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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 Notes.

    ERIC Educational Resources Information Center

    Nelson, Robert A.

    1983-01-01

    Discusses legislation related to SI (International Systems of Units) in the United States. Indicates that although SI metric units have been officially recognized by law in the United States, U.S. Customary Units have never received a statutory basis. (JN)

  4. 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.

  5. 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

  6. 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…

  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. A SiGe/Si multiple quantum well avalanche photodetector

    NASA Astrophysics Data System (ADS)

    Sun, Po-Hsing; Chang, Shu-Tong; Chen, Yu-Chun; Lin, Hongchin

    2010-10-01

    The present work investigates the performance of APDs with a SiGe/Si multi-quantum well (MQW) structure, which was fabricated using ultrahigh-vacuum chemical vapor deposition (UHV/CVD). Absorption of radiation and avalanche multiplication occur in both SiGe/Si MQW and the i-SiGe layer. Intense photoluminescence (PL) from strained, epitaxial SiGe alloys grown using UHV/CVD was reported with multiple SiGe/Si MQW and i-SiGe layer. It was found that the avalanche multiplication occurred at about 7 V, when exceeding 7 V, the responsiveness and quantum efficiency rapidly increased. An APD consisting of an epitaxial SiGe/Si MQW as the active absorption layer with intense response in the 800-1500 nm wavelength range is also demonstrated.

  10. 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.

  11. 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.

  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. Reactions of Hydrogen with Si-SiO2 Interfaces

    NASA Astrophysics Data System (ADS)

    Rashkeev, Sergey N.

    2001-11-01

    Three different types of behavior have been observed for H in Si-SiO2 structures: a) Radiation experiments established that H^+ released in SiO2 migrates to the Si-SiO2 interface where it induces new defects; b) For oxides exposed first to high-temperature annealing and then to molecular hydrogen, mobile positive charge believed to be H^+ can be cycled to and from the interface by reversing the oxide electric field; c) Hydrogen is known to passivate Si dangling bonds at the Si-SiO2 interface, but the subsequent arrival of H^+ at the interface causes depassivation of Si-H bonds. We report first-principles calculations that identify atomic-scale mechanisms for the different types of behavior and the conditions that are necessary for each. We show that the Si-Si bonds on the oxide side, i.e., ``suboxide bonds'', can trap H^+ in deep wells with asymmetric barrier (1.5 eV on the Si side, 1 eV on the SiO2 side). In radiation experiments these centers can act as fixed positive charge. In the mobile-positive-charge experiments, the protons can be cycled between opposite Si-SiO2 interfaces if the density of suboxide bonds is high. Also, we establish that H^+ is the only stable charge state at the interface and that H^+ reacts directly (without being neutralized by a Si electron) with a Si-H bond, forming an H2 molecule and a positively charged dangling bond (Pb center). As a result, H-induced interface-trap formation does not depend on the availability of Si electrons. This work was supported in part by AFOSR Grant F-49620-99-1-0289.

  15. Weakening of Sisbnd Si bonding in exohydrogenated Si60 nanoclusters

    NASA Astrophysics Data System (ADS)

    Bainglass, Edan; Mayfield, Cedric L.; Huda, Muhammad N.

    2017-09-01

    We performed density functional theory (DFT) analyses of several hollow cage-like Si60 nanoclusters and found a favoring of exohydrogenation in terms of reduced binding energies in all the structures except the Si60 fullerene. Further investigation into the effects of exohydrogenation on the Sisbnd Si bonding network revealed a level of weakening in Sisbnd Si bonds. A correlation was established between the magnitude of this weakening and the success of exohydrogenation in stabilizing the nanocluster. In addition, we found a slightly bent chain of individual Si20 units to exhibit the lowest binding energy among the present group of Si60 clusters studied here.

  16. 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.

  17. 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.

  18. 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.

  19. 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).

  20. 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.

  1. Lateral Si /SiO2 quantum well solar cells

    NASA Astrophysics Data System (ADS)

    Rölver, R.; Berghoff, B.; Bätzner, D. L.; Spangenberg, B.; Kurz, H.

    2008-05-01

    The photovoltaic properties of Si /SiO2 multiple quantum wells (QWs) embedded in lateral Schottky contacts are investigated. The QWs were fabricated by remote plasma enhanced chemical vapor deposition. By subsequent rapid thermal annealing, the two-dimensional Si layers are partially recrystallized, which gives rise to distinct quantum confinement effects. Although the current extraction along the quantum layers is hampered by the incomplete recrystallization, the data collected define the route to optimized Si based QW solar cells.

  2. Thermal expansion behavior of NiSi/NiSi2

    NASA Technical Reports Server (NTRS)

    Wilson, D. F.; Cavin, O. B.

    1992-01-01

    The thermal expansion of NiSi/NiSi2 for a range of temperatures from 293 to 1223 K was determined using high-temperature X-ray diffraction. While a linear relation with temperature was found for the lattice parameter of NiSi2, third-order relationships were found for the three lattice parameters of NiSi, with one of the parameters showing a decrease with increasing temperature. The volumetric expansion of both materials exhibited linear relationships.

  3. Composition determination of Si/Si1-xGex/Si by photoreflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, Changchun; Kelly, P. V.; Liu, Zhihong; Huang, Wentao; Dou, Weizhi; Tsien, Pei-Hsin

    2004-10-01

    UHVCVD-grown Si/Si1-xGex/Si heterostructure is investigated by photoreflectance spectroscopy (PR). The principle of PR in determining Ge content of a Si1-xGex epilayer is thoroughly described. The unambiguous E1 transition energy in the Si1-xGex epilayer is very useful to determine Ge content during PR analysis. R&R study with 10 repeats at the same point indicates that the measurements of PR are reproducible. These results demonstrate that PR is very promising for analysis of Si1-xGex epilayer characterization with constant Ge content.

  4. 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.

  5. 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.

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

    SciTech Connect

    Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.

    1994-08-01

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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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).

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. .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.

  17. Comparison of thermoelectric properties of nanostructured Mg2Si, FeSi2, SiGe, and nanocomposites of SiGe-Mg2Si, SiGe-FeSi2

    NASA Astrophysics Data System (ADS)

    Nozariasbmarz, Amin; Roy, Palash; Zamanipour, Zahra; Dycus, J. Houston; Cabral, Matthew J.; LeBeau, James M.; Krasinski, Jerzy S.; Vashaee, Daryoosh

    2016-10-01

    Thermoelectric properties of nanostructured FeSi2, Mg2Si, and SiGe are compared with their nanocomposites of SiGe-Mg2Si and SiGe-FeSi2. It was found that the addition of silicide nanoinclusions to SiGe alloy maintained or increased the power factor while further reduced the thermal conductivity compared to the nanostructured single-phase SiGe alloy. This resulted in ZT enhancement of Si0.88Ge0.12-FeSi2 by ˜30% over the broad temperature range of 500-950 °C compared to the conventional Si0.80Ge0.20 alloy. The Si0.88Ge0.12-Mg2Si nanocomposite showed constantly increasing ZT versus temperature up to 950 °C (highest measured temperature) reaching ZT ˜ 1.3. These results confirm the concept of silicide nanoparticle-in-SiGe-alloy proposed earlier by Mingo et al. [Nano Lett. 9, 711-715 (2009)].

  18. Epitaxial growth and characterization of Si/NiSi 2/Si(111) heterostructures

    NASA Astrophysics Data System (ADS)

    Rizzi, Angela; Förster, A.; Lüth, H.; Slijkerman, W.

    1989-04-01

    Si/NiSi 2/Si(111) heterostructures are grown under UHV conditions. The well known "template" method is used to produce the epitaxial NiSi 2 interlayer. On top of the suicide, the silicon epitaxial growth is obtained by means of gas phase reaction of SiH 4 at a surface temperature of 500° C. The Si growth rate is strongly enhanced by predissociation of SiH 4 using a hot tungsten filament in the vicinity of the surface. The single steps of the growth are followed in-situ by means of AES, HREELS and LEED analysis. Ex-situ high resolution RBS analysis is also applied for characterization.

  19. 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.

  20. Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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 SiNx/SiNy multilayers with high on/off ratio of 109. 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.

  1. 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.

  2. 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.

  3. Microstructural analysis of W-SiCf/SiC composite

    NASA Astrophysics Data System (ADS)

    Yoon, Hanki; Oh, Jeongseok; Kim, Gonho; Kim, Hyunsu; Takahashi, Heishichiro; Kohyama, Akira

    2015-03-01

    Continuous silicon carbide fiber-reinforced silicon carbide (SiCf/SiC) composites are promising structure candidates for future fusion power systems such as gas coolant fast channels, extreme high temperature reactor and fusion reactors, because of their intrinsic properties such as excellent mechanical properties, high thermal conductivity, good thermal-shock resistance as well as excellent physical and chemical stability in various environments under elevated temperature conditions. In this study, bonding of tungsten and SiCf/SiC was produced by hot-press method. Microstructure analyses were performed using SEM and TEM.

  4. 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.

  5. Bond dissociation energies of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi

    NASA Astrophysics Data System (ADS)

    Sevy, Andrew; Sorensen, Jason J.; Persinger, Thomas D.; Franchina, Jordan A.; Johnson, Eric L.; Morse, Michael D.

    2017-08-01

    Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi. It is argued that because of the high density of electronic states at the ground separated atom limit in these molecules, the predissociation threshold in each case corresponds to the thermochemical bond dissociation energy. The resulting bond dissociation energies are D0(TiSi) = 2.201(3) eV, D0(ZrSi) = 2.950(3) eV, D0(HfSi) = 2.871(3) eV, D0(VSi) = 2.234(3) eV, D0(NbSi) = 3.080(3) eV, and D0(TaSi) = 2.999(3) eV. The enthalpies of formation were also calculated as Δf,0KH°(TiSi(g)) = 705(19) kJ mol-1, Δf,0KH°(ZrSi(g)) = 770(12) kJ mol-1, Δf,0KH°(HfSi(g)) = 787(10) kJ mol-1, Δf,0KH°(VSi(g)) = 743(11) kJ mol-1, Δf,0KH°(NbSi(g)) = 879(11) kJ mol-1, and Δf,0KH°(TaSi(g)) = 938(8) kJ mol-1. Using thermochemical cycles, ionization energies of IE(TiSi) = 6.49(17) eV and IE(VSi) = 6.61(15) eV and bond dissociation energies of the ZrSi- and NbSi- anions, D0(Zr-Si-) ≤ 3.149(15) eV, D0(Zr--Si) ≤ 4.108(20) eV, D0(Nb-Si-) ≤ 3.525(31) eV, and D0(Nb--Si) ≤ 4.017(39) eV, have also been obtained. Calculations on the possible low-lying electronic states of each species are also reported.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. SI and Non-SI Units of Concentration: A Truce?

    ERIC Educational Resources Information Center

    Rich, Ronald L.

    1986-01-01

    Questions the current usage of the International System of Units (called SI units) in representing chemical notation and terminology. Suggests several additions to the system that relate to concentrations. Outlines new symbols for distinguishing between "concentration" and "molality." Includes tables to illustrate the proposed SI units. (TW)

  12. Strain in wavy SiGe/Si superlattices

    NASA Astrophysics Data System (ADS)

    Shin, Hongkee; Lockwood, David J.; Baribeau, Jean-Marc

    2000-03-01

    Coherent wave SiGe/Si multilayer structures are of current interest for use as optical waveguide photodetectors. The structural and optical properties of such strained undulated SiGe/Si superlattices grown by molecular beam epitaxy have been studied by x-ray diffraction and Raman spectroscopy. In these superlattices, the undulated SiGe layers are self-aligned along the growth direction, and the interface undulations are very regular and predominently oriented along [100] directions. X-ray diffraction measurements exhibit features normally seen in planar superlattices and indicate that the structures have retained their strain. Grazing incidence x-ray results are consistent with a long ( 100 nm) in-plane interface correlation and a well correlated vertical alignment of the undulations over the whole superlattice depth. In the optic mode Raman spectra, there are noticeable frequency shifts between corresponding alloy modes of the wavy and similar planar superlattices. These shifts of the Si-Si, Ge-Si, and Ge-Ge mode frequncies indicate that the "average" strain in the wavy superlattice is reduced from that in the planar case, which leads to greater thermal stability. The Raman spectra of the folded acoustic modes indicate atomically abrupt interfaces in the wavy superlattices. These undulated structures show considerable promise for device use.

  13. 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.

  14. 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.

  15. 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…

  16. 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)

  17. 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)

  18. 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…

  19. 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.

  20. Hermetic SiC-SiC composite tubes

    SciTech Connect

    Kowbel, W.; Liu, Y.; Bruce, C.; Withers, J.C.; Kolaya, L.E.; Lewis, N.

    1998-12-31

    SiC-SiC composites have good potential for structural applications but are limited by expensive forming techniques. A high purity {beta}-SiC fiber produced by MER, and a polymer derived SiC matrix were used to fabricate small diameter hermetic SiC-SiC tubes. The process was optimized to prevent the formation of a brittle structure while rapidly forming a dense matrix. This tube was made hermetic by first coating the surface of the tube with a silicon carbide particle filled polymer slurry, followed by a Chemical Vapor Infiltration/Deposition (CVI/CVD) SiC deposition which was performed to close any residual porosity on the composite tube surface. X-ray diffraction and Transmission Electron Microscopy (TEM) examination was performed to determine the fiber and matrix structures. These tubes were found to be impermeable to helium with leak rates below 10{sup {minus}9} cc/sec as determined by testing similar to MIL-STD-883D, method 1014.10. This high level of impermeability was sustained following thermal cycling between room temperature and 1,520 C.

  1. Compressively strained Si/Si1-xCx heterostructures formed on Ar ion implanted Si(100) substrates

    NASA Astrophysics Data System (ADS)

    Hoshi, Yusuke; Arisawa, You; Arimoto, Keisuke; Yamanaka, Junji; Nakagawa, Kiyokazu; Sawano, Kentarou; Usami, Noritaka

    2016-03-01

    We demonstrate that compressively strained Si/Si1-xCx heterostructures are epitaxially grown on Ar ion implanted Si substrates. The ion-implantation-induced defects are found to promote strain relaxation in the Si1-xCx layers, which accompanies an increase in the substitutional C concentrations. The top Si layers are strained on the Si1-xCx layers for all samples, and thus the increase in the substitutional C concentration based on strain relaxation in the Si1-xCx layers is very important for the control of the compressive strain in the top Si layer.

  2. 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.

  3. Hole mobility in strained Si/SiGe/vicinal Si(110) grown by gas source MBE

    NASA Astrophysics Data System (ADS)

    Arimoto, Keisuke; Yagi, Sosuke; Yamanaka, Junji; Hara, Kosuke O.; Sawano, Kentarou; Usami, Noritaka; Nakagawa, Kiyokazu

    2017-06-01

    Strained Si/SiGe heterostructures were grown on vicinal Si(110) substrates by using gas-source MBE, and relationship between structural aspects and effective hole mobility was investigated. The surface inclination was found to be effective in obtaining smoother surface. By growing the film at different substrate temperatures, samples which were significantly different in surface morphology and crystalline defects were obtained. Under a certain condition, the strain in the SiGe layer was found to be relaxed mainly by microtwin formation. It was found that this strain relaxation pathway was favorable for pMOSFETs with [1 ̅10 ] channel. As a result, the effective hole mobility as high as 350 cm2/Vs was achieved on conventional Si substrate.

  4. 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.

  5. 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.

  6. 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.

  7. Boron diffusion mechanism and effect of interface Ge atoms in Si/SiO2 and SiGe/SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Kim, Geun-Myeong; Oh, Young Jun; Lee, Chang Hwi; Chang, K. J.

    2014-03-01

    In metal-oxide-semiconductor field effect transistors (MOSFETs) it is known that implanted B dopants easily segregate to the oxide during thermal annealing after ion implantation, causing threshold voltage shift and sheet resistance increase. On the other hand, SiGe alloys have been considered as a promising material for p-type MOSFETs due to reduced B diffusion and high hole mobility. However, there is a lack of studies for B diffusion in Si/SiO2 and SiGe/SiO2 interfaces. In this work, we perform first-principles density functional calculations to study the mechanism for the B diffusion in Si/SiO2 and SiGe/SiO2 interfaces. We investigate the diffusion pathways and migration barriers by using the climbing nudged elastic band and dimer methods. For Si/SiO2 interface, B in Si turns into an interstitial B and tends to intervene between the Si and bridge O atoms at the interface. The overall migration barrier is calculated to be about 2 eV, comparable to that in bulk SiO2. In SiGe/SiO2, interface Ge atoms enhance the stability of B-related defects in the interface region, resulting in the higher migration barrier of about 3.7 eV. Our results indicate that Si/SiO2 interface does not hinder the B diffusion, however, the B diffusion is suppressed in the presence of interface Ge atoms.

  8. 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.

  9. 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.

  10. Electron Spin Qubits in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eriksson, Mark

    2010-10-01

    It is intriguing that silicon, the central material of modern classical electronics, also has properties well suited to quantum electronics. Recent advances in Si/SiGe quantum devices have enabled the creation of high-quality silicon quantum dots, also known as artificial atoms. Motivated in part by the potential for very long spin coherence times in this material, we are pursuing the development of individual electron spin qubits in silicon quantum dots. I will discuss recent demonstrations of single-shot spin measurement in a Si/SiGe quantum dot spin qubit, and the demonstration of spin-relaxation times longer than one second in such a system. These and similar measurements depend on a knowledge of tunnel rates between quantum dots and nearby reservoirs or between pairs of quantum dots. Measurements of such rates provide an opportunity to revisit classic experiments in quantum mechanics. At the same time, the unique features of the silicon conduction band lead to novel and unexpected effects, demonstrating that Si/SiGe quantum dots provide a highly controlled experimental system in which to study ideas at the heart of quantum physics.

  11. 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.

  12. 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.

  13. High Temperature Si-doped BN Interphases for Woven SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Hurwitz, Frances; Yun, Hee Mann; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    The hydrolytic stability of high-temperature deposited Si-doped BN has been shown in the past to be superior in comparison to "pure" BN processed at similar or even higher temperatures. This type of material would be very desirable as a SiC/SiC composite interphase that is formed by chemical infiltration into multi-ply woven preform. However, due to rapid deposition on the preform outer surface at the high processing temperature, this has proven very difficult. To overcome this issue, single plies of woven fabric were infiltrated with Si-doped BN. Three composite panels of different SiC fiber types were fabricated with Si-doped BN interphases including Sylramic, Hi-Nicalon Type S and Sylramic-iBN fiber-types. The latter fiber-type possesses a thin in-situ grown BN layer on the fiber surface. High Si contents (approx. 7 to 10 a/o) and low oxygen contents (less than 1 a/o) were achieved. All three composite systems demonstrated reasonable debonding and sliding properties. The coated Sylramic fabric and composites were weak due to fiber degradation apparently caused during interphase processing by the formation of TiN crystals on the fiber surface. The Hi-Nicalon Type S composites with Si-doped BN interphase were only slightly weaker than Hi-Nicalon Type S composites with conventional BN when the strength on the load-bearing fibers at failure was compared. On the other hand, the Sylramic-iBN fabric and composites with Si-doped BN showed excellent composite and intermediate temperature stress-rupture properties. Most impressive was the lack of any significant interphase oxidation on the fracture surface of stress-ruptured specimens tested well above matrix cracking at 815C.

  14. Three carbon pairs in Si

    NASA Astrophysics Data System (ADS)

    Docaj, A.; Estreicher, S. K.

    2012-08-01

    Carbon impurities in Si are common in floating-zone and cast-Si materials. The simplest and most discussed carbon complex is the interstitial-substitutional CiCs pair, which readily forms when self-interstitials are present in the material. This pair has three possible configurations, each of which is electrically active. The less common CsCs pair has been studied in irradiated material but has also recently been seen in as-grown C-rich cast-Si, which is commonly used to fabricate solar cells. The third pair consists of two interstitial C atoms: CiCi. Although its formation probability is low for several reasons, the CiCi pair is very stable and electrically inactive. In this contribution, we report preliminary results of first-principles calculations of these three C pairs in Si. The structures, binding energies, vibrational spectra, and electrical activity are predicted.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  16. Ab initio chemical kinetics for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the related unimolecular decomposition of Si3H8 under a-Si/H CVD conditions.

    PubMed

    Raghunath, P; Lin, M C

    2013-10-24

    The kinetics and mechanisms for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the related unimolecular decomposition of Si3H8 have been investigated by ab initio molecular orbital theory based on the QCISD(T)/CBS//QCISD/6-311++G(d,p) method in conjunction with quantum statistical variational Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. For the barrierless radical association processes, their variational transition states have been characterized by the CASPT2//CASSCF method. The species involved in the study are known to coexist under CVD conditions. The results show that the association reaction of SiH2 and Si2H6 producing Si3H8 occurs by insertion via its lowest-energy path forming a loose hydrogen-bonding molecular complex with 8.3 kcal/mol binding energy; the reaction is exothermic by 55.0 kcal/mol. The chemically activated Si3H8 adduct can fragment by several paths, producing SiH4 + SiH3SiH (-0.7 kcal/mol), Si(SiH3)2 + H2 (-1.4 kcal/mol), and SiH3SiH2SiH + H2 (-1.4 kcal/mol). The predicted enthalpy changes as given agree well with available thermochemical data. Three other decomposition channels of Si3H8 occurring by Si-H or Si-Si breaking were found to be highly endothermic, and the reactions take place without a well-defined barrier. The heats of formation of Si3H8, SiH2SiH, Si2H4, i-Si3H7, n-Si3H7, Si(SiH3)2, and SiH3SiH2SiH have been predicted and found to be in close agreement with those available data in the literature. The product branching rate constants for SiH2 + Si2H6 and SiH3 + Si2H5 reactions and the thermal unimolecular decomposition of Si3H8 for all low-energy paths have been calculated with multichannel variational RRKM theory covering varying P,T conditions typically employed in PECVD and Cat-CVD processes for hydrogenated amorphous silicon (a-Si/H) film growth. The results were also found to be in good agreement with available kinetic data. Our kinetic results may be employed to model and control very large-area a-Si/H film growth for a

  17. 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:

  18. 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.

  19. Energy shifts of Si oxidation states in the system of Si nanocrystals embedded in SiO2 matrix.

    PubMed

    Chen, T P; Liu, Y; Sun, C Q; Tseng, Ampere A; Fung, S

    2007-07-01

    Energy shifts in the Si 2p levels of the five Si oxidation states Sin+ (n = 0, 1, 2, 3, 4) in the system of Si nanocrystals embedded in SiO2 matrix have been determined. The thermal annealing effect on the energy shifts has been studied. The result suggests that the Si nanocrystals and the SiO2 are thermally stable but the annealing can cause some structural deformations such as changes in the bond lengths and bond angles for the suboxides Si2O and SiO. The energy shifts generally show a linear dependence on the oxidation state n, suggesting that the energy shifts could be mainly determined by the nearest-neighbor oxygen atoms. It is shown that the chemical structures of the system are similar to those of the conventional SiO2/Si system in terms of the energy shifts.

  20. Hydrogen reactions with dangling bonds in Si and Si-SiO sub 2 structures

    SciTech Connect

    Myers, S.M.; Brower, K.L.; Follstaedt, D.M.; Richards, P.M.; Stein, H.J.; Wampler, W.R.

    1991-01-01

    Hydrogen is highly mobile in Si and vitreous SiO{sub 2}, and it reacts strongly with dangling bonds residing on Si and O atoms. These interactions have important consequences for metal-oxide- semiconductor structures, with noteworthy effects including the passivation of electrically active defects, mediation of radiation sensitivity, chemical passivation of etched Si surfaces, and still poorly understood effects on epitaxial growth from H-containing media. Despite the significance of these H reactions, fundamental understanding of them has remained seriously deficient; the H bonding energies have been known semiquantitatively at best, and the detailed reaction paths and rate-determining energetics of intermediate states have remained largely speculative. We are addressing these issues through a coordinated program of experiment and theory with the goal of a unified, quantitatively predictive understanding. 3 figs.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

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

    PubMed

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

    2016-04-28

    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.

  7. 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.

  8. Electronic spectroscopy and photophysics of Si nanocrystals. Relationship to bulk c-Si and porous Si

    SciTech Connect

    Brus, L.E.; Szajowski, P.F.; Wilson, W.L.; Harris, T.D.; Schuppler, S.; Citrin, P.H.

    1995-03-15

    The structural characterization, electronic spectroscopy, and excited-state dynamics of surface-oxidized Si nanocrystals, prepared in a high-temperature aerosol apparatus, are studied to gain insight into the emission mechanism of visible light from these systems. The results are compared with direct-gap CdSe nanocrystals, indirect-gap AgBr nanocrystals, bulk crystalline silicon, and porous silicon thin films. As the size of the Si crystallites decreases to 1-2 nm in diameter, the band gap and luminescence energy correspondingly increase to near 2.0 eV, or 0.9 eV above the bulk 1.1-eV band gap. The absorption and luminescence spectra remain indirect-gap-like with strong transverse optical vibronic origins. The quantum yield increases to about 5% at room temperature, but the unimolecular radiative rate remains quite long, approximately 10{sup {minus}3}-10{sup {minus}4} s{sup {minus}1}. The luminescence properties of Si nanocrystals and porous Si are consistent, in most respects, with simple emission from size-dependent, volume-quantum-confined nanocrystal states. Room-temperature quantum yields increase not because coupling to the radiation field is stronger in confined systems, but because radiationless processes, which dominate bulk Si emission, are significantly weaker in nanocrystalline Si. An analogous series of changes occurs in nanocrystalline AgBr. 42 refs., 8 figs.

  9. 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.

  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. Interactions of transition metals with silicon(100): The Ni-Si, Co-Si and Au/Si(100) systems

    NASA Astrophysics Data System (ADS)

    Naftel, Steven James

    1999-11-01

    This thesis encompasses studies of the electronic and physical structure of three transition metal interfaces with Si(100) substrates. The first case concerns a high resolution photoemission (PES) study of the initial stages (0 to ˜ 25 ML) of the formation of the Au/Si(100) interface at room temperature. The interface was studied using Si 2p and Au 4f core-level PES, using synchrotron radiation. It was found that the Au and Si react immediately upon deposition to form a Au-Si phase. This initial Au-Si phase is seen to change to a second Au-Si phase by 3.6 ML (1 ML = 6.78 x 1014 atoms/cm 2) of Au coverage. As the coverage is increased a layer of the second Au-Si phase remains on the surface while pure Au layers form underneath it. Second we report a Si L3,2 -, Si K-, Co L3,2 - and Co K-edge X-ray absorption near-edge structures (XANES) study of a series of cobalt and cobalt silicide thin films prepared by thermally annealing deposited Co layers on Si(100) substrates. By collecting both Total Electron Yield (TEY) and Fluorescence Yield (FLY) XANES at the above edges we monitored the electronic and physical structural differences between films annealed under different conditions. It was found that the as deposited Co film exhibits noticeable intermixing at the Co-Si interface. The annealed films consisted of CoSi2; however, both SiO2 and metallic Co were found in the near surface region of these films. The origin of the metallic Co remains undetermined. Thirdly, we report a Si L3,2 -, Si K-, Ni L3,2 - and Ni K-edge, TEY and FLY XANES study of a series of nickel and nickel silicide thin films prepared by thermally annealing deposited Ni layers on Si(100) substrates. The unannealed films again showed noticeable intermixing at the Ni-Si interface. The annealed Ni films produced primarily NiSi and NiSi2 films depending on the final annealing temperature. Using the XANES spectra from the Ni-Si blanket films as a reference we determined that Ni-Si sub-micron lines formed

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Electroluminescence from Si/SiGe quantum cascade emitters

    NASA Astrophysics Data System (ADS)

    Paul, D. J.; Lynch, S. A.; Bates, R.; Ikonic, Z.; Kelsall, R. W.; Harrison, P.; Norris, D. J.; Liew, S. L.; Cullis, A. G.; Murzyn, P.; Pidgeon, C.; Arnone, D. D.; Robbins, D. J.

    2003-03-01

    Intersubband electroluminescence results are presented from Si/SiGe quantum cascade emitters at 3.2 THz and at temperatures up to 150 K. The effect of adding doping into the active quantum wells was studied in addition to reduced barrier widths from previous measurements. While the current through the sample is increased by the addition of doping, the emitted power is reduced through additional free carrier absorption and Coulombic scattering. Free electron laser measurements confirm the intersubband transitions in the quantum wells of the cascade devices and produce non-radiative lifetimes of ∼20 ps between 4 and 150 K.

  20. 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.

  1. Novel Si networks in Ca/Si phase diagram under pressure

    NASA Astrophysics Data System (ADS)

    Gao, Guoying; Ashcroft, Neil; Hoffmann, Roald

    2014-03-01

    In the Ca/Si phase diagram, many compositions are known. In these calcium silicides, silicon atoms form many different organizations, for example, at low pressure silicons are isolated silicon atoms in Ca2Si, Si chains in CaSi and corrugated hexagonal Si layers and a three-dimensional network of sp2 bonds in CaSi2. The crystal structures for these silicides under pressure have not been studied completely, and we are very interested in the new chemical and physical behavior of Si in these silicides under pressure. Therefore, we take a theoretical study of Ca2Si, CaSi and CaSi2 under pressure. We predicted many interesting Si networks in the calcium silicides under pressure. Si atoms form Si chains in Ca2Si, flat quadrangular and hexagonal Si layers in CaSi, and 6-coordinated Si tetrahedrons and 4, 8-coordinated Si octahedrons in CaSi2 at high pressure. All of these predicted structures are dynamically stable. Moreover, these calcium silicides are all metals. Some of them are good candidates to be superconductors. G. G., R. H., and N. W. A. acknowledge support by the NSF through research grant CHE-0910623 and DMR-0907425, and also EFree by the U.S. Department of Energy (Award No. DESC0001057 at Cornell).

  2. Ordered CaSi2 Microwall Arrays on Si Substrates Induced by the Kirkendall Effect.

    PubMed

    Meng, Xiang; Ueki, Akiko; Tatsuoka, Hirokazu; Itahara, Hiroshi

    2017-03-02

    We have specified the synthetic conditions to obtain one-directionally ordered CaSi2 microwall arrays vertically grown on a Si substrate. Our basic concept is based on the utilization of the Kirkendall effect for reactive deposition epitaxy (RDE). We found for the first time that: 1) a much larger Ca vapor supply on the Si substrate than the conventional RDE, 2) the adoption of a two-step heating process, and 3) the selection of the crystal axis of the Si surface are the keys to control the microstructures of CaSi2 on the Si substrate. The CaSi phase was first formed on Si, then the CaSi2 phase was formed at the CaSi/Si interface. Based on the Kirkendall effect, the interdiffusion of Ca and Si was enhanced in the vertical direction rather than in the parallel direction to the Si surface. CaSi2 tends to grow along four equivalent Si{111} planes, however, the specific orientation of the Si surface resulted in CaSi2 microwalls grown along its Si(111‾ ) plane, the only plane directing nearly vertical to the surface among the Si{111} planes. These results suggest that the Kirkendall effect under asymmetric growth of target materials would be a rational strategy to obtain their ordered microstructures. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. 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.

  4. On the Structure and Chemical Bonding of Si62- and Si62- in NaSi6- Upon Na+ Coordination

    SciTech Connect

    Zubarev, Dmitry Y.; Alexandrova, Anastassia N.; Boldyrev, Alexander I.; Cui, Lifeng; Li, Xi; Wang, Lai S.

    2006-03-23

    Photoelectron spectroscopy was combined with ab initio calculations to elucidate the structure and bonding in Si62- and NaSi6-. Well-resolved electronic transitions were observed in the photoelectron spectra of Si6- and NaSi6- at three photon energies (355, 266, and 193 nm). The spectra of NaSi6- were observed to be similar to those of Si6- except that the electron binding energies of the former are lower, suggesting that the Si6 motif in NaSi6- is structurally and electronically similar to that of Si6-. The electron affinity of Si6 and NaSi6 were measured fairly accurately to be 2.23 ± 0.03 eV and 1.80 ± 0.05 eV, respectively. Global minimum structure searches for Si62- and NaSi6- were performed using Gradient Embedded Genetic Algorithm followed by B3LYP, MP2 and CCSD(T) calculations. Vertical electron detachment energies (VDEs) were calculated for the lowest Si6- and NaSi6- structures at the CCSD(T)/6-311+G(2df), ROVGF/6-311+G(2df), UOVGF/6-311+G(2d), TD B3LYP/6-311+G(2df) levels of theory. Experimental VDEs were used to verify the global minimum structure for NaSi6-. Though the octahedral Si62-, analogous to the closo-form of borane B6H62-, is the most stable form for the bare hexa-silicon dianion, it is not the kernel for the NaSi6- global minimum. The most stable isomer of NaSi6- is based on a Si62- motif, which is distorted into C2v symmetry similar to the ground state structure of Si6-. The octahedral Si62- coordinated by a Na+ is a low-lying isomer and was also observed experimentally. The chemical bonding in Si62- and NaSi6- was understood using NBO, molecular orbital, and ELF analysis.

  5. 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.

  6. Comparison of low frequency charge noise in identically patterned Si/SiO{sub 2} and Si/SiGe quantum dots

    SciTech Connect

    Freeman, Blake M.; Schoenfield, Joshua S.; Jiang, HongWen

    2016-06-20

    We investigate and compare the charge noise in Si/SiO{sub 2} and Si/SiGe gate defined quantum dots with identically patterned gates by measuring the low frequency 1/f current noise through the biased quantum dots in the coulomb blockade regime. The current noise is normalized and used to extract a measurement of the potential energy noise in the system. Additionally, the temperature dependence of this noise is investigated. The measured charge noise in Si/SiO{sub 2} compares favorably with that of the SiGe device as well as previous measurements made on other substrates suggesting Si/SiO{sub 2} is a potential candidate for spin based quantum computing.

  7. 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.

  8. 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

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

    NASA Astrophysics Data System (ADS)

    González-González, A.; Alonso, M.; Navarro, E.; Sacedón, J. L.; Ruiz, A.

    2010-12-01

    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.

  10. Vibrationally Resolved Photoelectron Spectra of Si(3)- and Si(4)-

    DTIC Science & Technology

    1990-08-01

    3- and Si4- by T. N. Kitsopoulos, C. J. Chick, A. Weaver, and D. M. Neumark Submitted to the Journal of Chemical Physics : ’ " ., AUG 1 , ’J Ř...Diay ISAGE COUNT Interim Technical lpRIOM Jan 90 Y. July 90 190-7-31 15 1S. S..JPPLEMENTARY NOTATION Prepared for publication in the Journal of Chemical Physics 17

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

    PubMed

    González-González, A; Alonso, M; Navarro, E; Sacedón, J L; Ruiz, A

    2010-08-11

    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.

  12. 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.

  13. The epitaxial growth of (1 1 1) oriented monocrystalline Si film based on a 4:5 Si-to-SiC atomic lattice matching interface

    SciTech Connect

    Yang, Chen; Chen, Zhiming; Hu, Jichao; Ren, Zhanqiang; Lin, Shenghuang

    2012-06-15

    Highlights: ► A monocrystalline Si film was demonstrated by XRD to epitaxially grow on the 6H-SiC substrate. ► A 4:5 Si-to-SiC lattice matching structure was observed at the Si/SiC interface. ► The calculated value of the actual lattice mismatch is only 0.26%. ► Defects can be effectively reduced at the 4:5 Si-to-SiC lattice matching Si/SiC interface. -- Abstract: Due to a huge lattice mismatch of about 20% theoretically existing between SiC and Si, it is difficult for growing monocrystalline Si/SiC heterojunction to realize the light control of SiC devices. However, based on a 4:5 Si-to-SiC atomic lattice matching interface structure, the monocrystalline Si films were epitaxially prepared on the 6H-SiC (0 0 0 1) substrate by hot-wall chemical vapor deposition in our work. The film was characterized by X-ray diffraction analysis with only (1 1 1) orientation occurring. The X-ray rocking curves illustrated good symmetry with a full width at half maximum of 0.4339° omega. A 4:5 Si-to-SiC atomic matching structure of the Si/6H-SiC interface clearly observed by the transmission electron microscope revealed the essence of growing the monocrystalline Si film on the SiC substrate.

  14. 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.

  15. Acetonitrile adsorption on Si(001)

    NASA Astrophysics Data System (ADS)

    Miotto, R.; Oliveira, M. C.; Pinto, M. M.; de León-Pérez, F.; Ferraz, A. C.

    2004-06-01

    In this work we employ the state of the art pseudopotential method, within a generalized gradient approximation to the density-functional theory, to investigate the adsorption process of acetonitrile on the silicon surface. Our first-principles calculations indicate that CH3 CN adsorb via a [2+2] cycloaddition reaction through the CN group ( di- σCN model) with an adsorption energy around 37 kcal/mol . Although the di- σCN model is found to be the most probable adsorbed structure from the energetic point of view, we have also found that the adsorption via the Si-N dative bond ( Si-Ndat model) is also possible. Based in our energetic analysis, and in the spectroscopy data by Bournel and co-workers, we suggest the existence of a mixed domain surface composed by both the di- σCN and Si-Ndat adsorbates, although the existence of the latter structure is disregarded by the core level shift analysis by Tao and co-workers. Possible reasons for the contrast between available data are addressed. We present theoretical scanning tunneling microscopy images of the possible adsorbed systems and suggest that this experimental procedure could possibly identify the existence of the proposed mixed domain structure. In addition, the electronic structure and surface states for both the di- σCN and Si-Ndat models are discussed in detail.

  16. Using SI Units in Astronomy

    NASA Astrophysics Data System (ADS)

    Dodd, Richard

    2011-12-01

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

  17. 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…

  18. 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.

  19. 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.

  20. 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.

  1. Enhanced light emission from Si nanocrystals produced using SiOx/SiO2 multilayered silicon-rich oxides

    NASA Astrophysics Data System (ADS)

    Yoon, Jong-Hwan

    2015-07-01

    The light emission from Si nanocrystals (NCs) produced in SiO2 by annealing of SiOx/SiO2 multilayered silicon-rich oxide (SRO) is examined as a function of the SiOx layer thickness. Multilayered SRO structures are shown to produce a significant increase in emission intensities with a large redshift of spectra as compared with a single-layer SRO film. A multilayered SRO film with ∼6-nm thick SiO1.45 layers exhibits a 13-fold increase in the emission intensity with a redshift of ∼70 nm relative to a single-layer SiO1.45 SRO film with a thickness equivalent to the total SiO1.45 layer thickness in the multilayered film. The transmission electron microscopy analyses indicate that the enhancement of the emission intensity with the redshift of spectrum is caused by the enhanced aggregation of phase separated Si atoms in the former SiOx layers due to the hindering of interlayer diffusion of Si by the neighboring SiO2 layers.

  2. Thermal Evaporation Synthesis and Optical Properties of ZnS Microbelts on Si and Si/SiO2 Substrates

    NASA Astrophysics Data System (ADS)

    Nguyen, V. N.; Khoi, N. T.; Nguyen, D. H.

    2017-06-01

    In this study, we report on the differences in optical properties of zinc sulfide (ZnS) microbelts grown on Si and Si/SiO2 substrates by a thermal evaporation method. Our investigation suggests that the composition and luminescence of the microbelts are dependent on the growth substrate. Field emission scanning electron microscopy images show the formation of nanoparticles with a diameter of 300-400 nm on ZnS microbelts grown on Si substrate. In addition, energy dispersive x-ray spectroscopy analysis combined with x-ray diffraction and Raman measurements reveal the existence of Si on these microbelts which may bond with O to form SiO2 or amorphous silica. In contrast, no Si presents on the microbelts grown on Si/SiO2 substrate. Moreover, photoluminescence measurement at 300 K shows a narrow emission peak in the near-ultraviolet region from microbelts grown on Si/SiO2 substrate but a broad emission band with multi-peaks from microbelts grown on Si substrate. The origin of the luminescence distinction between microbelts is discussed in terms of the differences in the growth substrates and compositions.

  3. Superior solid solubility of MnSiO3 in CaSiO3 perovskite

    NASA Astrophysics Data System (ADS)

    Li, Lin; Nagai, Takaya; Seto, Yusuke; Fujino, Kiyoshi; Kawano, Jun; Itoh, Shoich

    2015-02-01

    The silicate perovskite phase relation between CaSiO3 and MnSiO3 was investigated at 35-52 GPa and at 1,800 K using laser-heated diamond anvil cells combined with angle-dispersive synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopic chemical analyses with scanning or transmission electron microscopy. We found that MnSiO3 can be incorporated into CaSiO3 perovskite up to 55, and 20 mol % of CaSiO3 is soluble in MnSiO3 perovskite. The range of 55-80 mol % of MnSiO3 in the CaSiO3-MnSiO3 perovskite system could be immiscible. We also observed that the two perovskite structured phases of the Mn-bearing CaSiO3 and the Ca-bearing MnSiO3 coexisted at these conditions. The Mn-bearing CaSiO3 perovskite has non-cubic symmetry and the Ca-bearing MnSiO3 perovskite has an orthorhombic structure with space group Pbnm. All the perovskite structured phases in the CaSiO3-MnSiO3 system convert to the amorphous phase during pressure release. MnSiO3 is the first chemical component confirmed to show such a superior solid solubility in CaSiO3 perovskite.

  4. Superior solid solubility of MnSiO3 in CaSiO3 perovskite

    NASA Astrophysics Data System (ADS)

    Li, Lin; Nagai, Takaya; Seto, Yusuke; Fujino, Kiyoshi; Kawano, Jun; Itoh, Shoich

    2014-08-01

    The silicate perovskite phase relation between CaSiO3 and MnSiO3 was investigated at 35-52 GPa and at 1,800 K using laser-heated diamond anvil cells combined with angle-dispersive synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopic chemical analyses with scanning or transmission electron microscopy. We found that MnSiO3 can be incorporated into CaSiO3 perovskite up to 55, and 20 mol % of CaSiO3 is soluble in MnSiO3 perovskite. The range of 55-80 mol % of MnSiO3 in the CaSiO3-MnSiO3 perovskite system could be immiscible. We also observed that the two perovskite structured phases of the Mn-bearing CaSiO3 and the Ca-bearing MnSiO3 coexisted at these conditions. The Mn-bearing CaSiO3 perovskite has non-cubic symmetry and the Ca-bearing MnSiO3 perovskite has an orthorhombic structure with space group Pbnm. All the perovskite structured phases in the CaSiO3-MnSiO3 system convert to the amorphous phase during pressure release. MnSiO3 is the first chemical component confirmed to show such a superior solid solubility in CaSiO3 perovskite.

  5. 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.

  6. 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.

  7. An inside job for siRNAs.

    PubMed

    Golden, Daniel E; Gerbasi, Vincent R; Sontheimer, Erik J

    2008-08-08

    Among the three main categories of small silencing RNAs in insects and mammals-siRNAs, miRNAs, and piRNAs-siRNAs were thought to arise primarily from exogenous sources, whereas miRNAs and piRNAs arise from endogenous loci. Recent work in flies and mice reveals several classes of endogenous siRNAs (endo-siRNAs) that contribute to functions previously reserved for miRNAs and piRNAs, including gene regulation and transposon suppression.

  8. 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

  9. Hydrogen-induced crystallization of amorphous Si thin films. II. Mechanisms and energetics of hydrogen insertion into Si-Si bonds

    SciTech Connect

    Valipa, Mayur S.; Sriraman, Saravanapriyan; Aydil, Eray S.; Maroudas, Dimitrios

    2006-09-01

    We report a detailed study of the mechanisms and energetics of hydrogen (H) insertion into strained Si-Si bonds during H-induced crystallization of hydrogenated amorphous Si (a-Si:H) thin films. Our analysis is based on molecular-dynamics (MD) simulations of exposure of a-Si:H films to H atoms from a H{sub 2} plasma through repeated impingement of H atoms. Hydrogen atoms insert into Si-Si bonds as they diffuse through the a-Si:H film. Detailed analyses of the evolution of Si-Si and Si-H bond lengths from the MD trajectories show that diffusing H atoms bond to one of the Si atoms of the strained Si-Si bond prior to insertion; upon insertion, a bridging configuration is formed with the H atom bonded to both Si atoms, which remain bonded to each other. After the H atom leaves the bridging configuration, the Si-Si bond is either further strained, or broken, or relaxed, restoring the Si-Si bond length closer to the equilibrium bond length in crystalline Si. In some cases, during its diffusion in the a-Si:H film, the H atom occupies a bond-center position between two Si atoms that are not bonded to each other; after the H diffuses away from this bond-center position, a Si-Si bond is formed between these previously nonbonded Si atoms. The activation energy barrier for the H insertion reaction depends linearly on both the initial strain in the corresponding Si-Si bond and a strain factor that takes into account the additional stretching of the Si-Si bond in the transition-state configuration. The role of the H insertion reactions in the structural relaxation of the a-Si:H network that results in disorder-to-order transitions is discussed.

  10. Cu-Si nanoobjects prepared by CVD on Cu/Cu5Si-substrates using various precursors (SiH4, EtSiH3, BuSiH3) with added H2 or air

    NASA Astrophysics Data System (ADS)

    Klementová, Mariana; Krabáč, Lubomír; Brázda, Petr; Palatinus, Lukáš; Dřínek, Vladislav

    2017-05-01

    The CVD method was employed to synthesize nanoobjects of Cu-Si phases at temperature of about 500 °C. Cu/Cu5Si-substrates and various Si-containing precursors (SiH4, EtSiH3, BuSiH3) with/without added H2 or air were used. Nanoobjects of various morphologies (nanoplatelets of η‧-Cu3Si, nanoribbons and nanorods of η″-Cu3Si, and nanowires of γ-Cu83Si17) were obtained depending on the experimental conditions, mainly type and pressure of precursor. A mixture of Si-containing precursor and H2/air promotes the growth of nanoobjects compared to using the pure Si-containing precursor. With increasing pressure of precursors the morphology changes from 1D (nanowires) to 2D (nanoribbons, nanoplatelets). Nanoobjects grow via the non-catalytic VS mechanism.

  11. 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.

  12. Nanostructure Effect in Si-MOSFETs

    DTIC Science & Technology

    2001-06-01

    tunneling MOS transistor made in Si and with properties like room temperature Coloumb oscillations. 1. Introduction The relentless scaling of Si MOSFET...During the talk we will present our results on e.g. room temperature Coloumb oscillations in Si based SETs [89, 90]. 5. Conclusions and future

  13. Microwave joining of SiC

    SciTech Connect

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

    1995-05-01

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

  14. Novel refractory phase, Ta7Si2(Si(x)B(1-x))2.

    PubMed

    Romaka, V; Fosodeder, V; Rogl, P F; Ramos, É C T; Nunes, C A; Coelho, G C; Giester, G

    2013-10-07

    X-ray single crystal (XSC) and powder diffraction data (XPD) were used to elucidate the crystal structure of a new refractory silicon boride Ta7Si2(Si(x)B(1-x))2 (x = 0.12). Tetragonal Ta7Si2(Si(x)B(1-x))2 (space group P4/mbm; a = 0.62219(2) nm, c = 0.83283(3) nm) with B atoms randomly sharing the 4g site with Si atoms is isotypic with the boride structure of (Re,Co)7B4. The architecture of the structure of Ta7Si2(Si(x)B(1-x))2 combines layers of three-capped triangular metal prisms (Si,B)[Ta(6+2)(Si,B)] alternating with double layers of two-capped Si[Ta(8+1)Si] Archimedian metal antiprisms. Consequently, the metal framework contains (B/Si) pairs and Si-Si dumbbells. These two types of coordination figures around the nonmetal atoms are typical for the system-inherent structures of Ta2B (or Ta2Si) and Ta3B2. DFT calculations showed strong B(Si)-B(Si) and Si-Si bonding and represent Ta7Si2(Si(x)B(1-x))2 as a covalent-ionic compound. This bonding behavior is reflected in the high hardness value of 1750 HV. The Sommerfeld constant, γ = 7.58 mJ/mol K(2), as derived from the electronic density of states, calculated at the Fermi level, suggests typical metallic behavior.

  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. Investigation of bonding characteristics between Si quantum dots and a SiO2 matrix.

    PubMed

    Park, Youngbin; Kim, Shinho; Moon, Jihyun; Lee, Jung Chul; Kim, Yangdo

    2012-02-01

    In order to understand and control the properties of Si quantum dot (QD) superlattice structures (SLS), it is necessary to investigate the bonding between the dots and their matrix and also the structures' crystallinities. In this study, a SiOx matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si QD SLS were prepared by alternating deposition of Si rich SiOx (x = 0.8) and SiO2 layers using RF magnetron co-sputtering and subsequent annealing at temperatures between 800 and 1,100 degrees C under nitrogen ambient. Annealing temperatures and times affected the formation of Si QDs in the SRO film. Raman and FTIR spectra revealed that nanocrystalline Si QDs started to precipitate after annealing at 1,100 degrees C for 1 hour. TEM images clearly showed SRO/SiO2 SLS and Si QDs formation in SRO layers after annealing at 1,100 degrees C for 2 hours. XPS analysis showed that Si-Si and Si-O bonding changes occurred above 1,100 degrees C. XPS analysis also revealed that Si QD SLSs started stabilizing after 2 hours' annealing and approached completion after 3 hours'. The systematic investigation of Si QDs in SiO2 matrices and their properties for solar cell application are presented.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  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. Characterization of Si nanostructured surfaces

    NASA Astrophysics Data System (ADS)

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

    1999-06-01

    Surface scattering of Si to enhanced 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 broad band reflection has been observed for triangular profiles with linewidths significantly less than 100 nm. Si nanostructures have been integrated into large (approximately 42 cm2) area solar cells. Internal quantum efficiency measurements in comparison with polished and conventionally textured cells show lower efficiency in the UV-visible (350 - 680 nm), but significantly higher IR (700 - 1200 nm) efficiency.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  6. Mechanism for Si-Si Bond Rupture in Single Molecule Junctions.

    PubMed

    Li, Haixing; Kim, Nathaniel T; Su, Timothy A; Steigerwald, Michael L; Nuckolls, Colin; Darancet, Pierre; Leighton, James L; Venkataraman, Latha

    2016-12-14

    The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si-Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si-Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si-Si bond is ruptured using an applied voltage. We investigate this voltage induced Si-Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation of molecular vibrational modes by tunneling electrons leads to homolytic Si-Si bond rupture.

  7. Si quantum dot structures and their applications

    NASA Astrophysics Data System (ADS)

    Shcherbyna, L.; Torchynska, T.

    2013-06-01

    This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented. The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.

  8. Photoelectron Spectroscopy of Si2

    DTIC Science & Technology

    1991-01-15

    of Si., as well as transitions to the higher-lying singlet states. Several possible- assignments of the anion and neutral triplet states are... neutral triplet states are presented. INTRODUCTION In recent years understanding chemical bonding in clusters has been the focus of intense research[I...spectroscopically identified. Using emission spectroscopy, Douglas[12] identified both the 3Xg" ground state and the ’l1 first excited state for the neutral

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Effect of tensile-strained Si layer on photoluminescence of Ge(Si) self-assembled islands grown on relaxed SiGe/Si(001) buffer layers

    SciTech Connect

    Shaleev, M. V. Novikov, A. V.; Yablonskii, A. N.; Kuznetsov, O. A.; Drozdov, Yu. N.; Krasil'nik, Z. F.

    2007-02-15

    The results of studying the photoluminescence of the structures with Ge(Si) self-assembled islands embedded into tensile-strained Si layer are reported. The structures were grown on smooth relaxed Si{sub 1-x}Ge{sub x}/Si(001) (x = 0.2-0.3) buffer layers. The photoluminescence peak found in the photoluminescence spectra of the studied structures is related to the indirect (in real space) optical transition between the holes localized in the Ge(Si) islands and electrons localized in the tensile-strained Si layers under and above an island. It is shown that one can efficiently control the position of the photoluminescence peak for a specified type of structure by varying the thickness of the strained Si layers. It is found that, at 77 K, the intensity of the photoluminescence signal from the heterostructures with Ge(Si) self-assembled islands contained between the tensile-strained Si layers exceeds by an order of magnitude the intensity of the photoluminescence signal from the GeSi structures with islands formed on the Si(001) substrates.

  17. 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.

  18. 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.

  19. 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.

  20. Abrasive wear behavior of MoSi(2)-SiC Composites

    SciTech Connect

    Alman, David E.; Hawk, Jeffrey A.; Petrovic, J.J.; Henager, C.H., Jr.; Singh, M.

    1998-01-01

    This paper investigates the influence of SiC volume fraction and composite processing route on the abrasive wear behavior of MoSi sub 2 -SiC composites. The MoSi sub 2 -SiC (10-67 vol%) particulate composites were produced by: (i) the conventional hot-pressing of mixtures of MoSi sub 2 powders and SiC whiskers; and (ii) through the solid-state displacement reaction between Mo sub 2 C and Si powders to form MoSi sub 2 and SiC during hot-pressing. A MoSi sub 2 -80 vol% SiC composite was also produced by the reactive melt infiltration of a carbon preform with a molten Si-Mo alloy. The incorporation of SiC into a MoSi sub 2 matrix is an effective way to enhance wear resistance, provided the composites are processed to as near full density as possible.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Photoluminescence Study of Si1-xGex/Si and Si/Ge Strained Layer Superlattices

    DTIC Science & Technology

    1992-07-13

    10 5. Superlattice Energy Bands as a Function of Well Width .... 12 6. Superlattice Minizones and Minibands ..................... 13 7. Bandgap vs...Vapor Deposition El = binding energy of bound exciton E, =conduction band minimum Eex = free exciton binding energy E9 = energy gap, bandgap EL...between the F and X 06 C Ot IC points (approximately G, FRACTION (Xý 0.8 times the distance Figure 3: Bulk Si 1 _xGe, bandgap vs. alloy concentration

  6. 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.

  7. 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.

  8. 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.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

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

    PubMed Central

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

    2017-01-01

    Memristors are promising building blocks for the next-generation memory and neuromorphic computing systems. Most memristors use materials that are incompatible with the silicon dominant complementary metal-oxide-semiconductor technology, and require external selectors in order for large memristor arrays to function properly. Here we demonstrate a fully foundry-compatible, all-silicon-based and self-rectifying memristor that negates the need for external selectors in large arrays. With a p-Si/SiO2/n-Si structure, our memristor exhibits repeatable unipolar resistance switching behaviour (105 rectifying ratio, 104 ON/OFF) and excellent retention at 300 °C. We further build three-dimensinal crossbar arrays (up to five layers of 100 nm memristors) using fluid-supported silicon membranes, and experimentally confirm the successful suppression of both intra- and inter-layer sneak path currents through the built-in diodes. The current work opens up opportunities for low-cost mass production of three-dimensional memristor arrays on large silicon and flexible substrates without increasing circuit complexity. PMID:28580928

  12. 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.

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

    DOEpatents

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

    2011-08-30

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

  14. 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.

  15. Photoluminescence line width of self-assembled Ge(Si) islands arranged between strained Si layers

    SciTech Connect

    Shaleev, M. V. Novikov, A. V.; Baydakova, N. A.; Yablonskiy, A. N.; Kuznetsov, O. A.; Lobanov, D. N.; Krasilnik, Z. F.

    2011-02-15

    The effect of variations in the strained Si layer thicknesses, measurement temperature, and optical excitation power on the width of the photoluminescence line produced by self-assembled Ge(Si) nanoislands, which are grown on relaxed SiGe/Si(001) buffer layers and arranged between strained Si layers, is studied. It is shown that the width of the photoluminescence line related to the Ge(Si) islands can be decreased or increased by varying the thickness of strained Si layers lying above and under the islands. A decrease in the width of the photoluminescence line of the Ge(Si) islands to widths comparable with the width of the photoluminescence line of quantum dot (QD) structures based on direct-gap InAs/GaAs semiconductors is attained with consideration of diffusive smearing of the strained Si layer lying above the islands.

  16. 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

  17. 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.

  18. Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

    DOE PAGES

    Kang, Joongoo; Park, Ji -Sang; Stradins, Pauls; ...

    2017-07-13

    In this paper, nonequilibrium growth of Si-III-V or Si-II-VI alloys is a promising approach to obtaining optically more active Si-based materials. We propose a new class of nonisovalent Si2AlP (or Si2ZnS) alloys in which the Al-P (or Zn-S) atomic chains are as densely packed as possible in the host Si matrix. As a hybrid of the lattice-matched parent phases, Si2AlP (or Si2ZnS) provides an ideal material system with tunable local chemical orders around Si atoms within the same composition and structural motif. Here, using first-principles hybrid functional calculations, we discuss how the local chemical orders affect the electronic and opticalmore » properties of the nonisovalent alloys.« less

  19. 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.

  20. 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

    2017-04-01

    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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. How to explain Si isotopes of chert?

    NASA Astrophysics Data System (ADS)

    Liu, Y.

    2016-12-01

    The variations of d30Si values in diagenetic chert and chert- associated BIFs over time can be used to reconstruct the environmental conditions of the early Earth, and become a hot topic in the Si isotope society. However, there are several different views of explaining the variation of d30Si values over time. Moreover, there are disputes in explaining the distribution of Si isotope in several main reservoirs in surface systems. Those disagreements are caused by lacking key Si isotope fractionation factors associated with the formation processes of chert and its altered products. There are many unexplained observations about Si isotope distributions in Earth's surface systems (Opfergelt and Delmelle, 2012). For example, the deduced Si isotope equilibrium fractionation factors by Rayleigh model at ambient temperature between clay and the solution D30Siclay-solution = -1.5 ‰ and -2.05 ‰ (Hughes et al., 2013) obviously disagree with common sense, which dictates that stiffer chemical bonds will enrich heavier isotopes, i.e., the precipitated minerals will preferentially incorporate heavy isotopes relative to aqueous H4SiO4 due to their shorter Si-O bonds. Another similar case is the fractionation between quartz and solution. Most field observations suggested that solution will be enriched with heavier Si isotope compared to quartz, conflicting to the fact that quartz is the one with much shorter Si-O bonds than aqueous H4SiO4 (ca. 1.610Å vs. 1.639Å). Here we provide equilibrium and kinetic Si isotope fractionation factors associated with the formation of amorphous quartz and other secondary minerals in polymerization, co-precipitation and adsorption processes. The adsorption processes of silica gel to Fe-hydroxides have been carefully examined. The Si isotope fractionations due to the formation of mono-dentate to quadru-dentate adsorbed Fe-Si complexes have been calculated. These data can explain well the experimental observations (e.g., Zheng et al., 2016) and

  6. 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.

  7. Low Activation Joining of SiC/SiC Composites for Fusion Applications: Tape Casting TiC+Si Powders

    SciTech Connect

    Henager, Charles H.; Kurtz, Richard J.; Canfield, Nathan L.; Shin, Yongsoon; Luscher, Walter G.; Mansurov, Jirgal; Roosendaal, Timothy J.; Borlaug, Brennan A.

    2013-08-06

    The use of SiC composites in fusion environments likely requires joining of plates using reactive joining or brazing. One promising reactive joining method uses solid-state displacement reactions between Si and TiC to produce Ti3SiC2 + SiC. We continue to explore the processing envelope for this joint for the TITAN collaboration in order to produce optimal joints to undergo irradiation studies in HFIR. One noted feature of the joints produced using tape-calendared powders of TiC+Si has been the large void regions that have been apparently unavoidable. Although the produced joints are very strong, these voids are undesirable. In addition, the tapes that were made for this joining were produced about 20 years ago and were aging. Therefore, we embarked on an effort to produce some new tape cast powders of TiC and Si that could replace our aging tape calendared materials.

  8. 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.

  9. 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.

  10. Characterization of spherical Si by photoluminescence measurement

    NASA Astrophysics Data System (ADS)

    Nagai, Takehiko; Liu, Zhengxin; Masuda, Atsushi; Kondo, Michio

    2007-05-01

    Spherical silicon (Si) with a size of ˜1mm diameter was fabricated by the dropping method for the applications of spherical Si solar cells. In this research work, we characterized spherical Si by means of photoluminescence (PL) measurement at 4 and 18K. The horn-type spherical Si crystals, formed under large undercooled conditions without a seeding technique, showed D-band luminescence originating from dislocations, whereas intrinsic PL bands of Si were not observed. In contrast, for the tear-type spherical Si crystals, formed under shadow undercooling by a seeding technique with Si powder, the boron (B) bound and Si intrinsic phonon-assisted PL bands were clearly observed both at 4 and 18K. Moreover, the intensity ratio of B bound exciton band to Si intrinsic phonon-assisted PL band showed good correlation to the minority carrier lifetime measured with microwave photoconductance decay method. These experimental results suggested that the crystallinity of the tear-type spherical Si is significantly improved by the seeding technique compared with the horn-type ones, which contain a large amount of B-related defects.

  11. 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.

  12. Thermoelectric transport in strained Si and Si/Ge heterostructures.

    PubMed

    Hinsche, N F; Mertig, I; Zahn, P

    2012-07-11

    The anisotropic thermoelectric transport properties of bulk silicon strained in the [111]-direction were studied by detailed first-principles calculations focusing on a possible enhancement of the power factor. Electron and hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high-temperature and high-doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of a [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole doping was drastically suppressed due to quantum-well effects, while under electron doping an enhanced power factor was found. For this, we state figures of merit of ZT = 0.2 and 1.4 at T = 300 and 900 K for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features.

  13. 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.

  14. 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.

  15. Epitaxial gallium oxide on a SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Nikolaev, V. I.; Osipov, A. V.; Osipova, E. V.; Pechnikov, A. I.; Feoktistov, N. A.

    2016-09-01

    Well-textured gallium oxide β-Ga2O3 layers with a thickness of 1 μm and a close to epitaxial layer structure were grown by the method of chloride vapor phase epitaxy on Si(111) wafers with a nano-SiC buffer layer. In order to improve the growth, a high-quality silicon carbide buffer layer 100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The β-Ga2O3 films were thoroughly investigated using reflection high-energy electron diffraction, ellipsometry, X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. The investigations revealed that the films are textured with a close to epitaxial structure and consist of a pure β-phase Ga2O3 with the (overline 2 01) orientation. The dependence of the dielectric constant of epitaxial β-Ga2O3 on the photon energy ranging from 0.7 to 6.5 eV in the isotropic approximation was measured.

  16. Mechanical Behavior of Notched SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    Gas turbine components such as combustor liners or turbine vanes are subject to regions of high stress-concentration, e.g., attachment to the frame or at cooling holes. Ceramic matrix composites (CMCs) are potential materials for high temperature applications in gas turbines. They offer some capability to relieve stress at regions of high stress-concentration via matrix damage accumulation. In this study notch sensitivity was examined for woven SiC fiber reinforced, melt-infiltrated SiC matrix composites with a BN interphase, utilizing either Hi-Nicalo(TM) fibers or the stiffer Sylramic fibers. The double-edge notched tensile test approach was used for a wide range of notch sizes and specimen widths. Both composite systems exhibited mild notch sensitivity similar to other CMC systems. Acoustic emission, detected during the tensile tests, indicated that matrix cracking occurred around notches at net-section stresses below the stress where matrix cracking first occurs in unnotched specimens. However, thermoelastic stress analysis did not show any measurable stress relief around notches after the specimens were preloaded.

  17. 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.

  18. 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.

  19. International system of units (SI)

    NASA Astrophysics Data System (ADS)

    Goldman, D. T.; Bell, R. J.

    1986-07-01

    The booklet is the United States edition of the English translation of the fifth edition of Le Systeme International d'Unites (SI), the definitive publication in the French language issued in 1985 by the International Bureau of Weights and Measures (BIPM). This U.S. edition, which conforms in substance with the British edition that follows the French text in the BIPM document is the result of a joint effort by the National Bureau of Standards (NBS) of the United States and the National Physical Laboratory (NPL) in the United Kingdom.

  20. Boron oxygen complexes in Si

    NASA Astrophysics Data System (ADS)

    Sanati, M.; Estreicher, S. K.

    2006-04-01

    The carrier lifetime in boron-doped Czochralski Si is strongly reduced by irradiation (space-based solar cells) or illumination (terrestrial cells). The culprits are believed to be boron-oxygen complexes. We use first-principles theory to predict the structure, electrical activity, and stability of complexes involving substitutional or interstitial B and interstitial O or oxygen dimers. Four complexes with comparable binding energies and thermodynamic gap levels are identified and their local vibrational modes predicted. Replacing B with Ga yields complexes with much smaller binding energies.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  2. 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.

  3. 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.

  4. 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.

  5. Comparison of Si and SiC Inverters for IPM Traction Drive

    SciTech Connect

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

    2010-01-01

    In this paper a comparison of performance of an hybrid electric vehicle with an all-silicon (Si), hybrid (Si and SiC), and an all-Silicon Carbide (SiC) inverters simulated for the standard US06 driving cycle is presented. The system model includes a motor/generator model, a boost converter model, and an inverter loss model developed using actual measured data. The drive train simulation results will provide an insight to the impact of SiC devices on overall system efficiency gains compared to Si devices over the drive cycle at different operating conditions.

  6. Mechanical behavior of MoSi{sub 2} and MoSi{sub 2} composites

    SciTech Connect

    Petrovic, J.J.

    1994-06-01

    MoSi{sub 2} is a key member of the new class high temperature structural silicide materials. Important features of the mechanical behavior of MoSi{sub 2} and MoSi{sub 2} composites are reviewed. The mechanical properties of MoSi{sub 2} single crystals, polycrystalline MoSi{sub 2}, and MoSi{sub 2}-based composites are discussed in association with properties such as elevated temperature deformation and low temperature fracture toughness. Interrelationships between single crystal, polycrystal, and composite mechanical behavior are identified.

  7. Ir/IrSi3/Si Schottky-Barrier Infrared Detector

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon

    1991-01-01

    Quantum efficiency increased. Proposed Schottky-barrier infrared detector has double metallic layer of Ir and IrSi3 instead of single metallic layer of Ir, IrSi, or IrSi3. Offers advantages of both relatively high infrared absorption in thin film of Ir and stability and reproducibility of layer of IrSi3 in contact with Si. Also serves as barrier to chemical reactions between Ir overlayer and Si substrate. Detectors used to form focal-plane array integrated with charge-coupled-device-addressing and image-processing circuitry.

  8. In-Plane Si Nanowire Growth Mechanism in Absence of External Si Flux.

    PubMed

    Curiotto, Stefano; Leroy, Frédéric; Cheynis, Fabien; Müller, Pierre

    2015-07-08

    We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au-Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

  9. 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.

  10. 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.

  11. Evolution of surface stress during oxygen exposure of clean Si(111), Si(100), and amorphous Si surfaces

    SciTech Connect

    Flötotto, D. Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

    2014-01-14

    The evolutions of the surface stress of Si(111)-7 × 7, Si(100)-2 × 1, and a-Si surfaces upon oxygen exposure at pO{sub 2} = 1 × 10{sup −4} Pa and room temperature have been investigated in a comparative manner using a specimen-curvature based technique. To this end, a generally applicable, dedicated set of experiments has been devised and performed to deduce and correct for the surface stress change owing to oxygen reaction(s) at the (poorly-defined) back face of the specimen only. On this basis, it could be demonstrated that exposure of clean Si(111)-7 × 7, Si(100)-2 × 1 and a-Si surfaces to pure oxygen gas results in compressive surface stress changes for all three surfaces due to the incorporation of oxygen into Si backbonds. The measured surface stress change decreases with decreasing atomic packing density at the clean Si surfaces, which complies well with the less-densily packed Si surface regions containing more free volume for the accommodation of adsorbed O atoms.

  12. 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

    2017-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  14. Emission efficiency limit of Si nanocrystals.

    PubMed

    Limpens, Rens; Luxembourg, Stefan L; Weeber, Arthur W; Gregorkiewicz, Tom

    2016-01-20

    One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. In this study we explore the limits of external quantum yield of photoluminescence of solid-state dispersions of Si nanocrystals in SiO2. By making use of a low-temperature hydrogen passivation treatment we demonstrate a maximum emission quantum efficiency of approximately 35%. This is the highest value ever reported for this type of material. By cross-correlating PL lifetime with EQE values, we obtain a comprehensive understanding of the efficiency limiting processes induced by Pb-defects. We establish that the observed record efficiency corresponds to an interface density of Pb-centers of 1.3 × 10(12) cm(12), which is 2 orders of magnitude higher than for the best Si/SiO2 interface. This result implies that Si nanocrystals with up to 100% emission efficiency are feasible.

  15. Interaction of metal layers with polycrystalline Si

    NASA Technical Reports Server (NTRS)

    Nakamura, K.; Olowolafe, J. O.; Lau, S. S.; Nicolet, M.-A.; Mayer, J. W.; Shima, R.

    1976-01-01

    Solid-phase reactions of metal films deposited on 0.5-micron-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 C were investigated by MeV He-4 backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at temperatures exceeding 550 C for Ag, at those exceeding 400 C for Al, and at those exceeding 200 C for Au films. For Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

  16. 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.

  17. Sputtering of NbSi 2 and CoSi 2

    NASA Astrophysics Data System (ADS)

    Hamdi, A. M.; Affolter, K.; Nicolet, M.-A.

    1985-03-01

    Sputtering of niobium and cobalt disilicide films on oxidized Si substrates interposed with an amorphous Si layer has been studied by backscattering spectrometry (BS). Thin NbSi 2 (600 Å) and CoSi 2 (370 Å) films were sputtered by Xe ions at energies of 200 and 260 keV, respectively. The sputtering process was carried out either at room temperature (RT), or at elevated temperatures, placing the samples in the radiation enhanced diffusion regime. The sputtering yields of Si, Ssi, and that of the metals, SNb or SCo, have been calculated from BS spectra. The measured ratios of the sputtering yields for both suicides, {S si}/{S Nb} and {S si}/{S Co}, imply that preferential sputtering of Si with respect to the stoichiometrical composition of these suicides had occurred. {S si}/{S Nb} is found to be about 13 and showed little change with dose and temperature. {S si}/{S Co} increased with both temperature or dose from about 4.3 for a dose of {5 × 10 16}/{cm 2} at RT to about 7.2 for {1 × 10 17}/{cm 2} at elevated temperature. These ratios are in contrast to that reported for CrSi 2 at high temperatures (i.e. {S si}/{S Cr} = 65 ). Possible reasons are thought to be related to the high affinity of Si to oxygen contamination.

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

    PubMed

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

    2017-05-25

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

  19. Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures.

    PubMed

    Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro; Sopinskyy, Mykola

    2016-12-01

    The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si-SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si-SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree (ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

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

    PubMed Central

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

    2017-01-01

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

  1. 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.

  2. NbOsSi and TaOsSi - Two new superconducting ternary osmium silicides

    NASA Astrophysics Data System (ADS)

    Benndorf, Christopher; Heletta, Lukas; Heymann, Gunter; Huppertz, Hubert; Eckert, Hellmut; Pöttgen, Rainer

    2017-06-01

    The new equiatomic silicides NbOsSi and TaOsSi as well as ZrOsSi, TIrSi (T = Zr, Hf, Nb, Ta) and TPtSi (T = Nb, Ta) were prepared from the elements by arc-melting. These silicides crystallize with the orthorhombic TiNiSi type structure, space group Pnma. Irregularly shaped crystals of ZrOsSi, NbOsSi, TaOsSi, ZrIrSi and HfIrSi were separated from the annealed samples and investigated by single-crystal X-ray diffraction (a = 640.46(7), b = 404.07(5), c = 743.66(8) pm, wR2 = 0.0285, 390 F2 values, 20 variables for ZrOsSi; a = 629.78(6), b = 388.72(4), c = 727.48(7) pm, wR2 = 0.0350, 397 F2 values, 20 variables for NbOsSi, a = 626.80(6), b = 389.36(4), c = 726.22(7) pm, wR2 = 0.0501, 385 F2 values, 20 variables for TaOsSi, a = 653.48(8), b = 395.35(4), c = 739.19(8) pm, wR2 = 0.0427, 413 F2 values, 20 variables for ZrIrSi and a = 646.34(12), b = 393.57(7), c = 736.8(14) pm, wR2 = 0.0582, 371 F2 values, 20 variables for HfIrSi). The striking structural motifs in the new osmium compounds are three-dimensional [OsSi] networks (Os-Si: 240-251 pm) in which the osmium atoms have strongly distorted tetrahedral silicon coordination. High-pressure/high-temperature experiments (9.5 GPa/1520 K) on TaOsSi gave no hint for a structural phase transition. Temperature dependent measurements of the magnetic susceptibility and the electrical conductivity of NbOsSi and TaOsSi showed superconductivity below TC = 3.5 and 5.5 K, respectively. 29Si solid state MAS NMR investigations of the prepared silicides approved the structural models and showed a correlation between the observed 29Si resonance shifts and the electronegativity of the involved refractory metal.

  3. Silicon isotope fractionations in pure Si and Fe-Si systems and their geological implications

    NASA Astrophysics Data System (ADS)

    Zheng, X. Y.; Beard, B. L.; Reddy, T. R.; Roden, E. E.; Johnson, C.

    2016-12-01

    Amorphous Si or Si-bearing materials are ubiquitous in nature, and are likely precursors to various rock types, such as cherts and banded iron formations (BIFs). Si isotope exchange kinetics and fractionation factors between these materials and aqueous Si, however, are poorly constrained, preventing a mechanistic or quantitative understanding of geological δ30Si records. A series of laboratory experiments were conducted to provide better estimates on Si isotope exchange kinetics and fractionation factors. Equilibrium Si isotope fractionation factors between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aq) in artificial Archean seawater (AAS), determined by a three-isotope method with a 29Si tracer, are -2.3‰ where Fe2+ is absent from the solution, and -3.2‰ where Fe2+ is present in the solution[1]. Aqueous Fe2+ catalyzes Si isotope exchange, and causes larger Si isotope fractionation due to incorporation into the solid that may have changed Si bonding. In contrast, our preliminary results show that Δ30Sigel-aq between pure Si gel and aqueous Si at equilibrium is -0.13‰. Ongoing experiments are intended to approach the isotope equilibrium from multiple directions to resolve potential kinetic effects, and to explore temperature dependence. Nonetheless, the contrast in Δ30Sigel-aq between Fe-Si and pure Si systems highlights a significant impact of Fe on Si isotope fractionations. These results have important implications for Si isotopes in Precambrian cherts and BIFs, as well as in weathering systems in general. Silicon isotope fractionation was also studied in experiments that involved dissimilatory iron reduction of Fe(III)-Si gel by Desulfuromonas acetoxidans in AAS[2], and was found to become larger with progression of Fe reduction. A Δ30Sigel-aq of -3.5‰ was observed at 32% reduction of Fe3+. This result explains lower δ30Si values in magnetite-associated quartz that those in hematite-associated quartz in some BIFs. The large Si isotope fractionation

  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. 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.

  6. Improved efficiency Si-photonic attenuator.

    PubMed

    Zheng, D W; Smith, B T; Asghari, M

    2008-10-13

    A forward-biased p-i-n diode integrated with a ridge waveguide forms a basic Si attenuator building block. Disruptive power improvement was achieved through a recessed contact configuration by limiting the amount of Si volume for carrier recombination. A device model was established by using realistic surface recombination velocities instead of effective carrier lifetime concept to understand the device physics of the afore-mentioned Si attenuator.

  7. Light-emitting Si nanostructures formed by swift heavy ions in a-Si:H/SiO2 multilayer heterostructures

    NASA Astrophysics Data System (ADS)

    Cherkova, S. G.; Volodin, V. A.; Cherkov, A. G.; Antonenko, A. Kh; Kamaev, G. N.; Skuratov, V. A.

    2017-08-01

    Light-emitting nanoclusters were formed in Si/SiO2 multilayer structures irradiated with 167 MeV Xe ions to the doses of 1011-3  ×  1014 cm-2 and annealed in the forming-gas at 500 °C and in nitrogen at 800-1100 °C, 30 min. The thicknesses were ~4 nm or ~7-8 for the Si, and ~10 nm for the SiO2 layers. The structures were studied using photoluminescence (PL), Raman spectroscopy, and the cross-sectional high resolution transmission electron microscopy (HRTEM). As-irradiated samples showed the PL, correlating with the growth of the ion doses. HRTEM found the layers to be partly disintegrated. The thickness of the amorphous Si layer was crucial. For 4 nm thick Si layers the PL was peaking at ~490 nm, and quenched by the annealing. It was ascribed to the structural imperfections. For the thicker Si layers the PL was peaking at ~600 nm and was attributed to the Si-rich nanoclusters in silicon oxide. The annealing increases the PL intensity and shifts the band to ~790 nm, typical of Si nanocrystals. Its intensity was proportional to the dose. Raman spectra confirmed the nanocrystals formation. All the results obtained evidence the material melting in the tracks for 10-11-10-10 s providing thereby fast diffusivities of the atoms. The thicker Si layers provide more excess Si to create the nanoclusters via a molten state diffusion.

  8. Ge/SiGe for silicon photonics

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yasuhiko

    2017-01-01

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

  9. 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.

  10. 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.

  11. 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.

  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. 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

  14. Contact formation in SiC devices

    NASA Astrophysics Data System (ADS)

    Pécz, B.

    2001-12-01

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

  15. 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.

  16. 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.

  17. 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)

  18. Lattice-matching of Si grown on 6H-SiC(000-1) C-face

    NASA Astrophysics Data System (ADS)

    Li, L. B.; Chen, Z. M.; Xie, L. F.; Yang, C.

    2014-01-01

    Si films with <111> preferred orientation have been prepared on 6H-SiC(000-1) C-face. HRTEM and SAED results indicate that the Si film has epitaxial connection with the 6H-SiC substrate and the parallel-plane relationship of the Si/6H-SiC heterostructure is (111)Si//(000-1)6H-SiC. Using fast Fourier transform and Fourier mask filtering technique, misfit dislocations are clearly observed at the Si/6H-SiC interface, which accommodate the most of lattice mismatch strain. Every four Si (111) lattice planes are registered with five 6H-SiC(000-1) lattice planes along the interface. Based on the 4:5 lattice matching mode, the lattice structure of the Si/6H-SiC interface and its stability were energetically investigated by molecular dynamics simulations. When the Si films grow preferentially along <111> orientation on 6H-SiC(000-1) C-face, the misfit strain in Si layer significantly reduces due to the relaxation of C atoms in SiC layer near the Si/6H-SiC interface, and thus the Si/6H-SiC heterostructure has a stable interface with a small interface formation energy of -14.24 eV.

  19. 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.

  20. 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.

  1. Characterization of SiO2/SiNx gate insulators for graphene based nanoelectromechanical systems

    NASA Astrophysics Data System (ADS)

    Tóvári, E.; Csontos, M.; Kriváchy, T.; Fürjes, P.; Csonka, S.

    2014-09-01

    The structural and magnetotransport characterization of graphene nanodevices exfoliated onto Si/SiO2/SiNx heterostructures are presented. Improved visibility of the deposited flakes is achieved by optimal tuning of the dielectric film thicknesses. The conductance of single layer graphene Hall-bar nanostructures utilizing SiO2/SiNx gate dielectrics were characterized in the quantum Hall regime. Our results highlight that, while exhibiting better mechanical and chemical stability, the effect of non-stoichiometric SiNx on the charge carrier mobility of graphene is comparable to that of SiO2, demonstrating the merits of SiNx as an ideal material platform for graphene based nanoelectromechanical applications.

  2. 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.

  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. 29 Si nuclear magnetic resonance study of URu 2 Si 2 under pressure

    SciTech Connect

    Shirer, K. R.; Dioguardi, A. P.; Bush, B. T.; Crocker, J.; Lin, C. H.; Klavins, P.; Cooley, J. C.; Maple, M. B.; Chang, K. B.; Poeppelmeier, K. R.; Curro, N. J.

    2016-01-01

    Wereport 29Si nuclearmagneticresonancemeasurementsofsinglecrystalsandalignedpowdersof URu2Si2 under pressureinthehiddenorderandparamagneticphases.We find thattheKnightshift decreases withappliedpressure,consistentwithpreviousmeasurementsofthestaticmagneticsus- ceptibility.Previousmeasurementsofthespinlatticerelaxationtimerevealedapartialsuppressionof the densityofstatesbelow30K.Thissuppressionpersistsunderpressure,andtheonsettemperatureis mildly enhanced.

  5. 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.

  6. Characterization of SiC-SiC composites for accident tolerant fuel cladding

    NASA Astrophysics Data System (ADS)

    Deck, C. P.; Jacobsen, G. M.; Sheeder, J.; Gutierrez, O.; Zhang, J.; Stone, J.; Khalifa, H. E.; Back, C. A.

    2015-11-01

    Silicon carbide (SiC) is being investigated for accident tolerant fuel cladding applications due to its high temperature strength, exceptional stability under irradiation, and reduced oxidation compared to Zircaloy under accident conditions. An engineered cladding design combining monolithic SiC and SiC-SiC composite layers could offer a tough, hermetic structure to provide improved performance and safety, with a failure rate comparable to current Zircaloy cladding. Modeling and design efforts require a thorough understanding of the properties and structure of SiC-based cladding. Furthermore, both fabrication and characterization of long, thin-walled SiC-SiC tubes to meet application requirements are challenging. In this work, mechanical and thermal properties of unirradiated, as-fabricated SiC-based cladding structures were measured, and permeability and dimensional control were assessed. In order to account for the tubular geometry of the cladding designs, development and modification of several characterization methods were required.

  7. 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+.

  8. 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.

  9. 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.

  10. 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.

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

    PubMed

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

    2015-11-25

    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/cm(2) 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. Photoluminescence from 20 MeV electron beam irradiated homogeneous SiOx and composite Si-SiOx films

    NASA Astrophysics Data System (ADS)

    Nesheva, D.; Šćepanović, M.; Grujić-Brojčin, M.; Dzhurkov, V.; Kaschieva, S.; Bineva, I.; Dmitriev, S. N.; Popović, Z. V.

    2016-10-01

    The effect of 20 MeV electron irradiation on the room temperature photoluminescence from homogeneous SiOx and composite Si-SiOx films, containing amorphous or crystalline Si nanoparticles, is studied. Layers with x = 1.5 and 1.7 and thickness of 200 nm were deposited on crystalline silicon substrates by thermal evaporation of SiO in vacuum. Film annealing in an inert atmosphere at 700 oC or 1000 oC for 60 min was applied to grow amorphous or crystalline silicon nanoparticles, respectively, in a SiOx matrix. Samples from all types of films were irradiated with 20 MeV electrons at close to room temperature and a fluence of 2.4x1014 el.cm-2. Photoluminescence was measured under excitation with the 488 nm line of an Ar+ laser. The electron irradiation causes a decrease of the integrated photoluminescence intensity in composite samples with initial x = 1.7 containing amorphous or crystalline nanoparticles and x = 1.5 samples with Si nanocrystals. The electron irradiation of x = 1.5 samples with amorphous nanoparticles slightly increases the photoluminescence intensity. The obtained results are discussed in terms of electron beam induced phase separation and Si nanoparticle size increase.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Further Developments in Modeling Creep Effects Within Structural SiC/SiC Components

    NASA Technical Reports Server (NTRS)

    Lang, Jerry; DiCarlo, James A.

    2008-01-01

    Anticipating the implementation of advanced SiC/SiC composites into turbine section components of future aero-propulsion engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly manipulate constituent materials and processes in order to minimize these effects. Focusing on SiC/SiC components experiencing through-thickness stress gradients (e.g., airfoil leading edge), prior NASA creep modeling studies showed that detrimental residual stress effects can develop globally within the component walls which can increase the risk of matrix cracking. These studies assumed that the SiC/SiC composites behaved as isotropic viscoelastic continuum materials with creep behavior that was linear and symmetric with stress and that the creep parameters could be obtained from creep data as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The present study expands on those prior efforts by including constituent behavior with non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Planetary and meteoritic Mg/Si and δ30 Si variations inherited from solar nebula chemistry

    NASA Astrophysics Data System (ADS)

    Dauphas, Nicolas; Poitrasson, Franck; Burkhardt, Christoph; Kobayashi, Hiroshi; Kurosawa, Kosuke

    2015-10-01

    The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at ∼1370 K in the solar nebula could have produced the observed Si isotope variations. Nebular fractionation of forsterite should be accompanied by correlated variations between the Si isotopic composition and Mg/Si ratio following a slope of ∼1, which is observed in meteorites. Consideration of this nebular process leads to a revised Si concentration in the Earth's core of 3.6 (+ 6.0 / - 3.6) wt% and provides estimates of Mg/Si ratios of bulk planetary bodies.

  10. 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.

  11. Boron distributions in individual core-shell Ge/Si and Si/Ge heterostructured nanowires.

    PubMed

    Han, Bin; Shimizu, Yasuo; Wipakorn, Jevasuwan; Nishibe, Kotaro; Tu, Yuan; Inoue, Koji; Fukata, Naoki; Nagai, Yasuyoshi

    2016-12-01

    Ge/Si and Si/Ge core-shell nanowires (NWs) have substantial potential for application in many kinds of devices. Because impurity distributions in Ge/Si and Si/Ge core-shell NWs strongly affect their electrical properties, which in turn affect device performance, this issue needs urgent attention. Here we report an atom probe tomographic study of the distribution of boron (B), one of the most important impurities, in two kinds of NWs. B atoms were doped into the Si regions of Ge/Si and Si/Ge core-shell NWs. It was found that the B atoms were randomly distributed in the Si shell of the Ge/Si core-shell NWs. In the Si/Ge core-shell NWs, on the other hand, the B distributions depended on the growth temperature and the B2H6 flux. With a higher growth temperature and an increased B2H6 flux, the B atoms piled up in the outer region of the Si core. However, the B atoms were observed to be randomly distributed in the Si core after decreasing both the growth temperature and the B2H6 flux.

  12. 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.

  13. Enhancement in thermoelectric performance of SiGe nanoalloys dispersed with SiC nanoparticles.

    PubMed

    Bathula, Sivaiah; Jayasimhadri, M; Gahtori, Bhasker; Kumar, Anil; Srivastava, A K; Dhar, Ajay

    2017-09-08

    SiGe is one of the most widely used thermoelectric materials for radioisotope thermoelectric generator applications for harnessing waste-heat at high temperatures. In the present study, we report a simple experimental strategy for enhancing the thermoelectric and mechanical properties of n-type SiGe nanoalloys by dispersing SiC nanoparticles in a SiGe nanoalloy matrix. This strategy yielded a high value of figure-of-merit (ZT) of ∼1.7 at 900 °C in the SiGe/SiC nanocomposite, which is nearly twice that reported for its pristine bulk counterpart and ∼15% higher than that of pristine SiGe nanoalloys. This significant enhancement in the ZT primarily originates from a reduction in the lattice thermal conductivity, owing to a high density of nano-scale interfaces, lattice-scale modulations and mass fluctuations, which lead to extensive scattering of heat-carrying phonons. The dispersion of SiC nanoparticles also significantly enhances the mechanical properties of the resulting SiGe/SiC nanocomposite, including fracture toughness and hardness. The enhancement in the thermoelectric and mechanical properties of the SiGe/SiC nanocomposites has been correlated with their microstructural features, elucidated employing X-ray diffraction, and scanning and transmission electron microscopy.

  14. Trapping of BTX compounds by SiO2, Ag-SiO2, Cu-SiO2, and Fe-SiO2 porous substrates.

    PubMed

    Hernández, M A; Asomoza, M; Rojas, F; Solís, S; Portillo, R; Salgado, M A; Felipe, C; Portillo, Y; Hernández, F

    2010-11-01

    Adsorption isotherms of BTX aromatic hydrocarbons (benzene, toluene, and p-xylene) on pristine (SiO2) and metal-doped (Ag-SiO2, Cu-SiO2 and Fe-SiO2) mesoporous and microporous substrates were measured and interpreted. These adsorbents were synthesized by the sol-gel procedure and their BTX sorption isotherms were obtained by the gas chromatographic technique (GC) at several temperatures in the range 423-593 K. The uptake amount of these hydrocarbon adsorptives on SiO2, Ag-SiO2, Cu-SiO2 and Fe-SiO2 mesoporous and microporous substrates was temperature-dependent. Additionally, the interaction of BTX molecules with the pore walls was evaluated by means of the corresponding isosteric heat of adsorption (qst), which was found to follow the next increasing sequence: qst (benzene)SiO2 structure leads to an increased adsorbed amount of BTX molecules on the solid surface if compared with the Cu-SiO2 adsorbent. The adsorption of benzene, but not of toluene and p-xylene, molecules on pristine SiO2 is facilitated by the pore size of this substrate since this is the highest of all materials. Copyright © 2010 Elsevier Ltd. All rights reserved.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. Monolithic integration of Si-MOSFET and GaN-LED using Si/SiO2/GaN-LED wafer

    NASA Astrophysics Data System (ADS)

    Tsuchiyama, Kazuaki; Yamane, Keisuke; Utsunomiya, Shu; Sekiguchi, Hiroto; Okada, Hiroshi; Wakahara, Akihiro

    2016-10-01

    In this report, we present a monolithic integration method for a Si-MOSFET and a GaN-LED onto a Si/SiO2/GaN-LED wafer as an elemental technology for monolithic optoelectronic integrated circuits. To enable a Si-MOSFET device process, we investigated the thermal tolerance of a thin top-Si and GaN-LED layer on a Si/SiO2/GaN-LED wafer. The high thermal tolerance of the Si/SiO2/GaN-LED structure allowed for the monolithic integration of a Si n-MOSFET and a GaN-µLED without degrading the performance of either device. A GaN-µLED driver circuit was fabricated using a Si n-MOSFET and a µLED of 30 × 30 µm2, with the modulation bandwidth of the circuit estimated to be over 10 MHz.

  3. 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.

  4. Inherent paramagnetic defects in layered nanocrystalline Si/SiO 2 superstructures

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

    With the view to fully disclose the nature of occurring paramagnetic defects, a detailed electron spin resonance (ESR) study has been carried out on entities comprised of regular arrays of Si nanoparticles (np's) (size ∼2 nm) embedded in an SiO 2 matrix, obtained by the SiO/SiO 2 superlattice method. The approach encompasses high-sensitivity first- and second-harmonic low-temperature X, K and Q-band ESR in combination with computer simulations. This enabled disentanglement of the common Si dangling-bond (DB) signal, observed in the as grown state as being composed solely of Si/SiO 2 interface-specific powder patterns of P b(0) and P b1 defects, indicating that the majority, if not all, of the np's are crystalline. The inferred densities are in the range of standard values obtained for thermal SiO 2 grown on Si and remain unchanged over different (V)UV irradiation treatments. Yet, upon (V)UV irradiation, SiO 2-specific defects ( Eγ‧ and EX) were activated, in numbers demonstrating standard SiO 2 quality. Only ∼71% of the Si nanocrystals (nc's) house a P b-type center, indicating the structure to be comprised of two subsystems, which may hence reflect in different defect-sensitive properties, such as, e.g., photoluminescence. Relying on the known properties of P b(0) and P b1 defects in standard microscopic Si/SiO 2, the data would comply with Si nc's, in average, predominantly bordered by (1 1 1) and (1 0 0) facets.

  5. 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.

  6. Effects of interface bonding and defects on boron diffusion at Si/SiO2 interface

    NASA Astrophysics Data System (ADS)

    Kim, Geun-Myeong; Oh, Young Jun; Chang, K. J.

    2013-12-01

    We perform first-principles density functional calculations to find the migration pathway and barrier for B diffusion at the Si/SiO2 interface. For various interface models, in which crystalline α-quartz or amorphous silica (a-SiO2) is placed on Si, we examine stable and metastable configurations of B-related defects which play a role in B diffusion. While a substitutional B alone is immobile in Si, it tends to diffuse to the interface via an interstitialcy mechanism in the presence of a self-interstitial and then changes into an interstitial B in oxide via a kick-out mechanism, leaving the self-interstitial at the interface. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, an interstitial B prefers to intervene between the interface Si and bridging O atoms and subsequently diffuses through the hollow space or along the network of the Si-O-Si bonds in oxide. The overall migration barriers are calculated to be 2.02-2.12 eV at the Si/α-quartz interface, while they lie in the range of 2.04 ± 0.44 eV at the Si/a-SiO2 interface, similar to that in α-quartz. The migration pathway and barrier are not significantly affected by interface defects such as suboxide bond and O protrusion, while dangling bonds in the suboxide region can increase the migration barrier by about 1.5 eV. The result that the interface generally does not hinder the B diffusion from Si to SiO2 assists in understanding the underlying mechanism for B segregation which commonly occurs at the Si/SiO2 interface.

  7. 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.

  8. Using Si in floriculture fertility programs

    USDA-ARS?s Scientific Manuscript database

    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...

  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. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

    2017-06-01

    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.

  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. 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.

  17. 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.

  18. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  20. 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.

  1. Minute SiGe quantum dots on Si(001) by a kinetic 3D island mode.

    PubMed

    Koch, R; Wedler, G; Schulz, J J; Wassermann, B

    2001-09-24

    We investigated the initial growth stages of Si(x)Ge(1-x)/Si(001) by real time stress measurements and in situ scanning tunneling microscopy at deposition temperatures, where intermixing effects are still minute (< or =900 K). Whereas Ge/Si(001) is a well known Stranski-Krastanow system, the growth of SiGe alloy films switches to a 3D island mode at Si content above 20%. The obtained islands are small (a few nanometers), are uniform in shape, and exhibit a narrow size distribution, making them promising candidates for future quantum dot devices.

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

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  3. Delivery materials for siRNA therapeutics

    NASA Astrophysics Data System (ADS)

    Kanasty, Rosemary; Dorkin, Joseph Robert; Vegas, Arturo; Anderson, Daniel

    2013-11-01

    RNA interference (RNAi) has broad potential as a therapeutic to reversibly silence any gene. To achieve the clinical potential of RNAi, delivery materials are required to transport short interfering RNA (siRNA) to the site of action in the cells of target tissues. This Review provides an introduction to the biological challenges that siRNA delivery materials aim to overcome, as well as a discussion of the way that the most effective and clinically advanced classes of siRNA delivery systems, including lipid nanoparticles and siRNA conjugates, are designed to surmount these challenges. The systems that we discuss are diverse in their approaches to the delivery problem, and provide valuable insight to guide the design of future siRNA delivery materials.

  4. 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.

  5. 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

    2017-08-01

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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Uniform SiGe/Si quantum well nanorod and nanodot arrays fabricated using nanosphere lithography

    PubMed Central

    2013-01-01

    This study fabricates the optically active uniform SiGe/Si multiple quantum well (MQW) nanorod and nanodot arrays from the Si0.4Ge0.6/Si MQWs using nanosphere lithography (NSL) combined with the reactive ion etching (RIE) process. Compared to the as-grown sample, we observe an obvious blueshift in photoluminescence (PL) spectra for the SiGe/Si MQW nanorod and nanodot arrays, which can be attributed to the transition of PL emission from the upper multiple quantum dot-like SiGe layers to the lower MQWs. A possible mechanism associated with carrier localization is also proposed for the PL enhancement. In addition, the SiGe/Si MQW nanorod arrays are shown to exhibit excellent antireflective characteristics over a wide wavelength range. These results indicate that SiGe/Si MQW nanorod arrays fabricated using NSL combined with RIE would be potentially useful as an optoelectronic material operating in the telecommunication range. PMID:23924368

  11. 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.

  12. 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.

  13. Si Purification by Removal of Entrapped Al during Electromagnetic Solidification Refining of Si-Al Alloy

    NASA Astrophysics Data System (ADS)

    Yu, Wenzhou; Ma, Wenhui; Zheng, Zhong; Lei, Yun; Jiang, Weiyan; Li, Jie

    2017-10-01

    To investigate the effect of the removal of entrapped Al on Si purity during Al-Si electromagnetic solidification refining, the formation mechanism and removal principle of entrapped Al in primary Si were studied. The results showed that the agglomeration and irregular shape of primary Si crystals during electromagnetic solidification were the main reasons for the formation of entrapped Al; a higher initial Si content in an Al-Si alloy may result in higher amounts of entrapped Al. The entrapped Al can be effectively removed by first grinding the primary Si to powder particles of 20 μm and then leaching the particles with acid, which can simultaneously remove other impurities concentrated in the entrapped Al such as Fe, Ca, Ti, and B. Hence, it is proposed that the combination of electromagnetic solidification, acid leaching, and vacuum directional solidification could be used to obtain solar-grade silicon.

  14. 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.

  15. 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.

  16. Si Purification by Removal of Entrapped Al during Electromagnetic Solidification Refining of Si-Al Alloy

    NASA Astrophysics Data System (ADS)

    Yu, Wenzhou; Ma, Wenhui; Zheng, Zhong; Lei, Yun; Jiang, Weiyan; Li, Jie

    2017-06-01

    To investigate the effect of the removal of entrapped Al on Si purity during Al-Si electromagnetic solidification refining, the formation mechanism and removal principle of entrapped Al in primary Si were studied. The results showed that the agglomeration and irregular shape of primary Si crystals during electromagnetic solidification were the main reasons for the formation of entrapped Al; a higher initial Si content in an Al-Si alloy may result in higher amounts of entrapped Al. The entrapped Al can be effectively removed by first grinding the primary Si to powder particles of 20 μm and then leaching the particles with acid, which can simultaneously remove other impurities concentrated in the entrapped Al such as Fe, Ca, Ti, and B. Hence, it is proposed that the combination of electromagnetic solidification, acid leaching, and vacuum directional solidification could be used to obtain solar-grade silicon.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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).

  5. Modeling Creep Effects within SiC/SiC Turbine Components

    NASA Technical Reports Server (NTRS)

    DiCarlo, J. A.; Lang, J.

    2008-01-01

    Anticipating the implementation of advanced SiC/SiC ceramic composites into the hot section components of future gas turbine engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly select and manipulate constituent materials, processes, and geometries in order to minimize these effects. In initial studies aimed at SiC/SiC components experiencing through-thickness stress gradients, creep models were developed that allowed an understanding of detrimental residual stress effects that can develop globally within the component walls. It was assumed that the SiC/SiC composites behaved as isotropic visco-elastic materials with temperature-dependent creep behavior as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The creep models and their key results are discussed assuming state-of-the-art SiC/SiC materials within a simple cylindrical thin-walled tubular structure, which is currently being employed to model creep-related effects for turbine airfoil leading edges subjected to through-thickness thermal stress gradients. Improvements in the creep models are also presented which focus on constituent behavior with more realistic non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

  6. 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. PMID:28347028

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. Effect of the SiCl4 Flow Rate on SiBN Deposition Kinetics in SiCl4-BCl3-NH3-H2-Ar Environment

    PubMed Central

    Li, Jianping; Qin, Hailong; Liu, Yongsheng; Ye, Fang; Li, Zan; Cheng, Laifei; Zhang, Litong

    2017-01-01

    To improve the thermal and mechanical stability of SiCf/SiC or C/SiC composites with SiBN interphase, SiBN coating was deposited by low pressure chemical vapor deposition (LPCVD) using SiCl4-BCl3-NH3-H2-Ar gas system. The effect of the SiCl4 flow rate on deposition kinetics was investigated. Results show that deposition rate increases at first and then decreases with the increase of the SiCl4 flow rate. The surface of the coating is a uniform cauliflower-like structure at the SiCl4 flow rate of 10 mL/min and 20 mL/min. The surface is covered with small spherical particles when the flow rate is 30 mL/min. The coatings deposited at various SiCl4 flow rates are all X-ray amorphous and contain Si, B, N, and O elements. The main bonding states are B-N, Si-N, and N-O. B element and B-N bonding decrease with the increase of SiCl4 flow rate, while Si element and Si-N bonding increase. The main deposition mechanism refers to two parallel reactions of BCl3+NH3 and SiCl4+NH3. The deposition process is mainly controlled by the reaction of BCl3+NH3. PMID:28772986

  12. Luminescence properties of Si-capped β-FeSi{sub 2} nanodots epitaxially grown on Si(001) and (111) substrates

    SciTech Connect

    Amari, Shogo; Ichikawa, Masakazu; Nakamura, Yoshiaki

    2014-02-28

    We studied the luminescence properties of Si-capped β-FeSi{sub 2} nanodots (NDs) epitaxially grown on Si substrates by using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Codepositing Fe and Si on ultrathin SiO{sub 2} films induced the self-assembly of epitaxial β-FeSi{sub 2} NDs. The PL spectra of the Si/β-FeSi{sub 2} NDs/Si structure depended on the crystal orientation of the Si substrate. These structures exhibited a broad PL peak near 0.8 eV on both Si(001) and (111) substrates. The PL intensity depended on the shape of the β-FeSi{sub 2} NDs. For the flat NDs, which exhibited higher PL intensity, we also recorded EL spectra. We explained the luminescence properties of these structures by the presence of nanostructured Si offering radiative electronic states in the Si cap layers, generated by nano-stressors for upper Si layer: the strain-relaxed β-FeSi{sub 2} NDs.

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

    PubMed

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

    2017-09-18

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

  14. 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.

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

    PubMed

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

    2016-04-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  17. 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

  18. Si microchannel plates for image intensification

    NASA Astrophysics Data System (ADS)

    Smith, Arlynn W.; Beetz, Charles P., Jr.; Boerstler, Robert W.; Winn, D. R.; Steinbeck, John W.

    2000-11-01

    Glass microchannel plates (MCPs) have been in use by numerous manufactuers in a variety of electron multiplication applications. Conventional fabrication of MCPs follow the lines of glass drawing and etching technology. Core and clad glass are drawn together, stacked, drawn again, and finally stacked in the desired pattern. The soluble core is removed with wet chemical processing. These techniques are beginning to run into their feasible limits in terms of channel size, open area ratio, uniformity, and material issues. A strong desire exists to fabricate MCPs with accepted lithographic techniques using Si as the base material to improve uniformity and throughput. Open area ratios of as high as 95% have been achieved using lithography. However, attempts to meet other channel plate characteristics met with little success due to thermal runaway or arcing during operation, high voltage is required for electron gain. Processing improvements have lead to the complete oxidation of the Si matrix eliminating the conducting Si in the channel walls of the Si MCPs allowing high voltages to be supported. Complete oxidation of the Si to silica allows processing temperatures high than conventional glass matrices can withstand. This fact allows for high temperature growth of conductive and secondary emissive materials on the channel walls of the structure. Si MCPs with gain have now been fabricated and tested with voltages comparable to conventional glass MCPs. Channel plate characteristics such as operating voltage, strip current, and gain for Si MCPs will be presented and compared to glass MCPs.

  19. 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.

  20. 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.

  1. 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.

  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. 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.

  4. 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.

  5. 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.

  6. Interstitial Functionalization in elemental Si

    NASA Astrophysics Data System (ADS)

    Kiefer, Boris; Fohtung, Edwin

    Societies in the 21st century will face many challenges. Materials science and materials design will be essential to address and master some if not all of these challenges. Semiconductors are among the most important technological material classes. Properties such as electrical transport are strongly affected by defects and a central goal continues to be the reduction of defect densities as much as possible in these compounds. Here we present results of interstitial Fe doping in elemental Si using first-principles DFT calculations. The preliminary results show that Fe will only occupy octahedral interstitial sites. The analysis of the electronic structure shows that the compounds are ferromagnetic and that a bandgap opens as interstitial Fe concentrations decrease, with a possible intermittent semi-metallic phase. The formation energy for interstitial Fe is unfavorable, as expected, by ~1.5 eV but becomes favorable as the chemical potential of Fe increases. Therefore, we expect that biasing the system with an external electrical field will lead to the formation of these materials. Thus, our results show that interstitial defects can be beneficial for the design of functionalities that differ significantly from those of the host material.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. SiGe quantum cascade structures for light emitting devices

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Li, X. B.; Neave, J. H.; Norris, D. J.; Cullis, A. G.; Kelsall, R. W.; Lynch, S.; Towsend, P.; Paul, D. J.; Fewster, P. F.

    2005-05-01

    The realisation of III-V quantum cascade lasers has initiated a strong interest in developing a Si/SiGe-based quantum cascade laser over the last 3 years. Most efforts were focused on the growth of strain-balanced Si/SiGe superlattices on strain-relaxed SiGe virtual substrates. This paper discusses the progress so far and addresses some of the material issues related to the epitaxy of Si/SiGe quantum cascade structures, including strain-stress balance and production of strain-relaxed SiGe virtual substrates.

  14. Completely CMOS compatible SiN-waveguide-based fiber coupling structure for Si wire waveguides.

    PubMed

    Maegami, Yuriko; Okano, Makoto; Cong, Guangwei; Ohno, Morifumi; Yamada, Koji

    2016-07-25

    For Si wire waveguides, we designed a highly efficient fiber coupling structure consisting of a Si inverted taper waveguide and a CMOS-compatible thin SiN waveguide with an SiO2 spacer inserted between them. By using a small SiN waveguide with a 310 nm-square core, the optical field can be expanded to correspond to a fiber with a 4.0-μm mode field diameter. A coupled waveguide system with the SiN waveguide and Si taper waveguide can provide low-loss and low-polarization-dependent mode conversion. Both losses in fiber-SiN waveguide coupling and SiN-Si waveguide mode conversion are no more than 1 dB in a wide wavelength bandwidth from 1.36 μm to 1.65 μm. Through a detailed analysis of the effective refractive indices in the coupled waveguide system, we can understand mode conversion accurately and also derive guidelines for reducing the polarization dependence and for shortening device length.

  15. The roles of Eu during the growth of eutectic Si in Al-Si alloys

    PubMed Central

    Li, Jiehua; Hage, Fredrik; Wiessner, Manfred; Romaner, Lorenz; Scheiber, Daniel; Sartory, Bernhard; Ramasse, Quentin; Schumacher, Peter

    2015-01-01

    Controlling the growth of eutectic Si and thereby modifying the eutectic Si from flake-like to fibrous is a key factor in improving the properties of Al-Si alloys. To date, it is generally accepted that the impurity-induced twinning (IIT) mechanism and the twin plane re-entrant edge (TPRE) mechanism as well as poisoning of the TPRE mechanism are valid under certain conditions. However, IIT, TPRE or poisoning of the TPRE mechanism cannot be used to interpret all observations. Here, we report an atomic-scale experimental and theoretical investigation on the roles of Eu during the growth of eutectic Si in Al-Si alloys. Both experimental and theoretical investigations reveal three different roles: (i) the adsorption at the intersection of Si facets, inducing IIT mechanism, (ii) the adsorption at the twin plane re-entrant edge, inducing TPRE mechanism or poisoning of the TPRE mechanism, and (iii) the segregation ahead of the growing Si twins, inducing a solute entrainment within eutectic Si. This investigation not only demonstrates a direct experimental support to the well-accepted poisoning of the TPRE and IIT mechanisms, but also provides a full picture about the roles of Eu atoms during the growth of eutectic Si, including the solute entrainment within eutectic Si. PMID:26328541

  16. The roles of Eu during the growth of eutectic Si in Al-Si alloys.

    PubMed

    Li, Jiehua; Hage, Fredrik; Wiessner, Manfred; Romaner, Lorenz; Scheiber, Daniel; Sartory, Bernhard; Ramasse, Quentin; Schumacher, Peter

    2015-09-02

    Controlling the growth of eutectic Si and thereby modifying the eutectic Si from flake-like to fibrous is a key factor in improving the properties of Al-Si alloys. To date, it is generally accepted that the impurity-induced twinning (IIT) mechanism and the twin plane re-entrant edge (TPRE) mechanism as well as poisoning of the TPRE mechanism are valid under certain conditions. However, IIT, TPRE or poisoning of the TPRE mechanism cannot be used to interpret all observations. Here, we report an atomic-scale experimental and theoretical investigation on the roles of Eu during the growth of eutectic Si in Al-Si alloys. Both experimental and theoretical investigations reveal three different roles: (i) the adsorption at the intersection of Si facets, inducing IIT mechanism, (ii) the adsorption at the twin plane re-entrant edge, inducing TPRE mechanism or poisoning of the TPRE mechanism, and (iii) the segregation ahead of the growing Si twins, inducing a solute entrainment within eutectic Si. This investigation not only demonstrates a direct experimental support to the well-accepted poisoning of the TPRE and IIT mechanisms, but also provides a full picture about the roles of Eu atoms during the growth of eutectic Si, including the solute entrainment within eutectic Si.

  17. Improved resistive switching characteristics in Ni/SiNx/p++-Si devices by tuning x

    NASA Astrophysics Data System (ADS)

    Kim, Sungjun; Chang, Yao-Feng; Kim, Min-Hwi; Park, Byung-Gook

    2017-07-01

    This letter studies the effect of the negative-set on the resistive switching performances of CMOS-compatible Ni/SiNx/p++-Si resistive memory devices by simply tuning x. A Ni/SiN1.07/p++-Si device showed lower power switching (20 μW) and better endurance cycles (103) compared to a Ni/SiN0.82/p++-Si device because of the improved negative set behavior and initially lower set and reset currents. In addition, we achieved fast switching speed for set (200 ns) and reset (100 ns) processes in the Ni/SiN1.07/p++-Si device. For the Ni/SiN1.07/p++-Si device, fine adjustment of resistance values is attainable by varying the pulse amplitude and width due to the gradual reset switching characteristics. The barrier-height-dependent conduction model is proposed to explain the change in the current level with the x value.

  18. Simulation of bipolar/MOSFET hybrid mode transistor with Si/GeSi heterojunction base

    NASA Astrophysics Data System (ADS)

    Guo, Wei-Lian; Niu, Ping-Juan; Li, Xiao-Yun; Mao, Lu-Hong

    2005-02-01

    Bipolar/MOSFET hybrid mode lateral transistor is a transistor in which both bipolar and MOSFET currents flow simultaneously. Because of (1) Good compatibility with CMOS technology; (2) Larger current driving capability and transconductance than MOSFET. So, it is suitable to be taken as a bipolar device in BiCMOS element. In this paper, the Si/SiGe heterostructure, under the gate, is introduced into the conventional bipolar/MOSFET hybrid mode transistor. So a hybrid mode transistor with a lateral n+-Si/p-SiGe/n+-Si structure parallel in base is formed, in which the heterostructure of E-B junction n+-Si/p-SiGe has a high injection electron current from E to B region and a low injection hole current from B to E region (result in by higher barrier for hole), then the total injection efficiency will increase. When this effect becomes a main mechanism than that of the barrier lowering in the surface depletion layer, the characteristics of the device will be dependent on the parameters of SiGe alloy, such as the mole number of Germanium etc. The device simulation of Si/SiGe heterojunction base hybrid mode transistor has been carried out by MEDICI program. The simulation results show that IC and hFE increase with Mole number of Ge increasing and WB decreasing, then the current gain and current capability are improved than that of conventional bipolar/MOSFET hybrid Mode transistor.

  19. Comparison of Schottky barrier heights of CoSi2 formed from evaporated or crystalline Si

    NASA Astrophysics Data System (ADS)

    Lien, C.-D.; Finetti, M.; Nicolet, M.-A.

    1984-09-01

    Three kinds of samples were used to form Co suicides by thermal annealing: firstly, a Co film of about 370 Å thick, evaporated on a (100) single crystal Si (Si c /Co); secondly, an evaporated boron-containing Si (Si e (B)) layer on the top of the first sample (Si c /Co/Si e (B)). The last sample is in the Co film of the first sample we deposited a Sie(B) layer (Si c /Co/Si e (B)/Co). A laterally uniform CoSi2 layer can be formed from the second and the third samples by annealing at 450 °C. In the first sample, the CoSi2 can be formed only at temperatures above 500 °C and the disilicide is laterally less uniform than in the second and third samples. The Schottky barrier heights of the three samples derived from the forward and reverse I V characteristics show that the barrier height is 0.01 0.02eV higher in the uniform case than in the nonuniform case.

  20. Low cost wavelength filter of SiGe photodetector with a-Si:H capped layer

    NASA Astrophysics Data System (ADS)

    Hwang, J. D.; Chang, W. T.; Chen, Y. H.; Hseih, K. H.; Chen, P. S.; Liu, J. C.

    2006-10-01

    The strained Si 0.8Ge 0.2 film has been prepared onto Si substrate by using an ultrahigh-vacuum chemical vapor deposition system. A low cost wavelength filter of photodetector has been demonstrated for the first time. This filter was simply carried out by just inserting a 60 nm thick a-Si:H capped layer onto Si 0.8Ge 0.2 thin film. The room-temperature photoluminescence shows that the sample with Si 0.8Ge 0.2 layer has a tendency to shift wavelength into longer regime than that of Si substrate. The full width at half maximum (FWHM) was 185 nm for Si 0.8Ge 0.2 photodetector without a-Si:H capped. By inserting a 60 nm thick a-Si:H capped layer, the FWHM was narrowed into 97 nm. This demonstrates that the a-Si:H capped layer has an ability acted as wavelength filter in our study.

  1. The Degradation Behavior of SiCf/SiO2 Composites in High-Temperature Environment

    NASA Astrophysics Data System (ADS)

    Yang, Xiang; Cao, Feng; Qing, Wang; Peng, Zhi-hang; Wang, Yi

    2017-08-01

    SiCf/SiO2 composites had been fabricated efficiently by Sol-Gel method. The oxidation behavior, thermal shock property and ablation behavior of SiCf/SiO2 composites was investigated. SiCf/SiO2 composites showed higher oxidation resistance in oxidation atmosphere, the flexural strength retention ratio was larger than 90.00%. After 1300 °C thermal shock, the mass retention ratio was 97.00%, and the flexural strength retention ratio was 92.60%, while after 1500 °C thermal shock, the mass retention ratio was 95.37%, and the flexural strength retention ratio was 83.34%. After 15 s ablation, the mass loss rate was 0.049 g/s and recession loss rate was 0.067 mm/s. The SiO2 matrix was melted in priority and becomes loosen and porous. With the ablation going on, the oxides were washed away by the shearing action of the oxyacetylene flame. The evaporation of SiO2 took away large amount of heat, which is also beneficial to the protection for SiCf/SiO2 composites.

  2. 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.

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

    PubMed

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

    2016-01-01

    A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al-Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al-Si melt was estimated to range from 4.9 × 10(-6) to 8.8 × 10(-7) for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (<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.

  4. 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

  5. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting

    NASA Astrophysics Data System (ADS)

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-01-01

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ~20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  6. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting.

    PubMed

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-02-07

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ∼20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  7. Ge dots embedded in SiO2 obtained by oxidation of Si/Ge/Si nanostructures

    NASA Astrophysics Data System (ADS)

    Stoica, T.; Sutter, E.

    2006-10-01

    Selective epitaxial growth was used to fabricate narrow Si/Ge/Si pillar nanostructures in small holes in ultrathin oxide (UTO) on Si(100). The self-assembled holes with diameters of 5-30 nm were obtained by in situ partial removal of the UTO at high temperature. The UTO formation and the annealing process were optimized for a high density of holes. The SiGe nanopillars were grown with sizes determined by the initial hole diameter in the UTO. Crystalline Ge dots embedded in oxide were formed by oxidation of the pillar nanostructures. High-resolution transmission electron microscopy (HRTEM) was used to study the pillar nanostructures and the dot shapes before and after oxidation. Capacitors obtained with the oxidized samples showed a hysteresis in their C-V curves attributed to charge retention in the Ge dots embedded in the oxide.

  8. 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

  9. Modified Raman confinement model for Si nanocrystals

    NASA Astrophysics Data System (ADS)

    Faraci, Giuseppe; Gibilisco, Santo; Russo, Paola; Pennisi, Agata R.; La Rosa, Salvo

    2006-01-01

    A modified one-phonon confinement model is developed for the calculation of micro-Raman spectra in Si nanocrystals, permitting the simultaneous determination of the Raman frequency, intensity, and linewidth. Using a specific spatial correlation function and the Si phonon dispersion relations, the Raman spectra are calculated under the limitations imposed on the wave vector by the spatial confinement. Results are obtained as a function of the Si nanocrystal size in the range 1.2 100 nm . The frequency shift and line broadening of the Raman spectra are compared with experimental results reported in the literature.

  10. 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.

  11. 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.

  12. Epitaxial graphene formation on 3C-SiC/Si thin films

    NASA Astrophysics Data System (ADS)

    Suemitsu, Maki; Jiao, Sai; Fukidome, Hirokazu; Tateno, Yasunori; Makabe, Isao; Nakabayashi, Takashi

    2014-03-01

    By forming a thin 3C-SiC film on Si substrates and by annealing it at ˜1500 K in vacuo, few-layer graphene is formed epitaxially on Si substrates. In this graphene-on-silicon (GOS) technology, graphene grows at least on three major low-index Si surfaces: (1 1 1), (1 0 0) and (1 1 0), which allows tuning of structural and electronic properties of epitaxial graphene by simply controlling the crystallographic orientation of the surface. A typical example can be found in the two types of graphene formed on 3C-SiC(1 1 1) surfaces; the one on 3C-SiC(1 1 1)/Si(1 1 1) shows a Bernal stacking with an interfacial buffer layer, while the one on 3C-SiC(1 1 1)/Si(1 1 0) shows a non-Bernal stacking without an interfacial buffer layer. Inserting an AlN interlayer between Si and 3C-SiC significantly contributes to improvement of the GOS quality. Moreover, thanks to the sealing effect of the AlN layer against Si out-diffusion, we can apply chemomechanical polishing of SiC surface to reduce the surface roughness, which can further accentuate the effect of H2 annealing of the surface. As a result, a D to G band intensity ratio as low as 0.4 is obtained.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Si-WEBS, a European network for the study of Si fluxes on continental margins

    NASA Astrophysics Data System (ADS)

    Ragueneau, O.; Si-Webs Team

    2003-04-01

    Diatoms play an essential role in the export of carbon (C) towards both higher trophic levels and the deep ocean. They have a crucial need for silicon (Si) to build their frustule, but this element has clearly been neglected in studies of carbon and nutrient (N, P) fluxes in continental margins. Over the last 20 years however, coastal ecosystems of temperate regions became particularly sensitive to declining Si:N and Si:P nutrient ratios. Such declines have been related to increased eutrophication and the build-up of dams in river systems. As a result of these anthropogenic perturbations, many ecosystems have switched from nitrate limitation to silicic acid (DSi) limitation, with important consequences for phytoplankton dynamics (from diatoms to less desirable species) and cascading effects on pelagic and benthic food webs. Short-term consequences of Si availability on the shelf mostly affect the resource whereas long-term consequences may affect carbon dioxide (CO2) sequestration on the shelf and the auxiliary biological pump. Continental margins also play a filtering role so that changes in Si delivery to the hydrosphere and/or retention along the Land-Ocean-Continuum (LOC) may have a long-term impact on the oceanic C cycle. Here, we suggest an approach to improve our understanding of (1) the role of Si in the functioning of coastal ecosystems and (2) Si delivery to the open ocean at global scale. This approach implies (1) extending the LOICZ budgeting approach to the element Si to derive worldwide Si budgets on continental margins; (2) improving our knowledge of the processes that control Si transformations along the LOC. The EU-SiWEBS Research Training Network (2002-2006) will work in this last direction, by (a) improving the parameterization of the Si cycle in three river, coastal zone and open ocean models, (b) building quantitative modeling tools to describe Si transformations along the land-ocean continuum, and (c) using these tools to evaluate the

  20. Formation of crystalline heteroepitaxial SiC films on Si by carbonization of polyimide Langmuir-Blodgett films

    NASA Astrophysics Data System (ADS)

    Luchinin, Viktor V.; Goloudina, Svetlana I.; Pasyuta, Vyacheslav M.; Panov, Mikhail F.; Smirnov, Alexander N.; Kirilenko, Demid A.; Semenova, Tatyana F.; Sklizkova, Valentina P.; Gofman, Iosif V.; Svetlichnyi, Valentin M.; Kudryavtsev, Vladislav V.

    2017-06-01

    High-quality crystalline nano-thin SiC films on Si substrates were prepared by carbonization of polyimide (PI) Langmuir-Blodgett (LB) films. The obtained films were characterized by Fourier transform-infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, Raman spectroscopy, transmission electon microscopy (TEM), transmission electron diffraction (TED), and scanning electron microscopy (SEM). We demonstrated that the carbonization of a PI film on a Si substrate at 1000 °C leads to the formation of a carbon film and SiC nanocrystals on the Si substrate. It was found that five planes in the 3C-SiC(111) film are aligned with four Si(111) planes. As a result of repeated annealing of PI films containing 121 layers at 1200 °C crystalline SiC films were formed on the Si substrate. It was shown that the SiC films (35 nm) grown on Si(111) at 1200 °C have a mainly cubic 3C-SiC structure with small amount of hexagonal polytypes. Only 3C-SiC films (30 nm) were formed on the Si(100) substrate at the same temperature. It was shown that the SiC films (30-35 nm) can cover the voids with size up to 10 µm in the Si substrate. The current-voltage (I-V) characteristics of the n-Si/n-SiC heterostructure were obtained by conductive atomic force microscopy.

  1. 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.

  2. Thermally Processed High-Mobility MOS Thin-Film Transistors on Transferable Single-Crystal Elastically Strain-Sharing Si/SiGe/Si Nanomembranes

    SciTech Connect

    Yuan, H.-C.; Kelly, M. M.; Savage, D. E.; Lagally, M. G.; Celler, G. K.; Zhenqiang, M.

    2008-03-01

    Demonstration of high-performance MOS thin-film transistors (TFTs) on elastically strain-sharing single-crystal Si/SiGe/Si nanomembranes (SiNMs) that are transferred to foreign substrates is reported. The transferable SiNMs are realized by first growing pseudomorphic SiGe and Si layers on silicon-on-insulator (SOI) substrates, and then, selectively removing the buried oxide (BOX) layer from the SOI. Before the release, only the SiGe layer is compressively strained. Upon release, part of the compressive strain in the SiGe layer is transferred to the thin Si layers, and the Si layers, thus, become tensile strained. Both the initial compressive strain state in the SiGe layer and the final strain sharing state between the SiGe and the Si layers are verified with X-ray diffraction measurements. The TFTs are fabricated employing the conventional high-temperature MOS process on the strain-shared SiNMs that are transferred to an oxidized Si substrate. The transferred strained-sharing SiNMs show outstanding thermal stability and can withstand the high-temperature TFT process on the new host substrate. The strained-channel TFTs fabricated on the new host substrate show high current drive capability and an average electron effective mobility of 270 cm{sup 2}/V ldr s. The results suggest that transferable and thermally stable single-crystal elastically strain- sharing SiNMs can serve as excellent active material for high-speed device application with a simple and scalable transfer method. The demonstration of MOS TFTs on the transferable nanomembranes may create the opportunity for future high-speed Si CMOS heterogeneous integration on any substrate.

  3. 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.

  4. 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.

  5. Optimum doping level in a-Si:H and a-SiC:H materials

    NASA Astrophysics Data System (ADS)

    Hadjadj, A.; St'ahel, P.; Roca i Cabarrocas, P.; Paret, V.; Bounouh, Y.; Martin, J. C.

    1998-01-01

    The changes in the optical and electrical properties of thick a-Si:H and a-SiC:H films doped with diborane are investigated. In situ spectroscopic ellipsometry measurements reveal that, at a ratio of diborane to silane Cg=[B2H6]/[SiH4]<10-3, the optical properties of both materials are not strongly modified by boron doping. However, in the case of a-Si:H films, an improvement of the morphological and optical properties is observed at Cg=0.45×10-3. The existence of an optimum doping level at Cg<10-3 in the case of an a-Si:H p layer is confirmed by the dependence of the open-circuit voltage of a-Si:H based solar cells on the doping level of the p layer.

  6. 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.

  7. Precipitation of (Si2-xAlx)Hf in an Al-Si-Mg-Hf Alloy.

    PubMed

    Wang, Xueli; Xie, Zhiqiang; Huang, Huilan; Jia, Zhihong; Yang, Guang; Gu, Lin; Liu, Qing

    2017-08-01

    The morphology, composition, and structure of precipitates in an Al-Si-Mg-Hf alloy after heat treatment at 560°C for 20 h were studied by means of C s -corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectrometry (EDS), high-resolution transmission electron microscopy (HRTEM), and first-principle calculations. Precipitates with three kinds of morphologies were observed. The rectangular and square precipitates were predominantly (Si2-x Al x )Hf phases, while the nanobelt-like precipitate is the Si2Hf phase. First-principle calculations were used to show that the Si6 and Si8 sites were the most favorable sites for Al incorporation in the orthorhombic Si2Hf phase.

  8. SiC/Si{sub 3}N{sub 4} nanotubes from peanut shells

    SciTech Connect

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

    2016-06-15

    Nanotubes and nanoparticles of SiC and Si{sub 3}N{sub 4} 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 Si{sub 3}N{sub 4}. Nanostructures formed by a single direct reaction provide a sustainable synthesis route for nanostructured SiC and Si{sub 3}N{sub 4}, for potential engineering applications due to their exceptional mechanical and electro-optic properties.

  9. 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.

  10. 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.

  11. Accurate D0 Values for SiF and SiF+

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Ricca, Alessandra; Arnold, James O. (Technical Monitor)

    1997-01-01

    Highly accurate D0 values are determined for SiF and SiF+ using the CCSD(T) approach in conjunction with basis set extrapolation. The results include the effect of spin-orbit coupling and core-valence correlation. Our best DO estimates for SiF and SiF+ are 141.5 and 159.7 kcal/mol, respectively, which we estimate to have an uncertainty of +/- 1.0 kcal/mol. For SiF, the value is significantly larger than the older experiments and only slightly larger than the most recent experiment. Our value is slightly larger than previous calculations. For SiF+ our best estimate is in good agreement with previous calculations and slightly smaller than the experimental value.

  12. 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.

  13. 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.

  14. Interaction of Si atoms and Si-based radicals with carbon nanotubes and graphene monolayers

    NASA Astrophysics Data System (ADS)

    Chang, Kiseok; Berber, Savas; Tománek, David

    2008-03-01

    We use ab initio density functional calculations to study the interaction of Si atoms and Si-based radicals, such as SiH3, with single-wall carbon nanotubes and graphene monolayers. We find that both Si atoms and radicals form a strong chemisorption bond, accompanied by a small relaxation and a locally increased sp^3 bond character of the graphitic nanostructure. We identify the optimum adsorption geometries at different adsorbate coverages and adsorbate-related changes in the electronic structure and vibration spectra of the systems. We propose that successful functionalization of carbon nanotubes or graphene by Si atoms or Si-based radicals can be verified by studying changes in the radial breathing mode of nanotubes and the G-band of graphitic nanocarbons using Raman spectroscopy.

  15. 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

  16. Selective removal of a Si0.7Ge0.3 layer from Si(100)

    NASA Astrophysics Data System (ADS)

    Krist, A. H.; Godbey, D. J.; Green, N. P.

    1991-04-01

    The selective removal of epitaxial Si0.7Ge0.3 from {100} silicon using an aqueous based etch is reported. An etch consisting of HNO3:H2O:HF(0.5%), 40:20:5 at 22 °C, removes Si0.7Ge0.3 at a rate of 207 Å/min, and removes {100} Si at a rate of 16 Å/min. This corresponds to a selectivity of 1321 where the selectivity is defined as the ratio of the Si0.7Ge0.3 to {100} Si etch rates. This etch leaves the surface smooth and free from pitting or trenching as observed by optical microscopy. The results obtained are consistent with a germanium enhanced oxidation mechanism of the Si0.7Ge0.3 alloy during semiconductor removal.

  17. 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.

  18. Effects of Proton Implantation on Amorphous SiO2 Predamaged by Si Implantation

    NASA Astrophysics Data System (ADS)

    Fujita, Tetsuo; Fukui, Minoru; Okada, Syunji; Iwayama-Shimizu, Tsutomu; Itoh, Noriaki

    1990-10-01

    The effects of H implantation on amorphous SiO2 preimplanted with Si have been studied through electron paramagnetic resonance (EPR). It is shown that both the width and intensity of the EPR spectra of the E1' centres generated by Si implantation increase upon H implantation, in contrast to the results for Ar and succeeding H implantation. The difference is ascribed to the difference in the effective cross section of annihilation under proton implantation of the E1' centres in Si- and Ar-implanted SiO2. The result supports the previously propsed model in which the combination of Si and interstitial O reduces the annihilation of the E1' centres.

  19. 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.

  20. 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.

  1. Experimental investigation of thermo-optic effects in SiC and Si photonic crystal nanocavities.

    PubMed

    Yamada, Shota; Song, Bong-Shik; Asano, Takashi; Noda, Susumu

    2011-10-15

    We experimentally investigate and compare the thermo-optic effects of silicon carbide (SiC) and silicon (Si) photonic crystal nanocavities on their resonant wavelengths over a temperature range of 25 °C to nearly 200 °C by using a laser source with a wavelength close to the telecommunication wavelength range of 1550 nm. The measured results clearly show that the shift in the resonant wavelength of the SiC cavity is significantly (by a factor of 3) less than that of the Si cavity for the same ambient temperature changes. In addition, the measured results provide direct estimates of the thermo-optic coefficients (dn/dT) for thin SiC and Si as 3.87×10(-5)/°C and 1.60×10(-4)/°C, respectively, for this temperature range.

  2. Solute embrittlement of SiC

    SciTech Connect

    Enrique, Raúl A.; Van der Ven, Anton

    2014-09-21

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

  3. 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.

  4. Adopting SI Units in Introductory Chemistry.

    ERIC Educational Resources Information Center

    Davies, William G.; Moore, John W.

    1980-01-01

    Discusses advantages to the use of SI units in dealing with proportionality problems, with particular emphasis on stoichiometric relationships. A table lists conversion relationships commonly used in chemistry, and a single-step "roadmap" is provided for each relationship. (CS)

  5. SI Units? A Camel is a Camel.

    ERIC Educational Resources Information Center

    Adamson, Arthur W.

    1978-01-01

    This paper is a summary of remarks made at a recent symposium on new directions in the teaching of physical chemistry. The author takes exception to the claims made for the International System of Units (SI). (HM)

  6. High-performance Si microwire photovoltaics

    SciTech Connect

    Kelzenberg, Michael D.; Turner-Evans, Daniel B.; Putnam, Morgan C.; Boettcher, Shannon W.; Briggs, Ryan M.; Baek, Jae Y.; Lewis, Nathan S.; Atwater, Harry A.

    2011-01-07

    Crystalline Si wires, grown by the vapor–liquid–solid (VLS) process, have emerged as promising candidate materials for low-cost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (Ln>> 30 µm) and low surface recombination velocities (S << 70 cm·s-1). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ~600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics.

  7. Disilicon complexes with two hexacoordinate Si atoms: paddlewheel-shaped isomers with (ClN4 )Si-Si(S4 Cl) and (ClN2 S2 )Si-Si(S2 N2 Cl) skeletons.

    PubMed

    Wagler, Jörg; Brendler, Erica; Heine, Thomas; Zhechkov, Lyuben

    2013-10-11

    The reaction of 1-methyl-3-trimethylsilylimidazoline-2-thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S-bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel-shaped complexes of the type ClSi(μ-mt)4 SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN4 )SiSi(S4 Cl), (ClN3 S)SiSi(S3 NCl), and (ClN2 S2 )SiSi(S2 N2 Cl) skeletons as so-called (4,0), (3,1), and cis-(2,2) paddlewheels) were detected in solution by using (29) Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X-ray diffraction studies. In accord with time-dependent NMR spectroscopy, computational analyses proved the cis-(2,2) isomer with a (ClN2 S2 )SiSi(S2 N2 Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two SiSi-bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Advances in SiGeSn Technology

    DTIC Science & Technology

    2007-12-01

    components for use in photonic integrated circuits (PICs) and optoelectronic integrated circuits (OEICs). The PICs offer “seamless” monolithic integration ...of photonic components, while OEICs give seamless integration of electronics and photonics in the same Si chip. An important benefit of such ICs is...perspective to be introduced into CMOS fabrication for integrated optoelectronics. We believe that this development represents a breakthrough in Si

  9. 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

  10. 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.

  11. 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.

  12. Adsorption and dynamics of Si atoms at the monolayer Pb/Si(111) surface

    NASA Astrophysics Data System (ADS)

    Kumar, Rakesh; Fang, Chuang-Kai; Lee, Chih-Hao; Hwang, Ing-Shouh

    2017-06-01

    In this work, we studied the adsorption behavior of deposited Si atoms along with their diffusion and other dynamic processes on a Pb monolayer-covered Si(111) surface from 125 to 230 K using a variable-temperature scanning tunneling microscope. The Pb-covered Si(111) surface forms a low-symmetry rowlike (√{7 }×√{3 } ) structure in this temperature range and the Si atoms bind favorably to two specific on-top sites (T1 A and T1 B) on the trimer row after deposition at the sample temperature of ˜125 K . The Si atoms were immobile at low temperatures and started to switch between the two neighboring T1 A and T1 B sites within the same trimer when the temperature was raised to ˜150 K . When the temperature was raised above ˜160 K , the adsorbed Si atoms could hop to other trimers along the same trimer row. Below ˜170 K , short hops to adjacent trimers dominated, but long hops dominated at temperatures above ˜170 K . The activation energy and prefactor for the Si atoms diffusion were derived through analysis of continuous-time imaging at temperatures from 160 to 174 K. In addition, irreversible aggregation of single Si atoms into Si clusters started to occur at the phase boundaries or defective sites at temperatures above ˜170 K . At temperature above ˜180 K , nearly all Si atoms aggregated into clusters, which may have important implications for the atomic mechanism of epitaxial growth of Si on the Pb-covered Si(111) surface. In addition, our study provides strong evidence for breaking in the mirror symmetry in the (√{7 }×√{3 } )-Pb structure, which has implications for the atomic model of this controversial structure.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Surface acoustic wave devices on AlN/3C-SiC/Si multilayer structures

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Ming; Chen, Yung-Yu; Felmetsger, Valery V.; Lien, Wei-Cheng; Riekkinen, Tommi; Senesky, Debbie G.; Pisano, Albert P.

    2013-02-01

    Surface acoustic wave (SAW) propagation characteristics in a multilayer structure including a piezoelectric aluminum nitride (AlN) thin film and an epitaxial cubic silicon carbide (3C-SiC) layer on a silicon (Si) substrate are investigated by theoretical calculation in this work. Alternating current (ac) reactive magnetron sputtering was used to deposit highly c-axis-oriented AlN thin films, showing the full width at half maximum (FWHM) of the rocking curve of 1.36° on epitaxial 3C-SiC layers on Si substrates. In addition, conventional two-port SAW devices were fabricated on the AlN/3C-SiC/Si multilayer structure and SAW propagation properties in the multilayer structure were experimentally investigated. The surface wave in the AlN/3C-SiC/Si multilayer structure exhibits a phase velocity of 5528 m s-1 and an electromechanical coupling coefficient of 0.42%. The results demonstrate the potential of AlN thin films grown on epitaxial 3C-SiC layers to create layered SAW devices with higher phase velocities and larger electromechanical coupling coefficients than SAW devices on an AlN/Si multilayer structure. Moreover, the FWHM values of rocking curves of the AlN thin film and 3C-SiC layer remained constant after annealing for 500 h at 540 °C in air atmosphere. Accordingly, the layered SAW devices based on AlN thin films and 3C-SiC layers are applicable to timing and sensing applications in harsh environments.

  19. Antioxidant migration resistance of SiOx layer in SiOx/PLA coated film.

    PubMed

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

    2017-08-23

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

  20. 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.

  1. 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.

  2. 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.

  3. X-ray absorption spectroscopy from H-passivated porous Si and oxidized Si nanocrystals

    SciTech Connect

    Schuppler, S.; Marcus, M.A.; Friedman, S.L.

    1994-11-01

    Quantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The IUSI ratios, as large as 1.2, were independently confirmed by ir-absorption and {alpha}-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 {Angstrom}. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.

  4. 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.

  5. 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.

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

    DTIC Science & Technology

    2015-10-09

    of direct-gap GeSn binaries grown on Ge buffered Si as well as light -emitting GeSiSn ternaries covering a broad band of tunable wavelengths from 1300...compounds. Emphasis was placed on the fabrication of direct-gap GeSn binaries grown on Ge buffered Si as well as light -emitting GeSiSn ternaries...Photoluminescence from Ge1-x-ySixSny, ternaries and LEDs: Synthesis of light emitting Ge1-x-ySixSny, materials with tunable wavelengths over a wide range in the

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

  10. 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.

  11. 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.

  12. Characterization of SiGe/Si multi-quantum wells for infrared sensing

    NASA Astrophysics Data System (ADS)

    Moeen, M.; Salemi, A.; Kolahdouz, M.; Östling, M.; Radamson, H. H.

    2013-12-01

    SiGe epitaxial layers are integrated as an active part in thermal detectors. To improve their performance, deeper understanding of design parameters, such as thickness, well periodicity, quality, and strain amount, of the layers/interfaces is required. Oxygen (2-2500 × 10-9 Torr) was exposed prior or during epitaxy of SiGe/Si multilayers. In this range, samples with 10 nTorr oxygen were processed to investigate layer quality and noise measurements. Temperature coefficient of resistance was also measured to evaluate the thermal response. These results demonstrate sensitivity of SiGe-based devices to size and location of defects in the structure.

  13. Straining of SiGe ultrathin films with mesoporous Si substrates

    SciTech Connect

    Boucherif, A.; Guillot, G.; Lysenko, V.; Blanchard, N. P.; Regreny, P.; Grenet, G.; Marty, O.

    2010-09-27

    We report on the fabrication and characterization of ultrathin (down to 50 nm) tensile strained SiGe films on mesoporous Si substrates. Low temperature oxidation of the porous substrate relaxes the compressive strain in the as grown monocrystalline (mc) SiGe. Applying this method to a 50 nm thick mc-Si{sub 0.72}Ge{sub 0.28} film, a tensile strain >0.78% can be achieved without compromising crystalline quality and up to 1.45 % without the appearance of cracks.

  14. 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.

  15. Thermodynamic Assessments of the Fe-Si-Cr and Fe-Si-Mg Systems

    NASA Astrophysics Data System (ADS)

    Cui, Senlin; Jung, In-Ho

    2017-06-01

    Thermodynamic assessments for the Fe-Si-Cr and Fe-Si-Mg ternary systems were conducted based on the critically evaluated and optimized thermodynamic and phase diagram data in the literature. The Gibbs energy of the liquid phase was described using the modified quasi-chemical model in pair approximation. The obtained thermodynamic descriptions of the Fe-Si-Cr and Fe-Si-Mg systems can be used to calculate any sections of the phase diagrams and thermodynamic properties of these two systems with high accuracy from room temperature to above the melting temperature.

  16. 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.

  17. Stress and its effect on the interdiffusion in Si(1-x)Ge(x)/Si superlattices

    NASA Astrophysics Data System (ADS)

    Prokes, S. M.; Glembocki, O. J.; Godbey, D. J.

    1992-03-01

    Effects of stress on the interdiffusion behavior in long-period Si(0.7)Ge(0.3)/Si is examined using X-ray diffraction and Raman spectroscopy. Symmetrically and asymmetrically strained superlattices are examined, and an activation energy for interdiffusion of 3.9 and 4.6 eV is obtained. Furthermore, an enhanced interdiffusion is measured for the asymmetrically strained superlattice when subjected to an external tensile stress during annealing. Thus, enhanced intermixing is measured whenever the Si barrier layers experience tensile stress during annealing. In addition, the Raman results confirm the enhancement of Ge diffusion into the Si barriers when annealed under tensile stress.

  18. Direct Imaging and First Principles Studies of Si3N4/SiO2 Interface

    NASA Astrophysics Data System (ADS)

    Walkosz, Weronika; Klie, Robert; Ogut, Serdar; Mikijelj, Bilijana; Pennycook, Stephen; Idrobo, Juan C.

    2010-03-01

    It is well known that the composition of the integranular films (IGFs) in sintered polycrystalline silicon nitride (Si3N4) ceramics controls many of their physical and mechanical properties. A considerable effort has been made to characterize these films on the atomic scale using both experimental and theoretical methods. In this talk, we present results from a combined atomic-resolution Z-contrast and annular bright field imaging, electron energy-loss spectroscopy, as well as ab initio studies of the interface between β-Si3N4 (10-10) and SiO2 intergranular film. Our results show that O replaces N at the interface between the two materials in agreement with our theoretical calculations and that N is present in the SiO2 IGF. Moreover, they indicate the presence of atomic columns completing Si3N4 open rings, which have not been observed experimentally at the recently imaged Si3N4/rare-earth oxides interfaces, but have been predicted theoretically on bare Si3N4 surfaces. The structural and electronic variations at the Si3N4/SiO2 interface will be discussed in detail, focusing in particular on bonding characteristics.

  19. 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.

  20. 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.

  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. 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.

  3. 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.

  4. Structural and Compositional Properties of Strain-Symmetrized SiGe/Si Heterostructures

    NASA Astrophysics Data System (ADS)

    Ross, I. M.; Gass, M.; Walther, T.; Bleloch, A.; Cullis, A. G.; Lever, L.; Ikonic, Z.; Califano, M.; Kelsall, R. W.; Zhang, J.; Paul, D. J.

    In this study, we have utilised conventional and aberration corrected (scanning) transmission electron microscopy to examine the Ge concentration across a series of technologically significant SiGe/Si prototype heterostructures. Electron energy loss line profiles show that the Ge concentration within the SiGe quantum wells approaches the nominal values. However, the Ge concentration profile shows that the interfaces are not abrupt and that the narrow 0.8nm barrier layer does not reach the nominal pure Si composition. Speculation as to the presence of Ge interdiffusion, surface segregation or interface roughness is discussed.

  5. Monte Carlo simulations of hole dynamics in SiGe/Si terahertz quantum-cascade structures

    NASA Astrophysics Data System (ADS)

    Ikonić, Z.; Kelsall, R. W.; Harrison, P.

    2004-06-01

    A detailed analysis of hole transport in cascaded p - Si/SiGe quantum well structures is performed using ensemble Monte Carlo simulations. The hole subband structure is calculated using the 6×6 k·p model, and then used to find carrier relaxation rates due to the alloy disorder, acoustic and optical phonon scattering. The simulation accounts for the in-plane k -space anisotropy of both the hole subband structure and the scattering rates. Results are presented for prototype terahertz Si/SiGe quantum cascade structures.

  6. Correlation between interface traps and paramagnetic defects in c-Si/a-Si:H heterojunctions

    NASA Astrophysics Data System (ADS)

    Thoan, N. H.; Jivanescu, M.; O'Sullivan, B. J.; Pantisano, L.; Gordon, I.; Afanas'ev, V. V.; Stesmans, A.

    2012-04-01

    Low-temperature (77 K) capacitance-voltage measurements are proposed as a technique to quantify the densities of traps in c-Si/a-Si:H heterojunction solar cell structures. By comparing the inferred trap densities to the results of electron spin resonance spectroscopy, we found that the dangling bonds of silicon atoms at the surface of the (100)Si substrate (Pb0 centers) and in a-Si:H layer (D-centers) provide the most significant contributions to the density of traps.

  7. Study of photoelectron spectroscopy from extremely uniform Si nanoislands on Si (111) 7×7 substrate

    NASA Astrophysics Data System (ADS)

    Negishi, R.; Suzuki, M.; Shigeta, Y.

    2004-11-01

    The electronic and structural properties of self-assembled Si nanoislands on a Si (111) 7×7 dimer-adatom-stacking fault substrate are investigated by photoelectron spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Uniform Si nanoislands are formed on the Si (111) 7×7 substrate by control of the growth conditions. For the nanoislands fabricated on the substrate, the photoelectron spectrum shows a significant peak shift of ≈0.1eV, which is caused by a surface state related to a dangling bond at the nanoisland.

  8. Thermodynamic Assessments of the Fe-Si-Cr and Fe-Si-Mg Systems

    NASA Astrophysics Data System (ADS)

    Cui, Senlin; Jung, In-Ho

    2017-09-01

    Thermodynamic assessments for the Fe-Si-Cr and Fe-Si-Mg ternary systems were conducted based on the critically evaluated and optimized thermodynamic and phase diagram data in the literature. The Gibbs energy of the liquid phase was described using the modified quasi-chemical model in pair approximation. The obtained thermodynamic descriptions of the Fe-Si-Cr and Fe-Si-Mg systems can be used to calculate any sections of the phase diagrams and thermodynamic properties of these two systems with high accuracy from room temperature to above the melting temperature.

  9. Investigation of GaP/Si Heteroepitaxy on MOCVD Prepared Si(100) Surfaces

    SciTech Connect

    Warren, Emily L.; Kibbler, Alan E.; France, Ryan M.; Norman, Andrew G.; Olson, Jerry M.; McMahon, William E.

    2015-06-14

    Antiphase-domain (APD) free growth of GaP on Si has been achieved on Si surfaces prepared in situ by etching with AsH3. The pre-nucleation AsH3 etching removes O and C contaminants at a relatively low temperature, and creates a single-domain arsenic-terminated Si surface. The As-As dimer rows are all parallel to the step edges, and subsequent GaP growth by MOCVD retains this dimerization orientation. Both LEED and TEM indicate that the resulting epilayer is APD-free, and could thereby serve as a template for III-V/Si multijunction solar cells.

  10. Photoconductivity of Si/Ge multilayer structures with Ge quantum dots pseudomorphic to the Si matrix

    SciTech Connect

    Talochkin, A. B. Chistokhin, I. B.

    2011-07-15

    Longitudinal photoconductivity spectra of Si/Ge multilayer structures with Ge quantum dots grown pseudomorphically to the Si matrix are studied. Lines of optical transitions between hole levels of quantum dots and Si electronic states are observed. This allowed us to construct a detailed energy-level diagram of electron-hole levels of the structure. It is shown that hole levels of pseudomorphic Ge quantum dots are well described by the simplest 'quantum box' model using actual sizes of Ge islands. The possibility of controlling the position of the long-wavelength photosensitivity edge by varying the growth parameters of Si/Ge structures with Ge quantum dots is determined.

  11. Cryogenic performance of lightweight SiC and C/SiC mirrors

    NASA Astrophysics Data System (ADS)

    Hadaway, James B.; Eng, Ron; Stahl, H. Philip; Carpenter, James R.; Kegley, Jeffrey R.; Hogue, William D.

    2004-10-01

    The technology associated with the use of silicon carbide (SiC) for high-performance mirrors has matured significantly over the past 10-20 years. More recently, the material has been considered for cryogenic applications such as space-based infrared telescopes. In light of this, NASA has funded several technology development efforts involving SiC mirrors. As part of these efforts, three lightweight SiC mirrors have been optically tested at cryogenic temperatures within the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC). The three mirrors consisted of a 0.50 m diameter carbon fiber-reinforced SiC, or C/SiC, mirror from IABG in Germany, a 0.51 m diameter SiC mirror from Xinetics, Inc., and a 0.25 m diameter SiC mirror from POCO Graphite, Inc. The surface figure error was measured interferometrically from room temperature (~290 K) to ~30 K for each mirror. The radius-of-curvature (RoC) was also measured over this range for the IABG C/SiC & Xinetics SiC mirrors. This paper will describe the test goals, the test instrumentation, and the test results for these cryogenic tests.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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}.

  18. Disilane-based cyclic deposition/etch of Si, Si:P and Si1-yCy:P layers: I. The elementary process steps

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Deguet, C.

    2013-02-01

    We have benchmarked the 550 °C, 20 Torr growth of Si:P and Si1-yCy:P using SiH4 and Si2H6. P segregation has prevented us from reaching P+ ion concentrations in Si higher than a few 1019 cm-3 using SiH4; the resulting surface ‘poisoning’ led to a severe growth rate reduction. Meanwhile, [P+] increased linearly with the phosphine flow when using Si2H6 as the Si precursor; values as high as 1.7 × 1020 cm-3 were obtained. The Si:P growth rate using Si2H6 was initially stable then increased as the PH3 flow increased. Mono-methylsilane flows 6.5-10 times higher were needed with Si2H6 than with SiH4 to reach the same substitutional C concentrations in intrinsic Si1-yCy layers ([C]subst. up to 1.9%). Growth rates were approximately six times higher with Si2H6 than with SiH4, however. 30 nm thick Si1-yCy layers became rough as [C]subst. exceeded 1.6% (formation of increasing numbers of islands). We have also studied the structural and electrical properties of ‘low’ and ‘high’ C content Si1-yCy:P layers (˜ 1.5 and 1.8%, respectively) grown with Si2H6. Adding significant amounts of PH3 led to a reduction of the tensile strain in the films. This was due to the incorporation of P atoms (at the expense of C atoms) in the substitutional sites of the Si matrix. Si1-yCy:P layers otherwise became rough as the PH3 flow increased. Resistivities lower than 1 mΩ cm were nevertheless associated with those Si1-yCy:P layers, with P atomic concentrations at most 3.9 × 1020 cm-3. Finally, we have quantified the beneficial impact of adding GeH4 to HCl for the low-temperature etching of Si. Etch rates 12-36 times higher with HCl + GeH4 than with pure HCl were achieved at 20 Torr. Workable etch rates close to 1 nm min-1 were obtained at 600 °C (versus 750 °C for pure HCl), enabling low-temperature cyclic deposition/etch strategies for the selective epitaxial growth of Si, Si:P and Si1-yCy:P layers on patterned wafers.

  19. {Ge9[Si(SiMe3)2(SiPh3)]3}(-): Ligand Modification in Metalloid Germanium Cluster Chemistry.

    PubMed

    Kysliak, Oleksandr; Schrenk, Claudio; Schnepf, Andreas

    2015-07-20

    The influence of the stabilizing ligand on the physical and chemical properties of a metalloid cluster compound is important for nanotechnology as metalloid clusters are ideal model compounds for metal nanoparticles. Here we present the synthesis of a differently substituted metalloid {Ge9R3}(-) cluster: {Ge9[Si(SiMe3)2(SiPh3)]3}(-) 1, which is obtained in good yield by the reaction of K4Ge9 with ClSi(SiMe3)2(SiPh3). 1 is characterized via NMR and mass spectrometry, but crystallization is hindered. However, the reaction with HgCl2 gives the neutral compound HgGe18[Si(SiMe3)2(SiPh3)]6 2, which can be crystallized and structurally characterized. The presented results are a first step for the investigation of the ligand's influence on the properties of a metalloid germanium cluster compound.

  20. Insight into the local density of states at Si sites at the submonolayer Si/Ge(001)-2 × 1 interface from Si KLV Auger spectroscopy.

    PubMed

    Unsworth, P; Weightman, P

    2010-03-03

    An analysis of the differences observed between the Si KLV Auger spectra of the Si/Ge(001)-2 × 1 interface and pure Si indicates that the electronic structure of the interface is characterized by a reduction in the local p DOS at the Si sites and a transfer of p valence charge from Si to Ge. As a result, the screening of core-ionized Si sites at the interface is significantly shifted towards s screening compared with the situation for pure Si. It is possible that there is an increase in the on-site electron correlation energy, UP, for Si sites at the interface as compared with pure Si.

  1. 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.

  2. 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.

  3. 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%.

  4. 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.

  5. 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.

  6. 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.

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

    SciTech Connect

    Takabe, Ryota; Takeuchi, Hiroki; Du, Weijie; Toko, Kaoru; Suemasu, Takashi; Ito, Keita; Ueda, Shigenori; Kimura, Akio

    2016-04-28

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

  8. Unambiguously distinguishing Si[3Si,1Al] and Si[3Si,1OH] stuctural units in zeolite by 1H/29Si/27Al triple resonance solid state NMR spectroscopy.

    PubMed

    Luo, Qing; Yang, Jun; Hu, Wei; Zhang, Mingjin; Yue, Yong; Ye, Chaohui; Deng, Feng

    2005-07-01

    We present an experimentally feasible triple-resonance NMR method that establishes the correlation among three different nuclei, avoiding the difficulty to directly explore the weak coupling between two NMR nuclei, such as (29)Si and (27)Al. Using this method, we are able to give an unambiguous assignment to the various peaks in (29)Si CP NMR spectrum of MCM-22 zeolite and discriminate (29)Si signals from SiOHAl and SiOH groups. In addition, in combination with (1)H/(27)Al double-resonance technique, the (1)H/(27)Al/(29)Si triple-resonance experiment suggests the presence of two different kinds of Brönsted acid sites in H-MCM-22 zeolite.

  9. 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.

  10. 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)

  11. 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.

  12. 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)

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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%.

  19. J(Si,H) Coupling Constants of Activated Si-H Bonds.

    PubMed

    Meixner, Petra; Batke, Kilian; Fischer, Andreas; Schmitz, Dominik; Eickerling, Georg; Kalter, Marcel; Ruhland, Klaus; Eichele, Klaus; Barquera-Lozada, José E; Casati, Nicola P M; Montisci, Fabio; Macchi, Piero; Scherer, Wolfgang

    2017-09-18

    We outline in this combined experimental and theoretical NMR study that sign and magnitude of J(Si,H) coupling constants provide reliable indicators to evaluate the extent of the oxidative addition of Si-H bonds in hydrosilane complexes. In combination with experimental electron density studies and MO analyses a simple structure-property relationship emerges: positive J(Si,H) coupling constants are observed in cases where M → L π-back-donation (M = transition metal; L = hydrosilane ligand) dominates. The corresponding complexes are located close to the terminus of the respective oxidative addition trajectory. In contrast negative J(Si,H) values signal the predominance of significant covalent Si-H interactions and the according complexes reside at an earlier stage of the oxidative addition reaction pathway. Hence, in nonclassical hydrosilane complexes such as Cp2Ti(PMe3)(HSiMe3-nCln) (with n = 1-3) the sign of J(Si,H) changes from minus to plus with increasing number of chloro substituents n and maps the rising degree of oxidative addition. Accordingly, the sign and magnitude of J(Si,H) coupling constants can be employed to identify and characterize nonclassical hydrosilane species also in solution. These NMR studies might therefore help to reveal the salient control parameters of the Si-H bond activation process in transition-metal hydrosilane complexes which represent key intermediates for numerous metal-catalyzed Si-H bond activation processes. Furthermore, experimental high-resolution and high-pressure X-ray diffraction studies were undertaken to explore the close relationship between the topology of the electron density displayed by the η(2)(Si-H)M units and their respective J(Si,H) couplings.

  20. 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.

  1. Sr-Al-Si co-segregated regions in eutectic Si phase of Sr-modified Al-10Si alloy.

    PubMed

    Timpel, M; Wanderka, N; Schlesiger, R; Yamamoto, T; Isheim, D; Schmitz, G; Matsumura, S; Banhart, J

    2013-09-01

    The addition of 200 ppm strontium to an Al-10 wt% Si casting alloy changes the morphology of the eutectic silicon phase from coarse plate-like to fine fibrous networks. In order to clarify this modification mechanism the location of Sr within the eutectic Si phase has been investigated by a combination of high-resolution methods. Whereas three-dimensional atom probe tomography allows us to visualise the distribution of Sr on the atomic scale and to analyse its local enrichment, transmission electron microscopy yields information about the crystallographic nature of segregated regions. Segregations with two kinds of morphologies were found at the intersections of Si twin lamellae: Sr-Al-Si co-segregations of rod-like morphology and Al-rich regions of spherical morphology. Both are responsible for the formation of a high density of multiple twins and promote the anisotropic growth of the eutectic Si phase in specific crystallographic directions during solidification. The experimental findings are related to the previously postulated mechanism of "impurity induced twinning". Copyright © 2012 Elsevier B.V. All rights reserved.

  2. 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.

  3. Eu-doped Si-SiO2 core-shell nanowires for Si-compatible red emission

    NASA Astrophysics Data System (ADS)

    Xu, Jinyou; Guo, Pengfei; Zou, Zhijun; Lu, Yang; Yan, Hailong; Luo, Yongsong

    2016-09-01

    The indirect bandgap of single-crystalline silicon has so far precluded the full integration of silicon microelectronics with photonics—which is expected to allow the realization of low-cost, high-speed optical information processing and communication in the future. Here we report the growth of europium (Eu)-doped Si-SiO2 core-shell nanowires by an oxide-assisted chemical vapor deposition method. The Eu concentration in these nanowires is effectively improved by intentionally increasing the thickness of SiO2 shells. As a result, a strong Si-compatible red emission from Eu3+ ions was observed under laser illumination. The effect of Eu3+ concentration on the emission efficiency was comprehensively studied, with the highest efficiency at Eu content about 0.8 at%. The relaxation mechanism of this concentration dependent luminescence was further explored through lifetime measurements. In light of the strong characteristic red emission and nanoscale footprint, these nanowires are promising Si-compatible light emission materials for future integrated nanophotonics.

  4. Structural and electronic properties of Si/Ge nanoparticles

    NASA Astrophysics Data System (ADS)

    Asaduzzaman, Abu Md.; Springborg, Michael

    2006-10-01

    Results of a theoretical study of the electronic properties of (Si)Ge and (Ge)Si core-shell nanoparticles, homogeneous SiGe clusters, and Ge∣Si clusters with an interphase separating the Si and Ge atoms are presented. In general, (Si)Ge particles are more stable than (Ge)Si ones, and SiGe systems are more stable than Ge∣Si ones. It is found that the frontier orbitals, that dictate the optical properties, are localized to the surface, meaning that saturating dangling bonds on the surface with ligands may influence the optical properties significantly. In the central parts we identify a weak tendency for the Si atoms to accept electrons, whereas Ge atoms donate electrons.

  5. Systemic siRNA-Mediated Gene Silencing

    PubMed Central

    Duxbury, Mark S.; Matros, Evan; Ito, Hiromichi; Zinner, Michael J.; Ashley, Stanley W.; Whang, Edward E.

    2004-01-01

    Objective: RNA interference (RNAi), mediated by small interfering RNA (siRNA), silences genes with a high degree of specificity and potentially represents a general approach for molecularly targeted anticancer therapy. The aim of this study was to evaluate the ability of systemically administered siRNA to silence gene expression in vivo and to assess the effect of this approach on tumor growth using a murine pancreatic adenocarcinoma xenograft model. Summary Background Data: Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is widely overexpressed in human gastrointestinal cancer. Overexpression of CEACAM6 promotes cell survival under anchorage independent conditions, a characteristic associated with tumorigenesis and metastasis. Methods: CEACAM6 expression was quantified by real-time polymerase chain reaction (PCR) and Western blot. Mice (n = 10/group) were subcutaneously xenografted with 2 × 106 BxPC3 cells (which inherently overexpress CEACAM6). Tumor growth, CEACAM6 expression, cellular proliferation (Ki-67 immunohistochemistry), apoptosis, angiogenesis (CD34 immunohistochemistry), and survival were compared for mice administered either systemic CEACAM6-specific or control single-base mismatch siRNA over 6 weeks, following orthotopic tumor implantation. Results: Treatment with CEACAM6-specific siRNA suppressed primary tumor growth by 68% versus control siRNA (P < 0.05) and was associated with a decreased proliferating cell index, impaired angiogenesis and increased apoptosis in the xenografted tumors. CEACAM6-specific siRNA completely inhibited metastasis (0% of mice versus 60%, P < 0.05) and significantly improved survival, without apparent toxicity. Conclusions: Our data demonstrate the efficacy of systemically administered siRNA as a therapeutic modality in experimental pancreatic cancer. This novel therapeutic strategy may be applicable to a broad range of cancers and warrants investigation in patients with refractory disease. PMID

  6. 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.

  7. 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.

  8. 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.

  9. Morphology of α-Si3N4 in Fe-Si3N4 prepared via flash combustion

    NASA Astrophysics Data System (ADS)

    Li, Bin; Chen, Jun-hong; Su, Jin-dong; Yan, Ming-wei; Sun, Jia-lin; Li, Yong

    2015-12-01

    The state and formation mechanism of α-Si3N4 in Fe-Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that α-Si3N4 crystals exist only in the Fe-Si3N4 dense areas. When FeSi75 particles react with N2, which generates substantial heat, a large number of Si solid particles evaporate. The product between Si gas and N2 is a mixture of α-Si3N4 and β-Si3N4. At the later stage of the flash combustion process, α-Si3N4 crystals dissolve and reprecipitate as β-Si3N4 and the β-Si3N4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-Si3N4 crystals cool before transforming into β-Si3N4 crystals in the dense areas of Fe-Si3N4. The phase composition of flash-combustion-synthesized Fe-Si3N4 is controllable through manipulation of the gas-phase reaction in the early stage and the α→β transformation in the later stage.

  10. 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

  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. Suppression of diabetic retinopathy with GLUT1 siRNA.

    PubMed

    You, Zhi-Peng; Zhang, Yu-Lan; Shi, Ke; Shi, Lu; Zhang, Yue-Zhi; Zhou, Yue; Wang, Chang-Yun

    2017-08-07

    To investigate the effect of glucose transporter-1 (GLUT1) inhibition on diabetic retinopathy, we divided forty-eight mice into scrambled siRNA, diabetic scrambled siRNA, and GLUT1 siRNA (intravitreally injected) groups. Twenty-one weeks after diabetes induction, we calculated retinal glucose concentrations, used electroretinography (ERG) and histochemical methods to assess photoreceptor degeneration, and conducted immunoblotting, leukostasis and vascular leakage assays to estimate microangiopathy. The diabetic scrambled siRNA and GLUT1 siRNA exhibited higher glucose concentrations than scrambled siRNA, but GLUT1 siRNA group concentrations were only 50.05% of diabetic scrambled siRNA due to downregulated GLUT1 expression. The diabetic scrambled siRNA and GLUT1 siRNA had lower ERG amplitudes and ONL thicknesses than scrambled siRNA. However, compared with diabetic scrambled siRNA, GLUT1 siRNA group amplitudes and thicknesses were higher. Diabetic scrambled siRNA cones were more loosely arranged and had shorter outer segments than GLUT1 siRNA cones. ICAM-1 and TNF-α expression levels, adherent leukocyte numbers, fluorescence leakage areas and extravasated Evans blue in diabetic scrambled siRNA were higher than those in scrambled siRNA. However, these parameters in the GLUT1 siRNA were lower than diabetic scrambled siRNA. Together, these results demonstrate that GLUT1 siRNA restricted glucose transport by inhibiting GLUT1 expression, which decreased retinal glucose concentrations and ameliorated diabetic retinopathy.

  13. Ballistic-Charge-Carrier Spectroscopy Of CoSi(2)/Si Interfaces

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Kaiser, William J.; Fathauer, Robert W.; Bell, Lloyd D.; Lee, Edwin Y.

    1993-01-01

    Report discusses experiments in which ballistic-electron-emission microscopy (BEEM) and related ballistic-hole and charge-carrier-scattering spectroscopies used to investigate transport of electric-charge carriers (electrons and holes) in epitaxial CoSi2/Si system.

  14. 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.

  15. 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

  16. 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.

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

    PubMed

    Zhao, Xiaofeng; Wen, Dianzhong; Li, Gang

    2012-01-01

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

  18. Carrier Mobility Enhancement of Tensile Strained Si and SiGe Nanowires via Surface Defect Engineering.

    PubMed

    Ma, J W; Lee, W J; Bae, J M; Jeong, K S; Oh, S H; Kim, J H; Kim, S-H; Seo, J-H; Ahn, J-P; Kim, H; Cho, M-H

    2015-11-11

    Changes in the carrier mobility of tensile strained Si and SiGe nanowires (NWs) were examined using an electrical push-to-pull device (E-PTP, Hysitron). The changes were found to be closely related to the chemical structure at the surface, likely defect states. As tensile strain is increased, the resistivity of SiGe NWs deceases in a linear manner. However, the corresponding values for Si NWs increased with increasing tensile strain, which is closely related to broken bonds induced by defects at the NW surface. Broken bonds at the surface, which communicate with the defect state of Si are critically altered when Ge is incorporated in Si NW. In addition, the number of defects could be significantly decreased in Si NWs by incorporating a surface passivated Al2O3 layer, which removes broken bonds, resulting in a proportional decrease in the resistivity of Si NWs with increasing strain. Moreover, the presence of a passivation layer dramatically increases the extent of fracture strain in NWs, and a significant enhancement in mobility of about 2.6 times was observed for a tensile strain of 5.7%.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  20. 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).