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Sample records for polycrystalline silicon promise

  1. Thin film polycrystalline silicon: Promise and problems in displays and solar cells

    SciTech Connect

    Fonash, S.J.

    1995-08-01

    Thin film polycrystalline Si (poly-Si) with its carrier mobilities, potentially good stability, low intragrain defect density, compatibility with silicon processing, and ease of doping activation is an interesting material for {open_quotes}macroelectronics{close_quotes} applications such as TFTs for displays and solar cells. The poly-Si films needed for these applications can be ultra-thin-in the 500{Angstrom} to 1000{Angstrom} thickness range for flat panel display TFTs and in the 4{mu}m to 10{mu}m thickness range for solar cells. Because the films needed for these microelectronics applications can be so thin, an effective approach to producing the films is that of crystallizing a-Si precursor material. Unlike cast materials, poly-Si films made this way can be produced using low temperature processing. Unlike deposited poly-Si films, these crystallized poly-Si films can have grain widths that are much larger than the film thickness and almost atomically smooth surfaces. This thin film poly-Si crystallized from a-Si precursor films, and its promise and problems for TFTs and solar cells, is the focus of this discussion.

  2. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1985-01-01

    Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells.

  3. Casting larger polycrystalline silicon ingots

    SciTech Connect

    Wohlgemuth, J.; Tomlinson, T.; Cliber, J.; Shea, S.; Narayanan, M.

    1995-08-01

    Solarex has developed and patented a directional solidification casting process specifically designed for photovoltaics. In this process, silicon feedstock is melted in a ceramic crucible and solidified into a large grained semicrystalline silicon ingot. In-house manufacture of low cost, high purity ceramics is a key to the low cost fabrication of Solarex polycrystalline wafers. The casting process is performed in Solarex designed casting stations. The casting operation is computer controlled. There are no moving parts (except for the loading and unloading) so the growth process proceeds with virtually no operator intervention Today Solarex casting stations are used to produce ingots from which 4 bricks, each 11.4 cm by 11.4 cm in cross section, are cut. The stations themselves are physically capable of holding larger ingots, that would yield either: 4 bricks, 15 cm by 15 an; or 9 bricks, 11.4 cm by 11.4 an in cross-section. One of the tasks in the Solarex Cast Polycrystalline Silicon PVMaT Program is to design and modify one of the castings stations to cast these larger ingots. If successful, this effort will increase the production capacity of Solarex`s casting stations by 73% and reduce the labor content for casting by an equivalent percentage.

  4. Losses in polycrystalline silicon waveguides

    NASA Astrophysics Data System (ADS)

    Foresi, J. S.; Black, M. R.; Agarwal, A. M.; Kimerling, L. C.

    1996-04-01

    The losses of polycrystalline silicon (polySi) waveguides clad by SiO2 are measured by the cutback technique. We report losses of 34 dB/cm at a wavelength of 1.55 μm in waveguides fabricated from chemical mechanical polished polySi deposited at 625 °C. These losses are two orders of magnitude lower than reported absorption measurements for polySi. Waveguides fabricated from unpolished polySi deposited at 625 °C exhibit losses of 77 dB/cm. We find good agreement between calculated and measured losses due to surface scattering.

  5. Polycrystalline Silicon: a Biocompatibility Assay

    SciTech Connect

    Pecheva, E.; Fingarova, D.; Pramatarova, L.; Hikov, T.; Laquerriere, P.; Bouthors, Sylvie; Dimova-Malinovska, D.; Montgomery, P.

    2010-01-21

    Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

  6. Polycrystalline silicon study: Low-cost silicon refining technology prospects and semiconductor-grade polycrystalline silicon availability through 1988

    NASA Technical Reports Server (NTRS)

    Costogue, E. N.; Ferber, R.; Lutwack, R.; Lorenz, J. H.; Pellin, R.

    1984-01-01

    Photovoltaic arrays that convert solar energy into electrical energy can become a cost effective bulk energy generation alternative, provided that an adequate supply of low cost materials is available. One of the key requirements for economic photovoltaic cells is reasonably priced silicon. At present, the photovoltaic industry is dependent upon polycrystalline silicon refined by the Siemens process primarily for integrated circuits, power devices, and discrete semiconductor devices. This dependency is expected to continue until the DOE sponsored low cost silicon refining technology developments have matured to the point where they are in commercial use. The photovoltaic industry can then develop its own source of supply. Silicon material availability and market pricing projections through 1988 are updated based on data collected early in 1984. The silicon refining industry plans to meet the increasing demands of the semiconductor device and photovoltaic product industries are overviewed. In addition, the DOE sponsored technology research for producing low cost polycrystalline silicon, probabilistic cost analysis for the two most promising production processes for achieving the DOE cost goals, and the impacts of the DOE photovoltaics program silicon refining research upon the commercial polycrystalline silicon refining industry are addressed.

  7. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  8. Polycrystalline silicon ion sensitive field effect transistors

    NASA Astrophysics Data System (ADS)

    Yan, F.; Estrela, P.; Mo, Y.; Migliorato, P.; Maeda, H.; Inoue, S.; Shimoda, T.

    2005-01-01

    We report the operation of polycrystalline silicon ion sensitive field effect transistors. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with a Si3N4 sensing layer. Nearly ideal pH sensitivity (54mV /pH) and stable operation have been achieved. Temperature effects have been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The sensitivity to penicillin G is about 10mV/mM, in solutions with concentration lower than the saturation value, which is about 7 mM.

  9. Process Research of Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1984-01-01

    A passivation process (hydrogenation) that will improve the power generation of solar cells fabricated from presently produced, large grain, cast polycrystalline silicon (Semix), a potentially low cost material are developed. The first objective is to verify the operation of a DC plasma hydrogenation system and to investigate the effect of hydrogen on the electrical performance of a variety of polycrystalline silicon solar cells. The second objective is to parameterize and optimize a hydrogenation process for cast polycrystalline silicon, and will include a process sensitivity analysis. The sample preparation for the first phase is outlined. The hydrogenation system is described, and some early results that were obtained using the hydrogenation system without a plasma are summarized. Light beam induced current (LBIC) measurements of minicell samples, and their correlation to dark current voltage characteristics, are discussed.

  10. Process for Polycrystalline film silicon growth

    DOEpatents

    Wang, Tihu; Ciszek, Theodore F.

    2001-01-01

    A process for depositing polycrystalline silicon on substrates, including foreign substrates, occurs in a chamber at about atmospheric pressure, wherein a temperature gradient is formed, and both the atmospheric pressure and the temperature gradient are maintained throughout the process. Formation of a vapor barrier within the chamber that precludes exit of the constituent chemicals, which include silicon, iodine, silicon diiodide, and silicon tetraiodide. The deposition occurs beneath the vapor barrier. One embodiment of the process also includes the use of a blanketing gas that precludes the entrance of oxygen or other impurities. The process is capable of repetition without the need to reset the deposition zone conditions.

  11. Process Research On Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Culik, J. S.

    1982-01-01

    The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented.

  12. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  13. Polycrystalline silicon on tungsten substrates

    NASA Technical Reports Server (NTRS)

    Bevolo, A. J.; Schmidt, F. A.; Shanks, H. R.; Campisi, G. J.

    1979-01-01

    Thin films of electron-beam-vaporized silicon were deposited on fine-grained tungsten substrates under a pressure of about 1 x 10 to the -10th torr. Mass spectra from a quadrupole residual-gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400 and 780 C, and deposition rates were between 20 and 630 A min. Surface contamination and interdiffusion were monitored by in situ Auger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, X-ray analysis, and SEM in the topographic and channeling modes were utilized to characterize the samples with respect to silicon-metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625 C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine-grain silicon films were obtained at lower temperatures.

  14. Hydrogen migration in phosphorous doped polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Kaiser, I.

    1998-12-31

    Hydrogen diffusion in phosphorous doped polycrystalline silicon was investigated by deuterium diffusion experiments. The presence of phosphorous enhances hydrogen diffusion. For high hydrogen concentrations the activation energy of the effective diffusion-coefficient amounts to 0.25--0.35 eV. At low hydrogen concentrations diffusion is governed by deep traps that are present in an appreciable concentration of 6 {times} 10{sup 18}--10{sup 19} cm{sup {minus}3}. The hydrogen chemical-potential, {mu}{sub H}, decreases with increasing temperature at a rate of {approx}0.002 eV/K. The data are discussed in terms of a two-level model used to describe hydrogen diffusion in amorphous and undoped polycrystalline silicon.

  15. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1984-01-01

    Results of hydrogen-passivated polycrystalline silicon solar cells are summarized. Very small grain or short minority-carrier diffusion length silicon was used. Hydrogenated solar cells fabricated from this material appear to have effective minority-carrier diffusion lengths that are still not very long, as shown by the open-circuit voltages of passivated cells that are still significantly less than those of single-crystal solar cells. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. However, the open-circuit voltage, which is sensitive to grain boundary recombination, is sometimes 20 to 40 mV less. The goal was to minimize variations in open-circuit voltage and fill-factor caused by defects by passivating these defects using a hydrogenation process. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystaline silicon solar cells.

  16. Equilibrium shapes of polycrystalline silicon nanodots

    SciTech Connect

    Korzec, M. D. Wagner, B.; Roczen, M.; Schade, M.; Rech, B.

    2014-02-21

    This study is concerned with the topography of nanostructures consisting of arrays of polycrystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a “dewetting” process of an amorphous Si (a-Si) layer from a SiO{sub 2} coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support “partial wetting” and grain boundaries for the polycrystalline case. We then use our method to predict the morphologies of silicon nanodots.

  17. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1982-01-01

    The investigation of the performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was continued by fabricating a set of minicell wafers on a selection of 10 cm x 10 cm wafers. A minicell wafer consists of an array of small (approximately 0.2 sq cm in area) photodiodes which are isolated from one another by a mesa structure. The junction capacitance of each minicell was used to obtain the dopant concentration, and therefore the resistivity, as a function of position across each wafer. The results indicate that there is no significant variation in resistivity with position for any of the polycrystalline wafers, whether Semix or Wacker. However, the resistivity of Semix brick 71-01E did decrease slightly from bottom to top.

  18. Solution-processed polycrystalline silicon on paper

    SciTech Connect

    Trifunovic, M.; Ishihara, R.; Shimoda, T.

    2015-04-20

    Printing electronics has led to application areas which were formerly impossible with conventional electronic processes. Solutions are used as inks on top of large areas at room temperatures, allowing the production of fully flexible circuitry. Commonly, research in these inks have focused on organic and metal-oxide ink materials due to their printability, while these materials lack in the electronic performance when compared to silicon electronics. Silicon electronics, on the other hand, has only recently found their way in solution processes. Printing of cyclopentasilane as the silicon ink has been conducted and devices with far superior electric performance have been made when compared to other ink materials. A thermal annealing step of this material, however, was necessary, which prevented its usage on inexpensive substrates with a limited thermal budget. In this work, we introduce a method that allows polycrystalline silicon (poly-Si) production directly from the same liquid silicon ink using excimer laser irradiation. In this way, poly-Si could be formed directly on top of paper even with a single laser pulse. Using this method, poly-Si transistors were created at a maximum temperature of only 150 °C. This method allows silicon device formation on inexpensive, temperature sensitive substrates such as polyethylene terephthalate, polyethylene naphthalate or paper, which leads to applications that require low-cost but high-speed electronics.

  19. Polycrystalline silicon semiconducting material by nuclear transmutation doping

    DOEpatents

    Cleland, John W.; Westbrook, Russell D.; Wood, Richard F.; Young, Rosa T.

    1978-01-01

    A NTD semiconductor material comprising polycrystalline silicon having a mean grain size less than 1000 microns and containing phosphorus dispersed uniformly throughout the silicon rather than at the grain boundaries.

  20. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  1. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  2. Deposited silicon photonics: Optical interconnect devices in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Preston, Kyle Jonathan

    Silicon photonics has tremendous potential to provide high-bandwidth and low-power data communication for applications such as computing and telecommunication, over length scales ranging from 100 kilometers over fiber to centimeter-length on-chip waveguides. Many silicon photonic building blocks have been demonstrated to date, but critical work remains to determine the best approaches for integrating together silicon photonics with microelectronics. In this thesis, I explore a novel method for integration of silicon photonics on the CMOS platform by using a deposited material: polycrystalline silicon. I will show the first demonstrations of electrically-active optical filters, modulators, and photodetectors in this material. In principle, this material platform would allow for the integration of silicon photonic devices and systems on top of any substrate, including complex CMOS and memory chips or even glass and plastic substrates. In Chapter 1, I introduce the state-of-the-art in silicon photonics, describe several integration schemes under development, and introduce the idea of using deposited materials. In Chapter 2, I demonstrate the use of polysilicon to make integrated microring resonators, and show the integration of different silicon materials together. Chapter 3 discusses the use of polysilicon as both an optical waveguiding layer and an electrode material in slot waveguides for the application of light emitters. Chapter 4 demonstrates the use of a pump-probe experiment to measure the free carrier lifetime in the material and demonstrate all-optical modulation. In Chapter 5, I demonstrate the first high-speed integrated electro-optic modulator in polysilicon, a necessary device for optical transmitters. In Chapter 6, I show how defects inside the same material enable integrated photodetectors at near-infrared telecommunication wavelengths. Chapter 7 shows initial results in adapting the material processing for lower temperatures, necessary for integration

  3. Effect of copper impurity on polycrystalline silicon solar cells

    NASA Technical Reports Server (NTRS)

    Daud, T.; Koliwad, K. M.

    1978-01-01

    The presence of copper impurity, up to 10 to the 15th atoms/cc, in single crystal silicon has been shown to have no deleterious effect on the p-n junction solar cell performance. However, in polycrystalline silicon, copper atoms tend to migrate to the defect sites because of the structural sensitive properties of copper. This study was undertaken to investigate the influence of this behavior of copper impurity on the performance of p-n junction solar cells fabricated from structurally imperfect silicon. Two sets of polycrystalline silicon substrates containing copper were examined. In one set of samples, copper was incorporated during growth, whereas in the other, copper was diffused. Solar cells were fabricated on both the sets of substrates by a standard process. Dark and light I-V and spectral response characteristics of the cells were measured and compared with copper-free polycrystalline silicon solar cells. The results and the model are discussed.

  4. Defect behavior of polycrystalline solar cell silicon

    SciTech Connect

    Schroder, D.K.; Park, S.H.; Hwang, I.G.; Mohr, J.B.; Hanly, M.P.

    1993-05-01

    The major objective of this study, conducted from October 1988 to September 1991, was to gain an understanding of the behavior of impurities in polycrystalline silicon and the influence of these impurities on solar cell efficiency. The authors studied edge-defined film-fed growth (EFG) and cast poly-Si materials and solar cells. With EFG Si they concentrated on chromium-doped materials and cells to determine the role of Cr on solar cell performance. Cast poly-Si samples were not deliberately contaminated. Samples were characterized by cell efficiency, current-voltage, deep-level transient spectroscopy (DLTS), surface photovoltage (SPV), open-circuit voltage decay, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy measurements. They find that Cr forms Cr-B pairs with boron at room temperature and these pairs dissociate into Cr{sub i}{sup +} and B{sup {minus}} during anneals at 210{degrees}C for 10 min. Following the anneal, Cr-B pairs reform at room temperature with a time constant of 230 h. Chromium forms CrSi{sub 2} precipitates in heavily contaminated regions and they find evidence of CrSi{sub 2} gettering, but a lack of chromium segregation or precipitation to grain boundaries and dislocations. Cr-B pairs have well defined DLTS peaks. However, DLTS spectra of other defects are not well defined, giving broad peaks indicative of defects with a range of energy levels in the band gap. In some high-stress, low-efficiency cast poly-Si they detect SiC precipitates, but not in low-stress, high-efficiency samples. SPV measurements result in nonlinear SPV curves in some materials that are likely due to varying optical absorption coefficients due to locally varying stress in the material.

  5. MIS and SIS solar cells on polycrystalline silicon

    SciTech Connect

    Cheek, G.; Mertens, R.

    1980-02-01

    MIS and SIS structured solar cells are receiving much attention in the photovoltaic community. Seemingly, these cells could be a viable alternative to thermally diffused p-n junctions for use on thin-film polycrystalline silicon substrates. This review describes MIS/SIS structured solar cells and the possible advantages of these structures for use with thin-film polycrystalline silicon. The results of efficiency calculations are presented. Also addressed are lifetime stability and fabrication techniques amenable to large scale production. Finally, the relative advantages and disadvantages of these cells and the results obtained are presented.

  6. Polycrystalline silicon material availability and market pricing outlook study for 1980 to 88: January 1983 update

    NASA Technical Reports Server (NTRS)

    Costogue, E.; Pellin, R.

    1983-01-01

    Photovoltaic solar cell arrays which convert solar energy into electrical energy can become a cost effective, alternative energy source provided that an adequate supply of low priced materials and automated fabrication techniques are available. Presently, silicon is the most promising cell material for achieving the near term cost goals of the Photovoltaics Program. Electronic grade silicon is produced primarily for the semiconductor industry with the photovoltaic industry using, in most cases, the production rejects of slightly lower grade material. Therefore, the future availability of adequate supplies of low cost silicon is one of the major concerns of the Photovoltaic Program. The supply outlook for silicon with emphasis on pricing is updated and is based primarily on an industry survey conducted by a JPL consultant. This survey included interviews with polycrystalline silicon manufacturers, a large cross section of silicon users and silicon solar cell manufacturers.

  7. Laser-induced amorphization of silicon during pulsed-laser irradiation of TiN/Ti/polycrystalline silicon/SiO2/silicon

    NASA Astrophysics Data System (ADS)

    Chong, Y. F.; Pey, K. L.; Wee, A. T. S.; Thompson, M. O.; Tung, C. H.; See, A.

    2002-11-01

    In this letter, we report on the complex solidification structures formed during laser irradiation of a titanium nitride/titanium/polycrystalline silicon/silicon dioxide/silicon film stack. Due to enhanced optical coupling, the titanium nitride/titanium capping layer increases the melt depth of polycrystalline silicon by more than a factor of 2. It is found that the titanium atoms diffuse through the entire polycrystalline silicon layer during irradiation. Contrary to the expected polycrystalline silicon growth, distinct regions of polycrystalline and amorphous silicon are formed instead. Possible mechanisms for the formation of these microstructures are proposed.

  8. A new directional solidification technique for polycrystalline solar grade silicon

    NASA Astrophysics Data System (ADS)

    Saito, T.; Shimura, A.; Ichikawa, S.

    A new directional solidification (casting) technique using powder mold releasing agent is described for producing polycrystalline solar grade silicon. Crack-free and stress-free growth of silicon was attainable with fused quartz crucibles coated with nitride powder, such as silicon nitride Si3 N4, on the inner crucible walls. The degree of nitrogen contamination was negligible because of the low nitrogen solubility in solid silicon. Other impurities contents were less than the ppm level. The average grain diameter was close to 0.1 cm. Diffused junction solar cells (n+/p structure) were fabricated by using this boron doped 1 ohm-cm material. An AM1 conversion efficiency of 12.4% on the cells of 20 cm sq area was obtained. The minority carrier diffusion length of this material was estimated to be greater than 80 microns.

  9. Thin-film polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Funghnan, B. W.; Blanc, J.; Phillips, W.; Redfield, D.

    1980-08-01

    Thirty-four new solar cells were fabricated on Wacker Sislo substrates and the AM-1 parameters were measured. A detailed comparison was made between the measurement of minority carrier diffusion length by the OE method and the penetrating light laser scan grain boundary photoresponse linewidth method. The laser scan method has more experimental uncertainty and agrees within 10 to 50% with the QE method. It allows determination of L over a large area. Atomic hydrogen passivation studies continued on Wacker material by three techniques. A method of determining surface recombination velocity, s, from laser scan data was developed. No change in s in completed solar cells after H-plasma treatment was observed within experimental error. H-passivation of bare silicon cars as measured by the new laser scan photoconductivity technique showed very large effects.

  10. Dependence of resistivity on the doping level of polycrystalline silicon

    NASA Technical Reports Server (NTRS)

    Fripp, A. L.

    1975-01-01

    The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as-deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 10 to the 16th atoms/per cu cm was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

  11. Reactive sticking coefficients for silane and disilane on polycrystalline silicon

    SciTech Connect

    Buss, R.J.; Ho, P.; Breiland, W.G.; Coltrin, M.E.

    1988-04-15

    Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition-rate measurements using molecular beam scattering and a very low-pressure cold-wall reactor. The RSCs have nonlinear Arrhenius temperature dependencies and decrease with increasing flux at low (710 /sup 0/C) temperatures. Several simple models are proposed to explain these observations. The results are compared with previous studies of the SiH/sub 4//Si(s) reaction and low-pressure chemical vapor deposition-rate measurements.

  12. Spherical silicon photonic microcavities: From amorphous to polycrystalline

    NASA Astrophysics Data System (ADS)

    Fenollosa, R.; Garín, M.; Meseguer, F.

    2016-06-01

    Shaping silicon as a spherical object is not an obvious task, especially when the object size is in the micrometer range. This has the important consequence of transforming bare silicon material in a microcavity, so it is able to confine light efficiently. Here, we have explored the inside volume of such microcavities, both in their amorphous and in their polycrystalline versions. The synthesis method, which is based on chemical vapor deposition, causes amorphous microspheres to have a high content of hydrogen that produces an onionlike distributed porous core when the microspheres are crystallized by a fast annealing regime. This substantially influences the resonant modes. However, a slow crystallization regime does not yield pores, and produces higher-quality-factor resonances that could be fitted to the Mie theory. This allows the establishment of a procedure for obtaining size calibration standards with relative errors of the order of 0.1%.

  13. Limiting mechanisms in large-grain polycrystalline silicon Spatial homogeneity

    NASA Technical Reports Server (NTRS)

    Culik, J.; Grimes, K.

    1984-01-01

    An experiment to investigate the spatial homogeneity of large-grain polycrystalline silicon shows a number of performance-loss mechanisms. Arrays of up to 400 small (about 0.2 sq cm in area) photodiodes were fabricated on a selection of 10 cm x 10 cm polycrystalline silicon wafers. Measurements of the illuminated current-voltage (J-V) characteristics were used to generate maps of Voc, Jsc, and FF as a function of position; and dark J-V and LBIC analysis were used to determine the cause of low performance in areas with significantly degraded J-V characteristics. In addition to the presence of inclusions, which act as resistive shunts, the performance of many of the cells is limited by quasineutral recombination current, which may vary by up to an order of magnitude across a wafer. The increase is the result of either electrically-active grain boundaries or numerous subgrain boundaries within the grain bulk. In other isolated instances, the open-circuit voltage is reduced by excess space-charge recombination current that is not correlated with either grain or subgrain boundary activity.

  14. Photoluminescence of silicon after deposition of polycrystalline diamond films

    SciTech Connect

    Aminev, D. F.; Bagaev, V. S.; Galkina, T. I.; Klokov, A. Yu. Krivobok, V. S.; Ralchenko, V. G.; Savel'ev, A. V.

    2009-09-15

    Low-temperature (5K) photoluminescence of silicon substrates in the range 0.8-1.2 eV is studied before and after deposition of polycrystalline diamond films. The diamond films were deposited in the microwave plasma onto high-purity dislocation-free silicon (with the resitivity {rho} {approx} 3 k{Omega} cm) subjected to mechanical polishing or more delicate chemical and mechanical polishing. The deposition temperature was 750-850 deg. C. In the photoluminescence spectra of the samples with the substrates polished chemically and mechanically, two lines, D{sub 1} and D{sub 2}, corresponding to the dislocation-related emission are recorded. Generation of dislocations in the substrates is caused by efficient adhesion of the diamond film and, as a result, by internal stresses that relax with the formation of dislocations. The experimental spectra are practically identical to the photoluminescence spectra observed in silicon ({rho} {approx} 100 {Omega} cm) with the density of dislocations {approx}10{sup 4} cm{sup -2}.

  15. Fabricating micro-instruments in surface-micromachined polycrystalline silicon

    SciTech Connect

    Comtois, J.H.; Michalicek, M.A.; Barron, C.C.

    1997-04-01

    Smaller, lighter instruments can be fabricated as Micro-Electro-Mechanical Systems (MEMS), having micron scale moving parts packaged together with associated control and measurement electronics. Batch fabrication of these devices will make economical applications such as condition-based machine maintenance and remote sensing. The choice of instrumentation is limited only by the designer`s imagination. This paper presents one genre of MEMS fabrication, surface-micromachined polycrystalline silicon (polysilicon). Two currently available but slightly different polysilicon processes are presented. One is the ARPA-sponsored ``Multi-User MEMS ProcesS`` (MUMPS), available commercially through MCNC; the other is the Sandia National Laboratories ``Sandia Ultra-planar Multilevel MEMS Technology`` (SUMMiT). Example components created in both processes will be presented, with an emphasis on actuators, actuator force testing instruments, and incorporating actuators into larger instruments.

  16. Predicting fracture in micron-scale polycrystalline silicon MEMS structures.

    SciTech Connect

    Hazra, Siddharth S.; de Boer, Maarten Pieter; Boyce, Brad Lee; Ohlhausen, James Anthony; Foulk, James W., III; Reedy, Earl David, Jr.

    2010-09-01

    Designing reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clear how to use a measured tensile strength distribution to predict the strength of a complex MEMS structure. To address such issues, two recently developed high throughput MEMS tensile test techniques have been used to measure strength distribution tails. The measured tensile strength distributions enable the definition of a threshold strength as well as an inferred maximum flaw size. The nature of strength-controlling flaws has been identified and sources of the observed variation in strength investigated. A double edge-notched specimen geometry was also tested to study the effect of a severe, micron-scale stress concentration on the measured strength distribution. Strength-based, Weibull-based, and fracture mechanics-based failure analyses were performed and compared with the experimental results.

  17. Fabrication of translucent boron nitride dispersed polycrystalline silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Fu, Z.; Niihara, K.; Lee, S. W.

    2011-03-01

    Optical transparency was achieved at infrared region and overall translucent silicon nitride was fabricated using hot press sintering (HPS). The increase in h-BN content decreased the optical transparency. Microstructral observations shows that the optical, mechanical and tribological properties of BN dispersed polycrystalline Si3N4 ceramics were affected by the density, α:β-phase ratio and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN at 1850°C. The composite contained from 0.25 to 2 mass % BN powder with sintering aids (9% AlN + 3% MgO). Maximum transmittance of 57% was achieved for 0.25 mass % BN doped Si3N4 ceramics. Fracture toughness was increased and wear volume and friction coefficient were decreased with increase in BN content.

  18. Properties of boron-doped thin films of polycrystalline silicon

    SciTech Connect

    Merabet, Souad

    2013-12-16

    The properties of polycrystalline-silicon films deposited by low pressure chemical vapor deposition and doped heavily in situ boron-doped with concentration level of around 2×10{sup 20}cm{sup −3} has been studied. Their properties are analyzed using electrical and structural characterization means by four points probe resistivity measurements and X-ray diffraction spectra. The thermal-oxidation process are performed on sub-micron layers of 200nm/c-Si and 200nm/SiO{sub 2} deposited at temperatures T{sub d} ranged between 520°C and 605°C and thermally-oxidized in dry oxygen ambient at 945°C. Compared to the as-grown resistivity with silicon wafers is known to be in the following sequence <ρ{sub 200nm/c−Si}> < <ρ{sub 200nm/SiO2}> and <ρ{sub 520}> < <ρ{sub 605}>. The measure X-ray spectra is shown, that the Bragg peaks are marked according to the crystal orientation in the film deposited on bare substrates (poly/c-Si), for the second series of films deposited on bare oxidized substrates (poly/SiO{sub 2}) are clearly different.

  19. Electrical measurements on ion-implanted LPCVD polycrystalline silicon films

    NASA Astrophysics Data System (ADS)

    Huang, Ruey-Shing; Cheng, Chin-Hsiung; Liu, J. C.; Lee, M. K.; Chen, C. T.

    1983-07-01

    The electrical conduction properties of ion implanted polycrystalline silicon films have been studied. The polysilicon films were deposited by pyrolysis of silane at 647°C in LPCVD system onto oxide-coated silicon wafers to a thickness of 0.6 μm. Dopants were itroducd by implanting with boron or phosphorus ions, accelerated to 145 keV; doses ranged from 1 × 10 12 cm -2 to 1 × 10 15 cm -2. Film resistivities spanning 8 orders of magnitude were obtained using this doping range. Current-voltage characteristics of polysilicon resistors were measured at temperatures ranging from 24 to 140°C. The associated barrier heights and activation energies were derived. The grain-boundary trapping states density was estimated to be 5 × 10 12 cm -2. We found that both dopant atom segregation and carrier trapping at the grain boundaries play important roles in polysilicon electrical conduction properties. However, within the dose range studies, the dopant atom segragation is most detrimental to the film conductivity for doses < 1 × 10 13 cm -2; as the dose is increased, carrier trapping effects become more pronounced for doses up to 5 × 10 14 cm -2. For doses ⩾ 5 × 10 14 cm -2, conduction due to carriers tunneling through the potential barriers at grain boundaries has to be considered.

  20. Improvements in cast polycrystalline silicon PV manufacturing technology

    NASA Astrophysics Data System (ADS)

    Wohlgemuth, John H.

    1997-02-01

    The objectives of this NREL sponsored Photovoltaic Manufacturing Technology (PVMaT) Program are to advance Solarex's cast polycrystalline silicon manufacturing technology, reduce module production cost in half, increase module performance and expand Solarex's commercial production capacity by a factor of three. To meet these objectives Solarex has: 1) Modified the casting process and stations and is now casting larger ingots in production; 2) Developed wire saw technology to cut wafers with less kerf loss and has transferred this technology to production; 3) Developed a laboratory process to increase cell efficiencies using back surface fields, mechanical texturing and gettering; 4) Modified the casting, wires saw and cell processes in order to fabricate larger (15.2 cm by 15.2 cm) wafers and cells; 5) Improved the automated assembly of modules, reducing labor requirements and increasing throughput; and 6) Developed a frameless module with a lower cost backsheet and a simple, low cost electrical termination system. Solarex is now in the process of developing the equipment necessary for automated handling of thin 15.2 cm by 15.2 cm wafers and cells. This paper will discuss the efforts during the first two and a half years of the program.

  1. Highly Doped Polycrystalline Silicon Microelectrodes Reduce Noise in Neuronal Recordings In Vivo

    PubMed Central

    Saha, Rajarshi; Jackson, Nathan; Patel, Chetan; Muthuswamy, Jit

    2013-01-01

    The aims of this study are to 1) experimentally validate for the first time the nonlinear current-potential characteristics of bulk doped polycrystalline silicon in the small amplitude voltage regimes (0–200 μV) and 2) test if noise amplitudes (0–15 μV) from single neuronal electrical recordings get selectively attenuated in doped polycrystalline silicon microelectrodes due to the above property. In highly doped polycrystalline silicon, bulk resistances of several hundred kilo-ohms were experimentally measured for voltages typical of noise amplitudes and 9–10 kΩ for voltages typical of neural signal amplitudes (>150–200 μV). Acute multiunit measurements and noise measurements were made in n = 6 and n = 8 anesthetized adult rats, respectively, using polycrystalline silicon and tungsten microelectrodes. There was no significant difference in the peak-to-peak amplitudes of action potentials recorded from either microelectrode (p > 0.10). However, noise power in the recordings from tungsten microelectrodes (26.36 ± 10.13 pW) was significantly higher (p < 0.001) than the corresponding value in polycrystalline silicon microelectrodes (7.49 ± 2.66 pW). We conclude that polycrystalline silicon microelectrodes result in selective attenuation of noise power in electrical recordings compared to tungsten microelectrodes. This reduction in noise compared to tungsten microelectrodes is likely due to the exponentially higher bulk resistances offered by highly doped bulk polycrystalline silicon in the range of voltages corresponding to noise in multiunit measurements. PMID:20667815

  2. The effect of heat treatment on the resistivity of polycrystalline silicon films

    NASA Technical Reports Server (NTRS)

    Fripp, A. L., Jr.

    1975-01-01

    The resistivity of doped polycrystalline silicon films has been studied as a function of post deposition heat treatments in an oxidizing atmosphere. It was found that a short oxidation cycle may produce a resistivity increase as large as three orders of magnitude in the polycrystalline films. The extent of change was dependent on the initial resistivity and the films' doping level and was independent of the total oxidation time.

  3. The effects of intragrain defects on the local photoresponse of polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Inoue, N.; Wilmsen, C. W.; Jones, K. A.

    1981-02-01

    Intragrain defects in Wacker cast and Monsanto zone-refined polycrystalline silicon materials were investigated using the electron-beam-induced current (EBIC) technique. The EBIC response maps were compared with etch pit, local diffusion length and local photoresponse measurements. It was determined that the Wacker polycrystalline silicon has a much lower density of defects than does the Monsanto polycrystalline silicon and that most of the defects in the Wacker material are not active recombination sites. A correlation was found between the recombination site density, as determined by EBIC, and the local diffusion length. It is shown that a large density of intragrain recombination sites greatly reduces the minority carrier diffusion length and thus can significantly reduce the photoresponse of solar cells.

  4. Refractive index and extinction coefficient of doped polycrystalline silicon films in infrared spectrum

    NASA Astrophysics Data System (ADS)

    Zhang, Xia; Zhang, Dacheng

    2016-03-01

    The refractive index and extinction coefficient in infrared spectrum of the polycrystalline silicon films with different doped dosages, base on the inverse calculation, are obtained by means of utilizing the measured reflectance and transmittance of a layer of material and multilayer films, and the equations derived from photonics and electromagnetic theory. The calculation results demonstrate that the refractive index of the doped polycrystalline silicon films decreases with the doped dosages increasing and the extinction coefficient increases with the doped dosages increasing for a given wavelength. This method used for determining the refractive index and extinction coefficient of the polycrystalline silicon films is effective and has the advantage of that the measured samples are fabricated simply.

  5. Boron- and phosphorus-doped polycrystalline silicon thin films prepared by silver-induced layer exchange

    SciTech Connect

    Antesberger, T.; Wassner, T. A.; Jaeger, C.; Algasinger, M.; Kashani, M.; Scholz, M.; Matich, S.; Stutzmann, M.

    2013-05-27

    Intentional boron and phosphorus doping of polycrystalline silicon thin films on glass prepared by the silver-induced layer exchange is presented. A silver/(titanium) oxide/amorphous silicon stack is annealed at temperatures below the eutectic temperature of the Ag/Si system, leading to a complete layer exchange and simultaneous crystallization of the amorphous silicon. Intentional doping of the amorphous silicon prior to the exchange process results in boron- or phosphorus-doped polycrystalline silicon. Hall effect measurements show carrier concentrations between 2 Multiplication-Sign 10{sup 17} cm{sup -3} and 3 Multiplication-Sign 10{sup 20} cm{sup -3} for phosphorus and 4 Multiplication-Sign 10{sup 18} cm{sup -3} to 3 Multiplication-Sign 10{sup 19} cm{sup -3} for boron-doped layers, with carrier mobilities up to 90 cm{sup 2}/V s.

  6. Process Research On Polycrystalline Silicon Material (PROPSM). [flat plate solar array project

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1983-01-01

    The performance-limiting mechanisms in large-grain (greater than 1 to 2 mm in diameter) polycrystalline silicon solar cells were investigated by fabricating a matrix of 4 sq cm solar cells of various thickness from 10 cm x 10 cm polycrystalline silicon wafers of several bulk resistivities. Analysis of the illuminated I-V characteristics of these cells suggests that bulk recombination is the dominant factor limiting the short-circuit current. The average open-circuit voltage of the polycrystalline solar cells is 30 to 70 mV lower than that of co-processed single-crystal cells; the fill-factor is comparable. Both open-circuit voltage and fill-factor of the polycrystalline cells have substantial scatter that is not related to either thickness or resistivity. This implies that these characteristics are sensitive to an additional mechanism that is probably spatial in nature. A damage-gettering heat-treatment improved the minority-carrier diffusion length in low lifetime polycrystalline silicon, however, extended high temperature heat-treatment degraded the lifetime.

  7. The properties of polycrystalline silicon solar cells with controlled titanium additions

    NASA Technical Reports Server (NTRS)

    Rohatgi, A.; Hopkins, R. H.; Davis, J. R., Jr.

    1981-01-01

    By coupling the results of electrical measurements, such as spectral response, lighted and dark I-V determinations, and deep-level-transient spectroscopy with optical and laser scan photomicroscopy, the effects of grain boundaries and impurities on silicon solar cells were evaluated. Titanium, which produces two deep levels in silicon, degrades cell performance by reducing bulk lifetime and thus cell short-circuit current. Electrically active grain boundaries induce carrier recombination in the bulk and depletion regions of the solar cell. Experimental data imply a small but measurable segregation of titanium into some grain boundaries of the polycrystalline silicon containing high Ti concentration. However, for the titanium-contaminated polycrystalline material used in this study, solar cell performance is dominated by the electrically active titanium concentration in the grains. Microstructural impacts on the devices are of secondary importance

  8. Investigation of lifetime limiting microdefects in polycrystalline silicon for photovoltaic applications

    SciTech Connect

    Werner, M.; Weber, E.R.; McHugo, S.; Bailey, J.

    1994-12-31

    Electron Microscopy techniques were applied to the study of intragranular microdefects in as-grown and intentionally Fe contaminated polycrystalline silicon solar cell material. Electron-Energy-Loss Spectroscopy (EELS) imaging revealed bright contrasts in metal diffused samples and with smaller concentration in as-grown material, probably due to metal precipitates. High-resolution and analytical electron microscopy identified Cu- and Fe-silicide particles in the contaminated specimen. These results demonstrate that intragranular microdefects exist in polycrystalline Si which act as nucleation sites for metal contaminants and lend support to the model that metal-decorated microdefects are decisive lifetime killers in as-grown material.

  9. Polycrystalline Silicon Sheets for Solar Cells by the Improved Spinning Method

    NASA Technical Reports Server (NTRS)

    Maeda, Y.; Yokoyama, T.; Hide, I.

    1984-01-01

    Cost reduction of silicon materials in the photovoltaic program of materials was examined. The current process of producing silicon sheets is based entirely on the conventional Czochralski ingot growth and wafering used in the semiconductor industry. The current technology cannot meet the cost reduction demands for producing low cost silicon sheets. Alternative sheet production processes such as unconventional crystallization are needed. The production of polycrystalline silicon sheets by unconventional ingot technology is the casting technique. Though large grain sheets were obtained by this technique, silicon ribbon growth overcomes deficiencies of the casting process by obtaining the sheet directly from the melt. The need to solve difficulties of growth stability and impurity effects are examined. The direct formation process of polycrystalline silicon sheets with large grain size, smooth surface, and sharp edges from the melt with a high growth rate which will yield low cost silicon sheets for solar cells and the photovoltaic characteristics associated with this type of sheet to include an EBIC study of the grain boundaries are described.

  10. Development of transparent polycrystalline beta-silicon carbide

    NASA Astrophysics Data System (ADS)

    Bayya, Shyam S.; Villalobos, Guillermo R.; Hunt, Michael P.; Sanghera, Jasbinder S.; Sadowski, Bryan M.; Aggarwal, Ishwar D.; Cinibulk, Michael; Carney, Carmen; Keller, Kristin

    2013-09-01

    Transparent beta-SiC is of great interest because its high strength, low coefficient of thermal expansion, very high thermal conductivity, and cubic crystal structure give it a very high thermal shock resistance. A transparent, polycrystalline beta-SiC window will find applications in armor, hypersonic missiles, and thermal control for thin disc lasers. SiC is currently available as either small transparent vapor grown disks or larger opaque shapes. Neither of which are useful in window applications. We are developing sintering technology to enable transparent SiC ceramics. This involves developing procedures to make high purity powders and studying their densification behavior. We have been successful in demonstrating transparency in thin sections using Field Assisted Sintering Technology (FAST). This paper will discuss the reaction mechanisms in the formation of beta-SiC powder and its sintering behavior in producing transparent ceramics.

  11. Defect engineering by ultrasound treatment in polycrystalline silicon

    SciTech Connect

    Ostapenko, S.; Jastrzebski, L.

    1995-08-01

    By applying ultrasound treatment (UST) to bulk and thin film polycrystalline Si (poly-Si) we have found a dramatic improvement of recombination and transport properties. The increasing of minority carrier lifetime by as much as one order of magnitude was found in short diffusion length regions, while exhibiting a strong dispersion for entire solar-grade poly-Si wafer. Relevant mechanisms are attributed to ultrasound processing on crystallographic defects, as well as UST stimulated dissociation of Fe-B pairs followed by Fe{sub i} gettering. A spectacular improvement of hydrogenation efficiency in poly-Si thin-films on glass substrate is demonstrated by resistivity study and confirmed using spatially resolved photoluminescence and nanoscale contact potential difference mapping. By applying UST to commercial solar cells we found the increasing of cell efficiency at low light excitation.

  12. Hot-Wire Chemical Vapor Deposition Of Polycrystalline Silicon : From Gas Molecule To Solar Cell

    NASA Astrophysics Data System (ADS)

    van Veenendaal, P. A. T. T.

    2002-10-01

    Although the effort to investigate the use of renewable energy sources, such as wind and solar energy, has increased, their contribution to the total energy consumption remains insignificant. The conversion of solar energy into electricity through solar cells is one of the most promising techniques, but the use of these cells is limited by the high cost of electricity. The major contributions to these costs are the material and manufacturing costs. Over the past decades, the development of silicon based thin film solar cells has received much attention, because the fabrication costs are low. A promising material for use in thin film solar cells is polycrystalline silicon (poly-Si:H). A relatively new technique to deposit poly-Si:H is Hot-Wire Chemical Vapor Deposition (Hot-Wire CVD), in which the reactant gases are catalytically decomposed at the surface of a hot filament, mainly tungsten and tantalum. The main advantages of Hot-Wire CVD over PE-CVD are absence of ion bombardment, high deposition rate, low equipment cost and high gas utilization. This thesis deals with the full spectrum of deposition, characterization and application of poly-Si:H thin films, i.e. from gas molecule to solar cell. Studies on the decomposition of silane on the filament showed that the process is catalytic of nature and that silane is decomposed into Si and 4H. The dominant gas phase reaction is the reaction of Si and H with silane, resulting in SiH3, Si2H6, Si3H6 and H2SiSiH2. The film growth precursors are Si, SiH3 and Si2H4. Also, XPS results on used tantalum and tungsten filaments are discussed. The position dependent measurements show larger silicon contents at the ends of the tungsten filament, as compared to the middle, due to a lower filament temperature. This effect is insignificant for a tantalum filament. Deposition time dependent measurements show an increase in silicon content of the tungsten filament with time, while the silicon content on the tantalum filament saturates

  13. Solar cells utilizing pulsed-energy crystallized microcrystalline/polycrystalline silicon

    DOEpatents

    Kaschmitter, James L.; Sigmon, Thomas W.

    1995-01-01

    A process for producing multi-terminal devices such as solar cells wherein a pulsed high energy source is used to melt and crystallize amorphous silicon deposited on a substrate which is intolerant to high processing temperatures, whereby to amorphous silicon is converted into a microcrystalline/polycrystalline phase. Dopant and hydrogenization can be added during the fabrication process which provides for fabrication of extremely planar, ultra shallow contacts which results in reduction of non-current collecting contact volume. The use of the pulsed energy beams results in the ability to fabricate high efficiency microcrystalline/polycrystalline solar cells on the so-called low-temperature, inexpensive plastic substrates which are intolerant to high processing temperatures.

  14. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Annual subcontract report, January 1, 1995--December 31, 1995

    SciTech Connect

    Wohlgemuth, J

    1996-06-01

    The objective of this three-year program is to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance and expand Solarex`s commercial production capacities. Two specific objectives of this program are to reduce the manufacturing cost for polycrystalline silicon PV modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three.

  15. New biomaterial as a promising alternative to silicone breast implants.

    PubMed

    Teck Lim, Goy; Valente, Stephanie A; Hart-Spicer, Cherie R; Evancho-Chapman, Mary M; Puskas, Judit E; Horne, Walter I; Schmidt, Steven P

    2013-05-01

    One in eight American women develops breast cancer. Of the many patients requiring mastectomy yearly as a consequence, most elect some form of breast reconstruction. Since 2006, only silicone breast implants have been approved by the FDA for the public use. Unfortunately, over one-third of women with these implants experience complications as a result of tissue-material biocompatibility issues, which may include capsular contracture, calcification, hematoma, necrosis and implant rupture. Our group has been working on developing alternatives to silicone. Linear triblock poly(styrene-b-isobutylene-b-styrene) (SIBS) polymers are self-assembling nanostructured thermoplastic rubbers, already in clinical practice as drug eluting stent coatings. New generations with a branched (arborescent or dendritic) polyisobutylene core show promising potential as a biomaterial alternative to silicone rubber. The purpose of this pre-clinical research was to evaluate the material-tissue interactions of a new arborescent block copolymer (TPE1) in a rabbit implantation model compared to a linear SIBS (SIBSTAR 103T) and silicone rubber. This study is the first to compare the molecular weight and molecular weight distribution, tensile properties and histological evaluation of arborescent SIBS-type materials with silicone rubber before implantation and after explantation. PMID:23466517

  16. Formation of polycrystalline-silicon films with hemispherical grains for capacitor structures with increased capacitance

    SciTech Connect

    Novak, A. V.

    2014-12-15

    The effect of formation conditions on the morphology of silicon films with hemispherical grains (HSG-Si) obtained by the method of low-pressure chemical vapor deposition (LPCVD) is investigated by atomic-force microscopy. The formation conditions for HSG-Si films with a large surface area are found. The obtained HSG-Si films make it possible to fabricate capacitor structures, the electric capacitance of which is twice as large in comparison to that of capacitors with “smooth” electrodes from polycrystalline silicon.

  17. Nano silver-catalyzed chemical etching of polycrystalline silicon wafer for solar cell application

    NASA Astrophysics Data System (ADS)

    Chen, S. R.; Liang, Z. C.; Wang, D. L.

    2016-03-01

    Silver nanoparticles were deposited on the surface of polycrystalline silicon wafer via vacuum thermal evaporation and metal-catalyzed chemical etching (MCCE) was conducted in a HF-H2O2 etching system. Treatment of the etched silicon wafer with HF transformed the textured structure on the surface from nanorods into nanocones. An etching time of 30 s and treatment with HF resulted in nanocones with uniform size distribution and a reflectivity as low as 1.98% across a spectral range from 300 to 1000 nm.

  18. Polycrystalline silicon thin-film solar cell prepared by the solid phase crystallization (SPC) method

    SciTech Connect

    Baba, T.; Matsuyama, T.; Sawada, T.; Takahama, T.; Wakisaka, K.; Tsuda, S.; Nakano, S.

    1994-12-31

    A solid phase crystallization (SPC) method was applied to the fabrication of thin-film polycrystalline silicon (poly-Si) for solar cells for the first time. Among crystalline silicon solar cells crystallized at a low temperature of less than 600 C, the world`s highest conversion efficiency of 8.5% was achieved in a solar cell using thin-film poly-Si with only 10 {micro}m thickness prepared by the SPC method. This solar cell showed high photosensitivity in the long-wavelength region of more than 800 nm and also exhibited no light-induced degradation after light exposure.

  19. The determination of minority carrier lifetime in polycrystalline silicon by the photoconductivity decay method

    NASA Astrophysics Data System (ADS)

    Singh, S. N.; Kishore, R.; Arora, N. K.

    1985-04-01

    Experiments were carried out to investigate the possible sources of error in estimates of the time constant of apparent minority carrier lifetime (tau-asterisk) in polycrystalline silicon. Tau-asterisk was measured in both single-crystal and polycrystalline silicon rods as a function of: (1) the intensity of background illumination; and (2) the temperature of the specimens. The background illumination source for the experiments was a tungsten-halogen lamp which operated in the intensity range 0-85 mW per sq cm. The temperatures of the specimens under illumination were in the range 25-140 C. The experimental results were explained on the basis of a theoretical analysis. It is shown that the photoconductivity of the specimens was generally dependent on the minority carrier mobility lifetime, as long as potential barriers were present at the grain boundaries of the specimens. On the basis of the theoretical analysis, it is concluded that the absence of potential barriers at the grain boundaries in polycrystalline silicon is a major source of error in estimates of minority carrier mobility lifetime. The apparent minority carrier mobility decay curves are reproduced in graphic form.

  20. Chemical mechanical polishing of boron-doped polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Pirayesh, Hamidreza; Cadien, Kenneth

    2014-03-01

    Chemical mechanical polishing (CMP) is a technique which helps to print a smaller depth of focus and smoother surface in micro fabrication industry. In this project, boron doped polysilicon is used as a fill material for Through Silicon Vias (TSV) creating a 3D package. It is shown that the presence of boron as dopant suppresses the polysilicon polish rate. To increase the polish rate, understanding the mechanism of polish rate retardation is essential. We believe that the electrical effects play the major role in this phenomenon and by reducing this effect we are able to increase the polish rate.

  1. Polycrystalline indium phosphide on silicon by indium assisted growth in hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Metaferia, Wondwosen; Sun, Yan-Ting; Pietralunga, Silvia M.; Zani, Maurizio; Tagliaferri, Alberto; Lourdudoss, Sebastian

    2014-07-01

    Polycrystalline InP was grown on Si(001) and Si(111) substrates by using indium (In) metal as a starting material in hydride vapor phase epitaxy (HVPE) reactor. In metal was deposited on silicon substrates by thermal evaporation technique. The deposited In resulted in islands of different size and was found to be polycrystalline in nature. Different growth experiments of growing InP were performed, and the growth mechanism was investigated. Atomic force microscopy and scanning electron microscopy for morphological investigation, Scanning Auger microscopy for surface and compositional analyses, powder X-ray diffraction for crystallinity, and micro photoluminescence for optical quality assessment were conducted. It is shown that the growth starts first by phosphidisation of the In islands to InP followed by subsequent selective deposition of InP in HVPE regardless of the Si substrate orientation. Polycrystalline InP of large grain size is achieved and the growth rate as high as 21 μm/h is obtained on both substrates. Sulfur doping of the polycrystalline InP was investigated by growing alternating layers of sulfur doped and unintentionally doped InP for equal interval of time. These layers could be delineated by stain etching showing that enough amount of sulfur can be incorporated. Grains of large lateral dimension up to 3 μm polycrystalline InP on Si with good morphological and optical quality is obtained. The process is generic and it can also be applied for the growth of other polycrystalline III-V semiconductor layers on low cost and flexible substrates for solar cell applications.

  2. Polycrystalline indium phosphide on silicon by indium assisted growth in hydride vapor phase epitaxy

    SciTech Connect

    Metaferia, Wondwosen; Sun, Yan-Ting Lourdudoss, Sebastian; Pietralunga, Silvia M.; Zani, Maurizio; Tagliaferri, Alberto

    2014-07-21

    Polycrystalline InP was grown on Si(001) and Si(111) substrates by using indium (In) metal as a starting material in hydride vapor phase epitaxy (HVPE) reactor. In metal was deposited on silicon substrates by thermal evaporation technique. The deposited In resulted in islands of different size and was found to be polycrystalline in nature. Different growth experiments of growing InP were performed, and the growth mechanism was investigated. Atomic force microscopy and scanning electron microscopy for morphological investigation, Scanning Auger microscopy for surface and compositional analyses, powder X-ray diffraction for crystallinity, and micro photoluminescence for optical quality assessment were conducted. It is shown that the growth starts first by phosphidisation of the In islands to InP followed by subsequent selective deposition of InP in HVPE regardless of the Si substrate orientation. Polycrystalline InP of large grain size is achieved and the growth rate as high as 21 μm/h is obtained on both substrates. Sulfur doping of the polycrystalline InP was investigated by growing alternating layers of sulfur doped and unintentionally doped InP for equal interval of time. These layers could be delineated by stain etching showing that enough amount of sulfur can be incorporated. Grains of large lateral dimension up to 3 μm polycrystalline InP on Si with good morphological and optical quality is obtained. The process is generic and it can also be applied for the growth of other polycrystalline III–V semiconductor layers on low cost and flexible substrates for solar cell applications.

  3. Electrodeposition of polycrystalline and amorphous silicon for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Rauh, R. D.

    1980-07-01

    Plating experiments with SiHCl3 solutions in propylene carbonate with 0.1 M tetrabutylammonium tetrafluoroborate are described. Silicon was deposited on ITO glass (Nesatron) as well as Mo substrates at temperatures from 25-80 C. Both potentiostatic and galvanostatic conditions were used. The high resistance of the films limited the thickness which could be deposited by either method to less than 5 micrometers. Deposition beyond this limit resulted in a deterioration of the film quality. X-ray analysis of the films confirmed that they were amorphous. SEM analysis of the films revealed a very porous structure with nodules about 1 micrometer in diameter. Annealing the deposit at 400 C in an Ar:H2 atmosphere resulted in a slightly smoother surface but the nodules remained. The films deposited on ITO glass had a band gap of about 1.0 eV and an EO4 value of 1.5-2.0 eV. The Auger analysis of the films showed the presence of large amounts of oxygen in the samples that had been exposed to air.

  4. Oxygen-aided synthesis of polycrystalline graphene on silicon dioxide substrates.

    PubMed

    Chen, Jianyi; Wen, Yugeng; Guo, Yunlong; Wu, Bin; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Wang, Dong; Yu, Gui; Liu, Yunqi

    2011-11-01

    We report the metal-catalyst-free synthesis of high-quality polycrystalline graphene on dielectric substrates [silicon dioxide (SiO(2)) or quartz] using an oxygen-aided chemical vapor deposition (CVD) process. The growth was carried out using a CVD system at atmospheric pressure. After high-temperature activation of the growth substrates in air, high-quality polycrystalline graphene is subsequently grown on SiO(2) by utilizing the oxygen-based nucleation sites. The growth mechanism is analogous to that of growth for single-walled carbon nanotubes. Graphene-modified SiO(2) substrates can be directly used in transparent conducting films and field-effect devices. The carrier mobilities are about 531 cm(2) V(-1) s(-1) in air and 472 cm(2) V(-1) s(-1) in N(2), which are close to that of metal-catalyzed polycrystalline graphene. The method avoids the need for either a metal catalyst or a complicated and skilled postgrowth transfer process and is compatible with current silicon processing techniques. PMID:21988639

  5. MIS and PN junction solar cells on thin-film polycrystalline silicon

    SciTech Connect

    Ariotedjo, A.; Emery, K.; Cheek, G.; Pierce, P.; Surek, T.

    1981-05-01

    The Photovoltaic Advanced Silicon (PVAS) Branch at the Solar Energy Research Institute (SERI) has initiated a comparative study to assess the potential of MIS-type solar cells for low-cost terrestrial photovoltaic systems in terms of performance, stability, and cost-effectiveness. Several types of MIS and SIS solar cells are included in the matrix study currently underway. This approach compares the results of MIS and p/n junction solar cells on essentially identical thin-film polycrystalline silicon materials. All cell measurements and characterizations are performed using uniform testing procedures developed in the Photovoltaic Measurements and Evaluation (PV M and E) Laboratory at SERI. Some preliminary data on the different cell structures on thin-film epitaxial silicon on metallurgical-grade substrates are presented here.

  6. CW Laser Annealing of Polycrystalline Silicon on SiO2 and Effects of Successive Furnace Annealing

    NASA Astrophysics Data System (ADS)

    Kugimiya, Koichi; Fuse, Genshu; Inoue, Kaoru

    1982-01-01

    CW Ar laser annealing was carried out to reduce the resistivity of polycrystalline silicon implanted with light doses of 1× 1012-5× 1014B+/cm2. Laser annealing, actually laser melting, and successive furnace annealing effectively reduced the resistivity to almost that of single crystal silicon. TEM, OM and stress observations revealed that the reduction was due primarily to the grain growth of polycrystalline silicon and secondarily to stress relief, from 9× 109 dyne/cm2 to 5× 109 dyne/cm2, caused by annealing. Grain growth of up to about 3× 100 μm and bamboo-joint-like growth were observed.

  7. Production of polycrystalline silicon from monosilane in the electron-beam plasma

    SciTech Connect

    Konstantinov, V. O.; Shchukin, V. G.; Sharafutdinov, R. G.; Karsten, V. M.; Gartvich, G. G.; Semenova, O. I.

    2010-12-15

    The results of experimental studies concerned with deposition of solar-grade silicon from monosilane in the electron-beam plasma are reported. With the laboratory equipment, the silicon deposition rate attains up to 40 g h{sup -1} at the expenditure of energy for the process 78 kW h kg{sup -1} and the efficiency of conversion of monosilane into silicon at about 50%. Analysis of the chemical composition of the resulting material shows that the material fits the requirements imposed on solar-grade silicon. The method suggested in the study holds promise in industrial-scale applications.

  8. Efficient organic light-emitting diodes using polycrystalline silicon thin films as semitransparent anode

    NASA Astrophysics Data System (ADS)

    Zhu, X. L.; Sun, J. X.; Peng, H. J.; Meng, Z. G.; Wong, M.; Kwok, H. S.

    2005-08-01

    Polycrystalline silicon (p-Si) is a good material for the construction of thin-film transistors (TFT). It is used for fabricating active-matrix organic light-emitting diode (AMOLED) displays. In this letter, we propose and demonstrate the application of boron-doped p-Si as a semi-transparent anode in making different color OLEDs. Without removing the ultrathin native oxide on the p-Si surface and employing p-doped hole transport layer to enhance holes injection, these OLEDs show comparable or even better performance to conventional OLEDs which use ITO as anodes. The present technique has the advantage of less masking steps in making AMOLED.

  9. Imaging of a Polycrystalline Silicon Solar Cell Using a Laser Terahertz Emission Microscope

    NASA Astrophysics Data System (ADS)

    Nakanishi, Hidetoshi; Fujiwara, Shogo; Takayama, Kazuhisa; Kawayama, Iwao; Murakami, Hironaru; Tonouchi, Masayoshi

    2012-11-01

    We employed a laser terahertz (THz) emission microscope (LTEM) as a novel tool for evaluating solar cells. LTEM images are obtained by exciting a polycrystalline silicon solar cell with femtosecond laser illumination and visualizing the local distribution of the optical response. THz emission signals also provide various types of information, such as the screening effect of the built-in electrical field near pn junctions. These results indicate that this technique can be used to evaluate the local photoelectric conversion efficiency distribution and dynamic behavior of optically excited carriers in solar cells.

  10. Investigation of diffusion length distribution on polycrystalline silicon wafers via photoluminescence methods.

    PubMed

    Lou, Shishu; Zhu, Huishi; Hu, Shaoxu; Zhao, Chunhua; Han, Peide

    2015-01-01

    Characterization of the diffusion length of solar cells in space has been widely studied using various methods, but few studies have focused on a fast, simple way to obtain the quantified diffusion length distribution on a silicon wafer. In this work, we present two different facile methods of doing this by fitting photoluminescence images taken in two different wavelength ranges or from different sides. These methods, which are based on measuring the ratio of two photoluminescence images, yield absolute values of the diffusion length and are less sensitive to the inhomogeneity of the incident laser beam. A theoretical simulation and experimental demonstration of this method are presented. The diffusion length distributions on a polycrystalline silicon wafer obtained by the two methods show good agreement. PMID:26364565

  11. Investigation of diffusion length distribution on polycrystalline silicon wafers via photoluminescence methods

    PubMed Central

    Lou, Shishu; Zhu, Huishi; Hu, Shaoxu; Zhao, Chunhua; Han, Peide

    2015-01-01

    Characterization of the diffusion length of solar cells in space has been widely studied using various methods, but few studies have focused on a fast, simple way to obtain the quantified diffusion length distribution on a silicon wafer. In this work, we present two different facile methods of doing this by fitting photoluminescence images taken in two different wavelength ranges or from different sides. These methods, which are based on measuring the ratio of two photoluminescence images, yield absolute values of the diffusion length and are less sensitive to the inhomogeneity of the incident laser beam. A theoretical simulation and experimental demonstration of this method are presented. The diffusion length distributions on a polycrystalline silicon wafer obtained by the two methods show good agreement. PMID:26364565

  12. Field-induced transition in the conductivity mechanism of polycrystalline silicon films

    NASA Astrophysics Data System (ADS)

    Ada-Hanifi, M.; Sicart, J.; Dusseau, J. M.; Robert, J. L.

    1988-04-01

    Current-voltage characteristics of polycrystalline silicon films highly doped with phosphorus and boron were studied over a wide range of temperatures (40-300 K) and applied electric fields (up to 5 kV cm-1). After the usual ohmic regime, we observed a large increase in dc current versus applied voltage. Moreover, at higher electric fields, a new ohmic conduction regime appeared which has not yet been reported in polycrystalline silicon. Thermoemission-based models cannot fully interpret our results. We present a new interpretation of current-voltage characteristics based on a model previously used to interpret the electrical properties of these films at low electric fields. This model takes into account the existence of fluctuations both in intergranular potential and in the grain boundary barrier heights. They result from all of the macroscopic inhomogeneities due to the growth conditions of the material. The high electric field detraps carriers from grain boundaries and extracts the carriers located in the valleys of potential created by the fluctuations, thus inducing transition in conductivity.

  13. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Semiannual subcontract report, January 1--June 30, 1995

    SciTech Connect

    Wohlgemuth, J.

    1996-02-01

    The objective of this three-year program is to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance and expand Solarex`s commercial production capacities. Two specific objectives of this program are to reduce the manufacturing cost for polycrystalline silicon PV modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three. To achieve these objectives, Solarex is working in the following technical areas: casting, wire saws, cell process, module assembly, frameless module development, and automated cell handling. Accomplishments reported include: Cast first successful larger ingot producing 73% larger volume of usable Si; Increased the size of the ingot even further and cast an ingot yielding nine 11.4 {times} 11.4 cm bricks, representing a 125% increase in usable Si from a single casting; Operated the wire-saw in a semi-operational mode, producing 459,000 wafers at 94.1% overall yield; Reduced the cost of wire-saw consumables, spare parts, and waste disposal; Developed a cost-effective back surface field process that increases cell efficiency by 5% and began production trials; Developed a plan for increasing the capacity in the module assembly area; Completed qualification testing of modules built using Spire`s automated tabbing and stringing machine; Selected, tested, and qualified a low-cost electrical termination system; Completed long-term UV testing of experimental back sheets; Qualified the structure and adhesive-tape system for mounting frameless modules; and ARRI completed a study of the fracture properties of cast polycrystalline Si wafers and provided the information necessary to calculate the maximum stresses allowable during wafer handling.

  14. Polycrystalline silicon thin-film solar cells with plasmonic-enhanced light-trapping.

    PubMed

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm(2), which can be increased up to 17-18 mA/cm(2) (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing

  15. The effect of grain boundaries on the resistivity of polycrystalline silicon. Ph.D. Thesis - Va. Univ.

    NASA Technical Reports Server (NTRS)

    Fripp, A. L., Jr.

    1974-01-01

    The electrical resistivity of polycrystalline silicon films was investigated. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity was found to be independent of dopant atom concentration in the lightly doped regions but was a strong function of dopant levels in the more heavily doped regions. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

  16. Cast polycrystalline silicon photovoltaic cell and module manufacturing technology improvements. Annual subcontract report, 1 December 1993--30 November 1994

    SciTech Connect

    Wohlgemuth, J.

    1995-09-01

    This report describes work performed under a 3-y contract to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance, and expand Solarex`s commercial production capacities. Specific objectives are to reduce manufacturing cost for polycrstalline silicon PV modules to less than $1.20/W and to increase manufacturing capacity by a factor of 3. Solarex is working on casting, wire saws, cell process, module assembly, frameless module development, and automated cell handling.

  17. Impurities analysis of polycrystalline silicon substrates: Neutronic Activation Analysis (NAA) and Secondary Ion Mass Spectrometry (SIMS)

    NASA Astrophysics Data System (ADS)

    Lounis, A.; Lenouar, K.; Gritly, Y.; Abbad, B.; Azzaz, M.; Taïbi, K.

    2010-01-01

    In this study we have determined the concentration of some impurities such as carbon, iron, copper, titanium, nickel of the flat product (polycrystalline silicon). These impurities generate a yield decrease in the photovoltaic components. The material (polycrystalline silicon) used in this work is manufactured by the Unit of Silicon Technology Development (UDTS Algiers, Algeria). The 80 kg ingot has been cutted into 16 briquettes in order to have plates (flat product) of 100 mm×100 mm dimensions. Each briquette is divided into three parts top (T), middle (M) and bottom (B). For this purpose, the following instrumental analysis techniques have been employed: neutronic analysis (neutronic activation analysis) and secondary ion mass spectrometry (SIMS). Masses of 80 mg are sampled and form of discs 18 mm in diameter, then exposed to a flux of neutron of 2.1012neutron cm-2 s-1 during 15 min. The energetic profile of incidental flux is constituted of fast neutrons (ΦR = 3.1012n.cm-2 s-1; E = 2 Mev), thermal neutrons (ΦTH = 1013n.cm-2 s-1; E = 0.025 ev) and epithermal neutrons (Φepi = 7.1011 n cm-2 s-1; E>4.9 ev), irradiation time 15 mn, after 20 mn of decrement, acquisitions of 300 s are carried out. The results are expressed by disintegration per second which does not exceed the 9000 Bq, 500 Bq and 2600 Bq, respectively for copper, titanium and nickel. It is observed that the impurities concentrations in the medium are higher. The impurities in the bottom of the ingots originate from the crucible. The impurities in the top originate from impurities dissolved in the liquid silicon, which have segregated to the top layer of the ingot and after solidification diffuse. Silicon corresponds to a mixture of three isotopes 28Si, 29Si and 30Si. These elements clearly appear on the mass spectrum (SIMS). The presence of iron and the one of nickel has been noticed.

  18. Vacuum deposited polycrystalline silicon films for solar cell applications. Quarterly report, September 15-December 31, 1979

    SciTech Connect

    Feldman, C.; Arrington, C. H.; Blum, N. A.; Satkiewicz, F. G.

    1980-03-01

    Polycrystalline silicon films 14-22 ..mu..m thick and with average grain diameters of 20-40 ..mu..m were deposited by vacuum deposition onto both ceramic and sapphire substrates which were previously coated with a thin (1-2 ..mu..m) TiB/sub 2/ conducting layer. The large grains are the result of an interaction in the initial growth stages between silicon and TiB/sub 2/. SIMS studies of B/Ti/Al/sub 2/O/sub 3/, B/Al/sub 2/O/sub 3/, and Ti/Al/sub 2/O/sub 3/, interactions are reported as part of a continuing investigation of TiB/sub 2/ formation and silicon interactions on the TiB/sub 2/ surface. The increase in grain size has led to an improvement in the open-circuit voltage V/sub oc/, but not to an increase in the short-circuit current J/sub sc/. Capacitance-voltage measurements give results characteristic of an abrupt junction and a build-in voltage V/sub D/ consistent with the measured doping levels. A simple method for measuring the minority carrier diffusion length in the base region L/sub n/ is described. The measurements indicate that there is little change in L/sub n/ between large (20-40 ..mu..m) and small (approx. 5 ..mu..m) grained samples.

  19. Vacuum deposited polycrystalline silicon films for solar cell applications. Quarterly report, 1 April-30 June 1980

    SciTech Connect

    Feldman, C.; Arrington, III, C. H.; Blum, N. A.; Satkiewicz, F. G.

    1980-08-01

    Polycrystalline p-type films were vacuum deposited onto TiB/sub 2/ coated alumina and sapphire substrates. Epitaxial layers were also formed on single crystal silicon substrates. Junctions in the layers were created by both gaseous diffusion in a tube furnace and by vacuum deposition. The TiB/sub 2/ vacuum deposited bottom electrodes have resistivities between 30 and 40 ..mu.. ..cap omega..-cm. All-vacuum-deposited solar cells were fabricated for the first time. Efficiencies approaching those in the diffused junction devices were achieved. The n-layers were deposited on the previously deposited p-layer/TiB/sub 2//ceramic sandwiches by vacuum deposition of silicon in a phosphine (PH/sub 3/) atmosphere. Photovoltaic data in diffused junction samples, including efficiency and spectral response measurements, indicate that crystallite size may no longer be the limiting factor in achieving high efficiency; rather, performance is now being limited by the presence of impurities in the vacuum deposition silicon base region.

  20. Comparison of boron precipitation in p-type bulk nanostructured and polycrystalline silicon germanium alloy

    NASA Astrophysics Data System (ADS)

    Zamanipour, Zahra; Krasinski, Jerzy S.; Vashaee, Daryoosh

    2013-04-01

    Boron precipitation process and its effect on electronic properties of p-type bulk nanostructured silicon germanium (Si0.8Ge0.2) compared with large grain polycrystalline Si0.8Ge0.2 have been studied. The structures were synthesized and their thermoelectric properties were measured versus temperature during heating and cooling cycles. The experimental data showed stronger temperature variation of Seebeck coefficient, carrier concentration, and conductivity in the nanostructured Si0.8Ge0.2 compared with the polycrystalline form indicating stronger boron precipitation in this structure. The electrical properties of both samples were calculated using a multi-band semi-classical model. The theoretical calculations confirm that the increase of boron precipitation in the nanostructured Si0.8Ge0.2 is responsible for its higher thermal instability. Since the thermoelectric properties of the nanostructured sample degrade as a result of thermal cycling, the material is appropriate only for continuous operation at high temperature without cooling.

  1. On properties of boundaries and electron conductivity in mesoscopic polycrystalline silicon films for memory devices

    SciTech Connect

    Berman, G.P.; Doolen, G.D.; Mainieri, R.; Rehacek, J.; Campbell, D.K.; Luchnikov, V.A.; Nagaev, K.E.

    1998-02-01

    The authors present the results of MD modeling on the structural properties of grain boundaries (GB) in thin polycrystalline films. The transition from crystalline boundaries with low mismatch angle to amorphous boundaries is investigated. It is shown that the structures of the GBs satisfy a thermodynamical criterion suggested in a cited reference. The potential energy of silicon atoms is closely related with a geometrical quantity -- tetragonality of their coordination with their nearest neighbors. A crossover of the length of localization is observed to analyze the crossover of the length of localization of the single electron states and properties of conductance of the thin polycrystalline film at low temperature. They use a two-dimensional Anderson localization model, with the random one site electron charging energy for a single grain (dot), random non-diagonal matrix elements, and random number of connections between the neighboring grains. The results on the crossover behavior of localization length of the single electron states and characteristic properties of conductance are presented in the region of parameters where the transition from an insulator to a conductor regimes takes place.

  2. Suppressing light reflection from polycrystalline silicon thin films through surface texturing and silver nanostructures

    SciTech Connect

    Akhter, Perveen; Huang, Mengbing Kadakia, Nirag; Spratt, William; Malladi, Girish; Bakhru, Hassarum

    2014-09-21

    This work demonstrates a novel method combining ion implantation and silver nanostructures for suppressing light reflection from polycrystalline silicon thin films. Samples were implanted with 20-keV hydrogen ions to a dose of 10¹⁷/cm², and some of them received an additional argon ion implant to a dose of 5×10¹⁵ /cm² at an energy between 30 and 300 keV. Compared to the case with a single H implant, the processing involved both H and Ar implants and post-implantation annealing has created a much higher degree of surface texturing, leading to a more dramatic reduction of light reflection from polycrystalline Si films over a broadband range between 300 and 1200 nm, e.g., optical reflection from the air/Si interface in the AM1.5 sunlight condition decreasing from ~30% with an untextured surface to below 5% for a highly textured surface after post-implantation annealing at 1000°C. Formation of Ag nanostructures on these ion beam processed surfaces further reduces light reflection, and surface texturing is expected to have the benefit of diminishing light absorption losses within large-size (>100 nm) Ag nanoparticles, yielding an increased light trapping efficiency within Si as opposed to the case with Ag nanostructures on a smooth surface. A discussion of the effects of surface textures and Ag nanoparticles on light trapping within Si thin films is also presented with the aid of computer simulations.

  3. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    SciTech Connect

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-17

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 {mu}m, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  4. Modeling and simulation of temperature effect in polycrystalline silicon PV cells

    NASA Astrophysics Data System (ADS)

    Marcu, M.; Niculescu, T.; Slusariuc, R. I.; Popescu, F. G.

    2016-06-01

    Due to the human needs of energy, there is a need to apply new technologies in energy conversion to supply the demand of clean and cheap energy in the context of environmental issues. Renewable energy sources like solar energy has one of the highest potentials. In this paper, solar panel is the key part of a photovoltaic system which converts solar energy to electrical energy. The purpose of this paper is to give a MATLAB/ Simulink simulation for photovoltaic module based on the one-diode model of a photovoltaic cell made of polycrystalline silicon. This model reveals the effect of the ambient temperature and the heating of the panel due to the solar infrared radiation. Also the measurements on the solar cell exposed to solar radiation can confirm the simulation.

  5. Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuits for Active Matrix Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yu-Sheng; Liu, Yan-Wei

    A new pixel design and driving method for active matrix organic light emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage programming method are proposed and verified using the SPICE simulator. We had employed an appropriate TFT model in SPICE simulation to demonstrate the performance of the pixel circuit. The OLED anode voltage variation error rates are below 0.35% under driving TFT threshold voltage deviation (Δ Vth =± 0.33V). The OLED current non-uniformity caused by the OLED threshold voltage degradation (Δ VTO =+0.33V) is significantly reduced (below 6%). The simulation results show that the pixel design can improve the display image non-uniformity by compensating for the threshold voltage deviation in the driving TFT and the OLED threshold voltage degradation at the same time.

  6. Graphitization of n-type polycrystalline silicon carbide for on-chip supercapacitor application

    NASA Astrophysics Data System (ADS)

    Liu, Fang; Gutes, Albert; Laboriante, Ian; Carraro, Carlo; Maboudian, Roya

    2011-09-01

    Synthesis of silicon carbide-derived carbon films with excellent supercapacitor characteristics is demonstrated by a process that is fully compatible with standard microfabrication technology. NiTi alloy deposited on nitrogen-doped polycrystalline SiC films is shown to result in the growth of a rough, porous, high conductivity, nanocrystalline graphitic carbon film upon rapid thermal annealing to 1050 °C. Electrodes fabricated in this manner exhibit high charge/discharge rates with a time constant of about 0.062 s. Analysis shows that the incorporated nitrogen in the carbon electrode may induce pseudo-capacitance, and the electrodes exhibit the capacitance/area values comparable to those reported on carbon nanotube-based supercapacitors.

  7. Design and test of reliable high strength ingressive polycrystalline silicon microgripper arrays

    NASA Astrophysics Data System (ADS)

    Hazra, S. S.; Beuth, J. L.; Myers, G. A.; DelRio, F. W.; de Boer, M. P.

    2015-01-01

    We present the design and validation of a micromachined gripper array that enables reliable transmission of forces of at least 14 mN. The gripper is constructed with polycrystalline silicon (polysilicon), a brittle material, and is compatible with polysilicon surface micromachining. Two ingressive snap-and-lock array designs are presented. After developing design guidelines, it is shown that the first gripper array is functional. However, a risk remains that the gripper array rather than the tensile bar that it grips in its intended application fails. Therefore, an improved geometry is designed and it is shown that it is robust with respect to failure. Scanning confocal Raman imaging directly confirms that the local peak tensile stresses in the robust gripper array are approximately 50% of the lower bound material strength, and also resolves a 25% stress variation across the array.

  8. Controllable electrical and physical breakdown of poly-crystalline silicon nanowires by thermally assisted electromigration

    NASA Astrophysics Data System (ADS)

    Park, Jun-Young; Moon, Dong-Il; Seol, Myeong-Lok; Jeon, Chang-Hoon; Jeon, Gwang-Jae; Han, Jin-Woo; Kim, Choong-Ki; Park, Sang-Jae; Lee, Hee Chul; Choi, Yang-Kyu

    2016-01-01

    The importance of poly-crystalline silicon (poly-Si) in semiconductor manufacturing is rapidly increasing due to its highly controllable conductivity and excellent, uniform deposition quality. With the continuing miniaturization of electronic components, low dimensional structures such as 1-dimensional nanowires (NWs) have attracted a great deal of attention. But such components have a much higher current density than 2- or 3- dimensional films, and high current can degrade device lifetime and lead to breakdown problems. Here, we report on the electrical and thermal characteristics of poly-Si NWs, which can also be used to control electrical and physical breakdown under high current density. This work reports a controllable catastrophic change of poly-Si NWs by thermally-assisted electromigration and underlying mechanisms. It also reports the direct and real time observation of these catastrophic changes of poly-Si nanowires for the first time, using scanning electron microscopy.

  9. Controllable electrical and physical breakdown of poly-crystalline silicon nanowires by thermally assisted electromigration

    PubMed Central

    Park, Jun-Young; Moon, Dong-Il; Seol, Myeong-Lok; Jeon, Chang-Hoon; Jeon, Gwang-Jae; Han, Jin-Woo; Kim, Choong-Ki; Park, Sang-Jae; Lee, Hee Chul; Choi, Yang-Kyu

    2016-01-01

    The importance of poly-crystalline silicon (poly-Si) in semiconductor manufacturing is rapidly increasing due to its highly controllable conductivity and excellent, uniform deposition quality. With the continuing miniaturization of electronic components, low dimensional structures such as 1-dimensional nanowires (NWs) have attracted a great deal of attention. But such components have a much higher current density than 2- or 3- dimensional films, and high current can degrade device lifetime and lead to breakdown problems. Here, we report on the electrical and thermal characteristics of poly-Si NWs, which can also be used to control electrical and physical breakdown under high current density. This work reports a controllable catastrophic change of poly-Si NWs by thermally-assisted electromigration and underlying mechanisms. It also reports the direct and real time observation of these catastrophic changes of poly-Si nanowires for the first time, using scanning electron microscopy. PMID:26782708

  10. Controllable electrical and physical breakdown of poly-crystalline silicon nanowires by thermally assisted electromigration.

    PubMed

    Park, Jun-Young; Moon, Dong-Il; Seol, Myeong-Lok; Jeon, Chang-Hoon; Jeon, Gwang-Jae; Han, Jin-Woo; Kim, Choong-Ki; Park, Sang-Jae; Lee, Hee Chul; Choi, Yang-Kyu

    2016-01-01

    The importance of poly-crystalline silicon (poly-Si) in semiconductor manufacturing is rapidly increasing due to its highly controllable conductivity and excellent, uniform deposition quality. With the continuing miniaturization of electronic components, low dimensional structures such as 1-dimensional nanowires (NWs) have attracted a great deal of attention. But such components have a much higher current density than 2- or 3-dimensional films, and high current can degrade device lifetime and lead to breakdown problems. Here, we report on the electrical and thermal characteristics of poly-Si NWs, which can also be used to control electrical and physical breakdown under high current density. This work reports a controllable catastrophic change of poly-Si NWs by thermally-assisted electromigration and underlying mechanisms. It also reports the direct and real time observation of these catastrophic changes of poly-Si nanowires for the first time, using scanning electron microscopy. PMID:26782708

  11. 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.

  12. Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

    NASA Astrophysics Data System (ADS)

    Saci, Lynda; Mahamdi, Ramdane; Mansour, Farida; Boucher, Jonathan; Collet, Maéva; Bedel Pereira, Eléna; Temple-Boyer, Pierre

    2011-05-01

    The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B-N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

  13. Polycrystalline silicon thin-film transistors fabricated by Joule-heating-induced crystallization

    NASA Astrophysics Data System (ADS)

    Hong, Won-Eui; Ro, Jae-Sang

    2015-01-01

    Joule-heating-induced crystallization (JIC) of amorphous silicon (a-Si) films is carried out by applying an electric pulse to a conductive layer located beneath or above the films. Crystallization occurs across the whole substrate surface within few tens of microseconds. Arc instability, however, is observed during crystallization, and is attributed to dielectric breakdown in the conductor/insulator/transformed polycrystalline silicon (poly-Si) sandwich structures at high temperatures during electrical pulsing for crystallization. In this study, we devised a method for the crystallization of a-Si films while preventing arc generation; this method consisted of pre-patterning an a-Si active layer into islands and then depositing a gate oxide and gate electrode. Electric pulsing was then applied to the gate electrode formed using a Mo layer. The Mo layer was used as a Joule-heat source for the crystallization of pre-patterned active islands of a-Si films. JIC-processed poly-Si thin-film transistors (TFTs) were fabricated successfully, and the proposed method was found to be compatible with the standard processing of coplanar top-gate poly-Si TFTs.

  14. Fracture toughness of low-pressure chemical-vapor-deposited polycrystalline silicon carbide thin films

    NASA Astrophysics Data System (ADS)

    Hatty, V.; Kahn, H.; Trevino, J.; Zorman, C. A.; Mehregany, M.; Ballarini, R.; Heuer, A. H.

    2006-01-01

    The fracture toughness of thin-film polycrystalline silicon carbide (poly-SiC) deposited on silicon (Si) wafers via low-pressure chemical-vapor deposition (LPCVD) has been measured on a scale useful for micromachined devices; the results are compared to previous studies on poly-SiC thin films deposited by atmospheric pressure chemical-vapor deposition (APCVD) [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)]. Samples in this study included those with and without silicon dioxide (SiO2) sacrificial release layers. The LPCVD processing technique induces residual tensile stresses in the films. Doubly clamped microtensile specimens were fabricated using standard micromachining processes, and microindentation was used to initiate atomically sharp precracks. The residual stresses in the films create stress intensity factors K at the crack tips; upon release, the precracks whose K exceeded a critical value, KIC, propagated to failure. The fracture toughness KIC was the same for both types of devices, 2.9+/-0.2 MPa m1/2 for the SiC on Si samples and 3.0+/-0.2 MPa m1/2 for the SiC on SiO2/Si samples, and similar to that found for APCVD poly-SiC, 2.8<=KIC<=3.4 MPa m1/2 [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)], indicating that KIC is truly a structure-insensitive material property. The fracture toughness of poly-SiC compares favorably with that for polysilicon, 0.85+/-0.05 MPa m1/2 [Kahn et al., Science 298, 1215 (2002)].

  15. The strength of polycrystalline silicon at the micro- and nano-scales with applications to MEMS

    NASA Astrophysics Data System (ADS)

    Chasiotis, Ioannis

    A new method for tensile testing of thin films by means of an improved apparatus has been developed to measure the elastic properties (Young's modulus, tensile strength) of surface micromachined polycrystalline silicon specimens. The newly designed tensile tester makes use of an Ultraviolet (UV) light curable adhesive to clamp micron-sized specimens. The properties determination utilizes surface topologies of deforming specimens, acquired with an Atomic Force Microscope (AFM), for determining strain fields by means of Digital Image Correlation (DIC). This full-field, direct and local measurements technique provides the capability of testing any type of thin film materials with nanometer resolution. A systematic study of small-scale size effects was thus performed by tensioning elliptically perforated specimens (minimum radius of curvature of 1 mum) so as to: (a) vary the stress concentration with constant radius of curvature, (b) increasing radius of curvature of micronotches relative to the grain size. The results demonstrate a strong influence of the size of the highly strained domain (decreasing notch radii) on the failure strength of MEMS scale specimens, while the effect of varying the stress concentration factor is rather insignificant. In addition, tests performed on unnotched tensile specimens of varying dimensions revealed a specimen size effect by which the values of strength scaled with the specimen length. The Young's modulus, however, is found to be rather insensitive to the specimen dimensions at the scale of microns. Contrary to the common belief that 49% HF wet release represents a safe post-process for manufacturing polycrystalline silicon, this study has clearly identified the release process as a key item in determining thin film failure properties. It is found that surface roughness as characterized by groove formation at the grain boundaries depends distinctly on the HF release time. In addition, while the actual failure mechanism in

  16. The effects of spatial location of defect states on the switching characteristics of amorphous and polycrystalline silicon thin film transistors: A numerical simulation using AMPS 2-D

    SciTech Connect

    Smith, J.; Fonash, S.; Kalkan, A.

    1994-06-01

    We demonstrate a two-dimensional device simulator for MOSFET structures that incorporates models for defect distributions and show predicted effects on device switching performance for various spatial distributions of defects in amorphous and polycrystalline silicon.

  17. Leakage Current Suppression on Metal-Induced Laterally Crystallized Polycrystalline Silicon Thin-Film Transistors by Asymmetrically Deposited Nickel

    NASA Astrophysics Data System (ADS)

    Byun, Chang Woo; Son, Se Wan; Lee, Yong Woo; Hyo Park, Jae; Vakilipour Takaloo, Ashkan; Joo, Seung Ki

    2013-10-01

    The electrical performance of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) fabricated by metal-induced lateral crystallization (MILC) is greatly affected by metal catalyst contaminations, such as Ni and Ni silicide trapped in the channel, since they concentrate in front of laterally grown crystallites. In the present work, the effect of the MILC/MILC boundary (MMB) on MILC polycrystalline silicon (poly-Si) TFTs is investigated by the comparison of MILC poly-Si TFTs with MMB at the center of the channel, and equivalent TFTs with MMB at a position ejected from the channel. The MMB location was controlled by the Ni catalyst position. Both a low off-state leakage current and a free from short channel effect (kink effect) were observed in high electric-field conditions. Furthermore, the field-effect mobility and drain current noise were drastically improved by ejecting the MILC boundary in the source direction.

  18. Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

    PubMed Central

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing

  19. High-Temperature Thermoelectric Properties of Polycrystalline Silicon Clathrate Ba8TM x Si46- x (TM = Ni, Pt)

    NASA Astrophysics Data System (ADS)

    Kikuchi, Daisuke; Fujimura, Koji; Tadokoro, Jun; Matsumoto, Miko; Yamazaki, Satoshi; Sasaki, Hirokazu; Eguchi, Tatsuhiko; Susai, Kyota

    2016-03-01

    The n-/ p-type stability of a silicon clathrate in which silicon was substituted with nickel or platinum was evaluated by density functional theory calculations. Then, Ba8Pt5Si41 and Ba8Pt1.5Ni3.5Si41 were synthesized, and their thermoelectric properties were investigated. The polycrystalline compounds, which have a type-I clathrate structure, were prepared through arc melting and spark-plasma-sintering. The crystal structures and elemental compositions of the synthesized samples were characterized via powder x-ray diffraction and electron microprobe analyses, respectively. The temperature dependence of both the electrical resistivity and the Seebeck coefficient was measured.

  20. Influence of Grain Size on the Thermoelectric Properties of Polycrystalline Silicon Nanowires

    NASA Astrophysics Data System (ADS)

    Suriano, F.; Ferri, M.; Moscatelli, F.; Mancarella, F.; Belsito, L.; Solmi, S.; Roncaglia, A.; Frabboni, S.; Gazzadi, G. C.; Narducci, D.

    2015-01-01

    The thermoelectric properties of doped polycrystalline silicon nanowires have been investigated using doping techniques that impact grain growth in different ways during the doping process. In particular, As- and P-doped nanowires were fabricated using a process flow which enables the manufacturing of surface micromachined nanowires contacted by Al/Si pads in a four-terminal configuration for thermal conductivity measurement. Also, dedicated structures for the measurement of the Seebeck coefficient and electrical resistivity were prepared. In this way, the thermoelectric figure of merit of the nanowires could be evaluated. The As-doped nanowires were heavily doped by thermal doping from spin-on-dopant sources, whereas predeposition from POCl3 was utilized for the P-doped nanowires. The thermal conductivity measured on the nanowires appeared to depend on the doping type. The P-doped nanowires showed, for comparable cross-sections, higher thermal conductivity values than As-doped nanowires, most probably because of their finer grain texture, resulting from the inhibition effect that such doping elements have on grain growth during high-temperature annealing.

  1. Polycrystalline silicon carbide dopant profiles obtained through a scanning nano-Schottky contact

    NASA Astrophysics Data System (ADS)

    Golt, M. C.; Strawhecker, K. E.; Bratcher, M. S.; Shanholtz, E. R.

    2016-07-01

    The unique thermo-electro-mechanical properties of polycrystalline silicon carbide (poly-SiC) make it a desirable candidate for structural and electronic materials for operation in extreme environments. Necessitated by the need to understand how processing additives influence poly-SiC structure and electrical properties, the distribution of lattice defects and impurities across a specimen of hot-pressed 6H poly-SiC processed with p-type additives was visualized with high spatial resolution using a conductive atomic force microscopy approach in which a contact forming a nano-Schottky interface is scanned across the sample. The results reveal very intricate structures within poly-SiC, with each grain having a complex core-rim structure. This complexity results from the influence the additives have on the evolution of the microstructure during processing. It was found that the highest conductivities localized at rims as well as at the interface between the rim and the core. The conductivity of the cores is less than the conductivity of the rims due to a lower concentration of dopant. Analysis of the observed conductivities and current-voltage curves is presented in the context of nano-Schottky contact regimes where the conventional understanding of charge transport to diode operation is no longer valid.

  2. A characterisation of electronic properties of alkaline texturized polycrystalline silicon solar cells using IBIC

    NASA Astrophysics Data System (ADS)

    Jakob, A. M.; Spemann, D.; Thies, R.; Barzola-Quiquia, J.; Vogt, J.; Butz, T.

    2011-10-01

    In this study, electronic properties of p-type alkaline texturized polycrystalline silicon solar cells were investigated using ion beam induced charge (IBIC) analysis. With this technique, quantitative information on electronic diffusion lengths and average electronic capture cross sections of lattice defects generated by high energy protons were obtained. Angular-resolved IBIC analysis was used to quantify the electronic diffusion lengths. For this purpose, the experimental data were fitted using a simulation based on the Ramo-Shockley-Gunn (RSG) theorem and the assumption of an abrupt pn-junction. In order to determine the average electronic capture cross section of proton-induced lattice defects, the loss of charge collection efficiency (CCE) was plotted vs. the accumulated ion fluence. As will be demonstrated, a simple model based on charge carrier diffusion and Shockley-Read-Hall (SRH) recombination is able to fit the CCE loss well. Furthermore, spatially and energetically highly resolved IBIC-maps of grain boundaries were recorded. A comparison with PIXE-maps shows that there is no correlation observable between CCE variations at grain boundaries and metallic impurities within the PIXE detection limits of a few ppm. On the contrary, there is an evident correlation to the morphology of the sample's surface as was observed by comparing IBIC-maps and SEM-micrographs. These local CCE fluctuations are dominated by the interplay of charge carrier diffusion processes and the sample surface morphology.

  3. Synthesis and characterization of large-grain solid-phase crystallized polycrystalline silicon thin films

    SciTech Connect

    Kumar, Avishek E-mail: dalapatig@imre.a-star.edu.sg; Law, Felix; Widenborg, Per I.; Dalapati, Goutam K. E-mail: dalapatig@imre.a-star.edu.sg; Subramanian, Gomathy S.; Tan, Hui R.; Aberle, Armin G.

    2014-11-01

    n-type polycrystalline silicon (poly-Si) films with very large grains, exceeding 30 μm in width, and with high Hall mobility of about 71.5 cm{sup 2}/V s are successfully prepared by the solid-phase crystallization technique on glass through the control of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The effect of this gas flow ratio on the electronic and structural quality of the n-type poly-Si thin film is systematically investigated using Hall effect measurements, Raman microscopy, and electron backscatter diffraction (EBSD), respectively. The poly-Si grains are found to be randomly oriented, whereby the average area weighted grain size is found to increase from 4.3 to 18 μm with increase of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The stress in the poly-Si thin films is found to increase above 900 MPa when the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio is increased from 0.025 to 0.45. Finally, high-resolution transmission electron microscopy, high angle annular dark field-scanning tunneling microscopy, and EBSD are used to identify the defects and dislocations caused by the stress in the fabricated poly-Si films.

  4. Strength and inelastic deformation in shocked polycrystalline silicon carbide. Final progress report, July 1992--June 1995

    SciTech Connect

    Gupta, Y.M.

    1998-07-10

    The objective of this research project was to quantify the response of shocked ceramics, including strength in the shocked state, to understand the mechanisms governing inelastic deformation at high stresses and high strain- rates in these materials. In-situ, piezoresistance stress gauge measurements were obtained in dense, polycrystalline silicon carbide (SiC) samples subjected to plane wave loading. A significant effort was carried out to ensure a self-consistent analysis of the lateral piezoresistance gauge data. Analysis of the longitudinal data revealed an inelastic response that could be modeled using either a strain hardening, plasticity model or a pressure-dependent strength model with stress relaxation. Experimental measurements and analysis of the lateral gauge data in SiC, currently underway, are needed to develop a comprehensive understanding of shocked SiC. Preliminary experiments and numerical calculations were completed to undertake combined compression and shear wave measurements in the SiC. The use of lateral piezoresistance gauges, and compression-shear measurements provide independent corroborations of material strength in the shocked state. This determination is important for understanding the differences in the compressive and tensile response of shocked ceramics.

  5. 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.

  6. Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs.

    PubMed

    Liang, Albert K; Koniczek, Martin; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua; Street, Robert A; Lu, Jeng Ping

    2016-03-01

    Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si)-a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance-information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% full width at half maximum (FWHM) at 70 keV; and the digital components should work well even in the presence of significant thin-film transistor (TFT) variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm. PMID:26878107

  7. Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua; Street, Robert A.; Lu, Jeng Ping

    2016-03-01

    Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si)—a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance—information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% full width at half maximum (FWHM) at 70 keV; and the digital components should work well even in the presence of significant thin-film transistor (TFT) variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm.

  8. Breakdown-induced thermochemical reactions in HfO2 high-κ/polycrystalline silicon gate stacks

    NASA Astrophysics Data System (ADS)

    Ranjan, R.; Pey, K. L.; Tung, C. H.; Tang, L. J.; Ang, D. S.; Groeseneken, G.; De Gendt, S.; Bera, L. K.

    2005-12-01

    The chemistry of dielectric-breakdown-induced microstructural changes in HfO2 high-κ/polycrystalline silicon gate nMOSFETs under constant voltage stress has been studied. Based on an electron energy loss spectrometry analysis, the hafnium and oxygen chemical bonding in the breakdown induced Hf-based compounds of a "ball-shaped" defect is found to be different compared to the stoichiometric HfO2 and SiO2. The formation of possibly HfSixOy and HfSix compounds in the "ball-shaped" defect is attributed to a thermochemical reaction triggered by the gate dielectric breakdown.

  9. Paradoxical Enhancement of the Power Factor of Polycrystalline Silicon as a Result of the Formation of Nanovoids

    NASA Astrophysics Data System (ADS)

    Lorenzi, B.; Narducci, D.; Tonini, R.; Frabboni, S.; Gazzadi, G. C.; Ottaviani, G.; Neophytou, N.; Zianni, X.

    2014-10-01

    Hole-containing silicon has been regarded as a viable candidate thermoelectric material because of its low thermal conductivity. However, because voids are efficient scattering centers not just for phonons but also for charge carriers, achievable power factors (PFs) are normally too low for its most common form, i.e. porous silicon, to be of practical interest. In this communication we report that high PFs can, indeed, be achieved with nanoporous structures obtained from highly doped silicon. High PFs, up to a huge 22 mW K-2 m-1 (more than six times higher than values for the bulk material), were observed for heavily boron-doped nanocrystalline silicon films in which nanovoids (NVs) were generated by He+ ion implantation. In contrast with single-crystalline silicon in which He+ implantation leads to large voids, in polycrystalline films implantation followed by annealing at 1000°C results in homogeneous distribution of NVs with final diameters of approximately 2 nm and densities of the order of 1019 cm-3 with average spacing of 10 nm. Study of its morphology revealed silicon nanograins 50 nm in diameter coated with 5-nm precipitates of SiB x . We recently reported that PFs up to 15 mW K-2 m-1 could be achieved for silicon-boron nanocomposites (without NVs) because of a simultaneous increase of electrical conductivity and Seebeck coefficient. In that case, the high Seebeck coefficient was achieved as a result of potential barriers on the grain boundaries, and high electrical conductivity was achieved as a result of extremely high levels of doping. The additional increase in the PF observed in the presence of NVs (which also include SiB x precipitates) might have several possible explanations; these are currently under investigation. Experimental results are reported which might clarify the reason for this paradoxical effect of NVs on silicon PF.

  10. Characterization of nanometer-thick polycrystalline silicon with phonon-boundary scattering enhanced thermoelectric properties and its application in infrared sensors

    NASA Astrophysics Data System (ADS)

    Zhou, Huchuan; Kropelnicki, Piotr; Lee, Chengkuo

    2014-12-01

    Although significantly reducing the thermal conductivity of silicon nanowires has been reported, it remains a challenge to integrate silicon nanowires with structure materials and electrodes in the complementary metal-oxide-semiconductor (CMOS) process. In this paper, we investigated the thermal conductivity of nanometer-thick polycrystalline silicon (poly-Si) theoretically and experimentally. By leveraging the phonon-boundary scattering, the thermal conductivity of 52 nm thick poly-Si was measured as low as around 12 W mK-1 which is only about 10% of the value of bulk single crystalline silicon. The ZT of n-doped and p-doped 52 nm thick poly-Si was measured as 0.067 and 0.024, respectively, while most previously reported data had values of about 0.02 and 0.01 for a poly-Si layer with a thickness of 0.5 μm and above. Thermopile infrared sensors comprising 128 pairs of thermocouples made of either n-doped or p-doped nanometer-thick poly-Si strips in a series connected by an aluminium (Al) metal interconnect layer are fabricated using microelectromechanical system (MEMS) technology. The measured vacuum specific detectivity (D*) of the n-doped and p-doped thermopile infrared (IR) sensors are 3.00 × 108 and 1.83 × 108 cm Hz1/2 W-1 for sensors of 52 nm thick poly-Si, and 5.75 × 107 and 3.95 × 107 cm Hz1/2 W-1 for sensors of 300 nm thick poly-Si, respectively. The outstanding thermoelectric properties indicate our approach is promising for diverse applications using ultrathin poly-Si technology.Although significantly reducing the thermal conductivity of silicon nanowires has been reported, it remains a challenge to integrate silicon nanowires with structure materials and electrodes in the complementary metal-oxide-semiconductor (CMOS) process. In this paper, we investigated the thermal conductivity of nanometer-thick polycrystalline silicon (poly-Si) theoretically and experimentally. By leveraging the phonon-boundary scattering, the thermal conductivity of 52 nm

  11. Exploration of maximum count rate capabilities for large-area photon counting arrays based on polycrystalline silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua

    2016-03-01

    Pixelated photon counting detectors with energy discrimination capabilities are of increasing clinical interest for x-ray imaging. Such detectors, presently in clinical use for mammography and under development for breast tomosynthesis and spectral CT, usually employ in-pixel circuits based on crystalline silicon - a semiconductor material that is generally not well-suited for economic manufacture of large-area devices. One interesting alternative semiconductor is polycrystalline silicon (poly-Si), a thin-film technology capable of creating very large-area, monolithic devices. Similar to crystalline silicon, poly-Si allows implementation of the type of fast, complex, in-pixel circuitry required for photon counting - operating at processing speeds that are not possible with amorphous silicon (the material currently used for large-area, active matrix, flat-panel imagers). The pixel circuits of two-dimensional photon counting arrays are generally comprised of four stages: amplifier, comparator, clock generator and counter. The analog front-end (in particular, the amplifier) strongly influences performance and is therefore of interest to study. In this paper, the relationship between incident and output count rate of the analog front-end is explored under diagnostic imaging conditions for a promising poly-Si based design. The input to the amplifier is modeled in the time domain assuming a realistic input x-ray spectrum. Simulations of circuits based on poly-Si thin-film transistors are used to determine the resulting output count rate as a function of input count rate, energy discrimination threshold and operating conditions.

  12. Experimental study of three-dimensional fin-channel charge trapping flash memories with titanium nitride and polycrystalline silicon gates

    NASA Astrophysics Data System (ADS)

    Liu, Yongxun; Matsukawa, Takashi; Endo, Kazuhiko; O'uchi, Shinichi; Tsukada, Junichi; Yamauchi, Hiromi; Ishikawa, Yuki; Mizubayashi, Wataru; Morita, Yukinori; Migita, Shinji; Ota, Hiroyuki; Masahara, Meishoku

    2014-01-01

    Three-dimensional (3D) fin-channel charge trapping (CT) flash memories with different gate materials of physical-vapor-deposited (PVD) titanium nitride (TiN) and n+-polycrystalline silicon (poly-Si) have successfully been fabricated by using (100)-oriented silicon-on-insulator (SOI) wafers and orientation-dependent wet etching. Electrical characteristics of the fabricated flash memories including statistical threshold voltage (Vt) variability, endurance, and data retention have been comparatively investigated. It was experimentally found that a larger memory window and a deeper erase are obtained in PVD-TiN-gated metal-oxide-nitride-oxide-silicon (MONOS)-type flash memories than in poly-Si-gated poly-Si-oxide-nitride-oxide-silicon (SONOS)-type memories. The larger memory window and deeper erase of MONOS-type flash memories are contributed by the higher work function of the PVD-TiN metal gate than of the n+-poly-Si gate, which is effective for suppressing electron back tunneling during erase operation. It was also found that the initial Vt roll-off due to the short-channel effect (SCE) is directly related to the memory window roll-off when the gate length (Lg) is scaled down to 46 nm or less.

  13. 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.

  14. Ultratough, Thermally Stable Polycrystalline Diamond/Silicon Carbide Nanocomposites for Drill Bits

    SciTech Connect

    2009-03-01

    This factsheet describes a research project whose goal is to develop and produce in quantity novel superhard and ultratough thermally stable polycrystalline (TSP) diamond/SiC nanocomposites reinforced with SiC/C nanofibers for drill-bit applications and multiple industrial functions.

  15. A method for polycrystalline silicon delineation applicable to a double-diffused MOS transistor

    NASA Technical Reports Server (NTRS)

    Halsor, J. L.; Lin, H. C.

    1974-01-01

    Method is simple and eliminates requirement for unreliable special etchants. Structure is graded in resistivity to prevent punch-through and has very narrow channel length to increase frequency response. Contacts are on top to permit planar integrated circuit structure. Polycrystalline shield will prevent creation of inversion layer in isolated region.

  16. Initial steps toward the realization of large area arrays of single photon counting pixels based on polycrystalline silicon TFTs

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua; Jiang, Hao; Street, Robert A.; Lu, Jeng Ping

    2014-03-01

    The thin-film semiconductor processing methods that enabled creation of inexpensive liquid crystal displays based on amorphous silicon transistors for cell phones and televisions, as well as desktop, laptop and mobile computers, also facilitated the development of devices that have become ubiquitous in medical x-ray imaging environments. These devices, called active matrix flat-panel imagers (AMFPIs), measure the integrated signal generated by incident X rays and offer detection areas as large as ~43×43 cm2. In recent years, there has been growing interest in medical x-ray imagers that record information from X ray photons on an individual basis. However, such photon counting devices have generally been based on crystalline silicon, a material not inherently suited to the cost-effective manufacture of monolithic devices of a size comparable to that of AMFPIs. Motivated by these considerations, we have developed an initial set of small area prototype arrays using thin-film processing methods and polycrystalline silicon transistors. These prototypes were developed in the spirit of exploring the possibility of creating large area arrays offering single photon counting capabilities and, to our knowledge, are the first photon counting arrays fabricated using thin film techniques. In this paper, the architecture of the prototype pixels is presented and considerations that influenced the design of the pixel circuits, including amplifier noise, TFT performance variations, and minimum feature size, are discussed.

  17. Nanophotonic light trapping in polycrystalline silicon thin-film solar cells using periodically nanoimprint-structured glass substrates

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Xavier, Jolly; Preidel, Veit; Wyss, Philippe; Sontheimer, Tobias; Rech, Bernd; Probst, Jürgen; Hülsen, Christoph; Löchel, Bernd; Erko, Alexei; Burger, Sven; Schmidt, Frank; Back, Franziska; Rudigier-Voigt, Eveline

    2013-09-01

    A smart light trapping scheme is essential to tap the full potential of polycrystalline silicon (poly-Si) thin-film solar cells. Periodic nanophotonic structures are of particular interest as they allow to substantially surpass the Lambertian limit from ray optics in selected spectral ranges. We use nanoimprint-lithography for the periodic patterning of sol-gel coated glass substrates, ensuring a cost-effective, large-area production of thin-film solar cell devices. Periodic crystalline silicon nanoarchitectures are prepared on these textured substrates by high-rate silicon film evaporation, solid phase crystallization and chemical etching. Poly-Si microhole arrays in square lattice geometry with an effective thickness of about 2μm and with comparatively large pitch (2 μm) exhibit a large absorption enhancement (A900nm = 52%) compared to a planar film (A900nm ~ 7%). For the optimization of light trapping in the desired spectral region, the geometry of the nanophotonic structures with varying pitch from 600 nm to 800 nm is tailored and investigated for the cases of poly-Si nanopillar arrays of hexagonal lattice geometry, exhibiting an increase in absorption in comparison to planar film attributed to nanophotonic wave optic effects. These structures inspire the design of prospective applications such as highly-efficient nanostructured poly-Si thin-film solar cells and large-area photonic crystals.

  18. Vacuum deposited polycrystalline silicon films for solar cell applications. Second quarterly technical progress report. January 1-March 31, 1980

    SciTech Connect

    Feldman, C.; Arlington, III, C. H.; Blum, N. A.; Satkiewicz, F. G.

    1980-05-01

    A careful study of a specially formed thin silicon layer on TiB/sub 2/-coated sapphire reveals that the interaction layer of TiSi/sub 2/ is composed of larger grains. Processing steps were developed which lead closer to the goal of fabricating polycrystalline silicon photovoltaic devices completely by vacuum deposition. Both n-type and p-type silicon are now being deposited. New deposition masks were made for depositing the n-regions upon the p-layers. New electrode deposition masks were also made for a direct electroding process to replace the photolithographic process used previously. The TiB/sub 2/ bottom electrode fabrication has been achieved in a single vacuum chamber. Reaction constants and activation energy for TiB/sub 2/ layer formation were determined to be less than those reported by other authors for bulk material. Studies of crystallite growth and interfacial interactions have continued. Major sources of undesirable impurities have been identified and removed from the vacuum chambers. The changes made this quarter have not been incorporated into a completed photovoltaic device.

  19. Rapid recovery of polycrystalline silicon from kerf loss slurry using double-layer organic solvent sedimentation method

    NASA Astrophysics Data System (ADS)

    Xing, Peng-fei; Guo, Jing; Zhuang, Yan-xin; Li, Feng; Tu, Gan-feng

    2013-10-01

    The rapid development of photovoltaic (PV) industries has led to a shortage of silicon feedstock. However, more than 40% silicon goes into slurry wastes due to the kerf loss in the wafer slicing process. To effectively recycle polycrystalline silicon from the kerf loss slurry, an innovative double-layer organic solvent sedimentation process was presented in the paper. The sedimentation velocities of Si and SiC particles in some organic solvents were investigated. Considering the polarity, viscosity, and density of solvents, the chloroepoxy propane and carbon tetrachloride were selected to separate Si and SiC particles. It is found that Si and SiC particles in the slurry waste can be successfully separated by the double-layer organic solvent sedimentation method, which can greatly reduce the sedimentation time and improve the purity of obtained Si-rich and SiC-rich powders. The obtained Si-rich powders consist of 95.04% Si, and the cast Si ingot has 99.06% Si.

  20. Deformation and fracture of single-crystal and sintered polycrystalline silicon carbide produced by cavitation

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Hattori, Shuji; Okada, Tsunenori; Buckley, Donald H.

    1987-01-01

    An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in the SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.

  1. Fatigue of polycrystalline silicon for MEMS applications: Crack growth and stability under resonant loading conditions

    SciTech Connect

    Muhlstein, C.L.; Howe, R.T.; Ritchie, R.O.

    2001-12-05

    Although bulk silicon is not known to exhibit susceptibility to cyclic fatigue, micron-scale structures made from silicon films are known to be vulnerable to degradation by fatigue in ambient air environments, a phenomenon that has been recently modeled in terms of a mechanism of sequential oxidation and stress-corrosion cracking of the native oxide layer.

  2. Mechanism of fatigue in micron-scale films of polycrystalline silicon for microelectromechanical applications

    SciTech Connect

    Muhlstein, C.L.; Stach, E.A.; Ritchie, R.O.

    2001-08-02

    Reported nearly a decade ago, cyclic fatigue failure in silicon thin films has remained a mystery. Silicon does not display the room temperature plasticity or extrinsic toughening mechanisms necessary to cause fatigue in either ductile (e.g., metals) or brittle (e.g., ceramics and ordered mintermetallic) materials.

  3. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Semiannual technical report, 1 January 1996--30 June 1996

    SciTech Connect

    Wohlgemuth, J

    1997-01-01

    Two specific objectives of Solarex`s program are to reduce the manufacturing cost for polycrystalline silicon photovoltaic modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three. This report highlights accomplishments during the period of January 1 through June 30, 1996. Accomplishments include: began the conversion of production casting stations to increase ingot size; operated the wire saw in a production mode with higher yields and lower costs than achieved on the ID saws; developed and qualified a new wire guide coating material that doubles the wire guide lifetime and produces significantly less scatter in wafer thickness; completed a third pilot run of the cost-effective Al paste back-surface-field (BSF) process, verifying a 5% increase in cell efficiency and demonstrating the ability to process and handle the BSF paste cells; completed environmental qualification of modules using cells produced by an all-print metallization process; optimized the design of the 15.2-cm by 15.2-cm polycrystalline silicon solar cells; demonstrated the application of a high-efficiency process in making 15.2-cm by 15.2-cm solar cells; demonstrated that cell efficiency increases with decreasing wafer thickness for the Al paste BSF cells; qualified a vendor-supplied Tedlar/ethylene vinyl acetate (EVA) laminate to replace the combination of separate sheets of EVA and Tedlar backsheet; demonstrated the operation of a prototype unit to trim/lead attach/test modules; and demonstrated the operation of a wafer pull-down system for cassetting wet wafers.

  4. Large-Scale PV Module Manufacturing Using Ultra-Thin Polycrystalline Silicon Solar Cells: Final Subcontract Report, 1 April 2002--28 February 2006

    SciTech Connect

    Wohlgemuth, J.; Narayanan, M.

    2006-07-01

    The major objectives of this program were to continue advances of BP Solar polycrystalline silicon manufacturing technology. The Program included work in the following areas. (1) Efforts in the casting area to increase ingot size, improve ingot material quality, and improve handling of silicon feedstock as it is loaded into the casting stations. (2) Developing wire saws to slice 100-..mu..m-thick silicon wafers on 290-..mu..m-centers. (3) Developing equipment for demounting and subsequent handling of very thin silicon wafers. (4) Developing cell processes using 100-..mu..m-thick silicon wafers that produce encapsulated cells with efficiencies of at least 15.4% at an overall yield exceeding 95%. (5) Expanding existing in-line manufacturing data reporting systems to provide active process control. (6) Establishing a 50-MW (annual nominal capacity) green-field Mega-plant factory model template based on this new thin polycrystalline silicon technology. (7) Facilitating an increase in the silicon feedstock industry's production capacity for lower-cost solar-grade silicon feedstock..

  5. Improvement in pH Sensitivity of Low-Temperature Polycrystalline-Silicon Thin-Film Transistor Sensors Using H2 Sintering

    PubMed Central

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si–OH2+ and Si–O− bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  6. Improvement in pH sensitivity of low-temperature polycrystalline-silicon thin-film transistor sensors using H2 sintering.

    PubMed

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si-OH2(+) and Si-O(-) bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  7. Thin film polycrystalline silicon solar cells. Second technical progress report, July 16, 1980-October 15, 1980

    SciTech Connect

    1980-10-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts have been directed to the purification of metallurgical silicon, the preparation and characterization of substrates and epitaxial silicon layers, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been further investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was determined and compared with the impurity content in metallurgical silicon. The effects of heat treatment on the impurity distribution in the substrate and in the epitaxial layer have also been investigated. Large area (30 to 60 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by depositing a p-n junction structure using the thermal reduction of trichlorosilane containing appropriate dopants. The AM1 efficiencies are about 9% for cells of 30 to 35 cm/sup 2/ area. Larger area, 60 cm/sup 2/, thin film solar cells have been fabricated for the first time, and their AM1 efficiencies are slightly higher than 8%. The spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation in a number of solr cells have been measured.

  8. Comparison between laser terahertz emission microscope and conventional methods for analysis of polycrystalline silicon solar cell

    SciTech Connect

    Nakanishi, Hidetoshi Ito, Akira; Takayama, Kazuhisa Kawayama, Iwao Murakami, Hironaru Tonouchi, Masayoshi

    2015-11-15

    A laser terahertz emission microscope (LTEM) can be used for noncontact inspection to detect the waveforms of photoinduced terahertz emissions from material devices. In this study, we experimentally compared the performance of LTEM with conventional analysis methods, e.g., electroluminescence (EL), photoluminescence (PL), and laser beam induced current (LBIC), as an inspection method for solar cells. The results showed that LTEM was more sensitive to the characteristics of the depletion layer of the polycrystalline solar cell compared with EL, PL, and LBIC and that it could be used as a complementary tool to the conventional analysis methods for a solar cell.

  9. Thin film polycrystalline silicon solar cells: first technical progress report, April 15, 1980-July 15, 1980

    SciTech Connect

    1980-07-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts during the past quarter have been directed to the purification of metallurgical silicon, the preparation of substrates, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was also determined. Large area (> 30 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by the thermal reduction of trichlorosilane containing appropriate dopants. Chemically deposited tin-dioxide films were used as antireflection coatings. Solar cells with AM1 efficiencies of about 8.5% have been obtained. Their spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation have been measured.

  10. Impurity segregation behavior in polycrystalline silicon ingot grown with variation of electron-beam power

    NASA Astrophysics Data System (ADS)

    Lee, Jun-Kyu; Lee, Jin-Seok; Jang, Bo-Yun; Kim, Joon-Soo; Ahn, Young-Soo; Cho, Churl-Hee

    2014-08-01

    Electron beam melting (EBM) systems have been used to improve the purity of metallurgical grade silicon feedstock for photovoltaic application. Our advanced EBM system is able to effectively remove volatile impurities using a heat source with high energy from an electron gun and to continuously allow impurities to segregate at the top of an ingot solidified in a directional solidification (DS) zone in a vacuum chamber. Heat in the silicon melt should move toward the ingot bottom for the desired DS. However, heat flux though the ingot is changed as the ingot becomes longer due to low thermal conductivity of silicon. This causes a non-uniform microstructure of the ingot, finally leading to impurity segregation at its middle. In this research, EB power irradiated on the silicon melt was controlled during the ingot growth in order to suppress the change of heat flux. EB power was reduced from 12 to 6.6 kW during the growth period of 45 min with a drop rate of 0.125 kW/min. Also, the silicon ingot was grown under a constant EB power of 12 kW to estimate the effect of the drop rate of EB power. When the EB power was reduced, the grains with columnar shape were much larger at the middle of the ingot compared to the case of constant EB power. Also, the present research reports a possible reason for the improvement of ingot purity by considering heat flux behaviors.

  11. Polycrystalline silicon material availability and market pricing outlook for 1980 through 1988

    NASA Technical Reports Server (NTRS)

    Costogue, E. N.; Ferber, R. R.

    1984-01-01

    The results of the second JPL update to an original report to assess the availability and prices of polycrystalline Si for solar cells in the 1983-88 interval are reported. It is noted that the demand for poly-Si for solar cells competes with the demand for the same material for semiconductors, although the solar cell industry can use material rejected from the semiconductor industry. A sufficient supply is projected for the 6 yr period, rising from 3224 metric tons to 10,220 metric tons in 1988, with prices dropping from the 1980 level of $140/kg to $25/kg. The price reduction and improved production are noted to be due in large part to DOE efforts at defining lower-cost production processes.

  12. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  13. Deposition and characterization of polycrystalline silicon films on glass for thin film solar cells

    SciTech Connect

    Bergmann, R.B.; Krinke, J.; Strunk, H.P.; Werner, J.H.

    1997-07-01

    The authors deposit phosphorus-doped, amorphous Si by low pressure chemical vapor deposition and subsequently crystallize the films by furnace annealing at a temperature of 600 C. Optical in-situ monitoring allows one to control the crystallization process. Phosphorus doping leads to faster crystallization and a grain size enhancement with a maximum grain size of 15 {micro}m. Using transmission electron microscopy they find a log-normal grain size distribution in their films. They demonstrate that this distribution not only arises from solid phase crystallization of amorphous Si but also from other crystallization processes based on random nucleation and growth. The log-normal grain size distribution seems to be a general feature of polycrystalline semiconductors.

  14. In-situ light-scattering measurements during the CVD of polycrystalline silicon carbide

    SciTech Connect

    Sheldon, B.W. |; Reichle, P.A.; Besmann, T.M.

    1992-12-31

    Light-scattering was used to monitor the chemical vapor deposition of silicon carbide from methyltrichlorosilane. Nucleation and growth of SiC caused changes in surface topography that altered the angular scattering spectrum generated by a He-Ne laser. These scattering spectra were analyzed to obtain information about the occurring nucleation and growth processes.

  15. 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.

  16. Experimental study and two-dimensional modeling of avalanche breakdown voltage in polycrystalline silicon p-n junctions

    NASA Astrophysics Data System (ADS)

    Amrani, Mohammed; Benamara, Zineb; Chellali, Mohammed; Tizi, Schahrazade; Mohammed-Brahim, Tayeb

    2007-05-01

    A two-dimensional (2D) model of the avalanche breakdown mechanism is examined to achieve a lateral polycrystalline silicon (polysilicon) p+-n diode with high forward current and high breakdown voltage (BV). Samples with different film thicknesses (tf) were deposited by low-pressure chemical vapor deposition process. The p+ zone and n zone are doped by ionic implantation with boron and phosphorus, respectively. The measured current-voltage (I-V) characteristics show that BV varies between 6.4, 7.5, and 8.25V when tf varies between 250, 350, and 450nm, respectively. These data also show that when tf decreases, the forward current is high, the leakage current becomes higher under reverse bias, and BV decreases. We reveal that the breakdown phenomenon of our samples is dominated by the impact ionization effect. A 2D simulation of avalanche breakdown voltage versus the critical parameters of polysilicon diodes is implemented. The algorithm is based on the solution of Poisson's equation and calculating the ionization integral along various electric field lines computed from the potential distribution. By taking into account the localization of trap states in the grain boundaries, the effects on the breakdown voltage of the doping concentration ND, the intergranular trap state density NT, the grain sizes Lg, the disposition of the grain boundaries, and the film thickness tf are investigated. The simulation results show that the impact ionization mechanism is more accelerated in polysilicon than in single-crystalline silicon, and the BV(Lg), BV(ND), BV(NT), and BV(tf) curves are characterized by a succession of descending stair shapes due to the trapping of free carries by trap states contained in grain boundaries that are parallel to the metallurgic junction. By comparing simulation results with experimental data, we select the electron-hole ionization coefficients characterizing our samples: αn∞=1.0×106cm-1, Encrit=5.87×106Vcm-1, αp∞=1.582×106cm-1, and EPcrit=2

  17. Three-dimensional study of a polycrystalline silicon solar cell: the influence of the applied magnetic field on the electrical parameters

    NASA Astrophysics Data System (ADS)

    Dieng, A.; Zerbo, I.; Wade, M.; Maiga, A. S.; Sissoko, G.

    2011-09-01

    In this paper, we present a theoretical 3D study of a polycrystalline silicon solar cell in frequency modulation under polychromatic illumination and applied magnetic field. The influence of the applied magnetic field on the diode current density, Jd, and both electric power-photovoltage and photocurrent-photovoltage characteristics are discussed. The Nyquist diagram permitted us to determine the electrical parameters such as the series resistance Rs and parallel equivalent resistance Rp of a polycrystalline silicon solar cell. The Bode diagram is then used to calculate the cut-off frequency, capacitance C and inductance L. It has been shown that, under a magnetic field, the solar cell behavior is like that of a low-pass filter.

  18. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  19. 3D determination of the minority carrier lifetime and the p-n junction recombination velocity of a polycrystalline silicon solar cell

    NASA Astrophysics Data System (ADS)

    Sam, R.; Zouma, B.; Zougmoré, F.; Koalaga, Z.; Zoungrana, M.; Zerbo, I.

    2012-02-01

    This work presents a theoretical and experimental transient tri-dimensional study conducted for the determination of the bulk component of the minority carrier lifetime and the p-n junction recombination velocity of a bifacial polycrystalline silicon solar cell. The theoretical analysis is based on the columnar model of the grains in the polycrystalline silicon solar cell. The boundaries conditions are defined in order to use Green's function to solve the three-dimensional diffusion equation. This leads to a new expression of the transient photovoltage. The value of the constraint coefficients at interfaces of the grain are computed while those of the effective minority carrier lifetime τeff is extracted from the experimental curve of transient voltage. The bulk lifetime and the p-n junction recombination velocity are deduced and have been compared to those obtained from transient state by one-dimensional modelling of carrier's diffusion. This comparative study permitted us to show grain effects on the lifetime and consequently the inadequacy of one-dimensional modelling of carrier's diffusion in the polycrystalline silicon solar cells.

  20. Low Temperature Deposition of PECVD Polycrystalline Silicon Thin Films using SiF4 / SiH4 mixture

    NASA Astrophysics Data System (ADS)

    Syed, Moniruzzaman; Inokuma, Takao; Kurata, Yoshihiro; Hasegawa, Seiichi

    2016-03-01

    Polycrystalline silicon films with a strong (110) texture were prepared at 400°C by a plasma-enhanced chemical vapor deposition using different SiF4 flow rates ([SiF4] = 0-0.5 sccm) under a fixed SiH4 flow rate ([SiH4] = 1 or 0.15 sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), Atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4] and their respective maxima reach 90% and 900 Å. However, for [SiH4] = 0.15 sccm, both the crystallinity and the grain size decreased with [SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning.

  1. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Semiannual subcontract report, 8 December 1993--30 June 1994

    SciTech Connect

    Wohlgemuth, J.

    1995-03-01

    This report describes work done under a 3-year program to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance, and expand Solarex`s commercial production capacities. The accomplishments described in this report are as follows: (1) the authors designed modifications to casting stations, ceramic molds, and sizing saws to allow for casting and sizing of larger ingots; (2) they demonstrated the casting of ingots with 17% larger volume; (3) the selected and purchased a new wire saw from HCT Shaping Systems; (4) they demonstrated wafering of eight bricks (2,400 wafers or {approximately}4.4 kilowatts at the cell level) in a 6.5-h run; (5) they demonstrated 14% average cell efficiency in the laboratory using an aluminum paste back surface field; (6) the Automation and Robotics Research Institute (ARRI) completed a modeling study of the Solarex module assembly process; (7) they identified and qualified three new lower-cost back sheet materials through accelerated environmental tests; and (8) they designed and built a test structure for mounting frameless modules, and selected two adhesives and began testing their ability to hold modules to the structure.

  2. Analysis of P-Doped Polycrystalline Silicon Missing of W-Polycide Gate for 2X nm NAND Flash

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Chi; Yang, Wen-Chung; Yin, Te-Yuan; Chien, Hung-Ju; Ying, Tzung-Hua

    2013-03-01

    We studied the control-gate (CG-Poly) missing behavior after post in-situ steam generation (ISSG) re-oxidation for W-polycide gate of 2X nm NAND Flash and attempted to determine the possible mechanism. On the other hand, various effective countermeasures were also been proposed. We found that Si atoms diffuse upward on WSi2.3 films, driven out of the underlying doped polycrystalline silicon film during steam radical oxidation process based on energy dispersive X-ray (EDX) analysis. A 2.5 nm remaining of SiN at least on sidewall before oxidation results in CG-Poly missing free and WSix deformation improvement simultaneously. A selective oxidation such as water vapor generator (WVG) and rapid thermal oxidation (RTO) can achieve the same efficient performance. Additionally, less intrinsic tensile stress of WSix film employment also shows immunity against CG-Poly missing. Satisfactory sidewall barrier utilization for ISSG oxidation, diverse thermal oxidation selection, and even by WSix film property modifying might avoid poly-Si missing occurrence and reduce the WSix film deformation extent for the narrower dimension of 2X nm and beyond.

  3. Interfacial Layer Control by Dry Cleaning Technology for Polycrystalline and Single Crystalline Silicon Growth.

    PubMed

    Im, Dong-Hyun; Kong-Soo Lee; Kang, Yoongoo; Jeong, Myoungho; Park, Kwang Wuk; Lee, Soon-Gun; Ma, Jin-Won; Kim, Youngseok; Kim, Bonghyun; Im, Ki-Vin; Lim, Hanjin; Lee, Jeong Yong

    2016-05-01

    Native oxide removal prior to poly-Si contact and epitaxial growth of Si is the most critical technology to ensure process and device performances of poly-Si plugs and selective epitaxial growth (SEG) layers for DRAM, flash memory, and logic device. Recently, dry cleaning process for interfacial oxide removal has attracted a world-wide attention due to its superior passivation properties to conventional wet cleaning processes. In this study, we investigated the surface states of Si substrate during and after dry cleaning process, and the role of atomic elements including fluorine and hydrogen on the properties of subsequent deposited silicon layer using SIMS, XPS, and TEM analysis. The controlling of residual fluorine on the Si surface after dry cleaning is a key factor for clean interface. The mechanism of native oxide re-growth caused by residual fluorine after dry cleaning is proposed based on analytical results. PMID:27483844

  4. Tribological behavior of micron-scale polycrystalline silicon structural films in ambient air

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; van der Hulst, R.; Stach, E. A.; Dugger, M. T.; De Hosson, J. Th. M.; Ritchie, R. O.

    2009-02-01

    As tribological properties are critical factors in the reliability of microelectromechanical systems, it is important to understand the physical processes and parameters governing wear and friction in silicon structural films. Dynamic friction, wear volumes and wear morphology have been studied for polysilicon devices from the Sandia SUMMiT VTM process actuated in ambient air at μN loads. A total of seven devices were tested. Roughly half of the devices showed a peak in the friction coefficient at three times the initial value with failure after 105 cycles. The other half of the devices behaved similarly initially; however, following the friction coefficient peak they displayed a lower steady-state friction regime with no failure for millions of cycles. Additionally, the nanoscale wear coefficient and roughness increased in the first ~105 cycles and then slowly decayed over several million cycles. Transmission electron microscopy studies revealed amorphous oxygen-rich debris. These measurements show that after a short adhesive wear regime, abrasive wear is the governing mechanism with failures attributed to differences in the local nanoscale surface morphology. Changing the relative humidity, sliding speed and load was found to influence the friction coefficient, but re-oxidation of worn polysilicon surfaces was only found to have an effect after periods of inactivity.

  5. Nanoscale Silicon as Anode for Li-ion Batteries: The Fundamentals, Promise, and Challenges

    SciTech Connect

    Gu, Meng; He, Yang; Zheng, Jianming; Wang, Chong M.

    2015-09-24

    Silicon (Si), associated with its natural abundance, low discharge voltage vs. Li/Li+, and extremely high theoretical discharge capacity (~ 4200 mAh g-1,), has been extensively explored as anode for lithium ion battery. One of the key challenges for using Si as anode is the large volume change upon lithiation and delithiation, which causes a fast capacity fading. Over the last few years, dramatic progress has been made for addressing this issue. In this paper, we summarize the progress towards tailoring of Si as anode for lithium ion battery. The paper is organized such that it covers the fundamentals, the promise offered based on nanoscale designing, and the remaining challenges that need to be attacked to allow using of Si based materials as anode for battery.

  6. Metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor technology and application to flat-panel displays

    NASA Astrophysics Data System (ADS)

    Meng, Zhiguo

    High quality flat-panel displays (FPD) typically use active-matrix (AM) addressing, with the optical state of each pixel controlled by one or more active devices such as amorphous silicon (a-Si) thin film transistors (TFT). The successful examples are portable computer and liquid-crystal television (LC-TV). A high level of system on panel (SoP) electronic integration is required for versatile and compact systems. Meanwhile, many self-emitting display technologies are developing fast, active matrix for self-emitting display is typically current driven. The a-Si TFTs suffer from limited current driving capability, polycrystalline silicon (poly-Si) device technology is required. A new technology employing metal-induced unilaterally crystallization (MIUC) is presently reported. The device characteristics are obviously better than those in rapid-thermal annealed (RTA) and solid-phase crystallization (SPC) TFTs and the fabrication equipment is much cheaper than excimer laser crystallization (ELC) technology. The field effect mobility (muFE) of p- and n-channel MIUC TFTs is about 100cm2/Vs. Ion/I off is more than seven orders. Gate-induced leakage current in LT-MIUC poly-Si TFTs has been reduced by crystallization before heavy junction implantation to improve material quality and incorporating a gate-modulated lightly-doped drain (gamo-LDD) structure to reduce the electric field near the drain/channel junction region. At the same time, recrystallized (RC) MIUC TFT was researched with device characteristics improved. The 6.6cm 120 x 160 active matrix for OLED display is fabricated using LT-MIUC TFT technology on glass substrate. This display has the advantages of self-emitting, large intrinsic view angle and very fast response. At the same time, 6.6cm 120X160 AM-reflective twist nematic (RTN) display is fabricated using RC-MIUC TFT technology. This display is capable of producing 16 grade levels, 10:1 contrast and video image. The SOP display for AM-OLED were designed

  7. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    SciTech Connect

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao Qihua; Li Yixin; Street, Robert A.; Lu Jengping

    2009-07-15

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of {approx}10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical

  8. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    PubMed Central

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao, Qihua; Li, Yixin; Street, Robert A.; Lu, Jeng-Ping

    2009-01-01

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and∕or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ∼10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill

  9. A New Approach of Polycrystalline Silicon Film on Plastic Substrate Prepared by Ion Beam Deposition Followed by Excimer Laser Crystallization at Room Temperature

    NASA Astrophysics Data System (ADS)

    Kwon, Jang Yeon; Lim, Hyuck; Park, Kyung Bae; Jung, Ji Sim; Kim, Do Young; Cho, Hans S.; Kim, Seok Pil; Park, Young Soo; Kim, Jong Man; Noguchi, Takashi

    2006-05-01

    In this work, we propose a new polycrystalline silicon (poly-Si) film of large grain for thin film transistor on flexible substrate. Thin films of amorphous silicon were deposited on plastic substrate by using ion beam deposition (IBD) and crystallized by excimer laser annealing. The entire process was carried out at room temperature. Si film formed by IBD has much lower impurity such as Ar, O, and H than that deposited by conventional sputtering method. This high purity of Si film makes large grain size (0.5 μm) and shows high endurance of excimer laser energy both on quartz and plastic substrate for flexible active matrix organic light emitting diode (AMOLED).

  10. Promises, Promises.

    PubMed

    McLean, Haydn

    2016-03-01

    Presenting a pledge to another establishes expectation in the recipient for the commitment to be fulfilled, particularly when a promise is devoid of coercion. Defaulting on a commitment may damage relationships between people and may predispose the disenchanted recipient to distrust those who proffer succeeding commitments. God's advocates who have been disappointed by God's evident under-delivery may experience a crisis of faith, exemplified in attachment distress, when disappointment intimates God has over-promised his providence, which questions the nature and, ultimately, the relevance of God. PMID:26956758

  11. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    NASA Astrophysics Data System (ADS)

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-04-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at ‑0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature.

  12. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    PubMed Central

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-01-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at −0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature. PMID:27098115

  13. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor.

    PubMed

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-01-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at -0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm(2)/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature. PMID:27098115

  14. Electrical Characteristics of Low-Temperature Polycrystalline Silicon Complementary Metal-Oxide-Semiconductor Thin-Film Transistors with Six-Step Photomask Structure

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Jin; Park, Jae-Hoon; Oh, Kum-Mi; Lee, Seok-Woo; Lee, Kyung-Eon; Shin, Woo-Sup; Jun, Myung-chul; Yang, Yong-Suk; Hwang, Yong-Kee

    2011-06-01

    We propose two types of six-step photomask, complementary metal-oxide-semiconductor (CMOS), thin-film transistor (TFT) PCT device structures in order to simplify their fabrication process compared with that of conventional, low-temperature, polycrystalline silicon (LTPS) CMOS TFT devices. The initial charge transfer characteristics of both types of six-step PCT are equivalent to those of the conventional nine-step PCT. Both types of six-step PCT are comparable to the conventional nine-step mask lightly doped drain (LDD) device in terms of the dc device lifetime of over 10 years at Vds=5 V for line inversion driving, which is the normally recognized duration time for semiconducting devices.

  15. The electrical conduction properties of poly-crystalline indium-zinc-oxide film

    SciTech Connect

    Tomai, S.; Terai, K.; Junke, T.; Tsuruma, Y.; Ebata, K.; Yano, K.; Uraoka, Y.

    2014-02-28

    We have developed a high-mobility and high-uniform oxide semiconductor using poly-crystalline semiconductor material composed of indium and zinc (p-IZO). A typical conduction mechanism of p-IZO film was demonstrated by the grain boundary scattering model as in polycrystalline silicon. The grain boundary potential of the 2-h-annealed IZO film was calculated to be 100 meV, which was comparable to that of the polycrystalline silicon. However, the p-IZO thin film transistor (TFT) measurement shows rather uniform characteristics. It denotes that the mobility deterioration around the grain boundaries is lower than the case for low-temperature polycrystalline silicon. This assertion was made based on the difference of the mobility between the polycrystalline and amorphous IZO film being much smaller than is the case for silicon transistors. Therefore, we conclude that the p-IZO is a promising material for a TFT channel, which realizes high drift mobility and uniformity simultaneously.

  16. Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

    DOEpatents

    Findikoglu, Alp T.; Jia, Quanxi; Arendt, Paul N.; Matias, Vladimir; Choi, Woong

    2009-10-27

    A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

  17. Fundamental studies of grain boundary passivation in polycrystalline silicon with application to improved photovoltaic devices. A final research report covering work completed from February-December 1979

    SciTech Connect

    Seager, C.H.; Ginley, D.S.

    1980-02-01

    Several aspects of the electrical properties of silicon grain boundaries have been studied. The temperature dependence of the zero-bias conductance and capacitance of single boundaries has been measured and shown to be in good agreement with a simple double depletion layer/thermal emission (DDL/TE) model developed to predict the transport properties of such structures. In addition, it has been shown that deconvolution of the I-V properties of some boundaries via a deconvolution scheme suggested by Pike and Seager yields effective one-electron densities of trapping states which are in good agreement with estimates obtained by low temperature electron emission measurements. Experiments have also been performed which indicate that diffusion of atomic hydrogen into silicon grain boundaries greatly reduces this density of trapping states. In properly prepared, large grained polycrystalline samples all measurable traces of grain boundary potential barriers can be removed to substantial penetration depths after several hours exposure to a hydrogen plasma at elevated temperatures. Initial experiments on prototype polysilicon solar cells have shown that this passivation process can improve AM1 efficiencies. In order to more fully understand and develop this process for improving practical multigrained cells, several device research efforts with other DOE/SERI funded contractors have been initiated.

  18. Deposition, fabrication and analysis of polycrystalline silicon MIS solar cells. Final Report, January 1-December 31, 1979

    SciTech Connect

    Anderson, W.A.

    1980-03-01

    Discussion of MIS cell fabrication techniques, protovoltaic response data, I-V-T analysis to reveal conduction mechanisms, a detailed computer model, optimum MIS solar cell design, surface state effects, Auger studies, reliability studies and e-beam deposition of thin silicon films are included. The most important features of the work during 1979 include the one pump-down fabrication process, establishing a consistent fabrication sequence, achieving 13% efficiency of 2 cm/sup 2/ area, an evaluation of conduction mechanisms, establishing a detailed computer model and setting up an improved e-beam system to deposit thin silicon films. Details are reported. (WHK)

  19. Photovoltaic mechanisms in polycrystalline thin film silicon solar cells. Final report, 30 June 1979-29 June 1980

    SciTech Connect

    Sopori, B.L.

    1980-11-01

    The objectives of this program were: (1) to develop appropriate measurement techniques to facilitate a quantitative study of the electrical activity of structural defects and at a grain boundary (G.B.) in terms of generation-recombination, barrier height, and G.B. conductivity; (2) to characterize G.B.s in terms of physical properties such as angle of misfit and local stress, and to correlate them with the electrical activity; (3) to determine the influence of solar cell processing on the electrical behavior of structural defects and G.B.s; and (4) to evaluate polycrystalline solar cell performance based on the above study, and to compare it with the experimentally measured performance. Progress is reported in detail. (WHK)

  20. Carrier mobility measurement across a single grain boundary in polycrystalline silicon using an organic gate thin-film transistor

    SciTech Connect

    Hashimoto, Masaki; Kanomata, Kensaku; Momiyama, Katsuaki; Kubota, Shigeru; Hirose, Fumihiko

    2012-01-09

    In this study, we developed a measurement method for field-effect-carrier mobility across a single grain boundary in polycrystalline Si (poly Si) used for solar cell production by using an organic gate field-effect transistor (FET). To prevent precipitation and the diffusion of impurities affecting the electronic characteristics of the grain boundary, all the processing temperatures during FET fabrication were held below 150 deg. C. From the grain boundary, the field-effect mobility was measured at around 21.4 cm{sup 2}/Vs at 297 K, and the temperature dependence of the field-effect mobility suggested the presence of a potential barrier of 0.22 eV at the boundary. The technique presented here is applicable for the monitoring of carrier conduction characteristics at the grain boundary in poly Si used for the production of solar cells.

  1. Thin film polycrystalline silicon solar cells. Quarterly technical progress report No. 3, 1 April 1980-30 June 1980

    SciTech Connect

    Sarma, K. R.; Rice, M. J.; Legge, R.; Ellis, R. J.

    1980-06-01

    During this third quarter of the program, the high pressure plasma (hpp) deposition process has been thoroughly evaluated using SiHCl/sub 3/ and SiCl/sub 4/ silicon source gases, by the gas chromatographic analysis of the effluent gases from the reactor. Both the deposition efficiency and reactor throughput rate were found to be consistently higher for hpp mode of operation compared to conventional CVD mode. The figure of merit for various chlorosilanes as a silicon source gas for hpp deposition is discussed. A new continuous silicon film deposition scheme is developed, and system design is initiated. This new system employs gas interlocks and eliminates the need for gas curtains which have been found to be problematic. Solar cells (2 cm x 2 cm area) with AM1 efficiencies of up to 12% were fabricated on RTR grain enhanced hpp deposited films. The parameters of a 12% cell under simulated AM1 illumination were: V/sub OC/ = 0.582 volts, J/sub SC/ = 28.3 mA/cm/sup 2/ and F.F. = 73.0%.

  2. Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Pagels, Marcel; Zachäus, Carolin; Pollakowski, Beatrix; Beckhoff, Burkhard; Kanngießer, Birgit; Rech, Bernd

    2013-01-01

    The combination of polycrystalline silicon (poly-Si) thin films with aluminum doped zinc oxide layers (ZnO:Al) as transparent conductive oxide enables the design of appealing optoelectronic devices at low costs, namely in the field of photovoltaics. The fabrication of both thin-film materials requires high-temperature treatments, which are highly desired for obtaining a high electrical material quality. Annealing procedures are typically applied during crystallization and defect-healing processes for silicon and can boost the carrier mobility and conductivity of ZnO:Al layers. In a combined poly-Si/ZnO:Al layer system, an in-depth knowledge of the interaction of both layers and the control of interface reactions upon thermal treatments is crucial. Therefore, we analyze the influence of rapid thermal treatments up to 1050 °C on solid phase crystallized poly-Si thin-film solar cells on ZnO:Al-coated glass, focusing on chemical interface reactions and modifications of the poly-Si absorber material quality. The presence of a ZnO:Al layer in the solar cell stack was found to limit the poly-Si solar cell performance with open circuit voltages only below 390 mV (compared to 435 mV without ZnO film), even if a silicon nitride (SiN) diffusion barrier was included. A considerable amount of diffused zinc inside the silicon was observed. By grazing-incidence X-ray fluorescence spectrometry, a depth-resolving analysis of the elemental composition close to the poly-Si/(SiN)/ZnO:Al interface was carried out. Temperatures above 1000 °C were found to promote the formation of new chemical compounds within about 10 nm of interface, such as zinc silicates (Zn2SiO4) and aluminium oxide (AlxOy). These results give valuable insights about the temperature-limitations of Si/ZnO thin-film solar cell fabrication and the formation of high-mobility ZnO-layers by thermal anneal.

  3. High-performance flexible thin-film transistors fabricated using print-transferrable polycrystalline silicon membranes on a plastic substrate

    NASA Astrophysics Data System (ADS)

    Qin, Guoxuan; Yuan, Hao-Chih; Yang, Hongjun; Zhou, Weidong; Ma, Zhenqiang

    2011-02-01

    Inexpensive polycrystalline Si (poly-Si) with large grain size is highly desirable for flexible electronics applications. However, it is very challenging to directly deposit high-quality poly-Si on plastic substrates due to processing constrictions, such as temperature tolerance and residual stress. In this paper, we present our study on poly-Si membranes that are stress free and most importantly, are transferrable to any substrate including a low-temperature polyethylene terephthalate (PET) substrate. We formed poly-Si-on-insulator by first depositing small-grain size poly-Si on an oxidized Si wafer. We then performed high-temperature annealing for recrystallization to obtain larger grain size. After selective doping on the poly-Si-on-insulator, buried oxide was etched away. By properly patterning the poly-Si layer, residual stress in the released poly-Si membranes was completely relaxed. The flat membrane topology allows the membranes to be print transferred to any substrates. High-performance TFTs were demonstrated on the transferred poly-Si membranes on a PET substrate.

  4. Process for utilizing low-cost graphite substrates for polycrystalline solar cells

    NASA Technical Reports Server (NTRS)

    Chu, T. L. (Inventor)

    1978-01-01

    Low cost polycrystalline silicon solar cells supported on substrates were prepared by depositing successive layers of polycrystalline silicon containing appropriate dopants over supporting substrates of a member selected from the group consisting of metallurgical grade polycrystalline silicon, graphite and steel coated with a diffusion barrier of silica, borosilicate, phosphosilicate, or mixtures thereof such that p-n junction devices were formed which effectively convert solar energy to electrical energy. To improve the conversion efficiency of the polycrystalline silicon solar cells, the crystallite size in the silicon was substantially increased by melting and solidifying a base layer of polycrystalline silicon before depositing the layers which form the p-n junction.

  5. Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique

    PubMed Central

    Lin, Hsin-Han; Chen, Wen-Hwa; Hong, Franklin C.-N.

    2013-01-01

    The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120–130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6–10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm2) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching. PMID:23847751

  6. High-speed and high-efficiency Si optical modulator with MOS junction, using solid-phase crystallization of polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Fujikata, Junichi; Takahashi, Masashi; Takahashi, Shigeki; Horikawa, Tsuyoshi; Nakamura, Takahiro

    2016-04-01

    We developed a high-speed and high-efficiency MOS-capacitor-type Si optical modulator (Si-MOD) by applying a low optical loss and a low resistivity of a polycrystalline silicon (poly-Si) gate with large grains. To achieve a low resistivity of a poly-Si film, a P-doped poly-Si film based on Si2H6 solid-phase crystallization (SPC) was developed, which showed a comparable resistivity to that of P-doped single-crystal Si. In addition, high-temperature annealing (HTA) after SPC was effective for realizing low optical loss. We designed the optimum Si-MOD structure and demonstrated a very high modulation efficiency of 0.3 V cm, which is very efficient among the Si-MODs developed thus far. High-speed (15 Gbps) operation was achieved with a small footprint of the 200-µm-long phase shifter and a low drive voltage of 1.5 Vpp at a low optical insertion loss of -2.2 dB and 1.55 µm wavelength.

  7. An effective approach for restraining electrochemical corrosion of polycrystalline silicon caused by an HF-based solution and its application for mass production of MEMS devices

    NASA Astrophysics Data System (ADS)

    Liu, Yunfei; Xie, Jing; Zhao, Hui; Luo, Wei; Yang, Jinling; An, Ji; Yang, Fuhua

    2012-03-01

    This paper presents a novel method to effectively protect the structural material polycrystalline silicon (polysilicon) from electrochemical corrosion, which often occurs when the MEMS device is released in HF-based solutions, especially when the device contains a noble metal. This corrosion seriously degrades the electrical and mechanical performance as well as the reliability of MEMS devices. In this method, a photoresist (PR) is employed to cover the noble metal, which is electrically coupled with the underlying polysilicon layer. This PR cover can effectually prevent an HF-based solution from diffusing through and arriving at the surface of the noble metal, thus cutting off the electrical current of the electrochemical corrosion reaction. The polysilicon is well protected for longer than 80 min in 49% concentrated HF solutions by a 3 µm-thick AZ 6130 PR film. This fabrication process is simple, reliable and suitable for mass production of high-end micromechanical disk resonators. Benefiting from the technology breakthrough mentioned above, a novel low-cost microfabrication method for disk resonators with high performance has been developed, and the VHF polysilicon disk resonators with resonance frequencies around 282 MHz and Q values larger than 2000 at atmosphere have been produced at wafer level.

  8. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Choi, Sung-Hwan; Kim, Sun-Jae; Mo, Yeon-Gon; Kim, Hye-Dong; Han, Min-Koo

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (ΔVTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (ΔVTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  9. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Sung-Hwan Choi,; Sun-Jae Kim,; Yeon-Gon Mo,; Hye-Dong Kim,; Min-Koo Han,

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (Δ VTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (Δ VTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  10. High quality SiO2/Si interfaces of poly-crystalline silicon thin film transistors by annealing in wet atmosphere

    NASA Astrophysics Data System (ADS)

    Sano, Naoki; Sekiya, Mitsunobu; Hara, Masaki; Kohno, Atsushi; Sameshima, Toshiyuki

    1995-05-01

    A new post-metallization annealing technique was developed to improve the quality of metal-oxide-semiconductor (MOS) devices using SiO2 films formed by a parallel-plate remote plasma chemical vapor deposition as gate insulators. The quality of the interface between SiO2 and crystalline Si was investigated by capacitance-voltage (C-V) measurements. An H2O vapor annealing at 270 C for 30 min efficiently decreased the interface trap density to 2.0 x 10(exp 10) cm(exp -2) eV(exp -1), and the effective oxide charge density from 1 x 10(exp 12) to 5 x 10(exp 9) cm(exp -2). This annealing process was also applied to the fabrication of Al-gate polycrystalline silicon thin film transistors (poly-Si TFT's) at 270 C. In p-channel poly-Si TFT's, the carrier mobility increased from 60-400 cm(exp 2) V(exp -1) s(exp - 1) and the threshold voltage decreased from - 5.5 to - 1.7 V.

  11. Stress-Induced Off-Current under On- and Off-State Stress Voltages in Low-Temperature n-Channel Polycrystalline Silicon Thin-Film Transistors

    NASA Astrophysics Data System (ADS)

    Seishiro Hirata,; Toshifumi Satoh,; Hiroyuki Tango,

    2010-03-01

    The changes in off-current under on- and off-state stress voltages in n-channel polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are investigated through measurements and simulations. It is found that the off-current increases markedly in the shallow-negative-gate-voltage region and decreases in the deep-gate-voltage region after applying both on- and off-state stresses, resulting in a weaker dependence on negative gate voltage. It can be supposed from the simulations and experiments that the donor-type trap states (positive charges) with a hump-type state profile, located at 0.1-0.2 eV below the midgap, and tail states are generated near the drain junction after applying both stresses. The amount of donor-type states increases in phonon-assisted tunneling with the Pool-Frenkel effect (PAT) and Schockley-Read-Hall generation (SRH) owing to the increase in the deep-trap-state density, and decreases in band-to-band tunneling (BBT) owing to the decrease in electric field, giving rise to a predominant PAT+SRH current in off-current in a wide-negative-gate-voltage region.

  12. Polycrystalline silicon thin-film transistor with nickel-titanium oxide by sol-gel spin-coating and nitrogen implantation

    NASA Astrophysics Data System (ADS)

    Wu, Shih-Chieh; Hou, Tuo-Hung; Chuang, Shiow-Huey; Chou, Hsin-Chih; Chao, Tien-Sheng; Lei, Tan-Fu

    2012-12-01

    This study demonstrates polycrystalline silicon thin-film transistors (poly-Si TFTs) integrated with a high-κ nickel-titanium oxide (NiTiO3) gate dielectric using sol-gel spin-coating and nitrogen channel implantation. This novel fabrication method of the high-κ NiTiO3 gate dielectric offers thin equivalent-oxide thickness and high gate capacitance density, favorable for increasing the current driving capability. Introducing nitrogen ions into the poly-Si using implantation effectively passivates the trap states not only in the poly-Si channel but also at the gate dielectric/poly-Si interface. The poly-Si NiTiO3 TFTs with nitrogen implantation exhibit significantly improved electrical characteristics, including lower threshold voltage, a steeper subthreshold swing, higher field-effect mobility, a larger on/off current ratio, and less threshold-voltage roll-off. Furthermore, the nitrogen implantation improves the reliability of poly-Si NiTiO3 TFTs against hot-carrier stress and positive bias temperature instability.

  13. Abnormal Threshold Voltage Shifts in P-Channel Low-Temperature Polycrystalline Silicon Thin Film Transistors Under Negative Bias Temperature Stress.

    PubMed

    Kim, Sang Sub; Choi, Pyung Ho; Baek, Do Hyun; Lee, Jae Hyeong; Choi, Byoung Deog

    2015-10-01

    In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiNx dielectrics. A negative gate bias temperature instability (NBTI) stress was applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (Vth). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNx/SiO2 dielectric interface being dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the Vth switches to the negative voltage direction, which is "turn-around" behavior. In the second stage, the Vth moves from -1.63 V to -2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps. PMID:26726370

  14. Exploratory development of thin-film polycrystalline silicon photovoltaic devices. Report No. 3. Electron beam ribbon-to-ribbon (EB RTR) recrystallization of microcrystalline silicon ribbons

    SciTech Connect

    Gurtler, R.W.

    1981-09-01

    The electron beam has been applied as the energy source for ribbon-to-ribbon (RTR) recrystallization of thin-film silicon with very small (approx. 1 ..mu..m) grains into sheets with very large grains (> 1 cm). The system described uses two e-guns, one for producing a thin molten region across the microcrystalline ribbon (except for the edges), the other for establishing desirable thermal profiles in the cool-down (and heat-up) regions. In this way, no furnace, heat shield, or cooling structures are present, in contrast to all the other ribbon growing techniques. This simple arrangement is gained at the (reasonable) expense of having to work in a vacuum. A CCTV camera observes the temperature distribution and melt shape during growth; its output is coupled to a real-time image analyzer system and a computer. When there is a need to alter the temperature or melt shape in a region, the deflection/modulation circuitry is appropriately instructed, and (closing the loop) the change is made. The vacuum chamber with cassette feed for ribbons, electron guns, and camera, was completed and placed in operation. The overall system was run with a fined temperature profile for small RTR samples; resulting thin-film silicon ribbon quality was comparable to that obtained with laser beam RTR. The entire electronic system was not finished, however, so potential utility of the system for improving silicon ribbon quality and economics could not be ascertained.

  15. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2015-06-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46- x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  16. Nanoscale deformation and fracture mechanics of polycrystalline silicon and diamond-like carbon for MEMS by the AFM/DIC method

    NASA Astrophysics Data System (ADS)

    Cho, Sung Woo

    A method for nanoscale experimental mechanics was developed to address problems in deformation and fracture of micron-scale components in Microelectromechanical Systems (MEMS). Specifically, the effective and local, elastic and fracture behavior of polycrystalline silicon (polysilicon) and tetrahedral amorphous diamond-like carbon (ta-C) were studied using freestanding thin films subject to uniaxial tension. In this method, direct measurements of local deformations were derived from Atomic Force Microscopy (AFM) images in specimen areas varying between 1x2 mum2 and 15x15 mum2 using Digital Image Correlation (DIC) to extract displacements and strains with spatial resolution of 1-2 nm. The effective elastic modulus and Poisson's ratio of polysilicon and ta-C from the Sandia National Laboratories (SUMMiT) were 155 +/- 6 GPa and 0.22 +/- 0.02, and 759 +/- 22 GPa and 0.17 +/- 0.03, respectively. Similarly, the elastic modulus and Poisson's ratio of polysilicon fabricated at MCNC via the Multi-User MEMS Processes (MUMPs) with <110> texture were 164 +/- 7 GPa and 0.22 +/- 0.02, respectively. A second problem studied using the AFM/DIC method was the fracture of polysilicon in the presence of atomically sharp cracks. The effective (macroscopic) Mode-I critical stress intensity factor for polysilicon from different MUMPs runs was 1.00 +/- 0.1 MPa√m, where 0.1 MPa√m was the standard deviation, attributed to local cleavage anisotropy and grain boundary toughening. The variation in the effective critical stress intensity factor and the subcritical crack growth of polysilicon that was spatially recorded and quantified for the first time were the result of the spatial variation of the 4 local stress intensity factor at the crack tip that controlled crack initiation and thus, the overall fracture process. The AFM/DIC method was also applied to determine the minimum size of a polysilicon domain whose effective mechanical behavior could be described by the isotropic elastic

  17. 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.

  18. Abnormality in fracture strength of polycrystalline silicene

    NASA Astrophysics Data System (ADS)

    Liu, Ning; Hong, Jiawang; Pidaparti, Ramana; Wang, Xianqiao

    2016-09-01

    Silicene, a silicon-based homologue of graphene, arouses great interest in nano-electronic devices due to its outstanding electronic properties. However, its promising electronic applications are greatly hindered by lack of understanding in the mechanical strength of silicene. Therefore, in order to design mechanically reliable devices with silicene, it is necessary to thoroughly explore the mechanical properties of silicene. Due to current fabrication methods, graphene is commonly produced in a polycrystalline form; the same may hold for silicene. Here we perform molecular dynamics simulations to investigate the mechanical properties of polycrystalline silicene. First, an annealing process is employed to construct a more realistic modeling structure of polycrystalline silicene. Results indicate that a more stable structure is formed due to the breaking and reformation of bonds between atoms on the grain boundaries. Moreover, as the grain size decreases, the efficiency of the annealing process, which is quantified by the energy change, increases. Subsequently, biaxial tensile tests are performed on the annealed samples in order to explore the relation between grain size and mechanical properties, namely in-plane stiffness, fracture strength and fracture strain etc. Results indicate that as the grain size decreases, the fracture strain increases while the fracture strength shows an inverse trend. The decreasing fracture strength may be partly attributed to the weakening effect from the increasing area density of defects which acts as the reservoir of stress-concentrated sites on the grain boundary. The observed crack localization and propagation and fracture strength are well-explained by a defect-pileup model.

  19. Upgrading Metallurgical-Grade Silicon

    NASA Technical Reports Server (NTRS)

    Woerner, L. M.; Moore, E. B.

    1985-01-01

    Closed-loop process produces semiconductor-grade silicon. Metallurgical-grade silicon converted to ultrapure silicon by reacting with hydrogen and silicon tetrahalide to form trihalosilane, purifying this intermediate and again decomposing to high purity silicon in third stage. Heterogeneously and homogeneously nucleated polycrystalline silicon used in semiconductor device applications and in silicon photovoltaic solar cell fabrication.

  20. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  1. Top-Coating Silicon Onto Ceramic

    NASA Technical Reports Server (NTRS)

    Heaps, J. D.; Nelson, L. D.; Zook, J. D.

    1985-01-01

    Polycrystalline silicon for solar cells produced at low cost. Molten silicon poured from quartz trough onto moving carbon-coated ceramic substrate. Doctor blade spreads liquid silicon evenly over substrate. Molten material solidifies to form sheet of polycrystalline silicon having photovoltaic conversion efficiency greater than 10 percent. Method produces 100-um-thick silicon coatings at speed 0.15 centimeter per second.

  2. Plastic flow of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Langer, James

    Leo Kadanoff had a long interest in fluid flows, especially fingering instabilities. This interest was one example of his insatiable curiosity about simple, fundamentally important, and often multidisciplinary phenomena. Here is an example of another class of such phenomena that I had hoped to show him this year. The experts in polycrystalline solid mechanics have insisted for decades that their central problem - dislocation-mediated strain hardening - is intrinsically unsolvable. I think they're wrong. My colleagues and I have made progress recently in theories of both amorphous and polycrystalline plasticity by introducing an effective disorder temperature as a dynamical variable in our equations of motion. In this way, we have been able to describe how the densities of flow defects or dislocations evolve in response to external forcing, and thus to develop theories that promise to become as predictive, and full of surprises, as the laws of fluid flow. For Kadanoff session.

  3. Silicon film solar cell process

    NASA Technical Reports Server (NTRS)

    Hall, R. B.; Mcneely, J. B.; Barnett, A. M.

    1984-01-01

    The most promising way to reduce the cost of silicon in solar cells while still maintaining performance is to utilize thin films (10 to 20 microns thick) of crystalline silicon. The method of solution growth is being employed to grow thin polycrystalline films of silicon on dissimilar substrates. The initial results indicate that, using tin as the solvent, this growth process only requires operating temperatures in the range of 800 C to 1000 C. Growth rates in the range of 0.4 to 2.0 microns per minute and grain sizes in the range of 20 to 100 microns were achieved on both quartz and coated steel substrates. Typically, an aspect ratio of two to three between the width and the Si grain thickness is seen. Uniform coverage of Si growth on quartz over a 2.5 x 2.5 cm area was observed.

  4. First-principles calculations of a promising intermediate-band photovoltaic material based on Co-hyperdoped crystalline silicon

    NASA Astrophysics Data System (ADS)

    Dong, Xiao; Song, Xiaohui; Wang, Yongyong; Wang, Jinfeng

    2015-08-01

    Among the various atomic structures of Co doped in the Si lattice, the substitutional Co is the most stable structure and can cause an impurity band in the band gap of crystalline Si. The impurity band is partially filled by electrons and isolated from the valence band (VB) and conduction band (CB), which fulfills the conditions of an intermediate-band (IB) photovoltaic material. The dielectric constant indicates that the substitutional Co-doped Si material can cause sub-band-gap light absorption. These properties will make the Co-hyperdoped Si a promising IB material in photovoltaic fields.

  5. Silicon and phosphorus dual doped graphene as the promising metal-free catalysts for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Lu, Zhansheng; Li, Shuo; Yang, Zongxian; Wu, Ruqian

    The pathways of oxygen reduction reaction (ORR) on the metal-free silicon and phosphorus dual doped graphene (Si-P-G) catalyst are systematically investigated based on the dispersion-corrected density functional theory (DFT-D) method. It is found that the Si-P-G can be stable at high temperature from the first-principles molecular dynamics simulation and the local region of dopants displays an important role in the adsorption and reduction of oxygen. Both of the four-electron O2 direct dissociation and the two-electron OOH dissociation pathways are probable for ORR on the Si-P-G, while the latter pathway is mainly followed by the pathway of the OH hydrogenation into H2O. For the OOH dissociation pathway, the hydrogenation of O2 to OOH is the rate-limiting step with a rather small barrier energy of 0.66 eV. The current results indicate that the Si-P-G is a novel metal-free catalyst for ORR, and which is comparable to that of the Pt catalyst. Work was supported by the National Science Foundation Center for Chemical Innovation on Chemistry at the Space-Time Limit (CaSTL) under Grant No. CHE-1414466, and the National Natural Science Foundation of China (Grant Nos. 51401078, and 11474086).

  6. Optical Sensing Circuit Using Low-Temperature Polycrystalline Silicon p-Type Thin-Film Transistors and p-Intrinsic-Metal Diode for Active Matrix Displays with Optical Input Functions

    NASA Astrophysics Data System (ADS)

    Lim, Han-Sin; Kwon, Oh-Kyong

    2009-03-01

    An optical sensing circuit composed of low-temperature polycrystalline silicon (LTPS) p-type thin-film transistors (TFTs) and a p-intrinsic-metal (p-i-m) diode is proposed for image scanning and touch sensing functions. Because it is a very difficult challenge to integrate both display pixels and optical sensing circuits into the restricted pixel area, the number of additional devices and control signal lines must be minimized. Therefore, two p-type TFTs, one p-i-m diode, one capacitor, and one signal line are added to display pixel for the proposed optical sensing circuit. Active matrix liquid crystal display (AMLCD) and active matrix organic light-emitting diode (AMOLED) pixels with the proposed optical sensing circuit have image scanning and touch sensing functions, respectively. Through the measurement of the proposed circuit under the condition of incident light varying from 0 to 10,000 lx, we verified that the dynamic and output ranges of the proposed circuit are 30 dB and 1.5 V, respectively.

  7. Role of surface-reaction layer in HBr/fluorocarbon-based plasma with nitrogen addition formed by high-aspect-ratio etching of polycrystalline silicon and SiO2 stacks

    NASA Astrophysics Data System (ADS)

    Iwase, Taku; Matsui, Miyako; Yokogawa, Kenetsu; Arase, Takao; Mori, Masahito

    2016-06-01

    The etching of polycrystalline silicon (poly-Si)/SiO2 stacks by using VHF plasma was studied for three-dimensional NAND fabrication. One critical goal is achieving both a vertical profile and high throughput for multiple-stack etching. While the conventional process consists of multiple steps for each stacked layer, in this study, HBr/fluorocarbon-based gas chemistry was investigated to achieve a single-step etching process to reduce process time. By analyzing the dependence on wafer temperature, we improved both the etching profile and rate at a low temperature. The etching mechanism is examined considering the composition of the surface reaction layer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption of N–H and Br was enhanced at a low temperature, resulting in a reduced carbon-based-polymer thickness and enhanced Si etching. Finally, a vertical profile was obtained as a result of the formation of a thin and reactive surface-reaction layer at a low wafer temperature.

  8. 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.

  9. Status of polycrystalline solar cell technologies

    NASA Astrophysics Data System (ADS)

    Kapur, Vijay K.; Basol, Bulent M.

    Thin-film cadmium telluride (CdTe) and thin-film copper indium diselenide (CIS) solar cells are discussed. The issues these technologies face before commercialization are addressed. High-efficiency (15-18 percent) polycrystalline silicon modules could dominate the market in the near future, and impressive results for thin-film CdTe and CIS solar cells and their outdoor stability can attract increased interest in these solar cells, which will accelerate their development.

  10. Development and evaluation of polycrystalline cadmium telluride dosimeters for accurate quality assurance in radiation therapy

    NASA Astrophysics Data System (ADS)

    Oh, K.; Han, M.; Kim, K.; Heo, Y.; Moon, C.; Park, S.; Nam, S.

    2016-02-01

    For quality assurance in radiation therapy, several types of dosimeters are used such as ionization chambers, radiographic films, thermo-luminescent dosimeter (TLD), and semiconductor dosimeters. Among them, semiconductor dosimeters are particularly useful for in vivo dosimeters or high dose gradient area such as the penumbra region because they are more sensitive and smaller in size compared to typical dosimeters. In this study, we developed and evaluated Cadmium Telluride (CdTe) dosimeters, one of the most promising semiconductor dosimeters due to their high quantum efficiency and charge collection efficiency. Such CdTe dosimeters include single crystal form and polycrystalline form depending upon the fabrication process. Both types of CdTe dosimeters are commercially available, but only the polycrystalline form is suitable for radiation dosimeters, since it is less affected by volumetric effect and energy dependence. To develop and evaluate polycrystalline CdTe dosimeters, polycrystalline CdTe films were prepared by thermal evaporation. After that, CdTeO3 layer, thin oxide layer, was deposited on top of the CdTe film by RF sputtering to improve charge carrier transport properties and to reduce leakage current. Also, the CdTeO3 layer which acts as a passivation layer help the dosimeter to reduce their sensitivity changes with repeated use due to radiation damage. Finally, the top and bottom electrodes, In/Ti and Pt, were used to have Schottky contact. Subsequently, the electrical properties under high energy photon beams from linear accelerator (LINAC), such as response coincidence, dose linearity, dose rate dependence, reproducibility, and percentage depth dose, were measured to evaluate polycrystalline CdTe dosimeters. In addition, we compared the experimental data of the dosimeter fabricated in this study with those of the silicon diode dosimeter and Thimble ionization chamber which widely used in routine dosimetry system and dose measurements for radiation

  11. Diffusion in polycrystalline microstructures

    SciTech Connect

    Swiler, T.P.; Holm, E.A.

    1995-07-01

    Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and the topological aspects of grain boundaries. In this study, a finite difference scheme is developed to study transient and steady-state mass transport through realistic two-dimensional polycrystalline microstructures. Effects of microstructural parameters such as average grain size and grain boundary topology are examined, as are effects due to limits of the model.

  12. Silicon materials outlook study for 1980-1985 calendar years

    NASA Technical Reports Server (NTRS)

    Costogue, E.; Ferber, R.; Hasbach, W.; Pellin, R.; Yaws, C.

    1979-01-01

    The polycrystalline silicon industry was studied in relation to future market needs. Analysis of the data obtained indicates that there is a high probability of polycrystalline silicon shortage by the end of 1982 and a strong seller's market after 1981 which will foster price competition for available silicon.

  13. Thin film polycrystalline silicon solar cells

    SciTech Connect

    Ghosh, A. K.; Feng, T.; Eustace, D. J.; Maruska, H. P.

    1980-01-01

    During the present quarter efficiency of heterostructure solar cells has been increased from 13 to 13.7% for single crystal and from 10.3 to 11.2% for polysilicon. For polysilicon the improvements can be attributed to reductions in grid-area coverage and in reflection losses and for single crystal to a combination of reduction in grid-area coverage and increase in fill factor. The heterostructure cells in both cases were IT0/n-Si solar cells. Degradation in Sn0/sub 2//n-Si solar cells can be greatly reduced to negligible proportions by proper encapsulation. The cells used in stability tests have an average initial efficiency of 11% which reduces to a value of about 10.5% after 6 months of exposure to sunlight and ambient conditions. This small degradation occurs within the first month, and the efficiency remains constant subsequently. The reduction in efficiency is due to a decrease in the open-circuit voltage only, while the short-circuit current and fill factor remain constant. The effects of grain-size on the Hall measurements in polysilicon have been analyzed and interpreted, with some modifications, using a model proposed by Bube. This modified model predicts that the measured effective Hall voltage is composed of components originating from the bulk and space-charge region. For materials with large grains, the carrier concentration is independent of the inter-grain boundary barrier, whereas the mobility is dependent on it. However, for small rains, both the carrier density and mobility depend on the barrier. These predictions are consistant with experimental results of mm-size Wacker polysilicon and ..mu..m-size NTD polysilicon.

  14. Thermal conductivity measurements of Summit polycrystalline silicon.

    SciTech Connect

    Clemens, Rebecca; Kuppers, Jaron D.; Phinney, Leslie Mary

    2006-11-01

    A capability for measuring the thermal conductivity of microelectromechanical systems (MEMS) materials using a steady state resistance technique was developed and used to measure the thermal conductivities of SUMMiT{trademark} V layers. Thermal conductivities were measured over two temperature ranges: 100K to 350K and 293K to 575K in order to generate two data sets. The steady state resistance technique uses surface micromachined bridge structures fabricated using the standard SUMMiT fabrication process. Electrical resistance and resistivity data are reported for poly1-poly2 laminate, poly2, poly3, and poly4 polysilicon structural layers in the SUMMiT process from 83K to 575K. Thermal conductivity measurements for these polysilicon layers demonstrate for the first time that the thermal conductivity is a function of the particular SUMMiT layer. Also, the poly2 layer has a different variation in thermal conductivity as the temperature is decreased than the poly1-poly2 laminate, poly3, and poly4 layers. As the temperature increases above room temperature, the difference in thermal conductivity between the layers decreases.

  15. Point defects in silicon carbide as a promising basis for spectroscopy of single defects with controllable quantum states at room temperature

    NASA Astrophysics Data System (ADS)

    Soltamov, V. A.; Tolmachev, D. O.; Il'in, I. V.; Astakhov, G. V.; Dyakonov, V. V.; Soltamova, A. A.; Baranov, P. G.

    2015-05-01

    The spin and optical properties of silicon vacancy defects in silicon carbide of the hexagonal 6 H polytype have been investigated using photoluminescence, electron paramagnetic resonance, and X-band optically detected magnetic resonance. It has been shown that different configurations of these defects can be used to create an optical alignment of their spin sublevels as in the case of low temperatures and at temperatures close to room temperature ( T = 293 K). The main specific feature of silicon vacancy centers in silicon carbide is that the zero-magnetic-field-splitting parameter of some centers remains constant with variations in the temperature, which indicates prospects for the use of these centers for quantum magnetometry. It has also been shown that a number of centers, on the contrary, are characterized by a strong dependence of the zero-magnetic-field-splitting parameter on the temperature, which indicates prospects for the use of these centers as temperature sensors.

  16. Polycrystalline photovoltaic cell

    SciTech Connect

    Jordan, J.F.; Lampkin, C.M.

    1983-10-25

    A photovoltaic cell is disclosed, having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6 /SUB u/ thick) of underlying polycrystalline semiconductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

  17. Polycrystalline thin film photovoltaics

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Ullal, H. S.; Mitchell, R. L.

    Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe2 and CdTe. The history of using CuInSe2 and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe2 and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.

  18. Patterned polycrystalline diamond microtip vacuum diode arrays

    SciTech Connect

    Kang, W.P.; Davidson, J.L.; Kinser, D.L.

    1995-12-31

    Electron field emission from an array of patterned pyramids of polycrystalline diamond for vacuum diode applications has been investigated. High current emission from the patterned diamond microtip arrays are obtained at low electric fields. A current density from the diamond microtips of 14mA/cm{sup 2} was observed for a field of <10 V/{mu}m. Field emission for these diamond microtips exhibits significant enhancement both in total emission current and stability compared to pure silicon emitters. Moreover, field emission from patterned polycrystalline diamond pyramidal tip arrays is unique in that the applied field is found to be lower (2-3 order of magnitude lower) compared to that required for emission from Si, Ge, GaAs, and metal surfaces. The fabrication process utilizing silicon shaping and micromachining techniques for the fabrication of diamond diaphragms with diamond microtip arrays for vacuum microelectronic applications has been developed. The processing techniques are compatible with IC fabrication technology. The effect of temperature annealing on the current emission characteristics were also investigated.

  19. Keeping Promises

    NASA Technical Reports Server (NTRS)

    Howell, Gregory A.

    2005-01-01

    Commitments are between people, not schedules. Project management as practiced today creates a "commitment-free zone," because it assumes that people will commit to centrally managed schedules without providing a mechanism to ensure their work can be done. So they give it their best, but something always seems to come up ..."I tried, but you know how it is." This form of project management does not provide a mechanism to ensure that what should be done, can in fact be done at the required moment. Too often, promises reliable promise. made in coordination meetings are conditional and unreliable. It has been my experience that at times trust can be low and hard to build in this environment. The absence of reliable promises explains why on well-run projects, people are often only completing 30-50 percent of the deliverables they d promised for the week. We all know what a promise is; we have plenty of experience making them and receiving them from others. So what s the problem? The sad fact is that the project environment-like many other work environments- is often so filled with systemic dishonesty, that we don t expect promises that are reliable. Project managers excel when they manage their projects as networks of commitments and help their people learn to elicit and make reliable promises.

  20. Polycrystalline thin-films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.

    1986-02-01

    This annual report summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Major subcontracted work in this area has concentrated on development of CuInSe2 and CdTe technologies. During FY 1985, major progress was achieved by subcontractors in: (1) developing a new, low-cost method of fabricating CuInSe2, and (2) improving the efficiency of CuInSe2 devices by about 10% (relative). The report also lists research planned to meet the Department of Energy's goals in these technologies.

  1. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

    1983-01-01

    A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

  2. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

    1983-04-05

    A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

  3. Phosphorus and boron diffusion paths in polycrystalline silicon gate of a trench-type three-dimensional metal-oxide-semiconductor field effect transistor investigated by atom probe tomography

    SciTech Connect

    Han, Bin Takamizawa, Hisashi Shimizu, Yasuo; Inoue, Koji; Nagai, Yasuyoshi; Yano, Fumiko; Kunimune, Yorinobu; Inoue, Masao; Nishida, Akio

    2015-07-13

    The dopant (P and B) diffusion path in n- and p-types polycrystalline-Si gates of trench-type three-dimensional (3D) metal-oxide-semiconductor field-effect transistors (MOSFETs) were investigated using atom probe tomography, based on the annealing time dependence of the dopant distribution at 900 °C. Remarkable differences were observed between P and B diffusion behavior. In the initial stage of diffusion, P atoms diffuse into deeper regions from the implanted region along grain boundaries in the n-type polycrystalline-Si gate. With longer annealing times, segregation of P on the grain boundaries was observed; however, few P atoms were observed within the large grains or on the gate/gate oxide interface distant from grain boundaries. These results indicate that P atoms diffuse along grain boundaries much faster than through the bulk or along the gate/gate oxide interface. On the other hand, in the p-type polycrystalline-Si gate, segregation of B was observed only at the initial stage of diffusion. After further annealing, the B atoms became uniformly distributed, and no clear segregation of B was observed. Therefore, B atoms diffuse not only along the grain boundary but also through the bulk. Furthermore, B atoms diffused deeper than P atoms along the grain boundaries under the same annealing conditions. This information on the diffusion behavior of P and B is essential for optimizing annealing conditions in order to control the P and B distributions in the polycrystalline-Si gates of trench-type 3D MOSFETs.

  4. Metal induced crystallization of amorphous silicon for photovoltaic solar cells

    NASA Astrophysics Data System (ADS)

    Van Gestel, D.; Gordon, I.; Poortmans, J.

    A silicon thin-film technology could lead to less expensive modules by the use of less silicon material and by the implementation of monolithic module processes. A technology based on polycrystalline-silicon thin-films with a grain size between 1 μm and 1 mm (pc-Si), seems particularly promising since it combines the low-cost potential of a thin-film technology with the high efficiency potential of crystalline silicon. One of the possible approaches to fabricate pc-Si absorber layers is metal induced crystallization (MIC). For solar cell applications mainly aluminium is investigated as metal because 1) it forms a eutectic system with silicon instead of a silicide-metal system like e.g. Ni 2) only shallow level defects are formed in the forbidden bandgap of silicon and 3) a layer exchange process can be obtained in combination with a-Si. Aluminum induced crystallization (AIC) of a-Si on non-silicon substrates can results in grains with a preferential (100) orientation and a maximum grain sizes above 50 micrometer. These layers can act as seed layers for further epitaxial growth. Based on this two-step approach (AIC + epitaxial growth) we made solar cells with an energy conversion efficiency of 8%. Based on TEM, EBIC, SEM, defect etch and EBSD measurements we showed that the efficiency is nowadays mainly limited by the presence of electrical intragrain defects.

  5. Gelcasting Polycrystalline Alumina

    SciTech Connect

    Janney, M.A.; Zuk, K.J.; Wei, G.C.

    2000-01-01

    OSRAM SYLVANIA INC. is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux TM line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency ({approximately}97% total transmittance in the visible), their refractoriness (inner wall temperature can reach l2OOC), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, up to 100 initial lumens per watt. (Compare incandescent lamps 10-20 lumens per watt, fluorescent lamps 25-90 lumens per watt.)

  6. Polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.; Ullal, H.

    1987-02-01

    This annual report for fiscal year 1986 summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Subcontracted work in this area has concentrated on the development of CuInSe2 and CdTe technologies. During FY 1986, major progress was achieved by subcontractors in (1) achieving 10.5% (SERI-verified) efficiency with CdTe, (2) improving the efficiency of selenized CuInSe2 solar cells to nearly 8%, and (3) developing a transparent contact to CdTe cells for potential use in the top cells of tandem structures.

  7. National solar technology roadmap: Film-silicon PV

    SciTech Connect

    Keyes, Brian

    2007-06-01

    Silicon photovoltaic (PV) technologies are addressed in two different technology roadmaps: Film-Silicon PV and Wafer-Silicon PV. This Film-Silicon PV roadmap applies to all silicon-film technologies that rely on a supporting substrate such as glass, polymer, aluminum, stainless steel, or metallurgical-grade silicon. Such devices typically use amorphous, nanocrystalline, fine-grained polycrystalline, or epitaxial silicon layers that are 1–20 μm thick.

  8. Silicon-on ceramic process. Silicon sheet growth and device developmentt for the Large-Area Silicon Sheet Task of the Low-Cost Solar Array Project. Quarterly report No. 13, October 1-December 31, 1979

    SciTech Connect

    Chapman, P W; Zook, J D; Grung, B L; McHenry, K; Schuldt, S B

    1980-02-15

    Research on the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating inexpensive ceramic substrates with a thin layer of polycrystalline silicon is reported. The coating methods to be developed are directed toward a minimum-cost process for producing solar cells with a terrestrial conversion efficiency of 11 percent or greater. By applying a graphite coating to one face of a ceramic substrate, molten silicon can be caused to wet only that graphite-coated face and produce uniform thin layers of large-grain polycrystalline silicon; thus, only a minimal quantity of silicon is consumed. A variety of ceramic materials have been dip coated with silicon. The investigation has shown that mullite substrates containing an excess of SiO/sub 2/ best match the thermal expansion coefficient of silicon and hence produce the best SOC layers. With such substrates, smooth and uniform silicon layers 25 cm/sup 2/ in area have been achieved with single-crystal grains as large as 4 mm in width and several cm in length. Crystal length is limited by the length of the substrate. The thickness of the coating and the size of the crystalline grains are controlled by the temperature of the melt and the rate at which the substrate is withdrawn from the melt. The solar-cell potential of this SOC sheet silicon is promising. To date, solar cells with areas from 1 to 10 cm/sup 2/ have been fabricated from material with an as-grown surface. Conversion efficiencies of about 10 percent with antireflection (AR) coating have been achieved. Such cells typically have open-circuit voltage and short-circuit current densities of 0.55V and 23 mA/cm/sup 2/, respectively.

  9. Computational characterizations on the grain-size-dependent properties of polycrystalline nanomaterials

    NASA Astrophysics Data System (ADS)

    Hyun, Sangil; Park, Youngho; Kim, Hyo-tae

    2015-12-01

    The microstructures of real nanomaterials can be quite complex with variety of grain sizes aligned in different crystal orientations and structural defects possibly created in a fabrication process. Material properties of these polycrystalline materials are generally known strongly dependent on the nanoscale morphology. First principle calculations based on the density functional theory need to be employed in these atomic characterizations; however, it may not be suitable for the polycrystalline nanomaterials for which large number of atoms is required in the simulation model. Instead, a mesoscale computer simulation scheme is employed to investigate these morphology-dependent mechanical properties of polycrystalline materials. We demonstrated the Voronoi construction of various polycrystalline atomic models such as two-dimensional graphene and three-dimensional silicon carbide. General behavior of the mechanical characteristics of the bulk nanostructured silicon carbide (SiC) was addressed, particularly the contribution of grain sizes. From this study, the optimal grain size was determined near 10 nm under tensile and compressive deformations.

  10. Silicon-on-ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project

    NASA Technical Reports Server (NTRS)

    Whitehead, A. B.; Zook, J. D.; Grung, B. L.; Heaps, J. D.; Schmit, F.; Schuldt, S. B.; Chapman, P. W.

    1981-01-01

    The technical feasibility of producing solar cell quality sheet silicon to meet the DOE 1986 cost goal of 70 cents/watt was investigated. The silicon on ceramic approach is to coat a low cost ceramic substrate with large grain polycrystalline silicon by unidirectional solidification of molten silicon. Results and accomplishments are summarized.

  11. Low temperature production of large-grain polycrystalline semiconductors

    DOEpatents

    Naseem, Hameed A.; Albarghouti, Marwan

    2007-04-10

    An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

  12. Silicon-rich SiO{sub 2}/SiO{sub 2} multilayers: A promising material for the third generation of solar cell

    SciTech Connect

    Gourbilleau, F.; Ternon, C.; Dufour, C.

    2009-07-01

    Si-rich-SiO{sub 2}(SRSO)/SiO{sub 2} multilayers (MLs) have been grown by reactive magnetron sputtering. The presence of silicon nanoclusters (Si-ncls) within the SRSO sublayer and annealing temperature influence optical absorption as well as photoluminescence. The optimized annealing temperature has been found to be 1100 deg. C, which allows the recovery of defects and thus enhances photoluminescence. Four MLs with Si-ncl size ranging from 1.5 to 8 nm have been annealed using the optimized conditions and then studied by transmission measurements. Optical absorption has been modeled so that a size effect in the linear absorption coefficient alpha (in cm{sup -1}) has been evidenced and correlated with TEM observations. It is demonstrated that amorphous Si-ncl absorption is fourfold higher than that of crystalline Si-ncls.

  13. Nucleation and growth studies of polycrystalline covalent materials

    NASA Astrophysics Data System (ADS)

    Yun, Jungheum

    The chemical vapor deposition of different covalent polycrystalline materials---including diamond, silicon carbide, and carbon nitride---in stagnation flow reactors was rigorously simulated to determine the nucleation and growth mechanisms of these materials. Kinetic models were used to predict the rates of gas-phase and surface chemistry, the temperature and velocity profiles, potential gaseous film growth precursors, the time evolution of nucleation and intermediate layer formation, and the morphological evolution of continuous polycrystalline films. Numerical studies were also carried out to determine the dependence of the kinetics of nucleation and subsequent polycrystalline film growth on operating conditions. The calculated results for carbon nitride deposition indicate that the experimentally measured bond types in the carbon nitride films must result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once gaseous film growth precursors, including C, CH2 , CH3, C2H2, N, NH, NH2, HCN, and H2CN, are adsorbed. Of these precursors, C and CH 3 dominate the carbon contribution to carbon nitride film growth, and atomic nitrogen is the principal nitrogen bearing species. When the evolution rates of a silicon carbide intermediate layer and diamond clusters are calculated by accounting for gas-phase and surface reactions, surface and bulk diffusion, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics, it is predicted that higher adsorption energies, in the range of 3.7 to 4.5 eV, lead to larger surface adatom densities, lower saturated nucleation densities, and larger silicon carbide intermediate layer thicknesses. The intermediate layer thickness becomes saturated while the growing diamond nuclei still cover a very small fraction of the silicon carbide. Reports of heteroepitaxial diamond nucleation without silicon carbide intermediate layer formation may be readily explained by a

  14. Continuous method of producing silicon carbide fibers

    NASA Technical Reports Server (NTRS)

    Barnard, Thomas Duncan (Inventor); Nguyen, Kimmai Thi (Inventor); Rabe, James Alan (Inventor)

    1999-01-01

    This invention pertains to a method for production of polycrystalline ceramic fibers from silicon oxycarbide (SiCO) ceramic fibers wherein the method comprises heating an amorphous ceramic fiber containing silicon and carbon in an inert environment comprising a boron oxide and carbon monoxide at a temperature sufficient to convert the amorphous ceramic fiber to a polycrystalline ceramic fiber. By having carbon monoxide present during the heating of the ceramic fiber, it is possible to achieve higher production rates on a continuous process.

  15. Gelcasting polycrystalline alumina

    SciTech Connect

    Janney, M.A.

    1997-04-01

    This work is being done as part of a CRADA with Osram-Sylvania, Inc. (OSI) OSI is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux{reg_sign} line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency (95% total transmittance in the visible region), their refractoriness (inner wall temperature can reach 1400{degrees}C), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, on the order of several hundred lumens / watt. (Compare - incandescent lamps -13 lumens/watt fluorescent lamps -30 lumens/watt.) Osram-Sylvania would like to explore using gelcasting to form PCA tubes for Lumalux{reg_sign} lamps, and eventually for metal halide lamps (known as quartz-halogen lamps). Osram-Sylvania, Inc. currently manufactures PCA tubes by isostatic pressing. This process works well for the shapes that they presently use. However, there are several types of tubes that are either difficult or impossible to make by isostatic pressing. It is the desire to make these new shapes and sizes of tubes that has prompted Osram-Sylvania`s interest in gelcasting. The purpose of the CRADA is to determine the feasibility of making PCA items having sufficient optical quality that they are useful in lighting applications using gelcasting.

  16. Process for forming retrograde profiles in silicon

    DOEpatents

    Weiner, Kurt H.; Sigmon, Thomas W.

    1996-01-01

    A process for forming retrograde and oscillatory profiles in crystalline and polycrystalline silicon. The process consisting of introducing an n- or p-type dopant into the silicon, or using prior doped silicon, then exposing the silicon to multiple pulses of a high-intensity laser or other appropriate energy source that melts the silicon for short time duration. Depending on the number of laser pulses directed at the silicon, retrograde profiles with peak/surface dopant concentrations which vary from 1-1e4 are produced. The laser treatment can be performed in air or in vacuum, with the silicon at room temperature or heated to a selected temperature.

  17. Process for forming retrograde profiles in silicon

    DOEpatents

    Weiner, K.H.; Sigmon, T.W.

    1996-10-15

    A process is disclosed for forming retrograde and oscillatory profiles in crystalline and polycrystalline silicon. The process consisting of introducing an n- or p-type dopant into the silicon, or using prior doped silicon, then exposing the silicon to multiple pulses of a high-intensity laser or other appropriate energy source that melts the silicon for short time duration. Depending on the number of laser pulses directed at the silicon, retrograde profiles with peak/surface dopant concentrations which vary are produced. The laser treatment can be performed in air or in vacuum, with the silicon at room temperature or heated to a selected temperature.

  18. Porous silicon gettering

    SciTech Connect

    Tsuo, Y.S.; Menna, P.; Pitts, J.R.

    1996-05-01

    The authors have studied a novel extrinsic gettering method that uses the large surface areas produced by a porous-silicon etch as gettering sites. The annealing step of the gettering used a high-flux solar furnace. They found that a high density of photons during annealing enhanced the impurity diffusion to the gettering sites. The authors used metallurgical-grade Si (MG-Si) prepared by directional solidification casing as the starting material. They propose to use porous-silicon-gettered MG-Si as a low-cost epitaxial substrate for polycrystalline silicon thin-film growth.

  19. Development of Novel Polycrystalline Ceramic Scintillators

    SciTech Connect

    Wisniewska, Monika; Boatner, Lynn A; Neal, John S; Jellison Jr, Gerald Earle; Ramey, Joanne Oxendine; North, Andrea L; Wisniewski, Monica; Payzant, E Andrew; Howe, Jane Y; Lempicki, Aleksander; Brecher, Charlie; Glodo, J.

    2008-01-01

    For several decades most of the efforts to develop new scintillator materials have concentrated on high-light-yield inorganic single-crystals while polycrystalline ceramic scintillators, since their inception in the early 1980 s, have received relatively little attention. Nevertheless, transparent ceramics offer a promising approach to the fabrication of relatively inexpensive scintillators via a simple mechanical compaction and annealing process that eliminates single-crystal growth. Until recently, commonly accepted concepts restricted the polycrystalline ceramic approach to materials exhibiting a cubic crystal structure. Here, we report our results on the development of two novel ceramic scintillators based on the non-cubic crystalline materials: Lu SiO:Ce (LSO:Ce) and LaBr:Ce. While no evidence for texturing has been found in their ceramic microstructures, our LSO:Ce ceramics exhibit a surprisingly high level of transparency/ translucency and very good scintillation characteristics. The LSO:Ce ceramic scintillation reaches a light yield level of about 86% of that of a good LSO:Ce single crystal, and its decay time is even faster than in single crystals. Research on LaBr:Ce shows that translucent ceramics of the high-light-yield rare-earth halides can also be synthesized. Our LaBr:Ce ceramics have light yields above 42 000 photons/MeV (i.e., 70%of the single-crystal light yield).

  20. Smart integration of silicon nanowire arrays in all-silicon thermoelectric micro-nanogenerators

    NASA Astrophysics Data System (ADS)

    Fonseca, Luis; Santos, Jose-Domingo; Roncaglia, Alberto; Narducci, Dario; Calaza, Carlos; Salleras, Marc; Donmez, Inci; Tarancon, Albert; Morata, Alex; Gadea, Gerard; Belsito, Luca; Zulian, Laura

    2016-08-01

    Micro and nanotechnologies are called to play a key role in the fabrication of small and low cost sensors with excellent performance enabling new continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). Harvesting devices providing energy autonomy to those large numbers of microsensors will be essential. In those scenarios where waste heat sources are present, thermoelectricity will be the obvious choice. However, miniaturization of state of the art thermoelectric modules is not easy with the current technologies used for their fabrication. Micro and nanotechnologies offer an interesting alternative considering that silicon in nanowire form is a material with a promising thermoelectric figure of merit. This paper presents two approaches for the integration of large numbers of silicon nanowires in a cost-effective and practical way using only micromachining and thin-film processes compatible with silicon technologies. Both approaches lead to automated physical and electrical integration of medium-high density stacked arrays of crystalline or polycrystalline silicon nanowires with arbitrary length (tens to hundreds microns) and diameters below 100 nm.

  1. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG&E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  2. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  3. Selective and low temperature synthesis of polycrystalline diamond

    NASA Technical Reports Server (NTRS)

    Ramesham, R.; Roppel, T.; Ellis, C.; Baugh, W.; Jaworske, D. A.

    1991-01-01

    Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

  4. Semi-transparent perovskite solar cells for tandems with silicon and CIGS

    SciTech Connect

    Bailie, Colin D.; Christoforo, M. Greyson; Mailoa, Jonathan P.; Bowring, Andrea R.; Unger, Eva L.; Nguyen, William H.; Burschka, Julian; Pellet, Norman; Lee, Jungwoo Z.; Grätzel, Michael; Noufi, Rommel; Buonassisi, Tonio; Salleo, Alberto; McGehee, Michael D.

    2014-12-23

    A promising approach for upgrading the performance of an established low-bandgap solar technology without adding much cost is to deposit a high bandgap polycrystalline semiconductor on top to make a tandem solar cell. We use a transparent silver nanowire electrode on perovskite solar cells to achieve a semi-transparent device. We place the semi-transparent cell in a mechanically-stacked tandem configuration onto copper indium gallium diselenide (CIGS) and low-quality multicrystalline silicon (Si) to achieve solid-state polycrystalline tandem solar cells with a net improvement in efficiency over the bottom cell alone. Furthermore, this work paves the way for integrating perovskites into a low-cost and high-efficiency (>25%) tandem cell.

  5. Semi-transparent perovskite solar cells for tandems with silicon and CIGS

    DOE PAGESBeta

    Bailie, Colin D.; Christoforo, M. Greyson; Mailoa, Jonathan P.; Bowring, Andrea R.; Unger, Eva L.; Nguyen, William H.; Burschka, Julian; Pellet, Norman; Lee, Jungwoo Z.; Grätzel, Michael; et al

    2014-12-23

    A promising approach for upgrading the performance of an established low-bandgap solar technology without adding much cost is to deposit a high bandgap polycrystalline semiconductor on top to make a tandem solar cell. We use a transparent silver nanowire electrode on perovskite solar cells to achieve a semi-transparent device. We place the semi-transparent cell in a mechanically-stacked tandem configuration onto copper indium gallium diselenide (CIGS) and low-quality multicrystalline silicon (Si) to achieve solid-state polycrystalline tandem solar cells with a net improvement in efficiency over the bottom cell alone. Furthermore, this work paves the way for integrating perovskites into a low-costmore » and high-efficiency (>25%) tandem cell.« less

  6. Polycrystalline Diamond Schottky Diodes and Their Applications.

    NASA Astrophysics Data System (ADS)

    Zhao, Ganming

    In this work, four-hot-filament CVD techniques for in situ boron doped diamond synthesis on silicon substrates were extensively studied. A novel tungsten filament shape and arrangement used to obtain large-area, uniform, boron doped polycrystalline diamond thin films. Both the experimental results and radiative heat transfer analysis showed that this technique improved the uniformity of the substrate temperature. XRD, Raman and SEM studies indicate that large area, uniform, high quality polycrystalline diamond films were obtained. Schottky diodes were fabricated by either sputter deposition of silver or thermal evaporation of aluminum or gold, on boron doped diamond thin films. High forward current density and a high forward-to-reverse current ratio were exhibited by silver on diamond Schottky diodes. Schottky barrier heights and the majority carrier concentrations of both aluminum and gold contacted diodes were determined from the C-V measurements. Furthermore, a novel theoretical C-V-f analysis of deep level boron doped diamond Schottky diodes was performed. The analytical results agree well with the experimental results. Compressive stress was found to have a large effect on the forward biased I-V characteristics of the diamond Schottky diodes, whereas the effect on the reverse biased characteristics was relatively small. The stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. This result shows that CVD diamond device has potential for mechanical transducer applications. The quantitative photoresponse characteristics of the diodes were studied in the spectral range of 300 -1050 nm. Semi-transparent gold contacts were used for better photoresponse. Quantum efficiency as high as 50% was obtained at 500 nm, when a reverse bias of over 1 volt was applied. The Schottky barrier heights between either gold or

  7. Research on polycrystalline thin-film materials, cells, and modules

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1990-11-01

    DOE supports research activities in polycrystalline thin films through the Polycrystalline Thin Film Program. This program includes includes R and D in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective is to support R and D of photovoltaic cells and modules that meet the DOE long term goals of high efficiency (15 to 20 percent), low cost ($50/sq cm), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin film CuInSe2 and CdTe solar cells and modules. These have become the leading thin film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe(sub 2) and CdTe modules. The recent progress and future directions are studied of the Polycrystalline Thin Film Program and the status of the subcontracted research on these promising photovoltaic materials.

  8. Research on polycrystalline thin-film materials, cells, and modules

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1990-11-01

    The US Department of Energy (DOE) supports research activities in polycrystalline thin films through the Polycrystalline Thin-Film Program at the Solar Energy Research Institute (SERI). This program includes research and development (R D) in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective of this program is to support R D of photovoltaic cells and modules that meet the DOE long-term goals of high efficiency (15%--20%), low cost ($50/m{sup 2}), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules. These have become the leading thin-film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe{sub 2} and CdTe modules. This paper focuses on the recent progress and future directions of the Polycrystalline Thin-Film Program and the status of the subcontracted research on these promising photovoltaic materials. 26 refs., 12 figs, 1 tab.

  9. Silicon on ceramic process. Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

    NASA Technical Reports Server (NTRS)

    Zook, J. D.; Heaps, J. D.; Maciolek, R. B.; Koepke, B. G.; Butter, C. D.; Schuldt, S. B.

    1977-01-01

    The technical and economic feasibility of producing solar-cell-quality sheet silicon was investigated. The sheets were made by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. Significant progress was made in all areas of the program.

  10. High temperature adsorption of nitrogen on a polycrystalline nickel surface

    NASA Astrophysics Data System (ADS)

    Boughaba, S.; Auvert, G.

    1994-01-01

    Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser-induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/<100> monosilicon substrates. As a heat source, a cw argon-ion laser was used. The laser-induced surface temperature was varied in the range 500-850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. On the basis of these results, the high temperature adsorption of nitrogen on a polycrystalline nickel surface was investigated. A model which accounts for the dependence of the nickel deposition rate and surface coverage with nitrogen adspecies on the N2 partial pressure was elaborated.

  11. Polycrystalline thin-film technology: Recent progress in photovoltaics

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe{sub 2}), cadmium telluride (CdTe), and thin-film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin-film CuInSe{sub 2}, has made some rapid advances in terms of high efficiency and long-term reliability. For CuInSe{sub 2} power modules, a world record has been reported on a 0.4-m{sup 2} module with an aperture-area efficiency of 10.4% and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe{sub 2} modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 cm{sup 2}. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10%; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  12. Polycrystalline thin-film technology: Recent progress in photovoltaics

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe2), cadmium telluride (CdTe), and thin film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin film CuInSe2, has made some rapid advances in terms of high efficiency and long term reliability. For CuInSe2 power modules, a world record has been reported on a 0.4 sq m module with an aperture-area efficiency of 10.4 pct. and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe2 modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 sq cm. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10 pct.; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  13. Transmutation doping of silicon solar cells

    NASA Technical Reports Server (NTRS)

    Wood, R. F.; Westbrook, R. D.; Young, R. T.; Cleland, J. W.

    1977-01-01

    Normal isotopic silicon contains 3.05% of Si-30 which transmutes to P-31 after thermal neutron absorption, with a half-life of 2.6 hours. This reaction is used to introduce extremely uniform concentrations of phosphorus into silicon, thus eliminating the areal and spatial inhomogeneities characteristic of chemical doping. Annealing of the lattice damage in the irradiated silicon does not alter the uniformity of dopant distribution. Transmutation doping also makes it possible to introduce phosphorus into polycrystalline silicon without segregation of the dopant at the grain boundaries. The use of neutron transmutation doped (NTD) silicon in solar cell research and development is discussed.

  14. Special Issue: The Silicon Age

    NASA Astrophysics Data System (ADS)

    Kittler, Martin; Yang, Deren

    2006-03-01

    The present issue of physica status solidi (a) contains a collection of articles about different aspects of current silicon research and applications, ranging from basic investigations of mono- and polycrystalline silicon materials and nanostructures to technologies for device fabrication in silicon photovoltaics, micro- and optoelectronics. Guest Editors are Martin Kittler and Deren Yang, the organizers of a recent Sino-German symposium held in Cottbus, Germany, 19-24 September 2005.The cover picture shows four examples of The Silicon Age: the structure of a thin film solar cell on low-cost SSP (silicon sheet from powder) substrate (upper left image) [1], a high-resolution transmission electron microscopy image and diffraction pattern of a single-crystalline Si nanowire (upper right) [2], a carrier lifetime map from an n-type multicrystalline silicon wafer after gettering by a grain boundary (lower left) [3], and a scanning acoustic microscopy image of a bonded 150 mm diameter wafer pair (upper right) [4].

  15. Polycrystalline diamond based detector for Z-pinch plasma diagnosis

    SciTech Connect

    Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan

    2010-08-15

    A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

  16. Progress and issues in polycrystalline thin-film PV technologies

    SciTech Connect

    Zweibel, K.; Ullal, H.S.; Roedern, B. von

    1996-05-01

    Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies in the past 18 months. However, the transition to first-time manufacturing is still under way, and technical problems continue. This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the U.S. Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

  17. Screen-Cage Ion Plating Of Silver On Polycrystalline Alumina

    NASA Technical Reports Server (NTRS)

    Spalvins, Talivaldis; Sliney, Harold E.; Deadmore, Daniel L.

    1995-01-01

    Screen-cage ion plating (SCIP) cost-effective technique offering high throwing power for deposition of adherent metal films on ceramic substrates. Applies silver films to complexly shaped substrates of polycrystalline alumina. Silver adheres tenaciously and reduces friction. SCIP holds promise for applying lubricating soft metallic films to high-temperature ceramic components of advanced combustion engines. Other potential uses include coating substrates with metal for protection against corrosion, depositing electrical conductors on dielectric substrates, making optically reflective or electrically or thermally conductive surface layers, and applying decorative metal coats to ceramic trophies or sculptures.

  18. Transformational silicon electronics.

    PubMed

    Rojas, Jhonathan Prieto; Torres Sevilla, Galo Andres; Ghoneim, Mohamed Tarek; Inayat, Salman Bin; Ahmed, Sally M; Hussain, Aftab Mustansir; Hussain, Muhammad Mustafa

    2014-02-25

    In today's traditional electronics such as in computers or in mobile phones, billions of high-performance, ultra-low-power devices are neatly integrated in extremely compact areas on rigid and brittle but low-cost bulk monocrystalline silicon (100) wafers. Ninety percent of global electronics are made up of silicon. Therefore, we have developed a generic low-cost regenerative batch fabrication process to transform such wafers full of devices into thin (5 μm), mechanically flexible, optically semitransparent silicon fabric with devices, then recycling the remaining wafer to generate multiple silicon fabric with chips and devices, ensuring low-cost and optimal utilization of the whole substrate. We show monocrystalline, amorphous, and polycrystalline silicon and silicon dioxide fabric, all from low-cost bulk silicon (100) wafers with the semiconductor industry's most advanced high-κ/metal gate stack based high-performance, ultra-low-power capacitors, field effect transistors, energy harvesters, and storage to emphasize the effectiveness and versatility of this process to transform traditional electronics into flexible and semitransparent ones for multipurpose applications. PMID:24476361

  19. Silicon research and technology

    NASA Technical Reports Server (NTRS)

    Meulenberg, A.

    1982-01-01

    The development of solar cells suitable for space applications are discussed, along with the advantages and disadvantages of silicon and gallium arsenide solar cells. The goal of a silicon solar cell with 18% efficiency has not been reached and does not appear promising in the near future.

  20. Morphology of polycrystalline cassiterite films

    NASA Astrophysics Data System (ADS)

    Tomaev, V. V.; Glazov, A. I.

    2014-09-01

    Polycrystalline cassiterite films have been grown by the hydropyrolytic method from a 10(H2O) + 5(SnCl2 · 2H2O) solution (in weight fractions) on corundum substrates. The crystallization regularities are considered and a comparative analysis of the properties of natural and artificial cassiterite crystals is performed. The surface morphology is investigated and the size of crystalline grains is determined by scanning electron microscopy. X-ray microprobe analysis showed that all films contain tin and oxygen atoms in a ratio corresponding (within the experimental error) to the chemical formula of tin dioxide. It is established that the surface morphology of cassiterite films is characterized by both single crystallites and aggregates of two or more crystals typical of twins. It is suggest that doping can efficiently be used to control the concentration of twins and the stability of their formation.

  1. Saturation magnetization of polycrystalline iron

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.; Hegland, D. E.

    1972-01-01

    The magnetic moment per gram, sigma (H sub I, T), where H sub I is the internal field and T is the temperature, was measured for a polycrystalline iron sphere with the vibrating-sample magnetometer. The instrument was calibrated by using a method utilizing the high permeability of an iron sphere. The spontaneous moment, sigma(0, T),was obtained from plots of sigma(H sub I, T) as a function of H sub I for temperatures from 4.2 K to room temperature. The value of the spontaneous moment, sigma(0, T), at 298.9 K was 217.5 + or -0.4 emu/g. The extrapolated moment, sigma(0, 0),at absolute zero from a plot of sigma(0, T) as a function of T to 3/2 power was 221.7 + or - 0.4 emu/g.

  2. Dip coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

    NASA Technical Reports Server (NTRS)

    Heaps, J. D.; Maciolek, R. B.; Zook, J. D.; Harrison, W. B.; Scott, M. W.; Hendrickson, G.; Wolner, H. A.; Nelson, L. D.; Schuller, T. L.; Peterson, A. A.

    1976-01-01

    The technical and economic feasibility of producing solar cell quality sheet silicon by dip-coating one surface of carbonized ceramic substrates with a thin layer of large grain polycrystalline silicon was investigated. The dip-coating methods studied were directed toward a minimum cost process with the ultimate objective of producing solar cells with a conversion efficiency of 10% or greater. The technique shows excellent promise for low cost, labor-saving, scale-up potentialities and would provide an end product of sheet silicon with a rigid and strong supportive backing. An experimental dip-coating facility was designed and constructed, several substrates were successfully dip-coated with areas as large as 25 sq cm and thicknesses of 12 micron to 250 micron. There appears to be no serious limitation on the area of a substrate that could be coated. Of the various substrate materials dip-coated, mullite appears to best satisfy the requirement of the program. An inexpensive process was developed for producing mullite in the desired geometry.

  3. Single molecule source reagents for chemical vapor deposition of b-silicon carbide. Final report, 1 June 1991-30 November 1992

    SciTech Connect

    Brown, D.W.

    1992-12-10

    Phase I conclusively showed the feasibility of rational design of single molecule-source reagents that could lead to improvements in the chemical vapor deposition of stoichiometric Beta silicon carbide. Four single molecule sources were synthesized, their decomposition pathways studied, and their utility in Beta-silicon carbide CVD investigated. Dramatic differences in the CVD process resulted from small changes in the reagent structure. A strained cyclic molecule, 1,3-disilacyclobutane, allowed growth of a Beta-silicon carbide film at a temperature >300 deg C lower than was possible with a similar straight chain reagent. Furthermore, the highest quality film was grown from the analogous chlorinated cyclic source reagent: 1,1,3,3 tetrachloro-1,3-disilacyclobutane. We propose that decomposition of the cyclic precursors directly produces intermediates that can lead to deposition of stoichiometric silicon carbide. The Phase I results clearly showed that Beta-silicon carbide CVD can be improved by molecular engineering of the source reagents. Cyclic precursors are promising for both the deposition of single crystal films at high temperature and for polycrystalline and single crystal films at low temperature. In Phase II we will optimize the precursor for low temperature deposition and the integration of silicon and silicon carbide HBT device structures.

  4. Conductive polycrystalline diamond probes for local anodic oxidation lithography

    NASA Astrophysics Data System (ADS)

    Ulrich, A. J.; Radadia, A. D.

    2015-11-01

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k Avg). The metal-coated and the DC tips with comparable k Avg showed comparable threshold voltages, whereas the MD tips with similar k Avg showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed (v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k Avg. This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography.

  5. Conductive polycrystalline diamond probes for local anodic oxidation lithography.

    PubMed

    Ulrich, A J; Radadia, A D

    2015-11-20

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k(Avg)). The metal-coated and the DC tips with comparable k(Avg) showed comparable threshold voltages, whereas the MD tips with similar k(Avg) showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed(v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k(Avg). This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography. PMID:26501841

  6. Theoretical study of the photovoltaic properties of polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Joshi, D. P.; Srivastava, R. S.

    1986-04-01

    By considering the variation of grain-boundary space-charge potential barrier height with grain size and doping level, the dependence of polysilicon solar cell parameters on the grain size (d) and substrate resistivity have been theoretically investigated. A new relation is presented for the effective diffusion length of minority carriers in polysilicon which predicts that the effective diffusion length is approximately proportional to d exp r, where r varies from 0 to 1. Computations show that as base resistivity decreases, the effect of the grain-boundary recombination process increases, and consequently the polysilicon cell parameters do not vary with resistivity in the same manner as has been observed for a single-crystal cell. The proposed theory also predicts the dominance of shunting effects of grain boundary at small grain sizes or low base resistivities. The available experimental data are found to be in good agreement with the predictions of the theory.

  7. Time-resolved photoluminescence of polycrystalline CdTe grown by close-spaced sublimation

    SciTech Connect

    Keyes, B.; Dhere, R.; Ramanathan, K. )

    1994-06-30

    Polycrystalline CdTe has shown great promise as a low-cost material for thin-film, terrestrial photovoltaic applications, with efficiencies approaching 16% achieved with close-spaced sublimation (CSS)-grown CdTe. Due to the inherent complexities of polycrystalline material, much of the progress in this area has occurred through a slow trial-and-error process. This report uses time-resolved photoluminescence (TRPL) to characterize the CdTe material quality as a function of one basic growth parameter---substrate temperature. This characterization is done for two different glass substrate materials, soda-lime silicate and borosilicate.

  8. Ceramic for Silicon-Shaping Dies

    NASA Technical Reports Server (NTRS)

    Sekercioglu, I.; Wills, R. R.

    1982-01-01

    Silicon beryllium oxynitride (SiBON) is a promising candidate material for manufacture of shaping dies used in fabricating ribbons or sheets of silicon. It is extremely stable, resists thermal shock, and has excellent resistance to molten silicon. SiBON is a solid solution of beryllium silicate in beta-silicon nitride.

  9. Electron microscopy of gallium nitride growth on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Cherns, D.; Kuball, M.; Jiang, Q.; Allsopp, D.

    2015-11-01

    Transmission and scanning electron microscopy were used to examine the growth of gallium nitride (GaN) on polycrystalline diamond substrates grown by metalorganic vapour phase epitaxy with a low-temperature aluminium nitride (AlN) nucleation layer. Growth on unmasked substrates was in the (0001) orientation with threading dislocation densities ≈7 × 109 cm-2. An epitaxial layer overgrowth technique was used to reduce the dislocation densities further, by depositing silicon nitride stripes on the surface and etching the unmasked regions down to the diamond substrate. A re-growth was then performed on the exposed side walls of the original GaN growth, reducing the threading dislocation density in the overgrown regions by two orders of magnitude. The resulting microstructures and the mechanisms of dislocation reduction are discussed.

  10. A New Polycrystalline Co-Ni Superalloy

    NASA Astrophysics Data System (ADS)

    Knop, M.; Mulvey, P.; Ismail, F.; Radecka, A.; Rahman, K. M.; Lindley, T. C.; Shollock, B. A.; Hardy, M. C.; Moody, M. P.; Martin, T. L.; Bagot, P. A. J.; Dye, D.

    2014-12-01

    In 2006, a new-ordered L12 phase, Co3(Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ/ γ' superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ' fraction of ~56% and a secondary γ' size of 88 nm were obtained, with a grain size of 2.5 μm. The solvus temperature was 1000°C. The density was found to be 8.52 g cm-3, which is similar to existing Ni alloys with this level of γ'. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ/ γ' Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm-2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.

  11. A reusable mold in directional solidification for silicon solar cells

    NASA Astrophysics Data System (ADS)

    Saito, T.; Shimura, A.; Ichikawa, S.

    1983-12-01

    Directional solidification of silicon was achieved by using a SiC coated carbon mold together with Si3N4 powder mold releasing agent. Crack-free polycrystalline silicon ingots were able to be extracted easily out of the mold. The mold was easily able to withstand more than 12 utilizations. Silicon ingot impurity contents were less than 3 ppm and the average polycrystalline grain diameter was 0.8 mm. Solar cells made of this material gave an AM1 maximum conversion of 10.8 deg.

  12. Composite polycrystalline semiconductor neutron detectors

    NASA Astrophysics Data System (ADS)

    Schieber, M.; Zuck, A.; Marom, G.; Khakhan, O.; Roth, M.; Alfassi, Z. B.

    2007-08-01

    Composite polycrystalline semiconductor detectors bound with different binders, both inorganic molten glasses, such as B 2O 3, PbO/B 2O 3, Bi 2O 3/PbO, and organic polymeric binders, such as isotactic polypropylene (iPP), polystyrene or nylon-6, and coated with different metal electrodes were tested at room temperature for α-particles and very weak thermal neutron sources. The detector materials tested were natural occurring hexagonal BN and cubic LiF, where both are not containing enriched isotopes of 10B or 6Li. The radiation sources were 5.5 MeV α's from 241Am, 5.3 MeV from 210Po and also 4.8 MeV from 226Ra. Some of these detectors were also tested with thermal neutrons from very weak 227Ac 9Be, 241Am- 10Be sources and also from a weak 238Pu+ 9Be and somewhat stronger 252Cf sources. The neutrons were thermalized with paraffin. Despite very low signal to noise ratio of only ˜2, the neutrons could be counted by subtracting the noise from the signal.

  13. High purity silane and silicon production

    NASA Technical Reports Server (NTRS)

    Breneman, William C. (Inventor)

    1987-01-01

    Silicon tetrachloride, hydrogen and metallurgical silicon are reacted at about 400.degree.-600.degree. C. and at pressures in excess of 100 psi, and specifically from about 300 up to about 600 psi to form di- and trichlorosilane that is subjected to disproportionation in the presence of an anion exchange resin to form high purity silane. By-product and unreacted materials are recycled, with metallurgical silicon and hydrogen being essentially the only consumed feed materials. The silane product may be further purified, as by means of activated carbon or cryogenic distillation, and decomposed in a fluid bed or free space reactor to form high purity polycrystalline silicon and by-product hydrogen which can be recycled for further use. The process results in simplified waste disposal operations and enhances the overall conversion of metallurgical grade silicon to silane and high purity silicon for solar cell and semiconductor silicon applications.

  14. Disposal of metal fragments released during polycrystalline slicing by multi-wire saw

    NASA Astrophysics Data System (ADS)

    Boutouchent-Guerfi, N.; Drouiche, N.; Medjahed, S.; Ould-Hamou, M.; Sahraoui, F.

    2016-08-01

    The environmental and economic impacts linked with solar systems are largely based on discharges of slurry generated during the various stages of sawing and cutting ingots. These discharges into the environment are subject to the general regulations on hazardous and special industrial waste disposal. Therefore, they should not be abandoned or burned in open air. The cutting of Silicon ingots leads to the production of Silicon wafers additional costs, losing more than 30% of Silicon material. Abrasive grains (Silicon Carbide) trapped between the wire and the block of Silicon need to be removed by various mechanisms to be later evacuated by slurry fragments. In the interest of decreasing operational costs during polycrystalline ingot slicing at Semiconductors Research Center, and, avoid environmental problems; it is necessary to recover the solar grade Silicon from the Silicon sawing waste. For this reason, the removal of metal fragments has become a preliminary requirement to regenerate the slurry; in addition, the solid phase needs to be separated from the liquid phase after the dissolution PEG with the solvent. In the present study, magnetic separation and centrifugation methods were adopted for metals removal, followed by the analysis of some operating parameters such as: washing time, pH, and initial concentration of Silicon. Finally, analytical, morphological and basic methods were performed in order to evaluate the efficiency of the process undertaken.

  15. Developing Mathematically Promising Students.

    ERIC Educational Resources Information Center

    Sheffield, Linda Jensen, Ed.

    This book, written on the recommendation of the Task Force on Mathematically Promising Students, investigates issues involving the development of promising mathematics students. Recommendations are made concerning topics such as the definition of promising students; the identification of such students; appropriate curriculum, instruction, and…

  16. Silicon Solar Cell Fabrication Technology

    NASA Technical Reports Server (NTRS)

    Stafsudd, O. M.

    1980-01-01

    Device fabrication and photoconductive lifetime decay measurements were used to characterize single and polycrystalline silicon substracts. The device characterization of the processed materials was done by spectral response measurements and absolute quantum efficiency at a single wavelength. The results were then reduced to yield the diffusion length of the various samples. The photoconductive lifetime decay method was implemented in order to determine the minority carrier lifetime in unprocessed wafers.

  17. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, K.H.

    1998-06-30

    A method is disclosed for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates. 1 fig.

  18. Method for producing silicon thin-film transistors with enhanced forward current drive

    DOEpatents

    Weiner, Kurt H.

    1998-01-01

    A method for fabricating amorphous silicon thin film transistors (TFTs) with a polycrystalline silicon surface channel region for enhanced forward current drive. The method is particularly adapted for producing top-gate silicon TFTs which have the advantages of both amorphous and polycrystalline silicon TFTs, but without problem of leakage current of polycrystalline silicon TFTs. This is accomplished by selectively crystallizing a selected region of the amorphous silicon, using a pulsed excimer laser, to create a thin polycrystalline silicon layer at the silicon/gate-insulator surface. The thus created polysilicon layer has an increased mobility compared to the amorphous silicon during forward device operation so that increased drive currents are achieved. In reverse operation the polysilicon layer is relatively thin compared to the amorphous silicon, so that the transistor exhibits the low leakage currents inherent to amorphous silicon. A device made by this method can be used, for example, as a pixel switch in an active-matrix liquid crystal display to improve display refresh rates.

  19. Aluminum additions in polycrystalline iron-gallium (Galfenol) alloys

    NASA Astrophysics Data System (ADS)

    Brooks, M. D.; Summers, E.; Meloy, R.; Mosley, J.

    2008-03-01

    Galfenol alloys show promise as a new magnetically activated smart material based on their unique combination of relatively high magnetostrictive performance and good mechanical robustness. Investigations of aluminum additions to single crystal iron-gallium alloys have been done previously, and the magnetostrictive response seems to follow the rule of mixtures with decreasing saturation magnetostriction with increasing aluminum content. Aluminum is assumed to substitute for Ga directly in the alloy. Directionally solidified polycrystalline Galfenol alloys with aluminum additions were produced to determine the effects on the magnetic properties. Iron-gallium-aluminum alloys were investigated for two primary reasons: (1) Fe-Al alloys are well established and are typically manufactured using conventional thermo-mechanical processing techniques such as rolling; it is anticipated that aluminum additions will aid in the development of Galfenol alloy rolled sheets (2) Gallium prices continue to rise and a cost effective alternative needs to be investigated. Several Fe-Ga-Al alloy compositions were prepared using the Free Stand Zone Melting (FSZM) directional solidification technique. Alloy composition ranges investigated include: Fe 80.5Ga xAl 19.5-x (4.9<=x<=13), Fe 81.6Ga yAl 18.4-y (4.6<=y<=13.8), and Fe 85Ga zAl 15-z (3.75<=z<=11.25). Alloys were studied using EDS (chemistry verification), EBSD (crystallite orientation), and magnetic characterization techniques to determine the effect of aluminum addition on the polycrystalline binary Fe-Ga system. Magnetic properties such as saturation magnetostriction (λ sat), piezomagnetic constant (d 33), and relative magnetic permeability (μ r) of directionally solidified Fe-Ga-Al polycrystalline alloys will be compared to binary Fe-Ga alloys including investigations into the crystal orientation effects on these properties. Results suggest that up to 50% aluminum can be substituted in the alloy while maintaining considerable

  20. Silicon heterojunction solar cell and crystallization of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Lu, Meijun

    they use less materials resulting in lower cost. Polycrystalline silicon (poly-Si) is one promising thin-film material. It has the potential advantages to not only retain the performance and stability of c-Si, but also use the well established manufacturing techniques on thin-film. One of the main difficulties of poly-Si thin-film solar cells is growing large-grained poly-Si films (grain sizes comparable to the film thickness of micrometers) onto foreign substrates. Aluminum-induced crystallization (AIC) is one technique that has been developed to transform the amorphous Si to large-grain poly-Si. In this dissertation, our systematic studies of AIC samples with different stack structures, with and without interface oxide layer, annealed both below and above eutectic temperature will be introduced, and a phenomenological model will be proposed to explain the experimental results.

  1. Making silicon stronger.

    SciTech Connect

    Boyce, Brad Lee

    2010-11-01

    Silicon microfabrication has seen many decades of development, yet the structural reliability of microelectromechanical systems (MEMS) is far from optimized. The fracture strength of Si MEMS is limited by a combination of poor toughness and nanoscale etch-induced defects. A MEMS-based microtensile technique has been used to characterize the fracture strength distributions of both standard and custom microfabrication processes. Recent improvements permit 1000's of test replicates, revealing subtle but important deviations from the commonly assumed 2-parameter Weibull statistical model. Subsequent failure analysis through a combination of microscopy and numerical simulation reveals salient aspects of nanoscale flaw control. Grain boundaries, for example, suffer from preferential attack during etch-release thereby forming failure-critical grain-boundary grooves. We will discuss ongoing efforts to quantify the various factors that affect the strength of polycrystalline silicon, and how weakest-link theory can be used to make worst-case estimates for design.

  2. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    NASA Astrophysics Data System (ADS)

    Abrams, K. J.; Hinks, J. A.; Pawley, C. J.; Greaves, G.; van den Berg, J. A.; Eyidi, D.; Ward, M. B.; Donnelly, S. E.

    2012-04-01

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  3. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  4. Orientation imaging microscopy of polycrystalline sodium chloride

    SciTech Connect

    Staiger, M.P.; Kolbeinsson, I.; Newman, J.; Woodfield, T.; Sato, T.

    2010-04-15

    A novel preparation technique is described that makes possible grain size analysis of polycrystalline NaCl using orientation imaging microscopy via electron backscatter diffraction (EBSD). The preparation methodology is specifically developed to overcome difficulties in preparing microporous NaCl for microscopy. The grain size and crystallographic texture of polycrystalline NaCl samples, prepared via solution pressure and sintered in the range of 650-780 deg. C, were able to be measured successfully with EBSD. The limitations of the preparation technique for EBSD analysis of NaCl are also discussed.

  5. The Kalamazoo Promise Scholarship

    ERIC Educational Resources Information Center

    Bartik, Timothy J.; Lachowska, Marta

    2014-01-01

    This study takes advantage of the unexpected announcement of the Kalamazoo Promise to study its effects on student achievement and behavior in high school. The Kalamazoo Promise provides college scholarships to graduates of Kalamazoo Public Schools (KPS), a midsized urban school district in Michigan that is racially and economically diverse.…

  6. Radiation hardness of three-dimensional polycrystalline diamond detectors

    SciTech Connect

    Lagomarsino, Stefano Sciortino, Silvio; Bellini, Marco; Corsi, Chiara; Cindro, Vladimir; Kanxheri, Keida; Servoli, Leonello; Morozzi, Arianna; Passeri, Daniele; Schmidt, Christian J.

    2015-05-11

    The three-dimensional concept in particle detection is based on the fabrication of columnar electrodes perpendicular to the surface of a solid state radiation sensor. It permits to improve the radiation resistance characteristics of a material by lowering the necessary bias voltage and shortening the charge carrier path inside the material. If applied to a long-recognized exceptionally radiation-hard material like diamond, this concept promises to pave the way to the realization of detectors of unprecedented performances. We fabricated conventional and three-dimensional polycrystalline diamond detectors, and tested them before and after neutron damage up to 1.2 ×10{sup 16 }cm{sup −2}, 1 MeV-equivalent neutron fluence. We found that the signal collected by the three-dimensional detectors is up to three times higher than that of the conventional planar ones, at the highest neutron damage ever experimented.

  7. Resistive switching in polycrystalline YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bogusz, A.; Müller, A. D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

    2014-10-01

    We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

  8. Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

    NASA Astrophysics Data System (ADS)

    Liang, Wei-Zheng; Ji, Yan-Da; Nan, Tian-Xiang; Huang, Jiang; Zeng, Hui-Zhong; Du, Hui; Chen, Chong-Lin; Lin, Yuan

    2012-06-01

    Barium titanate (BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition (PAD) technique. The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion. Crystal structures, surface morphologies, and dielectric performance were examined and compared for BTO thin films annealed under different temperatures. Correlations between the fabrication conditions, microstructures, and dielectric properties were discussed. BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with inr ~ 400 and tan δ < 0.025 at 100 kHz. The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

  9. Removing Undesired Fine Powder From Silicon Reactor

    NASA Technical Reports Server (NTRS)

    Flagella, Robert N.

    1992-01-01

    Fluidized-bed reactor produces highly pure polycrystalline silicon particles with diameters approximately greater than 400 micrometers. Operates by pyrolysis of silane in reaction zone, which is bed of silicon seed particles fluidized by flow of silane and carrier gas. Above reaction zone, gas mixture flows rapidly enough to entrain silicon powders, but not larger seed and product particles. Entrained particles swept out of reactor. Applicable to other processes such as production of fine metal and ceramic powders where control of sizes of product needed.

  10. The feasibility of silicon on garnet technology

    NASA Technical Reports Server (NTRS)

    Rasky, P. H. L.; Greve, D. W.; Kryder, M. H.; Dutta, S.

    1985-01-01

    The feasibility of combining silicon and magnetic bubble technologies is demonstrated. Functional MOSFETs have been fabricated on top of bubble films coated with 1-micron thick SiO2 layers. The large grain silicon necessary for these devices is obtained by laser recrystallization of polycrystalline silicon (polysilicon). The laser-recrystallization process causes changes in the magnetic properties of the bubble film; however, these changes can be reversed by subsequent thermal anneals. The required temperature treatments after laser annealing are compatible with the MOSFET fabrication process.

  11. High hole mobility tin-doped polycrystalline germanium layers formed on insulating substrates by low-temperature solid-phase crystallization

    NASA Astrophysics Data System (ADS)

    Takeuchi, Wakana; Taoka, Noriyuki; Kurosawa, Masashi; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2015-07-01

    We investigated the effects of incorporation of 0%-2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1-xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1-xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20-30 nm. The Hall hole mobility of a poly-Ge1-xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

  12. High-pressure deformation and failure of polycrystalline ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Dongmei

    2005-11-01

    High-strength polycrystalline ceramics are increasingly being used for armor applications because of their light weight and superior ballistic performance over conventional armor steels. However, accurate material modeling needed in ceramic armor design remains a challenge because of their complex behavior under impact loading. A ceramic may display extremely high strength during rapid compression but lose tensile strength when the load reverses from compression to tension. A good understanding of the mechanisms governing the deformation and failure of ceramics under high-stress impact and a capability to accurately predict the resulting effective strengths of both intact and damaged ceramics are critically needed. To this end, a computational methodology for micromechanical analysis of polycrystalline materials has been developed. It combines finite element analysis with microstructural modeling based on the Voronoi polycrystals, and material modeling that considers nonlinear elasticity, crystal plasticity, intergranular shear damage during compression and intergranular Mode-I cracking during tension. Using this method, simulations have been carried out on polycrystalline alpha-6H silicon carbide and alpha-phase aluminum oxide to determine if microplasticity is a viable mechanism of inelastic deformation in ceramics undergoing high-pressure uniaxial-strain compression. Further, the competing roles of in-grain microplasticity and intergranular microdamage during a sequence of dynamic compression and tension have been studied. The results show that microplasticity is a more plausible mechanism than microcracking under uniaxial-strain compression. The deformation by limited slip systems can be highly heterogeneous so that a significant amount of grains may remain elastic and thus result in high macroscopic compressive strength. On the other hand, the failure evolution during dynamic load reversal from compression to tension can be well predicted by intergranular Mode

  13. Progress and promise.

    PubMed

    Kamphaus, Randy W

    2012-12-01

    This editorial introduces the current issue of the journal School Psychology Quarterly (SPQ).There has been an impressive and promising progress of school psychology science has been reflected in every issue of SPQ, including the current one. PMID:23294232

  14. Stochastic multiscale modeling of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Wen, Bin

    Mechanical properties of engineering materials are sensitive to the underlying random microstructure. Quantification of mechanical property variability induced by microstructure variation is essential for the prediction of extreme properties and microstructure-sensitive design of materials. Recent advances in high throughput characterization of polycrystalline microstructures have resulted in huge data sets of microstructural descriptors and image snapshots. To utilize these large scale experimental data for computing the resulting variability of macroscopic properties, appropriate mathematical representation of microstructures is needed. By exploring the space containing all admissible microstructures that are statistically similar to the available data, one can estimate the distribution/envelope of possible properties by employing efficient stochastic simulation methodologies along with robust physics-based deterministic simulators. The focus of this thesis is on the construction of low-dimensional representations of random microstructures and the development of efficient physics-based simulators for polycrystalline materials. By adopting appropriate stochastic methods, such as Monte Carlo and Adaptive Sparse Grid Collocation methods, the variability of microstructure-sensitive properties of polycrystalline materials is investigated. The primary outcomes of this thesis include: (1) Development of data-driven reduced-order representations of microstructure variations to construct the admissible space of random polycrystalline microstructures. (2) Development of accurate and efficient physics-based simulators for the estimation of material properties based on mesoscale microstructures. (3) Investigating property variability of polycrystalline materials using efficient stochastic simulation methods in combination with the above two developments. The uncertainty quantification framework developed in this work integrates information science and materials science, and

  15. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2006-12-05

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  16. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2008-12-09

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  17. Improved toughness of silicon carbide

    NASA Technical Reports Server (NTRS)

    Palm, J. A.

    1975-01-01

    Several techniques were employed to apply or otherwise form porous layers of various materials on the surface of hot-pressed silicon carbide ceramic. From mechanical properties measurements and studies, it was concluded that although porous layers could be applied to the silicon carbide ceramic, sufficient damage was done to the silicon carbide surface by the processing required so as to drastically reduce its mechanical strength. It was further concluded that there was little promise of success in forming an effective energy absorbing layer on the surface of already densified silicon carbide ceramic that would have the mechanical strength of the untreated or unsurfaced material. Using a process for the pressureless sintering of silicon carbide powders it was discovered that porous layers of silicon carbide could be formed on a dense, strong silicon carbide substrate in a single consolidation process.

  18. Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films

    NASA Astrophysics Data System (ADS)

    Lin, Yuan-Hua; Ying, Minghao; Li, Ming; Wang, Xiaohui; Nan, Ce-Wen

    2007-05-01

    Polycrystalline ZnO-based thin films with Li and/or Co doping have been prepared by a sol-gel spin-coating method on silicon substrates. Magnetization measurements reveal that Li-doped ZnO film shows paramagnetic behavior. However, the Co-doped ZnO thin films show obvious room-temperature ferromagnetic properties, and ferromagnetic properties can be enhanced by the Li codoping, which may be ascribed to indirect exchange via Li-related defects. All ZnO-based films exhibit ferroelectric behavior, and ferroelectric properties can be tuned by the dopants.

  19. Promising More Information

    NASA Technical Reports Server (NTRS)

    2003-01-01

    When NASA needed a real-time, online database system capable of tracking documentation changes in its propulsion test facilities, engineers at Stennis Space Center joined with ECT International, of Brookfield, Wisconsin, to create a solution. Through NASA's Dual-Use Program, ECT developed Exdata, a software program that works within the company's existing Promise software. Exdata not only satisfied NASA s requirements, but also expanded ECT s commercial product line. Promise, ECT s primary product, is an intelligent software program with specialized functions for designing and documenting electrical control systems. An addon to AutoCAD software, Promis e generates control system schematics, panel layouts, bills of material, wire lists, and terminal plans. The drawing functions include symbol libraries, macros, and automatic line breaking. Primary Promise customers include manufacturing companies, utilities, and other organizations with complex processes to control.

  20. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting next-generation'' options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called government/industry partnerships'') that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  1. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting ``next-generation`` options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called ``government/industry partnerships``) that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  2. Low-cost-silicon-process development. Phase IV: process improvement. Second quarterly technical progress report

    SciTech Connect

    Giraudi, R. V.; Newman, C. G.

    1981-04-01

    A number of promising techniques for improving the overall yield and economics of the tribromosilane based process to produce solar cell grade silicon is investigated. The current work is aimed at the identification of an optimum process and the characterization of that process through mini-plant operation and analysis. The three project tasks include process improvement studies, kinetic studies, and process economic studies. During this second quarter reporting period process improvement studies continued in the mini-plant, focusing on the correlation of current mini-plant yield results with prior laboratory scale work. Silicon bromination in the synthesis unit and tribromosilane purification in the distillation unit proceeded efficiently and without complication during this reporting period. Tribromosilane yields in the synthesis unit were low due to unobtainable higher reaction temperatures. Initial polycrystalline silicon production studies have indicated consistent yields of 85%. The laboratory scale static bulb reactor system was calibrated by observing the decomposition of t-butyl chloride. These results compared very well to results obtained by previous investigators for the same decomposition. Upon the conclusion of the calibration tests, the tribromosilane decomposition rate study was initiated. Two decompositions were completed and it was concluded that the reaction order can not be determined at this time. A free space reactor apparatus was assembled and tribromosilane decompositions, as a function of dilution in argon, was studied.

  3. Grain-boundary resistance in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Reiss, G.; Vancea, J.; Hoffmann, H.

    1986-05-01

    Grain boundaries are known to reduce significantly the electrical dc conductivity of polycrystalline metallic materials. In this paper, we give a quantum mechanical calculation of the grain-boundary resistance based on the transfer matrix approach. The results show an exponential decrease of the conductivity with respect to the number of grain boundaries per mean free path in accord with an empirical model proposed recently.

  4. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  5. Application of neutron holography to polycrystalline samples

    NASA Astrophysics Data System (ADS)

    Szakál, A.; Markó, M.; Krexner, G.; Cser, L.

    2015-07-01

    Neutron holography can be an efficient tool to investigate the local real-space structure of crystalline materials around specific probe nuclei serving as radiation source or detector. The positions of atoms in the neighborhood of such nuclei are observable with high (picometry) accuracy. Measurements of this type require orientational order and, therefore, restrict the range of study essentially to single crystals. However, if the information searched for is limited to the distances between the probe and the surrounding nuclei instead of their positions, holographic techniques can be applied to polycrystalline samples as well. In order to prove this statement, the expected multi-wavelength holographic signal of a polycrystalline sample was calculated. The holographic signal can be obtained by applying time-of-flight techniques, and by using a proper mathematical procedure, the distances between the probe nucleus and the surrounding nuclei can be reconstructed. A model calculation taking into account real instrument parameters confirms this expectation. The experimental verification of the predictions can be undertaken at existing pulsed neutron sources being able to provide the required experimental conditions. This new method opens the way to expand the field of investigation towards gaining information about the local atomic structure of polycrystalline materials which are of importance also in various applications.

  6. Effective structural properties in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Hossain, Zubaer

    This talk will discuss effective structural properties in polycrystalline graphene under the presence of atomic scale heterogeneity. Polycrystallinity is ubiquitous in solids, but theories describing their effective behavior remain limited, particularly when heterogeneity is present in the form of nonuniform deformation or composition. Over the decades, exploration of the effective transport and strength properties of heterogeneous systems has been carried out mostly with random distribution of grains or regular periodic structures under various approximations, in translating the underlying physics into a single representative volume element. Although heterogeneity can play a critical role in modulating the basic behavior of low-dimensional materials, it is difficult to capture the local characteristics accurately by these approximations. Taking polycrystalline graphene as an example material, we study the effective structural properties (such as Young's Modulus, Poisson's ratio and Toughness) by using a combination of density functional theory and molecular dynamic simulations. We identify the key mechanisms that govern their effective behavior and exploit the understanding to engineer the behavior by doping with a carefully selected choice of chemical elements.

  7. Characterization of electrochemically modified polycrystalline platinum surfaces

    SciTech Connect

    Krebs, L.C.; Ishida, Takanobu.

    1991-12-01

    The characterization of electrochemically modified polycrystalline platinum surfaces has been accomplished through the use of four major electrochemical techniques. These were chronoamperometry, chronopotentiommetry, cyclic voltammetry, and linear sweep voltammetry. A systematic study on the under-potential deposition of several transition metals has been performed. The most interesting of these were: Ag, Cu, Cd, and Pb. It was determined, by subjecting the platinum electrode surface to a single potential scan between {minus}0.24 and +1.25 V{sub SCE} while stirring the solution, that the electrocatalytic activity would be regenerated. As a consequence of this study, a much simpler method for producing ultra high purity water from acidic permanganate has been developed. This method results in water that surpasses the water produced by pyrocatalytic distillation. It has also been seen that the wettability of polycrystalline platinum surfaces is greatly dependent on the quantity of oxide present. Oxide-free platinum is hydrophobic and gives a contact angle in the range of 55 to 62 degrees. We have also modified polycrystalline platinum surface with the electrically conducting polymer poly-{rho}-phenylene. This polymer is very stable in dilute sulfuric acid solutions, even under applied oxidative potentials. It is also highly resistant to electrochemical hydrogenation. The wettability of the polymer modified platinum surface is severely dependent on the choice of supporting electrolyte chosen for the electrochemical polymerization. Tetraethylammonium tetrafluoroborate produces a film that is as hydrophobic as Teflon, whereas tetraethylammonium perchlorate produces a film that is more hydrophilic than oxide-free platinum.

  8. Rapid epitaxy-free graphene synthesis on silicidated polycrystalline platinum

    PubMed Central

    Babenko, Vitaliy; Murdock, Adrian T.; Koós, Antal A.; Britton, Jude; Crossley, Alison; Holdway, Philip; Moffat, Jonathan; Huang, Jian; Alexander-Webber, Jack A.; Nicholas, Robin J.; Grobert, Nicole

    2015-01-01

    Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials. PMID:26175062

  9. Governing parameter for electromigration damage in the polycrystalline line covered with a passivation layer

    NASA Astrophysics Data System (ADS)

    Sasagawa, Kazuhiko; Hasegawa, Masataka; Saka, Masumi; Abé, Hiroyuki

    2002-02-01

    A governing parameter, called AFDgen*, which reflects electromigration damage in a polycrystalline line covered with a passivation layer is proposed. The formulation is based on the parameter AFDgen previously introduced in our studies. With the help of AFDgen we can calculate the atomic flux divergence due to electromigration by considering two-dimensional distributions of current density and temperature and also by simply considering the microstructure of polycrystalline lines and bamboo lines. AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline lines and bamboo lines through experimental verification. As the first step in the development of a practical and universal prediction method for electromigration damage, we treated metal lines not covered with a passivation layer. On the other hand, metal lines used in packaged silicon integrated circuits are covered with passivation. Electromigration induces a mechanical stress (atomic density) gradient in such lines. This gradient plays an important role in the mechanism of electromigration damage. The new parameter proposed here, AFDgen*, includes the effect of the atomic density gradient. We develop also an AFDgen*-based method for determination of film characteristics. This method is applied to both covered and uncovered metal lines made of the same Al film. The film characteristics of both line types are obtained experimentally. Based on a discussion about the validity of the obtained characteristic constants, we were finally able to conclude that the AFDgen* parameter and the proposed method for deriving film characteristics are useful.

  10. Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

    SciTech Connect

    Zhao, G.; Charlson, E.M.; Charlson, E.J.; Stacy, T.; Meese, J.M. ); Popovici, G.; Prelas, M. )

    1993-02-15

    Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

  11. Effect of top electrodes on photovoltaic properties of polycrystalline BiFeO3 based thin film capacitors

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Li, Mi; Liu, Yiwei; Zuo, Zhenghu; Zhuge, Fei; Zhan, Qing-Feng; Li, Run-Wei

    2011-05-01

    We investigated capacitors based on polycrystalline narrow-band-gap BiFeO3 (BFO) thin films with different top electrodes. The photovoltaic response for the capacitor with a Sn-doped In2O3 (ITO) top electrode is about 25 times higher than that with a Au top electrode, which indicates that the electrode plays a key role in determining the photovoltaic response of ferroelectric thin film capacitors, as simulated by Qin et al (2009 Appl. Phys. Lett. 95 22912). The light-to-electricity photovoltaic efficiency for the ITO/polycrystalline BFO/Pt capacitor can reach 0.125%. Furthermore, under incident light of 450 µW cm - 2 and zero bias, the corresponding photocurrent varies from 0.2 to 200 pA, that is, almost a 1000-fold photoconductivity enhancement. Our experiments suggest that polycrystalline BFO films are promising materials for application in photo-sensitive and energy-related devices.

  12. Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area sheet task of the low-cost solar array project

    NASA Technical Reports Server (NTRS)

    Baghdadi, A.; Gurtler, R. W.; Legge, R.; Sopori, B.; Ellis, R. J.

    1978-01-01

    A new calculation of the effects of thermal stresses during growth on silicon ribbon quality is reported. Thermal stress distributions are computed for ribbon growth under a variety of temperature profiles. A growth rate of 55 cu cm/min with a single ribbon was achieved. The growth of RTR ribbon with a fairly uniform parallel dendritic structure was demonstrated. Results with two approaches were obtained for reducing the Mo impurity level in polycrystalline feedstock. Coating the Mo substrate with Si3N4 does not effect thermal shear separation of the polyribbon; this process shows promise of improving cell efficiency and also increasing the useful life of the molybdenum substrate. A number of solar cells were fabricated on RTR silicon grown from CVD feedstock.

  13. Gaia: Status and Promises

    NASA Astrophysics Data System (ADS)

    Sozzetti, A.

    2015-10-01

    The power of micro-arcsecond (µas) astrometry is about to be unleashed. ESA's Gaia mission, now entering its second year of routine science operations, will soon fulfil its promise for revolutionary science in the countless aspects of Galactic astronomy and astrophysics. I will briefly review the Gaia mission status of operations, and the scenario for intermediate data releases. Iwill then illustrate the potential of µas astrometry for detection and improved characterization of planetary systems in the neighborhood of the Sun.

  14. Basic research challenges in crystalline silicon photovoltaics

    SciTech Connect

    Werner, J.H.

    1995-08-01

    Silicon is abundant, non-toxic and has an ideal band gap for photovoltaic energy conversion. Experimental world record cells of 24 % conversion efficiency with around 300 {mu}m thickness are only 4 % (absolute) efficiency points below the theoretical Auger recombination-limit of around 28 %. Compared with other photovoltaic materials, crystalline silicon has only very few disadvantages. The handicap of weak light absorbance may be mastered by clever optical designs. Single crystalline cells of only 48 {mu}m thickness showed 17.3 % efficiency even without backside reflectors. A technology of solar cells from polycrystalline Si films on foreign substrates arises at the horizon. However, the disadvantageous, strong activity of grain boundaries in Si could be an insurmountable hurdle for a cost-effective, terrestrial photovoltaics based on polycrystalline Si on foreign substrates. This talk discusses some basic research challenges related to a Si based photovoltaics.

  15. Light emission from porous silicon

    NASA Astrophysics Data System (ADS)

    Penczek, John

    The continuous evolution of silicon microelectronics has produced significant gains in electronic information processing. However, greater improvements in performance are expected by utilizing optoelectronic techniques. But these techniques have been severely limited in silicon- based optoelectronics due to the lack of an efficient silicon light emitter. The recent observation of efficient light emission from porous silicon offer a promising opportunity to develop a suitable silicon light source that is compatible with silicon microelectronics. This dissertation examined the porous silicon emission mechanism via photoluminescence, and by a novel device structure for porous silicon emitters. The investigation first examined the correlation between porous silicon formation conditions (and subsequent morphology) with the resulting photoluminescence properties. The quantum confinement theory for porous silicon light emission contends that the morphology changes induced by the different formation conditions determine the optical properties of porous silicon. The photoluminescence spectral shifts measured in this study, in conjunction with TEM analysis and published morphological data, lend support to this theory. However, the photoluminescence spectral broadening was attributed to electronic wavefunction coupling between adjacent silicon nanocrystals. An novel device structure was also investigated in an effort to improve current injection into the porous silicon layer. The selective etching properties of porous silicon were used to create a p-i-n structure with crystalline silicon contacts to the porous silicon layer. The resulting device was found to have unique characteristics, with a negative differential resistance region and current-induced emission that spanned from 400 nm to 5500 nm. The negative differential resistance was correlated to resistive heating effects in the device. A numerical analysis of thermal emission spectra from silicon films, in addition to

  16. Singlet exciton fission in polycrystalline pentacene: from photophysics toward devices.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Ehrler, Bruno; Friend, Richard H

    2013-06-18

    Singlet exciton fission is the process in conjugated organic molecules bywhich a photogenerated singlet exciton couples to a nearby chromophore in the ground state, creating a pair of triplet excitons. Researchers first reported this phenomenon in the 1960s, an event that sparked further studies in the following decade. These investigations used fluorescence spectroscopy to establish that exciton fission occurred in single crystals of several acenes. However, research interest has been recently rekindled by the possibility that singlet fission could be used as a carrier multiplication technique to enhance the efficiency of photovoltaic cells. The most successful architecture to-date involves sensitizing a red-absorbing photoactive layer with a blue-absorbing material that undergoes fission, thereby generating additional photocurrent from higher-energy photons. The quest for improved solar cells has spurred a drive to better understand the fission process, which has received timely aid from modern techniques for time-resolved spectroscopy, quantum chemistry, and small-molecule device fabrication. However, the consensus interpretation of the initial studies using ultrafast transient absorption spectroscopy was that exciton fission was suppressed in polycrystalline thin films of pentacene, a material that would be otherwise expected to be an ideal model system, as well as a viable candidate for fission-sensitized photovoltaic devices. In this Account, we review the results of our recent transient absorption and device-based studies of polycrystalline pentacene. We address the controversy surrounding the assignment of spectroscopic features in transient absorption data, and illustrate how a consistent interpretation is possible. This work underpins our conclusion that singlet fission in pentacene is extraordinarily rapid (∼80 fs) and is thus the dominant decay channel for the photoexcited singlet exciton. Further, we discuss our demonstration that triplet excitons

  17. Silicon applications in photonics

    NASA Astrophysics Data System (ADS)

    Jelenski, A. M.; Gawlik, G.; Wesolowski, M.

    2005-09-01

    Silicon technology enabled the miniaturization of computers and other electronic system for information storage, transmission and transformation allowing the development of the Knowledge Based Information Society. Despite the fact that silicon roadmap indicates possibilities for further improvement, already now the speed of electrons and the bandwidth of electronic circuits are not sufficient and photons are commonly utilized for signal transmission through optical fibers and purely photonic circuits promise further improvements. However materials used for these purposes II/V semiconductor compounds, glasses make integration of optoelectronic circuits with silicon complex an expensive. Therefore research on light generation, transformation and transmission in silicon is very active and recently, due to nanotechnology some spectacular results were achieved despite the fact that mechanisms of light generation are still discussed. Three topics will be discussed. Porous silicon was actively investigated due to its relatively efficient electroluminescence enabling its use in light sources. Its index of refraction, differs considerably from the index of silicon, and this allows its utilization for Bragg mirrors, wave guides and photonic crystals. The enormous surface enables several applications on medicine and biotechnology and in particular due to the effective chemo-modulation of its refracting index the design of optical chemosensors. An effective luminescence of doped and undoped nanocrystalline silicon opened another way for the construction of silicon light sources. Optical amplification was already discovered opening perspectives for the construction of nanosilicon lasers. Luminescences was observed at red, green and blue wavelengths. The used technology of silica and ion implantation are compatible with commonly used CMOS technology. Finally the recently developed and proved idea of optically pumped silicon Raman lasers, using nonlinearity and vibrations in the

  18. Prototyping and Development of Commercial Nano Crystalline and Thin Film Silicon for Photovoltaic Manufacturing

    SciTech Connect

    Haldar, Pradeep, Ph.D.; Pethuraja, Gopal, Ph.D.; Efstathiadis, Haralabos, Ph.D.

    2011-12-02

    The College of Nanoscale Science and Engineering (CNSE) at the University at Albany received funding from the Department of Energy for its proposal Prototyping and Development of Commercial Nanocrystalline and Thin Film Si for Photovoltaic Manufacturing. This project was created to identify growth rate, texture uniformity, process window, economics, composition and thickness uniformity solutions related to fabricating large area, high efficiency thin film silicon based solar cells. This document serves as a final report for the closure of this program and details the deliverables from CNSE against its original scope of work. Thin-film silicon solar cells are a promising candidate for electricity generation applications because of a combination of advantages. Nanocrystalline and poly-Si based thin films, reduces the use of expensive semiconductor material content, can be deposited onto a foreign substrate (e.g. glass or flexible stainless steel) and enables use of the cells in wide variety of applications. In addition, nano and poly-Si films have higher carrier mobility as well as reduce recombination effects, relative to traditional amorphous-silicon films. They can be mass-produced at low cost, and expected to have a strong position in the international photovoltaic industry, which is experiencing a compounded annual growth of 25%. The objectives included: • Demonstration of high rate VHF (Very High Frequency) growth of nc-Si over large areas with uniform thickness. • Demonstration of single chamber device growth that allows mass production processing. • Demonstration of uniform segmented electrodes. • Development of computer models to accelerate efforts. • Demonstration of large grain thin film polycrystalline silicon films fabrication. • Utilizing the AIC (Aluminum Induced Crystallization) process for large grain silicon film

  19. Polycrystalline gamma plutonium's elastic moduli versus temperature

    SciTech Connect

    Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I

    2009-01-01

    Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline {sup 239}Pu in the {gamma} phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease of all elastic moduli with increasing temperature was observed. They calculated the Poisson ratio and found that it increases from 0.242 at 519 K to 0.252 at 571 K. These measurements on extremely well characterized pure Pu are in agreement with other reported results where overlap occurs.

  20. Photoinduced conductivity changes in polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Prawer, S.; Jamieson, D.

    1996-02-01

    We report that the dark electrical properties of polycrystalline chemical vapor deposition diamond films are modified after exposure to UV light. UV illumination gives rise to an increase in the dark conductivity and to a change in the I-V characteristic from Iα exp (aV) for the as-grown material to IαV2 following UV irradiation. Thermally stimulated currents corresponding to an activation energy of about 1.9 eV are observed after UV illumination. The effects of UV irradiation can be totally reversed by thermal annealing and partially reversed by exposing the samples to white light.

  1. Poole-Frenkel conduction in polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Boiko, Y.; Prawer, S.; Jamieson, D.

    1996-04-01

    High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole-Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm-3.

  2. Shock-front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, J. L.; Kadau, K.

    2008-04-01

    We analyze a model for the evolution of shock fronts in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  3. Multilayer hexagonal silicon forming in slit nanopore

    PubMed Central

    He, Yezeng; Li, Hui; Sui, Yanwei; Qi, Jiqiu; Wang, Yanqing; Chen, Zheng; Dong, Jichen; Li, Xiongying

    2015-01-01

    The solidification of two-dimensional liquid silicon confined to a slit nanopore has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious transition from liquid to multilayer hexagonal film with the decrease of temperature, accompanied by dramatic change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the cooling process, some hexagonal islands randomly appear in the liquid first, then grow up to grain nuclei, and finally connect together to form a complete polycrystalline film. Moreover, it is found that the quenching rate and slit size are of vital importance to the freezing structure of silicon film. The results also indicate that the slit nanopore induces the layering of liquid silicon, which further induces the slit size dependent solidification behavior of silicon film with different electrical properties. PMID:26435518

  4. Multilayer hexagonal silicon forming in slit nanopore.

    PubMed

    He, Yezeng; Li, Hui; Sui, Yanwei; Qi, Jiqiu; Wang, Yanqing; Chen, Zheng; Dong, Jichen; Li, Xiongying

    2015-01-01

    The solidification of two-dimensional liquid silicon confined to a slit nanopore has been studied using molecular dynamics simulations. The results clearly show that the system undergoes an obvious transition from liquid to multilayer hexagonal film with the decrease of temperature, accompanied by dramatic change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the cooling process, some hexagonal islands randomly appear in the liquid first, then grow up to grain nuclei, and finally connect together to form a complete polycrystalline film. Moreover, it is found that the quenching rate and slit size are of vital importance to the freezing structure of silicon film. The results also indicate that the slit nanopore induces the layering of liquid silicon, which further induces the slit size dependent solidification behavior of silicon film with different electrical properties. PMID:26435518

  5. A silicon nanocrystal tunnel field effect transistor

    SciTech Connect

    Harvey-Collard, Patrick; Drouin, Dominique; Pioro-Ladrière, Michel

    2014-05-12

    In this work, we demonstrate a silicon nanocrystal Field Effect Transistor (ncFET). Its operation is similar to that of a Tunnelling Field Effect Transistor (TFET) with two barriers in series. The tunnelling barriers are fabricated in very thin silicon dioxide and the channel in intrinsic polycrystalline silicon. The absence of doping eliminates the problem of achieving sharp doping profiles at the junctions, which has proven a challenge for large-scale integration and, in principle, allows scaling down the atomic level. The demonstrated ncFET features a 10{sup 4} on/off current ratio at room temperature, a low 30 pA/μm leakage current at a 0.5 V bias, an on-state current on a par with typical all-Si TFETs and bipolar operation with high symmetry. Quantum dot transport spectroscopy is used to assess the band structure and energy levels of the silicon island.

  6. [Promising technologies in surgery].

    PubMed

    Kotiv, B N; Maĭstrenko, N A

    2013-06-01

    In modern conditions of local wars and armed conflicts, the basic principle of medical care is to reduce injuries stages of medical evacuation, aimed at accelerating the provision of specialized surgical care. In this regard, significantly increases the need for the development and implementation of new high-tech methods that can improve quality of care, both on the battlefield and on the stages of specialized surgical care. A promising direction is the introduction into clinical practice: minimally invasive technologies, the concept of hybrid navigation surgery, operations with the use of laser technology and robotics, advanced and extremely extensive interventions to cancer patients; technology reduces blood loss, use of cell therapy, transplantation techniques, the development of the concept of organ transplantation, lost in combat trauma, the creation of artificial organs and tissues, the creation of personal protective equipment, integrated with a system of combat, etc. PMID:24000635

  7. Credible threats and promises.

    PubMed Central

    McNamara, John M; Houston, Alasdair I

    2002-01-01

    We consider various implications of information about the other player in two-player evolutionary games. A simple model of desertion shows that information about the partner's behaviour can be disadvantageous, and highlights the idea of credible threats. We then discuss the general issue of whether the partner can convince the focal player that it will behave in a specific way, i.e. whether the focal player can make credible threats or promises. We show that when desertion decisions depend on reserves, a player can manipulate its reserves so as to create a credible threat of desertion. We then extend previous work on the evolution of trust and commitment, discussing conditions under which it is advantageous to assume that a partner will behave in a certain way even though it is not in its best interest. PMID:12495517

  8. Acoustic study of texture in polycrystalline brass

    SciTech Connect

    Foster, K.; Fairburn, S.L.; Leisure, R.G.; Kim, S.; Balzar, D.; Alers, G.; Ledbetter, H.

    1999-05-01

    Resonant ultrasound spectroscopy was used to measure the orthorhombic elastic constants of rolled, polycrystalline plates of Cu, Cu{endash}5{percent} Zn, and Cu{endash}15{percent} Zn. The experimental results were fit to theoretical expressions to determine the orientation-distribution coefficients W{sub 400}, W{sub 420}, and W{sub 440}. These coefficients are related to texture (the nonrandom orientation of crystallites). The experimental results were in good agreement with theory for the Cu and the Cu{endash}15{percent} Zn materials. The agreement was not as good for the more anisotropic Cu{endash}5{percent} Zn material, especially for the in-plane compressional constants C{sub 11} and C{sub 22}. The ultrasonically derived {ital W}{close_quote}s were compared to those obtained from neutron measurements for the Cu{endash}Zn alloys. Pole plots based on the two types of measurements, using W{sub 400}, W{sub 420}, and W{sub 440}, were in excellent agreement for the 15{percent} Zn material, and in qualitative agreement for the 5{percent} Zn material. The results support the idea that acoustic methods can be used to measure the low-order {ital W}{close_quote}s in polycrystalline materials. {copyright} {ital 1999 Acoustical Society of America.}

  9. US polycrystalline thin film solar cells program

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L. )

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the US Department of Energy's long-term goals by achieving high efficiencies (15%-20%), low-cost ($50/m{sup 2}), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The US Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe{sub 2} and CdTe with subcontracts to start in Spring 1990. 23 refs., 5 figs.

  10. Electrical properties of polycrystalline methane hydrate

    USGS Publications Warehouse

    Du Frane, W. L.; Stern, L.A.; Weitemeyer, K.A.; Constable, S.; Pinkston, J.C.; Roberts, J.J.

    2011-01-01

    Electromagnetic (EM) remote-sensing techniques are demonstrated to be sensitive to gas hydrate concentration and distribution and complement other resource assessment techniques, particularly seismic methods. To fully utilize EM results requires knowledge of the electrical properties of individual phases and mixing relations, yet little is known about the electrical properties of gas hydrates. We developed a pressure cell to synthesize gas hydrate while simultaneously measuring in situ frequency-dependent electrical conductivity (σ). Synthesis of methane (CH4) hydrate was verified by thermal monitoring and by post run cryogenic scanning electron microscope imaging. Impedance spectra (20 Hz to 2 MHz) were collected before and after synthesis of polycrystalline CH4 hydrate from polycrystalline ice and used to calculate σ. We determined the σ of CH4 hydrate to be 5 × 10−5 S/m at 0°C with activation energy (Ea) of 30.6 kJ/mol (−15 to 15°C). After dissociation back into ice, σ measurements of samples increased by a factor of ~4 and Ea increased by ~50%, similar to the starting ice samples.

  11. Polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  12. Reversible piezomagnetoelectric switching in bulk polycrystalline ceramics

    SciTech Connect

    Stevenson, T. Bennett, J.; Brown, A. P.; Wines, T.; Bell, A. J.; Comyn, T. P.; Smith, R. I.

    2014-08-01

    Magnetoelectric (ME) coupling in materials offer tremendous advantages in device functionality enabling technologies including advanced electronic memory, combining electronic speed, and efficiency with magnetic robustness. However, low cost polycrystalline ME materials are excluded from most commercial applications, operating only at cryogenic temperatures, impractically large electric/magnetic fields, or with low ME coefficients (1-100 mV/cm Oe). Despite this, the technological potential of single compound ME coupling has continued to drive research into multiferroics over the last two decades. Here we show that by manipulating the large induced atomic strain within the polycrystalline, room temperature multiferroic compound 0.7BiFeO{sub 3}–0.3PbTiO{sub 3}, we can induce a reversible, piezoelectric strain controlled ME effect. Employing an in situ neutron diffraction experiment, we have demonstrated that this piezomagnetoelectric effect manifests with an applied electric field >8 kV/mm at the onset of piezoelectric strain, engineered in to the compound by crystallographic phase mixing. This produces a remarkable intrinsic ME coefficient of 1276 mV/cm Oe, due to a strain driven modification to the oxygen sub-lattice, inducing an increase in magnetic moment per Fe{sup 3+} ion of +0.142 μ{sub B}. This work provides a framework for investigations into strain engineered nanostructures to realize low-cost ME devices designed from the atoms up, as well as contributing to the deeper understanding of single phase ME coupling mechanisms.

  13. US Polycrystalline Thin Film Solar Cells Program

    NASA Astrophysics Data System (ADS)

    Ullal, Harin S.; Zweibel, Kenneth; Mitchell, Richard L.

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R and D on copper indium diselenide and cadmium telluride thin films. The objective of the program is to support research to develop cells and modules that meet the U.S. Department of Energy's long-term goals by achieving high efficiencies (15 to 20 percent), low-cost ($50/m(sup 2)), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe2 and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The U.S. Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe2 and CdTe with subcontracts to start in spring 1990.

  14. High-Efficiency Polycrystalline Thin Film Tandem Solar Cells.

    PubMed

    Kranz, Lukas; Abate, Antonio; Feurer, Thomas; Fu, Fan; Avancini, Enrico; Löckinger, Johannes; Reinhard, Patrick; Zakeeruddin, Shaik M; Grätzel, Michael; Buecheler, Stephan; Tiwari, Ayodhya N

    2015-07-16

    A promising way to enhance the efficiency of CIGS solar cells is by combining them with perovskite solar cells in tandem devices. However, so far, such tandem devices had limited efficiency due to challenges in developing NIR-transparent perovskite top cells, which allow photons with energy below the perovskite band gap to be transmitted to the bottom cell. Here, a process for the fabrication of NIR-transparent perovskite solar cells is presented, which enables power conversion efficiencies up to 12.1% combined with an average sub-band gap transmission of 71% for photons with wavelength between 800 and 1000 nm. The combination of a NIR-transparent perovskite top cell with a CIGS bottom cell enabled a tandem device with 19.5% efficiency, which is the highest reported efficiency for a polycrystalline thin film tandem solar cell. Future developments of perovskite/CIGS tandem devices are discussed and prospects for devices with efficiency toward and above 27% are given. PMID:26266847

  15. Memristive Phenomena in Polycrystalline Single Layer MoS2

    NASA Astrophysics Data System (ADS)

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, ultrathin transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high carrier mobility and tunable band-gap. However, available growth methods produce polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Correlated electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism. This abstract is replacing MAR16-2015-004166 that had exceeded the character limit.

  16. Memristive Phenomena in Polycrystalline Single Layer MoS2

    NASA Astrophysics Data System (ADS)

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, single layer transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high electrical conductivity, tunable band-gap, and strong light-matter interaction. However, available growth methods produce large-area polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Complementary electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism.

  17. Progress in polycrystalline thin-film solar cells

    SciTech Connect

    Zweibel, K; Hermann, A; Mitchell, R

    1983-07-01

    Photovoltaic devices based on several polycrystalline thin-film materials have reached near and above 10% sunlight-to-electricity conversion efficiencies. This paper examines the various polycrystalline thin-film PV materials including CuInSe/sub 2/ and CdTe in terms of their material properties, fabrication techniques, problems, and potentials.

  18. Synchrotron X-ray Microdiffraction Analysis of Proton Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. I.; Davidson, J. L.; Ice, G. E.; Liu, W.

    2004-01-01

    X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with sub-micron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechanical Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2x10(exp 17) H(+)per square centimeter protons. Preliminary results indicate that a measurable strain, on the order of 10(exp -3), was introduced into the film near the End of Range (EOR) region of the protons.

  19. 1 Tbit/in.2 Very-High-Density Recording in Mass-Productive Polycrystalline Ferroelectric Thin Film Media

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kenjiro; Kawano, Takahiro; Onoe, Atsushi; Tamura, Masahiro; Umeda, Masaru; Toda, Masayuki

    2009-07-01

    We demonstrate very-high-density ferroelectric recording experiments of 1 Tbit/in.2 in polycrystalline Pb(Zr,Ti)O3 (PZT) thin film for the first time. A high-quality polycrystalline PZT thin film was successfully deposited on a silicon substrate with a SrRuO3 (SRO) electrode by metal-organic chemical vapor deposition (MOCVD). The roughness of the PZT film was reduced to less than 1 nm by chemical mechanical polishing (CMP). The PZT film has very high controllability for domain inversion. Our fabrication process also enables high productivity. Therefore, our PZT film has potential to be a mass-productive ferroelectric recording medium for high-density storage systems.

  20. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    NASA Astrophysics Data System (ADS)

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-08-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets.

  1. Modelling heat conduction in polycrystalline hexagonal boron-nitride films.

    PubMed

    Mortazavi, Bohayra; Pereira, Luiz Felipe C; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  2. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    PubMed Central

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  3. Plastic deformation of polycrystalline zirconium carbide

    NASA Technical Reports Server (NTRS)

    Darolia, R.; Archbold, T. F.

    1976-01-01

    The compressive yield strength of arc-melted polycrystalline zirconium carbide has been found to vary from 77 kg per sq mm at 1200 C to 19 kg per sq mm at 1800 C. Yield drops were observed with plastic strain-rates greater than 0.003/sec but not with slower strain rates. Strain-rate change experiments yielded values for the strain-rate sensitivity parameter m which range from 6.5 at 1500 C to 3.8 at 1800 C, and the product dislocation velocity stress exponent times T was found to decrease linearly with increasing temperature. The deformation rate results are consistent with the Kelly-Rowcliffe model in which the diffusion of carbon assists the motion of dislocations.

  4. Modeling of Irradiation Hardening of Polycrystalline Materials

    SciTech Connect

    Li, Dongsheng; Zbib, Hussein M.; Garmestani, Hamid; Sun, Xin; Khaleel, Mohammad A.

    2011-09-14

    High energy particle irradiation of structural polycrystalline materials usually produces irradiation hardening and embrittlement. The development of predict capability for the influence of irradiation on mechanical behavior is very important in materials design for next generation reactors. In this work a multiscale approach was implemented to predict irradiation hardening of body centered cubic (bcc) alpha-iron. The effect of defect density, texture and grain boundary was investigated. In the microscale, dislocation dynamics models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent model was applied to predict the irradiation hardening in samples with changes in texture and grain boundary. This multiscale modeling can guide performance evaluation of structural materials used in next generation nuclear reactors.

  5. Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

    SciTech Connect

    Martin, Guillaume; Desgardin, Pierre; Sauvage, Thierry; Barthe, Marie-France; Garcia, Philippe; Carlot, Gaelle

    2007-07-01

    This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO{sub 2} sintered samples presenting different microstructures were implanted with {sup 3}He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the {sup 3}He(d,{alpha}){sup 1}H reaction. {sup 3}He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

  6. High-temperature creep of polycrystalline chromium

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.; Klopp, W. D.

    1972-01-01

    The creep properties of high-purity, polycrystalline chromium were determined over the temperature range 0.51 to 0.78 T sub m, where T sub m is the melting temperature. Creep rates determined from step-load creep tests can be represented by the general creep equation; epsilon/D = k((sigma/E) to the nth power) where epsilon is the minimum creep rate, D is the diffusivity, k is the creep rate constant, sigma is the applied stress, E is the modulus, and n is the stress exponent, equal to 4.3 for chromium. This correlation and metallographic observations suggest a dislocation climb mechanism is operative in the creep of chromium over the temperature range investigated.

  7. Polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1996-02-01

    Thermophotovoltaic (TPV) cells convert thermal energy to electricity. Modularity, portability, silent operation, absence of moving parts, reduced air pollution, rapid start-up, high power densities, potentially high conversion efficiencies, choice of a wide range of heat sources employing fossil fuels, biomass, and even solar radiation are key advantages of TPV cells in comparison with fuel cells, thermionic and thermoelectric convertors, and heat engines. The potential applications of TPV systems include: remote electricity supplies, transportation, co-generation, electric-grid independent appliances, and space, aerospace, and military power applications. The range of bandgaps for achieving high conversion efficiencies using low temperature (1000-2000 K) black-body or selective radiators is in the 0.5-0.75 eV range. Present high efficiency convertors are based on single crystalline materials such as In1-xGaxAs, GaSb, and Ga1-xInxSb. Several polycrystalline thin films such as Hg1-xCdxTe, Sn1-xCd2xTe2, and Pb1-xCdxTe, etc., have great potential for economic large-scale applications. A small fraction of the high concentration of charge carriers generated at high fluences effectively saturates the large density of defects in polycrystalline thin films. Photovoltaic conversion efficiencies of polycrystalline thin films and PV solar cells are comparable to single crystalline Si solar cells, e.g., 17.1% for CuIn1-xGaxSe2 and 15.8% for CdTe. The best recombination-state density Nt is in the range of 10-15-10-16 cm-3 acceptable for TPV applications. Higher efficiencies may be achieved because of the higher fluences, possibility of bandgap tailoring, and use of selective emitters such as rare earth oxides (erbia, holmia, yttria) and rare earth-yttrium aluminium garnets. As compared to higher bandgap semiconductors such as CdTe, it is easier to dope the lower bandgap semiconductors. TPV cell development can benefit from the more mature PV solar cell and opto

  8. Residual Stress Predictions in Polycrystalline Alumina

    SciTech Connect

    VEDULA,VENKATA R.; GLASS,S. JILL; SAYLOR,DAVID M.; ROHRER,GREGORY S.; CARTER,W. CRAIG; LANGER,STEPHEN A.

    1999-12-13

    Microstructure-level residual stresses arise in polycrystalline ceramics during processing as a result of thermal expansion anisotropy and crystallographic disorientation across the grain boundaries. Depending upon the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking during the processing of these materials. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples were predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations. The crystallographic orientations were obtained by electron-backscattered diffraction (EBSD). The residual stresses were lower and the stress distributions were narrower in the textured samples compared to those in the untextured samples. Crack initiation and propagation were also simulated using the Griffith fracture criterion. The grain boundary to surface energy ratios required for computations were estimated using AFM groove measurements.

  9. Polycrystalline Thin Film Device Degradation Studies

    SciTech Connect

    Albin, D. S.; McMahon, T. J.; Pankow, J. W.; Noufi, R.; Demtsu, S. H.; Davies, A.

    2005-11-01

    Oxygen during vapor CdCl2 (VCC) treatments significantly reduced resistive shunts observed in CdS/CdTe polycrystalline devices using thinner CdS layers during 100 deg C, open-circuit, 1-sun accelerated stress testing. Cu oxidation resulting from the reduction of various trace oxides present in as-grown and VCC treated films is the proposed mechanism by which Cu diffusion, and subsequent shunts are controlled. Graphite paste layers between metallization and CdTe behave like diffusion barriers and similarly benefit device stability. Ni-based contacts form a protective Ni2Te3 intermetallic layer that reduces metal diffusion but degrades performance through increased series resistance.

  10. Shock front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, John; Kadau, Kai

    2008-03-01

    We analyze a model for the evolution of weak shock fronts (or elastic precursor waves) in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  11. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  12. Interaction of metal layers with polycrystalline Si

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  13. Dynamical electrophotoconductivity in polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.

    1982-01-01

    Polycrystalline cadmium sulfide (CdS) films were deposited on lithium niobate (LiNbO3) substrates by vacuum evaporation and annealed to obtain high photosensitivity. The change in photoconductivity of these films due to the penetration of electric fields associated with elastic waves propagating on their substrates was demonstrated and studied. The relationship between the acoustic electric field and the induced change in film conductivity was found to be a nonlinear one. The fractional change in conductivity is strongly dependent on the light intensity and the film temperature, showing a prominent maximum as a function of these quantities. The largest recorded fractional change in conductivity was about 25% at electric fields of the order of 1,000 volts per centimeter. A phenomological model was developed based on the interaction between the space charge created by the electric field and the electron trapping states in the photoconductor.

  14. Vacancy Formation Enthalpy in Polycrystalline Depleted Uranium

    NASA Astrophysics Data System (ADS)

    Lund, K. R.; Lynn, K. G.; Weber, M. H.; Okuniewski, M. A.

    2013-06-01

    Positron Annihilation Spectroscopy was performed as a function of temperature and beam energy on polycrystalline depleted uranium (DU) foil. Samples were run with varying heat profiles all starting at room temperature. While collecting Doppler-Broadening data, the temperature of the sample was cycled several times. The first heat cycle shows an increasing S-parameter near temperatures of 400K to 500K much lower than the first phase transition of 941K indicating increasing vacancies possibly due to oxygen diffusion from the bulk to the surface. Vacancy formation enthalpies were calculated fitting a model to the data to be 1.6± 0.16 eV. Results are compared to previous work [3,4].

  15. Electrical characterization of silicon produced by electrochemical purification

    SciTech Connect

    Kibbler, A.E.

    1981-12-01

    An overall procedure and specific methodology are described for the electrical characterization of small single crystal and polycrystalline silicon specimens. The tested material is manufactured by electrowinning or electrorefining processes in quantities ranging from 10 to 1000 milligrams. Since the specimen source is limited and individual samples vary in size, shape, and physical structure, specific techniques have to be employed for successful utilization of the measurement procedure. The development of this procedure, therefore, necessitates a measurement pressure which is nondestructive, and yet reliable, as possible. The ultimate goal of these measurements is to give an indication of the material's potential for application in solar cell fabrication. The minimum measurement format includes: majority carrier type, resistivity, minority carrier diffusion length, minority carrier lifetime, Hall mobility, and Hall carrier density. Existing techniques were either directly applied, modified, or totally discarded. In addition, specialized preparation techniques were experimentally developed, insuring measurement compatibility. After testing, the outlined methods prove to be reasonably reliable, reproducible (allowing for experimental variances), and usually successful in obtaining reportable results. Besides these essential measurements, the beginnings of device fabrication and measurement are being investigated with promising results for the materials in question. These include: Schottky diodes, diffused junction diodes, MOS structures, conventionally diffused photocells, and ITO or SnO/sub 2/ photocells.

  16. Nuclear spin relaxation of polycrystalline 129 xenon

    NASA Astrophysics Data System (ADS)

    Samuelson, Gary Lee, Jr.

    Through spin exchange optical pumping, it is possible to achieve upwards of 30% nuclear spin polarization in 129Xe with an NMR signal enhancement of some 5 orders of magnitude over typical thermal signals. Hyperpolarized 129Xe has thus found application in several leading-edge technologies. At 1 T and 4.2 K, the characteristic relaxation time of enriched polycrystalline 129Xe (86% 129Xe, 0.1% 131Xe) is well over 200 hrs, sufficient for long-term storage and transport. Longitudinal nuclear spin relaxation of 129Xe at more convenient fields from 1 to 200 G is studied in detail. Significant structure in relaxation times vs. magnetic field is seen; the most prominent new finding being a sharp local long-time T 1 maximum of 1000 mins at ≈3 G. Such structure has not been observed in previous measurements of natural Xe. Below temperatures of 10 K, relaxation can be attributed to cross relaxation with 131Xe, mediated by spin diffusion. Measurements of 129Xe relaxation as a function of magnetic field, temperature and Xe isotopic content are reported and compared with expected theoretical behaviors. It is seen that the characteristic nuclear spin relaxation of enriched 129Xe at 4.2 K is nonexponential at these low fields. For fields between 10 G and 200 G, these nonexponential relaxation curves can be fit well with a specific spin diffusion model. Below 10 G no such fit is possible and thus quantum mechanical details of the coupling between 129Xe, 131Xe and the bulk lattice are considered. These findings support the hypothesis that cross relaxation with 131Xe is indeed a dominant actor in the nuclear spin relaxation of polycrystalline 129 Xe at such low fields and low temperatures.

  17. ESR in CVD silicon and silicon-carbon alloys

    NASA Astrophysics Data System (ADS)

    Gaczi, P. J.; Booth, D. C.

    1981-03-01

    Electron spin resonance (ESR) is reported in three groups of chemical vapor deposited silicon films. It is noted that group I films are amorphous Si(x)C(100-x) alloys prepared from silane and acetylene at a substrate temperature of 630 C that have a spin density of 3 x 10 to the 19th/cu cm. The silicon-carbon films have been developed as structurally stable selective absorbers for photothermal solar energy conversion. Group II films are nonalloyed amorphous silicon films prepared below 660 C that have a spin density of 1 x 10 to the 19th, while group III films are polycrystalline films prepared above 670 C with a density of 0.5 x 10 to the 19th/cu cm. The exchange interaction between spins is sufficiently strong in the group I silicon-carbon alloys so that an average g value is observed and no evidence of superposition is found in agreement with the amorphous Si-Ge results of Kumeda et al. (1977). ESR saturation and line broadening as a function of microwave power in samples representative of the three groups is observed. A trend, in the order group III, II, I, is found of increasing spin system homogeneity, indicating that the exchange coupled spin clusters contain increasing numbers of spins.

  18. Heteroepitaxial film silicon solar cell grown on Ni-W foils

    SciTech Connect

    Wee, Sung Hun; Cantoni, Claudia; Fanning, Thomas; Teplin, Charles; Bogorin, Daniela Florentina; Bornstein, Jon; Bowers, Karen; Schroeter,; Hasoon, Falah; Branz, Howard; Paranthaman, Mariappan Parans; Goyal, Amit

    2013-01-01

    Today, silicon-wafer-based technology dominates the photovoltaic (PV) industry because it enables high efficiency, is produced from abundant, non-toxic materials and is proven in the PV marketplace.[1] However, costs associated with the wafer itself limit ultimate cost reductions.[1,2] PV based on absorber layers of crystalline Si with only 2 to 10 m thickness are a promising route to reduce these costs, while maintaining efficiencies above 15%.[3-5] With the goal of fabricating low-cost film crystalline Si (c-Si), recent research has explored wafer peeling,[6,7] crystallization of amorphous silicon films on glass,[4,8-10] and seed and epitaxy approaches.[3,5,11] In this third approach, one initially forms a seed layer that establishes the grain size and crystalline order. The Si layer is then grown heteroepitaxially on the seed layer, so that it replicates the seed crystal structure. In all of these film c-Si approaches, the critical challenge is to grow c-Si with adequate material quality: specifically, the diffusion length (LD) must be at least three times the film thickness.[12] In polycrystalline Si films, grain boundaries (GBs) are recombination-active and significantly reduce LD. This adverse effects of GBs motivates research into growth of large grained c-Si [13,14] (for a low density of GBs) and biaxially-textured c-Si [11] (for low-angle GBs).

  19. Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications.

    PubMed

    Wu, Jennifer Yun-Shin; Lin, Chih-Heng; Feng, Mei-Huei; Chen, Chien-Hung; Su, Ping-Chia; Yang, Po-Wen; Zheng, Jian-Ming; Fu, Chang-Wei; Yang, Yuh-Shyong

    2016-01-01

    Surveillance using biomarkers is critical for the early detection, rapid intervention, and reduction in the incidence of diseases. In this study, we describe the preparation of polycrystalline silicon nanowire field-effect transistors (pSNWFETs) that serve as biosensing devices for biomarker detection. A protocol for chemical and biomolecular sensing by using pSNWFETs is presented. The pSNWFET device was demonstrated to be a promising transducer for real-time, label-free, and ultra-high-sensitivity biosensing applications. The source/drain channel conductivity of a pSNWFET is sensitive to changes in the environment around its silicon nanowire (SNW) surface. Thus, by immobilizing probes on the SNW surface, the pSNWFET can be used to detect various biotargets ranging from small molecules (dopamine) to macromolecules (DNA and proteins). Immobilizing a bioprobe on the SNW surface, which is a multistep procedure, is vital for determining the specificity of the biosensor. It is essential that every step of the immobilization procedure is correctly performed. We verified surface modifications by directly observing the shift in the electric properties of the pSNWFET following each modification step. Additionally, X-ray photoelectron spectroscopy was used to examine the surface composition following each modification. Finally, we demonstrated DNA sensing on the pSNWFET. This protocol provides step-by-step procedures for verifying bioprobe immobilization and subsequent DNA biosensing application. PMID:27167162

  20. New Deep Reactive Ion Etching Process Developed for the Microfabrication of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Evans, Laura J.; Beheim, Glenn M.

    2005-01-01

    Silicon carbide (SiC) is a promising material for harsh environment sensors and electronics because it can enable such devices to withstand high temperatures and corrosive environments. Microfabrication techniques have been studied extensively in an effort to obtain the same flexibility of machining SiC that is possible for the fabrication of silicon devices. Bulk micromachining using deep reactive ion etching (DRIE) is attractive because it allows the fabrication of microstructures with high aspect ratios (etch depth divided by lateral feature size) in single-crystal or polycrystalline wafers. Previously, the Sensors and Electronics Branch of the NASA Glenn Research Center developed a DRIE process for SiC using the etchant gases sulfur hexafluoride (SF6) and argon (Ar). This process provides an adequate etch rate of 0.2 m/min and yields a smooth surface at the etch bottom. However, the etch sidewalls are rougher than desired, as shown in the preceding photomicrograph. Furthermore, the resulting structures have sides that slope inwards, rather than being precisely vertical. A new DRIE process for SiC was developed at Glenn that produces smooth, vertical sidewalls, while maintaining an adequately high etch rate.

  1. Expanding the versatility of silicon carbide thin films and nanowires

    NASA Astrophysics Data System (ADS)

    Luna, Lunet

    Silicon carbide (SiC) based electronics and sensors hold promise for pushing past the limits of current technology to achieve small, durable devices that can function in high-temperature, high-voltage, corrosive, and biological environments. SiC is an ideal material for such conditions due to its high mechanical strength, excellent chemical stability, and its biocompatibility. Consequently, SiC thin films and nanowires have attracted interest in applications such as micro- and nano-electromechanical systems, biological sensors, field emission cathodes, and energy storage devices. However to fully realize SiC in such technologies, the reliability of metal contacts to SiC at high temperatures must be improved and the nanowire growth mechanism must be understood to enable strict control of nanowire crystal structure and orientation. Here, we present a novel metallization scheme, utilizing solid-state graphitization of SiC, to improve the long-term reliability of Pt/Ti contacts to polycrystalline n-type SiC films at high temperature. The metallization scheme includes an alumina protection layer and exhibits low, stable contact resistivity even after long-term (500 hr) testing in air at 450 ºC. We also report the crystal structure and growth mechanism of Ni-assisted silicon carbide nanowires using single-source precursor, methyltrichlorosilane. The effects of growth parameters, such as substrate and temperature, on the structure and morphology of the resulting nanowires will also be presented. Overall, this study provides new insights towards the realization of novel SiC technologies, enabled by advanced electron microscopy techniques located in the user facilities at the Molecular Foundry in Berkeley, California. This work was performed in part at the Molecular Foundry, supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

  2. Synthesis of silane and silicon in a non-equilibrium plasma jet

    NASA Technical Reports Server (NTRS)

    Calcote, H. F.; Felder, W.

    1977-01-01

    The feasibility of using a non-equilibrium hydrogen plasma jet as a chemical synthesis tool was investigated. Four possible processes were identified for further study: (1) production of polycrystalline silicon photovoltaic surfaces, (2) production of SiHCl3 from SiCl4, (3) production of SiH4 from SiHCl3, and (4) purification of SiCl4 by metal impurity nucleation. The most striking result was the recognition that the strongly adhering silicon films, amorphous or polycrystalline, produced in our studies could be the basis for preparing a photovoltaic surface directly; this process has potential advantages over other vapor deposition processes.

  3. Mechanical Properties and Failure Mechanisms in Polycrystalline Graphene

    NASA Astrophysics Data System (ADS)

    Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Large-scale growth of graphene using chemical vapor deposition produces polycrystalline material containing grain boundaries. Recent experiments demonstrate that polycrystalline graphene is nearly as strong as pristine. In this work, the mechanical properties of bi-crystal and polycrystalline graphene samples are investigated by simulating nano-indentation of a circular membrane using classical molecular dynamics and a novel Screened Environment Dependent Reactive Bond Order (SED-REBO) potential. The failure mechanisms and crack propagation in graphene samples containing grain boundaries are also discussed.

  4. High-performance porous silicon solar cell development. Final report, October 1, 1993--September 30, 1995

    SciTech Connect

    Maruska, P

    1996-09-01

    The goal of the program was to demonstrate use of porous silicon in new solar cell structures. Porous silicon technology has been developed at Spire for producing visible light-emitting diodes (LEDs). The major aspects that they have demonstrated are the following: porous silicon active layers have been made to show photovoltaic action; porous silicon surface layers can act as antireflection coatings to improve the performance of single-crystal silicon solar cells; and porous silicon surface layers can act as antireflection coatings on polycrystalline silicon solar cells. One problem with the use of porous silicon is to achieve good lateral conduction of electrons and holes through the material. This shows up in terms of poor blue response and photocurrents which increase with increasing reverse bias applied to the diode.

  5. RF performances of inductors integrated on localized p+-type porous silicon regions

    NASA Astrophysics Data System (ADS)

    Capelle, Marie; Billoué, Jérôme; Poveda, Patrick; Gautier, Gaël

    2012-09-01

    To study the influence of localized porous silicon regions on radiofrequency performances of passive devices, inductors were integrated on localized porous silicon regions, full porous silicon sheet, bulk silicon and glass substrates. In this work, a novel strong, resistant fluoropolymer mask is introduced to localize the porous silicon on the silicon wafer. Then, the quality factors and resonant frequencies obtained with the different substrates are presented. A first comparison is done between the performances of inductors integrated on same-thickness localized and full porous silicon sheet layers. The effect of the silicon regions in the decrease of performances of localized porous silicon is discussed. Then, the study shows that the localized porous silicon substrate significantly reduces losses in comparison with high-resistivity silicon or highly doped silicon bulks. These results are promising for the integration of both passive and active devices on the same silicon/porous silicon hybrid substrate.

  6. Progress on monolithic integration of cheap IR FPAs of polycrystalline PbSe

    NASA Astrophysics Data System (ADS)

    Sanchez, F. J.; Rodrigo, M. T.; Vergara, G.; Lozano, M.; Santander, J.; Torquemada, M. C.; Gomez, L. J.; Villamayor, V.; Alvarez, M.; Verdu, M.; Almazan, R.; Plaza, J.; Rodriguez, P.; Catalan, I.; Diezhandino, J.; Montojo, M. T.

    2005-05-01

    Although IR detectors are old and well known devices, at present they have not reached the status of a mass-market product. The main reason is directly related to their lack of affordability. Fifteen years ago the latest generation of thermal infrared (IR) detectors, as large format focal plane arrays (FPA), appeared with very promising expectation. They have been called low cost detectors because they do not need cooling and, as a consequence, prices are sensitively lower. However, they are currently still not affordable. Issues related to packaging and processing are limiting the potential affordability of these type of devices. Meanwhile, the technology of uncooled photonic detectors such as polycrystalline lead salt detectors are evolving fast and now they are a real alternative in the field of cheap detectors. CIDA owns an innovative technology for processing low density polycrystalline PbSe FPAs. This technology presents some advantages compared to the standard technology, mainly for processing more complex devices, such as 2D arrays or multicolor detectors. Mass production and prices decrease depend strongly on the monolithic integration between detectors and read out electronics. The method developed makes possible to process monolithic devices without any fundamental limitation. This work presents the latest results obtained during a study of monolithic integration viability carried out in our laboratories. A complementary metal oxide semiconductor (CMOS) test circuitry was designed, processed and submitted to all PbSe processing with promising results. The next phase will consist of designing a proper CMOS circuitry and process sensors on top.

  7. Study of silicon strip waveguides with diffraction gratings and photonic crystals tuned to a wavelength of 1.5 µm

    SciTech Connect

    Barabanenkov, M. Yu. Vyatkin, A. F.; Volkov, V. T.; Gruzintsev, A. N.; Il’in, A. I.; Trofimov, O. V.

    2015-12-15

    Single-mode submicrometer-thick strip waveguides on silicon-on-insulator substrates, fabricated by silicon-planar-technology methods are considered. To solve the problem of 1.5-µm wavelength radiation input-output and its frequency filtering, strip diffraction gratings and two-dimensional photonic crystals are integrated into waveguides. The reflection and transmission spectra of gratings and photonic crystals are calculated. The waveguide-mode-attenuation coefficient for a polycrystalline silicon waveguide is experimentally estimated.

  8. Graphene film growth on polycrystalline metals.

    PubMed

    Edwards, Rebecca S; Coleman, Karl S

    2013-01-15

    Graphene, a true wonder material, is the newest member of the nanocarbon family. The continuous network of hexagonally arranged carbon atoms gives rise to exceptional electronic, mechanical, and thermal properties, which could result in the application of graphene in next generation electronic components, energy-storage materials such as capacitors and batteries, polymer nanocomposites, transparent conducting electrodes, and mechanical resonators. With one particularly attractive application, optically transparent conducting electrodes or films, graphene has the potential to rival indium tin oxide (ITO) and become a material for producing next generation displays, solar cells, and sensors. Typically, graphene has been produced from graphite using a variety of methods, but these techniques are not suitable for growing large-area graphene films. Therefore researchers have focused much effort on the development of methodology to grow graphene films across extended surfaces. This Account describes current progress in the formation and control of graphene films on polycrystalline metal surfaces. Researchers can grow graphene films on a variety of polycrystalline metal substrates using a range of experimental conditions. In particular, group 8 metals (iron and ruthenium), group 9 metals (cobalt, rhodium, and iridium), group 10 metals (nickel and platinum), and group 11 metals (copper and gold) can support the growth of these films. Stainless steel and other commercial copper-nickel alloys can also serve as substrates for graphene film growth. The use of copper and nickel currently predominates, and these metals produce large-area films that have been efficiently transferred and tested in many electronic devices. Researchers have grown graphene sheets more than 30 in. wide and transferred them onto display plastic ready for incorporation into next generation displays. The further development of graphene films in commercial applications will require high

  9. Time-resolved x-ray diffraction techniques for bulk polycrystalline materials under dynamic loading.

    PubMed

    Lambert, P K; Hustedt, C J; Vecchio, K S; Huskins, E L; Casem, D T; Gruner, S M; Tate, M W; Philipp, H T; Woll, A R; Purohit, P; Weiss, J T; Kannan, V; Ramesh, K T; Kenesei, P; Okasinski, J S; Almer, J; Zhao, M; Ananiadis, A G; Hufnagel, T C

    2014-09-01

    We have developed two techniques for time-resolved x-ray diffraction from bulk polycrystalline materials during dynamic loading. In the first technique, we synchronize a fast detector with loading of samples at strain rates of ~10(3)-10(4) s(-1) in a compression Kolsky bar (split Hopkinson pressure bar) apparatus to obtain in situ diffraction patterns with exposures as short as 70 ns. This approach employs moderate x-ray energies (10-20 keV) and is well suited to weakly absorbing materials such as magnesium alloys. The second technique is useful for more strongly absorbing materials, and uses high-energy x-rays (86 keV) and a fast shutter synchronized with the Kolsky bar to produce short (~40 μs) pulses timed with the arrival of the strain pulse at the specimen, recording the diffraction pattern on a large-format amorphous silicon detector. For both techniques we present sample data demonstrating the ability of these techniques to characterize elastic strains and polycrystalline texture as a function of time during high-rate deformation. PMID:25273733

  10. Time-resolved x-ray diffraction techniques for bulk polycrystalline materials under dynamic loading

    SciTech Connect

    Lambert, P. K.; Hustedt, C. J.; Zhao, M.; Ananiadis, A. G.; Hufnagel, T. C.; Vecchio, K. S.; Huskins, E. L.; Casem, D. T.; Gruner, S. M.; Tate, M. W.; Philipp, H. T.; Purohit, P.; Weiss, J. T.; Woll, A. R.; Kannan, V.; Ramesh, K. T.; Kenesei, P.; Okasinski, J. S.; Almer, J.

    2014-09-15

    We have developed two techniques for time-resolved x-ray diffraction from bulk polycrystalline materials during dynamic loading. In the first technique, we synchronize a fast detector with loading of samples at strain rates of ∼10{sup 3}–10{sup 4} s{sup −1} in a compression Kolsky bar (split Hopkinson pressure bar) apparatus to obtain in situ diffraction patterns with exposures as short as 70 ns. This approach employs moderate x-ray energies (10–20 keV) and is well suited to weakly absorbing materials such as magnesium alloys. The second technique is useful for more strongly absorbing materials, and uses high-energy x-rays (86 keV) and a fast shutter synchronized with the Kolsky bar to produce short (∼40 μs) pulses timed with the arrival of the strain pulse at the specimen, recording the diffraction pattern on a large-format amorphous silicon detector. For both techniques we present sample data demonstrating the ability of these techniques to characterize elastic strains and polycrystalline texture as a function of time during high-rate deformation.

  11. Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl2

    NASA Astrophysics Data System (ADS)

    Jensen, S. A.; Burst, J. M.; Duenow, J. N.; Guthrey, H. L.; Moseley, J.; Moutinho, H. R.; Johnston, S. W.; Kanevce, A.; Al-Jassim, M. M.; Metzger, W. K.

    2016-06-01

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  12. Time-resolved x-ray diffraction techniques for bulk polycrystalline materials under dynamic loading

    PubMed Central

    Lambert, P. K.; Hustedt, C. J.; Vecchio, K. S.; Huskins, E. L.; Casem, D. T.; Gruner, S. M.; Tate, M. W.; Philipp, H. T.; Woll, A. R.; Purohit, P.; Weiss, J. T.; Kannan, V.; Ramesh, K. T.; Kenesei, P.; Okasinski, J. S.; Almer, J.; Zhao, M.; Ananiadis, A. G.; Hufnagel, T. C.

    2014-01-01

    We have developed two techniques for time-resolved x-ray diffraction from bulk polycrystalline materials during dynamic loading. In the first technique, we synchronize a fast detector with loading of samples at strain rates of ∼103–104 s−1 in a compression Kolsky bar (split Hopkinson pressure bar) apparatus to obtain in situ diffraction patterns with exposures as short as 70 ns. This approach employs moderate x-ray energies (10–20 keV) and is well suited to weakly absorbing materials such as magnesium alloys. The second technique is useful for more strongly absorbing materials, and uses high-energy x-rays (86 keV) and a fast shutter synchronized with the Kolsky bar to produce short (∼40 μs) pulses timed with the arrival of the strain pulse at the specimen, recording the diffraction pattern on a large-format amorphous silicon detector. For both techniques we present sample data demonstrating the ability of these techniques to characterize elastic strains and polycrystalline texture as a function of time during high-rate deformation. PMID:25273733

  13. Partitioning Effects in Recrystallization of Silicon from Silicon-Metal Solutions

    SciTech Connect

    Good, E. A.; Wang, T. H.; Ciszek, T. F.; Frost, R. H.; Page, M. R.; Landry, M. D.

    2002-08-01

    The objective of this work is to investigate various silicon-metal eutectic systems that selectively retain detrimental impurities, such as Ni, Co, Fe, Cr, in the melt so that silicon may be purified. We studied possible interactions in the melt and in the silicon crystal between impurity elements and solvent metals that lead to reduced or enhanced impurity partition relative to the respective silicon-impurity binary systems. Systems such as Al- Si, Cu-Si, and In-Si show promises of reduced impurity incorporations in recrystallized silicon, which are good candidates for further investigation besides Ga-Si, Au-Si, and Ag-Si.

  14. A promising new thermoelectric material - Ruthenium silicide

    NASA Technical Reports Server (NTRS)

    Vining, Cronin B.; Mccormack, Joseph A.; Zoltan, Andrew; Zoltan, Leslie D.

    1991-01-01

    Experimental and theoretical efforts directed toward increasing thermoelectric figure of merit values by a factor of 2 or 3 have been encouraging in several respects. An accurate and detailed theoretical model developed for n-type silicon-germanium (SiGe) indicates that ZT values several times higher than currently available are expected under certain conditions. These new, high ZT materials are expected to be significantly different from SiGe, but not unreasonably so. Several promising candidate materials have been identified which may meet the conditions required by theory. One such candidate, ruthenium silicide, currently under development at JPL, has been estimated to have the potential to exhibit figure of merit values 4 times higher than conventional SiGe materials. Recent results are summarized.

  15. Piezoresistivity of polycrystalline p-type diamond films of various doping levels at different temperatures

    SciTech Connect

    Wang, W.L.; Jiang, X.; Taube, K.; Klages, C.

    1997-07-01

    The piezoresistivity of polycrystalline p-type diamond films has been studied. The films were grown by microwave plasma assisted chemical vapor deposition and {ital in situ} doped with different concentrations of boron. A four-point electrical measurement was performed to evaluate the film resistivity change upon straining in a four-point bending beam setup. Films were glued directly onto a stainless steel beam and the silicon substrates were selectively removed. A gauge factor (relative change of the resistivity divided by the elastic strain) of about 690 under 100 microstrains was obtained at room temperature for a film doped with 32 ppm boron. With increasing temperature and dopant concentration the gauge factor increases. The experimental results obtained are discussed. {copyright} {ital 1997 American Institute of Physics.}

  16. Epitaxial growth of cadmium sulfide films on silicon

    NASA Astrophysics Data System (ADS)

    Antipov, V. V.; Kukushkin, S. A.; Osipov, A. V.

    2016-03-01

    A 300-nm-thick cadmium sulfide epitaxial layer on silicon was grown for the first time. The grown was performed by the method of evaporation and condensation in a quasi-closed volume at a substrate temperature of 650°C and a growth time of 4 s. In order to avoid a chemical reaction between silicon and cadmium sulfide (at this temperature, the rate constant of the reaction is ~103) and to prevent etching of silicon by sulfur, a high-quality silicon carbide buffer layer ~100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The ellipsometric, Raman, electron diffraction, and trace element analyses showed a high structural perfection of the CdS layer and the absence of a polycrystalline phase.

  17. Estimating Geometric Dislocation Densities in Polycrystalline Materialsfrom Orientation Imaging Microscopy

    SciTech Connect

    Man, Chi-Sing; Gao, Xiang; Godefroy, Scott; Kenik, Edward A

    2010-01-01

    Herein we consider polycrystalline materials which can be taken as statistically homogeneous and whose grains can be adequately modeled as rigid-plastic. Our objective is to obtain, from orientation imaging microscopy (OIM), estimates of geometrically necessary dislocation (GND) densities.

  18. Polycrystalline neutron scattering for Geant4: NXSG4

    NASA Astrophysics Data System (ADS)

    Kittelmann, T.; Boin, M.

    2015-04-01

    An extension to Geant4 based on the nxs library is presented. It has been implemented in order to include effects of low-energy neutron scattering in polycrystalline materials, and is made available to the scientific community.

  19. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2013-06-01

    This National Center for Photovoltaics sheet describes the capabilities of its polycrystalline thin-film research in the area of cadmium telluride. The scope and core competencies and capabilities are discussed.

  20. Thermophysical Properties of Sodium (Beta)-Alumina Polycrystalline Ceramic

    NASA Technical Reports Server (NTRS)

    Ryan, M. A.; Williams, R. M.; Allevato, C. E.; Vining, C. B.; Lowe-Ma, C. K.; Robie, S. B.

    1994-01-01

    Teh thermal diffusivity, heat capacity and thermal conductivity of solid samples of new, Li-stabilized, sodium (Beta)-alumina polycrystalline ceramic have been determined in the temperature range 500-1200 K.

  1. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet that includes scope, core competencies and capabilities, and contact/web information for Polycrystalline Thin-Film Research: Cadmium Telluride at the National Center for Photovoltaics.

  2. Stability of polycrystalline Nextel 720 fiber

    SciTech Connect

    Das, G.

    1996-12-31

    The microstructure and tensile properties of polycrystalline Nextel 720 fiber (85 wt.% Al{sub 2}O{sub 3} - 15 wt-% SiO{sub 2}), both crystallized and precrystallized, were evaluated following prolonged thermal exposure at 982{degrees}C in air. The room temperature tensile strengths of Nextel 720 fibers did not appear to suffer degradation for exposures up to 3000 h and the microstructure remained unaffected by thermal exposures. The tensile strength of precrystallized Nextel 720 fiber was also determined at room temperature following heat treatments at 1093-1427{degrees}C in air. The precrystallized Nextel 720 fiber started to show a slight loss of strength after heat treatment at 1093{degrees}C/4 h and the strength deterioration was exacerbated for heat treatments at 1204{degrees}C/4 h and above. Microstructural characterization by x-ray and transmission electron microscopy (TEM) revealed the formation of mullite in heat treated precrystallized Nextel 720 fiber at 1204{degrees}C and a coarsening of microstructure above 1204{degrees}C. The degradation of strength in precrystallized Nextel 720 fiber heat treated at 1204{degrees}C/4 h and above may be attributed to phase instability and grain coarsening. Fractographs showed that fracture originated predominantly at the fiber surface.

  3. Texture and Anisotropy of Polycrystalline Piezoelectics

    SciTech Connect

    Jones,J.; Iverson, B.; Bowman, K.

    2007-01-01

    Piezoelectricity is manifested in ferroelectric ceramics by inducing a preferred volume fraction of one ferroelectric domain variant orientation at the expense of degenerate orientations. The piezoelectric effect is therefore largely controlled by the effectiveness of the electrical poling in producing a bias in ferroelectric (180{sup o}) and ferroelastic (non-180{sup o}) domain orientations. Further enhancement of the piezoelectric effect in bulk ceramics can be accomplished by inducing preferred orientation through grain-orientation processes such as hot forging or tape casting that precede the electrical-poling process. Coupled crystal orientation and domain orientation processing yields ceramics with an even greater piezoelectric response. In this paper, preferred orientations of domains and grains in polycrystalline piezoelectric ceramics generated through both domain- and grain-orientation processing are characterized through pole figures and orientation distribution functions obtained using data from a variety of diffraction techniques. The processing methods used to produce these materials and the methods used to evaluate preferred orientation and texture are described and discussed in the context of prior research. Different sample and crystal symmetries are explored across a range of commercial and laboratory-prepared materials. Some of the variables presented in this work include the effects of in situ thermal depoling and the detailed processing parameters used in tape casting of materials with preferred crystallite orientations. Preferred orientation is also correlated with anisotropic properties, demonstrating a clear influence of both grain and domain orientations on piezoelectricity.

  4. Nonlinear alternating current conduction in polycrystalline manganites

    NASA Astrophysics Data System (ADS)

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-01

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1-x -yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1-xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc˜Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf.

  5. Direct integration of a supercapacitor into the backside of a silicon photovoltaic device

    NASA Astrophysics Data System (ADS)

    Westover, Andrew S.; Share, Keith; Carter, Rachel; Cohn, Adam P.; Oakes, Landon; Pint, Cary L.

    2014-05-01

    We demonstrate a route to integrate active material for energy storage directly into a silicon photovoltaic (PV) device, and the synergistic operation of the PV and storage systems for load leveling. Porous silicon supercapacitors with 84% Coulombic efficiency are etched directly into the excess absorbing layer material in a commercially available polycrystalline silicon PV device and coupled with solid-state polymer electrolytes. Our work demonstrates the simple idea both that the PV device can charge the supercapacitor under an external load and that a constant current load can be maintained through periods of intermittent illumination, demonstrating the concept of an all-silicon integrated solar supercapacitor.

  6. Photovoltaic Cell Having A P-Type Polycrystalline Layer With Large Crystals

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes R.

    1996-03-26

    A photovoltaic cell has an n-type polycrystalline layer and a p-type polycrystalline layer adjoining the n-type polycrystalline layer to form a photovoltaic junction. The p-type polycrystalline layer comprises a substantially planar layer portion having relatively large crystals adjoining the n-type polycrystalline layer. The planar layer portion includes oxidized impurities which contribute to obtainment of p-type electrical properties in the planar layer portion.

  7. Mid-infrared silicon pillar waveguides

    NASA Astrophysics Data System (ADS)

    Singh, Neetesh; Hudson, Darren D.; Eggleton, Benjamin J.

    2015-12-01

    In this work silicon pillar waveguides have been proposed to exploit the entire transparent window of silicon. These geometries posses a broad and at dispersion (from 2 to 6 μm) with four zero dispersion wavelengths. We calculate supercontinuum generation spanning over two octaves (2 to >8 μm) with long wavelengths interacting weakly with the lossy substrate. These structures have higher mode confinement in the silicon - away from the substrate, which makes them substrate independent and are promising for exploring new nonlinear phenomena and highly sensitive molecular sensing over the entire silicon's transparency range

  8. Poly-crystalline thin-film by aluminum induced crystallization on aluminum nitride substrate

    NASA Astrophysics Data System (ADS)

    Bhopal, Muhammad Fahad; Lee, Doo Won; Lee, Soo Hong

    2016-07-01

    Thin-film polycrystalline silicon (pc-Si) on foreign (non-silicon) substrates has been researched by various research groups for the production of photovoltaic cells. High quality pc-Si deposition on foreign substrates with superior optical properties is considered to be the main hurdle in cell fabrication. Metal induced crystallization (MIC) is one of the renowned techniques used to produce this quality of material. In the current study, an aluminum induced crystallization (AIC) method was adopted to produce pc-Si thin-film on aluminum nitride (AlN) substrate by a seed layer approach. Aluminum and a-Si layer were deposited using an e-beam evaporator. Various annealing conditions were used in order to investigate the AIC grown pc-Si seed layers for process optimization. The effect of thermal annealing on grain size, defects preferentially crystallographic orientation of the grains were analyzed. Surface morphology was studied using an optical microscope. Poly-silicon film with a crystallinity fraction between 95-100% and an FWHM between 5-6 cm-1 is achievable at low temperatures and for short time intervals. A grain size of about 10 micron can be obtained at a low deposition rate on an AIN substrate. Similarly, Focused ion beam (FIB) also showed that at 425 °C sample B and at 400 °C sample A were fully crystallized. The crystalline quality of pc-Si was evaluated using µ-Raman spectroscopy as a function of annealed conditions and Grazing incidence X-ray diffraction (GIXRD) was used to determine the phase direction of the pc-Si layer. The current study implicates that a poly-silicon layer with good crystallographic orientation and crystallinity fraction is achievable on AIN substrate at low temperatures and short time frames.

  9. Nonlinear alternating current conduction in polycrystalline manganites

    SciTech Connect

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-28

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La{sub 1−x−y}Y{sub y}Ca{sub x}MnO{sub 3} with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn{sub 1−x}Fe{sub x}O{sub 3} with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ{sub 0} by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ{sub 0} up to a certain frequency, known as the onset frequency f{sub c} and increases from Σ{sub 0} as frequency is increased from f{sub c}. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. f{sub c} scales with Σ{sub 0} as f{sub c}∼Σ{sub 0}{sup x{sub f}}, where x{sub f} is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that x{sub f} is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent x{sub f}.

  10. Dip-coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

    NASA Technical Reports Server (NTRS)

    Zook, J. D.; Heaps, J. D.; Maciolek, R. B.; Koepke, B. G.; Gutter, C. D.; Schuldt, S. B.

    1977-01-01

    The objective of this research program is to investigate the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. The past quarter demonstrated significant progress in several areas. Seeded growth of silicon-on-ceramic (SOC) with an EFG ribbon seed was demonstrated. Different types of mullite were successfully coated with silicon. A new method of deriving minority carrier diffusion length, L sub n from spectral response measurements was evaluated. ECOMOD cost projections were found to be in good agreement with the interim SAMIS method proposed by JPL. On the less positive side, there was a decrease in cell performance which we believe to be due to an unidentified source of impurities.

  11. 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.

  12. 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.

  13. Label-Free Direct Detection of miRNAs with Poly-Silicon Nanowire Biosensors

    PubMed Central

    Gong, Changguo; Qi, Jiming; Xiao, Han; Jiang, Bin; Zhao, Yulan

    2015-01-01

    Background The diagnostic and prognostic value of microRNAs (miRNAs) in a variety of diseases is promising. The novel silicon nanowire (SiNW) biosensors have advantages in molecular detection because of their high sensitivity and fast response. In this study, poly-crystalline silicon nanowire field-effect transistor (poly-SiNW FET) device was developed to achieve specific and ultrasensitive detection of miRNAs without labeling and amplification. Methods The poly-SiNW FET was fabricated by a top–down Complementary Metal Oxide Semiconductor (CMOS) wafer fabrication based technique. Single strand DNA (ssDNA) probe was bind to the surface of the poly-SiNW device which was silanated and aldehyde-modified. By comparing the difference of resistance value before and after ssDNA and miRNA hybridization, poly-SiNW device can be used to detect standard and real miRNA samples. Results Poly-SiNW device with different structures (different line width and different pitch) was applied to detect standard Let-7b sample with a detection limitation of 1 fM. One-base mismatched sequence could be distinguished meanwhile. Furthermore, these poly-SiNW arrays can detect snRNA U6 in total RNA samples extracted from HepG2 cells with a detection limitation of 0.2 μg/mL. In general, structures with pitch showed better results than those without pitch in detection of both Let-7b and snRNA U6. Moreover, structures with smaller pitch showed better detection efficacy. Conclusion Our findings suggest that poly-SiNW arrays could detect standard and real miRNA sample without labeling or amplification. Poly-SiNW biosensor device is promising for miRNA detection. PMID:26709827

  14. Polycrystalline Garnet Porphyroblasts, an EBSD Study

    NASA Astrophysics Data System (ADS)

    Seaton, N. C.; Whitney, D. L.; Anderson, C.; Alpert, A.

    2008-12-01

    Polycrystalline garnet porphyroblasts (PGP's) are significant because their formation provides information about metamorphic crystalline mechanisms, in particular during early stages of crystal growth, which may differ from those governing later stages; and because their existence may affect the chemical and structural evolution of metamorphic rocks. For example, the extent of element exchange between the garnet interior and the matrix may be affected by the presence of grain boundaries within PGP's. There have been several previous studies of PGP's but important questions about them remain; e.g. whether early coalescence is a common method by which garnets crystallize, whether grains rotate during growth to attain an energetically favorable grain-grain contact, and whether deformation and/or precursor minerals or other chemical or mechanical heterogeneities influence the formation of PGP's. PGP's have been detected by us in several different localities including; micaschist from SE Vermont (USA), including locality S35j of Rosenfeld (1968); the Solitude Range (British Columbia, Canada); the Southern Menderes Massif (Turkey); and three zones (garnet, staurolite, kyanite) from the Dutchess County Barrovian sequence in NY (USA). We have identified two types of PGP: cryptic and morphologically distinct. Cryptic PGP have no obvious morphological expression of the high angle boundaries within them and appear to be a single crystal. Morphologically distinct PGP have an obvious depression in the outer grain boundary where it is intersected by the internal grain boundary. Most PGP's contain inclusion trails and the high angle grain boundaries crosscut the trend of these as well as the inclusions themselves. PGP also show major element growth zoning that is not influenced by the internal grain boundaries except in rare cases. PGP's comprise ~ 5-35% of the garnet populations analyzed. More than 95% of the PGP's we have analyzed are comprised of 2-3 domains; the rest contain

  15. Polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; Phillips, J. E.; Shafarman, W. N.; Hegedus, S. S.; McCandless, B. E.

    1991-11-01

    Results and conclusions of Phase 1 of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe2 and CdTe solar cells. The kinetics of the formation of CuInSe2 by selenization with hydrogen selenide was investigated and a CuInSe2/Cds solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe2 films and a cell efficiency of 7 percent. Detailed investigations of the open circuit voltage of CuInSe2 solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe2 thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe2 is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10 percent can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm(exp 2) are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  16. Reactive sticking coefficients of silane on silicon

    SciTech Connect

    Buss, R.J.; Ho, P.; Breiland, W.G.; Coltrin, M.E.

    1988-09-15

    Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition rate measurements using molecular beam scattering and a very low pressure cold wall reactor. The RSCs have non-Arrhenius temperature dependences and decreases with increasing flux at low (710/sup 0/) temperatures. A simple model involving dissociative adsorption of silane is consistent with these results. The results are compared with previous studies of the SiH/sub 4//Si(s) reaction.

  17. Sheet silicon cell/module technology

    NASA Technical Reports Server (NTRS)

    Morrison, A. D.

    1983-01-01

    The cost involved in the performance of the standard operations for the manufacture of silicon wafers is insignificant in the case of space photovoltaics applications. It is, however, a decisive factor with respect to terrestrial applications of silicon photovoltaic devices. In 1975, a program was, therefore, begun to develop low cost silicon solar arrays for terrestrial applications. The goal was silicon-based photovoltaic (PV) modules ready for installation at a selling price of $0.50/watt (1975 dollars). Sheet and ribbon silicon growth held out the promise of reduced cost through continuous operation, high material throughput, high material utilization efficiency, and a product whose shape lent itself to the assembly of high packing density modules. Attention is given to ribbon growth technologies, sheet technology generic problems, and ribbon cell and module technology status. It is concluded that the potential for crystalline ribbon silicon appears to be better today than ever before.

  18. Nanotechnology: Its Promise and Challenges

    SciTech Connect

    Vicki Colvin

    2009-05-14

    Vicki Colvin of Rice University talks about how nanotechnology-enabled systems, with dimensions on the scale of a billionth of a meter, offer great promise for solving difficult social problems and creating enormous possibilities.

  19. Recent developments in polycrystalline oxide fiber laser materials: production of Yb-doped polycrystalline YAG fiber

    NASA Astrophysics Data System (ADS)

    Lee, HeeDong; Keller, Kristin; Sirn, Brian; Parthasarathy, Triplicane; Cheng, Michael; Hopkins, Frank K.

    2011-09-01

    Laser quality, polycrystalline oxide fibers offer significant advantages over state-of-the-art silica fiber for high energy lasers. Advanced ceramic processing technology, along with a novel powder production process, has potential to produce oxide fibers with an outstanding optical quality for use in the fiber laser applications. The production of contaminant-free green fibers with a high packing density, as well as uniform packing distribution, is a key factor in obtaining laserquality fibers. High quality green fibers are dependent on the powder quality combined with the appropriate slurry formulation. These two fundamental technologies were successfully developed at UES, and used to produce Yb-doped yttrium aluminum garnet (YAG) fibers with high optical quality, high chemical purity, and suitable core diameters down to 20-30 microns.

  20. A holistic view of crystalline silicon module reliability

    SciTech Connect

    Hanoka, J.I.

    1995-11-01

    Several aspects of module reliability are discussed, particularly with reference to the encapsulant and its interaction with the metallization and interconnection of a module. A need to look at the module as a whole single unit is stressed. Also, the issue of a slight light degradation effect in crystalline silicon cells is discussed. A model for this is mentioned and it may well be that polycrystalline cells with dislocations may have an advantage.

  1. Silicon-on Ceramic Process: Silicon Sheet Growth and Device Development for the Large-area Silicon Sheet and Cell Development Tasks of the Low-cost Solar Array Project

    NASA Technical Reports Server (NTRS)

    Chapman, P. W.; Zook, J. D.; Heaps, J. D.; Grung, B. L.; Koepke, B.; Schuldt, S. B.

    1979-01-01

    The technical and economic feasibility of producing solar cell-quality silicon was investigated. This was done by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. Significant progress in the following areas was demonstrated: (1) fabricating a 10 sq cm cell having 9.9 percent conversion efficiency; (2) producing a 225 sq cm layer of sheet silicon; and (3) obtaining 100 microns thick coatings at pull speed of 0.15 cm/sec, although approximately 50 percent of the layer exhibited dendritic growth.

  2. Submicrometer-wide amorphous and polycrystalline anatase TiO2 waveguides for microphotonic devices.

    PubMed

    Bradley, Jonathan D B; Evans, Christopher C; Choy, Jennifer T; Reshef, Orad; Deotare, Parag B; Parsy, François; Phillips, Katherine C; Lončar, Marko; Mazur, Eric

    2012-10-01

    We demonstrate amorphous and polycrystalline anatase TiO(2) thin films and submicrometer-wide waveguides with promising optical properties for microphotonic devices. We deposit both amorphous and polycrystalline anatase TiO(2) using reactive sputtering and define waveguides using electron-beam lithography and reactive ion etching. For the amorphous TiO(2), we obtain propagation losses of 0.12 ± 0.02 dB/mm at 633 nm and 0.04 ± 0.01 dB/mm at 1550 nm in thin films and 2.6 ± 0.5 dB/mm at 633 nm and 0.4 ± 0.2 dB/mm at 1550 nm in waveguides. Using single-mode amorphous TiO(2) waveguides, we characterize microphotonic features including microbends and optical couplers. We show transmission of 780-nm light through microbends having radii down to 2 μm and variable signal splitting in microphotonic couplers with coupling lengths of 10 μm. PMID:23188347

  3. Reduction of Fermi level pinning and recombination at polycrystalline CdTe surfaces by laser irradiation

    SciTech Connect

    Simonds, Brian J.; Kheraj, Vipul; Palekis, Vasilios; Ferekides, Christos; Scarpulla, Michael A.

    2015-06-14

    Laser processing of polycrystalline CdTe is a promising approach that could potentially increase module manufacturing throughput while reducing capital expenditure costs. For these benefits to be realized, the basic effects of laser irradiation on CdTe must be ascertained. In this study, we utilize surface photovoltage spectroscopy (SPS) to investigate the changes to the electronic properties of the surface of polycrystalline CdTe solar cell stacks induced by continuous-wave laser annealing. The experimental data explained within a model consisting of two space charge regions, one at the CdTe/air interface and one at the CdTe/CdS junction, are used to interpret our SPS results. The frequency dependence and phase spectra of the SPS signal are also discussed. To support the SPS findings, low-temperature spectrally-resolved photoluminescence and time-resolved photoluminescence were also measured. The data show that a modest laser treatment of 250 W/cm{sup 2} with a dwell time of 20 s is sufficient to reduce the effects of Fermi level pinning at the surface due to surface defects.

  4. Silicon material task review

    NASA Technical Reports Server (NTRS)

    Lorenz, J. H.

    1986-01-01

    The objectives of the Flat-plate Solar Array (FSA) Project Silicon Material Task are to evaluate technologies, new and old; to develop the most promising technologies; to establish practicality of the processes to meet production, energy use, and economic criteria; and to develop an information base on impurities in polysilicon and to determine their effects on solar cell performance. The approach involves determining process feasibility, setting milestones for the forced selection of the processes, and establishing the technical readiness of the integrated process.

  5. Compact magnetooptical isolator with cobalt ferrite on silicon photonic circuits

    NASA Astrophysics Data System (ADS)

    Yanaga, Megumi; Shoji, Yuya; Takamura, Yota; Nakagawa, Shigeki; Mizumoto, Tetsuya

    2015-08-01

    In the telecom wavelength range, the magnetooptical effect of cobalt ferrites is approximately 10 times larger than that of conventional magnetooptical materials such as yttrium iron garnets. In this study, we focus on an application of cobalt ferrite to a magnetooptical isolator that is to be miniaturized and made suitable for integration. First, we prepare polycrystalline cobalt ferrite films deposited on a silicon substrate using a MgO buffer layer. Next, we fabricate a waveguide optical isolator of silicon waveguides by the partial deposition of the cobalt ferrite films. An optical isolation ratio of 5.5 dB is demonstrated.

  6. Orientation and Morphology Effects in Rapid Silicon Sheet Solidification

    NASA Technical Reports Server (NTRS)

    Ciszek, T. F.

    1984-01-01

    Radial growth anisotropies and equilibrium forms of point nucleated, dislocation free silicon sheets spreading horizontally on the free surface of a silicon melt were measured for (100), (110), (111), and (112) sheet planes. The growth process was recorded. Qualitative Wulff surface free energy polar plots were deduced from the equilibrium shapes for each sheet plane. Predicted geometries for the tip shape of unidirectional, dislocation free, horizontally grown sheets growing in various directions within the planes were analyzed. Polycrystalline sheets and dendrite propagation were analyzed. For dendrites, growth rates on the order of 2.5 m/min and growth rate anisotropies of 25 are measured.

  7. Silicon nitride/silicon carbide composite powders

    DOEpatents

    Dunmead, Stephen D.; Weimer, Alan W.; Carroll, Daniel F.; Eisman, Glenn A.; Cochran, Gene A.; Susnitzky, David W.; Beaman, Donald R.; Nilsen, Kevin J.

    1996-06-11

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  8. Scaling properties of charge transport in polycrystalline graphene.

    PubMed

    Van Tuan, Dinh; Kotakoski, Jani; Louvet, Thibaud; Ortmann, Frank; Meyer, Jannik C; Roche, Stephan

    2013-04-10

    Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD) growth at random nucleation sites on metallic substrates. The morphology of grain boundaries has become an important topic given its fundamental role in limiting the mobility of charge carriers in polycrystalline graphene, as compared to mechanically exfoliated samples. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We created realistic models of large CVD-grown graphene samples and then computed the corresponding charge carrier mobilities as a function of the average grain size and the coalescence quality between the grains. Our results reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations along grain boundaries. PMID:23448361

  9. Direct-patterned optical waveguides on amorphous silicon films

    DOEpatents

    Vernon, Steve; Bond, Tiziana C.; Bond, Steven W.; Pocha, Michael D.; Hau-Riege, Stefan

    2005-08-02

    An optical waveguide structure is formed by embedding a core material within a medium of lower refractive index, i.e. the cladding. The optical index of refraction of amorphous silicon (a-Si) and polycrystalline silicon (p-Si), in the wavelength range between about 1.2 and about 1.6 micrometers, differ by up to about 20%, with the amorphous phase having the larger index. Spatially selective laser crystallization of amorphous silicon provides a mechanism for controlling the spatial variation of the refractive index and for surrounding the amorphous regions with crystalline material. In cases where an amorphous silicon film is interposed between layers of low refractive index, for example, a structure comprised of a SiO.sub.2 substrate, a Si film and an SiO.sub.2 film, the formation of guided wave structures is particularly simple.

  10. Shielded silicon gate complementary MOS integrated circuit.

    NASA Technical Reports Server (NTRS)

    Lin, H. C.; Halsor, J. L.; Hayes, P. J.

    1972-01-01

    An electrostatic shield for complementary MOS integrated circuits was developed to minimize the adverse effects of stray electric fields created by the potentials in the metal interconnections. The process is compatible with silicon gate technology. N-doped polycrystalline silicon was used for all the gates and the shield. The effectiveness of the shield was demonstrated by constructing a special field plate over certain transistors. The threshold voltages obtained on an oriented silicon substrate ranged from 1.5 to 3 V for either channel. Integrated inverters performed satisfactorily from 3 to 15 V, limited at the low end by the threshold voltages and at the high end by the drain breakdown voltage of the n-channel transistors. The stability of the new structure with an n-doped silicon gate as measured by the shift in C-V curve under 200 C plus or minus 20 V temperature-bias conditions was better than conventional aluminum gate or p-doped silicon gate devices, presumably due to the doping of gate oxide with phosphorous.

  11. Silicon Film[trademark] photovoltaic manufacturing technology

    SciTech Connect

    Bottenberg, W.R.; Hall, R.B.; Jackson, E.L.; Lampo, S.; Mulligan, W.E.; Barnett, A.M. )

    1993-04-01

    This report describes work on a project to develop an advanced low-cost manufacturing process for a new utility-scale flatplate module based on thin active layers of polycrystalline silicon on a low-cost substrate. This is called the Silicon-Film[trademark] process. This new power module is based on a new large solar cell that is 675 cm[sup 2] in area. Eighteen of these solar cells form a 170-W module. Twelve ofthese modules form a 2-kW array. The program has three components: (1) development of a Silicon-Film[trademark] wafer machine that can manufacture wafer 675 cm[sup 2] in size with a total product cost reductionof 70%; (2) development of an advanced solar cell manufacturing process that will turn the Silicon-Film[trademark] wafer into a 14%-efficient solar cell; and (3) development of an advanced module design based on these large-area, efficient silicon solar cells with an average power of 170 watts. The completion of these three tasks will lead to a new power module designed for utility and other power applications with asubstantially lower cost.

  12. Electronic structure of polycrystalline Cd metal using 241Am radioisotope

    NASA Astrophysics Data System (ADS)

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Sharma, B. K.

    2014-04-01

    Electronic structure study of the polycrystalline cadmium metal is reported. The experimental measurement is undertaken on a polycrystalline sheet sample using 59.54 keV radioisotope of 241Am. These results are compared with the ab initio calculations. The theoretical calculations are performed using linear combination of atomic orbitals (LCAO) method employing the density functional theories (DFT) and Hartree-Fock (HF) and augmented plane wave (APW) methods. The spherically averaged APW and LCAO based theoretical Compton profiles are in good agreement with the experimental measurement however the APW based theoretical calculations show best agreement.

  13. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  14. Software optimization for electrical conductivity imaging in polycrystalline diamond cutters

    SciTech Connect

    Bogdanov, G.; Ludwig, R.; Wiggins, J.; Bertagnolli, K.

    2014-02-18

    We previously reported on an electrical conductivity imaging instrument developed for measurements on polycrystalline diamond cutters. These cylindrical cutters for oil and gas drilling feature a thick polycrystalline diamond layer on a tungsten carbide substrate. The instrument uses electrical impedance tomography to profile the conductivity in the diamond table. Conductivity images must be acquired quickly, on the order of 5 sec per cutter, to be useful in the manufacturing process. This paper reports on successful efforts to optimize the conductivity reconstruction routine, porting major portions of it to NVIDIA GPUs, including a custom CUDA kernel for Jacobian computation.

  15. Wavelength-tunable waveguides based on polycrystalline organic-inorganic perovskite microwires.

    PubMed

    Wang, Ziyu; Liu, Jingying; Xu, Zai-Quan; Xue, Yunzhou; Jiang, Liangcong; Song, Jingchao; Huang, Fuzhi; Wang, Yusheng; Zhong, Yu Lin; Zhang, Yupeng; Cheng, Yi-Bing; Bao, Qiaoliang

    2016-03-28

    Hybrid organic-inorganic perovskites have emerged as new photovoltaic materials with impressively high power conversion efficiency due to their high optical absorption coefficient and long charge carrier diffusion length. In addition to high photoluminescence quantum efficiency and chemical tunability, hybrid organic-inorganic perovskites also show intriguing potential for diverse photonic applications. In this work, we demonstrate that polycrystalline organic-inorganic perovskite microwires can function as active optical waveguides with small propagation loss. The successful production of high quality perovskite microwires with different halogen elements enables the guiding of light with different colours. Furthermore, it is interesting to find that out-coupled light intensity from the microwire can be effectively modulated by an external electric field, which behaves as an electro-optical modulator. This finding suggests the promising applications of perovskite microwires as effective building blocks in micro/nano scale photonic circuits. PMID:26508593

  16. Wavelength-tunable waveguides based on polycrystalline organic-inorganic perovskite microwires

    NASA Astrophysics Data System (ADS)

    Wang, Ziyu; Liu, Jingying; Xu, Zai-Quan; Xue, Yunzhou; Jiang, Liangcong; Song, Jingchao; Huang, Fuzhi; Wang, Yusheng; Zhong, Yu Lin; Zhang, Yupeng; Cheng, Yi-Bing; Bao, Qiaoliang

    2016-03-01

    Hybrid organic-inorganic perovskites have emerged as new photovoltaic materials with impressively high power conversion efficiency due to their high optical absorption coefficient and long charge carrier diffusion length. In addition to high photoluminescence quantum efficiency and chemical tunability, hybrid organic-inorganic perovskites also show intriguing potential for diverse photonic applications. In this work, we demonstrate that polycrystalline organic-inorganic perovskite microwires can function as active optical waveguides with small propagation loss. The successful production of high quality perovskite microwires with different halogen elements enables the guiding of light with different colours. Furthermore, it is interesting to find that out-coupled light intensity from the microwire can be effectively modulated by an external electric field, which behaves as an electro-optical modulator. This finding suggests the promising applications of perovskite microwires as effective building blocks in micro/nano scale photonic circuits.

  17. 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.

  18. Monolithic uncooled IR detectors of polycrystalline PbSe: a real alternative

    NASA Astrophysics Data System (ADS)

    Vergara, G.; Gómez, L. J.; Villamayor, V.; Álvarez, M.; Torquemada, M. C.; Rodrigo, M. T.; Verdú, M.; Sánchez, F. J.; Almazán, R. M.; Plaza, J.; Rodriguez, P.; Catalán, I.; Gutierrez, R.; Montojo, M. T.; Serra-Graells, F.; Margarit, J. M.; Terés, L.

    2007-04-01

    Paradoxically more than 50 years after being used in WWII, polycrystalline PbSe technology has turned today into an emerging technology. Without any doubt one of the main facts responsible for the PbSe resurgence is a new method for processing detectors based on a Vapour Phase Deposition (VPD) technique developed at CIDA. Using this method, the first low density 2D PbSe Focal Plane Array (FPA), an x-y addressed type device, was processed on silicon. Even though the last advances have been important they are not yet enough to consider this technology as a real alternative to other uncooled technologies. To reach technical relevance and commercial interest it is obligated to integrate monolithically or hybridize the sensors with their corresponding read out electronics (ROIC). Aiming to process monolithic devices, a proper CMOS read out electronics were designed. In parallel, enabled technologies were developed for adapting the material peculiarities to the CMOS substrates. In this work, the first monolithic device of VPD PbSe is presented. Even though it is a modest 16x16 FPA with a pitch of 200 μm, it represents an important milestone, allocating polycrystalline PbSe among the major players in the short list of uncooled IR detectors. Unlike microbolometers and ferroelectrics, it is a photonic detector suitable for being used as a detector in low cost IR imagers sensitive to the MWIR band and with frame rates as high as 1000 fps. The number of applications is therefore huge, some of them specific, unique and highly demanded in the military and security fields such as sensors applied to fast imagers, Active Protection Systems or low cost seekers.

  19. New Perspectives in Silicon Micro and Nanophotonics

    NASA Astrophysics Data System (ADS)

    Casalino, M.; Coppola, G.; De Stefano, L.; Calio, A.; Rea, I.; Mocella, V.; Dardano, P.; Romano, S.; Rao, S.; Rendina, I.

    2015-05-01

    In the last two decades, there has been growing interest in silicon-based photonic devices for many optical applications: telecommunications, interconnects and biosensors. In this work, an advance overview of our results in this field is presented. Proposed devices allow overcoming silicon intrinsic drawbacks limiting its application as a photonic substrate. Taking advantages of both non-linear and linear effects, size reduction at nanometric scale and new two-dimensional emerging materials, we have obtained a progressive increase in device performance along the last years. In this work we show that a suitable design of a thin photonic crystal slab realized in silicon nitride can exhibit a very strong field enhancement. This result is very promising for all photonic silicon devices based on nonlinear phenomena. Moreover we report on the fabrication and characterization of silicon photodetectors working at near-infrared wavelengths based on the internal photoemission absorption in a Schottky junction. We show as an increase in device performance can be obtained by coupling light into both micro-resonant cavity and waveguiding structures. In addition, replacing metal with graphene in a Schottky junction, a further improve in PD performance can be achieved. Finally, silicon-based microarray for biomedical applications, are reported. Microarray of porous silicon Bragg reflectors on a crystalline silicon substrate have been realized using a technological process based on standard photolithography and electrochemical anodization of the silicon. Our insights show that silicon is a promising platform for the integration of various optical functionalities on the same chip opening new frontiers in the field of low-cost silicon micro and nanophotonics.

  20. Is Technology Fulfilling Its Promise?

    ERIC Educational Resources Information Center

    Weinstein, Margery

    2011-01-01

    Technology has promised trainers so much--from the ability to train distant learners to new ways of keeping young employees engaged. But has it delivered? In this article, several trainers consider whether their investment in training technology has been worth it.

  1. The Promise of Transformative Partnerships

    ERIC Educational Resources Information Center

    Yendol-Hoppey, Diane

    2010-01-01

    The promise, potential, and problems associated with school-university partnerships interested in better preparing teachers for the challenges they face teaching in today's schools rest in educators' ability to actualize transformative practices within partnership contexts. To date, most partnerships have focused on less complex forms of…

  2. The Educational Promise of Logo.

    ERIC Educational Resources Information Center

    Maddux, Cleborne D.

    1984-01-01

    Discussion of Logo use to teach children computer programing covers the educational theory behind Logo, how it differs from other programing languages, its educational promise, its graphics capabilities, Logo research, and different versions available. It is argued that educational computing will succeed only if it provides new ways of teaching.…

  3. Promising Electric Aircraft Drive Systems

    NASA Technical Reports Server (NTRS)

    Dudley, Michael R.

    2010-01-01

    An overview of electric aircraft propulsion technology performance thresholds for key power system components is presented. A weight comparison of electric drive systems with equivalent total delivered energy is made to help identify component performance requirements, and promising research and development opportunities.

  4. America: No Promise Without Agony.

    ERIC Educational Resources Information Center

    Brown, Robert McAfee

    We may discover signs of promise in the midst of agony if we make some shifts of perspective. (1) "Our fear of overt violence must be countered by our acknowledgement of covert violence." Covert violence is subtle and more destructive than physical violence because it is the "denial of personhood"--the insinuation by an act or by neglect that a…

  5. Educating Homeless Students: Promising Practices.

    ERIC Educational Resources Information Center

    Stronge, James H., Ed.; Reed-Victor, Evelyn, Ed.

    This book is for educators who serve homeless students or students temporarily sharing houses with other families. It describes many promising strategies for working with these students. The chapters are: (1) "Educating Homeless Children and Youth: An Introduction" (James H. Stronge); (2) "Meeting the Developmental and Educational Needs of…

  6. Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition.

    PubMed

    Cheng, Qijin; Xu, S; Long, Jidong; Huang, Shiyong; Guo, Jun

    2007-11-21

    Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500 °C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49 at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6 nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films. PMID:21730481

  7. Raman Microscopic Characterization of Proton-Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. L.; Davidson, J. L.; Lance, M. J.

    2004-01-01

    The microstructural effects of irradiating polycrystalline diamond films with proton dosages ranging from 10(exp 15) to 10(exp 17) H(+) per square centimeter was examined. Scanning Electron Microscopy and Raman microscopy were used to examine the changes in the diamond crystalline lattice as a function of depth. Results indicate that the diamond lattice is retained, even at maximum irradiation levels.

  8. Electron transient transport in CdTe polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  9. System of polarization correlometry of biological liquids layers polycrystalline structure

    NASA Astrophysics Data System (ADS)

    Ushenko, A. G.; Boychuk, T. M.; Mincer, O. P.; Angelsky, P. O.; Bodnar, N. B.; Oleinichenko, B. P.; Bizer, L. I.

    2013-09-01

    A model of generalized optical anisotropy of human bile is suggested and a method of polarimetric of the module and phase Fourier of the image of the field of laser radiation is analytically substantiated, that is generated by the mechanisms of linear and circular birefringence of polycrystalline networks with a diagnosis and differentiation of cholelithiasis against a background of chronic cholecystitis.

  10. Anomalous photoelectric effect of a polycrystalline topological insulator film.

    PubMed

    Zhang, Hongbin; Yao, Jiandong; Shao, Jianmei; Li, Hai; Li, Shuwei; Bao, Dinghua; Wang, Chengxin; Yang, Guowei

    2014-01-01

    A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators. PMID:25069391

  11. Amorphous metallic films in silicon metallization systems

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.; Kattelus, H.; So, F.

    1984-01-01

    The general objective was to determine the potential of amorphous metallic thin films as a means of improving the stability of metallic contacts to a silicon substrate. The specific objective pursued was to determine the role of nitrogen in the formation and the resulting properties of amorphous thin-film diffusion barriers. Amorphous metallic films are attractive as diffusion barriers because of the low atomic diffusivity in these materials. Previous investigations revealed that in meeting this condition alone, good diffusion barriers are not necessarily obtained, because amorphous films can react with an adjacent medium (e.g., Si, Al) before they recrystallize. In the case of a silicon single-crystalline substrate, correlation exists between the temperature at which an amorphous metallic binary thin film reacts and the temperatures at which the films made of the same two metallic elements react individually. Amorphous binary films made of Zr and W were investigated. Both react with Si individually only at elevated temperatures. It was confirmed that such films react with Si only above 700 C when annealed in vacuum for 30 min. Amorphous W-N films were also investigated. They are more stable as barriers between Al and Si than polycrystalline W. Nitrogen effectively prevents the W-Al reaction that sets in at 500 C with polycrystalline W.

  12. Polyurethane and silicone: myths and misconceptions.

    PubMed

    Brown, J M

    1995-01-01

    Silicone elastomer has been the standard by which other catheter materials have been judged. In the past ten years, technical advances in polymer research have provided the medical manufacturer with a wide variety of new materials for catheter manufacture. Thermoplastic polyurethane has shown great promise as an alternative to silicone for vascular catheters. This article examines the basic properties of the two materials and describes the findings in the literature that show comparable biocompatibility properties for both materials. PMID:7776066

  13. Wetting and infiltration of nitride bonded silicon nitride by liquid silicon

    NASA Astrophysics Data System (ADS)

    Schneider, V.; Reimann, C.; Friedrich, J.

    2016-04-01

    Nitride bonded silicon nitride (NBSN) is a promising crucible material for the repeated use in the directional solidification of multicrystalline (mc) silicon ingots for photovoltaic applications. Due to wetting and infiltration, however, silicon nitride in its initial state does not offer the desired reusability. In this work the sessile drop method is used to systematically study the wetting and infiltration behavior of NBSN after applying different oxidation procedures. It is found that the wetting of the NBSN crucible by liquid silicon can be prevented by the oxidation of the geometrical surface. The infiltration of liquid silicon into the porous crucible can be suppressed by oxygen enrichment within the volume of the NBSN, i.e. at the pore walls of the crucibles. The realized reusability of the NBSN is demonstrated by reusing a NBSN crucible six times for the directional solidification of undoped multicrystalline silicon ingots.

  14. Fully-depleted, back-illuminated charge-coupled devices fabricated on high-resistivity silicon

    SciTech Connect

    Holland, Stephen E.; Groom, Donald E.; Palaio, Nick P.; Stover, Richard J.; Wei, Mingzhi

    2002-03-28

    Charge-coupled devices (CCD's) have been fabricated on high-resistivity silicon. The resistivity, on the order of 10,000 {Omega}-cm, allows for depletion depths of several hundred microns. Fully-depleted, back-illuminated operation is achieved by the application of a bias voltage to a ohmic contact on the wafer back side consisting of a thin in-situ doped polycrystalline silicon layer capped by indium tin oxide and silicon dioxide. This thin contact allows for good short wavelength response, while the relatively large depleted thickness results in good near-infrared response.

  15. Silicon microdosimetry.

    PubMed

    Agosteo, Stefano; Pola, Andrea

    2011-02-01

    Silicon detectors are being studied as microdosemeters since they can provide sensitive volumes of micrometric dimensions. They can be applied for assessing single-event effects in electronic instrumentation exposed to complex fields around high-energy accelerators or in space missions. When coupled to tissue-equivalent converters, they can be used for measuring the quality of radiation therapy beams or for dosimetry. The use of micrometric volumes avoids the contribution of wall effects to the measured spectra. Further advantages of such detectors are their compactness, cheapness, transportability and a low sensitivity to vibrations. The following problems need to be solved when silicon devices are used for microdosimetry: (i) the sensitive volume has to be confined in a region of well-known dimensions; (ii) the electric noise limits the minimum detectable energy; (iii) corrections for tissue-equivalency should be made; (iv) corrections for shape equivalency should be made when referring to a spherical simulated site of tissue; (v) the angular response should be evaluated carefully; (vi) the efficiency of a single detector of micrometric dimensions is very poor and detector arrays should be considered. Several devices have been proposed as silicon microdosemeters, based on different technologies (telescope detectors, silicon on insulator detectors and arrays of cylindrical p-n junctions with internal amplification), in order to satisfy the issues mentioned above. PMID:21112892

  16. The promise of quantum simulation

    DOE PAGESBeta

    Muller, Richard P.; Blume-Kohout, Robin

    2015-07-21

    In this study, quantum simulations promise to be one of the primary applications of quantum computers, should one be constructed. This article briefly summarizes the history of quantum simulation in light of the recent result of Wang and co-workers, demonstrating calculation of the ground and excited states for a HeH+ molecule, and concludes with a discussion of why this and other recent progress in the field suggest that quantum simulations of quantum chemistry have a bright future.

  17. The promise of quantum simulation

    SciTech Connect

    Muller, Richard P.; Blume-Kohout, Robin

    2015-07-21

    In this study, quantum simulations promise to be one of the primary applications of quantum computers, should one be constructed. This article briefly summarizes the history of quantum simulation in light of the recent result of Wang and co-workers, demonstrating calculation of the ground and excited states for a HeH+ molecule, and concludes with a discussion of why this and other recent progress in the field suggest that quantum simulations of quantum chemistry have a bright future.

  18. The Promise of Quantum Simulation.

    PubMed

    Muller, Richard P; Blume-Kohout, Robin

    2015-08-25

    Quantum simulations promise to be one of the primary applications of quantum computers, should one be constructed. This article briefly summarizes the history of quantum simulation in light of the recent result of Wang and co-workers, demonstrating calculation of the ground and excited states for a HeH(+) molecule, and concludes with a discussion of why this and other recent progress in the field suggest that quantum simulations of quantum chemistry have a bright future. PMID:26197037

  19. Thermodynamics of Volatile Silicon Hydroxides Studied

    NASA Technical Reports Server (NTRS)

    Copland, Evan H.; Opila, Elizabeth J.; Jacobson, Nathan S.

    2001-01-01

    Silicon-based ceramics are promising candidate structural materials for heat engines. The long-term stability of these materials to environmental degradation is dependent on the formation and retention of a protective SiO2 layer. It is well known that SiO2 forms stable volatile hydroxides in the presence of water vapor at elevated temperatures. Combustion conditions, which characteristically are at high velocities, contain significant water vapor pressures, and high temperatures tend to promote continuous formation of these hydroxides with resulting material degradation. For the degradation of silicon-based ceramics to be predicted, accurate thermodynamic data on the formation of silicon hydroxides are needed.

  20. Refining of metallurgical-grade silicon

    NASA Technical Reports Server (NTRS)

    Dietl, J.

    1986-01-01

    A basic requirement of large scale solar cell fabrication is to provide low cost base material. Unconventional refining of metallurical grade silicon represents one of the most promising ways of silicon meltstock processing. The refining concept is based on an optimized combination of metallurgical treatments. Commercially available crude silicon, in this sequence, requires a first pyrometallurgical step by slagging, or, alternatively, solvent extraction by aluminum. After grinding and leaching, high purity qualtiy is gained as an advanced stage of refinement. To reach solar grade quality a final pyrometallurgical step is needed: liquid-gas extraction.

  1. Silicon surface passivation by silicon nitride deposition

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.

    1984-01-01

    Silicon nitride deposition was studied as a method of passivation for silicon solar cell surfaces. The following three objectives were the thrust of the research: (1) the use of pecvd silicon nitride for passivation of silicon surfaces; (2) measurement techniques for surface recombination velocity; and (3) the importance of surface passivation to high efficiency solar cells.

  2. Microcrystalline silicon and micromorph tandem solar cells

    NASA Astrophysics Data System (ADS)

    Keppner, H.; Meier, J.; Torres, P.; Fischer, D.; Shah, A.

    ``Micromorph'' tandem solar cells consisting of a microcrystalline silicon bottom cell and an amorphous silicon top cell are considered as one of the most promising new thin-film silicon solar-cell concepts. Their promise lies in the hope of simultaneously achieving high conversion efficiencies at relatively low manufacturing costs. The concept was introduced by IMT Neuchâtel, based on the VHF-GD (very high frequency glow discharge) deposition method. The key element of the micromorph cell is the hydrogenated microcrystalline silicon bottom cell that opens new perspectives for low-temperature thin-film crystalline silicon technology. According to our present physical understanding microcrystalline silicon can be considered to be much more complex and very different from an ideal isotropic semiconductor. So far, stabilized efficiencies of about 12% (10.7% independently confirmed) could be obtained with micromorph solar cells. The scope of this paper is to emphasize two aspects: the first one is the complexity and the variety of microcrystalline silicon. The second aspect is to point out that the deposition parameter space is very large and mainly unexploited. Nevertheless, the results obtained are very encouraging and confirm that the micromorph concept has the potential to come close to the required performance criteria concerning price and efficiency.

  3. Manufacturing technologies for photovoltaics and possible means of their development in Russia (Review). Part 1: General approach to the development of photoelectric converters and basic silicon technologies

    NASA Astrophysics Data System (ADS)

    Tarasenko, A. B.; Popel', O. S.

    2015-11-01

    The state and key tendencies of the development of basic technologies for manufacture of photoelectric converters (PECs) in the world are considered, and their advantages and disadvantages are discussed. The first part of the review gives short information on the development of photovoltaics in the world and planes of the development of solar power plants in Russia. Total power of photoelectric plants operating in various countries in 2015 exceeded 150 GW and increased in the last ten years with a rate of approximately 50% per year. Russia made important state decisions on the support of the development of renewable power engineering and developed mechanisms, which were attractive for business, on the stimulation of building of the network of solar power plants with a total power to 1.5 GW in the country to 2020. At the same time, the rigid demands are made with respect to the localization of the production of components of these plants that opens new abilities for the development of the domestic production of photovoltaics manufacture. Data on the efficiency of PECs of various types that are attained in the leading laboratories of the world are given. Particular emphasis has been placed on the consideration of basic silicon technologies of PEC manufacture, which had the widest commercial application. The basic methods for production of polycrystalline silicon and making single-crystal and multicrystal silicon are described. Fundamentals of making techniques for plates, PECs, and photoelectric modules based on single-crystal and polycrystalline silicon are considered. The second part will be devoted to modifications of manufacturing techniques for photoelectric converters, enhancement methods for contact structures, and recommendations of authors with respect to the choice of prospective technologies for the expansion of PEC production in Russia. It will involve formulations and substantiations of the most promising lines of the development of photoelectric

  4. Epitaxy of silicon carbide on silicon: Micromorphological analysis of growth surface evolution

    NASA Astrophysics Data System (ADS)

    Shikhgasan, Ramazanov; Ştefan, Ţălu; Dinara, Sobola; Sebastian, Stach; Guseyn, Ramazanov

    2015-10-01

    The main purpose of our research was the study of evolution of silicon carbide films on silicon by micromorphological analysis. Surface micromorphologies of Silicon Carbide epilayers with two different thicknesses were compared by means of fractal geometry. Silicon Carbide films were prepared on Si substrates by magnetron sputtering of polycrystalline target SiC in Ar atmosphere (99.999% purity). Synthesis of qualitative SiC/Si templates solves the questions of large diameter SiC single-crystal wafers formation. This technology decreases financial expenditure and provides integration of SiC into silicon technology. These hybrid substrates with buffer layer of high oriented SiC are useful for growth of both wide band gap materials (SiC, AlN, GaN) and graphene. The main problem of SiC heteroepitaxy on Si (1 1 1) is the large difference (∼20%) of the lattice parameters. Fractal analysis of surface morphology of heteroepitaxial films could help to understand the films growth mechanisms. The 3D (three-dimensional) surfaces revealed a fractal structure at the nanometer scale. The fractal dimension (D) provided global quantitative values that characterize the scale properties of surface geometry.

  5. Carbonitriding of silicon using plasma focus device

    SciTech Connect

    Jabbar, S.; Khan, I. A.; Ahmad, R.; Zakaullah, M.; Pan, J. S.

    2009-03-15

    Carbonitride thin films have been deposited on silicon substrate by the irradiation of energetic nitrogen ions emanated from dense plasma focus device. The carbon ions are ablated by the irradiation of relativistic electrons from the insert material (graphite) placed at the anode tip. The x-ray diffraction analysis demonstrates that a polycrystalline thin film consisting of various compounds such as Si{sub 3}N{sub 4}, SiC, and C{sub 3}N{sub 4} is formed on the silicon (100) substrate. Crystallinity of different compounds decreases with the increase in angular positions (0 deg., 10 deg., and 20 deg. ). Raman spectroscopy shows the appearance of graphitic and disordered bands with silicon nitride and silicon carbide indicating the formation of carbonitride. Raman spectra also indicate that broadening of bands increases with the increase in focus deposition shots, leading to the amorphization of the thin film. The amorphization of the thin films depends on the ion energy flux as well as on the sample angular position. The scanning electron microscopy exhibits the damaging of the substrate surface at 0 deg. angular position. The microstructure shows the tubular shape for higher ion dose (40 focus shots). At 10 deg. angular position, a two phase phenomenon is observed with the ordered phase in the solid solution. A smooth and uniform surface morphology showing a small cluster is observed for the 20 deg. angular position.

  6. Increased medium-range order in amorphous silicon with increased substrate temperature

    SciTech Connect

    Voyles, P. M.; Gerbi, J. E.; Treacy, M. M. J.; Gibson, J. M.; Aberlson, J. R.

    2000-08-15

    Using fluctuation electron microscopy, the authors have measured the medium-range order of magnetron sputtered silicon thin films as a function of substrate temperature from the amorphous to polycrystalline regimes. They find a smooth increase in the medium-range order of the samples, which they interpret in the context of the paracrystalline structural model as an increase in the size of and/or volume fraction occupied by the paracrystalline grains. These data are counter to the long-standing belief that there is a sharp transition between amorphous and polycrystalline structures as a function of substrate temperature.

  7. [Study on the micro-infrared spectra and origin of polycrystalline diamonds from Mengyin kimberlite pipes].

    PubMed

    Yang, Zhi-Jun; Liang, Rong; Zeng, Xiang-Qing; Ge, Tie-Yan; Ai, Qun; Zheng, Yun-Long; Peng, Ming-Sheng

    2012-06-01

    The natural polycrystalline diamonds from the Mengyin kimberlite pipes can be classified as the euhedral faceted polycrystalline diamonds and anhedral rounded polycrystalline diamonds. The results of micro-FTIR spectra characterization of the polycrystalline diamonds show that the concentration of nitrogen is low, varying from 16.69 to 72.81 microgram per gram and is different among different diamond grains or position in polycrystalline diamonds. The euhedral faceted polycrystalline diamonds are Ia AB type and have higher concentration of A-center defects than B-center defects. Most of the anhedral rounded polycrystalline diamonds are Ia AB type and have higher content of B-center defects. A minority of the anhedral rounded polycrystalline diamonds have C-center, A-center and B-center defects simultaneously. The polycrystalline diamonds probably originated from the relatively deeper mantle and were not formed in diamond nucleation stage, but in the diamond growth period or some special conditions after the diamond grains were formed already. Furthermore, the euhedral faceted polycrystalline diamonds were formed slightly later and the anhedral rounded polycrystalline diamonds were formed obviously earlier than the diamond single crystals from the Mengyin kimberlite pipes. PMID:22870630

  8. Thermoelastic micromechanical stresses associated with a large alpha-silicon carbide grain in a polycrystalline beta-silicon carbide matrix

    NASA Technical Reports Server (NTRS)

    Li, Zhuang; Bradt, Richard C.

    1989-01-01

    The thermoelastic micromechanical stresses associated with a single large hexagonal alpha-SiC grain within a fine-grain-size cubic (3C) beta-SiC matrix were calculated. The naturally occurring residual stresses which are created during cooling from the processing temperatures and the effects of superimposed applied external stresses are both considered. A significant effect of the shape or geometry of the alpha-SiC grain is revealed, with the largest residual stresses associated with the naturally occurring tabular or platelet structure. The stresses are compared with the published strength results for these materials, which suggests that the residual stresses assume a significant role in the strength reduction that is observed.

  9. Slicing of single crystal and polycrystalline silicon ingots using multi-blade saws

    NASA Technical Reports Server (NTRS)

    Ross, J. B.

    1980-01-01

    Optimization of the Multi-Blade Slurry wafering technique was evaluated. Several wafering runs were made. Sufficient data necessary for a complete cost analysis of each of the three types of saw utilized are provided.

  10. Large gauge factor of hot wire chemical vapour deposition in-situ boron doped polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Grech, David; Tarazona, Antulio; De Leon, Maria Theresa; Kiang, Kian S.; Zekonyte, Jurgita; Wood, Robert J. K.; Chong, Harold M. H.

    2016-04-01

    Polysilicon piezoresistors with a large longitudinal gauge factor (GF) of 44 have been achieved using in-situ boron doped hot-wire chemical vapour deposition (HWCVD). This GF is a consequence of a high quality p-type doped polysilicon with a crystal volume of 97% and an average grain size of 150 nm, estimated using Raman spectroscopy and atomic force microscopy (AFM) respectively. The measured minimum Hooge factor associated to the 1/f noise of the polysilicon piezoresistors is 1.4 × 10‑3. These results indicate that HWCVD polysilicon is a suitable piezoresistive material for micro-electro-mechanical systems (MEMS) applications.

  11. Electrothermal actuators fabricated in four-level planarized surface-miromachined polycrystalline silicon

    SciTech Connect

    Comtois, J.H.; Michalicek, A.; Barron, C.C.

    1997-11-01

    This paper presents the results of tests performed on a variety of electrochemical microactuators and arrays of these actuators fabricated in the SUMMiT process at the U.S. Department of Energy`s Sandia National Laboratories. These results are intended to aid designers of thermally actuated mechanisms, and they apply to similar actuators made in other polysilicon MEMS processes such as the MUMPS process. Measurements include force and deflection versus input power, maximum operating frequency, effects of long term operation, and ideal actuator and array geometries for different applications` force requirements. Also, different methods of arraying these actuators together are compared. It is found that a method using rotary joints, enabled by the advanced features of the SUMMiT fabrication process, is the most efficient array design. The design and operation of a thermally actuated stepper motor is explained to illustrate a useful application of these arrays.

  12. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    NASA Astrophysics Data System (ADS)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  13. Thin film poly-crystalline silicon fabrication based on Rapid Thermal Annealing (RTA) process

    NASA Astrophysics Data System (ADS)

    Qian, Jun; Li, Jirong; Liao, Yang; Shi, Weimin; Kuang, Huahui; Ming, Xiuchun; Liu, Jin; Jin, Jing; Qin, Juan

    2013-12-01

    Rapid Thermal Annealing (RTA) process was introduced to the experiment of Aluminum-induced crystallization of a-Si, based on sputtering method, on low cost glass substrate. A stack of glass/Al (150 nm)/Si (220 nm) was deposited by sputtering sequentially. Samples were annealed under RTA process, then annealed in the tube annealing furnace at 400 °C for 5 h. The grain crystallization was inspected by optical microscopy (OM), ,Raman spectroscopy, X-ray diffraction (XRD),and energy dispersive spectroscopy (EDS). The preferential orientation (111) was observed, with a Raman Peak at 520.8cm-1, Different annealing periods were discussed.

  14. X-ray measurements of stresses and defects in EFG and large grained polycrystalline silicon ribbons

    NASA Technical Reports Server (NTRS)

    Wagner, C. N. J.

    1979-01-01

    The Bond method was employed to measure the lattice parameter in an area of 0.4 mm in diameter of EFG Si-ribbons to an accuracy of + or - 0.00008 A. A Bond goniometer was built which included a goniostat with a special specimen holder to mount ribbons 1 m in length and 75 mm in width which could be rotated about two orthogonal axes, and a Leitz microscope for precision alignment of a particular area into the center of the goniostat and the small primary X-ray beam. The (321) planes were found to be parallel to the surface of the ribbons with an angular spread of about 15 deg. The poles of the (111) planes clustered about an angle of 25 deg away from the surface normal, again with a spread of 10 deg. The lattice parameter of a small piece of ribbon material was found to be a sub o = 5.43075 A. A maximum stress of 115 MPa was observed in a fractured ribbon which corresponded to the fracture stress of single crystals of Si.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  16. Investigation of photovoltaic mechanisms in polycrystalline thin-film solar cells. Interim technical report, November 1, 1980-July 31, 1981

    SciTech Connect

    Temofonte, T. A.; Szedon, J. R.; O'Keeffe, T. W.

    1982-03-05

    Effort is reported on measurement technique development to assess the utility of Deep-Level Transient Spectroscopy (DLTS) methods in characterizing polycrystalline silicon that was deliberately doped with Ti during growth. Difficulties encountered with lateral DLTS measurements are discussed. In this approach, modulation of the grain boundary, double-depletion region produces the entire DLTS signal. Major effort has been applied in grain boundary characterization and control. The most significant accomplishments to date have involved laser scanning of slices of Wacker SILSO polysilicon having nearly identical grain structure. By using various kinds of treatments and by comparing treated and untreated substrates having nearly identical grain structure, control of grain boundary photocurrent suppression (..delta..I/sub ph/) over the range 1% less than or equal to ..delta..I/sub ph/ less than or equal to 40% was demonstrated.

  17. Polycrystalline InN thin films prepared by ion-beam-assisted filtered cathodic vacuum arc technique

    NASA Astrophysics Data System (ADS)

    Ji, X. H.; Lau, S. P.

    2005-09-01

    We report on the fabrication of indium nitride (InN) thin films on silicon (1 0 0) substrates by radio frequency ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The effects of nitrogen ion energy on the structural properties of InN films have been investigated by X-ray diffraction and Raman spectroscopy. The InN films exhibit polycrystalline wurtzite structure. At nitrogen ion energy of 100 eV, the film shows preferred (0 0 0 2) orientation. The preferred orientation is changed to ( 1 0 1¯ 1) when the nitrogen ion energy is more than 100 eV. Three Raman-active optical phonons have been clearly identified and assigned to A 1(LO) at ˜588 cm -1, E22 at ˜490 cm -1 and A 1(TO) at ˜449 cm -1 of InN films, which confirmed the hexagonal structure of InN.

  18. Mechanical instability of monocrystalline and polycrystalline methane hydrates.

    PubMed

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T; Kjelstrup, Signe; Vlugt, Thijs J H; He, Jianying; Skallerud, Bjørn H; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  19. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

    2014-03-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

  20. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    NASA Astrophysics Data System (ADS)

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-11-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments.

  1. Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

    SciTech Connect

    Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.; Lee, Michael V.; Qi, Yabing; Joo Shin, Tae; Ahn, Docheon; Lee, Han-Koo; Baik, Jaeyoon; Shin, Hyun-Joon

    2015-03-15

    Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

  2. Compton profile study of polycrystalline ZnBr{sub 2}

    SciTech Connect

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Kothari, R. K.; Sharma, B. K.

    2010-12-01

    The first ever Compton profile study of polycrystalline ZnBr{sub 2} is presented in this paper. The measurement of polycrystalline sample of ZnBr{sub 2} is performed using 59.54 keV gamma-rays emanating from an {sup 241}Am radioisotope. Theoretical calculations are performed following the Ionic model calculations for a number of configurations Zn{sup +x}Br{sub 2}{sup -x/2}(0.0{<=}x{<=}2.0 in step of 0.5) utilizing free atom profiles. The ionic model suggest transfer of 2.0 electrons from 4 s state of Zn to 4 p state of two Br atoms. The autocorrelation function B(z) is also derived from experiment and the most favoured ionic valence Compton profiles.

  3. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy

    PubMed Central

    Schmid, T.; Schäfer, N.; Levcenko, S.; Rissom, T.; Abou-Ras, D.

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  4. Further development and application of polycrystalline metal whiskers

    NASA Technical Reports Server (NTRS)

    Schladitz, H. J.

    1979-01-01

    High strength metal whiskers have a larger versatile field of application than monocrystalline whiskers. Although polycrystalline metal whiskers can be used for composites, preferably by extrusion in thermoplastics or by infiltration of resins or metals into whisker networks, the chief application at present may be the production and various use of whisker networks. Such networks can be produced up to high degrees of porosity and besides high mechanical strength, they have high inside surfaces and high electric conductivity. There are for instance, applications concerning construction of electrodes for batteries and fuel cells, catalysts and also new heat-exchanger material, capable of preparing fuel oil and gasoline in order to assist a high-efficiency combustion. The technical application of polycrystalline metal whiskers require their modification as well as the construction of a pilot production unit.

  5. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    PubMed Central

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  6. Boron doped polycrystalline diamond films for strain sensing applications

    SciTech Connect

    Wur, D.; Davidson, J.L.; Kang, W.P.

    1995-12-31

    It has been recently established in our work and others that boron-doped polycrystalline diamond films (PDF) have piezoresistivity (PZR). This property opens PDF to the field of sensor applications using strain sensing. Polycrystalline diamond films have been prepared with microwave plasma enhanced chemical vapor deposition (CVD) method and boron-doped to p-type semiconductors. In addition, by combining the piezoresistive effect in doped PDF and the insulating property of undoped PDF, whereby doped diamond resistors reside on a dielectric diamond substrate diaphragm, a monolithic all-diamond microstructure for examining the strain response of patterned p-doped diamond PZRs was fabricated and characterized. This work examines some critical issues of diamond for strain sensing applications such as its rupture stress and edge stress of diamond diaphragm and the high temperature responses of a diamond strain sensor.

  7. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-01-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  8. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy.

    PubMed

    Schmid, T; Schäfer, N; Levcenko, S; Rissom, T; Abou-Ras, D

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  9. Theranos phenomenon: promises and fallacies.

    PubMed

    Diamandis, Eleftherios P

    2015-06-01

    Recently, spectacular advances in diagnostic technologies, genomics, etc. offer unprecedented opportunities for widespread testing of asymptomatic individuals, in the hope that this testing will unravel early disease signs which could lead to preventative or more effective therapeutic measures. In particular, one commercial organization, Theranos, promises to revolutionize diagnostics by offering multi-analyte testing at low prices in commercial outlets, thus challenging the current paradigm of targeted and centralized diagnostic testing. In this paper, I analyze the Theranos technology and their promises, and contrast this information with the currently used technologies, to show that most of the company's claims are exaggerated. While it remains to be seen if this technology will revolutionize diagnostics, in this Opinion Paper, I also draw attention of associated issues, such as self-testing and self-interpretation of results, over-testing, over-diagnosis and over-treatment, along with their associated harms. As the public is bombarded daily with new and revolutionary health-related advances, it is time to balance the enthusiasm of the seemingly obvious huge gains, by also explaining the associated possible harms. PMID:26030792

  10. Oscillation of structure characteristics in polycrystalline nickel during plastic deformation

    SciTech Connect

    Dvorovienko, N.A.; Gernov, S.A.; Sirenko, A.F. . Dept. of Solid State Physics); Hamana, D. . Research Unit of Materiale Physic)

    1993-07-01

    The variation of X-ray diffraction characteristics (breadth at half maximum intensity, integrated intensity, dislocation density and residual stresses), as a function of plastic deformation rate, which occurs by uniaxial tensile test, has been studied. At room temperature the observed oscillation of studied characteristics in deformed polycrystalline nickel is due to the deformation mechanism change. The latter can be a translational displacement due to dislocations or a rotational displacement due to disclination.

  11. A characterization study of a hydroxylated polycrystalline tin oxide surface

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.; Grogan, Austin L., Jr.; Asbury, Douglas A.; Schryer, David R.

    1989-01-01

    In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

  12. Photoluminescence of polycrystalline ZnO under different annealing conditions

    NASA Astrophysics Data System (ADS)

    Hur, Tae-Bong; Jeen, Gwang Soo; Hwang, Yoon-Hwae; Kim, Hyung-Kook

    2003-11-01

    We investigated polycrystalline zinc oxide (ZnO) with different annealing conditions in air by x-ray photoelectron spectroscopy and photoluminescence. We found that the concentration of antisite oxide (OZn) increases when ZnO ceramics were in an O-rich condition. As the concentration of antisite oxide (OZn) increased, the photoluminescence intensity of the green band emission increased. The crossover temperature of the free and bound excitons was roughly estimated as 100 K.

  13. Polycrystalline organic thin film transistors for advanced chemical sensing

    NASA Astrophysics Data System (ADS)

    Torsi, Luisa; Tanese, Maria C.; Cioffi, Nicola; Sabbatini, Luigia; Zambonin, Pier G.

    2003-11-01

    Organic thin-film transistors have seen a dramatic improvement of their performance in the last decade. They have been also proposed as gas sensors. This paper deals with the interesting new aspects that polycrystalline based conducting polymer transistors present when operated as chemical sensors. Such devices are capable to deliver multi-parameter responses that are also extremely repeatable and fast at room temperature. Interesting are also the perspectives for their use as chemically selective devices in array type sensing systems.

  14. Silicon-on ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project

    NASA Technical Reports Server (NTRS)

    Grung, B. L.; Heaps, J. D.; Schmit, F. M.; Schuldt, S. B.; Zook, J. D.

    1981-01-01

    The technical feasibility of producing solar-cell-quality sheet silicon to meet the Department of Energy (DOE) 1986 overall price goal of $0.70/watt was investigated. With the silicon-on-ceramic (SOC) approach, a low-cost ceramic substrate is coated with large-grain polycrystalline silicon by unidirectional solidification of molten silicon. This effort was divided into several areas of investigation in order to most efficiently meet the goals of the program. These areas include: (1) dip-coating; (2) continuous coating designated SCIM-coating, and acronym for Silicon Coating by an Inverted Meniscus (SCIM); (3) material characterization; (4) cell fabrication and evaluation; and (5) theoretical analysis. Both coating approaches were successful in producing thin layers of large grain, solar-cell-quality silicon. The dip-coating approach was initially investigated and considerable effort was given to this technique. The SCIM technique was adopted because of its scale-up potential and its capability to produce more conventiently large areas of SOC.

  15. Silicene, a promising new 2D material

    NASA Astrophysics Data System (ADS)

    Oughaddou, Hamid; Enriquez, Hanna; Tchalala, Mohammed Rachid; Yildirim, Handan; Mayne, Andrew J.; Bendounan, Azzedine; Dujardin, Gérald; Ait Ali, Mustapha; Kara, Abdelkader

    2015-02-01

    Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies were the first to predict a puckered honeycomb structure with electronic properties resembling those of graphene. Though these studies were for free-standing silicene, experimental fabrication of silicene has been achieved so far only through epitaxial growth on crystalline surfaces. Indeed, it was only in 2010 that researchers presented the first experimental evidence of the formation of silicene on Ag(1 1 0) and Ag(1 1 1), which has launched silicene in a similar way to graphene. This very active field has naturally led to the recent growth of silicene on Ir(1 1 1), ZrB2(0 0 0 1) and Au(1 1 0) substrates. However, the electronic properties of epitaxially grown silicene on metal surfaces are influenced by the strong silicene-metal interactions. This has prompted experimental studies of the growth of multi-layer silicene, though the nature of its "silicene" structure remains questionable. Of course, like graphene, synthesizing free-standing silicene represents the ultimate challenge. A first step towards this has been reported recently through chemical exfoliation from calcium disilicide (CaSi2). In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries.

  16. Field-effect electroluminescence in silicon nanocrystals.

    PubMed

    Walters, Robert J; Bourianoff, George I; Atwater, Harry A

    2005-02-01

    There is currently worldwide interest in developing silicon-based active optical components in order to leverage the infrastructure of silicon microelectronics technology for the fabrication of optoelectronic devices. Light emission in bulk silicon-based devices is constrained in wavelength to infrared emission, and in efficiency by the indirect bandgap of silicon. One promising strategy for overcoming these challenges is to make use of quantum-confined excitonic emission in silicon nanocrystals. A critical challenge for silicon nanocrystal devices based on nanocrystals embedded in silicon dioxide has been the development of a method for efficient electrical carrier injection. We report here a scheme for electrically pumping dense silicon nanocrystal arrays by a field-effect electroluminescence mechanism. In this excitation process, electrons and holes are both injected from the same semiconductor channel across a tunnelling barrier in a sequential programming process, in contrast to simultaneous carrier injection in conventional pn-junction light-emitting-diode structures. Light emission is strongly correlated with the injection of a second carrier into a nanocrystal that has been previously programmed with a charge of the opposite sign. PMID:15665836

  17. Grain boundary engineering for improved thin silicon photovoltaics.

    PubMed

    Raghunathan, Rajamani; Johlin, Eric; Grossman, Jeffrey C

    2014-09-10

    In photovoltaic devices, the bulk disorder introduced by grain boundaries (GBs) in polycrystalline silicon is generally considered to be detrimental to the physical stability and electronic transport of the bulk material. However, at the extremum of disorder, amorphous silicon is known to have a beneficially increased band gap and enhanced optical absorption. This study is focused on understanding and utilizing the nature of the most commonly encountered Σ3 GBs, in an attempt to balance incorporation of the advantageous properties of amorphous silicon while avoiding the degraded electronic transport of a fully amorphous system. A combination of theoretical methods is employed to understand the impact of ordered Σ3 GBs on the material properties and full-device photovoltaic performance. PMID:24963798

  18. Subsurface damage of single crystalline silicon carbide in nanoindentation tests.

    PubMed

    Yan, Jiwang; Gai, Xiaohui; Harada, Hirofumi

    2010-11-01

    The response of single crystalline silicon carbide (SiC) to a Berkovich nanoindenter was investigated by examining the indents using a transmission electron microscope and the selected area electron diffraction technique. It was found that the depth of indentation-induced subsurface damage was far larger than the indentation depth, and the damaging mechanism of SiC was distinctly different from that of single crystalline silicon. For silicon, a broad amorphous region is formed underneath the indenter after unloading; for SiC, however, no amorphous phase was detected. Instead, a polycrystalline structure with a grain size of ten nanometer level was identified directly under the indenter tip. Micro cracks, basal plane dislocations and possible cross slips were also found around the indent. These finding provide useful information for ultraprecision manufacturing of SiC wafers. PMID:21138038

  19. Mechanical properties of irradiated multi-phase polycrystalline BCC materials

    NASA Astrophysics Data System (ADS)

    Song, Dingkun; Xiao, Xiazi; Xue, Jianming; Chu, Haijian; Duan, Huiling

    2015-04-01

    Structure materials under severe irradiations in nuclear environments are known to degrade because of irradiation hardening and loss of ductility, resulting from irradiation-induced defects such as vacancies, interstitials and dislocation loops, etc. In this paper, we develop an elastic-viscoplastic model for irradiated multi-phase polycrystalline BCC materials in which the mechanical behaviors of individual grains and polycrystalline aggregates are both explored. At the microscopic grain scale, we use the internal variable model and propose a new tensorial damage descriptor to represent the geometry character of the defect loop, which facilitates the analysis of the defect loop evolutions and dislocation-defect interactions. At the macroscopic polycrystal scale, the self-consistent scheme is extended to consider the multiphase problem and used to bridge the individual grain behavior to polycrystal properties. Based on the proposed model, we found that the work-hardening coefficient decreases with the increase of irradiation-induced defect loops, and the orientation/loading dependence of mechanical properties is mainly attributed to the different Schmid factors. At the polycrystalline scale, numerical results for pure Fe match well with the irradiation experiment data. The model is further extended to predict the hardening effect of dispersoids in oxide-dispersed strengthened steels by the considering the Orowan bowing. The influences of grain size and irradiation are found to compete to dominate the strengthening behaviors of materials.

  20. Physics of grain boundaries in polycrystalline photovoltaic semiconductors

    SciTech Connect

    Yan, Yanfa Yin, Wan-Jian; Wu, Yelong; Shi, Tingting; Paudel, Naba R.; Li, Chen; Poplawsky, Jonathan; Wang, Zhiwei; Moseley, John; Guthrey, Harvey; Moutinho, Helio; Al-Jassim, Mowafak M.; Pennycook, Stephen J.

    2015-03-21

    Thin-film solar cells based on polycrystalline Cu(In,Ga)Se{sub 2} (CIGS) and CdTe photovoltaic semiconductors have reached remarkable laboratory efficiencies. It is surprising that these thin-film polycrystalline solar cells can reach such high efficiencies despite containing a high density of grain boundaries (GBs), which would seem likely to be nonradiative recombination centers for photo-generated carriers. In this paper, we review our atomistic theoretical understanding of the physics of grain boundaries in CIGS and CdTe absorbers. We show that intrinsic GBs with dislocation cores exhibit deep gap states in both CIGS and CdTe. However, in each solar cell device, the GBs can be chemically modified to improve their photovoltaic properties. In CIGS cells, GBs are found to be Cu-rich and contain O impurities. Density-functional theory calculations reveal that such chemical changes within GBs can remove most of the unwanted gap states. In CdTe cells, GBs are found to contain a high concentration of Cl atoms. Cl atoms donate electrons, creating n-type GBs between p-type CdTe grains, forming local p-n-p junctions along GBs. This leads to enhanced current collections. Therefore, chemical modification of GBs allows for high efficiency polycrystalline CIGS and CdTe thin-film solar cells.

  1. 'Age-hardened alloy' based on bulk polycrystalline oxide ceramic

    NASA Astrophysics Data System (ADS)

    Gurnani, Luv; Singh, Mahesh Kumar; Bhargava, Parag; Mukhopadhyay, Amartya

    2015-05-01

    We report here for the first time the development of 'age-hardened/toughened' ceramic alloy based on MgO in the bulk polycrystalline form. This route allows for the facile development of a 'near-ideal' microstructure characterized by the presence of nanosized and uniformly dispersed second-phase particles (MgFe2O4) within the matrix grains, as well as along the matrix grain boundaries, in a controlled manner. Furthermore, the intragranular second-phase particles are rendered coherent with the matrix (MgO). Development of such microstructural features for two-phase bulk polycrystalline ceramics is extremely challenging following the powder metallurgical route usually adopted for the development of bulk ceramic nanocomposites. Furthermore, unlike for the case of ceramic nanocomposites, the route adopted here does not necessitate the usage of nano-powder, pressure/electric field-assisted sintering techniques and inert/reducing atmosphere. The as-developed bulk polycrystalline MgO-MgFe2O4 alloys possess considerably improved hardness (by ~52%) and indentation toughness (by ~35%), as compared to phase pure MgO.

  2. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials. PMID:26936563

  3. Optical Properties of Anisotropic Polycrystalline Ce+3 activated LSO

    PubMed Central

    Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod

    2012-01-01

    Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. PMID:23505329

  4. Grain-boundary-induced melting in quenched polycrystalline monolayers

    NASA Astrophysics Data System (ADS)

    Deutschländer, Sven; Boitard, Charlotte; Maret, Georg; Keim, Peter

    2015-12-01

    Melting in two dimensions can successfully be explained with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario which describes the formation of the high-symmetry phase with the thermal activation of topological defects within an (ideally) infinite monodomain. With all state variables being well defined, it should hold also as freezing scenario where oppositely charged topological defects annihilate. The Kibble-Zurek mechanism, on the other hand, shows that spontaneous symmetry breaking alongside a continuous phase transition cannot support an infinite monodomain but leads to polycrystallinity. For any nonzero cooling rate, critical fluctuations will be frozen out in the vicinity of the transition temperature. This leads to domains with different director of the broken symmetry, separated by a defect structure, e.g., grain boundaries in crystalline systems. After instantaneously quenching a colloidal monolayer from a polycrystalline to the isotropic fluid state, we show that such grain boundaries increase the probability for the formation of dislocations. In addition, we determine the temporal decay of defect core energies during the first few Brownian times after the quench. Despite the fact that the KTHNY scenario describes a continuous phase transition and phase equilibrium does not exist, melting in polycrystalline samples starts at grain boundaries similar to first-order phase transitions.

  5. Carbon Cryogel Silicon Composite Anode Materials for Lithium Ion Batteries

    NASA Technical Reports Server (NTRS)

    Woodworth James; Baldwin, Richard; Bennett, William

    2010-01-01

    A variety of materials are under investigation for use as anode materials in lithium-ion batteries, of which, the most promising are those containing silicon. 10 One such material is a composite formed via the dispersion of silicon in a resorcinol-formaldehyde (RF) gel followed by pyrolysis. Two silicon-carbon composite materials, carbon microspheres and nanofoams produced from nano-phase silicon impregnated RF gel precursors have been synthesized and investigated. Carbon microspheres are produced by forming the silicon-containing RF gel into microspheres whereas carbon nano-foams are produced by impregnating carbon fiber paper with the silicon containing RF gel to create a free standing electrode. 1-4,9 Both materials have demonstrated their ability to function as anodes and utilize the silicon present in the material. Stable reversible capacities above 400 mAh/g for the bulk material and above 1000 mAh/g of Si have been observed.

  6. Emerging heterogeneous integrated photonic platforms on silicon

    NASA Astrophysics Data System (ADS)

    Fathpour, Sasan

    2015-05-01

    Silicon photonics has been established as a mature and promising technology for optoelectronic integrated circuits, mostly based on the silicon-on-insulator (SOI) waveguide platform. However, not all optical functionalities can be satisfactorily achieved merely based on silicon, in general, and on the SOI platform, in particular. Long-known shortcomings of silicon-based integrated photonics are optical absorption (in the telecommunication wavelengths) and feasibility of electrically-injected lasers (at least at room temperature). More recently, high two-photon and free-carrier absorptions required at high optical intensities for third-order optical nonlinear effects, inherent lack of second-order optical nonlinearity, low extinction ratio of modulators based on the free-carrier plasma effect, and the loss of the buried oxide layer of the SOI waveguides at mid-infrared wavelengths have been recognized as other shortcomings. Accordingly, several novel waveguide platforms have been developing to address these shortcomings of the SOI platform. Most of these emerging platforms are based on heterogeneous integration of other material systems on silicon substrates, and in some cases silicon is integrated on other substrates. Germanium and its binary alloys with silicon, III-V compound semiconductors, silicon nitride, tantalum pentoxide and other high-index dielectric or glass materials, as well as lithium niobate are some of the materials heterogeneously integrated on silicon substrates. The materials are typically integrated by a variety of epitaxial growth, bonding, ion implantation and slicing, etch back, spin-on-glass or other techniques. These wide range of efforts are reviewed here holistically to stress that there is no pure silicon or even group IV photonics per se. Rather, the future of the field of integrated photonics appears to be one of heterogenization, where a variety of different materials and waveguide platforms will be used for different purposes with

  7. Silicon: the health benefits of a metalloid.

    PubMed

    Martin, Keith R

    2013-01-01

    Silicon is the second most abundant element in nature behind oxygen. As a metalloid, silicon has been used in many industrial applications including use as an additive in the food and beverage industry. As a result, humans come into contact with silicon through both environmental exposures but also as a dietary component. Moreover, many forms of silicon, that is, Si bound to oxygen, are water-soluble, absorbable, and potentially bioavailable to humans presumably with biological activity. However, the specific biochemical or physiological functions of silicon, if any, are largely unknown although generally thought to exist. As a result, there is growing interest in the potential therapeutic effects of water-soluble silica on human health. For example, silicon has been suggested to exhibit roles in the structural integrity of nails, hair, and skin, overall collagen synthesis, bone mineralization, and bone health and reduced metal accumulation in Alzheimer's disease, immune system health, and reduction of the risk for atherosclerosis. Although emerging research is promising, much additional, corroborative research is needed particularly regarding speciation of health-promoting forms of silicon and its relative bioavailability. Orthosilicic acid is the major form of bioavailable silicon whereas thin fibrous crystalline asbestos is a health hazard promoting asbestosis and significant impairment of lung function and increased cancer risk. It has been proposed that relatively insoluble forms of silica can also release small but meaningful quantities of silicon into biological compartments. For example, colloidal silicic acid, silica gel, and zeolites, although relatively insoluble in water, can increase concentrations of water-soluble silica and are thought to rely on specific structural physicochemical characteristics. Collectively, the food supply contributes enough silicon in the forms aforementioned that could be absorbed and significantly improve overall human health

  8. Selective deposition of polycrystalline diamond films using photolithography with addition of nanodiamonds as nucleation centers

    NASA Astrophysics Data System (ADS)

    Okhotnikov, V. V.; Linnik, S. A.; Gaidaichuk, A. V.; Shashev, D. V.; Nazarova, G. Yu; Yurchenko, V. I.

    2016-02-01

    A new method of selective deposition of polycrystalline diamond has been developed and studied. The diamond coatings with a complex, predetermined geometry and resolution up to 5 μm were obtained. A high density of polycrystallites in the coating area was reached (up to 32·107 pcs/cm2). The uniformity of the film reached 100%, and the degree of the surface contamination by parasitic crystals did not exceed 2%. The technology was based on the application of the standard photolithography with an addition of nanodiamond suspension into the photoresist that provided the creation of the centers of further nucleation in the areas which require further overgrowth. The films were deposited onto monocrystalline silicon substrates using the method of “hot filaments” in the CVD reactor. The properties of the coating and the impact of the nanodiamond suspension concentration in the photoresist were also studied. The potential use of the given method includes a high resolution, technological efficiency, and low labor costs compared to the standard methods (laser treatment, chemical etching in aggressive environments,).

  9. Local impedance imaging of boron-doped polycrystalline diamond thin films

    SciTech Connect

    Zieliński, A.; Ryl, J.; Burczyk, L.; Darowicki, K.

    2014-09-29

    Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 10{sup 16} to 2 × 10{sup 21} atoms cm{sup −3}. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp{sup 2} regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

  10. Cast Polycrystalline Photovoltaic Module Manufacturing Technology Improvements; Final Subcontract Report, 8 December 199330 April 1998

    SciTech Connect

    J. Wohlgemuth.

    1999-06-16

    This report summarizes work performed by Solarex, A Business Unit of Amoco/Enron Solar, under this subcontract. Among the accomplishments during the program are the following: Converting all of the production casting stations to increase ingot size, operating them at equivalent yields and cell efficiencies, and thus doubling the casting capacity at a 20% lower cost than the cost of new equipment. Developing a wire-saw process and transferring the process to production; as a result, more than 80% of wafering is now done using wire saws, at higher yields and lower costs than achieved on the internal diameter saws. Developing an aluminum paste back-surface field (BSF) process to increase cell efficiency by 5%; researchers also designed, procured, and transferred to manufacturing a fully automated printing system to produce the BSF cells. Fabricating 15.2-cm by 15.2-cm polycrystalline silicon solar cells and building modules using these cells. Modifying the module assembly area to increase capacity by a factor of three. Implementing a single-layer Tedlar backsheet that reduced backsheet cost by $0.50/ft2. Selecting, testing, and qualifying a low-cost (< $1.00 per module) electrical termination system. Qualifying the structure and adhesive system for mounting frameless modules and using the system to build several large arrays.

  11. Mechanical Properties of Polycrystalline Titanium Nitride Films Measured by XRD Tensile Testing

    NASA Astrophysics Data System (ADS)

    Namazu, Takahiro; Inoue, Shozo; Takemoto, Hideki; Koterazawa, Keiji

    This paper describes measurement of mechanical properties of micron-thin polycrystalline titanium nitride (TiN) films. We developed a novel tensile test technique that can directly measure lateral elastic strain of a microscale single/poly-crystalline specimen by means of X-ray diffraction (XRD), which enables evaluation of not only Young's modulus but also Poisson's ratio of TiN films. TiN films having thicknesses of 0.5 μm to 1.6 μm are deposited onto the top and bottom surfaces of a microscale single crystal silicon (Si) specimen. The deposition is carried out by r.f. reactive magnetron sputtering under Ar partial pressure ranging from 0.7 Pa to 1.0 Pa. Average values of Young's modulus and Poisson's ratio for the Si monolayer specimen are found to be 169 GPa and 0.35, respectively, which are in close agreement with analytical values. TiN films deposited under an Ar partial pressure of 0.7 Pa have average Young's modulus of 290 GPa and Poisson's ratio of 0.36. These values gradually decrease with increasing Ar partial pressure, but are independent of TiN film thickness. Fracture strength of a TiN/Si/TiN composite specimen shows dependence on film thickness, regardless of Ar partial pressure.

  12. Significant enhancement of the thermoelectric figure of merit of polycrystalline Si films by reducing grain size

    NASA Astrophysics Data System (ADS)

    Valalaki, K.; Vouroutzis, N.; Nassiopoulou, A. G.

    2016-08-01

    The thermoelectric properties of p-type polycrystalline silicon thin films deposited by low pressure chemical vapour deposition (LPCVD) were accurately determined at room temperature and the thermoelectric figure of merit was deduced as a function of film thickness, ranging from 100 to 500 nm. The effect of film thickness on their thermoelectric performance is discussed. More than threefold increase in the thermoelectric figure of merit of the 100 nm thick polysilicon film was observed compared to the 500 nm thick film, reaching a value as high as 0.033. This enhancement is mainly the result of the smaller grain size in the thinner films. With the decrease in grain size the resistivity of the films is increased twofold and electrical conductivity decreased, however the Seebeck coefficient is increased by 30% and the thermal conductivity is decreased eightfold, being mainly at the origin of the increased figure of merit of the 100 nm film. Our experimental results were compared to known theoretical models and the possible mechanisms involved are presented and discussed.

  13. Promising candidates for allergy prevention.

    PubMed

    Gern, James E

    2015-07-01

    Recent advances in understanding environmental risk factors for allergic diseases in children have led to renewed efforts aimed at prevention. Factors that modify the probability of developing allergies include prenatal exposures, mode of delivery, diet, patterns of medication use, and exposure to pets and farm animals. Recent advances in microbial detection techniques demonstrate that exposure to diverse microbial communities in early life is associated with a reduction in allergic disease. In fact, microbes and their metabolic products might be essential for normal immune development. Identification of these risk factors has provided new targets for prevention of allergic diseases, and possibilities of altering microbial exposure and colonization to reduce the incidence of allergies is a promising approach. This review examines the rationale, feasibility, and potential effect for the prevention of childhood allergic diseases and explores possible strategies for enhancing exposure to beneficial microbes. PMID:26145984

  14. Cultural Neuroscience: Progress and Promise

    PubMed Central

    Chiao, Joan Y.; Cheon, Bobby K.; Pornpattanangkul, Narun; Mrazek, Alissa J.; Blizinsky, Katherine D.

    2013-01-01

    The nature and origin of human diversity has been a source of intellectual curiosity since the beginning of human history. Contemporary advances in cultural and biological sciences provide unique opportunities for the emerging field of cultural neuroscience. Research in cultural neuroscience examines how cultural and genetic diversity shape the human mind, brain and behavior across multiple time scales: situation, ontogeny and phylogeny. Recent progress in cultural neuroscience provides novel theoretical frameworks for understanding the complex interaction of environmental, cultural and genetic factors in the production of adaptive human behavior. Here, we provide a brief history of cultural neuroscience, theoretical and methodological advances, as well as empirical evidence of the promise of and progress in the field. Implications of this research for population health disparities and public policy are discussed. PMID:23914126

  15. Mangiferin: a promising anticancer bioactive.

    PubMed

    Khurana, Rajneet K; Kaur, Ranjot; Lohan, Shikha; Singh, Kamalinder K; Singh, Bhupinder

    2016-05-01

    Of late, several biologically active antioxidants from natural products have been investigated by the researchers in order to combat the root cause of carcinogenesis, in other words, oxidative stress. Mangiferin, a therapeutically active C-glucosylated xanthone, is extracted from pulp, peel, seed, bark and leaf of Mangifera indica. These polyphenols of mangiferin exhibit antioxidant properties and tend to decrease the oxygen-free radicals, thereby reducing the DNA damage. Indeed, its capability to modulate several key inflammatory pathways undoubtedly helps in stalling the progression of carcinogenesis. The current review article emphasizes an updated account on the patents published on the chemopreventive action of mangiferin, apoptosis induction made on various cancer cells, along with proposed antioxidative activities and patent mapping of other important therapeutic properties. Considering it as promising polyphenol, this paper would also summarize the diverse molecular targets of mangiferin. PMID:27088726

  16. MFTF-progress and promise

    SciTech Connect

    Thomassen, K.I.

    1980-10-03

    The Mirror Fusion Test Facility (MFTF) has been in construction at Lawrence Livermore National Laboratory (LLNL) for 3 years, and most of the major subsystems are nearing completion. Recently, the scope of this project was expanded to meet new objectives, principally to reach plasma conditions corresponding to energy break-even. To fulfill this promise, the single-cell minimum-B mirror configuration will be replaced with a tandem mirror configuration (MFTF-B). The facility must accordingly be expanded to accomodate the new geometry. This paper briefly discusses the status of the major MFTF subsystems and describes how most of the technological objectives of MFTF will be demonstrated before we install the additional systems necessary to make the tandem. It also summarizes the major features of the expanded facility.

  17. International Collaboration: Promises and Challenges

    PubMed Central

    Widmer, R. Jay; Widmer, Jocelyn M.; Lerman, Amir

    2015-01-01

    We currently face a myriad of grand global challenges in fields such as poverty, the environment, education, science, and medicine. However, our current means of dealing with such challenges has fallen short, and ingenious solutions are required to overcome the inherent resistance to progress toward ameliorating such difficulties. Here, we highlight the promises and challenges of international collaboration in achieving success toward these trials. We note prior successes in fields such as education, medicine, science, and environmental issues made to date, yet at the same time we do note deficiencies and shortcomings in these efforts. Hence, the notion of international collaboration should be strengthened and encouraged by governments, non-profit organizations, and others moving forward using creative means to bring talented teams together to tackle these challenges across the globe. PMID:25973264

  18. Promising therapeutic targets in neuroblastoma.

    PubMed

    Matthay, Katherine K; George, Rani E; Yu, Alice L

    2012-05-15

    Neuroblastoma, the most common extracranial solid tumor in children, is derived from neural crest cells. Nearly half of patients present with metastatic disease and have a 5-year event-free survival of <50%. New approaches with targeted therapy may improve efficacy without increased toxicity. In this review we evaluate 3 promising targeted therapies: (i) (131)I-metaiodobenzylguanidine (MIBG), a radiopharmaceutical that is taken up by human norepinephrine transporter (hNET), which is expressed in 90% of neuroblastomas; (ii) immunotherapy with monoclonal antibodies targeting the GD2 ganglioside, which is expressed on 98% of neuroblastoma cells; and (iii) inhibitors of anaplastic lymphoma kinase (ALK), a tyrosine kinase that is mutated or amplified in ~10% of neuroblastomas and expressed on the surface of most neuroblastoma cells. Early-phase trials have confirmed the activity of (131)I-MIBG in relapsed neuroblastoma, with response rates of ~30%, but the technical aspects of administering large amounts of radioactivity in young children and limited access to this agent have hindered its incorporation into treatment of newly diagnosed patients. Anti-GD2 antibodies have also shown activity in relapsed disease, and a recent phase III randomized trial showed a significant improvement in event-free survival for patients receiving chimeric anti-GD2 (ch14.18) combined with cytokines and isotretinoin after myeloablative consolidation therapy. A recently approved small-molecule inhibitor of ALK has shown promising preclinical activity for neuroblastoma and is currently in phase I and II trials. This is the first agent directed to a specific mutation in neuroblastoma, and marks a new step toward personalized therapy for neuroblastoma. Further clinical development of targeted treatments offers new hope for children with neuroblastoma. PMID:22589483

  19. Promising therapeutic targets in neuroblastoma

    PubMed Central

    Matthay, Katherine K.; George, Rani E.; Yu, Alice L.

    2012-01-01

    Neuroblastoma, the most common extra- cranial solid tumor in children, is derived from neural crest cells. Nearly half of patients present with metastatic disease, and have 5-year EFS of less than 50%. New approaches with targeted therapy may improve efficacy without increased toxicity. The current review will evaluate three promising targeted therapies, including 131I-metaiodobenzylguanidine (MIBG), a radiopharmaceutical taken up by the human norepinephrine transporter expressed in 90% of neuroblastomas, immunotherapy with monoclonal antibodies targeting the GD2 ganglioside, expressed on 98% of neuroblastoma cells, and inhibitors of ALK, a tyrosine kinase which is mutated or amplified in approximately 10% of neuroblastoma and expressed on the surface of most neuroblastoma cells. Early phase trials have confirmed the activity of 131I-MIBG in relapsed neuroblastoma, with response rates of about 30%, but the technical aspects of administration of large amounts of radioactivity in young children and the limited access have hindered incorporation into treatment of newly diagnosed patients. Anti-GD2 antibodies have also demonstrated activity in relapsed disease, and a recent phase III randomized trial showed a significant improvement in event-free survival for patients receiving chimeric anti-GD2 (ch14.18) combined with cytokines and isotretinoin after myeloablative consolidation therapy. A recently approved small molecule inhibitor of ALK has promising pre-clinical activity for neuroblastoma, and is currently in phase I and II trials. This is the first agent directed to a specific mutation in neuroblastoma, and marks a new step toward personalized therapy for neuroblastoma. Further clinical development of targeted treatments offers new hope for children with neuroblastoma. PMID:22589483

  20. Monolithic integration of common mode filters with electrostatic discharge protection on silicon/porous silicon hybrid substrate

    NASA Astrophysics Data System (ADS)

    Capelle, M.; Billoué, J.; Concord, J.; Poveda, P.; Gautier, G.

    2014-02-01

    This work presents the integration of a common mode filter with ElectroStatic Discharge protection on a silicon/porous silicon hybrid substrate. The porous silicon fabrication was performed after the integration of active components. Thus, a fluoropolymer hard mask was used to protect the active devices during anodization and can be easily removed without damaging the porous silicon. Electrical characterization results have shown fully operational components and an increase of performance with the hybrid substrate regarding to p+-type silicon. Indeed, the cutoff frequency was increased by 8.8 GHz when porous silicon was fabricated below the bump pads and the inductors. This improvement is a promising result to extend the application of RF components for future communication standards with silicon technology.

  1. A novel preparation method for silicone oil nanoemulsions and its application for coating hair with silicone

    PubMed Central

    Hu, Zhenhua; Liao, Meiling; Chen, Yinghui; Cai, Yunpeng; Meng, Lele; Liu, Yajun; Lv, Nan; Liu, Zhenguo; Yuan, Weien

    2012-01-01

    Background Silicone oil, as a major component in conditioner, is beneficial in the moisture preservation and lubrication of hair. However, it is difficult for silicone oil to directly absorb on the hair surface because of its hydrophobicity. Stable nanoemulsions containing silicone oil may present as a potential solution to this problem. Methods Silicone oil nanoemulsions were prepared using the oil-in-water method with nonionic surfactants. Emulsion particle size and distribution were characterized by scanning electron microscopy. The kinetic stability of this nanoemulsion system was investigated under accelerated stability tests and long-term storage. The effect of silicone oil deposition on hair was examined by analyzing the element of hair after treatment of silicone oil nanoemulsions. Results Nonionic surfactants such as Span 80 and Tween 80 are suitable emulsifiers to prepare oil-in-water nanoemulsions that are both thermodynamically stable and can enhance the absorption of silicone oil on hair surface. Conclusion The silicone oil-in-water nanoemulsions containing nonionic surfactants present as a promising solution to improve the silicone oil deposition on the hair surface for hair care applications. PMID:23166436

  2. Micromachined silicon seismic transducers

    SciTech Connect

    Barron, C.C.; Fleming, J.G.; Sniegowski, J.J.; Armour, D.L.; Fleming, R.P.

    1995-08-01

    Batch-fabricated silicon seismic transducers could revolutionize the discipline of CTBT monitoring by providing inexpensive, easily depolyable sensor arrays. Although our goal is to fabricate seismic sensors that provide the same performance level as the current state-of-the-art ``macro`` systems, if necessary one could deploy a larger number of these small sensors at closer proximity to the location being monitored in order to compensate for lower performance. We have chosen a modified pendulum design and are manufacturing prototypes in two different silicon micromachining fabrication technologies. The first set of prototypes, fabricated in our advanced surface- micromachining technology, are currently being packaged for testing in servo circuits -- we anticipate that these devices, which have masses in the 1--10 {mu}g range, will resolve sub-mG signals. Concurrently, we are developing a novel ``mold`` micromachining technology that promises to make proof masses in the 1--10 mg range possible -- our calculations indicate that devices made in this new technology will resolve down to at least sub-{mu}G signals, and may even approach to 10{sup {minus}10} G/{radical}Hz acceleration levels found in the low-earth-noise model.

  3. The neural circuitry of a broken promise.

    PubMed

    Baumgartner, Thomas; Fischbacher, Urs; Feierabend, Anja; Lutz, Kai; Fehr, Ernst

    2009-12-10

    Promises are one of the oldest human-specific psychological mechanisms fostering cooperation and trust. Here, we study the neural underpinnings of promise keeping and promise breaking. Subjects first make a promise decision (promise stage), then they anticipate whether the promise affects the interaction partner's decision (anticipation stage) and are subsequently free to keep or break the promise (decision stage). Findings revealed that the breaking of the promise is associated with increased activation in the DLPFC, ACC, and amygdala, suggesting that the dishonest act involves an emotional conflict due to the suppression of the honest response. Moreover, the breach of the promise can be predicted by a perfidious brain activity pattern (anterior insula, ACC, inferior frontal gyrus) during the promise and anticipation stage, indicating that brain measurements may reveal malevolent intentions before dishonest or deceitful acts are actually committed. PMID:20005830

  4. Crystalline Silicon Solar Cells

    NASA Astrophysics Data System (ADS)

    Green, Martin A.

    2015-10-01

    The following sections are included: * Overview * Silicon cell development * Substrate production * Cell processing * Cell costs * Opportunities for improvement * Silicon-supported thin films * Summary * Acknowledgement * References

  5. Laser wafering for silicon solar.

    SciTech Connect

    Friedmann, Thomas Aquinas; Sweatt, William C.; Jared, Bradley Howell

    2011-03-01

    Current technology cuts solar Si wafers by a wire saw process, resulting in 50% 'kerf' loss when machining silicon from a boule or brick into a wafer. We want to develop a kerf-free laser wafering technology that promises to eliminate such wasteful wire saw processes and achieve up to a ten-fold decrease in the g/W{sub p} (grams/peak watt) polysilicon usage from the starting polysilicon material. Compared to today's technology, this will also reduce costs ({approx}20%), embodied energy, and green-house gas GHG emissions ({approx}50%). We will use short pulse laser illumination sharply focused by a solid immersion lens to produce subsurface damage in silicon such that wafers can be mechanically cleaved from a boule or brick. For this concept to succeed, we will need to develop optics, lasers, cleaving, and high throughput processing technologies capable of producing wafers with thicknesses < 50 {micro}m with high throughput (< 10 sec./wafer). Wafer thickness scaling is the 'Moore's Law' of silicon solar. Our concept will allow solar manufacturers to skip entire generations of scaling and achieve grid parity with commercial electricity rates. Yet, this idea is largely untested and a simple demonstration is needed to provide credibility for a larger scale research and development program. The purpose of this project is to lay the groundwork to demonstrate the feasibility of laser wafering. First, to design and procure on optic train suitable for producing subsurface damage in silicon with the required damage and stress profile to promote lateral cleavage of silicon. Second, to use an existing laser to produce subsurface damage in silicon, and third, to characterize the damage using scanning electron microscopy and confocal Raman spectroscopy mapping.

  6. Low cost silicon solar cell array

    NASA Technical Reports Server (NTRS)

    Bartels, F. T. C.

    1974-01-01

    The technological options available for producing low cost silicon solar cell arrays were examined. A project value of approximately $250/sq m and $2/watt is projected, based on mass production capacity demand. Recommendations are included for the most promising cost reduction options.

  7. High Q silicon carbide microdisk resonator

    SciTech Connect

    Lu, Xiyuan; Lee, Jonathan Y.; Feng, Philip X.-L.; Lin, Qiang

    2014-05-05

    We demonstrate a silicon carbide (SiC) microdisk resonator with optical Q up to 5.12 × 10{sup 4}. The high optical quality, together with the diversity of whispering-gallery modes and the tunability of external coupling, renders SiC microdisk a promising platform for integrated quantum photonics applications.

  8. Numerical simulation and fabrication of silicon sheet via spin casting.

    PubMed

    Lee, Jaewoo; Kim, Hyunhui; Lee, Changbum; Kim, Joonsoo; Jang, Bo-Yun; Lee, Jinseok; Ahn, Youngsoo; Yoon, Wooyoung

    2013-05-01

    A spin-casting process for fabricating polycrystalline silicon sheets for use as solar cell wafers is proposed, and the parameters that control the sheet thickness are investigated. A numerical study of the fluidity of molten silicon indicates that the formation of thin silicon sheets without a mold and via spin casting is feasible. The faster the rotation speed of graphite mold, the thinner the thickness of sheet. After the spread of the molten silicon to cover the graphite mold with rotation speed of above 500 rpm, the solidification has to start. Silicon sheets can be produced by using the centrifugal force under appropriate experimental conditions. The spin-cast sheet had a vertical columnar microstructure due to the normal heat extraction to the substrate, and the sheet lifetime varied from 0.1 microS to 0.3 microS measured by using the microwave photoconductance decay (MW-PCD) to confirm that the spin-cast silicon sheet is applicable to photovoltaics. PMID:23858887

  9. Promising ethanologens for xylose fermentation

    SciTech Connect

    Zhang, M.; Franden, M.A.; Newman, M.

    1995-12-31

    An economical biomass-to-ethanol process depends on the efficient conversion of both its cellulose and hemicellulose components. On a dry weight basis, the typical feedstock contains approx 25-50% (w/w) glucose, 10-30% (w/w) xylose, 15-30% (w/w) lignin, and 1-5% (w/w) of other minor pentose and hexose sugars. Although many microorganisms can ferment the glucose component in cellulose to ethanol, conversion of pentose sugars in the hemicellulose fraction, particularly xylose, has been hindered by the lack of a suitable biocatalyst. Despite the development of recombinant strains with improved fermentation performance, increased ethanol yields and concentrations and shorter fermentation times are key targets that have yet to be achieved from lignocellulosic hydrolyzates. Our objective is to develop biocatalysts for the rapid and efficient conversion of xylose by engineering key metabolic pathways in selected organisms. To identify promising biocatalysts for these efforts, we have surveyed several industrial microorganisms according to several primary traits considered to be essential, as well as a number of secondary traits considered to be desirable, in a commercial biomass-to-ethanol process.

  10. Importance sampling : promises and limitations.

    SciTech Connect

    West, Nicholas J.; Swiler, Laura Painton

    2010-04-01

    Importance sampling is an unbiased sampling method used to sample random variables from different densities than originally defined. These importance sampling densities are constructed to pick 'important' values of input random variables to improve the estimation of a statistical response of interest, such as a mean or probability of failure. Conceptually, importance sampling is very attractive: for example one wants to generate more samples in a failure region when estimating failure probabilities. In practice, however, importance sampling can be challenging to implement efficiently, especially in a general framework that will allow solutions for many classes of problems. We are interested in the promises and limitations of importance sampling as applied to computationally expensive finite element simulations which are treated as 'black-box' codes. In this paper, we present a customized importance sampler that is meant to be used after an initial set of Latin Hypercube samples has been taken, to help refine a failure probability estimate. The importance sampling densities are constructed based on kernel density estimators. We examine importance sampling with respect to two main questions: is importance sampling efficient and accurate for situations where we can only afford small numbers of samples? And does importance sampling require the use of surrogate methods to generate a sufficient number of samples so that the importance sampling process does increase the accuracy of the failure probability estimate? We present various case studies to address these questions.

  11. The Ambivalence of Promising Technology.

    PubMed

    Shelley-Egan, Clare

    2010-08-01

    Issues of responsibility in the world of nanotechnology are becoming explicit with the emergence of a discourse on 'responsible development' of nanoscience and nanotechnologies. Much of this discourse centres on the ambivalences of nanotechnology and of promising technology in general. Actors must find means of dealing with these ambivalences. Actors' actions and responses to ambivalence are shaped by their position and context, along with strategic games they are involved in, together with other actors. A number of interviews were conducted with industrial actors with the aim of uncovering their ethical stances towards responsible development of nanotechnology. The data shows that standard repertoires of justification of nanotechnological development were used. Thus, the industrial actors fell back on their position and associated responsibilities. Such responses reinforce a division of moral labour in which industrial actors and scientists can focus on the progress of science and technology, while other actors, such as NGOs, are expected to take care of broader considerations, such as ethical and social issues. PMID:20835398

  12. Kinetics and mechanisms of primary and steady state creep in B- and Al-containing alpha silicon carbide

    NASA Astrophysics Data System (ADS)

    Davis, Robert F.; Carter, Calvin H., Jr.

    1989-07-01

    The steady state creep behavior of a number of high temperature structural ceramics has been measured and the results analyzed to determine the controlling mechanism. Pure polycrystalline silicon carbide, devoid of sintering aids, creeps by dislocation motion and climb. Silicon carbide containing B- and Al- sintering aids, creeps by grain boundary sliding controlled by diffusion mechanisms (grain boundary diffusion - Coble creep - below 1920 K; lattice diffusion - Nabarro-Herring creep-above 1920 K). The difference in behavior is attributed to the high concentration of vacancies accompanying impurity substitution in the sintered silicon carbide. Experimental measurements of grain boundary sliding offsets on polycrystalline silicon carbide have shown that the primary, transient, creep stage in this material is primarily due to plastic strain within the grains, and that the secondary, steady state, creep stage is primarily due to grain boundary sliding between the grains. The creep of a single crystal and polycrystalline niobium carbide in the 1570 to 1850 K range is controlled by dislocation glide and climb. The creep of hot pressed silicon nitrate and mullite in the 1470 to 1800 K range is controlled by grain boundary sliding due to the amorphous phase present as a consequence of Y2O3 and Al2O3 sintering aids.

  13. Light harvesting by a spherical silicon microcavity

    NASA Astrophysics Data System (ADS)

    Garín, M.; Fenollosa, R.; Ortega, P.; Meseguer, F.

    2016-01-01

    Silicon colloids are presented as efficient absorbers in the VIS-NIR region. The theory of resonant absorption by Mie modes in a single high-index sphere is reviewed and engineering rules established. The presented model predicts enhanced absorption in the crystalline silicon band-to-band absorption region, with absorption efficiencies exceeding one in the VIS and excellent NIR response. A maximum resonant absorption efficiency close to 4 can be obtained at the violet region (425 nm), and values above 0.25 are possible in the bandgap edge at wavelengths up to 1400 nm. Silicon colloids are proposed as a promising cost-effective, silicon saving, sunlight harvesters with improved VIS and NIR response.

  14. Silicon-Based Optical Modulator with Ferroelectric Layer

    NASA Technical Reports Server (NTRS)

    Sheldon, Douglas

    2006-01-01

    According to a proposal, a silicon dioxide layer in a high-speed, low-power, silicon- based electro-optical modulator would be replaced by a layer of lead zirconate titanate or other ferroelectric oxide material. The purpose of this modification is to enhance the power performance and functionality of the modulator. In its unmodified form, the particular silicon- based electro-optical modulator is of an advanced design that overcomes the speed limitation of prior silicon-based electro- optical modulators. Whereas modulation frequencies of such devices had been limited to about 20 MHz, this modulator can operate at modulation frequencies as high as 1 GHz. This modulator can be characterized as a silicon-waveguide-based metal oxide/semiconductor (MOS) capacitor phase shifter in which modulation of the index of refraction in silicon is obtained by exploiting the free-charge-carrier-plasma dispersion effect. As shown in the figure, the modulator includes an n-doped crystalline silicon slab (the silicon layer of a silicon- on-insulator wafer) and a p-doped polycrystalline silicon rib with a gate oxide layer (the aforementioned silicon dioxide layer) sandwiched between them. Under accumulation conditions, the majority charge carriers in the silicon waveguide modify the index of refraction so that a phase shift is induced in the optical mode propagating in the waveguide. The advantage of using an MOS capacitor phase shifter is that it is possible to achieve high modulation speed because there are no slow carrier-generation or -recombination processes involved in the accumulation operation. The main advantage of the proposed substitution of a ferroelectric oxide layer for the silicon dioxide layer would arise from the spontaneous polarization effect of the ferroelectric layer: This spontaneous polarization would maintain accumulation conditions in the absence of applied voltage. Consequently, once the device had been switched to a given optical state, it would remain in

  15. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Declemy, A.; Pranevicius, L.; Milhet, X.

    2005-04-15

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm{sup -2}. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the <001> being more preferential for nitrogen diffusion than <011>. In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or {gamma}{sub N} phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

  16. Advances in polycrystalline thin-film photovoltaics for space applications

    SciTech Connect

    Lanning, B.R.; Armstrong, J.H.; Misra, M.S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 eV and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not `reactor-specific` and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a `substrate configuration` by physical vapor deposition techniques and CdTe cells/modules are fabricated in a `superstrate configuration` by wet chemical methods.

  17. Silicon nanomaterials platform for bioimaging, biosensing, and cancer therapy.

    PubMed

    Peng, Fei; Su, Yuanyuan; Zhong, Yiling; Fan, Chunhai; Lee, Shuit-Tong; He, Yao

    2014-02-18

    Silicon nanomaterials are an important class of nanomaterials with great potential for technologies including energy, catalysis, and biotechnology, because of their many unique properties, including biocompatibility, abundance, and unique electronic, optical, and mechanical properties, among others. Silicon nanomaterials are known to have little or no toxicity due to favorable biocompatibility of silicon, which is an important precondition for biological and biomedical applications. In addition, huge surface-to-volume ratios of silicon nanomaterials are responsible for their unique optical, mechanical, or electronic properties, which offer exciting opportunities for design of high-performance silicon-based functional nanoprobes, nanosensors, and nanoagents for biological analysis and detection and disease treatment. Moreover, silicon is the second most abundant element (after oxygen) on earth, providing plentiful and inexpensive resources for large-scale and low-cost preparation of silicon nanomaterials for practical applications. Because of these attractive traits, and in parallel with a growing interest in their design and synthesis, silicon nanomaterials are extensively investigated for wide-ranging applications, including energy, catalysis, optoelectronics, and biology. Among them, bioapplications of silicon nanomaterials are of particular interest. In the past decade, scientists have made an extensive effort to construct a silicon nanomaterials platform for various biological and biomedical applications, such as biosensors, bioimaging, and cancer treatment, as new and powerful tools for disease diagnosis and therapy. Nonetheless, there are few review articles covering these important and promising achievements to promote the awareness of development of silicon nanobiotechnology. In this Account, we summarize recent representative works to highlight the recent developments of silicon functional nanomaterials for a new, powerful platform for biological and

  18. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere. PMID:10947983

  19. An acoustic emission study of plastic deformation in polycrystalline aluminium

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Frederick, J. R.; Felbeck, D. K.

    1979-01-01

    Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminum while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.

  20. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-09-18

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.