Research on a Micro-Nano Si/SiGe/Si Double Heterojunction Electro-Optic Modulation Structure

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Song Feng

2018-01-01

Full Text Available The electro-optic modulator is a very important device in silicon photonics, which is responsible for the conversion of optical signals and electrical signals. For the electro-optic modulator, the carrier density of waveguide region is one of the key parameters. The traditional method of increasing carrier density is to increase the external modulation voltage, but this way will increase the modulation loss and also is not conducive to photonics integration. This paper presents a micro-nano Si/SiGe/Si double heterojunction electro-optic modulation structure. Based on the band theory of single heterojunction, the barrier heights are quantitatively calculated, and the carrier concentrations of heterojunction barrier are analyzed. The band and carrier injection characteristics of the double heterostructure structure are simulated, respectively, and the correctness of the theoretical analysis is demonstrated. The micro-nano Si/SiGe/Si double heterojunction electro-optic modulation is designed and tested, and comparison of testing results between the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation and the micro-nano Silicon-On-Insulator (SOI micro-ring electro-optic modulation, Free Spectrum Range, 3 dB Bandwidth, Q value, extinction ratio, and other parameters of the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation are better than others, and the modulation voltage and the modulation loss are lower.

Structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 phases from first-principles calculations

Science.gov (United States)

Li, X. D.; Li, K.; Wei, C. H.; Han, W. D.; Zhou, N. G.

2018-06-01

The structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 are systematically investigated by using first-principles calculations method based on density functional theory (DFT). The calculated formation enthalpies and cohesive energies show that CaSi2 possesses the greatest structural stability and CaSi has the strongest alloying ability. The structural stability of the three phases is compared according to electronic structures. Further analysis on electronic structures indicates that the bonding of these phases exhibits the combinations of metallic, covalent, and ionic bonds. The elastic constants are calculated, and the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor of polycrystalline materials are deduced. Additionally, the thermodynamic properties were theoretically predicted and discussed.

Structural insights into RNA processing by the human RISC-loading complex.

Science.gov (United States)

Wang, Hong-Wei; Noland, Cameron; Siridechadilok, Bunpote; Taylor, David W; Ma, Enbo; Felderer, Karin; Doudna, Jennifer A; Nogales, Eva

2009-11-01

Targeted gene silencing by RNA interference (RNAi) requires loading of a short guide RNA (small interfering RNA (siRNA) or microRNA (miRNA)) onto an Argonaute protein to form the functional center of an RNA-induced silencing complex (RISC). In humans, Argonaute2 (AGO2) assembles with the guide RNA-generating enzyme Dicer and the RNA-binding protein TRBP to form a RISC-loading complex (RLC), which is necessary for efficient transfer of nascent siRNAs and miRNAs from Dicer to AGO2. Here, using single-particle EM analysis, we show that human Dicer has an L-shaped structure. The RLC Dicer's N-terminal DExH/D domain, located in a short 'base branch', interacts with TRBP, whereas its C-terminal catalytic domains in the main body are proximal to AGO2. A model generated by docking the available atomic structures of Dicer and Argonaute homologs into the RLC reconstruction suggests a mechanism for siRNA transfer from Dicer to AGO2.

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

Energy Technology Data Exchange (ETDEWEB)

Naserifar, Saber [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211 (United States); Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125 (United States); Goddard, William A. [Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125 (United States); Tsotsis, Theodore T.; Sahimi, Muhammad, E-mail: moe@usc.edu [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211 (United States)

2015-05-07

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

Characterization of electronic structures from CdS/Si nanoheterostructure array based on silicon nanoporous pillar array

Energy Technology Data Exchange (ETDEWEB)

Li, Yong, E-mail: liyong@pdsu.edu.cn [Department of Physics and Solar Energy Research Center, Pingdingshan University, Pingdingshan 467000 (China); Song, Xiao Yan [Department of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450045 (China); Song, Yue Li; Ji, Peng Fei; Zhou, Feng Qun; Tian, Ming Li; Huang, Hong Chun [Department of Physics and Solar Energy Research Center, Pingdingshan University, Pingdingshan 467000 (China); Li, Xin Jian [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China)

2016-02-15

Highlights: • CdS/Si nanoheterostructure array has been fabricated through a CBD method. • The electronic properties have been investigated by the I–V and C–V techniques. • The onset voltages, characteristic frequency and built-in potential are investigated. • The electronic structures can be tuned through the annealing treatments. - Abstract: The electronic properties of heterostructures are very important to its applications in the field of optoelectronic devices. Understanding and control of electronic properties are very necessary. CdS/Si nanoheterostructure array have been fabricated through growing CdS nanocrystals on the silicon nanoporous pillar array using a chemical bath deposition method. The electronic properties of CdS nanoheterostructure array have been investigated by the current–voltage, complex impedance spectroscopy and capacitance–voltage techniques. The onset voltages, characteristic frequency and built-in potential are gradually increased with increasing the annealing temperature. It is indicated that the electronic structures of CdS/Si nanoheterostructure array can be tuned through the annealing treatments.

Characterization of electronic structures from CdS/Si nanoheterostructure array based on silicon nanoporous pillar array

International Nuclear Information System (INIS)

Li, Yong; Song, Xiao Yan; Song, Yue Li; Ji, Peng Fei; Zhou, Feng Qun; Tian, Ming Li; Huang, Hong Chun; Li, Xin Jian

2016-01-01

Highlights: • CdS/Si nanoheterostructure array has been fabricated through a CBD method. • The electronic properties have been investigated by the I–V and C–V techniques. • The onset voltages, characteristic frequency and built-in potential are investigated. • The electronic structures can be tuned through the annealing treatments. - Abstract: The electronic properties of heterostructures are very important to its applications in the field of optoelectronic devices. Understanding and control of electronic properties are very necessary. CdS/Si nanoheterostructure array have been fabricated through growing CdS nanocrystals on the silicon nanoporous pillar array using a chemical bath deposition method. The electronic properties of CdS nanoheterostructure array have been investigated by the current–voltage, complex impedance spectroscopy and capacitance–voltage techniques. The onset voltages, characteristic frequency and built-in potential are gradually increased with increasing the annealing temperature. It is indicated that the electronic structures of CdS/Si nanoheterostructure array can be tuned through the annealing treatments.

Surface acoustic wave devices on AlN/3C–SiC/Si multilayer structures

International Nuclear Information System (INIS)

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

2013-01-01

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. (paper)

Electrical properties of Si/Si1-xGex/Si inverted modulation doped structures

International Nuclear Information System (INIS)

Sadeghzadeh, M.A.

1998-12-01

This thesis is a report of experimental investigations of growth strategy and electrical properties of Si/Si 1-x Ge x /Si inverted Modulation Doped (MD) structures grown by solid source Molecular Beam Epitaxy (MBE). If the grown Si layer is B-doped at some distance (as spacer) before or after the alloy layer, this remote doping induces the formation of a quasi Two Dimensional Hole Gas (2-DHG) near to the inverted (SiGe on Si) or normal (Si on SiGe) heterointerfaces of the Si/Si 1-x Ge x /Si quantum well, respectively. The latter arrangement is the well known 'normal' MD structure but the former one is the so-called 'inverted' MD structure which is of great interest for Field Effect Transistor (FET) applications. A reproducible growth strategy was employed by the use of a thick (400nm) Si cap for inverted MD structures with Ge composition in the range of 16-23%. Boron segregation and cap surface charges are significant in these inverted structures with small ( 20nm) spacer layers, respectively. It was demonstrated by secondary ion mass spectroscopy (SIMS) that boron segregation, which causes a reduction in the effective spacer dimension, can be suppressed by growth interruption after boron doping. The enhancement in hole sheet density with increasing Si cap layer thickness, is attributed to a reduction in the influence of positive surface charges in these structures. Top-gated devices were fabricated using these structures and the hole sheet density could be varied by applying a voltage to the metal-semiconductor gate, and the maximum Hall mobility of 5550 cm 2 V -1 s -1 with 4.2x10 11 cm -2 was measured (at 1.6K) in these structures. Comparison of measured Hall mobility (at 4.2K) as a function of hole sheet density in normal and inverted MD structures implies that both 2-DHG confined at normal and/or inverted structures are subjected to very similar interface charge, roughness, and alloy scattering potentials. Low temperatures magnetotransport measurements (down to

Complex three-dimensional structures in Si{1 0 0} using wet bulk micromachining

International Nuclear Information System (INIS)

Pal, Prem; Sato, Kazuo

2009-01-01

Complex three-dimensional structures for microelectromechanical systems (MEMS) are fabricated in Si{1 0 0} wafers using wet bulk micromachining. The structures are divided into two categories: fixed and freestanding. The fabrication processes for both types utilize single wafers with sequentially deposited nitride and oxide layers, local oxidation of silicon (LOCOS) and two steps of wet anisotropic etching. The fixed structures contain perfectly sharp edges. Thermally deposited oxide is used as the material for the freestanding structures. Wet etching is performed in tetramethyl ammonium hydroxide (TMAH) with and without Triton X-100 (C 14 H 22 O(C 2 H 4 O) n , n = 9–10). For the fixed structures, both etching steps are performed either in 25 wt% TMAH + Triton or pure TMAH or both, depending upon the type of the structures. In the case of freestanding systems, TMAH + Triton is utilized first, followed by pure TMAH. The fabrication methods enable densely arrayed structures, allowing the manufacture of corrugated diaphragms, compact size liquid (or gas) flow delivery systems, newly shaped mold for soft MEMS structures (e.g. PDMS (polydimethylsiloxane)) and other applications. The present research is an approach to fabricate advanced MEMS structures, extending the range of 3D structures fabricated by silicon anisotropic etching

Structural and electronic properties of Si/SiO2 MOS structures with aligned 3C-SiC nanocrystals in the oxide

International Nuclear Information System (INIS)

Pongracz, A.; Battistig, G.; Duecso, Cs.; Josepovits, K.V.; Deak, P.

2007-01-01

Our group previously proved that a simple reactive annealing in CO containing gas produces 3C-SiC nanocrystals, which are epitaxially and void-free aligned in the Si substrate. By a further thermal oxidation step, these nanocrystals can be lifted from the Si and incorporated into the SiO 2 matrix, thereby creating a promising structure for charge storage. In this work the structural and electrical properties of such systems with nanocrystalline SiC will be presented. Prototype MOS structures with 3C-SiC nanocrystals were produced for current-voltage and capacitance-voltage measurements. The results indicate that the high-temperature annealing did not damage the MOS structure, despite the fact that the CO annealing changed the electrical properties of the system. There was a positive charge accumulation and a reversible carrier injection observed in the structure. We assume that the positive charges originated from oxygen vacancies and the charge injection is related to the presence of SiC nanocrystals

Improving the opto-microwave performance of SiGe/Si phototransistor through edge-illuminated structure

Science.gov (United States)

Tegegne, Z. G.; Viana, C.; Polleux, J. L.; Grzeskowiak, M.; Richalot, E.

2016-03-01

This paper demonstrates the experimental study of edge and top illuminated SiGe phototransistors (HPT) implemented using the existing industrial SiGe2RF Telefunken GmbH BiCMOS technology for opto-microwave (OM) applications using 850nm Multi-Mode Fibers (MMF). Its technology and structure are described. Two different optical window size HPTs with top illumination (5x5μm2, 10x10μm2) and an edge illuminated HPTs having 5μm x5μm size are presented and compared. A two-step post fabrication process was used to create an optical access on the edge of the HPT for lateral illumination with a lensed MMF through simple polishing and dicing techniques. We perform Opto-microwave Scanning Near-field Optical Microscopy (OM-SNOM) analysis on edge and top illuminated HPTs in order to observe the fastest and the highest sensitive regions of the HPTs. This analysis also allows understanding the parasitic effect from the substrate, and thus draws a conclusion on the design aspect of SiGe/Si HPT. A low frequency OM responsivity of 0.45A/W and a cutoff frequency, f-3dB, of 890MHz were measured for edge illuminated HPT. Compared to the top illuminated HPT of the same size, the edge illuminated HPT improves the f-3dB by a factor of more than two and also improves the low frequency responsivity by a factor of more than four. These results demonstrate that a simple etched HPT is still enough to achieve performance improvements compared to the top illuminated HPT without requiring a complex coupling structure. Indeed, it also proves the potential of edge coupled SiGe HPT in the ultra-low-cost silicon based optoelectronics circuits with a new approach of the optical packaging and system integration to 850nm MMF.

Magneto-transport phenomena in metal/SiO2/n(p)-Si hybrid structures

Science.gov (United States)

Volkov, N. V.; Tarasov, A. S.; Rautskii, M. V.; Lukyanenko, A. V.; Bondarev, I. A.; Varnakov, S. N.; Ovchinnikov, S. G.

2018-04-01

Present review touches upon a subject of magnetotransport phenomena in hybrid structures which consist of ferromagnetic or nonmagnetic metal layer, layer of silicon oxide and silicon substrate with n- or p-type conductivity. Main attention will be paid to a number gigantic magnetotransport effects discovered in the devices fabricated on the base of the M/SiO2/n(p)-Si (M is ferromagnetic or paramagnetic metal) hybrid structures. These effects include bias induced dc magnetoresistance, gigantic magnetoimpedance, dc magnetoresistance induced by an optical irradiation and lateral magneto-photo-voltaic effect. The magnetoresistance ratio in ac and dc modes for some of our devices can exceed 106% in a magnetic field below 1 T. For lateral magneto-photo-voltaic effect, the relative change of photo-voltage in magnetic field can reach 103% at low temperature. Two types of mechanisms are responsible for sensitivity of the transport properties of the silicon based hybrid structures to magnetic field. One is related to transformation of the energy structure of the (donor) acceptor states including states near SiO2/n(p)-Si interface in magnetic field. Other mechanism is caused by the Lorentz force action. The features in behaviour of magnetotransport effects in concrete device depend on composition of the used structure, device topology and experimental conditions (bias voltage, optical radiation and others). Obtained results can be base for design of some electronic devices driven by a magnetic field. They can also provide an enhancement of the functionality for existing sensors.

Two structure types based on Si6O15 rings: synthesis and structural and spectroscopic characterisation of Cs1.86K1.14DySi6O15 and Cs1.6K1.4SmSi6O15

International Nuclear Information System (INIS)

Wierzbicka-Wieczorek, Maria; Goeckeritz, Martin; Kolitsch, Uwe; Lenz, Christoph; Giester, Gerald

2015-01-01

The silicate Cs 1.86 K 1.14 DySi 6 O 15 represents a mixed tetrahedral-octahedral framework structure type based on roughly circular Si 6 O 15 rings and isolated DyO 6 octahedra. The silicate Cs 1.6 K 1.4 SmSi 6 O 15 has a layered atomic arrangement built from corrugated Si 6 O 15 layers containing four-, six- and eight-membered rings. The layers are connected by isolated SmO 6 octahedra to form a mixed tetrahedral-octahedral framework. This structure shows a close structural relationship to β-K 3 NdSi 6 O 15 and a less close one to dehydrated elpidite (Na 2 ZrSi 6 O 15 ). In both structures, Cs/K atoms occupy large voids. The silicates were obtained through high-temperature flux syntheses. Their crystal structures have been determined from single-crystal X-ray diffraction data. Cs 1.86 K 1.14 DySi 6 O 15 crystallises in R32 (no. 155) with a = 13.896(2), c = 35.623(7) Aa and V = 5957.2(17) Aa 3 , whereas Cs 1.6 K 1.4 SmSi 6 O 15 crystallises in Cmca (no. 64) with a = 14.474(3), b = 14.718(3), c = 15.231(3) Aa and V = 3244.7(11) Aa 3 . The Dy 3+ and Sm 3+ cations present in the silicates cause PL emission bands in the visible yellow-to-orange spectral range. (Copyright copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Comparative study on stress in AlGaN/GaN HEMT structures grown on 6H-SiC, Si and on composite substrates of the 6H-SiC/poly-SiC and Si/poly-SiC

International Nuclear Information System (INIS)

Guziewicz, M; Kaminska, E; Piotrowska, A; Golaszewska, K; Domagala, J Z; Poisson, M-A; Lahreche, H; Langer, R; Bove, P

2008-01-01

The stresses in GaN-based HEMT structures grown on both single crystal 6H SiC(0001) and Si(111) have been compared to these in the HEMT structures grown on new composite substrates engendered as a thin monocrystalline film attached to polycrystalline 3C-SiC substrate. By using HRXRD technique and wafer curvature method we show that stress of monocrystalline layer in composite substrates of the type mono-Si/poly-SiC is lower than 100 MPa and residual stress of epitaxial GaN buffer grown on the composite substrate does not exceed 0.31 GPa, but in the cases of single crystal SiC or Si substrates the GaN buffer stress is compressive in the range of -0.5 to -0.75 GPa. The total stress of the HEMT structure calculated from strains is consistent with the averaged stress of the multilayers stack measured by wafer curvature method. The averaged stress of HEMT structure grown on single crystals is higher than those in structures grown on composites substrates

Carbon redistribution and precipitation in high temperature ion-implanted strained Si/SiGe/Si multi-layered structures

DEFF Research Database (Denmark)

Gaiduk, Peter; Hansen, John Lundsgaard; Nylandsted Larsen, Arne

2014-01-01

Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects.......Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects....

The strain effect in the surface barrier structures prepared on the basis of n-Si and p-Si

International Nuclear Information System (INIS)

Mamatkarimov, O.O.; Tuychiev, U.A.

2004-01-01

Full text: One of the ways of creation of large deformations in small volume of the semiconductor is the deformation created by a needle. At insignificant change of external influence the large deformation under a needle in small volume of the semiconductor the significant change of electrophysical parameters of the semiconductor in small volume is created. Therefore, in the present work the results of researches of local pressure influence on physical properties of surface barrier structures has been performed on the basis of silicon with Ni and Mn impurity. The relative changes of a direct current made on the basis n-Si and p-Si from a different degree of compensation are given depending on size of local pressure are shown. Change of current in structures Au-Si -Sb with specific resistance of base ρ=80 Ω·cm and ρ=200 Ω·cm are I p /I 0 =3-3.5 times and I P /I ) =2-2.5 times at pressure P=1.6·10 8 Pa respectively. These data show, that in structures received on the basis of initial silicon, change of a direct current with pressure is in inverse proportion to size of resistance of base of the diode. And in structures Au-Si -Sb with specific resistance of base ρ=5·10 2 Ω·cm and ρ=3·10 3 Ω·cm these changes accordingly are I P /I 0 =7 and I P /I 0 =14. Changes of direct current relative to initial value for structures on the basis p-Si with specific resistance ρ=7·10 2 Ω·cm and ρ=4·10 3 Ω·cm) are I P /I 0 =9 and I P /I 0 =16 respectively. The same changes of direct current of structures on the basis P-Si at local pressure are I P /I 0 =2-2.5. The given values I P /I 0 testify that as in structures Au-Si -Sb, and structures Sb-p-Si -Au, unlike structures on the basis of initial silicon, the values I P /I 0 are increased with increase of specific resistance of base of structures

Solar cells based on InP/GaP/Si structure

Science.gov (United States)

Kvitsiani, O.; Laperashvil, D.; Laperashvili, T.; Mikelashvili, V.

2016-10-01

Solar cells (SCs) based on III-V semiconductors are reviewed. Presented work emphases on the Solar Cells containing Quantum Dots (QDs) for next-generation photovoltaics. In this work the method of fabrication of InP QDs on III-V semiconductors is investigated. The original method of electrochemical deposition of metals: indium (In), gallium (Ga) and of alloys (InGa) on the surface of gallium phosphide (GaP), and mechanism of formation of InP QDs on GaP surface is presented. The possibilities of application of InP/GaP/Si structure as SC are discussed, and the challenges arising is also considered.

Structure-based characterization of multiprotein complexes.

Science.gov (United States)

Wiederstein, Markus; Gruber, Markus; Frank, Karl; Melo, Francisco; Sippl, Manfred J

2014-07-08

Multiprotein complexes govern virtually all cellular processes. Their 3D structures provide important clues to their biological roles, especially through structural correlations among protein molecules and complexes. The detection of such correlations generally requires comprehensive searches in databases of known protein structures by means of appropriate structure-matching techniques. Here, we present a high-speed structure search engine capable of instantly matching large protein oligomers against the complete and up-to-date database of biologically functional assemblies of protein molecules. We use this tool to reveal unseen structural correlations on the level of protein quaternary structure and demonstrate its general usefulness for efficiently exploring complex structural relationships among known protein assemblies. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

Electro-physical properties of a Si-based MIS structure with a low-k SiOC(-H) film

Energy Technology Data Exchange (ETDEWEB)

Zakirov, Anvar Sagatovich; Navamathavan, Rangaswamy; Kim, Seung Hyun; Jang, Yong Jun; Jung, An Soo; Choi, Chi Kyu [Cheju National University, Jeju (Korea, Republic of)

2006-09-15

SiOC(-H) films with low dielectric constants have been prepared by using plasma enhanced chemical vapor deposition with a mixture of methyltriethoxysilane and oxygen precursors. The C-V characteristics of the structures, Al/SiOC(-H)/p-Si(100), were studied in the forward and the reverse directions by applying a polarizing potential. We found that the ratio of the maximum to the minimum capacitance (C{sub ma}x{sub /}C{sub min}) depended on the [MTES/(MTES+O{sub 2})] flow rate ratio. Annealed samples exhibited even greater reductions of the maximum capacitance and the dielectric constant of the SiOC(-H) samples. After annealing at 400 .deg. C, the measurement in the reverse direction revealed an interesting behavior in the form of strongly pronounced 'steps'. The bonds between Si-O and the -CH{sub 3} group reduced the surface charge density, and the distribution of the surface charge density depended on [MTES/(MTES+O{sub 2})] flow rate ratio and the annealing temperature because the fixed positive (Si-CH{sub 3}){sup +} and negative (Si-O){sup -} changed the configuration at the SiOC(-H)/p-Si(100) interface. The SiOC(-H) film had donor (O{sub 2}) and acceptor (Si-CH{sub 3} -groups) levels, and the electronic process at the SiOC(-H)/p-Si(100) interface was defined by the (Si-CH{sub 3}){sup +} and the (Si-O){sup -} bonds.

FEM Analysis of Sezawa Mode SAW Sensor for VOC Based on CMOS Compatible AlN/SiO2/Si Multilayer Structure

Directory of Open Access Journals (Sweden)

Muhammad Zubair Aslam

2018-05-01

Full Text Available A Finite Element Method (FEM simulation study is conducted, aiming to scrutinize the sensitivity of Sezawa wave mode in a multilayer AlN/SiO2/Si Surface Acoustic Wave (SAW sensor to low concentrations of Volatile Organic Compounds (VOCs, that is, trichloromethane, trichloroethylene, carbon tetrachloride and tetrachloroethene. A Complimentary Metal-Oxide Semiconductor (CMOS compatible AlN/SiO2/Si based multilayer SAW resonator structure is taken into account for this purpose. In this study, first, the influence of AlN and SiO2 layers’ thicknesses over phase velocities and electromechanical coupling coefficients (k2 of two SAW modes (i.e., Rayleigh and Sezawa is analyzed and the optimal thicknesses of AlN and SiO2 layers are opted for best propagation characteristics. Next, the study is further extended to analyze the mass loading effect on resonance frequencies of SAW modes by coating a thin Polyisobutylene (PIB polymer film over the AlN surface. Finally, the sensitivity of the two SAW modes is examined for VOCs. This study concluded that the sensitivity of Sezawa wave mode for 1 ppm of selected volatile organic gases is twice that of the Rayleigh wave mode.

Joining of SiCf/SiC composites for thermonuclear fusion reactors

International Nuclear Information System (INIS)

Ferraris, M.; Badini, C.; Montorsi, M.; Appendino, P.; Scholz, H.W.

1994-01-01

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

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

Science.gov (United States)

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

2017-05-25

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

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

Directory of Open Access Journals (Sweden)

Lianbi Li

2017-05-01

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

Structural and electronic properties of the transition layer at the SiO2/4H-SiC interface

Directory of Open Access Journals (Sweden)

Wenbo Li

2015-01-01

Full Text Available Using first-principles methods, we generate an amorphous SiO2/4H-SiC interface with a transition layer. Based this interface model, we investigate the structural and electronic properties of the interfacial transition layer. The calculated Si 2p core-level shifts for this interface are comparable to the experimental data, indicating that various SiCxOy species should be present in this interface transition layer. The analysis of the electronic structures reveals that the tetrahedral SiCxOy structures cannot introduce any of the defect states at the interface. Interestingly, our transition layer also includes a C-C=C trimer and SiO5 configurations, which lead to the generation of interface states. The accurate positions of Kohn-Sham energy levels associated with these defects are further calculated within the hybrid functional scheme. The Kohn-Sham energy levels of the carbon trimer and SiO5 configurations are located near the conduction and valence band of bulk 4H-SiC, respectively. The result indicates that the carbon trimer occurred in the transition layer may be a possible origin of near interface traps. These findings provide novel insight into the structural and electronic properties of the realistic SiO2/SiC interface.

A TEM study of strained SiGe/Si and related heteroepitaxial structures

International Nuclear Information System (INIS)

Benedetti, Alessandro

2002-01-01

The role of SiGe/Si heterostructures and related materials has become increasingly important within the last few decades. In order to increase the scale of integration, however, devices with active elements not larger than few tens of nanometer have been recently introduced. There is, therefore, a strong need for an analytical technique capable of giving information about submicron-sized components. An investigation on a nanometre scale can be performed by the combination of a fully equipped Transmission Electron Microscope (TEM) with a Field Emission Gun (PEG) electron source, which enables one to use a wide range of analytical techniques with an electron probe as small as 0.5 nm. In this work, two different types of SiGe/Si-based devices were investigated. Strained-Si n-channel MOSFETs. The use of Strained-Si n-channel grown on SiGe should improve both carrier mobility and transconductance with respect to conventional MOSFETs. Materials analysed in this work showed an extremely high transconductance but a rather low mobility. In order to relate their microstructural properties to their electrical performance, as well as to improve the device design, a full quantitative and qualitative structural characterisation was performed. SiGe Multiple Quantum Wells (MQW) IR detectors Light detection is achieved by collecting the photogenerated carriers, injected from the SiGe QWs layers into the Si substrate. A key factor is the Ge profile across a single QW, since it governs the band structure and therefore the device performances. Four different TEM techniques were used to determine the Ge distribution across a single well, showing an overall good agreement among the results. The Ge profiles broadening, consistent with data available in literature, was successfully explained and theoretically predicted by the combined effect of Ge segregation and gas dwell times within the reactor. (author)

High-speed Si/GeSi hetero-structure Electro Absorption Modulator.

Science.gov (United States)

Mastronardi, L; Banakar, M; Khokhar, A Z; Hattasan, N; Rutirawut, T; Bucio, T Domínguez; Grabska, K M; Littlejohns, C; Bazin, A; Mashanovich, G; Gardes, F Y

2018-03-19

The ever-increasing demand for integrated, low power interconnect systems is pushing the bandwidth density of CMOS photonic devices. Taking advantage of the strong Franz-Keldysh effect in the C and L communication bands, electro-absorption modulators in Ge and GeSi are setting a new standard in terms of device footprint and power consumption for next generation photonics interconnect arrays. In this paper, we present a compact, low power electro-absorption modulator (EAM) Si/GeSi hetero-structure based on an 800 nm SOI overlayer with a modulation bandwidth of 56 GHz. The device design and fabrication tolerant process are presented, followed by the measurement analysis. Eye diagram measurements show a dynamic ER of 5.2 dB at a data rate of 56 Gb/s at 1566 nm, and calculated modulator power is 44 fJ/bit.

A comparative study of three ternary complexes prepared in different mixing orders of siRNA/redox-responsive hyperbranched poly (amido amine/hyaluronic acid

Directory of Open Access Journals (Sweden)

Chen CJ

2012-07-01

gene silencing effects on vascular endothelial growth factor expression in MDA-MB-231 cells were as follows: mixing order III > mixing order I > mixing order II. Based on these results, a likely explanation for the difference in functionality dependent on mixing orders is the formation of different assembly structures. These results may help future optimization of siRNA ternary complexes for achieving better delivery efficiencies, especially for target-specific siRNA delivery to cells with HA receptor overexpression.Keywords: small interfering RNA, poly(amido amines, siRNA ternary complex, mixing order, hyaluronic acid, siRNA delivery

Kinetic analysis of the effects of target structure on siRNA efficiency

Science.gov (United States)

Chen, Jiawen; Zhang, Wenbing

2012-12-01

RNAi efficiency for target cleavage and protein expression is related to the target structure. Considering the RNA-induced silencing complex (RISC) as a multiple turnover enzyme, we investigated the effect of target mRNA structure on siRNA efficiency with kinetic analysis. The 4-step model was used to study the target cleavage kinetic process: hybridization nucleation at an accessible target site, RISC-mRNA hybrid elongation along with mRNA target structure melting, target cleavage, and enzyme reactivation. At this model, the terms accounting for the target accessibility, stability, and the seed and the nucleation site effects are all included. The results are in good agreement with that of experiments which show different arguments about the structure effects on siRNA efficiency. It shows that the siRNA efficiency is influenced by the integrated factors of target's accessibility, stability, and the seed effects. To study the off-target effects, a simple model of one siRNA binding to two mRNA targets was designed. By using this model, the possibility for diminishing the off-target effects by the concentration of siRNA was discussed.

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

Science.gov (United States)

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.

In-Situ Immobilization of Ni Complex on Amine-Grafted SiO₂ for Ethylene Polymerization.

Science.gov (United States)

Lee, Sang Yun; Ko, Young Soo

2018-02-01

The results on the In-Situ synthesis of Ni complex on amine-grafted SiO2 and its ethylene polymerization were explained. SiO2/2NS/(DME)NiBr2 and SiO2/3NS/(DME)NiBr2(Ni(II) bromide ethylene glycol dimethyl ether) catalysts were active for ethylene polymerization. The highest activity was shown at the polymerization temperature of 25 °C, and SiO2/2NS/(DME)NiBr2 exhibited higher activity than SiO2/3NS/(DME)NiBr2. The PDI values of SiO2/2NS/(DME)NiBr2 were in the range of 8~18. The aminosilane compounds and Ni were evenly grafted and distributed in the silica. It was proposed that DME ligand was mostly removed during the supporting process, and only NiBr2 was complexed with the amine group of 2NS based on the results of FT-IR and ethylene polymerization.

First-principles calculations of orientation dependence of Si thermal oxidation based on Si emission model

Science.gov (United States)

Nagura, Takuya; Kawachi, Shingo; Chokawa, Kenta; Shirakawa, Hiroki; Araidai, Masaaki; Kageshima, Hiroyuki; Endoh, Tetsuo; Shiraishi, Kenji

2018-04-01

It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study, we used first-principles calculations based on the density functional theory, and investigated the Si emission behavior at the various interfaces on the basis of the Si emission model including its atomistic structure and dependence on Si crystal orientation. The results show that the order in which Si atoms are more likely to be emitted during thermal oxidation is (111) > (110) > (310) > (100). Moreover, the emission of Si atoms is enhanced as the compressive strain increases. Therefore, the emission of Si atoms occurs more easily in V-MOSFETs than in planar MOSFETs. To reduce Si missing in V-MOSFETs, oxidation processes that induce less strain, such as wet or pyrogenic oxidation, are necessary.

Characterization of complex carbide–silicide precipitates in a Ni–Cr–Mo–Fe–Si alloy modified by welding

Energy Technology Data Exchange (ETDEWEB)

Bhattacharyya, D., E-mail: dhb@ansto.gov.au; Davis, J.; Drew, M.; Harrison, R.P.; Edwards, L.

2015-07-15

Nickel based alloys of the type Hastelloy-N™ are ideal candidate materials for molten salt reactors, as well as for applications such as pressure vessels, due to their excellent resistance to creep, oxidation and corrosion. In this work, the authors have attempted to understand the effects of welding on the morphology, chemistry and crystal structure of the precipitates in the heat affected zone (HAZ) and the weld zone of a Ni–Cr–Mo–Fe–Si alloy similar to Hastelloy-N™ in composition, by using characterization techniques such as scanning and transmission electron microscopy. Two plates of a Ni–Cr–Mo–Fe–Si alloy GH-3535 were welded together using a TiG welding process without filler material to achieve a joint with a curved molten zone with dendritic structure. It is evident that the primary precipitates have melted in the HAZ and re-solidified in a eutectic-like morphology, with a chemistry and crystal structure only slightly different from the pre-existing precipitates, while the surrounding matrix grains remained unmelted, except for the zones immediately adjacent to the precipitates. In the molten zone, the primary precipitates were fully melted and dissolved in the matrix, and there was enrichment of Mo and Si in the dendrite boundaries after solidification, and re-precipitation of the complex carbides/silicides at some grain boundaries and triple points. The nature of the precipitates in the molten zone varied according to the local chemical composition. - Graphical abstract: Display Omitted - Highlights: • Ni-based alloy with Cr, Mo, Si, Fe and C was welded, examined with SEM, EBSD, and TEM. • Original Ni{sub 2}(Mo,Cr){sub 4}(Si,C) carbides changed from equiaxed to lamellar shape in HAZ. • Composition and crystal structure remained almost unchanged in HAZ. • Original carbides changed to lamellar Ni{sub 3}(Mo,Cr){sub 3}(Si,C) in some cases in weld metal. • Precipitates were mostly incoherent, but semi-coherent in some cases in weld

Characterization of complex carbide–silicide precipitates in a Ni–Cr–Mo–Fe–Si alloy modified by welding

International Nuclear Information System (INIS)

Bhattacharyya, D.; Davis, J.; Drew, M.; Harrison, R.P.; Edwards, L.

2015-01-01

Nickel based alloys of the type Hastelloy-N™ are ideal candidate materials for molten salt reactors, as well as for applications such as pressure vessels, due to their excellent resistance to creep, oxidation and corrosion. In this work, the authors have attempted to understand the effects of welding on the morphology, chemistry and crystal structure of the precipitates in the heat affected zone (HAZ) and the weld zone of a Ni–Cr–Mo–Fe–Si alloy similar to Hastelloy-N™ in composition, by using characterization techniques such as scanning and transmission electron microscopy. Two plates of a Ni–Cr–Mo–Fe–Si alloy GH-3535 were welded together using a TiG welding process without filler material to achieve a joint with a curved molten zone with dendritic structure. It is evident that the primary precipitates have melted in the HAZ and re-solidified in a eutectic-like morphology, with a chemistry and crystal structure only slightly different from the pre-existing precipitates, while the surrounding matrix grains remained unmelted, except for the zones immediately adjacent to the precipitates. In the molten zone, the primary precipitates were fully melted and dissolved in the matrix, and there was enrichment of Mo and Si in the dendrite boundaries after solidification, and re-precipitation of the complex carbides/silicides at some grain boundaries and triple points. The nature of the precipitates in the molten zone varied according to the local chemical composition. - Graphical abstract: Display Omitted - Highlights: • Ni-based alloy with Cr, Mo, Si, Fe and C was welded, examined with SEM, EBSD, and TEM. • Original Ni 2 (Mo,Cr) 4 (Si,C) carbides changed from equiaxed to lamellar shape in HAZ. • Composition and crystal structure remained almost unchanged in HAZ. • Original carbides changed to lamellar Ni 3 (Mo,Cr) 3 (Si,C) in some cases in weld metal. • Precipitates were mostly incoherent, but semi-coherent in some cases in weld metal

A Method to Predict the Structure and Stability of RNA/RNA Complexes.

Science.gov (United States)

Xu, Xiaojun; Chen, Shi-Jie

2016-01-01

RNA/RNA interactions are essential for genomic RNA dimerization and regulation of gene expression. Intermolecular loop-loop base pairing is a widespread and functionally important tertiary structure motif in RNA machinery. However, computational prediction of intermolecular loop-loop base pairing is challenged by the entropy and free energy calculation due to the conformational constraint and the intermolecular interactions. In this chapter, we describe a recently developed statistical mechanics-based method for the prediction of RNA/RNA complex structures and stabilities. The method is based on the virtual bond RNA folding model (Vfold). The main emphasis in the method is placed on the evaluation of the entropy and free energy for the loops, especially tertiary kissing loops. The method also uses recursive partition function calculations and two-step screening algorithm for large, complicated structures of RNA/RNA complexes. As case studies, we use the HIV-1 Mal dimer and the siRNA/HIV-1 mutant (T4) to illustrate the method.

Filter optimization of Si and SiC semiconductor-based H5 and Conergy-NPC transformerless PV inverters

DEFF Research Database (Denmark)

Saridakis, Stefanos; Koutroulis, Eftichios; Blaabjerg, Frede

2013-01-01

Single-phase transformerless Photovoltaic (PV) inverters are synthesized by combining available solutions in terms of the power section topology, power semiconductors manufacturing technology and structure of the output filter. A design method is presented in this paper for optimizing the power......C-based PV inverters will inject more energy into the electric grid, compared to the Si-based structures and enable the reduction of the output filter size, weight and cost. Employing an LLCL-type output filter and simultaneously reducing the cost of SiC power semiconductors to the level of their Si...

Reaction of ReH sub 7 (PPh sub 3 ) sub 2 with silanes: Preparation and characterization of the first silyl polyhydride complexes, ReH sub 6 (SiR sub 3 )(PPh sub 3 ) sub 2 (SiR sub 3 = SiPh sub 3 , SiEt sub 3 , SiHEt sub 2 )

Energy Technology Data Exchange (ETDEWEB)

Luo, Xiaoliang; Baudry, D.; Boydell, P.; Charpin, P.; Nierlich, M.; Ephritikhine, M.; Crabtree, R.H. (Yale Univ., New Haven, CT (USA) CEA-CEN Saclay, Gif-sur-Yvette (France))

1990-04-18

Reaction of silanes with ReH{sub 7}(PPh{sub 3}){sub 2} (1) gives the novel rhenium silyl hexahydride complexes ReH{sub 6}(SiR{sub 3})(PPh{sub 3}){sub 2} (SiR{sub 3} = SiPh{sub 3} (2a), SiEt{sub 3} (2b), SiHEt{sub 2} (2c)), which have been fully characterized by IR and {sup 1}H, {sup 31}P, and {sup 13}C NMR spectroscopy and, in the case of 2a, by single-crystal x-ray crystallography. The spectroscopic and x-ray diffraction data suggest that 2a-c probably have a classical nine-coordinate tricapped trigonal-prismatic structure with the two phosphine ligands and the silyl group occupying the three equatorial sites and the six hydride ligands occupying the six axial positions. 2a has been obtained in two crystalline forms, one solvated (CH{sub 2}Cl{sub 2}) and the other unsolvated, and structures were determined on both. The crystal structures of crystals of unsolvated 2a and 2a {times} CH{sub 2} Cl{sub 2} are reported. The Re-Si bond lengths, 2.474 (4) {angstrom} (2a) and 2.475 (4) {angstrom} (2a {times} CH{sub 2}Cl{sub 2}), are shorter than the sum of the covalent radii of the Re and Si atoms (2.65 {angstrom}), which is unusual for a transition-metal silyl complex with a formal d{sup 0} configuration. 35 refs., 2 figs., 4 tabs.

In-situ synthesis of SiC particles by the structural evolution of TiCx in Al–Si melt

International Nuclear Information System (INIS)

Nie, Jinfeng; Li, Dakui; Wang, Enzhao; Liu, Xiangfa

2014-01-01

Highlights: • A facile method to in-situ synthesize SiC was developed utilizing the structural evolution of TiC x in Al–Si melt. • The SiC particles have the size range from 2.5 to 7.5 μm and a block-like morphology. • The SiC particles and (SiC + TiB 2 ) hybrid-particles reinforced Al–18Si composite were prepared. • The wear resistance effect of SiC on the based alloy was investigated. - Abstract: A facile method has been developed to in-situ synthesize SiC particles utilizing the structural instability and evolution of TiC x in Al–Si melt. It is considered that the synthesis of SiC particles occurs via the gradual reaction between TiC x and Si atoms, whilst Si content plays the crucial role in this approach. If the Si content in the melt is above 30%, TiC x directly reacts with Si and Al to form SiC, but the needle-like TiAl x Si y phase formed simultaneously will do harm to the mechanical properties of the composites. Thus, it is proposed to add B element in the melt to transform the TiAl x Si y into TiB 2 particles. Therefore, the SiC and (SiC + TiB 2 ) hybrid-particles reinforced Al–18Si composites were successfully prepared using the method. In the composites, the SiC particles have the size range from 2.5 to 7.5 μm and a block-like morphology. Furthermore, the mechanical properties of base alloy, including the wear resistance and macro-hardness, have been obviously improved by the in-situ SiC particles. Besides, the relevant underlying mechanisms are also discussed

High-dose MeV electron irradiation of Si-SiO2 structures implanted with high doses Si+

Science.gov (United States)

Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

2018-03-01

The influence was studied of 22-MeV electron irradiation on Si-SiO2 structures implanted with high-fluence Si+ ions. Our earlier works demonstrated that Si redistribution is observed in Si+-ion-implanted Si-SiO2 structures (after MeV electron irradiation) only in the case when ion implantation is carried out with a higher fluence (1016 cm-2). We focused our attention on the interaction of high-dose MeV electron irradiation (6.0×1016 cm-2) with n-Si-SiO2 structures implanted with Si+ ions (fluence 5.4×1016 cm-2 of the same order magnitude). The redistribution of both oxygen and silicon atoms in the implanted Si-SiO2 samples after MeV electron irradiation was studied by Rutherford back-scattering (RBS) spectroscopy in combination with a channeling technique (RBS/C). Our results demonstrated that the redistribution of oxygen and silicon atoms in the implanted samples reaches saturation after these high doses of MeV electron irradiation. The transformation of amorphous SiO2 surface into crystalline Si nanostructures (after MeV electron irradiation) was evidenced by atomic force microscopy (AFM). Silicon nanocrystals are formed on the SiO2 surface after MeV electron irradiation. The shape and number of the Si nanocrystals on the SiO2 surface depend on the MeV electron irradiation, while their size increases with the dose. The mean Si nanocrystals height is 16-20 nm after irradiation with MeV electrons at the dose of 6.0×1016 cm-2.

The structure modification of Si-SiO2 irradiated by Fe+ ion

International Nuclear Information System (INIS)

Jin Tao; Ma Zhongquan; Guo Qi

1992-01-01

The effect of the iron ion implantation on the oxide surface and SiO 2 -Si interface of MOS structure was studied by X-ray photo-electron spectroscopy (XPS), and the chemical states of compounds formed were examined. The results obtained show that in the surface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface thickness is almost doubled that leads to failure of MOS capacitors. The physical and chemical mechanisms of MOS structure change by Fe + ion implantation are also discussed and analyzed

Modular fabrication and characterization of complex silicon carbide composite structures Advanced Reactor Technologies (ART) Research Final Report (Feb 2015 – May 2017)

Energy Technology Data Exchange (ETDEWEB)

Khalifa, Hesham [General Atomics, San Diego, CA (United States)

2017-08-03

Advanced ceramic materials exhibit properties that enable safety and fuel cycle efficiency improvements in advanced nuclear reactors. In order to fully exploit these desirable properties, new processing techniques are required to produce the complex geometries inherent to nuclear fuel assemblies and support structures. Through this project, the state of complex SiC-SiC composite fabrication for nuclear components has advanced significantly. New methods to produce complex SiC-SiC composite structures have been demonstrated in the form factors needed for in-core structural components in advanced high temperature nuclear reactors. Advanced characterization techniques have been employed to demonstrate that these complex SiC-SiC composite structures provide the strength, toughness and hermeticity required for service in harsh reactor conditions. The complex structures produced in this project represent a significant step forward in leveraging the excellent high temperature strength, resistance to neutron induced damage, and low neutron cross section of silicon carbide in nuclear applications.

Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation.

Science.gov (United States)

Yang, Lina; Minnich, Austin J

2017-03-14

Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

Computer Aided Multi-scale Design of SiC-Si3N4 Nanoceramic Composites for High-Temperature Structural Applications

Energy Technology Data Exchange (ETDEWEB)

Vikas Tomer; John Renaud

2010-08-31

It is estimated that by using better and improved high temperature structural materials, the power generation efficiency of the power plants can be increased by 15% resulting in significant cost savings. One such promising material system for future high-temperature structural applications in power plants is Silicon Carbide-Silicon Nitride (SiC-Si{sub 3}N{sub 4}) nanoceramic matrix composites. The described research work focuses on multiscale simulation-based design of these SiC-Si{sub 3}N{sub 4} nanoceramic matrix composites. There were two primary objectives of the research: (1) Development of a multiscale simulation tool and corresponding multiscale analyses of the high-temperature creep and fracture resistance properties of the SiC-Si{sub 3}N{sub 4} nanocomposites at nano-, meso- and continuum length- and timescales; and (2) Development of a simulation-based robust design optimization methodology for application to the multiscale simulations to predict the range of the most suitable phase morphologies for the desired high-temperature properties of the SiC-Si{sub 3}N{sub 4} nanocomposites. The multiscale simulation tool is based on a combination of molecular dynamics (MD), cohesive finite element method (CFEM), and continuum level modeling for characterizing time-dependent material deformation behavior. The material simulation tool is incorporated in a variable fidelity model management based design optimization framework. Material modeling includes development of an experimental verification framework. Using material models based on multiscaling, it was found using molecular simulations that clustering of the SiC particles near Si{sub 3}N{sub 4} grain boundaries leads to significant nanocomposite strengthening and significant rise in fracture resistance. It was found that a control of grain boundary thicknesses by dispersing non-stoichiometric carbide or nitride phases can lead to reduction in strength however significant rise in fracture strength. The

Effects of the c-Si/a-SiO2 interfacial atomic structure on its band alignment: an ab initio study.

Science.gov (United States)

Zheng, Fan; Pham, Hieu H; Wang, Lin-Wang

2017-12-13

The crystalline-Si/amorphous-SiO 2 (c-Si/a-SiO 2 ) interface is an important system used in many applications, ranging from transistors to solar cells. The transition region of the c-Si/a-SiO 2 interface plays a critical role in determining the band alignment between the two regions. However, the question of how this interface band offset is affected by the transition region thickness and its local atomic arrangement is yet to be fully investigated. Here, by controlling the parameters of the classical Monte Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thicknesses, as well as containing Si at different oxidation states. A hybrid functional method, as shown by our calculations to reproduce the GW and experimental results for bulk Si and SiO 2 , was used to calculate the electronic structure of the heterojunction. This allowed us to study the correlation between the interface band characterization and its atomic structures. We found that although the systems with different thicknesses showed quite different atomic structures near the transition region, the calculated band offset tended to be the same, unaffected by the details of the interfacial structure. Our band offset calculation agrees well with the experimental measurements. This robustness of the interfacial electronic structure to its interfacial atomic details could be another reason for the success of the c-Si/a-SiO 2 interface in Si-based electronic applications. Nevertheless, when a reactive force field is used to generate the a-SiO 2 and c-Si/a-SiO 2 interfaces, the band offset significantly deviates from the experimental values by about 1 eV.

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-05-16

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

Research Progress on Preparation for Biomass-based SiC Ceramic

Directory of Open Access Journals (Sweden)

CUI He-shuai

2017-08-01

Full Text Available Silicon carbide (SiC ceramics prepared by the conventional process has excellent properties and wide application prospects, but the increased cost of high-temperature preparation process restricts its further development. In contrast, the abundant porous structure of biomass makes itself to be ideal replacement of SiC ceramic prepared at low temperature. This paper reviewed the structure characteristics, preparation methods, pyrolysis mechanism and influence parameters of biomass-based SiC ceramic, and eventually explored the current problems and development trends of the pretreatment of carbon source and silicon source, the pyrolysis process and the application research on the preparation for biomass-based SiC ceramic.

Formation, structure, and phonon confinement effect of nanocrystalline Si1-xGex in SiO2-Si-Ge cosputtered films

International Nuclear Information System (INIS)

Yang, Y.M.; Wu, X.L.; Siu, G.G.; Huang, G.S.; Shen, J.C.; Hu, D.S.

2004-01-01

Using magnetron cosputtering of SiO 2 , Ge, and Si targets, Si-based SiO 2 :Ge:Si films were fabricated for exploring the influence of Si target proportion (P Si ) and annealing temperature (Ta) on formation, local structure, and phonon properties of nanocrystalline Si 1-x Ge x (nc-Si 1-x Ge x ). At low P Si and Ta higher than 800 deg. C, no nc-Si 1-x Ge x but a kind of composite nanocrystal consisting of a Ge core, GeSi shell, and amorphous Si outer shell is formed in the SiO 2 matrix. At moderate P Si , nc-Si 1-x Ge x begins to be formed at Ta=800 deg. C and coexists with nc-Ge at Ta=1100 deg. C. At high P Si , it was disclosed that both optical phonon frequency and lattice spacing of nc-Si 1-x Ge x increase with raising Ta. The possible origin of this phenomenon is discussed by considering three factors, the phonon confinement, strain effect, and composition variation of nc-Si 1-x Ge x . This work will be helpful in understanding the growth process of ternary GeSiO films and beneficial to further investigations on optical properties of nc-Ge 1-x Si x in the ternary matrix

Characterization of μc-Si:H/a-Si:H tandem solar cell structures by spectroscopic ellipsometry

International Nuclear Information System (INIS)

Murata, Daisuke; Yuguchi, Tetsuya; Fujiwara, Hiroyuki

2014-01-01

In order to perform the structural characterization of Si thin-film solar cells having submicron-size rough textured surfaces, we have developed an optical model that can be utilized for the spectroscopic ellipsometry (SE) analysis of a multilayer solar cell structure consisting of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) layers fabricated on textured SnO 2 :F substrates. To represent the structural non-uniformity in the textured structure, the optical response has been calculated from two regions with different thicknesses of the Si layers. Moreover, in the optical model, the interface layers are modeled by multilayer structures assuming two-phase composites and the volume fractions of the phases in the layers are controlled by the structural curvature factor. The polarized reflection from the μc-Si:H layer that shows extensive surface roughening during the growth has also been modeled. In this study, a state-of-the-art solar cell structure with the textured μc-Si:H (2000 nm)/ZnO (100 nm)/a-Si:H (200 nm)/SnO 2 :F/glass substrate structure has been characterized. The μc-Si:H/a-Si:H textured structure deduced from our SE analysis shows remarkable agreement with that observed by transmission electron microscopy. From the above results, we have demonstrated the high-precision characterization of highly-textured μc-Si:H/a-Si:H solar cell structures. - Highlights: • Characterization of textured μc-Si:H/a-Si:H solar cell structures by ellipsometry • A new optical model using surface area and multilayer models • High precision characterization of submicron-range rough interface structures

Primary design of Si cooling arm structure in ICF cryogenic target

International Nuclear Information System (INIS)

Zhang Yong; Yi Yong; Tang Changhuan; Zhang Jicheng

2013-01-01

According to the requirement of the cryogenic target system to the Si cooling arm structure, the Si cooling arm was primarily designed based on the USA National Ignition Facility (NIF) target. A new three-dimensional model of Si cooling arm was developed by SolidWorks software, and the simulation and analysis of Si cooling arm in aspect of mechanical property, thermal response and assembly were made based on the model. A law about the effect of the arm length of Si cooling arm and the width and the length of bifurcation on Si cooling arm was achieved. The research may provide the theoretical foundation and reference for the further improvement of cryogenic target. (authors)

RNACompress: Grammar-based compression and informational complexity measurement of RNA secondary structure

Directory of Open Access Journals (Sweden)

Chen Chun

2008-03-01

Full Text Available Abstract Background With the rapid emergence of RNA databases and newly identified non-coding RNAs, an efficient compression algorithm for RNA sequence and structural information is needed for the storage and analysis of such data. Although several algorithms for compressing DNA sequences have been proposed, none of them are suitable for the compression of RNA sequences with their secondary structures simultaneously. This kind of compression not only facilitates the maintenance of RNA data, but also supplies a novel way to measure the informational complexity of RNA structural data, raising the possibility of studying the relationship between the functional activities of RNA structures and their complexities, as well as various structural properties of RNA based on compression. Results RNACompress employs an efficient grammar-based model to compress RNA sequences and their secondary structures. The main goals of this algorithm are two fold: (1 present a robust and effective way for RNA structural data compression; (2 design a suitable model to represent RNA secondary structure as well as derive the informational complexity of the structural data based on compression. Our extensive tests have shown that RNACompress achieves a universally better compression ratio compared with other sequence-specific or common text-specific compression algorithms, such as Gencompress, winrar and gzip. Moreover, a test of the activities of distinct GTP-binding RNAs (aptamers compared with their structural complexity shows that our defined informational complexity can be used to describe how complexity varies with activity. These results lead to an objective means of comparing the functional properties of heteropolymers from the information perspective. Conclusion A universal algorithm for the compression of RNA secondary structure as well as the evaluation of its informational complexity is discussed in this paper. We have developed RNACompress, as a useful tool

Electrochemically synthesized Si nano wire arrays and thermoelectric nano structures

International Nuclear Information System (INIS)

Khuan, N.I.; Ying, K.K.; Nur Ubaidah Saidin; Foo, C.T.

2012-01-01

Thermoelectric nano structures hold great promise for capturing and directly converting into electricity some vast amount of low-grade waste heats now being lost to the environment (for example from nuclear power plant, fossil fuel burning, automotive and household appliances). In this study, large-area vertically-aligned silicon nano wire (SiNW) arrays were synthesized in an aqueous solution containing AgNO 3 and HF on p-type Si (100) substrate by self-selective electroless etching process. The etching conditions were systematically varied in order to achieve different stages of nano wire formation. Diameters of the SiNWs obtained varied from approximately 50 to 200 nm and their lengths ranged from several to a few tens of μm. Te/ Bi 2 Te 3 -Si thermoelectric core-shell nano structures were subsequently obtained via galvanic displacement of SiNWs in acidic HF electrolytes containing HTeO 2 + and Bi 3+ / HTeO 2 + ions. The reactions were basically a nano-electrochemical process due to the difference in redox potentials between the materials. the surface-modified SiNWs of core-shell structures had roughened surface morphologies and therefore, higher surface-t-bulk ratios compared to unmodified SiNWs. They have potential applications in sensors, photovoltaic and thermoelectric nano devices. Growth study on the SiNWs and core-shell nano structures produced is presented using various microscopy, diffraction and probe-based techniques for microstructural, morphological and chemical characterizations. (Author)

Quasi-2D silicon structures based on ultrathin Me2Si (Me = Mg, Ca, Sr, Ba) films

Science.gov (United States)

Migas, D. B.; Bogorodz, V. O.; Filonov, A. B.; Borisenko, V. E.; Skorodumova, N. V.

2018-04-01

By means of ab initio calculations with hybrid functionals we show a possibility for quasi-2D silicon structures originated from semiconducting Mg2Si, Ca2Si, Sr2Si and Ba2Si silicides to exist. Such a 2D structure is similar to the one of transition metal chalcogenides where silicon atoms form a layer in between of metal atoms aligned in surface layers. These metal surface atoms act as pseudo passivation species stabilizing crystal structure and providing semiconducting properties. Considered 2D Mg2Si, Ca2Si, Sr2Si and Ba2Si have band gaps of 1.14 eV, 0.69 eV, 0.33 eV and 0.19 eV, respectively, while the former one is also characterized by a direct transition with appreciable oscillator strength. Electronic states of the surface atoms are found to suppress an influence of the quantum confinement on the band gaps. Additionally, we report Sr2Si bulk in the cubic structure to have a direct band gap of 0.85 eV as well as sizable oscillator strength of the first direct transition.

Revision of the Li13Si4 structure.

Science.gov (United States)

Zeilinger, Michael; Fässler, Thomas F

2013-11-06

Besides Li17Si4, Li16.42Si4, and Li15Si4, another lithium-rich representative in the Li-Si system is the phase Li13Si4 (trideca-lithium tetra-silicide), the structure of which has been determined previously [Frank et al. (1975 ▶). Z. Naturforsch. Teil B, 30, 10-13]. A careful analysis of X-ray diffraction patterns of Li13Si4 revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li13Si4 on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i) the introduction of a split position for one Li site [occupancy ratio 0.838 (7):0.162 (7)], (ii) the anisotropic refinement of atomic displacement parameters for all atoms, and (iii) a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li13Si4 contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si-Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in the ab plane at z = 0 and are strictly separated from the Si-Si dumbbells at z = 0.5.

Structure and magnetism in novel group IV element-based magnetic materials

Energy Technology Data Exchange (ETDEWEB)

Tsui, Frank [Univ. of North Carolina, Chapel Hill, NC (United States)

2013-08-14

The project is to investigate structure, magnetism and spin dependent states of novel group IV element-based magnetic thin films and heterostructures as a function of composition and epitaxial constraints. The materials systems of interest are Si-compatible epitaxial films and heterostructures of Si/Ge-based magnetic ternary alloys grown by non-equilibrium molecular beam epitaxy (MBE) techniques, specifically doped magnetic semiconductors (DMS) and half-metallic Heusler alloys. Systematic structural, chemical, magnetic, and electrical measurements are carried out, using x-ray microbeam techniques, magnetotunneling spectroscopy and microscopy, and magnetotransport. The work is aimed at elucidating the nature and interplay between structure, chemical order, magnetism, and spin-dependent states in these novel materials, at developing materials and techniques to realize and control fully spin polarized states, and at exploring fundamental processes that stabilize the epitaxial magnetic nanostructures and control the electronic and magnetic states in these complex materials. Combinatorial approach provides the means for the systematic studies, and the complex nature of the work necessitates this approach.

Nano-Ag complexes prepared by γ-radiolysis and their structures and physical properties

International Nuclear Information System (INIS)

Kim, Hwa-Jung; Choi, Seong-Ho; Park, Hae-Jun

2012-01-01

In this study, nano-silver (nano-Ag) complexes showing different properties have been synthesized as follows. Polypyrrolidone (PVP)-stabilized silver colloids (NAg), nano-Ag bound to silica (SiO 2 ) (NSS), and nano-Ag bound to a complex of SiO 2 and polyaniline (PANI) (NSSPAI) were prepared via γ-irradiation at room temperature. NAg and NSS used PVP as a colloidal stabilizer, while NSSPAI did not use PVP as a colloidal stabilizer. Interesting bonding properties occurred in the nano-Ag complex and anticipated structural changes were clearly shown through a surface analysis of x-ray photoelectron spectroscopy (XPS). The morphologies by field emission-scanning electron microscopy (FE-SEM) analysis showed that nano-Ag complexes have various particle sizes ranging from 10 to 30 nm. NSS (average, 10 nm) and NSSPAI (average, 30 nm) showed a uniformly spherical shape and size, while NAg did not. From the reflection peaks in the x-ray diffraction (XRD) patterns, surface crystallinity of the nano-Ag complexes was indicated to be in the same degree as that of NSSPAI>NSS>NAg. Also, in the contact angle (CA) determination, surface hydrophobicity of NSSPAI was stronger than those of NSS and NAg, relatively. The different nano-Ag complexes prepared by γ-irradiation can be applicable in various industry fields due to the increase in specific property. - Highlights: ► Nano-Ag complexes showing different properties have been synthesized via γ-irradiation. ► Nano-Ag colloid (NAg), nano-Ag bound to SiO 2 (NSS), nano-Ag bound to SiO 2 and PANI complex (NSSPAI). ► Nano-Ag complexes were the same based on Ag metal. ► Results clearly showed fascinating/different physical properties. ► Different nano-Ag complexes can be applicable in various industry fields.

Nano-structural properties of ZnO films for Si based heterojunction solar cells

Energy Technology Data Exchange (ETDEWEB)

Breivik, T.H. [University of Oslo, Department of Physics, P.O. Box 1048, Blindern, NO-0316, Oslo (Norway)], E-mail: t.h.breivik@fys.uio.no; Diplas, S. [University of Oslo, Department of Physics, P.O. Box 1048, Blindern, NO-0316, Oslo (Norway); University of Oslo, Center for Material Science and Nanotechnology, P.O. Box 1126, Blindern, NO-0318 Oslo (Norway); Ulyashin, A.G. [Section for Renewable Energy, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller (Norway); Gunnaes, A.E. [University of Oslo, Department of Physics, P.O. Box 1048, Blindern, NO-0316, Oslo (Norway); Olaisen, B.R.; Wright, D.N.; Holt, A. [Section for Renewable Energy, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller (Norway); Olsen, A. [University of Oslo, Department of Physics, P.O. Box 1048, Blindern, NO-0316, Oslo (Norway)

2007-10-15

Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.

Nano-structural properties of ZnO films for Si based heterojunction solar cells

International Nuclear Information System (INIS)

Breivik, T.H.; Diplas, S.; Ulyashin, A.G.; Gunnaes, A.E.; Olaisen, B.R.; Wright, D.N.; Holt, A.; Olsen, A.

2007-01-01

Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping

Revision of the Li13Si4 structure

Directory of Open Access Journals (Sweden)

Thomas F. Fässler

2013-12-01

Full Text Available Besides Li17Si4, Li16.42Si4, and Li15Si4, another lithium-rich representative in the Li–Si system is the phase Li13Si4 (tridecalithium tetrasilicide, the structure of which has been determined previously [Frank et al. (1975. Z. Naturforsch. Teil B, 30, 10–13]. A careful analysis of X-ray diffraction patterns of Li13Si4 revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li13Si4 on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i the introduction of a split position for one Li site [occupancy ratio 0.838 (7:0.162 (7], (ii the anisotropic refinement of atomic displacement parameters for all atoms, and (iii a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li13Si4 contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si–Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in the ab plane at z = 0 and are strictly separated from the Si–Si dumbbells at z = 0.5.

A spot laser modulated resistance switching effect observed on n-type Mn-doped ZnO/SiO2/Si structure.

Science.gov (United States)

Lu, Jing; Tu, Xinglong; Yin, Guilin; Wang, Hui; He, Dannong

2017-11-09

In this work, a spot laser modulated resistance switching (RS) effect is firstly observed on n-type Mn-doped ZnO/SiO 2 /Si structure by growing n-type Mn-doped ZnO film on Si wafer covered with a 1.2 nm native SiO 2 , which has a resistivity in the range of 50-80 Ω∙cm. The I-V curve obtained in dark condition evidences the structure a rectifying junction, which is further confirmed by placing external bias. Compared to the resistance state modulated by electric field only in dark (without illumination), the switching voltage driving the resistance state of the structure from one state to the other, shows clear shift under a spot laser illumination. Remarkably, the switching voltage shift shows a dual dependence on the illumination position and power of the spot laser. We ascribe this dual dependence to the electric filed produced by the redistribution of photo-generated carriers, which enhance the internal barrier of the hetero-junction. A complete theoretical analysis based on junction current and diffusion equation is presented. The dependence of the switching voltage on spot laser illumination makes the n-type Mn-doped ZnO/SiO 2 /Si structure sensitive to light, which thus allows for the integration of an extra functionality in the ZnO-based photoelectric device.

Structural and electrical properties of epitaxial Si layers prepared by E-beam evaporation

Energy Technology Data Exchange (ETDEWEB)

Dogan, P. [Hahn-Meitner-Institut Berlin, Kekulestr. 5, 12489 Berlin (Germany)], E-mail: pinar.dogan@hmi.de; Rudigier, E.; Fenske, F.; Lee, K.Y.; Gorka, B.; Rau, B.; Conrad, E.; Gall, S. [Hahn-Meitner-Institut Berlin, Kekulestr. 5, 12489 Berlin (Germany)

2008-08-30

In this work, we present structural and electrical properties of thin Si films which are homoepitaxially grown at low substrate temperatures (T{sub s} 450-700 deg. C) by high-rate electron beam evaporation. As substrates, monocrystalline Si wafers with (100) and (111) orientations and polycrystalline Si (poly-Si) seed layers on glass were used. Applying Secco etching, films grown on Si(111) wafers exhibit a decreasing etch pit density with increasing T{sub s}. The best structural quality of the films was obtained on Si(100) wafers. Defect etching on epitaxially grown poly-Si absorbers reveal regions with different crystalline quality. Solar cells have been prepared on both wafers and seed layers. Applying Rapid Thermal Annealing (RTA) and Hydrogen plasma passivation an open circuit voltage of 570 mV for wafer based and 346 mV for seed layer based solar cells have been reached.

Thermal characterization of tubular SiC/SiC composite structures for nuclear applications

International Nuclear Information System (INIS)

Duquesne, Loys

2015-01-01

Researches on the development on SiCf/SiC refractory composites for generation IV nuclear fuel cladding led the CEA to focus on the thermal behavior of these materials. In particular, knowledge of the thermal properties is essential for designing the components. Regarding the development of the 'sandwich' cladding concept, for which the complexity and the geometry differ from the conventionally used flat tubes, usual measurement methods are unsuitable. This study reports on the characterization and modeling of the thermal behavior of these structures. The first part deals with the identification of the global thermal parameters for the different layers of a 'sandwich' cladding. For this purpose, a flash method is used and an experimental device suitable for tubular geometries was developed. A new estimation method based on the combination of both collected signals in front and rear faces allows the identification of the thermal diffusivity of tubular composites using infrared thermography. The second part focuses on a virtual material approach, established to describe the thermal behavior of a 'sandwich' cladding, starting from the measured properties of the elementary components (fibers and matrix). They are then used as input data for the heat transfer modeling. Confrontations between experimental measurements and numerical results finally allow us to understand the importance of the various key parameters governing the heat transfer. (author) [fr

Biomimetic synthesis of cellular SiC based ceramics from plant ...

Indian Academy of Sciences (India)

Unknown

SiC based materials so derived can be used in structural applications and in designing high temperature filters and catalyst supports. Keywords. Biomimetic synthesis; carbonaceous biopreform; biomorphic Si–SiC ceramic composites; porous cellular SiC ceramics. 1. Introduction. In recent years, there has been tremendous ...

Geometric structure of thin SiO xN y films on Si(100)

Science.gov (United States)

Behrens, K.-M.; Klinkenberg, E.-D.; Finster, J.; Meiwes-Broer, K.-H.

1998-05-01

Thin films of amorphous stoichometric SiO xN y are deposited on radiation-heated Si(100) by rapid thermal low-pressure chemical vapour deposition. We studied the whole range of possible compositions. In order to determine the geometric structure, we used EXAFS and photoelectron spectroscopy. Tetrahedrons constitute the short-range units with a central Si atom connected to N and O. The distribution of the possible tetrahedrons can be described by a mixture of the Random Bonding Model and the Random Mixture Model. For low oxygen contents x/( x+ y)≤0.3, the geometric structure of the film is almost the structure of a-Si 3N 4, with the oxygen preferably on top of Si-N 3 triangles. Higher oxygen contents induce changes in the bond lengths, bond angles and coordination numbers.

Polyamidoamine-Decorated Nanodiamonds as a Hybrid Gene Delivery Vector and siRNA Structural Characterization at the Charged Interfaces.

Science.gov (United States)

Lim, Dae Gon; Rajasekaran, Nirmal; Lee, Dukhee; Kim, Nam Ah; Jung, Hun Soon; Hong, Sungyoul; Shin, Young Kee; Kang, Eunah; Jeong, Seong Hoon

2017-09-20

Nanodiamonds have been discovered as a new exogenous material source in biomedical applications. As a new potent form of nanodiamond (ND), polyamidoamine-decorated nanodiamonds (PAMAM-NDs) were prepared for E7 or E6 oncoprotein-suppressing siRNA gene delivery for high risk human papillomavirus-induced cervical cancer, such as types 16 and 18. It is critical to understand the physicochemical properties of siRNA complexes immobilized on cationic solid ND surfaces in the aspect of biomolecular structural and conformational changes, as the new inert carbon material can be extended into the application of a gene delivery vector. A spectral study of siRNA/PAMAM-ND complexes using differential scanning calorimetry and circular dichroism spectroscopy proved that the hydrogen bonding and electrostatic interactions between siRNA and PAMAM-NDs decreased endothermic heat capacity. Moreover, siRNA/PAMAM-ND complexes showed low cell cytotoxicity and significant suppressing effects for forward target E6 and E7 oncogenic genes, proving functional and therapeutic efficacy. The cellular uptake of siRNA/PAMAM-ND complexes at 8 h was visualized by macropinocytes and direct endosomal escape of the siRNA/PAMAM-ND complexes. It is presumed that PAMAM-NDs provided a buffering cushion to adjust the pH and hard mechanical stress to escape endosomes. siRNA/PAMAM-ND complexes provide a potential organic/inorganic hybrid material source for gene delivery carriers.

Interface Engineering for Atomic Layer Deposited Alumina Gate Dielectric on SiGe Substrates.

OpenAIRE

Zhang, L; Guo, Y; Hassan, VV; Tang, K; Foad, MA; Woicik, JC; Pianetta, P; Robertson, John; McIntyre, PC

2016-01-01

Optimization of the interface between high-k dielectrics and SiGe substrates is a challenging topic due to the complexity arising from the coexistence of Si and Ge interfacial oxides. Defective high-k/SiGe interfaces limit future applications of SiGe as a channel material for electronic devices. In this paper, we identify the surface layer structure of as-received SiGe and Al2O3/SiGe structures based on soft and hard X-ray photoelectron spectroscopy. As-received SiGe substrates have native Si...

Complex structural hierarchies observed in Y2O3–Al2O3–SiO2 eutectic ceramics prepared by laser melting

Directory of Open Access Journals (Sweden)

Dian-Zheng Wang

2015-03-01

Full Text Available Amorphous Y2O3–Al2O3–SiO2 beads were directly melted by a Nd:YAG laser. The structural features in multi-scale of the samples after solidification were investigated. The results showed that the cooling speed in the applied processing conditions was not high enough to retain the amorphous nature of ceramic beads into the consolidated bulks. In addition to an amorphous phase two crystalline phases, YAG and α-Al2O3, were formed yielding the formation of complex structural hierarchies.

Microscopic and macroscopic characterization of the charging effects in SiC/Si nanocrystals/SiC sandwiched structures

International Nuclear Information System (INIS)

Xu, Jie; Xu, Jun; Wang, Yuefei; Cao, Yunqing; Li, Wei; Yu, Linwei; Chen, Kunji

2014-01-01

Microscopic charge injection into the SiC/Si nanocrystals/SiC sandwiched structures through a biased conductive AFM tip is subsequently characterized by both electrostatic force microscopy and Kelvin probe force microscopy (KPFM). The charge injection and retention characteristics are found to be affected by not only the band offset at the Si nanocrystals/SiC interface but also the doping type of the Si substrate. On the other hand, capacitance–voltage (C–V) measurements investigate the macroscopic charging effect of the sandwiched structures with a thicker SiC capping layer, where the charges are injected from the Si substrates. The calculated macroscopic charging density is 3–4 times that of the microscopic one, and the possible reason is the underestimation of the microscopic charging density caused by the averaging effect and detection delay in the KPFM measurements. (paper)

Investigation of structural and electronic properties of epitaxial graphene on 3C–SiC(100/Si(100 substrates

Directory of Open Access Journals (Sweden)

Gogneau N

2014-09-01

Full Text Available Noelle Gogneau,1 Amira Ben Gouider Trabelsi,2 Mathieu G Silly,3 Mohamed Ridene,1 Marc Portail,4 Adrien Michon,4 Mehrezi Oueslati,2 Rachid Belkhou,3 Fausto Sirotti,3 Abdelkarim Ouerghi1 1Laboratoire de Photonique et de Nanostructures, Centre National de la Recherche Scientifique, Marcoussis, France; 2Unité des Nanomatériaux et Photonique, Faculté des Sciences de Tunis, Université de Tunis El Manar Campus Universitaire, Tunis, Tunisia; 3Synchrotron-SOLEIL, Saint-Aubin, BP48, F91192 Gif sur Yvette Cedex, France; 4Centre de Recherche sur l'HétéroEpitaxie et Ses Application, Centre National de la Recherche Scientifique, Valbonne, France Abstract: Graphene has been intensively studied in recent years in order to take advantage of its unique properties. Its synthesis on SiC substrates by solid-state graphitization appears a suitable option for graphene-based electronics. However, before developing devices based on epitaxial graphene, it is desirable to understand and finely control the synthesis of material with the most promising properties. To achieve these prerequisites, many studies are being conducted on various SiC substrates. Here, we review 3C–SiC(100 epilayers grown by chemical vapor deposition on Si(100 substrates for producing graphene by solid state graphitization under ultrahigh-vacuum conditions. Based on various characterization techniques, the structural and electrical properties of epitaxial graphene layer grown on 3C–SiC(100/Si(100 are discussed. We establish that epitaxial graphene presents properties similar to those obtained using hexagonal SiC substrates, with the advantage of being compatible with current Si-processing technology. Keywords: epitaxial graphene, electronic properties, structural properties, silicon carbide 

Correlation between structure and optical properties of Si-based alloys deposited by PECVD

Energy Technology Data Exchange (ETDEWEB)

Giangregorio, M.M. [Institute of Inorganic Methodologies and of Plasmas IMIP-CNR and INSTM-UdR Bari via Orabona, 4-70126 Bari (Italy)]. E-mail: michelaria@hotmail.com; Losurdo, M. [Institute of Inorganic Methodologies and of Plasmas IMIP-CNR and INSTM-UdR Bari via Orabona, 4-70126 Bari (Italy); Sacchetti, A. [Institute of Inorganic Methodologies and of Plasmas IMIP-CNR and INSTM-UdR Bari via Orabona, 4-70126 Bari (Italy); Capezzuto, P. [Institute of Inorganic Methodologies and of Plasmas IMIP-CNR and INSTM-UdR Bari via Orabona, 4-70126 Bari (Italy); Bruno, G. [Institute of Inorganic Methodologies and of Plasmas IMIP-CNR and INSTM-UdR Bari via Orabona, 4-70126 Bari (Italy)

2006-07-26

Si-based thin films, including {mu}c-Si, Si{sub 1-x}Ge {sub x} and Si{sub 1-x}C {sub x} alloys, have been deposited by plasma enhanced chemical vapor deposition (PECVD) using SiF{sub 4}:H{sub 2}:He, SiF{sub 4}:GeH{sub 4}:H{sub 2} and SiF{sub 4}:CH{sub 4}:H{sub 2} plasmas, respectively. When SiF{sub 4} is used as Si-precursor, it is found that a low flux of CH{sub 4} or GeH{sub 4} results in incorporation of C and Ge in alloys as high as 30%. Correlations between microstructure and optical properties of films are investigated using spectroscopic ellipsometry. The role of fluorine atoms in the growth chemistry and material microstructure is discussed.

Interface formation and defect structures in epitaxial La2Zr2O7 thin films on (111) Si

International Nuclear Information System (INIS)

Seo, J.W.; Fompeyrine, J.; Guiller, A.; Norga, G.; Marchiori, C.; Siegwart, H.; Locquet, J.-P.

2003-01-01

We have studied the growth of epitaxial La 2 Zr 2 O 7 thin films on (111) Si. Although the interface structure can be strongly affected by the Si oxidation during the deposition process, epitaxial growth of La 2 Zr 2 O 7 was obtained. A detailed study by means of transmission electron microscopy reveals two types of structures (pyrochlore and fluorite) with the same average chemical composition but strong differences in reactivity and interface formation. The structural complexity of the ordered pyrochlore structure seems to prevent excess oxygen diffusion and interfacial SiO 2 formation

Solving complex band structure problems with the FEAST eigenvalue algorithm

Science.gov (United States)

Laux, S. E.

2012-08-01

With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problems—as exemplified by the complex band-structure problem—even though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.

A new entropy based method for computing software structural complexity

CERN Document Server

Roca, J L

2002-01-01

In this paper a new methodology for the evaluation of software structural complexity is described. It is based on the entropy evaluation of the random uniform response function associated with the so called software characteristic function SCF. The behavior of the SCF with the different software structures and their relationship with the number of inherent errors is investigated. It is also investigated how the entropy concept can be used to evaluate the complexity of a software structure considering the SCF as a canonical representation of the graph associated with the control flow diagram. The functions, parameters and algorithms that allow to carry out this evaluation are also introduced. After this analytic phase follows the experimental phase, verifying the consistency of the proposed metric and their boundary conditions. The conclusion is that the degree of software structural complexity can be measured as the entropy of the random uniform response function of the SCF. That entropy is in direct relation...

Selective Epitaxy of InP on Si and Rectification in Graphene/InP/Si Hybrid Structure.

Science.gov (United States)

Niu, Gang; Capellini, Giovanni; Hatami, Fariba; Di Bartolomeo, Antonio; Niermann, Tore; Hussein, Emad Hameed; Schubert, Markus Andreas; Krause, Hans-Michael; Zaumseil, Peter; Skibitzki, Oliver; Lupina, Grzegorz; Masselink, William Ted; Lehmann, Michael; Xie, Ya-Hong; Schroeder, Thomas

2016-10-12

The epitaxial integration of highly heterogeneous material systems with silicon (Si) is a central topic in (opto-)electronics owing to device applications. InP could open new avenues for the realization of novel devices such as high-mobility transistors in next-generation CMOS or efficient lasers in Si photonics circuitry. However, the InP/Si heteroepitaxy is highly challenging due to the lattice (∼8%), thermal expansion mismatch (∼84%), and the different lattice symmetries. Here, we demonstrate the growth of InP nanocrystals showing high structural quality and excellent optoelectronic properties on Si. Our CMOS-compatible innovative approach exploits the selective epitaxy of InP nanocrystals on Si nanometric seeds obtained by the opening of lattice-arranged Si nanotips embedded in a SiO 2 matrix. A graphene/InP/Si-tip heterostructure was realized on obtained materials, revealing rectifying behavior and promising photodetection. This work presents a significant advance toward the monolithic integration of graphene/III-V based hybrid devices onto the mainstream Si technology platform.

Design guideline for Si/organic hybrid solar cell with interdigitated back contact structure

Science.gov (United States)

Bimo Prakoso, Ari; Rusli; Li, Zeyu; Lu, Chenjin; Jiang, Changyun

2018-03-01

We study the design of Si/organic hybrid (SOH) solar cells with interdigitated back contact (IBC) structure. SOH solar cells formed between n-Si and poly(3,4-ethylenedioxythiophene): polystyrenesulphonate (PEDOT:PSS) is a promising concept that combines the excellent electronic properties of Si with the solution-based processing advantage of an organic polymer. The IBC cell structure is employed to minimize parasitic absorption losses in the organic polymer, eliminate grid shadowing losses, and allow excellent passivation of the front Si surface in one step over a large area. The influence of Si thickness, doping concentration and contact geometry are simulated in this study to optimize the performance of the SOH-IBC solar cell. We found that a high power conversion efficiency of >20% can be achieved for optimized SOH-IBC cell based on a thin c-Si substrate of 40 μm thickness.

Hot spots based gold nanostar@SiO2@CdSe/ZnS quantum dots complex with strong fluorescence enhancement

Directory of Open Access Journals (Sweden)

Feng Shan

2018-02-01

Full Text Available In this paper, a novel gold nanostar (NS@SiO2@CdSe/ZnS quantum dots (QDs complex with plasmon-enhanced fluorescence synthesized using a step-by-step surface linkage method was presented. The gold NS was synthesized by the seed growth method. The synthesized gold NS with the apexes structure has a hot-spot effect due to the strong electric field distributed at its sharp apexes, which leads to a plasmon resonance enhancement. Because the distance between QDs and metal nanostructures can be precisely controlled by this method, the relationship between enhancement and distance was revealed. The thickness of SiO2 shell was also optimized and the optimum distance of about 21 nm was obtained. The highest fluorescence enhancement of 4.8-fold accompanied by a minimum fluorescence lifetime of 2.3 ns were achieved. This strong enhancement comes from the hot spots distributed at the sharp tip of our constructed nanostructure. Through the finite element method, we calculated the field distribution on the surface of NS and found that gold NS with the sharpest apexes exhibited the highest field enhancement, which matches well with our experiment result. This complex shows tremendous potential applications for liquid-dependent biometric imaging systems.

Hot spots based gold nanostar@SiO2@CdSe/ZnS quantum dots complex with strong fluorescence enhancement

Science.gov (United States)

Shan, Feng; Su, Dan; Li, Wei; Hu, Wei; Zhang, Tong

2018-02-01

In this paper, a novel gold nanostar (NS)@SiO2@CdSe/ZnS quantum dots (QDs) complex with plasmon-enhanced fluorescence synthesized using a step-by-step surface linkage method was presented. The gold NS was synthesized by the seed growth method. The synthesized gold NS with the apexes structure has a hot-spot effect due to the strong electric field distributed at its sharp apexes, which leads to a plasmon resonance enhancement. Because the distance between QDs and metal nanostructures can be precisely controlled by this method, the relationship between enhancement and distance was revealed. The thickness of SiO2 shell was also optimized and the optimum distance of about 21 nm was obtained. The highest fluorescence enhancement of 4.8-fold accompanied by a minimum fluorescence lifetime of 2.3 ns were achieved. This strong enhancement comes from the hot spots distributed at the sharp tip of our constructed nanostructure. Through the finite element method, we calculated the field distribution on the surface of NS and found that gold NS with the sharpest apexes exhibited the highest field enhancement, which matches well with our experiment result. This complex shows tremendous potential applications for liquid-dependent biometric imaging systems.

Alpha-particle irradiation induced defects in SiO2 films of Si-SiO2 structures

International Nuclear Information System (INIS)

Koman, B.P.; Gal'chynskyy, O.V.; Kovalyuk, R.O.; Shkol'nyy, A.K.

1996-01-01

The aim of the work was to investigate alpha-particle irradiation induced defects in Si-SiO 2 structures by means of the thermostimulated discharge currents (TSDC) analysis. The object of investigation were (p-Si)-SiO 2 structures formed by a combined oxidation of the industrial p-Si wafers in dry and wet oxygen at temperature of 1150 C. The TSD currents were investigated in the temperature range between 90 and 500 K under linear heating rate. Pu 238 isotopes were the source of alpha-particles with an energy of 4-5 MeV and a density of 5.10 7 s -1 cm -2 . The TSD current curves show two peculiar maxima at about 370 and 480 K. Alpha-particle irradiation doesn't affect the general shape of the TSDC curves but leads to a shift of the maximum at 370 K and reduces the total electret charge which is accumulated in the Si-SiO 2 structures during polarization. The energy distribution function of the defects which are involved in SiO 2 polarization has been calculated. It showes that defects with activation energies of about 0.8 and 1.0 eV take part in forming the electret state, and these activation energies have certain energy distributions. It has been found that the TSDC maximum at 370 K has space charge nature and is caused by migration of hydrogen ions. In irradiated samples hydrogen and natrium ions localize on deeper trapping centres induced by alpha-particle irradiation. (orig.)

In vitro and in vivo siRNA delivery to hepatocyte utilizing ternary complexation of lactosylated dendrimer/cyclodextrin conjugates, siRNA and low-molecular-weight sacran.

Science.gov (United States)

Hayashi, Yuya; Higashi, Taishi; Motoyama, Keiichi; Jono, Hirofumi; Ando, Yukio; Arima, Hidetoshi

2018-02-01

In this study, we newly developed the ternary complexes consisting of lactosylated dendrimer (generation 3)/α-cyclodextrin conjugate (Lac-α-CDE), siRNA and the anionic polysaccharide sacrans, and evaluated their utility as siRNA transfer carriers. Three kinds of the low-molecular-weight sacrans, i.e. sacran (100) (Mw 44,889Da), sacran (1000) (Mw 943,692Da) and sacran (10,000) (Mw 1,488,281Da) were used. Lac-α-CDE/siRNA/sacran ternary complexes were prepared by adding the low-molecular-weight sacrans to the Lac-α-CDE/siRNA binary complex solution. Cellular uptake of the ternary complex with sacran (100) was higher than that of the binary complex or the other ternary complexes with sacran (1000) and sacran (10,000) in HepG2 cells. Additionally, the ternary complex possessed high serum resistance and endosomal escaping ability in HepG2 cells. High liver levels of siRNA and Lac-α-CDE were observed after the intravenous administration of the ternary complex rather than that of the binary complex. Moreover, intravenous administration of the ternary complex (siRNA 5mg/kg) induced the significant RNAi effect in the liver of mice with negligible change of blood chemistry values. Therefore, a ternary complexation of the Lac-α-CDE/siRNA binary complex with sacran is useful as a hepatocyte-specific siRNA delivery system. Copyright © 2017 Elsevier B.V. All rights reserved.

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-08-15

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

Structure and magnetism in Co/X, Fe/Si, and Fe/(FeSi) multilayers

Science.gov (United States)

Franklin, Michael Ray

Previous studies have shown that magnetic behavior in multilayers formed by repeating a bilayer unit comprised of a ferromagnetic layer and a non-magnetic spacer layer can be affected by small structural differences. For example, a macroscopic property such as giant magnetoresistance (GMR) is believed to depend significantly upon interfacial roughness. In this study, several complimentary structural probes were used to carefully characterize the structure of several sputtered multilayer systems-Co/Ag, Co/Cu, Co/Mo, Fe/Si, and Fe//[FeSi/]. X-ray diffraction (XRD) studies were used to examine the long-range structural order of the multilayers perpendicular to the plane of the layers. Transmission electron diffraction (TED) studies were used to probe the long-range order parallel to the layer plane. X-ray Absorption Fine Structure (XAFS) studies were used to determine the average local structural environment of the ferromagnetic atoms. For the Co/X systems, a simple correlation between crystal structure and saturation magnetization is discovered for the Co/Mo system. For the Fe/X systems, direct evidence of an Fe-silicide is found for the /[FeSi/] spacer layer but not for the Si spacer layer. Additionally, differences were observed in the magnetic behavior between the Fe in the nominally pure Fe layer and the Fe contained in the /[FeSi/] spacer layers.

Photoluminescence, structural and electrical properties of passivated a-Si:H based thin films and corresponding solar cells

International Nuclear Information System (INIS)

Pincik, E.; Kobayashi, H.; Takahashi, M.; Fujiwara, N.; Brunner, R.; Gleskova, H.; Jergel, M.; Muellerova, J.; Kucera, M.; Falcony, C.; Ortega, L.; Rusnak, J.; Mikula, M.; Zahoran, M.; Jurani, R.; Kral, M.

2004-01-01

This paper deals with the photoluminescence, structural and electrical properties of chemically passivated a-Si:H based thin films and corresponding thin film solar cells. The structures were chemically passivated in three types of KCN and HCN solutions containing MeOH and/or with water. The photoluminescence measurements were performed at 6 K using Ar laser and lock-in signal recording device containing Ge and Si photodetectors. Optically determined band gap related photoluminescence signals were observed between 1.1 and 1.7 eV. The electrical properties were measured by a high-sensitive charge version of deep level transient spectroscopy (Q-DLTS). The evolution of three basic groups of defects was observed. The structural studies were realized by the standard X-ray diffraction analysis. The cyanide treatment improved significantly the electrical characteristics of both corresponding MOS structures and solar cells due to the passivation of some parts of the dangling bonds by CN group. Particularly, the passivation of the defects at interfaces in MOS or solar cell multilayer structures was achieved which is of primary practical importance

Reliability implications of defects in high temperature annealed Si/SiO2/Si structures

International Nuclear Information System (INIS)

Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.; Wilson, I.H.; Xu, J.B.

1994-01-01

High-temperature post-oxidation annealing of poly-Si/SiO 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 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 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 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 2 /Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies

Three-dimensional imaging for precise structural control of Si quantum dot networks for all-Si solar cells

Science.gov (United States)

Kourkoutis, Lena F.; Hao, Xiaojing; Huang, Shujuan; Puthen-Veettil, Binesh; Conibeer, Gavin; Green, Martin A.; Perez-Wurfl, Ivan

2013-07-01

All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to reduced inter-QD coupling in the layer. Efficient carrier transport via mini-bands is in this case more likely across the multilayers provided the SiO2 spacer layer is thin enough to allow coupling in the vertical direction.All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to

Band structure analysis in SiGe nanowires

Energy Technology Data Exchange (ETDEWEB)

Amato, Michele [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy); Palummo, Maurizia [European Theoretical Spectroscopy Facility (ETSF) (Italy); CNR-INFM-SMC, Dipartimento di Fisica, Universita di Roma, ' Tor Vergata' , via della Ricerca Scientifica 1, 00133 Roma (Italy); Ossicini, Stefano, E-mail: stefano.ossicini@unimore.it [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy) and Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy) and European Theoretical Spectroscopy Facility - ETSF (Italy) and Centro Interdipartimentale ' En and Tech' , Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy)

2012-06-05

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

Band structure analysis in SiGe nanowires

International Nuclear Information System (INIS)

Amato, Michele; Palummo, Maurizia; Ossicini, Stefano

2012-01-01

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

International Nuclear Information System (INIS)

Onojima, Norio; Kasamatsu, Akihumi; Hirose, Nobumitsu; Mimura, Takashi; Matsui, Toshiaki

2008-01-01

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g m ) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f T compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Energy Technology Data Exchange (ETDEWEB)

Onojima, Norio [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan)], E-mail: nonojima@nict.go.jp; Kasamatsu, Akihumi; Hirose, Nobumitsu [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan); Mimura, Takashi [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan); Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); Matsui, Toshiaki [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan)

2008-07-30

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g{sub m}) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f{sub T} compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.

Novel siRNA delivery system using a ternary polymer complex with strong silencing effect and no cytotoxicity.

Science.gov (United States)

Kodama, Yukinobu; Shiokawa, Yumi; Nakamura, Tadahiro; Kurosaki, Tomoaki; Aki, Keisei; Nakagawa, Hiroo; Muro, Takahiro; Kitahara, Takashi; Higuchi, Norihide; Sasaki, Hitoshi

2014-01-01

We developed a novel small interfering RNA (siRNA) delivery system using a ternary complex with polyethyleneimine (PEI) and γ-polyglutamic acid (γ-PGA), which showed silencing effect and no cytotoxicity. The binary complexes of siRNA with PEI were approximately 73-102 nm in particle size and 45-52 mV in ζ-potential. The silencing effect of siRNA/PEI complexes increased with an increase of PEI, and siRNA/PEI complexes with a charge ratio greater than 16 showed significant luciferase knockdown in a mouse colon carcinoma cell line regularly expressing luciferase (Colon26/Luc cells). However, strong cytotoxicity and blood agglutination were observed in the siRNA/Lipofectamine complex and siRNA/PEI16 complex. Recharging cationic complexes with an anionic compound was reported to be a promising method for overcoming these toxicities. We therefore prepared ternary complexes of siRNA with PEI (charge ratio 16) by the addition of γ-PGA to reduce cytotoxicity and deliver siRNA. As expected, the cytotoxicity of the ternary complexes decreased with an increase of γ-PGA content, which decreased the ζ-potential of the complexes. A strong silencing effect comparable to siRNA/Lipofectamine complex was discovered in ternary complexes including γ-PGA with an anionic surface charge. The high incorporation of ternary complexes into Colon26/Luc cells was confirmed with fluorescence microcopy. Having achieved knockdown of an exogenously transfected gene, the ability of the complex to mediate knockdown of an endogenous housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), was assessed in B16-F10 cells. The ternary complex (siRNA/PEI16/γ-PGA12 complex) exhibited a significant GAPDH knockdown effect. Thus, we developed a useful siRNA delivery system.

Ab initio CASSCF study of the electronic structure of the transition-metal alkylidene-like complexes Mo-M[prime]H[sub 2] (M[prime] = C, Si, Ge, and Sn)

Energy Technology Data Exchange (ETDEWEB)

Marquez, A.; Sanz, J.F. (Universidad de Sevilla (Spain))

1992-12-02

Experimental and theoretical research on the electronic and geometric structure of transition-metal-carbenes and -alkylidenes is an active area in chemistry nowadays due to their potential activity in catalysis and in organic and organometallic synthesis. A theoretical investigation of the electronic structure of the high-valent, transition-metal, alkylidene-like complexes MoM[prime]H[sub 2] (M[prime] = C, Si, Ge, and Sn) is reported. Based on ab initio calculations carried out at the complete active space multiconfiguration self-consistent field (CASSCF) level, the molecular structure of the ground state and some low-lying excited states have been determined. For M[prime] = C, Si, and Ge, the ground state has C[sub 2v] symmetry (state [sup 5]B[sub 1]) and corresponds to pairing each electron of the M[prime]H[sub 2] triplet [sup 3]B[sub 1] with an electron of Mo ([sup 7]S). In the case of MoSnH[sub 2], the lowest state is bent (C[sub s] symmetry, state [sup 7]A[prime]), the out-of-plane angle being 68[degrees], and dissociates into SnH[sub 2] ([sup 1]A[sub 1]) + Mo ([sup 7]S). Dissociation energies, potential energy profiles for the dissociation, harmonic force constants in terms of internal symmetry coordinates, and vibrational frequencies are reported. The comparison of these properties with those of their pentacarbonylated homologous (CO)[sub 5]M[double bond]M[prime]H[sub 2] shows that the carbene-like (Fischer) type of complexation is stronger than the alkylidene-like one (Schrock). 28 refs., 4 figs., 6 tabs.

Impact of target mRNA structure on siRNA silencing efficiency: A large-scale study.

Science.gov (United States)

Gredell, Joseph A; Berger, Angela K; Walton, S Patrick

2008-07-01

The selection of active siRNAs is generally based on identifying siRNAs with certain sequence and structural properties. However, the efficiency of RNA interference has also been shown to depend on the structure of the target mRNA, primarily through studies using exogenous transcripts with well-defined secondary structures in the vicinity of the target sequence. While these studies provide a means for examining the impact of target sequence and structure independently, the predicted secondary structures for these transcripts are often not reflective of structures that form in full-length, native mRNAs where interactions can occur between relatively remote segments of the mRNAs. Here, using a combination of experimental results and analysis of a large dataset, we demonstrate that the accessibility of certain local target structures on the mRNA is an important determinant in the gene silencing ability of siRNAs. siRNAs targeting the enhanced green fluorescent protein were chosen using a minimal siRNA selection algorithm followed by classification based on the predicted minimum free energy structures of the target transcripts. Transfection into HeLa and HepG2 cells revealed that siRNAs targeting regions of the mRNA predicted to have unpaired 5'- and 3'-ends resulted in greater gene silencing than regions predicted to have other types of secondary structure. These results were confirmed by analysis of gene silencing data from previously published siRNAs, which showed that mRNA target regions unpaired at either the 5'-end or 3'-end were silenced, on average, approximately 10% more strongly than target regions unpaired in the center or primarily paired throughout. We found this effect to be independent of the structure of the siRNA guide strand. Taken together, these results suggest minimal requirements for nucleation of hybridization between the siRNA guide strand and mRNA and that both mRNA and guide strand structure should be considered when choosing candidate si

Microcrystalline silicon oxides for silicon-based solar cells: impact of the O/Si ratio on the electronic structure

Science.gov (United States)

Bär, M.; Starr, D. E.; Lambertz, A.; Holländer, B.; Alsmeier, J.-H.; Weinhardt, L.; Blum, M.; Gorgoi, M.; Yang, W.; Wilks, R. G.; Heske, C.

2014-10-01

Hydrogenated microcrystalline silicon oxide (μc-SiOx:H) layers are one alternative approach to ensure sufficient interlayer charge transport while maintaining high transparency and good passivation in Si-based solar cells. We have used a combination of complementary x-ray and electron spectroscopies to study the chemical and electronic structure of the (μc-SiOx:H) material system. With these techniques, we monitor the transition from a purely Si-based crystalline bonding network to a silicon oxide dominated environment, coinciding with a significant decrease of the material's conductivity. Most Si-based solar cell structures contain emitter/contact/passivation layers. Ideally, these layers fulfill their desired task (i.e., induce a sufficiently high internal electric field, ensure a good electric contact, and passivate the interfaces of the absorber) without absorbing light. Usually this leads to a trade-off in which a higher transparency can only be realized at the expense of the layer's ability to properly fulfill its task. One alternative approach is to use hydrogenated microcrystalline silicon oxide (μc-SiOx:H), a mixture of microcrystalline silicon and amorphous silicon (sub)oxide. The crystalline Si regions allow charge transport, while the oxide matrix maintains a high transparency. To date, it is still unclear how in detail the oxygen content influences the electronic structure of the μc-SiOx:H mixed phase material. To address this question, we have studied the chemical and electronic structure of the μc-SiOx:H (0 0.5, we observe a pronounced decrease of Si 3s - Si 3p hybridization in favor of Si 3p - O 2p hybridization in the upper valence band. This coincides with a significant increase of the material's resistivity, possibly indicating the breakdown of the conducting crystalline Si network. Silicon oxide layers with a thickness of several hundred nanometres were deposited in a PECVD (plasma-enhanced chemical vapor deposition) multi chamber system

Carrier-microencapsulation using Si-catechol complex for suppressing pyrite floatability

Energy Technology Data Exchange (ETDEWEB)

Jha, R.K.T.; Satur, J.; Hiroyoshi, N.; Ito, M.; Tsunekawa, M. [Hokkaido University, Hokkaido (Japan). Graduate School of Engineering

2008-11-15

Pyrite (FeS{sub 2}) is a common sulfide mineral associated with valuable metal minerals and coal, and it is rejected as a gangue mineral using physical separation techniques such as froth flotation and discharged into tailing pond. In the flotation, pyrite is frequently entrapped in the froth due to its hydrophobic nature. Formation of acid mine drainage due to the air-oxidation of pyrite in the tailing pond is also a serious problem. The authors have proposed carrier-microencapsulation (CME) as a method for suppressing both the floatability and oxidation of pyrite. In this method, pyrite is coated with a thin layer of metal oxide or hydroxide using catechol solution as a carrier combined with metal ions. The layer converts the pyrite surface from hydrophobic to hydrophilic and acts as a protective coating against oxidation. The present study demonstrates the effect of CME using Si-catechol complex to suppress the pyrite floatability: The bubble pick-up experiments showed that attachment of pyrite particles to air bubble is suppressed by the CME treatment at pH 4-10, Si-catechol complex concentration over 0.5 mol m{sup -3} and treatment time within 2 min. The Hallimond tube flotation experiments showed that the pyrite floatability is suppressed by the CME treatment even in the presence of typical flotation collectors such as kerosene and xanthate. SEM-EDX analysis confirmed that Si present on the pyrite surface treated by Si-catechol complex, implying that SiO{sub 2} or SiOH{sub 4} layer formed by the CME treatment convert the pyrite surface hydrophobic to hydrophilic.

Reliability study of ultra-thin gate oxides on strained-Si/SiGe MOS structures

International Nuclear Information System (INIS)

Varzgar, John B.; Kanoun, Mehdi; Uppal, Suresh; Chattopadhyay, Sanatan; Tsang, Yuk Lun; Escobedo-Cousins, Enrique; Olsen, Sarah H.; O'Neill, Anthony; Hellstroem, Per-Erik; Edholm, Jonas; Ostling, Mikael; Lyutovich, Klara; Oehme, Michael; Kasper, Erich

2006-01-01

The reliability of gate oxides on bulk Si and strained Si (s-Si) has been evaluated using constant voltage stressing (CVS) to investigate their breakdown characteristics. The s-Si architectures exhibit a shorter life time compared to that of bulk Si, which is attributed to higher bulk oxide charges (Q ox ) and increased surface roughness in the s-Si structures. The gate oxide in the s-Si structure exhibits a hard breakdown (HBD) at 1.9 x 10 4 s, whereas HBD is not observed in bulk Si up to a measurement period of 1.44 x 10 5 s. The shorter lifetime of the s-Si gate oxide is attributed to a larger injected charge (Q inj ) compared to Q inj in bulk Si. Current-voltage (I-V) measurements for bulk Si samples at different stress intervals show an increase in stress induced leakage current (SILC) of two orders in the low voltage regime from zero stress time to up to 5 x 10 4 s. In contrast, superior performance enhancements in terms of drain current, maximum transconductance and effective channel mobility are observed in s-Si MOSFET devices compared to bulk Si. The results from this study indicate that further improvement in gate oxide reliability is needed to exploit the sustained performance enhancement of s-Si devices over bulk Si

Fluorescent SiC with pseudo-periodic moth-eye structures

DEFF Research Database (Denmark)

Ou, Yiyu; Aijaz, Imran; Ou, Haiyan

2012-01-01

White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising candidates for the general lighting applications as energy-saving sources. Recently, donor-acceptor doped fluorescent SiC has been proven as a highly efficient wavelength converter...... to enhance the extraction efficiency, we present a simple method to fabricate the pseudo-periodic moth-eye structures on the surface of the fluorescent SiC. A thin gold layer is deposited on the fluorescent SiC first. Then the thin gold layer is treated by rapid thermal processing. After annealing, the thin...... gold layer turns into discontinuous nano-islands. The average size of the islands is dependent on the annealing condition which could be well controlled. By using the reactive-ion etching, pseudo-periodic moth-eye structures would be obtained using the gold nano-islands as a mask layer. Reactive...

Spectroscopic and calorimetric investigation of short and intermediate-range structures and energetics of amorphous SiCO, SiCN, and SiBCN polymer-derived ceramics

Science.gov (United States)

Widgeon, Scarlett J.

Polymer-derived ceramics (PDCs) are a new class of amorphous ceramics in the Si-B-C-N system that are synthesized by the pyrolysis of silicon-based organic polymers. PDCs are lightweight and are resistant to creep, crystallization, and oxidation at temperatures near 1800 K making them ideal for a variety of high temperature applications. In spite of being X-ray amorphous, these materials display structural heterogeneity at the nanometer length scale. Their structure and resulting properties can be drastically altered by the utilization of preceramic polymers with differing chemistry and architectures. Fundamental understanding of the atomic structure is critical in deciphering the structure-property relationships and ultimately in controlling their properties for specific engineering applications. The short-range atomic structure has been extensively investigated using a variety of techniques, however, the structures at length scales beyond next-nearest neighbors remained highly controversial. Here we report the results of a spectroscopic and calorimetric study of short and intermediate -range structure and energetic of SiOC and SiBCN PDCs derived from a wide variety of precursors. SiOC PDCs with different carbon contents were synthesized from polysiloxane precurors and their structures were studied using high-resolution 13C and 29Si nuclear magnetic resonance (NMR) spectroscopy. The results suggest that these PDCs consists of a continuous mass fractal backbone of corner-shared SiC xO4-x tetrahedral units with "voids" occupied by sp 2-hybridized graphitic carbon. The oxygen-rich SiCxO 4-x units are located at the interior of this backbone with a mass fractal dimension of ~ 2.5, while the carbon-rich units occupy the two-dimensional interface between the backbone and the free carbon nanodomains. Such fractal topology is expected to give rise to unusual mechanical and transport properties characteristic of fractal percolation networks. For example, elastic moduli and

Electroluminescence of erbium in Al/α-Si:H(Er)/p-c-Si/Al structure

International Nuclear Information System (INIS)

Kon'kov, I.O.; Kuznetsov, A.N.; Pak, P.E.; Terukov, E.I.; Granitsyna, L.S.

2001-01-01

It is informed for the first time on the observation of the erbium intensive electroluminescence from the amorphous hydrated silicon layer by application of the Al/α-Si:H(Er)/p-c-Si/Al structure in the direct shift mode. The above structure is the n-p-heterostructure with the barrier values of 0.3-0.4 eV for the electrons and 0.9-1.1 eV for the holes. The electroluminescence efficiency is evaluated at the level ∼ 2 x 10 -5 . The electroluminescence effect in the Al/α-Si:H(Er)/p-c-Si/Al structure is connected with the hole tunneling from the crystal silicon by the amorphous silicon localized states with the subsequent release into the valent zone [ru

Annealing characteristics of SiO2-Si structures after incoherent light pulse processing

International Nuclear Information System (INIS)

Sieber, N.; Klabes, R.; Voelskow, M.; Fenske, F.

1982-01-01

The behaviour of oxide charges and interface charges in boron implanted and non-implanted SiO 2 -Si structures as well as the electrical activation of the dopants by the action of incoherent light pulses was studied. Depth profiles of electrically active boron ions are presented for different annealing conditions as measured by the pulsed C-V method. It can be concluded that exposure of MOS structures to intense radiation of flash lamps does not increase the fixed charge and the fast state density at the SiO 2 -Si interface if optimal annealing conditions (energy densities) are employed. Low dose boron implanted silicon can be electrically activated without diffusion or segregation of dopants

Effect of resonant tunneling on electroluminescence in nc-Si/SiO2 multilayers-based p-i-n structure

International Nuclear Information System (INIS)

Chen, D.Y.; Wang, Y.Y.; Sun, Y.; He, Y.J.; Zhang, G.

2015-01-01

P-i-n structures with SiO 2 /nc-Si/SiO 2 multilayers as intrinsic layer were prepared in conventional plasma enhanced chemical vapor deposition system. Their carrier transport and electroluminescence properties were investigated. Two resonant tunneling related current peaks with current dropping gradually under forward bias were observed in the current voltage curve. Non-uniformity of the interfaces might be responsible for the gradual dropping of the current. Electroluminescence intensity of the device under bias of 7 V which is near the resonant tunneling peak voltage of 7.2 V was weaker than that under 6.5 V. According to the Gaussian fitting results of the spectra, the intensity of the sub-peak of 650 nm originating from recombination of injected electrons and holes was decreased the most. When resonant tunneling conditions are met, it might be that most of the injected electrons participate in resonant tunneling and fewer in Pool–Frenkel tunneling, which is the main carrier transport mechanism, to contribute to electroluminescence intensity. - Highlights: • Two resonant tunneling peaks with current dropping gradually were observed. • The EL intensity of the structure under resonant tunneling peak voltage is weakened. • P–F tunneling is the main transport mechanism besides resonant tunneling

X-ray absorption spectroscopy study on SiC-side interface structure of SiO2–SiC formed by thermal oxidation in dry oxygen

Science.gov (United States)

Isomura, Noritake; Kosaka, Satoru; Kataoka, Keita; Watanabe, Yukihiko; Kimoto, Yasuji

2018-06-01

Extended X-ray absorption fine structure (EXAFS) spectroscopy is demonstrated to measure the fine atomic structure of SiO2–SiC interfaces. The SiC-side of the interface can be measured by fabricating thin SiO2 films and using SiC-selective EXAFS measurements. Fourier transforms of the oscillations of the EXAFS spectra correspond to radial-structure functions and reveal a new peak of the first nearest neighbor of Si for m-face SiC, which does not appear in measurements of the Si-face. This finding suggests that the m-face interface could include a structure with shorter Si–C distances. Numerical calculations provide additional support for this finding.

Si Thermoelectric Power Generator with an Unconventional Structure

Science.gov (United States)

Sakamoto, Tatsuya; Iida, Tsutomu; Ohno, Yota; Ishikawa, Masashi; Kogo, Yasuo; Hirayama, Naomi; Arai, Koya; Nakamura, Takashi; Nishio, Keishi; Takanashi, Yoshifumi

2014-06-01

We examine the mechanical stability of an unconventional Mg2Si thermoelectric generator (TEG) structure. In this structure, the angle θ between the thermoelectric (TE) chips and the heat sink is less than 90°. We examined the tolerance to an external force of various Mg2Si TEG structures using a finite-element method (FEM) with the ANSYS code. The output power of the TEGs was also measured. First, for the FEM analysis, the mechanical properties of sintered Mg2Si TE chips, such as the bending strength and Young's modulus, were measured. Then, two-dimensional (2D) TEG models with various values of θ (90°, 75°, 60°, 45°, 30°, 15°, and 0°) were constructed in ANSYS. The x and y axes were defined as being in the horizontal and vertical directions of the substrate, respectively. In the analysis, the maximum tensile stress in the chip when a constant load was applied to the TEG model in the x direction was determined. Based on the analytical results, an appropriate structure was selected and a module fabricated. For the TEG fabrication, eight TE chips, each with dimensions of 3 mm × 3 mm × 10 mm and consisting of Sb-doped n-Mg2Si prepared by a plasma-activated sintering process, were assembled such that two chips were connected in parallel, and four pairs of these were connected in series on a footprint of 46 mm × 12 mm. The measured power generation characteristics and temperature distribution with temperature differences between 873 K and 373 K are discussed.

Bis(imidazolin-2-iminato) rare earth metal complexes: synthesis, structural characterization, and catalytic application.

Science.gov (United States)

Trambitas, Alexandra G; Melcher, Daniel; Hartenstein, Larissa; Roesky, Peter W; Daniliuc, Constantin; Jones, Peter G; Tamm, Matthias

2012-06-18

Reaction of anhydrous rare earth metal halides MCl(3) with 2 equiv of 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im(Dipp)NH) and 2 equiv of trimethylsilylmethyl lithium (Me(3)SiCH(2)Li) in THF furnished the complexes [(Im(Dipp)N)(2)MCl(THF)(n)] (M = Sc, Y, Lu). The molecular structures of all three compounds were established by single-crystal X-ray diffraction analyses. The coordination spheres around the pentacoordinate metal atoms are best described as trigonal bipyramids. Reaction of YbI(2) with 2 equiv of LiCH(2)SiMe(3) and 2 equiv of the imino ligand Im(Dipp)NH in tetrahydrofuran did not result in a divalent complex, but instead the Yb(III) complex [(Im(Dipp)N)(2)YbI(THF)(2)] was obtained and structurally characterized. Treatment of [(Im(Dipp)N)(2)MCl(THF)(n)] with 1 equiv of LiCH(2)SiMe(3) resulted in the formation of [(Im(Dipp)N)(2)M(CH(2)SiMe(3))(THF)(n)]. The coordination arrangement of these compounds in the solid state at the metal atoms is similar to that found for the starting materials, although the introduction of the neosilyl ligand induces a significantly greater distortion from the ideal trigonal-bipyramidal geometry. [(Im(Dipp)N)(2)Y(CH(2)SiMe(3))(THF)(2)] was used as precatalyst in the intramolecular hydroamination/cyclization reaction of various terminal aminoalkenes and of one aminoalkyne. The complex showed high catalytic activity and selectivity. A comparison with the previously reported dialkyl yttrium complex [(Im(Dipp)N)Y(CH(2)SiMe(3))(2)(THF)(3)] showed no clear tendency in terms of activity.

Fabrication and structure of bulk nanocrystalline Al-Si-Ni-mishmetal alloys

International Nuclear Information System (INIS)

Latuch, Jerzy; Cieslak, Grzegorz; Kulik, Tadeusz

2007-01-01

Al-based alloys of structure consisting of nanosized Al crystals, embedded in an amorphous matrix, are interesting for their excellent mechanical properties, exceeding those of the commercial crystalline Al-based alloys. Recently discovered nanocrystalline Al alloys containing silicon (Si), rare earth metal (RE) and late transition metal (Ni), combine high tensile strength and good wear resistance. The aim of this work was to manufacture bulk nanocrystalline alloys from Al-Si-Ni-mishmetal (Mm) system. Bulk nanostructured Al 91-x Si x Ni 7 Mm 2 (x = 10, 11.6, 13 at.%) alloys were produced by ball milling of nanocrystalline ribbons followed by high pressure hot isostating compaction

Electronic structure and chemical bonding in LaIrSi-type intermetallics

Energy Technology Data Exchange (ETDEWEB)

Matar, Samir F. [Bordeaux Univ., Pessac (France). CNRS; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Nakhl, Michel [Univ. Libanaise, Fanar (Lebanon). Ecole Doctorale Sciences et Technologies

2017-05-01

The cubic LaIrSi type has 23 representatives in aluminides, gallides, silicides, germanides, phosphides, and arsenides, all with a valence electron count of 16 or 17. The striking structural motif is a three-dimensional network of the transition metal (T) and p element (X) atoms with TX{sub 3/3} respectively XT{sub 3/3} coordination. Alkaline earth or rare earth atoms fill cavities within the polyanionic [TX]{sup δ-} networks. The present work presents a detailed theoretical study of chemical bonding in LaIrSi-type representatives, exemplarily for CaPtSi, BaIrP, BaAuGa, LaIrSi, CeRhSi, and CeIrSi. DFT-GGA-based electronic structure calculations show weakly metallic compounds with itinerant small magnitude DOSs at E{sub F} except for CeRhSi whose large Ce DOS at E{sub F} leads to a finite magnetization on Ce (0.73 μ{sub B}) and induced small moments of opposite sign on Rh and Si in a ferromagnetic ground state. The chemical bonding analyses show dominant bonding within the [TX]{sup δ-} polyanionic networks. Charge transfer magnitudes were found in accordance with the course of the electronegativites of the chemical constituents.

The guanidinium group as a key part of water-soluble polymer carriers for siRNA complexation and protection against degradation.

Science.gov (United States)

Tabujew, Ilja; Freidel, Christoph; Krieg, Bettina; Helm, Mark; Koynov, Kaloian; Müllen, Klaus; Peneva, Kalina

2014-07-01

Here, the preparation of a novel block copolymer consisting of a statistical copolymer N-(2-hydroxypropyl) methacrylamide-s-N-(3-aminopropyl) methacrylamide and a short terminal 3-guanidinopropyl methacrylamide block is reported. This polymer structure forms neutral but water-soluble nanosized complexes with siRNA. The siRNA block copolymer complexes are first analyzed using agarose gel electrophoresis and their size is determined with fluorescence correlation spectroscopy. The protective properties of the polymer against RNA degradation are investigated by treating the siRNA block copolymer complexes with RNase V1. Heparin competition assays confirm the efficient release of the cargo in vitro. In addition, the utilization of microscale thermophoresis is demonstrated for the determination of the binding strength between a fluorescently labeled polyanion and a polymer molecule. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic structure and bonding in the ternary silicide YNiSi3

International Nuclear Information System (INIS)

Sung, Gi Hong; Kang, Dae Bok

2003-01-01

An analysis of the electronic structure and bonding in the ternary silicide YNiSi 3 is made, using extended Hueckel tight-binding calculations. The YNiSi 3 structure consists of Ni-capped Si 2 dimer layers and Si zigzag chains. Significant bonding interactions are present between the silicon atoms in the structure. The oxidation state formalism of (Y 3+ )(Ni 0 )(Si 3 ) 3- for YNiSi 3 constitutes a good starting point to describe its electronic structure. Si atoms receive electrons form the most electropositive Y in YNiSi 3 , and Ni 3d and Si 3p states dominate below the Fermi level. There is an interesting electron balance between the two Si and Ni sublattices. Since the π orbitals in the Si chain and the Ni d and s block levels are almost completely occupied, the charge balance for YNiSi 3 can be rewritten as (Y 3+ )(Ni 2- )(Si 2- )(Si-Si) + , making the Si 2 layers oxidized. These results suggest that the Si zigzag chain contains single bonds and the Si 2 double layer possesses single bonds within a dimer with a partial double bond character. Stronger Si-Si and Ni-Si bonding interactions are important for giving stability to the structure, while essentially no metal-metal bonding exists at all. The 2D metallic behavior of this compound is due to the Si-Si interaction leading to dispersion of the several Si 2 π bands crossing the Fermi level in the plane perpendicular to the crystallographic b axis

First-principles study of the Pd–Si system and Pd(001)/SiC(001) hetero-structure

Energy Technology Data Exchange (ETDEWEB)

Turchi, P.E.A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ivashchenko, V.I. [National Academy of Sciences of Ukraine (NASU), Kiev (Ukraine)

2014-11-01

First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3m, P6m2, Pm3m), Pd₂Si (P6⁻2m, P6₃/mmc, P3m1, P3⁻1m) and Pd₃Si (Pnma, P6₃22, Pm3m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd₂Si and D0₁₁-Pd₃Si fragments, in agreement with experiment.

Non-switching to switching transferring mechanism investigation for Ag/SiO x /p-Si structure with SiO x deposited by HWCVD

Science.gov (United States)

Liu, Yanhong; Wang, Ruoying; Li, Zhongyue; Wang, Song; Huang, Yang; Peng, Wei

2018-04-01

We proposed and fabricated an Ag/SiO x /p-Si sandwich structure, in which amorphous SiO x films were deposited through hot wire chemical vapor deposition (HWCVD) using tetraethylorthosilicate (TEOS) as Si and O precursor. Experimental results indicate that the I–V properties of this structure transfer from non-switching to switching operation as the SiO x deposition temperature increased. The device with SiO x deposited at high deposition temperature exhibits typical bipolar switching properties, which can be potentially used in resistive switching random accessible memory (RRAM). The transferring mechanism from non-switching to switching can be ascribed to the change of structural and electronic properties of SiO x active layer deposited at different temperatures, as evidenced by analyzing FTIR spectrum and fitting its I–V characteristics curves. This work demonstrates a safe and practicable low-temperature device-grade SiO x film deposition technology by conducting HWCVD from TEOS.

GaN nanorods and LED structures grown on patterned Si and AlN/Si substrates by selective area growth

Energy Technology Data Exchange (ETDEWEB)

Li, Shunfeng; Fuendling, Soenke; Soekmen, Uensal; Neumann, Richard; Merzsch, Stephan; Peiner, Erwin; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig (Germany); Hinze, Peter; Weimann, Thomas [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany); Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

2010-07-15

GaN nanorods (NRs) show promising applications in high-efficiency light emitting diodes, monolithic white light emission and optical interconnection due to their superior properties. In this work, we performed GaN nanostructures growth by pre-patterning the Si and AlN/Si substrates. The pattern was transferred to Si and AlN/Si substrates by photolithography and inductively-coupled plasma etching. GaN NRs were grown on these templates by metal-organic vapour phase epitaxy (MOVPE). GaN grown on Si pillar templates show a truncated pyramidal structure. Transmission electron microscopy measurements demonstrated clearly that the threading dislocations bend to the side facets of the GaN nanostructures and terminate. GaN growth can also be observed on the sidewalls and bottom surface between the Si pillars. A simple phenomenological model is proposed to explain the GaN nanostructure growth on Si pillar templates. Based on this model, we developed another growth method, by which we grow GaN rod structures on pre-patterned AlN/Si templates. By in-situ nitridation and decreasing of the V/III ratio, we found that GaN rods only grew on the patterned AlN/Si dots with an aspect ratio of about 1.5 - 2. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Three-dimensional imaging for precise structural control of Si quantum dot networks for all-Si solar cells.

Science.gov (United States)

Kourkoutis, Lena F; Hao, Xiaojing; Huang, Shujuan; Puthen-Veettil, Binesh; Conibeer, Gavin; Green, Martin A; Perez-Wurfl, Ivan

2013-08-21

All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to reduced inter-QD coupling in the layer. Efficient carrier transport via mini-bands is in this case more likely across the multilayers provided the SiO2 spacer layer is thin enough to allow coupling in the vertical direction.

Lipid-Based Liquid Crystalline Nanoparticles Facilitate Cytosolic Delivery of siRNA via Structural Transformation.

Science.gov (United States)

He, Shufang; Fan, Weiwei; Wu, Na; Zhu, Jingjing; Miao, Yunqiu; Miao, Xiaran; Li, Feifei; Zhang, Xinxin; Gan, Yong

2018-04-11

RNA interference (RNAi) technology has shown great promise for the treatment of cancer and other genetic disorders. Despite the efforts to increase the target tissue distribution, the safe and effective delivery of siRNA to the diseased cells with sufficient cytosolic transport is another critical factor for successful RNAi clinical application. Here, the constructed lipid-based liquid crystalline nanoparticles, called nano-Transformers, can transform thestructure in the intracellular acidic environment and perform high-efficient siRNA delivery for cancer treatment. The developed nano-Transformers have satisfactory siRNA loading efficiency and low cytotoxicity. Different from the traditional cationic nanocarriers, the endosomal membrane fusion induced by the conformational transition of lipids contributes to the easy dissociation of siRNA from nanocarriers and direct release of free siRNA into cytoplasm. We show that transfection with cyclin-dependent kinase 1 (CDK1)-siRNA-loaded nano-Transformers causes up to 95% reduction of relevant mRNA in vitro and greatly inhibits the tumor growth without causing any immunogenic response in vivo. This work highlights that the lipid-based nano-Transformers may become the next generation of siRNA delivery system with higher efficacy and improved safety profiles.

Fabrication of miniaturised Si-based electrocatalytic membranes

International Nuclear Information System (INIS)

D'Arrigo, G.; Spinella, C.; Arena, G.; Lorenti, S.

2003-01-01

The increasing interest for light and movable electronic systems, cell phones and small digital devices, drives the technological research toward integrated regenerating power sources with small dimensions and great autonomy. Conventional batteries are already unable to deliver power in more and more shrunk volumes maintaining the requirements of long duration and light weight. A possible solution to overcome these limits is the use of miniaturised fuel cell. The fuel cell offers a greater gravimetric energy density compared to conventional batteries. The micromachining technology of silicon is an important tool to reduce the fuel cell structure to micrometer sizes. The use of silicon also gives the opportunity to integrate the power source and the electronic circuits controlling the fuel cell on the same structure. This paper reports preliminary results concerning the micromachining procedure for fabricating a Si-based electrocatalytic membrane for miniaturised Si-based proton exchange membrane fuel cells (PEMFC)

Three dimensional (3D) microstructure-based finite element modeling of Al-SiC nanolaminates using focused ion beam (FIB) tomography

Energy Technology Data Exchange (ETDEWEB)

Mayer, Carl R. [Materials Science and Engineering, Arizona State University, Tempe, AZ 85287-6106 (United States); Molina-Aladareguia, Jon [IMDEA Materials Institute, c/Eric Kandel 2, Getafe, Madrid 28906 (Spain); Chawla, Nikhilesh, E-mail: nchawla@asu.edu [Materials Science and Engineering, Arizona State University, Tempe, AZ 85287-6106 (United States)

2016-10-15

Al-SiC nanolaminate composites show promise as high performance coating materials due to their combination of strength and toughness. Although a significant amount of modeling effort has been focused on materials with an idealized flat nanostructure, experimentally these materials exhibit complex undulating layer geometries. This work utilizes FIB tomography to characterize this nanostructure in 3D and finite element modeling to determine the effect that this complex structure has on the mechanical behavior of these materials. A sufficiently large volume was characterized such that a 1 × 2 μm micropillar could be generated from the dataset and compared directly to experimental results. The mechanical response from this nanostructure was then compared to pillar models using simplified structures with perfectly flat layers, layers with sinusoidal waviness, and layers with arc segment waviness. The arc segment based layer geometry showed the best agreement with the experimentally determined structure, indicating it would be the most appropriate geometry for future modeling efforts. - Highlights: •FIB tomography was used to determine the structure of an Al-SiC nanolaminate in 3D. •FEM was used to compare the deformation of the nanostructure to experimental results. •Idealized structures from literature were compared to the FIB determined structure. •Arc segment based structures approximated the FIB determined structure most closely.

Extremely high magnetic-field sensitivity of charge transport in the Mn/SiO2/p-Si hybrid structure

Directory of Open Access Journals (Sweden)

N. V. Volkov

2017-01-01

Full Text Available We report on abrupt changes in dc resistance and impedance of a diode with the Schottky barrier based on the Mn/SiO2/p-Si structure in a magnetic field. It was observed that at low temperatures the dc and ac resistances of the device change by a factor of more than 106 with an increase in a magnetic field to 200 mT. The strong effect of the magnetic field is observed only above the threshold forward bias across the diode. The ratios between ac and dc magnetoresistances can be tuned from almost zero to 108% by varying the bias. To explain the diversity of magnetotransport phenomena observed in the Mn/SiO2/p-Si structure, it is necessary to attract several mechanisms, which possibly work in different regions of the structure. The anomalously strong magnetotransport effects are attributed to the magnetic-field-dependent impact ionization in the bulk of a Si substrate. At the same time, the conditions for this process are specified by structure composition, which, in turn, affects the current through each structure region. The effect of magnetic field attributed to suppression of impact ionization via two mechanisms leads to an increase in the carrier energy required for initiation of impact ionization. The first mechanism is related to displacement of acceptor levels toward higher energies relative to the top of the valence band and the other mechanism is associated with the Lorentz forces affecting carrier trajectories between scatterings events. The estimated contributions of these two mechanisms are similar. The proposed structure is a good candidate for application in CMOS technology-compatible magnetic- and electric-field sensors and switching devices.

Structural and optical properties of Si-doped Ag clusters

KAUST Repository

Mokkath, Junais Habeeb

2014-03-06

The structural and optical properties of AgN and Ag N-1Si1 (neutral, cationic, and anionic) clusters (N = 5 to 12) are systematically investigated using the density functional based tight binding method and time-dependent density functional theory, providing insight into recent experiments. The gap between the highest occupied and lowest unoccupied molecular orbitals and therefore the optical spectrum vary significantly under Si doping, which enables flexible tuning of the chemical and optical properties of Ag clusters. © 2014 American Chemical Society.

Structural and optical properties of Si-doped Ag clusters

KAUST Repository

Mokkath, Junais Habeeb; Schwingenschlö gl, Udo

2014-01-01

The structural and optical properties of AgN and Ag N-1Si1 (neutral, cationic, and anionic) clusters (N = 5 to 12) are systematically investigated using the density functional based tight binding method and time-dependent density functional theory, providing insight into recent experiments. The gap between the highest occupied and lowest unoccupied molecular orbitals and therefore the optical spectrum vary significantly under Si doping, which enables flexible tuning of the chemical and optical properties of Ag clusters. © 2014 American Chemical Society.

Structure of Ti{sub 3}SiC{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Rawn, C.J.; Payzant, E.A.; Hubbard, C.R. [Oak Ridge National Lab., TN (United States); Barsoum, M.W.; El-Raghy, T. [Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Engineering

1998-11-01

Earlier high temperature structure analysis by neutron powder diffraction suggested that Si vacancies were created when Ti{sub 3}SiC{sub 2} was heated. A specimen that was heated to 906 C overnight was later examined at room temperature. For this subsequent room temperature data set refinement of the Si site occupancies in the Ti{sub 3}SiC{sub 2} structure did not support the hypothesis that Si vacancies were being created when the sample was held at elevated temperatures in a vacuum furnace.

Structural analysis of highly-durable Si-O-C composite anode prepared by electrodeposition for lithium secondary batteries

International Nuclear Information System (INIS)

Nara, Hiroki; Yokoshima, Tokihiko; Otaki, Mitsutoshi; Momma, Toshiyuki; Osaka, Tetsuya

2013-01-01

The structure of the highly durable silicon-based anode prepared by electrodeposition was investigated for volume change and chemical structure. With repeated charge–discharge cycles, the volume change resulting from the anode film thickness decreased, and, after 100 cycles, essentially no difference was observed between the charged and discharged states. The buffering effect of the volume change was considered to be achieved by the formation of Li 2 O, Li 2 CO 3 , and lithium silicates such as Li 4 SiO 4 , whose existence were supported by STEM, EELS, and XPS analyses. From the structural analyses, the main reactions related to the capacity of the silicon-based anode were considered to be the formation of Li x Si and Li 2 Si 2 O 5 . Li x Si and Li 2 Si 2 O 5 can be delithiated into Si and SiO 2 , respectively

A methodology of SiP testing based on boundary scan

Science.gov (United States)

Qin, He; Quan, Haiyang; Han, Yifei; Zhu, Tianrui; Zheng, Tuo

2017-10-01

System in Package (SiP) play an important role in portable, aerospace and military electronic with the microminiaturization, light weight, high density, and high reliability. At present, SiP system test has encountered the problem on system complexity and malfunction location with the system scale exponentially increase. For SiP system, this paper proposed a testing methodology and testing process based on the boundary scan technology. Combining the character of SiP system and referencing the boundary scan theory of PCB circuit and embedded core test, the specific testing methodology and process has been proposed. The hardware requirement of the under test SiP system has been provided, and the hardware platform of the testing has been constructed. The testing methodology has the character of high test efficiency and accurate malfunction location.

Subband Structure and Effective Mass in the Inversion Layer of a Strain Si-Based Alloy P-Type MOSFET.

Science.gov (United States)

Chen, Kuan-Ting; Fan, Jun Wei; Chang, Shu-Tong; Lin, Chung-Yi

2015-03-01

In this paper, the subband structure and effective mass of an Si-based alloy inversion layer in a PMOSFET are studied theoretically. The strain condition considered in our calculations is the intrinsic strain resulting from growth of the silicon-carbon alloy on a (001) Si substrate and mechanical uniaxial stress. The quantum confinement effect resulting from the vertically effective electric field was incorporated into the k · p calculation. The distinct effective mass, such as the quantization effective mass and the density-of-states (DOS) effective mass, as well as the subband structure of the silicon-carbon alloy inversion layer for a PMOSFET under substrate strain and various effective electric field strengths, were all investigated. Ore results show that subband structure of relaxed silicon-carbon alloys with low carbon content are almost the same as silicon. We find that an external stress applied parallel to the channel direction can efficiently reduce the effective mass along the channel direction, thus producing hole mobility enhancement.

MOVPE and characterization of GaN-based structures on alternative substrates

Energy Technology Data Exchange (ETDEWEB)

Dikme, Y.

2006-06-20

This study involves growth experiments of GaN-based layer structures on silicon (Si), lithium aluminate (LiAlO{sub 2}) and the composite substrate SiCOI. Substrate specific preparation and growth procedures were developed. Because of the different lattice constants and thermal expansion coefficients between GaN and the substrate materials and because of the high depositions temperatures (>1000 C) complex interlayers are required to create a crossover from the substrate to the GaN layer and to prevent substrate/layer bowing and cracks developing in the epitaxial layers. Crystallographic, thermal and electronic properties of these materials were investigated and the developed layers were used as buffer layers for electronic and opto electronic devices. On Si AlN/GaN distributed Bragg reflectors (DBR), InGaN/GaN multiple quantum well (MQW) and AlGaN/GaN HEMT (high electron mobility transistor) were demonstrated. The transistor structures showed high power densities, which were comparable to industrially fabricated devices. As well as the reflection of a certain wavelength region, the DBR layers additionally showed positive influence on succeeding GaN top layer optical properties. For the first time laser emission of an optically pumped InGaN/GaN MQW on Si was demonstrated with low excitation density and a high operating temperature. GaN-based structures were deposited on LiAlO2 in the m-plane crystal orientation; that do not exhibit polarization mechanisms in growth direction. For the deposition of coalesced GaN films a seal-coating of the LiAlO{sub 2} surface was developed and finally LED structures were grown on these substrates. For the first time electroluminescence of LED structures on LiAlO{sub 2} was achieved. The growth on the composite substrate SiCOI was initiated with an HT AlN layer and it was demonstrated that SiCOI is comparable to a bulk SiC substrate for the GaN-based epitaxy. The developed and investigated layer structure served as buffer for the

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

Directory of Open Access Journals (Sweden)

Alexander T Fleck

Full Text Available We studied the effect of Silicon (Si on Casparian band (CB development, chemical composition of the exodermal CB and Si deposition across the root in the Si accumulators rice and maize and the Si non-accumulator onion. Plants were cultivated in nutrient solution with and without Si supply. The CB development was determined in stained root cross-sections. The outer part of the roots containing the exodermis was isolated after enzymatic treatment. The exodermal suberin was transesterified with MeOH/BF3 and the chemical composition was measured using gas chromatography-mass spectroscopy (GC-MS and flame ionization detector (GC-FID. Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS was used to determine the Si deposition across root cross sections. Si promoted CB formation in the roots of Si-accumulator and Si non-accumulator species. The exodermal suberin was decreased in rice and maize due to decreased amounts of aromatic suberin fractions. Si did not affect the concentration of lignin and lignin-like polymers in the outer part of rice, maize and onion roots. The highest Si depositions were found in the tissues containing CB. These data along with literature were used to suggest a mechanism how Si promotes the CB development by forming complexes with phenols.

Dynamics of Defects and Dopants in Complex Systems: Si and Oxide Surfaces and Interfaces

Science.gov (United States)

Kirichenko, Taras; Yu, Decai; Banarjee, Sanjay; Hwang, Gyeong

2004-10-01

Fabrication of forthcoming nanometer scale electronic devices faces many difficulties including formation of extremely shallow and highly doped junctions. At present, ultra-low-energy ion implantation followed by high-temperature thermal annealing is most widely used to fabricate such ultra-shallow junctions. In the process, a great challenge lies in achieving precise control of redistribution and electrical activation of dopant impurities. Native defects (such as vacancies and interstitials) generated during implantation are known to be mainly responsible for the TED and also influence significantly the electrical activation/deactivation. Defect-dopant dynamics is rather well understood in crystalline Si and SiO2. However, little is known about their diffusion and annihilation (or precipitation) at the surfaces and interfaces, despite its growing importance in determining junction profiles as device dimensions get smaller. In this talk, we will present our density functional theory calculation results on the atomic and electronic structure and dynamical behavior of native defects and dopant-defect complexes in disordered/strained Si and oxide systems, such as i) clean and absorbent-modified Si(100) surface and subsurface layers, ii) amorphous-crystalline Si interfaces and iii) amorphous SiO2/Si interfaces. The fundamental understanding and data is essential in developing a comprehensive kinetic model for junction formation, which would contribute greatly in improving current process technologies.

An albumin-mediated cholesterol design-based strategy for tuning siRNA pharmacokinetics and gene silencing.

Science.gov (United States)

Bienk, Konrad; Hvam, Michael Lykke; Pakula, Malgorzata Maria; Dagnæs-Hansen, Frederik; Wengel, Jesper; Malle, Birgitte Mølholm; Kragh-Hansen, Ulrich; Cameron, Jason; Bukrinski, Jens Thostrup; Howard, Kenneth A

2016-06-28

Major challenges for the clinical translation of small interfering RNA (siRNA) include overcoming the poor plasma half-life, site-specific delivery and modulation of gene silencing. In this work, we exploit the intrinsic transport properties of human serum albumin to tune the blood circulatory half-life, hepatic accumulation and gene silencing; based on the number of siRNA cholesteryl modifications. We demonstrate by a gel shift assay a strong and specific affinity of recombinant human serum albumin (rHSA) towards cholesteryl-modified siRNA (Kd>1×10(-7)M) dependent on number of modifications. The rHSA/siRNA complex exhibited reduced nuclease degradation and reduced induction of TNF-α production by human peripheral blood mononuclear cells. The increased solubility of heavily cholesteryl modified siRNA in the presence of rHSA facilitated duplex annealing and consequent interaction that allowed in vivo studies using multiple cholesteryl modifications. A structural-activity-based screen of in vitro EGFP-silencing was used to select optimal siRNA designs containing cholesteryl modifications within the sense strand that were used for in vivo studies. We demonstrate plasma half-life extension in NMRI mice from t1/2 12min (naked) to t1/2 45min (single cholesteryl) and t1/2 71min (double cholesteryl) using fluorescent live bioimaging. The biodistribution showed increased accumulation in the liver for the double cholesteryl modified siRNA that correlated with an increase in hepatic Factor VII gene silencing of 28% (rHSA/siRNA) compared to 4% (naked siRNA) 6days post-injection. This work presents a novel albumin-mediated cholesteryl design-based strategy for tuning pharmacokinetics and systemic gene silencing. Copyright © 2016 Elsevier B.V. All rights reserved.

A new entropy based method for computing software structural complexity

International Nuclear Information System (INIS)

Roca, Jose L.

2002-01-01

In this paper a new methodology for the evaluation of software structural complexity is described. It is based on the entropy evaluation of the random uniform response function associated with the so called software characteristic function SCF. The behavior of the SCF with the different software structures and their relationship with the number of inherent errors is investigated. It is also investigated how the entropy concept can be used to evaluate the complexity of a software structure considering the SCF as a canonical representation of the graph associated with the control flow diagram. The functions, parameters and algorithms that allow to carry out this evaluation are also introduced. After this analytic phase follows the experimental phase, verifying the consistency of the proposed metric and their boundary conditions. The conclusion is that the degree of software structural complexity can be measured as the entropy of the random uniform response function of the SCF. That entropy is in direct relationship with the number of inherent software errors and it implies a basic hazard failure rate for it, so that a minimum structure assures a certain stability and maturity of the program. This metric can be used, either to evaluate the product or the process of software development, as development tool or for monitoring the stability and the quality of the final product. (author)

Single layer and multilayer vacuum-arc coatings based on the nitride TiAlSiYN: composition, structure, properties

International Nuclear Information System (INIS)

Beresnev, V.M.; Litovchenko, S.V.; Nemchenko, U.S.; Srebnyuk, P.A.; Mazilin, B.A.; Sobol, O.V.; Mejlekhov, A.A.; Barmin, A.E.; Serenko, TA.; Pogrebnyak, A.D.; Ivanov, O.N.; Kritsyna, E.V.; Stolbovoj, V.A.; Novikov, V.Yu.; Malikov, L.V.

2017-01-01

Using high-technological vacuum-arc evaporation in the atmosphere of nitrogen with ion bombardment, single- and multilayer coatings based on TiAlSiYN with high mechanical characteristics were obtained: hardness of the coatings reached 49.5 GPa, resistance to wear, with the value of the critical point L_C_5 reaching 184.92 N. The peculiarities of radiation-induced effect at applying bias potential U_b were found: formation of nitride coatings based on fcc metallic lattice with the preferred orientation of crystallites with the texture axis [111], as well as simultaneous growth of hardness. Hardness of both single- and multilayer coatings increases by 40...50% at the increase of U_b from 50 to 200 V. Formation of silicon-containing layers of TiAlSiYN during the deposition contributes to reaching increased hardness, which, in the case of single-layer coating obtained at U_b = -200 V is 49.5 GPa, which corresponds to superhard state. The mechanisms of structure formation, defining the resulting mechanical characteristics of single- and multi-layer coatings based on TiAlSiYN nitride have been discussed.

Gene silencing activity of siRNA polyplexes based on thiolated N,N,N-trimethylated chitosan.

Science.gov (United States)

Varkouhi, Amir K; Verheul, Rolf J; Schiffelers, Raymond M; Lammers, Twan; Storm, Gert; Hennink, Wim E

2010-12-15

N,N,N-Trimethylated chitosan (TMC) is a biodegradable polymer emerging as a promising nonviral vector for nucleic acid and protein delivery. In the present study, we investigated whether the introduction of thiol groups in TMC enhances the extracellular stability of the complexes based on this polymer and promotes the intracellular release of siRNA. The gene silencing activity and the cellular cytotoxicity of polyplexes based on thiolated TMC were compared with those based on the nonthiolated counterpart and the regularly used lipidic transfection agent Lipofectamine. Incubation of H1299 human lung cancer cells expressing firefly luciferase with siRNA/thiolated TMC polyplexes resulted in 60-80% gene silencing activity, whereas complexes based on nonthiolated TMC showed less silencing (40%). The silencing activity of the complexes based on Lipofectamine 2000 was about 60-70%. Importantly, the TMC-SH polyplexes retained their silencing activity in the presence of hyaluronic acid, while nonthiolated TMC polyplexes hardly showed any silencing activity, demonstrating their stability against competing anionic macromolecules. Under the experimental conditions tested, the cytotoxicity of the thiolated and nonthiolated siRNA complexes was lower than those based on Lipofectamine. Given the good extracellular stability and good silencing activity, it is concluded that polyplexes based on TMC-SH are attractive systems for further in vivo evaluations.

Structural and magnetic properties of Mn-implanted Si

International Nuclear Information System (INIS)

Zhou Shengqiang; Potzger, K.; Zhang Gufei; Muecklich, A.; Eichhorn, F.; Schell, N.; Groetzschel, R.; Schmidt, B.; Skorupa, W.; Helm, M.; Fassbender, J.; Geiger, D.

2007-01-01

Structural and magnetic properties in Mn-implanted, p-type Si were investigated. High resolution structural analysis techniques such as synchrotron x-ray diffraction revealed the formation of MnSi 1.7 nanoparticles already in the as-implanted samples. Depending on the Mn fluence, the size increases from 5 nm to 20 nm upon rapid thermal annealing. No significant evidence is found for Mn substituting Si sites either in the as-implanted or annealed samples. The observed ferromagnetism yields a saturation moment of 0.21μ B per implanted Mn at 10 K, which could be assigned to MnSi 1.7 nanoparticles as revealed by a temperature-dependent magnetization measurement

Formation of equiaxed crystal structures in directionally solidified Al-Si alloys using Nb-based heterogeneous nuclei

Science.gov (United States)

Bolzoni, Leandro; Xia, Mingxu; Babu, Nadendla Hari

2016-01-01

The design of chemical compositions containing potent nuclei for the enhancement of heterogeneous nucleation in aluminium, especially cast alloys such as Al-Si alloys, is a matter of importance in order to achieve homogeneous properties in castings with complex geometries. We identified that Al3Nb/NbB2 compounds are effective heterogeneous nuclei and are successfully produced in the form of Al-2Nb-xB (x = 0.5, 1 and 2) master alloys. Our study shows that the inoculation of Al-10Si braze alloy with these compounds effectively promotes the heterogeneous nucleation of primary α-Al crystals and reduces the undercooling needed for solidification to take place. Moreover, we present evidences that these Nb-based compounds prevent the growth of columnar crystals and permit to obtain, for the first time, fine and equiaxed crystals in directionally solidified Al-10Si braze alloy. As a consequence of the potent heterogeneous particles, the size of the α-Al crystals was found to be less dependent on the processing conditions, especially the thermal gradient. Finally, we also demonstrate that the enhanced nucleation leads to the refinement of secondary phases such as eutectic silicon and primary silicon particles. PMID:28008967

Analysis of PL spectrum shape of Si-based materials as a tool for determination of Si crystallites' distribution

Energy Technology Data Exchange (ETDEWEB)

Khomenkova, L., E-mail: khomen@isp.kiev.ua

2014-11-15

This paper represents the analysis of the shape of photoluminescence spectra of Si-based nano-materials vs. energy of excitation light and temperature of measurements as a tool for the estimation of Si nanocrystallites' distribution. The samples fabricated by electrochemical etching (allowed different termination of Si nanocrystallites to be obtained) were used as modeling material. Bright emission at room temperature was observed for oxygen-terminated Si nanocrytallites, whereas hydrogen-terminated samples emit at low temperatures only. For most samples the photoluminescence spectrum was found to be complex, demonstrating competitive emission from Si crystallites and oxide defects. In latter case to separate the contribution of each recombination channel and to obtain information about crystallite distribution, low-temperature measurements of photoluminescence spectra under different excitation light energy were performed.

On the Mass Fractal Character of Si-Based Structural Networks in Amorphous Polymer Derived Ceramics

Directory of Open Access Journals (Sweden)

Sabyasachi Sen

2015-03-01

Full Text Available The intermediate-range packing of SiNxC4−x (0 ≤ x ≤ 4 tetrahedra in polysilycarbodiimide and polysilazane-derived amorphous SiCN ceramics is investigated using 29Si spin-lattice relaxation nuclear magnetic resonance (SLR NMR spectroscopy. The SiCN network in the polysilylcarbodiimide-derived ceramic consists predominantly of SiN4 tetrahedra that are characterized by a 3-dimensional spatial distribution signifying compact packing of such units to form amorphous Si3N4 clusters. On the other hand, the SiCN network of the polysilazane-derived ceramic is characterized by mixed bonded SiNxC4−x tetrahedra that are inefficiently packed with a mass fractal dimension of Df ~2.5 that is significantly lower than the embedding Euclidean dimension (D = 3. This result unequivocally confirms the hypothesis that the presence of dissimilar atoms, namely, 4-coordinated C and 3-coordinated N, in the nearest neighbor environment of Si along with some exclusion in connectivity between SiCxN4−x tetrahedra with widely different N:C ratios and the absence of bonding between C and N result in steric hindrance to an efficient packing of these structural units. It is noted that similar inefficiencies in packing are observed in polymer-derived amorphous SiOC ceramics as well as in proteins and binary hard sphere systems.

Structural and optical modification in 4H-SiC following 30 keV silver ion irradiation

Science.gov (United States)

Kaushik, Priya Darshni; Aziz, Anver; Siddiqui, Azher M.; Lakshmi, G. B. V. S.; Syväjärvi, Mikael; Yakimova, Rositsa; Yazdi, G. Reza

2018-05-01

The market of high power, high frequency and high temperature based electronic devices is captured by SiC due to its superior properties like high thermal conductivity and high sublimation temperature and also due to the limitation of silicon based electronics in this area. There is a need to investigate effect of ion irradiation on SiC due to its application in outer space as outer space is surrounded both by low and high energy ion irradiations. In this work, effect of low energy ion irradiation on structural and optical property of 4H-SiC is investigated. ATR-FTIR is used to study structural modification and UV-Visible spectroscopy is used to study optical modifications in 4H-SiC following 30 keV Ag ion irradiation. FTIR showed decrease in bond density of SiC along the ion path (track) due to the creation of point defects. UV-Visible absorption spectra showed decrease in optical band gap from 3.26 eV to 2.9 eV. The study showed degradation of SiC crystallity and change in optical band gap following low energy ion irradiation and should be addressed while fabricationg devices based on SiC for outer space application. Additionally, this study provides a platform for introducing structural and optical modification in 4H-SiC using ion beam technology in a controlled manner.

Structural design principles of complex bird songs: a network-based approach.

Directory of Open Access Journals (Sweden)

Kazutoshi Sasahara

Full Text Available Bird songs are acoustic communication signals primarily used in male-male aggression and in male-female attraction. These are often monotonous patterns composed of a few phrases, yet some birds have extremely complex songs with a large phrase repertoire, organized in non-random fashion with discernible patterns. Since structure is typically associated with function, the structures of complex bird songs provide important clues to the evolution of animal communication systems. Here we propose an efficient network-based approach to explore structural design principles of complex bird songs, in which the song networks--transition relationships among different phrases and the related structural measures--are employed. We demonstrate how this approach works with an example using California Thrasher songs, which are sequences of highly varied phrases delivered in succession over several minutes. These songs display two distinct features: a large phrase repertoire with a 'small-world' architecture, in which subsets of phrases are highly grouped and linked with a short average path length; and a balanced transition diversity amongst phrases, in which deterministic and non-deterministic transition patterns are moderately mixed. We explore the robustness of this approach with variations in sample size and the amount of noise. Our approach enables a more quantitative study of global and local structural properties of complex bird songs than has been possible to date.

Model-based flaw localization from perturbations in the dynamic response of complex mechanical structures

Energy Technology Data Exchange (ETDEWEB)

Chambers, D H

2009-02-24

A new method of locating structural damage using measured differences in vibrational response and a numerical model of the undamaged structure has been presented. This method is particularly suited for complex structures with little or no symmetry. In a prior study the method successively located simulated damage from measurements of the vibrational response on two simple structures. Here we demonstrate that it can locate simulated damage in a complex structure. A numerical model of a complex structure was used to calculate the structural response before and after the introduction of a void. The method can now be considered for application to structures of programmatic interest. It could be used to monitor the structural integrity of complex mechanical structures and assemblies over their lifetimes. This would allow early detection of damage, when repair is relatively easy and inexpensive. It would also allow one to schedule maintenance based on actual damage instead of a time schedule.

Influence of Preparation Conditions on Electrical Properties of the Al/Alq3/Si Diode Structures

Directory of Open Access Journals (Sweden)

Irina ČERNIUKĖ

2013-12-01

Full Text Available Hybrid organic-inorganic diode structures, Al/Alq3/n-Si and Al/Alq3/p-Si based on thin films of tris(8-hydroxyquinoline aluminum (Alq3 have been investigated. The Alq3 films were evaporated in vacuum and spin coated onto patterned areas of crystalline n- and p-type Si substrates with chemically removed native SiO2 layer. Current-voltage characteristics of the diode structures demonstrated improved rectification property compared to similar Al/n-Si and Al/p-Si device structures. Increased barrier height values (0.90 eV ÷ 1.1 eV and 0.77 eV ÷ 0.91 eV for the Al/Alq3/n-Si and Al/Alq3/p-Si device structures, respectively certified presence of an interface dipole induced by the organic interlayer. Non-ideal behavior of forward current-voltage characteristics has been explained assuming non-uniformity of barrier height, presence of interface states, and influence of the organic film on diode series resistance and space charge limited current. DOI: http://dx.doi.org/10.5755/j01.ms.19.4.2733

Strain distribution analysis in Si/SiGe line structures for CMOS technology using Raman spectroscopy

International Nuclear Information System (INIS)

Hecker, M; Roelke, M; Hermann, P; Zschech, E; Vartanian, V

2010-01-01

Strained silicon underneath the field-effect transistor gate increases significantly the charge carrier mobility and thus improves the performance of leading-edge Complementary Metal Oxide Semiconductor (CMOS) devices. For better understanding of the structure-strain relationship on the nanoscale and for optimization of device structures, the measurement of the local strain state has become essential. Raman spectroscopy is used in the present investigation to analyze the strain distribution in and close to silicon/embedded silicon-germanium (SiGe) line structures in conjunction with strain modeling applying finite element analysis. Both experimental results and modeling indicate the impact of geometry on the stress state. An increase of compressive stress within the Si lines is obtained for increasing SiGe line widths and decreasing Si line widths. The stress state within the Si lines is shown to be a mixed one deviating from a pure uniaxial state. Underneath the SiGe cavities, the presence of a tensile stress was observed. To investigate a procedure to scale down the spatial resolution of the Raman measurements, tip-enhanced Raman scattering experiments have been performed on free-standing SiGe lines with 100nm line width and line distance. The results show superior resolution and strain information not attainable in conventional Raman scans.

Oxidation resistance coating for niobium base structural composites

International Nuclear Information System (INIS)

Tabaru, T.; Shobu, K.; Kim, J.H.; Hirai, H.; Hanada, S.

2003-01-01

Oxidation behavior of Al-rich Mo(Si,Al) 2 base alloys, which is a candidate material for the oxidation resistance coating on Nb base structural composites, were investigated by thermogravimetry. The Mo(Si,Al) 2 base alloys containing Mo 5 (Si,Al) 3 up to about 10 vol% exhibits excellent oxidation resistance at temperatures ranging from 780 to 1580 K, particularly at 1580 K due to continuous Al 2 O 3 layer development. To evaluate the applicability of the Mo(Si,Al) 2 base coating, plasma spraying on Nb base composites were undertaken. However, interface reaction layer was found to form during the following heat treatment. Preparation of Mo(Si,Al) 2 /Al 2 O 3 /Nb layered structures via powder metallurgical process was attempted to preclude diffusion reaction between coating and substrate. (orig.)

Application progress of solid 29Si, 27Al NMR in the research of cement-based materials

International Nuclear Information System (INIS)

Feng Chunhua; Wang Xijian; Li Dongxu

2014-01-01

Background: The solid-state Nuclear Magnetic Resonance (NMR) is an effective method for the research of cement-based materials. Now it focuses on using solid 29 Si and 27 Al NMR to research the hydration structure of the cement-based materials in cement chemistry. Purpose: A theoretical guidance is proposed for solid 29 Si and 27 Al NMR technology used in cement chemistry research. Methods: We reviewed the application of solid 29 Si and 27 Al NMR in the cement-based materials and analyzed the problem among the researches. Results: This paper introduced an fundamental, relevant-conditions and basic parameters of NMR, and studied the technical parameters of solid 29 Si and 27 Ai NMR together with the relationship among the hydration structure of cement based material. Moreover, this paper reviewed the related domestic and overseas achievements in the research of hydration structure of the cement-based materials using solid 29 Si and 27 Al NMR. Conclusion: There were some problems in the research on cement-based materials by technology of solid 29 Si and 27 Al NMR. NMR will promote the Hydration theory of cement-based material greatly. (authors)

On the Mass Fractal Character of Si-Based Structural Networks in Amorphous Polymer Derived Ceramics.

Science.gov (United States)

Sen, Sabyasachi; Widgeon, Scarlett

2015-03-17

The intermediate-range packing of SiN x C 4- x (0 ≤ x ≤ 4) tetrahedra in polysilycarbodiimide and polysilazane-derived amorphous SiCN ceramics is investigated using 29 Si spin-lattice relaxation nuclear magnetic resonance (SLR NMR) spectroscopy. The SiCN network in the polysilylcarbodiimide-derived ceramic consists predominantly of SiN₄ tetrahedra that are characterized by a 3-dimensional spatial distribution signifying compact packing of such units to form amorphous Si₃N₄ clusters. On the other hand, the SiCN network of the polysilazane-derived ceramic is characterized by mixed bonded SiN x C 4- x tetrahedra that are inefficiently packed with a mass fractal dimension of D f ~2.5 that is significantly lower than the embedding Euclidean dimension ( D = 3). This result unequivocally confirms the hypothesis that the presence of dissimilar atoms, namely, 4-coordinated C and 3-coordinated N, in the nearest neighbor environment of Si along with some exclusion in connectivity between SiC x N 4- x tetrahedra with widely different N:C ratios and the absence of bonding between C and N result in steric hindrance to an efficient packing of these structural units. It is noted that similar inefficiencies in packing are observed in polymer-derived amorphous SiOC ceramics as well as in proteins and binary hard sphere systems.

Performance improvement inpolymer-based thin film transistor using modified bottom-contact structures with etched SiO{sub 2} layers

Energy Technology Data Exchange (ETDEWEB)

Park, Jeong Woo [R and D Center, Samsung Corning Precision Materials Co., Ltd, Asan (Korea, Republic of); You, Young Jun; Shim, Jae Won [Dept. of Electronics and Electrical Engineering, Dongguk University-Seoul, Seoul (Korea, Republic of)

2017-02-15

Polymer-based thin film transistors (TFTs) with a modified bottom-contact structure and etched SiO{sub 2} layer were developed and investigated. An increase in the field-effect mobility in the developed TFTs compared to TFTs with a normal bottom-contact structure was ascertained. A bottom-contact structure and the photolithographic processing method were used to ensure that the developed TFTs were suitable for commercial applications. Increased mobility of the modified bottom-contact structure was attributed to direct contact of the Au electrode with the active polymer layer.

Structure and chemistry of the Si(111)/AlN interface

Science.gov (United States)

Radtke, G.; Couillard, M.; Botton, G. A.; Zhu, D.; Humphreys, C. J.

2012-01-01

We investigate the atomic structure and the chemistry of the Si(111)/AlN interface for an AlN film grown at low-temperature (735 °C) by metalorganic vapor phase epitaxy. A heterogeneous interface is formed from the alternation of crystallographically abrupt and partly amorphous regions. The polarity of the AlN film, along with the projected atomic structure of the crystalline interface, is retrieved using high-angle annular dark field imaging, and a model, based on these experimental observations, is proposed for the bonding at the interface. Electron energy-loss spectrum-imaging, however, also reveals a chemical intermixing, placing our growth conditions at the onset of SiNx interlayer formation.

Structural and tunneling properties of Si nanowires

KAUST Repository

Montes Muñoz, Enrique

2013-12-06

We investigate the electronic structure and electron transport properties of Si nanowires attached to Au electrodes from first principles using density functional theory and the nonequilibrium Green\\'s function method. We systematically study the dependence of the transport properties on the diameter of the nanowires, on the growth direction, and on the length. At the equilibrium Au-nanowire distance we find strong electronic coupling between the electrodes and nanowires, which results in a low contact resistance. With increasing nanowire length we study the transition from metallic to tunneling conductance for small applied bias. For the tunneling regime we investigate the decay of the conductance with the nanowire length and rationalize the results using the complex band structure of the pristine nanowires. The conductance is found to depend strongly on the growth direction, with nanowires grown along the ⟨110⟩ direction showing the smallest decay with length and the largest conductance and current.

Structural and tunneling properties of Si nanowires

KAUST Repository

Montes Muñ oz, Enrique; Gkionis, Konstantinos; Rungger, Ivan; Sanvito, Stefano; Schwingenschlö gl, Udo

2013-01-01

We investigate the electronic structure and electron transport properties of Si nanowires attached to Au electrodes from first principles using density functional theory and the nonequilibrium Green's function method. We systematically study the dependence of the transport properties on the diameter of the nanowires, on the growth direction, and on the length. At the equilibrium Au-nanowire distance we find strong electronic coupling between the electrodes and nanowires, which results in a low contact resistance. With increasing nanowire length we study the transition from metallic to tunneling conductance for small applied bias. For the tunneling regime we investigate the decay of the conductance with the nanowire length and rationalize the results using the complex band structure of the pristine nanowires. The conductance is found to depend strongly on the growth direction, with nanowires grown along the ⟨110⟩ direction showing the smallest decay with length and the largest conductance and current.

Structural and magnetic characterization of Fe2CrSi Heusler alloy nanoparticles as spin injectors and spin based sensors

Science.gov (United States)

Saravanan, G.; Asvini, V.; Kalaiezhily, R. K.; Parveen, I. Mubeena; Ravichandran, K.

2018-05-01

Half-metallic ferromagnetic [HMF] nanoparticles are of considerable interest in spintronics applications due to their potential use as a highly spin polarized current source. HMF exhibits a semiconductor in one spin band at the Fermi level Ef and at the other spin band they poses strong metallic nature which shows 100 % spin polarization at Ef. Fe based full Heusler alloys are primary interest due to high Curie temperature. Fe2CrSi Heusler alloys are synthesized using metallic powders of Fe, Cr and Si by mechanical alloying method. X-Ray diffractions studies were performed to analyze the structural details of Fe2CrSi nanoparticles with High resolution scanning electron microscope (HRSEM) studies for the morphological details of nanoparticles and magnetic properties were studied using Vibrating sample magnetometer (VSM). XRD Data analysis conforms the Heusler alloy phase showing the existence of L21 structure. Magnetic properties are measured for synthesized samples exhibiting a soft magnetic property possessing low coercivity (HC = 60.5 Oe) and saturation magnetic moment of Fe2CrSi is 3.16 µB, which is significantly higher than the ideal value of 2 µB from the Slater-Pauling rule due to room temperature measurement. The change in magnetic properties are half-metallic nature of Fe2CrSi is due to the shift of the Fermi level with respect to the gap were can be used as spin sensors and spin injectors in magnetic random access memories and other spin dependent devices.

Local atomic structure and chemical order in amorphous SiGe:H and SiC:H alloys

International Nuclear Information System (INIS)

Pisarkiewicz, T.; Stapinski, T.

1994-01-01

The local structure and chemical ordering in amorphous hydrogenated silicon-germanium and silicon-carbon alloys were analyzed mainly with the help of extended x-ray absorption fine structure (EXAFS) spectroscopy, Raman scattering and electron diffraction. Ge-Ge and Ge-Si distances were found to be independent of concentration and the composition of the first coordination shell around Ge is consistent with a random mixing of the two species in a-Si 1-x Ge:H alloy. The first-coordination-shell average bond lengths for Si-Si and SiC in a-Si 1-x C x :H are also constant with concentration x and the comparison of the first coordination shell composition around Si with average concentration indicates that the alloys tends to be chemically ordered. The degree of crystallinity in microcrystalline Si films determined by EXAFS is in agreement with that obtained in Raman scattering analysis. (author). 16 refs, 5 figs

Dislocation core structures in Si-doped GaN

International Nuclear Information System (INIS)

Rhode, S. L.; Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J.; Horton, M. K.; Pennycook, T. J.; Dusane, R. O.; Moram, M. A.

2015-01-01

Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10 8  and (10 ± 1) × 10 9  cm −2 . All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN

Dislocation core structures in Si-doped GaN

Energy Technology Data Exchange (ETDEWEB)

Rhode, S. L., E-mail: srhode@imperial.ac.uk; Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Horton, M. K. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Pennycook, T. J. [SuperSTEM, STFC Daresbury Laboratories, Warrington WA4 4AD (United Kingdom); Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Dusane, R. O. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076 (India); Moram, M. A. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)

2015-12-14

Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10{sup 8} and (10 ± 1) × 10{sup 9} cm{sup −2}. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN.

Electroluminescence properties of Si MOS structures with incorporation of FeSi2 precipitates formed by iron implantation

International Nuclear Information System (INIS)

Chow, C.F.; Wong, S.P.; Gao, Y.; Ke, N.; Li, Q.; Cheung, W.Y.; Lourenco, M.A.; Homewood, K.P.

2005-01-01

Silicon MOS structures with FeSi 2 precipitates embedded in the MOS active region have been fabricated and the electroluminescence (EL) properties from these FeSi 2 -Si MOS structures were measured as a function of temperature from 80 K to 300 K. Clear EL signals were observed even at room temperature for samples prepared at appropriate processing conditions. The EL spectra consist of two peaks, one attributed to FeSi 2 and the other attributed to Si band edge emission. While the intensity of the FeSi 2 peak showed the usual thermal quenching behavior, the Si band edge emission showed the opposite trend with its intensity increased with increasing temperature. Details of the line shapes and their temperature dependence are analyzed and discussed

The effect of disorder on electronic and magnetic properties of quaternary Heusler alloy CoFeMnSi with LiMgPbSb-type structure

International Nuclear Information System (INIS)

Feng, Yu; Chen, Hong; Yuan, Hongkuan; Zhou, Ying; Chen, Xiaorui

2015-01-01

Thin films based on Heusler alloy often lost their theoretical predicted ultra-high spin polarization owing to the appearance of disorder. Using the first-principles calculations within density functional theory (DFT), we investigate the effect of disorder including antisite and swap on electronic and magnetic properties of quaternary Heusler alloy CoFeMnSi with LiMgPbSb-type structure. Twelve kinds of antisites and six kinds of swap disorders are proposed and studied comprehensively. In our calculations, Co(Fe)-, Mn(Fe)-, Si(Mn)-antisite and Co–Fe swap disorders are most favorable due to their lowest formation energies. Moreover, the positive binding energies of Co–Fe, Co–Si, Fe–Si and Mn–Si swap disorders with respect to their corresponding antisite disorders indicate that these complex swap disorders are more stable compared with their corresponding isolated antisite disorders. The investigations on density of states (DOS) show that the spin down energy gap of disordered structures suffers contraction and their DOS entirely move towards lower zone. Besides, the 100% spin polarization is maintained in all structures with antisite and swap disorders except for those with Co(Mn)-, Co(Si)-antisite and Co–Mn, Co–Si swap disorders. Therefore, the half-metallicity of quaternary Heusler alloy CoFeMnSi is quite robust against interfering effects such as Si(Mn), Co(Fe) and Co–Fe disorders most possibly formed in the growth. - Highlights: • CoFeMnSi with LiMgPbSb-type structure is found to be a half-metallic ferromagnet. • Si(Mn), Co(Fe), Mn(Fe) antisites and Co–Fe swap disorders are most likely to form. • The half-metallicity of CoFeMnSi is robust against the most possible disorders. • The magnetic moments of the most possible disorders follow the Pauli-Slater rule

Oxide Structure Dependence of SiO2/SiOx/3C-SiC/n-Type Si Nonvolatile Resistive Memory on Memory Operation Characteristics

Science.gov (United States)

Yamaguchi, Yuichiro; Shouji, Masatsugu; Suda, Yoshiyuki

2012-11-01

We have investigated the dependence of the oxide layer structure of our previously proposed metal/SiO2/SiOx/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) resistive memory device on the memory operation characteristics. The current-voltage (I-V) measurement and X-ray photoemission spectroscopy results suggest that SiOx defect states mainly caused by the oxidation of 3C-SiC at temperatures below 1000 °C are related to the hysteresis memory behavior in the I-V curve. By restricting the SiOx interface region, the number of switching cycles and the on/off current ratio are more enhanced. Compared with a memory device formed by one-step or two-step oxidation of 3C-SiC, a memory device formed by one-step oxidation of Si/3C-SiC exhibits a more restrictive SiOx interface with a more definitive SiO2 layer and higher memory performances for both the endurance switching cycle and on/off current ratio.

Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2

Science.gov (United States)

Pikul, A. P.; Kaczorowski, D.; Gajek, Z.; Stȩpień-Damm, J.; Ślebarski, A.; Werwiński, M.; Szajek, A.

2010-05-01

Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific-heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The physical properties were analyzed in terms of crystalline electric field and compared with results of ab initio band-structure calculations performed within the density-functional theory approach. The compound was found to crystallize in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma No.74, Pearson symbol: oI24 ) with the lattice parameters a=7.1330(14)Å , b=9.7340(19)Å , and c=5.6040(11)Å . Analysis of the magnetic and XPS data revealed the presence of well-localized magnetic moments of trivalent cerium ions. All the physical properties were found to be highly anisotropic over the whole temperature range studied and influenced by exceptionally strong crystalline electric field with the overall splitting of the 4f1 ground multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic moments at TN=4.70(1)K and their subsequent spin rearrangement at Tt=4.48(1)K manifest themselves as distinct anomalies in the temperature characteristic of all the physical properties investigated and exhibit complex evolution in an external magnetic field. A tentative magnetic B-T phase diagram, constructed for B parallel to the b axis being the easy magnetization direction, shows very complex magnetic behavior of CeRh3Si2 , similar to that recently reported for an isostructural compound CeIr3Si2 . The electronic band-structure calculations corroborated the antiferromagnetic ordering of the cerium magnetic moments and well-reproduced the experimental XPS valence-band spectrum.

Structure and scintillation properties of CsI(Tl) films on Si single crystal substrates

Energy Technology Data Exchange (ETDEWEB)

Guo, Lina [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Liu, Shuang, E-mail: shuangliu@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Chen, Dejun; Zhang, Shangjian; Liu, Yong; Zhong, Zhiyong [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Falco, Charles M. [University of Arizona, College of Optical Sciences, AZ 85721 (United States)

2016-10-30

Highlights: • We obtained the desired micro-columnar structure of CsI(Tl) films on the orienting Si substrates. • We improved the micro-columnar structure of CsI(Tl) films under the relatively large deposition rate through using the substrate with a pre-deposited CsI nanolayer. • We modeled the interface structures between the CsI(Tl) films with (200) and (310) orientation and Si(111) substrates to explain the preferred orientation of film under the influence of the orienting substrate significantly. • We gained a new spectrum of the CsI(Tl) films peaked at 740 nm wavelength. - Abstract: CsI(Tl) scintillation films fabricated on glass substrates are widely applied for X-ray imaging because their ability to grow in micro-columnar structure and proper emission wavelength matching CCD cameras. But the coupling process between the CsI(Tl) films and Si-based photo detector would cause coupling loss. In this work, CsI(Tl) films were deposited on the orienting Si substrates and the Si substrates covered by the pre-deposited CsI nanolayers. Structure and scintillation properties of films were examined by using scanning electron microscopy, X-ray diffraction, photoluminescence and radioluminescent spectrum. The films deposited on the orienting Si substrates show the micro-columnar morphology with perfect single crystalline structure and the photoluminescence spectra with bimodal distribution. The performances of the films prepared on the pre-deposited CsI nanolayer, containing micro-columns structure and the light yield are improved.

Structure and scintillation properties of CsI(Tl) films on Si single crystal substrates

International Nuclear Information System (INIS)

Guo, Lina; Liu, Shuang; Chen, Dejun; Zhang, Shangjian; Liu, Yong; Zhong, Zhiyong; Falco, Charles M.

2016-01-01

Highlights: • We obtained the desired micro-columnar structure of CsI(Tl) films on the orienting Si substrates. • We improved the micro-columnar structure of CsI(Tl) films under the relatively large deposition rate through using the substrate with a pre-deposited CsI nanolayer. • We modeled the interface structures between the CsI(Tl) films with (200) and (310) orientation and Si(111) substrates to explain the preferred orientation of film under the influence of the orienting substrate significantly. • We gained a new spectrum of the CsI(Tl) films peaked at 740 nm wavelength. - Abstract: CsI(Tl) scintillation films fabricated on glass substrates are widely applied for X-ray imaging because their ability to grow in micro-columnar structure and proper emission wavelength matching CCD cameras. But the coupling process between the CsI(Tl) films and Si-based photo detector would cause coupling loss. In this work, CsI(Tl) films were deposited on the orienting Si substrates and the Si substrates covered by the pre-deposited CsI nanolayers. Structure and scintillation properties of films were examined by using scanning electron microscopy, X-ray diffraction, photoluminescence and radioluminescent spectrum. The films deposited on the orienting Si substrates show the micro-columnar morphology with perfect single crystalline structure and the photoluminescence spectra with bimodal distribution. The performances of the films prepared on the pre-deposited CsI nanolayer, containing micro-columns structure and the light yield are improved.

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

Science.gov (United States)

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.

Tuning by means of laser annealing of electronic and structural properties of nc-Si/a-Si:H

International Nuclear Information System (INIS)

Poliani, E.; Somaschini, C.; Sanguinetti, S.; Grilli, E.; Guzzi, M.; Le Donne, A.; Binetti, S.; Pizzini, S.; Chrastina, D.; Isella, G.

2009-01-01

We report the effect of laser annealing on the structural and electronic properties of nc-Si/a-Si:H samples grown close to the amorphous to nanocrystalline transition. The nc-Si/a-Si:H thin films were produced by low-energy plasma-enhanced chemical vapor deposition through a gas discharge containing SiH 4 . The samples were subjected to different laser fluencies and were characterized for changes in their structural and electronic properties via Raman spectroscopy and photoluminescence measurements. The laser annealing effects are twofold: i) the nanocrystalline phase grows, during the laser treatment, respect to the amorphous phase; ii) the photoluminescence spectra show the suppression, after laser annealing, of the frequencies above the crystalline Si band-gap.

New self-limiting assembly model for Si quantum rings on Si(100).

Science.gov (United States)

Yu, L W; Chen, K J; Song, J; Xu, J; Li, W; Li, X F; Wang, J M; Huang, X F

2007-04-20

We propose a new self-limiting assembly model for Si quantum rings on Si(100) where the ring's formation and evolution are driven by a growth-etching competition mechanism. The as-grown ring structure in a plasma enhanced chemical vapor deposition system has excellent rotational symmetry and superior morphology with a typical diameter, edge width, and height of 150-300, 10, and 5 nm, respectively. Based on this model, the size and morphology can be controlled well by simply tuning the timing procedure. We suggest that this growth model is not limited to certain material system, but provides a general scheme to control and tailor the self-assembly nanostructures into the desired size, shape, and complexity.

Electric-field-controlled interface dipole modulation for Si-based memory devices.

Science.gov (United States)

Miyata, Noriyuki

2018-05-31

Various nonvolatile memory devices have been investigated to replace Si-based flash memories or emulate synaptic plasticity for next-generation neuromorphic computing. A crucial criterion to achieve low-cost high-density memory chips is material compatibility with conventional Si technologies. In this paper, we propose and demonstrate a new memory concept, interface dipole modulation (IDM) memory. IDM can be integrated as a Si field-effect transistor (FET) based memory device. The first demonstration of this concept employed a HfO 2 /Si MOS capacitor where the interface monolayer (ML) TiO 2 functions as a dipole modulator. However, this configuration is unsuitable for Si-FET-based devices due to its large interface state density (D it ). Consequently, we propose, a multi-stacked amorphous HfO 2 /1-ML TiO 2 /SiO 2 IDM structure to realize a low D it and a wide memory window. Herein we describe the quasi-static and pulse response characteristics of multi-stacked IDM MOS capacitors and demonstrate flash-type and analog memory operations of an IDM FET device.

The effect of millisecond flash lamp annealing on electrical and structural properties of ZnO:Al/Si structures

Energy Technology Data Exchange (ETDEWEB)

Lindberg, P. F.; Riise, H. N.; Vines, L.; Svensson, B. G.; Monakhov, E. V. [Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048, Blindern, N-0316 Oslo (Norway); Lipp Bregolin, F.; Wiesenhütter, K.; Wiesenhütter, U.; Prucnal, S.; Skorupa, W. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany)

2016-05-14

The effect of millisecond flash lamp annealing (FLA) on aluminum doped ZnO (AZO) films and their interface with Si have been studied. The AZO films were deposited by magnetron sputtering on Si (100) substrates. The electrical and structural properties of the film and AZO/Si structures were characterized by current–voltage, capacitance–voltage, and deep level transient spectroscopy measurements, X-ray diffraction, and secondary ion mass spectrometry. The resistivity of the AZO film is reduced to a close to state-of-the-art value of 2 × 10{sup −4} Ω cm after FLA for 3 ms with an average energy density of 29 J/cm{sup 2}. In addition, most of the interfacial defects energy levels are simultaneously annealed out, except for one persisting shallow level, tentatively assigned to the vacancy-oxygen complex in Si, which was not affected by FLA. Subsequent to the FLA, the samples were treated in N{sub 2} or forming gas (FG) (N{sub 2}/H{sub 2}, 90/10%{sub mole}) ambient at 200–500 °C. The latter samples maintained the low resistivity achieved after the FLA, but not the former ones. The interfacial defect level persisting after the FLA is removed by the FG treatment, concurrently as another level emerges at ∼0.18 eV below the conduction band. The electrical data of the AZO films are discussed in term of point defects controlling the resistivity, and it is argued that the FLA promotes formation of electrically neutral clusters of Zink vacancies (V{sub Zn}'s) rather than passivating/compensating complexes between the Al donors and V{sub Zn}'s.

Electron density distribution and disordered crystal structure of 15R-SiAlON, SiAl4O2N4

International Nuclear Information System (INIS)

Banno, Hiroki; Hanai, Takaaki; Asaka, Toru; Kimoto, Koji; Fukuda, Koichiro

2014-01-01

The crystal structure of SiAl 4 O 2 N 4 was characterized by laboratory X-ray powder diffraction (CuKα 1 ). The title compound is trigonal with space group R3-bar m. The hexagonal unit-cell dimensions (Z=3) are a=0.301332(3) nm, c=4.18616(4) nm and V=0.3291825(5) nm 3 . The initial structural model was successfully derived by the charge-flipping method and further refined by the Rietveld method. The final structural model showed the positional disordering of one of the three (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R wp =5.05%, S (=R wp /R e )=1.21, R p =3.77%, R B =1.29% and R F =1.01%. The disordered crystal structure was successfully described by overlapping three types of domains with ordered atom arrangements. The distribution of atomic positions in one of the three types of domains can be achieved in the space group R3-bar m. The atom arrangements in the other two types of domains are noncentrosymmetrical with the space group R3m. These two structural configurations are related by the pseudo-symmetry inversion. -- Graphical abstract: A bird's eye view of electron densities up to 75.3% (0.133 nm −3 ) of the maximum on the plane parallel to (110) with the corresponding atomic arrangements of SiAl 4 O 2 N 4 . Highlights: • Crystal structure of SiAl 4 O 2 N 4 is determined by laboratory X-ray powder diffraction. • The atom arrangements are represented by the split-atom model. • The maximum-entropy method-based pattern fitting method is used to confirm the validity of the model. • The disordered structure is described by overlapping three types of domains with ordered atom arrangements

Structural stabilities and electronic properties of fully hydrogenated SiC sheet

International Nuclear Information System (INIS)

Wang, Xin-Quan; Wang, Jian-Tao

2011-01-01

The intriguing structural and electronic properties of fully hydrogenated SiC honeycomb sheet are studied by means of ab initio calculations. Based on structure optimization and phonon dispersion analysis, we find that both chair-like and boat-like configurations are dynamically stable, and the chair-like conformer is energetically more favored with an energy gain of 0.03 eV per C atom relative to the boat-like one. The chair-like and boat-like conformers are revealed to be nonmagnetic semiconductors with direct band gaps of 3.84 and 4.29 eV, respectively, both larger than 2.55 eV of pristine SiC sheet. The charge density distributions show that the bondings are characterized with covalency for both chair-like and boat-like conformers. -- Highlights: → Structural and electronic properties of fully hydrogenated SiC sheet are studied. → Both chair-like and boat-like configurations are dynamically stable. → While the chair-like conformer is energetically more favored. → The chair-like and boat-like conformers are nonmagnetic semiconductors. → The bondings are characterized with covalency.

Resistance Switching Memory Characteristics of Si/CaF2/CdF2 Quantum-Well Structures Grown on Metal (CoSi2) Layer

Science.gov (United States)

Denda, Junya; Uryu, Kazuya; Watanabe, Masahiro

2013-04-01

A novel scheme of resistance switching random access memory (ReRAM) devices fabricated using Si/CaF2/CdF2/CaF2/Si quantum-well structures grown on metal CoSi2 layer formed on a Si substrate has been proposed, and embryonic write/erase memory operation has been demonstrated at room temperature. It has been found that the oxide-mediated epitaxy (OME) technique for forming the CoSi2 layer on Si dramatically improves the stability and reproducibility of the current-voltage (I-V) curve. This technology involves 10-nm-thick Co layer deposition on a protective oxide prepared by boiling in a peroxide-based solution followed by annealing at 550 °C for 30 min for silicidation in ultrahigh vacuum. A switching voltage of lower than 1 V, a peak current density of 32 kA/cm2, and an ON/OFF ratio of 10 have been observed for the sample with the thickness sequence of 0.9/0.9/2.5/0.9/5.0 nm for the respective layers in the Si/CaF2/CdF2/CaF2/Si structure. Results of surface morphology analysis suggest that the grain size of crystal islands with flat surfaces strongly affects the quality of device characteristics.

Structural studies of n-type nc-Si-QD thin films for nc-Si solar cells

Science.gov (United States)

Das, Debajyoti; Kar, Debjit

2017-12-01

A wide optical gap nanocrystalline silicon (nc-Si) dielectric material is a basic requirement at the n-type window layer of nc-Si solar cells in thin film n-i-p structure on glass substrates. Taking advantage of the high atomic-H density inherent to the planar inductively coupled low-pressure (SiH4 + CH4)-plasma, development of an analogous material in P-doped nc-Si-QD/a-SiC:H network has been tried. Incorporation of C in the Si-network extracted from the CH4 widens the optical band gap; however, at enhanced PH3-dilution of the plasma spontaneous miniaturization of the nc-Si-QDs below the dimension of Bohr radius (∼4.5 nm) further enhances the band gap by virtue of the quantum size effect. At increased flow rate of PH3, dopant induced continuous amorphization of the intrinsic crystalline network is counterbalanced by the further crystallization promoted by the supplementary atomic-H extracted from PH3 (1% in H2) in the plasma, eventually holding a moderately high degree of crystallinity. The n-type wide band gap (∼1.93 eV) window layer with nc-Si-QDs in adequate volume fraction (∼52%) could furthermore be instrumental as an effective seed layer for advancing sequential crystallization in the i-layer of nc-Si solar cells with n-i-p structure in superstrate configuration.

Ge 3P 6Si 2O 25: A cage structure closely related to the intersecting tunnel structure KMo 3P 6Si 2O 25

Science.gov (United States)

Leclaire, A.; Raveau, B.

1988-08-01

A germanosilicophosphate Ge 3P 6Si 2O 25 has been isolated. Its structure was solved from a single-crystal study in the space group P overline31c . Its cell parameters are a = b = 7.994(1) Å, c = 16.513(2) Å, Z = 2. The refinement by full-matrix least-squares calculations leads to R = 0.043 with 686 independent reflections. The structure of this oxide is built up from corner-sharing PO 4 and SiO 4 tetrahedra and GeO 6 octahedra. One observes a feature common to several silicophosphates: the presence of the structural unit P 6Si 2O 25 built up from a disilicate group sharing its corners with six PO 4 tetrahedra. The structural relationships between this oxide and the silicophosphates AMo 3P 6Si 2O 25 and Si 3P 6Si 2O 25 (or Ge 3P 6 Ge 2O 25) are described.

Structural and optical properties of SiC-SiO2 nanocomposite thin films

Science.gov (United States)

Bozetine, I.; Keffous, A.; Kaci, S.; Menari, H.; Manseri, A.

2018-03-01

This study deals with the deposition of thin films of a SiC-SiO2nanocomposite deposited on silicon substrates. The deposition is carried out by a co-sputtering RF magnetron 13.56 MHz, using two targets a polycristallin 6H-SiC and sprigs of SiO2. In order to study the influence of the deposition time on the morphology, the structural and optical properties of the thin films produced, two series of samples were prepared, namely a series A with a 30 min deposition time and a series B of one hour duration. The samples were investigated using different characterization techniques such as Scanning Electron Microscope (SEM), X-ray Diffraction (DRX), Fourier Transform Infrared Spectroscopy (FTIR), Secondary Ion Mass Spectrometry (SIMS) and photoluminescence. The results obtained, reveal an optical gap varies between 1.4 and 2.4 eV depending on the thickness of the film; thus depending on the deposition time. The SIMS profile recorded the presence of oxygen (16O) on the surface, which the signal beneath the silicon signal (28Si) and carbon (12C) signals, which confirms that the oxide (SiO2) is the first material deposited at the interface film - substrate with an a-OSiC structure. The photoluminescence (PL) measurement exhibits two peaks, centred at 390 nm due to the oxide and at 416 nm due probably to the nanocrystals of SiC crystals, note that when the deposition time increases, the intensity of the PL drops drastically, result in agreement with dense and smooth film.

Ternary complexes of folate-PEG-appended dendrimer (G4)/α-cyclodextrin conjugate, siRNA and low-molecular-weight polysaccharide sacran as a novel tumor-selective siRNA delivery system.

Science.gov (United States)

Ohyama, Ayumu; Higashi, Taishi; Motoyama, Keiichi; Arima, Hidetoshi

2017-06-01

We previously developed a tumor-selective siRNA carrier by preparing polyamidoamine dendrimer (generation 4, G4) conjugates with α-cyclodextrin and folate-polyethylene glycol (Fol-PαC (G4)). In the present study, we developed ternary complexes of Fol-PαC (G4)/siRNA with low-molecular-weight-sacrans to achieve more effective siRNA transfer activity. Among the different molecular-weight sacrans, i.e. sacran 100, 1000 and 10,000 (MW 44,889Da, 943,692Da and 1,488,281Da, respectively), sacran 100 significantly increased the cellular uptake and the RNAi effects of Fol-PαC (G4)/siRNA binary complex with negligible cytotoxicity in KB cells (folate receptor-α positive cells). In addition, the ζ-potential and particle size of Fol-PαC (G4)/siRNA complex were decreased by the ternary complexation with sacran 100. Importantly, the in vivo RNAi effect of the ternary complex after the intravenous administration to tumor-bearing BALB/c mice was significantly higher than that of the binary complex. In conclusion, Fol-PαC (G4)/siRNA/sacran 100 ternary complex has a potential as a novel tumor-selective siRNA delivery system. Copyright © 2017 Elsevier B.V. All rights reserved.

Magnetic ordering in the monoclinic structure of Nd5Si1.45Ge2.55 and Pr5Si1.5Ge2.5 studied by means of neutron powder diffraction

International Nuclear Information System (INIS)

Magen, C; Ritter, C; Morellon, L; Algarabel, P A; Ibarra, M R

2004-01-01

The compounds Nd 5 Si 1.45 Ge 2.55 and Pr 5 Si 1.5 Ge 2.5 have been investigated by means of magnetization measurements and neutron powder diffraction techniques. These alloys present a room-temperature monoclinic Gd 5 Si 2 Ge 2 -type crystallographic structure and, on cooling, both systems order ferromagnetically, at T C = 56 and 32 K, respectively, from a high-temperature paramagnetic to a low-temperature complex canted ferromagnetic state. The monoclinic crystallographic structure remains unchanged upon cooling down to 4 K, demonstrating the existence of a monoclinic ferromagnetic phase, and the possibility of a full decoupling of magnetic and crystallographic degrees of freedom in the 5:4 lanthanide intermetallic compounds

Electric measurements of PV heterojunction structures a-SiC/c-Si

Science.gov (United States)

Perný, Milan; Šály, Vladimír; Janíček, František; Mikolášek, Miroslav; Váry, Michal; Huran, Jozef

2018-01-01

Due to the particular advantages of amorphous silicon or its alloys with carbon in comparison to conventional crystalline materials makes such a material still interesting for study. The amorphous silicon carbide may be used in a number of micro-mechanical and micro-electronics applications and also for photovoltaic energy conversion devices. Boron doped thin layers of amorphous silicon carbide, presented in this paper, were prepared due to the optimization process for preparation of heterojunction solar cell structure. DC and AC measurement and subsequent evaluation were carried out in order to comprehensively assess the electrical transport processes in the prepared a-SiC/c-Si structures. We have investigated the influence of methane content in deposition gas mixture and different electrode configuration.

The Effects of Al and Ti Additions on the Structural Stability, Mechanical and Electronic Properties of D8m-Structured Ta5Si3

Directory of Open Access Journals (Sweden)

Linlin Liu

2016-05-01

Full Text Available In the present study, the influence of substitutional elements (Ti and Al on the structural stability, mechanical properties, electronic properties and Debye temperature of Ta5Si3 with a D8m structure were investigated by first principle calculations. The Ta5Si3 alloyed with Ti and Al shows negative values of formation enthalpies, indicating that these compounds are energetically stable. Based on the values of formation enthalpies, Ti exhibits a preferential occupying the Ta4b site and Al has a strong site preference for the Si8h site. From the values of the bulk modulus (B, shear modulus (G and Young’s modulus (E, we determined that both Ti and Al additions decrease both the shear deformation resistance and the elastic stiffness of D8m structured Ta5Si3. Using the shear modulus/bulk modulus ratio (G/B, Poisson’s ratio (υ and Cauchy’s pressure, the effect of Ti and Al additions on the ductility of D8m-structured Ta5Si3 are explored. The results show that Ti and Al additions reduce the hardness, resulting in solid solution softening, but improve the ductility of D8m-structured Ta5Si3. The electronic calculations reveal that Ti and Al additions change hybridization between Ta-Si and Si-Si atoms for the binary D8m-structured Ta5Si3. The new Ta-Al bond is weaker than the Ta-Si covalent bonds, reducing the covalent property of bonding in D8m-structured Ta5Si3, while the new strong Ti4b-Ti4b anti-bonding enhances the metallic behavior of the binary D8m-structured Ta5Si3. The change in the nature of bonding can well explain the improved ductility of D8m-structured Ta5Si3 doped by Ti and Al. Moreover, the Debye temperatures, ΘD, of D8m-structured Ta5Si3 alloying with Ti and Al are decreased as compared to the binary Ta5Si3.

Ultra-low Thermal Conductivity in Si/Ge Hierarchical Superlattice Nanowire.

Science.gov (United States)

Mu, Xin; Wang, Lili; Yang, Xueming; Zhang, Pu; To, Albert C; Luo, Tengfei

2015-11-16

Due to interfacial phonon scattering and nanoscale size effect, silicon/germanium (Si/Ge) superlattice nanowire (SNW) can have very low thermal conductivity, which is very attractive for thermoelectrics. In this paper, we demonstrate using molecular dynamics simulations that the already low thermal conductivity of Si/Ge SNW can be further reduced by introducing hierarchical structure to form Si/Ge hierarchical superlattice nanowire (H-SNW). The structural hierarchy introduces defects to disrupt the periodicity of regular SNW and scatters coherent phonons, which are the key contributors to thermal transport in regular SNW. Our simulation results show that periodically arranged defects in Si/Ge H-SNW lead to a ~38% reduction of the already low thermal conductivity of regular Si/Ge SNW. By randomizing the arrangement of defects and imposing additional surface complexities to enhance phonon scattering, further reduction in thermal conductivity can be achieved. Compared to pure Si nanowire, the thermal conductivity reduction of Si/Ge H-SNW can be as large as ~95%. It is concluded that the hierarchical structuring is an effective way of reducing thermal conductivity significantly in SNW, which can be a promising path for improving the efficiency of Si/Ge-based SNW thermoelectrics.

Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation

DEFF Research Database (Denmark)

Dhiman, Rajnish; Rana, Kuldeep; Bengu, Erman

2012-01-01

We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process...

Theoretical study of the structure and reactivity of lanthanide and actinide based organometallic complexes

International Nuclear Information System (INIS)

Barros, N.

2007-06-01

In this PhD thesis, lanthanide and actinide based organometallic complexes are studied using quantum chemistry methods. In a first part, the catalytic properties of organo-lanthanide compounds are evaluated by studying two types of reactions: the catalytic hydro-functionalization of olefins and the polymerisation of polar monomers. The reaction mechanisms are theoretically determined and validated, and the influence of possible secondary non productive reactions is envisaged. A second part focuses on uranium-based complexes. Firstly, the electronic structure of uranium metallocenes is analysed. An analogy with the uranyl compounds is proposed. In a second chapter, two isoelectronic complexes of uranium IV are studied. After validating the use of DFT methods for describing the electronic structure and the reactivity of these compounds, it is shown that their reactivity difference can be related to a different nature of chemical bonding in these complexes. (author)

Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

Science.gov (United States)

Leung, T. C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K. G.

1993-01-01

Studies of SiO2-Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO2-Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown.

Study of SiO2-Si and metal-oxide-semiconductor structures using positrons

International Nuclear Information System (INIS)

Leung, T.C.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K.G.

1993-01-01

Studies of SiO 2 -Si and metal-oxide-semiconductor (MOS) structures using positrons are summarized and a concise picture of the present understanding of positrons in these systems is provided. Positron annihilation line-shape S data are presented as a function of the positron incident energy, gate voltage, and annealing, and are described with a diffusion-annihilation equation for positrons. The data are compared with electrical measurements. Distinct annihilation characteristics were observed at the SiO 2 -Si interface and have been studied as a function of bias voltage and annealing conditions. The shift of the centroid (peak) of γ-ray energy distributions in the depletion region of the MOS structures was studied as a function of positron energy and gate voltage, and the shifts are explained by the corresponding variations in the strength of the electric field and thickness of the depletion layer. The potential role of the positron annihilation technique as a noncontact, nondestructive, and depth-sensitive characterization tool for the technologically important, deeply buried interface is shown

Characterization of SiC–SiC composites for accident tolerant fuel cladding

Energy Technology Data Exchange (ETDEWEB)

Deck, C.P., E-mail: Christian.Deck@ga.com; Jacobsen, G.M.; Sheeder, J.; Gutierrez, O.; Zhang, J.; Stone, J.; Khalifa, H.E.; Back, C.A.

2015-11-15

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.

Copper-based metal coordination complexes with Voriconazole ligand: Syntheses, structures and antimicrobial properties

Science.gov (United States)

Zhao, Yan-Ming; Tang, Gui-Mei; Wang, Yong-Tao; Cui, Yue-Zhi; Ng, Seik Weng

2018-03-01

Three new chiral metal coordination complexes, namely, [Cu(FZ)2(CH3COO)2(H2O)]·2H2O (1), [Cu(FZ)2(NO3)2] (2), and [Cu2(FZ)2 (H2O)8](SO4)2·4H2O (3) [FZ = (2R,3S)-2-(2,4-difluorophenyl)-3-(5-fluoro-4-pyrimidiny)-1-(1H-1,2,4-triazol-1-yl)-2-butanol) (Voriconazole)] have been obtained by the reaction of Cu(II) salts and the free ligand FZ at room temperature. Complexes 1-3 were structurally characterized by X-ray single-crystal diffraction, IR, UV-vis, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Complex 1 crystallizes in the chiral space group C2, which exhibits a mono-nuclear structure. Both complexes 2 and 3 display a one-dimensional (1D) tape structure, which crystallize in chiral space group P21212 and P212121, respectively. Among these complexes, there exist a variety of hydrogen bonds and stacking interactions, through which a three-dimensional supramolecular architecture will be generated. Compared with the standard (Voriconazole), these Cu-based complexes show the more potent inhibiting efficiency against the species of Candida and Aspergillus. Moreover, among these complexes, complex 1 shows the most excellent efficiency.

Periodically structured Si pillars for high-performing heterojunction photodetectors

Science.gov (United States)

Melvin David Kumar, M.; Yun, Ju-Hyung; Kim, Joondong

2015-03-01

A periodical array of silicon (Si) micro pillar structures was fabricated on Si substrates using PR etching process. Indium tin oxide (ITO) layer of 80 nm thickness was deposited over patterned Si substrates so as to make ITO/n-Si heterojunction devices. The influences of width and period of pillars on the optical and electrical properties of prepared devices were investigated. The surface morphology of the Si substrates revealed the uniform array of pillar structures. The 5/10 (width/period) Si pillar pattern reduced the optical reflectance to 6.5% from 17% which is of 5/7 pillar pattern. The current rectifying ratio was found higher for the device in which the pillars are situated in optimum periods. At both visible (600 nm) and near infrared (900 nm) range of wavelengths, the 5/7 and 5/10 pillar patterned device exhibited the better photoresponses which are suitable for making advanced photodetectors. This highly transmittance and photoresponsive pillar patterned Si substrates with an ITO layer would be a promising device for various photoelectric applications.

Effect of oxide charge trapping on x-ray photoelectron spectroscopy of HfO2/SiO2/Si structures

International Nuclear Information System (INIS)

Abe, Yasuhiro; Miyata, Noriyuki; Suzuki, Haruhiko; Kitamura, Koji; Igarashi, Satoru; Nohira, Hiroshi; Ikenaga, Eiji

2009-01-01

We examined the effects of interfacial SiO 2 layers and a surface metal layer on the photoelectron spectra of HfO 2 /SiO 2 /Si structures by hard X-ray photoemission spectroscopy with synchrotron radiation as well as conventional X-ray photoelectron spectroscopy (XPS). The Hf 4f and Hf 3d photoelectron peaks broadened and shifted toward a higher binding energy with increasing thickness of the interfacial SiO 2 layer, even though photoelectrons may have been emitted from the HfO 2 layer with the same chemical composition. Thinning the interfacial Si oxide layer to approximately one monolayer and depositing a metal layer on the HfO 2 surface suppressed these phenomena. The O 1s photoelectron spectra revealed marked differences between the metal- and nonmetal-deposited HfO 2 /SiO 2 /Si structures; HfO 2 and SiO 2 components in the O 1s photoelectron spectra for the metal-deposited structures were observed at reasonably separated binding energies, but those for the nonmetal-deposited structures were not separated clearly. From this behavior concerning the effects of interfacial SiO 2 and surface metal layers, we concluded that the Hf 4f, Hf 3d, and O 1s spectra measured from the HfO 2 /SiO 2 /Si structures did not reflect actual chemical bonding states. We consider that potential variations in the HfO 2 film owing to charge trapping strongly affect the measured photoelectron spectra. On the basis of angle-resolved XPS measurements, we propose that positive charges are trapped at the HfO 2 surface and negative charges are trapped inside the HfO 2 layer. (author)

Antimony Influence on Shape of Eutectic Silicium in Al-Si Based Alloys

Directory of Open Access Journals (Sweden)

Bolibruchová D.

2017-12-01

Full Text Available Liquid AI-Si alloys are usually given special treatments before they are cast to obtain finer or modified matrix and eutectic structures, leading to improved properties. For many years, sodium additions to hypoeutectic and eutectic AI-Si melts have been recognized as the most effective method of modifying the eutectic morphology, although most of the group IA or IIA elements have significant effects on the eutectic structure. Unfortunately, many of these approaches also have associated several founding difficulties, such as fading, forming dross in presence of certain alloying elements, reduced fluidity, etc. ln recent years, antimony additions to AI-Si castings have attracted considerable attention as an alternative method of refining the eutectic structure. Such additions eliminate many of the difficulties listed above and provide permanent (i.e. non-fading refining ability. In this paper, the authors summarize work on antimony treatment of Al-Si based alloys.

3D complex: a structural classification of protein complexes.

Directory of Open Access Journals (Sweden)

Emmanuel D Levy

2006-11-01

Full Text Available Most of the proteins in a cell assemble into complexes to carry out their function. It is therefore crucial to understand the physicochemical properties as well as the evolution of interactions between proteins. The Protein Data Bank represents an important source of information for such studies, because more than half of the structures are homo- or heteromeric protein complexes. Here we propose the first hierarchical classification of whole protein complexes of known 3-D structure, based on representing their fundamental structural features as a graph. This classification provides the first overview of all the complexes in the Protein Data Bank and allows nonredundant sets to be derived at different levels of detail. This reveals that between one-half and two-thirds of known structures are multimeric, depending on the level of redundancy accepted. We also analyse the structures in terms of the topological arrangement of their subunits and find that they form a small number of arrangements compared with all theoretically possible ones. This is because most complexes contain four subunits or less, and the large majority are homomeric. In addition, there is a strong tendency for symmetry in complexes, even for heteromeric complexes. Finally, through comparison of Biological Units in the Protein Data Bank with the Protein Quaternary Structure database, we identified many possible errors in quaternary structure assignments. Our classification, available as a database and Web server at http://www.3Dcomplex.org, will be a starting point for future work aimed at understanding the structure and evolution of protein complexes.

SiGe Based Low Temperature Electronics for Lunar Surface Applications

Science.gov (United States)

Mojarradi, Mohammad M.; Kolawa, Elizabeth; Blalock, Benjamin; Cressler, John

2012-01-01

The temperature at the permanently shadowed regions of the moon's surface is approximately -240 C. Other areas of the lunar surface experience temperatures that vary between 120 C and -180 C during the day and night respectively. To protect against the large temperature variations of the moon surface, traditional electronics used in lunar robotics systems are placed inside a thermally controlled housing which is bulky, consumes power and adds complexity to the integration and test. SiGe Based electronics have the capability to operate over wide temperature range like that of the lunar surface. Deploying low temperature SiGe electronics in a lander platform can minimize the need for the central thermal protection system and enable the development of a new generation of landers and mobility platforms with highly efficient distributed architecture. For the past five years a team consisting of NASA, university and industry researchers has been examining the low temperature and wide temperature characteristic of SiGe based transistors for developing electronics for wide temperature needs of NASA environments such as the Moon, Titan, Mars and Europa. This presentation reports on the status of the development of wide temperature SiGe based electronics for the landers and lunar surface mobility systems.

Thermal stability of Cu/α-Ta/SiO2/Si structures

International Nuclear Information System (INIS)

Yuan, Z.L.; Zhang, D.H.; Li, C.Y.; Prasad, K.; Tan, C.M.

2004-01-01

The thermal stability of the Cu/α-Ta/SiO 2 /Si structures is investigated. Tantalum oxides are first observed at the interface between Cu and Ta due to residual oxygen in the annealing ambient at low annealing temperatures (about 600 deg. C). Ternary Cu-Ta oxides and/or Ta oxides rather than Cu oxides are found at the Cu top layer on account of the out diffusion of Ta. After high temperature annealing (up to 750 deg. C), polycrystalline Tantalum oxides (Ta 2 O 5 ) and Ta-rich silicides (Ta 5 Si 3 ) are found as dominant products due to the dissociation of SiO 2 . A severe intermixing of Cu, Ta and SiO 2 was observed after 800 deg. C annealing. First a drop and then an increase in sheet resistances were observed, the former possibly resulting from grain growth and impurities removal in Cu films, and the latter from the reduction of Cu thickness and formation of high resistivity products. The α-Ta films with a thickness of 25 nm have good barrier effectiveness up to 750 deg. C. The degradation of α-Ta film is mainly caused by self oxidation, silicidation and bidirectional diffusion

Parameters of thermoelectric power and electronic structure of Yb-based compounds of YbM2X2(M=Fe,Co,Ni,Cu; X=Si,Ge) type

International Nuclear Information System (INIS)

Levin, E.M.; Kuzhel', B.S.

1990-01-01

Thermoelectric power of Yb-based intermetallic alloys YbM 2 Si 2 (M-Co,Ni,Cu) and YbM 2 Ge 2 (M=Fe,Co,Ni) have been investigated and found to have anomalous low-temperature peaks conditioned by intermediate Yb valency. Calculation of electronic structure parameters performed in frames of the localized Fermi-liquid model using experimental data on the thermoelectric power is in good agreement with results of YbCu 2 Si 2 band structure calculation based on the experimental value of the electronic heat capacity with regard for the (2J+1) - fold Yb 2+ degeneration

First discovery and structural characterization of a new compound in Al-Si-O-C system

International Nuclear Information System (INIS)

Iwata, Tomoyuki; Kaga, Motoaki; Nakano, Hiromi; Fukuda, Koichiro

2009-01-01

A quaternary oxycarbide, [Al 16.77(5) Si 1.23(5) ] Σ 18 [O 3.04(9) C 10.96(9) ] Σ 14 , has been for the first time discovered in the Al-Si-O-C system. The crystal structure was characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The atom ratios [Al:Si] were determined by EDX, and the initial structural model was derived by the direct methods. The structural parameters as well as the atom ratios [O:C] were determined by the Rietveld method. The crystal is monoclinic (space group C2/m, Z=1) with lattice dimensions a=0.57404(1) nm, b=0.331435(5) nm, c=1.92410(2) nm, β=90.036(1) o and V=0.366076(9) nm 3 . The final structural model showed the positional disordering of Al/Si sites. The validity of the split-atom model was verified by the three-dimensional electron density distribution, the structural bias of which was reduced as much as possible using the maximum-entropy methods-based pattern fitting (MPF). The reliability indices calculated from the MPF were R wp =4.20% (S=1.14), R p =3.09%, R B =0.92% and R F =1.05%. The crystal was an inversion twin with nearly the same twin fraction. - Graphical abstract: A quaternary oxycarbide firstly discovered in the Al-Si-O-C system. The crystal is an inversion twin, and hence the structure is represented by a split-atom model. The three-dimensional electron density distribution is determined by the maximum-entropy methods-based pattern fitting, being consistent with the disordered structural model.

Two-dimensional layer architecture assembled by Keggin polyoxotungstate, Cu(II)-EDTA complex and sodium linker: Synthesis, crystal structures, and magnetic properties

International Nuclear Information System (INIS)

Liu Hong; Xu Lin; Gao Guanggang; Li Fengyan; Yang Yanyan; Li Zhikui; Sun Yu

2007-01-01

Reaction of Keggin polyoxotungstate with copper(II)-EDTA (EDTA=ethylenediamine tetraacetate) complex under mild conditions led to the formation of hybrid inorganic-organic compounds Na 4 (OH)[(Cu 2 EDTA)PW 12 O 40 ].17H 2 O (1) and Na 4 [(Cu 2 EDTA)SiW 12 O 40 ].19H 2 O (2). The single-crystal X-ray diffraction analyses reveal their two structural features: (1) one-dimensional chain structure consisting of Keggin polyoxotungstate and copper(II)-EDTA complex; (2) Two-dimensional layer architecture assembled by the one-dimensional chain structure and sodium linker. The results of magnetic measurements in the temperature range 300-2 K indicated the existence of ferromagnetic exchange interactions between the Cu II ions for both compounds. In addition, TGA analysis, IR spectra, and electrochemical properties were also investigated to well characterize these two compounds. - Graphical abstract: Two new polyoxometalate-based hybrids, Na 4 (OH)[Cu 2 (EDTA)PW 12 O 40 ].17H 2 O (1) and Na 4 [Cu 2 (EDTA)SiW 12 O 40 ].19H 2 O (2), have been synthesized and structurally characterized, which consist of one-dimensional chain structure assembled by Keggin polyoxotungstate and copper(II)-EDTA complex. The chains are further connected to form two-dimensional layer architecture assembled by the one-dimensional chain structure and sodium linker

Interconversion of η3-H2SiRR' σ-complexes and 16-electron silylene complexes via reversible H-H or C-H elimination.

Science.gov (United States)

Lipke, Mark C; Neumeyer, Felix; Tilley, T Don

2014-04-23

Solid samples of η(3)-silane complexes [PhBP(Ph)3]RuH(η(3)-H2SiRR') (R,R' = Et2, 1a; PhMe, 1b; Ph2, 1c, MeMes, 1d) decompose when exposed to dynamic vacuum. Gas-phase H2/D2 exchange between isolated, solid samples of 1c-d3 and 1c indicate that a reversible elimination of H2 is the first step in the irreversible decomposition. An efficient solution-phase trap for hydrogen, the 16-electron ruthenium benzyl complex [PhBP(Ph)3]Ru[η(3)-CH2(3,5-Me2C6H3)] (3) reacts quantitatively with H2 in benzene via elimination of mesitylene to form the η(5)-cyclohexadienyl complex [PhBP(Ph)3]Ru(η(5)-C6H7) (4). This H2 trapping reaction was utilized to drive forward and quantify the elimination of H2 from 1b,d in solution, which resulted in the decomposition of 1b,d to form 4 and several organosilicon products that could not be identified. Reaction of {[PhBP(Ph)3]Ru(μ-Cl)}2 (2) with (THF)2Li(SiHMes2) forms a new η(3)-H2Si species [PhBP(Ph)3]Ru[CH2(2-(η(3)-H2SiMes)-3,5-Me2C6H2)] (5) which reacts with H2 to form the η(3)-H2SiMes2 complex [PhBP(Ph)3]RuH(η(3)-H2SiMes2) (1e). Complex 1e was identified by NMR spectroscopy prior to its decomposition by elimination of Mes2SiH2 to form 4. DFT calculations indicate that an isomer of 5, the 16-electron silylene complex [PhBP(Ph)3]Ru(μ-H)(═SiMes2), is only 2 kcal/mol higher in energy than 5. Treatment of 5 with XylNC (Xyl = 2,6-dimethylphenyl) resulted in trapping of [PhBP(Ph)3]Ru(μ-H)(═SiMes2) to form the 18-electron silylene complex [PhBP(Ph)3]Ru(CNXyl)(μ-H)(═SiMes2) (6). A closely related germylene complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)](H)(═GeH(t)Bu) (8) was prepared from reaction of (t)BuGeH3 with the benzyl complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)][η(1)-CH2(3,5-Me2C6H3)] (7). Single crystal XRD analysis indicated that unlike for 6, the hydride ligand in 8 is a terminal hydride that does not engage in 3c-2e Ru-H → Ge bonding. Complex 1b is an effective precatalyst for the catalytic Ge-H dehydrocoupling

A single frequency component-based re-estimated MUSIC algorithm for impact localization on complex composite structures

International Nuclear Information System (INIS)

Yuan, Shenfang; Bao, Qiao; Qiu, Lei; Zhong, Yongteng

2015-01-01

The growing use of composite materials on aircraft structures has attracted much attention for impact monitoring as a kind of structural health monitoring (SHM) method. Multiple signal classification (MUSIC)-based monitoring technology is a promising method because of its directional scanning ability and easy arrangement of the sensor array. However, for applications on real complex structures, some challenges still exist. The impact-induced elastic waves usually exhibit a wide-band performance, giving rise to the difficulty in obtaining the phase velocity directly. In addition, composite structures usually have obvious anisotropy, and the complex structural style of real aircrafts further enhances this performance, which greatly reduces the localization precision of the MUSIC-based method. To improve the MUSIC-based impact monitoring method, this paper first analyzes and demonstrates the influence of measurement precision of the phase velocity on the localization results of the MUSIC impact localization method. In order to improve the accuracy of the phase velocity measurement, a single frequency component extraction method is presented. Additionally, a single frequency component-based re-estimated MUSIC (SFCBR-MUSIC) algorithm is proposed to reduce the localization error caused by the anisotropy of the complex composite structure. The proposed method is verified on a real composite aircraft wing box, which has T-stiffeners and screw holes. Three typical categories of 41 impacts are monitored. Experimental results show that the SFCBR-MUSIC algorithm can localize impact on complex composite structures with an obviously improved accuracy. (paper)

Violet-blue photoluminescence from Si nanoparticles with zinc-blende structure synthesized by laser ablation in liquids

Directory of Open Access Journals (Sweden)

P. Liu

2013-02-01

Full Text Available Violet-blue luminescence from Si nanostructures has been widely investigated, because of its potential use in optoelectronic and bioimaging devices. However, the emission mechanism in multiform Si nanomaterials remains unclear. In this contribution, Si nanocrystals (NCs with zincblende structure and visible violet-blue emission are prepared by electric field assisted laser ablation in liquids. While subsequent annealing of the Si NCs weakens their blue emission dramatically. We investigate the origin of the violet-blue emission by monitoring crystal structure transitions and photoluminescence during different treatments of the Si NCs. The results indicate that the violet-blue emission cannot simply be ascribed to quantum confinement effects or the presence of general surface states on the Si NCs. Instead, we propose that excitons are formed within the Si NCs by direct transitions at Γ or X points, which can be induced during the formation of the zincblende structure, and are a most possible origin of the violet-blue luminescence. Furthermore, defects in the metastable Si NCs are also expected to play an important role in violet-blue emission. This study not only gives clear and general insight into the physical origins of violet-blue emission from Si NCs, it also provides useful information for designing optoelectronic devices based on Si NCs.

Temperature stability of c-axis oriented LiNbO3/SiO2/Si thin film layered structures

International Nuclear Information System (INIS)

Tomar, Monika; Gupta, Vinay; Mansingh, Abhai; Sreenivas, K.

2001-01-01

Theoretical calculations have been performed for the temperature stability of the c-axis oriented LiNbO 3 thin film layered structures on passivated silicon (SiO 2 /Si) substrate with and without a non-piezoelectric SiO 2 overlayer. The phase velocity, electromechanical coupling coefficient and temperature coefficient of delay (TCD) have been calculated. The thicknesses of various layers have been determined for optimum SAW performance with zero TCD. The presence of a non-piezoelectric SiO 2 overlayer on LiNbO 3 film is found to significantly enhance the coupling coefficient. The optimized results reveal that a high coupling coefficient of K 2 =3.45% and a zero TCD can be obtained in the SiO 2 /LiNbO 3 /SiO 2 /Si structure with a 0.235λ thick LiNbO 3 layer sandwiched between 0.1λ thick SiO 2 layers. (author)

Extended x-ray absorption fine structure studies of amorphous and crystalline Si-Ge alloys with synchrotron radiation

International Nuclear Information System (INIS)

Kajiyama, Hiroshi

1988-01-01

Extended X-ray absorption fine structure (EXAFS) is a powerful probe to study the local structure around the atom of a specific element. In conventional EXAFS analysis, it has been known that reliable structures are obtained with the different values of absorption edge energy for different neighboring atoms. It is shown in this study that the Ge-K edge EXAFS resulting from the Ge-Ge and Ge-Si bonds in hydrogenated amorphous Si-Ge alloys was able to be excellently explained by a unique absorption edge energy value, provided that a newly developed formula based on the spherical wave function of photoelectrons is used. The microscopic structures of hydrogenated amorphous Si-Ge alloys and crystalline Si-Ge alloys have been determined using the EXAFS method. The lengths of Ge-Ge and Ge-Si bonds were constant throughout their entire composition range, and it was found that the length of Ge-Si bond was close to the average value of the bond lengths of both Ge and Si crystals. In crystalline Si-Ge alloys, it has been shown that the bonds relaxed completely, while the lattice constant varied monotonously with the composition. (Kako, I.)

Electronic structure of the boron fullerene B14 and its silicon derivatives B13Si(+), B13Si(-) and B12Si2: a rationalization using a cylinder model.

Science.gov (United States)

Van Duong, Long; Nguyen, Minh Tho

2016-06-29

Geometric and electronic structures of the boron cluster B14 and its silicon derivatives B13Si(+), B13Si(-), and B12Si2 were determined using DFT calculations (TPSSh/6-311+G(d)). The B12Si2 fullerene, which is formed by substituting two B atoms at two apex positions of the B14 fullerene by two Si atoms, was also found as the global minimum structure. We demonstrated that the electronic structure and orbital configuration of these small fullerenes can be predicted by the wavefunctions of a particle on a cylinder. The early appearance of high angular node MOs in B14 and B12Si2 can be understood by this simple model. Replacement of one B atom at a top position of B14 by one Si atom, followed by the addition or removal of one electron does not lead to a global minimum fullerene structure for the anion B13Si(-) and cation B13Si(+). The early appearance of the 5σ1 orbital in B13Si(+) causes a lower stability for the fullerene-type structure.

Effect of boron-doping on the luminescent and electrical properties of a CdS/Si heterostructure based on Si nanoporous pillar array

Energy Technology Data Exchange (ETDEWEB)

Yan, Ling Ling [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China); College of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China); Wang, Xiao Bo [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China); College of Physics and Electrical Engineering, Anyang Normal University, Anyang 455000 (China); Cai, Xiao Jun [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China); Li, Xin Jian, E-mail: lixj@zzu.edu.cn [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China)

2015-05-25

Highlights: • B-doped CdS/Si-NPA heterostructure was prepared by a CBD method. • B-doping does not affect the crystal structure and surface morphology of CdS/Si-NPA. • The optical/electrical properties of CdS/Si-NPA could be tuned by changing [B]/[Cd] ratio. • CdS/Si-NPA with optimal physical properties could be prepared with [B]/[Cd] = 0.01. • The method may find applications in preparing CdS/Si-NPA devices with high device performances. - Abstract: Using silicon nanoporous pillar array (Si-NPA) as substrates and boric acid as dopant source, a series of CdS/Si nanoheterostructures were prepared by growing B-doped CdS thin films on Si-NPA via a chemical bath deposition (CBD) method. The structural, optical and electrical properties of CdS/Si-NPA were studied as a function of the [B]/[Cd] ratio of the initial CBD solutions. Our results disclosed that B concentration could be tuned effectively through changing the ratio of [B]/[Cd], which would bring large variation on the optical and electrical properties of CdS/Si-NPA without affecting its crystal structure and surface morphology. The samples with optimal optical and electrical properties were prepared with [B]/[Cd] = 0.01, in which the physical properties of relatively strong light absorption, small electrical resistivity, low turn-on voltage, small leakage current density and high breakdown voltage could be obtained. These results indicated that B-doping might be an effective path for promoting the performance of the optoelectronic devices based on CdS/Si-NPA.

Electronic structure of divacancy-hydrogen complexes in silicon

International Nuclear Information System (INIS)

Coutinho, J; Torres, V J B; Jones, R; Oeberg, S; Briddon, P R

2003-01-01

Divacancy-hydrogen complexes (V 2 H and V 2 H 2 ) in Si are studied by ab initio modelling using large supercells. Here we pay special attention to their electronic structure, showing that these defects produce deep carrier traps. Calculated electrical gap levels indicate that V 2 H 2 is an acceptor, whereas V 2 H is amphoteric, with levels close to those of the well known divacancy. Finally our results are compared with the available data from deep level transient spectroscopy and electron paramagnetic resonance experiments

Topotactic synthesis of the overlooked multilayer silicene intercalation compound SrSi2.

Science.gov (United States)

Tokmachev, A M; Averyanov, D V; Karateev, I A; Parfenov, O E; Vasiliev, A L; Yakunin, S N; Storchak, V G

2016-09-28

Silicene, a 2D honeycomb lattice of Si atoms similar to graphene, is expected to be a platform for nanoelectronics and home to novel quantum phenomena. Unlike graphene, free-standing silicene is notoriously difficult to stabilize, while strong hybridization of silicene with substrates destroys its desirable properties. On the other hand, Dirac cones of silicene are effectively realized in a bulk - stoichiometric ionic multilayer silicene intercalation compound CaSi2. Besides, a number of new 2D silicene-based materials are synthesized employing CaSi2 as a precursor. However, the rather complex atomic structure of CaSi2 and fresh opportunities of physical and chemical breakthroughs drive the search for alternative compounds with silicene networks. Here, a new polymorph of SrSi2 is synthesized, enjoying both the structure of intercalated multilayer silicene and the simplest possible stacking of silicene sheets. The MBE-quality synthesis accomplished on Si(001) and Si(111) surfaces leads to epitaxial films of SrSi2 with orientation controlled by the substrate, as revealed by XRD, RHEED and electron microscopy studies. The structural SrSi2/Si relation is mirrored in the transport properties of the films.

Relaxation of mechanical stresses in Si-Ge/Si structures implanted by carbon ions. Study with optical methods

International Nuclear Information System (INIS)

Klyuj, M.Yi.

1998-01-01

Optical properties of Si-Ge/Si structures implanted by carbon ions with the energy of 20 keV and at the doses of 5 centre dot 10 15 - 1- 16 cm -2 are studied by spectro ellipsometry and Raman scattering techniques. From the comparison of experimental data with the results of theoretical calculations, it is shown that, as a result of implantation, a partial relaxation of mechanical stresses in the Si 1-x Ge x film due to introduction of carbon atoms with a small covalent radius into the Si-Ge lattice takes place. An elevated implantation temperature allows one to maintain a high structural perfection of the implanted film

Electrical characterizations of MIS structures based on variable-gap n(p)-HgCdTe grown by MBE on Si(0 1 3) substrates

Science.gov (United States)

Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.; Varavin, V. S.; Dvoretskii, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Sidorov, G. Yu.

2017-12-01

Metal-insulator-semiconductor (MIS) structures based on n(p)-Hg1-xCdxTe (x = 0.22-0.40) with near-surface variable-gap layers were grown by the molecular-beam epitaxy (MBE) technique on the Si (0 1 3) substrates. Electrical properties of MIS structures were investigated experimentally at various temperatures (9-77 K) and directions of voltage sweep. The ;narrow swing; technique was used to determine the spectra of fast surface states with the exception of hysteresis effects. It is established that the density of fast surface states at the MCT/Al2O3 interface at a minimum does not exceed 3 × 1010 eV-1 × cm-2. For MIS structures based on n-MCT/Si(0 1 3), the differential resistance of the space-charge region in strong inversion mode in the temperature range 50-90 K is limited by the Shockley-Read-Hall generation in the space-charge region.

Carbon nanotube on Si(001): structural and electronic properties

International Nuclear Information System (INIS)

Orellana, W.; Fazzio, A.; Miwa, R.W.

2003-01-01

Full text: The promising nanoscale technology based on carbon nanotubes has attracted much attention due to the unique electronic, chemical and mechanical properties of the nanotubes. Single-wall carbon nanotubes (SWCNs) provide an ideal atomically uniform one dimensional (1D) conductors, having a strong electronic confinement around its circumference, which can be retained up to room temperature[1]. This interesting property may lead one to consider SWCNs as 1D conductors for the development of nanoscale electronic devices. In this work the structural and electronic properties of the contact between a metallic (6,6) SWCN adsorbed on a silicon (001) surface are studied from first-principles total-energy calculations. We consider two adsorption sites for the tube on the Si(001) surface: on the top of the Si-dimer rows and on the surface 'trench' between two consecutive dimer rows. Our results show a chemical bond between the nanotube and Si(001) when the tube is located along the 'trench', which corresponds to the only bound structure. We find a binding energy per tube length of 0.21 eV/angstrom. We also verified that the binding energy depends on the rotation of the tube. Typically, a rotation of 15 deg can reduce the binding energy up to 0.07 eV/angstrom. Our calculated electronic properties indicate that the most stable structure shows a subband associated to the tube/surface bond that cross the Fermi level. This result indicates an enhanced metallic behavior along the tube/surface contact characterizing a 1D quantum wire. The charge transfer between the Si surface and the tube is also discussed. [1] Z. Yao, C. Dekker, and P. Avouris in Carbon Nanotubes, M. S. Dresselhaus, G. Dresselhaus, and P. Avouris Eds., (Springer, Berlin 2001), p. 147. (author)

Structural and electronic properties of metalloporphyrin (MP, M = Fe, Co and Zn) adsorbed on single walled BNNT and SiCNT

Energy Technology Data Exchange (ETDEWEB)

Rezvani, M. [Department of Chemistry, Faculty of Science, Arak Branch, Islamic Azad University, Arak (Iran, Islamic Republic of); Darvish Ganji, M., E-mail: ganji_md@yahoo.com [Department of Nanochemistry, Faculty of Pharmaceutical Chemistry, Pharmaceutical Sciences Branch, Islamic Azad University (IAUPS), Tehran (Iran, Islamic Republic of); Jameh-Bozorghi, S. [Department of Chemistry, Faculty of Science, Hamedan Branch, Islamic Azad University, Hamedan (Iran, Islamic Republic of)

2016-01-01

Graphical abstract: First-principles calculations showed that SiCNTs is a very promising candidate for metalloporphyrin adsorption and sensing/detection. - Highlights: • Theoretical study of MPs adsorption on SiCNT and BNNT were studied. • The interaction FeP with SiCNT is stronger than the other counterparts. • The interaction of FeP with SiCNT is six times stronger than with BNNT. • The FeP-BNNT complex might be suitable material for spintronics. • SiCNTs are very promising candidate for MPs adsorption and sensing. - Abstract: In the present work, we report a detailed theoretical investigation of a series of metalloporphyrin, MP (M = FeP, CoP and ZnP), molecules interacting with silicon carbide nanotube (SiCNT) by means of density functional theory (DFT) calculations. In all calculations, we used the Perdew–Burke–Erzenhof (PBE) functional as employed in the SIESTA package. The detailed analysis of the structural and electronical properties of various optimized configurations is performed. The results show that among the MPs, adsorption of FeP molecule on the Si site with zigzag orientation is the most energetically preferable with a binding energy of −2.10 eV. Compared to SiCNTs, boron nitride nanotubes (BNNTs) have weaker interaction strength with the FeP molecule with −0.34 eV of binding energy. We have analyzed charge transfer between two interacting species trough well-known Mulliken, Hirshfeld and Voronoi charges analysis for aforementioned systems. The spin-polarized DFT calculations showed that the density of states (DOSs) are spin-polarized for the Fe-BNNT complex while the spin-polarization of the DOS spectra turn out to be less notable for MP-SiCNT complexes. Our results propose that FeP-SiCNT complex could be used for interesting applications in solar cell technology and nano-biosensors while FeP-BNNT complex might be considered for spintronic molecular devices.

Study of reticular defects in V3Si (A15 structure)

International Nuclear Information System (INIS)

Ben Lamine, Abdelmottaleb

1980-01-01

The A15 crystal structure is that of superconductive compounds with high critical temperature. This research thesis aims at studying its possible reticular defects. In a first part, the author presents this structure and more particularly its crystallographic properties, reports the indexing of electronic diffraction diagrams (point diagrams and line diagrams of Kikuchi) in the case of V 3 Si. Then, after having described the sample preparation technique, the author reports the study of reticular defects by high voltage electronic microscopy on a raw V 3 Si crystal. The existence of a specific defect is highlighted and the crystallographic study of this defect is reported. It has been performed by means of computer-based simulation of contrast (TWODIS software). Results are then discussed

Correlations between atomic structure and giant magnetoresistance ratio in Co2(Fe,Mn)Si spin valves

International Nuclear Information System (INIS)

Lari, L; Sizeland, J; Gilks, D; Uddin, G M; Nedelkoski, Z; Hasnip, P J; Lazarov, V K; Yoshida, K; Galindo, P L; Sato, J; Oogane, M; Ando, Y; Hirohata, A

2014-01-01

We show that the magnetoresistance of Co 2 Fe x Mn 1−x Si-based spin valves, over 70% at low temperature, is directly related to the structural ordering in the electrodes and at the electrodes/spacer (Co 2 Fe x Mn 1−x Si/Ag) interfaces. Aberration-corrected atomic resolution Z-contrast scanning transmission electron microscopy of device structures reveals that annealing at 350 °C and 500 °C creates partial B2/L2 1 and fully L2 1 ordering of electrodes, respectively. Interface structural studies show that the Ag/Co 2 Fe x Mn 1−x Si interface is more ordered compared to the Co 2 Fe x Mn 1−x Si/Ag interface. The release of interface strain is mediated by misfit dislocations that localize the strain around the dislocation cores, and the effect of this strain is assessed by first principles electronic structure calculations. This study suggests that by improving the atomic ordering and strain at the interfaces, further enhancement of the magnetoresistance of CFMS-based current-perpendicular-to-plane spin valves is possible. (fast track communication)

Infrared Spectra and Structures of SiH{sub 2}-(CH{sub 2}){sub 2} and CH{sub 2}=CH-SiH{sub 3} Intermediates Prepared in Reactions of Laser-ablated Silicon Atoms with Ethane

Energy Technology Data Exchange (ETDEWEB)

Cho, Han-Gook [Incheon National University, Incheon (Korea, Republic of); Andrews, Lester [University of Virginia, Charlottesville (United States)

2016-03-15

SiH{sub 2}-(CH{sub 2}){sub 2} and CH{sub 2}=CH-SiH{sub 3} were observed in the matrix IR spectra following reactions of laser-ablated Si atoms with ethane on the basis of correlation with computed frequencies. Evidently photon energy is required for the formation of the cyclic Si compound. These Si complexes are similar to the primary products in the previous studies of group 4 metals, in line with the previous results that s{sup 2}p{sup 2} and s{sup 2}d{sup 2} electronic configurations yield similar products. The relatively long C–C bond in the cyclic Si product reflects the structural strain, and the short C-Si and C-C bonds of CH{sub 3}CH=SiH{sub 2} and CH{sub 2}=CH-SiH{sub 3} show that they are true double bonds in line with the natural bond orders. Reactions of transition-metal atoms with small alkanes and halomethanes have been studied in a series of recent investigations. High oxidation-state products (methylidenes and methylidynes) along with insertion complexes were identified in the matrix spectra. It is interesting whether or not Si, a group 14 metalloid, undergoes similar reactions with larger hydrocarbons to provide higher oxidation-state compounds.

A Corner-Point-Grid-Based Voxelization Method for Complex Geological Structure Model with Folds

Science.gov (United States)

Chen, Qiyu; Mariethoz, Gregoire; Liu, Gang

2017-04-01

3D voxelization is the foundation of geological property modeling, and is also an effective approach to realize the 3D visualization of the heterogeneous attributes in geological structures. The corner-point grid is a representative data model among all voxel models, and is a structured grid type that is widely applied at present. When carrying out subdivision for complex geological structure model with folds, we should fully consider its structural morphology and bedding features to make the generated voxels keep its original morphology. And on the basis of which, they can depict the detailed bedding features and the spatial heterogeneity of the internal attributes. In order to solve the shortage of the existing technologies, this work puts forward a corner-point-grid-based voxelization method for complex geological structure model with folds. We have realized the fast conversion from the 3D geological structure model to the fine voxel model according to the rule of isocline in Ramsay's fold classification. In addition, the voxel model conforms to the spatial features of folds, pinch-out and other complex geological structures, and the voxels of the laminas inside a fold accords with the result of geological sedimentation and tectonic movement. This will provide a carrier and model foundation for the subsequent attribute assignment as well as the quantitative analysis and evaluation based on the spatial voxels. Ultimately, we use examples and the contrastive analysis between the examples and the Ramsay's description of isoclines to discuss the effectiveness and advantages of the method proposed in this work when dealing with the voxelization of 3D geologic structural model with folds based on corner-point grids.

Enhanced lateral heat dissipation packaging structure for GaN HEMTs on Si substrate

International Nuclear Information System (INIS)

Cheng, Stone; Chou, Po-Chien; Chieng, Wei-Hua; Chang, E.Y.

2013-01-01

This work presents a technology for packaging AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate. The GaN HEMTs are attached to a V-groove copper base and mounted on a TO-3P leadframe. The various thermal paths from the GaN gate junction to the case are carried out for heat dissipation by spreading to protective coating; transferring through the bond wires; spreading in the lateral device structure through the adhesive layer, and vertical heat spreading of silicon chip bottom. Thermal characterization showed a thermal resistance of 13.72 °C/W from the device to the TO-3P package. Experimental tests of a 30 mm gate-periphery single chip packaged in a 5 × 3 mm V-groove Cu base with a 100 V drain bias showed power dissipation of 22 W. -- Highlights: ► An enhanced packaging structure designed for AlGaN/GaN HEMTs on an Si substrate. ► The V-groove copper base is designed on the device periphery surface heat conduction for enhancing Si substrate thermal dissipation. ► The proposed device shows a lower thermal resistance and upgrade in thermal conductivity capability. ► This work provides useful thermal IR imagery information to aid in designing high efficiency package for GaN HEMTs on Si

Fabrication of 3D SiO x structures using patterned PMMA sacrificial layer

Science.gov (United States)

Li, Zhiqin; Xiang, Quan; Zheng, Mengjie; Bi, Kaixi; Chen, Yiqin; Chen, Keqiu; Duan, Huigao

2018-02-01

Three-dimensional (3D) nanofabrication based on electron-beam lithography (EBL) has drawn wide attention for various applications with its high patterning resolution and design flexibility. In this work, we present a bilayer EBL process to obtain 3D freestanding SiO x structures via the release of the bottom sacrificial layer. This new kind of bilayer process enables us to define various 3D freestanding SiO x structures with high resolution and low edge roughness. As a proof of concept for applications, metal-coated freestanding SiO x microplates with an underlying air gap were fabricated to form asymmetric Fabry-Perot resonators, which can be utilized for colorimetric refractive index sensing and thus also have application potential for biochemical detection, anti-counterfeiting and smart active nano-optical devices.

Synthesis, structures and electroluminescence properties of CdS:In/Si nanoheterostructure array

Energy Technology Data Exchange (ETDEWEB)

Yan, Ling Ling; Cai, Hong Xin; Chen, Liang [Henan Polytechnic University, School of Physics and Electronic Information Engineering, Jiaozuo (China)

2017-10-15

An In-doped CdS/Si nanoheterojunction (CdS:In/Si-NPA) is prepared by depositing an In-doped CdS thin film onto a Si nanoporous pillar array (Si-NPA) via a successive ionic layer adsorption and reaction method. Based on the measured J-V characteristic curve, the nanoheterojunction exhibits a good rectifying behavior with a low forward turn-on voltage (2.2 V), a small leakage current density (0.5 mA/cm{sup 2} at - 3 V) and a high reverse breakdown voltage (> 8 V). The electroluminescence (EL) measurements reveal that a broadband emerges between 400 and 700 nm, and this band is confirmed as a white light emission based on the value of the chromaticity coordinate. The EL properties, including the CIE chromaticity coordinates, Colour Rendering Index and correlated color temperature, can be tuned by the applied voltage. The generation mechanism of the EL can be well interpreted depending on the energy band structure of CdS:In/Si-NPA. The green band should be attributed to the band-edge emission of CdS and the yellow emission may be related to Cd interstitial. These results highlight the potential of CdS:In/Si-NPA as a light source for future white light emitting devices. (orig.)

Synthesis and structural characterization of Al4SiC4-homeotypic aluminum silicon oxycarbide, [Al4.4Si0.6][O1.0C2.0]C

International Nuclear Information System (INIS)

Kaga, Motoaki; Iwata, Tomoyuki; Nakano, Hiromi; Fukuda, Koichiro

2010-01-01

A new quaternary layered oxycarbide, [Al 4.39(5) Si 0.61(5) ] Σ5 [O 1.00(2) C 2.00(2) ] Σ3 C, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The title compound was found to be hexagonal with space group P6 3 /mmc, Z=2, and unit-cell dimensions a=0.32783(1) nm, c=2.16674(7) nm and V=0.20167(1) nm 3 . The atom ratios Al:Si were determined by EDX, and the initial structural model was derived by the direct methods. The final structural model showed the positional disordering of one of the three types of Al/Si sites. The maximum-entropy methods-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R wp =3.73% (S=1.20), R p =2.94%, R B =1.04% and R F =0.81%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al 4 SiC 4 (space group P6 3 mc, Z=2). - Graphical abstract: A new oxycarbide discovered in the Al-Si-O-C system, Al 4 SiC 4 -homeotypic [Al 4.4 Si 0.6 ][O 1.0 C 2.0 ]C. The crystal is an inversion twin, and hence the structure is represented by a split-atom model. The three-dimensional electron density distributions are determined by the maximum-entropy methods-based pattern fitting, being consistent with the disordered structural model.

Ultraviolet-enhanced photodetection in a graphene/SiO2/Si capacitor structure with a vacuum channel

International Nuclear Information System (INIS)

Kim, Myungji; Kim, Hong Koo

2015-01-01

We report photodetection properties of a graphene/oxide/silicon capacitor structure with a nanoscale vacuum channel. The photogenerated two-dimensional electron gas (2DEG) inversion charges at SiO 2 /Si interface are extracted out to air and transported along the void channel at low bias voltage (<5 V). A monolayer graphene, placed on top of SiO 2 and suspended on the void channel, is utilized as a photon-transparent counter-electrode to the 2DEG layer and a collector electrode for the out-of-plane transported electrons, respectively. The photocurrent extracted through a void channel reveals high responsivity (1.0 A/W at 633 nm) as measured in a broad spectral range (325–1064 nm), especially demonstrating a UV-enhanced performance (0.43 A/W responsivity and 384% internal quantum efficiency at 325 nm). The mechanisms underlying photocarrier generation, emission, and transport in a suspended-graphene/SiO 2 /Si structure are proposed

Electronic structures and Eu3+ photoluminescence behaviors in Y2Si2O7 and La2Si2O7

International Nuclear Information System (INIS)

Zhang Zhiya; Wang Yuhua; Zhang Feng; Cao Haining

2011-01-01

Research highlights: → Host excitation near the band gap of Y 2 Si 2 O 7 and La 2 Si 2 O 7 is analyzed. → The calculated result well explains Eu 3+ PL behaviors in Y 2 Si 2 O 7 and La 2 Si 2 O 7 . → The electronic structure and Eu 3+ VUV PL in La 2 Si 2 O 7 are first estimated. - Abstract: The electronic structures and linear optical properties of Y 2 Si 2 O 7 (YSO) and La 2 Si 2 O 7 (LSO) are calculated by LDA method based on the theory of DFT. Both YSO and LSO are direct-gap materials with the direct band gap of 5.89 and 6.06 eV, respectively. The calculated total and partial density of states indicate that in both YSO and LSO the valence band (VB) is mainly constructed from O 2p and the conduction band (CB) is mostly formed from Y 4d or La 5d. Both the calculated VB and CB of YSO exhibit relatively wider dispersion than that of LSO. In addition, the CB of YSO presents more electronic states. Meanwhile, the VB of LSO shows narrower energy distribution with higher electronic states density. The theoretical absorption of YSO shows larger bandwidth and higher intensity than that of LSO. The results are compared with the experimental host excitations and impurity photoluminescence in Eu 3+ -doped YSO and LSO.

Effects of alloying on Co--Si eutectoid structures and properties

International Nuclear Information System (INIS)

Livingston, J.D.

1976-01-01

The effects of various ternary alloying elements on the microstructure and properties of directionally solidified and transformed Co-Si eutectoid alloys were studied. Aligned eutectoid structures were maintained with additions of up to 10 at. percent Ni. However, higher Ni additions led to changes in both the silicide and solid-solution phases, related changes in microstructure, and decreased tensile strength. Additions of 5 at. percent Cr, Cu, Fe, or Mn produced cellular eutectoid microstructures which deteriorated the mechanical properties. Additions of W, Ta, or Al led to eutectic, rather than eutectoid, microstructures. Alloys based on the Co-W-Si eutectic appear to have the most promising high-temperature mechanical properties

Electronic structure of C and Si fullerenes and fullerides

International Nuclear Information System (INIS)

Saito, S.

1996-01-01

Fullerenes, i.e., cage-structure clusters are now studied intensively as a building unit for a new class of materials. The electronic structure of C 60 and Si 20 fullerenes and their fullerides obtained in the framework of the density-functional theory is discussed with emphasis on the electronic as well as the geometrical hierarchy in superconducting fullerides. In both C 60 and Si 20 fullerides, the charge transfer from alkali atoms to fullerenes and the hybridization between alkaline-earth states and fullerene states are observed. Also A 3 C 60 and (Ba 3 Si 3 Na rate at Si 20 ) 2 superconductors are found to have high Fermi-level density of states, although the mechanism giving it is different in two materials. Interesting materials to be produced in the future are also discussed. (orig.)

Growth and coalescence control of inclined c-axis polar and semipolar GaN multilayer structures grown on Si(111), Si(112), and Si(115) by metalorganic vapor phase epitaxy

Energy Technology Data Exchange (ETDEWEB)

Szymański, Tomasz, E-mail: tomasz.szymanski@pwr.edu.pl; Wośko, Mateusz; Paszkiewicz, Bartłomiej; Paszkiewicz, Bogdan; Paszkiewicz, Regina [The Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw (Poland); Sankowska, Iwona [The Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warszawa (Poland)

2016-09-15

Herein, silicon substrates in alternative orientations from the commonly used Si(111) were used to enable the growth of polar and semipolar GaN-based structures by the metalorganic vapor phase epitaxy method. Specifically, Si(112) and Si(115) substrates were used for the epitaxial growth of nitride multilayer structures, while the same layer schemes were also deposited on Si(111) for comparison purposes. Multiple approaches were studied to examine the influence of the seed layers and the growth process conditions upon the final properties of the GaN/Si(11x) templates. Scanning electron microscope images were acquired to examine the topography of the deposited samples. It was observed that the substrate orientation and the process conditions allow control to produce an isolated GaN block growth or a coalesced layer growth, resulting in inclined c-axis GaN structures under various forms. The angles of the GaN c-axis inclination were determined by x-ray diffraction measurements and compared with the results obtained from the analysis of the atomic force microscope (AFM) images. The AFM image analysis method to determine the structure tilt was found to be a viable method to estimate the c-axis inclination angles of the isolated blocks and the not-fully coalesced layers. The quality of the grown samples was characterized by the photoluminescence method conducted at a wide range of temperatures from 77 to 297 K, and was correlated with the sample degree of coalescence. Using the free-excitation peak positions plotted as a function of temperature, analytical Bose-Einstein model parameters were fitted to obtain further information about the grown structures.

Synthesis and structure of the first fullerene complex of titanium Cp{sub 2}Ti({eta}{sup 2}-C{sub 60})

Energy Technology Data Exchange (ETDEWEB)

Burlakov, V.V.; Usatov, A.V.; Lyssenko, K.A.; Antipin, M.Yu.; Novikov, Yu.N.; Shur, V.B. [Russian Academy of Sciences, Moscow (Russian Federation). A.N. Nesmeyanov Inst. of Organoelement Compounds

1999-11-01

The first fullerene complex of titanium Cp{sub 2}Ti({eta}{sup 2}-C{sub 60}) has been synthesized by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene Cp{sub 2}Ti({eta}{sup 2}-Me{sub 3}SiC{sub 2}SiMe{sub 3}) with an equimolar amount of fullerene-60 in toluene at room temperature under argon. An X-ray diffraction study of the complex has shown that it has the structure of a titanacyclopropane derivative. (orig.)

Towards flexible asymmetric MSM structures using Si microwires through contact printing

Science.gov (United States)

Khan, S.; Lorenzelli, L.; Dahiya, R.

2017-08-01

This paper presents development of flexible metal-semiconductor-metal devices using silicon (Si) microwires. Monocrystalline Si in the shape of microwires are used which are developed through standard photolithography and etching. These microwires are assembled on secondary flexible substrates through a dry transfer printing by using a polydimethylsiloxane stamp. The conductive patterns on Si microwires are printed using a colloidal silver nanoparticles based solution and an organic conductor i.e. poly (3,4-ethylene dioxthiophene) doped with poly (styrene sulfonate). A custom developed spray coating technique is used for conductive patterns on Si microwires. A comparative study of the current-voltage (I-V) responses is carried out in flat and bent orientations as well as the response to the light illumination of the wires is explored. Current variations as high as 17.1 μA are recorded going from flat to bend conditions, while the highest I on/I off ratio i.e. 43.8 is achieved with light illuminations. The abrupt changes in the current response due to light-on/off conditions validates these devices for fast flexible photodetector switches. These devices are also evaluated based on transfer procedure i.e. flip-over and stamp-assisted transfer printing for manipulating Si microwires and their subsequent post-processing. These new developments were made to study the most feasible approach for transfer printing of Si microwires and to harvest their capabilities such as photodetection and several other applications in the shape of metal-semiconductor-metal structures.

TaSiN nanocomposite thin films: Correlation between structure, chemical composition, and physical properties

International Nuclear Information System (INIS)

Ramírez, G.; Oezer, D.; Rivera, M.; Rodil, S.E.; Sanjinés, R.

2014-01-01

The structural and electronic properties of fcc-TaN/SiN x nanocomposite thin films deposited by reactive magnetron sputtering have been investigated as function of the N and Si contents. Our studies have been mainly focused on three different types of nanocomposite Ta x Si y N z films based on: nitrogen deficient fcc-TaN 0.88 , nearly stoichiometric fcc-TaN, and over-stoichiometric fcc-TaN 1.2 with the Si contents in the range from 0 to about 15 at.%. The optical properties were investigated by ellipsometric measurements, while the DC. electrical resistivity was measured using the van der Pauw configuration at 300 K. The optical measurements were interpreted using the standard Drude–Lorentz model. The results showed that the electronic properties are closely correlated with both the compositional and the structural modifications of the Ta x Si y N z films induced by the addition of Si atoms, and also depending on the stoichiometry of the starting fcc-TaN system. Thus, depending on both the nitrogen and the silicon contents, the fcc-Ta x Si y N z films can exhibit room temperature resistivity values ranging from 10 2 μΩ cm to about 6 × 10 4 μΩ cm. - Highlights: • TaSiN films were grown using dual magnetron sputtering system. • The physical and structural properties were correlated with the deposition parameters. • The electrical properties were influenced by the nitrogen and silicon contents on the films

Structural stability, electronic and magnetic behaviour of spin-polarized YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) Heusler alloys

Energy Technology Data Exchange (ETDEWEB)

Rasool, Muhammad Nasir, E-mail: nasir4iub@gmail.com [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan); Hussain, Altaf, E-mail: altafiub@yahoo.com [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan); Javed, Athar [Department of Physics, University of the Punjab, Lahore, 54590 (Pakistan); Khan, Muhammad Azhar; Iqbal, F. [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan)

2016-11-01

The structural stability, electronic and magnetic behaviour of YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) Heusler alloys have been studied by first principle approach. Generalized gradient approximation (GGA) based on density functional theory (DFT) has been applied to investigate the properties of quaternary Heusler alloys. The YCoVSi, YCoVGe, YCoTiSi and YCoTiGe Heusler alloys of Type-3 structure are found to be stable in spin-polarized/magnetic phase. The YCoVSi and YCoVGe alloys exhibit nearly spin gapless semiconductor (SGS) behaviour while YCoTiSi and YCoTiGe alloys show half-metallic ferromagnetic (HMF) behaviour. For YCoVSi, YCoVGe, YCoTiSi and YCoTiGe alloys, the calculated energy band gaps in spin down (↓) channel are 0.60, 0.54, 0.68 and 0.44 eV, respectively. The YCoVZ and YCoTiZ alloys are found to have integral value of total magnetic moment (M{sub T}), thus obeying the Slater-Pauling rule, M{sub T} = (N{sub v}–18)μ{sub B}. - Highlights: • Four Heusler alloys i.e. YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) are studied. • Type-3 crystal structure of all four alloys is stable in magnetic phase. • The compressibility (S) follows the order: S{sub YCoVSi} > S{sub YCoTiSi} > S{sub YCoVGe} > S{sub YCoTiGe}. • Half metallic ferromagnetic behaviour is observed in all four alloys. • All four alloys obey the Slater-Pauling rule, M{sub T} = (N{sub v} – 18)μ{sub B}.

Structural and electrical properties of the GexSi1-x/Si heterojunctions obtained by the method of direct bonding

International Nuclear Information System (INIS)

Argunova, T. S.; Belyakova, E. I.; Grekhov, I. V.; Zabrodskii, A. G.; Kostina, L. S.; Sorokin, L. M.; Shmidt, N. M.; Yi, J. M.; Jung, J. W.; Je, J. H.; Abrosimov, N. V.

2007-01-01

The results of studying the structural and electrical properties of structures produced by the method of direct bonding of Ge x Si 1-x and Si wafers are reported. The wafers were cut from the crystals grown by the Czochralski method. Continuity of the interface and the crystal-lattice defects were studied by X-ray methods using synchrotron radiation and by scanning electron microscopy. Measurements of the forward and reverse current-voltage characteristics of the p-Ge x Si 1-x /n-Si diodes made it possible to assess the effect of the crystallattice defects on the electrical properties of heterojunctions. Satisfactory electrical parameters suggest that the technology of direct bonding is promising for the fabrication of large-area Ge x Si 1-x /Si heterojunctions

Crystal structure of the Hg4SiS6 and Hg4SiSe6 compounds

International Nuclear Information System (INIS)

Gulay, L.D.; Olekseyuk, I.D.; Parasyuk, O.V.

2002-01-01

The crystal structures of Hg 4 SiS 6 and Hg 4 SiSe 6 compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.23020(5), b=0.71031(4), c=1.22791(4) nm, β=109.721(3) deg. for Hg 4 SiS 6 and a=1.28110(4), b=0.74034(4), c=1.27471(1) nm, β=109.605(3) deg. for Hg 4 SiSe 6 . Atomic parameters were refined in the isotropic approximation (R I =0.0571 and R I =0.0555 for the Hg 4 SiS 6 and Hg 4 SiSe 6 , respectively)

High ink absorption performance of inkjet printing based on SiO2@Al13 core-shell composites

Science.gov (United States)

Chen, YiFan; Jiang, Bo; Liu, Li; Du, Yunzhe; Zhang, Tong; Zhao, LiWei; Huang, YuDong

2018-04-01

The increasing growth of the inkjet market makes the inkjet printing more necessary. A composite material based on core-shell structure has been developed and applied to prepare inkjet printing layer. In this contribution, the ink printing record layers based on SiO2@Al13 core-shell composite was elaborated. The prepared core-shell composite materials were characterized by X-ray photoelectron spectroscopy (XPS), zeta potential, X-ray diffraction (XRD), scanning electron microscopy (SEM). The results proved the presence of electrostatic adsorption between SiO2 molecules and Al13 molecules with the formation of the well-dispersed system. In addition, based on the adsorption and the liquid permeability analysis, SiO2@Al13 ink printing record layer achieved a relatively high ink uptake (2.5 gmm-1) and permeability (87%), respectively. The smoothness and glossiness of SiO2@Al13 record layers were higher than SiO2 record layers. The core-shell structure facilitated the dispersion of the silica, thereby improved its ink absorption performance and made the clear printed image. Thus, the proposed procedure based on SiO2@Al13 core-shell structure of dye particles could be applied as a promising strategy for inkjet printing.

Local Structures around Si, Al and Na in Hydrated Silicate Glasses

International Nuclear Information System (INIS)

Farges, Francois; Wispelaere, Sidoine de; Rossano, Stephanie; Munos, Manuel; Wilke, Max; Flank, Anne-Marie; Lagarde, Pierre

2007-01-01

XANES spectra were collected at the Si-, Al-, and Na K-edge in hydrous silicate glasses to understand the effect of water on the local structure around these cations. Around network forming Si and Al, no drastic changes are observed. Around Na, the dissolution of water creates more ordered environments in Al-bearing glasses and less ordered environment in Al-free glasses. Ab-initio XANES calculations were undertaken to understand the structural origins for these features. Based on these results, a bond valence model was refined that considers not only the present XANES experiments and models but also NMR information. The double percolation model refined explains, among others, the explosive properties of water-bearing hydrous melts, at the origin of a number of cataclysmic eruptions in subduction zones

Atomistic Origins of High Capacity and High Structural Stability of Polymer-Derived SiOC Anode Materials.

Science.gov (United States)

Sun, Hong; Zhao, Kejie

2017-10-11

Capacity and structural stability are often mutually exclusive properties of electrodes in Li-ion batteries (LIBs): a gain in capacity is usually accompanied by the undesired large volumetric change of the host material upon lithiation. Polymer-derived ceramics, such as silicon oxycarbide (SiOC) of hybrid Si-O-C bonds, show an exceptional combination of high capacity and superior structural stability. We investigate the atomistic origins of the unique chemomechanical performance of carbon-rich SiOC using the first-principles theoretical approach. The atomic model of SiOC is composed of continuous Si-O-C units caged by a graphene-like cellular network and percolated nanovoids. The segregated sp 2 carbon network serves as the backbone to maintain the structural stability of the lattice. Li insertion is first absorbed at the nanovoid sites, and then it is accommodated by the SiOC tetrahedral units, excess C atoms, and topological defects at the edge of or within the segregated carbon network. SiOC expands up to 22% in volumetric strain at the fully lithiated capacity of 1230 mA h/g. We examine in great detail the evolution of the microscopic features of the SiOC molecule in the course of Li reactions. The first-principles modeling provides a fundamental understanding of the physicochemical properties of Si-based glass ceramics for their application in LIBs.

Positron annihilation spectroscopy: Applications to Si, ZnO, and multilayer semiconductor structures

Science.gov (United States)

Schaffer, J. P.; Rohatgi, A.; Dewald, A. B.; Frost, R. L.; Pang, S. K.

1989-11-01

The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors is demonstrated for Si, ZnO, and multilayer structures, such as an AlGaAs/GaAs solar cell. The types of defects discussed include: i) vacancy complexes, oxygen impurities and dopants, ii) the influence of cooling rates on spatial non-uniformities in defects, and iii) characterization of buried interfaces. In sev-eral instances, the results of the PAS investigations are correlated with data from other established semiconductor characterization techniques.

Contribution to the study of metal-oxide-semiconductor devices with optical access. In2O3-SiO2-Si structure

International Nuclear Information System (INIS)

Thenoz, Yves.

1974-01-01

A general study of the fabrication of the structure In 2 O 3 /SiO 2 /Si was made encompassing the problems posed during the realization of these structures. The sputtering study enabled the influence of the main parameters on layer properties to be determined. The decisive importance of clean conditions throughout fabrication (especially during sputtering) on the properties of In 2 O 3 layers and on those of the structure and its stability was revealed. However, the problem of ageing of the structure were not investigated. Finally, the construction of MOS capacitors and transistors showed that In 2 O 3 /SiO 2 /Si structures can be used in MOS circuits [fr

Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure.

Science.gov (United States)

Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke

2016-12-01

It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.

Mo-based compounds for SiC-SiC joints

Energy Technology Data Exchange (ETDEWEB)

Magnani, G.; Beaulardi, L.; Mingazzini, C. [ENEA-Faenza (Italy). New Material Div.; Marmo, E. [Fabbricazioni Nucleari S.p.A., Bosco Mavengo (Italy)

2002-07-01

New method to joint silicon carbide-based material was developed. It was based on mixture composed mainly by molybdenum silicides. This mixture was tested as brazing mixture with several types of silicon carbide-based material. Microstructural examination of the joint showed that brazing mixture reacted with substrate to form silicon carbide on the surface, while two different molybdenum silicides were identified inside the joint (MoSi{sub 2} and Mo{sub 4.8}Si{sub 3}C{sub 0.6}). Preliminary oxidation tests performed by means of TGA showed high oxidation resistance of this joint over 1000 C making it very promising for high temperature application like ceramic heat exchanger. (orig.)

On the atomic structure of liquid Ni-Si alloys: a neutron diffraction study

Science.gov (United States)

Gruner, S.; Marczinke, J.; Hennet, L.; Hoyer, W.; Cuello, G. J.

2009-09-01

The atomic structure of the liquid NiSi and NiSi2 alloys is investigated by means of neutron diffraction experiments with isotopic substitution. From experimental data-sets obtained using four Ni isotopes, partial structure factors and pair correlation functions are obtained by applying a reverse Monte Carlo modelling approach. Both alloys were found to exhibit a strong tendency to hetero-coordination within the first coordination shell. In particular, covalent Si-Si bonds with somewhat greater distances seem to influence the structure of the liquid NiSi alloy.

On the atomic structure of liquid Ni-Si alloys: a neutron diffraction study

Energy Technology Data Exchange (ETDEWEB)

Gruner, S; Marczinke, J; Hoyer, W [Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany); Hennet, L [CNRS-CEMHTI, University of Orleans, F-45071 Orleans (France); Cuello, G J, E-mail: sascha.gruner@physik.tu-chemnitz.d [Institute Laue-Langevin, PO Box 156, F-38042 Grenoble (France)

2009-09-23

The atomic structure of the liquid NiSi and NiSi{sub 2} alloys is investigated by means of neutron diffraction experiments with isotopic substitution. From experimental data-sets obtained using four Ni isotopes, partial structure factors and pair correlation functions are obtained by applying a reverse Monte Carlo modelling approach. Both alloys were found to exhibit a strong tendency to hetero-coordination within the first coordination shell. In particular, covalent Si-Si bonds with somewhat greater distances seem to influence the structure of the liquid NiSi alloy.

A simple structure wavelet transform circuit employing function link neural networks and SI filters

Science.gov (United States)

Mu, Li; Yigang, He

2016-12-01

Signal processing by means of analog circuits offers advantages from a power consumption viewpoint. Implementing wavelet transform (WT) using analog circuits is of great interest when low-power consumption becomes an important issue. In this article, a novel simple structure WT circuit in analog domain is presented by employing functional link neural network (FLNN) and switched-current (SI) filters. First, the wavelet base is approximated using FLNN algorithms for giving a filter transfer function that is suitable for simple structure WT circuit implementation. Next, the WT circuit is constructed with the wavelet filter bank, whose impulse response is the approximated wavelet and its dilations. The filter design that follows is based on a follow-the-leader feedback (FLF) structure with multiple output bilinear SI integrators and current mirrors as the main building blocks. SI filter is well suited for this application since the dilation constant across different scales of the transform can be precisely implemented and controlled by the clock frequency of the circuit with the same system architecture. Finally, to illustrate the design procedure, a seventh-order FLNN-approximated Gaussian wavelet is implemented as an example. Simulations have successfully verified that the designed simple structure WT circuit has low sensitivity, low-power consumption and litter effect to the imperfections.

Nitric acid oxidation of Si (NAOS) method for low temperature fabrication of SiO{sub 2}/Si and SiO{sub 2}/SiC structures

Energy Technology Data Exchange (ETDEWEB)

Kobayashi, H., E-mail: koba771@ybb.ne.jp [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Imamura, K.; Kim, W.-B.; Im, S.-S.; Asuha [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2010-07-15

We have developed low temperature formation methods of SiO{sub 2}/Si and SiO{sub 2}/SiC structures by use of nitric acid, i.e., nitric acid oxidation of Si (or SiC) (NAOS) methods. By use of the azeotropic NAOS method (i.e., immersion in 68 wt% HNO{sub 3} aqueous solutions at 120 deg. C), an ultrathin (i.e., 1.3-1.4 nm) SiO{sub 2} layer with a low leakage current density can be formed on Si. The leakage current density can be further decreased by post-metallization anneal (PMA) at 200 deg. C in hydrogen atmosphere, and consequently the leakage current density at the gate bias voltage of 1 V becomes 1/4-1/20 of that of an ultrathin (i.e., 1.5 nm) thermal oxide layer usually formed at temperatures between 800 and 900 deg. C. The low leakage current density is attributable to (i) low interface state density, (ii) low SiO{sub 2} gap-state density, and (iii) high band discontinuity energy at the SiO{sub 2}/Si interface arising from the high atomic density of the NAOS SiO{sub 2} layer. For the formation of a relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer, we have developed the two-step NAOS method in which the initial and subsequent oxidation is performed by immersion in {approx}40 wt% HNO{sub 3} and azeotropic HNO{sub 3} aqueous solutions, respectively. In this case, the SiO{sub 2} formation rate does not depend on the Si surface orientation. Using the two-step NAOS method, a uniform thickness SiO{sub 2} layer can be formed even on the rough surface of poly-crystalline Si thin films. The atomic density of the two-step NAOS SiO{sub 2} layer is slightly higher than that for thermal oxide. When PMA at 250 deg. C in hydrogen is performed on the two-step NAOS SiO{sub 2} layer, the current-voltage and capacitance-voltage characteristics become as good as those for thermal oxide formed at 900 deg. C. A relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer can also be formed on SiC at 120 deg. C by use of the two-step NAOS method. With no treatment before the NAOS method

X-ray diffraction studies of structures of Be, Al, LiF, Fe+3%Si, Si, SiO2, KCl under dynamic pressures from 2 Gpa to 20 Gpa

International Nuclear Information System (INIS)

Egorov, L.A.; Barenboim, A.I.; Mokhova, V.V.; Dorohin, V.V.; Samoilov, A.I.

1997-01-01

Currently, the only direct method to study behaviour of solid crystal substance structures under dynamic compression is method to record X-rays diffraction pictures of crystal structures under shock compression. Thepaper presents results of X-rays diffraction measurements concerning structural parameters of shock compressed substances at pressures higher than Hugoniot elastic limit (Be, Al, LiF, Fe+3%Si), lower than Hugoniot elastic limit (Si, SiO 2 , LiF) and in the area of pressures of phase transformation beginning (KCl, Si). Recorded states of shock-compressed substance structures demonstrate identity of structural deformations at pressures higher and lower than Hugoniot elastic limit as well as at pressures above the phase transformation point, which can be characterized as single-axial deformations. (orig.)

Electrical and optical properties of Si-doped Ga2O3

Science.gov (United States)

Li, Yin; Yang, Chuanghua; Wu, Liyuan; Zhang, Ru

2017-05-01

The charge densities, band structure, density of states, dielectric functions of Si-doped β-Ga2O3 have been investigated based on the density functional theory (DFT) within the hybrid functional HSE06. The heavy doping makes conduction band split out more bands and further influences the band structure. It decreases the band gap and changes from a direct gap to an indirect gap. After doping, the top of the valence bands is mainly composed by the O-2p states, Si-3p states and Ga-4p states and the bottom of the conduction bands is almost formed by the Si-3s, Si-3p and Ga-4s orbits. The anisotropic optical properties have been investigated by means of the complex dielectric function. After the heavy Si doping, the position of absorption band edges did not change much. The slope of the absorption curve descends and indicates that the absorption became more slow for Si-doped β-Ga2O3 than undoped one due to the indirect gap of Si-doped β-Ga2O3.

Synthesis and Crystal Structures of Ni(II)/(III) and Zn(II) Complexes with Schiff Base Ligands

International Nuclear Information System (INIS)

Koo, Bon Kweon

2013-01-01

Coordination polymers are of great interest due to their intriguing structural motifs and potential applications in optical, electronic, magnetic, and porous materials. The most commonly used strategy for designing such materials relies on the utilization of multidentate N- or Odonor ligands which have the capacity to bridge between metal centers to form polymeric structures. The Schiff bases with N,O,S donor atoms are an useful source as they are readily available and easily form stable complexes with most transition metal ions. Schiff bases are also important intermediates in synthesis of some bioactive compounds and are potent anti-bacterial, anti-fungal, anticancer and antiviral compounds. In this work, the Schiff bases, Hapb and Hbpb, derived from 2-acetylpyridene or 2-benzoylpyridine and benzhydrazide were taken as trifunctional (N,N,O) monobasic ligand (Scheme 1). This ligand is of important because the π-delocalization of charge and the configurational flexibility of their molecular chain can give rise to a great variety of coordination modes. Although many metal.Schiff base complexes have been reported, the 1D, 2D, and 3D networks of coordination polymers linked through the bridging of ligands such as dicyanamide, N(CN) 2 - as coligand have been little published. In the process of working to extend the dimensionality of the metal-Schiff base complexes using benzilic acid as a bridging ligand, we obtained three simple metal (II)/(III) complexes of acetylpyridine/2-benzoyl pyridine based benzhydrazide ligand. Therefore, we report here the synthesis and crystal structures of the complexes

Si/ZnO NANO STRUCTURED HETEROJUNCTIONS BY APCVD METHOD

Directory of Open Access Journals (Sweden)

M. Maleki

2015-12-01

Full Text Available In this paper, polycrystalline pure zinc oxide nano structured thin films were deposited on two kinds of single crystal and polycrystalline of p and n type Si in three different substrate temperatures of 300, 400 and 500◦C by low cost APCVD method. Structural, electrical and optical properties of these thin films were characterized by X ray diffraction, two point probe method and UV visible spectrophotometer respectively. IV measurements of these heterojunctions showed that turn on voltage and series resistance will increase with increasing substrate temperature in polycrystalline Si, while in single crystal Si, turn on voltage will decrease. Although they are acceptable diodes, their efficiency as a heterojunction solar cell are so low

SiGe layer thickness effect on the structural and optical properties of well-organized SiGe/SiO2 multilayers

Science.gov (United States)

Vieira, E. M. F.; Toudert, J.; Rolo, A. G.; Parisini, A.; Leitão, J. P.; Correia, M. R.; Franco, N.; Alves, E.; Chahboun, A.; Martín-Sánchez, J.; Serna, R.; Gomes, M. J. M.

2017-08-01

In this work, we report on the production of regular (SiGe/SiO2)20 multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (t SiGe) from 3.5-2 nm results in a transition from continuous SiGe crystalline layer (t SiGe ˜ 3.5 nm) to layers consisting of isolated nanocrystals (t SiGe ˜ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ˜3-8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for t SiGe ˜ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K) photoluminescence measurements performed on annealed SiGe/SiO2 nanostructures show an emission band located between 0.7-0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix.

Ultraviolet-enhanced photodetection in a graphene/SiO{sub 2}/Si capacitor structure with a vacuum channel

Energy Technology Data Exchange (ETDEWEB)

Kim, Myungji; Kim, Hong Koo, E-mail: hkk@pitt.edu [Department of Electrical and Computer Engineering and Petersen Institute of NanoScience and Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 (United States)

2015-09-14

We report photodetection properties of a graphene/oxide/silicon capacitor structure with a nanoscale vacuum channel. The photogenerated two-dimensional electron gas (2DEG) inversion charges at SiO{sub 2}/Si interface are extracted out to air and transported along the void channel at low bias voltage (<5 V). A monolayer graphene, placed on top of SiO{sub 2} and suspended on the void channel, is utilized as a photon-transparent counter-electrode to the 2DEG layer and a collector electrode for the out-of-plane transported electrons, respectively. The photocurrent extracted through a void channel reveals high responsivity (1.0 A/W at 633 nm) as measured in a broad spectral range (325–1064 nm), especially demonstrating a UV-enhanced performance (0.43 A/W responsivity and 384% internal quantum efficiency at 325 nm). The mechanisms underlying photocarrier generation, emission, and transport in a suspended-graphene/SiO{sub 2}/Si structure are proposed.

First-principles study of the Pd–Si system and Pd(0 0 1)/SiC(0 0 1) hetero-structure

Energy Technology Data Exchange (ETDEWEB)

Turchi, P.E.A. [Lawrence Livermore National Laboratory (L-352), 7000 East Avenue, Livermore, CA 94551 (United States); Ivashchenko, V.I. [Institute of Problems of Materials Science, NAS of Ukraine, Krzhyzhanovsky str. 3, 03142 Kyiv (Ukraine)

2014-11-15

Highlights: • A large atomic mixing at the Pd/Si interface occurs at 1500–1800 K. • The Pd/C interface remains sharp even at the highest temperature of 2100 K. • At the Pd/C interface, voids and a graphite-like clustering are detected. • At the Pd/Si interface C22-Pd{sub 2}Si and D0{sub 11}-Pd{sub 3}Si fragments form, in agreement with experiment. - Abstract: First-principles molecular dynamics simulations of the Pd(0 0 1)/3C–SiC(0 0 1) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3{sup ¯}m, P6{sup ¯}m2, Pm3{sup ¯}m), Pd{sub 2}Si (P6{sup ¯}2m, P6{sub 3}/mmc, P3{sup ¯}m1, P3{sup ¯}1m) and Pd{sub 3}Si (Pnma, P6{sub 3}22, Pm3{sup ¯}m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd{sub 2}Si and D0{sub 11}-Pd{sub 3}Si fragments, in agreement with experiment.

Present status of SiCf/SiC composites as low-activation structural materials of fusion reactor in Japan

International Nuclear Information System (INIS)

Kohyama, A.; Katoh, Y.; Hasegawa, A.; Noda, T.

2001-01-01

The outline of research subjects on SiCf/SiC composites to apply to the structural components of fusion reactors are described and present status on material development of SiCf/SiC composites in Japan is reviewed. Irradiation experiments of the composites using fission reactors conducted by international collaborations to clarify their radiation response and to optimize the fabrication processes are introduced. (author)

The dependence of the interface and shape on the constrained growth of nc-Si in a-SiN sub x /a-Si:H/a-SiN sub x structures

CERN Document Server

Zhang Li; Wang Li; Li Wei; Xu Jun; Huang Xin Fan; Chen Kun Ji

2002-01-01

Size-controlled nanocrystalline silicon (nc-Si) has been prepared from a-SiN sub x /a-Si:H/a-SiN sub x ('a' standing for amorphous) structures by thermal annealing. Transmission electron microscope analyses show that the lateral size of the nc-Si is controlled by the annealing conditions and the a-Si sublayer thickness. The deviation of the nc-Si grain size distribution decreases with the a-Si sublayer thickness, so thinner a-Si sublayers are favourable for obtaining uniform nc-Si grains. In the a-Si:H (10 nm) sample annealed at 1000 deg. C for 30 min, an obvious bi-modal size distribution of nc-Si grains appears, but no obvious bi-modal size distribution is found in other samples with thinner a-Si:H sublayers. On the basis of the experimental results, we discuss the process of transition from the sphere-like shape to the disc-like shape in the growth model of the nc-Si crystallization. The critical thickness of the a-Si sublayer for the constrained crystallization can be determined by the present model. More...

Silicon electrodeposition from chloride-fluoride melts containing K2SiF6 and SiO2

Directory of Open Access Journals (Sweden)

Zhuk Sergey I.

2017-01-01

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

All-Si photodetector for telecommunication wavelength based on subwavelength grating structure and critical coupling

Directory of Open Access Journals (Sweden)

Alireza Taghizadeh

2017-09-01

Full Text Available We propose an efficient planar all-Si internal photoemission photodetector operating at the telecommunication wavelength of 1550 nm and numerically investigate its optical and electrical properties. The proposed polarization-sensitive detector is composed of an appropriately engineered subwavelength grating structure topped with a silicide layer of nanometers thickness as an absorbing material. It is shown that a nearly-perfect light absorption is possible for the thin silicide layer by its integration to the grating resonator. The absorption is shown to be maximized when the critical coupling condition is satisfied. Simulations show that the external quantum efficiency of the proposed photodetector with a 2-nm-thick PtSi absorbing layer at the center wavelength of 1550 nm can reach up to ∼60%.

Investigation of the atomic interface structure of mesotaxial Si/CoSi2(100) layers formed by high-dose implantation

International Nuclear Information System (INIS)

Bulle-Lieuwma, C.W.T.; Jong, A.F. de; Vandenhoudt, D.E.W.

1991-01-01

Aligned mesotaxial films of CoSi 2 in monocrystalline (100) oriented Si substrates have been formed by high-dose ion implantation of Co, followed by a high temperature treatment. The atomic structures of both the lower and upper Si/CoSi 2 (100) interfaces of the buried CoSi 2 layer have been investigated by high-resolution electron microscopy (HREM) combined with image simulations. A domain-like structure is observed consisting of areas with different interfaces. In order to derive the atomic configuration, image simulations of different proposed models are presented. By comparing simulated images and HREM images, two different atomic structure models for the Si/CoSi 2 (100) interface have been found. In the first model the interfacial Co atoms are six-fold coordinated and the tetrahedral coordination and bond lengths of silicon atoms are everywhere maintained. In the second model we found evidence for a 2 x 1 interface reconstruction, involving a difference in composition. The interfacial Co atoms are seven-fold coordinated. It is shown that the boundaries between the domains are associated with interfacial dislocations of edge-type with Burgers vectors b a/4 inclined and b = a/2 parallel to the interfacial plane. (author)

Stabilization of Si_60 Cage Structure: The Agony and the Ecstasy

Science.gov (United States)

Kawazoe, Y.; Sun, Q.; Wang, Q.; Rao, B. K.; Jena, P.

2003-03-01

The unique role of silicon in the micro-electronics industry has motivated many researchers to find ways to stabilize Si_60 with fullerene structure. In spite of numerous experimental attempts, synthesis of a theoretically predicted C_60-supported Si_60 cluster (C_60@Si_60) has not been possible. Using a state-of-the-art theoretical method, we provide the first answer for this long-standing contradiction between the experimental observation and the theoretical prediction. The flaws in earlier theoretical works are pointed out, and Si_60 is shown to be unstable in the fullerene structure either on its own or when supported on a C_60 fullerene (C_60@Si_60). On the other hand, we show that Si_60 cage can be stabilized by using magic clusters such as Al_12X (X = Si, Ge, Sn, Pb) as endohedral units, which have been identified in recent experiment as stable clusters and as suitable building blocks for cluster-assembled materials.

The formation of super-dislocation/micropipe complexes in 6H-SiC

Energy Technology Data Exchange (ETDEWEB)

Giocondi, J.; Rohrer, G.S.; Skowronski, M. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering; Balakrishna, V.; Augustine, G.; Hobgood, H.McD.; Hopkins, R.H. [Northrop Grumman Science and Technology Center, Pittsburgh PA (United States)

1998-06-01

Atomic force microscope images of surface/micropipe intersections on the (0001) growth surface of a 6H-SiC single crystal grown by the physical vapor transport method indicate that micropipes are associated with super-dislocations and that micron-scale deposits of a heterogeneous phase are frequently found in the vicinity of the defect. Based on our observations, we propose a model for the formation of super-dislocation/micropipe complexes that involves the coalescence of unit screw dislocations. The unit dislocations are forced together as large steps grow around heterogeneous material on the surface. (orig.) 5 refs.

Structures, phase stabilities, and electrical potentials of Li-Si battery anode materials

KAUST Repository

Tipton, William W.

2013-05-28

The Li-Si materials system holds promise for use as an anode in Li-ion battery applications. For this system, we determine the charge capacity, voltage profiles, and energy storage density solely by ab initio methods without any experimental input. We determine the energetics of the stable and metastable Li-Si phases likely to form during the charging and discharging of a battery. Ab initio molecular dynamics simulations are used to model the structure of amorphous Li-Si as a function of composition, and a genetic algorithm coupled to density-functional theory searches the Li-Si binary phase diagram for small-cell, metastable crystal structures. Calculations of the phonon densities of states using density-functional perturbation theory for selected structures determine the importance of vibrational, including zero-point, contributions to the free energies. The energetics and local structural motifs of these metastable Li-Si phases closely resemble those of the amorphous phases, making these small unit cell crystal phases good approximants of the amorphous phase for use in further studies. The charge capacity is estimated, and the electrical potential profiles and the energy density of Li-Si anodes are predicted. We find, in good agreement with experimental measurements, that the formation of amorphous Li-Si only slightly increases the anode potential. Additionally, the genetic algorithm identifies a previously unreported member of the Li-Si binary phase diagram with composition Li5Si2 which is stable at 0 K with respect to previously known phases. We discuss its relationship to the partially occupied Li7Si3 phase. © 2013 American Physical Society.

Tasks for development of SiC/SiC composites as structural material in a fusion reactor

International Nuclear Information System (INIS)

Yamada, Reiji

1997-01-01

SiC/SiC composites are chosen for a structural material of blankets in DREAM Reactor that has been proposed as a power reactor by JAERI. The main requirements and the target values in the DREAM conceptual design were described, and compared to available experimental data. (author)

Atomic structures of a monolayer of AlAs, GaAs, and InAs on Si(111)

International Nuclear Information System (INIS)

Lee, Geunjung; Yoon, Younggui

2010-01-01

We study atomic structures of a monolayer of AlAs, GaAs, and InAs on a Si(111) substrate from first-principles. The surface with the stacking sequence of ...SiSiMAsSiAs is energetically more stable than the surface with the stacking sequence of ...SiSiSiAsMAs, where M is Al, Ga, or In. The atomic structure of the three top layers of the low-energy surfaces are quite robust, irrespective of M, and the atomic structure of the AlAsSiAs terminated surface and that of the GaAsSiAs terminated surface are very similar. For the high-energy AsMAs terminated surfaces, the broken local tetrahedral symmetry plays an important role in the atomic structures. The calculated atomic structures of InAs on the Si(111) substrate depart most from the structure of crystalline Si.

Electronic structures and superconductivity in LuTE2Si2 phases (TE = d-electron transition metal)

Science.gov (United States)

Samsel-Czekała, M.; Chajewski, G.; Wiśniewski, P.; Romanova, T.; Hackemer, A.; Gorzelniak, R.; Pikul, A. P.; Kaczorowski, D.

2018-05-01

In the course of our search for unconventional superconductors amidst the 1:2:2 phases, we have re-investigated the LuTE2Si2 compounds with TE = Fe, Co, Ni, Ru, Pd and Pt. In this paper, we present the results of our fully relativistic ab initio calculations of the band structures, performed using the full-potential local-orbital code. The theoretical data are supplemented by the results of low-temperature electrical transport and specific heat measurements performed down to 0.35 K. All the materials studied but LuPt2Si2 crystallize with the body-centered tetragonal ThCr2Si2-type structure (space group I4/mmm). Their Fermi surfaces exhibit a three-dimensional multi-band character. In turn, the Pt-bearing compound adopts the primitive tetragonal CaBe2Ge2-type structure (space group P4/nmm), and its Fermi surface consists of predominantly quasi-two-dimensional sheets. Bulk superconductivity was found only in LuPd2Si2 and LuPt2Si2 (independent of the structure type and dimensionality of the Fermi surface). The key superconducting characteristics indicate a fully-gapped BCS type character. Though the electronic structure of LuFe2Si2 closely resembles that of the unconventional superconductor YFe2Ge2, this Lu-based silicide exhibits neither superconductivity nor spin fluctuations at least down to 0.35 K.

Structural Investigation of Fe-Ni-S and Fe-Ni-Si Melts by High-temperature Fluorescence XAFS Measurements

International Nuclear Information System (INIS)

Manghnani, Murli H.; Balogh, John; Hong Xinguo; Newville, Matthew; Amulele, G.

2007-01-01

Iron-nickel (Fe-Ni) alloy is regarded as the most abundant constituent of Earth's core, with an amount of 5.5 wt% Ni in the core based on geochemical and cosmochemical models. The structural role of nickel in liquid Fe-Ni alloys with light elements such as S or Si is poorly understood, largely because of the experimental difficulties of high-temperature melts. Recently, we have succeeded in acquiring Ni K-edge fluorescence x-ray absorption fine structure (XAFS) spectra of Fe-Ni-S and Fe-Ni-Si melts and alloys. Different structural environment of Ni atoms in Fe-Ni-S and Fe-Ni-Si melts is observed, supporting the effect of light elements in Fe-Ni melts

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

International Nuclear Information System (INIS)

Scholz, R.; Greeff, J. de; Vinche, C.

1998-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

1998-07-01

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

Growth process and structure of Er/Si(100) thin film

International Nuclear Information System (INIS)

Fujii, S.; Michishita, Y.; Miyamae, N.; Suto, H.; Honda, S.; Okado, H.; Oura, K.; Katayama, M.

2006-01-01

The solid-phase reactive epitaxial growth processes and structures of Er/Si(100) thin films were investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-deposited Er film grown at room temperature was transformed into crystalline rectangular-shaped islands after annealing at 900 deg. C. These islands have a hexagonal AlB 2 -type structure and the epitaxial relationship is determined to be ErSi 2 (011-bar0)[0001]//Si(100)[011-bar]. It has been revealed that the surface of the Er silicide island is terminated with an Er plane

Electronic structure of O-doped SiGe calculated by DFT + U method

Science.gov (United States)

Zhao, Zong-Yan; Yang, Wen; Yang, Pei-Zhi

2016-12-01

To more in depth understand the doping effects of oxygen on SiGe alloys, both the micro-structure and properties of O-doped SiGe (including: bulk, (001) surface, and (110) surface) are calculated by DFT + U method in the present work. The calculated results are as follows. (i) The (110) surface is the main exposing surface of SiGe, in which O impurity prefers to occupy the surface vacancy sites. (ii) For O interstitial doping on SiGe (110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers. (iii) The finding about decreased surface work function of O-doped SiGe (110) surface can confirm previous experimental observations. (iv) In all cases, O doing mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-SiGe-based solar cells in the future. Project supported by the Natural Science Foundation of Yunnan Province, China (Grant No. 2015FB123), the 18th Yunnan Province Young Academic and Technical Leaders Reserve Talent Project, China (Grant No. 2015HB015), and the National Natural Science Foundation of China (Grant No. U1037604).

Temperature stability of c-axis oriented LiNbO{sub 3}/SiO{sub 2}/Si thin film layered structures

Energy Technology Data Exchange (ETDEWEB)

Tomar, Monika [Department of Physics and Astrophysics, University of Delhi, Delhi (India)]. E-mail: mtomar@physics.du.ac.in; monikatomar@rediffmail.com; Gupta, Vinay; Mansingh, Abhai; Sreenivas, K. [Department of Physics and Astrophysics, University of Delhi, Delhi (India)

2001-08-07

Theoretical calculations have been performed for the temperature stability of the c-axis oriented LiNbO{sub 3} thin film layered structures on passivated silicon (SiO{sub 2}/Si) substrate with and without a non-piezoelectric SiO{sub 2} overlayer. The phase velocity, electromechanical coupling coefficient and temperature coefficient of delay (TCD) have been calculated. The thicknesses of various layers have been determined for optimum SAW performance with zero TCD. The presence of a non-piezoelectric SiO{sub 2} overlayer on LiNbO{sub 3} film is found to significantly enhance the coupling coefficient. The optimized results reveal that a high coupling coefficient of K{sup 2}=3.45% and a zero TCD can be obtained in the SiO{sub 2}/LiNbO{sub 3}/SiO{sub 2}/Si structure with a 0.235{lambda} thick LiNbO{sub 3} layer sandwiched between 0.1{lambda} thick SiO{sub 2} layers. (author)

Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

Science.gov (United States)

Korotchenkov, Oleg; Nadtochiy, Andriy; Kuryliuk, Vasyl; Wang, Chin-Chi; Li, Pei-Wen; Cantarero, Andres

2014-03-01

The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.

Alkane metathesis with the tantalum methylidene [(≡SiO)Ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4

KAUST Repository

Chen, Yin; Abou-Hamad, Edy; Hamieh, Ali Imad Ali; Hamzaoui, Bilel; Emsley, Lyndon; Basset, Jean-Marie

2015-01-01

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(≡SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(≡SiO)2Ta(=CH2)Me] and [(≡SiO)Ta(=CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(≡SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

Alkane metathesis with the tantalum methylidene [(≡SiO)Ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4

KAUST Repository

Chen, Yin

2015-01-21

By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(≡SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(≡SiO)2Ta(=CH2)Me] and [(≡SiO)Ta(=CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(≡SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

Role of the SiO2 buffer layer thickness in the formation of Si/SiO2/nc-Ge/SiO2 structures by dry oxidation

International Nuclear Information System (INIS)

Kling, A.; Ortiz, M.I.; Prieto, A.C.; Rodriguez, A.; Rodriguez, T.; Jimenez, J.; Ballesteros, C.; Soares, J.C.

2006-01-01

Nanomemories, containing Ge-nanoparticles in a SiO 2 matrix, can be produced by dry thermal oxidation of a SiGe layer deposited onto a Si-wafer with a barrier SiO 2 layer on its top. Rutherford backscattering spectrometry has been used to characterize the kinetics of the oxidation process, the composition profile of the growing oxide, the Ge-segregation and its diffusion into the barrier oxide in samples with thin and thick barrier oxide layers. The Ge segregated during the oxidation of the SiGe layer diffuses into the barrier oxide. In the first case the diffusion through the thin oxide is enhanced by the proximity of the substrate that acts as a sink for the Ge, resulting in the formation of a low Ge concentration SiGe layer in the surface of the Si-wafer. In the second case, the Ge-diffusion progresses as slowly as in bulk SiO 2 . Since barrier oxide layers as thin as possible are favoured for device fabrication, the structures should be oxidized at lower temperatures and the initial SiGe layer thickness reduced to minimize the Ge-diffusion

Interactions of atomic hydrogen with amorphous SiO2

Science.gov (United States)

Yue, Yunliang; Wang, Jianwei; Zhang, Yuqi; Song, Yu; Zuo, Xu

2018-03-01

Dozens of models are investigated by the first-principles calculations to simulate the interactions of an atomic hydrogen with a defect-free random network of amorphous SiO2 (a-SiO2) and oxygen vacancies. A wide variety of stable configurations are discovered due to the disorder of a-SiO2, and their structures, charges, magnetic moments, spin densities, and density of states are calculated. The atomic hydrogen interacts with the defect-free a-SiO2 in positively or negatively charged state, and produces the structures absent in crystalline SiO2. It passivates the neutral oxygen vacancies and generates two neutral hydrogenated E‧ centers with different Si dangling bond projections. Electron spin resonance parameters, including Fermi contacts, and g-tensors, are calculated for these centers. The atomic hydrogen interacts with the positive oxygen vacancies in dimer configuration, and generate four different positive hydrogenated defects, two of which are puckered like the Eγ‧ centers. This research helps to understand the interactions between an atomic hydrogen, and defect-free a-SiO2 and oxygen vacancies, which may generate the hydrogen-complexed defects that play a key role in the degeneration of silicon/silica-based microelectronic devices.

N-Heterocyclic Carbene Coinage Metal Complexes of the Germanium-Rich Metalloid Clusters [Ge9R3]− and [Ge9RI2]2− with R = Si(iPr3 and RI = Si(TMS3

Directory of Open Access Journals (Sweden)

Felix S. Geitner

2017-07-01

Full Text Available We report on the synthesis of novel coinage metal NHC (N-heterocyclic carbene compounds of the germanium-rich metalloid clusters [Ge9R3]− and [Ge9RI2]2− with R = Si(iPr3 and RI = Si(TMS3. NHCDippCu{η3Ge9R3} with R = Si(iPr3 (1 represents a less bulky silyl group-substituted derivative of the known analogous compounds with R = Si(iBu3 or Si(TMS3. The coordination of the [NHCDippCu]+ moiety to the cluster unit occurs via one triangular face of the tri-capped trigonal prismatic [Ge9] cluster. Furthermore, a series of novel Zintl cluster coinage metal NHC compounds of the type (NHCM2{η3Ge9RI2} (RI = Si(TMS3 M = Cu, Ag and Au; NHC = NHCDipp or NHCMes is presented. These novel compounds represent a new class of neutral dinuclear Zintl cluster coinage metal NHC compounds, which are obtained either by the stepwise reaction of a suspension of K12Ge17 with Si(TMS3Cl and the coinage metal carbene complexes NHCMCl (M = Cu, Ag, Au, or via a homogenous reaction using the preformed bis-silylated cluster K2[Ge9(Si(TMS32] and the corresponding NHCMCl (M = Cu, Ag, Au complex. The molecular structures of NHCDippCu{η3Ge9(Si(iPr33} (1 and (NHCDippCu2{η3-Ge9(Si(TMS32} (2 were determined by single crystal X-ray diffraction methods. In 2, the coordination of the [NHCDippCu]+ moieties to the cluster unit takes place via both open triangular faces of the [Ge9] entity. Furthermore, all compounds were characterized by means of NMR spectroscopy (1H, 13C, 29Si and ESI-MS.

Structural relaxation of Ni-Si-B amorphous ribbon

NARCIS (Netherlands)

Jurikova, A.; Csach, K.; Miskuf, J.; Ocelik, V.

The structural relaxation of the Ni-Si-B amorphous ribbon was studied by means of differential scanning calorimetry and thermomechanical analysis. It was shown that considerable length changes associated with reversible structural relaxation were revealed after a previous creep applied at higher

Structure of Ni-rich Ni--Cr--B--Si coating alloys

International Nuclear Information System (INIS)

Knotek, O.; Lugscheider, E.; Reimann, H.

1975-01-01

The structures of quaternary, nickel-rich Ni--Cr--B--Si alloys were analyzed at a constant boron content of 10 at. percent and a temperature of 850 0 C. The composition range for silicide formation was determined. In these quaternary alloys, known binary nickel silicides, nickel and chromium borides, and the ternary silico-boride Ni 6 Si 2 B were confirmed. A new composition for the W 5 Si 3 -type phase in the Ni--B--Si system was proposed. (U.S.)

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

Energy Technology Data Exchange (ETDEWEB)

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

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.

Effect of Carbon Doping on the Structure and Magnetic Phase Transition in (Mn,Fe2(P,Si))

Science.gov (United States)

Thang, N. V.; Yibole, H.; Miao, X. F.; Goubitz, K.; van Eijck, L.; van Dijk, N. H.; Brück, E.

2017-08-01

Given the potential applications of (Mn,Fe2(P,Si))-based materials for room-temperature magnetic refrigeration, several research groups have carried out fundamental studies aimed at understanding the role of the magneto-elastic coupling in the first-order magnetic transition and further optimizing this system. Inspired by the beneficial effect of the addition of boron on the magnetocaloric effect of (Mn,Fe2(P,Si))-based materials, we have investigated the effect of carbon (C) addition on the structural properties and the magnetic phase transition of Mn_{1.25}Fe_{0.70}P_{0.50}Si_{0.50}C_z and Mn_{1.25}Fe_{0.70}P_{0.55}Si_{0.45}C_z compounds by x-ray diffraction, neutron diffraction and magnetic measurements in order to find an additional control parameter to further optimize the performance of these materials. All samples crystallize in the hexagonal Fe_2P-type structure (space group P-62m), suggesting that C doping does not affect the phase formation. It is found that the Curie temperature increases, while the thermal hysteresis and the isothermal magnetic entropy change decrease by adding carbon. Room-temperature neutron diffraction experiments on Mn_{1.25}Fe_{0.70}P_{0.55}Si_{0.45}C_z compounds reveal that the added C substitutes P/Si on the 2 c site and/or occupies the 6 k interstitial site of the hexagonal Fe_2P-type structure.

Structure of MnSi on SiC(0001)

Science.gov (United States)

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

2016-11-01

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

SiC/SiC Cladding Materials Properties Handbook

Energy Technology Data Exchange (ETDEWEB)

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

2017-08-01

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

Use of SiCf/SiC ceramic composites as structure material of a fusion reactor toroid internal components

International Nuclear Information System (INIS)

Aiello, G.

2001-01-01

The use of low neutron-induced activation structural materials seems necessary in order to improve safety in future fusion power reactors. Among them, SiC f /SiC composites appear as a very promising solution because of their low activation characteristics coupled with excellent mechanical properties at high temperatures. With the main objective of evaluating the limit of present-day composites, a tritium breeding blanket using SiC f /SiC as structural material (the TAURO blanket) has been developed in the last years by the Commissariat a l'Energie Atomique (CEA). The purpose of this thesis was to modify the available design tools (computer codes, design criteria), normally used for the analyses of metallic structures, in order to better take into account the mechanical behaviour of SiC f /SiC. Alter a preliminary improvement of the calculation methods, two main topics of study could be identified: the modelling of the mechanical behaviour of the composite and the assessment of appropriate design criteria. The different behavioural models available in literature were analysed in order to find the one that was the best suited to the specific problems met in the field of fusion power. The selected model was then implemented in the finite elements code CASTEM 2000 used within the CEA for the thermo-mechanical analyses of the TAURO blanket. For the design of the blanket, we proposed a new resistance criterion whose main advantage, with respect to the other examined, lies in the easiness of identification. The suggested solutions were then applied in the design studies of the TAURO blanket. We then could show that the use of appropriate calculation methodologies is necessary in order to achieve a correct design of the blanket and a more realistic estimate of the limits of present day composites. The obtained results can also be extended to all nuclear components making use of SiC f /SiC structures. (author) [fr

AlGaInN-based ultraviolet light-emitting diodes grown on Si(111)

International Nuclear Information System (INIS)

Kipshidze, G.; Kuryatkov, V.; Borisov, B.; Holtz, M.; Nikishin, S.; Temkin, H.

2002-01-01

Ultraviolet light-emitting diodes grown on Si(111) by gas-source molecular-beam epitaxy with ammonia are described. The layers are composed of superlattices of AlGaN/GaN and AlN/AlGaInN. The layers are doped n and p type with Si and Mg, respectively. Hole concentration of 4x10 17 cm -3 , with a mobility of 8 cm2/Vs, is measured in Al 0.4 Ga 0.6 N/GaN. We demonstrate effective n- and p-type doping of structures based on AlN/AlGaInN. Light-emitting diodes based on these structures show light emission between 290 and 334 nm

Structural characterization of amorphous Fe-Si and its recrystallized layers

International Nuclear Information System (INIS)

Naito, Muneyuki; Ishimaru, Manabu; Hirotsu, Yoshihiko; Valdez, James A.; Sickafus, Kurt E.

2006-01-01

We have synthesized amorphous Fe-Si thin layers and investigated their microstructure using transmission electron microscopy (TEM). Si single crystals with (1 1 1) orientation were irradiated with 120 keV Fe + ions to a fluence of 4.0 x 10 17 cm -2 at cryogenic temperature (120 K), followed by thermal annealing at 1073 K for 2 h. A continuous amorphous layer with a bilayered structure was formed on the topmost layer of the Si substrate in the as-implanted specimen: the upper layer was an amorphous Fe-Si, while the lower one was an amorphous Si. After annealing, the amorphous bilayer crystallized into a continuous β-FeSi 2 thin layer

Band structure of hydrogenated Si nanosheets and nanotubes

International Nuclear Information System (INIS)

Guzman-Verri, G G; Lew Yan Voon, L C

2011-01-01

The band structures of fully hydrogenated Si nanosheets and nanotubes are elucidated by the use of an empirical tight-binding model. The hydrogenated Si sheet is a semiconductor with an indirect band gap of about 2.2 eV. The symmetries of the wavefunctions allow us to explain the origin of the gap. We predict that, for certain chiralities, hydrogenated Si nanotubes represent a new type of semiconductor, one with coexisting direct and indirect gaps of exactly the same magnitude. This behavior is different from that governed by the Hamada rule established for non-hydrogenated carbon and silicon nanotubes. A comparison to the results of an ab initio calculation is made.

Mechanically Activated Combustion Synthesis of MoSi₂-Based Composites

Energy Technology Data Exchange (ETDEWEB)

Shafirovich, Evgeny [Univ. of Texas, El Paso, TX (United States)

2015-09-30

The thermal efficiency of gas-turbine power plants could be dramatically increased by the development of new structural materials based on molybdenum silicides and borosilicides, which can operate at temperatures higher than 1300 °C with no need for cooling. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. One approach is based on the fabrication of MoSi2-Mo5Si3 composites that combine high oxidation resistance of MoSi2 and good mechanical properties of Mo5Si3. Another approach involves the addition of boron to Mo-rich silicides for improving their oxidation resistance through the formation of a borosilicate surface layer. In particular, materials based on Mo5SiB2 phase are promising materials that offer favorable combinations of high temperature mechanical properties and oxidation resistance. However, the synthesis of Mo-Si-B multi-phase alloys is difficult because of their extremely high melting temperatures. Mechanical alloying has been considered as a promising method, but it requires long milling times, leading to large energy consumption and contamination of the product by grinding media. In the reported work, MoSi2-Mo5Si3 composites and several materials based on Mo5SiB2 phase have been obtained by mechanically activated self-propagating high-temperature synthesis (MASHS). Short-term milling of Mo/Si mixture in a planetary mill has enabled a self-sustained propagation of the combustion front over the mixture pellet, leading to the formation of MoSi2-T1 composites. Combustion of Mo/Si/B mixtures for the formation of T2 phase becomes possible if the composition is designed for the addition of more exothermic reactions leading to the formation of MoB, TiC, or TiB2. Upon ignition, Mo/Si/B and Mo/Si/B/Ti mixtures exhibited spin combustion, but the products were porous, contained undesired secondary phases, and had low oxidation resistance. It has been shown that use of

Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots

Science.gov (United States)

Yang, Zhen

Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.

Band structure and unconventional electronic topology of CoSi

Science.gov (United States)

Pshenay-Severin, D. A.; Ivanov, Y. V.; Burkov, A. A.; Burkov, A. T.

2018-04-01

Semimetals with certain crystal symmetries may possess unusual electronic structure topology, distinct from that of the conventional Weyl and Dirac semimetals. Characteristic property of these materials is the existence of band-touching points with multiple (higher than two-fold) degeneracy and nonzero Chern number. CoSi is a representative of this group of materials exhibiting the so-called ‘new fermions’. We report on an ab initio calculation of the electronic structure of CoSi using density functional methods, taking into account the spin-orbit interactions. The linearized \

Properties of three-dimensional structures prepared by Ge dewetting from Si(111) at high temperatures

Energy Technology Data Exchange (ETDEWEB)

Shklyaev, Alexander, E-mail: shklyaev@isp.nsc.ru [A. V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Bolotov, Leonid; Poborchii, Vladimir; Tada, Tetsuya [National Institute of Advanced Industrial Science and Technology, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562 (Japan)

2015-05-28

The formation of three-dimensional (3D) structures during Ge deposition on Si(111) at about 800 °C is studied with scanning tunneling, Kelvin probe and electron microscopies, and scanning tunneling and Raman spectroscopies. The observed surface morphology is formed by dewetting of Ge from Si(111), since it occurs mainly by means of minimization of surface and interfacial energies. The dewetting proceeds through massive Si eroding around growing 3D structures, providing them to be composed of SiGe with about a 30% Ge content, and leads to the significant reduction of the SiGe/Si interface area. It is found that the SiGe top component of 3D structures forms sharp interfaces with the underlying Si. The minimization of interfacial and strain energies occurs on the way that the 3D structures appear to get the dendrite-like shape. The Ge distribution in the 3D SiGe structures is inhomogeneous in the lateral dimension with a higher Ge concentration in their central areas and Ge segregation on their surface.

Properties of three-dimensional structures prepared by Ge dewetting from Si(111) at high temperatures

International Nuclear Information System (INIS)

Shklyaev, Alexander; Bolotov, Leonid; Poborchii, Vladimir; Tada, Tetsuya

2015-01-01

The formation of three-dimensional (3D) structures during Ge deposition on Si(111) at about 800 °C is studied with scanning tunneling, Kelvin probe and electron microscopies, and scanning tunneling and Raman spectroscopies. The observed surface morphology is formed by dewetting of Ge from Si(111), since it occurs mainly by means of minimization of surface and interfacial energies. The dewetting proceeds through massive Si eroding around growing 3D structures, providing them to be composed of SiGe with about a 30% Ge content, and leads to the significant reduction of the SiGe/Si interface area. It is found that the SiGe top component of 3D structures forms sharp interfaces with the underlying Si. The minimization of interfacial and strain energies occurs on the way that the 3D structures appear to get the dendrite-like shape. The Ge distribution in the 3D SiGe structures is inhomogeneous in the lateral dimension with a higher Ge concentration in their central areas and Ge segregation on their surface

Improved designs of Si-based quantum wells and Schottky diodes for IR detection

Energy Technology Data Exchange (ETDEWEB)

Moeen, M., E-mail: moeen@kth.se [School of Information and Communication Technology, KTH Royal Institute of Technology, Stockholm, 16640, Kista (Sweden); Kolahdouz, M. [School of Electrical and Computer Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Salemi, A.; Abedin, A.; Östling, M. [School of Information and Communication Technology, KTH Royal Institute of Technology, Stockholm, 16640, Kista (Sweden); Radamson, H.H., E-mail: rad@kth.se [School of Information and Communication Technology, KTH Royal Institute of Technology, Stockholm, 16640, Kista (Sweden)

2016-08-31

Novel structures of intrinsic or carbon-doped multi quantum wells (MQWs) and intrinsic or carbon-doped Si Schottky diodes (SD), individually or in combination, have been manufactured to detect the infrared (IR) radiation. The carbon concentration in the structures was 5 × 10{sup 20} cm{sup −3} and the MQWs are located in the active part of the IR detector. A Schottky diode was designed and formed as one of the contacts (based on NiSi(C)/TiW) to MQWs where on the other side the structure had an Ohmic contact. The thermal response of the detectors is expressed in terms of temperature coefficient of resistance (TCR) and the quality of the electrical signal is quantified by the signal-to-noise ratio. The noise measurements provide the K{sub 1/f} parameter which is obtained from the power spectrum density. An excellent value of TCR = − 6%/K and K{sub 1/f} = 4.7 × 10{sup −14} was measured for the detectors which consist of the MQWs in series with the SD. These outstanding electrical results indicate a good opportunity to manufacture low cost Si-based IR detectors in the near future. - Highlights: • SiGe (C)/Si(C) multi quantum wells (MQWs) are evaluated to detect IR radiation. • Schottky diodes (SDs), individually or in series with MQWs are also fabricated. • Detectors consisted of MQWs in series with SD show excellent thermal sensing. • The noise values are also extremely low for MQWs in series with SD.

Improved designs of Si-based quantum wells and Schottky diodes for IR detection

International Nuclear Information System (INIS)

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

2016-01-01

Novel structures of intrinsic or carbon-doped multi quantum wells (MQWs) and intrinsic or carbon-doped Si Schottky diodes (SD), individually or in combination, have been manufactured to detect the infrared (IR) radiation. The carbon concentration in the structures was 5 × 10 20 cm −3 and the MQWs are located in the active part of the IR detector. A Schottky diode was designed and formed as one of the contacts (based on NiSi(C)/TiW) to MQWs where on the other side the structure had an Ohmic contact. The thermal response of the detectors is expressed in terms of temperature coefficient of resistance (TCR) and the quality of the electrical signal is quantified by the signal-to-noise ratio. The noise measurements provide the K 1/f parameter which is obtained from the power spectrum density. An excellent value of TCR = − 6%/K and K 1/f = 4.7 × 10 −14 was measured for the detectors which consist of the MQWs in series with the SD. These outstanding electrical results indicate a good opportunity to manufacture low cost Si-based IR detectors in the near future. - Highlights: • SiGe (C)/Si(C) multi quantum wells (MQWs) are evaluated to detect IR radiation. • Schottky diodes (SDs), individually or in series with MQWs are also fabricated. • Detectors consisted of MQWs in series with SD show excellent thermal sensing. • The noise values are also extremely low for MQWs in series with SD.

Obtaining of bilateral high voltage epitaxial p—i—n Si structures by LPE method

Directory of Open Access Journals (Sweden)

Vakiv N. M.

2013-12-01

Full Text Available Silicon p—i—n-structures are usually obtained using conventional diffusion method or liquid phase epitaxy (LPE. In both cases, the formation of p- and n-layers occurs in two stages. This technological approach is quite complex. Moreover, when forming bilateral high-voltage epitaxial layers, their parameters significantly deteriorate as a result of prolonged heat treatment of active high-resistivity layer. Besides, when using diffusion method, it is impossible to provide good reproducibility of the process. In this paper a technique of growing bilateral high-voltage silicon p—i—n-structures by LPE in a single process is proposed. The authors have obtained the optimum compounds of silicon-undersaturated molten solutions for highly doped (5•1018 cm–3 contact layers: 0.4—0.8 at. % aluminum in gallium melt for growing p-Si-layers and 0.03—0.15 at. % ytterbium in tin melt for n-Si-layers. Parameters of such structures provide for manufacturing of high-voltage diodes on their basis. Such diodes can be used in navigational equipment, communication systems for household and special purposes, on-board power supply systems, radar systems, medical equipment, etc.

An in situ XPS study of growth of ITO on amorphous hydrogenated Si: Initial stages of heterojunction formation upon processing of ITO/a-Si:H based solar cell structures

Energy Technology Data Exchange (ETDEWEB)

Diplas, Spyros; Thoegersen, Annett; Ulyashin, Alexander [SINTEF Materials and Chemistry, Oslo (Norway); Romanyuk, Andriy [University of Basel, Basel (Switzerland)

2015-01-01

In this work we studied the interface growth upon deposition of indium-tin oxide (ITO) on amorphous hydrogenated Si (a-Si:H)/crystalline Si (c-Si) structures. The analysis methods used were X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) in combination with in situ film growth with magnetron sputtering. The analysis was complemented with transmission electron microscopy (TEM) of the deposited films. The sputtering equipment was attached to the XPS spectrometer and hence early stage film growth was observed without breaking the vacuum. It was shown that during early deposition stages ITO is reduced by a-Si:H. The reduction is accompanied with formation of metallic In and Sn at the interface. Formation of Sn is more enhanced on a-Si substrates whilst formation of In is more dominant on c-Si substrates. The reduction effect is less intense for amorphous hydrogenated Si as compared to crystalline Si and this is attributed to stronger presence of dangling bonds in the latter than the former. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Study on the structure of Co/ZrO2-SiO2 catalysts by XAFS

International Nuclear Information System (INIS)

Gao Haiyan; Xiang Hongwei; Li Yongwang; Sun Yuhan; Liu Tao; Xie Yaning; Hu Tiandou

2002-01-01

The Co-based catalysts have been extensively used in converting CO to longer chain hydrocarbons which can then be hydrocracked to diesel oil with high grade. SiO 2 is one of the most commonly used carriers for Co-based catalysts. It is showed that commercial silica carrier after modification can lead to much high reaction activity and selectivity to heavy hydrocarbons. But the structure of Co-based catalysts supported on the modified carrier has not been clearly understood. XAFS is used to investigate the change of structure of cobalt species in Co-based catalysts supported on modified carriers. The result from XAFS indicate that the structure of Co-based catalysts supported on modified carrier has certain change in comparison with Co-based catalyst supported on commercial silica. The interaction between carrier and metal is woken in the modified catalysts. Especially, the structure of catalysts after reduction have distinct difference. The extent of reduction in modified catalysts is much more than the catalyst supported on commercial silica. Cobalt species of the catalyst supported commercial silica after reduction dose exist mainly in the form of cobalt metal forms and may exist in the form of Co 2 SiO 4 surface compound

Preparations, structures and properties of heterobimetallic complexes based on tetrahydrofuran-2,3,4,5-tetracarboxylate

International Nuclear Information System (INIS)

Jia, Tian-Jing; Li, Shu-Mu; Cao, Wei; Li, Li-Cun; Zheng, Xiang-Jun; Yuan, Da-Qiang

2013-01-01

Transition heterobimetallic metal-organic frameworks based on tetrahydrofuran-2,3,4,5-tetracarboxylicate (FTA), namely [M(H 2 O) 6 ][Cu 2 M(FTA) 2 (H 2 O) 2 ]·4H 2 O [M=Mn (1), Co (2)], and [CuZn(FTA)(H 2 O) 5 ]·H 2 O (3) have been synthesized and characterized. Single-crystal X-ray diffraction indicates that complexes 1 and 2 are isomorphic. In 1 and 2, FTA ligand links the metal ions to a 2-D wave-like negative-charged layer with a topology of (4;6 2 ) 2 (4;6 3 ;8 2 ) 2 (6). They possess 1-D channels with [M(H 2 O) 6 ] 2+ and lattice water molecules enclathrated. While in the complex 3, Cu 2+ and Zn 2+ ions are bridged by FTA to a 2-D neutral layer structure with a (8) 2 (8 4 ;12 2 ) topology. Magnetic properties of 1–3 were analyzed in connection with their structures, which show that there exist weak antiferromagnetic interactions between metal ions. - Graphical abstract: Three heterobimetallic MOFs were constructed through the size-selectivity of TFA coordination sites for different transition metal ions based on the concept of “Hard and Soft Acids and Bases”. Highlights: ► Complexes 1 and 3 contain 2-D wave-like negative-charged layers. ► Complex 2 is a 2-D neutral layer structure with a (8) 2 (8 4 ;12 2 ) topology. ► Complexes 1–3 are the first example of heterobimetallic MOFs based on FTA. ► The coordination sites of FTA show size-selectivity to metal ions

Preparations, structures and properties of heterobimetallic complexes based on tetrahydrofuran-2,3,4,5-tetracarboxylate

Energy Technology Data Exchange (ETDEWEB)

Jia, Tian-Jing; Li, Shu-Mu; Cao, Wei [College of Chemistry, Beijing Normal University, Beijing 100875 (China); Li, Li-Cun [College of Chemistry, Nankai University, Tianjin 300071 (China); Zheng, Xiang-Jun, E-mail: xjzheng@bnu.edu.cn [College of Chemistry, Beijing Normal University, Beijing 100875 (China); Yuan, Da-Qiang [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

2013-05-01

Transition heterobimetallic metal-organic frameworks based on tetrahydrofuran-2,3,4,5-tetracarboxylicate (FTA), namely [M(H₂O)₆][Cu₂M(FTA)₂(H₂O)₂]·4H₂O [M=Mn (1), Co (2)], and [CuZn(FTA)(H₂O)₅]·H₂O (3) have been synthesized and characterized. Single-crystal X-ray diffraction indicates that complexes 1 and 2 are isomorphic. In 1 and 2, FTA ligand links the metal ions to a 2-D wave-like negative-charged layer with a topology of (4;6²)₂(4;6³;8²)₂(6). They possess 1-D channels with [M(H₂O)₆]²⁺ and lattice water molecules enclathrated. While in the complex 3, Cu²⁺ and Zn²⁺ ions are bridged by FTA to a 2-D neutral layer structure with a (8)₂(8⁴;12²) topology. Magnetic properties of 1–3 were analyzed in connection with their structures, which show that there exist weak antiferromagnetic interactions between metal ions. - Graphical abstract: Three heterobimetallic MOFs were constructed through the size-selectivity of TFA coordination sites for different transition metal ions based on the concept of “Hard and Soft Acids and Bases”. Highlights: • Complexes 1 and 3 contain 2-D wave-like negative-charged layers. • Complex 2 is a 2-D neutral layer structure with a (8)₂(8⁴;12²) topology. • Complexes 1–3 are the first example of heterobimetallic MOFs based on FTA. • The coordination sites of FTA show size-selectivity to metal ions.

Effect of local atomic and electronic structures on thermoelectric properties of chemically substituted CoSi

Science.gov (United States)

Hsu, C. C.; Pao, C. W.; Chen, J. L.; Chen, C. L.; Dong, C. L.; Liu, Y. S.; Lee, J. F.; Chan, T. S.; Chang, C. L.; Kuo, Y. K.; Lue, C. S.

2014-05-01

We report the effects of Ge partial substitution for Si on local atomic and electronic structures of thermoelectric materials in binary compound cobalt monosilicides (\\text{CoSi}_{1-x}\\text{Ge}_{x}\\text{:}\\ 0 \\le x \\le 0.15 ). Correlations between local atomic/electronic structure and thermoelectric properties are investigated by means of X-ray absorption spectroscopy. The spectroscopic results indicate that as Ge is partially substituted onto Si sites at x \\le 0.05 , Co in CoSi1-xGex gains a certain amount of charge in its 3d orbitals. Contrarily, upon further replacing Si with Ge at x \\ge 0.05 , the Co 3d orbitals start to lose some of their charge. Notably, thermopower is strongly correlated with charge redistribution in the Co 3d orbital, and the observed charge transfer between Ge and Co is responsible for the variation of Co 3d occupancy number. In addition to Seebeck coefficient, which can be modified by tailoring the Co 3d states, local lattice disorder may also be beneficial in enhancing the thermoelectric properties. Extended X-ray absorption fine structure spectrum results further demonstrate that the lattice phonons can be enhanced by Ge doping, which results in the formation of the disordered Co-Co pair. Improvements in the thermoelectric properties are interpreted based on the variation of local atomic and electronic structure induced by lattice distortion through chemical substitution.

Mapping Optimal Charge Density and Length of ROMP-Based PTDMs for siRNA Internalization.

Science.gov (United States)

Caffrey, Leah M; deRonde, Brittany M; Minter, Lisa M; Tew, Gregory N

2016-10-10

A fundamental understanding of how polymer structure impacts internalization and delivery of biologically relevant cargoes, particularly small interfering ribonucleic acid (siRNA), is of critical importance to the successful design of improved delivery reagents. Herein we report the use of ring-opening metathesis polymerization (ROMP) methods to synthesize two series of guanidinium-rich protein transduction domain mimics (PTDMs): one based on an imide scaffold that contains one guanidinium moiety per repeat unit, and another based on a diester scaffold that contains two guanidinium moieties per repeat unit. By varying both the degree of polymerization and, in effect, the relative number of cationic charges in each PTDM, the performances of the two ROMP backbones for siRNA internalization were evaluated and compared. Internalization of fluorescently labeled siRNA into Jurkat T cells demonstrated that fluorescein isothiocyanate (FITC)-siRNA internalization had a charge content dependence, with PTDMs containing approximately 40 to 60 cationic charges facilitating the most internalization. Despite this charge content dependence, the imide scaffold yielded much lower viabilities in Jurkat T cells than the corresponding diester PTDMs with similar numbers of cationic charges, suggesting that the diester scaffold is preferred for siRNA internalization and delivery applications. These developments will not only improve our understanding of the structural factors necessary for optimal siRNA internalization, but will also guide the future development of optimized PTDMs for siRNA internalization and delivery.

A System Structure for a VHTR-SI Process Dynamic Simulation Code

International Nuclear Information System (INIS)

Chang, Jiwoon; Shin, Youngjoon; Kim, Jihwan; Lee, Kiyoung; Lee, Wonjae; Chang, Jonghwa; Youn, Cheung

2008-01-01

The VHTR-SI process dynamic simulation code embedded in a mathematical solution engine is an application software system that simulates the dynamic behavior of the VHTR-SI process. Also, the software system supports a user friendly graphical user interface (GUI) for user input/out. Structured analysis techniques were developed in the late 1970s by Yourdon, DeMarco, Gane and Sarson for applying a systematic approach to a systems analysis. It included the use of data flow diagrams and data modeling and fostered the use of an implementation-independent graphical notation for a documentation. In this paper, we present a system structure for a VHRT-SI process dynamic simulation code by using the methodologies of structured analysis

Suppressing Structural Colors of Photocatalytic Optical Coatings on Glass: The Critical Role of SiO2.

Science.gov (United States)

Li, Ronghua; Boudot, Mickael; Boissière, Cédric; Grosso, David; Faustini, Marco

2017-04-26

The appearance of structural colors on coated-glass is a critical esthetical drawback toward industrialization of photocatalytic coatings on windows for architecture or automobile. Herein we describe a rational approach to suppress the structural color of mesoporous TiO 2 -based coatings preserving photoactivity and mechanical stiffness. Addition of SiO 2 as third component is discussed. Ti x Si (1-x) O 2 mesoporous coatings were fabricated by one-step liquid deposition process through the evaporation induced self-assembling and characterized by GI-SAXS, GI-WAXS, electron microscopies, and in situ Environmental Ellipsometry Porosimetry. Guided by optical simulation, we investigated the critical role of SiO 2 on the optical responses of the films but also on the structural, mechanical, and photocatalytic properties, important requirements to go toward real applications. We demonstrate that adding SiO 2 to porous TiO 2 allows tuning and suppression of structural colors through refractive index matching and up to 160% increase in mechanical stiffening of the films. This study leads us to demonstrate an example of "invisible" coating, in which the light reflection is angle- and thickness-independent, and exhibiting high porosity, mechanical stiffness, and photoactivity.

Comparison between Si/SiO_2 and InP/Al_2O_3 based MOSFETs

International Nuclear Information System (INIS)

Akbari Tochaei, A.; Arabshahi, H.; Benam, M. R.; Vatan-Khahan, A.; Abedininia, M.

2016-01-01

Electron transport properties of InP-based MOSFET as a new channel material with Al_2O_3 as a high-k dielectric oxide layer in comparison with Si-based MOSFET are studied by the ensemble Monte Carlo simulation method in which the conduction band valleys in InP are based on three valley models with consideration of quantum effects (effective potential approach). I_d–V_d characteristics for Si-based MOSFET are in good agreement with theoretical and experimental results. Our results show that I_d of InP-based MOSFET is about 2 times that of Si-based MOSFET. We simulated the diagrams of longitudinal and transverse electric fields, conduction band edge, average electron velocity, and average electron energy for Si-based MOSFET and compared the results with those for InP-based MOSFET. Our results, as was expected, show that the transverse electric field, the conduction band edge, the electron velocity, and the electron energy in a channel in the InP-based MOSFET are greater than those for Si-based MOSFET. But the longitudinal electric field behaves differently at different points of the channel.

Synthesis, crystal structure and biological activity of the Schiff base organotin(IV) complexes based on salicylaldehyde-o-aminophenol

Science.gov (United States)

Tan, Yu-Xing; Zhang, Zhi-Jian; Liu, Yang; Yu, Jiang-Xi; Zhu, Xiao-Ming; Kuang, Dai-Zhi; Jiang, Wu-Jiu

2017-12-01

Schiff base organotin(IV) complexes C1 ∼ C5b have been synthesized via the reaction of the substituted salicylaldehyde-o-aminophenol Schiff base ligands (L1 ∼ L3) with the dibenzyltin dichloride, n-butyltin trichloride or dibutyltin oxide, respectively. The complexes have been characterized by IR, UV-Vis, 1H NMR, 13C NMR spectra, elemental analysis and the crystal structures have been determined by X-ray diffraction. The anticancer activity of the Schiff base ligand and complexes C1 ∼ C5b against five species of cancer cell which are Hela, MCF7, HepG2, Colo205, NCIsbnd H460 were tested respectively, the tests showed that C1 ∼ C5b exhibited significant anticancer activity for the cancer cells in comparison with the ligand, and the activity was greater than carboplatin.

Highly sensitive work function hydrogen gas sensor based on PdNPs/SiO2/Si structure at room temperature

Directory of Open Access Journals (Sweden)

G. Behzadi pour

Full Text Available In this study, fabrication of highly sensitive PdNPs/SiO2/Si hydrogen gas sensor using experimental and theoretical methods has been investigated. Using chemical method the PdNPs are synthesized and characterized by X-ray diffraction (XRD. The average size of PdNPs is 11 nm. The thickness of the oxide film was 20 nm and the surface of oxide film analyzed using Atomic-force microscopy (AFM. The C-V curve for the PdNPs/SiO2/Si hydrogen gas sensor in 1% hydrogen concentration and at the room temperature has been reported. The response time and recovery time for 1% hydrogen concentration at room temperature were 1.2 s and 10 s respectively. The response (R% for PdNPs/SiO2/Si MOS capacitor hydrogen sensor was 96%. The PdNPs/SiO2/Si MOS capacitor hydrogen sensor showed very fast response and recovery times compared to SWCNTs/PdNPs, graphene/PdNPs, nanorod/PdNPs and nanowire/PdNPs hydrogen gas sensors. Keywords: Sensitive, Oxide film, Capacitive, Resistance

Magnetic order and crystal structure study of YNi{sub 4}Si-type NdNi{sub 4}Si

Energy Technology Data Exchange (ETDEWEB)

Yao, Jinlei [Research Center for Solid State Physics and Materials, School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009 (China); Isnard, O. [Université Grenoble Alpes, Inst NEEL, BP166, Grenoble F-38042 (France); CNRS, Institut NEEL, 25 rue des martyrs, Grenoble F-38042 (France); Morozkin, A.V., E-mail: morozkin@tech.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation); Ivanova, T.I. [Physics Department, Moscow State University, Moscow 119992 (Russian Federation); Koshkid' ko, Yu.S. [International Laboratory of High Magnetic Fields and Low Temperatures, Wrocław (Poland); VSB-Technical University of Ostrava, Ostrava-Poruba 70833 (Czech Republic); Bogdanov, A.E.; Nikitin, S.A. [Physics Department, Moscow State University, Moscow 119992 (Russian Federation); Suski, W. [International Laboratory of High Magnetic Fields and Low Temperatures, Wrocław (Poland); Polish Academy of Sciences, Trzebiatowski Institute of Low Temperatures and Structure Research, P.O. Box 1410, 50-950 Wrocław 2 (Poland)

2015-02-15

Magnetic measurements and neutron powder diffraction investigation of the magnetic structure of the orthorhombic YNi{sub 4}Si-type (space group Cmmm) NdNi{sub 4}Si compound are presented. The magnetocaloric effect of NdNi{sub 4}Si is calculated in terms of the isothermal magnetic entropy change and it reaches the maximum value of –3.3 J/kg K for a field change of 50 kOe near T{sub C}=12 K. Below ∼12 K, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group in a zero magnetic field. At 1.5 K, the neodymium atoms have the magnetic moment of 2.37(5) μ{sub B}. The orthorhombic crystal structure and its thermal evolution are discussed in comparison with the CaCu{sub 5}-type compound. - Graphical abstract: The NdNi{sub 4}Si supplement the series of the orthorhombic derivative of the CaCu{sub 5}-type, namely the YNi{sub 4}Si-type, RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho). Below ∼12 K in a zero applied magnetic field, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group. Compared to the CaCu{sub 5}-type NdNi{sub 4}Si compound, the YNi{sub 4}Si-type counterpart has the relatively high ferromagnetic ordering temperature (9.2 K vs. 12 K), the small magnetocaloric effect (–7.3 J/kg K vs. –3.3 J/kg K for ∆H=50 kOe), and the large magnetic anisotropy at low temperatures. In contrast with CaCu{sub 5}-type NdNi{sub 4}Si, YNi{sub 4}Si-type NdNi{sub 4}Si shows distinct hysteresis loop at 2 K.We suggest that orthorhombic distortion may be used as a prospective route for optimization of permanent magnetic properties in the family of CaCu{sub 5}-type rare earth materials. - Highlights: • Below ∼12 K the YNi{sub 4}Si-type NdNi{sub 4}Si shows a ferromagnetic ordering. • MCE of NdNi{sub 4}Si reaches value of –3.3 J/kg K in 0–50 kOe near Curie point. • NdNi{sub 4}Si exhibits b-axis ferromagnetic order with the Cmm′m magnetic space

Tailoring the strain in Si nano-structures for defect-free epitaxial Ge over growth.

Science.gov (United States)

Zaumseil, P; Yamamoto, Y; Schubert, M A; Capellini, G; Skibitzki, O; Zoellner, M H; Schroeder, T

2015-09-04

We investigate the structural properties and strain state of Ge nano-structures selectively grown on Si pillars of about 60 nm diameter with different SiGe buffer layers. A matrix of TEOS SiO2 surrounding the Si nano-pillars causes a tensile strain in the top part at the growth temperature of the buffer that reduces the misfit and supports defect-free initial growth. Elastic relaxation plays the dominant role in the further increase of the buffer thickness and subsequent Ge deposition. This method leads to Ge nanostructures on Si that are free from misfit dislocations and other structural defects, which is not the case for direct Ge deposition on these pillar structures. The Ge content of the SiGe buffer is thereby not a critical parameter; it may vary over a relatively wide range.

An investigation of hydrogenized amorphous Si structures with Doppler broadening positron annihilation techniques

International Nuclear Information System (INIS)

Petkov, M.P.; Marek, T.; Asoka-Kumar, P.; Lynn, K.G.; Crandall, R.S.; Mahan, A.H.

1998-01-01

In this letter, we examine the feasibility of applying positron annihilation spectroscopy to the study of hydrogenized amorphous silicon (a-Si:H)-based structures produced by chemical vapor deposition techniques. The positron probe, sensitive to open volume formations, is used to characterize neutral and negatively charged silicon dangling bonds, typical for undoped and n-doped a-Si:H, respectively. Using depth profiling along the growth direction a difference was observed in the electronic environment of these defects, which enables their identification in a p-i-n device. copyright 1998 American Institute of Physics

Analysis of neutron irradiation effects on thermal conductivity of SiC-based composites and monolithic ceramics

Energy Technology Data Exchange (ETDEWEB)

Youngblood, G.E.; Senor, D.J. [Pacific Northwest National Lab., Richland, WA (United States)

1997-08-01

After irradiation of a variety of SiC-based materials to 33 or 43 dpa-SiC at 1000{degrees}C, their thermal conductivity values were degraded and became relatively temperature independent, which indicates that the thermal resistivity was dominated by point defect scattering. The magnitude of irradiation-induced conductivity degradation was greater at lower temperatures and typically was larger for materials with higher unirradiated conductivity. From these data, a K{sub irr}/K{sub unirr} ratio map which predicts the expected equilibrium thermal conductivity for most SiC-based materials as a function of irradiation temperature was derived. Due to a short-term EOC irradiation at 575{degrees} {+-} 60{degrees}C, a duplex irradiation defect structure was established. Based on an analysis of the conductivity and swelling recovery after post-irradiation anneals for these materials with the duplex defect structure, several consequences for irradiating SiC at temperatures of 1000{degrees}C or above are given. In particular, the thermal conductivity degradation in the fusion relevant 800{degrees}-1000{degrees}C temperature range may be more severe than inferred from SiC swelling behavior.

Analysis of neutron irradiation effects on thermal conductivity of SiC-based composites and monolithic ceramics

International Nuclear Information System (INIS)

Youngblood, G.E.; Senor, D.J.

1997-01-01

After irradiation of a variety of SiC-based materials to 33 or 43 dpa-SiC at 1000 degrees C, their thermal conductivity values were degraded and became relatively temperature independent, which indicates that the thermal resistivity was dominated by point defect scattering. The magnitude of irradiation-induced conductivity degradation was greater at lower temperatures and typically was larger for materials with higher unirradiated conductivity. From these data, a K irr /K unirr ratio map which predicts the expected equilibrium thermal conductivity for most SiC-based materials as a function of irradiation temperature was derived. Due to a short-term EOC irradiation at 575 degrees ± 60 degrees C, a duplex irradiation defect structure was established. Based on an analysis of the conductivity and swelling recovery after post-irradiation anneals for these materials with the duplex defect structure, several consequences for irradiating SiC at temperatures of 1000 degrees C or above are given. In particular, the thermal conductivity degradation in the fusion relevant 800 degrees-1000 degrees C temperature range may be more severe than inferred from SiC swelling behavior

Investigation of interface property in Al/SiO2/ n-SiC structure with thin gate oxide by illumination

Science.gov (United States)

Chang, P. K.; Hwu, J. G.

2017-04-01

The reverse tunneling current of Al/SiO2/ n-SiC structure employing thin gate oxide is introduced to examine the interface property by illumination. The gate current at negative bias decreases under blue LED illumination, yet increases under UV lamp illumination. Light-induced electrons captured by interface states may be emitted after the light sources are off, leading to the recovery of gate currents. Based on transient characteristics of gate current, the extracted trap level is close to the light energy for blue LED, indicating that electron capture induced by lighting may result in the reduction of gate current. Furthermore, bidirectional C- V measurements exhibit a positive voltage shift caused by electron trapping under blue LED illumination, while a negative voltage shift is observed under UV lamp illumination. Distinct trapping and detrapping behaviors can be observed from variations in I- V and C- V curves utilizing different light sources for 4H-SiC MOS capacitors with thin insulators.

Understanding lattice thermal conductivity in thermoelectric clathrates: A density functional theory study on binary Si-based type-I clathrates

Science.gov (United States)

Euchner, Holger; Pailhès, Stéphane; Giordano, Valentina M.; de Boissieu, Marc

2018-01-01

Despite their crystalline nature, thermoelectric clathrates exhibit a strongly reduced lattice thermal conductivity. While the reason for this unexpected behavior is known to lie in the peculiarities of the complex crystal structure and the interplay of the underlying guest-host framework, their respective roles are still not fully disentangled and understood. Our ab initio study of the most simple type-I clathrate phase, the binary compound Ba8Si46 and its derivatives Ba8 -xSi46 seeks to identify these mechanisms and provides insight into their origin. Indeed, the strongly decreased lattice thermal conductivity in thermoelectric clathrates is a consequence of a reduction of the acoustic phonon bandwidth, a lowering of the acoustic phonon group velocities, and the amplification of three-phonon-scattering processes. While the complexity of the crystal structure is demonstrated not to be the leading factor, the reasons are manifold. A modified Si-Si interaction causes a first decrease of the sound velocity, whereas the presence of flat Ba modes results in an additional lowering. These modes correspond to confined Bloch states that are localized on the Ba atoms and significantly increase the scattering phase space and, together with an increased anharmonicity of the interatomic interactions, strongly affect the phonon lifetimes.

High fluence swift heavy ion structure modification of the SiO{sub 2}/Si interface and gate insulator in 65 nm MOSFETs

Energy Technology Data Exchange (ETDEWEB)

Ma, Yao [Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Lab of Microelectronics Sichuan Province, Sichuan University, Chengdu, Sichuan 610064 (China); College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China); Gao, Bo, E-mail: gaobo@scu.edu.cn [Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Lab of Microelectronics Sichuan Province, Sichuan University, Chengdu, Sichuan 610064 (China); College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China); Gong, Min [Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Lab of Microelectronics Sichuan Province, Sichuan University, Chengdu, Sichuan 610064 (China); College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China); Willis, Maureen [College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China); Yang, Zhimei [Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Lab of Microelectronics Sichuan Province, Sichuan University, Chengdu, Sichuan 610064 (China); Guan, Mingyue [College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China); Li, Yun [Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Key Lab of Microelectronics Sichuan Province, Sichuan University, Chengdu, Sichuan 610064 (China); College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064 (China)

2017-04-01

In this work, a study of the structure modification, induced by high fluence swift heavy ion radiation, of the SiO{sub 2}/Si structures and gate oxide interface in commercial 65 nm MOSFETs is performed. A key and novel point in this study is the specific use of the transmission electron microscopy (TEM) technique instead of the conventional atomic force microscope (AFM) or scanning electron microscope (SEM) techniques which are typically performed following the chemical etching of the sample to observe the changes in the structure. Using this method we show that after radiation, the appearance of a clearly visible thin layer between the SiO{sub 2} and Si is observed presenting as a variation in the TEM intensity at the interface of the two materials. Through measuring the EDX line scans we reveal that the Si:O ratio changed and that this change can be attributed to the migration of the Si towards interface after the Si-O bond is destroyed by the swift heavy ions. For the 65 nm MOSFET sample, the silicon substrate, the SiON insulator and the poly-silicon gate interfaces become blurred under the same irradiation conditions.

Structural colors of the SiO2/polyethyleneimine thin films on poly(ethylene terephthalate) substrates

International Nuclear Information System (INIS)

Jia, Yanrong; Zhang, Yun; Zhou, Qiubao; Fan, Qinguo; Shao, Jianzhong

2014-01-01

The SiO 2 /polyethyleneimine (PEI) films with structural colors on poly(ethylene terephthalate) (PET) substrates were fabricated by an electrostatic self-assembly method. The morphology of the films was characterized by Scanning Electron Microscopy. The results showed that there was no distinguishable multilayered structure found of SiO 2 /PEI films. The optical behaviors of the films were investigated through the color photos captured by a digital camera and the color measurement by a multi-angle spectrophotometer. Different hue and brightness were observed at various viewing angles. The structural colors were dependent on the SiO 2 particle size and the number of assembly cycles. The mechanism of the structural colors generated from the assembled films was elucidated. The morphological structures and the optical properties proved that the SiO 2 /PEI film fabricated on PET substrate formed a homogeneous inorganic/organic SiO 2 /PEI composite layer, and the structural colors were originated from single thin film interference. - Highlights: • SiO 2 /PEI thin films were electrostatic self-assembled on PET substrates. • The surface morphology and optical behavior of the film were investigated. • The structural colors varied with various SiO 2 particle sizes and assembly cycles. • Different hue and lightness of SiO 2 /PEI film were observed at various viewing angles. • Structural color of the SiO 2 /PEI film originated from single thin film interference

Positron annihilation studies of the AlOx/SiO2/Si interface in solar cell structures

International Nuclear Information System (INIS)

Edwardson, C. J.; Coleman, P. G.; Li, T.-T. A.; Cuevas, A.; Ruffell, S.

2012-01-01

Film and film/substrate interface characteristics of 30 and 60 nm-thick AlO x films grown on Si substrates by thermal atomic layer deposition (ALD), and 30 nm-thick AlO x films by sputtering, have been probed using variable-energy positron annihilation spectroscopy (VEPAS) and Doppler-broadened spectra ratio curves. All samples were found to have an interface which traps positrons, with annealing increasing this trapping response, regardless of growth method. Thermal ALD creates an AlO x /SiO x /Si interface with positron trapping and annihilation occurring in the Si side of the SiO x /Si boundary. An induced positive charge in the Si next to the interface reduces diffusion into the oxides and increases annihilation in the Si. In this region there is a divacancy-type response (20 ± 2%) before annealing which is increased to 47 ± 2% after annealing. Sputtering seems to not produce samples with this same electrostatic shielding; instead, positron trapping occurs directly in the SiO x interface in the as-deposited sample, and the positron response to it increases after annealing as an SiO 2 layer is formed. Annealing the film has the effect of lowering the film oxygen response in all film types. Compared to other structural characterization techniques, VEPAS shows larger sensitivity to differences in film preparation method and between as-deposited and annealed samples.

Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition.

Science.gov (United States)

Zhang, Z; Wang, R F; Zhang, J; Li, H S; Zhang, J; Qiu, F; Yang, J; Wang, C; Yang, Y

2016-07-29

The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

Analysis of frequency-dependent series resistance and interface states of In/SiO{sub 2}/p-Si (MIS) structures

Energy Technology Data Exchange (ETDEWEB)

Birkan Selcuk, A. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey); Tugluoglu, N. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey)], E-mail: ntuglu@taek.gov.tr; Karadeniz, S.; Bilge Ocak, S. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey)

2007-11-15

In this work, the investigation of the interface state density and series resistance from capacitance-voltage (C-V) and conductance-voltage (G/{omega}-V) characteristics in In/SiO{sub 2}/p-Si metal-insulator-semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO{sub 2} film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 A. The forward and reverse bias C-V and G/{omega}-V characteristics of MIS structures have been studied at the frequency range 30 kHz-1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (R{sub s}) and interface state density (D{sub it}) values. Both the series resistance R{sub s} and density of interface states D{sub it} are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of R{sub s}-V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO{sub 2}/p-Si MIS structures. The interface state density value of In/SiO{sub 2}/p-Si MIS diode calculated at strong accumulation region is 1.11x10{sup 12} eV{sup -1} cm{sup -2} at 1 MHz. It is found that the calculated value of D{sub it} ({approx}10{sup 12} eV{sup -1} cm{sup -2}) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation.

Evolution of dislocation structure and fatigue crack behavior in Fe-Si alloys during cyclic bending test

International Nuclear Information System (INIS)

Ushioda, Kohsaku; Takebayashi, Shigeto; Goto, Shoji; Komatsu, Yoshinari; Hoshino, Akinori

2010-01-01

The evolution of dislocation structures was investigated by means of TEM in Fe-Si alloys with 0, 0.5 and 1.0 mass% Si during a cyclic bending test in conjunction with fatigue crack behavior. The addition of Si increased the fatigue strength. In steel without Si the cell structure develops, whereas in steel with 1%Si the vein structure evolves, which is considered to lead to the increased fatigue strength. The cell structure in 0%Si steel is postulated to be caused by the easy cross slip of dislocations, whereas the vein structure in the steels with Si is inferred to be caused by the difficulty in cross slip presumably due to the decrease in stacking fault energy. Furthermore, the steel containing Si shows a dislocation free zone (DFZ) along grain boundaries. A transgranular fracture takes place in 0%Si steel, while in 1%Si steel many intergranular cracks were observed just beneath the top surface, which was thought to be caused by the fact that a) strains are dispersed within grains owing to the vein structure and b) micro cracks are initiated and propagated along a DFZ.

Structure of a stacked anthraquinone–DNA complex

Science.gov (United States)

De Luchi, Daniela; Usón, Isabel; Wright, Glenford; Gouyette, Catherine; Subirana, Juan A.

2010-01-01

The crystal structure of the telomeric sequence d(UBrAGG) interacting with an anthraquinone derivative has been solved by MAD. In all previously studied complexes of intercalating drugs, the drug is usually sandwiched between two DNA base pairs. Instead, the present structure looks like a crystal of stacked anthraquinone molecules in which isolated base pairs are intercalated. Unusual base pairs are present in the structure, such as G·G and A·UBr reverse Watson–Crick base pairs. PMID:20823516

Structure and stability of BaTiSi₂O₇

DEFF Research Database (Denmark)

Viani, Alberto; Palermo, Andrea; Zanardi, Stefano

2015-01-01

emission) whose exhaustive explanation has been hampered to date by the lack of a structure model. In this work, BTS2 and the related compound BaTiSi4O11 (BTS4) were synthesized through conventional solid-state reaction methods. BTS2 invariably shows complex twinning patterns. Thus, its structure solution...... the triclinic phase has the space group  and unit cell a = 7.99385 (4), b = 10.01017 (5), c = 7.47514 (3) Å, α = 90.084 (8), β = 100.368 (8) and γ = 89.937 (9)º. These lattices can be seen as a distortion of that of tetragonal synthetic β-BaVSi2O7 with Ti in place of V. The structure models obtained from...

Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

Science.gov (United States)

Sasaki, Tomoyuki; Ando, Yuichiro; Kameno, Makoto; Tahara, Takayuki; Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-09-01

Spin transport in nondegenerate semiconductors is expected to pave the way to the creation of spin transistors, spin logic devices, and reconfigurable logic circuits, because room-temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in nondegenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observe the modulation of the Hanle-type spin-precession signals, which is a characteristic spin dynamics in nondegenerate semiconductors. We obtain long spin transport of more than 20 μm and spin rotation greater than 4π at RT. We also observe gate-induced modulation of spin-transport signals at RT. The modulation of the spin diffusion length as a function of a gate voltage is successfully observed, which we attribute to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to lead to the creation of practical Si-based spin MOSFETs.

Unusual antiferromagnetic structure of YbCo{sub 2}Si{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Mufti, N. [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany); Department of Physics, State University of Malang, Malang (Indonesia); Kaneko, K. [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany); Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai (Japan); Hoser, A. [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Gutmann, M. [ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot (United Kingdom); Geibel, C.; Stockert, O. [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany); Krellner, C. [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany); Physikalisches Institut, Goethe-Universitaet Frankfurt, Frankfurt (Germany)

2016-07-01

We report on extensive powder and single crystal neutron diffraction experiments to study the magnetic structure in YbCo{sub 2}Si{sub 2} below the Neel temperature T{sub N} = 1.7 K in detail. Representation analysis has been used to find the possible magnetic structure models compatible with the experiments. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k{sub 1} = (0.25 0.25 1) and equal moments or about 1.4 μ{sub B}/Yb is found, while the intermediate phase (T > 0.9 K) is characterized by an incommensurate amplitude-modulated magnetic structure with k{sub 2} = (0.25 0.086 1). The magnetic structure in YbCo{sub 2}Si{sub 2} is in stark contrast to all other compounds of the RCo{sub 2}Si{sub 2} family (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.

Factors influencing shape memory effect and phase transformation behaviour of Fe-Mn-Si based shape memory alloys

International Nuclear Information System (INIS)

Li, H.; Dunne, D.; Kennon, N.

1999-01-01

The objective of this research work was to investigate the factors influencing the shape memory effect and phase transformation behaviour of three Fe-Mn-Si based shape memory alloys: Fe-28Mn-6Si, Fe-13Mn-5Si-10Cr-6Ni and Fe-20Mn-6Si-7Cr-1Cu. The research results show that the shape memory capacity of Fe-Mn-Si based shape memory alloys varies with annealing temperature, and this effect can be explained in terms of the effect of annealing on γ ε transformation. The nature and concentration of defects in austenite are strongly affected by annealing conditions. A high annealing temperature results in a low density of stacking faults, leading to a low nucleation rate during stress induced γ→ε transformation. The growth of ε martensite plates is favoured rather than the formation of new ε martensite plates. Coarse martensite plates produce high local transformation strains which can be accommodated by local slip deformation, leading to a reduction in the reversibility of the martensitic transformation and to a degradation of the shape memory effect. Annealing at low temperatures (≤673 K) for reasonable times does not eliminate complex defects (dislocation jogs, kinks and vacancy clusters) created by hot and cold working strains. These defects can retard the movement and rearrangement of Shockley partial dislocations, i.e. suppress γ→ε transformation, also leading to a degradation of shape memory effect. Annealing at about 873 K was found to be optimal to form the dislocation structures which are favourable for stress induced martensitic transformation, thus resulting in the best shape memory behaviour. (orig.)

Si- and Sn-containing SiOCN-based nanocomposites as anode materials for lithium ion batteries. Synthesis, thermodynamic characterization and modeling

Energy Technology Data Exchange (ETDEWEB)

Rohrer, Jochen; Albe, Karsten [Technische Univ. Darmstadt (Germany). Materialmodellierung; Vrankovic, Dragoljub; Riedel, Ralf; Graczyk-Zajac, Magdalena [Technische Univ. Darmstadt (Germany). Disperse Feststoffe; Cupid, Damian; Seifert, Hans J. [Karlsruher Institut fuer Technologie, Eggenstein-Leopoldshafen (Germany). IAM - Angewandte Werkstoffphysik

2017-11-15

Novel nanocomposites consisting of silicon/tin nanoparticles (n-Si/n-Sn) embedded in silicon carbonitride (SiCN) or silicon oxycarbide (SiOC) ceramic matrices are investigated as possible anode materials for Li-ion batteries. The goal of our study is to exploit the large mass specific capacity of Si/Sn (3 579 mAh g{sup -1}/994 mAh g{sup -1}), while avoiding rapid capacity fading due to the large volume changes of Si/Sn during Li insertion. We show that a large amount (∝30-40 wt.%) of disordered carbon phase is dispersed within the SiOC/SiCN matrix and stabilizes the Si/Sn nanoparticles with respect to extended reversible lithium ion storage. Silicon nanocomposites are prepared by mixing of a polymeric precursor with commercial and ''home-synthesized'' crystalline and amorphous silicon. Tin nanocomposites, in contrast, are prepared using a single precursor approach, which allows the in-situ generation of Sn nanoparticles homogeneously dispersed within the SiOC host. The best electrochemical stability along with capacities of 600 - 700 mAh g{sup -1} is obtained when amorphous/porous silicon is used. Mechanisms contributing to the increase of storage capacity and the cycle stability are clarified by analyzing elemental composition, local solid-state structures, intercalation hosts and Li-ion mobility. Our work is supplemented by first-principles based atomistic modeling and thermochemical measurements.

Boron doping induced thermal conductivity enhancement of water-based 3C-Si(B)C nanofluids.

Science.gov (United States)

Li, Bin; Jiang, Peng; Zhai, Famin; Chen, Junhong; Bei, Guo-Ping; Hou, Xinmei; Chou, Kuo-Chih

2018-06-04

In this paper, the fabrication and thermal conductivity of water-based nanofluids using boron (B) doped SiC as dispersions are reported. Doping B into β-SiC phase leads to the shrinkage of SiC lattice due to the substitution of Si atoms (radius: 0.134 nm) by smaller B atoms (radius: 0.095 nm). The presence of B in SiC phase also promotes crystallization and grain growth of obtained particles. The tailored crystal structure and morphology of B doped SiC nanoparticles are beneficial for the thermal conductivity improvement of the nanofluids by using them as dispersions. Serving B doped SiC nanoparticles as dispersions for nanofluids, a remarkable improvement of the stability was achieved in SiC-B6 nanofluid at pH 11 by means of the Zeta potential measurement. Dispersing B doped SiC nanoparticles in water based fluids, the thermal conductivity of the as prepared nanofluids containing only 0.3 vol. % SiC-B6 nanoparticles is remarkably raised up to 39.3 % at 30 °C compared to the base fluids and is further enhanced with the increased temperature. The main reasons for the improvement of thermal conductivity of SiC-B6 nanofluids are more stable dispersion and intensive charge ions vibration around the surface of nanoparticles as well as the enhanced thermal conductivity of the SiC-B dispersions. © 2018 IOP Publishing Ltd.

New metal-organic complexes based on bis(tetrazole) ligands: Synthesis, structures and properties

Science.gov (United States)

Du, Ceng-Ceng; Fan, Jian-Zhong; Wang, Xin-Fang; Zhou, Sheng-Bin; Wang, Duo-Zhi

2017-04-01

In this paper, a series of new complexes, [Zn2(HL1)2(H2O)4]·H2O (1), [Co2(HL1)2]·TEA (2), [Co3(HL1)2(H2L1)2(H2O)4]n (3), [Cu(HL1)(H2O)2]n (4), {[Cu5(HL2)2(OH)4(ClO4)2]·4H2O}n (5) and [Cu2(L3)]n (6) were successfully prepared by utilizing three bis(tetrazole) ligands [bis-(1H-tetrazol-5-ylmethyl)-amine (H3L1), bis-(1H-tetrazol-5-ylethyl)-amine (H3L2) and 1,5-bis(5-tetrazolo)-3-thiapentane (H2L3)], all of which have been characterized by elemental analyses, FT-IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analyses as well as single-crystal X-ray diffraction analyses showing different dimensionalities (0D, 1D and 3D). Complexes 1 and 2 are 0D structures, 1 shows a dinuclear structure, 2 displays two crystallographically different mononuclear structures, 1 and 2 are further assembled to form 3D supramolecular framework and 2D supramolecular network by hydrogen-bonding interactions, respectively. Complexes 3, 4 and 5 are 1D structures, 3 features a mononuclear unit and a 1D chain, which are arranged into 3D supramolecular architecture by hydrogen-bonding interactions, 4 presents a zigzag chain, 5 shows an infinite chain structure constructed from pentanuclear Cu(II) subunits and ClO4- anions. Complex 6 exhibits a 3D coordination framework based on cyclic [Cu4(L3)2] dimmer subunits as nodes possessing an 8-connected network topology with the point symbol {424·64}. Further, semiconductor behaviors, the solid-state luminescent properties of the complexes 1-3 and 6 were measured and studied seriously at room temperature.

Growth of CoSi2 on Si(001) by reactive deposition epitaxy

International Nuclear Information System (INIS)

Lim, C.W.; Shin, C.-S.; Gall, D.; Zuo, J.M.; Petrov, I.; Greene, J.E.

2005-01-01

CaF 2 -structure CoSi 2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi 2 layers obtained by conventional solid phase growth (SPG). In both sets of experiments, Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi 2 formed at 600 deg. C. However, in the case of RDE, CoSi 2 formation occurred during Co deposition while for SPG, Co was deposited at 25 deg. C and silicidation took place during subsequent annealing. X-ray diffraction pole figures and transmission electron microscopy results demonstrate that RDE CoSi 2 layers are epitaxial with a cube-on-cube relationship (001) CoSi 2 parallel (001) Si and [100] CoSi 2 parallel[100] Si . In contrast, SPG films are polycrystalline with an average grain size of ≅1000 A and a mixed 111/002/022/112 orientation. We attribute the striking difference to rapid Co diffusion into the Si(001) substrate during RDE for which the high Co/Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. In contrast, sequential nucleation and transformation among increasingly Si-rich phases--from orthorhombic Co 2 Si to cubic CoSi to CoSi 2 --during SPG results in polycrystalline layers with a complex texture

Atomistic simulations of thermal transport in Si and SiGe based materials: From bulk to nanostructures

Science.gov (United States)

Savic, Ivana; Mingo, Natalio; Donadio, Davide; Galli, Giulia

2010-03-01

It has been recently proposed that Si and SiGe based nanostructured materials may exhibit low thermal conductivity and overall promising properties for thermoelectric applications. Hence there is a considerable interest in developing accurate theoretical and computational methods which can help interpret recent measurements, identify the physical origin of the reduced thermal conductivity, as well as shed light on the interplay between disorder and nanostructuring in determining a high figure of merit. In this work, we investigate the capability of an atomistic Green's function method [1] to describe phonon transport in several types of Si and SiGe based systems: amorphous Si, SiGe alloys, planar and nanodot Si/SiGe multilayers. We compare our results with experimental data [2,3], and with the findings of molecular dynamics simulations and calculations based on the Boltzmann transport equation. [1] I. Savic, N. Mingo, and D. A. Stewart, Phys. Rev. Lett. 101, 165502 (2008). [2] S.-M. Lee, D. G. Cahill, and R. Venkatasubramanian, Appl. Phys. Lett. 70, 2957 (1997). [3] G. Pernot et al., submitted.

Valence electron structure analysis of the cubic silicide intermetallics in rapidly solidified Al-Fe-V-Si alloy

International Nuclear Information System (INIS)

Wang, J.Q.; Qian, C.F.; Zhang, B.J.; Tseng, M.K.; Xiong, S.W.

1996-01-01

The application of rapid solidification for the development of elevated temperature aluminum alloys has resulted in the emergence of several alloys based on the Al-Fe alloy system. Of particular interest are Al-Fe-V-Si alloys which have excellent room temperature and high temperature mechanical properties. In a pioneering study, Skinner et al. showed the stabilization of the cubic phase in ternary Al-Fe-Si alloy by the addition of a quaternary element, vanadium. The evolution of the microstructure in these alloys both during rapid solidification and subsequent processing is of crucial importance. Kim has demonstrated that the composition of the silicide phase in rapidly solidified Al-Fe-V-Si alloy is very close to Al 12 (Fe,V) 3 Si with the body centered cubic (bcc) structure. The structure is closely related to that of quasicrystals.In view of the structural features and the relationship between the α 12 and α 13 phases, the researching emphasis should firstly be put on the α 12 phase. In this paper the authors analyzed the α -(AlFeSi)(α 12 -type) phase from the angle of atomic valence electron structure other than the traditional methods of obtaining the diffraction spots of the phase. Several pieces of information were obtained about the hybrid levels and bond natures of every kind of atom in the α -(AlFeSi) phase. Finally the authors explained the phenomenon which V atom can substitute for Fe atom in the α 12 phase and improve the thermal stability of the phase in Al-Fe-V-Si alloy

Effect of Ni on eutectic structural evolution in hypereutectic Al-Mg2Si cast alloys

International Nuclear Information System (INIS)

Li Chong; Wu Yaping; Li Hui; Wu Yuying; Liu Xiangfa

2010-01-01

Research highlights: → By the injection of rod-like NiAl 3 phase in Al-Mg 2 Si alloys, Al-Mg 2 Si binary eutectic structure gradually evolves into Al-Mg 2 Si-NiAl 3 ternary eutectic. → The ternary eutectic presents a unique double rod structure that rod-like NiAl 3 and Mg 2 Si uniformly distribute in Al matrix. → The mechanism of structural evolution was analyzed in terms of the detailed microstructural observations. → The high temperature (350 deg. C) tensile strength of the alloy increases by 23% due to the eutectic structural evolution. - Abstract: The aim of this work is to investigate the eutectic structural evolution of hypereutectic Al-20% Mg 2 Si with Ni addition under a gravity casting process. Three-dimensional morphologies of eutectic phases were observed in detail using field emission scanning electron microscopy, after Al matrix was removed by deep etching or extraction. The results show that Al-Mg 2 Si binary eutectic gradually evolves into Al-Mg 2 Si-NiAl 3 ternary eutectic with the increase of Ni content, and flake-like eutectic Mg 2 Si transforms into rods. The ternary eutectic presents a unique double rod structure that rod-like NiAl 3 and Mg 2 Si uniformly distribute in Al matrix. Further, the high temperature (350 deg. C) tensile strength of the alloy increases by 23% due to the eutectic structure evolution, and the mechanism of structural evolution was discussed and analyzed in terms of the detailed microstructural observations.

Electron transport in all-Heusler Co2CrSi/Cu2CrAl/Co2CrSi device, based on ab-initio NEGF calculations

Science.gov (United States)

Mikaeilzadeh, L.; Pirgholi, M.; Tavana, A.

2018-05-01

Based on the ab-initio non-equilibrium Green's function (NEGF) formalism based on the density functional theory (DFT), we have studied the electron transport in the all-Heusler device Co2CrSi/Cu2CrAl/Co2CrSi. Results show that the calculated transmission spectra is very sensitive to the structural parameters and the interface. Also, we obtain a range for the thickness of the spacer layer for which the MR effect is optimum. Calculations also show a perfect GMR effect in this device.

Optimization-based topology identification of complex networks

International Nuclear Information System (INIS)

Tang Sheng-Xue; Chen Li; He Yi-Gang

2011-01-01

In many cases, the topological structures of a complex network are unknown or uncertain, and it is of significance to identify the exact topological structure. An optimization-based method of identifying the topological structure of a complex network is proposed in this paper. Identification of the exact network topological structure is converted into a minimal optimization problem by using the estimated network. Then, an improved quantum-behaved particle swarm optimization algorithm is used to solve the optimization problem. Compared with the previous adaptive synchronization-based method, the proposed method is simple and effective and is particularly valid to identify the topological structure of synchronization complex networks. In some cases where the states of a complex network are only partially observable, the exact topological structure of a network can also be identified by using the proposed method. Finally, numerical simulations are provided to show the effectiveness of the proposed method. (general)

Theoretical study of the structure and reactivity of lanthanide and actinide based organometallic complexes; Etude theorique de la structure et de la reactivite de complexes organometalliques de lanthanides et d'actinides

Energy Technology Data Exchange (ETDEWEB)

Barros, N

2007-06-15

In this PhD thesis, lanthanide and actinide based organometallic complexes are studied using quantum chemistry methods. In a first part, the catalytic properties of organo-lanthanide compounds are evaluated by studying two types of reactions: the catalytic hydro-functionalization of olefins and the polymerisation of polar monomers. The reaction mechanisms are theoretically determined and validated, and the influence of possible secondary non productive reactions is envisaged. A second part focuses on uranium-based complexes. Firstly, the electronic structure of uranium metallocenes is analysed. An analogy with the uranyl compounds is proposed. In a second chapter, two isoelectronic complexes of uranium IV are studied. After validating the use of DFT methods for describing the electronic structure and the reactivity of these compounds, it is shown that their reactivity difference can be related to a different nature of chemical bonding in these complexes. (author)

Structural, thermal, dielectric spectroscopic and AC impedance properties of SiC nanoparticles doped PVK/PVC blend

Science.gov (United States)

Alghunaim, Naziha Suliman

2018-06-01

Nanocomposite films based on poly (N-vinylcarbazole)/polyvinylchloride (PVK/PVC) blend doped with different concentrations of Silicon Carbide (SiC) nanoparticles have been prepared. The X-ray diffraction, Ultra violet-visible spectroscopy, thermogravimetric analysis and electrical spectroscopic has been used to characterize these nanocomposites. The X-ray analysis confirms the semi-crystalline nature of the films. The intensity of the main X-ray peak is decreased due to the interaction between the PVK/PVC and SiC. The main SiC peaks are absent due to complete dissolution of SiC in polymeric matrices. The UV-Vis spectra indicated that the band gap optical energy is affected by adding SiC nanoparticles because the charges transfer complexes between PVK/PVC with amount of SiC. The thermal stability is improved and the estimated values of ε‧ and ε″ are increased with increasing for SiC content due to the free charge carriers which in turn increase the ionic conductivity of the doped samples. The plots of tan δ with frequency are studied. A single peak from the plot between tan δ and Log (f) is appeared and shifted towards the higher frequency confirmed the presence of relaxing dipoles moment.

Structural study of Na2O-B2O3-SiO2 glasses from molecular simulations using a polarizable force field.

Science.gov (United States)

Pacaud, Fabien; Delaye, Jean-Marc; Charpentier, Thibault; Cormier, Laurent; Salanne, Mathieu

2017-10-28

Sodium borosilicate glasses Na 2 O-B 2 O 3 -SiO 2 (NBS) are complex systems from a structural point of view. Three main building units are present: tetrahedral SiO 4 and BO 4 (B IV ) and triangular BO 3 (B III ). One of the salient features of these compounds is the change of the B III /B IV ratio with the alkali concentration, which is very difficult to capture in force fields-based molecular dynamics simulations. In this work, we develop a polarizable force field that is able to reproduce the boron coordination and more generally the structure of several NBS systems in the glass and in the melt. The parameters of the potential are fitted from density functional theory calculations only, in contrast with the existing empirical potentials for NBS systems. This ensures a strong improvement on the transferability of the parameters from one composition to another. Using this new force field, the structure of NBS systems is validated against neutron diffraction and nuclear magnetic resonance experiments. A special focus is given to the distribution of B III /B IV with respect to the composition and the temperature.

Features of carrier tunneling between the silicon valence band and metal in devices based on the Al/high-K oxide/SiO_2/Si structure

International Nuclear Information System (INIS)

Vexler, M. I.; Grekhov, I. V.

2016-01-01

The features of electron tunneling from or into the silicon valence band in a metal–insulator–semiconductor system with the HfO_2(ZrO_2)/SiO_2 double-layer insulator are theoretically analyzed for different modes. It is demonstrated that the valence-band current plays a less important role in structures with HfO_2(ZrO_2)/SiO_2 than in structures containing only silicon dioxide. In the case of a very wide-gap high-K oxide ZrO_2, nonmonotonic behavior related to tunneling through the upper barrier is predicted for the valence-band–metal current component. The use of an insulator stack can offer certain advantages for some devices, including diodes, bipolar tunnel-emitter transistors, and resonant-tunneling diodes, along with the traditional use of high-K insulators in a field-effect transistor.

Preliminary study in development of glass-ceramic based on SiO2-LiO2 system, starting of different SiO2 starting powders

International Nuclear Information System (INIS)

Daguano, J.K.M.F.; Santos, F.A.; Santos, C.; Marton, L.F.M.; Conte, R.A.; Rodrigues Junior, D.; Melo, F.C.L.

2009-01-01

In this work, lithium disilicate glass-ceramics were developed starting of the rice ash- SiO 2 and Li 2 CO 3 powders. The results were compared with glass ceramics based on the lithium disilicate obtained by commercial SiO 2 powders. Glass were melted at 1580 deg C, and annealed at 850 deg C. X-Ray diffraction and scanning electron microscopy were used for characterization of the materials, and hardness and fracture toughness were evaluated using Vickers indentation method. Glasses with amorphous structure were obtained in both materials. After annealing, 'rice-ash' samples presented Li 2 SiO 3 and residual SiO 2 as crystalline phases. On the other side, commercial SiO 2 - Samples presented only Li 2 Si 2 O 5 as crystalline phases and the better results of hardness and fracture toughness. (author)

Synthesis, structural, spectroscopic and biological studies of Schiff base complexes

Science.gov (United States)

Diab, M. A.; El-Sonbati, A. Z.; Shoair, A. F.; Eldesoky, A. M.; El-Far, N. M.

2017-08-01

Schiff base ligand 4-((pyridin-2- yl)methyleneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (PDMP) and its complexes were prepared and characterized on the basis of elemental analysis, IR, mass spectra and thermogravimetric analysis. All results confirm that the complexes have 1:1 (M: PMDP) stoichiometric formula [M(PMDP)Cl2H2O ] (M = Cu(II), Co(II), Ni(II) and Mn(II)), [Cd(PMDP)Cl2] and the ligand behaves as a bi/tridentate forming five-membered chelating ring towards the metal ions, bonding through azomethine nitrogen/exocyclic carbonyl oxygen, azomethine pyridine nitrogen and exocyclic carbonyl oxygen. The shift in the band positions of the groups involved in coordination has been utilized to estimate the metal-nitrogen and/or oxygen bond lengths. The complexes of Co(II), Ni(II) and Cu(II) are paramagnetic and the magnetic as well as spectral data suggest octahedral geometry, whereas the Cd(II) complex is tetrahedral. The XRD studies show that both the ligand and its metal complexes (1 and 3) show polycrystalline with crystal structure. Molecular docking was used to predict the binding between PMDP ligand and the receptors. The corrosion inhibition of mild steel in 2 M HCl solution by PDMP was explored utilizing potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and (EFM) electrochemical frequency modulation method. Potentiodynamic polarization demonstrated that PDMP compound is mixed-type inhibitor. EIS spectra exhibit one capacitive loop and confirm the protective ability. The percentage of inhibition efficiency was found to increase with increasing the inhibitor concentration.

"Equilibrium structure of monatomic steps on vicinal Si(001)

NARCIS (Netherlands)

Zandvliet, Henricus J.W.; Elswijk, H.B.; van Loenen, E.J.; Dijkkamp, D.