was readily applicable on large-scale-sized Si wafers. Also, the PSi acted as a down-shifter that absorbed the ultraviolet/violet light to which the Si solar cell responded poorly, and emitted a red one to which the cell responded well. Front and rear surface passivations were conducted by using SiO2 and Al2O3, respectively, to suppress the surface recombination and to facilitate the charge transfer. Indium-tin-oxide was used as the front electrode that was in good contact with the PSi, and Al was used as the rear one. For such a PSi-emitter crystalline-Si solar cell, enhancements of the photovoltaic responses from the ultraviolet to near-infrared regimes were observed; the open-circuit voltage was 606.8 mV, the short-circuit current density was 40.13 mA cm-2, the fill factor was 0.779 and the conversion efficiency was 18.97%.

  20. Diffusion of carbon oxides in SiO2 during SiC oxidation

    Science.gov (United States)

    Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori; Kageshima, Hiroyuki; Uematsu, Masashi

    2013-03-01

    SiC is a wide-band-gap semiconductor and has an advantage to fabricate electronic devices such as MOSFETs due to the ability to thermally oxidize to SiO2. Despite many studies conducted on the oxidation of SiC, the kinetics such as diffusion and interface reaction is not fully understood. Here, we focus on the diffusion process during SiC oxidation, and clarify the diffusion mechanism of carbon oxides (CO and CO2) in SiO2 by means of density functional calculations. Our calculations demonstrate that the CO without any chemical bonds with host SiO2 is stabilized while the CO2 is incorporated between Si-O bonds of SiO2 to form a carbonate group. The energy of CO2 is found to be lower than that of CO by 3.7 eV, indicating that the most stable form of carbon oxides in SiO2 is CO2. Furthermore, the calculated energy barriers for diffusion of CO and CO2 are found to be 0.1 and 1.8 eV, respectively. These results thus imply that CO molecules easily react with oxidant such as O2 to form CO2 and the outward diffusion of resultant CO2 is rate-limiting. Indeed, the estimated activation energy for CO2 diffusion (3.5 eV) reasonably agrees with that for Si-face SiC (3.1 eV) obtained by Deal-Grove model considering product gas out-diffusion. This work was supported in part by Grant-in-Aid for Scientific Research (No. 24560025) from the Japan Society for the Promotion of Science.

  1. Microstructural evolution of SiC/Cu-Si composites obtained through reactive infiltration; Evolucion microestructural de composites SiC/aleaciones CuSi obtenidos a traves de infiltracion ractiva

    Energy Technology Data Exchange (ETDEWEB)

    Cornejo, J.; Ordonez, S.; Iturriza, I.

    2010-07-01

    The microstructural evolution of composites of SiC/Cu-Si alloys obtained through process of reactive infiltration to 1400 degree centigrade was studied. Three zones were detected in the obtained composites: the reaction zone, the transition zone and the infiltrated zone. In the reaction zone and transition zone the resulting microstructure was composed of a metallic phase, graphite laminae and SiC particles. It was found that SiC decomposes into these areas because of the alloy Cu-Si, so the available Si forms a liquid solution that a room temperature consisted of a a solid solution and a {gamma} phase (Cu{sub 5}Si). The carbon resulting from the decomposition of SiC precipitated as graphite laminae. In addition, the SiC decomposition was decreasing as the initial amount of Si in the alloy increased. (Author) 37 refs.

  2. Diffusion mobilities in the fcc{sub A}1 Cu-Si, Al-Si and Al-Cu-Si alloys

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Dachun [School of Mechanical Engineering, Xiangtan University, Xiangtan, Hunan Province 411105 (China); Liu, Ya [School of Materials Science and Engineering, Changzhou University, 1 Gehu Road, Changzhou, Jiangsu Province 213164 (China); Su, Xuping, E-mail: sxping@cczu.edu.cn [School of Mechanical Engineering, Xiangtan University, Xiangtan, Hunan Province 411105 (China); School of Materials Science and Engineering, Changzhou University, 1 Gehu Road, Changzhou, Jiangsu Province 213164 (China); Wang, Jianhua; Tu, Hao [School of Materials Science and Engineering, Changzhou University, 1 Gehu Road, Changzhou, Jiangsu Province 213164 (China); Huang, Jianfeng [School of Mechanical Engineering, Xiangtan University, Xiangtan, Hunan Province 411105 (China)

    2013-02-25

    Highlights: Black-Right-Pointing-Pointer The atomic mobilities of fcc Cu-Si, Al-Si and Al-Cu-Si alloys have been assessed. Black-Right-Pointing-Pointer The calculated results agree well with various experimental diffusivities. Black-Right-Pointing-Pointer The temperature and concentration dependence are taken into consideration. Black-Right-Pointing-Pointer The mobility parameters obtained can be used to predict many diffusion phenomena. - Abstract: Based on the available thermodynamic parameters and experimental data of self-diffusivity, impurity diffusivity, intrinsic diffusivity, tracer diffusivity and interdiffusivity in the Cu-Si, Al-Si and Al-Cu-Si alloys, the atomic mobilities of Cu, Al and Si in face-centered cubic (fcc{sub A}1) Cu-Si, Al-Si and Al-Cu-Si alloys have been critically assessed as a function of temperature and composition using the CALPHAD-type and DICTRA software package. Comparisons between the calculated and measured coefficients reveal that most of the diffusivities can be reproduced satisfactorily. The obtained mobility parameters can be used to study diffusion-related characteristics for fcc{sub A}1 Cu-Si, Al-Si and Al-Cu-Si alloys.

  3. How to make the ionic Si-O bond more covalent and the Si-O-Si linkage a better acceptor for hydrogen bonding.

    Science.gov (United States)

    Grabowsky, Simon; Hesse, Maxie F; Paulmann, Carsten; Luger, Peter; Beckmann, Jens

    2009-05-18

    Variation of a bond angle can tune the reactivity of a chemical compound. To exemplify this concept, the nature of the siloxane linkage (Si-O-Si), the most abundant chemical bond in the earth's crust, was examined using theoretical calculations on the molecular model compounds H(3)SiOSiH(3), (H(3)Si)(2)OHOH, and (H(3)Si)(2)OHOSiH(3) and high-resolution synchrotron X-ray diffraction experiments on 5-dimethylhydroxysilyl-1,3-dihydro-1,1,3,3-tetramethyl-2,1,3-benzoxadisilole (1), a molecular compound that gives rise to the formation of very rare intermolecular hydrogen bonds between the silanol groups and the siloxane linkages. For theoretical calculations and experiment, electronic descriptors were derived from a topological analysis of the electron density (ED) distribution and the electron localization function (ELF). The topological analysis of an experimentally obtained ELF is a newly developed methodology. These descriptors reveal that the Si-O bond character and the basicity of the siloxane linkage strongly depend on the Si-O-Si angle. While the ionic bond character is dominant for Si-O bonds, covalent bond contributions become more significant and the basicity increases when the Si-O-Si angle is reduced from linearity to values near the tetrahedral angle. Thus, the existence of the exceptional intermolecular hydrogen bond observed for 1 can be explained by its very small strained Si-O-Si angle that adopts nearly a tetrahedral angle.

  4. Porous nC-Si/SiOx nanostructured layer on Si substrate with tunable photoluminescent properties fabricated by direct, precursor-free microplasma irradiation in air

    Science.gov (United States)

    Wang, Tao; Hu, Mingshan; Yang, Bin; Wang, Xiaolin; Liu, Jingquan

    2018-03-01

    Porous nC-Si/SiOx photoluminescent nanostructured layer is fabricated by direct, precursor-free microplasma irradiation on Si substrate in air. It is confirmed that the deposited layer has porous and cluster-like structures by scanning electron microscopy (SEM) and profile scanning. Fourier transform infrared transmission (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) results indicate the produced layer is actually composed of nanocrystalline silicon (nC-Si) embedded in SiOx matrix. Transmission electron microscopy (TEM) and Raman results show the mean particle size of nC-Si is mainly between 2 and 4 nm and the highest crystalline volume fraction reaches 86.9%. The photoluminescence (PL) measurement of nC-Si/SiOx layer exhibited a broad band centered at 1.7-1.9 eV, ranging from 1.2-2.4 eV, and could be tuned by varying the applied voltage. The synthetical mechanisms are discussed to explain the PL properties of the layers. We propose that the energetic ions bombing induced by high compressed electric field near the Si surface is the main reason for porous nC-Si/SiOx formation. Maskless deposition of the line pattern of nC-Si/SiOx layer was also successfully fabricated. This simple, maskless, vacuum-free and precursor-free technique could be used in various potential optoelectronics and biological applications in the future.

  5. Fluorescence enhancement of single DNA molecules confined in Si/SiO2 nanochannels

    DEFF Research Database (Denmark)

    Westerlund, F.; Persson, Karl Fredrik; Kristensen, Anders

    2010-01-01

    We demonstrate that the detected emission intensity from YOYO-labeled DNA molecules confined in 180 nm deep Si/SiO2 nano-funnels changes significantly and not monotonically with the width of the funnel. This effect may be of importance for quantitative fluorescence microscopy and for experiments...

  6. Green bean biofortification for Si through soilless cultivation: plant response and Si bioaccessibility in pods.

    Science.gov (United States)

    Montesano, Francesco Fabiano; D'Imperio, Massimiliano; Parente, Angelo; Cardinali, Angela; Renna, Massimiliano; Serio, Francesco

    2016-08-17

    Food plants biofortification for micronutrients is a tool for the nutritional value improvement of food. Soilless cultivation systems, with the optimal control of plant nutrition, represent a potential effective technique to increase the beneficial element content in plant tissues. Silicon (Si), which proper intake is recently recommended for its beneficial effects on bone health, presents good absorption in intestinal tract from green bean, a high-value vegetable crop. In this study we aimed to obtain Si biofortified green bean pods by using a Si-enriched nutrient solution in soilless system conditions, and to assess the influence of boiling and steaming cooking methods on Si content, color parameters and Si bioaccessibility (by using an in vitro digestion process) of pods. The Si concentration of pods was almost tripled as a result of the biofortification process, while the overall crop performance was not negatively influenced. The Si content of biofortified pods was higher than unbiofortified also after cooking, despite the cooking method used. Silicon bioaccessibility in cooked pods was more than tripled as a result of biofortification, while the process did not affect the visual quality of the product. Our results demonstrated that soilless cultivation can be successfully used for green bean Si biofortification.

  7. Atomic state and characterization of nitrogen at the SiC/SiO2 interface

    Science.gov (United States)

    Xu, Y.; Zhu, X.; Lee, H. D.; Xu, C.; Shubeita, S. M.; Ahyi, A. C.; Sharma, Y.; Williams, J. R.; Lu, W.; Ceesay, S.; Tuttle, B. R.; Wan, A.; Pantelides, S. T.; Gustafsson, T.; Garfunkel, E. L.; Feldman, L. C.

    2014-01-01

    We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO2 interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO2). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs.

  8. Thermographic Characterization of Impact Damage in SiC/SiC Composite Materials

    Science.gov (United States)

    Fox, Dennis S.; Cosgriff, Laura M.; Bhatt, Ramakrishna; Choi, Sung R.

    2005-01-01

    SiC/SiC composite materials targeted as turbine components for next-generation aero-engines are being investigated at NASA Glenn Research Center. In order to examine damage mechanisms in these materials, SiC/SiC coupons were impacted with 1.59 mm diameter steel spheres at increasing velocities from 115 m/s to 400 m/s. Pulsed thermography, a nondestructive evaluation technique that monitors the thermal response of a sample over time, was utilized to characterize the impact damage. A thermal standard of similar material was fabricated to aid in the interpretation of the thermographic data and to provide information regarding thermography system detection capabilities in 2.4 mm thick SiC/SiC composite materials. Flat bottom holes at various depths with aspect ratios greater than 2.5 were detectable in the thermal images. In addition, the edges of holes at depths of 1.93 mm into the sample were not as resolvable as flat bottom holes closer to the surface. Finally, cooling behavior was characterized in SiC/SiC materials and used to determine impact damage depth within an 8.5% error of a known depth.

  9. SiC-Si as a support material for oxygen evolution electrode in PEM steam electrolysers

    DEFF Research Database (Denmark)

    Nikiforov, Aleksey; Tomás García, Antonio Luis; Petrushina, Irina

    2011-01-01

    The need of higher energy efficiency in hydrogen production has promoted the research on improved catalysts for water electrolysis. In this work, a novel supported catalyst for oxygen evolution electrodes was prepared and characterized with different techniques. IrO2 supported on a SiC/Si composi...

  10. Computer aided cooling curve analysis for Al-5Si and Al-11Si alloys

    African Journals Online (AJOL)

    user

    The effect of grain refiner, modifier, and combination of grain refiner cum modifier was studied on Al-5Si and Al-11Si alloys using computer aided cooling curve analysis. For combined grain refinement and modification effect, Al-Ti-B-Sr single master alloy was developed that acted as both grain refiner and modifier.

  11. A Sensitive Optical Sensor Based on DNA Labeled Si@SiO 2 Core ...

    Indian Academy of Sciences (India)

    11

    A Sensitive Optical Sensor Based on DNA Labeled Si@SiO2 Core–Shell Nanoparticle for the Detection of Hg2+ ions in Environmental water samples. Krishnan Srinivasan1, Kathavarayan Subramanian1, Aruliah Rajasekar2, Kadarkarai Murugan3,. Giovanni Benelli4,5 and Kannaiyan Dinakaran6*. 1Department of ...

  12. Preparation of Si 3 N 4–SiC composites by microwave route

    Indian Academy of Sciences (India)

    Decrease in relative density has manifested in the reduction of fracture toughness and microhardness values of the composite with increase in SiC content although the good sintering of matrix Si3N4 limits the decrease of fracture toughness. Highest value of fracture toughness of 6.1 MPa m1/2 is observed in 10 vol.

  13. Current–voltage studies on β-FeSi2/Si heterojunction

    Indian Academy of Sciences (India)

    later treated by pulsed laser. Temperature of thermal annealing and diode area ... Silicide; semiconducting silicide; heterojunction; pulsed laser; I–V characteristics. 1. Introduction β-FeSi2 is a semiconducting silicide .... region and the electric field due to ionized impurities in Si yields a current in the opposite direction to that ...

  14. Structure of thin CrSi{sub 2} films on Si(0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Filonenko, O.; Falke, M.; Hortenbach, H.; Henning, A.; Beddies, G.; Hinneberg, H.-J

    2004-04-15

    The morphology and texture of CrSi{sub 2} films grown on Si(0 0 1) is reported. The films have been prepared under ultra high vacuum conditions by reactive codeposition and by the template method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses have been performed to investigate the influence of the substrate temperature and the template thickness on the silicide texture and morphology. XRD evidences that the major part of CrSi{sub 2} crystallites grows with an orientation of CrSi{sub 2}(0 0 1)[1 0 0] parallel Si(0 0 1)[1 1 0] within all present experiments. Considering the morphology and preferred orientation of the crystallites the substrate temperature of 700 deg. C is determined to be optimal for the codeposition growth method. A further improvement of the CrSi{sub 2}(0 0 1) texture and an increase of the grain size by an order of magnitude is observed after deposition of 0.5 nm Cr onto the Si(0 0 1) substrate at room temperature prior to the codeposition of Cr and Si at 700 deg. C.

  15. Weld microstructure in cast AlSi9/SiC(p metal matrix composites

    Directory of Open Access Journals (Sweden)

    J. Wysocki

    2009-04-01

    Full Text Available Welded joint in cast AlSi9/SiC/20(p metal matrix composite by manual TIG arc welding using AlMg5 filler metal has been described inhis paper. Cooling curves have been stated, and the influence in distribution of reinforced particles on crystallization and weldmicrostructure. Welded joint mechanical properties have been determined: hardness and tensile.

  16. Computer aided cooling curve analysis for Al-5Si and Al-11Si alloys ...

    African Journals Online (AJOL)

    The effect of grain refiner, modifier, and combination of grain refiner cum modifier was studied on Al-5Si and Al-11Si alloys using computer aided cooling curve analysis. For combined grain refinement and modification effect, Al-Ti-B-Sr single master alloy was developed that acted as both grain refiner and modifier.

  17. Proton conductivity and methanol permeability of Nafion-SiO2/SiWA composite membranes

    Science.gov (United States)

    Thiam, Hui San; Chia, Min Yan; Cheah, Qiao Rou; Koo, Charlene Chai Hoon; Lai, Soon Onn; Chong, Kok Chung

    2017-04-01

    Proton exchange membranes for a direct methanol fuel cell (DMFC) were prepared by incorporating silica/silicotungstic acid (SiO2/SiWA) inorganic composite into a Nafion polymer. The effects of SiO2/SiWA content on proton conductivity of membranes were investigated by using a four-probe conductivity cell. Methanol permeability of composite membrane was also determined by using a homemade diffusion cell and gas chromatography technique. It was found that proton conductivity of the composite membranes decreased with SiO2/SiWA content, however the highest proton conductivity achieved was 11% greater than the pure recast Nafion membrane. The methanol permeability of composite membrane was much lower than that of pure recast Nafion, in a reduction of 58% which indicated a better resistance to fuel crossover. Nafion-SiO2/SiWA composite membrane showed promising advantages over pure Nafion on electrochemical properties such as proton conductivity and fuel crossover and it is potentially attractive for use in DMFC.

  18. Direct observation of quantum confinement of Si nanocrystals in Si-rich nitrides

    Science.gov (United States)

    Nguyen, P. D.; Kepaptsoglou, D. M.; Ramasse, Q. M.; Olsen, A.

    2012-02-01

    The band gap of the active layers in stacked Si-based tandem solar cells can be fine tuned by changing the size of embedded silicon nanocrystals (Si NCs). Although SiO2 matrices have been predominantly used for such applications, nitride phases have recently emerged as a promising alternative. In this paper, we use high-resolution scanning transmission electron microscopy and energy-loss spectroscopy to report on the electronic structure of individual Si NCs embedded in silicon nitride films. Si NCs were produced by rf sputtering and exhibited controllable crystallite size and quality via different thermal annealing conditions. Quantum confinement effects were observed through a blue shift in both conduction band edges and volume plasmon energies as a function of particle size and structure. We show that, in good agreement with theoretical models, the volume plasmon energy Ep (eV) is related to the size d (nm) of Si NCs by Ep = 16.89+ 23.90/d2. Lattice distortion in twinned Si NCs and dangling bonds at defect centers are shown to be the cause of a weakening in quantum size effects and a reduction in the light emission efficiency of the films. Both electron spectroscopy and optical results are consistent in explaining the correlation between structure and optoelectronic properties of Si NCs.

  19. Fabrication and Characteristics of an nc-Si/c-Si Heterojunction MOSFETs Pressure Sensor

    Directory of Open Access Journals (Sweden)

    Xiaofeng Zhao

    2012-05-01

    Full Text Available A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor.

  20. Fabrication and characteristics of an nc-Si/c-Si heterojunction MOSFETs pressure sensor.

    Science.gov (United States)

    Zhao, Xiaofeng; Wen, Dianzhong; Li, Gang

    2012-01-01

    A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W) ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor.

  1. Reactivity and wettability of SiC by Ni and Ni-Si alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rado, C. [INPG, 38 - Saint Martin d`Heres (France). LTPCM; Kalogeropoulou, S. [INPG, 38 - Saint Martin d`Heres (France). LTPCM; Eustathopoulos, N. [INPG, 38 - Saint Martin d`Heres (France). LTPCM

    1996-08-01

    Wettability of SiC by Ni and Ni-Si alloys was studied at 1633K by the sessile drop technique under high vacuum or pure He. It is shown that reactivity in this system can be controlled and even nearly suppressed while obtaining good wetting and strong interface. (orig.)

  2. Progressive degradation in a-Si: H/SiN thin film transistors

    NARCIS (Netherlands)

    Merticaru, A.R.; Mouthaan, A.J.; Kuper, F.G.

    2003-01-01

    In this paper we present the study of gate-stress induced degradation in a-Si:H/SiN TFTs. The drain current transient during gate bias stress (forward or reverse bias) and subsequent relaxation cannot be fitted with the models existent in the literature but it shows to be described by a progressive

  3. Study of dynamics of charge trapping in a-Si:H/SiN TFTs

    NARCIS (Netherlands)

    Merticaru, A.R.; Mouthaan, A.J.; Kuper, F.G.

    2001-01-01

    In this paper we present the study of the failure mechanism responsible for long-term degradation that ultimately leads to instability in a-Si:H/SiN TFTs. The experimental data points we obtain by monitoring in-situ the drain current during gate bias stress (forward and reverse bias) and relaxation

  4. Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

    Directory of Open Access Journals (Sweden)

    David J. Lockwood

    2016-03-01

    Full Text Available Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 – 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots, two dimensions (corresponding to quantum wires, and one dimension (corresponding to quantum wells. The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW heterojunctions (HJs with a Si/Ge NW diameter in the range 50 – 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si

  5. SiGe growth on patterned Si(001) substrates : Surface evolution and evidence of modified island coarsening

    NARCIS (Netherlands)

    Zhang, J.J.; Stoffel, M.; Rastelli, A.; Schmidt, O.G.; Jovanovi?, V.; Nanver, L.K.; Bauer, G.

    2007-01-01

    The morphological evolution of both pits and SiGe islands on patterned Si(001) substrates is investigated. With increasing Si buffer layer thickness the patterned holes transform into multifaceted pits before evolving into inverted truncated pyramids. SiGe island formation and evolution are studied

  6. Synthesis and characterization of AlTiSiN/CrSiN multilayer coatings by cathodic arc ion-plating

    Science.gov (United States)

    Yang, B.; Tian, C. X.; Wan, Q.; Yan, S. J.; Liu, H. D.; Wang, R. Y.; Li, Z. G.; Chen, Y. M.; Fu, D. J.

    2014-09-01

    AlTiSiN/CrSiN multilayer coatings were deposited on Si (1 0 0) and cemented carbide substrates using Cr, AlTi cathodes and SiH4 gases by cathodic arc ion plating system. The influences of SiH4 gases flowrate on the structural and mechanical properties of the coatings were investigated, systematically. AlTiSiN/CrSiN coatings exhibit a B1 NaCl-type nano-multilayered structure in which the CrSiN nano-layers alternate with AlTiSiN nano-layers with multiple orientations of crystal planes indicated by XRD patterns and TEM. Si contents of the coatings increase with increasing SiH4 flowrate. The hardness of the coatings increases to the maximum value of 3500 Hv0.05 with increasing SiH4 flowrate from 20 to 40 sccm and then decreases with further addition of SiH4 gases. A higher adhesive force of 73 N is obtained at the flowrate of 48 sccm. The coatings exhibit different tribological performance when the mating materials were varied from Si3N4 to cemented carbide balls and the variation of friction coefficients of the coatings against Si3N4 influenced by SiH4 flowrate are not obvious as against cemented carbide balls.

  7. Realization of Colored Multicrystalline Silicon Solar Cells with SiO2/SiNx:H Double Layer Antireflection Coatings

    Directory of Open Access Journals (Sweden)

    Minghua Li

    2013-01-01

    Full Text Available We presented a method to use SiO2/SiNx:H double layer antireflection coatings (DARC on acid textures to fabricate colored multicrystalline silicon (mc-Si solar cells. Firstly, we modeled the perceived colors and short-circuit current density (Jsc as a function of SiNx:H thickness for single layer SiNx:H, and as a function of SiO2 thickness for the case of SiO2/SiNx:H (DARC with fixed SiNx:H (refractive index n=2.1 at 633 nm, and thickness = 80 nm. The simulation results show that it is possible to achieve various colors by adjusting the thickness of SiO2 to avoid significant optical losses. Therefore, we carried out the experiments by using electron beam (e-beam evaporation to deposit a layer of SiO2 over the standard SiNx:H for 156×156 mm2 mc-Si solar cells which were fabricated by a conventional process. Semisphere reflectivity over 300 nm to 1100 nm and I-V measurements were performed for grey yellow, purple, deep blue, and green cells. The efficiency of colored SiO2/SiNx:H DARC cells is comparable to that of standard SiNx:H light blue cells, which shows the potential of colored cells in industrial applications.

  8. Simulations of Proton Implantation in Silicon Carbide (SiC)

    Science.gov (United States)

    2016-03-31

    philip.feng@case.edu Abstract: We report on exploratory research effort with preliminary results on investigating fundamental radiation effects in...of implanting protons (hydrogen ions, H+) into SiC thin layers on silicon (Si) substrate, and explore the ion implantation conditions that are...create SiC-on-insulator (SiC-on-SiO2) films and structures [4,5]. It is important to understand and control the implantation depth. Presented here

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

    Science.gov (United States)

    Wang, Donghai; Yi, Ran; Dai, Fang

    2016-02-23

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

  10. Optical Diagnostics on HIT-SI3

    Science.gov (United States)

    Everson, Christopher; Jarboe, Thomas; Morgan, Kyle

    2016-10-01

    Interferometry and Thomson Scattering are implemented on the HIT-SI3 (Helicity Injected Torus - Steady Inductive 3) device to provide time resolved measurements of electron density and spatially resolved measurements of electron temperature, respectively. HIT-SI3 is a modification of the original HIT-SI apparatus that uses three injectors instead of two. The scientific aim of HIT-SI3 is to develop a deeper understanding of how injector behavior and interactions influence current drive and spheromak stability. The interferometer system makes use of an intermediate frequency between two parallel 184.3 μm Far-Infrared (FIR) laser cavities which are optically pumped by a CO2 laser. The phase shift in this beat frequency due to the plasma index of refraction is used to calculate the line-integrated electron density. To measure the electron temperature, Thomson Scattered light from a 20 J (1 GW pulse) Ruby laser off of free electrons in the HIT-SI3 plasma is measured simultaneously at four locations across the spheromak (nominally 23 cm minor radius). Polychromators bin the collected light into 3 spectral bands to detect the relative level of scattering. Work supported by the D.O.E.

  11. Formation and thermoelectric properties of Si/CrSi2/Si(001) heterostructures with stressed chromium disilicide nanocrystallites

    Science.gov (United States)

    Goroshko, Dmitry; Chusovitin, Evgeniy; Bezbabniy, Dmitry; Dózsa, Laszlo; Pécz, Bela; Galkin, Nikolay

    2015-05-01

    Three-layer heterostructures with embedded CrSi2 nanocrystallites were grown using molecular-beam epitaxy. The nanocrystallites have epitaxial orientation to the silicon lattice and are subjected to anisotropic compressive stress in the CrSi2 [001] direction. The thermoelectric power factor of the heterostructure is about 5 times higher than that in the substrate at 300-480 K. Taking into consideration the ratio of nanocomposite and substrate thickness, the real power factor is expected to be 2-3 orders higher than the measured one and it reaches 3200 μW K-2 m-1 at 470 K.[Figure not available: see fulltext.

  12. Carbon clusters as possible defects at the SiC-SiO2 interface

    Science.gov (United States)

    Liu, Yingdi; Dang, Hongli; Liu, Yang; Li, Ying; Chisholm, Matthew; Biggerstaff, Trinity; Duscher, Gerd; Wang, Sanwu

    2009-03-01

    High state densities in the band gap of the SiC-SiO2 interface significantly reduce the channel mobilities in SiC-based high-temperature/high-power microelectronics. Investigations of the nature of the interface defects are thus of great importance. While several possible defects including very small carbon clusters with up to four carbon atoms have been identified by first-principles theory, larger carbon clusters as possible defects have attracted less attention. Here, we report first-principles quantum-mechanical calculations for two larger carbon clusters, the C10 ring and the C20 fullerence, at the SiC-SiO2 interface. We find that both carbon clusters introduce significant states in the band gap. The states extend over the entire band gap with higher densities in the upper half of the gap, thus accounting for some of the interface trap densities observed experimentally.

  13. Relationship between 4H-SiC/SiO2 transition layer thickness and mobility

    Science.gov (United States)

    Biggerstaff, T. L.; Reynolds, C. L.; Zheleva, T.; Lelis, A.; Habersat, D.; Haney, S.; Ryu, S.-H.; Agarwal, A.; Duscher, G.

    2009-07-01

    The interfacial region between silicon carbide (SiC) and its native oxide contains a high density of interfacial traps, which is considered a major problem leading to a lower mobility that has hindered SiC metal oxide semiconductor field effect transistors from reaching their theoretical expectations. We investigate the microstructure and chemistry of the 4H-SiC/SiO2 interface due to variations in nitric oxide annealing and aluminum implantation using Z-contrast imaging and electron energy loss spectroscopy. A transition layer with a carbon to silicon ratio greater than 1 is consistently observed on the SiC side of the interface in each of these samples, and the width of this transition layer is found to be inversely related to the effective channel mobility measured on fabricated devices.

  14. Carbon Clusters as Possible Defects in the SiC-SiO2 Interface

    Energy Technology Data Exchange (ETDEWEB)

    Dang, Hongli [ORNL; Ramkumar, Gudipati [unknown; Yang, Liu [unknown; Li, Ying [ORNL; Peterson, Heather [unknown; Chisholm, Matthew F [ORNL; Biggerstaff, Trinity Leigh [ORNL; Duscher, Gerd [University of Tennessee, Knoxville (UTK); Wang, Sanwu [ORNL

    2009-01-01

    High state densities in the band gap of the SiC-SiO2 interface significantly reduce the channel mobilities in SiC-based high-temperature/high-power microelectronics. Investigations of the nature of the interface defects are thus of great importance. While several possible defects including very small carbon clusters with up to four carbon atoms have been identified by first-principles theory, larger carbon clusters as possible defects have attracted less attention. Here, we report first-principles quantum-mechanical calculations for two larger carbon clusters, the C10 ring and the C20 fullerence, in the SiC-SiO2 interface. We find that both carbon clusters introduce significant states in the band gap. The states extend over the entire band gap with higher densities in the upper half of the gap, thus accounting for some of the interface trap densities observed experimentally

  15. On the compliant behaviour of free-standing Si nanostructures on Si(001) for Ge nanoheteroepitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kozlowski, Grzegorz

    2012-04-24

    Selective chemical vapor deposition Ge heteroepitaxy approaches for high quality Ge nanostructure growth with reasonable thermal budget must be developed for local Ge photonic module integration. A promising vision is offered by the compliant substrate effects within nanometer scale Ge/Si heteroepitaxial structures. Here, in contrast to the classical Ge deposition on bulk Si substrates, the thermal and lattice mismatch strain energy accumulated in the Ge epilayer is partially shifted to the free-standing Si nanostructure. This strain partitioning phenomenon is at the very heart of the nanoheteroepitaxy theory (NHE) and, if strain energy levels are correctly balanced, offers the vision to grow defect-free nanostructures of lattice mismatched semiconductors on Si. In case of the Ge/Si heterosystem with a lattice mismatch of 4.2%, the strain partitioning phenomenon is expected to be triggered when free-standing Si nanopillars with the width of 50 nm and below are used. In order to experimentally verify NHE with its compliant substrate effects, a set of free-standing Ge/Si nanostructures with diameter ranging from 150 to 50 nm were fabricated and investigated. The main limitation corresponds to a simultaneous detection of (a) the strain partitioning phenomenon between Ge and Si and (b) the absence of defects on the nano-scale. In this respect, synchrotron-based grazing incidence X-ray diffraction was applied to study the epitaxial relationship, defect and strain characteristics with high resolution and sensitivity in a non-destructive way. Raman spectroscopy supported by finite element method calculations were used to investigate the strain distribution within a single Ge/Si nanostructure. Special focus was devoted to transmission electron microscopy to determine the quality of the Ge epilayer. It was found, that although high quality Ge nanoclusters can be achieved by thermal annealing on Si pillars bigger than 50 nm in width, no proof of strain partitioning

  16. Coadsorption of potassium and oxygen on thin β-FeSi2 overlayers on Si(111)

    Science.gov (United States)

    Kennou, S.; Tan, T. A. Nguyen

    1991-07-01

    We report UPS, AES and WF measurements on the interaction of K and O2 on thin semiconducting epitaxial layers of β-FeSi2 on Si(111). Oxygen was adsorbed on clean and K-covered β-FeSi2 at 300 K and the system was heated up to 900 K with the suicide remaining stable. A correlation of the experimental results indicates that at RT on clean β-FeSi2 oxygen chemisorbs dissociatively on silicon sites and does not interact with iron. In the presence of K oxygen chemisorbs on iron and on silicon sites with an increased sticking coefficient. No potassium oxide was formed. Upon heating up to 800 K SiO2 is formed on the suicide film under conditions in which the suicide remains stable.

  17. Joining of SiC[sub f]/SiC composites for thermonuclear fusion reactors

    Energy Technology Data Exchange (ETDEWEB)

    Ferraris, M. (Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C. Duca degli Abruzzi 24, I-10129 Torino (Italy)); Badini, C. (Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C. Duca degli Abruzzi 24, I-10129 Torino (Italy)); Montorsi, M. (Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C. Duca degli Abruzzi 24, I-10129 Torino (Italy)); Appendino, P. (Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C. Duca degli Abruzzi 24, I-10129 Torino (Italy)); Scholz, H.W. (Institute for Advanced Materials, CEC Joint Research Centre, I-21020 Ispra (Vatican City State, Holy See) (Italy))

    1994-09-01

    Due to their favourable radiological behaviour, SiC[sub f]/SiC composites are promising structural materials for future use in fusion reactors. A problem to cope with is the joining of the ceramic composite material (CMC) to itself for more complex structures. Maintenance concepts for a reactor made of SiC[sub f]/SiC will demand a method of joining. The joining agents should comply with the low-activation approach of the base material. With the acceptable elements Si and Mg, sandwich structures of composite/metal/composite were prepared in Ar atmosphere at temperatures just above the melting points of the metals. Another promising route is the use of joining agents of boro-silicate glasses: their composition can be tailored to obtain softening temperatures of interest for fusion applications. The glassy joint can be easily ceramised to improve thermomechanical properties. The joining interfaces were investigated by SEM-EDS, XRD and mechanical tests. ((orig.))

  18. Formation of permeation barriers on ceramic SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Racault, C. [Commission of the European Communities, Ispra (Italy). Joint Research Centre; Serra, E. [Safety Technology Institute, Ispra Establishment, I-21020 Ispra (Vatican City State, Holy See) (Italy); Fenici, P. [Commission of the European Communities, Ispra (Italy). Joint Research Centre

    1996-10-01

    The effectiveness as permeation barriers of the following CVD and PVD (sputtering) coatings has been investigated: TiC+Al{sub 2}O{sub 3}(CVD), SiC(CVD), SiO{sub 2}(CVD), TiN(CVD), TiN(CVD)+TiN(PVD) and SiC(CVD)+Al{sub 2}O{sub 3}(PVD). The substrate material was a SiC/SiC composite, proposed as low activation structural material for fusion applications. Permeation measurements were performed in the temperature range 300-750 K using deuterium at pressures in the range 0.5-150 kPa. A linear dependence of permeation rate on pressure was measured. The efficiency of the coatings as deuterium permeation barriers is discussed in terms of coating microstructure. The best result was obtained with a bilayer of TiN(CVD) (15 {mu}m) +TiN(PVD) (8 {mu}m). (orig.).

  19. Mechanoactivation of chromium silicide formation in the SiC-Cr-Si system

    Directory of Open Access Journals (Sweden)

    Vlasova M.

    2002-01-01

    Full Text Available The processes of simultaneous grinding of the components of a SiC-Cr-Si mixture and further temperature treatment in the temperature range 1073-1793 K were studied by X-ray phase analysis, IR spectroscopy, electron microscopy, and X-ray microanalysis. It was established that, during grinding of the mixture, chromium silicides form. A temperature treatment completes the process. Silicide formation proceeds within the framework of the diffusion of silicon into chromium. In the presence of SiO2 in the mixture, silicide formation occurs also as a result of the reduction of silica by silicon and silicon carbide. The sintering of synthesized composite SiC-chromium silicides powders at a high temperature under a high pressure (T = 2073 K, P = 5 GPa is accompanied by the destruction of cc-SiC particles, the cc/3 transition in silicon carbide and deformation distortions of the lattices of chromium silicides.

  20. Preparation and low temperature properties of FeSi-type RuSi

    Energy Technology Data Exchange (ETDEWEB)

    Buschinger, B. [Technische Hochschule Darmstadt (Germany). Inst. fuer Festkoerperphysik; Geibel, C. [Technische Hochschule Darmstadt (Germany). Inst. fuer Festkoerperphysik; Diehl, J. [Augsburg Univ. (Germany). Lehrstuhl fuer Experimentalphysik 2; Weiden, M. [Technische Hochschule Darmstadt (Germany). Inst. fuer Festkoerperphysik; Guth, W. [Technische Hochschule Darmstadt (Germany). Inst. fuer Festkoerperphysik; Wildbrett, A. [Augsburg Univ. (Germany). Lehrstuhl fuer Experimentalphysik 2; Horn, S. [Augsburg Univ. (Germany). Lehrstuhl fuer Experimentalphysik 2; Steglich, F. [Technische Hochschule Darmstadt (Germany). Inst. fuer Festkoerperphysik

    1997-07-05

    We have reinvestigated the metallographic RuSi phase diagram and could establish the transition temperature from the low temperature FeSi-type to the high temperature CsCl-type structure for stoichiometric samples. Magnetic and transport properties of the low temperature modification in the temperature range 1.5 KSi-type RuSi is found to be semiconducting but still in the extrinsic regime at room temperature. Below 100 K, an additional gap opens and at temperatures <40 K variable-range hopping conduction sets in as the dominant transport mechanism. In contrast, resistivity measurements on CsCl-type RuSi show simple metallic behavior. (orig.)

  1. Synthesis of biomorphic SiC and SiO2 ceramics

    Directory of Open Access Journals (Sweden)

    ADELA EGELJA

    2008-07-01

    Full Text Available Coniferous wood (fir was transformed by pyrolysis into carbon preforms, which were subsequently converted into biomorphic ceramics by the pressure infiltration technique with colloidal silica. An in situ reaction between the silica and the carbon template occurred in the cellular wall at a high sintering temperature. Depending on the employed atmosphere, non-oxide (SiC or oxide (SiO2 ceramics were obtained. The morphology of the resulting porous ceramics and their phase composition were investigated by scanning electron microscopy (SEM/EDX and X-ray diffraction (XRD. The experimental results showed that the biomorphic cellular morphology of the wood maintained in both the SiC and silica ceramics, which consisted of only the b-SiC phase and SiO2, respectively.

  2. Blue-light emission from sputtered Si:SiO2 films without annealing

    Science.gov (United States)

    Hanaizumi, Osamu; Ono, Kazutaka; Ogawa, Yuichi

    2003-01-01

    We observed a photoluminescence (PL) spectrum at room temperature that had a peak with full width of half maximum (FWHM) of 0.38 eV near the band gap energy of 3.2 eV from a Si:SiO2 sputtered film without annealing. Blue-light emission could be seen by the naked eye. A low-intensity PL peak with FWHM of 0.20 eV was also observed at around 1.6 eV. We have already demonstrated that our method automatically forms Si clusters contributing to visible emission. Our results did not contradict the well-founded conjecture that there were two mechanisms of emission from Si clusters: emission at 1.6-1.7 eV due to the surface state of the oxidized Si nanocrystals and emission at the band gap energy originating from the quantum confinement effect.

  3. Si nanocrystals embedded in SiO2: Optical studies in the vacuum ultraviolet range

    DEFF Research Database (Denmark)

    Pankratov, V.; Osinniy, Viktor; Kotlov, A.

    2011-01-01

    Photoluminescence excitation and transmission spectra of Si nanocrystals of different diameters embedded in a SiO2 matrix have been investigated in the broad visible-vacuum ultraviolet spectral range using synchrotron radiation. The dependence of the photoluminescence excitation spectra...... on the nanocrystals size was experimentally established. It is shown that the photoluminescence excitation and absorption spectra are significantly blueshifted with decreasing Si nanocrystal size. A detailed comparison of photoluminescence excitation and absorption spectra with data from theoretical modeling has been...... done. It is demonstrated that the experimentally determined blueshift of the photoluminescence excitation and absorption spectra is larger than the theoretical predictions. The influence of point defects in the SiO2 matrix on the optical and luminescence properties of the embedded Si nanocrystals...

  4. Processing and properties of SiCf/SiBOC ceramic matrix composites by polyborosiloxane impregnation and pyrolysis

    Science.gov (United States)

    Vijay, Vipin; Prabhakaran, P. V.; Devasia, Renjith

    2013-06-01

    SiCf/SiBOC Ceramic Matrix Composites (CMCs) were fabricated using polyborosiloxane as the matrix resin and Nicalon™ NL-202 silicon carbide fiber as the reinforcement via polymer infiltration/impregnation and pyrolysis process (PIP). Repeated PIP cycles resulted in CMCs with a density value of ≈ 2 g/cc and a maximum average flexural strength value of 108 MPa. Oxidation resistance of SiCf/SiBOC was compared with Cf/C and Cf/SiBOC at 1000°C. SiCf/SiBOC composite shows a better oxidation resistance due to the formation of a protective layer of amorphous borosilicate glass on oxidation.

  5. Determination of band offsets in strained-Si heterolayers

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, C.K.; Samanta, S.K.; Chatterjee, S.; Dalapati, G.K.; Bhattacharya, S.; Armstrong, B.M.; Gamble, H.S.; McCarthy, J.; Perova, T.S.; Moore, R.A

    2004-09-01

    Strained-Si/SiGe/Si structures are of increasing importance for microelectronic applications. A fully relaxed-SiGe buffer layer is required for growing strained-Si for applications towards high performance field effect transistors (FETs) having strained-Si as the channel. Preparation of epitaxial strained-Si layers on relaxed-SiGe (001) heterostructures using low pressure chemical vapor deposition (LPCVD) is reported. Gas source molecular beam epitaxy (GSMBE) grown strained-Si films are used to compare with LPCVD strained-Si films. Characterization of the strained-Si layers has been performed using AFM, TEM and Raman spectroscopy. Conduction and valence band offsets of strained-Si on relaxed-SiGe heterostructures have been extracted from measured capacitance-voltage (C-V) profiling of MOS capacitors fabricated on strained-Si using SiO{sub 2} as the dielectric. Extracted experimental values of the valence and conduction band offsets are in good agreement with theoretical predictions.

  6. Carrier recombination in tailored multilayer Si/Si{sub 1−x}Ge{sub x} nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Mala, S.A. [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Tsybeskov, L., E-mail: tsybesko@njit.edu [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Lockwood, D.J.; Wu, X.; Baribeau, J.-M. [National Research Council, Ottawa, ON, Canada KIA 0R6 (Canada)

    2014-11-15

    Photoluminescence (PL) measurements were performed in Si/Si{sub 1−x}Ge{sub x} nanostructures with a single Si{sub 0.92}Ge{sub 0.08} nanometer-thick layer incorporated into Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. Under pulsed laser excitation, the PL decay associated with the Si{sub 0.92}Ge{sub 0.08} nano-layer is found to be nearly a 1000 times faster compared to that in Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. A model considering Si/SiGe hetero-interface composition and explaining the fast and slow time-dependent recombination rates is proposed.

  7. Microhardness evaluation alloys Hf-Si-B; Avaliacao de microdureza de ligas Hf-Si-B

    Energy Technology Data Exchange (ETDEWEB)

    Gigolotti, Joao Carlos Janio; Costa, Eliane Fernandes Brasil [Centro Universitario de Volta Redonda (UNIFOA), Volta Redonda, RJ (Brazil); Nunes, Carlos Angelo; Rocha, Elisa Gombio; Coelho, Gilberto Carvalho, E-mail: carlosjanio@uol.com.br, E-mail: eliane-costabrasi@hotmail.com, E-mail: cnunes@demar.eel.usp.br, E-mail: elisarocha@alunos.eel.usp.br, E-mail: coelho@demar.eel.usp.br [Universidade de Sao Paulo (USP), Lorena, SP (Brazil)

    2014-08-15

    The technological advance has generated increasing demand for materials that can be used under high temperature, what includes intermetallic MR-Si-B (MR = refractory metal) alloys with multiphase structures, that can also be applied in oxide environments. Thus, this work had for objective the micro hardness study of the Hf-Si-B system alloys, heat treated at 1600 deg C, in the Hf rich region. Hf-Si-B alloys had been produced with blades of Hf (min. 99.8%), Si (min. 99.998%) and B (min. 99.5%), in the voltaic arc furnace and heat treated at 1600 deg C under argon atmosphere. The relationship of the phases had been previously identified by X-ray diffraction and contrast in backscattered electron imaging mode. The alloys had their hardness analyzed by method Vickers (micro hardness) with load of 0.05 kgf and 0.2 kgf and application time of 20 s. The results, obtained from the arithmetic mean of measurements for each alloy on the heterogeneous region, showed a mean hardness of 11.08 GPA, with small coefficient of variation of 3.8%. The borides HfB2 (19.34 GPa) e HfB - 11.76 GPa, showed the hardness higher than the silicides Hf2Si (8.57 GPa), Hf5Si3 (9.63 GPa), Hf3Si2 (11.66 GPa), Hf5Si4 (10.00 GPa), HfSi (10.02 GPa) e HfSi2 (8.61 GPa). (author)

  8. A DFT investigation on geometry and chemical bonding of isoelectronic Si8N6V-, Si8N6Cr, and Si8N6Mn+ clusters

    Science.gov (United States)

    Tam, Nguyen Minh; Pham, Hung Tan; Cuong, Ngo Tuan; Tung, Nguyen Thanh

    2017-10-01

    The geometric feature and chemical bonding of isoelectronic systems Si8N6Mq (M = V, Cr, Mn and q = -1, 0, 1, respectively) are investigated by means of density-functional-theory calculations. The encapsulated form is found for all ground-state structures, where the metal atom locates at the central site of the hollow Si8N6 cage. The Si8N6 cage is established by adding two Si atoms to a distorted Si6N6 prism, which is a combination of Si4N2 and Si2N4 strings. Chemical bonding of Si8N6Mq systems is explored by using the electron localization indicator and theory of atom in molecule, revealing the vital role of metal center in stabilizing the clusters.

  9. Computer simulation of CaSiO3 glass under compression: correlation between Si-Si pair radial distribution function and intermediate range order structure

    Science.gov (United States)

    Lan, Mai Thi; Thuy Duong, Tran; Iitaka, Toshiaki; Van Hong, Nguyen

    2017-06-01

    The structural organization of CaSiO3 glass at 600 K and under pressure of 0-100 GPa is investigated by molecular dynamics simulation (MDS). Results show that the atomic structure of CaSiO3 comprises SiO n and CaO m units considered as basic structural polyhedra. At low pressure, most of the basic structural polyhedra are SiO4, CaO5, CaO6 and CaO7. At high pressure most of the basic structural polyhedra are SiO5, SiO6 and CaO9, CaO10 and CaO11. The distribution of basic structural polyhedra is not uniform resulting in formation of Ca-rich and Si-rich regions. The distribution of SiO4, SiO5 and SiO6 polyhedra is also not uniform, but it tends to form SiO4-, SiO5-, and SiO6-clusters. For the Si-O network, under compression there is a gradual transition from the tetrahedral network (SiO4) to the octahedral network (SiO6) via SiO5 polyhedra. The SiO5-clusters are the same as immediate-phase in the transformation process. The size and shape of SiO4 tetrahedra change strongly under compression. While the size of SiO5 and SiO6 has also changed significantly, but the shape is almost unchanged under compression. The SiO n polyhedra can connect to each other via one common oxygen ion (corner-sharing bond), two common oxygen ions (edge-sharing bond) or three common oxygen ions (face-sharing bond). The Si-Si bond length in corner-sharing bonds is much longer than the ones in edge-sharing and face-sharing bonds. The change of intermediate range order (IRO) structure under compression relating to edge- and face-sharing bonds amongst SiO n at high pressure is the origin of the first peak splitting of the radial distribution functions of Si-Si pair. Under compression, the number of non-bridging oxygen (NBO) decreases. This makes the Si-O network more polymerized. At low pressure, most of the Ca2+ ions incorporate into the Si-O network via NBOs. At high pressure, the amount of NBO decreases, Ca2+ ions mainly incorporate into the Si-O network via bridging oxygen (BO) that

  10. Magnetism in nanocrystalline SiC films

    Science.gov (United States)

    Semenov, A. V.; Pashchenko, V. O.; Khirnyi, V. F.; Kozlovskyi, A. A.; Mateichenko, P. V.

    2015-11-01

    Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °C and 1200 C. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral VSiVC divacancies in separate nanocrystals. The estimated concentration of neutral VSiVC divacancies in nanocrystalline SiC films is ~1020 cm-3.

  11. XXe/XXIe siècles

    OpenAIRE

    Allemand-Cosneau, Claude; Chassey, Éric de; Corbel, Laurence; d’Anthenaise, Claude; Grammont, Claudine; Huber, Thomas; Krebs, Sophie; Pelizzari, Maria Antonella; Popelard, Johan; Réra, Nathan; Salomé, Laurent; Soulages, Pierre; Tillier, Bertrand

    2014-01-01

    XXe siècle Pierre Soulages, regard sur l’histoire de l’art. Réflexions autour des pratiques de mixité entre art actuel et art ancien dans les musées... Qu’en est-il du fauvisme cent ans après ? Quels enjeux pour les recherches sur le caricatural au xxe siècle ? et XXIe siècle Le futurisme et ses acceptions, l’art de l’Entre-deux-guerres, les rapports conceptuels entre photographie et architecture, les éditions d’artistes depuis les années 1960, et l’art contemporain à l’épreuve de la destruc...

  12. Ultra high vacuum growth of CrSi2 and β-FeSi2 nanoislands and Si top layers on the plasma modified monocrystalline silicon surfaces

    Science.gov (United States)

    Galkin, Nikolay G.; Astashynski, Valiantsin M.; Chusovitin, Evgenii A.; Galkin, Konstantin N.; Dergacheva, Tatyana A.; Kuzmitski, Anton M.; Kostyukevich, Evgenii A.

    A set of silicon substrates processed by compression plasma was studied by means of atomic force microscopy (AFM). AFM data revealed a threshold nature (in terms of plasma flow energy) of the formation of tube-like surface structures (SS) observed as "waves" regardless of the conductivity type, resistivity, and the substrate orientation ((111) or (100)). For the first time nanoheterostructures Si(111)/NC CrSi2/Si and Si(100)/NC β-FeSi2 / Si have been formed on silicon substrates processed by compression plasma flow. Avery high density of CrSi2 nanoislands - (2-3)×1011 cm-2 was obtained for Cr-Si system but in the case of Fe-Si system the β-FeSi2 nanoislands density was only about 2×109 cm-2. According to the optical spectroscopy data during the process of silicon capping layer formation the CrSi2 and β-FeSi2 nanocrystals move up to the surface.

  13. SiC/Si heterojunction diodes fabricated by self-selective and by blanket rapid thermal chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Yih, P.H.; Li, J.P.; Steckl, A.J. (Univ. of Cincinnati, OH (United States). Dept. of Electrical and Computer Engineering)

    1994-03-01

    SiC/Si heterojunction diodes have been fabricated by two different rapid thermal chemical vapor deposition (RTCVD) processes: a localized self-selective growth and blanket growth. The self-selective growth of crystalline cubic ([beta]) SiC was obtained by propane carbonization of the Si substrate in regions unprotected by an SiO[sub 2] layer, producing planar diodes. Mesa diodes were fabricated using the blanket growth of polycrystalline [beta]-SiC produced by the decomposition of methylsilane (CH[sub 3]SiH[sub 3]). The SiC/Si heterojunction diodes show good rectifying properties for both device structures. Reverse breakdown voltage of 50 V was obtained with the self-selective SiC/Si diode. The mesa diodes exhibited even higher breakdown voltages (V[sub br]) of 150 V and excellent ideality factors of 1.06 at 25 C. The high V[sub br] and good forward rectifying characteristics indicate that the SiC/Si heterojunction diode represents a promising approach for the fabrication of wide-gap emitter SiC/Si heterojunction bipolar transistors.

  14. Ag on Si(111) from basic science to application

    Energy Technology Data Exchange (ETDEWEB)

    Belianinov, Aleksey [Iowa State Univ., Ames, IA (United States)

    2012-01-01

    In our work we revisit Ag and Au adsorbates on Si(111)-7x7, as well as experiment with a ternary system of Pentacene, Ag and Si(111). Of particular interest to us is the Si(111)-(√3x√3)R30°}–Ag (Ag-Si-√3 hereafter). In this thesis I systematically explore effects of Ag deposition on the Ag-Si-√3 at different temperatures, film thicknesses and deposition fluxes. The generated insight of the Ag system on the Si(111) is then applied to generate novel methods of nanostructuring and nanowire growth. I then extend our expertise to the Au system on the Ag-Si(111) to gain insight into Au-Si eutectic silicide formation. Finally we explore behavior and growth modes of an organic molecule on the Ag-Si interface.

  15. Generation of siRNA Nanosheets for Efficient RNA Interference

    Science.gov (United States)

    Kim, Hyejin; Lee, Jae Sung; Lee, Jong Bum

    2016-04-01

    After the discovery of small interference RNA (siRNA), nanostructured siRNA delivery systems have been introduced to achieve an efficient regulation of the target gene expression. Here we report a new siRNA-generating two dimensional nanostructure in a formation of nanosized sheet. Inspired by tunable mechanical and functional properties of the previously reported RNA membrane, siRNA nanosized sheets (siRNA-NS) with multiple Dicer cleavage sites were prepared. The siRNA-NS has two dimensional structure, providing a large surface area for Dicer to cleave the siRNA-NS for the generation of functional siRNAs. Furthermore, downregulation of the cellular target gene expression was achieved by delivery of siRNA-NS without chemical modification of RNA strands or conjugation to other substances.

  16. Characteristics of Al-Si-Mg Reinforced SiC Composites Produced by Stir Casting Route

    Science.gov (United States)

    Zulfia, A.; Zhakiah, T.; Dhaneswara, D.; Sutopo

    2017-05-01

    Al-Si-Mg alloy that is strengthened by silicon carbide particles has the potential to have excellent mechanical properties with light weight. In this study, metal matrix composites reinforced silicon carbide from 2 vf-% to 15 vf-% and magnesium amounted to 10 wt-% as an external dopant were fabricated by stir casting route. The magnesium was added to promote the wetting between Al matrix and reinforced SiC. The process involved SiC blended inside the molten Al by a stirrer with a rotational speed of 500 rpm at 800 °C for 2 minutes and degassed with Ar gas for 4 minutes to remove all of the gas content in the molten Al. The molten composite was then cast into the plate and tensile test sample molds. The effect of SiC addition on the mechanical properties and microstructure of the composites was investigated. The result showed that the optimum tensile strength was reached at 8 vf-% SiC with the value of 175 MPa, while the elongation was 9.1%. The maximum hardness and wear rate were achieved at 10 vf-% SiC with the values of 57 HRB and 0.0022 mm3/m, respectively. Such increase was related to the microstructures dominated by the presence of Chinese script, primary and eutectic Mg2Si which were contributed to the mechanical properties of the composites.

  17. Formation of ZnO nanostructures grown on Si and SiO2 substrates.

    Science.gov (United States)

    Lee, Seungjin; Park, Eunkyung; Lee, Jongtack; Park, Taehee; Lee, Sang-Hwa; Kim, Jae-Yong; Yi, Whikun

    2013-09-01

    ZnO nanorods are grown on Si-based substrate by chemical bath deposition method in aqueous solution using zinc nitrate hexahydrate. Various substrates having different surface morphology are used to evaluate their effect on growing ZnO nanorods, such as flat Si(100) wafer, small and large textured-Si wafer, porous silicon, flat SiO2 wafer, small and large textured-SiO2 wafer. The length, diameter, geometry, and coverage density of ZnO nanorods are investigated by field-emission scanning electron microscopy and summarized. SiO2 is a preferred substrate for the growth of ZnO nanorods to Si if the surface morphology of substrate is same, and the textured surface has much higher coverage density (> 95%) than the flat surface. Each nanorod is vertically grown along the c-axis on the top of each pyramid face for textured substrate, and forms the 3D sea sponge-like ZnO structure. The characteristics of ZnO nanorods grown on various substrates are analyzed by grazing-angle X-ray diffraction (XRD) and photoluminescence (PL) measurements.

  18. Fiber creep rate and high-temperature properties of SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Lewinsohn, C.A.; Jones, R.H.; Youngblood, G.E.; Henager, C.H. Jr. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    Results of studies aimed at relating the fiber creep rate to the subcritical crack growth rate and fracture properties of SiC/SiC composites have demonstrated that the crack growth rate in a bulk composite is controlled by the fiber creep rate. This result was demonstrated for Nicalon-CG and Hi-Nicalon fiber reinforced material where a 50--75 c shift in the creep strength of the fiber resulted in a similar shift in the crack growth rate of the composite. Irradiation enhanced creep of SiC fibers and matrix must also be considered in the performance assessment of SiC/SiC composites. The shape of the displacement versus time curve for composites containing Hi-Nicalon fibers were similar to those of the previously tested materials, containing Ceramic-grade fibers, that exhibited subcritical crack growth controlled by time-dependent relaxation of the fiber-bridging stresses due to fiber creep. The crack velocity in the CG-C composites at 1100 C in argon was very close to that of the Hi-C materials at 1150--1175 C, this roughly corresponds to the temperature differential shown by DiCarlo et al. to obtain the same relaxation in 1 hour bend stress relaxation (BSR) tests in the two fibers. This supports the hypothesis that subcritical crack growth in SiC/SiC composites is controlled by fiber creep.

  19. Wetting and reaction characteristics of crystalline and amorphous SiO2 derived rice-husk ash and SiO2/SiC substrates with Al-Si-Mg alloys

    Science.gov (United States)

    Bahrami, A.; Pech-Canul, M. I.; Gutiérrez, C. A.; Soltani, N.

    2015-12-01

    A study of the wetting behavior of three substrate types (SiC, SiO2-derived RHA and SiC/SiO2-derived RHA) by two Al-Si-Mg alloys using the sessile drop method has been conducted, using amorphous and crystalline SiO2 in the experiment. Mostly, there is a transition from non-wetting to wetting contact angles, being the lowest θ values achieved with the alloy of high Mg content in contact with amorphous SiO2. The observed wetting behavior is attributed to the deposited Mg on the substrates. A strong diffusion of Si from the SiC/Amorphous RHA substrate into the metal drop explains the free Si segregated at the drop/substrate interface and drop surface. Although incorporation of both SiO2-derived RHA structures into the SiC powder compact substrates increases the contact angles in comparison with the SiC substrate alone, the still observed acute contact angles in RHA/SiC substrates make them promising for fabrication of composites with high volume fraction of reinforcement by the pressureless infiltration technique. The observed wetting characteristics, with decrease in surface tension and contact angles is explained by surface related phenomena. Based on contact angle changes, drop dimensions and surface tension values, as well as on the interfacial elemental mapping, and XRD analysis of substrates, some wetting and reaction pathways are proposed and discussed.

  20. Thickness and temperature depending intermixing of SiO{sub x}/SiO{sub 2} and SiO{sub x}N{sub y}/SiO{sub 2} superlattices: Experimental observation and thermodynamic modeling

    Energy Technology Data Exchange (ETDEWEB)

    Zhigunov, D. M. [Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow (Russian Federation); Sarikov, A. [IMDEA Materials Institute, c/ Eric Kandel, 2, 28906 Getafe, Madrid (Spain); V. Lashkarev Institute of Semiconductor Physics NAS Ukraine, 45 Nauki Avenue, 03028 Kiev (Ukraine); Chesnokov, Yu. M.; Vasiliev, A. L. [National Research Centre “Kurchatov Institute”, pl. Akademika Kurchatova 1, 123182 Moscow (Russian Federation); Zakharov, N. [Max-Planck-Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany); Kashkarov, P. K. [Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow (Russian Federation); National Research Centre “Kurchatov Institute”, pl. Akademika Kurchatova 1, 123182 Moscow (Russian Federation)

    2016-05-30

    Multilayered SiO{sub x}/SiO{sub 2} and SiO{sub x}N{sub y}/SiO{sub 2} thin films were fabricated using different techniques and subsequently annealed at high temperatures (≥1100 °C) in order to form Si nanocrystals by means of the well-known superlattice approach. The thickness of the SiO{sub x} and SiO{sub x}N{sub y} layers was varied from 1.5 to 5 nm, while for the SiO{sub 2} layers it was fixed at 4 nm. Using transmission electron microscopy, we showed that the multilayered structure generally sustains the high temperature annealing for both types of films. However, for samples with ultrathin SiO{sub x} or SiO{sub x}N{sub y} layers a breakdown of the superlattice structure and a complete intermixing of layers were observed at high temperatures. On the contrary, annealing at lower temperature (900 °C) preserves the multilayered structure even of such samples. Theoretical calculations showed that the intermixing of SiO{sub x}/SiO{sub 2} and SiO{sub x}N{sub y}/SiO{sub 2} superlattices in the ultrathin layers thickness limit may be explained thermodynamically by the gain in the Gibbs free energy, which depends in turn on the annealing temperature.

  1. Comparative Study of Thermal Shock Behavior with Fabrication Method of SiC{sub f}/SiC Composite

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dong Hee; Park, Kwang Heon [Kyunghee University, Seoul (Korea, Republic of); Kim, Weon Ju; Park, Ji Yeon; Kim, Dae Jong; Lee, Hyeon Geun [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    An active search is ongoing for an alternative material to be used for manufacturing of nuclear fuel cladding. Studies are currently aimed at improving the safety of this cladding. In particular, ceramic-based nuclear fuel cladding, such as SiC, is receiving much attention due to the excellent radiation resistance, high strength, chemical durability against oxidation and corrosion, and excellent thermal conduction of ceramics. SiC{sub f}f/SiC composite cladding is required to maintain soundness against destruction and corrosion, and have excellent thermal conductivity to remove sufficiently the heat generated by nuclear fuel in output operation. For the reason, SiCf/SiC composite layers with densification are needed in SiC fiber bundle. As manufacturing methods to fill SiC matrix phase, there are Liquid Silicon Infiltration (LSI), Chemical Vapor Infiltration (CVI), Slurry Infiltration and Hot Pressure Sintering (SI-HPS), Polymer Infiltration and Pyrolysis (PIP), and Hybrid processes in combination of multiple processes (CVI+PIP, CVI{sub R}S and PIP+RS). This study conducted a comparison analysis, based on the manufacturing method, of the thermal shock behavior of metal cladding that had an SiC composite protective film added. The SiC{sub f}/SiC composite layer and the Zry-4 surface were separated, and cracks occurred in the SiC{sub f}/SiC composite. In the case of the cladding that had the SiC{sub f}/SiC composite protective film manufactured by the CVI process, there was no microcrack inside the SiC{sub f}/SiC composite. A microcracks that penetrated the fiber was observed inside the SiC{sub f}/SiC composite when it was manufactured using the PIP process; this was due to the absence of an interphase coating that increased the fracture toughness of the fiber.

  2. Si/Fe flux ratio influence on growth and physical properties of polycrystalline β-FeSi2 thin films on Si(100) surface

    Science.gov (United States)

    Tarasov, I. A.; Visotin, M. A.; Aleksandrovsky, A. S.; Kosyrev, N. N.; Yakovlev, I. A.; Molokeev, M. S.; Lukyanenko, A. V.; Krylov, A. S.; Fedorov, A. S.; Varnakov, S. N.; Ovchinnikov, S. G.

    2017-10-01

    This work investigates the Si/Fe flux ratio (2 and 0.34) influence on the growth of β-FeSi2 polycrystalline thin films on Si(100) substrate at 630 °C. Lattice deformations for the films obtained are confirmed by X-ray diffraction analysis (XRD). The volume unit cell deviation from that of β-FeSi2 single crystal are 1.99% and 1.1% for Si/Fe =2 and Si/Fe =0.34, respectively. Absorption measurements show that the indirect transition ( 0.704 eV) of the Si/Fe =0.34 sample changes to the direct transition with a bandgap value of 0.816 eV for the sample prepared at Si/Fe =2. The absorption spectrum of the Si/Fe =0.34 sample exhibits an additional peak located below the bandgap energy value with the absorption maximum of 0.36 eV. Surface magneto-optic Kerr effect (SMOKE) measurements detect the ferromagnetic behavior of the β-FeSi2 polycrystalline films grown at Si/Fe =0.34 at T=10 K, but no ferromagnetism was observed in the samples grown at Si/Fe =2. Theoretical calculations refute that the cell deformation can cause the emergence of magnetization and argue that the origin of the ferromagnetism, as well as the lower absorption peak, is β-FeSi2 stoichiometry deviations. Raman spectroscopy measurements evidence that the film obtained at Si/Fe flux ratio equal to 0.34 has the better crystallinity than the Si/Fe =2 sample.

  3. Production of NiSi phase by grain boundary diffusion induced solid state reaction between Ni{sub 2}Si and Si(1 0 0) substrate

    Energy Technology Data Exchange (ETDEWEB)

    Shenouda, S.S., E-mail: shenouda_physics@yahoo.com [University of Debrecen, Department of Solid State Physics, H-4010, Debrecen, P.O. Box 2 (Hungary); Ain Shams University, Department of Physics, Faculty of Education, Roxy, Cairo (Egypt); Langer, G.A.; Katona, G.L.; Daróczi, L. [University of Debrecen, Department of Solid State Physics, H-4010, Debrecen, P.O. Box 2 (Hungary); Csik, A. [Institute Nuclear Research, Hungarian Academy of Sciences (ATOMKI), H-4001, Debrecen, P.O. Box 51 (Hungary); Beke, D.L. [University of Debrecen, Department of Solid State Physics, H-4010, Debrecen, P.O. Box 2 (Hungary)

    2014-11-30

    Graphical abstract: Sketch of grain boundary diffusion of Si (blue) into Ni{sub 2}Si film (yellow) forming NiSi (red). - Highlights: • New processing method for creation of homogeneous thin NiSi contacts from nanocrystalline-Ni{sub 2}Si/Si(1 0 0) substrate. • The NiSi forms by grain-boundary diffusion and reaction in a certain low temperature-time and thickness-time window. • The nucleated NiSi growths perpendicular to the grain boundaries and its velocity can also be determined. - Abstract: We report a process to obtain thin (5–20 nm thick) NiSi layers on Si(1 0 0) substrate from magnetron deposited Ni{sub 2}Si thin films at low temperatures (180–200°C). The time evolution of transformation was followed by means of Secondary Neutral Mass Spectrometry, transmission electron microscopy and resistance measurements. It is shown that there exist certain temperature-time and thickness-time windows inside of which the formation of NiSi takes place. The NiSi phase, formed along the grain boundaries of Ni{sub 2}Si and grew by the motion of these interfaces, gradually consumes the Ni{sub 2}Si phase. From the depth profiles of the first stage of the process, using the linear dependence of the average composition inside the film on the annealing time, the velocity of the grain boundary diffusion induced interface motion was also estimated. The normalized value of the resistance, proportional to the amount of the new phase, showed similar time evolution and yielded similar value for the interface velocity.

  4. Primary Crystals of AlfeMnSi Intermetallics in the Cast AlSi Alloys

    Directory of Open Access Journals (Sweden)

    Warmuzek M.

    2017-09-01

    Full Text Available In this paper the results of the microscopic observations of the intermetallic AlFeMnSi phases crystals formed in the liquid hypo- and eutectic AlSi alloys containing transition metals 3.0 wt.% Fe and 0.1, 0.5 and 2.0 wt.% Mn were presented. The crystals morphology has been revealed on both polished and deep etched microsections. The different stages of the primary AlFeMnSi phases particles formation in the solidifying alloy and their final morphology were shown as influenced by cooling rate and alloy chemical composition.

  5. Development of Readout Interconnections for the Si-W Calorimeter of SiD

    Energy Technology Data Exchange (ETDEWEB)

    Woods, M.; Fields, R.G.; Holbrook, B.; Lander, R.L.; Moskaleva, A.; Neher, C.; Pasner, J.; Tripathi, M.; /UC, Davis; Brau, J.E.; Frey, R.E.; Strom, D.; /Oregon U.; Breidenbach, M.; Freytag, D.; Haller, G.; Herbst, R.; Nelson, T.; /SLAC; Schier, S.; Schumm, B.; /UC, Santa Cruz

    2012-09-14

    The SiD collaboration is developing a Si-W sampling electromagnetic calorimeter, with anticipated application for the International Linear Collider. Assembling the modules for such a detector will involve special bonding technologies for the interconnections, especially for attaching a silicon detector wafer to a flex cable readout bus. We review the interconnect technologies involved, including oxidation removal processes, pad surface preparation, solder ball selection and placement, and bond quality assurance. Our results show that solder ball bonding is a promising technique for the Si-W ECAL, and unresolved issues are being addressed.

  6. Thermophysical and mechanical properties of SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-09-01

    The key thermophysical and mechanical properties for SiC/SiC composites are summarized, including temperature-dependent tensile properties, elastic constants, thermal conductivity, thermal expansion, and specific heat. The effects of neutron irradiation on the thermal conductivity and dimensional stability (volumetric swelling, creep) of SiC is discussed. The estimated lower and upper temperatures limits for structural applications in high power density fusion applications are 400 and 1000 C due to thermal conductivity degradation and void swelling considerations, respectively. Further data are needed to more accurately determine these estimated temperature limits.

  7. Development of readout interconnections for the Si-W calorimeter of SiD

    Science.gov (United States)

    Woods, M.; Fields, R. G.; Holbrook, B.; Lander, R. L.; Moskaleva, A.; Neher, C.; Pasner, J.; Tripathi, M.; Brau, J. E.; Frey, R. E.; Strom, D.; Breidenbach, M.; Freytag, D.; Haller, G.; Herbst, R.; Nelson, T.; Schier, S.; Schumm, B.

    2011-12-01

    The SiD collaboration is developing a Si-W sampling electromagnetic calorimeter, with anticipated application for the International Linear Collider. Assembling the modules for such a detector will involve special bonding technologies for the interconnections, especially for attaching a silicon detector wafer to a flex cable readout bus. We review the interconnect technologies involved, including oxidation removal processes, pad surface preparation, solder ball selection and placement, and bond quality assurance. Our results show that solder ball bonding is a promising technique for the Si-W ECAL, and unresolved issues are being addressed.

  8. Synthesis, characterization and luminescence of europium perchlorate with MABA-Si complex and coating structure SiO2@Eu(MABA-Si) luminescence nanoparticles.

    Science.gov (United States)

    Fu, Zhi-Fang; Li, Wen-Xian; Bai, Juan; Bao, Jin-Rong; Cao, Xiao-Fang; Zheng, Yu-Shan

    2017-05-01

    This article reports a novel category of coating structure SiO 2 @Eu(MABA-Si) luminescence nanoparticles (NPs) consisting of a unique organic shell, composed of perchlorate europium(III) complex, and an inorganic core, composed of silica. The binary complex Eu(MABA-Si) 3 ·(ClO 4 ) 3 ·5H 2 O was synthesized using HOOCC 6 H 4 N(CONH(CH 2 ) 3 Si(OCH 2 CH 3 ) 3 ) 2 (MABA-Si) and was used as a ligand. Furthermore, the as-prepared silica NPs were successfully coated with the -Si(OCH 2 CH 3 ) 3 group of MABA-Si to form Si-O-Si chemical bonds by means of the hydrolyzation of MABA-Si. The binary complexes were characterized by elemental analysis, molar conductivity and coordination titration analysis. The results indicated that the composition of the binary complex was Eu(MABA-Si) 3 ·(ClO 4 ) 3 ·5H 2 O. Coating structure SiO 2 @Eu(MABA-Si) NPs were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared (IR) spectra. Based on the SEM and TEM measurements, the diameter of core-SiO 2 particles was ~400 and 600 nm, and the thickness of the cladding layer Eu(MABA-Si) was ~20 nm. In the binary complex Eu(MABA-Si) 3 ·(ClO 4 ) 3 ·5H 2 O, the fluorescence spectra illustrated that the energy of the ligand MABA-Si transferred to the energy level for the excitation state of europium(III) ion. Coating structure SiO 2 @Eu(MABA-Si) NPs exhibited intense red luminescence compared with the binary complex. The fluorescence lifetime and fluorescence quantum efficiency of the binary complex and of the coating structure NPs were also calculated. The way in which the size of core-SiO 2 spheres influences the luminescence was also studied. Moreover, the luminescent mechanisms of the complex were studied and explained. Copyright © 2016 John Wiley & Sons, Ltd.

  9. Chemical bonding and charge redistribution - Valence band and core level correlations for the Ni/Si, Pd/Si, and Pt/Si systems

    Science.gov (United States)

    Grunthaner, P. J.; Grunthaner, F. J.; Madhukar, A.

    1982-01-01

    Via a systematic study of the correlation between the core and valence level X-ray photoemission spectra, the nature of the chemical bonding and charge redistribution for bulk transition metal silicides has been examined. Particular emphasis is placed on Pt2Si and PtSi. It is observed that the strength of the metal (d)-silicon (p) interaction increases in the order Ni2Si, Pd2Si, Pt2Si. It is also observed that both the metal and silicon core lines shift to higher binding energy as the silicides are formed. The notion of charge redistribution for metallic bonds is invoked to explain these data.

  10. A declaration of independence for Mg/Si. [Al/Si intensity ratio predictive usefulness for Mg/Si intensity ratio in lunar X-ray fluorescence

    Science.gov (United States)

    Hubbard, N.; Keith, J. E.

    1978-01-01

    The weak covariation that exists between Al/Si and Mg/Si for large areas of the lunar surface is little, if any, stronger than that forced on a random set of numbers that are subject to closure. The Mg and Al variations implied by the Mg/Si and Al/Si intensity ratio data are qualitatively like those seen in lunar soil sample data. Two petrogenetic provinces are suggested for terra materials; one appears to have 50% higher Mg values than the other. Using the improved data, Mg/Si variations can be studied at a signal-to-noise ratio greater than 5/1.

  11. Liquinert quartz crucible for the growth of multicrystalline Si ingots

    OpenAIRE

    Fujiwara, Kozo; Horioka, Yukichi; Sakuragi, Shiro

    2017-01-01

    The growth of a multicrystalline silicon (mc-Si) ingot for solar cell applications was attempted using a Liquinert quartz crucible. A mc-Si ingot was also grown in a quartz crucible coated with Si3N4 powder for comparison with that from the Liquinert quartz crucible. The mc-Si ingot grown in the Liquinert quartz crucible had a shinier surface which has few impurity particles and higher minority carrier lifetime than the mc-Si ingot grown in a quartz crucible coated with Si3N4 powder. These re...

  12. Materials and devices for quantum information processing in Si/SiGe

    Energy Technology Data Exchange (ETDEWEB)

    Sailer, Juergen

    2010-12-15

    In this thesis, we cover and discuss the complete way from material science, the fabrication of two-dimensional electron systems (2DES) in Si/SiGe heterostructures in molecular beam epitaxy (MBE), to quantum effects in few-electron devices based on these samples. We applied and compared two different approaches for the creation of pseudo-substrates that are as smooth, relaxed and defect free as possible. In the 'graded buffer' concept, starting from pure Si, the Ge content of the SiGe alloy is slowly and linearly increased until the desired Ge content is reached. In contrast, in the so-called 'low-temperature Si' concept, the SiGe alloy is deposited directly with the final Ge content, but onto a layer of highly defective Si. In terms of crystal defects, the 'graded buffer' turned out to be superior in comparison to the 'low-temperature Si' concept at the expense of a significantly higher material consumption. By continued optimization of the growth process, aiming at reducing the influence of the impurity, it nevertheless became possible to improve the charge carrier mobility from a mere 2000 cm{sup 2}/(Vs) to a record mobility exceeding 100 000 cm{sup 2}/(Vs). Within this work, we extended our MBE system with an electron beam evaporator for nuclear spin free {sup 28}Si. Together with the already existing effusion cell for {sup 70}Ge we were able to realize first 2DES in a nuclear spin free environment after successfully putting it to operation. The highest mobility 2DES in a nuclear spin free environment which have been realized in this thesis exhibited electron mobilities of up to 55 000 cm{sup 2}/(Vs). Quantum effects in Si/SiGe have been investigated in two- and zero-dimensional nanostructures. A remarkable phenomenon in the regime of the integer quantum Hall effect in Si/SiGe 2DES has been discovered and researched. For applications in quantum information processing and for the creation of qubits it is mandatory to

  13. $^{31}$Si Self-Diffusion in Si-Ge Alloys and Si-(B-)C-N Ceramics and Diffusion Studies for Al and Si Beam Developments

    CERN Multimedia

    Nylandsted larsen, A; Voss, T L; Strohm, A

    2002-01-01

    An invaluable method for studying diffusion in solids is the radiotracer technique. However, its applicability had been restricted to radiotracer atoms with half-lives $t_{1/2}$ of about 1~d or longer. Within the framework of IS372 a facility was developed in which short-lived radiotracer atoms ( 5min $\\scriptstyle{\\lesssim}$ $t_{1/2}\\scriptstyle{\\lesssim}$1 d ) can be used. For the implantation of the short-lived tracers the facility is flanged to the ISOLDE beamline, and all post-implantation steps required in the radiotracer technique are done in situ.\\\\ After successful application of this novel technique in diffusion studies of $^{11}$C ($t_{1/2}$ = 20.3 min), this experiment aims at performing self-diffusion studies of $^{31}$Si ($t_{1/2}$ = 2.6~h) in Si--Ge alloys and in amorphous Si--(B--)C--N ceramics.\\\\ Our motivation for measuring diffusion in Si--Ge alloys is their recent technological renaissance as well as the purpose to test the prediction that in these alloys the self-diffusion mechanism chang...

  14. Blistering behavior in Mo/Si multilayers

    NARCIS (Netherlands)

    Kuznetsov, Alexey; Gleeson, Michael; van de Kruijs, Robbert Wilhelmus Elisabeth; Bijkerk, Frederik; Kuznetsov, A.S.

    2011-01-01

    This paper is concerned with mapping the characteristics of blistering induced on Mo/Si multilayers as a result of irradiation by hydrogen species generated in a thermal capillary cracker. The nature and extent of the damage observed is dependent on exposure conditions such as the sample

  15. Universal Converter Using SiC

    Energy Technology Data Exchange (ETDEWEB)

    Dallas Marckx; Brian Ratliff; Amit Jain; Matthew Jones

    2007-01-01

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

  16. A porous SiC ammonia sensor

    NARCIS (Netherlands)

    Connolly, E.J.; Timmer, B.H.; Pham, H.T.M.; Groeneweg, J.; Sarro, P.M.; Olthuis, Wouter; French, P.J.

    2005-01-01

    When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to be extremely sensitive to the presence of ammonia (NH3) gas. The exact sensing method is still not clear, but NH3 levels as low as 0.5 ppm could be detected. We report the fabrication and preliminary

  17. SiD Letter of Intent

    CERN Document Server

    Aihara, H.; Oreglia, M.; Berger, E.L.; Guarino, V.; Repond, J.; Weerts, H.; Xia, L.; Zhang, J.; Zhang, Q.; Srivastava, A.; Butler, J.M.; Goldstein, Joel; Velthuis, J.; Radeka, V.; Zhu, R.-Y.; Lutz, P.; de Roeck, A.; Elsener, K.; Gaddi, A.; Gerwig, H.; Grefe, C.; Klempt, W.; Linssen, L.; Schlatter, D.; Speckmayer, P.; Thom, J.; Yang, J.; Christian, D.C.; Cihangir, S.; Cooper, W.E.; Demarteau, M.; Fisk, H.E.; Garren, L.A.; Krempetz, K.; Kutschke, R.K.; Lipton, R.; Para, A.; Tschirhart, R.; Wenzel, H.; Yarema, R.; Grunewald, M.; Pankov, A.; U., Gomel State Tech.; Dutta, T.; Dauncey, P.D.; Balbuena, J.P.; Fleta, C.; Lozano, M.; Ullan, M.; Christian, G.B.; Faus-Golfe, A.; Fuster, J.; Lacasta, C.; Marinnas, C.; Vos, M.; Duarte, J.; Fernandez, M.; Gonzalez, J.; Jaramillo, R.; Lopez, Virto A.; Martinez-Eivero, C.; Moya, D.; Ruiz-Mimeno, A.; Vila, I.; Colledani, C.; Dorokhov, A.; Hu-Guo, C.; Winter, M.; Moortgat-Pick, G.; Onoprienko, D.V.; Kim, G.N.; Park, H.; Adloff, C.; Blaha, J.; Blaising, J.-J.; Cap, S.; Chefdeville, M.; Drancourt, C.; Espargiliare, A.; Gaglione, R.; Geffroy, N.; Jacquemier, J.; Karyotakis, Y.; Prast, J.; Vouters, G.; Gronberg, J.; Walston, S.; Wright, D.; Sawyer, L.; Laloum, M.; Ciobanu, C.; Chauveau, J.; Savoy-Navarro, A.; Andricek, L.; Moser, H.-G.; Cowan, R.f.; Fisher, P.; Yamamoto, R.K.; Kenney, ClMl; Boos, E.E.; Merkin, M.; Chen, S.; Chakraborty, D.; Dyshkant, A.; Hedin, D.; Zutshi, V.; Galkin, V.; D'Ascenzo, N.; Ossetski, D.; Saveliev, V.; Kapusta, F.; De Masi, R.; Vrba, V.; Lu, C.; McDonald, K.T.; Smith, A.J.S.; Bortoletto, D.; Coath, R.; Crooks, J.; Damerell, C.; Gibson, M.; Nichols, A.; Stanitzki, M.; Strube, J.; Turchetta, R.; Tyndel, M.; Weber, M.; Worm, S.; Zhang, Z.; Barklow, T.L.; Belymam, A.; Breidenbach, M.; Cassell, R.; Craddock, W.; Deaconu, C.; Dragone, A.; Graf, N.A.; Haller, G.; Herbst, R.; Hewett, J.L.; Jaros, J.A.; Johnson, A.S.; Kim, P.C.; MacFarlane, D.B.; Markiewicz, T.; Maruyama, T.; McCormick, J.; Moffeit, K.; Neal, H.A.; Nelson, T.K.; Oriunno, M.; Partridge, R.; Peskin, M.E.; Rizzo, T.G.; Rowson, P.; Su, D.; Woods, M.; Chakrabarti, S.; Dieguez, A.; Garrido, Ll.; Kaminski, J.; Conway, J.S.; Chertok, M.; Gunion, J.; Holbrook, B.; Lander, R.L.; Tripathi, S.M.; Fadeyev, V.; Schumm, B.A.; Oreglia, M.; Gill, J.; Nauenberg, U.; Oleinik, G.; Wagner, S.R.; Ranjan, K.; Shivpuri, R.; Varner, G.S.; Orava, R.; Van Kooten, R.; Bilki, B.; Charles, M.; Kim, T.J.; Mallik, U.; Norbeck, E.; Onel, Y.; Brau, B.P.; Willocq, S.; Taylor, G.N.; Riles, Keith; Yang, H.-J.; Kriske, R.; Cremaldi, L.; Rahmat, R.; Lastovicka-Medin, G.; Seidel, S.; Hildreth, M.D.; Wayne, M.; Brau, J.E.; Frey, R.; Sinev, N.; Strom, D.M.; Torrence, E.; Banda, Y.; Burrows, P.N.; Devetak, E.; Foster, B.; Lastovicka, T.; Li, Y.-M.; Nomerotski, A.; Riera-Babures, J.; Vilasis-Cardona, X.; Manly, S.; Adeva, B.; Iglesias Escudero, C.; Vazquez Regueiro, P.; Saborido Silva, J.J.; Gallas Torreira, A.; Gao, D.; Jie, W.; Jungfeng, Y.; Li, C.; Liu, S.; Liu, Y.; Sun, Y.; Wang, Q.; Yi, J.; Yonggang, W.; Zhao, Z.; De, K.; Farbin, A.; Park, S.; Smith, J.; White, A.P.; Yu, J.; Lou, X.C.; Abe, T.; Iwasaki, M.; Lubatti, H.J.; Band, H.R.; Feyzi, F.; Prepost, R.; Karchin, P.E.; Milstene, C.; Baltay, C.; Dhawan, S.; Kwon, Y.-J.

    2009-01-01

    Letter of intent describing SiD (Silicon Detector) for consideration by the International Linear Collider IDAG panel. This detector concept is founded on the use of silicon detectors for vertexing, tracking, and electromagnetic calorimetry. The detector has been cost-optimized as a general-purpose detector for a 500 GeV electron-positron linear collider.

  18. siRNA for Influenza Therapy

    Directory of Open Access Journals (Sweden)

    Sailen Barik

    2010-07-01

    Full Text Available Influenza virus is one of the most prevalent and ancient infections in humans. About a fifth of world's population is infected by influenza virus annually, leading to high morbidity and mortality, particularly in infants, the elderly and the immunocompromised. In the US alone, influenza outbreaks lead to roughly 30,000 deaths each year. Current vaccines and anti-influenza drugs are of limited use due to high mutation rate of the virus and side effects. In recent years, RNA interference, triggered by synthetic short interfering RNA (siRNA, has rapidly evolved as a potent antiviral regimen. Properly designed siRNAs have been shown to function as potent inhibitors of influenza virus replication. The siRNAs outperform traditional small molecule antivirals in a number of areas, such as ease of design, modest cost, and fast turnaround. Although specificity and tissue delivery remain major bottlenecks in the clinical applications of RNAi in general, intranasal application of siRNA against respiratory viruses including, but not limited to influenza virus, has experienced significant success and optimism, which is reviewed here.

  19. siRNA for Influenza Therapy.

    Science.gov (United States)

    Barik, Sailen

    2010-07-01

    Influenza virus is one of the most prevalent and ancient infections in humans. About a fifth of world's population is infected by influenza virus annually, leading to high morbidity and mortality, particularly in infants, the elderly and the immunocompromised. In the US alone, influenza outbreaks lead to roughly 30,000 deaths each year. Current vaccines and anti-influenza drugs are of limited use due to high mutation rate of the virus and side effects. In recent years, RNA interference, triggered by synthetic short interfering RNA (siRNA), has rapidly evolved as a potent antiviral regimen. Properly designed siRNAs have been shown to function as potent inhibitors of influenza virus replication. The siRNAs outperform traditional small molecule antivirals in a number of areas, such as ease of design, modest cost, and fast turnaround. Although specificity and tissue delivery remain major bottlenecks in the clinical applications of RNAi in general, intranasal application of siRNA against respiratory viruses including, but not limited to influenza virus, has experienced significant success and optimism, which is reviewed here.

  20. Si diffusion in GaAs

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutional–.

  1. Ordering of vacancies on Si(001)

    NARCIS (Netherlands)

    Zandvliet, Henricus J.W.

    1997-01-01

    Missing dimer vacancies are always present on the clean Si(001) surface. The vacancy density can be increased by ion bombardment (Xe+, Ar+), etching (O2, Br2, I2, etc.) or Ni contamination. The equilibrium shape at low vacancy concentrations (<0.2¿0.3 monolayers) of these vacancy islands is

  2. Design of lentivirally expressed siRNAs

    NARCIS (Netherlands)

    Liu, Ying Poi; Berkhout, Ben

    2013-01-01

    RNA interference (RNAi) has been widely used as a tool for gene knockdown in fundamental research and for the development of new RNA-based therapeutics. The RNAi pathway is typically induced by expression of ∼22 base pair (bp) small interfering RNAs (siRNAs), which can be transfected into cells. For

  3. Shape modification of Si nanowires by using faceted silicide catalysts nucleated in Au-Si catalyst solution during the growth

    Directory of Open Access Journals (Sweden)

    Erchao Meng

    2013-09-01

    Full Text Available The shape modification of Si nanowires is demonstrated using faceted solid silicide catalysts. The Si nanowires were grown on Si(111 substrates covered with Au as a catalyst using MnCl2 and Si powders as source materials. The solid silicide catalysts were nucleated and formed in the Au-Si catalyst solution at the top of the nanowires during the growth. The faceted solid silicides grew larger with increased growth time and played a role as a solid catalyst. The faceted shape of the catalyst defines the shape of the faceted Si nanowire. The squared Si nanowires were grown with the growth direction of Si[111] and the sidewalls of {110} and {211} planes. The growth evolution of the faceted Si nanowires occurs by a vapor-liquid-solid mechanism followed by the silicide vapor-solid-solid mechanism.

  4. Band gap tuning in Si-SiO2 nanocomposite: Interplay of confinement effect and surface/interface bonding

    Science.gov (United States)

    Rani, Ekta; Ingale, Alka; Phase, D. M.; Chaturvedi, A.; Mukherjee, C.; Joshi, M. P.; Kukreja, L. M.

    2017-12-01

    Correlation between size, bonding of Si and O at the surface/interface of Si nanocrystals and frequency of Si phonons in Si-SiO2 nanocomposites is established using Raman mapping and X-ray photoelectron spectroscopy. Corroboration of these results with absorption spectroscopy shows that lowering of direct transition of light electron conduction band to heavy hole valence band ∼2.8 and 2.95 eV is a result of the interplay between effect of electron confinement (increases band gap) and oxidation bonding environment at the surface/interface (decreases band gap) of a nanocrystal in Si-SiO2 nanocomposites. These studies have generated deeper insight into the fundamental understanding of the nanocomposite, which can allow easy optical microscopy monitoring of Si-SiO2 based device fabrication.

  5. Effects of laser-induced quenching and restoration of photoluminescence in hybrid Si/SiOx nanoparticles

    Science.gov (United States)

    Bagratashvili, V. N.; Dorofeev, S. G.; Ischenko, A. A.; Kononov, N. N.; Panchenko, V. Ya; Rybaltovskii, A. O.; Sviridov, A. P.; Senkov, S. N.; Tsypina, S. I.; Yusupov, V. I.; Yuvchenko, S. A.; Zimnyakov, D. A.

    2013-09-01

    We studied the processes of pulsed and continuous-wave (CW) laser excitation of photoluminescence (PL) in nc-Si/SiOx nanoparticles. CW laser irradiation of the nc-Si/SiOx sol in dimethylsulfoxide (DMSO) and in a thin film was found to quench PL with an essentially nonexponential dynamics. The laser-induced variation of the Rayleigh scattering signal from the nc-Si/SiOx sol in DMSO was found to replicate that of the PL quenching. The IR and Raman spectra of the laser-exposed nc-Si/SiOx exhibited no new bands that could be evidence of their chemical transformations. There were also no perceptible effects pointing to laser-induced aggregation of the nc-Si/SiOx particles in the sol. 355 nm pulse-periodic laser irradiation of the nc-Si/SiOx particles preliminarily exposed to a 405 nm CW laser (which causes a strong PL quenching effect) was found to result in a rapid restoration of the original PL signal, which means that the effect of laser quenching of PL can be entirely reversible. We considered a mechanism of the reversible photosensitivity of nc-Si/SiOx, based on the processes of ionization of the photoluminescent oxygen-deficient centers in their suboxide shell and electron capture by traps, followed by their laser-assisted photorecombination.

  6. Purity and radioactive decay behaviour of industrial 2D-reinforced SiC[sub f]/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, H.W. (Institute for Advanced Materials, CEC Joint Research Centre, I-21020 Ispra (Vatican City State, Holy See) (Italy)); Zucchetti, M. (Dipartimento di Energetica, Politecnico di Torino, C. Duca degli Abruzzi 24, I-10129 Torino (Italy)); Casteleyn, K. (Institute for Advanced Materials, CEC Joint Research Centre, I-21020 Ispra (Vatican City State, Holy See) (Italy)); Adelhelm, C. (IMF I, Kernforschungszentrum Karlsruhe GmbH, Postfach 3640, D-76344 Karlsruhe (Germany))

    1994-09-01

    Ceramic matrix composites based on SiC with continuous fibres (SiC[sub f]/SiC) are considered promising structural materials for future fusion devices. It was still to clarify, whether impurities in industrial SiC[sub f]/SiC could jeopardise radiological advantages. Experimental impurity analyses revealed a two-dimensionally reinforced SiC[sub f]/SiC with the matrix produced by CVI as very pure. Chemo-spectrometric methods were combined with radioactivation methods (CPAA, NAA). A quantification of the main constituents Si, C and O was added. Calculations with the FISPACT-2.4 code and EAF-2 library identified elements detrimental for different low-activation criteria. For the neutron exposure, EEF reactor-study first wall and blanket conditions were simulated. The calculated SiC[sub f]/SiC included 48 trace elements. Even under conservative assumptions, all low-activation limits of European interest are fulfilled. Exclusively the hands-on recycling limit for the First Wall can intrinsically not be satisfied with SiC. The theoretical goal of a SiC[sub f]/SiC depleted of [sup 28]Si (isotopic tailoring) is critically discussed. ((orig.))

  7. New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics

    Directory of Open Access Journals (Sweden)

    Magdalena Graczyk-Zajac

    2015-02-01

    Full Text Available Within this work we define structural properties of the silicon carbonitride (SiCN and silicon oxycarbide (SiOC ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

  8. Electrical behavior of MIS devices based on Si nanoclusters embedded in SiOxNy and SiO2 films

    Directory of Open Access Journals (Sweden)

    Debieu Olivier

    2011-01-01

    Full Text Available Abstract We examined and compared the electrical properties of silica (SiO2 and silicon oxynitride (SiOxNy layers embedding silicon nanoclusters (Sinc integrated in metal-insulator-semiconductor (MIS devices. The technique used for the deposition of such layers is the reactive magnetron sputtering of a pure SiO2 target under a mixture of hydrogen/argon plasma in which nitrogen is incorporated in the case of SiOxNy layer. Al/SiOxNy-Sinc/p-Si and Al/SiO2-Sinc/p-Si devices were fabricated and electrically characterized. Results showed a high rectification ratio (>104 for the SiOxNy-based device and a resistive behavior when nitrogen was not incorporating (SiO2-based device. For rectifier devices, the ideality factor depends on the SiOxNy layer thickness. The conduction mechanisms of both MIS diode structures were studied by analyzing thermal and bias dependences of the carriers transport in relation with the nitrogen content.

  9. Synthesis of SiC decorated carbonaceous nanorods and its hierarchical composites Si@SiC@C for high-performance lithium ion batteries

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Chundong [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Li, Yi, E-mail: liyi@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Ostrikov, Kostya [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4000 (Australia); Plasma Nanoscience, Industrial Innovation Program, CSIRO Manufacturing Flagship, Lindfield, New South Wales 2070 (Australia); Yang, Yonggang [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Zhang, Wenjun, E-mail: apwjzh@cityu.edu.hk [Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China)

    2015-10-15

    SiC- based nanomaterials possess superior electric, thermal and mechanical properties. However, due to the tricky synthesis process, which needs to be carried out under high temperature with multi-step reaction procedures, the further application is dramatically limited. Herein, a simple as well as a controllable approach is proposed for synthesis of SiC- based nanostructures under low temperature. Phenyl-bridged polysilsesquioxane was chosen as the starting material to react with magnesium at 650 °C, following which SiC@C nanocomposites were finally obtained, and it maintains the original bent rod-like architecture of polysilsesquioxanes. The possible formation process for the nanocomposites can proposed as well. The electrochemical behaviour of nanocomposites was accessed, verifying that the synthesized SiC@C nanocomposites deliver good electrochemical performance. Moreover, SiC@C also shows to be a promising scaffold in supporting Si thin film electrode in achieving stable cycling performance in lithium ion batteries. - Highlights: • SiC@C bent nanorods were synthesized with a magnesium reaction approach. • Carbon nanorod spines studded with ultrafine β-SiC nanocrystallines was realized. • The synthesized SiC@C keeps the original rod-like structure of polysilsesquioxanes. • The possible formation process for the nanocomposites was analysed and proposed. • Si@SiC@C nanocomposites reveal good electrochemical performance in LIBs.

  10. Growth of strained Si/relaxed SiGe heterostructures on Si(110) substrates using solid-source molecular beam epitaxy

    Science.gov (United States)

    Arimoto, Keisuke; Nakazawa, Hiroki; Mitsui, Shohei; Utsuyama, Naoto; Yamanaka, Junji; Hara, Kosuke O.; Usami, Noritaka; Nakagawa, Kiyokazu

    2017-11-01

    A strained Si/relaxed SiGe heterostructure grown on Si(110) substrate is attractive as a platform for high-hole-mobility Si-based electronic devices. To improve the electrical property, a smoother surface is desirable. In this study, we investigated surface morphology and microstructural aspects of strained Si/relaxed SiGe/Si(110) heterostructures grown by solid-source (SS) molecular beam epitaxy (MBE). It was revealed that SSMBE provides a way to grow strained Si/relaxed SiGe heterostructures with smooth surfaces. In addition, it was found that the strain in the SiGe layer of the SSMBE-grown sample is highly anisotropic whereas that of the GSMBE-grown sample is almost biaxially relaxed. Along with the surface morphology, the symmetry in degree of strain relaxation has implications for the electrical property. Results of a calculation shows that anisotropic strain is preferable for device application since it confines holes solely in the strained Si layer where hole mobility is enhanced.

  11. Atomistic Modelling of Si Nanoparticles Synthesis

    Directory of Open Access Journals (Sweden)

    Giovanni Barcaro

    2017-02-01

    Full Text Available Silicon remains the most important material for electronic technology. Presently, some efforts are focused on the use of Si nanoparticles—not only for saving material, but also for improving the efficiency of optical and electronic devices, for instance, in the case of solar cells coated with a film of Si nanoparticles. The synthesis by a bottom-up approach based on condensation from low temperature plasma is a promising technique for the massive production of such nanoparticles, but the knowledge of the basic processes occurring at the atomistic level is still very limited. In this perspective, numerical simulations can provide fundamental information of the nucleation and growth mechanisms ruling the bottom-up formation of Si nanoclusters. We propose to model the low temperature plasma by classical molecular dynamics by using the reactive force field (ReaxFF proposed by van Duin, which can properly describe bond forming and breaking. In our approach, first-principles quantum calculations are used on a set of small Si clusters in order to collect all the necessary energetic and structural information to optimize the parameters of the reactive force-field for the present application. We describe in detail the procedure used for the determination of the force field and the following molecular dynamics simulations of model systems of Si gas at temperatures in the range 2000–3000 K. The results of the dynamics provide valuable information on nucleation rate, nanoparticle size distribution, and growth rate that are the basic quantities for developing a following mesoscale model.

  12. Reduction in interface defect density in p-BaSi2/n-Si heterojunction solar cells by a modified pretreatment of the Si substrate

    Science.gov (United States)

    Yamashita, Yudai; Yachi, Suguru; Takabe, Ryota; Sato, Takuma; Emha Bayu, Miftahullatif; Toko, Kaoru; Suemasu, Takashi

    2018-02-01

    We have investigated defects that occurred at the interface of p-BaSi2/n-Si heterojunction solar cells that were fabricated by molecular beam epitaxy. X-ray diffraction measurements indicated that BaSi2 (a-axis-oriented) was subjected to in-plane compressive strain, which relaxed when the thickness of the p-BaSi2 layer exceeded 50 nm. Additionally, transmission electron microscopy revealed defects in the Si layer near steps that were present on the Si(111) substrate. Deep level transient spectroscopy revealed two different electron traps in the n-Si layer that were located at 0.33 eV (E1) and 0.19 eV (E2) below the conduction band edge. The densities of E1 and E2 levels in the region close to the heterointerface were approximately 1014 cm‑3. The density of these electron traps decreased below the limits of detection following Si pretreatment to remove the oxide layers from the n-Si substrate, which involved heating the substrate to 800 °C for 30 min under ultrahigh vacuum while depositing a layer of Si (1 nm). The remaining traps in the n-Si layer were hole traps located at 0.65 eV (H1) and 0.38 eV (H2) above the valence band edge. Their densities were as low as 1010 cm‑3. Following pretreatment, the current versus voltage characteristics of the p-BaSi2/n-Si solar cells under AM1.5 illumination were reproducible with conversion efficiencies beyond 5% when using a p-BaSi2 layer thickness of 100 nm. The origin of the H2 level is discussed.

  13. Vertical charge-carrier transport in Si nanocrystal/SiO2 multilayer structures.

    Science.gov (United States)

    Osinniy, V; Lysgaard, S; Kolkovsky, Vl; Pankratov, V; Nylandsted Larsen, A

    2009-05-13

    Charge-carrier transport in multilayer structures of Si nanocrystals (NCs) embedded in a SiO(2) matrix grown by magnetron sputtering has been investigated. The presence of two types of Si NCs with different diameters after post-growth annealing is concluded from transmission-electron microscopy and photoluminescence measurements. Based on the electric field and temperature dependences of capacitance and resistivity, it is established that the carrier transport is best described by a combination of phonon-assisted and direct tunneling mechanisms. Poole-Frenkel tunneling seems to be a less suitable mechanism to explain the vertical carrier transport due to the very high values of refractive indices obtained within this model. The possibility to more effectively collect charge carriers generated by light in structures having Si NCs of different size is discussed.

  14. High-temperature tensile strength of near-stoichiometric SiC/SiC composites

    Science.gov (United States)

    Hironaka, K.; Nozawa, T.; Hinoki, T.; Igawa, N.; Katoh, Y.; Snead, L. L.; Kohyama, A.

    2002-12-01

    In an attempt to characterize mechanical properties of near-stoichiometric SiC/SiC composites, tensile tests were conducted at room temperature in air and at elevated temperature under mild oxidizing gases atmosphere. SiC/SiC composites were fabricated by forced-flow chemical vapor infiltration method using two-dimensional fabrics of carbon coated near-stoichiometric Tyranno™SA fibers. Tensile tests were conducted on composites with two types of lay-up schemes using edge-loading small specimens. The effect of lay-up orientation on the mechanical properties and fracture behavior of composites were also examined. Tensile strength of composite was slightly decreased at 1573 K, while it retained approximately 80% of the strength at room temperature. Porosity dependence on elastic modulus was clearly exhibited.

  15. Nitrogen Plasma Processing of SiO2/4H-SiC Interfaces

    Science.gov (United States)

    Modic, A.; Sharma, Y. K.; Xu, Y.; Liu, G.; Ahyi, A. C.; Williams, J. R.; Feldman, L. C.; Dhar, S.

    2014-04-01

    A nitrogen plasma annealing process for gate dielectric applications in 4H-SiC metal oxide semiconductor (MOS) technology has been investigated. This process results in substantially greater interfacial N coverage at the SiO2/4H-SiC interface and lower interface trap densities than the state-of-the-art nitric oxide (NO) annealing process. Despite these exciting results, the field-effect mobility of MOS field-effect transistors (MOSFETs) fabricated by use of this process is very similar to that of NO-annealed MOSFETs. These results emphasize the importance of understanding mobility-limiting mechanisms in addition to charge trapping in next-generation 4H-SiC MOSFETs.

  16. Simulation and performance comparison of Si and SiC-based interleaved boost converter

    Science.gov (United States)

    Almalaq, Yasser; Alateeq, Ayoob; Matin, Mohammad

    2017-08-01

    In this paper, simulation and performance comparison of Si and SiC based interleaved boost converter is presented. Wide bandgap devices such as silicon carbide and gallium nitride are desirable and recommended in high-power applications because of their capability of operating under high temperature, high switching frequency, and high voltage with reduced switching losses. The main advantage of using SiC materials is the ability to raise the switching frequency which will reduce the size. However, their cost is high compared to Si. In this paper, 60V input voltage is used to get 120V output voltage under 100 KHz switching frequency and 0.5 duty cycle. With the help of LTSpice software, an efficiency comparison between silicon and silicon carbide by considering interleaved boost converter are simulated and studied.

  17. 75-GHz SiGe Heterojunction Bipolor Transistors: GaAs Performance in Si Technology?

    Science.gov (United States)

    1992-05-22

    frequency results of the base-collector junction without penalty on cur- SiGe and Si epitaxial base transistors (cf. Figs. I and rent density...0.60x.3 0.604.3 20 / IT (GHz) 2, 2o . .. 50A SI BJT R(W/Ob) 3.8 s 10 k (0) 60 so’ ’ . . Re (a) is 1985 1990 R (0I) 18 8 Publication Date 0VCE0 M 2.4 3.2...ee ls "SIMS profile for the SiGe-base transistors of 0Fig. 1, The Ge grading is positioned precisely 20 in the most heavily doped region of the base NC

  18. How do students from Student Incubators (SI) use networks and how can SI support the activity?

    DEFF Research Database (Denmark)

    Andersen, Henrik Mariendal

    2015-01-01

    This paper examines Student Entrepreneur’s (SE) use of networks as part of their activities in a Student Incubator (SI). Recommendations are made as to how SI can create activities to support students' use of internal and external relationships and discusses the paradox between running a learning...... is on SEs because students are likely to have a smaller (in size), less well-founded and limited professional network. In addition, an SI is assumed to be characterized by “limitations” related to their student status. So far none has paid any attention to how SEs "compensate for" and/or develop relevant...... internal and external relationships and how SI supports an appropriate project and business development process with these assumptions and “limitations” in mind. To investigate this, a series of qualitative interviews with SEs are conducted, with an emphasis on the use of relationships...

  19. IBA study of SiGe/SiO{sub 2} nanostructured multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Barradas, Nuno P., E-mail: nunoni@ctn.ist.utl.pt [Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, E.N. 10 (ao km 139,7), 2695-066 Bobadela LRS (Portugal); Laboratório de Engenharia Nuclear, Instituto Superior Técnico, Universidade de Lisboa, E.N. 10 (ao km 139,7), 2695-066 Bobadela LRS (Portugal); Alves, E. [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Vieira, E.M.F. [Centre of Physics and Physics Department, University of Minho, 4710-057 Braga (Portugal); Parisini, A. [CNR-IMM Sezione di Bologna, via P. Gobetti 101, 40129 Bologna (Italy); Conde, O. [Physics Department and ICEMS, University of Lisbon, 1749-016 Lisboa (Portugal); Martín-Sánchez, J. [Laser Processing Group, Instituto de Óptica, CSIC, C/Serrano 121, 28006 Madrid (Spain); Rolo, A.G. [Centre of Physics and Physics Department, University of Minho, 4710-057 Braga (Portugal); Chahboun, A. [Centre of Physics and Physics Department, University of Minho, 4710-057 Braga (Portugal); FST Tanger, Physics Department, BP 416 Tanger (Morocco); Gomes, M.J.M. [Centre of Physics and Physics Department, University of Minho, 4710-057 Braga (Portugal)

    2014-07-15

    SiGe/SiO{sub 2} multilayers with layer thickness of 5 nm were deposited with RF magnetron sputtering. The as deposited samples had well defined SiGe amorphous layers. Different annealing treatments were made to promote the formation of SiGe nanocrystals. We report an ion beam analysis study with the Rutherford backscattering and elastic recoil analysis detection techniques, in order to determine the thickness and composition of the nanolayers, and gain insight into the evolution of the roughness of the layers. The results are correlated with other structural properties of the samples, as measured with complementary techniques such as grazing incidence X-ray diffraction annular dark field scanning transmission electron microscopy and high resolution transmission electron microscopy.

  20. Specific features of current flow in α-Si : H/Si heterojunction solar cells

    Science.gov (United States)

    Sachenko, A. V.; Kostylyov, V. P.; Sokolovskyi, I. O.; Bobyl', A. V.; Verbitskii, V. N.; Terukov, E. I.; Shvarts, M. Z.

    2017-02-01

    Specific features of the formation of dark I-V characteristics of α-Si: H/Si heterojunction solar cells are investigated taking account the ratio between silicon doping level N d and excess concentration Δ n of electron-hole pairs. It is demonstrated that, at Δ n ≥ Nd, the I-V characteristic is fundamentally different from the characteristic of a classical Shockley diode due the effect of the backside surface (additional drop of the applied voltage). The results of analysis are used to describe the experimental I-V characteristics reported in studies on α-Si: H/Si heterojunction solar cells. Numerical values of the ideality factors of the dark I-V characteristics are obtained by comparing the experimental and calculated curves.

  1. Magnetohydrodynamic (MHD) considerations for liquid metal blanket and a SiC/SiC composite structure

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, R.; Greeff, J. de; Vinche, C. [Commission Europeenne Community, JRC, Vatican City State, Holy See (Italy)

    1998-07-01

    The electrical conductivity was measured on SiC/SiC composite specimens, in the as-received conditions and after neutron irradiation, for temperatures between 20 deg. C and 1000 deg. C. The tests were aimed at estimating the magnitude of MHD effects in liquid metal blankets and a SiC/SiC composites structure. The electrical conductivity of the unirradiated samples increased continuously with temperature and ranged from 330 ({omega} m){sup -1} at 20 deg. C to 550 ({omega} m){sup -1} at 1000 deg.C. The irradiation reduced only slightly the magnitude of {sigma} indicating the materials tested cannot be treated as an electrical insulator in a MHD analysis for liquid metal blankets. (authors)

  2. Positive magnetoresistance in Co40Fe40B20/SiO2/Si heterostructure

    KAUST Repository

    Zhang, Y.

    2016-07-20

    Current-perpendicular-to-plane electronic transport properties and magnetoresistance of amorphous Co40Fe40B20/SiO2/Si heterostructures are investigated systematically. A backward diode-like rectifying behavior was observed due to the formation of a Schottky barrier between Co40Fe40B20 and Si. The junction resistance shows a metal-insulator transition with decreasing temperature in both the forward and reverse ranges. A large positive magnetoresistance (MR) of ∼2300% appears at 200 K. The positive MR can be attributed to the magnetic-field-controlled impact ionization process of carriers. MR shows a temperature-peak-type character under a constant bias current, which is related to the spin-dependent barrier in the Si near the interface. © CopyrightEPLA, 2016.

  3. Betavoltaic device in por-SiC/Si C-Nuclear Energy Converter

    Science.gov (United States)

    Akimchenko, Alina; Chepurnov, Victor; Dolgopolov, Mikhail; Gurskaya, Albina; Kuznetsov, Oleg; Mashnin, Alikhan; Radenko, Vitaliy; Radenko, Alexander; Surnin, Oleg; Zanin, George

    2017-10-01

    The miniature and low-power devices with long service life in hard operating conditions like the Carbon-14 beta-decay energy converters indeed as eternal resource for integrated MEMS and NEMS are considered. Authors discuss how to create the power supply for MEMS/NEMS devices, based on porous SiC/Si structure, which are tested to be used as the beta-decay energy converters of radioactive C-14 into electrical energy. This is based on the silicon carbide obtaining by self-organizing mono 3C-SiC endotaxy on the Si substrate. The new idea is the C-14 atoms including in molecules in the silicon carbide porous structure by this technology, which will increase the efficiency of the converter due to the greater intensity of electron-hole pairs generation rate in the space charge region. The synthesis of C-14 can be also performed by using the electronically controlled magneto-optic chamber.

  4. High-temperature tensile strength of near-stoichiometric SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Hironaka, K. E-mail: keisuke@iae.kyoto-u.ac.jp; Nozawa, T.; Hinoki, T.; Igawa, N.; Katoh, Y.; Snead, L.L.; Kohyama, A

    2002-12-01

    In an attempt to characterize mechanical properties of near-stoichiometric SiC/SiC composites, tensile tests were conducted at room temperature in air and at elevated temperature under mild oxidizing gases atmosphere. SiC/SiC composites were fabricated by forced-flow chemical vapor infiltration method using two-dimensional fabrics of carbon coated near-stoichiometric Tyranno SA fibers. Tensile tests were conducted on composites with two types of lay-up schemes using edge-loading small specimens. The effect of lay-up orientation on the mechanical properties and fracture behavior of composites were also examined. Tensile strength of composite was slightly decreased at 1573 K, while it retained approximately 80% of the strength at room temperature. Porosity dependence on elastic modulus was clearly exhibited.

  5. Physical studies of strained Si/SiGe heterostructures. From virtual substrates to nanodevices

    Energy Technology Data Exchange (ETDEWEB)

    Minamisawa, Renato Amaral

    2011-10-21

    During the past two decades, the decrease in intrinsic delay of MOSFETs has been driven by the scaling of the device dimensions. The performance improvement has relied mostly in the increase of source velocity with gate scaling, while the transport properties of the channel have remained constant, i.e., those of conventional Si. Starting at the 90 nm node, uniaxial strain has been introduced in the transistor channel in order to further increase the source velocity. Beyond the 32 nm node, novel channel materials, with superior carrier velocities, and novel device architectures are required in order to continue the performance enhancement of MOSFETs while preserving the electrostatic control. In this Thesis, different physical aspects of strained Si and SiGe materials are investigated as a mean to increase carrier velocity in MOSFET channels. Novel approaches for the fabrication of strained Si based on ion implantation and anneal induced relaxation of virtual substrates are developed. The strain relaxation of SiGe layers is improved using a buried thin Si:C layer in the Si(100) substrate. Further, a Si{sup +} ion implantation and annealing method is investigated for relaxing virtual substrates using lower implantation dose. Finally, the uniaxial relaxation of {l_brace}110{r_brace} surface oriented substrates is demonstrated using a He ion implantation and anneal technique. Apart of channel material studies, the fundamental and technological challenges involved in the integration of strained Si and SiGe into MOSFETs are assessed. The impact of source and drain formation on the elastic strain and electrical properties of strained Si layers and nanowires is examined. Also, the formation of ultra-shallow junction in strained Si/strained Si{sub 0.5}Ge{sub 0.5}/SSOI heterostructures is investigated using different types of ion implanted specie and annealing. The results show that BF{sup +}{sub 2} implantation and low temperature annealing are suitable approaches for

  6. Blue photoluminescence and local structure of Si nanostructures embedded in SiO2 matrices

    Science.gov (United States)

    Zhang, Qi; Bayliss, S. C.; Hutt, D. A.

    1995-04-01

    Strong and stable blue photoluminescence (PL), visible to the naked eye under 0.4 μW of 300 nm and 2.7 μW of 370 nm excitation, has been observed for samples of Si clusters embedded in SiO2 matrices, prepared by rf co-sputtering followed by N2 annealing at 800 °C. Si K-edge extended x-ray absorption fine structure (EXAFS) and near-edge x-ray absorption fine structure (NEXAFS) strongly suggest the existence of Si nanoclusters with crystalline cores in the efficient emitting material. The PL excitation dependence is explained by an increase in the conduction band density of states deep in the band, and the formation of a band tail.

  7. Si-H induced synthesis of Si/Cu2O nanowire arrays for photoelectrochemical water splitting

    Science.gov (United States)

    Zhang, Shaoyang; She, Guangwei; Li, Shengyang; Mu, Lixuan; Shi, Wensheng

    2018-01-01

    We report a facile and low-cost method to synthesize Si/Cu2O heterojunction nanowire arrays, without SiOx, at the Si/Cu2O interface. The reductive Si–H bonds on the surface of Si nanowires plays a key role in situ by reducing Cu(II) ions to Cu2O nanocubes and avoiding the SiOx interface layer. Different pH values would vary the electrochemical potential of reactions and as a result, different products would be formed. Utilized as a photoanode for water splitting, Si/Cu2O nanowire arrays exhibit good photoelectrochemical performance.

  8. Origin of multistate resistive switching in Ti/manganite/Si$O_x$/Si heterostructures

    OpenAIRE

    Acevedo, W. Román; Acha, C.; Sánchez, M. J.; Levy, P.; Rubi, D.

    2016-01-01

    We report on the growth and characterization of Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/Si$O_x$/n-Si memristive devices. We demonstrate that using current as electrical stimulus unveils an intermediate resistance state, in addition to the usual high and low resistance states that are observed in standard voltage controlled experiments. Based on thorough electrical characterization (impedance spectroscopy, current-voltage curves analysis), we disclose the contribution of three different microscopic reg...

  9. Vaporization of SiO2 and MgSiO3

    Science.gov (United States)

    Stixrude, L. P.; Xiao, B.

    2016-12-01

    Vaporization of SiO2 and MgSiO3B Xiaoa and L Stixrude*a, a Department of Earth Sciences, University College London, WC1E 6BT London, UK *presenting author, email: l.stixrude@ucl.ac.uk Vaporization is an important process in Earth's earliest evolution during which giant impacts are thought to have produced a transient silicate atmosphere. As experimental data are very limited, little is known of the near-critical vaporization of Earth's major oxide components: MgO and SiO2. We have performed novel ab initio molecular dynamics simulations of vapor-liquid coexistence in the SiO2 and MgSiO3 systems. The simulations, based on density functional theory using the VASP code, begin with a suitably prepared liquid slab embedded in a vacuum. During the dynamical trajectory in the canonical ensemble, we see spontaneous vaporization, leading eventually to a steady-state chemical equilibrium between the two coexisting phases. We locate the liquid-vapor critical point at 6600 K and 0.40 g/cm3 for MgSiO3 and 5300 K and 0.43 g/cm3 for SiO2. By carefully examining the trajectories, we determine the composition and speciation of the vapor. For MgSiO3, We find that the vapor is significantly richer in Mg, O, and atomic (non-molecular) species than extrapolation of low-temperature experimental data has suggested. These results will have important implications for our understanding of the initial chemistry of the Earth and Moon and the initial thermal state of Earth.

  10. Marbled texture of sputtered Al/Si alloy thin film on Si

    Energy Technology Data Exchange (ETDEWEB)

    Gentile, M.G. [Physics Department and NIS Interdepartmental Center, University of Torino, via P. Giuria 1, 10125 Torino (Italy); Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Muñoz-Tabares, J.A.; Chiodoni, A. [Istituto Italiano di Tecnologia, Center for Space Human Robotics, Corso Trento 21, 10129 Torino (Italy); Sgorlon, C. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Para, I. [Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Carta, R.; Richieri, G. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Bejtka, K. [Istituto Italiano di Tecnologia, Center for Space Human Robotics, Corso Trento 21, 10129 Torino (Italy); Merlin, L. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Vittone, E. [Physics Department and NIS Interdepartmental Center, University of Torino, via P. Giuria 1, 10125 Torino (Italy)

    2016-08-01

    DC magnetron sputtering is a commonly used technique for the fabrication of silicon based electronic devices, since it provides high deposition rates and uniform large area metallization. However, in addition to the thickness uniformity, coating optical uniformity is a crucial need for semiconductor industrial processes, due to the wide use of optical recognition tools. In the silicon-based technology, aluminum is one of the most used materials for the metal contact. Both the pre-deposition substrate cleaning and the sputtering conditions determine the quality and the crystalline properties of the final Al deposited film. In this paper is shown that not all the mentioned conditions lead to good quality and uniform Al films. In particular, it is shown that under certain standard process conditions, Al/Si alloy (1% Si) metallization on a [100] Si presents a non-uniform reflectivity, with a marbled texture caused by flakes with milky appearance. This optical inhomogeneity is found to be caused by the coexistence of randomly orient Al/Si crystal, with heteroepitaxial Al/Si crystals, both grown on Si substrate. Based on the microstructural analysis, some strategies to mitigate or suppress this marbled texture of the Al thin film are proposed and discussed. - Highlights: • Sputtered Al/Si layers deposited on Si present evident optical non-uniformity • It could be an issue for optical recognition tools used in semiconductor industries • Optical non-uniformity is due to randomly oriented growth of Al grains. • Substrate misorientation and process temperature can mitigate the problem.

  11. Nanoscale Structuring by Misfit Dislocations in Si1-xGex/Si Epitaxial Systems

    DEFF Research Database (Denmark)

    Shiryaev, S.Y.; Jensen, Flemming; Hansen, J. Lundsgaard

    1997-01-01

    New capabilities of misfit dislocations for spatial manipulation of islands in Si1-xGex/Si heteroepitaxial systems have been elucidated. Formation of highly ordered Ge-island patterns on substrates prestructured by slip bands of misfit dislocations is revealed. The major sources leading...... to the ordering are identified to be dislocation strain fields at the surface and modifications of the nearsurface-layer morphology induced by dislocation slip....

  12. Influence of Oxidation Parameters on Roughness at the Si-SiO2 Interface.

    Science.gov (United States)

    1980-01-01

    between Si and SiO 2 down to the resolution of 1 nm (corresponding to about 3 atomic layers). Krivanek and coworkers ( 21 ) demonstrated even with a...Buiocchi, M.S. Abrahams, W.E. Ham, Appl. Phys. Lett. 30 (1977) 120 21. O.L. Krivanek , T.T. Sheng and D.C. Tsui, Appl. Phys. Lett. 32 (1978) 437 22. H.H

  13. Modeling Environmental Degradation of SiC/BN/SiC CMCs (Preprint)

    Science.gov (United States)

    2017-04-28

    AFRL-RX-WP-JA-2017-0308 MODELING ENVIRONMENTAL DEGRADATION OF SIC/BN/SIC CMCS (PREPRINT) Craig Przybyla and Michael K Cinibulk...2017 Interim 22 July 2013 – 6 January 2017 4. TITLE AND SUBTITLE MODELING ENVIRONMENTAL DEGRADATION OF SIC/BN/SIC CMCS (PREPRINT) 5a. CONTRACT...91360 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 Modeling environmental degradation of SiC/BN/SiC CMCs Triplicane A

  14. A thermokinetic model for Mg-Si couple formation in Al-Mg-Si alloys

    Science.gov (United States)

    Svoboda, J.; Shan, Y. V.; Kozeschnik, E.; Fischer, F. D.

    2016-03-01

    Mg-Si couples formed from atomic Mg and Si represent the first step in Mg-Si cluster formation in a dilute Al-Mg-Si system. Based on the thermodynamic extremal principle, a kinetic model for Mg-Si couple formation is developed. The model utilizes the trapping concept for the calculation of Gibbs energy of the non-equilibrium system and provides a generalized (multiplicative) form of the Oriani equation for description of the equilibrium state. The dissipation in the system accounts for diffusion of both Mg and Si atoms in the lattice. The model is compared with the classical Lidiard and Howard equilibrium theory. Some demonstrative examples are presented. Finally the model is applied to an experimentally studied system. Good quantitative agreement with quenching experiments is obtained, if, simultaneously, the impact of excess quenched-in vacancies and their gradual annihilation in the system, which has been already treated in a previous paper, are accounted for. The model is generally applicable for any couple (and pair) formation.

  15. Comparative study by IBIC of Si and SiC diodes irradiated with high energy protons

    Energy Technology Data Exchange (ETDEWEB)

    Garcia Lopez, J., E-mail: fjgl@us.es [Dpto. Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41080 Sevilla (Spain); CNA (U. Sevilla, J. Andalucia, CSIC), Av. Thomas A. Edison 7, 41092 Sevilla (Spain); Jimenez-Ramos, M.C.; Rodriguez-Ramos, M. [CNA (U. Sevilla, J. Andalucia, CSIC), Av. Thomas A. Edison 7, 41092 Sevilla (Spain); Ceballos, J. [Institute of Microelectronics of Seville, IMSE-CNM (CSIC/University of Seville), Seville 41092 (Spain); Linez, F. [Department of Applied Physics, Aalto University, 02150 Espoo (Finland); Raisanen, J. [Department of Physics, University of Helsinki, Helsinki 00014 (Finland)

    2016-04-01

    The transport properties of a series of Si and SiC diodes have been studied using the Ion Beam Induced Charge (IBIC) technique. Structural defects were induced into the samples during the irradiation with 17 MeV protons. The experimental values of the charge collection efficiency (CCE) vs bias voltages have been analyzed using a modified drift-diffusion model, which takes into account the recombination of carriers in the neutral and depletion regions. From these simulations, we have obtained the values of the carrier’s lifetime for pristine and irradiated diodes, which are found to degrade faster in the case of the SiC samples. However, the decrease of the CCE at high bias voltages is more important for the Si detectors, indicative of the lower radiation hardness of this material compared to SiC. The nature of the proton-induced defects on Si wafers has been studied by Positron Annihilation Spectroscopy (PAS) and Doppler Broadening Spectroscopy (DBS). The results suggest that the main defect detected by the positrons in p-type samples is the divacancy while for n-type at least a fraction of the positron annihilate in another defect. The concentration of defects is much lower than the number of vacancies predicted by SRIM.

  16. Effect of High Si Content on U3Si2 Fuel Microstructure

    Science.gov (United States)

    Rosales, Jhonathan; van Rooyen, Isabella J.; Meher, Subhashish; Hoggan, Rita; Parga, Clemente; Harp, Jason

    2017-11-01

    The development of U3Si2 as an accident-tolerant nuclear fuel has gained research interest because of its promising high uranium density and improved thermal properties. In the present study, three samples of U3Si2 fuel with varying silicon content have been fabricated by a conventional powder metallurgical route. Microstructural characterization via scanning and transmission electron microscopy reveals the presence of other stoichiometry of uranium silicide such as USi and UO2 in both samples. The detailed phase analysis by x-ray diffraction shows the presence of secondary phases, such as USi, U3Si, and UO2. The samples with higher concentrations of silicon content of 7.5 wt.% display additional elemental Si. These samples also possess an increased amount of the USi phase as compared to that in the conventional sample with 7.3 wt.% silicon. The optimization of U3Si2 fuel performance through the understanding of the role of Si content on its microstructure has been discussed.

  17. Temperature determination of the Si-SiC eutectic fixed point using thermocouples

    Science.gov (United States)

    Suherlan; Kim, Yong-Gyoo; Joung, Wukchul; Yang, Inseok

    2015-04-01

    The temperature of the Si-SiC eutectic fixed point for use in thermocouple thermometry has been determined. Three Si-SiC cells were fabricated from pure silicon powder within separate graphite crucibles. Each of the three cells was cycled through 17 melt-freeze cycles and subjected to temperatures above 1400 °C for a period of approximately 73 h, and none showed any sign of mechanical failure. The melting transition was measured using three types of thermocouple: one type S, one type B, and two Pt/Pd thermocouples calibrated at the fixed points of Ag, Cu, Fe-C, Co-C, and Pd (only for type B). The transition temperature, measured using the type S and two Pt/Pd thermocouples, was (1410.0 ± 0.8) °C with k = 2. However, the measurement uncertainty using the type B thermocouple was as large as 1.5 °C (k = 2) due to the inhomogeneity of the thermocouple. The repeatability of the three Si-SiC cells was calculated to be 0.3 °C, and the extremes of the temperature measurement differed by 0.8 °C.

  18. Thermophysical properties of Si, Ge and Si-Ge melts under microgravity

    Energy Technology Data Exchange (ETDEWEB)

    Chathoth, Suresh Mavila; Damaschke, Bernd; Samwer, Konrad [I. Physikalisches Institut, Universitaet Goettingen, 37077 Goettingen (Germany)

    2007-07-01

    The liquid Si and Ge are highly reactive materials. Especially the liquid Si is known to reactive with almost all materials. To have an accurate values of thermophysical properties of these melts container less processing is required. The container less processing can be realized by electromagnetic or electrostatic levitation. These ground based levitation techniques have demerits of gravity driven convection and accuracy of the data depend on convection currents. The thermophysical properties of Si, Ge and Si-Ge alloy melts have been investigated in the TEMPUS facility on board of Zero-G plane during the parabolic flights. Unlike metallic alloys which can melt in a magnetic field, Si, Ge and Si-Ge are semiconductors in their sold state a laser pre-heating was necessary to melt these samples. The melted droplets were video taped and from the images the thermal expansion and surface tension of the samples were evaluated. Absence of gravity driven convection a separation of the influence of gravity induced convection become possible by comparing the data with ground based experiments.

  19. Drawing siRNAs of viral origin out from plant siRNAs libraries.

    Science.gov (United States)

    Miozzi, Laura; Pantaleo, Vitantonio

    2015-01-01

    Viruses are obligate intracellular entities that infect all forms of life. In plants, invading viral nucleic acids trigger RNA silencing machinery and it results in the accumulation of viral short interfering RNAs (v-siRNAs). The study of v-siRNAs population in biological samples has become a major part of many research projects aiming to identify viruses infecting them, including unknown viruses, even at extremely low titer. Currently, siRNA populations are investigated by high-throughput sequencing approaches, which generate very large data sets. The major difficulty in these studies is to properly analyze such huge amount of data. In this regard, easy-to-use bioinformatics tools to groom and decipher siRNA libraries and to draw out v-siRNAs are needed. Here we describe a workflow, which permit users with little experience in bioinformatics to draw out v-siRNAs from raw data sequences obtained by Illumina technology. Such pipeline has been released in the context of Galaxy, an open source Web-based platform for bioinformatics analyses.

  20. Spectroscopic ellipsometry of columnar porous Si thin films and Si nanowires

    Science.gov (United States)

    Fodor, Bálint; Defforge, Thomas; Agócs, Emil; Fried, Miklós; Gautier, Gaël; Petrik, Péter

    2017-11-01

    Columnar mesoporous Si thin films and dense nanowire (SiNW) carpets were investigated by spectroscopic ellipsometry in the visible-near-infrared wavelength range. Porous Si layers were formed by electrochemical etching while structural anisotropy was controlled by the applied current. Layers of highly oriented SiNWs, with length up to 4.1 μm were synthesized by metal-assisted chemical etching. Ellipsometric spectra were fitted with different multi-layered, effective medium approximation-based (EMA) models. Isotropic, in-depth graded, anisotropic and hybrid EMA models were investigated with the help of the root mean square errors obtained from the fits. Ellipsometric-fitted layer thicknesses were also cross-checked by scanning electron microscopy showing an excellent agreement. Furthermore, in the case of mesoporous silicon, characterization also revealed that, at low current densities (100 mA/cm2) this behavior turns around, and anisotropy becomes the dominant feature describing the spectra. Characterization of SiNW layers showed a very high geometrical anisotropy. However, the highest fitted geometrical anisotropy was obtained for the layer composed of ∼1 μm long SiNWs indicating that for thicker layers, collapse of the nanowires occurs.

  1. Small sensitivity to temperature variations of Si-photonic Mach-Zehnder interferometer using Si and SiN waveguides

    Directory of Open Access Journals (Sweden)

    Tatsurou eHiraki

    2015-03-01

    Full Text Available We demonstrated a small sensitivity to temperature variations of delay-line Mach-Zehnder interferometer (DL MZI on a Si photonics platform. The key technique is to balance a thermo-optic effect in the two arms by using waveguide made of different materials. With silicon and silicon nitride waveguides, the fabricated DL MZI with a free-spectrum range of ~40 GHz showed a wavelength shift of -2.8 pm/K with temperature variations, which is 24 times smaller than that of the conventional Si-waveguide DL MZI. We also demonstrated the decoding of the 40-Gbit/s differential phase-shift keying signals to on-off keying signals with various temperatures. The tolerable temperature variation for the acceptable power penalty was significantly improved due to the small wavelength shifts.

  2. Low Activation Joining of SiC/SiC Composites for Fusion Applications: Modeling Thermal and Irradiation-induced Swelling Effects on Integrity of Ti3SiC2/SiC Joint

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-03-31

    This work developed a continuum damage mechanics model that incorporates thermal expansion combined with irradiation-induced swelling effects to study the origin of cracking observed in recent irradiation experiments. Micromechanical modeling using an Eshelby-Mori-Tanaka approach was used to compute the thermoelastic properties of the Ti3SiC2/SiC joint needed for the model. In addition, a microstructural dual-phase Ti3SiC2/SiC model was developed to determine irradiation-induced swelling of the composite joint at a given temperature resulting from differential swelling of SiC and the Ti3SiC2 MAX phase. Three cases for the miniature torsion hourglass (THG) specimens containing a Ti3SiC2/SiC joint were analyzed corresponding to three irradiation temperatures: 800oC, 500oC, and 400oC.

  3. Oxidation of TaSi2-Containing ZrB2-SiC Ultra-High Temperature Materials

    Science.gov (United States)

    Opila, Elizabeth J.; Smith, Jim; Levine, Stanley R.; Lorincz, Jonathan; Reigel, Marissa

    2010-01-01

    Hot pressed coupons of composition ZrB2-20 v% SiC-5 v% TaSi2 and ZrB2-20 v% SiC-20 v% TaSi2 were oxidized in stagnant air at temperatures of 1627 and 1927C for one, five and ten 10-minute cycles. The oxidation reactions were characterized by weight change kinetics, x-ray diffraction, and SEM/EDS. Detailed WDS/microprobe quantitative analyses of the oxidation products were conducted for the ZrB2-20 v% SiC-20 v% TaSi2 sample oxidized for five 10-minute cycles at 1927C. Oxidation kinetics and product formation were compared to ZrB2-20 v% SiC with no TaSi2 additions. It was found that the 20 v% TaSi2 composition exhibited improved oxidation resistance relative to the material with no TaSi2 additions at 1627C. However, for exposures at 1927C less oxidation resistance and extensive liquid phase formation were observed compared to the material with no TaSi2 additions. Attempts to limit the liquid phase formation by reducing the TaSi2 content to 5 v% were unsuccessful. In addition, the enhanced oxidation resistance at 1627C due to 20 v% TaSi2 additions was not achieved at the 5 v% addition level. The observed oxidation product evolution is discussed in terms of thermodynamics and phase equilibria for the TaSi2-containing ZrB2-SiC material system. TaSi2-additions to ZrB2-SiC at any level are not recommended for ultra-high temperature (>1900C) applications due to excessive liquid phase formation.

  4. Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Xunxiang [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Ang, Caen K. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Singh, Gyanender P. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Katoh, Yutai [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

    2016-08-01

    Driven by the need to enlarge the safety margins of nuclear fission reactors in accident scenarios, research and development of accident-tolerant fuel has become an important topic in the nuclear engineering and materials community. A continuous-fiber SiC/SiC composite is under consideration as a replacement for traditional zirconium alloy cladding owing to its high-temperature stability, chemical inertness, and exceptional irradiation resistance. An important task is the development of characterization techniques for SiC/SiC cladding, since traditional work using rectangular bars or disks cannot directly provide useful information on the properties of SiC/SiC composite tubes for fuel cladding applications. At Oak Ridge National Laboratory, experimental capabilities are under development to characterize the modulus, microcracking, and hermeticity of as-fabricated, as-irradiated SiC/SiC composite tubes. Resonant ultrasound spectroscopy has been validated as a promising technique to evaluate the elastic properties of SiC/SiC composite tubes and microcracking within the material. A similar technique, impulse excitation, is efficient in determining the basic mechanical properties of SiC bars prepared by chemical vapor deposition; it also has potential for application in studying the mechanical properties of SiC/SiC composite tubes. Complete evaluation of the quality of the developed coatings, a major mitigation strategy against gas permeation and hydrothermal corrosion, requires the deployment of various experimental techniques, such as scratch indentation, tensile pulling-off tests, and scanning electron microscopy. In addition, a comprehensive permeation test station is being established to assess the hermeticity of SiC/SiC composite tubes and to determine the H/D/He permeability of SiC/SiC composites. This report summarizes the current status of the development of these experimental capabilities.

  5. Composite films of highly ordered Si nanowires embedded in SiGe0.3 for thermoelectric applications

    Science.gov (United States)

    Kikuchi, Akiou; Yao, Akifumi; Mori, Isamu; Ono, Takahito; Samukawa, Seiji

    2017-10-01

    We fabricated a high-density array of silicon nanowires (SiNWs) with a diameter of 10 nm embedded in silicon germanium (SiGe0.3) to give a composite thin film for thermoelectric device applications. The SiNW array was first fabricated by bio-template mask and neutral beam etching techniques. The SiNW array was then embedded in SiGe0.3 by thermal chemical vapor deposition. The cross-plane thermal conductivity of the SiNW-SiGe0.3 composite film with a thickness of 100 nm was 3.5 ± 0.3 W/mK in the temperature range of 300-350 K. Moreover, the temperature dependences of the in-plane electrical conductivity and in-plane Seebeck coefficient of the SiNW-SiGe0.3 composite were evaluated. The fabricated SiNW-SiGe0.3 composite film displayed a maximum power factor of 1 × 103 W/m K2 (a Seebeck coefficient of 4.8 × 103 μV/K and an electrical conductivity of 4.4 × 103 S/m) at 873 K. The present high-density SiNW array structure represents a new route to realize practical thermoelectric devices using mature Si processes without any rare metals.

  6. Transport properties of RuSi, RuGe, OsSi, and quasi-binary alloys of these compounds

    Energy Technology Data Exchange (ETDEWEB)

    Hohl, H.; Ramirez, A.P.; Goldmann, C.; Ernst, G.; Bucher, E. [Bell Labs., Holmdel, NJ (United States). Lucent Technologies

    1998-08-21

    RuSi, RuGe, OsSi and the solid solutions RuSi{sub 0.5}Ge{sub 0.5} and Ru{sub 0.5}Os{sub 0.5}Si are investigated. All of them crystallize in the cubic B20 structure. The systems RuSi-RuGe and RuSi-OsSi form solid solutions which obey Vegard`s law. RuSi, RuSi{sub 0.5}Ge{sub 0.5}, and RuGe are semiconductors with band gaps of 0.26,0.20 and 0.15 eV, respectively. OsSi and Ru{sub 0.5}Os{sub 0.5}Si are degenerate semiconductors; their band gaps are larger than 0.26 eV. The thermal conductivity of the materials is dominated by the contributions of the lattice. The magnetic behavior is temperature independent and diamagnetic. RuSi and RuSi{sub 0.5}Ge{sub 0.5} exhibit large Seebeck coefficients of almost 300 {mu}V K{sup -1}, but their dimensionless thermoelectric figure of merit ZT does not exceed 0.03. (orig.) 12 refs.

  7. Predicting siRNA efficacy based on multiple selective siRNA representations and their combination at score level

    Science.gov (United States)

    He, Fei; Han, Ye; Gong, Jianting; Song, Jiazhi; Wang, Han; Li, Yanwen

    2017-03-01

    Small interfering RNAs (siRNAs) may induce to targeted gene knockdown, and the gene silencing effectiveness relies on the efficacy of the siRNA. Therefore, the task of this paper is to construct an effective siRNA prediction method. In our work, we try to describe siRNA from both quantitative and qualitative aspects. For quantitative analyses, we form four groups of effective features, including nucleotide frequencies, thermodynamic stability profile, thermodynamic of siRNA-mRNA interaction, and mRNA related features, as a new mixed representation, in which thermodynamic of siRNA-mRNA interaction is introduced to siRNA efficacy prediction for the first time to our best knowledge. And then an F-score based feature selection is employed to investigate the contribution of each feature and remove the weak relevant features. Meanwhile, we encode the siRNA sequence and existed empirical design rules as a qualitative siRNA representation. These two kinds of siRNA representations are combined to predict siRNA efficacy by supported Vector Regression (SVR) at score level. The experimental results indicate that our method may select the features with powerful discriminative ability and make the two kinds of siRNA representations work at full capacity. The prediction results also demonstrate that our method can outperform other popular siRNA efficacy prediction algorithms.

  8. Effects of antimony (Sb) on electron trapping near SiO{sub 2}/4H-SiC interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Mooney, P. M.; Jiang, Zenan; Basile, A. F. [Physics Department, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Zheng, Yongju; Dhar, Sarit [Physics Department, Auburn University, Auburn, Alabama 36849 (United States)

    2016-07-21

    To investigate the mechanism by which Sb at the SiO{sub 2}/SiC interface improves the channel mobility of 4H-SiC MOSFETs, 1 MHz capacitance measurements and constant capacitance deep level transient spectroscopy (CCDLTS) measurements were performed on Sb-implanted 4H-SiC MOS capacitors. The measurements reveal a significant concentration of Sb donors near the SiO{sub 2}/SiC interface. Two Sb donor related CCDLTS peaks corresponding to shallow energy levels in SiC were observed close to the SiO{sub 2}/SiC interface. Furthermore, CCDLTS measurements show that the same type of near-interface traps found in conventional dry oxide or NO-annealed capacitors are present in the Sb implanted samples. These are O1 traps, suggested to be carbon dimers substituted for O dimers in SiO{sub 2}, and O2 traps, suggested to be interstitial Si in SiO{sub 2}. However, electron trapping is reduced by a factor of ∼2 in Sb-implanted samples compared with samples with no Sb, primarily at energy levels within 0.2 eV of the SiC conduction band edge. This trap passivation effect is relatively small compared with the Sb-induced counter-doping effect on the MOSFET channel surface, which results in improved channel transport.

  9. siRNA as an alternative therapy against viral infections

    Directory of Open Access Journals (Sweden)

    Hana A. Pawestri

    2012-07-01

    Full Text Available siRNA (small interfering ribonucleic acid adalah sebuah metode yang dapat digunakan untuk mengatasi infeksi virus yang prinsip kerjanya berdasarkan metode komplementer dsRNA (double stranded RNA pada RNA virus sehingga menyebabkan kegagalan proses transkripsi (silencing.  Untuk lebih memahami bagaimana proses kerja dan ulasan penelitian siRNA yang terkini, di dalam tulisan ini ditinjau siRNA sebagai metoda yang dikembangkan untuk mengatasi infeksi dan meneliti efeknya pada replikasi beberapa virus seperti Hepatitis C, Influenza, Polio, dan HIV. Kami menemukan bahwa urutan basa nukleotida dari target siRNA sangat penting. Hal tersebut harus homolog dengan target RNA virus dan tidak menganggu RNA sel inang. Untuk mengurangi kegagalan terapi siRNA oleh adanya mutasi, digunakan beberapa siRNA yang sekaligus menjadi target RNA virus yang berbeda. Namun demikian, terapi siRNA masih menghadapi beberapa kesulitan seperti pengiriman (transfer khusus ke jaringan yang terinfeksi dan perlindungan siRNA dari perusakan oleh nuklease. Berdasarkan beberapa penelitian yang telah dilakukan, siRNA dapat digunakan sebagai alternatif untuk mengobati infeksi yang disebabkan oleh virus. Terapi tersebut direkomendasikan untuk dilakukan uji klinis dengan memperhatikan beberapa aspek seperti desain siRNA dan mekanisme transfer. (Health Science Indones 2010; 1: 58 - 65 Kata kunci: siRNA, infeksi virus, target virus, alternatif terapi Abstract SiRNA is a promising method to deal with viral infections. The principle of siRNA is based on the complementarily of (synthetic dsRNA to an RNA virus which, in consequence, will be silenced. Many studies are currently examining the effects of siRNA on replication of diverse virus types like Hepatitis C, polio and HIV. The choice of the siRNA target sequence is crucial. It has to be very homologous to the target RNA, but it cannot target RNA of the host cell. To reduce the possibility for the virus to escape from the siRNA therapy by

  10. SiC device development for high temperature sensor applications

    Science.gov (United States)

    Shor, J. S.; Goldstein, David; Kurtz, A. D.; Osgood, R. M.

    1992-01-01

    Progress made in the processing and characterization of 3C-SiC for high temperature sensor applications is reviewed. Piezoresistance properties of silicon carbide and the temperature coefficient of resistivity of n-type beta-SiC are presented. In addition, photoelectrical etching and dopant selective etch-stops in SiC and high temperature Ohmic contacts for n-type beta-SiC sensors are discussed.

  11. Prospects for SiC electronics and sensors

    OpenAIRE

    Nick G. Wright; Alton B. Horsfall; Vassilevski, Konstantin

    2008-01-01

    There has been substantial international research effort in the development of SiC electronics over the last ten years. With promising applications in power electronics, hostile-environment electronics, and sensors, there is considerable industrial interest in SiC as a material for electronics. However, issues relating to crystal growth and the difficulties of material processing have restricted SiC devices to relatively limited use to date. The eventual success of SiC as an electronic techno...

  12. Fluorescent SiC for white light-emitting diodes

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Kamiyama, S.

    2012-01-01

    The strong photoluminescence from f-SiC was achieved after the optimization of the B and N concentrations. Surface nanostructures were successfully applied to enhance the extraction efficiency. f-SiC is a promising wavelength convertor for white LEDs.......The strong photoluminescence from f-SiC was achieved after the optimization of the B and N concentrations. Surface nanostructures were successfully applied to enhance the extraction efficiency. f-SiC is a promising wavelength convertor for white LEDs....

  13. Densification and mechanical properties of mullite–SiC ...

    Indian Academy of Sciences (India)

    Unknown

    Nanosize SiC (average size 180 nm) surface was first provided with a mullite precursor coating which was characterized by the X-ray analysis and TEM. ... load of 500 g. This value gradually decreased with an increase in SiC content. Keywords. Mullite–SiC nanocomposites; sol–gel; microstructure; Vicker's microhardness.

  14. SiGe thin-film structures for solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Bremond, G.; Daami, A.; Laugier, A. [Inst. National des Sciences Appliquees de Lyon, Villeurbanne (France). Lab. de Physique de la Matiere] [and others

    1998-12-31

    In order to study their applicability as the active base material in Si thin crystalline film solar cell technology, SiGe relaxed layers grown by Liquid Phase Epitaxy (LPE) and Chemical Vapor Deposition (CVD) on Si substrates are investigated by optical and electrical measurements (TEM, EXD, PL, EBIC). The main results of this work is to point out the improvement of the SiGe active base layer by using smooth Ge graded SiGe buffer layer and remote plasma hydrogenation. TEM, EXD, PL experiments show the effect of the Ge graded buffer layer grown using LPE, by confining the threading dislocations in the SiGe buffer layer close to the Si/SiGe interface. EBIC measurements reveal low recombination activity of dislocations at 300 K providing the diffusion length exceeds the 15 {micro}m layer thickness. The enhanced luminescence of SiGe near bandgap indicates that remote plasma hydrogenation induces a decrease of the non-radiative recombination pathways due to dislocations on CVD layers where defect recombinations dominate as indicated by EBIC measurements. This study points out the importance of controlling relaxed SiGe layers with good minority carrier recombination quality as a key issue for the optimization of new SiGe/Si based solar cells.

  15. Low Temperature Photoluminescence of 6H fluorescent SiC

    DEFF Research Database (Denmark)

    Wei, Yi; Künecke, Ulrike; Jokubavicius, Valdas

    We have presented the low temperature photoluminescence (PL) measurements of three 6H fluorescent Silicon Carbide (f-SiC) samples. The epilayers of the f-SiC samples were nitrogenboron co-doped and grown by fast sublimation growth process (FSGP) method on the bulk 6H SiC substrates. The doping...

  16. The growth and the electrical properties of epitaxial CrSi sub 2 films prepared on Si(111) substrates

    CERN Document Server

    Kim, K H; Lee, J J; Choi, C K; Lee, J Y; Lee, Y P

    1998-01-01

    About a 290-A-thick CrSi sub 2 film was epitaxially grown on a Si(111) substrate by Cr deposition on a Si(111)-7x7 substrate at approx 450 .deg. C followed by in suit annealing at approx 1000 .deg . C for 10 min. X-ray diffraction and transmission electron microscopy showed that the CrSi sub 2 (001) plane grew parallel to the Si(111) plane with a CrSi sub 2 llSi matching face relationship. CrSi sub 2 is a p-type degenerate semiconductor. The electrical resistivity at room temperature was approx 5 x approx 10 sup - sup 3 OMEGA cm, and the energy band gap deduced from the temperature dependence of resistivity was approx 0.3 eV.

  17. Study on Mechanical Behavior of CVD-SiC Coated C/SiC Composites under Simulated Space Environments

    Science.gov (United States)

    Yang, Xiang; Feng, Cao; Yi, Wang; Guang-de, Li; Jie, Cao

    2017-10-01

    SiC coating was prepared on the surface of C/SiC composites by chemical vapor deposition (CVD) method, and then mechanical behavior of CVD-SiC coated C/SiC composites under cold and thermal cycling had been investigated. Specimens were thermally cycled between the temperatures of -100 °C and 100 °C for up to 200 cycles, respectively. The coating was characterized by XRD, SEM and EDS. The results showed that there were no significant changes in the flexural property. CVD-SiC coated C/SiC composites had good mechanical stability in above simulated space environments. While great changes occurred on both elements and structure of the coating, from homogeneous single-phase of SiC into the inner layer of SiC and the outer of C, which caused the change of the bending strength.

  18. Enhanced optical second-harmonic generation from the current-biased graphene/SiO2/Si(001) structure.

    Science.gov (United States)

    An, Yong Q; Nelson, Florence; Lee, Ji Ung; Diebold, Alain C

    2013-05-08

    We find that optical second-harmonic generation (SHG) in reflection from a chemical-vapor-deposition graphene monolayer transferred onto a SiO2/Si(001) substrate is enhanced about 3 times by the flow of direct current electric current in graphene. Measurements of rotational-anisotropy SHG revealed that the current-induced SHG from the current-biased graphene/SiO2/Si(001) structure undergoes a phase inversion as the measurement location on graphene is shifted laterally along the current flow direction. The enhancement is due to current-associated charge trapping at the graphene/SiO2 interface, which introduces a vertical electric field across the SiO2/Si interface that produces electric field-induced SHG. The phase inversion is due to the positive-to-negative polarity switch in the current direction of the trapped charges at the current-biased graphene/SiO2 interface.

  19. Efficient fabrication of nanoporous si and Si/Ge enabled by a heat scavenger in magnesiothermic reactions

    National Research Council Canada - National Science Library

    Luo, Wei; Wang, Xingfeng; Meyers, Colin; Wannenmacher, Nick; Sirisaksoontorn, Weekit; Lerner, Michael M; Ji, Xiulei

    2013-01-01

    Magnesiothermic reduction can directly convert SiO2 into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature...

  20. Characterization of SiO{sub 2}/SiN{sub x} gate insulators for graphene based nanoelectromechanical systems

    Energy Technology Data Exchange (ETDEWEB)

    Tóvári, E.; Csontos, M., E-mail: csontos@dept.phy.bme.hu; Kriváchy, T.; Csonka, S. [Department of Physics, Budapest University of Technology and Economics and Condensed Matter Research Group of the Hungarian Academy of Sciences, Budafoki út 8, H-1111 Budapest (Hungary); Fürjes, P. [MEMS Lab, Institute for Technical Physics and Materials Science, RCNS, HAS, Konkoly-Thege út 29-33, H-1121 Budapest (Hungary)

    2014-09-22

    The structural and magnetotransport characterization of graphene nanodevices exfoliated onto Si/SiO{sub 2}/SiN{sub x} heterostructures are presented. Improved visibility of the deposited flakes is achieved by optimal tuning of the dielectric film thicknesses. The conductance of single layer graphene Hall-bar nanostructures utilizing SiO{sub 2}/SiN{sub x} gate dielectrics were characterized in the quantum Hall regime. Our results highlight that, while exhibiting better mechanical and chemical stability, the effect of non-stoichiometric SiN{sub x} on the charge carrier mobility of graphene is comparable to that of SiO{sub 2}, demonstrating the merits of SiN{sub x} as an ideal material platform for graphene based nanoelectromechanical applications.

  1. As escritas de si do punk

    Directory of Open Access Journals (Sweden)

    Everton de Oliveira Moraes

    2014-10-01

    Full Text Available O artigo tem por objetivo discutir e analisar a escrita dos fanzines, entendendo-a como um importante elemento na constituição de subjetividades e sensibilidades punks e como uma prática contestadora do regime contemporâneo de produção de subjetividades. Contestação realizada através de uma constante problematização das próprias condutas, pensamentos e dos significados do punk. Cria-se, desse modo, uma cultura do cuidado de si, da crítica constante de si mesmo através da escrita. Esta escapa ao modelo clássico do militante engajado, mas também as formas pelas quais o discurso exerce, na modernidade, um certo tipo de poder que, ao pretender dizer a verdade sobre as coisas, procurava conjurar qualquer possibilidade do acontecimento dessa escrita se efetuar de outra maneira.

  2. Vacancies in SiC nanopowders

    Energy Technology Data Exchange (ETDEWEB)

    Kityk, I.V.; Makowska-Janusik, M. [Technical Univ. of Czestochowa (Poland). Inst. of Phys.; Kassiba, A.; Charpentier, C. [Laboratoire de Physique de l' Etat Condense, UPRES-A6087, Universite du Maine, Avenue Olivier Messiaen, 72085 Cedex 9, LeMans (France); Tuesu, K. [Research Informatic Science Department, Tohoku University, 2-1-4 Katahira, Aoba-ku, 982-12, Sendai (Japan); Ling, Y. [Michigan Molecular Institute, 48640, Midland, MI (United States)

    2000-08-31

    Origin of vacancies in the large-sized SiC nanocrystals (higher than 10 nm) has been investigated using theoretical band structure calculations and experimental electronic paramagnetic resonance (EPR) measurements. Influence of geometry sizes on appearance of concrete vacancy has been studied. The theoretical approach includes self-consistent norm-conserving pseudopotential band energy calculations and geometry structure optimisation. The performed calculations show that the presence of the vacancies is a necessary attribute of the SiC nanocrystallites. Moreover, the type and concentration of the vacancies are dependent on the nanoparticle geometry. We have revealed that spin-polarised states of intracrystallite vacancies differ essentially from vacancies in the bulk crystals. A comparison between the performed theoretical simulations and obtained EPR experimental data shows the possibility of using the proposed methods for prediction of vacancy appearance in the binary nanocrystallites and possibility for their operation. (orig.)

  3. Sonochemical preparation of SbSI gel.

    Science.gov (United States)

    Nowak, M; Szperlich, P; Bober, L; Szala, J; Moskal, G; Stróz, D

    2008-07-01

    A novel sonochemical method for direct preparation of nanocrystalline antimony sulfoiodide (SbSI) has been established. The SbSI gel was synthesized using elemental Sb, S and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2 W/cm2) at 50 degrees C for 2 h. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and optical diffuse reflection spectroscopy (DRS). The SEM and HRTEM investigations exhibit that the as-prepared samples are made up of large quantity nanowires with diameters of about 10-50 nm and lengths reaching up to several micrometers and single-crystalline in nature.

  4. Dendrimers for siRNA Delivery

    Directory of Open Access Journals (Sweden)

    Swati Biswas

    2013-02-01

    Full Text Available Since the discovery of the “starburst polymer”, later renamed as dendrimer, this class of polymers has gained considerable attention for numerous biomedical applications, due mainly to the unique characteristics of this macromolecule, including its monodispersity, uniformity, and the presence of numerous functionalizable terminal groups. In recent years, dendrimers have been studied extensively for their potential application as carriers for nucleic acid therapeutics, which utilize the cationic charge of the dendrimers for effective dendrimer-nucleic acid condensation. siRNA is considered a promising, versatile tool among various RNAi-based therapeutics, which can effectively regulate gene expression if delivered successfully inside the cells. This review reports on the advancements in the development of dendrimers as siRNA carriers.

  5. The National Si-Soft Project

    Science.gov (United States)

    Chang, Chun-Yen; Trappey, Charles V.

    2003-06-01

    Taiwan's electronics industry emerged in the 1960s with the creation of a small but well planned integrated circuit (IC) packaging industry. This industry investment led to bolder investments in research, laboratories, and the island's first semiconductor foundries in the 1980s. Following the success of the emerging IC manufacturers and design houses, hundreds of service firms and related industries (software, legal services, substrate, chemical, and test firms among others) opened for business and completed Taiwan's IC manufacturing supply chain. The challenge for Taiwan's electronics industry is to take the lead in the design, manufacture, and marketing of name brand electronic products. This paper introduces the Si-Soft (silicon software) Project, a national initiative that builds on Taiwan's achievements in manufacturing (referred to as Si-Hard or silicon hardware) to launch a new wave of companies. These firms will contribute to the core underlying technology (intellectual property) used in the creation of electronic products.

  6. El operador discursivo ya si eso

    Directory of Open Access Journals (Sweden)

    Elvira Comas Leonés

    2015-12-01

    Full Text Available La pragmática es una ciencia en constante evolución y actualidad, tanto como el estudio del español coloquial, que, en nuestros días, supone enfocar la lengua a estructuras muy utilizadas por los hablantes pero que no poseen análisis exhaustivos por parte de la lingüística. En este uso mayoritariamente oral de la lengua, podemos encontrar determinados marcadores que los hablantes a menudo utilizan y que podemos considerar objetos de estudio. Los operadores discursivos si eso y sus variantes, como ya si eso, son construcciones que aún no se han lexicalizado pero que merecen ser objeto de estudio por cuanto su uso y connotaciones están aumentando en la actualidad. 

  7. Photonic Multitasking Interleaved Si Nanoantenna Phased Array.

    Science.gov (United States)

    Lin, Dianmin; Holsteen, Aaron L; Maguid, Elhanan; Wetzstein, Gordon; Kik, Pieter G; Hasman, Erez; Brongersma, Mark L

    2016-12-14

    Metasurfaces provide unprecedented control over light propagation by imparting local, space-variant phase changes on an incident electromagnetic wave. They can improve the performance of conventional optical elements and facilitate the creation of optical components with new functionalities and form factors. Here, we build on knowledge from shared aperture phased array antennas and Si-based gradient metasurfaces to realize various multifunctional metasurfaces capable of achieving multiple distinct functions within a single surface region. As a key point, we demonstrate that interleaving multiple optical elements can be accomplished without reducing the aperture of each subelement. Multifunctional optical elements constructed from Si-based gradient metasurface are realized, including axial and lateral multifocus geometric phase metasurface lenses. We further demonstrate multiwavelength color imaging with a high spatial resolution. Finally, optical imaging functionality with simultaneous color separation has been obtained by using multifunctional metasurfaces, which opens up new opportunities for the field of advanced imaging and display.

  8. Liposomes as siRNA delivery vectors.

    Science.gov (United States)

    Bochicchio, Sabrina; Dalmoro, Annalisa; Barba, Anna Angela; Grassi, Gabriele; Lamberti, Gaetano

    2014-01-01

    Nucleic Acid Based Drugs (NABDs) constitute a class of promising and powerful therapeutic new agents with limited side effects, potentially useable against a wide range of diseases, including cancer. Among them, the short interfering RNAs (siRNAs), represent very effective molecules. Despite their in vitro efficacy, the major drawback that limits siRNAs usage consists in a difficult delivery due to their very low stability in physiological fluids, and to their limited membrane-permeability through physiological barriers. On the other hand, the liposomes (lipid bilayers closed in vesicles of various sizes) represent interesting drug delivery systems (DDSs) which can be tailored in order to get the best performance in terms of load, vesicle size and transfection yield. In this work, the current state of study in these two fields, and the connections between them, are briefly summarized.

  9. Distribution of nitrogen and defects in SiO(x)N(y)/Si structures formed by the thermal nitridation of SiO2/Si

    Science.gov (United States)

    Vasquez, R. P.; Madhukar, A.; Grunthaner, F. J.; Naiman, M. L.

    1986-01-01

    Previously reported nitrogen distributions in SiO2 films on Si which have been thermally nitrided at 1000 C have been explained by a kinetic model of the nitridation process which rests upon the effects of interfacial strain. A critical test of this kinetic model is the validity of the predictions regarding nitrogen distributions obtained at other nitridation temperatures. In this work, nitrogen distributions determined via X-ray photoelectron spectroscopy are reported for samples nitrided at 800 and 1150 C, and are shown to be consistent with the kinetic model. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen distribution, and is postulated to be related to kinetically generated defects in the dielectric film, consistent with the strain-dependent energy of formation of defects proposed recently to explain electrical data.

  10. Magnetic properties of URu 2Si 2

    Science.gov (United States)

    Monachesi, Patrizia; Continenza, Alessandra

    1995-02-01

    We perform electronic structure calculations with the FLAPW method within LSD approximation for URu 2Si 2, including the spin—orbit interaction self-consistently. Considering spin and orbital contributions to the magnetic moment we get a result much closer to the experiments than in previous calculations. We also provide spin polarization density maps in the plane parallel and perpendicular to the tetragonal c-axis.

  11. Precise Half Life Measurement of ^26Si

    Science.gov (United States)

    Iacob, V. E.; Golovko, V.; Goodwin, J.; Hardy, J. C.; Nica, N.; Park, H. I.; Trache, L.; Tribble, R. E.

    2008-10-01

    As part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix via 0^+->0^+superallowed β transitions, we recently measured the half-life of ^26Si. The radioactive ^26Si beam was obtained with a ^27Al primary beam at 30A MeV, which bombarded a cryogenic hydrogen target held at a pressure of 2.0 atm. From the reaction products, a high-purity ^26Si beam at 25A MeV was selected with the MARS spectrograph. The beam was then extracted in air, passed through a 0.3-mm-thick BC-404 plastic scintillator and a set of Al degraders, which had been adjusted so that the radioactive nuclei stopped in the center of the 76-μm-thick aluminized-mylar tape of our fast tape-transport system. We collected ^26Si nuclei for 1.3 s; then the beam was switched off and the activity was moved in less than 0.2 s to the center of a 4π proportional counter, located in a well-shielded region. The observed decays were then multi-scaled over a 44 s time span. To ensure an unbiased result, we split the experiment into many runs, each differing from the others in its discriminator threshold, detector bias or dominant dead-time setting. The analysis of these separate runs showed no systematic bias with these parameters. Our preliminary result agrees with the currently accepted (average) value, and the full analysis is expected to yield an uncertainty of 0.05% or better.

  12. Equilibrium and kinetic Si isotope fractionation factors and their implications on Si isotope distributions in the Earth's surface environments

    Science.gov (United States)

    Tang, M.; Zhang, S.; Liu, Y.

    2015-12-01

    Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the H4SiO4 solution are complemented to facilitate explanation of distributions of Si isotope in the Earth's surface environments. The results reveal that heavy Si isotopes will be significantly enriched in the secondary silicate minerals in comparison to aqueous H4SiO4. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of 28Si-enrichment in hyper-coordinated organosilicon complexes is found the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer is calculated and the result supports previous statement that highly 28Si-enrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many surface systems of the Earth can be explained. For example, the change of bulk soil δ30Si can be predicted as a concave pattern with respect to weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesqui-oxides and poorly crystalline minerals reaches its maximum. When well-crystallized clays start to precipitate from pore solutions under equilibrium conditions, the bulk soil δ30Si will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain δ30Si variations in the ground water profile. Equilibrium Si isotope fractionations among quadra-coordinated organosilicon complexes and the H4SiO4 solution may also shed the light on the Si isotope distributions in Si-accumulating plants.

  13. Stress-induced indirect to direct band gap transition in β-FeSi2 nanocrystals embedded in Si

    Science.gov (United States)

    Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Balagan, S. A.; Dotsenko, S. A.; Galkin, K. N.; Galkin, N. G.; Shamirzaev, T. S.; Gutakovskii, A. K.; Iinuma, M.; Terai, Y.

    2017-09-01

    Embedded in silicon β-FeSi2 nanocrystals (NCs) were grown on Si(111) by solid phase epitaxy of a thin iron film followed by Si molecular beam epitaxy. After solid phase epitaxy, a mixture of β-FeSi2 and ɛ-FeSi nanocrystals is formed on the surface, sometimes β and ɛ phases coexist inside one nanocrystal. During initial stage of Si molecular beam epitaxy all ɛ-FeSi transforms into β-FeSi2. β-FeSi2 nanocrystals tend to move following Si growth front. By adjusting growth condition, we manage to prevent the nanocrystals from moving and to fabricate 7-layer n-Si(111)/β-FeSi2_NCs/p+-Si silicon heterostructure with embedded β-FeSi2 NCs. An epitaxial relationship and a stress induced in the nanocrystals by silicon matrix were found to be suitable for indirect to direct band gap transition in β-FeSi2. Of the heterostructure, a n-i-p avalanche photodetector and a light-emitting diode were formed. They have shown relatively good performance: ultrabroadband photoresponse from the visible (400 nm) to short-wavelength infrared (1800 nm) ranges owing to quantum-confined Stark effect in the nanocrystals and optical emission power of up to 25 µW at 9 A/cm2 with an external quantum efficiency of 0.009% at room temperature owing to a direct fundamental transition in stressed β-FeSi2 nanocrystals.

  14. Molecules on si: electronics with chemistry.

    Science.gov (United States)

    Vilan, Ayelet; Yaffe, Omer; Biller, Ariel; Salomon, Adi; Kahn, Antoine; Cahen, David

    2010-01-12

    Basic scientific interest in using a semiconducting electrode in molecule-based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test-bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor-molecule electronics we need reproducible, high-yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power.To consider these issues and questions we will, in this Progress Report, review junctions based on direct bonding of molecules to oxide-free Si.describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified.investigate to what extent imperfections in the monolayer are important for transport across the monolayer.revisit the concept of energy levels in such hybrid systems.

  15. Elastic and inelastic properties of SiC/Si biomorphic composites and biomorphic SiC based on oak and eucalyptus

    Science.gov (United States)

    Kardashev, B. K.; Nefagin, A. S.; Smirnov, B. I.; de Arellano-Lopez, A. R.; Martinez-Fernandez, J.; Sepulveda, R.

    2006-09-01

    This paper reports on the results of a comparative investigation into the elastic and microplastic properties of biomorphic SiC/Si composites and biomorphic SiC prepared by pyrolysis of oak and eucalyptus with subsequent infiltration of molten silicon into a carbon matrix and additional chemical treatment to remove excess silicon. The acoustic studies were performed by the composite oscillator technique using resonant longitudinal vibrations at frequencies of about 100 kHz. It is shown that, in biomorphic SiC (as in biomorphic SiC/Si) at small-amplitude strains ɛ, adsorption and desorption of the environmental (air) molecules determine to a considerable extent the Young’s modulus E and the internal friction (decrement of acoustic vibrations δ) and that the changes in E and δ at these amplitudes are irreversible. The stress-microplastic strain curves are constructed from the acoustic data for the materials under study at temperatures of 100 and 290 K.

  16. New class of Si-based superlattices - Alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) alloys

    Science.gov (United States)

    Fathauer, R. W.; George, T.; Jones, E. W.; Pike, W. T.; Ksendzov, A.; Vasquez, R. P.

    1992-01-01

    Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) have been fabricated. This is accomplished by first growing a Si/Si(0.7)Ge(0.3) superlattice by molecular beam epitaxy, followed by Ar-ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy-layer thickness and strain. Superlattices have been fabricated from 1-micron wide mesas with Si(0.7)Ge(0.3) layers fully converted to 5-nm thick porous amorphous material.

  17. On the radiative recombination and tunneling of charge carriers in SiGe/Si heterostructures with double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Yablonsky, A. N., E-mail: yablonsk@ipmras.ru; Zhukavin, R. Kh.; Bekin, N. A.; Novikov, A. V.; Yurasov, D. V.; Shaleev, M. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-12-15

    For SiGe/Si(001) epitaxial structures with two nonequivalent SiGe quantum wells separated by a thin Si barrier, the spectral and time characteristics of interband photoluminescence corresponding to the radiative recombination of excitons in quantum wells are studied. For a series of structures with two SiGe quantum wells different in width, the characteristic time of tunneling of charge carriers (holes) from the narrow quantum well, distinguished by a higher exciton recombination energy, to the wide quantum well is determined as a function of the Si barrier thickness. It is shown that the time of tunneling of holes between the Si{sub 0.8}5Ge{sub 0.15} layers with thicknesses of 3 and 9 nm steadily decreases from ~500 to <5 ns, as the Si barrier thickness is reduced from 16 to 8 nm. At intermediate Si barrier thicknesses, an increase in the photoluminescence signal from the wide quantum well is observed, with a characteristic time of the same order of magnitude as the luminescence decay time of the narrow quantum well. This supports the observation of the effect of the tunneling of holes from the narrow to the wide quantum well. A strong dependence of the tunneling time of holes on the Ge content in the SiGe layers at the same thickness of the Si barrier between quantum wells is observed, which is attributed to an increase in the effective Si barrier height.

  18. Study of low dimensional SiGe island on Si for potential visible Metal-Semiconductor-Metal photodetector

    Science.gov (United States)

    Rahim, Alhan Farhanah Abd; Zainal Badri, Nur'Amirah; Radzali, Rosfariza; Mahmood, Ainorkhilah

    2017-11-01

    In this paper, an investigation of design and simulation of silicon germanium (SiGe) islands on silicon (Si) was presented for potential visible metal semiconductor metal (MSM) photodetector. The characterization of the performances in term of the structural, optical and electrical properties of the structures was analyzed from the simulation results. The project involves simulation using SILVACO Technology Computer Aided Design (TCAD) tools. The different structures of the silicon germanium (SiGe) island on silicon substrate were created, which were large SiGe, small SiGe, combination SiGe and bulk Ge. All the structures were tested for potential Metal Semiconductor Metal (MSM) photodetector. The extracted data such as current versus voltage characteristic, current gain and spectral response were obtained using ATLAS SILVACO tools. The performance of SiGe island structures and bulk Ge on Si substrate as (MSM) photodetector was evaluated by photo and dark current-voltage (I-V) characteristics. It was found that SiGe islands exhibited higher energy band gap compared to bulk Ge. The SiGe islands current-voltage characteristics showed improved current gain compared to bulk Ge. Specifically the enhancement of the islands gain was contributed by the enhanced photo currents and lower dark currents. The spectral responses of the SiGe islands showed peak response at 590 nm (yellow) which is at the visible wavelength. This shows the feasibility of the SiGe islands to be utilized for visible photodetections.

  19. Study of low dimensional SiGe island on Si for potential visible Metal-Semiconductor-Metal photodetector

    Directory of Open Access Journals (Sweden)

    Abd Rahim Alhan Farhanah

    2017-01-01

    Full Text Available In this paper, an investigation of design and simulation of silicon germanium (SiGe islands on silicon (Si was presented for potential visible metal semiconductor metal (MSM photodetector. The characterization of the performances in term of the structural, optical and electrical properties of the structures was analyzed from the simulation results. The project involves simulation using SILVACO Technology Computer Aided Design (TCAD tools. The different structures of the silicon germanium (SiGe island on silicon substrate were created, which were large SiGe, small SiGe, combination SiGe and bulk Ge. All the structures were tested for potential Metal Semiconductor Metal (MSM photodetector. The extracted data such as current versus voltage characteristic, current gain and spectral response were obtained using ATLAS SILVACO tools. The performance of SiGe island structures and bulk Ge on Si substrate as (MSM photodetector was evaluated by photo and dark current-voltage (I-V characteristics. It was found that SiGe islands exhibited higher energy band gap compared to bulk Ge. The SiGe islands current-voltage characteristics showed improved current gain compared to bulk Ge. Specifically the enhancement of the islands gain was contributed by the enhanced photo currents and lower dark currents. The spectral responses of the SiGe islands showed peak response at 590 nm (yellow which is at the visible wavelength. This shows the feasibility of the SiGe islands to be utilized for visible photodetections.

  20. Investigation of the vertical electrical transport in a-Si:H/nc-Si:H superlattice thin films.

    Science.gov (United States)

    Das, Debajyoti; Kar, Debjit

    2015-07-14

    Tuning the size of silicon nano-crystallites (Si-ncs) has been realized simply by controlling the thickness of the nc-Si:H sub-layer (tnc) in the a-Si:H/nc-Si:H superlattice thin films grown by low temperature plasma processing in PE-CVD. The vertical electrical transport phenomena accomplished in superlattice films have been investigated in order to identify their effective utilization in practical device configuration. The reduced size of the Si-ncs at thinner tnc and the associated band gap widening due to quantum confinement effects generates the Coulomb potential barrier at the a-Si/nc-Si interface which in turn obstructs the transport of charge carriers to the allowed energy states in Si-ncs, leading to the Poole-Frenkel tunneling as the prevailing charge transport mechanism in force. The advantages of the conduction process governed by the Poole-Frenkel mechanism are two-fold. The lower barrier height caused by the a-Si:H sub-layer in the superlattice than the silicon oxide sub-layer in conventional structures enhances the conduction current. Moreover, increasing trapped charges in the a-Si:H sub-layer can arbitrarily increase the current conduction. Accordingly, a-Si:H/nc-Si:H superlattice structures could provide superior electrical transport in stacked layer devices e.g., multi-junction all silicon solar cells.

  1. Protection and systemic translocation of siRNA following oral administration of chitosan/siRNA nanoparticles

    DEFF Research Database (Denmark)

    Gonzalez, Borja Ballarin; Dagnæs-Hansen, Frederik; Fenton, Robert A.

    2013-01-01

    , gastrointestinal (GI) deposition, and translocation into peripheral tissue of nonmodified siRNA after oral gavage of chitosan/siRNA nanoparticles in mice. In contrast to naked siRNA, retained structural integrity and deposition in the stomach, proximal and distal small intestine, and colon was observed at 1 and 5...

  2. Silicon Promotes Exodermal Casparian Band Formation in Si-Accumulating and Si-Excluding Species by Forming Phenol Complexes

    Science.gov (United States)

    Hinrichs, Martin; Specht, André; Waßmann, Friedrich; Schreiber, Lukas; Schenk, Manfred K.

    2015-01-01

    We studied the effect of Silicon (Si) on Casparian band (CB) development, chemical composition of the exodermal CB and Si deposition across the root in the Si accumulators rice and maize and the Si non-accumulator onion. Plants were cultivated in nutrient solution with and without Si supply. The CB development was determined in stained root cross-sections. The outer part of the roots containing the exodermis was isolated after enzymatic treatment. The exodermal suberin was transesterified with MeOH/BF3 and the chemical composition was measured using gas chromatography-mass spectroscopy (GC-MS) and flame ionization detector (GC-FID). Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) was used to determine the Si deposition across root cross sections. Si promoted CB formation in the roots of Si-accumulator and Si non-accumulator species. The exodermal suberin was decreased in rice and maize due to decreased amounts of aromatic suberin fractions. Si did not affect the concentration of lignin and lignin-like polymers in the outer part of rice, maize and onion roots. The highest Si depositions were found in the tissues containing CB. These data along with literature were used to suggest a mechanism how Si promotes the CB development by forming complexes with phenols. PMID:26383862

  3. Low-dimensional structures generated by misfit dislocations in the bulk of Si1 - xGex/Si heteroepitaxial systems

    DEFF Research Database (Denmark)

    Shiryaev, Sergey Y.; Jensen, Flemming; Petersen, Jon Wulff

    1997-01-01

    The capability of misfit dislocations to generate nanostructures in the bulk of Si1-xGex/Si heteroepitaxial systems is demonstrated. It is shown that dislocation slip originating from compositionally graded Si1-xGex layers can produce a range of low-dimensional structures including nanowires...

  4. Surface modification of silicon nanowire field-effect devices with Si-C and Si-N bonded Monolayers

    NARCIS (Netherlands)

    Masood, M.N.

    2011-01-01

    The research work was mainly focused on the surface modification/surface functionalization of active-gate areas of silicon nanowire field-effect transistor devices (Si-NW FET) using hydrogen terminated surfaces, Si-C and Si-N bonded monolayers and subsequent bioimmobilization for biosensor

  5. Thermoelectric properties of Si/CoSi2 sub-micrometer composites prepared by melt-spinning technique

    Science.gov (United States)

    Xie, Jun; Ohishi, Yuji; Ichikawa, Satoshi; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke

    2017-05-01

    We here report on the influence of CoSi2 precipitates on the thermoelectric properties of heavily doped p-type Si. A simple self-assembly process using a melt-spinning technique followed by spark plasma sintering is introduced to prepare bulk Si/CoSi2 composites with a nominal composition of (Si0.99B0.01)95Co5. Scanning and transmission electron microscopy observations present clear evidence of a sub-micrometer CoSi2 phase with a size ranging from 50 to 500 nm. These sub-micrometer precipitates resulted in a retention of the high electrical performance of heavily doped Si, while simultaneously reducing thermal conductivity by over 20% compared to a coarse CoSi2 phase (1-10 μm) in a comparative sample prepared by arc melting and spark plasma sintering. As a result, a figure of merit ZT value of 0.21 at 1073 K was achieved in the sub-micrometer Si/CoSi2, an increase of 16% compared with the ZT value for homogeneous p-type Si with a similar carrier concentration. This suggests that the self-assembled sub-micrometer inclusions effectively enhanced the thermoelectric performance of Si-based thermoelectric materials.

  6. EELS measurements of boron concentration profiles in p-a-Si and nip a-Si solar cells

    DEFF Research Database (Denmark)

    Van Aken, Bas B.; Duchamp, Martial; Boothroyd, Chris

    2012-01-01

    The p-type Si layer in a-Si and μc-Si solar cells on foil needs to fulfil several important requirements. The layer is necessary to create the electric field that separates the photo-generated charge carriers; the doping also increases the conductivity to conduct the photocurrent to the front...

  7. Low cost sol–gel derived SiC–SiO{sub 2} nanocomposite as anti reflection layer for enhanced performance of crystalline silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jannat, Azmira [School of Semiconductor and Chemical Engineering, Solar Energy Research Center, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); Solar Energy Engineering, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); Lee, Woojin [School of Semiconductor and Chemical Engineering, Solar Energy Research Center, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); Akhtar, M. Shaheer, E-mail: shaheerakhtar@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Solar Energy Research Center, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); New & Renewable Energy Materials Development Center (NewREC), Chonbuk National University, Jeonbuk (Korea, Republic of); Li, Zhen Yu [School of Semiconductor and Chemical Engineering, Solar Energy Research Center, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); Yang, O.-Bong, E-mail: obyang@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Solar Energy Research Center, Chonbuk National University, Jeonju, Jeonbuk 54896 (Korea, Republic of); New & Renewable Energy Materials Development Center (NewREC), Chonbuk National University, Jeonbuk (Korea, Republic of)

    2016-04-30

    Graphical abstract: - Highlights: • Sol–gel derived SiC–SiO{sub 2} nanocomposite was prepared. • It effectively coated as AR layer on p-type Si-wafer. • SiC–SiO{sub 2} layer on Si solar cells exhibited relatively low reflectance of 7.08%. • Fabricated Si solar cell attained highly comparable performance of 16.99% to commercial device. - Abstract: This paper describes the preparation, characterizations and the antireflection (AR) coating application in crystalline silicon solar cells of sol–gel derived SiC–SiO{sub 2} nanocomposite. The prepared SiC–SiO{sub 2} nanocomposite was effectively applied as AR layer on p-type Si-wafer via two step processes, where the sol–gel of precursor solution was first coated on p-type Si-wafer using spin coating at 2000 rpm and then subjected to annealing at 450 °C for 1 h. The crystalline, and structural observations revealed the existence of SiC and SiO{sub 2} phases, which noticeably confirmed the formation of SiC–SiO{sub 2} nanocomposite. The SiC–SiO{sub 2} layer on Si solar cells was found to be an excellent AR coating, exhibiting the low reflectance of 7.08% at wavelengths ranging from 400 to 1000 nm. The fabricated crystalline Si solar cell with SiC–SiO{sub 2} nanocomposite AR coating showed comparable power conversion efficiency of 16.99% to the conventional Si{sub x}N{sub x} AR coated Si solar cell. New and effective sol–gel derived SiC–SiO{sub 2} AR layer would offer a promising technique to produce high performance Si solar cells with low-cost.

  8. A comparative study on electronic and structural properties of transition metal monosilicides, CrSi(B20-type), RhSi(B20-type), RhSi(B31-type) and RhSi(B2-type)

    Science.gov (United States)

    Altintas, Bahadir

    2011-11-01

    Transition metal based monosilicide compounds (CrSi and RhSi) have been investigated theoretically from ab initio calculations. The structural and electronic band calculations of CrSi and different phases of RhSi crystals show that the metallic property and hypothetically constructed structures of RhSi(Pnma) under different pressures from 0 GPa to 75 GPa show a certain difference only along Γ-Z directions of the high symmetry points of first Brillouin zone. The character of the bands around fermi level was determined by partial density of state calculations.

  9. Thermodynamic assessment of the Ru-Si system

    Energy Technology Data Exchange (ETDEWEB)

    Du Yong [State Key Lab. for Powder Metallurgy, Hunan, HN (China); Inst. fuer Physikalische Chemie, Wien (Austria); Chen, K.H.; Huang, B.Y.; Yuan, Z.H. [State Key Lab. for Powder Metallurgy, Hunan, HN (China); Schuster, J.C. [Inst. fuer Physikalische Chemie, Wien (Austria); Perring, L. [Nestle Research Center, Lausanne (Switzerland); Gachon, J.C. [Lab. de Chimie du Solide Mineral, Vandoeuvre-les-Nancy (France)

    2001-04-01

    A consistent thermodynamic data set for the Ru-Si system is obtained by a computer-aided least-squares method applied to the experimental phase diagram and thermodynamic data. The liquid phase is described by the Redlich-Kister formula. All of the compounds, Ru{sub 2}Si, Ru{sub 4}Si{sub 3}, RuSi, and Ru{sub 2}Si{sub 3}, are treated as stoichiometric phases. Comparisons between the calculated and measured phase diagram and thermodynamic quantities show that all of the accurate experimental information is well accounted for by the thermodynamic description. (orig.)

  10. Generation of endo-siRNAs in Xenopus laevis oocytes.

    Science.gov (United States)

    Alnumeir, Sammer; Werner, Andreas

    2014-01-01

    Endogenous siRNAs (endo-siRNAs) are well documented and characterized in C. elegans and Drosophila. Endo-siRNAs can also be found in vertebrates; however, their biology is much less clear. They are thought to be produced by Dicer and to contribute to transposon silencing. Because of their generally low abundance and their similarity with miRNAs and products of physiological RNA turn-over, endo-siRNAs are difficult to investigate. Here, we report a system, oocytes from Xenopus laevis, that allows for the generation and analysis of endo-siRNAs from double-stranded RNA precursors.

  11. Male germ cells express abundant endogenous siRNAs

    Science.gov (United States)

    Song, Rui; Hennig, Grant W.; Wu, Qiuxia; Jose, Charlie; Zheng, Huili; Yan, Wei

    2011-01-01

    In mammals, endogenous siRNAs (endo-siRNAs) have only been reported in murine oocytes and embryonic stem cells. Here, we show that murine spermatogenic cells express numerous endo-siRNAs, which are likely to be derived from naturally occurring double-stranded RNA (dsRNA) precursors. The biogenesis of these testicular endo-siRNAs is DROSHA independent, but DICER dependent. These male germ cell endo-siRNAs can potentially target hundreds of transcripts or thousands of DNA regions in the genome. Overall, our work has unveiled another hidden layer of regulation imposed by small noncoding RNAs during male germ cell development. PMID:21788498

  12. Preparation of SiO2-Protecting Metallic Fe Nanoparticle/SiO2 Composite Spheres for Biomedical Application

    Directory of Open Access Journals (Sweden)

    Pin-Wei Hsieh

    2015-11-01

    Full Text Available Functionalized Fe nanoparticles (NPs have played an important role in biomedical applications. In this study, metallic Fe NPs were deposited on SiO2 spheres to form a Fe/SiO2 composite. To protect the Fe from oxidation, a thin SiO2 layer was coated on the Fe/SiO2 spheres thereafter. The size and morphology of the SiO2@Fe/SiO2 composite spheres were examined by transmission electron microscopy (TEM. The iron form and its content and magnetic properties were examined by X-ray diffraction (XRD, inductively-coupled plasma mass spectrometry (ICP-MS and a superconducting quantum interference device (SQUID. The biocompatibility of the SiO2@Fe/SiO2 composite spheres was examined by Cell Counting Kit-8 (CCK-8 and lactate dehydrogenase (LDH tests. The intracellular distribution of the SiO2@Fe/SiO2 composite spheres was observed using TEM. XRD analysis revealed the formation of metallic iron on the surface of the SiO2 spheres. According to the ICP-MS and SQUID results, using 0.375 M FeCl3·6H2O for Fe NPs synthesis resulted in the highest iron content and magnetization of the SiO2@Fe/SiO2 spheres. Using a dye loading experiment, a slow release of a fluorescence dye from SiO2@Fe/SiO2 composite spheres was confirmed. The SiO2@Fe/SiO2 composite spheres co-cultured with L929 cells exhibit biocompatibility at concentrations <16.25 µg/mL. The TEM images show that the SiO2@Fe/SiO2 composite spheres were uptaken into the cytoplasm and retained in the endosome. The above results demonstrate that the SiO2@Fe/SiO2 composite spheres could be used as a multi-functional agent, such as a magnetic resonance imaging (MRI contrast agent or drug carriers in biomedical applications.

  13. Characterization of rare-earth doped Si 3 N4 /SiC micro/nanocomposites

    Directory of Open Access Journals (Sweden)

    Peter Tatarko

    2010-03-01

    Full Text Available Influence of various rare-earth oxide additives (La2O3, Nd2O3, Sm2O3, Y2O3, Yb2O3 and Lu2O3 on the mechanical properties of hot-pressed silicon nitride and silicon nitride/silicon carbide micro/nano-composites has been investigated. The bimodal character of microstructures was observed in all studied materials where elongated β-Si3N4 grains were embedded in the matrix of much finer Si3N4 grains. The fracture toughness values increased with decreasing ionic radius of rare-earth elements. The fracture toughness of composites was always lower than that of monoliths due to their finer Si3N4/SiC microstructures. Similarly, the hardness and bending strength values increased with decreasing ionic radius of rare-earth elements either in monoliths or composites. On the other hand, the positive influence of finer microstructure of the composites on strength was not observed due to the present defects in the form of SiC clusters and non-reacted carbon zones. Wear resistance at room temperature also increased with decreasing ionic radius of rare-earth element. Significantly improved creep resistance was observed in case either of composite materials or materials with smaller radius of RE3+.

  14. Origin of multistate resistive switching in Ti/manganite/SiOx/Si heterostructures

    Science.gov (United States)

    Román Acevedo, W.; Acha, C.; Sánchez, M. J.; Levy, P.; Rubi, D.

    2017-01-01

    We report on the growth and characterization of Ti/La1/3Ca3/2MnO3/SiO2/n-Si memristive devices. We demonstrate that using current as electrical stimulus unveils an intermediate resistance state, in addition to the usual high and low resistance states that are observed in the standard voltage controlled experiments. Based on thorough electrical characterization (impedance spectroscopy, current-voltage curves analysis), we disclose the contribution of three different microscopic regions of the device to the transport properties: an ohmic incomplete metallic filament, a thin manganite layer below the filament tip exhibiting Poole-Frenkel like conduction, and the SiOx layer with an electrical response well characterized by a Child-Langmuir law. Our results suggest that the existence of the SiOx layer plays a key role in the stabilization of the intermediate resistance level, indicating that the combination of two or more active resistive switching oxides adds functionalities in relation to the single-oxide devices. We understand that these multilevel devices are interesting and promising, as their fabrication procedure is rather simple and they are fully compatible with the standard Si-based electronics.

  15. Optical properties of GaN films grown on SiC/Si

    Energy Technology Data Exchange (ETDEWEB)

    Devrajan, J.; Steckl, A.J. [Cincinnati Univ., OH (United States); Tran, C.A.; Stall, R.A. [EMCORE Corp., Somerset, NJ (United States)

    1998-08-01

    3C SiC grown on Si and on SOI wafers have been used as substrates for GaN growth. The optical properties of GaN/3C SiC are compared to those of GaN grown on the commonly used sapphire substrates and on 6H SiC substrates. Mapping of the PL characteristics over {proportional_to}1 inch substrates indicate a fairly strong edge effect in terms of peak intensity for GaN/3C SiC. Interestingly, the wavelength of the peak intensity was quite uniform over the entire wafer area, with an average value of 365 nm and a standard deviation of {proportional_to}3.3 nm. Mapping of the FWHM of the emission peak exhibited some edge effect, with the lowest values in the center of the wafer. The average PL FWHM was {proportional_to}17 nm, with a standard deviation of {proportional_to}1.4 nm. (orig.) 3 refs.

  16. 29 Si NMR study of polycrystalline NaTiSi2O6

    Science.gov (United States)

    Stern, Raivo; Rästa, Riho; Heinmaa, Ivo; Joon, Enno; Silverlein, Harlyn J.; Wiebe, Christopher

    NaTiSi2O6 (NTSO) structure consists of quasi 1-D zig-zag chains of edge-sharing slightly distorted TiO6 octahedrons. The chains are separated by SiO4 tetrahedrons. At high T the distance between magnetic spin-1/2 Ti3+ ions in the chain is equal. At Tc = 210 K the compound undergoes orbital-Peierls transition. As a result, below 210 K TiO6 chain becomes dimerized having diamagnetic singlet ground state. Neutron spectroscopy provided singlet-triplet gap value 615(35) K, μSR 2 Δ = 700(100) K. Our 29Si magic angle spinning NMR spectra show in paramagnetic region one single resonance with paramagnetic shift K = 713 ppm at 300 K. The shift slightly increases with decreasing T and has maximum K = 796 ppm at T= 213 K. Below Tc the resonance transforms into two lines with different paramagnetic shifts. At T = 56 K the spectrum shows 2 sharp lines with diamagnetic chemical shifts -84 and -101 ppm corresponding to 2 different Si sites in the low-T unit cell. T-dependence of 29Si spin-lattice relaxation T1 in 70 K ETAg IUT23-7, PUT210; TK134.

  17. Improvement of the thermal conductivity of SiC{sub F}/SiC composite

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, G.E. [Pacific Northwest National Laboratory, Richland, WA (United States); Kowbel, W. [MER Corporation, Tucson, AZ (United States)

    1996-04-01

    The methods, high temperature annealing and doping, were examined for improving the thermal conductivity of simulated CVI/{Beta}-SiC matrix material. For instance, a two hour 1500{degrees}C anneal led to the increase of the room temperature (RT) thermal conductivity from 38 to 59 W.mK. Be doping was even more effective in causing the thermal conductivity to increase with RT conductivity values up to 160 W/mK attained. To further optimize the thermal conductivity, hot-pressed SiC materials with carefully controlled amounts of Be-and B{sub 4}C-doping were investigated. Although a small improvement ({approx} 8%) was achieved with 2.0 wt % Be-doping, the effort to refine the amount of doping needed was largely unsuccessful. Apparently, hot-pressing SiC introduced numerous substructural stacking faults which effectively scattered phonons on the intermediate temperature range and nullified the benefits of doping. Nevertheless, Be and B{sub 4}C-doping and/or thermal treatments appear to be promising strategies to achieve the goal of eventually improving the thermal conductivity of SiC{sub f}/SiC composite.

  18. Optimization of spectrally selective Si/SiO2 based filters for thermophotovoltaic devices

    Science.gov (United States)

    Khosroshahi, Farhad Kazemi; Ertürk, Hakan; Pınar Mengüç, M.

    2017-08-01

    Design of a spectrally selective filter based on one-dimensional Si/SiO2 layers is considered for improved performance of thermo-photovoltaic devices. Spectrally selective filters transmit only the convertible radiation from the emitter as non-convertible radiation leads to a reduction in cell efficiency due to heating. The presented Si/SiO2 based filter concept reflects the major part of the undesired range back to the emitter to minimize energy required for the process and it is adaptable to different types of cells and emitters with different temperatures since its cut-off wavelength can be tuned. While this study mainly focuses on InGaSb based thermo-photovoltaic cell, Si, GaSb, and Ga0.78In0.22As0.19Sb0.81 based cells are also examined. Transmittance of the structure is predicted by rigorous coupled wave approach. Genetic algorithm, which is a global optimization method, is used to find the best possible filter structure by considering the overall efficiency as an objective function that is maximized. The simulations show that significant enhancement in the overall system and device efficiency is possible by using such filters with TPV devices. The methodology described in this paper allows for an improved filter design procedure for selected applications.

  19. Issues on Fabrication and Evaluation of SiC/SiC Tubes With Various Fiber Architectures

    Science.gov (United States)

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

    2004-01-01

    SiC/SiC engine components, high-modulus Sylramic-iBN SiC fiber tows were used to form nine different tubular architectural preforms with 13 mm (0.5 in.) inner diameter and lengths of approx. 75 and 230 mm (approx. 3 and approx, 9 in.). The thin-walled preforms were then coated with a BN interphase and densified with a hybrid SiC matrix using nearly the same process steps previously established for slurry-cast melt-infiltrated Sylramic-iBN/BN/SiC flat panels. The as-fabricated CMC tubes were microstructurally evaluated and tested for tensile hoop and flexural behavior, and some of the tubes were also tested in a low-pressure burner rig test with a high thru-thickness thermal gradient. To date, four general tube scale-up issues have been identified: greater CVI deposits on outer wall than inner wall; increased ply thickness and reduced fiber fraction; poor test standards for accurately determining the hoop strength of a small-diameter tube; and poor hoop strength for architectures with seams or ply ends. The underlying mechanisms and possible methods for their minimization are discussed.

  20. Influence of oxygen doping on resistive-switching characteristic of a-Si/c-Si device

    Science.gov (United States)

    Zhang, Jiahua; Chen, Da; Huang, Shihua

    2017-12-01

    The influence of oxygen doping on resistive-switching characteristics of Ag/a-Si/p+-c-Si device was investigated. By oxygen doping in the growth process of amorphous silicon, the device resistive-switching performances, such as the ON/OFF resistance ratios, yield and stability were improved, which may be ascribed to the significant reduction of defect density because of oxygen incorporation. The device I–V characteristics are strongly dependent on the oxygen doping concentration. As the oxygen doping concentration increases, the Si-rich device gradually transforms to an oxygen-rich device, and the device yield, switching characteristics, and stability may be improved for silver/oxygen-doped a-Si/p+-c-Si device. Finally, the device resistive-switching mechanism was analyzed. Project supported by the Zhejiang Provincial Natural Science Foundation of China (No. LY17F040001), the Open Project Program of Surface Physics Laboratory (National Key Laboratory) of Fudan University (No. KF2015_02), the Open Project Program of National Laboratory for Infrared Physics, Chinese Academy of Sciences (No. M201503), the Zhejiang Provincial Science and Technology Key Innovation Team (No. 2011R50012), and the Zhejiang Provincial Key Laboratory (No. 2013E10022).

  1. Photoacoustic Fourier transform infrared spectroscopy of nanoporous SiOx/Si thin films with varying porosities

    Science.gov (United States)

    Yang, D.-Q.; Meunier, M.; Sacher, E.

    2005-12-01

    Nanostructured SiOx/Si thin films, over a large range of porosities, were deposited by the excimer laser ablation (KrF, 248nm) of Si targets in He; they have been characterized by photoacoustic Fourier transform infrared spectroscopy, which necessitates exposure to air with subsequent oxidation. In particular, the IR Si -O-Si asymmetric stretching region, from 1000 to 1300cm-1, has been found to be composed of four components: P1 at 1045cm-1, P2 at 1060cm-1, P3 at 1090cm-1, and P4 at 1170cm-1. The photoacoustic signals were enhanced with increasing film porosity, as previously found for larger scale porous materials; those for P2-4 also correlated with similar increases in the O -H and C -Hn surface contaminant stretching peaks, indicating their sources to be in the surface region. We demonstrate that the experimental data fully support a previously proposed theoretical relationship, originally developed for powders.

  2. Thermoelectric Properties of Sb-Doped Mg2Si Prepared Using Different Silicon Sources

    Science.gov (United States)

    Isoda, Yukihiro; Tada, Satoki; Kitagawa, Hiroyuki; Shinohara, Yoshikazu

    2016-03-01

    Magnesium silicide (Mg2Si) compounds doped with 8000 ppm Sb were prepared using different Si sources via liquid-solid reaction synthesis and hot pressing. The Si sources were solar-grade Si, metal-grade Si, and sludge Si. The Si sludge generated during the cutting of Si wafers was recycled as a Si source. The x-ray diffraction (XRD) patterns of the Si sludge corresponded to Si, silicon dioxide (SiO2), and C, whereas the solar-grade Si and metal-grade Si were indexed as a single Si phase. For the sintered compact samples, the Mg2Si phase was predominant in all the samples. However, small amounts of impurity phases, MgO and SiC, were identified in the sintered Mg2Si that used sludge Si. The thermoelectric properties of the Mg2Si produced using solar-grade Si or metal-grade Si were almost the same at the measured temperature. The efficacy of the low-purity metal-grade Si was demonstrated. However, the power factor and thermal conductivity of the Mg2Si produced using sludge Si were smaller than those of the other samples over the entire measured temperature range. However, the maximum value of ZT was almost the same.

  3. SEMICONDUCTOR DEVICES: An optically controlled SiC lateral power transistor based on SiC/SiCGe super junction structure

    Science.gov (United States)

    Hongbin, Pu; Lin, Cao; Jie, Ren; Zhiming, Chen; Yagong, Nan

    2010-04-01

    An optically controlled SiC/SiCGe lateral power transistor based on superjunction structure has been proposed, in which n-SiCGe/p-SiC superjunction structure is employed to improve device figure of merit. Performance of the novel optically controlled power transistor was simulated using Silvaco Atlas tools, which has shown that the device has a very good response to the visible light and the near infrared light. The optoelectronic responsivities of the device at 0.5 μm and 0.7 μm are 330 mA/W and 76.2 mA/W at 2 V based voltage, respectively.

  4. Corrosion characteristics of Al-Si-Mg/SiC{sub p} composites with varying Si/Mg molar ratio in neutral chloride solutions

    Energy Technology Data Exchange (ETDEWEB)

    Escalera-Lozano, R.; Pech-Canul, M.I. [Cinvestav Saltillo (Mexico); Pech-Canul, M.A.; Quintana, P. [Departamento de Fisica Aplicada, Merida, Yuc. (Mexico)

    2009-09-15

    The corrosion resistance of Al-Mg-Si/SiC{sub p} composites produced by the pressureless infiltration method [using SiC{sub p} preforms with 50% porosity containing rice hull ash (RHA) and four custom-made alloys with varying Si/Mg molar ratio] was evaluated in neutral 0.1 M NaCl solutions. The deleterious phase Al{sub 4}C{sub 3} was successfully suppressed in composites with Si/Mg molar ratios of 0.89 and 1.05, but not in those with lower Si/Mg molar ratios (0.12 and 0.49). Results of cyclic polarizations in deareated 0.1 M NaCl solutions showed that with increasing Si/Mg molar ratio, passive current density increased but pitting susceptibility decreased both for reinforced and unreinforced alloys. Immersion tests in aerated 0.1 M NaCl showed that for composites with Si/Mg molar ratios of 0.12 and 0.49 chemical degradation by hydrolysis of Al{sub 4}C{sub 3} was followed by intense anodic dissolution at the matrix-reinforcement interface, while composites corresponding to Si/Mg molar ratios of 0.89 and 1.05 did not exhibit intense localized attack. Possible reasons for the improvement in resistance to localized corrosion are discussed. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  5. Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers

    Directory of Open Access Journals (Sweden)

    Shichao Liu

    2017-07-01

    Full Text Available The effect of residual stresses on the strength, toughness and work of fracture of Si3N4/SiC multilayered composites with different SiC layers has been investigated. It may be an effective way to design and optimize the mechanical properties of Si3N4/SiC multilayered composites by controlling the properties of SiC layers. Si3N4/SiC multilayered composites with different SiC layers were fabricated by aqueous tape casting and pressureless sintering. Residual stresses were calculated by using ANSYS simulation, the maximum values of tensile and compressive stresses were 553.2 MPa and −552.1 MPa, respectively. Step-like fracture was observed from the fracture surfaces. Fraction of delamination layers increased with the residual stress, which can improve the reliability of the materials. Tensile residual stress was benefit to improving toughness and work of fracture, but the strength of the composites decreased.

  6. In-situ formation of SiC nanocrystals by high temperature annealing of SiO2/Si under CO: A photoemission study

    Science.gov (United States)

    D'angelo, M.; Deokar, G.; Steydli, S.; Pongrácz, A.; Pécz, B.; Silly, M. G.; Sirotti, F.; Cavellin, C. Deville

    2012-04-01

    We have studied CO interaction with SiO2/Si system at high temperature (~ 1100 °C) and 350 mbar by core-level photoemission. Even for short annealing time (5 min) the signal from Si2p and C1s core levels shows a clear change upon CO treatment. Shifted components are attributed to formation of SiC. This is confirmed by TEM imaging which further shows that the silicon carbide is in the form of nano-crystals of the 3C polytype. Photoemission spectroscopy moreover reveals the formation of silicon oxicarbide which could not be evidenced by other methods. Combining these results with previous Nuclear Resonance Profiling study gives a deeper insight into the mechanisms involved in the nanocrystals growth and especially for the reaction equation leading to SiC formation. We show that CO diffuses as a molecule through the silica layer and reacts with the silicon substrate according the following reaction: 4 CO + 4 SiSiO2 + 2SiC + SiO2C2.

  7. Three Crystalline Polymorphs of KFeSi04, Potassium Ferrisilicate

    DEFF Research Database (Denmark)

    Bentzen, Janet Jonna

    1983-01-01

    , and synthetic kaliophilite, KAISiO4, respectively, and it is proposed that β- and λ-KFeSiO4 are linked by Si-Fe order-disorder. Beta KFeSiO4 transforms slowly into α-KFeSi04 above 910°C but the transformation was not shown to be reversible in the present dry-heating experiments.......Orthorhombic α-KFeSi04 ( a =0.5478, b =0.9192, c =0.8580 nm), hexagonal β-KFeSiO4 (a =0.5309, c =0.8873 nm), and hexagonal γ-KFeSi04 (a =0.5319, c =0.8815 nm) were synthesized by devitrification of KFeSiO4 glass. Powder X-ray diffraction data are given for all three polymorphs. Alpha KFeSiO4......, the high-temperature polymorph, melts congruently at 1197”±2”C. Mössbauer spectroscopy of the α phase indicates that Fe3+ occupies two tetrahedral sites in the lattice. Beta KFeSiO4, the low-temperature polymorph, and γ-KFeSiO4, a metastable polymorph, appear to be isomorphous with kalsilite, KAISiO4...

  8. δ30Si systematics in a granitic saprolite, Puerto Rico

    Science.gov (United States)

    Ziegler, Karen; Chadwick, Oliver A.; White, Arthur F.; Brzezinski, Mark A.

    2005-01-01

    Granite weathering and clay mineral formation impart distinct and interpretable stable Si isotope (δ30Si) signatures to their solid and aqueous products. Within a saprolite, clay minerals have δ30Si values ∼2.0‰ more negative than their parent mineral and the δ30Si signature of the bulk solid is determined by the ratio of primary to secondary minerals. Mineral-specific weathering reactions predominate at different depths, driving changes in differing δ30Sipore watervalues. At the bedrock-saprolite interface, dissolution of plagioclase and hornblende creates δ30Sipore water signatures more positive than granite by up to 1.2‰; these reactions are the main contributor of Si to stream water and determine its δ30Si value. Throughout the saprolite, biotite weathering releases Si to pore waters but kaolinite overgrowth formation modulates its contribution to pore-water Si. The influence of biotite on δ30Sipore water is greatest near the bedrock where biotite-derived Si mixes with bulk pore water prior to kaolinite formation. Higher in the saprolite, biotite grains have become more isolated by kaolinite overgrowth, which consumes biotite-derived Si that would otherwise influence δ30Sipore water. Because of this isolation, which shifts the dominant source of pore-water Si from biotite to quartz, δ30Sipore water values are more negative than granite by up to 1.3‰ near the top of the saprolite.

  9. Kinetics and thermodynamics of Si(111) surface nitridation in ammonia

    Science.gov (United States)

    Mansurov, Vladimir G.; Malin, Timur V.; Galitsyn, Yurij G.; Shklyaev, Alexander A.; Zhuravlev, Konstantin S.

    2016-05-01

    Kinetics and thermodynamics of Si(111) surface nitridation under an ammonia flux at different substrate temperatures are investigated by reflection high-energy electron diffraction. Two different stages of the nitridation process were revealed. The initial stage is the fast (within few seconds) formation of ordered two-dimensional SiN phase, occuring due to the topmost active surface Si atom (Sisurf) interaction with ammonia molecules. It is followed by the late stage consisting in the slow (within few minutes) amorphous Si3N4 phase formation as a result of the interaction of Si atoms in the lattice site (Siinc) with chemisorbed ammonia molecules. It was found that the ordered SiN phase formation rate decreases, as the temperature increases. The kinetic model of the initial stage was developed, in which the ordered SiN phase formation is the two-dimensional phase transition in the lattice gas with SiN cells. The enthalpy of the active surface Si atom generation on the clean Si(111) surface was estimated to be about 1.5 eV. In contrast, the amorphous Si3N4 phase formation is the normal (thermally activated) chemical process with the first-order kinetics, whose activation energy and pre-exponential factor are 2.4 eV and 108 1/s, respectively.

  10. Three-dimensional hierarchical Te-Si nanostructures.

    Science.gov (United States)

    Lim, Jae-Hong; Shin, Gyeong-Jin; Hwang, Tae-Yeon; Lim, Hyo-Ryoung; Lee, Young-In; Lee, Kyu-Hwan; Kim, Sung-Dae; Oh, Min-Wook; Park, Su-Dong; Myung, Nosang V; Choa, Yong-Ho

    2014-10-21

    Three-dimensional hybrid nanostructures (i.e., Te "nanobranches" on a Si "nanotrunk" or Te "nanoleaves" on a Si "nanotrunk") were synthesized by combining the gold-assisted chemical etching of Si to form Si "nanotrunks" and the galvanic displacement of Si to form Te "nanobranches" or "nanoleaves." By adjusting the composition of the electrolyte used for the galvanic displacement reaction, the shape of the Te nanostructures could be changed from nanoleaves to nanobranches. The Si nanotrunks with Te nanobranches showed stronger luminescent emission in the visible region, with their Raman spectrum having a higher wave number, owing to their grain size being larger. This suggested that the optical and photoelectrochemical properties of Te-Si hybrid nanostructures depend on their shape and size. Using this approach, it should be possible to fabricate various hierarchical nanostructures for use in photoelectronic and photoelectrochemical devices.

  11. Analysis of poly-Si thin film p^+-n-n+ homojunction solar cell and heterojunction solar cell with and without a thin μc-Si layer at the interface of a-Si and poly-Si layers

    Science.gov (United States)

    Letha, A. J.; Hwang, H. L.

    2009-05-01

    In this study, new possibilities for higher efficiency poly-Si thin film solar cells are investigated using MEDICI^TM device simulator. The poly-Si p^+-n-n+ thin film solar cell with a thin a-Si p+ layer is found to have higher efficiency than the homojunction p^+-n-n+ cell. Further improvement in efficiency of the heterojunction p^+-n-n+ cell is achieved by introducing a thin μc-Si layer at the interface of a-Si emitter and poly-Si absorber layers. The μc-Si layer at the interface is found to reduce the recombination losses at the interface and improved the fill factor and efficiency of the cell. The photovoltaic parameters of the cell and the absorber layer thickness for optimum efficiency are highly influenced by grain size and passivation at the grain boundary.

  12. Electrical characterization of Si/InN nanowire heterojunctions

    Science.gov (United States)

    Alagha, S.; Zhao, S.; Mi, Z.; Watkins, S. P.; Kavanagh, K. L.

    2018-01-01

    We report on the electrical properties of undoped, Si-doped and Mg-doped InN nanowires measured directly on degenerate n-type and p-type Si substrates. The transport was measured with a nanoprobe technique inside a scanning electron microscope. The resulting average current density versus voltage characteristics are weakly rectifying for InN grown on n+–Si with similar ratios for all InN dopant types. On p+–Si, Mg-doped InN nanowires show a strong rectification behavior with opposite voltage polarity compared to n+–Si, while undoped and Si-doped nanowires show nearly symmetric transport. These characteristics are analyzed in terms of the properties of broken gap band offsets at the Si/InN heterojunction.

  13. Synthesis of biomorphic SiC ceramic from bamboo charcoal.

    Science.gov (United States)

    Zhu, Jiangtao; Kwong, Fung Luen; Ng, Dickon Hang Leung

    2009-02-01

    Biomorphic SiC ceramic was successfully synthesized by reaction sintering between bamboo charcoal and a Si/SiO2 powder mixture. The charcoal was converted into an entirely SiC ceramic inherited with the original bamboo structure. Samples were characterized according to their crystallinity, morphology, microstructures and pore structures. We found that various morphological SiC structures were formed in different parts of the charcoal which depended on the morphology of the textures. The length of SiC nanowires were up to micron size. They were grown in the direction. The number of micropores in the converted biomorphic SiC was less than the original bamboo charcoal, but the pore diameter was larger.

  14. Thermochemistry and growth mechanism of SiC nanowires

    Science.gov (United States)

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

    2017-09-01

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

  15. Inherent point defects at the thermal higher-Miller index (211)Si/SiO{sub 2} interface

    Energy Technology Data Exchange (ETDEWEB)

    Iacovo, S.; Stesmans, A., E-mail: andre.stesmans@fys.kuleuven.be [Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium)

    2014-12-29

    Electron spin resonance (ESR) studies were carried out on the higher-Miller index (211)Si/SiO{sub 2} interface thermally grown in the temperature range T{sub ox} = 400–1066 °C to assess interface quality in terms of inherently incorporated point defects. This reveals the presence predominantly of two species of a P{sub b}-type interface defect (interfacial Si dangling bond), which, based on pertinent ESR parameters, is typified as P{sub b0}{sup (211)} variant, close to the P{sub b0} center observed in standard (100)Si/SiO{sub 2}—known as utmost detrimental interface trap. T{sub ox} ≳ 750 °C is required to minimize the P{sub b0}{sup (211)} defect density (∼4.2 × 10{sup 12 }cm{sup −2}; optimized interface). The data clearly reflect the non-elemental nature of the (211)Si face as an average of (100) and (111) surfaces. It is found that in oxidizing (211)Si at T{sub ox} ≳ 750 °C, the optimum Si/SiO{sub 2} interface quality is retained for the two constituent low-index (100) and (111) faces separately, indicating firm anticipating power for higher-index Si/SiO{sub 2} interfaces in general. It implies that, as a whole, the quality of a thermal higher-index Si/SiO{sub 2} interface can never surmount that of the low-index (100)Si/SiO{sub 2} structure.

  16. Initial assessment of environmental effects on SiC/SiC composites in helium-cooled nuclear systems

    Energy Technology Data Exchange (ETDEWEB)

    Contescu, Cristian I [ORNL

    2013-09-01

    This report summarized the information available in the literature on the chemical reactivity of SiC/SiC composites and of their components in contact with the helium coolant used in HTGR, VHTR and GFR designs. In normal operation conditions, ultra-high purity helium will have chemically controlled impurities (water, oxygen, carbon dioxide, carbon monoxide, methane, hydrogen) that will create a slightly oxidizing gas environment. Little is known from direct experiments on the reactivity of third generation (nuclear grade) SiC/SiC composites in contact with low concentrations of water or oxygen in inert gas, at high temperature. However, there is ample information about the oxidation in dry and moist air of SiC/SiC composites at high temperatures. This information is reviewed first in the next chapters. The emphasis is places on the improvement in material oxidation, thermal, and mechanical properties during three stages of development of SiC fibers and at least two stages of development of the fiber/matrix interphase. The chemical stability of SiC/SiC composites in contact with oxygen or steam at temperatures that may develop in off-normal reactor conditions supports the conclusion that most advanced composites (also known as nuclear grade SiC/SiC composites) have the chemical resistance that would allow them maintain mechanical properties at temperatures up to 1200 1300 oC in the extreme conditions of an air or water ingress accident scenario. Further research is needed to assess the long-term stability of advanced SiC/SiC composites in inert gas (helium) in presence of very low concentrations (traces) of water and oxygen at the temperatures of normal operation of helium-cooled reactors. Another aspect that needs to be investigated is the effect of fast neutron irradiation on the oxidation stability of advanced SiC/SiC composites in normal operation conditions.

  17. Bragg reflector and laser fired back contact in a-Si:H/c-Si heterostructure solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Tucci, M. [ENEA, Research Center Casaccia, via Anguillarese 301, S. Maria di Galeria 00123, Rome (Italy)], E-mail: mario.tucci@casaccia.enea.it; Serenelli, L.; Salza, E.; Pirozzi, L. [ENEA, Research Center Casaccia, via Anguillarese 301, S. Maria di Galeria 00123, Rome (Italy); De Cesare, G.; Caputo, D.; Ceccarelli, M. [Department of Electronic Engineering, University ' Sapienza' , via Eudossiana 18 00184, Rome (Italy)

    2009-03-15

    The amorphous/crystalline silicon (a-Si/c-Si) heterostructure has recently attracted new interest due to higher open circuit voltage V{sub oc} and low temperature fabrication processes. By reducing the wafer thickness all these characteristics become a necessity, together with the requirement of a back reflecting mirror, to obtain an effective optical confinement. To this aim dielectric mirrors can be adopted in the rear side of the solar cells, together with a local process of laser fired back Al contact. Taking advantage of a-Si/SiN{sub x} passivation properties of c-Si surface a Bragg reflector configuration can be formed on the rear side of the c-Si wafer by Plasma Enhanced Chemical Vapor Deposition (PECVD) alternating several couples of a-Si/SiN{sub x} and choosing their thicknesses to maximize the reflectance inward the c-Si wafer in the NIR spectrum. In this work we have adopted this mirror on the rear side of an n-a-Si/i-a-Si/p-c-Si heterostructure solar cell to obtain a full low temperature process. The cell back contact has been ensured by an Al diffusion into the c-Si wafer promoted by Nd-YAG pulsed laser. The front cell contact has been enhanced by chromium silicide CrSi formation on top of the n-a-Si layer and ITO deposition followed by an Ag grid. A V{sub oc} of 681 mV and 94% of IQE at 1000 nm have been reached.

  18. PIE of nuclear grade SiC/SiC flexural coupons irradiated to 10 dpa at LWR temperature

    Energy Technology Data Exchange (ETDEWEB)

    Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-03-01

    Silicon carbide fiber-reinforced SiC matrix (SiC/SiC) composites are being actively investigated for accident-tolerant core structures of light water reactors (LWRs). Owing to the limited number of irradiation studies previously conducted at LWR-coolant temperature, this study examined SiC/SiC composites following neutron irradiation at 230–340°C to 2.0 and 11.8 dpa in the High Flux Isotope Reactor. The investigated materials are chemical vapor infiltrated (CVI) SiC/SiC composites with three different reinforcement fibers. The fiber materials were monolayer pyrolytic carbon (PyC)-coated Hi-NicalonTM Type-S (HNS), TyrannoTM SA3 (SA3), and SCS-UltraTM (SCS) SiC fibers. The irradiation resistance of these composites was investigated based on flexural behavior, dynamic Young’s modulus, swelling, and microstructures. There was no notable mechanical properties degradation of the irradiated HNS and SA3 SiC/SiC composites except for reduction of the Young’s moduli by up to 18%. The microstructural stability of these composites supported the absence of degradation. In addition, no progressive swelling from 2.0 to 11.8 dpa was confirmed for these composites. On the other hand, the SCS composite showed significant mechanical degradation associated with cracking within the fiber. This study determined that SiC/SiC composites with HNS or SA3 SiC/SiC fibers, a PyC interphase, and a CVI SiC matrix retain their properties beyond the lifetime dose for LWR fuel cladding at the relevant temperature.

  19. Metastable carbon phases from CF/sub 4/ reactions. Part I. Reactions with SiC and Si

    Energy Technology Data Exchange (ETDEWEB)

    Holcombe, C.E. Jr.; Condon, J.B.; Johnson, D.H.

    1978-09-01

    Reactions of CF/sub 4/ with ..beta..-SiC and Si powders were studied by thermal analysis techniques. Products were examined by x-ray and electron diffraction and electron microscopy. Two exotherms occur with ..beta..-SiC: at 874/sup 0/C, possibly from preferential reaction of the (111) planes; at 982/sup 0/C, presumably from rapid reaction on arbitrary planes. The primary product is amorphous carbon; however, graphite, carbon VI, or lonsdaleite single crystals also form. With Si powder, an exothermic reaction at 990/sup 0/C results from the formation of textured ..beta..-SiC.

  20. Thermal conductivity of hexagonal Si and hexagonal Si nanowires from first-principles

    Science.gov (United States)

    Raya-Moreno, Martí; Aramberri, Hugo; Seijas-Bellido, Juan Antonio; Cartoixà, Xavier; Rurali, Riccardo

    2017-07-01

    We calculate the thermal conductivity, κ, of the recently synthesized hexagonal diamond (lonsdaleite) Si using first-principles calculations and solving the Boltzmann Transport Equation. We find values of κ which are around 40% lower than in the common cubic diamond polytype of Si. The trend is similar for [111] Si nanowires, with reductions of the thermal conductivity that are even larger than in the bulk in some diameter range. The Raman active modes are identified, and the role of mid-frequency optical phonons that arise as a consequence of the reduced symmetry of the hexagonal lattice is discussed. We also show briefly that popular classic potentials used in molecular dynamics might not be suited to describe hexagonal polytypes, discussing the case of the Tersoff potential.

  1. Theory and simulation of photogeneration and transport in Si-SiOx superlattice absorbers

    Directory of Open Access Journals (Sweden)

    Aeberhard Urs

    2011-01-01

    Full Text Available Abstract Si-SiOx superlattices are among the candidates that have been proposed as high band gap absorber material in all-Si tandem solar cell devices. Owing to the large potential barriers for photoexited charge carriers, transport in these devices is restricted to quantum-confined superlattice states. As a consequence of the finite number of wells and large built-in fields, the electronic spectrum can deviate considerably from the minibands of a regular superlattice. In this article, a quantum-kinetic theory based on the non-equilibrium Green's function formalism for an effective mass Hamiltonian is used for investigating photogeneration and transport in such devices for arbitrary geometry and operating conditions. By including the coupling of electrons to both photons and phonons, the theory is able to provide a microscopic picture of indirect generation, carrier relaxation, and inter-well transport mechanisms beyond the ballistic regime.

  2. Impact of organic overlayers on a-Si:H/c-Si surface potential

    KAUST Repository

    Seif, Johannes P.

    2017-04-11

    Bilayers of intrinsic and doped hydrogenated amorphous silicon, deposited on crystalline silicon (c-Si) surfaces, simultaneously provide contact passivation and carrier collection in silicon heterojunction solar cells. Recently, we have shown that the presence of overlaying transparent conductive oxides can significantly affect the c-Si surface potential induced by these amorphous silicon stacks. Specifically, deposition on the hole-collecting bilayers can result in an undesired weakening of contact passivation, thereby lowering the achievable fill factor in a finished device. We test here a variety of organic semiconductors of different doping levels, overlaying hydrogenated amorphous silicon layers and silicon-based hole collectors, to mitigate this effect. We find that these materials enhance the c-Si surface potential, leading to increased implied fill factors. This opens opportunities for improved device performance.

  3. Formation of pyramid-like nanostructures in MBE-grown Si films on Si(001)

    Energy Technology Data Exchange (ETDEWEB)

    Galiana, N.; Martin, P.P.; Rodriguez-Canas, E.; Esteban-Betegon, F.; Alonso, M.; Ruiz, A. [CSIC, Instituto de Ciencia de Materiales de Madrid, Madrid (Spain); Garzon, L.; Ocal, C. [CSIC, Institut de Ciencia de Materials de Barcelona, Barcelona (Spain); Munuera, C. [CSIC, Instituto de Ciencia de Materiales de Madrid, Madrid (Spain); CSIC, Institut de Ciencia de Materials de Barcelona, Barcelona (Spain); Varela, M. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States)

    2011-03-15

    The growth of Si homoepitaxial layers on Si(001) substrates by molecular beam epitaxy is analyzed for a set of growth conditions in which diverse nanometer-scale features develop. Using Si substrates prepared by exposure to HF vapor and annealing in ultra-high vacuum, a rich variety of surface morphologies is found for different deposited layer thicknesses and substrate temperatures in a reproducible way, showing a critical dependence on both. Arrays of 3D islands (truncated pyramids), percolated ridge networks, and square pit (inverted pyramid) distributions are observed. We analyze the obtained arrangements and find remarkable similarities to other semiconductor though heteroepitaxial systems. The nanoscale entities (islands or pits) display certain self assembly and ordering, concerning size, shape, and spacing. Film growth sequence follows the 'islands-coalescence-2D growth' pathway, eventually leading to optimum flat morphologies for high enough thickness and temperature. (orig.)

  4. Oxidation-resistant interface coatings for SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Stinton, D.P.; Kupp, E.R.; Hurley, J.W. [and others

    1996-06-01

    The characteristics of the fiber-matrix interfaces in ceramic matrix composites control the mechanical behavior of these composites. Finite element modeling (FEM) was performed to examine the effect of interface coating modulus and coefficient of thermal expansion on composite behavior. Oxide interface coatings (mullite and alumina-titania) produced by a sol-gel method were chosen for study as a result of the FEM results. Amorphous silicon carbide deposited by chemical vapor deposition (CVD) is also being investigated for interface coatings in SiC-matrix composites. Processing routes for depositing coatings of these materials were developed. Composites with these interfaces were produced and tested in flexure both as-processed and after oxidation to examine the suitability of these materials as interface coatings for SiC/SiC composites in fossil energy applications.

  5. Oxidation-resistant interface coatings for SiC/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Stinton, D.P.; Kupp, E.R.; Hurley, J.W.; Lowden, R.A. [Oak Ridge National Lab., TN (United States)] [and others

    1996-08-01

    The characteristics of the fiber-matrix interfaces in ceramic matrix composites control the mechanical behavior of these composites. Finite element modeling (FEM) was performed to examine the effect of interface coating modulus and coefficient of thermal expansion on composite behavior. Oxide interface coatings (mullite and alumina-titania) produced by a sol-gel method were chosen for study as a result of the FEM results. Amorphous silicon carbide deposited by chemical vapor deposition (CVD) is also being investigated for interface coatings in SiC-matrix composites. Processing routes for depositing coatings of these materials were developed. Composites with these interfaces were produced and tested in flexure both as-processed and after oxidation to examine the suitability of these materials as interface coatings for SiC/SiC composites in fossil energy applications.

  6. Photoluminescence characterization of defects in Si and SiGe structures

    Energy Technology Data Exchange (ETDEWEB)

    Higgs, V.; Chin, F.; Wang, X.; Mosalski, J. [Bio-Rad Micromeasurements, Hemel Hempstead (United Kingdom); Beanland, R. [Marconi Caswell Ltd, Towcester, Northamptonshire (United Kingdom)

    2000-12-11

    Low-temperature photoluminescence (PL) spectroscopy is a very sensitive tool to investigate the presence of dislocations in Si. The main dislocation-related bands (D1-D4) have been attributed to a wide range of causes, either intrinsic properties of the dislocation or impurity related. PL is a competitive recombination process and the non-radiative processes need to be measured to understand the overall effect of impurities. PL spectroscopy samples a large volume in comparison to the dislocation itself and therefore gives an average effect. High-resolution room-temperature PL mapping (SiPHER) has been used to detect defects in both Si and SiGe wafers. Whole-wafer PL maps reveal the presence of slip on 300 mm Si wafers. Comparison studies with defect etching show that there is a one-to-one correlation between defects detected in the PL micro-scans and those revealed by defect etching. Whole-wafer mapping has revealed a number of different defect types in SiGe epilayers. The ability to record whole-wafer PL maps facilitates the rapid identification of inhomogeneities and defects. High-resolution PL micro-maps showed the defect area to contain a high density of misfit dislocations, and the nucleation site has strong non-radiative recombination. One common defect type was analysed using plan view transmission electron microscopy (TEM) and optical microscopy; these results revealed the presence of a high density of defect loops and stacking faults consistent with the high recombination rate at the defect site. (author)

  7. Photoluminescence characterization of defects in Si and SiGe structures

    Science.gov (United States)

    Higgs, V.; Chin, F.; Wang, X.; Mosalski, J.; Beanland, R.

    2000-12-01

    Low-temperature photoluminescence (PL) spectroscopy is a very sensitive tool to investigate the presence of dislocations in Si. The main dislocation-related bands (D1-D4) have been attributed to a wide range of causes, either intrinsic properties of the dislocation or impurity related. PL is a competitive recombination process and the non-radiative processes need to be measured to understand the overall effect of impurities. PL spectroscopy samples a large volume in comparison to the dislocation itself and therefore gives an average effect. High-resolution room-temperature PL mapping (SiPHER) has been used to detect defects in both Si and SiGe wafers. Whole-wafer PL maps reveal the presence of slip on 300 mm Si wafers. Comparison studies with defect etching show that there is a one-to-one correlation between defects detected in the PL micro-scans and those revealed by defect etching. Whole-wafer mapping has revealed a number of different defect types in SiGe epilayers. The ability to record whole-wafer PL maps facilitates the rapid identification of inhomogeneities and defects. High-resolution PL micro-maps showed the defect area to contain a high density of misfit dislocations, and the nucleation site has strong non-radiative recombination. One common defect type was analysed using plan view transmission electron microscopy (TEM) and optical microscopy; these results revealed the presence of a high density of defect loops and stacking faults consistent with the high recombination rate at the defect site.

  8. Dimensional stability and anisotropy of SiC and SiC-based composites in transition swelling regime

    Science.gov (United States)

    Katoh, Yutai; Koyanagi, Takaaki; McDuffee, Joel L.; Snead, Lance L.; Yueh, Ken

    2018-02-01

    Swelling, or volumetric expansion, is an inevitable consequence of the atomic displacement damage in crystalline silicon carbide (SiC) caused by energetic neutron irradiation. Because of its steep temperature and dose dependence, understanding swelling is essential for designing SiC-based components for nuclear applications. In this study, swelling behaviors of monolithic CVD SiC and nuclear grade SiC fiber - SiC matrix (SiC/SiC) composites were accurately determined, supported by the irradiation temperature determination for individual samples, following neutron irradiation within the lower transition swelling temperature regime. Slightly anisotropic swelling behaviors were found for the SiC/SiC samples and attributed primarily to the combined effects of the pre-existing microcracking, fiber architecture, and specimen dimension. A semi-empirical model of SiC swelling was calibrated and presented. Finally, implications of the refined model to selected swelling-related issues for SiC-based nuclar reactor components are discussed.

  9. Separation of primary Si and impurity boron removal from Al-30%Si-10%Sn melt under a traveling magnetic field

    Directory of Open Access Journals (Sweden)

    Jin-ling Sun

    2016-07-01

    Full Text Available Separation of primary Si phase and removal of boron in the primary Si phase during the solidification process of the Al-30%Si-10%Sn melt under a traveling magnetic field (TMF were investigated. The results showed that the agglomeration layer of the primary Si can be formed in the periphery of the ingot while the inner microstructures mainly consist of the eutectic α-Al+Si and β-Sn phases. The intense melt flow carries the bulk liquid with higher Si content to promote the growth of the primary Si phase which is first precipitated close to the inner wall of crucible with a relatively lower temperature, resulting in the remarkable segregation of the primary Si phase. The content of impurity B in the primary Si phase can be removed effectively with an increase in magnetic flux intensity. The results of electron probe microanalysis (EPMA clearly indicated that the average intensity of the B Ka line in the α-Al phase region of Al-Si-Sn alloy is higher in the case of solidification under TMF than that of normal solidification condition, suggesting that the electromagnetic stirring can promote the B removal from the primary Si phase.

  10. Comparative assessment of 3.3kV/400A SiC MOSFET and Si IGBT power modules

    DEFF Research Database (Denmark)

    Ionita, Claudiu; Nawaz, Muhammad; Ilves, Kalle

    2017-01-01

    In this paper, a comparative evaluation between a commercial 3.3 kV/400 A Si-IGBT and a 3.3 kV/400 A SiC MOSFET power module in half-bridge configuration is presented. With a constant current of 250 A, a lower forward voltage (VDS) drop of 1.6 V is obtained for SiC MOSFET at 300 K compared to Si...... IGBT. At 400 A, the difference is reduced to 1.3 V. SiC MOSFET offers an on-state resistance of 8.7 mΩ, and blocking voltage of 3.5 kV at 300 K. Compared to Si-IGBT, a significant lower leakage current for the SiC MOSFET is obtained with varying temperature from 300 K to 400 K. SiC MOSFET offers 7.......5 times lower switching losses compared to Si-IGBTs for a supply voltage of 2000 V at 300 K. The switching losses of the SiC MOSFET are not affected by the temperature. Total energy loss increases (3.5 times) linearly with variation of the gate resistance from 6 Ω to 27 Ω. The capability of the SiC MOSFET...

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

    Energy Technology Data Exchange (ETDEWEB)

    Cao, J. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering]|[Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

    1996-12-01

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

  12. Growth and characterization of textured well-faceted ZnO on planar Si(100), planar Si(111), and textured Si(100) substrates for solar cell applications.

    Science.gov (United States)

    Tsai, Chin-Yi; Lai, Jyong-Di; Feng, Shih-Wei; Huang, Chien-Jung; Chen, Chien-Hsun; Yang, Fann-Wei; Wang, Hsiang-Chen; Tu, Li-Wei

    2017-01-01

    In this work, textured, well-faceted ZnO materials grown on planar Si(100), planar Si(111), and textured Si(100) substrates by low-pressure chemical vapor deposition (LPCVD) were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and cathode luminescence (CL) measurements. The results show that ZnO grown on planar Si(100), planar Si(111), and textured Si(100) substrates favor the growth of ZnO(110) ridge-like, ZnO(002) pyramid-like, and ZnO(101) pyramidal-tip structures, respectively. This could be attributed to the constraints of the lattice mismatch between the ZnO and Si unit cells. The average grain size of ZnO on the planar Si(100) substrate is slightly larger than that on the planar Si(111) substrate, while both of them are much larger than that on the textured Si(100) substrate. The average grain sizes (about 10-50 nm) of the ZnO grown on the different silicon substrates decreases with the increase of their strains. These results are shown to strongly correlate with the results from the SEM, AFM, and CL as well. The reflectance spectra of these three samples show that the antireflection function provided by theses samples mostly results from the nanometer-scaled texture of the ZnO films, while the micrometer-scaled texture of the Si substrate has a limited contribution. The results of this work provide important information for optimized growth of textured and well-faceted ZnO grown on wafer-based silicon solar cells and can be utilized for efficiency enhancement and optimization of device materials and structures, such as heterojunction with intrinsic thin layer (HIT) solar cells.

  13. Effect of addition of Si on thermal and electrical properties of Al-Si-Al2O3 composites

    Science.gov (United States)

    Cao, R.; Jiang, J. X.; Wu, C.; Jiang, X. S.

    2017-06-01

    Al-5wt.%Si-Al2O3, Al-10wt.%Si-Al2O3, Al-20wt.%Si-Al2O3 composites were fabricated by powder metallurgy and in-situ reactive synthesis technology. The impact of the addition of Si on the thermal and electrical properties was tested and analysed for vary in silicon content in Al-Si-Al2O3 composites. Results show that both thermal expansion coefficient and thermal conductivity decreased as silicon content increased because Si and Al2O3 dispersed in the Al matrix uniformly to suppress the high thermal expansion of Al to a large extent as well as the interfacial thermal resistance which led to the decline in thermal conductivity. Electrical resistivity increased when silicon content was increased because low thermal expansion coefficient particles of Si and Al2O3 severely damaged the continuity of the Al matrix which hindered movement of electron in the matrix.

  14. Antimony segregation and n-type doping in Si/Si(111) films grown by molecular beam epitaxy

    Science.gov (United States)

    Yurasov, D. V.; Drozdov, M. N.; Schmagin, V. B.; Yunin, P. A.; Novikov, A. V.

    2017-10-01

    The temperature dependence of antimony segregation in Si/Si(111) films grown by molecular-beam epitaxy was investigated experimentally. The obtained results were found to be qualitatively similar to the previously reported data for Si(001) case, but rather significant quantitative differences were observed. It was obtained that segregation ratio, which is defined as surface-to-bulk impurity concentration ratio, varies by nearly 5 orders of magnitude in the relatively narrow temperature interval of 500-675 °C for Si(111). This finding allowed to disseminate the previously proposed technique of selective doping of Si(001) to the Si(111) case. Using this technique selectively n-type doped Si films were fabricated which have abrupt boundaries of the antimony concentration profiles. A profile abruptness as low as 1.5 nm/decade was obtained.

  15. Effect of simultaneous ion irradiation on microstructural change of SiC/SiC composites at high temperature

    Science.gov (United States)

    Taguchi, T.; Wakai, E.; Igawa, N.; Nogami, S.; Snead, L. L.; Hasegawa, A.; Jitsukawa, S.

    2002-12-01

    The effect of simultaneous triple ion irradiation of He, H and Si on microstructural evolution of two kinds of SiC/SiC composites (HNS composite (using Hi-Nicalon type S SiC fiber) and TSA composite (using Tyranno SA SiC fiber)) at 1000 °C has been investigated. The microstructure observations of SiC/SiC composites irradiated to 10 dpa were examined by transmission electron microscopy. He bubbles were hardly formed in matrix of TSA composite, but many helium bubbles and some cracks were observed at grain boundaries of matrix of HNS composite. He bubbles and cracks were not, on the other hand, observed in the both fiber fabrics of HNS and TSA composites. Debonding between fiber and carbon layer following irradiation region was not observed in the both composites. Under these irradiation conditions, TSA composite showed the better microstructural stability against ion beams irradiation than one of HNS composite.

  16. Syntheses and structural characterizations of CrSi2 nanostructures using Si substrates under CrCl2 vapor

    Science.gov (United States)

    Li, Wen; Meng, Erchao; Matsushita, Tomoji; Oda, Shingo; Ishikawa, Daisuke; Nakane, Kaito; Hu, Junhua; Guan, Shaokang; Ishida, Akihiro; Tatsuoka, Hirokazu

    2013-02-01

    Chromium disilicide (CrSi2) nanostructures were grown by the exposure of Si substrates to CrCl2 vapor at atmospheric pressure, and the growth condition dependence on the morphological and structural properties of CrSi2 was systemically investigated. The various structures of CrSi2, such as microrods, nanowire bundles along with microrods and dendritic nanowire structures, have been grown. It was found that the Si substrate temperature and the quantity of the CrCl2 source materials significantly affect the morphological and structural properties of the CrSi2 structures. The structural evolution of CrSi2 has been discussed on the basis of thermodynamic reactions, vapor deposition growth and dendritic growth phenomena. This growth process provides a simple and controllable method to grow novel nano-scaled structures of transition metal silicides for technological use.

  17. Growth of DySi sub 2 layers on Si surface by high-current Dy-ion implantation

    CERN Document Server

    Cheng, X Q

    2003-01-01

    We report, in this paper, the synthesis of DySi sub 2 layers on Si surfaces by high-current Dy-ion implantation in Si wafers using a metal vapor vacuum arc ion source. It was found that the continuous DySi sub 2 layers could grow at a relatively low formation temperature of 190degC and that the surface morphology varied with the variation of the implantation parameters. The formation mechanism of the equilibrium DySi sub 2 phase as well as the continuous DySi sub 2 layer on Si surface is proposed in terms of ion beam heating and the effect of ion dose on the Dy-ion implantation process. (author)

  18. Reaction-bonded Si3N4 and SiC matrix composites

    Science.gov (United States)

    Bhatt, Ramakrishna T.; Behrendt, Donald R.

    1992-01-01

    A development status evaluation is presented for the reaction-bonded SiC- and Si3N4-matrix types of fiber-reinforced ceramic-matrix composite (FRCMC). A variety of reaction-bonding methods are being pursued for FRCMC fabrication: CVI, CVD, directed metal oxidation, and self-propagating high-temperature synthesis. Due to their high specific modulus and strength, toughness, and fabricability, reaction-bonded FRCMC are important candidate materials for such heat-engine components as combustor liners, nozzles, and turbine and stator blading. The improvement of long-term oxidative stability in these composites is a major goal of current research.

  19. Metastable ultrathin crystal in thermally grown SiO2 film on Si substrate

    Directory of Open Access Journals (Sweden)

    Koji Kimoto

    2012-12-01

    Full Text Available A silicon dioxide film on a silicon substrate is the most essential element in semiconductor devices and various advanced materials. We have elucidated the atomic structure of SiO2 films using low-dose scanning transmission electron microscopy (STEM. We have visualized a metastable crystalline SiO2 layer near a silicon substrate, which was not revealed in previous studies probably due to the vitrification caused by electron irradiation. Our experimental results also suggest a crystallographic nature of various surface oxides.

  20. Comparative Study of Si and SiC MOSFETs for High Voltage Class D Audio Amplifiers

    DEFF Research Database (Denmark)

    Nielsen, Dennis; Knott, Arnold; Andersen, Michael A. E.

    2014-01-01

    Silicon (Si) Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are traditional utilised in class D audio amplifiers. It has been proposed to replace the traditional inefficient electrodynamic transducer with the electrostatic transducer. This imposes new high voltage requirements...... on the MOSFETs of class D amplifiers, and significantly reduces the selection of suitable MOSFETs. As a consequence it is investigated, if Silicon-Carbide (SiC) MOSFETs could represent a valid alternative. The theory of pulse timing errors are revisited for the application of high voltage and capactive loaded...

  1. Mechanism of Si intercalation in defective graphene on SiC

    KAUST Repository

    Kaloni, Thaneshwor P.

    2012-10-01

    Previously reported experimental findings on Si-intercalated graphene on SiC(0001) seem to indicate the possibility of an intercalation process based on the migration of the intercalant through atomic defects in the graphene sheet. We employ density functional theory to show that such a process is in fact feasible and obtain insight into its details. By means of total energy and nudged elastic band calculations we are able to establish the mechanism on an atomic level and to determine the driving forces involved in the different steps of the intercalation process through atomic defects.

  2. Magnetically tuned photoelectric response observed in nanoscale Co-SiO2-Si structures.

    Science.gov (United States)

    Zhang, Qian; Hu, Jieqiong; Zheng, Diyuan; Dong, Anhua; Wang, Hui

    2017-10-27

    We report a large magnetically tuned lateral photovoltaic effect (LPE) observed in nanoscale Co-SiO2-Si structures. This tunable effect strongly depends on the location of two electrodes. The change ratio of lateral photovoltage (LPV) can reach a considerable value of 94.15% under an external magnetic field of 1.77 Teslas. This phenomenon is mainly ascribed to the asymmetric Lorentz force acting on the photo-current in the region of the edge area of the nanostructure. It adds a new functionality to traditional LPE-based devices, and provides a potential prospect for the development of multifunctional high-sensitive photoelectric devices or sensors.

  3. Magnetically tuned photoelectric response observed in nanoscale Co-SiO2-Si structures

    Science.gov (United States)

    Zhang, Qian; Hu, Jieqiong; Zheng, Diyuan; Dong, Anhua; Wang, Hui

    2017-10-01

    We report a large magnetically tuned lateral photovoltaic effect (LPE) observed in nanoscale Co-SiO2-Si structures. This tunable effect strongly depends on the location of two electrodes. The change ratio of lateral photovoltage (LPV) can reach a considerable value of 94.15% under an external magnetic field of 1.77 Teslas. This phenomenon is mainly ascribed to the asymmetric Lorentz force acting on the photo-current in the region of the edge area of the nanostructure. It adds a new functionality to traditional LPE-based devices, and provides a potential prospect for the development of multifunctional high-sensitive photoelectric devices or sensors.

  4. Performance and Durability of Environmental Barrier Coatings on SiC/SiC Ceramic Matrix Composites

    Science.gov (United States)

    Zhu, Dongming; Harder, Bryan; Bhatt, Ramakrishna

    2016-01-01

    This presentation highlights advanced environmental barrier coating (EBC) and SiC-SiC Ceramic Matrix Composites (CMC) systems for next generation turbine engines. The emphasis will be placed on fundamental coating and CMC property evaluations; and the integrated system performance and degradation mechanisms in simulated laboratory turbine engine testing environments. Long term durability tests in laser rig simulated high heat flux the rmomechanical creep and fatigue loading conditions will also be presented. The results can help improve the future EBC-CMC system designs, validating the advanced EBC-CMC technologies for hot section turbine engine applications.

  5. Technology computer aided design for Si, SiGe and GaAs integrated circuits

    CERN Document Server

    Armstrong, GA

    2007-01-01

    The first book to deal with a broad spectrum of process and device design, and modelling issues related to semiconductor devices, bridging the gap between device modelling and process design using TCAD. Examples for types of Si-, SiGe-, GaAs- and InP-based heterostructure MOS and bipolar transistors are compared with experimental data from state-of-the-art devices. With various aspects of silicon heterostructures, this book presents a comprehensive perspective of emerging fields and covers topics ranging from materials to fabrication, devices, modelling and applications. Aimed at research-and-

  6. Effective stabilization and delivery of siRNA: reversible siRNA-phospholipid conjugate in nanosized mixed polymeric micelles.

    Science.gov (United States)

    Musacchio, Tiziana; Vaze, Onkar; D'Souza, Gerard; Torchilin, Vladimir P

    2010-08-18

    siRNA is a powerful tool to control cellular processes at the post-transcriptional level. However, its therapeutic potential is limited because of low stability in biological fluids and the lack of simple and efficient delivery systems. Chemical modification of siRNA could be used to increase its intracellular delivery, but may affect its specific activity. To overcome these obstacles, we suggest a simple and effective system capable of stabilization, delivery, and subsequent release of free active siRNA within cells. With this in mind, we reversibly modified the double-stranded GFP-siRNA with a phosphothioethanol (PE) portion via the reducible disulfide bond and incorporated the resulting siRNA-S-S-PE conjugate in nanosized PEG-PE micelles. In the mixed siRNA-S-S-PE/PEG-PE micelles obtained, siRNA was well-protected against degradation by nucleases for at least 24 h, and was released easily from these nanoparticles in free form in the presence of glutathione (GSH) at a concentration mimicking the intracellular levels. In GFP-C166 endothelial cells, mixed GFP-siRNA-S-S-PE/PEG-PE micelles down-regulate the GFP production 50-fold more effectively than free siRNA. In addition, siRNA-containing micelles showed none of the cytotoxic side effects typical for siRNA delivery systems that are based on electrostatic association of siRNA with cationic carriers. Thus, a reversible siRNA-phospholipid conjugate formulated into mixed micelles with PEG-PE can be an effective, nontoxic system for stabilization and delivery of siRNA.

  7. Formation Mechanism of SiO2-Type Inclusions in Si-Mn-Killed Steel Wires Containing Limited Aluminum Content

    Science.gov (United States)

    Wang, Kunpeng; Jiang, Min; Wang, Xinhua; Wang, Ying; Zhao, Haoqian; Cao, Zhanmin

    2015-10-01

    The origin, formation mechanism, and evolution of SiO2-type inclusions in Si-Mn-killed steel wires were studied by pilot trials with systematical samplings at the refining ladle, casting tundish, as-cast bloom, reheated bloom, and hot-rolled rods. It was found that the inclusions in tundish were well controlled in the low melting point region. By contrast, MnO-SiO2-Al2O3 inclusions in the as-cast bloom were with compositions located in the primary region of SiO2, and most CaO-SiO2-Al2O3-MnO inclusions lied in primary phase region of anorthite. Therefore, precipitation of SiO2 particles in MnO-SiO2-Al2O3 inclusions can be easier than in CaO-SiO2-Al2O3-MnO inclusions to form dual-phase inclusions in the as-cast bloom. Thermodynamic calculation by the software FactSage 6.4 (CRCT-ThermFact Inc., Montréal, Canada) showed that mass transfer between liquid steel and inclusions resulted in the rise of SiO2 content in inclusions from tundish to as-cast bloom and accelerated the precipitation of pure SiO2 phase in the formed MnO-SiO2-Al2O3 inclusions. As a result, the inclusions characterized by dual-phase structure of pure SiO2 in MnO-SiO2-Al2O3 matrix were observed in both as-cast and reheated blooms. Moreover, the ratio of such dual-phase SiO2-type inclusions witnessed an obvious increase from 0 to 25.4 pct before and after casting, whereas it changed little during the reheating and rolling. Therefore, it can be reasonably concluded that they were mainly formed during casting. Comparing the evolution of the inclusions composition and morphology in as-cast bloom and rolled products, a formation mechanism of the SiO2-type inclusions in wire rods was proposed, which included (1) precipitation of SiO2 in the formed MnO-SiO2-Al2O3 inclusion during casting and (2) solid-phase separation of the undeformed SiO2 precipitation from its softer MnO-SiO2-Al2O3 matrix during multipass rolling.

  8. The Stellar Imager (SI) Mission Concept

    Science.gov (United States)

    Carpenter, Kenneth S.; Schrijver, Carolus J.; Oegerle, William R. (Technical Monitor)

    2002-01-01

    The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5 approximately km. It will image stars and binaries with one hundred to one thousand resolution elements on their surface and enable long-term studies of stellar magnetic activity patterns and their evolution with time, for comparison with those on the sun. It will also sound their interiors through asteroseismology to image internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars in which these dynamos operate. The ultimate goal of the mission is to achieve the best possible forecasting of solar activity as a driver of climate and space weather on times scales ranging from months to decades, and an understanding of the impact of stellar magnetic activity on astrobiology and life in the Universe. The road to that goal will revolutionize our understanding of stars and stellar systems, the building blocks of the Universe. Fitting naturally within the NASA and ESA long-term time lines, SI complements defined missions, and with them will show us entire other solar systems, from the central star to their orbiting planets. In this paper we will describe the scientific goals of the mission, the performance requirements needed to address those goals, and the design concepts now under study.

  9. Electron Spectroscopy Study of SiC,

    Science.gov (United States)

    1983-09-01

    Liquid nitrogen cooling is supplied to the central copper block of the sample holder by flexible spiral stainless steel capillary. This cooling facility...sapphire disks from thinner copper blocks at both sides. The outer copper blocks hold 1.5 mm diameter W rods to which are welded a pair of 0.375 mm...sputtering was sufficient to implant F+ and Ar+ ions deep enough in the SiC surface layer, so that the implanted F and Ar could not be removed-by thermal

  10. SiNTO EWT silicon solar cells

    OpenAIRE

    Fallisch, A.; Keding, R.; Kästner, G.; Bartsch, J.; Werner, S; Stüwe, D.; Specht, J.; Preu, R.; Biro, D.

    2010-01-01

    In this work we combine the SiNTO cell process with the EWT cell concept. All masking steps are performed by inkjet printing technology. The via-holes and laser-fired contacts are created by high-speed laser drilling. A new polishing process, which is suitable for inkjet masking, to pattern the interdigitated grid on the rear side is developed. For passivation purposes a thermal silicon oxide is used for the rear surface and a silicon nitride antireflection coating for the front surface. An e...

  11. Como si fuera posible recoger sentimientos

    OpenAIRE

    Vayreda Puigvert, Marian; Vallès Villanueva, Joan

    2011-01-01

    Se trata de una propuesta como resultado del trabajo conjunto entre la escuela de Arte Pigment y el ESPAI ZERO1 del Museu Comarcal de la Garrotxa, destinado exclusivamente a exposiciones temporales de creación contemporánea y como continuidad de propuestas anteriores de colaboración: REPLICA23 y SONESNAT JUNIOR. Com si fos possible recollir el sofriment es un proyecto de la artista Anna Manel.la, y se consideró una propuesta interesante y un reto para conversar, intercambiar y crear con los a...

  12. Two-Zone Microstructures in Al-18Si Alloy Powders

    Science.gov (United States)

    Spinelli, J. E.; Bogno, A.-A.; Henein, H.

    2018-02-01

    Hypereutectic Al-18 wt pct Si alloy is widely used in automotive industry as a wear-resistant alloy for engine components. However, in the last few years, this traditional composition is being considered for processing by different rapid solidification methods. Positive points include its low thermal expansion and uniform distribution of surface oxides. Nevertheless, the microstructural aspects of Al-Si powders of 18 wt pct Si are still need to be addressed, such as, the eutectic Si morphology, size, and distribution generated by different process conditions during rapid solidification. Based on a detailed quantitative analysis of the microstructures of rapid solidified Al-18 wt pct Si in this work, solidification conditions that yield specific Si morphologies, Si spacing, and thermal cooling conditions are outlined. The focus is determining the solidification conditions that will yield a specified shape of eutectic Si. It is shown that Si morphology is dependent on a combination of growth velocity (based on modified JH model) and temperature gradient. Furthermore, the highest hardness is achieved with globular morphologies of Si. The processing conditions required to achieve these properties are outlined.

  13. Thermoelectric transport properties of Mn4 Si7 thin films

    Science.gov (United States)

    Shin, Yooleemi; Duong, Anh Tuan; Choi, Jeongyong; Cho, Sunglae

    2014-03-01

    The deposition of transition metal layers on silicon and their reaction with substrate are important issues in semiconductor device technology. The interface between metal and semiconductor determines the device performance. The 3d transition metal monosilicides such as FeSi, CoSi, MnSi and CrSi have attracted much attention because they are easily formed in the interface between transition metal and Si. On the other hand, the Mn4Si7 compound is well known a pseudo-direct band gap semiconductor (0.42 ~ 0.98 eV) with a fundamental gap increasing linearly with the compression along c- or a-axis. We have grown Mn thin films on Si (111) substrates at 600 °C using MBE, resulting in the formation of Mn4Si7. In order to investigate the correlation between magnetization and charge carrier transport, we performed magnetoresistance and Hall resistance measurements by using a physical property measurement system. Interestingly, we observed the Seebeck coefficient of -565 μV/K and electrical resistivity of 2.26 m Ω cm in Mn4Si7 films grown on Si substrate, resulting in the power factor of 14 mW/K2m.

  14. A Thermoelectric Generator Using Porous Si Thermal Isolation

    Directory of Open Access Journals (Sweden)

    Emmanouel Hourdakis

    2013-10-01

    Full Text Available In this paper we report on a thermoelectric generator (TEG using thermal isolation provided by a thick porous Si layer locally formed on the Si wafer and thermocouples composed of p-doped polycrystalline Si/Al. The “hot” contacts of the thermocouples lie on the porous Si layer, while the “cold” contacts lie on bulk crystalline Si. A housing was also designed and fabricated in order to transfer any external temperature change on the “hot” contacts of the thermocouples, the “cold” contacts being isolated from the “hot” contacts by a thick resist layer. The fabrication of the sensing element (Si die is fully compatible with batch Si processing. The output power of the thermoelectric generator depends on the porous Si isolation layer thickness, porosity, structure and morphology. For a mesoporous Si layer of 60% porosity and a macroscopic temperature differential of 10 K, an output power of 0.39 μW/cm2 was measured for a 50 μm thick porous Si layer.

  15. Single siRNA nanocapsules for enhanced RNAi delivery.

    Science.gov (United States)

    Yan, Ming; Liang, Min; Wen, Jing; Liu, Yang; Lu, Yunfeng; Chen, Irvin S Y

    2012-08-22

    Synthetic siRNA has been considered as a highly promising therapeutic agent for human diseases. However, clinical use of siRNA has been hampered by instability in the body and inability to deliver sufficient RNA interference compounds to the tissues or cells. To address this challenge, we present here a single siRNA nanocapsule delivery technology, which is achieved by encapsulating a single siRNA molecule within a degradable polymer nanocapsule with a diameter around 20 nm and positive surface charge. As proof-of-concept, since CCR5 is considered a major silencing target of HIV therapy, CCR5-siRNA nanocapsules were delivered into 293T cells and successfully downregulated the CCR5 RNA fused with mCherry reporter RNA. In the absence of human serum, nanocapsules and lipofectamine silenced expression of CCR5-mCherry expression to 8% and 15%, respectively. Such nanocapsules maintain the integrity of siRNA inside even after incubation with ribonuclease and serum for 1 h; under the same conditions, siRNA is degraded in the native form or when formulated with lipofectamine. In the presence of serum, CCR5-siRNA nanocapsules knocked down CCR5-mCherry expression to less than 15% while siRNAs delivered through lipofectamine slightly knocked down the expression to 55%. In summary, this work provides a novel platform for siRNA delivery that can be developed for therapeutic purposes.

  16. Functional gene silencing mediated by chitosan/siRNA nanocomplexes

    Energy Technology Data Exchange (ETDEWEB)

    Ji, A M; Su, D; Che, O; Li, W S; Sun, L; Zhang, Z Y; Xu, F [Department of Pharmaceutical Science, Zhujiang Hospital, Southern Medical University, Guangzhou 510282 (China); Yang, B, E-mail: andrewfxu1998@gmail.co [Department of Chemistry, Indiana University-Bloomington, Bloomington, IN 47405 (United States)

    2009-10-07

    Chitosan/siRNA nanoparticles to knock down FHL2 gene expression were reported in this work. The physicochemical properties such as particle size, surface charge, morphology and complex stability of chitosan nanoparticle-incorporated siRNA were evaluated. Nanoparticles which were formulated with chitosan/siRNA exhibited irregular, lamellar and dendritic structures with a hydrodynamic radius size of about 148 nm and net positive charges with zeta-potential value of 58.5 mV. The knockdown effect of the chitosan/siRNA nanoparticles on gene expression in FHL2 over-expressed human colorectal cancer Lovo cells was investigated. The result showed that FHL2 siRNA formulated within chitosan nanoparticles could knock down about 69.6% FHL2 gene expression, which is very similar to the 68.8% reduced gene expression when siRNA was transfected with liposome Lipofectamine. Western analysis further showed significant FHL-2 protein expression reduced by the chitosan/siRNA nanoparticles. The results also showed that blocking FHL2 expression by siRNA could also inhibit the growth and proliferation of human colorectal cancer Lovo cells. The current results demonstrated that chitosan-based siRNA nanoparticles were a very efficient delivery system for siRNA in vivo as previously reported.

  17. Functional gene silencing mediated by chitosan/siRNA nanocomplexes

    Science.gov (United States)

    Ji, A. M.; Su, D.; Che, O.; Li, W. S.; Sun, L.; Zhang, Z. Y.; Yang, B.; Xu, F.

    2009-10-01

    Chitosan/siRNA nanoparticles to knock down FHL2 gene expression were reported in this work. The physicochemical properties such as particle size, surface charge, morphology and complex stability of chitosan nanoparticle-incorporated siRNA were evaluated. Nanoparticles which were formulated with chitosan/siRNA exhibited irregular, lamellar and dendritic structures with a hydrodynamic radius size of about 148 nm and net positive charges with zeta-potential value of 58.5 mV. The knockdown effect of the chitosan/siRNA nanoparticles on gene expression in FHL2 over-expressed human colorectal cancer Lovo cells was investigated. The result showed that FHL2 siRNA formulated within chitosan nanoparticles could knock down about 69.6% FHL2 gene expression, which is very similar to the 68.8% reduced gene expression when siRNA was transfected with liposome Lipofectamine. Western analysis further showed significant FHL-2 protein expression reduced by the chitosan/siRNA nanoparticles. The results also showed that blocking FHL2 expression by siRNA could also inhibit the growth and proliferation of human colorectal cancer Lovo cells. The current results demonstrated that chitosan-based siRNA nanoparticles were a very efficient delivery system for siRNA in vivo as previously reported.

  18. Thin film properties of sputtered niobium silicide on SiO/sub 2/, Si/sub 3/N/sub 4/, and N/sup +/ poly-Si

    Energy Technology Data Exchange (ETDEWEB)

    Chow, T.P.; Lu, W.J.; Steckl, A.J.; Baliga, B.J.

    1986-01-01

    Thin film properties of niobium silicide sputtered from a slightly silicon-rich (Si/Nb approx. = 2.3), cold-pressed alloy target onto SiO/sub 2/, Si/sub 3/N/sub 4/, and n doped poly-Si have been investigated. The structural and compositional properties were examined with x-ray diffraction, Rutherford backscattering spectrometry (RBS), and secondary ion mass spectrometry (SIMS). X-ray diffraction revealed that NbSi/sub 2/ was the predominant silicide phase present, unlike those films reported previously, which contained significant amounts of an intermediate silicide phase (Nb/sub 5/Si/sub 3/). These films had a SiNb ratio of 2.1 as determined from RBS and contained lower levels of common contaminants (such as N/sub 2/, O/sub 2/, and carbon). Isochronal and isothermal annealing showed that the major decrease in resistivity occurred in the first 5 min, and a resistivity value of approx. =70 ..mu cap omega..-cm was obtained after annealing at 1000/sup 0/C. During annealing, phosphorus was found to diffuse through NbSi/sub 2/ rapidly, similar to other refractory silicides.

  19. Synthesis, electronic and optical properties of Si nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Dinh, L.N.

    1996-09-01

    Silicon and silicon oxide nanostructures have been deposited on solid substrates, in an ultra high vacuum (UHV) chamber, by laser ablation or thermal vaporization. Laser ablation followed by substrate post annealing produced Si clusters with average size of a few nanometers, on highly oriented pyrolytic graphite (HOPG) surfaces. This technique, which is based on surface diffusion, is limited to the production of less than one layer of clusters on a given surface. The low coverage of Si clusters and the possibility of nonradiative decay of excitation in the Si cores to the HOPG substrates in these samples rendered them unsuitable for many optical measurements. Thermal vaporization of Si in an Ar buffer gas, on the contrary, yielded multilayer coverage of Si nanoclusters with a fairly narrow size distribution of about 2 nm, full width at half maximum (FWHM). As a result, further study was performed only on Si nanoclusters synthesized by thermal vaporization in a buffer gas. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) revealed that these nanoclusters were crystalline. However, during synthesis, if oxygen was the buffer gas, a network of amorphous Si oxide nanostructures (an-SiO{sub x}) with occasional embedded Si dots was formed. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times from nanoseconds to microseconds depending on synthesis conditions. There were differences in PL spectra for hydrogen and oxygen passivated nc-Si, while many common PL properties between oxygen passivated nc-Si and an SiO{sub x} were observed. The observed experimental results can be best explained by a model involving absorption between quantum confined states in the Si cores and emission for which the decay times are very sensitive to surface and/or interface states.

  20. C-H and C-C activation of n -butane with zirconium hydrides supported on SBA15 containing N-donor ligands: [(≡SiNH-)(≡SiX-)ZrH2], [(≡SiNH-)(≡SiX-)2ZrH], and[(≡SiN=)(≡SiX-)ZrH] (X = -NH-, -O-). A DFT study

    KAUST Repository

    Pasha, Farhan Ahmad

    2014-07-01

    Density functional theory (DFT) was used to elucidate the mechanism of n-butane hydrogenolysis (into propane, ethane, and methane) on well-defined zirconium hydrides supported on SBA15 coordinated to the surface via N-donor surface pincer ligands: [(≡SiNH-)(≡SiO-)ZrH2] (A), [(≡SiNH-)2ZrH2] (B), [(≡SiNH-)(≡SiO-) 2ZrH] (C), [(≡SiNH-)2(≡SiO-)ZrH] (D), [(≡SiN=)(≡Si-O-)ZrH] (E), and [(≡SiN=)(≡SiNH-)ZrH] (F). The roles of these hydrides have been investigated in C-H/C-C bond activation and cleavage. The dihydride A linked via a chelating [N,O] surface ligand was found to be more active than B, linked to the chelating [N,N] surface ligand. Moreover, the dihydride zirconium complexes are also more active than their corresponding monohydrides C-F. The C-C cleavage step occurs preferentially via β-alkyl transfer, which is the rate-limiting step in the alkane hydrogenolysis. The energetics of the comparative pathways over the potential energy surface diagram (PES) reveals the hydrogenolysis of n-butane into propane and ethane. © 2014 American Chemical Society.

  1. High Performance Resistive Switching Characteristics of SiN Films with a Cu/Ta/SiN/Cu/SiN/TiN Multilayer Structure

    Science.gov (United States)

    Kumar, D.; Y Tseng, T.

    2017-12-01

    The bipolar resistive switching properties of SiN based conductive bridge random access memory (CBRAM) device are investigated for non-volatile memory applications in a Cu/Ta/SiN/Cu/SiN/TiN multilayer structure. The device shows good switching characteristics with set voltages between 0.8 V and 1.3 V and reset voltages between -0.3 V and - 0.7 V with a variation of less than 0.1 V. The Cu/Ta/SiN/Cu/SiN/TiN multilayer CBRAM device exhibits excellent memory performance, such as long stable endurance cycles (> 4.5x103) during the test without any degradation, good retention ability (>104 s) at a temperature of 120 °C with more than 102 on/off resistance ratio.

  2. Raman study of light-emitting SiN{sub x} films grown on Si by low-pressure chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Komarov, F. [A.N. Sevchenko Institute of Applied Physics Problems, Kurchatov Str. 7, 220045 Minsk (Belarus); Vlasukova, L. [Belarusian State University, Nezavisimosty Ave. 4, 220030 Minsk (Belarus); Parkhomenko, I., E-mail: irinaparkhomen@gmail.com [Belarusian State University, Nezavisimosty Ave. 4, 220030 Minsk (Belarus); Milchanin, O. [A.N. Sevchenko Institute of Applied Physics Problems, Kurchatov Str. 7, 220045 Minsk (Belarus); Mudryi, A. [Scientific and Practical Materials Research Center, National Academy of Sciences of Belarus, P. Brovki Str. 17, 220072 Minsk (Belarus); Togambaeva, A. [Al-Farabi Kazakh National University, Al-Farabiy Ave. 71, 050038 Almaty (Kazakhstan); Korolik, O. [Belarusian State University, Nezavisimosty Ave. 4, 220030 Minsk (Belarus)

    2015-03-31

    Si-rich silicon nitride (SRSN) films were deposited on Si wafers by low pressure chemical vapor deposition (LPCVD) technique and, subsequently, annealed at (800–1200) °C to form Si precipitates. The composition of SiN{sub x} films was measured by Rutherford backscattering spectrometry (RBS). Two sets of samples differed by the amount of excessive Si (Si{sub exc}) in silicon nitride were studied. Evolution of Si nanoclusters from amorphous to crystalline ones during high temperature treatment was examined by Raman scattering (RS) spectroscopy. The amorphous Si clusters were already revealed in as-deposited SiN{sub x} while the annealing results in their crystallization. The crystalline nanoprecipitates are only registered in nitride films after annealing at 1200 °C. A dependence of Raman scattering intensity from the Si wafer on the temperature of annealing of SiN{sub x}/Si structures was revealed. This information was used to explain the phase transformations in SRSNs during high temperature treatments. The peculiarities of photoluminescence (PL) spectra for two sets of Si-rich SiN{sub x} films are explained taking into account the contribution from the quantum confinement effect of Si nanocrystals and from the native defects in silicon nitride matrix, such as N- and K-centers. - Highlights: • The size of Si nanocrystals in Si-rich SiN{sub x} films depends on Si excess content. • Excess Si remains in SiN{sub 0.46} as randomly distributed Si atoms in atomic network. • In SiN{sub 1} films practically all excess Si is aggregated into Si nanoclusters.

  3. Three-dimensional imaging for precise structural control of Si quantum dot networks for all-Si solar cells

    Science.gov (United States)

    Kourkoutis, Lena F.; Hao, Xiaojing; Huang, Shujuan; Puthen-Veettil, Binesh; Conibeer, Gavin; Green, Martin A.; Perez-Wurfl, Ivan

    2013-07-01

    All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to reduced inter-QD coupling in the layer. Efficient carrier transport via mini-bands is in this case more likely across the multilayers provided the SiO2 spacer layer is thin enough to allow coupling in the vertical direction.All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to

  4. Bi surfactant mediated growth for fabrication of Si/Ge nanostructures and investigation of Si/Ge intermixing by STM

    Energy Technology Data Exchange (ETDEWEB)

    Paul, N.

    2007-10-26

    In the thesis work presented here, we show that Bi is more promising surfactant material than Sb. We demonstrate that by using Bi as a terminating layer on Ge/Si surface, it is possible to distinguish between Si and Ge in Scanning tunnelling microscope (STM). Any attempt to utilize surfactant mediated growth must be preceded by a thorough study of its effect on the the system being investigated. Thus, the third chapter of this thesis deals with an extensive study of the Bi surfactant mediated growth of Ge on Si(111) surface as a function of Ge coverage. The growth is investigated from the single bilayer Ge coverage till the Ge coverage of about 15 BL when the further Ge deposition leads to two-dimensional growth. In the fourth chapter, the unique property of Bi terminating layer on Ge/Si surface to result in an STM height contrast between Si and Ge is explained with possible explanations given for the reason of this apparent height contrast. The controlled fabrication of Ge/Si nanostructures such as nanowires and nanorings is demonstrated. A study on Ge-Si diffusion in the surface layers by a direct method such as STM was impossible previously because of the similar electronic structure of Ge and Si. Since with the Bi terminating surface layer, one is able to distinguish between Ge and Si, the study of intermixing between them is also possible using STM. This method to distinguish between Si and Ge allows one to study intermixing on the nanoscale and to identify the fundamental diffusion processes giving rise to the intermixing. In Chapter 5 we discuss how this could prove useful especially as one could get a local probe over a very narrow Ge-Si interface. A new model is proposed to estimate change in the Ge concentration in the surface layer with time. The values of the activation energies of Ge/Si exchange and Si/Ge exchange are estimated by fitting the experimental data with the model. The Ge/Si intermixing has been studied on a surface having 1 ML Bi ({radical

  5. Phosphorous passivation of the SiO 2/4H-SiC interface

    Science.gov (United States)

    Sharma, Y. K.; Ahyi, A. C.; Issacs-Smith, T.; Shen, X.; Pantelides, S. T.; Zhu, X.; Feldman, L. C.; Rozen, J.; Williams, J. R.

    2012-02-01

    We describe experimental and theoretical studies to determine the effects of phosphorous as a passivating agent for the SiO 2/4H-SiC interface. Annealing in a P 2O 5 ambient converts the SiO 2 layer to PSG (phosphosilicate glass) which is known to be a polar material. Higher mobility (approximately twice the value of 30-40 cm 2/V s obtained using nitrogen introduced with an anneal in nitric oxide) and lower threshold voltage are compatible with a lower interface defect density. Trap density, current-voltage and bias-temperature stress (BTS) measurements for MOS capacitors are also discussed. The BTS measurements point to the possibility of an unstable MOSFET threshold voltage caused by PSG polarization charge at the O-S interface. Theoretical considerations suggest that threefold carbon atoms at the interface can be passivated by phosphorous which leads to a lower interface trap density and a higher effective mobility for electrons in the channel. The roles of phosphorous in the passivation of correlated carbon dangling bonds, for SiC counter-doping, for interface band-tail state suppression, for Na-like impurity band formation and for substrate trap passivation are also discussed briefly.

  6. Compatibility of SiC and SiC Composites with Molten Lead

    Energy Technology Data Exchange (ETDEWEB)

    H Tunison

    2006-03-07

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

  7. Influence of Constituents on Creep Properties of SiC/SiC Composites

    Science.gov (United States)

    Bhatt, R.; DiCarlo, J.

    2016-01-01

    SiC-SiC composites are being considered as potential candidate materials for next generation turbine components such as combustor liners, nozzle vanes and blades because of their low density, high temperature capability, and tailorable mechanical properties. These composites are essentially fabricated by infiltrating matrix into a stacked array of fibers or fiber preform by one or a combination of manufacturing methods such as, Melt Infiltration (MI) of molten silicon metal, Chemical Vapor Infiltration (CVI), Polymer Infiltration and Pyrolysis (PIP). To understand the influence of constituents, the SiC-SiC composites fabricated by MI, CVI, and PIP methods were creep tested in air between 12000 and 14500 degrees Centigrade for up to 500 hours. The failed specimens were analyzed under a scanning electron microscope to assess damage mechanisms. Also, knowing the creep deformation parameters of the fiber and the matrix under the testing conditions, the creep behavior of the composites was modeled and compared with the measured data. The implications of the results on the long term durability of these composites will be discussed.

  8. Fully Si compatible SiN resistive switching memory with large self-rectification ratio

    Directory of Open Access Journals (Sweden)

    Sungjun Kim

    2016-01-01

    Full Text Available In this letter, we report unique unipolar resistive switching memory behaviors in the Ni/Si3N4/p-Si structure by controlling the impurity concentration of Si bottom electrode. It is found that we can decrease the reset current drastically by reducing dopant concentration by reducing dopant concentration, which helps low-power operation in the high density resistive switching memory array. Also, the samples with high impurity concentration exhibited ohmic conduction in the low-resistance state (LRS while those with low dopant concentration below 1018 cm−3 showed a remarkable self-rectifying behavior. The nonlinear metal-insulator-semiconductor (MIS diode characteristics in the samples with low doping concentration (∼1018 cm−3 are explained by the formation of Schottky barrier at the metal and semiconductor interface. As a result, we demonstrate high rectification ratio (>105 between forward and reverse currents along with the robust nonvolatile properties including endurance cycles and retention from the devices with large self-rectification ratio. The high self-rectifying characteristics of Si3N4-based RRAM cell would be one of the most virtuous merits in the high-density crossbar array.

  9. Advanced Environmental Barrier Coating Development for SiC-SiC Ceramic Matrix Composite Components

    Science.gov (United States)

    Zhu, Dongming; Harder, Bryan; Hurst, Janet B.; Halbig, Michael Charles; Puleo, Bernadette J.; Costa, Gustavo; Mccue, Terry R.

    2017-01-01

    This presentation reviews the NASA advanced environmental barrier coating (EBC) system development for SiC-SiC Ceramic Matrix Composite (CMC) combustors particularly under the NASA Environmentally Responsible Aviation, Fundamental Aeronautics and Transformative Aeronautics Concepts Programs. The emphases have been placed on the current design challenges of the 2700-3000F capable environmental barrier coatings for low NOX emission combustors for next generation turbine engines by using advanced plasma spray based processes, and the coating processing and integration with SiC-SiC CMCs and component systems. The developments also have included candidate coating composition system designs, degradation mechanisms, performance evaluation and down-selects; the processing optimizations using TriplexPro Air Plasma Spray Low Pressure Plasma Spray (LPPS), Plasma Spray Physical Vapor Deposition and demonstration of EBC-CMC systems. This presentation also highlights the EBC-CMC system temperature capability and durability improvements under the NASA development programs, as demonstrated in the simulated engine high heat flux, combustion environments, in conjunction with high heat flux, mechanical creep and fatigue loading testing conditions.

  10. Low Gilbert damping in Co2FeSi and Fe2CoSi films

    Science.gov (United States)

    Sterwerf, Christian; Paul, Soumalya; Khodadadi, Behrouz; Meinert, Markus; Schmalhorst, Jan-Michael; Buchmeier, Mathias; Mewes, Claudia K. A.; Mewes, Tim; Reiss, Günter

    2016-08-01

    Thin highly textured Fe1+xCo2-xSi (0 ≤ x ≤ 1) films were prepared on MgO (001) substrates by magnetron co-sputtering. Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance (FMR) measurements were used to investigate the composition dependence of the magnetization, the magnetic anisotropy, the gyromagnetic ratio, and the relaxation of the films. Both MOKE and FMR measurements reveal a pronounced fourfold anisotropy for all films. In addition, we found a strong influence of the stoichiometry on the anisotropy as the cubic anisotropy strongly increases with increasing Fe concentration. The gyromagnetic ratio is only weakly dependent on the composition. We find low Gilbert damping parameters for all films with values down to 0.0012 ±0.00010.0007 for Fe1.75Co1.25Si. The effective damping parameter for Co2FeSi is found to be 0.0018 ±0.00040.0034 . We also find a pronounced anisotropic relaxation, which indicates significant contributions of two-magnon scattering processes that is strongest along the easy axes of the films. This makes thin Fe1+xCo2-xSi films ideal materials for the application in spin transfer-torque magnetic RAM (STT-MRAM) devices.

  11. Betavoltaic device in por-SiC/Si C-Nuclear Energy Converter

    Directory of Open Access Journals (Sweden)

    Akimchenko Alina

    2017-01-01

    Full Text Available The miniature and low-power devices with long service life in hard operating conditions like the Carbon-14 beta-decay energy converters indeed as eternal resource for integrated MEMS and NEMS are considered. Authors discuss how to create the power supply for MEMS/NEMS devices, based on porous SiC/Si structure, which are tested to be used as the beta-decay energy converters of radioactive C-14 into electrical energy. This is based on the silicon carbide obtaining by self-organizing mono 3C-SiC endotaxy on the Si substrate. The new idea is the C-14 atoms including in molecules in the silicon carbide porous structure by this technology, which will increase the efficiency of the converter due to the greater intensity of electron-hole pairs generation rate in the space charge region. The synthesis of C-14 can be also performed by using the electronically controlled magneto-optic chamber.

  12. Thickness and composition of ultrathin SiO2 layers on Si

    NARCIS (Netherlands)

    van der Marel, C; Verheijen, M.A.; Tamminga, Y; Pijnenburg, RHW; Tombros, N; Cubaynes, F

    2004-01-01

    Ultrathin SiO2 layers are of importance for the semiconductor industry. One of the techniques that can be used to determine the chemical composition and thickness of this type of layers is x-ray photoelectron spectroscopy (XPS). As shown by Seah and Spencer [Surf. Interface Anal. 33, 640 (2002)], it

  13. Chitosan/siRNA nanoparticles encapsulated in PLGA nanofibers for siRNA delivery

    DEFF Research Database (Denmark)

    Chen, Menglin; Gao, Shan; Dong, Mingdong

    2012-01-01

    H 7.4, while a triphasic release profile involving both surface erosion and bulk erosion was obtained at pH 5.5. A short alkaline pretreatment provided a homogeneous hydrolysis and consequently a nearly zero-order release profile. The interesting release profile was further investigated for siRNA...

  14. Probabilistic Analysis of a SiC/SiC Ceramic Matrix Composite Turbine Vane

    Science.gov (United States)

    Murthy, Pappu L. N.; Nemeth, Noel N.; Brewer, David N.; Mital, Subodh

    2004-01-01

    To demonstrate the advanced composite materials technology under development within the Ultra-Efficient Engine Technology (UEET) Program, it was planned to fabricate, test, and analyze a turbine vane made entirely of silicon carbide-fiber-reinforced silicon carbide matrix composite (SiC/SiC CMC) material. The objective was to utilize a five-harness satin weave melt-infiltrated (MI) SiC/SiC composite material developed under this program to design and fabricate a stator vane that can endure 1000 hours of engine service conditions. The vane was designed such that the expected maximum stresses were kept within the proportional limit strength of the material. Any violation of this design requirement was considered as the failure. This report presents results of a probabilistic analysis and reliability assessment of the vane. Probability of failure to meet the design requirements was computed. In the analysis, material properties, strength, and pressure loading were considered as random variables. The pressure loads were considered normally distributed with a nominal variation. A temperature profile on the vane was obtained by performing a computational fluid dynamics (CFD) analysis and was assumed to be deterministic. The results suggest that for the current vane design, the chance of not meeting design requirements is about 1.6 percent.

  15. Effect of starting composition on formation of MoSi2–SiC ...

    Indian Academy of Sciences (India)

    traditional use as heating elements, materials based on MoSi2 appear to be promising candidates for a wide variety of ... ing is basically a dry and high energy ball milling process which has been used to synthesize oxide dispersion ... SEM operating at 25 kV. Heat treatment of as milled pow- ders was conducted in a tube ...

  16. Electrical properties of SiO{sub 2}/SiC interfaces on 2°-off axis 4H-SiC epilayers

    Energy Technology Data Exchange (ETDEWEB)

    Vivona, M., E-mail: marilena.vivona@imm.cnr.it [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy); Fiorenza, P. [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy); Sledziewski, T.; Krieger, M. [Friedrich-Alexander-University (FAU) Erlangen-Nuremberg, Department of Physics, Staudtstrasse 7/Bld. A3, D-91058 Erlangen (Germany); Chassagne, T.; Zielinski, M. [NOVASiC, Savoie Technolac, BP267, F-73375 Le Bourget-du-Lac Cedex (France); Roccaforte, F. [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy)

    2016-02-28

    Graphical abstract: - Highlights: • Processing and electrical characterization of MOS capacitors fabricated on 4H-SiC epilayers grown on 2°-off axis heavily doped substrates. • Excellent characteristics of the SiO{sub 2}/4H-SiC interface in terms of flatness, interface state density and oxide reliability. • Electrical behavior of the MOS devices comparable with that obtained for the state-of-the-art of 4°-off axis 4H-SiC material. • Demonstration of the maturity of the 2°-off axis material for application in 4H-SiC MOSFET device technology. - Abstract: In this paper, the electrical properties of the SiO{sub 2}/SiC interface on silicon carbide (4H-SiC) epilayers grown on 2°-off axis substrates were studied. After epilayer growth, chemical mechanical polishing (CMP) allowed to obtain an atomically flat surface with a roughness of 0.14 nm. Metal-oxide-semiconductor (MOS) capacitors, fabricated on this surface, showed an interface state density of ∼1 × 10{sup 12} eV{sup −1} cm{sup −2} below the conduction band, a value which is comparable to the standard 4°-off-axis material commonly used for 4H-SiC MOS-based device fabrication. Moreover, the Fowler–Nordheim and time-zero-dielectric breakdown analyses confirmed an almost ideal behavior of the interface. The results demonstrate the maturity of the 2°-off axis material for 4H-SiC MOSFET device fabrication.

  17. Z historii leksemów: gzić się, grzać się, parzyć się, bzykać się

    Directory of Open Access Journals (Sweden)

    Zuzanna Maria Krótki

    2016-12-01

    Full Text Available From the history of the lexemes gzić się, grzać się, parzyć się, bzykać się The present article undertakes a semasiological analysis of four Polish vulgarisms associated with sexual intercourse: gzić się, grzać się, parzyć się, bzykać się. Taking is the point of departure their etymology, it investigates the changes in the meanings of these units. It was discovered that initially the analysed lexemes communicated a very wide range of content, far from their contemporary semantic structure. Successively, some of their senses were rearranged, causing these units to become attributed to animal copulation and later to human sexual intercourse. However, it was until the mid-20th century that the analysed verbs have come to play the role of vulgarisms.   Z historii leksemów: gzić się, grzać się, parzyć się, bzykać się W artykule poddano analizie semazjologicznej cztery polskie wulgaryzmy wiązane ze stosunkiem seksualnym, tj.: gzić się, grzać się, parzyć się i bzykać się. Wychodząc od etymologii, badano zmiany w znaczeniach tych jednostek. Okazało się, że analizowane leksemy początkowo posiadały bardzo szerokie treści, dalekie ich współczesnej strukturze semantycznej. Sukcesywnie dochodziło jednak do przeszeregowania niektórych sensów, na skutek czego badane jednostki wpierw zaczęto odnosić do zwierzęcej kopulacji, natomiast nieco później do ludzkiego współżycia. Rolę wulgaryzmów analizowane czasowniki zaczęły odgrywać jednak dopiero w połowie XX wieku.

  18. Structural characterization of SiC nanoparticles

    Science.gov (United States)

    Sun, Baoxing; Xie, Ruobing; Yu, Cun; Li, Cheng; Xu, Hongjie

    2017-10-01

    The structure and size of SiC nanoparticles were studied by different characterization methods including small angle X-ray scattering (SAXS), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results showed that particle size distributions determined respectively from SAXS and TEM are comparable and follow the log-normal function. The size distribution of the particles is between 10 to 100 nm with most of them being in the range of 20–50 nm. The average particle size is around 42 nm. XRD identifies the phase of the SiC nanoparticles and suggests the average size of the single crystalline domain to be around 21 nm. The combined results from XRD and SAXS suggest the existence of many polycrystals, which is confirmed by the HRTEM observation of particles with twins and stacking faults. The material synthesis methods leading to various particle sizes are also discussed. Project supported by the National Natural Science Foundation of China (No. 11505273) and the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA02000000).

  19. Polarized Neutron on URu2Si2

    Science.gov (United States)

    Bourdarot, F.; Ressouche, E.; Ballou, R.; Raymond, S.; Aoki, D.; Martin, N.; Regnault, L.-P.; Simonet, V.; Fernandez-Diaz, M. T.; Stunault, A.; Taufour, V.; Flouquet, J.

    Polarized neutron scattering has shed a new light on URu2Si2. This compound studied for almost thirty years presents two tran- sitions: a superconducting state below 1.2K (Tsc) and a well-defined bulk transition at 17.8K (T0). In spite of intensive research, no local probe has defined the order parameter associated with this transition (the famous Hidden Order (HO)). Neutron Larmor diffraction measurements combined with uniaxial stress experiments have shown that the relevant parameter that governs the magnetic properties is the a-lattice parameter. Induced magnetization distribution measured by elastic polarized neutron scattering shows a subtle change when entering the HO state that suggests a freezing of rank 5 multipoles (i.e. dotriacontapole). Polarized inelastic neutron measurements have shown the existence of two well defined excitations on the top of a broad continuum. How- ever only the AF excitation vanishes at T0 and as well as when URu2Si2 switches between HO to AF state under pressure. These excitations seem to correspond also to transitions between singlet levels.

  20. SPHERICAL INDENTATION OF SiC

    Energy Technology Data Exchange (ETDEWEB)

    Wereszczak, Andrew A [ORNL; Johanns, Kurt E [ORNL

    2007-01-01

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

  1. Flex Fuel Optimized SI and HCCI Engine

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Guoming [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Schock, Harold [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Yang, Xiaojian [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Huisjen, Andrew [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Stuecken, Tom [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Moran, Kevin [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Zhen, Ren [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Zhang, Shupeng [Michigan State Univ., East Lansing, MI (United States). Mechanical Engineering; Opra, John [Chrysler Corporation, Auburn Hill, MI (United States); Reese, Ron [Chrysler Corporation, Auburn Hill, MI (United States)

    2013-12-20

    The central objective of the proposed work is to demonstrate an HCCI (homogeneous charge compression ignition) capable SI (spark ignited) engine that is capable of fast and smooth mode transition between SI and HCCI combustion modes. The model-based control technique was used to develop and validate the proposed control strategy for the fast and smooth combustion mode transition based upon the developed control-oriented engine; and an HCCI capable SI engine was designed and constructed using production ready two-step valve-train with electrical variable valve timing actuating system. Finally, smooth combustion mode transition was demonstrated on a metal engine within eight engine cycles. The Chrysler turbocharged 2.0L I4 direct injection engine was selected as the base engine for the project and the engine was modified to fit the two-step valve with electrical variable valve timing actuating system. To develop the model-based control strategy for stable HCCI combustion and smooth combustion mode transition between SI and HCCI combustion, a control-oriented real-time engine model was developed and implemented into the MSU HIL (hardware-in-the-loop) simulation environment. The developed model was used to study the engine actuating system requirement for the smooth and fast combustion mode transition and to develop the proposed mode transition control strategy. Finally, a single cylinder optical engine was designed and fabricated for studying the HCCI combustion characteristics. Optical engine combustion tests were conducted in both SI and HCCI combustion modes and the test results were used to calibrate the developed control-oriented engine model. Intensive GT-Power simulations were conducted to determine the optimal valve lift (high and low) and the cam phasing range. Delphi was selected to be the supplier for the two-step valve-train and Denso to be the electrical variable valve timing system supplier. A test bench was constructed to develop control strategies for

  2. By and for women. Nicaragua's Si Mujer.

    Science.gov (United States)

    1993-01-01

    In Nicaragua, a group of women physicians and health professionals created an alternative health service for women. "Si Mujer" (Yes Woman), which stands for Integrated Services for Women, provides: 1) gynecologic services (comprehensive check-up, early cancer detection, sterility counseling, and AIDS and sexually transmitted disease [STD] prevention); 2) obstetric services (prenatal care, normal and high-risk pregnancy care, and family planning); 3) counseling (for women, couples, and families, and for victims of sexual violence); and 4) sex education and training (in reproductive health, gynecology, and sexuality). The non-profit organization collects fees according to ability to pay (11% pay nothing) and serves approximately 800 clients per month. Special programs provide services to teenagers and to men. While the training program began as a secondary effort, it is now as important as the direct service provision, with training activities reaching more than 1600 people in the first year through courses on such topics as sexuality, gender and power, AIDS and STD prevention, and cancer prevention. Si Mujer is one of more than 52 women's health centers in Nicaragua that have arisen to fill the gap left by the deterioration of public health services and which apply a gender perspective to the manner in which they approach their clients.

  3. Processing of sintered alpha SiC

    Science.gov (United States)

    Storm, R. S.

    1984-01-01

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

  4. Study of radiation damage restoration and antimony ions redistribution in Si(1 0 0) and Si(1 1 1) crystals

    Science.gov (United States)

    Labbani, R.; Halimi, R.; Chafi, Z.

    2002-03-01

    In this work, we study the radiation damage restoration and antimony ions redistribution into and oriented silicon substrates. The samples are implanted with antimony to a dose of 5×10 14 Sb + cm -2 at 60 keV energy, then annealed under oxygen atmosphere at 900°C, 30 min. The thin layer of SiO 2 (which is formed on Si surface by dry oxidation and expected to prevent any loss of Sb + dopant during Si recovery) is removed by a 10% HF solution. The specimens are analyzed by H + Rutherford Backscattering Spectrometry (RBS) operating at 0.3 MeV energy in both random and channelling modes. The values of the projected range, Rp, the standard deviation, Δ Rp, and the dose of antimony ions, which are estimated with a simple program, are in agreement with tabulated ones. It is also shown that the surface damage restoration is better for Si(1 0 0) samples than for Si(1 1 1) ones, in other words, the radiation damage is more significant in Si(1 1 1) substrates. Moreover, for both Si(1 0 0) and Si(1 1 1), it has been noticed that an important quantity of implanted antimony is localized in substitutional silicon sites. This fact is more pronounced in Si(1 0 0). On the other hand, it has been found, for Si(1 0 0) substrates only, that antimony ions are redistributed into the silicon lattice following a Gaussian law.

  5. High-efficient production of SiC/SiO2 core-shell nanowires for effective microwave absorption

    KAUST Repository

    Zhong, Bo

    2017-02-21

    In the current report, we have demonstrated that the high-efficient production of SiC/SiO2 core-shell nanowires can be achieved through the introduction of trace of water vapor during the chemical vapor deposition process. The yield of the SiC/SiO2 core-shell nanowires is dramatically improved due to the introduction of water vapor. The SiC/SiO2 core-shell nanowires exhibit an excellent microwave absorption property in the frequency range of 2.0–18.0GHz with a very low weight percentage of 0.50wt.% in the absorbers. A minimum reflection loss value of −32.72dB (>99.99% attenuation) at 13.84GHz has been observed with the absorber thickness of 3.0mm. Moreover, the SiC/SiO2 core-shell nanowires based absorber can reach an effective absorption bandwidth (<−10dB) of 5.32GHz with the absorber thickness of 3.5mm. Furthermore, a possible absorption mechanism is also proposed in detail for such effective attenuation of microwave which can be attributed to the dielectric loss and magnetic loss of SiC/SiO2 core-shell nanowires.

  6. Albumin pre-coating enhances intracellular siRNA delivery of multifunctional amphiphile/siRNA nanoparticles

    Science.gov (United States)

    Kummitha, China M; Malamas, Anthony S; Lu, Zheng-Rong

    2012-01-01

    Nonspecific association of serum molecules with short-interfering RNA (siRNA) nanoparticles can change their physiochemical characteristics, and results in reduced cellular uptake in the target tissue during the systemic siRNA delivery process. Serum albumin is the most abundant protein in the body and has been used to modify the surface of nanoparticles, to inhibit association of other serum molecules. Here, we hypothesized that surface modification of lipid-based nanoparticular siRNA delivery systems with albumin could prevent their interaction with serum proteins, and improve intracellular uptake. In this study, we investigated the influence of albumin on the stability and intracellular siRNA delivery of the targeted siRNA nanoparticles of a polymerizable and pH-sensitive multifunctional surfactant N-(1-aminoethyl) iminobis[N-(oleoylcysteinylhistinyl-1-aminoethyl)propionamide] (EHCO) in serum. Serum resulted in a significant increase in the size of targeted EHCO/siRNA nanoparticles and inhibited cellular uptake of the nanoparticles. Coating of targeted EHCO/siRNA nanoparticles with bovine serum albumin at 9.4 μM prior to cell transfection improved cellular uptake and gene silencing efficacy of EHCO/siRNA targeted nanoparticles in serum-containing media, as compared with the uncoated nanoparticles. At a proper concentration, albumin has the potential to minimize interactions of serum proteins with siRNA nanoparticles for effective systemic in vivo siRNA delivery. PMID:23055731

  7. First-principles study of the Pd–Si system and Pd(001)/SiC(001) hetero-structure

    Energy Technology Data Exchange (ETDEWEB)

    Turchi, P.E.A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ivashchenko, V.I. [National Academy of Sciences of Ukraine (NASU), Kiev (Ukraine)

    2014-11-01

    First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3m, P6m2, Pm3m), Pd2Si (P6⁻2m, P63/mmc, P3m1, P3⁻1m) and Pd3Si (Pnma, P6322, Pm3m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd2Si and D011-Pd3Si fragments, in agreement with experiment.

  8. Highly selective chemical mechanical polishing of Si3N4 over SiO2 using advanced silica abrasive

    Science.gov (United States)

    Bae, KiHo; Baek, Kye Hyun; Kim, JaeSeok; Kim, Hoyoung; Yoon, Bo Un; Kim, Jae Jeong

    2017-05-01

    Highly selective chemical mechanical polishing (CMP) of Si3N4 over SiO2 is achieved by using a modified silica abrasive. Controlling the removal rate of Si3N4/SiO2, chemical reaction is a dominant factor for ceria abrasive, but physical force such as repulsion/attraction is a primary one for silica abrasive. In order to maximize mechanical action in CMP process using silica slurry, we modified the surface charge of silica abrasive into having more negative charge, which resulting in -50 mV of zeta potential in a low pH (< 3.0) slurry. This strong negative zeta potential of the modified silica abrasive enables enhancing attractive forces to Si3N4 and repulsive forces to SiO2 in a low pH environment. In addition, a cocoon shape silica abrasive shows 3 times higher Si3N4 RR than a spherical shape one. Consequently, selectivity of Si3N4 over SiO2 reaches 95.0, which is significantly improved from 0.0167 in the conventional silica abrasive case. When this modified silicon abrasive and the optimum pH condition are applied, in-chip uniformity at various pattern densities of Si3N4 (0, 12, and 32%) turns out to be well controlled under 100 Å. This result is an acceptable level for our semiconductor device integration.

  9. Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites.

    Science.gov (United States)

    Shevlyagin, A V; Goroshko, D L; Chusovitin, E A; Galkin, K N; Galkin, N G; Gutakovskii, A K

    2015-10-05

    By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p(+)-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3-4 and 15-20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 10(9) cm × Hz(1/2)/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.

  10. Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites

    Science.gov (United States)

    Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Galkin, K. N.; Galkin, N. G.; Gutakovskii, A. K.

    2015-01-01

    By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p+-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3–4 and 15–20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 109 cm × Hz1/2/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2. PMID:26434582

  11. Anomalously high yield of doubly charged Si ions sputtered from cleaned Si surface by keV neutral Ar impact

    Energy Technology Data Exchange (ETDEWEB)

    Shinde, N.; Morita, K. E-mail: k-morita@mail.nucl.nagoya-u.ac.jp; Dhole, S.D.; Ishikawa, D

    2001-08-01

    The energy spectra of positively charged and neutral species ejected from the Si(1 1 1) surfaces by keV Ar impact have been measured by means of a combined technique of the time-of-flight (TOF) analysis with the multi-photon resonance ionization spectroscopy (MPRIS). It is shown that positively charged species of Si{sup +}, Si{sup 2+} and SiO{sup +} are ejected from the as-cleaned 7x7 surface by 11 keV Ar impact. It is also shown that Ar sputter cleaning of the as-cleaned 7x7 surface for 14 min at the flux of 2x10{sup 13}/cm{sup 2}s removes completely the oxygen impurity and the yields of Si{sup 2+} is comparable to that of Si{sup +}. Moreover, the ionization probability of Si atoms sputtered is shown to be expressed as an exponential function of the inverse of their velocity. The production mechanism for the doubly charged Si ion is discussed based on the L-shell ionization of Si atoms due to quasi-molecule formation in the collisions of the surface atoms with energetic recoils and subsequent Auger decay of the L-shell vacancy to doubly ionized Si ions.

  12. Effect of different oxide thickness on the bending Young's modulus of SiO2@SiC nanowires.

    Science.gov (United States)

    Ma, Jinyao; Liu, Yanping; Hao, Peida; Wang, Jin; Zhang, Yuefei

    2016-01-07

    The surface or sheath effect on core-shell nanowires plays an important role in the nanomechanical test. In the past few years, SiC nanowires have been synthesized using various methods with an uneven and uncontrollable amorphous silicon dioxide sheath. The bending Young's modulus of the SiC nanowires has scarcely been measured, and the effect of the oxide sheath has not been taken into account. In this paper, SiO2-coated SiC (SiO2@SiC) nanowires were synthesized using the chemical vapor deposition method, followed by thermal reduction. Scanning electron microscopy and transmission electron microscopy show that the SiO2@SiC nanowires in this paper have diameters ranging from 130 ~ 150 nm, with the average thickness of SiO2 layer approximately 14 nm. After different processing times with 1 mol/L NaOH, approximately 5 nm, 9 nm, 14 nm silicon dioxide layers were obtained. The results of the three-point-bending test show that the modulus of SiO2@SiC nanowires is found to clearly decrease with the increase in oxide thickness and the influence of the oxide sheath should not be ignored when the layer thickness is above 5 nm. Young's modulus of the SiO2@SiC nanowires calculated in this study by the core-shell structure model is in good agreement with the theoretical value.

  13. Ultra-high current density thin-film Si diode

    Science.gov (United States)

    Wang, Qi [Littleton, CO

    2008-04-22

    A combination of a thin-film .mu.c-Si and a-Si:H containing diode structure characterized by an ultra-high current density that exceeds 1000 A/cm.sup.2, comprising: a substrate; a bottom metal layer disposed on the substrate; an n-layer of .mu.c-Si deposited the bottom metal layer; an i-layer of .mu.c-Si deposited on the n-layer; a buffer layer of a-Si:H deposited on the i-layer, a p-layer of .mu.c-Si deposited on the buffer layer; and a top metal layer deposited on the p-layer.

  14. Raman active modes of NiSi crystal

    Energy Technology Data Exchange (ETDEWEB)

    Wan Li, E-mail: liwan_china@yahoo.com.c [Department of Physics, Wenzhou University (China); Tang Bo; Cheng Xinhong; Ren Yiming; Zhang Xuefei; Xu Dapeng; Luo Haijun; Huang Yunmi [Department of Physics, Wenzhou University (China)

    2009-08-01

    Raman scattering intensities of the NiSi Raman-active modes have been calculated with three Raman measurement configurations, which can be used for the symmetry assignment of the NiSi Raman peaks. Raman-active vibrations of the NiSi crystal have also been theoretically studied. Results show that the lattices with A{sub g} and B{sub 2g} modes vibrate only in the plane normal to the NiSi[0 1 0] direction while the lattices with B{sub 1g} and B{sub 3g} modes vibrate only along the NiSi[0 1 0] axis. Based on such study, the relationship between the anisotropic strain distribution in the NiSi thin film and the Raman peak shifts has been briefly discussed.

  15. Microwave joining of SiC ceramics and composites

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, I.; Silberglitt, R.; Tian, Y.L. [FM Technologies, Inc., Fairfax, VA (United States); Katz, J.D. [Los Alamos National Lab., NM (United States)

    1997-04-01

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

  16. Vertical III-V nanowire device integration on Si(100).

    Science.gov (United States)

    Borg, Mattias; Schmid, Heinz; Moselund, Kirsten E; Signorello, Giorgio; Gignac, Lynne; Bruley, John; Breslin, Chris; Das Kanungo, Pratyush; Werner, Peter; Riel, Heike

    2014-01-01

    We report complementary metal-oxide-semiconductor (CMOS)-compatible integration of compound semiconductors on Si substrates. InAs and GaAs nanowires are selectively grown in vertical SiO2 nanotube templates fabricated on Si substrates of varying crystallographic orientations, including nanocrystalline Si. The nanowires investigated are epitaxially grown, single-crystalline, free from threading dislocations, and with an orientation and dimension directly given by the shape of the template. GaAs nanowires exhibit stable photoluminescence at room temperature, with a higher measured intensity when still surrounded by the template. Si-InAs heterojunction nanowire tunnel diodes were fabricated on Si(100) and are electrically characterized. The results indicate a high uniformity and scalability in the fabrication process.

  17. siRNA delivery with lipid-based systems

    DEFF Research Database (Denmark)

    Foged, Camilla

    2012-01-01

    A key hurdle for the further development of RNA interference (RNAi) therapeutics like small interfering RNA (siRNA) is their safe and effective delivery. Lipids are promising and versatile carriers because they are based on Nature's own building blocks and can be provided with properties which...... allow for protection of the siRNA, steric stabilization, targeting, membrane fusion and triggered drug release. At present a variety of lipid-based transfectants for siRNA delivery have been used for in vitro and in vivo purposes. The majority bears a cationic charge to electrostatically complex the siRNA...... into more hydrophobic lipoplexes, which promote passage of the siRNA across cellular membrane barriers, especially when lipids are added that facilitate membrane fusion. Despite these attractive features, siRNA delivery vehicles are facing a number of challenges such as the limited delivery efficiency...

  18. U(Al,Si){sub 3} stabilization by Zr addition

    Energy Technology Data Exchange (ETDEWEB)

    Pizarro, L.M.; Alonso, P.R.; Rubiolo, G.H. [Unidad de Actividad Materiales, Unidad de Energia Nuclear, CAC, CNEA, CP (Argentina)

    2007-07-01

    Four alloys were made within the quaternary system U-Al-Si-Zr in order to assert the minimum Zr content for fixed 0.1 wt. % Si content that could stabilize (U,Zr)(Al,Si){sub 3} against U(Al,Si){sub 4} formation. Heat treatments at 600 Celsius degrees were undertaken and samples analyzed by means of XRD (X-ray Diffraction), EPMA (Electron-Probe Micro-Analysis) and EDS (Energy Dispersive Spectroscopy) techniques. It was found evidence for Zr solubility in UAl{sub 3} and for the presence of UAl{sub 4} phase for a maximum of 6 wt. % Zr content in the alloy. A remarkable conclusion is that Zr was only found in the primary solidified phase (U,Zr)(Al,Si){sub 3}, which does not even partially transform to U(Al,Si){sub 4} under heat treatment. (authors)

  19. Metastability of a-SiO{sub x}:H thin films for c-Si surface passivation

    Energy Technology Data Exchange (ETDEWEB)

    Serenelli, L., E-mail: luca.serenelli@enea.it [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy); DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Martini, L. [DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Imbimbo, L. [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy); DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Asquini, R. [DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Menchini, F.; Izzi, M.; Tucci, M. [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy)

    2017-01-15

    Highlights: • a-SiO{sub x}:H film deposition by RF-PECVD is optimized from SiH{sub 4}, CO{sub 2} and H{sub 2} gas mixture. • Metastability of a-SiO{sub x}:H/c-Si passivation is investigated under thermal annealing and UV exposure. • A correlation between passivation metastability and Si−H bonds is found by FTIR spectra. • A metastability model is proposed. - Abstract: The adoption of a-SiO{sub x}:H films obtained by PECVD in heterojunction solar cells is a key to further increase their efficiency, because of its transparency in the UV with respect to the commonly used a-Si:H. At the same time this layer must guarantee high surface passivation of the c-Si to be suitable in high efficiency solar cell manufacturing. On the other hand the application of amorphous materials like a-Si:H and SiN{sub x} on the cell frontside expose them to the mostly energetic part of the sun spectrum, leading to a metastability of their passivation properties. Moreover as for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In this work we explored the reliability of a-SiO{sub x}:H thin film layers surface passivation on c-Si substrates under UV exposition, in combination with thermal annealing steps. Both p- and n-type doped c-Si substrates were considered. To understand the effect of UV light soaking we monitored the minority carriers lifetime and Si−H and Si−O bonding, by FTIR spectra, after different exposure times to light coming from a deuterium lamp, filtered to UV-A region, and focused on the sample to obtain a power density of 50 μW/cm{sup 2}. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiO{sub x}:H/c-Si/a-SiO{sub x}:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiO{sub x} passivation properties, was furthermore considered. In

  20. Environmentally Resistant Mo-Si-B-Based Coatings

    Science.gov (United States)

    Perepezko, J. H.; Sossaman, T. A.; Taylor, M.

    2017-06-01

    High-temperature applications have demonstrated aluminide-coated nickel-base superalloys to be remarkably effective, but are reaching their service limit. Alternate materials such as refractory (e.g., W, Mo) silicide alloys and SiC composites are being considered to extend high temperature capability, but the silica surfaces on these materials require coatings for enhanced environmental resistance. This can be accomplished with a Mo-Si-B-based coating that is deposited by a spray deposition of Mo followed by a chemical vapor deposition of Si and B by pack cementation to develop an aluminoborosilica surface. Oxidation of the as-deposited (Si + B)-pack coatings proceeds with partial consumption of the initial MoSi2 forming amorphous silica. This Si depletion leads to formation of a B-saturated Mo5Si3 (T1) phase. Reactions between the Mo and the B rich phases develop an underlying Mo5SiB2 (T2) layer. The T1 phase saturated with B has robust oxidation resistance, and the Si depletion is prevented by the underlying diffusion barrier (T2). Further, due to the natural phase transformation characteristics of the Mo-Si-B system, cracks or scratches to the outer silica and T1 layers can be repaired from the Si and B reservoirs of T2 + MoB layer to yield a self-healing characteristic. Mo-Si-B-based coatings demonstrate robust performance up to at least 1700 °C not only to the rigors of elevated temperature oxidation, but also to CMAS attack, hot corrosion attack, water vapor and thermal cycling.

  1. Status and Prospects of SiC Power Devices

    Science.gov (United States)

    Bakowski, Mietek

    Silicon Carbide (SiC) power devices offer significant benefits of improved efficiency, dynamic performance and reliability of electronic and electric systems. The challenges and prospects of SiC power device development are reviewed considering different device types. A close correlation between an exponential increase of current handling capability during the last ten years and improvement in substrate quality is demonstrated. The voltage range of silicon and SiC unipolar and bipolar power devices with respect to the on-state voltage is determined based on device simulations. 4H-SiC unipolar devices are potentially superior to all silicon devices up to 5kV design voltage and to all SiC bipolar devices up to 5-6kV design voltage for temperatures up to 150°C. The low end of SiC unipolar devices is determined to be around 200V design voltage provided substrate resistance is reduced by reducing the thickness of the substrate down to 100μm. The influence of reduced channel mobility on the specific on-resistance of 4H-SiC and 3C-SiC DMOSFETs is shown. It has been demonstrated that 3C-SiC DMOSFETs could be a better choice compared to 4H-SiC DMOSFETs in the voltage range below 1.2kV utilising better channel mobility and larger substrate size obtainable in the near future in 3C-SiC polytype. An impact of the super junction (SJ) concept on silicon and SiC MOSFET specific on-resistance limits is demonstrated.

  2. Analysis and recommendations for DPA calculations in SiC

    Energy Technology Data Exchange (ETDEWEB)

    Heinisch, H.L. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-09-01

    Recent modeling results, coupled with the implications of available experimental results, provide sufficient information to achieve consensus on the values of threshold displacement energies to use in displacements per atom (DPA) calculations. The values recommended here, 20 eV for C and 35 eV for Si, will be presented for adoption by the international fusion materials community at the next IEA SiC/SiC workshop.

  3. Atomic Scale Understanding of Poly-Si/SiO2/c-Si Passivated Contacts: Passivation Degradation Due to Metallization

    Energy Technology Data Exchange (ETDEWEB)

    Aguiar, Jeffery A.; Young, David; Lee, Benjamin; Nemeth, William; Harvey, Steve; Aoki, Toshihiro; Al-Jassim, Mowafak; Stradins, Paul

    2016-11-21

    The key attributes for achieving high efficiency crystalline silicon solar cells include class leading developments in the ability to approach the theoretical limits of silicon solar technology (29.4% efficiency). The push for high efficiency devices is further compounded with the clear need for passivation to reduce recombination at the metal contacts. At the same time there is stringent requirement to retain the same material device quality, surface passivation, and performance characteristics following subsequent processing. The development of passivated silicon cell structures that retain active front and rear surface passivation and overall material cell quality is therefore a relevant and active area of development. To address the potential outcomes of metallization on passivated silicon stack, we report on some common microstructural features of degradation due to metallization for a series of silicon device stacks. A fundamental materials understanding of the metallization process on retaining high-efficiency passivated Si devices is therefore gained over these series of results.

  4. Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers; Las tensiones residuales y las propiedades mecánicas de compuestos multicapa de Si3N4/SiC con diferentes capas de SiC

    Energy Technology Data Exchange (ETDEWEB)

    Liua, S.; Lia, Y.; Chena, P.; Lia, W.; Gaoa, S.; Zhang, B.; Yeb, F.

    2017-11-01

    The effect of residual stresses on the strength, toughness and work of fracture of Si3N4/SiC multilayered composites with different SiC layers has been investigated. It may be an effective way to design and optimize the mechanical properties of Si3N4/SiC multilayered composites by controlling the properties of SiC layers. Si3N4/SiC multilayered composites with different SiC layers were fabricated by aqueous tape casting and pressureless sintering. Residual stresses were calculated by using ANSYS simulation, the maximum values of tensile and compressive stresses were 553.2MPa and −552.1MPa, respectively. Step-like fracture was observed from the fracture surfaces. Fraction of delamination layers increased with the residual stress, which can improve the reliability of the materials. Tensile residual stress was benefit to improving toughness and work of fracture, but the strength of the composites decreased. [Spanish] Se ha investigado el efecto de las tensiones residuales en la resistencia, dureza y trabajo de fractura de los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC. Puede ser una manera eficaz de diseñar y optimizar las propiedades mecánicas de los compuestos multicapa de Si3N4/SiC mediante el control de las propiedades de las capas de SiC. Los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC se fabricaron por medio de colado en cinta en medio acuoso y sinterización sin presión. Las tensiones residuales se calcularon mediante el uso de la simulación ANSYS, los valores máximos de las fuerzas de tracción y compresión fueron 553,2 MPa y −552,1 MPa, respectivamente. Se observó una fractura escalonada a partir de las superficies de fractura. La fracción de capas de deslaminación aumenta con la tensión residual, lo que puede mejorar la fiabilidad de los materiales. La fuerza de tracción residual era beneficiosa para la mejora de la dureza y el trabajo de fractura, pero la resistencia de los compuestos disminuyó.

  5. Development of High Performance Sintered Si3N4

    Science.gov (United States)

    1980-09-01

    times up to 160 h. A thin oxide scale of alpha cristobalite was coherently-bonded to the GPS Si^NL material in all cases. There was no...polished and caustic-etched microstructure of GPS Si.,lSL showing the beta SioNL grains. SEM photomicrograph at a mag. = 3,500X ^2 17. Grain...that is crystalline about 92% is alpha and 8% is beta SiJ^. A trace of free Si can be detected in both the Sylvania and Starck SioNL powders by X-ray

  6. Ultrafast electron dynamics in GeSi nanostructures

    Science.gov (United States)

    Cavill, S. A.; Potenza, A.; Dhesi, S. S.

    2012-01-01

    The relaxation dynamics of photoexcited hot carriers in GexSi1-x islands grown on Si(111)-(7×7) have been studied with the spatial and temporal resolution of time-resolved two-photon photoemission electron microscopy. The relaxation dynamics of the excited electronic states within the Ge-rich GexSi1-x dots and the surrounding Si-rich wetting layer are found to vary significantly below the conduction-band minimum. These differences are ascribed to faster hot-carrier-diffusion rates for the islands compared to those for the wetting layer.

  7. Surface engineering of SiC via sublimation etching

    Energy Technology Data Exchange (ETDEWEB)

    Jokubavicius, Valdas, E-mail: valjo@ifm.liu.se [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden); Yazdi, Gholam R.; Ivanov, Ivan G. [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden); Niu, Yuran; Zakharov, Alexei [Max Lab, Lund University, S-22100 Lund (Sweden); Iakimov, Tihomir; Syväjärvi, Mikael; Yakimova, Rositsa [Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping (Sweden)

    2016-12-30

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

  8. Amorphization of SiC under ion and neutron irradiation

    Science.gov (United States)

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

    1998-05-01

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

  9. Interdiffusion processes at irradiated Cr/Si interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Luneville, L., E-mail: laurence.luneville@cea.fr [DEN/DANS/DM2S/SERMA/LLPR/LRC-CARMEN, CEA Saclay, 91191 Gif-sur-Yvette (France); Largeau, L. [LPN-UPR20/CNRS, Route de Nozay, 91460 Marcoussis (France); Deranlot, C. [Unite Mixte de Physique CNRS/Thales, 1 Avenue Augustin Fresnel, 91767 Palaiseau (France); Ribis, J. [DEN/DANS/DMN/SRMA/LA2M/LRC-CARMEN, CEA Saclay, 91191 Gif-sur-Yvette (France); Ott, F. [DSM/IRAMIS/LLB/CEA/CNRS, CEA Saclay, 91191 Gif-sur-Yvette (France); Moncoffre, N. [IPNL/CNRS, Domaine scientifique de la Doua, 69622 Villeurbanne (France); Baldinozzi, G. [CNRS-SPMS/UMR 8580/LRC CARMEN Ecole Centrale Paris, 92295 Chatenay-Malabry (France); Simeone, D. [DEN/DANS/DMN/SRMA/LA2M/LRC-CARMEN, CEA Saclay, 91191 Gif-sur-Yvette (France)

    2015-03-25

    Highlights: • Interdiffusion at Cr/Si interfaces induced by ion beam mixing at room temperature. • Creation of Cr/Si alloy metastable phases. • Reconstruction of Cr/Si interdiffusion profile by X-ray reflectometry. • Quantitative correlation between Cr and Si profiles extracted from XRR and measured by EDX–TEM. - Abstract: Chromium silicon CrSi alloys are foreseen as possible materials for spintronic devices. Ion beam mixing could be an efficient technique to produce thin films of such alloys at room temperature while avoiding thermal diffusion. In order to assess this point, we have irradiated 20 nm Cr layer on a (1 0 0) Si wafer with 70 keV Kr ions. The X-ray reflectometry technique combined with Transmission Electron Microscopy and Energy Dispersive X-ray analysis was applied to analyze, at the nanometric scale, the formation of Cr/Si blurred interfaces induced by ion beam mixing. From the analysis of reflectivity curves, it appears that nanometric Cr{sub 5}Si{sub 3} and CrSi{sub 2} phases are produced at the early stage of the process. The existence of these two paramagnetic phases gives some clues to explain the reason why the experimentally observed ferrimagnetism was weaker than predicted.

  10. SiC Power MOSFET with Improved Gate Dielectric

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-08-23

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

  11. Therapy of respiratory viral infections with intranasal siRNAs.

    Science.gov (United States)

    Barik, Sailen; Lu, Patrick

    2015-01-01

    Chemically synthesized short interfering RNA (siRNA) has ushered a new era in the application of RNA interference (RNAi) against viral genes. We have paid particular attention to respiratory viruses that wreak heavy morbidity and mortality worldwide. The clinically significant ones include respiratory syncytial virus (RSV), parainfluenza virus (PIV) (two Paramyxoviruses), and influenza virus (an Orthomyxovirus). As the infection by these viruses is clinically restricted to the respiratory tissues, mainly the lungs, the logical route for the application of the siRNA was also the same, i.e., via the nasal route. Following the initial success of single intranasal siRNA against RSV, we now offer two new strategies: (1) second-generation siRNAs, used against the paramyxoviral RNA polymerase large subunit (L), (2) siRNA cocktail with a novel transfection reagent, used against influenza virus. Based on these results, we propose the following consensus for designing intranasal antiviral siRNAs: (a) modified 19-27 nt-long double-stranded siRNAs are functional in the lung, (b) excessive 2'-OMe and 2'-F modifications in either or both strands of these siRNAs reduce efficacy, (c) limited modifications in the sense strand are beneficial, although their precise efficacy may be position-dependent, (d) cocktail of multiple siRNAs can be highly effective against multiple viral strains and subtypes.

  12. Metal organic vapor phase epitaxy growth of (Al)GaN heterostructures on SiC/Si(111) templates synthesized by topochemical method of atoms substitution

    DEFF Research Database (Denmark)

    Rozhavskaya, Mariia M.; Kukushkin, Sergey A.; Osipov, Andrey V.

    2017-01-01

    crystalline interfaces with epitaxial relationship between SiC/Si and AlN/SiC layers. Optimization of SiC morphology and AlN seed layer thickness facilitates the growth of GaN layers free of pits (v-defects). It is also found that Si doping eliminates these defects in the case of growth on SiC templates...... with non-optimized surface morphology. Thus, synthesis of thin SiC buffer layer is suggested as a solution for the interface problems at the initial stage of III-N on Si epitaxy....

  13. Effects of Surface Treatment Processes of SiC Ceramic on Interfacial Bonding Property of SiC-AFRP

    Directory of Open Access Journals (Sweden)

    WEI Ru-bin

    2016-12-01

    Full Text Available To improve the interfacial bonding properties of SiC-aramid fiber reinforced polymer matrix composites (SiC-AFRP, the influences of etching process of SiC ceramic, coupling treatment process, and the adhesives types on the interfacial peel strength of SiC-AFRP were studied. The results show that the surface etching process and coupling treatment process of silicon carbide ceramic can effectively enhance interfacial bonding property of the SiC-AFRP. After soaked the ceramic in K3Fe(CN6 and KOH mixed etching solution for 2 hours, and coupled with vinyl triethoxy silane coupling agent, the interfacial peel strength of the SiC-AFRP significantly increases from 0.45kN/m to 2.20kN/m. EVA hot melt film with mass fraction of 15%VA is ideal for interface adhesive.

  14. Improvement of Strength and Oxidation Resistance for SiC/graphite Composites by SiC coating

    Science.gov (United States)

    Yang, Wanli; Shi, Zhongqi; Li, Hongwei; Li, Zhen; Jin, Zhihao; Qiao, Guanjun

    2011-03-01

    SiC/graphite composites with exelent machinable properties and thermal shock behaviour were successfully fabricated by pressureless sintering at 1700°C in nitrogen atmosphere. A dipping infiltration process was applied to improve the strength and oxidation resistance of the composites. Dense SiC coating was covered on the composites' surface by heat-treating at 1400°C in nitrogen atmosphere with dipping infiltration of silica sol and phenolic resin solutions. The flexural strength of the SiC coated composites were improved from 60 MPa to 140 MPa obviously, and the weight loss of the SiC coated composites was reduced more than 20 % comparing with the uncoated composites by oxidation resistance testing at 1000 °C for 24 h in air. SEM micrographs shows that SiC coating was surrounded the surface of pores and XRD pattern revealed that the new layer was SiC.

  15. Characterization of Si particles and their effects on and recrystallization in a nanostructured cold rolled Al-1%Si alloy

    DEFF Research Database (Denmark)

    Huang, T.L.; Wu, G.L.; Huang, Xiaoxu

    2015-01-01

    An Al-1.08 vol.% Si alloy was cold rolled to a reduction of 98% (εvM = 4.5) and then annealed at different temperatures up to 210°C (0.52 Tm) for different times. The deformed structure is characterized by a nanoscale lamellar structure with the presence of Si particles of coarse (> 1 μm), medium...... (100 nm - 1 μm) and fine (formed around the coarse Si particles and the boundary spacing is finer in the deformation zone than in the matrix. The medium Si particles have little effect on the morphology and boundary spacing. The fine Si...... particles are aligned along the lamellar boundaries indicating a stabilizing effect on the structural refinement during cold rolling. After annealing, enhanced recovery occurs in the deformation zones around the coarse Si particles. However the reduction in stored energy during recovery and the pinning...

  16. Gettering of Co in Si by high-energy B ion-implantation and by p/p+ epitaxial Si

    Science.gov (United States)

    Benton, J. L.; Boone, T.; Jacobson, D. C.; Rafferty, C. S.

    2000-12-01

    Detection and gettering of Co contamination in processed Si is an important issue in integrated circuit fabrication. In this work, Co was intentionally introduced into Si by ion implantation, and its diffusion monitored by secondary ion mass spectroscopy. The surface layer recombination lifetime in p/p+ epitaxial Si is unaffected by the Co at doses of 1×1011cm-2 or 1×1012cm-2. In the case of 2.5 MeV, 4×1014B/cm2 ion implanted bulk Si, two mechanisms for Co redistribution during high temperature furnace, 900 °C, 30 min, processing are evident. First, regions of high boron concentration provide gettering sites for Co contamination. Second, the final distribution of Co in Si reflects ion-implantation induced defect evolution during annealing. Both mechanisms will operate during device processing and will control the effect of the metal on the electrical properties of the Si.

  17. Room-temperature ferromagnetism in CrSi2(core)/SiO2(shell) semiconducting nanocables

    Science.gov (United States)

    Hou, Te-Chien; Han, You-Hong; Lo, Shen-Chuan; Lee, Cheng-Tse; Ouyang, Hao; Chen, Lih-Juann

    2011-05-01

    Room-temperature ferromagnetism has been observed in high density free-standing CrSi2(core)/SiO2(shell) semiconducting nanocables, which is contrast to diamagnetic properties of both CrSi2 and SiO2 in bulk. The hexagonal CrSi2 C40-type nanowires, sheathed with a thin amorphous SiO2 layer, grow along [0001] direction. The results of first-principles simulations indicate that Cr atoms around the interface are with anomalously high magnetization (about 2 μB/atom), due to distorted/dangling bonds and surrounded oxygen atoms. Evaluations can be very consistent with measurements by further considering the effects of interfacial roughness and more distribution of oxygen around the interface. These results point toward a different way to tune nanomagnetism in core/shell nanowires.

  18. Sponge-like Si-SiO{sub 2} nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

    Energy Technology Data Exchange (ETDEWEB)

    Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R. [Helmholtz-Zentrum Dresden – Rossendorf, Bautzner Landstr. 400, 01328 Dresden (Germany); Wolf, D. [Triebenberg Laboratory, Institute of Structure Physics, Technische Universität Dresden, 01062 Dresden (Germany); Kölling, S. [Fraunhofer Center Nanoelectronic Technologies, Königsbrücker Str. 180, 01099 Dresden (Germany); Mikolajick, T. [NaMLab GmbH, Nöthnitzer Str. 64, 01187 Dresden (Germany); Technische Universität Dresden, Nöthnitzer Str. 64, 01187 Dresden (Germany)

    2013-09-23

    Sponge-like Si nanostructures embedded in SiO{sub 2} were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO{sub 2} nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

  19. M3FT-16OR020202112 - Report on viability of hydrothermal corrosion resistant SiC/SiC Joint development

    Energy Technology Data Exchange (ETDEWEB)

    Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Kiggans Jr, James O. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Terrani, Kurt A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-06-30

    Hydrothermal corrosion of four types of the silicon carbide (SiC) to SiC plate joints were investigated under PWR and BWR relevant chemical conditions without irradiation. The joints were formed by metal diffusion bonding using molybdenum or titanium interlayer, reaction sintering using Ti-Si-C system, and SiC nanopowder sintering. Most of the formed joints withstood the corrosion tests for five weeks. The recession of the SiC substrates was limited. Based on the recession rate of the bonding layers, it was concluded that all the joints except for the molybdenum diffusion bond are promising under the reducing activity environments. The SiC nanopowder sintered joint was the most corrosion tolerant under the oxidizing activity environment among the four joints.

  20. The high-temperature modification of ScRuSi - Structure, 29Si and 45Sc solid state NMR spectroscopy

    Science.gov (United States)

    Hoffmann, Rolf-Dieter; Rodewald, Ute Ch.; Haverkamp, Sandra; Benndorf, Christopher; Eckert, Hellmut; Heying, Birgit; Pöttgen, Rainer

    2017-10-01

    A polycrystalline sample of the TiNiSi type low-temperature (LT) modification of ScRuSi was synthesized by arc-melting. Longer annealing in a sealed silica tube (6 weeks at 1270 K) followed by quenching led to the high-temperature (HT) phase. HT-ScRuSi adopts the ZrNiAl structure type: P 6 bar 2 m , a = 688.27(9), c = 336.72(5) pm, wR2 = 0.0861, 260 F2 values, 14 variables. The striking structural building units are regular, tricapped trigonal prisms Si1@Ru3Sc6 and Si2@Ru6Sc3. Both polymorphs have been characterized by 29Si and 45Sc MAS-NMR spectroscopy. The local scandium environments in the two polymorphs are easily distinguished by their electric field gradient tensor values, in agreement with theoretically calculated values.

  1. Filter optimization of Si and SiC semiconductor-based H5 and Conergy-NPC transformerless PV inverters

    DEFF Research Database (Denmark)

    Saridakis, Stefanos; Koutroulis, Eftichios; Blaabjerg, Frede

    2013-01-01

    semiconductors type (Si- or SiC-based), switching frequency and output filter (LCL- or LLCL-type) employed in H5 and Conergy-NPC PV inverters, considering the simultaneous impact of the factors affecting the PV energy processing performance and PV inverter cost. According to the design results, the optimized Si......C-based PV inverters will inject more energy into the electric grid, compared to the Si-based structures and enable the reduction of the output filter size, weight and cost. Employing an LLCL-type output filter and simultaneously reducing the cost of SiC power semiconductors to the level of their Si......Single-phase transformerless Photovoltaic (PV) inverters are synthesized by combining available solutions in terms of the power section topology, power semiconductors manufacturing technology and structure of the output filter. A design method is presented in this paper for optimizing the power...

  2. Phase Stability and Thermal Conductivity of Composite Environmental Barrier Coatings on SiC/SiC Ceramic Matrix Composites

    Science.gov (United States)

    Benkel, Samantha; Zhu, Dongming

    2011-01-01

    Advanced environmental barrier coatings are being developed to protect SiC/SiC ceramic matrix composites in harsh combustion environments. The current coating development emphasis has been placed on the significantly improved cyclic durability and combustion environment stability in high-heat-flux and high velocity gas turbine engine environments. Environmental barrier coating systems based on hafnia (HfO2) and ytterbium silicate, HfO2-Si nano-composite bond coat systems have been processed and their stability and thermal conductivity behavior have been evaluated in simulated turbine environments. The incorporation of Silicon Carbide Nanotubes (SiCNT) into high stability (HfO2) and/or HfO2-silicon composite bond coats, along with ZrO2, HfO2 and rare earth silicate composite top coat systems, showed promise as excellent environmental barriers to protect the SiC/SiC ceramic matrix composites.

  3. Effect of the chromium layer thickness on the morphology and optical properties of heterostructures Si(111)/(CrSi2 nanocrystallites)/Si(111)

    Science.gov (United States)

    Galkin, N. G.; Turchin, T. V.; Goroshko, D. L.

    2008-02-01

    Growth and the optical properties of epitaxial heterostructures Si(111)/(CrSi2 nanocrystallites)/Si(111) based on nanosized islands of chromium disilicide (CrSi2) on Si(111) were studied using low-energy electron diffraction, atomic-force microscopy, and optical reflection and transmission spectroscopy. The heterostructures with thicknesses of 0.1, 0.3, 0.6, 1.0, and 1.5 nm were formed by reactive epitaxy at a temperature of 500°C followed by the epitaxial growth of silicon at 750°C. The specific features of changes in the density and sizes of CrSi2 islands on the silicon surface were determined at T = 750°C as the chromium layer thickness was increased. It was established that, in the heterostructures with chromium layer thicknesses exceeding 0.6 nm, a small part of faceted Cr2Si2 nanocrystallites (NCs) emerge into near-surface region of the silicon, which is confirmed by the data from optical reflectance spectroscopy and an analysis of the spectral dependence of the absorption coefficient. A critical size of NCs is shown to exist above which their shift to the silicon surface is hampered. The decreased density of emerging NCs at chromium layer thicknesses of 1.0-1.5 nm is associated with the formation of coarser NCs within a silicon layer, which is confirmed by the data from differential reflection spectroscopy.

  4. Performance Improvement of Microcrystalline p-SiC/i-Si/n-Si Thin Film Solar Cells by Using Laser-Assisted Plasma Enhanced Chemical Vapor Deposition

    Directory of Open Access Journals (Sweden)

    Hsin-Ying Lee

    2014-01-01

    Full Text Available The microcrystalline p-SiC/i-Si/n-Si thin film solar cells treated with hydrogen plasma were fabricated at low temperature using a CO2 laser-assisted plasma enhanced chemical vapor deposition (LAPECVD system. According to the micro-Raman results, the i-Si films shifted from 482 cm−1 to 512 cm−1 as the assisting laser power increased from 0 W to 80 W, which indicated a gradual transformation from amorphous to crystalline Si. From X-ray diffraction (XRD results, the microcrystalline i-Si films with (111, (220, and (311 diffraction were obtained. Compared with the Si-based thin film solar cells deposited without laser assistance, the short-circuit current density and the power conversion efficiency of the solar cells with assisting laser power of 80 W were improved from 14.38 mA/cm2 to 18.16 mA/cm2 and from 6.89% to 8.58%, respectively.

  5. Bias-polarity-dependent resistance switching in W/SiO2/Pt and W/SiO2/Si/Pt structures.

    Science.gov (United States)

    Jiang, Hao; Li, Xiang Yuan; Chen, Ran; Shao, Xing Long; Yoon, Jung Ho; Hu, Xiwen; Hwang, Cheol Seong; Zhao, Jinshi

    2016-02-26

    SiO2 is the most significantly used insulator layer in semiconductor devices. Its functionality was recently extended to resistance switching random access memory, where the defective SiO2 played an active role as the resistance switching (RS) layer. In this report, the bias-polarity-dependent RS behaviours in the top electrode W-sputtered SiO2-bottom electrode Pt (W/SiO2/Pt) structure were examined based on the current-voltage (I-V) sweep. When the memory cell was electroformed with a negative bias applied to the W electrode, the memory cell showed a typical electronic switching mechanism with a resistance ratio of ~100 and high reliability. For electroforming with opposite bias polarity, typical ionic-defect-mediated (conducting filament) RS was observed with lower reliability. Such distinctive RS mechanisms depending on the electroforming-bias polarity could be further confirmed using the light illumination study. Devices with similar electrode structures with a thin intervening Si layer between the SiO2 and Pt electrode, to improve the RS film morphology (root-mean-squared roughness of ~1.7 nm), were also fabricated. Their RS performances were almost identical to that of the single-layer SiO2 sample with very high roughness (root-mean-squared roughness of ~10 nm), suggesting that the reported RS behaviours were inherent to the material property.

  6. Effect of Si doping on the growth and microstructure of GaN grown on Si(1 1 1) using SiC as a buffer layer

    Science.gov (United States)

    Wang, D.; Yoshida, S.; Ichikawa, M.

    2002-07-01

    We studied the initial growth of Si-doped GaN (GaN:Si) epilayers grown under both N- and Ga-rich conditions. Upon Si doping, the surface polarity changed from N- to Ga-polarity. The surface diffusion kinetics of the Ga adatoms of the GaN:Si epilayers depended strongly on the Ga/N flux ratio. GaN:Si films with good crystal quality were obtained for a Ga/N flux ratio slightly larger than 1. The dislocation density decreased about one order of magnitude, while the stacking fault and cubic phase density near the interfacial region increased. The main types of dislocations in the undoped GaN were mixed and edge dislocations. In the GaN:Si, the main dislocations were pure-edge dislocations. The dislocation-density reduction in the GaN:Si may have been due to a low density of mixed dislocations in the presence of a high density of stacking faults and cubic phase.

  7. In situ synthesis and properties of self-reinforced Si3N4–SiO2 ...

    Indian Academy of Sciences (India)

    These composites with different compositions were prepared in a nitrogenatmosphere for comparison of phase transformation and mechanical properties. The results showed that SiO 2 –Al 2 O 3 –Y 2 O 3 (La 2 O 3 ) glass can effectively promote α - to β -Si 3 N 4 phase transformation. The crystallized Y 2 Si 2 O 7 –La 4.67 ...

  8. Back contact formation for p-type based a-Si:H/c-Si heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Tucci, Mario; Serenelli, Luca; De Iuliis, Simona; Izzi, Massimo [ENEA Research Center Casaccia, Via Anguillarese 301, 00123 Rome (Italy); De Cesare, Giampiero; Caputo, Domenico [Department of Electronic Engineering, University ' ' Sapienza' ' , Via Eudossiana 18, 00184 Rome (Italy)

    2011-03-15

    Even if p-type silicon is a more common PV material, heterojunction solar cells on p-type c-Si are less popular than on n-type. In turn, it has been difficult to achieve high efficiency with double-sided heterojunction with intrinsic thin layer structure on p-type c-Si. The double-sided silicon heterojunction solar cell is more appropriate for n-type crystalline silicon wafers than for p-type c-Si ones because of larger band offset at the valence band edge between the amorphous and crystalline semiconductors with respect to the conduction band edge. Indeed, it represents a large barrier for majority carrier holes flowing through to the back contact. In turn at the backside, the small conduction band offset provides a much less effective mirror for the minority carrier electrons. We have found an alternative way to obtain a quasi-ohmic contact promoting the formation of a CrSi film on top of p-a-Si:H layer. This reduces the problem of low p-a-Si:H doping value and the high activation energy, leading to a better carrier collection. In this work we present a detailed investigation of the p-c-Si/i-a-Si:H/p-a-Si:H contact, comparing the experimental transport measurements with numerical model of the stacked structure. We verify the effectiveness of p-c-Si/i-a-Si:H/p-a-Si:H as back side contact on the heterojunction solar cell performances. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Release of Si from Silicon, a Ferrosilicon (FeSi) Alloy and a Synthetic Silicate Mineral in Simulated Biological Media

    Science.gov (United States)

    Herting, Gunilla; Jiang, Tao; Sjöstedt, Carin; Odnevall Wallinder, Inger

    2014-01-01

    Unique quantitative bioaccessibility data has been generated, and the influence of surface/material and test media characteristics on the elemental release process were assessed for silicon containing materials in specific synthetic body fluids at certain time periods at a fixed loading. The metal release test protocol, elaborated by the KTH team, has previously been used for classification, ranking, and screening of different alloys and metals. Time resolved elemental release of Si, Fe and Al from particles, sized less than 50 µm, of two grades of metallurgical silicon (high purity silicon, SiHG, low purity silicon, SiLG), an alloy (ferrosilicon, FeSi) and a mineral (aluminium silicate, AlSi) has been investigated in synthetic body fluids of varying pH, composition and complexation capacity, simple models of for example dermal contact and digestion scenarios. Individual methods for analysis of released Si (as silicic acid, Si(OH)4) in synthetic body fluids using GF-AAS were developed for each fluid including optimisation of solution pH and graphite furnace parameters. The release of Si from the two metallurgical silicon grades was strongly dependent on both pH and media composition with the highest release in pH neutral media. No similar effect was observed for the FeSi alloy or the aluminium silicate mineral. Surface adsorption of phosphate and lactic acid were believed to hinder the release of Si whereas the presence of citric acid enhanced the release as a result of surface complexation. An increased presence of Al and Fe in the material (low purity metalloid, alloy or mineral) resulted in a reduced release of Si in pH neutral media. The release of Si was enhanced for all materials with Al at their outermost surface in acetic media. PMID:25225879

  10. Rapid thermal annealing of YBaCuO films on Si and SiO/sub 2/ substrates

    Energy Technology Data Exchange (ETDEWEB)

    Aslam, M.; Soltis, R.E.; Logothetis, E.M.; Ager, R.; Mikkor, M.; Win, W.; Chen, J.T.; Wenger, L.E.

    1988-07-11

    A very rapid thermal annealing technique has been employed on sputter-deposited YBaCuO films. After an O/sub 2/ anneal (with or without a N/sub 2/ preanneal) at temperatures as high as 920 /sup 0/C for 8--12 s, films on (100)Si and on SiO/sub 2/ /Si substrates exhibited superconductivity onsets above 95 K and zero resistance in the range 40--66 K.

  11. Release of Si from silicon, a ferrosilicon (FeSi alloy and a synthetic silicate mineral in simulated biological media.

    Directory of Open Access Journals (Sweden)

    Gunilla Herting

    Full Text Available Unique quantitative bioaccessibility data has been generated, and the influence of surface/material and test media characteristics on the elemental release process were assessed for silicon containing materials in specific synthetic body fluids at certain time periods at a fixed loading. The metal release test protocol, elaborated by the KTH team, has previously been used for classification, ranking, and screening of different alloys and metals. Time resolved elemental release of Si, Fe and Al from particles, sized less than 50 µm, of two grades of metallurgical silicon (high purity silicon, SiHG, low purity silicon, SiLG, an alloy (ferrosilicon, FeSi and a mineral (aluminium silicate, AlSi has been investigated in synthetic body fluids of varying pH, composition and complexation capacity, simple models of for example dermal contact and digestion scenarios. Individual methods for analysis of released Si (as silicic acid, Si(OH4 in synthetic body fluids using GF-AAS were developed for each fluid including optimisation of solution pH and graphite furnace parameters. The release of Si from the two metallurgical silicon grades was strongly dependent on both pH and media composition with the highest release in pH neutral media. No similar effect was observed for the FeSi alloy or the aluminium silicate mineral. Surface adsorption of phosphate and lactic acid were believed to hinder the release of Si whereas the presence of citric acid enhanced the release as a result of surface complexation. An increased presence of Al and Fe in the material (low purity metalloid, alloy or mineral resulted in a reduced release of Si in pH neutral media. The release of Si was enhanced for all materials with Al at their outermost surface in acetic media.

  12. Long-Term Reliability of High Speed SiGe/Si Heterojunction Bipolar Transistors

    Science.gov (United States)

    Ponchak, George E. (Technical Monitor); Bhattacharya, Pallab

    2003-01-01

    Accelerated lifetime tests were performed on double-mesa structure Si/Si0.7Ge0.3/Si npn heterojunction bipolar transistors, grown by molecular beam epitaxy, in the temperature range of 175C-275C. Both single- and multiple finger transistors were tested. The single-finger transistors (with 5x20 micron sq m emitter area) have DC current gains approximately 40-50 and f(sub T) and f(sub MAX) of up to 22 GHz and 25 GHz, respectively. The multiple finger transistors (1.4 micron finger width, 9 emitter fingers with total emitter area of 403 micron sq m) have similar DC current gain but f(sub T) of 50 GHz. It is found that a gradual degradation in these devices is caused by the recombination enhanced impurity diffusion (REID) of boron atoms from the p-type base region and the associated formation of parasitic energy barriers to electron transport from the emitter to collector layers. This REID has been quantitatively modeled and explained, to the first order of approximation, and the agreement with the measured data is good. The mean time to failure (MTTF) of the devices at room temperature is estimated from the extrapolation of the Arrhenius plots of device lifetime versus reciprocal temperature. The results of the reliability tests offer valuable feedback for SiGe heterostructure design in order to improve the long-term reliability of the devices and circuits made with them. Hot electron induced degradation of the base-emitter junction was also observed during the accelerated lifetime testing. In order to improve the HBT reliability endangered by the hot electrons, deuterium sintered techniques have been proposed. The preliminary results from this study show that a deuterium-sintered HBT is, indeed, more resistant to hot-electron induced base-emitter junction degradation. SiGe/Si based amplifier circuits were also subjected to lifetime testing and we extrapolate MTTF is approximately 1.1_10(exp 6) hours at 125iC junction temperature from the circuit lifetime data.

  13. Secondary growth mechanism of SiGe islands deposited on a mixed-phase microcrystalline Si by ion beam co-sputtering

    Science.gov (United States)

    Ke, S. Y.; Yang, J.; Qiu, F.; Wang, Z. Q.; Wang, C.; Yang, Y.

    2015-11-01

    We discuss the SiGe island co-sputtering deposition on a microcrystalline silicon (μc-Si) buffer layer and the secondary island growth based on this pre-SiGe island layer. The growth phenomenon of SiGe islands on crystalline silicon (c-Si) is also investigated for comparison. The pre-SiGe layer grown on μc-Si exhibits a mixed-phase structure, including SiGe islands and amorphous SiGe (a-SiGe) alloy, while the layer deposited on c-Si shows a single-phase island structure. The preferential growth and Ostwald ripening growth are shown to be the secondary growth mechanism of SiGe islands on μc-Si and c-Si, respectively. This difference may result from the effect of amorphous phase Si (AP-Si) in μc-Si on the island growth. In addition, the Si-Ge intermixing behavior of the secondary-grown islands on μc-Si is interpreted by constructing the model of lateral atomic migration, while this behavior on c-Si is ascribed to traditional uphill atomic diffusion. It is found that the aspect ratios of the preferential-grown super islands are higher than those of the Ostwald-ripening ones. The lower lateral growth rate of super islands due to the lower surface energy of AP-Si on the μc-Si buffer layer for the non-wetting of Ge at 700 °C and the stronger Si-Ge intermixing effect at 730 °C may be responsible for this aspect ratio difference.

  14. Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation

    DEFF Research Database (Denmark)

    Dhiman, Rajnish; Rana, Kuldeep; Bengu, Erman

    2012-01-01

    We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process...... ceramic material can be achieved, thus suggesting new industrial applications. The structure and composition of numerous as-synthesized samples were characterized in detail by using a wide range of techniques. Wear and friction properties were also investigated, with polished samples. The properties found...

  15. Ceramic Technology Project database: September 1990 summary report. [SiC, SiN, whisker-reinforced SiN, ZrO-toughened aluminas, zirconias, joints

    Energy Technology Data Exchange (ETDEWEB)

    Keyes, B.L.P.

    1992-06-01

    Data generated within the Ceramic Technology Project (CTP) represent a valuable resource for both research and industry. The CTP database was created to provide easy access to this information in electronic and hardcopy forms by using a computerized database and by issuing periodic hardcopy reports on the database contents. This report is the sixth in a series of semiannual database summaries and covers recent additions to the database, including joined brazed specimen test data. It covers 1 SiC, 34 SiN, 10 whisker-reinforced SiN, 2 zirconia-toughened aluminas, 8 zirconias, and 34 joints.

  16. Shakespeare au XXe siècle

    OpenAIRE

    Déprats, Jean-Michel; Desveaux, Paul; Drouet, Pascale; Drouet, Pascale; Falcon, Cécile; Guidicelli, Carole; Laroque, François; Laroque, François; Lekston, Édouard; Martinet, Marie-Madeleine; Rivère de Carles, Nathalie; Rivier, Estelle; Schwartz-Gastine, Isabelle; Thouret, Clotilde; Wilkinson, Kate

    2013-01-01

    King Richard II, pièce historique qui ouvre la seconde tétralogie de Shakespeare, est joué pour la première fois en 1595, par la troupe « The Chamberlain’s Men », sans doute dans le théâtre de James Burbage. Si la pièce a attiré de nombreux metteurs en scène britanniques depuis l’époque élisabéthaine jusqu’à nos jours, ce n’est qu’en 1947 qu’elle a été représentée en France sous la direction de Jean Vilar à Avignon - dans ces deux pays, cependant, les représentations de King Richard II se son...

  17. Sub-picosecond dynamics in liquid Si

    Energy Technology Data Exchange (ETDEWEB)

    Hosokawa, S [Institut fuer Physikalische-, Kern-, und Makromolekulare Chemie, Philipps Universitaet Marburg, D-35032 Marburg (Germany); Pilgrim, W-C [Institut fuer Physikalische-, Kern-, und Makromolekulare Chemie, Philipps Universitaet Marburg, D-35032 Marburg (Germany); Kawakita, Y [Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 810-8560 (Japan); Ohshima, K [Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 810-8560 (Japan); Takeda, S [Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 810-8560 (Japan); Ishikawa, D [SPring-8, Hyogo 679-5198 (Japan); Tsutsui, S [SPring-8, Hyogo 679-5198 (Japan); Tanaka, Y [SPring-8, Hyogo 679-5198 (Japan); Baron, A Q R [SPring-8, Hyogo 679-5198 (Japan)

    2003-10-15

    We are the first group to succeed in measuring the dynamic structure factor S(Q,{omega}) of liquid Si close to melting using high-resolution inelastic x-ray scattering. The spectra clearly demonstrate the existence of propagating short wavelength modes in the melt with a Q-{omega} relation similar to those in other liquid metal systems. A specific variation of the quasi-elastic line shape with increasing Q is observed close to the structure factor maximum. This observation is related to the onset of atomic correlations on the sub-picosecond timescale in the vicinity of a metal-to-insulator transition. Such observations have been made previously only in computer simulations of metallic systems with increasing covalent character. Our data provide the first experimental evidence for these ultrashort density correlations. (letter to the editor)

  18. On the structure of Si(100) surface

    DEFF Research Database (Denmark)

    Back, Seoin; Schmidt, Johan Albrecht; Ji, Hyunjun

    2013-01-01

    )]. Interestingly, however, the MRCI + Q, MRAQCC, and MRACPF results (which give a more refined description of electron correlation effects) suggest that the buckled dimer is marginally more stable than its symmetric counterpart. The present study underlines the significance of having an accurate description...... density functional based calculations predict the dimers to be buckled, while most wavefunction based correlated treatments prefer the symmetric configurations. Here, we use the doubly hybrid density functional (DHDF) geometry optimizations, in particular, XYGJ-OS, complete active space self...... of the electron-electron correlation as well as proper multireference wave functions when exploring the extremely delicate potential energy surfaces of the reconstructed Si(100) surface. (C) 2013 AIP Publishing LLC....

  19. Structural and tunneling properties of Si nanowires

    KAUST Repository

    Montes Muñoz, Enrique

    2013-12-06

    We investigate the electronic structure and electron transport properties of Si nanowires attached to Au electrodes from first principles using density functional theory and the nonequilibrium Green\\'s function method. We systematically study the dependence of the transport properties on the diameter of the nanowires, on the growth direction, and on the length. At the equilibrium Au-nanowire distance we find strong electronic coupling between the electrodes and nanowires, which results in a low contact resistance. With increasing nanowire length we study the transition from metallic to tunneling conductance for small applied bias. For the tunneling regime we investigate the decay of the conductance with the nanowire length and rationalize the results using the complex band structure of the pristine nanowires. The conductance is found to depend strongly on the growth direction, with nanowires grown along the ⟨110⟩ direction showing the smallest decay with length and the largest conductance and current.

  20. α clustering and superdeformation of 28Si

    Directory of Open Access Journals (Sweden)

    Kimura M.

    2010-04-01

    Full Text Available We have studied positive-parity states of 28Si using antisymmetrized molecular dynamics and multiconfiguration mixing with constrained variation. Applying constraints to the cluster distance and the quadrupole deformation of the variational calculation, we have obtained basis wave functions that have various structures such as α-24Mg and 12C-16O cluster structures as well as deformed structures. Superposing those basis wave functions, we have obtained a oblate ground state band, a β vibration band, a normal-deformed prolate band, and a superdeformed band. It is found that the superdeformed bands contain large amounts of the α-24Mg cluster components. The results also suggest the presence of two excited bands with the developed α-24Mg cluster structure, where the inter-cluster motion and the 24Mg-cluster deformation play important roles.