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Sample records for aligned silicon oxide

  1. Molten Pb as a catalyst for large-scale growth of highly aligned silicon oxide nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Jiang, Feihong; Yang, Yongdong; Li, Jianping

    2007-09-01

    Low melting point metal Pb can be used as an effective catalyst for the large-scale growth of highly aligned silicon oxide nanowire balls. Unlike any previously observed results using Au or Fe as catalyst, the molten Pb-catalyzed vapor-liquid-solid (VLS) growth exhibits many amazing growth phenomena. The scan electron microscopy (SEM) data indicate that the silicon oxide nanowires grow out perpendicularly from the surface of the metal Pb balls. For each ball, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. The pear-like, flower-like, chrysanthemum-like, and echinus-like SiO 2 nanostructures were formed. A growth model was proposed. The experimental results further expand the low melting point metal-catalyzed VLS mechanism to a broader range.

  2. Silicon oxides as alignment surfaces for vertically-aligned nematics in photonic devices

    NASA Astrophysics Data System (ADS)

    Oton, E.; López-Andrés, S.; Bennis, N.; Otón, J. M.; Geday, M. A.

    2014-06-01

    A comparative study on alignment performance and microstructure of inorganic layers used for liquid crystal cell conditioning has been carried out. The study has focused on two specific materials, SiOx and SiO2, deposited under different conditions. The purpose was to establish a relationship between layer microstructure and liquid crystal alignment. The surface morphology has been studied by FESEM and AFM. An analysis on liquid crystal alignment, pretilt angle, response time, contrast ratio and the conditions to develop backflow effect (significant rise time increase due to pure homeotropic alignment) on vertically-aligned nematic cells has been carried out. A technique to overcome the presence of backflow has been identified. The full comparative study of SiOx and SiO2 layer properties and their influence over liquid crystal alignment and electrooptic response is presented.

  3. Low-temperature growth of well-aligned zinc oxide nanorod arrays on silicon substrate and their photocatalytic application

    PubMed Central

    Azam, Ameer; Babkair, Saeed Salem

    2014-01-01

    Well-aligned and single-crystalline zinc oxide (ZnO) nanorod arrays were grown on silicon (Si) substrate using a wet chemical route for the photodegradation of organic dyes. Structural analysis using X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction confirmed the formation of ZnO nanorods grown preferentially oriented in the (001) direction and with a single phase nature with a wurtzite structure. Field emission scanning electron microscopy and transmission electron microscopy micrographs showed that the length and diameter of the well-aligned rods were about ~350–400 nm and ~80–90 nm, respectively. Raman scattering spectra of ZnO nanorod arrays revealed the characteristic E2 (high) mode that is related to the vibration of oxygen atoms in the wurtzite ZnO. The photodegradation of methylene blue (MB) using ZnO nanorod arrays was performed under ultraviolet light irradiation. The results of photodegradation showed that ZnO nanorod arrays were capable of degrading ~80% of MB within 60 minutes of irradiation, whereas ~92% of degradation was achieved in 120 minutes. Complete degradation of MB was observed after 270 minutes of irradiation time. Owing to enhanced photocatalytic degradation efficiency and low-temperature growth method, prepared ZnO nanorod arrays may open up the possibility for the successful utilization of ZnO nanorod arrays as a future photocatalyst for environmental remediation. PMID:24812511

  4. Band alignment of vanadium oxide as an interlayer in a hafnium oxide-silicon gate stack structure

    NASA Astrophysics Data System (ADS)

    Zhu, Chiyu; Kaur, Manpuneet; Tang, Fu; Liu, Xin; Smith, David J.; Nemanich, Robert J.

    2012-10-01

    Vanadium oxide (VO2) is a narrow band gap material (Eg = 0.7 eV) with a thermally induced insulator-metal phase transition at ˜343 K and evidence of an electric field induced transition at T < 343 K. To explore the electronic properties of VO2, a sandwich structure was prepared with a 2 nm VO2 layer embedded between an oxidized Si(100) surface and a 2 nm hafnium oxide (HfO2) layer. The layer structure was confirmed with high resolution transmission electron microscopy. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy, and the band alignment was deduced on both n-type and p-type Si substrates. The valence band offset between VO2 and SiO2 is measured to be 4.0 eV. The valence band offset between HfO2 and VO2 is measured to be ˜3.4 eV. The band relation developed from these results demonstrates the potential for charge storage and switching for the embedded VO2 layer.

  5. Preparation of Aligned Ultra-long and Diameter-controlled Silicon Oxide Nanotubes by Plasma Enhanced Chemical Vapor Deposition Using Electrospun PVP Nanofiber Template

    NASA Astrophysics Data System (ADS)

    Zhou, Ming; Zhou, Jinyuan; Li, Ruishan; Xie, Erqing

    2010-02-01

    Well-aligned and suspended polyvinyl pyrrolidone (PVP) nanofibers with 8 mm in length were obtained by electrospinning. Using the aligned suspended PVP nanofibers array as template, aligned ultra-long silicon oxide (SiO x) nanotubes with very high aspect ratios have been prepared by plasma-enhanced chemical vapor deposition (PECVD) process. The inner diameter (20-200 nm) and wall thickness (12-90 nm) of tubes were controlled, respectively, by baking the electrospun nanofibers and by coating time without sacrificing the orientation degree and the length of arrays. The micro-PL spectrum of SiO x nanotubes shows a strong blue-green emission with a peak at about 514 nm accompanied by two shoulders around 415 and 624 nm. The blue-green emission is caused by the defects in the nanotubes.

  6. Growth of well-aligned carbon nanotubes on a large area of Co Ni co-deposited silicon oxide substrate by thermal chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Cheol Jin; Park, Jeunghee; Kang, Seung Youl; Lee, Jin Ho

    2000-06-01

    We have grown vertically well-aligned multiwalled carbon nanotubes (CNT) on a large area of cobalt-nickel (Co-Ni) co-deposited silicon oxide substrate by thermal chemical vapor deposition using C 2H 2 gas, at 950°C. The diameter of CNTs is in the range of 50-120 nm and the length is about 130 μm. The grown CNTs have a bamboo structure and closed tip with no catalytic particles inside. As the particle size of Co-Ni catalyst decreases, the vertical alignment is enhanced. The CNTs exhibits a low turn-on voltage of 0.8 V/μm with an emission current density of 0.1 μA cm -2.

  7. Silicon on insulator self-aligned transistors

    DOEpatents

    McCarthy, Anthony M.

    2003-11-18

    A method for fabricating thin-film single-crystal silicon-on-insulator (SOI) self-aligned transistors. Standard processing of silicon substrates is used to fabricate the transistors. Physical spaces, between the source and gate, and the drain and gate, introduced by etching the polysilicon gate material, are used to provide connecting implants (bridges) which allow the transistor to perform normally. After completion of the silicon substrate processing, the silicon wafer is bonded to an insulator (glass) substrate, and the silicon substrate is removed leaving the transistors on the insulator (glass) substrate. Transistors fabricated by this method may be utilized, for example, in flat panel displays, etc.

  8. Buried oxide layer in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2001-01-01

    A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

  9. Oxidation resistance of silicon ceramics

    NASA Technical Reports Server (NTRS)

    Yasutoshi, H.; Hirota, K.

    1984-01-01

    Oxidation resistance, and examples of oxidation of SiC, Si3N4 and sialon are reviewed. A description is given of the oxidation mechanism, including the oxidation product, oxidation reaction and the bubble size. The oxidation reactions are represented graphically. An assessment is made of the oxidation process, and an oxidation example of silicon ceramics is given.

  10. Silicon oxidation in fluoride solutions

    NASA Technical Reports Server (NTRS)

    Sancier, K. M.; Kapur, V.

    1980-01-01

    Silicon is produced in a NaF, Na2SiF6, and Na matrix when SiF4 is reduced by metallic sodium. Hydrogen is evolved during acid leaching to separate the silicon from the accompanying reaction products, NaF and Na2SiF6. The hydrogen evolution reaction was studied under conditions simulating leaching conditions by making suspensions of the dry silicon powder in aqueous fluoride solutions. The mechanism for the hydrogen evolution is discussed in terms of spontaneous oxidation of silicon resulting from the cooperative effects of (1) elemental sodium in the silicon that reacts with water to remove a protective silica layer, leaving clean reactive silicon, and (2) fluoride in solution that complexes with the oxidized silicon in solution and retards formation of a protective hydrous oxide gel.

  11. ASM stepper alignment through thick epitaxial silicon films

    NASA Astrophysics Data System (ADS)

    Black, Iain

    1999-04-01

    High voltage bipolar and BiCMOS processes often use thick epitaxially grown layers of silicon. These films 12-24 micrometers thick offer a considerable challenge to the alignment of subsequent process layers due to the 'wash out' and image distortion, caused to any underlying pattern, which render automatic alignment mark recognition difficult it not impossible. Historically using projection aligner technology these immediately post Epi layers have been manually aligned with future automatic alignment target defined at the first opportunity post Epi. This is not possible using ASM steppers, as these depend upon marks etched into the silicon, before first processing, to create marks, to which all subsequent layers are registered. To allow the stepper to run wafers with these Epi films a new approach was required.

  12. Nanoporous silicon oxide memory.

    PubMed

    Wang, Gunuk; Yang, Yang; Lee, Jae-Hwang; Abramova, Vera; Fei, Huilong; Ruan, Gedeng; Thomas, Edwin L; Tour, James M

    2014-08-13

    Oxide-based two-terminal resistive random access memory (RRAM) is considered one of the most promising candidates for next-generation nonvolatile memory. We introduce here a new RRAM memory structure employing a nanoporous (NP) silicon oxide (SiOx) material which enables unipolar switching through its internal vertical nanogap. Through the control of the stochastic filament formation at low voltage, the NP SiOx memory exhibited an extremely low electroforming voltage (∼ 1.6 V) and outstanding performance metrics. These include multibit storage ability (up to 9-bits), a high ON-OFF ratio (up to 10(7) A), a long high-temperature lifetime (≥ 10(4) s at 100 °C), excellent cycling endurance (≥ 10(5)), sub-50 ns switching speeds, and low power consumption (∼ 6 × 10(-5) W/bit). Also provided is the room temperature processability for versatile fabrication without any compliance current being needed during electroforming or switching operations. Taken together, these metrics in NP SiOx RRAM provide a route toward easily accessed nonvolatile memory applications. PMID:24992278

  13. Structure, defects, and strain in silicon-silicon oxide interfaces

    SciTech Connect

    Kovačević, Goran Pivac, Branko

    2014-01-28

    The structure of the interfaces between silicon and silicon-oxide is responsible for proper functioning of MOSFET devices while defects in the interface can deteriorate this function and lead to their failure. In this paper we modeled this interface and characterized its defects and strain. MD simulations were used for reconstructing interfaces into a thermodynamically stable configuration. In all modeled interfaces, defects were found in the form of three-coordinated silicon atom, five coordinated silicon atom, threefold-coordinated oxygen atom, or displaced oxygen atom. Three-coordinated oxygen atom can be created if dangling bonds on silicon are close enough. The structure and stability of three-coordinated silicon atoms (P{sub b} defect) depend on the charge as well as on the electric field across the interface. The negatively charged P{sub b} defect is the most stable one, but the electric field resulting from the interface reduces that stability. Interfaces with large differences in periodic constants of silicon and silicon oxide can be stabilized by buckling of silicon layer. The mechanical stress resulted from the interface between silicon and silicon oxide is greater in the silicon oxide layer. Ab initio modeling of clusters representing silicon and silicon oxide shows about three time larger susceptibility to strain in silicon oxide than in silicon if exposed to the same deformation.

  14. Growth of silicon bump induced by swift heavy ion at the silicon oxide-silicon interface

    SciTech Connect

    Carlotti, J.-F.; Touboul, A.D.; Ramonda, M.; Caussanel, M.; Guasch, C.; Bonnet, J.; Gasiot, J.

    2006-01-23

    Thin silicon oxide layers on silicon substrates are investigated by scanning probe microscopy before and after irradiation with 210 MeV Au+ ions. After irradiation and complete chemical etching of the silicon oxide layer, silicon bumps grown on the silicon surface are observed. It is shown that each impinging ion induces one silicon bump at the interface. This observation is consistent with the thermal spike theory. Ion energy loss is transferred to the oxide and induces local melting. Silicon-bump formation is favored when the oxide and oxide-silicon interface are silicon rich.

  15. A study of the self-aligned nanometre scale palladium clusters on silicon formation process

    NASA Astrophysics Data System (ADS)

    Gavrilov, S.; Lemeshko, S.; Shevyakov, V.; Roschin, V.

    1999-06-01

    The possibility of the self-aligned formation of Pd/Pd2Si/Si nanostructures on a single-crystal silicon substrate is shown. A porous anodic oxide film of Al was used as a mask which determines the size and shape of the nanostructures. A thin Al film was first deposited on the silicon substrate and then transformed in a nanoporous oxide by the well known anodic treatment procedure in a sulfuric acid and water solution. It is shown by atomic force microscopy that nanoscale Pd clusters with diameters equal to the size of pores in anodic Al remain at the surface of silicon substrate after cathode deposition of Pd into the pores, vacuum thermal annealing and chemical etching of the Al2O3 mask. In addition, we determine the dependencies of the size and shape of the nanoclusters on the mask formation regimes and the Pd deposition conditions.

  16. Silicon Alignment Pins: An Easy Way to Realize a Wafer-to-Wafer Alignment

    NASA Technical Reports Server (NTRS)

    Jung-Kubiak, Cecile; Reck, Theodore J.; Lin, Robert H.; Peralta, Alejandro; Gill, John J.; Lee, Choonsup; Siles, Jose; Toda, Risaku; Chattopadhyay, Goutam; Cooper, Ken B.; Mehdi, Imran; Thomas, Bertrand

    2013-01-01

    Submillimeter heterodyne instruments play a critical role in addressing fundamental questions regarding the evolution of galaxies as well as being a crucial tool in planetary science. To make these instruments compatible with small platforms, especially for the study of the outer planets, or to enable the development of multi-pixel arrays, it is essential to reduce the mass, power, and volume of the existing single-pixel heterodyne receivers. Silicon micromachining technology is naturally suited for making these submillimeter and terahertz components, where precision and accuracy are essential. Waveguide and channel cavities are etched in a silicon bulk material using deep reactive ion etching (DRIE) techniques. Power amplifiers, multiplier and mixer chips are then integrated and the silicon pieces are stacked together to form a supercompact receiver front end. By using silicon micromachined packages for these components, instrument mass can be reduced and higher levels of integration can be achieved. A method is needed to assemble accurately these silicon pieces together, and a technique was developed here using etched pockets and silicon pins to align two wafers together.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

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

    PubMed

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

    2014-08-15

    Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices. PMID:25053702

  19. Silicon oxide films grown in microwave discharge

    NASA Technical Reports Server (NTRS)

    Kraitchman, J.

    1968-01-01

    Silicon oxide films thicker than 1000 angstrom are produced in the dense plasma of a microwave discharge. The oxide growth is characterized by a rate limiting diffusion process modified by sputtering effects produced by the discharge. Silicon is rapidly oxidized at temperatures estimated to be 500 degrees C or lower.

  20. Method of forming buried oxide layers in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2000-01-01

    A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

  1. Roads to ultrathin silicon oxides

    NASA Astrophysics Data System (ADS)

    Morgen, P.; Bahari, A.; Robenhagen, U.; Andersen, J. F.; Hansen, J.-K.; Pedersen, K.; Rao, M. G.; Li, Z. S.

    2005-01-01

    Ultrathin gate dielectrics for complementary metal-oxide-semiconductor (CMOS) devices, with suitable structural and electrical properties, are crucial for the further development of silicon based microelectronics. The effective (SiO2-equivalent) thickness of 10 A˚ or below needed in the next generations of CMOS devices has been found too low to prevent tunneling, and leakage, with current processes for SiO2 based gate insulators. Before abandoning SiO2 completely, however, there are good reasons to look for improved procedures or alternative processes to grow or form ultrathin SiO2 films on silicon, and possible improvements through the controlled addition of nitrogen. The present article initially describes an attempt to grow ultrathin oxides in a furnace, but this was limited to 50-A˚-thick layers or above. It then unveils some particularly simple, easily controlled, low-thermal budget, low-pressure based processes for thinner oxide layers, which have not been met earlier. These later processes are all done in an ultrahigh vacuum (UHV) based environment, starting from a clean and perfectly ordered Si surface. Thus we formed the thinnest possible (~4 A˚) uniformly covering oxide layers on the Si(111) and Si(001) surfaces. They are made very simply from cycles of oxygen adsorption at room temperature and short anneals, and are self-saturating at this thickness. Following these processes we explored isothermal methods in UHV at low temperatures and pressures. Such processes, at low pressures, were found to lead to a universal, self-limiting growth of an approximately 7-A˚-thick oxide at a range of temperatures between 300 and 700 °C. Further, up to about 10 A˚ oxides are grown in a series of steps, in each of which a layer of freshly deposited Cs on top of already grown oxide is retaining oxygen on this otherwise passivated surface. The Cs layer also catalyzes oxidation during a subsequent rapid annealing step. Higher thicknesses (up to 50 A˚) are obtained by

  2. Light trapping in horizontally aligned silicon microwire solar cells.

    PubMed

    Martinsen, Fredrik A; Smeltzer, Benjamin K; Ballato, John; Hawkins, Thomas; Jones, Max; Gibson, Ursula J

    2015-11-30

    In this study, we demonstrate a solar cell design based on horizontally aligned microwires fabricated from 99.98% pure silicon via the molten core fiber drawing method. A similar structure consisting of 50 μm diameter close packed wires (≈ 0.97 packing density) on a Lambertian white back-reflector showed 86 % absorption for incident light of wavelengths up to 850 nm. An array with a packing fraction of 0.35 showed an absorption of 58 % over the same range, demonstrating the potential for effective light trapping. Prototype solar cells were fabricated to demonstrate the concept. Horizontal wire cells offer several advantages as they can be flexible, and partially transparent, and absorb light efficiently over a wide range of incident angles. PMID:26698794

  3. Oxide-assisted growth of silicon nanowires by carbothermal evaporation

    NASA Astrophysics Data System (ADS)

    Hutagalung, Sabar D.; Yaacob, Khatijah A.; Aziz, Azma F. Abdul

    2007-11-01

    Silicon nanowires (SiNWs) have successfully been synthesized by carbothermal evaporation method. By ramping-up the furnace system at 20 °C min -1 to 1100 °C for 6 h, the vertically aligned coexist with crooked SiNWs were achieved on the silicon substrate located at 12 cm from source material. The processing parameters such as temperature, heating rate, duration, substrate position and location are very important to produce SiNWs. Morphology and chemical composition of deposited products were investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray analysis (EDX). The existence of small sphere silicon oxide capped nanowires suggested that the formation of SiNWs was governed by oxide-assisted growth (OAG) mechanism.

  4. A Ferroelectric Oxide Made Directly on Silicon

    SciTech Connect

    Warusawithana, M.; Cen, C; Sleasman, C; Woicik, J; Li, Y; Fitting Kourkoutis, L; Klug, J; Li, H; Ryan, P; et. al.

    2009-01-01

    Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, have undergone four decades of staggering technological advancement. With fundamental limits to this technology close at hand, alternatives to silicon dioxide are being pursued to enable new functionality and device architectures. We achieved ferroelectric functionality in intimate contact with silicon by growing coherently strained strontium titanate (SrTiO{sub 3}) films via oxide molecular beam epitaxy in direct contact with silicon, with no interfacial silicon dioxide. We observed ferroelectricity in these ultrathin SrTiO{sub 3} layers by means of piezoresponse force microscopy. Stable ferroelectric nanodomains created in SrTiO{sub 3} were observed at temperatures as high as 400 kelvin.

  5. Novel synthetic methodology for controlling the orientation of zinc oxide nanowires grown on silicon oxide substrates.

    PubMed

    Cho, Jinhyun; Salleh, Najah; Blanco, Carlos; Yang, Sungwoo; Lee, Chul-Jin; Kim, Young-Woo; Kim, Jungsang; Liu, Jie

    2014-04-01

    This study presents a simple method to reproducibly obtain well-aligned vertical ZnO nanowire arrays on silicon oxide (SiOx) substrates using seed crystals made from a mixture of ammonium hydroxide (NH4OH) and zinc acetate (Zn(O2CCH3)2) solution. In comparison, high levels of OH(-) concentration obtained using NaOH or KOH solutions lead to incorporation of Na or K atoms into the seed crystals, destroying the c-axis alignment of the seeds and resulting in the growth of misaligned nanowires. The use of NH4OH eliminates the metallic impurities and ensures aligned nanowire growth in a wide range of OH(-) concentrations in the seed solution. The difference of crystalline orientations between NH4OH- and NaOH-based seeds is directly observed by lattice-resolved images and electron diffraction patterns using a transmission electron microscope (TEM). This study obviously suggests that metallic impurities incorporated into the ZnO nanocrystal seeds are one of the factors that generates the misaligned ZnO nanowires. This method also enables the use of silicon oxide substrates for the growth of vertically aligned nanowires, making ZnO nanostructures compatible with widely used silicon fabrication technology. PMID:24584438

  6. Single crystal functional oxides on silicon

    PubMed Central

    Bakaul, Saidur Rahman; Serrao, Claudy Rayan; Lee, Michelle; Yeung, Chun Wing; Sarker, Asis; Hsu, Shang-Lin; Yadav, Ajay Kumar; Dedon, Liv; You, Long; Khan, Asif Islam; Clarkson, James David; Hu, Chenming; Ramesh, Ramamoorthy; Salahuddin, Sayeef

    2016-01-01

    Single-crystalline thin films of complex oxides show a rich variety of functional properties such as ferroelectricity, piezoelectricity, ferro and antiferromagnetism and so on that have the potential for completely new electronic applications. Direct synthesis of such oxides on silicon remains challenging because of the fundamental crystal chemistry and mechanical incompatibility of dissimilar interfaces. Here we report integration of thin (down to one unit cell) single crystalline, complex oxide films onto silicon substrates, by epitaxial transfer at room temperature. In a field-effect transistor using a transferred lead zirconate titanate layer as the gate insulator, we demonstrate direct reversible control of the semiconductor channel charge with polarization state. These results represent the realization of long pursued but yet to be demonstrated single-crystal functional oxides on-demand on silicon. PMID:26853112

  7. Liquid crystallinity driven highly aligned large graphene oxide composites

    SciTech Connect

    Lee, Kyung Eun; Oh, Jung Jae; Yun, Taeyeong; Kim, Sang Ouk

    2015-04-15

    Graphene is an emerging graphitic carbon materials, consisting of sp{sup 2} hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites.

  8. Oxide driven strength evolution of silicon surfaces

    SciTech Connect

    Grutzik, Scott J.; Zehnder, Alan T.; Milosevic, Erik; Boyce, Brad L.

    2015-11-21

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  9. Oxide driven strength evolution of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Grutzik, Scott J.; Milosevic, Erik; Boyce, Brad L.; Zehnder, Alan T.

    2015-11-01

    Previous experiments have shown a link between oxidation and strength changes in single crystal silicon nanostructures but provided no clues as to the mechanisms leading to this relationship. Using atomic force microscope-based fracture strength experiments, molecular dynamics modeling, and measurement of oxide development with angle resolved x-ray spectroscopy we study the evolution of strength of silicon (111) surfaces as they oxidize and with fully developed oxide layers. We find that strength drops with partial oxidation but recovers when a fully developed oxide is formed and that surfaces intentionally oxidized from the start maintain their high initial strengths. MD simulations show that strength decreases with the height of atomic layer steps on the surface. These results are corroborated by a completely separate line of testing using micro-scale, polysilicon devices, and the slack chain method in which strength recovers over a long period of exposure to the atmosphere. Combining our results with insights from prior experiments we conclude that previously described strength decrease is a result of oxidation induced roughening of an initially flat silicon (1 1 1) surface and that this effect is transient, a result consistent with the observation that surfaces flatten upon full oxidation.

  10. Optimizing Silicon Oxide Embedded Silicon Nanocrystal Inter-particle Distances.

    PubMed

    van Sebille, Martijn; Allebrandi, Jort; Quik, Jim; van Swaaij, René A C M M; Tichelaar, Frans D; Zeman, Miro

    2016-12-01

    We demonstrate an analytical method to optimize the stoichiometry and thickness of multilayer silicon oxide films in order to achieve the highest density of non-touching and closely spaced silicon nanocrystals after annealing. The probability of a nanocrystal nearest-neighbor distance within a limited range is calculated using the stoichiometry of the as-deposited film and the crystallinity of the annealed film as input parameters. Multiplying this probability with the nanocrystal density results in the density of non-touching and closely spaced silicon nanocrystals. This method can be used to estimate the best as-deposited stoichiometry in order to achieve optimal nanocrystal density and spacing after a subsequent annealing step. PMID:27492439

  11. Optimizing Silicon Oxide Embedded Silicon Nanocrystal Inter-particle Distances

    NASA Astrophysics Data System (ADS)

    van Sebille, Martijn; Allebrandi, Jort; Quik, Jim; van Swaaij, René A. C. M. M.; Tichelaar, Frans D.; Zeman, Miro

    2016-08-01

    We demonstrate an analytical method to optimize the stoichiometry and thickness of multilayer silicon oxide films in order to achieve the highest density of non-touching and closely spaced silicon nanocrystals after annealing. The probability of a nanocrystal nearest-neighbor distance within a limited range is calculated using the stoichiometry of the as-deposited film and the crystallinity of the annealed film as input parameters. Multiplying this probability with the nanocrystal density results in the density of non-touching and closely spaced silicon nanocrystals. This method can be used to estimate the best as-deposited stoichiometry in order to achieve optimal nanocrystal density and spacing after a subsequent annealing step.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  13. Liquid crystallinity driven highly aligned large graphene oxide composites

    NASA Astrophysics Data System (ADS)

    Lee, Kyung Eun; Oh, Jung Jae; Yun, Taeyeong; Kim, Sang Ouk

    2015-04-01

    Graphene is an emerging graphitic carbon materials, consisting of sp2 hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites.

  14. Silicon Carbide Nanotube Oxidation at High Temperatures

    NASA Technical Reports Server (NTRS)

    Ahlborg, Nadia; Zhu, Dongming

    2012-01-01

    Silicon Carbide Nanotubes (SiCNTs) have high mechanical strength and also have many potential functional applications. In this study, SiCNTs were investigated for use in strengthening high temperature silicate and oxide materials for high performance ceramic nanocomposites and environmental barrier coating bond coats. The high · temperature oxidation behavior of the nanotubes was of particular interest. The SiCNTs were synthesized by a direct reactive conversion process of multiwall carbon nanotubes and silicon at high temperature. Thermogravimetric analysis (TGA) was used to study the oxidation kinetics of SiCNTs at temperatures ranging from 800degC to1300degC. The specific oxidation mechanisms were also investigated.

  15. Functionalised silicon oxide nanoparticles for fingermark detection.

    PubMed

    Moret, Sébastien; Bécue, Andy; Champod, Christophe

    2016-02-01

    Over the past decade, the use of nanotechnology for fingermark detection has been attracting a lot of attention. A substantial number of nanoparticle types has thus been studied and applied with varying success. However, despite all efforts, few publications present clear supporting evidence of their superiority over standard and commonly used techniques. This paper focuses on a rarely studied type of nanoparticles that regroups all desired properties for effective fingermark detection: silicon oxide. These nanoparticles offer optical and surface properties that can be tuned to provide optimal detection. This study explores their potential as a new method for fingermark detection. Detection conditions, outer functionalisations and optical properties were optimised and a first evaluation of the technique is presented. Dye-doped silicon oxide nanoparticles were assessed against a one-step luminescent cyanoacrylate. Both techniques were compared on natural fingermarks from three donors collected on four different non-porous substrates. On average, the two techniques performed similarly but silicon oxide detected marks with a better homogeneity and was less affected by donor inter-variability. The technique remains to be further optimised and yet silicon oxide nanoparticles already show great promises for effective fingermark detection. PMID:26717406

  16. Photoluminescence mechanism model for oxidized porous silicon and nanoscale-silicon-particle-embedded silicon oxide

    NASA Astrophysics Data System (ADS)

    Qin, G. G.; Li, Y. J.

    2003-08-01

    There is much debate about the photoluminescence (PL) mechanisms of the nanoscale Si/Si oxide systems containing oxidized porous silicon and a nanoscale-Si-particle (NSP)—embedded Si oxide deposited by chemical vapor deposition, sputtering, or Si-ion implanting into Si oxide. In this paper, we suggest that two competitive processes, namely, the quantum confinement (QC) process and the quantum confinement-luminescence center (QCLC) process, take place in the PL. The photoexcitation occurs in the NSPs for both of the processes, while the photoemission occurs either in the NSPs for the QC process or in the luminescence centers (LCs) in Si oxide adjacent to the NSPs for the QCLC process. The rates of the two processes are compared quantitatively. Which process plays the major role in PL is determined by the capture cross section, the luminescence efficiency, and the density of the LCs, and the sizes of the NSPs. For a nanoscale Si/Si oxide system with the LCs having certain capture cross-section and luminescence efficiency, the higher the LC density and the larger the sizes of NSPs, the more beneficial for the QCLC process to surpass the QC process, and vice versa. For certain LC parameters, there is a critical most probable size for the NSPs. When the most probable size of the NSPs is larger than the critical one, the QCLC process dominates the PL, and when the most probable size of the NSPs is smaller than the critical one, the QC process dominates the PL. When the most probable size of the NSPs is close to the critical one, both the QC and QCLC processes should be taken into account. We have used this model to discuss PL experimental results reported for some nanoscale Si/Si oxide systems.

  17. Tailoring Silicon Oxycarbide Glasses for Oxidative Stability

    NASA Technical Reports Server (NTRS)

    Hurwitz, F. I.; Meador, M. A. B.

    1997-01-01

    Blackglas(Trademark) polysiloxane systems produce silicon oxycarbide glasses by pyrolysis in inert atmosphere. The silicon oxycarbides evidence oxidative degradation that limits their lifetime as composite matrices. The present study characterizes bonding rearrangements in the oxycarbide network accompanying increases in pyrolysis temperature. It also addresses the changes in susceptibility to oxidation due to variations in the distribution of Si bonded species obtained under different processing conditions. The study is carried out using Si-29 nuclear magnetic resonance (NMR) spectroscopy and a design of experiments approach to model the oxidation behavior. The NMR results are compared with those obtained by thermogravimetric analysis (TGA). Samples pyrolyzed under inert conditions are compared to those pyrolyzed in reactive ammonia environments.

  18. Fabricating vertically aligned sub-20 nm Si nanowire arrays by chemical etching and thermal oxidation

    NASA Astrophysics Data System (ADS)

    Li, Luping; Fang, Yin; Xu, Cheng; Zhao, Yang; Zang, Nanzhi; Jiang, Peng; Ziegler, Kirk J.

    2016-04-01

    Silicon nanowires (SiNWs) are appealing building blocks in various applications, including photovoltaics, photonics, and sensors. Fabricating SiNW arrays with diameters <100 nm remains challenging through conventional top-down approaches. In this work, chemical etching and thermal oxidation are combined to fabricate vertically aligned, sub-20 nm SiNW arrays. Defect-free SiNWs with diameters between 95 and 200 nm are first fabricated by nanosphere (NS) lithography and chemical etching. The key aspects for defect-free SiNW fabrication are identified as: (1) achieving a high etching selectivity during NS size reduction; (2) retaining the circular NS shape with smooth sidewalls; and (3) using a directional metal deposition technique. SiNWs with identical spacing but variable diameters are demonstrated by changing the reactive ion etching power. The diameter of the SiNWs is reduced by thermal oxidation, where self-limiting oxidation is encountered after oxidizing the SiNWs at 950 °C for 1 h. A second oxidation is performed to achieve vertically aligned, sub-20 nm SiNW arrays. Si/SiO2 core/shell NWs are obtained before removing the oxidized shell. HRTEM imaging shows that the SiNWs have excellent crystallinity.

  19. Fabricating vertically aligned sub-20 nm Si nanowire arrays by chemical etching and thermal oxidation.

    PubMed

    Li, Luping; Fang, Yin; Xu, Cheng; Zhao, Yang; Zang, Nanzhi; Jiang, Peng; Ziegler, Kirk J

    2016-04-22

    Silicon nanowires (SiNWs) are appealing building blocks in various applications, including photovoltaics, photonics, and sensors. Fabricating SiNW arrays with diameters <100 nm remains challenging through conventional top-down approaches. In this work, chemical etching and thermal oxidation are combined to fabricate vertically aligned, sub-20 nm SiNW arrays. Defect-free SiNWs with diameters between 95 and 200 nm are first fabricated by nanosphere (NS) lithography and chemical etching. The key aspects for defect-free SiNW fabrication are identified as: (1) achieving a high etching selectivity during NS size reduction; (2) retaining the circular NS shape with smooth sidewalls; and (3) using a directional metal deposition technique. SiNWs with identical spacing but variable diameters are demonstrated by changing the reactive ion etching power. The diameter of the SiNWs is reduced by thermal oxidation, where self-limiting oxidation is encountered after oxidizing the SiNWs at 950 °C for 1 h. A second oxidation is performed to achieve vertically aligned, sub-20 nm SiNW arrays. Si/SiO2 core/shell NWs are obtained before removing the oxidized shell. HRTEM imaging shows that the SiNWs have excellent crystallinity. PMID:26953775

  20. Evolution of the Band Alignment at Polar Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Burton, J. D.; Tsymbal, Evgeny

    2011-03-01

    The next generation of electronic devices and systems are envisioned to exploit the multifunctional properties of complex oxide interfaces. Fundamental to this endeavor is an understanding of the electronic band alignment across such interfaces. Engineering this band alignment in all-oxide systems by properly preparing the interfaces is highly desirable. Here we explore an all-oxide metal-insulator interface between, SrTi O3 (STO), and La 1-xAx Mn O3 (LAMO), where A is a divalent cation. The doping level of the manganite, x , offers a parameter which can be varied to engineer the band alignment. We use first-principles density-functional calculations to determine the evolution of the band alignment at La 0.7A0.3 Mn O3 | La 1-xAx O | Ti O2 | SrTi O3 (001) heterointerfaces as the interfacial composition, La 1-xAx , is varied. The position of the valence band maximum (VBM) with respect to the Fermi level increases linearly with interfacial composition x due to the linear dependence of the screened electrostatic interface dipole on the interfacial ionic charge. The importance of the polar nature of LAMO and its background dielectric properties will be discussed. Our results are agreement with recent experimental data reported by Hikita et al.

  1. Silicon carbide-silicon composite having improved oxidation resistance and method of making

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    1999-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  2. Method of making silicon carbide-silicon composite having improved oxidation resistance

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    2002-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  3. Alignment of the CMS silicon strip tracker during stand-alone commissioning

    SciTech Connect

    Adam, W.; et al.

    2009-07-01

    The results of the CMS tracker alignment analysis are presented using the data from cosmic tracks, optical survey information, and the laser alignment system at the Tracker Integration Facility at CERN. During several months of operation in the spring and summer of 2007, about five million cosmic track events were collected with a partially active CMS Tracker. This allowed us to perform first alignment of the active silicon modules with the cosmic tracks using three different statistical approaches; validate the survey and laser alignment system performance; and test the stability of Tracker structures under various stresses and temperatures ranging from +15C to -15C. Comparison with simulation shows that the achieved alignment precision in the barrel part of the tracker leads to residual distributions similar to those obtained with a random misalignment of 50 (80) microns in the outer (inner) part of the barrel.

  4. Silica substrate or portion formed from oxidation of monocrystalline silicon

    DOEpatents

    Matzke, Carolyn M.; Rieger, Dennis J.; Ellis, Robert V.

    2003-07-15

    A method is disclosed for forming an inclusion-free silica substrate using a monocrystalline silicon substrate as the starting material and oxidizing the silicon substrate to convert it entirely to silica. The oxidation process is performed from both major surfaces of the silicon substrate using a conventional high-pressure oxidation system. The resulting product is an amorphous silica substrate which is expected to have superior etching characteristics for microfabrication than conventional fused silica substrates. The present invention can also be used to convert only a portion of a monocrystalline silicon substrate to silica by masking the silicon substrate and locally thinning a portion the silicon substrate prior to converting the silicon portion entirely to silica. In this case, the silica formed by oxidizing the thinned portion of the silicon substrate can be used, for example, as a window to provide optical access through the silicon substrate.

  5. A Simple Nanoscale Interface Directs Alignment of a Confluent Cell Layer on Oxide and Polymer Surfaces

    PubMed Central

    Donnelly, Patrick E.; Jones, Casey M.; Bandini, Stephen B.; Singh, Shivani; Schwartz, Jeffrey; Schwarzbauer, Jean E.

    2013-01-01

    Templating of cell spreading and proliferation is described that yields confluent layers of cells aligned across an entire two-dimensional surface. The template is a reactive, two-component interface that is synthesized in three steps in nanometer thick, micron-scaled patterns on silicon and on several biomaterial polymers. In this method, a volatile zirconium alkoxide complex is first deposited at reduced pressure onto a surface pattern that is prepared by photolithography; the substrate is then heated to thermolyze the organic ligands to form surface-bound zirconium oxide patterns. The thickness of this oxide layer ranges from 10 to 70 nanometers, which is controlled by alkoxide complex deposition time. The oxide layer is treated with 1,4-butanediphosphonic acid to give a monolayer pattern whose composition and spatial conformity to the photolithographic mask are determined spectroscopically. NIH 3T3 fibroblasts and human bone marrow-derived mesenchymal stem cells attach and spread in alignment with the pattern without constraint by physical means or by arrays of cytophilic and cytophobic molecules. Cell alignment with the pattern is maintained as cells grow to form a confluent monolayer across the entire substrate surface. PMID:23936630

  6. Nanofabrication of arrays of silicon field emitters with vertical silicon nanowire current limiters and self-aligned gates

    NASA Astrophysics Data System (ADS)

    Guerrera, S. A.; Akinwande, A. I.

    2016-07-01

    We developed a fabrication process for embedding a dense array (108 cm‑2) of high-aspect-ratio silicon nanowires (200 nm diameter and 10 μm tall) in a dielectric matrix and then structured/exposed the tips of the nanowires to form self-aligned gate field emitter arrays using chemical mechanical polishing (CMP). Using this structure, we demonstrated a high current density (100 A cm‑2), uniform, and long lifetime (>100 h) silicon field emitter array architecture in which the current emitted by each tip is regulated by the silicon nanowire current limiter connected in series with the tip. Using the current voltage characteristics and with the aid of numerical device models, we estimated the tip radius of our field emission arrays to be ≈4.8 nm, as consistent with the tip radius measured using a scanning electron microscope (SEM).

  7. Nanofabrication of arrays of silicon field emitters with vertical silicon nanowire current limiters and self-aligned gates.

    PubMed

    Guerrera, S A; Akinwande, A I

    2016-07-22

    We developed a fabrication process for embedding a dense array (10(8) cm(-2)) of high-aspect-ratio silicon nanowires (200 nm diameter and 10 μm tall) in a dielectric matrix and then structured/exposed the tips of the nanowires to form self-aligned gate field emitter arrays using chemical mechanical polishing (CMP). Using this structure, we demonstrated a high current density (100 A cm(-2)), uniform, and long lifetime (>100 h) silicon field emitter array architecture in which the current emitted by each tip is regulated by the silicon nanowire current limiter connected in series with the tip. Using the current voltage characteristics and with the aid of numerical device models, we estimated the tip radius of our field emission arrays to be ≈4.8 nm, as consistent with the tip radius measured using a scanning electron microscope (SEM). PMID:27292120

  8. Complete magnesiothermic reduction reaction of vertically aligned mesoporous silica channels to form pure silicon nanoparticles

    PubMed Central

    Kim, Kyoung Hwan; Lee, Dong Jin; Cho, Kyeong Min; Kim, Seon Joon; Park, Jung-Ki; Jung, Hee-Tae

    2015-01-01

    Owing to its simplicity and low temperature conditions, magnesiothermic reduction of silica is one of the most powerful methods for producing silicon nanostructures. However, incomplete reduction takes place in this process leaving unconverted silica under the silicon layer. This phenomenon limits the use of this method for the rational design of silicon structures. In this effort, a technique that enables complete magnesiothermic reduction of silica to form silicon has been developed. The procedure involves magnesium promoted reduction of vertically oriented mesoporous silica channels on reduced graphene oxides (rGO) sheets. The mesopores play a significant role in effectively enabling magnesium gas to interact with silica through a large number of reaction sites. Utilizing this approach, highly uniform, ca. 10 nm sized silicon nanoparticles are generated without contamination by unreacted silica. The new method for complete magnesiothermic reduction of mesoporous silica approach provides a foundation for the rational design of silicon structures. PMID:25757800

  9. Complete magnesiothermic reduction reaction of vertically aligned mesoporous silica channels to form pure silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung Hwan; Lee, Dong Jin; Cho, Kyeong Min; Kim, Seon Joon; Park, Jung-Ki; Jung, Hee-Tae

    2015-03-01

    Owing to its simplicity and low temperature conditions, magnesiothermic reduction of silica is one of the most powerful methods for producing silicon nanostructures. However, incomplete reduction takes place in this process leaving unconverted silica under the silicon layer. This phenomenon limits the use of this method for the rational design of silicon structures. In this effort, a technique that enables complete magnesiothermic reduction of silica to form silicon has been developed. The procedure involves magnesium promoted reduction of vertically oriented mesoporous silica channels on reduced graphene oxides (rGO) sheets. The mesopores play a significant role in effectively enabling magnesium gas to interact with silica through a large number of reaction sites. Utilizing this approach, highly uniform, ca. 10 nm sized silicon nanoparticles are generated without contamination by unreacted silica. The new method for complete magnesiothermic reduction of mesoporous silica approach provides a foundation for the rational design of silicon structures.

  10. Method for making alignment-enhancing feed-through conductors for stackable silicon-on-sapphire

    NASA Technical Reports Server (NTRS)

    Anthony, Thomas R. (Inventor)

    1985-01-01

    Alignment-enhancing electrically conductive feed-through paths are provided for the high-speed low-loss transfer of electrical signals between integrated circuits of a plurality of silicon-on-sapphire bodies arrayed in a stack. The alignment-enhancing feed-throughs are made by a process of this invention involving the drilling of holes through the body, double-sided sputtering, electroplating, and the filling of the holes with solder by capillary action. The alignment-enhancing feed-throughs are activated by forming a stack of wafers and remelting the solder whereupon the wafers, and the feed-through paths, are pulled into alignment by surface tension forces.

  11. Graphene-Assisted Chemical Etching of Silicon Using Anodic Aluminum Oxides as Patterning Templates.

    PubMed

    Kim, Jungkil; Lee, Dae Hun; Kim, Ju Hwan; Choi, Suk-Ho

    2015-11-01

    We first report graphene-assisted chemical etching (GaCE) of silicon by using patterned graphene as an etching catalyst. Chemical-vapor-deposition-grown graphene transferred on a silicon substrate is patterned to a mesh with nanohole arrays by oxygen plasma etching using an anodic- aluminum-oxide etching mask. The prepared graphene mesh/silicon is immersed in a mixture solution of hydrofluoric acid and hydro peroxide with various molecular fractions at optimized temperatures. The silicon underneath graphene mesh is then selectively etched to form aligned nanopillar arrays. The morphology of the nanostructured silicon can be controlled to be smooth or porous depending on the etching conditions. The experimental results are systematically discussed based on possible mechanisms for GaCE of Si. PMID:26473800

  12. Mg-catalyzed autoclave synthesis of aligned silicon carbide nanostructures.

    PubMed

    Xi, Guangcheng; Liu, Yankuan; Liu, Xiaoyan; Wang, Xiaoqing; Qian, Yitai

    2006-07-27

    In this article, a novel magnesium-catalyzed co-reduction route was developed for the large-scale synthesis of aligned beta-SiC one-dimensional (1D) nanostructures at relative lower temperature (600 degrees C). By carefully controlling the reagent concentrations, we could synthesize beta-SiC rodlike and needlelike nanostructures. The possible growth mechanism of the as-synthesized beta-SiC 1D nanostructures has been investigated. The structure and morphology of the as-synthesized beta-SiC nanostructures are characterized using X-ray diffraction, Fourier transform infrared absorption, and scanning and transmission electron microscopes. Raman and photoluminescence properties are also investigated at room temperature. The as-synthesized beta-SiC nanostructures exhibit strong shape-dependent field emission properties. Corresponding to their shapes, the as-synthesized nanorods and nanoneedles display the turn-on fields of 12, 8.4, and 1.8 V/microm, respectively. PMID:16854116

  13. Microwave Characterization of a Field Effect Transistor with Dielectrophoretically-Aligned Single Silicon Nanowire

    NASA Astrophysics Data System (ADS)

    Kang, Myung-Gil; Ahn, Jae-Hyun; Lee, Jongwoon; Hwang, Dong-Hoon; Kim, Hee-Tae; Rieh, Jae-Seong; Whang, Dongmok; Son, Maeng-Ho; Ahn, Doyeol; Yu, Yun-Seop; Hwang, Sung-Woo

    2010-06-01

    Microwave (MW) characteristics of a field effect transistor (FET) incorporating a single silicon nanowire (SiNW) were obtained from S-parameter measurements in the frequency range of 0.05 to 20 GHz. The single SiNW was aligned, using the alternating current (ac) dielectrophoresis alignment method, between the drain and source electrode forming a coplanar waveguide (CPW) structure. Analysis of the FET was performed using equivalent circuit modeling by advanced device system (ADS) simulation. By fitting the measured data with the simulation results, the parameters of the single SiNW FET were obtained and the cutoff frequency was derived.

  14. Fouling Study of Silicon Oxide Pores Exposed to Tap Water

    SciTech Connect

    Nilsson, J.; Bourcier, W.L.; Lee, J.R.I.; Letant, S.E.; /LLNL, Livermore

    2007-07-12

    We report on the fouling of Focused Ion Beam (FIB)-fabricated silicon oxide nanopores after exposure to tap water for two weeks. Pore clogging was monitored by Scanning Electron Microscopy (SEM) on both bare silicon oxide and chemically functionalized nanopores. While fouling occurred on hydrophilic silicon oxide pore walls, the hydrophobic nature of alkane chains prevented clogging on the chemically functionalized pore walls. These results have implications for nanopore sensing platform design.

  15. Phonon processes in vertically aligned silicon nanowire arrays produced by low-cost all-solution galvanic displacement method

    NASA Astrophysics Data System (ADS)

    Banerjee, Debika; Trudeau, Charles; Gerlein, Luis Felipe; Cloutier, Sylvain G.

    2016-03-01

    The nanoscale engineering of silicon can significantly change its bulk optoelectronic properties to make it more favorable for device integration. Phonon process engineering is one way to enhance inter-band transitions in silicon's indirect band structure alignment. This paper demonstrates phonon localization at the tip of silicon nanowires fabricated by galvanic displacement using wet electroless chemical etching of a bulk silicon wafer. High-resolution Raman micro-spectroscopy reveals that such arrayed structures of silicon nanowires display phonon localization behaviors, which could help their integration into the future generations of nano-engineered silicon nanowire-based devices such as photodetectors and solar cells.

  16. Evaluation of transition metal oxide as carrier-selective contacts for silicon heterojunction solar cells

    SciTech Connect

    Ding, L.; Boccard, Matthieu; Holman, Zachary; Bertoni, M.

    2015-04-06

    "Reducing light absorption in the non-active solar cell layers, while enabling the extraction of the photogenerated minority carriers at quasi-Fermi levels are two key factors to improve current generation and voltage, and therefore efficiency of silicon heterojunction solar devices. To address these two critical aspects, transition metal oxide materials have been proposed as alternative to the n- and p-type amorphous silicon used as electron and hole selective contacts, respectively. Indeed, transition metal oxides such as molybdenum oxide, titanium oxide, nickel oxide or tungsten oxide combine a wide band gap typically over 3 eV with a band structure and theoretical band alignment with silicon that results in high transparency to the solar spectrum and in selectivity for the transport of only one carrier type. Improving carrier extraction or injection using transition metal oxide has been a topic of investigation in the field of organic solar cells and organic LEDs; from these pioneering works a lot of knowledge has been gained on materials properties, ways to control these during synthesis and deposition, and their impact on device performance. Recently, the transfer of some of this knowledge to silicon solar cells and the successful application of some metal oxide to contact heterojunction devices have gained much attention. In this contribution, we investigate the suitability of various transition metal oxide films (molybdenum oxide, titanium oxide, and tungsten oxide) deposited either by thermal evaporation or sputtering as transparent hole or electron selective transport layer for silicon solar cells. In addition to systematically characterize their optical and structural properties, we use photoemission spectroscopy to relate compound stoichiometry to band structure and characterize band alignment to silicon. The direct silicon/metal oxide interface is further analyzed by quasi-steady state photoconductance decay method to assess the quality of surface

  17. The Active Oxidation of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers, Dwight L.

    2009-01-01

    The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive

  18. Ultrafast laser functionalized rare phased gold-silicon/silicon oxide nanostructured hybrid biomaterials.

    PubMed

    Premnath, P; Tan, B; Venkatakrishnan, K

    2015-12-01

    We introduce a hybrid nanostructured biomaterial that is a combination of rare phases of immiscible gold and silicon oxide, functionalized via ultrafast laser synthesis. For the first time, we show cancer controlling properties of rare phases of gold silicides, which include Au7Si, Au5Si, Au0.7Si2.3 and Au8Si2. Conventionally, pure forms of gold and silicon/silicon oxide are extensively employed in targeted therapy and drug delivery systems due to their unique properties. While silicon and silicon oxide nanoparticles have shown biocompatibility, gold nanoparticles show conflicting results based on their size and material properties. Several studies have shown that gold and silicon combinations produce cell controlling properties, however, these studies were not able to produce a homogenous combination of gold and silicon, owing to its immiscibility. A homogenous combination of gold and silicon may potentially enable properties that have not previously been reported. We describe rare phased gold-silicon oxide nanostructured hybrid biomaterials and its unique cancer controlling properties, owing to material properties, concentration, size and density. The gold-silicon oxide nanostructured hybrid is composed of individual gold-silicon oxide nanoparticles in various concentrations of gold and silicon, some nanoparticles possess a gold-core and silicon-shell like structure. The individual nanoparticles are bonded together forming a three dimensional nanostructured hybrid. The interaction of the nanostructured hybrids with cervical cancer cells showed a 96% reduction in 24h. This engineered nanostructured hybrid biomaterial presents significant potential due to the combination of immiscible gold and silicon oxide in varying phases and can potentially satiate the current vacuum in cancer therapy. PMID:26539809

  19. Guided photoluminescence study of Nd-doped silicon rich silicon oxide and silicon rich silicon nitride waveguides

    NASA Astrophysics Data System (ADS)

    Pirasteh, Parastesh; Charrier, Joël; Dumeige, Yannick; Doualan, Jean-Louis; Camy, Patrice; Debieu, Olivier; Liang, Chuan-hui; Khomenkova, Larysa; Lemaitre, Jonathan; Boucher, Yann G.; Gourbilleau, Fabrice

    2013-07-01

    Planar waveguides made of Nd3+-doped silicon rich silicon oxide (SRSO) and silicon rich silicon nitride (SRSN) have been fabricated by reactive magnetron sputtering and characterized with special emphasis on the comparison of the guided photoluminescence (PL) properties of these two matrices. Guided fluorescence excited by top surface pumping at 488 nm on planar waveguides was measured as a function of the distance between the excitation area and the output of the waveguide, as well as a function of the pump power density. The PL intensity increased linearly with pump power without any saturation even at high power. The linear intensity increase of the Nd3+ guided PL under a non-resonant excitation (488 nm) confirms the efficient coupling between either Si-np and rare-earth ions for SRSO or radiative defects and rare earth ions for SRSN. The guided fluorescences at 945 and 1100 nm were observed until 4 mm and 8 mm of the output of the waveguide for Nd3+ doped SRSO and SRSN waveguides, respectively. The guided fluorescence decays of Nd3+-doped-SRSO and -SRSN planar waveguides have been measured and found equal to 97 μs ±7 and 5 μs ± 2, respectively. These results show notably that the Nd3+-doped silicon rich silicon oxide is a very promising candidate on the way to achieve a laser cavity at 1.06 μm.

  20. Infrared Dielectric Properties of Low-Stress Silicon Oxide

    NASA Technical Reports Server (NTRS)

    Cataldo, Giuseppe; Wollack, Edward J.; Brown, Ari D.; Miller, Kevin H.

    2016-01-01

    Silicon oxide thin films play an important role in the realization of optical coatings and high-performance electrical circuits. Estimates of the dielectric function in the far- and mid-infrared regime are derived from the observed transmittance spectrum for a commonly employed low-stress silicon oxide formulation. The experimental, modeling, and numerical methods used to extract the dielectric function are presented.

  1. Silicon radiation detectors with oxide charge state compensation

    NASA Technical Reports Server (NTRS)

    Walton, J. T.; Goulding, F. S.

    1987-01-01

    This paper discusses the use of boron implantation on high resistivity P type silicon before oxide growth to compensate for the presence of charge states in the oxide and oxide/silicon interface. The presence of these charge states on high resistivity P type silicon produces an inversion layer which causes high leakage currents on N(+)P junctions and high surface conductance. Compensating the surface region by boron implantation is shown to result in oxide passivated N(+)P junctions with very low leakage currents and with low surface conductance.

  2. Towards a full integration of vertically aligned silicon nanowires in MEMS using silane as a precursor

    NASA Astrophysics Data System (ADS)

    Gadea, G.; Morata, A.; Santos, J. D.; Dávila, D.; Calaza, C.; Salleras, M.; Fonseca, L.; Tarancón, A.

    2015-05-01

    Silicon nanowires present outstanding properties for electronics, energy, and environmental monitoring applications. However, their integration into microelectromechanical systems (MEMS) is a major issue so far due to low compatibility with mainstream technology, which complicates patterning and controlled morphology. This work addresses the growth of <111> aligned silicon nanowire arrays fully integrated into standard MEMS processing by means of the chemical vapor deposition-vapor liquid solid method (CVD-VLS) using silane as a precursor. A reinterpretation of the galvanic displacement method is presented for selectively depositing gold nanoparticles of controlled size and shape. Moreover, a comprehensive analysis of the effects of synthesis temperature and pressure on the growth rate and alignment of nanowires is presented for the most common silicon precursor, i.e., silane. Compared with previously reported protocols, the redefined galvanic displacement together with a silane-based CVD-VLS growth methodology provides a more standard and low-temperature (<650 °C) synthesis scheme and a compatible route to reliably grow Si nanowires in MEMS for advanced applications.

  3. Towards a full integration of vertically aligned silicon nanowires in MEMS using silane as a precursor.

    PubMed

    Gadea, G; Morata, A; Santos, J D; Dávila, D; Calaza, C; Salleras, M; Fonseca, L; Tarancón, A

    2015-05-15

    Silicon nanowires present outstanding properties for electronics, energy, and environmental monitoring applications. However, their integration into microelectromechanical systems (MEMS) is a major issue so far due to low compatibility with mainstream technology, which complicates patterning and controlled morphology. This work addresses the growth of 〈111〉 aligned silicon nanowire arrays fully integrated into standard MEMS processing by means of the chemical vapor deposition-vapor liquid solid method (CVD-VLS) using silane as a precursor. A reinterpretation of the galvanic displacement method is presented for selectively depositing gold nanoparticles of controlled size and shape. Moreover, a comprehensive analysis of the effects of synthesis temperature and pressure on the growth rate and alignment of nanowires is presented for the most common silicon precursor, i.e., silane. Compared with previously reported protocols, the redefined galvanic displacement together with a silane-based CVD-VLS growth methodology provides a more standard and low-temperature (<650 °C) synthesis scheme and a compatible route to reliably grow Si nanowires in MEMS for advanced applications. PMID:25902702

  4. Resistive switches and memories from silicon oxide.

    PubMed

    Yao, Jun; Sun, Zhengzong; Zhong, Lin; Natelson, Douglas; Tour, James M

    2010-10-13

    Because of its excellent dielectric properties, silicon oxide (SiO(x)) has long been used and considered as a passive, insulating component in the construction of electronic devices. In contrast, here we demonstrate resistive switches and memories that use SiO(x) as the sole active material and can be implemented in entirely metal-free embodiments. Through cross-sectional transmission electron microscopy, we determine that the switching takes place through the voltage-driven formation and modification of silicon (Si) nanocrystals (NCs) embedded in the SiO(x) matrix, with SiO(x) itself also serving as the source of the formation of this Si pathway. The small sizes of the Si NCs (d ∼ 5 nm) suggest that scaling to ultrasmall domains could be feasible. Meanwhile, the switch also shows robust nonvolatile properties, high ON/OFF ratios (>10(5)), fast switching (sub-100-ns), and good endurance (10(4) write-erase cycles). These properties in a SiO(x)-based material composition showcase its potentials in constructing memory or logic devices that are fully CMOS compatible. PMID:20806916

  5. Biomimetic alignment of zinc oxide nanoparticles along a peptide nanofiber.

    PubMed

    Tomizaki, Kin-ya; Kubo, Seiya; Ahn, Soo-Ang; Satake, Masahiko; Imai, Takahito

    2012-09-18

    Zinc oxide (ZnO) has potential applications in solar cells, chemical sensors, and piezoelectronic and optoelectronic devices due to its attractive physical and chemical properties. Recently, a solution-phase method has been used to synthesize ZnO crystals with diverse (from simple to hierarchical) nanostructures that is simple, of low cost, and scalable. This method requires template molecules to control the morphology of the ZnO crystals. In this paper, we describe the design and synthesis of two short peptides (RU-003,Ac-AIEKAXEIA-NH(2); RU-027, EAHVMHKVAPRPGGGAIEKAXEIA-NH(2); X = l-2-naphthylalanine) and the characterization of their self-assembled nanostructures. We also report their potential for ZnO mineralization and the alignment of ZnO nanoparticles along peptide nanostructures at room temperature. Interestingly, nonapeptide RU-003 predominantly formed a straight fibrous structure and induced the nucleation of ZnO at its surface, leading to an alignment of ZnO nanoparticles along a peptide nanofiber. This novel method holds promise for the room-temperature fabrication of ZnO catalysts with increased specific surface area, ZnO-gated transistors, and ZnO-based nanomaterials for optical applications. PMID:22954381

  6. Nitric oxide-releasing porous silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Kafshgari, Morteza Hasanzadeh; Cavallaro, Alex; Delalat, Bahman; Harding, Frances J.; McInnes, Steven JP; Mäkilä, Ermei; Salonen, Jarno; Vasilev, Krasimir; Voelcker, Nicolas H.

    2014-07-01

    In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment.

  7. Nitric oxide-releasing porous silicon nanoparticles

    PubMed Central

    2014-01-01

    In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment. PMID:25114633

  8. Self-aligned silicon quantum wires on Ag(1 1 0)

    NASA Astrophysics Data System (ADS)

    Leandri, C.; Lay, G. Le; Aufray, B.; Girardeaux, C.; Avila, J.; Dávila, M. E.; Asensio, M. C.; Ottaviani, C.; Cricenti, A.

    2005-01-01

    Upon deposition of silicon onto the (1 1 0) surface of a silver crystal we have grown massively parallel one-dimensional Si nanowires. They are imaged in scanning tunnelling microscopy as straight, high aspect ratio, nanostructures, all with the same characteristic width of 16 Å, perfectly aligned along the atomic troughs of the bare surface. Low energy electron diffraction confirms the massively parallel assembly of these self-organized nanowires. Photoemission reveals striking quantized states dispersing only along the length of the nanowires, and extremely sharp, two-components, Si 2p core levels. This demonstrates that in the large ensemble each individual nanowire is a well-defined quantum object comprising only two distinct silicon atomic environments. We suggest that this self-assembled array of highly perfect Si nanowires provides a simple, atomically precise, novel template that may impact a wide range of applications.

  9. Silicon solar cells made by a self-aligned, selective-emitter, plasma-etchback process

    DOEpatents

    Ruby, D.S.; Schubert, W.K.; Gee, J.M.

    1999-02-16

    A potentially low-cost process for forming and passivating a selective emitter. The process uses a plasma etch of the heavily doped emitter to improve its performance. The grids of the solar cell are used to mask the plasma etch so that only the emitter in the region between the grids is etched, while the region beneath the grids remains heavily doped for low contact resistance. This process is potentially low-cost because it requires no alignment. After the emitter etch, a silicon nitride layer is deposited by plasma-enhanced, chemical vapor deposition, and the solar cell is annealed in a forming gas. 5 figs.

  10. Silicon solar cells made by a self-aligned, selective-emitter, plasma-etchback process

    DOEpatents

    Ruby, Douglas S.; Schubert, William K.; Gee, James M.

    1999-01-01

    A potentially low-cost process for forming and passivating a selective emitter. The process uses a plasma etch of the heavily doped emitter to improve its performance. The grids of the solar cell are used to mask the plasma etch so that only the emitter in the region between the grids is etched, while the region beneath the grids remains heavily doped for low contact resistance. This process is potentially low-cost because it requires no alignment. After the emitter etch, a silicon nitride layer is deposited by plasma-enhanced, chemical vapor deposition, and the solar cell is annealed in a forming gas.

  11. Alignment of nanoparticles, nanorods, and nanowires during chemical vapor deposition of silicon

    NASA Astrophysics Data System (ADS)

    Swain, Bhabani Sankar; Park, Jin-Woo; Yang, Seung-Min; Mahmood, Khalid; Swain, Bibhu Prasad; Lee, Jae-Gab; Hwang, Nong-Moon

    2015-09-01

    We fabricated silicon nanostructures (Si-NSs) on SiO x /Si substrate in chemical vapor deposition. During the synthesis of Si-NSs, Si sunflower-shaped structures of one to hundred microns were observed, therein the nanoparticles (NPs), nanowires, and nanorods were aligned in an ordered manner. We suggest that the NSs reported here are evolved by the electrostatic force exerted by charged NPs in gas phase. This NS would help in understanding the role of spontaneous charging of NPs in the gas phase and the role of charged NPs in the gas phase for NSs growth.

  12. Planar polar liquid crystalline alignment in nanostructured porous silicon one-dimensional photonic crystals

    NASA Astrophysics Data System (ADS)

    Mor, Shahar; Torres-Costa, Vicente; Martín-Palma, Raúl J.; Abdulhalim, I.

    2010-09-01

    The ability of liquid crystals (LCs) to flow and fill nanopores assists in using them for infiltration into porous nanophotonic structures such as nanostructured porous silicon (nanoPS). The reflectivity spectra at normal incidence from periodic nanostructured nanoPS filters infiltrated with nematic LC is found to exhibit polarization dependence. This is experimental evidence that the LC molecules in the nanoPS matrix are aligned such that an effective anisotropy exists parallel to the substrate plane. From the theoretical fit the preferred configuration was found to be the planar-polar geometry which is shown to be biaxial.

  13. Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix

    SciTech Connect

    Kole, Arindam; Chaudhuri, Partha

    2014-10-15

    A moderately low temperature (≤800 °C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (μc-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of T{sub v} = 525 °C. The samples were then stepwise annealed at different temperatures T{sub a} in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the μc-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (D{sub XRD}) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in T{sub a} from 250 °C to 800 °C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.

  14. Self-aligned nanoforest in silicon nanowire for sensitive conductance modulation.

    PubMed

    Seol, Myeong-Lok; Ahn, Jae-Hyuk; Choi, Ji-Min; Choi, Sung-Jin; Choi, Yang-Kyu

    2012-11-14

    A self-aligned and localized nanoforest structure is constructed in a top-down fabricated silicon nanowire (SiNW). The surface-to-volume ratio (SVR) of the SiNW is enhanced due to the local nanoforest formation. The conductance modulation property of the SiNWs, which is an important characteristic in sensor and charge transfer based applications, can be largely enhanced. For the selective modification of the channel region, localized Joule-heating and subsequent metal-assisted chemical etching (mac-etch) are employed. The nanoforest is formed only in the channel region without misalignment due to the self-aligned process of Joule-heating. The modified SiNW is applied to a porphyrin-silicon hybrid device to verify the enhanced conductance modulation. The charge transfer efficiency between the porphyrin and the SiNW, which is caused by external optical excitation, is clearly increased compared to the initial SiNW. The effect of the local nanoforest formation is enhanced when longer etching times and larger widths are used. PMID:23066892

  15. Surface analytical studies of ion-implanted uni-directionally aligned silicon nitride for tribological applications

    NASA Astrophysics Data System (ADS)

    Nakamura, Naoki; Hirao, Kiyoshi; Yamauchi, Yukihiko

    2004-03-01

    Uni-directionally aligned silicon nitride, which exhibits both high strength and high toughness, was implanted with B +, N +, Si + and Ti + ions at a fluence of 2 × 10 17 ions/cm 2 and an energy of 200 keV. The effect of ion implantation on the surface structure of the uni-directionally aligned silicon nitride has been studied, in terms of surface analyses such as atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray absorption near edge structure (XANES). It was clarified that the ion-implanted layer was amorphized and the implantation profile showed good agreement with that estimated from a TRIM simulation. It was found that BN and TiN were formed in B +- and Ti +-implanted Si 3N 4, respectively. There was a slight difference in ion implantation depth among different structures of Si 3N 4, considered to be due to differences in ion channeling.

  16. Improved Retention Characteristic in Polycrystalline Silicon-Oxide-Hafnium Oxide-Oxide-Silicon-Type Nonvolatile Memory with Robust Tunnel Oxynitride

    NASA Astrophysics Data System (ADS)

    Hsieh, Chih Ren; Lai, Chiung Hui; Lin, Bo Chun; Zheng, Yuan Kai; Chung Lou, Jen; Lin, Gray

    2011-03-01

    In this paper, we present a simple novel process for forming a robust and reliable oxynitride dielectric with a high nitrogen content. It is highly suitable for n-channel metal-oxide-semiconductor field-effect transistor (nMOSFETs) and polycrystalline silicon-oxide-hafnium oxide-oxide-silicon (SOHOS)-type memory applications. The proposed approach is realized by using chemical oxide with ammonia (NH3) nitridation followed by reoxidation with oxygen (O2). The novel oxynitride process is not only compatible with the standard complementary metal-oxide-semiconductor (CMOS) process, but also can ensure the improvement of flash memory with low-cost manufacturing. The characteristics of nMOSFETs and SOHOS-type nonvolatile memories (NVMs) with a robust oxynitride as a gate oxide or tunnel oxide are studied to demonstrate their advantages such as the retardation of the stress-induced trap generation during constant-voltage stress (CVS), the program/erase behaviors, cycling endurance, and data retention. The results indicate that the proposed robust oxynitride is suitable for future nonvolatile flash memory technology application.

  17. Indium oxide/n-silicon heterojunction solar cells

    DOEpatents

    Feng, Tom; Ghosh, Amal K.

    1982-12-28

    A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.

  18. Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects.

    PubMed

    Sun, Shuangxi; Mu, Wei; Edwards, Michael; Mencarelli, Davide; Pierantoni, Luca; Fu, Yifeng; Jeppson, Kjell; Liu, Johan

    2016-08-19

    For future miniaturization of electronic systems using 3D chip stacking, new fine-pitch materials for through-silicon-via (TSV) applications are likely required. In this paper, we propose a novel carbon nanotube (CNT)/copper nanocomposite material consisting of high aspect ratio, vertically aligned CNT bundles coated with copper. These bundles, consisting of hundreds of tiny CNTs, were uniformly coated by copper through electroplating, and aspect ratios as high as 300:1 were obtained. The resistivity of this nanomaterial was found to be as low as ∼10(-8) Ω m, which is of the same order of magnitude as the resistivity of copper, and its temperature coefficient was found to be only half of that of pure copper. The main advantage of the composite TSV nanomaterial is that its coefficient of thermal expansion (CTE) is similar to that of silicon, a key reliability factor. A finite element model was set up to demonstrate the reliability of this composite material and thermal cycle simulations predicted very promising results. In conclusion, this composite nanomaterial appears to be a very promising material for future 3D TSV applications offering both a low resistivity and a low CTE similar to that of silicon. PMID:27383767

  19. Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects

    NASA Astrophysics Data System (ADS)

    Sun, Shuangxi; Mu, Wei; Edwards, Michael; Mencarelli, Davide; Pierantoni, Luca; Fu, Yifeng; Jeppson, Kjell; Liu, Johan

    2016-08-01

    For future miniaturization of electronic systems using 3D chip stacking, new fine-pitch materials for through-silicon-via (TSV) applications are likely required. In this paper, we propose a novel carbon nanotube (CNT)/copper nanocomposite material consisting of high aspect ratio, vertically aligned CNT bundles coated with copper. These bundles, consisting of hundreds of tiny CNTs, were uniformly coated by copper through electroplating, and aspect ratios as high as 300:1 were obtained. The resistivity of this nanomaterial was found to be as low as ∼10‑8 Ω m, which is of the same order of magnitude as the resistivity of copper, and its temperature coefficient was found to be only half of that of pure copper. The main advantage of the composite TSV nanomaterial is that its coefficient of thermal expansion (CTE) is similar to that of silicon, a key reliability factor. A finite element model was set up to demonstrate the reliability of this composite material and thermal cycle simulations predicted very promising results. In conclusion, this composite nanomaterial appears to be a very promising material for future 3D TSV applications offering both a low resistivity and a low CTE similar to that of silicon.

  20. Research on silicon microchannel arrays oxide insulation technology

    NASA Astrophysics Data System (ADS)

    Wu, Ke-xin; Duanmu, Qingduo; Wang, Guozheng; Yang, Ji-kai; Kou, Yang-qiang

    2015-03-01

    Silicon microchannel plates (Si-MCP) is widely used in the photomultiplier, night vision, X- ray intensifier and other areas. In order to meet the requirements of high voltage electron multiplier, Si-MCP need to prepare a layer of silicon dioxide in the microchannel to improve the insulating properties. There are many methods for preparing SiO2 layer, such as thermal growth, magnetron sputtering method and chemical vapor deposition etc. The thermal oxidation method is often used for preparation of insulating layer that it grows film thickness uniformity, compact structure, simple process and so on. There will be bending deformation phenomenon of silicon microchannel arrays in high temperature oxidation process. The warpage of Si-MCP has brought great for difficulties of subsequent processing. Silicon crystals has the properties of plastic deformation at high temperature, this article take full advantage of this properties by which the already bending deformation of silicon microchannel arrays can be restored to flat.

  1. Structure and method for controlling band offset and alignment at a crystalline oxide-on-semiconductor interface

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    2003-11-25

    A crystalline oxide-on-semiconductor structure and a process for constructing the structure involves a substrate of silicon, germanium or a silicon-germanium alloy and an epitaxial thin film overlying the surface of the substrate wherein the thin film consists of a first epitaxial stratum of single atomic plane layers of an alkaline earth oxide designated generally as (AO).sub.n and a second stratum of single unit cell layers of an oxide material designated as (A'BO.sub.3).sub.m so that the multilayer film arranged upon the substrate surface is designated (AO).sub.n (A'BO.sub.3).sub.m wherein n is an integer repeat of single atomic plane layers of the alkaline earth oxide AO and m is an integer repeat of single unit cell layers of the A'BO.sub.3 oxide material. Within the multilayer film, the values of n and m have been selected to provide the structure with a desired electrical structure at the substrate/thin film interface that can be optimized to control band offset and alignment.

  2. Integration of functional complex oxide nanomaterials on silicon

    NASA Astrophysics Data System (ADS)

    Vila-Fungueiriño, Jose Manuel; Bachelet, Romain; Saint-Girons, Guillaume; Gendry, Michel; Gich, Marti; Gazquez, Jaume; Ferain, Etienne; Rivadulla, Francisco; Rodriguez-Carvajal, Juan; Mestres, Narcis; Carretero-Genevrier, Adrian

    2015-06-01

    The combination of standard wafer-scale semiconductor processing with the properties of functional oxides opens up to innovative and more efficient devices with high value applications that can be produced at large scale. This review uncovers the main strategies that are successfully used to monolithically integrate functional complex oxide thin films and nanostructures on silicon: the chemical solution deposition approach (CSD) and the advanced physical vapor deposition techniques such as oxide molecular beam epitaxy (MBE). Special emphasis will be placed on complex oxide nanostructures epitaxially grown on silicon using the combination of CSD and MBE. Several examples will be exposed, with a particular stress on the control of interfaces and crystallization mechanisms on epitaxial perovskite oxide thin films, nanostructured quartz thin films, and octahedral molecular sieve nanowires. This review enlightens on the potential of complex oxide nanostructures and the combination of both chemical and physical elaboration techniques for novel oxide-based integrated devices.

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

    SciTech Connect

    Santella, M.L.; Moorhead, A.J.

    1987-01-01

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

  4. Formation of Mosaic Silicon Oxide Structure during Metal-Assisted Electrochemical Etching of Silicon at High Current Density

    NASA Astrophysics Data System (ADS)

    Cao, Dao Tran; Anh, Cao Tuan; Ngan, Luong Truc Quynh

    2016-05-01

    We have used constant-current, metal-assisted electrochemical etching of silicon in HF/H2O2/ethanol electrolyte to fabricate porous silicon. We found that, at large enough current density, the sponge-like porous silicon structure is replaced by a mosaic structure, which includes islands of various shapes emerging between trenches that have been etched downward. Energy-dispersive x-ray analysis showed that the surface of the mosaic pieces was covered with silicon oxide, while little silicon oxide developed on the surface of trenches. We suggest that the appearance of the mosaic structure can be explained by the increase in the oxidation rate of silicon when the anodic current density increases, combined with no change in the dissolution rate of silicon oxide into the solution. Consequently, above a certain value of anodic current density, there is sufficient residual silicon oxide on the etched surface to create a continuous thin film. However, if the silicon oxide layer is too thick (e.g., due to too high anodic current density or too long etching time), it will become cracked (formation of mosaic pieces), likely due to differences in thermal expansion coefficient between the amorphous silicon oxide layer and crystalline silicon substrate. The oxide is cracked at locations with many defects, and the cracks reveal the silicon substrate. Therefore, at the locations where cracks occur, etching will go sideways and downward, creating trenches.

  5. Extension of silicon emission model to silicon pillar oxidation

    NASA Astrophysics Data System (ADS)

    Kageshima, Hiroyuki; Shiraishi, Kenji; Endoh, Tetsuo

    2016-08-01

    Missing Si in the oxidation of Si pillar structures is investigated by extending the Si emission model to the oxidation of planar structures. The original Si emission model [H. Kageshima et al., Jpn. J. Appl. Phys. 38, L971 (1999)] assumes the emission of excess Si from the interface into the oxide during the oxidation process, the diffusion of the excess Si through the oxide, and the control of the oxidation rate by the concentration of remaining excess Si around the interface. By assuming the sublimation of the excess Si from the oxide surface in addition to the assumptions of the original Si emission model, the origin of the missing Si is consistently explained. It is suggested that the amount of the missing Si is enhanced by the geometrical effect of the pillar structure because the concentration of excess Si is inversely proportional to the radial position. This also suggests that the missing Si is inevitable for the thin pillar structures. Careful approaches to the oxidation process are recommended for pillar structures.

  6. Dopant segregation at silicon-oxide interfaces

    NASA Astrophysics Data System (ADS)

    Pei, Lirong

    . However, Z-contrast imaging shows a segregation of Sb to the interface. Unlike the As doped samples, pentagon-shaped Sb precipitates are also detected 8nm from interface on the Si side. For the As doped Si/HfxSi1-xO samples, an unexpected silicate interfacial layer is observed between hafnium oxide thin film and silicon substrate. Therefore, As segregation at the novel interface turns out to be exactly same as As at Si/SiO2 interfaces. Combining Z-contrast imaging and EELS analysis, the interfacial layer is determined to be introduced by the kinetic problem in the MOCVD deposition of HfxSi1-x O thin film.

  7. First stages of silicon oxidation with the activation relaxation technique

    NASA Astrophysics Data System (ADS)

    Ganster, Patrick; Béland, Laurent Karim; Mousseau, Normand

    2012-08-01

    Using the art nouveau method, we study the initial stages of silicon oxide formation. After validating the method's parameters with the characterization of point defects diffusion mechanisms in pure Stillinger-Weber silicon, which allows us to recover some known results and to detail vacancy and self-interstitial diffusion paths, the method is applied onto a system composed of an oxygen layer deposited on a silicon substrate. We observe the oxygen atoms as they move rapidly into the substrate. From these art nouveau simulations, we extract the energy barriers of elementary mechanisms involving oxygen atoms and leading to the formation of an amorphouslike silicon oxide. We show that the kinetics of formation can be understood in terms of the energy barriers between various coordination environments.

  8. Cycling endurance of silicon{endash}oxide{endash}nitride{endash}oxide{endash}silicon nonvolatile memory stacks prepared with nitrided SiO{sub 2}/Si(100) interfaces

    SciTech Connect

    Habermehl, S.; Nasby, R.D.; Rightley, M.J.

    1999-08-01

    The effects of nitrided SiO{sub 2}/Si(100) interfaces upon cycling endurance in silicon{endash}oxide{endash}nitride{endash}oxide{endash}silicon (SONOS) nonvolatile memory transistors are investigated. Analysis of metal{endash}oxide{endash}silicon field-effect transistor subthreshold characteristics indicate cycling degradation to be a manifestation of interface trap generation at the tunnel oxide/silicon interface. After 10{sup 6} write/erase cycles, SONOS film stacks prepared with nitrided tunnel oxides exhibit enhanced cycling endurance over stacks prepared with non-nitrided tunnel oxides. If the capping oxide is formed by steam oxidation, rather than by deposition, SONOS stacks prepared with non-nitrided tunnel oxides exhibit endurance characteristics similar to stacks with nitrided tunnel oxides. For this case, a mechanism for latent nitridation of the tunnel oxide/silicon interface is proposed. {copyright} {ital 1999 American Institute of Physics.}

  9. Liquid crystal alignment on zinc oxide nanowire arrays for LCDs applications.

    PubMed

    Chen, Mu-Zhe; Chen, Wei-Sheng; Jeng, Shie-Chang; Yang, Sheng-Hsiung; Chung, Yueh-Feng

    2013-12-01

    The zinc oxide (ZnO) nanowire arrays on the indium tin oxide (ITO) glass substrates were fabricated by using the two-step hydrothermal method. A high transmittance ~92% of ZnO nanowire arrays on ITO substrate in the visible region was obtained. It was observed that the liquid crystal (LC) directors were aligned vertically to the (ZnO) nanowire arrays. The properties of ZnO nanowire arrays as vertical liquid crystal (LC) alignment layers and their applications for hybrid-aligned nematic LC modes were investigated in this work. PMID:24514480

  10. Synthesis of nanoscale silicon oxide oxidation state distributions: The transformation from hydrophilicity to hydrophobicity

    NASA Astrophysics Data System (ADS)

    Laminack, William; Gole, James L.; White, Mark G.; Ozdemir, Serdar; Ogden, Andrew G.; Martin, Holly J.; Fang, Zongtang; Wang, Tsang-Hsiu; Dixon, David A.

    2016-06-01

    Silicon oxide nanostructures which span the range from hydrophilic to hydrophobic have been synthesized. The surface chemistry of these silicon-based nanostructures was analyzed using a combination of X-ray photoelectron spectroscopy, reflectance infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The dominant oxidation state for the nanostructured oxides shifts from an average oxidation state of +III to a combination of +II and +III oxidation states. A correlation of the ability to adsorb water with variations in the surface Si:O ratios was observed showing a transition from hydrophilic to hydrophobic character.

  11. Ion implantation reduces radiation sensitivity of metal oxide silicon /MOS/ devices

    NASA Technical Reports Server (NTRS)

    1971-01-01

    Implanting nitrogen ions improves hardening of silicon oxides 30 percent to 60 percent against ionizing radiation effects. Process reduces sensitivity, but retains stability normally shown by interfaces between silicon and thermally grown oxides.

  12. Oxide mediated liquid-solid growth of high aspect ratio aligned gold silicide nanowires on Si(110) substrates.

    PubMed

    Bhatta, Umananda M; Rath, Ashutosh; Dash, Jatis K; Ghatak, Jay; Yi-Feng, Lai; Liu, Chuan-Pu; Satyam, P V

    2009-11-18

    Silicon nanowires grown using the vapor-liquid-solid method are promising candidates for nanoelectronics applications. The nanowires grow from an Au-Si catalyst during silicon chemical vapor deposition. In this paper, the effect of temperature, oxide at the interface and substrate orientation on the nucleation and growth kinetics during formation of nanogold silicide structures is explained using an oxide mediated liquid-solid growth mechanism. Using real time in situ high temperature transmission electron microscopy (with 40 ms time resolution), we show the formation of high aspect ratio ( approximately 15.0) aligned gold silicide nanorods in the presence of native oxide at the interface during in situ annealing of gold thin films on Si(110) substrates. Steps observed in the growth rate and real time electron diffraction show the existence of liquid Au-Si nano-alloy structures on the surface besides the un-reacted gold nanostructures. These results might enable us to engineer the growth of nanowires and similar structures with an Au-Si alloy as a catalyst. PMID:19843987

  13. Oxide mediated liquid-solid growth of high aspect ratio aligned gold silicide nanowires on Si(110) substrates

    NASA Astrophysics Data System (ADS)

    Bhatta, Umananda M.; Rath, Ashutosh; Dash, Jatis K.; Ghatak, Jay; Yi-Feng, Lai; Liu, Chuan-Pu; Satyam, P. V.

    2009-11-01

    Silicon nanowires grown using the vapor-liquid-solid method are promising candidates for nanoelectronics applications. The nanowires grow from an Au-Si catalyst during silicon chemical vapor deposition. In this paper, the effect of temperature, oxide at the interface and substrate orientation on the nucleation and growth kinetics during formation of nanogold silicide structures is explained using an oxide mediated liquid-solid growth mechanism. Using real time in situ high temperature transmission electron microscopy (with 40 ms time resolution), we show the formation of high aspect ratio (≈15.0) aligned gold silicide nanorods in the presence of native oxide at the interface during in situ annealing of gold thin films on Si(110) substrates. Steps observed in the growth rate and real time electron diffraction show the existence of liquid Au-Si nano-alloy structures on the surface besides the un-reacted gold nanostructures. These results might enable us to engineer the growth of nanowires and similar structures with an Au-Si alloy as a catalyst.

  14. The Oxidation of CVD Silicon Carbide in Carbon Dioxide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Nguyen, QuynchGiao N.

    1997-01-01

    Chemically-vapor-deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO2) at temperatures of 1200-1400 C for times between 100 and 500 hours at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate limiting kinetic laws are discussed. Oxidation of SiC by CO2 is negligible compared to the rates measured for other oxidants typically found in combustion environments: oxygen and water vapor.

  15. Structure-thermal property correlation of aligned silicon dioxide nanorod arrays

    NASA Astrophysics Data System (ADS)

    Zhu, Jie; Zhu, Yu; Wu, Xuewang; Song, Helun; Zhang, Yaohui; Wang, Xiaojia

    2016-06-01

    Quantitative characterization of thermal properties of nanorod (NR) arrays appears to be challenging due to the complex combination of high volume of air voids, anisotropy, and structural non-uniformity. This work investigates the structure-thermal property correlation of arrays consisting of either vertically aligned or slanted silicon dioxide (SiO2) NRs, fabricated by the dynamic shadowing growth technique. We apply the frequency-dependent time-domain thermoreflectance method to quantify the thermal properties of SiO2 NR arrays that may possess inhomogeneity along the depth direction. The effective thermal conductivities of four SiO2 NR array films and one reference capping layer for the SiO2 NR array are obtained. The impact of the structure on the effective thermal conductivities of the SiO2 NR array is discussed. The lowest effective thermal conductivity among all samples in this work is found to be 0.13 W m-1 K-1 for the slanted NR array. We attribute the reduction in the effective thermal conductivity of the NR array to the discontinuous nature of SiO2 NRs, which reduces the density of the thermal transport channels and thus prevents heat flux from propagating downwards along the through-plane direction. The results from this work facilitate the potential applications of NR-array-based thermal insulators for micro-thermal devices.

  16. Analysis of multiple internal reflections in a parallel aligned liquid crystal on silicon SLM.

    PubMed

    Martínez, José Luis; Moreno, Ignacio; del Mar Sánchez-López, María; Vargas, Asticio; García-Martínez, Pascuala

    2014-10-20

    Multiple internal reflection effects on the optical modulation of a commercial reflective parallel-aligned liquid-crystal on silicon (PAL-LCoS) spatial light modulator (SLM) are analyzed. The display is illuminated with different wavelengths and different angles of incidence. Non-negligible Fabry-Perot (FP) effect is observed due to the sandwiched LC layer structure. A simplified physical model that quantitatively accounts for the observed phenomena is proposed. It is shown how the expected pure phase modulation response is substantially modified in the following aspects: 1) a coupled amplitude modulation, 2) a non-linear behavior of the phase modulation, 3) some amount of unmodulated light, and 4) a reduction of the effective phase modulation as the angle of incidence increases. Finally, it is shown that multiple reflections can be useful since the effect of a displayed diffraction grating is doubled on a beam that is reflected twice through the LC layer, thus rendering gratings with doubled phase modulation depth. PMID:25401619

  17. Arsenic silicide formation by oxidation of arsenic implanted silicon

    NASA Astrophysics Data System (ADS)

    Hagmann, D.; Euen, W.; Schorer, G.; Metzger, G.

    1989-07-01

    Wet oxidations of (100) silicon implanted with an arsenic dose of 2 × 1016 cm-2 and an energy of 30 keV were carried out in the temperature range between 600 and 900° C. The oxidation rate is increased on the arsenic implanted samples up to a factor of 2000 as compared to undoped samples. During these oxidations the arsenic suicide phase AsSi is precipitated at the oxide/silicon interface. After short oxidation times at 600° C, a continuous AsSi layer is found. It is dissolved during extended oxidation times and finally almost all As is incorporated in the oxide. After 900° C oxidations, substantial AsSi crystallites remain at the Si/SiO2 interface. They are still observed up to the larg-est oxide thickness grown (2.3 µm). The AsSi phase and the distribution of the im-planted arsenic were analyzed by TEM, SIMS and XRF measurements.

  18. Electron stimulated oxidation of silicon surfaces

    SciTech Connect

    Munoz, M.C.; Sacedon, J.L.

    1981-04-15

    Experimental evidence of electron stimulated oxidation (ESO) has been given for Si(111) 7 x 7 surface. In a first stage, the oxide thickness as a function of time shows a linear relationship; in a second stage, the growth rate quickly decreases and a pressure dependent saturation oxide thickness is reached. During the oxidation process an electrical potential does exist across the oxide, as is required in the Cabrera--Mott theory. The linear kinetics and the electrical potential are shown to be explicable in terms of a modified coupled-current approach based on the Cabrera--Mott theory, provided a semiphenomenological pressure dependent parameter is included. This represents a contribution of the surface reaction to the transport equation. The saturation has been explained as due to the decrease of the negative surface charge (donor levels) which produces a decrease of the electron current.

  19. Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces

    SciTech Connect

    Uçar, A.; Çopuroğlu, M.; Suzer, S.; Baykara, M. Z.; Arıkan, O.

    2014-10-28

    We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (∼0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45° before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO{sub 2} surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.

  20. Oxidation Protection of Porous Reaction-Bonded Silicon Nitride

    NASA Technical Reports Server (NTRS)

    Fox, D. S.

    1994-01-01

    Oxidation kinetics of both as-fabricated and coated reaction-bonded silicon nitride (RBSN) were studied at 900 and 1000 C with thermogravimetry. Uncoated RBSN exhibited internal oxidation and parabolic kinetics. An amorphous Si-C-O coating provided the greatest degree of protection to oxygen, with a small linear weight loss observed. Linear weight gains were measured on samples with an amorphous Si-N-C coating. Chemically vapor deposited (CVD) Si3N4 coated RBSN exhibited parabolic kinetics, and the coating cracked severely. A continuous-SiC-fiber-reinforced RBSN composite was also coated with the Si-C-O material, but no substantial oxidation protection was observed.

  1. Interaction at the silicon/transition metal oxide heterojunction interface and its effect on the photovoltaic performance.

    PubMed

    Liang, Zhimin; Su, Mingze; Zhou, Yangyang; Gong, Li; Zhao, Chuanxi; Chen, Keqiu; Xie, Fangyan; Zhang, Weihong; Chen, Jian; Liu, Pengyi; Xie, Weiguang

    2015-11-01

    The interfacial reaction and energy level alignment at the Si/transition metal oxide (TMO, including MoO3-x, V2O5-x, WO3-x) heterojunction are systematically investigated. We confirm that the interfacial reaction appears during the thermal deposition of TMO, with the reaction extent increasing from MoO3-x, to V2O5-x, and to WO3-x. The reaction causes the surface oxidation of silicon for faster electron/hole recombination, and the reduction of TMO for effective hole collection. The photovoltaic performance of the Si/TMO heterojunction devices is affected by the interface reaction. MoO3-x are the best hole selecting materials that induce least surface oxidation but strongest reduction. Compared with H-passivation, methyl group passivation is an effective way to reduce the interface reaction and improve the interfacial energy level alignment for better electron and hole collection. PMID:26422643

  2. Oxidation kinetics of coated silicon carbide fiber-reinforced silicon carbide (SiC/SiC)

    SciTech Connect

    Fox, D.S.

    1994-12-31

    Silicon carbide fiber-reinforced silicon carbide (SiC/SiC) was exposed for 100 hours to dry, flowing oxygen. Oxidation kinetics were determined via thermogravimetric analysis at 981{degrees}, 1204{degrees} and 1316{degrees}C (1800{degrees}, 2200{degrees} and 2400{degrees}F). The effectiveness of three external coating systems applied for oxidation protection is discussed. In all cases, weight gains were observed, and the pyrolytic carbon interface layer remained intact. A CVD SiC external coating is the most promising due to low oxidation kinetics resulting from solid silica formation. A borosilicate glass was observed on the surface of two of the materials that have boron-containing coatings.

  3. Charge trapping in low temperature MOS (Metal-Oxide-Silicon) oxides

    NASA Astrophysics Data System (ADS)

    Zvanut, M. E.; Feigl, F. J.; Butler, S. R.; Vogel, R. H.

    1984-08-01

    Metal-oxide-silicon (MOS) capacitors were fabricated on silicon dioxide films produced at 700 C by either low pressure chemical vapor deposition (LPCVD) or high pressure thermal oxidation (HIPOX). The LPCVD process involved reaction of dichlorosilane with nitrous oxide. The HIPOX process involved dry oxygen. The LPCVD and HIPOX films were subjected to a variety of annealing treatments. We have systematically investigated the effects of these treatments by measurement of oxide charge and interface trap density before and after electron current transport across films, grown and annealed at 700 C, were comparable to those of standard dry thermal oxides grown and annealed at 1000 C. However, charge trapping in the HIPOX films was an order of magnitude larger than in the standard oxides, although well-prepared HIPOX films exhibited specific electron traps characteristics of standard dry oxides.

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

    PubMed

    Zhang; Suenaga; Colliex; Iijima

    1998-08-14

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

  5. Fabrication of self-aligned, nanoscale, complex oxide varactors

    NASA Astrophysics Data System (ADS)

    Fu, Richard X.; Toonen, Ryan C.; Hirsch, Samuel G.; Ivill, Mathew P.; Cole, Melanie W.; Strawhecker, Kenneth E.

    2015-01-01

    Applications in ferroelectric random access memory and superparaelectric devices require the fabrication of ferroelectric capacitors at the nanoscale that exhibit extremely small leakage currents. To systematically study the material-size dependence of ferroelectric varactor performance, arrays of parallel-plate structures have been fabricated with nanoscale dielectric diameters. Electron beam lithography and inductively coupled plasma dry etching have been used to fabricate arrays of ferroelectric varactors using top electrodes as a self-aligned etch mask. Parallel-plate test structures using RF-sputtered Ba0.6Sr0.4TiO3 thin-films were used to optimize the fabrication process. Varactors with diameters down to 20 nm were successfully fabricated. Current-voltage (I-V) characteristics were measured to evaluate the significance of etch-damage and fabrication quality by ensuring low leakage currents through the structures.

  6. Efficient Direct Reduction of Graphene Oxide by Silicon Substrate

    PubMed Central

    Chan Lee, Su; Some, Surajit; Wook Kim, Sung; Jun Kim, Sun; Seo, Jungmok; Lee, Jooho; Lee, Taeyoon; Ahn, Jong-Hyun; Choi, Heon-Jin; Chan Jun, Seong

    2015-01-01

    Graphene has been studied for various applications due to its excellent properties. Graphene film fabrication from solutions of graphene oxide (GO) have attracted considerable attention because these procedures are suitable for mass production. GO, however, is an insulator, and therefore a reduction process is required to make the GO film conductive. These reduction procedures require chemical reducing agents or high temperature annealing. Herein, we report a novel direct and simple reduction procedure of GO by silicon, which is the most widely used material in the electronics industry. In this study, we also used silicon nanosheets (SiNSs) as reducing agents for GO. The reducing effect of silicon was confirmed by various characterization methods. Furthermore, the silicon wafer was also used as a reducing template to create a reduced GO (rGO) film on a silicon substrate. By this process, a pure rGO film can be formed without the impurities that normally come from chemical reducing agents. This is an easy and environmentally friendly method to prepare large scale graphene films on Si substrates. PMID:26194107

  7. Efficient Direct Reduction of Graphene Oxide by Silicon Substrate.

    PubMed

    Lee, Su Chan; Some, Surajit; Kim, Sung Wook; Kim, Sun Jun; Seo, Jungmok; Lee, Jooho; Lee, Taeyoon; Ahn, Jong-Hyun; Choi, Heon-Jin; Jun, Seong Chan

    2015-01-01

    Graphene has been studied for various applications due to its excellent properties. Graphene film fabrication from solutions of graphene oxide (GO) have attracted considerable attention because these procedures are suitable for mass production. GO, however, is an insulator, and therefore a reduction process is required to make the GO film conductive. These reduction procedures require chemical reducing agents or high temperature annealing. Herein, we report a novel direct and simple reduction procedure of GO by silicon, which is the most widely used material in the electronics industry. In this study, we also used silicon nanosheets (SiNSs) as reducing agents for GO. The reducing effect of silicon was confirmed by various characterization methods. Furthermore, the silicon wafer was also used as a reducing template to create a reduced GO (rGO) film on a silicon substrate. By this process, a pure rGO film can be formed without the impurities that normally come from chemical reducing agents. This is an easy and environmentally friendly method to prepare large scale graphene films on Si substrates. PMID:26194107

  8. Models and experiments on degradation of oxidized silicon

    NASA Astrophysics Data System (ADS)

    Sah, C. T.

    1990-02-01

    The concepts of electronic and protonic traps are introduced to delineate and classify the fundamental mechanisms of charging, generation, annealing and hydrogenation of electronic or electron and hole traps located in the interfacial (gate-conductor/oxide, oxide/nitride and oxide/silicon), insulator (oxide, nitride and oxynitride) and semiconductor surface layers of silicon MOS transistors and integrated circuits. Two matrix tables, one without tunneling (3 × 3) and one with tunneling (3 × 4) are used to classify the trap charging and electronic injection mechanisms according to the initial and final (band or bound) states of the electronic transition and the energy exchange mechanisms (thermal, optical and Auger-impact). The importance of tunneling to and from traps (TTT) as an oxide charge build-up mechanism is discussed. A theoretical tunneling rate to traps is given showing that traps shallower than about 2 eV from the oxide conduction band edge or 3 eV from the oxide valence band edge cannot be charged by the TTT transitions alone. Experimental examples illustrating the use of these mechanism tables as well as the importance of breaking hydrogen and strained intrinsic bonds by hot electron impact and by thermal hole capture are discussed, including: (i) annealing of the oxide/Si interface traps via hydrogenation during 380C chip bonding and during Fowler-Nordheim tunneling electron injection (FN-TEI) and avalanche electron injection (AEI) stresses, (ii) interface trap generation and positive oxide charge build-up during electron injection via FN-TEI or AEI, and (iii) electrical deactivation of boron and other group-III acceptors (Al, Ga, In) in the silicon surface layer during FNTEI or AEI stresses. Examples at three d.c. bias conditions to delineate the dominant degradation mechanisms in silicon MOS transistors are given showing that trap charging via tunneling (FNTEI, FNTHI and TTT) dominates below about 3.3 V in both n-MOS and p-MOS but trap generation

  9. Green light emission from terbium doped silicon rich silicon oxide films obtained by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Podhorodecki, A.; Zatryb, G.; Misiewicz, J.; Wojcik, J.; Wilson, P. R. J.; Mascher, P.

    2012-11-01

    The effect of silicon concentration and annealing temperature on terbium luminescence was investigated for thin silicon rich silicon oxide films. The structures were deposited by means of plasma enhanced chemical vapor deposition. The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy and Raman scattering. The optical properties were investigated by means of photoluminescence and photoluminescence decay spectroscopy. It was found that both the silicon concentration in the film and the annealing temperature have a strong impact on the terbium emission intensity. In this paper, we present a detailed discussion of these issues and determine the optimal silicon concentration and annealing temperature.

  10. Green light emission from terbium doped silicon rich silicon oxide films obtained by plasma enhanced chemical vapor deposition.

    PubMed

    Podhorodecki, A; Zatryb, G; Misiewicz, J; Wojcik, J; Wilson, P R J; Mascher, P

    2012-11-30

    The effect of silicon concentration and annealing temperature on terbium luminescence was investigated for thin silicon rich silicon oxide films. The structures were deposited by means of plasma enhanced chemical vapor deposition. The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy and Raman scattering. The optical properties were investigated by means of photoluminescence and photoluminescence decay spectroscopy. It was found that both the silicon concentration in the film and the annealing temperature have a strong impact on the terbium emission intensity. In this paper, we present a detailed discussion of these issues and determine the optimal silicon concentration and annealing temperature. PMID:23110801

  11. Silicon-silicon bonds in the oxide near the SiO 2/Si interface

    NASA Astrophysics Data System (ADS)

    Terada, Naozumi; Haga, Takashi; Miyata, Noriyuki; Moriki, Kazunori; Fujisawa, Masami; Morita, Mizuho; Ohmi, Tadahiro; Hattori, Takeo

    The contribution of the SiO 2/Si interface structure to optical absorption below the optical absorption edge of fused quartz was studied by measuring the reflectance of thermally grown ultrathin silicon oxide films. From the modified Kramers-Kronig analysis of reflectance, it was found that optical absorption at the photon energy of 7.8 eV arises from Si sbnd Si bonds in the oxide film within 1.4 nm of the interface. The approximate areal density of Si sbnd Si bonds is 7 × 10 14 cm -2 and is approximately equal to the areal density of silicon su☐ides determined by X-ray photoelectron spectroscopy.

  12. Hydrogen passivation and ozone oxidation of silicon surface

    SciTech Connect

    Kurokawa, Akira; Nakamura, Ken; Ichimura, Shingo

    1998-12-31

    The oxidation of H/Si(100) and H/Si(111) with high concentration ozone gas was investigated with X-ray photoelectron spectroscopy (XPS). The ozone oxidation of partially hydride-covered surface was observed. The hydrogen termination reduced the rate of oxygen insertion into silicon backbond. The reduction of oxygen insertion rate by the H-termination for H/Si(100) was larger than that for H/Si(111). The dissociation rate of ozone molecule on H/Si was estimated to be {approx_equal}0.2 with a directional mass analyzer.

  13. Oxidation induced precipitation in Al implanted epitaxial silicon

    NASA Astrophysics Data System (ADS)

    La Ferla, A.; Galvagno, G.; Giri, P. K.; Franzò, G.; Rimini, E.; Raineri, V.; Gasparotto, A.; Cali, D.

    2000-10-01

    The behavior of Al implanted in silicon has been investigated during thermal oxidation. It has been found that precipitation of Al into Al-O-defect complexes depends on the implant energy, i.e., on the distance of the dopant from the surface. It occurs at 650 keV, but it does not at 2.0 MeV or higher energies. This phenomenon has been explained taking into account the diffusivity of self-interstitials introduced during oxidation, the oxygen present in the Si, the Al concentration, and the annealing out of defects.

  14. New perspectives on thermal and hyperthermal oxidation of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Khalilov, Umedjon

    The growth of (ultra)thin silica (SiO2) layers on crystalline silicon (c-Si) and controlling the thickness of SiO2 is an important issue in the fabrication of microelectronics and photovoltaic devices (e.g., MOSFETs, solar cells, optical fibers etc.). Such ultrathin oxide can be grown and tuned even at low temperature (including room temperature), by hyperthermal oxidation or when performed on non-planar Si surfaces (e.g., Si nanowires or spheres). However, hyperthermal silica growth as well as small Si-NW oxidation in general and the initial stages in particular have not yet been investigated in full detail. This work is therefore devoted to controlling ultrathin silica thickness on planar and non-planar Si surfaces, which can open new perspectives in nanodevice fabrication. The simulation of hyperthermal (1-100 eV) Si oxidation demonstrate that at low impact energy (<10 eV), oxygen does not damage the Si surface and this energy region could thus beneficially be used for Si oxidation. In contrast to thermal oxidation, 10 eV species can directly oxidize Si subsurface layers. A transition temperature of about 700 K was found: below this temperature, the oxide thickness only depends on the impact energy of the impinging species. Above this temperature, the oxide thickness depends on the impact energy, type of oxidant and the surface temperature. The results show that control over the ultrathin oxide (a-SiO2) thickness is possible by hyperthermal oxidation of silicon surfaces at temperatures below the transition temperature. In small Si-NWs, oxidation is a self-limiting process that occurs at low temperature, resulting in small Si core - SiO2 shell (semiconductor + dielectric) or c-Si|SiOx| a-SiO2 nanowire, which has also being envisaged to be used as nanowire field-effect transistors and photovoltaic devices in near-future nanotechnology. Above the transition temperature such core-shell nanowires are completely converted to a-SiO2 nanowires. It can be concluded that

  15. Engineering functionalized multi-phased silicon/silicon oxide nano-biomaterials to passivate the aggressive proliferation of cancer

    PubMed Central

    Premnath, P.; Tan, B.; Venkatakrishnan, K.

    2015-01-01

    Currently, the use of nano silicon in cancer therapy is limited as drug delivery vehicles and markers in imaging, not as manipulative/controlling agents. This is due to limited properties that native states of nano silicon and silicon oxides offers. We introduce nano-functionalized multi-phased silicon/silicon oxide biomaterials synthesized via ultrashort pulsed laser synthesis, with tunable properties that possess inherent cancer controlling properties that can passivate the progression of cancer. This nanostructured biomaterial is composed of individual functionalized nanoparticles made of a homogenous hybrid of multiple phases of silicon and silicon oxide in increasing concentration outwards from the core. The chemical properties of the proposed nanostructure such as number of phases, composition of phases and crystal orientation of each functionalized nanoparticle in the three dimensional nanostructure is defined based on precisely tuned ultrashort pulsed laser-material interaction mechanisms. The amorphous rich phased biomaterial shows a 30 fold (95%) reduction in number of cancer cells compared to bulk silicon in 48 hours. Further, the size of the cancer cells reduces by 76% from 24 to 48 hours. This method exposes untapped properties of combination of multiple phases of silicon oxides and its applications in cancer therapy. PMID:26190009

  16. Novel junctionless silicon-oxide-nitride-oxide-silicon memory devices with field-enhanced poly-Si nanowire structure

    NASA Astrophysics Data System (ADS)

    Chou, Chia-Hsin; Chan, Wei-Sheng; Wu, Chun-Yu; Lee, I.-Che; Liao, Ta-Chuan; Wang, Chao-Lung; Wang, Kuang-Yu; Cheng, Huang-Chung

    2015-08-01

    In this work, a novel gate-all-around (GAA) low-temperature poly-Si (LTPS) junctionless (JL) silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory device with a field-enhanced nanowire (NW) structure has been proposed to improve the programing/erasing (P/E) performance. Each nanowire has three sharp corners fabricated by a sidewall spacer formation technique to obtain high local electrical fields. Owing to the higher carrier concentration in the channel and the high local electrical field from the three sharp corners, such a JL SONOS memory device exhibits a significantly enhanced P/E speed, a larger memory window, and better data retention properties than a conventional inversion mode NW-channel memory device.

  17. Oxidation of silicon with a 5 eV O(-) beam

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Orient, O. J.; Chutjian, A.; Vasquez, R. P.

    1989-01-01

    A silicon wafer has been oxidized at room temperature in vacuum using a pure, ground-state beam of O(-) ions. The beam was of sufficiently low energy that no displacement damage or implantation was energetically possible. The resulting SiO2 films were analyzed with X-ray photoelectron spectroscopy. A logarithmic dependence of oxide thickness on dose was observed, with an extrapolated oxidation efficiency of unity for the clean silicon surface. A distinct initial oxidation phase was observed, with an anomalously high level of silicon suboxides. In addition, the valence-band offset between the silicon and the oxide was unusually small, suggesting a large interfacial dipole.

  18. Selective growth and field emission of vertically well-aligned carbon nanotubes on hole-patterned silicon substrates

    NASA Astrophysics Data System (ADS)

    Huh, Y.; Lee, J. Y.; Lee, J. H.; Lee, T. J.; Lyu, S. C.; Lee, C. J.

    2003-07-01

    We have achieved selective growth of high-purity carbon nanotubes (CNTs) on iron-deposited hole-patterns by thermal chemical vapor deposition (CVD) of acetylene gas. The vertically well-aligned CNTs were uniformly synthesized with good selectivity on hole-patterned silicon substrates. The CNTs indicated multiwalled and bamboo-like structure. The turn-on gate voltage at the CNT-based triode structure was about 55 V and emission current density was 2.0 μA at the applied gate voltage of 100 V.

  19. Fabrication and characterization of copper oxide-silicon nanowire heterojunction photodiodes

    NASA Astrophysics Data System (ADS)

    Akgul, Guvenc; Aksoy Akgul, Funda; Mulazimoglu, Emre; Emrah Unalan, Husnu; Turan, Rasit

    2014-02-01

    In this study, copper oxide (CuO) thin film/silicon (Si) nanowire heterojunctions have been fabricated and their optoelectronic performances have been investigated. Vertically aligned n-type Si nanowires have been fabricated using metal-assisted etching (MAE) technique. CuO thin films were synthesized by the sol-gel method and deposited onto the nanowires through spin-coating. Fabricated nanowire heterojunction devices exhibited excellent diode behaviour compared to the planar heterojunction control device. The rectification ratios were found to be 105 and 101 for nanowire and planar heterojunctions, respectively. The improved electrical properties and photosensitivity of the nanowire heterojunction diode was observed, which was related to the three-dimensional nature of the interface between the Si nanowires and the CuO film. Results obtained in this work reveal the potential of Si nanowire-based heterojunctions for various optoelectronic devices.

  20. Method for removing oxide contamination from silicon carbide powders

    DOEpatents

    Brynestad, J.; Bamberger, C.E.

    1984-08-01

    The described invention is directed to a method for removing oxide contamination in the form of oxygen-containing compounds such as SiO/sub 2/ and B/sub 2/O/sub 3/ from a charge of finely divided silicon carbide. The silicon carbide charge is contacted with a stream of hydrogen fluoride mixed with an inert gas carrier such as argon at a temperature in the range of about 200/sup 0/ to 650/sup 0/C. The oxides in the charge react with the heated hydrogen fluoride to form volatile gaseous fluorides such as SiF/sub 4/ and BF/sub 3/ which pass through the charge along with unreacted hydrogen fluoride and the carrier gas. Any residual gaseous reaction products and hydrogen fluoride remaining in the charge are removed by contacting the charge with the stream of inert gas which also cools the powder to room temperature. The removal of the oxygen contamination by practicing the present method provides silicon carbide powders with desirable pressing and sintering characteristics. 1 tab.

  1. Aligned Carbon Nanotube Reinforced Silicon Carbide Composites by Chemical Vapor Infiltration

    SciTech Connect

    Gu, Zhan Jun; Yang, Ying Chao; Li, Kai Yuan; Tao, Xin Yong; Eres, Gyula; Howe, Jane Y; Zhang, Li Tong; Li, Xiao Dong; Pan, Zhengwei

    2011-01-01

    Owing to their exceptional stiffness and strength1 4, carbon nanotubes (CNTs) have long been considered to be an ideal reinforcement for light-weight, high-strength, and high-temperature-resistant ceramic matrix composites (CMCs)5 10. However, the research and development in CNT-reinforced CMCs have been greatly hindered due to the challenges related to manufacturing including poor dispersion, damages during dispersion, surface modification, densification and sintering, weak tube/matrix interfaces, and agglomeration of tubes at the matrix grain boundaries5,11. Here we report the fabrication of high-quality aligned CNT/SiC composites by chemical vapor infiltration (CVI), a technique that is being widely used to fabricate commercial continuous-filament CMCs12 15. Using the CVI technique most of the challenges previously encountered in the fabrication of CNT composites were readily overcome. Nanotube pullouts, an important toughening mechanism for CMCs, were consistently observed on all fractured CNT/SiC samples. Indeed, three-point bending tests conducted on individual CNT/SiC nanowires (diameters: 50 200 nm) using an atomic force microscope show that the CNT-reinforced SiC nanowires are about an order of magnitude tougher than the bulk SiC. The tube/matrix interface is so intimate and the SiC matrix is so dense that a ~50-nm-thick SiC coating can effectively protect the inside nanotubes from being oxidized at 1600 C in air. The CVI method may be extended to produce nanotube composites from a variety of matrix

  2. Alignment of graphene oxide nanostructures between microgap electrodes via dielectrophoresis for hydrogen gas sensing applications

    SciTech Connect

    Singh, Budhi; Wang, Jianwei; Rathi, Servin; Kim, Gil-Ho

    2015-05-18

    Graphene oxide (GO) nanostructures have been aligned between conducting electrodes via dielectrophoresis (DEP) with different electrical configurations. The arrangement of ground with respect to peak-to-peak voltage (V{sub pp}) plays a crucial role in manipulating the GO nanostructures. Grounds on both sides of the V{sub pp} electrode give an excellent linking of GO nanostructures which is explained by scanning electron microscopy and current-voltage characteristics. A finite element method simulation explains the electric field and voltage variation profile during DEP process. The optimized aligned GO nanostructures are used as hydrogen gas sensor with a sensitivity of 6.0% for 800 ppm hydrogen gas.

  3. Periodic alignment of Si quantum dots on hafnium oxide coated single wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Olmedo, Mario; Martinez-Morales, Alfredo A.; Liu, Gang; Yengel, Emre; Ozkan, Cengiz S.; Lau, Chun Ning; Ozkan, Mihrimah; Liu, Jianlin

    2009-03-01

    We demonstrate a bottom up approach for the aligned epitaxial growth of Si quantum dots (QDs) on one-dimensional (1D) hafnium oxide (HfO2) ridges created by the growth of HfO2 thin film on single wall carbon nanotubes. This growth process creates a high strain 1D ridge on the HfO2 film, which favors the formation of Si seeds over the surrounding flat HfO2 area. Periodic alignment of Si QDs on the 1D HfO2 ridge was observed, which can be controlled by varying different growth conditions, such as growth temperature, growth time, and disilane flow rate.

  4. Alignment of graphene oxide nanostructures between microgap electrodes via dielectrophoresis for hydrogen gas sensing applications

    NASA Astrophysics Data System (ADS)

    Singh, Budhi; Wang, Jianwei; Rathi, Servin; Kim, Gil-Ho

    2015-05-01

    Graphene oxide (GO) nanostructures have been aligned between conducting electrodes via dielectrophoresis (DEP) with different electrical configurations. The arrangement of ground with respect to peak-to-peak voltage (Vpp) plays a crucial role in manipulating the GO nanostructures. Grounds on both sides of the Vpp electrode give an excellent linking of GO nanostructures which is explained by scanning electron microscopy and current-voltage characteristics. A finite element method simulation explains the electric field and voltage variation profile during DEP process. The optimized aligned GO nanostructures are used as hydrogen gas sensor with a sensitivity of 6.0% for 800 ppm hydrogen gas.

  5. Temperature-dependent minority carrier lifetime of crystalline silicon wafers passivated by high quality amorphous silicon oxide

    NASA Astrophysics Data System (ADS)

    Inaba, Masahiro; Todoroki, Soichiro; Nakada, Kazuyoshi; Miyajima, Shinsuke

    2016-04-01

    We investigated the effects of annealing on the temperature-dependent minority carrier lifetime of a crystalline silicon wafer passivated by hydrogenated amorphous silicon oxide. The annealing significantly affects the lifetime and its temperature dependence. Our device simulations clearly indicate that valence band offset significantly affects the temperature dependence. We also found a slight increase in the interface defect density after annealing.

  6. In situ imaging of the conducting filament in a silicon oxide resistive switch

    PubMed Central

    Yao, Jun; Zhong, Lin; Natelson, Douglas; Tour, James M.

    2012-01-01

    The nature of the conducting filaments in many resistive switching systems has been elusive. Through in situ transmission electron microscopy, we image the real-time formation and evolution of the filament in a silicon oxide resistive switch. The electroforming process is revealed to involve the local enrichment of silicon from the silicon oxide matrix. Semi-metallic silicon nanocrystals with structural variations from the conventional diamond cubic form of silicon are observed, which likely accounts for the conduction in the filament. The growth and shrinkage of the silicon nanocrystals in response to different electrical stimuli show energetically viable transition processes in the silicon forms, offering evidence for the switching mechanism. The study here also provides insights into the electrical breakdown process in silicon oxide layers, which are ubiquitous in a host of electronic devices. PMID:22355755

  7. Low reflectance sputtered vanadium oxide thin films on silicon

    NASA Astrophysics Data System (ADS)

    Esther, A. Carmel Mary; Dey, Arjun; Rangappa, Dinesh; Sharma, Anand Kumar

    2016-07-01

    Vanadium oxide thin films on silicon (Si) substrate are grown by pulsed radio frequency (RF) magnetron sputtering technique at RF power in the range of 100-700 W at room temperature. Deposited thin films are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques to investigate microstructural, phase, electronic structure and oxide state characteristics. The reflectance and transmittance spectra of the films and the Si substrate are recorded at the solar region (200-2300 nm) of the spectral window. Substantial reduction in reflectance and increase in transmittance is observed for the films grown beyond 200 W. Further, optical constants viz. absorption coefficient, refractive index and extinction coefficient of the deposited vanadium oxide films are evaluated.

  8. Thermal oxidation of 3C silicon carbide single-crystal layers on silicon

    NASA Technical Reports Server (NTRS)

    Fung, C. D.; Kopanski, J. J.

    1984-01-01

    Thermal oxidation of thick single-crystal 3C SiC layers on silicon substrates was studied. The oxidations were conducted in a wet O2 atmosphere at temperatures from 1000 to 1250 C for times from 0.1 to 50 h. Ellipsometry was used to determine the thickness and index of refraction of the oxide films. Auger analysis showed them to be homogeneous with near stoichiometric composition. The oxide growth followed a linear parabolic relationship with time. Activation energy of the parabolic rate constant was found to be 50 kcal/mole, while the linear rate constant was 74 kcal/mole. The latter value corresponds approximately to the energy required to break a Si-C bond. Electrical measurements show an effective density of 4-6 x 10 to the 11th per sq cm for fixed oxide charges at the oxide-carbide interface, and the dielectric strength of the oxide film is aproximately 6 x 10 to the 6th V/cm.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  11. Effect of hydrogen passivation on the photoluminescence of Tb ions in silicon rich silicon oxide films

    NASA Astrophysics Data System (ADS)

    Zatryb, G.; Klak, M. M.; Wojcik, J.; Misiewicz, J.; Mascher, P.; Podhorodecki, A.

    2015-12-01

    In this work, silicon-rich silicon oxide films containing terbium were prepared by means of plasma enhanced chemical vapor deposition. The influence of hydrogen passivation on defects-mediated non-radiative recombination of excited Tb3+ ions was investigated by photoluminescence, photoluminescence excitation, and photoluminescence decay measurements. Passivation was found to have no effect on shape and spectral position of the excitation spectra. In contrast, a gradual increase in photoluminescence intensity and photoluminescence decay time was observed upon passivation for the main 5D4-7F5 transition of Tb3+ ions. This observation was attributed to passivation of non-radiative recombination defects centers with hydrogen. It was found that the number of emitted photons increases upon passivation as a result of two effects: (1) longer Tb3+ lifetime in the 5D4 excited state and (2) optical activation of new Tb3+ emitters. The obtained results were discussed and compared with other experimental reports.

  12. 4 channel × 10 Gb/s bidirectional optical subassembly using silicon optical bench with precise passive optical alignment.

    PubMed

    Kang, Eun Kyu; Lee, Yong Woo; Ravindran, Sooraj; Lee, Jun Ki; Choi, Hee Ju; Ju, Gun Wu; Min, Jung Wook; Song, Young Min; Sohn, Ik-Bu; Lee, Yong Tak

    2016-05-16

    We demonstrate an advanced structure for optical interconnect consisting of 4 channel × 10 Gb/s bidirectional optical subassembly (BOSA) formed using silicon optical bench (SiOB) with tapered fiber guiding holes (TFGHs) for precise and passive optical alignment of vertical-cavity surface-emitting laser (VCSEL)-to-multi mode fiber (MMF) and MMF-to-photodiode (PD). The co-planar waveguide (CPW) transmission line (Tline) was formed on the backside of silicon substrate to reduce the insertion loss of electrical data signal. The 4 channel VCSEL and PD array are attached at the end of CPW Tline using a flip-chip bonder and solder pad. The 12-channel ribbon fiber is simply inserted into the TFGHs of SiOB and is passively aligned to the VCSEL and PD in which no additional coupling optics are required. The fabricated BOSA shows high coupling efficiency and good performance with the clearly open eye patterns and a very low bit error rate of less than 10-12 order at a data rate of 10 Gb/s with a PRBS pattern of 231-1. PMID:27409898

  13. Oxidation Behavior of Carbon Fiber Reinforced Silicon Carbide Composites

    NASA Technical Reports Server (NTRS)

    Valentin, Victor M.

    1995-01-01

    Carbon fiber reinforced Silicon Carbide (C-SiC) composites offer high strength at high temperatures and good oxidation resistance. However, these composites present some matrix microcracks which allow the path of oxygen to the fiber. The aim of this research was to study the effectiveness of a new Silicon Carbide (SiC) coating developed by DUPONT-LANXIDE to enhance the oxidation resistance of C-SiC composites. A thermogravimetric analysis was used to determine the oxidation rate of the samples at different temperatures and pressures. The Dupont coat proved to be a good protection for the SiC matrix at temperatures lower than 1240 C at low and high pressures. On the other hand, at temperatures above 1340 C the Dupont coat did not seem to give good protection to the composite fiber and matrix. Even though some results of the tests have been discussed, because of time restraints, only a small portion of the desired tests could be completed. Therefore, no major conclusions or results about the effectiveness of the coat are available at this time.

  14. Origin of complex impact craters on native oxide coated silicon surfaces

    SciTech Connect

    Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B.

    2008-02-15

    Crater structures induced by impact of keV-energy Ar{sub n}{sup +} cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar{sub 12} cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

  15. Influence of Anodic Conditions on Self-ordered Growth of Highly Aligned Titanium Oxide Nanopores

    PubMed Central

    2007-01-01

    Self-aligned nanoporous TiO2templates synthesized via dc current electrochemical anodization have been carefully analyzed. The influence of environmental temperature during the anodization, ranging from 2 °C to ambient, on the structure and morphology of the nanoporous oxide formation has been investigated, as well as that of the HF electrolyte chemical composition, its concentration and their mixtures with other acids employed for the anodization. Arrays of self-assembled titania nanopores with inner pores diameter ranging between 50 and 100 nm, wall thickness around 20–60 nm and 300 nm in length, are grown in amorphous phase, vertical to the Ti substrate, parallel aligned to each other and uniformly disordering distributed over all the sample surface. Additional remarks about the photoluminiscence properties of the titania nanoporous templates and the magnetic behavior of the Ni filled nanoporous semiconductor Ti oxide template are also included.

  16. Effect of Graphene Oxide on the Properties of Porous Silicon.

    PubMed

    Olenych, Igor B; Aksimentyeva, Olena I; Monastyrskii, Liubomyr S; Horbenko, Yulia Yu; Partyka, Maryan V; Luchechko, Andriy P; Yarytska, Lidia I

    2016-12-01

    We studied an effect of the graphene oxide (GO) layer on the optical and electrical properties of porous silicon (PS) in hybrid PS-GO structure created by electrochemical etching of silicon wafer and deposition of GO from water dispersion on PS. With the help of scanning electron microscopy (SEM), atomic-force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy, it was established that GO formed a thin film on the PS surface and is partly embedded in the pores of PS. A comparative analysis of the FTIR spectra for the PS and PS-GO structures confirms the passivation of the PS surface by the GO film. This film has a sufficient transparency for excitation and emission of photoluminescence (PL). Moreover, GO modifies PL spectrum of PS, shifting the PL maximum by 25 nm towards lower energies. GO deposition on the surface of the porous silicon leads to the change in the electrical parameters of PS in AC and DC modes. By means of current-voltage characteristics (CVC) and impedance spectroscopy, it is shown that the impact of GO on electrical characteristics of PS manifests in reduced capacitance and lower internal resistance of hybrid structures. PMID:26831681

  17. Effect of Graphene Oxide on the Properties of Porous Silicon

    NASA Astrophysics Data System (ADS)

    Olenych, Igor B.; Aksimentyeva, Olena I.; Monastyrskii, Liubomyr S.; Horbenko, Yulia Yu.; Partyka, Maryan V.; Luchechko, Andriy P.; Yarytska, Lidia I.

    2016-02-01

    We studied an effect of the graphene oxide (GO) layer on the optical and electrical properties of porous silicon (PS) in hybrid PS-GO structure created by electrochemical etching of silicon wafer and deposition of GO from water dispersion on PS. With the help of scanning electron microscopy (SEM), atomic-force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy, it was established that GO formed a thin film on the PS surface and is partly embedded in the pores of PS. A comparative analysis of the FTIR spectra for the PS and PS-GO structures confirms the passivation of the PS surface by the GO film. This film has a sufficient transparency for excitation and emission of photoluminescence (PL). Moreover, GO modifies PL spectrum of PS, shifting the PL maximum by 25 nm towards lower energies. GO deposition on the surface of the porous silicon leads to the change in the electrical parameters of PS in AC and DC modes. By means of current-voltage characteristics (CVC) and impedance spectroscopy, it is shown that the impact of GO on electrical characteristics of PS manifests in reduced capacitance and lower internal resistance of hybrid structures.

  18. Enhanced room temperature oxidation in silicon and porous silicon under 10 keV x-ray irradiation

    SciTech Connect

    Ryckman, Judson D.; Reed, Robert A.; Weller, Robert A.; Fleetwood, D. M.; Weiss, S. M.

    2010-12-01

    We report the observation of enhanced oxidation on silicon and porous silicon samples exposed in air ambient to high-dose-rate 10 keV x-ray radiation at room temperature. The evolution of the radiation-induced oxide growth is monitored by ellipsometry and interferometric reflectance spectroscopy. Fourier transform infrared (FTIR) spectroscopy shows the emergence of Si-O-Si stretching modes and corresponding suppression of SiH{sub x} and Si-Si modes in the porous silicon samples. The radiation response depends strongly on initial native oxide thickness and Si-H surface species. The enhanced oxidation mechanism is attributed to photoinduced oxidation processes wherein energetic photons are used to dissociate molecular oxygen and promote the formation of more reactive oxygen species.

  19. Silicon and tungsten oxide nanostructures for water splitting

    NASA Astrophysics Data System (ADS)

    Reyes Gil, Karla R.; Spurgeon, Joshua M.; Lewis, Nathan S.

    2009-08-01

    Inorganic semiconductors are promising materials for driving photoelectrochemical water-splitting reactions. However, there is not a single semiconductor material that can sustain the unassisted splitting of water into H2 and O2. Instead, we are developing a three part cell design where individual catalysts for water reduction and oxidation will be attached to the ends of a membrane. The job of splitting water is therefore divided into separate reduction and oxidation reactions, and each catalyst can be optimized independently for a single reaction. Silicon might be suitable to drive the water reduction. Inexpensive highly ordered Si wire arrays were grown on a single crystal wafer and transferred into a transparent, flexible polymer matrix. In this array, light would be absorbed along the longer axial dimension while the resulting electrons or holes would be collected along the much shorter radial dimension in a massively parallel array resembling carpet fibers on a microscale, hence the term "solar carpet". Tungsten oxide is a good candidate to drive the water oxidation. Self-organized porous tungsten oxide was successfully synthesized on the tungsten foil by anodization. This sponge-like structure absorbs light efficiently due to its high surface area; hence we called it "solar sponge".

  20. Understanding the role of silicon oxide shell in oxide-assisted SiNWs growth

    SciTech Connect

    Wu, Shunqing; Wang, Cai-Zhuang Z; Zhu, Z Z; Ho, Kai-Ming

    2014-12-01

    The role of silicon oxide shell in oxide-assisted SiNWs growth is studied by performing ab initio molecular dynamics simulations on the structural and dynamical properties of the interface between crystalline Si(111) surface and disorder SiO thin film. Si atoms in the SiO film tends to aggregate into the vicinity of the Si(111)/SiO interface. In addition, the diffusion of Si atoms at the interface is anisotropic - the diffusion along the interface is several times faster than that perpendicular to the interface. The segregation and anisotropic diffusion of Si atoms at the Si(111)/SiO interface shed interesting light into the mechanism of oxide-assisted silicon nanowire growth.

  1. Study of the processes of carbonization and oxidation of porous silicon by Raman and IR spectroscopy

    SciTech Connect

    Vasin, A. V.; Okholin, P. N.; Verovsky, I. N.; Nazarov, A. N.; Lysenko, V. S.; Kholostov, K. I. Bondarenko, V. P.; Ishikawa, Y.

    2011-03-15

    Porous silicon layers were produced by electrochemical etching of single-crystal silicon wafers with the resistivity 10 {Omega} cm in the aqueous-alcohol solution of hydrofluoric acid. Raman spectroscopy and infrared absorption spectroscopy are used to study the processes of interaction of porous silicon with undiluted acetylene at low temperatures and the processes of oxidation of carbonized porous silicon by water vapors. It is established that, even at the temperature 550 Degree-Sign C, the silicon-carbon bonds are formed at the pore surface and the graphite-like carbon condensate emerges. It is shown that the carbon condensate inhibits oxidation of porous silicon by water vapors and contributes to quenching of white photoluminescence in the oxidized carbonized porous silicon nanocomposite layer.

  2. Enhanced photothermal effect of surface oxidized silicon nanocrystals anchored to reduced graphene oxide nanosheets

    NASA Astrophysics Data System (ADS)

    Afshani, Parichehr; Moussa, Sherif; Atkinson, Garrett; Kisurin, Vitaly Y.; Samy El-Shall, M.

    2016-04-01

    We demonstrate the coupling of the photothermal effects of silicon nanocrystals and graphene oxide (GO) dispersed in water. Using laser irradiation (532 nm or 355 nm) of suspended Si nanocrystals in an aqueous solution of GO, the synthesis of surface oxidized Si-reduced GO nanocomposites (SiOx/Si-RGO) is reported. The laser reduction of GO is accompanied by surface oxidation of the Si nanocrystals resulting in the formation of the SiOx/Si-RGO nanocomposites. The SiOx/Si-RGO nanocomposites are proposed as promising materials for photothermal therapy and for the efficient conversion of solar energy into usable heat for a variety of thermal and thermomechanical applications.

  3. Liquid crystal terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment

    SciTech Connect

    Yang, Chan-Shan; Tang, Tsung-Ta; Pan, Ru-Pin; Yu, Peichen; Pan, Ci-Ling

    2014-04-07

    Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer for liquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding π/2 at 1.0 THz was achieved in a ∼517 μm-thick cell. The phase shifter exhibits high transmittance (∼78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxide-semiconductor (CMOS) and thin-film transistor (TFT) technologies.

  4. Characterization of silicon carbide metal oxide semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Marinella, Matthew J.

    Only a few years after the invention of the transistor, William Shockley considered silicon carbide (SiC) an excellent material for high temperature semiconductor devices. Over a half century later, SiC technology is nearly mature enough that it may be considered for use in commercial electronic devices. Furthermore, since SiC has the ability to grow thermal silicon dioxide, significant research has been directed toward the creation of a commercial SiC metal oxide semiconductor field effect transistor (MOSFET). However, a number of significant hurdles still must be overcome before SiC devices can become commercially competitive, including the relatively high cost and low quality of materials. Another significant problem is the lack of understanding of factors which limit the minority carrier lifetime. The primary purpose of this work was to use the pulsed metal oxide semiconductor capacitor (MOS-C) technique to measure generation lifetime in SiC materials. It was found that many nonidealities corrupt the results obtained by this technique. One very interesting nonideality was negative bias temperature instability (NBTI), which has also been widely studied by the silicon industry in recent years. Methods to understand and minimize the effect of these nonidealities were developed. Furthermore, these methods allowed for further study of the oxide properties, such as leakage current. Even after accounting for nonidealities, generation lifetimes showed several peculiarities, such as a variation of as much as a factor of 1000 within a square cm area. In addition, the ratio of generation to recombination lifetime is less than unity, which is not predicted by classic theory, nor typically observed in silicon devices. Possible explanations are put forth to explain these observations. In addition, to further investigate these abnormalities, Schottky diodes were fabricated and characterized. When applied to the SiC MOS capacitor, the pulsed MOS-C technique involves

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    2014-12-15

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

  7. Enhancing field emission performance of aligned Si nanowires via in situ partial oxidization.

    PubMed

    Qian, Zhongjian; Liu, Xianyun; Yang, Ye; Yin, Qiaoxia

    2014-08-01

    Partially oxidized Si nanowire (NW) arrays have been achieved via a combinatorial process of selectively etching Si wafer to obtain vertically aligned single crystalline Si NW arrays and subsequent in situ partially oxidizing the as-etched bare Si NWs. The resultant Si products are Si-SiOx nanocable-like structures consisting of single-crystalline Si NW inner cores and outer shells of insulating SiOx. Field emission measurements demonstrate that surface partial oxidization enhances the field emission current of the as-etched bare Si NWs effectively, which can be ascribed to the outer shell of insulating SiOx that has small electron affinity (0.6-0.8 eV) and can protect Si NW inner cores. The results indicate that the partially oxidized Si NW arrays would act as the excellent field emitters in the future vacuum micro- and nano-electronic devices. PMID:25936088

  8. Single crystal ternary oxide ferroelectric integration with Silicon

    NASA Astrophysics Data System (ADS)

    Bakaul, Saidur; Serrao, Claudy; Youun, Long; Khan, Asif; Salahuddin, Sayeef

    2015-03-01

    Integrating single crystal, ternary oxide ferroelectric thin film with Silicon or other arbitrary substrates has been a holy grail for the researchers since the inception of microelectronics industry. The key motivation is that adding ferroelectric materials to existing electronic devices could bring into new functionality, physics and performance improvement such as non-volatility of information, negative capacitance effect and lowering sub-threshold swing of field effect transistor (FET) below 60 mV/decade in FET [Salahuddin, S, Datta, S. Nano Lett. 8, 405(2008)]. However, fabrication of single crystal ferroelectric thin film demands stringent conditions such as lattice matched single crystal substrate and high processing temperature which are incompatible with Silicon. Here we report on successful integration of PbZr0.2Ti0.8O3 in single crystal form with by using a layer transfer method. The lattice structure, surface morphology, piezoelectric coefficient d33, dielectric constant, ferroelectric domain switching and spontaneous and remnant polarization of the transferred PZT are as good as these characteristics of the best PZT films grown by pulsed laser deposition on lattice matched oxide substrates. We also demonstrate Si based, FE gate controlled FET devices.

  9. Phonon confinement in Ge nanocrystals in silicon oxide matrix

    NASA Astrophysics Data System (ADS)

    Jie, Yiaxiong; Wee, A. T. S.; Huan, C. H. A.; Shen, Z. X.; Choi, W. K.

    2011-02-01

    Spherical Ge nanocrystals well-dispersed in amorphous silicon oxide matrix have been synthesized with different sizes, and significant size-dependent Raman shift and broadening have been observed. The lattice constant of Ge nanocrystals well-bonded to silicon oxide matrix has been characterized nearly size-independent. With our proposed stress generation and relaxation mechanisms, stress effects in our samples have been analyzed to be insignificant with respect to phonon confinement effects. The phenomenological model introduced by [Richter, Wang, and Ley, Solid State Commun. 39, 625 (1981] with Gaussian weighting function and TO2 phonon dispersion function has been found to give a quite good description of the measured size-dependence of Raman shift and broadening. A 3-peak fitting method has been proposed to determine Ge nanocrystal size and film crystallinity. After physically quantizing quantum-confined one-dimensional elastic waves, we have deduced that each quantum-confined phonon possesses an instantaneous momentum of a given magnitude ℏk with an equal chance of being either positive or negative and momentum conservation is retained in an electron-phonon scattering process. Therefore, on the basis of the first-principle microscopic model and our experimental results, we deduced that Raman scattering in spherical nanocrystals is a concurrent two-phonon process, one phonon generation and one phonon transition.

  10. 22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector

    SciTech Connect

    Geissbühler, Jonas Werner, Jérémie; Martin de Nicolas, Silvia; Hessler-Wyser, Aïcha; Tomasi, Andrea; Niesen, Bjoern; De Wolf, Stefaan; Barraud, Loris; Despeisse, Matthieu; Nicolay, Sylvain; Ballif, Christophe

    2015-08-24

    Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.

  11. 22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector

    NASA Astrophysics Data System (ADS)

    Geissbühler, Jonas; Werner, Jérémie; Martin de Nicolas, Silvia; Barraud, Loris; Hessler-Wyser, Aïcha; Despeisse, Matthieu; Nicolay, Sylvain; Tomasi, Andrea; Niesen, Bjoern; De Wolf, Stefaan; Ballif, Christophe

    2015-08-01

    Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.

  12. Oxidation of silicon nanoparticles produced by nanosecond laser ablation in liquids

    NASA Astrophysics Data System (ADS)

    Vaccaro, L.; Camarda, P.; Messina, F.; Buscarino, G.; Agnello, S.; Gelardi, F. M.; Cannas, M.; Boscaino, R.

    2014-10-01

    We investigated nanoparticles produced by laser ablation of silicon in water by the fundamental harmonic (1064 nm) of a ns pulsed Nd:YAG. The silicon oxidation is evidenced by IR absorption features characteristic of amorphous SiO2 (silica). This oxide is highly defective and manifests a luminescence activity under UV excitation: two emission bands at 2.7 eV and 4.4 eV are associated with the twofold coordinated silicon, =SiO••.

  13. Fabrication of p-type porous silicon nanowire with oxidized silicon substrate through one-step MACE

    SciTech Connect

    Li, Shaoyuan; Ma, Wenhui; Zhou, Yang; Chen, Xiuhua; Xiao, Yongyin; Ma, Mingyu; Wei, Feng; Yang, Xi

    2014-05-01

    In this paper, the simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then MPSiNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO{sub 3} system. The PL spectrum of MPSiNWs obtained from the oxidized silicon wafers show a large blue-shift, which can be attributed to the deep Q. C. effect induced by numerous mesoporous structures. The effects of HF and AgNO{sub 3} concentration on formation of SiNWs were carefully investigated. The results indicate that the higher HF concentration is favorable to the growth of SiNWs, and the density of SiNWs is significantly reduced when Ag{sup +} ions concentrations are too high. The deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon surface were studied. According to the experimental results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon. - Graphical abstract: Schematic cross-sectional views of PSiNWs array formation by etching oxidized silicon wafer in HF/AgNO{sub 3} solution. (A) At the starting point; (B) during the etching process; and (C) after Ag dendrites remove. - Highlights: • Prior to etching, a simple pre-oxidation is firstly used to treat silicon substrate. • The medially doped p-type MPSiNWs are prepared by one-step MACE. • Deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon are studied. • A model is finally proposed to explain the formation mechanism of PSiNWs.

  14. Solid oxide membrane (SOM) process for ytterbium and silicon production from their oxides

    NASA Astrophysics Data System (ADS)

    Jiang, Yihong

    The Solid oxide membrane (SOM) electrolysis is an innovative green technology that produces technologically important metals directly from their respective oxides. A yttria-stabilized zirconia (YSZ) tube, closed at one end is employed to separate the molten salt containing dissolved metal oxides from the anode inside the YSZ tube. When the applied electric potential between the cathode in the molten salt and the anode exceeds the dissociation potential of the desired metal oxides, oxygen ions in the molten salt migrate through the YSZ membrane and are oxidized at the anode while the dissolved metal cations in the flux are reduced to the desired metal at the cathode. Compared with existing metal production processes, the SOM process has many advantages such as one unit operation, less energy consumption, lower capital costs and zero carbon emission. Successful implementation of the SOM electrolysis process would provide a way to mitigate the negative environmental impact of the metal industry. Successful demonstration of producing ytterbium (Yb) and silicon (Si) directly from their respective oxides utilizing the SOM electrolysis process is presented in this dissertation. During the SOM electrolysis process, Yb2O3 was reduced to Yb metal on an inert cathode. The melting point of the supporting electrolyte (LiF-YbF3-Yb2O3) was determined by differential thermal analysis (DTA). Static stability testing confirmed that the YSZ tube was stable with the flux at operating temperature. Yb metal deposit on the cathode was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). During the SOM electrolysis process for silicon production, a fluoride based flux based on BaF2, MgF2, and YF3 was engineered to serve as the liquid electrolyte for dissolving silicon dioxide. YSZ tube was used to separate the molten salt from an anode current collector in the liquid silver. Liquid tin was chosen as cathode to dissolve the reduced silicon during

  15. Fabrication of Vertically Aligned Carbon Nanotube or Zinc Oxide Nanorod Arrays for Optical Diffraction Gratings.

    PubMed

    Kim, Jeong; Kim, Sun Il; Cho, Seong-Ho; Hwang, Sungwoo; Lee, Young Hee; Hur, Jaehyun

    2015-11-01

    We report on new fabrication methods for a transparent, hierarchical, and patterned electrode comprised of either carbon nanotubes or zinc oxide nanorods. Vertically aligned carbon nanotubes or zinc oxide nanorod arrays were fabricated by either chemical vapor deposition or hydrothermal growth, in combination with photolithography. A transparent conductive graphene layer or zinc oxide seed layer was employed as the transparent electrode. On the patterned surface defined using photoresist, the vertically grown carbon nanotubes or zinc oxides could produce a concentrated electric field under applied DC voltage. This periodic electric field was used to align liquid crystal molecules in localized areas within the optical cell, effectively modulating the refractive index. Depending on the material and morphology of these patterned electrodes, the diffraction efficiency presented different behavior. From this study, we established the relationship between the hierarchical structure of the different electrodes and their efficiency for modulating the refractive index. We believe that this study will pave a new path for future optoelectronic applications. PMID:26726580

  16. Ion beam fabrication of aluminum-doped zinc oxide layer for high-performance liquid crystals alignment.

    PubMed

    Liu, Yang; Lee, Ju Hwan; Seo, Dae-Shik

    2016-07-25

    In this paper, a 1.8 keV ion beam (IB) sputtered thin layer of aluminum-doped zinc oxide (AZO) with columnar AZO bumps covering the surface working as an alignment layer for the homogeneous alignment of liquid crystals (LC) is investigated. Bumpy AZO alignment layers in twisted nematic (TN) cells generated larger LC pre-tilt angles and thus enabled accelerated switching of LC, and the highly conductive bumpy AZO thin layers allowed super-fast release of accumulated charges, and led to low residual DC performance. These results indicate the promising applications of AZO bumps layer as alignment layer in LC devices. PMID:27464189

  17. Self Aligned Cell: Scaling Up Manufacture of a Cost Effective Cell Architecture for Multicrystalline Silicon Photovoltaics

    SciTech Connect

    Gabor, A.; van Mierlo, F.

    2010-12-01

    Two areas of technology for fabrication of higher efficiency Si-wafer solar cells were addressed: (1) the formation of structured texturing that is an improvement over the industry-standard isotexture process for multicrystalline wafers. (2) the formation of fine line (<50 micron) metallization seed layers in a self-aligned manner where the fingers can be automatically and perfectly lined up to a selective emitter and where expensive silver screen printing paste can be mostly replaced by plating up the seed layers with silver or copper. The benefits are: a) Lower reflectivity , b) Decoupling the performance of the texture from the saw damage, thus allowing for better advances in sawing and a more robust wet process. 1366 Technologies developed 2 pilot machines for 1) deposition and patterning of low-cost resist layers to enable simultaneous Honeycomb front texturing and groove formation for multicrystalline Si wafers, and 2) fine-line dispensing of materials that are self aligned to the grooves.

  18. Liquid Crystal Alignment on Solution Derived Zinc Oxide Films via Ion Beam Irradiation.

    PubMed

    Park, Hong-Gyu; Han, Jae-Jun; Seo, Dae-Shik

    2016-03-01

    A 75-nm-thick ZnO film was deposited by a sol-gel method on indium-tin oxide (ITO)-coated glass. This film served as a liquid crystal (LC) alignment layer. We report the fabrication and characteristics of this film after ion-beam (IB) irradiation. Uniform LC alignment was achieved at an IB incident energy above 2400 eV. The IB-treated ZnO surface was analyzed by X-ray photoelectron spectroscopy (XPS), monitoring the intensity of the Zn 2p and O 1s peaks as a function of IB-irradiation energy density. The electro-optical (EO) characteristics of a twisted nematic-liquid crystal display (TN-LCD) were comparable to rubbed polyimide. PMID:27455726

  19. Biaxially aligned buffer layers of cerium oxide, yttria stabilized zirconia, and their bilayers

    NASA Astrophysics Data System (ADS)

    Gnanarajan, S.; Katsaros, A.; Savvides, N.

    1997-05-01

    Biaxially aligned cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) films were deposited on Ni-based metal (Hastelloy C276) substrates held at room temperature using ion beam assisted (IBAD) magnetron deposition with the ion beam directed at 55° to the normal of the film plane. In addition, we achieved, room-temperature epitaxial growth of CeO2 by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline structure and in-plane orientation of films was investigated by x-ray diffraction techniques. Both the IBAD CeO2 and YSZ films, and the CeO2/YSZ bilayers have a (111) pole in the ion beam direction.

  20. Periodic alignment of Si quantum dots on hafnium oxide coated single wall carbon nanotubes

    SciTech Connect

    Olmedo, Mario; Martinez-Morales, Alfredo A.; Ozkan, Mihrimah; Liu Jianlin; Liu Gang; Lau, C.N.; Yengel, Emre; Ozkan, Cengiz S.

    2009-03-23

    We demonstrate a bottom up approach for the aligned epitaxial growth of Si quantum dots (QDs) on one-dimensional (1D) hafnium oxide (HfO{sub 2}) ridges created by the growth of HfO{sub 2} thin film on single wall carbon nanotubes. This growth process creates a high strain 1D ridge on the HfO{sub 2} film, which favors the formation of Si seeds over the surrounding flat HfO{sub 2} area. Periodic alignment of Si QDs on the 1D HfO{sub 2} ridge was observed, which can be controlled by varying different growth conditions, such as growth temperature, growth time, and disilane flow rate.

  1. Investigations on the growth and characterization of vertically aligned zinc oxide nanowires by radio frequency magnetronsputtering

    SciTech Connect

    Venkatesh, P. Sundara; Jeganathan, K.

    2013-04-15

    Undoped vertically aligned ZnO nanowires have been grown on silicon (111) substrates by the rf magnetron sputtering technique without metal catalyst. The diameter, length and density distributions of the nanowires have been analyzed with respect to the different growth durations. The tapering of the nanowires is observed for the growth duration of 120 min owing to the insufficient adatoms on the growth front. In the X-ray diffraction pattern, the dominant (002) peak with narrow full width at half maximum (FWHM) of ZnO nanowires indicates the c-axis orientation and high crystalline nature with hexagonal wurtzite crystal structure. The narrow FWHM of E{sub 2}{sup low} and E{sub 2}{sup high} phonon modes (1.4 and 9.1 cm{sup −1}) provide an additional evidence for the high crystalline and optical properties of the nanowires. The low temperature photoluminescence spectra are dominated by the green emission at∼2.28 eV induced by the electron transitions between shallow donor and acceptor energy levels. - Graphical abstract: Coalescence free vertically aligned ZnO nanowires have been grown on silicon (111) substrate by the radio frequency magnetron sputtering technique. Highlights: ► ZnO nanowires have been grown by rf magnetron sputtering. ► A morphologically superior and coalescence free ZnO nanowires have been realized. ► ZnO nanowires exhibit hexagonal wurtzite crystal structure. ► A dominant visible emission indicates the presence of point defects in nanowires.

  2. Growth and characterization of vertically aligned ZnO nanorods grown on porous silicon: Effect of precursor concentration

    NASA Astrophysics Data System (ADS)

    Shabannia, R.; Abu Hassan, H.

    2013-10-01

    Vertically aligned ZnO nanorods were successfully synthesized on porous silicon (PS) substrates by chemical bath deposition method at low temperature. The effect of precursor concentration on the growth of ZnO nanorods were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), low and high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. The XRD results reveal that all the as-grown ZnO nanorod arrays grew preferentially oriented along the c-axis with a hexagonal wurtzite structure. The FESEM images show that the ZnO nanorods grown perpendicular to the PS substrates had diameters and lengths ranging from 13 nm to 69 nm and from 85 nm to 208 nm, respectively. The low-resolution TEM image indicates that the ZnO nanorod arrays had a uniform diameter along their whole length and a smooth surface. PL and Raman analyses reveal that the aligned ZnO nanorods exhibited a sharp ultraviolet peak and high E2 (high) at around 390 nm and 433.8 cm-1, respectively. Furthermore, the ZnO nanorods grew vertically under 0.050 M precursor concentration, resulting in a high structural and optical quality. These ZnO nanorods can be potentially used for fabricating nanoelectronic and nano-optical devices.

  3. Oxidatively Stable Nanoporous Silicon Photocathodes for Photoelectrochemical Hydrogen Evolution

    SciTech Connect

    Neale, Nathan R.; Zhao, Yixin; Zhu, Kai; Oh, Jihun; van de Lagemaat, Jao; Yuan, Hao-Chih; Branz, Howard M.

    2014-06-02

    Stable and high-performance nanoporous 'black silicon' photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit >20 mA/cm2 photocurrent density at +0.2 V vs. reversible hydrogen electrode (RHE) for photoelectrochemical hydrogen evolution under 1 sun illumination. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, this beneficial oxide layer becomes a kinetic barrier to proton reduction that inhibits hydrogen production after just 24 h. To mitigate this problem, we developed a novel second Pt-assisted etch process that buries the Pt NPs deeper into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V vs. RHE, and reduces the charge-transfer resistance with no performance decrease seen for at least two months.

  4. Atomistic modeling of bending properties of oxidized silicon nanowires

    SciTech Connect

    Ilinov, Andrey Kuronen, Antti

    2014-03-14

    In this work, we have modeled a three point bending test of monocrystalline Si nanowires using molecular dynamics simulations in order to investigate their elastic properties. Tested nanowires were about 30 nm in length and had diameters from 5 to 9 nm. To study the influence of a native oxide layer, nanowires were covered with a 1 nm thick silica layer. The bending force was applied by a carbon diamond half-sphere with a 5 nm diameter. The Si-O parametrization for the Tersoff potential was used to describe atomic interactions between Si and O atoms. In order to remove the indentation effect of the diamond half-sphere and to obtain a pure bending behavior, we have also performed a set of simulations with fixed bottoms of the nanowires. Our results show that the oxide layer reduces the nanowire stiffness when compared with a pure Si nanowire with the same number of silicon atoms—in spite of the fact that the oxidized nanowires had larger diameters.

  5. Formation of hybrid hafnium oxide by applying sacrifacial silicon film

    NASA Astrophysics Data System (ADS)

    Lin, Chiung-Wei; Zheng, Bo-Shen; Huang, Jing-Wei

    2016-01-01

    In the fabrication of hafnium oxide (HfO2)-based metal-insulator-semiconductor (MIS) devices, a sacrificial amorphous silicon (a-Si) film was used as silicon source for facilitating the formation of hafnium silicate (Hf-silicate; HfSiO) between HfO2 and crystallized Si (c-Si). HfSiO can assist in changing the phase of the HfO2 film into the tetragonal phase and achieve high dielectric constant. The combination of HfSiO and HfO2 was named as “Hybrid HfO2”. When this Hybrid HfO2 insulator was applied to MIS devices, it can form a good insulator/semiconductor interface with c-Si. Hybrid HfO2 cannot only suppress the leakage current but also show high dielectric strength. The Hybrid HfO2 film in this work exhibited a high dielectric constant of 25.5 and a high dielectric strength of 17.9 MV/cm.

  6. Shrinking of silicon nanocrystals embedded in an amorphous silicon oxide matrix during rapid thermal annealing in a forming gas atmosphere

    NASA Astrophysics Data System (ADS)

    van Sebille, M.; Fusi, A.; Xie, L.; Ali, H.; van Swaaij, R. A. C. M. M.; Leifer, K.; Zeman, M.

    2016-09-01

    We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.

  7. Efficient and sustained photoelectrochemical water oxidation by cobalt oxide/silicon photoanodes with nanotextured interfaces.

    PubMed

    Yang, Jinhui; Walczak, Karl; Anzenberg, Eitan; Toma, Francesca M; Yuan, Guangbi; Beeman, Jeffrey; Schwartzberg, Adam; Lin, Yongjing; Hettick, Mark; Javey, Ali; Ager, Joel W; Yano, Junko; Frei, Heinz; Sharp, Ian D

    2014-04-30

    Plasma-enhanced atomic layer deposition of cobalt oxide onto nanotextured p(+)n-Si devices enables efficient photoelectrochemical water oxidation and effective protection of Si from corrosion at high pH (pH 13.6). A photocurrent density of 17 mA/cm(2) at 1.23 V vs RHE, saturation current density of 30 mA/cm(2), and photovoltage greater than 600 mV were achieved under simulated solar illumination. Sustained photoelectrochemical water oxidation was observed with no detectable degradation after 24 h. Enhanced performance of the nanotextured structure, compared to planar Si, is attributed to a reduced silicon oxide thickness that provides more intimate interfacial contact between the light absorber and catalyst. This work highlights a general approach to improve the performance and stability of Si photoelectrodes by engineering the catalyst/semiconductor interface. PMID:24720554

  8. Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

    SciTech Connect

    Wan, Yimao Bullock, James; Cuevas, Andres

    2015-05-18

    This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta{sub 2}O{sub 5}) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN{sub x}). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta{sub 2}O{sub 5} and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm{sup 2} and 68 fA/cm{sup 2} are measured on 150 Ω/sq boron-diffused p{sup +} and 120 Ω/sq phosphorus-diffused n{sup +} c-Si, respectively. Capacitance–voltage measurements reveal a negative fixed insulator charge density of −1.8 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5} film and −1.0 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5}/SiN{sub x} stack. The Ta{sub 2}O{sub 5}/SiN{sub x} stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

  9. Film-edge-induced dislocation generation in silicon substrates. II. Application of the theoretical model for local oxidation processes on (001) silicon substrates

    NASA Astrophysics Data System (ADS)

    Vanhellemont, J.; Amelinckx, S.; Claeys, C.

    1987-03-01

    A theoretical model which allows prediction of the type and of the equilibrium configuration of dislocations generated or captured in fcc substrates at the edges of thin films is applied to local oxidation processes on (001) Czochralski silicon substrates. Nitride film structures aligned along the two most interesting crystallographic directions on the (001) surface, i.e., the <110> and the <100> directions, are studied by high-voltage electron microscopy. The model allows to explain the observed dislocation types including most of the previous reports in the literature. Some numerical examples are given which illustrate the strength of the model to obtain even quantitative information both on the film stresses and on the critical glide force from the observed equilibrium configuration of the defects. Good agreement is obtained between the observed shape and position of the defects and computer simulations based on the model.

  10. Damage at hydrogenated amorphous/crystalline silicon interfaces by indium tin oxide overlayer sputtering

    NASA Astrophysics Data System (ADS)

    Demaurex, Bénédicte; De Wolf, Stefaan; Descoeudres, Antoine; Charles Holman, Zachary; Ballif, Christophe

    2012-10-01

    Damage of the hydrogenated amorphous/crystalline silicon interface passivation during transparent conductive oxide sputtering is reported. This occurs in the fabrication process of silicon heterojunction solar cells. We observe that this damage is at least partially caused by luminescence of the sputter plasma. Following low-temperature annealing, the electronic interface properties are recovered. However, the silicon-hydrogen configuration of the amorphous silicon film is permanently changed, as observed from infra-red absorbance spectra. In silicon heterojunction solar cells, although the as-deposited film's microstructure cannot be restored after sputtering, no significant losses are observed in their open-circuit voltage.

  11. Improved performance of microcrystalline silicon solar cell with graded-band-gap silicon oxide buffer layer

    NASA Astrophysics Data System (ADS)

    Shi, Zhen-Liang; Ji, Yun; Yu, Wei; Yang, Yan-Bin; Cong, Ri-Dong; Chen, Ying-Juan; Li, Xiao-Wei; Fu, Guang-Sheng

    2015-07-01

    Microcrystalline silicon (μc-Si:H) solar cell with graded band gap microcrystalline silicon oxide (μc-SiOx:H) buffer layer is prepared by plasma enhanced chemical vapor deposition and exhibits improved performance compared with the cell without it. The buffer layer moderates the band gap mismatch by reducing the barrier of the p/i interface, which promotes the nucleation of the i-layer and effectively eliminates the incubation layer, and then enhances the collection efficiency of the cell in the short wavelength region of the spectrum. The p/i interface defect density also decreases from 2.2 × 1012 cm-2 to 5.0 × 1011 cm-2. This graded buffer layer allows to simplify the deposition process for the μc-Si:H solar cell application. Project supported by the Key Basic Research Project of Hebei Province, China (Grant Nos. 12963930D and 12963929D), the Natural Science Foundation of Hebei Province, China (Grant Nos. F2013201250 and E2012201059), and the Science and Technology Research Projects of the Education Department of Hebei Province, China (Grant No. ZH2012030).

  12. Microbridge testing of plasma-enhanced chemical-vapor deposited silicon oxide films on silicon wafers

    NASA Astrophysics Data System (ADS)

    Cao, Zhiqiang; Zhang, Tong-Yi; Zhang, Xin

    2005-05-01

    Plasma-enhanced chemical-vapor deposited (PECVD) silane-based oxides (SiOx) have been widely used in both microelectronics and microelectromechanical systems (MEMS) to form electrical and/or mechanical components. In this paper, a nanoindentation-based microbridge testing method is developed to measure both the residual stresses and Young's modulus of PECVD SiOx films on silicon wafers. Theoretically, we considered both the substrate deformation and residual stress in the thin film and derived a closed formula of deflection versus load. The formula fitted the experimental curves almost perfectly, from which the residual stresses and Young's modulus of the film were determined. Experimentally, freestanding microbridges made of PECVD SiOx films were fabricated using the silicon undercut bulk micromachining technique. Some microbridges were subjected to rapid thermal annealing (RTA) at a temperature of 400 °C, 600 °C, or 800 °C to simulate the thermal process in the device fabrication. The results showed that the as-deposited PECVD SiOx films had a residual stress of -155±17MPa and a Young's modulus of 74.8±3.3GPa. After the RTA, Young's modulus remained relatively unchanged at around 75 GPa, however, significant residual stress hysteresis was found in all the films. A microstructure-based mechanism was then applied to explain the experimental results of the residual stress changes in the PECVD SiOx films after the thermal annealing.

  13. Transparent Conducting Oxides for Photovoltaics: Manipulation of Fermi Level, Work Function and Energy Band Alignment

    SciTech Connect

    Klein, A.; Körber, C.; Wachau, A.; Säuberlich, F.; Gassenbauer, Y.; Harvey, S.P.; Proffit, Diana E.; Mason, Thomas O.

    2010-11-02

    Doping limits, band gaps, work functions and energy band alignments of undoped and donor-doped transparent conducting oxides ZnO, In{sub 2}O{sub 3}, and SnO{sub 2} as accessed by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) are summarized and compared. The presented collection provides an extensive data set of technologically relevant electronic properties of photovoltaic transparent electrode materials and illustrates how these relate to the underlying defect chemistry, the dependence of surface dipoles on crystallographic orientation and/or surface termination, and Fermi level pinning.

  14. GHz properties of magnetophoretically aligned iron-oxide nanoparticle doped polymers.

    PubMed

    Pisanello, Ferruccio; De Paolis, Rosa; Lorenzo, Daniela; Guardia, Pablo; Nitti, Simone; Monti, Giuseppina; Fragouli, Despina; Athanassiou, Athanassia; Tarricone, Luciano; Manna, Liberato; De Vittorio, Massimo; Martiradonna, Luigi

    2013-04-24

    We show that assembled domains of magnetic iron-oxide nanoparticles (IONPs) are effective at increasing the dielectric permittivity of polydimethylsiloxane (PDMS) nanocomposites in the GHz frequency range. The assembly has been achieved by means of magnetophoretic transport and its efficacy, as well as the electromagnetic properties of the nanocomposite, has been found to depend on IONPs diameter. Remarkably, the dielectric permittivity increase has been obtained by keeping dielectric and magnetic losses very low, making us envision the suitability of nanocomposites based on aligned IONPs as substrates for radiofrequency applications. PMID:23537058

  15. Silicon cells made by self-aligned selective-emitter plasma-etchback process

    DOEpatents

    Ruby, Douglas S.; Schubert, William K.; Gee, James M.; Zaidi, Saleem H.

    2000-01-01

    Photovoltaic cells and methods for making them are disclosed wherein the metallized grids of the cells are used to mask portions of cell emitter regions to allow selective etching of phosphorus-doped emitter regions. The preferred etchant is SF.sub.6 or a combination of SF.sub.6 and O.sub.2. This self-aligned selective etching allows for enhanced blue response (versus cells with uniform heavy doping of the emitter) while preserving heavier doping in the region beneath the gridlines needed for low contact resistance. Embodiments are disclosed for making cells with or without textured surfaces. Optional steps include plasma hydrogenation and PECVD nitride deposition, each of which are suited to customized applications for requirements of given cells to be manufactured. The techniques disclosed could replace expensive and difficult alignment methodologies used to obtain selectively etched emitters, and they may be easily integrated with existing plasma processing methods and techniques of the invention may be accomplished in a single plasma-processing chamber.

  16. Studies on Thermal and Mechanical Properties of Epoxy-Silicon Oxide Hybrid Materials

    NASA Astrophysics Data System (ADS)

    Ghosh, P. K.; Kumar, Kaushal; Kumar, Arun

    2015-11-01

    Ultrasonic dual mixing (UDM) process involving ultrasonic vibration with simultaneous stirring is used to prepare epoxy-silicon oxide hybrid materials with inorganic nanoscale building blocks by incorporating nanoscale silicon oxide network in epoxy matrix. The silicon oxide network is obtained from tetraethoxysilane (TEOS) by using the in situ sol-gel process. Same epoxy-silica hybrid materials were also prepared by mixing with simple impeller stirring, and its properties were compared with the material of same composition prepared by the UDM process. The epoxy-silicon oxide hybrid materials are characterized by using FT-IR, DSC, FESEM, and XRD techniques. The glass transition temperature, tensile strength, and elastic modulus of the epoxy-silicon oxide hybrid materials treated by UDM process are found comparatively better than those of the materials processed by a rotating impeller. FESEM studies confirm that amount of TEOS varies the distribution and size of silicon oxide network, which remains relatively finer at lower content of TEOS. Significant improvement of thermal and mechanical properties of the neat epoxy is noted in the presence of 3.05 wt.% TEOS content in it is giving rise to the formation of inorganic building block of silicon oxide of size 88 ± 45 nm in the matrix. In this regard, the use of UDM process is found superior to mixing by simple impeller stirring for enhancement of properties of epoxy-silicon oxide hybrid materials. Lowering of properties of the epoxy-silicon oxide hybrid materials with TEOS addition beyond 3.05 wt.% up to 6.1 wt.% occurs primarily due to increase of amount and size (up to 170 ± 82 nm) of the inorganic building block in the matrix.

  17. Serum protein layers on parylene-C and silicon oxide: Effect on cell adhesion

    PubMed Central

    Delivopoulos, Evangelos; Ouberai, Myriam M.; Coffey, Paul D.; Swann, Marcus J.; Shakesheff, Kevin M.; Welland, Mark E.

    2015-01-01

    Among the range of materials used in bioengineering, parylene-C has been used in combination with silicon oxide and in presence of the serum proteins, in cell patterning. However, the structural properties of adsorbed serum proteins on these substrates still remain elusive. In this study, we use an optical biosensing technique to decipher the properties of fibronectin (Fn) and serum albumin adsorbed on parylene-C and silicon oxide substrates. Our results show the formation of layers with distinct structural and adhesive properties. Thin, dense layers are formed on parylene-C, whereas thicker, more diffuse layers are formed on silicon oxide. These results suggest that Fn acquires a compact structure on parylene-C and a more extended structure on silicon oxide. Nonetheless, parylene-C and silicon oxide substrates coated with Fn host cell populations that exhibit focal adhesion complexes and good cell attachment. Albumin adopts a deformed structure on parylene-C and a globular structure on silicon oxide, and does not support significant cell attachment on either surface. Interestingly, the co-incubation of Fn and albumin at the ratio found in serum, results in the preferential adsorption of albumin on parylene-C and Fn on silicon oxide. This finding is supported by the exclusive formation of focal adhesion complexes in differentiated mouse embryonic stem cells (CGR8), cultured on Fn/albumin coated silicon oxide, but not on parylene-C. The detailed information provided in this study on the distinct properties of layers of serum proteins on substrates such as parylene-C and silicon oxide is highly significant in developing methods for cell patterning. PMID:25555155

  18. Preparation of silicon@silicon oxide core-shell nanowires from a silica precursor toward a high energy density Li-ion battery anode.

    PubMed

    Zhang, Chuanjian; Gu, Lin; Kaskhedikar, Nitin; Cui, Guanglei; Maier, Joachim

    2013-12-11

    Bulk-quantity silicon@silicon oxide nanowires have been successfully synthesized via a facile high-temperature approach using environment-friendly silica mixed with titanium powders. It is confirmed that the obtained nanowires process a crystalline core and amorphous oxide sheath. The obtained nanowires grow along the [111] direction which catalyzed by spherical silicon@siilcon oxide nanoparticles. The unique one-dimensional structure and thin oxide sheath result in the favorable electrochemical performances, which may be beneficial to the high energy density silicon anode for lithium ion batteries. PMID:24229329

  19. Electrical characterization of low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures

    NASA Astrophysics Data System (ADS)

    Ang, S. S.; Shi, Y. J.; Brown, W. D.

    1993-03-01

    The electrical characteristics of as-deposited and oxygen-annealed low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide (SiO2) metal-oxide-silicon (MOS) structures were investigated. As-deposited LPCVD SiO2 MOS structures exhibit a high oxide fixed charge density in the mid-1011 cm-2 and an interface state density in the low-1011 cm-2 eV-1 due to the large number of oxygen and silicon dangling bonds. A low electron barrier height in these structures (1.2 eV) is presumed to be due to lowering of the barrier by excess silicon microclusters. Oxygen-annealed LPCVD SiO2 MOS structures exhibit oxide fixed charge and interface state densities in the mid-1010 cm-2 and mid-1010 cm-2 eV-1, respectively. Both the as-deposited and annealed devices exhibit turnaround in flatband voltage shift with avalanche electron injection. However, the direction of shift is opposite for the two devices with the annealed device being very similar to that of thermally grown SiO2 MOS structures. Apparently, oxygen annealing restructures and oxidizes the partial SiOx in the as-deposited LPCVD oxide into stochiometric SiO2. However, the residual nonstochiometric SiO2 microclusters in the bulk result in an electron barrier height of only 2.3 eV.

  20. Photocurrent spectroscopy of Ge nanoclusters grown on oxidized silicon surface

    NASA Astrophysics Data System (ADS)

    Mykytiuk, A. A.; Kondratenko, S. V.; Lysenko, V. S.; Kozyrev, Yu. N.

    2014-05-01

    Germanium (Ge) nanoclusters are grown by a molecular-beam epitaxy technique on chemically oxidized Si(100) surface at 700ºC. Evidence for long-term photoinduced changes of surface conductivity in structures with Ge nanoclusters (NCs) grown on silicon oxide is presented. Photoexcitation NCs or Si by quanta with different energy allows observing two non-equilibrium steady-states with excess and shortage of conductivity values as compare to equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after interband excitation of electron-hole pairs in Si(001) substrate. This effect may be attributed to spatial carrier separation of photoexcited electron-hole pairs by macroscopic fields in the depletion layer of near-surface Si. Photoquenching of surface conductivity, driven by optical recharging of Ge NC's and Si/SiO2 interface states, is observed. Conductivity decay is discussed in the terms of hole`s accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.

  1. Enhanced field emission of vertically aligned core-shelled carbon nanotubes with molybdenum oxide encapsulation

    SciTech Connect

    Yu, J.; Chua, Daniel H. C.; Sow, C. H.; Wee, Andrew T. S.

    2009-06-01

    The field emission characteristics of the core-shelled nanostructures obtained by directly coating molybdenum oxide onto vertically aligned multiwalled carbon nanotubes (MWNTs) was investigated. A metal-organic chemical vapor deposition technique was used with Mo(CO){sub 6} as the precursor and films deposited at process temperatures of 200, 400, and 700 deg. C. X-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray diffraction were used to study and understand the material properties of the deposited coatings. Enhanced field emission performance was observed for molybdenum oxide coated MWNT samples at 400 deg. C with a turn-on field of 1.33 V mum{sup -1} and a field enhancement factor beta estimated to be approx7000. The enhanced performance may be due to both the shape of the coated emitters and a decrease in the effective barrier height.

  2. Self-aligned multi-channel silicon nanowire field-effect transistors

    NASA Astrophysics Data System (ADS)

    Zhu, Hao; Li, Qiliang; Yuan, Hui; Baumgart, Helmut; Ioannou, Dimitris E.; Richter, Curt A.

    2012-12-01

    Si nanowire field effect transistors (SiNW FETs) with multiple nanowire channels and different gate lengths have been fabricated by using a directed assembly approach combined with a standard photolithographic process. The electrical characteristics of SiNW FETs containing different numbers of nanowire channels were measured and compared. The multi-channel SiNW FETs show excellent performance: small subthreshold slope (≈75 mV/dec), large ON/OFF ratio (≈108), good break-down voltage (>30 V) and good carrier mobility (μp ≈ 100 cm2 V-1s-1). These excellent device properties were achieved by using a clean self-alignment process and an improved device structure with Schottky barriers at the source and drain contacts. Such high-performance multi-nanowire FETs are attractive for logic, memory, and sensor applications.

  3. Interstellar polarization and grain alignment: the role of iron and silicon

    NASA Astrophysics Data System (ADS)

    Voshchinnikov, N. V.; Henning, Th.; Prokopjeva, M. S.; Das, H. K.

    2012-05-01

    We compiled the polarimetric data for a sample of lines of sight with known abundances of Mg, Si, and Fe. We correlated the degree of interstellar polarization P and polarization efficiency (the ratio of P to the colour excess E(B - V) or extinction AV) with dust phase abundances. We detect an anticorrelation between P and the dust phase abundance of iron in non silicate-containing grains [Fe(rest)/H]d, a correlation between P and the abundance of Si, and no correlation between P/E(B - V) or P/AV and dust phase abundances. These findings can be explained if mainly the silicate grains aligned by the radiative mechanism are responsible for the observed interstellar linear polarization. Table 1 is available in electronic form at http://www.aanda.org

  4. Monolithic integration of rare-earth oxides and semiconductors for on-silicon technology

    SciTech Connect

    Dargis, Rytis Clark, Andrew; Erdem Arkun, Fevzi; Grinys, Tomas; Tomasiunas, Rolandas; O'Hara, Andy; Demkov, Alexander A.

    2014-07-01

    Several concepts of integration of the epitaxial rare-earth oxides into the emerging advanced semiconductor on silicon technology are presented. Germanium grows epitaxially on gadolinium oxide despite lattice mismatch of more than 4%. Additionally, polymorphism of some of the rare-earth oxides allows engineering of their crystal structure from hexagonal to cubic and formation of buffer layers that can be used for growth of germanium on a lattice matched oxide layer. Molecular beam epitaxy and metal organic chemical vapor deposition of gallium nitride on the rare-earth oxide buffer layers on silicon is discussed.

  5. High-temperature oxidation behavior of reaction-formed silicon carbide ceramics

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.; Singh, M.

    1995-01-01

    The oxidation behavior of reaction-formed silicon carbide (RFSC) ceramics was investigated in the temperature range of 1100 to 1400 C. The oxidation weight change was recorded by TGA; the oxidized materials were examined by light and electron microscopy, and the oxidation product by x-ray diffraction analysis (XRD). The materials exhibited initial weight loss, followed by passive weight gain (with enhanced parabolic rates, k(sub p)), and ending with a negative (logarithmic) deviation from the parabolic law. The weight loss arose from the oxidation of residual carbon, and the enhanced k(sub p) values from internal oxidation and the oxidation of residual silicon, while the logarithmic kinetics is thought to have resulted from crystallization of the oxide. The presence of a small amount of MoSi, in the RFSC material caused a further increase in the oxidation rate. The only solid oxidation product for all temperatures studied was silica.

  6. Method of fabricating conducting oxide-silicon solar cells utilizing electron beam sublimation and deposition of the oxide

    DOEpatents

    Feng, Tom; Ghosh, Amal K.

    1979-01-01

    In preparing tin oxide and indium tin oxide-silicon heterojunction solar cells by electron beam sublimation of the oxide and subsequent deposition thereof on the silicon, the engineering efficiency of the resultant cell is enhanced by depositing the oxide at a predetermined favorable angle of incidence. Typically the angle of incidence is between 40.degree. and 70.degree. and preferably between 55.degree. and 65.degree. when the oxide is tin oxide and between 40.degree. and 70.degree. when the oxide deposited is indium tin oxide. gi The Government of the United States of America has rights in this invention pursuant to Department of Energy Contract No. EY-76-C-03-1283.

  7. Silicon nanoprofiling with the use of a solid aluminum oxide mask and combined 'dry' etching

    SciTech Connect

    Belov, A. N.; Demidov, Yu. A.; Putrya, M. G.; Golishnikov, A. A.; Vasilyev, A. A.

    2009-12-15

    Technological features of nanoprofiling of silicon protected by a solid mask based on porous aluminum oxide are considered. It is shown that, for a nanoprofiled silicon surface to be formed, it is advisable that combined dry etching be used including preliminary bombardment of structures with accelerated neutral atoms of an inert gas followed by reactive ion etching.

  8. Mediator-less highly sensitive voltammetric detection of glutamate using glutamate dehydrogenase/vertically aligned CNTs grown on silicon substrate.

    PubMed

    Gholizadeh, Azam; Shahrokhian, Saeed; zad, Azam Iraji; Mohajerzadeh, Shamsoddin; Vosoughi, Manouchehr; Darbari, Sara; Sanaee, Zeinab

    2012-01-15

    A sensitive glutamate biosensor is prepared based on glutamate dehydrogenase/vertically aligned carbon nanotubes (GLDH, VACNTs). Vertically aligned carbon nanotubes were grown on a silicon substrate by direct current plasma enhanced chemical vapor deposition (DC-PECVD) method. The electrochemical behavior of the synthesized VACNTs was investigated by cyclic voltammetry and electrochemical impedance spectroscopic methods. Glutamate dehydrogenase covalently attached on tip of VACNTs. The electrochemical performance of the electrode for detection of glutamate was investigated by cyclic and differential pulse voltammetry. Differential pulse voltammetric determinations of glutamate are performed in mediator-less condition and also, in the presence of 1 and 5 μM thionine as electron mediator. The linear calibration curve of the concentration of glutamate versus peak current is investigated in a wide range of 0.1-500 μM. The mediator-less biosensor has a low detection limit of 57 nM and two linear ranges of 0.1-20 μM with a sensitivity of 0.976 mA mM(-1) cm(-2) and 20-300 μM with a sensitivity of 0.182 mA mM(-1) cm(-2). In the presence of 1 μM thionine as an electron mediator, the prepared biosensor shows a low detection limit of 68 nM and two linear ranges of 0.1-20 with a calibration sensitivity of 1.17 mA mM(-1) cm(-2) and 20-500 μM with a sensitivity of 0.153 mA mM(-1) cm(-2). The effects of the other biological compounds on the voltammetric behavior of the prepared biosensor and its response stability are investigated. The results are demonstrated that the GLDH/VACNTs electrode even without electron mediator is a suitable basic electrode for detection of glutamate. PMID:22040749

  9. Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes.

    PubMed

    Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M; Gambhir, Sanjeev; Wallace, Gordon G; Kozlov, Mikhail E; Baughman, Ray H; Kim, Seon Jeong

    2012-01-01

    The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g(-1), far exceeding spider dragline silk (165 J g(-1)) and Kevlar (78 J g(-1)). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs. PMID:22337128

  10. Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M.; Gambhir, Sanjeev; Wallace, Gordon G.; Kozlov, Mikhail E.; Baughman, Ray H.; Kim, Seon Jeong

    2012-01-01

    The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g-1, far exceeding spider dragline silk (165 J g-1) and Kevlar (78 J g-1). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs.

  11. Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes

    PubMed Central

    Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M.; Gambhir, Sanjeev; Wallace, Gordon G.; Kozlov, Mikhail E.; Baughman, Ray H.; Kim, Seon Jeong

    2012-01-01

    The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g−1, far exceeding spider dragline silk (165 J g−1) and Kevlar (78 J g−1). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs. PMID:22337128

  12. Role of atomic layer deposited aluminum oxide as oxidation barrier for silicon based materials

    SciTech Connect

    Fiorentino, Giuseppe Morana, Bruno; Forte, Salvatore; Sarro, Pasqualina Maria

    2015-01-15

    In this paper, the authors study the protective effect against oxidation of a thin layer of atomic layer deposited (ALD) aluminum oxide (Al{sub 2}O{sub 3}). Nitrogen doped silicon carbide (poly-SiC:N) based microheaters coated with ALD Al{sub 2}O{sub 3} are used as test structure to investigate the barrier effect of the alumina layers to oxygen and water vapor at very high temperature (up to 1000 °C). Different device sets have been fabricated changing the doping levels, to evaluate possible interaction between the dopants and the alumina layer. The as-deposited alumina layer morphology has been evaluated by means of AFM analysis and compared to an annealed sample (8 h at 1000 °C) to estimate the change in the grain structure and the film density. The coated microheaters are subjected to very long oxidation time in dry and wet environment (up to 8 h at 900 and 1000 °C). By evaluating the electrical resistance variation between uncoated reference devices and the ALD coated devices, the oxide growth on the SiC is estimated. The results show that the ALD alumina coating completely prevents the oxidation of the SiC up to 900 °C in wet environment, while an oxide thickness reduction of 50% is observed at 1000 °C compared to uncoated devices.

  13. The electroluminescence mechanism of Er3+ in different silicon oxide and silicon nitride environments

    NASA Astrophysics Data System (ADS)

    Rebohle, L.; Berencén, Y.; Wutzler, R.; Braun, M.; Hiller, D.; Ramírez, J. M.; Garrido, B.; Helm, M.; Skorupa, W.

    2014-09-01

    Rare earth doped metal-oxide-semiconductor (MOS) structures are of great interest for Si-based light emission. However, several physical limitations make it difficult to achieve the performance of light emitters based on compound semiconductors. To address this point, in this work the electroluminescence (EL) excitation and quenching mechanism of Er-implanted MOS structures with different designs of the dielectric stack are investigated. The devices usually consist of an injection layer made of SiO2 and an Er-implanted layer made of SiO2, Si-rich SiO2, silicon nitride, or Si-rich silicon nitride. All structures implanted with Er show intense EL around 1540 nm with EL power efficiencies in the order of 2 × 10-3 (for SiO2:Er) or 2 × 10-4 (all other matrices) for lower current densities. The EL is excited by the impact of hot electrons with an excitation cross section in the range of 0.5-1.5 × 10-15 cm-2. Whereas the fraction of potentially excitable Er ions in SiO2 can reach values up to 50%, five times lower values were observed for other matrices. The decrease of the EL decay time for devices with Si-rich SiO2 or Si nitride compared to SiO2 as host matrix implies an increase of the number of defects adding additional non-radiative de-excitation paths for Er3+. For all investigated devices, EL quenching cross sections in the 10-20 cm2 range and charge-to-breakdown values in the range of 1-10 C cm-2 were measured. For the present design with a SiO2 acceleration layer, thickness reduction and the use of different host matrices did not improve the EL power efficiency or the operation lifetime, but strongly lowered the operation voltage needed to achieve intense EL.

  14. Fabrication of p-type porous silicon nanowire with oxidized silicon substrate through one-step MACE

    NASA Astrophysics Data System (ADS)

    Li, Shaoyuan; Ma, Wenhui; Zhou, Yang; Chen, Xiuhua; Xiao, Yongyin; Ma, Mingyu; Wei, Feng; Yang, Xi

    2014-05-01

    In this paper, the simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then MPSiNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO3 system. The PL spectrum of MPSiNWs obtained from the oxidized silicon wafers show a large blue-shift, which can be attributed to the deep Q. C. effect induced by numerous mesoporous structures. The effects of HF and AgNO3 concentration on formation of SiNWs were carefully investigated. The results indicate that the higher HF concentration is favorable to the growth of SiNWs, and the density of SiNWs is significantly reduced when Ag+ ions concentrations are too high. The deposition behaviors of Ag+ ions on oxidized and unoxidized silicon surface were studied. According to the experimental results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon.

  15. Microstructure, toughness and flexural strength of self-reinforced silicon nitride ceramics doped with yttrium oxide and ytterbium oxide.

    PubMed

    Zheng, Y. S.; Knowles, K. M.; Vieira, J. M.; Lopes, A. B.; Oliveira, F. J.

    2001-02-01

    Self-reinforced silicon nitride ceramics with additions of either yttrium oxide or ytterbium oxide have been investigated at room temperature after various processing heat treatments. Devitrification of the intergranular phase in these materials is very sensitive to the heat treatment used during processing and does not necessarily improve their strength and toughness. Hot-pressed ceramics without a subsequent devitrification heat treatment were the strongest. The ytterbium oxide-doped silicon nitride ceramics were consistently tougher, but less strong, than the yttrium oxide-doped silicon nitride ceramics. In all the ceramics examined, the fracture toughness showed evidence for R-curve behaviour. This was most significant in pressureless sintered ytterbium oxide-doped silicon nitride ceramics. A number of toughening mechanisms, including crack deflection, bridging, and fibre-like grain pull-out, were observed during microstructural analysis of the ceramics. In common with other silicon nitride-based ceramics, thin amorphous films were found at the grain boundaries in each of the ceramics examined. Arrays of dislocations left in the elongated silicon nitride grains after processing were found to belong to the {101;0}<0001> primary slip system. PMID:11207926

  16. Structural alloy with a protective coating containing silicon or silicon-oxide

    DOEpatents

    Natesan, Ken

    1994-01-01

    An iron-based alloy containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100.degree. C.

  17. Structural alloy with a protective coating containing silicon or silicon-oxide

    DOEpatents

    Natesan, K.

    1992-01-01

    This invention is comprised of an iron-based alloy containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100{degrees}C.

  18. Structural alloy with a protective coating containing silicon or silicon-oxide

    DOEpatents

    Natesan, K.

    1994-12-27

    An iron-based alloy is described containing chromium and optionally, nickel. The alloy has a surface barrier of silicon or silicon plus oxygen which converts at high temperature to a protective silicon compound. The alloy can be used in oxygen-sulfur mixed gases at temperatures up to about 1100 C. 8 figures.

  19. Synchrotron x-ray reflectivity study of oxidation/passivation of copper and silicon.

    SciTech Connect

    Chu, Y.; Nagy, Z.; Parkhutik, V.; You, H.

    1999-07-21

    Synchrotron x-ray-scattering technique studies of copper and silicon electrochemical interfaces are reported. These two examples illustrate the application of synchrotron x-ray techniques for oxidation, passivation, and dissolution of metals and semiconductors.

  20. Method for forming indium oxide/n-silicon heterojunction solar cells

    DOEpatents

    Feng, Tom; Ghosh, Amal K.

    1984-03-13

    A high photo-conversion efficiency indium oxide/n-silicon heterojunction solar cell is spray deposited from a solution containing indium trichloride. The solar cell exhibits an Air Mass One solar conversion efficiency in excess of about 10%.

  1. Vertically aligned crystalline silicon nanowires with controlled diameters for energy conversion applications: Experimental and theoretical insights

    SciTech Connect

    Razek, Sara Abdel; Swillam, Mohamed A.; Allam, Nageh K.

    2014-05-21

    Vertically orientated single crystalline silicon nanowire (SiNW) arrays with controlled diameters are fabricated via a metal-assisted chemical etching method. The diameter of the fabricated nanowires is controlled by simply varying the etching time in HF/H{sub 2}O{sub 2} electrolytes. The fabricated SiNWs have diameters ranging from 117 to 650 nm and lengths from 8 to 18 μm. The optical measurements showed a significant difference in the reflectance/absorption of the SiNWs with different diameters, where the reflectance increases with increasing the diameter of the SiNWs. The SiNWs showed significant photoluminescence (PL) emission spectra with peaks lying between 380 and 670 nm. The PL intensity increases as the diameter increases and shows red shift for peaks at ∼670 nm. The increase or decrease of reflectivity is coincident with PL intensity at wavelength ∼660 nm. The x-ray diffraction patterns confirm the high crystallinity of the fabricated SiNWs. In addition, the Raman spectra showed a shift in the first order transverse band toward lower frequencies compared to that usually seen for c-Si. Finite difference time domain simulations have been performed to confirm the effect of change of diameter on the optical properties of the nanowires. The simulation results showed good agreement with the experimental results for the SiNWs of different diameters.

  2. Optimized lithography process for through-silicon vias-fabrication using a double-sided (structured) photomask for mask aligner lithography

    NASA Astrophysics Data System (ADS)

    Weichelt, Tina; Stuerzebecher, Lorenz; Zeitner, Uwe D.

    2015-07-01

    Through-silicon vias (TSV) are very important for wafer-level packaging as they provide patterning holes through thick silicon dies to integrate and interconnect devices which are stacked in the z-direction. For economic processing, TSV fabrication primarily needs to be cost effective, especially for a high throughput. Furthermore, a lithography process for TSV has to be stable enough to allow patterning on prestructured substrates with inhomogeneous topography. This can be addressed by an exposure process which offers a large depth of focus. We have developed a mask-aligner lithography process based on the use of a double-sided photomask to realize aerial images that meet these constraints.

  3. Mixed-phase p-type silicon oxide containing silicon nanocrystals and its role in thin-film silicon solar cells

    NASA Astrophysics Data System (ADS)

    Cuony, P.; Marending, M.; Alexander, D. T. L.; Boccard, M.; Bugnon, G.; Despeisse, M.; Ballif, C.

    2010-11-01

    Lower absorption, lower refractive index, and tunable resistance are three advantages of amorphous silicon oxide containing nanocrystalline silicon grains (nc-SiOx) compared to microcrystalline silicon (μc-Si), when used as a p-type layer in μc-Si thin-film solar cells. We show that p-nc-SiOx with its particular nanostructure increases μc-Si cell efficiency by reducing reflection and parasitic absorption losses depending on the roughness of the front electrode. Furthermore, we demonstrate that the p-nc-SiOx reduces the detrimental effects of the roughness on the electrical characteristics, and significantly increases μc-Si and Micromorph cell efficiency on substrates until now considered too rough for thin-film silicon solar cells.

  4. Alternative method for steam generation for thermal oxidation of silicon

    NASA Astrophysics Data System (ADS)

    Spiegelman, Jeffrey J.

    2010-02-01

    Thermal oxidation of silicon is an important process step in MEMS device fabrication. Thicker oxide layers are often used as structural components and can take days or weeks to grow, causing high gas costs, maintenance issues, and a process bottleneck. Pyrolytic steam, which is generated from hydrogen and oxygen combustion, was the default process, but has serious drawbacks: cost, safety, particles, permitting, reduced growth rate, rapid hydrogen consumption, component breakdown and limited steam flow rates. Results from data collected over a 24 month period by a MEMS manufacturer supports replacement of pyrolytic torches with RASIRC Steamer technology to reduce process cycle time and enable expansion previously limited by local hydrogen permitting. Data was gathered to determine whether Steamers can meet or exceed pyrolytic torch performance. The RASIRC Steamer uses de-ionized water as its steam source, eliminating dependence on hydrogen and oxygen. A non-porous hydrophilic membrane selectively allows water vapor to pass. All other molecules are greatly restricted, so contaminants in water such as dissolved gases, ions, total organic compounds (TOC), particles, and metals can be removed in the steam phase. The MEMS manufacturer improved growth rate by 7% over the growth range from 1μm to 3.5μm. Over a four month period, wafer uniformity, refractive index, wafer stress, and etch rate were tracked with no significant difference found. The elimination of hydrogen generated a four-month return on investment (ROI). Mean time between failure (MTBF) was increased from 3 weeks to 32 weeks based on three Steamers operating over eight months.

  5. Thromboresistance Characterization of Extruded Nitric Oxide-Releasing Silicone Catheters

    PubMed Central

    Amoako, Kagya A.; Archangeli, Christopher; Handa, Hitesh; Major, Terry; Meyerhoff, Mark E.; Annich, Gail M.; Bartlett, Robert H.

    2013-01-01

    Intravascular catheters used in clinical practice can activate platelets, leading to thrombus formation and stagnation of blood flow. Nitric oxide (NO)-releasing polymers have been shown previously to reduce clot formation on a number of blood contacting devices. In this work, trilaminar NO-releasing silicone catheters were fabricated and tested for their thrombogenicity. All catheters had specifications of L = 6 cm, inner diameter = 21 gauge (0.0723 cm), outer diameter = 12 gauge (0.2052 cm), and NO-releasing layer thickness = 200 ± 11 μm. Control and NO-releasing catheters were characterized in vitro for their NO flux and NO release duration by gas phase chemiluminescence measurements. The catheters were then implanted in the right and left internal jugular veins of (N = 6 and average weight = 3 kg) adult male rabbits for 4 hours thrombogenicity testing. Platelet counts and function, methemoglobin (metHb), hemoglobin (Hb), and white cell counts and functional time (defined as patency time of catheter) were monitored as measured outcomes. Nitric oxide-releasing catheters (N = 6) maintained an average flux above (2 ± 0.5) × 10−10 mol/min/cm2 for more than 24 hours, whereas controls showed no NO release. Methemoglobin, Hb, white cell, and platelet counts and platelet function at 4 hours were not significantly different from baseline (α = 0.05). However, clots on controls were visibly larger and prevented blood draws at a significantly (p < 0.05) earlier time (2.3 ± 0.7 hours) into the experiment, whereas all NO-releasing catheters survived the entire 4 hours test period. Results indicate that catheter NO flux levels attenuated thrombus formation in a short-term animal model. PMID:22395119

  6. Assembly and evaluation of a pyroelectric detector bonded to vertically aligned multiwalled carbon nanotubes over thin silicon.

    PubMed

    Theocharous, E; Theocharous, S P; Lehman, J H

    2013-11-20

    A novel pyroelectric detector consisting of a vertically aligned nanotube array on thin silicon (VANTA/Si) bonded to a 60 μm thick crystal of LiTaO₃ has been fabricated. The performance of the VANTA/Si-coated pyroelectric detector was evaluated using National Physical Laboratory's (NPL's) detector-characterization facilities. The relative spectral responsivity of the detector was found to be spectrally flat in the 0.8-24 μm wavelength range, in agreement with directional-hemispherical reflectance measurements of witness samples of the VANTA. The spatial uniformity of response of the test detector exhibited good uniformity, although the nonuniformity increased with increasing modulation frequency. The nonuniformity may be assigned either to the dimensions of the VANTA or the continuity of the bond between the VANTA/Si coating and the pyroelectric crystal substrate. The test detector exhibited a small superlinear response, which is similar to that of pyroelectric detectors coated with good quality gold-black coatings. PMID:24513757

  7. Silicon oxide permeation barrier coating of PET bottles and foils

    NASA Astrophysics Data System (ADS)

    Steves, Simon; Deilmann, Michael; Awakowicz, Peter

    2009-10-01

    Modern packaging materials such as polyethylene terephthalate (PET) have displaced established materials in many areas of food and beverage packaging. Plastic packing materials offer are various advantages concerning production and handling. PET bottles for instance are non-breakable and lightweight compared to glass and metal containers. However, PET offers poor barrier properties against gas permeation. Therefore, the shelf live of packaged food is reduced. Permeation of gases can be reduced by depositing transparent plasma polymerized silicon oxide (SiOx) barrier coatings. A microwave (2.45 GHz) driven low pressure plasma reactor is developed based on a modified Plasmaline antenna to treat PET foils or bottles. To increase the barrier properties of the coatings furthermore a RF substrate bias (13.56 MHz) is applied. The composition of the coatings is analyzed by means of Fourier transform infrared (FTIR) spectroscopy regarding carbon and hydrogen content. Influence of gas phase composition and substrate bias on chemical composition of the coatings is discussed. A strong relation between barrier properties and film composition is found: good oxygen barriers are observed as carbon content is reduced and films become quartz-like. Regarding oxygen permeation a barrier improvement factor (BIF) of 70 is achieved.

  8. Resistive Switching and Memory effects in Silicon Oxide Based Nanostructures

    NASA Astrophysics Data System (ADS)

    Yao, Jun

    Silicon oxide (SiOx 1 < x ≦2) has long been used and considered as a passive and insulating component in the construction of electronic devices. In contrast, here the active role of SiOx in constructing a type of resistive switching memory is studied. From electrode-independent electrical behaviors to the visualization of the conducting filament inside the SiOx matrix, the intrinsic switching picture in SiOx is gradually revealed. The thesis starts with the introduction of some similar phenomenological switching behaviors in different electronic structures (Chapter 1), and then generalizes the electrode-material-independent electrical behaviors on SiOx substrates, providing indirect evidence to the intrinsic SiOx switching (Chapter 2). From planar nanogap systems to vertical sandwiched structures, Chapter 3 further discusses the switching behaviors and properties in SiOx. By localization of the switching site, the conducting filament in SiOx is visualized under transmission electron microscope using both static and in situ imaging methods (Chapter 4). With the intrinsic conduction and switching in SiO x largely revealed, Chapter 5 discusses its impact and implications to the molecular electronics and nanoelectronics where SiOx is constantly used. As comparison, another type of memory effect in semiconductors (carbon nanotubes) based on charge trapping at the semiconductor/SiO x interface is discussed (Chapter 6).

  9. Crystalline Silicon/Graphene Oxide Hybrid Junction Solar Cells

    NASA Astrophysics Data System (ADS)

    Liu, Qiming; Wanatabe, Fumiya; Hoshino, Aya; Ishikawa, Ryo; Gotou, Takuya; Ueno, Keiji; Shirai, Hajime

    2012-10-01

    Soluble graphene oxide (GO) and plasma-reduced (pr-) GO were investigated using crystalline silicon (c-Si) (100)/GO/pr-GO hybrid junction solar cells. Their photovoltaic performances were compared with those of c-Si/GO/pristine conductive poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) heterojunction and c-Si/PEDOT:PSS:GO composite devices. The c-Si/GO/pr-GO and conductive PEDOT:PSS/Al heterojunction solar cells showed power conversion efficiencies of 6.5 and 8.2%, respectively, under illumination with AM 1.5 G 100 mW/cm2 simulated solar light. A higher performance of 10.7% was achieved using the PEDOT:PSS:GO (12.5 wt %) composite device. These findings imply that soluble GO, pr-GO, and the PEDOT:PSS:GO composite are promising materials as hole transport and transparent conductive layers for c-Si/organic hybrid junction solar cells.

  10. Electrical characterization of hydrogenated amorphous silicon oxide films

    NASA Astrophysics Data System (ADS)

    Itoh, Takashi; Katayama, Ryuichi; Yamakawa, Koki; Matsui, Kento; Saito, Masaru; Sugiyama, Shuhichiroh; Sichanugrist, Porponth; Nonomura, Shuichi; Konagai, Makoto

    2015-08-01

    The electrical characterization of hydrogenated amorphous silicon oxide (a-SiOx:H) films was performed by electron spin resonance (ESR) and electrical conductivity measurements. In the ESR spectra of the a-SiOx:H films, two ESR peaks with g-values of 2.005 and 2.013 were observed. The ESR peak with the g-value of 2.013 was not observed in the ESR spectra of a-Si:H films. The photoconductivity of the a-SiOx:H films decreased with increasing spin density estimated from the ESR peak with the g-value of 2.005. On the other hand, photoconductivity was independent of spin density estimated from the ESR peak with the g-value of 2.013. The optical absorption coefficient spectra of the a-SiOx:H films were also measured. The spin density estimated from the ESR peak with the g-value of 2.005 increased proportionally with increasing optical absorption owing to the gap-state defect.

  11. Degenerate epitaxy-driven defects in monolayer silicon oxide on ruthenium

    NASA Astrophysics Data System (ADS)

    Mathur, Shashank; Vlaic, Sergio; Machado-Charry, Eduardo; Vu, Anh-Duc; Guisset, Valérie; David, Philippe; Hadji, Emmanuel; Pochet, Pascal; Coraux, Johann

    2015-10-01

    The structure of the ultimately thin crystalline allotrope of silicon oxide, prepared on a ruthenium surface, is unveiled down to the atomic scale with chemical sensitivity, owing to high resolution scanning tunneling microscopy and first principles calculations. An ordered oxygen lattice is imaged which coexists with the two-dimensional monolayer oxide. This coexistence signals a displacive transformation from an oxygen-reconstructed Ru(0001) to silicon oxide, along which laterally shifted domains form, each with equivalent and degenerate epitaxial relationships with the substrate. The unavoidable character of defects at the boundaries between these domains appeals for the development of alternative methods capable of producing single-crystalline two-dimensional oxides.

  12. Correlation between density and oxidation temperature for pyrolytic-gas passivated ultrathin silicon oxide films

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroshi

    2004-01-01

    Pyrolytic-gas passivation (PGP) with a small amount nitrogen gas enhances the breakdown reliability of silicon oxide gate films. To clarify the reliability retention of the PGP-grown films oxidized at low temperature, densities (ρox's) of the 3.5-6.5-nm-thick PGP-grown films on Si(100) oxidized at 700-900 °C were investigated. Since ρox's correlate well with the reliability and are useful as an index of the intrinsic structural characteristics of the films. Moreover, changes in ρox and nitrogen content corresponding to oxidation temperature are similar to those in breakdown reliability and interface state density (Dit), respectively. In addition, ρox's of the 700 °C-grown PGP films do not deteriorate as much when compared with those of the films grown by normal ultradry oxidation at 800 °C and their Dit's are less than about 6×1010/eV cm2. This suggests that PGP probably improves the reliability by generating the higher-ρox microscopic structure with few Si dangling bonds and effective passivation. .

  13. Process for depositing an oxide epitaxially onto a silicon substrate and structures prepared with the process

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    1993-01-01

    A process and structure involving a silicon substrate utilizes an ultra high vacuum and molecular beam epitaxy (MBE) methods to grow an epitaxial oxide film upon a surface of the substrate. As the film is grown, the lattice of the compound formed at the silicon interface becomes stabilized, and a base layer comprised of an oxide having a sodium chloride-type lattice structure grows epitaxially upon the compound so as to cover the substrate surface. A perovskite may then be grown epitaxially upon the base layer to render a product which incorporates silicon, with its electronic capabilities, with a perovskite having technologically-significant properties of its own.

  14. Self-Assembled Epitaxial Au-Oxide Vertically Aligned Nanocomposites for Nanoscale Metamaterials.

    PubMed

    Li, Leigang; Sun, Liuyang; Gomez-Diaz, Juan Sebastian; Hogan, Nicki L; Lu, Ping; Khatkhatay, Fauzia; Zhang, Wenrui; Jian, Jie; Huang, Jijie; Su, Qing; Fan, Meng; Jacob, Clement; Li, Jin; Zhang, Xinghang; Jia, Quanxi; Sheldon, Matthew; Alù, Andrea; Li, Xiaoqin; Wang, Haiyan

    2016-06-01

    Metamaterials made of nanoscale inclusions or artificial unit cells exhibit exotic optical properties that do not exist in natural materials. Promising applications, such as super-resolution imaging, cloaking, hyperbolic propagation, and ultrafast phase velocities have been demonstrated based on mostly micrometer-scale metamaterials and few nanoscale metamaterials. To date, most metamaterials are created using costly and tedious fabrication techniques with limited paths toward reliable large-scale fabrication. In this work, we demonstrate the one-step direct growth of self-assembled epitaxial metal-oxide nanocomposites as a drastically different approach to fabricating large-area nanostructured metamaterials. Using pulsed laser deposition, we fabricated nanocomposite films with vertically aligned gold (Au) nanopillars (∼20 nm in diameter) embedded in various oxide matrices with high epitaxial quality. Strong, broad absorption features in the measured absorbance spectrum are clear signatures of plasmon resonances of Au nanopillars. By tuning their densities on selected substrates, anisotropic optical properties are demonstrated via angular dependent and polarization resolved reflectivity measurements and reproduced by full-wave simulations and effective medium theory. Our model predicts exotic properties, such as zero permittivity responses and topological transitions. Our studies suggest that these self-assembled metal-oxide nanostructures provide an exciting new material platform to control and enhance optical response at nanometer scales. PMID:27186652

  15. Chemical Bath Deposition of Aluminum Oxide Buffer on Curved Surfaces for Growing Aligned Carbon Nanotube Arrays.

    PubMed

    Wang, Haitao; Na, Chongzheng

    2015-07-01

    Direct growth of vertically aligned carbon nanotube (CNT) arrays on substrates requires the deposition of an aluminum oxide buffer (AOB) layer to prevent the diffusion and coalescence of catalyst nanoparticles. Although AOB layers can be readily created on flat substrates using a variety of physical and chemical methods, the preparation of AOB layers on substrates with highly curved surfaces remains challenging. Here, we report a new solution-based method for preparing uniform layers of AOB on highly curved surfaces by the chemical bath deposition of basic aluminum sulfate and annealing. We show that the thickness of AOB layer can be increased by extending the immersion time of a substrate in the chemical bath, following the classical Johnson-Mehl-Avrami-Kolmogorov crystallization kinetics. The increase of AOB thickness in turn leads to the increase of CNT length and the reduction of CNT curviness. Using this method, we have successfully synthesized dense aligned CNT arrays of micrometers in length on substrates with highly curved surfaces including glass fibers, stainless steel mesh, and porous ceramic foam. PMID:26053766

  16. Template-Assisted Hydrothermal Growth of Aligned Zinc Oxide Nanowires for Piezoelectric Energy Harvesting Applications

    PubMed Central

    2016-01-01

    A flexible and robust piezoelectric nanogenerator (NG) based on a polymer-ceramic nanocomposite structure has been successfully fabricated via a cost-effective and scalable template-assisted hydrothermal synthesis method. Vertically aligned arrays of dense and uniform zinc oxide (ZnO) nanowires (NWs) with high aspect ratio (diameter ∼250 nm, length ∼12 μm) were grown within nanoporous polycarbonate (PC) templates. The energy conversion efficiency was found to be ∼4.2%, which is comparable to previously reported values for ZnO NWs. The resulting NG is found to have excellent fatigue performance, being relatively immune to detrimental environmental factors and mechanical failure, as the constituent ZnO NWs remain embedded and protected inside the polymer matrix. PMID:27172933

  17. Template-Assisted Hydrothermal Growth of Aligned Zinc Oxide Nanowires for Piezoelectric Energy Harvesting Applications.

    PubMed

    Ou, Canlin; Sanchez-Jimenez, Pedro E; Datta, Anuja; Boughey, Francesca L; Whiter, Richard A; Sahonta, Suman-Lata; Kar-Narayan, Sohini

    2016-06-01

    A flexible and robust piezoelectric nanogenerator (NG) based on a polymer-ceramic nanocomposite structure has been successfully fabricated via a cost-effective and scalable template-assisted hydrothermal synthesis method. Vertically aligned arrays of dense and uniform zinc oxide (ZnO) nanowires (NWs) with high aspect ratio (diameter ∼250 nm, length ∼12 μm) were grown within nanoporous polycarbonate (PC) templates. The energy conversion efficiency was found to be ∼4.2%, which is comparable to previously reported values for ZnO NWs. The resulting NG is found to have excellent fatigue performance, being relatively immune to detrimental environmental factors and mechanical failure, as the constituent ZnO NWs remain embedded and protected inside the polymer matrix. PMID:27172933

  18. In situ transmission infrared spectroscopy of high-kappa oxide atomic layer deposition onto silicon surfaces

    NASA Astrophysics Data System (ADS)

    Ho, Ming-Tsung

    Ultra-thin aluminum oxide (Al2O3) and hafnium oxide (HfO2) layers have been grown by atomic layer deposition (ALD) using tri-methyl-aluminum (TMA) and tetrakis-ethyl-methyl-amino-hafnium (TEMAH) respectively with heavy water (D2O) as the oxidizing agent. Several different silicon surfaces were used as substrates such as hydrogen terminated silicon (H/Si), SC2 (or RCA 2) cleaned native silicon oxide (SiO 2/Si), and silicon (oxy)nitride. In-situ transmission Fourier transform infrared spectroscopy (FTIR) has been adopted for the study of the growth mechanisms during ALD of these films. The vibrational spectra of gas phase TEMAH and its reaction byproducts with oxidants have also been investigated. Density functional theory (DFT) normal mode calculations show a good agreement with the experimental data when it is combined with linear wave-number scaling method and Fermi resonance mechanism. Ether (-C-O-C-) and tertiary alkylamine (N(R1R 2R3)) compounds are the two most dominant products of TEMAH reacting with oxygen gas and water. When ozone is used as the oxidant, gas phase CH2O, CH3NO2, CH3-N=C=O and other compounds containing -(C=O)- and --C-O-C- (or --O-C-) segments are observed. With substrate temperatures less than 400°C and 300°C for TMA and TEMAH respectively, Al oxide and Hf oxide ALD can be appropriately performed on silicon surfaces. Thin silicon (oxy)nitride thermally grown in ammonia on silicon substrate can significantly reduce silicon oxide interlayer formation during ALD and post-deposition annealing. The crystallization temperature of amorphous ALD grown HfO2 on nitridized silicon is 600°C, which is 100°C higher than on the other silicon surfaces. When HfO2 is grown on H/Si(111) at 100°C deposition temperature, minimum 5--10 ALD cycles are required for the full surface coverage. The steric effect can be seen by the evolution of the H-Si stretching mode at 2083 cm-1. The observed red shift of H-Si stretching to ˜ 2060 cm-1 can be caused by Si

  19. Ethylene oxide-block-butylene oxide copolymer uptake by silicone hydrogel contact lens materials

    NASA Astrophysics Data System (ADS)

    Huo, Yuchen; Ketelson, Howard; Perry, Scott S.

    2013-05-01

    Four major types of silicone hydrogel contact lens material have been investigated following treatments in aqueous solutions containing poly(ethylene oxide) and poly(butylenes oxide) block copolymer (EO-BO). The extent of lens surface modification by EO-BO and the degree of bulk uptake were studied using X-ray photoelectron spectroscopy (XPS) and ultra-performance liquid chromatography (UPLC), respectively. The experimental results suggest that different interaction models exist for the lenses, highlighting the influence of both surface and bulk composition, which greatly differs between the lenses examined. Specifically, lenses with hydrophilic surface treatments, i.e., PureVision® (balafilcon A) and O2OPTIX (lotrafilcon B), demonstrated strong evidence of preferential surface adsorption within the near-surface region. In comparison, surface adsorption on ACUVUE® Oasys® (senofilcon A) and Biofinity® (comfilcon A) was limited. As for bulk absorption, the amount of EO-BO uptake was the greatest for balafilcon A and comfilcon A, and least for lotrafilcon B. These findings confirm the presence of molecular concentration gradients within the silicone hydrogel lenses following exposure to EO-BO solutions, with the nature of such concentration gradients found to be lens-specific. Together, the results suggest opportunities for compositional modifications of lenses for improved performance via solution treatments containing surface-active agents.

  20. High performance high-κ/metal gate complementary metal oxide semiconductor circuit element on flexible silicon

    NASA Astrophysics Data System (ADS)

    Torres Sevilla, G. A.; Almuslem, A. S.; Gumus, A.; Hussain, A. M.; Cruz, M. E.; Hussain, M. M.

    2016-02-01

    Thinned silicon based complementary metal oxide semiconductor (CMOS) electronics can be physically flexible. To overcome challenges of limited thinning and damaging of devices originated from back grinding process, we show sequential reactive ion etching of silicon with the assistance from soft polymeric materials to efficiently achieve thinned (40 μm) and flexible (1.5 cm bending radius) silicon based functional CMOS inverters with high-κ/metal gate transistors. Notable advances through this study shows large area of silicon thinning with pre-fabricated high performance elements with ultra-large-scale-integration density (using 90 nm node technology) and then dicing of such large and thinned (seemingly fragile) pieces into smaller pieces using excimer laser. The impact of various mechanical bending and bending cycles show undeterred high performance of flexible silicon CMOS inverters. Future work will include transfer of diced silicon chips to destination site, interconnects, and packaging to obtain fully flexible electronic systems in CMOS compatible way.

  1. Critical issues of complex, epitaxial oxide growth and integration with silicon by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lettieri, James

    Molecular beam epitaxy was used to grow epitaxial oxides on silicon substrates. The growth of BaO, SrO, EuO, and SrTiO3 are discussed with a focus on the general theme of integration of functional, epitaxial oxides into a silicon environment. Oxidation studies of various metal systems relevant for oxide on silicon epitaxy and integration are reported. Results demonstrate the catalytic nature of an alkaline earth metal at small concentrations to enable the oxidation of the poorly oxidizing metals at pressures lower than during deposition of the pure metal alone. Results from the deposition of various elements are presented. The aspects of the growth of alkaline earth oxides on silicon are explained. The transition from the silicon to the alkaline earth oxide as described through reflection high energy electron diffraction (RHEED) is presented and used to understand issues related to each stage of the growth. High quality, commensurate alkaline earth oxides are grown on silicon at room temperature and P O2 background ˜ 3 x 10-8 Torr. The growth of alkaline earth and rare earth oxide solid solutions and rare earth oxides (EuO) are described. The first reported epitaxial EuO on silicon is reported, enabled by the use of a thin buffer layer (13 A) of SrO. Using a strategy of transition from simple structures to the more complex, the growth of a perovskite (SrTiO3) on silicon is demonstrated. Growth of a structurally optimized perovskite structure entails the transformation of a thin interfacial alkaline earth oxide layer into the initial perovskite cells. SrTiO3 and La-doped SrTiO3 on silicon are used to integrate a piezoelectric relevant for microelectromechanical systems (MEMS) applications and a ferroelectric relevant for a ferroelectric random access memory (FRAM) architecture. A d33 value of over 400 pm/V under bias is measured for the piezoelectric (Pb(Mn1/3Nb 2/3)O3 -PbTiO3) and a remanent polarization of 25 muC/cm2 and fatigue free behavior (>1012 cycles) for a

  2. Gas-phase formation of silicon carbides, oxides, and sulphides from atomic silicon ions

    NASA Technical Reports Server (NTRS)

    Bohme, Diethard K.; Wlodek, Stanislaw; Fox, Arnold

    1989-01-01

    A systematic experimental study of the kinetics and mechanisms of the chemical reactions in the gas phase between ground-state Si(+)2p and a variety of astrophysical molecules. The aim of this study is to identify the reactions which trigger the formation of chemical bonds between silicon and carbon, oxygen and sulphur, and the chemical pathways which lead to further molecular growth. Such knowledge is valuable in the identification of new extraterrestrial silicon-bearing molecules and for an assessment of the gas-phase transition from atomic silicon to silicon carbide and silicate grain particles in carbon-rich and oxygen-rich astrophysical environments.

  3. Method for one-to-one polishing of silicon nitride and silicon oxide

    NASA Technical Reports Server (NTRS)

    Babu, Suryadevara V. (Inventor); Natarajan, Anita (Inventor)

    2009-01-01

    The present invention provides a method of removing silicon nitride at about the same removal rate as silicon dioxide by CMP. The method utilizes a polishing slurry that includes colloidal silica abrasive particles dispersed in water and additives that modulate the silicon dioxide and silicon nitride removal rates such that they are about the same. In one embodiment of the invention, the additive is lysine or lysine mono hydrochloride in combination with picolinic acid, which is effective at a pH of about 8. In another embodiment of the invention, the additive is arginine in combination with picolinic acid, which is effective at a pH of about 10.

  4. RF Reactive Magnetron Sputter Deposition of Silicon Sub-Oxides

    NASA Astrophysics Data System (ADS)

    van Hattum, E. D.

    2007-01-01

    RF reactive magnetron plasma sputter deposition of silicon sub oxide E.D. van Hattum Department of Physics and Astronomy, Faculty of Sciences, Utrecht University The work described in the thesis has been inspired and stimulated by the use of SiOx layers in the direct inductive printing technology, where the SiOx layer is used as the charge retention layer on the drums for copying and printing devices. The thesis describes investigations of the plasma and of processes taking place on the sputter target and on the SiOx growth surface in the room temperature, RF reactive magnetron plasma sputter deposition technology. The sputtering target consists of silicon and the reactive atmosphere consists of an Ar/O2 mixture. The composition of the grown SiOx layers has been varied between x=0 and x=2 by variation of the O2 partial pressure. The characteristics of the growth process have been related to the nanostructural properties of the grown films. The deposition system enables the characterisation of the plasma (Langmuir probe, energy resolved mass spectrometer) and of the growing film (Elastic Recoil Detection (ERD), Fourier transform infrared absorption spectroscopy) and is connected to a beamline of a 6MV tandem van de Graaff accelerator. Also Rutherford Backscattering Spectrometry and X-ray Photoelectron Spectroscopy have been applied. It is shown how ERD can be used as a real-time in-situ technique. The thesis presents spatially resolved values of the ion density, electron temperature and the quasi-electrostatic potential, determined using a Langmuir probe. The plasma potential has a maximum about 2 cm from the cathode erosion area, and decreases (more than 200 V typically) towards the floating sputter cathode. The potential decreases slightly in the direction towards the grounded growth surface and the positive, mainly Ar+, ions created in the large volume of the plasma closest to the substrate are accelerated towards the growth surface. These ions obtain a few eV of

  5. Electrical characterization of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures

    NASA Astrophysics Data System (ADS)

    Ang, S. S.; Shi, Y. J.; Brown, W. D.

    1996-02-01

    The electrical characteristics of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide metal-oxide-silicon (MOS) structures were investigated. Both nitridation temperature and time affect the properties of the MOS structures as revealed by capacitance-voltage characteristics. Nitridation at 1000 °C for 15 s followed by re-oxidation for 60 s at 1000 °C in an oxygen/nitrogen ambient was found to be superior to the same nitridation for 60 s with no re-oxidation. Typical values of fixed charge and interface state densities for devices subjected to nitridation and re-oxidation in a mixture of oxygen and nitrogen were 4×1010 cm-2 and 7×1010 eV-1 cm-2, respectively. Avalanche electron injection using electric fields of 3-3.5 MV/cm produced positive shifts in flatband voltage for devices nitrided at 1000 °C for 15 s followed by re-oxidation, whereas samples nitrided at 1000 °C for 60 s without the re-oxidation yielded negative shifts in flatband voltage. An electron barrier height of 2.4 eV was found for these nitrided samples. These results strongly suggest that device quality MOS dielectrics for high-voltage power MOS field-effect-transistors can be realized by nitridation/re-oxidation of LPCVD oxide.

  6. Comparison of Structural and Optoelectronic Properties of N-Type Microcrystalline Silicon and Silicon Oxide Films with Lowering of Thickness

    NASA Astrophysics Data System (ADS)

    Banerjee, Chandan; Sarker, Arindam; Barua, Asok K.

    2002-08-01

    We have compared the structural and optoelectronic properties of n-type microcrystalline hydrogenated silicon oxide (n-μc-SiO:H) and n-type microcrystalline hydrogenated silicon (n-μc-Si:H) films with lowering of thickness, prepared by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD, 13.56 MHz) method. At thickness ≤ 300 Å, the n-μc-SiO:H film has higher optical gap (E05) and lower optical absorption while retaining the photoconductivity (σph) and activation energy (Ea) similar to those for n-μc-Si:H film. Due to these advantages of n-μc-SiO:H film over that of n-μc-Si:H at low thickness this material has potential for use in improving the performance of single and double junction amorphous silicon solar cells.

  7. An Alignment Medium for Measuring Residual Dipolar Couplings in Pure DMSO: Liquid Crystals from Graphene Oxide Grafted with Polymer Brushes.

    PubMed

    Zong, Wen; Li, Gao-Wei; Cao, Jiang-Ming; Lei, Xinxiang; Hu, Mao-Lin; Sun, Han; Griesinger, Christian; Tan, Ren Xiang

    2016-03-01

    Residual dipolar couplings (RDCs) have attracted attention in light of their great impact on the structural elucidation of organic molecules. However, the effectiveness of RDC measurements is limited by the shortage of alignment media compatible with widely used organic solvents, such as DMSO. Herein, we present the first liquid crystal (LC) based alignment medium that is compatible with pure DMSO, thus enabling RDC measurements of polar and intermediate polarity molecules. The liquid crystals were obtained by grafting polymer brushes onto graphene oxide (GO) using free radical polymerization. The resulting new medium offers several advantages, such as absence of background signals, narrow line shapes, and tunable alignment. Importantly, this medium is compatible with π-conjugated molecules. Moreover, sonication-induced fragmentation can reduce the size of GO sheets. The resulting anisotropic medium has moderate alignment strength, which is a prerequisite for an accurate RDC measurement. PMID:26890579

  8. The complex interface chemistry of thin-film silicon/zinc oxide solar cell structures.

    PubMed

    Gerlach, D; Wimmer, M; Wilks, R G; Félix, R; Kronast, F; Ruske, F; Bär, M

    2014-12-21

    The interface between solid-phase crystallized phosphorous-doped polycrystalline silicon (poly-Si(n(+))) and aluminum-doped zinc oxide (ZnO:Al) was investigated using spatially resolved photoelectron emission microscopy. We find the accumulation of aluminum in the proximity of the interface. Based on a detailed photoemission line analysis, we also suggest the formation of an interface species. Silicon suboxide and/or dehydrated hemimorphite have been identified as likely candidates. For each scenario a detailed chemical reaction pathway is suggested. The chemical instability of the poly-Si(n(+))/ZnO:Al interface is explained by the fact that SiO2 is more stable than ZnO and/or that H2 is released from the initially deposited a-Si:H during the crystallization process. As a result, Zn (a deep acceptor in silicon) is "liberated" close to the silicon/zinc oxide interface presenting the inherent risk of forming deep defects in the silicon absorber. These could act as recombination centers and thus limit the performance of silicon/zinc oxide based solar cells. Based on this insight some recommendations with respect to solar cell design, material selection, and process parameters are given for further knowledge-based thin-film silicon device optimization. PMID:25363298

  9. Improvement of plasmonic enhancement of quantum dot emission via an intermediate silicon-aluminum oxide interface

    SciTech Connect

    Wing, Waylin J.; Sadeghi, Seyed M. Campbell, Quinn

    2015-01-05

    We studied the emission of quantum dots in the presence of plasmon-metal oxide substrates, which consist of arrays of metallic nanorods embedded in amorphous silicon coated with a nanometer-thin layer of aluminum oxide on the top. We showed that the combined effects of plasmons and the silicon-aluminum oxide interface can lead to significant enhancement of the quantum efficiency of quantum dots. Our results show that such an interface can significantly enhance plasmonic effects of the nanorods via quantum dot-induced exciton-plasmon coupling, leading to partial polarization of the quantum dots' emission.

  10. Vertically aligned graphitic carbon nanosheet arrays fabricated from graphene oxides for supercapacitors and Li-O2 batteries.

    PubMed

    Zhao, Guangyu; Zhang, Li; Lv, Jixian; Li, Changle; Sun, Kening

    2016-05-11

    Vertically aligned graphitic carbon nanosheet arrays were fabricated from graphene oxide solution by a hydrothermal method. The arrays exhibited a specific capacitance of 240 F g(-1) at 200 A g(-1) as a supercapacitor electrode and a capacity of 6500 mA h g(-1) as a Li-O2 battery cathode. PMID:27090965

  11. Study of charge control and gate tunneling in a ferroelectric-oxide-silicon field effect transistor: Comparison with a conventional metal-oxide-silicon structure

    NASA Astrophysics Data System (ADS)

    Lin, Yih-Yin; Zhang, Yifei; Singh, Jasprit; York, Robert; Mishra, Umesh

    2001-02-01

    It is known that conventional metal-oxide-silicon (MOS) devices will have gate tunneling related problems at very thin oxide thicknesses. Various high-dielectric-constant materials are being examined to suppress the gate currents. In this article we present theoretical results of a charge control and gate tunneling model for a ferroelectric-oxide-silicon field effect transistor and compare them to results for a conventional MOS device. The potential of high polarization charge to induce inversion without doping and high dielectric constant to suppress tunneling current is explored. The model is based on a self-consistent solution of the quantum problem and includes the ferroelectric hysteresis response self-consistently. We show that the polarization charge associated with ferroelectrics can allow greater controllability of the inversion layer charge density. Also the high dielectric constant of ferroelectrics results in greatly suppressed gate current.

  12. Rapid thermal chemical vapor deposition of thin silicon oxide films using silane and nitrous oxide

    NASA Astrophysics Data System (ADS)

    Xu, X. L.; Kuehn, R. T.; Wortman, J. J.; Öztürk, M. C.

    1992-06-01

    Thin (80-200 Å) silicon dioxide (SiO2) films have been deposited by low pressure rapid thermal chemical vapor deposition (RTCVD), using silane (SiH4) and nitrous oxide (N2O) as the reactive gases for the first time. A deposition rate of 55 Å/min has been achieved at 800 °C with a SiH4/N2O flow rate ratio of 2%. Auger electron spectroscopy (AES) and Rutherford back scattering spectroscopy (RBS) have shown a uniform and stoichiometric composition throughout the deposited oxide films. Electrical characterization of the films have shown an average catastrophic breakdown field of 13 MV/cm and a midgap interface trap density (Dit) of equal to or less than 5×1010 eV-1 cm-2. The results suggest that the deposited RTCVD SiO2 films using SiH4-N2O gas system may have the potential to be used as the gate dielectric in future low-temperature metal oxide semiconductor (MOS) device processes for ultralarge scale integration (ULSI).

  13. Crack healing behavior of hot pressed silicon nitride due to oxidation

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Tikare, V.

    1992-01-01

    It is shown that limited oxidation of an MgO-containing, hot-pressed silicon nitride ceramic at 800 deg C and above results in increased strength due to crack healing. Slight oxidation of the surface produces enstatite and cristobalite which fills in cracks. More extensive oxidation leads to strength degradation due to the formation of new flaws by the evolution of N2 gas at the surface. The apparent fracture toughness also increased at 800 deg C and above due to oxidation. Bonds formed between the two surfaces of the crack during oxidation leads to a reduction in stress intensity at the crack tip, suggesting that valid high-temperature toughness values cannot be obtained in an air environment. The increase in strength due to crack healing by oxidation can be achieved without compromising the fatigue properties of the silicon nitride ceramic.

  14. Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.

    PubMed

    Lee, Austin W H; Gates, Byron D

    2016-07-26

    We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces. PMID:27396288

  15. Synthesis of metal silicide at metal/silicon oxide interface by electronic excitation

    SciTech Connect

    Lee, J.-G.; Nagase, T.; Yasuda, H.; Mori, H.

    2015-05-21

    The synthesis of metal silicide at the metal/silicon oxide interface by electronic excitation was investigated using transmission electron microscopy. A platinum silicide, α-Pt{sub 2}Si, was successfully formed at the platinum/silicon oxide interface under 25–200 keV electron irradiation. This is of interest since any platinum silicide was not formed at the platinum/silicon oxide interface by simple thermal annealing under no-electron-irradiation conditions. From the electron energy dependence of the cross section for the initiation of the silicide formation, it is clarified that the silicide formation under electron irradiation was not due to a knock-on atom-displacement process, but a process induced by electronic excitation. It is suggested that a mechanism related to the Knotek and Feibelman mechanism may play an important role in silicide formation within the solid. Similar silicide formation was also observed at the palladium/silicon oxide and nickel/silicon oxide interfaces, indicating a wide generality of the silicide formation by electronic excitation.

  16. Optimization of contaminated oxide inversion layer solar cell. [considering silicon oxide coating

    NASA Technical Reports Server (NTRS)

    Call, R. L.

    1976-01-01

    Contaminated oxide cells have been fabricated with efficiencies of 8.6% with values of I sub sc = 120 ma, V sub oc = .54 volts, and curve factor of .73. Attempts to optimize the fabrication step to yield a higher output have not been successful. The fundamental limitation is the inadequate antireflection coating afforded by the silicon dioxide coating used to hold the contaminating ions. Coatings of SiO, therefore, were used to obtain a good antireflection coating, but the thinness of the coatings prevented a large concentration of the contaminating ions, and the cells was weak. Data of the best cell were .52 volts V sub oc, 110 ma I sub sc, .66 CFF and 6.7% efficiency.

  17. Surface-Assisted Laser Desorption Ionization of Low Molecular Organic Substances on Oxidized Porous Silicon

    NASA Astrophysics Data System (ADS)

    Shmigol, I. V.; Alekseev, S. A.; Lavrynenko, O. Yu.; Zaitsev, V. N.; Barbier, D.; Pokrovskiy, V. A.

    Desorption/ionization on silicon (DIOS) mass spectra of methylene blue (MB+Cl-) were studied using p+-type oxidized monofunctional porous silicon (PS-OX mono ) free layers. Reduction/protonation processes of methylene blue (MB) dye were investigated. It was shown that SiH x terminal sites on oxidized surface of porous silicon (PS-OX) are not the rate-determining factor for the reduction/protonation in DIOS. Tunneling of electron through the dielectric layer of nanostructures on silicon surface under effect of local electrostatic and electromagnetic fields is considered to be the most significant factor of adsorbate-adsorbent electron exchange and further laser-induced ion formation.

  18. Hybrid Integration of Graphene Analog and Silicon Complementary Metal-Oxide-Semiconductor Digital Circuits.

    PubMed

    Hong, Seul Ki; Kim, Choong Sun; Hwang, Wan Sik; Cho, Byung Jin

    2016-07-26

    We demonstrate a hybrid integration of a graphene-based analog circuit and a silicon-based digital circuit in order to exploit the strengths of both graphene and silicon devices. This mixed signal circuit integration was achieved using a three-dimensional (3-D) integration technique where a graphene FET multimode phase shifter is fabricated on top of a silicon complementary metal-oxide-semiconductor field-effect transistor (CMOS FET) ring oscillator. The process integration scheme presented here is compatible with the conventional silicon CMOS process, and thus the graphene circuit can successfully be integrated on current semiconductor technology platforms for various applications. This 3-D integration technique allows us to take advantage of graphene's excellent inherent properties and the maturity of current silicon CMOS technology for future electronics. PMID:27403730

  19. Corrosion resistant three-dimensional nanotextured silicon for water photo-oxidation

    NASA Astrophysics Data System (ADS)

    Carter, Rachel; Chatterjee, Shahana; Gordon, Evan; Share, Keith; Erwin, William R.; Cohn, Adam P.; Bardhan, Rizia; Pint, Cary L.

    2015-10-01

    We demonstrate the ability to chemically transform bulk silicon into a nanotextured surface that exhibits excellent electrochemical stability in aqueous conditions for water photo-oxidation. Conformal defective graphene coatings on nanotextured silicon formed by thermal treatment enable over 50× corrosion resistance in aqueous electrolytes based upon Tafel analysis and impedance spectroscopy. This enables nanotextured silicon as an effective oxygen-evolution photoanode for water splitting with saturation current density measured near 35 mA cm-2 under 100 mW cm-2 (1 sun) illumination. Our approach builds upon simple and scalable processing techniques with silicon to develop corrosion resistant electrodes that can benefit a broad range of catalytic and photocatalytic applications.We demonstrate the ability to chemically transform bulk silicon into a nanotextured surface that exhibits excellent electrochemical stability in aqueous conditions for water photo-oxidation. Conformal defective graphene coatings on nanotextured silicon formed by thermal treatment enable over 50× corrosion resistance in aqueous electrolytes based upon Tafel analysis and impedance spectroscopy. This enables nanotextured silicon as an effective oxygen-evolution photoanode for water splitting with saturation current density measured near 35 mA cm-2 under 100 mW cm-2 (1 sun) illumination. Our approach builds upon simple and scalable processing techniques with silicon to develop corrosion resistant electrodes that can benefit a broad range of catalytic and photocatalytic applications. Electronic supplementary information (ESI) available: (i) Experimental details, (ii) Nyquist plot from EIS data, (iii) FTIR of H-terminated silicon, (iv) reflectance measurements to quantify light trapping in nanotextured silicon, (v) LSV from Tafel analysis, and (vi) J-V curves for H-terminated flat samples, (vii) stability test of photoanode, and (viii) forward and reverse scans for each sample type. See DOI: 10

  20. Effective surface passivation of p-type crystalline silicon with silicon oxides formed by light-induced anodisation

    NASA Astrophysics Data System (ADS)

    Cui, Jie; Grant, Nicholas; Lennon, Alison

    2014-12-01

    Electronic surface passivation of p-type crystalline silicon by anodic silicon dioxide (SiO2) was investigated. The anodic SiO2 was grown by light-induced anodisation (LIA) in diluted sulphuric acid at room temperature, a process that is significantly less-expensive than thermal oxidation which is widely-used in silicon solar cell fabrication. After annealing in oxygen and then forming gas at 400 °C for 30 min, the effective minority carrier lifetime of 3-5 Ω cm, boron-doped Czochralski silicon wafers with a phosphorus-doped 80 Ω/□ emitter and a LIA anodic SiO2 formed on the p-type surface was increased by two orders of magnitude to 150 μs. Capacitance-voltage measurements demonstrated a very low positive charge density of 3.4 × 1011 cm-2 and a moderate density of interface states of 6 × 1011 eV-1 cm-2. This corresponded to a silicon surface recombination velocity of 62 cm s-1, which is comparable with values reported for other anodic SiO2 films, which required higher temperatures and longer growth times, and significantly lower than oxides grown by chemical vapour deposition techniques. Additionally, a very low leakage current density of 3.5 × 10-10 and 1.6 × 10-9 A cm-2 at 1 and -1 V, respectively, was measured for LIA SiO2 suggesting its potential application as insulation layer in IBC solar cells and a barrier for potential induced degradation.

  1. Dispersion engineering of high-Q silicon microresonators via thermal oxidation

    SciTech Connect

    Jiang, Wei C.; Zhang, Jidong; Usechak, Nicholas G.; Lin, Qiang

    2014-07-21

    We propose and demonstrate a convenient and sensitive technique for precise engineering of group-velocity dispersion in high-Q silicon microresonators. By accurately controlling the surface-oxidation thickness of silicon microdisk resonators, we are able to precisely manage the zero-dispersion wavelength, while simultaneously further improving the high optical quality of our devices, with the optical Q close to a million. The demonstrated dispersion management allows us to achieve parametric generation with precisely engineerable emission wavelengths, which shows great potential for application in integrated silicon nonlinear and quantum photonics.

  2. The effect of nanocrystalline silicon host on magnetic properties of encapsulated iron oxide nanoparticles.

    PubMed

    Granitzer, P; Rumpf, K; Gonzalez-Rodriguez, R; Coffer, J L; Reissner, M

    2015-12-21

    The purpose of this work is a detailed comparison of the fundamental magnetic properties of nanocomposite systems consisting of Fe3O4 nanoparticle-loaded porous silicon as well as silicon nanotubes. Such composite structures are of potential merit in the area of magnetically guided drug delivery. For magnetic systems to be utilized in biomedical applications, there are certain magnetic properties that must be fulfilled. Therefore magnetic properties of embedded Fe3O4-nanoparticles in these nanostructured silicon host matrices, porous silicon and silicon nanotubes, are investigated. Temperature-dependent magnetic investigations have been carried out for four types of iron oxide particle sizes (4, 5, 8 and 10 nm). The silicon host, in interplay with the iron oxide nanoparticle size, plays a sensitive role. It is shown that Fe3O4 loaded porous silicon and SiNTs differ significantly in their magnetic behavior, especially the transition between superparamagnetic behavior and blocked state, due to host morphology-dependent magnetic interactions. Importantly, it is found that all investigated samples meet the magnetic precondition of possible biomedical applications of exhibiting a negligible magnetic remanence at room temperature. PMID:26575478

  3. Large-area alignment of tungsten oxide nanowires over flat and patterned substrates for room-temperature gas sensing.

    PubMed

    Cheng, Wei; Ju, Yanrui; Payamyar, Payam; Primc, Darinka; Rao, Jingyi; Willa, Christoph; Koziej, Dorota; Niederberger, Markus

    2015-01-01

    Alignment of nanowires over a large area of flat and patterned substrates is a prerequisite to use their collective properties in devices such as gas sensors. In this work, uniform single-crystalline ultrathin W18 O49 nanowires with diameters less than 2 nm and aspect ratios larger than 100 have been synthesized, and, despite their flexibility, assembled into thin films with high orientational order over a macroscopic area by the Langmuir-Blodgett technique. Alignment of the tungsten oxide nanowires was also possible on top of sensor substrates equipped with electrodes. Such sensor devices were found to exhibit outstanding sensitivity to H2 at room temperature. PMID:25412600

  4. Designing high performance precursors for atomic layer deposition of silicon oxide

    SciTech Connect

    Mallikarjunan, Anupama Chandra, Haripin; Xiao, Manchao; Lei, Xinjian; Pearlstein, Ronald M.; Bowen, Heather R.; O'Neill, Mark L.; Derecskei-Kovacs, Agnes; Han, Bing

    2015-01-15

    Conformal and continuous silicon oxide films produced by atomic layer deposition (ALD) are enabling novel processing schemes and integrated device structures. The increasing drive toward lower temperature processing requires new precursors with even higher reactivity. The aminosilane family of precursors has advantages due to their reactive nature and relative ease of use. In this paper, the authors present the experimental results that reveal the uniqueness of the monoaminosilane structure [(R{sub 2}N)SiH{sub 3}] in providing ultralow temperature silicon oxide depositions. Disubstituted aminosilanes with primary amines such as in bis(t-butylamino)silane and with secondary amines such as in bis(diethylamino)silane were compared with a representative monoaminosilane: di-sec-butylaminosilane (DSBAS). DSBAS showed the highest growth per cycle in both thermal and plasma enhanced ALD. These findings show the importance of the arrangement of the precursor's organic groups in an ALD silicon oxide process.

  5. Vertically aligned zinc oxide nanowires electrodeposited within porous polycarbonate templates for vibrational energy harvesting

    NASA Astrophysics Data System (ADS)

    Boughey, Francesca L.; Davies, Timothy; Datta, Anuja; Whiter, Richard A.; Sahonta, Suman-Lata; Kar-Narayan, Sohini

    2016-07-01

    A piezoelectric nanogenerator has been fabricated using a simple, fast and scalable template-assisted electrodeposition process, by which vertically aligned zinc oxide (ZnO) nanowires were directly grown within a nanoporous polycarbonate (PC) template. The nanowires, having average diameter 184 nm and length 12 μm, are polycrystalline and have a preferred orientation of the [100] axis parallel to the long axis. The output power density of a nanogenerator fabricated from the as-grown ZnO nanowires still embedded within the PC template was found to be 151 ± 25 mW m‑3 at an impedance-matched load, when subjected to a low-level periodic (5 Hz) impacting force akin to gentle finger tapping. An energy conversion efficiency of ∼4.2% was evaluated for the electrodeposited ZnO nanowires, and the ZnO–PC composite nanogenerator was found to maintain good energy harvesting performance through 24 h of continuous fatigue testing. This is particularly significant given that ZnO-based nanostructures typically suffer from mechanical and/or environmental degradation that otherwise limits their applicability in vibrational energy harvesting. Our template-assisted synthesis of ZnO nanowires embedded within a protective polymer matrix through a single growth process is thus attractive for the fabrication of low-cost, robust and stable nanogenerators.

  6. Higher-power supercapacitor electrodes based on mesoporous manganese oxide coating on vertically aligned carbon nanofibers.

    PubMed

    Klankowski, Steven A; Pandey, Gaind P; Malek, Gary; Thomas, Conor R; Bernasek, Steven L; Wu, Judy; Li, Jun

    2015-05-14

    A study on the development of high-power supercapacitor materials based on formation of thick mesoporous MnO2 shells on a highly conductive 3D template using vertically aligned carbon nanofibers (VACNFs). Coaxial manganese shells of 100 to 600 nm nominal thicknesses are sputter-coated on VACNFs and then electrochemically oxidized into rose-petal-like mesoporous MnO2 structure. Such a 3D MnO2/VACNF hybrid architecture provides enhanced ion diffusion throughout the whole MnO2 shell and yields excellent current collection capability through the VACNF electrode. These two effects collectively enable faster electrochemical reactions during charge-discharge of MnO2 in 1 M Na2SO4. Thick MnO2 shells (up to 200 nm in radial thickness) can be employed, giving a specific capacitance up to 437 F g(-1). More importantly, supercapacitors employing such a 3D MnO2/VACNF hybrid electrode illustrate more than one order of magnitude higher specific power than the state-of-the-art ones based on other MnO2 structures, reaching ∼240 kW kg(-1), while maintaining a comparable specific energy in the range of 1 to 10 Wh kg(-1). This hybrid approach demonstrates the potential of 3D core-shell architectures for high-power energy storage devices. PMID:25894255

  7. Vertically aligned zinc oxide nanowires electrodeposited within porous polycarbonate templates for vibrational energy harvesting.

    PubMed

    Boughey, Francesca L; Davies, Timothy; Datta, Anuja; Whiter, Richard A; Sahonta, Suman-Lata; Kar-Narayan, Sohini

    2016-07-15

    A piezoelectric nanogenerator has been fabricated using a simple, fast and scalable template-assisted electrodeposition process, by which vertically aligned zinc oxide (ZnO) nanowires were directly grown within a nanoporous polycarbonate (PC) template. The nanowires, having average diameter 184 nm and length 12 μm, are polycrystalline and have a preferred orientation of the [100] axis parallel to the long axis. The output power density of a nanogenerator fabricated from the as-grown ZnO nanowires still embedded within the PC template was found to be 151 ± 25 mW m(-3) at an impedance-matched load, when subjected to a low-level periodic (5 Hz) impacting force akin to gentle finger tapping. An energy conversion efficiency of ∼4.2% was evaluated for the electrodeposited ZnO nanowires, and the ZnO-PC composite nanogenerator was found to maintain good energy harvesting performance through 24 h of continuous fatigue testing. This is particularly significant given that ZnO-based nanostructures typically suffer from mechanical and/or environmental degradation that otherwise limits their applicability in vibrational energy harvesting. Our template-assisted synthesis of ZnO nanowires embedded within a protective polymer matrix through a single growth process is thus attractive for the fabrication of low-cost, robust and stable nanogenerators. PMID:27256619

  8. Reduced graphene oxide and vertically aligned carbon nanotubes superhydrophilic films for supercapacitors devices

    SciTech Connect

    Zanin, H.; Saito, E.; Ceragioli, H.J.; Baranauskas, V.; Corat, E.J.

    2014-01-01

    Graphical abstract: - Highlights: • Graphene nanosheets were produced onto wire rods. • RGO and VACNT-O were evaluated and compared as supercapacitor electrode. • RGO and VACNT-O have structural and electrochemical properties quite similars. • The materials present good specific capacitance, energy storage and power delivery. - Abstract: Reduced graphene oxide (RGO) and vertically aligned carbon nanotubes (VACNT) superhydrophilic films were prepared by chemical vapor deposition techniques for electrical energy storage investigations. These electrodes were characterized in terms of their material and electrochemical properties by scanning electron microscopy (SEM), surface wettability, Fourier transform infrared spectroscopy (FTIR), energy dispersive and Raman spectroscopies, cyclic voltammetry (CV) and galvanostatic charge–discharge. We observed several physical structural and electrochemical similarities between these carbon-based materials with particular attention to very good specific capacitance, ultra-high energy storage and fast power delivery. Our results showed that the main difference between specific capacitance values is attributed to pseudocapacitive contribution and high density of multiwall nanotubes tips. In this work we have tested a supercapacitor device using the VACNT electrodes.

  9. Microstructural and physical properties of magnesium oxide-doped silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Sirota, V.; Lukianova, O.; Krasilnikov, V.; Selemenev, V.; Dokalov, V.

    Silicon nitride based ceramics with aluminum, yttrium and magnesium oxides were produced by cold isostatic pressing and free sintering. The phase composition of the starting MgO powder obtained by the novel technology has been studied. The effect of magnesium oxide content on the structure of the produced materials has been investigated. It was found, that obtained materials with 1 and 2 wt.% of magnesium oxide and without it have a typical β-silicon nitride structure with elongated grains. Ceramics with 5 wt.% magnesia has a duplex α/β-structure with elongated and equiaxed grains. Ceramics with 2 wt.% magnesium oxide has a maximum density of 2.91 g/cm3. The increases in magnesium oxide content upto 5% led to decrease in the shrinkage (from 16% to 12%) and density (from 2.88 to 2.37 g/cm3).

  10. High-Quality Solution-Processed Silicon Oxide Gate Dielectric Applied on Indium Oxide Based Thin-Film Transistors.

    PubMed

    Jaehnike, Felix; Pham, Duy Vu; Anselmann, Ralf; Bock, Claudia; Kunze, Ulrich

    2015-07-01

    A silicon oxide gate dielectric was synthesized by a facile sol-gel reaction and applied to solution-processed indium oxide based thin-film transistors (TFTs). The SiOx sol-gel was spin-coated on highly doped silicon substrates and converted to a dense dielectric film with a smooth surface at a maximum processing temperature of T = 350 °C. The synthesis was systematically improved, so that the solution-processed silicon oxide finally achieved comparable break downfield strength (7 MV/cm) and leakage current densities (<10 nA/cm(2) at 1 MV/cm) to thermally grown silicon dioxide (SiO2). The good quality of the dielectric layer was successfully proven in bottom-gate, bottom-contact metal oxide TFTs and compared to reference TFTs with thermally grown SiO2. Both transistor types have field-effect mobility values as high as 28 cm(2)/(Vs) with an on/off current ratio of 10(8), subthreshold swings of 0.30 and 0.37 V/dec, respectively, and a threshold voltage close to zero. The good device performance could be attributed to the smooth dielectric/semiconductor interface and low interface trap density. Thus, the sol-gel-derived SiO2 is a promising candidate for a high-quality dielectric layer on many substrates and high-performance large-area applications. PMID:26039187

  11. Resistance of Silicon Nitride Turbine Components to Erosion and Hot Corrosion/oxidation Attack

    NASA Technical Reports Server (NTRS)

    Strangmen, Thomas E.; Fox, Dennis S.

    1994-01-01

    Silicon nitride turbine components are under intensive development by AlliedSignal to enable a new generation of higher power density auxiliary power systems. In order to be viable in the intended applications, silicon nitride turbine airfoils must be designed for survival in aggressive oxidizing combustion gas environments. Erosive and corrosive damage to ceramic airfoils from ingested sand and sea salt must be avoided. Recent engine test experience demonstrated that NT154 silicon nitride turbine vanes have exceptional resistance to sand erosion, relative to superalloys used in production engines. Similarly, NT154 silicon nitride has excellent resistance to oxidation in the temperature range of interest - up to 1400 C. Hot corrosion attack of superalloy gas turbine components is well documented. While hot corrosion from ingested sea salt will attack silicon nitride substantially less than the superalloys being replaced in initial engine applications, this degradation has the potential to limit component lives in advanced engine applications. Hot corrosion adversely affects the strength of silicon nitride in the 850 to 1300 C range. Since unacceptable reductions in strength must be rapidly identified and avoided, AlliedSignal and the NASA Lewis Research Center have pioneered the development of an environmental life prediction model for silicon nitride turbine components. Strength retention in flexure specimens following 1 to 3300 hour exposures to high temperature oxidation and hot corrosion has been measured and used to calibrate the life prediction model. Predicted component life is dependent upon engine design (stress, temperature, pressure, fuel/air ratio, gas velocity, and inlet air filtration), mission usage (fuel sulfur content, location (salt in air), and times at duty cycle power points), and material parameters. Preliminary analyses indicate that the hot corrosion resistance of NT154 silicon nitride is adequate for AlliedSignal's initial engine

  12. Fabrication of OSOS cells by neutral ion beam sputtering. [Oxide Semiconductor On Silicon solar cells

    NASA Technical Reports Server (NTRS)

    Burk, D. E.; Dubow, J. B.; Sites, J. R.

    1976-01-01

    Oxide semiconductor on silicon (OSOS) solar cells have been fabricated from various indium tin oxide (In2O3)x(SnO2)1-x compositions sputtered onto p-type single crystal silicon substrates with a neutralized argon ion beam. High temperature processing or annealing was not required. The highest efficiency was achieved with x = 0.91 and was 12 percent. The cells are environmentally rugged, chemically stable, and show promise for still higher efficiencies. Moreover, the ion beam sputtering fabrication technique is amenable to low cost, continuous processing.

  13. Catalytically enhanced thermal decomposition of chemically grown silicon oxide layers on Si(001)

    NASA Astrophysics Data System (ADS)

    Leroy, F.; Passanante, T.; Cheynis, F.; Curiotto, S.; Bussmann, E. B.; Müller, P.

    2016-03-01

    The thermal decomposition of Si dioxide layers formed by wet chemical treatment on Si(001) has been studied by low-energy electron microscopy. Independent nucleations of voids occur into the Si oxide layers that open by reaction at the void periphery. Depending on the voids, the reaction rates exhibit large differences via the occurrence of a nonlinear growth of the void radius. This non-steady state regime is attributed to the accumulation of defects and silicon hydroxyl species at the SiO2/Si interface that enhances the silicon oxide decomposition at the void periphery.

  14. Superior optical properties of homogeneous liquid crystal alignment on a tin (IV) oxide surface sequentially modulated via ion beam irradiation.

    PubMed

    Kang, Young-Gu; Park, Hong-Gyu; Kim, Hyung-Jun; Kim, Young-Hwan; Oh, Byeong-Yun; Kim, Byoung-Yong; Kim, Dai-Hyun; Seo, Dae-Shik

    2010-10-11

    We first investigated the alignment characteristics of tin (IV) oxide (SnO(2)) thin films deposited by radio-frequency (RF) magnetron sputtering. This study demonstrates that liquid crystal (LC) molecules could be aligned homogeneously by controlling the Ion Beam (IB) irradiation energy densities. We also show that the pretilt angle of the LC molecules has a close relation with the surface energy. X-ray photoelectron spectroscopy (XPS) indicates that a non-stoichiometric SnO(2-x) surface converted by ion beam irradiation can horizontally align the LC molecules. The measured electro-optical (EO) characteristics showed high performance, comparable with those of rubbed and ion-beam irradiated polyimide (PI) layers. PMID:20941057

  15. Growth and characterization of aligned ultralong and diameter-controlled silicon nanotubes by hot wire chemical vapor deposition using electrospun poly(vinyl pyrrolidone) nanofiber template

    NASA Astrophysics Data System (ADS)

    Zhou, Ming; Li, Ruishan; Zhou, Jinyuan; Guo, Xiaosong; Liu, Bin; Zhang, Zhenxing; Xie, Erqing

    2009-12-01

    Using aligned suspended polyvinyl pyrrolidone nanofibers array as template, aligned ultralong (about 4 mm) silicon nanotubes have been prepared by a hot wire chemical vapor deposition process. Scanning electron microscopy and transmission electron microscopy demonstrate that the inner diameter (35-200 nm) and wall thickness (20-400 nm) of Si tubes are controlled, respectively, by baking the electrospun nanofibers and by coating time. The tube wall is composed of nanoparticle or nanopillar, and the inner surface of the wall is smoother than the outer surface of the wall. The microphotoluminescence spectra of the thinner Si nanotubes show three light emission bands in the red, green, and blue regions. And the luminescence mechanism is explained according to the quantum-confinement-luminescence center process and radiative recombination from the defect centers.

  16. Plasma-Sprayed Refractory Oxide Coatings on Silicon-Base Ceramics

    NASA Technical Reports Server (NTRS)

    Tewari, Surendra

    1997-01-01

    Silicon-base ceramics are promising candidate materials for high temperature structural applications such as heat exchangers, gas turbines and advanced internal combustion engines. Composites based on these materials are leading candidates for combustor materials for HSCT gas turbine engines. These materials possess a combination of excellent physical and mechanical properties at high temperatures, for example, high strength, high toughness, high thermal shock resistance, high thermal conductivity, light weight and excellent oxidation resistance. However, environmental durability can be significantly reduced in certain conditions such as when molten salts, H2 or water vapor are present. The oxidation resistance of silicon-base materials is provided by SiO2 protective layer. Molten salt reacts with SiO2 and forms a mixture of SiO2 and liquid silicate at temperatures above 800C. Oxygen diffuses more easily through the chemically altered layer, resulting in a catastrophic degradation of the substrate. SiC and Si3N4 are not stable in pure H2 and decompose to silicon and gaseous species such as CH4, SiH, SiH4, N2, and NH3. Water vapor is known to slightly increase the oxidation rate of SiC and Si3N4. Refractory oxides such as alumina, yttria-stabilized zirconia, yttria and mullite (3Al2O3.2SiO2) possess excellent environmental durability in harsh conditions mentioned above. Therefore, refractory oxide coatings on silicon-base ceramics can substantially improve the environmental durability of these materials by acting as a chemical reaction barrier. These oxide coatings can also serve as a thermal barrier. The purpose of this research program has been to develop refractory oxide chemical/thermal barrier coatings on silicon-base ceramics to provide extended temperature range and lifetime to these materials in harsh environments.

  17. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-04-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications.

  18. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

    PubMed Central

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J. Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  19. Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry.

    PubMed

    Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; Del Río, J Antonio; Tagüeña-Martínez, Julia

    2016-01-01

    Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

  20. Self-aligned graphene field-effect transistors on SiC (0001) substrates with self-oxidized gate dielectric

    NASA Astrophysics Data System (ADS)

    Jia, Li; Cui, Yu; Li, Wang; Qingbin, Liu; Zezhao, He; Shujun, Cai; Zhihong, Feng

    2014-07-01

    A scalable self-aligned approach is employed to fabricate monolayer graphene field-effect transistors on semi-insulated 4H-SiC (0001) substrates. The self-aligned process minimized access resistance and parasitic capacitance. Self-oxidized Al2O3, formed by deposition of 2 nm Al followed by exposure in air to be oxidized, is used as gate dielectric and shows excellent insulation. An intrinsic cutoff frequency of 34 GHz and maximum oscillation frequency of 36.4 GHz are realized for the monolayer graphene field-effect transistor with a gate length of 0.2 μm. These studies show a pathway to fabricate graphene transistors for future applications in ultra-high frequency circuits.

  1. Oxidation of Chemically-Vapor-Deposited Silicon Carbide in Carbon Dioxide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Nguyen, QuynhGiao N.

    1998-01-01

    Chemically-vapor-deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO2) at temperatures of 1200-1400 C for times between 96 and 500 h at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate limiting kinetic mechanisms are discussed. Passive oxidation of SiC by CO2 is negligible compared to the rates measured for other oxidants that are also found in combustion environments, oxygen and water vapor.

  2. Surface photovoltage analysis of iron contamination in silicon processing and the relation to gate oxide integrity

    NASA Astrophysics Data System (ADS)

    Henley, Worth B.

    1995-09-01

    Surface photovoltage (SPV), a contactless optical technique for measuring minority carrier lifetime, is used to quantify the relationship between silicon iron contamination level and thin gate oxide integrity. Iron concentration levels in the range of 1 X 1010 cm-3 to 5 X 1013 cm-3 are evaluated for oxide thicknesses of 8 to 20 nm. Ramp voltage electrical breakdown and time dependant dielectric breakdown measurement on the iron contaminated gate oxide capacitors are reported. Distinct iron contamination threshold limits based on defect density and gate oxide integrity evaluate cleaning efficiencies and metallic cross contamination effects during thermal processing contamination. Iron-silicide precipitation kinetics are investigated by the lifetime analysis procedure.

  3. Facile preparation of highly-dispersed cobalt-silicon mixed oxide nanosphere and its catalytic application in cyclohexane selective oxidation

    PubMed Central

    2011-01-01

    Highly dispersed cobalt-silicon mixed oxide [Co-SiO2] nanosphere was successfully prepared with a modified reverse-phase microemulsion method. This material was characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance spectra, X-ray absorption spectroscopy near-edge structure, and N2 adsorption-desorption measurements. High valence state cobalt could be easily obtained without calcination, which is fascinating for the catalytic application for its strong oxidation ability. In the selective oxidation of cyclohexane, Co-SiO2 acted as an efficient catalyst, and good activity could be obtained under mild conditions. PMID:22067075

  4. Synthesis of silicon oxide nanowires and nanotubes with cobalt-palladium or palladium catalysts

    NASA Astrophysics Data System (ADS)

    Esterina, Ria; Liu, X. M.; Ross, C. A.; Adeyeye, A. O.; Choi, W. K.

    2012-07-01

    The dewetting behaviors of cobalt (Co), cobalt palladium (CoPd), and palladium (Pd) thin films on oxidized silicon substrates were examined. We observed the formation of craters in the oxide layer and pits in the Si substrate for larger CoPd or Pd catalyst particles and thinner oxide. Nanowires and nanotubes were observed near the Si pits. The nanowires and nanotubes grow via a vapor-solid-solid or vapor-liquid-solid mechanism with the silicon vapor source provided from the substrate. The original Si atoms that form the nanowires or nanotubes were oxidized in situ by the residual oxygen atoms present in the chamber. Some of the nanotubes had a series of embedded sub-catalysts that formed branches from the primary nanotube.

  5. Higher-power supercapacitor electrodes based on mesoporous manganese oxide coating on vertically aligned carbon nanofibers

    NASA Astrophysics Data System (ADS)

    Klankowski, Steven A.; Pandey, Gaind P.; Malek, Gary; Thomas, Conor R.; Bernasek, Steven L.; Wu, Judy; Li, Jun

    2015-04-01

    A study on the development of high-power supercapacitor materials based on formation of thick mesoporous MnO2 shells on a highly conductive 3D template using vertically aligned carbon nanofibers (VACNFs). Coaxial manganese shells of 100 to 600 nm nominal thicknesses are sputter-coated on VACNFs and then electrochemically oxidized into rose-petal-like mesoporous MnO2 structure. Such a 3D MnO2/VACNF hybrid architecture provides enhanced ion diffusion throughout the whole MnO2 shell and yields excellent current collection capability through the VACNF electrode. These two effects collectively enable faster electrochemical reactions during charge-discharge of MnO2 in 1 M Na2SO4. Thick MnO2 shells (up to 200 nm in radial thickness) can be employed, giving a specific capacitance up to 437 F g-1. More importantly, supercapacitors employing such a 3D MnO2/VACNF hybrid electrode illustrate more than one order of magnitude higher specific power than the state-of-the-art ones based on other MnO2 structures, reaching ~240 kW kg-1, while maintaining a comparable specific energy in the range of 1 to 10 Wh kg-1. This hybrid approach demonstrates the potential of 3D core-shell architectures for high-power energy storage devices.A study on the development of high-power supercapacitor materials based on formation of thick mesoporous MnO2 shells on a highly conductive 3D template using vertically aligned carbon nanofibers (VACNFs). Coaxial manganese shells of 100 to 600 nm nominal thicknesses are sputter-coated on VACNFs and then electrochemically oxidized into rose-petal-like mesoporous MnO2 structure. Such a 3D MnO2/VACNF hybrid architecture provides enhanced ion diffusion throughout the whole MnO2 shell and yields excellent current collection capability through the VACNF electrode. These two effects collectively enable faster electrochemical reactions during charge-discharge of MnO2 in 1 M Na2SO4. Thick MnO2 shells (up to 200 nm in radial thickness) can be employed, giving a

  6. Effect of dielectric stoichiometry and interface chemical state on band alignment between tantalum oxide and platinum

    SciTech Connect

    Lebedinskii, Yu. Yu.; Chernikova, A. G.; Markeev, A. M.; Kuzmichev, D. S.

    2015-10-05

    The tantalum oxide–platinum interface electronic properties determined by X-ray photoelectron spectroscopy are found to depend on the dielectric stoichiometry and platinum chemical state. We demonstrate the slow charging of the tantalum oxide in cases of Ta{sub 2}O{sub 5}/Pt and Ta{sub 2}O{sub 5−y}/Pt interfaces under the X-ray irradiation. This behavior is proposed to be related to the charge accumulation at oxygen vacancies induced traps. Based on the proposed methodology, we define the intrinsic conductive band offset (CBO) ∼1.3 eV (both for Ta{sub 2}O{sub 5}/Pt and Ta{sub 2}O{sub 5−y}/Pt) and CBO after the full saturation of the traps charging ∼0.5 eV, while the last one defines the energy position of charged traps below the bottom of conduction band. We demonstrate also the pining at the both Ta{sub 2}O{sub 5}/Pt and Ta{sub 2}O{sub 5−y}/Pt interfaces even in the “intrinsic” state, apparently induced by the presence of additional interfacial states. No shifts of Ta4f line and band alignment in over stoichiometric Ta{sub 2}O{sub 5+x}/Pt structure during X-ray irradiation, as well as the absence of pinning, resulting in increase of CBO up to 2.3 eV are found. This behavior is related to the PtO{sub 2} interfacing layer formation at Ta{sub 2}O{sub 5+x}/Pt, blocking the charging of the surface states and associated dipole formation.

  7. Using size-selected gold clusters on graphene oxide films to aid cryo-transmission electron tomography alignment

    PubMed Central

    Arkill, Kenton P.; Mantell, Judith M.; Plant, Simon R.; Verkade, Paul; Palmer, Richard E.

    2015-01-01

    A three-dimensional reconstruction of a nano-scale aqueous object can be achieved by taking a series of transmission electron micrographs tilted at different angles in vitreous ice: cryo-Transmission Electron Tomography. Presented here is a novel method of fine alignment for the tilt series. Size-selected gold clusters of ~2.7 nm (Au561 ± 14), ~3.2 nm (Au923 ± 22), and ~4.3 nm (Au2057 ± 45) in diameter were deposited onto separate graphene oxide films overlaying holes on amorphous carbon grids. After plunge freezing and subsequent transfer to cryo-Transmission Electron Tomography, the resulting tomograms have excellent (de-)focus and alignment properties during automatic acquisition. Fine alignment is accurate when the evenly distributed 3.2 nm gold particles are used as fiducial markers, demonstrated with a reconstruction of a tobacco mosaic virus. Using a graphene oxide film means the fiducial markers are not interfering with the ice bound sample and that automated collection is consistent. The use of pre-deposited size-selected clusters means there is no aggregation and a user defined concentration. The size-selected clusters are mono-dispersed and can be produced in a wide size range including 2–5 nm in diameter. The use of size-selected clusters on a graphene oxide films represents a significant technical advance for 3D cryo-electron microscopy. PMID:25783049

  8. Using size-selected gold clusters on graphene oxide films to aid cryo-transmission electron tomography alignment

    NASA Astrophysics Data System (ADS)

    Arkill, Kenton P.; Mantell, Judith M.; Plant, Simon R.; Verkade, Paul; Palmer, Richard E.

    2015-03-01

    A three-dimensional reconstruction of a nano-scale aqueous object can be achieved by taking a series of transmission electron micrographs tilted at different angles in vitreous ice: cryo-Transmission Electron Tomography. Presented here is a novel method of fine alignment for the tilt series. Size-selected gold clusters of ~2.7 nm (Au561 +/- 14), ~3.2 nm (Au923 +/- 22), and ~4.3 nm (Au2057 +/- 45) in diameter were deposited onto separate graphene oxide films overlaying holes on amorphous carbon grids. After plunge freezing and subsequent transfer to cryo-Transmission Electron Tomography, the resulting tomograms have excellent (de-)focus and alignment properties during automatic acquisition. Fine alignment is accurate when the evenly distributed 3.2 nm gold particles are used as fiducial markers, demonstrated with a reconstruction of a tobacco mosaic virus. Using a graphene oxide film means the fiducial markers are not interfering with the ice bound sample and that automated collection is consistent. The use of pre-deposited size-selected clusters means there is no aggregation and a user defined concentration. The size-selected clusters are mono-dispersed and can be produced in a wide size range including 2-5 nm in diameter. The use of size-selected clusters on a graphene oxide films represents a significant technical advance for 3D cryo-electron microscopy.

  9. Heterojunction Solar Cells Based on Silicon and Composite Films of Graphene Oxide and Carbon Nanotubes.

    PubMed

    Yu, LePing; Tune, Daniel; Shearer, Cameron; Shapter, Joseph

    2015-09-01

    Graphene oxide (GO) sheets have been used as the surfactant to disperse single-walled carbon nanotubes (CNT) in water to prepare GO/CNT electrodes that are applied to silicon to form a heterojunction that can be used in solar cells. GO/CNT films with different ratios of the two components and with various thicknesses have been used as semitransparent electrodes, and the influence of both factors on the performance of the solar cell has been studied. The degradation rate of the GO/CNT-silicon devices under ambient conditions has also been explored. The influence of the film thickness on the device performance is related to the interplay of two competing factors, namely, sheet resistance and transmittance. CNTs help to improve the conductivity of the GO/CNT film, and GO is able to protect the silicon from oxidation in the atmosphere. PMID:25959241

  10. Nanopatterning of Crystalline Silicon Using Anodized Aluminum Oxide Templates for Photovoltaics

    NASA Astrophysics Data System (ADS)

    Chao, Tsu-An

    A novel thin film anodized aluminum oxide templating process was developed and applied to make nanopatterns on crystalline silicon to enhance the optical properties of silicon. The thin film anodized aluminum oxide was created to improve the conventional thick aluminum templating method with the aim for potential large scale fabrication. A unique two-step anodizing method was introduced to create high quality nanopatterns and it was demonstrated that this process is superior over the original one-step approach. Optical characterization of the nanopatterned silicon showed up to 10% reduction in reflection in the short wavelength range. Scanning electron microscopy was also used to analyze the nanopatterned surface structure and it was found that interpore spacing and pore density can be tuned by changing the anodizing potential.

  11. Silicon oxide nanowire growth mechanisms revealed by real-time electron microscopy

    NASA Astrophysics Data System (ADS)

    Kolíbal, Miroslav; Novák, Libor; Shanley, Toby; Toth, Milos; Šikola, Tomáš

    2015-12-01

    Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains contradictory results reported in prior studies. We also show that under wet atmospheres the Ga droplets can be mobile and promote nanowire growth as they traverse the silicon substrate.Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains

  12. Microstructure, oxidation behavior and mechanical behavior of lens deposited niobium-titanium-silicon and niobium-titanium-silicon based alloys

    NASA Astrophysics Data System (ADS)

    Dehoff, Ryan Richard

    With current high temperature structural materials such as nickel based superalloys being pushed to the limits of suitable operating conditions, there comes a need for replacement materials with even higher temperature capabilities. Niobium silicon based systems have been shown to have superior density normalized strength at elevated temperatures when compared to currently used alloys. The drawbacks associated with the niobium silicon system are due to catastrophic oxidation behavior at elevated temperatures. Alloying addition have been shown to increase the oxidation resistance near suitable levels, but also decrease the high temperature strength and increases creep rates when compared to the binary alloy system. The microstructure of the material is similar to metal matrix composites in which high melting temperature silicides are dispersed in a niobium based matrix phase. The silicides produce high temperature strength while the niobium based matrix increases the room temperature properties such as fracture toughness. The bulk of the research has been conducted on directionally solidified material which has a coarse microstructure due to the slow cooling rates associated with the processing condition. The current research uses a powder metallurgy process termed Laser Engineered Net Shaping, or LENS, to produce material with a significantly refined microstructure due to fast cooling rates associated with the laser process. Several compositions of alloys were examined and the ideal processing parameters were determined for each alloy. The resulting microstructures show a refinement of the microstructure as expected with a fine scale distribution of Nb5Si3 and Nb3Si dispersed in a niobium based matrix phase. The high temperature oxidation behavior of the LENS deposited alloys was comparable to alloys produced using other techniques. A non protective oxide scale formed on samples exposed for only 0.5 hours but was not protective and showed large amounts of

  13. Oxidation of silicon implanted with high-dose aluminum

    SciTech Connect

    Yang, Zunde; Du, Honghua; Withrow, S.P.

    1994-12-31

    Si(100) wafers were implanted with Al at 500 C to high doses at multi-energies and were oxidized in 1 atm flowing oxygen at 1000-1200 C. Morphology, structure, and oxidation behavior of the implanted and oxidized Si were studied using optical microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy in conjunction with selected area electron diffraction and energy dispersive x-ray analysis. Large Al precipitates were formed and embedded near the surface region of the implanted Si. Oxidation rate of the Al-implanted Si wafers was lower than that of virgin Si. The unique morphology of the implanted Si results from rpaid Al diffusion and segregation promoted by hot implantation. Reduction of the oxidation rate of Si by Al implantation is attributed to preferential oxidation of Al and formation of a continuous diffusion barrier of Al{sub 2}O{sub 3}.

  14. Scalable Preparation of Ternary Hierarchical Silicon Oxide-Nickel-Graphite Composites for Lithium-Ion Batteries.

    PubMed

    Wang, Jing; Bao, Wurigumula; Ma, Lu; Tan, Guoqiang; Su, Yuefeng; Chen, Shi; Wu, Feng; Lu, Jun; Amine, Khalil

    2015-12-01

    Silicon monoxide is a promising anode candidate because of its high theoretical capacity and good cycle performance. To solve the problems associated with this material, including large volume changes during charge-discharge processes, we report a ternary hierarchical silicon oxide-nickel-graphite composite prepared by a facile two-step ball-milling method. The composite consists of nano-Si dispersed silicon oxides embedded in nano-Ni/graphite matrices (Si@SiOx /Ni/graphite). In the composite, crystalline nano-Si particles are generated by the mechanochemical reduction of SiO by ball milling with Ni. These nano-Si dispersed oxides have abundant electrochemical activity and can provide high Li-ion storage capacity. Furthermore, the milled nano-Ni/graphite matrices stick well to active materials and interconnect to form a crosslinked framework, which functions as an electrical highway and a mechanical backbone so that all silicon oxide particles become electrochemically active. Owing to these advanced structural and electrochemical characteristics, the composite enhances the utilization efficiency of SiO, accommodates its large volume expansion upon cycling, and has good ionic and electronic conductivity. The composite electrodes thus exhibit substantial improvements in electrochemical performance. This ternary hierarchical Si@SiOx /Ni/graphite composite is a promising candidate anode material for high-energy lithium-ion batteries. Additionally, the mechanochemical ball-milling method is low cost and easy to reproduce, indicating potential for the commercial production of the composite materials. PMID:26548901

  15. Metal Oxide Silicon /MOS/ transistors protected from destructive damage by wire

    NASA Technical Reports Server (NTRS)

    Deboo, G. J.; Devine, E. J.

    1966-01-01

    Loop of flexible, small diameter, nickel wire protects metal oxide silicon /MOS/ transistors from a damaging electrostatic potential. The wire is attached to a music-wire spring, slipped over the MOS transistor case, and released so the spring tensions the wire loop around all the transistor leads, shorting them together. This allows handling without danger of damage.

  16. Improved reaction sintered silicon nitride. [protective coatings to improve oxidation resistance

    NASA Technical Reports Server (NTRS)

    Baumgartner, H. R.

    1978-01-01

    Processing treatments were applied to as-nitrided reaction sintered silicon nitride (RSSN) with the purposes of improving strength after processing to above 350 MN/m2 and improving strength after oxidation exposure. The experimental approaches are divided into three broad classifications: sintering of surface-applied powders; impregnation of solution followed by further thermal processing; and infiltration of molten silicon and subsequent carburization or nitridation of the silicon. The impregnation of RSSN with solutions of aluminum nitrate and zirconyl chloride, followed by heating at 1400-1500 C in a nitrogen atmosphere containing silicon monoxide, improved RSSN strength and oxidation resistance. The room temperature bend strength of RSSN was increased nearly fifty percent above the untreated strength with mean absolute strengths up to 420 MN/m2. Strengths of treated samples that were measured after a 12 hour oxidation exposure in air were up to 90 percent of the original as-nitrided strength, as compared to retained strengths in the range of 35 to 60 percent for untreated RSSN after the same oxidation exposure.

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

    NASA Astrophysics Data System (ADS)

    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 <= x = O/Si <=1) system with a combination of complementary x-ray and electron spectroscopies. The different surface sensitivities of the employed techniques help to reduce the impact of surface oxides on the spectral interpretation. For all samples, we find the valence band maximum to be located at a similar energy with respect to the Fermi energy. However, for x > 0.5, we observe a pronounced decrease of Si 3s - Si 3p hybridization in favor

  18. A Model for the Oxidation of Carbon Silicon Carbide Composite Structures

    NASA Technical Reports Server (NTRS)

    Sullivan, Roy M.

    2004-01-01

    A mathematical theory and an accompanying numerical scheme have been developed for predicting the oxidation behavior of carbon silicon carbide (C/SiC) composite structures. The theory is derived from the mechanics of the flow of ideal gases through a porous solid. The result of the theoretical formulation is a set of two coupled nonlinear differential equations written in terms of the oxidant and oxide partial pressures. The differential equations are solved simultaneously to obtain the partial vapor pressures of the oxidant and oxides as a function of the spatial location and time. The local rate of carbon oxidation is determined using the map of the local oxidant partial vapor pressure along with the Arrhenius rate equation. The nonlinear differential equations are cast into matrix equations by applying the Bubnov-Galerkin weighted residual method, allowing for the solution of the differential equations numerically. The numerical method is demonstrated by utilizing the method to model the carbon oxidation and weight loss behavior of C/SiC specimens during thermogravimetric experiments. The numerical method is used to study the physics of carbon oxidation in carbon silicon carbide composites.

  19. Enhancement of oxidation resistance of NBD 200 silicon nitride ceramics by aluminum implantation

    NASA Astrophysics Data System (ADS)

    Mukundhan, Priya

    Silicon nitride (Si3N4) ceramics are leading candidates for high temperature structural applications. They have already demonstrated functional capabilities well beyond the limits of conventional metals and alloys in advanced diesel and turbine engines. However, the practical exploitation of these benefits is limited by their oxidation and associated degradation processes in chemically aggressive environments. Additives and impurities in Si3N4 segregate to the surface of Si3N 4 and accelerate its high temperature oxidation process. This study aims to investigate the oxidation behavior of Norton NBD 200 silicon nitride (hot isostatically pressed with ˜1 wt.% MgO) and its modification by aluminum surface alloying. NBD 200 samples tribochemically polished to a mirror finish (10 nm) were implanted with 5, 10, 20 and 30 at.% aluminum at multienergies and multi-doses to achieve a uniform implant depth distribution to 200 nm. Unimplanted and aluminum-implanted samples were oxidized at 800°--1100°C in 1 atm O2 for 0.5--10 hours. Oxidation kinetics was determined using profilometry in conjunction with etch patterning. The morphological, structural and chemical characteristics of the oxide were characterized by various analytical techniques such as scanning electron microscope and energy dispersive x-ray analysis, secondary ion mass spectrometry and x-ray photoelectron spectroscopy. Oxidation of NBD 200 follows parabolic kinetics in the temperature range investigated and the process is diffusion-controlled. The oxide layers are enriched with sodium and magnesium from the bulk of the Si3N 4. The much higher oxidation rate for NBD 200 silicon nitride than for other silicon nitride ceramics with a similar amount of MgO is attributed to the presence of sodium. The rate-controlling mechanism is the outward diffusion of Mg2+ from the grain boundaries to the oxide scale. Aluminum implantation alleviates the detrimental effects of Na+ and Mg2+; not only is the rate of oxidation

  20. The effect of nanocrystalline silicon host on magnetic properties of encapsulated iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Granitzer, P.; Rumpf, K.; Gonzalez-Rodriguez, R.; Coffer, J. L.; Reissner, M.

    2015-11-01

    The purpose of this work is a detailed comparison of the fundamental magnetic properties of nanocomposite systems consisting of Fe3O4 nanoparticle-loaded porous silicon as well as silicon nanotubes. Such composite structures are of potential merit in the area of magnetically guided drug delivery. For magnetic systems to be utilized in biomedical applications, there are certain magnetic properties that must be fulfilled. Therefore magnetic properties of embedded Fe3O4-nanoparticles in these nanostructured silicon host matrices, porous silicon and silicon nanotubes, are investigated. Temperature-dependent magnetic investigations have been carried out for four types of iron oxide particle sizes (4, 5, 8 and 10 nm). The silicon host, in interplay with the iron oxide nanoparticle size, plays a sensitive role. It is shown that Fe3O4 loaded porous silicon and SiNTs differ significantly in their magnetic behavior, especially the transition between superparamagnetic behavior and blocked state, due to host morphology-dependent magnetic interactions. Importantly, it is found that all investigated samples meet the magnetic precondition of possible biomedical applications of exhibiting a negligible magnetic remanence at room temperature.The purpose of this work is a detailed comparison of the fundamental magnetic properties of nanocomposite systems consisting of Fe3O4 nanoparticle-loaded porous silicon as well as silicon nanotubes. Such composite structures are of potential merit in the area of magnetically guided drug delivery. For magnetic systems to be utilized in biomedical applications, there are certain magnetic properties that must be fulfilled. Therefore magnetic properties of embedded Fe3O4-nanoparticles in these nanostructured silicon host matrices, porous silicon and silicon nanotubes, are investigated. Temperature-dependent magnetic investigations have been carried out for four types of iron oxide particle sizes (4, 5, 8 and 10 nm). The silicon host, in interplay

  1. Oxidation and sulfidation resistant alloys with silicon additions

    SciTech Connect

    Dunning, John S.; Alman, David E.; Poston, J.A., Jr.; Siriwardane, R.

    2003-01-01

    The Albany Research Center (ARC) has considerable experience in developing lean chromium, austenitic stainless steels with improved high temperature oxidation resistance. Using basic alloy design principles, a baseline composition of Fe-16Cr-16Ni-2Mn-1Mo alloys with Si and Al addition at a maximum of 5 weight percent was selected for potential application at temperatures above 700ºC for supercritical and ultra-supercritical power plant application. The alloys were fully austenitic. Cyclic oxidation tests in air for 1000 hours were carried out on alloys with Si only or combined Si and Al additions in the temperature range 700ºC to 800ºC. Oxidation resistances of alloys with Si only additions were outstanding, particularly at 800ºC (i.e., these alloys possessed weight gains 4 times less than a standard type-304 alloy). In addition, Si alloys pre-oxidized at 800ºC, showed a zero weight gain in subsequent testing for 1000 hours at 700ºC. Similar improvements were observed for Si only alloy after H2S exposure at 700ºC compared with type 304 stainless steel. SEM and ESCA analysis of the oxide films and base material at the oxide/base metal interface were conducted to study potential rate controlling mechanisms at ARC. Depth profile analysis and element concentration profiles (argon ion etching/x-ray photoelectron spectroscopy) were conducted on oxidized specimens and base material at the National Energy Technology Laboratory.

  2. Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers.

    PubMed

    Rosso, Michel; Nguyen, Ai T; de Jong, Ed; Baggerman, Jacob; Paulusse, Jos M J; Giesbers, Marcel; Fokkink, Remko G; Norde, Willem; Schroën, Karin; van Rijn, Cees J M; Zuilhof, Han

    2011-03-01

    The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH═CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH═CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon

  3. Graphene oxide-immobilized NH₂-terminated silicon nanoparticles by cross-linked interactions for highly stable silicon negative electrodes.

    PubMed

    Sun, Cheng; Deng, Yuanfu; Wan, Lina; Qin, Xusong; Chen, Guohua

    2014-07-23

    There is a great interest in the utilization of silicon-based anodes for lithium-ion batteries. However, its poor cycling stability, which is caused by a dramatic volume change during lithium-ion intercalation, and intrinsic low electric conductivity hamper its industrial applications. A facile strategy is reported here to fabricate graphene oxide-immobilized NH2-terminated silicon nanoparticles (NPs) negative electrode (Si@NH2/GO) directed by hydrogen bonding and cross-linked interactions to enhance the capacity retention of the anode. The NH2-modified Si NPs first form strong hydrogen bonds and covalent bonds with GO. The Si@NH2/GO composite further forms hydrogen bonds and covalent bonds with sodium alginate, which acts as a binder, to yield a stable composite negative electrode. These two chemical cross-linked/hydrogen bonding interactions-one between NH2-modified Si NPs and GO, and another between the GO and sodium alginate-along with highly mechanically flexible graphene oxide, produced a robust network in the negative electrode system to stabilize the electrode during discharge and charge cycles. The as-prepared Si@NH2/GO electrode exhibits an outstanding capacity retention capability and good rate performance, delivering a reversible capacity of 1000 mAh g(-1) after 400 cycles at a current of 420 mA g(-1) with almost 100% capacity retention. The results indicated the importance of system-level strategy for fabricating stable electrodes with improved electrochemical performance. PMID:24922522

  4. Oxidation Kinetics of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.

    1994-01-01

    The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(sub H2O) = 0.1 atm) at temperatures between 1200 C and 1400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.

  5. Low temperature oxidation of silicon in a microwave-discharged oxygen plasma

    SciTech Connect

    Kimura, S.I.; Miyake, K.; Murakami, E.; Sunami, H.; Tokuyama, T.; Warabisako, T.

    1985-06-01

    Silicon dioxide growth in an oxygen plasma is investigated using newly developed microwave discharge equipment with electron cyclotron resonance. It is found that the plasma oxidation kinetics can be explained by the Cabrera-Mott model, in which the drift motion of ions is assumed, rather than by the Deal-Grove thermal oxidation model. The drift motion of oxygen ions across the oxide film under the influence of self-bias in the plasma is considered to be the plasma oxidation mechanism. Infrared absorption and etch-rate measurements reveal that the physica properties of plasma oxidized SiO/sub 2/ at 600/sup 0/C are structurally quite comparable to those of thermally oxidized SiO/sub 2/.

  6. Thermal radiative near field transport between vanadium dioxide and silicon oxide across the metal insulator transition

    NASA Astrophysics Data System (ADS)

    Menges, F.; Dittberner, M.; Novotny, L.; Passarello, D.; Parkin, S. S. P.; Spieser, M.; Riel, H.; Gotsmann, B.

    2016-04-01

    The thermal radiative near field transport between vanadium dioxide and silicon oxide at submicron distances is expected to exhibit a strong dependence on the state of vanadium dioxide which undergoes a metal-insulator transition near room temperature. We report the measurement of near field thermal transport between a heated silicon oxide micro-sphere and a vanadium dioxide thin film on a titanium oxide (rutile) substrate. The temperatures of the 15 nm vanadium dioxide thin film varied to be below and above the metal-insulator-transition, and the sphere temperatures were varied in a range between 100 and 200 °C. The measurements were performed using a vacuum-based scanning thermal microscope with a cantilevered resistive thermal sensor. We observe a thermal conductivity per unit area between the sphere and the film with a distance dependence following a power law trend and a conductance contrast larger than 2 for the two different phase states of the film.

  7. Crack healing in silicon nitride due to oxidation

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Tikare, Veena; Pawlik, Ralph

    1991-01-01

    The crack healing behavior of a commercial, MgO-containing, hot pressed Si3N4 was studied as a function of temperature in oxidizing and inert annealing environments. Crack healing occurred at a temperature 800 C or higher due to oxidation regardless of crack size, which ranged from 100 microns (indentation crack) to 1.7 mm (SEPB precrack). The resulting strength and apparent fracture toughness increased at crack healing temperature by 100 percent and 300 percent, respectively. The oxide layer present in the crack plane was found to be highly fatigue resistant, indicating that the oxide is not solely silicate glass, but a mixture of glass, enstatite, and/or cristobalite that was insensitive to fatigue in a room temperature water environment.

  8. Dependence of cryogenic strength of hydroxide catalysis bonded silicon on type of surface oxide

    NASA Astrophysics Data System (ADS)

    Beveridge, N. L.; van Veggel, A. A.; Cunningham, L.; Hough, J.; Martin, I. W.; Nawrodt, R.; Reid, S.; Rowan, S.

    2013-01-01

    Hydroxide catalysis bonding is a joining technique used in the construction of highly stable opto-mechanical systems including quasi-monolithic silica suspensions for first and second generation gravitational wave detectors. Future generations of detector are likely to operate at cryogenic temperatures necessitating a change in testmass/suspension material. A promising candidate material is silicon, which requires an oxide surface layer for hydroxide catalysis bonding to be reliable. Here, we present first results showing the influence of the type of oxide layer applied on bond strength, measured at room temperature and 77 K, and identify preferred oxide deposition methods.

  9. Destruction of monocrystalline silicon with nanosecond pulsed fiber laser accompanied by the oxidation of ablation microparticles

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Skvortsov, A. M.; Huynh, C. T.; Petrov, A. A.

    2013-11-01

    In this work, we report an observation of process of local destruction monocrystalline silicon with a scanning beam irradiation of pulse ytterbium fiber laser with a wavelength λ= 1062 nm, accompanied by the oxidation of ablation microparticles. It is shown that depending on the power density of irradiation was observed a large scatter size of the microparticles. From a certain average power density is observed beginning oxidation particulate emitted from the surface of the irradiated area. By varying the parameters of the laser beam such as scanning speed, pulse repetition rate, overlap of laser spot, radiation dose can be achieved almost complete oxidation of all formed during the ablation of microparticles.

  10. The effect of oxide precipitates on minority carrier lifetime in n-type silicon

    NASA Astrophysics Data System (ADS)

    Murphy, J. D.; Al-Amin, M.; Bothe, K.; Olmo, M.; Voronkov, V. V.; Falster, R. J.

    2015-12-01

    Supersaturated levels of interstitial oxygen in Czochralski silicon can lead to the formation of oxide precipitates. Although beneficial from an internal gettering perspective, oxygen-related extended defects give rise to recombination which reduces minority carrier lifetime. The highest efficiency silicon solar cells are made from n-type substrates in which oxide precipitates can have a detrimental impact on cell efficiency. In order to quantify and to understand the mechanism of recombination in such materials, we correlate injection level-dependent minority carrier lifetime data measured with silicon nitride surface passivation with interstitial oxygen loss and precipitate concentration measurements in samples processed under substantially different conditions. We account for surface recombination, doping level, and precipitate morphology to present a generalised parameterisation of lifetime. The lifetime data are analysed in terms of recombination activity which is dependent on precipitate density or on the surface area of different morphologies of precipitates. Correlation of the lifetime data with interstitial oxygen loss data shows that the recombination activity is likely to be dependent on the precipitate surface area. We generalise our findings to estimate the impact of oxide precipitates with a given surface area on lifetime in both n-type and p-type silicon.

  11. Self-aligned top-gate amorphous indium zinc oxide thin-film transistors exceeding low-temperature poly-Si transistor performance.

    PubMed

    Park, Jae Chul; Lee, Ho-Nyeon; Im, Seongil

    2013-08-14

    Thin-film transistor (TFT) is a key component of active-matrix flat-panel displays (AMFPDs). These days, the low-temperature poly silicon (LTPS) TFTs are to match with advanced AMFPDs such as the active matrix organic light-emitting diode (AMOLED) display, because of their high mobility for fast pixel switching. However, the manufacturing process of LTPS TFT is quite complicated, costly, and scale-limited. Amorphous oxide semiconductor (AOS) TFT technology is another candidate, which is as simple as that of conventioanl amorphous (a)-Si TFTs in fabrication but provides much superior device performances to those of a-Si TFTs. Hence, various AOSs have been compared with LTPS for active channel layer of the advanced TFTs, but have always been found to be relatively inferior to LTPS. In the present work, we clear the persistent inferiority, innovating the device performaces of a-IZO TFT by adopting a self-aligned coplanar top-gate structure and modifying the surface of a-IZO material. Herein, we demonstrate a high-performance simple-processed a-IZO TFT with mobility of ∼157 cm(2) V(-1) s(-1), SS of ∼190 mV dec(-1), and good bias/photostabilities, which overall surpass the performances of high-cost LTPS TFTs. PMID:23823486

  12. Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field

    PubMed Central

    Shah, Saqlain A.; Reeves, Daniel B.; Ferguson, R. Matthew; Weaver, John B.

    2015-01-01

    Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (ΔT ~ 20 °C) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging. PMID:26504371

  13. Interfacial energy level alignments between low-band-gap polymer PTB7 and indium zinc oxide anode

    NASA Astrophysics Data System (ADS)

    Shin, Dongguen; Lee, Jeihyun; Park, Soohyung; Jeong, Junkyeong; Seo, Ki-Won; Kim, Hyo-Joong; Kim, Han-Ki; Choi, Min-Jun; Chung, Kwun-Bum; Yi, Yeonjin

    2015-09-01

    The interfacial energy level alignments between poly(thieno[3,4-b]-thiophene)-co-benzodithiophene (PTB7) and indium zinc oxide (IZO) were investigated. In situ ultraviolet photoemission spectroscopy measurements were conducted with the step-by-step deposition of PTB7 on IZO substrate. All spectral changes were analyzed between each deposition step, and interfacial energy level alignments were estimated. The hole barrier of standard ultraviolet-ozone treated IZO is 0.58 eV, which is lower than the value of 1.09 eV obtained for bare IZO. The effect of barrier reduction on the hole transport was also confirmed with electrical measurements of hole-dominated devices.

  14. Surface chemistry, reactivity, and pore structure of porous silicon oxidized by various methods.

    PubMed

    Riikonen, Joakim; Salomäki, Mikko; van Wonderen, Jessica; Kemell, Marianna; Xu, Wujun; Korhonen, Ossi; Ritala, Mikko; MacMillan, Fraser; Salonen, Jarno; Lehto, Vesa-Pekka

    2012-07-17

    Oxidation is the most commonly used method of passivating porous silicon (PSi) surfaces against unwanted reactions with guest molecules and temporal changes during storage or use. In the present study, several oxidation methods were compared in order to find optimal methods able to generate inert surfaces free of reactive hydrides but would cause minimal changes in the pore structure of PSi. The studied methods included thermal oxidations, liquid-phase oxidations, annealings, and their combinations. The surface-oxidized samples were studied by Fourier transform infrared spectroscopy, isothermal titration microcalorimetry, nitrogen sorption, ellipsometry, X-ray diffraction, electron paramagnetic resonance spectroscopy, and scanning electron microscopy imaging. Treatment at high temperature was found to have two advantages. First, it enables the generation of surfaces free of hydrides, which is not possible at low temperatures in a liquid or a gas phase. Second, it allows the silicon framework to partially accommodate a volume expansion because of oxidation, whereas at low temperature the volume expansion significantly consumes the free pore volume. The most promising methods were further optimized to minimize the negative effects on the pore structure. Simple thermal oxidation at 700 °C was found to be an effective oxidation method although it causes a large decrease in the pore volume. A novel combination of thermal oxidation, annealing, and liquid-phase oxidation was also effective and caused a smaller decrease in the pore volume with no significant change in the pore diameter but was more complicated to perform. Both methods produced surfaces that were not found to react with a model drug cinnarizine in isothermal titration microcalorimetry experiments. The study enables a reasonable choice of oxidation method for PSi applications. PMID:22671967

  15. Indentation and oxidation studies on silicon nitride joints

    SciTech Connect

    Gopal, M.; De Jonghe, L.C.; Thomas, G. |

    1996-05-01

    Si nitride ceramics have been joined with a Y oxide-SiO{sub 2} interlayer. A 1:2 molar ratio of Y{sub 2}O{sub 3} to SiO{sub 2} was chosen to obtain the desired Y{sub 2}Si{sub 2}O{sub 7} stoichiometry, which should give the interlayer better oxidation resistance compared to other interlayer materials. Mechanical characterization of the joints performed by indentation shows it to have good room temperature strength.

  16. Extracting mechanical properties of copper coatings on oxidized silicon substrates by nanoindentation

    NASA Astrophysics Data System (ADS)

    Moharrami, N.; Oila, A.; Bull, S. J.

    2014-08-01

    The thickness of the copper coatings that are used for the manufacture of conducting tracks in microelectronic devices are being aggressively scaled down and there is a need to monitor the mechanical response of metallization at a scale comparable to the material microstructure. When using indentation tests to assess the properties of thin films, the plastic zone dimensions are of a similar scale to the grain size. For the purposes of designs based on continuum mechanics approaches it is usually required that the grain size is much smaller than the deforming volume, which is not always observed in practice. Considerable differences between predicted and observed performance can be seen depending on the material tested and its grain size; the extent of oxidation of the copper after deposition is critical, as is that of its underlying silicon substrate. Whereas it is possible to make good measurements of metallization properties on stiff substrates such as silicon there are serious issues with the reliability of Young's modulus and hardness data from coatings on device quality wafers which may have been oxidized prior to use. The effects of grain size, shape and orientation on the mechanical response of metallic thin films used for semiconductor metallization on oxidized silicon are presented in this paper. The appropriate conditions for the successful use of continuum mechanics are discussed and the importance of considering the consequences of crystallographic anisotropy and oxidation on the selection of suitable design data is presented with regards to copper coatings.

  17. The growth of microcrystalline silicon oxide thin films studied by in situ plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Kirner, S.; Gabriel, O.; Stannowski, B.; Rech, B.; Schlatmann, R.

    2013-02-01

    The crystallinity and refractive index of microcrystalline silicon oxide (μc-SiOx:H) n-layers and their dependence on the pressure and radio frequency power during the deposition process is correlated with plasma properties derived from in situ diagnostics. From process gas depletion measurements, the oxygen content of the layers was calculated. High crystallinities were observed for increased pressures and decreased powers, indicating clear differences to trends previously shown for microcrystalline silicon (μc-Si:H) material, which are explained by the varying oxygen incorporation. Amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cells with μc-SiOx:H intermediate reflector layers deposited at optimized pressures showed greatly improved series resistances.

  18. Exclusively Gas-Phase Passivation of Native Oxide-Free Silicon(100) and Silicon(111) Surfaces.

    PubMed

    Tao, Ye; Hauert, Roland; Degen, Christian L

    2016-05-25

    Reactions in the gas phase are of primary technological importance for applications in nano- and microfabrication technology and in the semiconductor industry. We present exclusively gas-phase protocols to chemically passivate oxide-free Si(111) and Si(100) surfaces with short-chain alkynes. The resulting surfaces showed equal or better oxidation resistance than most existing liquid-phase-derived surfaces and rivaled the outstanding stability of a full-coverage Si(111)-propenyl surface.1,2 The most stable surface (Si(111)-ethenyl) grew one-fifth of a monolayer of oxide (0.04 nm) after 1 month of air exposure. We monitored the regrowth of oxides on passivated Si(111) and Si(100) surfaces by X-ray photoelectron spectroscopy (XPS) and observed a significant crystal-orientation dependence of initial rates when total oxide thickness was below approximately one monolayer (0.2 nm). This difference was correlated with the desorption kinetics of residual surface Si-F bonds formed during HF treatment. We discuss applications of the technology and suggest future directions for process optimization. PMID:27153212

  19. Molecular dynamics simulation of silicon oxidation enhanced by energetic hydrogen ion irradiation

    NASA Astrophysics Data System (ADS)

    Mizotani, Kohei; Isobe, Michiro; Fukasawa, Masanaga; Nagahata, Kazunori; Tatsumi, Tetsuya; Hamaguchi, Satoshi

    2015-04-01

    Molecular dynamics numerical simulations have been performed to clarify the mechanism of enhanced oxidation in Si during silicon gate etching by HBr/O2 plasmas. Such enhanced oxidation sometimes manifests itself as Si recess during gate etching processes. When a Si substrate is subject to energetic ion bombardment together with a flux of radical species, our study has identified the cause of such enhanced oxidation in Si as enhanced O diffusion arising from the momentum transfer from energetic H atoms to O atoms on the surface or in the subsurface of the Si substrate. No chemical effect such as hydrogenation of Si plays a role for the enhanced oxidation. Simulation results are found to be in good agreement with earlier experimental observations of ion-irradiation-enhanced oxidation obtained by beam experiments.

  20. Thin film germanium on silicon created via ion implantation and oxide trapping

    NASA Astrophysics Data System (ADS)

    Anthony, R.; Knights, A. P.

    2015-06-01

    We present a novel process for integrating germanium with silicon-on-insulator (SOI) wafers. Germanium is implanted into SOI which is then oxidized, trapping the germanium between the two oxide layers (the grown oxide and the buried oxide). With careful control of the implantation and oxidation conditions this process creates a thin layer (current experiments indicate up to 20-30nm) of almost pure germanium. The layer can be used potentially for fabrication of integrated photo-detectors sensitive to infrared wavelengths, or may serve as a seed for further germanium growth. Results are presented from electron microscopy and Rutherford back-scattering analysis, as well as preliminary modelling using an analytical description of the process.

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

    NASA Astrophysics Data System (ADS)

    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 <= x = O/Si <=1) system with a combination of complementary x-ray and electron spectroscopies. The different surface sensitivities of the employed techniques help to reduce the impact of surface oxides on the spectral interpretation. For all samples, we find the valence band maximum to be located at a similar energy with respect to the Fermi energy. However, for x > 0.5, we observe a pronounced decrease of Si 3s - Si 3p hybridization in favor

  2. In situ silicon oxide based intermediate reflector for thin-film silicon micromorph solar cells

    NASA Astrophysics Data System (ADS)

    Buehlmann, P.; Bailat, J.; Dominé, D.; Billet, A.; Meillaud, F.; Feltrin, A.; Ballif, C.

    2007-10-01

    We show that SiO-based intermediate reflectors (SOIRs) can be fabricated in the same reactor and with the same process gases as used for thin-film silicon solar cells. By varying input gas ratios, SOIR layers with a wide range of optical and electrical properties are obtained. The influence of the SOIR thickness in the micromorph cell is studied and current gain and losses are discussed. Initial micromorph cell efficiency of 12.2% (Voc=1.40V, fill factor=71.9%, and Jsc=12.1mA/cm2) is achieved with top cell, SOIR, and bottom cell thicknesses of 270, 95, and 1800nm, respectively.

  3. High-temperature oxidation of CVD silicon-based ceramics

    SciTech Connect

    Goto, Takashi; Hirai, Toshio; Iguchi, Yasutaka

    1996-12-31

    Oxidation behavior of CVD SiC and CVD Si{sub 3}N{sub 4} was studied at 1773 to 2023 K in Ar-O{sub 2}, N{sub 2}-O{sub 2} and CO-CO{sub 2} atmospheres. In Ar-O{sub 2} and N{sub 2}-O{sub 2} atmospheres, the active oxidation rates for CVD SiC and CVD Si{sub 3}N{sub 4} were dominated by oxygen diffusion through a gas boundary layer. The active-to-passive transition oxygen partial pressures for CVD SiC were slightly greater than those for CVD Si{sub 3}N{sub 4}. In CO-CO{sub 2} atmospheres, at PCO{sub 2}/PCO < 10{sup -3} inward diffusion of CO{sub 2} gas controlled the active oxidation rates for CVD SiC; however, a chemical reaction controlled the rates for CVD Si{sub 3}N{sub 4}. At PCO{sub 2}/PCO > 10 {sup -2}, SiO{sub 2} particles or layers formed during the active oxidation; the decomposition of SiO{sub 2} could control the active oxidation rates. The Wagner model can be used to explain the active-to-passive transition in these atmospheres for both CVD SiC and CVD Si{sub 3}N{sub 4}. The volatility diagram and thermodynamic calculation, including mass balance relationship, were also useful to understand the transition behavior.

  4. Effect of W and WC on the oxidation resistance of yttria-doped silicon nitride

    NASA Technical Reports Server (NTRS)

    Schuon, S.

    1980-01-01

    The effect of tungsten and tungsten carbide contamination on the oxidation and cracking in air of yttria-doped silicon nitride ceramics is investigated. Silicon nitride powder containing 8 wt % Y2O3 was doped with 2 wt % W, 4 wt % W, 2 wt % WC or left undoped, and sintered in order to simulate contamination during milling, and specimens were exposed in air to 500, 750 and 1350 C for various lengths of time. Scanning electron and optical microscopy and X-ray diffraction of the specimens in the as-sintered state reveals that the addition of W or WC does not affect the phase relationships in the system, composed of alpha and beta Si3N4, melilite and an amorphous phase. Catastrophic oxidation is observed at 750 C in specimens containing 2 and 4 wt % W, accompanied by the disappearance of alpha Si3N4 and melilite from the structure. At 1350 C, the formation of a protective glassy oxide layer was observed on all specimens without catastrophic oxidation, and it is found that pre-oxidation at 1350 C also improved the oxidation resistance at 750 C of bars doped with 4 wt % W. It is suggested that tungsten contamination from WC grinding balls may be the major cause of the intermediate-temperature cracking and instability frequently observed in Si3N4-8Y2O3.

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

    PubMed

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

    2010-08-01

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

  6. Efficient processing of reaction-sintered silicon carbide by anodically oxidation-assisted polishing

    NASA Astrophysics Data System (ADS)

    Tu, Qunzhang; Shen, Xinmin; Zhou, Jianzhao; He, Xiaohui; Yamamura, Kazuya

    2015-10-01

    Reaction-sintered silicon carbide (RS-SiC) is a promising optical material for the space telescope systems. Anodically oxidation-assisted polishing is a method to machine RS-SiC. The electrolyte used in this study is a mixture of hydrogen peroxide (H2O2) and hydrochloric acid (HCl), and the oxidation potential has two modes: constant potential and high-frequency-square-wave potential. Oxide morphologies are compared by scanning electron microscope/energy dispersive x-ray spectroscopy and scanning white-light interferometer. The results indicate that anodic oxidation under constant potential can not only obtain a relatively smooth surface but also be propitious to obtain high material removal rate. The oxidation depth in anodic oxidation under constant potential is calculated by comparing surface morphologies before and after hydrofluoric acid etching. The theoretical oxidation rate is 5.3 nm/s based on the linear Deal-Grove model. Polishing of the oxidized RS-SiC is conducted to validate the machinability of the oxide layer. The obtained surface roughness root-mean-square is around 4.5 nm. Thus, anodically oxidation-assisted polishing can be considered as an efficient method, which can fill the performance gap between the rough figuring and fine finishing of RS-SiC. It can improve the machining quality of RS-SiC parts and promote the application of RS-SiC products.

  7. A template and catalyst-free metal-etching-oxidation method to synthesize aligned oxide nanowire arrays: NiO as an example.

    PubMed

    Wei, Zhi Peng; Arredondo, Miryam; Peng, Hai Yang; Zhang, Zhou; Guo, Dong Lai; Xing, Guo Zhong; Li, Yong Feng; Wong, Lai Mun; Wang, Shi Jie; Valanoor, Nagarajan; Wu, Tom

    2010-08-24

    Although NiO is one of the canonical functional binary oxides, there has been no report so far on the effective fabrication of aligned single crystalline NiO nanowire arrays. Here we report a novel vapor-based metal-etching-oxidation method to synthesize high-quality NiO nanowire arrays with good vertical alignment and morphology control. In this method, Ni foils are used as both the substrates and the nickel source; NiCl(2) powder serves as the additional Ni source and provides Cl(2) to initiate mild etching. No template is deliberately employed; instead a nanograined NiO scale formed on the NiO foil guides the vapor infiltration and assists the self-assembled growth of NiO nanowires via a novel process comprising simultaneous Cl(2) etching and gentle oxidation. Furthermore, using CoO nanowires and Co-doped NiO as examples, we show that this general method can be employed to produce nanowires of other oxides as well as the doped counterparts. PMID:20614899

  8. Kinetic study of the oxide-assisted catalyst-free synthesis of silicon nitride nanowires

    NASA Astrophysics Data System (ADS)

    Farjas, J.; Pinyol, A.; Rath, Chandana; Roura, P.; Bertran, E.

    2006-05-01

    The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles with N2 in the 1200-1440 °C temperature range is reported. The nitridation conditions are such that the reaction with nitrogen is favoured by the presence of silicon oxide in the particles and by the active oxidation of silicon without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on the amount of silicon particles used in the experiments and that, in general, the reaction slows down for greater amounts. This trend is explained by particle stacking, which restricts the exchange of gases between the furnace atmosphere and the atmosphere around the inner particles. In a first stage, local oxygen partial pressure increases around the inner particles and inhibits nitridation locally. If the amount of reactant Si nanoparticles is small enough, this extrinsic effect is avoided and the intrinsic nitridation kinetics can be measured. Experiments show that intrinsic kinetics does not depend on temperature.

  9. Novel Iron-oxide Catalyzed CNT Formation on Semiconductor Silicon Nanowire

    PubMed Central

    Adam, Tijjani; U, Hashim

    2014-01-01

    An aqueous ferric nitrate nonahydrate (Fe(NO3)3.9H2O) and magnesium oxide (MgO) were mixed and deposited on silicon nanowires (SiNWs), the carbon nanotubes (CNTs) formed by the concentration of Fe3O4/MgO catalysts with the mole ratio set at 0.15:9.85 and 600°C had diameter between 15.23 to 90nm with high-density distribution of CNT while those with the mole ratio set at 0.45:9.55 and 730°C had diameter of 100 to 230nm. The UV/Vis/NIR and FT-IR spectroscopes clearly confirmed the presence of the silicon-CNTs hybrid structure. UV/Vis/NIR, FT-IR spectra and FESEM images confirmed the silicon-CNT structure exists with diameters ranging between 15-230nm. Thus, the study demonstrated cost effective method of silicon-CNT composite nanowire formation via Iron-oxide Catalyze synthesis. PMID:25237290

  10. Growth Mechanisms of Vertically-aligned Carbon, Boron Nitride, and Zinc Oxide Nanotubes

    SciTech Connect

    Yap, Yoke Khin

    2009-07-07

    Nanotubes are one-dimensional nanomaterials with all atoms located near the surface. This article provides a brief review on the possible growth mechanisms of a series of inorganic nanotubes, in particular, vertically-aligned (VA) carbon nanotubes (CNTs), boron nitride nanotubes (BNNTs), and ZnO nanotubes (ZnO NTs).

  11. Hydrothermal growth and characterization of vertically well-aligned and dense ZnO nanorods on glass and silicon using a simple optimizer system

    NASA Astrophysics Data System (ADS)

    Mohammad, Sabah M.; Hassan, Z.; Ahmed, Naser M.; Talib, Rawnaq A.; Abd-Alghafour, Nabeel M.; Omar, A. F.

    2016-07-01

    Vertically, well-aligned and high density ZnO nanorods were successfully hydrothermally grown on glass and silicon substrates using a simple and low cost system. The mechanism of synthesis of ZnO nanorods, generated with our system under hydrothermal conditions, is investigated in this report. Field-emission scanning electron microscopy indicated that the fabricated ZnO nanorods on both substrates have hexagonal shape with diameters ranging from 20 nm to 70 nm which grew vertically from the substrate. XRD analysis confirms the formation of wurtzite ZnO phase with a preferred orientation along (002) direction perpendicular on the substrate and enhanced crystallinity. The low value of the tensile strain (0.126 %) revealed that ZnO nanorods preferred to grow along the c-axis for both substrates. Photoluminescence spectra exhibited a strong, sharp UV near band edge emission peak with narrow FWHM values for both samples.

  12. Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

    DOEpatents

    Sarin, Vinod K.

    1990-01-01

    An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al.sub.x N.sub.y O.sub.z layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al.sub.x N.sub.y O.sub.z layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

  13. Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

    DOEpatents

    Sarin, V.K.

    1990-08-21

    An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications is disclosed. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al[sub x]N[sub y]O[sub z] layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al[sub x]N[sub y]O[sub z] layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

  14. Complete coverage of reduced graphene oxide on silicon dioxide substrates

    NASA Astrophysics Data System (ADS)

    Huang, Jingfeng; Melanie, Larisika; Chen, Hu; Steve, Faulkner; Myra, A. Nimmo; Christoph, Nowak; Alfred Tok Iing, Yoong

    2014-08-01

    Reduced graphene oxide (RGO) has the advantage of an aqueous and industrial-scale production route. No other approaches can rival the RGO field effect transistor platform in terms of cost (oxide with ethanol, carbon islets are deposited preferentially at the edges of existing flakes. With a 2-h treatment, the standard deviation in electrical resistance of the treated chips can be reduced by 99.95%. Thus this process could enable RGO to be used in practical electronic devices.

  15. Tunable nanoporous silicon oxide templates by swift heavy ion tracks technology.

    PubMed

    Kaniukov, E Yu; Ustarroz, J; Yakimchuk, D V; Petrova, M; Terryn, H; Sivakov, V; Petrov, A V

    2016-03-18

    Nanoporous silicon oxide templates formed by swift heavy ion tracks technology have been investigated. The influence of the heavy ion characteristics, such as type of ion, energy, stopping power and irradiation fluence on the pore properties of the silicon oxide templates, has been studied. Furthermore, the process of pore formation by chemical etching with hydrofluoric acid has been thoroughly investigated by assessing the effect of etchant concentration and etching time. The outcome of this investigation enables us to have precise control over the resulting geometry of nanopores arrays. As a result, guidelines for the creation of a-SiO2/Si templates with tunable parameters and general recommendations for their further application are presented. PMID:26878691

  16. Tunable nanoporous silicon oxide templates by swift heavy ion tracks technology

    NASA Astrophysics Data System (ADS)

    Kaniukov, E. Yu; Ustarroz, J.; Yakimchuk, D. V.; Petrova, M.; Terryn, H.; Sivakov, V.; Petrov, A. V.

    2016-03-01

    Nanoporous silicon oxide templates formed by swift heavy ion tracks technology have been investigated. The influence of the heavy ion characteristics, such as type of ion, energy, stopping power and irradiation fluence on the pore properties of the silicon oxide templates, has been studied. Furthermore, the process of pore formation by chemical etching with hydrofluoric acid has been thoroughly investigated by assessing the effect of etchant concentration and etching time. The outcome of this investigation enables us to have precise control over the resulting geometry of nanopores arrays. As a result, guidelines for the creation of a-SiO2/Si templates with tunable parameters and general recommendations for their further application are presented.

  17. Production of Silicon Oxide like Thin Films by the Use of Atmospheric Plasma Torch

    NASA Astrophysics Data System (ADS)

    Ozono, E. M.; Fachini, E. R.; Silva, M. L. P.; Ruchko, L. F.; Galvão, R. M. O.

    2015-03-01

    The advantages of HMDS (hexamethyldisilazane) APT-plasma films for sensor applications were explored producing films in a three-turn copper coil APT equipment. HMDS was introduced into the argon plasma at four different conditions. Additional flux of oxygen could modulate the presence of organic components in the film, the composition varying from pure inorganic oxides to organo-silane polymers. Oxygen promoted deposition rates as high as 900 nm/min on silicon, acrylic or piezoelectric quartz crystal substrates. Films with a clustered morphology and refractive index of 1.45 were obtained, mainly due to a silicon oxide structure. Raman spectroscopy and XPS data showed the presence of CHn and amorphous carbon in the inorganic matrix. The films were sensitive to the humidity of the air. The adsorptive capabilities of outstanding films were tested in a Quartz Crystal Microbalance (QCM). The results support that those films can be a useful and simple alternative for the development of sensors.

  18. Dimensions of luminescent oxidized and porous silicon structures

    SciTech Connect

    Schuppler, S.; Friedman, S.L.; Marcus, M.A.; Adler, D.L.; Xie, Y.; Ross, F.M.; Harris, T.D.; Brown, W.L.; Chabal, Y.J.; Brus, L.E.; Citrin, P.H. National Center for Electron Microscopy, Lawrence Berkeley Laboratory, Berkeley, California 94720 )

    1994-04-18

    X-ray absorption measurements from H-passivated porous Si and from oxidized Si nanocrystals, combined with electron microscopy, ir absorption, [alpha] recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the visible luminescence observed in these samples. The mass-weighted average structures in por-Si are particles, not wires, with dimensions significantly smaller than previously reported or proposed.

  19. Silicon based solar cells using a multilayer oxide as emitter

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Wu, Weiliang; Liu, Zongtao; Shen, Hui

    2016-08-01

    In this work, n-type silicon based solar cells with WO3/Ag/WO3 multilayer films as emitter (WAW/n-Si solar cells) were presented via simple physical vapor deposition (PVD). Microstructure and composition of WAW/n-Si solar cells were studied by TEM and XPS, respectively. Furthermore, the dependence of the solar cells performances on each WO3 layer thickness was investigated. The results indicated that the bottom WO3 layer mainly induced band bending and facilitated charge-carriers separation, while the top WO3 layer degraded open-circuit voltage but actually improved optical absorption of the solar cells. The WAW/n-Si solar cells, with optimized bottom and top WO3 layer thicknesses, exhibited 5.21% efficiency on polished wafer with area of 4 cm2 under AM 1.5 condition (25 °C and 100 mW/cm2). Compared with WO3 single-layer film, WAW multilayer films demonstrated better surface passivation quality but more optical loss, while the optical loss could be effectively reduced by implementing light-trapping structures. These results pave a new way for dopant-free solar cells in terms of low-cost and facile process flow.

  20. Quantum Conductance in Silicon Oxide Resistive Memory Devices

    PubMed Central

    Mehonic, A.; Vrajitoarea, A.; Cueff, S.; Hudziak, S.; Howe, H.; Labbé, C.; Rizk, R.; Pepper, M.; Kenyon, A. J.

    2013-01-01

    Resistive switching offers a promising route to universal electronic memory, potentially replacing current technologies that are approaching their fundamental limits. In many cases switching originates from the reversible formation and dissolution of nanometre-scale conductive filaments, which constrain the motion of electrons, leading to the quantisation of device conductance into multiples of the fundamental unit of conductance, G0. Such quantum effects appear when the constriction diameter approaches the Fermi wavelength of the electron in the medium – typically several nanometres. Here we find that the conductance of silicon-rich silica (SiOx) resistive switches is quantised in half-integer multiples of G0. In contrast to other resistive switching systems this quantisation is intrinsic to SiOx, and is not due to drift of metallic ions. Half-integer quantisation is explained in terms of the filament structure and formation mechanism, which allows us to distinguish between systems that exhibit integer and half-integer quantisation. PMID:24048282

  1. Irradiation induced pulsations of reverse biased metal oxide/silicon structures

    SciTech Connect

    Fink, D.; Kiv, A.; Fuks, D.; Tabacnics, M.; Rizutto, M. de A; Silva, A. de O D; Chandra, A.; Golovanov, V.; Ivanovskaya, M.; Khirunenko, L.

    2007-08-20

    Specific electronic features have been found in structures consisting of metal oxide layers on silicon substrates upon swift heavy ion irradiation. These features are linked to the appearance of radiation-induced negative differential resistances in the structures. In the reversed bias direction they show high frequency current pulsations at around {approx}10 kHz frequency. Their amplitude increases with increasing applied voltage. The pulsation frequency also shows a small increase. The current amplitude depends on the ion fluence and flux.

  2. Window layer with p doped silicon oxide for high Voc thin-film silicon n-i-p solar cells

    NASA Astrophysics Data System (ADS)

    Biron, Rémi; Pahud, Celine; Haug, Franz-Josef; Escarré, Jordi; Söderström, Karin; Ballif, Christophe

    2011-12-01

    We investigate the influence of the oxygen content in boron-doped nanocrystalline silicon oxide films (p-nc-SiOx) and introduce this material as window layer in n-i-p solar cells. The dependence of both, optical and electrical properties on the oxygen content is consistent with a bi-phase model which describes the p-nc-SiOx material as a mixture of an oxygen-rich (O-rich) phase and a silicon-rich (Si-rich) phase. We observe that increasing the oxygen content enhances the optical gap E04 while deteriorating the activation energy and the planar conductivity. These trends are ascribed to a higher volume fraction of the O-rich phase. Incorporated into n-i-p a-Si:H cells, p-nc-SiOx layers with moderate oxygen content yield open circuit voltage (Voc) up to 945 mV, which corresponds to a relative gain of 11% compared to an oxygen-free p-layer. As a similar gain is obtained on planar and on textured substrates, we attribute the increase in Voc to the higher work function of the p-nc-SiOx layer made possible by its wider band gap. These results are attained without changing the dilution ratio of the 250 nm thick intrinsic layer. We also observe an enhancement of 0.6 mA cm-2 in short circuit current density in the short wavelengths due to the higher transparency of the p-nc-SiOx layer. Finally, an initial efficiency of 9.9% for a single junction 250 nm a-Si:H n-i-p solar cell on plastic foil is achieved with the optimization of the p layer thickness, the doping ratio of the front transparent conductive oxide, and the optical properties of the back reflector.

  3. Self-aligned process for forming microlenses at the tips of vertical silicon nanowires by atomic layer deposition

    SciTech Connect

    Dan, Yaping Chen, Kaixiang; Crozier, Kenneth B.

    2015-01-01

    The microlens is a key enabling technology in optoelectronics, permitting light to be efficiently coupled to and from devices such as image sensors and light-emitting diodes. Their ubiquitous nature motivates the development of new fabrication techniques, since existing methods face challenges as microlenses are scaled to smaller dimensions. Here, the authors demonstrate the formation of microlenses at the tips of vertically oriented silicon nanowires via a rapid atomic layer deposition process. The nature of the process is such that the microlenses are centered on the nanowires, and there is a self-limiting effect on the final sizes of the microlenses arising from the nanowire spacing. Finite difference time domain electromagnetic simulations are performed of microlens focusing properties, including showing their ability to enhance visible-wavelength absorption in silicon nanowires.

  4. Coaxial carbon/metal oxide/aligned carbon nanotube arrays as high-performance anodes for lithium ion batteries.

    PubMed

    Lou, Fengliu; Zhou, Haitao; Tran, Trung Dung; Melandsø Buan, Marthe Emelie; Vullum-Bruer, Fride; Rønning, Magnus; Walmsley, John Charles; Chen, De

    2014-05-01

    Coaxial carbon/metal oxide/aligned carbon nanotube (ACNT) arrays over stainless-steel foil are reported as high-performance binder-free anodes for lithium ion batteries. The coaxial arrays were prepared by growth of ACNTs over stainless-steel foil followed by coating with metal oxide and carbon. The carbon/manganese oxide/ACNT arrays can deliver an initial capacity of 738 mAh g(-1) with 99.9 % capacity retention up to 100 cycles and a capacity of 374 mAh g(-1) at a high current density of 6000 mA g(-1). The external carbon layer was recognized as a key component for high performance, and the mechanism of performance enhancement was investigated by electrochemical impedance spectroscopy, electron microscopy, and X-ray diffraction analysis. The layer increases rate capability by enhancing electrical conductivity and maintaining a low mass-transfer resistance and also improves cyclic stability by avoiding aggregation of metal-oxide particles and stabilizing the solid electrolyte interface. The resultant principle of rational electrode design was applied to an iron oxide-based system, and similar improvements were found. These coaxial nanotube arrays present a promising strategy for the rational design of high-performance binder-free anodes for lithium ion batteries. PMID:24578068

  5. Oxidation of chemically-vapor-deposited silicon nitride and single-crystal silicon

    NASA Technical Reports Server (NTRS)

    Choi, Doo J.; Fischbach, David B.; Scott, William D.

    1989-01-01

    The present 1000 C and 1300 C oxidation tests on 111-oriented single-crystal Si and dense CVD Si3N4 notes the oxidation rates of the latter in wet O2, dry O2, wet inert gas, and steam atmosphere conditions to be several orders of magnitude lower than the rates for the former in identical atmospheric conditions. Although the parabolic rate constant for Si increased linearly as the water vapor pressure increased, the parabolic rate constant for Si3N4 exhibited a nonlinear dependency on water vapor pressure in the presence of O2. NO and NH3 formation at the reaction interface of Si3N4, and the counterpermeation of these reaction products, are noted to dominate reaction kinetics.

  6. Electron-irradiation-induced crystallization at metallic amorphous/silicon oxide interfaces caused by electronic excitation

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Yamashita, Ryo; Lee, Jung-Goo

    2016-04-01

    Irradiation-induced crystallization of an amorphous phase was stimulated at a Pd-Si amorphous/silicon oxide (a(Pd-Si)/SiOx) interface at 298 K by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Under irradiation, a Pd-Si amorphous phase was initially formed at the crystalline face-centered cubic palladium/silicon oxide (Pd/SiOx) interface, followed by the formation of a Pd2Si intermetallic compound through irradiation-induced crystallization. The irradiation-induced crystallization can be considered to be stimulated not by defect introduction through the electron knock-on effects and electron-beam heating, but by the electronic excitation mechanism. The observed irradiation-induced structural change at the a(Pd-Si)/SiOx and Pd/SiOx interfaces indicates multiple structural modifications at the metal/silicon oxide interfaces through electronic excitation induced by the electron-beam processes.

  7. Thermal annealing of thin PECVD silicon-oxide films for airgap-based optical filters

    NASA Astrophysics Data System (ADS)

    Ghaderi, M.; de Graaf, G.; Wolffenbuttel, R. F.

    2016-08-01

    This paper investigates the mechanical and optical properties of thin PECVD silicon-oxide layers for optical applications. The different deposition parameters in PECVD provide a promising tool to manipulate and control the film structure. Membranes for use in optical filters typically are of ~λ/4n thickness and should be slightly tensile for remaining flat, thus avoiding scattering. The effect of the thermal budget of the process on the mechanical characteristics of the deposited films was studied. Films with compressive stress ranging from  ‑100 to 0 MPa were deposited. Multiple thermal annealing cycles were applied to wafers and the in situ residual stress and ex situ optical properties were measured. The residual stress in the films was found to be highly temperature dependent. Annealing during the subsequent process steps results in tensile stress from 100 to 300 MPa in sub-micron thick PECVD silicon-oxide films. However, sub-100 nm thick PECVD silicon-oxide layers exhibit a lower dependence on the thermal annealing cycles, resulting in lower stress variations in films after the annealing. It is also shown that the coefficient of thermal expansion, hence the residual stress in layers, varies with the thickness. Finally, several free-standing membranes were fabricated and the results are compared.

  8. Oxidation effects on the mechanical properties of SiC fiber-reinforced reaction-bonded silicon nitride matrix composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.

    1989-01-01

    The room temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite.

  9. Effect of carbon and boron on the high-temperature oxidation of silicon carbide

    SciTech Connect

    Fergus, J.W.; Worrel, W.L.

    1995-07-01

    Silicon carbide has good oxidation resistance, due to the formation of a protective silica layer. Although amorphous silica is an excellent oxygen barrier, it is very sensitive to impurity elements, which affect its viscosity, oxygen diffusivity,a nd crystallization kinetics. This paper compares the oxidation rates of CVD SiC, sintered {alpha}-SiC, and CVD SiC-coated graphite in 1 atm oxygen at 1,500 C to determine the effects of small additions of boron and carbon. the formation of bubbles in the silica scale formed on sintered {alpha}-Sic in oxygen between 1,230 and 1,550 C is also discussed.

  10. Patterns of discoloration and oxidation by direct and scattered fluxes, especially oxygen on silicon

    NASA Technical Reports Server (NTRS)

    Frederickson, A. R.; Filz, R. C.; Rich, F. J.; Sagalyn, Paul L.

    1991-01-01

    A number of interesting discoloration patterns are clearly evident on M0002-1 which resides on three faces of LDEF: front face, rear face, and earth face. Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by once-scattered ram oxygen atoms along the earth face. Most of the other patterns are seen in the Thermal Control Paint. Also, severe oxidation of CR-39 polycarbonate occurred on the front face of LDEF, as expected. A complete explanation for the patterns has not yet been obtained.

  11. Comparison of beryllium oxide and pyrolytic graphite crucibles for boron doped silicon epitaxy

    SciTech Connect

    Ali, Dyan; Richardson, Christopher J. K.

    2012-11-15

    This article reports on the comparison of beryllium oxide and pyrolytic graphite as crucible liners in a high-temperature effusion cell used for boron doping in silicon grown by molecular beam epitaxy. Secondary ion mass spectroscopy analysis indicates decomposition of the beryllium oxide liner, leading to significant incorporation of beryllium and oxygen in the grown films. The resulting films are of poor crystal quality with rough surfaces and broad x-ray diffraction peaks. Alternatively, the use of pyrolytic graphite crucible liners results in higher quality films.

  12. Simulation of Nanoscale Two-Bit Not-And-type Silicon-Oxide-Nitride-Oxide-Silicon Nonvolatile Memory Devices with a Separated Double-Gate Fin Field Effect Transistor Structure Containing Different Tunneling Oxide Thicknesses

    NASA Astrophysics Data System (ADS)

    Oh, Se Woong; Park, Sang Su; Kim, Dong Hun; Kim, Hyun Woo; Kim, Tae Whan

    2009-06-01

    Not-and (NAND)-type silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory (NVM) devices with a separated double-gate (SDG) Fin field effect transistor structure were proposed to reduce the unit cell size of such memory devices and increase their memory density in comparison with that of conventional NVM devices. The proposed memory device consisted of a pair of control gates separated along the length of the Fin channel direction. Each SDG had a different thickness of the tunneling oxide to operate the proposed memory device as a two-bit/cell device. A technology computer-aided design simulation was performed to investigate the program/erase and two-bit characteristics. The simulation results show that the proposed devices can be used to increase the scaling down capability and charge storage density of NAND-type SONOS NVM devices.

  13. Mechanisms for generation of oxide trapped charges in ultrathin silicon dioxide films during electrical stress

    NASA Astrophysics Data System (ADS)

    Samanta, Piyas

    2008-02-01

    Charge trapping characteristics of ultrathin silicon dioxide (SiO2) films during constant voltage stress (CVS) in direct tunneling regime have been presented. Both bulk and border traps have been segregated from oxide trapped charges. Our measurement results indicate that electron trapping in as fabricated traps in ultrathin samples was suppressed and/or absent during prolonged stress. In addition, the generation kinetics of "border" and "bulk" trapped positive oxide charges have been studied. From the bulk oxide charge relaxation experiments, nature of as-fabricated intrinsic hole traps in SiO2 has been determined. Our results show that both bulk and border trapped positive oxide charges are mostly contributed by proton related species possibly the [Si2dbnd OH]+ centers. Based on experimental observations, a physical model of stress-induced bulk positive charge generation/trapping has been proposed.

  14. The effectiveness of electron holography, microscopy, and energy-loss spectroscopy in characterizing thin silicon oxide-nitride-oxide structures

    NASA Astrophysics Data System (ADS)

    Waytena, G. L.; Hren, J.; Rez, P.

    1993-02-01

    High-resolution transmission electron microscopy, electron holography, and high-spatial- resolution (19 Å) computer-controlled parallel electron-energy-loss spectrometry (PEELS) were used to probe the structure of and chemical profile across two thin silicon oxide-nitride-oxide layered structures of nominal widths of 10 Å-50 Å-10 Å and 30 Å-50 Å-30 Å. It was found that the individual layers of the stacked structures could be clearly imaged using electron holography, but not with electron microscopy due to the behavior of the microscope transfer function and the shape of the potential profile of the structure. Holography revealed that the layers of the 10 Å-50 Å-10 Å system were in fact 14 Å-28 Å-18 ż5 Å, and the oxide layer in contact with the substrate (first oxide layer) was discontinuous. PEELS showed that the second oxide layer contained nitrogen, and the nitride layer had a silicon-to-nitrogen concentration ratio of 1.0±0.1. The 30 Å-50 Å-30 Å system was in fact 30 Å-20 Å-40 Å-15 ż5 Å. The second oxide layer was SiO1.6±0.2, and nitrogen was found near the film surface which made the structure appear to be four layers. These results show the power of holography in characterizing thin, light-element, amorphous layers and the importance of computer-controlled parallel energy-loss line scans for obtaining analytical information at the highest spatial resolution with minimum dose.

  15. Extended Frenkel pairs and band alignment at metal-oxide interfaces

    NASA Astrophysics Data System (ADS)

    Sharia, O.; Tse, K.; Robertson, J.; Demkov, Alexander A.

    2009-03-01

    We show how oxygen vacancies in metal oxides next to high-work-function metals are stabilized by an oxygen exchange reaction with the metal, and by a charge transfer from the vacancy energy level to the metal Fermi level. The results help explain some of the Fermi-level pinning problems in high- k dielectric gate stacks in complimentary metal oxide semiconductor technology and also explain the driving force behind the strong metal-support interaction in oxide-supported catalysts.

  16. Resistive switching characteristics and mechanisms in silicon oxide memory devices

    NASA Astrophysics Data System (ADS)

    Chang, Yao-Feng; Fowler, Burt; Chen, Ying-Chen; Zhou, Fei; Wu, Xiaohan; Chen, Yen-Ting; Wang, Yanzhen; Xue, Fei; Lee, Jack C.

    2016-05-01

    Intrinsic unipolar SiOx-based resistance random access memories (ReRAM) characterization, switching mechanisms, and applications have been investigated. Device structures, material compositions, and electrical characteristics are identified that enable ReRAM cells with high ON/OFF ratio, low static power consumption, low switching power, and high readout-margin using complementary metal-oxide semiconductor transistor (CMOS)-compatible SiOx-based materials. These ideas are combined with the use of horizontal and vertical device structure designs, composition optimization, electrical control, and external factors to help understand resistive switching (RS) mechanisms. Measured temperature effects, pulse response, and carrier transport behaviors lead to compact models of RS mechanisms and energy band diagrams in order to aid the development of computer-aided design for ultralarge-v scale integration. This chapter presents a comprehensive investigation of SiOx-based RS characteristics and mechanisms for the post-CMOS device era.

  17. Structural silicon nitride materials containing rare earth oxides

    DOEpatents

    Andersson, Clarence A.

    1980-01-01

    A ceramic composition suitable for use as a high-temperature structural material, particularly for use in apparatus exposed to oxidizing atmospheres at temperatures of 400 to 1600.degree. C., is found within the triangular area ABCA of the Si.sub.3 N.sub.4 --SiO.sub.2 --M.sub.2 O.sub.3 ternary diagram depicted in FIG. 1. M is selected from the group of Yb, Dy, Er, Sc, and alloys having Yb, Y, Er, or Dy as one component and Sc, Al, Cr, Ti, (Mg +Zr) or (Ni+Zr) as a second component, said alloy having an effective ionic radius less than 0.89 A.

  18. In situ investigation of mesoporous silicon oxidation kinetics using infrared emittance spectroscopy.

    PubMed

    Bardet, Benjamin; De Sousa Meneses, Domingos; Defforge, Thomas; Billoué, Jérôme; Gautier, Gaël

    2016-07-21

    In this paper, we study the thermal oxidation kinetics of mesoporous silicon layers, synthesized by electrochemical anodization, from 260 °C up to 1100 °C. A specific apparatus is employed to heat the mesoporous samples in air and to record at the same time their infrared emittance. Based on Bruggeman effective medium approximation, an optical model is set up to realistically approximate the dielectric function of the porous material with an emphasis on the surface chemistry and oxide content. A transition temperature of 600 °C is evidenced from data processing which gives evidence of two oxidation mechanisms with distinct kinetics. Between 260-600 °C, the oxidation is surface-limited with kinetics dependent on the hydrogen desorption rate. However, above 600 °C, the oxide growth is limited by oxygen diffusion through the existing oxide layer. A parabolic law is employed to fit the oxidation rate and to extract the high-temperature activation energy (EA = 1.5 eV). A precise control of the oxide growth can thus be achieved. PMID:27333267

  19. Alternating current surface photovoltage in thermally oxidized chromium-contaminated n-type silicon wafers

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Nagase, Shintarou; Ikeda, Masanori

    2011-09-01

    We investigated a variation of frequency-dependent alternating current (AC) surface photovoltages (SPVs) in thermally oxidized, chromium-contaminated, n-type silicon (Si) wafers. As previously reported, immediately after rinsing in Cr-contaminated solution, a Cr(OH)3-Si contact causes a Schottky-barrier-type AC SPV on n-type Si. Upon oxidation at 373 K for 10 min, the Schottky barrier collapses and, with further oxidation, a metal-induced negative oxide charge, due to atomic bridging of (CrOSi)- and/or CrO2- networks, definitely grows over time in SiO2. For samples oxidized at temperatures between 823 and 1023 K for 30 min, the observed AC SPV gives evidence that the metal-induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 1023 K and /or for an oxidation time longer than 60 min, the level height of the AC SPV is reduced, implying that the strongly inverted state changes into a less depleted state, whilst, finally, the AC SPV disappears. In this case, the collapse of the (CrOSi)- and/or CrO2- networks is anticipated, with a possible change into Cr2O3. The existence of the (CrOSi)- and/or CrO2- networks has also been confirmed in p-type Si wafers.

  20. Optical properties of hybrid plasmonic structure on silicon using transparent conducting-silver nanoparticles–silicon dioxide layers: the role of conducting oxide layer thickness in antireflection

    NASA Astrophysics Data System (ADS)

    Sardana, Sanjay K.; Komarala, Vamsi K.

    2016-07-01

    The hybrid plasmonic antireflection layer (HPAL) consisting of silver nanoparticles (Ag NPs) sandwiched between indium tin oxide (ITO) and silicon dioxide (SiO2) thin layers is investigated for enhancing light absorption within a silicon wafer. The optimization of HPAL for minimizing reflection losses from silicon is carried out by tuning the ITO layer thickness, which also affects Ag NP morphology during the growth process. Light reflectivity of ∼10% is observed from the silicon integrated with HPAL in the 300–1100 nm spectral region, due to enhanced light forward scattering as compared to a reflectivity of 26% from the bare silicon wafer. We have also investigated the ITO–SiO2 double layer (without Ag NPs) effect in reflection reduction from the silicon, but the HPAL performed better in Ag NPs’ surface plasmon resonance (<600 nm) and off-resonance (900–1100 nm) wavelength regions as compared to the double layer. With the Ag NPs, the ITO layer thickness can be reduced from 70 nm to 30 nm for the maximum reflectance reduction from the silicon surface. The thin SiO2 capping layer on Ag NPs provides a better refractive index match for further reflectance reduction, and also acts as a protective layer from degradation of Ag NPs with time.

  1. Enhancing the far-ultraviolet sensitivity of silicon complementary metal oxide semiconductor imaging arrays

    NASA Astrophysics Data System (ADS)

    Retherford, Kurt D.; Bai, Yibin; Ryu, Kevin K.; Gregory, James A.; Welander, Paul B.; Davis, Michael W.; Greathouse, Thomas K.; Winters, Gregory S.; Suntharalingam, Vyshnavi; Beletic, James W.

    2015-10-01

    We report our progress toward optimizing backside-illuminated silicon P-type intrinsic N-type complementary metal oxide semiconductor devices developed by Teledyne Imaging Sensors (TIS) for far-ultraviolet (UV) planetary science applications. This project was motivated by initial measurements at Southwest Research Institute of the far-UV responsivity of backside-illuminated silicon PIN photodiode test structures, which revealed a promising QE in the 100 to 200 nm range. Our effort to advance the capabilities of thinned silicon wafers capitalizes on recent innovations in molecular beam epitaxy (MBE) doping processes. Key achievements to date include the following: (1) representative silicon test wafers were fabricated by TIS, and set up for MBE processing at MIT Lincoln Laboratory; (2) preliminary far-UV detector QE simulation runs were completed to aid MBE layer design; (3) detector fabrication was completed through the pre-MBE step; and (4) initial testing of the MBE doping process was performed on monitoring wafers, with detailed quality assessments.

  2. Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping.

    PubMed

    Rossi, Alessandro; Tanttu, Tuomo; Hudson, Fay E; Sun, Yuxin; Möttönen, Mikko; Dzurak, Andrew S

    2015-01-01

    As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization. PMID:26067215

  3. Progress in complementary metal-oxide-semiconductor silicon photonics and optoelectronic integrated circuits

    NASA Astrophysics Data System (ADS)

    Hongda, Chen; Zan, Zhang; Beiju, Huang; Luhong, Mao; Zanyun, Zhang

    2015-12-01

    Silicon photonics is an emerging competitive solution for next-generation scalable data communications in different application areas as high-speed data communication is constrained by electrical interconnects. Optical interconnects based on silicon photonics can be used in intra/inter-chip interconnects, board-to-board interconnects, short-reach communications in datacenters, supercomputers and long-haul optical transmissions. In this paper, we present an overview of recent progress in silicon optoelectronic devices and optoelectronic integrated circuits (OEICs) based on a complementary metal-oxide-semiconductor-compatible process, and focus on our research contributions. The silicon optoelectronic devices and OEICs show good characteristics, which are expected to benefit several application domains, including communication, sensing, computing and nonlinear systems. Project supported by the National Basic Research Program of China (No. 2011CBA00608), the National Natural Science Foundation of China (Nos. 61178051, 61321063, 61335010, 61178048, 61275169), and the National High Technology Research and Development Program of China (Nos. 2013AA013602, 2013AA031903, 2013AA032204).

  4. Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

    PubMed Central

    Rossi, Alessandro; Tanttu, Tuomo; Hudson, Fay E.; Sun, Yuxin; Möttönen, Mikko; Dzurak, Andrew S.

    2015-01-01

    As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization. PMID:26067215

  5. Optimization of oxidation processes to improve crystalline silicon solar cell emitters

    SciTech Connect

    Shen, L.; Liang, Z. C. Liu, C. F.; Long, T. J.; Wang, D. L.

    2014-02-15

    Control of the oxidation process is one key issue in producing high-quality emitters for crystalline silicon solar cells. In this paper, the oxidation parameters of pre-oxidation time, oxygen concentration during pre-oxidation and pre-deposition and drive-in time were optimized by using orthogonal experiments. By analyzing experimental measurements of short-circuit current, open circuit voltage, series resistance and solar cell efficiency in solar cells with different sheet resistances which were produced by using different diffusion processes, we inferred that an emitter with a sheet resistance of approximately 70 Ω/□ performed best under the existing standard solar cell process. Further investigations were conducted on emitters with sheet resistances of approximately 70 Ω/□ that were obtained from different preparation processes. The results indicate that emitters with surface phosphorus concentrations between 4.96 × 10{sup 20} cm{sup −3} and 7.78 × 10{sup 20} cm{sup −3} and with junction depths between 0.46 μm and 0.55 μm possessed the best quality. With no extra processing, the final preparation of the crystalline silicon solar cell efficiency can reach 18.41%, which is an increase of 0.4%{sub abs} compared to conventional emitters with 50 Ω/□ sheet resistance.

  6. The role of oxide interlayers in back reflector configurations for amorphous silicon solar cells

    NASA Astrophysics Data System (ADS)

    Demontis, V.; Sanna, C.; Melskens, J.; Santbergen, R.; Smets, A. H. M.; Damiano, A.; Zeman, M.

    2013-02-01

    Thin oxide interlayers are commonly added to the back reflector of thin-film silicon solar cells to increase their current. To gain more insight in the enhancement mechanism, we tested different back reflector designs consisting of aluminium-doped zinc oxide (ZnO:Al) and/or hydrogenated silicon oxide (SiOx:H) interlayers with different metals (silver, aluminium, and chromium) in standard p-i-n a-Si:H solar cells. We use a unique inverse modeling approach to show that in most back reflectors the internal metal reflectance is lower than expected theoretically. However, the metal reflectance is increased by the addition of an oxide interlayer. Our experiments demonstrate that SiOx:H forms an interesting alternative interlayer because unlike the more commonly used ZnO:Al it can be deposited by plasma-enhanced chemical vapour deposition and it does not reduce the fill factor. The largest efficiency enhancement is obtained with a double interlayer of SiOx:H and ZnO:Al.

  7. Reply to ``Comment on `Dynamics of thermal growth of silicon oxide films on Si' ''

    NASA Astrophysics Data System (ADS)

    de Almeida, R. M. C.; Gonçalves, S.; Baumvol, I. J. R.; Stedile, F. C.

    2006-09-01

    In a Comment on “Dynamics of thermal growth of silicon oxide films on Si” [Phys. Rev. B 61, 12992 (2000)], Roura and Farjas argue that the values of the kinetics parameters obtained from the model proposed in that paper are not reliable and that the solutions given for different partial pressures are erroneous. Moreover, that the solution from such model is unable to predict the oxidation rate experimentally observed in the thin oxide regime neither the width of the interface. Resorting to experimental results, and old and new results obtained from our model, we show in this Reply that none of the criticisms are solid and that the results of the original paper represent indeed an improvement over the Deal-Grove model. Finally, motivated by one of the issues raised by Roura and Farjas, we present here new fittings of experimental data using our model together with experimental estimates for the interface width between the oxide layer and the silicon substrate. This turned a two parameter fitting problem into a much simpler one parameter procedure.

  8. Hydrothermal growth of vertically-aligned ordered mesoporous nickel oxide nanosheets on three-dimensional nickel framework for electrocatalytic oxidation of urea in alkaline medium

    NASA Astrophysics Data System (ADS)

    Wu, Mao-Sung; Lin, Guan-Wei; Yang, Run-Song

    2014-12-01

    Vertically-aligned α-Ni(OH)2 nanosheets are homogeneously covered on three-dimensional (3D) macroporous Ni foam and stainless steel (SS) sheet by a simple hydrothermal synthesis. After annealing at 300 °C, most of the α-Ni(OH)2 is transformed to cubic NiO. The NiO nanosheets exhibit ordered mesoporous structure. Electrolysis of urea is analyzed by cyclic voltammetry and potential step chronoamperometry in 1 M KOH electrolyte with 0.33 M urea. The electrocatalytic performance of NiO electrodes depends strongly on their configuration and substrate. Vertically-aligned NiO nanosheets favor the electrolysis of urea because they can provide more catalytic sites than the NiO powder with aggregated nanosheets. In addition, the large open space between vertically-aligned NiO nanosheets expedites the transport of electrolyte, urea, and gases. 3D macroporous Ni foam substrate is very helpful to the electrolysis of urea which allows for fast electron conduction, leading to a decrease of overpotential and the increase of oxidation current density. Consequently, the Ni foam-supported mesoporous NiO nanosheets can offer a much better electrocatalytic performance than SS-supported mesoporous NiO nanosheets and powder during electrolysis of urea.

  9. Elementary reaction schemes for physical and chemical vapor deposition of transition metal oxides on silicon for high-k gate dielectric applications

    NASA Astrophysics Data System (ADS)

    Niu, D.; Ashcraft, R. W.; Kelly, M. J.; Chambers, J. J.; Klein, T. M.; Parsons, G. N.

    2002-05-01

    This article describes the kinetics of reactions that result in substrate consumption during formation of ultrathin transition metal oxides on silicon. Yttrium silicate films (˜40 Å) with an equivalent silicon dioxide thickness of ˜11 Å are demonstrated by physical vapor deposition (PVD) routes. Interface reactions that occur during deposition and during postdeposition treatment are observed and compared for PVD and chemical vapor deposition (CVD) yttrium oxides and CVD aluminum-oxide systems. Silicon diffusion, metal-silicon bond formation, and reactions involving hydroxides are proposed as critical processes in interface layer formation. For PVD of yttrium silicate, oxidation is thermally activated with an effective barrier of 0.3 eV, consistent with the oxidation of silicide being the rate-limited step. For CVD aluminum oxide, interface oxidation is consistent with a process limited by silicon diffusion into the deposited oxide layer.

  10. Processing of uranium oxide and silicon carbide based fuel using polymer infiltration and pyrolysis

    NASA Astrophysics Data System (ADS)

    Singh, Abhishek K.; Zunjarrao, Suraj C.; Singh, Raman P.

    2008-09-01

    Ceramic composite pellets consisting of uranium oxide, UO 2, contained within a silicon carbide matrix, were fabricated using a novel processing technique based on polymer infiltration and pyrolysis (PIP). In this process, particles of depleted uranium oxide, in the form of U 3O 8, were dispersed in liquid allylhydridopolycarbosilane (AHPCS), and subjected to pyrolysis up to 900 °C under a continuous flow of ultra high purity argon. The pyrolysis of AHPCS, at these temperatures, produced near-stoichiometric amorphous silicon carbide ( a-SiC). Multiple polymer infiltration and pyrolysis (PIP) cycles were performed to minimize open porosity and densify the silicon carbide matrix. Analytical characterization was conducted to investigate chemical interaction between U 3O 8 and SiC. It was observed that U 3O 8 reacted with AHPCS during the very first pyrolysis cycle, and was converted to UO 2. As a result, final composition of the material consisted of UO 2 particles contained in an a-SiC matrix. The physical and mechanical properties were also quantified. It is shown that this processing scheme promotes uniform distribution of uranium fuel source along with a high ceramic yield of the parent matrix.

  11. Structural and optical properties of silicon metal-oxide-semiconductor light-emitting devices

    NASA Astrophysics Data System (ADS)

    Xu, Kaikai; Zhang, Zhengyuan; Zhang, Zhengping

    2016-01-01

    A silicon p-channel metal oxide semiconductor field-effect transistor (Si-PMOSFET) that is fully compatible with the standard complementary metal oxide semiconductor process is investigated based on the phenomenon of optical radiation observed in the reverse-biased p-n junction in the Si-PMOSFET device. The device can be used either as a two-terminal silicon diode light-emitting device (Si-diode LED) or as a three-terminal silicon gate-controlled diode light-emitting device (Si gate-controlled diode LED). It is seen that the three-terminal operating mode could provide much higher power transfer efficiency than the two-terminal operating mode. A new solution based on the concept of a theoretical quantum efficiency model combined with calculated results is proposed for interpreting the evidence of light intensity reduction at high operating voltages. The Si-LED that can be easily integrated into CMOS fabrication process is an important step toward optical interconnects.

  12. Role of interfacial oxide in high-efficiency graphene-silicon Schottky barrier solar cells.

    PubMed

    Song, Yi; Li, Xinming; Mackin, Charles; Zhang, Xu; Fang, Wenjing; Palacios, Tomás; Zhu, Hongwei; Kong, Jing

    2015-03-11

    The advent of chemical vapor deposition (CVD) grown graphene has allowed researchers to investigate large area graphene/n-silicon Schottky barrier solar cells. Using chemically doped graphene, efficiencies of nearly 10% can be achieved for devices without antireflective coatings. However, many devices reported in past literature often exhibit a distinctive s-shaped kink in the measured I/V curves under illumination resulting in poor fill factor. This behavior is especially prevalent for devices with pristine (not chemically doped) graphene but can be seen in some cases for doped graphene as well. In this work, we show that the native oxide on the silicon presents a transport barrier for photogenerated holes and causes recombination current, which is responsible for causing the kink. We experimentally verify our hypothesis and propose a simple semiconductor physics model that qualitatively captures the effect. Furthermore, we offer an additional optimization to graphene/n-silicon devices: by choosing the optimal oxide thickness, we can increase the efficiency of our devices to 12.4% after chemical doping and to a new record of 15.6% after applying an antireflective coating. PMID:25685934

  13. The correlation between electron density and anchoring strength in the inorganic vertical alignment layer

    SciTech Connect

    Hwang, Byoung Har; Yoo, Young Bum; Oh, Jin Young; Chae, Soo Sang; Baik, Hong Koo; Lee, Se Jong; Song, Kie Moon

    2009-08-24

    The relationship between the liquid crystal (LC) alignment and the density of the silicon oxide alignment layer was studied by theoretical and experimental approaches. The thin films were deposited by various methods and conditions, and then their densities were analyzed by x-ray reflectivity measurement. The alignment of LC was highly dependent on their densities, which we found to be closely related to the number of interacting dipoles. Ultimately, a-SiO{sub x} thin film with lower density gives rise to the uniform vertical alignment of liquid crystal.

  14. Oxidative stress in bacteria (Pseudomonas putida) exposed to nanostructures of silicon carbide.

    PubMed

    Borkowski, Andrzej; Szala, Mateusz; Kowalczyk, Paweł; Cłapa, Tomasz; Narożna, Dorota; Selwet, Marek

    2015-09-01

    Silicon carbide (SiC) nanostructures produced by combustion synthesis can cause oxidative stress in the bacterium Pseudomonas putida. The results of this study showed that SiC nanostructures damaged the cell membrane, which can lead to oxidative stress in living cells and to the loss of cell viability. As a reference, micrometric SiC was also used, which did not exhibit toxicity toward cells. Oxidative stress was studied by analyzing the activity of peroxidases, and the expression of the glucose-6-phosphate dehydrogenase gene (zwf1) using real-time PCR and northern blot techniques. Damage to nucleic acid was studied by isolating and hydrolyzing plasmids with the formamidopyrimidine [fapy]-DNA glycosylase (also known as 8-oxoguanine DNA glycosylase) (Fpg), which is able to detect damaged DNA. The level of viable microbial cells was investigated by propidium iodide and acridine orange staining. PMID:25965002

  15. Electrorheological properties of polyaniline-vanadium oxide nanostructures suspended in silicone oil

    NASA Astrophysics Data System (ADS)

    Goswami, Sumita; Brehm, Tiago; Filonovich, Sergej; Cidade, Maria Teresa

    2014-10-01

    In the present work, organic/inorganic hybrid nanostructures comprised of polyaniline and vanadium oxide were synthesized via a simple hydrothermal technique. The polyaniline/vanadium oxide hybrid morphology was tailored from rods to spheres by controlling the relative concentration of the reactants. The synthesized composites were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) for structural and morphological analyses. Electrorheological (ER) properties of the as-prepared nanocomposites suspended in silicone oil were investigated by a rotational viscometer under both steady and dynamic shear. The ER activity of the composite material suspensions showed higher ER effects for the product with the rod-like structures than for the product with the sphere-like structures. The typical ER behaviour showed by the polyaniline-vanadium oxide nanocomposites demonstrated their potential application as an ER smart material.

  16. Near-theoretical fracture strengths in native and oxidized silicon nanowires

    NASA Astrophysics Data System (ADS)

    DelRio, Frank W.; White, Ryan M.; Krylyuk, Sergiy; Davydov, Albert V.; Friedman, Lawrence H.; Cook, Robert F.

    2016-08-01

    In this letter, fracture strengths σ f of native and oxidized silicon nanowires (SiNWs) were determined via atomic force microscopy bending experiments and nonlinear finite element analysis. In the native SiNWs, σ f in the Si was comparable to the theoretical strength of Si<111>, ≈22 GPa. In the oxidized SiNWs, σ f in the SiO2 was comparable to the theoretical strength of SiO2, ≈6 to 12 GPa. The results indicate a change in the failure mechanism between native SiNWs, in which fracture originated via inter-atomic bond breaking or atomic-scale defects in the Si, and oxidized SiNWs, in which fracture initiated from surface roughness or nano-scale defects in the SiO2.

  17. Self-limiting and complete oxidation of silicon nanostructures produced by laser ablation in water

    NASA Astrophysics Data System (ADS)

    Vaccaro, L.; Popescu, R.; Messina, F.; Camarda, P.; Schneider, R.; Gerthsen, D.; Gelardi, F. M.; Cannas, M.

    2016-07-01

    Oxidized Silicon nanomaterials produced by 1064 nm pulsed laser ablation in deionized water are investigated. High-resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy allows to characterize the structural and chemical properties at a sub-nanometric scale. This analysis clarifies that laser ablation induces both self-limiting and complete oxidation processes which produce polycrystalline Si surrounded by a layer of SiO2 and amorphous fully oxidized SiO2, respectively. These nanostructures exhibit a composite luminescence spectrum which is investigated by time-resolved spectroscopy with a tunable laser excitation. The origin of the observed luminescence bands agrees with the two structural typologies: Si nanocrystals emit a μs-decaying red band; defects of SiO2 give rise to a ns-decaying UV band and two overlapping blue bands with lifetime in the ns and ms timescale.

  18. Effect of gate oxide thickness on the radiation hardness of silicon-gate CMOS

    SciTech Connect

    Nordstrom, T.V.; Gibbon, C.F.

    1981-01-01

    Significant improvements have been made in the radiation hardness of silicon-gate CMOS by reducing the gate oxide thickness. The device studied is an 8-bit arithmetic logic unit designed with Sandia's Expanded Linear Array (ELA) standard cells. Devices with gate oxide thicknesses of 400, 570 (standard), and 700 A were fabricated. Irradiations were done at a dose rate of 2 x 10/sup 6/ rads (Si) per hour. N- and P-channel maximum threshold shifts were reduced by 0.3 and 1.2 volts, respectively, for the thinnest oxide. Approximately, a linear relationship is found for threshold shift versus thickness. The functional radiation hardness of the full integrated circuit was also measured.

  19. Fabrication of piezodriven, free-standing, all-oxide heteroepitaxial cantilevers on silicon

    NASA Astrophysics Data System (ADS)

    Banerjee, N.; Houwman, E. P.; Koster, G.; Rijnders, G.

    2014-09-01

    We report on the fabrication and mechanical properties of all-oxide, free-standing, heteroepitaxial, piezoelectric, microelectromechanical systems (MEMS) on silicon, using PbZr0.52Ti0.48O3 as the key functional material. The fabrication was enabled by the development of an epitaxial lift-off strategy for the patterning of multilayer oxide heterostructures grown on Si(001), employing a high temperature stable, sacrificial oxide template mask to obtain freestanding cantilever MEMS devices after substrate etching. All cantilevers, with lengths in the range 25-325 μm, width 50 μm, and total thickness of 300 nm, can be actuated by an external AC-bias. For lengths 50-125 μm, the second order bending mode formed the dominant resonance, whereas for the other lengths different or multiple modes were present.

  20. Near-theoretical fracture strengths in native and oxidized silicon nanowires.

    PubMed

    DelRio, Frank W; White, Ryan M; Krylyuk, Sergiy; Davydov, Albert V; Friedman, Lawrence H; Cook, Robert F

    2016-08-01

    In this letter, fracture strengths σ f of native and oxidized silicon nanowires (SiNWs) were determined via atomic force microscopy bending experiments and nonlinear finite element analysis. In the native SiNWs, σ f in the Si was comparable to the theoretical strength of Si〈111〉, ≈22 GPa. In the oxidized SiNWs, σ f in the SiO2 was comparable to the theoretical strength of SiO2, ≈6 to 12 GPa. The results indicate a change in the failure mechanism between native SiNWs, in which fracture originated via inter-atomic bond breaking or atomic-scale defects in the Si, and oxidized SiNWs, in which fracture initiated from surface roughness or nano-scale defects in the SiO2. PMID:27325151

  1. Fabrication and evaluation of series-triple quantum dots by thermal oxidation of silicon nanowire

    SciTech Connect

    Uchida, Takafumi Jo, Mingyu; Tsurumaki-Fukuchi, Atsushi; Arita, Masashi; Takahashi, Yasuo; Fujiwara, Akira

    2015-11-15

    Series-connected triple quantum dots were fabricated by a simple two-step oxidation technique using the pattern-dependent oxidation of a silicon nanowire and an additional oxidation of the nanowire through the gap of the fine gates attached to the nanowire. The characteristics of multi-dot single-electron devices are obtained. The formation of each quantum dot beneath an attached gate is confirmed by analyzing the electrical characteristics and by evaluating the gate capacitances between all pairings of gates and quantum dots. Because the gate electrode is automatically attached to each dot, the device structure benefits from scalability. This technique promises integrability of multiple quantum dots with individual control gates.

  2. Enhanced electron-hole droplet emission from surface-oxidized silicon photonic crystal nanocavities.

    PubMed

    Sumikura, Hisashi; Kuramochi, Eiichi; Taniyama, Hideaki; Notomi, Masaya

    2016-01-25

    We have observed electron-hole droplet (EHD) emission enhanced by silicon photonic crystal (Si PhC) nanocavities with a surface oxide. The EHD is employed as a massive emitter that remains inside the nanocavity to achieve efficient cavity-emitter coupling. Time-resolved emission measurements demonstrate that the surface oxide greatly reduces the nonradiative annihilation of the EHDs and maintains them in the PhC nanocavities. It is found that the surface-oxidized Si PhC nanocavity enhances EHD emission in addition to the Purcell enhancement of the resonant cavity, which will contribute to works on Si light emission and the cavity quantum electrodynamics of electron-hole condensates. PMID:26832491

  3. Fabrication and evaluation of series-triple quantum dots by thermal oxidation of silicon nanowire

    NASA Astrophysics Data System (ADS)

    Uchida, Takafumi; Jo, Mingyu; Tsurumaki-Fukuchi, Atsushi; Arita, Masashi; Fujiwara, Akira; Takahashi, Yasuo

    2015-11-01

    Series-connected triple quantum dots were fabricated by a simple two-step oxidation technique using the pattern-dependent oxidation of a silicon nanowire and an additional oxidation of the nanowire through the gap of the fine gates attached to the nanowire. The characteristics of multi-dot single-electron devices are obtained. The formation of each quantum dot beneath an attached gate is confirmed by analyzing the electrical characteristics and by evaluating the gate capacitances between all pairings of gates and quantum dots. Because the gate electrode is automatically attached to each dot, the device structure benefits from scalability. This technique promises integrability of multiple quantum dots with individual control gates.

  4. Robust postfabrication trimming of ultracompact resonators on silicon on insulator with relaxed requirements on resolution and alignment.

    PubMed

    Alipour, Payam; Atabaki, Amir H; Askari, Murtaza; Adibi, Ali; Eftekhar, Ali A

    2015-10-01

    One of the main drawbacks of the high-index-contrast silicon-on-insulator platform in integrated photonics is the high sensitivity of the resonance wavelength of resonators to dimensional variations caused by fabrication imperfection. In this work, we experimentally demonstrate an accurate postfabrication trimming technique for compensating the fabrication-induced variations in the resonance properties of nanophotonic devices. Using this technique, we reduce the variation of the resonance wavelength of 4 μm diameter microdonut resonators by more than 1 order of magnitude to about 25 pm, which is adequate for most interconnect, optical signal processing, and sensing applications. In addition, our proposed technique has improved misalignment toleration and throughput compared to previous reports. PMID:26421560

  5. Electrochemically reduced graphene oxide on silicon nanowire arrays for enhanced photoelectrochemical hydrogen evolution.

    PubMed

    Meng, Huan; Fan, Ke; Low, Jingxiang; Yu, Jiaguo

    2016-09-21

    Photoelectrochemical (PEC) water splitting into hydrogen and oxygen by sunlight is a promising approach to solve energy and environmental problems. In this work, silicon nanowire arrays (SiNWs) photocathodes decorated with reduced graphene oxide (rGO) for PEC water splitting were successfully prepared by a flexible and scalable electrochemical reduction method. The SiNWs photocathode with the optimized rGO decoration (SiNWs/rGO20) shows an enhanced activity with a much higher photocurrent density and significantly positive shift of onset potential compared to the bare SiNWs arrays for the hydrogen evolution reaction (HER). The enhanced PEC activity is ascribed to the high electrical conductivity of rGO and improved separation of the photogenerated charge carriers. This work not only demonstrates a facile, rapid and tunable electrochemical reduction method to produce rGO, but also exhibits an efficient protocol to enhance the PEC water splitting of silicon-based materials. PMID:27461187

  6. A 200 V silicon-on-sapphire LDMOS structure with a step oxide extended field plate

    NASA Astrophysics Data System (ADS)

    Roig, J.; Flores, D.; Rebollo, J.; Hidalgo, S.; Millan, J.

    2004-02-01

    Fabrication of power integrated circuits on silicon-on-sapphire (SOS) substrates has rarely been considered before. Hence, there is a lack of research in lateral power devices integrated on SOS. Self-heating effects in existing silicon-on-insulator (SOI) lateral power devices degrade the device performance and their reliability. Use of SOS substrates could alleviate these problems though they would require a different approach in lateral power device engineering. This paper purposes a new power SOS LDMOS structure with reduced transient self-heating effects and enhanced current capability compared to the conventional SOI counterpart. The proposed lateral power structure integrated on SOS substrates is analyzed by electro-thermal simulations. The field plate is enlarged (extended field plate (EFP)) along the drift region, reaching the drain region. The EFP includes an oxide step which improves the "on-state resistance-breakdown voltage" trade-off ( RONxS- Vbr).

  7. Optically tunable microcavity in a planar photonic crystal silicon waveguide buried in oxide.

    PubMed

    Märki, Iwan; Salt, Martin; Herzig, Hans Peter; Stanley, Ross; El Melhaoui, L; Lyan, P; Fedeli, J M

    2006-02-15

    We present all-optical tuning and switching of a microcavity inside a two-dimensional photonic crystal waveguide. The photonic crystal structure is fabricated in silicon-on-insulator using complementary metal-oxide semiconductor processing techniques based on deep ultraviolet lithography and is completely buried in a silicon dioxide cladding that provides protection from the environment. By focusing a laser onto the microcavity region, both a thermal and a plasma dispersion effect are generated, allowing tuning and fast modulation of the in-plane transmission. By means of the temporal characteristics of the in-plane transmission, we experimentally identify a slower thermal and a fast plasma dispersion effect with modulation bandwidths of the order of several 100 kHz and up to the gigahertz level, respectively. PMID:16496904

  8. Corrosion behavior of silicon nitride, magnesium oxide, and several metals in molten calcium chloride with chlorine

    SciTech Connect

    McLaughlin, D. . Research and Development Center); Sesions, C.E.; Marra, J.E. )

    1992-08-01

    In this paper corrosion studies are described in a molten calcium chloride environment sparged with chlorine gas at 850{degrees}C, both in the melt and in the gas phase above the salt, in support of efforts at Westinghouse Savannah River Company to develop more resistant materials of construction for molten salt processing of plutonium. Corrosion rates and electron microscope analyses are reported for Inconel alloys 601 and 617, tantalum, tungsten, magnesium oxide, and silicon nitride. Silicon nitride exhibited the greatest resistance, showing {lt}0.1 mg/cm{sup 2} {center dot} h loss in both melt and vapor None of the metallic coupons withstood the chlorine vapor environment, although Inconel indicated resistance immersed in the melt if protected from chlorine gas.

  9. Method of making highly porous, stable aluminum oxides doped with silicon

    DOEpatents

    Khosravi-Mardkhe, Maryam; Woodfield, Brian F.; Bartholomew, Calvin H.; Huang, Baiyu

    2016-03-22

    The present invention relates to a method for making high surface area and large pore volume thermally stable silica-doped alumina (aluminum oxide) catalyst support and ceramic materials. The ability of the silica-alumina to withstand high temperatures in presence or absence of water and prevent sintering allows it to maintain good activity over a long period of time in catalytic reactions. The method of preparing such materials includes adding organic silicon reagents to an organic aluminum salt such as an alkoxide in a controlled quantity as a doping agent in a solid state, solvent deficient reaction followed by calcination. Alternatively, the organic silicon compound may be added after calcination of the alumina, followed by another calcination step. This method is inexpensive and simple. The alumina catalyst support material prepared by the subject method maintains high pore volumes, pore diameters and surface areas at very high temperatures and in the presence of steam.

  10. High-temperature mixed oxidation of nitride-bonded silicon carbide in oxidizing gas mixtures containing 2% Cl{sub 2}

    SciTech Connect

    Park, C.; McNallan, M.J.

    1995-04-01

    Nitride-bonded silicon carbide ceramics have lower processing costs than many other SiC-based ceramics and adequate properties for use as high-temperature heat exchangers in oxidizing environments. Silicon nitride has much better resistance to attack by chlorine at temperatures above 900 C than silicon carbide. When nitride bonded silicon carbide ceramics are exposed to gas mixtures containing 2% Cl{sub 2} and small amounts of oxygen in this temperature range, the SiC is selectively chlorinated, leaving behind a porous matrix of silicon nitride. The rate of corrosion is controlled by a combination of interfacial kinetics at the surfaces of the SiC grains and transport of volatile species through the silicon nitride skeleton. In more oxidizing environments, the rate of chlorination is suppressed by the formation of a protective SiO{sub 2} film. In more oxidizing environments at temperatures in excess of 1,200 C, the formation of volatile chloride reaction products at the interface between the SiC and the passivating SiO{sub 2} layer causes bubbles to form in the SiO{sub 2}, which accelerates the oxidation.

  11. Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications

    PubMed Central

    2013-01-01

    Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO2 QDs after 1, 3, and 7 days from their administration. QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection. Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO2 QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered. Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the

  12. Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications

    NASA Astrophysics Data System (ADS)

    Stanca, Loredana; Petrache, Sorina Nicoleta; Serban, Andreea Iren; Staicu, Andrea Cristina; Sima, Cornelia; Munteanu, Maria Cristina; Zărnescu, Otilia; Dinu, Diana; Dinischiotu, Anca

    2013-05-01

    Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO2 QDs after 1, 3, and 7 days from their administration. QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection. Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO2 QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered. Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the

  13. Oxide trap relaxation spectroscopy: A new difference method to determine trap in oxidized silicon

    NASA Astrophysics Data System (ADS)

    Tan, Changhua; Xu, Mingzhen; Liu, Xiaowei; He, Yandong; Wang, Yangyuan

    1995-03-01

    A difference analysis method has been presented to separate and characterize interface and oxide traps generated in the metal-oxide-semiconductor structure under Fowler-Nordheim stress. The oxide trap relaxation measurement has been performed in dynamic voltage mode. For a high constant voltage stress condition, the effective oxide traps can be obtained by the difference Fowler-Nordheim current relaxation characteristics. For a low-voltage condition, the interface and effective oxide traps can be separated and determined by the difference subthreshold voltage relaxation characteristics. Using combined difference Fowler-Nordheim current and subthreshold voltage measurements, the density, centroid, and generation/capture cross section of the oxide traps can be obtained without the double current-voltage technique, thus permitting more accurate and quick measurement of the generated oxide traps. All difference Fowler-Nordheim current and subthreshold voltage versus the electron-fluence characteristics exhibit spectrum features. Analytical expressions for computing the interface and oxide traps have been derived and experimental results have been presented for a Fowler-Nordheim tunnel metal-oxide-semiconductor structure. Two interface and two oxide traps generated at Fowler-Nordheim stress have been obtained by the new technique.

  14. Process for removal of water and silicon mu-oxides from chlorosilanes

    DOEpatents

    Tom, Glenn M.; McManus, James V.

    1992-03-10

    A scavenger composition having utility for removal of water and silicon mu-oxide impurities from chlorosilanes, such scavenger composition comprising: (a) a support; and (b) associated with the support, one or more compound(s) selected from the group consisting of compounds of the formula: R.sub.a-x MCl.sub.x wherein: M is a metal selected from the group consisting of the monovalent metals lithium, sodium, and potassium; the divalent metals magnesium, strontium, barium, and calcium; and the trivalent metal aluminum; R is alkyl; a is a number equal to the valency of metal M; and x is a number having a value of from 0 to a, inclusive; and wherein said compound(s) of the formula R.sub.a-x MCl.sub.x have been activated for impurity-removal service by a reaction scheme selected from those of the group consisting of: (i) reaction of such compound(s) with hydrogen chloride to form a first reaction product therefrom, followed by reaction of the first reaction product with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y, wherein y is a number having a value of from 1 to 3, inclusive; and (ii) reaction of such compound(s) with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y wherein y is a number having a value of 1 to 3, inclusive. A corresponding method of making the scavenger composition, and of purifying a chlorosilane which contains oxygen and silicon mu-oxide impurities, likewise are disclosed, together with a purifier apparatus, in which a bed of the scavenger composition is disposed. The composition, purification process, and purifier apparatus of the invention have utility in purifying gaseous chlorosilanes which are employed in the semiconductor industry as silicon source reagents for forming epitaxial silicon layers.

  15. Composition, process, and apparatus, for removal of water and silicon mu-oxides from chlorosilanes

    DOEpatents

    Tom, Glenn M.; McManus, James V.

    1991-10-15

    A scavenger composition having utility for removal of water and silicon mu-oxide impurities from chlorosilanes, such scavenger composition comprising: (a) a support; and (b) associated with the support, one or more compound(s) selected from the group consisting of compounds of the formula: R.sub.a-x MCl.sub.x wherein: M is a metal selected from the group consisting of the monovalent metals lithium, sodium, and potassium; the divalent metals magnesium, strontium, barium, and calcium; and the trivalent metal aluminum; R is alkyl; a is a number equal to the valency of metal M; and x is a number having a value from 0 to a, inclusive; and wherein said compound(s) of the formula R.sub.a-x MCl.sub.x have been activated for impurity-removal service by a reaction scheme selected from those of the group consisting of: (i) reaction of such compound(s) with hydrogen chloride to form a first reaction product therefrom, followed by reaction of the first reaction product with a chlorosilane of the formula: SiH.sub.4"y Cl.sub.y, wherein y is a number having a value of from 1 to 3, inclusive; and (ii) reaction of such compound(s) with a chlorosilane of the formula: SiH.sub.4-y Cl.sub.y wherein y is a number having a value of 1 to 3, inclusive. A corresponding method of making the scavenger composition, and of purifying a chlorosilane which contains oxygen and silicon mu-oxide impurities, likewise are disclosed, together with a purifier apparatus, in which a bed of the scavenger composition is disposed. The composition, purification process, and purifier apparatus of the invention have utility in purifying gaseous chlorosilanes which are employed in the semiconductor industry as silicon source reagents for forming epitaxial silicon layers.

  16. A Modified Oxidative Refinement Process for Removing Boron from Molten Silicon Under Enhanced Electromagnetic Force.

    PubMed

    Lee, Jun-Kyu; Lee, Jin-Seok; Jang, Bo-Yun; Kim, Joon-Soo; Ahn, Young-Soo; Kang, Gi-Hwan; Cho, Churl-Hee

    2015-11-01

    The removal of boron is one of the main challenges in the purification of metallurgical grade silicon destined for low-cost photovoltaic applications. However, boron is very difficult to remove in its elemental form due to its large segregation coefficient in silicon and its low vapor pressure. The removal of boron by slag treatment is today regarded as a highly promising method, but its refining efficiency is relatively low. Also, the reduction of boron by plasma treatment exhibits a high refining efficiency, but the processing cost is high due to the large amount of electricity consumed by the process. In this regard, the use of an oxidizing reactive gas in the refinement process offers some advantages both in terms of low energy consumption and promising refinement rates. Boron can be extracted in various gaseous forms as B(x)O(y) and/or B(x)H(z)O(y) phases, but the vapor pressure of B(x)H(z)O(y) is much greater than that of the other specie at a temperature of 1700 K. The present study reports a modified oxidative refining method designed to enhance the vaporization of boron as B(x)H(z)O(y) by blowing gaseous water onto the silicon melt in a segmented crucible to enhance the electromagnetic force, whereby the processing cost can be dramatically reduced due to the use of a reusable quartz crucible in a graphite crucible. An initial boron content of 13 ppm in the metallurgical grade silicon was significantly decreased to 0.3 ppm by the employment of 1.7SLM Ar + 100 ml/h H2O. Also, a mechanism capable of reducing boron based on thermodynamic considerations is proposed. PMID:26726550

  17. Nitric oxide-generating silicone as a blood-contacting biomaterial

    PubMed Central

    Amoako, Kagya A.; Cook, Keith E.

    2011-01-01

    Coagulation upon blood-contacting biomaterials remains a problem for short and long-term clinical applications. This study examined the ability of copper(II)-doped silicone surfaces to generate nitric oxide (NO) and locally inhibit coagulation. Silicone was doped with 3-micron copper (Cu(0)) particles yielding 3 to 10 weight percent (wt%) Cu in 70-μm thick Cu/Silicone polymeric matrix composites (Cu/Si PMCs). At 3, 5, 8 and 10 wt% Cu doping, the surface expression of Cu was 12.1 ± 2.8%, 19.7 ± 5.4%, 29.0 ± 3.8%, and 33.8 ± 6.5% respectively. After oxidizing Cu(0) to Cu(II) by spontaneous corrosion, NO flux, JNO (mol*cm−2*min−1), as measured by chemiluminescence, increased with surface Cu expression according to the relationship JNO =(1.63 %SACu −0.81) ×10−11, R2 = 0.98 where %SACu is the percentage of surface occupied by Cu. NO flux at 10 wt% Cu was 5.35± 0.74 ×10−10 mol*cm−2*min−1. The clotting time of sheep blood exposed to these surfaces was 80 ± 13s with pure silicone and 339 ± 44s when 10 wt% Cu(II) was added. SEMs of coatings showed clots occurred away from exposed Cu-dendrites. In conclusion, Cu/Si PMCs inhibit coagulation in a dose-dependent fashion related to the extent of copper exposure on the coated surface. PMID:22036723

  18. Hydrogen passivation of silicon(100) used as templates for low-temperature epitaxy and oxidation

    NASA Astrophysics Data System (ADS)

    Atluri, Vasudeva Prasad

    Epitaxial growth, oxidation and ohmic contacts require surfaces as free as possible of physical defects and chemical contaminants, especially, oxygen and hydrocarbons. Wet chemical cleaning typically involves a RCA clean to remove contaminants by stripping the native oxide and regrowing a chemical oxide with only trace levels of carbon and metallic impurities. Low temperature epitaxy, T<800sp° C, limits the thermal budget for the desorption of impurities and surface oxides, and can be performed on processed structures. But, silicon dioxide cannot be desorbed at temperatures lower than 800sp°C. Recently, hydrogen passivation of Si(111) has been reported to produce stable and ordered surfaces at low temperatures. Hydrogen can then be desorbed between 200sp°C and 600sp°C prior to deposition. In this work, Si(100) is passivated via a solution of hydrofluoric acid in alcohol (methanol, ethanol, or isopropyl alcohol) with HF concentrations between 0.5 to 10%. A rinse in water or alcohol is performed after etching to remove excess fluorine. This work investigates wet chemical cleaning of Si(100) to produce ordered, hydrogen-terminated, oxygen- and carbon-free surfaces to be used as templates for low temperature epitaxial growth and rapid thermal oxidation. Ion beam analysis, Tapping mode atomic force microscopy, Fourier transform infrared spectroscopy, Secondary ion mass spectroscopy, Chemical etching, Capacitance-voltage measurements and Ellipsometry are used to measure, at the surface and interface, impurities concentration, residual disorder, crystalline order, surface topography, roughness, chemical composition, defects density, electrical characteristics, thickness, and refractive index as a function of cleaning conditions for homoepitaxial silicon growth and oxidation. The wetting characteristics of the Si(100) surfaces are measured with a tilting plate technique. Different materials are analyzed by ion beam analysis for use as hydrogen standards in elastic

  19. Aligned ZnO/CdTe core-shell nanocable arrays on indium tin oxide: synthesis and photoelectrochemical properties.

    PubMed

    Wang, Xina; Zhu, Haojun; Xu, Yeming; Wang, Hao; Tao, Yin; Hark, Suikong; Xiao, Xudong; Li, Quan

    2010-06-22

    Vertically aligned ZnO/CdTe core-shell nanocable arrays-on-indium tin oxide (ITO) are fabricated by electrochemical deposition of CdTe on ZnO nanorod arrays in an electrolyte close to neutral pH. By adjusting the total charge quantity applied during deposition, the CdTe shell thickness can be tuned from several tens to hundreds of nanometers. The CdTe shell, which has a zinc-blende structure, is very dense and uniform both radially and along the axial direction of the nanocables, and forms an intact interface with the wurtzite ZnO nanorod core. The absorption of the CdTe shell above its band gap ( approximately 1.5 eV) and the type II band alignment between the CdTe shell and the ZnO core, respectively, demonstrated by absorption and photoluminescence measurements, make a nanocable array-on-ITO architecture a promising photoelectrode with excellent photovoltaic properties for solar energy applications. A photocurrent density of approximately 5.9 mA/cm(2) has been obtained under visible light illumination of 100 mW cm(-2) with zero bias potential (vs saturated calomel electrode). The neutral electrodeposition method can be generally used for plating CdTe on nanostructures made of different materials, which would be of interest in various applications. PMID:20446665

  20. Enhanced field emission properties from well-aligned zinc oxide nanoneedles grown on the Au/Ti/n-Si substrate

    SciTech Connect

    Park, Chan Jun; Choi, Duck-Kyun; Yoo, Jinkyoung; Yi, Gyu-Chul; Lee, Cheol Jin

    2007-02-19

    The authors investigated the field emission from vertically well-aligned zinc oxide (ZnO) nanoneedles grown on the Au/Ti/n-Si (100) substrate using metal organic chemical vapor deposition. The turn-on field of ZnO nanoneedles was about 0.85 V/{mu}m at the current density of 0.1 {mu}A/cm{sup 2}, and the emission current density of 1 mA/cm{sup 2} was achieved at the applied electric field of 5.0 V/{mu}m. The low turn-on field of the ZnO nanoneedles was attributed to very sharp tip morphology, and the high emission current density was mainly caused by the formation of the stable Ohmic contact between the ZnO nanoneedles and Au film.

  1. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

    NASA Astrophysics Data System (ADS)

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T.; Shinde, Dhanraj B.; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-03-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30-40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71+/-5 l m-2 hr-1 bar-1 for 150+/-15 nm thick membranes).

  2. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide.

    PubMed

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T; Shinde, Dhanraj B; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-01-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm(2)) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30-40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71 ± 5 l m(-2) hr(-1) bar(-1) for 150 ± 15 nm thick membranes). PMID:26947916

  3. Pull-test adhesion measurements of diamondlike carbon films on silicon carbide, silicon nitride, aluminum oxide, and zirconium oxide

    SciTech Connect

    Erck, R.A.; Nichols, F.A.; Dierks, J.F.

    1993-10-01

    Hydrogenated amorphous carbon films or diamondlike carbon (DLC) films were formed by ion-beam deposition of 400 eV methane (CH{sub 4}) ions on several smooth and rough ceramics, as well as on ceramics coated with a layer of Si and Ti. Adhesion was measured by the pin-pull method. Excellent adhesion was measured for smooth SiC and Si{sub 3}N{sub 4}, but adhesion of DLC to Al{sub 2}O{sub 3} and ZrO{sub 2} was negligible. The use of a Si bonding interlayer produced good adhesion to all the substrates, but a Ti layer was ineffective because bonding between the DLC film and Ti was poor. The presence of surface roughness appeared to greatly increase the measured adhesion in all cases. Bulk thermodynamic calculations are not directly applicable to bonding at the interface. If the standard enthalpy of formation for reaction between CH{sub 4} and substrate is calculated assumpting a carbide or carbon phase is produced, a relation is seen between reaction enthalpy and relative adhesion. Large positive enthalpies are associated with poor adhesion; negative or small positive enthalpies are associated with good adhesion. This relation between enthalpy and adhesion was also observed for DLC deposited on Si. Lack of adhesion to Ti was attributed to inadvertent formation of a surface oxide layer that rendered the enthalpy for reaction with CH{sub 4} strongly positive and similar in magnitude to that for Al{sub 2}O{sub 3} and ZrO{sub 2}.

  4. The influence of oxidation properties on the electron emission characteristics of porous silicon

    NASA Astrophysics Data System (ADS)

    He, Li; Zhang, Xiaoning; Wang, Wenjiang; Wei, Haicheng

    2016-09-01

    In order to investigate the influence of oxidation properties such as oxygen content and its distribution gradient on the electron emission characteristics of porous silicon (PS) emitters, emitters with PS thickness of 8 μm, 5 μm, and 3 μm were prepared and then oxidized by electrochemical oxidation (ECO) and ECO-RTO (rapid thermal oxidation) to get different oxidation properties. The experimental results indicated that the emission current density, efficiency, and stability of the PS emitters are mainly determined by oxidation properties. The higher oxygen content and the smaller oxygen distribution gradient in the PS layer, the larger emission current density and efficiency we noted. The most favorable results occurred for the PS emitter with the smallest oxygen distribution gradient and the highest level of oxygen content, with an emission current density of 212.25 μA/cm2 and efficiency of 59.21‰. Additionally, it also demonstrates that thick PS layer benefits to the emission stability due to its longer electron acceleration tunnel. The FN fitting plots indicated that the effective emission areas of PS emitters can be enlarged and electron emission thresholds is decreased because of the higher oxygen content and smaller distribution gradient, which were approved by the optical micrographs of top electrode of PS emitters before and after electron emission.

  5. Band offsets of a ruthenium gate on ultrathin high-{kappa} oxide films on silicon

    SciTech Connect

    Rangan, Sylvie; Bersch, Eric; Bartynski, Robert Allen; Garfunkel, Eric; Vescovo, Elio

    2009-02-15

    Valence-band and conduction-band edges of ultrathin oxides (SiO{sub 2}, HfO{sub 2}, Hf{sub 0.7}Si{sub 0.3}O{sub 2}, and Al{sub 2}O{sub 3} grown on silicon) and their shifts upon sequential metallization with ruthenium have been measured using synchrotron-radiation-excited x-ray, ultraviolet, and inverse photoemissions. From these techniques, the offsets between the valence-band and conduction-band edges of the oxides, and the ruthenium metal gate Fermi edge have been directly measured. In addition the core levels of the oxides and the ruthenium have been characterized. Upon deposition, Ru remains metallic and no chemical alteration of the underlying oxide gates, or interfacial SiO{sub 2} in the case of the high-{kappa} thin films, can be detected. However a clear shift of the band edges is measured for all samples due to the creation of an interface dipole at the ruthenium-oxide interface. Using the energy gap, the electron affinity of the oxides, and the ruthenium work function that have been directly measured on these samples, the experimental band offsets are compared to those predicted by the induced gap states model.

  6. Reliability of potassium ion electret in silicon oxide for vibrational energy harvester applications

    NASA Astrophysics Data System (ADS)

    Misawa, Kensuke; Sugiyama, Tatsuhiko; Hashiguchi, Gen; Toshiyoshi, Hiroshi

    2015-06-01

    In this paper, we report on the long-term reliability of potassium ion electret included in a thermally grown silicon oxide. The electret in this work is used in a microelectromechanical systems (MEMS) energy harvester to generate electrical current from mechanical vibration. A spring-mass system similar to a comb-drive electrostatic actuator is developed by silicon micromachining, and the surface is oxidized by wet-oxidation through a potassium hydroxide bubbler, thereby including potassium atoms at a high concentration. The potassium is then electrically polarized by an applied voltage of 150 V at 650 °C for 5 min. Degradation of the stored polarization potential is monitored in a vacuum of 1 × 10-3 Pa at elevated temperatures of 350, 400, and 450 °C. The time needed to cause a -1 dB decay of the potential is used as the lifetime of the electret, and the Arrhenius extrapolation plot suggested a life time of more than 400 years at 25 °C.

  7. In-Situ Transmission Electron Microscopy Probing of Native Oxide and Artificial Layers on Silicon Nanoparticles for Lithium Ion Batteries

    SciTech Connect

    He, Yang; Piper, Daniela M.; Gu, Meng; Travis, Jonathan J.; George, Steven M.; Lee, Se-Hee; Genc, Arda; Pullan, Lee; Liu, Jun; Mao, Scott X.; Zhang, Jiguang; Ban, Chunmei; Wang, Chong M.

    2014-11-25

    Surface modification of silicon nanoparticle via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism as how this thin layer of coating function is not known, which is even complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in-situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation, and therefore low coulombic efficiency. In contrast, the alucone MLD coated particles show extremely fast, thorough and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li+/e- conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer and therefore mitigates side reaction and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the coulombic efficiency and preserve capacity and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrated that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance as the coating layer itself.

  8. In situ transmission electron microscopy probing of native oxide and artificial layers on silicon nanoparticles for lithium ion batteries.

    PubMed

    He, Yang; Piper, Daniela Molina; Gu, Meng; Travis, Jonathan J; George, Steven M; Lee, Se-Hee; Genc, Arda; Pullan, Lee; Liu, Jun; Mao, Scott X; Zhang, Ji-Guang; Ban, Chunmei; Wang, Chongmin

    2014-11-25

    Surface modification of silicon nanoparticles via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism of how this thin layer of coating functions is not known, which is complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation and therefore low Coulombic efficiency. In contrast, the alucone MLD-coated particles show extremely fast, thorough, and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li(+)/e(-) conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer, and therefore mitigates side reactions and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the Coulombic efficiency, preserves capacity, and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrates that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance to the coating layer itself. PMID:25347792

  9. Characteristics of electro-refractive modulating based on Graphene-Oxide-Silicon waveguide.

    PubMed

    Xu, Chao; Jin, Yichang; Yang, Longzhi; Yang, Jianyi; Jiang, Xiaoqing

    2012-09-24

    Graphene has attracted a high level of research interest because of its outstanding electronic transport properties and optical properties. Based on the Kubo formalism and the Maxwell equations, it's demonstrated that the optical conductivity of graphene can be controlled through the applied voltage. And we find that the graphene-oxide-silicon (GOS) based waveguide can be made into either the electro-absorptive or electron-refractive modulators. Using graphene as the active medium, we present a new electro-refractive Mach-Zender interferometer based on the GOS structure. This new GOS-based electron-refractive modulation mechanism can enable novel architectures for on-chip optical communications. PMID:23037388

  10. Degradation of Gate Oxide Reliability due to Plasma-Deposited Silicon Nitride

    NASA Astrophysics Data System (ADS)

    Ogino, Masaaki; Sugahara, Yoshiyuki; Kuribayashi, Hitoshi; Yamabe, Kikuo

    2004-03-01

    The effects of plasma-enhanced chemical vapor deposition (PE-CVD) silicon nitride (p-SiN) passivation films on time dependent dielectric breakdown (TDDB) of gate oxide were studied. It was found that degradation of TDDB characteristics with p-SiN films was suppressed by the change in p-SiN deposition conditions. The correlation between trapped electron density and TDDB characteristics varied, depending on the p-SiN films. The degradation of TDDB characteristics was also enhanced with phosphosilicate glass (PSG) under the p-SiN passivation film.

  11. Performance and characteristics of double layer porous silicon oxide resistance random access memory

    NASA Astrophysics Data System (ADS)

    Tsai, Tsung-Ming; Chang, Kuan-Chang; Zhang, Rui; Chang, Ting-Chang; Lou, J. C.; Chen, Jung-Hui; Young, Tai-Fa; Tseng, Bae-Heng; Shih, Chih-Cheng; Pan, Yin-Chih; Chen, Min-Chen; Pan, Jhih-Hong; Syu, Yong-En; Sze, Simon M.

    2013-06-01

    A bilayer resistive switching memory device with an inserted porous silicon oxide layer is investigated in this letter. Compared with single Zr:SiOx layer structure, Zr:SiOx/porous SiOx structure outperforms from various aspects, including low operating voltages, tighter distributions of set voltage, higher stability of both low resistance state and high resistance state, and satisfactory endurance characteristics. Electric field simulation by comsolTM Multiphysics is applied, which corroborates that intensive electric field around the pore in porous SiOx layer guides the conduction of electrons. The constraint of conduction path leads to better stabilization and prominent performance of bilayer resistive switching devices.

  12. Oxidation behavior in reaction-bonded aluminum-silicon alloy/alumina powder compacts

    SciTech Connect

    Yokota, S.H.

    1992-12-01

    Goal of this research is to determine the feasibility of producing low-shrinkage mullite/alumina composites by applying the reaction-bonded alumina (RBAO) process to an aluminum-silicon alloy/alumina system. Mirostructural and compositional changes during heat treatment were studied by removing samples from the furnace at different steps in the heating schedule and then using optical and scanning electron microscopy, EDS and XRD to characterize the powder compacts. Results suggest that the oxidation behavior of the alloy compact is different from the model proposed for the pure Al/alumina system.

  13. Ultrasensitive food toxin biosensor using frequency based signals of silicon oxide nanoporous structure

    NASA Astrophysics Data System (ADS)

    Ghosh, H.; RoyChaudhuri, C.

    2013-06-01

    We report an electrochemically fabricated silicon oxide nanoporous structure for ultrasensitive detection of AfB1 in food by shift in peak frequency corresponding to maximum sensitivity. It has been observed that the impedance sensitivity changes from 19% to 40% (which is only twice) where as the peak frequency shifts from 500 Hz to 50 kHz, for a change in concentration from 1 fg/ml to 1 pg/ml. This has been attributed to the combined effect of the significant pore narrowing with increasing AfB1 concentration and the opposing nature of impedance change within the nanopores and the conducting substrate immediately below the nanoporous layer.

  14. Scattering strength of the scatterer inducing variability in graphene on silicon oxide

    NASA Astrophysics Data System (ADS)

    Katoch, Jyoti; Le, Duy; Singh, Simranjeet; Rao, Rahul; Rahman, Talat S.; Ishigami, Masa

    2016-03-01

    Large variability of carrier mobility of graphene-based field effect transistors hampers graphene science and technology. We show that the number of the scatterer responsible for the observed variability on graphene devices on silicon oxide can be determined by finding the number of hydrogen that can be chemisorbed on graphene. We use the relationship between the number of the scatterer and the mobility of graphene devices to determine that the variability-inducing scatterer possesses scattering strength 10 times smaller than that of adsorbed potassium atoms and 50 times smaller than that of ion-beam induced vacancies. Our results provide an important, quantitative input towards determining the origin of the variability.

  15. Epitaxial ferromagnetic oxide thin films on silicon with atomically sharp interfaces

    SciTech Connect

    Coux, P. de; Bachelet, R.; Fontcuberta, J.; Sánchez, F.; Warot-Fonrose, B.; Skumryev, V.; Lupina, L.; Niu, G.; Schroeder, T.

    2014-07-07

    A bottleneck in the integration of functional oxides with silicon, either directly grown or using a buffer, is the usual formation of an amorphous interfacial layer. Here, we demonstrate that ferromagnetic CoFe{sub 2}O{sub 4} films can be grown epitaxially on Si(111) using a Y{sub 2}O{sub 3} buffer layer, and remarkably the Y{sub 2}O{sub 3}/Si(111) interface is stable and remains atomically sharp. CoFe{sub 2}O{sub 4} films present high crystal quality and high saturation magnetization.

  16. Electrical and gas sensing properties of self-aligned copper-doped zinc oxide nanoparticles

    SciTech Connect

    Sonawane, Yogesh S.; Kanade, K.G.; Kale, B.B. Aiyer, R.C.

    2008-10-02

    Electrical and gas sensing properties of nanocrystalline ZnO:Cu, having Cu X wt% (X = 0.0, 0.5, 1.0, and 1.5) in ZnO, in the form of pellet were investigated. Copper chloride and zinc acetate were used as precursors along with oxalic acid as a precipitating reagent in methanol. Material characterization was done by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and inductive coupled plasma with optical emission spectrometry (ICP-OES). FE-SEM showed the self-aligned Cu-doped ZnO nano-clusters with particles in the range of 40-45 nm. The doping of 0.5% of copper changes the electrical conductivity by an order of magnitude whereas the temperature coefficient of resistance (TCR) reduces with increase in copper wt% in ZnO. The material has shown an excellent sensitivity for the H{sub 2}, LPG and CO gases with limited temperature selectivity through the optimized operating temperature of 130, 190 and 220 deg. C for H{sub 2}, LPG and CO gases, respectively at 625 ppm gas concentration. The %SF was observed to be 1460 for H{sub 2} at 1% Cu doping whereas the 0.5% Cu doping offered %SF of 950 and 520 for CO and LPG, respectively. The response and recovery time was found to be 6 to 8 s and 16 s, respectively.

  17. ZnO transparent conductive oxide for thin film silicon solar cells

    NASA Astrophysics Data System (ADS)

    Söderström, T.; Dominé, D.; Feltrin, A.; Despeisse, M.; Meillaud, F.; Bugnon, G.; Boccard, M.; Cuony, P.; Haug, F.-J.; Faÿ, S.; Nicolay, S.; Ballif, C.

    2010-03-01

    There is general agreement that the future production of electric energy has to be renewable and sustainable in the long term. Photovoltaic (PV) is booming with more than 7GW produced in 2008 and will therefore play an important role in the future electricity supply mix. Currently, crystalline silicon (c-Si) dominates the market with a share of about 90%. Reducing the cost per watt peak and energy pay back time of PV was the major concern of the last decade and remains the main challenge today. For that, thin film silicon solar cells has a strong potential because it allies the strength of c-Si (i.e. durability, abundancy, non toxicity) together with reduced material usage, lower temperature processes and monolithic interconnection. One of the technological key points is the transparent conductive oxide (TCO) used for front contact, barrier layer or intermediate reflector. In this paper, we report on the versatility of ZnO grown by low pressure chemical vapor deposition (ZnO LP-CVD) and its application in thin film silicon solar cells. In particular, we focus on the transparency, the morphology of the textured surface and its effects on the light in-coupling for micromorph tandem cells in both the substrate (n-i-p) and superstrate (p-i-n) configurations. The stabilized efficiencies achieved in Neuchâtel are 11.2% and 9.8% for p-i-n (without ARC) and n-i-p (plastic substrate), respectively.

  18. The oxidized porous silicon vacuum microtriode: A revolutionary new type of field emission array

    SciTech Connect

    Smith, D.D.; Demroff, H.P.; Elliott, T.S.; Faber, J.S.; Lee, B.; Mazumdar, T.; McIntyre, P.M.; Trost, H.J.; Pang, Y.

    1997-08-01

    Yue began studying porous silicon-based vacuum microelectronic devices i n1990. Results from a device he dubbed the Oxidized Porous Silicon Field Emission Diode (OPSFED) showed that porous silicon (PS) offered an attractive alternative to standard field emission devices. Emission sites are reduced to near-atomic dimensions and site density is increased by six orders of magnitude. Yue, and later Madduri extracted electrons into the vacuum in a diode configuration, but no attempt to build a triode device had ever been successful. Using a novel metallization technique developed by Dr. R.C. Jaklevic et al. for use in STM imaging, the authors have successfully fabricated the first working PS-based vacuum microtriodes. Results are extremely encouraging. Collector currents up to 700 {micro}A were extracted across {approximately}3mm of vacuum with a pulsed DC gate bias of less than 20V. Simultaneous measurement of the gate current showed current densities to 700A/cm{sup 2}. Modulation of the emission to 5MH: was observed. Fowler-Nordheim plots show a slight curvature, as would be expected from extremely sharp emission tips, although it is stressed that the electroemissive mechanism is as yet unknown. Fowler-Nordheim plots for OPSFED`s made from the same material show an opposite curvature as predicted for emission from a large number of sites. Density of emitters approach a true two-dimensional limit, and many applications exist if the technology can be matured.

  19. Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation

    SciTech Connect

    Kawase, Kazumasa; Uehara, Yasushi; Teramoto, Akinobu; Suwa, Tomoyuki; Hattori, Takeo; Ohmi, Tadahiro; Umeda, Hiroshi

    2012-02-01

    Silicon dioxide (SiO{sub 2}) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O{sub 2} plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO{sub 2} films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO{sub 2} films were increased near the SiO{sub 2} surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO{sub 2} film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.

  20. Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation

    NASA Astrophysics Data System (ADS)

    Kawase, Kazumasa; Teramoto, Akinobu; Umeda, Hiroshi; Suwa, Tomoyuki; Uehara, Yasushi; Hattori, Takeo; Ohmi, Tadahiro

    2012-02-01

    Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O2 plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO2 films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO2 films were increased near the SiO2 surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO2 film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O network with the radical oxidation.

  1. CO oxidation catalyzed by silicon carbide (SiC) monolayer: A theoretical study.

    PubMed

    Wang, Nan; Tian, Yu; Zhao, Jingxiang; Jin, Peng

    2016-05-01

    Developing metal-free catalysts for CO oxidation has been a key scientific issue in solving the growing environmental problems caused by CO emission. In this work, the potential of the silicon carbide (SiC) monolayer as a metal-free catalyst for CO oxidation was systematically explored by means of density functional theory (DFT) computations. Our results revealed that CO oxidation reaction can easily proceed on SiC nanosheet, and a three-step mechanism was proposed: (1) the coadsorption of CO and O2 molecules, followed by (2) the formation of the first CO2 molecule, and (3) the recovery of catalyst by a second CO molecule. The last step is the rate-determining one of the whole catalytic reaction with the highest barrier of 0.65eV. Remarkably, larger curvature is found to have a negative effect on the catalytic performance of SiC nanosheet for CO oxidation. Therefore, our results suggested that flat SiC monolayer is a promising metal-free catalyst for CO oxidation. PMID:27135172

  2. Impact of Silicon Nanocrystal Oxidation on the Nonmetallic Growth of Carbon Nanotubes.

    PubMed

    Rocks, Conor; Mitra, Somak; Macias-Montero, Manuel; Maguire, Paul; Svrcek, Vladimir; Levchenko, Igor; Ostrikov, Kostya; Mariotti, Davide

    2016-07-27

    Carbon nanotube (CNT) growth has been demonstrated recently using a number of nonmetallic semiconducting and metal oxide nanoparticles, opening up pathways for direct CNT synthesis from a number of more desirable templates without the need for metallic catalysts. However, CNT growth mechanisms using these nonconventional catalysts has been shown to largely differ and reamins a challenging synthesis route. In this contribution we show CNT growth from partially oxidized silicon nanocrystals (Si NCs) that exhibit quantum confinement effects using a microwave plasma enhanced chemical vapor deposition (PECVD) method. On the basis of solvent and a postsynthesis frgamentation process, we show that oxidation of our Si NCs can be easily controlled. We determine experimentally and explain with theoretical simulations that the Si NCs morphology together with a necessary shell oxide of ∼1 nm is vital to allow for the nonmetallic growth of CNTs. On the basis of chemical analysis post-CNT-growth, we give insight into possible mechanisms for CNT nucleation and growth from our partially oxidized Si NCs. This contribution is of significant importance to the improvement of nonmetallic catalysts for CNT growth and the development of Si NC/CNT interfaces. PMID:27362537

  3. Crystallographic plane-orientation dependent atomic force microscopy-based local oxidation of silicon carbide.

    PubMed

    Ahn, Jung-Joon; Jo, Yeong-Deuk; Kim, Sang-Cheol; Lee, Ji-Hoon; Koo, Sang-Mo

    2011-01-01

    The effect of crystalline plane orientations of Silicon carbide (SiC) (a-, m-, and c-planes) on the local oxidation on 4H-SiC using atomic force microscopy (AFM) was investigated. It has been found that the AFM-based local oxidation (AFM-LO) rate on SiC is closely correlated to the atomic planar density values of different crystalline planes (a-plane, 7.45 cm-2; c-plane, 12.17 cm-2; and m-plane, 6.44 cm-2). Specifically, at room temperature and under about 40% humidity with a scan speed of 0.5 μm/s, the height of oxides on a- and m-planes 4H-SiC is 6.5 and 13 nm, respectively, whereas the height of oxides on the c-plane increased up to 30 nm. In addition, the results of AFM-LO with thermally grown oxides on the different plane orientations in SiC are compared. PMID:21711752

  4. Crystallographic plane-orientation dependent atomic force microscopy-based local oxidation of silicon carbide

    PubMed Central

    2011-01-01

    The effect of crystalline plane orientations of Silicon carbide (SiC) (a-, m-, and c-planes) on the local oxidation on 4H-SiC using atomic force microscopy (AFM) was investigated. It has been found that the AFM-based local oxidation (AFM-LO) rate on SiC is closely correlated to the atomic planar density values of different crystalline planes (a-plane, 7.45 cm-2; c-plane, 12.17 cm-2; and m-plane, 6.44 cm-2). Specifically, at room temperature and under about 40% humidity with a scan speed of 0.5 μm/s, the height of oxides on a- and m-planes 4H-SiC is 6.5 and 13 nm, respectively, whereas the height of oxides on the c-plane increased up to 30 nm. In addition, the results of AFM-LO with thermally grown oxides on the different plane orientations in SiC are compared. PMID:21711752

  5. On the variation of magnetic anisotropy in Co/Pt(111) on silicon oxide

    NASA Astrophysics Data System (ADS)

    Winkler, G.; Kobs, A.; Chuvilin, A.; Lott, D.; Schreyer, A.; Oepen, H. P.

    2015-03-01

    The structural properties and magnetic anisotropy of Pt/Co/Pt trilayers grown on thermally oxidized (Si/SiO2) and naturally oxidized silicon (Si/Siox) are presented. Although similar substrates and identical preparation conditions are used distinct differences in the structural composition are found which stem from the Pt seed layer created via ion assisted sputtering. While for thermal oxidized Si a Pt/Co/Pt trilayer is formed, for systems grown on naturally oxidized Si a complex PtSi alloy formation within the seed layer is observed as a consequence of the high ion energies of ion assisted sputtering. The composition of the PtSi alloy varies along the growth direction with a low Si content at the interface to Co and the lattice constant is similar to bulk Pt. The latter provides a much higher magnetic interface anisotropy constant compared to Pt/Co/Pt on thermal oxidized Si of about 0.9 mJ/m2 which is comparable to the highest values found for MBE grown Co on single crystalline Pt(111).

  6. Fatigue failure in thin-film polycrystalline silicon is due to subcritical cracking within the oxide layer

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Stach, E. A.; Muhlstein, C. L.; Ritchie, R. O.

    2005-01-01

    It has been established that microelectromechanical systems created from polycrystalline silicon thin films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a "reaction-layer" process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoing moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the "reaction-layer" mechanism.

  7. Enhanced light emission from germanium microdisks on silicon by surface passivation through thermal oxidation

    NASA Astrophysics Data System (ADS)

    Xu, Xuejun; Hashimoto, Hideaki; Sawano, Kentarou; Nohira, Hiroshi; Maruizumi, Takuya

    2016-05-01

    We have observed enhanced direct-gap light emission from undoped and n-doped germanium microdisks on silicon. The enhancement is attributed mainly to increased carrier density due to surface passivation of the dry-etched sidewall. The enhancement factor increases as the disk size decreases, approaching 4 for microdisks with radii of 1 µm. To achieve maximum enhancement and not modify the geometric structure of resonators, 450-500 °C is found to be the best temperature window. Thermal oxidation is also effective for the degraded interface induced by sputtered Al2O3. These results indicate that thermal oxidation is a promising method suitable for fabrication of low-threshold germanium lasers.

  8. Low temperature growth of crystalline magnesium oxide on hexagonal silicon carbide (0001) by molecular beam epitaxy

    SciTech Connect

    Goodrich, T. L.; Parisi, J.; Cai, Z.; Ziemer, K. S.

    2007-01-22

    Magnesium oxide (111) was grown epitaxially on hexagonal silicon carbide (6H-SiC) (0001) substrates at low temperatures by molecular beam epitaxy and a remote oxygen plasma source. The films were characterized by reflection high-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. Crystal structure, morphology, and growth rate of the magnesium oxide (MgO) films were found to be dependent on the magnesium flux, indicating a magnesium adsorption controlled growth mechanism. The single crystalline MgO thin films had an epitaxial relationship where MgO (111) parallel 6H-SiC (0001) and were stable in both air and 10{sup -9} Torr up to 1023 K.

  9. Selective Growth of α-Sexithiophene by Using Silicon Oxides Patterns

    PubMed Central

    Albonetti, Cristiano; Barbalinardo, Marianna; Milita, Silvia; Cavallini, Massimiliano; Liscio, Fabiola; Moulin, Jean-François; Biscarini, Fabio

    2011-01-01

    A process for fabricating ordered organic films on large area is presented. The process allows growing sexithiophene ultra-thin films at precise locations on patterned Si/SiOx substrates by driving the orientation of growth. This process combines the parallel local anodic oxidation of Si/SiOx substrates with the selective arrangement of molecular ultra-thin film. The former is used to fabricate silicon oxide arrays of parallel lines of 400 nm in width over an area of 1 cm2. Selective growth arises from the interplay between kinetic growth parameters and preferential interactions with the patterned surface. The result is an ultra-thin film of organic molecules that is conformal to the features of the fabricated motives. PMID:22016622

  10. Charge separation technique for metal-oxide-silicon capacitors in the presence of hydrogen deactivated dopants

    SciTech Connect

    Witczak, Steven C.; Winokur, Peter S.; Lacoe, Ronald C.; Mayer, Donald C.

    2000-06-01

    An improved charge separation technique for metal-oxide-silicon (MOS) capacitors is presented which accounts for the deactivation of substrate dopants by hydrogen at elevated irradiation temperatures or small irradiation biases. Using high-frequency capacitance-voltage measurements, radiation-induced inversion voltage shifts are separated into components due to oxide trapped charge, interface traps, and deactivated dopants, where the latter is computed from a reduction in Si capacitance. In the limit of no radiation-induced dopant deactivation, this approach reduces to the standard midgap charge separation technique used widely for the analysis of room-temperature irradiations. The technique is demonstrated on a p-type MOS capacitor irradiated with {sup 60}Co {gamma} rays at 100 degree sign C and zero bias, where the dopant deactivation is significant.(c) 2000 American Institute of Physics.

  11. Hydrogenation kinetics in oxidized boron-doped silicon irradiated by keV electrons

    NASA Astrophysics Data System (ADS)

    Lin, Wallace Wan-Li; Sah, Chih-Tang

    1988-08-01

    Hydrogenation kinetics of boron acceptors in oxidized silicon during and after repeated 8-keV electron irradiation (225-2700-μC/cm2 stresses and 10-168-h interirradiation anneals) at room temperature are reported. Hydrogenation proceeds rapidly during irradiation but continues for many hours after the 8-keV electron beam is removed. Postoxidation process dependencies show that postoxidation and postmetallization annealing processes reduce the hydrogenation effect during the 8-keV electron irradiation, while exposure of the oxide to water prior to aluminum electrode deposition enhances it. The data can be interpreted by our two-reaction model consisting of the hydrogen capture reaction by the boron acceptor and the hydrogen recombination reaction to form hydrogen molecule.

  12. The fabrication of highly ordered block copolymer micellar arrays: control of the separation distances of silicon oxide dots.

    PubMed

    Yoo, Hana; Park, Soojin

    2010-06-18

    We demonstrate the fabrication of highly ordered silicon oxide dotted arrays prepared from polydimethylsiloxane (PDMS) filled nanoporous block copolymer (BCP) films and the preparation of nanoporous, flexible Teflon or polyimide films. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) films were annealed in toluene vapor to enhance the lateral order of micellar arrays and were subsequently immersed in alcohol to produce nano-sized pores, which can be used as templates for filling a thin layer of PDMS. When a thin layer of PDMS was spin-coated onto nanoporous BCP films and thermally annealed at a certain temperature, the PDMS was drawn into the pores by capillary action. PDMS filled BCP templates were exposed to oxygen plasma environments in order to fabricate silicon oxide dotted arrays. By addition of PS homopolymer to PS-b-P2VP copolymer, the separation distances of micellar arrays were tuned. As-prepared silicon oxide dotted arrays were used as a hard master for fabricating nanoporous Teflon or polyimide films by spin-coating polymer precursor solutions onto silicon patterns and peeling off. This simple process enables us to fabricate highly ordered nanoporous BCP templates, silicon oxide dots, and flexible nanoporous polymer patterns with feature size of sub-20 nm over 5 cm x 5 cm. PMID:20498523

  13. Reactive atomization of silicon to form in situ oxide sintering aids

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Zeng, X.; Lavernia, E. J.; Schoenung, J. M.

    1996-08-01

    The present investigation demonstrated the feasibility of using reactive atomization to produce Si powder with in situ oxide sintering aids. With further process optimization, this powder may be an alternative starting material to the conventional, mechanically blended, Si-plus-oxide powder used to produce commercial sintered reaction bonded silicon nitride (SRBSN). In the reactive atomization approach, yttrium and aluminum additives were introduced into silicon metal during induction melting. Reactive atomization was accomplished using a N2-5 pct O2 mixture as the atomization gas. During atomization, oxygen in the atomization gas reacted with Y and Al in the Si melt to produce Y2O3 and Al2O3, which act as in situ sintering aids. The reactive atomized powder demonstrated a Gaussian distribution with a mean diameter of 36 μm. The powder fines (<38 μm) were used to produce cold isostatically pressed compacts that were subsequently reaction bonded and sintered. The results demonstrate that β-Si3N4 formed during reaction bonding and sintering. The density of the SRBSN was 77 pct of theoretical. Transmission electron microscopy (TEM) studies indicated the presence of a glassy phase on the grain boundaries, which is typical in SRBSN and indicative of the presence of the in situ sintering aids. A kinetic model was used to study the influence of processing parameters, such as droplet temperature and oxygen partial pressure, on the kinetics of oxide formation during reactive atomization. The results suggest that the volume fraction of oxides increases with increasing droplet temperature and oxygen partial pressure in the atomization gas mixture.

  14. Silicon carbide: A unique platform for metal-oxide-semiconductor physics

    SciTech Connect

    Liu, Gang; Tuttle, Blair R.; Dhar, Sarit

    2015-06-15

    A sustainable energy future requires power electronics that can enable significantly higher efficiencies in the generation, distribution, and usage of electrical energy. Silicon carbide (4H-SiC) is one of the most technologically advanced wide bandgap semiconductor that can outperform conventional silicon in terms of power handling, maximum operating temperature, and power conversion efficiency in power modules. While SiC Schottky diode is a mature technology, SiC power Metal Oxide Semiconductor Field Effect Transistors are relatively novel and there is large room for performance improvement. Specifically, major initiatives are under way to improve the inversion channel mobility and gate oxide stability in order to further reduce the on-resistance and enhance the gate reliability. Both problems relate to the defects near the SiO{sub 2}/SiC interface, which have been the focus of intensive studies for more than a decade. Here we review research on the SiC MOS physics and technology, including its brief history, the state-of-art, and the latest progress in this field. We focus on the two main scientific problems, namely, low channel mobility and bias temperature instability. The possible mechanisms behind these issues are discussed at the device physics level as well as the atomic scale, with the support of published physical analysis and theoretical studies results. Some of the most exciting recent progress in interface engineering for improving the channel mobility and fundamental understanding of channel transport is reviewed.

  15. Silicon Carbide and Uranium Oxide Based Composite Fuel Preparation Using Polymer Infiltration and Pyrolysis

    SciTech Connect

    Singh, Abhishek K.; Zunjarrao, Suraj C.; Singh, Raman P.

    2006-07-01

    Ceramic composite pellets consisting of uranium oxide, U{sub 3}O{sub 8}, particles in a silicon carbide matrix are fabricated using a novel processing technique based on polymer infiltration and pyrolysis (PIP). In this process, spherical particles of depleted uranium oxide, in the form of U{sub 3}O{sub 8}, are dispersed in liquid allyl-hydrido-poly-carbo-silane (AHPCS), and subjected to pyrolysis up to 900 deg. C under a continuous flow of ultra high purity (UHP) argon. Pyrolysis of AHPCS produces near-stoichiometric amorphous SiC at 900 deg. C. Multiple polymer infiltration and pyrolysis (PIP) cycles are required to minimize open porosity and densify the silicon carbide matrix, in order to enhance the mechanical strength of the material. Structural characterization is carried out after first pyrolysis to investigate chemical interaction between U{sub 3}O{sub 8} and SiC. The physical and mechanical properties are also quantified, and it is shown that this processing scheme promotes uniform distribution of uranium fuel source along with a high ceramic yield of the parent matrix. Furthermore, the processing technique involves lower energy requirements than conventional sintering processes currently in practice. (authors)

  16. Inkjet printing as a tool for the patterned deposition of octadecylsiloxane monolayers on silicon oxide surfaces.

    PubMed

    Belgardt, Christian; Sowade, Enrico; Blaudeck, Thomas; Baumgärtel, Thomas; Graaf, Harald; von Borczyskowski, Christian; Baumann, Reinhard R

    2013-05-28

    We present a case study about inkjet printing as a tool for molecular patterning of silicon oxide surfaces with hydrophobic functionality, mediated by n-octadecyltrichlorosilane (OTS) molecules. In contrast to state-of-the-art techniques such as micro contact printing or chemical immersion with subsequent lithography processes, piezo drop-on-demand inkjet printing does not depend on physical masters, which allows an effective direct-write patterning of rigid or flexible substrates and enables short run-lengths of the individual pattern. In this paper, we used mesithylene-based OTS inks, jetted them in droplets of 10 pL on a silicon oxide surface, evaluated the water contact angle of the patterned areas and fitted the results with Cassie's law. For inks of 2.0 mM OTS concentration, we found that effective area coverages of 38% can be obtained. Our results hence show that contact times of the order of hundred milliseconds are sufficient to form a pattern of regions with OTS molecules adsorbed to the surface, representing at least a fragmented, inhomogeneous self-assembled OTS monolayer (OTS-SAM). PMID:23417102

  17. Carrier Selective, Passivated Contacts for High Efficiency Silicon Solar Cells based on Transparent Conducting Oxides

    DOE PAGESBeta

    Young, David L.; Nemeth, William; Grover, Sachit; Norman, Andrew; Yuan, Hao-Chih; Lee, Benjamin G.; LaSalvia, Vincenzo; Stradins, Paul

    2014-01-01

    We describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO2 and transparent conducting oxide layers. High temperature silicon dioxide is grown on both surfaces of an n-type wafer to a thickness <50 Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high J0,contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter of the contact (J0,contact) and the specificmore » contact resistivity (ρcontact) using a TLM pattern. The best ITO/SiO2 passivated contact in this study has J0,contact = 92.5 fA/cm2 and ρcontact = 11.5 mOhm-cm2. These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J0,contact, ρcontact) values. The ITO/SiO2 contacts are found to have a higher J0,contact, but a similar ρcontact compared to the best reported passivated contacts.« less

  18. Silicon carbide: A unique platform for metal-oxide-semiconductor physics

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Tuttle, Blair R.; Dhar, Sarit

    2015-06-01

    A sustainable energy future requires power electronics that can enable significantly higher efficiencies in the generation, distribution, and usage of electrical energy. Silicon carbide (4H-SiC) is one of the most technologically advanced wide bandgap semiconductor that can outperform conventional silicon in terms of power handling, maximum operating temperature, and power conversion efficiency in power modules. While SiC Schottky diode is a mature technology, SiC power Metal Oxide Semiconductor Field Effect Transistors are relatively novel and there is large room for performance improvement. Specifically, major initiatives are under way to improve the inversion channel mobility and gate oxide stability in order to further reduce the on-resistance and enhance the gate reliability. Both problems relate to the defects near the SiO2/SiC interface, which have been the focus of intensive studies for more than a decade. Here we review research on the SiC MOS physics and technology, including its brief history, the state-of-art, and the latest progress in this field. We focus on the two main scientific problems, namely, low channel mobility and bias temperature instability. The possible mechanisms behind these issues are discussed at the device physics level as well as the atomic scale, with the support of published physical analysis and theoretical studies results. Some of the most exciting recent progress in interface engineering for improving the channel mobility and fundamental understanding of channel transport is reviewed.

  19. Charge storage in a nitride-oxide-silicon medium by scanning capacitance microscopy

    NASA Astrophysics Data System (ADS)

    Barrett, R. C.; Quate, C. F.

    1991-09-01

    In this paper we describe a variant of the scanning capacitance microscope (SCaM) which is based on the atomic force microscope. Our SCaM involves a cantilever beam that is used to press a conducting tip against a conducting substrate coated with a dielectric film. A capacitance sensor is then used to measure the tip-sample capacitance as a function of lateral position. The deflection of the cantilever can also be used to measure independently the surface topography. This microscope can be used to measure electrical properties of dielectric films and their underlying substrates. We have applied this microscope to the study of the nitride-oxide-silicon (NOS) system. This system has been studied extensively because of its ability to store information by trapping charge in the silicon nitride. Commercial semiconductor nonvolatile memories have been designed using this NOS technology. We have used the SCaM tip to apply a localized bias to the NOS sample, causing charge to tunnel through the oxide layer and to be trapped in the nitride film. This trapped charge induces a depletion region in the silicon substrate, which can be detected by the resulting depletion capacitance between the tip and sample. The stored charge can be interpreted as a digital memory. Bit sizes as small as 750 Å full width at half maximum have been stored using this technique. The stored charge has been observed to be stable over a period of seven days. The stored charge can be removed by applying a reverse bias to the region, and the bit can be subsequently rewritten. By simultaneously measuring capacitance and topography images, we have demonstrated that the stored information is not the result of any topographic change to the surface. Simulations of the potential distributions resulting from this trapped charge have been performed and are compared with the experiments. Finally, a discussion is presented on the ultimate density and speed limits of such a storage technology.

  20. Comparative analysis on surface property in anodic oxidation polishing of reaction-sintered silicon carbide and single-crystal 4H silicon carbide

    NASA Astrophysics Data System (ADS)

    Shen, Xinmin; Tu, Qunzhang; Deng, Hui; Jiang, Guoliang; He, Xiaohui; Liu, Bin; Yamamura, Kazuya

    2016-04-01

    For effective machining of difficult-to-machine materials, such as reaction-sintered silicon carbide (RS-SiC) and single-crystal 4H silicon carbide (4H-SiC), a novel polishing technique named anodic oxidation polishing was proposed, which combined with the anodic oxidation of substrate and slurry polishing of oxide. By scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) observation and atomic force microscopy analysis, both the anodic oxidation behaviors of RS-SiC and 4H-SiC were investigated. Through comparison of the surfaces before and after hydrofluoric acid etching of the oxidized samples by the scanning white light interferometry (SWLI) measurement, the relationships between oxidation depth and oxidation time were obtained, and the calculated oxidation rate for RS-SiC was 5.3 nm/s and that for 4H-SiC was 5.8 nm/s based on the linear Deal-Grove model. Through anodic oxidation polishing of RS-SiC substrate and 4H-SiC substrate, respectively, the surface roughness rms obtained by SWLI was improved to 2.103 nm for RS-SiC and to 0.892 nm for 4H-SiC. Experimental results indicate that anodic oxidation polishing is an effective method for the machining of RS-SiC and 4H-SiC samples, which would improve the process level of SiC substrates and promote the application of SiC products in the fields of optics, ceramics, semiconductors, electronics, and so on.

  1. Amperometric Non-Enzymatic Hydrogen Peroxide Sensor Based on Aligned Zinc Oxide Nanorods

    PubMed Central

    Al-Hardan, Naif H.; Abdul Hamid, Muhammad Azmi; Shamsudin, Roslinda; Othman, Norinsan Kamil; Kar Keng, Lim

    2016-01-01

    Zinc oxide (ZnO) nanorods (NRs) have been synthesized via the hydrothermal process. The NRs were grown over a conductive glass substrate. A non-enzymatic electrochemical sensor for hydrogen peroxide (H2O2), based on the prepared ZnO NRs, was examined through the use of current-voltage measurements. The measured currents, as a function of H2O2 concentrations ranging from 10 μM to 700 μM, revealed two distinct behaviours and good performance, with a lower detection limit (LOD) of 42 μM for the low range of H2O2 concentrations (first region), and a LOD of 143.5 μM for the higher range of H2O2 concentrations (second region). The prepared ZnO NRs show excellent electrocatalytic activity. This enables a measurable and stable output current. The results were correlated with the oxidation process of the H2O2 and revealed a good performance for the ZnO NR non-enzymatic H2O2 sensor. PMID:27367693

  2. Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications

    NASA Astrophysics Data System (ADS)

    Li, V. Z.-Q.; Mirabedini, M. R.; Kuehn, R. T.; Wortman, J. J.; Öztürk, M. C.; Batchelor, D.; Christensen, K.; Maher, D. M.

    1997-12-01

    In situ boron-doped polycrystalline Si1-xGex (x>0.4) films have been formed on the thermally grown oxides in a rapid thermal chemical vapor deposition processor using SiH4-GeH4-B2H6-H2 gas system. Our results showed that in situ boron-doped Si1-xGex films can be directly deposited on the oxide surface, in contrast to the rapid thermal deposition of undoped silicon-germanium (Si1-xGex) films on oxides which is a partially selective process and requires a thin silicon film pre-deposition to form a continuous film. For the in situ boron-doped Si1-xGex films, we observed that with the increase of the germane percentage in the gas source, the Ge content and the deposition rate of the film are increased, while its resistivity is decreased down to 0.66 mΩ cm for a Ge content of 73%. Capacitance-voltage characteristics of p-type metal-oxide-semiconductor capacitors with p+-Si1-xGex gates showed negligible polydepletion effect for a 75 Å gate oxide, indicating that a high doping level of boron at the poly-Si1-xGex/oxide interface was achieved.

  3. Aligned poly(ε-caprolactone)/graphene oxide and reduced graphene oxide nanocomposite nanofibers: Morphological, mechanical and structural properties.

    PubMed

    Ramazani, Soghra; Karimi, Mohammad

    2015-11-01

    A number of studies have demonstrated that the mechanical properties of electrospun polymeric nanofibrous scaffolds are enhanced with the incorporation of graphene and its derivatives, thus developing their applications in hard tissue engineering. However, our understanding of the relationship between the microstructure and properties of these fibrous scaffolds and how they are influenced by graphene oxide (GO) and reduced graphene oxide (RGO) loading is much more limited. Thus, in this paper, poly(ε-caprolactone) (PCL)/GO and RGO nanocomposite nanofibers containing 0, 0.1, 0.5 and 1wt.% GO and RGO were prepared using an electrospinning technique. With the addition of 0.1wt.% of GO and RGO nanosheets in PCL, the tensile strength of PCL scaffolds increased over ~160 and 304% respectively and elastic modulus increased over 103 and 163% due to the good dispersion of the nanosheets and their interaction with the molecular chains of PCL. These were supported by the parallel increase in relaxation time and molecular orientation of PCL chains at the presence of nanosheets with a loading of 0.1wt.%. The enhancement effect of the nanosheets was weakened with an increase in GO and RGO loading up to 1wt.% in which it is connected to a partial exfoliation of the nanosheets. PMID:26249597

  4. An amorphous phase formation at palladium / silicon oxide (Pd/SiOx) interface through electron irradiation - electronic excitation process

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Yamashita, Ryo; Yabuuchi, Atsushi; Lee, Jung-Goo

    2015-11-01

    A Pd-Si amorphous phase was formed at a palladium/silicon oxide (Pd/SiOx) interface at room temperature by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Solid-state amorphization was stimulated without the electron knock-on effects. The total dose required for the solid-state amorphization decreases with decreasing acceleration voltage. This is the first report on electron irradiation induced metallic amorphous formation caused by the electronic excitation at metal/silicon oxide interface.

  5. Fast Responsive Gas Sensor of Vertically Aligned Fluorine-Doped Tin Oxide Nanorod Thin Film

    NASA Astrophysics Data System (ADS)

    Cho, Chan-Woo; Lee, Jong-Heun; Riu, Doh-Hyung; Kim, Chang-Yeoul

    2012-04-01

    We prepared fluorine-doped tin oxide (FTO) nanorod films and a conventional FTO thin film for the application of a semiconducting gas sensor by spray pyrolysis method. The lengths of FTO nanorods (FTON, 100 and 500 nm) were controlled by changing deposition times, and FTO thin film (FTOT) was also prepared as a reference. The gas sensitivity test shows FTON with long nanorods had higher sensitivity for both hydrogen and ethanol gases but slow response and recovery times, despite an advantage of the higher gas sensitivity. FTO nanorod film with short length about 100 nm showed relatively lower sensitivity, but fast gas response and recovery characteristics. The fast response and recovery for the analyte gases are attributed to the conductance of FTO nanorods, which is closely related to the diameter and length of nanorods.

  6. Optical and structural characterization of thermal oxidation effects of erbium thin films deposited by electron beam on silicon

    SciTech Connect

    Kamineni, Himani S.; Kamineni, Vimal K.; Moore, Richard L.; Gallis, Spyros; Diebold, Alain C.; Huang Mengbing; Kaloyeros, Alain E.

    2012-01-01

    Thermal oxidation effects on the structural, compositional, and optical properties of erbium films deposited on silicon via electron beam evaporation were analyzed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and spectroscopic ellipsometry. A gradual rise in oxidation temperature from 700 to 900 deg. C resulted in a transition from ErO- to Er{sub 2}O{sub 3}-rich phase. Additional increase in oxidation temperature above 1000 deg. C led to the formation of erbium silicate due to further oxygen incorporation, as well as silicon out-diffusion from the substrate. A silicon oxide interfacial layer was also detected, with its thickness increasing with higher oxidation temperature. Additionally, film refractive index decreased, while its Tauc bandgap value increased from {approx}5.2 eV to {approx}6.4 eV, as the oxidation temperature was raised from 700 deg. C to above 900 deg. C. These transformations were accompanied by the appearance of an intense and broad absorption band below the optical gap. Thermal oxidation effects are discussed in the context of film structural characteristics and defect states.

  7. The preparation and characterization of highly aligned poly(epsilon-caprolactone)/poly ethylene oxide/chitosan ultrafine fiber for the application to tissue scaffold.

    PubMed

    Nien, Yu-Hsun; Wang, Jia-Yi; Tsai, Yan-Sheng

    2013-07-01

    The purpose of this study was to fabricate poly(epsilon-caprolactone) (PCL)/poly ethylene oxid (PEO)/chitosan (CS) ultrafine fiber in both aligned and random structures using electrospinning technique and their process parameters were optimized. The aligned and random PCL/PEO/chitosan ultrafine fibers were also used as scaffold for tissue engineering and their cell affinity was investigated. In the first part, we inspected the effect of environment conditions, solution properties, process parameters on PCL/PEO/chitosan ultrafine fiber. In the second part, the apparatus of electrospinning to manufacture highly aligned PCL/PEO/chitosan ultrafine fiber was developed. The effects of process parameters such as flow rate, design of collector and rotation speed of collecting drum on the morphology of ultrafine fiber were discussed. In addition, the cross link of PCL/PEO/chitosan ultrafine fiber by cross-linking agent was examined, too. The physical properties, chemical properties, and cell affinities of the aligned PCL/PEO/chitosan ultrafine fiber with or without cross link were measured. The chemical analysis and tensile strength of the ultrafine fiber were characterized using Fourier Transfer Infared Spectrophotometer and Universal Tensile Machine, respectively. The results show that the aligned PCL/PEO/chitosan ultrafine fibrous mat had the capacity to induce cellular alignment and enhance cellular elongation. PMID:23901493

  8. Design, microstructure, and high-temperature behavior of silicon nitride sintered with rate-earth oxides

    SciTech Connect

    Ciniculk, M.K. . Dept. of Materials Science and Mineral Engineering)

    1991-08-01

    The processing-microstructure-property relations of silicon nitride ceramics sintered with rare-earth oxide additives have been investigated with the aim of improving their high-temperature behavior. The additions of the oxides of Y, Sm, Gd, Dy, Er, or Yb were compositionally controlled to tailor the intergranular phase. The resulting microstructure consisted of {beta}-Si{sub 3}N{sub 4} grains and a crystalline secondary phase of RE{sub 2}Si{sub 2}O{sub 7}, with a thin residual amorphous phase present at grain boundaries. The lanthanide oxides were found to be as effective as Y{sub 2}O{sub 3} in densifying Si{sub 3}N{sub 4}, resulting in identical microstructures. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a residual amorphous, observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification. The low resistance to oxidation of these materials was attributed to the minimization of amorphous phases via devitrification to disilicates, compatible with SiO{sub 2}, the oxidation product of Si{sub 3}N{sub 4}. The strength retention of these materials at 1300{degrees}C was found to be between 80% and 91% of room-temperature strength, due to crystallization of the secondary phase and a residual but refractory amorphous grain-boundary phase. The creep behavior was found to be strongly dependent on residual amorphous phase viscosity as well as on the oxidation behavior, as evidenced by the nonsteady-state creep rates of all materials. 122 refs., 51 figs., 12 tabs.

  9. Behavior of incorporated nitrogen in plasma-nitrided silicon oxide formed by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Shinoda, Nao; Itokawa, Hiroshi; Fujitsuka, Ryota; Sekine, Katsuyuki; Onoue, Seiji; Tonotani, Junichi

    2016-04-01

    The behavior of nitrogen (N) atoms in plasma-nitrided silicon oxide (SiO2) formed by chemical vapor deposition (CVD) was characterized by physical analysis and from electrical properties. The changes in the chemical bonding and distribution of N in plasma-nitrided SiO2 were investigated for different subsequent processes. N-Si3, N-Si2O, and N2 are formed in a SiO2 film by plasma nitridation. N2 molecules diffuse out during annealing at temperatures higher than 900 °C. NH species are generated from N2 molecules and H in the SiO2 film with subsequent oxide deposition using O3 as an oxidant. The capacitance-voltage (C-V) curves of metal-oxide-semiconductor (MOS) capacitors are obtained. The negative shift of the C-V curve is caused by the increase in the density of positive fix charge traps in CVD-SiO2 induced by plasma nitridation. The C-V curve of plasma-nitrided SiO2 subjected to annealing shifts to the positive direction and that subjected to the subsequent oxide deposition shifts markedly to the negative direction. It is clarified that the density of positive charge fixed traps in plasma-nitrided SiO2 films decrease because the amount of N2 molecules is decreased by annealing, and that the density of traps increases because NH species are generated and move to the interface between SiO2 and the Si substrate with the subsequent oxide deposition.

  10. Effective Infiltration of Gel Polymer Electrolyte into Silicon-Coated Vertically Aligned Carbon Nanofibers as Anodes for Solid-State Lithium-Ion Batteries.

    PubMed

    Pandey, Gaind P; Klankowski, Steven A; Li, Yonghui; Sun, Xiuzhi Susan; Wu, Judy; Rojeski, Ronald A; Li, Jun

    2015-09-23

    This study demonstrates the full infiltration of gel polymer electrolyte into silicon-coated vertically aligned carbon nanofibers (Si-VACNFs), a high-capacity 3D nanostructured anode, and the electrochemical characterization of its properties as an effective electrolyte/separator for future all-solid-state lithium-ion batteries. Two fabrication methods have been employed to form a stable interface between the gel polymer electrolyte and the Si-VACNF anode. In the first method, the drop-casted gel polymer electrolyte is able to fully infiltrate into the open space between the vertically aligned core-shell nanofibers and encapsulate/stabilize each individual nanofiber in the polymer matrix. The 3D nanostructured Si-VACNF anode shows a very high capacity of 3450 mAh g(-1) at C/10.5 (or 0.36 A g(-1)) rate and 1732 mAh g(-1) at 1C (or 3.8 A g(-1)) rate. In the second method, a preformed gel electrolyte film is sandwiched between an Si-VACNF electrode and a Li foil to form a half-cell. Most of the vertical core-shell nanofibers of the Si-VACNF anode are able to penetrate into the gel polymer film while retaining their structural integrity. The slightly lower capacity of 2800 mAh g(-1) at C/11 rate and ∼1070 mAh g(-1) at C/1.5 (or 2.6 A g(-1)) rate have been obtained, with almost no capacity fade for up to 100 cycles. Electrochemical impedance spectroscopy does not show noticeable changes after 110 cycles, further revealing the stable interface between the gel polymer electrolyte and the Si-VACNFs anode. These results show that the infiltrated flexible gel polymer electrolyte can effectively accommodate the stress/strain of the Si shell due to the large volume expansion/contraction during the charge-discharge processes, which is particularly useful for developing future flexible solid-state lithium-ion batteries incorporating Si-anodes. PMID:26325385

  11. Fabrication, strength and oxidation of molybdenum-silicon-boron alloys from reaction synthesis

    NASA Astrophysics Data System (ADS)

    Middlemas, Michael Robert

    Mo-Si-B alloys are a leading candidate for the next generation of jet turbine engine blades and have the potential to raise the operating temperatures by 300-400°C, which would dramatically increase power and efficiency. The alloys of interest are a three-phase mixture of the molybdenum solid solution (Moss) and two intermetallic phases, Mo3Si (A15) and Mo5SiB2 (T2). A novel powder metallurgical method was developed which uses the reaction of molybdenum, silicon nitride (Si3N4) and boron nitride (BN) powders to synthesize a fine dispersion of the intermetallic phases in a Moss matrix. The covalent nitrides are stable in oxidizing environments up to 1000ºC, allowing for fine particle processing without the formation of silicon and boron oxides. The process developed uses standard powder processing techniques to create Mo-Si-B alloys in a less complex and expensive manner than previously demonstrated. The formation of the intermetallic phases was examined by thermo-gravimetric analysis and x-ray diffraction. The start of the reactions to form the T2 and A15 phases were observed at 1140°C and 1193°C and the reactions have been demonstrated to be complete in as little as two hours at 1300°C. This powder metallurgy approach yields a fine dispersion of intermetallics in the Moss matrix, with average grain sizes of 2-4mum. Densities up to 95% of theoretical were attained from pressureless sintering at 1600°C and full theoretical density was achieved by hot-isostatic pressing (HIP). Low temperature sintering and HIPing was attempted to limit grain growth and to reduce the equilibrium silicon concentration in the Moss matrix. Sintering and HIPing at 1300°C reduced the grain sizes of all three phases by over a factor of two. Powder metallurgy provides an opportunity for microstructure control through changes in raw materials and processing parameters. Microstructure examination by electron back-scatter diffraction (EBSD) imaging was used to precisely define the

  12. Band Alignment at Molybdenum Disulphide/Boron Nitride/Aluminum Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    DiStefano, Jennifer; Lin, Yu-Chuan; Robinson, Joshua; Glavin, Nicholas R.; Voevodin, Andrey A.; Brockman, Justin; Kuhn, Markus; French, Benjamin; King, Sean W.

    2016-02-01

    To facilitate the design of future heterostructure devices employing two-dimensional (2D) materials such as molybdenum disulphide (MoS2) and hexagonal/sp2 boron nitride (BN), x-ray photoelectron spectroscopy (XPS) has been utilized to determine the valence band offset (VBO) present at interfaces formed between these materials. For MoS2 grown on a pulsed laser-deposited amorphous BN (a-BN) layer with sp2 bonding, the VBO was determined to be 1.4 ± 0.2 eV. Similarly, the VBO between the a-BN layer and the aluminum oxide (Al2O3) substrate was determined to be 1.1 ± 0.2 eV. Using the bandgaps established in the literature for MoS2, h-BN, and Al2O3, the conduction band offsets (CBOs) at the MoS2/a-BN and a-BN/Al2O3 interfaces were additionally calculated to be 3.3 ± 0.2 and 1.7 ± 0.2 eV, respectively. The resulting large VBOs and CBOs indicate BN and Al2O3 are attractive gate dielectrics and substrates for future 2D MoS2 devices.

  13. Facile synthesis of binder-free reduced graphene oxide/silicon anode for high-performance lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Zuo, Pengjian; Chen, Cheng; Ma, Yulin; Cheng, Xinqun; Du, Chunyu; Gao, Yunzhi; Yin, Geping

    2016-04-01

    A novel binder-free reduced graphene oxide/silicon (RGO/Si) composite anode has been fabricated by a facile doctor-blade coating method. The relatively low C/O ratio plays an important role for the fabrication of the bind-free multilayered RGO/Si electrode with silicon nanoparticles encapsulating among the RGO sheet layers. The RGO provides the electron transport pathway and prevents the electrode fracture caused by the volume changes of active silicon particles during cycling. The RGO/Si composite anode with a silicon content of 66.7% delivers a reversible capacity of 1931 mAh g-1 at 0.2 A g-1 and still remains 92% of the initial capacity after 50 cycles.

  14. Numerically controlled atmospheric-pressure plasma sacrificial oxidation using electrode arrays for improving silicon-on-insulator layer uniformity

    NASA Astrophysics Data System (ADS)

    Takei, Hiroyasu; Yoshinaga, Keinosuke; Matsuyama, Satoshi; Yamauchi, Kazuto; Sano, Yasuhisa

    2015-01-01

    Silicon-on-insulator (SOI) wafers are important semiconductor substrates in high-performance devices. In accordance with device miniaturization requirements, ultrathin and highly uniform top silicon layers (SOI layers) are required. A novel method involving numerically controlled (NC) atmospheric-pressure plasma sacrificial oxidation using an electrode array system was developed for the effective fabrication of an ultrathin SOI layer with extremely high uniformity. Spatial resolution and oxidation properties are the key factors controlling ultraprecision machining. The controllability of plasma oxidation and the oxidation properties of the resulting experimental electrode array system were examined. The results demonstrated that the method improved the thickness uniformity of the SOI layer over one-sixth of the area of an 8-in. wafer area.

  15. High performance of graphene oxide-doped silicon oxide-based resistance random access memory

    PubMed Central

    2013-01-01

    In this letter, a double active layer (Zr:SiO x /C:SiO x ) resistive switching memory device with outstanding performance is presented. Through current fitting, hopping conduction mechanism is found in both high-resistance state (HRS) and low-resistance state (LRS) of double active layer RRAM devices. By analyzing Raman and FTIR spectra, we observed that graphene oxide exists in C:SiO x layer. Compared with single Zr:SiO x layer structure, Zr:SiO x /C:SiO x structure has superior performance, including low operating current, improved uniformity in both set and reset processes, and satisfactory endurance characteristics, all of which are attributed to the double-layer structure and the existence of graphene oxide flakes formed by the sputter process. PMID:24261454

  16. High performance of graphene oxide-doped silicon oxide-based resistance random access memory.

    PubMed

    Zhang, Rui; Chang, Kuan-Chang; Chang, Ting-Chang; Tsai, Tsung-Ming; Chen, Kai-Huang; Lou, Jen-Chung; Chen, Jung-Hui; Young, Tai-Fa; Shih, Chih-Cheng; Yang, Ya-Liang; Pan, Yin-Chih; Chu, Tian-Jian; Huang, Syuan-Yong; Pan, Chih-Hung; Su, Yu-Ting; Syu, Yong-En; Sze, Simon M

    2013-01-01

    In this letter, a double active layer (Zr:SiOx/C:SiOx) resistive switching memory device with outstanding performance is presented. Through current fitting, hopping conduction mechanism is found in both high-resistance state (HRS) and low-resistance state (LRS) of double active layer RRAM devices. By analyzing Raman and FTIR spectra, we observed that graphene oxide exists in C:SiOx layer. Compared with single Zr:SiOx layer structure, Zr:SiOx/C:SiOx structure has superior performance, including low operating current, improved uniformity in both set and reset processes, and satisfactory endurance characteristics, all of which are attributed to the double-layer structure and the existence of graphene oxide flakes formed by the sputter process. PMID:24261454

  17. Silicon nanowire oxidation: the influence of sidewall structure and gold distribution

    NASA Astrophysics Data System (ADS)

    Sivakov, V. A.; Scholz, R.; Syrowatka, F.; Falk, F.; Gösele, U.; Christiansen, S. H.

    2009-10-01

    The oxidation behavior of Si nanowires (SiNWs) grown by the gold (Au) catalyzed vapor-liquid-solid (VLS) growth process in an electron beam evaporation (EBE) reactor is studied. The VLS SiNWs exhibit hexagonal shape with essentially {112} facets where each facet shows a saw-tooth faceting itself, consisting of alternating {111} and {113} facets. Depending on growth temperatures (450-750 °C) and evaporation currents (40-80 mA) that determine the silicon vapor supply, this facet formation is more or less pronounced. The diffusion of Au atoms on the faceted SiNW surfaces and the formation of Au nanoparticles on the SiNW facets during growth and during ex situ annealing are studied. Upon diffusion, the Au atoms agglomerate and form Au nanoparticles that preferably arrange themselves on {113} facets. Upon annealing in air at temperatures between 800 and 950 °C the gold nanoparticles agglomerate further and form bigger particles of a few tens of nm in diameter that reside at the interface between the growing silica (SiO2) layer and the SiNW itself, which in turn shrinks during SiNW oxidation. The oxide layer thickness and the oxide appearance depend on the annealing conditions (time and temperature) and systematically varied oxidation processing is described in this paper as investigated by cross-sectional transmission electron microscopy (TEM) including high resolution studies as well as scanning electron microscopy (SEM) studies. Our results strongly suggest that the SiNWs can be fully oxidized, thus forming silica NWs that can either keep their initial shape or, under certain annealing conditions, do not keep their initial wire shape but assume a bamboo-like shape that forms most likely as a result of locally high stresses that are related to nanocrack formation. The nanocracks form in the growing oxide layer mediated by the presence of Au nanoparticles that yield gold-enhanced SiNW oxidation and thus a faster oxidation rate.

  18. Silicon oxynitride films deposited by reactive high power impulse magnetron sputtering using nitrous oxide as a single-source precursor

    SciTech Connect

    Hänninen, Tuomas Schmidt, Susann; Jensen, Jens; Hultman, Lars; Högberg, Hans

    2015-09-15

    Silicon oxynitride thin films were synthesized by reactive high power impulse magnetron sputtering of silicon in argon/nitrous oxide plasmas. Nitrous oxide was employed as a single-source precursor supplying oxygen and nitrogen for the film growth. The films were characterized by elastic recoil detection analysis, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray reflectivity, scanning electron microscopy, and spectroscopic ellipsometry. Results show that the films are silicon rich, amorphous, and exhibit a random chemical bonding structure. The optical properties with the refractive index and the extinction coefficient correlate with the film elemental composition, showing decreasing values with increasing film oxygen and nitrogen content. The total percentage of oxygen and nitrogen in the films is controlled by adjusting the gas flow ratio in the deposition processes. Furthermore, it is shown that the film oxygen-to-nitrogen ratio can be tailored by the high power impulse magnetron sputtering-specific parameters pulse frequency and energy per pulse.

  19. Dielectric tunability of vertically aligned ferroelectric-metal oxide nanocomposite films controlled by out-of-plane misfit strain

    NASA Astrophysics Data System (ADS)

    Wu, Huaping; Ma, Xuefu; Zhang, Zheng; Zhu, Jun; Wang, Jie; Chai, Guozhong

    2016-04-01

    A nonlinear thermodynamic model based on the vertically aligned nanocomposite (VAN) thin films of ferroelectric-metal oxide system has been developed to investigate the physical properties of the epitaxial Ba0.6Sr0.4TiO3 (BST) films containing vertical Sm2O3 (SmO) nanopillar arrays on the SrTiO3 substrate. The phase diagrams of out-of-plane lattice mismatch vs. volume fraction of SmO are calculated by minimizing the total free energy. It is found that the phase transformation and dielectric response of BST-SmO VAN systems are extremely dependent on the in-plane misfit strain, the out-of-plane lattice mismatch, the volume fraction of SmO phase, and the external electric field applied to the nanocomposite films at room temperature. In particular, the BST-SmO VAN systems exhibit higher dielectric properties than pure BST films. Giant dielectric response and maximum tunability are obtained near the lattice mismatch where the phase transition occurs. Under the in-plane misfit strain of umf=0.3 % and the out-of-plane lattice mismatch of u3=0.002 , the dielectric tunability can be dramatically enhanced to 90% with the increase of SmO volume fraction, which is well consistent with previous experimental results. This work represents an approach to further understand the dependence of physical properties on the lattice mismatch (in-plane and out-of-plane) and volume fraction, and to manipulate or optimize functionalities in the nanocomposite oxide thin films.

  20. Magnetically aligned iron oxide/gold nanoparticle-decorated carbon nanotube hybrid structure as a humidity sensor.

    PubMed

    Lee, Jaewook; Mulmi, Suresh; Thangadurai, Venkataraman; Park, Simon S

    2015-07-22

    Functionalized carbon nanotubes (f-CNTs), particularly CNTs decorated with nanoparticles (NPs), are of great interest because of their synergic effects, such as surface-enhanced Raman scattering, plasmonic resonance energy transfer, magnetoplasmonic, magnetoelectric, and magnetooptical effects. In general, research has focused on a single type of NP, such as a metal or metal oxide, that has been modified on a CNT surface. In this study, however, a new strategy is introduced for the decoration of two different NP types on CNTs. In order to improve the functionality of modified CNTs, we successfully prepared binary NP-decorated CNTs, namely, iron oxide/gold (Au) NP-decorated CNTs (IA-CNTs), which were created through two simple reactions in deionized water, without high temperature, high pressure, or harsh reducing agents. The physicochemical properties of IA-CNTs were characterized by ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, a superconducting quantum interference device, scanning electron microscopy, and transmission electron microscopy. In this study, IA-CNTs were utilized to detect humidity. Magnetic IA-CNTs were aligned on interdigitated platinum electrodes under external magnetic fields to create a humidity-sensing channel, and its electrical conductivity was monitored. As the humidity increased, the electrical resistance of the sensor also increased. In comparison with various gases, for example, H2, O2, CO, CO2, SO2, and dry air, the IA-CNT-based humidity sensor exhibited high-selectivity performances. IA-CNTs also responded to heavy water (D2O), and it was established that the humidity detection mechanism had D2O-sensing capabilities. Further, the humidity from human out-breathing was also successfully detected by this system. In conclusion, these unique IA-CNTs exhibited potential application as gas detection materials. PMID:26112318

  1. Characterization of Interface State in Silicon Carbide Metal Oxide Semiconductor Capacitors

    NASA Astrophysics Data System (ADS)

    Kao, Wei-Chieh

    Silicon carbide (SiC) has always been considered as an excellent material for high temperature and high power devices. Since SiC is the only compound semiconductor whose native oxide is silicon dioxide (SiO2), it puts SiC in a unique position. Although SiC metal oxide semiconductor (MOS) technology has made significant progress in recent years, there are still a number of issues to be overcome before more commercial SiC devices can enter the market. The prevailing issues surrounding SiC MOSFET devices are the low channel mobility, the low quality of the oxide layer and the high interface state density at the SiC/SiO2 interface. Consequently, there is a need for research to be performed in order to have a better understanding of the factors causing the poor SiC/SiO2 interface properties. In this work, we investigated the generation lifetime in SiC materials by using the pulsed metal oxide semiconductor (MOS) capacitor method and measured the interface state density distribution at the SiC/SiO2 interface by using the conductance measurement and the high-low frequency capacitance technique. These measurement techniques have been performed on n-type and p-type SiC MOS capacitors. In the course of our investigation, we observed fast interface states at semiconductor-dielectric interfaces in SiC MOS capacitors that underwent three different interface passivation processes, such states were detected in the nitrided samples but not observed in PSG-passivated samples. This result indicate that the lack of fast states at PSG-passivated interface is one of the main reasons for higher channel mobility in PSG MOSFETs. In addition, the effect of mobile ions in the oxide on the response time of interface states has been investigated. In the last chapter we propose additional methods of investigation that can help elucidate the origin of the particular interface states, enabling a more complete understanding of the SiC/SiO2 material system.

  2. Metal Oxide Induced Charge Transfer Doping and Band Alignment of Graphene Electrodes for Efficient Organic Light Emitting Diodes

    PubMed Central

    Meyer, Jens; Kidambi, Piran R.; Bayer, Bernhard C.; Weijtens, Christ; Kuhn, Anton; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Robertson, John; Hofmann, Stephan

    2014-01-01

    The interface structure of graphene with thermally evaporated metal oxide layers, in particular molybdenum trioxide (MoO3), is studied combining photoemission spectroscopy, sheet resistance measurements and organic light emitting diode (OLED) characterization. Thin (<5 nm) MoO3 layers give rise to an 1.9 eV large interface dipole and a downwards bending of the MoO3 conduction band towards the Fermi level of graphene, leading to a near ideal alignment of the transport levels. The surface charge transfer manifests itself also as strong and stable p-type doping of the graphene layers, with the Fermi level downshifted by 0.25 eV and sheet resistance values consistently below 50 Ω/sq for few-layer graphene films. The combination of stable doping and highly efficient charge extraction/injection allows the demonstration of simplified graphene-based OLED device stacks with efficiencies exceeding those of standard ITO reference devices. PMID:24946853

  3. Ultra-violet Sensing Characteristic and Field Emission Properties of Vertically Aligned Aluminum Doped Zinc Oxide Nanorod Arrays

    SciTech Connect

    Mamat, M. H.; Malek, M. F.; Musa, M. Z.; Khusaimi, Z.; Rusop, M.

    2011-05-25

    Ultra-violet (UV) sensing behavior and field emission characteristic have been investigated on vertically aligned aluminum (Al) doped zinc oxide (ZnO) nanorod arrays prepared using sol-gel immersion method. Uniform and high coverage density of ZnO nanorod arrays have been successfully deposited on seeded-catalyst coated substrates. The synthesized nanorods have diameter sizes between 50 nm to 150 nm. The XRD spectra show Al doped ZnO nanorod array has high crystallinity properties with the dominancy of crystal growth along (002) plane or c-axis. UV photoresponse measurement indicates that Al doped ZnO nanorod array sensitively detects UV light as shown by conductance increment after UV illumination exposure. The nanorod array shows good field emission properties with low turn on field and threshold field at 2.1 V/{mu}m and 5.6 V/{mu}m, respectively. The result suggested that Al doped ZnO nanorod arrays prepared by low-cost sol-gel immersion method show promising result towards fabrication of multi applications especially in UV photoconductive sensor and field emission displays.

  4. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

    PubMed Central

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T.; Shinde, Dhanraj B.; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-01-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30–40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71±5 l m−2 hr−1 bar−1 for 150±15 nm thick membranes). PMID:26947916

  5. Energy level alignment of electrically doped hole transport layers with transparent and conductive indium tin oxide and polymer anodes

    NASA Astrophysics Data System (ADS)

    Fehse, Karsten; Olthof, Selina; Walzer, Karsten; Leo, Karl; Johnson, Robert L.; Glowatzki, Hendrik; Bröker, Benjamin; Koch, Norbert

    2007-10-01

    Using ultraviolet photoemission spectroscopy, we investigated the energy level alignment at the interfaces of typical anodes used in organic electronics, indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), with the oligomeric hole transport material N ,N,N',N'-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD), and studied the influence of electrical interface doping by the strong electron acceptor tetrafluoro tetracyanoquinodimethane (F4-TCNQ). The fundamentally different anode materials with work functions of 4.40eV (ITO) and 4.85eV (PEDOT:PSS) show different hole injection barriers, which also depend on the thickness of the F4-TCNQ interface dopant layer. PEDOT:PSS anodes exhibit a consistently lower hole injection barrier to MeO-TPD compared to ITO by 0.1eV. We attribute this low hole injection barrier to additional charge transfer reactions at the PEDOT:PSS/MeO-TPD interface. In contrast, the deposition of the electron acceptor at the interface helps significantly to lower the hole injection barrier for ITO anodes.

  6. Demonstration of nitric oxide on asbestos and silicon carbide fibers with a new ultraviolet spectrophotometric assay.

    PubMed Central

    Leanderson, P; Lagesson, V; Tagesson, C

    1997-01-01

    Nitric oxide (NO) has a number of important functions in biological systems and may play a role in the toxicity of mineral fibers. We investigated whether NO might be present on the surface of mineral fibers and if crocidolite could adsorb NO from NO gas or cigarette smoke. NO was determined with a new gas chromatography-ultraviolet spectrophotometric technique after thermal desorption from the fiber surface and injection in a gas flow cell. NO was found in different amounts on chrysotile B, crocidolite, amosite, and silicon carbide whiskers. There was a strong correlation between the amount of NO and the specific surface area of these fibers (r = 0.98). NO could not be demonstrated on rockwool fibers [man-made vitreous fiber(s) (MMVF)21 and MMVF22] or silicon nitride whiskers. NO on crocidolite, amosite, and silicon carbide whiskers was readily desorbed from the fibers at increased temperature, while NO on chrysotile B seemed to be more firmly adsorbed to the fiber and required a longer period of time to be desorbed. The amount of NO bound to crocidolite increased from 34 micrograms/g fiber to 85 and 474 micrograms/g after exposing the fibers to cigarette smoke and NO gas, respectively. These findings indicate that a) NO adsorbs to fiber surfaces, b) some fibers adsorb more NO than others, c) some fibers adsorb NO more strongly than others, and d) the amounts of NO on fibers may be increased after exposure of the fiber to cigarette smoke or other sources of NO. The biological significance of NO on mineral fibers remains to be investigated. Images Figure 3. PMID:9400696

  7. Tunnel oxide passivated contacts formed by ion implantation for applications in silicon solar cells

    NASA Astrophysics Data System (ADS)

    Reichel, Christian; Feldmann, Frank; Müller, Ralph; Reedy, Robert C.; Lee, Benjamin G.; Young, David L.; Stradins, Paul; Hermle, Martin; Glunz, Stefan W.

    2015-11-01

    Passivated contacts (poly-Si/SiOx/c-Si) doped by shallow ion implantation are an appealing technology for high efficiency silicon solar cells, especially for interdigitated back contact (IBC) solar cells where a masked ion implantation facilitates their fabrication. This paper presents a study on tunnel oxide passivated contacts formed by low-energy ion implantation into amorphous silicon (a-Si) layers and examines the influence of the ion species (P, B, or BF2), the ion implantation dose (5 × 1014 cm-2 to 1 × 1016 cm-2), and the subsequent high-temperature anneal (800 °C or 900 °C) on the passivation quality and junction characteristics using double-sided contacted silicon solar cells. Excellent passivation quality is achieved for n-type passivated contacts by P implantations into either intrinsic (undoped) or in-situ B-doped a-Si layers with implied open-circuit voltages (iVoc) of 725 and 720 mV, respectively. For p-type passivated contacts, BF2 implantations into intrinsic a-Si yield well passivated contacts and allow for iVoc of 690 mV, whereas implanted B gives poor passivation with iVoc of only 640 mV. While solar cells featuring in-situ B-doped selective hole contacts and selective electron contacts with P implanted into intrinsic a-Si layers achieved Voc of 690 mV and fill factor (FF) of 79.1%, selective hole contacts realized by BF2 implantation into intrinsic a-Si suffer from drastically reduced FF which is caused by a non-Ohmic Schottky contact. Finally, implanting P into in-situ B-doped a-Si layers for the purpose of overcompensation (counterdoping) allowed for solar cells with Voc of 680 mV and FF of 80.4%, providing a simplified and promising fabrication process for IBC solar cells featuring passivated contacts.

  8. Functionalization of oxidized silicon surfaces with methyl groups and their characterization

    NASA Astrophysics Data System (ADS)

    Schmohl, A.; Khan, A.; Hess, P.

    2004-07-01

    Oxidized silicon surfaces were functionalized with chemically bonded methyl end groups and characterized by means of Fourier transform infrared (FTIR) spectroscopy with the attenuated total reflection (ATR) method, contact angle measurements, scanning force microscopy (SFM), and thermal desorption spectroscopy (TDS). Detailed results are presented for trimethylsilyl (TMS) and pentamethyldisilyl (PMDS) terminated surfaces, which were prepared by silanization with suitable chloro compounds. The IR spectra of the TMS-terminated surface exhibit two CH stretching peaks at 2904 and 2963 cm -1. In the thermal desorption experiments desorption of trimethylsilanol and methane was observed at 550 ∘C. The IR spectra of the PMDS-terminated surface show two CH stretching peaks at 2898 and 2955 cm -1. The thermal desorption spectra indicate cleavage of Si-Si bonds and desorption of trimethylsilane at 530 ∘C. The wetting behavior, adhesion, and mechanical properties were studied by contact angle measurements and SFM. The results are compared with the well-defined Si(111)-(1×1):H surface and a self-assembled monolayer (SAM) on a silicon surface with long hydrocarbon chains, prepared with octadecyltrichlorosilane (OTS, H 3C(CH 2) 17SiCl 3). The water contact angle was 82 ∘ for TMS and 85 ∘ for PMDS end groups. The friction forces measured for the TMS- and PMDS-terminated surfaces were comparable and about 3 times higher than that of the H-terminated silicon and the OTS-SAM surface. The corresponding friction coefficients were 0.17, 0.18, 0.34, and 0.45 for Si(111)-(1×1):H, OTS SAM, TMS, and PMDS surfaces, respectively.

  9. Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films

    NASA Astrophysics Data System (ADS)

    Cao, Zhiqiang; Zhang, Xin

    2004-10-01

    The structural relaxation of plasma-enhanced chemical-vapor-deposited (PECVD) silane-based silicon oxide films during thermal cycling and annealing has been studied using wafer curvature measurements. These measurements, which determine stress in the amorphous silicon oxide films, are sensitive to both plastic deformation and density changes. A quantitative case study of such changes has been done based upon the experimental results. A microstructure-based mechanism elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then used to explain a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD silicon oxide films with a thickness varying from 1to40μm were studied, as certain demanding applications in microelectromechanical systems require such thick films serving as heat/electrical insulation layers.

  10. Aluminum-natural oxide-P type silicon /MIS/ solar cells

    NASA Astrophysics Data System (ADS)

    Badura, E.; Zdanowicz, W.

    1980-12-01

    MIS (metal-interfacial region-semiconductor) solar cells are attractive because of their relatively high conversion efficiency. Their performance, however, is strongly affected by device preparation. Two methods are described for preparing Al - natural SiO - p-type Si cells which exhibit high photovoltaic values. The first, involving a 'nonsintered oxide' process, entails etching the active silicon surfaces in HF acid and exposing them to air at room temperature for 48 hours. The second method differs from the first only in that it requires the additional step of sintering the oxidized surfaces in a vacuum at about 500 C. In both cases, a semitransparent Al film is then applied to the oxide, after which an Al grid electrode and 70-nm SiOx antireflection coatings are deposited on the device. Measured against both the nonsintered cell and the Schottky barrier cell, the sintered assembly shows the highest open-circuit voltage (0.46-0.492), the highest fill factor (0.66-0.73), and the most efficient dark parameters.

  11. Silicon dioxide nanoparticles increase macrophage atherogenicity: Stimulation of cellular cytotoxicity, oxidative stress, and triglycerides accumulation.

    PubMed

    Petrick, Lauren; Rosenblat, Mira; Paland, Nicole; Aviram, Michael

    2016-06-01

    Nanoparticle research has focused on their toxicity in general, while increasing evidence points to additional specific adverse effects on atherosclerosis development. Arterial macrophage cholesterol and triglyceride (TG) accumulation and foam cell formation are the hallmark of early atherogenesis, leading to cardiovascular events. To investigate the in vitro atherogenic effects of silicon dioxide (SiO2 ), J774.1 cultured macrophages (murine cell line) were incubated with SiO2 nanoparticle (SP, d = 12 nm, 0-20 µg/mL), followed by cellular cytotoxicity, oxidative stress, TG and cholesterol metabolism analyses. A significant dose-dependent increase in oxidative stress (up to 164%), in cytotoxicity (up to 390% measured by lactate dehydrogenase (LDH) release), and in TG content (up to 63%) was observed in SiO2 exposed macrophages compared with control cells. A smaller increase in macrophage cholesterol mass (up to 22%) was noted. TG accumulation in macrophages was not due to a decrease in TG cell secretion or to an increased TG biosynthesis rate, but was the result of attenuated TG hydrolysis secondary to decreased lipase activity and both adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) protein expression (by 42 and 25%, respectively). Overall, SPs showed pro-atherogenic effects on macrophages as observed by cytotoxicity, increased oxidative stress and TG accumulation. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 713-723, 2016. PMID:25448404

  12. Hot-pressed silicon nitride with various lanthanide oxides as sintering additives

    NASA Technical Reports Server (NTRS)

    Ueno, K.; Toibana, Y.

    1984-01-01

    The effects of addition of various lanthanide oxides and their mixture with Y2O3 on the sintering of Si3N4 were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si3N4 in hot-pressing at 1800 C under 300-400kg/ centimeters squared for 60 min. The crystallization of yttrium and lanthanide-silicon oxynitrides which was observed inn the sintered body containing yttrium-lanthanide mixed oxides as additives led to the formation of a highly refractory Si3N4 ceramic having a bending strength of 82 and 84 kg/millimeters squared at room temperature and 1300 C respectively. In a Y2O3+La2O3 system, a higher molar ratio of La2O3 to Y2O3 gave a higher hardness and strength at high temperatures. It was found that 90 min was an optimum sintering time for the highest strength.

  13. Electronic passivation of silicon surfaces by thin films of atomic layer deposited gallium oxide

    SciTech Connect

    Allen, T. G. Cuevas, A.

    2014-07-21

    This paper proposes the application of gallium oxide (Ga{sub 2}O{sub 3}) thin films to crystalline silicon solar cells. Effective passivation of n- and p-type crystalline silicon surfaces has been achieved by the application of very thin Ga{sub 2}O{sub 3} films prepared by atomic layer deposition using trimethylgallium (TMGa) and ozone (O{sub 3}) as the reactants. Surface recombination velocities as low as 6.1 cm/s have been recorded with films less than 4.5 nm thick. A range of deposition parameters has been explored, with growth rates of approximately 0.2 Å/cycle providing optimum passivation. The thermal activation energy for passivation of the Si-Ga{sub 2}O{sub 3} interface has been found to be approximately 0.5 eV. Depassivation of the interface was observed for prolonged annealing at increased temperatures. The activation energy for depassivation was measured to be 1.9 eV.

  14. Damp and dry heat degradation of thermal oxide passivation of p+ silicon

    NASA Astrophysics Data System (ADS)

    Thomson, Andrew; Gardner, Matthew; McIntosh, Keith; Shalav, Avi; Bullock, James

    2014-03-01

    Thermal SiO2 passivates both moderately and heavily doped silicon surfaces irrespective of the dopant type, which is advantageous in high-efficiency solar cell designs. Commercial photovoltaic cells are submitted to accelerated ageing tests, such as damp-heat exposure, to ensure they maintain their performance for at least 20 yr. We find damp-heat exposure causes a severe and rapid degradation of thermal SiO2 passivation on p+ silicon surfaces. The reaction is so severe that the diffused-region recombination in the degraded state is limited by the diffusion of minority carriers to the Si-SiO2 interface not the density of interface defects Dit. Certainly, this effect renders the thermal-oxide passivation useless if employed on a solar cell. To study the cause of the degradation, we also test the effects of storage in dry heat and room ambient conditions. Examination of the rate of degradation in the tested storage conditions in comparison with modelled diffusion of moisture in SiO2, we find a significant correlation between the time dependent J0e and moisture supplied to the interface, leading us to the conclusion that moisture ingression and subsequent reaction at the SiO2-Si interface are the cause of both damp-heat and room- ambient degradation.

  15. Preparation and characterization of n-type microcrystalline hydrogenated silicon oxide films

    NASA Astrophysics Data System (ADS)

    Sarker, Arindam; Banerjee, Chandan; Barua, A. K.

    2002-06-01

    We have developed n-type microcrystalline hydrogenated silicon oxide (n-µc-SiO : H) thin films by the radio frequency plasma enhanced chemical vapour deposition (RF-PECVD, 13.56 MHz) method having suitable characteristics for use in the fabrication of single or multijunction amorphous silicon (a-Si) solar cells. The films have been characterized in detail for the study of structural and optoelectronic properties. Transmission electron microscopy, Raman spectroscopy, x-ray diffraction, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy have been used for the structural studies. The dependence of the structure and optoelectronic properties of n-µc-SiO : H films on the various deposition parameters such as hydrogen dilution, chamber pressure, RF-power density etc have also been studied. Comparison of the properties between n-µc-SiO : H and n-µc-Si : H films have been studied, too, which shows that the former has higher optical gap (2.17 eV) and lower activation energy (0.015 eV) with similar electrical conductivity (12.08 S cm-1).

  16. Paralinear Oxidation of Silicon Nitride in a Water Vapor/Oxygen Environment

    NASA Technical Reports Server (NTRS)

    Fox, Dennis S.; Opila, Elizabeth J.; Nguyen, QuynhGiao; Humphrey, Donald L.; Lewton, Susan M.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    Three silicon nitride materials were exposed to dry oxygen flowing at 0.44 cm/s at temperatures between 1200 and 1400 C. Reaction kinetics were measured with a continuously recording microbalance. Parabolic kinetics were observed. When the same materials were exposed to a 50% H2O - 50% O2 gas mixture flowing at 4.4 cm/s, all three types exhibited paralinear kinetics. The material is oxidized by water vapor to form solid silica. The protective silica is in turn volatilized by water vapor to form primarily gaseous Si(OH)4. Nonlinear least squares analysis and a paralinear kinetic model were used to determine both parabolic and linear rate constants from the kinetic data. Volatilization of the protective silica scale can result in accelerated consumption of Si3N4. Recession rates under conditions more representative of actual combustors are compared to the furnace data.

  17. The formation of light emitting cerium silicates in cerium-doped silicon oxides

    SciTech Connect

    Li Jing; Zalloum, Othman; Roschuk, Tyler; Heng Chenglin; Wojcik, Jacek; Mascher, Peter

    2009-01-05

    Cerium-doped silicon oxides with cerium concentrations of up to 0.9 at. % were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition. Bright cerium related photoluminescence, easily seen even under room lighting conditions, was observed from the films and found to be sensitive to film composition and annealing temperature. The film containing 0.9 at. % Ce subjected to anneal in N{sub 2} at 1200 deg. C for 3 h showed the most intense cerium-related emission, easily visible under bright room lighting conditions. This is attributed to the formation of cerium silicate [Ce{sub 2}Si{sub 2}O{sub 7} or Ce{sub 4.667} (SiO{sub 4}){sub 3}O], the presence of which was confirmed by high resolution transmission electron microscopy.

  18. Characterization and simulation on antireflective coating of amorphous silicon oxide thin films with gradient refractive index

    NASA Astrophysics Data System (ADS)

    Huang, Lu; Jin, Qi; Qu, Xingling; Jin, Jing; Jiang, Chaochao; Yang, Weiguang; Wang, Linjun; Shi, Weimin

    2016-08-01

    The optical reflective properties of silicon oxide (SixOy) thin films with gradient refractive index are studied both theoretically and experimentally. The thin films are widely used in photovoltaic as antireflective coatings (ARCs). An effective finite difference time domain (FDTD) model is built to find the optimized reflection spectra corresponding to structure of SixOy ARCs with gradient refractive index. Based on the simulation analysis, it shows the variation of reflection spectra with gradient refractive index distribution. The gradient refractive index of SixOy ARCs can be obtained in adjustment of SiH4 to N2O ratio by plasma-enhanced chemical vapor deposition (PECVD) system. The optimized reflection spectra measured by UV-visible spectroscopy confirms to agree well with that simulated by FDTD method.

  19. Functionalization of Oxide-Free Silicon Surfaces with Redox-Active Assemblies.

    PubMed

    Fabre, Bruno

    2016-04-27

    This review provides a comprehensive survey of the derivatization of hydrogen-terminated, oxide-free silicon surfaces with electroactive assemblies (from molecules to polymers) attached through strong interactions (covalent, electrostatic, and chimisorption). Provided that surface modification procedures are thoroughly optimized, such an approach has appeared as a promising strategy toward high-quality functional interfaces exhibiting excellent chemical and electrochemical stabilities. The attachment of electroactive molecules exhibiting either two stable redox states (e.g., ferrocene and quinones) or more than two stable redox states (e.g., metalloporphyrins, polyoxometalates, and C60) is more particularly discussed. Attention is also paid to the immobilization of electrochemically polymerizable centers. Globally, these functional interfaces have been demonstrated to show great promise for the molecular charge storage and information processing or the elaboration of the electrochemically switchable devices. Besides, there are also some relevant examples dealing with their activity for other fields of interest, such as sensing and electrochemical catalysis. PMID:27064580

  20. Patterns of discoloration and oxidation by direct and scattered fluxes on LDEF, including oxygen on silicon

    NASA Technical Reports Server (NTRS)

    Frederickson, A. R.; Filz, R. C.; Rich, F. J.; Sagalyn, P. L.

    1992-01-01

    A number of interesting discoloration patterns are clearly evident on MOOO2-1 which resides on the three faces of the Long Duration Exposure Facility (LDEF). Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by scattered or direct ram oxygen atoms along the earth face. A complete explanation for the patterns has not yet been obtained. All honeycomb outgassing holes have a small discoloration ring around them that varies in color. The shadow cast by a suspended wire on the earth face surface is not easily explained by either solar photons or by ram flux. The shadows and the dark/light regions cannot be explained consistently by the process of solar ultraviolet paint-darkening modulated by ram flux oxygen bleaching of the paint.

  1. A multilayered silicon-reduced graphene oxide electrode for high performance lithium-ion batteries.

    PubMed

    Gao, Xianfeng; Li, Jianyang; Xie, Yuanyuan; Guan, Dongsheng; Yuan, Chris

    2015-04-22

    A multilayered structural silicon-reduced graphene oxide electrode with superior electrochemical performance was synthesized from bulk Si particles through inexpensive electroless etching and graphene self-encapsulating approach. The prepared composite electrode presents a stable charge-discharge performance with high rate, showing a reversible capacity of 2787 mAh g(-1) at a charging rate of 100 mA g(-1), and a stable capacity over 1000 mAh g(-1) was retained at 1 A g(-1) after 50 cycles with a high columbic efficiency of 99% during the whole cycling process. This superior performance can be attributed to its novel multilayered structure with porous Si particles encapsulated, which can effectively accommodate the large volume change during the lithiation process and provide increased electrical conductivity. This facile low-cost approach offers a promising route to develop an optimized carbon encapsulated Si electrode for future industrial applications. PMID:25826636

  2. Surface Modification of High Haze Front Transparent Conductive Oxide for Silicon Thin Film Solar Cell

    NASA Astrophysics Data System (ADS)

    Kim, Sun Ho; You, Dong Joo; Park, Jin Hee; Lee, Sung Eun; Lee, Heon-Min; Kim, Donghwan

    2012-10-01

    The aluminium-doped zinc oxide (ZnO:Al) films grown by sputtering method were etched to improve the light scattering property. The high haze value (diffuse transmission to total transmission) of above 40% at 850 nm wavelength was obtained by the increase of etching time. But the resistance of film increased and a lot of pin holes were created due to the over etch for high haze. In order to solve these problems, the additional ZnO layer was deposited on etched ZnO:Al film without sacrifice of high haze. This method was able to compensate the deteriorated properties without the change of optical properties. Amorphous based silicon solar cells showed the improvement of photovoltaic performances by the additional deposition.

  3. Acoustic Properties of Polyurethane Composition Reinforced with Carbon Nanotubes and Silicon Oxide Nano-powder

    NASA Astrophysics Data System (ADS)

    Orfali, Wasim A.

    This article demonstrates the acoustic properties of added small amount of carbon-nanotube and siliconoxide nano powder (S-type, P-Type) to the host material polyurethane composition. By adding CNT and/or nano-silica in the form of powder at different concentrations up to 2% within the PU composition to improve the sound absorption were investigated in the frequency range up to 1600 Hz. Sound transmission loss measurement of the samples were determined using large impedance tube. The tests showed that addition of 0.2 wt.% Silicon Oxide Nano-powder and 0.35 wt.% carbon nanotube to polyurethane composition improved sound transmissions loss (Sound Absorption) up to 80 dB than that of pure polyurethane foam sample.

  4. Light-induced water oxidation at silicon electrodes functionalized with a cobalt oxygen-evolving catalyst

    PubMed Central

    Pijpers, Joep J. H.; Winkler, Mark T.; Surendranath, Yogesh; Buonassisi, Tonio; Nocera, Daniel G.

    2011-01-01

    Integrating a silicon solar cell with a recently developed cobalt-based water-splitting catalyst (Co-Pi) yields a robust, monolithic, photo-assisted anode for the solar fuels process of water splitting to O2 at neutral pH. Deposition of the Co-Pi catalyst on the Indium Tin Oxide (ITO)-passivated p-side of a np-Si junction enables the majority of the voltage generated by the solar cell to be utilized for driving the water-splitting reaction. Operation under neutral pH conditions fosters enhanced stability of the anode as compared to operation under alkaline conditions (pH 14) for which long-term stability is much more problematic. This demonstration of a simple, robust construct for photo-assisted water splitting is an important step towards the development of inexpensive direct solar-to-fuel energy conversion technologies. PMID:21646536

  5. Nonvolatile memories by using charge traps in silicon-rich oxides

    NASA Astrophysics Data System (ADS)

    Lim, Keun Yong; Kim, Min Choul; Hong, Seung Hui; Choi, Suk-Ho; Kim, Kyung Joong

    2010-08-01

    The nonvolatile memory characteristics of silicon-rich oxide (SRO, SiOx) grown at room temperature for charge-trapping layer are first reported and shown to exhibit a strong dependence on oxygen content (x). The memory window that is estimated by capacitance-voltage curves monotonically decreases with increasing x from 1.0 to 1.8, possibly resulting from the x-dependent variation in the Si suboxide states responsible for the charge traps, as evidenced by x-ray photoelectron spectroscopy. The density of the charge traps is estimated to be (3.9-8.8)×1012 cm-2 for x=1.0-1.4. The charge-loss rate sharply decreases at x=1.2, but by further increase in x above 1.2, it gradually increases, which can be explained by the lowered SRO/SiO2 barrier due to the increased optical band gap of SRO at larger x

  6. A CMOS compatible Microbulk Micromegas-like detector using silicon oxide as spacer material

    NASA Astrophysics Data System (ADS)

    Blanco Carballo, V. M.; Fransen, M.; van der Graaf, H.; Lu, J.; Schmitz, J.

    2011-02-01

    We present a new Micro Pattern Gaseous Detector (MPGD) fabricated with nonpolymeric materials. The device structure is similar to a Microbulk Micromegas design, consisting of a punctured metal grid supported by a continuous perforated insulating structure. In this detector, the supporting structure is made out of silicon oxide. Devices were tested in He/ iC 4H 10 (80/20) and Ar/ iC 4H 10 (80/20) gas mixtures under 55Fe irradiation. Gas gain of 20,000 and energy resolution below 13% FWHM were achieved. The CMOS compatibility of the fabrication process has been studied in Timepix chips as well as individual 0.13-μm technology CMOS transistors. Complete detectors have been fabricated on top of Timepix chips. In an Ar/ iC 4H 10 (80/20) gas mixture 55Fe decay events were recorded operating the Timepix chip in 2D readout mode.

  7. Oxidized Porous Silicon Particles Covalently Grafted with Daunorubicin as a Sustained Intraocular Drug Delivery System

    PubMed Central

    Chhablani, Jay; Nieto, Alejandra; Hou, Huiyuan; Wu, Elizabeth C.; Freeman, William R.; Sailor, Michael J.; Cheng, Lingyun

    2013-01-01

    Purpose. To test the feasibility of covalent loading of daunorubicin into oxidized porous silicon (OPS) and to evaluate the ocular properties of sustained delivery of daunorubicin in this system. Methods. Porous silicon was heat oxidized and chemically functionalized so that the functional linker on the surface was covalently bonded with daunorubicin. The drug loading rate was determined by thermogravimetric analysis. Release of daunorubicin was confirmed in PBS and excised rabbit vitreous by mass spectrometry. Daunorubicin-loaded OPS particles (3 mg) were intravitreally injected into six rabbits, and ocular properties were evaluated through ophthalmic examinations and histology during a 3-month study. The same OPS was loaded with daunorubicin using physical adsorption and was evaluated similarly as a control for the covalent loading. Results. In the case of covalent loading, 67 ± 10 μg daunorubicin was loaded into each milligram of the particles while 27 ± 10 μg/mg particles were loaded by physical adsorption. Rapid release of daunorubicin was observed in both PBS and excised vitreous (∼75% and ∼18%) from the physical adsorption loading, while less than 1% was released from the covalently loaded particles. Following intravitreal injection, the covalently loaded particles demonstrated a sustained degradation of OPS with drug release for 3 months without evidence of toxicity; physical adsorption loading revealed a complete release within 2 weeks and localized retinal toxicity due to high daunorubicin concentration. Conclusions. OPS with covalently loaded daunorubicin demonstrated sustained intravitreal drug release without ocular toxicity, which may be useful to inhibit unwanted intraocular proliferation. PMID:23322571

  8. Carrier Selective, Passivated Contacts for High Efficiency Silicon Solar Cells based on Transparent Conducting Oxides

    SciTech Connect

    Young, David L.; Nemeth, William; Grover, Sachit; Norman, Andrew; Yuan, Hao-Chih; Lee, Benjamin G.; LaSalvia, Vincenzo; Stradins, Paul

    2014-01-01

    We describe the design, fabrication and results of passivated contacts to n-type silicon utilizing thin SiO2 and transparent conducting oxide layers. High temperature silicon dioxide is grown on both surfaces of an n-type wafer to a thickness <50 Å, followed by deposition of tin-doped indium oxide (ITO) and a patterned metal contacting layer. As deposited, the thin-film stack has a very high J0,contact, and a non-ohmic, high contact resistance. However, after a forming gas anneal, the passivation quality and the contact resistivity improve significantly. The contacts are characterized by measuring the recombination parameter of the contact (J0,contact) and the specific contact resistivity (ρcontact) using a TLM pattern. The best ITO/SiO2 passivated contact in this study has J0,contact = 92.5 fA/cm2 and ρcontact = 11.5 mOhm-cm2. These values are placed in context with other passivating contacts using an analysis that determines the ultimate efficiency and the optimal area fraction for contacts for a given set of (J0,contact, ρcontact) values. The ITO/SiO2 contacts are found to have a higher J0,contact, but a similar ρcontact compared to the best reported passivated contacts.

  9. Comparative cytotoxicity and genotoxicity of cobalt (II, III) oxide, iron (III) oxide, silicon dioxide, and aluminum oxide nanoparticles on human lymphocytes in vitro.

    PubMed

    Rajiv, S; Jerobin, J; Saranya, V; Nainawat, M; Sharma, A; Makwana, P; Gayathri, C; Bharath, L; Singh, M; Kumar, M; Mukherjee, A; Chandrasekaran, N

    2016-02-01

    Despite the extensive use of nanoparticles (NPs) in various fields, adequate knowledge of human health risk and potential toxicity is still lacking. The human lymphocytes play a major role in the immune system, and it can alter the antioxidant level when exposed to NPs. Identification of the hazardous NPs was done using in vitro toxicity tests and this study mainly focuses on the comparative in vitro cytotoxicity and genotoxicity of four different NPs including cobalt (II, III) oxide (Co3O4), iron (III) oxide (Fe2O3), silicon dioxide (SiO2), and aluminum oxide (Al2O3) on human lymphocytes. The Co3O4 NPs showed decrease in cellular viability and increase in cell membrane damage followed by Fe2O3, SiO2, and Al2O3 NPs in a dose-dependent manner after 24 h of exposure to human lymphocytes. The oxidative stress was evidenced in human lymphocytes by the induction of reactive oxygen species, lipid peroxidation, and depletion of catalase, reduced glutathione, and superoxide dismutase. The Al2O3 NPs showed the least DNA damage when compared with all the other NPs. Chromosomal aberration was observed at 100 µg/ml when exposed to Co3O4 NPs and Fe2O3 NPs. The alteration in the level of antioxidant caused DNA damage and chromosomal aberration in human lymphocytes. PMID:25829403

  10. Design, analysis, and characterization of stress-engineered 3D microstructures comprised of PECVD silicon oxide and nitride

    NASA Astrophysics Data System (ADS)

    Pi, Chia-Hsing; Turner, Kevin T.

    2016-06-01

    Microelectromechanical systems (MEMS) are typically 2D or quasi-3D structures fabricated using surface and bulk micromachining processes. In this work, an approach for 3D structure fabrication based on stress engineering is demonstrated. Specifically, sub-mm 3D spherical cage-like structures are realized through the deformation of bilayers of residually-stressed silicon oxide and silicon nitride with micrometer-scale thicknesses. Analytical and finite models to predict the shape of stress-engineered structures based on geometry and residual stress are described and used for structure design. A systematic experimental study was performed to quantify residual stresses in silicon nitride films made by plasma-enhanced chemical vapor deposition (PECVD). The measurements show that the residual stress of PECVD silicon nitride can be tuned over a wide range of tensile stresses through the control of deposition parameters, such as flow rate and power. Stress engineered 3D cage-like structures comprised of PECVD silicon nitride and oxide films were fabricated. 3D structures with a range of curvatures were demonstrated. The measured geometry of the fabricated structures are in good agreement with predictions from analytical and finite element models.

  11. Plasma surface oxidation of 316L stainless steel for improving adhesion strength of silicone rubber coating to metal substrate

    NASA Astrophysics Data System (ADS)

    Latifi, Afrooz; Imani, Mohammad; Khorasani, Mohammad Taghi; Daliri Joupari, Morteza

    2014-11-01

    Stainless steel 316L is one of the most widely used materials for fabricating of biomedical devices hence, improving its surface properties is still of great interest and challenging in biomaterial sciences. Plasma oxidation, in comparison to the conventional chemical or mechanical methods, is one of the most efficient methods recently used for surface treatment of biomaterials. Here, stainless steel specimens were surface oxidized by radio-frequency plasma irradiation operating at 34 MHz under pure oxygen atmosphere. Surface chemical composition of the samples was significantly changed after plasma oxidation by appearance of the chromium and iron oxides on the plasma-oxidized surface. A wettable surface, possessing high surface energy (83.19 mN m-1), was observed after plasma oxidation. Upon completion of the surface modification process, silicone rubber was spray coated on the plasma-treated stainless steel surface. Morphology of the silicone rubber coating was investigated by scanning electron microscopy (SEM). A uniform coating was formed on the oxidized surface with no delamination at polymer-metal interface. Pull-off tests showed the lowest adhesion strength of coating to substrate (0.12 MPa) for untreated specimens and the highest (0.89 MPa) for plasma-oxidized ones.

  12. Metal-oxide-semiconductor field-effect-transistors on indium phosphide using HfO2 and silicon passivation layer with equivalent oxide thickness of 18 A˚

    NASA Astrophysics Data System (ADS)

    Chen, Yen-Ting; Zhao, Han; Yum, Jung Hwan; Wang, Yanzhen; Lee, Jack C.

    2009-05-01

    In this letter, we demonstrate the electrical properties of metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field-effect transistors (MOSFETs) on InP using atomic layer deposited HfO2 gate dielectric and a thin silicon interface passivation layer (Si IPL). Compared with single HfO2, the use of Si IPL results in better interface quality with InP substrate, as illustrated by smaller frequency dispersion and reduced hysteresis. MOSFETs with Si IPL show much higher drive current and transconductance, improved subthreshold swing, interface-trap density and gate leakage current with equivalent oxide thickness scaling down to 18 Å.

  13. Valence band offset in heterojunctions between crystalline silicon and amorphous silicon (sub)oxides (a-SiO{sub x}:H, 0 < x < 2)

    SciTech Connect

    Liebhaber, M.; Mews, M.; Schulze, T. F.; Korte, L. Rech, B.; Lips, K.

    2015-01-19

    The heterojunction between amorphous silicon (sub)oxides (a-SiO{sub x}:H, 0 < x < 2) and crystalline silicon (c-Si) is investigated. We combine chemical vapor deposition with in-system photoelectron spectroscopy in order to determine the valence band offset ΔE{sub V} and the interface defect density, being technologically important junction parameters. ΔE{sub V} increases from ≈0.3 eV for the a-Si:H/c-Si interface to >4 eV for the a-SiO{sub 2}/c-Si interface, while the electronic quality of the heterointerface deteriorates. High-bandgap a-SiO{sub x}:H is therefore unsuitable for the hole contact in heterojunction solar cells, due to electronic transport hindrance resulting from the large ΔE{sub V}. Our method is readily applicable to other heterojunctions.

  14. Continuous-flow Mass Production of Silicon Nanowires via Substrate-Enhanced Metal-Catalyzed Electroless Etching of Silicon with Dissolved Oxygen as an Oxidant

    NASA Astrophysics Data System (ADS)

    Hu, Ya; Peng, Kui-Qing; Liu, Lin; Qiao, Zhen; Huang, Xing; Wu, Xiao-Ling; Meng, Xiang-Min; Lee, Shuit-Tong

    2014-01-01

    Silicon nanowires (SiNWs) are attracting growing interest due to their unique properties and promising applications in photovoltaic devices, thermoelectric devices, lithium-ion batteries, and biotechnology. Low-cost mass production of SiNWs is essential for SiNWs-based nanotechnology commercialization. However, economic, controlled large-scale production of SiNWs remains challenging and rarely attainable. Here, we demonstrate a facile strategy capable of low-cost, continuous-flow mass production of SiNWs on an industrial scale. The strategy relies on substrate-enhanced metal-catalyzed electroless etching (MCEE) of silicon using dissolved oxygen in aqueous hydrofluoric acid (HF) solution as an oxidant. The distinct advantages of this novel MCEE approach, such as simplicity, scalability and flexibility, make it an attractive alternative to conventional MCEE methods.

  15. Continuous-flow Mass Production of Silicon Nanowires via Substrate-Enhanced Metal-Catalyzed Electroless Etching of Silicon with Dissolved Oxygen as an Oxidant

    PubMed Central

    Hu, Ya; Peng, Kui-Qing; Liu, Lin; Qiao, Zhen; Huang, Xing; Wu, Xiao-Ling; Meng, Xiang-Min; Lee, Shuit-Tong

    2014-01-01

    Silicon nanowires (SiNWs) are attracting growing interest due to their unique properties and promising applications in photovoltaic devices, thermoelectric devices, lithium-ion batteries, and biotechnology. Low-cost mass production of SiNWs is essential for SiNWs-based nanotechnology commercialization. However, economic, controlled large-scale production of SiNWs remains challenging and rarely attainable. Here, we demonstrate a facile strategy capable of low-cost, continuous-flow mass production of SiNWs on an industrial scale. The strategy relies on substrate-enhanced metal-catalyzed electroless etching (MCEE) of silicon using dissolved oxygen in aqueous hydrofluoric acid (HF) solution as an oxidant. The distinct advantages of this novel MCEE approach, such as simplicity, scalability and flexibility, make it an attractive alternative to conventional MCEE methods. PMID:24413157

  16. Surface etching, chemical modification and characterization of silicon nitride and silicon oxide--selective functionalization of Si3N4 and SiO2.

    PubMed

    Liu, Li-Hong; Michalak, David J; Chopra, Tatiana P; Pujari, Sidharam P; Cabrera, Wilfredo; Dick, Don; Veyan, Jean-François; Hourani, Rami; Halls, Mathew D; Zuilhof, Han; Chabal, Yves J

    2016-03-01

    The ability to selectively chemically functionalize silicon nitride (Si3N4) or silicon dioxide (SiO2) surfaces after cleaning would open interesting technological applications. In order to achieve this goal, the chemical composition of surfaces needs to be carefully characterized so that target chemical reactions can proceed on only one surface at a time. While wet-chemically cleaned silicon dioxide surfaces have been shown to be terminated with surficial Si-OH sites, chemical composition of the HF-etched silicon nitride surfaces is more controversial. In this work, we removed the native oxide under various aqueous HF-etching conditions and studied the chemical nature of the resulting Si3N4 surfaces using infrared absorption spectroscopy (IRAS), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and contact angle measurements. We find that HF-etched silicon nitride surfaces are terminated by surficial Si-F and Si-OH bonds, with slightly subsurface Si-OH, Si-O-Si, and Si-NH2 groups. The concentration of surficial Si-F sites is not dependent on HF concentration, but the distribution of oxygen and Si-NH2 displays a weak dependence. The Si-OH groups of the etched nitride surface are shown to react in a similar manner to the Si-OH sites on SiO2, and therefore no selectivity was found. Chemical selectivity was, however, demonstrated by first reacting the -NH2 groups on the etched nitride surface with aldehyde molecules, which do not react with the Si-OH sites on a SiO2 surface, and then using trichloro-organosilanes for selective reaction only on the SiO2 surface (no reactivity on the aldehyde-terminated Si3N4 surface). PMID:26870908

  17. Size control, quantum confinement, and oxidation kinetics of silicon nanocrystals synthesized at a high rate by expanding thermal plasma

    SciTech Connect

    Han, Lihao E-mail: A.H.M.Smets@tudelft.nl; Zeman, Miro; Smets, Arno H. M. E-mail: A.H.M.Smets@tudelft.nl

    2015-05-25

    The growth mechanism of silicon nanocrystals (Si NCs) synthesized at a high rate by means of expanding thermal plasma chemical vapor deposition technique are studied in this letter. A bimodal Gaussian size distribution is revealed from the high-resolution transmission electron microscopy images, and routes to reduce the unwanted large Si NCs are discussed. Photoluminescence and Raman spectroscopies are employed to study the size-dependent quantum confinement effect, from which the average diameters of the small Si NCs are determined. The surface oxidation kinetics of Si NCs are studied using Fourier transform infrared spectroscopy and the importance of post-deposition passivation treatments of hydrogenated crystalline silicon surfaces are demonstrated.

  18. Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes

    PubMed Central

    Lorenzoni, Matteo; Matsui, Soichiro; Tanemura, Masaki; Perez-Murano, Francesc

    2015-01-01

    Summary Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency. PMID:25671165

  19. Double layer oxidation resistant coating for carbon fiber reinforced silicon carbide matrix composites

    NASA Astrophysics Data System (ADS)

    Zheng, X. H.; Du, Y. G.; Xiao, J. Y.; Zhang, W. J.; Zhang, L. C.

    2009-01-01

    Double layer coatings, with celsian-Y 2SiO 5 as inner layer and Y 2Si 2O 7 as outer layer, were prepared by microwave sintering on the surface of carbon fiber reinforced silicon carbide matrix composite. Both celsian, Y 2SiO 5 and Y 2Si 2O 7 were synthesized by in situ method using BAS glass, Y 2O 3 and SiO 2 as staring materials. The sintering temperature was 1500 °C, and little damage was induced to the composite. The composition and micrograph of the fired coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The oxidation and thermal shock resistance of samples with doubled-layered coating were characterized at 1400 °C in air. After 150 min oxidation and thermal cycling between 1400 °C and room temperature for 15 times, the weight loss of double layer-coated sample was 1.22% and there were no cracks in the coating.

  20. Vapor-phase silanization of oxidized porous silicon for stabilizing composition and photoluminescence

    NASA Astrophysics Data System (ADS)

    Li, Hong-Liang; Zhu, Yingchun; Xu, Dongsheng; Wan, Yong; Xia, Linhua; Zhao, Xiu-song

    2009-06-01

    A vapor-phase deposition approach to the silanization modification of the oxidized porous silicon (PSi) surface using (CH3O)3Si(CH2)3NH2 has been exploited. Standard clean (SC)-1 (NH3H2O/H2O2/H2O, 1:1:5,v/v) and SC-2 [HCl/H2O2/H2O (1:1:6,v/v)] solutions are utilized for the first time to obtain oxidized PSi and have been proved to be a very efficient combination for creating Si-OH species on the PSi surface. After the modification, an amine group terminated surface was successfully created as demonstrated by the contact angle with water, the x-ray photoelectron spectroscopy, and the Fourier transform infrared (FTIR) spectra. The influences of the surface derivatives on the composition stability of the PSi layer and on its photoluminescence properties were investigated by means of FTIR spectra, photoluminescence spectra, and time-resolved photoluminescence measurements.

  1. Transparent conducting oxide contacts and textured metal back reflectors for thin film silicon solar cells

    NASA Astrophysics Data System (ADS)

    Franken, R. H.-J.

    2006-09-01

    With the growing population and the increasing environmental problems of the 'common' fossil and nuclear energy production, the need for clean and sustainable energy sources is evident. Solar energy conversion, such as in photovoltaic (PV) systems, can play a major role in the urgently needed energy transition in electricity production. At the present time PV module production is dominated by the crystalline wafer technology. Thin film silicon technology is an alternative solar energy technology that operates at lower efficiencies, however, it has several significant advantages, such as the possibility of deposition on cheap (flexible) substrates and the much smaller silicon material consumption. Because of the small thickness of the solar cells, light trapping schemes are needed in order to obtain enough light absorption and current generation. This thesis describes the research on thin film silicon solar cells with the focus on the optimization of the transparent conducting oxide (TCO) layers and textured metal Ag substrate layers for the use as enhanced light scattering back reflectors in n-i-p type of solar cells. First we analyzed ZnO:Al (TCO) layers deposited in an radio frequent (rf) magnetron deposition system equipped with a 7 inch target. We have focused on the improvement of the electrical properties without sacrificing the optical properties by increasing the mobility and decreasing the grain boundary density. Furthermore, we described some of the effects on light trapping of ZnO:Al enhanced back reflectors. The described effects are able to explain the observed experimental data. Furthermore, we present a relation between the surface morphology of the Ag back contact and the current enhancement in microcrystalline (muc-Si:H) solar cells. We show the importance of the lateral feature sizes of the Ag surface on the light scattering and introduce a method to characterize the quality of the back reflector by combining the vertical and lateral feature sizes

  2. [Synergetic effects of silicon carbide and molecular sieve loaded catalyst on microwave assisted catalytic oxidation of toluene].

    PubMed

    Wang, Xiao-Hui; Bo, Long-Li; Liu, Hai-Nan; Zhang, Hao; Sun, Jian-Yu; Yang, Li; Cai, Li-Dong

    2013-06-01

    Molecular sieve loaded catalyst was prepared by impregnation method, microwave-absorbing material silicon carbide and the catalyst were investigated for catalytic oxidation of toluene by microwave irradiation. Research work examined effects of silicon carbide and molecular sieve loading Cu-V catalyst's mixture ratio as well as mixed approach changes on degradation of toluene, and characteristics of catalyst were measured through scanning electron microscope, specific surface area test and X-ray diffraction analysis. The result showed that the fixed bed reactor had advantages of both thermal storage property and low-temperature catalytic oxidation when 20% silicon carbide was filled at the bottom of the reactor, and this could effectively improve the utilization of microwave energy as well as catalytic oxidation efficiency of toluene. Under microwave power of 75 W and 47 W, complete-combustion temperatures of molecular sieve loaded Cu-V catalyst and Cu-V-Ce catalyst to toluene were 325 degrees C and 160 degrees C, respectively. Characteristics of the catalysts showed that mixture of rare-earth element Ce increased the dispersion of active components in the surface of catalyst, micropore structure of catalyst effectively guaranteed high adsorption capacity for toluene, while amorphous phase of Cu and V oxides increased the activity of catalyst greatly. PMID:23947020

  3. Tunnel oxide passivated contacts formed by ion implantation for applications in silicon solar cells

    SciTech Connect

    Reichel, Christian; Feldmann, Frank; Müller, Ralph; Hermle, Martin; Glunz, Stefan W.; Reedy, Robert C.; Lee, Benjamin G.; Young, David L.; Stradins, Paul

    2015-11-28

    Passivated contacts (poly-Si/SiO{sub x}/c-Si) doped by shallow ion implantation are an appealing technology for high efficiency silicon solar cells, especially for interdigitated back contact (IBC) solar cells where a masked ion implantation facilitates their fabrication. This paper presents a study on tunnel oxide passivated contacts formed by low-energy ion implantation into amorphous silicon (a-Si) layers and examines the influence of the ion species (P, B, or BF{sub 2}), the ion implantation dose (5 × 10{sup 14 }cm{sup −2} to 1 × 10{sup 16 }cm{sup −2}), and the subsequent high-temperature anneal (800 °C or 900 °C) on the passivation quality and junction characteristics using double-sided contacted silicon solar cells. Excellent passivation quality is achieved for n-type passivated contacts by P implantations into either intrinsic (undoped) or in-situ B-doped a-Si layers with implied open-circuit voltages (iV{sub oc}) of 725 and 720 mV, respectively. For p-type passivated contacts, BF{sub 2} implantations into intrinsic a-Si yield well passivated contacts and allow for iV{sub oc} of 690 mV, whereas implanted B gives poor passivation with iV{sub oc} of only 640 mV. While solar cells featuring in-situ B-doped selective hole contacts and selective electron contacts with P implanted into intrinsic a-Si layers achieved V{sub oc} of 690 mV and fill factor (FF) of 79.1%, selective hole contacts realized by BF{sub 2} implantation into intrinsic a-Si suffer from drastically reduced FF which is caused by a non-Ohmic Schottky contact. Finally, implanting P into in-situ B-doped a-Si layers for the purpose of overcompensation (counterdoping) allowed for solar cells with V{sub oc} of 680 mV and FF of 80.4%, providing a simplified and promising fabrication process for IBC solar cells featuring passivated contacts.

  4. Oxidation Behavior of Germanium- and/or Silicon-Bearing Near-α Titanium Alloys in Air

    NASA Astrophysics Data System (ADS)

    Kitashima, Tomonori; Yamabe-Mitarai, Yoko

    2015-06-01

    The effect of germanium (Ge) and/or silicon (Si) addition on the oxidation behavior of the near-α alloy Ti-5Al-2Sn-4Zr-2Mo was investigated in air at 973 K (700 °C). Ge addition decreased the oxidation resistance because of the formation of a Ge-rich layer in the substrate at the TiO2/substrate interface, enhancing Sn segregation at the interface. In addition, a small amount of Ge dissolved in the external Al2O3 layer. These results reduced the aluminum activity at the interface, suppressed the formation of Al2O3, and increased the diffusivity of oxygen in the oxide scales. The addition of 0.2 and 0.9 wt pct Si was beneficial for improving oxidation resistance. The effect of germanide and silicide precipitates in the matrix on the oxide growth process was also discussed.

  5. Current, charge, and capacitance during scanning probe oxidation of silicon. II. Electrostatic and meniscus forces acting on cantilever bending

    NASA Astrophysics Data System (ADS)

    Dagata, J. A.; Perez-Murano, F.; Martin, C.; Kuramochi, H.; Yokoyama, H.

    2004-08-01

    A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis identifies the electronic and ionic contributions to the total current, especially at the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In this work, we concentrate on noncontact SPM oxidation. We analyze simultaneous force-distance and current-distance curves to demonstrate that total current flow during noncontact oxidation is significantly less for noncontact mode than for contact oxidation, although the resulting oxide volume is nearly identical. Ionization of water layers and mobile charge reorganization prior to and following meniscus formation is also shown to alter the tip-substrate capacitance and, therefore, the bending of the SPM cantilever.

  6. Role of surface oxides in the formation of solid-electrolyte interphases at silicon electrodes for lithium-ion batteries.

    PubMed

    Schroder, Kjell W; Dylla, Anthony G; Harris, Stephen J; Webb, Lauren J; Stevenson, Keith J

    2014-12-10

    Nonaqueous solvents in modern battery technologies undergo electroreduction at negative electrodes, leading to the formation of a solid-electrolyte interphase (SEI). The mechanisms and reactions leading to a stable SEI on silicon electrodes in lithium-ion batteries are still poorly understood. This lack of understanding inhibits the rational design of electrolyte additives, active material coatings, and the prediction of Li-ion battery life in general. We prepared SEI with a common nonaqueous solvent (LiPF6 in PC and in EC/DEC 1:1 by wt %) on silicon oxide and etched silicon (001) surfaces in various states of lithiation to understand the role of surface chemistry on the SEI formation mechanism and SEI structure. Anhydrous and anoxic techniques were used to prevent air and moisture contamination of prepared SEI films, allowing for more accurate characterization of SEI chemical stratification and composition by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling. Additionally, multivariate statistical methods were used to better understand TOF-SIMS depth profiling studies. We conclude that the absence of native-oxide layer on silicon has a significant impact on the formation, composition, structure, and thickness of the SEI. PMID:25402271

  7. Cobalt-silicon mixed oxide nanocomposites by modified sol-gel method

    SciTech Connect

    Esposito, Serena; Turco, Maria; Ramis, Gianguido; Bagnasco, Giovanni; Pernice, Pasquale; Pagliuca, Concetta; Bevilacqua, Maria; Aronne, Antonio

    2007-12-15

    Cobalt-silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO{sub 3}){sub 2}.6H{sub 2}O and Si(OC{sub 2}H{sub 5}){sub 4} using a modified sol-gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV-vis, FT-IR spectroscopy and N{sub 2} adsorption at -196 deg. C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co{sup 2+} ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 deg. C, the sample with lowest Co content appeared amorphous and contained only Co{sup 2+} tetrahedral complexes, while at higher cobalt loading Co{sub 3}O{sub 4} was present as the only crystalline phase, besides Co{sup 2+} ions strongly interacting with siloxane matrix. At 850 deg. C, in all samples crystalline Co{sub 2}SiO{sub 4} was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 deg. C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity. - Graphical abstract: Highly dispersed cobalt-silicon mixed oxide nanocomposites (Co/Si=0.111, 0.250 and 0.428) were obtained by a modified sol-gel method using almost solely aqueous solutions. The nature of cobalt species and their interactions with the siloxane matrix are strongly depending on both the cobalt loading and the heat treatment. All materials retained high surface areas also after treatments at 600 deg. C and exhibited surface Lewis acidity.

  8. A Silicon-Based Nanothin Film Solid Oxide Fuel Cell Array with Edge Reinforced Support for Enhanced Thermal Mechanical Stability.

    PubMed

    Baek, Jong Dae; Yu, Chen-Chiang; Su, Pei-Chen

    2016-04-13

    A silicon-based micro-solid oxide fuel cell (μ-SOFC) with electrolyte membrane array embedded in a thin silicon supporting membrane, featuring a unique edge reinforcement structure, was demonstrated by utilizing simple silicon micromachining processes. The square silicon supporting membrane, fabricated by combining deep reactive ion etching and through-wafer wet etching processes, has thicker edges and corners than the center portion of the membrane, which effectively improved the mechanical stability of the entire fuel cell array during cell fabrication and cell operation. The 20 μm thick single crystalline silicon membrane supports a large number of 80 nm thick free-standing yttria-stabilized zirconia (YSZ) electrolytes. The fuel cell array was stably maintained at the open circuit voltage (OCV) of 1.04 V for more than 30 h of operation at 350 °C. A high peak power density of 317 mW/cm(2) was obtained at 400 °C. During a rigorous in situ thermal cycling between 150 and 400 °C at a fast cooling and heating rate of 25 °C/min, the OCV of the μ-SOFC recovered to its high value of 1.07 V without any drop caused by membrane failure, which justifies the superior thermal stability of this novel cell architecture. PMID:26990604

  9. Room temperature NO2 gas sensing of Au-loaded tungsten oxide nanowires/porous silicon hybrid structure

    NASA Astrophysics Data System (ADS)

    Deng-Feng, Wang; Ji-Ran, Liang; Chang-Qing, Li; Wen-Jun, Yan; Ming, Hu

    2016-02-01

    In this work, we report an enhanced nitrogen dioxide (NO2) gas sensor based on tungsten oxide (WO3) nanowires/porous silicon (PS) decorated with gold (Au) nanoparticles. Au-loaded WO3 nanowires with diameters of 10 nm-25 nm and lengths of 300 nm-500 nm are fabricated by the sputtering method on a porous silicon substrate. The high-resolution transmission electron microscopy (HRTEM) micrographs show that Au nanoparticles are uniformly distributed on the surfaces of WO3 nanowires. The effect of the Au nanoparticles on the NO2-sensing performance of WO3 nanowires/porous silicon is investigated over a low concentration range of 0.2 ppm-5 ppm of NO2 at room temperature (25 °C). It is found that the 10-Å Au-loaded WO3 nanowires/porous silicon-based sensor possesses the highest gas response characteristic. The underlying mechanism of the enhanced sensing properties of the Au-loaded WO3 nanowires/porous silicon is also discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274074 and 61271070) and the Key Research Program of Application Foundation and Advanced Technology of Tianjin, China (Grant No. 11JCZDJC15300).

  10. Improving the stability of nanostructured silicon thin film lithium-ion battery anodes through their controlled oxidation.

    PubMed

    Abel, Paul R; Lin, Yong-Mao; Celio, Hugo; Heller, Adam; Mullins, C Buddie

    2012-03-27

    Silicon and partially oxidized silicon thin films with nanocolumnar morphology were synthesized by evaporative deposition at a glancing angle, and their performance as lithium-ion battery anodes was evaluated. The incorporated oxygen concentration was controlled by varying the partial pressure of water during the deposition and monitored by quartz crystal microbalance, X-ray photoelectron spectroscopy. In addition to bulk oxygen content, surface oxidation and annealing at low temperature affected the cycling stability and lithium-storage capacity of the films. By simultaneously optimizing all three, films of ~2200 mAh/g capacity were synthesized. Coin cells made with the optimized films were reversibly cycled for ~120 cycles with virtually no capacity fade. After 300 cycles, 80% of the initial reversible capacity was retained. PMID:22372404

  11. Electronic devices containing switchably conductive silicon oxides as a switching element and methods for production and use thereof

    DOEpatents

    Tour, James M.; Yao, Jun; Natelson, Douglas; Zhong, Lin; He, Tao

    2015-09-08

    In various embodiments, electronic devices containing switchably conductive silicon oxide as a switching element are described herein. The electronic devices are two-terminal devices containing a first electrical contact and a second electrical contact in which at least one of the first electrical contact or the second electrical contact is deposed on a substrate to define a gap region therebetween. A switching layer containing a switchably conductive silicon oxide resides in the gap region between the first electrical contact and the second electrical contact. The electronic devices exhibit hysteretic current versus voltage properties, enabling their use in switching and memory applications. Methods for configuring, operating and constructing the electronic devices are also presented herein.

  12. Electronic devices containing switchably conductive silicon oxides as a switching element and methods for production and use thereof

    DOEpatents

    Tour, James M; Yao, Jun; Natelson, Douglas; Zhong, Lin; He, Tao

    2013-11-26

    In various embodiments, electronic devices containing switchably conductive silicon oxide as a switching element are described herein. The electronic devices are two-terminal devices containing a first electrical contact and a second electrical contact in which at least one of the first electrical contact or the second electrical contact is deposed on a substrate to define a gap region therebetween. A switching layer containing a switchably conductive silicon oxide resides in the the gap region between the first electical contact and the second electrical contact. The electronic devices exhibit hysteretic current versus voltage properties, enabling their use in switching and memory applications. Methods for configuring, operating and constructing the electronic devices are also presented herein.

  13. On the photoluminescence of as-deposited Tb-doped silicon oxides and oxynitrides fabricated by ECR-PECVD

    NASA Astrophysics Data System (ADS)

    Ramírez, J. M.; Wojcik, J.; Berencén, Y.; Mascher, P.; Garrido, B.

    2014-05-01

    In-situ doping of Tb3+ ions in silicon oxides and oxynitrides deposited by electron-cyclotron-resonance plasma enhanced chemical-vapour (ECR-PECVD) has been performed. Oxygen and nitrogen gas flow rates were changed to produce a gradual substitution of oxygen by nitrogen in the host matrix. Bright green luminescence from as-deposited layers is observed by the naked eye under daylight conditions. Tbdoped nitrogen-rich samples showed a considerable photoluminescence (PL) enhancement compared to Tb-doped silicon oxides. An optimum layer composition for efficient Tb3+ excitation under non-resonant optical pumping is obtained. The combination of a low temperature treatment with bright luminescence could be instrumental for the development of light emitting devices in other platforms with more restrictive temperature requirements.

  14. Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

    2007-01-01

    Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

  15. Fabrication and characterization of a fuel flexible micro-reformer fully integrated in silicon for micro-solid oxide fuel cell applications

    NASA Astrophysics Data System (ADS)

    Pla, D.; Salleras, M.; Garbayo, I.; Morata, A.; Sabaté, N.; Divins, N. J.; Llorca, J.; Tarancón, A.

    2015-05-01

    A novel design of a fuel-flexible micro-reactor for hydrogen generation from ethanol and methane is proposed in this work. The micro-reactor is fully fabricated with mainstream MEMS technology and consists of an array of more than 20000 through-silicon vertically aligned micro-channels per cm2 of 50 μm in diameter. Due to this unique configuration, the micro-reformer presents a total surface per projected area of 16 cm2/cm2 and per volume of 320 cm2/cm3. The active surface of the micro-reformer, i.e. the walls of the micro-channels, is homogenously coated with a thin film of Rh- Pd/CeO2 catalyst. Excellent steam reforming of ethanol and dry reforming of methane are presented with hydrogen production rates above 3 mL/min·cm2 and hydrogen selectivity of ca. 50% on a dry basis at operations conditions suitable for application in micro-solid oxide fuel cells (micro-SOFCs), i.e. 700-800ºC and fuel flows of 0.02 mLL/min for ethanol and 36 mLG/min for methane (corresponding to a system able to produce one electrical watt).

  16. A time-pulsed positronium beam and a study of oxides on silicon using positrons

    SciTech Connect

    Khatri, R.K.

    1993-01-01

    The studies on rare gas solid moderators were carried out with a 350 [mu]Ci [sup 22]Na radioactive source. The corrected efficiency for neon moderator in conical geometrical configuration was as high as (1.4 [+-] 0.2)%. The conical configuration moderator performed better by a factor of (2.2 [+-] 0.2) than the cylindrical configuration. A time pulsed positron beam was built to carry out investigations on the positronium formation processes and positronium beam. This beam has the capability to store low energy e[sup +] in a magnetic bottle, with a magnetic bottle at one end and an electrostatic mirror at the other. These stored e[sup +] are then bunched to form a pulse with a buncher. The bunched beam had a FWHM of 17 nsec and contained 1 to 2 e[sup +]/pulse. A thin carbon foil of 50 [angstrom] thickness was used for positronium formation by process of charge exchange. Positronium Annihilation Spectroscopy (PAS) was utilized to carry out studies on the activation energy of hydrogen at the interface of oxide and silicon substrate and the effect of irradiation on the oxides in SiO[sub 2]/Si(100) sample. The activation energy of hydrogen at the interface of SiO[sub 2]/Si(100) samples with n- and p-type substrate was measured to be 2.60(6) eV and 2.47(6) eV respectively. The investigations of the samples irradiated with x-ray and [gamma]-ray led to the first time identification of creation of E[prime] centers with PAS.

  17. Characterization of hybrid cobalt-porous silicon systems: protective effect of the Matrix in the metal oxidation

    PubMed Central

    2012-01-01

    In the present work, the characterization of cobalt-porous silicon (Co-PSi) hybrid systems is performed by a combination of magnetic, spectroscopic, and structural techniques. The Co-PSi structures are composed by a columnar matrix of PSi with Co nanoparticles embedded inside, as determined by Transmission Electron Microscopy (TEM). The oxidation state, crystalline structure, and magnetic behavior are determined by X-Ray Absorption Spectroscopy (XAS) and Alternating Gradient Field Magnetometry (AGFM). Additionally, the Co concentration profile inside the matrix has been studied by Rutherford Backscattering Spectroscopy (RBS). It is concluded that the PSi matrix can be tailored to provide the Co nanoparticles with extra protection against oxidation. PMID:22938050

  18. Fabrication of silicon nanowire/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-graphene oxide hybrid solar cells

    NASA Astrophysics Data System (ADS)

    Uma, Kasimayan; Subramani, Thiyagu; Syu, Hong-Jhang; Lin, Tzu-Ching; Lin, Ching-Fuh

    2015-03-01

    Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) Schottky junctions have shown great promise as high efficiency, cost effective solar cells. Here, hybrid SiNWs/PEDOT:PSS blended graphene oxide (GO) solar cells are prepared and investigated. The SiNWs/PEDOT:PSS blended GO cells show enhanced light trapping and a large junction area when compared to pure PEDOT:PSS structures. SiNWs combined with GO solar cells show energy conversion efficiencies of up to 9.57% under the AM 1.5G condition, opening the possibility of using semiconductor/graphene oxide in photovoltaic applications.

  19. Self-assembly-induced formation of high-density silicon oxide memristor nanostructures on graphene and metal electrodes.

    PubMed

    Park, Woon Ik; Yoon, Jong Moon; Park, Moonkyu; Lee, Jinsup; Kim, Sung Kyu; Jeong, Jae Won; Kim, Kyungho; Jeong, Hu Young; Jeon, Seokwoo; No, Kwang Soo; Lee, Jeong Yong; Jung, Yeon Sik

    2012-03-14

    We report the direct formation of ordered memristor nanostructures on metal and graphene electrodes by a block copolymer self-assembly process. Optimized surface functionalization provides stacking structures of Si-containing block copolymer thin films to generate uniform memristor device structures. Both the silicon oxide film and nanodot memristors, which were formed by the plasma oxidation of the self-assembled block copolymer thin films, presented unipolar switching behaviors with appropriate set and reset voltages for resistive memory applications. This approach offers a very convenient pathway to fabricate ultrahigh-density resistive memory devices without relying on high-cost lithography and pattern-transfer processes. PMID:22324809

  20. Oxidation Properties of Nitrogen-Doped Silicon Films Deposited from Si2H6 and NH3

    NASA Astrophysics Data System (ADS)

    Scheid, Emmanuel; Boyer, Pierre; Samitier, Josep; Hassani, Ahmed

    1994-03-01

    Si2H6/NH3 gas mixture was employed to obtain, by low-pressure chemical vapor deposition (LPCVD) at low temperature, nitrogen-doped silicon (NIDOS) films with various N/Si ratios. Thermal oxide was grown in dry oxygen at 900°C and 1100°C on NIDOS films. The result indicates that the nitrogen content of NIDOS films, assessed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), greatly influences their oxidation rate.