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Sample records for chemical vapor infiltration

  1. Overview of chemical vapor infiltration

    SciTech Connect

    Besmann, T.M.; Stinton, D.P.; Lowden, R.A.

    1993-06-01

    Chemical vapor infiltration (CVI) is developing into a commercially important method for the fabrication of continuous filament ceramic composites. Current efforts are focused on the development of an improved understanding of the various processes in CVI and its modeling. New approaches to CVI are being explored, including pressure pulse infiltration and microwave heating. Material development is also proceeding with emphasis on improving the oxidation resistance of the interfacial layer between the fiber and matrix. This paper briefly reviews these subjects, indicating the current state of the science and technology.

  2. Microwave assisted chemical vapor infiltration

    SciTech Connect

    Devlin, D.J.; Currier, R.P.; Barbero, R.S.; Espinoza, B.F.; Elliott, N.

    1991-12-31

    A microwave assisted process for production of continuous fiber reinforced ceramic matrix composites is described. A simple apparatus combining a chemical vapor infiltration reactor with a conventional 700 W multimode oven is described. Microwave induced inverted thermal gradients are exploited with the ultimate goal of reducing processing times on complex shapes. Thermal gradients in stacks of SiC (Nicalon) cloths have been measured using optical thermometry. Initial results on the ``inside out`` deposition of SiC via decomposition of methyltrichlorosilane in hydrogen are presented. Several key processing issues are identified and discussed. 5 refs.

  3. Chemical vapor infiltration using microwave energy

    DOEpatents

    Devlin, David J.; Currier, Robert P.; Laia, Jr., Joseph R.; Barbero, Robert S.

    1993-01-01

    A method for producing reinforced ceramic composite articles by means of chemical vapor infiltration and deposition in which an inverted temperature gradient is utilized. Microwave energy is the source of heat for the process.

  4. Fabrication of fiber-reinforced composites by chemical vapor infiltration

    SciTech Connect

    Matlin, W.M.; Stinton, D.P.; Besmann, T.M.

    1995-08-01

    A two-step forced chemical vapor infiltration process was developed that reduced infiltration times for 4.45 cm dia. by 1.27 cm thick Nicalon{sup +} fiber preforms by two thirds while maintaining final densities near 90 %. In the first stage of the process, micro-voids within fiber bundles in the cloth were uniformly infiltrated throughout the preform. In the second stage, the deposition rate was increased to more rapidly fill the macro-voids between bundles within the cloth and between layers of cloth. By varying the thermal gradient across the preform uniform infiltration rates were maintained and high final densities achieved.

  5. Fiber-reinforced ceramic composites made by chemical vapor infiltration

    SciTech Connect

    Caputo, A.J.; Lowden, R.A.; Stinton, D.P.

    1985-01-01

    A process was developed for the fabrication of ceramic-fiber-reinforced ceramic-matrix composites by chemical vapor infiltration. The ceramic composites were prepared by making fibrous preforms from multiple layers of SiC cloth and forming the silicon-carbide matrix for each component specimen by infiltrating the fibrous preform by a chemical vapor deposition process. A major goal of the work was achieved when infiltration was accomplished in hours instead of weeks by combining the thermal-gradient and forced-gas-flow techniques. Composites that possessed moderate flexural strength and high strain to failure were produced. In addition, the strength of the composites decreased gradually after the maximum strength was obtained, demonstrating that the composites had the desired high toughness and avoided the typical brittle behavior of monolithic ceramics.

  6. Scale-up and modeling of forced chemical vapor infiltration

    SciTech Connect

    Besmann, T.M.; McLaughlin, J.C.; Starr, T.L.

    1994-09-01

    The forced flow-thermal gradient chemical vapor infiltration (FCVI) process has been scaled-up from a maximum of 7.6 cm dia. disk to fabrication of 24 cm dia. disks, 1.6 cm in thickness. The components are turbine rotor subelements produced from polar weave Tyranno fibers preforms. The disks were subjected to non-destructive testing and spin-tested to high rpm. The processing conditions were modeled with the GTCVI code to aid in optimization.

  7. Modeling of chemical vapor infiltration for composite fabrication

    SciTech Connect

    Starr, T.L.; Besmann, T.M.

    1993-12-31

    We describe our ongoing efforts to develop a general, validated, 3-D, finite-volume model for the chemical vapor infiltration (CVI) process. The model simulates preform densification for both isothermal (ICVI) and forced flow-thermal gradient (FCVI) variations of the process, but is most useful for FCVI where specification and control of flow rates and temperature profiles are critical to rapid, uniform densification. The model has been validated experimentally for both ICVI and FCVI fabrication of SiC/SiC composites.

  8. Fabrication of fiber-reinforced composites by chemical vapor infiltration

    SciTech Connect

    Besmann, T.M.; McLaughlin, J.C.; Probst, K.J.; Anderson, T.J.; Starr, T.L.

    1997-12-01

    Silicon carbide-based heat exchanger tubes are of interest to energy production and conversion systems due to their excellent high temperature properties. Fiber-reinforced SiC is of particular importance for these applications since it is substantially tougher than monolithic SiC, and therefore more damage and thermal shock tolerant. This paper reviews a program to develop a scaled-up system for the chemical vapor infiltration of tubular shapes of fiber-reinforced SiC. The efforts include producing a unique furnace design, extensive process and system modeling, and experimental efforts to demonstrate tube fabrication.

  9. Measurement of gas transport properties for chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Hablutzel, N.

    1996-12-01

    In the chemical vapor infiltration (CVI) process for fabricating ceramic matrix composites (CMCs), transport of gas phase reactant into the fiber preform is a critical step. The transport can be driven by pressure or by concentration. This report describes methods for measuring this for CVI preforms and partially infiltrated composites. Results are presented for Nicalon fiber cloth layup preforms and composites, Nextel fiber braid preforms and composites, and a Nicalon fiber 3-D weave composite. The results are consistent with a percolating network model for gas transport in CVI preforms and composites. This model predicts inherent variability in local pore characteristics and transport properties, and therefore, in local densification during processing; this may lead to production of gastight composites.

  10. Chemical vapor deposited fiber coatings and chemical vapor infiltrated ceramic matrix composites

    SciTech Connect

    Kmetz, M.A.

    1992-01-01

    Conventional Chemical Vapor Deposition (CVD) and Organometallic Chemical Vapor Deposition (MOCVD) were employed to deposit a series of interfacial coatings on SiC and carbon yarn. Molybdenum, tungsten and chromium hexacarbonyls were utilized as precursors in a low temperature (350[degrees]C) MOCVD process to coat SiC yarn with Mo, W and Cr oxycarbides. Annealing studies performed on the MoOC and WOC coated SiC yarns in N[sub 2] to 1,000[degrees]C establish that further decomposition of the oxycarbides occurred, culminating in the formation of the metals. These metals were then found to react with Si to form Mo and W disilicide coatings. In the Cr system, heating in N[sub 2] above 800[degrees]C resulted in the formation of a mixture of carbides and oxides. Convention CVD was also employed to coat SiC and carbon yarn with C, Bn and a new interface designated BC (a carbon-boron alloy). The coated tows were then infiltrated with SiC, TiO[sub 2], SiO[sub 2] and B[sub 4]C by a chemical vapor infiltration process. The B-C coatings were found to provide advantageous interfacial properties over carbon and BN coatings in several different composite systems. The effectiveness of these different coatings to act as a chemically inert barrier layer and their relationship to the degree of interfacial debonding on the mechanical properties of the composites were examined. The effects of thermal stability and strength of the coated fibers and composites were also determined for several difference atmospheres. In addition, a new method for determining the tensile strength of the as-received and coated yarns was also developed. The coated fibers and composites were further characterized by AES, SEM, XPS, IR and X-ray diffraction analysis.

  11. Rapid fabrication of ceramic composite tubes using chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Chiang, D.; Besmann, T.M.; Stinton, D.P.; McLaughlin, J.C.; Matlin, W.M.

    1996-06-01

    Ceramic composite tubes can be fabricated with silicon carbide matrix and Nicalon fiber reinforcement using forced flow-thermal gradient chemical vapor infiltration (FCVI). The process model GTCVI is used to design the equipment configuration and to identify conditions for rapid, uniform densification. The initial injector and mandrel design produced radial and longitudinal temperature gradients too large for uniform densification. Improved designs have been evaluated with the model. The most favorable approach utilizes a free-standing preform and an insulated water-cooled gas injector. Selected process conditions are based on the temperature limit of the fiber, matrix stoichiometry and reagent utilization efficiency. Model runs for a tube 12 inches long, 4 inches OD and 1/4 inch wall thickness show uniform densification in approximately 15 hours.

  12. Chemical vapor infiltration of TiB{sub 2} composites

    SciTech Connect

    Besmann, T.M.

    1995-05-01

    This program is designed to develop a Hall-Heroult aluminum smelting cathode with substantially improved properties. The carbon cathodes in current use require significant anode-to-cathode spacing in order to prevent shorting, causing significant electrical inefficiencies. This is due to the non-wettability of carbon by aluminum which causes instability in the cathodic aluminum pad. It is suggested that a fiber reinforced-TiB{sub 2} matrix composite would have the requisite wettability, strength, strain-to-failure, cost, and lifetime to solve this problem. The approach selected to fabricate such a cathode material is chemical vapor infiltration (CVI). This program is designed to evaluate potential fiber reinforcements, fabricate test specimens, and test the materials in a static bath and lab-scale Hall cell.

  13. Mass transport measurements and modeling for chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Chiang, D.Y.; Fiadzo, O.G.; Hablutzel, N.

    1997-12-01

    This project involves experimental and modeling investigation of densification behavior and mass transport in fiber preforms and partially densified composites, and application of these results to chemical vapor infiltration (CVI) process modeling. This supports work on-going at ORNL in process development for fabrication of ceramic matrix composite (CMC) tubes. Tube-shaped composite preforms are fabricated at ORNL with Nextel{trademark} 312 fiber (3M Corporation, St. Paul, MN) by placing and compressing several layers of braided sleeve on a tubular mandrel. In terms of fiber architecture these preforms are significantly different than those made previously with Nicalon{trademark} fiber (Nippon Carbon Corp., Tokyo, Japan) square weave cloth. The authors have made microstructure and permeability measurements on several of these preforms and a few partially densified composites so as to better understand their densification behavior during CVI.

  14. Gas transport model for chemical vapor infiltration. Topical report

    SciTech Connect

    Starr, T.L.

    1995-05-01

    A node-bond percolation model is presented for the gas permeability and pore surface area of the coarse porosity in woven fiber structures during densification by chemical vapor infiltration (CVI). Model parameters include the number of nodes per unit volume and their spatial distribution, and the node and bond radii and their variability. These parameters relate directly to structural features of the weave. Some uncertainty exists in the proper partition of the porosity between {open_quotes}node{close_quotes} and{open_quote}bond{close_quotes} and between intra-tow and inter-tow, although the total is constrained by the known fiber loading in the structure. Applied to cloth layup preforms the model gives good agreement with the limited number of available measurements.

  15. Modeling of forced flow/thermal gradient chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Smith, A.W. )

    1992-09-01

    The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a finite volume'' model for FCVI.

  16. Modeling of forced flow/thermal gradient chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Smith, A.W.

    1992-09-01

    The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a ``finite volume`` model for FCVI.

  17. Chemical vapor infiltration of TiB{sub 2} composites

    SciTech Connect

    Besmann, T.M.; Miller, J.H.; Cooley, K.C.; Lowden, R.A.; Starr, T.L.

    1993-01-01

    Efficiency of the Hall-Heroult electrolytic reduction of aluminum can be substantially improved by the use of a TiB{sub 2} cathode surface. The use of TiB{sub 2}, however, has been hampered by the brittle nature of the material and the grain-boundary attack of sintering-aid phases by molten aluminum. In the current work, TiB{sub 2} is toughened through the use of reinforcing fibers, with chemical vapor infiltration (CVI) used to produce pure TiB{sub 2}. It has been observed, however, that the formation of TiB{sub 2} from chloride precursors at fabrication temperatures below 900 to 1000{degrees}C alloys the retention of destructive levels of chlorine in the material. At higher fabrication temperatures and under appropriate infiltration conditions, as determined from the use of a process model, a TIB{sub 2}THORNEL P-25 fiber composite, 45 mm in diam and 6 mm thick, has been fabricated in 20 h. The material has been demonstrated to be stable in molten aluminum in short-duration tests.

  18. Chemical vapor infiltration of TiB[sub 2] composites

    SciTech Connect

    Besmann, T.M.; Miller, J.H.; Cooley, K.C.; Lowden, R.A. ); Starr, T.L. )

    1993-01-01

    Efficiency of the Hall-Heroult electrolytic reduction of aluminum can be substantially improved by the use of a TiB[sub 2] cathode surface. The use of TiB[sub 2], however, has been hampered by the brittle nature of the material and the grain-boundary attack of sintering-aid phases by molten aluminum. In the current work, TiB[sub 2] is toughened through the use of reinforcing fibers, with chemical vapor infiltration (CVI) used to produce pure TiB[sub 2]. It has been observed, however, that the formation of TiB[sub 2] from chloride precursors at fabrication temperatures below 900 to 1000[degrees]C alloys the retention of destructive levels of chlorine in the material. At higher fabrication temperatures and under appropriate infiltration conditions, as determined from the use of a process model, a TIB[sub 2]THORNEL P-25 fiber composite, 45 mm in diam and 6 mm thick, has been fabricated in 20 h. The material has been demonstrated to be stable in molten aluminum in short-duration tests.

  19. Properties of chemical vapor infiltration diamond deposited in a diamond powder matrix

    SciTech Connect

    Panitz, J.K.G.; Tallant, D.R.; Hills, C.R.; Staley, D.J.

    1993-12-31

    Densifying non-mined diamond powder precursors with diamond produced by chemical vapor infiltration (CVI) is an attractive approach for forming thick diamond deposits that avoids many potential manufacturability problems associated with predominantly chemical vapor deposition (CVD) processes. The authors have developed two techniques: electrophoretic deposition and screen printing, to form nonmined diamond powder precursors on substrates. They then densify these precursors in a hot filament assisted reactor. Analysis indicated that a hot filament assisted chemical vapor infiltration process forms intergranular diamond deposits with properties that are to some degree different from predominantly hot-filament-assisted CVD material.

  20. Development of a two-step, forced chemical vapor infiltration process

    SciTech Connect

    Matlin, W.M.; Stinton, D.P.; Besmann, T.M.

    1995-12-01

    A two-step forced chemical vapor infiltration process was developed that reduced infiltration times for 4.45 cm dia. by 1.27 cm thick Nicalon{trademark} fiber pre-forms by two thirds while maintaining final densities near 90%. In the first stage of the process, micro-voids within fiber bundles in the cloth were uniformly infiltrated throughout the preform. In the second stage, the deposition rate was increased to more rapidly fill the macro-voids between bundles within the cloth and between layers of cloth. By varying the thermal gradient across the preform uniform infiltration rates were maintained and high final densities achieved.

  1. Radiation stable, hybrid, chemical vapor infiltration/preceramic polymer joining of silicon carbide components

    NASA Astrophysics Data System (ADS)

    Khalifa, Hesham E.; Koyanagi, Takaaki; Jacobsen, George M.; Deck, Christian P.; Back, Christina A.

    2017-04-01

    This paper reports on a nuclear-grade joining material for bonding of silicon carbide-based components. The joint material is fabricated via a hybrid preceramic polymer, chemical vapor infiltration process. The joint is comprised entirely of β-SiC and results in excellent mechanical and permeability performance. The joint strength, composition, and microstructure have been characterized before and after irradiation to 4.5 dpa at 730 °C in the High Flux Isotope Reactor. The hybrid preceramic polymer-chemical vapor infiltrated joint exhibited complete retention of shear strength and no evidence of microstructural evolution or damage was detected following irradiation.

  2. Fabrication of fiber-reinforced composites by chemical vapor infiltration

    SciTech Connect

    Besmann, T.M.; Matlin, W.M.; Stinton, D.P.; Liaw, P.K.

    1996-06-01

    Processing equipment for the infiltration of fiber-reinforced composite tubes is being designed that incorporates improvements over the equipment used to infiltrate disks. A computer-controlled machine-man interface is being developed to allow for total control of all processing variables. Additionally, several improvements are being made to the furnace that will reduce the complexity and cost of the process. These improvements include the incorporation of free standing preforms, cast mandrels, and simpler graphite heating elements.

  3. Fabrication of fiber-reinforced composites by chemical vapor infiltration

    SciTech Connect

    Besmann, T.M.; Stinton, D.P.; Matlin, W.M.; Liaw, P.K.

    1996-08-01

    Processing equipment for the infiltration of fiber-reinforced composite tubes is being designed that incorporates improvements over the equipment used to infiltrate disks. A computer-controlled machine-man interface is being developed to allow for total control of all processing variables. Additionally, several improvements are being made to the furnace that will reduce the complexity and cost of the process. These improvements include the incorporation of free standing preforms, cast mandrels, and simpler graphite heating elements.

  4. Simulates the Forced-Flow Chemical Vapor Infiltration in Steady State

    SciTech Connect

    Bessman, T. M.

    1997-12-12

    GTCVI is a finite volume model for steady-state simulation of forced-flow chemical vapor infiltration in either Cartesian or cylindrical coordinates. The model solves energy and momentum balances simultaneously over a given domain discretized into an array of finite volume elements. The species balances and deposition rates are determined after the energy and momentum balances converge. Density-dependent preform properties are included in the model. Transient average density, backpressure, temperature gradient, and average radial deposition rates can be summarized. Optimal infiltration conditions can be found by varying temperature, flow, and reactant concentration.

  5. Synthesis of active carbon-based catalysts by chemical vapor infiltration for nitrogen oxide conversion.

    PubMed

    Busch, Martin; Bergmann, Ulf; Sager, Uta; Schmidt, Wolfgang; Schmidt, Frank; Notthoff, Christian; Atakan, Burak; Winterer, Markus

    2011-09-01

    Direct reduction of nitrogen oxides is still a challenge. Strong efforts have been made in developing noble and transition metal catalysts on microporous support materials such as active carbons or zeolites. However, the required activation energy and low conversion rates still limit its breakthrough. Furthermore, infiltration of such microporous matrix materials is commonly performed by wet chemistry routes. Deep infiltration and homogeneous precursor distribution are often challenging due to precursor viscosity or electrostatic shielding and may be inhibited by pore clogging. Gas phase infiltration, as an alternative, can resolve viscosity issues and may contribute to homogeneous infiltration of precursors. In the present work new catalysts based on active carbon substrates were synthesized via chemical vapor infiltration. Iron oxide nano clusters were deposited in the microporous matrix material. Detailed investigation of produced catalysts included nitrogen oxide adsorption, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Catalytic activity was studied in a recycle flow reactor by time-resolved mass spectrometry at a temperature of 423 K. The infiltrated active carbons showed very homogeneous deposition of iron oxide nano clusters in the range of below 12 to 19 nm, depending on the amount of infiltrated precursor. The specific surface area was not excessively reduced, nor was the pore size distribution changed compared to the original substrate. Catalytic nitrogen oxides conversion was detected at temperatures as low as 423 K.

  6. Modeling of chemical vapor infiltration for ceramic composites reinforced with layered, woven fabrics

    NASA Technical Reports Server (NTRS)

    Chung, Gui-Yung; Mccoy, Benjamin J.

    1991-01-01

    A homogeneous model is developed for the chemical vapor infiltration by one-dimensional diffusion into a system of layered plies consisting of woven tows containing bundles of filaments. The model predictions of the amount of deposition and the porosity of the sample as a function of time are compared with the predictions of a recent nonhomogeneous model with aligned holes formed by the weave. The nonhomogeneous model allows for diffusion through the aligned holes, into the spaces between plies, and into the gaps around filaments; i.e., three diffusion equations apply. Relative to the nonhomogeneous results, the homogeneous model underestimates the amount of deposition, since the absence of holes and spaces allows earlier occlusion of gaps around filaments and restricts the vapor infiltration.

  7. Upscaling the Chemical Vapor Infiltration Process of Activated Carbon with TMS

    NASA Astrophysics Data System (ADS)

    Curdts, B.; Helmich, M.; Pasel, C.; Bathen, D.; Atakan, B.; Pflitsch, C.

    Activated carbons are important adsorbents covering a broad range of applications from gas to air purification. In order to improve their mechanical stability and their resistance against oxidation they are infiltrated here with an inert material, SiC or SiO2. For this process the chemical vapor infiltration technique with tetramethylsilane as precursor is used. The process is designed for the infiltration of larger quantities (up to 50 g) which allows further analysis of the materials produced: in comparison to the uncoated activated carbon the novel adsorbent have an increased breaking strength and the BET-surface areas and pore volumes are on high levels. The possibility of using the novel material for solvent adsorption is demonstrated for acetone.

  8. The preparation and economics of silicon carbide matrix composites by chemical vapor infiltration

    SciTech Connect

    Roman, Y.G.; Stinton, D.P.

    1995-10-01

    This paper describes a number of processing techniques that are currently in use for the development and production of continuous fiber reinforced ceramic composite materials. The limited number of available processing routes are compared with respect to the resulting material properties. As it appears the Chemical Vapor Infiltration technique is one of the most extensively developed methods. During the last decade, at least five different modifications of the isobaric isothermal CVI principle have been developed; each route having its own benefits. CVI techniques have now been developed to the extent that industrial commercialization is being realized. Projected cost aspects of the various CVI manufacturing techniques have been examined and compared.

  9. X-ray tomographic study of chemical vapor infiltration processing of ceramic composites

    SciTech Connect

    Kinney, J.H.; Haupt, D.; Saroyan, R.A. ); Breunig, T.M.; Nichols, M.C. ); Starr, T.L.; Stock, S.R.; Butts, M.D. )

    1993-05-07

    The fabrication of improved ceramic-matrix composites will require a better understanding of processing variables and how they control the development of the composite microstructure. Noninvasive, high-resolution methods of x-ray tomography have been used to measure the growth of silicon carbide in a woven Nicalon-fiber composite during chemical vapor infiltration. The high spatial resolution allows one to measure the densification within individual fiber tows and to follow the closure of macroscopic pores in situ. The experiments provide a direct test of a recently proposed model that describes how the surface area available for matrix deposition changes during infiltration. The measurements indicate that this surface area is independent of the fiber architecture and location within the preform and is dominated by large-scale macroporosity during the final stages of composite consolidation. The measured surface areas are in good agreement with the theoretical model. 12 refs., 4 figs.

  10. Finite volume model for forced flow/thermal gradient chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Smith, A.W.

    1991-03-01

    The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successfully technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by many to be unsuitable for such components. The major concern is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification.

  11. Measurement of gas transport through fiber preforms and densified composites for chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Hablutzel, N.

    1998-05-01

    Gas transport via pressure-driven permeation or via concentration-driven diffusion is a key step in the chemical vapor infiltration (CVI) process. This paper describes methods for the measurement of these properties for CVI preforms and partially infiltrated composites. Results are presented for Nicalon-fiber cloth layup preforms and composites, Nextel-fiber braid preforms and composites, and a Nicalon-fiber three-dimensional (3-D) weave composite. The permeability of Nicalon cloth layup preforms is strongly dependent on the packing density over the range of 29--40 vol% but is only weakly dependent on the orientation of the alternating cloth layers. The permeability of Nextel braid preforms is dependent on the thread count and the weight for cloths with similar construction and packing density. The gas permeability of the finer wave (6.3 tows/cm (16 tows/in.)) is approximately one-half that of the coarser weave (3.5 tows/cm (9 tows/in.)). Results are reported for a small number of infiltrated composites with Nextel fiber reinforcement. Attempts to mount a Nicalon-fiber 3-D weave preform specimen have been unsuccessful. Results for a small number of composite specimens with 3-D weave reinforcement are reported.

  12. Chemical vapor infiltration of TiB{sub 2} fibrous composites

    SciTech Connect

    Besmann, T.M.

    1997-04-01

    This program is designed to develop a Hall-Heroult aluminum smelting cathode with substantially improved properties. The carbon cathodes in current use require significant anode-to-cathode spacing in order to prevent shorting, causing significant electrical inefficiencies. This is due to the non-wettability of carbon by aluminum which causes instability in the cathodic aluminum pad. It is suggested that a fiber reinforced-TiB{sub 2} matrix composite would have the requisite wettability, strength, strain-to-failure, cost, and lifetime to solve this problem. The approach selected to fabricate such a cathode material is chemical vapor infiltration (CVI). This process produces high purity matrix TiB{sub 2} without damaging the relatively fragile fibers. The program is designed to evaluate potential fiber reinforcements, fabricate test specimens, and scale the process to provide demonstration components.

  13. Thermal expansion of laminated, woven, continuous ceramic fiber/chemical-vapor-infiltrated silicon carbide matrix composites

    NASA Technical Reports Server (NTRS)

    Eckel, Andrew J.; Bradt, Richard C.

    1990-01-01

    Thermal expansions of three two-dimensional laminate, continuous fiber/chemical-vapor-infiltrated silicon carbide matrix composites reinforced with either FP-Alumina (alumina), Nextel (mullite), or Nicalon (Si-C-O-N) fibers are reported. Experimental thermal expansion coefficients parallel to a primary fiber orientation were comparable to values calculated by the conventional rule-of-mixtures formula, except for the alumina fiber composite. Hysteresis effects were also observed during repeated thermal cycling of that composite. Those features were attributed to reoccurring fiber/matrix separation related to the micromechanical stresses generated during temperature changes and caused by the large thermal expansion mismatch between the alumina fibers and the silicon carbide matrix.

  14. High-strength carbon nanotube/carbon composite fibers via chemical vapor infiltration.

    PubMed

    Lee, Jaegeun; Kim, Teawon; Jung, Yeonsu; Jung, Kihoon; Park, Junbeom; Lee, Dong-Myeong; Jeong, Hyeon Su; Hwang, Jun Yeon; Park, Chong Rae; Lee, Kun-Hong; Kim, Seung Min

    2016-12-07

    In this study, we have developed an efficient and scalable method for improving the mechanical properties of carbon nanotube (CNT) fibers. The mechanical properties of as-synthesized CNT fibers are primarily limited by their porous structures and the weak bonding between adjacent CNTs. These result in inefficient load transfer, leading to low tensile strength and modulus. In order to overcome these limitations, we have adopted chemical vapor infiltration (CVI) to efficiently fill the internal voids of the CNT fibers with carbon species which are thermally decomposed from gas phase hydrocarbon. Through the optimization of the processing time, temperature, and gas flow velocity, we have confirmed that carbon species formed by the thermal decomposition of acetylene (C2H2) gas successfully infiltrated into porous CNT fibers and densified them at relatively low temperatures (650-750 °C). As a result, after CVI processing of the as-synthesized CNT fibers under optimum conditions, the tensile strength and modulus increased from 0.6 GPa to 1.7 GPa and from 25 GPa to 127 GPa, respectively. The CVI technique, combined with the direct spinning of CNT fibers, can open up a route to the fast and scalable fabrication of high performance CNT/C composite fibers. In addition, the CVI technique is a platform technology that can be easily adapted into other nano-carbon based yarn-like fibers such as graphene fibers.

  15. Forced chemical vapor infiltration of tubular geometries: Modeling, design, and scale-up

    SciTech Connect

    Stinton, D.P.; Besmann, T.M.; Matlin, W.M.

    1995-06-01

    In advanced indirectly fired coal combustion systems and externally fired combined cycle concepts, ceramic heat exchangers are required to transfer heat from the hot combustion gases to the clean air that drives the gas turbines. For high efficiencies, the temperature of the turbine inlet needs to exceed 1100{degrees}C and preferably be about 1260{degrees}C. The heat exchangers will operate under pressure and experience thermal and mechanical stresses during heating and cooling, and some transients will be severe under upset conditions. Silicon carbide-matrix composites are promising for such applications because of their high strength at elevated temperature, light weight, thermal and mechanical resistance, damage tolerance, and oxidation and corrosion resistance. Fiber-reinforced composite tubes of several fiber architectures were fabricated by forced chemical vapor infiltration (FCVI) and characterized. Unfortunately, long times ({approximately}150 hours) were required to thoroughly density the tubes. An objective of the current investigation was to optimize the forced CVI process so that composite tubes could be fabricated in much shorter times. To aid in such optimization, a computer code which models the CVI process was used to identify critical process parameters. Finally, successful demonstration of the utility of composite tubes for these applications will require the testing of near-full scale components. As a result a new infiltration system was designed and constructed to prepare 10-cm diameter tubes, and is described in this report.

  16. Expedient Respiratory and Physical Protection: Does a Wet Towel Work to Prevent Chemical Warfare Agent Vapor Infiltration?

    SciTech Connect

    Sorensen, J.H.

    2002-08-30

    The purpose of this paper is to examine the effectiveness of expedient protection strategies to reduce exposure to vapors from chemical warfare agents. This includes an examination of the physical and the psychological effectiveness of measures such as using a wet towel to seal a door jam against the infiltration of chemicals while sheltering in place or to provide expedient respiratory protection. Respiratory protection for civilians has never been considered a viable option for population protection in the CSEPP. Problems of storage, ability to effectively don respirators, and questionable fit have been primary factors in rejecting this option. Expedient respiratory protection seems to offer little benefits for population protection for chemical agent vapors. Furthermore, using wet towels as a vapor barrier at the bottom of a door should be discouraged. The wetted towel provides no vapor filtration and its effectiveness in infiltration reduction is unknown. Taping the bottom of the door will still likely provide greater infiltration reduction and is recommended as the current method for use in sheltering.

  17. Structure and properties of braided sleeve preforms for chemical vapor infiltration

    SciTech Connect

    Starr, T.L.; Fiadzo, O.G.; Hablutzel, N.

    1998-04-01

    In all composites the properties and structure of the reinforcement strongly influence the performance of the material. For some composites, however, the reinforcement also affects the fabrication process itself exerting an additional, second order influence on performance. This is the case for the chemical vapor infiltration (CVI) process for fabrication of ceramic matrix composites. In this process the matrix forms progressively as a solid deposit, first onto the fiber surfaces, then onto the previous layer of deposit, ultimately growing to fill the inter-fiber porosity. The transport of reactants to the surfaces and the evolved morphology of the matrix depend on the initial reinforcement structure. This structure can vary greatly and is controlled by such factors as fiber size and cross-section, the number of filaments and amount of twist per tow or yarn, and the weave or braid architecture. Often the choice of reinforcement is based on mechanical performance analysis or on the cost and availability of the material or on the temperature stability of the fiber. Given this choice, the composite densification process--CVI--must be optimized to attain a successful material. Ceramic fiber in the form of cylindrical braided sleeve is an attractive choice for fabrication of tube-form ceramic matrix composites. Multiple, concentric layers of sleeve can be placed over a tubular mandrel, compressed and fixed with a binder to form a freestanding tube preform. This fiber architecture is different than that created by layup of plain weave cloth--the material used in most previous CVI development. This report presents the results of the investigation of CVI densification of braided sleeve preforms and the evolution of their structure and transport properties during processing.

  18. Rapid processing of carbon-carbon composites by forced flow-thermal gradient chemical vapor infiltration (FCVI)

    SciTech Connect

    Vaidyaraman, S.; Lackey, W.J.; Agrawal, P.K.; Freeman, G.B.; Langman, M.D.

    1995-10-01

    Carbon fiber-carbon matrix composites were fabricated using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. Preforms were prepared by stacking 40 layers of plain weave carbon cloth in a graphite holder. The preforms were infiltrated using propylene, propane, and methane. The present work showed that the FCVI process is well suited for fabricating carbon-carbon composites; without optimization of the process, the authors have achieved uniform and thorough densification. Composites with porosities as low as 7% were fabricated in 8--12 h. The highest deposition rate obtained in the present study was {approximately}3 {micro}m/h which is more than an order of magnitude faster than the typical value of 0.1--0.25 {micro}m/h for the isothermal process. It was also found that the use of propylene and propane as reagents resulted in faster infiltration compared to methane.

  19. Interfacial studies of chemical vapor infiltrated (CVI) ceramic-matrix composites. Annual report, 1 August 1987-31 July 1988

    SciTech Connect

    Brennan, J.J.

    1988-10-01

    The objective of this program is to investigate the fiber/matrix interfacial chemistry in Chemical Vapor Infiltrated Silicon Carbide matrix composites utilizing Nicalon SiC and Nextel 440 mullite fibers and how this interface influences composite properties such as strength, toughness, and environmental stability. The SiC matrix was deposited using three different reactants; methyldichlorosilane (MDS), methyltrichlorosilane (MTS), and dimethyldichlorosilane (DMDS). It was found that by varying the reactant gas flow rates, the ratio of carrier gas to reactant gas, the type of carrier gas (hydrogen or argon), the flushing gas used in the reactor prior to deposition (hydrogen or argon), or the type of silane reactant gas used, the composition of the deposited SiC could be varied from very silicon rich (75 at %) to carbon rich (60%) to almost pure carbon. Stoichiometric SiC was found to bond very strongly to both Nicalon and Nextel fibers, resulting in a weak and brittle composite. A thin carbon interfacial layer deposited either deliberately by the decomposition of methane or inadvertently by the introduction of argon into the reactor prior to silane flow, resulted in a weakly bonded fiber/matrix interface and strong and tough composites. However, composites with this type of interface were not oxidatively stable. Preliminary results point to the use of a carbon-rich SiC interfacial zone to achieve a relatively weak, crack-deflecting fiber/matrix bond but also exhibiting oxidative stability.

  20. Thermal Shock Properties of a 2D-C/SiC Composite Prepared by Chemical Vapor Infiltration

    NASA Astrophysics Data System (ADS)

    Zhang, Chengyu; Wang, Xuanwei; Wang, Bo; Liu, Yongsheng; Han, Dong; Qiao, Shengru; Guo, Yong

    2013-06-01

    The thermal shock properties of a two-dimensional carbon fiber-reinforced silicon carbide composite with a multilayered self-healing coating (2D-C/SiC) were investigated in air. The composite was prepared by low-pressure chemical vapor infiltration. 2D-C/SiC specimens were thermally shocked for different cycles between 900 and 300 °C. The thermal shock resistance was characterized by residual tensile properties and mass variation. The change of the surface morphology and microstructural evolution of the composite were examined by a scanning electron microscope. In addition, the phase evolution on the surfaces was identified using an X-ray diffractometer. It is found that the composite retains its tensile strength within 20 thermal shock cycles. However, the modulus of 2D-C/SiC decreases gradually with increasing thermal shock cycles. Extensive pullout of fibers on the fractured surface and peeling off of the coating suggest that the damage caused by the thermal shock involves weakening of the bonding strength of coating/composite and fiber/matrix. In addition, the carbon fibers in the near-surface zone were oxidized through the matrix cracks, and the fiber/matrix interfaces delaminated when the composite was subjected to a larger number of thermal shock cycles.

  1. A novel procedure to obtain nanocrystalline diamond/porous silicon composite by chemical vapor deposition/infiltration processes.

    PubMed

    Miranda, C R B; Azevedo, A F; Baldan, M R; Beloto, A F; Ferreira, N G

    2009-06-01

    Nanocrystalline diamond (NCD) films were formed on porous silicon (PS) substrate by Chemical Vapor Deposition/Infiltration (CVD/CVI) process using a hot filament reactor. This innovative procedure is determinant to grow a controlled three-dimensional diamond structure with diamond grains formation in the pores, covering uniformly the different growth planes. In this CVI process, a piece of reticulated vitreous carbon (RVC) was used, under de PS substrate, as an additional solid source of hydrocarbon that ensures the production of pertinent carbon growth species directly on PS and into its pores. PS substrates were obtained by anodization etching process of n-type silicon wafer in a hydrofluoric acid (HF) solution containing acetonitrile (CH3CN) which result in an uniform and well controlled porous distribution and size when compared with the usual ethanol solution. Depositions were performed using Ar-H2-CH4 where the methane concentration varied from 0 up to 1.0 vol%, to analyze the influence of RVC use as an additional carbon source on growth mechanism. Scanning Electron Microscopy (SEM) and Field Emission Gun (FEG) were used to investigate PS and NCD film morphology. SEM images of NCD showed faceted nanograins with average size from 5 to 16 nm and uniform surface texture covering all the supports among the pores resulting in an apparent micro honeycomb structure. Raman spectra confirmed the existence of sp2-bonded carbon at the grain boundaries. The spectra showed a peak that may be deconvoluted in two components at 1332 cm(-1) (diamond) and 1345 cm(-1) (D band). Two shoulders at 1150 and 1490 cm(-1) also appear and are assigned to transpolyacetylene (TPA) segments at the grain boundaries of NCD surfaces. In addition, X-ray diffraction analyses of all films presented characteristic diamond diffraction peaks corresponding to (111), (220) and (311).

  2. Chemical vapor deposition growth

    NASA Technical Reports Server (NTRS)

    Ruth, R. P.; Manasevit, H. M.; Kenty, J. L.; Moudy, L. A.; Simpson, W. I.; Yang, J. J.

    1976-01-01

    A chemical vapor deposition (CVD) reactor system with a vertical deposition chamber was used for the growth of Si films on glass, glass-ceramic, and polycrystalline ceramic substrates. Silicon vapor was produced by pyrolysis of SiH4 in a H2 or He carrier gas. Preliminary deposition experiments with two of the available glasses were not encouraging. Moderately encouraging results, however, were obtained with fired polycrystalline alumina substrates, which were used for Si deposition at temperatures above 1,000 C. The surfaces of both the substrates and the films were characterized by X-ray diffraction, reflection electron diffraction, scanning electron microscopy optical microscopy, and surface profilometric techniques. Several experiments were conducted to establish baseline performance data for the reactor system, including temperature distributions on the sample pedestal, effects of carrier gas flow rate on temperature and film thickness, and Si film growth rate as a function of temperature.

  3. Chemical vapor deposition growth

    NASA Technical Reports Server (NTRS)

    Ruth, R. P.; Manasevit, H. M.; Kenty, J. L.; Moudy, L. A.; Simpson, W. I.; Yang, J. J.

    1976-01-01

    The chemical vapor deposition (CVD) method for the growth of Si sheet on inexpensive substrate materials is investigated. The objective is to develop CVD techniques for producing large areas of Si sheet on inexpensive substrate materials, with sheet properties suitable for fabricating solar cells meeting the technical goals of the Low Cost Silicon Solar Array Project. Specific areas covered include: (1) modification and test of existing CVD reactor system; (2) identification and/or development of suitable inexpensive substrate materials; (3) experimental investigation of CVD process parameters using various candidate substrate materials; (4) preparation of Si sheet samples for various special studies, including solar cell fabrication; (5) evaluation of the properties of the Si sheet material produced by the CVD process; and (6) fabrication and evaluation of experimental solar cell structures, using standard and near-standard processing techniques.

  4. Chemical vapor deposition growth

    NASA Technical Reports Server (NTRS)

    Ruth, R. P.; Manasevit, H. M.; Campbell, A. G.; Johnson, R. E.; Kenty, J. L.; Moudy, L. A.; Shaw, G. L.; Simpson, W. I.; Yang, J. J.

    1978-01-01

    The objective was to investigate and develop chemical vapor deposition (CVD) techniques for the growth of large areas of Si sheet on inexpensive substrate materials, with resulting sheet properties suitable for fabricating solar cells that would meet the technical goals of the Low Cost Silicon Solar Array Project. The program involved six main technical tasks: (1) modification and test of an existing vertical-chamber CVD reactor system; (2) identification and/or development of suitable inexpensive substrate materials; (3) experimental investigation of CVD process parameters using various candidate substrate materials; (4) preparation of Si sheet samples for various special studies, including solar cell fabrication; (5) evaluation of the properties of the Si sheet material produced by the CVD process; and (6) fabrication and evaluation of experimental solar cell structures, using impurity diffusion and other standard and near-standard processing techniques supplemented late in the program by the in situ CVD growth of n(+)/p/p(+) sheet structures subsequently processed into experimental cells.

  5. Simple Chemical Vapor Deposition Experiment

    ERIC Educational Resources Information Center

    Pedersen, Henrik

    2014-01-01

    Chemical vapor deposition (CVD) is a process commonly used for the synthesis of thin films for several important technological applications, for example, microelectronics, hard coatings, and smart windows. Unfortunately, the complexity and prohibitive cost of CVD equipment makes it seldom available for undergraduate chemistry students. Here, a…

  6. Simple Chemical Vapor Deposition Experiment

    ERIC Educational Resources Information Center

    Pedersen, Henrik

    2014-01-01

    Chemical vapor deposition (CVD) is a process commonly used for the synthesis of thin films for several important technological applications, for example, microelectronics, hard coatings, and smart windows. Unfortunately, the complexity and prohibitive cost of CVD equipment makes it seldom available for undergraduate chemistry students. Here, a…

  7. Microwave and RF assisted chemical vapor infiltration

    SciTech Connect

    Devlin, D.J.; Barbero, R.S.

    1995-05-01

    Work during this reporting period has focused on the development of a CVI technique for rapid production of carbon/carbon and alumina composite systems. The focus of the alumina effort is towards porous materials for membrane supports and hot gas filtration. Industrial interest in these applications include companies such as: Dow, Westinghouse, Amoco and DuPont. Applications for the carbon materials are numerous and include: brakes, sporting goods, biomedical materials, flaps and seals for thrust control, after burner nozzles, turbine engine flaps and rotors. This effort will focus on aircraft brakes. A collaboration is underway with Hitco a major producer of carbon/carbon materials.

  8. Hierarchical Process Control of Chemical Vapor Infiltration.

    DTIC Science & Technology

    1995-05-31

    convergence artificial neural network and used it to discover improved regions of the CVI processing parameter space; also, the Technology Assessment...identify in situ process sensors of considerable promise and as artificial neural network training pairs.

  9. Chemical vapor deposition of sialon

    DOEpatents

    Landingham, R.L.; Casey, A.W.

    A laminated composite and a method for forming the composite by chemical vapor deposition are described. The composite includes a layer of sialon and a material to which the layer is bonded. The method includes the steps of exposing a surface of the material to an ammonia containing atmosphere; heating the surface to at least about 1200/sup 0/C; and impinging a gas containing N/sub 2/, SiCl/sub 4/, and AlCl/sub 3/ on the surface.

  10. Chemical vapor deposition of sialon

    DOEpatents

    Landingham, Richard L.; Casey, Alton W.

    1982-01-01

    A laminated composite and a method for forming the composite by chemical vapor deposition. The composite includes a layer of sialon and a material to which the layer is bonded. The method includes the steps of exposing a surface of the material to an ammonia containing atmosphere; heating the surface to at least about 1200.degree. C.; and impinging a gas containing in a flowing atmosphere of air N.sub.2, SiCl.sub.4, and AlCl.sub.3 on the surface.

  11. Comparison of precursor infiltration into polymer thin films via atomic layer deposition and sequential vapor infiltration using in-situ quartz crystal microgravimetry

    SciTech Connect

    Padbury, Richard P.; Jur, Jesse S.

    2014-07-01

    Previous research exploring inorganic materials nucleation behavior on polymers via atomic layer deposition indicates the formation of hybrid organic–inorganic materials that form within the subsurface of the polymer. This has inspired adaptations to the process, such as sequential vapor infiltration, which enhances the diffusion of organometallic precursors into the subsurface of the polymer to promote the formation of a hybrid organic–inorganic coating. This work highlights the fundamental difference in mass uptake behavior between atomic layer deposition and sequential vapor infiltration using in-situ methods. In particular, in-situ quartz crystal microgravimetry is used to compare the mass uptake behavior of trimethyl aluminum in poly(butylene terephthalate) and polyamide-6 polymer thin films. The importance of trimethyl aluminum diffusion into the polymer subsurface and the subsequent chemical reactions with polymer functional groups are discussed.

  12. Thickness limitations in carbon nanotube reinforced silicon nitride coatings synthesized by vapor infiltration

    SciTech Connect

    Eres, Gyula

    2012-01-01

    Chemical vapor infiltration is a convenient method for synthesizing carbon nanotube (CNT)-reinforced ceramic coatings. The thickness over which infiltration is relatively uniform is limited by gas phase diffusion in the pore structure. These effects were investigated in two types of silicon nitride matrix composites. With CNTs that were distributed uniformly on the substrate surface dense coatings were limited to thicknesses of several microns. With dual structured CNT arrays produced by photolithography coatings up to 400 gm thick were obtained with minimal residual porosity. Gas transport into these dual structured materials was facilitated by creating micron sized channels between "CNT pillars" (i.e. each pillar consisted of a large number of individual CNTs). The experimental results are consistent with basic comparisons between the rates of gas diffusion and silicon nitride growth in porous structures. This analysis also provides a general insight into optimizing infiltration conditions during the fabrication of thick CNT-reinforced composite coatings. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  13. Water vapor mass balance method for determining air infiltration rates in houses

    Treesearch

    David R. DeWalle; Gordon M. Heisler

    1980-01-01

    A water vapor mass balance technique that includes the use of common humidity-control equipment can be used to determine average air infiltration rates in buildings. Only measurements of the humidity inside and outside the home, the mass of vapor exchanged by a humidifier/dehumidifier, and the volume of interior air space are needed. This method gives results that...

  14. Chemical vapor deposition coating for micromachines

    SciTech Connect

    MANI,SEETHAMBAL S.; FLEMING,JAMES G.; SNIEGOWSKI,JEFFRY J.; DE BOER,MAARTEN P.; IRWIN,LAWRENCE W.; WALRAVEN,JEREMY A.; TANNER,DANELLE M.; DUGGER,MICHAEL T.

    2000-04-21

    Two major problems associated with Si-based MEMS devices are stiction and wear. Surface modifications are needed to reduce both adhesion and friction in micromechanical structures to solve these problems. In this paper, the authors will present a process used to selectively coat MEMS devices with tungsten using a CVD (Chemical Vapor Deposition) process. The selective W deposition process results in a very conformal coating and can potentially solve both stiction and wear problems confronting MEMS processing. The selective deposition of tungsten is accomplished through silicon reduction of WF{sub 6}, which results in a self-limiting reaction. The selective deposition of W only on polysilicon surfaces prevents electrical shorts. Further, the self-limiting nature of this selective W deposition process ensures the consistency necessary for process control. Selective tungsten is deposited after the removal of the sacrificial oxides to minimize process integration problems. This tungsten coating adheres well and is hard and conducting, requirements for device performance. Furthermore, since the deposited tungsten infiltrates under adhered silicon parts and the volume of W deposited is less than the amount of Si consumed, it appears to be possible to release stuck parts that are contacted over small areas such as dimples. Results from tungsten deposition on MEMS structures with dimples will be presented. The effect of wet and vapor phase cleanings prior to the deposition will be discussed along with other process details. The W coating improved wear by orders of magnitude compared to uncoated parts. Tungsten CVD is used in the integrated-circuit industry, which makes this approach manufacturable.

  15. Photoluminescence Mechanism and Photocatalytic Activity of Organic-Inorganic Hybrid Materials Formed by Sequential Vapor Infiltration.

    PubMed

    Akyildiz, Halil I; Stano, Kelly L; Roberts, Adam T; Everitt, Henry O; Jur, Jesse S

    2016-05-03

    Organic-inorganic hybrid materials formed by sequential vapor infiltration (SVI) of trimethylaluminum into polyester fibers are demonstrated, and the photoluminescence of the fibers is evaluated using a combined UV-vis and photoluminescence excitation (PLE) spectroscopy approach. The optical activity of the modified fibers depends on infiltration thermal processing conditions and is attributed to the reaction mechanisms taking place at different temperatures. At low temperatures a single excitation band and dual emission bands are observed, while, at high temperatures, two distinct absorption bands and one emission band are observed, suggesting that the physical and chemical structure of the resulting hybrid material depends on the SVI temperature. Along with enhancing the photoluminescence intensity of the PET fibers, the internal quantum efficiency also increased to 5-fold from ∼4-5% to ∼24%. SVI processing also improved the photocatalytic activity of the fibers, as demonstrated by photodeposition of Ag and Au metal particles out of an aqueous metal salt solution onto fiber surfaces via UVA light exposure. Toward applications in flexible electronics, well-defined patterning of the metallic materials is achieved by using light masking and focused laser rastering approaches.

  16. Atmospheric pressure synthesis of photoluminescent hybrid materials by sequential organometallic vapor infiltration into polyethylene terephthalate fibers

    SciTech Connect

    Akyildiz, Halil I.; Mousa, Moataz Bellah M.; Jur, Jesse S.

    2015-01-28

    Exposing a polymer to sequential organometallic vapor infiltration (SVI) under low pressure conditions can significantly modify the polymer's chemical, mechanical, and optical properties. We demonstrate that SVI of trimethylaluminum into polyethylene terephthalate (PET) can also proceed readily at atmospheric pressure, and at 60 °C the extent of reaction determined by mass uptake is independent of pressure between 2.5 Torr and 760 Torr. At 120 °C, however, the mass gain is 50% larger at 2.5 Torr relative to that at 760 Torr, indicating that the precursor diffusion in the chamber and fiber matrix decreases at higher source pressure. Mass gain decreases, in general, as the SVI process temperature increases both at 2.5 Torr and 760 Torr attributed to the faster reaction kinetics forming a barrier layer, which prevents further diffusion of the reactive species. The resulting PET/Al-O{sub x} product shows high photoluminescence compared to untreated fibers. A physical mask on the polymer during infiltration at 760 Torr is replicated in the underlying polymer, producing an image in the polymer that is visible under UV illumination. Because of the reduced precursor diffusivity during exposure at 760 Torr, the image shows improved resolution compared to SVI performed under typical 2.5 Torr conditions.

  17. HANFORD CHEMICAL VAPORS WORKER CONCERNS & EXPOSURE EVALUATION

    SciTech Connect

    ANDERSON, T.J.

    2006-12-20

    Chemical vapor emissions from underground hazardous waste storage tanks on the Hanford site in eastern Washington State are a potential concern because workers enter the tank farms on a regular basis for waste retrievals, equipment maintenance, and surveillance. Tank farm contractors are in the process of retrieving all remaining waste from aging single-shell tanks, some of which date to World War II, and transferring it to newer double-shell tanks. During the waste retrieval process, tank farm workers are potentially exposed to fugitive chemical vapors that can escape from tank headspaces and other emission points. The tanks are known to hold more than 1,500 different species of chemicals, in addition to radionuclides. Exposure assessments have fully characterized the hazards from chemical vapors in half of the tank farms. Extensive sampling and analysis has been done to characterize the chemical properties of hazardous waste and to evaluate potential health hazards of vapors at the ground surface, where workers perform maintenance and waste transfer activities. Worker concerns. risk communication, and exposure assessment are discussed, including evaluation of the potential hazards of complex mixtures of chemical vapors. Concentrations of vapors above occupational exposure limits-(OEL) were detected only at exhaust stacks and passive breather filter outlets. Beyond five feet from the sources, vapors disperse rapidly. No vapors have been measured above 50% of their OELs more than five feet from the source. Vapor controls are focused on limited hazard zones around sources. Further evaluations of vapors include analysis of routes of exposure and thorough analysis of nuisance odors.

  18. Vapor Pressure of Coal Chemicals

    NASA Astrophysics Data System (ADS)

    Chao, J.; Lin, C. T.; Chung, T. H.

    1983-10-01

    The vapor pressure data on 324 coal compounds are collected and analyzed. The adopted data sets for each substance are weighted and combined to fit into a Cox vapor pressure equation, log10P=(1-D/T)×10(A+BT+CT2) by the least-squares method. The results of the literature review and the evaluated values of coefficients for the vapor pressure equations are presented in separate tables. For ease of presentation, the coal compounds are divided into seven groups, based upon their molecular structures. They are (1) benzene and its derivatives, (2) naphthalene and its derivatives, (3) saturated ring compounds, (4) unsaturated ring compounds, (5) heterocyclic sulfur compounds, (6) heterocyclic nitrogen compounds, and (7) heterocyclic oxygen compounds.

  19. Automated semiconductor vacuum chemical vapor deposition facility

    NASA Technical Reports Server (NTRS)

    1982-01-01

    A semiconductor vacuum chemical vapor deposition facility (totally automatic) was developed. Wafers arrived on an air track, automatically loaded into a furnace tube, processed, returned to the track, and sent on to the next operation. The entire process was controlled by a computer.

  20. CHEMICAL VAPOR DEPOSITED MATERIALS FOR ELECTRON TUBES.

    DTIC Science & Technology

    The combined techniques of chemical vapor deposition and photocopying offer the promise of new and useful slow -wave structures for microwave tubes...These slow -wave structures include conventional periodic structures such as the helix, meander line and interdigital line. In addition, structures

  1. Chemical vapor deposition of mullite coatings

    DOEpatents

    Sarin, Vinod; Mulpuri, Rao

    1998-01-01

    This invention is directed to the creation of crystalline mullite coatings having uniform microstructure by chemical vapor deposition (CVD). The process comprises the steps of establishing a flow of reactants which will yield mullite in a CVD reactor, and depositing a crystalline coating from the reactant flow. The process will yield crystalline coatings which are dense and of uniform thickness.

  2. Low-pressure, chemical vapor deposition polysilicon

    NASA Technical Reports Server (NTRS)

    Gallagher, B. D.; Crotty, G. C.

    1986-01-01

    The low-pressure chemical vapor deposition (LPCVD) of polycrystalline silicon was investigted. The physical system was described, as was the controlling process parameters and requirements for producing films for use as an integral portion of the solar cell contact system.

  3. Numerical modeling tools for chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Jasinski, Thomas J.; Childs, Edward P.

    1992-01-01

    Development of general numerical simulation tools for chemical vapor deposition (CVD) was the objective of this study. Physical models of important CVD phenomena were developed and implemented into the commercial computational fluid dynamics software FLUENT. The resulting software can address general geometries as well as the most important phenomena occurring with CVD reactors: fluid flow patterns, temperature and chemical species distribution, gas phase and surface deposition. The physical models are documented which are available and examples are provided of CVD simulation capabilities.

  4. DuPont Chemical Vapor Technical Report

    SciTech Connect

    MOORE, T.L.

    2003-10-03

    DuPont Safety Resources was tasked with reviewing the current chemical vapor control practices and providing preventive recommendations on best commercial techniques to control worker exposures. The increased focus of the tank closure project to meet the 2024 Tri-Party Agreement (TPA) milestones has surfaced concerns among some CH2MHill employees and other interested parties. CH2MHill is committed to providing a safe working environment for employees and desires to safely manage the tank farm operations using appropriate control measures. To address worker concerns, CH2MHill has chartered a ''Chemical Vapors Project'' to integrate the activities of multiple CH2MHill project teams, and solicit the expertise of external resources, including an independent Industrial Hygiene expert panel, a communications consultant, and DuPont Safety Resources. Over a three-month time period, DuPont worked with CH2MHill ESH&Q, Industrial Hygiene, Engineering, and the independent expert panel to perform the assessment. The process included overview presentations, formal interviews, informal discussions, documentation review, and literature review. DuPont Safety Resources concluded that it is highly unlikely that workers in the tank farms are exposed to chemicals above established standards. Additionally, the conventional and radiological chemistry is understood, the inherent chemical hazards are known, and the risk associated with chemical vapor exposure is properly managed. The assessment highlighted management's commitment to addressing chemical vapor hazards and controlling the associated risks. Additionally, we found the Industrial Hygiene staff to be technically competent and well motivated. The tank characterization data resides in a comprehensive database containing the tank chemical compositions and relevant airborne concentrations.

  5. Areal variation and chemical modification of weathered shale infiltration characteristics

    SciTech Connect

    Luxmoore, R.J.; Spalding, B.P.; Munro, I.M.

    1981-07-01

    Spatial variability of infiltration into a weathered shale subsoil was evaluated at a site proximal to one used for shallow land burial of low-level radioactive waste at Oak Ridge National Laboratory. Double-ring infiltometers were installed at 48 locations on a 2- by 2-m grid after the removal of 1 to 2 m of soil (Litz-Sequoia association, Typic Hapludults). Infiltration rates were measured before and during the 0- to 20- and 239- to 259-day periods following treatment with solutions of NaOH, KOH, NaF, NaAlO/sub 2/, and Na/sub 2/SiO/sub 3/ at rates of 151 equivalents/m/sup 2/. None of these chemical treatments significantly altered infiltration rate, indicating that chemical modification of soil exchange properties may be achieved without inducing hydrologic disturbance in these subsoils. A semivariogram analysis of infiltration data showed that areal variability was random; any spatial patterning must therefore occur at a smaller scale than 2 m.

  6. Silicon refinement by chemical vapor transport

    NASA Technical Reports Server (NTRS)

    Olson, J.

    1984-01-01

    Silicon refinement by chemical vapor transport is discussed. The operating characteristics of the purification process, including factors affecting the rate, purification efficiency and photovoltaic quality of the refined silicon were studied. The casting of large alloy plates was accomplished. A larger research scale reactor is characterized, and it is shown that a refined silicon product yields solar cells with near state of the art conversion efficiencies.

  7. Making Ceramic Fibers By Chemical Vapor

    NASA Technical Reports Server (NTRS)

    Revankar, Vithal V. S.; Hlavacek, Vladimir

    1994-01-01

    Research and development of fabrication techniques for chemical vapor deposition (CVD) of ceramic fibers presented in two reports. Fibers of SiC, TiB2, TiC, B4C, and CrB2 intended for use as reinforcements in metal-matrix composite materials. CVD offers important advantages over other processes: fibers purer and stronger and processed at temperatures below melting points of constituent materials.

  8. Chemical-Vapor-Deposited Diamond Film

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1999-01-01

    This chapter describes the nature of clean and contaminated diamond surfaces, Chemical-vapor-deposited (CVD) diamond film deposition technology, analytical techniques and the results of research on CVD diamond films, and the general properties of CVD diamond films. Further, it describes the friction and wear properties of CVD diamond films in the atmosphere, in a controlled nitrogen environment, and in an ultra-high-vacuum environment.

  9. Making Ceramic Fibers By Chemical Vapor

    NASA Technical Reports Server (NTRS)

    Revankar, Vithal V. S.; Hlavacek, Vladimir

    1994-01-01

    Research and development of fabrication techniques for chemical vapor deposition (CVD) of ceramic fibers presented in two reports. Fibers of SiC, TiB2, TiC, B4C, and CrB2 intended for use as reinforcements in metal-matrix composite materials. CVD offers important advantages over other processes: fibers purer and stronger and processed at temperatures below melting points of constituent materials.

  10. Laser Velocimetry of Chemical Vapor Deposition Flows

    NASA Technical Reports Server (NTRS)

    1993-01-01

    Laser velocimetry (LV) is being used to measure the gas flows in chemical vapor deposition (CVD) reactors. These gas flow measurements can be used to improve industrial processes in semiconductor and optical layer deposition and to validate numerical models. Visible in the center of the picture is the graphite susceptor glowing orange-hot at 600 degrees C. It is inductively heated via the copper cool surrounding the glass reactor.

  11. Chemical vapor deposition of epitaxial silicon

    DOEpatents

    Berkman, Samuel

    1984-01-01

    A single chamber continuous chemical vapor deposition (CVD) reactor is described for depositing continuously on flat substrates, for example, epitaxial layers of semiconductor materials. The single chamber reactor is formed into three separate zones by baffles or tubes carrying chemical source material and a carrier gas in one gas stream and hydrogen gas in the other stream without interaction while the wafers are heated to deposition temperature. Diffusion of the two gas streams on heated wafers effects the epitaxial deposition in the intermediate zone and the wafers are cooled in the final zone by coolant gases. A CVD reactor for batch processing is also described embodying the deposition principles of the continuous reactor.

  12. Interfacial Studies of Chemical Vapor Infiltrated (CVI) Ceramic Matrix Composites

    DTIC Science & Technology

    1990-03-31

    methyldichlorosilane (MDS), methyltrichlorosilane (MTS), and dimethyldichlorosilane (DMDS). The fibers utilized were Nicalon SiC and Nextel 440 mullite. During the... methyltrichlorosilane (MTS), and dimethyldichlorosilane (DMDS). The fibers utilized were Nicalon SiC and Nextel 440 mullite. The chemistry and...MOS), methyltrichlorosilane (MTS), and dimethyldichloro- silane (DMDS). The fiber/matrix interface was tailored by means of introducing a carbon, BN, or

  13. Interfacial Studies of Chemical Vapor Infiltrated (CVI) Ceramic Matrix Composites

    DTIC Science & Technology

    1988-10-01

    methyldichlorosilane (MDS), methyltrichlorosilane (MTS), and dimethyldichlorosilane (DMDS). The fibers utilized were Nicalon SiC and Nextel 440 mullite. The...transference of the saturated carrier to the reactor over long distances without heated lines. Methyltrichlorosilane (MTS), CH 3 SiCI 3 (B.P.= 66.4 0C), is...used extensively by other researchers to deposit SiC and was also used in this program along with dimethyldichlorosilane (DMDS), (CH3)2SiCI 2 (B.P

  14. Chemical vapor deposition of group IIIB metals

    DOEpatents

    Erbil, Ahmet

    1989-01-01

    Coatings of Group IIIB metals and compounds thereof are formed by chemical vapor deposition, in which a heat decomposable organometallic compound of the formula (I) ##STR1## where M is a Group IIIB metal, such as lanthanum or yttrium and R is a lower alkyl or alkenyl radical containing from 2 to about 6 carbon atoms, with a heated substrate which is above the decomposition temperature of the organometallic compound. The pure metal is obtained when the compound of the formula I is the sole heat decomposable compound present and deposition is carried out under nonoxidizing conditions. Intermetallic compounds such as lanthanum telluride can be deposited from a lanthanum compound of formula I and a heat decomposable tellurium compound under nonoxidizing conditions.

  15. Chemical Vapor Deposition Of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Larkin, David J.; Matus, Lawrence G.; Petit, Jeremy B.

    1993-01-01

    Large single-crystal SiC boules from which wafers of large area cut now being produced commerically. Availability of wafers opens door for development of SiC semiconductor devices. Recently developed chemical vapor deposition (CVD) process produces thin single-crystal SiC films on SiC wafers. Essential step in sequence of steps used to fabricate semiconductor devices. Further development required for specific devices. Some potential high-temperature applications include sensors and control electronics for advanced turbine engines and automobile engines, power electronics for electromechanical actuators for advanced aircraft and for space power systems, and equipment used in drilling of deep wells. High-frequency applications include communication systems, high-speed computers, and microwave power transistors. High-radiation applications include sensors and controls for nuclear reactors.

  16. Chemical vapor deposition of group IIIB metals

    DOEpatents

    Erbil, A.

    1989-11-21

    Coatings of Group IIIB metals and compounds thereof are formed by chemical vapor deposition, in which a heat decomposable organometallic compound of the formula given in the patent where M is a Group IIIB metal, such as lanthanum or yttrium and R is a lower alkyl or alkenyl radical containing from 2 to about 6 carbon atoms, with a heated substrate which is above the decomposition temperature of the organometallic compound. The pure metal is obtained when the compound of the formula 1 is the sole heat decomposable compound present and deposition is carried out under nonoxidizing conditions. Intermetallic compounds such as lanthanum telluride can be deposited from a lanthanum compound of formula 1 and a heat decomposable tellurium compound under nonoxidizing conditions.

  17. Chemical agent simulant release from clothing following vapor exposure.

    PubMed

    Feldman, Robert J

    2010-02-01

    Most ambulatory victims of a terrorist chemical attack will have exposure to vapor only. The study objective was to measure the duration of chemical vapor release from various types of clothing. A chemical agent was simulated using methyl salicylate (MeS), which has similar physical properties to sulfur mustard and was the agent used in the U.S. Army's Man-In-Simulant Test (MIST). Vapor concentration was measured with a Smiths Detection Advanced Portable Detector (APD)-2000 unit. The clothing items were exposed to vapor for 1 hour in a sealed cabinet; vapor concentration was measured at the start and end of each exposure. Clothing was then removed and assessed every 5 minutes with the APD-2000, using a uniform sweep pattern, until readings remained 0. Concentration and duration of vapor release from clothing varied with clothing composition and construction. Lightweight cotton shirts and jeans had the least trapped vapor; down outerwear, the most. Vapor concentration near the clothing often increased for several minutes after the clothing was removed from the contaminated environment. Compression of thick outerwear released additional vapor. Mean times to reach 0 ranged from 7 minutes for jeans to 42 minutes for down jackets. This simulation model of chemical vapor release demonstrates persistent presence of simulant vapor over time. This implies that chemical vapor may be released from the victims' clothing after they are evacuated from the site of exposure, resulting in additional exposure of victims and emergency responders. Insulated outerwear can release additional vapor when handled. If a patient has just moved to a vapor screening point, immediate assessment before additional vapor can be released from the clothing can lead to a false-negative assessment of contamination.

  18. The influence of vapor pressure of chemicals on dermal penetration.

    PubMed

    Gilpin, Sarah

    2014-01-01

    Dermal exposure is an important route of entry for chemicals in occupational and consumer settings. Key to this exposure is the penetration of the skin's barrier, and key to this penetration is a chemical's vapor pressure. Until now, vapor pressure and its effects on the skin have yet to be widely studied. This review aims to provide some historical background on early work on dermal penetration for volatile materials, which has helped form later research into the effects of vapor pressure on chemical risk assessment for dermal exposures. This review should be the start of an investigation into more in-depth coverage of vapor pressure and current prediction models.

  19. Modeling of Tungsten Thermal Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kim, Byunghoon; Akiyama, Yasunobu; Imaishi, Nobuyuki; Park, Heung-Chul

    1999-05-01

    Low-pressure chemical vapor deposition (LPCVD) of tungsten (W)film on silicon (Si) substrate was performed by reducting hexafluoride(WF6) with hydrogen. This CVD system is known for its nonlineardependence of growth rate on WF6 concentration. This study adopted asimple surface-reaction model which assumes that the precursor, i.e.,WF6, in the gas phase adsorbs on solid surfaces and then the adsorbedWF6 molecule is converted into tungsten solid film. The two kineticparameters involved in the model are derived from the experimentalresults. The solidification rate constant (ks) is equal to the growthrate at very high WF6 concentrations. The adsorption rate constant(ka) is derived from profile analyses of films grown in microtrenchesunder very low WF6 concentrations by applying the conventional MonteCarlo simulation code, which is valid for linear surface-reactionsystems. In the temperature range of 623 to 823 K, ka and ks haveactivation energies of 82 kJmol-1, 66.1 kJmol-1, respectively. A newlyproposed Monte Carlo simulation for nonlinear reaction systems, incombination with the two kinetic parameters, can quantitativelypredict the shape of film in microtrenches for a wide range oftemperatures and WF6 concentrations.

  20. Characterization of Metalorganic Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Jesser, W. A.

    1998-01-01

    A series of experimental and numerical investigations to develop a more complete understanding of the reactive fluid dynamics of chemical vapor deposition were conducted. In the experimental phases of the effort, a horizontal CVD reactor configuration was used for the growth of InP at UVA and for laser velocimetry measurements of the flow fields in the reactor at LaRC. This horizontal reactor configuration was developed for the growth of III-V semiconductors and has been used by our research group in the past to study the deposition of both GaAs and InP. While the ultimate resolution of many of the heat and mass transport issues will require access to a reduced-gravity environment, the series of groundbased research makes direct contributions to this area while attempting to answer the design questions for future experiments of how low must gravity be reduced and for how long must this gravity level be maintained to make the necessary measurements. It is hoped that the terrestrial experiments will be useful for the design of future microgravity experiments which likely will be designed to employ a core set of measurements for applications in the microgravity environment such as HOLOC, the Fluid Physics/Dynamics Facility, or the Schlieren photography, the Laser Imaging Velocimetry and the Laser Doppler Velocimetry instruments under development for the Advanced Fluids Experiment Module.

  1. Development of chemical vapor composites, CVC materials. Final report

    SciTech Connect

    1998-10-05

    Industry has a critical need for high-temperature operable ceramic composites that are strong, non-brittle, light weight, and corrosion resistant. Improvements in energy efficiency, reduced emissions and increased productivity can be achieved in many industrial processes with ceramic composites if the reaction temperature and pressure are increased. Ceramic composites offer the potential to meet these material requirements in a variety of industrial applications. However, their use is often restricted by high cost. The Chemical Vapor composite, CVC, process can reduce the high costs and multiple fabrication steps presently required for ceramic fabrication. CVC deposition has the potential to eliminate many difficult processing problems and greatly increase fabrication rates for composites. With CVC, the manufacturing process can control the composites` density, microstructure and composition during growth. The CVC process: can grow or deposit material 100 times faster than conventional techniques; does not require an expensive woven preform to infiltrate; can use high modulus fibers that cannot be woven into a preform; can deposit composites to tolerances of less than 0.025 mm on one surface without further machining.

  2. Preventing Chemical-Vapor Deposition In Selected Areas

    NASA Technical Reports Server (NTRS)

    Keeley, Joseph T.; Goela, Jitendra Singh; Pickering, Michael A.; Taylor, Raymond L.

    1991-01-01

    Method for prevention of chemical-vapor deposition of material in selected areas developed. Gas shroud isolates specific area from rest of deposition system. Inert gas flowing from beneath substrate prevents deposition between substrate and outer ring. Method extremely successful in selective deposition of SiC in chemical-vapor-deposition reactor. Used in deposition of SiC mirror blanks in Large Mirror Substrate and Lidar Mirror programs. Critical element in overall chemical-vapor-deposition process for producing large, lightweight mirrors.

  3. Chemical Vapor Deposition Epitaxy an Patternless and Patterned Substrates.

    ERIC Educational Resources Information Center

    Takoudis, Christos G.

    1990-01-01

    Discusses chemical vapor deposition epitaxy on patternless and patterned substrates for an electronic materials processing course. Describes the processs types and features of epitaxy. Presents some potential problems of epitaxy. Lists 38 references. (YP)

  4. Performance enhancement of hybrid solar cells through chemical vapor annealing.

    PubMed

    Wu, Yue; Zhang, Genqiang

    2010-05-12

    Improvement in power conversion efficiency has been observed in cadmium selenide nanorods/poly(3-hexylthiophene) hybrid solar cells through benzene-1,3-dithiol chemical vapor annealing. Phosphor NMR studies of the nanorods and TEM/AFM characterizations of the morphology of the blended film showed that the ligand exchange reaction and related phase separation happening during the chemical vapor annealing are responsible for the performance enhancement.

  5. Oxidation Protection Systems for Carbon-Carbon Composites Formed by Chemical Vapor Deposition and Plasma Assisted Chemical Vapor Deposition Techniques

    DTIC Science & Technology

    1992-04-22

    3 limitations. The most cow , ron technique used to deposit protective coatings is chemical vapor deposition (CVD). CVD is generally defined as "a... istalled in the gas feeding system. As illustrated in Figure 3-2, the vaporization device contains a Varian type tee adapter, in which ZrCl 4 powder was

  6. Chemical vapor deposition of copper films

    NASA Astrophysics Data System (ADS)

    Borgharkar, Narendra Shamkant

    We have studied the kinetics of copper chemical vapor deposition (CVD) for interconnect metallization using hydrogen (Hsb2) reduction of the Cu(hfac)sb2 (copper(II) hexafluoroacetylacetonate) precursor. Steady-state deposition rates were measured using a hot-wall microbalance reactor. For base case conditions of 2 Torr Cu(hfac)sb2, 40 Torr Hsb2, and 300sp°C, a growth rate of 0.5 mg cmsp{-2} hrsp{-1} (ca. 10 nm minsp{-1}) is observed. Reaction order experiments suggest that the deposition rate passes through a maximum at partial pressure of 2 Torr of Cu(hfac)sb2. The deposition rate has an overall half-order dependence on Hsb2 partial pressure. A Langmuir-Hinshelwood rate expression is used to describe the observed kinetic dependencies on Cu(hfac)sb2, Hsb2, and H(hfac). Based on the rate expression a mechanism is proposed in which the overall rate is determined by the surface reaction of adsorbed Cu(hfac)sb2 and H species. Additionally, the role of alcohols in enhancing the deposition rate has been investigated. Addition of isopropanol results in a six fold enhancement to yield a deposition rate of 3.3 mg cmsp{-2} hrsp{-1} (ca. 60 nm minsp{-1}) at 5 Torr of isopropanol, 0.4 Torr Cu(hfac)sb2, 40 Torr Hsb2, and 300sp°C. Ethanol and methanol give lower enhancements of 1.75 and 1.1 mg cmsp{-2} hrsp{-1}, respectively. A mechanism based on the ordering of the aqueous pKsba values of the alcohols is proposed to explain the observed results. Lastly, we have built a warm-wall Pedestal reactor apparatus to demonstrate copper CVD on TiN/Si substrates. The apparatus includes a liquid injection system for transport of isopropanol-diluted precursor solutions. At optimized conditions of precursor and substrate pre-treatments, we have deposited uniform films of copper on TiN/Si substrates at an average deposition rate of 3.0 mg cmsp{-2} hrsp{-1} (ca. 60 nm minsp{-1}).

  7. Differentiation of vapor mixture with chemical sensor arrays

    NASA Astrophysics Data System (ADS)

    Kim, Chulki; Jung, Youngmo; Moon, Hi Gyu; Lee, Ji Eun; Shin, Bum Ju; Lim, Chaehyun; Choi, Jaebin; Seo, Minah; Kim, Jae Hun; Jun, Seong Chan; Kim, Sang Kyung; Kang, Chong Yun; Lee, Taikjin; Lee, Seok

    2015-07-01

    Arrays of partially selective chemical sensors have been the focus of extensive research over the past decades because of their potential for widespread application in ambient air monitoring, health and safety, and biomedical diagnostics. Especially, vapor sensor arrays based on functionalized nanomaterials have shown great promise with their high sensitivity by dimensionality and outstanding electronic properties. Here, we introduce experiments where individual vapors and mixtures of them are examined by different chemical sensor arrays. The collected data from those sensor arrays are further analyzed by a principal component analysis (PCA) and targeted vapors are recognized based on prepared database.

  8. A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal.

    PubMed

    Zhang, Yuqi; Qiu, Jianhua; Hu, Rongrong; Li, Pei; Gao, Loujun; Heng, Liping; Tang, Ben Zhong; Jiang, Lei

    2015-04-21

    A photonic crystal (PC) sensor that can selectively detect organic vapors through visual color changes has been proposed. The sensor was fabricated by infiltrating a tetraphenylethene polymer (TPEP) into the voids of SiO2 inverse opal photonic crystal. When the sensor was exposed to tetrahydrofuran or acetone vapor, a red shift of the stopband of more than 50 nm could be clearly observed; meanwhile, the film's color changed from violet to cyan. Subsequently, when exposed to air, the stopband underwent a blue shift and the color returned to violet. The reason for the observed change is that a reversible adsorption-desorption process occurs on alternate exposure of the sensor to organic vapor and air, due to the high specific surface area of the inverse opal macroporous structure and the high affinity of TPEP to tetrahydrofuran and acetone. The adsorption of vapor analyte can increase the PC's effective refractive index, which will induce the stopband red shift and the resulting color change according to Bragg's Law. The reversible adsorption-desorption of organic vapors varied the effective refractive index of the sensor repeatedly, causing the reversible stopband shift and color change, and providing a general method for the design of visual vapor sensors.

  9. Chemical vapor deposition of graphene single crystals.

    PubMed

    Yan, Zheng; Peng, Zhiwei; Tour, James M

    2014-04-15

    As a two-dimensional (2D) sp(2)-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and low yields. Recently developed chemical vapor deposition (CVD) techniques have emerged as an important method for the scalable production of large-size and high-quality graphene for various applications. However, CVD-derived graphene is polycrystalline and demonstrates degraded properties induced by grain boundaries. Thus, the next critical step of graphene growth relies on the synthesis of large graphene single crystals. In this Account, we first discuss graphene grain boundaries and their influence on graphene's properties. Mechanical and electrical behaviors of CVD-derived polycrystalline graphene are greatly reduced when compared to that of exfoliated graphene. We then review four representative pathways of pretreating Cu substrates to make millimeter-sized monolayer graphene grains: electrochemical polishing and high-pressure annealing of Cu substrate, adding of additional Cu enclosures, melting and resolidfying Cu substrates, and oxygen-rich Cu substrates. Due to these pretreatments, the nucleation site density on Cu substrates is greatly reduced, resulting in hexagonal-shaped graphene grains that show increased grain domain size and comparable electrical properties as to exfoliated graphene. Also, the properties of graphene can be engineered by its shape, thickness and spatial structure. Thus, we further discuss recently developed methods of making graphene grains with special spatial structures, including snowflakes, six-lobed flowers, pyramids and hexagonal graphene onion rings. The fundamental growth mechanism and practical applications of these well-shaped graphene structures should be interesting topics and

  10. The chemical vapor deposition of zirconium carbide onto ceramic substrates

    SciTech Connect

    Glass, John A, Jr.; Palmisiano, Nick, Jr.; Welsh, R. Edward

    1999-07-01

    Zirconium carbide is an attractive ceramic material due to its unique properties such as high melting point, good thermal conductivity, and chemical resistance. The controlled preparation of zirconium carbide films of superstoichiometric, stoichiometric, and substoichiometric compositions has been achieved utilizing zirconium tetrachloride and methane precursor gases in an atmospheric pressure high temperature chemical vapor deposition system.

  11. Advanced chemical heat pumps using liquid-vapor reactions

    NASA Astrophysics Data System (ADS)

    Kirol, L.

    Chemical heat pumps utilizing liquid-vapor reactions can be configured in forms analogous to electric drive vapor-compression heat pumps and heat activated absorption heat pumps. Basic thermodynamic considerations eliminate some heat pumps and place restrictive working fluid requirements on others, but two thermodynamically feasible systems have significant potential advantage over conventional technology. An electric drive reactive heat pump can use smaller heat exchangers and compressor than a vapor-compression machine, and have more flexible operating characteristics. A waste heat driven heat pump (temperature amplifier) using liquid-vapor chemical reactions can operate with higher coefficient of performance and smaller heat exchangers than an absorption temperature amplifying heat pump. Higher temperatures and larger temperature lifts should also be possible.

  12. SAW Sensors for Chemical Vapors and Gases

    PubMed Central

    Devkota, Jagannath; Ohodnicki, Paul R.; Greve, David W.

    2017-01-01

    Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions. Based on previous publications, we suggest some appropriate sensing approaches for particular applications and identify new opportunities and needs for additional research in this area moving into the future. PMID:28397760

  13. Vaporization of a mixed precursors in chemical vapor deposition for YBCO films

    NASA Technical Reports Server (NTRS)

    Zhou, Gang; Meng, Guangyao; Schneider, Roger L.; Sarma, Bimal K.; Levy, Moises

    1995-01-01

    Single phase YBa2Cu3O7-delta thin films with T(c) values around 90 K are readily obtained by using a single source chemical vapor deposition technique with a normal precursor mass transport. The quality of the films is controlled by adjusting the carrier gas flow rate and the precursor feed rate.

  14. A novel chemically selective siloxane polymer for chemical vapor sensing

    NASA Astrophysics Data System (ADS)

    Huang, Jia; Jiang, Yadong; Du, Xiaosong; Bi, Juan

    2010-10-01

    A new hydrogen-bond acidic carbosiloxane polymer for quartz crystal microbalance sensors (QCMs) application was synthesized via O-alkylation, Claisen rearrange, hydrosilylation reaction and functionalized the polysiloxane with trifluoroacetone groups (TFA). The trifluoroisopropanol functionalized polysiloxane was characterized by FT-IR and 1HNMR. And this novel siloxane polymer was coated onto AT-cut 8 MHz QCM sensors to investigate its gas sensitive responses to the organophosphorus nerve agent stimulant dimethyl methylphosphonate (DMMP) vapor as well as other interfering organic vapors. The research work indicated that frequency shifts of the trifluoroisopropanol functionalized polysiloxane based QCM sensor to the DMMP vapor were completely linear, and with a regression coefficient of 0.9973 in the concentration range of 10-60 ppm. In addition, the sensitivity of the fabricated QCM sensors to DMMP was up to 10.64 Hz/ ppm, and much higher than the other interfering vapors, limits of detection (LODs) of the QCM sensors was 0.28 ppm, thus high selectivity to DMMP was demonstrated in this work.

  15. Chemical Vapor Deposition of Aluminum Oxide Thin Films

    ERIC Educational Resources Information Center

    Vohs, Jason K.; Bentz, Amy; Eleamos, Krystal; Poole, John; Fahlman, Bradley D.

    2010-01-01

    Chemical vapor deposition (CVD) is a process routinely used to produce thin films of materials via decomposition of volatile precursor molecules. Unfortunately, the equipment required for a conventional CVD experiment is not practical or affordable for many undergraduate chemistry laboratories, especially at smaller institutions. In an effort to…

  16. A novel induction heater for chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ong, C. W.; Wong, H. K.; Sin, K. S.; Yip, S. T.; Chik, K. P.

    1989-06-01

    We report how an induction cooker for household use can be modified for heating substrate or heating gases to high temperature in a chemical vapor deposition system. Only minor changes of the cooker are necessary. Stable substrate temperature as high as 900 °C was achieved with input power of about 1150 W.

  17. Chemical Vapor Deposition of Aluminum Oxide Thin Films

    ERIC Educational Resources Information Center

    Vohs, Jason K.; Bentz, Amy; Eleamos, Krystal; Poole, John; Fahlman, Bradley D.

    2010-01-01

    Chemical vapor deposition (CVD) is a process routinely used to produce thin films of materials via decomposition of volatile precursor molecules. Unfortunately, the equipment required for a conventional CVD experiment is not practical or affordable for many undergraduate chemistry laboratories, especially at smaller institutions. In an effort to…

  18. Quantitative Infrared Spectra of Vapor Phase Chemical Agents

    SciTech Connect

    Sharpe, Steven W.; Johnson, Timothy J.; Chu, P M.; Kleimeyer, J; Rowland, Brad; Gardner, Patrick J.

    2003-04-21

    Quantitative high resolution (0.1 cm -1) infrared spectra have been acquired for a number of pressure broadened (101.3 KPa N2), vapor phase chemicals including: Sarin (GB), Soman (GD), Tabun (GA), Cyclosarin (GF), VX, nitrogen mustard (HN3), sulfur mustard (HD) and Lewisite (L).

  19. Chemical vapor deposition for automatic processing of integrated circuits

    NASA Technical Reports Server (NTRS)

    Kennedy, B. W.

    1980-01-01

    Chemical vapor deposition for automatic processing of integrated circuits including the wafer carrier and loading from a receiving air track into automatic furnaces and unloading on to a sending air track is discussed. Passivation using electron beam deposited quartz is also considered.

  20. The Chemical Vapor Deposition of Iridium.

    DTIC Science & Technology

    1981-07-01

    accepted types are made of porous tungsten impregnated with barium calcium aluminates (Levi, 1955; Brodie and Jenkins, 1956). The emission capability of the...not only does the chemical composition of the pore ends and the bulk material undergo alteration, but the crystal structure of the tungsten (Maloney... hexafluoride to iridium metal or IrF 6 species. In our work, IrF 6 was prepared and stored in fluorine-passivated apparatus, and between runs maintained at

  1. Chemical vapor deposition reactor. [providing uniform film thickness

    NASA Technical Reports Server (NTRS)

    Chern, S. S.; Maserjian, J. (Inventor)

    1977-01-01

    An improved chemical vapor deposition reactor is characterized by a vapor deposition chamber configured to substantially eliminate non-uniformities in films deposited on substrates by control of gas flow and removing gas phase reaction materials from the chamber. Uniformity in the thickness of films is produced by having reactive gases injected through multiple jets which are placed at uniformally distributed locations. Gas phase reaction materials are removed through an exhaust chimney which is positioned above the centrally located, heated pad or platform on which substrates are placed. A baffle is situated above the heated platform below the mouth of the chimney to prevent downdraft dispersion and scattering of gas phase reactant materials.

  2. Chemical Vapor Deposition of Turbine Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Haven, Victor E.

    1999-01-01

    Ceramic thermal barrier coatings extend the operating temperature range of actively cooled gas turbine components, therefore increasing thermal efficiency. Performance and lifetime of existing ceram ic coatings are limited by spallation during heating and cooling cycles. Spallation of the ceramic is a function of its microstructure, which is determined by the deposition method. This research is investigating metalorganic chemical vapor deposition (MOCVD) of yttria stabilized zirconia to improve performance and reduce costs relative to electron beam physical vapor deposition. Coatings are deposited in an induction-heated, low-pressure reactor at 10 microns per hour. The coating's composition, structure, and response to the turbine environment will be characterized.

  3. Copper-vapor-catalyzed chemical vapor deposition of graphene on dielectric substrates

    NASA Astrophysics Data System (ADS)

    Yang, Chao; Wu, Tianru; Wang, Haomin; Zhang, Xuefu; Shi, Zhiyuan; Xie, Xiaoming

    2017-07-01

    Direct synthesis of high-quality graphene on dielectric substrates is important for its application in electronics. In this work, we report the process of copper-vapor-catalyzed chemical vapor deposition of high-quality and large graphene domains on various dielectric substrates. The copper vapor plays a vital role on the growth of transfer-free graphene. Both single-crystal domains that are much larger than previous reports and high-coverage graphene films can be obtained by adjusting the growth duration. The quality of the obtained graphene was verified to be comparable with that of graphene grown on Cu foil. The progress reported in this work will aid the development of the application of transfer-free graphene in the future.

  4. Synthesis of mullite coatings by chemical vapor deposition

    SciTech Connect

    Mulpuri, R.P.; Sarin, V.K.

    1996-06-01

    Formation of mullite on ceramic substrates via chemical vapor deposition was investigated. Mullite is a solid solution of Al{sub 2}O{sub 3} and SiO{sub 2} with a composition of 3Al{sub 2}O{sub 3}{center_dot}2SiO{sub 2}. Thermodynamic calculations performed on the AlCl{sub 3}{endash}SiCl{sub 4}{endash}CO{sub 2}{endash}H{sub 2} system were used to construct equilibrium chemical vapor deposition (CVD) phase diagrams. With the aid of these diagrams and consideration of kinetic rate limiting factors, initial process parameters were determined. Through process optimization, crystalline CVD mullite coatings have been successfully grown on SiC and Si{sub 3}N{sub 4} substrates. Results from the thermodynamic analysis, process optimization, and effect of various process parameters on deposition rate and coating morphology are discussed. {copyright} {ital 1996 Materials Research Society.}

  5. Metal Organic-Chemical Vapor Deposition fabrication of semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Thomas, C.

    1980-08-01

    The metal organic chemical vapor deposition (MO-CVD) process was studied and implemented in detail. Single crystal GaAs, and Ga(x)Al(1-x)As films were grown on GaAs by depositing metal organic alkyl gallium compounds in the presence of an arsine mixture. The metal organic chemical vapor deposition process allowed formation of the semiconductor compound directly on the heated substrate in only one hot temperature zone. With MO-CVD, semiconductor films can be efficiently produced by a more economical, less complicated process which will lend itself more easily than past fabrication procedures, to high quantity, high quality reproduction techniques of semiconductor lasers. Clearly MO-CVD is of interest to the communication industry where semiconductor lasers are used extensively in fiber optic communication systems, and similarly to the solar energy business where GaAs substrates are used as photoelectric cells.

  6. Finite Element Analysis Modeling of Chemical Vapor Deposition of Silicon Carbide

    DTIC Science & Technology

    2014-06-19

    Conference on Computational Fluid Dynamics . 6. de Jong, F. & M. Meyyappan. (1996). Numerical Simulation of Silicon Carbide Chemical Vapor Deposition...FINITE ELEMENT ANALYSIS MODELING OF CHEMICAL VAPOR DEPOSITION OF SILICON CARBIDE !! THESIS JUNE 2014 ! Brandon M. Allen...T-14-J-38 ! ! FINITE ELEMENT ANALYSIS MODELING OF CHEMICAL VAPOR DEPOSITION OF SILICON CARBIDE !! THESIS Presented to the Faculty Department of

  7. Laser Induced Chemical Vapor Deposition of Gallium Arsenide Films.

    DTIC Science & Technology

    1987-08-20

    be grown. The VPE processes can be subdivided into (a) the chloride and (b) the metalorganic chemical vapor deposition (MOCVD) processes. The... chloride VPE processes, utilizing 1= AsCl 3 -Ga-H 2 or HC1-Ga-AsH3 . are capable of producing epitazial layers with low carrier concentrations and high...electron mobilities. However. the chloride systems have not been successful for the growth of aluminum- containing III-V alloys because of the reactivity

  8. Processing Research on Chemically Vapor Deposited Silicon Nitride.

    DTIC Science & Technology

    1979-12-01

    the feasi- bility of synthesizing free-standing plate and figured geometries of phase-pure silicon nitride by the chemical vapor deposition (CVD) method...ates toward moisture and the probability that they all contain absorbed ammonium chloride and ammonia. A strong ammoniacal odor indicates that...solid (V- L -S) processes favored by high ammonia/silicon ratios, high concentrations and long times. Whisker formation would be favored by the opposite

  9. Combustion chemical vapor desposited coatings for thermal barrier coating systems

    SciTech Connect

    Hampikian, J.M.; Carter, W.B.

    1995-10-01

    The new deposition process, combustion chemical vapor deposition, shows a great deal of promise in the area of thermal barrier coating systems. This technique produces dense, adherent coatings, and does not require a reaction chamber. Coatings can therefore be applied in the open atmosphere. The process is potentially suitable for producing high quality CVD coatings for use as interlayers between the bond coat and thermal barrier coating, and/or as overlayers, on top of thermal barrier coatings.

  10. Chemical vapor deposition coating of fibers using microwave application

    NASA Technical Reports Server (NTRS)

    Barmatz, Martin B. (Inventor); Hoover, Gordon (Inventor); Jackson, Henry W. (Inventor)

    2000-01-01

    Chemical vapor deposition coating is carried out in a cylindrical cavity. The fibers are heated by a microwave source that is uses a TM0N0 mode, where O is an integer, and produces a field that depends substantially only on radius. The fibers are observed to determine their heating, and their position can be adjusted. Once the fibers are uniformly heated, a CVD reagent is added to process the fibers.

  11. Extraordinary magnetoresistance in shunted chemical vapor deposition grown graphene devices

    DTIC Science & Technology

    2011-07-01

    than 95% single-layer gra- phene using chemical vapor deposition (CVD) on copper foils.12 These large-area films are transferable to any arbi- trary...graphene will reconcile with the need for higher mobility, as mobility coupled the cleanliness and defectiveness of the graphene. Nonetheless, such devices...Wiesendagner, Science 320, 82 (2008). 21A. L. Friedman, H. Chun, Y. J. Jung, D. Heiman, E. R. Glaser , and L. Menon, Phys. Rev. B 81, 115461 (2010). FIG. 3

  12. Fabrication and evaluation of chemically vapor deposited tungsten heat pipe

    NASA Technical Reports Server (NTRS)

    Bacigalupi, R. J.

    1972-01-01

    A network of lithium-filled tungsten heat pipes is considered as a method of heat extraction from high temperature nuclear reactors. The need for material purity and shape versatility in these applications dictates the use of chemically vapor deposited (CVD) tungsten. Adaptability of CVD tungsten to complex heat pipe designs is shown. Deposition and welding techniques are described. Operation of two lithium-filled CVD tungsten heat pipes above 1800 K is discussed.

  13. Research on chemical vapor deposition processes for advanced ceramic coatings

    NASA Technical Reports Server (NTRS)

    Rosner, Daniel E.

    1993-01-01

    Our interdisciplinary background and fundamentally-oriented studies of the laws governing multi-component chemical vapor deposition (VD), particle deposition (PD), and their interactions, put the Yale University HTCRE Laboratory in a unique position to significantly advance the 'state-of-the-art' of chemical vapor deposition (CVD) R&D. With NASA-Lewis RC financial support, we initiated a program in March of 1988 that has led to the advances described in this report (Section 2) in predicting chemical vapor transport in high temperature systems relevant to the fabrication of refractory ceramic coatings for turbine engine components. This Final Report covers our principal results and activities for the total NASA grant of $190,000. over the 4.67 year period: 1 March 1988-1 November 1992. Since our methods and the technical details are contained in the publications listed (9 Abstracts are given as Appendices) our emphasis here is on broad conclusions/implications and administrative data, including personnel, talks, interactions with industry, and some known applications of our work.

  14. Fluid infiltration into fault zones: Chemical, isotopic, and mechanical effects

    NASA Astrophysics Data System (ADS)

    Kerrich, R.

    1986-01-01

    Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by δ18O=+6±2, δD=-50±20, δ13C=-4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher μ than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and δ13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 2≈0.1, neutral to slightly acidic pH, low salinity ≤3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years. At the Grenville front, translation was accommodated along two mylonite zones and an intervening

  15. Chemical vapor deposition modeling: An assessment of current status

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1991-01-01

    The shortcomings of earlier approaches that assumed thermochemical equilibrium and used chemical vapor deposition (CVD) phase diagrams are pointed out. Significant advancements in predictive capabilities due to recent computational developments, especially those for deposition rates controlled by gas phase mass transport, are demonstrated. The importance of using the proper boundary conditions is stressed, and the availability and reliability of gas phase and surface chemical kinetic information are emphasized as the most limiting factors. Future directions for CVD are proposed on the basis of current needs for efficient and effective progress in CVD process design and optimization.

  16. Temperature and exposure dependence of hybrid organic-inorganic layer formation by sequential vapor infiltration into polymer fibers.

    PubMed

    Akyildiz, Halil I; Padbury, Richard P; Parsons, Gregory N; Jur, Jesse S

    2012-11-06

    The characteristic processing behavior for growth of a conformal nanoscale hybrid organic-inorganic modification to polyamide 6 (PA6) by sequential vapor infiltration (SVI) is demonstrated. The SVI process is a materials growth technique by which exposure of organometallic vapors to a polymeric material promotes the formation of a hybrid organic-inorganic modification at the near surface region of the polymer. This work investigates the SVI exposure temperature and cycling times of sequential exposures of trimethylaluminum (TMA) on PA6 fiber mats. The result of TMA exposure is the preferential subsurface organic-inorganic growth by diffusion into the polymer and reaction with the carbonyl in PA6. Mass gain, infrared spectroscopy, and transmission electron microscopy analysis indicate enhanced materials growth and uniformity at lower processing temperatures. The inverse relationship between mass gain and exposure temperature is explained by the formation of a hybrid layer that prevents the diffusion of TMA into the polymer to react with the PA6 upon subsequent exposure cycles. As few as 10 SVI exposure cycles are observed to saturate the growth, yielding a modified thickness of ∼75 nm and mass increase of ∼14 wt %. Removal of the inherent PA6 moisture content reduces the mass gain by ∼4 wt % at low temperature exposures. The ability to understand the characteristic growth process is critical for the development of the hybrid materials fabrication and modification techniques.

  17. Chemical vapor deposition of conformal, functional, and responsive polymer films.

    PubMed

    Alf, Mahriah E; Asatekin, Ayse; Barr, Miles C; Baxamusa, Salmaan H; Chelawat, Hitesh; Ozaydin-Ince, Gozde; Petruczok, Christy D; Sreenivasan, Ramaswamy; Tenhaeff, Wyatt E; Trujillo, Nathan J; Vaddiraju, Sreeram; Xu, Jingjing; Gleason, Karen K

    2010-05-11

    Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

  18. Model for the Vaporization of Mixed Organometallic Compounds in the Metalorganic Chemical Vapor Deposition of High Temperature Superconducting Films

    NASA Technical Reports Server (NTRS)

    Meng, Guangyao; Zhou, Gang; Schneider, Roger L.; Sarma, Bimal K.; Levy, Moises

    1993-01-01

    A model of the vaporization and mass transport of mixed organometallics from a single source for thin film metalorganic chemical vapor deposition is presented. A stoichiometric gas phase can be obtained from a mixture of the organometallics in the desired mole ratios, in spite of differences in the volatilities of the individual compounds. Proper film composition and growth rates are obtained by controlling the velocity of a carriage containing the organometallics through the heating zone of a vaporizer.

  19. Fabrication of commercial-scale fiber-reinforced hot-gas filters by chemical vapor deposition

    SciTech Connect

    White, L.R. . New Products Dept.)

    1992-11-01

    Goal was to fabricate a filter for removing particulates from hot gases; principal applications would be in advanced utility processes such as pressurized fluidized bed combustion or coal gasification combined cycle systems. Filters were made in two steps: make a ceramic fiber preform and coat it with SiC by chemical vapor infiltration (CVD). The most promising construction was felt/filament wound. Light, tough ceramic composite filters can be made; reinforcement by continuous fibers is needed to avoid brittleness. Direct metal to filter contact does not damage the top which simplifies installation. However, much of the filter surface of felt/filament wound structures is closed over by the CVD coating, and the surface is rough and subject to delamination. Recommendations are given for improving the filters.

  20. Fabrication of commercial-scale fiber-reinforced hot-gas filters by chemical vapor deposition

    SciTech Connect

    White, L.R.

    1992-11-01

    Goal was to fabricate a filter for removing particulates from hot gases; principal applications would be in advanced utility processes such as pressurized fluidized bed combustion or coal gasification combined cycle systems. Filters were made in two steps: make a ceramic fiber preform and coat it with SiC by chemical vapor infiltration (CVD). The most promising construction was felt/filament wound. Light, tough ceramic composite filters can be made; reinforcement by continuous fibers is needed to avoid brittleness. Direct metal to filter contact does not damage the top which simplifies installation. However, much of the filter surface of felt/filament wound structures is closed over by the CVD coating, and the surface is rough and subject to delamination. Recommendations are given for improving the filters.

  1. Chemical vapor deposition modeling for high temperature materials

    NASA Technical Reports Server (NTRS)

    Goekoglu, Sueleyman

    1992-01-01

    The formalism for the accurate modeling of chemical vapor deposition (CVD) processes has matured based on the well established principles of transport phenomena and chemical kinetics in the gas phase and on surfaces. The utility and limitations of such models are discussed in practical applications for high temperature structural materials. Attention is drawn to the complexities and uncertainties in chemical kinetics. Traditional approaches based on only equilibrium thermochemistry and/or transport phenomena are defended as useful tools, within their validity, for engineering purposes. The role of modeling is discussed within the context of establishing the link between CVD process parameters and material microstructures/properties. It is argued that CVD modeling is an essential part of designing CVD equipment and controlling/optimizing CVD processes for the production and/or coating of high performance structural materials.

  2. Kinetics, Chemistry, and Morphology of Syngas Photoinitiated Chemical Vapor Deposition.

    PubMed

    Farhanian, Donya; De Crescenzo, Gregory; Tavares, Jason R

    2017-02-28

    Syngas is the product of gasification processes and is used for the production of petrochemicals. Little attention has been paid to its use in the production of oligomeric thin films under ambient conditions. Herein, the nature of the photoinitiated chemical vapor deposition of films made from syngas using high-wavelength ultraviolet light is discussed, including an exploration of the oligomeric films' structure, synthesis mechanism, and growth kinetics. Specifically, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses provide insight into the chemical structure, illustrating the effect of photogenerated radicals in the formation of aliphatic, anhydride, and cyclic structures. The films are covalently bonded to the substrate and chemically uniform. Electron and atomic force microscopy identify an islandlike morphology for the deposit. These insights into the mechanism and structure are linked to processing parameters through a study on the effect of residence time and treatment duration on the deposition rate, as determined through profilometry.

  3. Hazardous Chemical Vapor Handbook for Marine Tank Vessels,

    DTIC Science & Technology

    1983-10-01

    M3/MIN) 99.41 ENTER DIAMETER OF BUTTERWORTH OPENING IN METERS 0.305 HOW DO YOU WANT TO CALCULATE HENRY S CONSTANT? 1. HENRY S CONSTANT BY MACKAY S...METHOD 2. HENRY S CONSTANT BY DILLING S METHOD 4 SELECT A 1 OR 2 1 INPUT GAMINF, ACTIVITY COEFFICIENT AT INFINITE DILUTION (CHEMICAL IN WATER)li 7.78 Ko...TEMPERATURE (K) VAPOR PRESSURE(rMM HG) DIFFUSION COEFCICIENT(CM2/SEC) KINEMATIC VISCOSITY OF AIR(CM2/SEC) SCHMIDT NUMBER RHOF(GM/CM3) MDOTXZ(GM/CM"-SEC) TAUB

  4. Surface Acoustic Wave Devices as Chemical Vapor Sensors

    DTIC Science & Technology

    2009-03-26

    Plasma-Enhanced Chemical Vapor Deposited Surfaces,” Advanced Materials, 2006. 45. S . C. Huang, K. D. Caldwell , J. N. Lin, H . K. Wang, and J. N. Herron...exposure, 45 s develop, titanium. 59 Figure 4.4: SEM image of one of the devices from Series 3. 4.2 Testing AFRL- Designed SAW Devices Through...Approach for the Detection of Explosives,” Jour- nal of Hazardous Materials,, vol. 144, pp. 15–28, June 2007. 4. M. H . Ervin, S . J. Kilpatrick, C

  5. Chemical Vapor Deposited Zinc Sulfide. SPIE Press Monograph

    SciTech Connect

    McCloy, John S.; Tustison, Randal W.

    2013-04-22

    Zinc sulfide has shown unequaled utility for infrared windows that require a combination of long-wavelength infrared transparency, mechanical durability, and elevated-temperature performance. This book reviews the physical properties of chemical vapor deposited ZnS and their relationship to the CVD process that produced them. An in-depth look at the material microstructure is included, along with a discussion of the material's optical properties. Finally, because the CVD process itself is central to the development of this material, a brief history is presented.

  6. Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nam, Youngwoo; Sun, Jie; Lindvall, Niclas; Jae Yang, Seung; Rae Park, Chong; Woo Park, Yung; Yurgens, August

    2014-01-01

    We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.

  7. Highly sensitive wide bandwidth photodetectors using chemical vapor deposited graphene

    NASA Astrophysics Data System (ADS)

    Goo Kang, Chang; Kyung Lee, Sang; Jin Yoo, Tae; Park, Woojin; Jung, Ukjin; Ahn, Jinho; Hun Lee, Byoung

    2014-04-01

    A photodetector generating a nearly constant photocurrent in a very wide spectral range from ultraviolet (UV) to infrared has been demonstrated using chemical vapor deposited (CVD) graphene. Instability due to a photochemical reaction in the UV region has been minimized using an Al2O3 passivation layer, and a responsivity comparable to that of Highly Ordered Pyrolytic Graphite graphene photodetectors of ˜8 mA/W has been achieved at a 0.1 V bias, despite high defect density in the CVD graphene. A highly sensitive multi-band photodetector using graphene has many potential applications including optical interconnects, multi-band imaging sensors, highly sensitive motion detectors, etc.

  8. Combustion chemical vapor deposited coatings for thermal barrier coating systems

    SciTech Connect

    Hampikian, J.M.; Carter, W.B.

    1995-12-31

    The new deposition process, combustion chemical vapor deposition, shows a great deal of promise in the area of thermal barrier coating systems. This technique produces dense, adherent coatings, and does not require a reaction chamber. Coatings can therefore be applied in the open atmosphere. The process is potentially suitable for producing high quality CVD coatings for use as interlayers between the bond coat and thermal barrier coating, and/or as overlayers, on top of thermal barrier coatings. In this report, the evaluation of alumina and ceria coatings on a nickel-chromium alloy is described.

  9. Plasma-enhanced chemical vapor deposition of multiwalled carbon nanofibers

    NASA Technical Reports Server (NTRS)

    Matthews, Kristopher; Cruden, Brett A.; Chen, Bin; Meyyappan, M.; Delzeit, Lance

    2002-01-01

    Plasma-enhanced chemical vapor deposition is used to grow vertically aligned multiwalled carbon nanofibers (MWNFs). The graphite basal planes in these nanofibers are not parallel as in nanotubes; instead they exhibit a small angle resembling a stacked cone arrangement. A parametric study with varying process parameters such as growth temperature, feedstock composition, and substrate power has been conducted, and these parameters are found to influence the growth rate, diameter, and morphology. The well-aligned MWNFs are suitable for fabricating electrode systems in sensor and device development.

  10. Josephson tunnel junctions with chemically vapor deposited polycrystalline germanium barriers

    SciTech Connect

    Kroger, H.; Jillie, D.W.; Smith, L.N.; Phaneuf, L.E.; Potter, C.N.; Shaw, D.M.; Cukauskas, E.J.; Nisenoff, M.

    1984-03-01

    High quality Josephson tunnel junctions have been fabricated whose tunneling barrier is polycrystalline germanium chemically vapor deposited on a NbN base electrode and covered by a Nb counterelectrode. These junctions have excellent characteristics for device applications: values of V/sub m/ (the product of the critical current and the subgap resistance measured at 2 mV and 4.2 K) ranging between 35--48 mV, ideal threshold curves, a steep current rise at the gap voltage, and Josephson current densities from 100 to 1100 A/cm/sup 2/.

  11. Spectroscopic Observation of Chemical Interaction Between Impact-induced Vapor Clouds and the Ambient Atmosphere

    NASA Technical Reports Server (NTRS)

    Sugita, S.; Heineck, J. T.; Schultz, P. H.

    2000-01-01

    Chemical reactions within impact-induced vapor clouds were observed in laboratory experiments using a spectroscopic method. The results indicate that projectile-derived carbon-rich vapor reacts intensively with atmospheric nitrogen.

  12. Rapid Chemical Vapor Detection Using Optofluidic Ring Resonators

    NASA Astrophysics Data System (ADS)

    Sun, Yuze; Shopova, Siyka I.; White, Ian M.; Frye-Mason, Greg; Fan, Xudong

    The optofluidic ring resonator (OFRR) is a novel gas sensing technology platform. In an OFRR gas sensor, the OFRR interior surface is coated with a layer of vapor-sensitive polymer. The interaction between the polymer and the gas molecules flowing through the OFRR results in a change in polymer refractive index and thickness, which can be detected by the circulating waveguide modes supported by the circular cross section of the OFRR. Due to the excellent fluidics of a capillary, the OFRR is capable of detecting chemical vapors rapidly with very low sample volume. In addition, the OFRR is highly compatible with gas chromatography (GC) and is a promising platform for development of micro-GC (μGC) with unique multipoint, on-column detection capability. In this chapter, we will discuss the fundamental operational principles of the OFRR gas sensor, followed by examples of rapid detection of several representative vapor analytes. The development of an OFRR-based μGC system and its applications in explosive separation and detection will also be presented.

  13. Chemical etching of copper foils for single-layer graphene growth by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Yoshihara, Naoki; Noda, Masaru

    2017-10-01

    Chemical etching on copper surface is essential as a pre-treatment for single-layer graphene growth by chemical vapor deposition (CVD). Here, we investigated the effect of chemical etching treatment on copper foils for single-layer graphene CVD growth. The chemical etching conditions, such as the type of chemical etchants and the treatment time, were found to strongly influence the graphene domain size. Moreover, a drastic change in the layer structure of graphene sheets, which was attributed to the surface morphology of the etched copper foil, was confirmed by graphene transmittance and Raman mapping measurements.

  14. Chemical vapor deposited diamond-on-diamond powder composites (LDRD final report)

    SciTech Connect

    Panitz, J.K.; Hsu, W.L.; Tallant, D.R.; McMaster, M.; Fox, C.; Staley, D.

    1995-12-01

    Densifying non-mined diamond powder precursors with diamond produced by chemical vapor infiltration (CVI) is an attractive approach for forming thick diamond deposits that avoids many potential manufacturability problems associated with predominantly chemical vapor deposition (CVD) processes. The authors developed techniques for forming diamond powder precursors and densified these precursors in a hot filament-assisted reactor and a microwave plasma-assisted reactor. Densification conditions were varied following a fractional factorial statistical design. A number of conclusions can be drawn as a result of this study. High density diamond powder green bodies that contain a mixture of particle sizes solidify more readily than more porous diamond powder green bodies with narrow distributions of particle sizes. No composite was completely densified although all of the deposits were densified to some degree. The hot filament-assisted reactor deposited more material below the exterior surface, in the interior of the powder deposits; in contrast, the microwave-assisted reactor tended to deposit a CVD diamond skin over the top of the powder precursors which inhibited vapor phase diamond growth in the interior of the powder deposits. There were subtle variations in diamond quality as a function of the CVI process parameters. Diamond and glassy carbon tended to form at the exterior surface of the composites directly exposed to either the hot filament or the microwave plasma. However, in the interior, e.g. the powder/substrate interface, diamond plus diamond-like-carbon formed. All of the diamond composites produced were grey and relatively opaque because they contained flawed diamond, diamond-like-carbon and glassy carbon. A large amount of flawed and non-diamond material could be removed by post-CVI oxygen heat treatments. Heat treatments in oxygen changed the color of the composites to white.

  15. High activity redox catalysts synthesized by chemical vapor impregnation.

    PubMed

    Forde, Michael M; Kesavan, Lokesh; Bin Saiman, Mohd Izham; He, Qian; Dimitratos, Nikolaos; Lopez-Sanchez, Jose Antonio; Jenkins, Robert L; Taylor, Stuart H; Kiely, Christopher J; Hutchings, Graham J

    2014-01-28

    The use of precious metals in heterogeneous catalysis relies on the preparation of small nanoparticles that are stable under reaction conditions. To date, most conventional routes used to prepare noble metal nanoparticles have drawbacks related to surface contamination, particle agglomeration, and reproducibility restraints. We have prepared titania-supported palladium (Pd) and platinum (Pt) catalysts using a simplified vapor deposition technique termed chemical vapor impregnation (CVI) that can be performed in any standard chemical laboratory. These materials, composed of nanoparticles typically below 3 nm in size, show remarkable activity under mild conditions for oxidation and hydrogenation reactions of industrial importance. We demonstrate the preparation of bimetallic Pd-Pt homogeneous alloy nanoparticles by this new CVI method, which show synergistic effects in toluene oxidation. The versatility of our CVI methodology to be able to tailor the composition and morphology of supported nanoparticles in an easily accessible and scalable manner is further demonstrated by the synthesis of Pdshell-Aucore nanoparticles using CVI deposition of Pd onto preformed Au nanoparticles supported on titania (prepared by sol immobilization) in addition to the presence of monometallic Au and Pd nanoparticles.

  16. Flexible Electronics: High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells (Adv. Mater. 28/2016).

    PubMed

    He, Rongrui; Day, Todd D; Sparks, Justin R; Sullivan, Nichole F; Badding, John V

    2016-07-01

    On page 5939, J. V. Badding and co-workers describe the unrolling of a flexible hydrogenated amorphous silicon solar cell, deposited by high-pressure chemical vapor deposition. The high-pressure deposition process is represented by the molecules of silane infiltrating the small voids between the rolled up substrate, facilitating plasma-free deposition over a very large area. The high-pressure approach is expected to also find application for 3D nanoarchitectures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Modeling of InP metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Black, Linda R.; Clark, Ivan O.; Kui, J.; Jesser, William A.

    1991-01-01

    The growth of InP by metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor is being modeled with a commercially available computational fluid dynamics modeling code. The mathematical treatment of the MOCVD process has four primary areas of concern: 1) transport phenomena, 2) chemistry, 3) boundary conditions, and 4) numerical solution methods. The transport processes involved in CVD are described by conservation of total mass, momentum, energy, and atomic species. Momentum conservation is described by a generalized form of the Navier-Stokes equation for a Newtonian fluid and laminar flow. The effect of Soret diffusion on the transport of particular chemical species and on the predicted deposition rate is examined. Both gas-phase and surface chemical reactions are employed in the model. Boundary conditions are specified at the inlet and walls of the reactor for temperature, fluid flow and chemical species. The coupled set of equations described above is solved by a finite difference method over a nonuniform rectilinear grid in both two and three dimensions. The results of the 2-D computational model is presented for gravity levels of zero- and one-g. The predicted growth rates at one-g are compared to measured growth rates on fused silica substrates.

  18. Modeling of InP metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Black, Linda R.; Clark, Ivan O.; Kui, J.; Jesser, William A.

    1991-01-01

    The growth of InP by metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor is being modeled with a commercially available computational fluid dynamics modeling code. The mathematical treatment of the MOCVD process has four primary areas of concern: 1) transport phenomena, 2) chemistry, 3) boundary conditions, and 4) numerical solution methods. The transport processes involved in CVD are described by conservation of total mass, momentum, energy, and atomic species. Momentum conservation is described by a generalized form of the Navier-Stokes equation for a Newtonian fluid and laminar flow. The effect of Soret diffusion on the transport of particular chemical species and on the predicted deposition rate is examined. Both gas-phase and surface chemical reactions are employed in the model. Boundary conditions are specified at the inlet and walls of the reactor for temperature, fluid flow and chemical species. The coupled set of equations described above is solved by a finite difference method over a nonuniform rectilinear grid in both two and three dimensions. The results of the 2-D computational model is presented for gravity levels of zero- and one-g. The predicted growth rates at one-g are compared to measured growth rates on fused silica substrates.

  19. Chemiluminescent chemical sensors for inorganic and organic vapors

    SciTech Connect

    Collins, G.E.; Rose-Pehrsson, S.L.

    1995-12-31

    Chemiluminescent, chemical sensors for inorganic and organic vapors are being investigated via the immobilization of 3-aminophthalhydrazide (luminol) within hydrogels and polymeric, sorbent coatings. The films are supported behind a teflon membrane and positioned in front of a photomultiplier tube, permitting the sensitive detection of numerous toxic vapors. Some selectivity has been tailored into these devices by careful selection of the polymer type, pH and metal catalyst incorporated within the film. The incorporation of luminol and Fe(3) within a polyvinylalcohol hydrogel gave a film with superior sensitivity toward NO{sub 2} (detection limit of 0.46 ppb and a response time on the order of seconds). The use of the hydrogel matrix helped eliminate humidity problems associated with other polymeric films. Other chemiluminescent thin films prepared have demonstrated the detection of ppb levels of SO{sub 2}(g) and hydrazine, N{sub 2}H{sub 4}(g). Recently, the authors have begun investigating the incorporation of a heated Pt filament into the inlet line as a pre-oxidative step prior to passage of the gas stream across the teflon membrane. This has permitted the sensitive detection of ppm levels of CCl{sub 4}(g), CHCl{sub 3}(g) and CH{sub 2}Cl{sub 2}(g).

  20. Chemical vapor deposition coatings for oxidation protection of titanium alloys

    NASA Technical Reports Server (NTRS)

    Cunnington, G. R.; Robinson, J. C.; Clark, R. K.

    1991-01-01

    Results of an experimental investigation of the oxidation protection afforded to Ti-14Al-21Nb and Ti-14Al-23Nb-2V titanium aluminides and Ti-17Mo-3Al-3Nb titanium alloy by aluminum-boron-silicon and boron-silicon coatings are presented. These coatings are applied by a combination of physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. The former is for the application of aluminum, and the latter is for codeposition of boron and silicon. Coating thickness is in the range of 2 to 7 microns, and coating weights are 0.6 to 2.0 mg/sq cm. Oxidation testing was performed in air at temperatures to 1255 K in both static and hypersonic flow environments. The degree of oxidation protection provided by the coatings is determined from weight change measurements made during the testing and post test compositional analyses. Temperature-dependent total normal emittance data are also presented for four coating/substrate combinations. Both types of coatings provided excellent oxidation protection for the exposure conditions of this investigation. Total normal emittances were greater than 0.80 in all cases.

  1. Radio-frequency plasma chemical vapor deposition growth of diamond

    NASA Technical Reports Server (NTRS)

    Meyer, Duane E.; Dillon, Rodney O.; Woollam, John A.

    1989-01-01

    Plasma chemical vapor deposition (CVD) at 13.56 MHz has been used to produce diamond particles in two different inductively coupled systems with a mixture of methane and hydrogen. The effect of a diamondlike carbon (DLC) overcoating on silicon, niobium, and stainless-steel substrates has been investigated and in the case of silicon has been found to enhance particle formation as compared to uncoated polished silicon. In addition the use of carbon monoxide in hydrogen has been found to produce well-defined individual faceted particles as well as polycrystalline films on quartz and DLC coated silicon substrates. Plasma CVD is a competitive approach to production of diamond films. It has the advantage over microwave systems of being easily scaled to large volume and high power.

  2. Quantitative infrared spectra of vapor phase chemical agents

    NASA Astrophysics Data System (ADS)

    Sharpe, Steven W.; Johnson, Timothy J.; Chu, Pamela M.; Kleimeyer, James; Rowland, Brad

    2003-08-01

    Quantitative, high resolution (0.1 cm-1) infrared spectra have been acquired for a number of pressure broadened (101.3 KPa N2), vapor phase chemicals including: Sarin (GB), Soman (GD), Tabun (GA), Cyclosarin (GF), VX, nitrogen mustard (HN3), sulfur mustard (HD) and Lewisite (L). The spectra are acquired using a heated, flow-through White cell of 5.6 m optical path length. Each reported spectrum represents a statistical fit to Beer's law, which allows for a rigorous calculation of uncertainty in the absorption coefficients. As part of an ongoing collaboration with the National Institute of Standards and Technology (NIST), cross-laboratory validation is a critical aspect of this work. In order to identify possible errors in the Dugway flow-through system, quantitative spectra of isopropyl alcohol from both NIST and Pacific Northwest National Laboratory (PNNL) are compared to similar data taken at the Dugway Proving Ground (DPG).

  3. Chemical vapor synthesis and characterization of aluminum nanopowder

    NASA Astrophysics Data System (ADS)

    Choi, Jin Won; Sohn, Hong Yong; Choi, Young Joon; Fang, Zhigang Zak

    Aluminum is a component in many promising hydrogen storage materials such as aluminum hydride and complex aluminum hydrides. In this research, Al and TiAl 3-containing Al nanopowders were prepared by a chemical vapor synthesis (CVS) process using Mg as the reducing agent. XRD and EDS results indicated that the produced powder was composed of Al or Al with TiAl 3. The shape of the powder was spherical with the average size in the range of 10-50 nm measured by SEM, TEM, BET and ZetaPALS compared with the typically larger than 100 nm for commercially available fine Al powders. In addition, the effects of the operating conditions such as Ar flow rate, precursor feed rate and reaction temperature on the properties of the product powder were investigated.

  4. Low Temperature Chemical Vapor Deposition Of Thin Film Magnets

    DOEpatents

    Miller, Joel S.; Pokhodnya, Kostyantyn I.

    2003-12-09

    A thin-film magnet formed from a gas-phase reaction of tetracyanoetheylene (TCNE) OR (TCNQ), 7,7,8,8-tetracyano-P-quinodimethane, and a vanadium-containing compound such as vanadium hexcarbonyl (V(CO).sub.6) and bis(benzene)vanalium (V(C.sub.6 H.sub.6).sub.2) and a process of forming a magnetic thin film upon at least one substrate by chemical vapor deposition (CVD) at a process temperature not exceeding approximately 90.degree. C. and in the absence of a solvent. The magnetic thin film is particularly suitable for being disposed upon rigid or flexible substrates at temperatures in the range of 40.degree. C. and 70.degree. C. The present invention exhibits air-stable characteristics and qualities and is particularly suitable for providing being disposed upon a wide variety of substrates.

  5. Chemical vapor deposition of low reflective cobalt (II) oxide films

    NASA Astrophysics Data System (ADS)

    Amin-Chalhoub, Eliane; Duguet, Thomas; Samélor, Diane; Debieu, Olivier; Ungureanu, Elisabeta; Vahlas, Constantin

    2016-01-01

    Low reflective CoO coatings are processed by chemical vapor deposition from Co2(CO)8 at temperatures between 120 °C and 190 °C without additional oxygen source. The optical reflectivity in the visible and near infrared regions stems from 2 to 35% depending on deposition temperature. The combination of specific microstructural features of the coatings, namely a fractal ⿿cauliflower⿿ morphology and a grain size distribution more or less covering the near UV and IR wavelength ranges enhance light scattering and gives rise to a low reflectivity. In addition, the columnar morphology results in a density gradient in the vertical direction that we interpret as a refractive index gradient lowering reflectivity further down. The coating formed at 180 °C shows the lowest average reflectivity (2.9%), and presents an interesting deep black diffuse aspect.

  6. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  7. Strain relaxation in graphene grown by chemical vapor deposition

    SciTech Connect

    Troppenz, Gerald V. Gluba, Marc A.; Kraft, Marco; Rappich, Jörg; Nickel, Norbert H.

    2013-12-07

    The growth of single layer graphene by chemical vapor deposition on polycrystalline Cu substrates induces large internal biaxial compressive strain due to thermal expansion mismatch. Raman backscattering spectroscopy and atomic force microscopy were used to study the strain relaxation during and after the transfer process from Cu foil to SiO{sub 2}. Interestingly, the growth of graphene results in a pronounced ripple structure on the Cu substrate that is indicative of strain relaxation of about 0.76% during the cooling from the growth temperature. Removing graphene from the Cu substrates and transferring it to SiO{sub 2} results in a shift of the 2D phonon line by 27 cm{sup −1} to lower frequencies. This translates into additional strain relaxation. The influence of the processing steps, used etching solution and solvents on strain, is investigated.

  8. Chemical Vapor Deposition at High Pressure in a Microgravity Environment

    NASA Technical Reports Server (NTRS)

    McCall, Sonya; Bachmann, Klaus; LeSure, Stacie; Sukidi, Nkadi; Wang, Fuchao

    1999-01-01

    In this paper we present an evaluation of critical requirements of organometallic chemical vapor deposition (OMCVD) at elevated pressure for a channel flow reactor in a microgravity environment. The objective of using high pressure is to maintain single-phase surface composition for materials that have high thermal decomposition pressure at their optimum growth temperature. Access to microgravity is needed to maintain conditions of laminar flow, which is essential for process analysis. Based on ground based observations we present an optimized reactor design for OMCVD at high pressure and reduced gravity. Also, we discuss non-intrusive real-time optical monitoring of flow dynamics coupled to homogeneous gas phase reactions, transport and surface processes. While suborbital flights may suffice for studies of initial stages of heteroepitaxy experiments in space are essential for a complete evaluation of steady-state growth.

  9. Synthesis of mullite coatings by chemical vapor deposition

    SciTech Connect

    Mulpuri, R.P.; Auger, M.; Sarin, V.K.

    1996-08-01

    Formation of mullite on ceramic substrates via chemical vapor deposition was investigated. Mullite is a solid solution of Al{sub 2}O{sub 3} and SiO{sub 2} with a composition of 3Al{sub 2}O{sub 3}{circ}2SiO{sub 2}. Thermodynamic calculations performed on the AlCl{sub 3}-SiCl{sub 4}-CO{sub 2}-H{sub 2} system were used to construct equilibrium CVD phase diagrams. With the aid of these diagrams and consideration of kinetic rate limiting factors, initial process parameters were determined. Through process optimization, crystalline CVD mullite coatings have been successfully grown on SiC and Si{sub 3}N{sub 4} substrates. Results from the thermodynamic analysis, process optimization, and effect of various process parameters on deposition rate and coating morphology are discussed.

  10. Development and study of chemical vapor deposited tantalum base alloys

    NASA Technical Reports Server (NTRS)

    Meier, G. H.; Bryant, W. A.

    1976-01-01

    A technique for the chemical vapor deposition of alloys was developed. The process, termed pulsing, involves the periodic injection of reactant gases into a previously-evacuated reaction chamber where they blanket the substrate almost instantaneously. Formation of alternating layers of the alloy components and subsequent homogenization allows the formation of an alloy of uniform composition with the composition being determined by the duration and relative numbers of the various cycles. The technique has been utilized to produce dense alloys of uniform thickness and composition (Ta- 10 wt % W) by depositing alternating layers of Ta and W by the hydrogen reduction of TaCl5 and WCl6. A similar attempt to deposit a Ta - 8 wt % W - 2 wt% Hf alloy was unsuccessful because of the difficulty in reducing HfCl4 at temperatures below those at which gas phase nucleation of Ta and W occurred.

  11. Chemical Vapor Deposition Growth of Graphene and Related Materials

    NASA Astrophysics Data System (ADS)

    Kitaura, Ryo; Miyata, Yasumitsu; Xiang, Rong; Hone, James; Kong, Jing; Ruoff, Rodney S.; Maruyama, Shigeo

    2015-12-01

    Research on atomic layers including graphene, hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDCs) and their heterostructures has attracted a great deal of attention. Chemical vapor deposition (CVD) can provide large-area structure-defined high-quality atomic layer samples, which have considerably contributed to the recent advancement of atomic-layer research. In this article, we focus on the CVD growth of various atomic layers and review recent progresses including (1) the CVD growth of graphene using methane and ethanol as carbon sources, (2) the CVD growth of hBN using borazine and ammonia borane, (3) the CVD growth of various TMDCs using single and multi-furnace methods, and (4) CVD growth of vertical and lateral heterostructures such as graphene/hBN, MoS2/graphite, WS2/hBN and MoS2/WS2.

  12. Selective vapor detection of an integrated chemical sensor array

    NASA Astrophysics Data System (ADS)

    Jung, Youngmo; Kim, Young Jun; Choi, Jaebin; Lim, Chaehyun; Shin, Beom Ju; Moon, Hi Gyu; Lee, Taikjin; Kim, Jae Hun; Seo, Minah; Kang, Chong Yun; Jun, Seong Chan; Lee, Seok; Kim, Chulki

    2015-07-01

    Graphene is a promising material for vapor sensor applications because of its potential to be functionalized for specific chemical gases. In this work, we present a graphene gas sensor that uses single-stranded DNA (ssDNA) molecules as its sensing agent. We investigate the characteristics of graphene field effect transistors (FETs) coated with different ssDNAs. The sensitivity and recovery rate for a specific gas are modified according to the differences in the DNA molecules' Guanine (G) and Cytosine (C) content. ssDNA-functionalized devices show a higher recovery rate compared to bare graphene devices. Pattern analysis of a 2-by-2 sensor array composed of graphene devices functionalized with different-sequence ssDNA enables identification of NH3, NO2, CO, SO2 using Principle Component Analysis (PCA).

  13. Temperature-dependent morphology of chemical vapor grown molybdenum disulfide

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoyin; Wang, Yantao; Zhou, Jiadong; Liu, Zheng

    2017-04-01

    Monolayered molybdenum disulfide (MoS2) is a 2D direct band gap semiconductor with promising potential applications. In this work, we observed the temperature dependency of the morphologies of MoS2 monolayers from chemical vapor deposition. At a low growing temperature below 850 °C, MoS2 flakes tend to be trianglular in shape. At 850–950 °C, hexagonal MoS2 flakes can be observed. While at a temperature over 950 °C, MoS2 flakes can form rectangular shapes. Complementary characterizations have been made to these samples. We also proposed a mechanism for such temperature-dependent shape evolution based on thermodynamic simulation.

  14. Characterization of Carbon Nanotubes Grown by Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Cochrane, J. C.; Zhu, Shen; Su, Ching-Hua; Lehoczky, S. L.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Since the superior properties of multi-wall carbon nanotubes (MWCNT) could improve numerous devices such as electronics and sensors, many efforts have been made in investigating the growth mechanism of MWCNT to synthesize high quality MWCNT. Chemical vapor deposition (CVD) is widely used for MWCNT synthesis, and scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) are useful methods for analyzing the structure, morphology and composition of MWCNT. Temperature and pressure are two important growth parameters for fabricating carbon nanotubes. In MWCNT growth by CVD, the plasma assisted method is normally used for low temperature growth. However a high temperature environment is required for thermal CVD. A systematic study of temperature and pressure-dependence is very helpful to understanding MWCNT growth. Transition metal particles are commonly used as catalysis in carbon nanotube growth. It is also interesting to know how temperature and pressure affect the interface of carbon species and catalyst particles

  15. Quantitative Infrared Spectra of Vapor Phase Chemical Agents

    SciTech Connect

    Sharpe, Steven W.; Johnson, Timothy J.; Chu, P. M.; Kleimeyer, J.; Rowland, Brad

    2003-08-01

    Quantitative, moderately high resolution (0.1 cm-1) infrared spectra have been acquired for a number of nitrogen broadened (1 atm N2) vapor phase chemicals including: Sarin (GB), Soman (GD), Tabun (GA), Cyclosarin (GF), VX, Nitrogen Mustard (HN3), Sulfur Mustard (HD), and Lewisite (L). The spectra are acquired using a heated, flow-through White Cell1 of 5.6 meter optical path length. Each reported spectrum represents a statistical fit to Beer’s law, which allows for a rigorous calculation of uncertainty in the absorption coefficients. As part of an ongoing collaboration with the National Institute of Standards and Technology (NIST), cross-laboratory validation is a critical aspect of this work. In order to identify possible errors in the Dugway flow-through system, quantitative spectra of isopropyl alcohol from both NIST and Pacific Northwest National Laboratory (PNNL) are compared to similar data taken at Dugway proving Grounds (DPG).

  16. Chemical vapor deposition fluid flow simulation modelling tool

    NASA Technical Reports Server (NTRS)

    Bullister, Edward T.

    1992-01-01

    Accurate numerical simulation of chemical vapor deposition (CVD) processes requires a general purpose computational fluid dynamics package combined with specialized capabilities for high temperature chemistry. In this report, we describe the implementation of these specialized capabilities in the spectral element code NEKTON. The thermal expansion of the gases involved is shown to be accurately approximated by the low Mach number perturbation expansion of the incompressible Navier-Stokes equations. The radiative heat transfer between multiple interacting radiating surfaces is shown to be tractable using the method of Gebhart. The disparate rates of reaction and diffusion in CVD processes are calculated via a point-implicit time integration scheme. We demonstrate the use above capabilities on prototypical CVD applications.

  17. Field emission properties of chemical vapor deposited individual graphene

    SciTech Connect

    Zamri Yusop, Mohd; Kalita, Golap; Yaakob, Yazid; Takahashi, Chisato; Tanemura, Masaki

    2014-03-03

    Here, we report field emission (FE) properties of a chemical vapor deposited individual graphene investigated by in-situ transmission electron microscopy. Free-standing bilayer graphene is mounted on a cathode microprobe and FE processes are investigated varying the vacuum gap of cathode and anode. The threshold field for 10 nA current were found to be 515, 610, and 870 V/μm for vacuum gap of 400, 300, and 200 nm, respectively. It is observed that the structural stability of a high quality bilayer graphene is considerably stable during emission process. By contacting the nanoprobe with graphene and applying a bias voltage, structural deformation and buckling are observed with significant rise in temperature owing to Joule heating effect. The finding can be significant for practical application of graphene related materials in emitter based devices as well as understanding the contact resistance influence and heating effect.

  18. Patterned growth of tungsten diselenide flakes by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, Zhendong; Huang, Qi; Chen, Peng; Wang, Jianyu; Lu, Yan; Zhang, Sihong; Liang, Xuelei; Wang, Li

    2017-08-01

    By introducing prepatterned Pt/Ti dots, arrays of WSe2 flakes have been successfully grown on SiO2 substrates by chemical vapor deposition, opening a new pathway for the large-scale production of WSe2-based devices. The WSe2 flakes are high-quality single crystals characterized by transmission electron microscopy and Raman spectroscopy. Field-effect transistors were fabricated on these WSe2 flakes, and the field effect mobility was measured to be 11.0 cm2 V-1 s-1 and an on/off ratio of ˜106 was achieved. The growth of highly patterned WSe2 flake arrays facilitates the fabrication of WSe2 flake-based integrated devices.

  19. Sulfur Vapor-Infiltrated 3D Carbon Nanotube Foam for Binder-Free High Areal Capacity Lithium-Sulfur Battery Composite Cathodes.

    PubMed

    Li, Mengya; Carter, Rachel; Douglas, Anna; Oakes, Landon; Pint, Cary L

    2017-05-23

    Here, we demonstrate a strategy to produce high areal loading and areal capacity sulfur cathodes by using vapor-phase infiltration of low-density carbon nanotube (CNT) foams preformed by solution processing and freeze-drying. Vapor-phase capillary infiltration of sulfur into preformed and binder-free low-density CNT foams leads to a mass loading of ∼79 wt % arising from interior filling and coating of CNTs with sulfur while preserving conductive CNT-CNT junctions that sustain electrical accessibility through the thick foam. Sulfur cathodes are then produced by mechanically compressing these foams into dense composites (ρ > 0.2 g/cm(3)), revealing specific capacity of 1039 mAh/gS at 0.1 C, high sulfur areal loading of 19.1 mg/cm(2), and high areal capacity of 19.3 mAh/cm(2). This work highlights a technique broadly adaptable to a diverse group of nanostructured building blocks where preformed low-density materials can be vapor infiltrated with sulfur, mechanically compressed, and exhibit simultaneous high areal and gravimetric storage properties. This provides a route for scalable, low-cost, and high-energy density sulfur cathodes based on conventional solid electrode processing routes.

  20. Direct synthesis of large area graphene on insulating substrate by gallium vapor-assisted chemical vapor deposition

    SciTech Connect

    Murakami, Katsuhisa Hiyama, Takaki; Kuwajima, Tomoya; Fujita, Jun-ichi; Tanaka, Shunsuke; Hirukawa, Ayaka; Kano, Emi; Takeguchi, Masaki

    2015-03-02

    A single layer of graphene with dimensions of 20 mm × 20 mm was grown directly on an insulating substrate by chemical vapor deposition using Ga vapor catalysts. The graphene layer showed highly homogeneous crystal quality over a large area on the insulating substrate. The crystal quality of the graphene was measured by Raman spectroscopy and was found to improve with increasing Ga vapor density on the reaction area. High-resolution transmission electron microscopy observations showed that the synthesized graphene had a perfect atomic-scale crystal structure within its grains, which ranged in size from 50 nm to 200 nm.

  1. Precursors for chemical and photochemical vapor deposition of copper metal

    NASA Astrophysics Data System (ADS)

    James, Alicia Marie

    The colorless square-planar cluster [CuN(SiMe3)2] 4, which contains four Cu(I) ions with four bridging amide groups, was studied as a precursor for chemical and photochemical vapor deposition of Cu metal. The cluster phosphoresces in CH2Cl2 solution and in the solid state at room temperature. Its electronic spectrum in CH 2Cl2 consists of two intense bands which are assigned to symmetry-allowed 3d → 4p transitions; the phosphorescence is also likely to be metal-centered. Solid [CuN(SiMe3)2]4 luminesces with approximately the same spectrum as that of the CH2Cl2 solutions. At 77 K, the solid-state luminescence red-shifts slightly. The emission lifetime in glassy Et2O solution is 690 mus. [CuN(SiMe3) 2]4 deposits Cu metal via chemical vapor deposition under H2 carrier gas at substrate temperatures of 145--200°C. Deposition also occurs photochemically beginning at 136--138°C under near-UV irradiation. The preparation of monomeric derivatives of [CuN(SiMe3) 2]4 was attempted by using neutral donor ligands L (e.g. LnCuN(SiMe3)2; L = CO, PR3, CN-t-Bu; n = 1--3). The target compounds were expected to be more volatile than the copper cluster and still maintain photosensitivity. CuCl and [Cu(CH 3CN)4]PF6 were used as starting materials. Even in the presence of L, [CuN(SiMe3)2] 4 is a major product in reactions using CuCl and NaN(SiCH3) 2- [Cu(CH3CN)4]PF6 was a promising route for the monomeric Cu(I) complexes because of ready dissociation of its acetonitrile ligands. However, the characterization of these complexes was unsuccessful. Other Cu(I) amide clusters have been prepared; they may also be suitable for chemical and photochemical vapor deposition of Cu. [CuNEt2] 4, [CuN(i-Pr)2]4, and [CuN(t-Bu)(SiMe 3)]4 are phosphorescent though they are very air sensitive. They should be more volatile and produce Cu metal films more readily than [CuN(SiMe3)2]4 Cu(hfac)2 is a versatile Lewis acid, forming adducts with a variety of bases. The bases that were used were ethylene

  2. Chemical vapor deposition of magnetic oxide semiconductors for spintronic applications

    NASA Astrophysics Data System (ADS)

    Falco, Lucas

    2005-11-01

    Moore's law, which states that the number of transistor's per square inch on integrated circuits doubles every 18 months, has set the pace of progress for the electronics industry since the 1970's. This in turn has led to a significant reduction in the cost of computers and communications devices. However, because of quantum mechanic effects, a limit in the miniaturization of devices is rapidly approaching where any further reduction in size may hinder their operation. Taking advantage of the electron spin, a quantum effect, and integrating it with electronics design, a new field is emerging, known as spintronics. In this respect, a very active area of research is in dilute magnetic semiconductors (DMS). In this work the author examines the use of chemical vapor deposition (CVD) as a method for the preparation of magnetic oxide semiconductors for spintronic applications. CVD has been used extensively as an efficient and inexpensive method to deposit magnetic and semiconducting thin films. The author examined the chemical, structural, and morphological properties of hematite (alpha-Fe2O3) thin films prepared by plasma enhanced chemical vapor deposition (PECVD) on silicon oxide (SiO2) substrates. Using X-ray diffraction (XRD) it was determined that the films contain a alpha-Fe2O3 phase. The author also studied the deposition of SnO2 by atomic layer deposition (ALD) and CVD. The effect of SnI4 pulse time was analyzed and it was determined that ALD growth was achieved after an 8 second pulse time. Ultimately, the preparation of cobalt oxide and Co-doped SnO2 films was the objective of this work. After several cobalt precursors were tried, the author found a suitable precursor, cobalt (II) acetylacetonate, to grow cobalt oxide and Co-doped SnO2 films. Sn1-XCO XO2+delta films were epitaxial for Co at% < 1 and indicated ferromagnetism on both SiO2 and sapphire substrate. In general, it was observed that higher magnetic moments were found for samples with lower cobalt

  3. Chemical Analysis for Chitin as a Measure of Fungal Infiltration of Cellulosic Materials.

    DTIC Science & Technology

    1976-12-01

    the addition of 50 n’.illiliters of I 2N hydrochloric acid). Store at .~lO0 C. (11) Bushnell-Haas medium (12) Glucosamine hydrochloride (I milliliter...Infiltration Cellu!.jsic Materials Fungus-Induced Deterioration Glucosamine A TRACT (Cl~ i~s ,.v.ra. ia. ~V ~~~~~a . y d Sd.niIl ~ By block ni b.,) A chemical...EXPERIMENTAL PROCEDURE 3. Approach to the Problem. Carry out laboratory experiments to investigate variables as: shelf life of stock glucosamine , digestion

  4. Nanostructure Engineered Chemical Sensors for Hazardous Gas and Vapor Detection

    NASA Technical Reports Server (NTRS)

    Li, Jing; Lu, Yijiang

    2005-01-01

    A nanosensor technology has been developed using nanostructures, such as single walled carbon nanotubes (SWNTs) and metal oxides nanowires or nanobelts, on a pair of interdigitated electrodes (IDE) processed with a silicon based microfabrication and micromachining technique. The IDE fingers were fabricated using thin film metallization techniques. Both in-situ growth of nanostructure materials and casting of the nanostructure dispersions were used to make chemical sensing devices. These sensors have been exposed to hazardous gases and vapors, such as acetone, benzene, chlorine, and ammonia in the concentration range of ppm to ppb at room temperature. The electronic molecular sensing in our sensor platform can be understood by electron modulation between the nanostructure engineered device and gas molecules. As a result of the electron modulation, the conductance of nanodevice will change. Due to the large surface area, low surface energy barrier and high thermal and mechanical stability, nanostructured chemical sensors potentially can offer higher sensitivity, lower power consumption and better robustness than the state-of-the-art systems, which make them more attractive for defense and space applications. Combined with MEMS technology, light weight and compact size sensors can be made in wafer scale with low cost.

  5. Conversion Coatings for Aluminum Alloys by Chemical Vapor Deposition Mechanisms

    NASA Technical Reports Server (NTRS)

    Reye, John T.; McFadden, Lisa S.; Gatica, Jorge E.; Morales, Wilfredo

    2004-01-01

    With the rise of environmental awareness and the renewed importance of environmentally friendly processes, the United States Environmental Protection Agency has targeted surface pre-treatment processes based on chromates. Indeed, this process has been subject to regulations under the Clean Water Act as well as other environmental initiatives, and there is today a marked movement to phase the process out in the near future. Therefore, there is a clear need for new advances in coating technology that could provide practical options for replacing present industrial practices. Depending on the final application, such coatings might be required to be resistant to corrosion, act as chemically resistant coatings, or both. This research examined a chemical vapor deposition (CVD) mechanism to deposit uniform conversion coatings onto aluminum alloy substrates. Robust protocols based on solutions of aryl phosphate ester and multi-oxide conversion coating (submicron) films were successfully grown onto the aluminum alloy samples. These films were characterized by X-ray Photoelectron Spectroscopy (XPS). Preliminary results indicate the potential of this technology to replace aqueous-based chromate processes.

  6. Correlation of chemical evaporation rate with vapor pressure.

    PubMed

    Mackay, Donald; van Wesenbeeck, Ian

    2014-09-02

    A new one-parameter correlation is developed for the evaporation rate (ER) of chemicals as a function of molar mass (M) and vapor pressure (P) that is simpler than existing correlations. It applies only to liquid surfaces that are unaffected by the underlying solid substrate as occurs in the standard ASTM evaporation rate test and to quiescent liquid pools. The relationship has a sounder theoretical basis than previous correlations because ER is correctly correlated with PM rather than P alone. The inclusion of M increases the slope of previous log ER versus log P regressions to a value close to 1.0 and yields a simpler one-parameter correlation, namely, ER (μg m(-1) h(-1)) = 1464P (Pa) × M (g mol(-1)). Applications are discussed for the screening level assessment and ranking of chemicals for evaporation rate, such as pesticides, fumigants, and hydrocarbon carrier fluids used in pesticide formulations, liquid consumer products used indoors, and accidental spills of liquids. The mechanistic significance of the single parameter as a mass-transfer coefficient or velocity is discussed.

  7. Oxidative chemical vapor deposition of polyaniline thin films.

    PubMed

    Smolin, Yuriy Y; Soroush, Masoud; Lau, Kenneth K S

    2017-01-01

    Polyaniline (PANI) is synthesized via oxidative chemical vapor deposition (oCVD) using aniline as monomer and antimony pentachloride as oxidant. Microscopy and spectroscopy indicate that oCVD processing conditions influence the PANI film chemistry, oxidation, and doping level. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) indicate that a substrate temperature of 90 °C is needed to minimize the formation of oligomers during polymerization. Lower substrate temperatures, such as 25 °C, lead to a film that mostly includes oligomers. Increasing the oxidant flowrate to nearly match the monomer flowrate favors the deposition of PANI in the emeraldine state, and varying the oxidant flowrate can directly influence the oxidation state of PANI. Changing the reactor pressure from 700 to 35 mTorr does not have a significant effect on the deposited film chemistry, indicating that the oCVD PANI process is not concentration dependent. This work shows that oCVD can be used for depositing PANI and for effectively controlling the chemical state of PANI.

  8. Graphene-Based Chemical Vapor Sensors for Electronic Nose Applications

    NASA Astrophysics Data System (ADS)

    Nallon, Eric C.

    An electronic nose (e-nose) is a biologically inspired device designed to mimic the operation of the olfactory system. The e-nose utilizes a chemical sensor array consisting of broadly responsive vapor sensors, whose combined response produces a unique pattern for a given compound or mixture. The sensor array is inspired by the biological function of the receptor neurons found in the human olfactory system, which are inherently cross-reactive and respond to many different compounds. The use of an e-nose is an attractive approach to predict unknown odors and is used in many fields for quantitative and qualitative analysis. If properly designed, an e-nose has the potential to adapt to new odors it was not originally designed for through laboratory training and algorithm updates. This would eliminate the lengthy and costly R&D costs associated with materiel and product development. Although e-nose technology has been around for over two decades, much research is still being undertaken in order to find new and more diverse types of sensors. Graphene is a single-layer, 2D material comprised of carbon atoms arranged in a hexagonal lattice, with extraordinary electrical, mechanical, thermal and optical properties due to its 2D, sp2-bonded structure. Graphene has much potential as a chemical sensing material due to its 2D structure, which provides a surface entirely exposed to its surrounding environment. In this configuration, every carbon atom in graphene is a surface atom, providing the greatest possible surface area per unit volume, so that electron transport is highly sensitive to adsorbed molecular species. Graphene has gained much attention since its discovery in 2004, but has not been realized in many commercial electronics. It has the potential to be a revolutionary material for use in chemical sensors due to its excellent conductivity, large surface area, low noise, and versatile surface for functionalization. In this work, graphene is incorporated into a

  9. Advanced deposition model for thermal activated chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cai, Dang

    Thermal Activated Chemical Vapor Deposition (TACVD) is defined as the formation of a stable solid product on a heated substrate surface from chemical reactions and/or dissociation of gaseous reactants in an activated environment. It has become an essential process for producing solid film, bulk material, coating, fibers, powders and monolithic components. Global market of CVD products has reached multi billions dollars for each year. In the recent years CVD process has been extensively used to manufacture semiconductors and other electronic components such as polysilicon, AlN and GaN. Extensive research effort has been directed to improve deposition quality and throughput. To obtain fast and high quality deposition, operational conditions such as temperature, pressure, fluid velocity and species concentration and geometry conditions such as source-substrate distance need to be well controlled in a CVD system. This thesis will focus on design of CVD processes through understanding the transport and reaction phenomena in the growth reactor. Since the in situ monitor is almost impossible for CVD reactor, many industrial resources have been expended to determine the optimum design by semi-empirical methods and trial-and-error procedures. This approach has allowed the achievement of improvements in the deposition sequence, but begins to show its limitations, as this method cannot always fulfill the more and more stringent specifications of the industry. To resolve this problem, numerical simulation is widely used in studying the growth techniques. The difficulty of numerical simulation of TACVD crystal growth process lies in the simulation of gas phase and surface reactions, especially the latter one, due to the fact that very limited kinetic information is available in the open literature. In this thesis, an advanced deposition model was developed to study the multi-component fluid flow, homogeneous gas phase reactions inside the reactor chamber, heterogeneous surface

  10. Water-assisted chemical vapor deposition synthesis of boron nitride nanotubes and their photoluminescence property

    NASA Astrophysics Data System (ADS)

    Li, Juan; Li, Jianbao; Yin, Yanchun; Chen, Yongjun; Bi, Xiaofan

    2013-09-01

    A novel water-assisted chemical vapor deposition (CVD) method for the efficient synthesis of boron nitride (BN) nanotubes is demonstrated. The replacement of metal oxide by water vapor could continuously generate intermediate boron oxide vapor and enhance the production of BN nanotubes. The nanotubes synthesized when an appropriate amount of water vapor was introduced had an average diameter of about 80 nm and lengths of several hundred μm. The diameter and yield of nanotubes could be controlled by tuning the amount of water vapor. This simple water-assisted CVD approach paves a new path to the fabrication of BN nanotubes in large quantities.

  11. Water-assisted chemical vapor deposition synthesis of boron nitride nanotubes and their photoluminescence property.

    PubMed

    Li, Juan; Li, Jianbao; Yin, Yanchun; Chen, Yongjun; Bi, Xiaofan

    2013-09-13

    A novel water-assisted chemical vapor deposition (CVD) method for the efficient synthesis of boron nitride (BN) nanotubes is demonstrated. The replacement of metal oxide by water vapor could continuously generate intermediate boron oxide vapor and enhance the production of BN nanotubes. The nanotubes synthesized when an appropriate amount of water vapor was introduced had an average diameter of about 80 nm and lengths of several hundred μm. The diameter and yield of nanotubes could be controlled by tuning the amount of water vapor. This simple water-assisted CVD approach paves a new path to the fabrication of BN nanotubes in large quantities.

  12. Growth of graphene underlayers by chemical vapor deposition

    SciTech Connect

    Fabiane, Mopeli; Khamlich, Saleh; Bello, Abdulhakeem; Dangbegnon, Julien; Momodu, Damilola; Manyala, Ncholu; Charlie Johnson, A. T.

    2013-11-15

    We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth.

  13. Aerosol chemical vapor deposition of metal oxide films

    DOEpatents

    Ott, Kevin C.; Kodas, Toivo T.

    1994-01-01

    A process of preparing a film of a multicomponent metal oxide including: forming an aerosol from a solution comprised of a suitable solvent and at least two precursor compounds capable of volatilizing at temperatures lower than the decomposition temperature of said precursor compounds; passing said aerosol in combination with a suitable oxygen-containing carrier gas into a heated zone, said heated zone having a temperature sufficient to evaporate the solvent and volatilize said precursor compounds; and passing said volatilized precursor compounds against the surface of a substrate, said substrate having a sufficient temperature to decompose said volatilized precursor compounds whereby metal atoms contained within said volatilized precursor compounds are deposited as a metal oxide film upon the substrate is disclosed. In addition, a coated article comprising a multicomponent metal oxide film conforming to the surface of a substrate selected from the group consisting of silicon, magnesium oxide, yttrium-stabilized zirconium oxide, sapphire, or lanthanum gallate, said multicomponent metal oxide film characterized as having a substantially uniform thickness upon said FIELD OF THE INVENTION The present invention relates to the field of film coating deposition techniques, and more particularly to the deposition of multicomponent metal oxide films by aerosol chemical vapor deposition. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).

  14. Temperature admittance spectroscopy of boron doped chemical vapor deposition diamond

    SciTech Connect

    Zubkov, V. I. Kucherova, O. V.; Zubkova, A. V.; Ilyin, V. A.; Afanas'ev, A. V.; Bogdanov, S. A.; Vikharev, A. L.; Butler, J. E.

    2015-10-14

    Precision admittance spectroscopy measurements over wide temperature and frequency ranges were carried out for chemical vapor deposition epitaxial diamond samples doped with various concentrations of boron. It was found that the experimentally detected boron activation energy in the samples decreased from 314 meV down to 101 meV with an increase of B/C ratio from 600 to 18000 ppm in the gas reactants. For the heavily doped samples, a transition from thermally activated valence band conduction to hopping within the impurity band (with apparent activation energy 20 meV) was detected at temperatures 120–150 K. Numerical simulation was used to estimate the impurity DOS broadening. Accurate determination of continuously altering activation energy, which takes place during the transformation of conduction mechanisms, was proposed by numerical differentiation of the Arrhenius plot. With increase of boron doping level the gradual decreasing of capture cross section from 3 × 10{sup −13} down to 2 × 10{sup −17} cm{sup 2} was noticed. Moreover, for the hopping conduction the capture cross section becomes 4 orders of magnitude less (∼2 × 10{sup −20} cm{sup 2}). At T > T{sub room} in doped samples the birth of the second conductance peak was observed. We attribute it to a defect, related to the boron doping of the material.

  15. Chemical vapor deposition of high T sub c superconductors

    NASA Technical Reports Server (NTRS)

    Webb, G. W.; Engelhardt, J. J.

    1978-01-01

    The results are reported of an investigation into the synthesis and properties of high temperature superconducting materials. A chemical vapor deposition apparatus was designed and built which is suitable for the preparation of multicomponent metal films This apparatus was used to prepare a series of high T sub c A-15 structure superconducting films in the binary system Nb-Ge. The effect on T sub c of a variety of substrate materials was investigated. An extensive series of ternary alloys were also prepared. Conditions allowing the brittle high T sub c (approximately 18 K) A-15 structure superconductor Nb3A1 to be prepared in a low T sub c but ductile form were found. Some of the ways that the ductile (bcc) form can be cold worked or machined are described. Measurements of rate of transformation of cold worked bcc material to the high T sub c A-15 structure with low temperature annealing are given. Preliminary measurements indicate that this material has attractive high field critical current densities.

  16. A high temperature, plasma-assisted chemical vapor deposition system

    SciTech Connect

    Brusasco, R.M.; Britten, J.A.; Thorsness, C.B.; Scrivener, M.S.; Unites, W.G.; Campbell, J.H. ); Johnson, W.L. )

    1990-02-01

    We have designed and built a high-temperature, plasma-assisted, chemical vapor deposition system to deposit multilayer optical coatings of SiO{sub 2} and doped-SiO{sub 2} flat substrates. The coater concept and design is an outgrowth of our recent work with Schott Glasswerke demonstrating the use of plasma assisted CVD to prepare very high damage threshold optical coatings. The coater is designed to deposit up to several thousand alternating quarterwave layers of SiO{sub 2} and doped SiO{sub 2} substrate at deposition rates up to several microns per minute. The substrate is resistively heated to about 1000{degree}C during the deposition phase of the process. The plasma is driven by a 13.56 MHz RF unit capable of producing power densities of up to 140 W cm{sup {minus}3} in the reaction zone. The coater is designed to be adaptable to microwave generated plasmas, as well as RF. Reactant gas flow rates of up to 10 slm can be achieved at a 10 tar operating pressure. Reactants consist of O{sub 2}, SiCl{sub 4} and a volatile halogenated dopant. These gases react in the plasma volume producing SiO{sub 2} with dopant concentrations of up to a few percent. A variable dopant concentration is used to produce index differences between adjacent optical layers.

  17. Optical Diagnostics in the Combustion Chemical Vapor Deposition Proces

    NASA Astrophysics Data System (ADS)

    Luten, Henry; Oljaca, Miodrag; Tomov, Trifon; Metzger, Timothy

    1999-11-01

    Optical emission spectroscopy and IR temperature measurements are used to investigate the structure of a sub-micron droplet spray flame in the Combustion Chemical Vapor Deposition (CCVD) process. The specific system examined in this study is the deposition of barium-strontium-titanate (BaxSr1-xTiO3), a high performance ferroelectric. Spectral measurements were used to determine the decomposition rates of the precursors as well as the lifetimes and relative concentrations of the primary decomposition products. The emissions from atomic and unimolecular species reach a maximum value early in the flame and then decrease sharply, indicating very fast reaction rates. This data, however, is a function of the flame temperature. In order to arrive at proper relative concentration data, the optical emission data must be normalized using measured temperature. Two-dimensional temperature maps were obtained using a non-contact, infrared temperature sensor with peak sensitivity at 4.5 microns. It was found that the sodium emission intensity correlates with the flame temperature, and the sodium emission was used as an internal standard for removing the temperature factor and isolating the relative concentration data. While the flame temperature reaches maximum value at approximately 2 cm, the normalized emission for most species reaches peak intensity closer to the nozzle exit.

  18. Growth of graphene underlayers by chemical vapor deposition

    SciTech Connect

    Fabiane, Mopeli; Khamlich, Saleh; Bello, Abdulhakeem; Dangbegnon, Julien; Momodu, Damilola; Manyala, Ncholu; Charlie Johnson, A. T.

    2013-11-15

    We present a simple and very convincing approach to visualizing that subsequent layers of graphene grow between the existing monolayer graphene and the copper catalyst in chemical vapor deposition (CVD). Graphene samples were grown by CVD and then transferred onto glass substrates by the bubbling method in two ways, either direct-transfer (DT) to yield poly (methyl methacrylate) (PMMA)/graphene/glass or (2) inverted transfer (IT) to yield graphene/PMMA/glass. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to reveal surface features for both the DT and IT samples. The results from FE-SEM and AFM topographic analyses of the surfaces revealed the underlayer growth of subsequent layers. The subsequent layers in the IT samples are visualized as 3D structures, where the smaller graphene layers lie above the larger layers stacked in a concentric manner. The results support the formation of the so-called “inverted wedding cake” stacking in multilayer graphene growth.

  19. Application of chemical vapor composites (CVC) to terrestrial thermionics

    SciTech Connect

    Miskolczy, G.; Reagan, P.

    1995-01-20

    Terrestrial flame fired thermionics took a great leap forward in the earlier 1980`s with the development of reliable long-lived hot shells. These results were presented by Goodale (1981). The hot shell protects the fractory emitter from oxidizing in the combustion environment. In earlier efforts with supralloys emitters it was found that superalloys were poor thermionic emitters since they operated at too low a temperature for practical and economical use as discussed by Huffman (1978). With the development of Chemical Vapor Deposited (CVD) silicon carbide and CVD tungsten, it became possible to fabricate long-lived thermionic converters. These results were shown by Goodale (1980). Further improvements were achieved with the use of oxygen additives on the electrodes. These developments made thermionics attractive for topping a power plant or as the energy conversion part of a cogeneration plant as described by Miskolczy (1982) and Goodale (1983). The feasibility of a thermonic steam boiler and a thermionic topped gas turbine plant become a possibility, as shown by Miskolczy (1980). {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

  20. Carbon-assisted chemical vapor deposition of hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Ismach, Ariel; Chou, Harry; Mende, Patrick; Dolocan, Andrei; Addou, Rafik; Aloni, Shaul; Wallace, Robert; Feenstra, Randall; Ruoff, Rodney S.; Colombo, Luigi

    2017-06-01

    We show that in a low-pressure chemical vapor deposition (CVD) system, the residual oxygen and/or air play a crucial role in the mechanism of the growth of hexagonal boron nitride (h-BN) films on Ni foil ‘enclosures’. Hexagonal-BN films grow on the Ni foil surface via the formation of an intermediate boric-oxide (BO x ) phase followed by a thermal reduction of the BO x by a carbon source (either amorphous carbon powder or methane), leading to the formation of single- and bi-layer h-BN. Low energy electron microscopy (LEEM) and diffraction (LEED) were used to map the number of layers over large areas; Raman spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the structure and physical quality of the ultra-thin h-BN film. The growth procedure reported here leads to a better understanding and control of the synthesis of ultra-thin h-BN films.

  1. Testing of Wrought Iridium/Chemical Vapor Deposition Rhenium Rocket

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Schneider, Steven J.

    1996-01-01

    A 22-N class, iridium/rhenium (Ir/Re) rocket chamber, composed of a thick (418 miocrometer) wrought iridium (Ir) liner and a rhenium substrate deposited via chemical vapor deposition, was tested over an extended period on gaseous oxygen/gaseous hydrogen (GO2/GH2) propellants. The test conditions were designed to produce species concentrations similar to those expected in an Earth-storable propellant combustion environment. Temperatures attained in testing were significantly higher than those expected with Earth-storable propellants, both because of the inherently higher combustion temperature of GO2/GH2 propellants and because the exterior surface of the rocket was not treated with a high-emissivity coating that would be applied to flight class rockets. Thus the test conditions were thought to represent a more severe case than for typical operational applications. The chamber successfully completed testing (over 11 hr accumulated in 44 firings), and post-test inspections showed little degradation of the Ir liner. The results indicate that use of a thick, wrought Ir liner is a viable alternative to the Ir coatings currently used for Ir/Re rockets.

  2. Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

    PubMed Central

    Harberts, Megan; Lu, Yu; Yu, Howard; Epstein, Arthur J.; Johnston-Halperin, Ezekiel

    2015-01-01

    Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at <60 °C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics. PMID:26168285

  3. Chemical vapor deposited silica coatings for solar mirror protection

    NASA Technical Reports Server (NTRS)

    Gulino, Daniel A.; Dever, Therese M.; Banholzer, William F.

    1988-01-01

    A variety of techniques is available to apply protective coatings to oxidation susceptible spacecraft components, and each has associated advantages and disadvantages. Film applications by means of chemical vapor deposition (CVD) has the advantage of being able to be applied conformally to objects of irregular shape. For this reason, a study was made of the oxygen plasma durability of thin film (less than 5000 A) silicon dioxide coatings applied by CVD. In these experiments, such coatings were applied to silver mirrors, which are strongly subject to oxidation, and which are proposed for use on the space station solar dynamic power system. Results indicate that such coatings can provide adequate protection without affecting the reflectance of the mirror. Scanning electron micrographs indicated that oxidation of the silver layer did occur at stress crack locations, but this did not affect the measured solar reflectances. Oxidation of the silver did not proceed beyond the immediate location of the crack. Such stress cracks did not occur in thinner silica flims, and hence such films would be desirable for this application.

  4. Fundamental studies of the chemical vapor deposition of diamond

    SciTech Connect

    Stevenson, D.A.

    1991-01-01

    The plasma or thermally enhanced low pressure chemical vapor deposition of diamond films is an exciting development with many challenging fundamental problems. The early stages of nucleation is relevant to the initial growth rate and the perfection and morphology of the deposit. To isolate one of the factors that influence nucleation, we have studied the effect of surface topography on the nucleation process. Our earlier work has shown preferential nucleation on sharp convex features and we have proposed several possible reasons for this behavior, including dangling bonds at the convex features. In our recent work, we have extended our investigation to include a novel patterning of silicon substrates used to pattern silicon solar cells. The results are consistent with our earlier observations that the majority of nucleation events occur on protruding surface features. In an effort to establish whether dangling bonds at the protruding surfaces may be responsible for the selective nucleation, we have evaluated the dangling bond concentration using electron spin resonance. We have carried out deposition under nominally identical surface topography, but with different concentrations of dangling bonds at or near the surface. The results of this study indicate that dangling bonds play a minor role in enhancing nucleation, in contrast to a substantial role played by special surface topographical features. In the course of the past year, we have submitted four manuscripts for publication and have made six presentations.

  5. Metal film deposition by laser breakdown chemical vapor deposition

    SciTech Connect

    Jervis, T. R.; Newkirk, L. R.

    1986-06-01

    Dielectric breakdown of gas mixtures can be used to deposit thin films by chemical vapor deposition with appropriate control of flow and pressure conditions to suppress gas-phase nucleation and particle formation. Using a pulsed CO/sub 2/ laser operating at 10.6 ..mu.. where there is no significant resonant absorption in any of the source gases, homogeneous films from several gas-phase precursors have been sucessfully deposited by gas-phase laser pyrolysis. Nickel and molybdenum from the respective carbonyls representing decomposition chemistry and tungsten from the hexafluoride representing reduction chemistry have been demonstrated. In each case the gas precursor is buffered with argon to reduce the partial pressure of the reactants and to induce breakdown. Films have been characterized by Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, pull tests, and resistivity measurements. The highest quality films have resulted from the nickel depositions. Detailed x-ray diffraction analysis of these films yields a very small domain size consistent with the low temperature of the substrate and the formation of metastable nickel carbide. Transmission electron microscopy supports this analysis.

  6. Chemical vapor deposited silica coatings for solar mirror protection

    NASA Technical Reports Server (NTRS)

    Gulino, Daniel A.; Dever, Therese M.; Banholzer, William F.

    1988-01-01

    A variety of techniques is available to apply protective coatings to oxidation susceptible spacecraft components, and each has associated advantages and disadvantages. Film applications by means of chemical vapor deposition (CVD) has the advantage of being able to be applied conformally to objects of irregular shape. For this reason, a study was made of the oxygen plasma durability of thin film (less than 5000 A) silicon dioxide coatings applied by CVD. In these experiments, such coatings were applied to silver mirrors, which are strongly subject to oxidation, and which are proposed for use on the space station solar dynamic power system. Results indicate that such coatings can provide adequate protection without affecting the reflectance of the mirror. Scanning electron micrographs indicated that oxidation of the silver layer did occur at stress crack locations, but this did not affect the measured solar reflectances. Oxidation of the silver did not proceed beyond the immediate location of the crack. Such stress cracks did not occur in thinner silica films, and hence such films would be desirable for this application.

  7. High surface area graphene foams by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Drieschner, Simon; Weber, Michael; Wohlketzetter, Jörg; Vieten, Josua; Makrygiannis, Evangelos; Blaschke, Benno M.; Morandi, Vittorio; Colombo, Luigi; Bonaccorso, Francesco; Garrido, Jose A.

    2016-12-01

    Three-dimensional (3D) graphene-based structures combine the unique physical properties of graphene with the opportunity to get high electrochemically available surface area per unit of geometric surface area. Several preparation techniques have been reported to fabricate 3D graphene-based macroscopic structures for energy storage applications such as supercapacitors. Although reaserch has been focused so far on achieving either high specific capacitance or high volumetric capacitance, much less attention has been dedicated to obtain high specific and high volumetric capacitance simultaneously. Here, we present a facile technique to fabricate graphene foams (GF) of high crystal quality with tunable pore size grown by chemical vapor deposition. We exploited porous sacrificial templates prepared by sintering nickel and copper metal powders. Tuning the particle size of the metal powders and the growth temperature allow fine control of the resulting pore size of the 3D graphene-based structures smaller than 1 μm. The as-produced 3D graphene structures provide a high volumetric electric double layer capacitance (165 mF cm-3). High specific capacitance (100 Fg-1) is obtained by lowering the number of layers down to single layer graphene. Furthermore, the small pore size increases the stability of these GFs in contrast to the ones that have been grown so far on commercial metal foams. Electrodes based on the as-prepared GFs can be a boost for the development of supercapacitors, where both low volume and mass are required.

  8. Thirty Gigahertz Optoelectronic Mixing in Chemical Vapor Deposited Graphene.

    PubMed

    Montanaro, Alberto; Mzali, Sana; Mazellier, Jean-Paul; Bezencenet, Odile; Larat, Christian; Molin, Stephanie; Morvan, Loïc; Legagneux, Pierre; Dolfi, Daniel; Dlubak, Bruno; Seneor, Pierre; Martin, Marie-Blandine; Hofmann, Stephan; Robertson, John; Centeno, Alba; Zurutuza, Amaia

    2016-05-11

    The remarkable properties of graphene, such as broadband optical absorption, high carrier mobility, and short photogenerated carrier lifetime, are particularly attractive for high-frequency optoelectronic devices operating at 1.55 μm telecom wavelength. Moreover, the possibility to transfer graphene on a silicon substrate using a complementary metal-oxide-semiconductor-compatible process opens the ability to integrate electronics and optics on a single cost-effective chip. Here, we report an optoelectronic mixer based on chemical vapor-deposited graphene transferred on an oxidized silicon substrate. Our device consists in a coplanar waveguide that integrates a graphene channel, passivated with an atomic layer-deposited Al2O3 film. With this new structure, 30 GHz optoelectronic mixing in commercially available graphene is demonstrated for the first time. In particular, using a 30 GHz intensity-modulated optical signal and a 29.9 GHz electrical signal, we show frequency downconversion to 100 MHz. These results open promising perspectives in the domain of optoelectronics for radar and radio-communication systems.

  9. Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene.

    PubMed

    Harberts, Megan; Lu, Yu; Yu, Howard; Epstein, Arthur J; Johnston-Halperin, Ezekiel

    2015-07-03

    Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at <60 °C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

  10. Residual metallic contamination of transferred chemical vapor deposited graphene.

    PubMed

    Lupina, Grzegorz; Kitzmann, Julia; Costina, Ioan; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Vaziri, Sam; Östling, Mikael; Pasternak, Iwona; Krajewska, Aleksandra; Strupinski, Wlodek; Kataria, Satender; Gahoi, Amit; Lemme, Max C; Ruhl, Guenther; Zoth, Guenther; Luxenhofer, Oliver; Mehr, Wolfgang

    2015-05-26

    Integration of graphene with Si microelectronics is very appealing by offering a potentially broad range of new functionalities. New materials to be integrated with the Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etching and electrochemical delamination methods with respect to residual submonolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection X-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10(13) atoms/cm(2). These metal impurities appear to be partially mobile upon thermal treatment, as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics, these results reveal that further progress in synthesis, handling, and cleaning of graphene is required to advance electronic and optoelectronic applications.

  11. Chemical Vapor-Deposited (CVD) Diamond Films for Electronic Applications

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Diamond films have a variety of useful applications as electron emitters in devices such as magnetrons, electron multipliers, displays, and sensors. Secondary electron emission is the effect in which electrons are emitted from the near surface of a material because of energetic incident electrons. The total secondary yield coefficient, which is the ratio of the number of secondary electrons to the number of incident electrons, generally ranges from 2 to 4 for most materials used in such applications. It was discovered recently at the NASA Lewis Research Center that chemical vapor-deposited (CVD) diamond films have very high secondary electron yields, particularly when they are coated with thin layers of CsI. For CsI-coated diamond films, the total secondary yield coefficient can exceed 60. In addition, diamond films exhibit field emission at fields orders of magnitude lower than for existing state-of-the-art emitters. Present state-of-the-art microfabricated field emitters generally require applied fields above 5x10^7 V/cm. Research on field emission from CVD diamond and high-pressure, high-temperature diamond has shown that field emission can be obtained at fields as low as 2x10^4 V/cm. It has also been shown that thin layers of metals, such as gold, and of alkali halides, such as CsI, can significantly increase field emission and stability. Emitters with nanometer-scale lithography will be able to obtain high-current densities with voltages on the order of only 10 to 15 V.

  12. Chemical Vapor-Deposited (CVD) Diamond Films for Electronic Applications

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Diamond films have a variety of useful applications as electron emitters in devices such as magnetrons, electron multipliers, displays, and sensors. Secondary electron emission is the effect in which electrons are emitted from the near surface of a material because of energetic incident electrons. The total secondary yield coefficient, which is the ratio of the number of secondary electrons to the number of incident electrons, generally ranges from 2 to 4 for most materials used in such applications. It was discovered recently at the NASA Lewis Research Center that chemical vapor-deposited (CVD) diamond films have very high secondary electron yields, particularly when they are coated with thin layers of CsI. For CsI-coated diamond films, the total secondary yield coefficient can exceed 60. In addition, diamond films exhibit field emission at fields orders of magnitude lower than for existing state-of-the-art emitters. Present state-of-the-art microfabricated field emitters generally require applied fields above 5x10^7 V/cm. Research on field emission from CVD diamond and high-pressure, high-temperature diamond has shown that field emission can be obtained at fields as low as 2x10^4 V/cm. It has also been shown that thin layers of metals, such as gold, and of alkali halides, such as CsI, can significantly increase field emission and stability. Emitters with nanometer-scale lithography will be able to obtain high-current densities with voltages on the order of only 10 to 15 V.

  13. Chemical vapor deposition and characterization of tungsten boron alloy films

    SciTech Connect

    Smith, P.M.; Fleming, J.G.; Lujan, R.D.; Roherty-Osmun, E.; Reid, J.S.; Hochberg, A.K.; Roberts, D.A.

    1993-11-01

    A low pressure chemical vapor deposition (LPCVD) process for depositing W{sub X}B{sub (1-X)} films from WF{sub 6} and B{sub 2}H{sub 6} is described. The depositions were performed in a cold wall reactor on 6 in. Si wafers at 400C. During deposition, pressure was maintained at a fixed level in the range of 200 to 260 mTorr. Ratio of WF{sub 6}/B{sub 2}H{sub 6} was varied from 0.05 to 1.07. Carrier gas was either 100 sccm of Ar with a gas flow of 308 to 591 sccm, or 2000 sccm of Ar and 2000 sccm of H{sub 2} with the overall gas flow from 4213 to 4452 sccm. Two stable deposition regions were found separated by an unstable region that produced non-uniform films. The B-rich films produced in one of the stable deposition regions had W concentrations of 30 at.% and resistivities between 200 and 300 {mu}ohm{center_dot}cm. The W-rich films produced in the other stable deposition region had W concentrations of 80 at.% and resistivities of 100 {mu}ohm{center_dot}cm. As-deposited films had densities similar to bulk material of similar stoichiometry. Barrier properties of the films against diffusion of Cu to 700C in vacuum were measured by 4-point probe. Also, annealing was carried out to 900C in order to determine phases formed as the films crystallize. These studies indicate that W{sub X}B{sub (1-X)} films may be useful barriers in ULSI metallization applications.

  14. Investigation of diamond deposition by chemical vapor transport with hydrogen

    NASA Astrophysics Data System (ADS)

    Piekarczyk, Wladyslaw; Messier, Russell F.; Roy, Rustum; Engdahl, Chris

    1990-12-01

    The carbon-hydrogen chemical vapor transport system was examined in accordance with a four-stage transport model. A result of this examination is that graphite co-deposition could be avoided when diamond is deposited from gas solutions under-saturated with respect to diamond. Actual deposition experiments showed that this unusual requirement can be fulfilled but only for the condition that the transport distance between the carbon source and the substrate surface is short. In such a case diamond can be deposited equally from super-saturated as well as from under-saturated gas solutions. On the basis of thermodynamic considerations a possible explanation of this unusual phenomenon is given. It is shown that there is a possibility of deposition of diamond from both super-saturated as well as under-saturated gas solutions but only on the condition that they are in a non-equilibrium state generally called the activated state. A model of the diamond deposition process consisting of two steps is proposed. In the first step diamond and graphite are deposited simultaneously. The most important carbon deposition reaction is C2H2(g) + 2 H(g) C(diamond graphite) + CH(g). The amount of co-deposited graphite is not a direct function of the saturation state of the gas phase. In the second step graphite is etched according to the most probable reaction C(graphite) + 4 H(g) CH4(g). Atomic hydrogen in a super-equilibrium concentration is necessary not only to etch graphite but also to precipitate and graphite. 1.

  15. Metal film deposition by laser breakdown chemical vapor deposition

    SciTech Connect

    Jervis, T.R.

    1985-01-01

    Dielectric breakdown of gas mixtures can be used to deposit homogeneous thin films by chemical vapor deposition with appropriate control of flow and pressure conditions to suppress gas phase nucleation and particle formation. Using a pulsed CO/sub 2/ laser operating at 10.6 microns where there is no significant resonant absorption in any of the source gases, we have succeeded in depositing homogeneous films from several gas phase precursors by gas phase laser pyrolysis. Nickel and molybdenum from the respective carbonyls and tungsten from the hexafluoride have been examined to date. In each case the gas precursor is buffered to reduce the partial pressure of the reactants and to induce breakdown. The films are spectrally reflective and uniform over a large area. Films have been characterized by Auger electron spectroscopy, x-ray diffraction, pull tests, and resistivity measurements. The highest quality films have resulted from the nickel depositions. Detailed x-ray diffraction analysis of these films yields a very small domain size (approx. 50 A) consistent with rapid quenching from the gas phase reaction zone. This analysis also shows nickel carbide formation consistent with the temperature of the reaction zone and the Auger electron spectroscopy results which show some carbon and oxygen incorporation (8% and 1% respectively). Gas phase transport and condensation of the molybdenum carbonyl results in substantial carbon and oxygen contamination of the molybdenum films requiring heated substrates, a requirement not consistent with the goals of the program to maximize the quench rate of the deposition. Results from tungsten deposition experiments representing a reduction chemistry instead of the decomposition chemistry involved in the carbonyl experiments are also reported.

  16. Metal film deposition by laser breakdown chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jervis, T. R.

    1985-01-01

    Dielectric breakdown of gas mixtures can be used to deposit homogeneous thin films by chemical vapor deposition with appropriate control of flow and pressure conditions to suppress gas phase nucleation and particle formation. Using a pulsed CO2 laser operating at 10.6 microns where there is no significant resonant absorption in any of the source gases, we have succeeded in depositing homogeneous films from several gas phase precursors by gas phase laser pyrolysis. Nickel and molybdenum from the respective carbonyls and tungsten from the hexafluoride have been examined to date. In each case the gas precursor is buffered to reduce the partial pressure of the reactants and to induce breakdown. The films are spectrally reflective and uniform over a large area. Films have been characterized by Auger electron spectroscopy, X-ray diffraction, pull tests, and resistivity measurements. The highest quality films have resulted from the nickel depositions. Detailed X-ray diffraction analysis of these films yields a very small domain size (approx. 50 A) consistent with rapid quenching from the gas phase reaction zone. This analysis also shows nickel carbide formation consistent with the temperature of the reaction zone and the Auger electron spectroscopy results which show some carbon and oxygen incorporation (8% and 1% respectively). Gas phase transport and condensation of the molybdenum carbonyl results in substantial carbon and oxygen contamination of the molybdenum films requiring heated substrates, a requirement not consistent with the goals of the program to maximize the quench rate of the deposition. Results from tungsten deposition experiments representing a reduction chemistry instead of the decomposition chemistry involved in the carbonyl experiments are also reported.

  17. Review of chemical vapor deposition of graphene and related applications.

    PubMed

    Zhang, Yi; Zhang, Luyao; Zhou, Chongwu

    2013-10-15

    Since its debut in 2004, graphene has attracted enormous interest because of its unique properties. Chemical vapor deposition (CVD) has emerged as an important method for the preparation and production of graphene for various applications since the method was first reported in 2008/2009. In this Account, we review graphene CVD on various metal substrates with an emphasis on Ni and Cu. In addition, we discuss important and representative applications of graphene formed by CVD, including as flexible transparent conductors for organic photovoltaic cells and in field effect transistors. Growth on polycrystalline Ni films leads to both monolayer and few-layer graphene with multiple layers because of the grain boundaries on Ni films. We can greatly increase the percentage of monolayer graphene by using single-crystalline Ni(111) substrates, which have smooth surface and no grain boundaries. Due to the extremely low solubility of carbon in Cu, Cu has emerged as an even better catalyst for the growth of monolayer graphene with a high percentage of single layers. The growth of graphene on Cu is a surface reaction. As a result, only one layer of graphene can form on a Cu surface, in contrast with Ni, where more than one layer can form through carbon segregation and precipitation. We also describe a method for transferring graphene sheets from the metal using polymethyl methacrylate (PMMA). CVD graphene has electronic properties that are potentially valuable in a number of applications. For example, few-layer graphene grown on Ni can function as flexible transparent conductive electrodes for organic photovoltaic cells. In addition, because we can synthesize large-grain graphene on Cu foil, such large-grain graphene has electronic properties suitable for use in field effect transistors.

  18. Chemical reaction between water vapor and stressed glass

    NASA Technical Reports Server (NTRS)

    Soga, N.; Okamoto, T.; Hanada, T.; Kunugi, M.

    1979-01-01

    The crack velocity in soda-lime silicate glass was determined at room temperature at water-vapor pressures of 10 to 0.04 torr using the double torsion technique. A precracked glass specimen (70 x 16 x 1.6 mm) was placed in a vacuum chamber containing a four-point bending test apparatus. The plotted experimental results show that the crack propagation curve in water agrees fairly well with that of Wiederhorn (1967). Attention is given to the effect of water vapor pressure on crack velocity at K(I) = 550,000 N/m to the 3/2 power, with (Wiederhorn's data) or without N2 present. The plotted results reveal that the present crack velocity is about two orders of magnitude higher than that of Wiederhorn at high water-vapor conditions, but the difference decreases as the water-vapor concentration diminishes or the crack velocity slows down.

  19. Performance characteristics of a chemical oxygen-iodine laser without a water vapor trap

    NASA Astrophysics Data System (ADS)

    Kikuchi, Toshio; Tsuruyama, Toru; Uchiyama, Taro

    1988-09-01

    The effect of water vapor on the operation of a chemical oxygen-iodine laser without a water vapor trap is described. The maximum CW laser power of 87 W was obtained without the water vapor trap at a Cl2 flow rate of 740 mmol/min. An alkaline H2O2 solution (90 wt pct H2O2, 50 wt pct KOH) was cooled down to about -30 C in order to control the saturated H2O2-H2O vapor pressure to less than 100 mTorr. Two porous pipes made of carbon were utilized as a singlet oxygen generator.

  20. Experimental Study of Diamond Nucleation by Plasmon Assisted Chemical Vapor Deposition

    DTIC Science & Technology

    2012-05-18

    REPORT Final Technical Report for Proposal Number 59187MSDRP: Experimental Study of Diamond Nucleation by Plasmon Assisted Chemical Vapor Deposition 14...chemical vapor deposition , characterization of diamond nanoparticles, and direct conversion of the polymer poly(hydridocarbyne) to diamond. We adapted the...Raman spectroscopy. With the addition of the filament, we were able to observe carbon deposition and etching of amorphous carbon. We were 1. REPORT

  1. Year 2 Update: Investigation of Chemical Vapor Deposited Aluminum as a Replacement Coating for Cadmium

    DTIC Science & Technology

    2007-01-24

    1/29/2007 1 Year 2 Update: Investigation of Chemical Vapor Deposited Aluminum as a Replacement Coating for Cadmium Dr. Elizabeth Berman and Dr. Eric...Investigation of Chemical Vapor Deposited Aluminum as a Replacement Coating for Cadmium 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...13. SUPPLEMENTARY NOTES 27th Replacement of Hard Chrome and Cadmium Plating Program Review Meeting, January 23-25, 2007, New Orleans, LA. Sponsored

  2. Chemical Vapor Deposition of Atomically-Thin Molybdenum Disulfide (MoS2)

    DTIC Science & Technology

    2015-03-01

    UNCLASSIFIED AD-E403 625 Technical Report ARMET-TR-14041 CHEMICAL VAPOR DEPOSITION OF ATOMICALLY -THIN MOLYBDENUM...4. TITLE AND SUBTITLE CHEMICAL VAPOR DEPOSITION OF ATOMICALLY -THIN MOLYBDENUM DISULFIDE (MoS2) 5a. CONTRACT NUMBER 5b. GRANT NUMBER...materials, in their bulk form exist as lamellar structures, they can be exfoliated into individual, atomically -thin layers . While the exfoliated 2D materials

  3. Polymer-coated symmetrical metal-cladding waveguide for chemical vapor detection with high sensitivity

    NASA Astrophysics Data System (ADS)

    Xiao, PingPing; Deng, ManLan

    2012-11-01

    An optical platform for sensitive detection of chemical vapor based on a polymer-coated symmetrical metal-cladding waveguide is proposed. The diffusion of chemical vapor usually leads to a combinational effect in the polymer layer, i.e., swelling and refractive index change. Owing to the high sensitivity of ultrahigh-order modes, the vapor-induced effect will give rise to a dramatic variation of the reflected light intensity. For proof-of-concept, a good linearity and a low detection limit of toluene and benzene are experimentally demonstrated with an amorphous Teflon AF polymer layer.

  4. Interfacial studies of chemical-vapor-infiltrated (CVI) ceramic matrix composites. Final report

    SciTech Connect

    Brennan, J.J.

    1990-03-31

    The objective of this program was to investigate the fiber/matrix interfacial chemistry in CVI SiC matrix composites utilizing Nicalon SiC and Nextel 440 mullite fibers and to determine how this interface influences composite properties such as strength, toughness, and environmental stability. The SiC matrix was deposited using three different reactants; methyldichlorosilane (MDS), methyltrichlorosilane (MTS), and dimethyldichlorosilane (DMDS). The fiber/matrix interface was tailored by means of introducing a carbon, BN, or carbon rich SiC interfacial layer. It was found that applying a carbon interfacial layer to either NICALON or Nextel 440 fibers prior to deposition of SiC resulted in a weakly bonded interface that imparted toughness to CVI matrix composite through its ability to deflect matrix cracks. This carbon layer can be applied either deliberately by the decomposition of methane or by utilizing an argon flushing gas in the reactor that apparently interrupted the normal deposition of SiC from silane precursors and instead allowed carbon to deposit. It was found that this carbon interfacial layer, no matter how it was deposited, was not oxidatively stable at elevated temperatures, leading to severe degradation of composite properties.

  5. Forced chemical vapor infiltration of tubular geometries: Modeling, design, and scale-up

    SciTech Connect

    Stinton, D.P.; Besmann, T.M.; Matlin, W.M.; Starr, T.L.; Curtain, W.A.

    1995-10-01

    The development of thick-walled, tubular ceramic composites has involved investigations of different fiber architectures and fixturing to obtain optimal densification and mechanical properties. The current efforts entail modeling of the densification process in order to increase densification uniformity and decrease processing time. In addition, the process is being scaled to produce components with a 10 cm outer diameter.

  6. Chemical vapor deposition of fluorine-doped zinc oxide

    DOEpatents

    Gordon, Roy G.; Kramer, Keith; Liang, Haifan

    2000-06-06

    Fims of fluorine-doped zinc oxide are deposited from vaporized precursor compounds comprising a chelate of a dialkylzinc, such as an amine chelate, an oxygen source, and a fluorine source. The coatings are highly electrically conductive, transparent to visible light, reflective to infrared radiation, absorbing to ultraviolet light, and free of carbon impurity.

  7. Comparison of InGaAs(100) Grown by Chemical Beam Epitaxy and Metal Organic Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Greene, A. L.; Daniels-Race, T.; Lum, R. M.

    2000-01-01

    Secondary ion mass spectrometry is used to study the effects of substrate temperature on the composition and growth rate of InGaAs/InP(100) multilayers grown by chemical beam epitaxy, metal-organic chemical vapor deposition and solid source molecular beam epitaxy. The growth kinetics of the material grown by the different techniques are analyzed and compared.

  8. Comparison of InGaAs(100) Grown by Chemical Beam Epitaxy and Metal Organic Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Williams, M. D.; Greene, A. L.; Daniels-Race, T.; Lum, R. M.

    2000-01-01

    Secondary ion mass spectrometry is used to study the effects of substrate temperature on the composition and growth rate of InGaAs/InP(100) multilayers grown by chemical beam epitaxy, metal-organic chemical vapor deposition and solid source molecular beam epitaxy. The growth kinetics of the material grown by the different techniques are analyzed and compared.

  9. Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

    NASA Astrophysics Data System (ADS)

    Liang, Rongning; Chen, Lusi; Qin, Wei

    2015-07-01

    Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs.

  10. Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

    PubMed Central

    Liang, Rongning; Chen, Lusi; Qin, Wei

    2015-01-01

    Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs. PMID:26215887

  11. Organometallic Chemical Vapor Deposition Growth of Antimony Compounds

    NASA Astrophysics Data System (ADS)

    Chiang, Peng-Kuen

    This research is motivated by the desire to synthesize Sb III-V materials, including GaAs(,1-x)Sb(,x), InSb, and InAs(,1-x)Sb(,x). Ga-As-Sb system is known to have a significant solid phase miscibility gap from x = 0.2 to x = 0.8 at 600(DEGREES)C using a liquid phase epitaxy (LPE) growth technique. In this work, organometallic chemical vapor deposition (OM-CVD) has been shown to be a suitable growth technique for growing GaAs(,1-x)Sb(,x) alloys lying in the region of solid immiscibility. Conditions for growth of GaAs(,1-x)Sb(,x) layers with x as high as 0.7 on GaAs substrates are described for temperatures between 580 and 650(DEGREES)C. Effects of substrate orientation on growth characteristics are noted, and comparisons of growth on (511) and (100) GaAs faces are made. The experimental results indicate that growth is being controlled by surface reaction kinetics. A simple model based on kinetic control is presented. InSb is one of the most extensively examined semiconductors because of the small energy bandgap which is suitable for 3-5 (mu)m wavelength detection, and it also has highest mobility of any III-V compounds. OM-CVD has been used to epitaxially grow high quality InSb for the first time in this work. InSb with excellent morphology was achieved on both (100) and (111)B InSb substrates. The measured electron mobility at 300(DEGREES)K of undoped InSb grown on (100) GaAs semi-insulating substrates was 40,000 cm('2)/V -sec at a carrier concentration of N(,D)-N(,A) = 1.2 x 10('15)cm(' -3) has been measured at 77(DEGREES)K.Experimental data suggests that a dislocation scattering mechanism represents a significant mobility limiting process. InAs(,1-x)Sb(,x), with x (TURN) 0.6, has the lowest bandgap (=0.1 eV at 300(DEGREES)K) of any of the III-V ternary compounds. This bandgap is suitable for detectors in the 8-12 (mu)m wavelength region where an atmosphere window exists. So far, InAs(,1-x)Sb(,x) with 0.55 < x < 0.75 has not been achieved by LPE and molecular

  12. Magnetorheological finishing of chemical-vapor deposited zinc sulfide via chemically and mechanically modified fluids

    SciTech Connect

    Salzman, Sivan; Romanofsky, Henry J.; Giannechini, Lucca J.; Jacobs, Stephen D.; Lambropoulos, John C.

    2016-02-19

    In this study, we describe the anisotropy in the material removal rate (MRR) of the polycrystalline, chemical-vapor deposited zinc sulfide (ZnS).We define the polycrystalline anisotropy via microhardness and chemical erosion tests for four crystallographic orientations of ZnS: (100), (110), (111), and (311). Anisotropy in the MRR was studied under magnetorheological finishing (MRF) conditions. Three chemically and mechanically modified magnetorheological (MR) fluids at pH values of 4, 5, and 6 were used to test the MRR variations among the four single-crystal planes. When polishing the single-crystal planes and the polycrystalline with pH 5 and pH 6MR fluids, variations were found in the MRR among the four single-crystal planes and surface artifacts were observed on the polycrystalline material. When polishing the single-crystal planes and the polycrystalline with the modified MR fluid at pH 4, however, minimal variation was observed in the MRR among the four orientations and a reduction in surface artifacts was achieved on the polycrystalline material.

  13. Magnetorheological finishing of chemical-vapor deposited zinc sulfide via chemically and mechanically modified fluids

    DOE PAGES

    Salzman, Sivan; Romanofsky, Henry J.; Giannechini, Lucca J.; ...

    2016-02-19

    In this study, we describe the anisotropy in the material removal rate (MRR) of the polycrystalline, chemical-vapor deposited zinc sulfide (ZnS).We define the polycrystalline anisotropy via microhardness and chemical erosion tests for four crystallographic orientations of ZnS: (100), (110), (111), and (311). Anisotropy in the MRR was studied under magnetorheological finishing (MRF) conditions. Three chemically and mechanically modified magnetorheological (MR) fluids at pH values of 4, 5, and 6 were used to test the MRR variations among the four single-crystal planes. When polishing the single-crystal planes and the polycrystalline with pH 5 and pH 6MR fluids, variations were found inmore » the MRR among the four single-crystal planes and surface artifacts were observed on the polycrystalline material. When polishing the single-crystal planes and the polycrystalline with the modified MR fluid at pH 4, however, minimal variation was observed in the MRR among the four orientations and a reduction in surface artifacts was achieved on the polycrystalline material.« less

  14. Molecular restrictions for human eye irritation by chemical vapors

    SciTech Connect

    Cometto-Muniz, J. Enrique . E-mail: ecometto@ucsd.edu; Cain, William S.; Abraham, Michael H.

    2005-09-15

    Previous research showed a cut-off along homologous volatile organic compounds (VOCs) in their ability to produce acute human mucosal irritation. The present study sought to specify the particular cut-off homolog for sensory eye irritation in an acetate and n-alcohol series. A 1900-ml glass vessel system and a three-alternative forced-choice procedure served to test nonyl, decyl, and dodecyl acetate, and 1-nonanol, 1-decanol, and 1-undecanol. Flowrate to the eye ranged from 2 to 8 L/min and time of exposure from 3 to 24 s. Decyl acetate and 1-undecanol were the shortest homologs that failed to produce eye irritation under all conditions, producing a cut-off effect. Increasing the vapor concentration of decyl acetate and 1-undecanol by 3 and 8 times, respectively, via heating them to 37 deg C made either or both VOCs detectable to only half of the 12 subjects tested, even though the higher vapor concentration was well above a predicted eye irritation threshold. When eye irritation thresholds for homologous acetates and n-alcohols were plotted as a function of the longest unfolded length of the molecule, the values for decyl acetate and 1-undecanol fell within a restricted range of 18 to 19 A. The outcome suggests that the basis for the cut-off is biological, that is, the molecule lacks a key size or structure to trigger transduction, rather than physical, that is, the vapor concentration is too low to precipitate detection.

  15. Si Passivation and Chemical Vapor Deposition of Silicon Nitride: Final Technical Report, March 18, 2007

    SciTech Connect

    Atwater, H. A.

    2007-11-01

    This report investigated chemical and physical methods for Si surface passivation for application in crystalline Si and thin Si film photovoltaic devices. Overall, our efforts during the project were focused in three areas: i) synthesis of silicon nitride thin films with high hydrogen content by hot-wire chemical vapor deposition; ii) investigation of the role of hydrogen passivation of defects in crystalline Si and Si solar cells by out diffusion from hydrogenated silicon nitride films; iii) investigation of the growth kinetics and passivation of hydrogenated polycrystalline. Silicon nitride films were grown by hot-wire chemical vapor deposition and film properties have been characterized as a function of SiH4/NH3 flow ratio. It was demonstrated that hot-wire chemical vapor deposition leads to growth of SiNx films with controllable stoichiometry and hydrogen.

  16. Industrial Scale Synthesis of Carbon Nanotubes Via Fluidized Bed Chemical Vapor Deposition: A Senior Design Project

    ERIC Educational Resources Information Center

    Smith, York R.; Fuchs, Alan; Meyyappan, M.

    2010-01-01

    Senior year chemical engineering students designed a process to produce 10 000 tonnes per annum of single wall carbon nanotubes (SWNT) and also conducted bench-top experiments to synthesize SWNTs via fluidized bed chemical vapor deposition techniques. This was an excellent pedagogical experience because it related to the type of real world design…

  17. Industrial Scale Synthesis of Carbon Nanotubes Via Fluidized Bed Chemical Vapor Deposition: A Senior Design Project

    ERIC Educational Resources Information Center

    Smith, York R.; Fuchs, Alan; Meyyappan, M.

    2010-01-01

    Senior year chemical engineering students designed a process to produce 10 000 tonnes per annum of single wall carbon nanotubes (SWNT) and also conducted bench-top experiments to synthesize SWNTs via fluidized bed chemical vapor deposition techniques. This was an excellent pedagogical experience because it related to the type of real world design…

  18. Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor Deposition.

    PubMed

    Leyden, Matthew R; Meng, Lingqiang; Jiang, Yan; Ono, Luis K; Qiu, Longbin; Juarez-Perez, Emilio J; Qin, Chuanjiang; Adachi, Chihaya; Qi, Yabing

    2017-07-20

    Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22%, and perovskite light-emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m(2).

  19. Controlled VLS Growth of Indium, Gallium and Tin Oxide Nanowiresvia Chemical Vapor Transport

    SciTech Connect

    Johnson, M.C.; Aloni, S.; McCready, D.E.; Bourret-Courchesne, E.D.

    2006-03-13

    We utilized a vapor-liquid-solid growth technique to synthesize indium oxide, gallium oxide, and tin oxide nanowires using chemical vapor transport with gold nanoparticles as the catalyst. Using identical growth parameters we were able to synthesize single crystal nanowires typically 40-100 nm diameter and more than 10-100 microns long. The products were characterized by means of XRD, SEM and HRTEM. All the wires were grown under the same growth conditions with growth rates inversely proportional to the source metal vapor pressure. Initial experiments show that different transparent oxide nanowires can be grown simultaneously on a single substrate with potential application for multi-component gas sensors.

  20. A model for chemical and isotopic fractionation in the lunar regolith by impact vaporization

    NASA Technical Reports Server (NTRS)

    Housley, R. M.

    1979-01-01

    Up until now there has been no complete model of chemical and isotopic fractionation effects which could occur in the lunar regolith as a result of hypervelocity impact vaporization. Previous work on the outlines for such a model are extended and show that impact vaporization could be an efficient mechanism for producing heavy isotope enrichments. Rough qualitative predictions based on the model show a general similarity to the observations on lunar samples.

  1. A model for chemical and isotopic fractionation in the lunar regolith by impact vaporization

    NASA Technical Reports Server (NTRS)

    Housley, R. M.

    1979-01-01

    Up until now there has been no complete model of chemical and isotopic fractionation effects which could occur in the lunar regolith as a result of hypervelocity impact vaporization. Previous work on the outlines for such a model are extended and show that impact vaporization could be an efficient mechanism for producing heavy isotope enrichments. Rough qualitative predictions based on the model show a general similarity to the observations on lunar samples.

  2. From chemical agent alarm to fugitive vapor detection: development of a rugged commercial spectrometer

    NASA Astrophysics Data System (ADS)

    Costello, William E.; Simonds, Jo Ann; Milchling, Suzanne

    1996-06-01

    Intellitec, a division of Technical Products Group, Inc., is developing and testing a ruggedized commercial spectrometer for stable platform applications. This spectrometer design incorporates the key components utilized in the M21 remote sensing chemical agent alarm (RSCAAL). The spectrometer, which has a resolution of 4 wavenumbers (cm-1), can be used to remotely sense fugitive vapors with spectral features in the 8 - 12 micrometer region. Intellitec has initiated a parallel effort to complete the development of personal computer (PC) based vapor identification software. The spectrometer's detection capability was tested by placing small amounts of anhydrous hydrazine vapor in a cell positioned in front of a black body reference. The data collected from the spectrometer clearly showed characteristic spectral features of hydrazine vapor. A developmental set of hydrazine coefficients was generated for use with the vapor identification software utilized in the M21. The coefficients were programmed into the M21. The effectiveness of the coefficients in the M21 was then tested by attempting to detect hydrazine vapor contained in a cell positioned in front of a black body. The developmental coefficient set successfully detected the hydrazine vapor. Further testing is required to improve detection sensitivity and confirm the spectrometer's ability to detect these vapors in an open path environment.

  3. Metalorganic chemical vapor deposition of gallium nitride on sacrificial substrates

    NASA Astrophysics Data System (ADS)

    Fenwick, William Edward

    GaN-based light emitting diodes (LEDs) face several challenges if the technology is to continue to make a significant impact in general illumination, and on technology that has become known as solid state lighting (SSL). Two of the most pressing challenges for the continued penetration of SSL into traditional lighting applications are efficacy and total lumens from the device, and their related cost. The development of alternative substrate technologies is a promising avenue toward addressing both of these challenges, as both GaN-based device technology and the associated metalorganic chemical vapor deposition (MOCVD) technology are already relatively mature technologies with a well-understood cost base. Zinc oxide (ZnO) and silicon (Si) are among the most promising alternative substrates for GaN epitaxy. These substrates offer the ability to access both higher efficacy and lumen devices (ZnO) at a much reduced cost. This work focuses on the development of MOCVD growth processes to yield high quality GaN-based materials and devices on both ZnO and Si. ZnO is a promising substrate for growth of low defect-density GaN because of its similar lattice constant and thermal expansion coefficient. The major hurdles for GaN growth on ZnO are the instability of the substrate in a hydrogen atmosphere, which is typical of nitride growth conditions, and the inter-diffusion of zinc and oxygen from the substrate into the GaN-based epitaxial layer. A process was developed for the MOCVD growth of GaN and InxGa 1-xN on ZnO that attempted to address these issues. The structural and optical properties of these films were studied using various techniques. X-ray diffraction (XRD) showed the growth of wurtzite GaN on ZnO, and room-temperature photoluminescence (RT-PL) showed near band-edge luminescence from the GaN and InxGa1-xN layers. However, high zinc and oxygen concentrations due to interdiffusion near the ZnO substrate remained an issue; therefore, the diffusion of zinc and oxygen

  4. A chemical kinetic model for chemical vapor deposition of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Raji, K.; Thomas, Shijo; Sobhan, C. B.

    2011-10-01

    Carbon nanotubes (CNTs) are classified among the most promising novel materials due to their exceptional physical properties. Still, optimal fabrication of carbon nanotubes involves a number of challenges. Whatever be the fabrication method, a process optimization can be evolved only on the basis of a good theoretical model to predict the parametric influences on the final product. The work reported here investigates the dependence of the deposition parameters on the controllable parameters for carbon nanotube growth during Chemical vapor deposition (CVD), through a chemical kinetic model. The theoretical model consisted of the design equations and the energy balance equations, based on the reaction kinetics, for the plug flow and the batch reactor, which simulate the CVD system. The numerical simulation code was developed in-house in a g++ environment. The results predicted the growth conditions for CNT: the deposition temperature, pressure and number of atoms, which were found to be influenced substantially by the initial controllable parameters namely the temperature, volumetric flow rate of the carbon precursor, and the reaction time. An experimental study was also conducted on a CVD system developed in the laboratory, to benchmark the computational results. The experimental results were found to agree well with the theoretical predictions obtained from the model.

  5. Flux monitoring and control in epitaxy by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.; Brown, N.; Ricker, N. L.; Johnson, M.

    1998-06-01

    Atomic fluorescence spectroscopy is a promising technique to detect individual chemical species at typical growth pressures in chemical beam and metal-organic epitaxy. We report results of initial experiments to measure triethyl gallium and dimethylethylamine-alane. We have successfully detected both species, but further development is needed to adapt this measurement to the needs of real-time sensing and control in chemical beam epitaxy.

  6. Field emission property of hydrogenated chemical vapor deposited diamond films studied by scanning tunneling microscopy.

    PubMed

    Liu, Fengbin; Wang, Jiadao; Chen, Darong

    2010-11-01

    By using scanning tunneling microscopy, the plots of tunneling current versus applied voltage, at the local points for hydrogenated and oxygenated chemical vapor deposited diamond films, were investigated. For comparison, the measurement points were adopted on the centers of the crystalline grains and at the grain boundaries, respectively. The results indicated that, for the hydrogenated chemical vapor deposited diamond, the field emission character is much better on the center of the crystalline grains than at the grain boundary. In contrast, for the oxygenated samples, the crystalline grains show a poor field emission character. The two diamond surfaces exhibit similar field emission characters at the grain boundaries. The surface emission mechanisms of the hydrogenated chemical vapor deposited diamond films were also discussed.

  7. Sequential Vapor Infiltration Treatment Enhances the Ionic Current Rectification Performance of Composite Membranes Based on Mesoporous Silica Confined in Anodic Alumina.

    PubMed

    Liang, Yanyan; Liu, Zhengping

    2016-12-20

    Ionic current rectification of nanofluidic diode membranes has been studied widely in recent years because it is analogous to the functionality of biological ion channels in principle. We report a new method to fabricate ionic current rectification membranes based on mesoporous silica confined in anodic aluminum oxide (AAO) membranes. Two types of mesostructured silica nanocomposites, hexagonal structure and nanoparticle stacked structure, were used to asymmetrically fill nanochannels of AAO membranes by a vapor-phase synthesis (VPS) method with aspiration approach and were further modified via sequence vapor infiltration (SVI) treatment. The ionic current measurements indicated that SVI treatment can modulate the asymmetric ionic transport in prepared membranes, which exhibited clear ionic current rectification phenomenon under optimal conditions. The ionic current rectifying behavior is derived from the asymmetry of surface conformations, silica species components, and hydrophobic wettability, which are created by the asymmetrical filling type, silica depositions on the heterogeneous membranes, and the condensation of silanol groups. This article provides a considerable strategy to fabricate composite membranes with obvious ionic current rectification performance via the cooperation of the VPS method and SVI treatment and opens up the potential of mesoporous silica confined in AAO membranes to mimic fluid transport in biological processes.

  8. Application of laser Doppler velocimeter to chemical vapor laser system

    NASA Technical Reports Server (NTRS)

    Gartrell, Luther R.; Hunter, William W., Jr.; Lee, Ja H.; Fletcher, Mark T.; Tabibi, Bagher M.

    1993-01-01

    A laser Doppler velocimeter (LDV) system was used to measure iodide vapor flow fields inside two different-sized tubes. Typical velocity profiles across the laser tubes were obtained with an estimated +/-1 percent bias and +/-0.3 to 0.5 percent random uncertainty in the mean values and +/-2.5 percent random uncertainty in the turbulence-intensity values. Centerline velocities and turbulence intensities for various longitudinal locations ranged from 13 to 17.5 m/sec and 6 to 20 percent, respectively. In view of these findings, the effects of turbulence should be considered for flow field modeling. The LDV system provided calibration data for pressure and mass flow systems used routinely to monitor the research laser gas flow velocity.

  9. Solar-induced chemical vapor deposition of diamond-type carbon films

    DOEpatents

    Pitts, J. Roland; Tracy, C. Edwin; King, David E.; Stanley, James T.

    1994-01-01

    An improved chemical vapor deposition method for depositing transparent continuous coatings of sp.sup.3 -bonded diamond-type carbon films, comprising: a) providing a volatile hydrocarbon gas/H.sub.2 reactant mixture in a cold wall vacuum/chemical vapor deposition chamber containing a suitable substrate for said films, at pressure of about 1 to 50 Torr; and b) directing a concentrated solar flux of from about 40 to about 60 watts/cm.sup.2 through said reactant mixture to produce substrate temperatures of about 750.degree. C. to about 950.degree. C. to activate deposition of the film on said substrate.

  10. Solar-induced chemical vapor deposition of diamond-type carbon films

    DOEpatents

    Pitts, J.R.; Tracy, C.E.; King, D.E.; Stanley, J.T.

    1994-09-13

    An improved chemical vapor deposition method for depositing transparent continuous coatings of sp[sup 3]-bonded diamond-type carbon films, comprises: (a) providing a volatile hydrocarbon gas/H[sub 2] reactant mixture in a cold wall vacuum/chemical vapor deposition chamber containing a suitable substrate for said films, at pressure of about 1 to 50 Torr; and (b) directing a concentrated solar flux of from about 40 to about 60 watts/cm[sup 2] through said reactant mixture to produce substrate temperatures of about 750 C to about 950 C to activate deposition of the film on said substrate. 11 figs.

  11. Properties of Plasma Enhanced Chemical Vapor Deposition Barrier Coatings and Encapsulated Polymer Solar Cells

    NASA Astrophysics Data System (ADS)

    Qi, Lei; Zhang, Chunmei; Chen, Qiang

    2014-01-01

    In this paper, we report silicon oxide coatings deposited by plasma enhanced chemical vapor deposition technology (PECVD) on 125 μm polyethyleneterephthalate (PET) surfaces for the purpose of the shelf lifetime extension of sealed polymer solar cells. After optimization of the processing parameters, we achieved a water vapor transmission rate (WVTR) of ca. 10-3 g/m2/day with the oxygen transmission rate (OTR) less than 0.05 cc/m2/day, and succeeded in extending the shelf lifetime to about 400 h in encapsulated solar cells. And then the chemical structure of coatings related to the properties of encapsulated cell was investigated in detail.

  12. Classification Characteristics of Carbon Nanotube Polymer Composite Chemical Vapor Detectors

    DTIC Science & Technology

    2006-03-01

    eight- detector carbon black/polymer composite array was exposed to DMMP, DIMP, THF, benzene, methanol, toluene, water, lighter fluid, vinegar , or diesel... reaction of reagents, impregnated on the paper sensor, with the air. When a chemical agent is present, the reagent and chemical react and change the...toluene, water, lighter fluid, vinegar , or diesel fuel in an air background (Hopkins and Lewis, 2001:888). Additionally, the Jet Propulsion

  13. Ti-doped hydrogenated diamond like carbon coating deposited by hybrid physical vapor deposition and plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Na Rae; Sle Jun, Yee; Moon, Kyoung Il; Sunyong Lee, Caroline

    2017-03-01

    Diamond-like carbon films containing titanium and hydrogen (Ti-doped DLC:H) were synthesized using a hybrid technique based on physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD). The film was deposited under a mixture of argon (Ar) and acetylene gas (C2H2). The amount of Ti in the Ti-doped DLC:H film was controlled by varying the DC power of the Ti sputtering target ranging from 0 to 240 W. The composition, microstructure, mechanical and chemical properties of Ti-doped DLC:H films with varying Ti concentrations, were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nano indentation, a ball-on-disk tribometer, a four-point probe system and dynamic anodic testing. As a result, the optimum composition of Ti in Ti-doped DLC:H film using our hybrid method was found to be a Ti content of 18 at. %, having superior electrical conductivity and high corrosion resistance, suitable for bipolar plates. Its hardness value was measured to be 25.6 GPa with a low friction factor.

  14. The Relationship Between Chemical Structure and Dielectric Properties of Plasma-Enhanced Chemical Vapor Deposited Polymer Thin Films (Postprint)

    DTIC Science & Technology

    2007-01-01

    Materials Sci & Tech Applications, LLC) N. Venkatasubramanian and John T. Grant (University of Dayton) Kurt Eyink, Jesse Enlow, and Timothy J. Bunning...structure and dielectric properties of plasma-enhanced chemical vapor deposited polymer thin films Hao Jiang b,⁎, Lianggou Hong b, N. Venkatasubramanian c

  15. Reduced chemical warfare agent sorption in polyurethane-painted surfaces via plasma-enhanced chemical vapor deposition of perfluoroalkanes.

    PubMed

    Gordon, Wesley O; Peterson, Gregory W; Durke, Erin M

    2015-04-01

    Perfluoralkalation via plasma chemical vapor deposition has been used to improve hydrophobicity of surfaces. We have investigated this technique to improve the resistance of commercial polyurethane coatings to chemicals, such as chemical warfare agents. The reported results indicate the surface treatment minimizes the spread of agent droplets and the sorption of agent into the coating. The improvement in resistance is likely due to reduction of the coating's surface free energy via fluorine incorporation, but may also have contributing effects from surface morphology changes. The data indicates that plasma-based surface modifications may have utility in improving chemical resistance of commercial coatings.

  16. Selected area chemical vapor deposition of thin films for conductometric microelectronic chemical sensors

    NASA Astrophysics Data System (ADS)

    Majoo, Sanjeev

    Recent advances in microelectronics and silicon processing have been exploited to fabricate miniaturized chemical sensors. Although the capability of chemical sensing technology has grown steadily, it has been outpaced by the increasing demands for more reliable, inexpensive, and selective sensors. The diversity of applications requires the deployment of different sensing materials that have rich interfacial chemistry. However, several promising sensor materials are often incompatible with silicon micromachining and their deposition requires complicated masking steps. The new approach described here is to first micromachine a generic, instrumented, conductometric, microelectronic sensor platform that is fully functional except for the front-end sensing element. This generic platform contains a thin dielectric membrane, an integrated boron-doped silicon heater, and conductance electrodes. The membrane has low thermal mass and excellent thermal isolation. A proprietary selected-area chemical vapor deposition (SACVD) process in a cold-wall reactor at low pressures was then used to achieve maskless, self-lithographic deposition of thin films. The temperature-programmable integrated microheater initiates localized thermal decomposition/reaction of suitable CVD precursors confined to a small heated area (500 mum in diameter), and this creates the active sensing element. Platinum and titania (TiOsb2) films were deposited from pyrolysis of organometallic precursors, tetrakistrifluorophosphine platinum Pt(PFsb3)sb4 and titanium tetraisopropoxide Ti(OCH(CHsb3)sb2rbrack sb4, respectively. Deposition of gold metal films from chlorotriethylphosphine gold (Csb2Hsb5)sb3PAuCl precursor was also attempted but without success. The conductance electrodes permit in situ monitoring of film growth. The as-deposited films were characterized in situ by conductance measurements and optical microscopy and ex situ by electron microscopy and spectroscopy methods. Devices equipped with

  17. Evaluation of Chemical Warfare Agent Percutaneous Vapor Toxicity: Derivation of Toxicity Guidelines for Assessing Chemical Protective Ensembles.

    SciTech Connect

    Watson, A.P.

    2003-07-24

    Percutaneous vapor toxicity guidelines are provided for assessment and selection of chemical protective ensembles (CPEs) to be used by civilian and military first responders operating in a chemical warfare agent vapor environment. The agents evaluated include the G-series and VX nerve agents, the vesicant sulfur mustard (agent HD) and, to a lesser extent, the vesicant Lewisite (agent L). The focus of this evaluation is percutaneous vapor permeation of CPEs and the resulting skin absorption, as inhalation and ocular exposures are assumed to be largely eliminated through use of SCBA and full-face protective masks. Selection of appropriately protective CPE designs and materials incorporates a variety of test parameters to ensure operability, practicality, and adequacy. One aspect of adequacy assessment should be based on systems tests, which focus on effective protection of the most vulnerable body regions (e.g., the groin area), as identified in this analysis. The toxicity range of agent-specific cumulative exposures (Cts) derived in this analysis can be used as decision guidelines for CPE acceptance, in conjunction with weighting consideration towards more susceptible body regions. This toxicity range is bounded by the percutaneous vapor estimated minimal effect (EME{sub pv}) Ct (as the lower end) and the 1% population threshold effect (ECt{sub 01}) estimate. Assumptions of exposure duration used in CPE certification should consider that each agent-specific percutaneous vapor cumulative exposure Ct for a given endpoint is a constant for exposure durations between 30 min and 2 hours.

  18. Silicon epitaxy using tetrasilane at low temperatures in ultra-high vacuum chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hazbun, Ramsey; Hart, John; Hickey, Ryan; Ghosh, Ayana; Fernando, Nalin; Zollner, Stefan; Adam, Thomas N.; Kolodzey, James

    2016-06-01

    The deposition of silicon using tetrasilane as a vapor precursor is described for an ultra-high vacuum chemical vapor deposition tool. The growth rates and morphology of the Si epitaxial layers over a range of temperatures and pressures are presented. The layers were characterized using transmission electron microscopy, x-ray diffraction, spectroscopic ellipsometry, Atomic Force Microscopy, and secondary ion mass spectrometry. Based on this characterization, high quality single crystal silicon epitaxy was observed. Tetrasilane was found to produce higher growth rates relative to lower order silanes, with the ability to deposit crystalline Si at low temperatures (T=400 °C), with significant amorphous growth and reactivity measured as low as 325 °C, indicating the suitability of tetrasilane for low temperature chemical vapor deposition such as for SiGeSn alloys.

  19. Differentiation of complex vapor mixtures using versatile DNA-carbon nanotube chemical sensor arrays.

    PubMed

    Kybert, Nicholas J; Lerner, Mitchell B; Yodh, Jeremy S; Preti, George; Johnson, A T Charlie

    2013-03-26

    Vapor sensors based on functionalized carbon nanotubes (NTs) have shown great promise, with high sensitivity conferred by the reduced dimensionality and exceptional electronic properties of the NT. Critical challenges in the development of NT-based sensor arrays for chemical detection include the demonstration of reproducible fabrication methods and functionalization schemes that provide high chemical diversity to the resulting sensors. Here, we outline a scalable approach to fabricating arrays of vapor sensors consisting of NT field effect transistors functionalized with single-stranded DNA (DNA-NT). DNA-NT sensors were highly reproducible, with responses that could be described through equilibrium thermodynamics. Target analytes were detected even in large backgrounds of volatile interferents. DNA-NT sensors were able to discriminate between highly similar molecules, including structural isomers and enantiomers. The sensors were also able to detect subtle variations in complex vapors, including mixtures of structural isomers and mixtures of many volatile organic compounds characteristic of humans.

  20. Physico-chemical mechanism for the vapors sensitivity of photoluminescent InP quantum dots

    NASA Astrophysics Data System (ADS)

    Prosposito, P.; De Angelis, R.; De Matteis, F.; Hatami, F.; Masselink, W. T.; Zhang, H.; Casalboni, M.

    2016-03-01

    InP/InGaP surface quantum dots are interesting materials for optical chemical sensors since they present an intense emission at room temperature, whose intensity changes rapidly and reversibly depending on the composition of the environmental atmosphere. We present here their emission properties by time resolved photoluminescence spectroscopy investigation and we discuss the physico-chemical mechanism behind their sensitivity to the surrounding atmosphere. Photoluminescence transients in inert atmosphere (N2) and in solvent vapours of methanol, clorophorm, acetone and water were measured. The presence of vapors of clorophorm, acetone and water showed a very weak effect on the transient times, while an increase of up to 15% of the decay time was observed for methanol vapour exposure. On the basis of the vapor molecule nature (polarity, proticity, steric hindrance, etc.) and of the interaction of the vapor molecules with the quantum dots surface a sensing mechanism involving quantum dots non-radiative surface states is proposed.

  1. Ultrafine Microstructure Composites Prepared by Chemical Vapor Deposition

    DTIC Science & Technology

    1988-12-01

    deposition experiments reported in this paper, we performed numerous thermo- dynamic calculations using the SOLGASMIX - PV program [21]. In summary...Besmann, " SOLGASMIX - PV , A Computer Program to Calculate Equilibrium Relationships in Complex Chemical Systems," ORNL/TM-5775, Oak Ridge National

  2. Vapor Intrusion

    EPA Pesticide Factsheets

    Vapor intrusion occurs when there is a migration of volatile chemicals from contaminated groundwater or soil into an overlying building. Volatile chemicals can emit vapors that may migrate through subsurface soils and into indoor air spaces.

  3. Development of a Computational Chemical Vapor Deposition Model: Applications to Indium Nitride and Dicyanovinylaniline

    NASA Technical Reports Server (NTRS)

    Cardelino, Carlos

    1999-01-01

    A computational chemical vapor deposition (CVD) model is presented, that couples chemical reaction mechanisms with fluid dynamic simulations for vapor deposition experiments. The chemical properties of the systems under investigation are evaluated using quantum, molecular and statistical mechanics models. The fluid dynamic computations are performed using the CFD-ACE program, which can simulate multispecies transport, heat and mass transfer, gas phase chemistry, chemistry of adsorbed species, pulsed reactant flow and variable gravity conditions. Two experimental setups are being studied, in order to fabricate films of: (a) indium nitride (InN) from the gas or surface phase reaction of trimethylindium and ammonia; and (b) 4-(1,1)dicyanovinyl-dimethylaminoaniline (DCVA) by vapor deposition. Modeling of these setups requires knowledge of three groups of properties: thermodynamic properties (heat capacity), transport properties (diffusion, viscosity, and thermal conductivity), and kinetic properties (rate constants for all possible elementary chemical reactions). These properties are evaluated using computational methods whenever experimental data is not available for the species or for the elementary reactions. The chemical vapor deposition model is applied to InN and DCVA. Several possible InN mechanisms are proposed and analyzed. The CVD model simulations of InN show that the deposition rate of InN is more efficient when pulsing chemistry is used under conditions of high pressure and microgravity. An analysis of the chemical properties of DCVA show that DCVA dimers may form under certain conditions of physical vapor transport. CVD simulations of the DCVA system suggest that deposition of the DCVA dimer may play a small role in the film and crystal growth processes.

  4. Development of a Computational Chemical Vapor Deposition Model: Applications to Indium Nitride and Dicyanovinylaniline

    NASA Technical Reports Server (NTRS)

    Cardelino, Carlos

    1999-01-01

    A computational chemical vapor deposition (CVD) model is presented, that couples chemical reaction mechanisms with fluid dynamic simulations for vapor deposition experiments. The chemical properties of the systems under investigation are evaluated using quantum, molecular and statistical mechanics models. The fluid dynamic computations are performed using the CFD-ACE program, which can simulate multispecies transport, heat and mass transfer, gas phase chemistry, chemistry of adsorbed species, pulsed reactant flow and variable gravity conditions. Two experimental setups are being studied, in order to fabricate films of: (a) indium nitride (InN) from the gas or surface phase reaction of trimethylindium and ammonia; and (b) 4-(1,1)dicyanovinyl-dimethylaminoaniline (DCVA) by vapor deposition. Modeling of these setups requires knowledge of three groups of properties: thermodynamic properties (heat capacity), transport properties (diffusion, viscosity, and thermal conductivity), and kinetic properties (rate constants for all possible elementary chemical reactions). These properties are evaluated using computational methods whenever experimental data is not available for the species or for the elementary reactions. The chemical vapor deposition model is applied to InN and DCVA. Several possible InN mechanisms are proposed and analyzed. The CVD model simulations of InN show that the deposition rate of InN is more efficient when pulsing chemistry is used under conditions of high pressure and microgravity. An analysis of the chemical properties of DCVA show that DCVA dimers may form under certain conditions of physical vapor transport. CVD simulations of the DCVA system suggest that deposition of the DCVA dimer may play a small role in the film and crystal growth processes.

  5. VAPOR SAMPLING DEVICE FOR INTERFACE WITH MICROTOX ASSAY FOR SCREENING TOXIC INDUSTRIAL CHEMICALS

    EPA Science Inventory

    A time-integrated sampling system interfaced with a toxicity-based assay is reported for monitoring volatile toxic industrial chemicals (TICs). Semipermeable membrane devices (SPMDs) using dimethyl sulfoxide (DMSO) as the fill solvent accumulated each of 17 TICs from the vapor...

  6. Low temperature junction growth using hot-wire chemical vapor deposition

    DOEpatents

    Wang, Qi; Page, Matthew; Iwaniczko, Eugene; Wang, Tihu; Yan, Yanfa

    2014-02-04

    A system and a process for forming a semi-conductor device, and solar cells (10) formed thereby. The process includes preparing a substrate (12) for deposition of a junction layer (14); forming the junction layer (14) on the substrate (12) using hot wire chemical vapor deposition; and, finishing the semi-conductor device.

  7. Miscellaneous chemical basin treatability study: an analysis of passive soil vapor extraction wells (PSVE)

    SciTech Connect

    Riha, B.; Rossabi, J.

    1997-12-01

    A passive soil vapor extraction (PSVE) treatability study at the Miscellaneous Chemical Basin (MCB) of the Savannah River Site (SRS) has been progressing since September 1996. The results to date on the treatability study of the PSVE system indicate that the technology is performing well.

  8. Dopant gas effect on silicon chemical vapor depositions: A surface potential model

    NASA Technical Reports Server (NTRS)

    Chang, C. A.

    1975-01-01

    A surface potential model is proposed to consistently explain the known dopant gas effects on silicon chemical vapor deposition. This model predicts that the effects of the same dopant gases on the diamond deposition rate using methane and carbon tetrachloride should be opposite and similar to those of silane, respectively. Available data are in agreement with this prediction.

  9. Circular Graphene Platelets with Grain Size and Orientation Gradients Grown by Chemical Vapor Deposition.

    PubMed

    Xin, Xing; Fei, Zeyuan; Ma, Teng; Chen, Long; Chen, Mao-Lin; Xu, Chuan; Qian, Xitang; Sun, Dong-Ming; Ma, Xiu-Liang; Cheng, Hui-Ming; Ren, Wencai

    2017-02-27

    Monolayer circular graphene platelets with a grain structure gradient in the radial direction are synthesized by chemical vapor deposition on immiscible W-Cu substrates. Because of the different interactions and growth behaviors of graphene on Cu and tungsten carbide, such substrates cause the formation of grain size and orientation gradients through the competition between Cu and tungsten carbide in graphene growth.

  10. Chemical vapor detection and mapping with a multispectral forward-looking infrared (FLIR)

    NASA Astrophysics Data System (ADS)

    Althouse, Mark L.; Chang, Chein-I.

    1995-02-01

    Detection of chemical vapors with a remote sensor is a requirement for both military defense and civilian pollution control. The FLIR is a natural instrument from which to build a chemical sensor since most chemical vapors of interest are spectrally active within its operating wavelength range, it is widely distributed in the battlefield, and it is becoming a standard surveillance tool in police departments. Additionally, the output image provides a 2D concentration map of the cloud which is easily interpreted by a lightly trained operator. A system has been designed to provide the spectral sensitivity in a dedicated instrument or to place a chemical detection capability as an adjunct function in a military thermal imager. In the latter case an additional detector array which is spectrally filtered at the focal plane is added to the imager. Real-time autonomous detection and alarm is a military requirement and is desired for commercial use. A detection system model based on a Gaussian vapor concentration distribution has been the basis for detection algorithms. Image processing and analysis methods have been based upon information theory. These techniques extract the cloud image from a clutter scene and perform a limited vapor classification. These methods are suited to hyperspectral imagery.

  11. High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells.

    PubMed

    He, Rongrui; Day, Todd D; Sparks, Justin R; Sullivan, Nichole F; Badding, John V

    2016-07-01

    Thin films of hydrogenated amorphous silicon can be produced at MPa pressures from silane without the use of plasma at temperatures as low as 345 °C. High pressure chemical vapor deposition may open a new way to low cost deposition of amorphous silicon solar cells and other thin film structures over very large areas in very compact, simple reactors.

  12. VAPOR SAMPLING DEVICE FOR INTERFACE WITH MICROTOX ASSAY FOR SCREENING TOXIC INDUSTRIAL CHEMICALS

    EPA Science Inventory

    A time-integrated sampling system interfaced with a toxicity-based assay is reported for monitoring volatile toxic industrial chemicals (TICs). Semipermeable membrane devices (SPMDs) using dimethyl sulfoxide (DMSO) as the fill solvent accumulated each of 17 TICs from the vapor...

  13. Moire-Fringe Images of Twin Boundaries in Chemical Vapor Deposited Diamond

    DTIC Science & Technology

    1992-07-10

    Features in lattice image micrographs of chemical vapor deposited diamond can be interpreted as Moire fringes that occur when viewing twin boundaries that...are inclined to the electron beam. The periodicities in images of inclined twin boundaries with Sigma=3 and Sigma=9 misorientations have been modeled by computer graphic simulation.

  14. Volatile Barium Beta-Diketonate Polyether Adducts. Synthesis, Characterization and Metalorganic Chemical Vapor Deposition

    DTIC Science & Technology

    1991-05-31

    Volatile Barium 13- Diketonate Polyether Adducts.... Synthesis , Characterization and Metalorganic Chemical Vapor Deposition by Robin A. Gardiner...has been approved for public release and sale: its distribution is unlimited. Volatile, Barium B- Diketonate Polyether Adducts. Synthesis ...NO. NO. INO. ACCESSION NO. Arlington, VA 22217 II 11. TITLE (include Security Classification) Volatile Barium B- Diketonate Polyether Adducts

  15. Chemical vapor deposition of W-Si-N and W-B-N

    DOEpatents

    Fleming, J.G.; Roherty-Osmun, E.L.; Smith, P.M.; Custer, J.S.; Jones, R.V.; Nicolet, M.; Madar, R.; Bernard, C.

    1999-06-29

    A method of depositing a ternary, refractory based thin film on a substrate by chemical vapor deposition employing precursor sources of tungsten comprising WF[sub 6], either silicon or boron, and nitrogen. The result is a W-Si-N or W-B-N thin film useful for diffusion barrier and micromachining applications. 10 figs.

  16. Chemical vapor deposition of W-Si-N and W-B-N

    DOEpatents

    Fleming, James G.; Roherty-Osmun, Elizabeth Lynn; Smith, Paul M.; Custer, Jonathan S.; Jones, Ronald V.; Nicolet, Marc-A.; Madar, Roland; Bernard, Claude

    1999-01-01

    A method of depositing a ternary, refractory based thin film on a substrate by chemical vapor deposition employing precursor sources of tungsten comprising WF.sub.6, either silicon or boron, and nitrogen. The result is a W--Si--N or W--B--N thin film useful for diffusion barrier and micromachining applications.

  17. Chemical hazards present in liquids and vapors of electronic cigarettes.

    PubMed

    Hutzler, Christoph; Paschke, Meike; Kruschinski, Svetlana; Henkler, Frank; Hahn, Jürgen; Luch, Andreas

    2014-07-01

    Electronic (e-)cigarettes have emerged in recent years as putative alternative to conventional tobacco cigarettes. These products do not contain typical carcinogens that are present in tobacco smoke, due to the lack of combustion. However, besides nicotine, hazards can also arise from other constituents of liquids, such as solvents, flavors, additives and contaminants. In this study, we have analyzed 28 liquids of seven manufacturers purchased in Germany. We confirm the presence of a wide range of flavors to enhance palatability. Although glycerol and propylene glycol were detected in all samples, these solvents had been replaced by ethylene glycol as dominant compound in five products. Ethylene glycol is associated with markedly enhanced toxicological hazards when compared to conventionally used glycerol and propylene glycol. Additional additives, such as coumarin and acetamide, that raise concerns for human health were detected in certain samples. Ten out of 28 products had been declared "free-of-nicotine" by the manufacturer. Among these ten, seven liquids were identified containing nicotine in the range of 0.1-15 µg/ml. This suggests that "carry over" of ingredients may occur during the production of cartridges. We have further analyzed the formation of carbonylic compounds in one widely distributed nicotine-free brand. Significant amounts of formaldehyde, acetaldehyde and propionaldehyde were only found at 150 °C by headspace GC-MS analysis. In addition, an enhanced formation of aldehydes was found in defined puff fractions, using an adopted machine smoking protocol. However, this effect was delayed and only observed during the last third of the smoking procedure. In the emissions of these fractions, which represent up to 40 % of total vapor volume, similar levels of formaldehyde were detected when compared to conventional tobacco cigarettes. By contrast, carbonylic compounds were hardly detectable in earlier collected fractions. Our data demonstrate the

  18. A kinetic and equilibrium analysis of silicon carbide chemical vapor deposition on monofilaments

    NASA Technical Reports Server (NTRS)

    Gokoglu, S. A.; Kuczmarski, M. A.

    1993-01-01

    Chemical kinetics of atmospheric pressure silicon carbide (SiC) chemical vapor deposition (CVD) from dilute silane and propane source gases in hydrogen is numerically analyzed in a cylindrical upflow reactor designed for CVD on monofilaments. The chemical composition of the SiC deposit is assessed both from the calculated total fluxes of carbon and silicon and from chemical equilibrium considerations for the prevailing temperatures and species concentrations at and along the filament surface. The effects of gas and surface chemistry on the evolution of major gas phase species are considered in the analysis.

  19. Chemical vapor detection using a capacitive micromachined ultrasonic transducer.

    PubMed

    Lee, Hyunjoo J; Park, Kwan Kyu; Kupnik, Mario; Oralkan, O; Khuri-Yakub, Butrus T

    2011-12-15

    Distributed sensing of gas-phase chemicals using highly sensitive and inexpensive sensors is of great interest for many defense and consumer applications. In this paper we present ppb-level detection of dimethyl methylphosphonate (DMMP), a common simulant for sarin gas, with a ppt-level resolution using an improved capacitive micromachined ultrasonic transducer (CMUT) as a resonant chemical sensor. The improved CMUT operates at a higher resonant frequency of 47.7 MHz and offers an improved mass sensitivity of 48.8 zg/Hz/μm(2) by a factor of 2.7 compared to the previous CMUT sensors developed. A low-noise oscillator using the CMUT resonant sensor as the frequency-selective device was developed for real-time sensing, which exhibits an Allan deviation of 1.65 Hz (3σ) in the presence of a gas flow; this translates into a mass resolution of 80.5 zg/μm(2). The CMUT resonant sensor is functionalized with a 50-nm thick DKAP polymer developed at Sandia National Laboratory for dimethyl methylphosphonate (DMMP) detection. To demonstrate ppb-level detection of the improved chemical sensor system, the sensor performance was tested at a certified lab (MIT Lincoln Laboratory), which is equipped with an experimental chemical setup that reliably and accurately delivers a wide range of low concentrations down to 10 ppb. We report a high volume sensitivity of 34.5 ± 0.79 pptv/Hz to DMMP and a good selectivity of the polymer to DMMP with respect to dodecane and 1-octanol.

  20. Ultrafine Microstructure Composites Prepared by Chemical Vapor Deposition

    DTIC Science & Technology

    1987-12-01

    have performed numerous thermodynamic calculations for the BN + AIN and HfB2 + SiC systems. The calculations were performed usi..g the SOLGASMIX - PV ...CH3 SiCl 3 (methyltrichlorosilane or MTS1 again using the SOLGASMIX - PV program. A quantity of hydrogen was added equal to ten times the sum of the...Electro- chemical Society, Inc., Pennington, NJ, 1979, p.1. 7. T. M. Besmann, " SOLGASMIX - PV , A Computer Program to Calcu- late Equilibrium

  1. Removal of chemical oxygen demand and dissolved nutrients by a sunken lawn infiltration system during intermittent storm events.

    PubMed

    Hou, Lizhu; Yang, Huan; Li, Ming

    2014-01-01

    Urban surface water runoff typically contains high but varying amounts of organic matter and nutrients that require removal before reuse. Infiltration systems such as sunken lawns can improve water quality. However, there is currently insufficient information describing the treatment efficiency of lawn-based infiltration systems. In this study, novel sunken lawn infiltration systems (SLISs) were designed and their pollutant removal effectiveness was assessed. The results revealed that SLISs with Poa pratensis and Lolium perenne effectively removed most chemical oxygen demand (CODCr) and dissolved nutrients. Average CODCr, total nitrogen (TN), ammonium-nitrogen (NH4(+)-N) and total phosphorus (TP) concentrations were reduced by 78.93, 66.64, 71.86 and 75.83%, respectively, and the corresponding effluent concentrations met the standard for urban miscellaneous water consumption in China. The NH4(+)-N in the synthetic runoff was shown to be removed by adsorption during the stormwater dosing and nitrification during subsequent dry days, as well as through uptake by plants. Phosphorus was mainly removed by adsorption and chemical precipitation. The NH4(+)-N and phosphorus Langmuir isotherm model fitted the clay loam soil adsorption process better than the Freundlich model. Overall, these results indicate that an SLIS provides an alternative means of removing runoff pollutants owing to its efficiency, easy operation and maintenance.

  2. Mathematical Analysis and Optimization of Infiltration Processes

    NASA Technical Reports Server (NTRS)

    Chang, H.-C.; Gottlieb, D.; Marion, M.; Sheldon, B. W.

    1997-01-01

    A variety of infiltration techniques can be used to fabricate solid materials, particularly composites. In general these processes can be described with at least one time dependent partial differential equation describing the evolution of the solid phase, coupled to one or more partial differential equations describing mass transport through a porous structure. This paper presents a detailed mathematical analysis of a relatively simple set of equations which is used to describe chemical vapor infiltration. The results demonstrate that the process is controlled by only two parameters, alpha and beta. The optimization problem associated with minimizing the infiltration time is also considered. Allowing alpha and beta to vary with time leads to significant reductions in the infiltration time, compared with the conventional case where alpha and beta are treated as constants.

  3. Chemical vapor deposition and characterization of titanium dioxide thin films

    NASA Astrophysics Data System (ADS)

    Gilmer, David Christopher

    1998-12-01

    The continued drive to decrease the size and increase the speed of micro-electronic Metal-Oxide-Semiconductor (MOS) devices is hampered by some of the properties of the SiOsb2 gate dielectric. This research has focused on the CVD of TiOsb2 thin films to replace SiOsb2 as the gate dielectric in MOS capacitors and transistors. The relationship of CVD parameters and post-deposition anneal treatments to the physical and electrical properties of thin films of TiOsb2 has been studied. Structural and electrical characterization of TiOsb2 films grown from the CVD precursors tetraisopropoxotitanium (IV) (TTIP) and TTIP plus Hsb2O is described in Chapter 3. Both types of deposition produced stoichiometric TiOsb2 films comprised of polycrystalline anatase, but the interface properties were dramatically degraded when water vapor was added. Films grown with TTIP in the presence of Hsb2O contained greater than 50% more hydrogen than films grown using only TTIP and the hydrogen content of films deposited in both wet and dry TTIP environments decreased sharply with a post deposition Osb2 anneal. A significant thickness variation of the dielectric constant was observed which could be explained by an interfacial oxide and the finite accumulation thickness. Fabricated TiOsb2 capacitors exhibited electrically equivalent SiOsb2 gate dielectric thicknesses and leakage current densities as low as 38, and 1×10sp{-8} Amp/cmsp2 respectively. Chapter 4 discusses the low temperature CVD of crystalline TiOsb2 thin films deposited using the precursor tetranitratotitanium (IV), TNT, which produces crystalline TiOsb2 films of the anatase phase in UHV-CVD at temperatures as low as 184sp°C. Fabricated TiOsb2 capacitors exhibited electrically equivalent SiOsb2 gate dielectric thicknesses and leakage current densities as low as 17, and 1×10sp{-8} Amp/cmsp2 respectively. Chapter 5 describes the results of a comparison of physical and electrical properties between TiOsb2 films grown via LPCVD using

  4. Ballistic transport in graphene grown by chemical vapor deposition

    SciTech Connect

    Calado, V. E.; Goswami, S.; Xu, Q.; Vandersypen, L. M. K.; Zhu, Shou-En; Janssen, G. C. A. M.; Watanabe, K.; Taniguchi, T.

    2014-01-13

    In this letter, we report the observation of ballistic transport on micron length scales in graphene synthesised by chemical vapour deposition (CVD). Transport measurements were done on Hall bar geometries in a liquid He cryostat. Using non-local measurements, we show that electrons can be ballistically directed by a magnetic field (transverse magnetic focussing) over length scales of ∼1 μm. Comparison with atomic force microscope measurements suggests a correlation between the absence of wrinkles and the presence of ballistic transport in CVD graphene.

  5. Ultrafine Microstructure Composites Prepared by Chemical Vapor Deposition

    DTIC Science & Technology

    1989-12-01

    phase ceramic composites by CVD is that mechanical as well as chemical, electrical , optical, and thermal properties of the composites 2 can be favorably...while it is also an electrical insulator. Also, in Table 2-1, other important properties of BN are compared with those of AIN and other materials... Electrical Resistivity >10" >1016 >10" >10" >101 - (ncm) Density theo: 2.27 3.26 3.97 2.21 obs: 1.9 1.4 3.1 3.15 92% (g/cm’) to to to to 2.0 2.2 3.2

  6. A tunable MWIR laser remote sensor for chemical vapor detection

    NASA Astrophysics Data System (ADS)

    Bunn, Thomas L.; Noblett, Patricia M.; Otting, William D.

    1998-01-01

    The Air Force vision for Global Virtual Presence suggests a need for active remote sensing systems that provide both global coverage and the ability to detect multiple gaseous chemical species at low concentration from a significant standoff distance. The system will need to have acceptable weight, volume, and power characteristics, as well as a long operating lifetime for integration with various surveillance platforms. Laser based remote sensing systems utilizing the differential absorption lidar (DIAL) technique are promising for long range chemical sensing applications. Recent advancements in pulsed, diode pumped solid state laser (DPSSL) technology and in tunable optical parametric oscillators (OPO) make broadly tunable laser transmitters possible for the DIAL system. Also the characteristic narrow spectral bandwidth of these laser devices provides high measurement sensitivity and spectral selectivity with the potential to avoid interfering species. Rocketdyne has built and tested a tunable, midwave infrared (MWIR) DIAL system using DPSSL/OPO technology. The key to the system is a novel tuning and line narrowing technology developed for the OPO. The tuning system can quickly adjust to the desired wavelength and precisely locate a narrow spectral feature of interest. Once the spectral feature is located, a rapid dither tuning technique is employed. The laser pulses are tuned ``on'' and ``off'' the spectral resonance of a molecule with precise and repeatable performance as required to make the DIAL measurement. To date, the breadboard system has been tested by measuring methane, ethane, and sulfur dioxide in a calibrated gas cell at a range of 60 meters.

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

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Nguyen, QuynhGiao N.

    1998-01-01

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

  8. SiC nanofibers grown by high power microwave plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Honda, Shin-ichi; Baek, Yang-Gyu; Ikuno, Takashi; Kohara, Hidekazu; Katayama, Mitsuhiro; Oura, Kenjiro; Hirao, Takashi

    2003-05-01

    Silicon carbide (SiC) nanofibers have been synthesized on Si substrates covered by Ni thin films using high power microwave chemical vapor deposition (CVD). Characterization using transmission electron microscopy (TEM) combined with electron energy-dispersive X-ray spectroscopy (EDX) revealed that the resultant fibrous nanostructures were assigned to β-SiC with high crystallinity. The formation of SiC nanofibers can be explained by the vapor liquid solid (VLS) mechanism in which precipitation of SiC occurs from the supersaturated Ni nanoparticle containing Si and C.

  9. Chemical transformations during ambient air sampling for organic vapors

    SciTech Connect

    Pellizzari, E.D.; Drost, K.J.

    1984-09-01

    Potential chemical transformations of olefins in the presence of ozone and high levels (ppm) of halogens (Cl/sub 2/, Br/sub 2/) were demonstrated when sampling ambient air with a sorbent cartridge. The use of stryene-d/sub 8/ and cyclohexene-d/sub 10/ spiked sampling devices and capillary gas chromatography/mass spectrometry (GC/MS) analysis allowed the detection and identification of several deuteriated oxidation and halogenated products. Dimethylamine-d/sub 6/ was converted in trace quantities (5-10 mg) to dimethylnitrosamine-d/sub 6/ when sampling was conducted in the presence of NO/sub x/. Oxidation reactions were prevented when filters (2.5 cm) employed for removing particulates were impregnated with 5-10 mg of sodium thiosulfate and placed in front of the sorbent cartridge. Halogenation reactions were also consideraly reduced.

  10. Chemical vapor deposition of atomically thin materials for membrane dialysis applications

    NASA Astrophysics Data System (ADS)

    Kidambi, Piran; Mok, Alexander; Jang, Doojoon; Boutilier, Michael; Wang, Luda; Karnik, Rohit; Microfluidics; Nanofluidics Research Lab Team

    2015-11-01

    Atomically thin 2D materials like graphene and h-BN represent a new class of membranes materials. They offer the possibility of minimum theoretical membrane transport resistance along with the opportunity to tune pore sizes at the nanometer scale. Chemical vapor deposition has emerged as the preferable route towards scalable, cost effective synthesis of 2D materials. Here we show selective molecular transport through sub-nanometer diameter pores in graphene grown via chemical vapor deposition processes. A combination of pressure driven and diffusive transport measurements shows evidence for size selective transport behavior which can be used for separation by dialysis for applications such as desalting of biomolecular or chemical solutions. Principal Investigator

  11. Ultra-sensitive chemical vapor detection using micro-cavity photothermal spectroscopy.

    PubMed

    Hu, Juejun

    2010-10-11

    In this paper, I systematically investigated Micro-Cavity PhotoThermal Spectroscopy (MC-PTS), a novel technique for ultra-sensitive detection of chemical molecular species. I first derive the photothermal enhancement factor and noise characteristics of the technique using a generic theoretical model, followed by numerical analysis of a design example using chalcogenide glass micro-disk cavities. Guidelines for sensor material selection and device design are formulated based on the theoretical insight. The numerical analysis shows that this technique features a record photothermal enhancement factor of 10(4) with respect to conventional cavity-enhanced (multi-pass) infrared absorption spectroscopy, and is capable of detecting non-preconcentrated chemical vapor molecules down to the ppt level with a moderate cavity quality factor of 10(5) and a pump laser power of 0.1 W. Such performance qualifies this technique as one of the most sensitive methods for chemical vapor spectroscopic analysis.

  12. Vibrationally Excited Carbon Monoxide Produced via a Chemical Reaction Between Carbon Vapor and Oxygen

    NASA Astrophysics Data System (ADS)

    Jans, Elijah R.; Eckert, Zakari; Frederickson, Kraig; Rich, Bill; Adamovich, Igor V.

    2017-06-01

    Measurements of the vibrational distribution function of carbon monoxide produced via a reaction between carbon vapor and molecular oxygen has shown a total population inversion on vibrational levels 4-7. Carbon vapor, produced using an arc discharge to sublimate graphite, is mixed with an argon oxygen flow. The excited carbon monoxide is vibrationally populated up to level v=14, at low temperatures, T=400-450 K, in a collision-dominated environment, 15-20 Torr, with total population inversions between v=4-7. The average vibrational energy per CO molecule formed by the reaction is 0.6-1.2 eV/molecule, which corresponds to 10-20% of the reaction enthalpy. Kinetic modeling of the flow reactor, including state specific vibrational processes, was performed to infer the vibrational distribution of the products of the reaction. The results show viability of developing of a new chemical CO laser from the reaction of carbon vapor and oxygen.

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

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.

    1994-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.

    1994-01-01

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

  15. Removal of Water Vapor in a Mist Singlet Oxygen Generator for Chemical Oxygen Iodine Laser

    NASA Astrophysics Data System (ADS)

    Muto, Shigeki; Endo, Masamori; Nanri, Kenzo; Fujioka, Tomoo

    2004-02-01

    The mist singlet oxygen generator (Mist-SOG) for a chemical oxygen iodine laser (COIL) has been developed in order to increase basic hydrogen peroxide (BHP) utilization. It was clarified that the Mist-SOG generated much more water vapor than conventional SOGs because the heat capacity of BHP is small. The water vapor deactivates the excited iodine and depresses the laser power. Therefore, a jet-cold trap was developed in order to remove the water vapor while maintaining a minimum deactivation of singlet oxygen. In this method, a nozzle was used to spray chilled H2O2 at 238 K as a thin layer directly to the gas flow to achieve a large specific surface area for water vapor. As a result, the water vapor mole fraction was reduced to 7% from 18% with the BHP utilization of 21% at the Cl2 consumption rate of 3.5 mmol/s (Cl2 input flow rate of 8.0 mmol/s) for 65-μm-diameter BHP droplets.

  16. Diagnostic for Plasma Enhanced Chemical Vapor Deposition and Etch Systems

    NASA Technical Reports Server (NTRS)

    Cappelli, Mark A.

    1999-01-01

    In order to meet NASA's requirements for the rapid development and validation of future generation electronic devices as well as associated materials and processes, enabling technologies ion the processing of semiconductor materials arising from understanding etch chemistries are being developed through a research collaboration between Stanford University and NASA-Ames Research Center, Although a great deal of laboratory-scale research has been performed on many of materials processing plasmas, little is known about the gas-phase and surface chemical reactions that are critical in many etch and deposition processes, and how these reactions are influenced by the variation in operating conditions. In addition, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. The research described involves the study of plasmas used in semiconductor processes. An inductively coupled plasma (ICP) source in place of the standard upper electrode assembly of the Gaseous Electronics Conference (GEC) radio-frequency (RF) Reference Cell is used to investigate the discharge characteristics and chemistries. This ICP source generates plasmas with higher electron densities (approximately 10(exp 12)/cu cm) and lower operating pressures (approximately 7 mTorr) than obtainable with the original parallel-plate version of the GEC Cell. This expanded operating regime is more relevant to new generations of industrial plasma systems being used by the microelectronics industry. The motivation for this study is to develop an understanding of the physical phenomena involved in plasma processing and to measure much needed fundamental parameters, such as gas-phase and surface reaction rates. species

  17. Stretchable Electronic Sensors of Nanocomposite Network Films for Ultrasensitive Chemical Vapor Sensing.

    PubMed

    Yan, Hong; Zhong, Mengjuan; Lv, Ze; Wan, Pengbo

    2017-09-12

    A stretchable, transparent, and body-attachable chemical sensor is assembled from the stretchable nanocomposite network film for ultrasensitive chemical vapor sensing. The stretchable nanocomposite network film is fabricated by in situ preparation of polyaniline/MoS2 (PANI/MoS2 ) nanocomposite in MoS2 suspension and simultaneously nanocomposite deposition onto prestrain elastomeric polydimethylsiloxane substrate. The assembled stretchable electronic sensor demonstrates ultrasensitive sensing performance as low as 50 ppb, robust sensing stability, and reliable stretchability for high-performance chemical vapor sensing. The ultrasensitive sensing performance of the stretchable electronic sensors could be ascribed to the synergistic sensing advantages of MoS2 and PANI, higher specific surface area, the reliable sensing channels of interconnected network, and the effectively exposed sensing materials. It is expected to hold great promise for assembling various flexible stretchable chemical vapor sensors with ultrasensitive sensing performance, superior sensing stability, reliable stretchability, and robust portability to be potentially integrated into wearable electronics for real-time monitoring of environment safety and human healthcare. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Combinatorial Characterization of TiO2 Chemical Vapor Deposition Utilizing Titanium Isopropoxide.

    PubMed

    Reinke, Michael; Ponomarev, Evgeniy; Kuzminykh, Yury; Hoffmann, Patrik

    2015-07-13

    The combinatorial characterization of the growth kinetics in chemical vapor deposition processes is challenging because precise information about the local precursor flow is usually difficult to access. In consequence, combinatorial chemical vapor deposition techniques are utilized more to study functional properties of thin films as a function of chemical composition, growth rate or crystallinity than to study the growth process itself. We present an experimental procedure which allows the combinatorial study of precursor surface kinetics during the film growth using high vacuum chemical vapor deposition. As consequence of the high vacuum environment, the precursor transport takes place in the molecular flow regime, which allows predicting and modifying precursor impinging rates on the substrate with comparatively little experimental effort. In this contribution, we study the surface kinetics of titanium dioxide formation using titanium tetraisopropoxide as precursor molecule over a large parameter range. We discuss precursor flux and temperature dependent morphology, crystallinity, growth rates, and precursor deposition efficiency. We conclude that the surface reaction of the adsorbed precursor molecules comprises a higher order reaction component with respect to precursor surface coverage.

  19. Chemical vapor synthesis of nanocrystalline perovskites using laser flash evaporation of low volatility solid precursors.

    PubMed

    Winterer, Markus; Srdic, Vladimir V; Djenadic, Ruzica; Kompch, Alexander; Weirich, Thomas E

    2007-12-01

    One key requirement for the production of multinary oxide films by chemical vapor deposition (CVD) or nanocrystalline multinary oxides particles by chemical vapor synthesis (CVS) is the availability of precursors with high vapor pressure. This is especially the case for CVS where much higher production rates are required compared to thin films prepared by CVD. However, elements, which form low valent cations such as alkaline earth metals, are typically only available as solid precursors of low volatility, e.g., in form of beta-diketonates. This study describes laser flash evaporation as precursor delivery method for CVS of nanocrystalline perovskites. Laser flash evaporation exploits the nonequilibrium evaporation of solid metal organic precursors of low vapor pressure by absorption of the infrared radiation of a CO(2) laser. It is shown that stoichiometric, nanocrystalline particles consisting of SrZrO(3) and SrTiO(3) can be formed from corresponding mixtures of beta-diketonates which are evaporated nonselectively and with high rates by laser flash evaporation.

  20. Chemical vapor synthesis of nanocrystalline perovskites using laser flash evaporation of low volatility solid precursors

    NASA Astrophysics Data System (ADS)

    Winterer, Markus; Srdic, Vladimir V.; Djenadic, Ruzica; Kompch, Alexander; Weirich, Thomas E.

    2007-12-01

    One key requirement for the production of multinary oxide films by chemical vapor deposition (CVD) or nanocrystalline multinary oxides particles by chemical vapor synthesis (CVS) is the availability of precursors with high vapor pressure. This is especially the case for CVS where much higher production rates are required compared to thin films prepared by CVD. However, elements, which form low valent cations such as alkaline earth metals, are typically only available as solid precursors of low volatility, e.g., in form of β-diketonates. This study describes laser flash evaporation as precursor delivery method for CVS of nanocrystalline perovskites. Laser flash evaporation exploits the nonequilibrium evaporation of solid metal organic precursors of low vapor pressure by absorption of the infrared radiation of a CO2 laser. It is shown that stoichiometric, nanocrystalline particles consisting of SrZrO3 and SrTiO3 can be formed from corresponding mixtures of β-diketonates which are evaporated nonselectively and with high rates by laser flash evaporation.

  1. Electrical Performance of Monolayer MoS2 Field-Effect Transistors Prepared by Chemical Vapor Deposition

    DTIC Science & Technology

    2013-05-16

    REPORT Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical vapor deposition 14. ABSTRACT 16. SECURITY CLASSIFICATION...OF: Molybdenum disulfide ( MoS2 ) field effect transistors (FET) were fabricated on atomically smooth large-area single layers grown by chemical vapor...Standard Form 298 (Rev 8/98) Prescribed by ANSI Std. Z39.18 - Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical

  2. Chemically enhanced mixed region vapor stripping of TCE-contaminated saturated peat and silty clay soils

    SciTech Connect

    West, O.R.; Cameron, P.A.; Lucero, A.J.; Koran, L.J. Jr.

    1996-01-01

    The objective of this study was to conduct further testing of MRVS, chemically enhanced with calcium oxide conditioning, on field- contaminated soils collected from beneath the NASA Michoud Rinsewater Impoundment. In this study, residual soil VOC levels as a function of vapor stripping time were measured to quantify VOC removal rates. Physical and chemical soil parameters expected to affect MRVS efficiency were measures. The effects of varying the calcium oxide loadings as well as varying the vapor stripping flow rates on VOC removal were also evaluated. The results of this study will be used to determine whether acceptable removals can be achieved within reasonable treatment times, remediation costs being directly proportional to the latter. The purpose of this report is to document the experimental results of this study, as well as to address issues that were raised after completion of the previous Michoud treatability work.

  3. Development of Single Crystal Chemical Vapor Deposition Diamonds for Detector Applications

    SciTech Connect

    Harris Kagan; K.K. Gan; Richard Kass

    2009-03-31

    Diamond was studied as a possible radiation hard technology for use in future high radiation environments. With the commissioning of the LHC expected in 2009, and the LHC upgrades expected in 2013, all LHC experiments are planning for detector upgrades which require radiation hard technologies. Chemical Vapor Deposition (CVD) diamond has now been used extensively in beam conditions monitors as the innermost detectors in the highest radiation areas of BaBar, Belle and CDF and is installed in all LHC experiments. As a result, this material is now being discussed as an alternative sensor material for tracking very close to the interaction region of the super-LHC where the most extreme radiation conditions will exist. Our work addressed the further development of the new material, single-crystal Chemical Vapor Deposition diamond, towards reliable industrial production of large pieces and new geometries needed for detector applications.

  4. Development of Single Crystal Chemical Vapor Deposition Diamonds for Detector Applications

    SciTech Connect

    Rainer Wallny

    2012-10-15

    Diamond was studied as a possible radiation hard technology for use in future high radiation environments. With the commissioning of the LHC expected in 2010, and the LHC upgrades expected in 2015, all LHC experiments are planning for detector upgrades which require radiation hard technologies. Chemical Vapor Deposition (CVD) diamond has now been used extensively in beam conditions monitors as the innermost detectors in the highest radiation areas of BaBar, Belle and CDF and is installed and operational in all LHC experiments. As a result, this material is now being discussed as an alternative sensor material for tracking very close to the interaction region of the super-LHC where the most extreme radiation conditions will exist. Our work addressed the further development of the new material, single-crystal Chemical Vapor Deposition diamond, towards reliable industrial production of large pieces and new geometries needed for detector applications.

  5. Plasmon-enhanced photothermoelectric conversion in chemical vapor deposited graphene p-n junctions.

    PubMed

    Wu, Di; Yan, Kai; Zhou, Yu; Wang, Huan; Lin, Li; Peng, Hailin; Liu, Zhongfan

    2013-07-31

    Graphene p-n junctions grown by chemical vapor deposition hold great promise for the applications in high-speed, broadband photodetectors and energy conversion devices, where efficient photoelectric conversion can be realized by a hot-carrier-assisted photothermoelectric (PTE) effect and hot-carrier multiplication. However, the overall quantum efficiency is restricted by the low light absorption of single-layer graphene. Here, we present the first experimental demonstration of a plasmon-enhanced PTE conversion in chemical vapor deposited graphene p-n junctions. Surface plasmons of metallic nanostructures placed near the graphene p-n junctions were found to significantly enhance the optical field in the active layer and allow for a 4-fold increase in the photocurrent. Moreover, the utilization of localized plasmon enhancement facilitates the realization of efficient PTE conversion of graphene p-n junction devices under global illumination, which may offer an avenue for practical applications of graphene-based photodetectors and solar cells.

  6. Growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Uno, Kazuyuki; Yamasaki, Yuichiro; Tanaka, Ichiro

    2017-01-01

    The growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition (mist-CVD) were experimentally investigated from the viewpoint of mist behaviors and chemical reactions. The proper growth model, either vaporization or the Leidenfrost model, was studied by supplying two kinds of mists with different kinds of sources, such as H2 16O and H2 18O for ZnO growth and ZnCl2 and thiourea for ZnS growth. Moreover, the origin of the oxygen atoms of ZnO was investigated using a quantitative analysis. The role of chloro complex of zinc in the growth of ZnS from aqueous solutions was also examined by systematic studies.

  7. Electro-optic polymer waveguide fabricated using electric-field-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Tatsuura, Satoshi; Sotoyama, Wataru; Yoshimura, Tetsuzo

    1992-04-01

    The paper describes the fabrication of an electrooptic (EO) polymer channel waveguide using a new technique, electric-field-assisted chemical vapor deposition. A polymer film is deposited from epoxy and nonlinear optical (NLO) aliphatic amine, using chemical vapor deposition under an electric field applied by slit electrodes on a thermally oxidized Si wafer at room temperature. A clear propagating He-Ne laser beam is observed along the electrode gap. The propagated beam's near field pattern is bright for the TE mode, but very weak for the TM mode. This indicates the NLO side groups' in-plane alignment and the fabrication of a channel waveguide. The EO coefficient of this waveguide, measured in a Mach-Zehnder interferometer, is r(11) of about 0.1 pm/V. The polymer channel waveguide, which is poled at room temperature after film deposition, shows no EO response. This means NLO molecules are actually aligned during polymerizing, not after.

  8. Process for the preparation of fiber-reinforced ceramic composites by chemical vapor deposition

    DOEpatents

    Lackey, Jr., Walter J.; Caputo, Anthony J.

    1986-01-01

    A chemical vapor deposition (CVD) process for preparing fiber-reinforced ceramic composites. A specially designed apparatus provides a steep thermal gradient across the thickness of a fibrous preform. A flow of gaseous ceramic matrix material is directed into the fibrous preform at the cold surface. The deposition of the matrix occurs progressively from the hot surface of the fibrous preform toward the cold surface. Such deposition prevents the surface of the fibrous preform from becoming plugged. As a result thereof, the flow of reactant matrix gases into the uninfiltrated (undeposited) portion of the fibrous preform occurs throughout the deposition process. The progressive and continuous deposition of ceramic matrix within the fibrous preform provides for a significant reduction in process time over known chemical vapor deposition processes.

  9. Formation of catalyst nanoparticles and nucleation of carbon nanotubes in chemical vapor deposition.

    PubMed

    Verissimo, C; Aguiar, M R; Moshkalev, S A

    2009-07-01

    Multi-walled carbon nanotubes and other carbon nanostructures have been grown using catalytic thermal chemical vapor deposition method in a horizontal tubular quartz furnace at atmospheric pressure. The mechanisms of nanotubes/nanofibers nucleation and growth are analyzed. A new model explaining the nanotube nucleation as a specific instability occurring on the catalyst particle surface supersaturated with carbon is presented. It is also shown that an axially symmetric instability, giving rise to the nanotube nucleation, is developed when certain critical conditions such as temperature, supersaturation and catalyst volume are achieved. For smaller temperatures, another mechanism of carbon segregation from supersaturated catalyst particles has been observed. In this case, flat rather than tubular graphitic layers are formed. These findings are important for better understanding and control of the synthesis of different carbon nanoforms using chemical vapor deposition.

  10. Modeling Vapor Transport Through Partially Saturated Porous Media at the Pore Scale Using Chemical Potential

    NASA Astrophysics Data System (ADS)

    Schreyer, L. G.; Addassi, M.; Johannesson, B.; Lin, H.

    2016-12-01

    Vapor transport in variably saturated soils is traditionally modeled using a system of equations including the conservation of mass, multiphase Darcy equation, and a version of the Philip and deVries equation for heat transfer. Typically the continuity equations and multiphase Darcy equation are combined to form one equation with one unknown, usually moisture content or capillary pressure. Here we introduce chemical potential as an alternate dependent variable and show that it simplifies conceptually and mathematically the modeling of vapor transport. Here we revisit the fundamentals of chemical potential, provide a simple one-dimensional pore-scale model, and compare the model with experimental results. In the process we explain simply the physics of enhanced diffusion due to liquid bridges.

  11. Low pressure chemical vapor deposition of niobium coating on silicon carbide

    NASA Astrophysics Data System (ADS)

    Liu, Qiaomu; Zhang, Litong; Cheng, Laifei; Liu, Jinling; Wang, Yiguang

    2009-07-01

    Nb coatings were prepared on a SiC substrate by low pressure chemical vapor deposition using NbCl 5. Thermodynamic calculations were performed to study the effect of temperature and partial pressure of NbCl 5 on the final products. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy. The Nb coatings are oriented and grow in the preferred (2 0 0) plane and (2 1 1) plane, at 1173 K and 1223-1423 K, respectively. At 1123-1273 K, the deposition is controlled by the surface kinetic processes. The activation energy is found to be 133 kJ/mol. At 1273-1373 K, the deposition is controlled by the mass transport processes. The activation energy is found to be 46 kJ/mol. The growth mechanism of the chemical vapor deposited Nb is also discussed based on the morphologies and the deposition rates.

  12. Detection and characterization of chemical vapor fugitive emissions by nonlinear optimal estimation: theory and simulation.

    PubMed

    Gittins, Christopher M

    2009-08-10

    This paper addresses detection and characterization of chemical vapor fugitive emissions in a nonscattering atmosphere by processing of remotely-sensed long-wavelength infrared spectra. The analysis approach integrates a parameterized signal model based on the radiative transfer equation with a statistical model for the infrared background. The maximum likelihood model parameter values are defined as those that maximize a Bayesian posterior probability and are estimated using a Gauss-Newton algorithm. For algorithm performance evaluation we simulate observation of fugitive emissions by augmenting plume-free measured spectra with synthetic plume signatures. As plumes become optically thick, the Gauss-Newton algorithm yields significantly more accurate estimates of chemical vapor column density and significantly more favorable plume detection statistics than clutter-matched-filter-based and adaptive-subspace-detector-based plume characterization and detection.

  13. Investigations of chemical vapor deposition of GaN using synchrotron radiation

    SciTech Connect

    Thompson, C.; Stephenson, G. B.; Eastman, J. A.; Munkholm, A.; Auciello, O.; Murty, M. V. R.; Fini, P.; DenBaars, S. P.; Speck, J. S.

    2000-05-25

    The authors apply synchrotron x-ray analysis techniques to probe the surface structure of GaN films during synthesis by metal-organic chemical vapor deposition (MOCVD). Their approach is to observe the evolution of surface structure and morphology in real time using grazing incidence x-ray scattering (GIXS). This technique combines the ability of x-rays to penetrate the chemical vapor deposition environment for in situ measurements, with the sensitivity of GIXS to atomic scale structure. In this paper they present examples from some of their studies of growth modes and surface evolution as a function of process conditions that illustrate the capabilities of synchrotron x-ray analysis during MOCVD growth. They focus on studies of the homoepitaxial growth mode, island coarsening dynamics, and effects of impurities.

  14. Calibrated In Situ Measurement of UT/LS Water Vapor Using Chemical Ionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Thornberry, T. D.; Rollins, A.; Gao, R.; Watts, L. A.; Ciciora, S. J.; McLaughlin, R. J.; Fahey, D. W.

    2011-12-01

    Over the past several decades there has been considerable disagreement among in situ water vapor measurements by different instruments at the low part per million (ppm) mixing ratios found in the upper troposphere and lower stratosphere (UT/LS). These discrepancies contribute to uncertainty in our understanding of the microphysics related to cirrus cloud particle nucleation and growth and affect our ability to determine the effect of climate changes on the radiatively important feedback from UT/LS water vapor. To address the discrepancies observed in measured UT/LS water vapor, a new chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor at low mixing ratios. The instrument utilizes a radioactive α particle source to ionize a flow of sample air drawn into the instrument. A cascade of ion-molecule reactions results in the production of protonated water ions proportional to the water vapor mixing ratio that are then detected by the mass spectrometer. The multi-step nature of the ionization mechanism results in a non-linear sensitivity to water vapor, necessitating calibration across the full range of values to be measured. To accomplish this calibration, we have developed a novel calibration scheme using catalytic oxidation of hydrogen to produce well-defined water vapor mixing ratios that can be introduced into the instrument inlet during flight. The CIMS instrument was deployed for the first time aboard the NASA WB-57 high altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The sensitivity of the instrument to water vapor was calibrated every ~45 minutes in flight from < 1 to 150 ppm. Analysis of in-flight data demonstrates a typical sensitivity of 2000 Hz/ppm at 4.5 ppm with a signal to noise ratio (2 σ) > 50 for a 1 second measurement. The instrument and its calibration system performed successfully in

  15. Effect of irrigation with treated wastewater on soil chemical properties and infiltration rate.

    PubMed

    Bedbabis, Saida; Ben Rouina, Béchir; Boukhris, Makki; Ferrara, Giuseppe

    2014-01-15

    In Tunisia, water scarcity is one of the major constraints for agricultural activities. The reuse of treated wastewater (TWW) in agriculture can be a sustainable solution to face water scarcity. The research was conducted for a period of four years in an olive orchard planted on a sandy soil and subjected to irrigation treatments: a) rain-fed conditions (RF), as control b) well water (WW) and c) treated wastewater (TWW). In WW and TWW treatments, an annual amount of 5000 m(3) ha(-1) of water was supplied to the orchard. Soil samples were collected at the beginning of the study and after four years for each treatment. The main soil properties such as electrical conductivity (EC), pH, soluble cations, chloride (Cl(-)), sodium adsorption ratio (SAR), organic matter (OM) as well as the infiltration rate were investigated. After four years, either a significant decrease of pH and infiltration rate or a significant increase of OM, SAR and EC were observed in the soil subjected to treated wastewater treatment.

  16. Proposed Occupational Exposure Limits for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals

    SciTech Connect

    Poet, Torka S.; Timchalk, Chuck

    2006-03-24

    A large number of volatile chemicals have been identified in the headspaces of tanks used to store mixed chemical and radioactive waste at the U.S. Department of Energy (DOE) Hanford Site, and there is concern that vapor releases from the tanks may be hazardous to workers. Contractually established occupational exposure limits (OELs) established by the Occupational Safety and Health Administration (OSHA) and American Conference of Governmental Industrial Hygienists (ACGIH) do not exist for all chemicals of interest. To address the need for worker exposure guidelines for those chemicals that lack OSHA or ACGIH OELs, a procedure for assigning Acceptable Occupational Exposure Limits (AOELs) for Hanford Site tank farm workers has been developed and applied to a selected group of 57 headspace chemicals.

  17. Using chemical vapor deposition diamond finishing burs for conservative esthetic procedures.

    PubMed

    Furuse, Adilson Yoshio; da Cunha, Leonardo Fernandes; Runnacles, Patricio; Pirolo, Rodrigo; Zielak, Joao Cesar

    2013-07-01

    The article demonstrates how chemical vapor deposition (CVD) diamond burs were used in a simple esthetic and cosmetic procedure to treat discolored anterior teeth. A patient who experienced discoloration after bleaching was treated with direct resin composite veneers. Excess restorative material close to the periodontium was removed with a CVD diamond bur attached to an ultrasonic handpiece. The results indicate that CVD diamond burs are appropriate for removing excess material at the gingival margins of resin composite restorations without damaging the periodontium.

  18. Bandgap tuning of mixed organic cation utilizing chemical vapor deposition process

    PubMed Central

    Kim, Jeongmo; Kim, Hyeong Pil; Teridi, Mohd Asri Mat; Yusoff, Abd. Rashid bin Mohd; Jang, Jin

    2016-01-01

    Bandgap tuning of a mixed organic cation perovskite is demonstrated via chemical vapor deposition process. The optical and electrical properties of the mixed organic cation perovskite can be manipulated by varying the growth time. A slight shift of the absorption band to shorter wavelengths is demonstrated with increasing growth time, which results in the increment of the current density. Hence, based on the optimized growth time, our device exhibits an efficiency of 15.86% with negligible current hysteresis. PMID:27874026

  19. Electrochromic properties of molybdenum trioxide thin films prepared by chemical vapor deposition

    SciTech Connect

    Maruyama, Toshiro; Kanagawa, Tetsuya

    1995-05-01

    Electrochromic molybdenum trioxide thin films were prepared by chemical vapor deposition. The source material was molybdenum carbonyl. Amorphous molybdenum trioxide thin films were produced at a substrate temperature 300 C. Reduction and oxidation of the films in a 0.3M LiClO{sub 4} propylene carbonate solution caused desirable changes in optical absorption. Coulometry indicated that the coloration efficiency was 25.8 cm{sup 2}/C.

  20. Metal organic chemical vapor deposition of 111-v compounds on silicon

    DOEpatents

    Vernon, Stanley M.

    1986-01-01

    Expitaxial composite comprising thin films of a Group III-V compound semiconductor such as gallium arsenide (GaAs) or gallium aluminum arsenide (GaAlAs) on single crystal silicon substrates are disclosed. Also disclosed is a process for manufacturing, by chemical deposition from the vapor phase, epitaxial composites as above described, and to semiconductor devices based on such epitaxial composites. The composites have particular utility for use in making light sensitive solid state solar cells.

  1. Synthesis of Cobalt Oxides Thin Films Fractal Structures by Laser Chemical Vapor Deposition

    PubMed Central

    Haniam, P.; Kunsombat, C.; Chiangga, S.; Songsasen, A.

    2014-01-01

    Thin films of cobalt oxides (CoO and Co3O4) fractal structures have been synthesized by using laser chemical vapor deposition at room temperature and atmospheric pressure. Various factors which affect the density and crystallization of cobalt oxides fractal shapes have been examined. We show that the fractal structures can be described by diffusion-limited aggregation model and discuss a new possibility to control the fractal structures. PMID:24672354

  2. Monolayer Graphene Growth on Ni(111) by Low Temperature Chemical Vapor Deposition

    SciTech Connect

    Batzill, M.; Sutter, P.; Addou, R.; Dahal, A.

    2012-01-09

    In contrast to the commonly employed high temperature chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the bulk, we demonstrate that below 600 C graphene can be grown in a self-limiting monolayer growth process. Optimum growth is achieved at {approx}550 C. Above this temperature, carbon diffusion into the bulk is limiting the surface growth rate, while at temperatures below {approx}500 C a competing surface carbide phase impedes graphene formation.

  3. Characterization of single crystal chemical vapor deposition diamond detectors for neutron spectrometry.

    PubMed

    Gagnon-Moisan, F; Zimbal, A; Nolte, R; Reginatto, M; Schuhmacher, H

    2012-10-01

    Detectors made from artificial chemical vapor deposition single crystal diamond have shown great potential for fast neutron spectrometry. In this paper, we present the results of measurements made at the Physikalisch-Technische Bundesanstalt accelerator using neutron fields in the energy range from 7 MeV to 16 MeV. This study presents the first results of the characterization of the detector in this energy range.

  4. Negative Electron Affinity Effect on the Surface of Chemical Vapor Deposited Diamond Polycrystalline Films

    NASA Technical Reports Server (NTRS)

    Krainsky, I. L.; Asnin, V. M.; Mearini, G. T.; Dayton, J. A., Jr.

    1996-01-01

    Strong negative electron affinity effects have been observed on the surface of as-grown chemical vapor deposited diamond using Secondary Electron Emission. The test samples were randomly oriented and the surface was terminated with hydrogen. The effect appears as an intensive peak in the low energy part of the spectrum of the electron energy distribution and may be described in the model of effective negative electron affinity.

  5. Plasma-enhanced chemical vapor deposition of low-resistive tungsten thin films

    SciTech Connect

    Kim, Y.T.; Min, S.; Hong, J.S. ); Kim, C.K. )

    1991-02-25

    Controlling the wafer temperatures from 200 to 500 {degree}C at H{sub 2}/WF{sub 6} flow ratio equal to 24, low-resistive (about 11 {mu}{Omega} cm) tungsten thin films are deposited by plasma-enhanced chemical vapor deposition. The as-deposited tungsten films have (110), (200), and (211) oriented bcc structures and Auger depth profile shows that fluorine and oxygen impurities are below the detection limit of Auger electron spectroscopy.

  6. Chemical Vapor Deposition of Cu Film on SiO2 Using Cyclopentadienylcoppertriethylphosphine

    NASA Astrophysics Data System (ADS)

    Chichibu, Shigefusa; Yoshida, Nobuhide; Higuchi, Hirofumi; Matsumoto, Satoru

    1992-12-01

    Chemical vapor deposition of Cu film on SiO2 has been studied using cyclopentadienylcoppertriethylphosphine (C5H5CuP(C2H5)3), which contains no oxygen atom itself. The deposited Cu films had complete (111) preferred orientation for deposition temperatures below 450°C. From Auger electron spectroscopy measurements, no simultaneous incorporation of oxygen during the deposition has been confirmed. Relatively low temperature deposition is preferable to reduce the condensation of deposited Cu.

  7. Chemical Vapor Deposition Growth of Linked Carbon Monolayers with Acetylenic Scaffoldings on Silver Foil.

    PubMed

    Liu, Rong; Gao, Xin; Zhou, Jingyuan; Xu, Hua; Li, Zhenzhu; Zhang, Shuqing; Xie, Ziqian; Zhang, Jin; Liu, Zhongfan

    2017-03-02

    Graphdiyne analogs, linked carbon monolayers with acetylenic scaffoldings, are fabricated by adopting low-temperature chemical vapor deposition which provides a route for the synthesis of two-dimensional carbon materials via molecular building blocks. The electrical conductivity of the as-grown films can reach up to 6.72 S cm(-1) . Moreover, the films show potential as promising substrates for fluorescence suppressing and Raman advancement.

  8. GaN Stress Evolution During Metal-Organic Chemical Vapor Deposition

    SciTech Connect

    Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Hunter, J.; Tsong, I.

    1998-10-14

    The evolution of stress in gallium nitride films on sapphire has been measured in real- time during metal organic chemical vapor deposition. In spite of the 161%0 compressive lattice mismatch of GaN to sapphire, we find that GaN consistently grows in tension at 1050"C. Furthermore, in-situ stress monitoring indicates that there is no measurable relaxation of the tensile growth stress during annealing or thermal cycling.

  9. Mathematical Modeling of Chemical Vapor Deposition of Material on a Curvilinear Surface

    NASA Astrophysics Data System (ADS)

    Kuvyrkin, G. N.; Zhuravskii, A. V.; Savel‧eva, I. Yu.

    2016-11-01

    In this work, a mathematical model has been constructed that describes the process of chemical vapor deposition of material on a curvilinear plate. On the boundary where the deposition occurs, account is taken of convective heat transfer, heat transfer by radiation, and heat and mass transfer during the attachment of the substance to the surface. A numerical algorithm is proposed for finding the temperature profile at any instant of time; results and an analysis of numerical calculation are given for different materials.

  10. Fabrication of lightweight ceramic mirrors by means of a chemical vapor deposition process

    NASA Technical Reports Server (NTRS)

    Goela, Jitendra S. (Inventor); Taylor, Raymond L. (Inventor)

    1991-01-01

    A process to fabricate lightweigth ceramic mirrors, and in particular, silicon/silicon carbide mirrors, involves three chemical vapor deposition steps: one to produce the mirror faceplate, the second to form the lightweight backstructure which is deposited integral to the faceplate, and the third and final step which results in the deposition of a layer of optical grade material, for example, silicon, onto the front surface of the faceplate. The mirror figure and finish are fabricated into this latter material.

  11. The development of chemically vapor deposited mullite coatings for the corrosion protection of SiC

    SciTech Connect

    Auger, M.; Hou, P.; Sengupta, A.; Basu, S.; Sarin, V.

    1998-05-01

    Crystalline mullite coatings have been chemically vapor deposited onto SiC substrates to enhance the corrosion and oxidation resistance of the substrate. Current research has been divided into three distinct areas: (1) Development of the deposition processing conditions for increased control over coating`s growth rate, microstructure, and morphology; (2) Analysis of the coating`s crystal structure and stability; (3) The corrosion resistance of the CVD mullite coating on SiC.

  12. Synthesis of cobalt oxides thin films fractal structures by laser chemical vapor deposition.

    PubMed

    Haniam, P; Kunsombat, C; Chiangga, S; Songsasen, A

    2014-01-01

    Thin films of cobalt oxides (CoO and Co3O4) fractal structures have been synthesized by using laser chemical vapor deposition at room temperature and atmospheric pressure. Various factors which affect the density and crystallization of cobalt oxides fractal shapes have been examined. We show that the fractal structures can be described by diffusion-limited aggregation model and discuss a new possibility to control the fractal structures.

  13. High index of refraction films for dielectric mirrors prepared by metal-organic chemical vapor deposition

    SciTech Connect

    Brusasco, R.M.

    1989-01-01

    A wide variety of metal oxides with high index of refraction can be prepared by Metal-Organic Chemical Vapor Deposition. We present some recent optical and laser damage results on oxide films prepared by MOCVD which could be used in a multilayer structure for highly reflecting (HR) dielectric mirror applications. The method of preparation affects both optical properties and laser damage threshold. 10 refs., 8 figs., 4 tabs.

  14. Investigation of the Hazards Posed by Chemical Vapors Released in Marine Operations - Phase II.

    DTIC Science & Technology

    1983-04-01

    at San Antonio, Texas . 307 U.S. COAST GUARDf SOUTHWEST RESEARCH INSTITUTE, SAN ANTONIO, TEXAS , USA UNIVERSITY OF TEXAS SCHOOL OF PUBLIC HEALTH, HOUSTON... TEXAS , USA SUBJECT CONSENT FOR PARTICIPATION IN AN INVESTIGATION OF "HAZARDS POSED BY CHEMICAL VAPORS RELEASED IN MARINE OPERATIONS: TASK V...write to the following persons: Dr. Stanley M. Pier Mr. William J. Astleford 5326 Dora Street Southwest Research Institute Houston, Texas , 77005, USA

  15. Chemical Vapor Deposition of Monolayer Rhenium Disulfide (ReS2).

    PubMed

    Keyshar, Kunttal; Gong, Yongji; Ye, Gonglan; Brunetto, Gustavo; Zhou, Wu; Cole, Daniel P; Hackenberg, Ken; He, Yongmin; Machado, Leonardo; Kabbani, Mohamad; Hart, Amelia H C; Li, Bo; Galvao, Douglas S; George, Antony; Vajtai, Robert; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

    2015-08-19

    The direct synthesis of monolayer and multilayer ReS2 by chemical vapor deposition at a low temperature of 450 °C is reported. Detailed characterization of this material is performed using various spectroscopy and microscopy methods. Furthermore initial field-effect transistor characteristics are evaluated, which highlight the potential in being used as an n-type semiconductor. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Chemical Vapor Deposition of Large-Sized Hexagonal WSe₂ Crystals on Dielectric Substrates.

    PubMed

    Chen, Jianyi; Liu, Bo; Liu, Yanpeng; Tang, Wei; Nai, Chang Tai; Li, Linjun; Zheng, Jian; Gao, Libo; Zheng, Yi; Shin, Hyun Suk; Jeong, Hu Young; Loh, Kian Ping

    2015-11-01

    High-quality large-sized hexagoal WSe2 crystals can be grown on dielectric substrates using atmospheric chemical vapor deposition in the presence of hydrogen gas. These hexagonal crystals (lateral width >160 um) have a carrier mobility of 100 cm(2) V(-1) s(-1) and a photoresponsivity of ≈1100 mA W(-1), which is comparable to that of exfoliated flakes.

  17. Deposition of thermal and hot-wire chemical vapor deposition copper thin films on patterned substrates.

    PubMed

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    In this work we study the hot-wire chemical vapor deposition (HWCVD) of copper films on blanket and patterned substrates at high filament temperatures. A vertical chemical vapor deposition reactor was used in which the chemical reactions were assisted by a tungsten filament heated at 650 degrees C. Hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) vapors were used, directly injected into the reactor with the aid of a liquid injection system using N2 as carrier gas. Copper thin films grown also by thermal and hot-wire CVD. The substrates used were oxidized silicon wafers on which trenches with dimensions of the order of 500 nm were formed and subsequently covered with LPCVD W. HWCVD copper thin films grown at filament temperature of 650 degrees C showed higher growth rates compared to the thermally ones. They also exhibited higher resistivities than thermal and HWCVD films grown at lower filament temperatures. Thermally grown Cu films have very uniform deposition leading to full coverage of the patterned substrates while the HWCVD films exhibited a tendency to vertical growth, thereby creating gaps and incomplete step coverage.

  18. [The discussion of the infiltrative model of chemical knowledge stepping into genetics teaching in agricultural institute or university].

    PubMed

    Zou, Ping; Luo, Pei-Gao

    2010-05-01

    Chemistry is an important group of basic courses, while genetics is one of the important major-basic courses in curriculum of many majors in agricultural institutes or universities. In order to establish the linkage between the major course and the basic course, the ability of application of the chemical knowledge previously learned in understanding genetic knowledge in genetics teaching is worthy of discussion for genetics teachers. In this paper, the authors advocate to apply some chemical knowledge previously learned to understand genetic knowledge in genetics teaching with infiltrative model, which could help students learn and understand genetic knowledge more deeply. Analysis of the intrinsic logistic relationship among the knowledge of different courses and construction of the integral knowledge network are useful for students to improve their analytic, comprehensive and logistic abilities. By this way, we could explore a new teaching model to develop the talents with new ideas and comprehensive competence in agricultural fields.

  19. Chemical vapor deposition of high T(sub c) superconducting films in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Levy, Moises; Sarma, Bimal K.

    1994-01-01

    Since the discovery of the YBaCuO bulk materials in 1987, Metalorganic Chemical Vapor Deposition (MOCVD) has been proposed for preparing HTSC high T(sub c) films. This technique is now capable of producing high-T(sub c) superconducting thin films comparable in quality to those prepared by any other methods. The MOCVD technique has demonstrated its superior advantage in making large area high quality HTSC thin films and will play a major role in the advance of device applications of HTSC thin films. The organometallic precursors used in the MOCVD preparation of HTSC oxide thin films are most frequently metal beta-diketonates. High T(sub c) superconductors are multi-component oxides which require more than one component source, with each source, containing one kind of precursor. Because the volatility and stability of the precursors are strongly dependent on temperature, system pressure, and carrier gas flow rate, it has been difficult to control the gas phase composition, and hence film stoichiometry. In order circumvent these problems we have built and tested a single source MOCVD reactor in which a specially designed vaporizer was employed. This vaporizer can be used to volatilize a stoichiometric mixture of diketonates of yttrium, barium and copper to produce a mixed vapor in a 1:2:3 ratio respectively of the organometellics. This is accomplished even though the three compounds have significantly different volatilities. We have developed a model which provides insight into the process of vaporizing mixed precursors to produce high quality thin films of Y1Ba2Cu3O7. It shows that under steady state conditions the mixed organometallic vapor must have a stoichiometric ratio of the individual organometallics identical to that in the solid mixture.

  20. High rate chemical vapor deposition of carbon films using fluorinated gases

    DOEpatents

    Stafford, Byron L.; Tracy, C. Edwin; Benson, David K.; Nelson, Arthur J.

    1993-01-01

    A high rate, low-temperature deposition of amorphous carbon films is produced by PE-CVD in the presence of a fluorinated or other halide gas. The deposition can be performed at less than 100.degree. C., including ambient room temperature, with a radio frequency plasma assisted chemical vapor deposition process. With less than 6.5 atomic percent fluorine incorporated into the amorphous carbon film, the characteristics of the carbon film, including index of refraction, mass density, optical clarity, and chemical resistance are within fifteen percent (15%) of those characteristics for pure amorphous carbon films, but the deposition rates are high.

  1. Removal characteristics of plasma chemical vaporization machining with a pipe electrode for optical fabrication

    SciTech Connect

    Takino, Hideo; Yamamura, Kazuya; Sano, Yasuhisa; Mori, Yuzo

    2010-08-10

    Plasma chemical vaporization machining (CVM) is a high-precision chemical shaping method using rf plasma generated in the proximity of an electrode in an atmospheric environment. The purpose of the present study is to clarify the removal characteristics of plasma CVM using a pipe electrode. Polished fused silica plates were processed by plasma CVM, polishing, and precision grinding under various conditions. The removal rate of plasma CVM was about 4 to 1100 times faster than that of polishing, and the maximum removal rate was almost equal to that of precision grinding. The roughness of the resultant surfaces was almost the same as that of the polished surfaces.

  2. Chemical vapor generation for sample introduction into inductively coupled plasma atomic emission spectroscopy: vaporization of antimony(III) with bromide.

    PubMed

    Lopez-Molinero, A; Mendoza, O; Callizo, A; Chamorro, P; Castillo, J R

    2002-10-01

    A new method for antimony determination in soils is proposed. It is based on the chemical vapor generation of Sb(III) with bromide, after a reaction in sulfuric acid media and transport of the gaseous phase into an inductively coupled plasma for atomic emission spectrometry. The experimental variables influencing the method were delimited by experimental design and the most important were finally optimized by the modified Simplex method. In optimized conditions the method involves the reaction of 579 microl concentrated sulfuric acid with 120 microl 5% w/v KBr and 250 microl antimony solution. Measurement of antimony emission intensity at 217.581 nm provides a method with an absolute detection limit of 3.5 ng and a precision (RSD) of 5.8% for the injection of five replicates of 175 ng Sb(III) (250 microl of 0.7 microg ml(-1) solution). The interference of common anions and cations on the antimony signal was evaluated. A 21% Sb(III) volatilization efficiency was calculated from the mean of six experiments at optimum conditions. The accuracy of the methodology was checked by the analysis of one standard reference soil after acid decomposition heating in a microwave oven.

  3. Low power, lightweight vapor sensing using arrays of conducting polymer composite chemically-sensitive resistors.

    PubMed

    Ryan, M A; Lewis, N S

    2001-01-01

    Arrays of broadly responsive vapor detectors can be used to detect, identify, and quantify vapors and vapor mixtures. One implementation of this strategy involves the use of arrays of chemically-sensitive resistors made from conducting polymer composites. Sorption of an analyte into the polymer composite detector leads to swelling of the film material. The swelling is in turn transduced into a change in electrical resistance because the detector films consist of polymers filled with conducting particles such as carbon black. The differential sorption, and thus differential swelling, of an analyte into each polymer composite in the array produces a unique pattern for each different analyte of interest, Pattern recognition algorithms are then used to analyze the multivariate data arising from the responses of such a detector array. Chiral detector films can provide differential detection of the presence of certain chiral organic vapor analytes. Aspects of the spaceflight qualification and deployment of such a detector array, along with its performance for certain analytes of interest in manned life support applications, are reviewed and summarized in this article.

  4. Determination of cadmium in water samples by fast pyrolysis-chemical vapor generation atomic fluorescence spectrometry

    NASA Astrophysics Data System (ADS)

    Zhang, Jingya; Fang, Jinliang; Duan, Xuchuan

    2016-08-01

    A pyrolysis-vapor generation procedure to determine cadmium by atomic fluorescence spectrometry has been established. Under fast pyrolysis, cadmium ion can be reduced to volatile cadmium species by sodium formate. The presence of thiourea enhanced the efficiency of cadmium vapor generation and eliminated the interference of copper. The possible mechanism of vapor generation of cadmium was discussed. The optimization of the parameters for pyrolysis-chemical vapor generation, including pyrolysis temperature, amount of sodium formate, concentration of hydrochloric acid, and carrier argon flow rate were carried out. Under the optimized conditions, the absolute and concentration detection limits were 0.38 ng and 2.2 ng ml- 1, respectively, assuming that 0.17 ml of sample was injected. The generation efficiency of was 28-37%. The method was successfully applied to determine trace amounts of cadmium in two certified reference materials of Environmental Water (GSB07-1185-2000 and GSBZ 50009-88). The results were in good agreement with the certified reference values.

  5. Low power, lightweight vapor sensing using arrays of conducting polymer composite chemically-sensitive resistors

    NASA Technical Reports Server (NTRS)

    Ryan, M. A.; Lewis, N. S.

    2001-01-01

    Arrays of broadly responsive vapor detectors can be used to detect, identify, and quantify vapors and vapor mixtures. One implementation of this strategy involves the use of arrays of chemically-sensitive resistors made from conducting polymer composites. Sorption of an analyte into the polymer composite detector leads to swelling of the film material. The swelling is in turn transduced into a change in electrical resistance because the detector films consist of polymers filled with conducting particles such as carbon black. The differential sorption, and thus differential swelling, of an analyte into each polymer composite in the array produces a unique pattern for each different analyte of interest, Pattern recognition algorithms are then used to analyze the multivariate data arising from the responses of such a detector array. Chiral detector films can provide differential detection of the presence of certain chiral organic vapor analytes. Aspects of the spaceflight qualification and deployment of such a detector array, along with its performance for certain analytes of interest in manned life support applications, are reviewed and summarized in this article.

  6. Prediction of Chemical Vapor Deposition Rates on Monofilaments and Its Implications for Fiber Properties

    NASA Technical Reports Server (NTRS)

    Gokoglu, S. A.; Kuczmarski, M.; Veitch, L. C.

    1992-01-01

    Deposition rates are predicted in a cylindrical upflow reactor designed for chemical vapor deposition (CVD) on monofilaments. Deposition of silicon from silane in a hydrogen carrier gas is chosen as a relevant example. The effects of gas and surface chemistry are studied in a two-dimensional axisymmetric flow field for this chemically well-studied system. Model predictions are compared to experimental CVD rate measurements. The differences in some physical and chemical phenomena between such small diameter (about 150 microns) fiber substrates and other typical CVD substrates are highlighted. The influence of the Soret mass transport mechanism is determined to be extraordinarily significant. The difficulties associated with the accurate measurement and control of the fiber temperature are discussed. Model prediction sensitivities are investigated with respect to fiber temperatures, fiber radii, Soret transport, and chemical kinetic parameters. The implications of the predicted instantaneous rates are discussed relative to the desired fiber properties for both the batch and the continuous processes.

  7. Aerosol-Assisted Chemical Vapor Deposited Thin Films for Space Photovoltaics

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; McNatt, Jeremiah; Dickman, John E.; Jin, Michael H.-C.; Banger, Kulbinder K.; Kelly, Christopher V.; AquinoGonzalez, Angel R.; Rockett, Angus A.

    2006-01-01

    Copper indium disulfide thin films were deposited via aerosol-assisted chemical vapor deposition using single source precursors. Processing and post-processing parameters were varied in order to modify morphology, stoichiometry, crystallography, electrical properties, and optical properties in order to optimize device-quality material. Growth at atmospheric pressure in a horizontal hot-wall reactor at 395 C yielded best device films. Placing the susceptor closer to the evaporation zone and flowing a more precursor-rich carrier gas through the reactor yielded shinier, smoother, denser-looking films. Growth of (112)-oriented films yielded more Cu-rich films with fewer secondary phases than growth of (204)/(220)-oriented films. Post-deposition sulfur-vapor annealing enhanced stoichiometry and crystallinity of the films. Photoluminescence studies revealed four major emission bands (1.45, 1.43, 1.37, and 1.32 eV) and a broad band associated with deep defects. The highest device efficiency for an aerosol-assisted chemical vapor deposited cell was 1.03 percent.

  8. Flexible electrochemical capacitors based on polypyrrole/carbon fibers via chemical polymerization of pyrrole vapor

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Han, Gaoyi; Xiao, Yaoming; Chang, Yunzhen; Liu, Cuixian; Li, Miaoyu; Li, Yanping; Zhang, Ying

    2016-07-01

    Polypyrrole (PPy) has been deposited on the carbon fibers (CFs) via chemical oxidation of monomer vapor strategy, during which FeCl3·6H2O in acetonitrile adsorbed on CFs acts as oxidant to polymerize the pyrrole vapor. The morphologies and capacitive properties of the PPy deposited on CFs (PPy/CFs) are strongly influenced by the concentration of oxidant used in the process. The assembled flexible capacitors by using PPy/CFs as electrodes and LiCl/polyvinyl alcohol as gel electrolyte have been evaluated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results show that the composites of PPy/CFs prepared by using 350 mg mL-1 FeCl3·6H2O as oxidant (PPy/CFs-350) exhibit relatively higher specific capacitance and good rate capability. Compared with PPy/CFs prepared by electrochemical deposition (retaining 5% of the initial capacitance), the PPy/CFs prepared by chemically polymerizing monomer vapor shows excellent stability (retaining 85% of initial capacitance after 5000 cycles). Furthermore, cells fabricated by PPy/CFs show a fairly good performance under various bending states, three cells of PPy/CFs-350 connected in series can light up a light emitting diode with a voltage threshold of about 2.5 V for approximate 10 min after being charged for about 3 min, revealing the potential of the cells' practical applications.

  9. Influence of Geometry on a High Surface Area-Solid Phase Microextraction Sampler for Chemical Vapor Collection

    DTIC Science & Technology

    2007-06-04

    Title of Thesis: Influence of Geometry on a High Surface Area-Solid Phase Microextraction Sampler for Chemical Vapor Collection Name of...TITLE AND SUBTITLE Influence of Geometry on a High Surface Area-Solid Phase Microextraction Sampler for Chemical Vapor Collection 5a. CONTRACT...SUPPLEMENTARY NOTES 14. ABSTRACT The High Surface Area Solid Phase Microextraction (HSA-SPME) device is an internally heated sampling device designed for

  10. MICHIGAN SOIL VAPOR EXTRACTION REMEDIATION (MISER) MODEL: A COMPUTER PROGRAM TO MODEL SOIL VAPOR EXTRACTION AND BIOVENTING OF ORGANIC CHEMICALS IN UNSATURATED GEOLOGICAL MATERIAL

    EPA Science Inventory

    Soil vapor extraction (SVE) and bioventing (BV) are proven strategies for remediation of unsaturated zone soils. Mathematical models are powerful tools that can be used to integrate and quantify the interaction of physical, chemical, and biological processes occurring in field sc...

  11. MICHIGAN SOIL VAPOR EXTRACTION REMEDIATION (MISER) MODEL: A COMPUTER PROGRAM TO MODEL SOIL VAPOR EXTRACTION AND BIOVENTING OF ORGANIC CHEMICALS IN UNSATURATED GEOLOGICAL MATERIAL

    EPA Science Inventory

    Soil vapor extraction (SVE) and bioventing (BV) are proven strategies for remediation of unsaturated zone soils. Mathematical models are powerful tools that can be used to integrate and quantify the interaction of physical, chemical, and biological processes occurring in field sc...

  12. Uptake rate constants and partition coefficients for vapor phase organic chemicals using semipermeable membrane devices (SPMDs)

    USGS Publications Warehouse

    Cranor, W.L.; Alvarez, D.A.; Huckins, J.N.; Petty, J.D.

    2009-01-01

    To fully utilize semipermeable membrane devices (SPMDs) as passive samplers in air monitoring, data are required to accurately estimate airborne concentrations of environmental contaminants. Limited uptake rate constants (kua) and no SPMD air partitioning coefficient (Ksa) existed for vapor-phase contaminants. This research was conducted to expand the existing body of kinetic data for SPMD air sampling by determining kua and Ksa for a number of airborne contaminants including the chemical classes: polycyclic aromatic hydrocarbons, organochlorine pesticides, brominated diphenyl ethers, phthalate esters, synthetic pyrethroids, and organophosphate/organosulfur pesticides. The kuas were obtained for 48 of 50 chemicals investigated and ranged from 0.03 to 3.07??m3??g-1??d-1. In cases where uptake was approaching equilibrium, Ksas were approximated. Ksa values (no units) were determined or estimated for 48 of the chemicals investigated and ranging from 3.84E+5 to 7.34E+7. This research utilized a test system (United States Patent 6,877,724 B1) which afforded the capability to generate and maintain constant concentrations of vapor-phase chemical mixtures. The test system and experimental design employed gave reproducible results during experimental runs spanning more than two years. This reproducibility was shown by obtaining mean kua values (n??=??3) of anthracene and p,p???-DDE at 0.96 and 1.57??m3??g-1??d-1 with relative standard deviations of 8.4% and 8.6% respectively.

  13. Remote catalyzation for growth of boron nitride nanotubes by low pressure chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, Liangjie; Li, Taotao; Ling, Lin; Luo, Jie; Zhang, Kai; Xu, Yancui; Lu, Huifen; Yao, Yagang

    2016-05-01

    Direct deposition of high purity and quality boron nitride nanotubes (BNNTs) on Si substrate were obtained using low pressure chemical vapor deposition (LPCVD). We find Fe-Mg-O species may act as catalysts for growing BNNTs. This synthesis process conforms to vapor-liquid-solid (VLS) growth mechanism. As-grown BNNTs also show a large optical energy band gap of 6.12 eV, approaching to hexagonal phase BN single crystals. Meanwhile, as-grown BNNTs exhibit an intense UV-emission band located at 345 nm and a weak deep band at 237 nm. Their optoelectronic properties make them have promising for future nanoscale deep-UV light emitting devices.

  14. Chemical vapor deposition of carbon nanotubes: a review on growth mechanism and mass production.

    PubMed

    Kumar, Mukul; Ando, Yoshinori

    2010-06-01

    This review article deals with the growth mechanism and mass production of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). Different aspects of CNT synthesis and growth mechanism are reviewed in the light of latest progresses and understandings in the field. Materials aspects such as the roles of hydrocarbon, catalyst and catalyst support are discussed. Many new catalysts and new carbon sources are described. Growth-control aspects such as the effects of temperature, vapor pressure and catalyst concentration on CNT diameter distribution and single- or multi-wall formation are explained. Latest reports of metal-catalyst-free CNT growth are considered. The mass-production aspect is discussed from the perspective of a sustainable CNT technology. Existing problems and challenges of the process are addressed with future directions.

  15. Growth of high mobility InSb by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Partin, D. L.; Green, L.; Heremans, J.

    1994-02-01

    Thin films of InSb have been grown on insulating GaAs substrates using the metalorganic chemical vapor deposition technique with trimethyl indium and trimethyl antimony as reactants. We find that the mobilities obtained are usually low unless indium is predeposited onto the substrate. This indium predeposition technique greatly improves the yield of InSb films with mobilities of ~50000 crn2V-1S-1 at room temperature and a typical thickness of 2 microns. With this predeposition technique, the electron mobilities of these films become relatively independent of the vapor stroichiometry during growth and of the growth temperature. The electron mobilities are also very uniform across a wafer. These properties are obtained even when the film growth rate exceeds 2 μm/h.

  16. Continuous growth of single-wall carbon nanotubes using chemical vapor deposition

    DOEpatents

    Grigorian, Leonid; Hornyak, Louis; Dillon, Anne C; Heben, Michael J

    2014-09-23

    The invention relates to a chemical vapor deposition process for the continuous growth of a carbon single-wall nanotube where a carbon-containing gas composition is contacted with a porous membrane and decomposed in the presence of a catalyst to grow single-wall carbon nanotube material. A pressure differential exists across the porous membrane such that the pressure on one side of the membrane is less than that on the other side of the membrane. The single-wall carbon nanotube growth may occur predominately on the low-pressure side of the membrane or, in a different embodiment of the invention, may occur predominately in between the catalyst and the membrane. The invention also relates to an apparatus used with the carbon vapor deposition process.

  17. Continuous growth of single-wall carbon nanotubes using chemical vapor deposition

    DOEpatents

    Grigorian, Leonid [Raymond, OH; Hornyak, Louis [Evergreen, CO; Dillon, Anne C [Boulder, CO; Heben, Michael J [Denver, CO

    2008-10-07

    The invention relates to a chemical vapor deposition process for the continuous growth of a carbon single-wall nanotube where a carbon-containing gas composition is contacted with a porous membrane and decomposed in the presence of a catalyst to grow single-wall carbon nanotube material. A pressure differential exists across the porous membrane such that the pressure on one side of the membrane is less than that on the other side of the membrane. The single-wall carbon nanotube growth may occur predominately on the low-pressure side of the membrane or, in a different embodiment of the invention, may occur predominately in between the catalyst and the membrane. The invention also relates to an apparatus used with the carbon vapor deposition process.

  18. Direct measurement of chemical composition of SOx in impact vapor using a laser gun

    NASA Astrophysics Data System (ADS)

    Ohno, Sohsuke; Kadono, Toshihiko; Kurosawa, Kosuke; Hamura, Taiga; Sakaiya, Tatsuhiro; Sugita, Seiji; Shigemori, Keisuke; Hironaka, Yoichiro; Watari, Takeshi; Matsui, Takafumi

    2011-06-01

    The SO3/SO2 ratio of the impact vapor cloud is a key parameter for understanding the environmental perturbation caused by the impact-induced SOx and the killing mechanism of. the mass extinction at the K-Pg boundary. We conducted hypervelocity impact experiments using a high-speed laser gun (GEKKO XII-HIPER, ILE, Osaka University) and measured the chemical compositions of the SOx released from CaSO4. The experimental result indicates that SOx are dominated by SO3. It implies that the SOx generated by the K-Pg impact would have been also dominated by SO3, because the SO3/SO2 ratio of natural planetary scale impact vapor clouds would have been larger than that of the experimental result of this study.

  19. Copper-vapor-assisted chemical vapor deposition for high-quality and metal-free single-layer graphene on amorphous SiO2 substrate.

    PubMed

    Kim, Hyungki; Song, Intek; Park, Chibeom; Son, Minhyeok; Hong, Misun; Kim, Youngwook; Kim, Jun Sung; Shin, Hyun-Joon; Baik, Jaeyoon; Choi, Hee Cheul

    2013-08-27

    We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.

  20. Research and development of CVD (chemical vapor deposition) composite heat exchanger: Phase 1 report for the period August 1984-April 1985: (Final report)

    SciTech Connect

    Cole, W.; Metcalfe, C.; Nathanson, D.; Reagan, P.; Shimko, M.

    1985-05-17

    There is significant potential for energy and cost savings in high-temperature industrial processes by recovering the heat from flue-gas streams and using it to preheat combustion air. Although heat exchangers are available to preheat combustion air when the flue gases are clean, heat exchangers to recover heat from dirty and corrosive flue gas do not exist. Thermo Electron Corporation has developed a novel concept for a composite heat exchanger utilizing a ceramic composite material. This integrated concept relates to the one-piece construction of the heat exchanger panels which contain both headers and flow passages in one integrated panel. The ceramic composite material utilizes a woven ceramic cloth substrate which is first infiltrated and then overcoated with silicon carbide using the chemical vapor deposition (CVD) process. In this report, the accomplishments of the Phase 1 efforts are discussed and a description of the Phase 2 development program is presented.

  1. Test Operations Procedure (TOP) 10-2-022A Chemical Vapor and Aerosol System-Level Testing of Chemical/Biological Protective Suits

    DTIC Science & Technology

    2013-12-16

    Level Testing of Chemical/ Biological Protective Suits 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHORS 5d...designing and conducting tests estimating penetration of chemical agent vapor and aerosol simulant through chemical/ biological (CB) protective suit... Biological ; CB; Defense Testing 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 188 19a

  2. Chemical and physical sputtering effects on the surface morphology of carbon films grown by plasma chemical vapor deposition

    SciTech Connect

    Vazquez, Luis

    2009-08-01

    We have studied the influence of chemical and physical sputtering on the surface morphology of hydrogenated carbon films deposited on silicon substrates by bias-enhanced electron cyclotron resonance chemical vapor deposition. Atomic force microscopy based power spectrum density (PSD) and roughness analysis have been used to investigate the film morphology. This study has been possible due to the appropriate choice of the experimental variables, in particular, gas mixture, resulting in either nitrogen-free (a-C:H) or nitrogenated carbon (a-CN:H) films, and substrate bias (V{sub b}). Under these conditions, chemical sputtering is present for a-CN:H deposition but it is negligible for a-C:H film growth, while physical sputtering processes appear for both systems for V{sub b}<=-85 V. When physical sputtering does not operate, the film growth with simultaneous chemical sputtering leads to a characteristic a-CN:H granular surface morphology. Furthermore, PSD analysis reveals that a spatial correlation of the a-CN:H film surface roughness, up to distances approx300 nm, becomes a fingerprint of the coexistence of growth and chemical erosion processes on the film morphology. However, once physical sputtering takes place, the influence of chemical sputtering by reactive nitrogen species on the final surface morphology becomes negligible and both a-CN:H and a-C:H film morphologies are ultrasmooth.

  3. SiO2 coating of silver nanoparticles by photoinduced chemical vapor deposition.

    PubMed

    Boies, Adam M; Roberts, Jeffrey T; Girshick, Steven L; Zhang, Bin; Nakamura, Toshitaka; Mochizuki, Amane

    2009-07-22

    Gas-phase silver nanoparticles were coated with silicon dioxide (SiO2) by photoinduced chemical vapor deposition (photo-CVD). Silver nanoparticles, produced by inert gas condensation, and a SiO2 precursor, tetraethylorthosilicate (TEOS), were exposed to vacuum ultraviolet (VUV) radiation at atmospheric pressure and varying temperatures. The VUV photons dissociate the TEOS precursor, initiating a chemical reaction that forms SiO2 coatings on the particle surfaces. Coating thicknesses were measured for a variety of operation parameters using tandem differential mobility analysis and transmission electron microscopy. The chemical composition of the particle coatings was analyzed using energy dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The highest purity films were produced at 300-400 degrees C with low flow rates of additional oxygen. The photo-CVD coating technique was shown to effectively coat nanoparticles and limit core particle agglomeration at concentrations up to 10(7) particles cm(-3).

  4. Hydrological, chemical, and isotopic budgets of Lake Chad: a quantitative assessment of evaporation, transpiration and infiltration fluxes

    NASA Astrophysics Data System (ADS)

    Bouchez, Camille; Goncalves, Julio; Deschamps, Pierre; Vallet-Coulomb, Christine; Hamelin, Bruno; Doumnang, Jean-Claude; Sylvestre, Florence

    2016-04-01

    In the Sahelian belt, Lake Chad is a key water body for 13 million people, who live on its resources. It experiences, however, substantial and frequent surface changes. Located at the centre of one of the largest endorheic basins in the world, its waters remain surprisingly fresh. Its low salinity has been attributed to a low infiltration flow whose value remains poorly constrained. Understanding the lake's hydrological behaviour in response to climate variability requires a better constraint of the factors that control its water and chemical balance. Based on the three-pool conceptualization of Lake Chad proposed by Bader et al. (2011), this study aims to quantify the total water outflow from the lake, the respective proportions of evaporation (E), transpiration (T), and infiltration (I), and the associated uncertainties. A Bayesian inversion method based on lake-level data was used, leading to total water loss estimates in each pool (E + T + I = ETI). Sodium and stable isotope mass balances were then used to separate total water losses into E, T, and I components. Despite the scarcity of representative data available on the lake, the combination of these two geochemical tracers is relevant to assess the relative contribution of these three outflows involved in the control of the hydrological budget. Mean evapotranspiration rates were estimated at 2070 ± 100 and 2270 ± 100 mm yr-1 for the southern and northern pools, respectively. Infiltration represents between 100 and 300 mm yr-1 but most of the water is evapotranspirated in the first few kilometres from the shorelines and does not efficiently recharge the Quaternary aquifer. Transpiration is shown to be significant, around 300 mm yr-1 and reaches 500 mm yr-1 in the vegetated zone of the archipelagos. Hydrological and chemical simulations reproduce the marked hydrological change between the normal lake state that occurred before 1972 and the small lake state after 1972 when the lake surface shrunk to a one

  5. Hydrological, chemical and isotopic budgets of Lake Chad: a quantitative assessment of evaporation, transpiration and infiltration fluxes

    NASA Astrophysics Data System (ADS)

    Bouchez, C.; Goncalves, J.; Deschamps, P.; Vallet-Coulomb, C.; Hamelin, B.; Doumnang, J.-C.; Sylvestre, F.

    2015-10-01

    In the Sahelian belt, Lake Chad is a key water body for 13 million people who live on its resources. It experiences, however, substantial and frequent surface changes. Located at the center of one of the largest endorheic basins in the world, its waters remain surprisingly fresh. Its low salinity has been attributed to a low infiltration flow whose value remains poorly constrained. Understanding the lake's hydrological behavior in response to climate variability requires a better constraint of the factors that control its water and chemical balance. Based on the three-pool conceptualization of Lake Chad proposed by J. C. Bader, J. Lemoalle, and M. Leblanc (Bader et al., 2011), this study aims to quantify the total water outflow from the lake, the respective proportions of evaporation (E), transpiration (T) and infiltration (I), and the associated uncertainties. A Bayesian inversion method based on lake-level data was used, leading to total water loss estimates in each pool (ETI). Sodium and stable isotope mass balances were then used to separate total water losses into E, T and I components. Despite the scarcity of representative data available on the lake, the combination of these two geochemical tracers is relevant to assess the relative contribution of these three outflows involved in the control of the hydrological budget. Mean evapotranspiration rates were estimated at 2070 ± 100 and 2270 ± 100 mm yr-1 for the southern and northern pools respectively. Infiltration represents between 100 and 300 mm yr-1 but most of the water is evapotranspirated in the first few kilometers from the shorelines and does not efficiently recharge the Quaternary aquifer. Transpiration is shown to be significant, around 300 mm yr-1 and reaches 500 mm yr-1 in the vegetated zone of the archipelagos. Hydrological and chemical simulations reproduce the marked hydrological change between the normal lake state that occurred before 1972 and the small lake state after 1972 when the lake

  6. Chemical Species in the Vapor Phase of Hanford Double-Shell Tanks: Potential Impacts on Waste Tank Corrosion Processes

    SciTech Connect

    Felmy, Andrew R.; Qafoku, Odeta; Arey, Bruce W.; Boomer, Kayle D.

    2010-09-22

    The presence of corrosive and inhibiting chemicals on the tank walls in the vapor space, arising from the waste supernatant, dictate the type and degree of corrosion that occurs there. An understanding of how waste chemicals are transported to the walls and the affect on vapor species from changing supernatant chemistry (e.g., pH, etc.), are basic to the evaluation of risks and impacts of waste changes on vapor space corrosion (VSC). In order to address these issues the expert panel workshop on double-shell tank (DST) vapor space corrosion testing (RPP-RPT-31129) participants made several recommendations on the future data and modeling needs in the area of DST corrosion. In particular, the drying of vapor phase condensates or supernatants can form salt or other deposits at the carbon steel interface resulting in a chemical composition at the near surface substantially different from that observed directly in the condensates or the supernatants. As a result, over the past three years chemical modeling and experimental studies have been performed on DST supernatants and condensates to predict the changes in chemical composition that might occur as condensates or supernatants equilibrate with the vapor space species and dry at the carbon steel surface. The experimental studies included research on both the chemical changes that occurred as the supernatants dried as well as research on how these chemical changes impact the corrosion of tank steels. The chemical modeling and associated experimental studies were performed at the Pacific Northwest National Laboratory (PNNL) and the research on tank steel corrosion at the Savannah River National Laboratory (SRNL). This report presents a summary of the research conducted at PNNL with special emphasis on the most recent studies conducted in FY10. An overall summary of the project results as well as their broader implications for vapor space corrosion of the DST’s is given at the end of this report.

  7. Chemical vapor deposition of ceramic coatings on metals and ceramic fibers

    NASA Astrophysics Data System (ADS)

    Nable, Jun Co

    2005-07-01

    The research presented in this study consists of two major parts. The first part is about the development of ceramic coatings on metals by chemical vapor deposition (CVD) and metal-organic chemical vapor deposition (MOCVD). Ceramics such as Al2O3 and Cr2O3, are used as protective coatings for materials used at elevated temperatures (>700°C). These metal oxides either exhibit oxidation resistance or have been used as environmental bond coats. Conventional methods of coating by chemical vapor deposition requires deposition temperatures of >950°C which could damage the substrate material during the coating process. Lower deposition temperatures (400 to 600°C) by MOCVD of these metal oxides were successful on Ni metal substrates. Surface modification such as pre-oxidation and etching were also investigated. In addition, a novel approach for the CVD of TiN on metals was developed. This new approach utilizes ambient pressure conditions which lead to deposition temperatures of 800°C or lower compared to conventional CVD of TiN at 1000°C. Titanium nitride can be used as an abrasive and wear coating on cutting and grinding tools. This nitride can also serve as a diffusion coating in metals. The second major part of this research involves the synthesis of interfacial coatings on ceramic reinforcing fibers for ceramic matrix composites. Aluminum and chromium oxides were deposited onto SiC, and Al2O3-SiO 2 fibers by MOCVD. The effects of the interface coatings on the tensile strength of ceramic fibers are also discussed. New duplex interface coatings consisting of BN or TiN together with Al2O3 or ZrO 2 were also successfully deposited and evaluated on SiC fibers.

  8. Diamond-coated fiber Bragg grating through the hot filament chemical vapor process for chemical durability improvement.

    PubMed

    Alberto, Nélia; José Kalinowski, Hypolito; Neto, Victor; Nogueira, Rogério

    2017-02-20

    In recent years, the coating of fiber Bragg gratings (FBGs) with a specific material has opened up the possibility to broaden the limits of applicability of this technology. Diamond has a set of properties that makes it an attractive candidate to protect the optical fiber against chemically harsh environments, whose sensing is also a great challenge. One of the most used techniques to obtain these coatings is through the hot filament chemical vapor deposition (HFCVD); in this process, the temperature reaches, typically, around 850°C-900°C. In this work, the regeneration of a seed FBG during its coating with a nanocrystalline diamond thin film through the HFCVD process is presented. Simultaneously, the thermal monitoring of the process was also performed using the same grating. The resistance test in a corrosive medium reveals an improvement on the durability of the sensing properties of the diamond-coated FBG compared with an uncoated FBG, foreseeing a vast range of applications.

  9. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  10. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  11. The use of electrophoretically deposited diamond powder coatings as a precursor for chemically vapor deposited diamond

    SciTech Connect

    Panitz, J.K.G.

    1991-12-31

    It has generally been observed that in order in expedite the formation of chemical vapor deposited (CVD) diamond coatings, it is desirable to prepare a substrate by ``seeding`` it with diamond powder. We have determined that thick, stress free, shaped, diamond powder coatings can be electrophoretically deposited in a relatively short amounts of time. These diamond powder precursor coatings are then densified in a hot filament assisted CVD reactor to produce good quality CVD diamond/diamond powder composites. This combination of deposition techniques avoids many potential problems associated with predominantly CVD diamond.

  12. Textured (100) yttria-stabilized zirconia thin films deposited by plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Holzschuh, H.; Suhr, H.

    1991-07-01

    Thin films of yttria-stabilized zirconia were deposited by plasma-enhanced chemical vapor deposition on quartz Si(100), Si(111), Ni, and the steels V2A and Hastelloy at substrate temperatures (Ts): 673-873 K. The metal beta-diketonates Y (thd)3 and Zr(thd)4 were used as precursors. The fully stabilized fluorite-type cubic structure was obtained over a wide range of yttria contents from 3.5 to 80 mol pct (Ts = 773 K). The quality of the films depended on the match of the thermal expansion coefficients of substrate and deposit.

  13. High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ootera, Yasuaki; Shimada, Takuya; Kado, Masaki; Quinsat, Michael; Morise, Hirofumi; Nakamura, Shiho; Kondo, Tsuyoshi

    2015-11-01

    A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ∼1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ∼105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.

  14. Synthesis and Characterization of Tin(IV) Oxide Obtained by Chemical Vapor Deposition Method

    NASA Astrophysics Data System (ADS)

    Nagirnyak, Svitlana V.; Lutz, Victoriya A.; Dontsova, Tatiana A.; Astrelin, Igor M.

    2016-07-01

    The effect of precursors on the characteristics of tin oxide obtained by chemical vapor deposition (CVD) method was investigated. The synthesis of nanosized tin(IV) oxide was carried out with the use of two different precursors: tin(II) oxalate obtained using tin chloride(II) and oxalic acid; tin(II) oxalate obtained using tin chloride(II); and ammonium oxalate. The synthesized tin(IV) oxide samples were studied by electron microscopy, X-ray diffraction and optical spectra. The lattice parameters of tin(IV) oxide samples were defined, the bandgap of samples were calculated.

  15. Electrochromic Property of MoO3 Thin Films Deposited by Chemical Vapor Transport Synthesis

    NASA Astrophysics Data System (ADS)

    Kim, Dae-Gun; Kim, Se Hoon; Do Kim, Young

    2011-10-01

    The transmittance of electrochromic MoO3 thin films by chemical vapor transport (CVT) deposition and post-annealing on indium tin oxide (ITO) glass reached 80% with low reflectivity. Optical analysis demonstrated a 3.60 eV band gap energy in MoO3 thin film. Transmittance changes of 50% between coloration and decoloration (˜30 and ˜80%) at 533 nm under the bias change frequency revealed reversible electrochromic properties and stability. A coloration efficiency of the annealed MoO3 thin film was 23.7 cm2/C. Coloration responsibility was predominant with reliable performances by bias change.

  16. Double-walled boron nitride nanotubes grown by floating catalyst chemical vapor deposition.

    PubMed

    Kim, Myung Jong; Chatterjee, Shahana; Kim, Seung Min; Stach, Eric A; Bradley, Mark G; Pender, Mark J; Sneddon, Larry G; Maruyama, Benji

    2008-10-01

    One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.

  17. Formation of needlelike crystallites during growth of diamond films by chemical vapor deposition

    SciTech Connect

    Kopylov, P. G.; Obraztsov, A. N. Shvets, P. V.

    2010-07-15

    Diamond polycrystalline films have been grown by chemical vapor deposition from a hydrogenmethane mixture. The phase composition and structure of the films were studied using Raman spectroscopy, electron microscopy, and thermogravimetry. It is found that, upon heating in air, the oxidation of the carbon material forming the films occurs at significantly different temperatures, depending on the degree of its order and the crystallite size. This difference is used for selective oxidation of the least ordered fine-grained component of the films. The material obtained by this selective oxidation of the films consists of diamond crystallites shaped like regular micrometer-sized tetragonal pyramids with a radius of tip curvature of several nanometers.

  18. Boron coating on boron nitride coated nuclear fuels by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Durmazuçar, Hasan H.; Gündüz, Güngör

    2000-12-01

    Uranium dioxide-only and uranium dioxide-gadolinium oxide (5% and 10%) ceramic nuclear fuel pellets which were already coated with boron nitride were coated with thin boron layer by chemical vapor deposition to increase the burn-up efficiency of the fuel during reactor operation. Coating was accomplished from the reaction of boron trichloride with hydrogen at 1250 K in a tube furnace, and then sintering at 1400 and 1525 K. The deposited boron was identified by infrared spectrum. The morphology of the coating was studied by using scanning electron microscope. The plate, grainy and string (fiber)-like boron structures were observed.

  19. Electrical transport properties of microcrystalline silicon grown by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Pinto, Nicola; Ficcadenti, Marco; Morresi, Lorenzo; Murri, Roberto; Ambrosone, Giuseppina; Coscia, Ubaldo

    2004-12-01

    The dark conductivity and Hall mobility of hydrogenated silicon films deposited varying the silane concentration f =SiH4/(SiH4+H2) in a conventional plasma enhanced chemical vapor deposition system have been investigated as a function of temperature, taking into account their structural properties. The electrical properties have been studied in terms of a structural two-phase model. A clear transition from the electrical transport governed by a crystalline phase, in the range 1%⩽f⩽3%, to that controlled by an amorphous phase, for f >3%, has been evidenced. Some metastable effects of the dark conductivity have been noticed.

  20. Characteristics of epitaxial garnets grown by CVD using single metal alloy sources. [Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Besser, P. J.; Hamilton, T. N.; Mee, J. E.; Stermer, R. L.

    1974-01-01

    Single metal alloys have been explored as the cation source in the chemical vapor deposition (CVD) of iron garnets. Growth of good quality single crystal garnet films containing as many as five different cations has been achieved over a wide range of deposition conditions. The relationship of film composition to alloy compositions and deposition conditions has been determined for several materials. By proper choice of the alloy composition and the deposition conditions, uncrazed deposits were grown on (111) gadolinium gallium garnet (GGG) substrates. Data on physical, magnetic and optical properties of representative films is presented and discussed.

  1. Simulation of chemical-vapor-deposited silicon carbide for a cold wall vertical reactor

    NASA Astrophysics Data System (ADS)

    Lee, Y. L.; Sanchez, J. M.

    1997-07-01

    The growth rate of silicon carbide obtained by low-pressure chemical vapor deposition from tetramethylsilane is numerically simulated for a cold wall vertical reactor. The transport equations for momentum, heat, and mass transfer are simultaneously solved by employing the finite volume method. A model for reaction rate is also proposed in order to predict the measured growth rates [A. Figueras, S. Garelik, J. Santiso, R. Rodroguez-Clemente, B. Armas, C. Combescure, R. Berjoan, J.M. Saurel and R. Caplain, Mater. Sci. Eng. B 11 (1992) 83]. Finally, the effects of thermal diffusion on the growth rate are investigated.

  2. Oxygen and hydrogen effects on the chemical vapor deposition of aluminum nitride films

    SciTech Connect

    Aspar, B.; Armas, B.; Combescure, C. ); Figueras, A.; Rodriguez-Clemente, R. ); Mazel, A.; Kihn, Y.; Sevely, J. )

    1993-06-01

    Aluminum nitride has been obtained by chemical vapor deposition using AlCl[sub 3] and NH[sub 3] as precursors. Progressive introduction of N[sub 2]0 in the gas mixture has shown the possibility of inserting oxygen in the AlN lattice. This involves strong changes of surface morphology of the deposit and the formation of less-crystallized materials. When hydrogen is added to the gas mixture, these effects are reduced, Electron energy loss spectroscopy has shown that, in this case, oxygen is mainly concentrated on the external parts of AlN crystals, the structure of which has been found consistent with the wurtzite structure.

  3. Chemical vapor deposition techniques and related methods for manufacturing microminiature thermionic converters

    DOEpatents

    King, Donald B.; Sadwick, Laurence P.; Wernsman, Bernard R.

    2002-06-25

    Methods of manufacturing microminiature thermionic converters (MTCs) having high energy-conversion efficiencies and variable operating temperatures using MEMS manufacturing techniques including chemical vapor deposition. The MTCs made using the methods of the invention incorporate cathode to anode spacing of about 1 micron or less and use cathode and anode materials having work functions ranging from about 1 eV to about 3 eV. The MTCs also exhibit maximum efficiencies of just under 30%, and thousands of the devices can be fabricated at modest costs.

  4. Thermal conductivity of ultra-thin chemical vapor deposited hexagonal boron nitride films

    NASA Astrophysics Data System (ADS)

    Alam, M. T.; Bresnehan, M. S.; Robinson, J. A.; Haque, M. A.

    2014-01-01

    Thermal conductivity of freestanding 10 nm and 20 nm thick chemical vapor deposited hexagonal boron nitride films was measured using both steady state and transient techniques. The measured value for both thicknesses, about 100 ± 10 W m-1 K-1, is lower than the bulk basal plane value (390 W m-1 K-1) due to the imperfections in the specimen microstructure. Impressively, this value is still 100 times higher than conventional dielectrics. Considering scalability and ease of integration, hexagonal boron nitride grown over large area is an excellent candidate for thermal management in two dimensional materials-based nanoelectronics.

  5. Development of chemical vapor composite (CVC) ceramic materials. Status report, April 1995--June 1997

    SciTech Connect

    1997-07-25

    The objective of the 94 DOE Chemical Vapor Composites (CVC) ceramics materials grant is to develop a reliable and flexible process to produce, in a single step, ceramic composites to final shape. This report is a brief summary of activities in the development of the CVC ceramics materials. Equipment has been designed and built to fabricate CVC silicon carbides with fibers such as Nextel, Nicalon, and carbon. Materials and shapes have been fabricated and characterized as to physical and mechanical properties and microstructure. Details will be given in the final report.

  6. Porous tungsten prepared by atmospheric-pressure chemical vapor deposition with WF6 and its characterization

    NASA Astrophysics Data System (ADS)

    Li, Ying; Yu, Xiaodong; Tan, Chengwen; Wang, Fuchi; Ma, Honglei; Yue, Jintao

    2017-05-01

    Porous tungsten (W) is used in aeronautic and aerospace engineering, power electronics field and metallurgical industry. In this study, porous W with 98wt% W was prepared on a carbon foam substrate by atmospheric-pressure chemical vapor deposition (CVD) with tungsten fluoride (WF6) as the precursor. The porous W with 78.1346% porosity displayed a pure α-W phase and the uniform surface. The mode pore diameter of porous W is 208.0 µm. In a compression test, the fracture strength of porous W is 20.3 MPa.

  7. Simulation of catalyst behavior during chemical vapor deposition processing of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Nishi, Kazuki; Inoue, Shuhei; Matsumura, Yukihiko

    2014-06-01

    Nucleation of carbon nanotubes is considered to start with the supersaturation of carbon atoms dissolved in a catalyst. In chemical vapor deposition synthesis, it is believed that condensation of the source gas terminates the growth. However, some experimental studies have suggested that termination is primarily affected by catalyst behavior. We modified the potential functions and observed the behavior of carbon-iron mixed nanoparticles by a molecular dynamics method and found that the iron fraction melted at the equivalent temperature of growth termination. Thus, we concluded that the catalyst fusion prevented nucleation that would normally occur as a consequence of solution supersaturation.

  8. Influence of Alumina Reaction Tube Impurities on the Oxidation of Chemically-Vapor-Deposited Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth

    1995-01-01

    Pure coupons of chemically vapor deposited (CVD) SiC were oxidized for 100 h in dry flowing oxygen at 1300 C. The oxidation kinetics were monitored using thermogravimetry (TGA). The experiments were first performed using high-purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences were attributed to impurities in the alumina tubes. Investigators interested in high-temperature oxidation of silica formers should be aware that high-purity alumina can have significant effects on experiment results.

  9. Microstructure and properties of multiphase and functionally graded materials prepared by chemical vapor deposition

    SciTech Connect

    Lee, W.Y.

    1996-05-01

    The synthesis of multiphase and functionally graded materials by chemical vapor deposition is discussed from a perspective of controlling their composition and microstructure at a nano-scale level, and ultimately, tailoring their material properties. Prior research is briefly reviewed to address the current state of this novel material concept. Recent experimental results relating to controlling the selected properties of two multiphase systems, TiN + MoS{sub 2} and NiAl + Al{sub 2}O{sub 3}, are described to illustrate this concept`s potential merits and challenges for use in realistic applications.

  10. Monolayer graphene growth on Ni(111) by low temperature chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Addou, Rafik; Dahal, Arjun; Sutter, Peter; Batzill, Matthias

    2012-01-01

    In contrast to the commonly employed high temperature chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the bulk, we demonstrate that below 600 °C graphene can be grown in a self-limiting monolayer growth process. Optimum growth is achieved at ˜550 °C. Above this temperature, carbon diffusion into the bulk is limiting the surface growth rate, while at temperatures below ˜500 °C a competing surface carbide phase impedes graphene formation.

  11. Optical properties of silicon nitride films formed by plasma-chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Vlasukova, L. A.; Komarov, F. F.; Parkhomenko, I. N.; Milchanin, O. V.; Leont'ev, A. V.; Mudryi, A. V.; Togambaeva, A. K.

    2013-03-01

    The optical properties and structure of layers of silicon nitride deposited on silicon substrates by plasma-aided chemical vapor deposition at 300°C are studied by ellipsometry, Raman scattering, IR spectroscopy, and photoluminescence techniques. It is found that immediately after deposition the silicon nitride contains hydrogen in the form of Si-H bonds. Annealing (1100°C, 30 min) leads to dehydrogenation and densification of the nitride layer. An intense Si3N4 photoluminescence signal is detected in the green. Immediately after deposition the photoluminescence peak appears at 542 nm and annealing shifts it to shorter wavelengths.

  12. Spectroscopic signatures of AA' and AB stacking of chemical vapor deposited bilayer MoS2

    DOE PAGES

    Xia, Ming; Li, Bo; Yin, Kuibo; ...

    2015-11-04

    We discuss prominent resonance Raman and photoluminescence spectroscopic differences between AA'and AB stacked bilayer molybdenum disulfide (MoS2) grown by chemical vapor deposition are reported. Bilayer MoS2 islands consisting of the two stacking orders were obtained under identical growth conditions. Also, resonance Raman and photoluminescence spectra of AA' and AB stacked bilayer MoS2 were obtained on Au nanopyramid surfaces under strong plasmon resonance. Both resonance Raman and photoluminescence spectra show distinct features indicating clear differences in interlayer interaction between these two phases. The implication of these findings on device applications based on spin and valley degrees of freedom.

  13. Enhancement of field emission of CNTs array by CO2-assisted chemical vapor deposition.

    PubMed

    Wu, Jun; Ma, Yanfeng; Tang, Daiming; Liu, Chang; Huang, Qinwen; Huang, Yi; Cheng, Huiming; Chen, Dapeng; Chen, Yongsheng

    2009-05-01

    We present a new process to get in-situ-growth carbon nanotubes (CNTs) array device with good FE properties by CO2-assisted thermal chemical vapor deposition (CVD). Field Emission measurement shows that introducing CO2 into CNTs growth system leads to a significant enhancement in the emission properties, both the turn-on field and threshold field decrease. Raman, SEM and TEM investigation results showed that in this CO2-assisted thermal CVD, CO2 can remove amorphous carbon during CNTs growth process, and at the same time, it also creates more defects on the CNTs wall. Both can enhance FE properties of the CNTs at suitable CO2 concentrations.

  14. Chemical Vapor Deposition of Phosphorous- and Boron-Doped Graphene Using Phenyl-Containing Molecules.

    PubMed

    Mekan Ovezmyradov; Magedov, Igor V; Frolova, Liliya V; Chandler, Gary; Garcia, Jill; Bethke, Donald; Shaner, Eric A; Kalugin, Nikolai G

    2015-07-01

    Simultaneous chemical vapor deposition (CVD) of graphene and "in-situ" phosphorous or boron doping of graphene was accomplished using Triphenylphosphine (TPP) and 4-Methoxyphenylboronic acid (4-MPBA). The TPP and 4-MPBA molecules were sublimated and supplied along with CH4 molecules during graphene growth at atmospheric pressure. The grown graphene samples were characterized using Raman spectroscopy. Phosphorous and boron presence in phosphorous and boron doped graphene was confirmed with Auger electron spectroscopy. The possibility of obtaining phosphorous and boron doped graphene using solid-source molecule precursors via CVD can lead to an easy and rapid production of modified large area graphene.

  15. Microstructural modification of nc-Si/SiOx films during plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, X. W.

    2005-07-01

    Nanocrystalline-silicon embedded silicon oxide films are prepared by plasma-enhanced chemical vapor deposition (PECVD) at 300 °C without post-heat treatment. Measurements of XPS, IR, XRD, and HREM are performed. Microstructural modifications are found occurring throughout the film deposition. The silica network with a high oxide state is suggested to be formed directly under the abduction of the former deposited layer, rather than processing repeatedly from the original low-oxide state of silica. Nanocrystalline silicon particles with a size of 6-10 nm are embedded in the SiOx film matrix, indicating the potential application in Si-based optoelectronic integrity.

  16. Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kim, Chan-Soo; Youn, Woong-Kyu; Lee, Dong-Kwon; Seol, Kwang-Soo; Hwang, Nong-Moon

    2009-07-01

    The nanocrystalline alpha silicon nitride (α-Si 3N 4) was deposited on a silicon substrate by hot-wire chemical vapor deposition at the substrate temperature of 700 °C under 4 and 40 Torr at the wire temperatures of 1430 and 1730 °C, with a gas mixture of SiH 4 and NH 3. The size and density of crystalline nanoparticles on the substrate increased with increasing wire temperature. With increasing reactor pressure, the crystallinity of α-Si 3N 4 nanoparticles increased, but the deposition rate decreased.

  17. Plasma-enhanced chemical vapor deposition of β-tungsten, a metastable phase

    NASA Astrophysics Data System (ADS)

    Tang, C. C.; Hess, D. W.

    1984-09-01

    Plasma-enhanced chemical vapor deposition of a metastable phase of tungsten ( β-W) is performed using tungsten hexafluoride and hydrogen as source gases. At 350 °C, the as-deposited resistivity of these films is ˜50 μΩ cm. After heat treatments between 650 and 750 °C in forming gas, the resistivity drops below 11 μΩ cm. Concomitant with this resistivity change is a phase change to α-W, the equilibrium, body-centered-cubic form.

  18. Convection and mass-transport in laser-induced chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Patnaik, S.; Brown, R. A.

    1988-01-01

    Gas flow and energy and species transport in laser-induced chemical vapor deposition (LICVD) of amorphous silicon films by silane pyrolysis are analyzed by finite element analysis of a two-dimensional model for the process. Spatial nonuniformity of the deposited film is shown to result from diffusion controlled transport of products between the beam and substrate. Deposition profiles are affected by buoyancy-driven convection only at increased gas pressures. Horizontal orientation of the reactor with respect to gravity is optimal because the stagnation-like flow, that results adjacent to the substrate, enhances mixing, and smoothes the film profile.

  19. Chemically vapor deposited silicon carbide (SiC) for optical applications

    NASA Astrophysics Data System (ADS)

    Pickering, Michael A.; Taylor, Raymond L.; Keeley, Joseph T.; Graves, George A.

    1989-10-01

    Important physical, optical, thermal, and mechanical properties of cubic (beta) silicon carbide produced via a bulk chemical vapor deposition (CVD) process, developed at CVD Incorporated, are presented in this paper. The material's properties make it an ideal candidate material for optical components for lidar mirrors, solar collectors and concentrators, and astronomical telescopes. The CVD process has been scaled to produce large monolithic pieces of bulk SiC, i.e., disks up to 60-cm (24-in.) diameter and plates up to 76-cm (30-in.) long by 46-cm (18-in.) wide with thickness up to 13 mm (0.5 in.).

  20. Current Rectification by As-Grown Chemical Vapor Deposited Single-Walled Carbon Nanotubes

    DTIC Science & Technology

    2008-08-01

    Prescribed by ANSI Std Z39-18 Current Rectification by As-Grown Chemical Vapor Deposited Single- Walled Carbon Nanotubes Govind Mallick1*, Mark Griep1,2...nanowelding,” J. Nanoparticle Res., v. 5, pp. 395-400, 2003. [3] P. G. Collins, A. Zettl, H. Bando, A. Thess, and R . E. Smalley, “Nanotube Nanodevice...Science, v. 278, pp. 100-103, 1997. [4] B. C. Satishkumar, P. J. Thomas, A. Govindraj, and C. N. R . Rao, “Y-Junction Carbon Nanotubes,” Appl. Phys

  1. Low temperature deposition of inorganic films by excimer laser assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kuk, Seungkuk; Park, Jongmin; Zhang, Tao; Hwang, David J.

    2017-02-01

    In this study, silicon nitride film is deposited by laser assisted chemical vapor deposition technique based on the direct photolysis of SiH4/NH3 gas mixture using argon fluoride excimer laser of 193 nm wavelength at low substrate temperature around 100°C. By illuminating laser beam in parallel to sample surface, sample damage or heating can be avoided allowing compatibility of temperature sensitive device architectures. A wide range of processing parameters for laser and reactant gases are examined in correlation with deposition mechanisms.

  2. Synthesize of N-doped Carbon nanotube according to gas flow rate by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kim, J. B.; Kim, C. D.; Kong, S. J.; Kim, J. H.; Min, B. K.; Jung, W. S.; Lee, H. R.

    2011-12-01

    Nitrogen-doped (N-doped) Carbon nanotubes (CNTs) have been prepared by Thermal Chemical Vapor Deposition (CVD). As doping accompanies with the recombination of carbon atoms into CNTs in the CVD process, N atoms can be substitutionally doped into the CNTs lattice, which is hard to realize by other synthetic methods. The synthesis technique and the characteristic analysis of N-doped CNT will move up the industrialization and the basic study of CNT. We will elucidate the basic properties of CNT such as the structural characteristics of the N-doped CNT material and study for the industrial application of the N-doped CNTs to the electrode of fuel cell.

  3. Ultrathin SnSe2 Flakes Grown by Chemical Vapor Deposition for High-Performance Photodetectors.

    PubMed

    Zhou, Xing; Gan, Lin; Tian, Wenming; Zhang, Qi; Jin, Shengye; Li, Huiqiao; Bando, Yoshio; Golberg, Dmitri; Zhai, Tianyou

    2015-12-22

    High-quality ultrathin single-crystalline SnSe2 flakes are synthesized under atmospheric-pressure chemical vapor deposition for the first time. A high-performance photodetector based on the individual SnSe2 flake demonstrates a high photoresponsivity of 1.1 × 10(3) A W(-1), a high EQE of 2.61 × 10(5)%, and superb detectivity of 1.01 × 10(10) Jones, combined with fast rise and decay times of 14.5 and 8.1 ms, respectively.

  4. Method of making AlInSb by metal-organic chemical vapor deposition

    DOEpatents

    Biefeld, Robert M.; Allerman, Andrew A.; Baucom, Kevin C.

    2000-01-01

    A method for producing aluminum-indium-antimony materials by metal-organic chemical vapor deposition (MOCVD). This invention provides a method of producing Al.sub.X In.sub.1-x Sb crystalline materials by MOCVD wherein an Al source material, an In source material and an Sb source material are supplied as a gas to a heated substrate in a chamber, said Al source material, In source material, and Sb source material decomposing at least partially below 525.degree. C. to produce Al.sub.x In.sub.1-x Sb crystalline materials wherein x is greater than 0.002 and less than one.

  5. Growth mechanism of carbon nanotubes grown by microwave plasma-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Muneyoshi, T.; Okai, M.; Yaguchi, T.; Sasaki, S.

    2001-10-01

    To investigate the most suitable deposition conditions and growth mechanism, we grew carbon nanotubes (CNTs) by microwave plasma-assisted chemical vapor deposition under various conditions. The experimental parameters we varied were (a) the mixture ratio of methane in hydrogen, (b) the total gas pressure, and (c) the bias electric current. We found that the bias electric current was the most influential parameter in determining the shape of CNTs. We believe that the growth process of CNTs can be explained by using the solid solubility curves of metal-carbon phase diagrams. Selective growth and low-temperature growth of CNTs can also be understood from these phase diagrams.

  6. Structure of carbon nanotubes grown by microwave-plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Okai, M.; Muneyoshi, T.; Yaguchi, T.; Sasaki, S.

    2000-11-01

    Carbon nanotubes grown on a Ni substrate and an Fe-Ni-Cr alloy substrate by plasma-enhanced chemical vapor deposition were investigated by transmission electron microscope (TEM) and energy dispersive x-ray (EDX) analysis. TEM showed that the nanotubes on both substrates have a piled-cone structure with metal particles on top which determine the diameter of the nanotubes. Their diameter ranges from 60 to 80 nm. Moreover, EDX showed that the metal particles are composed of Ni when the nanotubes are grown on Ni substrate and of Fe and Ni in the case of the Fe-Ni-Cr alloy substrate.

  7. MgB2 ultrathin films fabricated by hybrid physical chemical vapor deposition and ion milling

    NASA Astrophysics Data System (ADS)

    Acharya, Narendra; Wolak, Matthäus A.; Tan, Teng; Lee, Namhoon; Lang, Andrew C.; Taheri, Mitra; Cunnane, Dan; Karasik, Boris. S.; Xi, X. X.

    2016-08-01

    In this letter, we report on the structural and transport measurements of ultrathin MgB2 films grown by hybrid physical-chemical vapor deposition followed by low incident angle Ar ion milling. The ultrathin films as thin as 1.8 nm, or 6 unit cells, exhibit excellent superconducting properties such as high critical temperature (Tc) and high critical current density (Jc). The results show the great potential of these ultrathin films for superconducting devices and present a possibility to explore superconductivity in MgB2 at the 2D limit.

  8. The fabrication of ReS2 flowers at controlled locations by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Wang, Jianyu; Lu, Yan; Zhang, Sihong; Liu, Xiaoshuo; Hou, Weiwei; Wang, Zhendong; Wang, Li

    2017-05-01

    Here we report a metal induced nucleation to realize the growth of ReS2 flowers at controlled locations. The ordered arrays of ReS2 flowers have been successfully prepared on SiO2/Si substrate using Pt metal dots as nucleation sites and S, NH4ReO4 powders as precursors by a chemical vapor depostion method. The NH4ReO4 powders are used as the rhenium sources. The ReS2 flowers are grown above the pre-patterned Pt dots, Raman and transmission electron microscopy measurements indicated that the prepared ReS2 flowers have excellent crystalline quality.

  9. Nanoimprint mold fabrication and replication by room-temperature conformal chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Murphy, Patrick F.; Morton, Keith J.; Fu, Zengli; Chou, Stephen Y.

    2007-05-01

    The authors present a technique for the replication of molds for nanoimprint lithography (NIL) without solvents or etching. A thin hard amorphous silicon film is deposited onto imprinted or self-assembled polymer nanostructures by room-temperature conformal plasma-enhanced chemical vapor deposition. After attachment to another substrate and separation from the polymer original, the thin hard film forms a NIL mold that is the inverse of the polymer original. Using this technology, the authors demonstrate the replication of a 200nm pitch grating mold and sub-50-nm features over wafer-scale areas without introducing additional line edge roughness associated with conventional replication methods.

  10. Chemical vapor deposition of methane for single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kong, Jing; Cassell, Alan M.; Dai, Hongjie

    1998-08-01

    We report the synthesis of high-quality single-walled carbon nanotubes (SWNT) by chemical vapor deposition (CVD) of methane at 1000°C on supported Fe 2O 3 catalysts. The type of catalyst support is found to control the formation of individual or bundled SWNTs. Catalysts supported on crystalline alumina nanoparticles produce abundant individual SWNTs and small bundles. Catalysts supported by amorphous silica particles produce only SWNT bundles. Studies of the ends of SWNTs lead to an understanding of their growth mechanism. Also, we present the results of methane CVD on supported NiO, CoO and NiO/CoO catalysts.

  11. Formation of Iron Carbide Nanorod by Pulsed Plasma Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Yooyen, S.; Kawamura, T.; Kotake, S.; Suzuki, Y.

    2010-11-01

    Iron carbide nanorods were produced on the surface of pure iron sheet by means of pulsed plasma chemical vapor deposition. Hydrogen plasma was used in the initial state, varied from 10 to 60 minute, for the purpose of cleaning and preparing nanoparticles. The formation was done under methane atmosphere, varied from 2 to 30 minute. X-ray diffraction (XRD) patterns analysis showed that iron carbide was found on all of these experiment conditions. By field emission scanning electron micro spectroscopy (FESEM) observation, iron carbide nanorods, however, were found neatly only on the methane plasma treating at 10 minute.

  12. Characteristics of epitaxial garnets grown by CVD using single metal alloy sources. [Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Besser, P. J.; Hamilton, T. N.; Mee, J. E.; Stermer, R. L.

    1974-01-01

    Single metal alloys have been explored as the cation source in the chemical vapor deposition (CVD) of iron garnets. Growth of good quality single crystal garnet films containing as many as five different cations has been achieved over a wide range of deposition conditions. The relationship of film composition to alloy compositions and deposition conditions has been determined for several materials. By proper choice of the alloy composition and the deposition conditions, uncrazed deposits were grown on (111) gadolinium gallium garnet (GGG) substrates. Data on physical, magnetic and optical properties of representative films is presented and discussed.

  13. Tunneling characteristics in chemical vapor deposited graphene–hexagonal boron nitride–graphene junctions

    SciTech Connect

    Roy, T.; Hesabi, Z. R.; Joiner, C. A.; Vogel, E. M.; Liu, L.; Gu, G.; Barrera, S. de la; Feenstra, R. M.; Chakrabarti, B.

    2014-03-24

    Large area chemical vapor deposited graphene and hexagonal boron nitride was used to fabricate graphene–hexagonal boron nitride–graphene symmetric field effect transistors. Gate control of the tunneling characteristics is observed similar to previously reported results for exfoliated graphene–hexagonal boron nitride–graphene devices. Density-of-states features are observed in the tunneling characteristics of the devices, although without large resonant peaks that would arise from lateral momentum conservation. The lack of distinct resonant behavior is attributed to disorder in the devices, and a possible source of the disorder is discussed.

  14. Synthesis and Characterization of Tin(IV) Oxide Obtained by Chemical Vapor Deposition Method.

    PubMed

    Nagirnyak, Svitlana V; Lutz, Victoriya A; Dontsova, Tatiana A; Astrelin, Igor M

    2016-12-01

    The effect of precursors on the characteristics of tin oxide obtained by chemical vapor deposition (CVD) method was investigated. The synthesis of nanosized tin(IV) oxide was carried out with the use of two different precursors: tin(II) oxalate obtained using tin chloride(II) and oxalic acid; tin(II) oxalate obtained using tin chloride(II); and ammonium oxalate. The synthesized tin(IV) oxide samples were studied by electron microscopy, X-ray diffraction and optical spectra. The lattice parameters of tin(IV) oxide samples were defined, the bandgap of samples were calculated.

  15. Chemical vapor deposition of Ti-Si-N films for diffusion barrier applications

    SciTech Connect

    Smith, P.M.; Custer, J.S.; Jones, R.V.

    1995-11-01

    Structurally disordered refractory ternary films such as titanium silicon nitride (Ti-Si-N) have potential as advanced diffusion barriers in future ULSI metallization schemes. The authors demonstrate chemical vapor deposition (CVD) of Ti-Si-N-containing films in a commercially available single-wafer CVD system using two different Ti precursors, TiCl{sub 4} and tetrakis(diethylamino)titanium (TDEAT). In particular, the TDEAT-based films can be grown conformally with low impurity content, and are promising candidates for advanced diffusion barrier applications.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  17. Fabrication of AIN Nano-Structures Using Polarity Control by High Temperature Metalorganic Chemical Vapor Deposition.

    PubMed

    Eom, Daeyong; Kim, Jinwan; Lee, Kyungjae; Jeon, Minhwan; Heo, Cheon; Pyeon, Jaedo; Nam, Okhyun

    2015-07-01

    This study investigates the crystallographic polarity transition of AIN layers grown by high temperature metalorganic chemical vapor deposition (HT-MOCVD), with varying trimethylaluminum (TMAI) pre-flow rates. AIN layers grown without TMAI pre-flow had a mixed polarity, consisting of Al- and N-polarity, and exhibited a rough surface. With an increasing rate of TMAI pre-flow, the AIN layer was changed to an Al-polarity, with a smooth surface morphology. Finally, AIN nano-pillars and nano-rods of Al-polarity were fabricated by etching a mixed polarity AIN layer using an aqueous KOH solution.

  18. Fabrication of highly ultramicroporous carbon nanofoams by SF6-catalyzed laser-induced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hattori, Yoshiyuki; Shuhara, Ai; Kondo, Atsushi; Utsumi, Shigenori; Tanaka, Hideki; Ohba, Tomonori; Kanoh, Hirofumi; Takahashi, Kunimitsu; Vallejos-Burgos, Fernando; Kaneko, Katsumi

    2016-05-01

    We have developed a laser-induced chemical vapor deposition (LCVD) method for preparing nanocarbons with the aid of SF6. This method would offer advantages for the production of aggregates of nanoscale foams (nanofoams) at high rates. Pyrolysis of the as-grown nanofoams induced the high surface area (1120 m2 g-1) and significantly enhanced the adsorption of supercritical H2 (16.6 mg g-1 at 77 K and 0.1 MPa). We also showed that the pyrolized nanofoams have highly ultramicroporous structures. The pyrolized nanofoams would be superior to highly microporous nanocarbons for the adsorption of supercritical gases.

  19. Metal organic chemical vapor deposition of phase change Ge1Sb2Te4 nanowires.

    PubMed

    Longo, Massimo; Fallica, Roberto; Wiemer, Claudia; Salicio, Olivier; Fanciulli, Marco; Rotunno, Enzo; Lazzarini, Laura

    2012-03-14

    The self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V.

  20. Fabrication of graphene with CuO islands by chemical vapor deposition.

    PubMed

    Qi, Yun; Eskelsen, Jeremy R; Mazur, Ursula; Hipps, K W

    2012-02-21

    Graphene prepared on Cu foil by chemical vapor deposition was studied as a function of post growth cooling conditions. CuO islands embedded in the graphene film were discovered and studied by scanning electron microscopy, atomic force microscopy, and X-ray photoemission spectroscopy. It is shown that nanostructured holes can be formed within a graphene film by reduction using hydrogen cooling immediately after film growth. We also observe the formation of symmetrical oxide islands in these holes. This study provides an easy way to fabricate a graphene + CuO composite, and the method may be extended to other graphene based structures.

  1. Self-assembled patterns of iron oxide nanoparticles by hydrothermal chemical-vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengjun; Wei, B. Q.; Ajayan, P. M.

    2001-12-01

    Here, we report a hydrothermal chemical-vapor deposition process, which produces self-assembled patterns of iron oxide nanoparticles. By exposing a planar silica substrate to a prevaporized mixture of water, ferrocene [Fe(C5H5)2] and xylene (C8H10), at temperatures of ˜1000 °C, Fe2O3 nanoparticles are deposited on the substrate surface, in regular circular patterns. The particle sizes are less than 100 nm, and are organized into submicron-size patterns. The same process without water produces arrays of carbon nanotubes catalyzed by iron nanoparticles that are formed by the decomposition of ferrocene molecules.

  2. Development of a polysilicon process based on chemical vapor deposition, phase 1

    NASA Technical Reports Server (NTRS)

    Plahutnik, F.; Arvidson, A.; Sawyer, D.

    1982-01-01

    The goal of this program is to demonstrate that a dichlorosilane-based reductive chemical vapor deposition (CVD) process is capable of producing, at low cost, high quality polycrystalline silicon. Physical form and purity of this material will be consistent with LSA material requirements for use in the manufacture of high efficiency solar cells. Four polysilicon deposition runs were completed in an intermediate size reactor using dichlorosilane fed from 250 pound cylinders. Results from the intermediate size reactor are consistent with those obtained earlier with a small experimental reactor. Modifications of two intermediate size reactors were completed to interface with the dichlorosilane process demonstration unit (PDU).

  3. Aromatic chemicals by iron-catalyzed hydrotreatment of lignin pyrolysis vapor.

    PubMed

    Olcese, Roberto Nicolas; Lardier, George; Bettahar, Mohammed; Ghanbaja, Jaafar; Fontana, Sébastien; Carré, Vincent; Aubriet, Frédéric; Petitjean, Dominique; Dufour, Anthony

    2013-08-01

    Lignin is a potential renewable material for the production of bio-sourced aromatic chemicals. We present the first hydrotreatment of lignin pyrolysis vapors, before any condensation, using inexpensive and sustainable iron-silica (Fe/SiO2 ) and iron-activated carbon (Fe/AC) catalysts. Lignin pyrolysis was conducted in a tubular reactor and vapors were injected in a fixed bed of catalysts (673 K, 1 bar) with stacks to investigate the profile of coke deposit. More than 170 GC-analyzable compounds were identified by GCxGC (heart cutting)/flame ionization detector mass spectrometry. Lignin oligomers were analyzed by very high resolution mass spectrometry, called the "petroleomic" method. They are trapped by the catalytic fixed bed and, in particular, by the AC. The catalysts showed a good selectivity for the hydrodeoxygenation of real lignin vapors to benzene, toluene, xylenes, phenol, cresols, and alkyl phenols. The spent catalysts were characterized by temperature-programmed oxidation, transmission electron microscopy (TEM), and N2 sorption. Micropores in the Fe/AC catalyst are completely plugged by coke deposits, whereas the mesoporous structure of Fe/SiO2 is unaffected. TEM images reveal two different types of coke deposit: 1) catalytic coke deposited in the vicinity of iron particles and 2) thermal coke (carbonaceous particles ≈1 μm in diameter) formed from the gas-phase growth of lignin oligomers.

  4. Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koh; Yamaoka, Yuya; Ubukata, Akinori; Arimura, Tadanobu; Piao, Guanxi; Yano, Yoshiki; Tokunaga, Hiroki; Tabuchi, Toshiya

    2016-05-01

    The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm-3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm-3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

  5. Highly scalable, atomically thin WSe2 grown via metal-organic chemical vapor deposition.

    PubMed

    Eichfeld, Sarah M; Hossain, Lorraine; Lin, Yu-Chuan; Piasecki, Aleksander F; Kupp, Benjamin; Birdwell, A Glen; Burke, Robert A; Lu, Ning; Peng, Xin; Li, Jie; Azcatl, Angelica; McDonnell, Stephen; Wallace, Robert M; Kim, Moon J; Mayer, Theresa S; Redwing, Joan M; Robinson, Joshua A

    2015-02-24

    Tungsten diselenide (WSe2) is a two-dimensional material that is of interest for next-generation electronic and optoelectronic devices due to its direct bandgap of 1.65 eV in the monolayer form and excellent transport properties. However, technologies based on this 2D material cannot be realized without a scalable synthesis process. Here, we demonstrate the first scalable synthesis of large-area, mono and few-layer WSe2 via metal-organic chemical vapor deposition using tungsten hexacarbonyl (W(CO)6) and dimethylselenium ((CH3)2Se). In addition to being intrinsically scalable, this technique allows for the precise control of the vapor-phase chemistry, which is unobtainable using more traditional oxide vaporization routes. We show that temperature, pressure, Se:W ratio, and substrate choice have a strong impact on the ensuing atomic layer structure, with optimized conditions yielding >8 μm size domains. Raman spectroscopy, atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) confirm crystalline monoto-multilayer WSe2 is achievable. Finally, TEM and vertical current/voltage transport provide evidence that a pristine van der Waals gap exists in WSe2/graphene heterostructures.

  6. A mathematical model and simulation results of plasma enhanced chemical vapor deposition of silicon nitride films

    NASA Astrophysics Data System (ADS)

    Konakov, S. A.; Krzhizhanovskaya, V. V.

    2015-01-01

    We developed a mathematical model of Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon nitride thin films from SiH4-NH3-N2-Ar mixture, an important application in modern materials science. Our multiphysics model describes gas dynamics, chemical physics, plasma physics and electrodynamics. The PECVD technology is inherently multiscale, from macroscale processes in the chemical reactor to atomic-scale surface chemistry. Our macroscale model is based on Navier-Stokes equations for a transient laminar flow of a compressible chemically reacting gas mixture, together with the mass transfer and energy balance equations, Poisson equation for electric potential, electrons and ions balance equations. The chemical kinetics model includes 24 species and 58 reactions: 37 in the gas phase and 21 on the surface. A deposition model consists of three stages: adsorption to the surface, diffusion along the surface and embedding of products into the substrate. A new model has been validated on experimental results obtained with the "Plasmalab System 100" reactor. We present the mathematical model and simulation results investigating the influence of flow rate and source gas proportion on silicon nitride film growth rate and chemical composition.

  7. Microstructure-property relationships of chemically vapor deposited zirconia fiber coating for environmentally durable silicon carbide/silicon carbide composites

    NASA Astrophysics Data System (ADS)

    Li, Hao

    In SiC/SiC ceramic matrix composites, toughness is obtained by adding a fiber coating, which provides a weak interface for crack deflection and debonding between the fiber and the matrix. However, the most commonly used fiber coatings, carbon and boron nitride, are unstable in oxidative environments. In the present study, the feasibility of using a chemically vapor deposited zirconia (CVD-ZrO2) fiber coating as an oxidation-resistant interphase for SiC/SiC composites was investigated. A study of morphological evolution in the CVD-ZrO2 coating suggested that a size-controlled displacive phase transformation from tetragonal ZrO2 ( t-ZrO2) to monoclinic ZrO2 (m-ZrO 2) was the key mechanism responsible for the weak interface behavior exhibited by the ZrO2 coating. It appeared that a low oxygen partial pressure in the CVD reactor chamber was essential for the nucleation of t-ZrO2 and therefore was responsible for the delamination behavior. With this understanding of the weak interface mechanism, minicomposite specimens containing various ZrO2 fiber coating morphologies were fabricated and tested. A fractographic analysis showed that in-situ fiber strength and minicomposite failure loads were strongly dependent on the phase contents and microstructure of the ZrO2 coating. We determined that an optimum microstructure of the ZrO2 coating should contain a predelaminated interface surrounded by a dense outer layer. The outer layer was needed to protect the fiber from degradation during the subsequent SiC matrix infiltration procedure. A preliminary tensile stress-rupture study indicated that the ZrO2 coating exhibited promising performance in terms of providing the weak interface behavior and maintaining the thermal and oxidative stability at elevated temperatures.

  8. Chemical sensing of copper phthalocyanine sol-gel glass through organic vapors

    SciTech Connect

    Ridhi, R.; Gawri, Isha; Abbas, Saeed J.; Saini, G. S. S.; Tripathi, S. K.

    2015-05-15

    The sensitivities of metallophthalocyanine to vapor phase electron donors has gained significance in many areas and disciplines due to their sensing properties and ease of operation. In the present study the interaction mechanism of organic vapors in Copper Phthalocyanine (CuPc) sol-gel glass has been studied. The interaction mechanism is affected by many factors like morphology, electrical or optical properties of film. CuPc sol-gel glass has been synthesized using chemical route sol-gel method. Its structural characterization was conducted using XRD and the amorphous nature of the silicate glass was observed with characteristic α polymorph phase of CuPc at around 6.64° with 13.30Å interplanar spacing. The size of the particle as determined using Debbye Scherre’s formula comes out around 15.5 nm. The presence of α phase of CuPc was confirmed using FTIR with the appearance of crystal parameter marker band at 787 cm-1. Apart from this A2u and Eu symmetry bands of CuPc have also been observed. The UV absorption spectrum of CuPc exhibits absorption peaks owing to π→ π* and n→ π* transitions. A blue shift in the prepared CuPc glass has been observed as compared to the dopant CuPc salt indicating increase of band gap. A split in B (Soret) band and Q band appears as observed with the help of Lorentzian fitting. CuPc sol gel glass has been exposed with chemical vapors of Methanol, Benzene and Bromine individually and the electrical measurements have been carried out. These measurements show the variation in conductivity and the interaction mechanism has been analyzed.

  9. Reactivity of monolayer chemical vapor deposited graphene imperfections studied using scanning electrochemical microscopy.

    PubMed

    Tan, Cen; Rodríguez-López, Joaquín; Parks, Joshua J; Ritzert, Nicole L; Ralph, Daniel C; Abruña, Héctor D

    2012-04-24

    Imperfections that disrupt the sp(2) conjugation of graphene can alter its electrical, chemical, and mechanical properties. Here we report on the examination of monolayer chemical vapor deposited graphene imperfections using scanning electrochemical microscopy in the feedback mode. It was found that the sites with a large concentration of defects are approximately 1 order of magnitude more reactive, compared to more pristine graphene surfaces, toward electrochemical reactions. Furthermore, we successfully passivated the activity of graphene defects by carefully controlling the electropolymerization conditions of o-phenylenediamine. With further electropolymerization, a thin film of the polymer was formed, and it was found to be insulating in nature toward heterogeneous electron transfer processes. The use of spatially resolved scanning electrochemical microscopy for detecting the presence and the "healing" of defects on graphene provides a strategy for in situ characterization and control of this attractive surface, enabling optimization of its properties for application in electronics, sensing, and electrocatalysis.

  10. Temperature dependence of chemical-vapor deposition of pure boron layers from diborane

    NASA Astrophysics Data System (ADS)

    Mohammadi, V.; de Boer, W. B.; Nanver, L. K.

    2012-09-01

    Surface reaction mechanisms are investigated to determine the activation energies of pure boron (PureB) layer deposition at temperatures from 350 °C to 850 °C when using chemical-vapor deposition from diborane in a commercial Si/SiGe epitaxial reactor with either hydrogen or nitrogen as carrier gas. Three distinguishable regions are identified to be related to the dominance of specific chemical reaction mechanisms. Activation energies in H2 are found to be 28 kcal/mol below 400 °C and 6.5 kcal/mol from 400 °C to 700 °C. In N2, the value decreases to 2.1 kcal/mol for all temperatures below 700 °C. The rate of hydrogen desorption is decisive for this behavior.

  11. Nanowatt chemical vapor detection with a self-sensing, piezoelectric microcantilever array

    NASA Astrophysics Data System (ADS)

    Adams, J. D.; Parrott, G.; Bauer, C.; Sant, T.; Manning, L.; Jones, M.; Rogers, B.; McCorkle, D.; Ferrell, T. L.

    2003-10-01

    The portability, compactness, price, and deployment of sensing systems are determined in large part by the power consumption and simplicity of the sensing platform used. We demonstrate a microcantilever chemical detection platform based on an array of piezoelectric microcantilevers. The sensor-element array power consumption, including actuation, is measured in nanowatts, with impedance of the order of megohms. This is four to five orders of magnitude lower power dissipation than current cantilever chemical detection platforms using optical or piezoresistive detection. The sensor is further characterized in the picowatt regime. The platform comprises three cantilevers wired in series, where variations in the resonant frequency and quality factor of selectively coated cantilevers, during successive impedance measurements, enable detection of ethanol vapor.

  12. Simultaneous Chemical and Optical Patterning of Polyacrylonitrile Film by Vapor-Based Reaction.

    PubMed

    Shin, Jae-Won; Lee, Choonghyeon; Cha, Sang-Ho; Jang, Jyongsik; Lee, Kyung Jin

    2015-06-01

    The surface of polyacrylonitrile (PAN) film is treated with ethyleneamines (EDA) in a simple chemical vapor phase reaction. Successful introduction of amine functional groups on the cyano group of PAN backbone is verified by FT-IR and NMR measurements. Further UV-vis and photoluminescence analyses show a red shift of the emission peak after repeated EDA treatment, which might be attributed to the formation of imine conjugation from newly formed carbon-nitrogen bonds on the PAN backbone. Further confocal laser scanning microscopy reveals that selective patterning of EDA on PAN films is possible via local polydimethylsiloxane masking. The results indicate that both chemical and optical patterning on PAN film can be realized via a single reaction and show the potential of this novel methodology in selective patterning. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Fabrication of ultrathin and highly uniform silicon on insulator by numerically controlled plasma chemical vaporization machining.

    PubMed

    Sano, Yasuhisa; Yamamura, Kazuya; Mimura, Hidekazu; Yamauchi, Kazuto; Mori, Yuzo

    2007-08-01

    Metal-oxide semiconductor field-effect transistors fabricated on a silicon-on-insulator (SOI) wafer operate faster and at a lower power than those fabricated on a bulk silicon wafer. Scaling down, which improves their performances, demands thinner SOI wafers. In this article, improvement on the thinning of SOI wafers by numerically controlled plasma chemical vaporization machining (PCVM) is described. PCVM is a gas-phase chemical etching method in which reactive species generated in atmospheric-pressure plasma are used. Some factors affecting uniformity are investigated and methods for improvements are presented. As a result of thinning a commercial 8 in. SOI wafer, the initial SOI layer thickness of 97.5+/-4.7 nm was successfully thinned and made uniform at 7.5+/-1.5 nm.

  14. Nucleation Chemical Physics: From Vapor Phase Clusters to Crystals in Solution

    SciTech Connect

    Kathmann, Shawn M.

    2007-08-03

    Both vapor-phase clusters and condensed-phase crystals are important in a wide variety of fundamental and applied problems in chemical physics. Favorable fluctuations in a supersaturated phase generate clusters of the new phase – exactly how one defines these new clusters as distinct from the mother phase represents a continuing challenge in molecular theories of nucleation. These incipient clusters can form homogeneously within the mother phase or heterogeneously on seeds, dust, impurities, ions, or others stability-inducing atomic/molecular structures (e.g., steps, edges, vacancies, etc.). Upon reaching a critical size the clusters may grow to macroscopic dimensions if enough nucleating material is present in surrounding environment or until relaxation processes dominate bringing the phase transformation to completion. This work was supported by the Chemical and Material Sciences Division, Office of Basic Energy Sciences, Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  15. Patterned growth of carbon nanotubes obtained by high density plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Mousinho, A. P.; Mansano, R. D.

    2015-03-01

    Patterned growth of carbon nanotubes by chemical vapor deposition represents an assembly approach to place and orient nanotubes at a stage as early as when they are synthesized. In this work, the carbon nanotubes were obtained at room temperature by High Density Plasmas Chemical Vapor Deposition (HDPCVD) system. This CVD system uses a new concept of plasma generation, where a planar coil coupled to an RF system for plasma generation was used with an electrostatic shield for plasma densification. In this mode, high density plasmas are obtained. We also report the patterned growth of carbon nanotubes on full 4-in Si wafers, using pure methane plasmas and iron as precursor material (seed). Photolithography processes were used to pattern the regions on the silicon wafers. The carbon nanotubes were characterized by micro-Raman spectroscopy, the spectra showed very single-walled carbon nanotubes axial vibration modes around 1590 cm-1 and radial breathing modes (RBM) around 120-400 cm-1, confirming that high quality of the carbon nanotubes obtained in this work. The carbon nanotubes were analyzed by atomic force microscopy and scanning electron microscopy too. The results showed that is possible obtain high-aligned carbon nanotubes with patterned growth on a silicon wafer with high reproducibility and control.

  16. Opening of triangular hole in triangular-shaped chemical vapor deposited hexagonal boron nitride crystal

    PubMed Central

    Sharma, Subash; Kalita, Golap; Vishwakarma, Riteshkumar; Zulkifli, Zurita; Tanemura, Masaki

    2015-01-01

    In-plane heterostructure of monolayer hexagonal boron nitride (h-BN) and graphene is of great interest for its tunable bandgap and other unique properties. Here, we reveal a H2-induced etching process to introduce triangular hole in triangular-shaped chemical vapor deposited individual h-BN crystal. In this study, we synthesized regular triangular-shaped h-BN crystals with the sizes around 2-10 μm on Cu foil by chemical vapor deposition (CVD). The etching behavior of individual h-BN crystal was investigated by annealing at different temperature in an H2:Ar atmosphere. Annealing at 900 °C, etching of h-BN was observed from crystal edges with no visible etching at the center of individual crystals. While, annealing at a temperature ≥950 °C, highly anisotropic etching was observed, where the etched areas were equilateral triangle-shaped with same orientation as that of original h-BN crystal. The etching process and well-defined triangular hole formation can be significant platform to fabricate planar heterostructure with graphene or other two-dimensional (2D) materials. PMID:25994455

  17. Synthesis of silicon nanowires using tin catalyst by hot wire chemical vapor processing

    SciTech Connect

    Meshram, Nagsen; Kumbhar, Alka; Dusane, R.O.

    2013-06-01

    Highlights: ► Silicon nanowires are grown by hot wire chemical vapor processing at 400 °C using Sn as catalyst material via VLS. ► For nanowire synthesis Sn nanotemplates are formed with hot wire generated atomic hydrogen. ► The TEM image reveals the crystalline nature of nanowire. - Abstract: Silicon nanowires (SiNWs) have been synthesized at temperatures in the range 300–400 °C by the hot wire chemical vapor processing (HWCVP) using tin nanotemplate. The tin nano-template is formed by hot wire atomic hydrogen treatment of thermally evaporated Sn films (∼300 nm thick) on glass substrates. Silicon nanowires are then grown using hot wire induced dissociation of SiH{sub 4} gas over the nanotemplate. Growth conditions like growth time and temperature were varied to study their effect on the tin nanoparticle size and on the silicon nanowire dimensions thereafter. From the observations, it is clear that the nanowire diameters and lengths depend on the size of nanoparticles and the growth time respectively. Though SiNWs were observed to grow at temperatures as low as 300 °C, nanowires with a narrow diameter distribution were achieved at 400 °C. Raman spectra and transmission electron microscope (TEM) reveal the crystalline nature of the silicon nanowires.

  18. Large improvement of phosphorus incorporation efficiency in n-type chemical vapor deposition of diamond

    SciTech Connect

    Ohtani, Ryota; Yamamoto, Takashi; Janssens, Stoffel D.; Yamasaki, Satoshi

    2014-12-08

    Microwave plasma enhanced chemical vapor deposition is a promising way to generate n-type, e.g., phosphorus-doped, diamond layers for the fabrication of electronic components, which can operate at extreme conditions. However, a deeper understanding of the doping process is lacking and low phosphorus incorporation efficiencies are generally observed. In this work, it is shown that systematically changing the internal design of a non-commercial chemical vapor deposition chamber, used to grow diamond layers, leads to a large increase of the phosphorus doping efficiency in diamond, produced in this device, without compromising its electronic properties. Compared to the initial reactor design, the doping efficiency is about 100 times higher, reaching 10%, and for a very broad doping range, the doping efficiency remains highly constant. It is hypothesized that redesigning the deposition chamber generates a higher flow of active phosphorus species towards the substrate, thereby increasing phosphorus incorporation in diamond and reducing deposition of phosphorus species at reactor walls, which additionally reduces undesirable memory effects.

  19. Development of Single Crystal Chemical Vapor Deposition Diamonds for Detector Applications

    SciTech Connect

    Kagan, Harris; Kass, Richard; Gan, K. K.

    2014-01-23

    With the LHC upgrades in 2013, and further LHC upgrades scheduled in 2018, most LHC experiments are planning for detector upgrades which require more radiation hard technologies than presently available. At present all LHC experiments now have some form of diamond detector. As a result Chemical Vapor Deposition (CVD) diamond has now been used extensively in beam conditions monitors as the innermost detectors in the highest radiation areas of all LHC experiments. Moreover CVD diamond is now being discussed as an alternative sensor material for tracking very close to the interaction region of the HL-LHC where the most extreme radiation conditions will exist. Our work addressed the further development of the new material, single-crystal Chemical Vapor Deposition diamond, towards reliable industrial production of large pieces and new geometries needed for detector applications. Our accomplishments include: • Developed a two U.S.companies to produce electronic grade diamond, • Worked with companies and acquired large area diamond pieces, • Performed radiation hardness tests using various proton energies: 70 MeV (Cyric, Japan), 800 MeV (Los Alamos), and 24 GeV (CERN).

  20. Noncatalytic thermocouple coatings produced with chemical vapor deposition for flame temperature measurements

    NASA Astrophysics Data System (ADS)

    Bahlawane, N.; Struckmeier, U.; Kasper, T. S.; Oßwald, P.

    2007-01-01

    Chemical vapor deposition (CVD) and metal-organic chemical vapor deposition (MOCVD) have been employed to develop alumina thin films in order to protect thermocouples from catalytic overheating in flames and to minimize the intrusion presented to the combustion process. Alumina films obtained with a CVD process using AlCl3 as the precursor are dense, not contaminated, and crystallize in the corundum structure, while MOCVD using Al(acetylwidth="0.3em"/>acetone)3 allows the growth of corundum alumina with improved growth rates. These films, however, present a porous columnar structure and show some carbon contamination. Therefore, coated thermocouples using AlCl3-CVD were judged more suitable for flame temperature measurements and were tested in different fuels over a typical range of stoichiometries. Coated thermocouples exhibit satisfactory measurement reproducibility, no temporal drifts, and do not suffer from catalytic effects. Furthermore, their increased radiative heat loss (observed by infrared spectroscopy) allows temperature measurements over a wider range when compared to uncoated thermocouples. A flame with a well-known temperature profile established with laser-based techniques was used to determine the radiative heat loss correction to account for the difference between the apparent temperature measured by the coated thermocouple and the true flame temperature. The validity of the correction term was confirmed with temperature profile measurements for several flames previously studied in different laboratories with laser-based techniques.

  1. Electronic Properties of Large-scale Graphene Chemical Vapor Synthesized on Nickel and on Sapphire

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Zhang, Liyuan; Chen, Yong; Yu, Qingkai; Li, Hao

    2009-03-01

    We have studied the electronic transport properties of large area few-layer graphene/graphitic films grown by two different chemical vapor based methods. The first type of samples (metal-transfer graphene) is synthesized by carbon segregation from Ni, then transferred to SiO2/Si substrates. The second type of samples is synthesized by direct chemical vapor deposition (CVD) on sapphire. We measured these samples under variable temperatures (from 2K to 300 K) and transverse magnet fields (from 0 to 7 T). For both types of samples, we found a negative magnetoresistance at low field, and carrier mobilities on the order of several hundreds of cm^2/V-s. For metal-transfer graphene in particular, we were able to measure a moderate field effect response, using the highly doped Si substrate as back gate. The observed magnetoresistance shows characteristic features of weak localization, from which we extract various carrier scattering lengths in the metal-transfer graphene samples. Comparison with those measured in mechanically exfoliated graphene suggests possibly different carrier scattering mechanisms for graphene materials prepared with different methods.

  2. Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization

    NASA Astrophysics Data System (ADS)

    Chang, Kow-Ming; Yeh, Ta-Hsun; Deng, I.-Chung

    1997-04-01

    A novel tungsten nitride (WNx) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300 °C in a low pressure chemical vapor deposition reactor with a SiH4/WF6 flow rate of 12.5/5 sccm under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300 °C without breaking vacuum. The thickness of WNx layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WNx layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n+p junction leakage current, the Al/WNx/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575 °C for 30 min. The effectiveness of W2N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminates the rapid diffusion paths in fine grain CVD-W films.

  3. Nitridation of fine grain chemical vapor deposited tungsten film as diffusion barrier for aluminum metallization

    SciTech Connect

    Chang, K.; Yeh, T.; Deng, I.

    1997-04-01

    A novel tungsten nitride (WN{sub x}) film for diffusion barrier applications has been prepared by nitridation of a fine grain chemical vapor deposited tungsten (CVD-W) film. The fine grain CVD-W is deposited at 300{degree}C in a low pressure chemical vapor deposition reactor with a SiH{sub 4}/WF{sub 6} flow rate of 12.5/5 sccm under a total gas pressure of 100 mTorr. The subsequent nitridation process is executed in nitrogen plasma at 300{degree}C without breaking vacuum. The thickness of WN{sub x} layer as examined by secondary ion mass spectroscopy is 50 nm after 5 min exposure to nitrogen plasma. X-ray photoelectron spectroscopy spectra shows that the atomic ratio of tungsten to nitrogen in WN{sub x} layer is 2:1. According to the analysis by Auger electron spectroscopy and the measurement of n{sup +}p junction leakage current, the Al/WN{sub x}/W/Si multilayer maintains excellent interfacial stability after furnace annealing at 575{degree}C for 30 min. The effectiveness of W{sub 2}N barrier is attributed to stuffing grain boundaries with nitrogen atoms which eliminates the rapid diffusion paths in fine grain CVD-W films. {copyright} {ital 1997 American Institute of Physics.}

  4. Polymer Thin Films and Surface Modification by Chemical Vapor Deposition: Recent Progress.

    PubMed

    Chen, Nan; Kim, Do Han; Kovacik, Peter; Sojoudi, Hossein; Wang, Minghui; Gleason, Karen K

    2016-06-07

    Chemical vapor deposition (CVD) polymerization uses vapor phase monomeric reactants to synthesize organic thin films directly on substrates. These thin films are desirable as conformal surface engineering materials and functional layers. The facile tunability of the films and their surface properties allow successful integration of CVD thin films into prototypes for applications in surface modification, device fabrication, and protective films. CVD polymers also bridge microfabrication technology with chemical and biological systems. Robust coatings can be achieved via CVD methods as antifouling, anti-icing, and antihydrate surfaces, as well as stimuli-responsive or biocompatible polymers and novel nanostructures. Use of low-energy input, modest vacuum, and room-temperature substrates renders CVD polymerization compatible with thermally sensitive substrates and devices. Compared with solution-based methods, CVD is particularly useful for insoluble materials, such as electrically conductive polymers and controllably crosslinked networks, and has the potential to reduce environmental, health, and safety impacts associated with solvents. This review discusses the relevant background and selected applications of recent advances by two methods that display and use the high retention of the organic functional groups from their respective monomers, initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.

  5. X-ray photoelectron spectroscopic study of the chemical vapor deposited W/Al interface

    NASA Astrophysics Data System (ADS)

    Ohshima, H.; Katayama, M.; Onoda, K.; Hattori, T.; Suzuki, H.; Tokuda, Y.

    1993-07-01

    The dependence of the amount of aluminum trifluoride (AlF3) piled up at the interface of chemical vapor deposited tungsten and the aluminum under layer on the deposition time and subsequent annealing in ultrahigh vacuum (UHV) or in monosilane (SiH4) gas has been studied. AlF3 is formed by the reaction of the aluminum under layer with tungsten hexafluoride (WF6) during the initial state of tungsten chemical vapor deposition. Tungsten was deposited on an Al layer under selective deposition conditions by SiH4 reduction at 250 °C. X-ray photoelectron spectroscopy measurement reveals that the amount of AlF3 decreases with an increase in the tungsten deposition time and that the reduction of AlF3 by volatilization of aluminum fluorides, which occurs at higher temperatures (≳400 °C) is not observed at low temperature (270 °C). Annealing in SiH4 gas after the tungsten deposition was effective to reduce the amount of AlF3 compared with annealing in UHV. This result and thermochemical data would suggest that the dependence of the amount of AlF3 on the tungsten deposition time is explained by the reduction of AlF3 with hydrogen atoms supplied from the dissociation of SiH4.

  6. Large improvement of phosphorus incorporation efficiency in n-type chemical vapor deposition of diamond

    NASA Astrophysics Data System (ADS)

    Ohtani, Ryota; Yamamoto, Takashi; Janssens, Stoffel D.; Yamasaki, Satoshi; Koizumi, Satoshi

    2014-12-01

    Microwave plasma enhanced chemical vapor deposition is a promising way to generate n-type, e.g., phosphorus-doped, diamond layers for the fabrication of electronic components, which can operate at extreme conditions. However, a deeper understanding of the doping process is lacking and low phosphorus incorporation efficiencies are generally observed. In this work, it is shown that systematically changing the internal design of a non-commercial chemical vapor deposition chamber, used to grow diamond layers, leads to a large increase of the phosphorus doping efficiency in diamond, produced in this device, without compromising its electronic properties. Compared to the initial reactor design, the doping efficiency is about 100 times higher, reaching 10%, and for a very broad doping range, the doping efficiency remains highly constant. It is hypothesized that redesigning the deposition chamber generates a higher flow of active phosphorus species towards the substrate, thereby increasing phosphorus incorporation in diamond and reducing deposition of phosphorus species at reactor walls, which additionally reduces undesirable memory effects.

  7. Suitable alkaline for graphene peeling grown on metallic catalysts using chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Karamat, S.; Sonuşen, S.; Çelik, Ü.; Uysallı, Y.; Oral, A.

    2016-04-01

    In chemical vapor deposition, the higher growth temperature roughens the surface of the metal catalyst and a delicate method is necessary for the transfer of graphene from metal catalyst to the desired substrates. In this work, we grow graphene on Pt and Cu foil via ambient pressure chemical vapor deposition (AP-CVD) method and further alkaline water electrolysis was used to peel off graphene from the metallic catalyst. We used different electrolytes i.e., sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH) and barium hydroxide Ba(OH)2 for electrolysis, hydrogen bubbles evolved at the Pt cathode (graphene/Pt/PMMA stack) and as a result graphene layer peeled off from the substrate without damage. The peeling time for KOH and LiOH was ∼6 min and for NaOH and Ba(OH)2 it was ∼15 min. KOH and LiOH peeled off graphene very efficiently as compared to NaOH and Ba(OH)2 from the Pt electrode. In case of copper, the peeling time is ∼3-5 min. Different characterizations like optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy were done to analyze the as grown and transferred graphene samples.

  8. Heteroepitaxial growth of 3-5 semiconductor compounds by metal-organic chemical vapor deposition for device applications

    NASA Technical Reports Server (NTRS)

    Collis, Ward J.; Abul-Fadl, Ali

    1988-01-01

    The purpose of this research is to design, install and operate a metal-organic chemical vapor deposition system which is to be used for the epitaxial growth of 3-5 semiconductor binary compounds, and ternary and quaternary alloys. The long-term goal is to utilize this vapor phase deposition in conjunction with existing current controlled liquid phase epitaxy facilities to perform hybrid growth sequences for fabricating integrated optoelectronic devices.

  9. Fabrication of carbon nanofiber-reinforced aluminum matrix composites assisted by aluminum coating formed on nanofiber surface by in situ chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ogawa, Fumio; Masuda, Chitoshi

    2015-01-01

    The van der Waals agglomeration of carbon nanofibers (CNFs) and the weight difference and poor wettability between CNFs and aluminum hinder the fabrication of dense CNF-reinforced aluminum matrix composites with superior properties. In this study, to improve this situation, CNFs were coated with aluminum by a simple and low-cost in situ chemical vapor deposition (in situ CVD). Iodine was used to accelerate the transport of aluminum atoms. The coating layer formed by the in situ CVD was characterized using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Fourier transform-infrared spectroscopy, and x-ray photoelectron spectroscopy. The results confirmed that the CNFs were successfully coated with aluminum. The composites were fabricated to investigate the effect of the aluminum coating formed on the CNFs. The dispersion of CNFs, density, Vickers micro-hardness and thermal conductivity of the composites fabricated by powder metallurgy were improved. Pressure-less infiltration experiments were conducted to fabricate composites by casting. The results demonstrated that the wettability and infiltration were dramatically improved by the aluminum coating layer on CNFs. The aluminum coating formed by the in situ CVD technique was proved to be effective for the fabrication of CNF-reinforced aluminum matrix composites.

  10. Through thickness mechanical properties of chemical vapor infiltration and nano-infiltration and transient eutectic-phase processed SiC/SiC composites

    SciTech Connect

    Shih, Chunghao Phillip; Katoh, Yutai; Ozawa, Kazumi; Lara-Curzio, Edgar; Snead, Lance Lewis

    2014-04-08

    The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. Furthermore, the 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure.

  11. Through thickness mechanical properties of chemical vapor infiltration and nano-infiltration and transient eutectic-phase processed SiC/SiC composites

    DOE PAGES

    Shih, Chunghao Phillip; Katoh, Yutai; Ozawa, Kazumi; ...

    2014-04-08

    The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. Furthermore, the 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure.

  12. Chemical etching and organometallic chemical vapor deposition on varied geometries of GaAs

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Landis, Geoffrey A.; Wilt, David M.

    1989-01-01

    Results of micron-spaced geometries produced by wet chemical etching and subsequent OMCVD growth on various GaAs surfaces are presented. The polar lattice increases the complexity of the process. The slow-etch planes defined by anisotropic etching are not always the same as the growth facets produced during MOCVD deposition, especially for deposition on higher-order planes produced by the hex groove etching.

  13. Adhesion and chemical vapor testing of second surface silver/glass solar mirrors

    SciTech Connect

    Dake, L.S.; Lind, M.A.

    1980-09-01

    Second surface silvered glass mirrors supplied by four different commercial manufacturers were evaluated for silver-to-glass adhesion and resistance to chemical vapor attack. The mirrors were chemically silvered on identical substrates of low iron float glass. Experiments were performed in order to assess the viability of using adhesion and chemical attack as screening tests for predicting the relative long-term durability of solar mirrors. The results of these tests will be compared at a future time with the survivability of field mirrors deployed in stationary exposure racks at ten locations throughout the United States. The adhesion tests were performed using a commercially-available thin film tensile pull tester in which a stud bonded to the film is pulled and the yield load recorded. Numerous subtleties regarding the selection of the adhesive used to bond the study and the validity of the testing procedure are discussed. Several different methods of normalizing the results were attempted in an effort to reduce the scatter in the data. The same set of samples were exposed to salt spray, water, HCl, H/sub 2/SO/sub 4/, and HNO/sub 3/ vapors and then ranked according to their performance. Visual comparison of tested samples did not yield consistent results; however, definite trends were observed favoring one of the manufacturers. Some SEM/EDX analysis was performed on these mirrors subject to accelerated degradation in order to compare them to mirrors subject to natural degradation. However, insufficient data has been collected to show that any of the tests performed will accurately predict the relative life expectancy of the mirrors in an outdoor environment.

  14. Improved detection and false alarm rejection for chemical vapors using passive hyperspectral imaging

    NASA Astrophysics Data System (ADS)

    Marinelli, William J.; Miyashiro, Rex; Gittins, Christopher M.; Konno, Daisei; Chang, Shing; Farr, Matt; Perkins, Brad

    2013-05-01

    Two AIRIS sensors were tested at Dugway Proving Grounds against chemical agent vapor simulants. The primary objectives of the test were to: 1) assess performance of algorithm improvements designed to reduce false alarm rates with a special emphasis on solar effects, and 3) evaluate performance in target detection at 5 km. The tests included 66 total releases comprising alternating 120 kg glacial acetic acid (GAA) and 60 kg triethyl phosphate (TEP) events. The AIRIS sensors had common algorithms, detection thresholds, and sensor parameters. The sensors used the target set defined for the Joint Service Lightweight Chemical Agent Detector (JSLSCAD) with TEP substituted for GA and GAA substituted for VX. They were exercised at two sites located at either 3 km or 5 km from the release point. Data from the tests will be presented showing that: 1) excellent detection capability was obtained at both ranges with significantly shorter alarm times at 5 km, 2) inter-sensor comparison revealed very comparable performance, 3) false alarm rates < 1 incident per 10 hours running time over 143 hours of sensor operations were achieved, 4) algorithm improvements eliminated both solar and cloud false alarms. The algorithms enabling the improved false alarm rejection will be discussed. The sensor technology has recently been extended to address the problem of detection of liquid and solid chemical agents and toxic industrial chemical on surfaces. The phenomenology and applicability of passive infrared hyperspectral imaging to this problem will be discussed and demonstrated.

  15. Surface modification of silicon-containing fluorocarbon films prepared by plasma-enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jin, Yoonyoung; Desta, Yohannes; Goettert, Jost; Lee, G. S.; Ajmera, P. K.

    2005-07-01

    Surface modification of silicon-containing fluorocarbon (SiCF) films achieved by wet chemical treatments and through x-ray irradiation is examined. The SiCF films were prepared by plasma-enhanced chemical vapor deposition, using gas precursors of tetrafluoromethane and disilane. As-deposited SiCF film composition was analyzed by x-ray photoelectron spectroscopy. Surface modification of SiCF films utilizing n-lithiodiaminoethane wet chemical treatment is discussed. Sessile water-drop contact angle changed from 95°+/-2° before treatment to 32°+/-2° after treatment, indicating a change in the film surface characteristics from hydrophobic to hydrophilic. For x-ray irradiation on the SiCF film with a dose of 27.4 kJ/cm3, the contact angle of the sessile water drop changed from 95°+/-2° before radiation to 39°+/-3° after x-ray exposure. The effect of x-ray exposure on chemical bond structure of SiCF films is studied using Fourier transform infrared measurements. Electroless Cu deposition was performed to test the applicability of the surface modified films. The x-ray irradiation method offers a unique advantage in making possible surface modification in a localized area of high-aspect-ratio microstructures. Fabrication of a Ti-membrane x-ray mask is introduced here for selective surface modification using x-ray irradiation.

  16. CHEMICALLY VAPOR DEPOSITED YTTRIA-STABILIZED ZIRCONIA (YSZ) FOR THERMAL AND ENVIRONMENTAL BARRIER COATING

    SciTech Connect

    Varanasi, V.G.; Besmann, T.M.; Lothian, J.L.; Xu, W.; Starr, T.L.

    2003-04-22

    Yttria-stabilized zirconia (YSZ) is used as a thermal barrier coating (TBC) to protect super-alloy blades such as Mar-M247 or Rene-N5 during engine operation. The current method for YSZ fabrication for TBC applications is by air-plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) (Haynes 1997). APS gives reasonable deposition rates, but has a limited life and aging effects due to its porous and lamellar structure. The EB-PVD coatings are more stable and can accommodate thermomechanical stresses due to their characteristic strain-tolerant, columnar microstructure. EB-PVD, however, is primarily line-of-sight, which often leaves ''hidden areas'' uncoated, has low throughput, and has high capital cost. The process of metal-organic chemical vapor deposition (MOCVD) is investigated here as an economical alternative to EB-PVD and APS, with the potential for better overall coverage as well as the ability to produce thick (100-250 {micro}m), strain-tolerant, columnar coatings. MOCVD of YSZ involves the use of zirconium and yttrium organometallic precursors reacting with an oxygen source. Previous researchers have used diketonate or chloride precursors and oxygen (Wahl et al. 2001a, Wahl et al. 2001b, Yamane and Harai 1989). These precursors have low transport rates due to their low carrier solvent solubility (Varanasi et al. 2003). Solvated zirconium and yttrium butoxide precursors were investigated here due to their higher vapor pressures and high solvent solubility. This work uses predictive equilibrium modeling and experiments involving butoxide precursors for tetragonal YSZ fabrication.

  17. a Design of Experiment Study of the Nucleation of Chemical Vapor Deposited Diamond Films.

    NASA Astrophysics Data System (ADS)

    Tang, Chi

    1995-01-01

    Because of its property, diamond has a unique role in the semiconductor and tool industry. As diamond synthesis technology advances, more and more applications are emerging. However, in order to take advantage of its exceptional property, reliable control of nucleation and growth must be accomplished. In this study, the author systematically studies the nucleation process in chemical vapor deposition (CVD) of diamonds. Among many important intricacies concerning diamond nucleation on foreign surfaces, this study addresses the following issues: the role of ultrasonic pre-treatment in CVD; the correlation between hot filament chemical vapor deposition (HFCVD) and microwave assisted chemical vapor deposition (MACVD) control parameters and the nucleation processes; the role of biasing substrates on the nucleation density in MACVD; the correlation between parameters of biasing substrates and the nucleation density; the reliable control of nucleation in CVD diamond synthesis. To achieve the goal of this research, a multi -purpose deposition system was built enabling the author to eliminate unnecessary variables in the deposition process. To ensure the accuracy of the nucleation effects of parameters investigated, great effort was made to calibrate measurement instruments so that noise or fluctuations in the experiments were minimized. The implementation of design of experiments (DOE), a systematic investigating technique, vastly improved the efficiency of this study over the less sophisticated empirical approach. In addition, DOE allowed the author to quantitatively estimate the effects of control parameters. Finally, diamond deposition was confirmed by Scanning Electron microscope, Micro Raman Scattering and Rutherford Backscattering. This research has successfully implemented DOE in estimating the effects of diamond nucleation quantitatively. The mechanism of ultrasonic pre-treatment is explained, and its effects are ascribed to seeding. The effects of primary CVD

  18. Thermal and chemical vapor deposition of Si nanowires: Shape control, dispersion, and electrical properties

    SciTech Connect

    Colli, A.; Fasoli, A.; Beecher, P.; Servati, P.; Pisana, S.; Fu, Y.; Flewitt, A. J.; Milne, W. I.; Robertson, J.; Ducati, C.; De Franceschi, S.; Hofmann, S.; Ferrari, A. C.

    2007-08-01

    We investigate and compare complementary approaches to SiNW production in terms of yield, morphology control, and electrical properties. Vapor-phase techniques are considered, including chemical vapor deposition (with or without the assistance of a plasma) and thermal evaporation. We report Au-catalyzed nucleation of SiNWs at temperatures as low as 300 deg. C using SiH{sub 4} as precursor. We get yields up to several milligrams by metal-free condensation of SiO powders. For all processes, we control the final nanostructure morphology. We then report concentrated and stable dispersions of SiNWs in solvents compatible with semiconducting organic polymers. Finally, we investigate the electrical response of intrinsic SiNWs grown by different methods. All our SiNWs exhibit p-type behavior and comparable performance, though in some cases ambipolar devices are observed. Thus, processing and morphology, rather than the growth technique, are key to achieve optimal samples for applications.

  19. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor.

    PubMed

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnO(x)-CVD layers.

  20. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor

    NASA Astrophysics Data System (ADS)

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G.

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnOx-CVD layers.

  1. Enhanced chemical vapor deposition of copper from (hfac)Cu(TMVS) using liquid coinjection of TMVS

    SciTech Connect

    Peterson, G.A.; Parmeter, J.E.; Apblett, C.A.; Gonzales, M.F.; Smith, P.M.; Omstead, T.R.; Norman, J.A.T.

    1995-03-01

    A direct liquid connection system has been applied to the chemical vapor deposition of copper using the commercially available Cu(I) precursor (hfac)Cu(TMVS), where hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate and TMVS = trimethylvinyl-silane. Precursor delivery was enhanced through the use of a coinjection system wherein additional TMVS was mixed with tire copper precursor before injection into the vaporization chamber. The results reported here demonstrate the capability of depositing blanket cooper for high purity (on the order of 99.99% copper) and low resistivity (1.85 {+-} 0.1 {mu}{Omega}-cm). These copper films have been deposited at rates up to and exceeding 1,500 {angstrom}/min. The effects of temperature and carrier gas on deposition rate and resistivity are examined. The as-deposited films demonstrate and dependence of grain size with thickness and little structural or morphological change with annealing. This study suggests that liquid coinjection is an effective method for enhancing deposition rates and for producing high quality copper films from copper(I) precursors.

  2. Growth of aligned ZnO nanowires via modified atmospheric pressure chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Yuping; Li, Chengchen; Chen, Mingming; Yu, Xiao; Chang, Yunwei; Chen, Anqi; Zhu, Hai; Tang, Zikang

    2016-12-01

    In this work, we report the growth of high-quality aligned ZnO nanowires via a facile atmospheric pressure chemical vapor deposition (CVD) method. The CVD reactor chamber used was more complicated than a conventional one due to the quartz boats loaded with sources (ZnO/C) and substrates being inserted into a semi-open quartz tube, and then placed inside the CVD reactor. The semi-open quartz tube played a very important role in growing the ZnO nanowires, and demonstrated that the transportation properties of Zn and O vapor differ from those in the conventional CVD reactor chamber. Aligned ZnO nanowires were successfully obtained, though they were only found at substrates located upstream. The very high crystalline quality of the obtained ZnO nanowires was demonstrated by high-resolution transmission electron microscopy and room temperature photoluminescence investigations. Such ZnO nanowires with high crystalline quality may provide opportunities for the fabrication of ZnO-based nano-devices in future.

  3. Regioselective Atomic Rearrangement of Ag-Pt Octahedral Catalysts by Chemical Vapor-Assisted Treatment.

    PubMed

    Pan, Yung-Tin; Yan, Linqing; Shao, Yu-Tsun; Zuo, Jian-Min; Yang, Hong

    2016-12-14

    Thermal annealing is a common, and often much-needed, process to optimize the surface structure and composition of bimetallic nanoparticles for high catalytic performance. Such thermal treatment is often carried out either in air or under an inert atmosphere by a trial-and-error approach. Herewith, we present a new chemical vapor-assisted treatment, which can preserve the octahedral morphology of Ag-Pt nanoparticles while modifying the surface into preferred composition arrangements with site-selectivity for high catalytic activity. In situ environmental transmission electron microscope (ETEM) study reveals a relatively homogeneous distribution of Ag and Pt is generated on the surface of Ag-Pt nanoparticles upon exposure to carbon monoxide (CO), whereas Pt atoms preferably segregate to the edge regions when the gas atmosphere is switched to argon. Density functional theory (DFT) calculations suggest stabilization of Pt atoms is energetically favored in the form of mixed surface alloys when CO vapor is present. Without CO, Ag and Pt phase separate under the similar mild treatment condition. There exists a close correlation between the tunable surface structures and the catalytic activities of Ag-Pt octahedral nanoparticles.

  4. Initiated chemical vapor deposition of thermoresponsive poly(N-vinylcaprolactam) thin films for cell sheet engineering.

    PubMed

    Lee, Bora; Jiao, Alex; Yu, Seungjung; You, Jae Bem; Kim, Deok-Ho; Im, Sung Gap

    2013-08-01

    Poly(N-vinylcaprolactam) (PNVCL) is a thermoresponsive polymer known to be nontoxic, water soluble and biocompatible. Here, PNVCL homopolymer was successfully synthesized for the first time by use of a one-step vapor-phase process, termed initiated chemical vapor deposition (iCVD). Fourier transform infrared spectroscopy results showed that radical polymerization took place from N-vinylcaprolactam monomers without damaging the functional caprolactam ring. A sharp lower critical solution temperature transition was observed at 31°C from the iCVD poly(N-vinylcaprolactam) (PNVCL) film. The thermoresponsive PNVCL surface exhibited a hydrophilic/hydrophobic alteration with external temperature change, which enabled the thermally modulated attachment and detachment of cells. The conformal coverage of PNVCL film on various substrates with complex topography, including fabrics and nanopatterns, was successfully demonstrated, which can further be utilized to fabricate cell sheets with aligned cell morphology. The advantage of this system is that cells cultured on such thermoresponsive surfaces could be recovered as an intact cell sheet by simply lowering the temperature, eliminating the need for conventional enzymatic treatments.

  5. Synthesis of Novel Sr Sources for Metalorganic Chemical Vapor Deposition of SrTiO3

    NASA Astrophysics Data System (ADS)

    Kimura, Takafumi; Yamauchi, Hideaki; Machida, Hideaki; Kokubun, Hiroshi; Yamada, Masao

    1994-09-01

    Novel Sr source materials for metalorganic chemical vapor deposition (MOCVD) of SrTiO3 have been developed. They were synthesized by adding amine, triethylenetetramine (trien) or tetraethylenepentamine (tetraen), to bis-dipivaloylmethanato strontium ( Sr(DPM)2, or strontium-bis-2,2,6,6-tetramethyl-3,5-heptanedionate). The new sources, Sr(DPM)2-trien2 and Sr(DPM)2-tetraen2, have a low melting point (43 75° C), and are liquid in phase when they are vaporized at 120 130° C. SrTiO3 thin films were prepared on Pt/Ta/ SiO2/Si substrates by MOCVD using the new Sr sources. The dielectric constant of films prepared with Sr(DPM)2-trien2 was 215 for 125 nm thick SrTiO3 films, and leakage current densities were below 10-6 A/cm2 at 1.5 V for 80 nm thick SrTiO3 films. The new Sr sources did not change in quality after 20-time heat cycles between room temperature and 130° C in Ar atmosphere at 40 Torr.

  6. Preparation Of Electrochromic Metal Oxide Films By Plasma-Enhanced Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Benson, D. K.; Tracy, C. E.; Svensson, J. S. E. M.; Liebert, B. E.

    1987-11-01

    Laboratory procedures have been developed for depositing thin films of electrochromic metal oxides by plasma-enhanced chemical vapor deposition (PE-CVD). In this process, vapor phase reactants, such as tungsten hexafluotIde, are mixed with oxygen and excited by RF energy at a frequency of 13.56 MHz and power levels up to≍1W/cm2 substrate area. Large rates of oxide deposition have been achieved (> 8 nm/s) making this process a candidate for high-speed coating of large area substrates, such as window glass. Amorphous WO1 films prepared by PE-CVD have been shown to have electrochromic responses virtually identical to films prepared by vacuum evaporation. The lithium ion diffusion rate, for example, is approximately 1.3 x 10-11 cm2 /s at x = 0.03 in LixWO3 prepared by PE-CVD. On the other hand, molybdenum oxide films and mixed molybdenum/tungsten oxide films prepared by PE-CVD from the hexafluorides differ markedly from vacuum evaporated films. Their electrochromic responses are spectrally different and are much slower. Lithium ion diffusion rates in such Mo03 films are lower by about three orders of magnitude. These differences are tentatively attributed to a large fraction of fluorine (Mo:F ratios of the order of 2:1) which are incorporated into the molybdenum and mixed oxides, but are not incorporated into the tungsten oxides.

  7. Determination of cadmium by flow injection-chemical vapor generation-atomic absorption spectrometry.

    PubMed

    Vargas-Razo, C; Tyson, J F

    2000-01-01

    A method was developed for the generation of a "cold vapor" of cadmium by means of flow injection-chemical vapor generation from aqueous samples, the determination being conducted with an atomic absorption spectrometer (Pyrex glass T-cell). Several gas-liquid separator designs, atomizer designs, and the effect of several reagents previously reported as sensitivity enhancers (including cobalt, nickel, thiourea and didodecyl-dimethylammonium bromide) were investigated. The limit of detection, calculated as the concentration giving a signal equal to three times the standard deviation of the blank, was 16 ng L(-1), and the relative standard deviation was 1.4% for a concentration of 2 microg L(-1) and 3.8% for 0.1 microg L(-1). The addition of nickel and thiourea to the samples provided improved tolerance to the interference of coexisting ions. Two NIST certified reference materials, Montana Soil and Apple Leaves (respectively containing 41.7+/-0.25 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd) were accurately analyzed. The interference of lead was overcome by coprecipitation with barium sulfate, and the experimental values obtained were 41+/-1 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd, respectively.

  8. Temperature regulated-chemical vapor deposition for incorporating NiO nanoparticles into mesoporous media

    NASA Astrophysics Data System (ADS)

    Han, Sang Wook; Kim, Il Hee; Kim, Dae Han; Park, Ki Jung; Park, Eun Ji; Jeong, Myung-Geun; Kim, Young Dok

    2016-11-01

    We have developed a novel strategy for incorporating NiO nanoparticles into mesoporous Al2O3 with a mean pore size of ∼12 nm and particle size of ∼1 mm. Ni-precursor vapor and ambient atmosphere were filled in a closed chamber with mesoporous Al2O3, and the chamber was initially heated at ∼100 °C, at which no chemical reaction between the inorganic precursor, oxygen, water vapor in the atmosphere, and the surface of Al2O3 took place. Next, the temperature of the system was increased to 260 °C for deposition of NiO. We found that NiO nanoparticles were not only deposited on the surface, but were also incorporated in a 50 μm-deep region of the mesoporous Al2O3 gel. We also demonstrated high CO oxidation activity and reusability of the deactivated NiO/Al2O3 catalysts prepared by the aforementioned method. These results suggest that our strategy could be widely applicable to the incorporation of various nanoparticles into mesoporous supports.

  9. A predictive model for the chemical vapor deposition of polysilicon in a cold wall, rapid thermal system

    SciTech Connect

    Toprac, A.J.; Trachtenberg, I.; Edgar, T.F. . Dept. of Chemical Engineering)

    1994-06-01

    The chemical vapor deposition of polysilicon from thermally activated silane in a cold wall, single-wafer rapid thermal system was studied by experimentation at a variety of low pressure conditions, including very high temperatures. The effect of diluent gas on polysilicon deposition rates was examined using hydrogen, helium, and krypton. A mass-transfer model for the chemical vapor deposition of polysilicon in a cold wall, rapid thermal system was developed. This model was used to produce an empirical rate expression for silicon deposition from silane by regressing kinetic parameters to fit experimental data. The resulting model provided accurate predictions over widely varying conditions in the experimental data.

  10. The Vapor Pressure of Environmentally Significant Organic Chemicals: A Review of Methods and Data at Ambient Temperature

    SciTech Connect

    Delle Site, A.

    1997-01-01

    The experimental techniques and the prediction procedures for the determination or evaluation of the vapor pressure of environmentally relevant organic compounds are described; with 259 references examined. For each of them the characteristics of precision and accuracy are given, when available from the literature. The experimental methods are classified as {open_quotes}direct{close_quotes} and {open_quotes}indirect.{close_quotes} The first class includes all those which can measure directly the vapor pressure, while the second concerns those which need {open_quotes}known{close_quotes} vapor pressures of reference compounds for the calibration. Prediction methods are based on the application of the Clapeyron{endash}Clausius equation or on the quantitative structure-property relationships. Also correlation methods require a suitable calibration. The vapor pressures at ambient temperature for several polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and furans, selected pesticides, and some reference compounds are tabulated together with the vapor pressure equations and the enthalpy values in the temperature range of measurement. A critical comparison, based on a statistical analysis of the data obtained with different methods and derived from 152 references, is also carried out. {copyright} {ital 1996 American Institute of Physics and American Chemical Society.}{ital Key words:} chlorinated biphenyls; chlorinated dioxins; critically reviewed data; critically reviewed methods; pesticides; polynuclear aromatics; vapor pressure. {copyright} {ital 1996} {ital American Institute of Physics and American Chemical Society}

  11. Optical properties of InP doping superlattices grown by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Gal, M.; Viner, J. M.; Taylor, P. C.; Yaun, J. S.; Stringfellow, G. B.

    1987-04-01

    Photoluminescence (PL), time-resolved PL, and photoreflectance spectroscopy are applied to InP doping superlattices grown by metal organic chemical vapor deposition. It is observed that the emission peak and line shape depend on the optical excitation intensity; the peak of the CW PL spectrum increases in energy with the intensity of the pumping light; the highest energy peak is at 888 nm; and the time-resolved PL exhibits long decay times. The energy separation of the quantized subbands is studied by measuring the PR spectra of two samples. The measurements reveal that PR line shapes are explained by photomodulation of the subbands in the conduction band; these line shapes account for the dependence of the spectrum on the power of the exciting light and on the layer thickness.

  12. Environmental effects on the tensile strength of chemically vapor deposited silicon carbide fibers

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Kraitchman, M. D.

    1985-01-01

    The room temperature and elevated temperature tensile strengths of commercially available chemically vapor-deposited (CVD) silicon carbide fibers were measured after 15 min heat treatment to 1600 C in various environments. These environments included oxygen, air, argon and nitrogen at one atmosphere and vacuum at 10/9 atmosphere. Two types of fibers were examined which differed in the SiC content of their carbon-rich coatings. Threshold temperature for fiber strength degradation was observed to be dependent on the as-received fiber-flaw structure, on the environment and on the coating. Fractographic analyses and flexural strength measurements indicate that tensile strength losses were caused by surface degradation. Oxidation of the surface coating is suggested as one possible degradation mechanism. The SiC fibers containing the higher percentage of SiC near the surface of the carbon-rich coating show better strength retention and higher elevated temperature strength.

  13. Hybrid physical-chemical vapor deposition of Bi2Se3 films

    NASA Astrophysics Data System (ADS)

    Brom, Joseph E.; Weiss, Lauren; Choudhury, Tanushree H.; Redwing, Joan M.

    2016-10-01

    Bi2Se3 thin films were grown on c-plane sapphire substrates by hybrid physical-chemical vapor deposition (HPCVD) using trimethyl bismuth (TMBi) and Se pellets. A Se-rich environment is created by evaporating Se pellets in the vicinity of the substrate, which is used to suppress the formation of Se vacancies. The effects of pre-cracking temperature and substrate/Se temperature on the growth rate, structural and electrical properties of the Bi2Se3 films were investigated. C-axis oriented films were obtained which show a reduction in the carrier concentration as pre-cracking temperature was increased from 290 °C (1.6×1019 cm-3) to 350 °C (8.4×1018 cm-3). An additional reduction in carrier concentration (7.28×1018 cm-3) was observed on increasing the substrate temperature from 200 to 260 °C.

  14. Low Temperature Metal Free Growth of Graphene on Insulating Substrates by Plasma Assisted Chemical Vapor Deposition.

    PubMed

    Muñoz, R; Munuera, C; Martínez, J I; Azpeitia, J; Gómez-Aleixandre, C; García-Hernández, M

    2017-03-01

    Direct growth of graphene films on dielectric substrates (quartz and silica) is reported, by means of remote electron cyclotron resonance plasma assisted chemical vapor deposition r-(ECR-CVD) at low temperature (650°C). Using a two step deposition process- nucleation and growth- by changing the partial pressure of the gas precursors at constant temperature, mostly monolayer continuous films, with grain sizes up to 500 nm are grown, exhibiting transmittance larger than 92% and sheet resistance as low as 900 Ω·sq(-1). The grain size and nucleation density of the resulting graphene sheets can be controlled varying the deposition time and pressure. In additon, first-principles DFT-based calculations have been carried out in order to rationalize the oxygen reduction in the quartz surface experimentally observed. This method is easily scalable and avoids damaging and expensive transfer steps of graphene films, improving compatibility with current fabrication technologies.

  15. Reducing flicker noise in chemical vapor deposition graphene field-effect transistors

    NASA Astrophysics Data System (ADS)

    Arnold, Heather N.; Sangwan, Vinod K.; Schmucker, Scott W.; Cress, Cory D.; Luck, Kyle A.; Friedman, Adam L.; Robinson, Jeremy T.; Marks, Tobin J.; Hersam, Mark C.

    2016-02-01

    Single-layer graphene derived from chemical vapor deposition (CVD) holds promise for scalable radio frequency (RF) electronic applications. However, prevalent low-frequency flicker noise (1/f noise) in CVD graphene field-effect transistors is often up-converted to higher frequencies, thus limiting RF device performance. Here, we achieve an order of magnitude reduction in 1/f noise in field-effect transistors based on CVD graphene transferred onto silicon oxide substrates by utilizing a processing protocol that avoids aqueous chemistry after graphene transfer. Correspondingly, the normalized noise spectral density (10-7-10-8 μm2 Hz-1) and noise amplitude (4 × 10-8-10-7) in these devices are comparable to those of exfoliated and suspended graphene. We attribute the reduction in 1/f noise to a decrease in the contribution of fluctuations in the scattering cross-sections of carriers arising from dynamic redistribution of interfacial disorder.

  16. Stress hysteresis and mechanical properties of plasma-enhanced chemical vapor deposited dielectric films

    NASA Astrophysics Data System (ADS)

    Thurn, Jeremy; Cook, Robert F.; Kamarajugadda, Mallika; Bozeman, Steven P.; Stearns, Laura C.

    2004-02-01

    A comprehensive survey is described of the responses of three plasma-enhanced chemical vapor deposited dielectric film systems to thermal cycling and indentation contact. All three films—silicon oxide, silicon nitride, and silicon oxy-nitride—exhibited significant nonequilibrium permanent changes in film stress on thermal cycling or annealing. The linear relationship between stress and temperature changed after the films were annealed at 300 °C, representing a structural alteration in the film reflecting a change in coefficient of thermal expansion or biaxial modulus. A double-substrate method was used to deduce both thermoelastic properties before and after the anneal of selected films and the results were compared with the modulus deconvoluted from small-scale depth-sensing indentation experiments (nanoindentation). Rutherford backscattering spectrometry and hydrogen forward scattering were used to deduce the composition of the films and it was found that all the films contained significant amounts of hydrogen.

  17. Thermoelectric Power of Nanocrystalline Silicon Prepared by Hot-Wire Chemical-Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kearney, Brian; Liu, Xiao; Jugdersuren, Battogtokh; Queen, Daniel; Metcalf, Thomas; Culbertson, James; Chervin, Christopher; Stroud, Rhonda; Nemeth, William; Wang, Qi

    Although doped bulk silicon possesses a favorable Seebeck coefficient and electrical conductivity, its thermal conductivity is too large for practical thermoelectric applications. Thin film nanocrystalline silicon prepared by hot-wire chemical-vapor deposition (HWCVD) is an established material used in multijunction amorphous silicon solar cells. Its potential in low cost and scalable thermoelectric applications depends on achieving a low thermal conductivity without sacrificing thermoelectric power and electrical conductivity. We examine the thermoelectric power of boron-doped HWCVD nanocrystalline silicon and find that it is comparable to doped nanostructured silicon alloys prepared by other methods. Given the low thermal conductivity and high electrical conductivity of these materials, they can achieve a high thermoelectric figure of merit, ZT. Work supported by the Office of Naval Research.

  18. Spectroscopic measurements of the surface stoichiometry of chemical vapor deposited GaN

    NASA Astrophysics Data System (ADS)

    Craft, H. S.; Rice, A. L.; Collazo, R.; Sitar, Z.; Maria, J.-P.

    2011-02-01

    We report on the surface stoichiometry of Ga-polar GaN films grown by metalorganic chemical vapor deposition as studied by x-ray photoelectron spectroscopy. GaN film surfaces are found to be Ga-rich, with Ga:N ratios ranging from 1.3:1 to 3.2:1. In vacuo ion-beam sputter/annealing studies show that these treatments drive the apparent Ga:N surface composition farther from unity, either through a decrease in surface contamination, oxidation of the surface, or both. Simple annealing experiments decrease the Ga:N ratio. The measured GaN ratio is correlated with the GaN growth time, suggesting that residual Ga precursor after growth interacts with the GaN surface as it cools.

  19. Ultrahigh-mobility graphene devices from chemical vapor deposition on reusable copper

    PubMed Central

    Banszerus, Luca; Schmitz, Michael; Engels, Stephan; Dauber, Jan; Oellers, Martin; Haupt, Federica; Watanabe, Kenji; Taniguchi, Takashi; Beschoten, Bernd; Stampfer, Christoph

    2015-01-01

    Graphene research has prospered impressively in the past few years, and promising applications such as high-frequency transistors, magnetic field sensors, and flexible optoelectronics are just waiting for a scalable and cost-efficient fabrication technology to produce high-mobility graphene. Although significant progress has been made in chemical vapor deposition (CVD) and epitaxial growth of graphene, the carrier mobility obtained with these techniques is still significantly lower than what is achieved using exfoliated graphene. We show that the quality of CVD-grown graphene depends critically on the used transfer process, and we report on an advanced transfer technique that allows both reusing the copper substrate of the CVD growth and making devices with mobilities as high as 350,000 cm2 V–1 s–1, thus rivaling exfoliated graphene. PMID:26601221

  20. Spiral Growth of Few-Layer MoS2 by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Dong, Xi; Tomer, Dushyant; Li, Lian

    Monolayer and few-layer transition metal dichalcogenide MoS2 are grown by chemical vapor deposition on SiO2/Si substrates using MoO3 and S powder as precursors. Before growth, the substrates are pretreated with perylene-3, 4, 9, 10-tetracarboxylic acid tetrapotassium salt to promote nucleation. Monolayer MoS2 islands are triangularly shaped with sizes ranging from a few to tens of micrometers, which also exhibits the characteristic Raman bands at 403.36 and 385.05 cm-1 corresponding to the A1g and E2g modes, respectively. Atomic force microscopy imaging further confirms the monolayer thickness to be 0.8 nm. For few-layer MoS2 films, triangular spirals are observed with both left- and right-handed chirality. Raman spectra showed interesting features of these growth spirals, the details of which will be presented at the meeting. NSF DMR-1508560.

  1. Plasma-enhanced chemical vapor deposition of amorphous Si on graphene

    NASA Astrophysics Data System (ADS)

    Lupina, G.; Strobel, C.; Dabrowski, J.; Lippert, G.; Kitzmann, J.; Krause, H. M.; Wenger, Ch.; Lukosius, M.; Wolff, A.; Albert, M.; Bartha, J. W.

    2016-05-01

    Plasma-enhanced chemical vapor deposition of thin a-Si:H layers on transferred large area graphene is investigated. Radio frequency (RF, 13.56 MHz) and very high frequency (VHF, 140 MHz) plasma processes are compared. Both methods provide conformal coating of graphene with Si layers as thin as 20 nm without any additional seed layer. The RF plasma process results in amorphization of the graphene layer. In contrast, the VHF process keeps the high crystalline quality of the graphene layer almost intact. Correlation analysis of Raman 2D and G band positions indicates that Si deposition induces reduction of the initial doping in graphene and an increase of compressive strain. Upon rapid thermal annealing, the amorphous Si layer undergoes dehydrogenation and transformation into a polycrystalline film, whereby a high crystalline quality of graphene is preserved.

  2. Diameter Tuning of β -Ga2O3 Nanowires Using Chemical Vapor Deposition Technique

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Kumar, Vikram; Singh, R.

    2017-03-01

    Diameter tuning of β -Ga2O3 nanowires using chemical vapor deposition technique have been investigated under various experimental conditions. Diameter of root grown β -Ga2O3 nanowires having monoclinic crystal structure is tuned by varying separation distance between metal source and substrate. Effect of gas flow rate and mixer ratio on the morphology and diameter of nanowires has been studied. Nanowire diameter depends on growth temperature, and it is independent of catalyst nanoparticle size at higher growth temperature (850-900 °C) as compared to lower growth temperature (800 °C). These nanowires show changes in structural strain value with change in diameter. Band-gap of nanowires increases with decrease in the diameter.

  3. Synthesis of boron nitride nanotubes by Argon supported Thermal Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Ahmad, Pervaiz; Khandaker, Mayeen Uddin; Amin, Yusoff Mohd

    2015-03-01

    Thermal Chemical Vapor Deposition technique is modified with the use of Argon gas flow inside the chamber as an alternative for vacuum and orientation of one end closed quartz test tube. The use of Argon gas not only simplified the experimental set up, but also made it ~ 18 % cost effective compared to the conventional set up. Field Emission Scanning Electron Microscopy micrographs show straight and long BNNTs along with some cotton like morphologies. Transmission electron microscopy revealed bamboo like structure inside the tube and ~0.34 nm interlayer spacing for highly crystalline nature of boron nitride nanotubes. X-ray photon spectroscopy shows B 1s peak at 191.08 eV and N 1s peak at 398.78 eV that represents h-BN. Whereas, Raman spectrum indicates a major peak at ~1379.60 (cm-1) that correspond to E2g mode of h-BN.

  4. Specific heat capacity and density of multi-walled boron nitride nanotubes by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhi, Chunyi; Bando, Yoshio; Tang, Chengchun; Golberg, Dmitri

    2011-01-01

    We report on the basic physical quantities of boron nitride nanotubes (BNNTs), namely specific heat capacity and density, which have not been measured to date. A series of differential scanning calorimetry experiments were performed, and specific heat capacity was calculated for multi-walled BNNTs synthesized by chemical vapor deposition using boron and metal oxide as precursor. Very close specific heat capacity values were revealed for BNNTs and a BN powder of hexagonal (h-BN) phase. Densities of BNNTs were measured through density analyses of their epoxy composites. Our work is important as far as bulk properties of large amounts of BNNTs are crucial, for example, thermal property and density prediction for composite materials with BNNTs embedded.

  5. Controllable Synthesis of Graphene by Plasma‐Enhanced Chemical Vapor Deposition and Its Related Applications

    PubMed Central

    Li, Menglin; Liu, Donghua; Song, Xuefen; Wei, Dapeng; Wee, Andrew Thye Shen

    2016-01-01

    Graphene and its derivatives hold a great promise for widespread applications such as field‐effect transistors, photovoltaic devices, supercapacitors, and sensors due to excellent properties as well as its atomically thin, transparent, and flexible structure. In order to realize the practical applications, graphene needs to be synthesized in a low‐cost, scalable, and controllable manner. Plasma‐enhanced chemical vapor deposition (PECVD) is a low‐temperature, controllable, and catalyst‐free synthesis method suitable for graphene growth and has recently received more attentions. This review summarizes recent advances in the PECVD growth of graphene on different substrates, discusses the growth mechanism and its related applications. Furthermore, the challenges and future development in this field are also discussed. PMID:27980983

  6. Growth inhibition to enhance conformal coverage in thin film chemical vapor deposition.

    PubMed

    Kumar, Navneet; Yanguas-Gil, Angel; Daly, Scott R; Girolami, Gregory S; Abelson, John R

    2008-12-31

    We introduce the use of a growth inhibitor to enhance thin film conformality in low temperature chemical vapor deposition. Films of TiB(2) grown from the single source precursor Ti(BH(4))(3)(dme) are much more highly conformal when grown in the presence of one of the film growth byproducts, 1,2-dimethoxyethane (dme). This effect can be explained in terms of two alternative inhibitory mechanisms: one involving blocking of surface reactive sites, which is equivalent to reducing the rate of the forward reaction leading to film growth, the other analogous to Le Chatelier's principle, in which the addition of a reaction product increases the rate of the back reaction. The reduction in growth rate corresponds to a reduction in the sticking probability of the precursor, which enhances conformality by enabling the precursor to diffuse deeper into a recessed feature before it reacts.

  7. Elastic and anelastic properties of chemical vapor deposited epitaxial 3C-SiC

    NASA Astrophysics Data System (ADS)

    Su, C. M.; Wuttig, Manfred; Fekade, A.; Spencer, M.

    1995-06-01

    Chemical vapor deposited 3C-SiC films were micromachined into free standing cantilevers and their anelastic and elastic properties were determined by a vibrating reed technique. Despite a high density of defects, epitaxial 3C-SiC exhibits extremely high mechanical Q which is essential for resonator sensors and actuators. An anelastic relaxation peak was found with an associated activation energy of 0.94 eV. Doping caused splitting of this peak. The mechanism of the mechanical relaxation peak is discussed in relation to defect movement under stress. Young's modulus of epitaxial undoped 3C-SiC was found to be 694 GPa, p-doping reduced it to 474 Gpa.

  8. Preparation of γ-Al2O3 films by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Gao, Ming; Ito, Akihiko; Goto, Takashi

    2015-06-01

    γ- and α-Al2O3 films were prepared by chemical vapor deposition using CO2, Nd:YAG, and InGaAs lasers to investigate the effects of varying the laser wavelength and deposition conditions on the phase composition and microstructure. The CO2 laser was found to mostly produce α-Al2O3 films, whereas the Nd:YAG and InGaAs lasers produced γ-Al2O3 films when used at a high total pressure. γ-Al2O3 films had a cauliflower-like structure, while the α-Al2O3 films had a dense and columnar structure. Of the three lasers, it was the Nd:YAG laser that interacted most with intermediate gas species. This promoted γ-Al2O3 nucleation in the gas phase at high total pressure, which explains the cauliflower-like structure of nanoparticles observed.

  9. Diamond synthesis at atmospheric pressure by microwave capillary plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hemawan, Kadek W.; Gou, Huiyang; Hemley, Russell J.

    2015-11-01

    Polycrystalline diamond has been synthesized on silicon substrates at atmospheric pressure, using a microwave capillary plasma chemical vapor deposition technique. The CH4/Ar plasma was generated inside of quartz capillary tubes using 2.45 GHz microwave excitation without adding H2 into the deposition gas chemistry. Electronically excited species of CN, C2, Ar, N2, CH, Hβ, and Hα were observed in the emission spectra. Raman measurements of deposited material indicate the formation of well-crystallized diamond, as evidenced by the sharp T2g phonon at 1333 cm-1 peak relative to the Raman features of graphitic carbon. Field emission scanning electron microscopy images reveal that, depending on the growth conditions, the carbon microstructures of grown films exhibit "coral" and "cauliflower-like" morphologies or well-facetted diamond crystals with grain sizes ranging from 100 nm to 10 μm.

  10. Low temperature metal free growth of graphene on insulating substrates by plasma assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Muñoz, R.; Munuera, C.; Martínez, J. I.; Azpeitia, J.; Gómez-Aleixandre, C.; García-Hernández, M.

    2017-03-01

    Direct growth of graphene films on dielectric substrates (quartz and silica) is reported, by means of remote electron cyclotron resonance plasma assisted chemical vapor deposition r-(ECR-CVD) at low temperature (650 °C). Using a two step deposition process- nucleation and growth- by changing the partial pressure of the gas precursors at constant temperature, mostly monolayer continuous films, with grain sizes up to 500 nm are grown, exhibiting transmittance larger than 92% and sheet resistance as low as 900 Ω sq-1. The grain size and nucleation density of the resulting graphene sheets can be controlled varying the deposition time and pressure. In additon, first-principles DFT-based calculations have been carried out in order to rationalize the oxygen reduction in the quartz surface experimentally observed. This method is easily scalable and avoids damaging and expensive transfer steps of graphene films, improving compatibility with current fabrication technologies.

  11. Thermal conductivity of ultra-thin chemical vapor deposited hexagonal boron nitride films

    SciTech Connect

    Alam, M. T.; Haque, M. A.; Bresnehan, M. S.; Robinson, J. A.

    2014-01-06

    Thermal conductivity of freestanding 10 nm and 20 nm thick chemical vapor deposited hexagonal boron nitride films was measured using both steady state and transient techniques. The measured value for both thicknesses, about 100 ± 10 W m{sup −1} K{sup −1}, is lower than the bulk basal plane value (390 W m{sup −1} K{sup −1}) due to the imperfections in the specimen microstructure. Impressively, this value is still 100 times higher than conventional dielectrics. Considering scalability and ease of integration, hexagonal boron nitride grown over large area is an excellent candidate for thermal management in two dimensional materials-based nanoelectronics.

  12. Spiral growth of few-layer MoS{sub 2} by chemical vapor deposition

    SciTech Connect

    Dong, X.; Yan, C.; Tomer, D.; Li, L.; Li, C. H.

    2016-08-01

    Growth spirals exhibit appealing properties due to a preferred layer stacking and lack of inversion symmetry. Here, we report spiral growth of MoS{sub 2} during chemical vapor deposition on SiO{sub 2}/Si and epitaxial graphene/SiC substrates, and their physical and electronic properties. We determine the layer-dependence of the MoS{sub 2} bandgap, ranging from 2.4 eV for the monolayer to a constant of 1.3 eV beyond the fifth layer. We further observe that spirals predominantly initiate at the step edges of the SiC substrate, based on which we propose a growth mechanism driven by screw dislocation created by the coalescence of two growth fronts at steps.

  13. Antireflective silica nanoparticle array directly deposited on flexible polymer substrates by chemical vapor deposition.

    PubMed

    Yun, Jungheum; Bae, Tae-Sung; Kwon, Jung-Dae; Lee, Sunghun; Lee, Gun-Hwan

    2012-11-21

    We report the direct coating of a novel antireflective (AR) nanoarray structure of silica nanoparticles on highly flexible polymer substrates by a conventional vacuum coating method using plasma-enhanced chemical vapor deposition. Globular-shaped silica nanoparticles are found to be self-arranged in a periodic pattern on subwavelength scales without the use of artificial assemblies that typically require complicated nanolithography or solution-based nanoparticle fabrication approaches. Highly efficient AR characteristics in the visible spectral range are obtained at optimized refractive indices by controlling the dimensions and average distances of the silica nanoparticle arrays in a level accuracy of tens of nanometers. The AR nanoarrays exhibit sufficient structural durability against the very high strain levels that arise from the flexibility of polymer substrates. This simple coating process provides a cost-effective, high-throughput, room-temperature fabrication solution for producing large-area polymer substrates with AR characteristics.

  14. The response of the ionosphere to the injection of chemically reactive vapors

    NASA Technical Reports Server (NTRS)

    Bernhardt, P. A.

    1976-01-01

    As a gas released in the ionosphere expands, it is rapidly cooled. When the vapor becomes sufficiently tenuous, it is reheated by collisions with the ambient atmosphere and its flow is then governed by diffusive expansion. As the injected gas becomes well mixed with the plasma, a hole is created by chemical processes. In the case of diatomic hydrogen release, depression of the electron concentrations is governed by the charge exchange reaction between oxygen ions and hydrogen, producing positive hydroxyl ions. Hydroxyl ions rapidly react with the electron gas to produce excited oxygen and hydrogen atoms. Enhanced airglow emissions result from the transition of the excited atoms to lower energy states. The electron temperature in the depleted region rises sharply causing a thermal expansion of the plasma and a further reduction in the local plasma concentration.

  15. Edge oxidation effect of chemical-vapor-deposition-grown graphene nanoconstriction.

    PubMed

    Iqbal, Muhammad Waqas; Iqbal, Muhammad Zahir; Jin, Xiaozhan; Hwang, Chanyong; Eom, Jonghwa

    2014-03-26

    The edge oxidation effects of chemical-vapor-deposition-grown graphene devices with nanoconstrictions of different sizes are presented. The effects of edge oxidation on the doping level of a nanoconstriction graphene device were identified by Raman spectroscopy and using the back-gate-voltage-dependent resistance. Strong p-type doping was observed as the size of nanoconstriction decreased. The Dirac point of the graphene device shifted toward positive voltage, and the positions of the G and 2D peaks in Raman spectroscopy shifted toward a higher wave number, indicating the p-type doping effect of the graphene device. p-type doping was lifted by deep-ultraviolet light illumination under a nitrogen atmosphere at room temperature. p-type doping was restored by deep-ultraviolet light illumination under an oxygen atmosphere at room temperature. Edge oxidation in the narrow structures explains the origin of the p-type doping effect widely observed in graphene nanodevices.

  16. Growth of FePt encapsulated carbon nanotubes by thermal chemical vapor deposition

    SciTech Connect

    Fujiwara, Yuji Kaneko, Tetsuya; Hori, Kenta; Takase, Sho; Sato, Hideki; Maeda, Kohji; Kobayashi, Tadashi; Kato, Takeshi; Iwata, Satoshi; Jimbo, Mutsuko

    2014-03-15

    FePt encapsulated carbon nanotubes (CNTs) were grown by thermal chemical vapor deposition using an Fe/Pt bilayer catalyst. The CNTs were grown according to the base growth model. Selected area electron diffraction results revealed that the encapsulated particles were A1-FePt, L1{sub 0}-FePt, and Fe{sub 3}PtC. The crystal structures of particles found at the root parts of CNTs were not able to be identified, however. The layered structure of catalytic films seemed to be responsible for the difference in Pt content between particles found at tip and root parts of CNTs. Approximately 60% of CNTs grown at 800 °C had particles at their tip parts, compared to only 30% when the growth temperature was 700 °C, indicating that higher process temperatures promote particle encapsulation in CNTs.

  17. Carbon agent chemical vapor transport growth of Ga2O3 crystal

    NASA Astrophysics Data System (ADS)

    Jie, Su; Tong, Liu; Jingming, Liu; Jun, Yang; Guiying, Shen; Yongbiao, Bai; Zhiyuan, Dong; Youwen, Zhao

    2016-10-01

    Beta-type gallium oxide (β-Ga2O3) is a new attractive material for optoelectronic devices. Different methods had been tried to grow high quality β-Ga2O3 crystals. In this work, crystal growth of Ga2O3 has been carried out by chemical vapor transport (CVT) method in a closed quartz tube using C as transport agent and sapphire wafer as seed. The CVT mass flux has been analyzed by theoretical calculations based on equilibrium thermodynamics and 1D diffusional mass transport. The crystal growth experimental results are in agreement with the theoretical predictions. Influence factors of Ga2O3 crystal growth, such as temperature distribution, amount of C as transport agent used, have also been discussed. Structural (XRD) and optical (Raman spectroscopy, photoluminescence spectrum) properties of the CVT-Ga2O3 crystal are presented. Project supported by the National Natural Science Foundation of China (Nos. 61474104, 61504131).

  18. Identification of reaction products in the low-pressure chemical vapor deposition of molybdenum silicide

    SciTech Connect

    Gaczi, P.J.; Reynolds, G.J. )

    1989-09-01

    The gaseous species produced by low-pressure chemical vapor deposition of molybdenum silicide in a cold wall reactor were identified by mass spectroscopy. Lowering the ionizing electron energy made possible the unambiguous assignment of the mass spectra to individual species and also permitted useful quantitative estimates to be made. Thermodynamic calculations using the computer program SOLGASMIX were carried out on the M-Si-H-F (M = Mo, W) quaternary system. Both experiment and calculation indicate that the fluorosilanes were the major gaseous reaction by-products, with SiHF{sub 3} being the most abundant for the experimental conditions investigated here. The changes in the process with substrate temperature were also investigated and are discussed with reference to both thermodynamic and kinetic effects.

  19. Plasma-enhanced chemical vapor deposition method to coat micropipettes with diamond-like carbon

    SciTech Connect

    Kakuta, Naoto; Watanabe, Mayu; Yamada, Yukio; Okuyama, Naoki; Mabuchi, Kunihiko

    2005-07-15

    This article provides a simple method for coating glass micropipettes with diamond-like carbon (DLC) through plasma-enhanced chemical vapor deposition. The apparatus uses a cathode that is a thin-metal-coated micropipette itself and an anode that is a meshed cylinder with its cylinder axis along the micropipette length. To produce a uniform plasma and prevent a temperature increase at the tip due to ion collision concentration, we investigated the effect of the height and diameter of the meshed cylindrical anode on the plasma. Intermittent deposition is also effective for inhibiting the temperature rise and producing high quality DLC films. Measured Raman spectra and electric resistivity indicate that a DLC film suitable for use as an insulating film can be produced on the micropipette. This coating method should also be useful for other extremely small probes.

  20. Contamination-free graphene by chemical vapor deposition in quartz furnaces.

    PubMed

    Lisi, Nicola; Dikonimos, Theodoros; Buonocore, Francesco; Pittori, Martina; Mazzaro, Raffaello; Rizzoli, Rita; Marras, Sergio; Capasso, Andrea

    2017-08-30

    Although the growth of graphene by chemical vapor deposition is a production technique that guarantees high crystallinity and superior electronic properties on large areas, it is still a challenge for manufacturers to efficiently scale up the production to the industrial scale. In this context, issues related to the purity and reproducibility of the graphene batches exist and need to be tackled. When graphene is grown in quartz furnaces, in particular, it is common to end up with samples contaminated by heterogeneous particles, which alter the growth mechanism and affect graphene's properties. In this paper, we fully unveil the source of such contaminations and explain how they create during the growth process. We further propose a modification of the widely used quartz furnace configuration to fully suppress the sample contamination and obtain identical and clean graphene batches on large areas.

  1. Development of a polysilicon process based on chemical vapor deposition, phase 1

    NASA Technical Reports Server (NTRS)

    Mccormick, J.; Sharp, K.; Arvidson, A.; Sawyer, D.

    1981-01-01

    The development of a dichlorosilane-based reductive chemical vapor deposition process for the production of polycrystalline silicon is discussed. Experimental data indicate that the ease of ignition and explosion severity of dichlorosilane (DCS)/air mixtures is substantially attenuated if the DCS is diluted with hydrogen. Redesign of the process development unit to accommodate safety related information is described. Several different sources of trichlorosilane were used to generate a mixture of redistributed chlorosilanes via Dowex ion exchange resin. The unseparated mixtures were then fed to an experimental reactor in which silicon was deposited and the deposited silicon analyzed for electrically active impurities. At least one trichlorosilane source provided material of requisite purity. Silicon grown in the experimental reactor was converted to single crystal material and solar cells fabricated and tested.

  2. Electronic properties of monolayer tungsten disulfide grown by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Alharbi, Abdullah; Shahrjerdi, Davood

    2016-11-01

    We demonstrate chemical vapor deposition of large monolayer tungsten disulfide (WS2) (>200 μm). Photoluminescence and Raman spectroscopy provide insight into the structural and strain heterogeneity of the flakes. We observe exciton quenching at grain boundaries that originate from the nucleation site at the center of the WS2 flakes. Temperature variable transport measurements of top-gated WS2 transistors show an apparent metal-to-insulator transition. Variable range and thermally activated hopping mechanisms can explain the carrier transport in the insulating phase at low and intermediate temperatures. The devices exhibit room-temperature field-effect electron mobility as high as 48 cm2/V.s. The mobility increases with decreasing temperature and begins to saturate at below 100 °K, possibly due to Coulomb scattering or defects.

  3. Silicon Chemical Vapor Deposition on macro and submicron powders in a fluidized bed

    SciTech Connect

    Cadoret, L.; Reuge, N; Pannala, Sreekanth; Syamlal, M; Rossignol, C; Dexpert-Ghys, J; Coufort, C; Caussat, B

    2009-01-01

    Titanium oxide (TiO2) submicron powders have been treated by Chemical Vapor Deposition (CVD) in a vibro-fluidized bed in order to deposit silicon layers of nanometer scale on each individual grain from silane (SiH4). Experimental results show that for the conditions tested, the original granular structure of the powders is preserved for 90% of the initial bed weight while the remaining 10% consisted of agglomerates in millimetre range found near the distributor of the reactor. A comparison between experimental and modelling results using the MFIX code shows that for Geldart's Group B alumina particles (Al2O3), the model represents both the bed hydrodynamics and silane conversion rates quite well. The future objective is to extend the simulation capability to cohesive submicron powders in order to achieve better predictability of the phenomena governing ultrafine particles.

  4. Growth of well-oriented VACNTs using thermal chemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Yousefi, Amin Termeh; Mahmood, Mohamad Rusop; Ikeda, Shoichiro

    2016-07-01

    The remarkable properties of carbon nanotubes (CNTs) make them attractive for biosensor applications, especially for medical detecting devices. In this paper, we describe a process to grow high oriented ratio CNT arrays to improve the electrical properties of the devices based on CNTs. Chemical vapor deposition (CVD) was used to grow highly oriented CNT using camphor as the carbon source, and argon and hydrogen as carrier gases to grow perpendicular CNTs on the surface of the silicon substrate in presence of ferrocene as a metallic catalyst. Images were revealed by FESEM indicates that the formation mechanism of oriented CNTs with high morphological purity nanotubes, which is depends significantly on deposition time and applied temperature to the furnaces. This method might be an effective method to produce oriented MWCNT in different length.

  5. High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Cui, Linfan; Chen, Jiangtao; Yang, Bingjun; Jiao, Tifeng

    2015-12-01

    Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm2. The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.

  6. High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition.

    PubMed

    Cui, Linfan; Chen, Jiangtao; Yang, Bingjun; Jiao, Tifeng

    2015-12-01

    Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm(2). The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.

  7. Influence of Carbon in Metalorganic Chemical Vapor Deposition of Few-Layer WSe2 Thin Films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaotian; Al Balushi, Zakaria Y.; Zhang, Fu; Choudhury, Tanushree H.; Eichfeld, Sarah M.; Alem, Nasim; Jackson, Thomas N.; Robinson, Joshua A.; Redwing, Joan M.

    2016-12-01

    Metalorganic chemical vapor deposition (MOCVD) is a promising technique to form large-area, uniform films of monolayer or few-layer transition metal dichalcogenide (TMD) thin films; however, unintentional carbon incorporation is a concern. In this work, we report the presence of a defective graphene layer that forms simultaneously during MOCVD growth of tungsten diselenide (WSe2) on sapphire at high growth temperature and high Se:W ratio when using tungsten hexacarbonyl (W(CO)6) and dimethyl selenide ((CH3)2Se, DMSe) as precursors. The graphene layer alters the surface energy of the substrate reducing the lateral growth and coalescence of WSe2 domains. The use of hydrogen selenide (H2Se) instead of DMSe eliminates the defective graphene layer enabling coalesced monolayer and few-layer WSe2 films.

  8. Nanoscale arrays of antimony telluride single crystals by selective chemical vapor deposition

    PubMed Central

    Huang, Ruomeng; Benjamin, Sophie L.; Gurnani, Chitra; Wang, Yudong; Hector, Andrew L.; Levason, William; Reid, Gillian; De Groot, C. H. (Kees)

    2016-01-01

    Arrays of individual single nanocrystals of Sb2Te3 have been formed using selective chemical vapor deposition (CVD) from a single source precursor. Crystals are self-assembled reproducibly in confined spaces of 100 nm diameter with pitch down to 500 nm. The distribution of crystallite sizes across the arrays is very narrow (standard deviation of 15%) and is affected by both the hole diameter and the array pitch. The preferred growth of the crystals in the <1 1 0> orientation along the diagonal of the square holes strongly indicates that the diffusion of adatoms results in a near thermodynamic equilibrium growth mechanism of the nuclei. A clear relationship between electrical resistivity and selectivity is established across a range of metal selenides and tellurides, showing that conductive materials result in more selective growth and suggesting that electron donation is of critical importance for selective deposition. PMID:27283116

  9. Controlling nucleation of monolayer WSe2 during metal-organic chemical vapor deposition growth

    NASA Astrophysics Data System (ADS)

    Eichfeld, Sarah M.; Oliveros Colon, Víctor; Nie, Yifan; Cho, Kyeongjae; Robinson, Joshua A.

    2016-06-01

    Tungsten diselenide (WSe2) is a semiconducting, two-dimensional (2D) material that has gained interest in the device community recently due to its electronic properties. The synthesis of atomically thin WSe2, however, is still in its infancy. In this work we elucidate the requirements for large selenium/tungsten precursor ratios and explain the effect of nucleation temperature on the synthesis of WSe2 via metal-organic chemical vapor deposition (MOCVD). The introduction of a nucleation-step prior to growth demonstrates that increasing nucleation temperature leads to a transition from a Volmer-Weber to Frank-van der Merwe growth mode. Additionally, the nucleation step prior to growth leads to an improvement of WSe2 layer coverage on the substrate. Finally, we note that the development of this two-step technique may allow for improved control and quality of 2D layers grown via CVD and MOCVD processes.

  10. Experimental and Theoretical Analysis of Chemical Vapor Deposition with Prediction of Gravity Effects

    NASA Technical Reports Server (NTRS)

    Stinespring, C. D.; Spear, K. E.

    1985-01-01

    A combined experimental and theoretical study to characterize the effects of gravitationally-induced transport on atmospheric pressure silicon epitaxy by SiH4 pyrolysis is planned. Experimentally, flow regimes in which free convective transport contributes to the Chemical Vapor Deposition (CVD) process will be identified, and, for these conditions, the flow and deposition process will be characterized. Specifically, this will include measurements of three dimensional temperature variations using in situ Rayleigh scattering, gas phase composition profiles using laser absorption and fluorescence techniques, and deposition rates and defect densities. Subsequently, the free convective transport contribution to the CVD process will be minimized and/or altered while leaving deposition chemistry unaltered, and the characterization will be repeated. Based on these analyses, the effects of gravitationally-induced transport on atmospheric pressure CVD will be assessed.

  11. Carbon impurities on graphene synthesized by chemical vapor deposition on platinum

    SciTech Connect

    Ping, Jinglei; Fuhrer, Michael S.

    2014-07-28

    We report nanocrystalline carbon impurities coexisting with graphene synthesized via chemical vapor deposition on platinum. For certain growth conditions, we observe micron-size island-like impurity layers which can be mistaken for second graphene layers in optical microscopy or scanning electron microscopy. The island orientation depends on the crystalline orientation of the Pt, as shown by electron backscatter diffraction, indicating growth of carbon at the platinum surface below graphene. Dark-field transmission electron microscopy indicates that in addition to uniform single-crystal graphene, our sample is decorated with nanocrystalline carbon impurities with a spatially inhomogeneous distribution. The impurity concentration can be reduced significantly by lowering the growth temperature. Raman spectra show a large D peak, however, electrical characterization shows high mobility (∼8000 cm{sup 2}/Vs), indicating a limitation for Raman spectroscopy in characterizing the electronic quality of graphene.

  12. Large single-domain growth of monolayer WS2 by rapid-cooling chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Li, Chao; Yamaguchi, Yoshiki; Kaneko, Toshiro; Kato, Toshiaki

    2017-07-01

    A novel method for the synthesis of large monolayer and single-crystal tungsten disulfide (WS2) has been developed by introducing a rapid-cooling stage to the conventional chemical vapor deposition (CVD). The maximum size of single-crystal WS2 can be increased up to 320 µm by adjusting the growth parameters during the rapid-cooling CVD. This is one of the largest sizes of single-crystal transition metal dichalcogenides directly grown on an insulating substrate. A theoretical model reveals that the increase in WS2 size can be explained by the enhanced nucleation probability and the growth velocity, caused by the additional precursors supplied during the rapid cooling.

  13. Boron nitride nanowires synthesis via a simple chemical vapor deposition at 1200 °C

    SciTech Connect

    Ahmad, Pervaiz; Khandaker, Mayeen Uddin; Amin, Yusoff Mohd; Khan, Ziaul Raza

    2015-04-24

    A very simple chemical vapor deposition technique is used to synthesize high quality boron nitride nanowires at 1200 °C within a short growth duration of 30 min. FESEM micrograph shows that the as-synthesized boron nitride nanowires have a clear wire like morphology with diameter in the range of ∼20 to 150 nm. HR-TEM confirmed the wire-like structure of boron nitride nanowires, whereas XPS and Raman spectroscopy are used to find out the elemental composition and phase of the synthesized material. The synthesized boron nitride nanowires have potential applications as a sensing element in solid state neutron detector, neutron capture therapy and microelectronic devices with uniform electronic properties.

  14. Development of a polysilicon process based on chemical vapor deposition (phase 1)

    NASA Technical Reports Server (NTRS)

    Mccormick, J.; Arvidson, A.; Sawyer, D.; Plahutnik, F.

    1981-01-01

    A dichlorosilane-based reductive chemical vapor deposition (CVD) process demonstrated is capable of producing, at low cost, high quality polycrystalline silicon. Testing of decomposition reactor heat shields to insure that the shield provides adequate personnel protection assuming a worst case explosion was completed. Minor modifications to a production reactor heat shield provided adequate heat shield integrity. Construction of the redesigned PDU (Process Development Unit) to accommodate all safety related information proceeded on schedule. Structural steel work was completed as is the piping and instrumentation design work. Major pieces of process equipment were received and positioned in the support structure and all transfer piping and conduits to the PDU were installed. Construction was completed on a feed system for supplying DCS to an intermediate sized reactor. The feed system was successfully interfaced with a reactor equipped with a modified heat shield. Reactor checkout was completed.

  15. Atmospheric Pressure Chemical Vapor Deposition of Graphene Using a Liquid Benzene Precursor.

    PubMed

    Kang, Cheong; Jung, Da Hee; Lee, Jin Seok

    2015-11-01

    Graphene has attracted great attention owing to its unique structural and electrical properties. Among various synthetic approaches of the graphene, metal assisted chemical vapor deposition (CVD) is the most reasonable and proper method to produce large-scale and low-defect graphene films. Until now, CVD from gaseous hydrocarbon sources has shown great promises for large-scale graphene growth, but high growth temperature is required for such growth. A recent work by using liquid benzene precursor has shown that monolayer graphene could be obtained at 300 degrees C by low pressure, required for high vacuum equipment. Here, we report the first successful attempt of atmospheric pressure CVD graphene growth on Cu foil using liquid benzene as a precursor. We investigated the effect of hydrogen partial pressure, growth time, and precursor temperature on the domain size of as-grown graphene. Also, micro-Raman analysis confirmed that these reaction parameters influenced the number of layer and uniformity of the graphene.

  16. Non-classical crystallization of silicon thin films during hot wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Jung, Jae-Soo; Lee, Sang-Hoon; Kim, Da-Seul; Kim, Kun-Su; Park, Soon-Won; Hwang, Nong-Moon

    2017-01-01

    The deposition behavior of silicon films by hot wire chemical vapor deposition (HWCVD) was approached by non-classical crystallization, where the building block of deposition is a nanoparticle generated in the gas phase of the reactor. The puzzling phenomenon of the formation of an amorphous incubation layer on glass could be explained by the liquid-like property of small charged nanoparticles (CNPs), which are generated in the initial stage of the HWCVD process. Using the liquid-like property of small CNPs, homo-epitaxial growth as thick as 150 nm could be successfully grown on a silicon wafer at 600 °C under the processing condition where CNPs as small as possible could be supplied steadily by a cyclic process which periodically resets the process. The size of CNPs turned out to be an important parameter in the microstructure evolution of thin films.

  17. Structure and magnetic properties of iron nanoparticles synthesized by chemical vapor condensation

    NASA Astrophysics Data System (ADS)

    Lee, D. H.; Jang, T. S.; Lee, D. W.; Kim, B. K.

    2004-06-01

    Iron nanoparticles were synthesized by chemical vapor condensation (CVC) without the aid of LN2 chiller. The powder synthesized at 400 °C was a mixture of amorphous and crystalline -Fe. Fully crystallized iron particles were then obtained at and above 600 °C. When the reactor temperature was 1000 °C, however, nonmagnetic -Fe was stabilized together with -Fe. The synthesized particles, mostly possessing the core-shell type structure, were all nearly spherical, but the average particle size rapidly increased as the temperature increased. The surface layer that enclosed the iron core and became thicker in smaller particles was Fe3O4 or Fe3O4-related amorphous. Except for the one synthesized at 1000 °C, the iron nanoparticles were not fully saturated. The iron nanoparticles (20 nm) synthesized at 600 °C exhibited iHc 1.0 kOe and Ms 170 emu/g.

  18. Auger Recombination in Chemical Vapor Deposition-Grown Monolayer WS2.

    PubMed

    Cunningham, Paul D; McCreary, Kathleen M; Jonker, Berend T

    2016-12-15

    Reduced dimensionality and strong Coulombic interactions in monolayer semiconductors lead to enhanced many-body interactions. Here, we report Auger recombination, i.e., exciton-exciton annihilation, in large-area chemical vapor deposition-grown monolayer WS2. Using ultrafast spectroscopy, we experimentally determine the Auger rate to be 0.089 ± 0.001 cm(2)/s at room temperature, which is an order of magnitude greater than the bulk value. This nonradiative recombination pathway dominates, regardless of excitation energy, for exciton densities greater than 8.0 ± 0.6 × 10(10) cm(-2) and below the Mott density. Higher-energy excitation above the A exciton resonance may initially produce a hot electron-hole gas that precedes exciton formation. Therefore, we use resonant excitation of the A exciton to ensure accuracy and avoid artifacts associated with other photogenerated species.

  19. Influence of gas phase equilibria on the chemical vapor deposition of graphene.

    PubMed

    Lewis, Amanda M; Derby, Brian; Kinloch, Ian A

    2013-04-23

    We have investigated the influence of gas phase chemistry on the chemical vapor deposition of graphene in a hot wall reactor. A new extended parameter space for graphene growth was defined through literature review and experimentation at low pressures (≥0.001 mbar). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy, and dark field optical microscopy, with the latter showing promise as a rapid and nondestructive characterization technique for graphene films. The equilibrium gas compositions have been calculated across this parameter space. Correlations between the graphene films grown and prevalent species in the equilibrium gas phase revealed that deposition conditions associated with a high acetylene equilibrium concentration lead to good quality graphene deposition, and conditions that stabilize large hydrocarbon molecules in the gas phase result in films with multiple defects. The transition between lobed and hexagonal graphene islands was found to be linked to the concentration of the monatomic hydrogen radical, with low concentrations associated with hexagonal islands.

  20. Study of surface morphology and alignment of MWCNTs grown by chemical vapor deposition

    SciTech Connect

    Shukrullah, S. E-mail: noranimuti-mohamed@petronas.com.my Mohamed, N. M. E-mail: noranimuti-mohamed@petronas.com.my Shaharun, M. S. E-mail: noranimuti-mohamed@petronas.com.my; Yasar, M.

    2014-10-24

    In this research work, Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized successfully by using floating catalytic chemical vapor deposition (FCCVD) method. Different ferrocene amounts (0.1, 0.125 and 0.15 g) were used as catalyst and ethylene was used as a carbon precursor at reaction temperature of 800°C. Characterization of the grown MWCNTs was carried out by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained data showed that the catalyst weight affects the nanotubes diameter, alignment, crystallinity and growth significantly, whereas negligible influence was noticed on CNTs forest length. The dense, uniform and meadow like patterns of grown CNTs were observed for 0.15 g ferrocene. The average diameter of the grown CNTs was found in the range of 32 to 75 nm. Close inspection of the TEM images also confirmed the defects in some of the grown CNTs, where few black spots were evident in CNTs structure.