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Sample records for isotopically engineered silicon

  1. Phonon coherence in isotopic silicon superlattices

    SciTech Connect

    Frieling, R.; Radek, M.; Eon, S.; Bracht, H.; Wolf, D. E.

    2014-09-29

    Recent experimental and theoretical investigations have confirmed that a reduction in thermal conductivity of silicon is achieved by isotopic silicon superlattices. In the present study, non-equilibrium molecular dynamics simulations are performed to identify the isotope doping and isotope layer ordering with minimum thermal conductivity. Furthermore, the impact of isotopic intermixing at the superlattice interfaces on phonon transport is investigated. Our results reveal that the coherence of phonons in isotopic Si superlattices is prevented if interfacial mixing of isotopes is considered.

  2. Oxygen and silicon isotopes in ALHA 81005

    NASA Astrophysics Data System (ADS)

    Mayeda, T. K.; Clayton, R. N.; Molini-Velsko, C. A.

    1983-09-01

    The Antarctic meteorite ALHA81005 has oxygen and silicon isotopic compositions identical with lunar highland rocks. The oxygen is distinctly unlike that in calcium-rich achondrites. The isotopic data are entirely consistent with a lunar origin for the meteorite.

  3. Isotopically engineered semiconductors

    NASA Astrophysics Data System (ADS)

    Haller, E. E.

    1995-04-01

    Scientific interest, technological promise, and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This review of mostly recent activities begins with an introduction to some past classical experiments which have been performed on isotopically controlled semiconductors. A review of the natural isotopic composition of the relevant elements follows. Some materials aspects resulting in part from the high costs of enriched isotopes are discussed next. Raman spectroscopy studies with a number of isotopically pure and deliberately mixed Ge bulk crystals show that the Brillouin-zone-center optical phonons are not localized. Their lifetime is almost independent of isotopic disorder, leading to homogeneous Raman line broadening. Studies with short period isotope superlattices consisting of alternating layers of n atomic planes of 70Ge and 74Ge reveal a host of zone-center phonons due to Brillouin-zone folding. At n≳40 one observes two phonon lines at frequencies corresponding to the bulk values of the two isotopes. In natural diamond, isotope scattering of the low-energy phonons, which are responsible for the thermal conductivity, is very strongly affected by small isotope disorder. Isotopically pure 12C diamond crystals exhibit thermal conductivities as high as 410 W cm-1 K-1 at 104 K, leading to projected values of over 2000 W cm-1 K-1 near 80 K. The changes in phonon properties with isotopic composition also weakly affect the electronic band structures and the lattice constants. The latter isotope dependence is most relevant for future standards of length based on crystal lattice constants. Capture of thermal neutrons by isotope nuclei followed by nuclear decay produces new elements, resulting in a very large number of possibilities for isotope selective doping of semiconductors. This neutron transmutation of isotope nuclei, already used

  4. Control mechanisms for the oceanic distribution of silicon isotopes

    NASA Astrophysics Data System (ADS)

    Wischmeyer, André G.; de La Rocha, Christina L.; Maier-Reimer, Ernst; Wolf-Gladrow, Dieter A.

    2003-09-01

    Marine diatoms take up silicic acid for the buildup of their opaline shells and discriminate against the heavier silicon isotope. For the first time, the overall oceanic distribution of silicon isotopes has been estimated by integration of the Hamburg Model of the Ocean Carbon Cycle, version 4 (HAMOCC4). It is shown that the relationship between the silicic acid concentration and its silicon isotope composition is not a simple Rayleigh distillation curve. Only the Southern Ocean and the equatorial Pacific show a clear functional dependency similar to the Rayleigh distillation curve. Model results can be used to predict opal silicon isotope compositions in the sediment and constrain the use of silicon isotopes as a proxy for silicic acid utilization. Owing to the structure of the Pacific current system, it might be valid to apply a relationship between surface silicic acid concentrations and the silicon isotope signal in the equatorial Pacific sediments.

  5. Diffusion in silicon isotope heterostructures

    SciTech Connect

    Silvestri, Hughes Howland

    2004-05-14

    The simultaneous diffusion of Si and the dopants B, P, and As has been studied by the use of a multilayer structure of isotopically enriched Si. This structure, consisting of 5 pairs of 120 nm thick natural Si and {sup 28}Si enriched layers, enables the observation of {sup 30}Si self-diffusion from the natural layers into the {sup 28}Si enriched layers, as well as dopant diffusion from an implanted source in an amorphous Si cap layer, via Secondary Ion Mass Spectrometry (SIMS). The dopant diffusion created regions of the multilayer structure that were extrinsic at the diffusion temperatures. In these regions, the Fermi level shift due to the extrinsic condition altered the concentration and charge state of the native defects involved in the diffusion process, which affected the dopant and self-diffusion. The simultaneously recorded diffusion profiles enabled the modeling of the coupled dopant and self-diffusion. From the modeling of the simultaneous diffusion, the dopant diffusion mechanisms, the native defect charge states, and the self- and dopant diffusion coefficients can be determined. This information is necessary to enhance the physical modeling of dopant diffusion in Si. It is of particular interest to the modeling of future electronic Si devices, where the nanometer-scale features have created the need for precise physical models of atomic diffusion in Si. The modeling of the experimental profiles of simultaneous diffusion of B and Si under p-type extrinsic conditions revealed that both species are mediated by neutral and singly, positively charged Si self-interstitials. The diffusion of As and Si under extrinsic n-type conditions yielded a model consisting of the interstitialcy and vacancy mechanisms of diffusion via singly negatively charged self-interstitials and neutral vacancies. The simultaneous diffusion of P and Si has been modeled on the basis of neutral and singly negatively charged self-interstitials and neutral and singly positively charged P

  6. High-purity, isotopically enriched bulk silicon

    SciTech Connect

    Ager III, J.W.; Beeman, J.W.; Hansen, W.L.; Haller, E.E.; Sharp, I.D.; Liao, C.; Yang, A.; Thewalt, M.L.W.; Riemann, H.

    2004-11-17

    The synthesis and characterization of dislocation-free, undoped, single crystals of Si enriched in all 3 stable isotopes is reported: {sup 28}Si (99.92%), {sup 29}Si (91.37%), and {sup 30}Si (89.8%). A silane-based process compatible with the relatively small amounts of isotopically enriched precursors that are practically available was used. The silane is decomposed to silicon on a graphite starter rod heated to 700-750 C in a recirculating flow reactor. A typical run produces 35 gm of polycrystalline Si at a growth rates of 5 {micro}m/min and conversion efficiency >95%. Single crystals are grown by the floating zone method and characterized by electrical and optical measurements. Concentrations of shallow dopants (P and B) are as low as mid-10{sup 13} cm{sup -3}. Concentrations of C and O lie below 10{sup 16} and 10{sup 15} cm{sup -3}, respectively.

  7. Nebular fractionation of silicon isotopes and implications for silicon in Earth's core

    NASA Astrophysics Data System (ADS)

    Dauphas, N.; Poitrasson, F.; Burkhardt, C.

    2014-12-01

    The silicate Earth has a heavy silicon isotopic composition relative to all chondrite groups, which was taken as evidence for the presence of sufficient amounts of silicon in Earth's core to explain its density deficit. A difficulty remains, however, in that chondrites themselves show variable silicon isotopic composition. For example, enstatite chondrites, the only group of meteorites that matches the Earth's composition for 17O, 48Ca, 50Ti, 54Cr, and 92Mo, have very light silicon isotopic compositions that would require unrealistic amounts of silicon in Earth's core if they were its main constituents. We have measured the silicon isotopic composition of several achondrites that had not been measured before. In particular, we have found that angrites have a heavy silicon isotopic composition, similar to the Earth and the Moon. These meteorites formed under relatively oxidizing conditions (~IW+1) and core formation in their parent-body occurred at relatively low pressure (<0.1 GPa), so core-mantle silicon isotopic fractionation is excluded as a cause for their Earth-like silicon isotopic composition. Angrites are among the most volatile-depleted meteorites and their heavy silicon isotope signature most likely reflects isotopic fractionation by nebular processes. All chondrite groups and the bulk silicate Earth form a trend in silicon isotopic composition vs. Mg/Si ratio, which we will show quantitatively can be explained by a simple nebular process. This can also explain the similarity in silicon isotopic composition between lunar and terrestrial rocks. Therefore, silicon isotopes in terrestrial rocks provide no constraints on the amount of Si in the core and are consistent with the presence of other light elements such as oxygen.

  8. Silicon isotope fractionation during nutrient utilization in the North Pacific

    NASA Astrophysics Data System (ADS)

    Reynolds, Ben C.; Frank, M.; Halliday, A. N.

    2006-04-01

    The distribution of silicon in the North Pacific is controlled by the utilization of silicic acid by diatoms, a process that fractionates silicon (Si) isotopic compositions. Silicon isotope variations are presented for six water column profiles from the surface mixed layer down to the deep waters of the North Pacific Ocean. Although the observed Si isotopic variations display an apparently simple inverse relationship with dissolved nutrient concentrations, in fact they reflect mixing of surface waters undergoing active Si isotope fractionation and deep-waters with more uniform concentrations and isotope compositions. Samples from the surface of the subtropical gyre have the lowest dissolved Si concentrations and heaviest Si isotope compositions of marine waters measured thus far. Fractionation in the surface waters follows a typical Rayleigh-type distillation curve for a 'closed' surface water reservoir resulting from stratification of the surface layer in the subarctic region. In contrast, an 'open' system prevails within the subtropical gyre where there is significant recycling of silicic acid in the upper water column and lateral transport of silicon within surface currents. For deep waters, the Si isotope composition distinguishes between the northern North Pacific Deep Water (NPDW) and the southerly-derived bottom water. The relatively light Si isotope compositions measured from waters within the subarctic gyre provides evidence for isolation of the nutrient pool in the North Pacific.

  9. Silicon Isotopic Fractionation of CAI-like Vacuum Evaporation Residues

    SciTech Connect

    Knight, K; Kita, N; Mendybaev, R; Richter, F; Davis, A; Valley, J

    2009-06-18

    Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquids (Richter et al., 2002, 2007a). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, {alpha}{sub Si}, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that {alpha}{sub Si} = 0.98985 {+-} 0.00044 (2{sigma}) for {sup 29}Si/{sup 28}Si with no resolvable variation with temperature over the temperature range of the experiments, 1600-1900 C. This value is different from what has been reported for evaporation of liquid Mg{sub 2}SiO{sub 4} (Davis et al., 1990) and of a melt with CI chondritic proportions of the major elements (Wang et al., 2001). There appears to be some compositional control on {alpha}{sub Si}, whereas no compositional effects have been reported for {alpha}{sub Mg}. We use the values of {alpha}Si and {alpha}Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose

  10. Silicon isotope fractionation in bamboo and its significance to the biogeochemical cycle of silicon

    NASA Astrophysics Data System (ADS)

    Ding, T. P.; Zhou, J. X.; Wan, D. F.; Chen, Z. Y.; Wang, C. Y.; Zhang, F.

    2008-03-01

    A systematic investigation on silica contents and silicon isotope compositions of bamboos was undertaken. Seven bamboo plants and related soils were collected from seven locations in China. The roots, stem, branch and leaves for each plant were sampled and their silica contents and silicon isotope compositions were determined. The silica contents and silicon isotope compositions of bulk and water-soluble fraction of soils were also measured. The silica contents of studied bamboo organs vary from 0.30% to 9.95%. Within bamboo plant the silica contents show an increasing trend from stem, through branch, to leaves. In bamboo roots the silica is exclusively in the endodermis cells, but in stem, branch and leaves, the silica is accumulated mainly in epidermal cells. The silicon isotope compositions of bamboos exhibit significant variation, from -2.3‰ to 1.8‰, and large and systematic silicon isotope fractionation was observed within each bamboo. The δ 30Si values decrease from roots to stem, but then increase from stem, through branch, to leaves. The ranges of δ 30Si values within each bamboo vary from 1.0‰ to 3.3‰. Considering the total range of silicon isotope composition in terrestrial samples is only 7‰, the observed silicon isotope variation in single bamboo is significant and remarkable. This kind of silicon isotope variation might be caused by isotope fractionation in a Rayleigh process when SiO 2 precipitated in stem, branches and leaves gradually from plant fluid. In this process the Si isotope fractionation factor between dissolved Si and precipitated Si in bamboo ( αpre-sol) is estimated to be 0.9981. However, other factors should be considered to explain the decrease of δ 30Si value from roots to stem, including larger ratio of dissolved H 4SiO 4 to precipitated SiO 2 in roots than in stem. There is a positive correlation between the δ 30Si values of water-soluble fractions in soils and those of bulk bamboos, indicating that the dissolved

  11. Silicon isotopes in sponge spicules: the story of a proxy

    NASA Astrophysics Data System (ADS)

    Hendry, K. R.; Maldonado, M.; Goodwin, C.; Berman, J.; De La Rocha, C. L.

    2014-12-01

    The silicon isotope composition of deep-sea sponges has been shown to reflect the concentration of dissolved silicon, silicic acid, in seawater. This discovery has lead to the development of a novel geochemical proxy for past deep water nutrient status, which has already been applied to a wide range of palaeoceanographic questions ranging from Southern Ocean silicic acid leakage on glacial-interglacial and millennial timescales, to the proliferation of diatoms at the Eocene-Oligocene boundary. The initial calibrations based on modern sponge samples showed some scatter in the relationship between sponge silicon isotopes and silicic acid concentration, but without any apparent systematic influence from other environmental factors (temperature, pH, or other nutrients), morphology or species. However, a silicon isotope calibration of core top spicules, based on measurements made on a large number of spicules extracted from sediments, shows a tighter relationship with silicic acid concentrations, indicating that there are variations between and within individuals that are "averaged out" during palaeoceanographic studies. As is the case for all novel geochemical proxies, there is a need to test the proxy rigorously to ensure robust interpretation of any downcore signal. Here, we will present new studies of modern sponge specimens that have been carried out to shed light on the processes that could result in differences in silicon isotopic fractionation between and within individual sponges. Our findings highlight where caution is required in order to produce robust downcore records of past ocean silicic acid concentrations.

  12. Engineered Adhesion Peptides for Improved Silicon Adsorption.

    PubMed

    Ramakrishnan, Sathish Kumar; Jebors, Said; Martin, Marta; Cloitre, Thierry; Agarwal, Vivechana; Mehdi, Ahmad; Martinez, Jean; Subra, Gilles; Gergely, Csilla

    2015-11-01

    Engineering peptides that present selective recognition and high affinity for a material is a major challenge for assembly-driven elaboration of complex systems with wide applications in the field of biomaterials, hard-tissue regeneration, and functional materials for therapeutics. Peptide-material interactions are of vital importance in natural processes but less exploited for the design of novel systems for practical applications because of our poor understanding of mechanisms underlying these interactions. Here, we present an approach based on the synthesis of several truncated peptides issued from a silicon-specific peptide recovered via phage display technology. We use the photonic response provided by porous silicon microcavities to evaluate the binding efficiency of 14 different peptide derivatives. We identify and engineer a short peptide sequence (SLVSHMQT), revealing the highest affinity for p(+)-Si. The molecular recognition behavior of the obtained peptide fragment can be revealed through mutations allowing identification of the preferential affinity of certain amino acids toward silicon. These results constitute an advance in both the engineering of peptides that reveal recognition properties for silicon and the understanding of biomolecule-material interactions. PMID:26440047

  13. INSTRUMENTS AND METHODS OF INVESTIGATION: Isotope engineering

    NASA Astrophysics Data System (ADS)

    Plekhanov, Vladimir G.

    2000-11-01

    Major applications of the novel and extremely promising technology of isotope engineering are reviewed which, along with basic research, also include — by no means exhaustively — optical fibers, optoelectronics, tunable solid-state lasers, neutron transmutation doping, and information storage.

  14. Silicon isotopes in angrites and volatile loss in planetesimals

    PubMed Central

    Moynier, Frédéric; Savage, Paul S.; Badro, James; Barrat, Jean-Alix

    2014-01-01

    Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation from the solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium–aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50–100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal–silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion. PMID:25404309

  15. Silicon isotopes in angrites and volatile loss in planetesimals.

    PubMed

    Pringle, Emily A; Moynier, Frédéric; Savage, Paul S; Badro, James; Barrat, Jean-Alix

    2014-12-01

    Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation from the solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium-aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50-100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal-silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion. PMID:25404309

  16. Isotopic Study of Silicon Carbide in Semarkona

    NASA Astrophysics Data System (ADS)

    Smith, J. B.; Huss, G. R.

    2002-03-01

    We have measured Si and C isotopes for individual SiC grains from Semarkona. Our results are compared with those of previous studies on SiC from Murchison and Orgueil. Metamorphism and grain-size distribution can affect these comparisons.

  17. Silicon and oxygen isotopic trends in Mesozoic radiolarites

    NASA Astrophysics Data System (ADS)

    Bôle, Maximlien; Baumgartner Peter, O.; Lukas, Baumgartner; Anne-Sophie, Bouvier; Rie, Hori; Masayuki, Ikeda

    2016-04-01

    Silicon and oxygen isotopes (δ30Si and δ18O) of siliceous tests (diatoms, sponges and radiolarians) preserve environmental signatures in unconsolidated sediments, but few studies show such signatures for ancient biosilicieous rocks. In Precambrian cherts from greenstone belts, small scaled isotopic variations were interpreted as a primary diagenetic feature. They were used, coupled to mean δ18O, to reconstruct seawater temperature at which cherts precipitated. Here, we examine stable isotopes in Mesozoic biogenic cherts that may also preserve an environmental signature. We measured δ30Si and δ18O in situ by SIMS, in the chalcedony of individual radiolarian tests preserved in Mesozoic radiolarites. Microanalysis of chalcedony, rather than the bulk rock isotopic composition, is likely to reveal a palaeoenvironmental signal, since it is derived from biogenic opal, the most mobile silica phase during earliest diagenesis. Our data reveal clear trends through several Mesozoic radiolarite sections from Panthalassa (Kiso River, Japan) and Western Tethys (Sogno, Italy). δ18O records measured in radiolarites show a relatively good correlation to δ18O-variations of Mesozoic low magnesium calcite shells, which are commonly used as a palaeotemperature proxy. Once these variations, attributed to seawater temperature, are removed, the residual δ18O trends are opposite to the δ30Si trends. δ30Si increases from Middle Triassic to Early Jurassic in the Kiso River sections and decrease during the Middle Jurassic in the Sogno section. The observed d30Si-trends are likely to represent a palaeoenvironmental signal, because they are not compatible with simple models of progressive diagenesis along P/T-paths (or depth below sea bottom in drill holes). Among the palaeoenvironmental factors that may have influenced these trends are the oceanic silica cycle changing though time, oceanic circulation and/or the palaeogeographic location of each studied site. Siliceous organisms are

  18. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1988-01-01

    This is the third annual technical report for the program entitled, Improved Silicon Carbide for Advanced Heat Engines, for the period February 16, 1987 to February 15, 1988. The objective of the original program was the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. Injection molding is the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals of the revised program are to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in 4-point loading. Two tasks are discussed: Task 1 which involves materials and process improvements, and Task 2 which is a MOR bar matrix to improve strength and reliability. Many statistically designed experiments were completed under task 1 which improved the composition of the batches, the mixing of the powders, the sinter and anneal cycles. The best results were obtained by an attritor mixing process which yielded strengths in excess of 550 MPa (80 ksi) and an individual Weibull modulus of 16.8 for a 9-sample group. Strengths measured at 1200 and 1400 C were equal to the room temperature strength. Annealing of machined test bars significantly improved the strength. Molding yields were measured and flaw distributions were observed to follow a Poisson process. The second iteration of the Task 2 matrix experiment is described.

  19. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1987-01-01

    This is the second annual technical report entitled, Improved Silicon Carbide for Advanced Heat Engines, and includes work performed during the period February 16, 1986 to February 15, 1987. The program is conducted for NASA under contract NAS3-24384. The objective is the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. The fabrication methods used are to be adaptable for mass production of such parts on an economically sound basis. Injection molding is the forming method selected. This objective is to be accomplished in a two-phase program: (1) to achieve a 20 percent improvement in strength and a 100 percent increase in Weibull modulus of the baseline material; and (2) to produce a complex shaped part, a gas turbine rotor, for example, with the improved mechanical properties attained in the first phase. Eight tasks are included in the first phase covering the characterization of the properties of a baseline material, the improvement of those properties and the fabrication of complex shaped parts. Activities during the first contract year concentrated on two of these areas: fabrication and characterization of the baseline material (Task 1) and improvement of material and processes (Task 7). Activities during the second contract year included an MOR bar matrix study to improve mechanical properties (Task 2), materials and process improvements (Task 7), and a Ford-funded task to mold a turbocharger rotor with an improved material (Task 8).

  20. The silicon isotope record of early silica diagenesis

    NASA Astrophysics Data System (ADS)

    Tatzel, Michael; von Blanckenburg, Friedhelm; Oelze, Marcus; Schuessler, Jan A.; Bohrmann, Gerhard

    2015-10-01

    The heavy isotopes of silicon are strongly enriched in some of the youngest, early diagenetically formed porcellanite layers from the Southwest Indian Ridge (Pleistocene) and the Maud Rise (Pliocene). These porcellanite layers are composed of opal-CT and were formed by the conversion of amorphous silica (opal-A) from siliceous sediment via dissolution-reprecipitation. Their bulk δ30Si values range between 1.7 and 2.3‰. Detritus-poor siliceous sediment surrounding these layers is significantly lower at -0.3 to 1.5‰. Sequential chemical extractions of bulk siliceous sediment show (i) preferential dissolution of diatoms featuring higher δ30Si than radiolaria and Al-Si components. The detailed investigation of porcellanite layers by micro-scale Si isotope and Al/Si analyses using UV femtosecond laser ablation ICP mass spectrometry show that (ii) precipitation of authigenic aluminum silicates enriched in light Si isotopes drives pore waters to even higher δ30Si. We suggest that the same processes redistributed stable silicon isotopes in precursor siliceous sediments of ancient chert. We infer that past environmental conditions can be reconstructed with high fidelity from the stable Si isotope composition of chert when initial seawater Si concentrations were high (such as in the Precambrian). Exchange of Si between layers during phase transformation (from opal-A to opal-CT and from opal-CT to quartz) is impeded when variable amounts of detrital minerals are present, because they control rates of silica phase transformation and hence the timing of dissolution-reprecipitation during burial.

  1. A Paleogene Silicon Stable Isotope Record: Long-Term Carbon and Silicon Cycling Interaction Revealed By Sponges and Radiolarians

    NASA Astrophysics Data System (ADS)

    Fontorbe, G.; De La Rocha, C. L.; Hendry, K. R.; Frings, P.; Conley, D. J.

    2014-12-01

    Silicon and carbon cycling are related both on short time scales via the uptake of carbon dioxide and dissolved silica (DSi) by diatoms, and on geological time scales via weathering of silicate rocks consuming carbon dioxide. Long-term changes in oceanic silicon cycling and DSi concentration have been mostly attributed to the evolution of siliceous organisms, especially the colonization of the surface waters by diatoms and their diversification. Thus, impacts of geological mechanisms and changes in carbon cycling have been, in our opinion, overlooked. During the past decade, progress has been made in using silicon isotopes in marine archives to investigate the paleo-silicon cycle. Silicon isotope fractionation in siliceous sponges is closely related to ambient DSi concentration. It follows from this relationship that sponge spicules from marine sediment cores provide a good proxy for reconstructing the paleo-DSi concentration and isotopic composition. The Paleogene period (65.5 to 23Ma) is highly relevant for studying the long-term silicon and carbon cycling relationship due to radiance of diatoms, high variability in the carbon cycle and initiation of the Himalayan orogeny. Here, we will present a sponge spicules and radiolarian silicon isotopes record from ODP Leg 171B (Blake Nose, Western North Atlantic) spanning most of the Paleogene. Our data show similar patterns in both foraminiferal carbon and spicule silicon stable isotopes, providing information on the mechanisms coupling the long-term silicon and carbon cycle.

  2. The silicon isotopic composition of the Ganges and its tributaries

    NASA Astrophysics Data System (ADS)

    Fontorbe, Guillaume; De La Rocha, Christina L.; Chapman, Hazel J.; Bickle, Michael J.

    2013-11-01

    The silicon isotopic composition (δSi30) of the headwaters of the Ganges River, in the Himalaya, ranged from +0.49±0.01‰ to +2.17±0.04‰ at dissolved silicon (DSi) concentrations of 38 to 239 μM. Both the concentration and isotopic composition of DSi in the tributaries increased between the highest elevations to where the Ganges leaves the Himalayas at Rishikesh. The tributaries exhibit a linear correlation between δSi30 and DSi that may represent mixing between a low DSi, low δSi30 (e.g., 40 μM, +0.5‰) component potentially reflecting fractionation during adsorption of a small fraction of silicon onto iron oxides and a high DSi, high δSi30 component (e.g., 240 μM, +1.7‰) produced during higher intensity weathering with a greater proportional sequestration of weathered silicon into secondary minerals or biogenic silica. On the Ganges alluvial plain, in the Ganges and the Yamuna, Gomati, and their tributaries, DSi ranged from 122 to 218 μM while δSi30 ranged from +1.03±0.03‰ to +2.46±0.06‰. Highest values of δSi30 occurred in the Gomati and its tributaries. In general, the lower DSi and higher δSi30 of DSi in these rivers suggests control of both by removal of DSi by secondary mineral formation and/or biogenic silica production. A simple 1-dimensional model with flow through a porous medium is introduced and provides a useful framework for understanding these results.

  3. Improved silicon nitride for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Wimmer, J. M.

    1986-01-01

    Silicon nitride is a high temperature material currently under consideration for heat engine and other applications. The objective is to improve the net shape fabrication technology of Si3N4 by injection molding. This is to be accomplished by optimizing the process through a series of statistically designed matrix experiments. To provide input to the matrix experiments, a wide range of alternate materials and processing parameters was investigated throughout the whole program. The improvement in the processing is to be demonstrated by a 20 percent increase in strength and a 100 percent increase in the Weibull modulus over that of the baseline material. A full characterization of the baseline process was completed. Material properties were found to be highly dependent on each step of the process. Several important parameters identified thus far are the starting raw materials, sinter/hot isostatic pressing cycle, powder bed, mixing methods, and sintering aid levels.

  4. Silicon Isotope Fractionation During Acid Water-Igneous Rock Interaction

    NASA Astrophysics Data System (ADS)

    van den Boorn, S. H.; van Bergen, M. J.; Vroon, P. Z.

    2007-12-01

    Silica enrichment by metasomatic/hydrothermal alteration is a widespread phenomenon in crustal environments where acid fluids interact with silicate rocks. High-sulfidation epithermal ore deposits and acid-leached residues at hot-spring settings are among the best known examples. Acid alteration acting on basalts has also been invoked to explain the relatively high silica contents of the surface of Mars. We have analyzed basaltic-andesitic lavas from the Kawah Ijen volcanic complex (East Java, Indonesia) that were altered by interaction with highly acid (pH~1) sulfate-chloride water of its crater lake and seepage stream. Quantitative removal of major elements during this interaction has led to relative increase in SiO2 contents. Our silicon isotope data, obtained by HR-MC-ICPMS and reported relative to the NIST RM8546 (=NBS28) standard, show a systematic increase in &δ&&30Si from -0.2‰ (±0.3, 2sd) for unaltered andesites and basalts to +1.5‰ (±0.3, 2sd) for the most altered/silicified rocks. These results demonstrate that silicification induced by pervasive acid alteration is accompanied by significant Si isotope fractionation, so that alterered products become isotopically heavier than the precursor rocks. Despite the observed enrichment in SiO2, the rocks have experienced an overall net loss of silicon upon alteration, if Nb is considered as perfectly immobile. The observed &δ&&30Si values of the alteration products appeared to correlate well with the inferred amounts of silicon loss. These findings would suggest that &28Si is preferentially leached during water-rock interaction, implying that dissolved silica in the ambient lake and stream water is isotopically light. However, layered opaline lake sediments, that are believed to represent precipitates from the silica-saturated water show a conspicuous &30Si-enrichment (+1.2 ± 0.2‰). Because anorganic precipitation is known to discriminate against the heavy isotope (e.g. Basile- Doelsch et al., 2006

  5. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1989-01-01

    The development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines is studied. Injection molding was the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals were to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in four-point loading. Statistically designed experiments were performed throughout the program and a fluid mixing process employing an attritor mixer was developed. Compositional improvements in the amounts and sources of boron and carbon used and a pressureless sintering cycle were developed which provided samples of about 99 percent of theoretical density. Strengths were found to improve significantly by annealing in air. Strengths in excess of 550 MPa (80 ksi) with Weibull modulus of about 9 were obtained. Further improvements in Weibull modulus to about 16 were realized by proof testing. This is an increase of 86 percent in strength and 100 percent in Weibull modulus over the baseline data generated at the beginning of the program. Molding yields were improved and flaw distributions were observed to follow a Poisson process. Magic angle spinning nuclear magnetic resonance spectra were found to be useful in characterizing the SiC powder and the sintered samples. Turbocharger rotors were molded and examined as an indication of the moldability of the mixes which were developed in this program.

  6. Improved silicon nitride for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Yeh, Hun C.; Fang, Ho T.

    1987-01-01

    The technology base required to fabricate silicon nitride components with the strength, reliability, and reproducibility necessary for actual heat engine applications is presented. Task 2 was set up to develop test bars with high Weibull slope and greater high temperature strength, and to conduct an initial net shape component fabrication evaluation. Screening experiments were performed in Task 7 on advanced materials and processing for input to Task 2. The technical efforts performed in the second year of a 5-yr program are covered. The first iteration of Task 2 was completed as planned. Two half-replicated, fractional factorial (2 sup 5), statistically designed matrix experiments were conducted. These experiments have identified Denka 9FW Si3N4 as an alternate raw material to GTE SN502 Si3N4 for subsequent process evaluation. A detailed statistical analysis was conducted to correlate processing conditions with as-processed test bar properties. One processing condition produced a material with a 97 ksi average room temperature MOR (100 percent of goal) with 13.2 Weibull slope (83 percent of goal); another condition produced 86 ksi (6 percent over baseline) room temperature strength with a Weibull slope of 20 (125 percent of goal).

  7. Species-dependent silicon isotope fractionation by marine diatoms

    NASA Astrophysics Data System (ADS)

    Sutton, Jill N.; Varela, Diana E.; Brzezinski, Mark A.; Beucher, Charlotte P.

    2013-03-01

    Fractionation of silicon (Si) isotopes was measured in seven species (nine strains) of polar and sub-polar marine diatoms grown in semi-continuous unialgal cultures under optimal irradiance and temperature for each diatom strain. Results from this work provide the first evidence that Si isotope fractionation by diatoms is species-dependent. The greatest difference in the Si isotope fractionation factor (ɛ) was observed between two Southern Ocean diatoms, Fragilariopsis kerguelensis (-0.54‰, average for two strains) and Chaetoceros brevis (-2.09‰). The ɛ for the other species, both polar and sub-polar, ranged from -0.72‰ to -1.21‰. The two remaining polar diatoms had ɛ values of -0.74 ± 0.05‰ for Thalassiosira antarctica, and -1.21 ± 0.04‰ for Thalassiosira nordenskioeldii, while the sub-polar species had ɛ values of -0.72 ± 0.04‰ for Thalassiosira weissflogii, -0.88 ± 0.06‰ for Thalassiosira pseudonana (CCCM58), -0.97 ± 0.14‰ for Thalassiosira pseudonana (CCMP1014), and -1.15 ± 0.03‰ for Porosira glacialis. The range in ɛ for the diatoms evaluated in this study may be large enough to significantly impact the Si isotope composition measured in diatom opal (δ30Si-bSiO2) from marine sediments and its subsequent interpretation. To test the influence of diatom taxonomic composition on δ30Si-bSiO2, we developed a model that considered the relative abundance of diatom species and the ɛ values (from this study) for each species present within the sediment core (i.e. weighted-average ɛ). The model was applied to records from a Southern Ocean sediment core (TN057-13) where both diatom abundance and δ30Si-bSiO2 data were available. The analysis indicated that 67% of the variation in δ30Si-bSiO2 could be explained by species-dependent Si isotope fractionation. We suggest that future work should assess phytoplankton taxonomic composition when using δ30Si-bSiO2 as a proxy for Si utilization.

  8. Silicon Isotopic Fractionation in a Tropical Soil-Plant System

    NASA Astrophysics Data System (ADS)

    Opfergelt, S.; Delstanche, S.; Cardinal, D.; Andre, L.; Delvaux, B.

    2006-12-01

    -0.33 (Ovs) and -0.56 permil (Yvs), close to the fractionation factor previously measured in hydroponics (-0.40 permil). The average delta29Si of phytoliths in banana plants was +0.17 permil. In the topsoil, the isotopic composition of Yvs ( 0.21 permil) was close to that of unweathered pumice (-0.20 permil). The Ovs were significantly lighter (-0.73 permil), confirming published data pointing to lighter isotopic composition with increased weathering. Heavier bulk plants at Ovs might be related to a heavier residual soil solution due to: (i) the formation of lighter clay minerals at Ovs (clay fraction: -0.94 permil) than at Yvs (-0.60 permil), and (ii) the quantitative adsorption of silica onto iron oxides (see Delstanche et al., 2006, AGU), more abundant in weathered Ovs. Our data support the view that plants can induce a strong imprint on the continental cycle of silicon, just as clay formation and possibly Si adsorption onto iron oxides can do. The quantification of Si-isotopic fractionation in the soil-plant system requires, however, further studies involving all the Si pools to achieve a comprehensive understanding of this cycle.

  9. Energetic Beam Processing of Silicon to Engineer Optoelectronically Active Defects

    NASA Astrophysics Data System (ADS)

    Recht, Daniel

    This thesis explores ways to use ion implantation and nanosecond pulsed laser melting, both energetic beam techniques, to engineer defects in silicon. These defects are chosen to facilitate the use of silicon in optoelectronic applications for which its indirect bandgap is not ideal. Chapter 2 develops a kinetic model for the use of point defects as luminescence centers for light-emitting diodes and demonstrates an experimental procedure capable of high-throughput screening of the electroluminescent properties of such defects. Chapter 3 discusses the dramatic change in optical absorption observed in silicon highly supersaturated (i.e., hyperdoped) with the chalcogens sulfur, selenium, and tellurium and reports the first measurements of the optical absorption of such materials for photon energies greater than the bandgap of silicon. Chapter 3 examines the use of silicon hyperdoped with chalcogens in light detectors and concludes that while these devices display strong internal gain that is coupled to a particular type of surface defect, hyperdoping with chalcogens does not lead directly to measurable sub-bandgap photoconductivity. Chapter 4 considers the potential for Silicon to serve as the active material in an intermediate-band solar cell and reports experimental progress on two proposed approaches for hyperdoping silicon for this application. The main results of this chapter are the use of native-oxide etching to control the surface evaporation rate of sulfur from silicon and the first synthesis of monocrystalline silicon hyperdoped with gold.

  10. All-Optical dc Nanotesla Magnetometry Using Silicon Vacancy Fine Structure in Isotopically Purified Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Simin, D.; Soltamov, V. A.; Poshakinskiy, A. V.; Anisimov, A. N.; Babunts, R. A.; Tolmachev, D. O.; Mokhov, E. N.; Trupke, M.; Tarasenko, S. A.; Sperlich, A.; Baranov, P. G.; Dyakonov, V.; Astakhov, G. V.

    2016-07-01

    We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-28SiC) and reveal not yet considered terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin-3 /2 color center. These terms give rise to additional spin transitions, which would be otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity better than 100 nT /√{Hz } within a volume of 3 ×10-7m m3 at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radio-frequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3 mm3 , the projection noise limit is below 100 fT /√{Hz } .

  11. Silicon Isotopes in Achondrites and Planetary Accretion and Differentiation

    NASA Astrophysics Data System (ADS)

    Pringle, E. A.; Savage, P. S.; Badro, J.; Barrat, J.-A.; Moynier, F.

    2015-07-01

    We present new high-precision Si isotope data for an extended suite of achondrites to assess the processes affecting the Si isotope system during the accretion and early geochemical modification of planetesimals.

  12. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, T. J.; Winterbottom, W. L.

    1986-01-01

    Work performed to develop silicon carbide materials of high strength and to form components of complex shape and high reliability is described. A beta-SiC powder and binder system was adapted to the injection molding process and procedures and process parameters developed capable of providing a sintered silicon carbide material with improved properties. The initial effort has been to characterize the baseline precursor materials (beta silicon carbide powder and boron and carbon sintering aids), develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures have been carried out in order to distinguish process routes for improving material properties. A total of 276 MOR bars of the baseline material have been molded, and 122 bars have been fully processed to a sinter density of approximately 95 percent. The material has a mean MOR room temperature strength of 43.31 ksi (299 MPa), a Weibull characteristic strength of 45.8 ksi (315 MPa), and a Weibull modulus of 8.0. Mean values of the MOR strengths at 1000, 1200, and 14000 C are 41.4, 43.2, and 47.2 ksi, respectively. Strength controlling flaws in this material were found to consist of regions of high porosity and were attributed to agglomerates originating in the initial mixing procedures. The mean stress rupture lift at 1400 C of five samples tested at 172 MPa (25 ksi) stress was 62 hours and at 207 MPa (30 ksi) stress was 14 hours. New fluid mixing techniques have been developed which significantly reduce flaw size and improve the strength of the material. Initial MOR tests indicate the strength of the fluid-mixed material exceeds the baseline property by more than 33 percent.

  13. Isotopic homojunction band engineering from diamond.

    PubMed

    Watanabe, H; Nebel, C E; Shikata, S

    2009-06-12

    Confinement of charge carriers in semiconductors by quantum wells is usually accomplished with layers that vary in elemental composition, such as aluminum gallium arsenide and gallium arsenide. We fabricated diamond superlattices by creating multilayer structures of isotopically pure carbon isotopes carbon-12 (12C) and carbon-13 (13C), which confine electrons by a difference in band-gap energy of 17 millielectron volts. Cathodoluminescence experiments performed at 80 kelvin showed that excitonic recombination in the higher-energy band of 13C vanishes in favor of increased recombination in the lower-energy 12C material. Carrier confinement was achieved in diamond superlattices made up of both thinner (30 nanometers) and thicker (up to 350 nanometers) layers. PMID:19520955

  14. Silicon isotopes in granulite xenoliths: Insights into isotopic fractionation during igneous processes and the composition of the deep continental crust

    NASA Astrophysics Data System (ADS)

    Savage, Paul S.; Georg, R. Bastian; Williams, Helen M.; Halliday, Alex N.

    2013-03-01

    The silicon (Si) cycle is of great current interest but the isotopic composition of the continental crust has not been determined. Magmatic differentiation generates liquids with heavier Si and the lower crust, thought to be dominated by cumulates and restites, is predicted to have a light isotopic composition. This is borne out by the composition of many types of granite, which appear to have relative light Si for their silica content. Here we report the Si isotopic compositions of two granulite facies xenolith suites, from the Chudleigh and McBride volcanic provinces, Australia, providing new constraints on deep crustal processes and the average composition of the deep continental crust. The xenoliths display a range of isotopic compositions (δ30Si=-0.43‰ to -0.15‰) comparable to that measured previously for igneous rocks. The isotopic compositions of the McBride xenoliths reflect assimilation and fractional crystallisation (AFC) and/or partial melting processes. Silicon and O isotopes are correlated in the McBride suite and can be explained by AFC of various evolved parent melts. In contrast, the Chudleigh xenoliths have Si isotope compositions predominantly controlled by the specific mineralogy of individual cumulates. Using the xenolith data and a number of weighting methods, the Si isotope compositions of the lower and middle crust are calculated to be δ30Si=-0.29±0.04‰ (95% s.e.) and -0.23±0.04‰ (95% s.e.) respectively. These values are almost identical to the composition of the Bulk Silicate Earth, implying minimal isotope fractionation associated with continent formation and no light lower crustal reservoir.

  15. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.; Mangels, J. A.

    1986-01-01

    The development of silicon carbide materials of high strength was initiated and components of complex shape and high reliability were formed. The approach was to adapt a beta-SiC powder and binder system to the injection molding process and to develop procedures and process parameters capable of providing a sintered silicon carbide material with improved properties. The initial effort was to characterize the baseline precursor materials, develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures were performed in order to distinguish process routes for improving material properties. A total of 276 modulus-of-rupture (MOR) bars of the baseline material was molded, and 122 bars were fully processed to a sinter density of approximately 95 percent. Fluid mixing techniques were developed which significantly reduced flaw size and improved the strength of the material. Initial MOR tests indicated that strength of the fluid-mixed material exceeds the baseline property by more than 33 percent. the baseline property by more than 33 percent.

  16. Nanoscale engineering of radiation tolerant silicon carbide.

    PubMed

    Zhang, Yanwen; Ishimaru, Manabu; Varga, Tamas; Oda, Takuji; Hardiman, Chris; Xue, Haizhou; Katoh, Yutai; Shannon, Steven; Weber, William J

    2012-10-14

    Radiation tolerance is determined by how effectively the microstructure can remove point defects produced by irradiation. Engineered nanocrystalline SiC with a high-density of stacking faults (SFs) has significantly enhanced recombination of interstitials and vacancies, leading to self-healing of irradiation-induced defects. While single crystal SiC readily undergoes an irradiation-induced crystalline to amorphous transformation at room temperature, the nano-engineered SiC with a high-density of SFs exhibits more than an order of magnitude increase in radiation resistance. Molecular dynamics simulations of collision cascades show that the nano-layered SFs lead to enhanced mobility of interstitial Si atoms. The remarkable radiation resistance in the nano-engineered SiC is attributed to the high-density of SFs within nano-sized grain structures that significantly enhance point defect annihilation. PMID:22948711

  17. Improved silicon nitride for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Yeh, Harry C.; Fang, Ho T.

    1991-01-01

    The results of a four year program to improve the strength and reliability of injection-molded silicon nitride are summarized. Statistically designed processing experiments were performed to identify and optimize critical processing parameters and compositions. Process improvements were monitored by strength testing at room and elevated temperatures, and microstructural characterization by optical, scanning electron microscopes, and scanning transmission electron microscope. Processing modifications resulted in a 20 percent strength and 72 percent Weibull slope improvement of the baseline material. Additional sintering aids screening and optimization experiments succeeded in developing a new composition (GN-10) capable of 581.2 MPa at 1399 C. A SiC whisker toughened composite using this material as a matrix achieved a room temperature toughness of 6.9 MPa m(exp .5) by the Chevron notched bar technique. Exploratory experiments were conducted on injection molding of turbocharger rotors.

  18. STATUS OF HIGH FLUX ISOTOPE REACTOR IRRADIATION OF SILICON CARBIDE/SILICON CARBIDE JOINTS

    SciTech Connect

    Katoh, Yutai; Koyanagi, Takaaki; Kiggans, Jim; Cetiner, Nesrin; McDuffee, Joel

    2014-09-01

    Development of silicon carbide (SiC) joints that retain adequate structural and functional properties in the anticipated service conditions is a critical milestone toward establishment of advanced SiC composite technology for the accident-tolerant light water reactor (LWR) fuels and core structures. Neutron irradiation is among the most critical factors that define the harsh service condition of LWR fuel during the normal operation. The overarching goal of the present joining and irradiation studies is to establish technologies for joining SiC-based materials for use as the LWR fuel cladding. The purpose of this work is to fabricate SiC joint specimens, characterize those joints in an unirradiated condition, and prepare rabbit capsules for neutron irradiation study on the fabricated specimens in the High Flux Isotope Reactor (HFIR). Torsional shear test specimens of chemically vapor-deposited SiC were prepared by seven different joining methods either at Oak Ridge National Laboratory or by industrial partners. The joint test specimens were characterized for shear strength and microstructures in an unirradiated condition. Rabbit irradiation capsules were designed and fabricated for neutron irradiation of these joint specimens at an LWR-relevant temperature. These rabbit capsules, already started irradiation in HFIR, are scheduled to complete irradiation to an LWR-relevant dose level in early 2015.

  19. Improved silicon nitride for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Wimmer, J. M.; Huang, H. H.; Rorabaugh, M. E.; Schienle, J.; Styhr, K. H.

    1985-01-01

    The AiResearch Casting Company baseline silicon nitride (92 percent GTE SN-502 Si sub 3 N sub 4 plus 6 percent Y sub 2 O sub 3 plus 2 percent Al sub 2 O sub 3) was characterized with methods that included chemical analysis, oxygen content determination, electrophoresis, particle size distribution analysis, surface area determination, and analysis of the degree of agglomeration and maximum particle size of elutriated powder. Test bars were injection molded and processed through sintering at 0.68 MPa (100 psi) of nitrogen. The as-sintered test bars were evaluated by X-ray phase analysis, room and elevated temperature modulus of rupture strength, Weibull modulus, stress rupture, strength after oxidation, fracture origins, microstructure, and density from quantities of samples sufficiently large to generate statistically valid results. A series of small test matrices were conducted to study the effects and interactions of processing parameters which included raw materials, binder systems, binder removal cycles, injection molding temperatures, particle size distribution, sintering additives, and sintering cycle parameters.

  20. Silicon isotope fractionation between rice plants and nutrient solution and its significance to the study of the silicon cycle

    NASA Astrophysics Data System (ADS)

    Ding, T. P.; Tian, S. H.; Sun, L.; Wu, L. H.; Zhou, J. X.; Chen, Z. Y.

    2008-12-01

    The silicon isotope fractionation between rice plant and nutrient solution was studied experimentally. Rice plants were grown to maturity with the hydroponic culture in a naturally lit glasshouse. The nutrient solution was sampled for 14 times during the whole rice growth period. The rice plants were collected at various growth stages and different parts of the plants were sampled separately. The silica contents of the samples were determined by the gravimetric method and the silicon isotope compositions were measured using the SiF 4 method. In the growth process, the silicon content in the nutrient solution decreased gradually from 16 mM at starting stage to 0.1-0.2 mM at harvest and the amount of silica in single rice plant increased gradually from 0.00013 g at start to 4.329 g at harvest. Within rice plant the SiO 2 fraction in roots reduced continuously from 0.23 at the seedling stage, through 0.12 at the tiller stage, 0.05 at the jointing stage, 0.023 at the heading stage, to 0.009 at the maturity stage. Accordingly, the fraction of SiO 2 in aerial parts increased from 0.77, through 0.88, 0.95, 0.977, to 0.991 for the same stages. The silicon content in roots decreased from the jointing stage, through the heading stage, to the maturity stage, parallel to the decrease of silicon content in the nutrient solution. At the maturity stage, the silicon content increased from roots, through stem and leaves, to husks, but decreased drastically from husks to grains. These observations show that transpiration and evaporation may play an important role in silica transportation and precipitation within rice plants. It was observed that the δ30Si of the nutrient solution increased gradually from -0.1‰ at start to 1.5‰ at harvest, and the δ30Si of silicon absorbed by bulk rice plant increased gradually from -1.72‰ at start to -0.08‰ at harvest, reflecting the effect of the kinetic silicon isotope fractionation during silicon absorption by rice plants from nutrient

  1. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors

    NASA Astrophysics Data System (ADS)

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W.; Chatterjee, Shahana; Erwin, William R.; Bardhan, Rizia; Weiss, Sharon M.; Pint, Cary L.

    2013-10-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10-40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage.

  2. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors.

    PubMed

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W; Chatterjee, Shahana; Erwin, William R; Bardhan, Rizia; Weiss, Sharon M; Pint, Cary L

    2013-01-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10-40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage. PMID:24145684

  3. Surface engineered porous silicon for stable, high performance electrochemical supercapacitors

    PubMed Central

    Oakes, Landon; Westover, Andrew; Mares, Jeremy W.; Chatterjee, Shahana; Erwin, William R.; Bardhan, Rizia; Weiss, Sharon M.; Pint, Cary L.

    2013-01-01

    Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface. This graphene coating simultaneously passivates surface charge traps and provides an ideal electrode-electrolyte electrochemical interface. This leads to 10–40X improvement in energy density, and a 2X wider electrochemical window compared to identically-structured unpassivated P-Si. This work demonstrates a technique generalizable to mesoporous and nanoporous materials that decouples the engineering of electrode structure and electrochemical surface stability to engineer performance in electrochemical environments. Specifically, we demonstrate P-Si as a promising new platform for grid-scale and integrated electrochemical energy storage. PMID:24145684

  4. Thermo-acoustic engineering of silicon microresonators via evanescent waves

    SciTech Connect

    Tabrizian, R.; Ayazi, F.

    2015-06-29

    A temperature-compensated silicon micromechanical resonator with a quadratic temperature characteristic is realized by acoustic engineering. Energy-trapped resonance modes are synthesized by acoustic coupling of propagating and evanescent extensional waves in waveguides with rectangular cross section. Highly different temperature sensitivity of propagating and evanescent waves is used to engineer the linear temperature coefficient of frequency. The resulted quadratic temperature characteristic has a well-defined turn-over temperature that can be tailored by relative energy distribution between propagating and evanescent acoustic fields. A 76 MHz prototype is implemented in single crystal silicon. Two high quality factor and closely spaced resonance modes, created from efficient energy trapping of extensional waves, are excited through thin aluminum nitride film. Having different evanescent wave constituents and energy distribution across the device, these modes show different turn over points of 67 °C and 87 °C for their quadratic temperature characteristic.

  5. Thermo-acoustic engineering of silicon microresonators via evanescent waves

    NASA Astrophysics Data System (ADS)

    Tabrizian, R.; Ayazi, F.

    2015-06-01

    A temperature-compensated silicon micromechanical resonator with a quadratic temperature characteristic is realized by acoustic engineering. Energy-trapped resonance modes are synthesized by acoustic coupling of propagating and evanescent extensional waves in waveguides with rectangular cross section. Highly different temperature sensitivity of propagating and evanescent waves is used to engineer the linear temperature coefficient of frequency. The resulted quadratic temperature characteristic has a well-defined turn-over temperature that can be tailored by relative energy distribution between propagating and evanescent acoustic fields. A 76 MHz prototype is implemented in single crystal silicon. Two high quality factor and closely spaced resonance modes, created from efficient energy trapping of extensional waves, are excited through thin aluminum nitride film. Having different evanescent wave constituents and energy distribution across the device, these modes show different turn over points of 67 °C and 87 °C for their quadratic temperature characteristic.

  6. Isotopic Composition of Presolar Silicon Carbide Grains Analyzed with CHILI

    NASA Astrophysics Data System (ADS)

    Stephan, T.; Trappitsch, R.; Davis, A. M.; Pellin, M. J.; Rost, D.; Savina, M. R.; Jadhav, M.; Kelly, C. H.

    2015-07-01

    Twenty-two presolar SiC grains were analyzed for Sr, Zr, and Ba isotopes with the Chicago Instrument for Laser Ionization. Most grains showed isotope patterns consistent with formation in AGB star like observed previously. One grain is a supernova grain.

  7. Isotopic Composition of Barium in Single Presolar Silicon Carbide Grains

    NASA Technical Reports Server (NTRS)

    Savina, M. R.; Tripa, C. E.; Pellin, M. J.; Davis, A. M.; Clayton, R. N.; Lewis, R. S.; Amari, S.

    2002-01-01

    We have measured Ba isotope distributions in individual presolar SiC grains. We find that the Ba isotopic composition in mainstream SiC grains is consistent with models of nucleosynthesis in low to intermediate mass asymptotic giant branch (AGB) stars. Additional information is contained in the original extended abstract.

  8. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications, phase 2

    NASA Astrophysics Data System (ADS)

    Sundberg, G. J.; Vartabedian, A. M.; Wade, J. A.; White, C. S.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP'ed Si3N4 with 4wt% Y2O3 (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  9. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications Phase 2. Final report

    SciTech Connect

    Sundberg, G.J.; Vartabedian, A.M.; Wade, J.A.; White, C.S.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP`ed Si{sub 3}N{sub 4} with 4wt% Y{sub 2}O{sub 3} (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  10. Silicon isotope fractionation during abiotic silica precipitation at low temperatures: Inferences from flow-through experiments

    NASA Astrophysics Data System (ADS)

    Geilert, Sonja; Vroon, Pieter Z.; Roerdink, Desiree L.; Van Cappellen, Philippe; van Bergen, Manfred J.

    2014-10-01

    Silicon isotopes have considerable potential as proxy for (near-) surface processes and environmental conditions. However, unambiguous interpretations of isotope signatures in natural silica deposits are often hampered by a lack of independent quantitative information on isotopic fractionations operating under the environmental conditions of interest. We performed seeded silica precipitation experiments using flow-through reactors in the 10-60 °C temperature range to alleviate this problem. The principal objective was to quantify the silicon isotope fractionations during controlled precipitation of amorphous silica from a flowing aqueous solution. The experiments were designed to simulate silica deposition induced by a temperature drop, with particular relevance for (near-) surface hydrothermal systems associated with steep temperature gradients. Monitored differences in silicon isotope ratios (30Si/28Si and 29Si/28Si) between input and output solutions demonstrated a systematic sequence in behavior. During an initial time interval, that is, before the reaction system reached steady state, the observed isotope shifts were influenced by dissolution of the seed material, the saturation state of the solution and the specific surface area of the seeds. After reaching steady state, the selective incorporation of silicon isotopes by the solid phase exhibited an explicit temperature dependency: the lighter isotopes were preferentially incorporated, and apparent fractionation magnitudes increased with decreasing temperature. Calculated magnitudes of silicon isotope fractionations between precipitated and dissolved silica (Δ30Si = δ30Siprecipitate (calculated) - δ30Siinput solution) were -2.1‰ at 10 °C, -1.2‰ at 20 °C, -1.0‰ at 30 °C, -0.5‰ at 40 °C, 0.1‰ at 50 °C, and 0.2‰ at 60 °C (s.d. ⩽ 0.6‰, based on replicate experiments). Hence, fractionation was nearly insignificant at temperatures ⩾50 °C. Apart from this relationship with temperature

  11. An Earth-Moon silicon isotope model to track silicic magma origins

    NASA Astrophysics Data System (ADS)

    Poitrasson, Franck; Zambardi, Thomas

    2015-10-01

    A comparison between terrestrial and lunar igneous rocks reveals that Si isotope compositions become slightly, though significantly enriched in heavy isotopes from basalts to granites and anorthosites as a function of the rock SiO2 concentration and/or tectosilicate content. This is interpreted as the result of a global igneous differentiation process that leads to an increased amount of tectosilicates in the rocks. This relationship of increasing degree of melt polymerization with increasingly heavy silicon isotope composition is particularly apparent in lunar rocks. The terrestrial trend, however, is more scattered. Given the sensitivity of Si isotopes to water-rock interactions, it is likely that the more erratic terrestrial trend reveals the involvement of water that does not occur on the Moon. Hence, Si isotopes appear to reflect the occurrence of low temperature water-rock interaction products, like clay minerals, in the source of peraluminous leucogranites. Conversely, the heavy silicon isotope composition of some andesites possibly trace the input of fluids involved in subduction zones and/or interaction of the oceanic crust with isotopically heavy seawater before subduction.

  12. A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts.

    PubMed

    Robert, François; Chaussidon, Marc

    2006-10-26

    The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago. PMID:17066030

  13. Valley-engineered ultra-thin silicon for high-performance junctionless transistors.

    PubMed

    Kim, Seung-Yoon; Choi, Sung-Yool; Hwang, Wan Sik; Cho, Byung Jin

    2016-01-01

    Extremely thin silicon show good mechanical flexibility because of their 2-D like structure and enhanced performance by the quantum confinement effect. In this paper, we demonstrate a junctionless FET which reveals a room temperature quantum confinement effect (RTQCE) achieved by a valley-engineering of the silicon. The strain-induced band splitting and a quantum confinement effect induced from ultra-thin-body silicon are the two main mechanisms for valley engineering. These were obtained from the extremely well-controlled silicon surface roughness and high tensile strain in silicon, thereupon demonstrating a device mobility increase of ~500% in a 2.5 nm thick silicon channel device. PMID:27389874

  14. Valley-engineered ultra-thin silicon for high-performance junctionless transistors

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Yoon; Choi, Sung-Yool; Hwang, Wan Sik; Cho, Byung Jin

    2016-07-01

    Extremely thin silicon show good mechanical flexibility because of their 2-D like structure and enhanced performance by the quantum confinement effect. In this paper, we demonstrate a junctionless FET which reveals a room temperature quantum confinement effect (RTQCE) achieved by a valley-engineering of the silicon. The strain-induced band splitting and a quantum confinement effect induced from ultra-thin-body silicon are the two main mechanisms for valley engineering. These were obtained from the extremely well-controlled silicon surface roughness and high tensile strain in silicon, thereupon demonstrating a device mobility increase of ~500% in a 2.5 nm thick silicon channel device.

  15. Valley-engineered ultra-thin silicon for high-performance junctionless transistors

    PubMed Central

    Kim, Seung-Yoon; Choi, Sung-Yool; Hwang, Wan Sik; Cho, Byung Jin

    2016-01-01

    Extremely thin silicon show good mechanical flexibility because of their 2-D like structure and enhanced performance by the quantum confinement effect. In this paper, we demonstrate a junctionless FET which reveals a room temperature quantum confinement effect (RTQCE) achieved by a valley-engineering of the silicon. The strain-induced band splitting and a quantum confinement effect induced from ultra-thin-body silicon are the two main mechanisms for valley engineering. These were obtained from the extremely well-controlled silicon surface roughness and high tensile strain in silicon, thereupon demonstrating a device mobility increase of ~500% in a 2.5 nm thick silicon channel device. PMID:27389874

  16. Can silicon isotopes be used to assess anthropogenic impacts and nutrient utilisation in Lake Baikal, Siberia?

    NASA Astrophysics Data System (ADS)

    Swann, G. E. A.; Panizzo, V. N.; Mackay, A. W.; Roberts, S.; Vologina, E.; Horstwood, M. S.

    2014-12-01

    Silicon isotope geochemistry (28Si, 29Si, 30Si) represents a growing field in Earth Sciences providing information to constrain and understand biogeochemical cycling on land and in oceans. Here we present records of δ30Si (30Si/28Si) from the Lake Baikal drainage basin in central Siberia to understand silicon cycling through the dominant river tributaries and into Lake Baikal itself, the world's deepest and most voluminous lake containing one fifth of all freshwater not stored in glaciers and ice caps.Waters were collected along an upstream transect for the five dominant Lake Baikal inflows as well as from the Selenga Delta which account for >50% of the annual riverine flow to the lake. Samples for dissolved silicon (DSi) concentrations and silicon isotopic signatures (δ30SiDSi) were filtered and acidified in the field with isotopic analyses conducted on a Neptune + Multi-Collector ICP-MS using wet plasma mode with Mg doping of samples and standard-sample-standard bracketing. Analytical reproducibility is 0.11‰ (2σ) and blanks are <1% of signal intensity. The DSi concentration of all river inflow samples varies from c. 2.5-6.3 ppm, which contrasts with concentrations of < 1ppm from the Angara River, the lake's only outflow. Combined with river δ30SiDSi values of c. + 0.94 to +1.52‰ and lake water and outflow values of c. +2.50‰, the results show significant (up to 60%) biological utilisation of silicon entering the lake.With the Lake Baikal having been designated a World Heritage Site since 1996, due to its high level of biological endemicity, the work in combination with sediment cores from the lake provides an insight into the transportation and fate of silicon in the basin and an assessment of how climate change and expanding anthropogenic activities in the region including urbanisation, deforestation, agriculture and mining have impacted biogeochemical cycling.

  17. Silicon Isotope Fractionation by Banana Under Continuous Nutrient and Silica Flux

    NASA Astrophysics Data System (ADS)

    Opfergelt, S.; Cardinal, D.; Henriet, C.; Delvaux, B.; André, L.

    2004-12-01

    Silicon is absorbed by plants as aqueous H4SiO4 with other essential nutrients, and precipitates in aerial parts of the plant as phytolith, a biogenic opal. Phytoliths are restored to the soil by decomposition of organic debris from plant material. The role of higher plants in the biogeochemical cycle of silicon is therefore major although it is still poorly studied. Biomineralization processes are known to fractionate the three stable silicon isotopes with a preferential uptake of light isotopes. Therefore, following some preliminary results from Douthitt (1982), and studies presented in recent conferences (Ziegler et al., 2002; Ding et al., 2003), we suspect that phytolith production by plants could also fractionate the silicon isotopes. Inversely, intensity of phytolith-related isotopic fractionations might contribute to a better understanding of the soil-plant silicon cycle. Our study focused on banana, a silicon accumulating plant (>1% Si, dry weight).Musa acuminata cv Grande Naine has been grown in hydroponics under controlled conditions (light, temperature, humidity, nutrients) during six weeks. The nutrient supply was kept constant: three batches of five plants were grown with a continuous nutrient solution flow of 5, 50 and 100 ppm SiO2 respectively. Si isotopic compositions were measured in the source solution, and in silica extracted from the various parts of banana (roots, pseudostems, midribs and petioles, leaves), using a Nu Plasma multicollector mass spectrometer (MC-ICP-MS) operating in dry plasma mode. The results are expressed as δ 29Si relatively to the NBS28 standard, with an average precision of ± 0.03‰ . Silicon contents and morphological studies of phytoliths were also achieved. Banana δ 29Si varied between -0.18 and -0.76‰ with a source solution at -0.02‰ . Values of δ 29Si were less fractionated, relatively to the nutrient solution, in roots, where no phytoliths have been observed until now, than in upper parts of banana where

  18. Joining and Integration of Silicon Carbide for Turbine Engine Applications

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay; Coddington, Bryan; Asthana, Rajiv

    2010-01-01

    The critical need for ceramic joining and integration technologies is becoming better appreciated as the maturity level increases for turbine engine components fabricated from ceramic and ceramic matrix composite materials. Ceramic components offer higher operating temperatures and reduced cooling requirements. This translates into higher efficiencies and lower emissions. For fabricating complex shapes, diffusion bonding of silicon carbide (SiC) to SiC is being developed. For the integration of ceramic parts to the surrounding metallic engine system, brazing of SiC to metals is being developed. Overcoming the chemical, thermal, and mechanical incompatibilities between dissimilar materials is very challenging. This presentation will discuss the types of ceramic components being developed by researchers and industry and the benefits of using ceramic components. Also, the development of strong, crack-free, stable bonds will be discussed. The challenges and progress in developing joining and integration approaches for a specific application, i.e. a SiC injector, will be presented.

  19. Silicon isotopes reveal recycled altered oceanic crust in the mantle sources of Ocean Island Basalts

    NASA Astrophysics Data System (ADS)

    Pringle, Emily A.; Moynier, Frédéric; Savage, Paul S.; Jackson, Matthew G.; Moreira, Manuel; Day, James M. D.

    2016-09-01

    The study of silicon (Si) isotopes in Ocean Island Basalts (OIB) has the potential to discern between different models for the origins of geochemical heterogeneities in the mantle. Relatively large (∼several per mil per atomic mass unit) Si isotope fractionation occurs in low-temperature environments during biochemical and geochemical precipitation of dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes relative to the dissolved Si. In contrast, only a limited range (∼tenths of a per mil) of Si isotope fractionation has been observed from high-temperature igneous processes. Therefore, Si isotopes may be useful as tracers for the presence of crustal material within OIB mantle source regions that experienced relatively low-temperature surface processes in a manner similar to other stable isotope systems, such as oxygen. Characterizing the isotopic composition of the mantle is also of central importance to the use of the Si isotope system as a basis for comparisons with other planetary bodies (e.g., Moon, Mars, asteroids). Here we present the first comprehensive suite of high-precision Si isotope data obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from ocean islands in the Pacific, Atlantic, and Indian Ocean basins and include representative end-members for the EM-1, EM-2, and HIMU mantle components. On average, δ30Si values for OIB (-0.32 ± 0.09‰, 2 sd) are in general agreement with previous estimates for the δ30Si value of Bulk Silicate Earth (-0.29 ± 0.07‰, 2 sd; Savage et al., 2014). Nonetheless, some small systematic variations are present; specifically, most HIMU-type (Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in the lighter isotopes of Si (δ30Si values lower than MORB), consistent with recycled altered oceanic crust and lithospheric mantle in their mantle sources.

  20. Evaluation of the silicon isotopes for ENDF/B-VI

    SciTech Connect

    Hetrick, D.M.; Larson, D.C.; Larson, N.M.; Fu, C.Y.; Epperson, S.J.

    1991-01-01

    Isotopic evaluations for {sup 28,29,30}Si performed for ENDF/B-VI are briefly reviewed. The evaluations are based on analysis of experimental data and results of model calculations. Evaluated data are given for neutron induced reaction cross sections, angular and energy distributions, and gamma-ray production cross sections. All necessary data are given to allow KERMA (Kinetic Energy Released in MAterials) and displacement cross sections to be calculated directly from information available in the evaluations. These quantities are fundamental to studies of neutron heating and radiation damage. 20 refs., 4 figs.

  1. Si isotopic structure of the infrared absorption of the fully hydrogenated vacancy in silicon

    NASA Astrophysics Data System (ADS)

    Clerjaud, B.; Pajot, B.

    2013-05-01

    An infrared absorption spectrum consisting in three lines observed around 2223 cm-1 at liquid helium temperature characterizes a defect common in silicon crystals containing hydrogen. Several investigations of this spectrum have converged towards its assignment to a fully hydrogenated lattice vacancy defect V(Si-H)4. However, the fact that the ratios of the intensities of the three lines have been reported to be proportional to the natural abundances of the three silicon isotopes suggests that only one Si atom is involved in the defect, apparently contradicting the above assignment. In this paper, the spectroscopic investigation of this defect is revisited and the Si-related isotopic structures of V(Si-H)4 and V(Si-D)4 defects are modeled. It is shown that the near proportionalities observed between the intensities of these lines and the abundances of the Si isotopes are fortuitous. Our analysis of the isotope dependence of the 2223 cm-1 line finds the V(Si-H)4 model to be correct and that the model of a single interstitial Si atom complexed with H can be rejected. The investigation is extended to the analysis of tetra-hydrogenated vacancy trapped by a carbon atom.

  2. Si isotopic structure of the infrared absorption of the fully hydrogenated vacancy in silicon.

    PubMed

    Clerjaud, B; Pajot, B

    2013-05-14

    An infrared absorption spectrum consisting in three lines observed around 2223 cm(-1) at liquid helium temperature characterizes a defect common in silicon crystals containing hydrogen. Several investigations of this spectrum have converged towards its assignment to a fully hydrogenated lattice vacancy defect V(Si-H)4. However, the fact that the ratios of the intensities of the three lines have been reported to be proportional to the natural abundances of the three silicon isotopes suggests that only one Si atom is involved in the defect, apparently contradicting the above assignment. In this paper, the spectroscopic investigation of this defect is revisited and the Si-related isotopic structures of V(Si-H)4 and V(Si-D)4 defects are modeled. It is shown that the near proportionalities observed between the intensities of these lines and the abundances of the Si isotopes are fortuitous. Our analysis of the isotope dependence of the 2223 cm(-1) line finds the V(Si-H)4 model to be correct and that the model of a single interstitial Si atom complexed with H can be rejected. The investigation is extended to the analysis of tetra-hydrogenated vacancy trapped by a carbon atom. PMID:23676054

  3. High resolution measurements of galactic cosmic-ray neon, magnesium, and silicon isotopes

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.

    1980-01-01

    High-resolution measurements of the abundances of individual isotopes of neon, magnesium and silicon in galactic cosmic rays are reported. The Caltech Heavy Isotope Spectrometer Telescope on board the ISEE 3 spacecraft was used to obtain measurements in the range 30 to 180 MeV/n at an rms mass resolution of 0.20 amu. Results indicate excesses of Ne-22 as well as Mg-25 and Mg-26 in galactic cosmic rays with respect to their solar system abundances. Calculations of the effects of interstellar propagation and solar modulation on cosmic-ray isotope abundances also imply an Mg-25 + Mg-26 cosmic ray source fraction significantly greater than the solar system fraction, and it is suggested that the cosmic ray source material and solar system material were synthesized under different conditions.

  4. Adsorption Behavior of Metasilicate on N-Methyl d-Glucamine Functional Groups and Associated Silicon Isotope Fractionation.

    PubMed

    Wang, Wei; Wei, Hai-Zhen; Jiang, Shao-Yong; Eastoe, Christopher J; Guo, Qi; Lin, Yi-Bo

    2016-09-01

    Significant isotope fractionation of silicon provides a powerful geochemical tracer for biological and physicochemical processes in terrestrial and marine environments. The exact mechanism involved in silicon uptake as part of the biological process is not well known. The silicon uptake in biological processes is investigated using silicate adsorption onto the N-methylglucamine functional group (sugarlike structure, abbreviated as L) of Amberlite IRA-743 resin as an analogue of the formation of silicate-sugar complexes in plants. This study provides new evidence that certain sugars can react readily with basic silicic acid to form sugar-silicate chelating complexes, and the equilibrium adsorption behavior of silicate can be well described by the Langmuir isotherm with a Gibbs free energy (ΔG) of -11.94 ± 0.21 kJ·mol(-1) at 293 K. The adsorption kinetics corresponds well to a first-order kinetic model in which the adsorption rate constant ka of 1.25 × 10(-4) s(-1) and the desorption rate constant kd of 4.00 × 10(-6) s(-1) are obtained at 293 K. Both ka and kd increase with increasing temperature. The bonding configurations of silicate-sugar complexes imply the principal coordination complex of hexacoordinated silicon (silicon/L = 1:3) in the liquid phase and the dominant tetracoordinated silicon in the solid phase. Similar to those of many natural processes, the biological uptake via the sugar-silicate chelating complexes favors the preferential enrichment of light Si isotopes into solids, and the Rayleigh model controls the dynamic isotope fractionation with an estimated silicon isotope fractionation factor (i.e., αsolid-solution = [Formula: see text]) of 0.9971. This study advanced the fundamental understanding of the dynamic isotope fractionation of silicon during silicon cycling from the lithosphere to the biosphere and hydrosphere in surficial processes. PMID:27499230

  5. Fractionation of silicon isotopes by marine diatoms during biogenic silica formation

    NASA Astrophysics Data System (ADS)

    de la Rocha, Christina L.; Brzezinski, Mark A.; DeNiro, Michael J.

    1997-12-01

    The fractionation of silicon isotopes by three species of marine diatoms, Skeletonema costatum, Thalassiosira weissflogii, and Thalassiosira sp., grown in batch culture, is reported. Fractionation was observed for all species. The δ 30Si value of the diatom silica and that of the initial silicic acid in the culture medium were used to compute a fractionation factor (α). The values of a for the three species were nearly identical, averaging 0.9989 ± 0.0004 (s.d., n = 13), which corresponds to the production of diatom silica with a δ 30Si value that is 1.1‰ more negative than that of the dissolved silicon utilized for growth. The fractionation factor did not vary with temperature and the consequent change in growth rate (ANOVA, p =0.61; tested at 12°, 15°, and 22°C with Thalassiosira sp.). The observation of fractionation of silicon isotopes by diatoms is an essential step in establishing δ 30Si variations in biogenic silica as a potential oceanographic tracer.

  6. Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai'i

    NASA Astrophysics Data System (ADS)

    Chemtob, Steven M.; Rossman, George R.; Young, Edward D.; Ziegler, Karen; Moynier, Fréderic; Eiler, John M.; Hurowitz, Joel A.

    2015-11-01

    Silicon stable isotopes are fractionated by a host of low-temperature aqueous processes, making them potentially useful as a weathering proxy. Here we characterize the silicon isotope signature of surficial chemical weathering of glassy basaltic lava flows at Kilauea Volcano, Hawaii. Fresh basalt flow surfaces (<40 years old) frequently feature opaque amorphous silica surface coatings up to 80 μm thick. These silica coatings and associated silica cements are enriched in the heavier isotopes of Si (δ30SiNBS-28 = +0.92‰ to +1.36‰) relative to their basaltic substrate (δ30SiNBS-28 = -0.3‰ to -0.2‰). Secondary clays and opals are typically depleted in 30Si relative to the dissolved reservoirs from which they precipitated, so this sense of isotopic fractionation is unusual. Mechanisms capable of producing isotopically heavy secondary minerals were explored by conducting batch alteration experiments on fresh basaltic glass. Batch acidic alteration of basalt glass in HCl, H2SO4, and HF produced silica-rich surface layers resembling the Hawaiian surface coatings. Differences in fluid chemical composition affected the direction and magnitude of Si isotope fractionation. Basalt leaching in HCl or H2SO4 produced 30Si-enriched fluids (1000 ln αprecip-Si(aq) ≅ -0.8‰) and 30Si-depleted secondary silica layers. In contrast, HF-bearing experiments produced highly 30Si-depleted fluid compositions (1000 ln αprecip-Si(aq) up to +8‰). Larger isotopic fractionations were observed in experiments with lower fluid-rock ratios. In Hawaii, where altering fluids contain H2SO4 and HCl but minimal HF, high δ30Si values for the silica coatings were likely achieved by Rayleigh fractionation. Aqueous 30Si-enriched silica was released during incongruent basalt dissolution then subsequently transported and deposited from an evaporating solution at the flow surface. Our results indicate that (1) altering fluid chemistry and fluid-rock ratio impact the Si isotope signature of

  7. Substitution of ceramics for high temperature alloys. [advantages of using silicon carbides and silicon nitrides in gas turbine engines

    NASA Technical Reports Server (NTRS)

    Probst, H. B.

    1978-01-01

    The high temperature capability of ceramics such as silicon nitride and silicon carbide can result in turbine engines of improved efficiency. Other advantages when compared to the nickel and cobalt alloys in current use are raw material availability, lower weight, erosion/corrosion resistance, and potentially lower cost. The use of ceramics in three different sizes of gas turbine is considered; these are the large utility turbines, advanced aircraft turbines, and small automotive turbines. Special consideration, unique to each of these applications, arise when one considers substituting ceramics for high temperature alloys. The effects of material substitutions are reviewed in terms of engine performance, operating economy, and secondary effects.

  8. In-Situ Silicon Isotope Analysis of Archean Cherts by Laser Ablation MC-ICPMS

    NASA Astrophysics Data System (ADS)

    Vroon, P. Z.; van den Boorn, S. H.; van der Wagt, B. J.; van Bergen, M. J.

    2007-12-01

    We present in-situ stable silicon isotope results for Archean Cherts from the Pilbara region, Western Australia. Analyses were performed using a Geolas Laser Ablation (LA) system equipped with a 193nm Excimer laser and a ThermoFinnigan Neptune MC-ICPMS. The MC-ICPMS was used in medium resolution mode (RP=4000) to resolve molecular isobaric interferences (e.g., 12C16O+, 14N2+, 14N16O+). We used an ablation pit size of 49 by 300μm with a 7Hz repetition rate and 5 J.cm-2. Tuning conditions and cup settings were similar as those described by Van den Boorn et al. (2006; 2007) for solution work. To assess precision and accuracy of the LA technique, chert samples were analyzed that were previously characterized for silicon isotopes by micro-drilling and subsequent liquid chromatographic purification. A chemically homogenous chert sample that is well characterized for silicon isotopes was used as a standard. This in-house standard has a δ30Si of 0.50 ± 20 (2sd, n=4) relative to NIST RM8546 (=NBS28). Our precision with the LA technique of 0.2° (2sd, n=11), based on repeated measurements of the standard, is slightly better than the long-term precision of 0.3‰ for solution work (Van den Boorn et al. 2006). Micro-drill and laser data are in excellent agreement (less than 0.4‰), which is well within the variations recorded in individual mm-cm sized chert laminae. By producing 3cm scans across chert bands, inhomogeneities of up to 0.5‰ can be resolved within a single band. Matrix effects might be significant in LA work. For example, borate silicate glass was up to 2.15‰ heavier than values obtained by solution work. This suggests that ablation induces isotopic fractionation and/or that matrix elements cause a shift in mass bias for silicon in the plasma. Because Archean cherts generally contain more than 95% SiO2, offsets due to matrix effects will be small. However, the use of a standard with a composition close to samples is recommended. References: Van den Boorn

  9. The silicon isotope composition of enstatite meteorites and their importance as proto-Earth components

    NASA Astrophysics Data System (ADS)

    Savage, P. S.; Moynier, F.

    2012-12-01

    Of the major primitive meteorite groups, the enstatite chondrites (EC) are the most chemically dissimilar to terrestrial composition [1]. This might preclude them as major components of the proto-Earth; however, for many isotope systems (most notably oxygen, ref. 2), enstatite chondrites and the Earth are compositionally alike. This has led some authors to infer that a significant proportion of Earth accreted from such meteorites [3]. In contrast to many isotope systems, silicon (Si) apparently exhibits significant mass-dependent variations between EC and Bulk Silicate Earth (BSE), which has been used as further evidence against the EC Earth model [4]. However, these conclusions are based on scant data, only 8 analyses of 6 separate meteorites. Here we present a comprehensive investigation into the Si isotope composition of enstatite chondrites and their differentiated counterparts, the aubrites. Our results confirm that enstatite meteorites have Si isotope compositions that are significantly lighter than both ordinary and carbonaceous chondrites and BSE; as such, the EC are the lightest macroscale objects, relative to Si isotopes, so far analysed from the solar system. The data also show that EH (high iron) chondrites have significantly lighter Si isotope compositions than EL (low iron) chondrites, supporting the assertion that these meteorite groups formed on separate bodies. Silicon isotope analyses of the metal-free components of EH and EL chondrites are identical, within error, to each other and with carbonaceous/ordinary chondrite bulk composition [5]. From this we infer that elemental fractionation in the nebular gas is not the cause of the light Si isotope enrichment in enstatite chondrites. A good negative correlation between bulk δ30Si and Si content in kamacite (Fe-Ni metal) in enstatite chondrites indicates that the presence of isotopically light Si in the metal phase (as the result of formation under reducing conditions) is the principle cause of the

  10. Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes

    NASA Astrophysics Data System (ADS)

    Frings, Patrick J.; De La Rocha, Christina; Struyf, Eric; van Pelt, Dimitri; Schoelynck, Jonas; Hudson, Mike Murray; Gondwe, Mangaliso J.; Wolski, Piotr; Mosimane, Keotsheple; Gray, William; Schaller, Jörg; Conley, Daniel J.

    2014-10-01

    Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (δ30Si) may be a useful tool to investigate these processes. Here, we present 82 δ30Si measurements from surface waters, pore waters, biogenic silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. δ30Si in dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36-1.19‰), implying the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi δ30Si (n = 30) ranges from -1.49‰ to +0.31‰ and during dissolution, residual BSi tends towards higher δ30Si. The data permit a field-based estimate of the fractionation associated with BSi dissolution, ε30BSi-DSi = -0.26‰, though it is unclear if this is an artefact of the process of dissolution. Clay δ30Si ranges from -0.97‰ to +0.10‰, (n = 15, mean = -0.31‰) and include the highest values yet published, which we speculate may be due to an equilibrium isotope effect during diagenetic transformation of BSi. Two key trends in surface water DSi δ30Si merit further examination: declining δ30Si in an area roughly corresponding to the permanent floodplains despite net DSi removal, and increasing δ30Si in the area corresponding to the seasonal floodplains

  11. Conversion electron spectrometry of Pu isotopes with a silicon drift detector.

    PubMed

    Pommé, S; Paepen, J; Peräjärvi, K; Turunen, J; Pöllänen, R

    2016-03-01

    An electron spectrometry set-up was built at IRMM consisting of a vacuum chamber with a moveable source holder and windowless Peltier-cooled silicon drift detector (SDD). The SDD is well suited for measuring low-energy x rays and electrons emitted from thin radioactive sources with low self-absorption. The attainable energy resolution is better than 0.5keV for electrons of 30keV. It has been used to measure the conversion electron spectra of three plutonium isotopes, i.e. (238)Pu, (239)Pu, (240)Pu, as well as (241)Am (being a decay product of (241)Pu). The obtained mixed x-ray and electron spectra are compared with spectra obtained with a close-geometry set-up using another SDD in STUK and spectra measured with a Si(Li) detector at IRMM. The potential of conversion electron spectrometry for isotopic analysis of mixed plutonium samples is investigated. With respect to the (240)Pu/(239)Pu isotopic ratio, the conversion electron peaks of both isotopes are more clearly separated than their largely overlapping peaks in alpha spectra. PMID:26651177

  12. Shape-engineered multifunctional porous silicon nanoparticles by direct imprinting.

    PubMed

    Mares, Jeremy W; Fain, Joshua S; Beavers, Kelsey R; Duvall, Craig L; Weiss, Sharon M

    2015-07-10

    A versatile and scalable method for fabricating shape-engineered nano- and micrometer scale particles from mesoporous silicon (PSi) thin films is presented. This approach, based on the direct imprinting of porous substrates (DIPS) technique, facilitates the generation of particles with arbitrary shape, ranging in minimum dimension from approximately 100 nm to several micrometers, by carrying out high-pressure (>200 MPa) direct imprintation, followed by electrochemical etching of a sub-surface perforation layer and ultrasonication. PSi particles (PSPs) with a variety of geometries have been produced in quantities sufficient for biomedical applications (≫10 μg). Because the stamps can be reused over 150 times, this process is substantially more economical and efficient than the use of electron beam lithography and reactive ion etching for the fabrication of nanometer-scale PSPs directly. The versatility of this fabrication method is demonstrated by loading the DIPS-imprinted PSPs with a therapeutic peptide nucleic acid drug molecule, and by vapor deposition of an Au coating to facilitate the use of PSPs as a photothermal contrast agent. PMID:26081802

  13. Shape-Engineered multifunctional porous silicon nanoparticles by direct imprinting

    NASA Astrophysics Data System (ADS)

    Mares, Jeremy W.; Fain, Joshua S.; Beavers, Kelsey R.; Duvall, Craig L.; Weiss, Sharon M.

    2015-07-01

    A versatile and scalable method for fabricating shape-engineered nano- and micrometer scale particles from mesoporous silicon (PSi) thin films is presented. This approach, based on the direct imprinting of porous substrates (DIPS) technique, facilitates the generation of particles with arbitrary shape, ranging in minimum dimension from approximately 100 nm to several micrometers, by carrying out high-pressure (>200 MPa) direct imprintation, followed by electrochemical etching of a sub-surface perforation layer and ultrasonication. PSi particles (PSPs) with a variety of geometries have been produced in quantities sufficient for biomedical applications (≫10 μg). Because the stamps can be reused over 150 times, this process is substantially more economical and efficient than the use of electron beam lithography and reactive ion etching for the fabrication of nanometer-scale PSPs directly. The versatility of this fabrication method is demonstrated by loading the DIPS-imprinted PSPs with a therapeutic peptide nucleic acid drug molecule, and by vapor deposition of an Au coating to facilitate the use of PSPs as a photothermal contrast agent.

  14. Silicon isotope fractionation in silicate minerals: Insights from first-principles models of phyllosilicates, albite and pyrope

    NASA Astrophysics Data System (ADS)

    Méheut, Merlin; Schauble, Edwin A.

    2014-06-01

    Isotopic fractionation factors for oxygen and silicon in phyllosilicates (pyrophyllite, talc), albite and pyrope have been calculated using first-principles methods based on density functional theory. Based on exhaustive analysis of numerical convergence, we also update our previous calculations on enstatite and forsterite silicon fractionation properties. Calculated oxygen isotope fractionations agree well with existing estimates for talc and albite. In the case of silicon, qualitative agreement is found with natural data. For phyllosilicates (kaolinite, lizardite, pyrophyllite, talc), Si isotope fractionation properties appear to be correlated with stoichiometry: 1000 ln α30Si={aMg(T)·Mg+aAl(T)·Al}/{Si}, where Sieq. =#Si, Al={3}/{4}#Al and Mg={1}/{2}#Mg (cation equivalents) are the charge-weighed stoichiometric coefficients of each cation, normalized to the charge of the silicon atom, and aX(T) are proportionality coefficients depending on temperature. It is suggested that the effect of cation X on Si isotope fractionation (i.e. aX(T)) will increase with decreasing electronegativity of X. Si isotope fractionation is further correlated with Si-O distances, suggesting a crystal chemical explanation for relation (1) in terms of electron donation effects. This relationship appears valid for quartz, pyrope and enstatite (R2=0.99, n=7), but forsterite is strongly anomalous (error of 0.7‰ at 600 °C). These models indicate that attention should be given to chemical compositions in Si isotope studies. Relation (1) would explain the enrichment in heavy silicon isotopes accompanying magmatic differentiation.

  15. Large isotopic anomalies of Si, C, N and noble gases in interstellar silicon carbide from the Murray meteorite

    NASA Astrophysics Data System (ADS)

    Zinner, E.; Ming, T.; Anders, E.

    1987-12-01

    Primitive meteorites contain several noble gas components with anomalous isotopic compositions which imply that they - and their solid 'carrier' phases - are of exotic, pre-solar origin. The authors found that minor fractions of the Murray meteorite contain two minerals not previously seen in meteorites: silicon carbide and an amorphous Si-O phase. They report ion microprobe analyses of these phases which reveal very large isotopic anomalies in silicon, nitrogen and carbon, exceeding the highest anomalies previously measured by factors of up to ≡50. It is concluded that these phases are circumstellar grains from carbon-rich stars, whose chemical inertness allowed them to survive in exceptionally well-preserved form.

  16. Dopant and self-diffusion in extrinsic n-type silicon isotopically controlled heterostructures

    SciTech Connect

    Silvestri, Hughes H.; Sharp, Ian D.; Bracht, Hartmut A.; Nicols, Sam P.; Beeman, Jeff W.; Hansen, John; Nylandsted-Larsen, Arme; Haller, Eugene E.

    2002-04-01

    We present experimental results of dopant- and self-diffusion in extrinsic silicon doped with As. Multilayers of isotopically controlled {sup 28}Si and natural silicon enable simultaneous analysis of {sup 30}Si diffusion into the {sup 28}Si enriched layers and dopant diffusion throughout the multilayer structure. In order to suppress transient enhanced self- and dopant diffusion caused by ion implantation, we adopted a special approach to dopant introduction. First, an amorphous 250-nm thick Si layer was deposited on top of the Si isotope heterostructure. Then the dopant ions were implanted to a depth such that all the radiation damage resided inside this amorphous cap layer. These samples were annealed for various times and temperatures to study the impact of As diffusion and doping on Si self-diffusion. The Si self-diffusion coefficient and the dopant diffusivity for various extrinsic n-type conditions were determined over a wide temperature range. We observed increased diffusivities that we attribute to the increase in the concentration of the native defect promoting the diffusion.

  17. Plasmonic engineering of spontaneous emission from silicon nanocrystals

    PubMed Central

    Goffard, Julie; Gérard, Davy; Miska, Patrice; Baudrion, Anne-Laure; Deturche, Régis; Plain, Jérôme

    2013-01-01

    Silicon nanocrystals offer huge advantages compared to other semi-conductor quantum dots as they are made from an abundant, non-toxic material and are compatible with silicon devices. Besides, among a wealth of extraordinary properties ranging from catalysis to nanomedicine, metal nanoparticles are known to increase the radiative emission rate of semiconductor quantum dots. Here, we use gold nanoparticles to accelerate the emission of silicon nanocrystals. The resulting integrated hybrid emitter is 5-fold brighter than bare silicon nanocrystals. We also propose an in-depth analysis highlighting the role of the different physical parameters in the photoluminescence enhancement phenomenon. This result has important implications for the practical use of silicon nanocrystals in optoelectronic devices, for instance for the design of efficient down-shifting devices that could be integrated within future silicon solar cells. PMID:24037020

  18. Silicon isotope fractionation during silica precipitation from hot-spring waters

    NASA Astrophysics Data System (ADS)

    Geilert, Sonja; Vroon, Pieter; Keller, Nicole; Gudbrnadsson, Snorri; Stefánsson, Andri; van Bergen, Manfred

    2014-05-01

    Hot-spring systems in the Geysir geothermal area, Iceland, have been studied to explore silicon isotope fractionation in a natural setting where sinter deposits are actively formed over a temperature interval between 20° and 100° C. The SiO2(aq)concentrations in spring and stream waters range between 290 and 560ppm and stay relatively constant along downstream trajectories, irrespective of significant cooling gradients. The waters are predominantly oversaturated in amorphous silica at the temperatures measured in the field. Correlations between the saturation indices, temperature and amounts of evaporative water loss suggest that cooling and evaporation are the main causes of subaqueous silica precipitation. The δ30Si values of dissolved silica in spring water and outflowing streams average around +1o probably due to the small quantities of instantaneously precipitating silica relative to the dissolved amount. Siliceous sinters, in contrast, range between -0.1o to -4.0o consistent with a preferred incorporation of the light silicon isotope and with values for precipitated silica becoming more negative with downstream decreasing temperatures. Larger fractionation magnitudes are inversely correlated with the precipitation rate, which itself is dependent on temperature, saturation state and the extent of a system. The resulting magnitudes of solid-fluid isotopic fractionation generally decline from -3.5o at 10° C to -2.0o at 90° C. These values confirm a similar relationship between fractionation magnitude and temperature that we found in laboratory-controlled silica-precipitation experiments. However, a relatively constant offset of ca. -2.9o between field and experimental fractionation values indicates that temperature alone cannot be responsible for the observed shifts. We infer that precipitation kinetics are a prominent control of silicon isotope fractionation in aqueous environments, whereby the influence of the extent of the system on the precipitation

  19. Self- and dopant diffusion in extrinsic boron doped isotopically controlled silicon multilayer structures

    SciTech Connect

    Sharp, Ian D.; Bracht, Hartmut A.; Silvestri, Hughes H.; Nicols, Samuel P.; Beeman, Jeffrey W.; Hansen, John L.; Nylandsted Larsen, Arne; Haller, Eugene E.

    2002-04-01

    Isotopically controlled silicon multilayer structures were used to measure the enhancement of self- and dopant diffusion in extrinsic boron doped silicon. {sup 30}Si was used as a tracer through a multilayer structure of alternating natural Si and enriched {sup 28}Si layers. Low energy, high resolution secondary ion mass spectrometry (SIMS) allowed for simultaneous measurement of self- and dopant diffusion profiles of samples annealed at temperatures between 850 C and 1100 C. A specially designed ion- implanted amorphous Si surface layer was used as a dopant source to suppress excess defects in the multilayer structure, thereby eliminating transient enhanced diffusion (TED) behavior. Self- and dopant diffusion coefficients, diffusion mechanisms, and native defect charge states were determined from computer-aided modeling, based on differential equations describing the diffusion processes. We present a quantitative description of B diffusion enhanced self-diffusion in silicon and conclude that the diffusion of both B and Si is mainly mediated by neutral and singly positively charged self-interstitials under p-type doping. No significant contribution of vacancies to either B or Si diffusion is observed.

  20. ESR Experiments on a Single Donor Electron in Isotopically Enriched Silicon

    NASA Astrophysics Data System (ADS)

    Tracy, Lisa; Luhman, Dwight; Carr, Stephen; Borchardt, John; Bishop, Nathaniel; Ten Eyck, Gregory; Pluym, Tammy; Wendt, Joel; Witzel, Wayne; Blume-Kohout, Robin; Nielsen, Erik; Lilly, Michael; Carroll, Malcolm

    In this talk we will discuss electron spin resonance experiments in single donor silicon qubit devices fabricated at Sandia National Labs. A self-aligned device structure consisting of a polysilicon gate SET located adjacent to the donor is used for donor electron spin readout. Using a cryogenic HEMT amplifier next to the silicon device, we demonstrate spin readout at 100 kHz bandwidth and Rabi oscillations with 0.96 visibility. Electron spin resonance measurements on these devices show a linewidth of 30 kHz and coherence times T2* = 10 us and T2 = 0.3 ms. We also discuss estimates of the fidelity of our donor electron spin qubit measurements using gate set tomography. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. ESR Experiments on a Single Donor Electron in Isotopically Enriched Silicon.

  1. Transformation of Silicon in a Coastal Sandy Beach Ecosystem: Insights from Stable Silicon Isotopes in Ground- and Porewaters

    NASA Astrophysics Data System (ADS)

    Ehlert, C.; Paffrath, R.; Reckhardt, A.; Pahnke, K.

    2014-12-01

    Wave and tide dominated sandy beach ecosystems have a major effect on coastal carbon, nutrient, and trace element cycling. The coarse-grained sediments are characterized by a high permeability, which permits advective porewater transport. Due to the fast porewater flow in the sandy sediment, organic matter remineralization products (i.e. nutrients and trace metals) are only slightly enriched in the porewater and rapidly discharged to the coastal zone where they can potentially stimulate primary production. Here we present stable silicon isotope (δ30Si) data from groundwaters and porewaters from Spiekeroog Island, a barrier island in the southern North Sea, Germany. Groundwater was sampled in the freshwater lens down to 70 m depth in the center of the island. The beach porewaters were taken along a transect from the dune belt to the low water line at depths between 0.5 and 5.2 m. This transect represents the mixing zone of fresh and saline groundwater with seawater, whereby the terrestrial driven groundwater flow provides a potential source of terrestrially derived Si isotope compositions resulting in a modification of the marine-dominated porewater composition. The groundwater is characterized by high Si concentrations of up to 750 µM and rather low δ30Si signatures between +0.6‰ and +1.2‰, which decrease with depth (and age) within the freshwater lens. The porewaters have much lower Si concentrations around 50-60 µM and higher and more variable δ30Si between +1.0‰ and +2.5‰. The lower δ30Si values are found closer to the dunes and at greater depths in the beach sediments. These signatures possibly reflect the outflow of the fresh groundwater to the coastal zone. The higher values represent the influence of seawater, which delivers water with a high δ30Si signature previously enriched by phytoplankton growth.

  2. Dual role of seawater and hydrothermal fluids in Early Archean chert formation: Evidence from silicon isotopes

    NASA Astrophysics Data System (ADS)

    van den Boorn, Sander H. J. M.; van Bergen, Manfred J.; Nijman, Wouter; Vroon, Pieter Z.

    2007-10-01

    The great variety and abundance of chert deposits in Archean terrains constitute one of the most unusual features that mark Earth's early geological history. Proposed explanations for their origin largely relying on field observations, trace element patterns, or oxygen isotope signatures have not yielded an encompassing model. Here we document silicon isotope systematics in cherts from 3.5-3.0 Ga units in the Pilbara Craton (Western Australia) as evidence of their formation by several distinct processes in Early Archean near-surface environments. Our δ30Si results, in combination with geochemical and mineralogical signatures and field relations, point to three end-member sources of silica derivation. One chert type is inferred to have originated through massive transformation of precursor material by silica added from sea water. At least 2‰ differences in δ30Si between the two other types, produced by direct chemical precipitation on the seafloor or in conduits, discriminate seawater from hydrothermal fluid as a source of silica. A virtually continuous Si isotope trend in cherts from this group is consistent with interaction between silica-carrying fluids at submarine vent systems.

  3. Silicon Isotopic Composition in Large Meteoritic SiC Particles and 22Na Origin of 22Ne.

    PubMed

    Brown, L E; Clayton, D D

    1992-11-01

    Large silicon carbide (SiC) particles extracted from acid-insoluble residues of carbonaceous chondrites are isotopically anomalous in both silicon and carbon and contain isotopically extreme noble gases. These particles are thought to have originated in mass outflows from red giant stars and to have existed in the interstellar medium at the time the solar system formed from an interstellar cloud. Calculations show that the silicon isotope correlations in those large SiC particles can be generated only in the most massive carbon stars. Consequently, the almost pure neon-22 ((22)Ne) in those particles must be interpreted as the condensation of radioactive sodium-22 ((22)Na) in the particles as they flowed away from the stars. The (22)Na is produced through proton capture by (21)Ne at the base of the surface convection zone. Neon-22 does not exist abundantly in helium shells hot enough to burn magnesium, which is necessary to establish the measured silicon isotopic composition. PMID:17794592

  4. Nanoscale contact engineering for Silicon/Silicide nanowire devices

    NASA Astrophysics Data System (ADS)

    Lin, Yung-Chen

    attributed to the high compressive stress built-in in the core/shell NW structure that retards the diffusion of the nickel atom as well as limits the volume expansion of the metal-rich phases. As a result, the high stress at this finite scale hinders the continuous growth of Ni31Si 12 into the core/shell NWs and totally eliminates the formation of Ni 2Si in core/shell NWs with thick oxide shells (˜ 50 nm). Through these studies, we have demonstrated first time the phase formation sequences of nickel silicides in Si and Si/SiOx NW structures, which is of great importance for reliable contact engineering for Si NW devices. Furthermore, we have provided a clear picture of the hindered nickel silicide growth in confined nanoscale environment and showed the deviated behavior of silicides growth under stress. The information rendered here will be useful for Si NW device applications as well as for the silicon device engineering at nanoscale in general. To further investigate the oxide shell effect, Mn5Si 3 and Fe5Ge3 NW were grown within various oxide thickness to explore the nucleation and growth in the nanowire structure. A oxide shell exerted a compressive stress on the silicide or germanide materials will make those materials with single-crystal properties. Interestingly, single-crystal growth of contact materials can be also implemented for germanide materials. The iron-rich germanide, Fe5Ge3, was successfully grown with single-crystal properties. It shows ferromagnetic properties with a Curie temperature above the room temperature verified by magnetic force microscope (MFM). Two different epitaxial relations found at germanide/germanium interface due to the different sizes of the germanium NW templates. These two different crystal structures exhibited magnetic anisotropy in magnetic force microscope (MFM) measurement, showing differently preferred domain orientations. In-plane and out-of-plane magnetization in the Fe5Ge3 NWs are observed in our experiment. The crystal

  5. Fingerprints of carbon, nitrogen, and silicon isotopes in small interstellar SiC grains from the Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Hoppe, Peter; Geiss, Johannes; Buehler, Fritz; Neuenschwander, Juerg; Amari, Sachiko; Lewis, Roy S.

    1993-01-01

    We report ion microprobe determinations of the carbon, nitrogen, and silicon isotopic compositions of small SiC grains from the Murchison CM2 chondrite. Analyses were made on samples containing variable numbers of grains and on 14 individual grains. In some cases the multiple-grain sample compositions were probably dominated by only one or two grains. Total ranges observed are given. Only a few grains show values near the range limits. Both the total ranges of carbon and nitrogen isotopic compositions, and even the narrower ranges typical for the majority of the grains, are similar to those observed for larger SiC grains. Two rare components appear to be present in the smaller-size fraction, one characterized by C-12/C-13 about 12-16 and the other by very heavy nitrogen. The carbon and nitrogen isotopic compositions qualitatively may reflect hydrostatic H-burning via the CNO cycle and He-burning in red giants, as well as explosive H-burning in novae. The silicon isotopic compositions of most grains qualitatively show what is the signature of He-burning. The silicon isotopic composition of one grain, however, suggests a different process.

  6. Nuclear magnetic resonance linewidth and spin diffusion in {sup 29}Si isotopically controlled silicon

    SciTech Connect

    Hayashi, Hiroshi; Itoh, Kohei M.; Vlasenko, Leonid S.

    2008-10-15

    A nuclear magnetic resonance (NMR) study was performed with n-type silicon single crystals containing {sup 29}Si isotope abundance f ranges from 1.2% to 99.2%. The nuclear spin diffusion coefficient D has been determined from the linewidth of significantly enhanced {sup 29}Si NMR signals utilizing a developed dynamic nuclear polarization (DNP) method. The {sup 29}Si NMR linewidth depends linearly on f, at least when f<10%, and approaches {proportional_to}f{sup 1/2} dependence when f>50%. The estimated {sup 29}Si nuclear spin diffusion time T{sub sd} between phosphorus atoms used for DNP is more than ten times shorter than the nuclear polarization time T{sub 1}{sup p} of {sup 29}Si nuclei around phosphorus. Therefore, the regime of 'rapid spin diffusion' is realized in the DNP experiments.

  7. Magnesium and Silicon Isotopes in HASP Glasses from Apollo 16 Lunar Soil 61241

    NASA Technical Reports Server (NTRS)

    Herzog, G. F.; Delaney, J. S.; Lindsay, F.; Alexander, C. M. O'D; Chakrabarti, R.; Jacobsen, S. B.; Whattam, S.; Korotev, R.; Zeigler, R. A.

    2012-01-01

    The high-Al (>28 wt %), silica-poor (<45 wt %) (HASP) feldspathic glasses of Apollo 16 are widely regarded as the evaporative residues of impacts in the lunar regolith [1-3]. By virtue of their small size, apparent homogeneity, and high inferred formation temperatures, the HASP glasses appear to be good samples in which to study fractionation processes that may accompany open system evaporation. Calculations suggest that HASP glasses with present-day Al2O3 concentrations of up to 40 wt% may have lost 19 wt% of their original masses, calculated as the oxides of iron and silicon, via evaporation [4]. We report Mg and Si isotope abundances in 10 HASP glasses and 2 impact-glass spherules from a 64-105 m grain-size fraction taken from Apollo 16 soil sample 61241.

  8. Correlated Strontium and Barium Isotopic Compositions of Acid-cleaned Single Mainstream Silicon Carbides from Murchison

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Savina, Michael R.; Gallino, Roberto; Davis, Andrew M.; Bisterzo, Sara; Gyngard, Frank; Käppeler, Franz; Cristallo, Sergio; Dauphas, Nicolas; Pellin, Michael J.; Dillmann, Iris

    2015-04-01

    We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated 88Sr/86Sr and 138Ba/136Ba ratios in mainstream SiC grains, we are able to resolve the effect of 13C concentration from that of 13C-pocket mass on s-process nucleosynthesis, which points toward the existence of large 13C pockets with low 13C concentrations in asymptotic giant branch stars. The presence of such large 13C pockets with a variety of relatively low 13C concentrations seems to require multiple mixing processes in parent asymptotic giant branch stars of mainstream SiC grains.

  9. Inductive Measurement of Optically Hyperpolarized Phosphorous Donor Nuclei in an Isotopically Enriched Silicon-28 Crystal

    NASA Astrophysics Data System (ADS)

    Gumann, P.; Patange, O.; Ramanathan, C.; Haas, H.; Moussa, O.; Thewalt, M. L. W.; Riemann, H.; Abrosimov, N. V.; Becker, P.; Pohl, H.-J.; Itoh, K. M.; Cory, D. G.

    2014-12-01

    We experimentally demonstrate the first inductive readout of optically hyperpolarized phosphorus-31 donor nuclear spins in an isotopically enriched silicon-28 crystal. The concentration of phosphorus donors in the crystal was 1.5 ×1 015 cm-3 , 3 orders of magnitude lower than has previously been detected via direct inductive detection. The signal-to-noise ratio measured in a single free induction decay from a 1 cm3 sample (≈1015 spins) was 113. By transferring the sample to an X -band ESR spectrometer, we were able to obtain a lower bound for the nuclear spin polarization at 1.7 K of ˜64 % . The 31P -T2 measured with a Hahn echo sequence was 420 ms at 1.7 K, which was extended to 1.2 s with a Carr Purcell cycle. The T1 of the 31P nuclear spins at 1.7 K is extremely long and could not be determined, as no decay was observed even on a time scale of 4.5 h. Optical excitation was performed with a 1047 nm laser, which provided above-band-gap excitation of the silicon. The buildup of the hyperpolarization at 4.2 K followed a single exponential with a characteristic time of 577 s, while the buildup at 1.7 K showed biexponential behavior with characteristic time constants of 578 and 5670 s.

  10. Dynamic nuclear polarization of {sup 29}Si nuclei in isotopically controlled phosphorus doped silicon

    SciTech Connect

    Hayashi, Hiroshi; Itahashi, Tatsumasa; Itoh, Kohei M.; Vlasenko, Leonid S.; Vlasenko, Marina P.

    2009-07-15

    Dynamic nuclear polarization (DNP) of {sup 29}Si nuclei in isotopically controlled silicon single crystals with the {sup 29}Si isotope abundance f{sub 29Si} varied from 1.2% to 99.2% is reported. It was found that both the DNP enhancement and {sup 29}Si nuclear spin-lattice relaxation time under saturation of the electron paramagnetic resonance transitions of phosphorus donors increase with the decrease in the {sup 29}Si abundance. A remarkably large steady-state DNP enhancement, E{sup ss}=2680 which is comparable to the theoretical upper limit of 3310, has been achieved through the ''resolved'' solid effect that has been identified clearly in the f{sub 29Si}=1.2% sample. The DNP enhancement depends not only on the {sup 29}Si abundance but also on the electron spin-lattice relaxation time that can be controlled by temperature and/or illumination. The linewidth of {sup 29}Si NMR spectra after DNP shows a linear dependence on f{sub 29Si} for f{sub 29Si}{<=}10% and changes to a square-root dependence for f{sub 29Si}{>=}50%. Comparison of experimentally determined nuclear polarization time with nuclear spin diffusion coefficients indicates that the rate of DNP is limited by the polarization transfer rather than by spin diffusion.

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

    SciTech Connect

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

    2014-07-21

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

  12. Factors controlling the silicon isotope distribution in waters and surface sediments of the Peruvian coastal upwelling

    NASA Astrophysics Data System (ADS)

    Ehlert, Claudia; Grasse, Patricia; Mollier-Vogel, Elfi; Böschen, Tebke; Franz, Jasmin; de Souza, Gregory F.; Reynolds, Ben C.; Stramma, Lothar; Frank, Martin

    2012-12-01

    We present the first systematic study of the silicon isotope composition in the water column (δ30Si) and in diatoms (δ30Sidiatom) from the underlying surface sediments in a coastal upwelling region. The surface waters upwelling on the shelf off Peru are mainly fed by southward flowing subsurface waters along the coast, which show a mean δ30Si of +1.5‰. The concentration of dissolved silicic acid (Si(OH)4) increases towards the south in these waters and with increasing water depth, suggesting lateral mixing with water masses from the south and intense remineralisation of particulate biogenic silica (bSiO2) in the water column and in the surface sediments. Surface waters in the realm of the most intense upwelling between 5°S and 15°S have only marginally elevated δ30Si values (δ30Si = +1.7‰) with respect to the source Si isotope composition, whereas further north and south, where upwelling is less pronounced, surface waters are more strongly fractionated (δ30Si up to +2.8‰) due to the stronger utilisation of the smaller amounts of available Si(OH)4. The degree of Si(OH)4 utilisation in the surface waters along the shelf estimated from the Si(OH)4 concentration data ranges from 51% to 93%. The δ30Sidiatom values of hand-picked diatoms in the underlying surface sediments vary from +0.6‰ to +2.0‰, which is within the range of the expected fractionation between surface waters and diatoms. The fractionation signal in the surface waters produced during formation of the diatoms is reflected by the δ30Sidiatom values in the underlying sediments, with the lowest δ30Sidiatom values in the main upwelling region. The silicon isotope compositions of bSiO2 (δ30Si) from the same surface sediment samples are generally much lower than the δ30Sidiatom signatures indicating a significant contamination of the bSiO2 with biogenic siliceous material other than diatoms, such as sponge spicules. This shift towards lighter δ30Si values by up to -1.3‰ compared to

  13. 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

  14. Silicon subsystem mechanical engineering work for the solenoidal detector collaboration

    SciTech Connect

    Miller, W.O.; Barney, M.; Byrd, D.; Christensen, R.W.; Dransfield, G.; Elder, M.; Gamble, M.; Crastataro, C.; Hanlon, J.; Jones, D.C.

    1995-02-01

    The silicon tracking system (STS) for the Solenoidal Detector Collaboration (SDC) represented an order of magnitude increase in size over any silicon system that had been previously built or even planned. In order to meet its performance requirements, it could not simply be a linear scaling of earlier systems, but instead required completely new concepts. The small size of the early systems made it possible to simply move the support hardware and services largely outside the active volume of the system. For a system five meters long, that simply is not an option. The design of the STS for the SDC experiment was the result of numerous compromises between the capabilities required to do the physics and the limitations imposed by cost, material properties, and silicon strip detector characteristics. From the point of view of the physics, the silicon system should start as close to the interaction point as possible. In addition, the detectors should measure the position of particles passing through them with no errors, and should not deflect or interact with the particles in any way. However, cost, radiation damage, and other factors limiting detector performance dictated, other, more realistic values. Radiation damage limited the inner radius of the silicon detectors to about 9 cm, whereas cost limited the outer radius of the detectors to about 50 cm. Cost also limits the half length of the system to about 250 cm. To control the effects of radiation damage on the detectors required operating the system at a temperature of 0{degrees}C or below, and maintaining that temperature throughout life of the system. To summarize, the physics and properties of the silicon strip detectors requires that the detectors be operated at or below 0{degrees}C, be positioned very accurately during assembly and remain positionally stable throughout their operation, and that all materials used be radiation hard and have a large thickness for one radiation length.

  15. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals.

    PubMed

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-01-01

    In this work we report on temperature-dependent photoluminescence measurements (15-300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system. PMID:27296771

  16. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-06-01

    In this work we report on temperature-dependent photoluminescence measurements (15–300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system.

  17. Temperature-dependent photoluminescence of surface-engineered silicon nanocrystals

    PubMed Central

    Mitra, Somak; Švrček, Vladimir; Macias-Montero, Manual; Velusamy, Tamilselvan; Mariotti, Davide

    2016-01-01

    In this work we report on temperature-dependent photoluminescence measurements (15–300 K), which have allowed probing radiative transitions and understanding of the appearance of various transitions. We further demonstrate that transitions associated with oxide in SiNCs show characteristic vibronic peaks that vary with surface characteristics. In particular we study differences and similarities between silicon nanocrystals (SiNCs) derived from porous silicon and SiNCs that were surface-treated using a radio-frequency (RF) microplasma system. PMID:27296771

  18. Processing study of injection molding of silicon nitride for engine applications

    NASA Technical Reports Server (NTRS)

    Rorabaugh, M. E.; Yeh, H. C.

    1985-01-01

    The high hardness of silicon nitride, which is currently under consideration as a structural material for such hot engine components as turbine blades, renders machining of the material prohibitively costly; the near net shape forming technique of injection molding is accordingly favored as a means for component fabrication. Attention is presently given to the relationships between injection molding processing parameters and the resulting microstructural and mechanical properties of the resulting engine parts. An experimental program has been conducted under NASA sponsorship which tests the quality of injection molded bars of silicon nitride at various stages of processing.

  19. Analysing the isotopic evolution of Silicon in the weathering zone by numerical modelling

    NASA Astrophysics Data System (ADS)

    Georg, B.; Opfergelt, S.

    2010-12-01

    The role of plant biological activity for the continental silicon cycle has been extensively discussed, and the overall consensus is that biological processes in terrestrial ecosystems play an important role in global Si mass balances. Biologically recycled Si fluxes are supposed to rival or in some cases exceed Si fluxes that stem from the dissolution of primary silicates (ALEXANDRE et al., 1997; DERRY et al., 2005). Discrepancies between Si weathering rates and denudation are mostly ascribed to the lock-up of Si in biogenic silica. However, for most settings it can be found that biological turnover is rather fast, and only a small proportion of biogenic Si is stored in long-term sinks, such as ‘old’ phytolith assemblages in soils (ALEXANDRE et al., 1997). The gross of the annually produced biogenic silica is returned to the topsoil as litter fall and subsequently re-dissolved during organic matter degradation. Previous models balanced the mass-fluxes between different Si pools. However, by only using Si fluxes, it is not possible to actually trace the material flux through various pools. In recent years a growing number of Si isotope data for weathering systems became available, and thus a new level of information is available to trace the reaction pathways of Si in the soil-biosphere-river system. Numerical models can be used to simulate matter exchange between pools and to simulate the isotopic fractionation and distribution in such an interlinked system in a temporal context. Preliminary results show that the formation of secondary minerals is the main process driving positive isotope composition in rivers. Although more Si is recycled through the biosphere, a fast turnover means that any significant isotope fractionation is counterbalanced when biogenic silica is returned to the soil system. The clay-pool is isotopically the lightest pool, followed by biosphere and finally dissolved Si in rivers. Once the biological cycle is in steady-state, it is mostly

  20. Coupling of the distribution of silicon isotopes to the meridional overturning circulation of the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Brzezinski, Mark A.; Jones, Janice L.

    2015-06-01

    The distribution of silicon isotopes within silicic acid, δ30Si(OH)4, was examined along a section in the North Atlantic from the Cape Verde Islands off Africa to Cape Cod, Massachusetts in North America. Surface water displayed elevated δ30Si(OH)4 associated with biological fractionation of Si during silica production. Below 300 m variations in δ30Si(OH)4 were closely tied to the distribution of water masses as diagnosed through optimum multiparameter analysis, confirming a tight relationship between δ30Si(OH)4 and the meridional overturning circulation in the Atlantic. A linear relationship between δ30Si(OH)4 and the inverse of silicic acid concentration supported control of Si isotope distribution by conservative mixing of end member water masses of different isotopic composition in the Atlantic. There was a suggestion of a weak local minimum in δ30Si(OH)4 in deep waters above the Trans-Atlantic Geotraverse hydrothermal zone on the mid-Atlantic Ridge consistent with the light δ30Si(OH)4 of hydrothermal waters. The lightest δ30Si(OH)4 values were observed in the deep western and deep eastern basins where Antarctic Bottom Water (AABW) dominated. The heaviest values in subsurface waters occurred in North Atlantic Deep Water due to strong ventilation and the contribution of heavy northern source waters that are influenced by the Arctic Ocean. The concept of a silicon isotope bipole is introduced to explain how the isotopic differences between the northern and southern end-member water masses arise, and how they influence Si isotope distributions. Northern end-member water masses are heavy due to the influence of the Arctic Ocean. Bottom topography prevents light deep waters from entering the Arctic and the further removal of light isotopes through local biological productivity results in extremely heavy δ30Si(OH)4 within the Arctic. Light AABW dominates the southern end member. The Southern Ocean silicic acid trap distills heavier isotopes of Si out of the

  1. Analytical and experimental evaluation of joining silicon nitride to metal and silicon carbide to metal for advanced heat engine applications

    SciTech Connect

    Kang, S.; Selverian, J.H.; Kim, H.; O'Niel, D.; Kim, K. )

    1990-04-01

    This report summarizes the results of Phase I of Analytical and Experimental Evaluation of Joining Silicon Nitride to Metal and Silicon Carbide to Metal and Silicon Carbide to Metal for Advanced Heat Engine Applications. A general methodology was developed to optimize the joint geometry and material systems for 650 and 950{degree}C applications. Failure criteria were derived to predict the fracture of the braze and ceramic. Extensive finite element analyses (FEA), using ABAQUS code, were performed to examine various joint geometries and to evaluate the affect of different interlayers on the residual stress state. Also, material systems composed of coating materials, interlayers, and braze alloys were developed for the program based on the chemical stability and strength of the joints during processing and service. Finally, the FEA results were compared with experiments using an idealized strength relationship. The results showed that the measured strength of the joint reached 30--90% of the strength by predicted by FEA. Overall results demonstrated that FEA is an effective tool for designing the geometries of ceramic-metal joints and that joining by brazing is a relevant method for advanced heat engine applications. 33 refs., 54 figs., 36 tabs.

  2. Astrophysics of CAI formation as revealed by silicon isotope LA-MC-ICPMS of an igneous CAI

    NASA Astrophysics Data System (ADS)

    Shahar, Anat; Young, Edward D.

    2007-05-01

    Silicon isotope ratios of a typical CAI from the Leoville carbonaceous chondrite, obtained in situ by laser ablation MC-ICPMS, together with existing 25Mg/ 24Mg data, reveal a detailed picture of the astrophysical setting of CAI melting and subsequent heating. Models for the chemical and isotopic effects of evaporation of the molten CAI are used to produce a univariant relationship between PH 2 and time during melting. The result shows that this CAI was molten for a cumulative time of no more than 70 days and probably less than 15 days depending on temperature. The object could have been molten for an integrated time of just a few hours if isotope ratio zoning was eliminated after melting by high subsolidus temperatures (e.g., > 1300 K) for ˜ 500 yr. In all cases subsolidus heating sufficient to produce diffusion-limited isotope fractionation at the margin of the solidified CAI is required. These stable isotope data point to a two-stage history for this igneous CAI involving melting for a cumulative timescale of hours to months followed by subsolidus heating for years to hundreds of years. The thermobarometric history deduced from combining Si and Mg isotope ratio data implicates thermal processing in the disk, perhaps by passage through shockwaves, following melting. This study underscores the direct link between the meaning of stable isotope ratio zoning, or lack thereof, and the inferred astrophysical setting of melting and subsequent processing of CAIs.

  3. Quantum engineering at the silicon surface using dangling bonds

    PubMed Central

    Schofield, S. R.; Studer, P.; Hirjibehedin, C. F.; Curson, N. J.; Aeppli, G.; Bowler, D. R.

    2013-01-01

    Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image. Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy. PMID:23552064

  4. Silicon isotope fractionation during silica precipitation from hot-spring waters: Evidence from the Geysir geothermal field, Iceland

    NASA Astrophysics Data System (ADS)

    Geilert, Sonja; Vroon, Pieter Z.; Keller, Nicole S.; Gudbrandsson, Snorri; Stefánsson, Andri; van Bergen, Manfred J.

    2015-09-01

    This study aims to explore the extent and controls of silicon isotope fractionation in hot spring systems of the Geysir geothermal area (Iceland), a setting where sinter deposits are actively formed. The δ30Si values of dissolved silica measured in the spring water and sampling sites along outflowing streams, covering a temperature range between 20 and 100 °C, were relatively constant around +0.2‰, whereas the δ30Si signatures of associated opaline sinters from the streambeds were between -0.1‰ and -4.0‰, becoming progressively more negative in the downstream parts of the aprons. Here, the deposited sinters represent some of the most 30Si depleted abiotically produced terrestrial materials documented to date. Compared to the data reported for Icelandic basalts, considered to be the source of the silicon, the δ30Si values of the fluids and sinter deposits are higher and lower, respectively. The resulting values for apparent solid-water isotope fractionation (Δ30Sisolid-water) decreased with decreasing temperature from ca. -0.7‰ at ∼80 °C to -3.7‰ at ∼20 °C, locally down to -4.4‰. This temperature relationship was reproducible in each of the investigated hot spring systems and is qualitatively consistent with recent findings in laboratory experiments on kinetic fractionation for a flowing fluid. However, the apparent fractionation magnitudes observed in the field are ca. -2‰ more negative and thus significantly larger. We infer that solid-water silicon isotope fractionation during deposition of amorphous silica from a flowing fluid correlates inversely with temperature, but is essentially a function of the precipitation rate, such that the fractionation factor decreases with increasing rate. As an important corollary, the effective fractionation behavior during precipitation of silica from saturated solutions is a system-dependent feature, which should be taken into account when using silicon isotopes for paleo-environmental reconstructions.

  5. Engineering near-infrared single-photon emitters with optically active spins in ultrapure silicon carbide.

    PubMed

    Fuchs, F; Stender, B; Trupke, M; Simin, D; Pflaum, J; Dyakonov, V; Astakhov, G V

    2015-01-01

    Vacancy-related centres in silicon carbide are attracting growing attention because of their appealing optical and spin properties. These atomic-scale defects can be created using electron or neutron irradiation; however, their precise engineering has not been demonstrated yet. Here, silicon vacancies are generated in a nuclear reactor and their density is controlled over eight orders of magnitude within an accuracy down to a single vacancy level. An isolated silicon vacancy serves as a near-infrared photostable single-photon emitter, operating even at room temperature. The vacancy spins can be manipulated using an optically detected magnetic resonance technique, and we determine the transition rates and absorption cross-section, describing the intensity-dependent photophysics of these emitters. The on-demand engineering of optically active spins in technologically friendly materials is a crucial step toward implementation of both maser amplifiers, requiring high-density spin ensembles, and qubits based on single spins. PMID:26151881

  6. Silicon Isotope Geochemistry of Ocean Island Basalts: Search for Deep Mantle Heterogeneities and Evidence for Recycled Altered Oceanic Crust

    NASA Astrophysics Data System (ADS)

    Pringle, E. A.; Savage, P. S.; Jackson, M. G.; Moreira, M. A.; Day, J. M.; Moynier, F.

    2014-12-01

    Analyses of Ocean Island Basalts (OIB) have shown that the Earth's mantle contains isotopically distinct components, but debate about the degree and cause of variability persists. The study of silicon (Si) isotopes in OIBs has the potential to elucidate mantle heterogeneities. Relatively large (~several per mil) Si isotopic fractionation occurs in low-temperature environments during precipitation from dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes [1], but only a limited range (~tenths of a per mil) of Si isotope fractionation has been observed due to high-temperature igneous processes [2]. Therefore, Si isotopes may be useful as tracers for the presence of crustal material in OIB source regions in a manner similar to more conventional stable isotope systems, such as oxygen. Here we present the first comprehensive suite of high-precision Si isotopic data obtained by MC-ICP-MS for a diverse set of OIBs representing the EM-1, EM-2, and HIMU mantle components. In general, the Si isotopic compositions of OIBs analyzed here are agreement with previous estimates for Bulk Silicate Earth (BSE). However, small systematic variations are present; the HIMU end-member Mangaia and HIMU-type Cape Verde island São Nicolau are enriched in the light isotopes of Si (δ30Si = -0.37 ± 0.06‰ and δ30Si = -0.39 ± 0.04‰, respectively; errors are 2sd), with compositions intermediary between Mid Ocean Ridge Basalts and chondritic values. Additionally, Iceland samples from volcanic complexes in the Northern Rift Zone show similar Si isotope compositions (on average, δ30Si = -0.40 ± 0.06‰). In contrast, the δ30Si averages of the EM-1 end-member Pitcairn (-0.28 ± 0.07‰), the EM-2 end-member Samoa (-0.31 ± 0.07‰) and other OIB localities do not show any significant difference from previous estimates for the δ30Si value of BSE [3]. The Si isotopic variability in some HIMU-type and Icelandic OIBs most likely reflects the incorporation of

  7. Analytical and Experimental Evaluation of Joining Silicon Carbide to Silicon Carbide and Silicon Nitride to Silicon Nitride for Advanced Heat Engine Applications Phase II

    SciTech Connect

    Sundberg, G.J.

    1994-01-01

    Techniques were developed to produce reliable silicon nitride to silicon nitride (NCX-5101) curved joins which were used to manufacture spin test specimens as a proof of concept to simulate parts such as a simple rotor. Specimens were machined from the curved joins to measure the following properties of the join interlayer: tensile strength, shear strength, 22 C flexure strength and 1370 C flexure strength. In parallel, extensive silicon nitride tensile creep evaluation of planar butt joins provided a sufficient data base to develop models with accurate predictive capability for different geometries. Analytical models applied satisfactorily to the silicon nitride joins were Norton's Law for creep strain, a modified Norton's Law internal variable model and the Monkman-Grant relationship for failure modeling. The Theta Projection method was less successful. Attempts were also made to develop planar butt joins of siliconized silicon carbide (NT230).

  8. SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE {sup 32}Si IN SUPERNOVAE

    SciTech Connect

    Pignatari, M.; Rauscher, T.; Thielemann, F.-K.; Zinner, E.; Bertolli, M. G.; Trappitsch, R.; Hoppe, P.; Fryer, C.; Herwig, F.; Hirschi, R.; Timmes, F. X.

    2013-07-01

    Carbon-rich grains are observed to condense in the ejecta of recent core-collapse supernovae (SNe) within a year after the explosion. Silicon carbide grains of type X are C-rich grains with isotopic signatures of explosive SN nucleosynthesis have been found in primitive meteorites. Much rarer silicon carbide grains of type C are a special sub-group of SiC grains from SNe. They show peculiar abundance signatures for Si and S, isotopically heavy Si, and isotopically light S, which appear to be in disagreement with model predictions. We propose that C grains are formed mostly from C-rich stellar material exposed to lower SN shock temperatures than the more common type X grains. In this scenario, extreme {sup 32}S enrichments observed in C grains may be explained by the presence of short-lived {sup 32}Si ({tau}{sub 1/2} = 153 yr) in the ejecta, produced by neutron capture processes starting from the stable Si isotopes. No mixing from deeper Si-rich material and/or fractionation of Si from S due to molecular chemistry is needed to explain the {sup 32}S enrichments. The abundance of {sup 32}Si in the grains can provide constraints on the neutron density reached during the SN explosion in the C-rich He shell material. The impact of the large uncertainty of the neutron capture cross sections in the {sup 32}Si region is discussed.

  9. Tritium trapping in silicon carbide in contact with solid breeder under high flux isotope reactor irradiation

    SciTech Connect

    H. Katsui; Y. Katoh; A. Hasegawa; M. Shimada; Y. Hatano; T. Hinoki; S. Nogami; T. Tanaka; S. Nagata; T. Shikama

    2013-11-01

    The trapping of tritium in silicon carbide (SiC) injected from ceramic breeding materials was examined via tritium measurements using imaging plate (IP) techniques. Monolithic SiC in contact with ternary lithium oxide (lithium titanate and lithium aluminate) as a ceramic breeder was irradiated in the High Flux Isotope Reactor (HFIR) in Oak Ridge, Tennessee, USA. The distribution of photo-stimulated luminescence (PSL) of tritium in SiC was successfully obtained, which separated the contribution of 14C ß-rays to the PSL. The tritium incident from ceramic breeders was retained in the vicinity of the SiC surface even after irradiation at 1073 K over the duration of ~3000 h, while trapping of tritium was not observed in the bulk region. The PSL intensity near the SiC surface in contact with lithium titanate was higher than that obtained with lithium aluminate. The amount of the incident tritium and/or the formation of a Li2SiO3 phase on SiC due to the reaction with lithium aluminate under irradiation likely were responsible for this observation.

  10. Silicon Isotope Geochemistry of Ocean Island Basalts: Mantle Heterogeneities and Contribution of Recycled Oceanic Crust and Lithosphere

    NASA Astrophysics Data System (ADS)

    Pringle, E. A.; Moynier, F.; Savage, P. S.; Jackson, M. G.; Moreira, M. A.; Day, J. M.

    2015-12-01

    The study of Silicon (Si) isotopes in Ocean Island Basalts (OIB) has the potential to elucidate between possible heterogeneities in the mantle. Relatively large (~several per mil per atomic mass unit) Si isotope fractionation occurs in low-temperature environments during biochemical and geochemical precipitation of dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes [1]. In contrast, only a limited range (~tenths of a per mil) of Si isotope fractionation has been observed in high-temperature igneous processes [2]. Therefore, Si isotopes may be useful as tracers for the presence of crustal material (derived from low-temperature surface processes) in OIB source regions in a manner similar to more conventional stable isotope systems, such as O. Here we present the first comprehensive set of high-precision Si isotope data obtained by MC-ICP-MS for a diverse suite of OIBs, including new data for the Canary Islands. Samples represent the Pacific, Atlantic, and Indian Ocean basins and include representative end-members for the EM-1, EM-2, and HIMU mantle components. Average δ30Si values for OIBs representing the EM-1 (-0.32 ± 0.06‰, 2 sd), EM-2 (-0.30 ± 0.01‰, 2 sd), and HIMU (-0.34 ± 0.09‰, 2 sd) mantle components are all in general agreement with previous estimates for the δ30Si value of Bulk Silicate Earth [3]. However, small systematic variations are present; HIMU (Mangaia, Cape Verde, La Palma) and Iceland OIBs are enriched in the lighter isotopes of Si (δ30Si values lower than MORB). Further, the difference in Si isotope composition between La Palma and El Heirro (Canary Islands) has previously been observed for O isotopes [4], suggesting a relationship between the Si and O isotope mantle systematics. The Si isotope variations among OIBs may be explained by the sampling of a primitive mantle reservoir enriched in the light isotopes of Si, as suggested by [5], but most likely reflects the incorporation of recycled

  11. Evaluation and silicon nitride internal combustion engine components. Final report, Phase I

    SciTech Connect

    Voldrich, W.

    1992-04-01

    The feasibility of silicon nitride (Si{sub 3}N{sub 4}) use in internal combustion engines was studied by testing three different components for wear resistance and lower reciprocating mass. The information obtained from these preliminary spin rig and engine tests indicates several design changes are necessary to survive high-stress engine applications. The three silicon nitride components tested were valve spring retainers, tappet rollers, and fuel pump push rod ends. Garrett Ceramic Components` gas-pressure sinterable Si{sub 3}N{sub 4} (GS-44) was used to fabricate the above components. Components were final machined from densified blanks that had been green formed by isostatic pressing of GS-44 granules. Spin rig testing of the valve spring retainers indicated that these Si{sub 3}N{sub 4} components could survive at high RPM levels (9,500) when teamed with silicon nitride valves and lower spring tension than standard titanium components. Silicon nitride tappet rollers showed no wear on roller O.D. or I.D. surfaces, steel axles and lifters; however, due to the uncrowned design of these particular rollers the cam lobes indicated wear after spin rig testing. Fuel pump push rod ends were successful at reducing wear on the cam lobe and rod end when tested on spin rigs and in real-world race applications.

  12. Interface Engineering of High Efficiency Organic-Silicon Heterojunction Solar Cells.

    PubMed

    Yang, Lixia; Liu, Yaoping; Chen, Wei; Wang, Yan; Liang, Huili; Mei, Zengxia; Kuznetsov, Andrej; Du, Xiaolong

    2016-01-13

    Insufficient interface conformity is a challenge faced in hybrid organic-silicon heterojunction solar cells because of using conventional pyramid antireflection texturing provoking the porosity of interface. In this study, we tested alternative textures, in particular rounded pyramids and inverted pyramids to compare the performance. It was remarkably improved delivering 7.61%, 8.91% and 10.04% efficiency employing conventional, rounded, and inverted pyramids, respectively. The result was interpreted in terms of gradually improving conformity of the Ag/organic/silicon interface, together with the gradually decreasing serial resistance. Altogether, the present data may guide further efforts arising the interface engineering for mastering high efficient heterojunction solar cells. PMID:26701061

  13. Selective modulation of cell response on engineered fractal silicon substrates

    PubMed Central

    Gentile, Francesco; Medda, Rebecca; Cheng, Ling; Battista, Edmondo; Scopelliti, Pasquale E.; Milani, Paolo; Cavalcanti-Adam, Elisabetta A.; Decuzzi, Paolo

    2013-01-01

    A plethora of work has been dedicated to the analysis of cell behavior on substrates with ordered topographical features. However, the natural cell microenvironment is characterized by biomechanical cues organized over multiple scales. Here, randomly rough, self-affinefractal surfaces are generated out of silicon,where roughness Ra and fractal dimension Df are independently controlled. The proliferation rates, the formation of adhesion structures, and the morphology of 3T3 murine fibroblasts are monitored over six different substrates. The proliferation rate is maximized on surfaces with moderate roughness (Ra ~ 40 nm) and large fractal dimension (Df ~ 2.4); whereas adhesion structures are wider and more stable on substrates with higher roughness (Ra ~ 50 nm) and lower fractal dimension (Df ~ 2.2). Higher proliferation occurson substrates exhibiting densely packed and sharp peaks, whereas more regular ridges favor adhesion. These results suggest that randomly roughtopographies can selectively modulate cell behavior. PMID:23492898

  14. Strain engineering of diamond silicon vacancy centers in MEMS cantilevers

    NASA Astrophysics Data System (ADS)

    Meesala, Srujan; Sohn, Young-Ik; Atikian, Haig; Holzgrafe, Jeffrey; Zhang, Mian; Burek, Michael; Loncar, Marko

    2016-05-01

    The silicon vacancy (SiV) center in diamond has recently attracted attention as a solid state quantum emitter due to its attractive optical properties. We fabricate diamond MEMS cantilevers, and use electrostatic actuation to apply controlled strain fields to single SiV centers implanted in these devices. The strain response of the four electronic transitions of the SiV at 737 nm is measured via cryogenic (4 K) photoluminescence excitation. We demonstrate over 300 GHz of tuning for the mean transition frequency between the ground and excited states, and over 100 GHz of tuning for the orbital splittings within the ground and excited states. The interaction Hamiltonian for strain fields is inferred, and large strain susceptibilities of the order 1 PHz/strain are measured. We discuss prospects to utilize our device to reduce phonon-induced decoherence in SiV spin qubits, and to exploit the large strain susceptibilities for hybrid quantum systems based on nanomechanical resonators.

  15. Carbon, nitrogen, magnesium, silicon, and titanium isotopic compositions of single interstellar silicon carbide grains from the Murchison carbonaceous chondrite

    NASA Technical Reports Server (NTRS)

    Hoppe, Peter; Amari, Sachiko; Zinner, Ernst; Ireland, Trevor; Lewis, Roy S.

    1994-01-01

    Seven hundred and twenty SiC grains from the Murchison CM2 chondrite, ranging in size from 1 to 10 micrometers, were analyzed by ion microprobe mass spectrometry for their C-isotopic compositions. Subsets of the grains were also analyzed for N (450 grains), Si (183 grains), Mg (179 grains), and Ti (28 grains) isotopes. These results are compared with previous measurements on 41 larger SiC grains (up to 15 x 26 micrometers) from a different sample of Murchison analyzed by Virag et al. (1992) and Ireland, Zinner, & Amari (1991a). All grains of the present study are isotopically anomalous with C-12/C-13 ratios ranging from 0.022 to 28.4 x solar, N-14/N-15 ratios from 0.046 to 30 x solar, Si-29/Si-28 from 0.54 to 1.20 x solar, Si-30/Si-28 from 0.42 to 1.14 x solar, Ti-49/Ti-48 from 0.96 to 1.95 x solar, and Ti-50/Ti-48 from 0.94 to 1.39 x solar. Many grains have large Mg-26 excesses from the decay of Al-26 with inferred Al-26/Al-27 ratios ranging up to 0.61, or 12,200 x the ratio of 5 x 10(exp -5) inferred for the early solar system. Several groups can be distinguished among the SiC grains. Most of the grains have C-13 and N-14 excesses, and their Si isotopic compositions (mostly excesses in Si-29 and Si-30) plot close to a slope 1.34 line on a Delta Si-29/Si-28 versus Delta Si-30/Si-28 three-isotope plot. Grains with small C-12/C-13 ratios (less than 10) tend to have smaller or no N-14 excesses and high Al-26/Al-27 ratios (up to 0.01). Grains with C-12/C-13 greater than 150 fall into two groups: grains X have N-15 excesses and Si-29 and Si-30 deficits and the highest (0.1 to 0.6) Al-26/Al-27 ratios; grains Y have N-14 excesses and plot on a slope 0.35 line on a Si three-isotope plot. In addition, large SiC grains of the Virag et al. (1992) study fall into three-distinct clusters according to their C-, Si-, and Ti-isotopic compositions. The isotopic diversity of the grains and the clustering of their isotopic compositions imply distinct and multiple stellar sources

  16. SIMS analyses of silicon and oxygen isotope ratios for quartz from Archean and Paleoproterozoic banded iron formations

    NASA Astrophysics Data System (ADS)

    Heck, Philipp R.; Huberty, Jason M.; Kita, Noriko T.; Ushikubo, Takayuki; Kozdon, Reinhard; Valley, John W.

    2011-10-01

    Banded iron formations (BIFs) are chemical marine sediments dominantly composed of alternating iron-rich (oxide, carbonate, sulfide) and silicon-rich (chert, jasper) layers. Isotope ratios of iron, carbon, and sulfur in BIF iron-bearing minerals are biosignatures that reflect microbial cycling for these elements in BIFs. While much attention has focused on iron, banded iron formations are equally banded silica formations. Thus, silicon isotope ratios for quartz can provide insight on the sources and cycling of silicon in BIFs. BIFs are banded by definition, and microlaminae, or sub-mm banding, are characteristic of many BIFs. In situ microanalysis including secondary ion mass spectrometry is well-suited for analyzing such small features. In this study we used a CAMECA IMS-1280 ion microprobe to obtain highly accurate (±0.3‰) and spatially resolved (˜10 μm spot size) analyses of silicon and oxygen isotope ratios for quartz from several well known BIFs: Isua, southwest Greenland (˜3.8 Ga); Hamersley Group, Western Australia (˜2.5 Ga); Transvaal Group, South Africa (˜2.5 Ga); and Biwabik Iron Formation, Minnesota, USA (˜1.9 Ga). Values of δ 18O range from +7.9‰ to +27.5‰ and include the highest reported δ 18O values for BIF quartz. Values of δ 30Si have a range of ˜5‰ from -3.7‰ to +1.2‰ and extend to the lowest δ 30Si values for Precambrian cherts. Isua BIF samples are homogeneous in δ 18O to ±0.3‰ at mm- to cm-scale, but are heterogeneous in δ 30Si up to 3‰, similar to the range in δ 30Si found in BIFs that have not experienced high temperature metamorphism (up to 300 °C). Values of δ 30Si for quartz are homogeneous to ±0.3‰ in individual sub-mm laminae, but vary by up to 3‰ between multiple laminae over mm-to-cm of vertical banding. The scale of exchange for Si in quartz in BIFs is thus limited to the size of microlaminae, or less than ˜1 mm. We interpret differences in δ 30Si between microlaminae as preserved from primary

  17. Engineering Interfacial Silicon Dioxide for Improved Metal-Insulator-Semiconductor Silicon Photoanode Water Splitting Performance.

    PubMed

    Satterthwaite, Peter F; Scheuermann, Andrew G; Hurley, Paul K; Chidsey, Christopher E D; McIntyre, Paul C

    2016-05-25

    Silicon photoanodes protected by atomic layer deposited (ALD) TiO2 show promise as components of water splitting devices that may enable the large-scale production of solar fuels and chemicals. Minimizing the resistance of the oxide corrosion protection layer is essential for fabricating efficient devices with good fill factor. Recent literature reports have shown that the interfacial SiO2 layer, interposed between the protective ALD-TiO2 and the Si anode, acts as a tunnel oxide that limits hole conduction from the photoabsorbing substrate to the surface oxygen evolution catalyst. Herein, we report a significant reduction of bilayer resistance, achieved by forming stable, ultrathin (<1.3 nm) SiO2 layers, allowing fabrication of water splitting photoanodes with hole conductances near the maximum achievable with the given catalyst and Si substrate. Three methods for controlling the SiO2 interlayer thickness on the Si(100) surface for ALD-TiO2 protected anodes were employed: (1) TiO2 deposition directly on an HF-etched Si(100) surface, (2) TiO2 deposition after SiO2 atomic layer deposition on an HF-etched Si(100) surface, and (3) oxygen scavenging, post-TiO2 deposition to decompose the SiO2 layer using a Ti overlayer. Each of these methods provides a progressively superior means of reliably thinning the interfacial SiO2 layer, enabling the fabrication of efficient and stable water oxidation silicon anodes. PMID:27096845

  18. Light emission from rare-earths in dislocation engineered silicon substrates

    NASA Astrophysics Data System (ADS)

    Lourenço, Manon A.; Ludurczak, Willy; Prins, Andrew D.; Milosavljević, Momir; Gwilliam, Russell M.; Homewood, Kevin P.

    2015-07-01

    We report and compare the luminescence, both photo- and electroluminescence, in the near-infrared of a wide range of rare earths (Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) doped dislocation engineered silicon light emitting devices. The rare earths are introduced using ion implantation into standard Czochralski (CZ) n-type silicon wafers pre-implanted with boron to form both the p-n junction and an engineered dislocation loop array. Rare earth internal transitions are observed in samples co-doped with Dy, Ho, Er, and Tm. We show that for each rare earth optimizing the optical activity depends critically on the rare earth implant parameters and post-implant process conditions. Room temperature operation in the 1.5 and 2.0 µm spectral regions is observed from the internal rare earth transitions in Er and Tm.

  19. Nanoscale contact engineering for Silicon/Silicide nanowire devices

    NASA Astrophysics Data System (ADS)

    Lin, Yung-Chen

    Metal silicides have been used in silicon technology as contacts to achieve high device performance and desired device functions. The growth and applications of silicide materials have recently attracted increasing interest for nanoscale device applications. Nanoscale silicide materials have been demonstrated with various synthetic approaches. Solid state reaction wherein high quality silicides form through diffusion of metal atoms into silicon nano-templates and the subsequent phase transformation caught significant attention for the fabrication of nanoscale Si devices. Very interestingly, studies on the diffusion and phase transformation processes at nanoscale have indicated possible deviations from the bulk and the thin film system. Here we studied growth kinetics, electronic properties and device applications of nanoscale silicides formed through solid state reaction. We have grown single crystal PtSi nanowires and PtSi/Si/PtSi nanowire heterostructures through solid state reaction. TEM studies show that the heterostructures have atomically sharp interfaces free of defects. Electrical measurement of PtSi nanowires shows a low resistivity of ˜28.6 μΩ·cm and a high breakdown current density beyond 108 A/cm2. Furthermore, using single-crystal PtSi/Si/PtSi nanowire heterostructures with atomically clean interfaces, we have fabricated p-channel enhancement mode transistors with the best reported performance for intrinsic silicon nanowires to date. In our results, silicide can provide a clean and no Fermi level pinning interface and then silicide can form Ohmic-contact behavior by replacing the source/drain metal with PtSi. It has been proven by our experiment by contacting PtSi with intrinsic Si nanowires (no extrinsic doping) to achieve high performance p-channel device. By utilizing the same approach, single crystal MnSi nanowires and MnSi/Si/MnSi nanowire heterojunction with atomically sharp interfaces can also been grown. Electrical transport studies on Mn

  20. Silicon subsystem mechanical engineering closeout report for the Solenoidal Detector Collaboration

    SciTech Connect

    Hanlon, J.; Christensen, R.W.; Hayman, G.; Jones, D.C.; Ross, R.; Wilds, W.; Yeamans, S.; Ziock, H.J.

    1995-02-01

    The authors group at Los Alamos National Laboratory was responsible for the mechanical engineering of the silicon tracking system of the Solenoidal Detector Collaboration (SDC) experiment of the Superconducting Super Collider (SSC) project. The responsibility included the overall design of the system from the mechanical point of view, development and integration of the cooling system, which was required to remove the heat generated by the front-end electronics, assembly of the system to extremely tight tolerances, and verification that the construction and operational stability and alignment tolerances would be met. A detailed description of the concepts they developed and the work they performed can be found in a report titled ``Silicon Subsystem Mechanical Engineering Work for the Solenoidal Detector Collaboration`` which they submitted to the SSC Laboratory. In addition to the mechanical engineering work, they also performed activation, background, and shielding studies for the SSC program. Much of the work they performed was potentially useful for other future high energy physics (HEP) projects. This report describes the closeout work that was performed for the Los Alamos SDC project. Four major tasks were identified for completion: (1) integration of the semi-automated assembly station being developed and construction of a precision part to demonstrate solutions to important general assembly problems (the station was designed to build precision silicon tracker subassemblies); (2) build a state-of-the-art TV holography (TVH) system to use for detector assembly stability tests; (3) design, build, and test a water based cooling system for a full silicon shell prototype; and (4) complete and document the activation, background, and shielding studies, which is covered in a separate report.

  1. NanoSIMS studies of Ba isotopic compositions in single presolar silicon carbide grains from AGB stars and supernovae

    NASA Astrophysics Data System (ADS)

    Marhas, K. K.; Hoppe, P.; Ott, U.

    2007-08-01

    We have studied 74 single presolar silicon carbide grains with sizes between 0.2 and 2.6 μm from the Murchison and Murray meteorites for Ba isotopic compositions using NanoSIMS. We also analyzed 7 SiC particles either consisting of sub-micron-size SiC grains or representing a morphologically and isotopically distinct subgroup. Of the 55 (likely) mainstream grains, originating from asymptotic giant branch (AGB) stars, 32 had high enough Ba contents for isotopic analysis. For 26 of them, CsHx interferences were either negligible or could be corrected with confidence. They exhibit typical s-process Ba isotopic patterns with slightly higher than solar 134Ba/136Ba and lower than solar 135,137,138Ba/136Ba ratios. Results are generally well explained in the context of neutron capture nucleosynthesis in low mass (1-3 M⊙) AGB stars and provide constraints on AGB models, by reducing the needed 13C spread from factor of ˜20 down to 2. Out of the 19 supernova X grains, three had sufficient concentrations for isotopic analysis. They tend to exhibit higher than solar 134Ba/136Ba and 138Ba/136Ba ratios, close to solar 137Ba/136Ba, and 135Ba/136Ba lower than solar but higher than in mainstream grains. This signature could indicate a mixture of n-burst type Ba with either "normal Ba" more s-process-rich than solar, or normal Ba plus weak s-process Ba. In the n-burst component Cs may have to be separated from Ba at ˜10 years after the SN explosion. Depending on predictions for its composition, another possibility is early separation (at ˜1 year) coupled with addition of some unfractionated n-burst matter. Abundances of trace elements (Sr, Zr, Cs, La, and Ce) analyzed along with Ba signify that implantation may have been an important process for their introduction.

  2. Atomic-Scale Engineering of Abrupt Interface for Direct Spin Contact of Ferromagnetic Semiconductor with Silicon.

    PubMed

    Averyanov, Dmitry V; Karateeva, Christina G; Karateev, Igor A; Tokmachev, Andrey M; Vasiliev, Alexander L; Zolotarev, Sergey I; Likhachev, Igor A; Storchak, Vyacheslav G

    2016-01-01

    Control and manipulation of the spin of conduction electrons in industrial semiconductors such as silicon are suggested as an operating principle for a new generation of spintronic devices. Coherent injection of spin-polarized carriers into Si is a key to this novel technology. It is contingent on our ability to engineer flawless interfaces of Si with a spin injector to prevent spin-flip scattering. The unique properties of the ferromagnetic semiconductor EuO make it a prospective spin injector into silicon. Recent advances in the epitaxial integration of EuO with Si bring the manufacturing of a direct spin contact within reach. Here we employ transmission electron microscopy to study the interface EuO/Si with atomic-scale resolution. We report techniques for interface control on a submonolayer scale through surface reconstruction. Thus we prevent formation of alien phases and imperfections detrimental to spin injection. This development opens a new avenue for semiconductor spintronics. PMID:26957146

  3. Atomic-Scale Engineering of Abrupt Interface for Direct Spin Contact of Ferromagnetic Semiconductor with Silicon

    PubMed Central

    Averyanov, Dmitry V.; Karateeva, Christina G.; Karateev, Igor A.; Tokmachev, Andrey M.; Vasiliev, Alexander L.; Zolotarev, Sergey I.; Likhachev, Igor A.; Storchak, Vyacheslav G.

    2016-01-01

    Control and manipulation of the spin of conduction electrons in industrial semiconductors such as silicon are suggested as an operating principle for a new generation of spintronic devices. Coherent injection of spin-polarized carriers into Si is a key to this novel technology. It is contingent on our ability to engineer flawless interfaces of Si with a spin injector to prevent spin-flip scattering. The unique properties of the ferromagnetic semiconductor EuO make it a prospective spin injector into silicon. Recent advances in the epitaxial integration of EuO with Si bring the manufacturing of a direct spin contact within reach. Here we employ transmission electron microscopy to study the interface EuO/Si with atomic-scale resolution. We report techniques for interface control on a submonolayer scale through surface reconstruction. Thus we prevent formation of alien phases and imperfections detrimental to spin injection. This development opens a new avenue for semiconductor spintronics. PMID:26957146

  4. Atomic-Scale Engineering of Abrupt Interface for Direct Spin Contact of Ferromagnetic Semiconductor with Silicon

    NASA Astrophysics Data System (ADS)

    Averyanov, Dmitry V.; Karateeva, Christina G.; Karateev, Igor A.; Tokmachev, Andrey M.; Vasiliev, Alexander L.; Zolotarev, Sergey I.; Likhachev, Igor A.; Storchak, Vyacheslav G.

    2016-03-01

    Control and manipulation of the spin of conduction electrons in industrial semiconductors such as silicon are suggested as an operating principle for a new generation of spintronic devices. Coherent injection of spin-polarized carriers into Si is a key to this novel technology. It is contingent on our ability to engineer flawless interfaces of Si with a spin injector to prevent spin-flip scattering. The unique properties of the ferromagnetic semiconductor EuO make it a prospective spin injector into silicon. Recent advances in the epitaxial integration of EuO with Si bring the manufacturing of a direct spin contact within reach. Here we employ transmission electron microscopy to study the interface EuO/Si with atomic-scale resolution. We report techniques for interface control on a submonolayer scale through surface reconstruction. Thus we prevent formation of alien phases and imperfections detrimental to spin injection. This development opens a new avenue for semiconductor spintronics.

  5. Silicon-slurry/aluminide coating. [protecting gas turbine engine vanes and blades

    NASA Technical Reports Server (NTRS)

    Deadmore, D. L.; Young, S. G. (Inventor)

    1983-01-01

    A low cost coating protects metallic base system substrates from high temperatures, high gas velocity ovidation, thermal fatigue and hot corrosion and is particularly useful fo protecting vanes and blades in aircraft and land based gas turbine engines. A lacquer slurry comprising cellulose nitrate containing high purity silicon powder is sprayed onto the superalloy substrates. The silicon layer is then aluminized to complete the coating. The Si-Al coating is less costly to produce than advanced aluminides and protects the substrates from oxidation and thermal fatigue for a much longer period of time than the conventional aluminide coatings. While more expensive Pt-Al coatings and physical vapor deposited MCrAlY coatings may last longer or provide equal protection on certain substrates, the Si-Al coating exceeded the performance of both types of coatings on certain superalloys in high gas velocity oxidation and thermal fatigue and increased the resistance of certain superalloys to hot corrosion.

  6. Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.

    SciTech Connect

    Savina, M. R.; Davis, A. M.; Tripa, C. E.; Pellin, M. J.; Clayton, R. N.; Lewis, R. S.; Amari, S.; Gallino, R.; Lugaro, M.; Univ. of Chicago; Washington Univ.; Univ. di Torino; Cambridge Univ.

    2003-09-01

    Barium isotopic compositions of single 2.3-5.3 {mu}m presolar SiC grains from the Murchison meteorite were measured by resonant ionization mass spectrometry. Mainstream SiC grains are enriched in s-process barium and show a spread in isotopic composition from solar to dominantly s-process. In the relatively coarse grain size fraction analyzed, there are large grain-to-grain variations of barium isotopic composition. Comparison of single grain data with models of nucleosynthesis in asymptotic giant branch (AGB) stars indicates that the grains most likely come from low mass carbon-rich AGB stars (1.5 to 3 solar masses) of about solar metallicity and with approximately solar initial proportions of r- and s-process isotopes. Measurements of single grains imply a wide variety of neutron-to-seed ratios, in agreement with previous measurements of strontium, zirconium and molybdenum isotopic compositions of single presolar SiC grains.

  7. Combination of Silicon and Neodymium Isotopes for a better understanding of past changes in bioproductivity and water mass mixing in the upwelling area off Peru

    NASA Astrophysics Data System (ADS)

    Grasse, P.; Ehlert, C.; Frank, M.; Stramma, L.

    2010-12-01

    The Peru coastal upwelling area is characterized by one of the most pronounced Oxygen Minimum Zones (OMZ). Oxygen concentrations are controlled by consumption through decomposition of organic matter versus ventilation via ocean circulation. Surface productivity is a function of both nutrient supply and upwelling intensity. The isotopic composition of Neodymium (Nd) is a powerful proxy for the reconstruction of past ocean circulation due to its intermediate oceanic residence time and the fact that it is independent of biological fractionation. This is in contrast to Silicon (Si) isotopes, which are fractionated during utilization in a way that the lighter Si isotopes are preferentially incorporated into the diatom frustules. The upwelling area off Peru is mainly influenced by water masses from the Central Pacific, which show more radiogenic values (ɛNd = -2), than water masses from the Northern Pacific (ɛNd = -5 to -3) or water masses from the south, which carry an unradiogenic Nd isotope signature originating from the Southern Ocean (ɛNd = -8 to -9). Upwelled Waters on the shelf are mainly supplied from the Equatorial Under Current (EUC) a strong southward flowing water mass originating in the western pacific. Therefore the δ30Si signal of diatoms is mainly influenced by the isotopic signal of the EUC. Past changes in the hydrography therefore would also influence the Si isotopic signal of this productivity proxy independent of silicic acid utilization. For a better understanding of the influence of water mass mixing on the isotopic signatures in the coastal upwelling area and the OMZ, we directly compare the Nd isotope signatures with dissolved stable Silicon isotope data. The information obtained from the unique combination of the biologically influenced Si isotopes and the Nd isotopes will lead to a better understanding of reconstruction of past ocean circulation and productivity.

  8. Guided cell patterning on gold-silicon dioxide substrates by surface molecular engineering.

    PubMed

    Veiseh, Mandana; Wickes, Bronwyn T; Castner, David G; Zhang, Miqin

    2004-07-01

    We report an effective approach to patterning cells on gold-silicon dioxide substrates with high precision, selectivity, stability, and reproducibility. This technique is based on photolithography and surface molecular engineering and requires no cell positioning or delivery devices, thus significantly reducing the potential damage to cells. The cell patterning was achieved by activating the gold regions of the substrate with functionalized thiols that covalently bind proteins onto the gold regions to guide subsequent cell adhesion while passivating the silicon dioxide background with polyethylene glycol to resist cell adhesion. Fourier transform infrared reflectance spectroscopy verified the successful immobilization of proteins on gold surfaces. Protein patterns were visualized by tagging proteins with Rhodamine fluorescent probes. Time-of-flight secondary ion mass spectrometry was used to characterize the chemistry of both the cell-adhesive and cell-resistant regions of surfaces after each key chemical reaction occurring during the molecular surface engineering. The ability of the engineered surfaces to guide cell adhesion was illustrated by differential interference contrast (DIC) reflectance microscopy. The cell patterning technique introduced in this study is compatible with micro- and photo-electronics, and may have many medical, environmental, and defense applications. PMID:14980426

  9. The elemental and isotopic composition of cosmic rays - Silicon to nickel

    NASA Technical Reports Server (NTRS)

    Young, J. S.; Freier, P. S.; Waddington, C. J.; Brewster, N. R.; Fickle, R. K.

    1981-01-01

    The reported observations were made with the aid of the Cosmic Ray Isotope Instrument System (CRISIS) which had been designed to detect and resolve the isotopes of cosmic ray nuclei with atomic numbers equal to or greater than 10. The CRISIS detector was flown on a balloon launched from Aberdeen, South Dakota on 1977 May 20. The period 1977 May 19-22 has been classified by Mason et al. (1979) as one of 'superquiet' solar activity, characterized by the lowest fluxes of low-energy solar particles ever observed. The obtained results are presented in a number of graphs and tables. It was found that the elemental and isotopic abundances of Si are solar-like. Elemental S is underabundant in the cosmic rays by a factor of approximately 3 relative to the solar system, but its isotopic composition resembles the solar composition with S-32 being the dominant isotope. Elemental Ar is virtually absent in the source, and the observed isotopic composition is consistent with a secondary origin. Elemental Ni has a solar-like abundance.

  10. Interface Engineering to Create a Strong Spin Filter Contact to Silicon

    PubMed Central

    Caspers, C.; Gloskovskii, A.; Gorgoi, M.; Besson, C.; Luysberg, M.; Rushchanskii, K. Z.; Ležaić, M.; Fadley, C. S.; Drube, W.; Müller, M.

    2016-01-01

    Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on silicon is a perfect route to enrich silicon nanotechnology with spin filter functionality. To date, the inherent chemical reactivity between EuO and Si has prevented a heteroepitaxial integration without significant contaminations of the interface with Eu silicides and Si oxides. We present a solution to this long-standing problem by applying two complementary passivation techniques for the reactive EuO/Si interface: (i) an in situ hydrogen-Si (001) passivation and (ii) the application of oxygen-protective Eu monolayers–without using any additional buffer layers. By careful chemical depth profiling of the oxide-semiconductor interface via hard x-ray photoemission spectroscopy, we show how to systematically minimize both Eu silicide and Si oxide formation to the sub-monolayer regime–and how to ultimately interface-engineer chemically clean, heteroepitaxial and ferromagnetic EuO/Si (001) in order to create a strong spin filter contact to silicon. PMID:26975515

  11. Microwave Nitridation of Sintered Reaction Bonded Silicon Parts for Natural Gas Fueled Diesel Engines

    SciTech Connect

    Edler, J.; Kiggans, J.O.; Suman, A.W.; Tiegs, T.N.

    1999-01-01

    This cooperative project was a joint development program between Eaton Corporation and Lockheed Martin Energy Research (LMER). Cooperative work was of benefit to both parties. ORNL was able to assess up-scale of the microwave nitridation process using a more intricate-shaped part designed for application in advanced diesel engines. Eaton Corporation mined access to microwave facilities and expertise for the nitridation of SRBSN materials. The broad objective of the CRADA established with Eaton Corporation and ORNL was to develop cost-effective silicon nitride ceramics compared to the current materials available. The following conclusions can be made from the work performed under the CRADA: (1) Demonstrated that the binder burnout step can be incorporated into the SRBSN processing in the microwave furnace. (2) Scale-up of the microwave nitridation process using Eaton Corporation parts showed that the nitridation weight gains were essentially identical to those obtained by conventional heating. (3) Combined nitridation and sintering processes using silicon nitride beads as packing powders results in degradation of the mechanical properties. (4) Gelcasting of silicon nitride materials using Eaton Si mixtures was demonstrated.

  12. Interface Engineering to Create a Strong Spin Filter Contact to Silicon.

    PubMed

    Caspers, C; Gloskovskii, A; Gorgoi, M; Besson, C; Luysberg, M; Rushchanskii, K Z; Ležaić, M; Fadley, C S; Drube, W; Müller, M

    2016-01-01

    Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on silicon is a perfect route to enrich silicon nanotechnology with spin filter functionality. To date, the inherent chemical reactivity between EuO and Si has prevented a heteroepitaxial integration without significant contaminations of the interface with Eu silicides and Si oxides. We present a solution to this long-standing problem by applying two complementary passivation techniques for the reactive EuO/Si interface: (i) an in situ hydrogen-Si (001) passivation and (ii) the application of oxygen-protective Eu monolayers-without using any additional buffer layers. By careful chemical depth profiling of the oxide-semiconductor interface via hard x-ray photoemission spectroscopy, we show how to systematically minimize both Eu silicide and Si oxide formation to the sub-monolayer regime-and how to ultimately interface-engineer chemically clean, heteroepitaxial and ferromagnetic EuO/Si (001) in order to create a strong spin filter contact to silicon. PMID:26975515

  13. Interface Engineering to Create a Strong Spin Filter Contact to Silicon

    NASA Astrophysics Data System (ADS)

    Caspers, C.; Gloskovskii, A.; Gorgoi, M.; Besson, C.; Luysberg, M.; Rushchanskii, K. Z.; Ležaić, M.; Fadley, C. S.; Drube, W.; Müller, M.

    2016-03-01

    Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on silicon is a perfect route to enrich silicon nanotechnology with spin filter functionality. To date, the inherent chemical reactivity between EuO and Si has prevented a heteroepitaxial integration without significant contaminations of the interface with Eu silicides and Si oxides. We present a solution to this long-standing problem by applying two complementary passivation techniques for the reactive EuO/Si interface: (i) an in situ hydrogen-Si (001) passivation and (ii) the application of oxygen-protective Eu monolayers–without using any additional buffer layers. By careful chemical depth profiling of the oxide-semiconductor interface via hard x-ray photoemission spectroscopy, we show how to systematically minimize both Eu silicide and Si oxide formation to the sub-monolayer regime–and how to ultimately interface-engineer chemically clean, heteroepitaxial and ferromagnetic EuO/Si (001) in order to create a strong spin filter contact to silicon.

  14. The silicon isotope composition of Ethmodiscus rex laminated diatom mats from the tropical West Pacific: Implications for silicate cycling during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xiong, Zhifang; Li, Tiegang; Algeo, Thomas; Doering, Kristin; Frank, Martin; Brzezinski, Mark A.; Chang, Fengming; Opfergelt, Sophie; Crosta, Xavier; Jiang, Fuqing; Wan, Shiming; Zhai, Bin

    2015-07-01

    The cause of massive blooms of Ethmodiscus rex laminated diatom mats (LDMs) in the eastern Philippine Sea (EPS) during the Last Glacial Maximum (LGM) remains uncertain. In order to better understand the mechanism of formation of E. rex LDMs from the perspective of dissolved silicon (DSi) utilization, we determined the silicon isotopic composition of single E. rex diatom frustules (δ30SiE. rex) from two sediment cores in the Parece Vela Basin of the EPS. In the study cores, δ30SiE. rex varies from -1.23‰ to -0.83‰ (average -1.04‰), a range that is atypical of marine diatom δ30Si and that corresponds to the lower limit of reported diatom δ30Si values of any age. A binary mixing model (upwelled silicon versus eolian silicon) accounting for silicon isotopic fractionation during DSi uptake by diatoms was constructed. The binary mixing model demonstrates that E. rex dominantly utilized DSi from eolian sources (i.e., Asian dust) with only minor contributions from upwelled seawater sources (i.e., advected from Subantarctic Mode Water, Antarctic Intermediate Water, or North Pacific Intermediate Water). E. rex utilized only ~24% of available DSi, indicating that surface waters of the EPS were eutrophic with respect to silicon during the LGM. Our results suggest that giant diatoms did not always use a buoyancy strategy to obtain nutrients from the deep nutrient pool, thus revising previously proposed models for the formation of E. rex LDMs.

  15. Molecular isotopic engineering (MIE): industrial manufacture of naproxen of predetermined stable carbon-isotopic compositions for authenticity and security protection and intellectual property considerations

    NASA Astrophysics Data System (ADS)

    Jasper, J. P.; Farina, P.; Pearson, A.; Mezes, P. S.; Sabatelli, A. D.

    2016-05-01

    Molecular Isotopic Engineering (MIE) is the directed stable-isotopic synthesis of chemical products for reasons of product identification and of product security, and also for intellectual property considerations. We report here a generally excellent correspondence between the observed and predicted stable carbon-isotopic (δ13C) results for a successful directed synthesis of racemic mixture from its immediate precursors. The observed results are readily explained by the laws of mass balance and isotope mass balance. Oxygen- and hydrogen isotopic results which require an additional assessment of the effects of O and H exchange, presumably due to interaction with water in the reaction solution, are addressed elsewhere. A previous, cooperative study with the US FDA-DPA showed that individual manufacturers of naproxen could readily be differentiated by their stable-isotopic provenance (δ13C, δ18O, and δD ref. 1). We suggest that MIE can be readily employed in the bio/pharmaceutical industry without alteration of present manufacturing processes other than isotopically selecting and/or monitoring reactants and products.

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

    PubMed Central

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

    2015-01-01

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

  17. Automated isotopic measurements of micron-sized dust: application to meteoritic presolar silicon carbide

    NASA Astrophysics Data System (ADS)

    Nittler, Larry R.; Alexander, Conel M. O'D.

    2003-12-01

    We report the development of a new analytical system allowing the fully automated measurement of isotopic ratios in micrometer-sized particles by secondary ion mass spectrometry (SIMS) in a Cameca ims-6f ion microprobe. Scanning ion images and image processing algorithms are used to locate individual particles dispersed on sample substrates. The primary ion beam is electrostatically deflected to and focused onto each particle in turn, followed by a peak-jumping isotopic measurement. Automatic measurements of terrestrial standards indicate similar analytical uncertainties to traditional manual particle analyses (e.g., ˜3‰/amu for Si isotopic ratios). We also present an initial application of the measurement system to obtain Si and C isotopic ratios for ˜3300 presolar SiC grains from the Murchison CM2 carbonaceous chondrite. Three rare presolar Si 3N 4 grains were also identified and analyzed. Most of the analyzed grains were extracted from the host meteorite using a new chemical dissolution procedure. The isotopic data are broadly consistent with previous observations of presolar SiC in the same size range (˜0.5-4 μm). Members of the previously identified SiC AB, X, Y, and Z subgroups were identified, as was a highly unusual grain with an extreme 30Si enrichment, a modest 29Si enrichment, and isotopically light C. The stellar source responsible for this grain is likely to have been a supernova. Minor differences in isotopic distributions between the present work and prior data can be partially explained by terrestrial contamination and grain aggregation on sample mounts, though some of the differences are probably intrinsic to the samples. We use the large new SiC database to explore the relationships between three previously identified isotopic subgroups—mainstream, Y, and Z grains—all believed to originate in asymptotic giant branch stars. The isotopic data for Z grains suggest that their parent stars experienced strong CNO-cycle nucleosynthesis during

  18. Isotopic composition of trace elements in presolar silicon carbide A+B grains

    NASA Astrophysics Data System (ADS)

    Savina, M.; Tripa, C.; Pellin, M.; Davis, A.; Clayton, R.; Lewis, R.; Amari, S.

    2003-04-01

    Presolar SiC are classified into several types based on C, N, and Si isotopic compositions. Most are mainstream, which are generally believed to derive from low-mass asymptotic giant branch (AGB) stars. Among the less common grains, A+B grains, which comprise ˜3-4% of presolar SiC, are perhaps the least well understood. Recent measurements of trace element concentration patterns in individual grains suggest that A+B grains can be divided into at least 4 groups, and thus have multiple astrophysical sites of origin^1. We report here our Resonant Ionization Mass Spectrometry (RIMS) measurements of Zr, Mo, Ba, and Fe isotopic compositions in individual mainstream and type A+B presolar SiC. While the mainstream grains show isotopic compositions compatible with condensation around low-mass AGB stars, most A+B grains have near-solar isotopic compositions, though some show Zr, Mo, and Fe isotope patterns that have not been observed in other types of presolar SiC grains. We discuss these results in terms of possible astrophysical sites for the production of these unusual grains. This work was supported in part by the Department of Energy, BES-Materials Sciences through Contract No. W-31-109-ENG-38. ^1 Amari S., Nittler L. R., Zinner E., Lodders K., and Lewis R. S. (2001) Astrophys. J. 559, 463-483.

  19. Differences between mono-generic and mixed diatom silicon isotope compositions trace present and past nutrient utilisation off Peru

    NASA Astrophysics Data System (ADS)

    Doering, Kristin; Ehlert, Claudia; Grasse, Patricia; Crosta, Xavier; Fleury, Sophie; Frank, Martin; Schneider, Ralph

    2016-03-01

    In this study we combine for the first time silicon (Si) isotope compositions of small mixed diatom species (δ30SibSiO2) and of large handpicked mono-generic (i.e. genus = Coscinodiscus) diatom samples (δ30SiCoscino) with diatom assemblages extracted from marine sediments in the Peruvian upwelling region in order to constrain present and past silicate utilisation. The extension of a previous core-top data set from the Peruvian shelf demonstrates that δ30SiCoscino values record near-complete Si utilisation, as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling. In contrast, the δ30SibSiO2 of small mixed diatom species increase southward along the shelf as well as towards the shore. We attribute highest δ30SibSiO2 values partly to transient iron limitation but primarily to the gradual increase of Si isotope fractionation within the seasonal diatom succession, which are mainly recorded by small diatom species during intense bloom events. In contrast, lower δ30SibSiO2 values are related to initial Si isotope utilisation during periods of weak upwelling, when low Si(OH)4 concentrations do not permit intense blooms and small diatom species record substantially lower δ30Si signatures. As such, we propose that the intensity of the upwelling can be deduced from the offset between δ30SibSiO2 and δ30SiCoscino (Δ30Sicoscino-bSiO2), which is low for strong upwelling conditions and high for prevailing weak upwelling. We apply the information extracted from surface sediments to generate a record of the present-day main upwelling region covering the past 17,700 years and find that this location has also been characterized by a persistent offset (Δ30Sicoscino-bSiO2). By comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions. In addition, our model calculations to quantify species-specific Si isotope fractionation effects based on the

  20. Barium Isotopic Composition of Mainstream Silicon Carbides from Murchison: Constraints for s-process Nucleosynthesis in Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Savina, Michael R.; Davis, Andrew M.; Gallino, Roberto; Straniero, Oscar; Gyngard, Frank; Pellin, Michael J.; Willingham, David G.; Dauphas, Nicolas; Pignatari, Marco; Bisterzo, Sara; Cristallo, Sergio; Herwig, Falk

    2014-05-01

    We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ(138Ba/136Ba) values are found, down to -400‰, which can only be modeled with a flatter 13C profile within the 13C pocket than is normally used. The dependence of δ(138Ba/136Ba) predictions on the distribution of 13C within the pocket in asymptotic giant branch (AGB) models allows us to probe the 13C profile within the 13C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the 22Ne(α, n)25Mg rate in the stellar temperature regime relevant to AGB stars, based on δ(134Ba/136Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ(134Ba/136Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, 130Ba and 132Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of 135Ba, we conclude that there is no measurable decay of 135Cs (t 1/2 = 2.3 Ma) to 135Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before 135Cs decayed.

  1. Chromium and Iron Isotopic Composition of Presolar Silicon Carbide Stardust Grains

    NASA Astrophysics Data System (ADS)

    Savina, M.; Levine, J.; Dauphas, N.; Pellin, M.; Willingham, D.; Stephan, T.; Trappitsch, R.; Davis, A. M.

    2011-12-01

    Most presolar SiC stardust grains derive from Asymptotic Giant Branch (AGB) stars, which are the main source of s-process nuclides in the galaxy. s-Process nucleosynthesis is not a major contributor to iron peak nuclides. The most interesting of these isotopes from an AGB nucleosynthetic standpoint are the trace isotopes 54Cr and 58Fe, which are predicted to have deviations from average Solar System ratios of ~100% and >200%, respectively. The other isotopes of Cr and Fe are essentially unchanged by AGB stars, and are representative of the isotopic composition of the protostellar cloud from which the SiC grains formed. They are thus tracers of Galactic Chemical Evolution, and provide a benchmark for the isotopic composition of the galaxy some five to seven billion years ago. SiC grains were isolated from the Murchison meteorite using high purity reagents and techniques specifically designed to prevent contamination with terrestrial Cr and Fe. Grains from the 2-4 μm size fraction were pressed into a high purity gold foil. Chromium and iron isotopic compositions were measured by Resonance Ionization Mass Spectrometry (RIMS) using new techniques specifically developed for high precision isotopic analysis of iron-peak elements. The Cr isotopic compositions of 19 grains form a distinct group. Several grains had resolvable (>2σ) 50Cr and 53Cr deficits ranging as low as -178%. The 54Cr/ 52Cr δ-values were all within 2σ of the Solar System value, though most were slightly higher. The average δ-values for the grains were -45±31% for 50Cr, -37±21% for 53Cr, and +25±26% for 54Cr. Iron results are pending. Given that AGB stars change most Fe and Cr isotope ratios very little, and that these grains' progenitor stars formed from a few hundred million to about three billion years before the Solar System formed (assuming their initial masses were 1.5 - 3 solar masses), and that grain interstellar residence times are likely less than ~100 - 200 million years, the Fe and Cr

  2. Design, analysis, and characterization of stress-engineered 3D microstructures comprised of PECVD silicon oxide and nitride

    NASA Astrophysics Data System (ADS)

    Pi, Chia-Hsing; Turner, Kevin T.

    2016-06-01

    Microelectromechanical systems (MEMS) are typically 2D or quasi-3D structures fabricated using surface and bulk micromachining processes. In this work, an approach for 3D structure fabrication based on stress engineering is demonstrated. Specifically, sub-mm 3D spherical cage-like structures are realized through the deformation of bilayers of residually-stressed silicon oxide and silicon nitride with micrometer-scale thicknesses. Analytical and finite models to predict the shape of stress-engineered structures based on geometry and residual stress are described and used for structure design. A systematic experimental study was performed to quantify residual stresses in silicon nitride films made by plasma-enhanced chemical vapor deposition (PECVD). The measurements show that the residual stress of PECVD silicon nitride can be tuned over a wide range of tensile stresses through the control of deposition parameters, such as flow rate and power. Stress engineered 3D cage-like structures comprised of PECVD silicon nitride and oxide films were fabricated. 3D structures with a range of curvatures were demonstrated. The measured geometry of the fabricated structures are in good agreement with predictions from analytical and finite element models.

  3. Turbine engine lubricant foaming due to silicone basestock used in non-specification spline lubricant

    SciTech Connect

    Centers, P.W.

    1995-05-01

    Dependent upon molecular weight and distribution, concentration, temperature, air flow, and test details or field application, polydimethylsiloxane (PDMS) may be neutral, profoamant or antifoamant in polyolesters. This understanding was critical in the solution of a turbine engine lubrication system foaming problem occurring at several military locations. Suspect turbine engine-accessory gearbox assembly materials gathered from several sites were evaluated. One non-specification PDMS-based spline lubricant caused copious foaming of the lubricant at less than ten parts-per-million concentration, while a specification polymethyl-phenylsiloxane (PMPS)-based lubricant required a concentration nearly 2000 times greater to generate equivalent foam. Use of the profoamant PDMS spline lubricant was then prohibited. Since prohibition, foaming of turbine engine lubricants used in the particular application has not been reported. PMPS impact on foaming of ester lubricants is similar to a much more viscous PDMS attributed to the reduced interaction of PMPS in esters due to pendant phenyl structure of PMPS absent in PDMS. These data provide significant additional insight and methodology to investigate foaming tendencies of partially miscible silicone-ester and other fluid systems. 7 refs., 2 figs., 1 tab.

  4. High-Performance Silicon Battery Anodes Enabled by Engineering Graphene Assemblies.

    PubMed

    Zhou, Min; Li, Xianglong; Wang, Bin; Zhang, Yunbo; Ning, Jing; Xiao, Zhichang; Zhang, Xinghao; Chang, Yanhong; Zhi, Linjie

    2015-09-01

    We propose a novel material/electrode design formula and develop an engineered self-supporting electrode configuration, namely, silicon nanoparticle impregnated assemblies of templated carbon-bridged oriented graphene. We have demonstrated their use as binder-free lithium-ion battery anodes with exceptional lithium storage performances, simultaneously attaining high gravimetric capacity (1390 mAh g(-1) at 2 A g(-1) with respect to the total electrode weight), high volumetric capacity (1807 mAh cm(-3) that is more than three times that of graphite anodes), remarkable rate capability (900 mAh g(-1) at 8 A g(-1)), excellent cyclic stability (0.025% decay per cycle over 200 cycles), and competing areal capacity (as high as 4 and 6 mAh cm(-2) at 15 and 3 mA cm(-2), respectively). Such combined level of performance is attributed to the templated carbon bridged oriented graphene assemblies involved. This engineered graphene bulk assemblies not only create a robust bicontinuous network for rapid transport of both electrons and lithium ions throughout the electrode even at high material mass loading but also allow achieving a substantially high material tap density (1.3 g cm(-3)). Coupled with a simple and flexible fabrication protocol as well as practically scalable raw materials (e.g., silicon nanoparticles and graphene oxide), the material/electrode design developed would propagate new and viable battery material/electrode design principles and opportunities for energy storage systems with high-energy and high-power characteristics. PMID:26308100

  5. Isotopic compositions of s-process elements in acid-cleaned mainstream presolar silicon carbide

    NASA Astrophysics Data System (ADS)

    Liu, Nan

    Pristine meteorites contain ancient stellar relicts that survived destructions in the early solar system. Isotopic studies of these presolar grains have proven to be a unique method to understand various known and unknown nucleosynthetic processes occurred in their parent stars. Previous studies of isotopic compositions of heavy elements in mainstream SiC grains from low-mass asymptotic giant branch (AGB) stars reported contamination from solar system materials with normal isotopic compositions on grain surfaces and prevented the authors from obtaining the pure nucleosynthetic isotopic signature from stars. In addition, in these previous studies uncertainties in the major neutron source 13C within the 13C-pocket were underestimated because only the 13C mass fraction was considered as a parameter with the 13C-pocket mass and the 13C profile fixed in model calculations. The oversimplified treatment of the 13C-pocket mainly resulted from the fact that it was unclear if there exists any tracer to distinguish different effects of the 13C concentration, the 13C-pocket mass, and the 13C profile within the 13C-pocket. To address these issues, we acid-cleaned all the presolar SiC grains used in this study after their separation from the bulk Murchison meteorite. In addition, we chose to measure strontium and barium isotopic compositions in these acid-cleaned SiC grains, because both elements sit at the first and second s-process peaks along the s-process path, and are sensitive to varying parameters for the s-process in model calculations. By comparing our new acid-cleaned grain data with single grain data from previous studies for barium isotopes, we conclude that the acid-cleaning procedure is quite effective in removing surface barium contamination. For the first time, we find that model predictions for 138Ba/ 136Ba are sensitive to all three variables of the 13C-pocket adopted in AGB model calculations. In order to match the low 138Ba/ 136Ba values in a minor group of

  6. Si transfers during Archean weathering processes traced by silicon isotopes and Ge/Si ratios

    NASA Astrophysics Data System (ADS)

    Delvigne, Camille; Opfergelt, Sophie; Hofmann, Axel; Cardinal, Damien; André, Luc

    2015-04-01

    Weathering conditions in the Mesoarchean are poorly constrained. Recent advances in analytical capabilities have added Si isotopes and Ge/Si ratios to the repertoire of tracers used in the study of soil formation processes: neoformation of secondary clay minerals is associated with large Si isotope and Ge/Si fractionation in response to desilication processes and the weathering degree [1, 2, 3, 4]. Here we combine Si isotopes and Ge/Si ratios of a Mesoarchean paleosol (~2.95 Ga) and of nearly coeval but younger shales as proxies of weathering processes and Si mass transfer at the early Earth's surface. The paleosol is developed on andesite and shows a well defined mineralogical and chemical differentiation. In a first step, similar to modern soils, neoformation of secondary clay minerals in the paleosol was associated with fractionation of Si isotopes and Ge/Si ratios in response to chemical weathering degree and soil desilication. In a second step, the loss of Fe(II)-rich minerals, likely Fe-rich smectites, due to low pO2 conditions produced additional control on Si and Ge mobilities. Opposite fractionation behaviors are observed: products of desilication acted as 28Si and Ge sink while the leaching of Fe(II)-rich minerals released 28Si and Ge to soil solutions. Furthermore, the shales deposited immediately after the paleosol display δ30Si and Ge/Si compositions which may be explained as mixtures of the recognized Archean paleosols components. Their recording within the sedimentary pile suggests that the observed weathering-induced desilication might have been widely effective during the Mesoarchean as well as Fe(II)-rich minerals leaching in a lesser extent and pointing out these processes as determinant in the Si transfers from continents to hydrosphere. [1] Kurtz et al., (2002) Geochim. Cosmochim. Acta 66, 1525-1537 [2] Ziegler et al., (2005) Geochim. Cosmochim. Acta 69, 4597-4610. [3] Opfergelt et al., (2010) Geochim. Cosmochim. Acta 74, 225-240. [4

  7. Silicon Isotope Variations in Giant Spicules of the Deep-sea Sponge Monorhaphis chuni

    NASA Astrophysics Data System (ADS)

    Jochum, K. P.; Schuessler, J. A.; Wang, X.; Müller, W. E.; Andreae, M. O.

    2012-12-01

    The astonishing longevity of the deep-sea sponge Monorhaphis chuni and the stability of their spicules (Wang et al. 2009) provide the potential that single giant basal spicules can be used as paleoenvironmental archives spanning the entire Holocene (Jochum et al. 2012). According to Wille et al. (2010), the Si isotope fractionation is influenced by seawater Si concentration with lower values associated with sponges collected from waters high in Si. In order to track possible secular variations during the last 10000 years in the deep sea, we have therefore determined Si isotope ratios and trace element ratios along center-to-surface sections at a high resolution by femtosecond LA-(MC)-ICP-MS. Samples came from different locations of the East and South China Sea as well as the South Pacific Ocean (near New Caledonia) and were collected at depths between 1100 m and 2100 m. The external reproducibility of the fs LA-(MC)-ICP-MS method was found to be 0.14 ‰ and 0.27 ‰ (2 SD) for δ29Si and δ30Si, respectively. The relative uncertainty on trace element abundance ratios, such as Mg/Ca, is about 5 % (RSD). Significant variations in Si isotope ratios were observed in the giant spicules Q-B and SCS-4 from the East and South China Sea, respectively. The δ30Si values for the largest spicule collected so far (SCS-4, 2.5 m long) from a depth of 2100 m in the South China Sea, span a large range from -1.9 to -3.7 ‰. No obvious trend in Si isotope variability outside external reproducibility could be identified in smaller and presumably younger spicules; average δ30Si values of 4 different segments of the spicule MC from the South China Sea are about -1.3 ‰. Low δ30Si values of about -0.88 ‰ are found in the giant spicule V from the South Pacific. Mg/Ca ratios of most spicules show small, but significant trends from higher values at the rim to lower values in the core, which can be interpreted as an increase in seawater temperature of several degrees Celsius during

  8. Barium isotopic composition of mainstream silicon carbides from Murchison: Constraints for s-process nucleosynthesis in asymptotic giant branch stars

    SciTech Connect

    Liu, Nan; Davis, Andrew M.; Pellin, Michael J.; Dauphas, Nicolas; Savina, Michael R.; Gallino, Roberto; Bisterzo, Sara; Straniero, Oscar; Cristallo, Sergio; Gyngard, Frank; Willingham, David G.; Pignatari, Marco; Herwig, Falk

    2014-05-01

    We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ({sup 138}Ba/{sup 136}Ba) values are found, down to –400‰, which can only be modeled with a flatter {sup 13}C profile within the {sup 13}C pocket than is normally used. The dependence of δ({sup 138}Ba/{sup 136}Ba) predictions on the distribution of {sup 13}C within the pocket in asymptotic giant branch (AGB) models allows us to probe the {sup 13}C profile within the {sup 13}C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the {sup 22}Ne(α, n){sup 25}Mg rate in the stellar temperature regime relevant to AGB stars, based on δ({sup 134}Ba/{sup 136}Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ({sup 134}Ba/{sup 136}Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, {sup 130}Ba and {sup 132}Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of {sup 135}Ba, we conclude that there is no measurable decay of {sup 135}Cs (t {sub 1/2} = 2.3 Ma) to {sup 135}Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before {sup 135}Cs decayed.

  9. The isotopic abundances of neon, magnesium and silicon nuclei accelerated in solar flares

    NASA Technical Reports Server (NTRS)

    Dietrich, W. F.; Simpson, J. A.

    1980-01-01

    Direct measurements of the relative abundance of the isotopes Ne-20 and Ne-22 are reported along with a preliminary value for the Mg-26/Mg-24 ratio and an upper limit to the abundance of Si-30 in solar flare accelerated nuclei. A Ne-20/Ne-22 ratio of 7.7 plus 2.3 or minus 1.7 is in agreement with the ratio for the component Neon-A found in carbonaceous chondrites, while a preliminary value of 0.22 plus or minus 0.07 for Mg-26/Mg-24 is larger by approximately one standard deviation than the expected ratio of 0.14 given by Cameron (1973).

  10. Vibrational lifetimes and isotope effects of interstitial oxygen in silicon and germanium

    NASA Astrophysics Data System (ADS)

    Sun, Baozhou; Yang, Qiguang; Newman, Ron; Pajot, Bernard; Marie, Tolk, Norman; Feldman, Len; Luepke, Gunter

    2004-03-01

    The lifetimes of the asymmetric stretch mode of interstitial ^16O and ^17O isotopes in Si are measured directly by time-resolved, transient bleaching spectroscopy to be 11.5 and 4.5 ps, respectively. We calculated the three-phonon density of states and found that the ^17O mode lies in the highest phonon density resulting from 2TO + 1TA phonon combinations. The lifetime of the ^16O mode in Ge is measured to be 125 ps, i.e., ˜ 10 times longer than in Si. The interaction between the local modes and the lattice vibrations is discussed according to the activity of phonon combinations. This work was supported in part by DOE through grant DE-FG02-99ER45781 (C.W.M. and V.U.), ONR (C.W.M. and V.U.), NSF through grants DMR-00-76027, DMR-02-42316 (C.W.M.), and the Thomas F. and Kate Miller Jeffress Memorial Trust through grant J-545 (C.W.M.).

  11. NOx and ammonium isotopic fingerprints of anammox in natural and engineered systems: Implications for N isotope budgets and the use of NOx isotopes to diagnose process stability in wastewater treatment

    NASA Astrophysics Data System (ADS)

    Lehmann, M. F.; Stöcklin, N.; Brunner, B.; Frame, C. H.; Joss, A.; Kipf, M.; Kuhn, T.; Wunderlin, P.

    2014-12-01

    The anaerobic oxidation of ammonium with nitrite (anammox) has been identified as a very important fixed nitrogen (N) sink, accounting for a large fraction of global fixed N loss in marine, freshwater, and semi-terrestrial environments. In engineered systems, combined nitritation-anammox is an efficient process to remove N from ammonium-rich wastewater, with nitrite as the central intermediate. During the anammox process, nitrate is being produced, providing reducing equivalents for carbon fixation. Measuring the N isotope ratios in fixed N species (i.e., ammonium, nitrite, nitrate) has proven to be a valuable tool to track N cycling in freshwater and marine ecosystems, yet its application in wastewater treatment as a tool to diagnose nitrate production pathways is novel. In this presentation we will elucidate, and compare, the N isotope effects associated with anammox 1) in vitro, 2) in a lacustrine setting, and 3) in a small-scale batch reactor for wastewater treatment. We demonstrate that the anammox nitrite/nitrate isotopic signatures are modulated by the superposition of strong kinetic (normal and inverse) and equilibrium (nitrite-nitrate) N isotope fractionation. The ammonium N isotope effect is driven by kinetic N isotope fractionation, and is similar to that of nitrification. We will discuss the possible controls on the expression of the anammox N isotope effects in the natural environment. We will also evaluate the use of nitrate/nitrite N (and O) isotope signatures to distinguish between nitrate production by anammox versus nitrite oxidation, which is important for optimizing process efficiency during wastewater treatment.

  12. Processing and characterization of diatom nanoparticles and microparticles as potential source of silicon for bone tissue engineering.

    PubMed

    Le, Thi Duy Hanh; Bonani, Walter; Speranza, Giorgio; Sglavo, Vincenzo; Ceccato, Riccardo; Maniglio, Devid; Motta, Antonella; Migliaresi, Claudio

    2016-02-01

    Silicon plays an important role in bone formation and maintenance, improving osteoblast cell function and inducing mineralization. Often, bone deformation and long bone abnormalities have been associated with silica/silicon deficiency. Diatomite, a natural deposit of diatom skeleton, is a cheap and abundant source of biogenic silica. The aim of the present study is to validate the potential of diatom particles derived from diatom skeletons as silicon-donor materials for bone tissue engineering applications. Raw diatomite (RD) and calcined diatomite (CD) powders were purified by acid treatments, and diatom microparticles (MPs) and nanoparticles (NPs) were produced by fragmentation of purified diatoms under alkaline conditions. The influence of processing on the surface chemical composition of purified diatomites was evaluated by X-ray photoelectron spectroscopy (XPS). Diatoms NPs were also characterized in terms of morphology and size distribution by transmission electron microscopy (TEM) and Dynamic light scattering (DLS), while diatom MPs morphology was analyzed by scanning electron microscopy (SEM). Surface area and microporosity of the diatom particles were evaluated by nitrogen physisorption methods. Release of silicon ions from diatom-derived particles was demonstrated using inductively coupled plasma optical emission spectrometry (ICP/OES); furthermore, silicon release kinetic was found to be influenced by diatomite purification method and particle size. Diatom-derived microparticles (MPs) and nanoparticles (NPs) showed limited or no cytotoxic effect in vitro depending on the administration conditions. PMID:26652398

  13. Distal and proximal controls on the silicon stable isotope signature of North Atlantic Deep Water

    NASA Astrophysics Data System (ADS)

    de Souza, Gregory F.; Slater, Richard D.; Hain, Mathis P.; Brzezinski, Mark A.; Sarmiento, Jorge L.

    2015-12-01

    It has been suggested that the uniquely high δ30Si signature of North Atlantic Deep Water (NADW) results from the contribution of isotopically fractionated silicic acid by mode and intermediate waters that are formed in the Southern Ocean and transported to the North Atlantic within the upper limb of the meridional overturning circulation (MOC). Here, we test this hypothesis in a suite of ocean general circulation models (OGCMs) with widely varying MOCs and related pathways of nutrient supply to the upper ocean. Despite their differing MOC pathways, all models reproduce the observation of a high δ30Si signature in NADW, as well showing a major or dominant (46-62%) contribution from Southern Ocean mode/intermediate waters to its Si inventory. These models thus confirm that the δ30Si signature of NADW does indeed owe its existence primarily to the large-scale transport of a distal fractionation signal created in the surface Southern Ocean. However, we also find that more proximal fractionation of Si upwelled to the surface within the Atlantic Ocean must also play some role, contributing 20-46% of the deep Atlantic δ30Si gradient. Finally, the model suite reveals compensatory effects in the mechanisms contributing to the high δ30Si signature of NADW, whereby less export of high-δ30Si mode/intermediate waters to the North Atlantic is compensated by production of a high-δ30Si signal during transport to the NADW formation region. This trade-off decouples the δ30Si signature of NADW from the pathways of deep water upwelling associated with the MOC. Thus, whilst our study affirms the importance of cross-equatorial transport of Southern Ocean-sourced Si in producing the unique δ30Si signature of NADW, it also shows that the presence of a deep Atlantic δ30Si gradient does not uniquely constrain the pathways by which deep waters are returned to the upper ocean.

  14. Electrostatic actuated strain engineering in monolithically integrated VLS grown silicon nanowires

    NASA Astrophysics Data System (ADS)

    Wagesreither, Stefan; Bertagnolli, Emmerich; Kawase, Shinya; Isono, Yoshitada; Lugstein, Alois

    2014-11-01

    In this paper we demonstrate the fabrication and application of an electrostatic actuated tensile straining test (EATEST) device enabling strain engineering in individual suspended nanowires (NWs). Contrary to previously reported approaches, this special setup guarantees the application of pure uniaxial tensile strain with no shear component of the stress while e.g. simultaneously measuring the resistance change of the NW. To demonstrate the potential of this approach we investigated the piezoresistivity of about 3 μm long and 100 nm thick SiNWs but in the same way one can think about the application of such a device on other geometries, other materials beyond Si as well as the use of other characterization techniques beyond electrical measurements. Therefore single-crystal SiNWs were monolithically integrated in a comb drive actuated MEMS device based on a silicon-on-insulator (SOI) wafer using the vapor-liquid-solid (VLS) growth technique. Strain values were verified by a precise measurement of the NW elongation with scanning electron microscopy (SEM). Further we employed confocal μ-Raman microscopy for in situ, high spatial resolution measurements of the strain in individual SiNWs during electrical characterization. A giant piezoresistive effect was observed, resulting in a fivefold increase in conductivity for 3% uniaxially strained SiNWs. As the EATEST approach can be easily integrated into an existing Si technology platform this architecture may pave the way toward a new generation of nonconventional devices by leveraging the strain degree of freedom.

  15. Contact effects and quantum interference in engineered dangling bond loops on silicon surfaces.

    PubMed

    Kleshchonok, Andrii; Gutierrez, Rafael; Cuniberti, Gianaurelio

    2015-09-01

    Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in the dangling bond loops. Our results reveal a strong sensitivity of the low-energy quantum transmission to the loop topology and to the atomistic details of the electrode-loop contact. Varying the length of the loop or the spatial position of at least one of the electrodes has a drastic impact on the quantum interference pattern; depending on whether constructive or destructive interference within the loop takes place, the conductance of the system can be tuned over several orders of magnitude, thus suggesting the possibility of exploiting such quantum mechanical effects in the design of two-dimensional, atomic-scale electronic devices such as logic gates. PMID:26228007

  16. Electrostatic actuated strain engineering in monolithically integrated VLS grown silicon nanowires.

    PubMed

    Wagesreither, Stefan; Bertagnolli, Emmerich; Kawase, Shinya; Isono, Yoshitada; Lugstein, Alois

    2014-11-14

    In this paper we demonstrate the fabrication and application of an electrostatic actuated tensile straining test (EATEST) device enabling strain engineering in individual suspended nanowires (NWs). Contrary to previously reported approaches, this special setup guarantees the application of pure uniaxial tensile strain with no shear component of the stress while e.g. simultaneously measuring the resistance change of the NW. To demonstrate the potential of this approach we investigated the piezoresistivity of about 3 μm long and 100 nm thick SiNWs but in the same way one can think about the application of such a device on other geometries, other materials beyond Si as well as the use of other characterization techniques beyond electrical measurements. Therefore single-crystal SiNWs were monolithically integrated in a comb drive actuated MEMS device based on a silicon-on-insulator (SOI) wafer using the vapor-liquid-solid (VLS) growth technique. Strain values were verified by a precise measurement of the NW elongation with scanning electron microscopy (SEM). Further we employed confocal μ-Raman microscopy for in situ, high spatial resolution measurements of the strain in individual SiNWs during electrical characterization. A giant piezoresistive effect was observed, resulting in a fivefold increase in conductivity for 3% uniaxially strained SiNWs. As the EATEST approach can be easily integrated into an existing Si technology platform this architecture may pave the way toward a new generation of nonconventional devices by leveraging the strain degree of freedom. PMID:25337772

  17. Isotopically controlled semiconductors

    SciTech Connect

    Haller, Eugene E.

    2006-06-19

    The following article is an edited transcript based on the Turnbull Lecture given by Eugene E. Haller at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his 'pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations'. The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin-film heterostructures. Isotopic composition affects several properties such as phonon energies, band structure, and lattice constant in subtle, but, for their physical understanding, significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photoluminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for simultaneous self- and dopant-diffusion studies. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.

  18. Insights into the transfer of silicon isotopes into the sediment record

    NASA Astrophysics Data System (ADS)

    Panizzo, V. N.; Swann, G. E. A.; Mackay, A. W.; Vologina, E.; Sturm, M.; Pashley, V.; Horstwood, M. S. A.

    2016-01-01

    The first δ30Sidiatom data from lacustrine sediment traps are presented from Lake Baikal, Siberia. Data are compared with March surface water (upper 180 m) δ30SiDSi compositions for which a mean value of +2.28 ± 0.09 (95 % confidence) is derived. This value acts as the pre-diatom bloom baseline silicic acid isotopic composition of waters (δ30SiDSi initial). Open traps were deployed along the depth of the Lake Baikal south basin water column between 2012 and 2013. Diatom assemblages display a dominance ( > 85 %) of the spring/summer bloom species Synedra acus var radians, so that δ30Sidiatom compositions reflect predominantly spring/summer bloom utilisation. Diatoms were isolated from open traps and, in addition, from 3-monthly (sequencing) traps (May, July and August 2012) for δ30Sidiatom analyses. Mean δ30Sidiatom values for open traps are +1.23 ± 0.06 (at 95 % confidence and MSWD of 2.9, n = 10). Total dry mass sediment fluxes are highest in June 2012, which we attribute to the initial export of the dominant spring diatom bloom. We therefore argue that May δ30Sidiatom signatures (+0.67 ± 0.06, 2σ) when compared with mean upper water δ30SiDSi initial (e.g. pre-bloom) signatures can be used to provide a snapshot estimation of diatom uptake fractionation factors (ɛuptake) in Lake Baikal. A ɛuptake estimation of -1.61 ‰ is therefore derived, although we emphasise that synchronous monthly δ30SiDSi and δ30Sidiatom data would be needed to provide more robust estimations and therefore more rigorously test this, particularly when taking into consideration any progressive enrichment of the DSi pool as blooms persist. The near-constant δ30Sidiatom composition in open traps

  19. Silicon isotopic abundance toward evolved stars and its application for presolar grains

    NASA Astrophysics Data System (ADS)

    Peng, T.-C.; Humphreys, E. M. L.; Testi, L.; Baudry, A.; Wittkowski, M.; Rawlings, M. G.; de Gregorio-Monsalvo, I.; Vlemmings, W.; Nyman, L.-A.; Gray, M. D.; de Breuck, C.

    2013-11-01

    Aims: Galactic chemical evolution (GCE) is important for understanding the composition of the present-day interstellar medium (ISM) and of our solar system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in evolved stars and tentatively relate this to presolar grain composition. Methods: We used the APEX telescope to detect thermal SiO isotopologue emission toward four oxygen-rich M-type stars. Together with the data retrieved from the Herschel science archive and from the literature, we were able to obtain the 29Si/30Si ratios for a total of 15 evolved stars inferred from their optically thin 29SiO and 30SiO emission. These stars cover a range of masses and ages, and because they do not significantly alter 29Si/30Si during their lifetimes, they provide excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of time. Results: The 29Si/30Si ratios inferred from the thermal SiO emission tend to be lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya), and close to an interstellar or solar value of 1.5 for the higher-mass carbon star IRC+10216 and two red supergiants. There is a tentative correlation between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we take the mass-loss rate as a proxy for the initial stellar mass or current stellar age. This is consistent with the different abundance ratios found in presolar grains. Before the formation of the Sun, the presolar grains indicate that the bulk of presolar grains already had 29Si/30Si ratios of about 1.5, which is also the ratio we found for the objects younger than the Sun, such as VY CMa and IRC+10216. However, we found that older objects (up to possibly 10 Gyr old) in our sample trace a previous, lower 29Si/30Si value of about 1. Material with this isotopic ratio is present in two subclasses of presolar grains, providing independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived from the SiO emission of

  20. Silicon isotope and trace element constraints on the origin of ˜3.5 Ga cherts: Implications for Early Archaean marine environments

    NASA Astrophysics Data System (ADS)

    van den Boorn, S. H. J. M.; van Bergen, M. J.; Vroon, P. Z.; de Vries, S. T.; Nijman, W.

    2010-02-01

    Silicon (Si) isotope variability in Precambrian chert deposits is significant, but proposed explanations for the observed heterogeneity are incomplete in terms of silica provenance and fractionation mechanisms involved. To address these issues we investigated Si isotope systematics, in conjunction with geochemical and mineralogical data, in three well-characterised and approximately contemporaneous, ˜3.5 Ga chert units from the Pilbara greenstone terrane (Western Australia). We show that Si isotope variation in these cherts is large (-2.4‰ to +1.3‰) and was induced by near-surface processes that were controlled by ambient conditions. Cherts that formed by chemical precipitation of silica show the largest spread in δ 30Si (-2.4‰ to +0.6‰) and are characterised by positive Eu, La and Y anomalies and overall depletions in lithophile trace elements. Silicon isotope systematics in these orthochemical deposits are explained by (1) mixing between hydrothermal fluids and seawater, and/or (2) fractionation of hydrothermal fluids by subsurface losses of silica due to conductive cooling. Rayleigh-type fractionation of hydrothermal fluids was largely controlled by temperature differences between these fluids and seawater. Lamina-scale Si isotope heterogeneity within individual chemical chert samples up to 2.2‰ is considered to reflect the dynamic nature of hydrothermal activity. Silicified volcanogenic sediments lack diagnostic REE+Y anomalies, are enriched in lithophile elements, and exhibit a much more restricted range of positive δ 30Si (+0.1‰ to +1.1‰), which points to seawater as the dominant source of silica. The proposed model for Si isotope variability in the Early Archaean implies that chemical cherts with the most negative δ 30Si formed from pristine hydrothermal fluids, whereas silicified or chemical sediments with positive δ 30Si are closest to pure seawater deposits. Taking the most positive value found in this study (+1.3‰), and assuming that

  1. Contact effects and quantum interference in engineered dangling bond loops on silicon surfaces

    NASA Astrophysics Data System (ADS)

    Kleshchonok, Andrii; Gutierrez, Rafael; Cuniberti, Gianaurelio

    2015-08-01

    Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in the dangling bond loops. Our results reveal a strong sensitivity of the low-energy quantum transmission to the loop topology and to the atomistic details of the electrode-loop contact. Varying the length of the loop or the spatial position of at least one of the electrodes has a drastic impact on the quantum interference pattern; depending on whether constructive or destructive interference within the loop takes place, the conductance of the system can be tuned over several orders of magnitude, thus suggesting the possibility of exploiting such quantum mechanical effects in the design of two-dimensional, atomic-scale electronic devices such as logic gates.Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in

  2. Atom probe microscopy of three-dimensional distribution of silicon isotopes in {sup 28}Si/{sup 30}Si isotope superlattices with sub-nanometer spatial resolution

    SciTech Connect

    Shimizu, Yasuo; Kawamura, Yoko; Uematsu, Masashi; Itoh, Kohei M.; Tomita, Mitsuhiro; Sasaki, Mikio; Uchida, Hiroshi; Takahashi, Mamoru

    2009-10-01

    Laser-assisted atom probe microscopy of 2 nm period {sup 28}Si/{sup 30}Si isotope superlattices (SLs) is reported. Three-dimensional distributions of {sup 28}Si and {sup 30}Si stable isotopes are obtained with sub-nanometer spatial resolution. The depth resolution of the present atom probe analysis is much higher than that of secondary ion mass spectrometry (SIMS) even when SIMS is performed with a great care to reduce the artifact due to atomic mixing. Outlook of Si isotope SLs as ideal depth scales for SIMS and three-dimensional position standards for atom probe microscopy is discussed.

  3. The role of nanostructured mesoporous silicon in discriminating in vitro calcification for electrospun composite tissue engineering scaffolds

    NASA Astrophysics Data System (ADS)

    Fan, Dongmei; Akkaraju, Giridhar R.; Couch, Ernest F.; CanhamCurrent Address, Intrinsiq Materials Ltd, Geraldine Road, Malvern Wr14 3SZ Uk, Leigh T.; Coffer, Jeffery L.

    2011-02-01

    The impact of mesoporous silicon (PSi) particles-embedded either on the surface, or totally encapsulated within electrospun poly (ε-caprolactone) (PCL) fibers-on its properties as a tissue engineering scaffold is assessed. Our findings suggest that the resorbable porous silicon component can sensitively accelerate the necessary calcification process in such composites. Calcium phosphate deposition on the scaffolds was measured via in vitro calcification assays both at acellular and cellular levels. Extensive attachment of fibroblasts, human adult mesenchymal stem cells, and mouse stromal cells to the scaffold were observed. Complementary cell differentiation assays and ultrastructural measurements were also carried out; the levels of alkaline phosphatase expression, a specific biomarker for mesenchymal stem cell differentiation, show that the scaffolds have the ability to mediate such processes, and that the location of the Si plays a key role in levels of expression.

  4. Insights on formation mechanism of colorful silica coatings on Kilauean basalts from field observations and silicon isotopes

    NASA Astrophysics Data System (ADS)

    Chemtob, S. M.; Stebbins, J. F.; Guan, Y.; Ziegler, K. G.; Hurowitz, J. A.; Eiler, J. M.; Rossman, G. R.

    2011-12-01

    Many young basalts from Kilauea, on the big island of Hawai'i, feature visually striking white, yellow, orange and blue coatings. These coatings represent an opportunity to study the early onset of acid-sulfate weathering in volcanic environments. The coatings, first investigated on 1974 flows in the Ka'u Desert, consist of a 10-50 μm thick layer of amorphous silica, capped, in some cases, by a ~1 μm layer of Fe-Ti oxide. Both layers contain %-level enrichments of S, and jarosite is present as a minor phase. The coatings often display residual morphologies consistent with formation by leaching, but occasionally demonstrate depositional or accumulative morphology. Coated basalts of various ages (1969-2010) were collected from several sites along the SW and E rift zones of Kilauea to characterize variability in coating properties and the timing of coating formation. As early as one month after emplacement, some lava surfaces feature translucent, discontinuous 2-3 μm silica glazes, and lavas emplaced as recently as 2007 feature mature coating morphologies. Coatings tend to occur most prominently on smooth, low-vesicularity lavas, such as spatter and volcanic bombs. Rougher surfaces tend not to preserve coatings due to enhanced erosion. Older but recently exposed or broken surfaces away from active eruptions appear to regrow bright glazes with similar qualities, suggesting the importance of regional vog or acid rain in coating formation. Field observations illustrate the timing and complexity of silica coating growth, but do not address the coating formation mechanism and degree of Si mobility. Recent work, including in situ silicon isotope analysis via SIMS and detailed structural analysis via 29Si NMR and Raman spectroscopy, strongly suggests that the coatings are depositional and that Si was mobile during coating formation. 29Si NMR spectra indicate that the coating is structurally identical to amorphous silica gel and contains unusually high structural water

  5. Analytical and experimental evaluation of joining silicon nitride to metal and silicon carbide to metal for advanced heat engine applications. Final report

    SciTech Connect

    Kang, S.; Selverian, J.H.; O`Neil, D.; Kim, H.; Kim, K.

    1993-05-01

    This report summarizes the results of Phase 2 of Analytical and Experimental Evaluation of Joining Silicon Nitride to Metal and Silicon Carbide to Metal for Advanced Heat Engine Applications. A general methodology was developed to optimize the joint geometry and material systems for 650{degrees}C applications. Failure criteria were derived to predict the fracture of the braze and ceramic. Extensive finite element analyses (FEA) were performed to examine various joint geometries and to evaluate the affect of different interlayers on the residual stress state. Also, material systems composed of coating materials, interlayers, and braze alloys were developed for the program based on the chemical stability and strength of the joints during processing, and service. The FEA results were compared with experiments using two methods: (1) an idealized strength relationship of the ceramic, and (2) a probabilistic analysis of the ceramic strength (NASA CARES). The results showed that the measured strength of the joint reached 30--80% of the strength predicted by FEA. Also, potential high-temperature braze alloys were developed and evaluated for the high-temperature application of ceramic-metal joints. 38 tabs, 29 figs, 20 refs.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  7. Silicon isotopic chemistry in the Changjiang Estuary and coastal regions: Impacts of physical and biogeochemical processes on the transport of riverine dissolved silica

    NASA Astrophysics Data System (ADS)

    Zhang, A. Y.; Zhang, J.; Hu, J.; Zhang, R. F.; Zhang, G. S.

    2015-10-01

    The dissolved silica (DSi) concentration and silicon isotopic composition (δ30Si) of surface water samples from the Changjiang Estuary was measured in summer and winter to study the behavior of DSi fluvial inputs into the estuary. The DSi concentration decreased away from the estuary and had a linear relationship with salinity, suggesting that mixing between river water and seawater is the dominant effect on DSi levels in the study area. Measured δ30Si in the Changjiang Estuary ranged from +1.48‰ to +2.35‰ in summer, and from +1.54‰ to +1.95‰ in winter. As a result of low light levels and abundant DSi riverine inputs, DSi remains relatively unaffected by biological utilization and fractionation in the near-shore region, and the isotopic imprint of water from the Changjiang can still be detected up to a salinity level of 20 in summer. An obvious increase in δ30Si was observed beyond this salinity level, indicating a significant increase in biological utilization and fractionation of DSi in high salinity waters. Lower water temperatures and light levels that prevail over the winter lead to the reduced fractionation of DSi compared with that in summer. The fractionation factor (30ɛ) was estimated using a steady state model to the high salinity waters, yielding a value of -0.95‰, which is in agreement with previous results obtained for Skeletonema costatum in cultivation experiments. The results of this study suggest that silicon isotopes can be used to identify the impact of biological utilization on the behavior of DSi in highly dynamic estuarine environments.

  8. Raman spectroscopy and in situ Raman spectroelectrochemistry of isotopically engineered graphene systems.

    PubMed

    Frank, Otakar; Dresselhaus, Mildred S; Kalbac, Martin

    2015-01-20

    CONSPECTUS: The special properties of graphene offer immense opportunities for applications to many scientific fields, as well as societal needs, beyond our present imagination. One of the important features of graphene is the relatively simple tunability of its electronic structure, an asset that extends the usability of graphene even further beyond present experience. A direct injection of charge carriers into the conduction or valence bands, that is, doping, represents a viable way of shifting the Fermi level. In particular, electrochemical doping should be the method of choice, when higher doping levels are desired and when a firm control of experimental conditions is needed. In this Account, we focus on the electrochemistry of graphene in combination with in situ Raman spectroscopy, that is, in situ Raman spectroelectrochemistry. Such a combination of methods is indeed very powerful, since Raman spectroscopy not only can readily monitor the changes in the doping level but also can give information on eventual stress or disorder in the material. However, when Raman spectroscopy is employed, one of its main strengths lies in the utilization of isotope engineering during the chemical vapor deposition (CVD) growth of the graphene samples. The in situ Raman spectroelectrochemical study of multilayered systems with smartly designed isotope compositions in individual layers can provide a plethora of knowledge about the mutual interactions (i) between the graphene layers themselves, (ii) between graphene layers and their directly adjacent environment (e.g., substrate or electrolyte), and (iii) between graphene layers and their extended environment, which is separated from the layer by a certain number of additional graphene layers. In this Account, we show a few examples of such studies, from monolayer to two-layer and three-layer specimens and considering both turbostratic and AB interlayer ordering. Furthermore, the concept and the method can be extended further

  9. Subwavelength engineered fiber-to-chip silicon-on-sapphire interconnects for mid-infrared applications (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Alonso-Ramos, Carlos; Han, Zhaohong; Le Roux, Xavier; Lin, Hongtao; Singh, Vivek; Lin, Pao Tai; Tan, Dawn; Cassan, Eric; Marris-Morini, Delphine; Vivien, Laurent; Wada, Kazumi; Hu, Juejun; Agarwal, Anuradha; Kimerling, Lionel C.

    2016-05-01

    The mid-Infrared wavelength range (2-20 µm), so-called fingerprint region, contains the very sharp vibrational and rotational resonances of many chemical and biological substances. Thereby, on-chip absorption-spectrometry-based sensors operating in the mid-Infrared (mid-IR) have the potential to perform high-precision, label-free, real-time detection of multiple target molecules within a single sensor, which makes them an ideal technology for the implementation of lab-on-a-chip devices. Benefiting from the great development realized in the telecom field, silicon photonics is poised to deliver ultra-compact efficient and cost-effective devices fabricated at mass scale. In addition, Si is transparent up to 8 µm wavelength, making it an ideal material for the implementation of high-performance mid-IR photonic circuits. The silicon-on-insulator (SOI) technology, typically used in telecom applications, relies on silicon dioxide as bottom insulator. Unfortunately, silicon dioxide absorbs light beyond 3.6 µm, limiting the usability range of the SOI platform for the mid-IR. Silicon-on-sapphire (SOS) has been proposed as an alternative solution that extends the operability region up to 6 µm (sapphire absorption), while providing a high-index contrast. In this context, surface grating couplers have been proved as an efficient means of injecting and extracting light from mid-IR SOS circuits that obviate the need of cleaving sapphire. However, grating couplers typically have a reduced bandwidth, compared with facet coupling solutions such as inverse or sub-wavelength tapers. This feature limits their feasibility for absorption spectroscopy applications that may require monitoring wide wavelength ranges. Interestingly, sub-wavelength engineering can be used to substantially improve grating coupler bandwidth, as demonstrated in devices operating at telecom wavelengths. Here, we report on the development of fiber-to-chip interconnects to ZrF4 optical fibers and integrated SOS

  10. Probing degradation in complex engineering silicones by 1H multiple quantum NMR

    SciTech Connect

    Maxwell, R S; Chinn, S C; Giuliani, J; Herberg, J L

    2007-09-05

    Static {sup 1}H Multiple Quantum Nuclear Magnetic Resonance (MQ NMR) has recently been shown to provide detailed insight into the network structure of pristine silicon based polymer systems. The MQ NMR method characterizes the residual dipolar couplings of the silicon chains that depend on the average molecular weight between physical or chemical constraints. Recently, we have employed MQ NMR methods to characterize the changes in network structure in a series of complex silicone materials subject to numerous degradation mechanisms, including thermal, radiative, and desiccative. For thermal degradation, MQ NMR shows that a combination of crosslinking due to post-curing reactions as well as random chain scissioning reactions occurs. For radiative degradation, the primary mechanisms are via crosslinking both in the network and at the interface between the polymer and the inorganic filler. For samples stored in highly desiccating environments, MQ NMR shows that the average segmental dynamics are slowed due to increased interactions between the filler and the network polymer chains.

  11. Engineering of silicon/HfO2 interface by variable energy proton irradiation

    NASA Astrophysics Data System (ADS)

    Maurya, Savita; Tribedi, L. C.; Maringanti, Radhakrishna

    2014-08-01

    Surfaces and interfaces between materials are of paramount importance for various phenomena, such as painting a house, catalyst driven chemical reactions, intricate life processes, corrosion of materials, and fabrication of various semiconductor devices. Interface of silicon or other such substrates with any of the oxides has profound effect on the performance of metal oxide field effect transistors and other similar devices. Since a surface is an abrupt termination of a periodic crystal, surface atoms will have some unsaturated valence electrons and these unsaturated bonds at the semiconductor surface make it chemically highly reactive. Other than annealing, there is not much that can be done to manage these unsaturated bonds. This study was initiated to explore the possibility of repairing these unsaturated dangling bonds that are formed at the silicon and oxide interface during the deposition of oxide layer above silicon, by the use of proton irradiation. In order to improve the interface characteristics, we present a method to modify the interface of silicon and hafnium dioxide after its fabrication, through proton irradiation. Results of the study are promising and probably this method might be used along with other methods such as annealing to modify the interface, after its fabrication.

  12. Engineering of silicon/HfO{sub 2} interface by variable energy proton irradiation

    SciTech Connect

    Maurya, Savita Maringanti, Radhakrishna; Tribedi, L. C.

    2014-08-18

    Surfaces and interfaces between materials are of paramount importance for various phenomena, such as painting a house, catalyst driven chemical reactions, intricate life processes, corrosion of materials, and fabrication of various semiconductor devices. Interface of silicon or other such substrates with any of the oxides has profound effect on the performance of metal oxide field effect transistors and other similar devices. Since a surface is an abrupt termination of a periodic crystal, surface atoms will have some unsaturated valence electrons and these unsaturated bonds at the semiconductor surface make it chemically highly reactive. Other than annealing, there is not much that can be done to manage these unsaturated bonds. This study was initiated to explore the possibility of repairing these unsaturated dangling bonds that are formed at the silicon and oxide interface during the deposition of oxide layer above silicon, by the use of proton irradiation. In order to improve the interface characteristics, we present a method to modify the interface of silicon and hafnium dioxide after its fabrication, through proton irradiation. Results of the study are promising and probably this method might be used along with other methods such as annealing to modify the interface, after its fabrication.

  13. Surface Engineering of Silicon and Carbon by Pulsed-Laser Ablation

    SciTech Connect

    Fowlkes, J.D.; Geohegan, D.B.; Jellison, G.E., Jr.; Lowndes, D.H.; Merkulov, V.I.; Pedraza, A.J.; Puretzky, A.A.

    1999-02-28

    Experiments are described in which a focused pulsed-excimer laser beam is used either to ablate a graphite target and deposit hydrogen-free amorphous carbon films, or to directly texture a silicon surface and produce arrays of high-aspect-ratio silicon microcolumns. In the first case, diamond-like carbon (or tetrahedral amorphous carbon, ta-C) films were deposited with the experimental conditions selected so that the masses and kinetic energies of incident carbon species were reasonably well controlled. Striking systematic changes in ta-C film properties were found. The sp{sup 3}-bonded carbon fraction, the valence electron density, and the optical (Tauc) energy gap ail reach their maximum values in films deposited at a carbon ion kinetic energy of {approximately}90 eV. Tapping-mode atomic force microscope measurements also reveal that films deposited at 90 eV are extremely smooth (rms roughness {approximately}1 {angstrom} over several hundred nm) and relatively free of particulate, while the surface roughness increases in films deposited at significantly lower energies. In the second set of experiments, dense arrays of high-aspect-ratio silicon microcolumns {approximately}20-40 {micro}m tall and {approximately}2 {micro}m in diameter were formed by cumulative nanosecond pulsed excimer laser irradiation of silicon wafers in air and other oxygen-containing atmospheres. It is proposed that microcolumn growth occurs through a combination of pulsed-laser melting of the tips of the columns and preferential redeposition of silicon on the molten tips from the ablated flux of silicon-rich vapor. The common theme in this research is that a focused pulsed-laser beam can be used quite generally to create an energetic flux, either the energetic carbon ions needed to form sp{sup 3} (diamond-like) bonds or the overpressure of silicon-rich species needed for microcolumn growth. Thus, new materials synthesis opportunities result from the access to nonequilibrium growth conditions

  14. Identification of volatile and semivolatile compounds in chemical ionization GC-MS using a mass-to-structure (MTS) Search Engine with integral isotope pattern ranking.

    PubMed

    Liao, Wenta; Draper, William M

    2013-02-21

    The mass-to-structure or MTS Search Engine is an Access 2010 database containing theoretical molecular mass information for 19,438 compounds assembled from common sources such as the Merck Index, pesticide and pharmaceutical compilations, and chemical catalogues. This database, which contains no experimental mass spectral data, was developed as an aid to identification of compounds in atmospheric pressure ionization (API)-LC-MS. This paper describes a powerful upgrade to this database, a fully integrated utility for filtering or ranking candidates based on isotope ratios and patterns. The new MTS Search Engine is applied here to the identification of volatile and semivolatile compounds including pesticides, nitrosoamines and other pollutants. Methane and isobutane chemical ionization (CI) GC-MS spectra were obtained from unit mass resolution mass spectrometers to determine MH(+) masses and isotope ratios. Isotopes were measured accurately with errors of <4% and <6%, respectively, for A + 1 and A + 2 peaks. Deconvolution of interfering isotope clusters (e.g., M(+) and [M - H](+)) was required for accurate determination of the A + 1 isotope in halogenated compounds. Integrating the isotope data greatly improved the speed and accuracy of the database identifications. The database accurately identified unknowns from isobutane CI spectra in 100% of cases where as many as 40 candidates satisfied the mass tolerance. The paper describes the development and basic operation of the new MTS Search Engine and details performance testing with over 50 model compounds. PMID:23248816

  15. Slow light engineering for high Q high sensitivity photonic crystal microcavity biosensors in silicon

    PubMed Central

    Chakravarty, Swapnajit; Zou, Yi; Lai, Wei-Cheng; Chen, Ray T.

    2012-01-01

    Current trends in photonic crystal microcavity biosensors in silicon-on-insulator (SOI), that focus on small and smaller sensors have faced a bottleneck trying to balance two contradictory requirements of resonance quality factor and sensitivity. By simultaneous control of the radiation loss and optical mode volumes, we show that both requirements can be satisfied simultaneously. Microcavity sensors are designed in which resonances show highest Q ~9,300 in the bio-ambient phosphate buffered saline (PBS) as well as highest sensitivity among photonic crystal biosensors. We experimentally demonstrated mass sensitivity 8.8 atto-grams with sensitivity per unit area of 0.8 picograms/mm2 Highest sensitivity, irrespective of the dissociation constant Kd, is demonstrated among all existing label-free optical biosensors in silicon at the concentration of 0.1μg/ml. PMID:22748964

  16. Defect Engineering, Cell Processing, and Modeling for High-Performance, Low-Cost Crystalline Silicon Photovoltaics

    SciTech Connect

    Buonassisi, Tonio

    2013-02-26

    The objective of this project is to close the efficiency gap between industrial multicrystalline silicon (mc-Si) and monocrystalline silicon solar cells, while preserving the economic advantage of low-cost, high-volume substrates inherent to mc-Si. Over the course of this project, we made significant progress toward this goal, as evidenced by the evolution in solar-cell efficiencies. While most of the benefits of university projects are diffuse in nature, several unique contributions can be traced to this project, including the development of novel characterization methods, defect-simulation tools, and novel solar-cell processing approaches mitigate the effects of iron impurities ("Impurities to Efficiency" simulator) and dislocations. In collaboration with our industrial partners, this project contributed to the development of cell processing recipes, specialty materials, and equipment that increased cell efficiencies overall (not just multicrystalline silicon). Additionally, several students and postdocs who were either partially or fully engaged in this project (as evidenced by the publication record) are currently in the PV industry, with others to follow.

  17. Follow the Money: Engineering at Stanford and UC Berkeley during the Rise of Silicon Valley

    ERIC Educational Resources Information Center

    Adams, Stephen B.

    2009-01-01

    A comparison of the engineering schools at UC Berkeley and Stanford during the 1940s and 1950s shows that having an excellent academic program is necessary but not sufficient to make a university entrepreneurial (an engine of economic development). Key factors that made Stanford more entrepreneurial than Cal during this period were superior…

  18. Method of protecting a surface with a silicon-slurry/aluminide coating. [coatings for gas turbine engine blades and vanes

    NASA Technical Reports Server (NTRS)

    Deadmore, D. L.; Young, S. G. (Inventor)

    1982-01-01

    A low cost coating for protecting metallic base system substrates from high temperatures, high gas velocity oxidation, thermal fatigue and hot corrosion is described. The coating is particularly useful for protecting vanes and blades in aircraft and land based gas turbine engines. A lacquer slurry comprising cellulose nitrate containing high purity silicon powder is sprayed onto the superalloy substrates. The silicon layer is then aluminized to complete the coating. The Si-Al coating is less costly to produce than advanced aluminides and protects the substrate from oxidation and thermal fatigue for a much longer period of time than the conventional aluminide coatings. While more expensive Pt-Al coatings and physical vapor deposited MCrAlY coatings may last longer or provide equal protection on certain substrates, the Si-Al coating exceeded the performance of both types of coatings on certain superalloys in high gas velocity oxidation and thermal fatigue. Also, the Si-Al coating increased the resistance of certain superalloys to hot corrosion.

  19. Antimicrobial functionalization of silicone surfaces with engineered short peptides having broad spectrum antimicrobial and salt-resistant properties.

    PubMed

    Li, Xiang; Li, Peng; Saravanan, Rathi; Basu, Anindya; Mishra, Biswajit; Lim, Suo Hon; Su, Xiaodi; Tambyah, Paul Anantharajah; Leong, Susanna Su Jan

    2014-01-01

    Catheter-associated urinary tract infections (CAUTIs) are often preceded by pathogen colonization on catheter surfaces and are a major health threat facing hospitals worldwide. Antimicrobial peptides (AMPs) are a class of new antibiotics that hold promise in curbing CAUTIs caused by antibiotic-resistant pathogens. This study aims to systematically evaluate the feasibility of immobilizing two newly engineered arginine/lysine/tryptophan-rich AMPs with broad antimicrobial spectra and salt-tolerant properties on silicone surfaces to address CAUTIs. The peptides were successfully immobilized on polydimethylsiloxane and urinary catheter surfaces via an allyl glycidyl ether (AGE) polymer brush interlayer, as confirmed by X-ray photoelectron spectroscopy and water contact angle analyses. The peptide-coated silicone surfaces exhibited excellent microbial killing activity towards bacteria and fungi in urine and in phosphate-buffered saline. Although both the soluble and immobilized peptides demonstrated membrane disruption capabilities, the latter showed a slower rate of kill, presumably due to reduced diffusivity and flexibility resulting from conjugation to the polymer brush. The synergistic effects of the AGE polymer brush and AMPs prevented biofilm formation by repelling cell adhesion. The peptide-coated surface showed no toxicity towards smooth muscle cells. The findings of this study clearly indicate the potential for the development of AMP-based coating platforms to prevent CAUTIs. PMID:24056098

  20. Subwavelength index engineered surface grating coupler with sub-decibel efficiency for 220-nm silicon-on-insulator waveguides.

    PubMed

    Benedikovic, Daniel; Cheben, Pavel; Schmid, Jens H; Xu, Dan-Xia; Lamontagne, Boris; Wang, Shurui; Lapointe, Jean; Halir, Robert; Ortega-Moñux, Alejandro; Janz, Siegfried; Dado, Milan

    2015-08-24

    Surface grating couplers are fundamental components in chip-based photonic devices to couple light between photonic integrated circuits and optical fibers. In this work, we report on a grating coupler with sub-decibel experimental coupling efficiency using a single etch process in a standard 220-nm silicon-on-insulator (SOI) platform. We specifically demonstrate a subwavelength metamaterial refractive index engineered nanostructure with backside metal reflector, with the measured peak fiber-chip coupling efficiency of -0.69 dB (85.3%) and 3 dB bandwidth of 60 nm. This is the highest coupling efficiency hitherto experimentally achieved for a surface grating coupler implemented in 220-nm SOI platform. PMID:26368230

  1. Band-Structure Engineering of Gold Atomic Wires on Silicon by Controlled Doping

    NASA Astrophysics Data System (ADS)

    Choi, Won Hoon; Kang, Pil Gyu; Ryang, Kyung Deuk; Yeom, Han Woong

    2008-03-01

    We report on the systematic tuning of the electronic band structure of atomic wires by controlling the density of impurity atoms. The atomic wires are self-assembled on Si(111) by substitutional gold adsorbates and extra silicon atoms are deposited as the impurity dopants. The one-dimensional electronic band of gold atomic wires, measured by angle-resolved photoemission, changes from a fully metallic to semiconducting one with its band gap increasing above 0.3 eV along with an energy shift as a linear function of the Si dopant density. The gap opening mechanism is suggested to be related to the ordering of the impurities.

  2. Silicon-based elementary particle tracking system: Materials science and mechanical engineering design

    SciTech Connect

    Miller, W.O.; Gamble, M.T.; Thompson, T.C.; Hanlon, J.A.

    1993-01-01

    Research and development of the mechanical, cooling, and structural design aspects of a silicon detector-based elementary particle tracking system has been performed. Achieving stringent system precision, stability, and mass requirements necessitated the use of graphite fiber-reinforced cyanate-ester (C-E) resins. Mechanical test results of the effects of butane, ionizing radiation, and a combination of both on the mechanical properties of these materials are presented, as well as progress on developing compression molding of an ultralightweight graphite composite ring structure and TV holography-based noninvasive evaluation.

  3. Silicon-based elementary particle tracking system: Materials science and mechanical engineering design

    SciTech Connect

    Miller, W.O.; Gamble, M.T.; Thompson, T.C.; Hanlon, J.A.

    1993-05-01

    Research and development of the mechanical, cooling, and structural design aspects of a silicon detector-based elementary particle tracking system has been performed. Achieving stringent system precision, stability, and mass requirements necessitated the use of graphite fiber-reinforced cyanate-ester (C-E) resins. Mechanical test results of the effects of butane, ionizing radiation, and a combination of both on the mechanical properties of these materials are presented, as well as progress on developing compression molding of an ultralightweight graphite composite ring structure and TV holography-based noninvasive evaluation.

  4. Rear interface engineering of hybrid organic-silicon nanowire solar cells via blade coating.

    PubMed

    Lai, Yi-Chun; Chang, Yu-Fan; Tsai, Pei-Ting; Chang, Jan-kai; Tseng, Wei-Hsuan; Lin, Yi-Cheng; Hsiao, Chu-Yen; Zan, Hsiao-Wen; Wu, Chih-I; Chi, Gou-Chung; Meng, Hsin-Fei; Yu, Peichen

    2016-01-25

    In this work, we investigate blade-coated organic interlayers at the rear surface of hybrid organic-silicon photovoltaics based on two small molecules: Tris(8-hydroxyquinolinato) aluminium (Alq(3)) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl) benzene (OXD-7). In particular, soluble Alq(3) resulting in a uniform thin film with a root-mean-square roughness < 0.2nm is demonstrated for the first time. Both devices with the Alq(3) and OXD-7 interlayers show notable enhancement in the open-circuit voltage and fill-factor, leading to a net efficiency increase by over 2% from the reference, up to 11.8% and 12.5% respectively. The capacitance-voltage characteristics confirm the role of the small-molecule interlayers resembling a thin interfacial oxide layer for the Al-Si Schottky barrier to enhance the built-in potential and facilitate charge transport. Moreover, the Alq(3) interlayer in optimized devices exhibits isolated phases with a large surface roughness, in contrast to the OXD-7 which forms a continuous uniform thin film. The distinct morphological differences between the two interlayers further suggest different enhancement mechanisms and hence offer versatile functionalities to the advent of hybrid organic-silicon photovoltaics. PMID:26832593

  5. Observation of silicon self-diffusion enhanced by the strain originated from end-of-range defects using isotope multilayers

    SciTech Connect

    Isoda, Taiga; Uematsu, Masashi; Itoh, Kohei M.

    2015-09-21

    Si self-diffusion in the presence of end-of-range (EOR) defects is investigated using {sup nat}Si/{sup 28}Si isotope multilayers. The isotope multilayers were amorphized by Ge ion implantation, and then annealed at 800–950 °C. The behavior of Si self-interstitials is investigated through the {sup 30}Si self-diffusion. The experimental {sup 30}Si profiles show further enhancement of Si self-diffusion at the EOR defect region, in addition to the transient enhanced diffusion via excess Si self-interstitials by EOR defects. To explain this additional enhanced diffusion, we propose a model which takes into account enhanced diffusion by tensile strain originated from EOR defects. The calculation results based on this model have well reproduced the experimental {sup 30}Si profiles.

  6. Effect of plastic deformation on the magnetic properties and dislocation luminescence of isotopically enriched silicon {sup 29}Si:B

    SciTech Connect

    Koplak, O. V.; Shteynman, E. A.; Tereschenko, A. N.; Morgunov, R. B.

    2015-09-15

    A correlation between the temperature dependences of the D1-line intensity of dislocation luminescence and the magnetic moment of plastically deformed isotopically enriched crystals {sup 29}Si:B is found. It is established that the magnetic susceptibility of the deformed crystals obtained by integration of the spectra of electron spin resonance and the D1-line intensity undergo similar nonmonotonic variations with temperature varying in the range of 20–32 K.

  7. Isotopic Composition of Molybdenum and Barium in Single Presolar Silicon Carbide Grains of Type A+B

    NASA Technical Reports Server (NTRS)

    Savina, M. R.; Tripa, C. E.; Pellin, M. J.; Davis, A. M.; Clayton, R. N.; Lewis, R. S.; Amari, S.

    2003-01-01

    Presolar SiC grains fall into several groups based on C, N, and Si isotopic compositions. Approximately 93% are defined as mainstream, having 10 less than C-12/C-13 less than 100 and N-14/N-15 ranging from 50 to 20,000. A number of studies have shown that the most likely sources of mainstream grains are low mass asymptotic giant branch stars. Models of nucleosynthesis in AGB stars reproduce the s-process enhancements seen in the heavy elements in mainstream SiC grains. Among the less common grains, A+B grains, which comprise approximately 3-4% of presolar SiC, are perhaps the least well understood. Recent studies by Amari et al. show that A+B grains can be divided into at least 4 groups based on their trace element concentration patterns. Of 20 grains studied, 7 showed trace element patterns consistent with condensation from a gas of solar system composition, while the rest had varying degrees of process enhancements. Our previous measurements on 3 A+B grains showed Mo of solar isotopic composition, but Zr with a strong enhancement in 96Zr, which is an r-process isotope but can be made in an sprocess if the neutron density is high enough to bridge the unstable Zr-95 (T(sub 1/2)= 64 d). The observation of Mo with solar system isotopic composition in the same grains is puzzling however. Meyer et al. have recently shown that a neutron burst mechanism can produce a high Zr-96/Zr-94 without enhancing Mo-100, however this model leads to enhancements in Mo-95 and Mo-97 not observed in A+B grains. We report here results of Mo measurements on 7 additional A+B grains, and Ba measurements on 2 A+B grains, and compare these to the previous studies.

  8. Silicon isotopes in ˜3.8 Ga West Greenland rocks as clues to the Eoarchaean supracrustal Si cycle

    NASA Astrophysics Data System (ADS)

    André, Luc; Cardinal, Damien; Alleman, Laurent Y.; Moorbath, Stephen

    2006-05-01

    We report MC-ICP-MS Si-isotopic measurements ( δ29Si recalculated as δ30Si) on micro-subsamples (at 500 μm scale) from several major rock types of the ˜3.8-Ga-old Isua Greenstone Belt (IGB, southern West Greenland) and surrounding Eoarchaean terrains. With a large overall range of variations (- 2.80‰ < δ30Si < + 0.68‰), they demonstrate strong involvement of surface fluids enriched with dissolved Si. The resistance of Si-isotopes to metamorphic resettings and metasomatic overprints is also established. Metabasaltic pillows and metasediments display similar 30Si-enriched signatures, suggesting that emergent surfaces of the Eoarchaean protocrust were composed of slightly weathered, hydrothermally altered, mafic-ultramafic bodies. Isua magnetite-quartz Banded Iron Formation (BIF) is strongly depleted in 30Si relative to all coeval rocks. This depletion supports Rayleigh-controlled precipitation from seafloor-vented hydrothermal fluids. In contrast, banded quartz-pyroxene rocks (from Akilia Island, some 150 km southwest of the IGB), which some authors have identified as BIF-related, yield quartz with Si-isotopic composition ( δ30Si = - 0.36‰) similar to metamorphic-derived quartz ( δ30Si = - 0.50‰). This supports their derivation from tectonic reworking of ultramafic protoliths penetrated by metamorphic silica and is at variance with their proposed role as harboring earliest biogenic tracers.

  9. Development of Innovative Radioactive Isotope Production Techniques at the Pennsylvania State University Radiation Science and Engineering Center

    SciTech Connect

    Johnsen, Amanda M.; Heidrich, Brenden; Durrant, Chad; Bascom, Andrew; Unlu, Kenan

    2013-08-15

    The Penn State Breazeale Nuclear Reactor (PSBR) at the Radiation Science and Engineering Center (RSEC) has produced radioisotopes for research and commercial purposes since 1956. With the rebirth of the radiochemistry education and research program at the RSEC, the Center stands poised to produce a variety of radioisotopes for research and industrial work that is in line with the mission of the DOE Office of Science, Office of Nuclear Physics, Isotope Development and Production Research and Application Program. The RSEC received funding from the Office of Science in 2010 to improve production techniques and develop new capabilities. Under this program, we improved our existing techniques to provide four radioisotopes (Mn-56, Br-82, Na-24, and Ar-41) to researchers and industry in a safe and efficient manner. The RSEC is also working to develop new innovative techniques to provide isotopes in short supply to researchers and others in the scientific community, specifically Cu-64 and Cu-67. Improving our existing radioisotopes production techniques and investigating new and innovative methods are two of the main initiatives of the radiochemistry research program at the RSEC.

  10. Heavy silicon isotopic composition of silicic acid and biogenic silica in Arctic waters over the Beaufort shelf and the Canada Basin

    NASA Astrophysics Data System (ADS)

    Varela, D. E.; Brzezinski, M. A.; Beucher, C. P.; Jones, J. L.; Giesbrecht, K. E.; Lansard, B.; Mucci, A.

    2016-06-01

    The silicon isotopic composition of silicic acid (δ30Si(OH)4) and biogenic silica (δ30Si-bSiO2) were measured for the first time in marine Arctic waters from the Mackenzie River delta to the deep Canada Basin in the late summer of 2009. In the upper 100 m of the water column, δ30Si(OH)4 signals (+1.82‰ to +3.08‰) were negatively correlated with the relative contribution of Mackenzie River water. The biogenic Si isotope fractionation factor estimated using an open system model, 30ɛ = -0.97 ± 0.17‰, agrees well with laboratory and global-ocean estimates. Nevertheless, the δ30Si dynamics of this region may be better represented by closed system isotope models that yield lower values of 30ɛ, between -0.33‰ and -0.41‰, depending on how the contribution of sea-ice diatoms is incorporated. In the upper 400 m, δ30Si-bSiO2 values were among the heaviest ever measured in marine suspended bSiO2 (+2.03‰ to +3.51‰). A positive correlation between δ30Si-bSiO2 and sea-ice cover implies that heavy signals can result from isotopically heavy sea-ice diatoms introduced to pelagic assemblages. Below the surface bSiO2 production zone, the δ30Si(OH)4 distribution followed that of major water masses. Vertical δ30Si(OH)4 profiles showed a minimum (average of +1.84 ± 0.10‰) in the upper halocline (125-200 m) composed of modified Pacific water and heavier average values (+2.04 ± 0.11‰) in Atlantic water (300-500 m deep). In the Canada Basin Deep Water (below 2000 m), δ30Si(OH)4 averaged +1.88 ± 0.12‰, which represents the most positive value ever measured anywhere in the deep ocean. Since most Si(OH)4 enters the Arctic from shallow depths in the Atlantic Ocean, heavy deep Arctic δ30Si(OH)4 signals likely reflect the influx of relatively heavy intermediate Atlantic waters. A box model simulation of the global marine δ30Si(OH)4 distribution successfully reproduced the observed patterns, with the δ30Si(OH)4 of the simulated deep Arctic Ocean being the

  11. Strain engineering on silicon/germanium nanoscale heterostructures using molecular dynamics

    NASA Astrophysics Data System (ADS)

    Park, Yumi

    Nanoscale architectures provide additional variables to engineer electronic/mechanical properties of material systems due to their high surface volume ratio and physics that arise from their extremely small size. To date, the device performance of microelectronics has been improved largely by miniaturization. However, with feature sizes below 100 nm, the fundamental challenges demand development of new architectures, new materials, and strain engineering. Strain engineering has been one of the most widely used techniques to achieve desired electronic properties of materials. For example, uniaxial compression and tension are desirable for high speed p-and n-MOSFET, respectively. However, accurate experimental characterization of strain in nanomaterials remains challenges such as resolving strain components and quantifying strain gradient which can affect electronic properties. Molecular dynamics (MD) describe materials with atomic resolution and it can provide invaluable information and insight into nanoscale strain engineering. MD simulations are used to study strain relaxation in Si/Ge heteroepitaxial structures of interest to nanoelectonic applications. Nanopatterning is considered as an avenue for strain engineering to achieve uniaxial strain state from epitaxially integrated Si/Ge heterostructures. Using MD, it is studied how size affect strain relaxation on strained Si/Ge/Si nanobars representing the structures obtained by patterning the films in nanoscale. The MD results demonstrate that Ge with a roughly square cross section has a uniaxial strain state desirable for hole mobility enhancement. Also, process-induced strain relaxation on Si/Ge heterostructures is discussed. The simulations suggest that, by engineering the aspect ratio of Si/Ge nanolaminates, local amorphization followed by recrystallization can be used for either preserving the engineered strain or achieving the desired strain state in crystalline region, showing a possibility as a new avenue

  12. Controllable surface-plasmon resonance in engineered nanometer epitaxial silicide particles embedded in silicon

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; Ksendzov, A.; Iannelli, J. M.; George, T.

    1991-01-01

    Epitaxial CoSi2 particles in a single-crystal silicon matrix are grown by molecular-beam epitaxy using a technique that allows nanometer control over particle size in three dimensions. These composite layers exhibit resonant absorption predicted by effective-medium theory. Selection of the height and diameter of disklike particles through a choice of growth conditions allows tailoring of the depolarization factor and hence of the surface-plasmon resonance energy. Resonant absorption from 0.49 to 1.04 eV (2.5 to 1.2 micron) is demonstrated and shown to agree well with values predicted by the Garnett (1904, 1906) theory using the bulk dielectric constants for CoSi2 and Si.

  13. A nickel-gold bilayer catalyst engineering technique for self-assembled growth of highly ordered silicon nanotubes (SiNT).

    PubMed

    Taghinejad, M; Taghinejad, H; Abdolahad, M; Mohajerzadeh, S

    2013-03-13

    We report the growth of vertically aligned high-crystallinity silicon nanotube (SiNT) arrays on silicon substrate by means of a Ni-Au bilayer catalyst engineering technique. Nanotubes were synthesized through solid-liquid-solid method as well as vapor-liquid-solid. A precise evaluation utilizing atomic force microscopy and lateral force microscopy describes that the gold profile in Ni regions leads to the construction of multiwall SiNTs. The agreement of the structural geometry and stiffness of the obtained SiNTs with previous theoretical predictions suggest sp(3) hybridization as the mechanism of tube formation. Apart from scanning electron and transmission electron microscopy techniques, photoluminescence spectroscopy (PL) has been conducted to investigate the formation of nanostructures. PL spectroscopy confirms the evolution of ultrafine walls of the silicon nanotubes, responsible for the observed photoemission properties. PMID:23394626

  14. Consolidation of silicon nitride without additives. [for gas turbine engine efficiency increase

    NASA Technical Reports Server (NTRS)

    Sikora, P. F.; Yeh, H. C.

    1976-01-01

    The use of ceramics for gas turbine engine construction might make it possible to increase engine efficiency by raising operational temperatures to values beyond those which can be tolerated by metallic alloys. The most promising ceramics being investigated in this connection are Si3N4 and SiC. A description is presented of a study which had the objective to produce dense Si3N4. The two most common methods of consolidating Si3N4 currently being used include hot pressing and reaction sintering. The feasibility was explored of producing a sound, dense Si3N4 body without additives by means of conventional gas hot isostatic pressing techniques and an uncommon hydraulic hot isostatic pressing technique. It was found that Si3N4 can be densified without additions to a density which exceeds 95% of the theoretical value

  15. Patterning human neuronal networks on photolithographically engineered silicon dioxide substrates functionalized with glial analogues.

    PubMed

    Hughes, Mark A; Brennan, Paul M; Bunting, Andrew S; Cameron, Katherine; Murray, Alan F; Shipston, Mike J

    2014-05-01

    Interfacing neurons with silicon semiconductors is a challenge being tackled through various bioengineering approaches. Such constructs inform our understanding of neuronal coding and learning and ultimately guide us toward creating intelligent neuroprostheses. A fundamental prerequisite is to dictate the spatial organization of neuronal cells. We sought to pattern neurons using photolithographically defined arrays of polymer parylene-C, activated with fetal calf serum. We used a purified human neuronal cell line [Lund human mesencephalic (LUHMES)] to establish whether neurons remain viable when isolated on-chip or whether they require a supporting cell substrate. When cultured in isolation, LUHMES neurons failed to pattern and did not show any morphological signs of differentiation. We therefore sought a cell type with which to prepattern parylene regions, hypothesizing that this cellular template would enable secondary neuronal adhesion and network formation. From a range of cell lines tested, human embryonal kidney (HEK) 293 cells patterned with highest accuracy. LUHMES neurons adhered to pre-established HEK 293 cell clusters and this coculture environment promoted morphological differentiation of neurons. Neurites extended between islands of adherent cell somata, creating an orthogonally arranged neuronal network. HEK 293 cells appear to fulfill a role analogous to glia, dictating cell adhesion, and generating an environment conducive to neuronal survival. We next replaced HEK 293 cells with slower growing glioma-derived precursors. These primary human cells patterned accurately on parylene and provided a similarly effective scaffold for neuronal adhesion. These findings advance the use of this microfabrication-compatible platform for neuronal patterning. PMID:23733444

  16. Effect of carbon situating at end-of-range defects on silicon self-diffusion investigated using pre-amorphized isotope multilayers

    NASA Astrophysics Data System (ADS)

    Isoda, Taiga; Uematsu, Masashi; Itoh, Kohei M.

    2016-03-01

    The effect of implanted carbon (C) on silicon (Si) self-diffusion has been investigated using pre-amorphized 28Si/natSi multilayers. The isotope multilayers were pre-amorphized by Ge implantation followed by C implantation, and annealed at 950 °C. Because of the presence of C, the Si self-diffusion was slower in 30 min annealing than the self-diffusion without C. This was attributed to the trapping of Si self-interstitials by C. On the other hand, the Si self-diffusion with C was faster in 2 h annealing than the self-diffusion without C, except in the end-of-range (EOR) defect region. The cause of this enhanced diffusion was understood as the retardation of Ostwald ripening of EOR defects by C trapped at the defects. In the EOR defect region, however, Si self-diffusion was slower than the self-diffusion without C in both 30 min and 2 h annealing owing to the presence of C. Relaxation of the tensile strain associated with the EOR defects by the trapped C was proposed to be the main cause of the retarded diffusion in the EOR region.

  17. Lattice thermal conductivity of crystalline and amorphous silicon with and without isotopic effects from the ballistic to diffusive thermal transport regime

    SciTech Connect

    Park, Minkyu; Lee, In-Ho; Kim, Yong-Sung

    2014-07-28

    Thermal conductivity of a material is an important physical parameter in electronic and thermal devices, and as the device size shrinks down, its length-dependence becomes unable to be neglected. Even in micrometer scale devices, materials having a long mean free path of phonons, such as crystalline silicon (Si), exhibit a strong length dependence of the thermal conductivities that spans from the ballistic to diffusive thermal transport regime. In this work, through non-equilibrium molecular-dynamics (NEMD) simulations up to 17 μm in length, the lattice thermal conductivities are explicitly calculated for crystalline Si and up to 2 μm for amorphous Si. The Boltzmann transport equation (BTE) is solved within a frequency-dependent relaxation time approximation, and the calculated lattice thermal conductivities in the BTE are found to be in good agreement with the values obtained in the NEMD. The isotopic effects on the length-dependent lattice thermal conductivities are also investigated both in the crystalline and amorphous Si.

  18. Silicon-Based Ceramic-Matrix Composites for Advanced Turbine Engines: Some Degradation Issues

    NASA Technical Reports Server (NTRS)

    Thomas-Ogbuji, Linus U. J.

    2000-01-01

    SiC/BN/SiC composites are designed to take advantage of the high specific strengths and moduli of non-oxide ceramics, and their excellent resistance to creep, chemical attack, and oxidation, while circumventing the brittleness inherent in ceramics. Hence, these composites have the potential to take turbine engines of the future to higher operating temperatures than is achievable with metal alloys. However, these composites remain developmental and more work needs to be done to optimize processing techniques. This paper highlights the lingering issue of pest degradation in these materials and shows that it results from vestiges of processing steps and can thus be minimized or eliminated.

  19. Patterning human neuronal networks on photolithographically engineered silicon dioxide substrates functionalized with glial analogues

    PubMed Central

    Hughes, Mark A; Brennan, Paul M; Bunting, Andrew S; Cameron, Katherine; Murray, Alan F; Shipston, Mike J

    2014-01-01

    Interfacing neurons with silicon semiconductors is a challenge being tackled through various bioengineering approaches. Such constructs inform our understanding of neuronal coding and learning and ultimately guide us toward creating intelligent neuroprostheses. A fundamental prerequisite is to dictate the spatial organization of neuronal cells. We sought to pattern neurons using photolithographically defined arrays of polymer parylene-C, activated with fetal calf serum. We used a purified human neuronal cell line [Lund human mesencephalic (LUHMES)] to establish whether neurons remain viable when isolated on-chip or whether they require a supporting cell substrate. When cultured in isolation, LUHMES neurons failed to pattern and did not show any morphological signs of differentiation. We therefore sought a cell type with which to prepattern parylene regions, hypothesizing that this cellular template would enable secondary neuronal adhesion and network formation. From a range of cell lines tested, human embryonal kidney (HEK) 293 cells patterned with highest accuracy. LUHMES neurons adhered to pre-established HEK 293 cell clusters and this coculture environment promoted morphological differentiation of neurons. Neurites extended between islands of adherent cell somata, creating an orthogonally arranged neuronal network. HEK 293 cells appear to fulfill a role analogous to glia, dictating cell adhesion, and generating an environment conducive to neuronal survival. We next replaced HEK 293 cells with slower growing glioma-derived precursors. These primary human cells patterned accurately on parylene and provided a similarly effective scaffold for neuronal adhesion. These findings advance the use of this microfabrication-compatible platform for neuronal patterning. © 2013 The Authors. Journal ofBiomedicalMaterials Research Part APublished byWiley Periodicals, Inc.Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1350–1360, 2014. PMID:23733444

  20. Probing Structure Property Relationships in Complex Engineering Silicones by 1H NMR

    SciTech Connect

    Chinn, S C; Gjersing, E L; Maxwell, R S; Eastwood, E; Bowen, D; Stephens, T

    2006-07-14

    It is generally accepted that the properties of polymeric materials are controlled by the network structure and the reactions by which they have been constructed. These properties include the bulk moduli at creation, but also the properties as a function of age during use. In order to interpret mechanical properties and predict the time dependent changes in these properties, detailed knowledge of the effect of structural changes must be obtained. The degree and type of crosslinking, the molecular weight between crosslinks, the number of elastically ineffective chains (loops, dangling chain ends, sol-fraction) must be characterized. A number of theoretical and experimental efforts have been reported in the last few years on model networks prepared by endlinking reactions and the relationships of those structures with the ultimate mechanical properties. A range of experimental methods have been used to investigate structure including rheometric, scattering, infrared, {sup 29}Si MAS and CPMAS, {sup 1}H relaxation measurements, and recently {sup 1}H multiple quantum methods. Characterization of the growth of multiple quantum coherences have recently been shown to provide detailed insight into silicone network structure by the ability to selective probe the individual components of the polymer network, such as the polymer-filler interface or network chains. We have employed recently developed MQ methods to investigate the structure-property relationships in a series of complex, endlinked filled-PDMS blends. Here, a systematic study of the relationship between the molecular formulation, as dictated by the amount and type of crosslinks present and by the remaining network chains, and the segmental dynamics as observed by MQ NMR was performed.

  1. An engineer at AeroVironment's Design Development Center inspects a set of silicon solar cells for p

    NASA Technical Reports Server (NTRS)

    2000-01-01

    An engineer at AeroVironment's Design Development Center in Simi Valley, California, closely inspects a set of silicon solar cells for potential defects. The cells, fabricated by SunPower, Inc., of Sunnyvale, California, are among 64,000 solar cells which have been installed on the Helios Prototype solar-powered aircraft to provide power to its 14 electric motors and operating systems. Developed by AeroVironment under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project, the Helios Prototype is the forerunner of a planned fleet of slow-flying, long duration, high-altitude aircraft which can perform atmospheric science missions and serve as telecommunications relay platforms in the stratosphere. Target goals set by NASA for the giant 246-foot span flying wing include reaching and sustaining subsonic horizontal flight at 100,000 feet altitude in 2001, and sustained continuous flight for at least four days and nights in 2003 with the aid of a regenerative fuel cell-based energy storage system now in development.

  2. Surface Engineering of Porous Silicon Microparticles for Intravitreal Sustained Delivery of Rapamycin

    PubMed Central

    Nieto, Alejandra; Hou, Huiyuan; Moon, Sang Woong; Sailor, Michael J.; Freeman, William R.; Cheng, Lingyun

    2015-01-01

    Purpose. To understand the relationship between rapamycin loading/release and surface chemistries of porous silicon (pSi) to optimize pSi-based intravitreal delivery system. Methods. Three types of surface chemical modifications were studied: (1) pSi-COOH, containing 10-carbon aliphatic chains with terminal carboxyl groups grafted via hydrosilylation of undecylenic acid; (2) pSi-C12, containing 12-carbon aliphatic chains grafted via hydrosilylation of 1-dodecene; and (3) pSiO2-C8, prepared by mild oxidation of the pSi particles followed by grafting of 8-hydrocarbon chains to the resulting porous silica surface via a silanization. Results. The efficiency of rapamycin loading follows the order (micrograms of drug/milligrams of carrier): pSiO2-C8 (105 ± 18) > pSi-COOH (68 ± 8) > pSi-C12 (36 ± 6). Powder X-ray diffraction data showed that loaded rapamycin was amorphous and dynamic drug-release study showed that the availability of the free drug was increased by 6-fold (compared with crystalline rapamycin) by using pSiO2-C8 formulation (P = 0.0039). Of the three formulations in this study, pSiO2-C8-RAP showed optimal performance in terms of simultaneous release of the active drug and carrier degradation, and drug-loading capacity. Released rapamycin was confirmed with the fingerprints of the mass spectrometry and biologically functional as the control of commercial crystalline rapamycin. Single intravitreal injections of 2.9 ± 0.37 mg pSiO2-C8-RAP into rabbit eyes resulted in more than 8 weeks of residence in the vitreous while maintaining clear optical media and normal histology of the retina in comparison to the controls. Conclusions. Porous silicon–based rapamycin delivery system using the pSiO2-C8 formulation demonstrated good ocular compatibility and may provide sustained drug release for retina. PMID:25613937

  3. Intravitreal Controlled Release of Dexamethasone from Engineered Microparticles of Porous Silicon Dioxide

    PubMed Central

    Wang, Chengyun; Hou, Huiyuan; Nan, Kaihui; Sailor, Michael J; Freeman, William R.; Cheng, Lingyun

    2014-01-01

    Dexamethasone is a glucocorticoid that is widely used in the ophthalmic arena. The recent FDA approved dexamethasone implant can provide a three month efficacy but with high rate of drug related cataract and high intraocular pressure (IOP). It seems that higher steroid in aqueous humor and around lens may be associated with these complications based on clinical fact that higher IOP was observed with intravitreal triamcinolone acetonide (TA) than with subtenon TA. We hypothesize that placing a sustained dexamethasone release system near back of the eye through a fine needle can maximize efficacy while mitigate higher rate of IOP rise and cataract. To develop a sustained intravitreal dexamethasone delivery system, porous silicon dioxide (pSiO2) microparticles were fabricated and functionalized with amines as well as carboxyl groups. Dexamethasone was conjugated to pSiO2 through the Steglich Esterificaion Reaction between hydroxyl of dexamethasone and carboxyl groups on the pSiO2. The drug loading was confirmed by Fourier transform infrared spectroscopy (FTIR) and loading efficiency was quantitated using thermogravimetric analysis (TGA). In vitro release was conducted for three months and dexamethasone was confirmed in the released samples using liquid chromatography-tandem mass spectrometry (LC/MS/MS). A pilot ocular safety and determination of vitreous drug level was performed in rabbit eyes. The drug loading study demonstrated that loading efficiency was from 5.96% to 10.77% depending on the loading reaction time, being higher with longer loading reaction time before reaching saturation around 7 days. In vitro drug release study revealed that dexamethasone release from pSiO2 particles was sustainable for over 90 days and was 80 days longer than free dexamethasone or infiltration-loaded pSiO2 particle formulation in the same setting. Pilot in vivo study demonstrated no sign of ocular adverse reaction in rabbit eyes following a single 3 mg intravitreal injection and

  4. Intravitreal controlled release of dexamethasone from engineered microparticles of porous silicon dioxide.

    PubMed

    Wang, Chengyun; Hou, Huiyuan; Nan, Kaihui; Sailor, Michael J; Freeman, William R; Cheng, Lingyun

    2014-12-01

    Dexamethasone is a glucocorticoid that is widely used in the ophthalmic arena. The recent FDA approved dexamethasone implant can provide a three month efficacy but with high rate of drug related cataract and high intraocular pressure (IOP). It seems that higher steroid in aqueous humor and around lens may be associated with these complications based on clinical fact that higher IOP was observed with intravitreal triamcinolone acetonide (TA) than with subtenon TA. We hypothesize that placing a sustained dexamethasone release system near back of the eye through a fine needle can maximize efficacy while mitigate higher rate of IOP rise and cataract. To develop a sustained intravitreal dexamethasone delivery system, porous silicon dioxide (pSiO2) microparticles were fabricated and functionalized with amines as well as carboxyl groups. Dexamethasone was conjugated to pSiO2 through the Steglich Esterification Reaction between hydroxyl of dexamethasone and carboxyl groups on the pSiO2. The drug loading was confirmed by Fourier transform infrared spectroscopy (FTIR) and loading efficiency was quantitated using thermogravimetric analysis (TGA). In vitro release was conducted for three months and dexamethasone was confirmed in the released samples using liquid chromatography-tandem mass spectrometry (LC/MS/MS). A pilot ocular safety and determination of vitreous drug level was performed in rabbit eyes. The drug loading study demonstrated that loading efficiency was from 5.96% to 10.77% depending on the loading reaction time, being higher with longer loading reaction time before reaching saturation around 7 days. In vitro drug release study revealed that dexamethasone release from pSiO2 particles was sustainable for over 90 days and was 80 days longer than free dexamethasone or infiltration-loaded pSiO2 particle formulation in the same setting. Pilot in vivo study demonstrated no sign of ocular adverse reaction in rabbit eyes following a single 3 mg intravitreal injection and

  5. Dissolved silicon and its isotopes in the water column of the Bay of Bengal: Internal cycling versus lateral transport

    NASA Astrophysics Data System (ADS)

    Singh, Satinder Pal; Singh, Sunil Kumar; Bhushan, Ravi; Rai, Vinai Kumar

    2015-02-01

    The concentration of dissolved Si and its isotope composition are measured in the Bay of Bengal (BoB) region of the northern Indian Ocean; the isotope data are the first data set from the northern Indian Ocean. The measurements are made in eight depth profiles closely along the 87°E transect (GIO1 section of the international GEOTRACES program) and in a few samples from the northern shelf of the bay. Dissolved Si in the water column varies from ∼0.6 to ∼152.5 μmol/kg, whereas the δ30Si data cover a range +1.2‰ to +3.6‰. The depth profiles of dissolved Si show generally lower values in the surface increasing with depth, whereas the pattern reverses in the case of δ30Si. These vertical distribution patterns of Si and δ30Si are similar to those reported in other oceanic regions and suggestive of the significant role of biological processes in governing Si biogeochemistry in the upper layers (top ∼1500 m). In contrast, dissolved Si in near surface waters of the northern shelf and the southernmost station is exceptionally high. These results indicate a continental supply of dissolved Si from the Ganga-Brahmaputra river system (G-B) and submarine groundwater discharge (SGD) to the shelf region, and an intrusion of high salinity waters from the Arabian Sea in the southern bay. The δ30Si values of ∼1.34 ± 0.10‰ for deep/bottom waters of the BoB (depth >1500 m) are similar to those reported for the deep Southern Ocean and indicate the dominant control of water mass mixing. The dissolved Si concentrations in the bottom waters of the BoB are generally higher than those of the water mass endmembers, which suggest the need for an additional source of Si; in situ particle dissolution and/or benthic release in the central bay seem to be the potential candidate. The annual Si budget in the top ∼100 m of the BoB seems to suggest that meso-scale eddies frequently occurring during non-monsoon periods can supply at the most ∼2.6 g Si/m2/year, which is about 33

  6. Germanium-on-Silicon Strain Engineered Materials for Improved Device Performance Grown by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Bharathan, Jayesh Moorkoth

    The primary goal of this research is to develop a chemical vapor deposition process for growing epitaxial films of germanium on silicon (001) substrates with two-dimensional (2-D) morphology, and a low density of threading dislocations. Growth was carried out in a reduced-pressure chemical vapor deposition (RPCVD) system by a two-step growth technique. An accurate knowledge of elastic constants of thin films is important in understanding the effect of strain on material properties. Residual thermal strain was used to measure the Poisson ratio of Ge films grown on Si(001) substrates, by the sin2Psi method and highresolution x-ray diffraction. The Poisson ratio of the Ge films was measured to be 0.25, compared to the bulk value of 0.27. The result was found to be independent of film thickness and defect density, which confirmed that the strain is associated with the elastic response of the film. The study showed that the use of Poisson ratio instead of bulk compliance values yields a more accurate description of the state of in-plane strain present in the film. The experimentally measured in-plane strain in Ge films was found to be lower than the theoretical calculations based on the differential thermal expansion coefficients of Si and Ge. The mechanism of thermal misfit strain relaxation in epitaxial Ge films grown on Si(001) substrates was investigated by x-ray diffraction, and transmission electron microscopy. Lattice misfit strain associated with Ge/(001)Si mismatched epitaxy is relieved by a network of Lomer edge misfit dislocations during the first step of the growth technique. However, thermal misfit strain energy during growth is relieved by interdiffusion mechanism at the heterointerface. Two SiGe compositions containing 0.5 and 6.0 atomic percent Si were detected that relieve the thermal mismatch strain associated with the two steps of the growth process. This study discusses the importance of interdiffusion mechanism in relieving small misfit strains

  7. Experimental calibration of silicon and oxygen isotope fractionations between quartz and water at 250°C by in situ microanalysis of experimental products and application to zoned low δ30Si quartz overgrowths

    DOE PAGESBeta

    Pollington, Anthony D.; Kozdon, Reinhard; Anovitz, Lawrence M.; Georg, R. Bastian; Spicuzza, Michael J.; Valley, John W.

    2015-12-01

    The interpretation of silicon isotope data for quartz is hampered by the lack of experimentally determined fractionation factors between quartz and fluid. Further, there is a large spread in published oxygen isotope fractionation factors at low temperatures, primarily due to extrapolation from experimental calibrations at high temperature. We report the first measurements of silicon isotope ratios from experimentally precipitated quartz and estimate the equilibrium fractionation vs. dissolved silica using a novel in situ analysis technique applying secondary ion mass spectrometry to directly analyze experimental products. These experiments also yield a new value for oxygen isotope fractionation. Quartz overgrowths up tomore » 235 μm thick were precipitated in silica–H2O–NaOH–NaCl fluids, at pH 12–13 and 250 °C. At this temperature, 1000lnα30Si(Qtz–fluid) = 0.55 ± 0.10‰ and 1000lnα18O(Qtz–fluid) = 10.62 ± 0.13‰, yielding the relations 1000lnα30Si(Qtz–fluid) = (0.15 ± 0.03) * 106/T2 and 1000lnα18O(Qtz–fluid) = (2.91 ± 0.04) * 106/T2 when extended to zero fractionation at infinite temperature. Values of δ30Si(Qtz) from diagenetic cement in sandstones from the basal Cambrian Mt. Simon Formation in central North America range from 0 to ₋5.4‰. Paired δ18O and δ30Si values from individual overgrowths preserve a record of Precambrian weathering and fluid transport. In conclusion, the application of the experimental quartz growth results to observations from natural sandstone samples suggests that precipitation of quartz at low temperatures in nature is dominated by kinetic, rather than equilibrium, processes.« less

  8. Using Carbon-14 Isotope Tracing to Investigate Molecular Structure Effects of the Oxygenate Dibutyl Maleate on Soot Emissions from a DI Diesel Engine

    SciTech Connect

    Buchholz, B A; Mueller, C J; Upatnieks, A; Martin, G C; Pitz, W J; Westbrook, C K

    2004-01-07

    The effect of oxygenate molecular structure on soot emissions from a DI diesel engine was examined using carbon-14 ({sup 14}C) isotope tracing. Carbon atoms in three distinct chemical structures within the diesel oxygenate dibutyl maleate (DBM) were labeled with {sup 14}C. The {sup 14}C from the labeled DBM was then detected in engine-out particulate matter (PM), in-cylinder deposits, and CO{sub 2} emissions using accelerator mass spectrometry (AMS). The results indicate that molecular structure plays an important role in determining whether a specific carbon atom either does or does not form soot. Chemical-kinetic modeling results indicate that structures that produce CO{sub 2} directly from the fuel are less effective at reducing soot than structures that produce CO before producing CO{sub 2}. Because they can follow individual carbon atoms through a real combustion process, {sup 14}C isotope tracing studies help strengthen the connection between actual engine emissions and chemical-kinetic models of combustion and soot formation/oxidation processes.

  9. Evidence of low temperature fractionation of silicon in Archean cherts: SIMS Si and O isotope measurements of 3.42-3.26 Ga banded carbonaceous cherts from the Onverwacht Group, Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

    Stefurak, E. J.; Fischer, W. W.; Lowe, D. R.

    2012-12-01

    The striking abundance of chert in Early Archean sedimentary successions highlights a major difference between younger Archean and Proterozoic successions, engendering a number of questions regarding the behavior of the Earth's early silica cycle. Though previously applied largely for the purpose of paleothermometry, Si isotopes are emerging as a new tool for understanding mass flux and mechanisms of silica concentration, precipitation, diagenesis, and metamorphism. In addition, most previous studies lack a detailed petrographic context, laboring under the assumption that the cherts are isotopically homogeneous on a centimeter scale. We present a new suite of high resolution SIMS Si and O isotope ratio data from banded carbonaceous chert from the Onverwacht Group of the Barberton Greenstone Belt, South Africa - collected from the 3.42 Ga Buck Reef Chert and 3.33-3.26 Ga Mendon Formation. These materials contain several distinct silica phases, including carbonaceous bands (with or without well-defined grains), pure chert bands, early cavity filling cements, and later quartz-filled veins, which provide for isotopic comparisons between different textures. δ30Si values from all samples span a range of almost 7‰, from -3.38 to +3.42, with an overall mean of 0.36, median of 0.46, and standard deviation of 0.87. Within individual samples, isotope ratio data displays systematic texture-specific δ30Si variations both between phases and within phases. The observed variations occur on a ~100μm scale and likely reflect isotopically distinct fluids from which different silica phases originated, in addition to fractionation during precipitation. To constrain the causes of the silicon isotope trends, we made 18O/16O measurements on spots placed just adjacent to measured Si spots. SIMS δ18O values are generally 18O-depleted and fall in a range consistent with previously published data from bulk gas source mass spectrometry. Measurements from all samples span a range of ~6

  10. Orbital forcing of glacial/interglacial variations in chemical weathering and silicon cycling within the upper White Nile basin, East Africa: Stable-isotope and biomarker evidence from Lakes Victoria and Edward

    NASA Astrophysics Data System (ADS)

    Cockerton, Helen E.; Street-Perrott, F. Alayne; Barker, Philip A.; Leng, Melanie J.; Sloane, Hilary J.; Ficken, Katherine J.

    2015-12-01

    On Quaternary time scales, the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae (notably diatoms, for which Si is an essential nutrient). Large tropical river systems dominate the export of Si from the continents to the oceans. Here, we investigate variations in Si cycling in the upper White Nile basin over the last 15 ka, using sediment cores from Lakes Victoria and Edward. Coupled measurements of stable O and Si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and Si cycling, while the abundances of lipid biomarkers characteristic of terrestrial/emergent higher plants, submerged/floating aquatic macrophytes and freshwater algae document past ecosystem changes. During the late-glacial to mid-Holocene, 15-5.5 ka BP, orbital forcing greatly enhanced monsoon rainfall, forest cover and chemical weathering. Riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower Si-isotope values. Since 5.5 ka BP, increasingly dry climates and more open vegetation, reinforced by the spread of agricultural cropland over the last 3-4 ka, have reduced dissolved silica inputs into the lakes. Centennial-to millennial-scale dry episodes are also evident in the isotopic records and merit further investigation.

  11. Using Environmental Isotopes, Geochemistry, and Aquifer Temperature to Address Flow Regimes Within the Eastern Snake River Plain Aquifer at the Idaho National Engineering and Environmental Laboratory.

    NASA Astrophysics Data System (ADS)

    McLing, T. L.; Smith, R. P.; Roback, R. C.; Elizabeth, J. G.; Blackwell, D. D.

    2002-12-01

    Beginning in 1997 a series of studies utilizing uranium and strontium isotopes were undertaken to characterize the Eastern Snake River Plain (ESRP) aquifer at the Idaho National Engineering and Environmental Laboratory (INEEL). These studies identified fast flow and slow flow zones within the ESRP aquifer at the INEEL. The work presented here is the result of continued study to characterize the physical properties of the aquifer. Especially the implications and origins of large-scale (10's of kilometers) slow flow zones located beneath the 2300 km2 site. Coupling strontium and uranium isotope data from water samples with regional temperature, geophysical, and geologic data has proven to be a robust way to investigate large-scale flow characteristics in the aquifer. Depth-temperature profiles show that effective aquifer thickness varies dramatically across the INEEL from less than 100-m to over 350-m. Isotopic ratios support the conclusion that the thinner portions of the aquifer are "slow flow" zones in which the residence time of groundwater in the rock matrix is sufficient to allow significant water rock interactions to take place. The "slow flow" zones may be zones of increased diagenesis and pore filling mineralization caused by large volumes of upwelling geothermal waters penetrating into the upper, conductive portion of the aquifer. Our current compilation of the large database of isotope, chemical, temperature, hydrologic, and geophysical data in a GIS format enables us to use 50 years of data collected from observation wells and regional surveys to increase our understanding of a complex fractured-rock aquifer

  12. Experimental calibration of silicon and oxygen isotope fractionations between quartz and water at 250°C by in situ microanalysis of experimental products and application to zoned low δ30Si quartz overgrowths

    SciTech Connect

    Pollington, Anthony D.; Kozdon, Reinhard; Anovitz, Lawrence M.; Georg, R. Bastian; Spicuzza, Michael J.; Valley, John W.

    2015-12-01

    The interpretation of silicon isotope data for quartz is hampered by the lack of experimentally determined fractionation factors between quartz and fluid. Further, there is a large spread in published oxygen isotope fractionation factors at low temperatures, primarily due to extrapolation from experimental calibrations at high temperature. We report the first measurements of silicon isotope ratios from experimentally precipitated quartz and estimate the equilibrium fractionation vs. dissolved silica using a novel in situ analysis technique applying secondary ion mass spectrometry to directly analyze experimental products. These experiments also yield a new value for oxygen isotope fractionation. Quartz overgrowths up to 235 μm thick were precipitated in silica–H2O–NaOH–NaCl fluids, at pH 12–13 and 250 °C. At this temperature, 1000lnα30Si(Qtz–fluid) = 0.55 ± 0.10‰ and 1000lnα18O(Qtz–fluid) = 10.62 ± 0.13‰, yielding the relations 1000lnα30Si(Qtz–fluid) = (0.15 ± 0.03) * 106/T2 and 1000lnα18O(Qtz–fluid) = (2.91 ± 0.04) * 106/T2 when extended to zero fractionation at infinite temperature. Values of δ30Si(Qtz) from diagenetic cement in sandstones from the basal Cambrian Mt. Simon Formation in central North America range from 0 to ₋5.4‰. Paired δ18O and δ30Si values from individual overgrowths preserve a record of Precambrian weathering and fluid transport. In conclusion, the application of the experimental quartz growth results to observations from natural sandstone samples suggests that precipitation of quartz at low temperatures in nature is dominated by kinetic, rather than equilibrium, processes.

  13. Material and device engineering in fully depleted silicon-on-insulator transistors to realize a steep subthreshold swing using negative capacitance

    NASA Astrophysics Data System (ADS)

    Ota, Hiroyuki; Migita, Shinji; Hattori, Junichi; Fukuda, Koichi; Toriumi, Akira

    2016-08-01

    This paper discusses material and device engineering in field-effect transistors (FETs) with HfO2-based ferroelectric gate insulators to attain a precipitous subthreshold swing (SS) by exploiting negative capacitance. Our physical analysis based on a new concept of a negative dielectric constant reveals that fully depleted silicon-on-insulator (FD-SOI) channels with a modest remnant polarization P r (3 µC/cm2 at most) are more suitable for realizing SS < 60 mV/decade than a higher P r of 10 µC/cm2, which is commonly reported for HfO2-based ferroelectric materials. We also confirm SS < 60 mV/decade in more than 5 orders of the subthreshold current in FD-SOI FETs with ferroelectric HfO2 gate insulators by device simulation.

  14. Silicon isotope fractionation during the precipitation of quartz and the adsorption of H4SiO4(aq) on Fe(Ⅲ)-oxyhydroxide surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Y.; He, H.; Zhang, S.

    2015-12-01

    Equilibrium Si isotope fractionation factors among orthosilicic acid (i.e.,H4SiO4(aq)), quartz and the adsorption complexes of H4SiO4(aq) on Fe (Ⅲ)-oxyhydroxide surface were calculated using the full-electron wave-function quantum chemistry methods (i.e., B3LYP/6-311G(2df,p)) with a new cluster-model-based treatment. Solvation effects were carefully included in our calculations via water-droplet method combined with implicit solvent models (e.g., PCM). The results revealed that, if it is under equilibrium conditions, heavy Si isotopes would be significantly enriched in quartz in comparison to H4SiO4(aq). However, most of the field observations suggested that quartz would have identical or even depleted d30Si values compared to that of H4SiO4(aq). To explain this discrepancy between the equilibrium calculation results and the field observations, the kinetic isotope effect (KIE) associated with the formation of amorphous silica, which usually is the precursor of crystalline quartz, was investigated using quantum chemistry methods. The KIE results showed that amorphous silica would be significantly enriched in light Si isotopes during its formation. Our equilibrium fractionation results, however, matched a special type of quartz (i.e., Herkimer "diamond") very well, due to its nearly equilibrated precipitation condition. Opposite to the case of precipitated quartz, a large equilibrium Si isotope fractionation (i.e., -3.0‰) was found between the absorbed bidentate Si surface complexes (i.e., 2C>Fe2O2Si(OH)2) and H4SiO4(aq). This calculated equilibrium Si isotope fractionation factor largely differed from a previous experimental result (ca. -1.08‰). We found that the formation of transient or temporary surface complexes (e.g., 1V>Fe2OSi(OH)3) may have accounted for the smaller net fractionation observed. With the equilibrium and kinetic Si isotope fractionation factors provided here, the distributions and changes of Si isotope compositions in the Earth's surface

  15. Influence of gate metal engineering on small-signal and noise behaviour of silicon nanowire MOSFET for low-noise amplifiers

    NASA Astrophysics Data System (ADS)

    Gupta, Neha; Chaujar, Rishu

    2016-08-01

    In this paper, we have investigated the small-signal behaviour and RF noise performance of gate electrode workfunction engineered (GEWE) silicon nanowire (SiNW) MOSFET, and the results so obtained are simultaneously compared with SiNW and conventional MOSFET at THz frequency range. This work examines reflection and transmission coefficients, noise conductance, minimum noise figure and cross-correlation factor. Results reveal significant reduction in input/output reflection coefficient and an increase in forward/reverse transmission coefficient owing to improved transconductance in GEWE-SiNW in comparison with conventional counterparts. It is also observed that minimum noise figure and noise conductance of GEWE-SiNW is reduced by 17.4 and 31.2 %, respectively, in comparison with SiNW, thus fortifying its potential application for low-noise amplifiers (LNAs) at radio frequencies. Moreover, the efficacy of gate metal workfunction engineering is also studied and the results validate that tuning of workfunction difference results further improvement in device small-signal behaviour and noise performance.

  16. 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.

  17. 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.

  18. Toward Complete Isotopic Analysis of Individual Presolar Silicon Carbide Grains: C, N, Si, Sr, Zr, Mo, and Ba in Single Grains of Type X

    NASA Technical Reports Server (NTRS)

    Pellin, M. J.; Calaway, W. F.; Davis, A. M.; Lewis, R. S.; Amari, S.; Clayton, R. N.

    2000-01-01

    The isotopic compositions of Sr, Ba, Zr and Mo in single presolar SiC grains from supernovae are different from those expected from either of the dominant heavy element neutron capture nucleosynthesis mechanisms, the s-process and the r-process.

  19. In(x)Ga(₁-x)As nanowires on silicon: one-dimensional heterogeneous epitaxy, bandgap engineering, and photovoltaics.

    PubMed

    Shin, Jae Cheol; Kim, Kyou Hyun; Yu, Ki Jun; Hu, Hefei; Yin, Leijun; Ning, Cun-Zheng; Rogers, John A; Zuo, Jian-Min; Li, Xiuling

    2011-11-01

    We report on the one-dimensional (1D) heteroepitaxial growth of In(x)Ga(1-x)As (x = 0.2-1) nanowires (NWs) on silicon (Si) substrates over almost the entire composition range using metalorganic chemical vapor deposition (MOCVD) without catalysts or masks. The epitaxial growth takes place spontaneously producing uniform, nontapered, high aspect ratio NW arrays with a density exceeding 1 × 10(8)/cm(2). NW diameter (∼30-250 nm) is inversely proportional to the lattice mismatch between In(x)Ga(1-x)As and Si (∼4-11%), and can be further tuned by MOCVD growth condition. Remarkably, no dislocations have been found in all composition In(x)Ga(1-x)As NWs, even though massive stacking faults and twin planes are present. Indium rich NWs show more zinc-blende and Ga-rich NWs exhibit dominantly wurtzite polytype, as confirmed by scanning transmission electron microscopy (STEM) and photoluminescence spectra. Solar cells fabricated using an n-type In(0.3)Ga(0.7)As NW array on a p-type Si(111) substrate with a ∼ 2.2% area coverage, operates at an open circuit voltage, V(oc), and a short circuit current density, J(sc), of 0.37 V and 12.9 mA/cm(2), respectively. This work represents the first systematic report on direct 1D heteroepitaxy of ternary In(x)Ga(1-x)As NWs on silicon substrate in a wide composition/bandgap range that can be used for wafer-scale monolithic heterogeneous integration for high performance photovoltaics. PMID:21967406

  20. 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.

  1. Theory-guided nano-engineering of organic electro-optic materials for hybrid silicon photonic, plasmonic, and metamaterial devices

    NASA Astrophysics Data System (ADS)

    Dalton, Larry R.

    2013-03-01

    Coarse-grained Monte Carlo/molecular dynamic calculations are employed to explore the effect of various of intermolecular electrostatic interactions upon chromophore order, lattice dimensionality, and viscoelasticity in electrically-poled organic second order nonlinear optical materials. The following classes of organic macromolecular materials are considered: (1) Chromophore-polymer composites, (2) chromophores covalently incorporated into polymers and dendrimers, (3) chromophores incorporating additional dipolar or quadrupolar interactions that enhance poling efficiency, and (4) binary chromophore materials. For chromophore-polymer composites, the competition of chromophore-chromophore dipolar interactions and nuclear repulsive (steric) interactions define poling-induced acentric order. For covalently incorporated chromophores, covalent bond potentials also influence poling-induced order. These first two classes of materials basically behave as Langevin (3-D) lattice materials. Dipolar (e.g., coumarin) and quadrupolar (arene-perfluoroarene) interactions act to influence lattice dimensionality and thus enhance poling efficiency (the ratio of electro-optic activity to electric poling field strength). The long-range molecular cooperativity associated with these interactions influences viscoelastic properties critical to material processing and integration into silicon photonic, plasmonic, and metamaterial devices. The interaction between different chromophore species in binary chromophore materials also enhances poling efficiency. Polarized laser radiation applied to certain binary chromophore materials can also be used to enhance poling efficiency through control of lattice dimensionality. Poling efficiency approaching 5 (nm/V)2 has been achieved for these latter two classes of materials. Improvement in poling efficiency and control of material viscosity is particular important for integration of organic materials into complex device structures.

  2. Silicon Micromachining

    NASA Astrophysics Data System (ADS)

    Elwenspoek, Miko; Jansen, Henri V.

    2004-08-01

    This comprehensive book provides an overview of the key techniques used in the fabrication of micron-scale structures in silicon. Recent advances in these techniques have made it possible to create a new generation of microsystem devices, such as microsensors, accelerometers, micropumps, and miniature robots. The authors underpin the discussion of each technique with a brief review of the fundamental physical and chemical principles involved. They pay particular attention to methods such as isotropic and anisotropic wet chemical etching, wafer bonding, reactive ion etching, and surface micromachining. There is a special section on bulk micromachining, and the authors also discuss release mechanisms for movable microstructures. The book is a blend of detailed experimental and theoretical material, and will be of great interest to graduate students and researchers in electrical engineering and materials science whose work involves the study of micro-electromechanical systems (MEMS).

  3. Engine

    SciTech Connect

    Shin, H.B.

    1984-02-28

    An internal combustion engine has a piston rack depending from each piston. This rack is connected to a power output shaft through a mechanical rectifier so that the power output shaft rotates in only one direction. A connecting rod is pivotally connected at one end to the rack and at the other end to the crank of a reduced function crankshaft so that the crankshaft rotates at the same angular velocity as the power output shaft and at the same frequency as the pistons. The crankshaft has a size, weight and shape sufficient to return the pistons back into the cylinders in position for the next power stroke.

  4. Seasonal variations, origin, and fate of settling diatoms in the Southern Ocean tracked by silicon isotope records in deep sediment traps

    NASA Astrophysics Data System (ADS)

    Closset, Ivia; Cardinal, Damien; Bray, Stephen G.; Thil, François; Djouraev, Irina; Rigual-Hernández, Andrés. S.; Trull, Thomas W.

    2015-09-01

    The Southern Ocean plays a pivotal role in the control of atmospheric CO2 levels, via both physical and biological sequestration processes. The biological carbon transfer to the ocean interior is tightly coupled to the availability of other elements, especially iron as a trace-limiting nutrient and dissolved silicon as the mineral substrate that allows diatoms to dominate primary production. Importantly, variations in the silicon cycling are large but not well understood. Here we use δ30Si measurements to track seasonal flows of silica to the deep sea, as captured by sediment trap time series, for the three major zones (Antarctic, AZ; Polar Frontal, PFZ; and Sub-Antarctic, SAZ) of the open Southern Ocean. Variations in the exported flux of biogenic silica (BSi) and its δ30Si composition reveal a range of insights, including that (i) the sinking rate of BSi exceeds 200 m d-1 in summer in the AZ yet decreases to very low values in winter that allow particles to remain in the water column through to the following spring, (ii) occasional vertical mixing events affect the δ30Si composition of exported BSi in both the SAZ and AZ, and (iii) the δ30Si signature of diatoms is well conserved through the water column despite strong BSi and particulate organic carbon (POC) attenuation at depth and is closely linked to the Si consumption in surface waters. With the strong coupling observed between BSi and POC fluxes in PFZ and AZ, these data provide new constraints for application to biogeochemical models of seasonal controls on production and export.

  5. Silicon production process evaluations

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Engineering design of the third distillation column in the process was accomplished. The initial design is based on a 94.35% recovery of dichlorosilane in the distillate and a 99.9% recovery of trichlorosilane in the bottoms. The specified separation is achieved at a reflux ratio of 15 with 20 trays (equilibrium stages). Additional specifications and results are reported including equipment size, temperatures and pressure. Specific raw material requirements necessary to produce the silicon in the process are presented. The primary raw materials include metallurgical grade silicon, silicon tetrachloride, hydrogen, copper (catalyst) and lime (waste treatment). Hydrogen chloride is produced as by product in the silicon deposition. Cost analysis of the process was initiated during this reporting period.

  6. Isotopic tracing study of the growth of silicon carbide nanocrystals at the SiO{sub 2}/Si interface by CO annealing

    SciTech Connect

    Pongracz, A.; Hoshino, Y.; D'Angelo, M.; Ganem, J.-J.; Trimaille, I.; Vickridge, I.; Cavellin, C. Deville; Battistig, G.; Josepovits, K. V.

    2009-07-15

    The epitaxial growth of beta-Sic nanocrystals at the Si{sup 16}O{sub 2}/Si(100) interface under CO annealing has been studied using {sup 13}C{sup 18}O and isotopically sensitive nuclear reaction analysis and secondary ion mass spectrometry analysis. The results show that the amount of SiC increases linearly with the CO pressure and the annealing time. We demonstrate that the CO diffuses as a molecule in the silica and that for each C atom reacting to form SiC, an oxygen atom is incorporated in the vicinity of the interface. The linear and the parabolic rate constants corresponding to an adapted Deal and Grove model are also determined.

  7. Isotopic Tracing of Fuel Carbon in the Emissions of a Compression-Ignition Engine Fueled with Biodiesel Blends

    SciTech Connect

    Buchholz, B A; Cheng, A S; Dibble, R W

    2003-03-03

    Experimental tests were conducted on a Cummins 85.9 direct-injected diesel engine fueled with biodiesel blends. 20% and 50% blend levels were tested, as was 100% (neat) biodiesel. Emissions of particulate matter (PM), nitrogen oxides (NO{sub x}), hydrocarbons (HC) and CO were measured under steady-state operating conditions. The effect of biodiesel on PM emissions was mixed; however, the contribution of the volatile organic fraction to total PM was greater for the higher biodiesel blend levels. When only non-volatile PM mass was considered, reductions were observed for the biodiesel blends as well as for neat biodiesel. The biodiesel test fuels increased NO{sub x}, while HC and CO emissions were reduced. PM collected on quartz filters during the experimental runs were analyzed for carbon-14 content using accelerator mass spectrometry (AMs). These measurements revealed that carbon from the biodiesel portion of the blended fuel was marginally less likely to contribute to PM, compared to the carbon from the diesel portion of the fuel. The results are different than those obtained in previous tests with the oxygenate ethanol, which was observed to be far less likely contribute to PM than the diesel component of the blended fuel. The data suggests that chemical structure of the oxygen- carbon bonds in an oxygenate affects the PM formation process.

  8. Sr, C and O isotopes as markers of alkaline disturbances in the Toarcian argillites of the Tournemire experimental platform (France). Case of a 15-years old engineered analogue.

    NASA Astrophysics Data System (ADS)

    Techer, I.; Boulvais, P.; Bartier, D.; Tinseau, E.

    2009-04-01

    In France, the concept of a geological disposal of high-activity and long-period nuclear wastes requires the use of concrete and cement-bearing materials as building structures or as waste containment packages, in conjunction with clayey barriers (e.g., compacted bentonite as an engineered barrier and/or argillite-type rocks as a geological barrier). Hydrolysis of cementitious phases is however known to produce hyper-alkaline pore fluids with pH ranging from 10 to 13.5 that will be in disequilibrium with the geological setting environment (argillite pore-water pH around 8). The disturbance of clayey rocks in contact with such materials is thus an important task in safety assessment studies of deep geological storage. This concerns the knowledge of mineral / solution paths but also the spatial extent of the alkaline plume into the clayey material. Experimental and modelling approaches were performed this last decade to answer these questions. In addition to these approaches, natural or engineered contexts in which a clayey formation has been in contact with cementitious materials can be considered as analogues of a deep geological storage for the study of argillite /cement interaction. Such contexts can be found in the IRSN Tournemire experimental platform in Aveyron (France). This platform is based on a tunnel, excavated between 1882 and 1886 through Domerian marls and Toarcian argillites, which is dedicated since 1990 to multidisciplinary research programs. In the frameworks of these programs, exploration boreholes were realized from the basement of the tunnel in the 1990 years. The boreholes were then filled with concrete and cement that are presently in contact with the Toarcian argillites for 15-20 years. One of this borehole - DM borehole - was overcored in 2005 in order to collect the Toarcian argillites in contact with the cement and the concrete. Mineralogical, petrographic and microstructural analyses have argued for a clear disturbance of the Toarcian

  9. Isotopic Biogeochemistry

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.

    1985-01-01

    An overview is provided of the biogeochemical research. The funding, productivity, personnel and facilities are reviewed. Some of the technical areas covered are: carbon isotopic records; isotopic studies of banded iron formations; isotope effects in microbial systems; studies of organic compounds in ancient sediments; and development in isotopic geochemistry and analysis.

  10. Low-lying spectroscopy of a few even-even silicon isotopes investigated with the multiparticle-multihole Gogny energy density functional

    NASA Astrophysics Data System (ADS)

    Pillet, N.; Zelevinsky, V. G.; Dupuis, M.; Berger, J.-F.; Daugas, J. M.

    2012-04-01

    A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even 26-32Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of generator coordinate method (GCM) type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force tailored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of 26Si, 28Si, and 32Si, but gives a systematic energy shift in 30Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large proton-neutron matrix elements supplied by the Gogny interaction at the level of the approximate resolution of the multiparticle-multihole configuration mixing method done in the present study. These proton-neutron matrix elements enter in the definition of both single-particle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in 28Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments toward an implicit treatment of highly excited configurations.

  11. Sr, C and O isotopes as markers of alkaline disturbances in the Toarcian argillites of the Tournemire experimental platform (France). Case of a 15-years old engineered analogue.

    NASA Astrophysics Data System (ADS)

    Techer, I.; Boulvais, P.; Bartier, D.; Tinseau, E.

    2009-04-01

    In France, the concept of a geological disposal of high-activity and long-period nuclear wastes requires the use of concrete and cement-bearing materials as building structures or as waste containment packages, in conjunction with clayey barriers (e.g., compacted bentonite as an engineered barrier and/or argillite-type rocks as a geological barrier). Hydrolysis of cementitious phases is however known to produce hyper-alkaline pore fluids with pH ranging from 10 to 13.5 that will be in disequilibrium with the geological setting environment (argillite pore-water pH around 8). The disturbance of clayey rocks in contact with such materials is thus an important task in safety assessment studies of deep geological storage. This concerns the knowledge of mineral / solution paths but also the spatial extent of the alkaline plume into the clayey material. Experimental and modelling approaches were performed this last decade to answer these questions. In addition to these approaches, natural or engineered contexts in which a clayey formation has been in contact with cementitious materials can be considered as analogues of a deep geological storage for the study of argillite /cement interaction. Such contexts can be found in the IRSN Tournemire experimental platform in Aveyron (France). This platform is based on a tunnel, excavated between 1882 and 1886 through Domerian marls and Toarcian argillites, which is dedicated since 1990 to multidisciplinary research programs. In the frameworks of these programs, exploration boreholes were realized from the basement of the tunnel in the 1990 years. The boreholes were then filled with concrete and cement that are presently in contact with the Toarcian argillites for 15-20 years. One of this borehole - DM borehole - was overcored in 2005 in order to collect the Toarcian argillites in contact with the cement and the concrete. Mineralogical, petrographic and microstructural analyses have argued for a clear disturbance of the Toarcian

  12. The GEM Silicon Tracking System

    SciTech Connect

    Mills, G.B.

    1993-09-01

    The GEM Collaboration has produced a baseline design for the GEM detector. The baseline design of the GEM Silicon Tracking System (STS) is discussed in this article. Mechanical and electrical engineering progress on the GEM STS is described. Results from simulations of detector performance and the implications on engineering issues are described.

  13. Isotopic anomalies in extraterrestrial grains.

    PubMed

    Ireland, T R

    1996-03-01

    Isotopic compositions are referred to as anomalous if the isotopic ratios measured cannot be related to the terrestrial (solar) composition of a given element. While small effects close to the resolution of mass spectrometric techniques can have ambiguous origins, the discovery of large isotopic anomalies in inclusions and grains from primitive meteorites suggests that material from distinct sites of stellar nucleosynthesis has been preserved. Refractory inclusions, which are predominantly composed of the refractory oxides of Al, Ca, Ti, and Mg, in chondritic meteorites commonly have excesses in the heaviest isotopes of Ca, Ti, and Cr which are inferred to have been produced in a supernova. Refractory inclusions also contain excess 26Mg from short lived 26Al decay. However, despite the isotopic anomalies indicating the preservation of distinct nucleosynthetic sites, refractory inclusions have been processed in the solar system and are not interstellar grains. Carbon (graphite and diamond) and silicon carbide grains from the same meteorites also have large isotopic anomalies but these phases are not stable in the oxidized solar nebula which suggests that they are presolar and formed in the circumstellar atmospheres of carbon-rich stars. Diamond has a characteristic signature enriched in the lightest and heaviest isotopes of Xe, and graphite shows a wide range in C isotopic compositions. SiC commonly has C and N isotopic signatures which are characteristic of H-burning in the C-N-O cycle in low-mass stars. Heavier elements such as Si, Ti, Xe, Ba, and Nd, carry an isotopic signature of the s-process. A minor population of SiC (known as Grains X, ca. 1%) are distinct in having decay products of short lived isotopes 26Al (now 26Mg), 44Ti (now 44Ca), and 49V (now 49Ti), as well as 28Si excesses which are characteristic of supernova nucleosynthesis. The preservation of these isotopic anomalies allows the examination of detailed nucleosynthetic pathways in stars. PMID

  14. Low cost silicon solar array project silicon materials task

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A program was established to develop a high temperature silicon production process using existing electric arc heater technology. Silicon tetrachloride and a reductant will be injected into an arc heated mixture of hydrogen and argon. Under these high temperature conditions, a very rapid reaction is expected to occur and proceed essentially to completion, yielding silicon and gaseous sodium chloride. Techniques for high temperature separation and collection of the molten silicon will be developed using standard engineering approaches, and the salt vapor will later be electrolytically separated into its elemental constituents for recycle. Preliminary technical evaluations and economic projections indicate not only that this process appears to be feasible, but that it also has the advantages of rapid, high capacity production of good quality molten silicon at a nominal cost.

  15. Determination of Silicon in Hydrazine

    NASA Technical Reports Server (NTRS)

    McClure, Mark B.; Mast, Dion; Greene, Ben; Maes, Miguel J.

    2006-01-01

    Inductively coupled plasma-mass spectrometry (ICP-MS) is a highly sensitive technique sometimes used for the trace determination of silicon at a mass-to-charge (m/z) ratio of 28, the most abundant natural isotope of silicon. Unfortunately, ICP-MS is unable to differentiate between other sources of m/z 28 and false positive results for silicon will result when other sources of m/z 28 are present. Nitrogen was a major source of m/z 28 and contributes to the m/z 28 signal when hydrazine sample or nitric acid preservative is introduced into the plasma. Accordingly, this work was performed to develop a sample preparation step coupled with an ICP-MS analysis that minimized non-silicon sources of m/z 28. In the preparatory step of this method, the hydrazine sample was first decomposed predominately to nitrogen gas and water with copper-catalyzed hydrogen peroxide. In the analysis step, ICP-MS was used without nitric acid preservative in samples or standards. Glass, a potential source of silicon contamination, was also avoided where possible. The method was sensitive, accurate, and reliable for the determination of silicon in monopropellant grade hydrazine (MPH) in AF-E-332 elastomer leaching tests. Results for silicon in MPH were comparable to those reported in the literature for other studies.

  16. Making a Silicon-Nitride/Silicon-Carbide Composite

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.

    1987-01-01

    Hot pressing and nitriding produce strong fiber/matrix material. Fabrication method developed for processing strong and tough silicon-based ceramic composite material, SiC/RBSN, which consists of reaction-bonded Si3N4 (RBSN) reinforced by continuous-length, high-modulus, high strength silicon carbide (SiC) fibers prepared by chemical-vapor deposition method. Increased toughness and ultimate strength of SiC/RBSN composite makes it potential structural material for advanced heat engines.

  17. Silicon polymer encapsulation of high level calcine waste for transportation or disposal

    SciTech Connect

    G. G. Loomis

    2000-02-27

    Engineers at the Idaho National Engineering and Environmental Laboratory (INEEL) are investigating the use of a proprietary silicon-polymer to encapsulate high-level calcine waste stored at the INEEL's Idaho Nuclear Technology and Engineering Center (INTEC). The silicon-polymer-encapsulated waste may be suitable for direct disposal at a radioactive waste disposal facility or for transport to an offsite melter for further processing. In connection with silicon-polymer encapsulation, the University of Akron, under special arrangement with Orbit Technologies, the originator of the Polymer Encapsulation Technology (PET), has studied a simulated waste material from INTEC called pilot-scale calcine that contains hazardous materials but no radioactive isotopes. In this study, Toxicity Characteristic Leaching Procedure (TCLP) and Materials Characterization Center Test 1P were performed to test the waste form for disposal. In addition, a maximum waste loading was established for transporting the calcine waste at INTEC to an offsite melter. For this maximum waste loading, compressive strength testing, 10-m drop testing, melt testing, and a Department of Transportation (DOT) oxidizer test were performed.

  18. Silicon Polymer Encapsulation of High Level Calcine Waste for Transportation or Disposal

    SciTech Connect

    Loomis, Guy George; Miller, Carla Jean; Kimmel, Richard John

    2000-03-01

    Engineers at the Idaho National Engineering and Environmental Laboratory (INEEL) are investigating the use of a proprietary silicon-polymer to encapsulate high-level calcine waste stored at the INEEL's Idaho Nuclear Technology and Engineering Center (INTEC). The silicon-polymer-encapsulated waste may be suitable for direct disposal at a radioactive waste disposal facility or for transport to an offsite melter for further processing. In connection with silicon-polymer encapsulation, the University of Akron, under special arrangement with Orbit Technologies, the originator of the Polymer Encapsulation Technology (PET), has studied a simulated waste material from INTEC called pilot-scale calcine that contains hazardous materials but no radioactive isotopes. In this study, Toxicity Characteristic Leaching Procedure (TCLP) and Materials Characterization Center Test 1P were performed to test the waste form for disposal. In addition, a maximum waste loading was established for transporting the calcine waste at INTEC to an offsite melter. For this maximum waste loading, compressive strength testing, 10-m drop testing, melt testing, and a Department of Transportation (DOT) oxidizer test were performed.

  19. Mass-independent isotope effects.

    PubMed

    Buchachenko, Anatoly L

    2013-02-28

    Three fundamental properties of atomic nuclei-mass, spin (and related magnetic moment), and volume-are the source of isotope effects. The mostly deserved and popular, with almost hundred-year history, is the mass-dependent isotope effect. The first mass-independent isotope effect which chemically discriminates isotopes by their nuclear spins and nuclear magnetic moments rather than by their masses was detected in 1976. It was named as the magnetic isotope effect because it is controlled by magnetic interaction, i.e., electron-nuclear hyperfine coupling in the paramagnetic species, the reaction intermediates. The effect follows from the universal physical property of chemical reactions to conserve angular momentum (spin) of electrons and nuclei. It is now detected for oxygen, silicon, sulfur, germanium, tin, mercury, magnesium, calcium, zinc, and uranium in a great variety of chemical and biochemical reactions including those of medical and ecological importance. Another mass-independent isotope effect was detected in 1983 as a deviation of isotopic distribution in reaction products from that which would be expected from the mass-dependent isotope effect. On the physical basis, it is in fact a mass-dependent effect, but it surprisingly results in isotope fractionation which is incompatible with that predicted by traditional mass-dependent effects. It is supposed to be a function of dynamic parameters of reaction and energy relaxation in excited states of products. The third, nuclear volume mass-independent isotope effect is detected in the high-resolution atomic and molecular spectra and in the extraction processes, but there are no unambiguous indications of its importance as an isotope fractionation factor in chemical reactions. PMID:23301791

  20. Silicon production process evaluations

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Chemical engineering analyses involving the preliminary process design of a plant (1,000 metric tons/year capacity) to produce silicon via the technology under consideration were accomplished. Major activities in the chemical engineering analyses included base case conditions, reaction chemistry, process flowsheet, material balance, energy balance, property data, equipment design, major equipment list, production labor and forward for economic analysis. The process design package provided detailed data for raw materials, utilities, major process equipment and production labor requirements necessary for polysilicon production in each process.

  1. Silicon production process evaluations

    NASA Astrophysics Data System (ADS)

    1982-07-01

    Chemical engineering analyses involving the preliminary process design of a plant (1,000 metric tons/year capacity) to produce silicon via the technology under consideration were accomplished. Major activities in the chemical engineering analyses included base case conditions, reaction chemistry, process flowsheet, material balance, energy balance, property data, equipment design, major equipment list, production labor and forward for economic analysis. The process design package provided detailed data for raw materials, utilities, major process equipment and production labor requirements necessary for polysilicon production in each process.

  2. Another continental pool in the terrestrial silicon cycle.

    PubMed

    Basile-Doelsch, Isabelle; Meunier, Jean Dominique; Parron, Claude

    2005-01-27

    Silicon is the second most abundant element on Earth. It is an important nutrient for phytoplankton and is readily absorbed by terrestrial vegetation; it also assists the removal of carbon dioxide from the atmosphere through the weathering of silicates. But the continental cycle of silicon is not well known, and only a few studies have attempted to use silicon stable isotopes (28Si, 29Si and 30Si) to quantify the continental silicon reservoirs. Dissolved silicon in sea and river waters forms a reservoir of mean isotopic value +1.1 per thousand (refs 7, 10). It is enriched in 30Si with respect to the igneous rocks reservoir, which has a mean isotopic value of -0.3 per thousand (refs 4, 9). This enrichment can only be produced by a major fractionation during weathering, and should result in the formation of a continental 30Si-depleted reservoir. Such a reservoir, however, has not been identified to date. Here we analyse silicon isotopes of in situ quartz from a sandstone series in France, using a new-generation secondary ion mass spectrometry apparatus. We show that quartz that precipitates as siliceous cements forms a strongly 30Si-depleted reservoir with isotopic values down to -5.7 per thousand, a more negative value than any previously published for terrestrial samples. Our findings suggest that quartz re-precipitation plays an important role in the biogeochemical cycle of silicon. PMID:15674287

  3. Isotope separation

    DOEpatents

    Bartlett, Rodney J.; Morrey, John R.

    1978-01-01

    A method and apparatus is described for separating gas molecules containing one isotope of an element from gas molecules containing other isotopes of the same element in which all of the molecules of the gas are at the same electronic state in their ground state. Gas molecules in a gas stream containing one of the isotopes are selectively excited to a different electronic state while leaving the other gas molecules in their original ground state. Gas molecules containing one of the isotopes are then deflected from the other gas molecules in the stream and thus physically separated.

  4. Silicon Self-Diffusion in Isotope Heterostructures

    SciTech Connect

    Bracht, H.; Haller, E.E.; Clark-Phelps, R.

    1998-02-06

    Structural and electronic properties as well as thestability of MoS2 nanotubes are studied using thedensity-functional-based tight-binding method. It is found that MoS2zigzag (n,0) nanotubes exhibit a narrow direct band gap and MoS2 armchair(n,n) possess a nonzero moderate direct gap. Interestingly, the (n,n)tubes show a small indirect gap similar to the direct gap of (n,0)nanotubes. Simulated electron diffraction patterns confirm the existenceof armchair and zigzag disulphide nanotubes. The structure of the MoS2nanotube tips is explained by introducing topological defects whichproduce positive and negative curvature.

  5. 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.

  6. Technical Note: Silica stable isotopes and silicification in a carnivorous sponge Asbestopluma sp.

    NASA Astrophysics Data System (ADS)

    Hendry, K. R.; Swann, G. E. A.; Leng, M. J.; Sloane, H. J.; Goodwin, C.; Berman, J.; Maldonado, M.

    2015-06-01

    The stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotope composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the vital effects on silica, silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that are related to unusual spicule silicification. The largest variation in both isotope systems was associated with the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotope signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotope signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements.

  7. Technical Note: Silica stable isotopes and silicification in a carnivorous sponge Asbestopluma sp.

    NASA Astrophysics Data System (ADS)

    Hendry, K. R.; Swann, G. E. A.; Leng, M. J.; Sloane, H. J.; Goodwin, C.; Berman, J.; Maldonado, M.

    2014-12-01

    The stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotopic composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the biological vital effects on silica silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that appear related to unusual spicule silicification. The largest variation in both isotope systems was associated to the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence of an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotopic signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotopic signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements.

  8. Chemical and Isotopic Composition and Gas Concentrations of Ground Water and Surface Water from Selected Sites At and Near the Idaho National Engineering and Environmental Laboratory, Idaho, 1994-97

    SciTech Connect

    E. Busenberg; L. N. Plummer; M. W. Doughten; P. K. Widman; R. C. Bartholomay

    2000-05-30

    >From May 1994 through May 1997, the US Geological Survey, in cooperation with the US Department of Energy, collected water samples from 86 wells completed in the Snake River Plain aquifer at and near the Idaho National Engineering and Environmental Laboratory. The samples were analyzed for a variety of chemical constituents including all major elements and 22 trace elements. Concentrations of scandium, yttrium, and the lanthanide series were measured in samples from 11 wells and 1 hot spring. The data will be used to determine the fraction of young water in the ground water. The fraction of young water must be known to calculate the ages of ground water using chlorofluorocarbons. The concentrations of the isotopes deuterium, oxygen-18, carbon-13, carbon-14, and tritium were measured in many ground water, surface-water and spring samples. The isotopic composition will provide clues to the origin and sources of water in the Snake River Plain aquifer. Concentrations ! of helium-3 , helium-4, total helium, and neon were measured in most groundwater samples, and the results will be used to determine the recharge temperature, and to date the ground waters.

  9. Radionuclides, stable isotopes, inorganic constituents, and organic compounds in water from selected wells and springs from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman Area, Idaho, 1994

    SciTech Connect

    Bartholomay, R.C.; Williams, L.M.; Campbell, L.J.

    1995-10-01

    The US Geological Survey and the Idaho Department of Water Resources, in response to a request from the US Department of Energy, samples 18 sites as part of a long-term project to monitor water quality of the Snake River Plain aquifer from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman area. Water samples were collected and analyzed for selected radionuclides, stable isotopes, inorganic constituents, and organic compounds. The samples were collected from seven irrigation wells, seven domestic wells, two springs, one stock well, and one observation well. Two quality assurance samples also were collected and analyzed. None of the radionuclide, inorganic constituent, or organic compound concentrations exceeded the established maximum contaminant levels for drinking water. Many of the radionuclide and inorganic constituent concentrations exceeded their respective reporting levels. All samples analyzed for dissolved organic carbon had concentrations that exceeded their minimum reporting levels.

  10. Radionuclides, stable isotopes, inorganic constituents, and organic compounds in water from selected wells and springs from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman Area, Idaho, 1995

    SciTech Connect

    Bartholomay, R.C.; Williams, L.M.; Campbell, L.J.

    1996-09-01

    The US Geological Survey and the Idaho Department of Water Resources, in cooperation with the US Department of Energy, sampled 17 sites as part of a long-term project to monitor water quality of the Snake River Plain aquifer from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman area. Water samples were collected and analyzed for selected radionuclides, stable isotopes, inorganic constituents, and organic compounds. The samples were collected from 11 irrigation wells, 2 domestic wells, 2 stock wells, 1 spring, and 1 public-supply well. Two quality assurance samples also were collected and analyzed. None of the radionuclide, inorganic constituents, or organic compound concentrations exceeded the established maximum contaminant levels for drinking water. Many of the radionuclide and inorganic constituent concentrations were greater than their respective reporting levels. All samples analyzed for dissolved organic carbon had concentrations that were greater than the minimum reporting level.