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Sample records for si rezultatele imediate

  1. Topoisomerase I-Mediated DNA Cleavage Induced by the Minor Groove-Directed Binding of Bibenzimidazoles to a Distal Site

    PubMed Central

    Khan, Qasim A.; Pilch, Daniel S.

    2007-01-01

    Summary Many agents (e.g., camptothecins, indolocarbazoles, indenoisoquinolines, and dibenzonaphthyridines) stimulate topoisomerase I-mediated DNA cleavage (a behavior termed topoisomerase I poisoning) by interacting with both the DNA and the enzyme at the site of cleavage (typically by intercalation between the −1 and +1 base pairs). The bibenzimidazoles, which include Hoechst 33258 and 33342, are a family of DNA minor groove-directed agents that also stimulate topoisomerase I-mediated DNA cleavage. However, the molecular mechanism by which these ligands poison TOP1 is poorly understood. Toward this goal, we have used a combination of mutational, footprinting, and DNA binding affinity analyses to define the DNA binding site for Hoechst 33258 and a related derivative that results in optimal induction of TOP1-mediated DNA cleavage. We show that this DNA binding site is located downstream from the site of DNA cleavage, encompassing the base pairs from position +4 to +8. The distal nature of this binding site relative to the site of DNA cleavage suggests that minor groove-directed agents like the bibenzimidazoles poison TOP1 via a mechanism distinct from compounds like the camptothecins, which interact at the site of cleavage. PMID:17095016

  2. Triple helix-forming oligonucleotides conjugated to indolocarbazole poisons direct topoisomerase I-mediated DNA cleavage to a specific site.

    PubMed

    Arimondo, P B; Bailly, C; Boutorine, A S; Moreau, P; Prudhomme, M; Sun, J S; Garestier, T; Hélène, C

    2001-01-01

    Topoisomerase I is an ubiquitous DNA-cleaving enzyme and an important therapeutic target in cancer chemotherapy for camptothecins as well as for indolocarbazole antibiotics such as rebeccamycin. To achieve a sequence-specific cleavage of DNA by topoisomerase I, a triple helix-forming oligonucleotide was covalently linked to indolocarbazole-type topoisomerase I poisons. The three indolocarbazole-oligonucleotide conjugates investigated were able to direct topoisomerase I cleavage at a specific site based upon sequence recognition by triplex formation. The efficacy of topoisomerase I-mediated DNA cleavage depends markedly on the intrinsic potency of the drug. We show that DNA cleavage depends also upon the length of the linker arm between the triplex-forming oligonucleotide and the drug. Based on a known structure of the DNA-topoisomerase I complex, a molecular model of the oligonucleotide conjugates bound to the DNA-topoisomerase I complex was elaborated to facilitate the design of a potent topoisomerase I inhibitor-oligonucleotide conjugate with an optimized linker between the two moieties. The resulting oligonucleotide-indolocarbazole conjugate at 10 nM induced cleavage at the triple helix site 2-fold more efficiently than 5 microM of free indolocarbazole, while the other drug-sensitive sites were not cleaved. The rational design of drug-oligonucleotide conjugates carrying a DNA topoisomerase poison may be exploited to improve the efficacy and selectivity of chemotherapeutic cancer treatments by targeting specific genes and reducing drug toxicity.

  3. Si/SiGe MMIC's

    NASA Astrophysics Data System (ADS)

    Luy, Johann-Friedrich; Strohm, Karl M.; Sasse, Hans-Eckard; Schueppen, Andreas; Buechler, Josef; Wollitzer, Michael; Gruhle, Andreas; Schaeffler, Friedrich; Guettich, Ulrich; Klaassen, Andreas

    1995-04-01

    Silicon-based millimeter-wave integrated circuits (SIMMWIC's) can provide new solutions for near range sensor and communication applications in the frequency range above 50 GHz. This paper gives a survey on the state-of-the-art performance of this technology and on first applications. The key devices are IMPATT diodes for mm-wave power generation and detection in the self-oscillating mixer mode, p-i-n diodes for use in switches and phase shifters, and Schottky diodes in detector and mixer circuits. The silicon/silicon germanium heterobipolar transistor (SiGe HBT) with f(sub max) values of more than 90 GHz is now used for low-noise oscillators at Ka-band frequencies. First system applications are discussed.

  4. Repair of Topoisomerase I-Mediated DNA Damage

    PubMed Central

    Pommier, Yves; Barcelo, Juana; Rao, V. Ashutosh; Sordet, Olivier; Jobson, Andrew G.; Thibaut, Laurent; Miao, Zheyong; Seiler, Jennifer; Zhang, Hongliang; Marchand, Christophe; Agama, Keli; Redon, Christophe

    2008-01-01

    Topoisomerase I (Top1) is an abundant and essential enzyme. Top1 is the selective target of camptothecins, which are effective anticancer agents. Top1-DNA cleavage complexes can also be trapped by various endogenous and exogenous DNA lesions including mismatches, abasic sites and carcinogenic adducts. Tyrosyl-DNA phosphodiesterase (Tdp1) is one of the repair enzymes for Top1-DNA covalent complexes. Tdp1 forms a multiprotein complex that includes poly(ADP) ribose polymerase (PARP). PARP-deficient cells are hypersensitive to camptothecins and functionally deficient for Tdp1. We will review recent developments in several pathways involved in the repair of Top1 cleavage complexes and the role of Chk1 and Chk2 checkpoint kinases in the cellular responses to Top1 inhibitors. The genes conferring camptothecin hypersensitivity are compiled for humans, budding yeast and fission yeast. PMID:16891172

  5. The Basic SI Model

    ERIC Educational Resources Information Center

    Hurley, Maureen; Jacobs, Glen; Gilbert, Melinda

    2006-01-01

    A general overview of the SI model is provided, including the SI philosophy, essential components of the program, program structures, key roles, outcomes, and evaluation. A review of what we have learned about the importance of planning SI sessions, providing ongoing training for leaders, conducting regular SI program assessments, and implementing…

  6. Characterization of Si/CoSi2/Si(111) heterostructures using Auger plasmon losses

    NASA Technical Reports Server (NTRS)

    Schowengerdt, F. D.; Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

    1989-01-01

    The Si/CoSi2/Si heterostructures prepared by codeposition and solid-phase epitaxy on Si(111) substrates were characterized using Auger plasmon data as a measure of Si overlayer thickness. The method of calibration is described, and the results of two studies, including a study of islanding in Si/CoSi2/Si and a study of diffusion in CoSi2/Si are presented, illustrating the utility of the Auger plasmon loss technique. It is shown that, most likely, the diffusion proceeds through residual defects in the CoSi2.

  7. Aperiodic SiSn/Si multilayers for thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Tonkikh, A. A.; Zakharov, N. D.; Eisenschmidt, C.; Leipner, H. S.; Werner, P.

    2014-04-01

    We report on novel defect-free SiSn/Si heterostructures grown pseudomorphically on Si(001) substrates using temperature-modulated molecular beam epitaxy. This approach results in a sustainable epitaxial growth for SiSn/Si multilayers. Transmission electron microscopy and electron diffraction manifest that SiSn layers possess a diamond lattice structure. X-ray diffraction reveals up to 9.5 at% Sn in the crystal lattice of SiSn layers.

  8. Photocurrent saturation and negative differential photoconductivity in Mn4Si7-Si-Mn4Si7 and Mn4Si7-Si- M heterojunctions

    NASA Astrophysics Data System (ADS)

    Kamilov, T. S.; Klechkovskaya, V. V.; Sharipov, B. Z.; Ivakin, G. I.

    2013-06-01

    A mechanism behind the saturation of the photocurrent and occurrence of negative differential photoconductivity in Mn4Si7-Si-Mn4Si7 and Mn4Si7-Si- M heterojunctions is found. Mn4Si7-Si-Mn4Si7 and Mn4Si7-Si- M structures are studied with a model of back-to-back diodes. Photocurrent-voltage characteristics are taken at high constant and pulsed applied biases. It is found that the nonlinearity of the photocurrent-voltage characteristics and photoconductivity kinetics are due to the quenching of photoconductivity by Joule self-heating.

  9. Endotaxial Si nanolines in Si(001):H

    NASA Astrophysics Data System (ADS)

    Owen, James; Bianco, François; Köster, Sigrun A.; Mazur, Daniel; Renner, Christoph; Bowler, David

    2011-03-01

    The study of one dimensional wires is of great interest in the area of low-dimensional physics, and these structures also have potential applications in future nanodevices. A perfectly straight nanoline embedded in a H-terminated silicon surface has been fabricated by a process of hydrogenation of a Bi nanoline surface using an atomic H beam source, and comprises a triangular core of Si embedded in the top five layers of the Si substrate. The defect density of this nanoline is extremely low, and being H- terminated, it is stable in air for limited periods of time. Scanning Tunnelling Microscopy experimental data and Density Functional Theory calculations have been used to determine the atomic structure of this nanoline, so-called the Haiku Stripe, and have revealed that there exists a 1D state localised to the nanoline core, lying just above the conduction band minimum. This work is supported by the Swiss National Science Fundation.

  10. SiC Technology

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.

    1998-01-01

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

  11. Synthesis and characterization of Si-SiO 2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhou, W. M.; Liu, X.; Zhang, Y. F.; Lai, Y. J.; Guo, X. Q.

    2007-01-01

    The bulk SiC/SiO 2 nanocomposites were synthesized without the presence of catalyst by high-frequency induction heating of SiO and activated carbon fibers in the temperature of 1400 °C for 20 min. The as-synthesized materials exhibit the morphologies of self-assembly nanograss, nanocolumn and Pine-tree-branch-like nanostructure. The Si-SiO 2 nanocomposites would open up new opportunities for fundamental nanodevice studies and applications.

  12. Interfacial reaction of eutectic AuSi solder with Si (100) and Si (111) surfaces

    NASA Astrophysics Data System (ADS)

    Jang, Jin-Wook; Hayes, Scott; Lin, Jong-Kai; Frear, Darrel R.

    2004-06-01

    The dissolution behavior of Si (100) and (111) dies by eutectic AuSi solder was investigated. On the Si (100) surface, the dissolution primarily occurred by the formation of craters resulting in a rough surface. The dissolution of the Si (111) resulted in a relatively smooth surface. The morphology of the Si (100) surface during a AuSi soldering reaction exhibited more time-dependent behavior and the etching craters on a Si (100) surface grew larger with time whereas Si (111) did not significantly change. This difference was ascribed to the surface energy differences between Si (111) and (100) surfaces that resulted in the two- and three-dimensional dissolution behaviors, respectively. This difference plays an important role in the formation of voids during the AuSi die bonding. The etching craters on Si (100) act as a AuSi solder sink and the regions surrounded by etch pits tend to become voids. For Si (111), flat surfaces were observed in the voided regions. Cross section analysis showed that no solder reaction occurred in the voided region of the Si (111) surface. This suggests the possibility of the formation of a thin inert layer in a potentially voided region prior to assembly. To achieve void-free die bonding, different parameters must be adjusted to the Si (100) and Si (111) surfaces with the AuSi alloy.

  13. Kapitza resistance of Si/SiO2 interface

    SciTech Connect

    Bowen Deng; Aleksandr Chenatynskiy; Marat Khafizov; David Hurley; Simon Phillpot

    2014-02-01

    A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO2 interface in a Si/SiO2/Si heterostructure. By varying the thickness of SiO2 layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO2 interface from both wave packet dynamics and a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interface and their contribution to the Kapitza resistance.

  14. SI (Metric) handbook

    NASA Astrophysics Data System (ADS)

    Artusa, Elisa A.

    1994-03-01

    This guide provides information for an understanding of SI units, symbols, and prefixes; style and usage in documentation in both the US and in the international business community; conversion techniques; limits, fits, and tolerance data; and drawing and technical writing guidelines. Also provided is information of SI usage for specialized applications like data processing and computer programming, science, engineering, and construction. Related information in the appendixes include legislative documents, historical and biographical data, a list of metric documentation, rules for determining significant digits and rounding, conversion factors, shorthand notation, and a unit index.

  15. SI (Metric) handbook

    NASA Technical Reports Server (NTRS)

    Artusa, Elisa A.

    1994-01-01

    This guide provides information for an understanding of SI units, symbols, and prefixes; style and usage in documentation in both the US and in the international business community; conversion techniques; limits, fits, and tolerance data; and drawing and technical writing guidelines. Also provided is information of SI usage for specialized applications like data processing and computer programming, science, engineering, and construction. Related information in the appendixes include legislative documents, historical and biographical data, a list of metric documentation, rules for determining significant digits and rounding, conversion factors, shorthand notation, and a unit index.

  16. Endotaxial Si nanolines in Si(001):H

    NASA Astrophysics Data System (ADS)

    Bianco, F.; Owen, J. H. G.; Köster, S. A.; Mazur, D.; Renner, Ch.; Bowler, D. R.

    2011-07-01

    We present a detailed study of the structural and electronic properties of a self-assembled silicon nanoline embedded in the H-terminated silicon (001) surface, known as the Haiku stripe. The nanoline is a perfectly straight and defect-free endotaxial structure of huge aspect ratio; it can grow micrometer long at a constant width of exactly four Si dimers (1.54 nm). Another remarkable property is its capacity to be exposed to air without suffering any degradation. The nanoline grows independently of any step edges at tunable densities from isolated nanolines to a dense array of nanolines. In addition to these unique structural characteristics, scanning tunneling microscopy and density functional theory reveal a one-dimensional state confined along the Haiku core. This nanoline is a promising candidate for the long-sought-after electronic solid-state one-dimensional model system to explore the fascinating quantum properties emerging in such reduced dimensionality.

  17. SI: The Stellar Imager

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

    2006-01-01

    The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

  18. U-Mo/Al-Si interaction: Influence of Si concentration

    NASA Astrophysics Data System (ADS)

    Allenou, J.; Palancher, H.; Iltis, X.; Cornen, M.; Tougait, O.; Tucoulou, R.; Welcomme, E.; Martin, Ph.; Valot, C.; Charollais, F.; Anselmet, M. C.; Lemoine, P.

    2010-04-01

    Within the framework of the development of low enriched nuclear fuels for research reactors, U-Mo/Al is the most promising option that has however to be optimised. Indeed at the U-Mo/Al interfaces between U-Mo particles and the Al matrix, an interaction layer grows under irradiation inducing an unacceptable fuel swelling. Adding silicon in limited content into the Al matrix has clearly improved the in-pile fuel behaviour. This breakthrough is attributed to an U-Mo/Al-Si protective layer around U-Mo particles appeared during fuel manufacturing. In this work, the evolution of the microstructure and composition of this protective layer with increasing Si concentrations in the Al matrix has been investigated. Conclusions are based on the characterization at the micrometer scale (X-ray diffraction and energy dispersive spectroscopy) of U-Mo7/Al-Si diffusion couples obtained by thermal annealing at 450 °C. Two types of interaction layers have been evidenced depending on the Si content in the Al-Si alloy: the threshold value is found at about 5 wt.% but obviously evolves with temperature. It has been shown that for Si concentrations ranging from 2 to 10 wt.%, the U-Mo7/Al-Si interaction is bi-layered and the Si-rich part is located close to the Al-Si for low Si concentrations (below 5 wt.%) and close to the U-Mo for higher Si concentrations. For Si weight fraction in the Al alloy lower than 5 wt.%, the Si-rich sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2Al 20, when the other sub-layer (close to U-Mo) is silicon free and made of UAl 3 and U 6Mo 4Al 43. For Si weight concentrations above 5 wt.%, the Si-rich part becomes U 3(Si, Al) 5 + U(Al, Si) 3 (close to U-Mo) and the other sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2Al 20. On the basis of these results and of a literature survey, a scheme is proposed to explain the formation of different types of ILs between U-Mo and Al-Si alloys (i.e. different protective layers).

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Thermoelectric properties of BaSi2, SrSi2, and LaSi

    NASA Astrophysics Data System (ADS)

    Hashimoto, Kohsuke; Kurosaki, Ken; Imamura, Yasushi; Muta, Hiroaki; Yamanaka, Shinsuke

    2007-09-01

    We studied the thermoelectric properties of BaSi2, SrSi2, and LaSi. The polycrystalline samples were prepared by spark plasma sintering (SPS). The electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were measured above room temperature. The power factor (S2/ρ) is quite low (below 10-5 Wm-1 K-2 over the whole temperature range) for BaSi2 and LaSi, while relatively high (1.19×10-3 Wm-1 K-2 at 331 K) for SrSi2. BaSi2 exhibits quite low κ. The κ values at room temperature are 1.56, 5.25, and 6.71 Wm-1 K-1 for BaSi2, SrSi2, and LaSi, respectively. The maximum values of the dimensionless figure of merit, ZT =S2T/ρ/κ, are 0.01 at 954 K for BaSi2, 0.09 at 417 K for SrSi2, and 0.002 at 957 K for LaSi.

  1. Long-Wavelength Stacked SiGe/Si Heterojunction Internal Photoemission Infrared Detectors Using Multiple SiGe/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; Gunapala, S. D.

    1994-01-01

    Utilizing low temperature silicon molecular beam epitaxy (MBE) growth, long-wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentrations (approximately equal to 4 x 10(sup 20) cm(sup -3)) has been achieved and high crystalline quality multiple Si(sub 0.7)Ge(sub 0.3)/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (approximately equal to 4 x 10(sup 20) cm(sup -3)) thin (less than or equal to 50 u Si(sub 0.7)Ge(sub 0.3) layers and undoped thick (approximately equal to 300u Si layers. The multiple p(sup +) - Si(sub 0.7)Ge(sub 0.3)/undoped-Si layers show strong infrared absorption in the long-wavelength regime mainly through free carrier absorption. The stacked Si(sub 0.7)Ge(sub 0.3)/Si HIP detectors with p = 4 x 10(sup 20) cm(sup -3) exhibit strong photoresponse at wavelengths ranging from 2 to 20 (micro)m with quantum efficiencies of about 4% and 1.5% at 10 and 15 (micro)m wavelengths, respectively. The detectors show near ideal thermionic-emission limited dark current characteristics.

  2. FeSi diffusion barriers in Fe/FeSi/Si/FeSi/Fe multilayers and oscillatory antiferromagnetic exchange coupling

    NASA Astrophysics Data System (ADS)

    Stromberg, F.; Bedanta, S.; Antoniak, C.; Keune, W.; Wende, H.

    2008-10-01

    We study the diffusion of 57Fe probe atoms in Fe/FeSi/Si/FeSi/Fe multilayers on Si(111) prepared by molecular beam epitaxy by means of 57Fe conversion electron Mössbauer spectroscopy (CEMS). We demonstrate that the application of FeSi boundary layers successfully inhibits the diffusion of 57Fe into the Si layer. The critical thickness for the complete prevention of Fe diffusion takes place at a nominal FeSi thickness of tFeSi = 10-12 Å, which was confirmed by the evolution of the isomer shift δ of the crucial CEM subspectrum. The formation of the slightly defective c-FeSi phase for thicker FeSi boundary layers (~20 Å) was confirmed by CEMS and reflection high-energy electron diffraction (RHEED). Ferromagnetic resonance (FMR) shows that, for tFeSi = 0-14 Å, the Fe layers in all samples are antiferromagnetically coupled and we observe an oscillatory antiferromagnetic coupling strength with FMR and superconducting quantum interference device (SQUID) magnetometry for varying FeSi thickness with a period of ~6 Å.

  3. Processing and Properties of SiC/MoSi2-SiC Composites Fabricated by Melt Infiltration

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.; Hebsur, Mohan G.

    2000-01-01

    Hi-Nicalon SiC fiber reinforced MoSi2-SiC matrix composites (SiC/MoSi2-SiC) have been fabricated by the melt infiltration approach. The composite consists of approximately 60 vol%, 2-D woven BN/SiC coated Hi-Nicalon SiC fibers and approximately 40 vol% MoSi2-SiC matrix. The room temperature tensile properties and thermal conductivity of the SiC/MoSi2-SiC composites were measured and compared with those of the melt infiltrated SiC/SiC composites. The influence oi fiber architecture on tensile properties was also evaluated. Results indicate that the primary modulus, stress corresponding to deviation from linearity, and transverse thermal conductivity values for the SiC/MoSi2-SiC composites are significantly lower than those for the SiC/SiC composites. Microcracking of the matrix due to the large difference in thermal expansion between MoSi2 and SiC appears to be the reason for the lower matrix dominated properties of SiC/MoSi2-SiC composites.

  4. Near interface oxide degradation in high temperature annealed Si/SiO{sub 2}/Si structures

    SciTech Connect

    Devine, R.A.B.; Mathiot, D.; Warren, W.L.; Fleetwood, D.M.

    1993-12-31

    Degradation of 430 nm thick SiO{sub 2} layers in Si/SiO{sub 2}/Si structures which results from high temperature annealing (1320 C) has been studied using electron spin resonance, infra-red and refractive index measurements. Large numbers of oxygen vacancies are found in a region {le}100 nm from each Si/SiO{sub 2} interface. Two types of paramagnetic defects are observed following {gamma} or x-irradiation or hole injection. The 1106 cm{sup {minus}1} infra-red absorption associated with O interstitials in the Si substrate is found to increase with annealing time. The infra-red and spin resonance observations can be explained qualitatively and quantitatively in terms of a model in which oxygen atoms are gettered from the oxide into the under or overlying Si, the driving force being the increased O solubility limit associated with the anneal temperature.

  5. Positron diffusion in Si

    SciTech Connect

    Nielsen, B.; Lynn, K.G.; Vehanen, A.; Schultz, P.J.

    1985-06-01

    Positron diffusion in Si(100) and Si(111) has been studied using a variable energy positron beam. The positron diffusion coefficient is found to be D/sub +/ = 2.7 +- 0.3 cm/sup 2//sec using a Makhov-type positron implantation profile, which is demonstrated to fit the data more reliably than the more commonly applied exponential profile. The diffusion related parameter, E/sub 0/, which results from the exponential profile, is found to be 4.2 +- 0.2 keV, significantly longer than previously reported values. A drastic reduction in E/sub 0/ is found after annealing the sample at 1300 K, showing that previously reported low values of E/sub 0/ are probably associated with the thermal history of the sample.

  6. Large Area and Depth-Profiling Dislocation Imaging and Strain Analysis in Si/SiGe/Si Heterostructures

    DTIC Science & Technology

    2014-01-01

    by high-resolution X-ray 387 diffraction. In Characterization of Semiconductor Heterostructures 388and Nanostructures , Lamberti C. (Ed.), pp. 93–132...combined advantage of Si semiconductor 29 technology and band gap engineering (Kittler et al., 1995). 30 Inside the Si/SiGe/Si heterostructure , SiGe is...and Depth-Profiling Dislocation Imaging and Strain Analysis in Si/SiGe/Si Heterostructures Report Title We demonstrate the combined use of large area

  7. Brazing SiC/SiC Composites to Metals

    NASA Technical Reports Server (NTRS)

    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.

  8. Highly sensitive NIR PtSi/Si-nanostructure detectors

    NASA Astrophysics Data System (ADS)

    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).

  9. SiC-Si interfacial thermal and mechanical properties of reaction bonded SiC/Si ceramic composites

    NASA Astrophysics Data System (ADS)

    Hsu, Chun-Yen; Deng, Fei; Karandikar, Prashant; Ni, Chaoying

    Reaction bonded SiC/Si (RBSC) ceramic composites are broadly utilized in military, semiconductor and aerospace industries. RBSC affords advanced specific stiffness, hardness and thermal. Interface is a key region that has to be considered when working with any composites. Both thermal and mechanical behaviors of the RBSC are highly dependent on the SiC-Si interface. The SiC-Si interface had been found to act as a thermal barrier in restricting heat transferring at room temperature and to govern the energy absorption ability of the RBSC. However, up to present, the role of the SiC-Si interface to transport heat at higher temperatures and the interfacial properties in the nanoscale have not been established. This study focuses on these critically important subjects to explore scientific phenomena and underlying mechanisms. The RBSC thermal conductivity with volume percentages of SiC at 80 and 90 vol% was measured up to 1,200 °C, and was found to decrease for both samples with increasing environmental temperature. The RBSC with 90 vol% SiC has a higher thermal conductivity than that of the 80 vol%; however, is still significantly lower than that of the SiC. The interfacial thermal barrier effect was found to decrease at higher temperatures close 1200 °C. A custom-made in-situ tensile testing device which can be accommodated inside a ZEISS Auriga 60 FIB/SEM has been setup successfully. The SiC-Si interfacial bonding strength was measured at 98 MPa. The observation and analysis of crack propagation along the SiC-Si interface was achieved with in-situ TEM.

  10. Nanoscale η-NiSi formation via ion irradiation of Si/Ni/Si

    NASA Astrophysics Data System (ADS)

    Banu, Nasrin; Satpati, Biswarup; Bhukta, Anjan; Dev, B. N.

    2017-01-01

    Nickel monosilicide (NiSi) has emerged as an excellent material of choice for source-drain contact applications below 45 nm node complementary metal-oxide-semiconductor technology. We have investigated the formation of nanoscale NiSi by ion irradiation of Si (˜5 nm)/Ni(˜15 nm)/Si, grown in an ultrahigh vacuum environment. Irradiation was carried out at room temperature with 1 MeV Si+ ions. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed for analysis. With increasing ion fluence, ion beam mixing occurs and more and more Si is incorporated into the Ni layer, and this layer gets amorphized. At an even higher fluence, a recrystallized uniform nickel monosilicide (η-NiSi) layer is formed. Several planar spacings of different Miller indices of η-NiSi have been observed in XRD and TEM. Additionally, an interesting amorphization and recrystallization behavior has been observed in the substrate Si with increasing ion fluence. To our knowledge, this has never been observed in ion irradiation of bare Si in decades of work in this area. This kind of amorphization/recrystallization in Si is apparently Ni-induced. Irradiation displaces Ni and produces a distribution of Ni in amorphized Si. Irradiation at a higher fluence produces two recrystallized Si bands in amorphous Si with concomitant accumulation of Ni at the amorphous/crystalline interfaces. On a further increase in irradiation fluence, the recrystallized Si bands again pass through amorphization and recrystallization. The total thickness of recrystallized, as well as amorphous Si, shows an oscillatory behavior as a function of ion fluence.

  11. Nanofabricated SiO{sub 2}-Si-SiO{sub 2} Resonant Tunneling Diodes

    SciTech Connect

    FLEMING,JAMES G.; CHOW,KAI-CHEUNG; LIN,SHAWN-YU

    2000-04-06

    Resonance Tunneling Diodes (RTDs) are devices that can demonstrate very high-speed operation. Typically they have been fabricated using epitaxial techniques and materials not consistent with standard commercial integrated circuits. The authors report here the first demonstration of SiO{sub 2}-Si-SiO{sub 2} RTDs. These new structures were fabricated using novel combinations of silicon integrated circuit processes.

  12. .Si≡Si3 defect at thermally grown (111)Si/Si3N4 interfaces

    NASA Astrophysics Data System (ADS)

    Stesmans, A.; van Gorp, G.

    1995-09-01

    Electron-spin resonance on various dehydrogenated (111)Si/(oxy)nitride structures, thermally grown at 1000-1150 °C in NH3, reveals the presence of two defects. The major one, called PbN, is identified as a Si dangling bond (.Si≡Si3) at the (111)Si/nitride interface aligned perpendicular to the interface; x-ray photoelectron spectroscopy actually shows that the in situ removal of the native Si oxide prior to nitridation is a prerequisite to obtaining stoichiometric Si3N4 films. The identification is based on strong similarities with the Pb defect at the (111)Si/SiO2 interface, such as the g matrix, the location at the interface, and linewidth anisotropy. This observation of the .Si≡Si3 defect at a natural Si/solid interface other than the Si/SiO2 one confirms Pb as a prototype dangling-bond center, its salient properties being set by the underside Si matrix-not by the overlaying insulator. Yet, secondary ESR signatures do differ as the large interface strain, resulting from the greater rigidity of the (oxy)nitrides as compared to SiO2 films, causes a slight perturbation of the Pb(N) symmetry, thereby lifting its C3v symmetry. This is born out at 4.3 K by specific distortions of the PbN line shape. Upon increasing temperature, the perturbation of the defect's symmetry is smoothed due to thermally activated averaging over the various defect distortions. The properties of the Pb and PbN defects at higher temperatures become largely identical. Comparison of the extracted unresolved 14N PbN and 17O Pb hf broadenings shows that their relative strengths comply with the known isotopic properties. A second defect, the intrinsic K center (.Si≡N3), with isotropic g=2.0028+/-0.0001, is observed only in stoichiometric Si3N4 films.

  13. Absorption in a-Si/SiO2 Superlattices

    NASA Astrophysics Data System (ADS)

    Kilpelä, O.; Karppinen, M.; Novikov, S.; Sokolov, V.; Yliniemi, S.

    a-Si/SiO2 superlattices were grown on quartz by MBD (Molecular Beam Deposition) using in situ oxidation by an RF-plasma source. The a-Si layer thicknesses were varied from 0.5-2.5nm while the SiO2 layer thicknesses (1.0nm) were kept constant. Optical transmission and reflection measurements were performed on these samples at room temperature. The recorded spectra were then analyzed with a commercial optical thin film analysis program. The band gaps were derived from constant-n and non-constant-n forms of Tauc and Cody laws. The observed blueshift of the band gap, with decreasing a-Si layer thickness, is attributed to quantum confinement in the a-Si sublayers.

  14. Synthesis and characterization of laminated Si/SiC composites

    PubMed Central

    Naga, Salma M.; Kenawy, Sayed H.; Awaad, Mohamed; Abd El-Wahab, Hamada S.; Greil, Peter; Abadir, Magdi F.

    2012-01-01

    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. PMID:25685404

  15. Study of Si/Si, Si/SiO sub 2 , and metal-oxide-semiconductor (MOS) using positrons

    SciTech Connect

    Leung, To Chi.

    1991-01-01

    A variable-energy positron beam is used to study Si/Si, Si/SiO{sub 2}, and metal-oxide-semiconductor (MOS) structures. The capability of depth resolution and the remarkable sensitivity to defects have made the positron annihilation technique a unique tool in detecting open-volume defects in the newly innovated low temperature (300C) molecular-beam-epitaxy (MBE) Si/Si. These two features of the positron beam have further shown its potential role in the study of the Si/SiO{sub 2}. Distinct annihilation characteristics has been observed at the interface and has been studied as a function of the sample growth conditions, annealing (in vacuum), and hydrogen exposure. The MOS structure provides an effective way to study the electrical properties of the Si/SiO{sub 2} interface as a function of applied bias voltage. The annihilation characteristics show a large change as the device condition is changed from accumulation to inversion. The effect of forming gas (FG) anneal is studied using positron annihilation and the result is compared with capacitance-voltage (C-V) measurements. The reduction in the number of interface states is found correlated with the changes in the positron spectra. The present study shows the importance of the positron annihilation technique as a non-contact, non-destructive, and depth-sensitive characterization tool to study the Si-related systems, in particular, the Si/SiO{sub 2} interface which is of crucial importance in semiconductor technology, and fundamental understanding of the defects responsible for degradation of the electrical properties.

  16. Fabrication of lightweight Si/SiC LIDAR mirrors

    NASA Technical Reports Server (NTRS)

    Goela, Jitendra S.; Taylor, Raymond L.

    1991-01-01

    A new, chemical vapor deposition (CVD) process was developed for fabricating lightweight, polycrystalline silicon/silicon-carbide (Si/SiC) mirrors. The process involves three CVD steps: (1) to produce the mirror faceplate; (2) to form the lightweight backstructure, which is deposited integral to the faceplate; and (3) to deposit a layer of optical-grade material, e.g., Si, onto the front surface of the faceplate. The mirror figure and finish are fabricated into the faceplate.

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

    SciTech Connect

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

    2015-01-07

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

  18. SiGe/Si Monolithically Integrated Amplifier Circuits

    NASA Technical Reports Server (NTRS)

    Katehi, Linda P. B.; Bhattacharya, Pallab

    1998-01-01

    With recent advance in the epitaxial growth of silicon-germanium heterojunction, Si/SiGe HBTs with high f(sub max) and f(sub T) have received great attention in MMIC applications. In the past year, technologies for mesa-type Si/SiGe HBTs and other lumped passive components with high resonant frequencies have been developed and well characterized for circuit applications. By integrating the micromachined lumped passive elements into HBT fabrication, multi-stage amplifiers operating at 20 GHz have been designed and fabricated.

  19. Inherent paramagnetic defects in layered Si/SiO{sub 2} superstructures with Si nanocrystals

    SciTech Connect

    Jivanescu, M.; Stesmans, A.; Zacharias, M.

    2008-11-15

    An extensive electron spin resonance (ESR) analysis has been carried out on structures comprised of Si nanoparticles ({approx}2 nm across) embedded in a regular pattern in an amorphous SiO{sub 2} matrix, fabricated by the SiO/SiO{sub 2} superlattice approach, with the intent to reveal and quantify occurring paramagnetic defects. The as-grown state is found to exhibit only a Si dangling bond (DB) signal, which through combination of first and second harmonic X-, K-, and Q-band observations in combination with computer spectra simulation, could be conclusively disentangled as solely comprised of overlapping powder pattern spectra of P{sub b(0)} and P{sub b1} defects, the archetypal intrinsic defects of the Si/SiO{sub 2} interface, with no evidence for a D line (Si DBs in disordered Si). This indicates a full crystalline system of randomly oriented Si nanocrystals (NCs). The P{sub b(0)}/P{sub b1} defect system, pertaining to the NC-Si/SiO{sub 2} interfaces, is found to be both qualitatively and quantitatively much alike that of standard (high-quality) thermal Si/SiO{sub 2}. The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of P{sub b}-type defects in standard microscopic Si/SiO{sub 2}, the data would comply with Si nanocrystallites, in average, predominantly bordered by (111) and (100) facets, perhaps with morphology, schematically, of [100] truncated (111) octahedrons. Based on independent NC particles counting, there appears a P{sub b}-type center at {approx}71% of the Si NCs indicating the latter to be comprised of two subsystems-with or without an incorporated strain relaxing interface defect-which in that case will exhibit drastically different defect-sensitive properties, such as, e.g., photoluminescence (PL). Upon additional optical irradiation, two more defects appear, i.e., the SiO{sub 2}-associated E{sub {gamma}}{sup '} and EX centers, where the observed density of the former, taken as

  20. Joining of SiC ceramics and SiC/SiC composites

    SciTech Connect

    Rabin, B.H.

    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.

  1. Joining of SiC ceramics and SiC/SiC composites

    SciTech Connect

    Rabin, B.H.

    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.

  2. Fabrication of SiO2/c-Si/SiO2 Double Barrier Structure Using Lateral Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Sinkkonen, J.

    Formation of an ultra-thin-film silicon-on-insulator structure by lateral solid state epitaxy (LSPE) of amorphous Si on SiO2 has been investigated. The LSPE growth length was found. The SiO2/Si/SiO2 double barrier structure with single crystalline silicon well has been grown.

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

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.

    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.

  4. SiC-SiC composites for optical applications

    NASA Astrophysics Data System (ADS)

    Kowbel, Witold; Woida, Rigel; Withers, J. C.

    2005-08-01

    SiC optics has been considered for a very long time. Today, there are a few military and commercial applications. Future imaging and energy transfer applications require robustness on a par with metallic systems. Intrinsic, low fracture toughness of several classes of monolithic SiC is the key impediment in these applications. A new form of SiC-SiC composite for optical applications has been developed. It features high modulus combined with high fracture toughness. This new, highly innovative technology offers the potential in demanding government applications, as well as large surveillance optics (increased toughness can translate into lower aerial density) and high energy commercial lasers. SiC-SIC is a novel technology for optical structures consisting of integrated composite materials and structures which exhibits excellent fracture toughness and homogeneous CTE.

  5. MoSi2-Base Composites

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.

    2003-01-01

    Addition of 30 to 50 vol% of Si3N4 particulate to MoSi2 eliminated its low temperature catastrophic failure, improved room temperature fracture toughness and the creep resistance. The hybrid composite SCS-6/MoSi2-Si3N4 did not show any matrix cracking and exhibited excellent mechanical and environmental properties. Hi-Nicalon continuous fiber reinforced MoSi2-Si3N4 also showed good strength and toughness. A new MoSi2-base composite containing in-situ whisker-type (Beta)Si3N4 grains in a MoSi2 matrix is also described.

  6. Measurements, Standards, and the SI.

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 1983

    1983-01-01

    Highlights six papers presented at the Seventh Biennial Conference on Chemical Education (Stillwater, Oklahoma 1982). Topics addressed included history, status, and future of SI units, algebra of SI units, periodic table, new standard-state pressure unit, and suggested new names for mole concept ("numerity" and "chemical amount"). (JN)

  7. SI: Prognosis for the Future.

    ERIC Educational Resources Information Center

    Goldman, David T.

    1981-01-01

    Presents a survey of the International System of Units, usually denoted by its French abbreviation, SI (Systeme International), how it came about, and how it is likely to develop in the future. Describes SI units (base, derived, and supplementary) and new definitions for base units. (Author/SK)

  8. Using SI Units in Mechanics.

    ERIC Educational Resources Information Center

    Meriam, J. L.

    This paper provides an historical account of the development of the International System of Units (SI), a complete listing of these units, and rules concerning their use and proper abbreviation. Ambiguities concerning the use of the system are explained. Appendices contain conversion factors for U.S. - British to SI units along with several…

  9. The localization and crystallographic dependence of Si suboxide species at the SiO2/Si interface

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Hecht, M. H.; Grunthaner, F. J.; Johnson, N. M.

    1987-01-01

    X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si(+), Si(2+), and Si(3+) suboxide states at the SiO2/Si interface for (100)and (111)-oriented substrates with gate oxide quality thermal oxides. The Si(+) and Si(2+) states are localized within 6-10 A of the interface while the Si(3+) state extends about 30 A into the bulk SiO2. The distribution of Si(+) and Si(2+) states shows a strong crystallographic dependence with Si(2+) dominating on (100) substrates and Si(+) dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si(+) and Si(2+) states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94 and 83 percent of a monolayer for these (100) and (111) substrates, respectively.

  10. Properties of SiC-SiC composites produced using CVR converted graphite cloth to SiC cloth

    SciTech Connect

    Kowbel, W.; Kyriacou, C.; Gao, F.; Bruce, C.A.; Withers, J.C.

    1995-10-01

    Nicalon fiber is the primary reinforcement in SiC-SiC composites currently produced by a variety of techniques including CVI and polymer infiltration. Low strength retention at high temperatures of the Nicalon fibers limits the choice of manufacturing processes which can be employed to produce low cost SiC-SiC composites. MER has developed a new SiC reinforcement based upon a conversion of low cost carbon fabric to SiC via a Chemical Vapor Reaction (CVR) process. This new SiC filaments exhibit an excellent creep resistance at temperatures up to 1,600 C. Several SiC-SiC composites were fabricated using graphite fabric converted to SiC fabric utilizing the CVR process combined with a slurry infiltration and CVI densification. A correlation between processing conditions, microstructure and properties of the SiC-SiC composites are discussed in detail.

  11. Improvement of parameters in a-Si(p)/c-Si(n)/a-Si(n) solar cells

    NASA Astrophysics Data System (ADS)

    Moustafa Bouzaki, Mohammed; Aillerie, Michel; Ould Saad Hamady, Sidi; Chadel, Meriem; Benyoucef, Boumediene

    2016-10-01

    We analyzed and discussed the influence of thickness and doping concentration of the different layers in a-Si(p)/c-Si(n)/a-Si(n) photovoltaic (PV) cells with the aim of increasing its efficiency while decreasing its global cost. Compared to the efficiency of a standard marketed PV cell, elaborated with a ZnO transparent conductive oxide (TCO) layer but without Back Surface Field (BSF) layer, an optimization of the thickness and dopant concentration of both the emitter a-Si(p) and absorber c-Si(n) layers will gain about 3% in the global efficiency of the cell. The results also reveal that with introduction of the third layer, i.e. the BSF layer, the efficiency always achieves values above 20% and all other parameters of the cell, such as the open-circuit voltage, the short-circuit current and the fill-factor, are strongly affected by the thickness and dopant concentration of the layers. The values of all parameters are given and discussed in the paper. Thereby, the simulation results give for an optimized a-Si(p)/c-Si(n)/a-Si(n) PV cells the possibility to decrease the thickness of the absorber layer down to 50 μm which is lower than in the state-of-the-art. This structure of the cell achieves suitable properties for high efficiency, cost-effectiveness and reliable heterojunction (HJ) solar cell applications.

  12. Si Isotopes of Brownleeite

    NASA Technical Reports Server (NTRS)

    Nakamura-Messenger, K.; Messenger, Scott R.; Ito, M.; Keller, L. P.; Clemett, S. J.; Jones, J. H.; Tatsuoka, H.; Zolensky, M. E.; Tatsuoka, H.

    2010-01-01

    Brownleeite is a manganese silicide, ideally stoichiometric MnSi, not previously observed in nature until its discovery within an interplanetary dust particle (IDP) that likely originated from a comet [1]. Three discrete brownleeite grains in the IDP L2055 I3 (4 microns in size, hereafter IDP I3) were identified with maximum dimensions of 100, 250 and 600 nm and fully analyzed using scanning-transmission electron microscopy (STEM) [1]. One of the grains (100 nm in size) was poikilitically enclosed by low-Fe, Mn-enriched (LIME) olivine. LIME olivine is epitaxial to the brownleeite with the brownleeite (200) parallel to the olivine c* [1]. LIME olivine is an enigmatic phase first reported from chondritic porous IDPs and some unequilibrated ordinary chondrites [ 2], that is commonly observed in chondritic-porous IDPs. Recently, LIME olivine has been also found in comet Wild-2 (Stardust) samples [3], indicating that LIME olivine is a common mineral component of comets. LIME olivine has been proposed to form as a high temperature condensate in the protosolar nebula [2]. Brownleeite grains also likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion [1]. The isotopic composition of the brownleeite grains may strongly constrain their ultimate source. To test this hypothesis, we performed isotopic analyses of the brownleeite and the associated LIME olivine, using the NASA/JSC NanoSIMS 50L ion microprobe.

  13. Epitaxial growth of Si deposited on (100) Si

    NASA Astrophysics Data System (ADS)

    Hung, L. S.; Lau, S. S.; von Allmen, M.; Mayer, J. W.; Ullrich, B. M.; Baker, J. E.; Williams, P.; Tseng, W. F.

    1980-11-01

    Epitaxial growth of deposited amorphous Si on chemically cleaned (100) Si has been found and layer-by-layer growth occurred at rates comparable to those in self-ion-implanted-amorphous Si. There is no evidence for appreciable oxygen penetration into the deposited layer during storage in air. The critical factors in achieving epitaxial growth are fast (˜50 Å/sec) deposition of Si onto a surface cleaned with a HF dip as a last rinse before loading into the vacuum system. Channeling and transmission electron microscopy measurements indicated that the epitaxial layers are essentially defect free. Secondary-ion mass spectroscopic analysis showed about 1014 oxygen/cm2 at the amorphous/crystal interface. With either higher interfacial oxygen coverage or slow (˜2 Å/sec) deposition, epitaxial growth rates are significantly slower.

  14. Synthesis and structural property of Si nanosheets connected to Si nanowires using MnCl2/Si powder source

    NASA Astrophysics Data System (ADS)

    Meng, Erchao; Ueki, Akiko; Meng, Xiang; Suzuki, Hiroaki; Itahara, Hiroshi; Tatsuoka, Hirokazu

    2016-08-01

    Si nanosheets connected to Si nanowires were synthesized using a MnCl2/Si powder source with an Au catalyst. The synthesis method has benefits in terms of avoiding conventionally used air-sensitive SiH4 or SiCl4. 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.

  15. Luminescence of Degraded Si-SiO2 Structures

    NASA Astrophysics Data System (ADS)

    Baraban, A. P.; Dmitriev, V. A.; Gadzhala, A. A.

    2014-09-01

    Possibilities of using electroluminescence (EL) and cathodoluminescence (CL) in the spectral range 250-800 nm to investigate physical-chemical processes taking place in Si-SiO2 structures as a result of extreme external actions (strong electric fields or γ-radiation) are considered. It is found that degradation processes along with changes in the electrophysical characteristics of Si-SiO2 structures are revealed in changes in the luminescence spectra, especially in the red region. The similarity of the changes in the CL and EL spectra of Si-SiO2 structures exposed to field and radiation points to a similarity in the processes taking place during degradation, which is confirmed by the qualitative similarity of the changes in the charge characteristics. The near-invariance of the spectral composition of the luminescence is an indication that the processes taking place during degradation do not lead to the formation of new luminescence centers, but modify the concentration of already existing biographical defects. This is evidence of the existence of a direct link between resistance to degradation and the technology of formation of the oxide layer on the silicon surface.

  16. Formation of microtubes from strained SiGe/Si heterostructures

    NASA Astrophysics Data System (ADS)

    Qin, H.; Shaji, N.; Merrill, N. E.; Kim, H. S.; Toonen, R. C.; Blick, R. H.; Roberts, M. M.; Savage, D. E.; Lagally, M. G.; Celler, G.

    2005-11-01

    We report the formation of micrometre-sized SiGe/Si tubes by releasing strained SiGe/Si bilayers from substrates in a wet chemical-etching process. In order to explore statistical studies of dynamic formation of microtubes, we fabricated arrays of square bilayers. Due to the dynamic change in curvature of the bilayers, and hence the underlying etch channels, the etching process deviates from a transport-controlled regime to one of kinetic controlled. We identified two distinct modes of etching. A slow etching mode is associated with symmetric surface deformation in which the bilayers mostly retain their initial pattern. In the fast mode, bilayers are asymmetrically deformed while large etch channels are induced and etching becomes kinetically controlled. Etch rate dispersion is directly related to the degree of asymmetry in surface deformation. When the dimensions of the bilayers become significantly larger than the curvature radius, kinetic etching dominates. During the formation of tubes, SiGe/Si bilayers strongly interact with the liquid environment of etchant and solvent. Assisted by the surface tension of evaporating liquids, the tubes are drawn near the substrate and eventually fixed to it because of van der Waals forces. Our study illuminates the dynamic etching and curling processes involved with and provides insight on how a uniform etch rate and consistent curling directions can be maintained.

  17. Fabrication and characterization of CuxSi1-x films on Si (111) and Si (100) by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Wu, Jun; He, Zhiqiang; Xie, Jun; Lu, Jingqi; Tu, Rong; Zhang, Lianmeng; Shi, Ji

    2016-05-01

    The CuxSi1-x thin films have been successfully fabricated by pulsed laser deposition (PLD). The influences of laser energy fluency (I0) and deposition temperature (Td) on the phase structure were investigated. The results show that Cu deposited on Si (001) at I0 = 0.5-2.0 J/cm2, and η"-Cu3Si formed on Si (111) at I0 = 1.0-2.0 J/cm2. The films were consisted of Cu, η'-Cu3Si, ɛ-Cu15Si4 and δ-Cu0.83Si0.17 at Td = 100-500 °C on Si (001). The films were the single phase of η-Cu3Si at Td = 700 °C. In the case of Si (111), the phase structures transformed from Cu to Cu + η'-Cu3Si to η'-Cu3Si to η'-Cu3Si + η-Cu3Si with the increasing of Td. Rectangular grains were formed on Si (001), whereas triangular grains on Si (111). Cu (001) film was epitaxially grown on Si (001) at I0 = 1.5 J/cm2 and Td = 20 °C. η-Cu3Si (001) epitaxial layer was formed on Si (111) at I0 = 1.5 J/cm2 and Td = 700 °C. The epitaxial relationships of Cu (001)[100]//Si (001)[110] and η-Cu3Si (001)[-110]//Si (111)[11-2] were identified.

  18. Nitriding kinetics of Si-SiC powder mixtures as simulations of reaction bonded Si3N4-SiC composites

    NASA Technical Reports Server (NTRS)

    Lightfoot, A.; Sheldon, B. W.; Flint, J. H.; Haggerty, J. S.

    1989-01-01

    The nitriding kinetics of Si and Si plus SiC powder mixtures were studied to simulate the fabrication of RBSN-SiC ceramic matrix composites. Very clean, assynthesized, and solvent-exposed powders were studied; C-rich and Si-rich SiC 0.04-0.05 micron diameter powders were mixed in varying concentrations with SiH4-derived 0.2-0.3 micron diameter Si powder. Complete nitridation is achieved with C-rich SiC powders in 140 min at 1250 C, and in the centers of Si-rich SiC powders in 15 min. The effects on the incubation periods, fast reaction periods, and slow reaction periods that characterize these nitriding processes were studied to explain unusual reverse reaction gradients and other effects of contamination.

  19. Ag-Pd-Si (009)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/97.etType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Ag-Pd-Si (009)' with the content:

  20. Kinetics of a-Si:H bulk defect and a-Si:H/c-Si interface-state reduction

    NASA Astrophysics Data System (ADS)

    de Wolf, Stefaan; Ballif, Christophe; Kondo, Michio

    2012-03-01

    Low-temperature annealing of hydrogenated amorphous silicon (a-Si:H) is investigated. An identical energy barrier is found for the reduction of deep defects in the bulk of a-Si:H films and at the interface such layers form with crystalline Si (c-Si) surfaces. This finding gives direct physical evidence that the defects determining a-Si:H/c-Si interface recombination are silicon dangling bonds and that also kinetically this interface has no unique features compared to the a-Si:H bulk.

  1. Improving Thermomechanical Properties of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    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

  2. Atractylenolide I-mediated Notch pathway inhibition attenuates gastric cancer stem cell traits.

    PubMed

    Ma, Li; Mao, Rurong; Shen, Ke; Zheng, Yuanhong; Li, Yueqi; Liu, Jianwen; Ni, Lei

    2014-07-18

    Atractylenolide I (AT-I), one of the main naturally occurring compounds of Rhizoma Atractylodis Macrocephalae, has remarkable anti-cancer effects on various cancers. However, its effects on the treatment of gastric cancer remain unclear. Via multiple cellular and molecular approaches, we demonstrated that AT-I could potently inhibit cancer cell proliferation and induce apoptosis through inactivating Notch pathway. AT-I treatment led to the reduction of expressions of Notch1, Jagged1, and its downstream Hes1/ Hey1. Our results showed that AT-I inhibited the self-renewal capacity of gastric stem-like cells (GCSLCs) by suppression of their sphere formation capacity and cell viability. AT-I attenuated gastric cancer stem cell (GCSC) traits partly through inactivating Notch1, leading to reducing the expressions of its downstream target Hes1, Hey1 and CD44 in vitro. Collectively, our results suggest that AT-I might develop as a potential therapeutic drug for the treatment of gastric cancer.

  3. Enhancement of topoisomerase I-mediated unwinding of supercoiled DNA by the radioprotector WR-33278

    SciTech Connect

    Holwitt, E.A.; Koda, E.; Swenberg, C.E. )

    1990-10-01

    The radioprotector WR-33278, the disulfide of WR-1065 (N-(2-mercaptoethyl)-1,3-diaminopropane), is shown to stimulate eukaryotic topoisomerase I unwinding of negatively supercoiled DNA. This observation suggests the possibility that some protection may be conferred to DNA either by a decrease in its supercoiled state or by altering directly other enzymatic processes. This is the first report of a radioprotective compound stimulating an enzyme involved in DNA structure and synthesis.

  4. Atractylenolide I-mediated Notch pathway inhibition attenuates gastric cancer stem cell traits

    SciTech Connect

    Ma, Li; Mao, Rurong; Shen, Ke; Zheng, Yuanhong; Li, Yueqi; Liu, Jianwen; Ni, Lei

    2014-07-18

    Highlights: • This paper supports the anti-tumor effects of AT-I on gastric cancer in vitro. • AT-I attenuates gastric cancer stem cell traits. • It is the systematic study regarding AT-I suppression of Notch pathway in GC and GCSLCs. - Abstract: Atractylenolide I (AT-I), one of the main naturally occurring compounds of Rhizoma Atractylodis Macrocephalae, has remarkable anti-cancer effects on various cancers. However, its effects on the treatment of gastric cancer remain unclear. Via multiple cellular and molecular approaches, we demonstrated that AT-I could potently inhibit cancer cell proliferation and induce apoptosis through inactivating Notch pathway. AT-I treatment led to the reduction of expressions of Notch1, Jagged1, and its downstream Hes1/ Hey1. Our results showed that AT-I inhibited the self-renewal capacity of gastric stem-like cells (GCSLCs) by suppression of their sphere formation capacity and cell viability. AT-I attenuated gastric cancer stem cell (GCSC) traits partly through inactivating Notch1, leading to reducing the expressions of its downstream target Hes1, Hey1 and CD44 in vitro. Collectively, our results suggest that AT-I might develop as a potential therapeutic drug for the treatment of gastric cancer.

  5. Cytosolic aminopeptidases influence MHC class I-mediated antigen presentation in an allele-dependent manner.

    PubMed

    Kim, Eunkyung; Kwak, Heechun; Ahn, Kwangseog

    2009-12-01

    Antigenic peptides presented by MHC class I molecules are generated mainly by the proteasome in the cytosol. Several cytosolic aminopeptidases further trim proteasomal products to form mature epitopes or individual amino acids. However, the distinct function of cytosolic aminopeptidases in MHC class I Ag processing remains to be elucidated. In this study, we show that cytosolic aminopeptidases differentially affect the cell surface expression of MHC class I molecules in an allele-dependent manner in human cells. In HeLa cells, knockdown of puromycin-sensitive aminopeptidase (PSA) by RNA interference inhibited optimal peptide loading of MHC class I molecules, and their cell surface expression was correspondingly reduced. In contrast, depletion of bleomycin hydrolase (BH) enhanced optimal peptide loading and cell surface expression of MHC class I molecules. We did not find evidence on the effect of leucine aminopeptidase knockdown on the MHC class I Ag presentation. Moreover, we demonstrated that PSA and BH influence the peptide loading and surface expression of MHC class I in an allele-specific manner. In the absence of either PSA or BH, the surface expression and peptide-dependent stability of HLA-A68 were reduced, whereas those of HLA-B15 were enhanced. The surface expression and peptide-dependent stability of HLA-A3 were enhanced by BH knockdown, although those of HLA-B8 were increased in PSA-depleted conditions.

  6. An Introduction to the New SI

    ERIC Educational Resources Information Center

    Knotts, Sandra; Mohr, Peter J.; Phillips, William D.

    2017-01-01

    Plans are under way to redefine the International System of Units (SI) around 2018. The new SI specifies the values of certain physical constants to define units. This article explains the new SI in order to provide a resource for high school teachers as well as for advanced students already familiar with the pre-2018 SI.

  7. Crystallinity control of SiC grown on Si by sputtering method

    NASA Astrophysics Data System (ADS)

    Watanabe, Ryosuke; Tsukamoto, Takahiro; Kamisako, Koichi; Suda, Yoshiyuki

    2017-04-01

    We investigated a method of controlling the crystallinity of an n-type SiC (n-SiC) layer grown on a p-type 4°-off-axis Si(1 1 1) (p-Si) substrate by our sputtering method for use as SiC/Si devices. An n-SiC layer grown on p-Si at 810 °C exhibits columnar 3C-SiC(1 1 1) crystal growth. However, it contains many defects near the n-SiC/p-Si interface. We then propose a method in which a 10-nm-thick nondoped SiC (i-SiC) interlayer is grown at a low temperature of 640 °C prior to the growth of the n-SiC layer at 810 °C, which results in a decrease in the number of defects at the SiC/p-Si interface and an intensive increase in the crystallinity of the n-SiC, compared with that of n-SiC grown at 810 °C without the interlayer, probably via effective interlayer reconstruction and an enhancement in the crystallinity of the i-SiC interlayer itself during the n-SiC growth. Furthermore, the n-SiC/i-SiC-interlayer/p-Si structure was applied as a Si-based solar cell and the energy conversion efficiency of the n-SiC/p-Si solar cell effectively increased with the insertion of the i-SiC interlayer.

  8. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    PubMed Central

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-01-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption. PMID:27120994

  9. Revealing heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys

    NASA Astrophysics Data System (ADS)

    Li, Jiehua; Hage, Fredrik S.; Liu, Xiangfa; Ramasse, Quentin; Schumacher, Peter

    2016-04-01

    The heterogeneous nucleation of primary Si and eutectic Si can be attributed to the presence of AlP. Although P, in the form of AlP particles, is usually observed in the centre of primary Si, there is still a lack of detailed investigations on the distribution of P within primary Si and eutectic Si in hypereutectic Al-Si alloys at the atomic scale. Here, we report an atomic-scale experimental investigation on the distribution of P in hypereutectic Al-Si alloys. P, in the form of AlP particles, was observed in the centre of primary Si. However, no significant amount of P was detected within primary Si, eutectic Si and the Al matrix. Instead, P was observed at the interface between the Al matrix and eutectic Si, strongly indicating that P, in the form of AlP particles (or AlP ‘patch’ dependent on the P concentration), may have nucleated on the surface of the Al matrix and thereby enhanced the heterogeneous nucleation of eutectic Si. The present investigation reveals some novel insights into heterogeneous nucleation of primary Si and eutectic Si by AlP in hypereutectic Al-Si alloys and can be used to further develop heterogeneous nucleation mechanisms based on adsorption.

  10. Thermodynamics of Si-C-O system

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Opila, E. J.

    1993-01-01

    The Si-C-O predominance diagram, in conjunction with a free-energy minimum of the gas phase, has been used to explain several observations in the reactions of SiC and/or carbon with SiO2. In the predominance diagram, the axes are chosen as the primary activity units for carbon and oxygen. The predominance diagram shows only the stable condensed phases SiO2, SiC, carbon, and silicon. It also shows the isobars for SiO(g) and CO(g), which are the primary gas-phase species. Only the thermodynamics of the system is considered. The observations explained include the general adjustment of carbon-rich SiC to a free-energy minimum on the SiC/SiO2 coexistence line and the inability to form free silicon from SiO2 and carbon, except at very high temperatures.

  11. Construction and characterization of spherical Si solar cells combined with SiC electric power inverter

    NASA Astrophysics Data System (ADS)

    Oku, Takeo; Matsumoto, Taisuke; Hiramatsu, Kouichi; Yasuda, Masashi; Shimono, Akio; Takeda, Yoshikazu; Murozono, Mikio

    2015-02-01

    Spherical silicon (Si) photovoltaic solar cell systems combined with an electric power inverter using silicon carbide (SiC) field-effect transistor (FET) were constructed and characterized, which were compared with an ordinary Si-based converter. The SiC-FET devices were introduced in the direct current-alternating current (DC-AC) converter, which was connected with the solar panels. The spherical Si solar cells were used as the power sources, and the spherical Si panels are lighter and more flexible compared with the ordinary flat Si solar panels. Conversion efficiencies of the spherical Si solar cells were improved by using the SiC-FET.

  12. Pourous Si(x)Ge(1-x) Layers Within Single Crystals Of Si

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W.; George, Thomas

    1994-01-01

    Layers of porous Si(x)Ge(1-x) buried within single crystals of Si formed by epitaxial growth of Si/Si(x)Ge(1-x)/Si structures followed by etching in solutions of HF:HNO3:H2O. Electroluminescence from these layers utilized in novel optoelectronic devices.

  13. Long-Wavelength Stacked Si(sub 1-x)/Si Heterojunction Internal Photoemission Infrared Detectors

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; George, T.; Gunapala, S. D.

    1993-01-01

    Utilizing the low temperature silicon molecular beam epitaxy (MBE) growth of degenerately doped SiGe layers on Si, long wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Se layers have been fabricated and demonstrated.

  14. Selective Growth of Nanocrystalline 3C-SiC Thin Films on Si

    NASA Astrophysics Data System (ADS)

    Beke, D.; Pongrácz, A.; Battistig, G.; Josepovits, K.; Pécz, B.

    2010-11-01

    Epitaxial formation of SiC nanocrystals has been investigated on single crystal silicon surfaces. A simple and cheap method using reactive annealing in CO has been developed and patented by our group (BME AFT and MTA MFA). By this technique epitaxial 3C-SiC nanocrystals can be grown at the Si side of a SiO2/Si interface without void formation at the SiC/Si interface. CO diffusion and SiC nanocrystal formation on different silicon based systems (SiO2/Si, Si3N4/3Si and SiO2/LPCVD poly-Si) after CO treatment at 105 Pa at elevated temperatures (T>1000° C) will be presented. By optimizing the annealing time a thin continuous nanocrystalline SiC layer has been formed. Applying a patterned Si3N4 capping layer as a barrier layer against CO diffusion, SiC nanocrystal formation at the Si3N4/Si interface is inhibited. We will present the selective growth of SiC nanocrystals using the before mentioned technique.

  15. Optimum condition to fabricate 5-10 nm SiO2/Si structure using advanced nitric acid oxidation of Si method with Si source

    NASA Astrophysics Data System (ADS)

    Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

    2012-12-01

    A low temperature (≦120 °C) fabrication method to form relatively thick SiO2/Si structure with a Si source has been developed using the advanced nitric acid oxidation of Si (NAOS) method, and the formation mechanism has been investigated. The reaction mechanism consists of direct oxidation of Si, dissolution of Si sources, and surface reaction of the dissolved Si species. The dissolved Si species is present in HNO3 solutions as mono-silicic acid and reacts with oxidizing species formed by decomposition of HNO3 on an ultrathin SiO2 layer (i.e., 1.4 nm) produced by the direct oxidation of Si substrates with HNO3 solutions. To achieve a uniform thickness of SiO2 layer with a smooth surface, HNO3 solutions with concentrations higher than 60 wt. % are needed because the dissolved Si species polymerizes in HNO3 solutions when the concentration is below 60 wt. %, resulting in the formation of SiO2 particles in HNO3, which are deposited afterwards on the SiO2 layer. In spite of the low temperature formation at 120 °C, the electrical characteristics of the advanced NAOS SiO2 layer formed with 68 wt. % HNO3 and subsequent post-metallization anneal at 250 °C are nearly identical to those of thermal oxide formed at 900 °C.

  16. Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar

    NASA Astrophysics Data System (ADS)

    Li, L.-G.; Rubino, S.; Vallin, Ö.; Olsson, J.

    2014-02-01

    Silicon-on-silicon-carbide substrates could be ideal for high-power and radiofrequency silicon devices. Such hybrid wafers, when made by wafer bonding, contain an intermediate silicon dioxide layer with poor thermal characteristics, which can be removed by high-temperature annealing in an inert atmosphere. To understand the dynamics of this process, removal of 2.4-nm-thick SiO2 layers from Si-SiO2-Si and Si-SiO2-SiC substrates has been studied at temperatures ranging from 1100°C to 1200°C. The substrates were analyzed by transmission electron microscopy, electron energy-loss spectroscopy, secondary-ion mass spectroscopy, and ellipsometry, before and after annealing. For oxide thickness less than 2.4 nm, the activation energy for oxide removal was estimated to be 6.4 eV, being larger than the activation energy reported for removal of thicker oxides (4.1 eV). Under the same conditions, the SiO2 layer became discontinuous. In the time domain, three steps could be distinguished: bulk diffusion, bulk diffusion with void formation, and bulk diffusion with disintegration. The void formation, predominant here, has an energetic cost that could explain the larger activation energy. The oxide remaining after prolonged annealing corresponds to one layer of oxygen atoms.

  17. Mo-Si alloy development

    SciTech Connect

    Liu, C.T.; Heatherly, L.; Wright, J.L.

    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.

  18. High thermal conductivity SiC/SiC composites for fusion applications -- 2

    SciTech Connect

    Kowbel, W.; Tsou, K.T.; Withers, J.C.; Youngblood, G.E.

    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. An unirradiated SiC/SiC composite made with MER-developed CVR SiC fiber and a hybrid PIP/CVI SiC matrix exhibited room temperature transverse thermal conductivity of 45 W/mK. An unirradiated SiC/SiC composite made from C/C composite totally CVR-converted to a SiC/SiC composite exhibited transverse thermal conductivity values of 75 and 35 W/mK at 25 and 1000 C, respectively. Both types of SiC/SiC composites exhibited non-brittle failure in flexure testing.

  19. Enhancing elastic stress relaxation in SiGe/Si heterostructures by Si pillar necking

    NASA Astrophysics Data System (ADS)

    Isa, F.; Salvalaglio, M.; Arroyo Rojas Dasilva, Y.; Jung, A.; Isella, G.; Erni, R.; Timotijevic, B.; Niedermann, P.; Gröning, P.; Montalenti, F.; von Känel, H.

    2016-10-01

    We demonstrate that the elastic stress relaxation mechanism in micrometre-sized, highly mismatched heterostructures may be enhanced by employing patterned substrates in the form of necked pillars, resulting in a significant reduction of the dislocation density. Compositionally graded Si1-xGex crystals were grown by low energy plasma enhanced chemical vapour deposition, resulting in tens of micrometres tall, three-dimensional heterostructures. The patterned Si(001) substrates consist of micrometre-sized Si pillars either with the vertical {110} or isotropically under-etched sidewalls resulting in narrow necks. The structural properties of these heterostructures were investigated by defect etching and transmission electron microscopy. We show that the dislocation density, and hence the competition between elastic and plastic stress relaxation, is highly influenced by the shape of the substrate necks and their proximity to the mismatched epitaxial material. The SiGe dislocation density increases monotonically with the crystal width but is significantly reduced by the substrate under-etching. The drop in dislocation density is interpreted as a direct effect of the enhanced compliance of the under-etched Si pillars, as confirmed by the three-dimensional finite element method simulations of the elastic energy distribution.

  20. Ozone cleaning of the Si-SiO2 system

    NASA Astrophysics Data System (ADS)

    Baumgärtner, H.; Fuenzalida, V.; Eisele, I.

    1987-07-01

    The cleaning of monocrystalline silicon substrates and thin thermally grown SiO2 layers on silicon by electrochemically produced ozone has been investigated. In both cases organics are removed very effectively. In comparison with other dry cleaning methods no radiation damage occurs.

  1. Morphology Analysis of Si Island Arrays on Si(001)

    PubMed Central

    2010-01-01

    The formation of nanometer-scale islands is an important issue for bottom-up-based schemes in novel electronic, optoelectronic and magnetoelectronic devices technology. In this work, we present a detailed atomic force microscopy analysis of Si island arrays grown by molecular beam epitaxy. Recent reports have shown that self-assembled distributions of fourfold pyramid-like islands develop in 5-nm thick Si layers grown at substrate temperatures of 650 and 750°C on HF-prepared Si(001) substrates. Looking for wielding control and understanding the phenomena involved in this surface nanostructuring, we develop and apply a formalism that allows for processing large area AFM topographic images in a shot, obtaining surface orientation maps with specific information on facets population. The procedure reveals some noticeable features of these Si island arrays, e.g. a clear anisotropy of the in-plane local slope distributions. Total island volume analysis also indicates mass transport from the substrate surface to the 3D islands, a process presumably related to the presence of trenches around some of the pyramids. Results are discussed within the framework of similar island arrays in homoepitaxial and heteroepitaxial semiconductor systems. PMID:21170139

  2. Infrared Detectors Containing Stacked Si(1-x)Ge(x)/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, Jin S.; Lin, True-Lon; Jones, Eric; Del Castillo, Hector; Gunapala, Sarath

    1996-01-01

    Long-wavelength-infrared detectors containing multiple layers of high-quality crystalline p(+) Si(1-x)Ge(x) alternating with layers of Si undergoing development. Each detector comprises stack of Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) photodetectors. In comparison with older HIP detectors containing single Si(1-x)Ge(x)/Si heterojunctions, developmental detectors feature greater quantum efficiencies and stronger photoresponses.

  3. Performance improvement for epitaxially grown SiGe on Si solar cell using a compositionally graded SiGe base

    NASA Astrophysics Data System (ADS)

    Li, Dun; Zhao, Xin; Wang, Li; Conrad, Brianna; Soeriyadi, Anastasia; Lochtefeld, Anthony; Gerger, Andrew; Perez-Wurfl, Ivan; Barnett, Allen

    2016-12-01

    Silicon germanium (SiGe) is a material with high mobility and relatively low bandgap making it an attractive candidate for the bottom subcell in a III-V tandem solar cell grown on silicon (Si) substrate. This paper reports on the performance improvement of an epitaxially grown SiGe on Si solar cell by growing a higher Ge composition SiGe layer in the base. The purpose of growing a higher Ge composition SiGe layer in the base is to improve the light absorption. The first iteration of this structure was an Si0.18Ge0.82 solar cell fabricated with a 1 μm thick Si0.12Ge0.88 layer in the base. This solar cell had a lower efficiency compared with the reference solar cell without the Si0.12Ge0.88 layer. One of the main reasons for the lower efficiency is believed to be the high threading dislocation density (TDD) caused by the abrupt change of lattice constant between Si0.18Ge0.82 and Si0.12Ge0.88 in the base. In order to reduce the TDD, the second iteration of the structure was fabricated with a compositionally graded SiGe base. With the new structure, an SiGe on Si solar cell with an efficiency of 3.1%, when filtered by a GaAs0.79P0.21 top cell, was fabricated. The Ge composition in the base of this solar cell gradually increased from 82% to 85% and then decreased again to 82%. The developed SiGe solar cell with graded base provides more flexibility for a highly efficient GaAsP/SiGe dual junction solar cell grown on an Si substrate.

  4. Microwave joining of SiC

    SciTech Connect

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

    1997-04-01

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

  5. The Use of SI Units.

    ERIC Educational Resources Information Center

    British Standards Institution, London (England).

    This booklet (referred to as PD 5686:1969) replaces the 1967 edition by including subsequent recommendations of the International Organization for Standardization (ISO) and the General Conference on Weights and Measures (CGPM). The International System of Units (SI) is described and rules are given for the formation of derived units and decimal…

  6. A Si Integrated Waveguiding Polarimeter

    NASA Astrophysics Data System (ADS)

    Kevorkian, A. P.

    1987-09-01

    The technology and characteristics of a silicon-based polarimeter are presented. This device features guided mode polarization splitting, non-taper solution for guided light detection and electronic signal processing. The overall fabrication process is fully compatible with standard Si technology.

  7. Interactions of Cu with CoSi2, CrSi2 and TiSi2 with and without TiNx barrier layers

    NASA Astrophysics Data System (ADS)

    Olowolafe, J. O.; Li, Jian; Mayer, J. W.

    1990-12-01

    Interactions of Cu with CoSi2, CrSi2, and TiSi2 with and without interposed TiNx layers have been studied using Rutherford backscattering spectrometry, Auger electron spectrometry, x-ray diffraction, and in situ sheet resistivity measurements. Cu diffuses through a preformed CoSi2 layer to form the structure CoSi2/Cu3Si/Si(100). No dissociation of CoSi2 has been observed. For the Cu/CrSi2/Si system, the outdiffusion of Si leads to the formation of Cu3Si/CrSi2/Si at temperatures above 300 °C. At about the same temperature, Cu diffuses into a TiSi2 layer and to the TiSi2/Si interface to react with both Ti and Si forming Cu3Ti, Cu3Si, and Cu4Si phases. A 50-nm TiNx layer prepared by reactive sputtering was observed to be an effective diffusion barrier between Cu and CoSi2 or CrSi2. A 30-nm layer of TiNx simultaneously grown with TiSi2 by rapid thermal annealing proved effective between Cu and TiSi2 up to 500 °C.

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

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira; Katoh, Yutai; Hasegawa, Akira; Snead, L.; 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.

  9. Electronic structure of Si vacancy centers in SiC

    NASA Astrophysics Data System (ADS)

    Soykal, Oney; Dev, Pratibha; Economou, Sophia

    2015-03-01

    The spin state of silicon vacancies in SiC is a promising candidate for applications in solid state quantum information technologies due to its long coherence time at room temperature, its technological availability and wide range of polytypism. Until recently, the electronic structure of this vacancy was not well understood. We have developed a group theoretical model that correctly predicts the spin 3/2 structure seen in recent experiments for the 4H-SiC defect. We have included several different mechanisms involved in the mixing of its spin states, such as crystal field splitting, spin-orbit coupling, spin-spin coupling, strain and Jahn-Teller interactions. We have also carried out DFT calculations that support and complement our analytical results.

  10. Si(1-x)Ge(x)/Si Infrared Photodiodes

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon

    1991-01-01

    Cutoff wavelengths depend on x and also adjusted somewhat via reverse bias. Si1-xGex photodiodes with cutoff wavelengths in and beyond practically important range of 8 to 12 micrometers made by molecular-beam epitaxy. Compatible (in terms of fabrication processes) with silicon readout circuitry, exhibit long-term stability, manufactured with sufficient uniformity for use in focal-plane arrays; and operate at temperatures approximately greater than 65 K, for which temperatures small, portable refrigerators available.

  11. High Refractive Index Si/SiOx Based Nanocomposites

    DTIC Science & Technology

    2000-01-01

    also provide the means for performing chemistry, in the presence of oxidizing agents such as benzoyl peroxide or 3- 328 chloroperbenzoic acid.[32,33...A small amount of benzoyl peroxide (1.79x10" 4 M) was found to produce the optimum results in terms of concentration of Si nanoparticles. Scheme 1...benzoylethyl ester and tetraethoxysilane (TEOS), along with unreacted benzoyl peroxide indicate that sonication can provide considerable amount of

  12. In situ control of atomic-scale Si layer with huge strain in the nanoheterostructure NiSi/Si/NiSi through point contact reaction.

    PubMed

    Lu, Kuo-Chang; Wu, Wen-Wei; Wu, Han-Wei; Tanner, Carey M; Chang, Jane P; Chen, Lih J; Tu, K N

    2007-08-01

    Nanoheterostructures of NiSi/Si/NiSi in which the length of the Si region can be controlled down to 2 nm have been produced using in situ point contact reaction between Si and Ni nanowires in an ultrahigh vacuum transmission electron microscope. The Si region was found to be highly strained (more than 12%). The strain increases with the decreasing Si layer thickness and can be controlled by varying the heating temperature. It was observed that the Si nanowire is transformed into a bamboo-type grain of single-crystal NiSi from both ends following the path with low-activation energy. We propose the reaction is assisted by interstitial diffusion of Ni atoms within the Si nanowire and is limited by the rate of dissolution of Ni into Si at the point contact interface. The rate of incorporation of Ni atoms to support the growth of NiSi has been measured to be 7 x 10(-4) s per Ni atom. The nanoscale epitaxial growth rate of single-crystal NiSi has been measured using high-resolution lattice-imaging videos. On the basis of the rate, we can control the consumption of Si and, in turn, the dimensions of the nanoheterostructure down to less than 2 nm, thereby far exceeding the limit of conventional patterning process. The controlled huge strain in the controlled atomic scale Si region, potential gate of Si nanowire-based transistors, is expected to significantly impact the performance of electronic devices.

  13. Si clusters are more metallic than bulk Si

    NASA Astrophysics Data System (ADS)

    Jackson, Koblar; Jellinek, Julius

    2016-12-01

    Dipole polarizabilities were computed using density functional theory for silicon clusters over a broad range of sizes up to N = 147 atoms. The calculated total effective polarizabilities, which include contributions from permanent dipole moments of the clusters, are in very good agreement with recently measured values. We show that the permanent dipole contributions are most important for clusters in the intermediate size range and that the measured polarizabilities can be used to distinguish between energetically nearly degenerate cluster isomers at these sizes. We decompose the computed total polarizabilities α into the so-called dipole and charge transfer contributions, αp and αq, using a site-specific analysis. When the per-atom values of these quantities are plotted against N-1 /3, clear linear trends emerge that can be extrapolated to the large size limit (N-1 /3→0 ), resulting in a value for α/N of 30.5 bohrs3/atom that is significantly larger than the per-atom polarizability of semiconducting bulk Si, 25.04 bohrs3/atom. This indicates that Si clusters possess a higher degree of metallicity than bulk Si, a conclusion that is consistent with the strong electrostatic screening of the cluster interiors made evident by the analysis of the calculated atomic polarizabilities.

  14. Microwave joining of SiC

    SciTech Connect

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

    1995-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  16. Si@SiOx/graphene hydrogel composite anode for lithium-ion battery

    NASA Astrophysics Data System (ADS)

    Bai, Xuejun; Yu, Yueyang; Kung, Harold H.; Wang, Biao; Jiang, Jianming

    2016-02-01

    A porous 3D graphene hydrogel (GH) composite embedded with Si nanoparticles coated with an ultrathin SiOx layer (Si@SiOx/GH) is successfully synthesized using a solution-based self-assembly process. The thickness of the SiOx coating, formed by an ozone treatment of the 30-50 nm diameter Si particles, increases with the treatment temperature, and its formation results in the presence of Si2+ and Si4+ on the surface of the Si nanoparticles. The GH provides an electrically conducting network of interconnecting, micron-size open cells bounded by ultrathin stacked graphene sheets onto which the coated Si nanoparticles are dispersed. The agglomeration among the Si particles decreases with increasing extent of surface oxidation. Electrodes constructed with the Si@SiOx/GH containing 71 wt.% Si@SiOx exhibit a stable storage capacity of 1020 mAh g-1 at 4 A g-1 and 1640 mAh g-1 after 140 cycles at 0.1 A g-1. The outstanding electrochemical performance can be attributed to the porous, open cell 3D structure of GH, which provides a large internal space and flexible and electrically conductive graphenic matrix that can accommodate volumetric changes of Si nanoparticles and a highly porous 3D structure of high specific surface area that allows rapid diffusion of Li-ions and easy penetration of electrolyte.

  17. Location and Electronic Nature of Phosphorus in the Si Nanocrystal − SiO2 System

    PubMed Central

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

    2015-01-01

    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. PMID:25997696

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

    PubMed

    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.

  19. Absence of quantum confinement effects in the photoluminescence of Si3N4-embedded Si nanocrystals

    NASA Astrophysics Data System (ADS)

    Hiller, D.; Zelenina, A.; Gutsch, S.; Dyakov, S. A.; López-Conesa, L.; López-Vidrier, J.; Estradé, S.; Peiró, F.; Garrido, B.; Valenta, J.; Kořínek, M.; Trojánek, F.; Malý, P.; Schnabel, M.; Weiss, C.; Janz, S.; Zacharias, M.

    2014-05-01

    Superlattices of Si-rich silicon nitride and Si3N4 are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 °C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si3N4. Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 105 times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si3N4 reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si3N4 band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si3N4 interface defect literature. In addition, the role of Si3N4 valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si3N4-embedded Si NCs are suggested.

  20. Characterization of Si Nanostructured Surfaces

    SciTech Connect

    Brueck, S.R.J.; Gee, James M.; Ruby, Douglas S.; Zaidi, Saleem H.

    1999-07-20

    Surface texturing of Si to enhance absorption particularly in the IR spectral region has been extensively investigated. Previous research chiefly examined approaches based on geometrical optics. These surface textures typically consist of pyramids with dimensions much larger than optical wavelengths. We have investigated a physical optics approach that relies on surface texture features comparable to, or smaller than, the optical wavelengths inside the semiconductor material. Light interaction at this are strongly dependent on incident polarization and surface profile. Nanoscale textures can be tuned for either narrow band, or broad band absorptive behavior. Lowest broadband reflection has been observed for triangular profiles with linewidths significantly less than 100 nm. Si nanostructures have been integrated into large ({approximately}42 cm{sup 2}) area solar cells, Internal quantum efficiency measurements in comparison with polished and conventionally textured cells show lower efficiency in the UV-visible (350-680 mu), but significantly higher IR (700-1200 nm) efficiency.

  1. Very fast light-induced degradation of a-Si:H/c-Si(100) interfaces

    NASA Astrophysics Data System (ADS)

    de Wolf, Stefaan; Demaurex, Bénédicte; Descoeudres, Antoine; Ballif, Christophe

    2011-06-01

    Light-induced degradation (LID) of crystalline silicon (c-Si) surfaces passivated with hydrogenated amorphous silicon (a-Si:H) is investigated. The initial passivation decays on polished c-Si(100) surfaces on a time scale much faster than usually associated with bulk a-Si:H LID. This phenomenon is absent for the a-Si:H/c-Si(111) interface. We attribute these differences to the allowed reconstructions on the respective surfaces. This may point to a link between the presence of so-called “fast” states and (internal) surface reconstruction in bulk a-Si:H.

  2. Columnar growth of CoSi2 on Si(111), Si(100) and Si(110) by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Codeposition of silicon and cobalt on heated silicon substrates in ratios several times the silicide stoichiometry is found to result in epitaxial columns of CoSi2 surrounded by a matrix of epitaxial silicon. For (111)-oriented wafers, nearly cylindrical columns are formed, where both columns and surrounding silicon are defect free, as deduced from transmission electron microscopy. Independent control of the column diameter and separation is possible, and diameters of 27-135 nm have been demonstrated.

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

    SciTech Connect

    Ping Wang, Y. 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.; Stodolna, J.; Ponchet, A.; Bahri, M.; Largeau, L.; Patriarche, G.; Magen, C.

    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.

  4. Observations of Si field evaporation.

    PubMed

    Thompson, Keith; Sebastian, Jason; Gerstl, Stephan

    2007-01-01

    Field evaporation studies of crystalline <100> Si were performed in a three-dimensional atom-probe, which utilized a local electrode geometry. Several distinct phenomena were observed. Si field evaporation rates showed: (1) no measurable dependence on temperature below 110K, (2) an exponential dependence on evaporation rate as a function of temperature above 110K, and (3) no dependence on substrate doping (i.e., electrical conductivity) as high as 10 Omega cm in the temperature range of 40-150K. Two distinct evaporation modes were observed. The first was associated with approximately 1at% H+ in the mass spectrum. Negligible amounts of H were detected in the mass spectra of the second mode. When the pulse fraction (pf) was increased from 5% to 30%, the presence of H+ in the mass spectra, i.e. operation in the first mode, was associated with a degradation in mass resolution by as much as 80% for the 10 Omega cm Si samples. Conversely, no loss in mass resolution was detected for the approximately 0.001 Omega cm samples over the pf range studied.

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

    SciTech Connect

    Hasanah, Lilik Suhendi, Endi; Tayubi, Yuyu Rahmat; Yuwono, Heru; Nandiyanto, Asep Bayu Dani; Murakami, Hideki; Khairrurijal

    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.

  6. Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  7. PtSi/Si LWIR Detectors Made With p+ Doping Spikes

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Park, Jin S.; George, Thomas; Fathauer, Robert W.; Jones, Eric W.; Maserjian, Joseph

    1996-01-01

    PtSi/Si Schottky-barrier devices detecting long-wavelength infrared (LWIR) photons demonstrated. Essential feature of one of these devices is p+ "doping spike"; layer of Si about 10 Angstrom thick, located at PtSi/Si interface, and doped with electron acceptors (boron atoms) at concentration between 5 x 10(19) and 2 x 10(20) cm(-3). Doping spikes extend cutoff wavelengths of devices to greater values than otherwise possible.

  8. GeSi photonics for telecommunication applications

    NASA Astrophysics Data System (ADS)

    Chaisakul, Papichaya; Vakarin, Vladyslav; Marris-Morini, Delphine; Frigerio, Jacopo; Wada, Kazumi; Isella, Giovanni; Vivien, Laurent

    2014-11-01

    We experimentally and theoretically investigate GeSi-based photonics for future on-chip optical interconnect on bulk Silicon substrates with dense wavelength division multiplexing (WDM) system. We experimentally show that Ge-rich Si1-xGex can be used as both a passive low loss waveguide and a substrate to facilitate low-temperature epitaxial growth of Ge-based active devices working at low optical loss wavelength of Ge-rich Si1-xGex waveguides. We also theoretically discussed the possibilities to realize a compact passive component based on Ge-rich Si1-xGex material system on bulk Si wafer. From simulation the system based on Ge-rich Si1-xGex waveguide and the Si1-yGey (y < x) lower cladding layer is good enough to ensure compactness of important on-chip photonic components including passive waveguide and GeSi-based array waveguide grating (AWG). The small refractive index contrast between Ge-rich Si1-xGex waveguide and the Si1-yGey lower cladding layer potentially avoid the polarization dependent loss and detrimental fabrication tolerance of WDM system. Our studies show that GeSi-based photonics could uniquely provide both passive and active functionalities for dense WDM system.

  9. Atomistic study of the structural and electronic properties of a-Si:H/c-Si interfaces.

    PubMed

    Santos, Iván; Cazzaniga, Marco; Onida, Giovanni; Colombo, Luciano

    2014-03-05

    We investigate the structural and electronic properties of the interface between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) by combining tight-binding molecular dynamics and DFT ab initio electronic structure calculations. We focus on the c-Si(100)(1×1)/a-Si:H, c-Si(100)(2×1)/a-Si:H and c-Si(111)/a-Si:H interfaces, due to their technological relevance. The analysis of atomic rearrangements induced at the interface by the interaction between H and Si allowed us to identify the relevant steps that lead to the transformation from c-Si(100)(1×1)/a-Si:H to c-Si(100)(2×1)/a-Si:H. The interface electronic structure is found to be characterized by spatially localized mid-gap states. Through them we have identified the relevant atomic structures responsible for the interface defect states, namely: dangling-bonds, H bridges, and strained bonds. Our analysis contributes to a better understanding of the role of such defects in c-Si/a-Si:H interfaces.

  10. The Schottky barrier modulation at PtSi/Si interface by strain and structural deformation

    SciTech Connect

    Srivastava, Pooja; Lee, Kwang-Ryeol; Mizuseki, Hiroshi; Kim, Seungchul; Shin, Mincheol

    2015-08-15

    We show, using density functional theory (DFT) calculations, that the Schottky barrier height (SBH) at the PtSi/Si interface can be lowered by uniaxial strain applied not only on Si but also on PtSi. The strain was applied to the (001) direction of Si and PtSi, which is normal for the interface. The SBH of the hole is lowered by 0.08 eV under 2% of tensile strain on Si and by 0.09 eV under 4 % of compressive strain on PtSi. Because the SBH at PtSi/Si contact is approximately 0.2 eV, this amount of reduction can significantly lower the resistance of the PtSi/Si contact; thus applying uniaxial strain on both PtSi and Si possibly enhances the performance of Schottky barrier field effect transistors. Theoretical models of SB formation and conventional structure model are evaluated. It is found that Pt penetration into Si stabilizes the interface and lowers the SBH by approximately 0.1 eV from the bulk-terminated interface model, which implies that conventionally used bulk-terminated interface models have significant errors. Among the theoretical models of SB formation, the model of strong Fermi level pining adequately explains the electron transfer phenomena and SBH, but it has limited ability to explain SBH changes induced by changes of interface structure.

  11. Development of SiAlON materials

    NASA Technical Reports Server (NTRS)

    Layden, G. K.

    1979-01-01

    Cold pressing and sintering techniques were used to produce ceramic test specimens in which the major phase was either Si3N4 or a solid solution having the beta Si3N4 structure. Additional components were incorporated to promote liquid phase sintering. Glass and/or crystalline phase were consequently retained in boundaries between Si3N4 grains which largely determined the physical properties of the bodies. Systems investigated most extensively included R-Si-Al-O-N (R = rare earth element) Zr-Si-Al-O-N, Y-Si-Be-O-N, and R1-R2-Si-O-N. Room temperature and 1370 C modulus of ruptured, 1370 C creep, and oxidation behavior are discussed in terms of phase relationships in a parent quinery, and relavent oxide systems.

  12. Differential cross sections measurement of 28Si(p,p/γ)28Si and 29Si(p,p/γ)29Si reactions for PIGE applications

    NASA Astrophysics Data System (ADS)

    Jokar, A.; Kakuee, O.; Lamehi-Rachti, M.

    2016-03-01

    Differential cross sections for gamma-ray emission from the 28Si(p,p/γ)28Si (Eγ = 1779 keV) and the 29Si(p,p/γ)29Si (Eγ = 1273 keV) nuclear reactions were measured in the energy range of 2.0-3.2 MeV and 2.0-3.0 MeV, respectively. The thin Si targets were prepared by evaporating natural SiO onto self-supporting Ag films. The gamma-rays and backscattered protons were detected simultaneously. An HPGe detector placed at an angle of 90° with respect to beam direction was employed to collect gamma-rays while an ion implanted Si detector placed at a scattering angle of 165° was used to detect backscattered protons. The great advantage of this work is that differential cross sections were obtained with a procedure irrespective of absolute value of the collected beam charge.

  13. High temperature compounds for turbine vanes. [of SiC, Si3N4, and Si composites

    NASA Technical Reports Server (NTRS)

    Rhodes, W. H.; Cannon, R. M., Jr.

    1974-01-01

    Fabrication and microstructure control studies were conducted on SiC, Si3N and composites based on Si3N. Charpy mode impact testing to 2400 F established that Si3N4/Mo composites have excellent potential. Attempts to fabricate composites of Si3N4 with superalloys, both by hot pressing and infiltration were largely unsuccessful in comparison to using Mo, Re, and Ta which are less reactive. Modest improvements in impact strength were realized for monolithic Si3N4; however, SiC strengths increased by a factor of six and now equal values achieved for Si3N4. Correlations of impact strength with material properties are discussed. Reduced MgO densification aid additions to Si3N4 were found to decrease densification kinetics, increase final porosity, decrease room temperature bend strength, increase high temperature bend strength, and decrease bend stress rupture properties. The decrease in bend strength at high temperature for fine grain size SiC suggested that a slightly larger grain size material with a nearly constant strength-temperature relation may prove desirable in the creep and stress rupture mode.

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  15. Magnetic ordering of YPd2Si-type HoNi2Si and ErNi2Si compounds

    NASA Astrophysics Data System (ADS)

    Morozkin, A. V.; Isnard, O.; Nirmala, R.; Quezado, S.; Malik, S. K.

    2016-12-01

    Magnetic properties of YPd2Si-type HoNi2Si and ErNi2Si were investigated via neutron diffraction and magnetisation measurements. HoNi2Si and ErNi2Si show ferromagnetic-like ordering at TC of 9 K and 7 K, respectively. The paramagnetic Weiss temperatures are 9 K and 11 K and the effective magnetic moments are 10.76 μB/fu and 9.79 μB/fu for HoNi2Si and ErNi2Si compounds, respectively. The HoNi2Si and ErNi2Si are soft ferromagnets with saturation magnetization of 8.1 μB/fu and 7.5 μB/fu, respectively at 2 K and in field of 140 kOe. The isothermal magnetic entropy change, ΔSm, has a maximum value of -15.6 J/kg·K at 10 K for HoNi2Si and -13.9 J/kg·K at 6 K for ErNi2Si for a field change of 50 kOe. Neutron diffraction study in zero applied field shows mixed ferromagnetic-antiferromagnetic ordering of HoNi2Si at 9 K and its magnetic structure is a sum of a-axis ferromagnetic Fa, b-axis antiferromagnetic AFb and c-axis antiferrromagnetic AFc components of Pn‧a21‧={1, mx‧/[1/2, 1/2, 1/2], 2y‧/[0, 1/2, 0], mz/[1/2, 0, 1/2]} magnetic space group and propagation vector K0=[0, 0, 0]. The holmium magnetic moment reaches a value of 9.23(9) μB at 1.5 K and the unit cell of HoNi2Si undergoes isotropic contraction around the temperature of magnetic transition.

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

    SciTech Connect

    Halverson, H.; Curtin, W.A.

    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.

  17. Similarity of Stranski-Krastanow growth of Ge/Si and SiGe/Si (001)

    SciTech Connect

    Norris, D. J.; Qiu, Y.; Walther, T.; Dobbie, A.; Myronov, M.

    2014-01-07

    This study investigates the onset of islanding (Stranski-Krastanow transition) in strained pure germanium (Ge) and dilute silicon-germanium (SiGe) alloy layers grown by chemical vapour deposition on Si(001) substrates. Integration of compositional profiles is compared to a novel method for quantification of X-ray maps acquired in cross-sectional scanning transmission electron microscopy, together with simulations of surface segregation of Ge. We show that Si{sub 1−x}Ge{sub x} alloys for germanium concentrations x ≤ 0.27 grow two-dimensionally and stay flat up to considerable layer thicknesses, while layers with concentrations in the range 0.28 < x ≤ 1 form islands after deposition of ∼3.0/x monolayers (=quarter unit cells in the diamond lattice, ML). The uncertainty in the amount of deposited material for pure Ge is ±(0.2–0.3) ML. Modelling shows that of the amount of germanium deposited, 0.7 ML segregate towards the free surface so that only ∼2.3/x ML are directly incorporated in the layer within a few nanometres, in good agreement with our measurements. For pure Ge (x = 1), this thickness is smaller than most values quoted in the literature, which we attribute to the high sensitivity of our method to fractional monolayer changes in the effective chemical width of such thin layers.

  18. Electron impact collision strengths in Si IX, Si X, and Si XI

    SciTech Connect

    Liang Guiyun; Zhao Gang . E-mail: gzhao@bao.ac.cn; Zeng Jiaolong

    2007-05-15

    Electron impact collision strengths among 560 levels of Si IX, 320 levels of Si X, and 350 levels of Si XI have been calculated using the Flexible Atomic Code of Gu [M.F. Gu, Astrophys. J. 582 (2003) 1241]. Collision strengths {omega} at 10 scattered electron energies, namely 10, 50, 100, 200, 400, 600, 800, 1000, 1500, and 2000 eV, are reported. Assuming a Maxwellian energy distribution, effective collision strengths Y are obtained on a finer electron temperature grid of 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 MK, which covers the typical temperature range of astrophysical hot plasmas. Additionally, radiative rates A and weighted oscillator strengths gf are given for the more probable transitions among these levels. Comparisons of our results with available predictions reported in earlier literature are made and the accuracy of the data is assessed. Most transitions exhibit a good agreement, but large differences in gf appear for a few cases, which are due to the different configuration interactions included in different theoretical calculations. For excitations among levels of the ground and lower excited configurations, large discrepancies of Y may have resulted from the consideration of resonance effects in earlier works.

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

    PubMed

    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.

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

    DOEpatents

    Liliental-Weber, Zuzanna; Maltez, Rogerio Luis; Morkoc, Hadis; Xie, Jinqiao

    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.

  1. Fusion of Si28+Si28,30: Different trends at sub-barrier energies

    NASA Astrophysics Data System (ADS)

    Montagnoli, G.; Stefanini, A. M.; Esbensen, H.; Jiang, C. L.; Corradi, L.; Courtin, S.; Fioretto, E.; Grebosz, J.; Haas, F.; Jia, H. M.; Mazzocco, M.; Michelagnoli, C.; Mijatović, T.; Montanari, D.; Parascandolo, C.; Scarlassara, F.; Strano, E.; Szilner, S.; Torresi, D.

    2014-10-01

    Background: The fusion excitation function of the system Si28+Si28 at energies near and below the Coulomb barrier is known only down to ≃15 mb. This precludes any information on both coupling effects on sub-barrier cross sections and the possible appearance of hindrance. For Si28+Si30 even if the fusion cross section is measured down to ≃50 μb, the evidence of hindrance is marginal. Both systems have positive fusion Q values. While Si28 has a deformed oblate shape, Si30 is spherical. Purpose: We investigate 1. the possible influence of the different structure of the two Si isotopes on the fusion excitation functions in the deep sub-barrier region and 2. whether hindrance exists in the Si+Si systems and whether it is strong enough to generate an S-factor maximum, thus allowing a comparison with lighter heavy-ion systems of astrophysical interest. Methods: Si28 beams from the XTU Tandem accelerator of the INFN Laboratori Nazionali di Legnaro were used. The setup was based on an electrostatic beam separator, and fusion evaporation residues (ER) were detected at very forward angles. Angular distributions of ER were measured. Results: Fusion cross sections of Si28+Si28 have been obtained down to ≃600 nb. The slope of the excitation function has a clear irregularity below the barrier, but no indication of a S-factor maximum is found. For Si28+Si30 the previous data have been confirmed and two smaller cross sections have been measured down to ≃4 μb. The trend of the S-factor reinforces the previous weak evidence of hindrance. Conclusions: The sub-barrier cross sections for Si28+Si28 are overestimated by coupled-channels calculations based on a standard Woods-Saxon potential, except for the lowest energies. Calculations using the M3Y+repulsion potential are adjusted to fit the Si28+Si28 and the existing Si30+Si30 data. An additional weak imaginary potential (probably simulating the effect of the oblate Si28 deformation) is required to fit the low-energy trend of

  2. Microstructures and Properties of Ti-Coated SiCp Reinforced Al-Si Alloy Composites

    NASA Astrophysics Data System (ADS)

    Feng, Yan; Ren, Junpeng; Dong, Cuige; Wang, Richu

    2016-12-01

    A double-layer structure of Ti coating was plated on the surface of SiC particles using a diffusion method in a vacuum reactor, which is a new method to fabricate a Ti-coating layer on the SiC particles. The phase structure of Ti coating on the surface of SiC particles was composed inside of Ti5Si3 and outside of TiC investigated by x-ray diffraction. The Ti5Si3 and TiC double-layer structure realizes the tight chemical bonding between SiC particles and the Ti coating, and significantly promotes the wettability between the aluminum matrix and the Ti-coated SiC particles. The Ti-coated SiCp-reinforced Al-Si composites are prepared by a powder metallurgy method, and express excellent relative densities, desirable mechanical properties and frictional wear resistance.

  3. Catalytic oxidation of (001)Si in the presence of Cu3Si at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, C. S.; Chen, L. J.

    1993-09-01

    Room temperature oxidation of (001)Si catalyzed by Cu3Si has been investigated by transmission electron microscopy (TEM) and x-ray diffractometry (XRD). For η`-Cu3Si thin layer on (001)Si, XRD analysis showed that volume fractions η`-Cu3Si and Cu decrease and increase with the exposure time in air, respectively. TEM revealed the presence of a high density of Cu precipitates in the SiO2 layer. After prolonged exposure in air, the Cu precipitates were observed to form an irregular network. The thickness of starting Cu, hence Cu3Si, layer on silicon was found to be a critical factor in determining the oxidation behavior. Based on the microstructural evolution data, a partial reconstitution of catalytic Cu3Si mechanism is proposed to be the dominant process for the room-temperature oxidation of silicon catalyzed by Cu3Si.

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

    PubMed

    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.

  5. Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    George, T.; Fathauer, R. W.

    1992-01-01

    The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

  6. First-principles study of the interfacial adhesion between Si O2 and Mo Si2

    NASA Astrophysics Data System (ADS)

    Jiang, D. E.; Carter, Emily A.

    2005-10-01

    Upon oxidation, a silica scale forms on MoSi2 , a potential high-temperature coating material for metals. This silica scale protects MoSi2 against high-temperature corrosive gases or liquids. We use periodic density functional theory to examine the interface between SiO2 and MoSi2 . The interfacial bonding is localized, as evidenced by an adhesion energy that changes only slightly with the thickness of the SiO2 layer. Moreover, the adhesion energy displays a relatively large (0.40J/m2) variation with the relative lateral position of the SiO2 and MoSi2 lattices due to changes in Si-O bonding across the interface. The most stable interfacial structure yields an ideal work of adhesion of 5.75J/m2 within the local density approximation ( 5.02J/m2 within the generalized-gradient approximation) to electron exchange and correlation, indicating extremely strong adhesion. Local densities of states and electron density difference plots demonstrate that the interfacial Si-O bonds are covalent in character. Mo-O interactions are not found in the SiO2/MoSi2 interface investigated here. Our work predicts that the SiO2 scale strongly adheres to MoSi2 , and further supports the potential of MoSi2 as a high-temperature structural material and coating.

  7. Lateral Ge Diffusion During Oxidation of Si/SiGe Fins.

    PubMed

    Brewer, William M; Xin, Yan; Hatem, C; Diercks, D; Truong, V Q; Jones, K S

    2017-04-12

    This Letter reports on the unusual diffusion behavior of Ge during oxidation of a multilayer Si/SiGe fin. It is observed that oxidation surprisingly results in the formation of vertically stacked Si nanowires encapsulated in defect free epitaxial strained SixGe1-x. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that extremely enhanced diffusion of Ge occurs along the vertical Si/SiO2 oxidizing interface and is responsible for the encapsulation process. Further oxidation fully encapsulates the Si layers in defect free single crystal SixGe1-x (x up to 0.53), which results in Si nanowires with up to -2% strain. Atom probe tomography reconstructions demonstrate that the resultant nanowires run the length of the fin. We found that the oxidation temperature plays a significant role in the formation of the Si nanowires. In the process range of 800-900 °C, pure strained and rounded Si nanowires down to 2 nm in diameter can be fabricated. At lower temperatures, the Ge diffusion along the oxidizing Si/SiO2 interface is slow, and rounding of the nanowire does not occur, while at higher temperatures, the diffusivity of Ge into Si is sufficient to result in dilution of the pure Si nanowire with Ge. The use of highly selective etchants to remove the SiGe could provide a new pathway for the creation of highly controlled vertically stacked nanowires for gate all around transistors.

  8. Oxidation Embrittlement Observed in SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.

    1997-01-01

    As part of a comprehensive materials characterization program at the NASA Lewis Research Center, tensile creep-rupture tests were performed on a SiC-fiber-reinforced SiC-matrix composite. The results of these tests and subsequent analysis revealed an oxidation embrittlement phenomena that occurs readily at a discreet temperature range below the maximum use temperature. The graph shows rupture lives for a creep stress of 83 MPa as a function of temperature. Note that the rupture time is constant at an intermediate temperature range of 700 to 982 C. This graph also shows the failure location, as measured from the center of the specimen. Whereas for temperatures of 500 to 700 C, failure occurred in the specimen gage section; at higher temperatures, the failure location migrated toward the cooled grip ends. Although the results initially suggested that the test procedure was influencing the measured creep rupture lives and driving the failure location out of the gage section, subsequent experiments and thermal stress analyses verified the robustness of the test method employed.

  9. Airborne Emissions from Si/FeSi Production

    NASA Astrophysics Data System (ADS)

    Kero, Ida; Grådahl, Svend; Tranell, Gabriella

    2017-02-01

    The management of airborne emissions from silicon and ferrosilicon production is, in many ways, similar to the management of airborne emissions from other metallurgical industries, but certain challenges are highly branch-specific, for example the dust types generated and the management of NO X emissions by furnace design and operation. A major difficulty in the mission to reduce emissions is that information about emission types and sources as well as abatement and measurement methods is often scarce, incomplete and scattered. The sheer diversity and complexity of the subject presents a hurdle, especially for new professionals in the field. This article focuses on the airborne emissions from Si and FeSi production, including greenhouse gases, nitrogen oxides, airborne particulate matter also known as dust, polyaromatic hydrocarbons and heavy metals. The aim is to summarize current knowledge in a state-of-the-art overview intended to introduce fresh industry engineers and academic researchers to the technological aspects relevant to the reduction of airborne emissions.

  10. Impact Resistance of Uncoated SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    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.

  11. Electron mobility enhancement in epitaxial multilayer Si-Si/1-x/Ge/x/ alloy films on /100/Si

    NASA Technical Reports Server (NTRS)

    Manasevit, H. M.; Gergis, I. S.; Jones, A. B.

    1982-01-01

    Enhanced Hall-effect mobilities have been measured in epitaxial (100)-oriented multilayer n-type Si/Si(1-x)Ge(x) films grown on single-crystal Si substrates by chemical vapor deposition. Mobilities from 20 to 40% higher than that of epitaxial Si layers and about 100% higher than that of epitaxial SiGe layers on Si were measured for the doping range 8 x 10 to the 15th to 10 to the 17th/cu cm. No mobility enhancement was observed in multilayer p-type (100) films and n-type (111)-oriented films. Experimental studies included the effects upon film properties of layer composition, total film thickness, doping concentrations, layer thickness, and growth temperature.

  12. Resonance Raman mapping as a tool to monitor and manipulate Si nanocrystals in Si-SiO{sub 2} nanocomposite

    SciTech Connect

    Rani, Ekta; Ingale, Alka A.; Chaturvedi, A.; Joshi, M. P.; Kukreja, L. M.

    2015-10-19

    Specially designed laser heating experiment along with Raman mapping on Si-SiO{sub 2} nanocomposites elucidates the contribution of core and surface/interface in the intermediate frequency range (511–514 cm{sup −1}) Si phonons. The contribution of core to surface/interface increases with the size of Si nanocrystal, which itself increases on laser irradiation. Further, it is found that resonance Raman is crucial to the observance of surface/interface phonons and wavelength dependent Raman mapping can be corroborated with band edges observed in absorption spectra. This understanding can be gainfully used to manipulate and characterize Si-SiO{sub 2} nanocomposite, simultaneously for photovoltaic device applications.

  13. Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

    SciTech Connect

    Jiang, Xiaofan; Ma, Zhongyuan Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

    2014-09-28

    Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

  14. Solution plasma synthesis of Si nanoparticles

    NASA Astrophysics Data System (ADS)

    Saito, Genki; Sakaguchi, Norihito

    2015-06-01

    Silicon nanoparticles (Si-NPs) were directly synthesized from a Si bar electrode via a solution plasma. In order to produce smaller Si-NPs, the effects of different electrolytes and applied voltages on the product were investigated in the experiments detailed in this paper. The results demonstrated that the use of an acidic solution of 0.1 M HCl or HNO3 produced Si-NPs without SiO2 formation. According to the transmission electron microscopy and electron energy-loss spectroscopy, the obtained Si-NPs contained both amorphous and polycrystalline Si particles, among which the smaller Si-NPs tended to be amorphous. When an alkaline solution of K2CO3 was used instead, amorphous SiO2 particles were synthesized owing to the corrosion of Si in the high-temperature environment. The pH values of KCl and KNO3 increased during electrolysis, and the products were partially oxidized in the alkaline solutions. The particle size increased with an increasing applied voltage because the excitation temperature of the plasma increased.

  15. SI PC104 Performance Test Report

    SciTech Connect

    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.

  16. Modelling the influence of high currents on the cutoff frequency in Si/SiGe/Si heterojunction transistors

    NASA Astrophysics Data System (ADS)

    Briggs, P. J.; Walker, A. B.; Herbert, D. C.

    1998-05-01

    A one-dimensional self-consistent bipolar Monte Carlo simulation code has been used to model carrier mobilities in strained doped SiGe and the base-collector region of Si/SiGe/Si and SiC/Si heterojunction bipolar transistors (HBTs) with wide collectors, to study the variation of the cutoff frequency 0268-1242/13/5/005/img6 with collector current density 0268-1242/13/5/005/img7. Our results show that while the presence of strain enhances the electron mobility, the scattering from alloy disorder and from ionized impurities reduces the electron mobility so much that it is less than that of Si at the same doping level, leading to larger base transit times 0268-1242/13/5/005/img8 and hence poorer 0268-1242/13/5/005/img6 performance for large 0268-1242/13/5/005/img7 for an Si/SiGe/Si HBT than for an SiC/Si HBT. At high values of 0268-1242/13/5/005/img7, we demonstrate the formation of a parasitic electron barrier at the base-collector interface which causes a sharp increase in 0268-1242/13/5/005/img8 and hence a dramatic reduction in 0268-1242/13/5/005/img6. Based on a comparison of the height of this parasitic barrier with estimates from an analytical model, we suggest a physical mechanism for base pushout after barrier formation that differs somewhat from that given for the analytical model.

  17. An inert marker study for palladium silicide formation - Si moves in polycrystalline Pd2Si

    NASA Technical Reports Server (NTRS)

    Ho, K. T.; Lien, C.-D.; Shreter, U.; Nicolet, M.-A.

    1985-01-01

    A novel use of Ti marker is introduced to investigate the moving species during Pd2Si formation on 111 and 100 line-type Si substrates. Silicide formed from amorphous Si is also studied using a W marker. Although these markers are observed to alter the silicide formation in the initial stage, the moving species can be identified once a normal growth rate is resumed. It is found that Si is the dominant moving species for all three types of Si crystallinity. However, Pd will participate in mass transport when Si motion becomes obstructed.

  18. Molecular-Beam Epitaxy Of CrSi2 on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W.; Grunthaner, Paula J.; Lin, True-Lon; Jamieson, David N.; Mazur, Jurek H.

    1989-01-01

    Crystalline layers grown in commercial apparatus. Experiments show CrSi2 grown on (111) face of single-crystal Si substrate by molecular-beam epitaxy. Epitaxial CrSi2 produced thus far not in desired single-crystal form. Because CrSi2 semiconductor with band gap of 0.3 eV, experimental process potential for monolitic integration of microelectronic devices based on CrSi2 (e.g., infrared detectors) with signal-processing circuitry based on Si.

  19. Elimination of SiC/SiO2 interface states by preoxidation ultraviolet-ozone cleaning

    NASA Astrophysics Data System (ADS)

    Afanas'ev, V. V.; Stesmans, A.; Bassler, M.; Pensl, G.; Schulz, M. J.; Harris, C. I.

    1996-04-01

    The preoxidation cleaning of silicon carbide surfaces (3C, 4H, 6H polytypes) by exposing them to ultraviolet radiation and oxygen is shown to produce a significant improvement in the electronic properties of SiC/SiO2 interfaces. It is found that this treatment results in a removal of defect species, otherwise present at the SiC surface after thermal oxidation of SiC. Carbon clusters are proposed as the attacked species responsible for a substantial part of the SiC/SiO2 interface states.

  20. Influence of the Si/SiO2 interface on the charge carrier density of Si nanowires

    NASA Astrophysics Data System (ADS)

    Schmidt, V.; Senz, S.; Gösele, U.

    2007-02-01

    The electrical properties of Si nanowires covered by a SiO2 shell are influenced by the properties of the Si/SiO2 interface. This interface can be characterized by the fixed oxide charge density Qf and the interface trap level density Dit. We derive expressions for the effective charge carrier density in silicon nanowires as a function of Qf, Dit, the nanowire radius, and the dopant density. It is found that a nanowire is fully depleted when its radius is smaller than a critical radius acrit. An analytic expression for acrit is derived.

  1. Effect of Si Growth Temperature on Fabrication of Si-ZnO Coaxial Nanorod Heterostructure on (100) Si Substrate

    NASA Astrophysics Data System (ADS)

    Yoon, Im Taek; Cho, Hak Dong; Cho, Hoon Young; Kwak, Dong Wook; Lee, Sejoon

    2017-02-01

    The realization and application of optoelectronics, photonics, and sensing, such as in solar diode sensors and photodiodes, which are potentially useful from ultraviolet to infrared light sensing, is dramatically advanced when ZnO is integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Here, we compare and analyze the fundamental features of the Si-ZnO coaxial nanorod heterostructures (Si@ZnO NRs) grown on semi-insulating (100)-oriented Si substrates at growing temperatures of 500°C, 600°C, 650°C, and 700°C of the Si layer for device applications. ZnO NRs were grown by a vapor phase transport, and Si layers were made by rapid thermal chemical vapor deposition. X-ray diffraction, field emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy, and Raman experiments showed that ZnO NRs were single crystals with a würtzite structure, while the Si layer was polysilicon with a zincblende structure. Furthermore, FESEM revealed that Si shell thickness of the Si@ZnO NRs increases with increasing growing temperatures of Si from 500°C to 700°C.

  2. SiLix-C Nanocomposites

    NASA Technical Reports Server (NTRS)

    Henry, Francois

    2015-01-01

    For this Phase II project, Superior Graphite Co., in collaboration with the Georgia Institute of Technology and Streamline Nanotechnologies, Inc., developed, explored the properties of, and demonstrated the enhanced capabilities of novel nanostructured SiLix-C anodes. These anodes can retain high capacity at a rapid 2-hour discharge rate and at 0 C when used in Li-ion batteries. In Phase I, these advanced anode materials had specific capacity in excess of 1,000 mAh/g, minimal irreversible capacity losses, and stable performance for 20 cycles at C/1. The goals in Phase II were to develop and apply a variety of novel nanomaterials, fine-tune the properties of composite particles at the nanoscale, optimize the composition of the anodes, and select appropriate binder and electrolytes. In order to achieve a breakthrough in power characteristics of Li-ion batteries, the team developed new nanostructured SiLix-C anode materials to offer up to 1,200 mAh/g at C/2 at 0 C.

  3. Growth and reactions of SiOx/Si nanostructures on surface-templated molecule corrals.

    PubMed

    Liu, Yi; Zhang, Zhanping; Wells, Matthew C; Beebe, Thomas P

    2005-09-13

    Surface-templated nanostructures on the highly oriented pyrolytic graphite (HOPG) basal plane were created by controlled Cs+- or Ga+)ion bombardment, followed by subsequent oxidation at high temperature, forming molecule corrals. The corrals were then used for template growth of SiOx/Si nanostructures. We demonstrate here that, for SiOx/Si nanostructures formed in controlled molecule corrals, the amount of silicon deposited on the surface is directly correlated with the corral density, making it possible to generate patterned SiOx/Si nanostructures on HOPG. Since the size, depth, position, and surface density of the nanostructures can be controlled on the HOPG, it is possible to produce surfaces with patterned or gradient functionalities for applications in fields such as biosensors, microelectronics, and biomaterials (e.g., neuron pathfinding). If desired, the SiOx structures can be reduced in size by etching in dilute HF, and further oxidation of the nanostructures is slow enough to provide plenty of time to functionalize them using ambient and solution reactions and to perform surface analysis. Organosilane monolayers on surface-templated SiOx/Si nanostructures were examined by X-ray photoelectron spectroscopy, time-of-flight secondary ion mas spectrometry, and atomic force microscopy. Silanes with long alkyl chains such as n-octadecyltrichlorosilane (C18) were found to both react on SiOx/Si nanostructures and to condense on the HOPG basal plane. Shorter-chain silanes, such as 11-bromoundicyltrimethoxysilane (C11) and 3-mercaptopropyltrimethoxysilane (C3) were found to react preferentially with SiOx/Si nanostructures, not HOPG. The SiOx/Si nanostructures were also found to be stable toward multiple chemical reactions. Selective modification of SiOx/Si nanostructures on the HOPG basal plane is thus achievable.

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

    SciTech Connect

    Wilson, Dane F.

    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.

  5. SiC Deep Ultraviolet Avalanche Photodetectors

    DTIC Science & Technology

    2010-10-01

    filters and SEM cross-section of dielectric stack filter. • GE SiC Solar blind detector demonstrated the best response in deep UV spectral region...Bolotnikov, A., Frechette, J., Verghese, S., Grossmann, P., Shaw, G.A. SiC APDs and arrays for UV and solar blind detection (2009) Conference Proceedings...optimized using optical and electrical device simulations , and associated fabrication methods for solar - blind SiC APD arrays have been developed

  6. Probing the valence orbitals of transition metal-silicon diatomic anions: ZrSi, NbSi, MoSi, PdSi and WSi.

    PubMed

    Gunaratne, K Don Dasitha; Berkdemir, Cuneyt; Harmon, C L; Castleman, A W

    2013-04-28

    Evolution of electronic properties and the nature of bonding of the 4d-transition metal silicides (ZrSi, NbSi, MoSi and PdSi) are discussed, revealing interesting trends in the transition metal-silicon interactions across the period. The electronic properties of select transition metal silicide diatomics have been determined by anion photoelectron imaging spectroscopy and theoretical methods. The electron binding energy spectra and photoelectron angular distributions obtained by 2.33 eV (532 nm) photons have revealed the distinct features of these diatomics. The theoretical calculations were performed at the density functional theory (DFT) level using the unrestricted B3LYP hybrid functional and at the ab initio unrestricted coupled cluster singles and doubles (triplets) (UCCSD(T)) methods to assign the ground electronic states of the neutral and anionic diatomics. The excited electronic states were calculated by the DFT (TD-DFT)/UB3LYP method. We have observed that the valence molecular orbital configuration of the ZrSi and NbSi anions are significantly different from that of the MoSi and PdSi anions. By combining our experimental and theoretical results, we report that the composition of the highest occupied molecular orbitals shift from a majority of transition metal s- and d-orbital contribution in ZrSi and NbSi, to mainly silicon p-orbital contribution for MoSi and PdSi. We expect these observed atomic scale transition metal-silicon interactions to be of increasing importance with the miniaturization of devices approaching the sub-nanometer size regime.

  7. Room Temperature Creep Of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Gyekenyesi, Andrew; Levine, Stanley (Technical Monitor)

    2001-01-01

    During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time dependent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the interfacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interfacial shear stress with time at room temperature as measured by fiber push-in experiments.

  8. One-dimensional Si nanolines in hydrogenated Si(001)

    NASA Astrophysics Data System (ADS)

    François, Bianco; Köster, Sigrun A.; Owen, James G. H.; Renner, Christoph; Bowler, David R.

    2012-02-01

    We present a detailed study of the structural and electronic properties of a self-assembled silicon nanoline embedded in the H-terminated silicon (001) surface, known as the Haiku stripe. The nanoline is a perfectly straight and defect free endotaxial structure of huge aspect ratio; it can grow micrometre long at a constant width of exactly four Si dimers (1.54 nm). Another remarkable property is its capacity to be exposed to air without suffering any degradation. The nanoline grows independently of any step edges at tunable densities, from isolated nanolines to a dense array of nanolines. In addition to these unique structural characteristics, scanning tunnelling microscopy and density functional theory reveal a one-dimensional state confined along the Haiku core. This nanoline is a promising candidate for the long sought after electronic solid-state one-dimensional model system to explore the fascinating quantum properties emerging in such reduced dimensionality. Phys. Rev. B, 84, 035328 (2011)

  9. The Si/Si_3N4 Interface and Si/Si_3N4 Submicron Mesa: A Multi-million Atom Molecular Dynamics Study

    NASA Astrophysics Data System (ADS)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam

    1998-03-01

    Using molecular dynamics simulations on parallel computers, the interface structure, stress distribution, crack propagation and fracture in a Si_3N4 film on Si substrate are studied. Bulk Si is described by Stillinger-Weber potential and Si_3N4 is represented by a combination of two- and three-body covalent interactions. At the interface, the charge transfer is taken from LCAO electronic structure calculations (G.-L. Zhao and M.E. Bachlechner, Europhys. Lett. 36, 287 (1997)). Results for structural correlations at the interface and 3D stress distribution for the submicron mesa are presented.

  10. Graphene/Si-nanowire heterostructure molecular sensors

    PubMed Central

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

    2014-01-01

    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. PMID:24947403

  11. Si isotope homogeneity of the solar nebula

    SciTech Connect

    Pringle, Emily A.; Savage, Paul S.; Moynier, Frédéric; Jackson, Matthew G.; Barrat, Jean-Alix E-mail: savage@levee.wustl.edu E-mail: moynier@ipgp.fr E-mail: Jean-Alix.Barrat@univ-brest.fr

    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.

  12. Engineering approaches in siRNA delivery.

    PubMed

    Barba, Anna Angela; Cascone, Sara; Caccavo, Diego; Lamberti, Gaetano; Chiarappa, Gianluca; Abrami, Michela; Grassi, Gabriele; Grassi, Mario; Tomaiuolo, Giovanna; Guido, Stefano; Brucato, Valerio; Carfì Pavia, Francesco; Ghersi, Giulio; La Carrubba, Vincenzo; Abbiati, Roberto Andrea; Manca, Davide

    2017-02-14

    siRNAs are very potent drug molecules, able to silence genes involved in pathologies development. siRNAs have virtually an unlimited therapeutic potential, particularly for the treatment of inflammatory diseases. However, their use in clinical practice is limited because of their unfavorable properties to interact and not to degrade in physiological environments. In particular they are large macromolecules, negatively charged, which undergo rapid degradation by plasmatic enzymes, are subject to fast renal clearance/hepatic sequestration, and can hardly cross cellular membranes. These aspects seriously impair siRNAs as therapeutics. As in all the other fields of science, siRNAs management can be advantaged by physical-mathematical descriptions (modeling) in order to clarify the involved phenomena from the preparative step of dosage systems to the description of drug-body interactions, which allows improving the design of delivery systems/processes/therapies. This review analyzes a few mathematical modeling approaches currently adopted to describe the siRNAs delivery, the main procedures in siRNAs vectors' production processes and siRNAs vectors' release from hydrogels, and the modeling of pharmacokinetics of siRNAs vectors. Furthermore, the use of physical models to study the siRNAs vectors' fate in blood stream and in the tissues is presented. The general view depicts a framework maybe not yet usable in therapeutics, but with promising possibilities for forthcoming applications.

  13. SiC-Based Gas Sensor Development

    NASA Technical Reports Server (NTRS)

    Hunter, G. W.; Neudeck, P. G.; Gray, M.; Androjna, D.; Chen, L.-Y.; Hoffman, R. W., Jr.; Liu, C. C.; Wu, Q. H.

    2000-01-01

    Silicon carbide based Schottky diode gas sensors are being developed for applications such as emission measurements and leak detection. The effects of the geometry of the tin oxide film in a Pd/SnO2/SiC structure will be discussed as well as improvements in packaging SiC-based sensors. It is concluded that there is considerable versatility in the formation of SiC-based Schottky diode gas sensing structures which will potentially allow the fabrication of a SiC-based gas sensor array for a variety of gases and temperatures.

  14. SiD Letter of Intent

    SciTech Connect

    Aihara, H.,; Burrows, P.,; 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.; /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.

  15. Sputtered Ta-Si-N diffusion barriers in Cu metallizations for Si

    NASA Technical Reports Server (NTRS)

    Kolawa, E.; Pokela, P. J.; Reid, J. S.; Chen, J. S.; Nicolet, Marc A.; Ruiz, R. P.

    1991-01-01

    Electrical measurements on shallow Si n+-p junction diodes with a 30-nm TiSi2 contacting layer demonstrate that an 80-nm-thick amorphous Ta36Si14N50 film prepared by reactive RF sputtering of a Ta5Si3 target in an Ar/N2 plasma very effectively prevents the interaction between the Si substrate with the TiSi2 contacting layer and a 500-nm Cu overlayer. The Ta36Si14N50 diffusion barrier maintains the integrity of the I-V characteristics up to 900 C for 30-min annealing in vacuum. It is concluded that the amorphous Ta36Si14N50 alloy is not only a material with a very low reactivity for copper, titanium, and silicon, but must have a small diffusivity for copper as well.

  16. Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

    NASA Astrophysics Data System (ADS)

    Ogawa, Shuichi; Tang, Jiayi; Takakuwa, Yuji

    2015-08-01

    Kinetics of Si atoms emission during the oxidation of Si(001) surfaces have been investigated using reflection high energy electron diffraction combined with Auger electron spectroscopy. The area ratio of the 1 × 2 and the 2 × 1 domains on a clean Si(001) surface changed with the oxidation of the surface by Langmuir-type adsorption. This change in the domain ratio is attributed to the emission of Si atoms. We can describe the changes in the domain ratio using the Si emission kinetics model, which states that (1) the emission rate is proportional to the oxide coverage, and (2) the emitted Si atoms migrate on the surface and are trapped at SB steps. Based on our model, we find experimentally that up to 0.4 ML of Si atoms are emitted during the oxidation of a Si(001) surface at 576 °C.

  17. Experimental estimation of oxidation-induced Si atoms emission on Si(001) surfaces

    SciTech Connect

    Ogawa, Shuichi Tang, Jiayi; Takakuwa, Yuji

    2015-08-15

    Kinetics of Si atoms emission during the oxidation of Si(001) surfaces have been investigated using reflection high energy electron diffraction combined with Auger electron spectroscopy. The area ratio of the 1 × 2 and the 2 × 1 domains on a clean Si(001) surface changed with the oxidation of the surface by Langmuir-type adsorption. This change in the domain ratio is attributed to the emission of Si atoms. We can describe the changes in the domain ratio using the Si emission kinetics model, which states that (1) the emission rate is proportional to the oxide coverage, and (2) the emitted Si atoms migrate on the surface and are trapped at S{sub B} steps. Based on our model, we find experimentally that up to 0.4 ML of Si atoms are emitted during the oxidation of a Si(001) surface at 576 °C.

  18. Oxidation instability of SiC and Si3N4 following thermal excursions

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.

    1991-01-01

    The effect of thermal excursion and thermal cycling on the oxidation stability of chemical vapor-deposited (CVD) SiC and Si3N4 was studied at 1350 C. Thermal cycling alone produced no noticeable change in oxidation kinetics. However, TEM showed that oxide scales grown in cycles consist of alternating layers of SiO2 and Si2N2O. When the oxidation of CVD SiC or Si3N4 at 1350 C was interrupted with a 1.5-h annealing in Ar at 1500 C, the kinetics of reoxidation at 1350 C were found to be drastically increased. The SiC and Si3N4 then oxidized essentially at the same rate, which is over 50 times the preannealing rate, and comparable to the expected oxidation rate of these materials at 1500 C.

  19. 26Si Excited States via One-Neutron Removal from 27Si Using Radioactive Beam

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, A. A.; Amthor, A. M.; Bazin, D.; Becerril, A. D.; Gade, A.; Galaviz, D.; Glasmacher, T.; Kahl, D.; Lorusso, G.; Matos, M.; Ouellet, C. V.; Pereira, J.; Schatz, H.; Smith, K. M.; Wales, B.; Weisshaar, D.; Zegers, R. G. T.

    2013-03-01

    A measurement of the p(27Si, d)26Si reaction has been performed to study levels of 26Si, with connections to the stellar 25Al(p, γ)26Si reaction rate. A beam of adioactive 27Si of energy 84.3 MeV/A was impinged on a polypropylene foil (CH2) of 180 mg/cm2 in thickness. De-excitation γ-rays were detected with a highly-segmented germanium detector array, in coincidence with the 26Si recoils. Our results are an independent measurement of states used in the energy calibration of other experiments on 26Si structure. They also suggest that the spin-parity of the Ex(26Si) = 6454 keV (Er = 940 keV) state should be 4+ instead of the previously adopted assignment of 0+.

  20. Vertically Conductive Single-Crystal SiC-Based Bragg Reflector Grown on Si Wafer

    PubMed Central

    Massoubre, David; Wang, Li; Hold, Leonie; Fernandes, Alanna; Chai, Jessica; Dimitrijev, Sima; Iacopi, Alan

    2015-01-01

    Single-crystal silicon carbide (SiC) thin-films on silicon (Si) were used for the fabrication and characterization of electrically conductive distributed Bragg reflectors (DBRs) on 100 mm Si wafers. The DBRs, each composed of 3 alternating layers of SiC and Al(Ga)N grown on Si substrates, show high wafer uniformity with a typical maximum reflectance of 54% in the blue spectrum and a stopband (at 80% maximum reflectance) as large as 100 nm. Furthermore, high vertical electrical conduction is also demonstrated resulting to a density of current exceeding 70 A/cm2 above 1.5 V. Such SiC/III-N DBRs with high thermal and electrical conductivities could be used as pseudo-substrate to enhance the efficiency of SiC-based and GaN-based optoelectronic devices on large Si wafers. PMID:26601894

  1. Crystallization of amorphous Si nanoclusters in SiO(x) films using femtosecond laser pulse annealings.

    PubMed

    Korchagina, T T; Gutakovsky, A K; Fedina, L I; Neklyudova, M A; Volodin, V A

    2012-11-01

    The SiO(x) films of various stoichiometries deposited on Si substrates with the use of the co-sputtering from two separate Si and SiO2 targets were annealed by femtosecond laser pulses. Femtosecond laser treatments were applied for crystallization of amorphous silicon nanoclusters in the silicon-rich oxide films. The treatments were carried out with the use of Ti-Sapphire laser with wavelength 800 nm and pulse duration about 30 fs. Regimes of crystallization of amorphous Si nanoclusters in the initial films were found. Ablation thresholds for SiO(x) films of various stoichiometries were discovered. The effect of laser assisted formation of a-Si nanoclusters in the non-stoichiometric dielectric films with relatively low concentration of additional Si atoms was also observed. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters on non-refractory substrates.

  2. Recycling of Al-Si die casting scraps for solar Si feedstock

    NASA Astrophysics Data System (ADS)

    Seo, Kum-Hee; Jeon, Je-Beom; Youn, Ji-Won; Kim, Suk Jun; Kim, Ki-Young

    2016-05-01

    Recycling of aluminum die-casting scraps for solar-grade silicon (SOG-Si) feedstock was performed successfully. 3 N purity Si was extracted from A383 die-casting scrap by using the combined process of solvent refining and an advanced centrifugal separation technique. The efficiency of separating Si from scrap alloys depended on both impurity level of scraps and the starting temperature of centrifugation. Impurities in melt and processing temperature governed the microstructure of the primary Si. The purity of Si extracted from the scrap melt was 99.963%, which was comparable to that of Si extracted from a commercial Al-30 wt% Si alloy, 99.980%. The initial purity of the scrap was 2.2% lower than that of the commercial alloy. This result confirmed that die-casting scrap is a potential source of high-purity Si for solar cells.

  3. Thermogravimetric and microscopic analysis of SiC/SiC materials with advanced interfaces

    SciTech Connect

    Windisch, C.F. Jr.; Jones, R.H.; Snead, L.L.

    1997-04-01

    The chemical stability of SiC/SiC composites with fiber/matrix interfaces consisting of multilayers of SiC/SiC and porous SiC have been evaluated using a thermal gravimetric analyzer (TGA). Previous evaluations of SiC/SiC composites with carbon interfacial layers demonstrated the layers are not chemically stable at goal use temperatures of 800-1100{degrees}C and O{sub 2} concentrations greater than about 1 ppm. No measureable mass change was observed for multilayer and porous SiC interfaces at 800-1100{degrees}C and O{sub 2} concentrations of 100 ppm to air; however, the total amount of oxidizable carbon is on the order of the sensitivity of the TGA. Further studies are in progress to evaluate the stability of these materials.

  4. Photovoltaic characteristics of Pd doped amorphous carbon film/SiO{sub 2}/Si

    SciTech Connect

    Ma Ming; Xue Qingzhong; Chen Huijuan; Zhou Xiaoyan; Xia Dan; Lv Cheng; Xie Jie

    2010-08-09

    The Pd doped amorphous carbon (a-C:Pd) films were deposited on n-Si substrates with or without a native SiO{sub 2} layer using magnetron sputtering. The photovoltaic characteristics of the a-C:Pd/SiO{sub 2}/Si and a-C:Pd/Si junctions were studied. It is found that under light illumination of 15 mW/cm{sup 2} at room temperature, the a-C:Pd/SiO{sub 2}/Si solar cell fabricated at 350 deg. C has a high power conversion efficiency of 4.7%, which is much better than the a-C/Si junctions reported before. The enhanced conversion efficiency is ascribed to the Pd doping and the increase in sp{sup 2}-bonded carbon clusters in the carbon film caused by the high temperature deposition.

  5. Theoretical investigation of intersubband hole transitions in Si/SiGe/Si quantum wells

    NASA Astrophysics Data System (ADS)

    Boujdaria, K.; Ridene, S.; Radhia, S. Ben; Zitouni, O.; Bouchriha, H.; Fishman, G.

    2002-09-01

    We study the effects of the pc-pc coupling in intersubband hole optical transitions in SiGe/Si quantum wells for x and z polarizations. We have used a k[middle dot]p model taking into account both the p-like first conduction band and the s-like second conduction band. First, we have found a unitary transformation that block diagonalizes the 14 x14 Hamiltonian (or 12 x12 Hamiltonian) into two 7 x7 (or 6 x6) blocks that are real symmetric in the finite difference formulation. We find that pc-pc interaction plays a minimal role in intersubband optical transition for x and z polarizations. Moreover, our calculations clearly confirm that the pc-pv coupling favors intersubband transitions for an optical polarization parallel to the layer plane (x polarization). In addition, for z polarization, both s-pv and pc-pv interactions play an equal footing role in intervalence band transitions.

  6. Optical gain in Si/SiO2 lattice: Experimental evidence with nanosecond pulses

    NASA Astrophysics Data System (ADS)

    Khriachtchev, Leonid; Räsänen, Markku; Novikov, Sergei; Sinkkonen, Juha

    2001-08-01

    Experimental evidence of population inversion and amplified spontaneous emission was found for Si nanocrystallites embedded in SiO2 surrounding under pumping with 5 ns light pulses at 380, 400, and 500 nm. As an important property, our experiments show a short lifetime of the population inversion allowing a generation of short (a few nanosecond) amplified light pulses in the Si/SiO2 lattice. The estimate for optical gain in the present samples is 6 cm-1 at 720 nm.

  7. C-V and DLTS studies of radiation induced Si-SiO2 interface defects

    NASA Astrophysics Data System (ADS)

    Capan, I.; Janicki, V.; Jacimovic, R.; Pivac, B.

    2012-07-01

    Interface traps at the Si-SiO2 interface have been and will be an important performance limit in many (future) semiconductor devices. In this paper, we present a study of fast neutron radiation induced changes in the density of Si-SiO2 interface-related defects. Interface related defects (Pb centers) are detected before and upon the irradiation. The density of interface-related defects is increasing with the fast neutron fluence.

  8. High Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films

    DTIC Science & Technology

    2013-04-01

    REPORT High Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: We...Energy Effects on Thermoelectric and Optical Properties of Si/Si+Sb Nanolayered Thin Films Report Title ABSTRACT We have prepared thermoelectric...the cross plane Seebeck coefficient and increase the cross plane electrical conductivity to increase the figure of merit. Some optical

  9. Vanadium, Cr, Si, and the Mg/Si Ratio of the Earth

    NASA Technical Reports Server (NTRS)

    Drake, Michael J.; Domanik, Kenneth; Bailey, Edward

    2003-01-01

    Experiments investigating the partitioning of V, Cr, and Si between metal and silicate at various pressures, temperatures, redox state, and composition demonstrate that V and Cr are always more siderophile than Si. The relatively high abundances of V and Cr in the Earth's upper mantle indicate that the high Mg/Si ratio of the Earth's upper mantle cannot be attributed to extraction of Si into the core and must be an intrinsic bulk property of the silicate Earth.

  10. Minimum bar size for flexure testing of irradiated SiC/SiC composite

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.

    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. The minimum bar size for 4-point flexure testing of SiC/SiC composite recommended by PNNL for irradiation effects studies is 30 {times} 6 {times} 2 mm{sup 3} with a span-to-depth ratio of 10/1.

  11. Electroluminescence and Photoluminescence from Scored Si-Rich SiO2 Film/p-Si Structure

    NASA Astrophysics Data System (ADS)

    Ran, Guang-Zhao; Sun, Yong-Ke; Chen, Yuan; Dai, Lun; Cui, Xiao-Ming; Zhang, Bo-Rui; Qiao, Yong-Ping; Ma, Zhen-Chang; Zong, Wan-Hua; Qin, Guo-Gang

    2003-02-01

    Electroluminescence (EL) is observed from the Au/Si-rich SiO2 film/p-Si diodes, in which the Si-rich SiO2 films are scored deliberately by a diamond tip. The EL intensity of the scored diode annealed at 800°C is about 6 times of that of the unscored counterpart. The EL spectrum of the unscored diode could be decomposed into two Gaussian luminescence bands with peaks at about 1.83 and 2.23 eV, while for the EL spectrum of the scored diode, an additional Gaussian band at about 3.0 eV appears, and the 1.83-eV peak increases significantly in intensity. The photoluminescence (PL) spectrum of an unscored Si-rich SiO2 film has only one band peaking at about 1.48 eV, whereas the PL spectrum of the scored one has two bands at about 1.48 and 1.97 eV. We consider that the high-density defect regions produced by the scoring provide new luminescence centres and become some types of nonradiative centres in the Si oxide layer, which thus result in changes of the EL and PL spectra.

  12. Time-resolved photoluminescence properties of ion-beam-synthesized β-FeSi2 and Si-implanted Si

    NASA Astrophysics Data System (ADS)

    Terai, Yoshikazu; Maeda, Yoshihito

    2015-07-01

    Temporal decay characteristics of 1.54 µm photoluminescence (PL) were investigated in β-FeSi2 and Si-implanted Si samples grown by ion-beam-synthesis (IBS). In the samples, the band-edge PL of β-FeSi2 (A-band) and the dislocation-related PL (D1-band) of Si were both observed at ˜0.8 eV. Regarding the dependence of the PL decay curves on excitation power density (P), PL decay curves without extrinsic effects were obtained at a low P of P ≤ 4.3 mW/cm2. The PL decay times obtained at a low P showed clear differences between the A-band and the D1-line. The result showed that the band-edge PL of β-FeSi2 was distinguished from the dislocation-related PL of Si by the PL decay times. The intrinsic PL decay times of β-FeSi2 were determined to be τ1 = 70-100 ns and τ2 = 550-670 ns at 5 K.

  13. Structure of Si-capped Ge/SiC/Si (001) epitaxial nanodots: Implications for quantum dot patterning

    SciTech Connect

    Petz, C. W.; Floro, J. A.; Yang, D.; Levy, J.

    2012-04-02

    Artificially ordered quantum dot (QD) arrays, where confined carriers can interact via direct exchange coupling, may create unique functionalities such as cluster qubits and spintronic bandgap systems. Development of such arrays for quantum computing requires fine control over QD size and spatial arrangement on the sub-35 nm length scale. We employ electron-beam irradiation to locally decompose ambient hydrocarbons onto a bare Si (001) surface. These carbonaceous patterns are annealed in ultra-high vacuum (UHV), forming ordered arrays of nanoscale SiC precipitates that have been suggested to template subsequent epitaxial Ge growth to form ordered QD arrays. We show that 3C-SiC nanodots form, in cube-on-cube epitaxial registry with the Si substrate. The SiC nanodots are fully relaxed by misfit dislocations and exhibit small lattice rotations with respect to the substrate. Ge overgrowth at elevated deposition temperatures, followed by Si capping, results in expulsion of the Ge from SiC template sites due to the large chemical and lattice mismatch between Ge and C. Maintaining an epitaxial, low-defectivity Si matrix around the quantum dots is important for creating reproducible electronic and spintronic coupling of states localized at the QDs.

  14. Surface Second Harmonic Studies of Si(111)/Electrolyte and Si(111)/SiO2/ Electrolyte Interfaces

    DTIC Science & Technology

    1994-05-13

    both H-terminated Si(111) surfaces in NJ4F, and oxide covered surfaces biased in H2SO4, the phase and the amplitude display a potential dependence ...demonstrate that for Si(1110)/oxide samples the potential dependence in the SH phase can be correlated with oxide thickness as demonstrated by

  15. About the International System of Units (SI) Part III. SI Table

    ERIC Educational Resources Information Center

    Aubrecht, Gordon J., II; French, Anthony P.; Iona, Mario

    2012-01-01

    Before discussing more details of SI, we will summarize the essentials in a few tables that can serve as ready references. If a unit isn't listed in Tables I-IV, it is not part of SI or specifically allowed for use with SI. The units and symbols that are sufficient for most everyday applications are given in bold.

  16. Process dependent morphology of the Si/SiO2 interface measured with scanning tunneling microscopy

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Bell, L. D.; Grunthaner, F. J.; Kaiser, W. J.

    1988-01-01

    A new experimental technique to determine Si/SiO2 interface morphology is described. Thermal oxides of silicon are chemically removed, and the resulting surface topography is measured with scanning tunneling microscopy. Interfaces prepared by oxidation of Si (100) and (111) surfaces, followed by postoxidation anneal (POA) at different temperatures, have been characterized. Correlations between interface structure, chemistry, and electrical characteristics are described.

  17. Fabrication of nanometer single crystal metallic CoSi2 structures on Si

    NASA Technical Reports Server (NTRS)

    Nieh, Kai-Wei (Inventor); Lin, True-Lon (Inventor); Fathauer, Robert W. (Inventor)

    1991-01-01

    Amorphous Co:Si (1:2 ratio) films are electron gun-evaporated on clean Si(111), such as in a molecular beam epitaxy system. These layers are then crystallized selectively with a focused electron beam to form very small crystalline Co/Si2 regions in an amorphous matrix. Finally, the amorphous regions are etched away selectively using plasma or chemical techniques.

  18. Silicon interstitial injection during dry oxidation of SiGe /Si layers

    NASA Astrophysics Data System (ADS)

    Napolitani, E.; Di Marino, M.; De Salvador, D.; Carnera, A.; Spadafora, M.; Mirabella, S.; Terrasi, A.; Scalese, S.

    2005-02-01

    The injection of Si self-interstitial atoms during dry oxidation at 815°C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe /Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2/SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.

  19. Mechanism of photoluminescence investigation of Si nano-crystals embedded in SiOx

    NASA Astrophysics Data System (ADS)

    Vivas Hernández, A.; Torchynska, T. V.; Guerrero Moreno, I.

    2010-05-01

    Nanoscaled Si (Ge) systems continue to be of interest for their potential application as Si (Ge) based light emiting materials and photonic structures. Optical properties of such systems are sensitive to nanocrystallite (NC) size fluctuations as well as to defects effects due to large surface to volume ratio in small NCs. Intensive research of Si (Ge) NCs is focused on the elucidation of the mechanism of radiative recombination with the aim to provide high efficient emission at room temperature in different spectral range. The bright visible photoluminescence (PL) of the Si (Ge)-SiOX system was investigated during last 15 years and several models were proposed. It was shown that blue (~2.64 eV) and green (~2.25 eV) PL are caused by various emitting centers in silicon oxide [1], while the nature of the more intensive red (1.70-2.00 eV) and infrared (0.80-1.60 eV) PL bands steel is no clear. These include PL model connected whit quantum confinement effects in Si (Ge) nanocrystallites [2-4], surface states on Si (Ge) nanocrystallites, as well as defects at the Si/SiOX (Ge/SiOX) interface and in the SiO2 layer [5-11]. It should be noted, that even investigation of PL on single Si quantum dots [12] cannot undoubtedly confirm the quantum confinement nature of red emission.

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

    NASA Technical Reports Server (NTRS)

    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.

  1. Thermochemical instability effects in SiC-based fibers and SiC{sub f}/SiC composites

    SciTech Connect

    Youngblood, G.E.; Henager, C.H.; Jones, R.H.

    1997-08-01

    Thermochemical instability in irradiated SiC-based fibers with an amorphous silicon oxycarbide phase leads to shrinkage and mass loss. SiC{sub f}/SiC composites made with these fibers also exhibit mass loss as well as severe mechanical property degradation when irradiated at 800{degrees}C, a temperature much below the generally accepted 1100{degrees}C threshold for thermomechanical degradation alone. The mass loss is due to an internal oxidation mechanism within these fibers which likely degrades the carbon interphase as well as the fibers in SiC{sub f}/SiC composites even in so-called {open_quotes}inert{close_quotes} gas environments. Furthermore, the mechanism must be accelerated by the irradiation environment.

  2. Tunneling magnetoresistance in Si nanowires

    NASA Astrophysics Data System (ADS)

    Montes, E.; Rungger, I.; Sanvito, S.; Schwingenschlögl, U.

    2016-11-01

    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.

  3. Metastability of a-SiOx:H thin films for c-Si surface passivation

    NASA Astrophysics Data System (ADS)

    Serenelli, L.; Martini, L.; Imbimbo, L.; Asquini, R.; Menchini, F.; Izzi, M.; Tucci, M.

    2017-01-01

    The adoption of a-SiOx: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 SiNx 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-SiOx: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 Sisbnd H and Sisbnd 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/cm2. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiOx:H/c-Si/a-SiOx:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiOx passivation properties, was furthermore considered. In particular we monitored the UV light soaking effect on c-Si wafers after a-SiOx:H coating by PECVD and after a thermal annealing treatment at 300 °C for 30 min, having selected these conditions on the basis of the study of the effect due to different temperatures and durations. We correlated the lifetime evolution and the metastability effect of thermal annealing to the a-SiOx:H/c-Si interface considering the evolution

  4. Experimental PDT: studies on new Si-phthalocyanines and Si-naphthalocyanines in Cremophor emulsions

    NASA Astrophysics Data System (ADS)

    Shopova, Maria; Mantareva, Vanya; Woehrle, Dieter; Mueller, Silke

    1996-12-01

    In the present work the following silicon (IV) - phthalocyanines and -naphthalocyanines bearing methoxyethylene glycol or methoxypolyethylene glycol covalently bound at the silicon are investigated: SiPc[OCH2CH2OCH3]2 (SiPc1), SiNc[OCH2CH2OCH3]2 (SiNc), SiPc[(OCH2CH2)nOCH3] with n approximately 115 (SiPc2). The phototherapeutic effect was shown at Lewis lung carcinoma implanted in mice. SiPc2 is monomeric soluble in water whereas the other two compounds aggregated in this solvent. Therefore these compounds were dissolved monomer in in aqueous Cremophor solution before in vivo administration. Laser irradiation was applied 7 days after implantation and 24 h after drug administration at the following wavelength (eta) ext: 672 nm for SiPc1 and SiPc2, 782 nm for SiNc. In all cases a fluence rate of 370 mW/cm2 at fluence of 360 J/cm2 was used. The assessment criteria for the tumor response were the changes in the mean tumor diameter with time, regrowth delay and average survival time (AST). According to the first parameter the most promising result was obtained after treatment with SiPc1. For example the mean tumor diameter increases as follows: SiPc1 less than SiPc2 less than SiNc very much less than control group without photosensitizer. The regrowth delay showed the same trend. however, for AST another dependence was observed. AST was the longest for SiPc2 (26 days) and shortest for SiNc (22 days). Compared to the control group (without sensitizer and irradiation) the AST was 9 days longer after SiPc2 treatment. Comparing SiPc1 and SiPc2 the chain length of the substituents does not influence the phototherapeutic properties. The detected therapeutic results probably are connected with the long wavelength absorption of the photosensitizers. The relatively lower affectivity of SiNc may be due to a lower degree of tumor accumulation as it was observed in our preliminary pharmacokinetic studies. It is also possible that the shorter AST after treatment with SiNc is

  5. Annealing effects of tantalum films on Si and SiO2/Si substrates in various vacuums

    NASA Astrophysics Data System (ADS)

    Liu, Ling; Wang, Yue; Gong, Hao

    2001-07-01

    The annealing effects of 550 nm thick β-Ta films sputtered on Si and SiO2 substrates have been investigated under various vacuum conditions. Phase transformation from the tetragonal β-Ta into body-centered-cubic α-Ta of much higher conductivity occurred at annealing temperatures lower than 500 °C and 80% of β-Ta transformed into α-Ta after annealing at 600 °C for Ta on a Si substrate. For Ta on a SiO2 substrate, no phase transformation was observed at 500 °C annealing, and only 20% of β-Ta transformed into α-Ta at 600 °C. Oxygen diffusion into the Ta film at the interface of Ta/SiO2 could hinder β-Ta to α-Ta transformation. Both Ta on Si and Ta on SiO2 samples have smooth surfaces after annealing in 2×10-5 Torr. After annealing in a vacuum lower than 2×10-4 Torr, surface oxidation of the Ta thin films was detected. The increase of oxygen content in the Ta films caused higher compressive stress, and resulted in the film peeling in a serpentine pattern during annealing at 500 °C in 2×10-2 Torr for Ta on a SiO2 substrate. The Ta films cracked and detached from the SiO2 substrate after being annealed at 750 °C in 2×10-2 Torr. In contrast, no crack was found in Ta on Si, probably because of the relief of film stress due to more β-Ta being transformed into α-Ta during annealing. The residual oxygen and moisture in low vacuum may build up stress in Ta thin films during thermal processes, which can cause major reliability problems in electronic and other applications.

  6. Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

  7. Using Si in floriculture fertility programs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Silicon (Si) is not considered to be an essential plant nutrient because most plant species can complete their life cycle without it. A clear benefit of Si for many ornamental crops has been reported including improved salt and drought tolerance, especially during post-harvest environments; stronger...

  8. Comparison of Ultrathin SiO2/Si(100) and SiO2/Si(111) Interfaces from Soft X-ray Photoelectron Spectroscopy

    SciTech Connect

    Ulrich,M.; Rowe, J.; Keister, J.; Niimi, H.; Fleming, L.; Lucovsky, G.

    2006-01-01

    The limitations of soft x-ray photoelectron spectroscopy (SXPS) for determining structural information of the SiO{sub 2}/Si interface for device-grade ultrathin ({approx}6-22 Angstroms) films of SiO{sub 2} prepared from crystalline silicon by remote plasma assisted oxidation are explored. The main focus of this article is the limitation of data analysis and sensitivity to structural parameters. In particular, annealing data shows a significant decrease in the integrated density of suboxide bonding arrangements as determined from analysis of SXPS data. These decreases and changes are interpreted as evidence for reorganization of specific interface bonding arrangements due to the annealing process. Moreover, these results suggest that sample preparation and processing history are both critical for defining the nature of the SiO{sub 2}/Si interface, and therefore its electrical properties. Quantitative estimates of the interface state densities are derived from SXPS data revealing {approx}2 monolayers (ML) of suboxide as prepared and {approx}1.5 ML of suboxide after rapid thermal annealing at 900 degrees C for both Si(100) and Si(111) substrates. Comparison of the individual suboxide bonding state densities indicate for both Si substrate crystallographic orientations that annealing causes a self-organization of the suboxide consistent with bond constraint theory.

  9. LARC-SI Flatwire Twin Conduction Circuits

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Eight 2-line, L-shaped gold flex circuits have been imprinted on 1-mil LARC-SI. Each circuit was embedded in a space-applications trapezoidal truss made of carbon fiber reinforced resin composite (with protruding ends) to facilitate electrical connection of electronic devices mounted on the truss. LARC-SI is an advanced polymer highly suitable for multi layered electrical circuits.

  10. Optical properties of passivated Si nanocrystals and SiOx nanostructures

    NASA Astrophysics Data System (ADS)

    Dinh, L. N.; Chase, L. L.; Balooch, M.; Siekhaus, W. J.; Wooten, F.

    1996-08-01

    Thin films of Si nanoclusters passivated with oxygen or hydrogen, with an average size of a few nanometers, have been synthesized by thermal vaporization of Si in an Ar buffer gas, followed by subsequent exposure to oxygen or atomic hydrogen. High-resolution transmission electron microscopy and x-ray diffraction revealed that these nanoclusters were crystalline. However, during synthesis, if oxygen was the buffer gas, a network of amorphous Si oxide nanostructures (an-SiOx) 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. Absorption in the Si cores for surface passivated Si nano- crystals (nc-Si), but mainly in oxygen related defect centers for an-SiOx, was observed by photoluminescence excitation spectroscopy. The visible components of PL spectra were noted to blueshift and broaden as the size of the nc-Si was reduced. There were differences in PL spectra for hydrogen and oxygen passivated nc-Si. Many common PL properties between oxygen passivated nc-Si and an-SiOx were observed. Our data can be 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. The emission could involve a simple band-to-band recombination mechanism within the Si cores. The combined evidence of all of our experimental results suggests, however, that emission between surface or interface states is a more likely mechanism.

  11. Modification of Mg{sub 2}Si in Mg–Si alloys with gadolinium

    SciTech Connect

    Ye, Lingying; Hu, Jilong Tang, Changping; Zhang, Xinming; Deng, Yunlai; Liu, Zhaoyang; Zhou, Zhile

    2013-05-15

    The modification effect of gadolinium (Gd) on Mg{sub 2}Si in the hypereutectic Mg–3 wt.% Si alloy has been investigated using optical microscope, scanning electron microscope, X-ray diffraction and hardness measurements. The results indicate that the morphology of the primary Mg{sub 2}Si is changed from coarse dendrite into fine polygon with the increasing Gd content. The average size of the primary Mg{sub 2}Si significantly decreases with increasing Gd content up to 1.0 wt.%, and then slowly increases. Interestingly, when the Gd content is increased to 4.0 and 8.0 wt.%, the primary and eutectic Mg{sub 2}Si evidently decrease and even disappear. The modification and refinement of the primary Mg{sub 2}Si is mainly attributed to the poisoning effect. The GdMg{sub 2} phase in the primary Mg{sub 2}Si is obviously coarsened as the Gd content exceeds 2.0 wt.%. While the decrease and disappearance of the primary and eutectic Mg{sub 2}Si are ascribed to the formation of vast GdSi compound. Therefore, it is reasonable to conclude that proper Gd (1.0 wt.%) addition can effectively modify and refine the primary Mg{sub 2}Si. - Highlights: ► Proper Gd (1.0 wt.%) addition can effectively modify and refine the primary Mg{sub 2}Si. ► We studied the reaction feasibility between Mg and Si, Gd and Si in Mg–Gd–Si system. ► We explored the modification mechanism of Gd modifier on Mg{sub 2}Si.

  12. Electrical and memory properties of Si3N4 MIS structures with embedded Si nanocrystals.

    PubMed

    Horváth, Z J; Basa, P; Jászi, T; Pap, A E; Dobos, L; Pécz, B; Tóth, L; Szöllosi, P; Nagy, K

    2008-02-01

    Memory structures with an embedded sheet of separated Si nanocrystals were prepared by low pressure chemical vapour deposition using a Si3N4 control layer and different Si2O2 or Si3N4 tunnel layers. It was obtained that Si nanocrystals improve the charging behaviour of the MNOS structures. Memory window width of 1.3 V and 2.0 V were obtained for pulse amplitudes of +/-9 V and +/-10 V, 100 ms, respectively. The extrapolated memory window after 10 years is about 15% of its initial value.

  13. Molecular-beam epitaxy of CrSi2 on Si(111)

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Grunthaner, P. J.; Lin, T. L.; Chang, K. T.; Mazur, J. H.

    1988-01-01

    The growth of CrSi2 on Si(111) in a commercial MBE system with a base pressure in the low 10 to the -11th torr range is reported. CrSi2 layers grown on Si(111) exhibit a strong tendency to form islands. Two particular epitaxial relationships are identified. Thick (210 nm) layers have been grown by four different techniques, with best results obtained by codepositing Cr and Si at elevated temperature. The grain size is observed to increase with substrate temperature, reaching 1-2 microns in a layer deposited at 825 C.

  14. Isotropic plasma etching of Ge Si and SiNx films

    SciTech Connect

    Henry, Michael David; Douglas, Erica Ann

    2016-08-31

    This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching.

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

    PubMed

    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%.

  16. Structural and Optical Properties of Si-Core/SiO x -Shell Nanowires

    NASA Astrophysics Data System (ADS)

    Thuy, Nguyen Thi; Tho, Do Duc; Tu, Nguyen Cong; Vuong, Dang Duc; Chien, Nguyen Duc; Lam, Nguyen Huu

    2017-01-01

    Si-core/SiO x -shell nanowires (NWs) have been synthesized on Si(111) surfaces using the vapor-liquid-solid technique. A 2-nm-thick Au layer was deposited by electron-beam evaporation as a metal catalyst. Au nanoparticles were formed by annealing at high temperature, resulting in subsequent formation of NWs. The Si-core/SiO x -shell structure of the NWs was investigated via scanning electron microscopy, transmission electron microscopy, x-ray diffraction analysis, and Raman spectroscopy. Photoluminescence measurements demonstrated a quantum confinement effect because of the reduced diameter of the NWs.

  17. Monolayer-induced band shifts at Si(100) and Si(111) surfaces

    SciTech Connect

    Mäkinen, A. J. Kim, Chul-Soo; Kushto, G. P.

    2014-01-27

    We report our study of the interfacial electronic structure of Si(100) and Si(111) surfaces that have been chemically modified with various organic monolayers, including octadecene and two para-substituted benzene derivatives. X-ray photoelectron spectroscopy reveals an upward band shift, associated with the assembly of these organic monolayers on the Si substrates, that does not correlate with either the dipole moment or the electron withdrawing/donating character of the molecular moieties. This suggests that the nature and quality of the self-assembled monolayer and the intrinsic electronic structure of the semiconductor material define the interfacial electronic structure of the functionalized Si(100) and Si(111) surfaces.

  18. Isotropic plasma etching of Ge Si and SiNx films

    DOE PAGES

    Henry, Michael David; Douglas, Erica Ann

    2016-08-31

    This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching.

  19. High Mobility SiGe/Si n-MODFET Structures and Devices on Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Mueller, Carl; Alterovitz, Samuel; Croke, Edward; Ponchak, George

    2004-01-01

    Si/Ge/Si n-type modulation doped field effect structures and transistors (n-MODFET's) have been fabricated on r-plane sapphire substrates. Mobilities as high as 1380 cm(exp 2)/Vs were measured at room temperature. Excellent carrier confinement was shown by Shubnikov-de Haas measurements. Atomic force microscopy indicated smooth surfaces, with rm's roughness less than 4 nm, similar to the quality of SiGe/Si n-MODFET structures made on Si substrates. Transistors with 2 micron gate lengths and 200 micron gate widths were fabricated and tested.

  20. Si-based blue light emitting diode

    NASA Astrophysics Data System (ADS)

    Namavar, Fereydoon

    1994-05-01

    Phase 1 results demonstrated for the first time a strong, stable blue-green emission from C-implanted red-emitting porous silicon. The objective of Phase 1 was to obtain blue-green emission from porous Si structure either by increasing the bandgap of the substrate by growth of Si-C random alloys prior to forming nanostructures with quantum confined properties, or by increasing the confinement energy of red-emitting Si nanostructures. Porous structures fabricated from group 4 alloys epitaxially grown by chemical vapor deposition (CVD) resulted in an enhancement in light emission of about one order of magnitude after incorporation of a very small amount of carbon in the epitaxial grown films. Strong blue-green light emission was observed by the naked eye from C-implanted and annealed porous Si. Using AlGaAs as a reference, we observed that the intensity of blue-green emission was one order of magnitude higher than that of the original red-emitting porous Si. Catholuminescence measurements of our samples performed at the University of Colorado show blue emission at 1.80 eV and 2.80 eV. Fourier transform infrared (FTIR) spectra of a blue-green emitting porous structure shows an IR absorption line identical to that of SiC and electron diffraction studies clearly show reflections corresponding to beta-SiC. Phase 1 results indicate that blue-green light is from SiC nanostructures with quantum confined properties. This material may be used to fabricate blue light-emitting Si-based devices which can be easily integrated into Si technology.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    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.

  2. Analysis of the dynamics of reactions of SiCl2 at Si(100) surfaces

    NASA Astrophysics Data System (ADS)

    Anzai, Keisuke; Kunioshi, Nílson; Fuwa, Akio

    2017-01-01

    The dynamics of reactions of SiCl2 at Si(100) surfaces was investigated through the molecular orbital method at the B3LYP/6-31G(d,p) level of theory, with the surface being modeled using clusters of silicon atoms. The intradimer adsorption of a SiCl2 molecule proceeded with no energy barrier, and in the structure of the product of the adsorption reaction the Si atom of the SiCl2 adsorbate formed a triangular structure with the two Si atoms of the surface dimer, in agreement with theoretical predictions published recently in the literature for a small cluster. However, the dynamics reported in this work indicates that SiCl2 undergoes molecular adsorption at the silicon surface, in contrast with the dissociative adsorption suggested by some available kinetic models. Intradimer adsorption of a second SiCl2 molecule, and interdimer adsorptions of a first, a second, and a third SiCl2 molecule were also seen to proceed without significant energy barriers, suggesting that the formation of the first additional layer of silicon atoms on the surface would be fast if the adsorption of SiCl2 were the only type of reaction proceeding in the system. The diffusion of the SiCl2 adsorbate over the surface and its desorption from the surface were found to have comparable activation energies, so that these reactions are expected to compete at high temperatures.

  3. Size-dependent electroluminescence from Si quantum dots embedded in amorphous SiC matrix

    NASA Astrophysics Data System (ADS)

    Rui, Yunjun; Li, Shuxin; Xu, Jun; Song, Chao; Jiang, Xiaofan; Li, Wei; Chen, Kunji; Wang, Qimin; Zuo, Yuhua

    2011-09-01

    Si quantum dots (QDs) were formed by thermal annealing the hydrogenated amorphous silicon carbide films (a-SiCx:H) with different C/Si ratio x, which were controlled by using a different gas ratio R of methane to silane during the deposition process. By adjusting x and post annealing temperature, the QD size can be changed from 1.4 to 4.2 nm accordingly, which was verified by the Raman spectra and transmission electron microscopy images. Size-dependent electroluminescence (EL) was observed, and the EL intensity was higher for the sample containing small-sized Si QDs due to the quantum confinement effect (QCE). The EL peak energy as a function of the Si QDs size was in good agreement with a modified effective mass approximation (EMA) model. The calculated finite barrier potential of the Si QDs embedded in SiC matrix is 0.4 and 0.8 eV for conduction and valence band, respectively. Moreover, the current-voltage properties and the linear relationship between the integrated EL intensity and injection current indicate that the carrier transport is dominated by Fowler-Nordheim tunneling and the EL mechanism is originated from the bipolar recombination of electron-hole pairs at Si QDs. Our results demonstrate Si QDs embedded in amorphous SiC matrix has the potential application in Si-based light emitting devices and the third-generation solar cells.

  4. Refinement of Eutectic Si Phase in Al-5Si Alloys with Yb Additions

    NASA Astrophysics Data System (ADS)

    Li, J. H.; Suetsugu, S.; Tsunekawa, Y.; Schumacher, P.

    2013-02-01

    A series of Al-5 wt pct Si alloys with Yb additions (up to 6100 ppm) have been investigated using thermal analysis and multiscale microstructure characterization techniques. The addition of Yb was found to cause no modification effect to a fibrous morphology involving Si twinning; however, a refined plate-like eutectic structure was observed. The Al2Si2Yb phase was observed with Yb addition level of more than 1000 ppm. Within the eutectic Al and Si phases, the Al2Si2Yb phase was also found as a precipitation from the remained liquid. No Yb was detected in the α-Al matrix or plate-like Si particle, even with Yb addition up to 6100 ppm. The absence of Yb inside the eutectic Si particle may partly explain why no significant Si twinning was observed along {111}Si planes in the eutectic Si particle. In addition, the formation of the thermodynamic stable YbP phases is also proposed to deteriorate the potency of AlP phase in Al alloys. This investigation highlights to distinguish the modification associated with the ever present P in Al alloys. We define modification as a transition from faceted to fibrous morphology, while a reduction of the Si size is termed refinement.

  5. Fabrication and measurement of devices in Si/SiGe nanomembranes

    NASA Astrophysics Data System (ADS)

    Mohr, Robert

    Silicon/silicon-germanium (Si/SiGe) heterostructures are useful as hosts for gated quantum dots. The quality of the as-grown Si/SiGe heterostructure has a large impact on the final quality of the quantum dot as a qubit host. For many years, quantum dots have been fab- ricated on strain-graded heterostructures. Commonly used strain-graded heterostructures inevitably develop plastic defects that lead to interface roughness, crosshatch, and mosaic tilt. All of these factors are sources of disorder in Si/SiGe quantum electronics. In this dissertation, I report the fabrication of Hall bars and gated quantum dots on heterostructures grown on fully elastically relaxed SiGe nanomembranes, rather than strain-graded heterostructures. I report measurements of Hall bars demonstrating the creation of two-dimensional electron gases in these structures. I report the fabrication procedures used to create pairs of Hall bars and quantum dots on individual membranes. In addition, I explain a general process flow for the creation of Si/SiGe quantum devices. I focus especially on an ion-implantation technique I implemented for the fabrication of Hall bars and quantum dots in Si/SiGe heterostructures without modulation doping layers.

  6. Effects of SiC on Properties of Cu-SiC Metal Matrix Composites

    NASA Astrophysics Data System (ADS)

    Efe, G. Celebi; Altinsoy, I.; Ipek, M.; Zeytin, S.; Bindal, C.

    2011-12-01

    This paper was focused on the effects of particle size and distribution on some properties of the SiC particle reinforced Cu composites. Copper powder produced by cementation method was reinforced with SiC particles having 1 and 30 μm particle size and sintered at 700 °C. SEM studies showed that SiC particles dispersed in copper matrix homogenously. The presence of Cu and SiC components in composites were verified by XRD analysis technique. The relative densities of Cu-SiC composites determined by Archimedes' principle are ranged from 96.2% to 90.9% for SiC with 1 μm particle size, 97.0 to 95.0 for SiC with 30 μm particle size. Measured hardness of sintered compacts varied from 130 to 155 HVN for SiC having 1 μm particle size, 188 to 229 HVN for SiC having 1 μm particle size. Maximum electrical conductivity of test materials was obtained as 80.0% IACS (International annealed copper standard) for SiC with 1 μm particle size and 83.0% IACS for SiC with 30 μm particle size.

  7. SiC and Si3N4 Recession Due to SiO2 Scale Volatility Under Combustor Conditions

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Robinson, Raymond C.; Opila, Elizabeth J.; Fox, Dennis S.; Jacobson, Nathan S.

    1999-01-01

    Silicon carbide (SiC) and Si3N4 materials were tested in various turbine engine combustion environments chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high-speed aircraft. Representative chemical vapor-deposited (CVD), sintered, and composite materials were evaluated by furnace and high-pressure burner rig exposures. Although protective SiO2 scales formed in all cases, the evidence presented supports a model based on paralinear growth kinetics (i.e., parabolic growth moderated simultaneously by linear volatilization). The volatility rate is dependent on temperature, moisture content, system pressure, and gas velocity. The burner tests were thus used to map SiO2 volatility (and SiC recession) over a range of temperatures, pressures, and velocities. The functional dependency of material recession (volatility) that emerged followed the form A[exp(-Q / RT)](P(sup x)v(sup y). These empirical relations were compared with rates predicted from the thermodynamics of volatile SiO and SiOxHy reaction products and a kinetic model of diffusion through a moving boundary layer. For typical combustion conditions, recession of 0.2 to 2 micrometers/hr is predicted at 1200 to 1400 C, far in excess of acceptable long-term limits.

  8. SiC and Si3N4 Recession Due to SiO2 Scale Volatility Under Combustor Conditions

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Robinson, R. Craig; Opila, Elizabeth J.; Fox, Dennis S.; Jacobson, Nathan S.

    1999-01-01

    SiC and Si3N4 materials were tested under various turbine engine combustion environments, chosen to represent either conventional fuel-lean or fuel-rich mixtures proposed for high speed aircraft. Representative CVD, sintered, and composite materials were evaluated in both furnace and high pressure burner rig exposure. While protective SiO2 scales form in all cases, evidence is presented to support paralinear growth kinetics, i.e. parabolic growth moderated simultaneously by linear volatilization. The volatility rate is dependent on temperature, moisture content, system pressure, and gas velocity. The burner tests were used to map SiO2 volatility (and SiC recession) over a range of temperature, pressure, and velocity. The functional dependency of material recession (volatility) that emerged followed the form: exp(-QIRT) * P(exp x) * v(exp y). These empirical relations were compared to rates predicted from the thermodynamics of volatile SiO and SiO(sub x)H(sub Y) reaction products and a kinetic model of diffusion through a moving, boundary layer. For typical combustion conditions, recession of 0.2 to 2 micron/h is predicted at 1200- 1400C, far in excess of acceptable long term limits.

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

    NASA Astrophysics Data System (ADS)

    Kunimune, Yorinobu; Shimada, Yasuhiro; Sakurai, Yusuke; Inoue, Masao; Nishida, Akio; Han, Bin; Tu, Yuan; Takamizawa, Hisashi; Shimizu, Yasuo; Inoue, Koji; Yano, Fumiko; Nagai, Yasuyoshi; Katayama, Toshiharu; Ide, Takashi

    2016-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Localization of electrons in dome-shaped GeSi/Si islands

    SciTech Connect

    Yakimov, A. I.; Kirienko, V. V.; Bloshkin, A. A.; Armbrister, V. A.; Kuchinskaya, P. A.; Dvurechenskii, A. V.

    2015-01-19

    We report on intraband photocurrent spectroscopy of dome-shaped GeSi islands embedded in a Si matrix with n{sup +}-type bottom and top Si layers. An in-plane polarized photoresponse in the 85–160 meV energy region has been observed and ascribed to the optical excitation of electrons from states confined in the strained Si near the dome apexes to the continuum states of unstrained Si. The electron confinement is caused by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried GeSi quantum dots. Sensitivity of the device to the normal incidence radiation proves a zero-dimensional nature of confined electronic wave functions.

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

    PubMed

    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.

  13. Silicon Effects on Properties of Melt Infiltrated SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.; Gyekenyesi, John Z.; Hurst, Janet B.

    2000-01-01

    Silicon effects on tensile and creep properties, and thermal conductivity of Hi-Nicalon SiC/SiC composites have been investigated. The composites consist of 8 layers of 5HS 2-D woven preforms of BN/SiC coated Hi-Nicalon fiber mats and a silicon matrix, or a mixture of silicon matrix and SiC particles. The Hi-Nicalon SiC/silicon and Hi-Nicalon SiC/SiC composites contained about 24 and 13 vol% silicon, respectively. Results indicate residual silicon up to 24 vol% has no significant effect on creep and thermal conductivity, but does decrease the primary elastic modulus and stress corresponding to deviation from linear stress-strain behavior.

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

    NASA Astrophysics Data System (ADS)

    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).

  15. Inherent interface defects in thermal (211)Si/SiO{sub 2}:{sup 29}Si hyperfine interaction

    SciTech Connect

    Iacovo, Serena E-mail: andre.stesmans@fys.kuleuven.be; Stesmans, Andre E-mail: andre.stesmans@fys.kuleuven.be

    2014-10-21

    Low temperature electron spin resonance (ESR) studies were carried out on ‘higher index’ (211)Si/SiO{sub 2} interfaces thermally grown in the temperature range T{sub ox} = 400–1066°C. The data reveal the presence of two species of a P{sub b}-type interface defect, exhibiting a significant difference in defect density. On the basis of the pertinent ESR parameters and interface symmetry, the basic defect is typified as P{sub b0}{sup (211)}, close to the Pb0 center observed in standard (100)Si/SiO{sub 2}. The dominant type is found to pertain to defected Si atoms at (111)Si-face terraces with the dangling bond along the [111] direction at ∼19.5°C with the interface normal, these sites thus apparently predominantly accounting for interface mismatch adaptation. The total of the P{sub b}-type defect appearance clearly reflects the higher-index nature of the interface. It is found that T{sub ox} = 750°C is required to minimize the P{sub b0}{sup (211)} defect density through relaxation of the oxide (interface). Q-band ESR saturation spectroscopy reveals an anisotropic {sup 29}Si (nuclear spin I=1/2) hyperfine (hf) doublet associated with the central P{sub b0}{sup (211)} Zeeman signal, with hf parameters closest to those of the similar hf structure of the P{sub b0}{sup (110)} defect in thermal (110)Si/SiO{sub 2}, adducing independent support to the P{sub b0}{sup (211)} typification.

  16. p-n Junction Diodes Fabricated on Si-Si/Ge Heteroepitaxial Films

    NASA Technical Reports Server (NTRS)

    Das, K.; Mazumder, M. D. A.; Hall, H.; Alterovitz, Samuel A. (Technical Monitor)

    2000-01-01

    A set of photolithographic masks was designed for the fabrication of diodes in the Si-Si/Ge material system. Fabrication was performed on samples obtained from two different wafers: (1) a complete HBT structure with an n (Si emitter), p (Si/Ge base), and an n/n+ (Si collector/sub-collector) deposited epitaxially (MBE) on a high resistivity p-Si substrate, (2) an HBT structure where epitaxial growth was terminated after the p-type base (Si/Ge) layer deposition. Two different process runs were attempted for the fabrication of Si-Si/Ge (n-p) and Si/Ge-Si (p-n) junction diodes formed between the emitter-base and base-collector layers, respectively, of the Si-Si/Ge-Si HBT structure. One of the processes employed a plasma etching step to expose the p-layer in the structure (1) and to expose the e-layer in structure (2). The Contact metallization used for these diodes was a Cu-based metallization scheme that was developed during the first year of the grant. The plasma-etched base-collector diodes on structure (2) exhibited well-behaved diode-like characteristics. However, the plasma-etched emitter-base diodes demonstrated back-to-back diode characteristics. These back-to back characteristics were probably due to complete etching of the base-layer, yielding a p-n-p diode. The deep implantation process yielded rectifying diodes with asymmetric forward and reverse characteristics. The ideality factor of these diodes were between 1.6 -2.1, indicating that the quality of the MBE grown epitaxial films was not sufficiently high, and also incomplete annealing of the implantation damage. Further study will be conducted on CVD grown films, which are expected to have higher epitaxial quality.

  17. Optical and Structural Properties of Si Nanocrystals in SiO2 Films

    PubMed Central

    Nikitin, Timur; Khriachtchev, Leonid

    2015-01-01

    Optical and structural properties of Si nanocrystals (Si-nc) in silica films are described. For the SiOx (x < 2) films annealed above 1000 °C, the Raman signal of Si-nc and the absorption coefficient are proportional to the amount of elemental Si detected by X-ray photoelectron spectroscopy. A good agreement is found between the measured refractive index and the value estimated by using the effective-medium approximation. The extinction coefficient of elemental Si is found to be between the values of crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the crystallization and the Si–SiO2 phase separation are not complete after annealing at 1200 °C. The 1.5-eV PL quantum yield increases as the amount of elemental Si decreases; thus, this PL is probably not directly from Si-nc responsible for absorption and detected by Raman spectroscopy. Continuous-wave laser light can produce very high temperatures in the free-standing films, which changes their structural and optical properties. For relatively large laser spots, the center of the laser-annealed area is very transparent and consists of amorphous SiO2. Large Si-nc (up to ~300 nm in diameter) are observed in the ring around the central region. These Si-nc lead to high absorption and they are typically under compressive stress, which is connected with their formation from the liquid phase. By using strongly focused laser beams, the structural changes in the free-standing films can be made in submicron areas.

  18. Mushroom-free selective epitaxial growth of Si, SiGe and SiGe:B raised sources and drains

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Lafond, D.; Damlencourt, J. F.; Morvan, S.; Prévitali, B.; Andrieu, F.; Loubet, N.; Dutartre, D.

    2013-05-01

    We have evaluated various Cyclic Selective Epitaxial Growth/Etch (CSEGE) processes in order to grow "mushroom-free" Si and SiGe:B Raised Sources and Drains (RSDs) on each side of ultra-short gate length Extra-Thin Silicon-On-Insulator (ET-SOI) transistors. The 750 °C, 20 Torr Si CSEGE process we have developed (5 chlorinated growth steps with four HCl etch steps in-between) yielded excellent crystalline quality, typically 18 nm thick Si RSDs. Growth was conformal along the Si3N4 sidewall spacers, without any poly-Si mushrooms on top of unprotected gates. We have then evaluated on blanket 300 mm Si(001) wafers the feasibility of a 650 °C, 20 Torr SiGe:B CSEGE process (5 chlorinated growth steps with four HCl etch steps in-between, as for Si). As expected, the deposited thickness decreased as the total HCl etch time increased. This came hands in hands with unforeseen (i) decrease of the mean Ge concentration (from 30% down to 26%) and (ii) increase of the substitutional B concentration (from 2 × 1020 cm-3 up to 3 × 1020 cm-3). They were due to fluctuations of the Ge concentration and of the atomic B concentration [B] in such layers (drop of the Ge% and increase of [B] at etch step locations). Such blanket layers were a bit rougher than layers grown using a single epitaxy step, but nevertheless of excellent crystalline quality. Transposition of our CSEGE process on patterned ET-SOI wafers did not yield the expected results. HCl etch steps indeed helped in partly or totally removing the poly-SiGe:B mushrooms on top of the gates. This was however at the expense of the crystalline quality and 2D nature of the ˜45 nm thick Si0.7Ge0.3:B recessed sources and drains selectively grown on each side of the imperfectly protected poly-Si gates. The only solution we have so far identified that yields a lesser amount of mushrooms while preserving the quality of the S/D is to increase the HCl flow during growth steps.

  19. Electrical Characteristics of Ni-CNT-SiO2-SiC Structured 4H-SiC MIS Capacitors.

    PubMed

    Lee, Taeseop; Kang, Min-Seok; Ha, Tae-Jun; Koo, Sang-Mo

    2015-10-01

    In this study, the electrical characteristics of Ni-CNT-SiO2-SiC structured 4H-SiC MIS capacitors were investigated. The effect of CNTs in the gate/insulator interface have been characterized by C-V measurement at 300 to 500K and J-V have also been measured. The experimental flat-band voltage tends to change with or without CNTs. Current densities of both devices are observed a negligible difference up to 3 V. It has been found that adding CNTs and/or change of temperature can help to control the positive and/or negative flat-band voltage shift.

  20. Multi-Step Bidirectional NDR Characteristics in Si/Si1-xGex/Si DHBTs and Their Temperature Dependence

    NASA Astrophysics Data System (ADS)

    Xu, D. X.; Shen, G. D.; Willander, M.; Hansson, G. V.

    1988-11-01

    Novel bidirectional negative differential resistance (NDR) phenomena have been observed at room temperature in strained base n-Si/p-Si1-xGex/n-Si double heterojunction bipolar transistors (DHBTs). A strong and symmetric bidirectional NDR modulated by base bias, together with a multi-step characteristic in collector current IC vs emitter-collector bias voltage VCE, was obtained in the devices with very thin base. The temperature dependence of the NDR and the multi-step IC-VCE characteristics has been measured to identify the possible transport mechanism. The physical origins of these phenomena are discussed.

  1. Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.

    2016-08-01

    Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ˜70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ˜10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2σ). Equilibrium

  2. Silicon photonics cloud (SiCloud)

    NASA Astrophysics Data System (ADS)

    DeVore, Peter T. S.; Jiang, Yunshan; Lynch, Michael; Miyatake, Taira; Carmona, Christopher; Chan, Andrew C.; Muniam, Kuhan; Jalali, Bahram

    2015-02-01

    We present SiCloud (Silicon Photonics Cloud), the first free, instructional web-based research and education tool for silicon photonics. SiCloud's vision is to provide a host of instructional and research web-based tools. Such interactive learning tools enhance traditional teaching methods by extending access to a very large audience, resulting in very high impact. Interactive tools engage the brain in a way different from merely reading, and so enhance and reinforce the learning experience. Understanding silicon photonics is challenging as the topic involves a wide range of disciplines, including material science, semiconductor physics, electronics and waveguide optics. This web-based calculator is an interactive analysis tool for optical properties of silicon and related material (SiO2, Si3N4, Al2O3, etc.). It is designed to be a one stop resource for students, researchers and design engineers. The first and most basic aspect of Silicon Photonics is the Material Parameters, which provides the foundation for the Device, Sub-System and System levels. SiCloud includes the common dielectrics and semiconductors for waveguide core, cladding, and photodetection, as well as metals for electrical contacts. SiCloud is a work in progress and its capability is being expanded. SiCloud is being developed at UCLA with funding from the National Science Foundation's Center for Integrated Access Networks (CIAN) Engineering Research Center.

  3. Optical characterization of SiC wafers

    SciTech Connect

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

    1999-07-01

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

  4. SiC-Based Gas Sensors

    NASA Technical Reports Server (NTRS)

    Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Knight, Dak; Liu, C. C.; Wu, Q. H.

    1997-01-01

    Electronic grade Silicon Carbide (SiC) is a ceramic material which can operate as a semiconductor at temperatures above 600 C. Recently, SiC semiconductors have been used in Schottky diode gas sensor structures. These sensors have been shown to be functional at temperatures significantly above the normal operating range of Si-based devices. SiC sensor operation at these higher temperatures allows detection of gases such as hydrocarbons which are not detectable at lower temperatures. This paper discusses the development of SiC-based Schottky diode gas sensors for the detection of hydrogen, hydrocarbons, and nitrogen oxides (NO(x)). Sensor designs for these applications are discussed. High sensitivity is observed for the hydrogen and hydrocarbon sensors using Pd on SiC Schottky diodes while the NO(x) sensors are still under development. A prototype sensor package has been fabricated which allows high temperature operation in a room temperature ambient by minimizing heat loss to that ambient. It is concluded that SiC-based gas sensors have considerable potential in a variety of gas sensing applications.

  5. Si Wire-Array Solar Cells

    NASA Astrophysics Data System (ADS)

    Boettcher, Shannon

    2010-03-01

    Micron-scale Si wire arrays are three-dimensional photovoltaic absorbers that enable orthogonalization of light absorption and carrier collection and hence allow for the utilization of relatively impure Si in efficient solar cell designs. The wire arrays are grown by a vapor-liquid-solid-catalyzed process on a crystalline (111) Si wafer lithographically patterned with an array of metal catalyst particles. Following growth, such arrays can be embedded in polymethyldisiloxane (PDMS) and then peeled from the template growth substrate. The result is an unusual photovoltaic material: a flexible, bendable, wafer-thickness crystalline Si absorber. In this paper I will describe: 1. the growth of high-quality Si wires with controllable doping and the evaluation of their photovoltaic energy-conversion performance using a test electrolyte that forms a rectifying conformal semiconductor-liquid contact 2. the observation of enhanced absorption in wire arrays exceeding the conventional light trapping limits for planar Si cells of equivalent material thickness and 3. single-wire and large-area solid-state Si wire-array solar cell results obtained to date with directions for future cell designs based on optical and device physics. In collaboration with Michael Kelzenberg, Morgan Putnam, Joshua Spurgeon, Daniel Turner-Evans, Emily Warren, Nathan Lewis, and Harry Atwater, California Institute of Technology.

  6. p-Cu2O/SiO x /n-SiC/n-Si memory diode fabricated with room-temperature-sputtered n-SiC and SiO x

    NASA Astrophysics Data System (ADS)

    Yamashita, Atsushi; Tsukamoto, Takahiro; Suda, Yoshiyuki

    2016-12-01

    We investigated low-temperature fabrication processes for our previously proposed pn memory diode with a p-Cu2O/SiC x O y /n-SiC/n-Si structure having resistive nonvolatile memory and rectifying behaviors suitable for a cross-point memory array with the highest theoretical density. In previous fabrication processes, n-SiC was formed by sputtering at 1113 K, and SiC x O y and p-Cu2O were formed by the thermal oxidation of n-SiC and Cu at 1073 and 473 K, respectively. In this study, we propose a pn memory diode with a p-Cu2O/SiO x /n-SiC/n-Si structure, where n-SiC and SiO x layers are deposited by sputtering at room temperature. The proposed processes enable the fabrication of the pn memory diode at temperatures of not more than 473 K, which is used for the formation of p-Cu2O. This memory diode exhibits good nonvolatile memory and rectifying characteristics. These proposed low-temperature fabrication processes are expected to expand the range of fabrication processes applicable to current LSI fabrication processes.

  7. Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal

    PubMed Central

    Chan, Ya-Ting; Kuan, Wen-Hui; Tzou, Yu-Min; Chen, Tsan-Yao; Liu, Yu-Ting; Wang, Ming-Kuang; Teah, Heng-Yi

    2016-01-01

    Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates. PMID:27095071

  8. Electronic structure, charge distribution, and charge transfer in α- and β-Si3N4 and at the Si(111)/Si3N4(001) interface

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bachlechner, M. E.

    1997-02-01

    The electronic structure, charge distribution, and charge transfer in α- and β- Si3N4 and at the Si(111)/Si3N4(001) interface have been studied using a self-consistent first-principles LCAO method. The calculated charge transfer suggests that both in α- and β-phases, the ionic formula may be written as Si3+1.24N4-0.93. For the Si(111)/Si3N4(001) interface, the silicon atoms from the Si(111) side give some electrons to the N atoms of Si3N4 forming the Si-N bonds at the interface. One Si-N bond is associated with a charge transfer of about 0.31 electrons.

  9. Carbon Diffusion through SiO2 from a Hydrogenated Amorphous Carbon Layer and Accumulation at the SiO2/Si Interface

    NASA Astrophysics Data System (ADS)

    Krafcsik, Olga H.; Vida, György; Pócsik, István; Josepovits, Katalin V.; Deák, Péter

    2001-04-01

    Carbon diffusion in a SiO2/Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190°C@. If the O content was high, the diffusion would start suddenly at 1140°C, and carbon accumulation would be found on the Si side of the SiO2/Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO2 and an exothermic reaction of CO with Si. No carbon segregation was found in SiO2. Consequences of carbon island formation during SiC oxidation are pointed out.

  10. Dependence of Morphology of SiOx Nanowires on the Supersaturation of Au-Si Alloy Liquid Droplets Formed on the Au-Coated Si Substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Li, Ji-Xue; Jin, Ai-Zi; Zhang, Ze

    2001-11-01

    A thermodynamic theory about the dependence of morphology of SiOx nanowires on the super-saturation of alloy liquid droplets has been proposed on the basis of the vapour-liquid-solid growth mechanism and has been supported experimentally. By changing the Si concentration in the Au-Si liquid droplets formed on the Au-coated Si substrate, firework-, tulip- and bud-shaped SiOx nanowires were synthesized by a thermal evaporation method and distributed concentrically around some void defects in the Si substrate. Voids were formed underneath the surface of the Si substrate during the thermal evaporation at 850°C and resulted in the Si-concentration deficient thus different saturation of Au-Si droplets. Electron microscopy analysis showed that the nanowires had an amorphous structure and were terminated by Au-Si particles.

  11. SiC for Space Optics

    NASA Astrophysics Data System (ADS)

    Wellman, John

    2012-01-01

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

  12. Mo-Si-B Alloy Development

    SciTech Connect

    Schneibel, J.H.; Kruzie, J.J.; Ritchie, R.O.

    2003-04-24

    Mo-Si-B silicides consisting of the phases {alpha}-Mo (Mo solid solution), Mo{sub 3}Si, and Mo{sub 5}SiB{sub 2} have melting points on the order of 2000 C and have potential as ultra-high temperature structural materials. Mo-Si-B alloys can be processed such that the {alpha}-Mo is present in the form of isolated particles in a silicide matrix, or as a continuous matrix ''cementing'' individual silicide particles together. The latter microstructure is similar to that of WC-Co hard metals. This paper focuses on the relationship between the topology as well as scale of the microstructure of Mo-Mo{sub 3}Si-Mo{sub 5}SiB{sub 2} alloys, and their creep strength and fracture toughness. For example, the creep strength of Mo-Si-B alloys is improved by reducing the {alpha}-Mo volume fraction and by making the {alpha}-Mo phase discontinuous. The fracture toughness is improved by increasing the {alpha}-Mo volume fraction and by making the {alpha}-Mo phase continuous. Room temperature stress intensity factors as high as 21 MPa m{sup 1/2} were obtained. The room temperature fracture toughness of Mo-Si-B alloys can also be improved by microalloying with Zr. The room temperature ductility of Mo itself can be improved by adding MgAl{sub 2}O{sub 4} spinel particles suggesting yet another way to improve the ductile phase toughening of Mo-Si-B alloys.

  13. Influence of the permeability of networked primary Si on the ejection of hypereutectic Al-Si melts by centrifugation

    NASA Astrophysics Data System (ADS)

    Youn, Ji Won; Jeon, Je-Beom; Park, Jin Man; Seo, Seok Yong; Lim, Jeon Taik; Kim, Suk Jun; Kim, Ki Young

    2017-02-01

    The separation of high purity Si for solar cells from Al-Si alloy melt in the mushy zone was investigated using an advanced centrifugal technique. The efficiency of separating Si, based on the weight ratio of separated Si to Si in alloy melt, was maximized by optimizing the permeability of a porous structure of Si (Si foam.) For the optimization of the permeability, two fundamental microstructure variables, size and the solid fraction of primary Si platelets, were controlled by adjusting the Si content in the melts and the rotation start temperature, respectively. The best separation efficiency (48.3% with 3N purity) was achieved when Si content in melt was 24% and the solid fraction was 8.7%. The melt with 23% Si led to a higher separation efficiency (69.8%) for a solid fraction of 10.4%, but Al sandwiched between the Si platelets resulted in a decrease in the purity to 2N.

  14. SEMICONDUCTOR TECHNOLOGY: SBH adjustment characteristic of the dopant segregation process for NiSi/n-Si SJDs

    NASA Astrophysics Data System (ADS)

    Haiping, Shang; Qiuxia, Xu

    2010-05-01

    By means of analyzing the I-V characteristic curve of NiSi/n-Si Schottky junction diodes (NiSi/n-Si SJDs), abstracting the effective Schottky barrier height (varphiB, eff) and the ideal factor of NiSi/n-Si SJDs and measuring the sheet resistance of NiSi films (RNiSi), we study the effects of different dopant segregation process parameters, including impurity implantation dose, segregation annealing temperature and segregation annealing time, on the varphiB, eff of NiSi/n-Si SJDs and the resistance characteristic of NiSi films. In addition, the changing rules of varphiB, eff and RNiSi are discussed.

  15. Influence of the permeability of networked primary Si on the ejection of hypereutectic Al-Si melts by centrifugation

    NASA Astrophysics Data System (ADS)

    Youn, Ji Won; Jeon, Je-Beom; Park, Jin Man; Seo, Seok Yong; Lim, Jeon Taik; Kim, Suk Jun; Kim, Ki Young

    2017-03-01

    The separation of high purity Si for solar cells from Al-Si alloy melt in the mushy zone was investigated using an advanced centrifugal technique. The efficiency of separating Si, based on the weight ratio of separated Si to Si in alloy melt, was maximized by optimizing the permeability of a porous structure of Si (Si foam.) For the optimization of the permeability, two fundamental microstructure variables, size and the solid fraction of primary Si platelets, were controlled by adjusting the Si content in the melts and the rotation start temperature, respectively. The best separation efficiency (48.3% with 3N purity) was achieved when Si content in melt was 24% and the solid fraction was 8.7%. The melt with 23% Si led to a higher separation efficiency (69.8%) for a solid fraction of 10.4%, but Al sandwiched between the Si platelets resulted in a decrease in the purity to 2N.

  16. Si(hhm) surfaces: Templates for developing nanostructures

    SciTech Connect

    Bozhko, S. I. Ionov, A. M.; Chaika, A. N.

    2015-06-15

    The fabrication of ordered low-dimensional structures on clean and metal-atom-decorated stepped Si(557) and Si(556) surfaces is discussed. The formation conditions and atomic structure of regular step systems on clean Si(557) 7 × 7 and Si(556) 7 × 7 surfaces are studied. The atomic structure of stepped Si(hhm), Ag/Si(557), and Gd/Si(557) surfaces is studied using high-resolution scanning tunneling microscopy and low-energy electron diffraction. The possibility of fabricating 1D and 2D structures of gadolinium and silver atoms on the Si(557) surface is demonstrated.

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

    PubMed Central

    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 (<1025 parts per million atoms, ppma) significantly improved the B removal. It was confirmed that the use of an increased 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

  18. Refinement of primary Si grains in Al-20%Si alloy slurry through serpentine channel pouring process

    NASA Astrophysics Data System (ADS)

    Zheng, Zhi-kai; Mao, Wei-min; Liu, Zhi-yong; Wang, Dong; Yue, Rui

    2016-05-01

    In this study, a serpentine channel pouring process was used to prepare the semi-solid Al-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the serpentine channel, and material of the serpentine channel on the size of primary Si grains in the semi-solid Al-20%Si alloy slurry were investigated. The results showed that the pouring temperature, number of the curves, and material of the channel strongly affected the size and distribution of the primary Si grains. The pouring temperature exerted the strongest effect, followed by the number of the curves and then the material of the channel. Under experimental conditions of a four-curve copper channel and a pouring temperature of 701°C, primary Si grains in the semi-solid Al-20%Si alloy slurry were refined to the greatest extent, and the lath-like grains were changed into granular grains. Moreover, the equivalent grain diameter and the average shape coefficient of primary Si grains in the satisfactory semi-solid Al-20%Si alloy slurry were 24.4 μm and 0.89, respectively. Finally, the refinement mechanism and distribution rule of primary Si grains in the slurry prepared through the serpentine channel pouring process were analyzed and discussed.

  19. SiS in Circumstellar Shells

    NASA Astrophysics Data System (ADS)

    Sahai, R.; Wootten, A.; Clegg, R. E. S.

    1985-07-01

    The author has observed the spectrum of SiS toward the Mira variable IRC+10216, and made a detailed model incorporating a radial SiS abundance gradient due to photodissociation by interstellar UV (Sahai, Wootten, and Clegg 1984). The sensitive search for SiS J = 7-6 and J = 6-5 lines in other carbon-rich, oxygen-rich, and S-type envelopes has revealed three new sources, CIT 6, CRL 2688 and IRC+20370, all of which are carbon-rich.

  20. SiC MEMS For Harsh Environments

    DTIC Science & Technology

    2003-12-01

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

  1. Si cycling in a forest biogeosystem - the importance of transient state biogenic Si pools

    NASA Astrophysics Data System (ADS)

    Sommer, M.; Jochheim, H.; Höhn, A.; Breuer, J.; Zagorski, Z.; Busse, J.; Barkusky, D.; Meier, K.; Puppe, D.; Wanner, M.; Kaczorek, D.

    2013-07-01

    The relevance of biological Si cycling for dissolved silica (DSi) export from terrestrial biogeosystems is still in debate. Even in systems showing a high content of weatherable minerals, like Cambisols on volcanic tuff, biogenic Si (BSi) might contribute > 50% to DSi (Gerard et al., 2008). However, the number of biogeosystem studies is rather limited for generalized conclusions. To cover one end of controlling factors on DSi, i.e., weatherable minerals content, we studied a forested site with absolute quartz dominance (> 95%). Here we hypothesise minimal effects of chemical weathering of silicates on DSi. During a four year observation period (05/2007-04/2011), we quantified (i) internal and external Si fluxes of a temperate-humid biogeosystem (beech, 120 yr) by BIOME-BGC (version ZALF), (ii) related Si budgets, and (iii) Si pools in soil and beech, chemically as well as by SEM-EDX. For the first time two compartments of biogenic Si in soils were analysed, i.e., phytogenic and zoogenic Si pool (testate amoebae). We quantified an average Si plant uptake of 35 kg Si ha-1 yr-1 - most of which is recycled to the soil by litterfall - and calculated an annual biosilicification from idiosomic testate amoebae of 17 kg Si ha-1. The comparatively high DSi concentrations (6 mg L-1) and DSi exports (12 kg Si ha-1 yr-1) could not be explained by chemical weathering of feldspars or quartz dissolution. Instead, dissolution of a relictic, phytogenic Si pool seems to be the main process for the DSi observed. We identified canopy closure accompanied by a disappearance of grasses as well as the selective extraction of pine trees 30 yr ago as the most probable control for the phenomena observed. From our results we concluded the biogeosystem to be in a transient state in terms of Si cycling.

  2. Process-Induced Carbon and Sub-Layer in SiC/BN/SiC Composites: Characterization and Consequences

    NASA Technical Reports Server (NTRS)

    Ogbuji, L. U. J. T; Wheeler, D. R.; McCue, T. R.

    2001-01-01

    Following our detection of films of elemental carbon in the Hi-Nicalon TM/BN/SiC composite and its deleterious effect on oxidative durability, we have examined other SiC/BN/SiC systems. The problem is pervasive, and significant residues of free carbon are confirmed in Sylramic /BN/SiC materials. Effective techniques for routine detection and characterization of adventitious carbon in SiC/BN/SiC composites are discussed.

  3. Synthesis, Structure and Properties of BN Nanotubes, BN/SiC and CBN/SiC Micro/Nano-Whiskers

    DTIC Science & Technology

    2003-12-01

    Synthesis, Structure and Properties of BN Nanotubes, BN/SiC and CBN/SiC Micro / Nano -Whiskers 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER 5d...Synthesis, Structure and Properties of BN Nanotubes, BN/SiC and CBN/SiC Micro / Nano -Whiskers CRDF COOPERATIVE GRANTS PROGRAM: FINAL PROJECT...SiC and CBN/SiC micro - nano -whiskers. In the result variety of BN nanostructures have been synthesized by carbothermal technique and characterized

  4. Cooling effect on the electron states of Si(III)Pd and Si(III)Pt interfaces

    NASA Astrophysics Data System (ADS)

    Abbati, I.; Braicovich, L.; Michelis, B. De; Pennino, U. Del; Valeri, S.

    1980-09-01

    Photoemission and Auger results are given for Si(III)Pd and Si(III)Pt interfaces prepared by depositing 10 ml metal onto cleaved Si(III). Thermal cycling between room temperature and liquid nitrogen temperature originates a reversible effect in the spectra due to metal concentration increase in {Si}/{Pt} and decrease in {Si}/{Pd}. The results are discussed in connection with open problems on Si d-metal interfaces.

  5. Large area and depth-profiling dislocation imaging and strain analysis in Si/SiGe/Si heterostructures.

    PubMed

    Chen, Xin; Zuo, Daniel; Kim, Seongwon; Mabon, James; Sardela, Mauro; Wen, Jianguo; Zuo, Jian-Min

    2014-10-01

    We demonstrate the combined use of large area depth-profiling dislocation imaging and quantitative composition and strain measurement for a strained Si/SiGe/Si sample based on nondestructive techniques of electron beam-induced current (EBIC) and X-ray diffraction reciprocal space mapping (XRD RSM). Depth and improved spatial resolution is achieved for dislocation imaging in EBIC by using different electron beam energies at a low temperature of ~7 K. Images recorded clearly show dislocations distributed in three regions of the sample: deep dislocation networks concentrated in the "strained" SiGe region, shallow misfit dislocations at the top Si/SiGe interface, and threading dislocations connecting the two regions. Dislocation densities at the top of the sample can be measured directly from the EBIC results. XRD RSM reveals separated peaks, allowing a quantitative measurement of composition and strain corresponding to different layers of different composition ratios. High-resolution scanning transmission electron microscopy cross-section analysis clearly shows the individual composition layers and the dislocation lines in the layers, which supports the EBIC and XRD RSM results.

  6. Large Area and Depth-Profiling Dislocation Imaging and Strain Analysis in Si/SiGe/Si Heterostructures

    SciTech Connect

    Chen, Xin; Zuo, Daniel; Kim, Seongwon; Mabon, James; Sardela, Mauro; Wen, Jianguo; Zuo, Jian-Min

    2014-08-27

    We demonstrate the combined use of large area depth-profiling dislocation imaging and quantitative composition and strain measurement for a strained Si/SiGe/Si sample based on nondestructive techniques of electron beam-induced current (EBIC) and X-ray diffraction reciprocal space mapping (XRD RSM). Depth and improved spatial resolution is achieved for dislocation imaging in EBIC by using different electron beam energies at a low temperature of ~7 K. Images recorded clearly show dislocations distributed in three regions of the sample: deep dislocation networks concentrated in the “strained” SiGe region, shallow misfit dislocations at the top Si/SiGe interface, and threading dislocations connecting the two regions. Dislocation densities at the top of the sample can be measured directly from the EBIC results. XRD RSM reveals separated peaks, allowing a quantitative measurement of composition and strain corresponding to different layers of different composition ratios. High-resolution scanning transmission electron microscopy cross-section analysis clearly shows the individual composition layers and the dislocation lines in the layers, which supports the EBIC and XRD RSM results.

  7. Growth kinetics of SiO2 on (001) Si catalyzed by Cu3Si at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Huang, H. Y.; Chen, L. J.

    2000-08-01

    The oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy, glancing angle x-ray diffraction, and Auger electron spectroscopy. For wet oxidation at 140-180 °C, the thickness of the oxide was found to increase parabolically with time with an activation energy of 0.4±0.2 eV. The activation energy is close to that of diffusivity of Cu in Si. At 180-200 °C, the growth rate became slower with increasing temperature. The growth of oxide tended to be discontinuous at the surface as the oxidation temperature was increased to a temperature at or higher than 300 °C. The anomalously fast growth of oxide at low temperatures is attributed to the presence of filamentary structures of Cu clusters in the oxide to expedite the diffusion of the oxidants through oxide. At 200-250 °C, more Cu atoms diffuse to the Cu3Si/Si interface and less Cu atoms stay in the oxide, which slows down the oxide growth. The lack of filamentary structures of Cu as diffusion paths retards the growth of SiO2. At 300 °C or higher temperatures, the lack of filamentary structures of Cu clusters stopped the growth of continuous oxide layer altogether.

  8. Si-based Nanoparticles: a biocompatibility study

    NASA Astrophysics Data System (ADS)

    Rivolta, I.; Lettiero, B.; Panariti, A.; D'Amato, R.; Maurice, V.; Falconieri, M.; Herlein, N.; Borsella, E.; Miserocchi, G.

    2010-10-01

    Exposure to silicon nanoparticles (Si-NPs) may occur in professional working conditions or for people undergoing a diagnostic screening test. Despite the fact that silicon is known as a non-toxic material, in the first case the risk is mostly related to the inhalation of nanoparticles, thus the most likely route of entry is across the lung alveolar epithelium. In the case of diagnostic imaging, nanoparticles are usually injected intravenously and Si-NPs could impact on the endothelial wall. In our study we investigated the interaction between selected Si-based NPs and an epithelial lung cell line. Our data showed that, despite the overall silicon biocompatibility, however accurate studies of the potential toxicity induced by the nanostructure and engineered surface characteristics need to be accurately investigated before Si nanoparticles can be safely used for in vivo applications as bio-imaging, cell staining and drug delivery.

  9. Photo and electroluminescence from PECVD grown a-Si:H/SiO 2 multilayers

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, V.; Malinin, A.; Sokolov, V.; Kilpelä, O.; Sinkkonen, J.

    2001-06-01

    Multilayers (ML) of a-Si:H/SiO 2 have been grown using plasma enhanced chemical vapor deposition. Room-temperature photoluminescence (PL) and electroluminescence (EL) in the range 1.35-1.8 eV has been observed in as-deposited and annealed samples. A noticeable redshift of the PL peak has been detected by increasing the a-Si:H layer thickness in the range 0.7-2.1 nm, as well as the annealing temperature (700-1200°C). The strong correlation between PL and EL spectra indicates that light emission from a-Si:H/SiO 2 ML can be attributed to the same luminescence centers in Si layers and nanoclusters. The luminescence mechanism can be interpreted in terms of quantum and spatial confinement of carriers.

  10. Ferroelectric modulation of terahertz waves with graphene/ultrathin-Si:HfO2/Si structures

    NASA Astrophysics Data System (ADS)

    Jiang, Ran; Han, Zuyin; Sun, Weideng; Du, Xianghao; Wu, Zhengran; Jung, Hyung-Suk

    2015-10-01

    Ferroelectric-field-effect-tunable modulation of terahertz waves in graphene/Si:HfO2/Si stack structure was observed. The modulation shows distinct behaviors when the samples under different gate polarities. At a negative voltage, a transmission modulation depth up to ˜74% was present without depending on the photo illumination power, whereas, at a positive voltage, the modulation of Thz wave shows dependence on the illumination power, which is ascribed to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfO2 layer. Considering the good compatibility of HfO2 on Si-based semiconductor process, the ferroelectricity layer of Si:HfO2 may open up an avenue for the tunable modulation of Thz wave.

  11. n-ZnO/p-Si 3D heterojunction solar cells in Si holey arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Mei; Golberg, Dmitri; Bando, Yoshio; Fukata, Naoki

    2012-01-01

    A wafer-scale, low-cost solar cell based on n-ZnO/p-Si 3D heterojunction arrays on holey Si substrates has been fabricated. This device shows a power-conversion efficiency of 1.2% and high photosensitivity. The present n-ZnO/p-Si heterojunction architectures are envisaged as potentially valuable candidates for next-generation photovoltaics.A wafer-scale, low-cost solar cell based on n-ZnO/p-Si 3D heterojunction arrays on holey Si substrates has been fabricated. This device shows a power-conversion efficiency of 1.2% and high photosensitivity. The present n-ZnO/p-Si heterojunction architectures are envisaged as potentially valuable candidates for next-generation photovoltaics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr11752e

  12. SiC/Si3N4 nanotubes from peanut shells

    NASA Astrophysics Data System (ADS)

    Qadri, S. B.; Rath, B. B.; Gorzkowski, E. P.; Feng, C. R.

    2016-06-01

    Nanotubes and nanoparticles of SiC and Si3N4 were produced from the thermal treatment of peanut shells in argon and nitrogen atmospheres respectively, at temperatures in excess of 1350°C. Using x-ray diffraction, Raman spectroscopy and transmission electron microscopy analysis, the processed samples in argon atmosphere were shown to consist of 2H and 3C polytypes of SiC nanoparticles and nanotubes. Whereas the samples prepared in nitrogen atmosphere consisted of α-phase of Si3N4. Nanostructures formed by a single direct reaction provide a sustainable synthesis route for nanostructured SiC and Si3N4, for potential engineering applications due to their exceptional mechanical and electro-optic properties.

  13. Charge trapping properties and retention time in amorphous SiGe/SiO2 nanolayers

    NASA Astrophysics Data System (ADS)

    Vieira, E. M. F.; Diaz, R.; Grisolia, J.; Parisini, A.; Martín-Sánchez, J.; Levichev, S.; Rolo, A. G.; Chahboun, A.; Gomes, M. J. M.

    2013-03-01

    In this paper, we report on the electrical properties of metal-oxide-semiconductor (MOS) capacitors containing a well-confined 8 nm-thick SiGe amorphous layer (a-SiGe) embedded in a SiO2 matrix grown by RF magnetron sputtering at a low temperature (350 °C). Capacitance-voltage measurements show that the introduction of the SiGe layer leads to a significant enhancement of the charge trapping capabilities, with the memory effect and charge retention time larger for hole carriers. The presented results demonstrate that amorphous floating-gate SiGe layers embedded in SiO2 may constitute a suitable alternative for memory applications.

  14. Creep behavior of MoSi{sub 2}-SiC composites

    SciTech Connect

    Butt, D.P.; Maloy, S.A.; Kung, H.; Korzekwa, D.A.; Petrovic, J.J.

    1993-12-31

    Using a cylindrical indenter, indentation creep behavior of hot pressed and HIPed MoSi{sub 2}-SiC composites containing 0--40% SiC by volume, was characterized at 1000--1200C, 258--362 MPa. Addition of SiC affects the creep behavior of MoSi{sub 2} in a complex manner by pinning grain boundaries during pressing, thus leading to smaller MoSi{sub 2} grains; by obstructing or altering both dislocation motion and grain boundary sliding; and by increasing the overall yield stress of the material. Comparisons are made between indentation and compressive creep studies. It is shown that under certain conditions, compressive creep and indentation creep measurements yield comparable results after correcting for effective stresses and strain rates beneath the indenter.

  15. N 2O oxidation of strained-Si/relaxed-SiGe heterostructure grown by UHVCVD

    NASA Astrophysics Data System (ADS)

    Tan, C. S.; Choi, W. K.; Bera, L. K.; Pey, K. L.; Antoniadis, D. A.; Fitzgerald, E. A.; Currie, M. T.; Maiti, C. K.

    2001-11-01

    Oxidation of strained-Si/relaxed-SiGe heterostructure grown by UHVCVD method using a rapid thermal processing technique in N 2O ambient is investigated. The electrical properties of the grown oxide have been characterized using a MOS structure. Hole confinement in the SiGe layer at low field is observed from the capacitance-voltage curve and this suggests that the strain in the initially strained Si epilayer is retained after oxidation. The experimental results are compared with simulation results obtained from a 1D Poisson solver. Dit and Qf/ q values are estimated to be 3×10 11 cm -2 eV -1 and -1.2×10 11 cm -2, respectively. These high values of Dit and negative Qf/ q could possibly be due to Ge out diffusion and pile up at the SiO 2/strained-Si interface. The oxide exhibits an excellent breakdown field of 15 MV cm -1.

  16. Advanced Environmental Barrier Coatings Developed for SiC/SiC Composite Vanes

    NASA Technical Reports Server (NTRS)

    Lee, Kang N.; Fox, Dennis S.; Eldridge, Jeffrey I.; Zhu, Dongming; Bansal, Narottam P.; Miller, Robert A.

    2003-01-01

    Ceramic components exhibit superior high-temperature strength and durability over conventional component materials in use today, signifying the potential to revolutionize gas turbine engine component technology. Silicon-carbide fiber-reinforced silicon carbide ceramic matrix composites (SiC/SiC CMCs) are prime candidates for the ceramic hotsection components of next-generation gas turbine engines. A key barrier to the realization of SiC/SiC CMC hot-section components is the environmental degradation of SiC/SiC CMCs in combustion environments. This is in the form of surface recession due to the volatilization of silica scale by water vapor. An external environmental barrier coating (EBC) is a logical approach to achieve protection and long-term durability.

  17. Determination of the SiO(2)/Si interface roughness by diffuse reflectance measurements.

    PubMed

    Roos, A; Bergkvist, M; Ribbing, C G

    1988-11-15

    The problem of determining the roughness of the SiO(2)/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO(2)/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO(2) on Si.

  18. Determination of the SiO(2)/Si interface roughness by diffuse reflectance measurements.

    PubMed

    Roos, A; Bergkvist, M; Ribbing, C G

    1988-10-15

    The problem of determining the roughness of the SiO(2)/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO(2)/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO(2) on Si.

  19. Investigation of Si-substrate preparation for GaAs-on-Si MBE growth

    NASA Astrophysics Data System (ADS)

    Kayambaki, M.; Callec, R.; Constantinidis, G.; Papavassiliou, Ch.; Löchtermann, E.; Krasny, H.; Papadakis, N.; Panayotatos, P.; Georgakilas, A.

    1995-12-01

    Auger electron spectroscopy (AES) and material characterization techniques have been used to investigate different chemical treatments for the preparation of Si substrates for GaAs-on-Si molecular beam epitaxy (MBE). The need for a Si surface passivating oxide is justified and three different oxidizing solutions are compared for substrate cleanliness and oxide volatility. It is shown that the SC2 solution HCl : H 2O 2 : H 2O (1 : 1 : 6) at 75°C is an appropriate treatment for the final Si cleaning step, since it results to a very volatile oxide that can be desorbed at 750°C, without compromising Si surface cleanliness and GaAs purity. Si wafers with optimized preparation/packaging may also be used as "EPI-ready" substrates within some time after manufacturing.

  20. Formation process of Si3N4 particles on surface of Si ingots grown using silica crucibles with Si3N4 coating by noncontact crucible method

    NASA Astrophysics Data System (ADS)

    Nakajima, Kazuo; Morishita, Kohei; Murai, Ryota; Usami, Noritaka

    2014-03-01

    A noncontact crucible method was used to investigate the process by which a Si3N4 coating material forms Si3N4 particles or precipitates on the surface of Si melts and ingots. Si ingots were grown using crucibles with and without a mixture of α- and β-Si3N4 particles. The oxygen and nitrogen concentrations in the ingots were measured by Fourier transform infrared spectrometry analysis. The nitrogen concentration in the ingots grown using crucibles with a Si3N4 coating was significantly higher than that in ingots grown using crucibles without a Si3N4 coating because the nitrogen from the Si3N4 coating material dissolved into the Si melt. From orientation image maps analyzed using electron backscattering diffraction patterns of SixNy particles on the surface of the ingots, it was clarified that most of the SixNy particles were β-Si3N4. This was also confirmed by X-ray diffraction measurements. The Si3N4 particles on the surface of the ingots had several morphologies such as needle-like, columnar, leaf-like, and hexagonal structures. There were two cases in which floating Si3N4 particles were formed on the surface of the Si melts, i.e., the removal and dissolution of the Si3N4 coating material. The removed or dissolved Si3N4 coating materials, which consisted of a mixture of α- and β-Si3N4 particles, are considered to have finally changed into β-Si3N4 in the form of transformers or precipitates on the surface of the Si melt, and these β-Si3N4 particles became attached to the surface of the ingots.

  1. Development and Characterization of SiC)/ MoSi2-Si3N4(p) Hybrid Composites

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.

    1998-01-01

    Intermetallic compound MoSi2 has long been known as a high temperature material that has excellent oxidation resistance and electrical/thermal conductivity. Also its low cost, high melting point (2023 C), relatively low density (6.2 g/cu cm versus 9 g/cu cm for current engine materials), and ease of machining, make it an attractive structural material. However, the use of MoSi2 has been hindered due to its poor toughness at low temperatures, poor creep resistance at high temperatures, and accelerated oxidation (also known as 'pest' oxidation) at temperatures between approximately 450 and 550 C. Continuous fiber reinforcing is very effective means of improving both toughness and strength. Unfortunately, MoSi2 has a relatively high coefficient of thermal expansion (CTE) compared to potential reinforcing fibers such as SiC. The large CTE mismatch between the fiber and the matrix resulted in severe matrix cracking during thermal cycling. Addition of about 30 to 50 vol % of Si3N4 particulate to MoSi2 improved resistance to low temperature accelerated oxidation by forming a Si2ON2 protective scale and thereby eliminating catastrophic 'pest failure'. The Si3N4 addition also improved the high temperature creep strength by nearly five orders of magnitude, doubled the room temperature toughness and significantly lowered the CTE of the MoSi2 and eliminated matrix cracking in SCS-6 reinforced composites even after thermal cycling. The SCS-6 fiber reinforcement improved the room temperature fracture toughness by seven times and impact resistance by five times. The composite exhibited excellent strength and toughness improvement up to 1400 C. More recently, tape casting was adopted as the preferred processing of MoSi2-base composites for improved fiber spacing, ability to use small diameter fibers, and for lower cost. Good strength and toughness values were also obtained with fine diameter Hi-Nicalon tow fibers. This hybrid composite remains competitive with ceramic matrix

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

    PubMed

    Hu, Liangbing; Wu, Hui; Hong, Seung Sae; Cui, Lifeng; McDonough, James R; Bohy, Sy; Cui, Yi

    2011-01-07

    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.

  3. Processing and characterization of SiC platelet/SiC composites

    SciTech Connect

    Cao, J.J.; MoberlyChan, W.J.; De Jonghe, L.C.; Dalgleish, B.; Niu, M.Y.

    1995-03-01

    Hot pressed {beta}-SiC and SiC matrix composites containing encapsulated {alpha}-SiC platelets were prepared and investigated. The Microstructures were characterized using electron microscopy, Auger electron spectroscopy, and x-ray diffraction. Prior to hot pressing, the platelets were either encapsulated with hydrated aluminum sulfate or yttrium hydroxycarbonate (later calcined to form alumina or yttria) from aqueous solutions, or oxidized to form a silica layer. The effect of these interfacial layers on toughness was described.

  4. B Removal by Zr Addition in Electromagnetic Solidification Refinement of Si with Si-Al Melt

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    This study investigated a new process of enhancing B removal by adding small amounts of Zr in the electromagnetic solidification refinement of Si with Si-Al melt. B in Si was removed by as much as 97.2 pct by adding less than 1057 ppma Zr, and the added Zr was removed by as much as 99.7 pct. In addition, Zr is more effective in enhancing B removal than Ti in the same electromagnetic solidification refining process.

  5. Heterogeneous integration of SiGe/Ge and III-V for Si photonics

    NASA Astrophysics Data System (ADS)

    Takenaka, Mitsuru; Kim, Younghyun; Han, Jaehoon; Kang, Jian; Ikku, Yuki; Cheng, Yongpeng; Park, Jinkwon; Takagi, Shinichi

    2016-05-01

    The heterogeneous integration of SiGe/Ge and III-V semiconductors gives us an opportunity to enhance functionalities of Si photonics platform through their superior material properties which lack in Si. In this paper we discuss what SiGe/Ge and III-V can bring to Si photonics. We have predicted that the light effective hole mass in strained SiGe results in the enhanced the free-carrier effects such as the plasma dispersion effect and free-carrier absorption. We observed significantly larger free-carrier absorption in the SiGe optical modulator than in the control Si device. By fabricating asymmetric Mach-Zehnder interferometer (MZI) SiGe optical modulators, the enhancement of the plasma dispersion effect in strained SiGe has been successfully demonstrated. Mid-infrared integrated photonics based on Ge waveguides on Si have also been investigated. Since Ge is transparent to the entire mid-infrared range, Ge photonic integrated circuits on the Ge-on-Insulator (GeOI) wafer are quite attractive. We have successfully fabricated the GeOI wafer with 2-μm-thick buried oxide (BOX) layer by wafer bonding. The passive waveguide components based on Ge strip waveguides have been demonstrated on the GeOI. We have also demonstrated carrier-injection Ge variable optical attenuators. We have proposed and investigate the III-V CMOS photonics platform by using the III-V on Insulator (IIIV- OI) on a Si wafer. The strong optical confinement in the III-V-OI enables us to achieve high-performance photonic devices. We have successfully demonstrated InGaAsP MZI optical switch with the low on-state crosstalk on the III-V-OI. Ultra-low dark current waveguide InGaAs PDs integrated with an InP grating coupler are also achieved.

  6. Metal Induced Growth of Si Thin Films and NiSi Nanowires

    DTIC Science & Technology

    2010-02-25

    Zinc Oxide Over MIG Silicon- We have been studying the formation of ZnO films by RF sputtering. Part of this study deals with...about 50 nm. 15. SUBJECT TERMS Thin film silicon, solar cells, thin film transistors , nanowires, metal induced growth 16. SECURITY CLASSIFICATION...to achieve, µc-Si is more desirable than a-Si due to its increased mobility. Thin film µc-Si is also a popular material for thin film transistors

  7. Precautions toward XTEM of Si3N4/SiO2

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.

    1991-01-01

    Severe difficulties are encountered in the preparation of oxidized Si3N4 specimens for XTEM transmission electromicroscopic inspection, in virtue of the extreme difference between Si3N4 and SiO2 mechanical properties. Attention is presently given to a preparation method in which an overlayer of the nitride is always occluded; this protects the oxide through most of the thinning that specimen preparation entails. An XTEM image of the oxide/nitride interface is presented.

  8. X-ray scattering studies of the Si-SiO2 interface

    NASA Astrophysics Data System (ADS)

    Fuoss, P. H.; Norton, L. J.; Brennan, S.; Fischer-Colbrie, A.

    1988-02-01

    We report observation of microcrystalline interface phases at the SiO2-Si(001) interface. The crystallites have varying degrees of orientational order with respect to the substrate depending on preparation techniques. Most of the diffraction peaks from these phases can be indexed as due to the α-cristobalite structure. Data are presented for oxides prepared on Si(001) surfaces by thermal oxidation, by electron beam evaporation, and by native oxide formation.

  9. Thermo-Oxidative Degradation Of SiC/Si3N4 Composites

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Batt, Ramakrishna T.; Rokhlin, Stanislav I.

    1995-01-01

    Experimental study conducted on thermo-oxidative degradation of composite-material specimens made of silicon carbide fibers in matrices of reaction-bonded silicon nitride. In SiC/Si3N4 composites of study, interphase is 3-micrometers-thick carbon-rich coat on surface of each SiC fiber. Thermo-oxidative degradation of these composites involves diffusion of oxygen through pores of composites to interphases damaged by oxidation. Nondestructive tests reveal critical exposure times.

  10. Roll Casting of Al-25%Si

    SciTech Connect

    Haga, Toshio; Harada, Hideto; Watari, Hisaki

    2011-05-04

    Strip casting of Al-25%Si strip was tried using an unequal diameter twin roll caster. The diameter of the lower roll (large roll) was 1000 mm and the diameter of the upper roll (small roll) was 250 mm. Roll material was mild steel. The sound strip could be cast at the speeds ranging from 8 m/min to 12 m/min. The strip did not stick to the roll without the parting material. The primary Si, which existed at centre area of the thickness direction, was larger than that which existed at other area. The size of the primary Si was smaller than 0.2 mm. Eutectic Si was smaller 5 {mu}m. The as-cast strip was ranging from 2 mm to 3 mm thick and its width was 100 mm. The as-cast strip could be hot rolled down to 1 mm. The hot rolled strip was cold rolled. The primary Si became smaller and the pore occurred around the primary Si after the rolling.

  11. Transparent conductor-Si pillars heterojunction photodetector

    SciTech Connect

    Yun, Ju-Hyung; Kim, Joondong; Park, Yun Chang

    2014-08-14

    We report a high-performing heterojunction photodetector by enhanced surface effects. Periodically, patterned Si substrates were used to enlarge the photo-reactive regions and yield proportionally improved photo-responses. An optically transparent indium-tin-oxide (ITO) was deposited on a Si substrate and spontaneously formed an ITO/Si heterojunction. Due to an electrical conductive ITO film, ITO/Si heterojunction device can be operated at zero-bias, which effectively suppresses the dark current, resulting in better performances than those by a positive or a negative bias operation. This zero-bias operating heterojunction device exhibits a short response time (∼ 22.5 ms) due to the physical reaction to the incident light. We revealed that the location of the space charge region (SCR) is crucial for a specific photon-wavelength response. The SCR space has the highest collection efficiency of the photo-generated carriers. The photo-response can be maximized when we design the photodetector by superposing the SCR space over a corresponding photon-absorption length. The surface enhanced Si pillar devices significantly improved the photo-responses ratios from that of a planar Si device. According to this design scheme, a high photo-response ratio of 5560% was achieved at a wavelength of 600 nm. This surfaced-enhanced heterojunction design scheme would be a promising approach for various photoelectric applications.

  12. Toward 17µm pitch heterogeneously integrated Si/SiGe quantum well bolometer focal plane arrays

    NASA Astrophysics Data System (ADS)

    Ericsson, Per; Fischer, Andreas C.; Forsberg, Fredrik; Roxhed, Niclas; Samel, Björn; Savage, Susan; Stemme, Göran; Wissmar, Stanley; Öberg, Olof; Niklaus, Frank

    2011-06-01

    Most of today's commercial solutions for un-cooled IR imaging sensors are based on resistive bolometers using either Vanadium oxide (VOx) or amorphous Silicon (a-Si) as the thermistor material. Despite the long history for both concepts, market penetration outside high-end applications is still limited. By allowing actors in adjacent fields, such as those from the MEMS industry, to enter the market, this situation could change. This requires, however, that technologies fitting their tools and processes are developed. Heterogeneous integration of Si/SiGe quantum well bolometers on standard CMOS read out circuits is one approach that could easily be adopted by the MEMS industry. Due to its mono crystalline nature, the Si/SiGe thermistor material has excellent noise properties that result in a state-ofthe- art signal-to-noise ratio. The material is also stable at temperatures well above 450°C which offers great flexibility for both sensor integration and novel vacuum packaging concepts. We have previously reported on heterogeneous integration of Si/SiGe quantum well bolometers with pitches of 40μm x 40μm and 25μm x 25μm. The technology scales well to smaller pixel pitches and in this paper, we will report on our work on developing heterogeneous integration for Si/SiGe QW bolometers with a pixel pitch of 17μm x 17μm.

  13. Effect of Adventitious Carbon on the Environmental Degradation of SiC/BN/SiC Composites

    NASA Technical Reports Server (NTRS)

    Ogbuji, L. U. J. T.; Yun, H. M.; DiCarlo, J.

    2002-01-01

    Pesting remains a major obstacle to the application of SiC/SiC composites in engine service and selective degradation of the boron nitride interphase at intermediate temperatures is of primary concern. However, significant progress has been made on interphase improvement recently and we now know more about the phenomenon and ways to suppress it. By screening SiC/BN/SiC materials through characterization of strength and microstructures after exposure in a burner rig, some factors that control pesting in these composites have been determined. A key precaution is careful control of elemental carbon presence in the interphase region.

  14. Si, Ge, and SiGe quantum wires and quantum dots

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses Si, Ge, and SiGe quantum wire and quantum dot structures, the synthesis of quantum wires and quantum dots, and applications of SiGe quantum-dot structures as photodetectors, light-emitting diodes, for optical amplification and as Si quantum-dot memories.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Monolithically Integrated SiGe/Si PIN-HBT Front-End Transimpedance Photoreceivers

    NASA Technical Reports Server (NTRS)

    Rieh, J.-S.; Qasaimeh, O.; Klotzkin, D.; Lu, L.-H.; Katehi, L. P. B.; Yang, K.; Bhattacharya, P.; Croke, E. T.

    1997-01-01

    The demand for monolithically integrated photoreceivers based on Si-based technology keeps increasing as low cost and high reliability products are required for the expanding commercial market. Higher speed and wider operating frequency range are expected when SiGe/Si heterojunction is introduced to the circuit design. In this paper, a monolithic SiGe/Si PIN-HBT front-end transimpedance photoreceiver is demonstrated for the first time. For this purpose, mesa-type SiGe/Si PIN-HBT technology was developed. Fabricated HBTs exhibit f(sub max) of 34 GHz with DC gain of 25. SiGe/Si PIN photodiodes, which share base and collector layers of HBTs, demonstrate responsivity of 0.3 A/W at lambda=850 nm and bandwidth of 450 MHz. Based on these devices, single- and dual-feedback transimpedance amplifiers were fabricated and they exhibited the bandwidth of 3.2 GHz and 3.3 GHz with the transimpedance gain of 45.2 dB(Omega) and 47.4 dB(Omega) respectively. Monolithically integrated single-feedback PIN-HBT photoreceivers were implemented and the bandwidth was measured to be approx. 0.5 GHz, which is limited by the bandwidth of PIN photodiodes.

  17. 26Si excited states via one-neutron removal from a 27Si radioactive ion beam

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, A. A.; Amthor, A. M.; Bazin, D.; Becerril, A. D.; Gade, A.; Galaviz, D.; Glasmacher, T.; Kahl, D.; Lorusso, G.; Matos, M.; Ouellet, C. V.; Pereira, J.; Schatz, H.; Smith, K.; Wales, B.; Weisshaar, D.; Zegers, R. G. T.

    2012-04-01

    A study of 26Si states by neutron removal from a fast radioactive beam of 27Si has been performed. A beam of 27Si of energy 84.3 MeV/nucleon impinged on a polypropylene foil (C3H6) of 180 mg/cm2 thickness. Deexcitation γ rays were detected with a highly segmented germanium detector array, in coincidence with the 26Si recoils, and the corresponding 26Si level energies were determined. In comparing our results to two previous γ-ray spectroscopic studies of 26Si level structures, we find good agreement with a recent measurement of the 12C(16O,2nγ)26Si reaction. Our results support the use of excitation energies from that study in helping determine the important resonance energies for the thermonuclear 25Al(p,γ)26Si reaction rate. We do not observe a bound state at 4093 keV reported in an earlier study of the 24Mg(3He,nγ)26Si reaction.

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

    SciTech Connect

    Youngblood, G.E.; Henager, C.H. Jr.; Jones, R.H.

    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}.

  19. Amorphous Si waveguides with high-quality stacked gratings for multi-layer Si optical circuits

    NASA Astrophysics Data System (ADS)

    Tokushige, H.; Endo, T.; Saiki, K.; Hiidome, K.; Kitamura, S.; Katsuyama, T.; Tokuda, M.; Takagi, H.; Morita, M.; Ito, Y.; Tsutsui, K.; Wada, Y.; Ikeda, N.; Sugimoto, Y.

    2014-11-01

    To realize a stacked multi-layer silicon-based photonic device, a waveguide with a stacked grating was fabricated by using amorphous Si (a-Si) material, which is suitable for constructing layered structures. The fabrication method was based on forming a flat a-Si layer on a non-flat structure by using only spin-on-glass (SOG) coating technique. The a-Si grating was precisely constructed on the a-Si waveguide with gold alignment marks for electron beam lithography. Transmitted and reflected light power dependence on the grating period, wavelength, and polarization was systematically measured and compared with the designed dependence. As a result, the reflected light power exhibited a characteristic peak structure at a particular wavelength. Remarkable transverse electric/transverse magnetic (TE/TM) mode dependence was also observed. Furthermore, the measured and the designed properties were in excellent agreement with each other. Consequently, the designed structure was well reproduced in the actual stacked structure based on the a-Si material. These results pave the way for novel a-Si based integrated photonic devices such as polarization selectors and wavelength filters, indicating that a-Si is an excellent material for implementing Si-based multi-layer optical circuits.

  20. ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars

    SciTech Connect

    Wang, Dong Yan, Yong; Schaaf, Peter; Sharp, Thomas; Schönherr, Sven; Ronning, Carsten; Ji, Ran

    2015-01-01

    Porous Si nanopillar arrays are used as templates for atomic layer deposition of ZnO and TiO{sub 2}, and thus, ZnO/porous-Si and TiO{sub 2}/porous-Si nanocomposite nanopillars are fabricated. The diffusion of the precursor molecules into the inside of the porous structure occurs via Knudsen diffusion and is strongly limited by the small pore size. The luminescence of the ZnO/porous-Si nanocomposite nanopillars is also investigated, and the optical emission can be changed and even quenched after a strong plasma treatment. Such nanocomposite nanopillars are interesting for photocatalysis and sensors.

  1. Modeled optical properties of SiGe and Si layers compared to spectroscopic ellipsometry measurements

    NASA Astrophysics Data System (ADS)

    Kriso, C.; Triozon, F.; Delerue, C.; Schneider, L.; Abbate, F.; Nolot, E.; Rideau, D.; Niquet, Y.-M.; Mugny, G.; Tavernier, C.

    2017-03-01

    The optical response of strained SiGe alloys, as well as thin Si layers, is analyzed using a sp3d5s∗ tight-binding model within the independent particle approximation. The theoretical results are compared to measurements obtained on samples with various Ge content and layer thicknesses. The dielectric function is extracted from spectroscopic ellipsometry allowing a separation of its real and imaginary parts. Theory and simulation show similar trends for the variation of the dielectric function of SiGe with varying Ge content. Variations are also well reproduced for thin Si layers with varying thickness and are attributed to quantum confinement.

  2. Dislocation engineering in SiGe heteroepitaxial films on patterned Si (001) substrates

    NASA Astrophysics Data System (ADS)

    Gatti, R.; Boioli, F.; Grydlik, M.; Brehm, M.; Groiss, H.; Glaser, M.; Montalenti, F.; Fromherz, T.; Schäffler, F.; Miglio, Leo

    2011-03-01

    We demonstrate dislocation engineering without oxide masks. By using finite element simulations we show how nanopatterning of Si substrates with {111} trenches provides anisotropic elastic relaxation in a SiGe film, generates preferential nucleation sites for dislocation loops, and allows for dislocation trapping, leaving wide areas free of threading dislocations. These predictions are confirmed by atomic force and transmission electron microscopy performed on overcritical Si0.7Ge0.3 films. These were grown by molecular beam epitaxy on a Si(001) substrate patterned with periodic arrays of selectively etched {111}-terminated trenches.

  3. Performance Comparison Study of SiC and Si Technology for an IPM Drive System

    SciTech Connect

    Chinthavali, Madhu Sudhan; Otaduy, Pedro J; Ozpineci, Burak

    2010-01-01

    The impact of the new SiC material based devices on a full system needs to be evaluated in order to assess the benefits of replacing Silicon (Si) devices with WBG devices. In this paper the results obtained with a full-system model simulated for an aggressive US06 drive cycle are presented. The system model includes a motor/generator model and inverter loss model developed using actual measured data. The results provide an insight to the difference in performance of a permanent magnet traction drive system using SiC versus Si devices.

  4. Resonant raman scattering in complexes of nc-Si/SiO2 quantum dots and oligonucleotides

    NASA Astrophysics Data System (ADS)

    Bairamov, F. B.; Poloskin, E. D.; Kornev, A. A.; Chernev, A. L.; Toporov, V. V.; Dubina, M. V.; Röder, C.; Sprung, C.; Lipsanen, H.; Bairamov, B. Kh.

    2014-11-01

    We report on the functionalization of nanocrystalline nc-Si/SiO2 semiconductor quantum dots (QDs) by short d(20G, 20T) oligonucleotides. The obtained complexes have been studied by Raman spectroscopy techniques with high spectral and spatial resolution. A new phenomenon of multiband resonant light scattering on single oligonucleotide molecules has been discovered, and peculiarities of this effect related to the nonradiative transfer of photoexcitation from nc-Si/SiO2 quantum dots to d(20G, 20T) oligonucleotide molecules have been revealed.

  5. Dislocation engineering in SiGe heteroepitaxial films on patterned Si (001) substrates

    SciTech Connect

    Gatti, R.; Boioli, F.; Montalenti, F.; Miglio, Leo; Grydlik, M.; Brehm, M.; Groiss, H.; Glaser, M.; Fromherz, T.; Schaeffler, F.

    2011-03-21

    We demonstrate dislocation engineering without oxide masks. By using finite element simulations we show how nanopatterning of Si substrates with (111) trenches provides anisotropic elastic relaxation in a SiGe film, generates preferential nucleation sites for dislocation loops, and allows for dislocation trapping, leaving wide areas free of threading dislocations. These predictions are confirmed by atomic force and transmission electron microscopy performed on overcritical Si{sub 0.7}Ge{sub 0.3} films. These were grown by molecular beam epitaxy on a Si(001) substrate patterned with periodic arrays of selectively etched (111)-terminated trenches.

  6. Wetting of polycrystalline SiC by molten Al and Al-Si alloys

    NASA Astrophysics Data System (ADS)

    Cong, Xiao-Shuang; Shen, Ping; Wang, Yi; Jiang, Qichuan

    2014-10-01

    The wetting of α-SiC by molten Al and Al-Si alloys was investigated using a dispensed sessile drop method in a high vacuum. In the Al-SiC system, representative wetting stages were identified. The liquid spreading was initially controlled by the deoxidation of the SiC surface and then by the formation of Al4C3 at the interface. The intrinsic contact angle for molten Al on the polycrystalline α-SiC surface was suggested to be lower than 90̊ provided that the oxide films covering the Al and SiC surfaces were removed, i.e., the system is partial wetting in nature. An increase in the Si concentration in liquid Al weakened the interfacial reaction but improved the final wettability. The role of the Si addition on the wetting was presumably attributed to its segregation at the interface and the formation of strong chemical bonds with the SiC surface.

  7. One-dimensional Si-in-Si(001) template for single-atom wire growth

    NASA Astrophysics Data System (ADS)

    Owen, J. H. G.; Bianco, F.; Köster, S. A.; Mazur, D.; Bowler, D. R.; Renner, Ch.

    2010-08-01

    Single atom metallic wires of arbitrary length are of immense technological and scientific interest. We present atomic-resolution scanning tunneling microscope data of a silicon-only template, which modeling predicts to enable the self-organized growth of isolated micrometer long surface and subsurface single-atom chains. It consists of a one-dimensional, defect-free Si reconstruction four dimers wide—the Haiku core—formed by hydrogenation of self-assembled Bi-nanolines on Si(001) terraces, independent of any step edges. We discuss the potential of this Si-in-Si template as an appealing alternative to vicinal surfaces for nanoscale patterning.

  8. High thermal conductivity SiC/SiC composites for fusion applications

    SciTech Connect

    Withers, J.C.; Kowbel, W.; Loutfy, R.O.

    1997-04-01

    SiC/SiC composites are considered for fusion applications due to their neutron irradiation stability, low activation, and good mechanical properties at high temperatures. The projected magnetic fusion power plant first wall and the divertor will operate with surface heat flux ranges of 0.5 to 1 and 4 to 6 MW/m{sup 2}, respectively. To maintain high thermal performance at operating temperatures the first wall and divertor coolant channels must have transverse thermal conductivity values of 5 to 10 and 20 to 30 W/mK, respectively. For these components exposed to a high energy neutron flux and temperatures perhaps exceeding 1000{degrees}C, SiC/SiC composites potentially can meet these demanding requirements. The lack of high-purity SiC fiber and a low through-the-thickness (transverse) thermal conductivity are two key technical problems with currently available SiC/SiC. Such composites, for example produced from Nicalon{trademark} fiber with a chemical vapor infiltrated (CVI) matrix, typically exhibit a transverse conductivity value of less than 8 W/mK (unirradiated) and less than 3 W/mK after neutron irradiation at 800{degrees}C. A new SiC/SiC composite fabrication process has been developed at MER Corp. This paper describes this process, and the thermal and mechanical properties which are observed in this new composite material.

  9. Optical anisotropies of Si grown on step-graded SiGe(110) layers

    NASA Astrophysics Data System (ADS)

    Balderas-Navarro, R. E.; Lastras-Martínez, L. F.; Arimoto, K.; Castro-García, R.; Villalobos-Aguilar, O.; Lastras-Martínez, A.; Nakagawa, K.; Sawano, K.; Shiraki, Y.; Usami, N.; Nakajima, K.

    2010-03-01

    Macroreflectance and microreflectance difference spectroscopies have been used to measure the strain induced optical anisotropies of semiconductor structures comprised of strained Si(110) thin films deposited on top of step-graded SiGe virtual substrates. The stress relaxation mechanism mainly occurs by the introduction of microtwin formation, whose fluctuation depends strongly on growth conditions. Correlations of such optical diagnostics with x-ray diffraction measurements and atomic force microscopy images, allow for the in situ study of the strain within both the top Si layer and the SiGe underneath with an spatial resolution of at least 5 μm.

  10. Fundamental Properties and Devices Applications of Ge(x)Si(1-x)/Si Superlattices.

    DTIC Science & Technology

    1987-01-01

    atomic fractions of the reaction species, Si, Si oxide, 0, have been plotted as a function of the silicon flux and are shown in Fig. 9. With this study...v.c 0 0 8 I0 12 Ai’ SILICON FLUX (;irmn) Fig. 9 Evolution of the Si, Si oxide and 0 atomic fractions in function of the silicon flux (O<Jsi᝾.5 A/min...G. Karunasiri, J. S. Park, C. H. Chern, and K. L. Wang, "Reflection High-Energy Electron Diffraction Observation of Substrate Cleaning During Silicon

  11. Electronic structure and charge transfer in α- and β-Si3N4 and at the Si(111)/Si3N4(001) interface

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bachlechner, M. E.

    1998-07-01

    Using a self-consistent linear combination of atomic orbitals method based on density-functional theory in a local-density approximation, the electronic structure in the high-temperature ceramics α-Si3N4 and β-Si3N4 and at the Si(111)/Si3N4(001) interface have been calculated. The resulting charge transfer suggests that the ionic formula can be written as Si+1.243N-0.934. For the Si(111)/Si3N4(001) interface, the silicon atoms from the silicon side lose some electrons to the nitrogen atoms of the silicon nitride side forming Si-N bonds at the interface. The calculated electronic density of states spectrum of Si 2p core levels for this interface is in good agreement with x-ray photoemission spectroscopy experiments.

  12. Size dependent optical properties of Si quantum dots in Si-rich nitride/Si{sub 3}N{sub 4} superlattice synthesized by magnetron sputtering

    SciTech Connect

    So, Yong-Heng; Huang, Shujuan; Conibeer, Gavin; Green, Martin A.; Gentle, Angus

    2011-03-15

    A spectroscopic ellipsometry compatible approach is reported for the optical study of Si quantum dots (QDs) in Si-rich nitride/silicon nitride (SRN/Si{sub 3}N{sub 4}) superlattice, which based on Tauc-Lorentz model and Bruggeman effective medium approximation. It is shown that the optical constants and dielectric functions of Si QDs are strongly size dependent. The suppressed imaginary dielectric function of Si QDs exhibits a single broad peak analogous to amorphous Si, which centered between the transition energies E{sub 1} and E{sub 2} of bulk crystalline Si and blue shifted toward E{sub 2} as the QD size reduced. A bandgap expansion observed by the TL model when the size of Si QD reduced is in good agreement with the PL measurement. The bandgap expansion with the reduction of Si QD size is well supported by the first-principles calculations based on quantum confinement.

  13. Deep ultraviolet photodetectors based on p-Si/ i-SiC/ n-Ga2O3 heterojunction by inserting thin SiC barrier layer

    NASA Astrophysics Data System (ADS)

    An, Yuehua; Zhi, Yusong; Wu, Zhenping; Cui, Wei; Zhao, Xiaolong; Guo, Daoyou; Li, Peigang; Tang, Weihua

    2016-12-01

    Deep ultraviolet photodetectors based on p-Si/ n-Ga2O3 and p-Si/ i-SiC/ n-Ga2O3 heterojunctions were fabricated by laser molecular beam epitaxial (L-MBE), respectively. In compare with p-Si/ n-Ga2O3 heterostructure-based photodetector, the dark current of p-Si/ i-SiC/ n-Ga2O3-based photodetector decreased by three orders of magnitude, and the rectifying behavior was tuned from reverse to forward. In order to improve the quality of the photodetector, we reduced the oxygen vacancies of p-Si/ i-SiC/ n-Ga2O3 heterostructures by changing the oxygen pressure during annealing. As a result, the rectification ratio ( I F/ I R) of the fabricated photodetectors was 36 at 4.5 V and the photosensitivity was 5.4 × 105% under the 254 nm light illumination at -4.5 V. The energy band structure of p-Si/ n-Ga2O3 and p-Si/ i-SiC/ n-Ga2O3 heterostructures was schematic drawn to explain the physic mechanism of enhancement of the performance of p-Si/ i-SiC/ n-Ga2O3 heterostructure-based deep UV photodetector by introduction of SiC layer.

  14. Synthesis of several millimeters long SiC-SiO2 nanowires by a catalyst-free technique

    NASA Astrophysics Data System (ADS)

    Dong, Shun; Li, Minglun; Hu, Ping; Cheng, Yuan; Sun, Boqian

    2016-11-01

    In situ synthesis of ultra-long SiC-SiO2 nanowires were successfully conducted with the raw materials of silicon and phenolic resin by an effective and catalyst-free technique. Several millimeters long SiC-SiO2 nanowires with the diameters in the range of 50-200 nm were mainly composed of Si, C and a small amount of O, and the formation of several millimeters long SiC-SiO2 nanowires was attributed to a low flow rate and carbon sources supplied continuously by the pyrolysis of phenolic resin. A catalyst-free vapor-solid (VS) growth mechanism was proposed to illustrate the growth process of ultra-long SiC-SiO2 nanowires in present experiment, which provides a promising method for in situ fabrication of SiC-SiO2 nanowires as reinforcements into composites.

  15. Crystallization mechanisms and recording characteristics of Si/CuSi bilayer for write-once blu-ray disc

    NASA Astrophysics Data System (ADS)

    Ou, Sin-Liang; Kuo, Po-Cheng; Chen, Sheng-Chi; Tsai, Tsung-Lin; Yeh, Chin-Yen; Chang, Han-Feng; Lee, Chao-Te; Chiang, Donyau

    2011-09-01

    The crystallization mechanisms of Si/CuSi bilayer and its recording characteristics for write-once blu-ray disc (BD-R) were investigated. It was found that Cu3Si phase appeared during the room temperature sputtered deposition. Then, the Si atoms in CuSi layer segregated and crystallized to cubic Si in Cu3Si nucleation sites as the film was annealed at 270 °C. After heating to 500 °C, the grains size of cubic Si phase grew and the hexagonal Si phase was observed. The dynamic tests show that the Si/CuSi bilayer has great feasibility for 1-4× BD-R with the bottom jitter values below 6.5%.

  16. Formation mechanisms of Si3N4 and Si2N2O in silicon powder nitridation

    NASA Astrophysics Data System (ADS)

    Yao, Guisheng; Li, Yong; Jiang, Peng; Jin, Xiuming; Long, Menglong; Qin, Haixia; Kumar, R. Vasant

    2017-04-01

    Commercial silicon powders are nitrided at constant temperatures (1453 K; 1513 K; 1633 K; 1693 K). The X-ray diffraction results show that small amounts of Si3N4 and Si2N2O are formed as the nitridation products in the samples. Fibroid and short columnar Si3N4 are detected in the samples. The formation mechanisms of Si3N4 and Si2N2O are analyzed. During the initial stage of silicon powder nitridation, Si on the outside of sample captures slight amount of O2 in N2 atmosphere, forming a thin film of SiO2 on the surface which seals the residual silicon inside. And the oxygen partial pressure between the SiO2 film and free silicon is decreasing gradually, so passive oxidation transforms to active oxidation and metastable SiO(g) is produced. When the SiO(g) partial pressure is high enough, the SiO2 film will crack, and N2 is infiltrated into the central section of the sample through cracks, generating Si2N2O and short columnar Si3N4 in situ. At the same time, metastable SiO(g) reacts with N2 and form fibroid Si3N4. In the regions where the oxygen partial pressure is high, Si3N4 is oxidized into Si2N2O.

  17. Microstructural Properties of NC-Si/SiO2 Films IN SITU Grown by Reactive Magnetron Co-Sputtering

    NASA Astrophysics Data System (ADS)

    Lu, Wanbing; Guo, Shaogang; Wang, Jiantao; Li, Yun; Wang, Xinzhan; Yu, Gengxi; Fan, Shanshan; Fu, Guangsheng

    2012-01-01

    Nanocrystalline silicon embedded in silicon oxide (nc-Si/SiO2) films have been in situ grown at a low substrate temperature of 300°C by reactive magnetron co-sputtering of Si and SiO2 targets in a mixed Ar/H2 discharge. The influences of H2 flow rate (FH) on the microstructural properties of the deposited nc-Si/SiO2 films were investigated. The results of XRD and the deposition rate of nc-Si/SiO2 films show that the introduction of H2 contributes to the growth of nc-Si grains in silicon oxide matrix. With further increasing FH, the average size of nc-Si grains increases and the deposition rate of nc-Si/SiO2 films decreases gradually. Fourier transform infrared spectra analyses reveal that introduction of hydrogen contributes to the phase separation of nc-Si and SiOx in the deposited films. Moreover, the Si-O4-nSin(n = 0, 1) concentration of the deposited nc-Si/SiO2 films reduces with the increase of FH, while that of Si-O4-nSin(n = 2, 3) concentration increases. These results can be explained by that active hydrogen atoms increase the probability of reducing oxygen from precursor in the plasma and prompting oxygen desorption from the growing surface. This low-temperature procedure for preparing nc-Si/SiO2 films opens up the possibility of fabricating the silicon-based thin-film solar cells onto low-cost glass substrates using nc-Si/SiO2 films.

  18. Ultraviolet responses of a heterojunction Si quantum dot solar cell.

    PubMed

    Lee, Seong Hyun; Kwak, Gyea Young; Hong, Songwoung; Kim, Chanhong; Kim, Sung; Kim, Ansoon; Kim, Kyung Joong

    2017-01-20

    We investigated the ultraviolet (UV) responses of a heterojunction Si quantum dot (QD) solar cell consisting of p-type Si-QDs fabricated on a n-type crystalline Si (p-Si-QD/n-c-Si HJSC). The UV responses were compared with a conventional n-type crystalline Si solar cell (n-c-Si SC). The external and internal quantum efficiency results of the p-Si-QD/n-c-Si HJSC exhibited a clear enhancement in the UV responses (300-400 nm), which was not observed in the n-c-Si SC. Based on the results of the cell reflectance and bias-dependent responses, we expect that almost all UV responses occur in the p-Si-QD layer, and the generated carriers can be transported via the Si-QD layer due to the formation of a sufficient electric filed. As a result, a high power conversion efficiency of 14.5% was achieved from the p-Si-QD/n-c-Si HJSC. By reducing the thickness of the n-Si substrate from 650 μm to 300 μm, more enhanced power conversion efficiency of 14.8% was obtained which is the highest value among the reported Si-QD based solar cells to date.

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

    SciTech Connect

    Doug Schulz

    2010-12-09

    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.

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

    SciTech Connect

    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.

  1. Ultraviolet responses of a heterojunction Si quantum dot solar cell

    NASA Astrophysics Data System (ADS)

    Lee, Seong Hyun; Kwak, Gyea Young; Hong, Songwoung; Kim, Chanhong; Kim, Sung; Kim, Ansoon; Kim, Kyung Joong

    2017-01-01

    We investigated the ultraviolet (UV) responses of a heterojunction Si quantum dot (QD) solar cell consisting of p-type Si-QDs fabricated on a n-type crystalline Si (p-Si-QD/n-c-Si HJSC). The UV responses were compared with a conventional n-type crystalline Si solar cell (n-c-Si SC). The external and internal quantum efficiency results of the p-Si-QD/n-c-Si HJSC exhibited a clear enhancement in the UV responses (300-400 nm), which was not observed in the n-c-Si SC. Based on the results of the cell reflectance and bias-dependent responses, we expect that almost all UV responses occur in the p-Si-QD layer, and the generated carriers can be transported via the Si-QD layer due to the formation of a sufficient electric filed. As a result, a high power conversion efficiency of 14.5% was achieved from the p-Si-QD/n-c-Si HJSC. By reducing the thickness of the n-Si substrate from 650 μm to 300 μm, more enhanced power conversion efficiency of 14.8% was obtained which is the highest value among the reported Si-QD based solar cells to date.

  2. Use of SI Metric Units Misrepresented in College Physics Texts.

    ERIC Educational Resources Information Center

    Hooper, William

    1980-01-01

    Summarizes results of a survey that examined 13 textbooks claiming to use SI units. Tables present data concerning the SI and non-SI units actually used in each text in discussion of fluid pressure and thermal energy, and data concerning which texts do and do not use SI as claimed. (CS)

  3. Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1989-01-01

    The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by an Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    A p-n junction was made on p-type Si<100> wafer (15 × 15 × 0.2 mm3 in size) via phosphorous diffusion at 900 °C. Porous Si (PSi) with ultralow reflectivity (<0.3% in the 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%.

  5. Comparative study of SiC- and Si-based photovoltaic inverters

    NASA Astrophysics Data System (ADS)

    Ando, Yuji; Oku, Takeo; Yasuda, Masashi; Shirahata, Yasuhiro; Ushijima, Kazufumi; Murozono, Mikio

    2017-01-01

    This article reports comparative study of 150-300 W class photovoltaic inverters (Si inverter, SiC inverter 1, and SiC inverter 2). In these sub-kW class inverters, the ON-resistance was considered to have little influence on the efficiency. The developed SiC inverters, however, have exhibited an approximately 3% higher direct current (DC)-alternating current (AC) conversion efficiency as compared to the Si inverter. Power loss analysis indicated a reduction in the switching and reverse recovery losses of SiC metal-oxide-semiconductor field-effect transistors used for the DC-AC converter is responsible for this improvement. In the SiC inverter 2, an increase of the switching frequency up to 100 kHz achieved a state-of-the-art combination of the weight (1.25 kg) and the volume (1260 cm3) as a 150-250 W class inverter. Even though the increased switching frequency should cause the increase of the switching losses, the SiC inverter 2 exhibited an efficiency comparable to the SiC inverter 1 with a switching frequency of 20 kHz. The power loss analysis also indicated a decreased loss of the DC-DC converter built with SiC Schottky barrier diodes led to the high efficiency for its increased switching frequency. These results clearly indicated feasibility of SiC devices even for sub-kW photovoltaic inverters, which will be available for the applications where compactness and efficiency are of tremendous importance.

  6. Wetting behavior of Al Si Mg alloys on Si3N4/Si substrates: optimization of processing parameters

    NASA Astrophysics Data System (ADS)

    de La Peña, J. L.; Pech-Canul, M. I.

    2008-06-01

    The wetting behavior of Al Si Mg alloys on Si3N4/Si substrates has been investigated using the sessile drop technique. Based on a Taguchi experiment design, the effect of the following processing parameters on the contact angle (θ) and surface tension (σLV) was studied: processing time and temperature, atmosphere (Ar and N2), substrate surface condition (with and without a silicon wafer), as well as the Mg and Si contents in the aluminium alloy. In nitrogen, non-wetting conditions prevail during the isothermal events while in argon a remarkable non-wetting to wetting transition leads to contact angles θ as low as 11±3° and a liquid surface tension σLV of 33± 10×10-5 kJ/m2. According to the multiple analysis of variance (Manova), the optimum conditions for minimizing the values of θ and σLV are as follows: temperature of 1100 °C, processing time of 90 min, argon atmosphere, no use of a silicon wafer, and the use of the Al-18% Mg-1% Si alloy. A verification test conducted under the optimized conditions resulted in a contact angle of θ=9±3° and a surface tension of σLV=29± 9×10-5 kJ/m2, both indicative of excellent wetting.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Lockwood, David; Wu, Xiaohua; Baribeau, Jean-Marc; Mala, Selina; Wang, Xialou; Tsybeskov, Leonid

    2016-03-01

    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 Si0.6Ge0.4 wavy

  9. Microstructure and Hot Oxidation Resistance of SiMo Ductile Cast Irons Containing Si-Mo-Al

    NASA Astrophysics Data System (ADS)

    Ibrahim, Mervat M.; Nofal, Adel; Mourad, M. M.

    2017-04-01

    SiMo ductile cast irons are used as high-temperature materials in automotive components, because they are microstructurally stable at high operating temperatures. The effect of different amounts of Si and Mo as well as the addition of 3 wt pct Al on the microstructure, high-temperature oxidation, and mechanical properties of SiMo ductile cast iron was studied. Dilatometric measurements of SiMo ductile iron exhibited obvious differences in the transformation temperature A 1 due to presence of Al and the increase of Si. The microstructure of the SiMo alloys without Al addition showed outstanding nodularity and uniform nodule distribution. However, by adding 3 wt pct Al to low Si-SiMo ductile iron, some compacted graphite was observed. The results of oxidation experiments indicated that high Si-SiMo ductile iron containing 4 and 4.9 wt pct Si had superior resistance to lower Si-SiMo and SiMo ductile iron containing 3 wt pct Al. The results showed also that with increasing Si up to 4.9 wt pct or by replacing a part of Si with 3 wt pct Al, tensile strength increased while elongation and impact toughness decreased.

  10. Microstructure and Hot Oxidation Resistance of SiMo Ductile Cast Irons Containing Si-Mo-Al

    NASA Astrophysics Data System (ADS)

    Ibrahim, Mervat M.; Nofal, Adel; Mourad, M. M.

    2016-12-01

    SiMo ductile cast irons are used as high-temperature materials in automotive components, because they are microstructurally stable at high operating temperatures. The effect of different amounts of Si and Mo as well as the addition of 3 wt pct Al on the microstructure, high-temperature oxidation, and mechanical properties of SiMo ductile cast iron was studied. Dilatometric measurements of SiMo ductile iron exhibited obvious differences in the transformation temperature A 1 due to presence of Al and the increase of Si. The microstructure of the SiMo alloys without Al addition showed outstanding nodularity and uniform nodule distribution. However, by adding 3 wt pct Al to low Si-SiMo ductile iron, some compacted graphite was observed. The results of oxidation experiments indicated that high Si-SiMo ductile iron containing 4 and 4.9 wt pct Si had superior resistance to lower Si-SiMo and SiMo ductile iron containing 3 wt pct Al. The results showed also that with increasing Si up to 4.9 wt pct or by replacing a part of Si with 3 wt pct Al, tensile strength increased while elongation and impact toughness decreased.

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

    DOEpatents

    Wang, Donghai; Yi, Ran; Dai, Fang

    2016-02-23

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

  12. Short communication: Enhancement of topoisomerase I-mediated unwinding of supercoiled DNA by the radioprotector WR-33278

    SciTech Connect

    Holwitt, E.A.; Koda, E.; Swenberg, C.E.

    1990-01-01

    Cellular DNA is one of the critical targets for ionizing radiation. To mitigate the effects of ionizing radiation, the U.S. Army Medical Research and Development Command has synthesized several radioprotective drugs, primarily aminothiol compounds. Many mechanisms responsible for their radioprotective action have been proposed, including radical scavenging, hydrogen atom donation to DNA carbon center radicals, enhancement of DNA repair process, and reduction in the target volume. All of these processes require that the radioprotector or its metabolite be located within molecular distances, less than 50A, from DNA.

  13. Molecular mechanisms of HLA class I-mediated immune evasion of human tumors and their role in resistance to immunotherapies.

    PubMed

    Seliger, B

    2016-11-01

    Although the human immune system can recognize and eradicate tumor cells, tumors have also been shown to develop different strategies to escape immune surveillance, which has been described for the first time in different mouse models. The evasion of immune recognition was often associated with a poor prognosis and reduced survival of patients. During the last years the molecular mechanisms, which protect tumor cells from this immune attack, have been identified and appear to be more complex than initially expected. However, next to the composition of cellular, soluble and physical components of the tumor microenvironment, the tumor cells changes to limit immune responses. Of particular importance are classical and non-classical human leukocyte antigen (HLA) class I antigens, which often showed a deregulated expression in cancers of distinct origin. Furthermore, HLA class I abnormalities were linked to defects in the interferon signaling, which have both been shown to be essential for mounting immune responses and are involved in resistances to T cell-based immunotherapies. Therefore this review summarizes the expression, regulation, function and clinical relevance of HLA class I antigens in association with the interferon signal transduction pathway and its role in adaptive resistances to immunotherapies.

  14. Atomic state and characterization of nitrogen at the SiC/SiO{sub 2} interface

    SciTech Connect

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

    2014-01-21

    We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO{sub 2} 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 (SiO{sub 2}). 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.

  15. Comparison of Nanocarbon-Silicon Solar Cells with Nanotube-Si or Graphene-Si Contact.

    PubMed

    Xu, Wenjing; Deng, Bing; Shi, Enzheng; Wu, Shiting; Zou, Mingchu; Yang, Liusi; Wei, Jinquan; Peng, Hailin; Cao, Anyuan

    2015-08-12

    Nanocarbon structures such as carbon nanotubes (CNTs) and graphene (G) have been combined with crystalline silicon wafers to fabricate nanocarbon-Si solar cells. Here, we show that the contact between the nanocarbon and Si plays an important role in the solar cell performance. An asymmetrically configured CNT-G composite film was used to create either CNT-Si dominating or G-Si dominating junctions, resulting in obviously different solar cell behavior in pristine state. Typically, solar cells with direct G-Si contacts (versus CNT-Si) exhibit better characteristics due to improved junction quality and larger contact area. On the basis of the composite film, the obtained CNT-G-Si solar cells reach power conversion efficiencies of 14.88% under air mass 1.5, 88 mW/cm2 illumination through established techniques such as acid doping and colloidal antireflection. Engineering the nanocarbon-Si contact is therefore a possible route for further improving the performance of this type of solar cells.

  16. Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate.

    PubMed

    Lee, Jeong-Hoon; Song, Kwan-Woo; Park, Min-Ho; Kim, Hyung-Kyu; Yang, Cheol-Woong

    2011-07-01

    Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.

  17. Visible light emission from MBD-grown {Si}/{SiO2} superlattices

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Sinkkonen, J.; Kilpelä, O.; Gastev, S. V.

    1997-05-01

    {Si}/{SiO2} superlattices were grown by MBD using in situ oxidation by RF-plasma source. Room temperature photoluminescence (PL) was observed in the spectral range 1.9-2.3 eV. PL spectra show blueshifts due to the quantum confinement of the energy states in ultrathin silicon layers.

  18. Morphological, compositional, structural, and optical properties of Si-nc embedded in SiOx films

    PubMed Central

    2012-01-01

    Structural, compositional, morphological, and optical properties of silicon nanocrystal (Si-nc) embedded in a matrix of non-stoichiometric silicon oxide (SiOx) films were studied. SiOx films were prepared by hot filament chemical vapor deposition technique in the 900 to 1,400°C range. Different microscopic and spectroscopic characterization techniques were used. The film composition changes with the growth temperature as Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy reveal. High-resolution transmission electron microscopy supports the existence of Si-ncs with a diameter from 1 to 6.5 nm in the matrix of SiOx films. The films emit in a wide photoluminescent spectrum, and the maximum peak emission shows a blueshift as the growth temperature decreases. On the other hand, transmittance spectra showed a wavelength shift of the absorption border, indicating an increase in the energy optical bandgap, when the growth temperature decreases. A relationship between composition, Si-nc size, energy bandgap, PL, and surface morphology was obtained. According to these results, we have analyzed the dependence of PL on the composition, structure, and morphology of the Si-ncs embedded in a matrix of non-stoichiometric SiOx films. PMID:23110990

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

    PubMed

    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.

  20. Foreign Object Damage Resistance of Uncoated and EBC Coated SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Choi, S. R.; Cosgriff, L. M.; Fox, D.; Lee, K. N.

    2004-01-01

    SiC/SiC composites fabricated by the melt infiltration method are candidate materials for the turbine components such as combustor liners, nozzle vanes and blades because of their high temperature strength, and thermal conductivity. To avoid surface recession in a combustion environment containing moisture, these materials also require an environmental barrier coating (EBC). Under thermal loading condition alone, the EBC coated SiC/SiC components show microstructural and strength stability after -1 5000 hr exposure to 12OO0C in combustion environment. However, the stability of SiC/SiC composites under impact conditions is not fully understood. In this study, both uncoated and EBC coated SiC/SiC composite specimens were impact tested by steel-ball projectiles at room temperature and at 1300 C in air. After impact, the specimens were analyzed under a scanning electron microscope to assess coating damage, and then tensile and bend tested at room temperature to determine their residual strength. The extent of coating and substrate damage with increasing projectile velocity was imaged and analyzed using nondestructive evaluation (NDE) methods such as micro focus x-ray radiography, tomography, and thermal wave imaging. The mechanical property results of impacted specimens are correlated with the NDE results and the scanning electron microscopy (SEM) observations. Influence of projectile velocity on impact damage of the coating/substrate, and the implication coating damage on durability of the composite will be discussed.

  1. Semipolar (202̅3) nitrides grown on 3C-SiC/(001) Si substrates

    NASA Astrophysics Data System (ADS)

    Dinh, Duc V.; Presa, S.; Akhter, M.; Maaskant, P. P.; Corbett, B.; Parbrook, P. J.

    2015-12-01

    Heteroepitaxial growth of GaN buffer layers on 3C-SiC/(001) Si templates (4°-offcut towards [110]) by metalorganic vapour phase epitaxy has been investigated. High-temperature grown Al0.5Ga0.5N/AlN interlayers were employed to produce a single (202̅3) GaN surface orientation. Specular crack-free GaN layers showed undulations along [11̅0]{}3{{C}-{SiC}/{Si}} with a root mean square roughness of about 13.5 nm (50 × 50 μm2). The orientation relationship determined by x-ray diffraction (XRD) was found to be [1̅21̅0]GaN ∥[11̅0]{}3{{C}-{SiC}/{Si}} and [3̅034]GaN ∥[110]3C - SiC/Si . Low-temperature photoluminescence (PL) and XRD measurements showed the presence of basal-plane stacking faults in the layers. PL measurements of (202̅3) multiple-quantum-well and light-emitting diode structures showed uniform luminescence at about 500 nm emission wavelength. A small peak shift of about 3 nm was observed in the electroluminescence when the current was increased from 5 to 50 mA (25-250 A cm-2).

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

    PubMed Central

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

    2016-01-01

    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. PMID:27530434

  3. MBE fabrication of self-assembled Si and metal nanostructures on Si surfaces

    SciTech Connect

    Galiana, Natalia; Martin, Pedro-Pablo; Munuera, Carmen; Varela del Arco, Maria; Soria, Federico; Ocal, Carmen; Ruiz, Ana; Alonso, Maria

    2006-01-01

    Two types of fairly regular distributions of Si nanostructures, of interest as templates to grow spatially controlled ensembles of metal (Co, Fe, Ag, etc.) nanostructures, are presented in this paper. Both of them are achieved by self-assembling processes during Si homoepitaxy. One corresponds to films grown by molecular beam epitaxy (MBE) on Si(0 0 1)-2 x 1 surfaces with low (<1 degree) miscut angles. In this case, arrays of 3D Si-islands displaying well defined pyramid-like shapes can be obtained, as evidenced by Scanning Force Microscopy (SFM) and Scanning Transmission Electron Microscopy (STEM). Such arrays exhibit strong similarities with those reported for Ge and SiGe islands on Si(0 0 1), and may thus serve as a simpler route to produce ordered distributions of metallic nanodots. On the other hand, on Si(1 1 1)-7 x 7 vicinal substrates misoriented 4 degrees toward the View the MathML source direction, step rearrangement during homoepitaxy permits to produce nanopatterned surfaces, the building-blocks of which are triangular (1 1 1) platforms, with lateral dimensions of hundreds of nanometers, bound by step bunches about 30 nm high. Furthermore, different Ag deposition experiments support this spontaneous patterning on Si(1 1 1) as a promising approach to achieve regular distributions of metallic nanocrystals with an overall homogeneity in sizes, shapes and spacing.

  4. SiC/Si diode trigger circuit provides automatic range switching for log amplifier

    NASA Technical Reports Server (NTRS)

    1967-01-01

    SiC/Si diode pair provides automatic range change to extend the operating range of a logarithmic amplifier-conversion circuit and assures stability at or near the range switch-over point. the diode provides hysteresis for a trigger circuit that actuates a relay at the desired range extension point.

  5. Film Si Solar Cells with Nano Si: Cooperative Research and Development Final Report, CRADA Number CRD-09-00356

    SciTech Connect

    Wang, Q.

    2011-05-01

    Nevada Nanotechnology Center and Si group at NREL will work together to develop a-Si based solar cells with nano-Si technique. We will explore the existing a-Si based film solar cell technology at NREL and nano scale Si technology at Nevada Nanotechnology Center. By exchanging information, we will come; up with some new cell structures using nano-Si. We expect the new a-Si based cells will have optical enhancement or better electronic or optical properties of absorber layer to improve solar cell performance.

  6. Diffusional kinetics of SiGe Dimers on Si(100) using atom-tracking scanning tunneling microscopy

    SciTech Connect

    QIN,X.R.; SWARTZENTRUBER,BRIAN S.; LAGALLY,M.G.

    2000-06-14

    Quantitative measurements of the diffusion of adsorbed mixed Ge-Si dimers on the Si(100) surface have been made as a function of temperature using atom-tracking scanning tunneling microscopy. These mixed dimers are distinguishable from pure Si-Si dimers by their characteristic kinetics--a 180-degree rotation between two highly buckled configurations. At temperatures at which the mixed dimers diffuse, atomic-exchange events occur, in which the Ge atom in the adsorbed dimer exchanges with a substrate Si atom. Re-exchange can also occur when the diffusing Si-Si dimer revisits the original site of exchange.

  7. Molecular dynamics simulation of C/Si ratio effect on the irradiation swelling of β-SiC

    NASA Astrophysics Data System (ADS)

    Li, Yingying; Xiao, Wei; Li, Huailin

    2016-11-01

    The C/Si atom ratio effect on the irradiation swelling of β-SiC is studied using molecular dynamics (MD) simulations. The irradiation swelling decreases with the increase of C/Si ratio under the same irradiation conditions. The carbon cluster is the key issue for the irradiation swelling of non-stoichiometric SiC. The carbon cluster size increases with the increase of C/Si ratio and the number of cluster decreases with the increase of C/Si ratio after irradiation process. An analytical model is established to describe the C/Si ratio effect on irradiation swelling and it fits the MD data well.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Optical Diagnostics on HIT-SI3

    NASA Astrophysics Data System (ADS)

    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.

  10. Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long-wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Maserjian, J.

    1990-01-01

    The feasibility of a novel p(+)-Si(1-x)Ge(x)-p-Si heterojunction internal photoemission (HIP) IR detector is demonstrated. A degenerately doped p(x)-Si(1-x)Ge(x) layer is required for strong IR absorption to generate photoexcited holes. The Si(1-x)Ge(x) layers are grown by molecular beam epitaxy, with boron concentrations up to 10 to the 20th/cu cm achieved by using an HBO2 source. Photoresponse at wavelengths ranging from 2 to 10 microns has been obtained with quantum efficiencies above 1 percent. The tailorable cutoff wavelength of the HIP detector has been demonstrated by varying the Ge composition ratio in the Si(1-x)Ge(x) layers.

  11. Metal/silicon interface formation - The Ni/Si and Pd/Si systems

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    The valence level spectra of the Ni/Si and Pd/Si systems have been investigated using high resolution X-ray photoelectron spectroscopy. Temperature dependence studies for Ni deposited on thin thermal SiO2 demonstrate the importance of metal aggregation effects in the interpretation of binding energies as chemical shifts. Temperature studies for the Ni/Si system indicate that substantial chemical interaction occurs at the interface at temperatures as low as 100 K. These studies also show the presence of Ni in interstitial voids in the Si near the interface. A comparative study of the core and valence band features for the Ni and Pd silicides provides many valuable insights and a self-consistent picture of the attendent valence charge redistribution and its influence on the observed chemical shifts.

  12. Photoresponse Model for Si_(1-x)Ge_x/Si Heterojunction Internal Photoemission Infrared Detector

    NASA Technical Reports Server (NTRS)

    Lin, T.; Park, J. S.; Gunapala, S. D.; Jones, E. W.; Castillo, H. M. Del

    1993-01-01

    A photoresponse model has been developed for the Si_(1-x)Ge_x/Si heterojunction internalphotoemission (HIP) infrared detector at wavelengths corresponding to photon energies less than theFermi energy. A Si_(0.7)Ge_(0.3)/Si HIP detector with a cutoff wavelength of 23 micrometers andan emission coefficient of 0.4 eV^(-1) has been demonstrated. The model agrees with the measureddetector response at lambda greater than 8 micrometers. The potential barrier determined by themodel is in close agreement (difference similar to 4 meV) with the potential barrier determined by theRichardson plot, compared to the discrepancies of 20-50 meV usually observed for PtSi Schottkydetectors.

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

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

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

  14. 193 nm Excimer laser processing of Si/Ge/Si(100) micropatterns

    NASA Astrophysics Data System (ADS)

    Gontad, F.; Conde, J. C.; Chiussi, S.; Serra, C.; González, P.

    2016-01-01

    193 nm Excimer laser assisted growth and crystallization of amorphous Si/Ge bilayer patterns with circular structures of 3 μm diameter and around 25 nm total thickness, is presented. Amorphous patterns were grown by Laser induced Chemical Vapor Deposition, using nanostencils as shadow masks and then irradiated with the same laser to induce structural and compositional modifications for producing crystalline SiGe alloys through fast melting/solidification cycles. Compositional and structural analyses demonstrated that pulses of 240 mJ/cm2 lead to graded SiGe alloys with Si rich discs of 2 μm diameter on top, a buried Ge layer, and Ge rich SiGe rings surrounding each feature, as predicted by previous numerical simulation.

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

    SciTech Connect

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

    2010-08-04

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

  16. Production of Si by vacuum carbothermal reduction of SiO2 using concentrated solar energy

    NASA Astrophysics Data System (ADS)

    Loutzenhiser, Peter G.; Tuerk, Ozan; Steinfeld, Aldo

    2010-09-01

    Using concentrated solar radiation as the energy source of high-temperature process heat, the carbothermal reduction of silica to silicon was examined thermodynamically and demonstrated experimentally at vacuum pressures. Reducing the system pressure favors Si(g) formation, enabling its vacuum distillation. Experimentation in a solar reactor was performed in the range 1,997-2,263 K at ˜3×10-3 bar with mixtures of charcoal and silica directly exposed to radiative flux intensities equivalent to 6,500 suns, yielding Si purities ranging from 66.1-79.2 wt.%. The Si purity increased with temperature. Solid characterizations showed SiC and SiO as important reaction intermediaries.

  17. Elastic and inelastic scattering of 50-MeV pions from 28Si and 30Si

    NASA Astrophysics Data System (ADS)

    Wienands, U.; Hessey, N.; Barnett, B. M.; Rozon, F. M.; Roser, H. W.; Altman, A.; Johnson, R. R.; Gill, D. R.; Smith, G. R.; Wiedner, C. A.; Manley, D. M.; Berman, B. L.; Crawford, H. J.; Grion, N.

    1987-02-01

    Angular distributions of the differential cross section for elastic and inelastic scattering of 50-MeV π+ and π- on 28Si and 30Si have been measured to a relative accuracy of 5-10 We fitted the cross section of elastic π+ and π- scattering from 28Si simultaneously with an optical model using a second-order potential of the Michigan State University form. Our best-fit parameters differ from those given previously. The ratio of the neutron and proton transition-matrix elements for the first Jπ=2+ state in 28Si is found from the inelastic cross section to be 1.13+/-0.09. For 30Si, the ratio is found to be 0.93+/-0.09, which differs significantly from the value derived from lifetime measurements on mirror nuclei.

  18. Interface nature of oxidized single-crystal arrays of etched Si nanowires on (100)Si

    NASA Astrophysics Data System (ADS)

    Jivanescu, M.; Stesmans, A.; Kurstjens, R.; Dross, F.

    2012-02-01

    Low temperature electron spin resonance studies have been carried out on single crystalline arrays of sub-10 nm Si nanowires (NWs) manufactured on (100)Si by top down etching and oxidation thinning. This reveals the presence of a substantial inherent density of Pb0 (Si3 ≡ Si•) defects (traps) at the NW Si/SiO2 interfaces, due to particular faceting and enhanced interface strain, leaving NW interfaces of reduced electrical quality. Perusal of the specific properties of the occurring Pb-type defect system points to a nanopillar morphology compatible with NWs predominantly bordered by {110} facets, with cross sectional shape of <100> truncated {110} squares. The inherent interface quality appears limited by the wire-narrowing thermal oxidation procedure.

  19. A model for thermal oxidation of Si and SiC including material expansion

    SciTech Connect

    Christen, T. Ioannidis, A.; Winkelmann, C.

    2015-02-28

    A model based on drift-diffusion-reaction kinetics for Si and SiC oxidation is discussed, which takes the material expansion into account with an additional convection term. The associated velocity field is determined self-consistently from the local reaction rate. The approach allows a calculation of the densities of volatile species in an nm-resolution at the oxidation front. The model is illustrated with simulation results for the growth and impurity redistribution during Si oxidation and for carbon and silicon emission during SiC oxidation. The approach can be useful for the prediction of Si and/or C interstitial distribution, which is particularly relevant for the quality of metal-oxide-semiconductor electronic devices.

  20. SiC/SiC Ceramic Matrix Composites Developed for High-Temperature Space Transportation Applications

    NASA Technical Reports Server (NTRS)

    Kiser, J. Douglas; Bhatt, Ramakrishna, T.; Morscher, Gregory N.; Yun, Hee Mann; DiCarlo, James A.; Petko, Jeanne F.

    2005-01-01

    Researchers at the NASA Glenn Research Center have been developing durable, high-temperature ceramic matrix composites (CMCs) with silicon carbide (SiC) matrices and SiC or carbon fibers for use in advanced reusable launch vehicle propulsion and airframe applications in the Next Generation Launch Technology (NGLT) Program. These CMCs weigh less and are more durable than competing metallic alloys, and they are tougher than silicon-based monolithic ceramics. Because of their high specific strength and durability at high temperatures, CMCs such as C/SiC (carbon- fiber-reinforced silicon carbide) and SiC/SiC (silicon-carbide-fiber-reinforced silicon carbide) may increase vehicle performance and safety significantly and reduce the cost of transporting payloads to orbit.

  1. Measurements of Local Strain Variation in Si(1-x)Ge(x)/Si Heterostructures

    NASA Technical Reports Server (NTRS)

    Bell, L. D.; Kaiser, W. J.; Manion, S. J.; Milliken, S. J.; Pike, W. T.; Fathauer, R. W.

    1995-01-01

    The energy splitting of the conduction-band minimum of Si(1-x), Ge(x), due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si(1-x), Ge(x) structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si(1-x), Ge(x), however, heterogeneity in the strain of the Si(1-x), Ge(x) layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si(1-x)Ge(x) surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.

  2. Epitaxial ternary RexMo1 - xSi2 thin films on Si(100)

    NASA Astrophysics Data System (ADS)

    Vantomme, André; Nicolet, Marc-A.; Long, Robert G.; Mahan, John E.

    1994-04-01

    Reactive deposition epitaxy was used to synthesize thin layers of RexMo1-xSi2 on Si(100). In the case of x=1, ReSi2 layers of excellent crystalline quality have been reported previously [J. E. Mahan, K. M. Geib, G. Y. Robinson, R. G. Long, Y. Xinghua, G. Bai, and M.-A. Nicolet, Appl. Phys. Lett. 56, 2439 (1990)]. In the case of x=0, however, virtually no alignment of the MoSi2 and the substrate is found, although this silicide is nearly isomorphic to ReSi2. For intermediate values of x, highly epitaxial ternary silicides are obtained, at least for a Mo fraction up to 1/3.

  3. Hysteresis in the Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  4. Microstructural characterization of as-cast Cr-Si alloys

    SciTech Connect

    Chad, V.M. Faria, M.I.S.T.; Coelho, G.C.; Nunes, C.A.; Suzuki, P.A.

    2008-01-15

    This work presents results of microstructural characterization of as-cast Cr-Si alloys. The alloys were prepared by arc melting pure Cr (min. 99.996%) and Si (min. 99.998%) powder mixtures under argon atmosphere in a water-cooled copper crucible with nonconsumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy (SEM), using the back-scattered electron (BSE) image mode and X-ray diffraction (XRD). The results confirm the currently accepted Cr-Si phase diagram in terms of the invariant reactions and solid phases present in this system. Small corrections are proposed for the compositions of the liquid phase in the following reactions: (i) L {r_reversible} Cr{sub SS}+Cr{sub 3}Si, from 15 to 16 at.% Si; (ii) L+{alpha}Cr{sub 5}Si{sub 3} {r_reversible} CrSi, from 51 at.% Si to slightly above 53 at.% Si; (iii) L {r_reversible} CrSi+CrSi{sub 2}, from 56 to slightly above 57 at.% Si; (iv) L {r_reversible} CrSi{sub 2}+Si, from 82 to slightly above 85 at.% Si.

  5. Investigation of structural and electrical properties of flat a-Si/c-Si heterostructure fabricated by EBPVD technique

    SciTech Connect

    Demiroğlu, D.; Tatar, B.; Kazmanli, K.; Urgen, M.

    2013-12-16

    Flat amorphous silicon - crystal silicon (a-Si/c-Si) heterostructure were prepared by ultra-high vacuum electron beam evaporation technique on p-Si (111) and n-Si (100) single crystal substrates. Structural analyses were investigated by XRD, Raman and FEG-SEM analysis. With these analyses we determined that at the least amorphous structure shows modification but amorphous structure just protected. The electrical and photovoltaic properties of flat a-Si/c-Si heterojunction devices were investigated with current-voltage characteristics under dark and illumination conditions. Electrical properties of flat a-Si/c-Si heterorojunction; such as barrier height Φ{sub B}, diode ideality factor η were determined from current-voltage characteristics in dark conditions. These a-Si/c-Si heterostructure have good rectification behavior as a diode and exhibit high photovoltaic sensitivity.

  6. A novel method to form conducting channels in SiOx(Si ) films for field emission application

    NASA Astrophysics Data System (ADS)

    Semenenko, M.; Evtukh, A.; Yilmazoglu, O.; Hartnagel, H. L.; Pavlidis, D.

    2010-01-01

    The electrical and field emission properties of SiOx(Si ) films are studied. SiOx(Si ) films of 40-100nm thick are obtained by plasma-enhanced chemical vapor deposition and thermal evaporation of Si powder onto Si substrates. Nanosized electrical conducting channels are formed in SiOx(Si ) films by electrical conditioning at high current densities. The structures with conducting channels demonstrate increased field emission current and decreased threshold voltage compared to as-deposited SiOx(Si ) films. The decrease in threshold voltage for electron field emission is explained by local enhancement of electric field. The diameters of conducting channels are estimated from the effective emission area to be in the range of 1-2nm.

  7. High-efficiency heterojunction crystalline Si solar cell and optical splitting structure fabricated by applying thin-film Si technology

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kenji; Adachi, Daisuke; Uzu, Hisashi; Ichikawa, Mitsuru; Terashita, Toru; Meguro, Tomomi; Nakanishi, Naoaki; Yoshimi, Masashi; Hernández, José Luis

    2015-08-01

    Thin-film Si technology for solar cells has been developed for over 40 years. Improvements in the conversion efficiency and industrialization of thin-film Si solar cells have been realized through continuous research and development of the thin-film Si technology. The thin-film Si technology covers a wide range of fields such as fundamental understanding of the nature of thin-film Si, cell/module production, simulation, and reliability technologies. These technologies are also significant for solar cells other than the thin-film Si solar cells. Utilizing the highly developed thin-film Si solar cell technology, we have achieved ∼24% efficiency heterojunction crystalline Si solar cells using 6-in. wafers and >26% efficiency solar cells with an optical splitting structure. These results indicate that further improvement of thin-film Si technology and its synergy with crystalline Si solar cell technology will enable further improvement of solar cells with efficiencies above 26%.

  8. Finite element simulation for ultraviolet excimer laser processing of patterned Si/SiGe/Si(100) heterostructures

    SciTech Connect

    Conde, J. C.; Chiussi, S.; Gontad, F.; Gonzalez, P.; Martin, E.; Serra, C.

    2010-07-05

    Ultraviolet (UV) Excimer laser assisted processing is an alternative strategy for producing patterned silicon germanium heterostructures. We numerically analyzed the effects caused by pulsed 193 Excimer laser radiation impinging on patterned amorphous hydrogenated silicon (a-Si:H) and germanium (a-Ge:H) bilayers deposited on a crystalline silicon substrate [Si(100)]. The proposed two dimensional axisymmetric numerical model allowed us to estimate the temperature and concentration gradients caused by the laser induced rapid melting and solidification processes. Energy density dependence of maximum melting depth and melting time evolution as well as three dimensional temperature and element distribution have been simulated and compared with experimentally obtained results.

  9. Photoemission study on electrical dipole at SiO2/Si and HfO2/SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Fujimura, Nobuyuki; Ohta, Akio; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

    2017-04-01

    Electrical dipole at SiO2/Si and HfO2/SiO2 interfaces have been investigated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. From the analysis of the cut-off energy for secondary photoelectrons measured at each thinning step of a dielectric layer by wet-chemical etching, an abrupt potential change caused by electrical dipole at SiO2/Si and HfO2/SiO2 interfaces has been clearly detected. Al-gate MOS capacitors with thermally-grown SiO2 and a HfO2/SiO2 dielectric stack were fabricated to evaluate the Al work function from the flat band voltage shift of capacitance–voltage (C–V) characteristics. Comparing the results of XPS and C–V measurements, we have verified that electrical dipole formed at the interface can be directly measured by photoemission measurements.

  10. Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Maserjian, Joseph; Ksendzov, A.; Huberman, Mark L.; Terhune, R.; Krabach, T. N.

    1990-01-01

    There is a major need for long-wavelength-infrared (LWIR) detector arrays in the range of 8 to 16 microns which operate with close-cycle cryocoolers above 65 K. In addition, it would be very attractive to have Si-based infrared (IR) detectors that can be easily integrated with Si readout circuitry and have good pixel-to-pixel uniformity, which is critical for focal plane array (FPA) applications. Here, researchers report a novel Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) detector approach with a tailorable long wavelength infrared cutoff wavelength, based on internal photoemission over the Si(1-x)Ge(x)/Si heterojunction. The HIP detectors were grown by molecular beam epitaxy (MBE), which allows one to optimize the device structure with precise control of doping profiles, layer thickness and composition. The feasibility of a novel Si(1-x)Ge(x)/Si HIP detector has been demonstrated with tailorable cutoff wavelength in the LWIR region. Photoresponse at wavelengths 2 to 10 microns are obtained with quantum efficiency (QE) above approx. 1 percent in these non-optimized device structures. It should be possible to significantly improve the QE of the HIP detectors by optimizing the thickness, composition, and doping concentration of the Si(1-x)Ge(x) layers and by configuring the detector for maximum absorption such as the use of a cavity structure. With optimization of the QE and by matching the barrier energy to the desired wavelength cutoff to minimize the thermionic current, researchers predict near background limited performance in the LWIR region with operating temperatures above 65K. Finally, with mature Si processing, the relatively simple device structure offers potential for low-cost producible arrays with excellent uniformity.

  11. MeV electron irradiation of Si-SiO2 structures with magnetron sputtered oxide

    NASA Astrophysics Data System (ADS)

    Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

    2016-03-01

    MeV electrons influence on the characteristics of Si-SiO2 structure with magnetron sputtered oxide was studied by ellipsometry and the thermally stimulated current (TSC) method. The MOS structures used in this study were fabricated on <100> oriented p-Si wafers of 12.75-17,25 Ω.cm resistivity. Magnetron sputtered oxides with different thicknesses of 20 and 100 nm were deposited on p-Si substrates. Both groups of samples were irradiated by 23 MeV electrons. The oxide thicknesses and TSC characteristics of the MOS samples were measured before and after MeV electron irradiation with doses of 4.8×1015 and 4.8×1016 el.cm-2. The oxide thicknesses of both groups of samples increased after irradiation. The main defects generated by the MeV electrons were evaluated. It was shown that the trap concentration increases with the electron irradiation dose. The main peak in the TSC characteristics gives information about the main radiation defects at the Si-SiO2 interface of the MOS structures. These defects can be related to the vacancy-boron complexes which are associated with the main impurities in the p-Si substrate. These results correspond to our results reported earlier for MeV electron irradiated Si-SiO2 structures with thermally grown oxide. But (in this case) the effects observed are more pronounced for the magnetron sputtered oxide. A possible reason is the higher defect concentration generated in the magnetron sputtered oxide during its deposition on Si-substrates.

  12. Flexible micromorph tandem a-Si/{mu}c-Si solar cells

    SciTech Connect

    Soederstroem, T.; Haug, F.-J.; Terrazzoni-Daudrix, V.; Ballif, C.

    2010-01-15

    The deposition of a stack of amorphous (a-Si:H) and microcrystalline ({mu}c-Si:H) tandem thin film silicon solar cells (micromorph) requires at least twice the time used for a single junction a-Si:H cell. However, micromorph devices have a higher potential efficiency, thanks to the broader absorption spectrum of {mu}c-Si:H material. High efficiencies can only be achieved by mitigating the nanocracks in the {mu}c-Si:H cell and the light-induced degradation of the a-Si:H cell. As a result, {mu}c-Si:H cell has to grow on a smooth substrate with large periodicity (>1 {mu}m) and the a-Si:H cell on sharp pyramids with smaller feature size ({approx}350 nm) to strongly scatter the light in the weak absorption spectra of a-Si:H material. The asymmetric intermediate reflector introduced in this work uncouples the growth and light scattering issues of the tandem micromorph solar cells. The stabilized efficiency of the tandem n-i-p/n-i-p micromorph is increased by a relative 15% compared to a cell without AIR and 32% in relative compared to an a-Si:H single junction solar cells. The overall process (T<200 deg. C) is kept compatible with low cost plastic substrates. The best stabilized efficiency of a cell deposited on polyethylene-naphthalate plastic substrate is 9.8% after 1000 h of light soaking at V{sub oc}, 1 sun, and 50 deg. C.

  13. Effects of silicon-on-insulator substrate on the residual stress within 3C-SiC/Si thin films

    NASA Astrophysics Data System (ADS)

    Park, J.-H.; Kim, J. H.; Kim, Y.; Lee, B.-T.; Jang, S.-J.; Moon, C.-K.; Song, H.-J.

    2003-09-01

    Single-crystalline 3C-SiC heteroepitaxial layers were grown on silicon-on-insulator (SOI) and Si wafers, to investigate effects of SOI substrates on the film quality. Residual stress measurement using a laser scan method and the Raman scattering spectroscopy indicated that internal stress within SiC films on SOI were indeed reduced, when compared with that of SiC films on Si.

  14. SiC Composite Turbine Vanes

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Verilli, Michael J.

    2006-01-01

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

  15. ICP Etching of SiC

    SciTech Connect

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

    1999-02-04

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

  16. Recent advances in siRNA delivery.

    PubMed

    Sarisozen, Can; Salzano, Giuseppina; Torchilin, Vladimir P

    2015-12-01

    In the 1990s an unexpected gene-silencing phenomena in plants, the later called RNA interference (RNAi), perplexed scientists. Following the proof of activity in mammalian cells, small interfering RNAs (siRNAs) have quickly crept into biomedical research as a new powerful tool for the potential treatment of different human diseases based on altered gene expression. In the past decades, several promising data from ongoing clinical trials have been reported. However, despite surprising successes in many pre-clinical studies, concrete obstacles still need to be overcome to translate therapeutic siRNAs into clinical reality. Here, we provide an update on the recent advances of RNAi-based therapeutics and highlight novel synthetic platforms for the intracellular delivery of siRNAs.

  17. DNA repair investigations using siRNA.

    PubMed

    Miller, Holly; Grollman, Arthur P

    2003-06-11

    Small interfering RNA (siRNA) is a revolutionary tool for the experimental modulation of gene expression, in many cases making redundant the need for specific gene mutations and allowing examination of the effect of modulating essential genes. It has now been shown that siRNA phenotypes resulting from stable transfection with short hairpin RNA (shRNA) can be transmitted through the mouse germ line and Rosenquist and his colleagues have used shRNA, which is processed in vivo to siRNA, to create germline transgenic mice in which a target DNA repair gene has been silenced. Here, Holly Miller and Arthur P. Grollman give the background of these discoveries, provide an overview of current uses, and look at future applications of this research.

  18. Transparent films for heterojunction Si photovoltaics.

    PubMed

    Kim, Joondong; Park, Yun Chang

    2013-06-01

    A heterojunction of Al-doped ZnO (AZO) and Si was applied as a photodiode. A Co-sputtering system was used to deposit a quality AZO film following an n-type Si thin film coating. Al is an n-doping element for ZnO and thus the Al content significantly controls the mobility and the crystalline structure of AZO films. In order to provide the highest mobility, the optimum Al-content was found to be 5.22 wt%. X-ray diffraction analysis also showed a release of the compressive stress for the Al-5.22 wt% AZO film. Due to the excellent electrical conductivity of the AZO film, the heterojunction diode showed an enhanced rectifying ratio of 87.7 from 59.9 of the bare Si diode according to the reduction of the series resistance. This scheme may provide a route to reducing the contact resistance and subsequently improving photovoltaic devices.

  19. The Stellar Imager (SI) "Vision Mission"

    NASA Technical Reports Server (NTRS)

    Carpenter, K.; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Schrijver, C.; Kilston, S.

    2004-01-01

    The Stellar Imager (SI) is a Vision Mission in the Sun-Earth Connection (SEC) NASA Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, a t ultraviolet wavelengths, on the order of 100 micro-arcsec and baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (>20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. In this paper, we present an update on the ongoing SI mission concept and technology development studies.

  20. The Stellar Imager (SI) "Vision Mission"

    NASA Technical Reports Server (NTRS)

    Carpenter, K.; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Schrijver, C.; Kilston, S.

    2004-01-01

    The Stellar Imager (SI) is a Vision Mission in the Sun-Earth Connection (SEC) NASA Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (greater than 20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. In this paper, we present an update on the ongoing SI mission concept and technology development studies.

  1. Role of Si2N2O in the passive oxidation of chemically-vapor-deposited Si3N4

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.

    1992-01-01

    The results of two-step oxidation experiments on chemically-vapor-deposited Si3N4 and SiC at 1350 C show that a correlation exists between the presence of a Si2N2O interphase and the strong oxidation resistance of Si3N4. During normal oxidation, k sub p for SiC was 15 times higher than that for Si3N4, and the oxide scale on Si3N4 was found by SEM and TEM to contain a prominent Si2N2O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500 C and reoxidized at 1350 C as before, three things happen: the oxidation k sub p increases over 55-fold for Si3N4, and 3.5-fold for SiC; the Si3N4 and SiC oxidize with nearly equal k sub p's; and, most significantly, the oxide scale on Si3N4 is found to be lacking an inner Si2N2O layer. The implications of this correlation for the competing models of Si3N4 oxidation are discussed.

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

    NASA Astrophysics Data System (ADS)

    Kleykamp, H.

    2000-12-01

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

  3. Thermodynamic analysis of the W--F--Si--H and W--F--Si--H--Cl systems

    SciTech Connect

    Rode, E.J. ); Harshbarger, W.R. )

    1990-01-01

    Chemical vapor deposition of WSi{sub 2} was studied through thermodynamic equilibrium calculations for the W--F--Si--H and W--F--Si--H--Cl systems. The calculations were made with a computer program that minimizes the Gibbs free energy by Langrangian multiplier techniques. The parameter range for these system analyses were: temperature 473 to 1073 K, pressure from 50 to 500 mTorr, and Si/W ratios of 3 to 1000. 21 gas phase species and eight solid species were included in the calculations for the W--F--Si--H system and 39 gas phase species and 15 solid species were considered for the W--F--Si--H--Cl system. At the equilibrium condition, H{sub 2}, SiF{sub 4}, and SiF{sub 2}H{sub 2} are the most prominent gaseous species for the W--F--Si--H system while WSi{sub 2} and Si are formed in the solid phase. For the W--F--Si--H--Cl system, WSi{sub 2} and Si are formed in the solid phase, while H{sub 2}, SiCl{sub 4}, HCl, SiF{sub 4} and SiHCl{sub 3} are the most prominent gas phase species. The SiCl{sub 2} intermediate plays a key role in the surface activated reaction for this system.

  4. Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour-liquid-solid mechanism from the Al-Ge-Si ternary system

    NASA Astrophysics Data System (ADS)

    Lorenzzi, Jean; Ferro, Gabriel; Cauwet, François; Souliere, Véronique; Carole, Davy

    2011-03-01

    In this work, we present and compare the results obtained from different Si-based melts (Ge-Si, Al-Si and Al-Ge-Si) for growing SiC layers on α-SiC substrate by vapour-liquid-solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al-Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge-Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge-Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes.

  5. GaP/Si heterojunction Solar Cells

    SciTech Connect

    Saive, R.; Chen, C.; Emmer, H.; Atwater, H.

    2015-05-11

    Improving the efficiency of solar cells requires the introduction of novel device concepts. Recent developments have shown that in Si solar cell technology there is still room for tremendous improvement. Using the heterojunction with intrinsic thin layer (HIT) approach 25.6 % power conversion efficiency was achieved. However, a-Si as a window and passivation layer comes with disadvantages as a-Si shows low conductivity and high parasitic absorption. Therefore, it is likely that using a crystalline material as window layer with high band gab and high mobility can further improve efficiency. We have studied GaP grown by MOCVD on Si with (001) and (112) orientation. We obtained crystalline layers with carrier mobility around 100 cm2/Vs and which passivate Si as confirmed by carrier lifetime measurements. We performed band alignment studies by X-ray photoelectron spectroscopy yielding a valence band offset of 0.3 eV. Comparing this value with the Schottky-model leads to an interface dipole of 0.59 eV. The open circuit voltage increases with increasing doping and is consistent with the theoretical open circuit voltage deduced from work function difference and interface dipole. We obtain an open circuit voltage of 0.38 V for n-doped GaP with doping levels in the order of 10^17 1/cm^3. In our next steps we will increase the doping level further in order to gain higher open circuit voltage. We will discuss the implications of these findings for GaP/Si heterojunction solar cells.

  6. C60 on SiC nanomesh.

    PubMed

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

    2006-11-02

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

  7. The use of Ge/Si ratios to quantify Si transformations in grassland ecosystems

    NASA Astrophysics Data System (ADS)

    Blecker, S. W.; Derry, L. A.; Chadwick, O. A.; Kelly, E. F.

    2005-12-01

    Germanium (Ge) has been shown to behave as a heavy isotope of silicon (Si), enabling the use of Ge/Si ratios as a weathering tracer in terrestrial environments. The two major mechanisms of Ge/Si fractionation in soils result from mineral weathering reactions and biogenic silica formation by plants. The role of plants in Ge fractionation has been deduced from relatively few field studies, and geochemical Ge fractionation data in temperate systems are lacking. The objectives of this research were to quantify biologic Ge fractionation, and to utilize differences in Ge/Si values among the major biogeochemical pools across a grassland bioclimosequence to examine stream water silica provenance. Quantification of biological Ge fractionation was carried out under controlled experimental conditions. Plant phytoliths grown in hydroponic solutions fractionated against Ge (comparing Ge/Sisolution with Ge/Siphytolith) by an average of 82%. Differences in Ge/Si values between roots, stems, and leaves indicate fractionation likely occurs at the root/solution interface. Phytoliths from plants grown in two different soil mediums fractionated against Ge, averaging 44% to 63%, with no clear trends among the species. From the field study, the greater fractionation factor (Kw, where Kw = (Ge/Siclay)/(Ge/Sibedrock)) of the tallgrass (Kw =2.8) vs. shortgrass sites (Kw =1.4) results from the increased weathering intensity across the bioclimosequence. Plant phytoliths exhibit relatively low Ge/Si values (0.15-0.44; x =0.29; n=15), compared to those of the corresponding surface soil water Ge/Si (0.22-0.94; x =0.66; n=6). Stream water Ge/Si values along the grassland climosequence (0.07-1.29, x = 0.34; n = 20) are typical of natural water Ge/Si values. Higher groundwater Ge values (0.42-3.4; x = 1.3; n=16) may represent an increased residence time or contact with minerals of higher Ge/Si ratios. The lack of Ge/Si separation among the major terrestrial pools confounds stream Si provenance

  8. Ab initio quantum chemical investigation of several isomers of anionic Si 6

    NASA Astrophysics Data System (ADS)

    Takahashi, Masae; Kawazoe, Yoshiyuki

    2006-02-01

    Eight isomers (planar hexagon, benzvalene, Dewar benzene, triangular prismane, bicyclopropenyl, octahedron, chair form, and twist boat form) of Si 6, Si62-, Si64-, and Si66-, have been searched for by the MP2 and B3LYP electronic structure calculations. Totally 14 isomers were found: two Si 6, six Si62-, five Si64-, and one Si66-. Two of them are different from the eight isomers: deformed triangle Si62-; pentagonal pyramidal Si64-. We discovered that the predicted stable shapes of Si62-, Si64-, and Si66- are octahedral, pentagonal pyramidal, and hexagonal, respectively, which agrees well with Wade rule.

  9. CBED and FE Study of Thin Foil Relaxation in Cross-Section Samples of Si /Si1-xGex and Si /Si1-xGex /Si Heterostructures

    NASA Astrophysics Data System (ADS)

    Alexandre, L.; Jurczak, G.; Alfonso, C.; Saikly, W.; Grosjean, C.; Charai, A.; Thibault, J.

    In order to determine residual stress/strain fields in CMOS devices and validate tools used to quantify the strain field, we first studied residual strains in Si/Si1-xGex and Si/Si1-xGex/Si TEM samples. Because of sample thinning for TEM observations, elastic relaxation occurs and modifies the initial stress present in the bulk sample. Nevertheless, if the main parameters which play a role on the elastic relaxation process can be determined, we show that it is possible to reproduce from FE and diffraction simulations the complex profile of the HOLZ lines observed on experimental CBED patterns which makes possible the determination of the initial stress state.

  10. SiO Maser Emission in Miras

    DTIC Science & Technology

    2008-09-01

    Mon. Not. R. Astron. Soc. 394, 51–66 (2009) doi:10.1111/j.1365-2966.2008.14237.x SiO maser emission in Miras M. D. Gray,1 M. Wittkowski,2 M. Scholz...October 27; in original form 2008 September 1 ABSTRACT We describe a combined dynamic atmosphere and maser propagation model of SiO maser emission in...brightest at an optical phase of 0.1–0.25, which is consistent with observed phase lags. Dust can have both mild and profound effects on the maser emission

  11. Bond-orientational order in liquid Si

    NASA Technical Reports Server (NTRS)

    Wang, Z. Q.; Stroud, D.

    1991-01-01

    Bond-orientational order in liquid Si via Monte Carlo simulation in conjuncation with empirical two- and three-body potentials of the form proposed by Stillinger and Weber are studied. Bond-orientational order (BOO) is described in terms of combinations of spherical harmonic functions. Liquid Si is found to have pronounced short-range BOO corresponding to l = 3, as expected for a structure with local tetrahedral order. No long-range BOO is found either in the equilibrium or the supercooled liquid. When the three-body potential is artificially removed, the tetrahedral bond-orientation order disappears and the liquid assumes a close-packed structure.

  12. Direct growth of graphene on Si(111)

    SciTech Connect

    Thanh Trung, Pham Joucken, Frédéric; Colomer, Jean-François; Robert, Sporken; Campos-Delgado, Jessica; Raskin, Jean-Pierre; Hackens, Benoît; Santos, Cristiane N.

    2014-06-14

    Due to the need of integrated circuit in the current silicon technology, the formation of graphene on Si wafer is highly desirable, but is still a challenge for the scientific community. In this context, we report the direct growth of graphene on Si(111) wafer under appropriate conditions using an electron beam evaporator. The structural quality of the material is investigated in detail by reflection high energy electron diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy, Raman spectroscopy, high resolution scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. Our experimental results confirm that the quality of graphene is strongly dependent on the growth time during carbon atoms deposition.

  13. Experience with SI units in biochemistry.

    PubMed Central

    Karnauchow, P. N.; Suvanto, L.

    1976-01-01

    Use of Système International d'Unités (SI) for laboratory measurements was instituted Jan. 1, 1975 at two community hospitals. Beforehand, talks were given, pamphlets, conversion tables, new calibration curves and new master record cards were printed, computer cards were reprogrammed and conversion kits were prepared; the total cost was less than $200. After 6 months 16% of the medical staff had stopped converting SI units into conventional units, 78% were still occasionally converting units and 6% were routinely converting units. Changeover had been difficult for 25%, only a nuisance for 49% and easy for 26%. The patients' lives were not endangered by conversion. PMID:1260590

  14. Ion Beam Synthesis Of Metal - Silicon Carbide - Si Multilayer Structures

    NASA Astrophysics Data System (ADS)

    Lindner, J. K. N.; Tsang, W. M.; Stritzker, B.; Wong, S. P.

    2003-08-01

    High doses of Ti, Ni, Mo, or W ions were implanted at elevated temperatures either conventionally or using a MEVVA ion source into ion beam synthesized Si/SiC/Si or SiC/Si layer structures in order to create metallic layers contacting the SiC. The depth distribution of metal atoms and the formation of silicide and carbide phases as well as the formation of cavities at the lower SiC/Si interface are studied by Rutherford backscattering spectroscopy (RBS) and cross-sectional transmission electron microscopy (XTEM). A brief survey of the effects ocurring in the ion beam metallization of SiC films is given and the benefit of using ion beams for metallization of thin films is elucidated.

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

    SciTech Connect

    Belianinov, Aleksey

    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.

  16. Hybrid Si nanocones/PEDOT:PSS solar cell

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Wang, Jianxiong; Rusli, ᅟ

    2015-04-01

    Periodic silicon nanocones (SiNCs) with different periodicities are fabricated by dry etching of a Si substrate patterned using monolayer polystyrene (PS) nanospheres as a mask. Hybrid Si/PEDOT:PSS solar cells based on the SiNCs are then fabricated and characterized in terms of their optical, electrical, and photovoltaic properties. The optical properties of the SiNCs are also investigated using theoretical simulation based on the finite element method. The SiNCs reveal excellent light trapping ability as compared to a planar Si substrate. It is found that the power conversion efficiency (PCE) of the hybrid cells decreases with increasing periodicity of the SiNCs. The highest PCE of 7.1% is achieved for the SiNC hybrid cell with a 400-nm periodicity, due to the strong light trapping near the peak of the solar spectrum and better current collection efficiency.

  17. Generation of siRNA Nanosheets for Efficient RNA Interference

    NASA Astrophysics Data System (ADS)

    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.

  18. Revision of the Li13Si4 structure

    PubMed Central

    Zeilinger, Michael; Fässler, Thomas F.

    2013-01-01

    Besides Li17Si4, Li16.42Si4, and Li15Si4, another lithium-rich representative in the Li–Si system is the phase Li13Si4 (trideca­lithium tetra­silicide), the structure of which has been determined previously [Frank et al. (1975 ▶). Z. Naturforsch. Teil B, 30, 10–13]. A careful analysis of X-ray diffraction patterns of Li13Si4 revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li13Si4 on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i) the introduction of a split position for one Li site [occupancy ratio 0.838 (7):0.162 (7)], (ii) the anisotropic refinement of atomic displacement parameters for all atoms, and (iii) a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li13Si4 contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si–Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in the ab plane at z = 0 and are strictly separated from the Si–Si dumbbells at z = 0.5. PMID:24454148

  19. Ferroelectric functionality in SrTiO3/Si heterojunctions

    NASA Astrophysics Data System (ADS)

    Yu, H. L.; Wu, Y. Z.; Jiang, X. F.; Cai, M. Q.; Gu, L. P.; Yang, G. W.

    2013-11-01

    By the first-principles calculations, various SrTiO3/Si interface architectures have been studied in this work and the computed results showed that the stable ferroelectricity can be realized in the SrTiO3/Si system. The Si/SrO interface architecture with the Si-O configuration showed predominately the ferroelectric nature and the height of the potential barrier between the negative and positive poled states (0.77 eV per interfacial unit cell). The presence of the covalent bond between the substrate Si and O of SrO layer adjacent to the substrate Si leads to the disappearance of the electronic dipoles at the interface, and the reason is that the Si-O configuration of the Si/SrO interface architecture exhibits ferroelectric nature. In order to further understand the influence of the interfacial bonding nature on the ferroelectricity of the oxide layer, the BaTiO3/Si heterojunction with the same interface architectures also have been studied. Indeed, the Si/BaO interface architecture with the Si-O configuration showed predominately the ferroelectric nature too. Certainly, a full SrO (or BaO) layer directly grown on the substrate Si is benefit to the realization of the ferroelectric functionality in the ferroelectric-Si heterojunction. These findings are useful for the understanding of the basic physics of the ferroelectric-Si heterojunction and the silicon-based functional oxide device design.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Simulation of electron transmittance and tunnel current in n{sup +} Poly-Si/HfSiO{sub x}N/Trap/SiO{sub 2}/Si(100) capacitors using analytical and numerical approaches

    SciTech Connect

    Noor, Fatimah A. Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal

    2015-04-16

    In this paper, we discuss the electron transmittance and tunneling current in high-k-based-MOS capacitors with trapping charge by including the off-diagonal effective-mass tensor elements and the effect of coupling between transverse and longitudinal energies represented by an electron velocity in the gate. The HfSiO{sub x}N/SiO{sub 2} dual ultrathin layer is used as the gate oxide in an n{sup +} poly- Si/oxide/Si capacitor to replace SiO{sub 2}. The main problem of using HfSiO{sub x}N is the charge trapping formed at the HfSiO{sub x}N/SiO{sub 2} interface that can influence the performance of the device. Therefore, it is important to develop a model taking into account the presence of electron traps at the HfSiO{sub x}N/SiO{sub 2} interface in the electron transmittance and tunneling current. The transmittance and tunneling current in n{sup +} poly- Si/HfSiO{sub x}N/trap/SiO2/Si(100) capacitors are calculated by using Airy wavefunctions and a transfer matrix method (TMM) as analytical and numerical approaches, respectively. The transmittance and tunneling current obtained from the Airy wavefunction are compared to those computed by the TMM. The effects of the electron velocity on the transmittance and tunneling current are also discussed.

  2. Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

    NASA Technical Reports Server (NTRS)

    Hauenstein, Robert J.; Miles, Richard H.; Young, Mary H.

    1990-01-01

    Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

  3. Intersubband absorption in Si(1-x)Ge(x/Si superlattices for long wavelength infrared detectors

    NASA Technical Reports Server (NTRS)

    Rajakarunanayake, Yasantha; Mcgill, Tom C.

    1990-01-01

    Researchers calculated the absorption strengths for intersubband transitions in n-type Si(1-x)Ge(x)/Si superlattices. These transitions can be used for the detection of long-wavelength infrared radiation. A significant advantage in Si(1-x)Ge(x)/Si supperlattice detectors is the ability to detect normally incident light; in Ga(1-x)Al(x)As/GaAs superlattices, intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. Researchers present detailed calculation of absorption coefficients, and peak absorption wavelengths for (100), (111) and (110) Si(1-x)Ge(x)/Si superlattices. Peak absorption strengths of about 2000 to 6000 cm(exp -1) were obtained for typical sheet doping concentrations (approx. equals 10(exp 12)cm(exp -2)). Absorption comparable to that in Ga(1-x)Al(x)As/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.

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

    SciTech Connect

    Lewinsohn, C.A.; Jones, R.H.; Youngblood, G.E.; Henager, C.H. Jr.

    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.

  5. Variational calculations for the rovibrational states of Si 212C and Si 213C

    NASA Astrophysics Data System (ADS)

    Wang, Feng; von Nagy-Felsobuki, Ellak I.

    1996-11-01

    Rovibrational states of the ground electronic state of Si 212C and Si 213C isotopomers have been calculated variationally. The potential energy surface used in the calculations was obtained from an MP2/TZ2Pf ab initio surface of Barone et al. (V. Barone, P. Jensen and C. Minichino, J. Mol. Spectrosc., 154 (1992) 252) by applying the restrictions of 100° ⩽ α < 150°. The ab initio surface was refitted to a fourth-order polynomial with an Ogilvie-Tipping variable using a multi-dimensional least-squares procedure. The force field was then embedded in an Eckart-Watson vibration-rotation Hamiltonian, from which low-lying vibrational states and rovibrational states of Si 212C and Si 213C were obtained. The calculated vibrational states (100) and (001) of Si 212C and the 13C isotopic shifts agree well with a recent experiment (J.D. Presilla-Marquez and W.R.M. Graham, J. Chem. Phys., 95 (1991) 5612). Also, the calculations support the vibrational transition at 658.2 cm -1 found by Kafafi et al. (Z.H. Kafafi, R.H. Hauge, L. Fredin and J.L. Margrave, J. Chem. Phys., 87 (1983) 797). The rotational energies of these isotopomers for the lowest six vibrational states are given as are the rotational constants for Si 212C and Si 213C.

  6. Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Zhen

    Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.

  7. Revised nomenclature for defects at or near the Si/SiO{sub 2} interface

    SciTech Connect

    Fleetwood, D.M.

    1992-09-01

    A revised nomenclature for defects in MOS devices is described which clearly distinguishes the language used to describe the physical location of defects from that used to describe their electrical response. ``Oxide traps`` are simply defects in the SiO{sub 2} layer, and ``interface traps`` are defects at the Si/SiO{sub 2} interface; nothing is presumed about how either communicates with the underlying Si. ``Fixed states`` are defined electrically as trap levels that do not communicate with the Si on the time scale, but ``switching states`` can exchange charge with the Si. Fixed states presumably are oxide traps, but switching states can either be interface traps or near-interfacial oxide traps that can communicate with the Si, i.e. ``border traps.`` Thus the term ``traps`` is reserved for defect location, and the term ``states`` for electrical response. This defect picture is used to provide new insight into the response of MOS capacitors with 45-nm radiation-hardened oxides to electrical stress and annealing; capacitance-voltage and thermally-stimulated-current measurements are used. 2 figs, 14 refs. (DLC)

  8. Advanced Woven SiC/SiC Composites for High Temperature Applications

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    2007-01-01

    The temperature, stress, and environmental conditions of many gas turbine, hypersonic, and even nuclear applications make the use of woven SiC/SiC composites an attractive enabling material system. The development in SiC/SiC composites over the past few years has resulted in significant advances in high temperature performance so that now these materials are being pursued for several turbine airfoil and reusable hypersonic applications. The keys to maximizing stress capability and maximizing temperature capability will be outlined for SiC/SiC. These include the type of SiC fiber, the fiber-architecture, and the matrix processing approach which leads to a variety of matrix compositions and structure. It will also be shown that a range of mechanical, thermal, and permeability properties can be attained and tailored depending on the needs of an application. Finally, some of the remaining challenges will be discussed in order for the use of these composite systems to be fully realized.

  9. Electron Spin Relaxation and Coherence Times in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Jock, R. M.; He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

    2013-03-01

    Single electron spin states in Si/SiGe quantum dots have shown promise as qubits for quantum information processing. Recently, electron spins in gated Si/SiGe quantum dots have displayed relaxation (T1) and coherence (T2) times of 250 μs at 350mK. The experiments used conventional X-band (10 GHz) pulsed Electron Spin Resonance (pESR) on a large area (3.5 x 20 mm2) , double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 108 quantum dots using e-beam lithography. Dots with 150 nm radii and 700 nm period are induced in a natural Si quantum well by the gates. Smaller dots are expected to reduce the effects of nearly degenerate valley states and spin-orbit coupling on the electron spin coherence. However, the small number of spins makes signal recovery extremely challenging. We have implemented a broadband cryogenic HEMT low-noise-amplifier and a high-speed single-pole double-throw switch operating at liquid helium temperatures. The switch and preamp have improved our signal to noise by an order of magnitude, allowing for smaller samples and shorter measurement times. We will describe these improvements and the data they have enabled. supported by the ARO

  10. High Mobility SiGe/Si Transistor Structures on Sapphire Substrates Using Ion Implantation

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Mueller, C. H.; Croke, E. T.

    2003-01-01

    High mobility n-type SiGe/Si transistor structures have been fabricated on sapphire substrates by ion implanting phosphorus ions into strained 100 Angstrom thick silicon channels for the first time. The strained Si channels were sandwiched between Si(sub 0.7)Ge(sub 0.3) layers, which, in turn, were deposited on Si(sub 0.7)Ge(sub 0.3) virtual substrates and graded SiGe buffer layers. After the molecular beam epitaxy (MBE) film growth process was completed, ion thick silicon channels implantation and post-annealing were used to introduce donors. The phosphorous ions were preferentially located in the Si channel at a peak concentration of approximately 1x10(exp 18)/cu cm. Room temperature electron mobilities exceeding 750 sq cm/V-sec at carrier densities of 1x10(exp 12)/sq cm were measured. Electron concentration appears to be the key factor that determines mobility, with the highest mobility observed for electron densities in the 1 - 2x10(exp 12)/sq cm range.

  11. Photoresponse properties of BaSi2 film grown on Si (100) by vacuum evaporation

    NASA Astrophysics Data System (ADS)

    Thi Trinh, Cham; Nakagawa, Yoshihiko; Hara, Kosuke O.; Takabe, Ryota; Suemasu, Takashi; Usami, Noritaka

    2016-07-01

    We have succeeded in the observation of high photoresponsivity of orthorhombic BaSi2 film grown on crystalline Si by a vacuum evaporation method, raising the prospect of its promising application in high-efficiency thin-film solar cells. Photocurrent was observed at photon energies larger than 1.28 eV, which corresponds to the band gap of evaporated BaSi2 film, indicating that the photoresponsivity originates from the BaSi2 film. The effect of the substrate temperature on the film’s properties was also investigated. The films grown at a substrate temperature larger than 500 °C are single-phase polycrystalline BaSi2 films, while those grown at a substrate temperature of 400 °C is a mixture of phases. We confirmed that undoped evaporated BaSi2 films are an n-type material with high carrier concentration. High carrier lifetime of 4.8 and 2.7 μs can be found for the films grown at 500 °C and 400 °C, respectively. BaSi2 film grown at a substrate temperature of 500 °C, which is crack-free and single-phase, shows the best photoresponsivity. The maximum value of photocurrent was obtained at photon energy of 1.9 eV, corresponding to an external quantum efficiency of 22% under reverse applied voltage of 2 V.

  12. Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

    2012-02-01

    Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 μs relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 μs and T2 to be 6.5 μs in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 μs at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.

  13. Partitioning of Si and platinum group elements between liquid and solid Fe-Si alloys

    NASA Astrophysics Data System (ADS)

    Morard, G.; Siebert, J.; Badro, J.

    2014-05-01

    Crystallization of the Earth's inner core fractionates major and minor elements between the solid and liquid metal, leaving physical and geochemical imprints on the Earth's core. For example, the density jump observed at the Inner Core Boundary (ICB) is related to the preferential partitioning of lighter elements in the liquid outer core. The fractionation of Os, Re and Pt between liquid and solid during inner core crystallization has been invoked as a process that explains the observed Os isotopic signature of mantle plume-derived lavas (Brandon et al., 1998; Brandon and Walker, 2005) in terms of core-mantle interaction. In this article we measured partitioning of Si, Os, Re and Pt between liquid and solid metal. Isobaric (2 GPa) experiments were conducted in a piston-cylinder press at temperatures between 1250 °C and 1600 °C in which an imposed thermal gradient through the sample provided solid-liquid coexistence in the Fe-Si system. We determined the narrow melting loop in the Fe-Si system using Si partitioning values and showed that order-disorder transition in the Fe-Si solid phases can have a large effect on Si partitioning. We also found constant partition coefficients (DOs, DPt, DRe) between liquid and solid metal, for Si concentrations ranging from 2 to 12 wt%. The compact structure of Fe-Si liquid alloys is compatible with incorporation of Si and platinum group elements (PGEs) elements precluding solid-liquid fractionation. Such phase diagram properties are relevant for other light elements such as S and C at high pressure and is not consistent with inter-elemental fractionation of PGEs during metal crystallization at Earth's inner core conditions. We therefore propose that the peculiar Os isotopic signature observed in plume-derived lavas is more likely explained by mantle source heterogeneity (Meibom et al., 2002; Baker and Krogh Jensen, 2004; Luguet et al., 2008).

  14. Electric field control and analyte transport in Si/SiO2 fluidic nanochannels.

    PubMed

    Zhang, Yi; Gamble, Thomas C; Neumann, Alexander; Lopez, Gabriel P; Brueck, Steven R J; Petsev, Dimiter N

    2008-10-01

    This article presents an analysis of the electric field distribution and current transport in fluidic nanochannels fabricated by etching of a silicon chip. The channels were overcoated by a SiO2 layer. The analysis accounts for the current leaks across the SiO2 layer into the channel walls. Suitable voltage biasing of the Si substrate allows eliminating of the leaks or using them to modify the potential distribution of the fluid. Shaping the potential in the fluid can be utilized for solute focusing and separations in fluidic nanochannels.

  15. Hot Corrosion Behavior of Stainless Steel with Al-Si/Al-Si-Cr Coating

    NASA Astrophysics Data System (ADS)

    Fu, Guangyan; Wu, Yongzhao; Liu, Qun; Li, Rongguang; Su, Yong

    2017-03-01

    The 1Cr18Ni9Ti stainless steel with Al-Si/Al-Si-Cr coatings is prepared by slurry process and vacuum diffusion, and the hot corrosion behavior of the stainless steel with/without the coatings is studied under the condition of Na2SO4 film at 950 °C in air. Results show that the corrosion kinetics of stainless steel, the stainless steel with Al-Si coating and the stainless steel with Al-Si-Cr coating follow parabolic laws in several segments. After 24 h corrosion, the sequence of the mass gain for the three alloys is the stainless steel with Al-Si-Cr coating < the stainless steel with Al-Si coating < the stainless steel without any coating. The corrosion products of the three alloys are layered. Thereinto, the corrosion products of stainless steel without coating are divided into two layers, where the outside layer contains a composite of Fe2O3 and FeO, and the inner layer is Cr2O3. The corrosion products of the stainless steel with Al-Si coating are also divided into two layers, of which the outside layer mainly consists of Cr2O3, and the inner layer is mainly SiO2. The corrosion film of the stainless steel with Al-Si-Cr coating is thin and dense, which combines well with substrate. Thereinto, the outside layer is mainly Cr2O3, and the inside layer is Al2O3. In the matrix of all of the three alloys, there exist small amount of sulfides. Continuous and protective films of Cr2O3, SiO2 and Al2O3 form on the surface of the stainless steel with Al-Si and Al-Si-Cr coatings, which prevent further oxidation or sulfide corrosion of matrix metals, and this is the main reason for the much smaller mass gain of the two alloys than that of the stainless steel without any coatings in the 24 h hot corrosion process.

  16. Thermophysical and mechanical properties of SiC/SiC composites

    SciTech Connect

    Zinkle, S.J.; Snead, L.L.

    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.

  17. Particle size reduction of Si3N4 with Si3N4 milling hardware

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Freedman, M. R.; Kiser, J. D.

    1986-01-01

    The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.

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

    SciTech Connect

    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.; /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.

  19. Misfit dislocation gettering by substrate pit-patterning in SiGe films on Si(001)

    SciTech Connect

    Grydlik, Martyna; Groiss, Heiko; Brehm, Moritz; Schaeffler, Friedrich; Boioli, Francesca; Montalenti, Francesco; Miglio, Leo; Gatti, Riccardo; Devincre, Benoit

    2012-07-02

    We show that suitable pit-patterning of a Si(001) substrate can strongly influence the nucleation and the propagation of dislocations during epitaxial deposition of Si-rich Si{sub 1-x}Ge{sub x} alloys, preferentially gettering misfit segments along pit rows. In particular, for a 250 nm layer deposited by molecular beam epitaxy at x{sub Ge} = 15%, extended film regions appear free of dislocations, by atomic force microscopy, as confirmed by transmission electron microscopy sampling. This result is quite general, as explained by dislocation dynamics simulations, which reveal the key role of the inhomogeneous distribution in stress produced by the pit-patterning.

  20. SiC reinforced-MoSi sub 2 based matrix composites

    SciTech Connect

    Petrovic, J.J.; Honnell, R.E.

    1990-01-01

    SiC reinforced-MoSi{sub 2} based matrix composites possess very significant potential as high temperature structural materials for temperatures above 1200{degree}C in oxidizing environments, due to their combination of oxidation resistance, thermodynamic stability, machinability, elevated temperature ductility and strength, and ability to alloy the MoSi{sub 2} matrix with other silicides. The fabrication, microstructures, oxidation, and mechanical properties of these materials are described, and their current properties are compared to high temperature metals and structural ceramics. 22 refs., 5 figs., 2 tabs.

  1. Superimposed grating wavelength division multiplexing in Ge-doped SiO2/Si planar waveguides

    NASA Astrophysics Data System (ADS)

    Othonos, Andreas; Bismuth, J.; Sweeny, M.; Kevorkian, Antoine P.; Xu, Jing Ming M.

    1998-02-01

    An improved model of wavelength division multiplexing (WDM) by superimposed gratings in planar waveguides has been developed. Based on this theory, principal design rules of N- channel WDM are established and a fanout capacity of 100 is estimated. Finally, four-channel WDM at 840 nm has been demonstrated on a Ge:SiO(subscript 2)/SiO(subscript 2)/Si planar waveguide, which was hydrogenated to enhance its photosensitivity. The superimposed gratings were written using a narrow linewidth KrF excimer laser in an interferometric setup used in inscribing fiber Bragg gratings.

  2. Amorphization and recrystallization of epitaxial ReSi2 films grown on Si(100)

    NASA Technical Reports Server (NTRS)

    Kim, Kun HO; Bai, G.; Nicolet, MARC-A.; Mahan, John E.; Geib, Kent M.

    1991-01-01

    The effects of implantation damage and the chemical species of the implant on structural and electrical properties of epitaxial ReSi2 films on Si(100) implanted with Si-28 or Ar-40 ions, at doses ranging from 10 to the 13th/sq cm to 10 to the 15th/sq cm, were investigated using the backscattering spectrometry, XRD, and the van der Pauw techniques. Results showed that ion implantation produces damage in the film, which increases monotonically with dose; the resistivity of the film decreases monotonically with dose.

  3. 29Si NMR spin-echo decay in YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Kambe, S.; Sakai, H.; Tokunaga, Y.; Hattori, T.; Lapertot, G.; Matsuda, T. D.; Knebel, G.; Flouquet, J.; Walstedt, R. E.

    2016-02-01

    29Si nuclear magnetic resonance (NMR) has been measured in a 29Si-enriched single crystal sample of YbRh2Si2. The spin-echo decay for applied field H ∥, ⊥ the c-axes has been measured at 100 K. A clear spin-echo decay oscillation is observed for both cases, possibly reflecting the Ruderman-Kittel (RK) interaction. Since the observed oscillation frequency depends on the direction of applied magnetic field, anisotropic RK coupling and pseudo-dipolar (PD) interactions may not be negligible in this compound. The origin of spin-echo decay oscillations is discussed.

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

    NASA Technical Reports Server (NTRS)

    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.

  5. Subsurface Growth of CoSi2 by Deposition of Co on Si-Capped CoSi2 Seed Regions

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; George, T.; Pike, W. T.

    1991-01-01

    At a growth temperature of 800 C, Co deposited on Si(111) diffuses through a Si cap and exhibits oriented growth on buried CoSi2 grains, a process referred to as endotaxy. This occurs preferentially to surface nucleation of CoSi2 provided the thickness of the Si cap is less than a critical value between 100 and 200 nm for a deposition rate of 0.01 nm/s. Steady-state endotaxy is modeled under the assumption that the process is controlled by Co diffusion.

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

    PubMed

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

    2016-07-19

    This article reports a novel category of coating structure SiO2 @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 ·(ClO4 )3 ·5H2 O was synthesized using HOOCC6 H4 N(CONH(CH2 )3 Si(OCH2 CH3 )3 )2 (MABA-Si) and was used as a ligand. Furthermore, the as-prepared silica NPs were successfully coated with the -Si(OCH2 CH3 )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 ·(ClO4 )3 ·5H2 O. Coating structure SiO2 @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-SiO2 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 ·(ClO4 )3 ·5H2 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 SiO2 @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-SiO2 spheres influences the luminescence was also studied. Moreover, the luminescent mechanisms of the complex were studied and explained.

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

    NASA Technical Reports Server (NTRS)

    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.

  8. Fracture toughness in SiC/Al composite material

    NASA Technical Reports Server (NTRS)

    Flom, Y.; Wu, S. B.; Arsenault, R. J.

    1989-01-01

    Crack initiation fracture toughness does not depend on SiC particle size. Crack growth fracture toughness increases as the size of the SiC particle increases. The fracture process is confined to a very narrow band and takes place within the matrix. In the case of composite reinforced with SiC particles of 20 microns and above, fracture of SiC begins to dominate. The matrix is influenced by a triaxial tension in the matrix and a high density of dislocations generated at SiC/Al interfaces due to the difference in coefficient of thermal expansion between SiC and the Al matrix.

  9. Bubble formation in oxide scales on SiC

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  10. Epitaxial Growth of Silicon Films on SiO2 Patterned Si(100) Substrates by Atmospheric Pressure Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Duan, Chunyan; Deng, Youjun; Ai, Bin; Liu, Chao; Zhuang, Lin; Shen, Hui

    2012-09-01

    In order to investigate the effect of selective area nucleation on epitaxial growth of silicon (Si) films, 35 µm thick Si films were deposited by atmospheric pressure chemical vapor deposition (APCVD) under the standard condition on two kinds of SiO2 patterned Si(100) wafers. One was circular patterns, and the other was striated patterns. Then, the structural properties of the as-deposited silicon thin films were investigated by metallurgical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The results show that normal epitaxial growth occurs on the exposed Si(100) regions, while just polycrystalline Si deposition happens on the SiO2 regions. Moreover, for the substrates with circular patterns, the as-deposited Si thin films possess pyramid surface morphology thus excellent light trapping performance being spontaneously formed, and the sizes of the pyramid grains approximately equal to the sum of the diameter and spacing of the round exposed Si regions.

  11. On-Demand Fabrication of Si/SiO2 Nanowire Arrays by Nanosphere Lithography and Subsequent Thermal Oxidation

    NASA Astrophysics Data System (ADS)

    Cao, Huaxiang; Li, Xinhua; Zhou, Bukang; Chen, Tao; Shi, Tongfei; Zheng, Jianqiang; Liu, Guangqiang; Wang, Yuqi

    2017-02-01

    We demonstrate the fabrication of the large-area arrays of vertically aligned Si/SiO2 nanowires with full tunability of the geometry of the single nanowires by the metal-assisted chemical etching technique and the following thermal oxidation process. To fabricate the geometry controllable Si/SiO2 nanowire (NW) arrays, two critical issues relating with the size control of polystyrene reduction and oxide thickness evolution are investigated. Through analyzing the morphology evolutions of polystyrene particles, we give a quantitative description on the diameter variations of polystyrene particles with the etching time of plasma etching. Based on this, pure Si NW arrays with controllable geometry are generated. Then the oxide dynamic of Si NW is analyzed by the extended Deal-Grove model. By control, the initial Si NWs and the thermal oxidation time, the well-aligned Si/SiO2 composite NW arrays with controllable geometry are obtained.

  12. Characterization and Adhesion in Cu/Ru/SiO2/Si Multilayer Nano-scale Structure for Cu Metallization

    NASA Astrophysics Data System (ADS)

    Chawla, N.; Venkatesh, S. H.; Singh, D. R. P.; Alford, T. L.

    2013-04-01

    In this study, we have characterized the microstructure, resistivity, and dynamic deformation behavior of Cu/Ru/SiO2 and Cu/SiO2 samples under scratch loading conditions. Cu/Ru/SiO2 samples showed higher elastic recovery and hardness when compared to the Cu/SiO2 samples. In the case of Cu/Ru/SiO2 samples, Ru acts as a glue layer between the Cu and the SiO2 substrate providing both strength and toughness against dynamic loading. Hence, the critical load for delamination is higher for Cu/Ru/SiO2 samples compared to Cu/SiO2 samples. Our results show that Cu/Ru/SiO2 thin films present significant potential to be used in Cu metallization.

  13. On-Demand Fabrication of Si/SiO2 Nanowire Arrays by Nanosphere Lithography and Subsequent Thermal Oxidation.

    PubMed

    Cao, Huaxiang; Li, Xinhua; Zhou, Bukang; Chen, Tao; Shi, Tongfei; Zheng, Jianqiang; Liu, Guangqiang; Wang, Yuqi

    2017-12-01

    We demonstrate the fabrication of the large-area arrays of vertically aligned Si/SiO2 nanowires with full tunability of the geometry of the single nanowires by the metal-assisted chemical etching technique and the following thermal oxidation process. To fabricate the geometry controllable Si/SiO2 nanowire (NW) arrays, two critical issues relating with the size control of polystyrene reduction and oxide thickness evolution are investigated. Through analyzing the morphology evolutions of polystyrene particles, we give a quantitative description on the diameter variations of polystyrene particles with the etching time of plasma etching. Based on this, pure Si NW arrays with controllable geometry are generated. Then the oxide dynamic of Si NW is analyzed by the extended Deal-Grove model. By control, the initial Si NWs and the thermal oxidation time, the well-aligned Si/SiO2 composite NW arrays with controllable geometry are obtained.

  14. Control of epitaxial growth at a-Si:H/c-Si heterointerface by the working pressure in PECVD

    NASA Astrophysics Data System (ADS)

    Shen, Yanjiao; Chen, Jianhui; Yang, Jing; Chen, Bingbing; Chen, Jingwei; Li, Feng; Dai, Xiuhong; Liu, Haixu; Xu, Ying; Mai, Yaohua

    2016-11-01

    The epitaxial-Si (epi-Si) growth on the crystalline Si (c-Si) wafer could be tailored by the working pressure in plasma-enhanced chemical vapor deposition (PECVD). It has been systematically confirmed that the epitaxial growth at the hydrogenated amorphous silicon (a-Si:H)/c-Si interface is suppressed at high pressure (hp) and occurs at low pressure (lp). The hp a-Si:H, as a purely amorphous layer, is incorporated in the lp-epi-Si/c-Si interface. We find that: (i) the epitaxial growth can also occur at a-Si:H coated c-Si wafer as long as this amorphous layer is thin enough; (ii) with the increase of the inserted hp layer thickness, lp epi-Si at the interface is suppressed, and the fraction of a-Si:H in the thin films increases and that of c-Si decreases, corresponding to the increasing minority carrier lifetime of the sample. Not only the epitaxial results, but also the quality of the thin films at hp also surpasses that at lp, leading to the longer minority carrier lifetime of the hp sample than the lp one although they have the same amorphous phase. Project supported by the Natural Science Foundation of Hebei Province, China (Grant No. E2015201203) and the International Society for Theoretical Chemical Physics of China (Grant No. 2015DFE62900).

  15. Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

    PubMed Central

    2014-01-01

    Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%. PACS 81.07.Ta; 78.67.Pt; 88.40.jj PMID:25489285

  16. Fabrication and characterization of SiC f/SiC composites produced by the slurry infiltration process

    NASA Astrophysics Data System (ADS)

    Lee, S. P.; Lee, M. H.; Lee, J. K.; Byun, J. H.; Kohyama, A.

    2011-10-01

    The mechanical properties of SiC f/SiC composites have been investigated, based on detailed analyses of their microstructure. SiC f/SiC composites were prepared from fiber preforms by a slurry infiltration technique, in which a mixture with SiC, Al 2O 3, and Y 2O 3 particles was impregnated into the fabric structure. SiC f/SiC composites were consolidated by liquid phase sintering process, associated with the creation of secondary phases by the addition of Al 2O 3 and Y 2O 3 particles. The reinforcing material was a plain weave Tyranno SA SiC fabric with a carbon interfacial layer. The sintered density and the pore volume fraction of SiC f/SiC composites were about 3.0 Mg/m 3 and about 10%, respectively. These SiC f/SiC composites had an average flexural strength of about 250 MPa at room temperature. They exhibited pseudo-ductile fracture behavior, due to the carbon interfacial layer. The introduction of the carbon interfacial layer greatly improved the fracture energy of SiC f/SiC composites.

  17. Laser-induced Mg production from magnesium oxide using Si-based agents and Si-based agents recycling

    NASA Astrophysics Data System (ADS)

    Liao, S. H.; Yabe, T.; Mohamed, M. S.; Baasandash, C.; Sato, Y.; Fukushima, C.; Ichikawa, M.; Nakatsuka, M.; Uchida, S.; Ohkubo, T.

    2011-01-01

    We succeeded in laser-induced magnesium (Mg) production from magnesium oxide (MgO) using Si-based agents, silicon (Si) and silicon monoxide (SiO). In these experiments, a cw CO2 laser irradiated a mixture of Mg and Si-based agents. Both experimental studies and theoretical analysis help not only understand the function of reducing agents but also optimize Mg extraction in laser-induced Mg production. The optimal energy efficiencies 12.1 mg/kJ and 4.5 mg/kJ of Mg production were achieved using Si and SiO, respectively. Besides, the possibility of recycling Si and SiO was preliminarily investigated without reducing agents but only with laser-irradiation. As for the Si-based agents recycling, we succeed in removing 36 mol % of oxygen fraction from SiO2 , obtaining 0.7 mg/kJ of Si production efficiency as well as 15.6 mg/kJ of SiO one at the same time. In addition, the laser irradiation to MgO-SiO mixture produced 24 mg/kJ of Si with more than 99% purity.

  18. Purity and radioactive decay behaviour of industrial 2D-reinforced SiC f/SiC composites

    NASA Astrophysics Data System (ADS)

    Scholz, H. W.; Zucchetti, M.; Casteleyn, K.; Adelhelm, C.

    1994-09-01

    Ceramic matrix composites based on SiC with continuous fibres (SiC f/SiC) are considered promising structural materials for future fusion devices. It was still to clarify, whether impurities in industrial SiC f/SiC could jeopardise radiological advantages. Experimental impurity analyses revealed a two-dimensionally reinforced SiC 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 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 f/SiC depleted of 28Si (isotopic tailoring) is critically discussed.

  19. Growth and characterization of GaN thin films on Si(111) substrates using SiC intermediate layer

    SciTech Connect

    Lim, K.Y.; Lee, K.J.; Park, C.I.; Kim, K.C.; Choi, S.C.; Lee, W.H.; Suh, E.K.; Yang, G.M.; Nahm, K.S.

    2000-07-01

    GaN films have been grown atop Si-terminated 3C-SiC intermediate layer on Si(111) substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). The SiC intermediate layer was grown by chemical vapor deposition (CVD) using tetramethylsilane (TMS) as the single source precursor. The Si terminated SiC surface was obtained by immediately flow of SiH{sub 4} gas after growth of SiC film. LP-MOCVD growth of GaN on 3C-SiC/Si(111) was carried out with trimethylgallium (TMG) and NH{sub 3}. Single crystalline hexagonal GaN layers can be grown on Si terminated SiC intermediate layer using an AlN or GaN buffer layer. Compared with GaN layers grown using a GaN buffer layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The GaN films were characterized by x-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). Full width at half maximum (FWHM) of double crystal x-ray diffraction (DCXD) rocking curve for GaN (0002) on 3C-SiC/Si(111) was 890 arcsec. PL near band edge emission peak position and FWHM at room temperature are 3.38 eV and 79.35 meV, respectively.

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

    PubMed Central

    Graczyk-Zajac, Magdalena; Reinold, Lukas Mirko; Kaspar, Jan; Sasikumar, Pradeep Vallachira Warriam; Soraru, Gian-Domenico; Riedel, Ralf

    2015-01-01

    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.

  1. Atomic scale quantum circuits in Si

    NASA Astrophysics Data System (ADS)

    Dusko, A.; Korkusinski, M.; Saraiva, A.; Delgado, A.; Koiller, B.; Hawrylak, P.

    The atomic scale circuits in Si are now realized by manipulation of dangling bonds on Si surface or incorporating dopant atoms in Si by STM techniques. We describe the electronic properties of these atomic scale quantum dot circuits (QDC) by the extended Hubbard-Kanamori Hamiltonian (HK), including on site Coulomb repulsion (U) and interdot hopping (t) , direct interaction (V) and exchange (J) terms. The interdot terms strongly depend on dopant position (RD) in Si lattice--small changes in RD strongly impact t, Vand J. We study how disorder in RD impacts QDC electronic properties, in particular the interplay of disorder and interactions. With no disorder in RD the energy spectrum (ES) of quantum dot chain at half-filling as a function of U / t (V , J = 0) shows a transition from ES dominated by kinetic energy (U / t < < 1) to ES dominated by Coulomb interactions for U / t > > 1 . The excited states group by single particle energy spacing (Hubbard bands) for weak (strong) interactions. In the weak interaction regime, disorder leads to localization, which strongly affects the electronic properties. We explore the effect of interactions and disorder on HK atomic scale circuits and potential many-body localized phases using Lanczos and Density Matrix Renormalization Group approaches.

  2. Si-nanocrystal-based nanofluids for nanothermometry.

    PubMed

    Cardona-Castro, M A; Morales-Sánchez, A; Licea-Jiménez, L; Alvarez-Quintana, J

    2016-06-10

    The measurement of local temperature in nanoscale volumes is becoming a technological frontier. Photoluminescent nanoparticles and nanocolloids are the natural choice for nanoscale temperature probes. However, the influence of a surrounding liquid on the cryogenic behavior of oxidized Si-nanocrystals (Si-NCs) has never been investigated. In this work, the photoluminescence (PL) of oxidized Si-NCs/alcohol based nanocolloids is measured as a function of the temperature and the molecule length of monohydric alcohols above their melting-freezing point. The results unveil a progressive blue shift on the emission peak which is dependent on the temperature as well as the dielectric properties of the surrounding liquid. Such an effect is analyzed in terms of thermal changes of the Si-NCs bandgap, quantum confinement and the polarization effects of the embedding medium; revealing an important role of the dielectric constant of the surrounding liquid. These results are relevant because they offer a general insight to the fundamental behavior of photoluminescent nanocolloids under a cooling process and moreover, enabling PL tuning based on the dielectric properties of the surrounding liquid. Hence, the variables required to engineer PL of nanofluids are properly identified for use as temperature sensors at the nanoscale.

  3. Spatially Selective Graphene Formation on Si Substrate

    NASA Astrophysics Data System (ADS)

    Yue, Naili; Zhang, Yong; Tsu, Raphael

    2012-02-01

    A uniform large area graphene is useful for applications such as electrode in a touch screen or substrate for growing another material. For applications where graphene is used either as active material (FET for instance) or electrode in a 2-D device array, to form a 2D (electronic) superlattice or photonic crystal, it is critically important to be able to form graphene at selective locations, in desirable size and shape on a substrate, without relying on mechanical cutting. It would be even more significant if the substrate is a Si wafer for coupling with the mature microelectronic technology. We have developed a technique that can achieve these goals. A thin SiC film is first deposited on a Si substrate using MBE. Then, at ambient condition, a focused laser beam is used to convert SiC to graphene at the selected location with the shape and size that can be defined by either a lithographic method or simply by a focused laser beam. The graphene conversion has been verified by structural characterization (TEM, SEM/EDS, etc.) and Raman spectroscopy.

  4. siRNA for Influenza Therapy

    PubMed Central

    Barik, Sailen

    2010-01-01

    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. PMID:21994689

  5. Bioengineered nanoparticles for siRNA delivery.

    PubMed

    Kozielski, Kristen L; Tzeng, Stephany Y; Green, Jordan J

    2013-01-01

    Short interfering RNA (siRNA) has been an important laboratory tool in the last two decades and has allowed researchers to better understand the functions of nonprotein-coding genes through RNA interference (RNAi). Although RNAi holds great promise for this purpose as well as for treatment of many diseases, efforts at using siRNA have been hampered by the difficulty of safely and effectively introducing it into cells of interest, both in vitro and in vivo. To overcome this challenge, many biomaterials and nanoparticles (NPs) have been developed and optimized for siRNA delivery, often taking cues from the DNA delivery field, although different barriers exist for these two types of molecules. In this review, we discuss general properties of biomaterials and nanoparticles that are necessary for effective nucleic acid delivery. We also discuss specific examples of bioengineered materials, including lipid-based NPs, polymeric NPs, inorganic NPs, and RNA-based NPs, which clearly illustrate the problems and successes in siRNA delivery.

  6. COMPUTING SI AND CCPP USING SPREADSHEET PROGRAMS

    EPA Science Inventory

    Lotus 1-2-3 worksheets for calculating the calcite saturation index (SI) and calcium carbonate precipitation potential of a water sample are described. A simplified worksheet illustrates the principles of the method, and a more complex worksheet suitable for modeling most potabl...

  7. Porous Si structure as moisture sensor

    SciTech Connect

    Peterson, D.W.; Nguyen, L.T.

    1996-12-31

    Development and characterization of a capacitive moisture sensor made from porous Si is presented. The sensor development was in support of the DoD funded Plastic Package Availability program and was intended for the detection of pinholes and defects in moisture barrier coatings applied to ICs during fabrication or during the plastic encapsulation assembly process.

  8. Universal Converter Using SiC

    SciTech Connect

    Dallas Marckx; Brian Ratliff; Amit Jain; Matthew Jones

    2007-01-01

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

  9. Peculiar magnetism of UAu2Si2

    NASA Astrophysics Data System (ADS)

    Tabata, Chihiro; Miura, Naoyuki; Uhlířová, Klára; Vališka, Michal; Saito, Hiraku; Hidaka, Hiroyuki; Yanagisawa, Tatsuya; Sechovský, Vladimír; Amitsuka, Hiroshi

    2016-12-01

    Single-crystalline UAu2Si2 has been grown by a floating-zone melting method, and its magnetic, thermal, and transport properties have been investigated through measurements of magnetization, specific heat, and electrical resistivity to reveal its peculiar magnetism. It is shown that UAu2Si2 undergoes a second-order phase transition at Tm = 19 K, which had been believed to be ferromagnetic ordering in the literature, from a paramagnetic phase to an uncompensated antiferromagnetic phase with spontaneous magnetization along the tetragonal c axis (the easy magnetization direction). The magnetic entropy analysis points to the itinerant character of 5 f electrons in the magnetic ordered state of UAu2Si2 with large enhancement of the electronic specific heat coefficient of γ ˜150 mJ/K2mol at 2 K. It also reveals the relatively isotropic crystalline electric field effect of this compound, with contrast to the other relative isostructural compounds. The observed magnetization curves strongly suggest that there is a parasitic ferromagnetic component developing below ˜50 K in high coercivity with the easy axis along the tetragonal c axis. The results are discussed in the context of evolution of magnetism within the entire family of isostructural U T2Si2 compounds.

  10. A study of the Pt/Ti/SiO_2/Si and Pt/TiO/SiO_2/Si systems for ferroelectric device electrodes

    NASA Astrophysics Data System (ADS)

    Siqueiros, Jesús M.; Machorro, R.; Valenzuela, J.; Hirata, G. A.; Cruz, M.; Portelles, J.; Fundora, A.

    1998-03-01

    Well adhered Pt films were deposited on Ti and TiO coated SiO_2/Si substrates by DC and RF sputtering, respectively at temperatures between room and 700^oC. X-ray diffraction showed highly drectional growth in the Pt (111) direction. A narrowing of the peaks was observed as the substrate temperature was risen. STM studies showed an increase in grain size with temperature and a change from grains to terraces for temperatures aboce 600^oC. In the Pt/Ti/SiO_2/Si system Auger Electron Spectroscopy Showed that Ti diffuses to the top of the Pt film through its grain boundaries. Spectroellipsometry measurements evidenced a decrease in the packing density of the Pt films as the substrate temperature was risen. Supported by CoNaCyT Proj. No. 4143E and 3025P-E9607 and DGAPA Proj. No. IN108995. We thank, I.Gradilla, F. Ruiz and E. Aparicio for their technical help. A. Fundora thanks the Foreign Ministry of Mexico.

  11. Uncertainty assessment of Si molar mass measurements

    NASA Astrophysics Data System (ADS)

    Mana, G.; Massa, E.; Valkiers, S.; Willenberg, G.-D.

    2010-01-01

    The uncertainty of the Si molar mass measurement is theoretically investigated by means of a two-isotope model, with particular emphasis to the role of this measurement in the determination of the Avogadro constant. This model allows an explicit calibration formula to be given and propagation of error analysis to be made. It also shows that calibration cannot correct for non-linearity.

  12. Interface-mediated intervalley coupling in Si

    NASA Astrophysics Data System (ADS)

    Koiller, Belita; Saraiva, A. L.; Calderon, M. J.; Hu, Xuedong; Das Sarma, S.

    2011-03-01

    The conduction band degeneracy in Si is detrimental to spin qubits, for which a nondegenerate ground orbital state is desirable. The Si valley degeneracy is reduced to 2 near an interface with an insulator, and it may be lifted by the spatially abrupt change in the crystal potential. Basic physical mechanisms for Si/barrier mediated valley coupling in different situations are addressed here. Theoretical studies of the interface-induced valley splitting in Si are presented. Abrupt and smooth interface profiles are considered, and the full plane wave expansions of the Bloch functions at the conduction band minima are included. Simple criteria are suggested for optimal fabrication parameters affecting the valley splitting, emphasizing the relevance of different interface-related properties. Refs: A.L.Saraiva et al, PRB 80, 081305 R (2009); arXiv:1006.3338 Support: BK and ALS thank CNPq, FUJB, INCT on Quantum Information, and FAPERJ. M.J.C. acknowledges Ministerio de Ciencia e Innovación (Spain). XH amd SDS thank NSA and L PS. S.D.S. also thanks CMTC.

  13. Bioengineered Nanoparticles for siRNA delivery

    PubMed Central

    Kozielski, Kristen L.; Tzeng, Stephany Y.; Green, Jordan J.

    2014-01-01

    Short interfering RNA (siRNA) has been an important laboratory tool in the last two decades and has allowed researchers to better understand the functions of non-protein-coding genes through RNA interference (RNAi). Although RNAi holds great promise for this purpose as well as for treatment of many diseases, efforts at using siRNA have been hampered by the difficulty of safely and effectively introducing it into cells of interest, both in vitro and in vivo. To overcome this challenge, many biomaterials and nanoparticles (NPs) have been developed and optimized for siRNA delivery, often taking cues from the DNA delivery field, although different barriers exist for these two types of molecules. In this review, we discuss general properties of biomaterials and nanoparticles that are necessary for effective nucleic acid delivery. We also discuss specific examples of bioengineered materials, including lipid-based NPs, polymeric NPs, inorganic NPs, and RNA-based NPs, which clearly illustrate the problems and successes in siRNA delivery. PMID:23821336

  14. Passive SiC irradiation temperature monitor

    SciTech Connect

    Youngblood, G.E.

    1996-04-01

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

  15. Si/Cu Interface Structure and Adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John

    2006-03-01

    An ab initio investigation of the Si(111)/Cu(111) interfacial atomic structure and adhesion is reported [1]. Misfit dislocations appear naturally, as do hcp interfacial silicide phases that vary with temperature. The silicides form in the interface even at relatively low temperatures. These results are consistent with available experimental data. [1] Xiao-Gang Wang, John Smith, Physical Review Letters 95, 156102 (2005).

  16. Role of CF2 in the etching of SiO2, Si3N4 and Si in fluorocarbon plasma

    NASA Astrophysics Data System (ADS)

    Lele, Chen; Liang, Zhu; Linda, Xu; Dongxia, Li; Hui, Cai; Tod, Pao

    2009-03-01

    The CF2 density and etch rate of SiO2, Si3N4 and Si are investigated as a function of gas pressure and O2 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO2 etch rate increases. Previous study has shown that SiO2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO2 etching. Generally, the CF2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO2 etching. When more CF2 radical in plasma, SiO2 etch rate is increased because more fluorine can be provided. In this case, CF2 is considered as a reactant for SiO2 etching. The etch rate of Si3N4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF2 density in plasma. Etching results obtained by varying O2 flow rate also support the proposition.

  17. Reaction mechanism for in-situ β-SiAlON formation in Fe3Si-Si3N4-Al2O3 composites

    NASA Astrophysics Data System (ADS)

    Qin, Hai-xia; Li, Yong; Bai, Li-xiong; Long, Meng-long; Xue, Wen-dong; Chen, Jun-hong

    2017-03-01

    In this work, Fe3Si-Si3N4-Al2O3 composites were prepared at 1300°C in an N2 atmosphere using fused corundum and tabular alumina particles, Al2O3 fine powder, and ferrosilicon nitride (Fe3Si-Si3N4) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe3Si-Si3N4-Al2O3 composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe2C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si5AlON7 indicated that the ferrosilicon alloy accelerated the reactions between Si3N4 and α-Al2O3 fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si3N4 because of its low reactivity.

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

    PubMed Central

    2011-01-01

    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. PMID:21711698

  19. Geminal (2)J((29)Si-O-(29)Si) couplings in oligosiloxanes and their relation to direct (1)J((29) Si-(13)C) couplings.

    PubMed

    Kurfürst, Milan; Blechta, Vratislav; Schraml, Jan

    2011-08-01

    Absolute values of (79) geminal (2)J((29) Si-O-(29)Si) couplings were measured in an extensive series of (55) unstrained siloxanes dissolved in chloroform-d. Signs of (2)J((29)Si-O-(29)Si) in some (9) silicon hydrides were determined relative to (1)J((29)Si-(1)H) which are known to be negative. It is supposed that positive sign of the (2)J((29)Si-O-(29)Si) coupling found in all studied hydrides is common to all siloxanes. Theoretical calculations for simple model compounds failed to reproduce this sign and so their predictions of bond length and angle dependences cannot be taken as reliable. Useful empirical correlations were found between the (2)J((29)Si-O-(29)Si) couplings on one side and the total number m of oxygen atoms bonded to the silicon atoms, sum of (29)Si chemical shifts or product of (1)J((29)Si-(13)C) couplings on the other side. The significance of these correlations is briefly discussed.

  20. High-performance Si sbnd SiGe HBTs SiGe-technology development in Esprit Project 8001 TIBIA: An overview

    NASA Astrophysics Data System (ADS)

    Terpstra, D.; De Boer, W. B.; Slotboom, J. W.

    1997-10-01

    Five major European Semiconductor Companies have cooperated on the development of technologies for the fabrication of Si sbnd SiGe-based Heterojunction Bipolar Transistors. This cooperation was part of the European Community Esprit Project 8001 TIBIA, on BICMOS Technology Development and Applications. This article presents an overview of the various concepts studied by the projet-partners, the fabrication processes and the results obtained on single devices and preliminary test-circuits (which already demonstrate the added value of Si sbnd SiGe HBTs in existing Si-technology). A more detailed description is given of the process studied at Philips, which involves double-polysilicon transistors with a selectively deposited Si sbnd SiGe base.

  1. Effects of MeV Si ions bombardment on the thermoelectric generator from SiO 2/SiO 2 + Cu and SiO 2/SiO 2 + Au nanolayered multilayer films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Chacha, J.; Smith, C.; Pugh, M.; Colon, T.; Heidary, K.; Johnson, R. B.; Ila, D.

    2011-12-01

    The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO 2/SiO 2 + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO 2/SiO 2 + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO 2, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.

  2. siMS Score: Simple Method for Quantifying Metabolic Syndrome

    PubMed Central

    Soldatovic, Ivan; Vukovic, Rade; Culafic, Djordje; Gajic, Milan; Dimitrijevic-Sreckovic, Vesna

    2016-01-01

    Objective To evaluate siMS score and siMS risk score, novel continuous metabolic syndrome scores as methods for quantification of metabolic status and risk. Materials and Methods Developed siMS score was calculated using formula: siMS score = 2*Waist/Height + Gly/5.6 + Tg/1.7 + TAsystolic/130—HDL/1.02 or 1.28 (for male or female subjects, respectively). siMS risk score was calculated using formula: siMS risk score = siMS score * age/45 or 50 (for male or female subjects, respectively) * family history of cardio/cerebro-vascular events (event = 1.2, no event = 1). A sample of 528 obese and non-obese participants was used to validate siMS score and siMS risk score. Scores calculated as sum of z-scores (each component of metabolic syndrome regressed with age and gender) and sum of scores derived from principal component analysis (PCA) were used for evaluation of siMS score. Variants were made by replacing glucose with HOMA in calculations. Framingham score was used for evaluation of siMS risk score. Results Correlation between siMS score with sum of z-scores and weighted sum of factors of PCA was high (r = 0.866 and r = 0.822, respectively). Correlation between siMS risk score and log transformed Framingham score was medium to high for age groups 18+,30+ and 35+ (0.835, 0.707 and 0.667, respectively). Conclusions siMS score and siMS risk score showed high correlation with more complex scores. Demonstrated accuracy together with superior simplicity and the ability to evaluate and follow-up individual patients makes siMS and siMS risk scores very convenient for use in clinical practice and research as well. PMID:26745635

  3. A comparative study of three-terminal Hanle signals in CoFe/SiO{sub 2}/n{sup +}-Si and Cu/SiO{sub 2}/n{sup +}-Si tunnel junctions

    SciTech Connect

    Lee, Jeong-Hyeon; Cho, B. K.; He, Shumin; Grünberg, Peter; Jin, Mi-Jin; Yoo, Jung-Woo

    2016-01-18

    We performed three-terminal (3T) Hanle measurement for two types of sample series, CoFe/SiO{sub 2}/n{sup +}-Si and Cu/SiO{sub 2}/n{sup +}-Si, with various tunnel resistances. Clear Hanle signal and anomalous scaling between spin resistance-area product and tunnel resistance-area product were observed in CoFe/SiO{sub 2}/n{sup +}-Si devices. In order to explore the origin of the Hanle signal and the impurity-assisted tunneling effect on the Hanle signal in our devices, Hanle measurement in Cu/SiO{sub 2}/n{sup +}-Si devices was performed as well. However, no detectable Hanle signal was observed in Cu/SiO{sub 2}/n{sup +}-Si, even though a lot of samples with various tunnel resistances were studied in wide temperature and bias voltage ranges. Through a comparative study, it is found that the impurity-assisted tunneling magnetoresistance mechanism would not play a dominant role in the 3T Hanle signal in CoFe/SiO{sub 2}/n{sup +}-Si tunnel junctions, where the SiO{sub 2} was formed by plasma oxidation to minimize impurities.

  4. Comparison of Fatigue Life Between C/SiC and SiC/SiC Ceramic-Matrix Composites at Room and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Longbiao, Li

    2016-10-01

    In this paper, the comparison of fatigue life between C/SiC and SiC/SiC ceramic-matrix composites (CMCs) at room and elevated temperatures has been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S-N curves and fatigue limits of cross-ply, 2D and 3D C/SiC and SiC/SiC composites at room temperature, 550 °C in air, 750 °C in dry and humid condition, 800 °C in air, 1000 °C in argon and air, 1100 °C, 1300 °C and 1500 °C in vacuum, have been predicted. At room temperature, the fatigue limit of 2D C/SiC composite with ECFL of 20 % lies between 0.78 and 0.8 tensile strength; and the fatigue limit of 2D SiC/SiC composite with ECFL of 20 % lies between 0.75 and 0.85 tensile strength. The fatigue limit of 2D C/SiC composite increases to 0.83 tensile strength with ECFL increasing from 20 to 22.5 %, and the fatigue limit of 3D C/SiC composite is 0.85 tensile strength with ECFL of 37 %. The fatigue performance of 2D SiC/SiC composite is better than that of 2D C/SiC composite at elevated temperatures in oxidative environment.

  5. Growth of chemically deposited ZnO and ZnO-SiO2 on Pt buffered Si substrate

    NASA Astrophysics Data System (ADS)

    Peguit, A. D. M. V.; Candidato, R. T., Jr.; Bagsican, F. R. G.; Odarve, M. K. G.; Jabian, M. E.; Sambo, B. R. B.; Vequizo, R. M.; Alguno, A. C.

    2015-06-01

    Growing ZnO on Si via low-cost CBD is difficult owing to the large lattice mismatch between ZnO and Si and the intricate control of nanoparticle aggregation. In this work, a Pt buffer layer and addition of SiO2 on the chemical solution were introduced. The effect of these parameters on the resulting morphology and composition were investigated using SEM-EDX and FTIR. Pt-coated Si showed higher density of ZnO nanostructure growth than bare Si due to the additional nucleation sites provided by Pt. Moreover, SiO2 addition resulted to a different ZnO nanostructure.

  6. Compositional and optical properties of SiO x films and (SiO x /SiO y ) junctions deposited by HFCVD

    PubMed Central

    2014-01-01

    In this work, non-stoichiometric silicon oxide (SiO x ) films and (SiO x /SiO y ) junctions, as-grown and after further annealing, are characterized by different techniques. The SiO x films and (SiO x /SiO y ) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiO x films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiO x /SiO y ) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiO x matrix. For the case of the as-grown SiO x films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiO x /SiO y ) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiO x matrix is present. After thermal annealing, a phase separation into Si and SiO2 occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices. PACS 61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh PMID:25342935

  7. Growth and characterization of cubic SiC single-crystal films on Si

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Matus, L. G.; Kuczmarski, Maria A.

    1987-01-01

    Morphological and electrical characterization results are presented for cubic SiC films grown by chemical vapor deposition on single-crystal Si substrates. The films, up to 40 microns thick, were characterized by optical microscopy, (SEM), (TEM), electron channeling, surface profilometry, and Hall measurements. A variety of morphological features observed on the SiC films are described. Electrical measurements showed a decrease in the electron mobility with increasing electron carrier concentration, similar to that observed in Si. Room-temperature electron mobilities up to 520 sq cm/V-s (at an electron carrier concentration of 5 x 10 to the 16th/cu cm) were measured. Finally, a number of parameters believed to be important in the growth process were investigated, and some discussion is given of their possible effects on the film characteristics.

  8. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

  9. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    We present an ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer superlattices grown by MBE at low temperature (500 C), and compare our results with X-ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. We show that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. We also note that we do not observe any strain effect on the E1 critical point.

  10. Excitonic luminescence of SiGe/Si quantum wells δ-doped with boron

    SciTech Connect

    Bagaev, V. S.; Nikolaev, S. N.; Onishchenko, E. E.; Pruchkina, A. A.; Krivobok, V. S.; Novikov, A. V.

    2015-05-14

    Low-temperature photoluminescence of undoped and moderately δ-doped Si{sub 1−x}Ge{sub x}/Si (x < 0.1) quantum wells has been studied. The influence of boron δ-layer on the excitonic luminescence and the luminescence caused by a dense electron plasma was demonstrated. The conditions under which the luminescence spectra of quantum wells are dominated by impurity-bound excitons (BE) have been established. Some unusual properties of these BE are explained in terms of type II band-offset in Si{sub 1−x}Ge{sub x}/Si (x < 0.1) quantum wells, which favors a spatial separation of electrons and holes. It is shown that the temperature dependence of an excitonic emission in the quantum wells allows to calculate the BE-related density of states and, thus, can be used for contactless estimation of the impurity concentration in quantum wells.

  11. Measurement of interfacial shear strength in SiC-fiber/Si3N4 composites

    NASA Technical Reports Server (NTRS)

    Laughner, James W.; Bhatt, Rham T.

    1989-01-01

    An indentation method for measuring shear strength in brittle matrix composites was applied to SiC-fiber/Si3N4-matrix samples. Three methods were used to manufacture the composites: reaction bonding of a Si/SiC preform, hot-pressing, and nitrogen-overpressure sintering. An indentation technique developed by Marshall for thin specimens was used to measure the shear strength of the interface and the interfacial friction stresses. This was done by inverting the sample after the initial push through and retesting the pushed fibers. SEM observations showed that the shear strength was determined by the degree of reaction between the fiber and the matrix unless the fiber was pushed out of its (well-bonded) sheath.

  12. An Insidious Mode of Oxidative Degradation in a SiC-SiC Composite

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.

    1997-01-01

    The oxidative durability of a SiC-SiC composite with Hi-Nicalon fiber and BN interphase was investigated at 800 C (where pesting is known to occur in SiC-SiC composites) for exposure durations of up to 500 hours and in a variety of oxidant mixes and flow rates, ranging from quasi-stagnant room air, through slow flowing O2 containing 30-90% H2O, to the high-velocity flame of a burner rig. Degradation of the composite was determined from residual strength and fracture strain in post-exposure mechanical tests and correlated with microstructural evidence of damage to fiber and interphase. The severest degradation of composite behavior was found to occur in the bumer rig, and is shown to be connected with the high oxidant velocity and substantial moisture content, as well as a thin sublayer of carbon indicated to form between fiber and interphase during composite processing.

  13. Hoop Tensile Characterization Of SiC/SiC Cylinders Fabricated From 2D Fabric

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Yun, HeeMann; DiCarlo, James A.; Barnett, Terry R.

    2002-01-01

    Tensile stress-strain properties in the hoop direction were obtained for 100-mm diameter SiC/SiC cylinders using ring specimens machined from the cylinder ends. The cylinders were fabricated from 2D balanced fabric with several material variants, including wall thickness (6, 8, and 12 plies), Sic fiber type (Sylramic, Sylramic-iBN, Hi-Nicalon, and Hi-Nicalon S), fiber sizing type, and matrix type (full CVI Sic, and partial CVI plus melt-infiltrated SiC-Si). Fiber ply splices existed in the all the hoops. Tensile hoop measurements were made at room temperature and 1200 C using hydrostatic ring test facilities. The hoop results are compared with in-plane data measured on flat panels using same material variants, but containing no splices.

  14. Current status and recent research achievements in SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Katoh, Y.; Snead, L. L.; Henager, C. H.; Nozawa, T.; Hinoki, T.; Iveković, A.; Novak, S.; Gonzalez de Vicente, S. M.

    2014-12-01

    The silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite system for fusion applications has seen a continual evolution from development a fundamental understanding of the material system and its behavior in a hostile irradiation environment to the current effort which is directed at a broad-based program of technology maturation program. In essence, over the past few decades this material system has steadily moved from a laboratory curiosity to an engineering material, both for fusion structural applications and other high performance application such as aerospace. This paper outlines the recent international scientific and technological achievements towards the development of SiC/SiC composite material technologies for fusion application and discusses future research directions. It also reviews the materials system in the larger context of progress to maturity as an engineering material for both the larger nuclear community and broader engineering applications.

  15. Stress relaxation in sputtered W films and W/GeSi/Si heterostructures

    SciTech Connect

    Ross, F.M.; Kola, R.R.; Hull, R.; Bean, J.C.

    1993-11-01

    We have investigated stress relaxation in GeSi/Si heterostructures on which thin W films have been sputtered with different stress states. Real-time electron microscope observations of the relaxation process demonstrate that the presence of the stressed metal film changes the relaxation kinetics of the GeSi/Si heterostructures. We discuss the significance of this result for the processing of strained layer heterostructures into devices. We have investigated the relationship between microstructure and stress in these sputtered W films, and, by developing a novel specimen geometry for the transmission electron microscope (TEM), we present dynamic observations of the evolution of microstructure and stress during the {beta}-W{yields}{alpha}-W transformation.

  16. Effect of neutron irradiation on fracture resistance of advanced SiC/SiC composites

    NASA Astrophysics Data System (ADS)

    Ozawa, Kazumi; Katoh, Yutai; Nozawa, Takashi; Snead, Lance L.

    2011-10-01

    In order to identify the neutron irradiation effects on fracture resistance of advanced SiC/SiC composites, unloading-reloading single edge notched bend tests were conducted and an analytical model based on non-linear fracture mechanics was applied. As a result of the analysis, energy release rate contributed by macro-crack initiation of 3.1 kJ/m 2 for both unirradiated and irradiated advanced SiC/SiC composites (Hi-Nicalon Type-S (0°/90° plain woven)/multilayer/chemically vapor infiltration) is estimated. This result indicates no significant degradation in fracture resistance after neutron irradiation to 5.9 × 10 25 n/m 2 at 800 °C.

  17. Ni-Si Alloys for the S-I Reactor-Hydrogen Production Process Interface

    SciTech Connect

    Joseph W. Newkirk; Richard K. Brow

    2010-01-21

    The overall goal of this project was to develop Ni-Si alloys for use in vessels to contain hot, pressurized sulfuric acid. The application was to be in the decomposition loop of the thermochemical cycle for production of hydrogen.

  18. In situ observation of mechanical damage within a SiC-SiC ceramic matrix composite

    NASA Astrophysics Data System (ADS)

    Saucedo-Mora, L.; Lowe, T.; Zhao, S.; Lee, P. D.; Mummery, P. M.; Marrow, T. J.

    2016-12-01

    SiC-SiC ceramic matrix composites are candidate materials for fuel cladding in Generation IV nuclear fission reactors and as accident tolerant fuel clad in current generation plant. Experimental methods are needed that can detect and quantify the development of mechanical damage, to support modelling and qualification tests for these critical components. In situ observations of damage development have been obtained of tensile and C-ring mechanical test specimens of a braided nuclear grade SiC-SiC ceramic composite tube, using a combination of ex situ and in situ computed X-ray tomography observation and digital volume correlation analysis. The gradual development of damage by matrix cracking and also the influence of non-uniform loading are examined.

  19. Incubation time for sub-critical crack propagation in SiC-SiC composites

    SciTech Connect

    El-Azab, A.; Ghoniem, N.M.

    1995-04-01

    The objective of this work is to investigate the time for sub-critical crack propagation is SiC-SiC composites at high temperatures. The effects of fiber thermal creep on the relaxation of crack bridging tractions in SiC-SiC ceramic matrix composites (CMCs) is considered in the present work, with the objective of studying the time-to propagation of sub-critical matrix cracks in this material at high temperatures. Under the condition of fiber stress relaxation in the bridiging zone, it is found that the crack opening and the stress intensity factor increase with time for sub-critical matrix cracks. The time elapsed before the stress intensity reaches the critical value for crack propagation is calculated as a function of the initial crack length, applied stress and temperature. Stability domains for matrix cracks are defined, which provide guidelines for conducting high-temperature crack propagation experiments.

  20. Architectural Effects on Impact Resistance of Uncoated MI SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Cosgriff, L. M.; Fox, D. S.

    2009-01-01

    Impact tests were conducted on uncoated 2D and 2.5D MI SiC/SiC composite specimens at room temperature and 1316 C in air. The specimens were analyzed before and after impact using optical microscopy, pulsed thermography (PT) and computed tomography (CT). Preliminary results indicate the following. Both 2-D and 2.5D composites show increase in surface and volumetric damages with increasing impact velocity. However, 2-D composites are prone to delamination cracks. In both 2D and 2.5D composites, the magnitude of impact damage at a fixed impact velocity is slightly greater at room temperature than at 1315 C. At a fixed projectile velocity and test temperature, the depth of penetration of the projectile into the substrate is significantly lower in 2.5D composites than in 2D composites. Fiber architecture plays a significant role controlling impact damage in MI SiC/SiC composites.

  1. SiC/SiC Composites for 1200 C and Above

    NASA Technical Reports Server (NTRS)

    DiCarlo, J. A.; Yun, H.-M.; Morscher, G. N.; Bhatt, R. T.

    2004-01-01

    The successful replacement of metal alloys by ceramic matrix composites (CMC) in high-temperature engine components will require the development of constituent materials and processes that can provide CMC systems with enhanced thermal capability along with the key thermostructural properties required for long-term component service. This chapter presents information concerning processes and properties for five silicon carbide (SiC) fiber-reinforced SiC matrix composite systems recently developed by NASA that can operate under mechanical loading and oxidizing conditions for hundreds of hours at 1204, 1315, and 1427 C, temperatures well above current metal capability. This advanced capability stems in large part from specific NASA-developed processes that significantly improve the creep-rupture and environmental resistance of the SiC fiber as well as the thermal conductivity, creep resistance, and intrinsic thermal stability of the SiC matrices.

  2. Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling

    NASA Technical Reports Server (NTRS)

    Maserjian, J.; Zamani, N.

    1982-01-01

    Thin-oxide (40-50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, before large levels of electron tunnel injection, the near-ideal behavior predicted for a uniform trapezoidal barrier with thick-oxide properties. The oscillatory field dependence caused by electron-wave interference at the Si/SiO2 interface suggests an abrupt, one-monolayer barrier transition (approximately 2.5 A) consistent with earlier work. After tunnel injection of 10 to the 17th - 5 x 10 to the 18th electrons/sq cm, the barrier undergoes appreciable degradation, leading to enhanced tunneling conductance. Reproducible behavior is observed among different samples. This effect is found to be consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (less than 20 A), where the tunneling electrons emerge into the oxide conduction band.

  3. Strain Accumulation and Damage Evolution During Creep of SiCf/SiC Composites

    NASA Astrophysics Data System (ADS)

    Wilshire, Brian; Burt, Howard

    For many high-performance applications, worldwide research efforts continue to be focussed on ceramic-fibre-reinforced ceramic-matrix composites (CFCMCs), with numerous studies featuring SiC-fibre-reinforced SiC-matrix materials (termed SiCf/SiC type products). In particular, because these CFCMCs are being considered for components which must operate for long periods without failure under load in hostile high-temperature environments, special attention has then been directed to characterization of their creep and creep fracture behaviour. In turn, many of these studies have been concerned with clarification of the damage processes which cause creep failure, aiming to acquire the understanding needed for future product development and component design.

  4. Current Status and Recent Research Achievements in SiC/SiC Composites

    SciTech Connect

    Katoh, Yutai; Snead, Lance L.; Henager, Charles H.; Nozawa, T.; Hinoki, Tetsuya; Ivekovic, Aljaz; Novak, Sasa; Gonzalez de Vicente, Sehila M.

    2014-12-01

    The development and maturation of the silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite system for fusion applications has seen the evolution from fundamental development and understanding of the material system and its behavior in a hostile irradiation environment to the current effort which essentially is a broad-based program of technology, directed at moving this material class from a laboratory curiosity to an engineering material. This paper lays out the recent international scientific and technological achievements in the development of SiC/SiC composite material technologies for fusion application and will discuss future research directions. It also reviews the materials system in the larger context of progress to maturity as an engineering material for both the larger nuclear community and for general engineering applications.

  5. Crack initiation and growth characteristics in SiC/SiC under indentation test

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Hinoki, T.; Katoh, Y.; Kohyama, A.; Noda, T.; Muroga, T.; Yu, J.

    1998-10-01

    The mechanical behavior of ceramic matrix composites (CMC) is known to be strongly influenced by fiber-matrix interfacial properties and there have been many efforts to clarify the interfacial characteristics. To understand the fracture mechanism of the materials it is necessary to clarify how the cracks initiate and propagate among fibers, interphase (coating) and matrix. The objective of this study is to investigate crack initiation and growth characteristics in SiC/SiC composites with variations in coating thickness and coating methods by means of micro-indentation technique. Micro-indentation tests and hardness tests were carried out on SiC/SiC composites produced by the chemical vapour infiltration (CVI) process. The intrinsic catastrophic mode of failure of the brittle composite was prevented by application of single carbon and multiple coatings on fibers. Thinner coatings are sensitive to make fibers debonded and may improve the toughness of the composites.

  6. Laser induced sponge-like Si in Si-rich oxides for photovoltaics.

    PubMed

    Gundogdu, S; Ozen, E Sungur; Hübner, R; Heinig, K H; Aydinli, A

    2013-10-07

    We show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3rd generation thin-film solar cells. Well passivated by the SiO₂ dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar⁺ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon.

  7. Inelastic light scattering spectroscopy in Si/SiGe nanostructures: Strain, chemical composition and thermal properties

    NASA Astrophysics Data System (ADS)

    Tsybeskov, L.; Mala, S. A.; Wang, X.; Baribeau, J.-M.; Wu, X.; Lockwood, D. J.

    2016-11-01

    We present a review of recent studies of inelastic light scattering spectroscopy in two types of Si/SiGe nanostructures: planar superlattices and cluster (dot) multilayers including first- and second-order Raman scattering, polarized Raman scattering and low-frequency inelastic light scattering associated with folded acoustic phonons. The results are used in semi-quantitative analysis of chemical composition, strain and thermal conductivity in these technologically important materials for electronic and optoelectronic devices.

  8. Pinhole-free growth of epitaxial CoSi.sub.2 film on Si(111)

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon (Inventor); Fathauer, Robert W. (Inventor); Grunthaner, Paula J. (Inventor)

    1991-01-01

    Pinhole-free epitaxial CoSi.sub.2 films (14') are fabricated on (111)-oriented silicon substrates (10) with a modified solid phase epitaxy technique which utilizes (1) room temperature stoichiometric (1:2) codeposition of Co and Si followed by (2) room temperature deposition of an amorphous silicon capping layer (16), and (3) in situ annealing at a temperature ranging from about 500.degree. to 750.degree. C.

  9. Electronic structure of Fe{sub 3}Si on Si(100) substrates

    SciTech Connect

    Lal, Chhagan; Di Santo, G.; Caputo, M.; Panighel, M.; Goldoni, A.; Taleatu, B. A.; Jain, I. P.

    2014-04-24

    The improved performance of large-scale integrated circuits (LSIs) by the shrinking of devices is becoming difficult due to physical limitations. Here we report, the growth and formation of Fe{sub 3}Si on Si(100) and characterized by x-ray photoemission, UV photoemission and low energy electron diffraction to study the electronic structure. The results revealed that the DO{sub 3} phase formation is exist and photoemission results also support the electron diffraction outcome.

  10. Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1972-01-01

    Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

  11. SEGR in SiO$${}_2$$ –Si$$_3$$ N$$_4$$ Stacks

    DOE PAGES

    Javanainen, Arto; Ferlet-Cavrois, Veronique; Bosser, Alexandre; ...

    2014-04-17

    This work presents experimental SEGR data for MOS-devices, where the gate dielectrics are are made of stacked SiO2–Si3N4 structures. Also a semi-empirical model for predicting the critical gate voltage in these structures under heavy-ion exposure is proposed. Then statistical interrelationship between SEGR cross-section data and simulated energy deposition probabilities in thin dielectric layers is discussed.

  12. Design of a creep experiment for SiC/SiC composites in HFIR

    SciTech Connect

    Hecht, S.L.; Hamilton, M.L.; Jones, R.H.

    1997-08-01

    A new specimen was designed for performing in-reactor creep tests on composite materials, specifically on SiC/SiC composites. The design was tailored for irradiation at 800{degrees}C in a HFIR RB position. The specimen comprises a composite cylinder loaded by a pressurized internal bladder that is made of Nb1Zr. The experiment was designed for approximately a one year irradiation.

  13. Synthesis and characterization of polyurethane/SiO2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Gao, Xiaoyan; Zhu, Yanchao; Zhao, Xu; Wang, Zichen; An, Dongmin; Ma, Yuejia; Guan, Shuang; Du, Yanyan; Zhou, Bing

    2011-03-01

    In order to achieve good dispersion of nano-SiO2 and increase the interactions between nano-SiO2 and PU matrix, nano-SiO2 was firstly modified with poly(propylene glycol) phosphate ester (PPG-P) which was a new polymeric surfactant synthesized through the esterification of poly(propylene glycol) (PPG) and polyphosphoric acid (PPA). Then a series of polyurethane (PU)/SiO2 nanocomposites were prepared via in situ polymerization. The surface modification of nano-SiO2, the microstructure and the properties of nanocomposites were investigated by FTIR, SEM, XRD and TGA. It was found that good dispersion of nano-SiO2 achieved in PU/SiO2 nanocomposite after the modification with PPG-P. The segmented structures of PU were not interfered by the presence of nano-SiO2 in these nanocomposites.

  14. Single photoresist masking for local porous Si formation

    NASA Astrophysics Data System (ADS)

    Hourdakis, E.; Nassiopoulou, A. G.

    2014-11-01

    A simple process for local electrochemical porous Si formation on a Si wafer using a photoresist mask was developed. In this respect, the AZ9260 photoresist from MicroChemicals was used, which is easily removed by simple immersion in acetone after the electrochemical process. The photoresist layer thickness and its adhesion to the Si substrate were optimized for increased etch resistance to the anodization solution. Using the above process, mesoporous Si layers as thick as 50 μm were locally formed on the Si wafer through the photoresist mask. The developed process paves the way towards a simple industrial batch Si technology process for the fabrication of mixed Si wafers containing local porous Si areas. These wafers are very interesting for future system-on-chip (SoC) applications, including RF analog/digital and sensors/electronics SoCs.

  15. Implementation of SI Units in Chemical Engineering Education

    ERIC Educational Resources Information Center

    Youngquist, Gordon R.

    1976-01-01

    Discusses the results of a survey of U.S. Chemical Engineering Departments to determine established policy concerning the use of SI units in courses and plans for future implementation of the SI system of units. (MLH)

  16. Scanning nonlinear dielectric microscopy observation of accumulated charges in metal-SiO2-SiN-SiO2-Si flash memory by detecting higher-order nonlinear permittivity

    NASA Astrophysics Data System (ADS)

    Honda, Koichiro; Cho, Yasuo

    2012-12-01

    Using scanning nonlinear dielectric microscopy with high-sensitivity capacitance variation detection capability, we succeeded in the high-resolution visualization of accumulated charges in metal-SiO2-SiN-SiO2-Si flash memory by detecting the higher-order (2-4 order) nonlinear permittivity. The obtained image contrast can be interpreted using a higher-order differential coefficient (dnC/dVn) of a quasi-static C-V curve of the SiO2-SiN-SiO2-Si interface capacitance as a function of externally applied voltage. Moreover, by using a higher-order nonlinear image, the charge concentration resolution can be improved. Thus, improved resolution of the spatial charge distribution is expected through improvement of the concentration resolution by the imaging of higher-order nonlinear dielectric terms.

  17. Metal-semiconductor interfacial reactions - Ni/Si system

    NASA Technical Reports Server (NTRS)

    Cheung, N. W.; Grunthaner, P. J.; Grunthaner, F. J.; Mayer, J. W.; Ullrich, B. M.

    1981-01-01

    X-ray photoelectron spectroscopy and channeling measurements with MeV He-4(+) ions have been used to probe the structure of the interface in the Ni/Si system. It is found that reactions occur where Ni is deposited on Si at 10 to the -10th torr: Si atoms are displaced from lattice sites, the Ni atoms are in an Si-rich environment, and the Ni/Si interface is graded in composition. Composition gradients are present at both interfaces in the Si/Ni2/Si/Ni system. For the Ni-Si system, cooling the substrate to 100 K slows down the reaction rate. The temperature dependence of the interfacial reactivity indicates the kinetic nature of metal-semiconductor interfaces.

  18. Advanced Si IR detectors using molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Jones, E. W.; George, T.; Ksendzov, A.; Huberman, M. L.

    1991-01-01

    SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

  19. New Si-based multilayers for solar cell applications

    PubMed Central

    2011-01-01

    In this article, we have fabricated and studied a new multilayer structure Si-SiO2/SiNx by reactive magnetron sputtering. The comparison between SiO2 and SiNx host matrices in the optical properties of the multilayers is detailed. Structural analysis was made on the multilayer structures using Fourier transform infrared spectroscopy. The effect of specific annealing treatments on the optical properties is studied and we report a higher visible luminescence with a control over the thermal budget when SiO2 is replaced by the SiNx matrix. The latter seems to be a potential candidate to replace the most sought SiO2 host matrix. PMID:21711661

  20. The energy band structure of Si and Ge nanolayers

    NASA Astrophysics Data System (ADS)

    Wu, Xueke; Huang, Weiqi; Huang, Zhongmei; Qin, Chaojie; Tang, Yanlin

    2016-12-01

    First-principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA) were carried out to investigate the energy band gap structure of Si and Ge nanofilms. Calculation results show that the band gaps of Si(111) and Ge(110) nanofilms are indirect structures and independent of film thickness, the band gaps of Si(110) and Ge(100) nanofilms could be transfered into the direct structure for nanofilm thickness of less than a certain value, and the band gaps of Si(100) and Ge(111) nanofilms are the direct structures in the present model thickness range (about 7 nm). Moreover, the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects. It will be a good way to obtain direct band gap emission in Si and Ge materials, and to develop Si and Ge laser on Si chip.

  1. Enhanced silicon oxidation on titanium-covered Si(001).

    PubMed

    Ohno, S; Shudo, K; Nakayama, F; Yamazaki, K; Ichikawa, Y; Tanaka, M; Okuda, T; Harasawa, A; Matsuda, I; Kakizaki, A

    2011-08-03

    We report on a core level photoemission study of the formation of an ultrathin SiO(x) layer grown at the interface of a titanium-covered Si(001) surface. Oxygen exposure at room temperature induces a large chemical shift of the Si 2p state, predominantly assigned to Si(4+). The results indicate that a SiO(2 - δ) layer, close to the stoichiometry of SiO(2), is formed below the TiO(x) film. The thickness of the SiO(2 - δ) layer is estimated to be ∼ 0.9 nm, corresponding to three to four oxide layers. Further chemical shift caused by annealing is attributed to the formation of titanium silicate (TiSi(x)O(y)).

  2. Thermal oxidation of Si/SiGe heterostructures for use in quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Neyens, Samuel F.; Foote, Ryan H.; Knapp, T. J.; McJunkin, Thomas; Savage, D. E.; Lagally, M. G.; Coppersmith, S. N.; Eriksson, M. A.

    Here we demonstrate dry thermal oxidation of a Si/SiGe heterostructure at 700°C and use a Hall bar device to measure the mobility after oxidation to be 43,000 cm2V-1s-1 at a carrier density of 4.1 ×1011 cm-2. Surprisingly, we find no significant reduction in mobility compared with an Al2O3 device made with atomic layer deposition on the same heterostructure, indicating thermal oxidation can be used to process Si/SiGe quantum dot devices. This result provides a path for investigating improvements to the gate oxide in Si/SiGe qubit devices, whose performance is believed to be limited by charge noise in the oxide layer. This work was supported in part by ARO (W911NF-12-0607) and NSF (DMR-1206915 and PHY-1104660). Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-03ER46028). This research utilized NSF-supported shared facilities at the University of Wisconsin-Madison.

  3. Advanced Environmental Barrier Coating Development for SiC/SiC Ceramic Matrix Composites: NASA's Perspectives

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming

    2016-01-01

    This presentation reviews NASA environmental barrier coating (EBC) system development programs and the coating materials evolutions for protecting the SiC/SiC Ceramic Matrix Composites in order to meet the next generation engine performance requirements. The presentation focuses on several generations of NASA EBC systems, EBC-CMC component system technologies for SiC/SiC ceramic matrix composite combustors and turbine airfoils, highlighting the temperature capability and durability improvements in simulated engine high heat flux, high pressure, high velocity, and with mechanical creep and fatigue loading conditions. The current EBC development emphasis is placed on advanced NASA 2700F candidate environmental barrier coating systems for SiC/SiC CMCs, their performance benefits and design limitations in long-term operation and combustion environments. Major technical barriers in developing environmental barrier coating systems, the coating integrations with next generation CMCs having the improved environmental stability, erosion-impact resistance, and long-term fatigue-environment system durability performance are described. The research and development opportunities for advanced turbine airfoil environmental barrier coating systems by utilizing improved compositions, state-of-the-art processing methods, and simulated environment testing and durability modeling are discussed.

  4. Characterization of interfaces of metal/amorphized (by implantation) Si/c-Si structures

    NASA Astrophysics Data System (ADS)

    Golan, A.; Fastow, R.; Eizenberg, M.

    1990-02-01

    The electrical properties of metal/implanted (amorphous) Si contacts were studied, emphasizing the effects of the doping level, of the metal type, and of the heat treatments applied prior to the metal deposition. The implantation was carried out using 60-keV Ar+ ions at a dose of 1016 cm-2, and resulted in the formation of a thin (1000-Å-thick) amorphous layer on top of the crystalline substrate. The doping level of the implanted Si affected the current-voltage (I-V) characteristics of the contacts mainly in the reverse bias (low doping-low currents), while the forward bias characteristics were quite independent of this parameter. The device characteristics were very sensitive to the metal type, Al, Ti-W, or Pt. Thermal treatments applied prior to the metal deposition affected the characteristics by lowering the device resistance in correspondence with the thinning of the amorphous layer as a result of epitaxial regrowth. The I-V characteristics, as well as their dependence on the different process parameters, are explained using a model of charge injection into a thin layer of trap rich amorphous Si bounded by a metal/a-Si interface on one side and by an a-Si/c-Si heterojunction on the other side.

  5. Dielectric Properties of Porous Si3N4-SiO2-BN Composites

    NASA Astrophysics Data System (ADS)

    Sun, Yinbao; Zhang, Yumin; Li, Dihong; Han, Jiecai

    Porous Si3N4-SiO2-BN composites were prepared by adding starch as both pore former and consolidator. Bruggeman effective-medium model, Maxwell-Garnett model and logarithmic model were used to describe and predict the dielectric constant of porous Si3N4-SiO2-BN ceramics. Relative dielectric constant of porous Si3N4-SiO2-BN composites decreases with the increase of apparent porosity within limits, and these models can forecast the change of the dielectric constant of the porous ceramics quite well. The minimum relative dielectric constant is 2.5 at the apparent porosity of 0.555 at room-temperature. The relationship between dielectric constant and temperature were investigated. It was found dielectric constant varied a lot with the increase of temperature, and Debye relaxation theory was employed to explain the variation of the dielectric constant with temperature increment. But the Debye relaxation theory can not explain the reason of variation of dielectric constant at the temperature range from 300°C to 900°C. To ascertain the cause of changes of dielectric constant at this temperature region, differential scanning calorimentry (DSC) measurement was performed. In this temperature region, phase transition behavior occurs at nearly 300°C in the porous composites. The new phase probably has a tidy large dielectric constant, and the dielectric constant increases sharply.

  6. SiN-SiC nanofilm: A nano-functional ceramic with bipolar magnetic semiconducting character

    SciTech Connect

    Zhang, Jiahui; Li, Xingxing; Yang, Jinlong

    2014-04-28

    Nowadays, functional ceramics have been largely explored for application in various fields. However, magnetic functional ceramics for spintronics remain little studied. Here, we propose a nano-functional ceramic of sphalerite SiN-SiC nanofilm with intrinsic ferromagnetic order. Based on first principles calculations, the SiN-SiC nanofilm is found to be a ferromagnetic semiconductor with an indirect band gap of 1.71 eV. By mean field theory, the Curie temperature is estimated to be 304 K, close to room temperature. Furthermore, the valence band and conduction band states of the nanofilm exhibit inverse spin-polarization around the Fermi level. Thus, the SiN-SiC nanofilm is a typical bipolar magnetic semiconductor in which completely spin-polarized currents with reversible spin polarization can be created and controlled by applying a gate voltage. Such a nano-functional ceramic provides a possible route for electrical manipulation of carrier's spin orientation.

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

    PubMed

    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.

  8. Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

    1993-01-01

    Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

  9. Optical and structural properties of Si nanocrystals produced by Si hot implantation

    SciTech Connect

    Sias, U. S.; Behar, M.; Boudinov, H.; Moreira, E. C.

    2007-08-15

    It was already demonstrated that Si hot implantation followed by high-temperature annealing induces the formation of Si nanocrystals (Si NCs) which when excited in a linear excitation regime present two photoluminescence (PL) bands (at 780 and 1000 nm). We have undertaken the present work in order to investigate three features: First, to determine the origin of each band. With this aim we have changed the implantation fluence and the high-temperature annealing time. Second, to investigate the influence of the postannealing atmosphere on the PL recovering process after bombarding the Si NCs. Third, we have annealed the as-produced Si NCs in a forming gas (FG) atmosphere in order to observe the PL behavior of each band. The results have shown that the 780 nm PL band has its origin in radiative interfacial states, while the 1000 nm one is due to quantum size effects. From the experiments we have concluded that the PL recovery after the Si NCs irradiation strongly depends on the type of postannealing atmosphere. Finally, it was found that the FG treatment strongly affects the line shape of the PL spectrum.

  10. Abrasive Wear Behaviour of COPPER-SiC and COPPER-SiO2 Composites

    NASA Astrophysics Data System (ADS)

    Umale, Tejas; Singh, Amarjit; Reddy, Y.; Khatitrkar, R. K.; Sapate, S. G.

    The present paper reports abrasive wear behaviour of copper matrix composites reinforced with silicon carbide and silica particles. Copper - SiC (12%) and Copper-SiO2 (9%) composites were prepared by powder metallurgical technique. Metallography, image analysis and hardness studies were carried out on copper composites. The abrasive wear experiments were carried out using pin on disc apparatus. The effect of sliding distance and load was studied on Copper - SiC (12%) and Copper-SiO2 (9%) composites. The abrasive wear volume loss increased with sliding distance in both the composites although the magnitude of increase was different in each case. Copper - SiC (12%) composites exhibited relatively better abrasion resistance as compared to and Copper-SiO2 (9%) composites. The abraded surfaces were observed under scanning electron microscope to study the morphology of abraded surfaces and operating wear mechanism. The analysis of wear debris particles was also carried out to substantiate the findings of the investigation.

  11. Electrical transport mechanisms in a-Si:H/c-Si heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Schulze, T. F.; Korte, L.; Conrad, E.; Schmidt, M.; Rech, B.

    2010-01-01

    We present temperature-dependent measurements of I-V curves in the dark and under illumination in order to elucidate the dominant transport mechanisms in amorphous silicon-crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. ZnO:Al/(p )a-Si:H/(n)c-Si/(n+)a-Si:H cells are compared with inversely doped structures and the impact of thin undoped a-Si:H buffer layers on charge carrier transport is explored. The solar cell I-V curves are analyzed employing a generalized two-diode model which allows fitting of the experimental data for a broad range of samples. The results obtained from the fitting are discussed using prevalent transport models under consideration of auxiliary data from constant-final-state-yield photoelectron spectroscopy, surface photovoltage, and minority carrier lifetime measurements. Thus, an in-depth understanding of the device characteristics is developed in terms of the electronic properties of the interfaces and thin films forming the heterojunction. It is shown that dark I-V curve fit parameters can unequivocally be linked to the open circuit voltage under illumination which opens a way to a simplified device assessment.

  12. Absolute Calibration of Si iRMs used for Si Paleo-nutrient proxies

    NASA Astrophysics Data System (ADS)

    Vocke, Robert; Rabb, Savelas

    2016-04-01

    The Avogadro Project is an ongoing international effort, coordinated by the International Bureau of Weights and Measures (BIPM) and the International Avogadro Coordination (IAC) to redefine the SI unit mole in terms of the Avogadro constant and the SI unit kg in terms of the Planck constant. One of the outgrowths of this effort has been the development of a novel, precise and highly accurate method to measure calibrated (absolute) isotopic ratios that are traceable to the SI (Vocke et al., 2014 Metrologia 51, 361, Azuma et al., 2015 Metrologia 52 360). This approach has also been able to produce absolute Si isotope ratio data with lower levels of uncertainty when compared to the traditional "Atomic Weights" method of absolute isotope ratio measurement. Silicon isotope variations (reported as delta(Si30)and delta(Si29)) in silicic acid dissolved in ocean waters, in biogenic silica and in diatoms are extremely informative paleo-nutrient proxies. The utility and comparability of such measurements however depends on calibration with artifact isotopic Reference Materials (iRMs). We will be reporting new measurements on the iRMs NBS-28 (RM 8546 - Silica Sand), Diatomite, Big Batch and SRM 990 using the Avogadro measurement approach, comparing them with prior assessments of these iRMs.

  13. Determination of Near-surface Ge and Si Site Occupation in Ge/Si(100)

    NASA Astrophysics Data System (ADS)

    Leskovar, M.; Meng, S.; Hessinger, Uwe; Olmstead, Marjorie A.

    1996-03-01

    When Ge is deposited on Si(001), the larger size and lower surface energy of the Ge should impede intermixing. However, the strain induced by the surface reconstruction has been predicted to result in a preference for Si in some near-surface sites. The specifics of the predicted site segregation depend on whether an empirical or ab-initio potential is used. We have investigated the near-surface site occupation of well-annealed <= 2 ML Ge films on single-domain Si(100)4 deg 2x1 surfaces using X-ray photoelectron diffraction (XPD) and low energy electron diffraction (LEED). Sub-monolayer Ge deposition at 500 degC results in the Ge residing in the top layer (no forward scattering in Ge XPD) while the LEED pattern remains mostly 2x1. This implies Ge exchange with the surface Si layer, followed by transport of the displaced Si to preserve the dimer row orientation relative to that of the steps. At higher temperatures and/or coverages some Si-Ge intermixing may be observed.

  14. Self-assembled strained GeSiSn nanoscale structures grown by MBE on Si(100)

    NASA Astrophysics Data System (ADS)

    Nikiforov, A. I.; Timofeev, V. A.; Tuktamyshev, A. R.; Yakimov, A. I.; Mashanov, V. I.; Gutakovskii, A. K.

    2017-01-01

    Gradual relaxation of elastic deformations in a silicon layer at the growth of a covering layer on strained layers was established. The dependence of the thickness of a silicon film, where full elastic strain relaxation occurs, on the germanium layer thickness was determined. The dependence of the critical thickness of 2D-3D transition of temperature and composition of the GeSiSn film on Si(100) was studied. Regularities of the formation of multilayer structures on quantum wells comprising pseudomorphous GeSiSn layers without relaxed buffer layers but creating the structures directly on Si. A possibility of synthesizing multilayer structures by molecular beam epitaxy was shown, and the crystal lattice constants using the high-resolution transmission electron microscopy were determined. Based on multilayer GeSiSn/Si structures the p-i-n-diodes, which demonstrated the photoresponse increasing by several orders of magnitude compared to the Sn-free structures at an increase in the Sn content, were created.

  15. Enhanced and Retarded SiO2 Growth on Thermally Oxidized Fe-Contaminated n-Type Si(001) Surfaces

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Hagiwara, Hiroyuki

    2013-04-01

    At the beginning of the oxidation of Fe-contaminated n-type Si(001) surfaces, Fe reacted with oxygen (O2) on the silicon (Si) substrate to form Fe2O3 and oxygen-induced point defects (emitted Si + vacancies). SiO2 growth was mainly enhanced by catalytic action of Fe. At 650 °C, SiO2 growth of the contaminated samples was faster than in reference samples rinsed in RCA solution during the first 60 min. However, it substantially slowed and became less than that of the reference samples. As the oxidation advanced, approximately half of the contaminated Fe atoms became concentrated close to the surface area of the SiO2 film layer. This Fe2O3-rich SiO2 layer acted as a diffusion barrier against oxygen species. The diffusion of oxygen atoms toward the SiO2/Si interface may have been reduced, and in turn, the emission of Si self-interstitials owing to oxidation-induced strain may have been decreased at the SiO2/Si interface, resulting in the retarded oxide growth. These results are evidence that emitted Si self-interstitials are oxidized not in the Fe2O3-rich SiO2 layer, but at the SiO2/Si interface in accordance with a previously proposed model. A possible mechanism based on the interfacial Si emission model is discussed. The activation energies for the oxide growth are found to be in accord with the enhanced and reduced growths of the Fe-contaminated samples.

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

    NASA Technical Reports Server (NTRS)

    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.

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

    SciTech Connect

    Hu, Xunxiang; Ang, Caen K.; Singh, Gyanender P.; Katoh, Yutai

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Ksendzov, A.; Dejewski, Suzan M.; Jones, Eric W.; Fathauer, Robert W.; Krabach, Timothy N.; Maserjian, Joseph

    1991-01-01

    A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p+-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-micron) regime. Detectors were fabricated by growing p+-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10 to the 19th/cu cm to 4 x 10 to the 20th/cu cm. Infrared absorption of 5-25 percent in a 30-nm-thick p+-SiGe layer was measured in the 3-20-micron range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5 percent have been obtained from test devices in the 8-12-micron range.

  20. Fiber/Matrix Interfacial Thermal Conductance Effect on the Thermal Conductivity of SiC/SiC Composites

    SciTech Connect

    Nguyen, Ba Nghiep; Henager, Charles H.

    2013-04-20

    SiC/SiC composites used in fusion reactor applications are subjected to high heat fluxes and require knowledge and tailoring of their in-service thermal conductivity. Accurately predicting the thermal conductivity of SiC/SiC composites as a function of temperature will guide the design of these materials for their intended use, which will eventually include the effects of 14-MeV neutron irradiations. This paper applies an Eshelby-Mori-Tanaka approach (EMTA) to compute the thermal conductivity of unirradiated SiC/SiC composites. The homogenization procedure includes three steps. In the first step EMTA computes the homogenized thermal conductivity of the unidirectional (UD) SiC fiber embraced by its coating layer. The second step computes the thermal conductivity of the UD composite formed by the equivalent SiC fibers embedded in a SiC matrix, and finally the thermal conductivity of the as-formed SiC/SiC composite is obtained by averaging the solution for the UD composite over all possible fiber orientations using the second-order fiber orientation tensor. The EMTA predictions for the transverse thermal conductivity of several types of SiC/SiC composites with different fiber types and interfaces are compared to the predicted and experimental results by Youngblood et al.