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Sample records for nitrogen silicon chalcogen

  1. Sub-bandgap absorptance in chalcogen-hyperdoped silicon

    NASA Astrophysics Data System (ADS)

    Newman, Bonna

    2011-03-01

    ~It has been shown that optical doping with pulsed lasers~can achieve non-equilibrium concentrations up to one atomic % of heavy chalcogens in silicon.~~Compared to intrinsic silicon, this material exhibits near-unity absorption of sub-bandgap photons and has potential use in silicon infrared photodetectors and high-efficiency photovoltaics.~~Successful application of this material, however, requires better understanding of the exact mechanism responsible for sub-bandgap absorptance.~~Using a variety of techniques, we probe the chemical structure of this material system.~~We find that the short range structure of the dopant atom is correlated to the amount of sub-bandgap absorptance.~~We also compare the structure of different dopant species (S and Se) as well as different hyperdoping mechanisms (fs-laser doping vs. ion implantation followed by pulsed laser melting).~~In conjunction with theoretical modeling of expected chalcogen defect states, we identify dominant structural characteristics related to the observation of sub-bandgap absorptance. ~ Expanding on previous results, we demonstrate control of sub-bandgap absorptance through thermal processing. ~~In addition to suggesting a method to engineer the optical properties of the material, this result provides further insight into the thermodynamics of formation of a possible dopant-related defect state.~~We compare the thermodynamics measurements to the dopant structural measurements and posit a model of sub-bandgap absorptance and defect dynamics. ~These results provide a better understanding of the phenomena of sub-bandgap absorptance in chalcogen-hyperdoped silicon and a pathway to explore other hyperdoped semiconductors. ~~ We acknowledge the support of the Clare B. Luce Foundation and the Chesonis Family Foundation.

  2. Reactivation of sub-bandgap absorption in chalcogen-hyperdoped silicon

    SciTech Connect

    Newman, Bonna K.; Buonassisi, Tonio; Sher, Meng-Ju; Mazur, Eric

    2011-06-20

    Silicon doped with nonequilibrium concentrations of chalcogens using a femtosecond laser exhibits near-unity absorption of sub-bandgap photons to wavelengths of at least 2500 nm. Previous studies have shown that sub-bandgap absorptance decreases with thermal annealing up to 1175 K and that the absorption deactivation correlates with chalcogen diffusivity. In this work, we show that sub-bandgap absorptance can be reactivated by annealing at temperatures between 1350 and 1550 K followed by fast cooling (>50 K/s). Our results suggest that the defects responsible for sub-bandgap absorptance are in equilibrium at high temperatures in hyperdoped Si:chalcogen systems.

  3. Possible atomic structures responsible for the sub-bandgap absorption of chalcogen-hyperdoped silicon

    SciTech Connect

    Wang, Ke-Fan; Shao, Hezhu; Liu, Kong; Qu, Shengchun E-mail: wangyx@henu.edu.cn; Wang, Zhanguo; Wang, Yuanxu E-mail: wangyx@henu.edu.cn

    2015-09-14

    Single-crystal silicon was hyperdoped with sulfur, selenium, and tellurium using ion implantation and nanosecond laser melting. The hyperdoping of such chalcogen elements led to strong and wide sub-bandgap light absorption. Annealing the hyperdoped silicon, even at low temperatures (such as 200–400 °C), led to attenuation of the sub-bandgap absorption. To explain the attenuation process, we modeled it as chemical decomposition reaction from an optically absorbing structure to a non-absorbing structure. Attenuation of the experimental absorption coefficient was fit using the Arrhenius equation. From the fitted data, we extracted the reaction activation energies of S-, Se-, and T-hyperdoped silicon as 0.338 ± 0.029 eV, 0.471 ± 0.040 eV, and 0.357 ± 0.028 eV, respectively. We discuss these activation energies in terms of the bond energies of chalcogen–Si metastable bonds, and suggest that several high-energy interstitial sites, rather than substitutional sites, are candidates for the atomic structures that are responsible for the strong sub-bandgap absorption of chalcogen hyperdoped silicon.

  4. Fabrication and subband gap optical properties of silicon supersaturated with chalcogens by ion implantation and pulsed laser melting

    SciTech Connect

    Bob, Brion P.; Aziz, Michael J.; Kohno, Atsushi; Charnvanichborikarn, Supakit; Williams, James S.; Warrender, Jeffrey M.; Umezu, Ikurou; Tabbal, Malek

    2010-06-15

    Topographically flat, single crystal silicon supersaturated with the chalcogens S, Se, and Te was prepared by ion implantation followed by pulsed laser melting and rapid solidification. The influences of the number of laser shots on the atomic and carrier concentration-depth profiles were measured with secondary ion mass spectrometry and spreading resistance profiling, respectively. We found good agreement between the atomic concentration-depth profiles obtained from experiments and a one-dimensional model for plane-front melting, solidification, liquid-phase diffusion, with kinetic solute trapping, and surface evaporation. Broadband subband gap absorption is exhibited by all dopants over a wavelength range from 1 to 2.5 microns. The absorption did not change appreciably with increasing number of laser shots, despite a measurable loss of chalcogen and of electronic carriers after each shot.

  5. Oxygen, carbon, hydrogen and nitrogen in crystalline silicon

    SciTech Connect

    Mikkelsen, J.C.; Pearton, S.J.; Corbett, J.W.; Pennycook, S.J

    1986-01-01

    These proceedings collect papers on interstitial material in silicon. Topics include: hydrogen in crystalline silicon, low energy hydrogen ion bombarded silicon, oxygen in silicon, oxygen thermal donor formation, thermal donor generation and annihilation effects on oxygen precipitation oxygen effects on plastic flow during growth of dendrixic web silicon, nitrogen in silicon, off-center nitrogen and oxygen in silicon, and thermal donor hierarchies in silicon and germanium.

  6. The potential of hydrogenated amorphous silicon-chalcogen alloys for photovoltaic applications: The role of persistent photoconductivity

    SciTech Connect

    Wang, S.L.; Viner, J.M.; Taylor, P.C.; Itoh, T.; Nitta, S.

    1997-02-01

    The potential improvement in stability of hydrogenated silicon-sulfur alloys (a-SiS{sub x}:H) with respect to ordinary hydrogenated amorphous silicon (a-Si:H) has been attributed to the introduction of an additional metastability known as persistent photoconductivity (PPC). In order to examine the PPC process in more detail we examine a series of alloys with large sulfur concentrations (x{gt}0.01). Although these alloys are not useful in photovoltaic devices, the high sulfur concentrations accentuate the PPC effect and allow one to study this effect with little competition from the ordinary Staebler-Wronski effect that dominates the metastable processes that occur in a -Si:H. {copyright} {ital 1997 American Institute of Physics.}

  7. Study of Nitrogen Concentration in Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Yan, Cheng-Feng; Kong, Hai-Kuan; Chen, Jian-Jun; Xin, Jun; Shi, Er-Wei; Yang, Jian-Hua

    2013-06-01

    This work focused on studying the nitrogen concentration ( C N) in SiC. The variations of C N in the synthesis of SiC powder as well as the transport during SiC crystal growth have been investigated for broad ranges of temperature and Ar pressure. Before SiC crystal growth, SiC powders were synthesized from high-purity silicon and carbon powders. The concentrations of nitrogen, free C, and free Si in the as-prepared powders were all measured. C N in the SiC source powder decreased with increasing temperature and decreasing Ar pressure, whereas it did not show a remarkable trend with the molar ratio of free Si to free C. SiC crystal was then grown by the physical vapor transport (PVT) technique using the as-prepared powder. The distribution of C N in the remaining material indirectly indicated the temperature field of crystal growth. In addition, compared with introducing N2 during SiC crystal growth, doping with nitrogen during synthesis of the SiC source powder might be a better method to control C N in SiC crystals.

  8. Supramolecular Wiring of Benzo-1,3-chalcogenazoles through Programmed Chalcogen Bonding Interactions.

    PubMed

    Kremer, Adrian; Fermi, Andrea; Biot, Nicolas; Wouters, Johan; Bonifazi, Davide

    2016-04-11

    The high-yielding synthesis of 2-substituted benzo-1,3-tellurazoles and benzo-1,3-selenazoles through a dehydrative cyclization reaction has been reported, giving access to a large variety of benzo-1,3-chalcogenazoles. Exceptionally, these aromatic heterocycles proved to be very stable and thus very handy to form controlled solid-state organizations in which wire-like polymeric structures are formed through secondary N⋅⋅⋅Y bonding interactions (SBIs) engaging the chalcogen (Y=Se or Te) and nitrogen atoms. In particular, it has been shown that the recognition properties of the chalcogen centre at the solid state could be programmed by selectively barring one of its σ-holes through a combination of electronic and steric effects exerted by the substituent at the 2-position. As predicted by the electrostatic potential surfaces calculated by quantum chemical modelling, the pyridyl groups revealed to be the stronger chalcogen bonding acceptors, and thus the best ligand candidate for programming the molecular organization at the solid state. In contrast, the thiophenyl group is an unsuitable substituent for establishing SBIs in this molecular system as it gives rise to chalcogen-chalcogen repulsion. The weaker chalcogen donor properties of the Se analogues trigger the formation of feeble N⋅⋅⋅Se contacts, which are manifested in similar solid-state polymers featuring longer nitrogen-chalcogen distances. PMID:26899235

  9. Anion Transport with Chalcogen Bonds.

    PubMed

    Benz, Sebastian; Macchione, Mariano; Verolet, Quentin; Mareda, Jiri; Sakai, Naomi; Matile, Stefan

    2016-07-27

    In this report, we introduce synthetic anion transporters that operate with chalcogen bonds. Electron-deficient dithieno[3,2-b;2',3'-d]thiophenes (DTTs) are identified as ideal to bind anions in the focal point of the σ holes on the cofacial endocyclic sulfur atoms. Anion binding in solution and anion transport across lipid bilayers are found to increase with the depth of the σ holes of the DTT anionophores. These results introduce DTTs and related architectures as a privileged motif to engineer chalcogen bonds into functional systems, complementary in scope to classics such as 2,2'-bipyrroles or 2,2'-bipyridines that operate with hydrogen bonds and lone pairs, respectively. PMID:27433964

  10. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers

    NASA Astrophysics Data System (ADS)

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-07-01

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10-15 cm2 s-1, 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value.

  11. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers

    PubMed Central

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-01-01

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10−15 cm2 s−1, 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value. PMID:26227342

  12. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers.

    PubMed

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-01-01

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10(-15) cm(2) s(-1), 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value. PMID:26227342

  13. Generalized Valence Bond Description of Chalcogen-Nitrogen Compounds. III. Why the NO-OH and NS-OH Bonds Are So Different.

    PubMed

    Takeshita, Tyler Y; Dunning, Thom H

    2016-09-01

    Crabtree et al. recently reported the microwave spectrum of nitrosyl-O-hydroxide (trans-NOOH), an isomer of nitrous acid, and found that this molecule has the longest O-O bond ever observed: 1.9149 Å ± 0.0005 Å. This is in marked contrast to the structure of the valence isoelectronic trans-NSOH molecule, which has a normal NS-OH bond length and strength. Generalized valence bond calculations show that the long bond in trans-NOOH is the result of a weak through-pair interaction that singlet couples the spins of the electrons in singly occupied orbitals on the hydroxyl radical and nitrogen atom, an interaction that is enhanced by the intervening lone pair of the oxygen atom in NO. The NS-OH bond is the result of the formation of a stable recoupled pair bond dyad, which accounts for both its length and strength. PMID:27501366

  14. Chalcogen nanowires: synthesis and properties

    NASA Astrophysics Data System (ADS)

    Mayers, Brian T.; Gates, Byron D.; Xia, Younan

    2002-11-01

    We have demonstrated a solution-phase approach based on homogeneous nucleation and controlled growth for the synthesis of 1-dimensional nanostructures from a chalcogens such as Se, Te, and Se/Te alloys. These nanostructures include monodispersed nanowires, nanorods, and nanotubes with good dimensional control (lateral dimensions from 10 to 1000 nm, and lengths ranging from a 0.25 to >20 μm). These nanomaterials are ideal components for fabricating devices or composites for photoconductive and piezoelectric applications. In this presentation, we will discuss the mechanisms (as revealed by our SEM and TEM studies) for the formation of these 1-dimensional nanostructures, as well as some preliminary measurements on their properties.

  15. Enzyme mimics: Halogen and chalcogen team up

    NASA Astrophysics Data System (ADS)

    Metrangolo, Pierangelo; Resnati, Giuseppe

    2012-06-01

    The behaviour of di-selenol enzyme mimics indicates that a halogen bond between selenium and iodine, and a chalcogen interaction between the two selenium atoms, play an important role in the activation of thyroid hormones.

  16. Boron/Carbon/Silicon/Nitrogen Ceramics And Precursors

    NASA Technical Reports Server (NTRS)

    Riccitiello, Salvatore; Hsu, Ming TA; Chen, Timothy S.

    1996-01-01

    Ceramics containing various amounts of boron, carbon, silicon, and nitrogen made from variety of polymeric precursors. Synthesized in high yield from readily available and relatively inexpensive starting materials. Stable at room temperature; when polymerized, converted to ceramics in high yield. Ceramics resist oxidation and other forms of degradation at high temperatures; used in bulk to form objects or to infiltrate other ceramics to obtain composites having greater resistance to oxidation and high temperatures.

  17. A nitrogen-hyperdoped silicon material formed by femtosecond laser irradiation

    SciTech Connect

    Dong, Xiao; Zhu, Zhen; Shao, Hezhu; Rong, Ximing; Zhuang, Jun; Li, Ning; Liang, Cong; Sun, Haibin; Zhao, Li; Feng, Guojin

    2014-03-03

    A supersaturation of nitrogen atoms is found in the surface layer of microstructured silicon after femtosecond (fs) laser irradiation in NF{sub 3}. The average nitrogen concentration in the uppermost 50 nm is about 0.5 ± 0.2 at. %, several orders of magnitude higher than the solid solubility of nitrogen atoms in silicon. The nitrogen-hyperdoped silicon shows high crystallinity in the doped layer, which is due to the repairing effect of nitrogen on defects in silicon lattices. Nitrogen atoms and vacancies can be combined into thermal stable complexes after fs laser irradiation, which makes the nitrogen-hyperdoped silicon exhibit good thermal stability of optical properties.

  18. Nature of chalcogen hor ellipsis chalcogen contact interactions in organic donor-molecule salts

    SciTech Connect

    Novoa, J.J.; Whangbo, Myung-Hwan . Dept. of Chemistry); Williams, J.M. )

    1990-01-01

    The nature of chalcogen{hor ellipsis}chalcogen contact interactions in organic donor-molecule salts was examined by performing ab initio SCF-MO/MP2 calculations on H{sub 2}X{hor ellipsis}XH{sub 2}(X = O, S, SE, Te) and MM2 calculations on donor dimers (TXF){sub 2} (X = S, SE, Te) and (BEDX-TTF){sub 2} (X = O, S). 14 refs., 4 figs., 4 tabs.

  19. Chalcogen catalysts for polymer electrolyte fuel cell

    DOEpatents

    Zelenay, Piotr; Choi, Jong-Ho; Alonso-Vante, Nicolas; Wieckowski, Andrzej; Cao, Dianxue

    2010-08-24

    A methanol-tolerant cathode catalyst and a membrane electrode assembly for fuel cells that includes such a cathode catalyst. The cathode catalyst includes a support having at least one transition metal in elemental form and a chalcogen disposed on the support. Methods of making the cathode catalyst and membrane electrode assembly are also described.

  20. Nitrogen effects on silicon growth, defects, and carrier lifetime

    SciTech Connect

    Ciszek, T.F.; Wang, T.H.; Burrows, R.W.

    1995-08-01

    Silicon crystal or multicrystal growth in N{sub 2} or partial-N{sub 2} atmospheres can provide mechanical strengthening, lower purge-gas costs (nitrogen from liquid sources is about a factor of 4 less expensive than argon from liquid sources), and reduce swirl-type microdefect formation in dislocation-free (DF) crystals. There is not much literature on electrical effects of N in Si, including lifetime effects. We studied the effects of Si growth in atmospheres containing N{sub 2} on minority charge carrier lifetime E using the float-zone (FZ) crystal growth method. Ingots were grown with purge gases that ranged from pure argon (99.9995%) to pure N{sub 2} (99-999%). We found that multicrystalline silicon ingot growth in a partial or total nitrogen ambient has a negligible effect on {tau}. Values of 40 {mu}s < {tau} < 100 {mu}s were typical regardless of ambient. For DF growth, the degradation of {tau} is minimal and {tau} values above 1000 {mu}s are obtained if the amount of N{sub 2} in the purge gas is below the level at which nitride compounds form in the melt and disrupt DF growth.

  1. Process for producing high purity silicon nitride by the direct reaction between elemental silicon and nitrogen-hydrogen liquid reactants

    DOEpatents

    Pugar, E.A.; Morgan, P.E.D.

    1987-09-15

    A process is disclosed for producing, at a low temperature, a high purity reaction product consisting essentially of silicon, nitrogen, and hydrogen which can then be heated to produce a high purity alpha silicon nitride. The process comprises: reacting together a particulate elemental high purity silicon with a high purity nitrogen-hydrogen reactant in its liquid state (such as ammonia or hydrazine) having the formula: N/sub n/H/sub (n+m)/ wherein: n = 1--4 and m = 2 when the nitrogen-hydrogen reactant is straight chain, and 0 when the nitrogen-hydrogen reactant is cyclic. High purity silicon nitride can be formed from this intermediate product by heating the intermediate product at a temperature of from about 1200--1700/degree/C for a period from about 15 minutes up to about 2 hours to form a high purity alpha silicon nitride product. The discovery of the existence of a soluble Si/endash/N/endash/H intermediate enables chemical pathways to be explored previously unavailable in conventional solid-state approaches to silicon-nitrogen ceramics

  2. Process for producing high purity silicon nitride by the direct reaction between elemental silicon and nitrogen-hydrogen liquid reactants

    DOEpatents

    Pugar, Eloise A.; Morgan, Peter E. D.

    1990-01-01

    A process is disclosed for producing, at a low temperature, a high purity reaction product consisting essentially of silicon, nitrogen, and hydrogen which can then be heated to produce a high purity alpha silicon nitride. The process comprises: reacting together a particulate elemental high purity silicon with a high purity nitrogen-hydrogen reactant in its liquid state (such as ammonia or hydrazine) having the formula: N.sub.n H.sub.(n+m) wherein: n=1-4 and m=2 when the nitrogen-hydrogen reactant is straight chain, and 0 when the nitrogen-hydrogen reactant is cyclic. High purity silicon nitride can be formed from this intermediate product by heating the intermediate product at a temperature of from about 1200.degree.-1700.degree. C. for a period from about 15 minutes up to about 2 hours to form a high purity alpha silicon nitride product. The discovery of the existence of a soluble Si-N-H intermediate enables chemical pathways to be explored previously unavailable in conventional solid state approaches to silicon-nitrogen ceramics.

  3. Locally induced laminar convection in liquid nitrogen and silicone oils.

    PubMed

    Dubois, C; Duchesne, A; Vanderheyden, B; Vanderbemden, P; Caps, H

    2016-08-01

    We present an experimental study of a laminar convective phenomenon induced by a centimetric heater totally immersed in a liquid pool (Rayleigh number ranging from 10(4) to 10(7)). This local heating is observed to induce a laminar convection that differs from the classical Rayleigh-Bénard cells created by heating the whole bottom of the fluid: the convection pattern is no more periodic. In order to obtain a complete map of the velocity field, we use Particle Image Velocimetry technique. The vertical velocity between the counter-rotating convective cells is used as the relevant physical parameter to describe the phenomenon. The potential cooling applications of this problem lead us to choose liquid nitrogen as an experimental fluid. We thus compare the results obtained for various temperature gradients in liquid nitrogen with experiments performed at room temperature with silicone oils of various viscosities. The theoretical law for the maximal vertical velocity from classical Rayleigh-Bénard experiments is adapted to the specific geometry investigated by using a new definition for the characteristic wavelength. This length is studied and appears to be dependent on the liquid properties. We finally obtain a remarkable agreement between theory and experimental data. PMID:27562830

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

  5. Powder containing 2H-type silicon carbide produced by reacting silicon dioxide and carbon powder in nitrogen atmosphere in the presence of aluminum

    NASA Technical Reports Server (NTRS)

    Kuramoto, N.; Takiguchi, H.

    1984-01-01

    The production of powder which contains silicon carbide consisting of 40% of 2H-type silicon carbide, beta type silicon carbide and less than 3% of nitrogen is discussed. The reaction temperature to produce the powder containing 40% of 2H-type silicon carbide is set at above 1550 degrees C in an atmosphere of aluminum or aluminum compounds and nitrogen gas or an antioxidation atmosphere containing nitrogen gas. The mixture ratio of silicon dioxide and carbon powder is 0.55 - 1:2.0 and the contents of aluminum or aluminum compounds within silicon dioxide is less than 3% in weight.

  6. Role of nitrogen in the downstream etching of silicon nitride

    SciTech Connect

    Blain, M.G.; Meisenheimer, T.L.; Stevens, J.E.

    1996-07-01

    Chemical downstream etching of silicon nitride (Si{sub 3}N{sub 4}) requires the addition of nitrogen to the discharge for obtaining efficient etch rates. A 10{percent} addition of N{sub 2} to a CF{sub 4}/O{sub 2} discharge (CF{sub 4}/O{sub 2} = 1.2, 0.525 Torr) causes a factor of 6 increase in the Si{sub 3}N{sub 4} etch rate and a 8{percent} decrease in the silicon dioxide etch rate. The result is selectivities approaching 9:1. Importantly, the conversion of CF{sub 4} to F and F-containing reactive species by the discharge decreases or remains constant as nitrogen is added to the discharge mix, indicating that the etching reaction is not limited by delivery of these species to the substrate. By measuring the amount of NO and NO{sub 2} in the etch chamber, it is found that the NO concentration increases by a factor of 6 as N{sub 2} is added, while the amount of NO{sub 2} remains small and constant. The NO signal is significantly reduced during nitride etching compared to the signal observed during a discharge with an empty etch chamber, implying that the increase in Si{sub 3}N{sub 4} etch rate is related to the formation of NO in the discharge. This view is consistent with the observation that an NF{sub 3} plasma in a quartz discharge tube results in a nitride etch rate which is a factor of 2 higher than for the same discharge in a sapphire tube. The conclusion is that the oxygen liberated by erosion of the quartz tube allows the formation of NO. That NO is a key Si{sub 3}N{sub 4} etch reactant was confirmed by performing a series of experiments in which N{sub 2}, NO, NO{sub 2}, and N{sub 2}O were injected into the discharge and then downstream in the reaction chamber during a CF{sub 4}/O{sub 2} discharge. Nitride etch rates increased significantly upon injection of NO into both discharge and etch chamber as compared to injection of the other N{sub {ital x}}O{sub {ital y}} species. {copyright} {ital 1996 American Vacuum Society}

  7. Enhanced surface hardness in nitrogen-implanted silicon carbide

    SciTech Connect

    Uslu, C.; Lee, D.H.; Berta, Y.

    1995-06-01

    Preliminary studies have been performed on the feasibility of carbon-silicon nitride formation ({beta}-Si{sub 1.5}C{sub 1.5}N{sub 4}, the homologue of equilibrium {beta}-Si{sub 3}N{sub 4} or hypothetical {beta}-C{sub 3}N{sub 4}) by high dose N{sup +}-implantation into polycrystalline {beta}-SiC (cubic). Thin films were formed using 100 keV implantations with varying ion doses in the range from 1.1 x 10{sup 17} to 27.1 x 10{sup 17} N/cm{sup 2}, and target temperatures between -196{degrees}C and 980{degrees}C. X-ray diffraction with a position-sensitive detector and cross-sectional transmission electron microscopy revealed that the as-implanted surfaces (up to 860{degrees}C) contained {approximately}0.1 {mu}m thick buried amorphous layers. Rutherford backscattering spectroscopy showed that the peak concentration of nitrogen saturated up to approximately 54 at. % with increasing doses, suggesting formation of a new phase. Implantation to doses of 1.1 x 10{sup 17} and 2.3 x 10{sup 17} N/cm{sup 2} at 980{degrees}C caused enhanced surface hardness compared to SiC.

  8. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon

    PubMed Central

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-01-01

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369

  9. Electron trap level of hydrogen incorporated nitrogen vacancies in silicon nitride

    SciTech Connect

    Sonoda, Ken'ichiro Tsukuda, Eiji; Tanizawa, Motoaki; Yamaguchi, Yasuo

    2015-03-14

    Hydrogen incorporation into nitrogen vacancies in silicon nitride and its effects on electron trap level are analyzed using simulation based on density functional theory with temperature- and pressure-dependent hydrogen chemical potential. If the silicon dangling bonds around a nitrogen vacancy are well separated each other, hydrogen incorporation is energetically stable up to 900 °C, which is in agreement with the experimentally observed desorption temperature. On the other hand, if the dangling bonds strongly interact, the incorporation is energetically unfavorable even at room temperature because of steric hindrance. An electron trap level caused by a nitrogen vacancy becomes shallow by the hydrogen incorporation. An electron is trapped in a deep level created by a silicon dangling bond before hydrogen incorporation, whereas it is trapped in a shallow level created by an anti-bonding state of a silicon-silicon bond after hydrogen incorporation. The simulation results qualitatively explain the experiment, in which reduced hydrogen content in silicon nitride shows superior charge retention characteristics.

  10. Ab Initio Identification of the Nitrogen Diffusion Mechanism in SIlicon

    SciTech Connect

    Stoddard, Nathan; Pichler, Peter; Duscher, Gerd J M; Windl, Wolfgang

    2005-01-01

    In this Letter, we present ab initio results identifying a new diffusion path for the nitrogen pair complex in silicon, resulting in an effective diffusivity of 67exp(-2.38 eV/kT) cm{sup 2}/s. This nudged elastic band result is compared with other nitrogen diffusion paths and mechanisms, and is determined to have unmatched agreement with experimental results. It is also shown that careful consideration of total energy corrections and use of a fully temperature-dependent diffusion prefactor have modest but important effects on the calculation of diffusivity for paired and for interstitial nitrogen.

  11. Local bonding environment of plasma deposited nitrogen-rich silicon nitride thin films

    NASA Astrophysics Data System (ADS)

    Soh, Martin T. K.; Savvides, N.; Musca, Charles A.; Martyniuk, Mariusz P.; Faraone, Lorenzo

    2005-05-01

    Plasma deposited nitrogen-rich silicon nitride thin films were prepared at temperatures between 80 and 300 °C. The infrared transmission (400-4000cm-1) was measured, and selected absorption bands were quantified through a multiple Lorentzian oscillator parametric analysis. It is observed that the concentration of silicon-centered tetrahedra bonded together through nitrogen atoms increases monotonically with increasing deposition temperature. A qualitative model is presented to highlight the impact of the active adsorption site density on the degree of stepped (ordered) nucleation at the vapor-film interface. The importance of this growth profile, in particular for micro-systems-technology, is discussed in conjunction with measurements of the biaxial modulus and residual stress of the thin films. A mechanism for residual stress controllability is also presented. The atomic concentrations of silicon, nitrogen, and hydrogen in the thin films were calculated using infrared calibration factors derived from the deposition temperature dependent condensation processes. The results for silicon nitride thin films deposited at 300 °C were observed to be similar in composition to silicon diimide. Additional observations of the infrared transmission characteristics are reported, which include the identification of silazane bridge characteristics for the absorption feature around 610cm-1, which is typically associated with Si-H (bending) absorption.

  12. Segregation and enhanced diffusion of nitrogen in silicon induced by low energy ion bombardment

    SciTech Connect

    Stoddard, N.; Duscher, G.; Karoui, A.; Stevie, F.; Rozgonyi, G.

    2005-04-15

    A sample of nitrogen-doped, single crystal Czochralski silicon was subjected to several different surface preparations. Secondary ion mass spectrometry depth profiling has shown that prolonged glancing-angle bombardment by 3-5 kV Ar{sup +} ions significantly increases the nitrogen concentration in the near surface by up to an order of magnitude over the bulk value. Concentrations are observed to be elevated over the bulk value to a depth up to 25 {mu}m. Nitrogen-implanted samples and samples with a 1 nm surface nitride did not exhibit nitrogen segregation under the same conditions, but a sample with 100 nm of surface nitride did exhibit ion bombardment induced drive-in. In nitride-free samples, the source of the nitrogen is indicated to be a nitrogen-rich layer in the first micron of material. The diffusion behavior of nitrogen in silicon is discussed and the Crowdion mechanism for diffusion is suggested as the enabling mechanism for the enhanced low temperature diffusion.

  13. Se···N chalcogen bond and Se···X halogen bond involving F2C═Se: influence of hybridization, substitution, and cooperativity.

    PubMed

    Guo, Xin; An, Xiulin; Li, Qingzhong

    2015-04-01

    Quantum-chemical calculations have been performed for the chalcogen- and halogen-bonded complexes of F2CSe with a series of nitrogen bases (N2, NCH, NH3, NHCH2, NCLi, and NMe3) and dihalogen molecules (BrCl, ClF, and BrF), respectively. Both types of interactions are mainly driven by the electrostatic and orbital interactions. The chalcogen bond becomes stronger in the order of NCH (sp) < NH3 (sp(3)) < NHCH2 (sp(2)), showing some inconsistence with the electronegativity of the hybridized N atom. The Li and methyl groups have an enhancing effect on the strength of chalcogen bond; however, the former is jointly achieved through the electrostatic and orbital interactions, whereas the orbital interaction has dominant contribution to the latter enhancement. The halogen bond with F2CX (X = O, S, Se) as the electron donor is stronger for the heavier chalcogen atom, exhibiting a reverse dependence on the chalcogen atom with that in hydrogen bonds. The halogen bond is further strengthened by the presence of chalcogen bond in the ternary complexes. In addition, CSD research confirms the abundance of Se···N interaction in crystal materials. PMID:25797149

  14. Chemical modification of a porous silicon surface induced by nitrogen dioxide adsorption.

    PubMed

    Sharov, Constantine S; Konstantinova, Elizaveta A; Osminkina, Lyubov A; Timoshenko, Victor Yu; Kashkarov, Pavel K

    2005-03-17

    The effect of gaseous and liquid nitrogen dioxide on the composition and electronic properties of porous silicon (PS) is investigated by means of optical spectroscopy and electron paramagnetic resonance. It is detected that the interaction process is weak and strong forms of chemisorption on the PS surface, and the process may be regarded as an actual chemical reaction between PS and NO(2). It is found that NO(2) adsorption consists in forming different surface nitrogen-containing molecular groups and dangling bonds of Si atoms (P(b)-centers) as well as in oxidizing and hydrating the PS surface. Also observed are the formation of ionic complexes of P(b)-centers with NO(2) molecules and the generation of free charge carriers (holes) in the volume of silicon nanocrystals forming PS. PMID:16851549

  15. Etch-stop behavior of buried layers formed by substoichiometric nitrogen ion implantation into silicon

    SciTech Connect

    Perez-Rodriguez, A.; Romano-Rodriguez, A.; Morante, J.R.; Acero, M.C. Esteve, J.; Montserrat, J.; El-Hassani, A.

    1996-03-01

    In this work the etch-stop behavior of buried layers formed by substoichiometric nitrogen ion implantation into silicon is studied as a function of the processing parameters, the implantation dose and temperature, and the presence of capping layers during implantation. Etching characteristics have been probed using tetramethylammonium hydroxide or KOH solutions for different times up to 6 h. Results show that, after annealing, the minimum dose required for the formation of an efficient etch-stop layer is about 4 {times} 10{sup 17} cm{sup {minus}2}, for an implantation energy of 75 keV. This is defined as a layer with an efficient etch selectivity in relation to Si of s {ge} 100. For larger implantation doses efficient etch selectivities larger than 100 are obtained. However, for these doses a considerable density of pits is observed in the etch-stop layer. These are related to the presence of nitrogen poor Si regions in the buried layer after annealing, due to a partial separation of silicon and silicon nitride phases during the annealing process. The influence of this separation of phases as well as nitrogen gettering in the buried layer on the etch-stop behavior is discussed as a function of the processing parameters.

  16. Annealing effect on thermodynamic and physical properties of mesoporous silicon: A simulation and nitrogen sorption study

    NASA Astrophysics Data System (ADS)

    Kumar, Pushpendra; Huber, Patrick

    2016-04-01

    Discovery of porous silicon formation in silicon substrate in 1956 while electro-polishing crystalline Si in hydrofluoric acid (HF), has triggered large scale investigations of porous silicon formation and their changes in physical and chemical properties with thermal and chemical treatment. A nitrogen sorption study is used to investigate the effect of thermal annealing on electrochemically etched mesoporous silicon (PS). The PS was thermally annealed from 200˚C to 800˚C for 1 hr in the presence of air. It was shown that the pore diameter and porosity of PS vary with annealing temperature. The experimentally obtained adsorption / desorption isotherms show hysteresis typical for capillary condensation in porous materials. A simulation study based on Saam and Cole model was performed and compared with experimentally observed sorption isotherms to study the physics behind of hysteresis formation. We discuss the shape of the hysteresis loops in the framework of the morphology of the layers. The different behavior of adsorption and desorption of nitrogen in PS with pore diameter was discussed in terms of concave menisci formation inside the pore space, which was shown to related with the induced pressure in varying the pore diameter from 7.2 nm to 3.4 nm.

  17. A Revival of Waste: Atmospheric Pressure Nitrogen Plasma Jet Enhanced Jumbo Silicon/Silicon Carbide Composite in Lithium Ion Batteries.

    PubMed

    Chen, Bing-Hong; Chuang, Shang-I; Liu, Wei-Ren; Duh, Jenq-Gong

    2015-12-30

    In this study, a jumbo silicon/silicon carbide (Si/SiC) composite (JSC), a novel anode material source, was extracted from solar power industry cutting waste and used as a material for lithium-ion batteries (LIBs), instead of manufacturing the nanolized-Si. Unlike previous methods used for preventing volume expansion and solid electrolyte interphase (SEI), the approach proposed here simply entails applying surface modification to JSC-based electrodes by using nitrogen-atmospheric pressure plasma jet (N-APPJ) treatment process. Surface organic bonds were rearranged and N-doped compounds were formed on the electrodes through applying different plasma treatment durations, and the qualitative examinations of before/after plasma treatment were identified by X-ray photoelectron spectroscopy (XPS) and electron probe microanalyzer (EPMA). The surface modification resulted in the enhancement of electrochemical performance with stable capacity retention and high Coulombic efficiency. In addition, depth profile and scanning electron microscope (SEM) images were executed to determine the existence of Li-N matrix and how the nitrogen compounds change the surface conditions of the electrodes. The N-APPJ-induced rapid surface modification is a major breakthrough for processing recycled waste that can serve as anode materials for next-generation high-performance LIBs. PMID:26462014

  18. Highly Strained Heterocycles Constructed from Boron-Boron Multiple Bonds and Heavy Chalcogens.

    PubMed

    Braunschweig, Holger; Constantinidis, Philipp; Dellermann, Theresa; Ewing, William C; Fischer, Ingo; Hess, Merlin; Knight, Fergus R; Rempel, Anna; Schneider, Christoph; Ullrich, Stefan; Vargas, Alfredo; Woollins, J Derek

    2016-04-25

    The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B-B double bond enables reactions with Se(0) and Te(0) . The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions. PMID:27027522

  19. A study of silicon-on-insulator structures formed by heavy-dose nitrogen implantation

    SciTech Connect

    Polchlopek, S.W.

    1991-01-01

    Silicon substrates were implanted with heavy doses of high-energy nitrogen. After implantation, the substrates underwent high-temperature annealing. The resulting substrates were studied in an effort to determine the processing parameters necessary to create the optimum-buried silicon nitride insulating layer. Atomic concentration depth profiles were obtained with the use of Auger Electron Spectroscopy. The van der Pauw technique was used to determine carrier Hall mobility, dopant activation, and sheet resistivity in the top layer. Buried-layer leakage was studied using both electron-beam-induced-current (EBIC) analysis and direct front-to-back current-voltage measurements. Implant parameters studied include dose, temperature, and energy. Annealing conditions studied include time and temperature. Samples implanted with lower doses of nitrogen (dose < 1.4 {times} 10{sup 18} cm{sup {minus}2}) possess very leaky buried layers. Higher-dose implants (dose = 1.4 {times} 10{sup 18} cm{sup {minus}2} or greater) produce substrates with good-quality buried dielectrics. It is discovered that very-high-dose nitrogen implantation is necessary to produce good-quality buried insulators.

  20. Potential energy landscapes of elemental and heterogeneous chalcogen clusters

    SciTech Connect

    Mauro, John C.; Loucks, Roger J.; Balakrishnan, Jitendra; Varshneya, Arun K.

    2006-02-15

    We describe the potential energy landscapes of elemental S{sub 8}, Se{sub 8}, and Te{sub 8} clusters using disconnectivity graphs. Inherent structures include both ring and chain configurations, with rings especially dominant in Se{sub 8}. We also map the potential energy landscapes of heterogeneous Se{sub n}(S,Te){sub 8-n} clusters, which offer insights into the structure of heterogeneous chalcogen glasses.

  1. Regenerable antioxidants-introduction of chalcogen substituents into tocopherols.

    PubMed

    Poon, Jia-Fei; Singh, Vijay P; Yan, Jiajie; Engman, Lars

    2015-02-01

    To improve the radical-trapping capacity of the natural antioxidants, alkylthio-, alkylseleno-, and alkyltelluro groups were introduced into all vacant aromatic positions in β-, γ- and δ-tocopherol. Reaction of the tocopherols with electrophilic chalcogen reagents generated by persulfate oxidation of dialkyl dichalcogenides provided convenient but low-yielding access to many sulfur and selenium derivatives, but failed in the case of tellurium. An approach based on lithiation of the appropriate bromo-tocopherol, insertion of chalcogen into the carbon-lithium bond, air-oxidation to a dichalcogenide, and final borohydride reduction/alkylation turned out to be generally applicable to the synthesis of all chalcogen derivatives. Whereas alkylthio- and alkylseleno analogues were generally poorer quenchers of lipid peroxyl radicals than the corresponding parents, all tellurium compounds showed a substantially improved radical-trapping activity. Introduction of alkyltelluro groups into the tocopherol scaffold also caused a dramatic increase in the regenerability of the antioxidant. In a two-phase lipid peroxidation system containing N-acetylcysteine as a water-soluble co-antioxidant the inhibition time was up to six-fold higher than that recorded for the natural antioxidants. PMID:25504664

  2. Strain profile of (001) silicon implanted with nitrogen by plasma immersion

    SciTech Connect

    Diaz, B.; Abramof, E.; Castro, R. M.; Ueda, M.; Reuther, H.

    2007-05-15

    In this work, we investigate the strain and defect state of silicon implanted with nitrogen by plasma immersion ion implantation, with doses between 4.5x10{sup 16} and 8.7x10{sup 16} cm{sup -2}. For this purpose, we have used Auger electron spectroscopy, x-ray reflectivity, and high-resolution x-ray diffraction. Auger spectra showed that nitrogen concentration profiles broaden and shift deeper into the substrate as the dose increases. High oxygen concentration in the first 20 nm suggested the presence of an amorphous oxide layer at the sample surface, which was confirmed by x-ray reflectivity measurements. Reciprocal space maps revealed a tensile strain perpendicular to the surface, while no in-plane strain was detected. Since no significant diffuse scattering was found, randomly distributed point defects must be predominant in the strained region compared to large displacement field defects such as clusters and dislocations. {omega}/2{theta} scans around (004) Bragg reflection were fitted using dynamical theory of x-ray diffraction. The strain profiles obtained from the best fits correlated well with nitrogen concentration depth profiles, signaling interstitial nitrogen as the main source of strain.

  3. Process for producing organic products containing silicon, hydrogen, nitrogen, and carbon by the direct reaction between elemental silicon and organic amines

    DOEpatents

    Pugar, Eloise A.; Morgan, Peter E. D.

    1990-04-03

    A process is disclosed for producing, at a low temperature, a high purity organic reaction product consisting essentially of silicon, hydrogen, nitrogen, and carbon. The process comprises reacting together a particulate elemental high purity silicon with a high purity reactive amine reactant in a liquid state at a temperature of from about 0.degree. C. up to about 300.degree. C. A high purity silicon carbide/silicon nitride ceramic product can be formed from this intermediate product, if desired, by heating the intermediate product at a temperature of from about 1200.degree.-1700.degree. C. for a period from about 15 minutes up to about 2 hours or the organic reaction product may be employed in other chemical uses.

  4. Process for producing organic products containing silicon, hydrogen, nitrogen, and carbon by the direct reaction between elemental silicon and organic amines and products formed thereby

    DOEpatents

    Pugar, E.A.; Morgan, P.E.D.

    1988-04-04

    A process is disclosed for producing, at a low temperature, a high purity organic reaction product consisting essentially of silicon, hydrogen, nitrogen, and carbon. The process comprises reacting together a particulate elemental high purity silicon with a high purity reactive amine reactant in a liquid state at a temperature of from about O/degree/C up to about 300/degree/C. A high purity silicon carbide/silicon nitride ceramic product can be formed from this intermediate product, if desired, by heating the intermediate product at a temperature of from about 1200-1700/degree/C for a period from about 15 minutes up to about 2 hours or the organic reaction product may be employed in other chemical uses.

  5. Formation of size controlled silicon nanocrystals in nitrogen free silicon dioxide matrix prepared by plasma enhanced chemical vapor deposition

    SciTech Connect

    Laube, J. Gutsch, S.; Hiller, D.; Zacharias, M.; Bruns, M.; Kübel, C.; Weiss, C.

    2014-12-14

    This paper reports the growth of silicon nanocrystals (SiNCs) from SiH4–O{sub 2} plasma chemistry. The formation of an oxynitride was avoided by using O{sub 2} instead of the widely used N{sub 2}O as precursor. X-ray photoelectron spectroscopy is used to prove the absence of nitrogen in the layers and determine the film stoichiometry. It is shown that the Si rich film growth is achieved via non-equilibrium deposition that resembles a interphase clusters mixture model. Photoluminescence and Fourier transformed infrared spectroscopy are used to monitor the formation process of the SiNCs, to reveal that the phase separation is completed at lower temperatures as for SiNCs based on oxynitrides. Additionally, transmission electron microscopy proves that the SiNC sizes are well controllable by superlattice configuration, and as a result, the optical emission band of the Si nanocrystal can be tuned over a wide range.

  6. Surface and morphological features of laser-irradiated silicon under vacuum, nitrogen and ethanol

    NASA Astrophysics Data System (ADS)

    Hayat, Asma; Bashir, Shazia; Akram, Mahreen; Mahmood, Khaliq; Iqbal, Muhammad Hassan

    2015-12-01

    Laser-induced surface and structural modification of silicon (Si) has been investigated under three different environments of vacuum, nitrogen (100 Torr) and ethanol. The interaction of 1000 pulses of KrF (λ ≈ 248 nm, τ ≈ 18 ns, repetition rate ≈ 30 Hz) Excimer laser at two different fluences of 2.8 J/cm2 and 4 J/cm2 resulted in formation of various kinds of features such as laser induced periodic surface structures (LIPSS), spikes, columns, cones and cracks. Surface morphology has been observed by Scanning Electron Microscope (SEM). Whereas, structural modification of irradiated targets is explored by Raman spectroscopy. SEM analysis exhibits a non-uniform distribution of micro-scale pillars and spikes at the central ablated regime of silicon irradiated at low laser fluence of 2.8 J/cm2 under vacuum. Whereas cones, pits, cavities and ripples like features are seen at the boundaries. At higher fluence of 4 J/cm2, laser induced periodic structures as well as micro-columns are observed. In the case of ablation in nitrogen environment, melting, splashing, self-organized granular structures and cracks along with redeposition are observed at lower fluence. Such types of small scaled structures in nitrogen are attributed to confinement and shielding effects of nitrogen plasma. Whereas, a crater with multiple ablative layers is formed in the case of ablation at higher fluence. Significantly different surface morphology of Si is observed in the case of ablation in ethanol. It reveals the formation of cavities along with small scale pores and less redeposition. These results reveal that the growth of surface and morphological features of irradiated Si are strongly dependent upon the laser fluence as well as environmental conditions. The difference in surface morphology is attributable to cooling, confinement and shielding effects as well as difference in plasma temperature, density and pressure of environmental media that corresponds to different energy deposition

  7. Silicon carbide nanocones: Computational analysis of chemical shieldings for pristine and boron/nitrogen decorated models

    NASA Astrophysics Data System (ADS)

    Mirzaei, Mahmoud

    2012-09-01

    Density functional theory (DFT) calculations were performed to investigate the electronic and structural properties of pristine and boron/nitrogen (B/N) decorated models of a representative silicon carbide nanocone (SiCNC). The atoms of apexes and tips were differently decorated by B/N atoms to make all possible decorations of the investigated SiCNC. The evaluated parameters by the optimization processes and nuclear magnetic resonance (NMR) calculations indicated that the overall and atomic scale properties of the investigated SiCNCs are significantly dependent on the ways of decorations of Si/C atoms by B/N atoms. The Si/C atoms close to the decorated regions also exhibited notable changes in comparison to the pristine model.

  8. Nano-Scale Analysis of Precipitates in Nitrogen-Doped Czochralski SIlicon

    SciTech Connect

    Rozgonyi, G. A.; Karoui, A.; Kvit, A.; Duscher, Gerd J M

    2003-01-01

    Nitrogen-doped Czochralski (CZ) silicon wafers were heat treated with Lo-Hi annealing in argon. Nanoscale defects were then examined by high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in the Z-contrast mode, and electron energy loss spectroscopy (EELS) analyses using a field emission JEOL 2010 with a resolution below 2 {angstrom}. The structures of precipitates, stacking faults and interstitial aggregates were found to depend on their location relative to the wafer surface. Precipitate composition, strain at the interface and interface roughness were obtained and are discussed in connection with the point defects generated during crystal growth and modified during wafer annealing. An excellent correlation was found between Z-contrast line scans across the precipitates and the N to O concentration ratio determined with EELS. In the precipitate central region that ratio is between 1 and 6%, whereas at precipitate boundaries it reaches 17%.

  9. Thermal Stability of Hi-Nicalon SiC Fiber in Nitrogen and Silicon Environments

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Garg, A.

    1995-01-01

    The room temperature tensile strength of uncoated and two types of pyrolytic boron nitride coated (PBN and Si-rich PBN) Hi-Nicalon SiC fibers was determined after 1 to 400 hr heat treatments to 1800 C under N2 pressures of 0.1, 2, and 4 MPa, and under 0.1 Mpa argon and vacuum environments. In addition, strength stability of both uncoated and coated fibers embedded in silicon powder and exposed to 0.1 MPa N2 for 24 hrs at temperatures to 1400 C was investigated. The uncoated and both types of BN coated fibers exposed to N2 for 1 hr showed noticeable strength degradation above 1400 C and 1600 C, respectively. The strength degradation appeared independent of nitrogen pressure, time of heat treatment, and surface coatings. TEM microstructural analysis suggests that flaws created due to SiC grain growth are responsible for the strength degradation. In contact with silicon powder, the uncoated and both types of PBN coated fibers degrade rapidly above 1350 C.

  10. 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.

  11. Organometallic chemical vapor deposition of silicon nitride films enhanced by atomic nitrogen generated from surface-wave plasma

    SciTech Connect

    Okada, H.; Kato, M.; Ishimaru, T.; Sekiguchi, H.; Wakahara, A.; Furukawa, M.

    2014-02-20

    Organometallic chemical vapor deposition of silicon nitride films enhanced by atomic nitrogen generated from surface-wave plasma is investigated. Feasibility of precursors of triethylsilane (TES) and bis(dimethylamino)dimethylsilane (BDMADMS) is discussed based on a calculation of bond energies by computer simulation. Refractive indices of 1.81 and 1.71 are obtained for deposited films with TES and BDMADMS, respectively. X-ray photoelectron spectroscopy (XPS) analysis of the deposited film revealed that TES-based film coincides with the stoichiometric thermal silicon nitride.

  12. Oxidation Properties of Nitrogen-Doped Silicon Films Deposited from Si2H6 and NH3

    NASA Astrophysics Data System (ADS)

    Scheid, Emmanuel; Boyer, Pierre; Samitier, Josep; Hassani, Ahmed

    1994-03-01

    Si2H6/NH3 gas mixture was employed to obtain, by low-pressure chemical vapor deposition (LPCVD) at low temperature, nitrogen-doped silicon (NIDOS) films with various N/Si ratios. Thermal oxide was grown in dry oxygen at 900°C and 1100°C on NIDOS films. The result indicates that the nitrogen content of NIDOS films, assessed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), greatly influences their oxidation rate.

  13. Supramolecular macrocycles reversibly assembled by Te…O chalcogen bonding

    PubMed Central

    Ho, Peter C.; Szydlowski, Patrick; Sinclair, Jocelyn; Elder, Philip J. W.; Kübel, Joachim; Gendy, Chris; Lee, Lucia Myongwon; Jenkins, Hilary; Britten, James F.; Morim, Derek R.; Vargas-Baca, Ignacio

    2016-01-01

    Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te…O–N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal. PMID:27090355

  14. A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond

    SciTech Connect

    Zhang, Xianping.

    1990-09-21

    The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

  15. Nanoindentation of plasma-deposited nitrogen-rich silicon nitride thin films

    NASA Astrophysics Data System (ADS)

    Soh, Martin T. K.; Fischer-Cripps, A. C.; Savvides, N.; Musca, C. A.; Faraone, L.

    2006-07-01

    Nanoindentation was performed on plasma-deposited nitrogen-rich silicon nitride thin films deposited on various substrates between 150 and 300°C. A very simple and effective depth-profiling method is introduced, which involves indentation of thin films deposited on substrates with different mechanical properties. The primary advantage of this method is that it avoids the complications associated with many of the complex mathematical models available to deconvolve thin film mechanical properties, while nevertheless allowing the user to visually identify thin film properties. This method is demonstrated on our thin films, which have a hardness between 14 and 21GPa, and reduced modulus between 120 and 160GPa. The initial rise in hardness at low contact depths, commonly attributed to an indentation-size effect, is shown to be due to elastic contact between the indenter and thin film surface. This demonstrates the perils of blindly following the 10% rule for hardness calculation. The contribution of elastic and plastic deformations from nanoindentation is used to clarify the physical meaning of hardness and reduced modulus.

  16. Study of stress in tensile nitrogen-plasma-treated multilayer silicon nitride films

    SciTech Connect

    Morin, Pierre; Raymond, Gaetan; Benoit, Daniel; Guiheux, Denis; Pantel, Roland; Volpi, Fabien; Braccini, Muriel

    2011-07-15

    The authors conducted a physico-chemical analysis of tensile sequential-nitrogen-plasma-treated silicon nitride films, which function as stressor liners in complementary metal oxide semiconductor (CMOS) technologies. These films are made of stacked nanometer-thick, plasma-enhanced, chemical vapor-deposited layers which were individually treated with N{sub 2}-plasma, to increase stress. This study allowed us to monitor the evolution of the films' chemical composition and stress as a function of process parameters such as deposition and post-N{sub 2}-plasma duration. Consistent with secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM) and other physico-chemical analysis results, it was shown that the elementary component of the films can be modeled with a bi-layer consisting of an untreated slice at the bottom that is covered by a more tensile post-treated film. In addition, we observed that longer plasma treatments increase residual stress, SiN bond concentration and layer density, while reducing hydrogen content. The stress increase induced by the plasma treatment was shown to correlate with the increase in SiN bonds following a percolation mechanism that is linked to hydrogen dissociation. Kinetics laws describing both SiN bond generation and stress increase are proposed and it is demonstrated that stress increase follows first-order kinetics.

  17. Characterization of nitrogen-rich silicon nitride films grown by the electron cyclotron resonance plasma technique

    NASA Astrophysics Data System (ADS)

    Wang, L.; Reehal, H. S.; Martínez, F. L.; San Andrés, E.; del Prado, A.

    2003-07-01

    Amorphous hydrogenated silicon nitride films have been deposited by the electron cyclotron resonance plasma technique, using N2 and SiH4 as precursor gases. The gas flow ratio, deposition temperature and microwave power have been varied in order to study their effect on the properties of the films, which were characterized by Rutherford back-scattering spectrometry, elastic recoil detection analysis (ERDA), Fourier transform infrared spectroscopy and ellipsometry. All samples show N/Si ratios near or above the stoichiometric value (N/Si = 1.33). The hydrogen content determined from ERDA measurements is significantly higher than the amount detected by infrared spectroscopy, evidencing the presence of non-bonded H. As the N2/SiH4 gas flow ratio is increased (by decreasing the SiH4 partial pressure), the Si content decreases and the N-H concentration increases, while the N content remains constant, resulting in an increase of the N/Si ratio. The decrease of the Si content causes a decrease of the refractive index and the density of the film, while the growth ratio also decreases due to the limiting factor of the SiH4 partial pressure. The infrared Si-N stretching band shifts to higher wavenumbers as the N-H concentration increases. The increase of deposition temperature promotes the release of H, resulting in a higher incorporation of N and Si into the film and a decrease of the N/Si ratio. The effect of increasing the microwave power is analogous to increasing the N2/SiH4 ratio, due to the increase in the proportion of nitrogen activated species.

  18. Behavior of incorporated nitrogen in plasma-nitrided silicon oxide formed by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Shinoda, Nao; Itokawa, Hiroshi; Fujitsuka, Ryota; Sekine, Katsuyuki; Onoue, Seiji; Tonotani, Junichi

    2016-04-01

    The behavior of nitrogen (N) atoms in plasma-nitrided silicon oxide (SiO2) formed by chemical vapor deposition (CVD) was characterized by physical analysis and from electrical properties. The changes in the chemical bonding and distribution of N in plasma-nitrided SiO2 were investigated for different subsequent processes. N-Si3, N-Si2O, and N2 are formed in a SiO2 film by plasma nitridation. N2 molecules diffuse out during annealing at temperatures higher than 900 °C. NH species are generated from N2 molecules and H in the SiO2 film with subsequent oxide deposition using O3 as an oxidant. The capacitance-voltage (C-V) curves of metal-oxide-semiconductor (MOS) capacitors are obtained. The negative shift of the C-V curve is caused by the increase in the density of positive fix charge traps in CVD-SiO2 induced by plasma nitridation. The C-V curve of plasma-nitrided SiO2 subjected to annealing shifts to the positive direction and that subjected to the subsequent oxide deposition shifts markedly to the negative direction. It is clarified that the density of positive charge fixed traps in plasma-nitrided SiO2 films decrease because the amount of N2 molecules is decreased by annealing, and that the density of traps increases because NH species are generated and move to the interface between SiO2 and the Si substrate with the subsequent oxide deposition.

  19. Chalcogen-Based Aerogels as Sorbents for Radionuclide Remediation

    SciTech Connect

    Riley, Brian J.; Chun, Jaehun; Um, Wooyong; Lepry, William C.; Matyas, Josef; Olszta, Matthew J.; Li, Xiaohong; Polychronopoulou, Kyriaki; Kanatzidis, Mercouri G.

    2013-06-13

    The efficient capture of radionuclides having long half-lives such as technetium-99 (99Tc), uranium-238 (238U), and iodine-129 (129I) is pivotal to prevent their transport into groundwater and/or release into the atmosphere. While different sorbents have been considered for capturing each of them, in the current work, a new nanostructured chalcogen-based aerogel, called a chalcogel, is shown to be very effective to capture ionic forms of 99Tc and 238U, as well as nonradioactive gaseous iodine (i.e., a surrogate for 129I), irrespective of the sorbent polarity. Some of the chalcogels performed better than others but the PtGeS sorbent performed the best with capture efficiencies of 98% and 99.4% for 99Tc and 238U, respectively. All sorbents showed >99% capture efficiency for iodine over the test duration. This unified sorbent would be an attractive option in environmental remediation for various radionuclides associated with legacy wastes from nuclear weapons production, wastes from nuclear power production, or potential future nuclear fuel reprocessing.

  20. Complex Boron Redistribution in P+ Doped-polysilicon / Nitrogen Doped Silicon Bi-layers during Activation Annealing

    NASA Astrophysics Data System (ADS)

    Abadli, S.; Mansour, F.; Perrera, E. Bedel

    We have investigated and modeled the complex phenomenon of boron (B) redistribution process in strongly doped silicon bilayers structure. A one-dimensional two stream transfer model well adapted to the particular structure of bi- layers and to the effects of strong-concentrations has been developed. This model takes into account the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi-layers have been obtained by low pressure chemical vapor deposition (LPCVD) method, using in-situ nitrogen- doped-silicon (NiDoS) layer and strongly B doped polycrystalline-silicon (P+) layer. To avoid long redistributions, thermal annealing was carried out at relatively lowtemperatures (600 °C and 700 °C) for various times ranging between 30 minutes and 2 hours. The good adjustment of the simulated profiles with the experimental secondary ion mass spectroscopy (SIMS) profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles-shoulders kinetics.

  1. Low resistance Ohmic contact to p-type crystalline silicon via nitrogen-doped copper oxide films

    NASA Astrophysics Data System (ADS)

    Zhang, Xinyu; Wan, Yimao; Bullock, James; Allen, Thomas; Cuevas, Andres

    2016-08-01

    This work explores the application of transparent nitrogen doped copper oxide (CuOx:N) films deposited by reactive sputtering to create hole-selective contacts for p-type crystalline silicon (c-Si) solar cells. It is found that CuOx:N sputtered directly onto crystalline silicon is able to form an Ohmic contact. X-ray photoelectron spectroscopy and Raman spectroscopy measurements are used to characterise the structural and physical properties of the CuOx:N films. Both the oxygen flow rate and the substrate temperature during deposition have a significant impact on the film composition, as well as on the resulting contact resistivity. After optimization, a low contact resistivity of ˜10 mΩ cm2 has been established. This result offers significant advantages over conventional contact structures in terms of carrier transport and device fabrication.

  2. Chalcogen-based aerogels as sorbents for radionuclide remediation.

    PubMed

    Riley, Brian J; Chun, Jaehun; Um, Wooyong; Lepry, William C; Matyas, Josef; Olszta, Matthew J; Li, Xiaohong; Polychronopoulou, Kyriaki; Kanatzidis, Mercouri G

    2013-07-01

    The efficient capture of radionuclides with long half-lives such as technetium-99 ((99)Tc), uranium-238 ((238)U), and iodine-129 ((129)I) is pivotal to prevent their transport into groundwater and/or release into the atmosphere. While different sorbents have been considered for capturing each of them, in the current work, nanostructured chalcogen-based aerogels called chalcogels are shown to be very effective at capturing ionic forms of (99)Tc and (238)U, as well as nonradioactive gaseous iodine (i.e., a surrogate for (129)I2), irrespective of the sorbent polarity. The chalcogel chemistries studied were Co0.7Bi0.3MoS4, Co0.7Cr0.3MoS4, Co0.5Ni0.5MoS4, PtGe2S5, and Sn2S3. The PtGe2S5 sorbent performed the best overall with capture efficiencies of 98.0% and 99.4% for (99)Tc and (238)U, respectively, and >99.0% for I2(g) over the duration of the experiment. The capture efficiencies for (99)Tc and (238)U varied between the different sorbents, ranging from 57.3-98.0% and 68.1-99.4%, respectively. All chalcogels showed >99.0% capture efficiency for iodine over the test duration. This versatile nature of chalcogels can provide an attractive option for the environmental remediation of the radionuclides associated with legacy wastes from nuclear weapons production as well as wastes generated during nuclear power production or nuclear fuel reprocessing. PMID:23763706

  3. Chalcogen- and halogen-bonds involving SX2 (X = F, Cl, and Br) with formaldehyde.

    PubMed

    Mo, Lixin; Zeng, Yanli; Li, Xiaoyan; Zhang, Xueying; Meng, Lingpeng

    2016-07-01

    The capacity of SX2 (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl2 (SBr2) has two σ-holes upon extension of Cl (Br)-S bonds, and two σ-holes upon extension of S-Cl (Br) bonds. SF2 contains only two σ-holes upon extension of the F-S bond. Consequently, SCl2 and SBr2 form chalcogen and halogen bonds with the electron donor H2CO while SF2 forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF2:H2CO complex. The S···O chalcogen bond between SF2 and H2CO is the strongest, while the strongest halogen bond is Br···O between SBr2 and H2CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X2S···H2CO···SX'2 (X = F, Cl, Br, and X' = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds. Graphical Abstract Molecular electrostatic potential and contour map of the Laplacian of the electron density in Cl2S···H2CO···SCl2 complex. PMID:27342252

  4. Influences of nitrogen, phosphorus and silicon addition on plant productivity and species richness in an alpine meadow

    PubMed Central

    Xu, Danghui; Fang, Xiangwen; Zhang, Renyi; Gao, Tianpeng; Bu, Haiyan; Du, Guozhen

    2015-01-01

    Fertilization, especially with nitrogen (N), increases aboveground primary productivity (APP), but reduces plant species richness at some level. Silicon (Si) fertilization alone, or with addition of N or phosphorus (P), has multiple direct and indirect beneficial effects on plant growth and development, both for individuals and the whole community. This study aimed to examine the effects of Si, N, P, NSi and PSi combinations on APP and species richness of the community and of four functional groups in an alpine meadow. The results showed that plots fertilized with Si in combination with either N or P had higher APP than when fertilized with N or P alone. Addition of N or P increased APP, and the higher APP occurred when the highest level of N was added, indicating co-limitation of N and P, with N being most limiting. Silicon fertilization alone or with addition of N increased the APP of grasses and forbs. Nitrogen addition decreased the community species richness; Si with addition of N alleviated the loss of species richness of the whole community and the forbs group. For the four functional groups, N or P addition increased the species richness of grasses and decreased that of forbs. Our findings highlight the importance of Si in improving APP and alleviating N fertilization-induced biodiversity loss in grasslands, and will help improve our ability to predict community composition and biomass dynamics in alpine meadow ecosystems subject to changing nutrient availability. PMID:26574603

  5. Influences of nitrogen, phosphorus and silicon addition on plant productivity and species richness in an alpine meadow.

    PubMed

    Xu, Danghui; Fang, Xiangwen; Zhang, Renyi; Gao, Tianpeng; Bu, Haiyan; Du, Guozhen

    2015-01-01

    Fertilization, especially with nitrogen (N), increases aboveground primary productivity (APP), but reduces plant species richness at some level. Silicon (Si) fertilization alone, or with addition of N or phosphorus (P), has multiple direct and indirect beneficial effects on plant growth and development, both for individuals and the whole community. This study aimed to examine the effects of Si, N, P, NSi and PSi combinations on APP and species richness of the community and of four functional groups in an alpine meadow. The results showed that plots fertilized with Si in combination with either N or P had higher APP than when fertilized with N or P alone. Addition of N or P increased APP, and the higher APP occurred when the highest level of N was added, indicating co-limitation of N and P, with N being most limiting. Silicon fertilization alone or with addition of N increased the APP of grasses and forbs. Nitrogen addition decreased the community species richness; Si with addition of N alleviated the loss of species richness of the whole community and the forbs group. For the four functional groups, N or P addition increased the species richness of grasses and decreased that of forbs. Our findings highlight the importance of Si in improving APP and alleviating N fertilization-induced biodiversity loss in grasslands, and will help improve our ability to predict community composition and biomass dynamics in alpine meadow ecosystems subject to changing nutrient availability. PMID:26574603

  6. Nitrogen

    USGS Publications Warehouse

    Kramer, D.A.

    2006-01-01

    In 2005, ammonia was produced by 15 companies at 26 plants in 16 states in the United States. Of the total ammonia production capacity, 55% was centered in Louisiana, Oklahoma and Texas because of their large reserves of natural gas. US producers operated at 66% of their rated capacity. In descending order, Koch Nitrogen, Terra Industries, CF Industries, Agrium and PCS Nitrogen accounted for 81% of the US ammonia production capacity.

  7. 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.

  8. Nitrogen

    USGS Publications Warehouse

    Kramer, D.A.

    2004-01-01

    Ammonia is the principal source of fixed nitrogen. It was produced by 17 companies at 34 plants in the United States during 2003. Fifty-three percent of U.S. ammonia production capacity was centered in Louisiana, Oklahoma and Texas because of their large reserves of natural gas, the dominant domestic feedstock.

  9. Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters.

    PubMed

    Kremer, Adrian; Aurisicchio, Claudia; De Leo, Federica; Ventura, Barbara; Wouters, Johan; Armaroli, Nicola; Barbieri, Andrea; Bonifazi, Davide

    2015-10-19

    The synthesis, X-ray crystal structures, ground- and excited-state UV/Vis absorption spectra, and luminescence properties of chalcogen-doped organic emitters equipped on both extremities with benzoxa-, benzothia-, benzoselena- and benzotellurazole (1X and 2X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal-structure analyses provide evidence of similar packing for 2O -2Se , in which the benzoazoles are engaged in π-π stacking and, for the heavier atoms, in secondary X⋅⋅⋅X and X⋅⋅⋅N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium-doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters. PMID:26471446

  10. Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy

    PubMed Central

    Zhou, Shengqiang; Liu, Fang; Prucnal, S.; Gao, Kun; Khalid, M.; Baehtz, C.; Posselt, M.; Skorupa, W.; Helm, M.

    2015-01-01

    Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ~ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability. PMID:25660096

  11. Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy.

    PubMed

    Zhou, Shengqiang; Liu, Fang; Prucnal, S; Gao, Kun; Khalid, M; Baehtz, C; Posselt, M; Skorupa, W; Helm, M

    2015-01-01

    Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ~ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability. PMID:25660096

  12. 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.

  13. STEM EDX Nitrogen Mapping of Nanoinclusions in Milky Diamonds from Juina, Brazil, Using a Windowless Silicon Drift Detector System.

    PubMed

    Rudloff-Grund, J; Brenker, F E; Marquardt, K; Kaminsky, F V; Schreiber, A

    2016-06-01

    Energy-dispersive X-ray spectroscopy (EDX) performed using scanning transmission electron microscopy (STEM) in combination with a windowless detector setup allows high-resolution imaging and chemical composition mapping even of light elements present in low concentrations. The used TEM-system combines a field emission electron source with four silicon drift detectors allowing for high detection sensitivity. We used this enhanced system to investigate 20 to 200 nm sized inclusions in milky diamonds from Rio Soriso, Juina area, Brazil. The diamonds act as a chemical inert container and therefore protect their inclusions from further chemical reactions with their surroundings. We visualize the presence and distribution of nitrogen within focused ion beam (FIB) slices containing these nanoinclusions. The investigation of these specific diamonds may open a new window to deeper parts of the Earth (>660 km) as they represent pristine material of this deep mantle environment. PMID:27128863

  14. Nitrogen

    USGS Publications Warehouse

    Kramer, D.A.

    2007-01-01

    Ammonia was produced by 15 companies at 25 plants in 16 states in the United States during 2006. Fifty-seven percent of U.S. ammonia production capacity was centered in Louisiana, Oklahoma and Texas because of their large reserves of natural gas, the dominant domestic feedstock. In 2006, U.S. producers operated at about 72 percent of their rated capacity (excluding plants that were idle for the entire year). Five companies, Koch Nitrogen, Terra Industries, CF Industries, PCS Nitro-gen, and Agrium, in descending order, accounted for 79 percent U.S. ammonia production capacity. The United States was the world's fourth-ranked ammonia producer and consumer following China, India and Russia. Urea, ammonium nitrate, ammonium phosphates, nitric acid and ammonium sulfate were the major derivatives of ammonia in the United States, in descending order of importance.

  15. Synthesizing photovoltaic thin films of high quality copper-zinc-tin alloy with at least one chalcogen species

    DOEpatents

    Teeter, Glenn; Du, Hui; Young, Matthew

    2013-08-06

    A method for synthesizing a thin film of copper, zinc, tin, and a chalcogen species ("CZTCh" or "CZTSS") with well-controlled properties. The method includes depositing a thin film of precursor materials, e.g., approximately stoichiometric amounts of copper (Cu), zinc (Zn), tin (Sn), and a chalcogen species (Ch). The method then involves re-crystallizing and grain growth at higher temperatures, e.g., between about 725 and 925 degrees K, and annealing the precursor film at relatively lower temperatures, e.g., between 600 and 650 degrees K. The processing of the precursor film takes place in the presence of a quasi-equilibrium vapor, e.g., Sn and chalcogen species. The quasi-equilibrium vapor is used to maintain the precursor film in a quasi-equilibrium condition to reduce and even prevent decomposition of the CZTCh and is provided at a rate to balance desorption fluxes of Sn and chalcogens.

  16. Effects of nitrogen impurities on the microstructure and electronic properties of P-doped Si nanocrystals emebedded in silicon-rich SiNx films

    NASA Astrophysics Data System (ADS)

    Ma, Deng-Hao; Zhang, Wei-Jia; Luo, Rui-Ying; Jiang, Zhao-Yi; Ma, Qiang; Ma, Xiao-Bo; Fan, Zhi-Qiang; Song, Deng-Yuan; Zhang, Lei

    2016-05-01

    Phosphorus doped Si nanocrystals (SNCs) emebedded in silicon-rich SiNx:H films were prepared using plasma enhanced chemical vapor deposition technique, and the effects of nitrogen incorporation on the microstructure and electronic properties of the thin films have been systematically studied. Transmission electron microscope and Raman observation revealed that nitrogen incorporation prevents the growth of Si nanocrystals, and that their sizes can be adjusted by varying the flow rate of NH3. The reduction of photoluminescence (PL) intensity in the range of 2.1-2.6 eV of photon energy was observed with increasing nitrogen impurity, and a maximal PL intensity in the range 1.6-2.0 eV was obtained when the incorporation flow ratio NH3/(SiH4+H2+PH3) was 0.02. The conductivity of the films is improved by means of proper nitrogen impurity doping, and proper doping causes the interface charge density of the heterojunction (H-J) device to be lower than the nc-Si:H/c-Si H-J device. As a result, the proper incorporation of nitrogen could not only reduce the silicon banding bond density, but also fill some carrier capture centers, and suppress the nonradiative recombination of electrons.

  17. On the ultrafast charge migration dynamics in isolated ionized halogen, chalcogen, pnicogen, and tetrel bonded clusters

    NASA Astrophysics Data System (ADS)

    Chandra, Sankhabrata; Rana, Bhaskar; Periyasamy, Ganga; Bhattacharya, Atanu

    2016-06-01

    Here we demonstrate, compare and contrast relaxation- and correlation-driven charge migration dynamics in halogen, chalcogen, pnicogen and tetrel bonded clusters, following their vertical ionization. For this work, we have selected different isolated A-X:NH3 clusters, where A represents F, Cl, CN and NH2 substituents and X features Cl, SH, PH2 and SiH3 to exhibit specific noncovalent bonding interaction. The charge migration dynamics in these clusters is studied using the density functional theory (DFT) with the wB97XD functional and the 6-31+G(d,p) basis set. Approximately 400-600 attosecond time scale is predicted for charge migration in (1:1) AX:NH3 complexes. Effects of basis set and intermolecular distance on the ultrafast charge migration dynamics through the halogen, chalcogen, pnicogen, and tetrel bonded clusters are also discussed. This is the first report on pure relaxation- and correlation-driven charge migration dynamics in chalcogen, pnicogen and tetrel bonded clusters.

  18. Application of INEPT nitrogen-15 and silicon-29 nuclear magnetic resonance spectrometry to derivatized fulvic acids

    USGS Publications Warehouse

    Thorn, K.A.; Folan, D.W.; Arterburn, J.B.; Mikita, M.A.; MacCarthy, P.

    1989-01-01

    Use of the INEPT experiment has been examined in two derivatization studies of the Suwannee River fulvic acid. In the first study, the fulvic acid was derivatized with 15N enriched hydroxylamine. The quantitative 15N NMR spectrum, acquired with a 45° pulse angle, 2.0 second pulse delay and inverse gated decoupling, showed that oximes (390-340 ppm) were the major derivatives, followed by nitriles (270-240 ppm), hydroxamic acids (170-160 ppm), secondary amides (150-115 ppm), and lactams (115-90 ppm). The INEPT 15N NMR spectrum was acquired using refocussing delays and polarization transfer times optimized for signal enhancement of singly protonated nitrogens. INEPT greatly enhanced the amide and lactam resonances, and showed that resonances downfield of 180 ppm in the quantitative spectrum represented nonprotonated nitrogens. In the second study, the fulvic acid was first methylated with diazomethane and then silylated with hexamethyldisilazane. The 29Si NMR spectra exhibited two major peaks, from approximately 33 to 22 ppm, representing silyl esters of carboxylic acids, and from 22 to 13 ppm, representing silyl ethers of alcohols and phenols. The INEPT 29Si NMR spectrum was virtually identical to the quantitative 29Si spectrum, acquired with a 90° pulse angle, 5.0 second pulse delay, inverse gated decoupling, and relaxation reagent. INEPT therefore can be used for quantitative analysis of trimethylsilyl derivatives of the fulvic acid, saving spectrometer time and eliminating the need for relaxation reagents.

  19. Atmospheric Pressure Plasma CVD of Amorphous Hydrogenated Silicon Carbonitride (a-SiCN:H) Films Using Triethylsilane and Nitrogen

    SciTech Connect

    Srinivasan Guruvenket; Steven Andrie; Mark Simon; Kyle W. Johnson; Robert A. Sailer

    2011-10-04

    Amorphous hydrogenated silicon carbonitride (a-SiCN:H) thin films are synthesized by atmospheric pressure plasma enhanced chemical vapor (AP-PECVD) deposition using the Surfx Atomflow{trademark} 250D APPJ source with triethylsilane (HSiEt{sub 3}, TES) and nitrogen as the precursor and the reactive gases, respectively. The effect of the substrate temperature (T{sub s}) on the growth characteristics and the properties of a-SiCN:H films was evaluated. The properties of the films were investigated via scanning electron microscopy (SEM), atomic force microscopy (AFM) for surface morphological analyses, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) for chemical and compositional analyses; spectroscopic ellipsometry for optical properties and thickness determination and nanoindentation to determine the mechanical properties of the a-SiCN:H films. Films deposited at low T{sub s} depict organic like features, while the films deposited at high T{sub s} depict ceramic like features. FTIR and XPS studies reveal that an increases in T{sub s} helps in the elimination of organic moieties and incorporation of nitrogen in the film. Films deposited at T{sub s} of 425 C have an index of refraction (n) of 1.84 and hardness (H) of 14.8 GPa. A decrease in the deposition rate between T{sub s} of 25 and 250 C and increase in deposition rate between T{sub s} of 250 and 425 C indicate that the growth of a-SiCN:H films at lower T{sub s} are surface reaction controlled, while at high temperatures film growth is mass-transport controlled. Based on the experimental results, a potential route for film growth is proposed.

  20. Molecular dynamics simulations of shallow nitrogen and silicon implantation into diamond

    NASA Astrophysics Data System (ADS)

    Lehtinen, Ossi; Naydenov, Boris; Börner, Pia; Melentjevic, Kristina; Müller, Christoph; McGuinness, Liam Paul; Pezzagna, Sebastien; Meijer, Jan; Kaiser, Ute; Jelezko, Fedor

    2016-01-01

    A solid understanding of the implantation process of N and Si ions into diamond is needed for the controlled creation of shallow color centers for quantum computing, simulation, and sensing applications. Here, molecular dynamics simulations of the shallow implantation of N and Si ions into diamond is simulated at 100-5000 eV kinetic energies and different angles of incidence. We find that ion channeling is an important effect with an onset energy depending on the crystal orientation. Consequently, the molecular dynamics simulations produce improved predictions as compared to standard Monte Carlo simulations. When implanting in a channeling direction, the spatial distribution of the channeled ions becomes markedly narrow, allowing a higher degree of control over the location of the nitrogen vacancy (NV-) centers. A contamination layer on the ion entry surface reduces the fraction of channeled ions. A comparison to an experimentally determined depth profile based on a NMR signal from protons yields a quantitative agreement, validating the simulation approach.

  1. Phase stability and lattice thermal conductivity reduction in CoSb3 skutterudites, doped with chalcogen atoms

    NASA Astrophysics Data System (ADS)

    Battabyal, M.; Priyadarshini, B.; Pradipkanti, L.; Satapathy, Dillip K.; Gopalan, R.

    2016-07-01

    We report a significant reduction in the lattice thermal conductivity of the CoSb3 skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb3 skutterudite samples (Te0.1Co4Sb12, Se0.1Co4Sb12, Te0.05Se0.05Co4Sb12) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb3 skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773 K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb3 skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb3 skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb3 skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ˜ 0.9 W/mK at 773 K is achieved in Te0.1Co4Sb12 skutterudites, which is the lowest value reported so far in CoSb3 skutterudites, doped with single Te chalcogen atom.

  2. Proton induced gamma-ray production cross sections and thick-target yields for boron, nitrogen and silicon

    NASA Astrophysics Data System (ADS)

    Marchand, Benoît; Mizohata, Kenichiro; Räisänen, Jyrki

    2016-07-01

    The excitation functions for the reactions 14N(p,p‧γ)14N, 28Si(p,p‧γ)28Si and 29Si(p,p‧γ)29Si were measured at an angle of 55° by bombarding a thin Si3N4 target with protons in the energy range of 3.6-6.9 MeV. The deduced γ-ray production cross section data is compared with available literature data relevant for ion beam analytical work. Thick-target γ-ray yields for boron, nitrogen and silicon were measured at 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5 MeV proton energies utilizing thick BN and Si3N4 targets. The measured yield values are put together with available yield data found in the literature. The experimental yield data has been used to cross-check the γ-ray production cross section values by comparing them with calculated thick-target yields deduced from the present and literature experimental excitation curves. All values were found to be in reasonable agreement taking into account the experimental uncertainties.

  3. Response of northern San Francisco Bay to riverine inputs of dissolved inorganic carbon, silicon, nitrogen and phosphorus

    USGS Publications Warehouse

    Schemel, Laurence E.; Harmon, Dana D.; Eager, Stephen W.; Peterson, David H.

    1984-01-01

    Estuarine processes can be effective in modifying (filtering) distributions of dissolved inorganic forms of carbon (DIC), silicon (DIS), nitrogen (DIN), and phosphorus (DIP) in northern San Francisco Bay. During winter, high inflow from the Sacramento-San Joaquin river system supplied these nutrients to the estuary at rates that exceeded potential rates of estuarine supply and removal processes. During spring and summer, when inflow rates were lower, the estuary was an effective “filter” of the river inflow “signal” because rates of estuarine processes were high relative to river and other supply rates. At lower inflow rates, the river apparently influenced estuarine hydrodynamic features that controlled rates of phytoplankton nutrient removal. Largest biological removal effects were localized in San Pablo Bay during spring and Suisun Bay during summer, and they were generally more pronounced in shallow water areas of the bays. In San Pablo Bay, effects of biological removal appeared soon after river inflow decreased from high winter rates, but persisted for only a short time. During the following summer months, DIN and DIP distributions in San Pablo Bay indicated that estuarine sources contributed to higher concentrations of these nutrients.

  4. Hierarchically porous silicon-carbon-nitrogen hybrid materials towards highly efficient and selective adsorption of organic dyes

    NASA Astrophysics Data System (ADS)

    Meng, Lala; Zhang, Xiaofei; Tang, Yusheng; Su, Kehe; Kong, Jie

    2015-01-01

    The hierarchically macro/micro-porous silicon-carbon-nitrogen (Si-C-N) hybrid material was presented with novel functionalities of totally selective and highly efficient adsorption for organic dyes. The hybrid material was conveniently generated by the pyrolysis of commercial polysilazane precursors using polydivinylbenzene microspheres as sacrificial templates. Owing to the Van der Waals force between sp-hybridized carbon domains and triphenyl structure of dyes, and electrostatic interaction between dyes and Si-C-N matrix, it exhibites high adsorption capacity and good regeneration and recycling ability for the dyes with triphenyl structure, such as methyl blue (MB), acid fuchsin (AF), basic fuchsin and malachite green. The adsorption process is determined by both surface adsorption and intraparticle diffusion. According to the Langmuir model, the adsorption capacity is 1327.7 mg.g-1 and 1084.5 mg.g-1 for MB and AF, respectively, which is much higher than that of many other adsorbents. On the contrary, the hybrid materials do not adsorb the dyes with azo benzene structures, such as methyl orange, methyl red and congro red. Thus, the hierarchically porous Si-C-N hybrid material from a facile and low cost polymer-derived strategy provides a new perspective and possesses a significant potential in the treatment of wastewater with complex organic pollutants.

  5. Nanostructured photoelectrochemical solar cell for nitrogen reduction using plasmon-enhanced black silicon.

    PubMed

    Ali, Muataz; Zhou, Fengling; Chen, Kun; Kotzur, Christopher; Xiao, Changlong; Bourgeois, Laure; Zhang, Xinyi; MacFarlane, Douglas R

    2016-01-01

    Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO2 emissions (0.57  Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N2 to ammonia producing yields of 13.3 mg m(-2) h(-1) under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m(-2) h(-1) at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell. PMID:27093916

  6. Nanostructured photoelectrochemical solar cell for nitrogen reduction using plasmon-enhanced black silicon

    NASA Astrophysics Data System (ADS)

    Ali, Muataz; Zhou, Fengling; Chen, Kun; Kotzur, Christopher; Xiao, Changlong; Bourgeois, Laure; Zhang, Xinyi; Macfarlane, Douglas R.

    2016-04-01

    Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO2 emissions (0.57 Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N2 to ammonia producing yields of 13.3 mg m-2 h-1 under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m-2 h-1 at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell.

  7. Nanostructured photoelectrochemical solar cell for nitrogen reduction using plasmon-enhanced black silicon

    PubMed Central

    Ali, Muataz; Zhou, Fengling; Chen, Kun; Kotzur, Christopher; Xiao, Changlong; Bourgeois, Laure; Zhang, Xinyi; MacFarlane, Douglas R.

    2016-01-01

    Ammonia (NH3) is one of the most widely produced chemicals worldwide. It has application in the production of many important chemicals, particularly fertilizers. It is also, potentially, an important energy storage intermediate and clean energy carrier. Ammonia production, however, mostly uses fossil fuels and currently accounts for more than 1.6% of global CO2 emissions (0.57  Gt in 2015). Here we describe a solar-driven nanostructured photoelectrochemical cell based on plasmon-enhanced black silicon for the conversion of atmospheric N2 to ammonia producing yields of 13.3 mg m−2 h−1 under 2 suns illumination. The yield increases with pressure; the highest observed in this work was 60 mg m−2 h−1 at 7 atm. In the presence of sulfite as a reactant, the process also offers a direct solar energy route to ammonium sulfate, a fertilizer of economic importance. Although the yields are currently not sufficient for practical application, there is much scope for improvement in the active materials in this cell. PMID:27093916

  8. Bacterial attachment and removal properties of silicon- and nitrogen-doped diamond-like carbon coatings.

    PubMed

    Zhao, Qi; Su, Xueju; Wang, Su; Zhang, Xiaoling; Navabpour, Parnia; Teer, Dennis

    2009-01-01

    Si- and N-doped diamond-like carbon (DLC) coatings with various Si and N contents were deposited on glass slides using magnetron sputter ion-plating and plasma-enhanced chemical vapour deposition. Surface energy analysis of the DLC coatings revealed that with increasing Si content, the electron acceptor gamma(s)(+) value decreased while the electron donor gamma(s)(-) value increased. The antifouling property of DLC coatings was evaluated with the bacterium, Pseudomonas fluorescens, which is one of the most common microorganisms forming biofilms on the surface of heat exchangers in cooling water systems. P. fluorescens had a high value of the gamma(s)(-) component (69.78 mN m(-1)) and a low value of the gamma(s)(+) component (5.97 mN m(-1)), and would be negatively charged with the zeta potential of -16.1 mV. The experimental results showed that bacterial removal by a standardised washing procedure increased significantly with increasing electron donor gamma(s)(-) values and with decreasing electron acceptor gamma(s)(+) values of DLC coatings. The incorporation of 2%N into the Si-doped DLC coatings further significantly reduced bacterial attachment and significantly increased ease of removal. The best Si-N-doped DLC coatings reduced bacterial attachment by 58% and increased removal by 41%, compared with a silicone coating, Silastic T2. Bacterial adhesion strength on the DLC coatings is explained in terms of thermodynamic work of adhesion. PMID:19283517

  9. D0 Silicon Upgrade: Liquid & Gas Nitrogen Line Sizing for D-Zero Upgrade

    SciTech Connect

    Rucinski, Russ; /Fermilab

    1995-09-14

    This engineering note documents the calculations done to properly size the liquid/gas nitrogen piping system for the D-Zero refrigerator, solenoid, and VLPC upgrade. See the line sketch of the system on the next page. The sketch shows the chosen line sizes, estimated lengths of piping runs, estimated steady state flow rates and pressure drops for each pipe section. The raw calculations are attached as an appendix. The estimated steady state flow rates were developed in D-Zero EN-421, 'Helium and LN2 Storage Requirements for the D-Zero Upgrade'. The pressure drop calculations take into account the two phase property of the fluid on the inlet piping. The outlet piping is sized for saturated vapor. These calculations supplement sizing that was done in D-Zero EN-416, rev. 6/26/95, 'Pipe Sizing for Solenoid/VLPC Cryogenic Systems', EN-416 only looked at the Solenoid and VLPC sections of the system. In a previous EN-430, 'LN2 control valve sizing', a calculation was done to address the cool down flow rate necessary. The minimum cooldown flow rate needed for a simultaneous, serial cooldown of the refrigerator, solenoid and VLPC system was 6.4 g/s. This warm flow would get choked by an opening less than 0.175-inch in diameter. All the piping/tubing sizes exceed this size, so cooldown will not be a problem. The available pressure drop for the VLPC and solenoid control valves was calculated to be 5.5 psid and 27 psid respectively. The actual delta P is expected to be larger because the conservativeness of using maximum flow rates and fluid properties that yield pressure drops on the high side.

  10. The influence of changes in nitrogen: silicon ratios on diatom growth dynamics

    NASA Astrophysics Data System (ADS)

    Gilpin, L. C.; Davidson, K.; Roberts, E.

    2004-02-01

    Nitrate loading to coastal waters has increased over recent decades while silicon loading has remained relatively constant or decreased. As the N:Si ratio in coastal waters shifts due to these anthropogenic influences, silicate limitation of diatom biomass may become a feature of the biogeochemistry in coastal waters especially in regions of reduced exchange. Two sets of nutrient enrichment mesocosm experiments were conducted in successive years using a natural planktonic assemblage obtained from the Trondheimsfjord, Norway. The inorganic nutrient concentrations at the start of the experiments were manipulated to give a variety of N:Si concentrations at ratios representative of current and possible future values, should N loading continue. In June 1999 experiments were conducted with a gradient of inorganic N:Si ratios (1:2, 1:1, 2:1, 4:1) to investigate the influence of low and high N:Si ratio conditions and to determine the conditions that would generate Si limitation of diatom growth. In June 2000, based on 1999 data, highly replicated experiments were conducted at N:Si ratios of 1:1 and 4:1 which were expected to result in N and Si limitation of diatom growth, respectively; statistical differences in cellular composition were recorded. N limitation of diatom biomass increase was observed under the three lowest N:Si ratios: particulate carbon (C) accumulation continued to occur following N exhaustion resulting in an increase in the organic C:N ratio. Silicate limitation of diatom biomass increase only occurred at the highest N:Si ratio of 4:1. Silicate exhaustion was followed by continued nitrate uptake for several days, at a slower rate than previously. The resulting increase in organic N was accompanied by an increase in organic C such that the C:N ratio of the organic material at the highest N:Si ratio failed to increase to the extent observed under the N limited conditions. Statistically significant differences in chlorophyll-a yield per unit nitrate, C

  11. Provision of nitrogen as ammonium rather than nitrate increases silicon uptake in sugarcane

    PubMed Central

    Keeping, Malcolm G.; Rutherford, R. Stuart; Sewpersad, C.; Miles, Neil

    2015-01-01

    Silicon (Si) is important in mitigating abiotic and biotic plant stresses, yet many agricultural soils, such as those of the rainfed production areas of the South African sugar industry, are deficient in plant-available Si, making Si supplementation necessary. However, Si uptake by sugarcane (Saccharum spp. hybrids) is limited even where silicate amendments improve soil Si status. Rhizosphere pH, which can affect Si uptake, can be manipulated using different N-form fertilizers. We tested whether (i) fertilization with NH4+ (rhizosphere acidification) increased Si uptake compared with NO3− (rhizosphere alkalinization); and (ii) uptake differed between an N-efficient, more acid-tolerant cultivar (N12) and an N-inefficient, less acid-tolerant cultivar (N14). Two pot trials with low-Si soil were fertilized with calcium silicate (Ca2SiO4) slag, plus N from ammonium sulphate [(NH4)2SO4], ammonium thiosulphate [(NH4)2S2O3] and calcium nitrate [Ca(NO3)2] (Trial 1) or N from (NH4)2S2O3 and Ca(NO3)2 only (Trial 2). Trial 2 included cultivars N12 and N14. Nitrate treatments significantly increased soil pH and soil Si compared with NH4+. However, NH4+ treatments significantly increased leaf and stalk Si content compared with NO3−, reflected in a significant negative relationship between soil pH and leaf Si. Acid-extracted soil Si was negatively related to leaf and stalk Si, likely due to adsorption of silicic acid to soil surfaces under higher pH of the NO3− treatment and its reduced availability for plant uptake. We conclude that NH4+ increased Si uptake into leaf and stalk, and propose that reduced rhizosphere pH solubilized Si from Ca2SiO4 and increased silicic acid availability for plant uptake. By contrast, NO3− may have reduced Si uptake due to adsorption of Si to soil surfaces at higher pH. Our results indicate that ammoniacal fertilizers, such as (NH4)2SO4 and urea, have potential for promoting dissolution of applied Ca2SiO4 and subsequent uptake of Si by

  12. D0 Silicon Upgrade: Liquid Nitrogen Valve Sizing for D-Zero Upgrade

    SciTech Connect

    Rucinski, Russ; /Fermilab

    1995-09-13

    There were 5 control valves and 2 manual valves for the liquid nitrogen distribution system that needed to be sized and procured for the upgrade. This engineering note documents the calculations done to properly size these valves. A table summarizes the valve choices. The raw calculations are attached as an appendix. The calculations jump around a bit. No effort was made to re-organize or rewrite them for the reader. The sizing calcs. on Pages 1 through 4 were first pass calcs. based on pure liquid to the valves with no attention to flashing/choking. The calcs on pages 5 through 8 then refine the calculations by considering the LN2 to the valve inlets to be two phase with quality of 0.032. This is a real situation if the LN2 subcooler is out of service for use as a He cooldown heat exchanger. Also, flashing would occur for this situation and is taken into account. The end result of this refinement pushed the Cv values up by about a factor of 3 over the initial calcs. of pages 1 through 4. The results of the refined (correct) calculations pages 5 through 8 appear in the table above. The required operating Cv's are smaller than commercially available LN2 control valves. Therefore it has been decided to use Fermilab Saver type control valve assemblies with the valve bullet Cv1s listed above. The bullets are 100: 1 equal percentage types and provide better control at the lower percentage of valve Cv values. See flow characteristic data and curve for these valves in appendix B. The manual valves will be commercially purchased, probably a Cryolab model CV3-84-5WPG2 or CV8-84-5WPG2 or CVI model V-1060-050-VJ. Pages 8-10 calculate a minimum required cooldown flowrate as referenced in Cryogenic Systems by Barron. This was done to be sure the valves and piping system did not choke the warm flow so much that cooldown could not be achieved. The minimum mass flow rate needed for a simultaneous, serial cooldown of the refrigerator, solenoid and VLPC system was 6.4 g/s. This warm

  13. Defect chemistry and chalcogen diffusion in thin-film Cu{sub 2}ZnSnSe{sub 4} materials

    SciTech Connect

    Harvey, Steven P.; Repins, Ingrid; Teeter, Glenn

    2015-02-21

    Selenium diffusion in polycrystalline thin-film Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSe) on molybdenum-coated soda-lime glass substrates was investigated by in situ monitoring of the molybdenum back-contact resistance during high-temperature selenization treatments. In these measurements, selenium diffusion through the CZTSe layer results in conversion of the molybdenum layer to MoSe{sub 2}, increasing the sheet resistance of the film stack. By monitoring the rate of MoSe{sub 2} formation as a function of annealing temperature, an activation energy of 0.5 ± 0.1 eV has been measured for selenium diffusion in CZTSe. The partial pressure dependence of chalcogen diffusion suggests that chalcogen vacancies are not the defect controlling chalcogen diffusion in thin-film CZTSe.

  14. Ab initio theoretical study of hydrogen and its interaction with boron acceptors and nitrogen donors in single-wall silicon carbide nanotubes

    NASA Astrophysics Data System (ADS)

    Gali, A.

    2007-02-01

    Silicon carbide nanotubes have a great potential for biological applications. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. Hydrogen is a common impurity that can appear during the growth of silicon carbide nanotubes or in the environment. In this paper we studied the properties of one and two hydrogen atoms in armchair and zigzag silicon carbide nanotubes by ab initio supercell calculations beyond the standard density functional theory. We found that a single hydrogen atom is an amphoteric defect: it can act as a donor as well as an acceptor, depending on the adsorption site. However, both sites are nearly equally stable; therefore these defects compensate each other in SiC nanotube semiconductors. We found that hydrogen can absorb onto SiC nanotubes when atomic hydrogen is present in the environment. In addition, we investigated the incorporation of hydrogen by applying BH and NH molecules in the environment of SiC nanotubes. The simulations predict that boron dissolves into SiC nanotubes together with hydrogen; thus boron can be used to raise the concentration of hydrogen in SiC nanotubes. Nitrogen is also incorporated with hydrogen. We predict that the shallow boron acceptor and the nitrogen donor may be activated in these processes.

  15. Nitrogen Plasma Instabilities and the Growth of Silicon Nitride by Electron Cyclotron Resonance Microwave Plasma Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Pool, F. S.

    1996-01-01

    Nitrogen plasma instabilities have been identified through fluctuations in the ion current density and substrate floating potential. The plasma characteristics for both nitrogen and silane-nitrogen plasmas are consistent with a transition from an underdense to overdense plasma at 0.9 and 1.0 mTorr respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  17. Reactions Between Chalcogen Donors and Dihalogens/Interalogens: Typology of Products and Their Characterization by FT-Raman Spectroscopy.

    PubMed

    Arca, Massimiliano; Aragoni, M Carla; Devillanova, Francesco A; Garau, Alessandra; Isaia, Francesco; Lippolis, Vito; Mancini, Annalisa; Verani, Gaetano

    2006-01-01

    The chemical bond and structural features for the most important classes of solid products obtained by reacting chalcogen donors with dihalogens and interhalogens are reviewed. Particular attention is paid to the information the FT-Raman spectroscopy can confidently give about each structural motif considered in the absence of X-ray structural analyses. PMID:17497008

  18. Regioselective, Solvent- and Metal-Free Chalcogenation of Imidazo[1,2-a]pyridines by Employing I2 /DMSO as the Catalytic Oxidation System.

    PubMed

    Rafique, Jamal; Saba, Sumbal; Rosário, Alisson R; Braga, Antonio L

    2016-08-01

    Highly efficient molecular-iodine-catalyzed chalcogenations (S and Se) of imidazo[1,2-a]pyridines were achieved by using diorganoyl dichalcogenides under solvent-free conditions. This approach afforded the desired products that had been chalcogenated regioselectively at the C3 position in up to 96 % yield by using DMSO as an oxidant, in the absence of a metal catalyst, and under an inert atmosphere. This mild, green approach allowed the preparation of different types of chalcogenated imidazo[1,2-a]pyridines with structural diversity. Furthermore, the current protocol was also extended to other N-heterocyclic cores. PMID:27388454

  19. Fractionation of highly siderophile and chalcogen elements in components of EH3 chondrites

    NASA Astrophysics Data System (ADS)

    Kadlag, Yogita; Becker, Harry

    2015-07-01

    Abundances of highly siderophile elements (HSE: Re, platinum group elements and Au), chalcogens (Te, Se and S), 187Os/188Os and the major and minor elements Mg, Ca, Mn, Fe, Ni and Co were determined in the components of Sahara 97072 (EH3, find) and Kota Kota (EH3, find) in order to understand the element fractionation processes. In a 187Re-187Os isochron diagram, most magnetic components lie close to the 4.56 Ga IIIA iron meteorite isochron, whereas most other components show deviations from the isochron caused by late redistribution of Re, presumably during terrestrial weathering. Metal- and sulfide rich magnetic fractions and metal-sulfide nodules are responsible for the higher 187Os/188Os in bulk rocks of EH chondrites compared to CI chondrites. The HSE and chalcogens are enriched in magnetic fractions relative to slightly magnetic and nonmagnetic fractions and bulk compositions, indicating that Fe-Ni metal is the main host phase of the HSE in enstatite chondrites. HSE abundance patterns indicate mixing of two components, a CI chondrite like end member and an Au-enriched end member. Because of the decoupled variations of Au from those of Pd or the chalcogens, the enrichment of Au in EH metal cannot be due to metal-sulfide-silicate partitioning processes. Metal and sulfide rich nodules may have formed by melting and reaction of pre-existing refractory element rich material with volatile rich gas. A complex condensation and evaporation history is required to account for the depletion of elements having very different volatility than Au in EH chondrites. The depletions of Te relative to HSE, Se and S in bulk EH chondrites are mainly caused by the depletion of Te in metal. S/Se and S/Mn are lower than in CI chondrites in almost all components and predominantly reflect volatility-controlled loss of sulfur. The latter most likely occurred during thermal processing of dust in the solar nebula (e.g., during chondrule formation), followed by the non-systematic loss of S

  20. Suppression Effect and Mechanism of Platinum and Nitrogen-Containing Silane on the Tracking and Erosion of Silicone Rubber for High-Voltage Insulation.

    PubMed

    Chen, Wan Juan; Zeng, Xingrong; Lai, Xuejun; Li, Hongqiang; Fang, Wei Zhen; Hou, Fei

    2016-08-17

    How to effectively improve the tracking and erosion resistance of silicone rubber (SR) was an urgent topic in the field of high-voltage insulation. In this work, the tracking and erosion resistance of SR was significantly improved by incorporating platinum (Pt) catalyst and nitrogen-containing silane (NS). The suppression effect and mechanism of Pt/NS on tracking and erosion were studied by inclined plane (IP) test, thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry, laser Raman spectroscopy, and scanning electron microscopy. It revealed that when 1.4 phr of NS and 6.7 ppm of Pt were added, the tracking resistance of SR was improved from 2.5 to 4.5 kV level in the IP test, and the eroded mass was significantly reduced. This might be attributed to the synergistic effect of Pt/NS on silicone chains. At a high temperature produced by arc discharge, Pt/NS would catalyze radical cross-linking, meanwhile suppressing oxidation and depolymerization of silicone chains. Hence, a tightly cross-linked network was formed and protected inner materials from arc ablation. Moreover, carbon deposit during pyrolysis was suppressed by Pt/NS, which served as the secondary mechanism of tracking suppression. PMID:27462876

  1. Supramolecular macrocycles reversibly assembled by Te(…)O chalcogen bonding.

    PubMed

    Ho, Peter C; Szydlowski, Patrick; Sinclair, Jocelyn; Elder, Philip J W; Kübel, Joachim; Gendy, Chris; Lee, Lucia Myongwon; Jenkins, Hilary; Britten, James F; Morim, Derek R; Vargas-Baca, Ignacio

    2016-01-01

    Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te(…)O-N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal. PMID:27090355

  2. Chalcogen vacancies in monolayer transition metal dichalcogenides and Fermi level pinning at contacts

    NASA Astrophysics Data System (ADS)

    Guo, Y.; Liu, D.; Robertson, J.

    2015-04-01

    It is predicted that Schottky barriers of the transition metal dichalcogenides MoSe2, MoTe2, WS2, WSe2, and WTe2 will suffer less from Fermi level pinning by chalcogen vacancies than does MoS2, because their vacancy formation energies are larger. The reduction in vacancy numbers will allow a greater degree of Schottky barrier height tuning by varying metal work function of the contacts in these compounds. The vacancy levels of WS2, WSe2 and MoSe2, and MoTe2 are also calculated to lie nearer midgap, so that ambipolar conduction will be easier in these compounds than in MoS2.

  3. Modulating the Electronic and Optical Properties of Tetragonal ZnSe Monolayers by Chalcogen Dopants.

    PubMed

    Zhou, Jia; Li, Yang; Wu, Xiaohong; Qin, Wei

    2016-07-01

    The recently proposed three-atom-thick single-layer ZnSe sheet demonstrates a strong quantum confinement effect by exhibiting a large enhancement of band gap relative to the zinc blende (ZB) bulk phase. In this work, we aim at investigating the electronic and optical properties of this ultrathin tetragonal ZnSe single-layer sheet with various chalcogen dopant atoms, based on density functional theory (DFT). We find that these single-layer sheets with dopant atoms are still direct-band semiconductors with tunable band gaps, which can lead to strong light absorption and potential applications in solar energy harvesting. Theoretical optical absorbance results show that the S-doped ZnSe monolayer exhibits a higher absorption performance compared to other doped and undoped ZnSe monolayers. These findings pave a way for the modulation of novel ultrathin tetragonal ZnSe monolayers for a wealth of potential optoelectronic applications. PMID:26972924

  4. Improving dielectric properties of epitaxial Gd{sub 2}O{sub 3} thin films on silicon by nitrogen doping

    SciTech Connect

    Roy Chaudhuri, Ayan; Osten, H. J.; Fissel, A.; Archakam, V. R.

    2013-01-14

    We report about the effect of nitrogen doping on the electrical properties of epitaxial Gd{sub 2}O{sub 3} thin films. Epitaxial Gd{sub 2}O{sub 3}:N thin films were grown on Si (111) substrates by solid source molecular beam epitaxy using nitrous oxide as the nitridation agent. Substitutional nitrogen incorporation into the dielectric layer was confirmed by secondary ion mass spectroscopy and X-ray photoelectron spectroscopy analysis. Substantial reduction of the leakage current density and disappearance of hysteresis in capacitance-voltage characteristics observed in the Gd{sub 2}O{sub 3}:N layers indicate that nitrogen incorporation in Gd{sub 2}O{sub 3} effectively eliminates the adverse effects of the oxygen vacancy induced defects in the oxide layer.

  5. Method for producing silicon nitride/silicon carbide composite

    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.

    1996-07-23

    Silicon carbide/silicon nitride composites are prepared by carbothermal reduction of crystalline silica powder, carbon powder and optionally crsytalline silicon nitride powder. The crystalline silicon carbide portion of the composite has a mean number diameter less than about 700 nanometers and contains nitrogen.

  6. Highly siderophile and chalcogen element constraints on the origin of components of the Allende and Murchison meteorites

    NASA Astrophysics Data System (ADS)

    Kadlag, Yogita; Becker, Harry

    2016-06-01

    187Re-187Os systematics, abundances of highly siderophile elements (HSE: Re, PGE, and Au), chalcogen elements (Te, Se, and S), and some major and minor elements were determined in physically separated components of the Allende (CV3) and Murchison (CM2) carbonaceous chondrites. Substantial differences exist in the absolute and relative abundances of elements in the components, but the similarity of calculated and literature bulk rock abundances of HSE and chalcogens indicate that chemical complementarity exists among the components, with CI chondrite-like ratios for many elements. Despite subsequent alteration and oxidation, the overall cosmochemical behavior of most moderately to highly siderophile elements during high-temperature processing has been preserved in components of Allende at the sampling scale of the present study. The 187Re-187Os systematics and element variations of Allende are less disturbed compared with Murchison, which reflects different degrees of oxidation and alteration of these meteorites. The HSE systematics (with the exception of Au) is controlled by two types of materials: Pd-depleted condensates and CI chondrite-like material. Enrichment and heterogeneous distribution of Au among the components is likely the result of hydrothermal alteration. Chalcogen elements are depleted compared with HSE in all components, presumably due to their higher volatility. Small systematic variations of S, Se, and Te in components bear the signature of fractional condensation/partial evaporation and metal-sulfide-silicate partitioning.

  7. Highly siderophile and chalcogen element constraints on the origin of components of the Allende and Murchison meteorites

    NASA Astrophysics Data System (ADS)

    Kadlag, Yogita; Becker, Harry

    2016-04-01

    187Re-187Os systematics, abundances of highly siderophile elements (HSE: Re, PGE, and Au), chalcogen elements (Te, Se, and S), and some major and minor elements were determined in physically separated components of the Allende (CV3) and Murchison (CM2) carbonaceous chondrites. Substantial differences exist in the absolute and relative abundances of elements in the components, but the similarity of calculated and literature bulk rock abundances of HSE and chalcogens indicate that chemical complementarity exists among the components, with CI chondrite-like ratios for many elements. Despite subsequent alteration and oxidation, the overall cosmochemical behavior of most moderately to highly siderophile elements during high-temperature processing has been preserved in components of Allende at the sampling scale of the present study. The 187Re-187Os systematics and element variations of Allende are less disturbed compared with Murchison, which reflects different degrees of oxidation and alteration of these meteorites. The HSE systematics (with the exception of Au) is controlled by two types of materials: Pd-depleted condensates and CI chondrite-like material. Enrichment and heterogeneous distribution of Au among the components is likely the result of hydrothermal alteration. Chalcogen elements are depleted compared with HSE in all components, presumably due to their higher volatility. Small systematic variations of S, Se, and Te in components bear the signature of fractional condensation/partial evaporation and metal-sulfide-silicate partitioning.

  8. Advances in the development of complexes that contain a group 13 element chalcogen multiple bond.

    PubMed

    Franz, Daniel; Inoue, Shigeyoshi

    2016-06-21

    Inorganic group 13 element (M) chalcogenides (E) based on the general formular M2E3 are ubiquitous in synthesis, catalysis and material science. The parent ME fragment which aggregates to form three dimensional networks in the condensed phase can be expected to exhibit multiple bond character between the elements. Low temperature matrix isolation techniques are required to investigate the nature of this elusive species. An alternate approach for respective studies is the synthesis of electron-precise molecular complexes that contain the ME entity and for which isolation at ambient temperature is possible. This is realized by kinetic stabilization with bulky ligands and thermodynamic stabilization using electron donor, as well as acceptor groups attached to the ME functionality (i.e. donor-acceptor stabilization). In this article we revise the literature on complex compounds that exhibit a bonding interaction between a group 13 element atom and a chalcogen atom that is reasonably to be interpreted in terms of a double- or triple bond. PMID:27216700

  9. Uranium (VI)Bis(imido) chalcogenate complexes:synthesis and density functional theory analysis

    SciTech Connect

    Spencer, Liam P; Batista, Enrique R; Boncella, James M; Yang, Ping; Scott, Brian L

    2009-01-01

    Bis(imido) uranium(VI) trans- and cis-dichalcogenate complexes with the general formula U(NtBu)2(EAr)2(OPPh3)2 (EAr = O-2-tBuC6H4, SPh, SePh, TePh) and U(NtBu)2(EAr)2(R2bpy) (EAr = SPh, SePh, TePh) (R2bpy = 4,4'-disubstituted-2,2'-bipyridyl, R = Me, tBu) have been prepared. This family of complexes includes the first reported monodentate selenolate and tellurolate complexes of uranium(VI). Density functional theory calculations show that covalent interactions in the U-E bond increase in the trans-dichalcogenate series U(NtBu)2(EAr)2(OPPh3)2 as the size of the chalcogenate donor increases and that both 5f and 6d orbital participation is important in the M-E bonds of U-S, U-Se, and U-Te complexes.

  10. Chalcogen bonding interactions between reducible sulfur and selenium compounds and models of zinc finger proteins.

    PubMed

    Lutz, Patricia B; Bayse, Craig A

    2016-04-01

    Reducible sulfur and selenium (r-S/Se) compounds, defined as sulfur and selenium compounds not in the lowest -2 oxidation state (e.g., -1 to +6), release Zn(2+) from zinc-sulfur proteins such as zinc fingers (ZFs) and metallothionein. A series of density functional theory calculations was performed on donor-acceptor complexes between r-S/Se compounds and models of the Cys2His2, Cys3His and Cys4 ZF sites. These S⋯S/Se chalcogen bonding interactions consist of the donation of electron density from a S lone pair on the ZF model to a S/Se-X antibonding molecular orbital of the r-S/Se compound. The strength of the interaction was shown to be dependent upon the Lewis basicity of the ZF model (Cys4>Cys3His>Cys2His2) and the Lewis acidity of the r-S/Se compound as measured by the energy of the S/Se-X antibonding orbital. Interactions with the softer r-Se compounds were stronger than the r-S compounds, consistent with the greater reactivity of the former with ZF proteins. PMID:26877152

  11. Preparation of nitrogen doped silicon oxides thin films by plasma polymerization of 3-aminopropyltriethoxylsilane using atmospheric pressure plasma jet

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chun; Wang, Meng-Jiy

    2016-01-01

    Surface modification techniques have been applied in various applications including self-cleaning surface, antibacterial filter, and biomaterials. In this study we employed the atmospheric pressure plasma jet (APPJ) deposition, a dry process for surface modification, to deposit 3-aminopropyltriethoxylsilane (APTES) on stainless steel (SS) on the purposes of simultaneously incorporating SiOx and nitrogen containing functionalities for the modulation of biofunctionality. The APPJ deposition allowed to form a thin layer of APTES with linear growth rate by controlling the deposition time. In addition, the surface chemical and physical properties, such as surface chemical composition, wettability, film thickness, and interactions with mammalian cells were evaluated by using different analytical methods. The results showed that the surface wettability was improved significantly due to the APTES deposition along with the increase of the incorporated nitrogen content. Moreover, the viability of L-929 fibroblasts was clearly promoted on the APTES deposited SS, which is most probably due to the thicker deposited films and higher density of nitrogen-containing functional groups. The outcomes of this research showed great potential to apply on metallic substrates in real time for biomedical related applications.

  12. Silicon reduces impact of plant nitrogen in promoting stalk borer (Eldana saccharina) but not sugarcane thrips (Fulmekiola serrata) infestations in sugarcane

    PubMed Central

    Keeping, Malcolm G.; Miles, Neil; Sewpersad, Chandini

    2014-01-01

    The stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae) is a major limiting factor in South African sugarcane production, while yield is also reduced by sugarcane thrips Fulmekiola serrata Kobus (Thysanoptera: Thripidae). Borer management options include appropriate nitrogen (N) and enhanced silicon (Si) nutrition; the effect of N on sugarcane thrips is unknown. We tested the effects of these nutrients, in combination with resistant (N33) and susceptible (N27) sugarcane cultivars, on E. saccharina and F. serrata infestation. Two pot trials with three levels of N (60, 120, and 180 kg ha-1) and two levels each of calcium silicate and dolomitic lime (5 and 10 t ha-1) were naturally infested with thrips, then artificially water stressed and infested with borer. Higher N levels increased borer survival and stalk damage, while Si reduced these compared with controls. Silicon significantly reduced stalk damage in N27 but not in N33; hence, Si provided relatively greater protection for susceptible cultivars than for resistant ones. High N treatments were associated with greater thrips numbers, while Si treatments did not significantly influence thrips infestation. The reduction in borer survival and stalk damage by Si application at all N rates indicates that under field conditions, the opportunity exists for optimizing sugarcane yields through maintaining adequate N nutrition, while reducing populations of E. saccharina using integrated pest management (IPM) tactics that include improved Si nutrition of the crop and reduced plant water stress. Improved management of N nutrition may also provide an option for thrips IPM. The contrasting effects of Si on stalk borer and thrips indicate that Si-mediated resistance to insect herbivores in sugarcane has mechanical and biochemical components that are well developed in the stalk tissues targeted by E. saccharina but poorly developed in the young leaf spindles where F. serrata occurs. PMID:24999349

  13. Studies of hot B subdwarfs. III - Carbon, nitrogen, and silicon abundances in three sdB stars

    NASA Technical Reports Server (NTRS)

    Lamontagne, R.; Wesemael, F.; Fontaine, G.; Sion, E. M.

    1985-01-01

    Optical and high-dispersion IUE observations of three hot B subdwarfs (UV 1758 + 36, Ton S-227, and Feige 65) are presented. These data are analyzed with model atmosphere techniques, and element abundances for C, N, and Si are derived. The abundances are either near (N) or below (C, Si) the solar value; large variations (1) in the extent of underabundances of carbon and silicon among the objects, as well as (2) in the abundances (with respect to the solar values) characterizing each star are observed. A preliminary interpretation of the observed variations in these and other hot subdwarfs in terms of radiative forces disrupting the downward diffusion of heavy elements is presented.

  14. The roles of lithium-philic giant nitrogen-doped graphene in protecting micron-sized silicon anode from fading.

    PubMed

    Liu, Xiaoxu; Chao, Dongliang; Zhang, Qiang; Liu, Hai; Hu, Hailong; Zhao, Jiupeng; Li, Yao; Huang, Yizhong; Lin, Jianyi; Shen, Ze Xiang

    2015-01-01

    A stable Si-based anode with a high initial coulombic efficiency (ICE) for lithium-ion batteries (LIB) is critical for energy storage. In the present paper, a new scalable method is adopted in combination with giant nitrogen-doped graphene and micron-size electrode materials. We first synthesize a new type of freestanding LIB anode composed of micron-sized Si (mSi) particles wrapped by giant nitrogen-doped graphene (mSi@GNG) film. High ICE (>85%) and long cycle life (more than 80 cycles) are obtained. In the mSi@GNG composite, preferential formation of a stable solid electrolyte interphase (SEI) on the surface of graphene sheets is achieved. The formation and components of SEI are identified for the first time by using UV-resonance Raman spectroscopy and Raman mapping, which will revive the study of formation and evolution of SEI by Raman. New mechanism is proposed that the giant graphene sheets protect the mSi particles from over-lithiation and fracture. Such a simple and scalable method may also be applied to other anode systems to boost their energy and power densities for LIB. PMID:26497729

  15. The roles of lithium-philic giant nitrogen-doped graphene in protecting micron-sized silicon anode from fading

    PubMed Central

    Liu, Xiaoxu; Chao, Dongliang; Zhang, Qiang; Liu, Hai; Hu, Hailong; Zhao, Jiupeng; Li, Yao; Huang, Yizhong; Lin, Jianyi; Shen, Ze Xiang

    2015-01-01

    A stable Si-based anode with a high initial coulombic efficiency (ICE) for lithium-ion batteries (LIB) is critical for energy storage. In the present paper, a new scalable method is adopted in combination with giant nitrogen-doped graphene and micron-size electrode materials. We first synthesize a new type of freestanding LIB anode composed of micron-sized Si (mSi) particles wrapped by giant nitrogen-doped graphene (mSi@GNG) film. High ICE (>85%) and long cycle life (more than 80 cycles) are obtained. In the mSi@GNG composite, preferential formation of a stable solid electrolyte interphase (SEI) on the surface of graphene sheets is achieved. The formation and components of SEI are identified for the first time by using UV-resonance Raman spectroscopy and Raman mapping, which will revive the study of formation and evolution of SEI by Raman. New mechanism is proposed that the giant graphene sheets protect the mSi particles from over-lithiation and fracture. Such a simple and scalable method may also be applied to other anode systems to boost their energy and power densities for LIB. PMID:26497729

  16. The roles of lithium-philic giant nitrogen-doped graphene in protecting micron-sized silicon anode from fading

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoxu; Chao, Dongliang; Zhang, Qiang; Liu, Hai; Hu, Hailong; Zhao, Jiupeng; Li, Yao; Huang, Yizhong; Lin, Jianyi; Shen, Ze Xiang

    2015-10-01

    A stable Si-based anode with a high initial coulombic efficiency (ICE) for lithium-ion batteries (LIB) is critical for energy storage. In the present paper, a new scalable method is adopted in combination with giant nitrogen-doped graphene and micron-size electrode materials. We first synthesize a new type of freestanding LIB anode composed of micron-sized Si (mSi) particles wrapped by giant nitrogen-doped graphene (mSi@GNG) film. High ICE (>85%) and long cycle life (more than 80 cycles) are obtained. In the mSi@GNG composite, preferential formation of a stable solid electrolyte interphase (SEI) on the surface of graphene sheets is achieved. The formation and components of SEI are identified for the first time by using UV-resonance Raman spectroscopy and Raman mapping, which will revive the study of formation and evolution of SEI by Raman. New mechanism is proposed that the giant graphene sheets protect the mSi particles from over-lithiation and fracture. Such a simple and scalable method may also be applied to other anode systems to boost their energy and power densities for LIB.

  17. Synthesis of silicon oxynitride by ion beam sputtering and the effects of nitrogen ion-assisted bombardment

    NASA Astrophysics Data System (ADS)

    Lambrinos, M. F.; Valizadeh, R.; Colligon, J. S.

    1997-05-01

    Thin silicon oxynitride (SiO xN y) films were synthesised without substrate heating by means of N 2+ ion-beam sputtering of a silicon nitride target at an energy of 1000 eV in a N 2 and O 2 ambient with and without 200 eV N 2+ ion assistance. Unassisted films were deposited in a controlled O 2 partial pressure ranging from ambient to 5.0 × 10 -3 Pa whereas assisted films were deposited at a fixed O 2 partial pressure of 1.0 × 10 -3 Pa. The O/(O+N) atomic fraction and the SiO xN y asymmetric stretch mode IR absorption peak wavenumber of unassisted films increased almost linearly with increasing O 2 partial pressure, from 0.2 to 1.0 and 860 cm -1 to 1050 cm -1, respectively, while their refractive indices decreased from 1.92 to 1.46. The behaviour of the SiO xN y film refractive index with the SiO 2 fraction has been compared to that predicted by Drude, Lorentz-Lorenz and Bruggeman models under the assumption that the film is a mixture of SiO 2 and Si 3N 4 phases. For a fixed O 2 partial pressure, the O content of the N 2+ ion-assisted films increased with an increase in the N + ion to Si atom arrival ratio from 0 to 3. This increase in O content correlate with changes in the film refractive index and SiO xN y asymmetric stretch mode absorption peak position, from 1.56 to 1.43 and 1014 cm -1 to 1054 cm -1, respectively, indicating that the O/N atomic ratio increases with increasing N + ion to Si atom ratio until film properties consistent with stoichiometric SiO 2 are obtained.

  18. Chalcogen (O2, S, Se, Te) atmosphere annealing induced bulk superconductivity in Fe1+yTe1-xSex single crystal

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Tsuchiya, Y.; Yamada, T.; Taen, T.; Pyon, S.; Shi, Z. X.; Tamegai, T.

    2014-09-01

    We reported a detailed study of Fe1+yTe0.6Se0.4 single crystals annealed in the atmosphere of chalcogens (O2, S, Se, Te). After annealing with appropriate amount of chalcogens, Fe1+yTe0.6Se0.4 single crystals show Tc higher than 14 K with a sharp transition width ∼1 K. Critical current density Jc for the annealed crystals reach a very high value ∼2-4 × 105 A/cm2 under zero field, and is also robust under applied field at low temperatures. Magneto-optical imaging reveal that the Jc is homogeneously distributed in the annealed crystals and isotropic in the ab-plane. Our results show that annealing in the atmosphere of chalcogens can successfully induce bulk superconductivity in Fe1+yTe0.6Se0.4.

  19. Chalcogenation of the 1,4-C2P4 ring: oxidation, isomerization, insertion, and ring contraction.

    PubMed

    Elder, Philip J W; Chivers, Tristram

    2013-07-01

    The reaction of H2C(PCl2)2 with 4 equiv of (t)BuMgCl in tetrahydrofuran (THF) produces 1,4-(CH2)2(P(t)Bu)4, 1, in about 65% yield. This six-membered ring reacts directly with elemental sulfur or selenium in toluene at low temperatures to give the mono- and dichalcogenides 1,4-(CH2)2(P(t)BuE)(P(t)Bu)3 (E = S, 2a, E = Se, 2b) and 1,4-(CH2)2-2,5-(P(t)BuE)2(P(t)Bu)2 (E = S, 3a, E = Se, 3b). X-ray structural determinations showed that 3a and 3b are isostructural in the solid state; the six-membered C2P4 ring exhibits a twist-boat geometry with chalcogen substituents in syn positions in each case. Density functional theory (DFT) calculations for the three possible isomers of disubstitution were performed to elucidate the factors that favor the 2,5-isomer. Thermal isomerism was observed in solutions of 3b or 3a in toluene at 60 and 95 °C, respectively, to give the corresponding 2,6-isomers. With an excess of chalcogen in toluene at reflux, the four-membered rings (H2C)(P(t)BuE)2E (E = S, 4a, E = Se, 4b) were obtained and identified by multinuclear NMR spectroscopy and single crystal X-ray crystallography, which showed the (t)Bu groups in a trans orientation with respect to the CP2E ring. With a large excess of chalcogen, the five-membered rings (H2C)(P(t)BuE)2E2 (E = S, 5a, E = Se, 5b) were also observed; the X-ray structure of 5b revealed a half-envelope conformation for the CP2Se2 ring. The direct reaction of 4a with sulfur in boiling toluene does not produce 5a, whereas 5b is formed slowly and in low yields from 4b and selenium under similar conditions. On the basis of DFT calculations of the relative energies of likely intermediates, chalcogen insertion into the P-P bonds of 3a and 3b to give eight-membered C2P4E2 rings, followed by monomerization, is proposed as a feasible pathway for the formation of the four-membered CP2E heterocycles 4a and 4b. PMID:23786389

  20. Weak O-Assistance Outcompeting Strong N,N-Bidentate Directing Groups in Copper-Catalyzed C-H Chalcogenation.

    PubMed

    Cera, Gianpiero; Ackermann, Lutz

    2016-06-13

    A copper-mediated C-H chalcogenation of triazoles has been achieved by weak coordination. The user-friendly protocol showed high functional-group tolerance and ample substrate scope, yielding fully substituted 1,2,3-triazoles with complete positional site-selectivity. The C-H selenylation could likewise be achieved by means of copper catalysis. Our findings highlight for the first time that weak O-coordination can outcompete the strong N,N-bidentate coordination mode in C-H functionalization technology. PMID:27124082

  1. Crystallization Behavior of Virgin TR-55 Silicone Rubber Measured Using Dynamic Mechanical Thermal Analysis with Liquid Nitrogen Cooling

    SciTech Connect

    Small IV, W; Wilson, T S

    2010-02-11

    Dynamic mechanical thermal analysis (DMTA) of virgin TR-55 silicone rubber specimens was conducted. Two dynamic temperature sweep tests, 25 to -100 C and 25 to -70 to 0 C (ramp rate = 1 C/min), were conducted at a frequency of 6.28 rad/s (1 Hz) using a torsion rectangular test geometry. A strain of 0.1% was used, which was near the upper limit of the linear viscoelastic region of the material based on an initial dynamic strain sweep test. Storage (G{prime}) and loss (G{double_prime}) moduli, the ratio G{double_prime}/G{prime} (tan {delta}), and the coefficient of linear thermal expansion ({alpha}) were determined as a function of temperature. Crystallization occurred between -40 and -60 C, with G{prime} increasing from {approx}6 x 10{sup 6} to {approx}4 x 10{sup 8} Pa. The value of {alpha} was fairly constant before ({approx}4 x 10{sup -4} mm/mm- C) and after ({approx}3 x 10{sup -4} mm/mm- C) the transition, and peaked during the transition ({approx}3 x 10{sup -3} mm/mm- C). Melting occurred around -30 C upon heating.

  2. Silicon nitride/silicon carbide composite densified materials prepared using composite powders

    DOEpatents

    Dunmead, S.D.; Weimer, A.W.; Carroll, D.F.; Eisman, G.A.; Cochran, G.A.; Susnitzky, D.W.; Beaman, D.R.; Nilsen, K.J.

    1997-07-01

    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.

  3. Use of silicon in liquid sintered silicon nitrides and sialons

    DOEpatents

    Raj, R.; Baik, S.

    1984-12-11

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic. 4 figs.

  4. Use of silicon in liquid sintered silicon nitrides and sialons

    DOEpatents

    Raj, Rishi; Baik, Sunggi

    1984-12-11

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic.

  5. PERSONAL MONITOR FOR NITROGEN DIOXIDE

    EPA Science Inventory

    An attempt was made to develop a personal monitor to measure nitrogen dioxide. Sampling of nitrogen dioxide is accomplished by permeation through a silicone membrane into a alkaline thymol blue solution. The nitrogen dioxide is converted to nitrite and is then quantitated by colo...

  6. Evaluation of momentum effects on material properties of titanium-silicon-nitrogen nanocrystalline composites prepared by pulsed dc reactive sputtering

    NASA Astrophysics Data System (ADS)

    Sunal, Paul Dennis

    The investigation had as a general goal the deposition of thin films that possess high erosion wear resistance. The fabrication technique used for this purpose was an industry-compatible process called reactive sputtering physical vapor deposition (PVD). The study specifically involved depositing Ti-Si-N nc-composite thin films according to generic design principles that specify using a transition metal nitride and a covalent nitride material system in order to produce hard coatings (˜50 GPa Vickers hardness). Thin films were deposited using reactive pulsed, do sputtering to avoid arcing issues and for wider control over the process properties such as the deposition rate and level of bombardment. Two sputter guns used synchronized pulsed do signals, which were asymmetric and bipolar with positive voltages of less than +100 V and negative voltages of -500 to -1000 V. The pulsing frequency was varied in this co-deposition system as a possible means to control the nanocrystalline composite thin film properties by controlling the level of bombardment. The thin films were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) to determine the crystallinity of the films. XRD results show the presence of the (111), (220), and (200) orientations with the later being most common. TEM bright-field images show nanocrystals in the 10 to 40 nm range, depending on the pulsing frequency. A columnar morphology (50--120 nm diameters) was observed in the nc-composite films from images taken with a scanning electron microscope. Verification of the TiN and SiN phases was accomplished using XPS to analyze the binding energies of Ti 2p and Si 2p electrons, respectively. Oxygen was detected in the films, (2--9 at.%) depending on pulsing frequency, and it severely worsened the mechanical properties, specifically the hardness, by reacting with some of the silicon in the SiN phase. A maximum Vickers hardness, Hv, of 32 GPa and reduced elastic modulus, Er, of

  7. S···O chalcogen bonding in sulfa drugs: insights from multipole charge density and X-ray wavefunction of acetazolamide.

    PubMed

    Thomas, Sajesh P; Jayatilaka, Dylan; Guru Row, T N

    2015-10-14

    Experimental charge density analysis combined with the quantum crystallographic technique of X-ray wavefunction refinement (XWR) provides quantitative insights into the intra- and intermolecular interactions formed by acetazolamide, a diuretic drug. Firstly, the analysis of charge density topology at the intermolecular level shows the presence of exceptionally strong interaction motifs such as a DDAA-AADD (D-donor, A-acceptor) type quadruple hydrogen bond motif and a sulfonamide dimer synthon. The nature and strength of intra-molecular S···O chalcogen bonding have been characterized using descriptors from the multipole model (MM) and XWR. Although pure geometrical criteria suggest the possibility of two intra-molecular S···O chalcogen bonded ring motifs, only one of them satisfies the "orbital geometry" so as to exhibit an interaction in terms of an electron density bond path and a bond critical point. The presence of 'σ-holes' on the sulfur atom leading to the S···O chalcogen bond has been visualized on the electrostatic potential surface and Laplacian isosurfaces close to the 'reactive surface'. The electron localizability indicator (ELI) and Roby bond orders derived from the 'experimental wave function' provide insights into the nature of S···O chalcogen bonding. PMID:26365207

  8. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    DOE PAGESBeta

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Wang, Jun; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show thatmore » the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.« less

  9. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1 +yTe1 -xSex

    NASA Astrophysics Data System (ADS)

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Wang, Jun; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1 +yTe1 -xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon, we performed a combination of magnetic susceptibility, specific heat, and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1 +yTe1 -xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥1 ) complexes. We show that the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.

  10. Electrochemical Kinetics and X-ray Absorption Spectroscopic Investigations of Oxygen Reduction on Chalcogen-Modified Ruthenium Catalysts in Alkaline Media

    SciTech Connect

    N Ramaswamy; R Allen; S Mukerjee; Y

    2011-12-31

    The oxygen reduction reaction (ORR) in alkaline media has been investigated on chalcogen-modified ruthenium nanoparticles (Ru/C, Se/Ru/C, Se/RuMo/C, S/Ru/C, S/RuMo/C) synthesized in-house via aqueous routes. In acidic medium, it is well known that modification by a chalcogen prevents the oxidation of the underlying transition-metal (Ru) surface, thereby promoting direct molecular O{sub 2} adsorption on the Ru metal. On an unmodified Ru catalyst in alkaline media, the surface oxides on Ru mediate the 2e{sup -} reduction of molecular O{sub 2} to a stable peroxide anion (HO{sub 2}{sup -}) intermediate via an outer-sphere electron-transfer mechanism. This increases the activity of HO{sub 2}{sup -} near the electrode surface and decreases the overpotential for ORR by effectively carrying out the reduction of HO{sub 2}{sup -} to OH{sup -} at the oxide-free ruthenium metal site. An increase in ORR activity of Ru is observed by modification with a chalcogen; however, the increase is not as significant as observed in acidic media. Ternary additives, such as Mo, were found to significantly improve the stability of the chalcogen-modified catalysts. Detailed investigations of the ORR activity of this class of catalyst have been carried out in alkaline media along with comparisons to acidic media wherever necessary. A combination of electrochemical and X-ray absorption spectroscopic (EXAFS, XANES, {Delta}{mu}) studies has been performed in order to understand the structure/property relationships of these catalysts within the context of ORR in alkaline electrolytes.

  11. Role of axial base coordination in isonitrile binding and chalcogen atom transfer to vanadium(III) complexes.

    PubMed

    Majumdar, Subhojit; Stauber, Julia M; Palluccio, Taryn D; Cai, Xiaochen; Velian, Alexandra; Rybak-Akimova, Elena V; Temprado, Manuel; Captain, Burjor; Cummins, Christopher C; Hoff, Carl D

    2014-10-20

    The enthalpy of oxygen atom transfer (OAT) to V[(Me3SiNCH2CH2)3N], 1, forming OV[(Me3SiNCH2CH2)3N], 1-O, and the enthalpies of sulfur atom transfer (SAT) to 1 and V(N[t-Bu]Ar)3, 2 (Ar = 3,5-C6H3Me2), forming the corresponding sulfides SV[(Me3SiNCH2CH2)3N], 1-S, and SV(N[t-Bu]Ar)3, 2-S, have been measured by solution calorimetry in toluene solution using dbabhNO (dbabhNO = 7-nitroso-2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) and Ph3SbS as chalcogen atom transfer reagents. The V-O BDE in 1-O is 6.3 ± 3.2 kcal·mol(-1) lower than the previously reported value for 2-O and the V-S BDE in 1-S is 3.3 ± 3.1 kcal·mol(-1) lower than that in 2-S. These differences are attributed primarily to a weakening of the V-Naxial bond present in complexes of 1 upon oxidation. The rate of reaction of 1 with dbabhNO has been studied by low temperature stopped-flow kinetics. Rate constants for OAT are over 20 times greater than those reported for 2. Adamantyl isonitrile (AdNC) binds rapidly and quantitatively to both 1 and 2 forming high spin adducts of V(III). The enthalpies of ligand addition to 1 and 2 in toluene solution are -19.9 ± 0.6 and -17.1 ± 0.7 kcal·mol(-1), respectively. The more exothermic ligand addition to 1 as compared to 2 is opposite to what was observed for OAT and SAT. This is attributed to less weakening of the V-Naxial bond in ligand binding as opposed to chalcogen atom transfer and is in keeping with structural data and computations. The structures of 1, 1-O, 1-S, 1-CNAd, and 2-CNAd have been determined by X-ray crystallography and are reported. PMID:25280113

  12. Copper-catalyzed C-H bond direct chalcogenation of aromatic compounds leading to diaryl sulfides, selenides, and diselenides by using elemental sulfur and selenium as chalcogen sources under oxidative conditions.

    PubMed

    Shibahara, Fumitoshi; Kanai, Takafumi; Yamaguchi, Eiji; Kamei, Akika; Yamauchi, Takayuki; Murai, Toshiaki

    2014-01-01

    The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3-substituted imidazo[1,5-a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N-methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield. PMID:24347073

  13. New dimensions in chemistry of materials with lanthanide-chalcogen bonds: Highly emissive molecules, clusters and composites

    NASA Astrophysics Data System (ADS)

    Banerjee, Santanu

    This thesis presents the synthesis and characterization of materials having bonds between hard, electropositive lanthanide metal cations and soft, covalent chalcogen based ligands and a study of their electronic properties. Molecular Ln chalcogenido chalcogenolate clusters LnxEy(ER) z(Ln=La-Lu; E=S,Se,Te; R=C6H5, C6F 5), oxo-ligand containing clusters [LnxEyO z(ER)n,LnxEyOz] and heterovalent clusters [Ln(II)/Ln(III)x (ER)y, Ln(II)/Ln(III) xEy(ER)z, Ln(II)/Ln'(III)x(ER) z Ln(II)/Ln'(III)xEy(ER)z] have been isolated and characterized. These compounds are useful in terms of interpreting the nature of the Ln-E bond and for correlating the physical properties of molecular lanthanide chalcogenolates [Ln(EPh)x] with those of LnxEy solid state materials. Also thermal decomposition of these clusters was investigated to establish the utility of the molecular materials as precursors to solid state materials. In addition to synthesis and structural chemistry, the photoluminescence properties of these compounds were studied in detail. The results of optical studies of different lanthanide compounds with chalcogenido, fluorinated thiolate and mu-Oxo ligands are reported here. Electronic characterization of these materials involves UV-Visible absorption spectroscopy, emission spectroscopy using LASER diode sources, optical gain and fluorescence decay time measurements.

  14. "Pnicogen bonds" or "chalcogen bonds": exploiting the effect of substitution on the formation of PSe noncovalent bonds.

    PubMed

    Shukla, Rahul; Chopra, Deepak

    2016-05-18

    In this article, we have analyzed the nature and characteristics of PSe noncovalent interactions by studying the effect of substitution on XH2PSeH2, H3PSeHX and XH2PSeHX (X= -H, -F, -CH3, -CF3, -Cl, -OH, -OCH3, -NH2, -NHCH3, and -CN) as our systems of interest at MP2/aug-cc-pVDZ level of theory. Binding energy calculations depict that binding energy increases in the order XH2PSeH2 < H3PSeHX < XH2PSeHX with the nature of the substituent having a direct effect on the strength of the interactions. PSe contacts as short as 2.52 Å were observed and analyzed in our study. The energy values for PSe contacts were found to exist in the range of -1.20 kcal mol(-1) to -7.89 kcal mol(-1). The topological analysis confirms the presence of PSe contacts in all the complexes with characteristics similar to hydrogen bonds. NBO analysis helped in categorizing these interactions into pnicogen and chalcogen bonds, depending on the strength of P(lp) to σ*(Se-X) orbitals or Se(lp) to σ*(P-X) orbitals. PMID:27145973

  15. Phenyl substituted Mg porphyrazines: The effect of annulation of a chalcogen-containing heterocycle on the spectral-luminescent properties

    NASA Astrophysics Data System (ADS)

    Knyukshto, V. N.; Volkovich, D. I.; Gladkov, L. L.; Kuzmitsky, V. A.; Ul-Haque, A.; Popkova, I. A.; Stuzhin, P. A.; Solovyov, K. N.

    2012-10-01

    We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield φ F , and lifetime τ F . Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Q x (0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield φ F and lifetime τ F decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle γ between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle γ = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ˜2000 cm-1.

  16. Use of free silicon in liquid phase sintering of silicon nitrides and sialons

    DOEpatents

    Raj, Rishi; Baik, Sunggi

    1985-11-12

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic.

  17. Use of free silicon in liquid phase sintering of silicon nitrides and sialons

    DOEpatents

    Raj, R.; Baik, S.

    1985-11-12

    This invention relates to the production of improved high density nitrogen based ceramics by liquid-phase densification of silicon nitride or a compound of silicon-nitrogen-oxygen-metal, e.g. a sialon. In the process and compositions of the invention minor amounts of finely divided silicon are employed together with the conventional liquid phase producing additives to enhance the densification of the resultant ceramic. 4 figs.

  18. Effects of stress annealing in nitrogen on the index of refraction of silicon dioxide layers in metal-oxide-semiconductor devices

    NASA Astrophysics Data System (ADS)

    Massoud, Hisham Z.; Przewlocki, Henryk M.

    2002-08-01

    In this article, we report the results of a study of the effects of high-temperature stress annealing in nitrogen on the index of refraction of SiO2 layers in metal/oxide/semiconductor (MOS) devices. In this study, we have experimentally characterized the dependence of mechanical stress in the Si-SiO2 system on the oxidation and annealing conditions and correlated such properties with the dependence of the index of refraction on processing conditions and oxide thickness. We consider the contributions of the thermal-relaxation and nitrogen-incorporation processes in determining changes in the index of refraction with annealing time. This description is consistent with other annealing studies carried out in argon where only the thermal-relaxation process is present. Correlations of these experimental observations with the electrical properties of the same MOS devices are presented in a companion article.

  19. 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.

  20. 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.

  1. Molecular dynamics studies of the bonding properties of amorphous silicon nitride coatings on crystalline silicon

    NASA Astrophysics Data System (ADS)

    Butler, Keith T.; Lamers, Machteld P. W. E.; Weeber, Arthur W.; Harding, John H.

    2011-12-01

    In this paper we present molecular dynamics simulations of silicon nitride, both in bulk and as an interface to crystalline silicon. We investigate, in particular, the bonding structure of the silicon nitride and analyze the simulations to search for defective geometries which have been identified as potential charge carrier traps when silicon nitride forms an interface with silicon semiconductors. The simulations reveal how the bonding patterns in silicon nitride are dependent upon the stoichiometry of the system. Furthermore we demonstrate how having an "interphase", where the nitrogen content in silicon gradually reduces toward pure silicon across a boundary region, as opposed to an interface where there is an abrupt drop in nitrogen concentration at the boundary, can result in significantly different numbers of certain important carrier trap.

  2. Studies of pure and nitrogen-incorporated hydrogenated amorphous carbon thin films and their possible application for amorphous silicon solar cells

    SciTech Connect

    Dwivedi, Neeraj; Kumar, Sushil; Malik, Hitendra K.

    2012-01-01

    Hydrogenated amorphous carbon (a-C:H) and nitrogen-incorporated a-C:H (a-C:N:H) thin films were deposited using radio frequency-plasma-enhanced chemical vapor deposition technique and studied for their electrical, optical, and nano-mechanical properties. Introduction of nitrogen and increase of self bias enhanced the conductivity of a-C:H and a-C:N:H films, whereas current-voltage measurement reveals heterojunction formation due to their rectifying behavior. The bandgap of these films was changed over wide range from 1.9 eV to 3.45 eV by varying self bias and the nitrogen incorporation. Further, activation energy was correlated with the electronic structure of a-C:H and a-C:N:H films, and conductivity was discussed as a function of bandgap. Moreover, a-C:N:H films exhibited high hardness and elastic modulus, with maximum values as 42 GPa and 430 GPa, respectively, at -100 V. Observed fascinating electrical, optical, and nano-mechanical properties made it a material of great utility in the development of optoelectronic devices, such as solar cells. In addition, we also performed simulation study for an a-Si:H solar cell, considering a-C:H and C:N:H as window layers, and compared their performance with the a-Si:H solar cell having a-SiC:H as window layer. We also proposed several structures for the development of a near full-spectrum solar cell. Moreover, due to high hardness, a-C:N:H films can be used as a protective and encapsulate layer on solar cells, especially in n-i-p configuration on metal substrate. Nevertheless, a-C:H and a-C:N:H as a window layer can avoid the use of additional hard and protective coating and, hence, minimize the cost of the product.

  3. One-Pot Approach to Organo-Phosphorus-Chalcogen Macrocycles Incorporating Double OP(S)SCn or OP(Se)SeCn Scaffolds: A Synthetic and Structural Study.

    PubMed

    Hua, Guoxiong; Du, Junyi; Slawin, Alexandra M Z; Woollins, J Derek

    2016-06-01

    The development of new methodology for the preparation of functional macrocycles with practical applications is an important research area in macromolecular science. In this study, we report a new one-pot route for the synthesis of a series of macro-heterocycles by incorporating two phosphorus atoms and two chalcogen atoms and two oxygen atoms (double OP(S)SCn or OP(Se)SeCn scaffolds). The three-component condensation reactions of 2,4-diferrocenyl-1,3,2,4-diathiadiphosphetane 2,4-disulfide (FcLR, a ferrocene analogue of Lawesson's reagent) or 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (LR, Lawesson's reagent), or 2,4-diphenyl-1,3,2,4-diselenadiphosphetane 2,4-diselenide (WR, Woollins' reagent), disodium alkenyl-diols, and dihalogenated alkanes are performed, giving rise to soluble and air or moisture-stable macrocycles in good-to-excellent yields (up to 92 %). This is the first systemically preparative and readily scalable example of one-pot ring opening/ring extending reaction of three-components to prepare phosphorus-chalcogen containing macrocycles. We also provide a systematic crystallographic study. PMID:27112964

  4. Chalcogenization-Derived Band Gap Grading in Solution-Processed CuIn(x)Ga(1-x)(Se,S)₂ Thin-Film Solar Cells.

    PubMed

    Park, Se Jin; Jeon, Hyo Sang; Cho, Jin Woo; Hwang, Yun Jeong; Park, Kyung Su; Shim, Hyeong Seop; Song, Jae Kyu; Cho, Yunae; Kim, Dong-Wook; Kim, Jihyun; Min, Byoung Koun

    2015-12-16

    Significant enhancement of solution-processed CuIn(x)Ga(1-x)(Se,S)2 (CIGSSe) thin-film solar cell performance was achieved by inducing a band gap gradient in the film thickness, which was triggered by the chalcogenization process. Specifically, after the preparation of an amorphous mixed oxide film of Cu, In, and Ga by a simple paste coating method chalcogenization under Se vapor, along with the flow of dilute H2S gas, resulted in the formation of CIGSSe films with graded composition distribution: S-rich top, In- and Se-rich middle, and Ga- and S-rich bottom. This uneven compositional distribution was confirmed to lead to a band gap gradient in the film, which may also be responsible for enhancement in the open circuit voltage and reduction in photocurrent loss, thus increasing the overall efficiency. The highest power conversion efficiency of 11.7% was achieved with J(sc) of 28.3 mA/cm(2), V(oc) of 601 mV, and FF of 68.6%. PMID:26595379

  5. Chalcogen-bonded complexes. Selenium-bound adducts of NH3, H2O, PH3, and H2S with OCSe, SCSe, and CSe2.

    PubMed

    Ramasami, Ponnadurai; Ford, Thomas A

    2015-02-01

    Recent ab initio investigations of some complexes formed between carbon dioxide and its analogues carbonyl sulfide, carbonyl selenide, carbon disulfide, and thiocarbonyl selenide and the common bases ammonia, water, phosphine, and hydrogen sulfide have revealed significant differences between the properties of those complexes bound through the oxygen atom of the electron acceptor and their counterparts in which the interaction takes place through a sulfur atom. In each case the interaction is weak, but the structures, interaction energies, and vibrational spectra of the complexes show some regular variations in behavior as the base and the acid are systematically changed. The adducts bound through sulfur present examples of the type of non-covalent interaction known as the chalcogen bond. In this paper we extend the range of electron acceptors to include carbon diselenide, and we explore the effects of substituting selenium for sulfur as the acceptor atom in the complexes of OCSe, SCSe, and CSe2. These adducts are also classified as chalcogen-bonded complexes, and have many features in common with the sulfur-bonded species, but also exhibit some noticeable differences between the two series. PMID:25644370

  6. Partial re-equilibration of highly siderophile elements and the chalcogens in the mantle: A case study on the Baldissero and Balmuccia peridotite massifs (Ivrea Zone, Italian Alps)

    NASA Astrophysics Data System (ADS)

    Wang, Zaicong; Becker, Harry; Gawronski, Timo

    2013-05-01

    The conditions at which melt percolation and reactive infiltration of depleted mantle peridotites fractionate highly siderophile elements (HSE) and cause re-equilibration of 187Os/188Os in mantle rocks are still poorly constrained. In a comparative study of the Paleozoic Balmuccia (BM) and Baldissero (BD) peridotite tectonites (Ivrea-Verbano Zone, Northern Italy), the influence of partial melting and melt infiltration on abundances of HSE, chalcogens (S, Se and Te) and 187Os/188Os have been studied. At BM, Re depletion ages (TRD) of lherzolites and replacive dunites display a uniform distribution with a maximum near 400-500 Ma. BD peridotites also display a Paleozoic distribution peak but a significant number of samples yielded Proterozoic TRD. The predominance of Paleozoic Re depletion ages in both bodies is consistent with Sm-Nd ages and the late Paleozoic magmatic and geodynamic evolution of the Ivrea-Verbano Zone. The different extents of preservation of ancient 187Os/188Os in BM and BD peridotites are interpreted to reflect different degrees of isotopic homogenization and chemical re-equilibration with incompatible element-depleted infiltrating melt during the Paleozoic. The differences between the two bodies are also reflected by differences in HSE and chalcogen abundances, with BD displaying large scatter among HSE patterns, slight re-enrichment of Re relative to Au, and linear trends of Pd, Se and Te with Al2O3. The differences in distributions of model ages and heterogeneity in HSE abundances support the view that the lithophile element, HSE and chalcogen variations of different suites of lherzolites likely reflect different extents of reactive melt infiltration in mantle peridotites, with partial re-equilibration and melt extraction in open system environments. However, the variable re-equilibration of BM and BD lherzolites apparently did not produce significant differences in HSE ratios such as Os/Ir, Ru/Ir, Rh/Ir, and Pd/Pt, which are in the range of

  7. Metallization of Large Silicon Wafers

    NASA Technical Reports Server (NTRS)

    Pryor, R. A.

    1978-01-01

    A metallization scheme was developed which allows selective plating of silicon solar cell surfaces. The system is comprised of three layers. Palladium, through the formation of palladium silicide at 300 C in nitrogen, makes ohmic contact to the silicon surface. Nickel, plated on top of the palladium silicide layer, forms a solderable interface. Lead-tin solder on the nickel provides conductivity and allows a convenient means for interconnection of cells. To apply this metallization, three chemical plating baths are employed.

  8. Silicon integrated microsensor incorporating a metal-doped phthalocyanine organic semiconductor used to selectively detect nitrogen dioxide and an organophosphorus compound

    NASA Astrophysics Data System (ADS)

    Kolesar, Edward S., Jr.; Wiseman, John M.

    1996-09-01

    A novel gas-sensitive microsensor, whose design is based upon the interdigitated-gate-electrode field-effect transistor was realized by integrating it with ia selectively-deposited, chemically-active, electron-beam evaporated copper phthalocyanine (CuPc) thin film. When isothermally operated at 150 degrees C, the microsensor can selectively and reversibly detect parts-per-billion (ppb) concentration levels of two environmentally-sensitive pollutants, nitrogen dioxide (NO2) and diisopropyl methylphosphonate (DIMP). Although the CuPc thin film chemically and electrically interacts with NO2 and DIMP, just as it will likely interact with other electrically- active gases, or combinations thereof, the selectivity feature of the microsensor was established by operating it with a 5-V peak amplitude, 2-microsecond(s) duration, 1000 Hz repetition frequency pulse, and then analyzing its time- and frequency-domain responses. As a direct consequence of this analysis, the envelopes associated with the normalized- difference Fourier transform magnitude frequency spectra reveal features which unambiguously distinguish the NO2 and DIMP challenge gas responses. Furthermore, the area beneath each response envelope may correspondingly be interpreted as a metric for the microsensor's sensitivity to a specific challenge gas concentration. Scanning electron microscopy was used to characterize the CuPc thin film's morphology. Additionally, infrared spectroscopy was employed to verify the (alpha) - and (beta) -phases of the sublimed CuPc thin films and to study the NO2- and DIMP-CuPc interactions.

  9. Control of silicon nanoparticle size embedded in silicon oxynitride dielectric matrix

    SciTech Connect

    Ehrhardt, F.; Ferblantier, G.; Muller, D.; Slaoui, A.; Ulhaq-Bouillet, C.; Rinnert, H.

    2013-07-21

    In this study, silicon rich silicon oxynitride layers containing more than 15% nitrogen were deposited by electron cyclotron resonance assisted plasma enhanced vapor deposition in order to form silicon nanoparticles after a high temperature thermal annealing. The effect of the flows of the precursor gases on the composition and the structural properties of the layers was assessed by Rutherford backscattering spectroscopy, elastic recoil detection analysis, and infrared spectroscopic measurements. The morphological and crystallinity properties were investigated by energy filtered transmission electron microscopy and Raman spectroscopy. We show that the excess of silicon in the silicon oxynitride layer controls the silicon nanoparticles size. On the other hand, the crystalline fraction of particles is found to be strongly correlated to the nanoparticle size. Finally, the photoluminescence measurements show that it is also possible to tune the photoluminescence peak position between 400 and 800 nm and its intensity by changing the silicon excess in the silicon rich silicon oxynitride matrix.

  10. Silicon on sapphire for ion implantation studies

    NASA Technical Reports Server (NTRS)

    Pisciotta, B. P.

    1974-01-01

    Van der Pauw or bridge samples are ultrasonically cut from silicon on sapphire wafers. Contact pad regions are implanted with moderately heavy dose of ions. Ion of interest is implanted into sample; and, before being annealed in vacuum, sample is sealed with sputtered layer of silicon dioxide. Nickel or aluminum is sputtered onto contact pad areas and is sintered in nitrogen atmosphere.

  11. 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.

  12. Molybdenum enhanced low-temperature deposition of crystalline silicon nitride

    SciTech Connect

    Lowden, Richard A.

    1994-01-01

    A process for chemical vapor deposition of crystalline silicon nitride which comprises the steps of: introducing a mixture of a silicon source, a molybdenum source, a nitrogen source, and a hydrogen source into a vessel containing a suitable substrate; and thermally decomposing the mixture to deposit onto the substrate a coating comprising crystalline silicon nitride containing a dispersion of molybdenum silicide.

  13. Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites

    SciTech Connect

    Ranmohotti, K.G. Sanjaya; Montasserasadi, M. Dariush; Choi, Jonglak; Yao, Yuan; Mohanty, Debasish; Josepha, Elisha A.; Adireddy, Shiva; Caruntu, Gabriel; Wiley, John B.

    2012-06-15

    Highlights: ► Topochemical reactions involving intercalation allow construction of metal chalcogenide arrays within perovskite hosts. ► Gaseous chalcogen hydrides serve as effect reactants for intercalation of sulfur and selenium. ► New compounds prepared by a two-step intercalation strategy are presented. -- Abstract: A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb{sub 2}O{sub 7}, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb{sub 2}LaNb{sub 2}O{sub 7}. This compound is then reacted at room-temperature with in situ generated H{sub 2}S gas to create Rb-S layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) Å, c = 15.256(1) Å; space group P4/mmm) shows the compound to be isostructural with (Rb{sub 2}Cl)LaNb{sub 2}O{sub 7} where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (∼0.8) of the product indicate a higher sulfur content than expected for S{sup 2−} alone. This combined with the Raman studies, which show evidence for an H-S stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H{sub 2}Se{sub (g)} were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.

  14. Partitioning of platinum-group elements (PGE) and chalcogens (Se, Te, As, Sb, Bi) between monosulfide-solid solution (MSS), intermediate solid solution (ISS) and sulfide liquid at controlled fO2-fS2 conditions

    NASA Astrophysics Data System (ADS)

    Liu, Yanan; Brenan, James

    2015-06-01

    In order to better understand the behavior of highly siderophile elements (HSEs: Os, Ir, Ru, Rh, Pt, Pd, Au, Re), Ag, Pb and chalcogens (As, Se, Sb, Te and Bi) during the solidification of sulfide magmas, we have conducted a series of experiments to measure partition coefficients (D values) between monosulfide solid solution (MSS) and sulfide melt, as well as MSS and intermediate solid solution (ISS), at 0.1 MPa and 860-926 °C, log fS2 -3.0 to -2.2 (similar to the Pt-PtS buffer), with fO2 controlled at the fayalite-magnetite-quartz (FMQ) buffer. The IPGEs (Os, Ir, Ru), Rh and Re are found to be compatible in MSS relative to sulfide melt with D values ranging from ∼20 to ∼5, and DRe/DOs of ∼0.5. Pd, Pt, Au, Ag, Pb, as well as the chalcogens, are incompatible in MSS, with D values ranging from ∼0.1 to ∼1 × 10-3. For the same metal/sulfur ratio, D values for the IPGEs, Rh and Re are systematically larger than most past studies, correlating with higher oxygen content in the sulfide liquid, reflecting the significant effect of oxygen on increasing the activity coefficients for these elements in the melt phase. MSS/ISS partitioning experiments reveal that Ru, Os, Ir, Rh and Re are partitioned into MSS by a factor of >50, whereas Pd, Pt, Ag, Au and the chalcogens partition from weakly (Se, As) to strongly (Ag, Au) into ISS. Uniformly low MSS- and ISS- melt partition coefficients for the chalcogens, Pt, Pd, Ag and Au will lead to enrichment in the residual sulfide liquid, but D values are generally too large to reach early saturation in Pt-Pd-chalcogen-rich accessory minerals, based on current solubility estimates. Instead, these phases likely precipitate at the last dregs of crystallization. Modeled evolution curves for the PGEs and chalcogens are in reasonably good agreement with whole-rock sulfide compositions for the McCreedy East deposit (Sudbury, Ontario), consistent with an origin by crystallization of MSS, then MSS + ISS from sulfide magma.

  15. Cryostable lightweight frit bonded silicon mirror

    NASA Astrophysics Data System (ADS)

    Anthony, F.; McCarter, D.; Tangedahl, M.; Content, D.

    The excellent polishability, low density and relatively high stiffness of silicon make it an attractive candidate for optical applications that require superior performance. Assembly of silicon details by means of glass frit bonding permits significant light weighting thus enhancing the benefit of silicon mirrors. To demonstrate the performance potential, a small lightweight glass frit bonded silicon mirror was fabricated and tested for cryoability. The test mirror was 12.5cm in diameter with a 60cm spherical radius and a maximum thickness, at the perimeter, of 2.5cm. A machined silicon core was used to stiffen the two face sheets of the silicon sandwich. These three elements were assembled, by glass frit bonding, to form the substrate that was polished. The experimental evaluation in a liquid nitrogen cryostat, demonstrated cryostability performance significantly better than required by the mirror specification. Key WordsCryostable, Lightweight, Silicon, Frit Bond, Spherical, Mirror

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

    NASA Technical Reports Server (NTRS)

    1971-01-01

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

  17. Fractionation of highly siderophile and chalcogen elements during magma transport in the mantle: Constraints from pyroxenites of the Balmuccia peridotite massif

    NASA Astrophysics Data System (ADS)

    Wang, Zaicong; Becker, Harry

    2015-06-01

    Sulfide segregation from sulfur saturated basic magmas affects the compositions of chalcophile elements such as the highly siderophile elements (HSE) and the chalcogens S, Se, Te to variable extent. Whether this process predominantly occurs in the lower crust or in the mantle and how segregation of liquid sulfide and accumulation affects concentrations and ratios of these elements at different mantle depths and in presumed primitive basic magmas remains uncertain. Abundances of the HSE, S, Se and Te and Os isotopes in websterites and spinel clinopyroxenites of the Balmuccia peridotite massif (Ivrea-Verbano Zone, Italian Alps) provide new insight on sulfide segregation and the compositional change of melt and peridotite during magma transport in the mantle. Balmuccia websterites and clinopyroxenites formed from late Paleozoic and Mesozoic melt influx into stretched continental lithospheric mantle of the Ivrea-Verbano Zone, respectively. The HSE and chalcogen element compositions of websterites and clinopyroxenites reflect the segregation and accumulation of sulfide melt from S saturated silicate melts with different abundances and ratios of chalcogens and the HSE. The pyroxenites display large variations in abundances of the platinum group elements (PGE) and Te whereas abundances of less chalcophile elements S, Se and Re are much less variable. The fractionation between the PGE and fractionation of Re/Os, S/Se and Se/Te in the mantle pyroxenites are consistent with sulfide melt-silicate melt partitioning with a sequence of apparent coefficients of DPGE > DAu ⩾ DTe > DSe ⩾ DS ≈ DRe. Concentrations in ocean ridge basalts and in gabbros of the lower oceanic crust are also consistent with such fractionation. Websterites which have formed during refertilization of depleted peridotites display ratios of the HSE and moderately suprachondritic initial 187Os/188Os similar to interstitial sulfides of refertilized peridotites. These compositions are different from

  18. Benzodipyrrolidone (BDP)-based polymer semiconductors containing a series of chalcogen atoms: comprehensive investigation of the effect of heteroaromatic blocks on intrinsic semiconducting properties.

    PubMed

    Lee, Kyu Cheol; Park, Won-Tae; Noh, Yong-Young; Yang, Changduk

    2014-04-01

    In order to determine the effects of actual 'chalcogen atoms' on semiconducting properties for application in a variety of optoelectronic devices, a class of donor (D)-acceptor (A) polymer semiconductors, namely PBDP-Fu, PBDP-Th, and PBDP-Se, containing the recently formulated benzodipyrrolidone (BDP) accepting unit and furan (Fu), thiophene (Th), or selenophene (Se) as a donating unit has been synthesized, characterized, and used in an active layer of organic field-effect transistors (OFETs). With the LUMO levels being comparatively consistent for all three polymers (-3.58 to -3.60 eV) due to the dominant BDP contribution to the polymer backbone, the HOMO energies are somewhat sensitive to the structurally distinctive feature of the donor counits used. Utilizing a combination of X-ray diffraction (XRD) and atomic force microscopy (AFM), it is apparent that further crystalline domains occur with edge-on orientation for the polymers (PBDP-Th and PBDP-Se) with relatively heavier chalcogen atoms such as Th and Se, compared with PBDP-Fu which has a rather amorphous nature. Investigation of their OFET performance indicates that all the polymers show well balanced ambipolar operations. The desirable morphological structures of both the PBDP-Th and PBDP-Se result in higher mobilities in OFETs than those of PBDP-Fu. In particular, 200 °C annealed PBDP-Se OFETs results in ambipolarity being mobile for both holes of up to 1.7 × 10(-2) cm(2)/V·s and electrodes of up to 1.9 × 10(-2) cm(2)/V·s. In addition, OFETs with PBDP-Th show nearly equivalent charge carrier mobilities for both holes (μ(h) = 1.2 × 10(-2) cm(2)/V·s) and electrons (μ(e) = 1.1 × 10(-2) cm(2)/V·s). Consequently, we systematically demonstrate how the manipulation of existing heteroaromatics can modulate the electronic properties of conjugated D-A polymers, elucidating structure-property relationships that are desirable for the rational design of next generation materials. PMID:24620709

  19. Nitrogen Index

    Technology Transfer Automated Retrieval System (TEKTRAN)

    There is a need to improve the management of nitrogen inputs to agricultural systems because they increase the potential for losses of reactive nitrogen to the environment, resulting in negative impacts to water and air resources. There is a need to reduce nitrate leaching, emissions of N2O from agr...

  20. Cryostable lightweight frit-bonded silicon mirror

    NASA Astrophysics Data System (ADS)

    Anthony, Frank M.; McCarter, Douglas R.; Tangedahl, Matt; Content, David A.

    2002-11-01

    The excellent polishability, low density and relatively high stiffness of silicon make it an attractive candidate for optical applications that require superior performance. Assembly of silicon details by means of glass frit bonding permits significant weight reduction thus enhancing the benefit of silicon mirrors. To demonstrate the performance potential, a small lightweight glass frit bonded silicon mirror was fabricated and tested for cryostability. The test mirror was 12.5cm in diameter with a 60cm spherical radius and a maximum thickness, at the perimeter, of 2.5cm. A machined silicon core was used to stiffen the two face sheets of the silicon sandwich. These three elements were assembled, by glass frit bonding, to form the substrate that was polished. The experimental evaluation, in a liquid nitrogen cryostat, demonstrated cryostability performance significantly better than required by the mirror specification.

  1. Silicon Nitride Equation of State

    NASA Astrophysics Data System (ADS)

    Swaminathan, Pazhayannur; Brown, Robert

    2015-06-01

    This report presents the development a global, multi-phase equation of state (EOS) for the ceramic silicon nitride (Si3N4) . Structural forms include amorphous silicon nitride normally used as a thin film and three crystalline polymorphs. Crystalline phases include hexagonal α-Si3N4, hexagonalβ-Si3N4, and the cubic spinel c-Si3N4. Decomposition at about 1900 °C results in a liquid silicon phase and gas phase products such as molecular nitrogen, atomic nitrogen, and atomic silicon. The silicon nitride EOS was developed using EOSPro which is a new and extended version of the PANDA II code. Both codes are valuable tools and have been used successfully for a variety of material classes. Both PANDA II and EOSPro can generate a tabular EOS that can be used in conjunction with hydrocodes. The paper describes the development efforts for the component solid phases and presents results obtained using the EOSPro phase transition model to investigate the solid-solid phase transitions in relation to the available shock data. Furthermore, the EOSPro mixture model is used to develop a model for the decomposition products and then combined with the single component solid models to study the global phase diagram. Sponsored by the NASA Goddard Space Flight Center Living With a Star program office.

  2. Tetrel, chalcogen, and CH⋅⋅O hydrogen bonds in complexes pairing carbonyl-containing molecules with 1, 2, and 3 molecules of CO{sub 2}

    SciTech Connect

    Azofra, Luis M.; Scheiner, Steve

    2015-01-21

    The complexes formed by H{sub 2}CO, CH{sub 3}CHO, and (CH{sub 3}){sub 2}CO with 1, 2, and 3 molecules of CO{sub 2} are studied by ab initio calculations. Three different types of heterodimers are observed, most containing a tetrel bond to the C atom of CO{sub 2}, and some supplemented by a CH⋅⋅O H-bond. One type of heterodimer is stabilized by an anti-parallel arrangement of the C=O bonds of the two molecules. The binding energies are enhanced by methyl substitution on the carbonyl, and vary between 2.4 and 3.5 kcal/mol. Natural bond orbital analysis identifies a prime source of interaction as charge transfer into the π*(CO) antibonding orbital. Heterotrimers and tetramers carry over many of the geometrical and bonding features of the binary complexes, but also introduce O⋅⋅O chalcogen bonds. These larger complexes exhibit only small amounts of cooperativity.

  3. Application of copper(I) iodide/diorganoyl dichalcogenides to the synthesis of 4-organochalcogen isoquinolines by regioselective C-N and C-chalcogen bond formation.

    PubMed

    Stein, André L; Bilheri, Filipe N; da Rocha, Juliana T; Back, Davi F; Zeni, Gilson

    2012-08-20

    A copper-catalyzed cyclization of (ortho-alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4-organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4-position. The cyclization reaction was carried out by using CuI (20 %) as a catalyst with diorganoyl dichalcogenides (1.5 equiv) in the presence of DMF at 100 °C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho-alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six-membered heterocyclic ring exclusively through a 6-endo-dig cyclization process. The organochalcogen group present at the 4-position of the isoquinoline ring was further subjected to a selective chalcogen-lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C-C bond formation. PMID:22807116

  4. Production of electronic grade lunar silicon by disproportionation of silicon difluoride

    NASA Astrophysics Data System (ADS)

    Agosto, William N.

    1993-03-01

    Waldron has proposed to extract lunar silicon by sodium reduction of sodium fluorosilicate derived from reacting sodium fluoride with lunar silicon tetrafluoride. Silicon tetrafluoride is obtained by the action of hydrofluoric acid on lunar silicates. While these reactions are well understood, the resulting lunar silicon is not likely to meet electronic specifications of 5 nines purity. Dale and Margrave have shown that silicon difluoride can be obtained by the action of silicon tetrafluoride on elemental silicon at elevated temperatures (1100-1200 C) and low pressures (1-2 torr). The resulting silicon difluoride will then spontaneously disproportionate into hyperpure silicon and silicon tetrafluoride in vacuum at approximately 400 C. On its own merits, silicon difluoride polymerizes into a tough waxy solid in the temperature range from liquid nitrogen to about 100 C. It is the silicon analog of teflon. Silicon difluoride ignites in moist air but is stable under lunar surface conditions and may prove to be a valuable industrial material that is largely lunar derived for lunar surface applications. The most effective driver for lunar industrialization may be the prospects for industrial space solar power systems in orbit or on the moon that are built with lunar materials. Such systems would require large quantities of electronic grade silicon or compound semiconductors for photovoltaics and electronic controls. Since silicon is the most abundant semimetal in the silicate portion of any solar system rock (approximately 20 wt percent), lunar silicon production is bound to be an important process in such a solar power project. The lunar silicon extraction process is discussed.

  5. Production of electronic grade lunar silicon by disproportionation of silicon difluoride

    NASA Technical Reports Server (NTRS)

    Agosto, William N.

    1993-01-01

    Waldron has proposed to extract lunar silicon by sodium reduction of sodium fluorosilicate derived from reacting sodium fluoride with lunar silicon tetrafluoride. Silicon tetrafluoride is obtained by the action of hydrofluoric acid on lunar silicates. While these reactions are well understood, the resulting lunar silicon is not likely to meet electronic specifications of 5 nines purity. Dale and Margrave have shown that silicon difluoride can be obtained by the action of silicon tetrafluoride on elemental silicon at elevated temperatures (1100-1200 C) and low pressures (1-2 torr). The resulting silicon difluoride will then spontaneously disproportionate into hyperpure silicon and silicon tetrafluoride in vacuum at approximately 400 C. On its own merits, silicon difluoride polymerizes into a tough waxy solid in the temperature range from liquid nitrogen to about 100 C. It is the silicon analog of teflon. Silicon difluoride ignites in moist air but is stable under lunar surface conditions and may prove to be a valuable industrial material that is largely lunar derived for lunar surface applications. The most effective driver for lunar industrialization may be the prospects for industrial space solar power systems in orbit or on the moon that are built with lunar materials. Such systems would require large quantities of electronic grade silicon or compound semiconductors for photovoltaics and electronic controls. Since silicon is the most abundant semimetal in the silicate portion of any solar system rock (approximately 20 wt percent), lunar silicon production is bound to be an important process in such a solar power project. The lunar silicon extraction process is discussed.

  6. Selenium segregation in femtosecond-laser hyperdoped silicon revealed by electron tomography.

    PubMed

    Haberfehlner, Georg; Smith, Matthew J; Idrobo, Juan-Carlos; Auvert, Geoffroy; Sher, Meng-Ju; Winkler, Mark T; Mazur, Eric; Gambacorti, Narciso; Gradečak, Silvija; Bleuet, Pierre

    2013-06-01

    Doping of silicon with chalcogens (S, Se, Te) by femtosecond laser irradiation to concentrations well above the solubility limit leads to near-unity optical absorptance in the visible and infrared (IR) range and is a promising route toward silicon-based IR optoelectronics. However, open questions remain about the nature of the IR absorptance and in particular about the impact of the dopant distribution and possible role of dopant diffusion. Here we use electron tomography using a high-angle annular dark-field (HAADF) detector in a scanning transmission electron microscope (STEM) to extract information about the three-dimensional distribution of selenium dopants in silicon and correlate these findings with the optical properties of selenium-doped silicon. We quantify the tomography results to extract information about the size distribution and density of selenium precipitates. Our results show correlation between nanoscale distribution of dopants and the observed sub-band gap optical absorptance and demonstrate the feasibility of HAADF-STEM tomography for the investigation of dopant distribution in highly-doped semiconductors. PMID:23570747

  7. Sputtered silicon nitride coatings for wear protection

    NASA Technical Reports Server (NTRS)

    Grill, A.; Aron, P. R.

    1982-01-01

    Silicon nitride films were deposited by RF sputtering on 304 stainless steel substrates in a planar RF sputtering apparatus. The sputtering was performed from a Si3N4 target in a sputtering atmosphere of argon and nitrogen. The rate of deposition, the composition of the coatings, the surface microhardness and the adhesion of the coatings to the substrates were investigated as a function of the process parameters, such as: substrate target distance, fraction nitrogen in the sputtering atmosphere and sputtering pressure. Silicon rich coating was obtained for fraction nitrogen below 0.2. The rate of deposition decreases continuously with increasing fraction nitrogen and decreasing sputtering pressure. It was found that the adherence of the coatings improves with decreasing sputtering pressure, almost independently of their composition.

  8. Silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    Lau, Sai-Kwing (Inventor); Calandra, Salvatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    2001-01-01

    This invention relates to a process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  9. Nitrogen in germanium

    NASA Astrophysics Data System (ADS)

    Chambouleyron, I.; Zanatta, A. R.

    1998-07-01

    The known properties of nitrogen as an impurity in, and as an alloy element of, the germanium network are reviewed in this article. Amorphous and crystalline germanium-nitrogen alloys are interesting materials with potential applications for protective coatings and window layers for solar conversion devices. They may also act as effective diffusion masks for III-V electronic devices. The existing data are compared with similar properties of other group IV nitrides, in particular with silicon nitride. To a certain extent, the general picture mirrors the one found in Si-N systems, as expected from the similar valence structure of both elemental semiconductors. However, important differences appear in the deposition methods and alloy composition, the optical properties of as grown films, and the electrical behavior of nitrogen-doped amorphous layers. Structural studies are reviewed, including band structure calculations and the energies of nitrogen-related defects, which are compared with experimental data. Many important aspects of the electronic structure of Ge-N alloys are not yet completely understood and deserve a more careful investigation, in particular the structure of defects associated with N inclusion. The N doping of the a-Ge:H network appears to be very effective, the activation energy of the most effectively doped samples becoming around 120 meV. This is not the case with N-doped a-Si:H, the reasons for the difference remaining an open question. The lack of data on stoichiometric β-Ge3N4 prevents any reasonable assessment on the possible uses of the alloy in electronic and ceramic applications.

  10. The Nature of the Chemical Bond in Linear Three-Body Systems: From I3− to Mixed Chalcogen/Halogen and Trichalcogen Moieties

    PubMed Central

    Aragoni, M. Carla; Arca, Massimiliano; Devillanova, Francesco A.; Garau, Alessandra; Isaia, Francesco; Lippolis, Vito; Mancini, Annalisa

    2007-01-01

    The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3− and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I3− anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom. PMID:18389065

  11. Molybdenum enhanced low-temperature deposition of crystalline silicon nitride

    DOEpatents

    Lowden, R.A.

    1994-04-05

    A process for chemical vapor deposition of crystalline silicon nitride is described which comprises the steps of: introducing a mixture of a silicon source, a molybdenum source, a nitrogen source, and a hydrogen source into a vessel containing a suitable substrate; and thermally decomposing the mixture to deposit onto the substrate a coating comprising crystalline silicon nitride containing a dispersion of molybdenum silicide. 5 figures.

  12. Nitrogen species

    NASA Astrophysics Data System (ADS)

    Harries, J. E.; Brasseur, G.; Coffey, M. T.; Fischer, H.; Gille, J.; Jones, R.; Louisnard, N.; McCormick, M. P.; Noxon, J.; Owens, A. J.

    Total odd nitrogen, NO(y), may be defined as the sum of all active nitrogen species that interchange photochemically with one another on a time scale of the order of weeks or less. As noted, NO + NO2 reactions dominate the processes controlling the ozone balance in the contemporary stratosphere. The observational data from non-satellite platforms are reviewed. The growth in available satellite data in the past four years is considered. Some of the most important scientific issues are discussed, taking into account new results from atmospheric models (mainly 2-D). The model results are compared with the observational data.

  13. Nitrogen species

    NASA Technical Reports Server (NTRS)

    Harries, J. E.; Brasseur, G.; Coffey, M. T.; Fischer, H.; Gille, J.; Jones, R.; Louisnard, N.; Mccormick, M. P.; Noxon, J.; Owens, A. J.

    1985-01-01

    Total odd nitrogen, NO(y), may be defined as the sum of all active nitrogen species that interchange photochemically with one another on a time scale of the order of weeks or less. As noted, NO + NO2 reactions dominate the processes controlling the ozone balance in the contemporary stratosphere. The observational data from non-satellite platforms are reviewed. The growth in available satellite data in the past four years is considered. Some of the most important scientific issues are discussed, taking into account new results from atmospheric models (mainly 2-D). The model results are compared with the observational data.

  14. Nitrogen dioxide

    Integrated Risk Information System (IRIS)

    Nitrogen dioxide ; CASRN 10102 - 44 - 0 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogeni

  15. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    SciTech Connect

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show that the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.

  16. Method of densifying an article formed of reaction bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Mangels, John A. (Inventor)

    1982-01-01

    A method of densifying an article formed of reaction bonded silicon nitride is disclosed. The reaction bonded silicon nitride article is packed in a packing mixture consisting of silicon nitride powder and a densification aid. The reaction bonded silicon nitride article and packing powder are sujected to a positive, low pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause any open porosity originally found in the reaction bonded silicon nitride article to be substantially closed. Thereafter, the reaction bonded silicon nitride article and packing powder are subjected to a positive high pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause a sintering of the reaction bonded silicon nitride article whereby the strength of the reaction bonded silicon nitride article is increased.

  17. Nitridation of silicon /111/ - Auger and LEED results

    NASA Technical Reports Server (NTRS)

    Delord, J. F.; Schrott, A. G.; Fain, S. C., Jr.

    1980-01-01

    Clean silicon (111) (7x7) surfaces at up to 1050 C have been reacted with nitrogen ions and neutrals produced by a low energy ion gun. The LEED patterns observed are similar to those previously reported for reaction of silicon (111) (7x7) with NH3. The nitrogen KLL peak exhibits no shift or change in shape with nitride growth. At the same time the magnitude of the elemental silicon LVV peak at 92 eV decreases progressively as a new peak at 84 eV increases. The position of both peaks appears to be independent of the degree of nitridation. Since the Auger spectra are free of oxygen and other impurities, these features can be attributed only to silicon, nitrogen, and their reaction products. Characteristic features of the Auger spectra are related to LEED observations and to the growth of microcrystals of Si3N4.

  18. Deposition of reactively ion beam sputtered silicon nitride coatings

    NASA Technical Reports Server (NTRS)

    Grill, A.

    1982-01-01

    An ion beam source was used to deposit silicon nitride films by reactively sputtering a silicon target with beams of Ar + N2 mixtures. The nitrogen fraction in the sputtering gas was 0.05 to 0.80 at a total pressure of 6 to 2 millionth torr. The ion beam current was 50 mA at 500 V. The composition of the deposited films was investigated by auger electron spectroscopy and the rate of deposition was determined by interferometry. A relatively low rate of deposition of about 2 nm. one-tenth min. was found. AES spectra of films obtained with nitrogen fractions higher than 0.50 were consistent with a silicon to nitrogen ratio corresponding to Si3N4. However the AES spectra also indicated that the sputtered silicon nitride films were contaminated with oxygen and carbon and contained significant amounts of iron, nickel, and chromium, most probably sputtered from the holder of the substrate and target.

  19. Corrosion of silicon nitride in high temperature alkaline solutions

    NASA Astrophysics Data System (ADS)

    Qiu, Liyan; Guzonas, Dave A.; Qian, Jing

    2016-08-01

    The corrosion of silicon nitride (Si3N4) in alkaline solutions was studied at temperatures from 60 to 300 °C. Si3N4 experienced significant corrosion above 100 °C. The release rates of silicon and nitrogen follow zero order reaction kinetics and increase with increasing temperature. The molar ratio of dissolved silicon and nitrogen species in the high temperature solutions is the same as that in the solid phase (congruent dissolution). The activation energy for silicon and nitrogen release rates is 75 kJ/mol which agrees well with that of silica dissolution. At 300 °C, the release of aluminum is observed and follows first order reaction kinetics while other minor constituents including Ti and Y are highly enriched on the corrosion films due to the low solubility of their oxides.

  20. Prokaryotic silicon utilizing microorganisms in the biosphere

    NASA Astrophysics Data System (ADS)

    Gupta, D.; Das, S.

    2012-12-01

    Although a little study has been done to determine the silicon utilizing prokaryotes, our previous experiments indicated that almost all Gram-positive bacteria are silicon utilizing; one of them, Streptococci survived exposure on the lunar surface for a long period in experiment done by others. Our initial experiments with these Gram positive microorganisms showed that there were limited growths of these microorganisms on carbon free silicate medium probably with the help of some carry over carbon and nitrogen during cultivation procedures. However, increase in growth rate after repeated subcultures could not be explained at present. The main groups of prokaryotes which were found silicon utilizing microorganisms were Mycobacterium, Bacillus, Nocardia, Streptomyces, Staphylococcus, Streptococcus, Lactobacillus, and Clostridium. In a another previous study by us when silicon level was studied in such grown up cells on carbon "free" silicate medium by electron prove microanalyser, it was found that silicon in cells grown on carbon "free" silicate medium was much higher (24.9%) than those grown on conventional carbon based medium (0.84%). However, these initial findings are encouraging for our future application of this group of organisms on extraterrestrial surfaces for artificial micro-ecosystem formation. It was found that when electropositive elements are less in extraterrestrial situation, then polymerization of silicon-oxygen profusion may occur easily, particularly in carbon and nitrogen paucity in the rocky worlds of the Universe.

  1. Silicon microdosimetry.

    PubMed

    Agosteo, Stefano; Pola, Andrea

    2011-02-01

    Silicon detectors are being studied as microdosemeters since they can provide sensitive volumes of micrometric dimensions. They can be applied for assessing single-event effects in electronic instrumentation exposed to complex fields around high-energy accelerators or in space missions. When coupled to tissue-equivalent converters, they can be used for measuring the quality of radiation therapy beams or for dosimetry. The use of micrometric volumes avoids the contribution of wall effects to the measured spectra. Further advantages of such detectors are their compactness, cheapness, transportability and a low sensitivity to vibrations. The following problems need to be solved when silicon devices are used for microdosimetry: (i) the sensitive volume has to be confined in a region of well-known dimensions; (ii) the electric noise limits the minimum detectable energy; (iii) corrections for tissue-equivalency should be made; (iv) corrections for shape equivalency should be made when referring to a spherical simulated site of tissue; (v) the angular response should be evaluated carefully; (vi) the efficiency of a single detector of micrometric dimensions is very poor and detector arrays should be considered. Several devices have been proposed as silicon microdosemeters, based on different technologies (telescope detectors, silicon on insulator detectors and arrays of cylindrical p-n junctions with internal amplification), in order to satisfy the issues mentioned above. PMID:21112892

  2. Synthesis of silicon nitride films by ion beam enhanced deposition

    NASA Astrophysics Data System (ADS)

    Xianghuai, Liu; Bin, Xue; Zhihong, Zheng; Zuyao, Zhou; Shichang, Zou

    1989-03-01

    Silicon nitride films with stoichiometric ratio of Si 3N 4 have been synthesized by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions. The results show that the component ratio of nitrogen to silicon in IBED silicon nitride films can be controlled and predicted by the atomic arrival rate ratio of nitrogen to silicon. IR measurement shows that the characteristic absorption peak of IBED Si 3N 4 is located at a wavenumber of 840 cm -1. The refractive index ranges from 2.2 to 2.6. RBS, AES, TEM, SEM, ED and spreading resistance measurement were used for investigation of the depth profiles of composition and structure of silicon nitride films synthesized by IBED. An intermixed layer is formed at the interface by the knock on effect, and a silicon enriched layer is observed at the surface region of the film. Normally the films were found to be amorphous, but electron diffraction patterns taken from deposited layer showed a certain crystallinity. The silicon nitride films prepared by IBED have dramatically less oxygen content than that formed by non-ion-assisted deposition.

  3. Silicon surface passivation by silicon nitride deposition

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.

    1984-01-01

    Silicon nitride deposition was studied as a method of passivation for silicon solar cell surfaces. The following three objectives were the thrust of the research: (1) the use of pecvd silicon nitride for passivation of silicon surfaces; (2) measurement techniques for surface recombination velocity; and (3) the importance of surface passivation to high efficiency solar cells.

  4. PECVD silicon-rich nitride and low stress nitride films mechanical characterization using membrane point load deflection

    NASA Astrophysics Data System (ADS)

    Bagolini, Alvise; Picciotto, Antonino; Crivellari, Michele; Conci, Paolo; Bellutti, Pierluigi

    2016-02-01

    An analysis of the mechanical properties of plasma enhanced chemical vapor (PECVD) silicon nitrides is presented, using micro fabricated silicon nitride membranes under point load deflection. The membranes are made of PECVD silicon-rich nitride and low stress nitride films. The mechanical performance of the bended membranes is examined both with analytical models and finite element simulation in order to extract the elastic modulus and residual stress values. The elastic modulus of low stress silicon nitride is calculated using stress free analytical models, while for silicon-rich silicon nitride and annealed low stress silicon nitride it is estimated with a pre-stressed model of point-load deflection. The effect of annealing both in nitrogen and hydrogen atmosphere is evaluated in terms of residual stress, refractive index and thickness variation. It is demonstrated that a hydrogen rich annealing atmosphere induces very little change in low stress silicon nitride. Nitrogen annealing effects are measured and shown to be much higher in silicon-rich nitride than in low stress silicon nitride. An estimate of PECVD silicon-rich nitride elastic modulus is obtained in the range between 240-320 GPa for deposited samples and 390 GPa for samples annealed in nitrogen atmosphere. PECVD low stress silicon nitride elastic modulus is estimated to be 88 GPa as deposited and 320 GPa after nitrogen annealing.

  5. The Effect of Polymer Char on Nitridation Kinetics of Silicon

    NASA Technical Reports Server (NTRS)

    Chan, Rickmond C.; Bhatt, Ramakrishna T.

    1994-01-01

    Effects of polymer char on nitridation kinetics of attrition milled silicon powder have been investigated from 1200 to 1350 C. Results indicate that at and above 1250 C, the silicon compacts containing 3.5 wt percent polymer char were fully converted to Si3N4 after 24 hr exposure in nitrogen. In contrast, the silicon compacts without polymer char could not be fully converted to Si3N4 at 1350 C under similar exposure conditions. At 1250 and 1350 C, the silicon compacts with polymer char showed faster nitridation kinetics than those without the polymer char. As the polymer char content is increased, the amount of SiC in the nitrided material is also increased. By adding small amounts (approx. 2.5 wt percent) of NiO, the silicon compacts containing polymer char can be completely nitrided at 1200 C. The probable mechanism for the accelerated nitridation of silicon containing polymer char is discussed.

  6. Crystalline Silicon Solar Cells

    NASA Astrophysics Data System (ADS)

    Green, Martin A.

    2015-10-01

    The following sections are included: * Overview * Silicon cell development * Substrate production * Cell processing * Cell costs * Opportunities for improvement * Silicon-supported thin films * Summary * Acknowledgement * References

  7. Nitrogen Supply Uses Hydrazine

    NASA Technical Reports Server (NTRS)

    Heppner, D. B.

    1984-01-01

    Liquid hydrazine dissociated and residual gas removed to produce almost pure nitrogen. Nitrogen-generation module catalytically dissociates liquid hydrazine then dissociates and separates product gases to yield almost pure nitrogen.

  8. Silicon oxynitride: A field emission suppression coating

    NASA Astrophysics Data System (ADS)

    Theodore, Nimel D.

    We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work had shown that the field emission from polished stainless steel (27 muA of field-emitted current at 15 MV/m) could be drastically reduced with simultaneous deposition of sputtered silicon dioxide during nitrogen implantation (167 pA of field-emitted current at 30 MV/m). We have determined that this unique implantation and deposition procedure produces high-purity silicon oxynitride films that can suppress field emission from stainless steel regardless of their initial surface polish. However, when this implantation procedure was applied to large, 3-D substrates, arcs occurred, damaging the coating and causing unreliable and unrepeatable field emission suppression. We have developed a novel reactive sputtering procedure to deposit high-purity silicon oxynitride coatings without nitrogen ion implantation. We can control the stoichometry and deposition rate of these coatings by adjusting the nitrogen pressure and incident RF-power. Using profilometry, Auger electron spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection analysis, and current-voltage measurements, we have determined that the elemental composition, chemical bonding, density, and electrical properties of the reactively-sputtered silicon oxynitride coatings are similar to those produced by nitrogen implantation during silicon dioxide deposition. Furthermore, high voltage tests determined that both coatings similarly suppress field emission from 6" diameter, polished

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

    NASA Astrophysics Data System (ADS)

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

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

  10. Silicon Crystal Growth and Wafer Processing for High Efficiency Solar Cells and High Mechanical Yield: Preprint

    SciTech Connect

    Karoui, A.; Rozgonyi, G. A.; Zhang, R.; Ciszek, T.

    2001-10-01

    Presented at the 2001 NCPV Program Review Meeting: Preliminary work on a novel process for external gettering by creating a band of silicon dioxide precipitation on top of a denuded zone via nitrogen doping is presented.

  11. Intermediate band properties of femtosecond-laser hyperdoped silicon

    NASA Astrophysics Data System (ADS)

    Sher, Meng-Ju

    This thesis explores using femtosecond-laser pulses to hyperdope silicon with chalcogen dopants at concentrations above the maximum equilibrium solubility. Hyperdoped silicon is promising for improving efficiencies of solar cells: the material exhibits broad-band light absorption to wavelengths deep below the corresponding bandgap energy of silicon. The high concentration of dopants forms an intermediate band (IB), instead of discrete energy levels, and the IB enables sub-bandgap light absorption. This thesis is divided into two primary studies: the dopant incorporation and the IB properties. First, we study dopant incorporation with a gas-phase dopant precursor (SF6) using secondary ion mass spectrometry. By varying the pressure of SF6, we find that the surface adsorbed molecules are the dominant source of the dopant. Furthermore, we show the hyperdoped layer is single crystalline. The results demonstrate that the dopant incorporation depth, concentration, and crystallinity are controlled respectively by the number of laser pulses, pressure of the dopant precursor, and laser fluence. Second, we study the IB properties of hyperdoped silicon using optical and electronic measurements. We use Fourier transform infrared spectroscopy to study light absorption. The absorption extends to wavelengths as far as 6 mum before thermal annealing and we find the upper bound of the IB location at 0.2 eV below the conduction band edge. For electronic measurements, we anneal the samples to form a diode between the hyperdoped layer and the substrate, allowing us to probe the IB using temperature-dependent electronic transport measurements. The measurement data indicate that these samples form a localized IB at concentrations below the insulator-to-metal transition. Using a two-band model, we obtain the location of the localized IB at >0.07 eV below the conduction band edge. After femtosecond-laser hyperdoping, annealing is necessary to reduce the laser-induced defects; however

  12. Pressure-induced phase transformations during femtosecond-laser doping of silicon

    NASA Astrophysics Data System (ADS)

    Smith, Matthew J.; Lin, Yu-Ting; Sher, Meng-Ju; Winkler, Mark T.; Mazur, Eric; Gradečak, Silvija

    2011-09-01

    Silicon hyperdoped with chalcogens via femtosecond-laser irradiation exhibits unique near-unity sub-bandgap absorptance extending into the infrared region. The intense light-matter interactions that occur during femtosecond-laser doping produce pressure waves sufficient to induce phase transformations in silicon, resulting in the formation of metastable polymorphic phases, but their exact formation mechanism and influence on the doping process are still unknown. We report direct observations of these phases, describe their formation and distribution, and consider their potential impact on sub-bandgap absorptance. Specifically, the transformation from diamond cubic Si-I to pressure-induced polymorphic crystal structures (amorphous Si, Si-XII, and Si-III) during femtosecond-laser irradiation was investigated using scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Amorphous Si, Si-XII, and Si-III were found to form in femtosecond-laser doped silicon regardless of the presence of a gaseous or thin-film dopant precursor. The rate of pressure loading and unloading induced by femtosecond-laser irradiation kinetically limits the formation of pressure-induced phases, producing regions of amorphous Si 20 to 200 nm in size and nanocrystals of Si-XII and Si-III. The surface texturing that occurs during femtosecond-laser irradiation produces inhomogeneous pressure distributions across the surface and causes delayed development of high-pressure silicon polymorphs over many laser pulses. Finally, we find that the polymorph phases disappear during annealing more rapidly than the sub-bandgap absorptance decreases, enabling us to decouple these two processes through post-treatment annealing.

  13. Upgrading Metallurgical-Grade Silicon

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  14. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  16. Thin silicon solar cells

    SciTech Connect

    Hall, R.B.; Bacon, C.; DiReda, V.; Ford, D.H.; Ingram, A.E.; Cotter, J.; Hughes-Lampros, T.; Rand, J.A.; Ruffins, T.R.; Barnett, A.M.

    1992-12-01

    The silicon-film design achieves high performance by using a dun silicon layer and incorporating light trapping. Optimally designed thin crystalline solar cells (<50 microns thick) have performance advantages over conventional thick devices. The high-performance silicon-film design employs a metallurgical barrier between the low-cost substrate and the thin silicon layer. Light trapping properties of silicon-film on ceramic solar cells are presented and analyzed. Recent advances in process development are described here.

  17. Buried oxide layer in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2001-01-01

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

  18. Mechanical Properties of Silicon Carbonitride Thin Films

    NASA Astrophysics Data System (ADS)

    Peng, Xiaofeng; Hu, Xingfang; Wang, Wei; Song, Lixin

    2003-02-01

    Silicon carbonitride thin films were synthesized by reactive rf sputtering a silicon carbide target in nitrogen and argon atmosphere, or sputtering a silicon nitride target in methane and argon atmosphere, respectively. The Nanoindentation technique (Nanoindenter XP system with a continuous stiffness measurement technique) was employed to measure the hardness and elastic modulus of thin films. The effects of sputtering power on the mechanical properties are different for the two SiCN thin films. With increasing sputtering power, the hardness and the elastic modulus decrease for the former but increase for the latter. The tendency is similar to the evolution trend of Si-C bonds in SiCN materials. This reflects that Si-C bonds provide greater hardness for SiCN thin films than Si-N and C-N bonds.

  19. Nonvolatile memory characteristics of nickel-silicon-nitride nanocrystal

    SciTech Connect

    Chen, W.-R.; Chang, T.-C.; Liu, P.-T.; Yeh, J.-L.; Tu, C.-H.; Lou, J.-C.; Yeh, C.-F.; Chang, C.-Y.

    2007-08-20

    The formation of nickel-silicon-nitride nanocrystals by sputtering a comixed target in the argon and nitrogen environment is proposed in this letter. High resolution transmission electron microscope analysis clearly shows the nanocrystals embedded in the silicon nitride and x-ray photoelectron spectroscopy also shows the chemical material analysis of nanocrystals. The memory window of nickel-silicon-nitride nanocrystals enough to define 1 and 0 states is obviously observed, and a good data retention characteristic to get up to 10 years is exhibited for the nonvolatile memory application.

  20. Micropatterning of porous silicon films by direct laser writing.

    PubMed

    Khung, Yit-Lung; Graney, Sean D; Voelcker, Nicolas H

    2006-01-01

    In this study, we demonstrate that porous silicon films can be ablated by the pulsed nitrogen laser of a commercial MALDI mass spectrometer. The extent of laser-induced ablation was found to depend on the doping level and surface chemistry of the porous silicon film. Using direct laser writing with or without a mask, micropatterns were generated on the porous silicon surface. These micropatterns were subsequently used to guide the growth of mammalian cells including neuroblastoma. Excellent selectivity of cell growth toward the laser-ablated regions was established. PMID:17022678

  1. Meteoritic silicon carbide and its stellar sources - Implications for galactic chemical evolution

    NASA Technical Reports Server (NTRS)

    Ming, Tang; Anders, Edward; Hoppe, Peter; Zinner, Ernst

    1989-01-01

    Interstellar silicon carbide grains in meteorites provide a novel means for studying the carbon-star population of about 5 x 10 to the 9th years ago. Their C-12/C-13 ratios differ greatly from the solar value but resemble those of present-day csrbon stars, implying little change in the galactic C-13 inventory. Isotope data on nitrogen and silicon suggest that the silicon carbide grains come mainly from red giants, with small contributions from novae.

  2. Silicon (100)/SiO2 by XPS

    SciTech Connect

    Jensen, David S.; Kanyal, Supriya S.; Madaan, Nitesh; Vail, Michael A.; Dadson, Andrew; Engelhard, Mark H.; Linford, Matthew R.

    2013-09-25

    Silicon (100) wafers are ubiquitous in microfabrication and, accordingly, their surface characteristics are important. Herein, we report the analysis of Si (100) via X-ray photoelectron spectroscopy (XPS) using monochromatic Al K radiation. Survey scans show that the material is primarily silicon and oxygen, and the Si 2p region shows two peaks that correspond to elemental silicon and silicon dioxide. Using these peaks the thickness of the native oxide (SiO2) was estimated using the equation of Strohmeier.1 The oxygen peak is symmetric. The material shows small amounts of carbon, fluorine, and nitrogen contamination. These silicon wafers are used as the base material for subsequent growth of templated carbon nanotubes.

  3. Purified silicon production system

    DOEpatents

    Wang, Tihu; Ciszek, Theodore F.

    2004-03-30

    Method and apparatus for producing purified bulk silicon from highly impure metallurgical-grade silicon source material at atmospheric pressure. Method involves: (1) initially reacting iodine and metallurgical-grade silicon to create silicon tetraiodide and impurity iodide byproducts in a cold-wall reactor chamber; (2) isolating silicon tetraiodide from the impurity iodide byproducts and purifying it by distillation in a distillation chamber; and (3) transferring the purified silicon tetraiodide back to the cold-wall reactor chamber, reacting it with additional iodine and metallurgical-grade silicon to produce silicon diiodide and depositing the silicon diiodide onto a substrate within the cold-wall reactor chamber. The two chambers are at atmospheric pressure and the system is open to allow the introduction of additional source material and to remove and replace finished substrates.

  4. Effect of iron on nitriding rate of silicon

    SciTech Connect

    Kijima, Kazunori

    1996-12-31

    The present paper investigates reasons why iron doping promotes the nitriding reaction rate of silicon. Kinetic studies on silicon nitridation indicated that the nitriding rate was increased by one order of magnitude with iron addition and that a diffusion controlling process existed at the initial stage. Since nitrogen self-diffusion in silicon nitride may play an important role in silicon nitridation, it was measured by a gas-solid isotope exchange method using {sup 15}N isotope. Diffusion results showed that the self-diffusion coefficient increased by one order of magnitude with iron addition, and that the apparent activation energy did not change with or without additive. In order to understand why iron increases diffusion, the Moessbaur effect of iron doped silicon nitride was investigated. The isomer shift indicated that iron atoms were in the Fe{sup 3+} state. The quadrupole splitting could be explained by the presence of nitrogen vacancies in silicon nitride and the solubility limit of iron into silicon nitride lies around 0.6 at.% at 1430{degrees}C.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  6. Optimization of sinter/HIP parameters of multiphase silicon nitride/silicon carbide ceramics

    SciTech Connect

    Perera, D.S.; Moricca, S.; Drennan, J.; Fan, Q.S.; Gu, P.Z.

    1996-12-31

    Multiphase silicon carbide reinforced silicon nitride materials were sintered using 3 techniques, (1) pressureless sintering, (2) post-sinter HIPing and (3) sintering and HIPing in the same cycle (sinter/HIP). The materials have been characterized with respect to their microstructure, phase relationships and mechanical properties. The materials reached almost the theoretical density using the 3 sintering methods, but this was achieved at a lower temperature with sinter/HIPing. A balance should be sought between the high pressure required for high density and the prevention of excessive nitrogen (pressurizing gas) dissolution in the glassy grain boundary phases. The optimization of sinter/HIP parameters are discussed with respect to sintering mechanisms.

  7. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air-exposed powder was compacted, prefired in helium, and reaction-sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degree of nitridation during sintering increased. Iron content remained constant.

  8. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air exposed powder was compacted, prefired in helium, and reaction sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degreee of nitridation during sintering increased. Iron content remained constant.

  9. Thermal stresses in the microchannel heatsink cooled by liquid nitrogen

    SciTech Connect

    Riddle, R.A.

    1993-06-30

    Microchannel heatsinks represent a highly efficient and compact method for heat removal in high heat flux components. Excellent thermal performance of a silicon microchannel heatsink has been demonstrated using liquid nitrogen as the coolant. For the heating of a 1 square centimeter area, at a heat dissipation of 500 W, a typical silicon heatsink cooled by liquid nitrogen has a thermal resistance of 0.046 cm{sup 2}{degrees}K/W. The actual heatsink structure in this case is only 0.1 cm high. Silicon, although it has excellent thermal properties at liquid nitrogen temperatures, may fracture with very little plastic deformation due to mechanical and thermal stresses. Because the fracture strength of silicon depends on the presence of small defects, strength of the heatsink structures must be addressed to insure highly reliable heatsink devices. Microchannel heatsink reliability can be affected by thermal stresses that arise due to temperature gradients between the base and fin and along the film length. These stresses are combined with the bonding stresses that arise in attaching components at elevated temperatures to the silicon heatsink and then cooling the structure to the cryogenic operating temperatures. These bonding stresses are potentially large because of the differences in the values of the coefficients of thermal expansion in silicon heatsink material, and the attached component materials. The stress results are shown for a 17:1 aspect ratio heatsink cooled in liquid nitrogen. The temperature gradients are a result of a surface heat flux of 1.3 kW/cm{sup 2}, approximating the heat dissipation of an RF power chip. The chip is connected to an aluminum nitride substrate, then the chip and substrate module are attached to the heatsink at a bonding temperature of 600{degrees}K, as for a gold tin eutectic bond. The stresses are shown to be within the allowables of the materials involved.

  10. Structural properties of silicon nanoparticles formed by pulsed laser ablation in liquid media

    NASA Astrophysics Data System (ADS)

    Eroshova, O. I.; Perminov, P. A.; Zabotnov, S. V.; Gongal'skii, M. B.; Ezhov, A. A.; Golovan', L. A.; Kashkarov, P. K.

    2012-11-01

    Silicon nanoparticles have been formed as a result of the irradiation of single-crystal silicon targets in distilled water and liquid nitrogen, by, respectively, picosecond and femtosecond laser pulses. The main structural properties of these nanoparticles have been investigated by atomic force microscopy, transmission electron microscopy, electron diffraction, Raman scattering, and photoluminescence spectroscopy. These particles are found to be mainly spherical. The presence of crystalline and amorphous silicon phases under picosecond ablation in water is established experimentally. Irradiation by femtosecond pulses in liquid nitrogen can yield nanoparticles smaller than 5 nm in size, which are quantum dots with a characteristic photoluminescence peak near 750 nm.

  11. New adamantane-like mercury-chalcogen cages. 2. Synthetic and multinuclear ( sup 31 P, sup 77 Se, sup 125 Te, sup 199 Hg) magnetic resonance study of tellurolate-bridged mercury(III) clusters ((. mu. -TeR) sub 6 (HgPR prime sub 3 ) sub 4 ) sup 2+ and ((. mu. -TeR) sub 6 (Hg)(HgPR prime sub 3 ) sub 3 ) sup 2+ and related species with mixed-bridging chalcogenates

    SciTech Connect

    Dean, P.A.W.; Manivannan, V.; Vittal, J.J. )

    1989-06-14

    The salts (({mu}-TePh){sub 6}(HgPR{prime}{sub 3}){sub 3}(Hg))(ClO{sub 4}){sub 2} (R{prime} = Ph, 4-C{sub 6}H{sub 4}Me, 4-C{sub 6}H{sub 4}Cl) are preparable from Hg(TePh){sub 2}, Mg(PR{prime}{sub 3}){sub 2}(ClO{sub 4}){sub 2}, and PR{prime}P{sub 3} in a 3:1:1 ratio in CH{sub 2}Cl{sub 2} or CHCl{sub 3}. The new cations have been characterized in CH{sub 2}Cl{sub 2} and DMF by multinuclear ({sup 31}P, {sup 125}Te, {sup 199}Hg) magnetic resonance and shown to be of adamantanoid structure with novel tellurolate bridging. These spectra provide clear evidence for preferential formation of one (R{prime} = Ph) or a mixture of both (R{prime} = 4-C{sub 6}H{sub 4}Cl, in DMF solution) of the two C{sub 3} isomers that are possible for adamantane-like ({mu}-TeR){sub 6}M{sub 4} as a result of inversion at the pyramidal Te atoms. Such preferential isomer formation has not been demonstrated previously for any adamantanoid chalcogenate-bridge ({mu}-ER){sub 6}M{sub 4} in solution. Isomer formation at various temperatures is reported. For the cations with R = Ph, the rate of inversion at Te varies with R{prime} in the order alkyl > 4-C{sub 6}H{sub 4}Me > Ph > 4-C{sub 6}H{sub 4}Cl. When R = Ph, R{prime} = 4-C{sub 6}H{sub 4}Me, NMR spectra ({sup 31}P, {sup 77}Se, {sup 125}Te, {sup 199}Hg) of mixtures of ((TeR){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} and (({mu}-ER){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} (E = S, Se) provide evidence for the formation of the mixed-chalcogen cores ({mu}-Te){sub 6-m}({mu}-E){sub m}Hg{sub 4}. 35 refs., 8 figs., 3 tabs.

  12. Process for producing silicon

    DOEpatents

    Olson, Jerry M.; Carleton, Karen L.

    1984-01-01

    A process for producing silicon includes forming an alloy of copper and silicon and positioning the alloy in a dried, molten salt electrolyte to form a solid anode structure therein. An electrically conductive cathode is placed in the electrolyte for plating silicon thereon. The electrolyte is then purified to remove dissolved oxides. Finally, an electrical potential is applied between the anode and cathode in an amount sufficient to form substantially pure silicon on the cathode in the form of substantially dense, coherent deposits.

  13. Does Silicon Have a Role in Ornamental Crop Production?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Silicon (Si) is not considered to be an essential plant nutrient because most plant species can complete their life cycle without it. Still, some plants can accumulate Si at concentrations greater than nitrogen and potassium, and all species evaluated so far have concentrations of Si in tissue grea...

  14. Electrodeposition of molten silicon

    DOEpatents

    De Mattei, Robert C.; Elwell, Dennis; Feigelson, Robert S.

    1981-01-01

    Silicon dioxide is dissolved in a molten electrolytic bath, preferably comprising barium oxide and barium fluoride. A direct current is passed between an anode and a cathode in the bath to reduce the dissolved silicon dioxide to non-alloyed silicon in molten form, which is removed from the bath.

  15. Nitrogen dioxide detection

    DOEpatents

    Sinha, Dipen N.; Agnew, Stephen F.; Christensen, William H.

    1993-01-01

    Method and apparatus for detecting the presence of gaseous nitrogen dioxide and determining the amount of gas which is present. Though polystyrene is normally an insulator, it becomes electrically conductive in the presence of nitrogen dioxide. Conductance or resistance of a polystyrene sensing element is related to the concentration of nitrogen dioxide at the sensing element.

  16. Nitrogen segregation in nanocarbons.

    PubMed

    Ewels, C P; Erbahar, D; Wagner, Ph; Rocquefelte, X; Arenal, R; Pochet, P; Rayson, M; Scardamaglia, M; Bittencourt, C; Briddon, P

    2014-01-01

    We explore the behaviour of nitrogen doping in carbon nanomaterials, notably graphene, nanotubes, and carbon thin films. This is initially via a brief review of the literature, followed by a series of atomistic density functional calculations. We show that at low concentrations, substitutional nitrogen doping in the sp(2)-C graphenic basal plane is favoured, however once the nitrogen concentration reaches a critical threshold there is a transition towards the formation of the more thermodynamically-favoured nitrogen terminated 'zigzag' type edges. These can occur either via formation of finite patches (polycyclic aromatic azacarbons), strips of sp(2) carbon with zigzag nitrogen edges, or internal nitrogen-terminated hole edges within graphenic planes. This transition to edge formation is especially favoured when the nitrogen can be partially functionalised with, e.g. hydrogen. By comparison with available literature results, notably from electron energy loss spectroscopy and X-ray spectroscopy, the current results suggest that much of the nitrogen believed to be incorporated into carbon nanoobjects is instead likely to be present terminating the edges of carbonaceous impurities attached to nanoobject's surface. By comparison to nitrogen-doped tetrahedrally amorphous carbon, we suggest that this transition at around 10-20% nitrogen concentration and above towards sp(2) coordination via internal nitrogen-terminated edge formation may be a general property of nitrogen-doped carbon materials. PMID:25468305

  17. Reaction bonded silicon nitride prepared from wet attrition-milled silicon

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Shaw, N. J.

    1980-01-01

    Silicon powder wet milled in heptane was dried, compacted into test bar shape, helium-sintered, and then reaction bonded in nitrogen-4 vol% hydrogen. As-nitrided bend strengths averaged approximately 290 MPa at both room temperature and 1400 C. Fracture initiation appeared to be associated with subsurface flaws in high-strength specimens and both subsurface and surface flaws in low-strength specimens.

  18. Reaction bonded silicon nitride prepared from wet attrition-milled silicon. [fractography

    NASA Technical Reports Server (NTRS)

    Herball, T. P.; Glasgow, T. K.; Shaw, N. J.

    1980-01-01

    Silicon powder wet milled in heptane was dried, compacted into test bar shape, helium-sintered, and then reaction bonded in nitrogen-4 volume percent hydrogen. As-nitrided bend strengths averaged approximately 290 MPa at both room temperature and 1400 C. Fracture initiation appeared to be associated with subsurface flaws in high strength specimens and both subsurface and surface flaws in low strength specimens.

  19. First-principles study of silicon nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Gao, Guohua; Kang, Hong Seok

    2008-10-01

    We have made a first-principles calculation of the topological, geometric, and electronic structures of nitrogen-doped armchair and zigzag silicon carbide nanotubes, where we have assumed that all carbon atoms have been substituted by nitrogen atoms. The doping was found to be substantially easier than for analogous carbon nanotubes. In addition, the doping process is cooperative, leading us to theoretically predict the stable existence of silicon nitride nanotubes (SiNNTs). For (n,n) SiNNTs, all kinds of chiral indices n are possible. These armchair tubes are semiconductors with much smaller band gaps than those of corresponding silicon carbide nanotubes, and the gap decreases with the tube diameter. For (n,0) chirality, only even-numbered chiral indices (n=2l) are possible. These nanotubes are also semiconductors with band gaps larger than those of armchair SiNNTs of similar diameters.

  20. Process for making silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    Lau, Sai-Kwing (Inventor); Calandra, Salavatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    1998-01-01

    A process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  1. Two-dimensional silicon and carbon monochalcogenides with the structure of phosphorene

    NASA Astrophysics Data System (ADS)

    Rocca, Dario; Abboud, Ali; Lebègue, Sébastien; Vaitheeswaran, Ganapathy

    Phosphorene has recently attracted interest for applications in transistors and photodetectors. Inspired by this material we carried out an ab initio study to predict new binary materials with a structure similar to phosphorene. Specifically, carbon or silicon atoms and chalcogen atoms (up to Te) were combined to form a phosphorene-like monolayer. The structure of these new compounds was then optimized and the dynamical stability of the structures was demonstrated by computing phonon dispersion curves. A series of materials were found to be stable: CS, CSe, CTe, SiO, SiS, SiSe, and SiTe. Electronic properties such as band gaps and effective masses were computed at the density functional theory level. By using the accurate HSE hybrid functional it was found that these materials span a broad range of bandgaps, going from the 2.1 eV of SiS to the 0.55 eV of SiTe. The effective masses were also computed; similarly to phosphorene, a strong anisotropy was found when comparing the zigzag and armchair directions. The variety of electronic properties found for these systems will contribute to broaden the technological applicability of two dimensional materials.

  2. Synthesis of fine-grained .alpha.-silicon nitride by a combustion process

    DOEpatents

    Holt, J. Birch; Kingman, Donald D.; Bianchini, Gregory M.

    1990-01-01

    A combustion synthesis process for the preparation of .alpha.-silicon nitride and composites thereof is disclosed. Preparation of the .alpha.-silicon nitride comprises the steps of dry mixing silicon powder with an alkali metal azide, such as sodium azide, cold-pressing the mixture into any desired shape, or loading the mixture into a fused, quartz crucible, loading the crucible into a combustion chamber, pressurizing the chamber with nitrogen and igniting the mixture using an igniter pellet. The method for the preparation of the composites comprises dry mixing silicon powder (Si) or SiO.sub.2, with a metal or metal oxide, adding a small amount of an alkali metal azide such as sodium azide, introducing the mixture into a suitable combustion chamber, pressurizing the combustion chamber with nitrogen, igniting the mixture within the combustion chamber, and isolating the .alpha.-silicon nitride formed as a reaction product.

  3. Glass-silicon column

    DOEpatents

    Yu, Conrad M.

    2003-12-30

    A glass-silicon column that can operate in temperature variations between room temperature and about 450.degree. C. The glass-silicon column includes large area glass, such as a thin Corning 7740 boron-silicate glass bonded to a silicon wafer, with an electrode embedded in or mounted on glass of the column, and with a self alignment silicon post/glass hole structure. The glass/silicon components are bonded, for example be anodic bonding. In one embodiment, the column includes two outer layers of silicon each bonded to an inner layer of glass, with an electrode imbedded between the layers of glass, and with at least one self alignment hole and post arrangement. The electrode functions as a column heater, and one glass/silicon component is provided with a number of flow channels adjacent the bonded surfaces.

  4. Porous silicon gettering

    SciTech Connect

    Tsuo, Y.S.; Menna, P.; Al-Jassim, M.

    1995-08-01

    We have studied a novel extrinsic gettering method that utilizes the very large surface areas, produced by porous silicon etch on both front and back surfaces of the silicon wafer, as gettering sites. In this method, a simple and low-cost chemical etching is used to generate the porous silicon layers. Then, a high-flux solar furnace (HFSF) is used to provide high-temperature annealing and the required injection of silicon interstitials. The gettering sites, along with the gettered impurities, can be easily removed at the end the process. The porous silicon removal process consists of oxidizing the porous silicon near the end the gettering process followed by sample immersion in HF acid. Each porous silicon gettering process removes up to about 10 {mu}m of wafer thickness. This gettering process can be repeated so that the desired purity level is obtained.

  5. Boron and nitrogen impurities in SiC nanoribbons: an ab initio investigation

    NASA Astrophysics Data System (ADS)

    Costa, C. D.; Morbec, J. M.

    2011-05-01

    Using ab initio calculations based on density-functional theory we have performed a theoretical investigation of substitutional boron and nitrogen impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag and armchair edges. In both systems we verify that the boron and nitrogen atoms energetically prefer to be localized at the edges of the nanoribbons. However, while boron preferentially substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, our electronic-structure calculations indicate that (i) substitutional boron and nitrogen impurities do not affect the semiconducting character of the armchair SiC nanoribbons, and (ii) the half-metallic behavior of the zigzag nanoribbons is maintained in the presence of substitutional boron impurities. In contrast, nitrogen atoms occupying edge carbon sites transform half-metallic zigzag nanoribbons into metallic systems.

  6. Boron and nitrogen impurities in SiC nanoribbons: an ab initio investigation.

    PubMed

    Costa, C D; Morbec, J M

    2011-05-25

    Using ab initio calculations based on density-functional theory we have performed a theoretical investigation of substitutional boron and nitrogen impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag and armchair edges. In both systems we verify that the boron and nitrogen atoms energetically prefer to be localized at the edges of the nanoribbons. However, while boron preferentially substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, our electronic-structure calculations indicate that (i) substitutional boron and nitrogen impurities do not affect the semiconducting character of the armchair SiC nanoribbons, and (ii) the half-metallic behavior of the zigzag nanoribbons is maintained in the presence of substitutional boron impurities. In contrast, nitrogen atoms occupying edge carbon sites transform half-metallic zigzag nanoribbons into metallic systems. PMID:21540516

  7. Silicon surface periodic structures produced by plasma flow induced capillary waves

    SciTech Connect

    Dojcinovic, I. P.; Kuraica, M. M.; Obradovic, B. M.; Puric, J.

    2006-08-14

    Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations.

  8. Nitrogen spark denoxer

    DOEpatents

    Ng, Henry K.; Novick, Vincent J.; Sekar, Ramanujam R.

    1997-01-01

    A NO.sub.X control system for an internal combustion engine includes an oxygen enrichment device that produces oxygen and nitrogen enriched air. The nitrogen enriched air contains molecular nitrogen that is provided to a spark plug that is mounted in an exhaust outlet of an internal combustion engine. As the nitrogen enriched air is expelled at the spark gap of the spark plug, the nitrogen enriched air is exposed to a pulsating spark that is generated across the spark gap of the spark plug. The spark gap is elongated so that a sufficient amount of atomic nitrogen is produced and is injected into the exhaust of the internal combustion engine. The injection of the atomic nitrogen into the exhaust of the internal combustion engine causes the oxides of nitrogen to be reduced into nitrogen and oxygen such that the emissions from the engine will have acceptable levels of NO.sub.X. The oxygen enrichment device that produces both the oxygen and nitrogen enriched air can include a selectively permeable membrane.

  9. Flameless nitrogen skid unit

    SciTech Connect

    Loesch, S.B.; John, J.C.; Mints, D.K.

    1984-03-27

    A flameless nitrogen vaporizing unit includes a first internal combustion engine driving a nitrogen pump through a transmission. A second internal combustion engine drives three hydraulic oil pumps against a variable back pressure so that a variable load may be imposed upon the second engine. Liquid nitrogen is pumped from the nitrogen pump driven by the first engine into a first heat exchanger where heat is transferred from exhaust gases from the first and second internal combustion engines to the liquid nitrogen to cause the nitrogen to be transformed into a gaseous state. The gaseous nitrogen then flows into a second heat exchanger where it is superheated by an engine coolant fluid to heat the gaseous nitrogen to essentially an ambient temperature. The superheated nitrogen is then injected into the well. The engine coolant fluid flows in a coolant circulation system. Heat is transferred to the coolant fluid directly from the internal combustion engine. Heat is also provided to the coolant fluid from lubrication oil pumped by the three pumps attached to the second internal combustion engine. The coolant fluid circulating system includes a comingling chamber for comingling warmer coolant fluid flowing from the internal combustion engines to the second heat exchanger with cooler coolant fluids flowing from the second heat exchanger to the internal combustion engines. Methods of vaporizing nitrogen are also disclosed.

  10. Silicon Nitride For Gallium Arsenide Integrated Circuits

    NASA Astrophysics Data System (ADS)

    Nagle, J.; Morgan, David V.

    1987-04-01

    Gallium Arsenide, unlike silicon does not have a natural oxide with the dielectric and interface qualities of SiO2. As a consequence alternative techniques have to be developed for device and IC processing applications. Plasma deposited silicon nitride films are currently being investigated in many laboratories. This paper will deal with the characterization of such films deposited under a range of gas and plasma deposition conditions. The techniques of Infra Red Spectroscopy and Rutherford backscattering have been used for characterization of both "as deposited layers" and layers which have been annealed up to temperatures of 800 °C, after deposition. The use of RBS for silicon nitride on GaAs is limited since the relatively small nitride spectrum is superimposed on much larger GaAs spectrum. The problem can be removed by placing carbon test substrates alongside the GaAs wafers. This separates the silicon and nitrogen spectra from the substrate enabling enhanced accuracy to be obtained. In this paper the range of results obtained will be discussed in the context of the deposition condition in order to identify the optimum conditions for obtaining a stoichiometric compound and a high quality interface.

  11. Silicon abundances in population I giants

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika

    1992-01-01

    Silicon to carbon abundance ratios for population I giants were determined from emission lines originating in the transition layers between stellar chromospheres and coronae. For effective temperatures larger than 6200 K we find a group of stars with increased silicon to carbon but normal nitrogen to carbon abundance ratios. These stars are presumably descendents from Ap stars with increased surface silicon to carbon abundance ratios. For G stars this anomaly disappears as is to be expected due to the increased depth of the convection zone and therefore deeper mixing which dilutes the surface overabundances. The disappearance of the abundance anomalies proves that the anomalous abundances observed for the F giants are indeed only a surface phenomenon. It also proves that the same holds for their progenitors, the Ap and Am stars, as has been generally believed. Unexplained is the increased silicon to carbon abundance ratio observed for several stars cooler than 5100 L. RS CVn and related stars do not show this increased abundance ratio. There are also some giants which appear to be enriched in carbon, perhaps due to a helium flash with some mixing if the star is a clump star.

  12. Carbonitriding of silicon using plasma focus device

    SciTech Connect

    Jabbar, S.; Khan, I. A.; Ahmad, R.; Zakaullah, M.; Pan, J. S.

    2009-03-15

    Carbonitride thin films have been deposited on silicon substrate by the irradiation of energetic nitrogen ions emanated from dense plasma focus device. The carbon ions are ablated by the irradiation of relativistic electrons from the insert material (graphite) placed at the anode tip. The x-ray diffraction analysis demonstrates that a polycrystalline thin film consisting of various compounds such as Si{sub 3}N{sub 4}, SiC, and C{sub 3}N{sub 4} is formed on the silicon (100) substrate. Crystallinity of different compounds decreases with the increase in angular positions (0 deg., 10 deg., and 20 deg. ). Raman spectroscopy shows the appearance of graphitic and disordered bands with silicon nitride and silicon carbide indicating the formation of carbonitride. Raman spectra also indicate that broadening of bands increases with the increase in focus deposition shots, leading to the amorphization of the thin film. The amorphization of the thin films depends on the ion energy flux as well as on the sample angular position. The scanning electron microscopy exhibits the damaging of the substrate surface at 0 deg. angular position. The microstructure shows the tubular shape for higher ion dose (40 focus shots). At 10 deg. angular position, a two phase phenomenon is observed with the ordered phase in the solid solution. A smooth and uniform surface morphology showing a small cluster is observed for the 20 deg. angular position.

  13. Silicon micro-mold

    DOEpatents

    Morales, Alfredo M.

    2006-10-24

    The present invention describes a method for rapidly fabricating a robust 3-dimensional silicon-mold for use in preparing complex metal micro-components. The process begins by depositing a conductive metal layer onto one surface of a silicon wafer. A thin photoresist and a standard lithographic mask are then used to transfer a trace image pattern onto the opposite surface of the wafer by exposing and developing the resist. The exposed portion of the silicon substrate is anisotropically etched through the wafer thickness down to conductive metal layer to provide an etched pattern consisting of a series of rectilinear channels and recesses in the silicon which serve as the silicon micro-mold. Microcomponents are prepared with this mold by first filling the mold channels and recesses with a metal deposit, typically by electroplating, and then removing the silicon micro-mold by chemical etching.

  14. [Silicone breast implants].

    PubMed

    Nielsen, M; Brandt, B; Breiting, V B; Christensen, L H; Thomsen, J L

    1989-12-18

    A brief review of the use of silicone breast implants, their structure, methods of implantation and complications is presented. Acute complications are rare, being mainly infection and hematoma. Long-term complications, on the contrary, are common, consisting mainly of capsular contracture around the prosthesis with subsequent pain and deformation of the breast. More rarely silicone granulomas form, and prosthesis rupture or herniation occurs. The importance of silicone leakage for these complications is discussed separately as well as the treatment of and prevention of capsular contracture and demonstration of silicone in tissue. A critical attitude towards the use of silicone breast implants, when these are used for purely cosmetic purposes, is recommended at present. New improved types of silicone breast implants are currently being tested clinically. PMID:2692262

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

    SciTech Connect

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

    2006-01-23

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

  16. Nitrogen In Saturn's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Smith, H. T.; Sittler, E. C.; Johnson, R. E.; McComas, D. J.; Reisenfeld, D.; Shappirio, M. D.; Baragiola, R.; Michael, M.; Shematovich, V. I.; Crary, F.; Young, D. T.

    2004-12-01

    We are analyzing CAPS instrument data on Cassini to look for nitrogen ions in Saturn's magnetosphere. Because Voyager could not separate oxygen and nitrogen, there has been considerable controversy on nitrogen's presence and relative importance. Two principal sources have been suggested: Titan's atmosphere and nitrogen species trapped in Saturn's icy satellite surfaces (Sittler et al 2004). The latter may be primordial nitrogen, likely as NH3 in ice (Stevenson 1982; Squyers et al. 1983) or nitrogen ions that have been implanted in the surface (Delitsky and Lane 2002). We will present the results of Saturnian nitrogen cloud modeling and relevant CAPS observations. We recently described the Titan source (Michael, et al. 2004; Shematovich et al. 2003; Smith et al. 2004; Sittler et al. 2004) in preparation for Cassini's Saturnian plasma measurements. Two components were identified: energetic nitrogen ions formed near Titan and energized as they diffused inward (Sittler et al. 2004) and neutrals in orbits with small perigee that became ionized in the inner magnetosphere (Smith et al 2004). The latter component would be a source of lower energy, co-rotating nitrogen ions in the inner magnetosphere. Such a component would have an energy spectrum similar to nitrogen species sputtered from the icy satellite surfaces (Johnson and Sittler 1990). However, the mass spectrum would differ, likely containing NHx and NOx species also, and, hence, may be separated from the Titan source. Our preliminary analysis for nitrogen species in the CAPS data will be compared to our models. Of interest will be the energy spectra, which can indicate whether any nitrogen present is formed locally or near Titan's orbit and diffused inward. This work is supported by the NASA Planetary Atmospheres, NASA Graduate Student Research, Virginia Space Grant Consortium Graduate Research Fellowship and CAPS Cassini instrument team programs.

  17. Preparation and thermal stability of silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Wang, H.; Ong, P. P.

    2001-02-01

    Silicon nanoparticles were prepared in a homemade apparatus by means of a dc sputtering method in which the condensates were collected directly from the cold surface of a liquid nitrogen trap. They were dispersed in 2-propanol under ultrasonic agitation, and dried in the atmosphere. The particles were found to compose of tiny silicon crystals and were only mildly oxidized. Various samples were prepared with different annealing times and temperatures in ultrahigh vacuum. XPS results show that, in the particles, the Si-O bonds of the Si 4+ state are the most stable, followed next by the unoxidised state Si 0. The intermediate oxidation states are the least stable; they exist only at sufficiently low temperatures (300°C or lower) and are converted to either Si 0 or Si 4+ at higher temperatures.

  18. Mist Ejection of Silicon Microparticle Using a Silicon Nozzle

    NASA Astrophysics Data System (ADS)

    Yokoyama, Yoshinori; Murakami, Takaaki; Yoshida, Yukihisa; Itoh, Toshihiro

    The novel mist-jet technology using a silicon nozzle and a silicon reflector has been developed. Ejection of water mist containing the silicon microparticles is demonstrated. Impurities of the silicon microparticles ejected on the substrate are analyzed. It has been verified for the first time that the contamination is reduced by the silicon head. The silicon pattern drawn by the head is successfully formed.

  19. Micromachined Silicon Waveguides

    NASA Technical Reports Server (NTRS)

    Mcgrath, William R.; Tai, Yu-Chong; Yap, Markus; Walker, Christopher K.

    1994-01-01

    Components that handle millimeter and submillimeter wavelengths fabricated conveniently. Micromachining rectangular waveguide involves standard steps of masking, etching, and deposition of metal on silicon. Parts made assembled into half-waveguide and finally into full waveguide. Silicon-micromachining approach enables simultaneous fabrication of several versions of waveguide, with variations in critical parameter, on single wafer of silicon. Performances of versions compared and optimized more quickly and at lower cost than is possible if different versions are fabricated sequentially, by conventional machining techniques.

  20. Highly porous silicon membranes fabricated from silicon nitride/silicon stacks.

    PubMed

    Qi, Chengzhu; Striemer, Christopher C; Gaborski, Thomas R; McGrath, James L; Fauchet, Philippe M

    2014-07-23

    Nanopore formation in silicon films has previously been demonstrated using rapid thermal crystallization of ultrathin (15 nm) amorphous Si films sandwiched between nm-thick SiO2 layers. In this work, the silicon dioxide barrier layers are replaced with silicon nitride, resulting in nanoporous silicon films with unprecedented pore density and novel morphology. Four different thin film stack systems including silicon nitride/silicon/silicon nitride (NSN), silicon dioxide/silicon/silicon nitride (OSN), silicon nitride/silicon/silicon dioxide (NSO), and silicon dioxide/silicon/silicon dioxide (OSO) are tested under different annealing temperatures. Generally the pore size, pore density, and porosity positively correlate with the annealing temperature for all four systems. The NSN system yields substantially higher porosity and pore density than the OSO system, with the OSN and NSO stack characteristics fallings between these extremes. The higher porosity of the Si membrane in the NSN stack is primarily due to the pore formation enhancement in the Si film. It is hypothesized that this could result from the interfacial energy difference between the silicon/silicon nitride and silicon/silicon dioxide, which influences the Si crystallization process. PMID:24623562

  1. Silicon web process development

    NASA Technical Reports Server (NTRS)

    Duncan, C. S.; Seidensticker, R. G.; Mchugh, J. P.; Skutch, M. E.; Driggers, J. M.; Hopkins, R. H.

    1981-01-01

    The silicon web process takes advantage of natural crystallographic stabilizing forces to grow long, thin single crystal ribbons directly from liquid silicon. The ribbon, or web, is formed by the solidification of a liquid film supported by surface tension between two silicon filaments, called dendrites, which border the edges of the growing strip. The ribbon can be propagated indefinitely by replenishing the liquid silicon as it is transformed to crystal. The dendritic web process has several advantages for achieving low cost, high efficiency solar cells. These advantages are discussed.

  2. The CDFII Silicon Detector

    SciTech Connect

    Julia Thom

    2004-07-23

    The CDFII silicon detector consists of 8 layers of double-sided silicon micro-strip sensors totaling 722,432 readout channels, making it one of the largest silicon detectors in present use by an HEP experiment. After two years of data taking, we report on our experience operating the complex device. The performance of the CDFII silicon detector is presented and its impact on physics analyses is discussed. We have already observed measurable effects from radiation damage. These results and their impact on the expected lifetime of the detector are briefly reviewed.

  3. Compounding with Silicones.

    PubMed

    Allen, Loyd V

    2015-01-01

    Since the 1940s, methylchlorosilanes have been used to treat glassware to prevent blood from clotting. The use of silicones in pharmaceutical and medical applications has grown to where today they are used in many life-saving devices (pacemakers, hydrocephalic shunts) and pharmaceutical applications from tubing, to excipients in topical formulations, to adhesives to affix transdermal drug delivery systems, and are also being used in products as active pharmaceutical ingredients, such as antiflatulents. About 60% of today's skin-care products now contain some type of silicone where they are considered safe and are known to provide a pleasant "silky-touch," non-greasy, and non-staining feel. Silicones exhibit many useful characteristics, and the safety of these agents supports their numerous applications; their biocompatibility is partially due to their low-chemical reactivity displayed by silicones, low-surface energy, and their hydrophobicity. Silicones are used both as active ingredients and as excipients. In addition is their use for "siliconization," or surface treatment, of many parenteral packaging components. Dimethicone and silicone oil are used as lubricants on stoppers to aid machineability, in syringes to aid piston movement, or on syringe needles to reduce pain upon injection. Silicones are also useful in pharmaceutical compounding as is discussed in this artiele included with this article are in developing formulations with silicones. PMID:26714363

  4. Micromachined silicon electrostatic chuck

    DOEpatents

    Anderson, Robert A.; Seager, Carleton H.

    1996-01-01

    An electrostatic chuck is faced with a patterned silicon plate 11, created y micromachining a silicon wafer, which is attached to a metallic base plate 13. Direct electrical contact between the chuck face 15 (patterned silicon plate's surface) and the silicon wafer 17 it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands 19 that protrude less than 5 micrometers from the otherwise flat surface of the chuck face 15. The islands 19 may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face 15 and wafer 17 contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands 19 are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face 15, typically 0.5 to 5 percent. The pattern of the islands 19, together with at least one hole 12 bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas.

  5. Micromachined silicon electrostatic chuck

    DOEpatents

    Anderson, R.A.; Seager, C.H.

    1996-12-10

    An electrostatic chuck is faced with a patterned silicon plate, created by micromachining a silicon wafer, which is attached to a metallic base plate. Direct electrical contact between the chuck face (patterned silicon plate`s surface) and the silicon wafer it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands that protrude less than 5 micrometers from the otherwise flat surface of the chuck face. The islands may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face and wafer contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face, typically 0.5 to 5 percent. The pattern of the islands, together with at least one hole bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas. 6 figs.

  6. Effect of high-energy electron-beam irradiation on the optical properties of ion-beam-sputtered silicon oxynitride thin films.

    PubMed

    Karanth, Shivaprasad; Shanbhogue, Ganesh H; Nagendra, C L

    2005-10-10

    Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings. PMID:16237933

  7. Variation in optical-absorption edge in SiN{sub x} layers with silicon clusters

    SciTech Connect

    Efremov, M. D. Volodin, V. A.; Marin, D. V.; Arzhannikova, S. A.; Kamaev, G. N.; Kochubei, S. A.; Popov, A. A.

    2008-02-15

    Using optical methods, data on optical constants are obtained for silicon nitride films synthesized by plasma-chemical vapor deposition (PCVD). Models for calculating the permittivity in the model of inhomogeneous phase mixture of silicon and silicon nitride are considered. It is found that the optical-absorption edge (E{sub g}) and the photoluminescence peak shift to longer wavelengths with increasing nitrogen atomic fraction x in sin{sub x} films. When x approaches the value 4/3 characteristic for stoichiometric silicon nitride Si{sub 3}N{sub 4}, a nonlinear sharp increase in E{sub g} is observed. Using Raman scattering, Si-Si bonds are revealed, which confirms the direct formation of silicon clusters during the film deposition. The relation between the composition of nonstoichiometric silicon nitride films, values of permittivity, and the optical-band width is established for light transmission.

  8. Use of (77)Se and (125)Te NMR Spectroscopy to Probe Covalency of the Actinide-Chalcogen Bonding in [Th(En){N(SiMe3)2}3](-) (E = Se, Te; n = 1, 2) and Their Oxo-Uranium(VI) Congeners.

    PubMed

    Smiles, Danil E; Wu, Guang; Hrobárik, Peter; Hayton, Trevor W

    2016-01-27

    Reaction of [Th(I)(NR2)3] (R = SiMe3) (1) with 1 equiv of either [K(18-crown-6)]2[Se4] or [K(18-crown-6)]2[Te2] affords the thorium dichalcogenides, [K(18-crown-6)][Th(η(2)-E2)(NR2)3] (E = Se, 2; E = Te, 3), respectively. Removal of one chalcogen atom via reaction with Et3P, or Et3P and Hg, affords the monoselenide and monotelluride complexes of thorium, [K(18-crown-6)][Th(E)(NR2)3] (E = Se, 4; E = Te, 5), respectively. Both 4 and 5 were characterized by X-ray crystallography and were found to feature the shortest known Th-Se and Th-Te bond distances. The electronic structure and nature of the actinide-chalcogen bonds were investigated with (77)Se and (125)Te NMR spectroscopy accompanied by detailed quantum-chemical analysis. We also recorded the (77)Se NMR shift for a U(VI) oxo-selenido complex, [U(O)(Se)(NR2)3](-) (δ((77)Se) = 4905 ppm), which features the highest frequency (77)Se NMR shift yet reported, and expands the known (77)Se chemical shift range for diamagnetic substances from ∼3300 ppm to almost 6000 ppm. Both (77)Se and (125)Te NMR chemical shifts of given chalcogenide ligands were identified as quantitative measures of the An-E bond covalency within an isoelectronic series and supported significant 5f-orbital participation in actinide-ligand bonding for uranium(VI) complexes in contrast to those involving thorium(IV). Moreover, X-ray diffraction studies together with NMR spectroscopic data and density functional theory (DFT) calculations provide convincing evidence for the actinide-chalcogen multiple bonding in the title complexes. Larger An-E covalency is observed in the [U(O)(E)(NR2)3](-) series, which decreases as the chalcogen atom becomes heavier. PMID:26667146

  9. Nitrogen and aluminum implantation in high resistivity silicon carbide

    SciTech Connect

    Dwight, D.; Rao, M.V.; Holland, O.W.; Kelner, G.; Chi, P.H.; Kretchmer, J.; Ghezzo, M.

    1997-12-01

    In this article, the results on N and Al implantations into undoped high-resistance and vanadium doped semi-insulating bulk 6H-SiC are reported for the first time. The N implants were performed at 700{degree}C and the Al implants at 800{degree}C to create n- and p-type layers, respectively. For comparison, implants were performed into epitaxial layers at the above temperatures and, for N, also at room temperature. The implanted/annealed material was characterized by van der Pauw Hall, secondary ion mass spectrometry, and Rutherford backscattering (RBS) measurements. After annealing, the room temperature N implantation gave similar electrical and RBS results as the 700{degree}C implantation for a total implant dose of 8{times}10{sup 14}cm{sup {minus}2} which corresponds to a volume concentration of 2{times}10{sup 19}cm{sup {minus}3}. The Al implant redistributed in the bulk crystals during annealing, resulting in a shoulder formation at the tail of the implant profile. Lower implant activation was obtained in V-doped material compared to the undoped bulk and epitaxial layers, but the results were promising enough to use implantation technology for making planar high frequency devices in the bulk V-doped substrates, especially as the quality of the substrates continue to improve. {copyright} {ital 1997 American Institute of Physics.}

  10. Method and apparatus for stable silicon dioxide layers on silicon grown in silicon nitride ambient

    NASA Technical Reports Server (NTRS)

    Cohen, R. A.; Wheeler, R. K. (Inventor)

    1974-01-01

    A method and apparatus for thermally growing stable silicon dioxide layers on silicon is disclosed. A previously etched and baked silicon nitride tube placed in a furnace is used to grow the silicon dioxide. First, pure oxygen is allowed to flow through the tube to initially coat the inside surface of the tube with a thin layer of silicon dioxide. After the tube is coated with the thin layer of silicon dioxide, the silicon is oxidized thermally in a normal fashion. If the tube becomes contaminated, the silicon dioxide is etched off thereby exposing clean silicon nitride and then the inside of the tube is recoated with silicon dioxide. As is disclosed, the silicon nitride tube can also be used as the ambient for the pyrolytic decomposition of silane and ammonia to form thin layers of clean silicon nitride.