Method and apparatus for removing and preventing window deposition during photochemical vapor deposition (photo-CVD) processes

DOEpatents

Tsuo, Simon; Langford, Alison A.

1989-01-01

Unwanted build-up of the film deposited on the transparent light-transmitting window of a photochemical vacuum deposition (photo-CVD) chamber is eliminated by flowing an etchant into the part of the photolysis region in the chamber immediately adjacent the window and remote from the substrate and from the process gas inlet. The respective flows of the etchant and the process gas are balanced to confine the etchant reaction to the part of the photolysis region proximate to the window and remote from the substrate. The etchant is preferably one that etches film deposit on the window, does not etch or affect the window itself, and does not produce reaction by-products that are deleterious to either the desired film deposited on the substrate or to the photolysis reaction adjacent the substrate.

Chemical vapor deposition and characterization of polysilanes polymer based thin films and their applications in compound semiconductors and silicon devices

NASA Astrophysics Data System (ADS)

Oulachgar, El Hassane

As the semiconductors industry is moving toward nanodevices, there is growing need to develop new materials and thin films deposition processes which could enable strict control of the atomic composition and structure of thin film materials in order to achieve precise control on their electrical and optical properties. The accurate control of thin film characteristics will become increasingly important as the miniaturization of semiconductor devices continue. There is no doubt that chemical synthesis of new materials and their self assembly will play a major role in the design and fabrication of next generation semiconductor devices. The objective of this work is to investigate the chemical vapor deposition (CVD) process of thin film using a polymeric precursor as a source material. This process offers many advantages including low deposition cost, hazard free working environment, and most importantly the ability to customize the polymer source material through polymer synthesis and polymer functionalization. The combination between polymer synthesis and CVD process will enable the design of new generation of complex thin film materials with a wide range of improved chemical, mechanical, electrical and optical properties which cannot be easily achieved through conventional CVD processes based on gases and small molecule precursors. In this thesis we mainly focused on polysilanes polymers and more specifically poly(dimethylsilanes). The interest in these polymers is motivated by their distinctive electronic and photonic properties which are attributed to the delocalization of the sigma-electron along the Si-Si backbone chain. These characteristics make polysilane polymers very promising in a broad range of applications as a dielectric, a semiconductor and a conductor. The polymer-based CVD process could be eventually extended to other polymer source materials such as polygermanes, as well as and a variety of other inorganic and hybrid organic-inorganic polymers. This work has demonstrated that a polysilane polymeric source can be used to deposit a wide range of thin film materials exhibiting similar properties with conventional ceramic materials such as silicon carbide (SiC), silicon oxynitride (SiON), silicon oxycarbide (SiOC) silicon dioxide (SiO2) and silicon nitride (Si3N4). The strict control of the deposition process allows precise control of the electrical, optical and chemical properties of polymer-based thin films within a broad range. This work has also demonstrated for the first time that poly(dimethylsilmaes) polymers deposited by CVD can be used to effectively passivate both silicon and gallium arsenide MOS devices. This finding makes polymer-based thin films obtained by CVD very promising for the development of high-kappa dielectric materials for next generation high-mobility CMOS technology. Keywords. Thin films, Polymers, Vapor Phase Deposition, CVD, Nanodielectrics, Organosilanes, Polysilanes, GaAs Passivation, MOSFET, Silicon Oxynitride, Integrated Waveguide, Silicon Carbide, Compound Semiconductors.

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.

Optimal Magnetorheological Fluid for Finishing of Chemical-Vapor-Deposited Zinc Sulfide

NASA Astrophysics Data System (ADS)

Salzman, Sivan

Magnetorheological finishing (MRF) of polycrystalline, chemical-vapor- deposited zinc sulfide (ZnS) optics leaves visible surface artifacts known as "pebbles". These artifacts are a direct result of the material's inner structure that consists of cone-like features that grow larger (up to a few millimeters in size) as deposition takes place, and manifest on the top deposited surface as "pebbles". Polishing the pebble features from a CVD ZnS substrate to a flat, smooth surface to below 10 nm root-mean-square is challenging, especially for a non-destructive polishing process such as MRF. This work explores ways to improve the surface finish of CVD ZnS processed with MRF through modification of the magnetorheological (MR) fluid's properties. A materials science approach is presented to define the anisotropy of CVD ZnS through a combination of chemical and mechanical experiments and theoretical predictions. Magnetorheological finishing experiments with single crystal samples of ZnS, whose cuts and orientations represent most of the facets known to occur in the polycrystalline CVD ZnS, were performed to explore the influence of material anisotropy on the material removal rate during MRF. By adjusting the fluid's viscosity, abrasive type concentration, and pH to find the chemo-mechanical conditions that equalize removal rates among all single crystal facets during MRF, we established an optimized, novel MR formulation to polish CVD ZnS without degrading the surface finish of the optic.

Room temperature chemical vapor deposition of c-axis ZnO

NASA Astrophysics Data System (ADS)

Barnes, Teresa M.; Leaf, Jacquelyn; Fry, Cassandra; Wolden, Colin A.

2005-02-01

Highly (0 0 2) oriented ZnO films have been deposited at temperatures between 25 and 230 °C by high-vacuum plasma-assisted chemical vapor deposition (HVP-CVD) on glass and silicon substrates. The HVP-CVD process was found to be weakly activated with an apparent activation energy of ∼0.1 eV, allowing room temperature synthesis. Films deposited on both substrates displayed a preferential c-axis texture over the entire temperature range. Films grown on glass demonstrated high optical transparency throughout the visible and near infrared.

Initiated chemical vapor deposition polymers for high peak-power laser targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baxamusa, Salmaan H.; Lepro, Xavier; Lee, Tom

2016-12-05

Here, we report two examples of initiated chemical vapor deposition (iCVD) polymers being developed for use in laser targets for high peak-power laser systems. First, we show that iCVD poly(divinylbenzene) is more photo-oxidatively stable than the plasma polymers currently used in laser targets. Thick layers (10–12 μm) of this highly crosslinked polymer can be deposited with near-zero intrinsic film stress. Second, we show that iCVD epoxy polymers can be crosslinked after deposition to form thin adhesive layers for assembling precision laser targets. The bondlines can be made as thin as ~ 1 μm, approximately a factor of 2 thinner thanmore » achievable using viscous resin-based adhesives. These bonds can withstand downstream coining and stamping processes.« less

Chemical Vapor Deposited Zinc Sulfide. SPIE Press Monograph

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.

A Comparative Study of Three Different Chemical Vapor Deposition Techniques of Carbon Nanotube Growth on Diamond Films

DTIC Science & Technology

2012-11-01

microwave plasma-enhanced CVD (MPE-CVD) with presputtered metal catalyst, and floating catalyst thermal CVD (FCT-CVD) with xylene and ferrocene liquid...processes with nickel and iron catalysts, respectively. For the FCT-CVD approach, ferrocene is used as an iron source to promoteCNT growth. Based on...furnace is ramped up to the growth temperature of 750∘C. Ferrocene was dissolved into a xylene solvent in a 0.008 : 1molar volume ratio.The xylene

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.

Friction and Wear of Ion-Beam-Deposited Diamondlike Carbon on Chemical-Vapor-Deposited, Fine-Grain Diamond

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Wu, Richard L. C.; Lanter, William C.

1996-01-01

Friction and wear behavior of ion-beam-deposited diamondlike carbon (DLC) films coated on chemical-vapor-deposited (CVD), fine-grain diamond coatings were examined in ultrahigh vacuum, dry nitrogen, and humid air environments. The DLC films were produced by the direct impact of an ion beam (composed of a 3:17 mixture of Ar and CH4) at ion energies of 1500 and 700 eV and an RF power of 99 W. Sliding friction experiments were conducted with hemispherical CVD diamond pins sliding on four different carbon-base coating systems: DLC films on CVD diamond; DLC films on silicon; as-deposited, fine-grain CVD diamond; and carbon-ion-implanted, fine-grain CVD diamond on silicon. Results indicate that in ultrahigh vacuum the ion-beam-deposited DLC films on fine-grain CVD diamond (similar to the ion-implanted CVD diamond) greatly decrease both the friction and wear of fine-grain CVD diamond films and provide solid lubrication. In dry nitrogen and in humid air, ion-beam-deposited DLC films on fine-grain CVD diamond films also had a low steady-state coefficient of friction and a low wear rate. These tribological performance benefits, coupled with a wider range of coating thicknesses, led to longer endurance life and improved wear resistance for the DLC deposited on fine-grain CVD diamond in comparison to the ion-implanted diamond films. Thus, DLC deposited on fine-grain CVD diamond films can be an effective wear-resistant, lubricating coating regardless of environment.

Improved synthesis of carbon-clad silica stationary phases.

PubMed

Haidar Ahmad, Imad A; Carr, Peter W

2013-12-17

Previously, we described a novel method for cladding elemental carbon onto the surface of catalytically activated silica by a chemical vapor deposition (CVD) method using hexane as the carbon source and its use as a substitute for carbon-clad zirconia.1,2 In that method, we showed that very close to exactly one uniform monolayer of Al (III) was deposited on the silica by a process analogous to precipitation from homogeneous solution in order to preclude pore blockage. The purpose of the Al(III) monolayer is to activate the surface for subsequent CVD of carbon. In this work, we present an improved procedure for preparing the carbon-clad silica (denoted CCSi) phases along with a new column packing process. The new method yields CCSi phases having better efficiency, peak symmetry, and higher retentivity compared to carbon-clad zirconia. The enhancements were achieved by modifying the original procedure in three ways: First, the kinetics of the deposition of Al(III) were more stringently controlled. Second, the CVD chamber was flushed with a mixture of hydrogen and nitrogen gas during the carbon cladding process to minimize generation of polar sites by oxygen incorporation. Third, the fine particles generated during the CVD process were exhaustively removed by flotation in an appropriate solvent.

Photochemical CVD of Ru on functionalized self-assembled monolayers from organometallic precursors

NASA Astrophysics Data System (ADS)

Johnson, Kelsea R.; Arevalo Rodriguez, Paul; Brewer, Christopher R.; Brannaka, Joseph A.; Shi, Zhiwei; Yang, Jing; Salazar, Bryan; McElwee-White, Lisa; Walker, Amy V.

2017-02-01

Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)2Me, (η3-allyl)Ru(CO)3Br, and (COT)Ru(CO)3, were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.

Chemical vapour deposition growth and Raman characterization of graphene layers and carbon nanotubes

NASA Astrophysics Data System (ADS)

Lai, Y.-C.; Rafailov, P. M.; Vlaikova, E.; Marinova, V.; Lin, S. H.; Yu, P.; Yu, S.-C.; Chi, G. C.; Dimitrov, D.; Sveshtarov, P.; Mehandjiev, V.; Gospodinov, M. M.

2016-02-01

Single-layer graphene films were grown by chemical vapour deposition (CVD) on Cu foil. The CVD process was complemented by plasma enhancement to grow also vertically aligned multiwalled carbon nanotubes using Ni nanoparticles as catalyst. The obtained samples were characterized by Raman spectroscopy analysis. Nature of defects in the samples and optimal growth conditions leading to achieve high quality of graphene and carbon nanotubes are discussed.

75 FR 74773 - Mandatory Reporting of Greenhouse Gases: Additional Sources of Fluorinated GHGs

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-01

..., Methods for Estimating Air Emissions from Chemical Manufacturing Facilities; Protocol for Equipment Leak... chemical vapor deposition process (CVD) or other manufacturing processes use N 2 O. Production processes.... N 2 O emissions from chemical vapor deposition and other electronics manufacturing processes...

MOCVD of aluminium oxide films using aluminium β-diketonates as precursors

NASA Astrophysics Data System (ADS)

Devi, A.; Shivashankar, S. A.; Samuelson, A. G.

2002-06-01

Deposition of Al203 coatings by CVD is of importance because they are often used as abrading material in cemented carbide cutting tools. The conventionally used CVD process for Al203 involves the corrosive reactant AICl3. In this paper, we report on the thermal characterisation of the metalorganic precursors namely aluminium tris-tetramethyl-heptanedionate [ Al(thd)3] and aluminium tris-acetylacetonate [ Al(acac)3] and their application to the CVD of Al203 films. Crystalline A1203 films were deposited by MOCVD at low temperatures by the pyrolysis of Al(thd)3 and AI(acac)3. The films were deposited on a TiN-coated tungsten carbide (TiN/WC) and Si(100) substrates in the temperature range 500-1100 °C. The as-deposited films were characterised by x-ray diffraction, optical microscopy, scanning and transmission electron microscopy, Auger electron spectroscopy. The observed crystallinity of films grown at low temperatures, their microstructure, and composition may be interpreted in terms of a growth process that involves the melting of the metalorganic precursor on the hot growth surface.

Inductively and capacitively coupled plasmas at interface: A comparative study towards highly efficient amorphous-crystalline Si solar cells

NASA Astrophysics Data System (ADS)

Guo, Yingnan; Ong, Thiam Min Brian; Levchenko, I.; Xu, Shuyan

2018-01-01

A comparative study on the application of two quite different plasma-based techniques to the preparation of amorphous/crystalline silicon (a-Si:H/c-Si) interfaces for solar cells is presented. The interfaces were fabricated and processed by hydrogen plasma treatment using the conventional plasma-enhanced chemical vacuum deposition (PECVD) and inductively coupled plasma chemical vapour deposition (ICP-CVD) methods The influence of processing temperature, radio-frequency power, treatment duration and other parameters on interface properties and degree of surface passivation were studied. It was found that passivation could be improved by post-deposition treatment using both ICP-CVD and PECVD, but PECVD treatment is more efficient for the improvement on passivation quality, whereas the minority carrier lifetime increased from 1.65 × 10-4 to 2.25 × 10-4 and 3.35 × 10-4 s after the hydrogen plasma treatment by ICP-CVD and PECVD, respectively. In addition to the improvement of carrier lifetimes at low temperatures, low RF powers and short processing times, both techniques are efficient in band gap adjustment at sophisticated interfaces.

Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration

NASA Astrophysics Data System (ADS)

Chang, Sung-Jin; Hyun, Moon Seop; Myung, Sung; Kang, Min-A.; Yoo, Jung Ho; Lee, Kyoung G.; Choi, Bong Gill; Cho, Youngji; Lee, Gaehang; Park, Tae Jung

2016-03-01

Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties.

Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration.

PubMed

Chang, Sung-Jin; Hyun, Moon Seop; Myung, Sung; Kang, Min-A; Yoo, Jung Ho; Lee, Kyoung G; Choi, Bong Gill; Cho, Youngji; Lee, Gaehang; Park, Tae Jung

2016-03-10

Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties.

Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration

PubMed Central

Chang, Sung-Jin; Hyun, Moon Seop; Myung, Sung; Kang, Min-A; Yoo, Jung Ho; Lee, Kyoung G.; Choi, Bong Gill; Cho, Youngji; Lee, Gaehang; Park, Tae Jung

2016-01-01

Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties. PMID:26961409

CVD Polymers for Devices and Device Fabrication.

PubMed

Wang, Minghui; Wang, Xiaoxue; Moni, Priya; Liu, Andong; Kim, Do Han; Jo, Won Jun; Sojoudi, Hossein; Gleason, Karen K

2017-03-01

Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high-purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro- and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radio frequency and microwave plasma for optical thin-film deposition

NASA Astrophysics Data System (ADS)

Otto, Juergen; Paquet, Volker; Kersten, Ralf T.; Etzkorn, Heinz-Werner; Brusasco, Raymond M.; Britten, Jerald A.; Campbell, Jack H.; Thorsness, J. B.

1990-12-01

For the next generation of fusion lasers reflecting mirrors with laser damage thresholds of at least 40 J/cm2 for 1 0 ns laser pulses at 1 .064 pm are needed. Up to now, no deposition technique has been developed to produce such mirrors. Best R&D-values realized today are around 30 J/cm2 for e-beam evaporated mirrors. R&D on conventional e-beam coating processes over the last 1 0 years has come up with marginal improvements in laser damage thresholds only. However, new technologies, like PICVD (Plasma-Impulse CVD) developed for the fabrication of ultra-low loss fiber preforms, seem to offer the potential to solve this problem. First results have been reported already [1-3]. It is well known that fused silica produced by CVD processes can have laser damage thresholds as high as 80 J/cm2. However, the thickness of a single deposited film is in the pm-range for most of the CVD-processes used for preform manufacturing; since interference optics need films in the ; /4n range (where n is the refractive index of the dielectric material) the use of preform-fabrication processes for the purpose of interference mirror fabrication is limited to a few plasma based CVD technologies, namely PCVD (Plasma-CVD, Philips [4]; PICVD, SCHOTT [5]). Especially PICVD is a very powerful technology to fabricate thin film multilayers for interference mirrors, because this technique is able to produce films down to monolayer thickness with nearly perfect stoichiometry and morphology. In first and preliminary experiments the usual deposition in a circular tube at high temperatures has been used for simplicity. However, to produce large area high quality laser mirrors this principle know-how has to be transfered from circular to planar geometry. Experiments showed, that there may be some limitations with respect to the homogeneity of a planar deposition using microwave excitation for the plasma. Therefore experiments have been performed in parallel with both RF and microwave excitation for comparison. In the following we will restrict ourselves to the description and discussions of the planar processes; the principle and details of the PICVD-process are described elsewhere [5] while RF-plasma technology is a well known process.

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.

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.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ioakeimidis, Apostolos; Christodoulou, Christos; Lux-Steiner, Martha

In this work we fabricate all-vacuum processed methyl ammonium lead halide perovskite by a sequence of physical vapour deposition of PbI{sub 2} and chemical vapour deposition (CVD) of CH{sub 3}NH{sub 3}I under a static atmosphere. We demonstrate that for higher deposition rate the (001) planes of PbI{sub 2} film show a higher degree of alignment parallel to the sample's surface. From X-ray diffraction data of the resulted perovskite film we derive that the intercalation rate of CH{sub 3}NH{sub 3}I is fostered for PbI{sub 2} films with higher degree of (001) planes alignment. The stoichiometry of the produced perovskite film ismore » also studied by Hard X-ray photoelectron spectroscopy measurements. Complete all-vacuum perovskite solar cells were fabricated on glass/ITO substrates coated by an ultra-thin (5 nm) Zn-phthalocyanine film as hole selective layer. A dependence of residual PbI{sub 2} on the solar cells performance is displayed, while photovoltaic devices with efficiency up to η=11.6% were achieved. - Graphical abstract: A two-step PVD/CVD processed perovskite film with the CVD intercalation rate of CH{sub 3}NCH{sub 3} molecules been fostered by increasing the PVD rate of PbI{sub 2} and prolonging the CVD time. - Highlights: • A simple PVD/CVD process for perovskite film production. • Increased PVD rate yields better alignment of the PbI{sub 2} (001) crystallite planes. • CH{sub 3}NH{sub 3}I intercalation process fostered by increased PbI{sub 2} PVD rate. • Stoichiometric CH{sub 3}NH{sub 3}PbI{sub 3} suitable as absorber in photovoltaic applications • Reduced PbI{sub 2} residue at the bottom of CH{sub 3}NH{sub 3}PbI{sub 3} improves device performance.« less

Diffusion mechanisms in chemical vapor-deposited iridium coated on chemical vapor-deposited rhenium

NASA Technical Reports Server (NTRS)

Hamilton, J. C.; Yang, N. Y. C.; Clift, W. M.; Boehme, D. R.; Mccarty, K. F.; Franklin, J. E.

1992-01-01

Radiation-cooled rocket thruster chambers have been developed which use CVD Re coated with CVD Ir on the interior surface that is exposed to hot combustion gases. The Ir serves as an oxidation barrier which protects the structural integrity-maintaining Re at elevated temperatures. The diffusion kinetics of CVD materials at elevated temperatures is presently studied with a view to the prediction and extension of these thrusters' performance limits. Line scans for Ir and Re were fit on the basis of a diffusion model, in order to extract relevant diffusion constants; the fastest diffusion process is grain-boundary diffusion, where Re diffuses down grain boundaries in the Ir overlayer.

Gaalas/Gaas Solar Cell Process Study

NASA Technical Reports Server (NTRS)

Almgren, D. W.; Csigi, K. I.

1980-01-01

Available information on liquid phase, vapor phase (including chemical vapor deposition) and molecular beam epitaxy growth procedures that could be used to fabricate single crystal, heteroface, (AlGa) As/GaAs solar cells, for space applications is summarized. A comparison of the basic cost elements of the epitaxy growth processes shows that the current infinite melt LPE process has the lower cost per cell for an annual production rate of 10,000 cells. The metal organic chemical vapor deposition (MO-CVD) process has the potential for low cost production of solar cells but there is currently a significant uncertainty in process yield, i.e., the fraction of active material in the input gas stream that ends up in the cell. Additional work is needed to optimize and document the process parameters for the MO-CVD process.

Giving Bigger Satellites a Boost

NASA Technical Reports Server (NTRS)

2000-01-01

Ultramet, Inc. has spurred a new process for producing rocket engine thrust chambers, through SBIR funding and the Glenn Research Center. High-temperature oxidation-resistant thruster materials are being produced in order to achieve high-temperature capability without sacrificing reliability. These thruster materials lead to an estimated three-percent improvement in propulsion system performance. To develop this material, Ultramet used a process called chemical vapor deposition (CVD). CVD involves heating precursors for metals, like iridium and rhenium, to temperatures at which they become gaseous. They are then deposited onto a mandrel, or spindle, layer-by-layer to produce high-density, highly resistant materials from the inside out.

Mixed Convection Flow in Horizontal CVD Reactors

NASA Astrophysics Data System (ADS)

Chiu, Wilson K. S.; Richards, Cristy J.; Jaluria, Yogesh

1998-11-01

Increasing demands for high quality films and production rates are challenging current Chemical Vapor Deposition (CVD) technology. Since film quality and deposition rates are strongly dependent on gas flow and heat transfer (W.K.S. Chiu and Y. Jaluria, ASME HTD-Vol. 347, pp. 293-311, 1997.), process improvement is obtained through the study of mixed convection flow and temperature distribution in a CVD reactor. Experimental results are presented for a CVD chamber with a horizontal or inclined resistance heated susceptor. Vaporized glycol solution illuminated by a light sheet is used for flow visualization. Temperature measurements are obtained by inserting thermocouple probes into the gas stream or embedding probes into the reactor walls. Flow visualization and temperature measurements show predominantly two dimensional flow and temperature distributions along the streamwise direction under forced convection conditions. Natural convection dominates under large heating rates and low flow rates. Over the range of parameters studied, several distinct flow regimes, characterized by instability, separation, and turbulence, are evident. Different flow regimes alter the flow pattern and temperature distribution, and in consequence, significantly modify deposition rates and uniformity.

iCVD Cyclic Polysiloxane and Polysilazane as Nanoscale Thin-Film Electrolyte: Synthesis and Properties.

PubMed

Chen, Nan; Reeja-Jayan, B; Liu, Andong; Lau, Jonathan; Dunn, Bruce; Gleason, Karen K

2016-03-01

A group of crosslinked cyclic siloxane (Si-O) and silazane (Si-N) polymers are synthesized via solvent-free initiated chemical vapor deposition (iCVD). Notably, this is the first report of cyclic polysilazanes synthesized via the gas-phase iCVD method. The deposited nanoscale thin films are thermally stable and chemically inert. By iCVD, they can uniformly and conformally cover nonplanar surfaces having complex geometry. Although polysiloxanes are traditionally utilized as dielectric materials and insulators, our research shows these cyclic organosilicon polymers can conduct lithium ions (Li(+) ) at room temperature. The conformal coating and the room temperature ionic conductivity make these cyclic organosilicon polymers attractive for use as thin-film electrolytes in solid-state batteries. Also, their synthesis process and properties have been systemically studied and discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical reactivity of CVC and CVD SiC with UO2 at high temperatures

NASA Astrophysics Data System (ADS)

Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; Snead, Lance L.

2015-05-01

Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO2 pellets and evaluated for their potential chemical reaction with UO2. While minor reactivity between chemical-vapor-composited (CVC) SiC and UO2 was observed at comparatively low temperatures of 1100 and 1300 °C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity. However, both CVD and CVC SiCs showed some reaction with UO2 at a higher temperature (1500 °C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive than CVD SiC at 1500 °C. Furthermore, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi2, and U3Si2 as a result of SiC reaction with UO2.

Iridium-coated rhenium thrusters by CVD

NASA Technical Reports Server (NTRS)

Harding, J. T.; Kazaroff, J. M.; Appel, M. A.

1989-01-01

Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the melting temperature of iridium, 2400 C (4350 F).

Iridium-coated rhenium thrusters by CVD

NASA Technical Reports Server (NTRS)

Harding, John T.; Kazaroff, John M.; Appel, Marshall A.

1988-01-01

Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the meltimg temperature of iridium, 2400 C (4350 F).

The optical properties of transferred graphene and the dielectrics grown on it obtained by ellipsometry

NASA Astrophysics Data System (ADS)

Kasikov, Aarne; Kahro, Tauno; Matisen, Leonard; Kodu, Margus; Tarre, Aivar; Seemen, Helina; Alles, Harry

2018-04-01

Graphene layers grown by chemical vapour deposition (CVD) method and transferred from Cu-foils to the oxidized Si-substrates were investigated by spectroscopic ellipsometry (SE), Raman and X-Ray Photoelectron Spectroscopy (XPS) methods. The optical properties of transferred CVD graphene layers do not always correspond to the ones of the exfoliated graphene due to the contamination from the chemicals used in the transfer process. However, the real thickness and the mean properties of the transferred CVD graphene layers can be found using ellipsometry if a real thickness of the SiO2 layer is taken into account. The pulsed laser deposition (PLD) and atomic layer deposition (ALD) methods were used to grow dielectric layers on the transferred graphene and the obtained structures were characterized using optical methods. The approach demonstrated in this work could be useful for the characterization of various materials grown on graphene.

Silicon-on-Insulator Pin Diodes.

DTIC Science & Technology

1987-12-01

Thin (0.5 Micron) Silicon-on-Oxidized Silicon Fig. 2.8 SEM Photographs of CVD Silicon Dioxide on Aluminum 28 After 1500 0 C Anneal in Oxygen...silicon nitride over the silicon dioxide encapsu- -9- lation layer and by depositing the silicon dioxide with a plasma CVD process which uses N20 as...relief via thermal expansion matching varies lin- -27- A B Figure 2.8: SEM Photographs of CVD Silicon Dioxide on Aluminum after 15000 C Anneal in Oxygen

DOE Office of Scientific and Technical Information (OSTI.GOV)

MANI,SEETHAMBAL S.; FLEMING,JAMES G.; WALRAVEN,JEREMY A.

Two major problems associated with Si-based MEMS (MicroElectroMechanical Systems) 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 present a CVD (Chemical Vapor Deposition) process that selectively coats MEMS devices with tungsten and significantly enhances device durability. Tungsten CVD is used in the integrated-circuit industry, which makes this approach manufacturable. This selective deposition process results in a very conformal coating and can potentially address both stiction and wear problems confronting MEMS processing. The selective deposition of tungsten is accomplished through the siliconmore » reduction of WF{sub 6}. The self-limiting nature of the process ensures consistent process control. The tungsten is deposited after the removal of the sacrificial oxides to minimize stress and process integration problems. The tungsten coating adheres well and is hard and conducting, which enhances performance for numerous devices. 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 adhered parts that are contacted over small areas such as dimples. The wear resistance of tungsten coated parts has been shown to be significantly improved by microengine test structures.« less

Computational Modeling in Structural Materials Processing

NASA Technical Reports Server (NTRS)

Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

1997-01-01

High temperature materials such as silicon carbide, a variety of nitrides, and ceramic matrix composites find use in aerospace, automotive, machine tool industries and in high speed civil transport applications. Chemical vapor deposition (CVD) is widely used in processing such structural materials. Variations of CVD include deposition on substrates, coating of fibers, inside cavities and on complex objects, and infiltration within preforms called chemical vapor infiltration (CVI). Our current knowledge of the process mechanisms, ability to optimize processes, and scale-up for large scale manufacturing is limited. In this regard, computational modeling of the processes is valuable since a validated model can be used as a design tool. The effort is similar to traditional chemically reacting flow modeling with emphasis on multicomponent diffusion, thermal diffusion, large sets of homogeneous reactions, and surface chemistry. In the case of CVI, models for pore infiltration are needed. In the present talk, examples of SiC nitride, and Boron deposition from the author's past work will be used to illustrate the utility of computational process modeling.

Laser assisted processing; Proceedings of the Meeting, Hamburg, Federal Republic of Germany, Sept. 19, 20, 1988

NASA Astrophysics Data System (ADS)

Laude, Lucien D.; Rauscher, Gerhard

The use of lasers in industrial material processing is discussed in reviews and reports. Sections are devoted to high-precision laser machining, deposition methods, ablation and polymers, and synthesis and oxidation. Particular attention is given to laser cutting of steel sheets, laser micromachining of material surfaces, process control in laser soldering, laser-induced CVD of doped Si stripes on SOS and their characterization by piezoresistivity measurements, laser CVD of Pt spots on glass, laser deposition of GaAs, UV-laser photoablation of polymers, ArF excimer-laser ablation of HgCdTe semiconductor, pulsed laser synthesis of Ti silicides and nitrides, the kinetics of laser-assisted oxidation of metallic films, and excimer-laser-assisted etching of solids for microelectronics.

The Chemistry of Inorganic Precursors during the Chemical Deposition of Films on Solid Surfaces.

PubMed

Barry, Seán T; Teplyakov, Andrew V; Zaera, Francisco

2018-03-20

The deposition of thin solid films is central to many industrial applications, and chemical vapor deposition (CVD) methods are particularly useful for this task. For one, the isotropic nature of the adsorption of chemical species affords even coverages on surfaces with rough topographies, an increasingly common requirement in microelectronics. Furthermore, by splitting the overall film-depositing reactions into two or more complementary and self-limiting steps, as it is done in atomic layer depositions (ALD), film thicknesses can be controlled down to the sub-monolayer level. Thanks to the availability of a vast array of inorganic and metalorganic precursors, CVD and ALD are quite versatile and can be engineered to deposit virtually any type of solid material. On the negative side, the surface chemistry that takes place in these processes is often complex, and can include undesirable side reactions leading to the incorporation of impurities in the growing films. Appropriate precursors and deposition conditions need to be chosen to minimize these problems, and that requires a proper understanding of the underlying surface chemistry. The precursors for CVD and ALD are often designed and chosen based on their known thermal chemistry from inorganic chemistry studies, taking advantage of the vast knowledge developed in that field over the years. Although a good first approximation, however, this approach can lead to wrong choices, because the reactions of these precursors at gas-solid interfaces can be quite different from what is seen in solution. For one, solvents often aid in the displacement of ligands in metalorganic compounds, providing the right dielectric environment, temporarily coordinating to the metal, or facilitating multiple ligand-complex interactions to increase reaction probabilities; these options are not available in the gas-solid reactions associated with CVD and ALD. Moreover, solid surfaces act as unique "ligands", if these reactions are to be viewed from the point of view of the metalorganic complexes used as precursors: they are bulky and rigid, can provide multiple binding sites for a single reaction, and can promote unique bonding modes, especially on metals, which have delocalized electronic structures. The differences between the molecular and surface chemistry of CVD and ALD precursors can result in significant variations in their reactivity, ultimately leading to unpredictable properties in the newly grown films. In this Account, we discuss some of the main similarities and differences in chemistry that CVD/ALD precursors follow on surfaces when contrasted against their known behavior in solution, with emphasis on our own work but also referencing other key contributions. Our approach is unique in that it combines expertise from the inorganic, surface science, and quantum-mechanics fields to better understand the mechanistic details of the chemistry of CVD and ALD processes and to identify new criteria to consider when designing CVD/ALD precursors.

Report of work done for technical assistance agreement 1269 between Sandia National Laboratories and the Watkins-Johnson Company: Chemical reaction mechanisms for computational models of SiO{sub 2} CVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, P.; Johannes, J.; Kudriavtsev, V.

The use of computational modeling to improve equipment and process designs for chemical vapor deposition (CVD) reactors is becoming increasingly common. Commercial codes are available that facilitate the modeling of chemically-reacting flows, but chemical reaction mechanisms must be separately developed for each system of interest. One f the products of the Watkins-Johnson Company (WJ) is a reactor marketed to semiconductor manufacturers for the atmospheric-pressure chemical vapor deposition (APCVD) of silicon oxide films. In this process, TEOS (tetraethoxysilane, Si(OC{sub 2}H{sub 5}){sub 4}) and ozone (O{sub 3}) are injected (in nitrogen and oxygen carrier gases) over hot silicon wafers that are beingmore » carried through the system on a moving belt. As part of their equipment improvement process, WJ is developing computational models of this tool. In this effort, they are collaborating with Sandia National Laboratories (SNL) to draw on Sandia`s experience base in understanding and modeling the chemistry of CVD processes.« less

Effect of process conditions and chemical composition on the microstructure and properties of chemically vapor deposited SiC, Si, ZnSe, ZnS and ZnS(x)Se(1-x)

NASA Technical Reports Server (NTRS)

Pickering, Michael A.; Taylor, Raymond L.; Goela, Jitendra S.; Desai, Hemant D.

1992-01-01

Subatmospheric pressure CVD processes have been developed to produce theoretically dense, highly pure, void-free and large area bulk materials, SiC, Si, ZnSe, ZnS and ZnS(x)Se(1-x). These materials are used for optical elements, such as mirrors, lenses and windows, over a wide spectral range from the VUV to the IR. We discuss the effect of CVD process conditions on the microstructure and properties of these materials, with emphasis on optical performance. In addition, we discuss the effect of chemical composition on the properties of the composite material ZnS(x)Se(1-x). We first present a general overview of the bulk CVD process and the relationship between process conditions, such as temperature, pressure, reactant gas concentration and growth rate, and the microstructure, morphology and properties of CVD-grown materials. Then we discuss specific results for CVD-grown SiC, Si, ZnSe, ZnS and ZnS(x)Se(1-x).

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.

Effects of etchants in the transfer of chemical vapor deposited graphene

NASA Astrophysics Data System (ADS)

Wang, M.; Yang, E. H.; Vajtai, R.; Kono, J.; Ajayan, P. M.

2018-05-01

The quality of graphene can be strongly modified during the transfer process following chemical vapor deposition (CVD) growth. Here, we transferred CVD-grown graphene from a copper foil to a SiO2/Si substrate using wet etching with four different etchants: HNO3, FeCl3, (NH4)2S2O8, and a commercial copper etchant. We then compared the quality of graphene after the transfer process in terms of surface modifications, pollutions (residues and contaminations), and electrical properties (mobility and density). Our tests and analyses showed that the commercial copper etchant provides the best structural integrity, the least amount of residues, and the smallest doping carrier concentration.

Surface structuring of boron doped CVD diamond by micro electrical discharge machining

NASA Astrophysics Data System (ADS)

Schubert, A.; Berger, T.; Martin, A.; Hackert-Oschätzchen, M.; Treffkorn, N.; Kühn, R.

2018-05-01

Boron doped diamond materials, which are generated by Chemical Vapor Deposition (CVD), offer a great potential for the application on highly stressed tools, e. g. in cutting or forming processes. As a result of the CVD process rough surfaces arise, which require a finishing treatment in particular for the application in forming tools. Cutting techniques such as milling and grinding are hardly applicable for the finish machining because of the high strength of diamond. Due to its process principle of ablating material by melting and evaporating, Electrical Discharge Machining (EDM) is independent of hardness, brittleness or toughness of the workpiece material. EDM is a suitable technology for machining and structuring CVD diamond, since boron doped CVD diamond is electrically conductive. In this study the ablation characteristics of boron doped CVD diamond by micro electrical discharge machining are investigated. Experiments were carried out to investigate the influence of different process parameters on the machining result. The impact of tool-polarity, voltage and discharge energy on the resulting erosion geometry and the tool wear was analyzed. A variation in path overlapping during the erosion of planar areas leads to different microstructures. The results show that micro EDM is a suitable technology for finishing of boron doped CVD diamond.

Fast method for reactor and feature scale coupling in ALD and CVD

DOEpatents

Yanguas-Gil, Angel; Elam, Jeffrey W.

2017-08-08

Transport and surface chemistry of certain deposition techniques is modeled. Methods provide a model of the transport inside nanostructures as a single-particle discrete Markov chain process. This approach decouples the complexity of the surface chemistry from the transport model, thus allowing its application under general surface chemistry conditions, including atomic layer deposition (ALD) and chemical vapor deposition (CVD). Methods provide for determination of determine statistical information of the trajectory of individual molecules, such as the average interaction time or the number of wall collisions for molecules entering the nanostructures as well as to track the relative contributions to thin-film growth of different independent reaction pathways at each point of the feature.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allendorf, M.D.; Arsenlis, A.; Bastasz, R.

Titanium nitride (TiN) films deposited by chemical vapor deposition (CVD) techniques are of interest for a wide range of commercial applications. In this report, the authors describe a mechanism that predicts Tin film growth rates from TiCl{sub 4}/NH{sub 3} mixtures as a function of process parameters, including inlet reactant concentrations, substrate temperatures, reactor pressures, and total gas flow rates. Model predictions were verified by comparison with the results of TiN deposition experiments in the literature and with measurements made in a new stagnation-flow reactor developed for the purpose of testing deposition mechanisms such as this. In addition, they describe abmore » initio calculations that predict thermodynamic properties for titanium-containing compounds. The results of calculations using Moeller-Plesset perturbation theory, density functional theory, and coupled cluster theory are encouraging and suggest that these methods can be used to estimate thermodynamic data that are essential for the development of CVD models involving transition-metal compounds. Finally, measurements of the adsorption and desorption kinetics of NH{sub 3} on TiN films using temperature-programmed desorption are described and their relevance to TiN CVD and mechanism development are discussed.« less

Engineering Nanoscale Polymers in Photovoltaics and Supercapacitors: Experimental and Theoretical Studies

NASA Astrophysics Data System (ADS)

Smolin, Yuriy Y.

Dye sensitized solar cells (DSSCs) and carbon-based supercapacitors are promising energy conversion and storage systems, respectively, because they can be made inexpensively, have good performance, and can be integrated into portable and flexible electronics. Both systems utilize nanostructured porous electrodes, leading to fewer diffusion limitations and higher active surface areas for interfacial processes compared to planar electrodes. A major drawback of the DSSC design is the use of a liquid electrolyte, since it is prone to leakage and evaporation--hindering DSSC applications, durability, and thermal stability. A polymer electrolyte (PE) can overcome these shortcomings; however, the integration of a PE within the mesoporous TiO2 photoanode of DSSCs with pore openings of 10-20 nm and photoanode thicknesses of 10 microm is very challenging. Solution-based deposition methods such as spin coating and drop casting to deposit PEs has led to incomplete pore filling inside the mesoporous photoanode, resulting in lower than optimal efficiencies. To overcome these challenges, a solvent-free method called initiated chemical vapor deposition (iCVD) was adopted to deposit PEs within the porous TiO2 electrode. In iCVD, the monomer and initiator are vapors which easily penetrate into the porous electrode. By carefully controlling the iCVD processing parameters, complete pore filling of PEs into the TiO2 photoanode was achieved, leading to 50% improvement in conversion efficiency. Polymers with ether, ester, pyridine, pyrrolidone, imidazole and epoxy functionality were synthesized and integrated. The findings indicated that DSSC characteristics, including open circuit voltage, short circuit current density and fill factor, can be tuned by polymer chemistry. A promising approach to improve the energy density of supercapacitor electrodes is to integrate inexpensive conducting polymers (CPs), such as polyaniline (PANI). Unfortunately, most CPs are insoluble, and integrating CPs into tortuous electrode pores with aspect ratios of >10,000 while preserving the intrinsic pore structures, to retain the double layer capacitance, is very challenging. Therefore, similarly to the iCVD process, oxidative CVD (oCVD) was chosen to bypass the limited solubility of CPs to deposit thin conformal CP films onto porous electrodes. By controlling the oCVD deposition parameters, PANI films on the order of a few nm were integrated into carbide-derived-carbon (CDC) electrodes, leading to a doubling of the capacitance. This yielded a PANI-only capacitance of 690 F/g, close to the theoretical value of 750 F/g. This work also combined experiments with first-principles modeling to develop a model-guided design and optimization framework, allowing for optimal device design and the intelligent selection of polymer chemistries with minimal experimental investigations. For example, to determine the effects of PE chemistry on DSSC processes, parameter estimation and parametric sensitivity studies were conducted which indicated that a shift in the conduction band of TiO2 and a suppression of the back electron transfer at the dye-TiO2-PE interface was induced by the side group PE chemistry. Furthermore, optimal design specifications for a PE DSSC were calculated using the model, and optimally performing DSSCs were subsequently fabricated and tested, validating the model.

Formation of Aluminide Coatings on Fe-Based Alloys by Chemical Vapor Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ying; Pint, Bruce A; Cooley, Kevin M

2008-01-01

Aluminide and Al-containing coatings were synthesized on commercial ferritic (P91) and austenitic (304L) alloys via a laboratory chemical vapor deposition (CVD) procedure for rigorous control over coating composition, purity and microstructure. The effect of the CVD aluminizing parameters such as temperature, Al activity, and post-aluminizing anneal on coating growth was investigated. Two procedures involving different Al activities were employed with and without including Cr-Al pellets in the CVD reactor to produce coatings with suitable thickness and composition for coating performance evaluation. The phase constitution of the as-synthesized coatings was assessed with the aid of a combination of X-ray diffraction, electronmore » probe microanalysis, and existing phase diagrams. The mechanisms of formation of these CVD coatings on the Fe-based alloys are discussed, and compared with nickel aluminide coatings on Ni-base superalloys. In addition, Cr-Al pellets were replaced with Fe-Al metals in some aluminizing process runs and similar coatings were achieved.« less

Chemical reactivity of CVC and CVD SiC with UO 2 at high temperatures

DOE PAGES

Silva, Chinthaka M.; Katoh, Yutai; Voit, Stewart L.; ...

2015-02-11

Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO 2 pellets and evaluated for their potential chemical reaction with UO 2. While minor reactivity between chemical-vapor-composited (CVC) SiC and UO 2 was observed at comparatively low temperatures of 1100 and 1300 C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity, according to microstructural investigations. But, both CVD and CVC SiCs showed some reaction with UO 2 at a higher temperature (1500 C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive thanmore » CVD SiC at 1500 C. Moreover, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi 2, and U 3Si 2 as a result of SiC reaction with UO 2.« less

A novel Mo-W interlayer approach for CVD diamond deposition on steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kundrát, Vojtěch; Sullivan, John; Ye, Haitao, E-mail: h.ye@aston.ac.uk

Steel is the most widely used material in engineering for its cost/performance ratio and coatings are routinely applied on its surface to further improve its properties. Diamond coated steel parts are an option for many demanding industrial applications through prolonging the lifetime of steel parts, enhancement of tool performance as well as the reduction of wear rates. Direct deposition of diamond on steel using conventional chemical vapour deposition (CVD) processes is known to give poor results due to the preferential formation of amorphous carbon on iron, nickel and other elements as well as stresses induced from the significant difference inmore » the thermal expansion coefficients of those materials. This article reports a novel approach of deposition of nanocrystalline diamond coatings on high-speed steel (M42) substrates using a multi-structured molybdenum (Mo) – tungsten (W) interlayer to form steel/Mo/Mo-W/W/diamond sandwich structures which overcome the adhesion problem related to direct magnetron sputtering deposition of pure tungsten. Surface, interface and tribology properties were evaluated to understand the role of such an interlayer structure. The multi-structured Mo-W interlayer has been proven to improve the adhesion between diamond films and steel substrates by acting as an effective diffusion barrier during the CVD diamond deposition.« less

A novel Mo-W interlayer approach for CVD diamond deposition on steel

NASA Astrophysics Data System (ADS)

Kundrát, Vojtěch; Zhang, Xiaoling; Cooke, Kevin; Sun, Hailin; Sullivan, John; Ye, Haitao

2015-04-01

Steel is the most widely used material in engineering for its cost/performance ratio and coatings are routinely applied on its surface to further improve its properties. Diamond coated steel parts are an option for many demanding industrial applications through prolonging the lifetime of steel parts, enhancement of tool performance as well as the reduction of wear rates. Direct deposition of diamond on steel using conventional chemical vapour deposition (CVD) processes is known to give poor results due to the preferential formation of amorphous carbon on iron, nickel and other elements as well as stresses induced from the significant difference in the thermal expansion coefficients of those materials. This article reports a novel approach of deposition of nanocrystalline diamond coatings on high-speed steel (M42) substrates using a multi-structured molybdenum (Mo) - tungsten (W) interlayer to form steel/Mo/Mo-W/W/diamond sandwich structures which overcome the adhesion problem related to direct magnetron sputtering deposition of pure tungsten. Surface, interface and tribology properties were evaluated to understand the role of such an interlayer structure. The multi-structured Mo-W interlayer has been proven to improve the adhesion between diamond films and steel substrates by acting as an effective diffusion barrier during the CVD diamond deposition.

Investigation of chemical vapor deposition of garnet films for bubble domain memories

NASA Technical Reports Server (NTRS)

Besser, P. J.; Hamilton, T. N.

1973-01-01

The important process parameters and control required to grow reproducible device quality ferrimagnetic films by chemical vapor deposition (CVD) were studied. The investigation of the critical parameters in the CVD growth process led to the conclusion that the required reproducibility of film properties cannot be achieved with individually controlled separate metal halide sources. Therefore, the CVD growth effort was directed toward replacement of the halide sources with metallic sources with the ultimate goal being the reproducible growth of complex garnet compositions utilizing a single metal alloy source. The characterization of the YGdGaIG films showed that certain characteristics of this material, primarily the low domain wall energy and the large temperature sensitivity, severely limited its potential as a useful material for bubble domain devices. Consequently, at the time of the change from halide to metallic sources, the target film compositions were shifted to more useful materials such as YGdTmGaIG, YEuGaIG and YSmGaIG.

Synthesis of high performance ceramic fibers by chemical vapor deposition for advanced metallics reinforcing

NASA Technical Reports Server (NTRS)

Revankar, Vithal; Hlavacek, Vladimir

1991-01-01

The chemical vapor deposition (CVD) synthesis of fibers capable of effectively reinforcing intermetallic matrices at elevated temperatures which can be used for potential applications in high temperature composite materials is described. This process was used due to its advantage over other fiber synthesis processes. It is extremely important to produce these fibers with good reproducible and controlled growth rates. However, the complex interplay of mass and energy transfer, blended with the fluid dynamics makes this a formidable task. The design and development of CVD reactor assembly and system to synthesize TiB2, CrB, B4C, and TiC fibers was performed. Residual thermal analysis for estimating stresses arising form thermal expansion mismatch were determined. Various techniques to improve the mechanical properties were also performed. Various techniques for improving the fiber properties were elaborated. The crystal structure and its orientation for TiB2 fiber is discussed. An overall view of the CVD process to develop CrB2, TiB2, and other high performance ceramic fibers is presented.

Process stability and morphology optimization of very thick 4H-SiC epitaxial layers grown by chloride-based CVD

NASA Astrophysics Data System (ADS)

Yazdanfar, M.; Stenberg, P.; Booker, I. D.; Ivanov, I. G.; Kordina, O.; Pedersen, H.; Janzén, E.

2013-10-01

The development of a chemical vapor deposition (CVD) process for very thick silicon carbide (SiC) epitaxial layers suitable for high power devices is demonstrated by epitaxial growth of 200 μm thick, low doped 4H-SiC layers with excellent morphology at growth rates exceeding 100 μm/h. The process development was done in a hot wall CVD reactor without rotation using both SiCl4 and SiH4+HCl precursor approaches to chloride based growth chemistry. A C/Si ratio <1 and an optimized in-situ etch are shown to be the key parameters to achieve 200 μm thick, low doped epitaxial layers with excellent morphology.

Superhydrophobic Copper Surfaces with Anticorrosion Properties Fabricated by Solventless CVD Methods.

PubMed

Vilaró, Ignasi; Yagüe, Jose L; Borrós, Salvador

2017-01-11

Due to continuous miniaturization and increasing number of electrical components in electronics, copper interconnections have become critical for the design of 3D integrated circuits. However, corrosion attack on the copper metal can affect the electronic performance of the material. Superhydrophobic coatings are a commonly used strategy to prevent this undesired effect. In this work, a solventless two-steps process was developed to fabricate superhydrophobic copper surfaces using chemical vapor deposition (CVD) methods. The superhydrophobic state was achieved through the design of a hierarchical structure, combining micro-/nanoscale domains. In the first step, O 2 - and Ar-plasma etchings were performed on the copper substrate to generate microroughness. Afterward, a conformal copolymer, 1H,1H,2H,2H-perfluorodecyl acrylate-ethylene glycol diacrylate [p(PFDA-co-EGDA)], was deposited on top of the metal via initiated CVD (iCVD) to lower the surface energy of the surface. The copolymer topography exhibited a very characteristic and unique nanoworm-like structure. The combination of the nanofeatures of the polymer with the microroughness of the copper led to achievement of the superhydrophobic state. AFM, SEM, and XPS were used to characterize the evolution in topography and chemical composition during the CVD processes. The modified copper showed water contact angles as high as 163° and hysteresis as low as 1°. The coating withstood exposure to aggressive media for extended periods of time. Tafel analysis was used to compare the corrosion rates between bare and modified copper. Results indicated that iCVD-coated copper corrodes 3 orders of magnitude slower than untreated copper. The surface modification process yielded repeatable and robust superhydrophobic coatings with remarkable anticorrosion properties.

Low-temperature-grown continuous graphene films from benzene by chemical vapor deposition at ambient pressure

NASA Astrophysics Data System (ADS)

Jang, Jisu; Son, Myungwoo; Chung, Sunki; Kim, Kihyeun; Cho, Chunhum; Lee, Byoung Hun; Ham, Moon-Ho

2015-12-01

There is significant interest in synthesizing large-area graphene films at low temperatures by chemical vapor deposition (CVD) for nanoelectronic and flexible device applications. However, to date, low-temperature CVD methods have suffered from lower surface coverage because micro-sized graphene flakes are produced. Here, we demonstrate a modified CVD technique for the production of large-area, continuous monolayer graphene films from benzene on Cu at 100-300 °C at ambient pressure. In this method, we extended the graphene growth step in the absence of residual oxidizing species by introducing pumping and purging cycles prior to growth. This led to continuous monolayer graphene films with full surface coverage and excellent quality, which were comparable to those achieved with high-temperature CVD; for example, the surface coverage, transmittance, and carrier mobilities of the graphene grown at 300 °C were 100%, 97.6%, and 1,900-2,500 cm2 V-1 s-1, respectively. In addition, the growth temperature was substantially reduced to as low as 100 °C, which is the lowest temperature reported to date for pristine graphene produced by CVD. Our modified CVD method is expected to allow the direct growth of graphene in device manufacturing processes for practical applications while keeping underlying devices intact.

Cerebrovascular disease, beta-amyloid and cognition in aging

PubMed Central

Marchant, Natalie L.; Reed, Bruce R.; DeCarli, Charles S.; Madison, Cindee M.; Weiner, Michael W.; Chui, Helena C.; Jagust, William J.

2011-01-01

The present study evaluated cerebrovascular disease (CVD), β-amyloid (Aβ), and cognition in clinically normal elderly adults. Fifty-four participants underwent MRI, PIB-PET imaging, and neuropsychological evaluation. High white matter hyperintensity burden and/or presence of infarct defined CVD status (CVD−: N = 27; CVD+: N = 27). PIB-PET ratios of Aβ deposition were extracted using Logan plotting (cerebellar reference). Presence of high levels of Aβ in prespecified regions determined PIB status (PIB−: N = 33; PIB+: N = 21). Executive functioning and episodic memory were measured using composite scales. CVD and Aβ, defined as dichotomous or continuous variables, were unrelated to one another. CVD+ participants showed lower executive functioning (P = 0.001) when compared to CVD− individuals. Neither PIB status nor amount of Aβ affected cognition (Ps ≥ .45), and there was no statistical interaction between CVD and PIB on either cognitive measure. Within this spectrum of normal aging CVD and Aβ aggregation appear to be independent processes with CVD primarily affecting cognition. PMID:22048124

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 reactions on the substrate surface, conductive, convective, inductive and radiative heat transfer, species transport and thereto-elastic stress distributions. Gas phase and surface reactions are studied thermodynamically and kinetically. Based on experimental results, detailed reaction mechanisms are proposed and the deposition rates are predicted. The deposition model proposed could be used for other experiments with similar operating conditions. Four different growth systems are presented in this thesis to discuss comprehensive transport phenomena in crystal growth from vapor. The first is the polysilicon bulk growth by modified Siemens technique in which a silicon tube is used as the starting material. The research effort has been focused on system design, geometric and operating parameters optimization, and heterogeneous and homogeneous silane pyrolysis analysis. The second is the GaN thin film growth by iodine vapor phase epitaxy technique. Heat and mass transport is studied analytically and numerically. Gas phase and surface reactions are analyzed thermodynamically and kinetically. Quasi-equilibrium and kinetic deposition models are developed to predict the growth rate. The third one is the AlN thin film growth by halide vapor phase epitaxy technique. The effects of gas phase and surface reactions on the crystal growth rate and deposition uniformity are studied. The last one is the AlN sublimation growth system. The research effort has been focused on the effect of thermal environment evolution on the crystal growth process. The thermoelastic stress formed in the as-grown AlN crystal is also calculated.

Mirror Technology

NASA Technical Reports Server (NTRS)

1992-01-01

Under a NASA contract, MI-CVD developed a process for producing bulk silicon carbide by means of a chemical vapor deposition process. The technology allows growth of a high purity material with superior mechanical/thermal properties and high polishability - ideal for mirror applications. The company employed the technology to develop three research mirrors for NASA Langley and is now marketing it as CVD SILICON CARBIDE. Its advantages include light weight, thermal stability and high reflectivity. The material has nuclear research facility applications and is of interest to industrial users of high power lasers.

Graphene Synthesis by Plasma-Enhanced CVD Growth with Ethanol

DOE PAGES

Campo, Teresa; Cotto, María; Márquez, Francisco; ...

2016-03-01

A modified route to synthesize graphene flakes is proposed using the Chemical Vapor Deposition (CVD) technique, by using copper substrates as supports. The carbon source used was ethanol, the synthesis temperature was 950°C and the pressure was controlled along the whole process. In this CVD synthesis process the incorporation of the carbon source was produced at low pressure and 950°C inducing the appearance of a plasma blue flash inside the quartz tube. Apparently, the presence of this plasma blue flash is required for obtaining graphene flakes. The synthesized graphene was characterized by different techniques, showing the presence of non-oxidized graphenemore » with high purity.« less

Fabrication of nanostructured electrodes and interfaces using combustion CVD

NASA Astrophysics Data System (ADS)

Liu, Ying

Reducing fabrication and operation costs while maintaining high performance is a major consideration for the design of a new generation of solid-state ionic devices such as fuel cells, batteries, and sensors. The objective of this research is to fabricate nanostructured materials for energy storage and conversion, particularly porous electrodes with nanostructured features for solid oxide fuel cells (SOFCs) and high surface area films for gas sensing using a combustion CVD process. This research started with the evaluation of the most important deposition parameters: deposition temperature, deposition time, precursor concentration, and substrate. With the optimum deposition parameters, highly porous and nanostructured electrodes for low-temperature SOFCs have been then fabricated. Further, nanostructured and functionally graded La0.8Sr0.2MnO2-La 0.8SrCoO3-Gd0.1Ce0.9O2 composite cathodes were fabricated on YSZ electrolyte supports. Extremely low interfacial polarization resistances (i.e. 0.43 Ocm2 at 700°C) and high power densities (i.e. 481 mW/cm2 at 800°C) were generated at operating temperature range of 600°C--850°C. The original combustion CVD process is modified to directly employ solid ceramic powder instead of clear solution for fabrication of porous electrodes for solid oxide fuel cells. Solid particles of SOFC electrode materials suspended in an organic solvent were burned in a combustion flame, depositing a porous cathode on an anode supported electrolyte. Combustion CVD was also employed to fabricate highly porous and nanostructured SnO2 thin film gas sensors with Pt interdigitated electrodes. The as-prepared SnO2 gas sensors were tested for ethanol vapor sensing behavior in the temperature range of 200--500°C and showed excellent sensitivity, selectivity, and speed of response. Moreover, several novel nanostructures were synthesized using a combustion CVD process, including SnO2 nanotubes with square-shaped or rectangular cross sections, well-aligned ZnO nanorods, and two-dimensional ZnO flakes. Solid-state gas sensors based on single piece of these nanostructures demonstrated superior gas sensing performances. These size-tunable nanostructures could be the building blocks of or a template for fabrication of functional devices. In summary, this research has developed new ways for fabrication of high-performance solid-state ionic devices and has helped generating fundamental understanding of the correlation between processing conditions, microstructure, and properties of the synthesized structures.

Beam Technologies for Integrated Processing

DTIC Science & Technology

1992-03-01

Ohki et al., 1988). Initially, they were used in ion Table 3-3 Ceramic Materials Produced by CVD Coating Chemical Mixture Deposition Temp. (* C ) Method...inner coating , deposited from tungsten hexafluoride, providing strength and creep resistance , and the outer layer, deposited from the chloride, has a (110...1971. Structure and Mechanical Properties of Co - deposited Pyrolytic C -SiC Alloys. Journal of the American Ceramic Society 54:605. Kashu, S., M. Nagase

Structural analysis of ion-implanted chemical-vapor-deposited diamond by transmission electron microscope

NASA Astrophysics Data System (ADS)

Jiang, N.; Deguchi, M.; Wang, C. L.; Won, J. H.; Jeon, H. M.; Mori, Y.; Hatta, A.; Kitabatake, M.; Ito, T.; Hirao, T.; Sasaki, T.; Hiraki, A.

1997-04-01

A transmission electron microscope (TEM) study of ion-implanted chemical-vapor-deposited (CVD) diamond is presented. CVD diamond used for transmission electron microscope observation was directly deposited onto Mo TEM grids. As-deposited specimens were irradiated by C (100 keV) ions at room temperature with a wide range of implantation doses (10 12-10 17/cm 2). Transmission electron diffraction (TED) patterns indicate that there exists a critical dose ( Dc) for the onset of amorphization of CVD diamond as a result of ion induced damage and the value of critical dose is confirmed to be about 3 × 10 15/cm 2. The ion-induced transformation process is clearly revealed by high resolution electron microscope (HREM) images. For a higher dose implantation (7 × 10 15/cm 2) a large amount of diamond phase is transformed into amorphous carbon and many tiny misoriented diamond blocks are found to be left in the amorphous solid. The average size of these misoriented diamond blocks is only about 1-2 nm. Further bombardment (10 17/cm 2) almost kills all of the diamond phase within the irradiated volume and moreover leads to local formation of micropolycrystalline graphite.

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.

Status of the secondary mirrors (M2) for the Gemini 8-m telescopes

NASA Astrophysics Data System (ADS)

Knohl, Ernst-Dieter; Schoeppach, Armin; Pickering, Michael A.

1998-08-01

The 1-m diameter lightweight secondary mirrors (M2) for the Gemini 8-m telescopes will be the largest CVD-SiC mirrors ever produced. The design and manufacture of these mirrors is a very challenging task. In this paper we will discuss the mirror design, structural and mechanical analysis, and the CVD manufacturing process used to produce the mirror blanks. The lightweight design consist of a thin faceplate (4-mm) and triangular backstructure cells with ribs of varying heights. The main drivers in the design were weight (40 kg) and manufacturing limitations imposed on the backstructure cells and mirror mounts. Finite element modeling predicts that the mirror design will meet all of the Gemini M2 requirements for weight, mechanical integrity, resonances, and optical performance. Special design considerations were necessary to avoid stress concentration in the mounting areas and to meet the requirement that the mirror survive an 8-g earthquake. The highest risk step in the mirror blank manufacturing process is the near-net-shape CVD deposition of the thin, curved faceplate. Special tooling and procedures had to be developed to produce faceplates free of fractures, cracks, and stress during the cool-down from deposition temperature (1350 C) to room temperature. Due to time delay with the CVD manufacturing process in the meantime a backup solution from Zerodur has been started. This mirror is now in the advanced polishing process. Because the design of both mirrors is very similar an excellent comparison of both solutions is possible.

A Route Towards Sustainability Through Engineered Polymeric Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reeja-Jayan, B; Kovacik, P; Yang, R

2014-05-30

Chemical vapor deposition (CVD) of polymer films represent the marriage of two of the most important technological innovations of the modern age. CVD as a mature technology for growing inorganic thin films is already a workhorse technology of the microfabrication industry and easily scalable from bench to plant. The low cost, mechanical flexibility, and varied functionality offered by polymer thin films make them attractive for both macro and micro scale applications. This review article focuses on two energy and resource efficient CVD polymerization methods, initiated Chemical Vapor Deposition (iCVD) and oxidative Chemical Vapor Deposition (oCVD). These solvent-free, substrate independent techniquesmore » engineer multi-scale, multi-functional and conformal polymer thin film surfaces and interfaces for applications that can address the main sustainability challenges faced by the world today.« less

Injection doping of ultrathin microcrystalline silicon films prepared by CC-CVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koynov, S.; Grebner, S.; Schwarz, R.

1997-07-01

Recently, the authors have proposed a cyclic method, referred to as Closed Chamber CVD (CC-CVD), for the preparation of {micro}c-Si films of high crystalline fraction at increased deposition rates. In this work, they first report new process conditions of CC-CVD, which result in growth of highly crystalline films with a sharp interface on a foreign substrate. Then these conditions are further used together with a pulsed injection of B{sub 2}H{sub 6} in an appropriate moment of each cycle, so that the disturbance of the crystallization process is prevented. A series of ultrathin {micro}c-Si films, doped by this technique, is characterizedmore » by conductivity measurements, SEM, Raman Scattering, optical transmission and UV reflection. A strong reduction of the transient interface layer is achieved and conductivity as high as 2 S/cm with an activation energy of 27 meV is reached.« less

CVD Growth of Carbon Nanotubes: Structure, Catalyst, and Growth

NASA Technical Reports Server (NTRS)

Delzeit, Lance

2003-01-01

Carbon nanotubes (CNTs) exhibit extraordinary mechanical and unique electronic properties and hence have been receiving much attention in recent years for their potential in nanoelectronics, field emission devices, scanning probes, high strength composites and many more applications. Catalytic decomposition of hydrocarbon feedstock with the aid of supported transition metal catalysts - also known as chemical vapor deposition (CVD) - has become popular to produce single-walled and multi-walled nanotubes (SWNTs, MWNTs) and multiwalled nanofibers (MWNFs). The ability to grow CNTs on patterned substrates and in vertically aligned arrays, and the simplicity of the process, has made CVD growth of CNTs an attractive approach.

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.

Selective growth of titanium dioxide by low-temperature chemical vapor deposition.

PubMed

Reinke, Michael; Kuzminykh, Yury; Hoffmann, Patrik

2015-05-13

A key factor in engineering integrated optical devices such as electro-optic switches or waveguides is the patterning of thin films into specific geometries. In particular for functional oxides, etching processes are usually developed to a much lower extent than for silicon or silicon dioxide; therefore, selective area deposition techniques are of high interest for these materials. We report the selective area deposition of titanium dioxide using titanium isopropoxide and water in a high-vacuum chemical vapor deposition (HV-CVD) process at a substrate temperature of 225 °C. Here—contrary to conventional thermal CVD processes—only hydrolysis of the precursor on the surface drives the film growth as the thermal energy is not sufficient to thermally decompose the precursor. Local modification of the substrate surface energy by perfluoroalkylsilanization leads to a reduced surface residence time of the precursors and, consequently, to lower reaction rate and a prolonged incubation period before nucleation occurs, hence, enabling selective area growth. We discuss the dependence of the incubation time and the selectivity of the deposition process on the presence of the perfluoroalkylsilanization layer and on the precursor impinging rates—with selectivity, we refer to the difference of desired material deposition, before nucleation occurs in the undesired regions. The highest measured selectivity reached (99 ± 5) nm, a factor of 3 superior than previously reported in an atomic layer deposition process using the same chemistry. Furthermore, resolution of the obtained patterns will be discussed and illustrated.

Comparison of tungsten films grown by CVD and hot-wire assisted atomic layer deposition in a cold-wall reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Mengdi, E-mail: M.Yang@utwente.nl; Aarnink, Antonius A. I.; Kovalgin, Alexey Y.

2016-01-15

In this work, the authors developed hot-wire assisted atomic layer deposition (HWALD) to deposit tungsten (W) with a tungsten filament heated up to 1700–2000 °C. Atomic hydrogen (at-H) was generated by dissociation of molecular hydrogen (H{sub 2}), which reacted with WF{sub 6} at the substrate to deposit W. The growth behavior was monitored in real time by an in situ spectroscopic ellipsometer. In this work, the authors compare samples with tungsten grown by either HWALD or chemical vapor deposition (CVD) in terms of growth kinetics and properties. For CVD, the samples were made in a mixture of WF{sub 6} and molecularmore » or atomic hydrogen. Resistivity of the WF{sub 6}-H{sub 2} CVD layers was 20 μΩ·cm, whereas for the WF{sub 6}-at-H-CVD layers, it was 28 μΩ·cm. Interestingly, the resistivity was as high as 100 μΩ·cm for the HWALD films, although the tungsten films were 99% pure according to x-ray photoelectron spectroscopy. X-ray diffraction reveals that the HWALD W was crystallized as β-W, whereas both CVD films were in the α-W phase.« less

Photo-oxidation of Polymers Synthesized by Plasma and Initiated CVD

DOE PAGES

Baxamusa, Salmaan H.; Suresh, Aravind; Ehrmann, Paul; ...

2015-11-09

Plasma polymers are often limited by their susceptibility to spontaneous and photo-oxidation. We show that the unusual photoluminescence (PL) behavior of a plasma polymer of trans-2-butene is correlated with its photoluminescence strength. These photo-processes occur under blue light illumination (λ=405 nm), distinguishing them from traditional ultraviolet degradation of polymers. These photo-active defects are likely formed during the plasma deposition process and we show that a polymer synthesized using initiated (i)CVD, non-plasma method, has 1000× lower PL signal and enhanced photo-stability. In conclusion, non-plasma methods such as iCVD may therefore be a route to overcoming material aging issues that limit themore » adoption of plasma polymers.« less

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via an efficient chemical deposition

PubMed Central

Yang, Che-Yuan; Som, Sudipta; Das, Subrata; Lu, Chung-Hsin

2017-01-01

Novel chemical vapor deposition (CVD) process was successfully developed for the growth of Sr2Si5N8:Ce3+ phosphors with elevated luminescent properties. Metallic strontium was used as a vapor source for producing Sr3N2 vapor to react with Si3N4 powder via a homogeneous gas-solid reaction. The phosphors prepared via the CVD process showed high crystallinity, homogeneous particle size ranging from 8 to 10 μm, and high luminescence properties. In contrast, the phosphors prepared via the conventional solid-state reaction process exhibited relative low crystallinity, non-uniform particle size in the range of 0.5–5 μm and relatively lower luminescent properties than the phosphors synthesized via the CVD process. Upon the blue light excitation, Sr2−xCexSi5N8 phosphors exhibited a broad yellow band. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions from x = 0.02 to x = 0.10. The maximum emission was observed at x = 0.06, and the external and internal quantum efficiencies were calculated to be 51% and 71%, respectively. Furthermore, the CVD derived optimum Sr1.94Ce0.06Si5N8 phosphor exhibited sufficient thermal stability for blue-LEDs and the activation energy was calculated to be 0.33 eV. The results demonstrate a potential synthesis process for nitride phosphors suitable for light emitting diodes. PMID:28361999

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via an efficient chemical deposition

NASA Astrophysics Data System (ADS)

Yang, Che-Yuan; Som, Sudipta; Das, Subrata; Lu, Chung-Hsin

2017-03-01

Novel chemical vapor deposition (CVD) process was successfully developed for the growth of Sr2Si5N8:Ce3+ phosphors with elevated luminescent properties. Metallic strontium was used as a vapor source for producing Sr3N2 vapor to react with Si3N4 powder via a homogeneous gas-solid reaction. The phosphors prepared via the CVD process showed high crystallinity, homogeneous particle size ranging from 8 to 10 μm, and high luminescence properties. In contrast, the phosphors prepared via the conventional solid-state reaction process exhibited relative low crystallinity, non-uniform particle size in the range of 0.5-5 μm and relatively lower luminescent properties than the phosphors synthesized via the CVD process. Upon the blue light excitation, Sr2-xCexSi5N8 phosphors exhibited a broad yellow band. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions from x = 0.02 to x = 0.10. The maximum emission was observed at x = 0.06, and the external and internal quantum efficiencies were calculated to be 51% and 71%, respectively. Furthermore, the CVD derived optimum Sr1.94Ce0.06Si5N8 phosphor exhibited sufficient thermal stability for blue-LEDs and the activation energy was calculated to be 0.33 eV. The results demonstrate a potential synthesis process for nitride phosphors suitable for light emitting diodes.

Amorphous alumina thin films deposited on titanium: Interfacial chemistry and thermal oxidation barrier properties

DOE PAGES

Baggetto, Loic; Charvillat, Cedric; Thebault, Yannick; ...

2015-12-02

Ti/Al 2O 3 bilayer stacks are used as model systems to investigate the role of atomic layer deposition (ALD) and chemical vapor deposition (CVD) to prepare 30-180 nm thick amorphous alumina films as protective barriers for the medium temperature oxidation (500-600⁰C) of titanium, which is employed in aeronautic applications. X-ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) results show that the films produced from the direct liquid injection (DLI) CVD of aluminum tri-isopropoxide (ATI) are poor oxygen barriers. The films processed using the ALD of trimethylaluminum (TMA) show good barriermore » properties but an extensive intermixing with Ti which subsequently oxidizes. In contrast, the films prepared from dimethyl aluminum isopropoxide (DMAI) by CVD are excellent oxygen barriers and show little intermixing with Ti. Overall, these measurements correlate the effect of the alumina coating thickness, morphology, and stoichiometry resulting from the preparation method to the oxidation barrier properties, and show that compact and stoichiometric amorphous alumina films offer superior barrier properties.« less

The synthesis of graphene at different deposition time from palm oil via thermal chemical vapor deposition

NASA Astrophysics Data System (ADS)

Salifairus, M. J.; Soga, T.; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop, M.

2018-05-01

The basic building of graphitic materials is graphene that can range from zero-dimensional to three-dimensional. Graphene is a single atomic layer of sp2 bonded carbon atoms. It becomes most potential new materials to replace silicon due to its fascinating properties. In this study, the graphene growth was observed at different deposition time. The 1cm x 1cm polycrystalline nickel substrate was cleaned by etching process. The palm oil, carbon source, was placed in the precursor furnace and the nickel substrate was placed in the second furnace (deposition furnace). The palm oil will mix with Argon and Hydrogen gas was used as carrier gas in the CVD under certain temperature and pressure to undergo pyrolysis process. The deposition temperature was set at 900 °C and the deposition time was varied from 5 - 60 minutes. The graphene was growth at ambient pressure in the CVD system. Raman spectrometer and atomic force microscopy revealed the structural properties and surface topography of the grapheme on the nickel substrate. The D, G and 2D band appear approximately at 1378 cm-1, 1580 cm-1 and 2696 cm-1. It can be concluded that the graphene has successfully synthesized at different deposition time.

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Sun, Haibin; Fu, Can; Gao, Yanli; Guo, Pengfei; Wang, Chunlei; Yang, Wenchao; Wang, Qishang; Zhang, Chongwu; Wang, Junya; Xu, Junqi

2018-07-01

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 103 S m‑1. These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

CVD diamond substrate for microelectronics. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burden, J.; Gat, R.

1996-11-01

Chemical Vapor Deposition (CVD) of diamond films has evolved dramatically in recent years, and commercial opportunities for diamond substrates in thermal management applications are promising. The objective of this technology transfer initiative (TTI) is for Applied Science and Technology, Inc. (ASTEX) and AlliedSignal Federal Manufacturing and Technologies (FM&T) to jointly develop and document the manufacturing processes and procedures required for the fabrication of multichip module circuits using CVD diamond substrates, with the major emphasis of the project concentrating on lapping/polishing prior to metallization. ASTEX would provide diamond films for the study, and FM&T would use its experience in lapping, polishing,more » and substrate metallization to perform secondary processing on the parts. The primary goal of the project was to establish manufacturing processes that lower the manufacturing cost sufficiently to enable broad commercialization of the technology.« less

Vapor deposition routes to conformal polymer thin films

PubMed Central

Moni, Priya; Al-Obeidi, Ahmed

2017-01-01

Vapor phase syntheses, including parylene chemical vapor deposition (CVD) and initiated CVD, enable the deposition of conformal polymer thin films to benefit a diverse array of applications. This short review for nanotechnologists, including those new to vapor deposition methods, covers the basic theory in designing a conformal polymer film vapor deposition, sample preparation and imaging techniques to assess film conformality, and several applications that have benefited from vapor deposited, conformal polymer thin films. PMID:28487816

Surface functionalization of 3D-printed plastics via initiated chemical vapor deposition

PubMed Central

Cheng, Christine

2017-01-01

3D printing is a useful fabrication technique because it offers design flexibility and rapid prototyping. The ability to functionalize the surfaces of 3D-printed objects allows the bulk properties, such as material strength or printability, to be chosen separately from surface properties, which is critical to expanding the breadth of 3D printing applications. In this work, we studied the ability of the initiated chemical vapor deposition (iCVD) process to coat 3D-printed shapes composed of poly(lactic acid) and acrylonitrile butadiene styrene. The thermally insulating properties of 3D-printed plastics pose a challenge to the iCVD process due to large thermal gradients along the structures during processing. In this study, processing parameters such as the substrate temperature and the filament temperature were systematically varied to understand how these parameters affect the uniformity of the coatings along the 3D-printed objects. The 3D-printed objects were coated with both hydrophobic and hydrophilic polymers. Contact angle goniometry and X-ray photoelectron spectroscopy were used to characterize the functionalized surfaces. Our results can enable the use of iCVD to functionalize 3D-printed materials for a range of applications such as tissue scaffolds and microfluidics. PMID:28875099

Lubrication by Diamond and Diamondlike Carbon Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1997-01-01

Regardless of environment (ultrahigh vacuum, humid air, dry nitrogen, or water), ion-beam-deposited diamondlike carbon (DLC) and nitrogen-ion-implanted, chemical-vapor-deposited (CVD) diamond films had low steady-state coefficients of friction (less than 0.1) and low wear rates (less than or equal to 10(exp -6)cu mm/N(dot)m). These films can be used as effective wear-resistant, self-lubricating coatings regardless of environment. On the other hand, as-deposited, fine-grain CVD diamond films; polished, coarse-grain CVD diamond films; and polished and then fluorinated, coarse-grain CVD diamond films can be used as effective wear-resistant, self-lubricating coatings in humid air, in dry nitrogen, and in water, but they had a high coefficient of friction and a high wear rate in ultrahigh vacuum. The polished, coarse-grain CVD diamond film revealed an extremely low wear rate, far less than 10(exp 10) cu mm/N(dot)m, in water.

Plasma boriding of a cobalt-chromium alloy as an interlayer for nanostructured diamond growth

NASA Astrophysics Data System (ADS)

Johnston, Jamin M.; Jubinsky, Matthew; Catledge, Shane A.

2015-02-01

Chemical vapor deposited (CVD) diamond coatings can potentially improve the wear resistance of cobalt-chromium medical implant surfaces, but the high cobalt content in these alloys acts as a catalyst to form graphitic carbon. Boriding by high temperature liquid baths and powder packing has been shown to improve CVD diamond compatibility with cobalt alloys. We use the microwave plasma-enhanced (PE) CVD process to deposit interlayers composed primarily of the borides of cobalt and chromium. The use of diborane (B2H6) in the plasma feedgas allows for the formation of a robust boride interlayer for suppressing graphitic carbon during subsequent CVD of nano-structured diamond (NSD). This metal-boride interlayer is shown to be an effective diffusion barrier against elemental cobalt for improving nucleation and adhesion of NSD coatings on a CoCrMo alloy. Migration of elemental cobalt to the surface of the interlayer is significantly reduced and undetectable on the surface of the subsequently-grown NSD coating. The effects of PECVD boriding are compared for a range of substrate temperatures and deposition times and are evaluated using glancing-angle X-ray diffraction (XRD), cross-sectional scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-Raman spectroscopy. Boriding of CoCrMo results in adhered nanostructured diamond coatings with low surface roughness.

A Comparative Study of Three Different Chemical Vapor Deposition (CVD) Techniques of Carbon Nanotube Growth on Diamond Films

DTIC Science & Technology

2013-01-01

FCT-CVD) with xylene and ferrocene liquid mixture without any prior catalyst deposition. T-CVD is a low cost system that can easily be set up to grow...iron catalysts, respectively. For the FCT-CVD approach, ferrocene is used as an iron source to promote CNT growth. Based on these repeatable results...kept at 250 ° C while the high temperature furnace is ramped up to the growth temperature of 750 ° C. Ferrocene was dissolved into xylene solvent in

Direct synthesis of vertically aligned ZnO nanowires on FTO substrates using a CVD method and the improvement of photovoltaic performance

PubMed Central

2012-01-01

In this work, we report a direct synthesis of vertically aligned ZnO nanowires on fluorine-doped tin oxide-coated substrates using the chemical vapor deposition (CVD) method. ZnO nanowires with a length of more than 30 μm were synthesized, and dye-sensitized solar cells (DSSCs) based on the as-grown nanowires were fabricated, which showed improvement of the device performance compared to those fabricated using transferred ZnO nanowires. Dependence of the cell performance on nanowire length and annealing temperature was also examined. This synthesis method provided a straightforward, one-step CVD process to grow relatively long ZnO nanowires and avoided subsequent nanowire transfer process, which simplified DSSC fabrication and improved cell performance. PMID:22673046

Development Status of a CVD System to Deposit Tungsten onto UO2 Powder via the WCI6 Process

NASA Technical Reports Server (NTRS)

Mireles, O. R.; Kimberlin, A.; Broadway, J.; Hickman, R.

2014-01-01

Nuclear Thermal Propulsion (NTP) is under development for deep space exploration. NTP's high specific impulse (> 850 second) enables a large range of destinations, shorter trip durations, and improved reliability. W-60vol%UO2 CERMET fuel development efforts emphasize fabrication, performance testing and process optimization to meet service life requirements. Fuel elements must be able to survive operation in excess of 2850 K, exposure to flowing hydrogen (H2), vibration, acoustic, and radiation conditions. CTE mismatch between W and UO2 result in high thermal stresses and lead to mechanical failure as a result UO2 reduction by hot hydrogen (H2) [1]. Improved powder metallurgy fabrication process control and mitigated fuel loss can be attained by coating UO2 starting powders within a layer of high density tungsten [2]. This paper discusses the advances of a fluidized bed chemical vapor deposition (CVD) system that utilizes the H2-WCl6 reduction process.

Noncatalytic thermocouple coatings produced with chemical vapor deposition for flame temperature measurements.

PubMed

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 AlCl(3) as the precursor are dense, not contaminated, and crystallize in the corundum structure, while MOCVD using Al(acetyl 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 AlCl(3)-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.

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.

CVD Diamond, DLC, and c-BN Coatings for Solid Film Lubrication

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Murakawa, Masao; Watanabe, Shuichi; Takeuchi, Sadao; Miyake, Shojiro; Wu, Richard L. C.

1998-01-01

The main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1 and 10(exp -6) cubic MM /(N*m), respectively. Carbon- and nitrogen-ion-implanted, fine-grain, chemical-vapor-deposited (CVD) diamond and diamondlike carbon (DLC) ion beam deposited on fine-grain CVD diamond met the criteria regardless of environment (vacuum, nitrogen, and air).

Process in manufacturing high efficiency AlGaAs/GaAs solar cells by MO-CVD

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.; Chang, K. I.; Tandon, J.

1984-01-01

Manufacturing technology for mass producing high efficiency GaAs solar cells is discussed. A progress using a high throughput MO-CVD reactor to produce high efficiency GaAs solar cells is discussed. Thickness and doping concentration uniformity of metal oxide chemical vapor deposition (MO-CVD) GaAs and AlGaAs layer growth are discussed. In addition, new tooling designs are given which increase the throughput of solar cell processing. To date, 2cm x 2cm AlGaAs/GaAs solar cells with efficiency up to 16.5% were produced. In order to meet throughput goals for mass producing GaAs solar cells, a large MO-CVD system (Cambridge Instrument Model MR-200) with a susceptor which was initially capable of processing 20 wafers (up to 75 mm diameter) during a single growth run was installed. In the MR-200, the sequencing of the gases and the heating power are controlled by a microprocessor-based programmable control console. Hence, operator errors can be reduced, leading to a more reproducible production sequence.

Evaluation of infrared thermography as a diagnostic tool in CVD applications

NASA Astrophysics Data System (ADS)

Johnson, E. J.; Hyer, P. V.; Culotta, P. W.; Clark, I. O.

1998-05-01

This research is focused on the feasibility of using infrared temperature measurements on the exterior of a chemical vapor deposition (CVD) reactor to ascertain both real-time information on the operating characteristics of a CVD system and provide data which could be post-processed to provide quantitative information for research and development on CVD processes. Infrared thermography techniques were used to measure temperatures on a horizontal CVD reactor of rectangular cross section which were correlated with the internal gas flow field, as measured with the laser velocimetry (LV) techniques. For the reactor tested, thermal profiles were well correlated with the gas flow field inside the reactor. Correlations are presented for nitrogen and hydrogen carrier gas flows. The infrared data were available to the operators in real time with sufficient sensitivity to the internal flow field so that small variations such as misalignment of the reactor inlet could be observed. The same data were post-processed to yield temperature measurements at known locations on the reactor surface. For the experiments described herein, temperatures associated with approximately 3.3 mm 2 areas on the reactor surface were obtained with a precision of ±2°C. These temperature measurements were well suited for monitoring a CVD production reactor, development of improved thermal boundary conditions for use in CFD models of reactors, and for verification of expected thermal conditions.

Growth of hybrid carbon nanostructures on iron-decorated ZnO nanorods

NASA Astrophysics Data System (ADS)

Mbuyisa, Puleng N.; Rigoni, Federica; Sangaletti, Luigi; Ponzoni, Stefano; Pagliara, Stefania; Goldoni, Andrea; Ndwandwe, Muzi; Cepek, Cinzia

2016-04-01

A novel carbon-based nanostructured material, which includes carbon nanotubes (CNTs), porous carbon, nanostructured ZnO and Fe nanoparticles, has been synthetized using catalytic chemical vapour deposition (CVD) of acetylene on vertically aligned ZnO nanorods (NRs). The deposition of Fe before the CVD process induces the presence of dense CNTs in addition to the variety of nanostructures already observed on the process done on the bare NRs, which range from amorphous graphitic carbon up to nanostructured dendritic carbon films, where the NRs are partially or completely etched. The combination of scanning electron microscopy and in situ photoemission spectroscopy indicate that Fe enhances the ZnO etching, and that the CNT synthesis is favoured by the reduced Fe mobility due to the strong interaction between Fe and the NRs, and to the presence of many defects, formed during the CVD process. Our results demonstrate that the resulting new hybrid shows a higher sensitivity to ammonia gas at ambient conditions (∼60 ppb) than the carbon nanostructures obtained without the aid of Fe, the bare ZnO NRs, or other one-dimensional carbon nanostructures, making this system of potential interest for environmental ammonia monitoring. Finally, in view of the possible application in nanoscale optoelectronics, the photoexcited carrier behaviour in these hybrid systems has been characterized by time-resolved reflectivity measurements.

Optimization of operating parameters in polysilicon chemical vapor deposition reactor with response surface methodology

NASA Astrophysics Data System (ADS)

An, Li-sha; Liu, Chun-jiao; Liu, Ying-wen

2018-05-01

In the polysilicon chemical vapor deposition reactor, the operating parameters are complex to affect the polysilicon's output. Therefore, it is very important to address the coupling problem of multiple parameters and solve the optimization in a computationally efficient manner. Here, we adopted Response Surface Methodology (RSM) to analyze the complex coupling effects of different operating parameters on silicon deposition rate (R) and further achieve effective optimization of the silicon CVD system. Based on finite numerical experiments, an accurate RSM regression model is obtained and applied to predict the R with different operating parameters, including temperature (T), pressure (P), inlet velocity (V), and inlet mole fraction of H2 (M). The analysis of variance is conducted to describe the rationality of regression model and examine the statistical significance of each factor. Consequently, the optimum combination of operating parameters for the silicon CVD reactor is: T = 1400 K, P = 3.82 atm, V = 3.41 m/s, M = 0.91. The validation tests and optimum solution show that the results are in good agreement with those from CFD model and the deviations of the predicted values are less than 4.19%. This work provides a theoretical guidance to operate the polysilicon CVD process.

Influence of low energy argon plasma treatment on the moisture barrier performance of hot wire-CVD grown SiNx multilayers

NASA Astrophysics Data System (ADS)

Majee, Subimal; Fátima Cerqueira, Maria; Tondelier, Denis; Geffroy, Bernard; Bonnassieux, Yvan; Alpuim, Pedro; Bourée, Jean Eric

2014-01-01

The reliability and stability are key issues for the commercial utilization of organic photovoltaic devices based on flexible polymer substrates. To increase the shelf-lifetime of these devices, transparent moisture barriers of silicon nitride (SiNx) films are deposited at low temperature by hot wire CVD (HW-CVD) process. Instead of the conventional route based on organic/inorganic hybrid structures, this work defines a new route consisting in depositing multilayer stacks of SiNx thin films, each single layer being treated by argon plasma. The plasma treatment allows creating smoother surface and surface atom rearrangement. We define a critical thickness of the single layer film and focus our attention on the effect of increasing the number of SiNx single-layers on the barrier properties. A water vapor transmission rate (WVTR) of 2 × 10-4 g/(m2·day) is reported for SiNx multilayer stack and a physical interpretation of the plasma treatment effect is given.

In-situ sensing using mass spectrometry and its use for run-to-run control on a W-CVD cluster tool

NASA Astrophysics Data System (ADS)

Gougousi, T.; Sreenivasan, R.; Xu, Y.; Henn-Lecordier, L.; Rubloff, G. W.; Kidder, , J. N.; Zafiriou, E.

2001-01-01

A 300 amu closed-ion-source RGA (Leybold-Inficon Transpector 2) sampling gases directly from the reactor of an ULVAC ERA-1000 cluster tool has been used for real time process monitoring of a W CVD process. The process involves H2 reduction of WF6 at a total pressure of 67 Pa (0.5 torr) to produce W films on Si wafers heated at temperatures around 350 °C. The normalized RGA signals for the H2 reagent depletion and the HF product generation were correlated with the W film weight as measured post-process with an electronic microbalance for the establishment of thin-film weight (thickness) metrology. The metrology uncertainty (about 7% for the HF product) was limited primarily by the very low conversion efficiency of the W CVD process (around 2-3%). The HF metrology was then used to drive a robust run-to-run control algorithm, with the deposition time selected as the manipulated (or controlled) variable. For that purpose, during a 10 wafer run, a systematic process drift was introduced as a -5 °C processing temperature change for each successive wafer, in an otherwise unchanged process recipe. Without adjustment of the deposition time the W film weight (thickness) would have declined by about 50% by the 10th wafer. With the aid of the process control algorithm, an adjusted deposition time was computed so as to maintain constant HF sensing signal, resulting in weight (thickness) control comparable to the accuracy of the thickness metrology. These results suggest that in-situ chemical sensing, and particularly mass spectrometry, provide the basis for wafer state metrology as needed to achieve run-to-run control. Furthermore, since the control accuracy was consistent with the metrology accuracy, we anticipate significant improvements for processes as used in manufacturing, where conversion rates are much higher (40-50%) and corresponding signals for metrology will be much larger.

Spray CVD for Making Solar-Cell Absorber Layers

NASA Technical Reports Server (NTRS)

Banger, Kulbinder K.; Harris, Jerry; Jin, Michael H.; Hepp, Aloysius

2007-01-01

Spray chemical vapor deposition (spray CVD) processes of a special type have been investigated for use in making CuInS2 absorber layers of thin-film solar photovoltaic cells from either of two subclasses of precursor compounds: [(PBu3) 2Cu(SEt)2In(SEt)2] or [(PPh3)2Cu(SEt)2 In(SEt)2]. The CuInS2 films produced in the experiments have been characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and four-point-probe electrical tests.

Ultratough CVD single crystal diamond and three dimensional growth thereof

DOEpatents

Hemley, Russell J [Washington, DC; Mao, Ho-kwang [Washington, DC; Yan, Chih-shiue [Washington, DC

2009-09-29

The invention relates to a single-crystal diamond grown by microwave plasma chemical vapor deposition that has a toughness of at least about 30 MPa m.sup.1/2. The invention also relates to a method of producing a single-crystal diamond with a toughness of at least about 30 MPa m.sup.1/2. The invention further relates to a process for producing a single crystal CVD diamond in three dimensions on a single crystal diamond substrate.

Gene expression profile in cardiovascular disease and preeclampsia: a meta-analysis of the transcriptome based on raw data from human studies deposited in Gene Expression Omnibus.

PubMed

Sitras, V; Fenton, C; Acharya, G

2015-02-01

Cardiovascular disease (CVD) and preeclampsia (PE) share common clinical features. We aimed to identify common transcriptomic signatures involved in CVD and PE in humans. Meta-analysis of individual raw microarray data deposited in GEO, obtained from blood samples of patients with CVD versus controls and placental samples from women with PE versus healthy women with uncomplicated pregnancies. Annotation of cases versus control samples was taken directly from the microarray documentation. Genes that showed a significant differential expression in the majority of experiments were selected for subsequent analysis. Hypergeometric gene list analysis was performed using Bioconductor GOstats package. Bioinformatic analysis was performed in PANTHER. Seven studies in CVD and 5 studies in PE were eligible for meta-analysis. A total of 181 genes were found to be differentially expressed in microarray studies investigating gene expression in blood samples obtained from patients with CVD compared to controls and 925 genes were differentially expressed between preeclamptic and healthy placentas. Among these differentially expressed genes, 22 were common between CVD and PE. Bioinformatic analysis of these genes revealed oxidative stress, p-53 pathway feedback, inflammation mediated by chemokines and cytokines, interleukin signaling, B-cell activation, PDGF signaling, Wnt signaling, integrin signaling and Alzheimer disease pathways to be involved in the pathophysiology of both CVD and PE. Metabolism, development, response to stimulus, immune response and cell communication were the associated biologic processes in both conditions. Gene set enrichment analysis showed the following overlapping pathways between CVD and PE: TGF-β-signaling, apoptosis, graft-versus-host disease, allograft rejection, chemokine signaling, steroid hormone synthesis, type I and II diabetes mellitus, VEGF signaling, pathways in cancer, GNRH signaling, Huntingtons disease and Notch signaling. CVD and PE share same common traits in their gene expression profile indicating common pathways in their pathophysiology. Copyright © 2014 Elsevier Ltd. All rights reserved.

Initiated Chemical Vapor Deposition (iCVD) of Highly Cross-Linked Polymer Films for Advanced Lithium-Ion Battery Separators.

PubMed

Yoo, Youngmin; Kim, Byung Gon; Pak, Kwanyong; Han, Sung Jae; Song, Heon-Sik; Choi, Jang Wook; Im, Sung Gap

2015-08-26

We report an initiated chemical vapor deposition (iCVD) process to coat polyethylene (PE) separators in Li-ion batteries with a highly cross-linked, mechanically strong polymer, namely, polyhexavinyldisiloxane (pHVDS). The highly cross-linked but ultrathin pHVDS films can only be obtained by a vapor-phase process, because the pHVDS is insoluble in most solvents and thus infeasible with conventional solution-based methods. Moreover, even after the pHVDS coating, the initial porous structure of the separator is well preserved owing to the conformal vapor-phase deposition. The coating thickness is delicately controlled by deposition time to the level that the pore size decreases to below 7% compared to the original dimension. The pHVDS-coated PE shows substantially improved thermal stability and electrolyte wettability. After incubation at 140 °C for 30 min, the pHVDS-coated PE causes only a 12% areal shrinkage (versus 90% of the pristine separator). The superior wettability results in increased electrolyte uptake and ionic conductivity, leading to significantly improved rate performance. The current approach is applicable to a wide range of porous polymeric separators that suffer from thermal shrinkage and poor electrolyte wetting.

Minimizing artifact formation in magnetorheological finishing of chemical vapor deposition ZnS flats.

PubMed

Kozhinova, Irina A; Romanofsky, Henry J; Maltsev, Alexander; Jacobs, Stephen D; Kordonski, William I; Gorodkin, Sergei R

2005-08-01

The polishing performance of magnetorheological (MR) fluids prepared with a variety of magnetic and nonmagnetic ingredients was studied on four types of initial surface for chemical vapor deposition (CVD) ZnS flats from domestic and foreign sources. The results showed that it was possible to greatly improve smoothing performance of magnetorheological finishing (MRF) by altering the fluid composition, with the best results obtained for nanoalumina abrasive used with soft carbonyl iron and altered MR fluid chemistry. Surface roughness did not exceed 20 nm peak to valley and 2 nm rms after removal of 2 microm of material. The formation of orange peel and the exposure of a pebblelike structure inherent in ZnS from the CVD process were suppressed.

TaC-coated graphite prepared via a wet ceramic process: Application to CVD susceptors for epitaxial growth of wide-bandgap semiconductors

NASA Astrophysics Data System (ADS)

Nakamura, Daisuke; Kimura, Taishi; Narita, Tetsuo; Suzumura, Akitoshi; Kimoto, Tsunenobu; Nakashima, Kenji

2017-11-01

A novel sintered tantalum carbide coating (SinTaC) prepared via a wet ceramic process is proposed as an approach to reducing the production cost and improving the crystal quality of bulk-grown crystals and epitaxially grown films of wide-bandgap semiconductors. Here, we verify the applicability of the SinTaC components as susceptors for chemical vapor deposition (CVD)-SiC and metal-organic chemical vapor deposition (MOCVD)-GaN epitaxial growth in terms of impurity incorporation from the SinTaC layers and also clarify the surface-roughness controllability of SinTaC layers and its advantage in CVD applications. The residual impurity elements in the SinTaC layers were confirmed to not severely incorporate into the CVD-SiC and MOCVD-GaN epilayers grown using the SinTaC susceptors. The quality of the epilayers was also confirmed to be equivalent to that of epilayers grown using conventional susceptors. Furthermore, the surface roughness of the SinTaC components was controllable over a wide range of average roughness (0.4 ≤ Ra ≤ 5 μm) and maximum height roughness (3 ≤ Rz ≤ 36 μm) through simple additional surface treatment procedures, and the surface-roughened SinTaC susceptor fabricated using these procedures was predicted to effectively reduce thermal stress on epi-wafers. These results confirm that SinTaC susceptors are applicable to epitaxial growth processes and are advantageous over conventional susceptor materials for reducing the epi-cost and improving the quality of epi-wafers.

Diagnostic Techniques Used to Study Chemical-Vapor-Deposited Diamond Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

2000-01-01

The advantages and utility of chemical-vapor-deposited (CVD) diamond as an industrial ceramic can only be realized if the price and quality are right. Until recently, this technology was of interest only to the academic and basic research community. However, interest has grown because of advances made by leading CVD diamond suppliers: 1) Reduction of the cost of CVD polycrystalline diamond deposition below $5/carat ($8/sq cm); 2) Installation of production capacity; 3) Epitaxial growth of CVD single-crystal diamond. Thus, CVD diamond applications and business are an industrial reality. At present, CVD diamond is produced in the form of coatings or wafers. CVD diamond film technology offers a broader technological potential than do natural and high-pressure synthetic diamonds because size, geometry, and eventually cost will not be as limiting. Now that they are cost effective, diamond coatings - with their extreme properties - can be used in a variety of applications. Diamond coatings can improve many of the surface properties of engineering substrate materials, including erosion, corrosion, and wear resistance. Examples of actual and potential applications, from microelectromechanical systems to the wear parts of diamond coatings and related superhard coatings are described. For example, diamond coatings can be used as a chemical and mechanical barrier for the space shuttles check valves, particularly on the guide pins and seat assemblies.

Electrical property of macroscopic graphene composite fibers prepared by chemical vapor deposition.

PubMed

Sun, Haibin; Fu, Can; Gao, Yanli; Guo, Pengfei; Wang, Chunlei; Yang, Wenchao; Wang, Qishang; Zhang, Chongwu; Wang, Junya; Xu, Junqi

2018-07-27

Graphene fibers are promising candidates in portable and wearable electronics due to their tiny volume, flexibility and wearability. Here, we successfully synthesized macroscopic graphene composite fibers via a two-step process, i.e. first electrospinning and then chemical vapor deposition (CVD). Briefly, the well-dispersed PAN nanofibers were sprayed onto the copper surface in an electrified thin liquid jet by electrospinning. Subsequently, CVD growth process induced the formation of graphene films using a PAN-solid source of carbon and a copper catalyst. Finally, crumpled and macroscopic graphene composite fibers were obtained from carbon nanofiber/graphene composite webs by self-assembly process in the deionized water. Temperature-dependent conduct behavior reveals that electron transport of the graphene composite fibers belongs to hopping mechanism and the typical electrical conductivity reaches 4.59 × 10 3 S m -1 . These results demonstrated that the graphene composite fibers are promising for the next-generation flexible and wearable electronics.

Chemical vapor deposition on chabazite (CHA) zeolite membranes for effective post-combustion CO2 capture.

PubMed

Kim, Eunjoo; Lee, Taehee; Kim, Hyungmin; Jung, Won-Jin; Han, Doug-Young; Baik, Hionsuck; Choi, Nakwon; Choi, Jungkyu

2014-12-16

Chabazite (CHA) zeolites with a pore size of 0.37 × 0.42 nm(2) are expected to separate CO2 (0.33 nm) from larger N2 (0.364 nm) in postcombustion flue gases by recognizing their minute size differences. Furthermore, the hydrophobic siliceous constituent in CHA membranes can allow for maintaining the CO2/N2 separation performance in the presence of H2O in contrast with the CO2 affinity-based membranes. In an attempt to increase the molecular sieving ability, the pore mouth size of all silica CHA (Si-CHA) particles was reduced via the chemical vapor deposition (CVD) of a silica precursor (tetraethyl orthosilicate). Accordingly, an increase of the CVD treatment duration decreased the penetration rate of CO2 into the CVD-treated Si-CHA particles. Furthermore, the CVD process was applied to siliceous CHA membranes in order to improve their CO2/N2 separation performance. Compared to the intact CHA membranes, the CO2/N2 maximum separation factor (max SF) for CVD-treated CHA membranes was increased by ∼ 2 fold under dry conditions. More desirably, the CO2/N2 max SF was increased by ∼ 3 fold under wet conditions at ∼ 50 °C, a representative temperature of the flue gas stream. In fact, the presence of H2O in the feed disfavored the permeation of N2 more than that of CO2 through CVD-modified CHA membranes and thus, contributed to the increased CO2/N2 separation factor.

25th anniversary article: CVD polymers: a new paradigm for surface modification and device fabrication.

PubMed

Coclite, Anna Maria; Howden, Rachel M; Borrelli, David C; Petruczok, Christy D; Yang, Rong; Yagüe, Jose Luis; Ugur, Asli; Chen, Nan; Lee, Sunghwan; Jo, Won Jun; Liu, Andong; Wang, Xiaoxue; Gleason, Karen K

2013-10-11

Well-adhered, conformal, thin (<100 nm) coatings can easily be obtained by chemical vapor deposition (CVD) for a variety of technological applications. Room temperature modification with functional polymers can be achieved on virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. In CVD polymerization, the monomer(s) are delivered to the surface through the vapor phase and then undergo simultaneous polymerization and thin film formation. By eliminating the need to dissolve macromolecules, CVD enables insoluble polymers to be coated and prevents solvent damage to the substrate. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, and thickness control. Initiated-CVD shows successful results in terms of rationally designed micro- and nanoengineered materials to control molecular interactions at material surfaces. The success of oxidative-CVD is mainly demonstrated for the deposition of organic conducting and semiconducting polymers. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Processing of SiO2 protective layer using HMDS precursor by combustion CVD.

PubMed

Park, Kyoung-Soo; Kim, Youngman

2011-08-01

Hexamethyldisilazane (HMDS, [(CH3)3Si]2NH) was used as a precursor to form SiO2 protective coatings on IN738LC alloys by combustion chemical vapor deposition (CCVD). SEM and XPS showed that the processed coatings were composed mainly of SiO2. The amount of HMDS had the largest effect on the size of the SiO2 agglomerates and the thickness of the deposited coatings. The specimens coated with SiO2 using the 0.05 mol/l HMDS solution showed a significantly higher temperature oxidation resistance than those deposited under other conditions.

Low-temperature growth of nitrogen-doped carbon nanofibers by acetonitrile catalytic CVD using Ni-based catalysts

NASA Astrophysics Data System (ADS)

Iwasaki, Tomohiro; Makino, Yuri; Fukukawa, Makoto; Nakamura, Hideya; Watano, Satoru

2016-11-01

To synthesize nitrogen-doped carbon nanofibers (N-CNFs) at high growth rates and low temperatures less than 673 K, nickel species (metallic nickel and nickel oxide) supported on alumina particles were used as the catalysts for an acetonitrile catalytic chemical vapor deposition (CVD) process. The nickel:alumina mass ratio in the catalysts was fixed at 0.05:1. The catalyst precursors were prepared from various nickel salts (nitrate, chloride, sulfate, acetate, and lactate) and then calcined at 1073 K for 1 h in oxidative (air), reductive (hydrogen-containing argon), or inert (pure argon) atmospheres to activate the nickel-based catalysts. The effects of precursors and calcination atmosphere on the catalyst activity at low temperatures were studied. We found that the catalysts derived from nickel nitrate had relatively small crystallite sizes of nickel species and provided N-CNFs at high growth rates of 57 ± 4 g-CNF/g-Ni/h at 673 K in the CVD process using 10 vol% hydrogen-containing argon as the carrier gas of acetonitrile vapor, which were approximately 4 times larger than that of a conventional CVD process. The obtained results reveal that nitrate ions in the catalyst precursor and hydrogen in the carrier gas can contribute effectively to the activation of catalysts in low-temperature CVD. The fiber diameter and nitrogen content of N-CNFs synthesized at high growth rates were several tens of nanometers and 3.5 ± 0.3 at.%, respectively. Our catalysts and CVD process may lead to cost reductions in the production of N-CNFs.

Corrosion Fatigue and Environmentally Assisted Cracking in Aging Military Vehicles (La fatigue-corrosion et la fissuration en milieu ambiant des vehicules militaires vieillissants)

DTIC Science & Technology

2011-03-01

deposition temperature is above 260°C (500°F), CVD Al cannot be applied to many structural alloys used in aerospace [12]. 23.3.4 Spray Deposited Cadmium...Alternatives There are several different aluminum-based coatings that can be deposited by spraying : aluminum and Al alloys , metallic-ceramic coatings...and Al - and Zn-filled polymers [12]. Thermal spray (flame or arc) is a very flexible and cost-effective process for deposition of pure

Corrosion Fatigue and Environmentally Assisted Cracking in Aging Military Vehicles (le fatigue-corrosion et la fissuration en milieu ambiant des vehicules militaires vieillissants)

DTIC Science & Technology

2011-03-01

deposition temperature is above 260°C (500°F), CVD Al cannot be applied to many structural alloys used in aerospace [12]. 23.3.4 Spray Deposited Cadmium...Alternatives There are several different aluminum-based coatings that can be deposited by spraying : aluminum and Al alloys , metallic-ceramic coatings...and Al - and Zn-filled polymers [12]. Thermal spray (flame or arc) is a very flexible and cost-effective process for deposition of pure

Chemical vapor deposition of yttria-stabilized zirconia as a thermal barrier coating for gas turbine engines

NASA Astrophysics Data System (ADS)

Varanasi, Venu Gopal

The gas turbine engine uses an yttria-stabilized zirconia (YSZ) coating to provide thermal insulation for its turbine blades. This YSZ coating must be tetragonal in crystal structure, columnar in microstructure, and be 100--250 mum thick to provide for adequate protection for the turbine blades in the severe engine environment. Currently, YSZ coatings are fabricated by electron-beam physical vapor deposition (EB-PVD), but this fabrication method is cost intensive. Chemical vapor deposition (CVD) is a more commercially viable processing method and a possible alternative to EB-PVD. The deposition of tetragonal YSZ from gaseous metal and oxidation sources were studied. A chemical equilibrium analysis modeled the feasibility of depositing tetragonal YSZ for both chloride CVD (Zr-Y-C-O-Cl-H-Inert system) and metal-organic CVD (MOCVD) (Zr-Y-C-O-H system). Pure thermochemical properties and the assessed YSZ phase diagram were used in this analysis. Using the molar input of metals ((nY + nZr) and ( nY/(nY + nZr ) = 0.08)) as bases, equilibrium calculations showed that tetragonal YSZ formation was feasible. Tetragonal YSZ formation was feasible with high oxygen content (nO/(nY + nZr) > 8) and high temperature (T > 100°C) in the case of chloride CVD (Zr-Y-C-O-Cl-H-Inert). Tetragonal YSZ formation was feasible with high oxygen content (nO/( nY + nZr) > 5) and high temperature (T > 950°C) in the case of MOCVD (Zr-Y-C-O-H). Although solid carbon formation did not appear in chloride CVD, additional oxygen (nO/( nY + nZr) > 32) and low hydrogen content relative to carbon (nH/nC < 2) were required to avoid solid carbon formation in MOCVD. Coatings were deposited using a set of base conditions derived from the chemical equilibrium analysis. In chloride CVD, YCl3 was not included because of its low vapor pressure, thus, ZrCl4 was oxidized with the H2-CO2 gas mixture. Monoclinic ZrO2 coatings were deposited at the thermochemically optimized conditions (n O/(nY + nZr) > 8, T > 1004°C) with approximately 5.5 mum h-1 growth rate. In metal-organic CVD (MOCVD), liquid precursor solutions of Y- and Zr-beta-diketonate and Y- and Zr-n-butoxide precursors were used as the metal sources and O2 gas was used as the oxidation source. Using the Y- and Zr-beta-diketonate liquid precursor solution, tetragonal YSZ was deposited with a layered microstructure apparent and a maximum growth rate of approximately 14 mum h-1 (activation energy (E a) of 50.9 +/- 4.3 kJ mol-1). The growth rate (approximately 43 mum h-1 with Ea = 53.8 +/- 7.9 kJ mol-1) was improved using Y- and Zr- n-butoxide liquid precursor solutions, and the microstructure was columnar. Yet, two-phase deposition of monoclinic ZrO2 and tetragonal YSZ occurred. Results of electron-probe micro-analysis showed that the nY/(nY + nZr ) ratio was less than 45% of the nY/( nY + nZr) ratio in the liquid precursor solution.

Micro-strip sensors based on CVD diamond

NASA Astrophysics Data System (ADS)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K. K.; Gheeraert, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; mac Lynne, L.; Manfredotti, C.; Meier, D.; Mishina, M.; Moroni, L.; Oh, A.; Pan, L. S.; Pernicka, M.; Peitz, A.; Perera, L.; Pirollo, S.; Procario, M.; Riester, J. L.; Roe, S.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R. J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Walsh, A. M.; Wedenig, R.; Weilhammer, P.; Wetstein, M.; White, C.; Zeuner, W.; Zoeller, M.; RD42 Collaboration

2000-10-01

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

Processing - microstructure relationships of chemically vapor deposited zirconia fiber coating for environmentally durable silicon carbide/silicon carbide composites

NASA Astrophysics Data System (ADS)

Lee, Jinil

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-ZrO 2) fiber coating as an oxidation-resistant interphase for SiC/SiC composites was investigated. The feasibility of the CVD-ZrO2 coating as a useful interphase for SiC/SiC composites was investigated with emphasis on developing critical processing-microstructure relationships. 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-ZrO2) was the key mechanism responsible for the weak interface behavior exhibited by the ZrO2 coating. The pre-delamination occurred as a result of (i) continuous formation of t-ZrO2 nuclei on the deposition surface; (ii) martensitic transformation of the tetragonal phase to a monoclinic phase upon reaching a critical grain size; and (iii) development of significant compressive hoop stresses due to the volume dilation associated with the transformation. We also discovered that low oxygen partial pressure in the CVD reactor was required for the nucleation of t-ZrO2 and was ultimately responsible for the delamination behavior. The effects of oxygen partial pressure on the nucleation behavior of the CVD-ZrO2 coating was systematically studied by intentionally adding the controlled amount of O2 into the CVD chamber. Characterization results suggested that the number density of t-ZrO2 nuclei apparently decreased with increasing the oxygen partial pressure from 0.004 to 1.6 Pa. Also, the coating layer became more columnar and contained larger m-ZrO2 grains. The observed relationships between the oxygen partial pressure and the morphological characteristics of the ZrO 2 coating were explained in the context of the grain size and oxygen deficiency effects which have been previously reported to cause the stabilization of the t-ZrO2 phase in bulk ZrO2 specimens.

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.

Advances in the Development of a WCl6 CVD System for Coating UO2 Powders with Tungsten

NASA Technical Reports Server (NTRS)

Mireles, Omar R.; Tieman, Alyssa; Broadway, Jeramie; Hickman, Robert

2013-01-01

W-UO2 CERMET fuels are under development to enable Nuclear Thermal Propulsion (NTP) for deep space exploration. Research efforts with an emphasis on fuel fabrication, testing, and identification of potential risks is underway. One primary risk is fuel loss due to CTE mismatch between W and UO2 and the grain boundary structure of W particles resulting in higher thermal stresses. Mechanical failure can result in significant reduction of the UO2 by hot hydrogen. Fuel loss can be mitigated if the UO2 particles are coated with a layer of high density tungsten before the consolidation process. This paper discusses the work to date, results, and advances of a fluidized bed chemical vapor deposition (CVD) system that utilizes the H2-WCl6 reduction process. Keywords: Space, Nuclear, Thermal, Propulsion, Fuel, CERMET, CVD, Tungsten, Uranium

Rhenium material properties

NASA Technical Reports Server (NTRS)

Biaglow, James A.

1995-01-01

Tensile data were obtained from four different types of rhenium at ambient and elevated temperatures. The four types of rhenium included chemical vapor deposition (CVD) and three powder metallurgy (PM) types, i.e., rolled sheet and pressed and sintered bars, with and without hot isostatic pressure (HIP) treatment. Results revealed a wide range of values with ultimate strengths at ambient temperatures varying from 663 MPa for CVD rhenium to 943 MPa for rolled sheet. A similar spread was also obtained for material tested at 1088 K and 1644 K. The wide variance observed with the different materials indicated that the rhenium manufacturing process, material composition and prior handling strongly dictated its properties. In addition to tensile properties, CVD, pressed and sintered material and HIP rhenium successfully completed 100 cycles of low cycle fatigue. Creep data were also obtained showing that CVD and pressed and sintered rhenium could sustain five hours of testing under a tension of 27.5 MPa at 1922 K.

Metal Organic Chemical Vapor Deposition of Oxide Films for Advanced Applications

DTIC Science & Technology

2000-06-01

coatings , photovoltaics, touch sensitive controls, electromagnetic shielding (as found on microwave ovens and stealth fighters), static dissipaters, and so...depositing high quality films. The methods are physical vapor deposition ( PVD ), spin/mist deposition, (CVD), and alternating layer (AL) CVD. PVD ...PZT & SBT, YBa2Cu3O, CeO, InO, TCOs, Varistors Ta2O5 , ZrO, MnO, HfO, CeO, MnO, MgO SAW/microwave Silicon/: Si, SiGe, SiGeC, �. Opto-electronics

Strain transfer across grain boundaries in MoS2 monolayers grown by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Niehues, Iris; Blob, Anna; Stiehm, Torsten; Schmidt, Robert; Jadriško, Valentino; Radatović, Borna; Čapeta, Davor; Kralj, Marko; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf

2018-07-01

Monolayers of transition metal dichalcogenides (TMDC) mechanically exfoliated from bulk crystals have exceptional mechanical and optical properties. They are extremely flexible, sustaining mechanical strain of about 10% without breaking. Their optical properties dramatically change with applied strain. However, the fabrication of a large number of mechanical devices is tedious due to the micromechanical exfoliation process. Alternatively, monolayers can be grown by chemical vapor deposition (CVD) on the wafer scale, with the drawback of cracks and grain boundaries in the material. Therefore, it is important to investigate the mechanical properties of CVD-grown material and its potential as a material for mass production of nanomechanical devices. Here, we measure the optical absorption of CVD-grown MoS2 monolayers with applied uniaxial tensile strain. We derive a strain-dependent shift for the A exciton of  ‑42 meV/%. This value is identical to MoS2 monolayers, which are mechanically exfoliated from natural molybdenite crystals. Using angle-resolved second-harmonic generation spectroscopy, we find that the applied uniaxial tensile strain is fully transferred across grain boundaries of the CVD-grown monolayer. Our work demonstrates that large-area artificially grown MoS2 monolayers are promising for mass-produced nanomechanical devices.

Vertical heterostructures of MoS2 and graphene nanoribbons grown by two-step chemical vapor deposition for high-gain photodetectors.

PubMed

Yunus, Rozan Mohamad; Endo, Hiroko; Tsuji, Masaharu; Ago, Hiroki

2015-10-14

Heterostructures of two-dimensional (2D) layered materials have attracted growing interest due to their unique properties and possible applications in electronics, photonics, and energy. Reduction of the dimensionality from 2D to one-dimensional (1D), such as graphene nanoribbons (GNRs), is also interesting due to the electron confinement effect and unique edge effects. Here, we demonstrate a bottom-up approach to grow vertical heterostructures of MoS2 and GNRs by a two-step chemical vapor deposition (CVD) method. Single-layer GNRs were first grown by ambient pressure CVD on an epitaxial Cu(100) film, followed by the second CVD process to grow MoS2 over the GNRs. The MoS2 layer was found to grow preferentially on the GNR surface, while the coverage could be further tuned by adjusting the growth conditions. The MoS2/GNR nanostructures show clear photosensitivity to visible light with an optical response much higher than that of a 2D MoS2/graphene heterostructure. The ability to grow a novel 1D heterostructure of layered materials by a bottom-up CVD approach will open up a new avenue to expand the dimensionality of the material synthesis and applications.

Low temperature growth of diamond films on optical fibers using Linear Antenna CVD system

NASA Astrophysics Data System (ADS)

Ficek, M.; Drijkoningen, S.; Karczewski, J.; Bogdanowicz, R.; Haenen, K.

2016-01-01

It is not trivial to achieve a good quality diamond-coated fibre interface due to a large difference in the properties and composition of the diamond films (or use coating even) and the optical fibre material, i.e. fused silica. One of the biggest problems is the high temperature during the deposition which influences the optical fibre or optical fibre sensor structure (e.g. long-period gratings (LPG)). The greatest advantage of a linear antenna microwave plasma enhanced chemical vapor deposition system (LA MW CVD) is the fact that it allows to grow the diamond layers at low temperature (below 300°C) [1]. High quality nanocrystalline diamond (NCD) thin films with thicknesses ranging from 70 nm to 150 nm, were deposited on silicon, glass and optical fibre substrates [2]. Substrates pretreatment by dip-coating and spin coating process with a dispersion consisting of detonation nanodiamond (DND) in dimethyl sulfoxide (DMSO) with polyvinyl alcohol (PVA) has been applied. During the deposition process the continuous mode of operation of the LA MW CVD system was used, which produces a continuous wave at a maximum power of 1.9 kW (in each antenna). Diamond films on optical fibres were obtained at temperatures below 350°C, providing a clear improvement of results compared to our earlier work [3]. The samples were characterized by scanning electron microscopy (SEM) imaging to investigate the morphology of the nanocrystalline diamond films. The film growth rate, film thickness, and optical properties in the VIS-NIR range, i.e. refractive index and extinction coefficient will be discussed based on measurements on reference quartz plates by using spectroscopic ellipsometry (SE).

Photoinitiated chemical vapor deposition of cytocompatible poly(2-hydroxyethyl methacrylate) films.

PubMed

McMahon, Brian J; Pfluger, Courtney A; Sun, Bing; Ziemer, Katherine S; Burkey, Daniel D; Carrier, Rebecca L

2014-07-01

Poly(2-hydroxyethyl methacrylate) (pHEMA) is a widely utilized biomaterial due to lack of toxicity and suitable mechanical properties; conformal thin pHEMA films produced via chemical vapor deposition (CVD) would thus have broad biomedical applications. Thin films of pHEMA were deposited using photoinitiated CVD (piCVD). Incorporation of ethylene glycol diacrylate (EGDA) into the pHEMA polymer film as a crosslinker, confirmed via Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, resulted in varied swelling and degradation behavior. 2-Hydroxyethyl methacrylate-only films showed significant thickness loss (up to 40%), possibly due to extraction of low-molecular-weight species or erosion, after 24 h in aqueous solution, whereas films crosslinked with EGDA (9.25-12.4%) were stable for up to 21 days. These results differ significantly from those obtained with plasma-polymerized pHEMA, which degraded steadily over a 21-day period, even with crosslinking. This suggests that the piCVD films differ structurally from those fabricated via plasma polymerization (plasma-enhanced CVD). piCVD pHEMA coatings proved to be good cell culture materials, with Caco-2 cell attachment and viability comparable to results obtained on tissue-culture polystyrene. Thus, thin film CVD pHEMA offers the advantage of enabling conformal coating of a cell culture substrate with tunable properties depending on method of preparation and incorporation of crosslinking agents. © 2013 Wiley Periodicals, Inc.

The growth and in situ characterization of chemical vapor deposited SiO2

NASA Technical Reports Server (NTRS)

Iyer, R.; Chang, R. R.; Lile, D. L.

1987-01-01

This paper reports the results of studies of the kinetics of remote (indirect) plasma enhanced low pressure CVD growth of SiO2 on Si and InP and of the in situ characterization of the electrical surface properties of InP during CVD processing. In the latter case photoluminescence was employed as a convenient and sensitive noninvasive method for characterizing surface trap densities. It was determined that, provided certain precautions are taken, the growth of SiO2 occurs in a reproducible and systematic fashion that can be expressed in an analytic form useful for growth rate prediction. Moreover, the in situ photoluminescence studies have yielded information on sample degradation resulting from heating and chemical exposure during the CVD growth.

Observation of Charge Generation and Transfer during CVD Growth of Carbon Nanotubes.

PubMed

Wang, Jiangtao; Liu, Peng; Xia, Bingyu; Wei, Haoming; Wei, Yang; Wu, Yang; Liu, Kai; Zhang, Lina; Wang, Jiaping; Li, Qunqing; Fan, Shoushan; Jiang, Kaili

2016-07-13

Carbon nanotube (CNT) is believed to be the most promising material for next generation IC industries with the prerequisite of chirality specific growth. For various approaches to controlling the chiral indices of CNTs, the key is to deepen the understanding of the catalytic growth mechanism in chemical vapor deposition (CVD). Here we show our discovery that the as-grown CNTs are all negatively charged after Fe-catalyzed CVD process. The extra electrons come from the charge generation and transfer during the growth of CNTs, which indicates that an electrochemical process happens in the surface reaction step. We then designed an in situ measurement equipment, verifying that the CVD growth of CNTs can be regarded as a primary battery system. Furthermore, we found that the variation of the Fermi level in Fe catalysts have a significant impact on the chirality of CNTs when different external electric fields are applied. These findings not only provide a new perspective on the growth of CNTs but also open up new possibilities for controlling the growth of CNTs by electrochemical methods.

Modeling chemical vapor deposition of silicon dioxide in microreactors at atmospheric pressure

NASA Astrophysics Data System (ADS)

Konakov, S. A.; Krzhizhanovskaya, V. V.

2015-01-01

We developed a multiphysics mathematical model for simulation of silicon dioxide Chemical Vapor Deposition (CVD) from tetraethyl orthosilicate (TEOS) and oxygen mixture in a microreactor at atmospheric pressure. Microfluidics is a promising technology with numerous applications in chemical synthesis due to its high heat and mass transfer efficiency and well-controlled flow parameters. Experimental studies of CVD microreactor technology are slow and expensive. Analytical solution of the governing equations is impossible due to the complexity of intertwined non-linear physical and chemical processes. Computer simulation is the most effective tool for design and optimization of microreactors. Our computational fluid dynamics model employs mass, momentum and energy balance equations for a laminar transient flow of a chemically reacting gas mixture at low Reynolds number. Simulation results show the influence of microreactor configuration and process parameters on SiO2 deposition rate and uniformity. We simulated three microreactors with the central channel diameter of 5, 10, 20 micrometers, varying gas flow rate in the range of 5-100 microliters per hour and temperature in the range of 300-800 °C. For each microchannel diameter we found an optimal set of process parameters providing the best quality of deposited material. The model will be used for optimization of the microreactor configuration and technological parameters to facilitate the experimental stage of this research.

Enhanced cold wall CVD reactor growth of horizontally aligned single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Mu, Wei; Kwak, Eun-Hye; Chen, Bingan; Huang, Shirong; Edwards, Michael; Fu, Yifeng; Jeppson, Kjell; Teo, Kenneth; Jeong, Goo-Hwan; Liu, Johan

2016-05-01

HASynthesis of horizontally-aligned single-walled carbon nanotubes (HA-SWCNTs) by chemical vapor deposition (CVD) directly on quartz seems very promising for the fabrication of future nanoelectronic devices. In comparison to hot-wall CVD, synthesis of HA-SWCNTs in a cold-wall CVD chamber not only means shorter heating, cooling and growth periods, but also prevents contamination of the chamber. However, since most synthesis of HA-SWCNTs is performed in hot-wall reactors, adapting this well-established process to a cold-wall chamber becomes extremely crucial. Here, in order to transfer the CVD growth technology from a hot-wall to a cold-wall chamber, a systematic investigation has been conducted to determine the influence of process parameters on the HA-SWCNT's growth. For two reasons, the cold-wall CVD chamber was upgraded with a top heater to complement the bottom substrate heater; the first reason to maintain a more uniform temperature profile during HA-SWCNTs growth, and the second reason to preheat the precursor gas flow before projecting it onto the catalyst. Our results show that the addition of a top heater had a significant effect on the synthesis. Characterization of the CNTs shows that the average density of HA-SWCNTs is around 1 - 2 tubes/ μm with high growth quality as shown by Raman analysis. [Figure not available: see fulltext.

Robofurnace: A semi-automated laboratory chemical vapor deposition system for high-throughput nanomaterial synthesis and process discovery

PubMed Central

Oliver, C. Ryan; Westrick, William; Koehler, Jeremy; Brieland-Shoultz, Anna; Anagnostopoulos-Politis, Ilias; Cruz-Gonzalez, Tizoc; Hart, A. John

2013-01-01

Laboratory research and development on new materials, such as nanostructured thin films, often utilizes manual equipment such as tube furnaces due to its relatively low cost and ease of setup. However, these systems can be prone to inconsistent outcomes due to variations in standard operating procedures and limitations in performance such as heating and cooling rates restrict the parameter space that can be explored. Perhaps more importantly, maximization of research throughput and the successful and efficient translation of materials processing knowledge to production-scale systems, relies on the attainment of consistent outcomes. In response to this need, we present a semi-automated lab-scale chemical vapor deposition (CVD) furnace system, called “Robofurnace.” Robofurnace is an automated CVD system built around a standard tube furnace, which automates sample insertion and removal and uses motion of the furnace to achieve rapid heating and cooling. The system has a 10-sample magazine and motorized transfer arm, which isolates the samples from the lab atmosphere and enables highly repeatable placement of the sample within the tube. The system is designed to enable continuous operation of the CVD reactor, with asynchronous loading/unloading of samples. To demonstrate its performance, Robofurnace is used to develop a rapid CVD recipe for carbon nanotube (CNT) forest growth, achieving a 10-fold improvement in CNT forest mass density compared to a benchmark recipe using a manual tube furnace. In the long run, multiple systems like Robofurnace may be linked to share data among laboratories by methods such as Twitter. Our hope is Robofurnace and like automation will enable machine learning to optimize and discover relationships in complex material synthesis processes. PMID:24289435

Synthesis and characterization of catalysts based on mesoporous silica partially hydrophobized for technological applications.

PubMed

Martins, Amanda R; Salviano, Adriana B; Oliveira, Aline A S; Mambrini, Raquel V; Moura, Flávia C C

2017-03-01

In this work, mesoporous silica mobil composition of matter no. 41 (MCM-41) was synthesized by the sol-gel method. Two different surface modifications were made to transform this material into a very active adsorbent and catalyst support: (i) impregnation of iron nanoparticles and (ii) hydrophobization via chemical vapor deposition (CVD) with ethanol. The materials prepared with different iron contents, i.e., 2.5, 5, and 10 %, after hydrophobization, were characterized by several techniques. CHN analysis and Raman spectroscopy proved that approximately 15 % of carbon is deposited during CVD process mainly as organized carbonaceous structures. The specific surface area was determined by the BET method as up to 1080 m 2  g -1 , which explains the excellent results of the materials in the adsorption of model dyes methylene blue and indigo carmine. Mössbauer spectroscopy, thermogravimetric (TG)/DTG analysis, and transmission electron microscopy (TEM) images showed that the iron supported may be partially reduced during the CVD process to Fe 2+ species, which are stabilized by the carbon coating. This iron species plays an important role in the oxidation of different contaminants, such as quinoline and methylene blue. The results obtained in the catalytic tests showed to be very promising.

Thermal barrier coatings on gas turbine blades: Chemical vapor deposition (Review)

NASA Astrophysics Data System (ADS)

Igumenov, I. K.; Aksenov, A. N.

2017-12-01

Schemes are presented for experimental setups (reactors) developed at leading scientific centers connected with the development of technologies for the deposition of coatings using the CVD method: at the Technical University of Braunschweig (Germany), the French Aerospace Research Center, the Materials Research Institute (Tohoku University, Japan) and the National Laboratory Oak Ridge (USA). Conditions and modes for obtaining the coatings with high operational parameters are considered. It is established that the formed thermal barrier coatings do not fundamentally differ in their properties (columnar microstructure, thermocyclic resistance, thermal conductivity coefficient) from standard electron-beam condensates, but the highest growth rates and the perfection of the crystal structure are achieved in the case of plasma-chemical processes and in reactors with additional laser or induction heating of a workpiece. It is shown that CVD reactors can serve as a basis for the development of rational and more advanced technologies for coating gas turbine blades that are not inferior to standard electron-beam plants in terms of the quality of produced coatings and have a much simpler and cheaper structure. The possibility of developing a new technology based on CVD processes for the formation of thermal barrier coatings with high operational parameters is discussed, including a set of requirements for industrial reactors, high-performance sources of vapor precursors, and promising new materials.

Microspheres and their methods of preparation

DOEpatents

Bose, Anima B; Yang, Junbing

2015-03-24

Carbon microspheres are doped with boron to enhance the electrical and physical properties of the microspheres. The boron-doped carbon microspheres are formed by a CVD process in which a catalyst, carbon source and boron source are evaporated, heated and deposited onto an inert substrate.

XPS study of thermal and electron-induced decomposition of Ni and Co acetylacetonate thin films for metal deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, Theodor; Warneke, Jonas; Zielasek, Volkmar, E-mail: zielasek@uni-bremen.de

2016-07-15

Optimizing thin metal film deposition techniques from metal-organic precursors such as atomic layer deposition, chemical vapor deposition (CVD), or electron beam-induced deposition (EBID) with the help of surface science analysis tools in ultrahigh vacuum requires a contamination-free precursor delivery technique, especially in the case of the less volatile precursors. For this purpose, the preparation of layers of undecomposed Ni(acac){sub 2} and Co(acac){sub 2} was tried via pulsed spray evaporation of a liquid solution of the precursors in ethanol into a flow of nitrogen on a CVD reactor. Solvent-free layers of intact precursor molecules were obtained when the substrate was heldmore » at a temperature of 115 °C. A qualitative comparison of thermally initiated and electron-induced precursor decomposition and metal center reduction was carried out. All deposited films were analyzed with respect to chemical composition quasi in situ by x-ray photoelectron spectroscopy. Thermally initiated decomposition yielded higher metal-to-metal oxide ratios in the deposit than the electron-induced process for which ratios of 60:40 and 20:80 were achieved for Ni and Co, resp. Compared to continuous EBID processes, all deposits showed low levels of carbon impurities of ∼10 at. %. Therefore, postdeposition irradiation of metal acetylacetonate layers by a focused electron beam and subsequent removal of intact precursor by dissolution in ethanol or by heating is proposed as electron beam lithography technique on the laboratory scale for the production of the metal nanostructures.« less

Anisotropic electrical conduction and reduction in dangling-bond density for polycrystalline Si films prepared by catalytic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Niikura, Chisato; Masuda, Atsushi; Matsumura, Hideki

1999-07-01

Polycrystalline Si (poly-Si) films with high crystalline fraction and low dangling-bond density were prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD. Directional anisotropy in electrical conduction, probably due to structural anisotropy, was observed for Cat-CVD poly-Si films. A novel method to separately characterize both crystalline and amorphous phases in poly-Si films using anisotropic electrical conduction was proposed. On the basis of results obtained by the proposed method and electron spin resonance measurements, reduction in dangling-bond density for Cat-CVD poly-Si films was achieved using the condition to make the quality of the included amorphous phase high. The properties of Cat-CVD poly-Si films are found to be promising in solar-cell applications.

Interface Properties of Wide Bandgap Semiconductor Structures

DTIC Science & Technology

1993-12-01

oxyacetylene torch and a water cooled substrate. Studying and controlling this chemical vapor deposition (CVD) process, however, can be frustrating because the...the carbide heat of formation. The precursors of chlorinated methylsilanes coupled with bias were used to deposit C films on Si(100). Textured C (lll...films were also achieved using an oxyacetylene torch . Cu forms an epitaxial rectifyingIcontact to diamond with a Schottky barrier height (SBH) of

Surface-texture evolution of different chemical-vapor-deposited zinc sulfide flats polished with various magnetorheological fluids

DOE PAGES

Salzman, S.; Romanofsky, H. J.; Jacobs, S. D.; ...

2015-08-19

The macro-structure of chemical-vapor-deposited (CVD) zinc sulfide (ZnS) substrates is characterizedby cone-like structures that start growing at the early stages of deposition. As deposition progresses,these cones grow larger and reach centimeter size in height and millimeter size in width. It is challengingto polish out these features from the top layer, particularly for the magnetorheological finishing (MRF)process. A conventional MR fluid tends to leave submillimeter surface artifacts on the finished surface,which is a direct result of the cone-like structure. Here we describe the MRF process of polishing four CVD ZnS substrates, manufactured by four differentvendors, with conventional MR fluid at pHmore » 10 and zirconia-coated-CI (carbonyl iron) MR fluids at pH 4, 5,and 6. We report on the surface–texture evolution of the substrates as they were MRF polished with thedifferent fluids. We show that performances of the zirconia-coated-CI MR fluid at pH 4 are significantlyhigher than that of the same fluid at pH levels of 5 and 6 and moderately higher than that of a conventionalMR fluid at pH 10. An improvement in surface–texture variability from part to part was also observedwith the pH 4 MR fluid.« less

Fabrication of AlN/BN bishell hollow nanofibers by electrospinning and atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haider, Ali; Kayaci, Fatma; Uyar, Tamer

2014-09-01

Aluminum nitride (AlN)/boron nitride (BN) bishell hollow nanofibers (HNFs) have been fabricated by successive atomic layer deposition (ALD) of AlN and sequential chemical vapor deposition (CVD) of BN on electrospun polymeric nanofibrous template. A four-step fabrication process was utilized: (i) fabrication of polymeric (nylon 6,6) nanofibers via electrospinning, (ii) hollow cathode plasma-assisted ALD of AlN at 100 °C onto electrospun polymeric nanofibers, (iii) calcination at 500 °C for 2 h in order to remove the polymeric template, and (iv) sequential CVD growth of BN at 450 °C. AlN/BN HNFs have been characterized for their chemical composition, surface morphology, crystal structure, and internal nanostructuremore » using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction. Measurements confirmed the presence of crystalline hexagonal BN and AlN within the three dimensional (3D) network of bishell HNFs with relatively low impurity content. In contrast to the smooth surface of the inner AlN layer, outer BN coating showed a highly rough 3D morphology in the form of BN nano-needle crystallites. It is shown that the combination of electrospinning and plasma-assisted low-temperature ALD/CVD can produce highly controlled multi-layered bishell nitride ceramic hollow nanostructures. While electrospinning enables easy fabrication of nanofibrous template, self-limiting reactions of plasma-assisted ALD and sequential CVD provide control over the wall thicknesses of AlN and BN layers with sub-nanometer accuracy.« less

Characterization of thin film deposits on tungsten filaments in catalytic chemical vapor deposition using 1,1-dimethylsilacyclobutane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Yujun, E-mail: shiy@ucalgary.ca; Tong, Ling; Mulmi, Suresh

Metal filament plays a key role in the technique of catalytic chemical vapor deposition (Cat-CVD) as it serves as a catalyst in dissociating the source gas to form reactive species. These reactive species initiate the gas-phase reaction chemistry and final thin film and nanostructure formation. At the same time, they also react with the metal itself, leading to the formation of metal alloys and other deposits. The deposits on the tungsten filaments when exposed to 1,1-dimethylsilacyclobutane (DMSCB), a single-source precursor for silicon carbide thin films, in the process of Cat-CVD were studied in this work. It has been demonstrated thatmore » a rich variety of deposits, including tungsten carbides (W{sub 2}C and WC), tungsten silicide (W{sub 5}Si{sub 3}), silicon carbide, amorphous carbon, and graphite, form on the W filament surfaces. The structural and morphological changes in the tungsten filaments depend strongly on the DMSCB pressure and filament temperature. At 1000 and 2000 °C, the formation of WC and W{sub 2}C dominates. In addition, a thin amorphous carbon layer has been found at 1500 °C with the 0.12 and 0.24 Torr of DMSCB and a lower temperature of 1200 °C with the 0.48 Torr of DMSCB. An increase in the DMSCB sample pressure gives rise to higher Si and C contents. As a result, the formation of SiC and W{sub 5}Si{sub 3} has been observed with the two high-pressure DMSCB samples (i.e., 0.24 and 0.48 Torr). The rich decomposition chemistry of DMSCB on the W surfaces is responsible for the extensive changes in the structure of the W filament, providing support for the close relationship between the gas-phase decomposition chemistry and the nature of alloy formation on the metal surface. The understanding of the structural changes obtained from this work will help guide the development of efficient methods to solve the filament aging problem in Cat-CVD and also to achieve a controllable deposition process.« less

A Comparative Study of Three Different Chemical Vapor Deposition Techniques of Carbon Nanotube Growth on Diamond Films

DTIC Science & Technology

2013-01-01

catalyst thermal CVD (FCT-CVD) with xylene and ferrocene liquid mixture without any prior catalyst deposition. T-CVD is a low-cost system that can... ferrocene is used as an iron source to promoteCNT growth. Based on these repeatable results, the CNT growth parameters were used to grow CNTs on the...temperature furnace is ramped up to the growth temperature of 750∘C. Ferrocene was dissolved into a xylene solvent in a 0.008 : 1molar volume ratio.The xylene

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.

Origin of the relatively low transport mobility of graphene grown through chemical vapor deposition

PubMed Central

Song, H. S.; Li, S. L.; Miyazaki, H.; Sato, S.; Hayashi, K.; Yamada, A.; Yokoyama, N.; Tsukagoshi, K.

2012-01-01

The reasons for the relatively low transport mobility of graphene grown through chemical vapor deposition (CVD-G), which include point defect, surface contamination, and line defect, were analyzed in the current study. A series of control experiments demonstrated that the determinant factor for the low transport mobility of CVD-G did not arise from point defects or surface contaminations, but stemmed from line defects induced by grain boundaries. Electron microscopies characterized the presence of grain boundaries and indicated the polycrystalline nature of the CVD-G. Field-effect transistors based on CVD-G without the grain boundary obtained a transport mobility comparative to that of Kish graphene, which directly indicated the detrimental effect of grain boundaries. The effect of grain boundary on transport mobility was qualitatively explained using a potential barrier model. Furthermore, the conduction mechanism of CVD-G was also investigated using the temperature dependence measurements. This study can help understand the intrinsic transport features of CVD-G. PMID:22468224

Comparison of the quality of single-crystal diamonds grown on two types of seed substrates by MPCVD

NASA Astrophysics Data System (ADS)

Zhao, Yun; Guo, Yanzhao; Lin, Liangzhen; Zheng, Yuting; Hei, Lifu; Liu, Jinlong; Wei, Junjun; Chen, Liangxian; Li, Chengming

2018-06-01

Microwave plasma chemical vapor deposition (MPCVD) was used to grow single-crystal diamonds on two types of single-crystal diamond seed substrates prepared by high-pressure, high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The quality of diamonds grown on the different seed substrates was compared. Fluorescence characteristics showed that the sectors of the HPHT seed substrates were obviously partitioned. Raman and absorption spectra showed that the CVD seed substrate produced higher-quality crystals with fewer nitrogen impurities. X-ray topography showed that the HPHT seed substrate had obvious growth sector boundaries, inclusions, dislocations, and stacking faults. The polarization characteristics of HPHT seed substrate were obvious, and the stress distribution was not uniform. When etching HPHT and CVD seed substrates using the same parameters, the etching morphology and extent of different growth sectors of the two substrates differed. Although extended defects were inevitably formed at the interface and propagated in the CVD layer, the dislocation density of a 1 mm-thick CVD layer grown on a CVD seed substrate was only half that of a 1 mm-thick CVD layer grown on an HPHT seed substrate. Therefore, the use of CVD seed substrate enabled the growth of a relatively higher-quality CVD single-crystal diamond.

Electrically insulating films deposited on V-4%Cr-4%Ti by reactive CVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J.H.

1998-04-01

In the design of liquid-metal blankets for magnetic fusion reactors, corrosion resistance of structural materials and the magnetohydrodynamic forces and their influence on thermal hydraulics and corrosion are major concerns. Electrically insulating CaO films deposited on V-4%Cr-4%Ti exhibit high-ohmic insulator behavior even though a small amount of vanadium from the alloy become incorporated into the film. However, when vanadium concentration in the film is > 15 wt.%, the film becomes conductive. When the vanadium concentration is high in localized areas, a calcium vanadate phase that exhibits semiconductor behavior can form. The objective of this study is to evaluate electrically insulatingmore » films that were deposited on V-4%Cr-4%Ti by a reactive chemical vapor deposition (CVD) method. To this end, CaO and Ca-V-O coatings were produced on vanadium alloys by CVD and by a metallic-vapor process to investigate the electrical resistance of the coatings. The authors found that the Ca-V-O films exhibited insulator behavior when the ratio of calcium concentration to vanadium concentration R in the film > 0.9, and semiconductor or conductor behavior when R < 0.8. However, in some cases, semiconductor behavior was observed when CaO-coated samples with R > 0.98 were exposed in liquid lithium. Based on these studies, they conclude that semiconductor behavior occurs if a conductive calcium vanadate phase is present in localized regions in the CaO coating.« less

Silicon carbide, a semiconductor for space power electronics

NASA Technical Reports Server (NTRS)

Powell, J. Anthony; Matus, Lawrence G.

1991-01-01

After many years of promise as a high temperature semiconductor, silicon carbide (SiC) is finally emerging as a useful electronic material. Recent significant progress that has led to this emergence has been in the areas of crystal growth and device fabrication technology. High quality single-crystal SiC wafers, up to 25 mm in diameter, can now be produced routinely from boules grown by a high temperature (2700 K) sublimation process. Device fabrication processes, including chemical vapor deposition (CVD), in situ doping during CVD, reactive ion etching, oxidation, metallization, etc. have been used to fabricate p-n junction diodes and MOSFETs. The diode was operated to 870 K and the MOSFET to 770 K.

Intelligent process control of fiber chemical vapor deposition

NASA Astrophysics Data System (ADS)

Jones, John Gregory

Chemical Vapor Deposition (CVD) is a widely used process for the application of thin films. In this case, CVD is being used to apply a thin film interface coating to single crystal monofilament sapphire (Alsb2Osb3) fibers for use in Ceramic Matrix Composites (CMC's). The hot-wall reactor operates at near atmospheric pressure which is maintained using a venturi pump system. Inert gas seals obviate the need for a sealed system. A liquid precursor delivery system has been implemented to provide precise stoichiometry control. Neural networks have been implemented to create real-time process description models trained using data generated based on a Navier-Stokes finite difference model of the process. Automation of the process to include full computer control and data logging capability is also presented. In situ sensors including a quadrupole mass spectrometer, thermocouples, laser scanner, and Raman spectrometer have been implemented to determine the gas phase reactants and coating quality. A fuzzy logic controller has been developed to regulate either the gas phase or the in situ temperature of the reactor using oxygen flow rate as an actuator. Scanning electron microscope (SEM) images of various samples are shown. A hierarchical control structure upon which the control structure is based is also presented.

Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides

NASA Technical Reports Server (NTRS)

Collins, J.; Rosner, D. E.; Castillo, J.

1992-01-01

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

Cold cathode vacuum discharge tube

DOEpatents

Boettcher, Gordon E.

1998-01-01

A cold cathode vacuum discharge tube, and method for making same, with an interior surface of the trigger probe coated with carbon deposited by carbon vapor deposition (CVD) or diamond-like carbon (DLC) deposition. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging.

Revealing the microscopic CVD growth mechanism of MoSe2 and the role of hydrogen gas during the growth procedure.

PubMed

Wang, Hulian; Zhu, Dancheng; Jiang, Feng; Zhao, Pei; Wang, Hongtao; Zhang, Ze; Chen, Xin; Jin, Chuanhong

2018-08-03

Understanding the microscopic mechanisms for the nucleation and growth of two-dimensional molybdenum diselenide (2D MoSe 2 ) via chemical vapor deposition (CVD) is crucial towards the precisely controlled growth of the 2D material. In this work, we employed a joint use of transmission electron microscopy and CVD, in which the 2D MoSe 2 were directly grown on a graphene membrane based on grids, that enables the microstructural characterization of as-grown MoSe 2 flakes. We further explore the role of hydrogen gas and find: in an argon ambient, the primary products are few-layer MoSe 2 flakes, along with MoO x nanoparticles; while with the introduction of H 2 , single-layer MoSe 2 became the dominant product during the CVD growth. Quantitative analysis of the effects of H 2 flow rate on the flake sizes, and areal coverage was also given. Nevertheless, we further illuminated the evolution of shape morphology and edge structures of single-layer MoSe 2 , and proposed the associated growth routes during a typical CVD process.

Growth of ZnOx:Al by high-throughput CVD at atmospheric pressure

NASA Astrophysics Data System (ADS)

Illiberi, A.; Simons, P. J. P. M.; Kniknie, B.; van Deelen, J.; Theelen, M.; Zeman, M.; Tijssen, M.; Zijlmans, W.; Steijvers, H. L. A. H.; Habets, D.; Janssen, A. C.; Beckers, E. H. A.

2012-05-01

Aluminum doped zinc oxide films (ZnOx:Al) have been deposited on a moving glass substrate by a metalorganic CVD process at atmospheric pressure in an in-line industrial type reactor. Tertiary-butanol has been used as an oxidant for diethylzinc and trimethylaluminium as the dopant gas. The effect of the deposition temperature (from 380 to 540 °C) on the deposition rate has been investigated by a numerical code, where a gas phase reaction among tertiary-butanol and diethylzinc is assumed to occur. The structural (crystallinity and morphology) properties of the films as a function of the deposition temperature have been analyzed by using X-ray diffraction and Scanning Electron Microscopy. A maximum growth rate of ˜11 nm/s was found at a deposition temperature of 480 °C, for which ZnOx:Al films show (002) preferential orientation, good crystalline quality and a naturally rough surface. ZnOx:Al films deposited at 480 °C are also highly conductive (R<10 Ω/□ for film thicknesses above 1050 nm) and transparent (>85% in the visible range). These films have been used as front transparent conductive oxide layers in p i n a-Si:H solar cells, achieving an initial efficiency approaching 8%.

Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

NASA Technical Reports Server (NTRS)

Bronikowski, Michael; Manohara, Harish

2008-01-01

This innovation consists of a set of methodologies for preparing large area (greater than 1 cm(exp 2)) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought. Another method for creating the graphene lattice includes metal-catalyzed CVD, in which the decomposition of the precursor molecules is initiated by the catalytic action of a catalytic metal upon the substrate surface. Another type of metal-catalyzed CVD has the entire substrate composed of catalytic metal, or other material, either as a bulk crystal or as a think layer of catalyst deposited upon another surface. In this case, the precursor molecules decompose directly upon contact with the substrate, releasing their atoms and forming the graphene sheet. Atomic layer deposition (ALD) can also be used. In this method, a substrate surface at low temperature is covered with exactly one monolayer of precursor molecules (which may be of more than one type). This is heated up so that the precursor molecules decompose and form one monolayer of the target material.

Surface modification for interaction study with bacteria and preosteoblast cells

NASA Astrophysics Data System (ADS)

Song, Qing

Surface modification plays a pivotal role in bioengineering. Polymer coatings can provide biocompatibility and biofunctionalities to biomaterials through surface modification. In this dissertation, initiated chemical vapor deposition (iCVD) was utilized to coat two-dimensional (2D) and three-dimensional (3D) substrates with differently charged polyelectrolytes in order to generate antimicrobial and osteocompatible biomaterials. ICVD is a modified CVD technique that enables surface modification in an all-dry condition without substrate damage and solvent contamination. The free-radical polymerization allows the vinyl polymers to conformally coat on various micro- and nano-structured substrates and maintains the delicate structure of the functional groups. The vapor deposition of polycations provided antimicrobial activity to planar and porous substrates through destroying the negatively charged bacterial membrane and brought about high contact-killing efficiency (99.99%) against Gram-positive Bacillus subtilis and Gram-negative Escherichia coli. Additionally, the polyampholytes synthesized by iCVD exhibited excellent antifouling performance against the adhesion of Gram-positive Listeria innocua and Gram-negative E. coli in phosphate buffered saline (PBS). Their antifouling activities were attributed to the electrostatic interaction and hydration layers that served as physical and energetic barriers to prevent bacterial adhesion. The contact-killing and antifouling polymers synthesized by iCVD can be applied to surface modification of food processing equipment and medical devices with the aim of reducing foodborne diseases and medical infections. Moreover, the charged polyelectrolyte modified 2D polystyrene surfaces displayed good osteocompatibility and enhanced osteogenesis of preosteoblast cells than the un-modified polystyrene surface. In order to promote osteoinduction of hydroxyapatite (HA) scaffolds, bioinspired polymer-controlled mineralization was conducted on the polyelectrolyte modified HA scaffolds. The mineralized scaffolds stimulated osteogenesis of preosteoblast cells compared with the control HA scaffolds. Therefore, the surface modification through vapor deposition of polyelectrolytes and polymer-controlled mineralization can improve osteoinduction of bone materials. In summary, the iCVD-mediated surface modification is a simple and promising approach to biofunctionalizing various structured substrates and generating antimicrobial and biocompatible biomaterials.

Chemical vapor deposition of Mo tubes for fuel cladding applications

DOE PAGES

Beaux, Miles F.; Vodnik, Douglas R.; Peterson, Reuben J.; ...

2018-01-31

In this study, chemical vapor deposition (CVD) techniques have been evaluated for fabrication of free-standing 0.25 mm thick molybdenum tubes with the end goal of nuclear fuel cladding applications. In order to produce tubes with the wall thickness and microstructures desirable for this application, long deposition durations on the order of 50 h with slow deposition rates were employed. A standard CVD method, involving molybdenum pentachloride reduction by hydrogen, as well as a fluidized-bed CVD (FBCVD) method was applied towards these objectives. Characterization of the tubes produced in this manner revealed regions of material with fine grain microstructure and wallmore » thickness suitable for fuel cladding applications, but lacking necessary uniformity across the length of the tubes. Finally, a path forward for the production of freestanding molybdenum tubes that possess the desired properties across their entire length has been identified and can be accomplished by future optimization of the deposition system.« less

Chemical vapor deposition of Mo tubes for fuel cladding applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaux, Miles F.; Vodnik, Douglas R.; Peterson, Reuben J.

In this study, chemical vapor deposition (CVD) techniques have been evaluated for fabrication of free-standing 0.25 mm thick molybdenum tubes with the end goal of nuclear fuel cladding applications. In order to produce tubes with the wall thickness and microstructures desirable for this application, long deposition durations on the order of 50 h with slow deposition rates were employed. A standard CVD method, involving molybdenum pentachloride reduction by hydrogen, as well as a fluidized-bed CVD (FBCVD) method was applied towards these objectives. Characterization of the tubes produced in this manner revealed regions of material with fine grain microstructure and wallmore » thickness suitable for fuel cladding applications, but lacking necessary uniformity across the length of the tubes. Finally, a path forward for the production of freestanding molybdenum tubes that possess the desired properties across their entire length has been identified and can be accomplished by future optimization of the deposition system.« less

Tractable Chemical Models for CVD of Silicon and Carbon

NASA Technical Reports Server (NTRS)

Blanquet, E.; Gokoglu, S. A.

1993-01-01

Tractable chemical models are validated for the CVD of silicon and carbon. Dilute silane (SiH4) and methane (CH4) in hydrogen are chosen as gaseous precursors. The chemical mechanism for each systems Si and C is deliberately reduced to three reactions in the models: one in the gas phase and two at the surface. The axial-flow CVD reactor utilized in this study has well-characterized flow and thermal fields and provides variable deposition rates in the axial direction. Comparisons between the experimental and calculated deposition rates are made at different pressures and temperatures.

Cold cathode vacuum discharge tube

DOEpatents

Boettcher, G.E.

1998-03-10

A cold cathode vacuum discharge tube, and method for making same, are disclosed with an interior surface of the trigger probe coated with carbon deposited by carbon vapor deposition (CVD) or diamond-like carbon (DLC) deposition. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging. 15 figs.

Cold cathode vacuum discharge tube

DOEpatents

Boettcher, G.E.

1998-04-14

A cold cathode vacuum discharge tube, and method for making same, with an interior surface of the trigger probe coated with carbon deposited by chemical vapor deposition (CVD) or diamond-like carbon (DLC) deposition are disclosed. Preferably a solid graphite insert is employed in the probe-cathode structure in place of an aluminum bushing employed in the prior art. The CVD or DLC probe face is laser scribed to allow resistance trimming to match available trigger voltage signals and to reduce electrical aging. 14 figs.

Microstructural Effects on the Corrosion Behavior of Alloys and Ceramics

DTIC Science & Technology

2008-06-30

Cr ferritic- martensitic steel HCMI2A, and silicon carbide fabricated by means of chemical vapor deposition (CVD). The study focused on the effect of...12%Cr ferritic- martensitic steel HCM12A, and silicon carbide fabricated by means of chemical vapor deposition (CVD). The study focused on the effect...3 1.4.3. Ferritic/ martensitic steel H CM 12A

Sub-10-nm patterning via directed self-assembly of block copolymer films with a vapour-phase deposited topcoat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suh, Hyo Seon; Kim, Do Han; Moni, Priya

2017-03-27

Directed self-assembly (DSA) of the domain structure in block copolymer (BCP) thin films is a promising approach for sub-10-nm surface patterning. DSA requires the control of interfacial properties on both interfaces of a BCP film to induce the formation of domains that traverse the entire film with a perpendicular orientation. Here we show a methodology to control the interfacial properties of BCP films that uses a polymer topcoat deposited by initiated chemical vapour deposition (iCVD). The iCVD topcoat forms a crosslinked network that grafts to and immobilizes BCP chains to create an interface that is equally attractive to both blocksmore » of the underlying copolymer. The topcoat, in conjunction with a chemically patterned substrate, directs the assembly of the grating structures in BCP films with a half-pitch dimension of 9.3 nm. As the iCVD topcoat can be as thin as 7 nm, it is amenable to pattern transfer without removal. As a result, the ease of vapour-phase deposition, applicability to high-resolution BCP systems and integration with pattern-transfer schemes are attractive properties of iCVD topcoats for industrial applications.« less

Optimization of chemical vapor deposition diamond films growth on steel: correlation between mechanical properties, structure, and composition.

PubMed

Laikhtman, A; Rapoport, L; Perfilyev, V; Moshkovich, A; Akhvlediani, R; Hoffman, A

2011-09-01

In the present work we perform optimization of mechanical and crystalline properties of CVD microcrystalline diamond films grown on steel substrates. A chromium-nitride (Cr-N) interlayer had been previously proposed to serve as a buffer for carbon and iron inter-diffusion and as a matching layer for the widely differing expansion coefficients of diamond and steel. However, adhesion and wear as well as crystalline perfection of diamond films are strongly affected by conditions of both Cr-N interlayer preparation and CVD diamond deposition. In this work we assess the effects of two parameters. The first one is the temperature of the Cr-N interlayer preparation: temperatures in the range of 500 degrees C-800 degrees C were used. The second one is diamond film thickness in the 0.5 microm-2 microm range monitored through variation of the deposition time from approximately 30 min to 2 hours. The mechanical properties of so deposited diamond films were investigated. For this purpose, scratch tests were performed at different indentation loads. The friction coefficient and wear loss were assessed. The mechanical and tribological properties were related to structure, composition, and crystalline perfection of diamond films which were extensively analyzed using different microscopic and spectroscopic techniques. It was found that relatively thick diamond film deposited on the Cr-N interlayer prepared at the temperature similar to that of the CVD process has the best mechanical and adhesion strength. This film was stable without visible cracks around the wear track during all scratch tests with different indentation loads. In other cases, cracking and delamination of the films took place at low to moderate indentation loads.

Role of hydrogen in the chemical vapor deposition growth of MoS2 atomic layers

NASA Astrophysics Data System (ADS)

Li, Xiao; Li, Xinming; Zang, Xiaobei; Zhu, Miao; He, Yijia; Wang, Kunlin; Xie, Dan; Zhu, Hongwei

2015-04-01

Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials.Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials. Electronic supplementary information (ESI) available: Low-magnification optical images; Raman spectra of 0% and 5% H2 samples; AFM characterization; Schematic of the film before and after sulfurization annealing; Schematic illustrations of two typical Raman-active phonon modes (E12g, A1g); Raman (mapping) spectra for 40% and 80% H2 samples before and after sulfurization annealing; PL spectra. See DOI: 10.1039/c5nr00904a

Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating

NASA Astrophysics Data System (ADS)

Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Seán. T.

2014-09-01

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

Microstructure and electroluminescent performance of chemical vapor deposited zinc sulfide doped with manganese films for integration in thin film electroluminescent devices

NASA Astrophysics Data System (ADS)

Topol, Anna Wanda

Zinc sulfide (ZnS) doped with manganese (Mn), ZnS:Mn, is widely recognized as the brightest and most effective electroluminescent (EL) phosphor used in current thin film electroluminescent (TFEL) devices. ZnS acts as a host lattice for the luminescent activator, Mn, leading to a highly efficient yellow-orange EL emission, and resulting in a wide array of applications in monochrome, multi-color and full color displays. Although this wide band dap (3.7 eV) material can be prepared by several deposition techniques, the chemical vapor deposition (CVD) is the most promising for TFEL applications in terms of viable deposition rates, high thickness and composition uniformity, and excellent yield over large area panels. This study describes the development and optimization of a CVD ZnS:Mn process using diethylzinc [(C2H5)2Zn, DEZ], di-pi-cyclopentadienylmanganese [(C5H5)2Mn, CPMn], and hydrogen sulfide [H2S] as the chemical sources for, respectively, Zn, Mn, and S. The effects of key deposition parameters on resulting Film microstructure and performance are discussed, primarily in the context of identifying an optimized process window for best electroluminescence behavior. In particular, substrate temperature was observed to play a key role in the formation of high quality crystalline ZnS:Mn films leading to improved brightness and EL efficiency. Further investigations of the influence of temperature treatment on the structural characteristics and EL performance of the CVD ZnS:Mn film were carried out. In this study, the influence of post-deposition annealing both in-situ and ex-situ annealing processes, on chemical, structural, and electroluminescent characteristics of the phosphor layer are described. The material properties of the employed dielectric are among the key factors determining the performance, stability and reliability of the TFEL display and therefore, the choice of dielectric material for use in ACTFEL displays is crucial. In addition, the luminous efficiency depends on the density of the interface states and their depth at the insulator-phosphor interfaces. Hence, critical integration issues are discussed in terms of the incorporation of ZnS:Mn films in dielectricsemiconductor-dielectric (DSD) structures with silicon nitride (SiNx) and aluminum titanium oxide (ATO) as top and bottom insulators.

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.

Large scale integration of CVD-graphene based NEMS with narrow distribution of resonance parameters

NASA Astrophysics Data System (ADS)

Arjmandi-Tash, Hadi; Allain, Adrien; (Vitto Han, Zheng; Bouchiat, Vincent

2017-06-01

We present a novel method for the fabrication of the arrays of suspended micron-sized membranes, based on monolayer pulsed-CVD graphene. Such devices are the source of an efficient integration of graphene nano-electro-mechanical resonators, compatible with production at the wafer scale using standard photolithography and processing tools. As the graphene surface is continuously protected by the same polymer layer during the whole process, suspended graphene membranes are clean and free of imperfections such as deposits, wrinkles and tears. Batch fabrication of 100 μm-long multi-connected suspended ribbons is presented. At room temperature, mechanical resonance of electrostatically-actuated devices show narrow distribution of their characteristic parameters with high quality factor and low effective mass and resonance frequencies, as expected for low stress and adsorbate-free membranes. Upon cooling, a sharp increase of both resonant frequency and quality factor is observed, enabling to extract the thermal expansion coefficient of CVD graphene. Comparison with state-of-the-art graphene NEMS is presented.

Evaluation of CVD silicon carbide for synchrotron radiation mirrors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takacs, P.Z.

1981-07-01

Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense x-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, andmore » few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods.« less

Evaluation of CVD silicon carbide for synchrotron radiation mirrors

NASA Astrophysics Data System (ADS)

Takacs, Peter Z.

1982-04-01

Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense X-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, and few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods.

The Chemical Vapor Deposition of Thin Metal Oxide Films

NASA Astrophysics Data System (ADS)

Laurie, Angus Buchanan

1990-01-01

Chemical vapor deposition (CVD) is an important method of preparing thin films of materials. Copper (II) oxide is an important p-type semiconductor and a major component of high T_{rm c} superconducting oxides. By using a volatile copper (II) chelate precursor, copper (II) bishexafluoroacetylacetonate, it has been possible to prepare thin films of copper (II) oxide by low temperature normal pressure metalorganic chemical vapor deposition. In the metalorganic CVD (MOCVD) production of oxide thin films, oxygen gas saturated with water vapor has been used mainly to reduce residual carbon and fluorine content. This research has investigated the influence of water-saturated oxygen on the morphology of thin films of CuO produced by low temperature chemical vapor deposition onto quartz, magnesium oxide and cubic zirconia substrates. ZnO is a useful n-type semiconductor material and is commonly prepared by the MOCVD method using organometallic precursors such as dimethyl or diethylzinc. These compounds are difficult to handle under atmospheric conditions. In this research, thin polycrystalline films of zinc oxide were grown on a variety of substrates by normal pressure CVD using a zinc chelate complex with zinc(II) bishexafluoroacetylacetonate dihydrate (Zn(hfa)_2.2H _2O) as the zinc source. Zn(hfa) _2.2H_2O is not moisture - or air-sensitive and is thus more easily handled. By operating under reduced-pressure conditions (20-500 torr) it is possible to substantially reduce deposition times and improve film quality. This research has investigated the reduced-pressure CVD of thin films of CuO and ZnO. Sub-micron films of tin(IV) oxide (SnO _2) have been grown by normal pressure CVD on quartz substrates by using tetraphenyltin (TPT) as the source of tin. All CVD films were characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).

Gas-Phase and Surface Chemistry in Electronic Materials Processing. Materials Research Society Symposium Proceedings Held in Boston, Massachusetts on November 29-December 2, 1993. Volume 334

DTIC Science & Technology

1994-01-01

CHEMISTRY IN THE PULSL’ LASER DEPOSITION OF OXIDE DIELECTRIC THIN FILMS ........................ 305 John W. Hastie, David W. Bonnell, Albert J. Paul...INVESTIGATIONS OF TiN AND Ti FILM DEPOSITION BY PLASMA ACTIVATED CVD USING CYCLOPENTADIENYL CYCLOHEPTATRIENYL TITANIUM, A LOW OXIDATION STATE PRECURSOR...Zhong Lu, Yi Ma, Scott Habertnehl, and Gerry Lucovsky ........ SPECTROSCOPIC INVESTIGATIONS OF LASER ABLATED GERMANIUM OXIDE

Chemical vapour deposition growth of carbon nanotube forests: kinetics, morphology, composition, and their mechanisms

NASA Astrophysics Data System (ADS)

Vinten, Phillip

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. in situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

Mass-Spectrometric Studies of Catalytic Chemical Vapor Deposition Processes of Organic Silicon Compounds Containing Nitrogen

NASA Astrophysics Data System (ADS)

Morimoto, Takashi; Ansari, S. G.; Yoneyama, Koji; Nakajima, Teppei; Masuda, Atsushi; Matsumura, Hideki; Nakamura, Megumi; Umemoto, Hironobu

2006-02-01

The mechanism of catalytic chemical vapor deposition (Cat-CVD) processes for hexamethyldisilazane (HMDS) and trisdimethylaminosilane (TDMAS), which are used as source gases to prepare SiNx or SiCxNy films, was studied using three different mass spectrometric techniques: ionization by Li+ ion attachment, vacuum-ultraviolet radiation and electron impact. The results for HMDS show that Si-N bonds dissociate selectively, although Si-C bonds are weaker, and (CH3)3SiNH should be one of the main precursors of deposited films. This decomposition mechanism did not change when NH3 was introduced, but the decomposition efficiency was slightly increased. Similar results were obtained for TDMAS.

Synthesis of carbon nanostructures from high density polyethylene (HDPE) and polyethylene terephthalate (PET) waste by chemical vapour deposition

NASA Astrophysics Data System (ADS)

Hatta, M. N. M.; Hashim, M. S.; Hussin, R.; Aida, S.; Kamdi, Z.; Ainuddin, AR; Yunos, MZ

2017-10-01

In this study, carbon nanostructures were synthesized from High Density Polyethylene (HDPE) and Polyethylene terephthalate (PET) waste by single-stage chemical vapour deposition (CVD) method. In CVD, iron was used as catalyst and pyrolitic of carbon source was conducted at temperature 700, 800 and 900°C for 30 minutes. Argon gas was used as carrier gas with flow at 90 sccm. The synthesized carbon nanostructures were characterized by FESEM, EDS and calculation of carbon yield (%). FESEM micrograph shows that the carbon nanostructures were only grown as nanofilament when synthesized from PET waste. The synthesization of carbon nanostructure at 700°C was produced smooth and the smallest diameter nanofilament compared to others. The carbon yield of synthesized carbon nanostructures from PET was lower from HDPE. Furthermore, the carbon yield is recorded to increase with increasing of reaction temperature for all samples. Elemental study by EDS analysis were carried out and the formation of carbon nanostructures was confirmed after CVD process. Utilization of polymer waste to produce carbon nanostructures is beneficial to ensure that the carbon nanotechnology will be sustained in future.

Properties of the carbon-palladium nanocomposites studied by Raman spectroscopy method

NASA Astrophysics Data System (ADS)

Belka, Radosław; Suchańska, Małgorzata

2013-10-01

In this paper, the results for thin carbon-palladium (C-Pd) nanocomposites obtained by PVD (Physical Vapour Deposition) and PVD/CVD (Chemical Vapour Deposition) method, carried out using Raman spectroscopy method are presented. Studies reveal the dominance of fullerene-like structure for PVD samples and graphite-like structures for CVD samples. The type of substrate and metal content have great impact on spectra shapes.

Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential

NASA Astrophysics Data System (ADS)

Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

2015-12-01

To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06016h

Nucleation and growth of single layer graphene on electrodeposited Cu by cold wall chemical vapor deposition

NASA Astrophysics Data System (ADS)

Das, Shantanu; Drucker, Jeff

2017-03-01

The nucleation density and average size of graphene crystallites grown using cold wall chemical vapor deposition (CVD) on 4 μm thick Cu films electrodeposited on W substrates can be tuned by varying growth parameters. Growth at a fixed substrate temperature of 1000 °C and total pressure of 700 Torr using Ar, H2 and CH4 mixtures enabled the contribution of total flow rate, CH4:H2 ratio and dilution of the CH4/H2 mixture by Ar to be identified. The largest variation in nucleation density was obtained by varying the CH4:H2 ratio. The observed morphological changes are analogous to those that would be expected if the deposition rate were varied at fixed substrate temperature for physical deposition using thermal evaporation. The graphene crystallite boundary morphology progresses from irregular/jagged through convex hexagonal to regular hexagonal as the effective C deposition rate decreases. This observation suggests that edge diffusion of C atoms along the crystallite boundaries, in addition to H2 etching, may contribute to shape evolution of the graphene crystallites. These results demonstrate that graphene grown using cold wall CVD follows a nucleation and growth mechanism similar to hot wall CVD. As a consequence, the vast knowledge base relevant to hot wall CVD may be exploited for graphene synthesis by the industrially preferable cold wall method.

Parameter Space of Atomic Layer Deposition of Ultrathin Oxides on Graphene

PubMed Central

2016-01-01

Atomic layer deposition (ALD) of ultrathin aluminum oxide (AlOx) films was systematically studied on supported chemical vapor deposition (CVD) graphene. We show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene using standard H2O and trimethylaluminum (TMA) precursors even at a high deposition temperature of 200 °C, without the use of surfactants or other additional graphene surface modifications. To obtain conformal nucleation, a precursor residence time of >2s is needed, which is not prohibitively long but sufficient to account for the slow adsorption kinetics of the graphene surface. In contrast, a shorter residence time results in heterogeneous nucleation that is preferential to defect/selective sites on the graphene. These findings demonstrate that careful control of the ALD parameter space is imperative in governing the nucleation behavior of AlOx on CVD graphene. We consider our results to have model system character for rational two-dimensional (2D)/non-2D material process integration, relevant also to the interfacing and device integration of the many other emerging 2D materials. PMID:27723305

ZnO synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen

NASA Astrophysics Data System (ADS)

Barnes, Teresa M.; Hand, Steve; Leaf, Jackie; Wolden, Colin A.

2004-09-01

Zinc oxide thin films were produced by high vacuum plasma-assisted chemical vapor deposition (HVP-CVD) from dimethylzinc (DMZn) and atomic oxygen. HVP-CVD is differentiated from conventional remote plasma-enhanced CVD in that the operating pressures of the inductively coupled plasma (ICP) source and the deposition chamber are decoupled. Both DMZn and atomic oxygen effuse into the deposition chamber under near collisionless conditions. The deposition rate was measured as a function of DMZn and atomic oxygen flux on glass and silicon substrates. Optical emission spectroscopy and quadrupole mass spectrometry (QMS) were used to provide real time analysis of the ICP source and the deposition chamber. The deposition rate was found to be first order in DMZn pressure and zero order in atomic oxygen density. All films demonstrated excellent transparency and were preferentially orientated along the c-axis. The deposition chemistry occurs exclusively through surface-mediated reactions, since the collisionless transport environment eliminates gas-phase chemistry. QMS analysis revealed that DMZn was almost completely consumed, and desorption of unreacted methyl radicals was greatly accelerated in the presence of atomic oxygen. Negligible zinc was detected in the gas phase, suggesting that Zn was efficiently consumed on the substrate and walls of the reactor.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Randolph, B.

Composite liners have been fabricated for the Los Alamos liner driven HEDP experiments using impactors formed by physical vapor deposition (PVD), electroplating, machining and shrink fitting. Chemical vapor deposition (CVD) has been proposed for some ATLAS liner applications. This paper describes the processes used to fabricate machined and shrink fitted impactors which have been used for copper impactors in 1100 aluminum liners and 6061 T-6 aluminum impactors in 1100 aluminum liners. The most successful processes have been largely empirically developed and rely upon a combination of shrink fitted and light press fitting. The processes used to date will be describedmore » along with some considerations for future composite liners requirements in the HEDP Program.« less

Development of CVD-W coatings on CuCrZr and graphite substrates with a PVD intermediate layer

NASA Astrophysics Data System (ADS)

Song, Jiupeng; Lian, Youyun; Lv, Yanwei; Liu, Junyong; Yu, Yang; Liu, Xiang; Yan, Binyou; Chen, Zhigang; Zhuang, Zhigang; Zhao, Ximeng; Qi, Yang

2014-12-01

In order to apply tungsten (W) coatings by chemical vapor deposition (CVD) for repairing or updating the plasma facing components (PFCs) of the first wall and divertor in existing or future tokomaks, where CuCrZr or graphite is the substrate material, an intermediate layer by physical vapor deposition (PVD) has been used to accommodate the interface stress due to the mismatch of thermal expansion or act as a diffusion barrier between the CVD-W coating and the substrate. The prepared CuCrZr/PVD-Cu/CVD-W sample with active cooling has passed thermal fatigue tests by electron beam with an absorbed power of 2.2 MW/m2, 50 s on/50 s off, for 100 cycles. Another graphite/PVD-Si/CVD-W sample without active cooling underwent thermal fatigue testing with an absorbed power density of 4.62 MW/m2, 5 s on/25 s off, for 200 cycles, and no catastrophic failure was found.

Water-Assisted Vapor Deposition of PEDOT Thin Film.

PubMed

Goktas, Hilal; Wang, Xiaoxue; Ugur, Asli; Gleason, Karen K

2015-07-01

The synthesis and characterization of poly(3,4-ethylenedioxythiophene) (PEDOT) using water-assisted vapor phase polymerization (VPP) and oxidative chemical vapor deposition (oCVD) are reported. For the VPP PEDOT, the oxidant, FeCl3 , is sublimated onto the substrate from a heated crucible in the reactor chamber and subsequently exposed to 3,4-ethylenedioxythiophene (EDOT) monomer and water vapor in the same reactor. The oCVD PEDOT was produced by introducing the oxidant, EDOT monomer, and water vapor simultaneously to the reactor. The enhancement of doping and crystallinity is observed in the water-assisted oCVD thin films. The high doping level observed at UV-vis-NIR spectra for the oCVD PEDOT, suggests that water acts as a solubilizing agent for oxidant and its byproducts. Although the VPP produced PEDOT thin films are fully amorphous, their conductivities are comparable with that of the oCVD produced ones. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interface properties of SiO2/GaN structures formed by chemical vapor deposition with remote oxygen plasma mixed with Ar or He

NASA Astrophysics Data System (ADS)

Truyen, Nguyen Xuan; Taoka, Noriyuki; Ohta, Akio; Makihara, Katsunori; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Shimizu, Mitsuaki; Miyazaki, Seiichi

2018-06-01

The impacts of noble gas species (Ar and He) on the formation of a SiO2/GaN structure formed by a remote oxygen plasma-enhanced chemical vapor deposition (ROPE-CVD) method were systematically investigated. Atomic force microscopy revealed that ROPE-CVD with He leads to a smooth SiO2 surface compared with the case of Ar. We found that no obvious oxidations of the GaN surfaces after the SiO2 depositions with the both Ar and He cases were observed. The capacitance–voltage (C–V) curves of the GaN MOS capacitors formed by ROPE-CVD with the Ar and He dilutions show good interface properties with no hysteresis and good agreement with the ideal C–V curves even after post deposition annealing at 800 °C. Besides, we found that the current density–oxide electric field characteristics shows a gate leakage current for the Ar case lower than the He case.

Optical materials characterization final technical report february 1, 1978-september 30, 1978. Technical note

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feldman, A.; Horowitz, D.; Waxter, R.M.

1979-02-01

Data obtained as part of the Optical Materials Characterization Program are summarized in this report. Room temperature values of refractive index as a function of wavelength are presented for the following materials: commercially grown KCl, reactive atmosphere processed (RAP) KCl, KCl nominally doped with 1.5% KI, hot forged CaF2, fusion cast CaF2, CaF2 doped with Er (0.001% to 3% Er), SrF2, chemical vapor deposited (CVD) ZnSe (2 specimens), and ZnS (CVD, 2 specimens). Data for the thermo-optic constant (dn/dT) and the linear thermal expansion coefficient are given for the following materials over the temperature range -180 degrees C to 200more » degrees C: Al2O3, BaF2, CaF2, CdF2, KBr, KCl, LiF, MgF2, NaCl, NaF, SrF2, ZnS (CVD), and ZnSe (CVD). The piezo-optic constants of the following materials are presented: As2S3 glass, CaF2, BaF2, Ge, KCl, fused SiO2, SrF2, a chalcogenide glass (Ge 33%, As 12%, Se 55%) and ZnSe (CVD).« less

An overview on tritium permeation barrier development for WCLL blanket concept

NASA Astrophysics Data System (ADS)

Aiello, A.; Ciampichetti, A.; Benamati, G.

2004-08-01

The reduction of tritium permeation through blanket structural materials and cooling tubes has to be carefully evaluated to minimise radiological hazards. A strong effort has been made in the past to select the best technological solution for the realisation of tritium permeation barriers (TPB) on complex structures not directly accessible after the completion of the manufacturing process. The best solution was identified in aluminium rich coatings, which form Al 2O 3 at their surface. Two technologies were selected as reference for the realisation of coating in the WCLL blanket concept: the chemical vapour deposition (CVD) process developed on laboratory scale by CEA, and the hot dipping (HD) process developed by FZK. The results obtained during three years of tests on CVD and HD coated specimens in gas and liquid metal phase are summarised and discussed.

Industrially-Situated Project-Based Learning: A Study of Feedback and Diffusion

ERIC Educational Resources Information Center

Gilbuena, Debra M.

2013-01-01

The Virtual Chemical Vapor Deposition (CVD) Process Development Project provides the context for the two areas of the research presented in this dissertation. The first area, generally referred to as feedback in this dissertation, focuses on student learning and the interactions of students and instructors that take place in the project,…

Equilibrium chemical vapor deposition growth of Bernal-stacked bilayer graphene.

PubMed

Zhao, Pei; Kim, Sungjin; Chen, Xiao; Einarsson, Erik; Wang, Miao; Song, Yenan; Wang, Hongtao; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

2014-11-25

Using ethanol as the carbon source, self-limiting growth of AB-stacked bilayer graphene (BLG) has been achieved on Cu via an equilibrium chemical vapor deposition (CVD) process. We found that during this alcohol catalytic CVD (ACCVD) a source-gas pressure range exists to break the self-limitation of monolayer graphene on Cu, and at a certain equilibrium state it prefers to form uniform BLG with a high surface coverage of ∼94% and AB-stacking ratio of nearly 100%. More importantly, once the BLG is completed, this growth shows a self-limiting manner, and an extended ethanol flow time does not result in additional layers. We investigate the mechanism of this equilibrium BLG growth using isotopically labeled (13)C-ethanol and selective surface aryl functionalization, and results reveal that during the equilibrium ACCVD process a continuous substitution of graphene flakes occurs to the as-formed graphene and the BLG growth follows a layer-by-layer epitaxy mechanism. These phenomena are significantly in contrast to those observed for previously reported BLG growth using methane as precursor.

Synthesis of ultrathin polymer insulating layers by initiated chemical vapour deposition for low-power soft electronics.

PubMed

Moon, Hanul; Seong, Hyejeong; Shin, Woo Cheol; Park, Won-Tae; Kim, Mincheol; Lee, Seungwon; Bong, Jae Hoon; Noh, Yong-Young; Cho, Byung Jin; Yoo, Seunghyup; Im, Sung Gap

2015-06-01

Insulating layers based on oxides and nitrides provide high capacitance, low leakage, high breakdown field and resistance to electrical stresses when used in electronic devices based on rigid substrates. However, their typically high process temperatures and brittleness make it difficult to achieve similar performance in flexible or organic electronics. Here, we show that poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) prepared via a one-step, solvent-free technique called initiated chemical vapour deposition (iCVD) is a versatile polymeric insulating layer that meets a wide range of requirements for next-generation electronic devices. Highly uniform and pure ultrathin films of pV3D3 with excellent insulating properties, a large energy gap (>8 eV), tunnelling-limited leakage characteristics and resistance to a tensile strain of up to 4% are demonstrated. The low process temperature, surface-growth character, and solvent-free nature of the iCVD process enable pV3D3 to be grown conformally on plastic substrates to yield flexible field-effect transistors as well as on a variety of channel layers, including organics, oxides, and graphene.

Initiated chemical vapor deposited nanoadhesive for bonding National Ignition Facility's targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Tom

Currently, the target fabrication scientists in National Ignition Facility Directorate at Lawrence Livermore National Laboratory (LLNL) is studying the propagation force resulted from laser impulses impacting a target. To best study this, they would like the adhesive used to glue the target substrates to be as thin as possible. The main objective of this research project is to create adhesive glue bonds for NIF’s targets that are ≤ 1 μm thick. Polyglycidylmethacrylate (PGMA) thin films were coated on various substrates using initiated chemical vapor deposition (iCVD). Film quality studies using white light interferometry reveal that the iCVD PGMA films weremore » smooth. The coated substrates were bonded at 150 °C under vacuum, with low inflow of Nitrogen. Success in bonding most of NIF’s mock targets at thicknesses ≤ 1 μm indicates that our process is feasible in bonding the real targets. Key parameters that are required for successful bonding were concluded from the bonding results. They include inert bonding atmosphere, sufficient contact between the PGMA films, and smooth substrates. Average bond strength of 0.60 MPa was obtained from mechanical shearing tests. The bonding failure mode of the sheared interfaces was observed to be cohesive. Future work on this project will include reattempt to bond silica aerogel to iCVD PGMA coated substrates, stabilize carbon nanotube forests with iCVD PGMA coating, and kinetics study of PGMA thermal crosslinking.« less

Continuous, highly flexible, and transparent graphene films by chemical vapor deposition for organic photovoltaics.

PubMed

Gomez De Arco, Lewis; Zhang, Yi; Schlenker, Cody W; Ryu, Koungmin; Thompson, Mark E; Zhou, Chongwu

2010-05-25

We report the implementation of continuous, highly flexible, and transparent graphene films obtained by chemical vapor deposition (CVD) as transparent conductive electrodes (TCE) in organic photovoltaic cells. Graphene films were synthesized by CVD, transferred to transparent substrates, and evaluated in organic solar cell heterojunctions (TCE/poly-3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS)/copper phthalocyanine/fullerene/bathocuproine/aluminum). Key to our success is the continuous nature of the CVD graphene films, which led to minimal surface roughness ( approximately 0.9 nm) and offered sheet resistance down to 230 Omega/sq (at 72% transparency), much lower than stacked graphene flakes at similar transparency. In addition, solar cells with CVD graphene and indium tin oxide (ITO) electrodes were fabricated side-by-side on flexible polyethylene terephthalate (PET) substrates and were confirmed to offer comparable performance, with power conversion efficiencies (eta) of 1.18 and 1.27%, respectively. Furthermore, CVD graphene solar cells demonstrated outstanding capability to operate under bending conditions up to 138 degrees , whereas the ITO-based devices displayed cracks and irreversible failure under bending of 60 degrees . Our work indicates the great potential of CVD graphene films for flexible photovoltaic applications.

Numerical Simulations of a 96-rod Polysilicon CVD Reactor

NASA Astrophysics Data System (ADS)

Guoqiang, Tang; Cong, Chen; Yifang, Cai; Bing, Zong; Yanguo, Cai; Tihu, Wang

2018-05-01

With the rapid development of the photovoltaic industry, pressurized Siemens belljar-type polysilicon CVD reactors have been enlarged from 24 rods to 96 rods in less than 10 years aimed at much greater single-reactor productivity. A CFD model of an industry-scale 96-rod CVD reactor was established to study the internal temperature distribution and the flow field of the reactor. Numerical simulations were carried out and compared with actual growth results from a real CVD reactor. Factors affecting polysilicon depositions such as inlet gas injections, flow field, and temperature distribution in the CVD reactor are studied.

Deposition and Characterization of Thin Films on Metallic Substrates

NASA Technical Reports Server (NTRS)

Gatica, Jorge E.

2005-01-01

A CVD method was successfully developed to produce conversion coatings on aluminum alloys surfaces with reproducible results with a variety of precursors. A well defined protocol to prepare the precursor solutions formulated in a previous research was extended to other additives. It was demonstrated that solutions prepared following such a protocol could be used to systematically generate protective coatings onto aluminum surfaces. Experiments with a variety of formulations revealed that a refined deposition protocol yields reproducible conversion coatings of controlled composition. A preliminary correlation between solution formulations and successful precursors was derived. Coatings were tested for adhesion properties enhancement for commercial paints. A standard testing method was followed and clear trends were identified. Only one precursors was tested systematically. Anticipated work on other precursors should allow a better characterization of the effect of intermetallics on the production of conversion/protective coatings on metals and ceramics. The significance of this work was the practical demonstration that chemical vapor deposition (CVD) techniques can be used to systematically generate protective/conversion coating on non-ferrous surfaces. In order to become an effective approach to replace chromate-based pre- treatment processes, namely in the aerospace or automobile industry, the process parameters must be defined more precisely. Moreover, the feasibility of scale-up designs necessitates a more comprehensive characterization of the fluid flow, transport phenomena, and chemical kinetics interacting in the process. Kinetic characterization showed a significantly different effect of magnesium-based precursors when compared to iron-based precursors. Future work will concentrate on refining the process through computer simulations and further experimental studies on the effect of other transition metals to induce deposition of conversion/protective films on aluminum and other metallic substrates.

CVD-Enabled Graphene Manufacture and Technology

PubMed Central

2015-01-01

Integrated manufacturing is arguably the most challenging task in the development of technology based on graphene and other 2D materials, particularly with regard to the industrial demand for “electronic-grade” large-area films. In order to control the structure and properties of these materials at the monolayer level, their nucleation, growth and interfacing needs to be understood to a level of unprecedented detail compared to existing thin film or bulk materials. Chemical vapor deposition (CVD) has emerged as the most versatile and promising technique to develop graphene and 2D material films into industrial device materials and this Perspective outlines recent progress, trends, and emerging CVD processing pathways. A key focus is the emerging understanding of the underlying growth mechanisms, in particular on the role of the required catalytic growth substrate, which brings together the latest progress in the fields of heterogeneous catalysis and classic crystal/thin-film growth. PMID:26240694

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulberg, M.T.; Allendorf, M.D.; Outka, D.A.

NH{sub 3} is an important component of many chemical vapor deposition (CVD) processes for TiN films, which are used for diffusion barriers and other applications in microelectronic circuits. In this study, the interaction of NH{sub 3} with TiN surfaces is examined with temperature programmed desorption (TPD) and Auger electron spectroscopy. NH{sub 3} has two adsorption states on TiN: a chemisorbed state and a multilayer state. A new method for analyzing TPD spectra in systems with slow pumping speeds yields activation energies for desorption for the two states of 24 kcal/mol and 7.3 kcal/mol, respectively. The sticking probability into the chemisorptionmore » state is {approximately}0.06. These results are discussed in the context of TiN CVD. In addition, the high temperature stability of TiN is investigated. TiN decomposes to its elements only after heating to 1300 K, showing that decomposition is unlikely to occur under CVD conditions.« less

Graphene growth with ‘no’ feedstock

NASA Astrophysics Data System (ADS)

Qing, Fangzhu; Jia, Ruitao; Li, Bao-Wen; Liu, Chunlin; Li, Congzhou; Peng, Bo; Deng, Longjiang; Zhang, Wanli; Li, Yanrong; Ruoff, Rodney S.; Li, Xuesong

2017-06-01

Synthesis of graphene by chemical vapor deposition (CVD) from hydrocarbons on Cu foil substrates can yield high quality and large area graphene films. In a typical CVD process, a hydrocarbon in the gas phase is introduced for graphene growth and hydrogen is usually required to achieve high quality graphene. We have found that in a low pressure CVD system equipped with an oil mechanical vacuum pump located downstream, graphene can be grown without deliberate introduction of a carbon feedstock but with only trace amounts of C present in the system, the origin of which we attribute to the vapor of the pump oil. This finding may help to rationalize the differences in graphene growth reported by different research groups. It should also help to gain an in-depth understanding of graphene growth mechanisms with the aim to improve the reproducibility and structure control in graphene synthesis, e.g. the formation of large area single crystal graphene and uniform bilayer graphene.

Mechanical properties of ultrahigh molecular weight PHEMA hydrogels synthesized using initiated chemical vapor deposition.

PubMed

Bose, Ranjita K; Lau, Kenneth K S

2010-08-09

In this work, poly(2-hydroxyethyl methacrylate) (PHEMA), a widely used hydrogel, is synthesized using initiated chemical vapor deposition (iCVD), a one-step surface polymerization that does not use any solvents. iCVD synthesis is capable of producing linear stoichiometric polymers that are free from entrained unreacted monomer or solvent and, thus, do not require additional purification steps. The resulting films, therefore, are found to be noncytotoxic and also have low nonspecific protein adsorption. The kinetics of iCVD polymerization are tuned so as to achieve rapid deposition rates ( approximately 1.5 microm/min), which in turn yield ultrahigh molecular weight polymer films that are mechanically robust with good water transport and swellability. The films have an extremely high degree of physical chain entanglement giving rise to high tensile modulus and storage modulus without the need for chemical cross-linking that compromises hydrophilicity.

High Yield Chemical Vapor Deposition Growth of High Quality Large-Area AB Stacked Bilayer Graphene

PubMed Central

Liu, Lixin; Zhou, Hailong; Cheng, Rui; Yu, Woo Jong; Liu, Yuan; Chen, Yu; Shaw, Jonathan; Zhong, Xing; Huang, Yu; Duan, Xiangfeng

2012-01-01

Bernal stacked (AB stacked) bilayer graphene is of significant interest for functional electronic and photonic devices due to the feasibility to continuously tune its band gap with a vertical electrical field. Mechanical exfoliation can be used to produce AB stacked bilayer graphene flakes but typically with the sizes limited to a few micrometers. Chemical vapor deposition (CVD) has been recently explored for the synthesis of bilayer graphene but usually with limited coverage and a mixture of AB and randomly stacked structures. Herein we report a rational approach to produce large-area high quality AB stacked bilayer graphene. We show that the self-limiting effect of graphene growth on Cu foil can be broken by using a high H2/CH4 ratio in a low pressure CVD process to enable the continued growth of bilayer graphene. A high temperature and low pressure nucleation step is found to be critical for the formation of bilayer graphene nuclei with high AB stacking ratio. A rational design of a two-step CVD process is developed for the growth of bilayer graphene with high AB stacking ratio (up to 90 %) and high coverage (up to 99 %). The electrical transport studies demonstrated that devices made of the as-grown bilayer graphene exhibit typical characteristics of AB stacked bilayer graphene with the highest carrier mobility exceeding 4,000 cm2/V·s at room temperature, comparable to that of the exfoliated bilayer graphene. PMID:22906199

Ion beam figuring of CVD silicon carbide mirrors

NASA Astrophysics Data System (ADS)

Gailly, P.; Collette, J.-P.; Fleury Frenette, K.; Jamar, C.

2017-11-01

Optical and structural elements made of silicon carbide are increasingly found in space instruments. Chemical vapor deposited silicon carbide (CVD-SiC) is used as a reflective coating on SiC optics in reason of its good behavior under polishing. The advantage of applying ion beam figuring (IBF) to CVD-SiC over other surface figure-improving techniques is discussed herein. The results of an IBF sequence performed at the Centre Spatial de Liège on a 100 mm CVD-SiC mirror are reported. The process allowed to reduce the mirror surface errors from 243 nm to 13 nm rms . Beside the surface figure, roughness is another critical feature to consider in order to preserve the optical quality of CVD-SiC . Thus, experiments focusing on the evolution of roughness were performed in various ion beam etching conditions. The roughness of samples etched at different depths down to 3 ≠m was determined with an optical profilometer. These measurements emphasize the importance of selecting the right combination of gas and beam energy to keep roughness at a low level. Kaufman-type ion sources are generally used to perform IBF but the performance of an end-Hall ion source in figuring CVD-SiC mirrors was also evaluated in this study. In order to do so, ion beam etching profiles obtained with the end-Hall source on CVD-SiC were measured and used as a basis for IBF simulations.

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.

Development and evaluation of die materials for use in the growth of silicon ribbons by the inverted ribbon growth process, task 2. LSSA project

NASA Technical Reports Server (NTRS)

Duffy, M. T.; Berkman, S.; Moss, H. S.; Cullen, G. W.

1978-01-01

The results of emission spectroscopic analysis indicate that molten silicon can remain in contact with hot-pressed Si3N4 (99.2 percent theoretical density) for prolonged periods without attaining the impurity content level of the nitride. Although MgO was used as binder, Mg was not found present in the silicon sessile drop in quantities much above the level initially present in the silicon source material. Preliminary experiments with EFG-type dies coated with CVD Si3N4 or CVD SiOxNy indicate that capillary rise does not occur readily in these dies. The same was found to be true of hot-pressed and reaction-sintered Si3N4 obtained commercially. However, when dies were formed by depositing CVD layers on shaped silicon slabs, a column of molten silicon was maintained in each CVD die while being heated in contact with a crucible of molten silicon. Preliminary wetting of dies appears necessary for EFG growth. Several ribbon growth experiments were performed from V-shaped dies.

Surface modification of pitch-based spherical activated carbon by CVD of NH 3 to improve its adsorption to uric acid

NASA Astrophysics Data System (ADS)

Liu, Chaojun; Liang, Xiaoyi; Liu, Xiaojun; Wang, Qin; Zhan, Liang; Zhang, Rui; Qiao, Wenming; Ling, Licheng

2008-08-01

Surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by chemical vapor deposition of NH 3 (NH 3-CVD) to improve the adsorption properties of uric acid. The texture and surface chemistry of PSAC were studied by N 2 adsorption, pH PZC (point of zero charge), acid-base titration and X-ray photoelectron spectroscopy (XPS). NH 3-CVD has a limited effect on carbon textural characteristics but it significantly changed the surface chemical properties, resulting in positive effects on uric acid adsorption. After modification by NH 3-CVD, large numbers of nitrogen-containing groups (especially valley-N and center-N) are introduced on the surface of PSAC, which is responsible for the increase of pH PZC, surface basicity and uric acid adsorption capacity. Pseudo-second-order kinetic model can be used to describe the dynamic adsorption of uric acid on PSAC, and the thermodynamic parameters show that the adsorption of uric acid on PSAC is spontaneous, endothermic and irreversible process in nature.

CVD-graphene for low equivalent series resistance in rGO/CVD-graphene/Ni-based supercapacitors.

PubMed

Kwon, Young Hwi; Kumar, Sunil; Bae, Joonho; Seo, Yongho

2018-05-11

Reduced equivalent series resistance (ESR) is necessary, particularly at a high current density, for high performance supercapacitors, and the interface resistance between the current collector and electrode material is one of the main components of ESR. In this report, we have optimized chemical vapor deposition-grown graphene (CVD-G) on a current collector (Ni-foil) using reduced graphene oxide as an active electrode material to fabricate an electric double layer capacitor with reduced ESR. The CVD-G was grown at different cooling rates-20 °C min -1 , 40 °C min -1 and 100 °C min -1 -to determine the optimum conditions. The lowest ESR, 0.38 Ω, was obtained for a cell with a 100 °C min -1 cooling rate, while the sample without a CVD-G interlayer exhibited 0.80 Ω. The CVD-G interlayer-based supercapacitors exhibited fast CD characteristics with high scan rates up to 10 Vs -1 due to low ESR. The specific capacitances deposited with CVD-G were in the range of 145.6 F g -1 -213.8 F g -1 at a voltage scan rate of 0.05 V s -1 . A quasi-rectangular behavior was observed in the cyclic voltammetry curves, even at very high scan rates of 50 and 100 V s -1 , for the cell with optimized CVD-G at higher cooling rates, i.e. 100 °C min -1 .

CVD-graphene for low equivalent series resistance in rGO/CVD-graphene/Ni-based supercapacitors

NASA Astrophysics Data System (ADS)

Kwon, Young Hwi; Kumar, Sunil; Bae, Joonho; Seo, Yongho

2018-05-01

Reduced equivalent series resistance (ESR) is necessary, particularly at a high current density, for high performance supercapacitors, and the interface resistance between the current collector and electrode material is one of the main components of ESR. In this report, we have optimized chemical vapor deposition-grown graphene (CVD-G) on a current collector (Ni-foil) using reduced graphene oxide as an active electrode material to fabricate an electric double layer capacitor with reduced ESR. The CVD-G was grown at different cooling rates—20 °C min‑1, 40 °C min‑1 and 100 °C min‑1—to determine the optimum conditions. The lowest ESR, 0.38 Ω, was obtained for a cell with a 100 °C min‑1 cooling rate, while the sample without a CVD-G interlayer exhibited 0.80 Ω. The CVD-G interlayer-based supercapacitors exhibited fast CD characteristics with high scan rates up to 10 Vs‑1 due to low ESR. The specific capacitances deposited with CVD-G were in the range of 145.6 F g‑1–213.8 F g‑1 at a voltage scan rate of 0.05 V s‑1. A quasi-rectangular behavior was observed in the cyclic voltammetry curves, even at very high scan rates of 50 and 100 V s‑1, for the cell with optimized CVD-G at higher cooling rates, i.e. 100 °C min‑1.

CVD Diamond, DLC, and c-BN Coatings for Solid Film Lubrication

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1998-01-01

When the main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1 and 10(exp -6) mm(exp 3)/N-m, respectively, carbon- and nitrogen-ion-implanted, fine-grain CVD diamond and DLC ion beam deposited on fine-grain CVD diamond met the requirements regardless of environment (vacuum, nitrogen, and air).

Densification control and analysis of outer shell of new high-temperature vacuum insulated composite

NASA Astrophysics Data System (ADS)

Wang, Yang; Chen, Zhaofeng; Jiang, Yun; Yu, Shengjie; Xu, Tengzhou; Li, Binbin; Chen, Zhou

2017-11-01

A novel high temperature vacuum insulated composite with low thermal conductivity composed of SiC foam core material and sealing outer shell is discussed, which will have a great potential to be used as thermal protection system material. In this composite, the outer shell is the key to maintain its internal vacuum, which is consisted of 2.5D C/C and SiC coating. So the densification processes of outer shell, including 2.5D braiding process, chemical vapor infiltration (CVI) pyrolytic carbon (PyC) process, polymer infiltration and pyrolysis (PIP) glassy carbon (GC) process and chemical vapor deposition (CVD) SiC process, are focused in this paper. The measuring result of the gas transmission quantity of outer shell is only 0.14 cm3/m2 · d · Pa after 5 times CVD processes, which is two order of magnitude lower than that sample deposited one time. After 10 times thermal shock cycles, the gas transmission quantity increases to 1.2 cm3/m2 · d · Pa. The effective thermal conductivity of high temperature vacuum insulated composite ranged from 0.19 W m-1 K-1 to 0.747 W m-1 K-1 within the temperature from 20 °C to 900 °C. Even after 10 thermal shock cycles, the variation of the effective thermal conductivity is still consistent with that without treatments.

Effects of Fiber Coatings on Tensile Properties of Hi-Nicalon SiC/RBSN Tow Composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Hull, David R.

1997-01-01

Uncoated Hi-Nicalon silicon carbide (SiC) fiber tows and those coated with a single surface layer of pyrolytic boron nitride (PBN), double layers of PBN/Si-rich PBN, and boron nitride (BN)/SiC coatings deposited by chemical vapor deposition (CVD) method were infiltrated with silicon slurry and then exposed to N2, for 4 hr at 1200 and 1400 C. Room temperature ultimate tensile fracture loads and microstructural characterization of uncoated and CVD coated Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride (RBSN) tow composites were measured to select suitable interface coating(s) stable under RBSN processing conditions. Results indicate that room temperature ultimate fracture loads of the uncoated Hi-Nicalon SiC/RBSN tow composites nitrided at both temperatures were significantly lower than those of the uncoated Hi-Nicalon tows without slurry infiltration. In contrast, all CVD coated Hi-Nicalon SiC/RBSN tow composites retained a greater fraction of the dry tow fracture load after nitridation at 1200 C, but degraded significantly after nitridation at 1400 C. Reaction between metal impurities (Fe and Ni) present in the attrition milled silicon powder and uncoated regions of SiC fibers appears to be the probable cause for fiber degradation.

Chemical Vapor Deposition Synthesis of Graphene-Based Materials and Chemical Modulation of Graphene Electronics

NASA Astrophysics Data System (ADS)

Yan, Zheng

Graphene, a two-dimensional sp2-bonded carbon material, has attracted enormous attention due to its excellent electrical, optical and mechanical properties. Recently developed chemical vapor deposition (CVD) methods could produce large-size and uniform polycrystalline graphene films, limited to gas carbon sources, metal catalyst substrates and degraded properties induced by grain boundaries. Meanwhile, pristine monolayer graphene exhibits a standard ambipolar behavior with a zero neutrality point in field-effect transistors (FETs), limiting its future electronic applications. This thesis starts with the investigation of CVD synthesis of pristine and N-doped graphene with controlled thickness using solid carbon sources on metal catalyst substrates (chapter 1), and then discusses the direct growth of bilayer graphene on insulating substrates, including SiO2, h-BN, Si3N4 and Al2O3, without needing further transfer-process (chapter 2). Chapter 3 discusses the synthesis of high-quality graphene single crystals and hexagonal onion-ring-like graphene domains, and also explores the basic growth mechanism of graphene on Cu substrates. To extend graphene's potential applications, both vertical and planar graphene-carbon nanotube hybrids are fabricated using CVD method and their interesting properties are investigated (chapter 4). Chapter 5 discusses how to use chemical methods to modulate graphene's electronic behaviors.

On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abrutis, Adulfas, E-mail: adulfas.abrutis@chf.vu.lt; Silimavicus, Laimis; Kubilius, Virgaudas

Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In{sub 2}O{sub 3} films; at a current of 6–10 A, growth rates weremore » increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10{sup −3} Ωcm and transparency of >90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs.« less

Room Temperature Sensing Achieved by GaAs Nanowires and oCVD Polymer Coating.

PubMed

Wang, Xiaoxue; Ermez, Sema; Goktas, Hilal; Gradečak, Silvija; Gleason, Karen

2017-06-01

Novel structures comprised of GaAs nanowire arrays conformally coated with conducting polymers (poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3,4-ethylenedioxythiophene-co-3-thiophene acetic acid) display both sensitivity and selectivity to a variety of volatile organic chemicals. A key feature is room temperature operation, so that neither a heater nor the power it would consume, is required. It is a distinct difference from traditional metal oxide sensors, which typically require elevated operational temperature. The GaAs nanowires are prepared directly via self-seeded metal-organic chemical deposition, and conducting polymers are deposited on GaAs nanowires using oxidative chemical vapor deposition (oCVD). The range of thickness for the oCVD layer is between 100 and 200 nm, which is controlled by changing the deposition time. X-ray diffraction analysis indicates an edge-on alignment of the crystalline structure of the PEDOT coating layer on GaAs nanowires. In addition, the positive correlation between the improvement of sensitivity and the increasing nanowire density is demonstrated. Furthermore, the effect of different oCVD coating materials is studied. The sensing mechanism is also discussed with studies considering both nanowire density and polymer types. Overall, the novel structure exhibits good sensitivity and selectivity in gas sensing, and provides a promising platform for future sensor design. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A New Commercializable Route for the Preparation of Single-Source Precursors for Bulk, Thin-Film, and Nanocrystallite I-III-IV Semiconductors

NASA Technical Reports Server (NTRS)

Banger, Kulbinder K.; Jin, Michael H. C.; Harris, Jerry D.; Fanwick, Philip E.; Hepp, Aloysius F.

2004-01-01

We report a new simplified synthetic procedure for commercial manufacture of ternary single source precursors (SSP). This new synthetic process has been successfully implemented to fabricate known SSPs on bulk scale and the first liquid SSPs to the semiconductors CuInSe2 and AgIn(x)S(y). Single crystal X-ray determination reveals the first unsolvated ternary AgInS SSP. SSPs prepared via this new route have successfully been used in a spray assisted chemical vapor deposition (CVD) process to deposit polycrystalline thin films, and for preparing ternary nanocrystallites.

New developments in CVD diamond for detector applications

NASA Astrophysics Data System (ADS)

Adam, W.; Berdermann, E.; Bergonzo, P.; de Boer, W.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Dulinski, W.; Doroshenko, J.; van Eijk, B.; Fallou, A.; Fischer, P.; Fizzotti, F.; Furetta, C.; Gan, K. K.; Ghodbane, N.; Grigoriev, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kaplon, J.; Kass, R.; Keil, M.; Knoepfle, K. T.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D.; Menichelli, D.; Meuser, S.; Mishina, M.; Moroni, L.; Noomen, J.; Oh, A.; Pernicka, M.; Perera, L.; Potenza, R.; Riester, J. L.; Roe, S.; Rudge, A.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Sutera, C.; Trischuk, W.; Tromson, D.; Tuve, C.; Vincenzo, B.; Weilhammer, P.; Wermes, N.; Wetstein, M.; Zeuner, W.; Zoeller, M.

Chemical Vapor Deposition (CVD) diamond has been discussed extensively as an alternative sensor material for use very close to the interaction region of the LHC and other machines where extreme radiation conditions exist. During the last seven years the RD42 collaboration has developed diamond detectors and tested them with LHC electronics towards the end of creating a device usable by experiments. The most recent results of this work are presented. Recently, a new form of CVD diamond has been developed: single crystal CVD diamond which resolves many of the issues associated with poly-crystalline CVD material. The first tests of this material are also presented.

Extraction of volatiles and metals from extraterrestrial materials

NASA Technical Reports Server (NTRS)

Lewis, J. S.

1992-01-01

Recent progress in defining the physical, orbital, and chemical properties of the Earth-crossing asteroid and comet population was integrated into an elaborate Monte Carlo model of the fluxes of bodies in the inner Solar System. This model is of use in projecting flight opportunities to as-yet undiscovered near-Earth objects and in assessing the impact hazard to life on Earth and the evolutionary consequences of impacts on the other terrestrial planets. Further progress was made in defining desirable transportation system architectures for the use of non-terrestrial volatiles and metals, including the delivery of propellants to near-Earth space for fueling of space exploration initiative (SEI) type expeditions, the construction and resupply of Solar Power Satellite constellations in various Earth orbits (including geosynchronous earth orbit (GEO) and Highly Eccentric Earth Orbit (HEEO)), and retrieval of He-3 for use as a clean fusion fuel on Earth. These studies suggest a greater future role for SERC in the exploration of space energy sources to meet Earth's 21st-century energy requirements. Laboratory studies of volatilization and deposition of ferrous metal alloys demonstrated deposition of strong iron films from carbonyl chemical vapor deposition (CVD), showing the crucial role of additive gases in governing the CVD process, and pointing the way to specific experiments on extraction and deposition of ferrous metals from nonterrestrial materials.

Calculation of residual principal stresses in CVD boron on carbon filaments

NASA Technical Reports Server (NTRS)

Behrendt, D. R.

1980-01-01

A three-dimensional finite element model of the chemical vapor deposition (CVD) of boron on a carbon substrate (B/C) is developed. The model includes an expansion of the boron after deposition due to atomic rearrangement and includes creep of the boron and carbon. Curves are presented to show how the principal residual stresses and the filament elongation vary as the parameters defining deposition strain and creep are varied. The calculated results are compared with experimental axial residual stress and elongation measurements made on B/C filaments. This comparison requires that for good agreement between calculated and experimental results, the deposited boron must continue to expand after deposition, and that the build-up of residual stresses is limited by significant boron and carbon creep rates.

Surface Design and Engineering Toward Wear-Resistant, Self-Lubricant Diamond Films and Coatings. Chapter 10

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1999-01-01

This chapter describes three studies on the surface design, surface engineering, and tribology of chemical-vapor-deposited (CVD) diamond films and coatings toward wear-resistant, self-lubricating diamond films and coatings. Friction mechanisms and solid lubrication mechanisms of CVD diamond are stated. Effects of an amorphous hydrogenated carbon on CVD diamond, an amorphous, nondiamond carbon surface layer formed on CVD diamond by carbon and nitrogen ion implantation, and a materials combination of cubic boron nitride and CVD diamond on the adhesion, friction, and wear behaviors of CVD diamond in ultrahigh vacuum are described. How surface modification and the selected materials couple improved the tribological functionality of coatings, giving low coefficient of friction and good wear resistance, is explained.

Spin-on metal oxide materials with high etch selectivity and wet strippability

NASA Astrophysics Data System (ADS)

Yao, Huirong; Mullen, Salem; Wolfer, Elizabeth; McKenzie, Douglas; Rahman, Dalil; Cho, JoonYeon; Padmanaban, Munirathna; Petermann, Claire; Hong, SungEun; Her, YoungJun

2016-03-01

Metal oxide or metal nitride films are used as hard mask materials in semiconductor industry for patterning purposes due to their excellent etch resistances against the plasma etches. Chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques are usually used to deposit the metal containing materials on substrates or underlying films, which uses specialized equipment and can lead to high cost-of-ownership and low throughput. We have reported novel spin-on coatings that provide simple and cost effective method to generate metal oxide films possessing good etch selectivity and can be removed by chemical agents. In this paper, new spin-on Al oxide and Zr oxide hard mask formulations are reported. The new metal oxide formulations provide higher metal content compared to previously reported material of specific metal oxides under similar processing conditions. These metal oxide films demonstrate ultra-high etch selectivity and good pattern transfer capability. The cured films can be removed by various chemical agents such as developer, solvents or wet etchants/strippers commonly used in the fab environment. With high metal MHM material as an underlayer, the pattern transfer process is simplified by reducing the number of layers in the stack and the size of the nano structure is minimized by replacement of a thicker film ACL. Therefore, these novel AZ® spinon metal oxide hard mask materials can potentially be used to replace any CVD or ALD metal, metal oxide, metal nitride or spin-on silicon-containing hard mask films in 193 nm or EUV process.

Foldable and Disposable Memory on Paper

PubMed Central

Lee, Byung-Hyun; Lee, Dong-Il; Bae, Hagyoul; Seong, Hyejeong; Jeon, Seung-Bae; Seol, Myung-Lok; Han, Jin-Woo; Meyyappan, M.; Im, Sung-Gap; Choi, Yang-Kyu

2016-01-01

Foldable organic memory on cellulose nanofibril paper with bendable and rollable characteristics is demonstrated by employing initiated chemical vapor deposition (iCVD) for polymerization of the resistive switching layer and inkjet printing of the electrode, where iCVD based on all-dry and room temperature process is very suitable for paper electronics. This memory exhibits a low operation voltage of 1.5 V enabling battery operation compared to previous reports and wide memory window. The memory performance is maintained after folding tests, showing high endurance. Furthermore, the quick and complete disposable nature demonstrated here is attractive for security applications. This work provides an effective platform for green, foldable and disposable electronics based on low cost and versatile materials. PMID:27922094

Dimensionless Numbers Expressed in Terms of Common CVD Process Parameters

NASA Technical Reports Server (NTRS)

Kuczmarski, Maria A.

1999-01-01

A variety of dimensionless numbers related to momentum and heat transfer are useful in Chemical Vapor Deposition (CVD) analysis. These numbers are not traditionally calculated by directly using reactor operating parameters, such as temperature and pressure. In this paper, these numbers have been expressed in a form that explicitly shows their dependence upon the carrier gas, reactor geometry, and reactor operation conditions. These expressions were derived for both monatomic and diatomic gases using estimation techniques for viscosity, thermal conductivity, and heat capacity. Values calculated from these expressions compared well to previously published values. These expressions provide a relatively quick method for predicting changes in the flow patterns resulting from changes in the reactor operating conditions.

Tribological Characteristics and Applications of Superhard Coatings: CVD Diamond, DLC, and c-BN

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Murakawa, Masao; Watanabe, Shuichi; Takeuchi, Sadao; Wu, Richard L. C.

1999-01-01

Results of fundamental research on the tribological properties of chemical-vapor-deposited (CVD) diamond, diamondlike carbon, and cubic boron nitride films in sliding contact with CVD diamond in ultrahigh vacuum, dry nitrogen, humid air, and water are discussed. Furthermore, the actual and potential applications of the three different superhard coatings in the field of tribology technology, particularly for wear parts and tools, are reviewed.

Thermal chemical vapor deposition (T-CVD) growth of carbon nanotubes on different metallic underlayers

NASA Astrophysics Data System (ADS)

Kim, S. M.; Gangloff, L.

2011-06-01

The synthesis of carbon nanotubes (CNTs) on various substrates by thermal chemical vapor deposition (T-CVD) (500-800 °C) is described. C 2H 2 (98% purity) is used as the carbon feedstock and the metallic underlayers, i.e., AlCu, Cu, Ag, Ta, and NiV are used. A crucial component is the insertion (or inclusion) of an Al layer between the metal and the catalyst, which then leads to the effective growth of CNTs. The types of CNTs (single or multi walled) could be dependent on the diameter of Al xO y nanoparticles that are formed during the annealing process. In situ mass spectroscopy reveals that the increase in CO 2 and H 2O with temperature, during the growth, could be correlated to the formation of longer CNTs (∼2 μm) on NiV and Ta due to their etching effects (i.e. C+CO 2→2CO and C+H 2O→CO+H 2).

Magnetic whiskers of p-aminobenzoic acid and their use for preparation of filled and microchannel silicone rubbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semenov, V. V., E-mail: vvsemenov@iomc.ras.ru; Loginova, V. V.; Zolotareva, N. V.

A thin cobalt layer has been formed on the surface of p-aminobenzoic acid whiskers by chemical vapor deposition (CVD). The metallized crystals have been oriented in liquid polydimethylsiloxane rubber by applying a dc magnetic field. After vulcanization, the filler has been removed by processing in an alcohol solution of trifluoroacetic acid. The cobalt deposition on the surface of the organic compound and the properties of metallized whiskers are investigated by optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Surface chemistry relevant to material processing for semiconductor devices

NASA Astrophysics Data System (ADS)

Okada, Lynne Aiko

Metal-oxide-semiconductor (MOS) structures are the core of many modern integrated circuit (IC) devices. Each material utilized in the different regions of the device has its own unique chemistry. Silicon is the base semiconductor material used in the majority of these devices. With IC device complexity increasing and device dimensions decreasing, understanding material interactions and processing becomes increasingly critical. Hsb2 desorption is the rate-limiting step in silicon growth using silane under low temperature conditions. Activation energies for Hsb2 desorption measured during Si chemical vapor deposition (CVD) versus single-crystal studies are found to be significantly lower. It has been proposed that defect sites on the silicon surface could explain the observed differences. Isothermal Hsb2 desorption studies using laser induced thermal desorption (LITD) techniques have addressed this issue. The growth of low temperature oxides is another relevant issue for fabrication of IC devices. Recent studies using 1,4-disilabutane (DSB) (SiHsb3CHsb2CHsb2SiHsb3) at 100sp°C in ambient Osb2 displayed the successful low temperature growth of silicon dioxide (SiOsb2). However, these studies provided no information about the deposition mechanism. We performed LITD and Fourier transform infrared (FTIR) studies on single-crystal and porous silicon surfaces to examine the adsorption, decomposition, and desorption processes to determine the deposition mechanism. Titanium nitride (TiN) diffusion barriers are necessary in modern metallization structures. Controlled deposition using titanium tetrachloride (TiClsb4) and ammonia (NHsb3) has been demonstrated using atomic layered processing (ALP) techniques. We intended to study the sequential deposition method by monitoring the surface intermediates using LITD techniques. However, formation of a Cl impurity source, ammonium chloride (NHsb4sp+Clsp-), was observed, thereby, limiting our ability for effective studies. Tetrakis(dimethylamino)titanium (Tilbrack N\\{CHsb3\\}sb2rbracksb4) (TDMAT) is another precursor used in the CVD deposition of TiN films in IC devices. Thermal decomposition studies have demonstrated deviations from conformal deposition. Successful conformal deposition may be affected by readsorption of the reaction product, dimethylamine (HNlbrack CHsb3rbracksb2). Detailed studies were performed using LITD techniques in order to understand the adsorption and desorption kinetics of TDMAT and dimethylamine to gain insights about the conformal deposition of TiN.

NEXAFS Study of the Annealing Effect on the Local Structure of FIB-CVD DLC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saikubo, Akihiko; Kato, Yuri; Igaki, Jun-ya

2007-01-19

Annealing effect on the local structure of diamond like carbon (DLC) formed by focused ion beam-chemical vapor deposition (FIB-CVD) was investigated by the measurement of near edge x-ray absorption fine structure (NEXAFS) and energy dispersive x-ray (EDX) spectra. Carbon K edge absorption NEXAFS spectrum of FIB-CVD DLC was measured in the energy range of 275-320 eV. In order to obtain the information on the location of the gallium in the depth direction, incidence angle dependence of NEXAFS spectrum was measured in the incident angle range from 0 deg. to 60 deg. . The peak intensity corresponding to the resonance transitionmore » of 1s{yields}{sigma}* originating from carbon-gallium increased from the FIB-CVD DLC annealed at 200 deg. C to the FIB-CVD DLC annealed at 400 deg. C and decreased from that at 400 deg. C to that at 600 deg. C. Especially, the intensity of this peak remarkably enhanced in the NEXAFS spectrum of the FIB-CVD DLC annealed at 400 deg. C at the incident angle of 60 deg. . On the contrary, the peak intensity corresponding to the resonance transition of 1s{yields}{pi}* originating from carbon double bonding of emission spectrum decreased from the FIB-CVD DLC annealed at 200 deg. C to that at 400 deg. C and increased from that at 400 deg. C to that at 600 deg. C. Gallium concentration in the FIB-CVD DLC decreased from {approx_equal}2.2% of the as-deposited FIB-CVD DLC to {approx_equal}1.5% of the FIB-CVD DLC annealed at 600 deg. C from the elementary analysis using EDX. Both experimental results indicated that gallium atom departed from FIB-CVD DLC by annealing at the temperature of 600 deg. C.« less

CVD apparatus and process for the preparation of fiber-reinforced ceramic composites

DOEpatents

Caputo, A.J.; Devore, C.E.; Lowden, R.A.; Moeller, H.H.

1990-01-23

An apparatus and process for the chemical vapor deposition of a matrix into a preform having circumferentially wound ceramic fibers, comprises heating one surface of the preform while cooling the other surface thereof. The resulting product may have fibers that are wound on radial planes or at an angle from the radial planes. The fibers can also be precoated with pyrolytic carbon before application of the matrix. The matrix is applied by passing reactant gas through the preform thereof to the other side thereof for the initial deposition of matrix near such other surface of the preform. The matrix fills in the preform from the other side surface thereof to the surface of the side of application thereof until a desired amount of matrix has been deposited. 6 figs.

CVD apparatus and process for the preparation of fiber-reinforced ceramic composites

DOEpatents

Caputo, Anthony J.; Devore, Charles E.; Lowden, Richard A.; Moeller, Helen H.

1990-01-01

An apparatus and process for the chemical vapor deposition of a matrix into a preform having circumferentially wound ceramic fibers, comprises heating one surface of the preform while cooling the other surface thereof. The resulting product may have fibers that are wound on radial planes or at an angle from the radial planes. The fibers can also be precoated with pyrolytic carbon before application of the matrix. The matrix is applied by passing reactant gas through the preform thereof to the other side thereof for the initial deposition of matrix near such other surface of the preform. The matrix fills in the preform from the other side surface thereof to the surface of the side of application thereof until a desired amount of matrix has been deposited.

Ballistic transport in graphene grown by chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calado, V. E.; Goswami, S.; Xu, Q.

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.

Method for localized deposition of noble metal catalysts with control of morphology

DOEpatents

Ricco, Antonio J.; Manginell, Ronald P.; Huber, Robert J.

1998-01-01

A combustible gas sensor that uses a resistively heated, noble metal-coated, micromachined polycrystalline Si filament to calorimetrically detect the presence and concentration of combustible gases. A thin catalytic Pt film was deposited by CVD from the precursor Pt(acac).sub.2 onto microfilaments resistively heated to approximately 500 .degree. C.; Pt deposits only on the hot filament. The filaments tested to date are 2 .mu.m thick .times.10 .mu.m wide .times.100, 250, 500, or 1000 .mu.m-long polycrystalline Si; some are overcoated with a 0.25 .mu.m-thick protective CVD Si.sub.3 N.sub.4 layer.

Thickness-controlled direct growth of nanographene and nanographite film on non-catalytic substrates

NASA Astrophysics Data System (ADS)

Du, Lei; Yang, Liu; Hu, Zhiting; Zhang, Jiazhen; Huang, Chunlai; Sun, Liaoxin; Wang, Lin; Wei, Dacheng; Chen, Gang; Lu, Wei

2018-05-01

Metal-catalyzed chemical vapor deposition (CVD) has been broadly employed for large-scale production of high-quality graphene. However, a following transfer process to targeted substrates is needed, which is incompatible with current silicon technology. We here report a new CVD approach to form nanographene and nanographite films with accurate thickness control directly on non-catalytic substrates such as silicon dioxide and quartz at 800 °C. The growth time is as short as a few seconds. The approach includes using 9-bis(diethylamino)silylanthracene as the carbon source and an atomic layer deposition (ALD) controlling system. The structure of the formed nanographene and nanographite films were characterized using atomic force microscopy, high resolution transmission electron microscopy, Raman scattering, and x-ray photoemission spectroscopy. The nanographite film exhibits a transmittance higher than 80% at 550 nm and a sheet electrical resistance of 2000 ohms per square at room temperature. A negative temperature-dependence of the resistance of the nanographite film is also observed. Moreover, the thickness of the films can be precisely controlled via the deposition cycles using an ALD system, which promotes great application potential for optoelectronic and thermoelectronic-devices.

Thickness-controlled direct growth of nanographene and nanographite film on non-catalytic substrates.

PubMed

Du, Lei; Yang, Liu; Hu, Zhiting; Zhang, Jiazhen; Huang, Chunlai; Sun, Liaoxin; Wang, Lin; Wei, Dacheng; Chen, Gang; Lu, Wei

2018-05-25

Metal-catalyzed chemical vapor deposition (CVD) has been broadly employed for large-scale production of high-quality graphene. However, a following transfer process to targeted substrates is needed, which is incompatible with current silicon technology. We here report a new CVD approach to form nanographene and nanographite films with accurate thickness control directly on non-catalytic substrates such as silicon dioxide and quartz at 800 °C. The growth time is as short as a few seconds. The approach includes using 9-bis(diethylamino)silylanthracene as the carbon source and an atomic layer deposition (ALD) controlling system. The structure of the formed nanographene and nanographite films were characterized using atomic force microscopy, high resolution transmission electron microscopy, Raman scattering, and x-ray photoemission spectroscopy. The nanographite film exhibits a transmittance higher than 80% at 550 nm and a sheet electrical resistance of 2000 ohms per square at room temperature. A negative temperature-dependence of the resistance of the nanographite film is also observed. Moreover, the thickness of the films can be precisely controlled via the deposition cycles using an ALD system, which promotes great application potential for optoelectronic and thermoelectronic-devices.

Remote catalyzation for direct formation of graphene layers on oxides.

PubMed

Teng, Po-Yuan; Lu, Chun-Chieh; Akiyama-Hasegawa, Kotone; Lin, Yung-Chang; Yeh, Chao-Hui; Suenaga, Kazu; Chiu, Po-Wen

2012-03-14

Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth. © 2012 American Chemical Society

Convection and chemistry effects in CVD: A 3-D analysis for silicon deposition

NASA Technical Reports Server (NTRS)

Gokoglu, S. A.; Kuczmarski, M. A.; Tsui, P.; Chait, A.

1989-01-01

The computational fluid dynamics code FLUENT has been adopted to simulate the entire rectangular-channel-like (3-D) geometry of an experimental CVD reactor designed for Si deposition. The code incorporated the effects of both homogeneous (gas phase) and heterogeneous (surface) chemistry with finite reaction rates of important species existing in silane dissociation. The experiments were designed to elucidate the effects of gravitationally-induced buoyancy-driven convection flows on the quality of the grown Si films. This goal is accomplished by contrasting the results obtained from a carrier gas mixture of H2/Ar with the ones obtained from the same molar mixture ratio of H2/He, without any accompanying change in the chemistry. Computationally, these cases are simulated in the terrestrial gravitational field and in the absence of gravity. The numerical results compare favorably with experiments. Powerful computational tools provide invaluable insights into the complex physicochemical phenomena taking place in CVD reactors. Such information is essential for the improved design and optimization of future CVD reactors.

One-dimensional surface-imprinted polymeric nanotubes for specific biorecognition by initiated chemical vapor deposition (iCVD).

PubMed

Ince, Gozde Ozaydin; Armagan, Efe; Erdogan, Hakan; Buyukserin, Fatih; Uzun, Lokman; Demirel, Gokhan

2013-07-24

Molecular imprinting is a powerful, generic, and cost-effective technique; however, challenges still remain related to the fabrication and development of these systems involving nonhomogeneous binding sites, insufficient template removing, incompatibility with aqueous media, low rebinding capacity, and slow mass transfer. The vapor-phase deposition of polymers is a unique technique because of the conformal nature of coating and offers new possibilities in a number of applications including sensors, microfluidics, coating, and bioaffinity platforms. Herein, we demonstrated a simple but versatile concept to generate one-dimensional surface-imprinted polymeric nanotubes within anodic aluminum oxide (AAO) membranes based on initiated chemical vapor deposition (iCVD) technique for biorecognition of immunoglobulin G (IgG). It is reported that the fabricated surface-imprinted nanotubes showed high binding capacity and significant specific recognition ability toward target molecules compared with the nonimprinted forms. Given its simplicity and universality, the iCVD method can offer new possibilities in the field of molecular imprinting.

Fabrication of high quality carbonaceous coating on Cu nanoparticle using poly(vinyl pyrrolidone) and its application for oxidation prevention

NASA Astrophysics Data System (ADS)

Pyo, Youngjun; Choi, Dahyun; Son, Yeon-Ho; Kang, Suhee; Yoon, Eric H.; Jung, Seung-Boo; Kim, Yongil; Sunyong Lee, Caroline

2016-05-01

A novel method of carbonaceous coating on the surface of copper particles was developed through a chemical vapor deposition (CVD) process to prevent the oxidation of copper nanoparticles (CNPs). The types of poly(vinyl pyrrolidone) (PVP) used were K-12 (M W 3,500) and K-30 (M W 45,000). The amounts of PVP used ranged from 10 to 50 wt %. Additionally, processing temperatures of 900 and 875 °C were tested and compared. The optimum CVD process conditions for the carbonaceous coating were as follows: 875 °C processing temperature, 50 wt % K12 PVP solution, and gas conditions of \\text{Ar}:\\text{H}2 = 1:1. The resistivity change in the fabricated copper pattern was confirmed that the initial resistivity value of the ink with a mixing ratio of carbonaceous-coated CNPs to 1-octanethiol-coated CNPs of 4:6 (w/w) maintained its initial resistivity value of 2.93 × 10-7 Ω·m for more than 210 days.

Graphene growth on Ge(100)/Si(100) substrates by CVD method.

PubMed

Pasternak, Iwona; Wesolowski, Marek; Jozwik, Iwona; Lukosius, Mindaugas; Lupina, Grzegorz; Dabrowski, Pawel; Baranowski, Jacek M; Strupinski, Wlodek

2016-02-22

The successful integration of graphene into microelectronic devices is strongly dependent on the availability of direct deposition processes, which can provide uniform, large area and high quality graphene on nonmetallic substrates. As of today the dominant technology is based on Si and obtaining graphene with Si is treated as the most advantageous solution. However, the formation of carbide during the growth process makes manufacturing graphene on Si wafers extremely challenging. To overcome these difficulties and reach the set goals, we proposed growth of high quality graphene layers by the CVD method on Ge(100)/Si(100) wafers. In addition, a stochastic model was applied in order to describe the graphene growth process on the Ge(100)/Si(100) substrate and to determine the direction of further processes. As a result, high quality graphene was grown, which was proved by Raman spectroscopy results, showing uniform monolayer films with FWHM of the 2D band of 32 cm(-1).

Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe 2

DOE PAGES

Li, Xufan; Puretzky, Alexander A.; Sang, Xiahan; ...

2017-05-18

Chemical vapor deposition (CVD) is one of the most promising, scalable synthetic techniques to enable large-area synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) for the realization of next generation optoelectronic devices. However, defects formed during the CVD growth process currently limit the quality and electronic properties of 2D TMDs. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed. In this work, isoelectrnic doping to produce stable alloy is presented as a new strategy to suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The random, isoelectronic substitution of Wmore » atoms for Mo atoms in CVD-grown monolayers of Mo 1-xW xSe 2 (02 monolayers. The resultant decrease in defect-medicated non-radiative recombination in the Mo 0.82W 0.18Se 2 monolayers yielded ~10 times more intense PL and extended the carrier lifetime by a factor of 3 compared to pristine CVD-grown MoSe 2 monolayers grown under similar conditions. Low temperatures (4 125 K) PL from defect-related localized states confirms theoretical predictions that isoelectronic W alloying should suppress deep levels in MoSe 2, showing that the defect levels in Mo 1-xW xSe 2 monolayers are higher in energy and quenched more quickly than in MoSe 2. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.« less

Suppression of Defects and Deep Levels Using Isoelectronic Tungsten Substitution in Monolayer MoSe 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xufan; Puretzky, Alexander A.; Sang, Xiahan

Chemical vapor deposition (CVD) is one of the most promising, scalable synthetic techniques to enable large-area synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) for the realization of next generation optoelectronic devices. However, defects formed during the CVD growth process currently limit the quality and electronic properties of 2D TMDs. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed. In this work, isoelectrnic doping to produce stable alloy is presented as a new strategy to suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The random, isoelectronic substitution of Wmore » atoms for Mo atoms in CVD-grown monolayers of Mo 1-xW xSe 2 (02 monolayers. The resultant decrease in defect-medicated non-radiative recombination in the Mo 0.82W 0.18Se 2 monolayers yielded ~10 times more intense PL and extended the carrier lifetime by a factor of 3 compared to pristine CVD-grown MoSe 2 monolayers grown under similar conditions. Low temperatures (4 125 K) PL from defect-related localized states confirms theoretical predictions that isoelectronic W alloying should suppress deep levels in MoSe 2, showing that the defect levels in Mo 1-xW xSe 2 monolayers are higher in energy and quenched more quickly than in MoSe 2. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices.« less

CVD of SiC and AlN using cyclic organometallic precursors

NASA Technical Reports Server (NTRS)

Interrante, L. V.; Larkin, D. J.; Amato, C.

1992-01-01

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

A platform for large-scale graphene electronics--CVD growth of single-layer graphene on CVD-grown hexagonal boron nitride.

PubMed

Wang, Min; Jang, Sung Kyu; Jang, Won-Jun; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Ruoff, Rodney S; Song, Young Jae; Lee, Sungjoo

2013-05-21

Direct chemical vapor deposition (CVD) growth of single-layer graphene on CVD-grown hexagonal boron nitride (h-BN) film can suggest a large-scale and high-quality graphene/h-BN film hybrid structure with a defect-free interface. This sequentially grown graphene/h-BN film shows better electronic properties than that of graphene/SiO2 or graphene transferred on h-BN film, and suggests a new promising template for graphene device fabrication. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Systems-oriented survey of noncontact temperature measurement techniques for rapid thermal processing

NASA Astrophysics Data System (ADS)

Peyton, David; Kinoshita, Hiroyuki; Lo, G. Q.; Kwong, Dim-Lee

1991-04-01

Rapid Thermal Processing (RTP) is becoming a popular approach for future ULSI manufacturing due to its unique low thermal budget and process flexibility. Furthermore when RTP is combined with Chemical Vapor Deposition (CVD) the so-called RTP-CVD technology it can be used to deposit ultrathin films with extremely sharp interfaces and excellent material qualities. One major consequence of this type of processing however is the need for extremely tight control of wafer temperature both to obtain reproducible results for process control and to minimize slip and warpage arising from nonuniformities in temperature. Specifically temperature measurement systems suitable for RiP must have both high precision--within 1-2 degrees--and a short response time--to output an accurate reading on the order of milliseconds for closedloop control. Any such in-situ measurement technique must be non-contact since thermocouples cannot meet the response time requirements and have problems with conductive heat flow in the wafer. To date optical pyrometry has been the most widely used technique for RiP systems although a number of other techniques are being considered and researched. This article examines several such techniques from a systems perspective: optical pyrometry both conventional and a new approach using ellipsometric techniques for concurrent emissivity measurement Raman scattering infrared laser thermometry optical diffraction thermometry and photoacoustic thermometry. Each approach is evaluated in terms of its actual or estimated manufacturing cost remote sensing capability precision repeatability dependence on processing history range

Effect of irradiation with MeV protons and electrons on the conductivity compensation and photoluminescence of moderately doped p-4H-SiC (CVD)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlovski, V. V.; Lebedev, A. A., E-mail: shura.lebe@mail.ioffe.ru; Bogdanova, E. V.

The compensation of moderately doped p-4H-SiC samples grown by the chemical vapor deposition (CVD) method under irradiation with 0.9-MeV electrons and 15-MeV protons is studied. The experimentally measured carrier removal rates are 1.2–1.6 cm{sup –1} for electrons and 240–260 cm{sup –1} for protons. The dependence of the concentration of uncompensated acceptors and donors, measured in the study, demonstrates a linear decrease with increasing irradiation dose to the point of complete compensation. This run of the dependence shows that compensation of the samples is due to the transition of carriers to deep centers formed by primary radiation-induced defects. It is demonstratedmore » that, in contrast to n-SiC (CVD), primary defects in the carbon sublattice of moderately doped p-SiC (CVD) only cannot account for the compensation process. In p-SiC, either primary defects in the silicon sublattice, or defects in both sublattices are responsible for conductivity compensation. Also, photoluminescence spectra are examined in relation to the irradiation dose.« less

Electronic transport in heterostructures of chemical vapor deposited graphene and hexagonal boron nitride.

PubMed

Qi, Zhengqing John; Hong, Sung Ju; Rodríguez-Manzo, Julio A; Kybert, Nicholas J; Gudibande, Rajatesh; Drndić, Marija; Park, Yung Woo; Johnson, A T Charlie

2015-03-25

CVD graphene devices on stacked CVD hexagonal boron nitride (hBN) are demonstrated using a novel low-contamination transfer method, and their electrical performance is systematically compared to devices on SiO(2). An order of magnitude improvement in mobility, sheet resistivity, current density, and sustained power is reported when the oxide substrate is covered with five-layer CVD hBN. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zinc sulfide and zinc selenide immersion gratings for astronomical high-resolution spectroscopy: evaluation of internal attenuation of bulk materials in the short near-infrared region

NASA Astrophysics Data System (ADS)

Ikeda, Yuji; Kobayashi, Naoto; Kondo, Sohei; Yasui, Chikako; Kuzmenko, Paul J.; Tokoro, Hitoshi; Terada, Hiroshi

2009-08-01

We measure the internal attenuation of bulk crystals of chemical vapor deposition zinc selenide (CVD-ZnS), chemical vapor deposition zinc sulfide (CVD-ZnSe), Si, and GaAs in the short near-infrared (sNIR) region to evaluate the possibility of astronomical immersion gratings with those high refractive index materials. We confirm that multispectral grade CVD-ZnS and CVD-ZnSe are best suited for the immersion gratings, with the smallest internal attenuation of αatt=0.01 to 0.03 cm-1 among the major candidates. The measured attenuation is roughly in proportion to λ-2, suggesting it is dominated by bulk scattering due to the polycrystalline grains rather than by absorption. The total transmittance in the immersion grating is estimated to be at least >80%, even for the spectral resolution of R=300,000. Two potential problems, the scattered light by the bulk material and the degradation of the spectral resolution due to the gradient illumination in the diffracted beam, are investigated and found to be negligible for usual astronomical applications. Since the remaining problem, the difficulty of cutting grooves on CVD-ZnS and CVD-ZnSe, has recently been overcome by the nanoprecision fly-cutting technique, ZnS and ZnSe immersion gratings for astronomy can be technically realized.

Composition and Morphology Control of Metal Dichalcogenides via Chemical Vapor Deposition for Photovoltaic and Nanoelectronic Applications

NASA Astrophysics Data System (ADS)

Samad, Leith L. J.

The body of work reviewed here encompasses a variety of metal dichalcogenides all synthesized using chemical vapor deposition (CVD) for solar and electronics applications. The first reported phase-pure CVD synthesis of iron pyrite thin films is presented with detailed structural and electrochemical analysis. The phase-pure thin film and improved crystal growth on a metallic backing material represents one of the best options for potential solar applications using iron pyrite. Large tin-sulfur-selenide solid solution plates with tunable bandgaps were also synthesized via CVD as single-crystals with a thin film geometry. Solid solution tin-sulfur-selenide plates were demonstrated to be a new material for solar cells with the first observed solar conversion efficiencies up to 3.1%. Finally, a low temperature molybdenum disulfide vertical heterostructure CVD synthesis with layered controlled growth was achieved with preferential growth enabled by Van der Waals epitaxy. Through recognition of additional reaction parameters, a fully regulated CVD synthesis enabled the controlled growth of 1-6 molybdenum disulfide monolayers for nanoelectronic applications. The improvements in synthesis and materials presented here were all enabled by the control afforded by CVD such that advances in phase purity, growth, and composition control of several metal dichalcogenides were achieved. Further work will be able to take full advantage of these advances for future solar and electronics technologies.

Reduced graphene oxide nanoshells for flexible and stretchable conductors

NASA Astrophysics Data System (ADS)

Jiang, Wen-Shuai; Liu, Zhi-Bo; Xin, Wei; Chen, Xu-Dong; Tian, Jian-Guo

2016-03-01

Graphene has been extensively investigated for its use in flexible electronics, especially graphene synthesized by chemical vapor deposition (CVD). To enhance the flexibility of CVD graphene, wrinkles are often introduced. However, reports on the flexibility of reduced graphene oxide (RGO) films are few, because of their weak conductivity and, in particular, poor flexibility. To improve the flexibility of RGO, reduced graphene oxide nanoshells are fabricated, which combine self-assembled polystyrene nanosphere arrays and high-temperature thermal annealing processes. The resulting RGO films with nanoshells present a better resistance stabilization after stretching and bending the devices than RGO without nanoshells. The sustainability and performance advances demonstrated here are promising for the adoption of flexible electronics in a wide variety of future applications.

Guided growth of large-scale, horizontally aligned arrays of single-walled carbon nanotubes and their use in thin-film transistors.

PubMed

Kocabas, Coskun; Hur, Seung-Hyun; Gaur, Anshu; Meitl, Matthew A; Shim, Moonsub; Rogers, John A

2005-11-01

A convenient process for generating large-scale, horizontally aligned arrays of pristine, single-walled carbon nanotubes (SWNTs) is described. The approach uses guided growth, by chemical vapor deposition (CVD), of SWNTs on miscut single-crystal quartz substrates. Studies of the growth reveal important relationships between the density and alignment of the tubes, the CVD conditions, and the morphology of the quartz. Electrodes and dielectrics patterned on top of these arrays yield thin-film transistors that use the SWNTs as effective thin-film semiconductors. The ability to build high-performance devices of this type suggests significant promise for large-scale aligned arrays of SWNTs in electronics, sensors, and other applications.

Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature

NASA Astrophysics Data System (ADS)

Park, Jae-Won; Kim, Eung-Seon; Kim, Jae-Un; Kim, Yootaek; Windes, William E.

2016-08-01

The potential of reducing the oxidation of the supporting graphite components during normal and/or accident conditions in the Very High Temperature Reactor (VHTR) design has been studied. In this work efforts have been made to slow the oxidation process of the graphite with a thin SiC coating (∼ 10 μm). Upon heating at ≥ 1173 K in air, the spallations and cracks were formed in the dense columnar structured SiC coating layer grown on the graphite with a functionally gradient electron beam physical vapor deposition (EB-PVD. In accordance with the formations of these defects, the sample was vigorously oxidized, leaving only the SiC coating layer. Then, efforts were made to heal the surface defects using additional EB-PVD with ion beam bombardment and chemical vapor deposition (CVD). The EB-PVD did not effectively heal the cracks. But, the CVD was more appropriate for crack healing, likely due to its excellent crack line filling capability with a high density and high aspect ratio. It took ∼ 34 min for the 20% weight loss of the CVD crack healed sample in the oxidation test with annealing at 1173 K, while it took ∼ 8 min for the EB-PVD coated sample, which means it took ∼4 times longer at 1173 K for the same weight reduction in this experimental set-up.

Controllable poly-crystalline bilayered and multilayered graphene film growth by reciprocal chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wu, Qinke; Jung, Seong Jun; Jang, Sung Kyu; Lee, Joohyun; Jeon, Insu; Suh, Hwansoo; Kim, Yong Ho; Lee, Young Hee; Lee, Sungjoo; Song, Young Jae

2015-06-01

We report the selective growth of large-area bilayered graphene film and multilayered graphene film on copper. This growth was achieved by introducing a reciprocal chemical vapor deposition (CVD) process that took advantage of an intermediate h-BN layer as a sacrificial template for graphene growth. A thin h-BN film, initially grown on the copper substrate using CVD methods, was locally etched away during the subsequent graphene growth under residual H2 and CH4 gas flows. Etching of the h-BN layer formed a channel that permitted the growth of additional graphene adlayers below the existing graphene layer. Bilayered graphene typically covers an entire Cu foil with domain sizes of 10-50 μm, whereas multilayered graphene can be epitaxially grown to form islands a few hundreds of microns in size. This new mechanism, in which graphene growth proceeded simultaneously with h-BN etching, suggests a potential approach to control graphene layers for engineering the band structures of large-area graphene for electronic device applications.We report the selective growth of large-area bilayered graphene film and multilayered graphene film on copper. This growth was achieved by introducing a reciprocal chemical vapor deposition (CVD) process that took advantage of an intermediate h-BN layer as a sacrificial template for graphene growth. A thin h-BN film, initially grown on the copper substrate using CVD methods, was locally etched away during the subsequent graphene growth under residual H2 and CH4 gas flows. Etching of the h-BN layer formed a channel that permitted the growth of additional graphene adlayers below the existing graphene layer. Bilayered graphene typically covers an entire Cu foil with domain sizes of 10-50 μm, whereas multilayered graphene can be epitaxially grown to form islands a few hundreds of microns in size. This new mechanism, in which graphene growth proceeded simultaneously with h-BN etching, suggests a potential approach to control graphene layers for engineering the band structures of large-area graphene for electronic device applications. Electronic supplementary information (ESI) available: The growth conditions, statistical studies of OM images and high-resolution STM/TEM measurements for multi-/bi-layered graphene are discussed in detail. See DOI: 10.1039/c5nr02716k

Tungsten Contact and Line Resistance Reduction with Advanced Pulsed Nucleation Layer and Low Resistivity Tungsten Treatment

NASA Astrophysics Data System (ADS)

Chandrashekar, Anand; Chen, Feng; Lin, Jasmine; Humayun, Raashina; Wongsenakhum, Panya; Chang, Sean; Danek, Michal; Itou, Takamasa; Nakayama, Tomoo; Kariya, Atsushi; Kawaguchi, Masazumi; Hizume, Shunichi

2010-09-01

This paper describes electrical testing results of new tungsten chemical vapor deposition (CVD-W) process concepts that were developed to address the W contact and bitline scaling issues on 55 nm node devices. Contact resistance (Rc) measurements in complementary metal oxide semiconductor (CMOS) devices indicate that the new CVD-W process for sub-32 nm and beyond - consisting of an advanced pulsed nucleation layer (PNL) combined with low resistivity tungsten (LRW) initiation - produces a 20-30% drop in Rc for diffused NiSi contacts. From cross-sectional bright field and dark field transmission electron microscopy (TEM) analysis, such Rc improvement can be attributed to improved plugfill and larger in-feature W grain size with the advanced PNL+LRW process. More experiments that measured contact resistance for different feature sizes point to favorable Rc scaling with the advanced PNL+LRW process. Finally, 40% improvement in line resistance was observed with this process as tested on 55 nm embedded dynamic random access memory (DRAM) devices, confirming that the advanced PNL+LRW process can be an effective metallization solution for sub-32 nm devices.

Growth-substrate induced performance degradation in chemically synthesized monolayer MoS{sub 2} field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amani, Matin; Chin, Matthew L.; Mazzoni, Alexander L.

2014-05-19

We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS{sub 2}) field-effect transistors (FETs) on Si/SiO{sub 2} substrates. MoS{sub 2} has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS{sub 2} samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS{sub 2}. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS{sub 2} is equal or superior to that of exfoliated material and has been possibly masked by a combinationmore » of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS{sub 2} devices following an identical fabrication process demonstrate the improvement in field-effect mobility.« less

Nonaligned carbon nanotubes anchored on porous alumina: formation, process modeling, gas-phase analysis, and field-emission properties.

PubMed

Lysenkov, Dmitry; Engstler, Jörg; Dangwal, Arti; Popp, Alexander; Müller, Günter; Schneider, Jörg J; Janardhanan, Vinod M; Deutschmann, Olaf; Strauch, Peter; Ebert, Volker; Wolfrum, Jürgen

2007-06-01

We have developed a chemical vapor deposition (CVD) process for the catalytic growth of carbon nanotubes (CNTs), anchored in a comose-type structure on top of porous alumina substrates. The mass-flow conditions of precursor and carrier gases and temperature distributions in the CVD reactor were studied by transient computational fluid dynamic simulation. Molecular-beam quadrupole mass spectroscopy (MB-QMS) has been used to analyze the gas phase during ferrocene CVD under reaction conditions (1073 K) in the boundary layer near the substrate. Field-emission (FE) properties of the nonaligned CNTs were measured for various coverages and pore diameters of the alumina. Samples with more dense CNT populations provided emitter-number densities up to 48,000 cm(-2) at an electric field of 6 V microm(-1). Samples with fewer but well-anchored CNTs in 22-nm pores yielded the highest current densities. Up to 83 mA cm(-2) at 7 V microm(-1) in dc mode and more than 200 mA cm(-2) at 11 V microm(-1) in pulsed diode operation have been achieved from a cathode size of 24 mm2.

Microstructure fabrication process induced modulations in CVD graphene

NASA Astrophysics Data System (ADS)

Matsubayashi, Akitomo; Zhang, Zhenjun; Lee, Ji Ung; LaBella, Vincent P.

2014-12-01

The systematic Raman spectroscopic study of a "mimicked" graphene device fabrication is presented. Upon photoresist baking, compressive stress is induced in the graphene which disappears after it is removed. The indirect irradiation from the electron beam (through the photoresist) does not significantly alter graphene characteristic Raman peaks indicating that graphene quality is preserved upon the exposure. The 2D peak shifts and the intensity ratio of 2D and G band, I(2D)/I(G), decreases upon direct metal deposition (Co and Py) suggesting that the electronic modulation occurs due to sp2 C-C bond weakening. In contrast, a thin metal oxide film deposited graphene does not show either the significant 2D and G peaks shift or I(2D)/I(G) decrease upon the metal deposition suggesting the oxide protect the graphene quality in the fabrication process.

Electrical and optical performance of transparent conducting oxide films deposited by electrostatic spray assisted vapour deposition.

PubMed

Hou, Xianghui; Choy, Kwang-Leong; Liu, Jun-Peng

2011-09-01

Transparent conducting oxide (TCO) films have the remarkable combination of high electrical conductivity and optical transparency. There is always a strong motivation to produce TCO films with good performance at low cost. Electrostatic Spray Assisted Vapor Deposition (ESAVD), as a variant of chemical vapour deposition (CVD), is a non-vacuum and low-cost deposition method. Several types of TCO films have been deposited using ESAVD process, including indium tin oxide (ITO), antimony-doped tin oxide (ATO), and fluorine doped tin oxide (FTO). This paper reports the electrical and optical properties of TCO films produced by ESAVD methods, as well as the effects of post treatment by plasma hydrogenation on these TCO films. The possible mechanisms involved during plasma hydrogenation of TCO films are also discussed. Reduction and etching effect during plasma hydrogenation are the most important factors which determine the optical and electrical performance of TCO films.

Nano- and microcrystalline diamond deposition on pretreated WC-Co substrates: structural properties and adhesion

NASA Astrophysics Data System (ADS)

Fraga, M. A.; Contin, A.; Rodríguez, L. A. A.; Vieira, J.; Campos, R. A.; Corat, E. J.; Trava Airoldi, V. J.

2016-02-01

Many developments have been made to improve the quality and adherence of CVD diamond films onto WC-Co hard metal tools by the removing the cobalt from the substrate surface through substrate pretreatments. Here we compare the efficiency of three chemical pretreatments of WC-Co substrates for this purpose. First, the work was focused on a detailed study of the composition and structure of as-polished and pretreated substrate surfaces to characterize the effects of the substrate preparation. Considering this objective, a set of WC-9% Co substrates, before and after pretreatment, was analyzed by FEG-SEM, EDS and x-ray diffraction (XRD). The second stage of the work was devoted to the evaluation of the influence of seeding process, using 4 nm diamond nanoparticles, on the morphology and roughness of the pretreated substrates. The last and most important stage was to deposit diamond coatings with different crystallite sizes (nano and micro) by hot-filament CVD to understand fully the mechanism of growth and adhesion of CVD diamond films on pretreated WC-Co substrates. The transition from nano to microcrystalline diamond was achieved by controlling the CH4/H2 gas ratio. The nano and microcrystalline samples were grown under same time at different substrate temperatures 600 °C and 800 °C, respectively. The different substrate temperatures allowed the analysis of the cobalt diffusion from the bulk to the substrate surface during CVD film growth. Furthermore, it was possible to evaluate how the coating adhesion is affected by the diffusion. The diamond coatings were characterized by Raman spectroscopy, XRD, EDS, FEG-SEM, atomic force microscope and 1500 N Rockwell indentation to evaluate the adhesion.

Blue light emitting thiogallate phosphor

DOEpatents

Dye, Robert C.; Smith, David C.; King, Christopher N.; Tuenge, Richard T.

1998-01-01

A crystalline blue emitting thiogallate phosphor of the formula RGa.sub.2 S.sub.4 :Ce.sub.x where R is selected from the group consisting of calcium, strontium, barium and zinc, and x is from about 1 to 10 atomic percent, the phosphor characterized as having a crystalline microstructure on the size order of from about 100 .ANG. to about 10,000 .ANG. is provided together with a process of preparing a crystalline blue emitting thiogallate phosphor by depositing on a substrate by CVD and resultant thin film electroluminescent devices including a layer of such deposited phosphor on an ordinary glass substrate.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors.

PubMed

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J; Mijowska, Ewa

2012-05-29

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

NASA Astrophysics Data System (ADS)

Wilgosz, Karolina; Chen, Xuecheng; Kierzek, Krzysztof; Machnikowski, Jacek; Kalenczuk, Ryszard J.; Mijowska, Ewa

2012-05-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

A quantitative comparison of resolution, scanning speed and lifetime behavior of CVD grown Single Wall Carbon Nanotubes and silicon SPM probes using spectral methods

NASA Astrophysics Data System (ADS)

Krause, O.; Bouchiat, V.; Bonnot, A. M.

2007-03-01

Due to their extreme aspect ratios and exceptional mechanical properties Carbon Nanotubes terminated silicon probes have proven to be the ''ideal'' probe for Atomic Force Microscopy. But especially for the manufacturing and use of Single Walled Carbon Nanotubes there are serious problems, which have not been solved until today. Here, Single and Double Wall Carbon Nanotubes, batch processed and used as deposited by Chemical Vapor Deposition without any postprocessing, are compared to standard and high resolution silicon probes concerning resolution, scanning speed and lifetime behavior.

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

PubMed

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

2011-11-09

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

Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohammadi, V., E-mail: V.Mohammadi@tudelft.nl; Nihtianov, S.

The lateral gas phase diffusion length of boron atoms, L{sub B}, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B{sub 2}H{sub 6}) is reported. The value of L{sub B} is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A L{sub B} = 2.2 mm was determined for boron deposition at 700 °C, while a L{sub B}more » of less than 1 mm was observed at temperatures lower than 500 °C.« less

Advanced zirconia-coated carbonyl-iron particles for acidic magnetorheological finishing of chemical-vapor-deposited ZnS and other IR materials

NASA Astrophysics Data System (ADS)

Salzman, S.; Giannechini, L. J.; Romanofsky, H. J.; Golini, N.; Taylor, B.; Jacobs, S. D.; Lambropoulos, J. C.

2015-10-01

We present a modified version of zirconia-coated carbonyl-iron (CI) particles that were invented at the University of Rochester in 2008. The amount of zirconia on the coating is increased to further protect the iron particles from corrosion when introduced to an acidic environment. Five low-pH, magnetorheological (MR) fluids were made with five acids: acetic, hydrochloric, nitric, phosphoric, and hydrofluoric. All fluids were based on the modified zirconia-coated CI particles. Off-line viscosity and pH stability were measured for all acidic MR fluids to determine the ideal fluid composition for acidic MR finishing of chemical-vapor-deposited (CVD) zinc sulfide (ZnS) and other infrared (IR) optical materials, such as hot-isostatic-pressed (HIP) ZnS, CVD zinc selenide (ZnSe), and magnesium fluoride (MgF2). Results show significant reduction in surface artifacts (millimeter-size, pebble-like structures on the finished surface) for several standard-grade CVD ZnS substrates and good surface roughness for the non-CVD MgF2 substrate when MR finished with our advanced acidic MR fluid.

CVD of silicon carbide on structural fibers - Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

CVD of silicon carbide on structural fibers: Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

Chemical vapor deposition growth

NASA Technical Reports Server (NTRS)

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

1976-01-01

A laboratory type CVD reactor system with a vertical deposition chamber and sample pedestal heated by an external RF coil has been extensively modified by installation of mass flow controllers, automatic process sequence timers, and special bellows-sealed air-operated valves for overall improved performance. Various film characterization procedures, including classical metallography, SEM analyses, X ray diffraction analyses, surface profilometry, and electrical measurements (resistivity, carrier concentration, mobility, spreading resistance profiles, and minority-carrier lifetime by the C-V-t method) area used to correlate Si sheet properties with CVD parameters and substrate properties. Evaluation procedures and measurements are given. Experimental solar cell structures were made both in epitaxial Si sheet (on sapphire substrates) and in polycrystalline material on alumina substrates, the former to provide an indication of what might be an upper limit on performance of the latter. Preliminary results are given, as obtained in cell structures not specially designed to allow for the unique properties of the sheet material, and fabricated in material known to be far from optimum for photovoltaic performance. Low power conversion efficiencies have been obtained in the epitaxial as well as the polycrystalline Si sheet.

Synthesis and Characterization of Hexagonal Boron Nitride as a Gate Dielectric

PubMed Central

Jang, Sung Kyu; Youn, Jiyoun; Song, Young Jae; Lee, Sungjoo

2016-01-01

Two different growth modes of large-area hexagonal boron nitride (h-BN) film, a conventional chemical vapor deposition (CVD) growth mode and a high-pressure CVD growth mode, were compared as a function of the precursor partial pressure. Conventional self-limited CVD growth was obtained below a critical partial pressure of the borazine precursor, whereas a thick h-BN layer (thicker than a critical thickness of 10 nm) was grown beyond a critical partial pressure. An interesting coincidence of a critical thickness of 10 nm was identified in both the CVD growth behavior and in the breakdown electric field strength and leakage current mechanism, indicating that the electrical properties of the CVD h-BN film depended significantly on the film growth mode and the resultant film quality. PMID:27458024

Growth Mechanism of Transition Metal Dichalcogenide Monolayers: The Role of Self-Seeding Fullerene Nuclei.

PubMed

Cain, Jeffrey D; Shi, Fengyuan; Wu, Jinsong; Dravid, Vinayak P

2016-05-24

Due to their unique optoelectronic properties and potential for next generation devices, monolayer transition metal dichalcogenides (TMDs) have attracted a great deal of interest since the first observation of monolayer MoS2 a few years ago. While initially isolated in monolayer form by mechanical exfoliation, the field has evolved to more sophisticated methods capable of direct growth of large-area monolayer TMDs. Chemical vapor deposition (CVD) is the technique used most prominently throughout the literature and is based on the sulfurization of transition metal oxide precursors. CVD-grown monolayers exhibit excellent quality, and this process is widely used in studies ranging from the fundamental to the applied. However, little is known about the specifics of the nucleation and growth mechanisms occurring during the CVD process. In this study, we have investigated the nucleation centers or "seeds" from which monolayer TMDs typically grow. This was accomplished using aberration-corrected scanning transmission electron microscopy to analyze the structure and composition of the nuclei present in CVD-grown MoS2-MoSe2 alloys. We find that monolayer growth proceeds from nominally oxi-chalcogenide nanoparticles which act as heterogeneous nucleation sites for monolayer growth. The oxi-chalcogenide nanoparticles are typically encased in a fullerene-like shell made of the TMD. Using this information, we propose a step-by-step nucleation and growth mechanism for monolayer TMDs. Understanding this mechanism may pave the way for precise control over the synthesis of 2D materials, heterostructures, and related complexes.

The use of CVD diamond burs for ultraconservative cavity preparations: a report of two cases.

PubMed

Carvalho, Carlos Augusto R; Fagundes, Ticiane C; Barata, Terezinha J E; Trava-Airoldi, Vladimir Jesus; Navarro, Maria Fidela L

2007-01-01

During the past decades, scientific developments in cutting instruments have changed the conventional techniques used to remove caries lesions. Ultrasound emerged as an alternative for caries removal since the 1950s. However, the conventional technology for diamond powder aggregation with nickel metallic binders could not withstand ultrasonic power. Around 5 years ago, an alternative approach using chemical vapor deposition (CVD) resulted in synthetic diamond technology. CVD diamond burs are obtained with high adherence of the diamond as a unique stone on the metallic surface with excellent abrading performance. This technology allows for diamond deposition with coalescent granulation in different formats of substrates. When connected to an ultrasonic handpiece, CVD diamond burs become an option for cavity preparation, maximizing preservation of tooth structure. Potential advantages such as reduced noise, minimal damage to the gingival tissue, extended bur durability, improved proximal cavity access, reduced risk of hitting the adjacent tooth resulting from the high inclination angles, and minimal patient's risk of metal contamination. These innovative instruments also potentially eliminate some problems regarding decreased cutting efficiency of conventional diamond burs. This clinical report presents the benefits of using CVD diamond burs coupled with an ultrasonic handpiece in the treatment of incipient caries. CVD diamond burs coupled with an ultrasonic device offer a promising alternative for removal of carious lesions when ultraconservative cavity preparations are required. Additionally, this system provides a less-painful technique for caries removal, with minimal noise.

The role of NH3 and hydrocarbon mixtures in GaN pseudo-halide CVD: a quantum chemical study.

PubMed

Gadzhiev, Oleg B; Sennikov, Peter G; Petrov, Alexander I; Kachel, Krzysztof; Golka, Sebastian; Gogova, Daniela; Siche, Dietmar

2014-11-01

The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons-NH3-Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located π-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis.

Effects of Temperature and Steam Environment on Fatigue Behavior of Three SIC/SIC Ceramic Matrix Composites

DTIC Science & Technology

2008-09-01

Infiltration (CVI), Chemical Vapor Deposition (CVD) and polymer impregnation/ pyrolysis (PIP) [5:20, 32]. The SiC fibers currently... composite was infiltrated with a mixture of polymer , filler particles and solvent. During pyrolysis under nitrogen at temperatures > 1000 °C, the...using polymer infiltration and pyrolysis (PIP) method. Polymer infiltration and pyrolysis processing method allows near-net-shape molding and

Chemical vapor deposition of mesoporous graphene nanoballs for supercapacitor.

PubMed

Lee, Jung-Soo; Kim, Sun-I; Yoon, Jong-Chul; Jang, Ji-Hyun

2013-07-23

A mass-producible mesoporous graphene nanoball (MGB) was fabricated via a precursor-assisted chemical vapor deposition (CVD) technique for supercapacitor application. Polystyrene balls and reduced iron created under high temperature and a hydrogen gas environment provide a solid carbon source and a catalyst for graphene growth during the precursor-assisted CVD process, respectively. Carboxylic acid and sulfonic acid functionalization of the polystyrene ball facilitates homogeneous dispersion of the hydrophobic polymer template in the metal precursor solution, thus, resulting in a MGB with a uniform number of graphene layers. The MGB is shown to have a specific surface area of 508 m(2)/g and is mesoporous with a mean mesopore diameter of 4.27 nm. Mesopores are generated by the removal of agglomerated iron domains, permeating down through the soft polystyrene spheres and providing the surface for subsequent graphene growth during the heating process in a hydrogen environment. This technique requires only drop-casting of the precursor/polystyrene solution, allowing for mass-production of multilayer MGBs. The supercapacitor fabricated by the use of the MGB as an electrode demonstrates a specific capacitance of 206 F/g and more than 96% retention of capacitance after 10,000 cycles. The outstanding characteristics of the MGB as an electrode for supercapacitors verify the strong potential for use in energy-related areas.

A Review of Carbon Nanomaterials' Synthesis via the Chemical Vapor Deposition (CVD) Method.

PubMed

Manawi, Yehia M; Samara, Ayman; Al-Ansari, Tareq; Atieh, Muataz A

2018-05-17

Carbon nanomaterials have been extensively used in many applications owing to their unique thermal, electrical and mechanical properties. One of the prime challenges is the production of these nanomaterials on a large scale. This review paper summarizes the synthesis of various carbon nanomaterials via the chemical vapor deposition (CVD) method. These carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbide-derived carbon (CDC), carbon nano-onion (CNO) and MXenes. Furthermore, current challenges in the synthesis and application of these nanomaterials are highlighted with suggested areas for future research.

High efficiency epitaxial GaAs/GaAs and GaAs/Ge solar cell technology using OM/CVD

NASA Technical Reports Server (NTRS)

Wang, K. L.; Yeh, Y. C. M.; Stirn, R. J.; Swerdling, S.

1980-01-01

A technology for fabricating high efficiency, thin film GaAs solar cells on substrates appropriate for space and/or terrestrial applications was developed. The approach adopted utilizes organometallic chemical vapor deposition (OM-CVD) to form a GaAs layer epitaxially on a suitably prepared Ge epi-interlayer deposited on a substrate, especially a light weight silicon substrate which can lead to a 300 watt per kilogram array technology for space. The proposed cell structure is described. The GaAs epilayer growth on single crystal GaAs and Ge wafer substrates were investigated.

A Review of Carbon Nanomaterials’ Synthesis via the Chemical Vapor Deposition (CVD) Method

PubMed Central

Manawi, Yehia M.; Samara, Ayman; Al-Ansari, Tareq; Atieh, Muataz A.

2018-01-01

Carbon nanomaterials have been extensively used in many applications owing to their unique thermal, electrical and mechanical properties. One of the prime challenges is the production of these nanomaterials on a large scale. This review paper summarizes the synthesis of various carbon nanomaterials via the chemical vapor deposition (CVD) method. These carbon nanomaterials include fullerenes, carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, carbide-derived carbon (CDC), carbon nano-onion (CNO) and MXenes. Furthermore, current challenges in the synthesis and application of these nanomaterials are highlighted with suggested areas for future research. PMID:29772760

Electrical Characterization of Amorphous Silicon MIS-Based Structures for HIT Solar Cell Applications.

PubMed

García, Héctor; Castán, Helena; Dueñas, Salvador; Bailón, Luis; García-Hernansanz, Rodrigo; Olea, Javier; Del Prado, Álvaro; Mártil, Ignacio

2016-12-01

A complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used. A rapid thermal annealing in forming gas atmosphere at 200 °C during 10 min was applied after the metallization process. The evolution of interfacial state density with the deposition temperature indicates a better interface passivation at higher growth temperatures. However, in these cases, an important contribution of slow states is detected as well. Thus, using intermediate growth temperatures (100-150 °C) might be the best choice.

Electrical Characterization of Amorphous Silicon MIS-Based Structures for HIT Solar Cell Applications

NASA Astrophysics Data System (ADS)

García, Héctor; Castán, Helena; Dueñas, Salvador; Bailón, Luis; García-Hernansanz, Rodrigo; Olea, Javier; del Prado, Álvaro; Mártil, Ignacio

2016-07-01

A complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used. A rapid thermal annealing in forming gas atmosphere at 200 °C during 10 min was applied after the metallization process. The evolution of interfacial state density with the deposition temperature indicates a better interface passivation at higher growth temperatures. However, in these cases, an important contribution of slow states is detected as well. Thus, using intermediate growth temperatures (100-150 °C) might be the best choice.

Microstructure fabrication process induced modulations in CVD graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsubayashi, Akitomo, E-mail: amatsubayashi@albany.edu; Zhang, Zhenjun; Lee, Ji Ung

The systematic Raman spectroscopic study of a “mimicked” graphene device fabrication is presented. Upon photoresist baking, compressive stress is induced in the graphene which disappears after it is removed. The indirect irradiation from the electron beam (through the photoresist) does not significantly alter graphene characteristic Raman peaks indicating that graphene quality is preserved upon the exposure. The 2D peak shifts and the intensity ratio of 2D and G band, I(2D)/I(G), decreases upon direct metal deposition (Co and Py) suggesting that the electronic modulation occurs due to sp{sup 2} C-C bond weakening. In contrast, a thin metal oxide film deposited graphenemore » does not show either the significant 2D and G peaks shift or I(2D)/I(G) decrease upon the metal deposition suggesting the oxide protect the graphene quality in the fabrication process.« less

Diamond and diamondlike carbon as wear-resistant, self-lubricating coatings for silicon nitride

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1995-01-01

Recent work on the friction and wear properties of as-deposited fine-grain diamond, polished coarse-grain diamond, and as-deposited diamondlike carbon (DLC) films in humid air at a relative humidity of approximately 40 percent and in dry nitrogen is reviewed. Two types of chemical vapor deposition (CVD) processes are used to deposit diamond films on silicon nitride (Si3N4) substrates: microwave-plasma and hot-filament. Ion beams are used to deposit DLC films of Si3N4 substrates. The diamond and DLC films in sliding contact with hemispherical bare Si3N4 pins have low steady-state coefficients of friction (less than 0.2) and low wear rates (less than 10(exp -7) mm(exp 2)/N-m), and thus, can be used effectively as wear-resistant, self-lubricating coatings for Si3N4 in the aforementioned two environments.

Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition.

PubMed

Xie, Fan; Deng, Xiaopei; Kratzer, Domenic; Cheng, Kenneth C K; Friedmann, Christian; Qi, Shuhua; Solorio, Luis; Lahann, Joerg

2017-01-02

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone-degradable polymer directly synthesized via CVD. The CVD co-polymerization of [2.2]para-cyclophanes with cyclic ketene acetals, specifically 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), results in well-defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para-cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vertical graphene nanosheets synthesized by thermal chemical vapor deposition and the field emission properties

NASA Astrophysics Data System (ADS)

Guo, Xin; Qin, Shengchun; Bai, Shuai; Yue, Hongwei; Li, Yali; Chen, Qiang; Li, Junshuai; He, Deyan

2016-09-01

In this paper, we explored synthesis of vertical graphene nanosheets (VGNs) by thermal chemical vapor deposition (CVD). Through optimizing the experimental condition, growth of well aligned VGNs with uniform morphologies on nickel-coated stainless steel (SS) was realized for the first time by thermal CVD. In the meantime, influence of growth parameters on the VGN morphology was understood based on the balancing between the concentration and kinetic energy of carbon-containing radicals. Structural characterizations demonstrate that the achieved VGNs are normally composed of several graphene layers and less corrugated compared to the ones synthesized by other approaches, e.g. plasma enhanced (PE) CVD. The field emission measurement indicates that the VGNs exhibit relatively stable field emission and a field enhancement factor of about 1470, which is comparable to the values of VGNs prepared by PECVD can be achieved.

Measurements and Diagnostics of Diamond Films and Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Wu, Richard L. C.

1999-01-01

The commercial potential of chemical-vapor-deposited (CVD) diamond films has been established and a number of applications have been identified through university, industry, and government research studies. This paper discusses the methodologies used for property measurement and diagnostic of CVD diamond films and coatings. Measurement and diagnostic techniques studied include scanning electron microscopy, transmission electron microscopy, atomic force microscopy, stylus profilometry, x-ray diffraction, electron diffraction, Raman spectroscopy, Rutherford backscattering, elastic recoil spectroscopy, and friction examination. Each measurement and diagnostic technique provides unique information. A combination of techniques can provide the technical information required to understand the quality and properties of CVD diamond films, which are important to their application in specific component systems and environments. In this study the combination of measurement and diagnostic techniques was successfully applied to correlate deposition parameters and resultant diamond film composition, crystallinity, grain size, surface roughness, and coefficient of friction.

Long distance spin communication in chemical vapour deposited graphene

NASA Astrophysics Data System (ADS)

Kamalakar, M. Venkata; Groenveld, Christiaan; Dankert, André; Dash, Saroj P.

2015-04-01

Graphene is an ideal medium for long-distance spin communication in future spintronic technologies. So far, the prospect is limited by the smaller sizes of exfoliated graphene flakes and lower spin transport properties of large-area chemical vapour-deposited (CVD) graphene. Here we demonstrate a high spintronic performance in CVD graphene on SiO2/Si substrate at room temperature. We show pure spin transport and precession over long channel lengths extending up to 16 μm with a spin lifetime of 1.2 ns and a spin diffusion length ~6 μm at room temperature. These spin parameters are up to six times higher than previous reports and highest at room temperature for any form of pristine graphene on industrial standard SiO2/Si substrates. Our detailed investigation reinforces the observed performance in CVD graphene over wafer scale and opens up new prospects for the development of lateral spin-based memory and logic applications.

Effect of the fabrication conditions of SiGe LEDs on their luminescence and electrical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalyadin, A. E.; Sobolev, N. A., E-mail: nick@sobolev.ioffe.rssi.ru; Strel’chuk, A. M.

2016-02-15

SiGe-based n{sup +}–p–p{sup +} light-emitting diodes (LEDs) with heavily doped layers fabricated by the diffusion (of boron and phosphorus) and CVD (chemical-vapor deposition of polycrystalline silicon layers doped with boron and phosphorus) techniques are studied. The electroluminescence spectra of both kinds of LEDs are identical, but the emission intensity of CVD diodes is ∼20 times lower. The reverse and forward currents in the CVD diodes are substantially higher than those in diffusion-grown diodes. The poorer luminescence and electrical properties of the CVD diodes are due to the formation of defects at the interface between the emitter and base layers.

Ultrasensitive label-free detection of DNA hybridization by sapphire-based graphene field-effect transistor biosensor

NASA Astrophysics Data System (ADS)

Xu, Shicai; Jiang, Shouzhen; Zhang, Chao; Yue, Weiwei; Zou, Yan; Wang, Guiying; Liu, Huilan; Zhang, Xiumei; Li, Mingzhen; Zhu, Zhanshou; Wang, Jihua

2018-01-01

Graphene has attracted much attention in biosensing applications for its unique properties. Because of one-atom layer structure, every atom of graphene is exposed to the environment, making the electronic properties of graphene are very sensitive to charged analytes. Therefore, graphene is an ideal material for transistors in high-performance sensors. Chemical vapor deposition (CVD) method has been demonstrated the most successful method for fabricating large area graphene. However, the conventional CVD methods can only grow graphene on metallic substrate and the graphene has to be transferred to the insulating substrate for further device fabrication. The transfer process creates wrinkles, cracks, or tears on the graphene, which severely degrade electrical properties of graphene. These factors severely degrade the sensing performance of graphene. Here, we directly fabricated graphene on sapphire substrate by high temperature CVD without the use of metal catalysts. The sapphire-based graphene was patterned and make into a DNA biosensor in the configuration of field-effect transistor. The sensors show high performance and achieve the DNA detection sensitivity as low as 100 fM (10-13 M), which is at least 10 times lower than prior transferred CVD G-FET DNA sensors. The use of the sapphire-based G-FETs suggests a promising future for biosensing applications.

High-rate deposition of LiNb 1- xTa xO 3 films by thermal plasma spray CVD

NASA Astrophysics Data System (ADS)

Majima, T.; Yamamoto, H.; Kulinich, S. A.; Terashima, K.

2000-12-01

LiNb 1- xTa xO 3 films were prepared by a thermal plasma spray CVD method using liquid source materials. Preferentially (0 0 1)-oriented LiNb 1- xTa xO 3 films with satisfactory in-plane and out-of-plane alignment were fabricated on sapphire (0 0 1) substrates. The full-width at half-maximum (FWHM) of the (0 0 6) rocking curve could achieve 0.12°, which was comparable with those of LiNbO 3 and LiTaO 3 films prepared by other conventional vapor-phase deposition methods. The deposition rate was up to 0.07 μm/min, which was 5-40 times faster than those for most other conventional vapor-phase deposition methods. From inductively coupled plasma atomic emission spectroscopy analysis, x values of these films were estimated to be 0.36-0.49.

The thickness effect of pre-deposited catalyst film on carbon nanotube growth by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Lowndes, Douglas H.

2001-03-01

Chemical vapor deposition (CVD) of multi wall carbon nanotubes (MWCNTs) was realized on a substrate with a layer of iron film used as a catalyst. The catalyst film was pre-deposited in an electron-gun evaporator equipped with a movable shutter which partially blocks the beam during the evaporation process to produce a catalyst film with a continuously changing thickness from 0 to 60 nm. This technique creates a growth environment in which the film thickness is the only variable and eliminates sample-to-sample variations, enabling a systematic study of the thickness effect of the catalyst film on CNT growth. After the deposition of the catalyst film, the sample was immediately transferred into a CVD chamber where CNT growth was performed. Using Acetylene (C_2H_2) as a carbon-source gas, at the substrate temperature of around 700^oC, MWCNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature from 640^oC to 800^oC. There appears to be no strong correlation between the film thickness and the diameter of the tubes. At the substrate temperature of over 900^oC, the deposited carbon formed graphite sheets surrounding the catalyst particles and no CNTs were observed. A plot of the critical thickness of the catalyst film where CNTs start to grow as a function of the substrate temperature has obtained, which can be served as a reference for selecting the growth parameter in MWCNT growth. The significance of these experimental trends is discussed within the framework of the diffusion model for MWCNT growth.

Single liquid source plasma-enhanced metalorganic chemical vapor deposition of high-quality YBa2Cu3O(7-x) thin films

NASA Technical Reports Server (NTRS)

Zhang, Jiming; Gardiner, Robin A.; Kirlin, Peter S.; Boerstler, Robert W.; Steinbeck, John

1992-01-01

High quality YBa2Cu3O(7-x) films were grown in-situ on LaAlO3 (100) by a novel single liquid source plasma-enhanced metalorganic chemical vapor deposition process. The metalorganic complexes M(thd) (sub n), (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate; M = Y, Ba, Cu) were dissolved in an organic solution and injected into a vaporizer immediately upstream of the reactor inlet. The single liquid source technique dramatically simplifies current CVD processing and can significantly improve the process reproducibility. X-ray diffraction measurements indicated that single phase, highly c-axis oriented YBa2Cu3O(7-x) was formed in-situ at substrate temperature 680 C. The as-deposited films exhibited a mirror-like surface, had transition temperature T(sub cO) approximately equal to 89 K, Delta T(sub c) less than 1 K, and Jc (77 K) = 10(exp 6) A/sq cm.

Recent Development of Advanced Electrode Materials by Atomic Layer Deposition for Electrochemical Energy Storage.

PubMed

Guan, Cao; Wang, John

2016-10-01

Electrode materials play a decisive role in almost all electrochemical energy storage devices, determining their overall performance. Proper selection, design and fabrication of electrode materials have thus been regarded as one of the most critical steps in achieving high electrochemical energy storage performance. As an advanced nanotechnology for thin films and surfaces with conformal interfacial features and well controllable deposition thickness, atomic layer deposition (ALD) has been successfully developed for deposition and surface modification of electrode materials, where there are considerable issues of interfacial and surface chemistry at atomic and nanometer scale. In addition, ALD has shown great potential in construction of novel nanostructured active materials that otherwise can be hardly obtained by other processing techniques, such as those solution-based processing and chemical vapor deposition (CVD) techniques. This review focuses on the recent development of ALD for the design and delivery of advanced electrode materials in electrochemical energy storage devices, where typical examples will be highlighted and analyzed, and the merits and challenges of ALD for applications in energy storage will also be discussed.

A sub-atmospheric chemical vapor deposition process for deposition of oxide liner in high aspect ratio through silicon vias.

PubMed

Lisker, Marco; Marschmeyer, Steffen; Kaynak, Mehmet; Tekin, Ibrahim

2011-09-01

The formation of a Through Silicon Via (TSV) includes a deep Si trench etching and the formation of an insulating layer along the high-aspect-ratio trench and the filling of a conductive material into the via hole. The isolation of the filling conductor from the silicon substrate becomes more important for higher frequencies due to the high coupling of the signal to the silicon. The importance of the oxide thickness on the via wall isolation can be verified using electromagnetic field simulators. To satisfy the needs on the Silicon dioxide deposition, a sub-atmospheric chemical vapor deposition (SA-CVD) process has been developed to deposit an isolation oxide to the walls of deep silicon trenches. The technique provides excellent step coverage of the 100 microm depth silicon trenches with the high aspect ratio of 20 and more. The developed technique allows covering the deep silicon trenches by oxide and makes the high isolation of TSVs from silicon substrate feasible which is the key factor for the performance of TSVs for mm-wave 3D packaging.

Recent Development of Advanced Electrode Materials by Atomic Layer Deposition for Electrochemical Energy Storage

PubMed Central

2016-01-01

Electrode materials play a decisive role in almost all electrochemical energy storage devices, determining their overall performance. Proper selection, design and fabrication of electrode materials have thus been regarded as one of the most critical steps in achieving high electrochemical energy storage performance. As an advanced nanotechnology for thin films and surfaces with conformal interfacial features and well controllable deposition thickness, atomic layer deposition (ALD) has been successfully developed for deposition and surface modification of electrode materials, where there are considerable issues of interfacial and surface chemistry at atomic and nanometer scale. In addition, ALD has shown great potential in construction of novel nanostructured active materials that otherwise can be hardly obtained by other processing techniques, such as those solution‐based processing and chemical vapor deposition (CVD) techniques. This review focuses on the recent development of ALD for the design and delivery of advanced electrode materials in electrochemical energy storage devices, where typical examples will be highlighted and analyzed, and the merits and challenges of ALD for applications in energy storage will also be discussed. PMID:27840793

Process for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, P.L.; Giammarise, A.W.

1991-10-29

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figures.

Apparatus and process for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, Paul L.; Giammarise, Anthony W.

1994-01-01

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

Process for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, Paul L.; Giammarise, Anthony W.

1991-01-01

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance toerosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

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.

Processing and optimization of functional ceramic coatings and inorganic nanomaterials

NASA Astrophysics Data System (ADS)

Nyutu, Edward Kennedy G.

Processing of functional inorganic materials including zero (0-D) dimensional (e.g. nanoparticles), 1-D (nanorods, nanofibers), and 2-D (films/coating) structures is of fundamental and technological interest. This research will have two major sections. The first part of section one focuses on the deposition of silicon dioxide onto a pre-deposited molybdenum disilicide coating on molybdenum substrates for both high (>1000 °C) and moderate (500-600 °C) temperature oxidation protection. Chemical vapor deposition (CVD/MOCVD) techniques will be utilized to deposit the metal suicide and oxide coatings. The focus of this study will be to establish optimum deposition conditions and evaluate the metal oxide coating as oxidation - thermal barriers for Mo substrates under both isothermal (static) and cyclic oxidation conditions. The second part of this section will involve a systematic evaluation of a boron nitride (BN) interface coating prepared by chemical vapor deposition. Ceramic matrix composites (CMCs) are prospective candidates for high (>1000 °C) temperature applications and fiber- matrix interfaces are the dominant design parameters in ceramic matrix composites (CMCs). An important goal of the study is to determine a set of process parameters, which would define a boron nitride (BN) interface coating by a chemical vapor deposition (CVD) process with respect to coating. In the first part of the second section, we will investigate a new approach to synthesize ultrafine metal oxides that combines microwave heating and an in-situ ultrasonic mixing of two or more liquid precursors with a tubular flow reactor. Different metal oxides such as nickel ferrite and zinc aluminate spinels will be studied. The synthesis of metal oxides were investigated in order to study the effects of the nozzle and microwave (INM process) on the purity, composition, and particle size of the resulting powders. The second part of this research section involves a study of microwave frequency effects on the synthesis of nanocrystalline tetragonal barium titanate. The effects of microwave frequency (fixed and variable), microwave bandwidths sweep time, and aging time on the microstructure, particle sizes, phase purity, surface areas, and porosities of the as-prepared BaTiO3 were systematically investigated. The final part of the research involves a new rapid and facile synthetic route to prepare size-tunable, ultranarrow, high surface area OMS-2 nanomaterials via open-vessel microwave-assisted refluxing preparations without employing templates or surfactants. The particle size control is achieved by varying the concentration or type of non-aqueous co-solvent. The structural, textural, and catalytic application properties of the prepared nanomaterials are investigated.

Morphological Evolution and Weak Interface Development within CVD-Zirconia Coating Deposited on Hi-Nicalon Fiber

NASA Technical Reports Server (NTRS)

Li, Hao; Lee, Jinil; Libera, Matthew R.; Lee, Woo Y.; Kebbede, Anteneh; Lance, Michael J.; Wang, Hongyu; Morscher, Gregory N.; Gray, Hugh R. (Technical Monitor)

2002-01-01

The phase contents and morphology of a ZrO2 fiber coating deposited at 1050 C on Hi-Nicalon(Tm) by chemical vapor deposition were examined as a function of deposition time from 5 to 120 min. The morphological evolution in the ZrO2 coating was correlated to the development of delamination within the ZrO2 coating. The delamination appears to occur as a result of: (1) continuous formation of tetragonal ZrO2 nuclei on the deposition surface; (2) martensitic transformation of the tetragonal phase to a monoclinic phase upon reaching a critical grain size; and (3) development of significant compressive hoop stresses due to the volume dilation associated with the transformation. Our observations suggest that it will be of critical importance to further understand and eventually control the nucleation and grain growth behavior of CVD ZrO2 and its phase transformation behavior for its potential applications for composites.

Design of Inorganic Water Repellent Coatings for Thermal Protection Insulation on an Aerospace Vehicle

NASA Technical Reports Server (NTRS)

Fuerstenau, D. W.; Ravikumar, R.

1997-01-01

In this report, thin film deposition of one of the model candidate materials for use as water repellent coating on the thermal protection systems (TPS) of an aerospace vehicle was investigated. The material tested was boron nitride (BN), the water-repellent properties of which was detailed in our other investigation. Two different methods, chemical vapor deposition (CVD) and pulsed laser deposition (PLD), were used to prepare the BN films on a fused quartz substrate (one of the components of thermal protection systems on aerospace vehicles). The deposited films were characterized by a variety of techniques including X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The BN films were observed to be amorphous in nature, and a CVD-deposited film yielded a contact angle of 60 degrees with water, similar to the pellet BN samples investigated previously. This demonstrates that it is possible to use the bulk sample wetting properties as a guideline to determine the candidate waterproofing material for the TPS.

Variability in Chemical Vapor Deposited Zinc Sulfide: Assessment of Legacy and International CVD ZnS Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCloy, John S.; Korenstein, Ralph

2009-10-06

Samples of CVD ZnS from the United States, Germany, Israel, and China were evaluated using transmission spectroscopy, x-ray diffraction, photoluminescence, and biaxial flexure testing. Visible and near-infrared scattering, 6 μm absorption, and ultraviolet cut-on edge varied substantially in tested materials. Crystallographic hexagonality and texture was determined and correlated with optical scattering. Transmission cut-on (ultraviolet edge) blue-shifts with annealing and corresponds to visible color but not the 6 μm absorption. Photoluminescence results suggest that CVD ZnS exhibits a complex suite of electronic bandgap defects. All CVD ZnS tested with biaxial flexure exhibit similar fracture strength values and Weibull moduli. This surveymore » suggests that technical understanding of the structure and optical properties CVD ZnS is still in its infancy.« less

Surface passivation of InGaP/GaAs HBT using silicon-nitride film deposited by ECR CVD plasma

NASA Astrophysics Data System (ADS)

Manera, L. T.; Zoccal, L. B.; Diniz, J. A.; Tatsch, P. J.; Doi, I.

2008-07-01

In this paper we have developed a passivation technique with silicon-nitride (SiN X) film that requires no surface pre-treatment, and is fully compatible to monolithic microwave integrated circuits (MMICs). The nitride depositions were carried out by ECR-CVD (electron cyclotron resonance-chemical vapor deposition) directly over InGaP/GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Optical emission spectrometry (OES) was used for plasma characterization, and low formation of H and NH molecules in the gas phase was detected at pressure of 2.5 mTorr. These molecules can degrade III-V semiconductor surfaces due to the preferential loss of As or P and hydrogen incorporation at the substrate. The substrates were cleaned with organic solvents using a Sox-let distillate. The ECR depositions were carried out at a fixed substrate temperature of 20 °C, SiH 4/N 2 flow ratio of 1, Ar flow of 5 sccm pressure of 2.5 mTorr and microwave (2.45 GHz) power of 250 W and RF (13.56 MHz) power of 4 W. We have applied this film for InGaP/GaAs HBT fabrication process with excellent results, where two major contribuiton is related to this passivation technique, the enhancement in the transistor dc gain β and the improvement in the signal-to-noise ratio when compared unpassivated and passivated devices.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

PubMed Central

2012-01-01

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors. PMID:22643113

Growth of nitrogen-doped graphene on copper: Multiscale simulations

NASA Astrophysics Data System (ADS)

Gaillard, P.; Schoenhalz, A. L.; Moskovkin, P.; Lucas, S.; Henrard, L.

2016-02-01

We used multiscale simulations to model the growth of nitrogen-doped graphene on a copper substrate by chemical vapour deposition (CVD). Our simulations are based on ab-initio calculations of energy barriers for surface diffusion, which are complemented by larger scale Kinetic Monte Carlo (KMC) simulations. Our results indicate that the shape of grown doped graphene flakes depends on the temperature and deposition flux they are submitted during the process, but we found no significant effect of nitrogen doping on this shape. However, we show that nitrogen atoms have a preference for pyridine-like sites compared to graphite-like sites, as observed experimentally.

Delaminated Transfer of CVD Graphene

NASA Astrophysics Data System (ADS)

Clavijo, Alexis; Mao, Jinhai; Tilak, Nikhil; Altvater, Michael; Andrei, Eva

Single layer graphene is commonly synthesized by dissociation of a carbonaceous gas at high temperatures in the presence of a metallic catalyst in a process known as Chemical Vapor Deposition or CVD. Although it is possible to achieve high quality graphene by CVD, the standard transfer technique of etching away the metallic catalyst is wasteful and jeopardizes the quality of the graphene film by contamination from etchants. Thus, development of a clean transfer technique and preservation of the parent substrate remain prominent hurdles to overcome. In this study, we employ a copper pretreatment technique and optimized parameters for growth of high quality single layer graphene at atmospheric pressure. We address the transfer challenge by utilizing the adhesive properties between a polymer film and graphene to achieve etchant-free transfer of graphene films from a copper substrate. Based on this concept we developed a technique for dry delamination and transferring of graphene to hexagonal boron nitride substrates, which produced high quality graphene films while at the same time preserving the integrity of the copper catalyst for reuse. DOE-FG02-99ER45742, Ronald E. McNair Postbaccalaureate Achievement Program.

Thermoelectic properties of CVD grown large area graphene

NASA Astrophysics Data System (ADS)

Sherehiy, Andriy

This thesis is based on experimental work on thermoelectric properties of CVD grown large area graphene. The thermoelectric power (TEP) of CVD (Chemical Vapor Deposition) grown large area graphene transferred onto a Si/SiO 2_substrate was measured by simply attaching two miniature thermocouples and a resistive heater. Availability of such large area graphene facilitates straight forward TEP measurement without the use of any microfabrication processes. All investigated graphene samples showed a positive TEP S ≈ 20 mVK in ambient conditions and saturated at a negative value as low as S ≈ -50 mVK after vacuum-annealing at 500 K in a vacuum of 10-7 Torr. The observed p-type behavior under ambient conditions is attributed to the oxygen doping, while the n-type behavior under degassed conditions is due to electron doping from SiO2 surface states. It was observed that the sign of the TEP switched from negative to positive for the degassed graphene when exposed to acceptor gases. Conversely, the TEP of vacuum-annealed graphene exposed to the donor gases became even more negative than the TEP of vacuum-annealed sample.

Immobilization of glucoamylase on ceramic membrane surfaces modified with a new method of treatment utilizing SPCP-CVD.

PubMed

Ida; Matsuyama; Yamamoto

2000-07-01

Glucoamylase, as a model enzyme, was immobilized on a ceramic membrane modified by surface corona discharge induced plasma chemical process-chemical vapor deposition (SPCP-CVD). Characterizations of the immobilized enzyme were then discussed. Three kinds of ceramic membranes with different amounts of amino groups on the surface were prepared utilizing the SPCP-CVD method. Each with 1-time, 3-times and 5-times surface modification treatments and used for supports in glucoamylase immobilization. The amount of immobilized glucoamylase increased with the increase in the number of surface modification treatments and saturated to a certain maximum value estimated by a two-dimensional random packing. The operational stability of the immobilized glucoamylase also increased with the increase in the number of the surface treatment. It was almost the same as the conventional method, while the activity of immobilized enzyme was higher. The results indicated the possibility of designing the performance of the immobilized enzyme by controlling the amount of amino groups. The above results showed that the completely new surface modification method using SPCP was effective in modifying ceramic membranes for enzyme immobilization.

Ternary Precursors for Depositing I-III-VI2 Thin Films for Solar Cells via Spray CVD

NASA Technical Reports Server (NTRS)

Banger, K. K.; Hollingsworth, J. A.; Jin, M. H.-C.; Harris, J. D.; Duraj, S. A.; Smith, M.; Scheiman, D.; Bohannan, E. W.; Switzer, J. A.; Buhro, W. E.

2002-01-01

The development of thin-film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power (W/kg). Thin-film fabrication studies demonstrate that ternary single source precursors (SSP's) can be used in either a hot or cold-wall spray chemical vapour deposition (CVD) reactor, for depositing CuInS2, CuGaS2, and CuGaInS2 at reduced temperatures (400 to 450 C), which display good electrical and optical properties suitable for photovoltaic (PV) devices. X-ray diffraction studies, energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) confirmed the formation of the single phase CIS, CGS, CIGS thin-films on various substrates at reduced temperatures.

Chemical vapor deposition growth of two-dimensional heterojunctions

NASA Astrophysics Data System (ADS)

Cui, Yu; Li, Bo; Li, JingBo; Wei, ZhongMing

2018-01-01

The properties of two-dimensional (2D) layered materials with atom-smooth surface and special interlayer van der Waals coupling are different from those of traditional materials. Due to the absence of dangling bonds from the clean surface of 2D layered materials, the lattice mismatch influences slightly on the growth of 2D heterojunctions, thus providing a flexible design strategy. 2D heterojunctions have attracted extensive attention because of their excellent performance in optoelectronics, spintronics, and valleytronics. The transfer method was utilized for the fabrication of 2D heterojunctions during the early stage of fundamental research on these materials. This method, however, has limited practical applications. Therefore, chemical vapor deposition (CVD) method was recently developed and applied for the preparation of 2D heterojunctions. The CVD method is a naturally down-top growth strategy that yields 2D heterojunctions with sharp interfaces. Moreover, this method effectively reduces the introduction of contaminants to the fabricated heterojunctions. Nevertheless, the CVD-growth method is sensitive to variations in growth conditions. In this review article, we attempt to provide a comprehensive overview of the influence of growth conditions on the fabrication of 2D heterojunctions through the direct CVD method. We believe that elucidating the effects of growth conditions on the CVD method is necessary to help control and improve the efficiency of the large-scale fabrication of 2D heterojunctions for future applications in integrated circuits.

D.C. Arcjet Diamond Deposition

NASA Astrophysics Data System (ADS)

Russell, Derrek Andrew

1995-01-01

Polycrystalline diamond films synthesized by a D.C. (direct current) arcjet device was reported for the first time in 1988. This device is capable of higher diamond growth rates than any other form of diamond CVD (chemical vapor deposition) process due to its inherent versatility with regard to the enthalpy and fluid properties of the diamond-depositing vapor. Unfortunately, the versatility of this type of device is contrasted by many difficulties such as arc stability and large heat fluxes which make applying it toward diamond deposition a difficult problem. The purpose of this work was to convert the dc arcjet, which is primarily a metallurgical device, into a commercially viable diamond CVD process. The project was divided into two parts: process development and diagnostics. The process development effort concentrated on the certain engineering challenges. Among these was a novel arcjet design that allowed the carbon-source gas to be injected downstream of the tungsten cathode while still facilitating mixture with the main gas feed. Another engineering accomplishment was the incorporation of a water -cooled substrate cooler/spinner that maintained the substrate at the proper temperature, provided the substrate with a large thermal time constant to reduce thermal shock of the diamond film, and enabled the system to achieve a four -inch diameter growth area. The process diagnostics effort concentrated on measurements aimed at developing a fundamental understanding of the properties of the plasma jet such as temperature, plasma density, Mach number, pressure at the substrate, etc. The plasma temperature was determined to be 5195 K by measuring the rotational temperature of C _2 via optical emission spectroscopy. The Mach number of the plasma jet was determined to be ~6.0 as determined by the ratio of the stagnation pressures before and after the shock wave in the plasma jet. The C_2 concentration in the plasma jet was determined to be {~10 }^{12} cm^ {-3} by counting the number of radiated Swan band photons. This is big enough to account for a significant amount (10%) of the diamond growth.

Vapor Phase Deposition Using Plasma Spray-PVD™

NASA Astrophysics Data System (ADS)

von Niessen, K.; Gindrat, M.; Refke, A.

2010-01-01

Plasma spray—physical vapor deposition (PS-PVD) is a low pressure plasma spray technology to deposit coatings out of the vapor phase. PS-PVD is a part of the family of new hybrid processes recently developed by Sulzer Metco AG (Switzerland) on the basis of the well-established low pressure plasma spraying (LPPS) technology. Included in this new process family are plasma spray—chemical vapor deposition (PS-CVD) and plasma spray—thin film (PS-TF) processes. In comparison to conventional vacuum plasma spraying and LPPS, these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats, but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional PVD technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and EB-PVD coatings. This paper reports on the progress made at Sulzer Metco to develop functional coatings build up from vapor phase of oxide ceramics and metals.

From Bench Top to Market: Growth of Multi-Walled Carbon Nanotubes by Injection CVD Using Fe Organometallics - Production of a Commercial Reactor

NASA Technical Reports Server (NTRS)

Rowsell, J.; Hepp, A. F.; Harris, J. D.; Raffaelle, R. P.; Cowen, J. C.; Scheiman, D. A.; Flood, D. M.; Flood, D. J.

2009-01-01

Preferential oriented multiwalled carbon nanotubes were prepared by the injection chemical vapor deposition (CVD) method using either cyclopentadienyliron dicarbonyl dimer or cyclooctatetraene iron tricarbonyl as the iron catalyst source. The catalyst precursors were dissolved in toluene as the carrier solvent for the injections. The concentration of the catalyst was found to influence both the growth (i.e., MWNT orientation) of the nanotubes, as well as the amount of iron in the deposited material. As deposited, the multiwalled carbon nanotubes contained as little as 2.8% iron by weight. The material was deposited onto tantalum foil and fused silica substrates. The nanotubes were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. This synthetic route provides a simple and scalable method to deposit MWNTs with a low defect density, low metal content and a preferred orientation. Subsequently, a small start-up was founded to commercialize the deposition equipment. The contrast between the research and entrepreneurial environments will be discussed.

Synthesizing and Characterizing Graphene via Raman Spectroscopy: An Upper-Level Undergraduate Experiment That Exposes Students to Raman Spectroscopy and a 2D Nanomaterial

ERIC Educational Resources Information Center

Parobek, David; Shenoy, Ganesh; Zhou, Feng; Peng, Zhenbo; Ward, Michelle; Liu, Haitao

2016-01-01

In this upper-level undergraduate experiment, students utilize micro-Raman spectroscopy to characterize graphene prepared by mechanical exfoliation and chemical vapor deposition (CVD). The mechanically exfoliated samples are prepared by the students while CVD graphene can be purchased or obtained through outside sources. Owing to the intense Raman…

Ethylene Gas Sensing Properties of Tin Oxide Nanowires Synthesized via CVD Method

NASA Astrophysics Data System (ADS)

Akhir, Maisara A. M.; Mohamed, Khairudin; Rezan, Sheikh A.; Arafat, M. M.; Haseeb, A. S. M. A.; Uda, M. N. A.; Nuradibah, M. A.

2018-03-01

This paper studies ethylene gas sensing performance of tin oxide (SnO2) nanowires (NWs) as sensing material synthesized using chemical vapor deposition (CVD) technique. The effect of NWs diameter on ethylene gas sensing characteristics were investigated. SnO2 NWs with diameter of ∼40 and ∼240 nm were deposited onto the alumina substrate with printed gold electrodes and tested for sensing characteristic toward ethylene gas. From the finding, the smallest diameter of NWs (42 nm) exhibit fast response and recovery time and higher sensitivity compared to largest diameter of NWs (∼240 nm). Both sensor show good reversibility features for ethylene gas sensor.

Transport mechanisms through PE-CVD coatings: influence of temperature, coating properties and defects on permeation of water vapour

NASA Astrophysics Data System (ADS)

Kirchheim, Dennis; Jaritz, Montgomery; Mitschker, Felix; Gebhard, Maximilian; Brochhagen, Markus; Hopmann, Christian; Böke, Marc; Devi, Anjana; Awakowicz, Peter; Dahlmann, Rainer

2017-03-01

Gas transport mechanisms through plastics are usually described by the temperature-dependent Arrhenius-model and compositions of several plastic layers are represented by the CLT. When it comes to thin films such as plasma-enhanced chemical vapour deposition (PE-CVD) or plasma-enhanced atomic layer deposition (PE-ALD) coatings on substrates of polymeric material, a universal model is lacking. While existing models describe diffusion through defects, these models presume that permeation does not occur by other means of transport mechanisms. This paper correlates the existing transport models with data from water vapour transmission experiments.

Ultrashort pulse laser deposition of thin films

DOEpatents

Perry, Michael D.; Banks, Paul S.; Stuart, Brent C.

2002-01-01

Short pulse PLD is a viable technique of producing high quality films with properties very close to that of crystalline diamond. The plasma generated using femtosecond lasers is composed of single atom ions with no clusters producing films with high Sp.sup.3 /Sp.sup.2 ratios. Using a high average power femtosecond laser system, the present invention dramatically increases deposition rates to up to 25 .mu.m/hr (which exceeds many CVD processes) while growing particulate-free films. In the present invention, deposition rates is a function of laser wavelength, laser fluence, laser spot size, and target/substrate separation. The relevant laser parameters are shown to ensure particulate-free growth, and characterizations of the films grown are made using several diagnostic techniques including electron energy loss spectroscopy (EELS) and Raman spectroscopy.

Single Source Precursors for Thin Film Solar Cells

NASA Technical Reports Server (NTRS)

Banger, Kulbinder K.; Hollingsworth, Jennifer A.; Harris, Jerry D.; Cowen, Jonathan; Buhro, William E.; Hepp, Aloysius F.

2002-01-01

The development of thin film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power, (W/kg). The use of a polycrystalline chalcopyrite absorber layer for thin film solar cells is considered as the next generation photovoltaic devices. At NASA GRC we have focused on the development of new single source precursors (SSP) and their utility to deposit the chalcopyrite semi-conducting layer (CIS) onto flexible substrates for solar cell fabrication. The syntheses and thermal modulation of SSPs via molecular engineering is described. Thin-film fabrication studies demonstrate the SSPs can be used in a spray CVD (chemical vapor deposition) process, for depositing CIS at reduced temperatures, which display good electrical properties, suitable for PV (photovoltaic) devices.

Highly Crystalline CVD-grown Multilayer MoSe2 Thin Film Transistor for Fast Photodetector

PubMed Central

Jung, Chulseung; Kim, Seung Min; Moon, Hyunseong; Han, Gyuchull; Kwon, Junyeon; Hong, Young Ki; Omkaram, Inturu; Yoon, Youngki; Kim, Sunkook; Park, Jozeph

2015-01-01

Hexagonal molybdenum diselenide (MoSe2) multilayers were grown by chemical vapor deposition (CVD). A relatively high pressure (>760 Torr) was used during the CVD growth to achieve multilayers by creating multiple nuclei based on the two-dimensional crystal growth model. Our CVD-grown multilayer MoSe2 thin-film transistors (TFTs) show p-type-dominant ambipolar behaviors, which are attributed to the formation of Se vacancies generated at the decomposition temperature (650 °C) after the CVD growth for 10 min. Our MoSe2 TFT with a reasonably high field-effect mobility (10 cm2/V · s) exhibits a high photoresponsivity (93.7 A/W) and a fast photoresponse time (τrise ~ 0.4 s) under the illumination of light, which demonstrates the practical feasibility of multilayer MoSe2 TFTs for photodetector applications. PMID:26477744

CVD Fiber Coatings for Al2O3/NiAl Composites

NASA Technical Reports Server (NTRS)

Boss, Daniel E.

1995-01-01

While sapphire-fiber-reinforced nickel aluminide (Al2O3/NiAl) composites are an attractive candidate for high-temperature structures, the significant difference in the coefficient of thermal expansion between the NiAl matrix and the sapphire fiber creates substantial residual stresses in the composite. This study seeks to produce two fiber-coating systems with the potential to reduce the residual stresses in the sapphire/NiAl composite system. Chemical vapor deposition (CVD) was used to produce both the compensating and compliant-fiber coatings for use in sapphire/NiAl composites. A special reactor was designed and built to produce the FGM and to handle the toxic nickel precursors. This process was successfully used to produce 500-foot lengths of fiber with coating thicknesses of approximately 3 microns, 5 microns, and 10 microns.

Identifying suitable substrates for high-quality graphene-based heterostructures

NASA Astrophysics Data System (ADS)

Banszerus, L.; Janssen, H.; Otto, M.; Epping, A.; Taniguchi, T.; Watanabe, K.; Beschoten, B.; Neumaier, D.; Stampfer, C.

2017-06-01

We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphene-based heterostuctures on a large number of different substrate materials, including hexagonal boron nitride (hBN), transition metal dichalcogenides, silicon, different oxides and nitrides, as well as polymers. By applying a hBN-assisted, contamination free, dry transfer process for CVD graphene, high-quality heterostructures with low doping densities and low strain variations are assembled. The Raman spectra of these pristine heterostructures are sensitive to substrate-induced doping and strain variations and are thus used to probe the suitability of the substrate material for potential high-quality graphene devices. We find that the flatness of the substrate material is a key figure for gaining, or preserving high-quality graphene.

Catalyst Interface Engineering for Improved 2D Film Lift-Off and Transfer

PubMed Central

2016-01-01

The mechanisms by which chemical vapor deposited (CVD) graphene and hexagonal boron nitride (h-BN) films can be released from a growth catalyst, such as widely used copper (Cu) foil, are systematically explored as a basis for an improved lift-off transfer. We show how intercalation processes allow the local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material (2DM) film. Interfacial composition change and selective dissolution can thereby be achieved in a single step or split into two individual process steps. We demonstrate that this method is not only highly versatile but also yields graphene and h-BN films of high quality regarding surface contamination, layer coherence, defects, and electronic properties, without requiring additional post-transfer annealing. We highlight how such transfers rely on targeted corrosion at the catalyst interface and discuss this in context of the wider CVD growth and 2DM transfer literature, thereby fostering an improved general understanding of widely used transfer processes, which is essential to numerous other applications. PMID:27934130

Nanoscale plasma chemistry enables fast, size-selective nanotube nucleation.

PubMed

Ostrikov, Kostya Ken; Mehdipour, Hamid

2012-03-07

The possibility of fast, narrow-size/chirality nucleation of thin single-walled carbon nanotubes (SWCNTs) at low, device-tolerant process temperatures in a plasma-enhanced chemical vapor deposition (CVD) is demonstrated using multiphase, multiscale numerical experiments. These effects are due to the unique nanoscale reactive plasma chemistry (NRPC) on the surfaces and within Au catalyst nanoparticles. The computed three-dimensional process parameter maps link the nanotube incubation times and the relative differences between the incubation times of SWCNTs of different sizes/chiralities to the main plasma- and precursor gas-specific parameters and explain recent experimental observations. It is shown that the unique NRPC leads not only to much faster nucleation of thin nanotubes at much lower process temperatures, but also to better selectivity between the incubation times of SWCNTs with different sizes and chiralities, compared to thermal CVD. These results are used to propose a time-programmed kinetic approach based on fast-responding plasmas which control the size-selective, narrow-chirality nucleation and growth of thin SWCNTs. This approach is generic and can be used for other nanostructure and materials systems. © 2012 American Chemical Society

Electrical applications of CVD diamond films

NASA Astrophysics Data System (ADS)

Fujimori, Naoji

Electronics applications of CVD diamond films are reported. The properties of epitaxial diamond films are affected by the orientation of the substrate and the deposition conditions. Boron-doped epitaxial films are found to have the same characteristics as natural IIb diamonds. An LED and an FET were successfully fabricated using boron-doped epitaxial films and Schottky junctions. However, these devices did not exhibit satisfactory properties. Other applications of CVD diamond films include speaker diaphragms (as both a thin-film coating and a free-standing film), and as an ideal packaging material (due to its high thermal conductivity and low dielectric constant).

Development of a polysilicon process based on chemical vapor deposition, phase 1 and phase 2

NASA Technical Reports Server (NTRS)

Plahutnik, F.; Arvidson, A.; Sawyer, D.; Sharp, K.

1982-01-01

High-purity polycrystalline silicon was produced in an experimental, intermediate and advanced CVD reactor. Data from the intermediate and advanced reactors confirmed earlier results obtained in the experimental reactor. Solar cells were fabricated by Westinghouse Electric and Applied Solar Research Corporation which met or exceeded baseline cell efficiencies. Feedstocks containing trichlorosilane or silicon tetrachloride are not viable as etch promoters to reduce silicon deposition on bell jars. Neither are they capable of meeting program goals for the 1000 MT/yr plant. Post-run CH1 etch was found to be a reasonably effective method of reducing silicon deposition on bell jars. Using dichlorosilane as feedstock met the low-cost solar array deposition goal (2.0 gh-1-cm-1), however, conversion efficiency was approximately 10% lower than the targeted value of 40 mole percent (32 to 36% achieved), and power consumption was approximately 20 kWh/kg over target at the reactor.

Low Temperature Metal Free Growth of Graphene on Insulating Substrates by Plasma Assisted Chemical Vapor Deposition

PubMed Central

Muñoz, R.; Munuera, C.; Martínez, J. I.; Azpeitia, J.; Gómez-Aleixandre, C.; García-Hernández, M.

2016-01-01

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. PMID:28070341

Control of Reaction Surface in Low Temperature CVD to Enhance Nucleation and Conformal Coverage

ERIC Educational Resources Information Center

Kumar, Navneet

2009-01-01

The Holy Grail in CVD community is to find precursors that can afford the following: good nucleation on a desired substrate and conformal deposition in high AR features. Good nucleation is not only necessary for getting ultra-thin films at low thicknesses; it also offers films that are smooth at higher thickness values. On the other hand,…

Improved Single-Source Precursors for Solar-Cell Absorbers

NASA Technical Reports Server (NTRS)

Banger, Kulbinder K.; Harris, Jerry; Hepp, Aloysius

2007-01-01

Improved single-source precursor compounds have been invented for use in spray chemical vapor deposition (spray CVD) of chalcopyrite semiconductor absorber layers of thin-film cells. A "single-source precursor compound" is a single molecular compound that contains all the required elements, which when used under the spray CVD conditions, thermally decomposes to form CuIn(x)Ga(1-x)S(y)Se(2-y).

Raman studies of the interactions of fibrous carbon nanomaterials with albumin

NASA Astrophysics Data System (ADS)

Wesełucha-Birczyńska, Aleksandra; Morajka, Krzysztof; Stodolak-Zych, Ewa; Długoń, Elżbieta; Dużyja, Maria; Lis, Tomasz; Gubernat, Maciej; Ziąbka, Magdalena; Błażewicz, Marta

2018-05-01

Adsorption or immobilization of proteins on synthetic surfaces is a key issue in the context of the biocompatibility of implant materials, especially those intended for the needs of cardiac surgery but also for the construction of biosensors or nanomaterials used as drug carriers. The subject of research was the analysis of Raman spectra of two types of fibrous carbon nanomaterials, of great potential for biomedical applications, incubated with human serum albumin (HSA). The first nanomaterial has been created on the layer of MWCNTs deposited by electrophoretic method (EPD) and then covered by thin film of pyrolytic carbon introduced by chemical vapor deposition process (CVD). The second material was formed from carbonized nanofibers prepared via electrospinning (ESCNFs) of polyacrylonitrile (PAN) precursor and then covered with pyrolytic carbon (CVD). The G-band blue-shift towards the position of about 1600 cm-1, observed for both studied surfaces, clearly indicates the albumin (HSA) adhesion to the surface. The G and G' (2D) peak shift was employed to assess the stress build up on the carbon nanomaterials. The surface nano- and micro-topography as well as the method of ordering the carbon nanomaterial has a significant influence on the mode of surface-protein interaction.

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. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Epitaxial ferromagnetic single clusters and smooth continuous layers on large area MgO/CVD graphene substrates

NASA Astrophysics Data System (ADS)

Godel, Florian; Meny, Christian; Doudin, Bernard; Majjad, Hicham; Dayen, Jean-François; Halley, David

2018-02-01

We report on the fabrication of ferromagnetic thin layers separated by a MgO dielectric barrier from a graphene-covered substrate. The growth of ferromagnetic metal layers—Co or Ni0.8Fe0.2—is achieved by Molecular Beam Epitaxy (MBE) on a 3 nm MgO(111) epitaxial layer deposited on graphene. In the case of a graphene, grown by chemical vapor deposition (CVD) over Ni substrates, an annealing at 450 °C, under ultra-high-vacuum (UHV) conditions, leads to the dewetting of the ferromagnetic layers, forming well-defined flat facetted clusters whose shape reflects the substrate symmetry. In the case of CVD graphene transferred on SiO2, no dewetting is observed after same annealing. We attribute this difference to the mechanical stress states induced by the substrate, illustrating how it matters for epitaxial construction through graphene. Controlling the growth parameters of such magnetic single objects or networks could benefit to new architectures for catalysis or spintronic applications.

Time dependent 14 MeV neutrons measurement using a polycrystalline chemical vapor deposited diamond detector at the JET tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angelone, M.; Pillon, M.; Bertalot, L.

A polycrystalline chemical vapor deposited (CVD) diamond detector was installed on a JET tokamak in order to monitor the time dependent 14 MeV neutron emission produced by D-T plasma pulses during the Trace Tritium Experiment (TTE) performed in October 2003. This was the first tentative ever attempted to use a CVD diamond detector as neutron monitor in a tokamak environment. Despite its small active volume, the detector was able to detect the 14 MeV neutron emission (>1.0x10{sup 15} n/shot) with good reliability and stability during the experimental campaign that lasted five weeks. The comparison with standard silicon detectors presently usedmore » at JET as 14 MeV neutron monitors is reported, showing excellent correlation between the measurements. The results prove that CVD diamond detectors can be reliably used in a tokamak environment and therefore confirm the potential of this technology for next step machines like ITER.« less

Physics and chemistry in the process of hot-wire deposition of thin film silicon

NASA Astrophysics Data System (ADS)

Zheng, Wengang

Hotwire Chemical Vapor Deposition (CVD) has been used in preparing high quality low hydrogen content hydrogenated amorphous or polycrystalline silicon thin film in recent years. Comparing to the most commonly used glow discharge method, Hotwire CVD has the potential of high speed deposition avoiding the damage caused by ion bombardment associated with plasma. Although device quality thin films have been prepared by this method, and some empirical optimized deposition conditions have been established, the mechanisms controlling this technique are not clear. A homebuild threshold ionization mass spectrometer was constructed in this lab, allowing the radicals to be observed with high sensitivity. Hydrogen dissociation on the hot metal surface was studied first both by the direct detection of hydrogen atoms from the hot surface and the temperature change due to the hydrogen dissociation, it was confirmed that the activation energy of this process is around 2.25eV, the same as the dissociation in the gas phase. Further, we observed a first order dependence of hydrogen dissociation probability on the hydrogen pressure. This observation contradicts previously reported models of second order desorption. The monosilicon radicals Si and SiH3 were observed. It was observed that the silane decomposition on the hot surface is mainly a function of filament temperature, but the species released from that surface also depend on the surface condition, and thus on the silane exposure history of that piece of filament. Si is believed to deteriorate the film quality, by comparing the depleted silane and the Si flux, it is observed that Si experienced a lot of gas phase reactions before reaching the substrate, which leads to less reactive precursors. This observation is consistence with Molenbroek's study on the optimization of deposition condition. The dominant disilicon radical is identified as Si2H2, which in the form of lowest energy isomer, is suppose to be much less reactive than Si, and thus contributes to good quality thin film deposition. The corresponding Si insert reaction Si + SiH4 was also studied and an effective reaction coefficient of KSeff = 5 x 10-12( cm3/s was established.

A comparative study of the thermoluminescent response to beta irradiation of CVD diamond and LiF dosimeters

NASA Astrophysics Data System (ADS)

Bogani, F.; Borchi, E.; Bruzzi, M.; Leroy, C.; Sciortino, S.

1997-02-01

The thermoluminescent (TL) response of Chemical Vapour Deposited (CVD) diamond films to beta irradiation has been investigated. A numerical curve-fitting procedure, calibrated by means of a set of LiF TLD100 experimental spectra, has been developed to deconvolute the complex structured TL glow curves. The values of the activation energy and of the frequency factor related to each of the TL peaks involved have been determined. The TL response of the CVD diamond films to beta irradiation has been compared with the TL response of a set of LiF TLD100 and TLD700 dosimeters. The results have been discussed and compared in view of an assessment of the efficiency of CVD diamond films in future applications as in vivo dosimeters.

Epitaxial Growth of GaN Films by Pulse-Mode Hot-Mesh Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Komae, Yasuaki; Yasui, Kanji; Suemitsu, Maki; Endoh, Tetsuo; Ito, Takashi; Nakazawa, Hideki; Narita, Yuzuru; Takata, Masasuke; Akahane, Tadashi

2009-07-01

Intermittent gas supplies for hot-mesh chemical vapor deposition (CVD) for the epitaxial growth of gallium nitride (GaN) films were investigated to improve film crystallinity and optical properties. The GaN films were deposited on SiC/Si(111) substrates using an alternating-source gas supply or an intermittent supply of source gases such as ammonia (NH3) and trimethylgallium (TMG) in hot-mesh CVD after deposition of an aluminum nitride (AlN) buffer layer. The AlN layer was deposited using NH3 and trimethylaluminum (TMA) on a SiC layer grown by carbonization of a Si substrate using propane (C3H8). GaN films were grown on the AlN layer by a reaction between NHx radicals generated on a ruthenium (Ru)-coated tungsten (W) mesh and TMG molecules. After testing various gas supply modes, GaN films with good crystallinity and surface morphology were obtained using an intermittent supply of TMG and a continuous supply of NH3 gas. An optimal interval for the TMG gas supply was also obtained for the apparatus employed.

Direct growth of ZnO tetrapod on glass substrate by Chemical Vapor Deposition Technique

NASA Astrophysics Data System (ADS)

Fadzil, M. F. M.; Rahman, R. A.; Azhar, N. E. A.; Aziz, T. N. T. A.; Zulkifli, Z.

2018-03-01

This research demonstrates the growth of ZnO tetrapod structure on glass substrate for different types of flow gas and at different growth temperatures. The study on the morphological structure and electrical properties of ZnO thin film growth by Chemical Vapour Deposition (CVD) technique showed that the optimum growth temperature was obtained at 750°C with ZnO nanotetrapod morphological structure. Introducing Nitrogen gas flow during the growth process exhibited leg-to-leg linking ZnO tetrapods morphology. The electrical properties of ZnO tetrapods film were measured by using two point probes and it shows that, the sample growth in Ar and O2 atmosphere have better I-V characteristic.

Use of Kelvin probe force microscopy for identification of CVD grown graphene flakes on copper foil

NASA Astrophysics Data System (ADS)

Kumar, Rakesh; Mehta, B. R.; Kanjilal, D.

2017-05-01

Graphene flakes have been grown by chemical vapour deposition (CVD) method on Cu foils. The obtained graphene flakes have been characterized by optical microscopy, field emission scanning electron microscopy, Kelvin probe force microscopy (KPFM) and Raman spectroscopy. The graphene flakes grown on Cu foil comprise mainly single layer graphene and confirm that the nucleation for graphene growth starts very quickly. Moreover, KPFM has been found to be a valuable technique to differentiate between covered and uncovered portion of Cu foil by graphene flakes deposited for shorter duration. The results show that KPFM can be a very useful technique in understanding the mechanism of graphene growth.

Apparatus and process for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, P.L.; Giammarise, A.W.

1994-12-20

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figures.

Exposure monitoring of graphene nanoplatelets manufacturing workplaces.

PubMed

Lee, Ji Hyun; Han, Jong Hun; Kim, Jae Hyun; Kim, Boowook; Bello, Dhimiter; Kim, Jin Kwon; Lee, Gun Ho; Sohn, Eun Kyung; Lee, Kyungmin; Ahn, Kangho; Faustman, Elaine M; Yu, Il Je

2016-01-01

Graphenes have emerged as a highly promising, two-dimensional engineered nanomaterial that can possibly substitute carbon nanotubes. They are being explored in numerous R&D and industrial applications in laboratories across the globe, leading to possible human and environmental exposures to them. Yet, there are no published data on graphene exposures in occupational settings and no readily available methods for their detection and quantitation exist. This study investigates for the first time the potential exposure of workers and research personnel to graphenes in two research facilities and evaluates the status of the control measures. One facility manufactures graphene using graphite exfoliation and chemical vapor deposition (CVD), while the other facility grows graphene on a copper plate using CVD, which is then transferred to a polyethylene terephthalate (PET) sheet. Graphene exposures and process emissions were investigated for three tasks - CVD growth, exfoliation, and transfer - using a multi-metric approach, which utilizes several direct reading instruments, integrated sampling, and chemical and morphological analysis. Real-time instruments included a dust monitor, condensation particle counter (CPC), nanoparticle surface area monitor, scanning mobility particle sizer, and an aethalometer. Morphologically, graphenes and other nanostructures released from the work process were investigated using a transmission electron microscope (TEM). Graphenes were quantified in airborne respirable samples as elemental carbon via thermo-optical analysis. The mass concentrations of total suspended particulate at Workplaces A and B were very low, and elemental carbon concentrations were mostly below the detection limit, indicating very low exposure to graphene or any other particles. The real-time monitoring, especially the aethalometer, showed a good response to the released black carbon, providing a signature of the graphene released during the opening of the CVD reactor at Workplace A. The TEM observation of the samples obtained from Workplaces A and B showed graphene-like structures and aggregated/agglomerated carbon structures. Taken together, the current findings on common scenarios (exfoliation, CVD growth, and transfer), while not inclusive of all graphene manufacturing processes, indicate very minimal graphene or particle exposure at facilities manufacturing graphenes with good manufacturing practices.

Chemical vapor deposition of aluminum oxide

DOEpatents

Gordon, Roy; Kramer, Keith; Liu, Xinye

2000-01-01

An aluminum oxide film is deposited on a heated substrate by CVD from one or more alkylaluminum alkoxide compounds having composition R.sub.n Al.sub.2 (OR').sub.6-n, wherein R and R' are alkyl groups and n is in the range of 1 to 5.

Controlled growth of CNT in mesoporous AAO through optimized conditions for membrane preparation and CVD operation

NASA Astrophysics Data System (ADS)

Ciambelli, P.; Arurault, L.; Sarno, M.; Fontorbes, S.; Leone, C.; Datas, L.; Sannino, D.; Lenormand, P.; Le Blond Du Plouy, S.

2011-07-01

Anodic aluminium oxide (RAAO) membranes with a mesoporous structure were prepared under strictly controlling experimental process conditions, and physically and chemically characterized by a wide range of experimental techniques. Commercial anodic aluminium oxide (CAAO) membranes were also investigated for comparison. We demonstrated that RAAO membranes have lower content of both water and phosphorus and showed better porosity shape than CAAO. The RAAO membranes were used for template growth of carbon nanotubes (CNT) inside its pores by ethylene chemical vapour deposition (CVD) in the absence of a catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and an external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity and quality of CNTs in terms of diameter, length and arrangement (i.e. number of tubes for each channel) were optimized by investigating the effect of changing the experimental conditions for the CVD process. We showed that upon thermal treatment RAAO membranes were made up of crystallized allotropic alumina phases, which govern the subsequent CNT growth, because of their catalytic activity, likely due to their Lewis acidity. The strict control of experimental conditions for membrane preparation and CNT growth allowed us to enhance the carbon structural order, which is a critical requisite for CNT application as a substitute for copper in novel nano-interconnects.

Controlled growth of CNT in mesoporous AAO through optimized conditions for membrane preparation and CVD operation.

PubMed

Ciambelli, P; Arurault, L; Sarno, M; Fontorbes, S; Leone, C; Datas, L; Sannino, D; Lenormand, P; Du Plouy, S Le Blond

2011-07-01

Anodic aluminium oxide (RAAO) membranes with a mesoporous structure were prepared under strictly controlling experimental process conditions, and physically and chemically characterized by a wide range of experimental techniques. Commercial anodic aluminium oxide (CAAO) membranes were also investigated for comparison. We demonstrated that RAAO membranes have lower content of both water and phosphorus and showed better porosity shape than CAAO. The RAAO membranes were used for template growth of carbon nanotubes (CNT) inside its pores by ethylene chemical vapour deposition (CVD) in the absence of a catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and an external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity and quality of CNTs in terms of diameter, length and arrangement (i.e. number of tubes for each channel) were optimized by investigating the effect of changing the experimental conditions for the CVD process. We showed that upon thermal treatment RAAO membranes were made up of crystallized allotropic alumina phases, which govern the subsequent CNT growth, because of their catalytic activity, likely due to their Lewis acidity. The strict control of experimental conditions for membrane preparation and CNT growth allowed us to enhance the carbon structural order, which is a critical requisite for CNT application as a substitute for copper in novel nano-interconnects.

Highly crystalline lithium titanium oxide sheets coated with nitrogen-doped carbon enable high-rate lithium-ion batteries.

PubMed

Han, Cuiping; He, Yan-Bing; Li, Baohua; Li, Hongfei; Ma, Jun; Du, Hongda; Qin, Xianying; Yang, Quan-Hong; Kang, Feiyu

2014-09-01

Sheets of Li4Ti5O12 with high crystallinity are coated with nitrogen-doped carbon (NC-LTO) using a controlled process, comprising hydrothermal reaction followed by chemical vapor deposition (CVD). Acetonitrile (CH3 CN) vapor is used as carbon and nitrogen source to obtain a thin coating layer of nitrogen-doped carbon. The layer enables the NC-LTO material to maintain its sheet structure during the high-temperature CVD process and to achieve high crystallinity. Doping with nitrogen introduces defects into the carbon coating layer, and this increased degree of disorder allows fast transportation of lithium ions in the layer. An electrode of NC-LTO synthesized at 700 °C exhibits greatly improved rate and cycling performance due to a markedly decreased total cell resistance and enhanced Li-ion diffusion coefficient (D(Li)). Specific capacities of 159.2 and 145.8 mA h g(-1) are obtained using the NC-LTO sheets, at charge/discharge rates of 1 and 10 C, respectively. These values are much higher than values for LTO particles did not undergo the acetonitrile CVD treatment. A capacity retention value as high as 94.7% is achieved for the NC-LTO sheets after 400 cycles in a half-cell at 5 C discharge rate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Oxidation of Boron Nitride in Composites

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.

1998-01-01

Boron nitride (BN) is a prime candidate for fiber coatings in silicon carbide (SiC) fiber-reinforced SiC matrix composites. The properties of BN allow the fiber to impart beneficial composite properties to the matrix, even at elevated temperatures. The problem with BN is that it is readily attacked by oxygen. Although BN is an internal component of the composite, a matrix crack or pore can create a path for hot oxygen to attack the BN. This type of attack is not well understood. A variety of phenomena have been observed. These include borosilicate glass formation, volatilization of the BN, and under some conditions, preservation of the BN. In this study at the NASA Lewis Research Center, a series of BN materials and BN-containing model composites were methodically examined to understand the various issues dealing with the oxidation of BN in composites. Initial studies were done with a series of monolithic BN materials prepared by hot pressing and chemical vapor deposition (CVD). From these studies, we found that BN showed a strong orientation effect in oxidation and was extremely sensitive to the presence of water vapor in the environment. In addition, CVD material deposited at a high temperature showed much better oxidation behavior than CVD material deposited at a lower temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chundong; Zhou, Yungang; He, Lifang

Due to its unique electronic properties and wide spectrum of promising applications, graphene has attracted much attention from scientists in various fields. Control and engineering of graphene’s semiconducting properties is considered to be the key of its applications in electronic devices. Here, we report a novel method to prepare in situ nitrogen-doped graphene by microwave plasma assisted chemical vapor deposition (CVD) using PDMS (Polydimethylsiloxane) as a solid carbon source. Based on this approach, the concentration of nitrogen-doping can be easily controlled via the flow rate of nitrogen during the CVD process. X-ray photoelectron spectroscopy results indicated that the nitrogen atomsmore » doped into graphene lattice were mainly in the forms of pyridinic and pyrrolic structures. Moreover, first-principles calculations show that the incorporated nitrogen atoms can lead to p-type doping of graphene. This in situ approach provides a promising strategy to prepare graphene with controlled electronic properties.« less

Transition Metal Dichalcogenide Growth via Close Proximity Precursor Supply

NASA Astrophysics Data System (ADS)

O'Brien, Maria; McEvoy, Niall; Hallam, Toby; Kim, Hye-Young; Berner, Nina C.; Hanlon, Damien; Lee, Kangho; Coleman, Jonathan N.; Duesberg, Georg S.

2014-12-01

Reliable chemical vapour deposition (CVD) of transition metal dichalcogenides (TMDs) is currently a highly pressing research field, as numerous potential applications rely on the production of high quality films on a macroscopic scale. Here, we show the use of liquid phase exfoliated nanosheets and patterned sputter deposited layers as solid precursors for chemical vapour deposition. TMD monolayers were realized using a close proximity precursor supply in a CVD microreactor setup. A model describing the growth mechanism, which is capable of producing TMD monolayers on arbitrary substrates, is presented. Raman spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and electrical transport measurements reveal the high quality of the TMD samples produced. Furthermore, through patterning of the precursor supply, we achieve patterned growth of monolayer TMDs in defined locations, which could be adapted for the facile production of electronic device components.

Raman spectra boron doped amorphous carbon thin film deposited by bias assisted-CVD

NASA Astrophysics Data System (ADS)

Ishak, A.; Fadzilah, A. N.; Dayana, K.; Saurdi, I.; Malek, M. F.; Nurbaya, Z.; Shafura, A. K.; Rusop, M.

2018-05-01

Boron doped amorphous carbon thin film carbon was deposited at 200°C-350°C by bias assisted-CVD using palm oil as a precursor material. The structural boron doped amorphous carbon films were discussed by Raman analysis through the evolution of D and G bands. The spectral evolution observed showed the increase of upward shift of D and G peaks as substrate deposition temperatures increased. These structural changes were further correlated with optical gap and the results obtained are discussed and compared. The estimated optical band gap is found to be 1.9 to 2.05 eV and conductivity is to be in the range of 10-5 Scm-1 to 10-4 Scm-1. The decrease of optical band gap is associated to conductivity increased which change the characteristic parameters of Raman spectra including the position of G peak, full width at half maximum of G peak, and ID/IG.

Multi-Energy Processing for Novel Coating Technologies

DTIC Science & Technology

2014-12-18

tungsten carbide (WC) substrate (BS-6S, Basic Carbide Corp.) with a dimension of 25.4 x 25.4 x 1.6 mm^ and a cobalt composition of 6% was placed on a...as dopant sources. (a) No NH3 + No laser (b) NH3 added, No laser (c) 10.591 ^m Figure 4.4 SEM micrographs of the diamond films deposited using...typed 37 diamond. Nitrogen was widely used as n-typed dopant . Nitrogen-containing additives in CVD diamond growth led to severe deterioration of the

VOx effectively doping CVD-graphene for transparent conductive films

NASA Astrophysics Data System (ADS)

Ji, Qinghua; Shi, Liangjing; Zhang, Qinghong; Wang, Weiqi; Zheng, Huifeng; Zhang, Yuzhi; Liu, Yangqiao; Sun, Jing

2016-11-01

Chemical vapor deposition(CVD)-synthesized graphene is potentially an alternative for tin-doped indium oxide (ITO) transparent conductive films (TCFs), however its sheet resistance is still too high to meet many demands. Vanadium oxide has been widely applied as smart window materials, however, no study has been reported to use it as dopant to improve the conductivity of graphene TCFs. In this study, we firstly reported that VOx doping can effectively lower the sheet resistance of CVD-graphene films while keeping its good optical properties, whose transmittance is as high as 86-90%. The optimized VOx-doped graphene exhibits a sheet resistance as low as 176 Ω/□, which decreases by 56% compared to the undoped graphene films. The doping process is convenient, stable, economical and easy to operate. What is more, VOx can effectively increase the work function(WF) of the film, making it more appropriate for use in solar cells. The evolution of the VOx species annealed at different temperatures below 400 °C has been detailed studied for the first time, based on which the doping mechanism is proposed. The prepared VOx doped graphene is expected to be a promising candidate for transparent conductive film purposes.

Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

NASA Technical Reports Server (NTRS)

Perez, Jose M.

1996-01-01

We present a summary of the research, citations of publications resulting from the research and abstracts of such publications. We have made no inventions in the performance of the work in this project. The main goals of the project were to set up a Chemical Vapor Deposition (CVD) diamond growth system attached to an UltraHigh Vacuum (UHV) atomic resolution Scanning Tunneling Microscopy (STM) system and carry out experiments aimed at studying the properties and growth of diamond films using atomic resolution UHV STM. We successfully achieved these goals. We observed, for the first time, the atomic structure of the surface of CVD grown epitaxial diamond (100) films using UHV STM. We studied the effects of atomic hydrogen on the CVD diamond growth process. We studied the electronic properties of the diamond (100) (2x1) surface, and the effect of alkali metal adsorbates such as Cs on the work function of this surface using UHV STM spectroscopy techniques. We also studied, using STM, new electronic materials such as carbon nanotubes and gold nanostructures. This work resulted in four publications in refereed scientific journals and five publications in refereed conference proceedings.

Large-scale synthesis of high-quality hexagonal boron nitride nanosheets for large-area graphene electronics.

PubMed

Lee, Kang Hyuck; Shin, Hyeon-Jin; Lee, Jinyeong; Lee, In-yeal; Kim, Gil-Ho; Choi, Jae-Young; Kim, Sang-Woo

2012-02-08

Hexagonal boron nitride (h-BN) has received a great deal of attention as a substrate material for high-performance graphene electronics because it has an atomically smooth surface, lattice constant similar to that of graphene, large optical phonon modes, and a large electrical band gap. Herein, we report the large-scale synthesis of high-quality h-BN nanosheets in a chemical vapor deposition (CVD) process by controlling the surface morphologies of the copper (Cu) catalysts. It was found that morphology control of the Cu foil is much critical for the formation of the pure h-BN nanosheets as well as the improvement of their crystallinity. For the first time, we demonstrate the performance enhancement of CVD-based graphene devices with large-scale h-BN nanosheets. The mobility of the graphene device on the h-BN nanosheets was increased 3 times compared to that without the h-BN nanosheets. The on-off ratio of the drain current is 2 times higher than that of the graphene device without h-BN. This work suggests that high-quality h-BN nanosheets based on CVD are very promising for high-performance large-area graphene electronics. © 2012 American Chemical Society

Coatings for Graphite Fibers

NASA Technical Reports Server (NTRS)

Galasso, F. S.; Scola, D. A.; Veltri, R. D.

1980-01-01

Several approaches for applying high resistance coatings continuously to graphite yarn were investigated. Two of the most promising approaches involved (1) chemically vapor depositing (CVD) SiC coatings on the surface of the fiber followed by oxidation, and (2) drawing the graphite yarn through an organo-silicone solution followed by heat treatments. In both methods, coated fibers were obtained which exhibited increased electrical resistances over untreated fibers and which were not degraded. This work was conducted in a previous program. In this program, the continuous CVD SiC coating process used on HTS fiber was extended to the coating of HMS, Celion 6000, Celion 12000 and T-300 graphite fiber. Electrical resistances three order of magnitude greater than the uncoated fiber were measured with no significant degradation of the fiber strength. Graphite fibers coated with CVD Si3N4 and BN had resistances greater than 10(exp 6) ohm/cm. Lower pyrolysis temperatures were used in preparing the silica-like coatings also resulting in resistances as high as three orders of magnitude higher than the uncoated fiber. The epoxy matrix composites prepared using these coated fibers had low shear strengths indicating that the coatings were weak.

CVD Rhenium Engines for Solar-Thermal Propulsion Systems

NASA Technical Reports Server (NTRS)

Williams, Brian E.; Fortini, Arthur J.; Tuffias, Robert H.; Duffy, Andrew J.; Tucker, Stephen P.

1999-01-01

Solar-thermal upper-stage propulsion systems have the potential to provide specific impulse approaching 900 seconds, with 760 seconds already demonstrated in ground testing. Such performance levels offer a 100% increase in payload capability compared to state-of-the-art chemical upper-stage systems, at lower cost. Although alternatives such as electric propulsion offer even greater performance, the 6- to 18- month orbital transfer time is a far greater deviation from the state of the art than the one to two months required for solar propulsion. Rhenium metal is the only material that is capable of withstanding the predicted thermal, mechanical, and chemical environment of a solar-thermal propulsion device. Chemical vapor deposition (CVD) is the most well-established and cost-effective process for the fabrication of complex rhenium structures. CVD rhenium engines have been successfully constructed for the Air Force ISUS program (bimodal thrust/electricity) and the NASA Shooting Star program (thrust only), as well as under an Air Force SBIR project (thrust only). The bimodal engine represents a more long-term and versatile approach to solar-thermal propulsion, while the thrust-only engines provide a potentially lower weight/lower cost and more near-term replacement for current upper-stage propulsion systems.

Perovskite Solar Cells for High-Efficiency Tandems

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGehee, Michael; Buonassisi, Tonio

The first monolithic perovskite/silicon tandem was made with a diffused silicon p-n junction, a tunnel junction made of n ++ hydrogenated amorphous silicon, a titania electron transport layer, a methylammonium lead iodide absorber, and a Spiro-OMeTAD hole transport layer (HTL). The power conversion efficiency (PCE) was only 13.7% due to excessive parasitic absorption of light in the HTL, limiting the matched current density to 11.5 mA/cm 2. Werner et al. 15 raised the PCE to a record 21.2% by switching to a silicon heterojunction bottom cell and carefully tuning layer thicknesses to achieve lower optical loss and a higher currentmore » density of 15.9 mA/cm 2. It is clear from these reports that minimizing parasitic absorption in the window layers is crucial to achieving higher current densities and efficiencies in monolithic tandems. To this end, the window layers through which light first passes before entering the perovskite and silicon absorber materials must be highly transparent. The front electrode must also be conductive to carry current laterally across the top of the device. Indium tin oxide (ITO) is widely utilized as a transparent electrode in optoelectronic devices such as flat-panel displays, smart windows, organic light-emitting diodes, and solar cells due to its high conductivity and broadband transparency. ITO is typically deposited through magnetron sputtering; however, the high kinetic energy of sputtered particles can damage underlying layers. In perovskite solar cells, a sputter buffer layer is required to protect the perovskite and organic carrier extraction layers from damage during sputter deposition. The ideal buffer layer should also be energetically well aligned so as to act as a carrier-selective contact, have a wide bandgap to enable high optical transmission, and have no reaction with the halides in the perovskite. Additionally, this buffer layer should act as a diffusion barrier layer to prevent both organic cation evolution and moisture penetration to overcome the often-reported thermal and environmental instability of metal halide perovskites. Previous perovskite-containing tandems utilized molybdenum oxide (MoO x) as a sputter buffer layer, but this has raised concerns over long-term stability, as the iodide in the perovskite can chemically react with MoO x. Mixed-cation perovskite solar cells have consistently outperformed their single-cation counterparts. The first perovskite device to exceed 20% PCE was fabricated with a mixture of methylammonium (MA) and formamidinium (FA). Recent reports have shown promising results with the introduction of cesium mixtures, enabling high efficiencies with improved photo-, moisture, and thermal stability. The increased moisture and thermal stability are especially important as they broaden the parameter space for processing on top of the perovskite, enabling the deposition of metal oxide contacts through atomic layer deposition (ALD) or chemical vapor deposition (CVD) that may require elevated temperatures or water as a counter reagent. Both titanium dioxide (TiO 2) and tin oxide (SnO 2) have consistently proven to be effective electron-selective contacts for perovskite solar cells and both can be deposited via ALD at temperatures below 150 °C. We introduced a bilayer of SnO 2 and zinc tin oxide (ZTO) that can be deposited by either low-temperature ALD or pulsed-CVD as a window layer with minimal parasitic absorption, efficient electron extraction, and sufficient buffer properties to prevent the organic and perovskite layers from damage during the subsequent sputter deposition of a transparent ITO electrode. We explored pulsed-CVD as a modified ALD process with a continual, rather than purely step-wise, growth component in order to considerably reduce the process time of the SnO 2 deposition process and minimize potential perovskite degradation. These layers, when used in an excellent mixed-cation perovskite solar cell atop a silicon solar cell tuned to the infrared spectrum, enable highly efficient perovskite-silicon tandem solar cells with enhanced thermal and environmental stability.« less

Growth of InAs NWs with controlled morphology by CVD

NASA Astrophysics Data System (ADS)

Huang, Y. S.; Li, M.; Wang, J.; Xing, Y.; Xu, H. Q.

2017-06-01

We report on the growth of single crystal InAs NWs on Si/SiOx substrates by chemical vapor deposition (CVD). By adjusting growth parameters, the diameters, morphology, length and the proportion of superlattice ZB InAs NWs (NWs) can be controlled on a Si/SiOx substrate. Our work provides a low-cost route to grow and phase-engineer single crystal InAs NWs for a wide range of potential applications.

Nanocrystalline sp{sup 2} and sp{sup 3} carbons: CVD synthesis and applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Terranova, M. L.; Rossi, M.; Tamburri, E., E-mail: emanuela.tamburri@uniroma2.it

The design and production of innovative materials based on nanocrystalline sp{sup 2}- and sp{sup 3}-coordinated carbons is presently a focus of the scientific community. We present a review of the nanostructures obtained in our labs using a series of synthetic routes, which make use of chemical vapor deposition (CVD) techniques for the selective production of non-planar graphitic nanostructures, nanocrystalline diamonds, and hybrid two-phase nanostructures.

Irradiation test of tungsten clad uranium carbide-zirconium carbide ((U,Zr)C) specimens for thermionic reactor application at conditions conductive to long-term performance

NASA Technical Reports Server (NTRS)

Creagh, J. W. R.; Smith, J. R.

1973-01-01

Uranium carbide fueled, thermionic emitter configurations were encapsulated and irradiated. One capsule contained a specimen clad with fluoride derived chemically vapor deposited (CVD) tungsten. The other capsule used a duplex clad specimen consisting of chloride derived on floride derived CVD tungsten. Both fuel pins were 16 millimeters in diameter and contained a 45.7-millimeter length of fuel.

Reactive polymer coatings: A robust platform towards sophisticated surface engineering for biotechnology

NASA Astrophysics Data System (ADS)

Chen, Hsien-Yeh

Functionalized poly(p-xylylenes) or so-called reactive polymers can be synthesized via chemical vapor deposition (CVD) polymerization. The resulting ultra-thin coatings are pinhole-free and can be conformally deposited to a wide range of substrates and materials. More importantly, the equipped functional groups can served as anchoring sites for tailoring the surface properties, making these reactive coatings a robust platform that can deal with sophisticated challenges faced in biointerfaces. In this work presented herein, surface coatings presenting various functional groups were prepared by CVD process. Such surfaces include aldehyde-functionalized coating to precisely immobilize saccharide molecules onto well-defined areas and alkyne-functionalized coating to click azide-modified molecules via Huisgen 1,3-dipolar cycloaddition reaction. Moreover, CVD copolymerization has been conducted to prepare multifunctional coatings and their specific functions were demonstrated by the immobilization of biotin and NHS-ester molecules. By using a photodefinable coating, polyethylene oxides were immobilized onto a wide range of substrates through photo-immobilization. Spatially controlled protein resistant properties were characterized by selective adsorption of fibrinogen and bovine serum albumin as model systems. Alternatively, surface initiator coatings were used for polymer graftings of polyethylene glycol) methyl ether methacrylate, and the resultant protein- and cell- resistant properties were characterized by adsorption of kinesin motor proteins, fibrinogen, and murine fibroblasts (NIH3T3). Accessibility of reactive coatings within confined microgeometries was systematically studied, and the preparation of homogeneous polymer thin films within the inner surface of microchannels was demonstrated. Moreover, these advanced coatings were applied to develop a dry adhesion process for microfluidic devices. This process provides (i) excellent bonding strength, (ii) extended storage time prior to bonding, and (iii) well-defined surface functionalities for subsequent surface modifications. Finally, we have also prepared surface microstructures and surface patterns using reactive coatings via photopatterning, projection lithography, supramolecular nanostamping (SuNS), and vapor-assisted micropatterning in replica structures (VAMPIR). These patterning techniques can be complimentarily used and provide access to precisely confined microenvironments on flat and curved geometries. Reactive coatings provide a technology platform that creates active, long-term control and may lead to improved mimicry of biological systems for effective bio-functional modifications.

Direct growth of high crystallinity graphene from water-soluble polymer powders

NASA Astrophysics Data System (ADS)

Chen, Qiao; Zhong, Yujia; Huang, Meirong; Zhao, Guoke; Zhen, Zhen; Zhu, Hongwei

2018-07-01

The use of solid-state carbon sources is effective to produce graphene by safe and low-cost chemical vapor deposition (CVD) process. Water-soluble polymers are generally environmentally friendly and have great potential on large-scale green production of graphene. Here, we systematically study the growth of graphene from water-soluble polymers on copper foils. Two different conversion ways are adopted to investigate the growth mechanism of graphene from water-soluble polymers. We find that the metal-binding functional group hydroxyl strongly influences the vaporization of water-soluble polymers on Cu foils, which hinders the formation of graphene films by rapid thermal treatment. In direct CVD process using water-soluble polymer powders as precursors, oxygenated functional groups in polymers can enhance the crystallinity of as-grown graphene in contrast to solid hydrocarbons without containing oxygen (e.g. polyethylene). Large and continuous graphene films of high quality are synthesized from polyvinyl alcohol and polyethylene glycol. Nitrogen doping in graphene can be easily realized by using nitrogen-containing water-soluble polymers (e.g. polyvinyl pyrrolidone).

A chemical and fluid dynamic study of the chemical vapor deposition of aluminum nitride in a vertical reactor

NASA Astrophysics Data System (ADS)

Bather, Wayne Anthony

The metalorganic chemical vapor deposition (MOCVD) growth of compound semiconductors has become important in producing many high performance electronic and optoelectronic devices from the wide bandgaps III-V nitrides, for example, aluminum nitride (AlN). A systematic theoretical and experimental investigation of the chemistry and mass transport process in a MOCVD system can yield predictive models of the deposition process. The chemistries and fluid dynamics of the MOCVD growth of AlN in a vertical reactor is analyzed and characterized in order to parameterize and model the deposition process. A Fourier Transform Infrared (FTIR) spectroscopic study of the predeposition reactions between trimethylaluminum (TMAl) and ammonia (NHsb3) is carried out in a static gas cell to examine the primary homogeneous gas phase reactions, pyrolysis of the reactants, and adduct formation, possibly accompanied by elimination reactions. A series of reactions, based on laboratory studies and literature review, is then proposed to model the deposition process. All pertinent kinetic, thermochemical, and transport properties were obtained. Utilizing a mass transport model, we performed computational fluid dynamics calculations using the FLUENT software package. We determined temperature, velocity, and concentration profiles, along with deposition rates inside the experimental vertical CVD reactor in the Howard University Material Science Research Center of Excellence. Experimental deposition rate data were found to be in good agreement with those predicted from the simulations, thus validating the proposed model. The control of the homogeneous gas phase reaction leading to the formation and subsequent decomposition of the adduct is critical to the formation of device-grade AlN films. Many basic processes occurring during MOCVD of AlN are still not completely understood, and none of the detailed surface reaction mechanisms are known.

Effect of catalyst film thickness on carbon nanotube growth by selective area chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wei, Y. Y.; Eres, Gyula; Merkulov, V. I.; Lowndes, D. H.

2001-03-01

The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe and Ni as catalyst. To eliminate sample-to-sample variations and create a growth environment in which the film thickness is the sole variable, samples with continuously changing catalyst film thickness from 0 to 60 nm were fabricated by electron-gun evaporation. Using thermal CVD CNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature. There appears to be no strong correlation between the film thickness and the diameter of the tubes. In contrast, using plasma enhanced CVD with Ni as catalyst, vertically oriented CNTs grow in the entire range of catalyst film thickness. The diameter of these CNTs shows a strong correlation with the catalyst film thickness. The significance of these experimental trends is discussed within the framework of the diffusion model for CNT growth.

High-efficiency thin-film GaAs solar cells, phase2

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.

1981-01-01

Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

Fabrication of Nanocarbon Composites Using In Situ Chemical Vapor Deposition and Their Applications.

PubMed

He, Chunnian; Zhao, Naiqin; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun

2015-09-23

Nanocarbon (carbon nanotubes (CNTs) and graphene (GN)) composites attract considerable research interest due to their fascinating applications in many fields. Here, recent developments in the field of in situ chemical vapor deposition (CVD) for the design and controlled preparation of advanced nanocarbon composites are highlighted, specifically, CNT-reinforced bulk structural composites, as well as CNT, GN, and CNT/GN functional composites, together with their practical and potential applications. In situ CVD is a very attractive approach for the fabrication of composites because of its engaging features, such as its simplicity, low-cost, versatility, and tunability. The morphologies, structures, dispersion, and interface of the resulting nanocarbon composites can be easily modulated by varying the experimental parameters (such as temperature, catalysts, carbon sources, templates or template catalysts, etc.), which enables a great potential for the in situ synthesis of high-quality nanocarbons with tailored size and dimension for constructing high-performance composites, which has not yet been achieved by conventional methods. In addition, new trends of the in situ CVD toward nanocarbon composites are discussed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High pressure studies using two-stage diamond micro-anvils grown by chemical vapor deposition

DOE PAGES

Vohra, Yogesh K.; Samudrala, Gopi K.; Moore, Samuel L.; ...

2015-06-10

Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two stage diamond anvil with 300 μm culet and with a CVD diamond second stage ofmore » 50 μm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86 GPa. Furthermore, the micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86 GPa.« less

Fabrication of efficient planar perovskite solar cells using a one-step chemical vapor deposition method

PubMed Central

Tavakoli, Mohammad Mahdi; Gu, Leilei; Gao, Yuan; Reckmeier, Claas; He, Jin; Rogach, Andrey L.; Yao, Yan; Fan, Zhiyong

2015-01-01

Organometallic trihalide perovskites are promising materials for photovoltaic applications, which have demonstrated a rapid rise in photovoltaic performance in a short period of time. We report a facile one-step method to fabricate planar heterojunction perovskite solar cells by chemical vapor deposition (CVD), with a solar power conversion efficiency of up to 11.1%. We performed a systematic optimization of CVD parameters such as temperature and growth time to obtain high quality films of CH3NH3PbI3 and CH3NH3PbI3-xClx perovskite. Scanning electron microscopy and time resolved photoluminescence data showed that the perovskite films have a large grain size of more than 1 micrometer, and carrier life-times of 10 ns and 120 ns for CH3NH3PbI3 and CH3NH3PbI3-xClx, respectively. This is the first demonstration of a highly efficient perovskite solar cell using one step CVD and there is likely room for significant improvement of device efficiency. PMID:26392200

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.

Study on fabrication technology of silicon-based silica array waveguide grating

NASA Astrophysics Data System (ADS)

Sun, Yanjun; Dong, Lianhe; Leng, Yanbing

2009-05-01

Array waveguide grating (AWG) is an important plane optical element in dense wavelength division multiplex/demultiplex system. There are many virtue, channel quantity larger,lower loss, lower crosstalk, size smaller and high reliability etc. This article describs AWG fabrication technics utilizing IC(Integrated Circles) techniques, based on sixteen channel Silicon-Based Silica Array Waveguide Grating, put emphasis on discussing doping and deposition of waveguide core film,technics theory and interrelated parameter condition of photoetch and ion etching. Experiment result indicates that it depens on electrode structure, energy of radio-frequency electrode gas component, pressure ,flowing speed and substrate temperature by CVD depositing film .During depositing waveguide film by PE-CVD, the silicon is not reacted, When temperature becomes lower,it is reacted and it is easy to realize the control of film thickness and time with a result of film thickness uniformity reaching about 4% after optimizing deposition parameter and condition. We get the result of high etching speed rate, outline zoom, and side frame smooth by photoresist/Cr multiple mask and optimizing etching technics.

A Scalable Route to Nanoporous Large-Area Atomically Thin Graphene Membranes by Roll-to-Roll Chemical Vapor Deposition and Polymer Support Casting.

PubMed

Kidambi, Piran R; Mariappan, Dhanushkodi D; Dee, Nicholas T; Vyatskikh, Andrey; Zhang, Sui; Karnik, Rohit; Hart, A John

2018-03-28

Scalable, cost-effective synthesis and integration of graphene is imperative to realize large-area applications such as nanoporous atomically thin membranes (NATMs). Here, we report a scalable route to the production of NATMs via high-speed, continuous synthesis of large-area graphene by roll-to-roll chemical vapor deposition (CVD), combined with casting of a hierarchically porous polymer support. To begin, we designed and built a two zone roll-to-roll graphene CVD reactor, which sequentially exposes the moving foil substrate to annealing and growth atmospheres, with a sharp, isothermal transition between the zones. The configurational flexibility of the reactor design allows for a detailed evaluation of key parameters affecting graphene quality and trade-offs to be considered for high-rate roll-to-roll graphene manufacturing. With this system, we achieve synthesis of uniform high-quality monolayer graphene ( I D / I G < 0.065) at speeds ≥5 cm/min. NATMs fabricated from the optimized graphene, via polymer casting and postprocessing, show size-selective molecular transport with performance comparable to that of membranes made from conventionally synthesized graphene. Therefore, this work establishes the feasibility of a scalable manufacturing process of NATMs, for applications including protein desalting and small-molecule separations.

Low work function materials for microminiature energy conversion and recovery applications

DOEpatents

Zavadil, Kevin R.; Ruffner, Judith A.; King, Donald B.

2003-05-13

Low work function materials are disclosed together with methods for their manufacture and integration with electrodes used in thermionic conversion applications (specifically microminiature thermionic conversion applications). The materials include a mixed oxide system and metal in a compositionally modulated structure comprised of localized discontinuous structures of material that are deposited using techniques suited to IC manufacture, such as rf sputtering or CVD. The structures, which can include layers are then heated to coalescence yielding a thin film that is both durable and capable of electron emission under thermionic conversion conditions used for microminiature thermionic converters. Using the principles of the invention, thin film electrodes (emitters and collectors) required for microconverter technology are manufactured using a single process deposition so as to allow for full fabrication integration consistent with batch processing, and tailoring of emission/collection properties. In the preferred embodiment, the individual layers include mixed BaSrCaO, scandium oxide and tungsten.

Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

DOEpatents

Sarin, V.K.

1990-08-21

An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications is disclosed. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al[sub x]N[sub y]O[sub z] layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al[sub x]N[sub y]O[sub z] layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

Oxidation resistant high temperature thermal cycling resistant coatings on silicon-based substrates and process for the production thereof

DOEpatents

Sarin, Vinod K.

1990-01-01

An oxidation resistant, high temperature thermal cycling resistant coated ceramic article for ceramic heat engine applications. The substrate is a silicon-based material, i.e. a silicon nitride- or silicon carbide-based monolithic or composite material. The coating is a graded coating of at least two layers: an intermediate AlN or Al.sub.x N.sub.y O.sub.z layer and an aluminum oxide or zirconium oxide outer layer. The composition of the coating changes gradually from that of the substrate to that of the AlN or Al.sub.x N.sub.y O.sub.z layer and further to the composition of the aluminum oxide or zirconium oxide outer layer. Other layers may be deposited over the aluminum oxide layer. A CVD process for depositing the graded coating on the substrate is also disclosed.

Chemical Vapor-Deposited Hexagonal Boron Nitride as a Scalable Template for High-Performance Organic Field-Effect Transistors

DOE PAGES

Lee, Tae Hoon; Kim, Kwanpyo; Kim, Gwangwoo; ...

2017-02-27

Organic field-effect transistors have attracted much attention because of their potential use in low-cost, large-area, flexible electronics. High-performance organic transistors require a low density of grain boundaries in their organic films and a decrease in the charge trap density at the semiconductor–dielectric interface for efficient charge transport. In this respect, the role of the dielectric material is crucial because it primarily determines the growth of the film and the interfacial trap density. Here, we demonstrate the use of chemical vapor-deposited hexagonal boron nitride (CVD h-BN) as a scalable growth template/dielectric for high-performance organic field-effect transistors. The field-effect transistors based onmore » C60 films grown on single-layer CVD h-BN exhibit an average mobility of 1.7 cm 2 V –1 s –1 and a maximal mobility of 2.9 cm 2 V –1 s –1 with on/off ratios of 10 7. The structural and morphology analysis shows that the epitaxial, two-dimensional growth of C 60 on CVD h-BN is mainly responsible for the superior charge transport behavior. In conclusion, we believe that CVD h-BN can serve as a growth template for various organic semiconductors, allowing the development of large-area, high-performance flexible electronics.« less

Chemical Vapor-Deposited Hexagonal Boron Nitride as a Scalable Template for High-Performance Organic Field-Effect Transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Tae Hoon; Kim, Kwanpyo; Kim, Gwangwoo

Organic field-effect transistors have attracted much attention because of their potential use in low-cost, large-area, flexible electronics. High-performance organic transistors require a low density of grain boundaries in their organic films and a decrease in the charge trap density at the semiconductor–dielectric interface for efficient charge transport. In this respect, the role of the dielectric material is crucial because it primarily determines the growth of the film and the interfacial trap density. Here, we demonstrate the use of chemical vapor-deposited hexagonal boron nitride (CVD h-BN) as a scalable growth template/dielectric for high-performance organic field-effect transistors. The field-effect transistors based onmore » C60 films grown on single-layer CVD h-BN exhibit an average mobility of 1.7 cm 2 V –1 s –1 and a maximal mobility of 2.9 cm 2 V –1 s –1 with on/off ratios of 10 7. The structural and morphology analysis shows that the epitaxial, two-dimensional growth of C 60 on CVD h-BN is mainly responsible for the superior charge transport behavior. In conclusion, we believe that CVD h-BN can serve as a growth template for various organic semiconductors, allowing the development of large-area, high-performance flexible electronics.« less

Plasma CVD of hydrogenated boron-carbon thin films from triethylboron

NASA Astrophysics Data System (ADS)

Imam, Mewlude; Höglund, Carina; Schmidt, Susann; Hall-Wilton, Richard; Birch, Jens; Pedersen, Henrik

2018-01-01

Low-temperature chemical vapor deposition (CVD) of B—C thin films is of importance for neutron voltaics and semiconductor technology. The highly reactive trialkylboranes, with alkyl groups of 1-4 carbon atoms, are a class of precursors that have been less explored for low-temperature CVD of B—C films. Herein, we demonstrate plasma CVD of B—C thin films using triethylboron (TEB) as a single source precursor in an Ar plasma. We show that the film density and B/C ratio increases with increasing plasma power, reaching a density of 2.20 g/cm3 and B/C = 1.7. This is attributed to a more intense energetic bombardment during deposition and more complete dissociation of the TEB molecule in the plasma at higher plasma power. The hydrogen content in the films ranges between 14 and 20 at. %. Optical emission spectroscopy of the plasma shows that BH, CH, C2, and H are the optically active plasma species from TEB. We suggest a plasma chemical model based on β-hydrogen elimination of C2H4 to form BH3, in which BH3 and C2H4 are then dehydrogenated to form BH and C2H2. Furthermore, C2H2 decomposes in the plasma to produce C2 and CH, which together with BH and possibly BH3-x(C2H5)x are the film forming species.

Are tomorrow's micro-supercapacitors hidden in a forest of silicon nanotrees?

NASA Astrophysics Data System (ADS)

Thissandier, Fleur; Gentile, Pascal; Brousse, Thierry; Bidan, Gérard; Sadki, Saïd

2014-12-01

Silicon nanotrees (SiNTrs) have been grown by Chemical Vapor Deposition (CVD) via gold catalysis and a three steps process: trunks and branches growth are separated by a new gold catalyst deposition. The influence of growth conditions and the second gold catalyst deposition method on SiNTrs morphology are investigated. SiNTrs based electrodes show a capacitive behavior and better capacitance than the corresponding silicon nanowires (SiNWs) electrode. Electrode capacitance is increased up to 900 μF cm-2, i.e. 150 fold higher than for bulk silicon. Micro-supercapacitors with SiNTrs electrodes have a remarkable stability (only 1.2% loses of their initial capacitance after more than one million cycles). The use of an ionic liquid based electrolyte leads to a high maximum power density (around 225 mW cm-2) which is competitive with Onion Like Carbon based micro-supercapacitors.

Chemical Vapor Deposition for Ultra-lightweight Thin-film Solar Arrays for Space

NASA Technical Reports Server (NTRS)

Hepp, Aloysius F.; Raffaelle, Ryne P.; Banger, Kulbinder K.; Jin, Michael H.; Lau, Janice E.; Harris, Jerry D.; Cowen, Jonathan E.; Duraj, Stan A.

2002-01-01

The development of thin-film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power, (W/kg). The use of a polycrystalline chalcopyrite absorber layer for thin film solar cells is considered as the next generation photovoltaic devices. A key technical issues outlined in the 2001 U.S. Photovoltaic Roadmap, is the need to develop low cost, high throughput manufacturing for high-efficiency thin film solar cells. At NASA GRC we have focused on the development of new single-source-precursors (SSPs) and their utility to deposit the chalcopyrite semi-conducting layer (CIS) onto flexible substrates for solar cell fabrication. The syntheses and thermal modulation of SSPs via molecular engineering is described. Thin-film fabrication studies demonstrate the SSPs can be used in a spray CVD process, for depositing CIS at reduced temperatures, which display good electrical properties, suitable for PV devices.

CVD aluminiding process for producing a modified platinum aluminide bond coat for improved high temperature performance

NASA Technical Reports Server (NTRS)

Nagaraj, Bangalore A. (Inventor); Williams, Jeffrey L. (Inventor)

2003-01-01

A method of depositing by chemical vapor deposition a modified platinum aluminide diffusion coating onto a superalloy substrate comprising the steps of applying a layer of a platinum group metal to the superalloy substrate; passing an externally generated aluminum halide gas through an internal gas generator which is integral with a retort, the internal gas generator generating a modified halide gas; and co-depositing aluminum and modifier onto the superalloy substrate. In one form, the modified halide gas is hafnium chloride and the modifier is hafnium with the modified platinum aluminum bond coat comprising a single phase additive layer of platinum aluminide with at least about 0.5 percent hafnium by weight percent and about 1 to about 15 weight percent of hafnium in the boundary between a diffusion layer and the additive layer. The bond coat produced by this method is also claimed.

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.

Mechanical design of thin-film diamond crystal mounting apparatus with optimized thermal contact and crystal strain for coherence preservation x-ray optics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shu, Deming; Shvydko, Yury; Stoupin, Stanislav

A method and mechanical design for a thin-film diamond crystal mounting apparatus for coherence preservation x-ray optics with optimized thermal contact and minimized crystal strain are provided. The novel thin-film diamond crystal mounting apparatus mounts a thin-film diamond crystal supported by a thick chemical vapor deposition (CVD) diamond film spacer with a thickness slightly thicker than the thin-film diamond crystal, and two groups of thin film thermal conductors, such as thin CVD diamond film thermal conductor groups separated by the thick CVD diamond spacer. The two groups of thin CVD film thermal conductors provide thermal conducting interface media with themore » thin-film diamond crystal. A piezoelectric actuator is integrated into a flexural clamping mechanism generating clamping force from zero to an optimal level.« less

Catalytic CVD synthesis of boron nitride and carbon nanomaterials - synergies between experiment and theory.

PubMed

McLean, Ben; Eveleens, Clothilde A; Mitchell, Izaac; Webber, Grant B; Page, Alister J

2017-10-11

Low-dimensional carbon and boron nitride nanomaterials - hexagonal boron nitride, graphene, boron nitride nanotubes and carbon nanotubes - remain at the forefront of advanced materials research. Catalytic chemical vapour deposition has become an invaluable technique for reliably and cost-effectively synthesising these materials. In this review, we will emphasise how a synergy between experimental and theoretical methods has enhanced the understanding and optimisation of this synthetic technique. This review examines recent advances in the application of CVD to synthesising boron nitride and carbon nanomaterials and highlights where, in many cases, molecular simulations and quantum chemistry have provided key insights complementary to experimental investigation. This synergy is particularly prominent in the field of carbon nanotube and graphene CVD synthesis, and we propose here it will be the key to future advances in optimisation of CVD synthesis of boron nitride nanomaterials, boron nitride - carbon composite materials, and other nanomaterials generally.

An efficient synthesis of graphenated carbon nanotubes over the tailored mesoporous molecular sieves by chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atchudan, R.; Department of Chemistry, CEG Campus, Anna University, Chennai 600025; Joo, Jin., E-mail: joojin@knu.ac.kr

2013-06-01

Highlights: ► Tailored 3D cubic Ni/KIT-6 with large pores was synthesized successfully. ► The new hybrid g-CNTs in large scale were synthesized using Ni/KIT-6 by CVD method. ► The use of mesoporous material by CVD method would be an ideal choice to prepare g-CNTs at reasonable cost. ► This type of g-CNTs might be a new avenue for nano-electronic applications. - Abstract: The new hybrid of graphenated carbon nanotubes (g-CNTs) was superior to either CNTs or graphene. Mesoporous 3D cubic Ni/KIT-6 were synthesized hydrothermally through organic template route and then were used as catalytic template for the production of g-CNTsmore » using acetylene as a carbon precursor by chemical vapor deposition (CVD) method. The deposited new hybrid carbon materials were purified and analyzed by various physico-chemical techniques such as XRD, TGA, SEM, TEM and Raman spectroscopy techniques. The graphitization of CNTs was confirmed by TGA and HRTEM studies. Thermal stability, surface morphology, and structural morphology of these materials were revealed by TGA, SEM and TEM analysis, respectively. Moreover, the tailored mesoporous Ni/KIT-6 molecular sieves were found to possess better quality and massive quantity of g-CNTs produced compared to other catalytic template route.« less

Upscaling high-quality CVD graphene devices to 100 micron-scale and beyond

NASA Astrophysics Data System (ADS)

Lyon, Timothy J.; Sichau, Jonas; Dorn, August; Zurutuza, Amaia; Pesquera, Amaia; Centeno, Alba; Blick, Robert H.

2017-03-01

We describe a method for transferring ultra large-scale chemical vapor deposition-grown graphene sheets. These samples can be fabricated as large as several cm2 and are characterized by magneto-transport measurements on SiO2 substrates. The process we have developed is highly effective and limits damage to the graphene all the way through metal liftoff, as shown in carrier mobility measurements and the observation of the quantum Hall effect. The charge-neutral point is shown to move drastically to near-zero gate voltage after a 2-step post-fabrication annealing process, which also allows for greatly diminished hysteresis.

Surface studies relevant to silicon carbide chemical vapor deposition

NASA Technical Reports Server (NTRS)

Stinespring, C. D.; Wormhoudt, J. C.

1989-01-01

Reactions of C2H4, C3H8, and CH4 on the Si(111) surface and C2H4 on the Si(100) surface were investigated for surface temperatures in the range of 1062-1495 K. Results led to the identification of the reaction products, a characterization of the solid-state transport process, a determination of the nucleation mechanism and growth kinetics, and an assessment of orientation effects. Based on these results and on the modeling studies of Stinespring and Wormhoudt (1988) on the associated gas phase chemistry, a physical model for the two-step beta-SiC CVD process is proposed.

Alkaline fuel cell with nitride membrane

NASA Astrophysics Data System (ADS)

Sun, Shen-Huei; Pilaski, Moritz; Wartmann, Jens; Letzkus, Florian; Funke, Benedikt; Dura, Georg; Heinzel, Angelika

2017-06-01

The aim of this work is to fabricate patterned nitride membranes with Si-MEMS-technology as a platform to build up new membrane-electrode-assemblies (MEA) for alkaline fuel cell applications. Two 6-inch wafer processes based on chemical vapor deposition (CVD) were developed for the fabrication of separated nitride membranes with a nitride thickness up to 1 μm. The mechanical stability of the perforated nitride membrane has been adjusted in both processes either by embedding of subsequent ion implantation step or by optimizing the deposition process parameters. A nearly 100% yield of separated membranes of each deposition process was achieved with layer thickness from 150 nm to 1 μm and micro-channel pattern width of 1μm at a pitch of 3 μm. The process for membrane coating with electrolyte materials could be verified to build up MEA. Uniform membrane coating with channel filling was achieved after the optimization of speed controlled dip-coating method and the selection of dimethylsulfoxide (DMSO) as electrolyte solvent. Finally, silver as conductive material was defined for printing a conductive layer onto the MEA by Ink-Technology. With the established IR-thermography setup, characterizations of MEAs in terms of catalytic conversion were performed successfully. The results of this work show promise for build up a platform on wafer-level for high throughput experiments.

Correlations between properties and applications of the CVD amorphous silicon carbide films

NASA Astrophysics Data System (ADS)

Kleps, Irina; Angelescu, Anca

2001-12-01

The aim of this paper is to emphasise the correlation between film preparation conditions, film properties and their applications. Low pressure chemical vapour deposition amorphous silicon carbide (a-SiC) and silicon carbonitride (SiCN) films obtained from liquid precursors have different structure and composition depending on deposition conditions. Thus, the films deposited under kinetic working conditions reveal a stable structure and composition. Deposition at moderate temperature leads to stoichiometric SiC, while the films deposited at high temperatures have a composition closer to Si 1- xC x, with x=0.75. These films form a very reactive interface with metallic layers. The films realised under kinetic working regime can be used in Si membrane fabrication process or as coating films for field emission applications. SiC layers field emission properties were investigated; the field emission current density of the a-SiC/Si structures was 2.4 mA/cm 2 at 25 V/μm. An Si membrane technology based on moderate temperatures (770-850 °C) a-SiC etching mask is presented.

Apparatus for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, P.L.; Giammarise, A.W.

1995-02-21

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice`s interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figs.

Apparatus for depositing hard coating in a nozzle orifice

DOEpatents

Flynn, Paul L.; Giammarise, Anthony W.

1995-01-01

The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

Measuring the proton selectivity of graphene membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker, Michael I.; Keyser, Ulrich F., E-mail: ufk20@cam.ac.uk; Braeuninger-Weimer, Philipp

2015-11-23

By systematically studying the proton selectivity of free-standing graphene membranes in aqueous solutions, we demonstrate that protons are transported by passing through defects. We study the current-voltage characteristics of single-layer graphene grown by chemical vapour deposition (CVD) when a concentration gradient of HCl exists across it. Our measurements can unambiguously determine that H{sup +} ions are responsible for the selective part of the ionic current. By comparing the observed reversal potentials with positive and negative controls, we demonstrate that the as-grown graphene is only weakly selective for protons. We use atomic layer deposition to block most of the defects inmore » our CVD graphene. Our results show that a reduction in defect size decreases the ionic current but increases proton selectivity.« less

Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

NASA Technical Reports Server (NTRS)

Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

1994-01-01

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

A beam radiation monitor based on CVD diamonds for SuperB

NASA Astrophysics Data System (ADS)

Cardarelli, R.; Di Ciaccio, A.

2013-08-01

Chemical Vapor Deposition (CVD) diamond particle detectors are in use in the CERN experiments at LHC and at particle accelerator laboratories in Europe, USA and Japan mainly as beam monitors. Nowadays it is considered a proven technology with a very fast signal read-out and a very high radiation tolerance suitable for measurements in high radiation environment zones i.e. near the accelerators beam pipes. The specific properties of CVD diamonds make them a prime candidate for measuring single particles as well as high-intensity particle cascades, for timing measurements on the sub-nanosecond scale and for beam protection systems in hostile environments. A single-crystalline CVD (scCVD) diamond sensor, read out with a new generation of fast and high transition frequency SiGe bipolar transistor amplifiers, has been tested for an application as radiation monitor to safeguard the silicon vertex tracker in the SuperB detector from excessive radiation damage, cumulative dose and instantaneous dose rates. Test results with 5.5 MeV alpha particles from a 241Am radioactive source and from electrons from a 90Sr radioactive source are presented in this paper.

Thermally Stable and Electrically Conductive, Vertically Aligned Carbon Nanotube/Silicon Infiltrated Composite Structures for High-Temperature Electrodes.

PubMed

Zou, Qi Ming; Deng, Lei Min; Li, Da Wei; Zhou, Yun Shen; Golgir, Hossein Rabiee; Keramatnejad, Kamran; Fan, Li Sha; Jiang, Lan; Silvain, Jean-Francois; Lu, Yong Feng

2017-10-25

Traditional ceramic-based, high-temperature electrode materials (e.g., lanthanum chromate) are severely limited due to their conditional electrical conductivity and poor stability under harsh circumstances. Advanced composite structures based on vertically aligned carbon nanotubes (VACNTs) and high-temperature ceramics are expected to address this grand challenge, in which ceramic serves as a shielding layer protecting the VACNTs from the oxidation and erosive environment, while the VACNTs work as a conductor. However, it is still a great challenge to fabricate VACNT/ceramic composite structures due to the limited diffusion of ceramics inside the VACNT arrays. In this work, we report on the controllable fabrication of infiltrated (and noninfiltrated) VACNT/silicon composite structures via thermal chemical vapor deposition (CVD) [and laser-assisted CVD]. In laser-assisted CVD, low-crystalline silicon (Si) was quickly deposited at the VACNT subsurfaces/surfaces followed by the formation of high-crystalline Si layers, thus resulting in noninfiltrated composite structures. Unlike laser-assisted CVD, thermal CVD activated the precursors inside and outside the VACNTs simultaneously, which realized uniform infiltrated VACNT/Si composite structures. The growth mechanisms for infiltrated and noninfiltrated VACNT/ceramic composites, which we attributed to the different temperature distributions and gas diffusion mechanism in VACNTs, were investigated. More importantly, the as-farbicated composite structures exhibited excellent multifunctional properties, such as excellent antioxidative ability (up to 1100 °C), high thermal stability (up to 1400 °C), good high velocity hot gas erosion resistance, and good electrical conductivity (∼8.95 Sm -1 at 823 K). The work presented here brings a simple, new approach to the fabrication of advanced composite structures for hot electrode applications.

Study of the interaction mechanisms between absorbed NO{sub 2} and por-Si/SnO{sub x} nanocomposite layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolotov, V. V.; Kan, V. E., E-mail: kan@obisp.oscsbras.ru; Makushenko, R. K.

2013-10-15

The interaction mechanisms between NO{sub 2} molecules and the surface of por-Si/SnO{sub x} nanocomposites obtained by magnetron deposition and chemical vapor deposition (CVD) are studied by infrared absorption spectroscopy and electron paramagnetic resonance methods. The observed increase in the free carrier concentration in the por-Si/SnO{sub x} nanocomposite layers is explained by a change in the charge state of P{sub b} centers due to the formation of neutral 'surface defect-adsorbed NO{sub 2} molecule' complexes with free carrier generation in the crystallite bulk. In the nanocomposite layers grown by the CVD method, the increase in the free hole concentration during NO{sub 2}more » adsorption is much less pronounced in comparison with the composite grown by magnetron deposition, which is caused by the competing interaction channel of NO{sub 2} molecules with electrically neutral P{sub b} centers.« less

Approaching the resolution limit of W-C nano-gaps using focused ion beam chemical vapour deposition

NASA Astrophysics Data System (ADS)

Dai, Jun; Chang, Hui; Maeda, Etsuo; Warisawa, Shin'ichi; Kometani, Reo

2018-01-01

Nano-gaps are fundamental building blocks for nanochannels, plasmonic nanostructures and superconducting Josephson junctions. We present a systematic study on the formation mechanism and resolution limit of W-C nano-gaps fabricated using focused-ion-beam chemical vapour deposition (FIB-CVD). First, the deposition size of the nanostructures is evaluated. The size averaged over 100 dots is 32 nm at FWHM. Line and space are also fabricated with the smallest size, having a spacing of only 5 nm at FWHM. Then, a model is developed to study the formation mechanism and provides the design basis for W-C nano-gaps. Both experimental and simulation results reveal that the shrinkage of W-C nano-gaps is accelerated as the Gaussian parts of the nano-wire profiles overlap. A Nano-gap with a length of 5 nm and height difference as high as 42 nm is synthesized. We believe that FIB-CVD opens avenues for novel functional nanodevices that can be potentially used for biosensing, photodetecting, or quantum computing.

Study of the Physics of Insulating Films as Related to the Reliability of Metal-Oxide Semiconductor Devices

DTIC Science & Technology

1980-05-01

York 10598 Technical assistance of F.L. Pesavento and J.A. Calse Typed by Steila B. Havreluk (3277) Abstract: Chemically vapor deposited (CVD) Si rich...wish to acknowledge the critical reading of this manuscript by D.R. Young and M.I. Nathan; the technical assistance of F.L. Pesavento and L.A. Calise...rendered by J.A. Calise and F.L. Pesavento . Samples have been prepared by the I.B.M. Yorktown Si Process Facility and the work has been supported in part

Self-heating and failure in scalable graphene devices

DOE PAGES

Beechem, Thomas E.; Shaffer, Ryan A.; Nogan, John; ...

2016-06-09

Self-heating induced failure of graphene devices synthesized from both chemical vapor deposition (CVD) and epitaxial means is compared using a combination of infrared thermography and Raman imaging. Despite a larger thermal resistance, CVD devices dissipate >3x the amount of power before failure than their epitaxial counterparts. The discrepancy arises due to morphological irregularities implicit to the graphene synthesis method that induce localized heating. As a result, morphology, rather than thermal resistance, therefore dictates power handling limits in graphene devices.

The Oxidation of CVD Silicon Carbide in Carbon Dioxide

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Nguyen, QuynchGiao N.

1997-01-01

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

Depressed scattering across grain boundaries in single crystal graphene

NASA Astrophysics Data System (ADS)

Chen, Jiao; Jin, Zhi; Ma, Peng; Wang, Hong; Wang, Haomin; Shi, Jingyuan; Peng, Songang; Liu, Xinyu; Ye, Tianchun

2012-10-01

We investigated the electrical and quantum properties of single-crystal graphene (SCG) synthesized by chemical vapor deposition (CVD). Quantum Hall effect and Shubnikov de Hass oscillation, a distinguishing feature of a 2-dimensional electronic material system, were observed during the low temperature transport measurements. Decreased scattering from grain boundaries in SCG was proven through extracting information from weak localization theory. Our results facilitate understanding the electrical properties of SCG grown by CVD and its applications in high speed transistor and quantum devices.

Status of the R&D activity on diamond particle detectors

NASA Astrophysics Data System (ADS)

Adam, W.; Bellini, B.; Berdermann, E.; Bergonzo, P.; de Boer, W.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Doroshenko, J.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fischer, P.; Fizzotti, F.; Furetta, C.; Gan, K. K.; Ghodbane, N.; Grigoriev, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kaplon, J.; Karl, C.; Kass, R.; Keil, M.; Knöpfle, K. T.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; mac Lynne, L.; Manfredotti, C.; Marshall, R. D.; Meier, D.; Menichelli, D.; Meuser, S.; Mishina, M.; Moroni, L.; Noomen, J.; Oh, A.; Perera, L.; Pernicka, M.; Polesello, P.; Potenza, R.; Riester, J. L.; Roe, S.; Rudge, A.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Sutera, C.; Trischuk, W.; Tromson, D.; Tuve, C.; Weilhammer, P.; Wermes, N.; Wetstein, M.; Zeuner, W.; Zoeller, M.; RD42 Collaboration

2003-09-01

Chemical Vapor Deposited (CVD) polycrystalline diamond has been proposed as a radiation-hard alternative to silicon in the extreme radiation levels occurring close to the interaction region of the Large Hadron Collider. Due to an intense research effort, reliable high-quality polycrystalline CVD diamond detectors, with up to 270 μm charge collection distance and good spatial uniformity, are now available. The most recent progress on the diamond quality, on the development of diamond trackers and on radiation hardness studies are presented and discussed.

High-efficiency solar cells fabricated by vacuum MO-CVD

NASA Technical Reports Server (NTRS)

Fraas, L. M.; Cape, J. A.; Partain, L. D.; Mcleod, P. S.

1984-01-01

High-efficiency, monolithic, two-color, three-terminal solar cells were fabricated by a novel growth technique, vacuum metal-organic chemical vapor deposition. The technique uses the expensive metal alkyls efficiently and toxic gases sparingly. The fact that the outer chamber is constructed of nonbreakable stainless steel is an attractive safety feature associated with this deposition system.

X Ray Mask Of Gold-Carbon Mixture Absorber On BCN Compound Substrate Fabricated By Plasma Processes

NASA Astrophysics Data System (ADS)

Aiyer, Chandrasekhar R.; Itoh, Satoshi; Yamada, Hitomi; Morita, Shinzo; Hattori, Shuzo

1988-06-01

X-ray mask fabrication based on BCN compound membrane and gold containing polymeric carbon ( Au-C ) absorber by totally dry processes is proposed. The Au-C films were depo-sited by plasma polymerization of propylene or styrene monomers and co-evaporation of gold. These films have 2 to 5 times higher etching rate than that of pure gold for 09 RIE, depending on the Au content. The stress in the films could be reduced to 1.9 E 7 N/m2 by annealing. The BCN films were deposited on silicon wafers by rf (13.56 MHz) plasma CVD with diborane, methane and nitrogen as source gases at typical deposition rate of 30 nm/min. The optical (633nm) and X ray (Pd L~) transparencies were nearly 80% for film thickness of 6 um. Patterning of Au-C was achieved by using tungsten as intermediate layer and PMMA electron beam resist. CF4 RIE was used to etch the tungsten layer which in turn acted as mask for the gold carbide 02 RIE. The process parameters and the characteristics of the Au-C and BCN films are presented.

Synthesis and properties of SiN coatings as stable fluorescent markers on vertically aligned carbon nanofibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearce, Ryan; Klein, Kate L; Ivanov, Ilia N

2014-01-01

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains mostly Si and N. In fluorescent microscopy experiments, imaging VACNF interfacing to live cell cultures it turned out that this material is broadly fluorescent, which made VACNFs useful as spatial markers, or created nuisance when DNA-labeling got masked. In this paper we provide insight into nature of this silicon/nitrogen in situ coatings. Here we have proposed a potential mechanism for deposition of SiNx coating on the sidewalls of VACNFs during PECVD synthesismore » in addition to exploring the origin of the coatings fluorescence. It seems most likely that the substrate reacts with the process gases through both processes similar to reactive sputtering and CVD to form silane and other silicon bearing compounds before being deposited isotropically as a SiNx coating onto the VACNFs. The case for the presence of Si-NCs is made strong through a combination of the strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies.« less

Synthesis of length-controlled aerosol carbon nanotubes and their dispersion stability in aqueous solution.

PubMed

Moon, Young Kyun; Lee, Jaebeom; Lee, Jae Keun; Kim, Tae Kyu; Kim, Soo H

2009-02-03

A one-step method combining spray pyrolysis and thermal chemical vapor deposition (CVD) processes was developed to grow hybrid carbon nanotube (CNT)-bimetallic composite particles. Nickel, aluminum, and acetylene were used as the catalytic site, noncatalytic matrix, and hydrocarbon source, respectively. The bimetallic particles (i.e., Al-Ni) were spray pyrolized and subsequently passed through thermal CVD. During the thermal CVD, the catalytic decomposition of acetylene occurred on the free-floating bimetallic particles so that sea urchin-like CNTs were radially grown. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed the CNTs to have a uniform diameter of approximately 10 +/- 2 nm. The length of the CNTs was controlled by varying the residence time of the bimetallic nanoparticles with a length of 200-1000 nm. After nitric acid treatment, the CNTs were released by melting the bimetallic particles. The resulting CNTs were then dispersed in an aqueous solution to examine the effect of the length of CNTs on their dispersion stability, which is a critical issue for the stability and repeatability of the heat transfer performance in nanofluids. Ultraviolet-visible (UV-vis) spectrometer analysis showed that shorter CNTs were less stable than the longer CNTs due to the higher mobility-induced agglomeration of the shorter CNTs.

CVD growth of large-area and high-quality HfS2 nanoforest on diverse substrates

NASA Astrophysics Data System (ADS)

Zheng, Binjie; Wang, Zegao; Qi, Fei; Wang, Xinqiang; Yu, Bo; Zhang, Wanli; Chen, Yuanfu

2018-03-01

Two-dimensional layered transition metal dichalcogenides (TMDs) have attracted burgeoning attention due to their various properties and wide potential applications. As a new TMD, hafnium disulfide (HfS2) is theoretically predicted to have better electrical performance than widely studied MoS2. The experimental researches also confirmed the extraordinary feature in electronics and optoelectronics. However, the maximal device performance may not be achieved due to its own limitation of planar structure and challenge of transfer without contamination. Here, through the chemical vapor deposition (CVD) technique, inch-size HfS2 nanoforest has been directly grown on diverse objective substrates covering insulating, semiconducting and conducting substrates. This direct CVD growth without conventional transfer process avoids contamination and degradation in quality, suggesting its promising and wide applications in high-quality and multifarious devices. It is noted that all the HfS2 nanoforests grown on diverse substrates are constructed with vertically aligned few-layered HfS2 nanosheets with high crystalline quality and edge orientation. Moreover, due to its unique structure, the HfS2 nanoforest owns abundant exposed edge sites and large active surface area, which is essential to apply in high-performance catalyst, sensor, and energy storage or field emitter.

Ultrathin Nanocrystalline Diamond Films with Silicon Vacancy Color Centers via Seeding by 2 nm Detonation Nanodiamonds.

PubMed

Stehlik, Stepan; Varga, Marian; Stenclova, Pavla; Ondic, Lukas; Ledinsky, Martin; Pangrac, Jiri; Vanek, Ondrej; Lipov, Jan; Kromka, Alexander; Rezek, Bohuslav

2017-11-08

Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5-6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4-6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 10 13 cm -2 ), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiO x substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

Alternative group V precursors for CVD applications

NASA Astrophysics Data System (ADS)

Lum, R. M.; Klingert, J. K.

1991-01-01

The chemical vapor deposition (CVD) techniques used to grow III/V semiconductors films, such as metalorganic vapor phase epitaxy (MOVPE), hydride VPE, chemical beam epitaxy (CBE) and gas source molecular beam epitaxy (GS-MBE), all use hydrides (AsH 3 and PH 3) as the Group V source. However, the hydrides are extremely toxic gases which are stored under high pressure (200-2000 psi). To reduce the safety hazards associated with these gases, alternative Group V precursors have been investigated. Organoarsenic and phosphorous compounds have received the most attention as replacements for AsH 3 and PH 3 because they are typically low vapor pressure liquids, and thus present significantly lower exposure risks than the hydrides. For AsH 3 these have included the methyl, ethyl and butyl-based derivatives RnAsH 3- n, with varying degrees ( n = 1-3) of hydrogen atom substitution. In this paper the growth properties, thermochemistry and toxicity of the various alkylarsine precursors are compared with arsine. Data are presented on the impact of the thermochemistry of these compounds on film electrical properties, and on the effects of precursor composition and purity on overall film quality. The suitability of alternative As-precursors for device applications is demonstrated, and selection criteria are presented for the most effective alkylarsine compound for a particular CVD growth process.

Creep and Rupture Strength of an Advanced CVD SiC Fiber

NASA Technical Reports Server (NTRS)

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

1997-01-01

In the as-produced condition the room temperature strength (approx. 6 GPa) of Textron Specialty Materials' 50 microns CVD SiC fiber represents the highest value thus far obtained for commercially produced polycrystalline SiC fibers. To understand whether this strength can be maintained after composite processing conditions, high temperature studies were performed on the effects of time, stress, and environment on 1400 deg. C tensile creep strain and stress rupture on as-produced, chemically vapor deposited SiC fibers. Creep strain results were consistent, allowing an evaluation of time and stress effects. Test environment had no influence on creep strain but I hour annealing at 1600 deg. C in argon gas significantly reduced the total creep strain and increased the stress dependence. This is attributed to changes in the free carbon morphology and its distribution within the CVD SiC fiber. For the as-produced and annealed fibers, strength at 1400 deg. C was found to decrease from a fast fracture value of 2 GPa to a 100-hr rupture strength value of 0. 8 GPa. In addition a loss of fast fracture strength from 6 GPa is attributed to thermally induced changes in the outer carbon coating and microstructure. Scatter in rupture times made a definitive analysis of environmental and annealing effects on creep strength difficult.

Localized growth of carbon nanotubes via lithographic fabrication of metallic deposits

PubMed Central

Tu, Fan; Drost, Martin; Szenti, Imre; Kiss, Janos; Kónya, Zoltan

2017-01-01

We report on the fabrication of carbon nanotubes (CNTs) at predefined positions and controlled morphology, for example, as individual nanotubes or as CNT forests. Electron beam induced deposition (EBID) with subsequent autocatalytic growth (AG) was applied to lithographically produce catalytically active seeds for the localized growth of CNTs via chemical vapor deposition (CVD). With the precursor Fe(CO)5 we were able to fabricate clean iron deposits via EBID and AG. After the proof-of-principle that these Fe deposits indeed act as seeds for the growth of CNTs, the influence of significant EBID/AG parameters on the deposit shape and finally the yield and morphology of the grown CNTs was investigated in detail. Based on these results, the parameters could be optimized such that EBID point matrixes (6 × 6) were fabricated on a silica surface whereby at each predefined site only one CNT was produced. Furthermore, the localized fabrication of CNT forests was targeted and successfully achieved on an Al2O3 layer on a silicon sample. A peculiar lift-up of the Fe seed structures as “flakes” was observed and the mechanism was discussed. Finally, a proof-of-principle was presented showing that EBID deposits from the precursor Co(CO)3NO are also very effective catalysts for the CNT growth. Even though the metal content (Co) of the latter is reduced in comparison to the Fe deposits, effective CNT growth was observed for the Co-containing deposits at lower CVD temperatures than for the corresponding Fe deposits. PMID:29259874

Nanocrystalline diamond micro-anvil grown on single crystal diamond as a generator of ultra-high pressures

DOE PAGES

Samudrala, Gopi K.; Moore, Samuel L.; Velisavljevic, Nenad; ...

2016-09-29

By combining mask-less lithography and chemical vapor deposition (CVD) techniques, a novel two-stage diamond anvil has been fabricated. A nanocrystalline diamond (NCD) micro-anvil 30 μm in diameter was grown at the center of a [100]-oriented, diamond anvil by utilizing microwave plasma CVD method. The NCD micro-anvil has a diamond grain size of 115 nm and micro-focused Raman and X-ray Photoelectron spectroscopy analysis indicate sp3-bonded diamond content of 72%. Lastly, these CVD grown NCD micro-anvils were tested in an opposed anvil configuration and the transition metals osmium and tungsten were compressed to high pressures of 264 GPa in a diamond anvilmore » cell.« less

Charging effect at grain boundaries of MoS2

NASA Astrophysics Data System (ADS)

Yan, Chenhui; Dong, Xi; Li, Connie H.; Li, Lian

2018-05-01

Grain boundaries (GBs) are inherent extended defects in chemical vapor deposited (CVD) transition metal dichalcogenide (TMD) films. Characterization of the atomic structure and electronic properties of these GBs is crucial for understanding and controlling the properties of TMDs via defect engineering. Here, we report the atomic and electronic structure of GBs in CVD grown MoS2 on epitaxial graphene/SiC(0001). Using scanning tunneling microscopy/spectroscopy, we find that GBs mostly consist of arrays of dislocation cores, where the presence of mid-gap states shifts both conduction and valence band edges by up to 1 eV. Our findings demonstrate the first charging effect near GBs in CVD grown MoS2, providing insights into the significant impact GBs can have on materials properties.

Diamond detectors for high energy physics experiments

NASA Astrophysics Data System (ADS)

Bäni, L.; Alexopoulos, A.; Artuso, M.; Bachmair, F.; Bartosik, M.; Beacham, J.; Beck, H.; Bellini, V.; Belyaev, V.; Bentele, B.; Berdermann, E.; Bergonzo, P.; Bes, A.; Brom, J.-M.; Bruzzi, M.; Cerv, M.; Chiodini, G.; Chren, D.; Cindro, V.; Claus, G.; Collot, J.; Cumalat, J.; Dabrowski, A.; D'Alessandro, R.; Dauvergne, D.; de Boer, W.; Dorfer, C.; Dünser, M.; Eremin, V.; Eusebi, R.; Forcolin, G.; Forneris, J.; Frais-Kölbl, H.; Gallin-Martel, L.; Gallin-Martel, M. L.; Gan, K. K.; Gastal, M.; Giroletti, C.; Goffe, M.; Goldstein, J.; Golubev, A.; Gorišek, A.; Grigoriev, E.; Grosse-Knetter, J.; Grummer, A.; Gui, B.; Guthoff, M.; Haughton, I.; Hiti, B.; Hits, D.; Hoeferkamp, M.; Hofmann, T.; Hosslet, J.; Hostachy, J.-Y.; Hügging, F.; Hutton, C.; Jansen, H.; Janssen, J.; Kagan, H.; Kanxheri, K.; Kasieczka, G.; Kass, R.; Kassel, F.; Kis, M.; Konovalov, V.; Kramberger, G.; Kuleshov, S.; Lacoste, A.; Lagomarsino, S.; Lo Giudice, A.; Lukosi, E.; Maazouzi, C.; Mandic, I.; Mathieu, C.; Menichelli, M.; Mikuž, M.; Morozzi, A.; Moss, J.; Mountain, R.; Murphy, S.; Muškinja, M.; Oh, A.; Oliviero, P.; Passeri, D.; Pernegger, H.; Perrino, R.; Picollo, F.; Pomorski, M.; Potenza, R.; Quadt, A.; Re, A.; Reichmann, M.; Riley, G.; Roe, S.; Sanz, D.; Scaringella, M.; Schaefer, D.; Schmidt, C. J.; Schnetzer, S.; Sciortino, S.; Scorzoni, A.; Seidel, S.; Servoli, L.; Smith, S.; Sopko, B.; Sopko, V.; Spagnolo, S.; Spanier, S.; Stenson, K.; Stone, R.; Sutera, C.; Tannenwald, B.; Taylor, A.; Traeger, M.; Tromson, D.; Trischuk, W.; Tuve, C.; Uplegger, L.; Velthuis, J.; Venturi, N.; Vittone, E.; Wagner, S.; Wallny, R.; Wang, J. C.; Weingarten, J.; Weiss, C.; Wengler, T.; Wermes, N.; Yamouni, M.; Zavrtanik, M.

2018-01-01

Beam test results of the radiation tolerance study of chemical vapour deposition (CVD) diamond against different particle species and energies is presented. We also present beam test results on the independence of signal size on incident particle rate in charged particle detectors based on un-irradiated and irradiated poly-crystalline CVD diamond over a range of particle fluxes from 2 kHz/cm2 to 10 MHz/cm2. The pulse height of the sensors was measured with readout electronics with a peaking time of 6 ns. In addition functionality of poly-crystalline CVD diamond 3D devices was demonstrated in beam tests and 3D diamond detectors are shown to be a promising technology for applications in future high luminosity experiments.

Rheumatologist and Primary Care Management of Cardiovascular Disease Risk in Rheumatoid Arthritis: Patient and Provider Perspectives.

PubMed

Bartels, Christie M; Roberts, Tonya J; Hansen, Karen E; Jacobs, Elizabeth A; Gilmore, Andrea; Maxcy, Courtney; Bowers, Barbara J

2016-04-01

Despite increased cardiovascular disease (CVD) risk, rheumatoid arthritis (RA) patients often lack CVD preventive care. We examined CVD preventive care processes from RA patient and provider perspectives to develop a process map for identifying targets for future interventions to improve CVD preventive care. Thirty-one participants (15 patients, 7 rheumatologists, and 9 primary care physicians [PCPs]) participated in interviews that were coded using NVivo software and analyzed using grounded theory techniques. Patients and providers reported that receipt of preventive care depends upon identifying and acting on risk factors, although most noted that both processes rarely occurred. Engagement in these processes was influenced by various provider-, system-, visit-, and patient-related conditions, such as patient activation or patients' knowledge about their risk. While nearly half of patients and PCPs were unaware of RA-CVD risk, all rheumatologists were aware of risk. Rheumatologists reported not systematically identifying risk factors, or, if identified, they described communicating about CVD risk factors via clinic notes to PCPs instead of acting directly due to perceived role boundaries. PCPs suggested that scheduling PCP visits could improve CVD risk management, and all participants viewed comanagement positively. Findings from this study illustrate important gaps and opportunities to support identifying and acting on CVD risk factors in RA patients from the provider, system, visit, and patient levels. Future work should investigate professional role support through improved guidelines, patient activation, and system-based RA-CVD preventive care strategies. © 2016, American College of Rheumatology.

Interwell coupling effect in Si/SiGe quantum wells grown by ultra high vacuum chemical vapor deposition

PubMed Central

Wang, Rui; Lu, Fen; Fan, Wei Jun; Liu, Chong Yang; Loh, Ter-Hoe; Nguyen, Hoai Son; Narayanan, Balasubramanian

2007-01-01

Si/Si0.66Ge0.34coupled quantum well (CQW) structures with different barrier thickness of 40, 4 and 2 nm were grown on Si substrates using an ultra high vacuum chemical vapor deposition (UHV-CVD) system. The samples were characterized using high resolution x-ray diffraction (HRXRD), cross-sectional transmission electron microscopy (XTEM) and photoluminescence (PL) spectroscopy. Blue shift in PL peak energy due to interwell coupling was observed in the CQWs following increase in the Si barrier thickness. The Si/SiGe heterostructure growth process and theoretical band structure model was validated by comparing the energy of the no-phonon peak calculated by the 6 + 2-bandk·pmethod with experimental PL data. Close agreement between theoretical calculations and experimental data was obtained.

Low temperature ECR-CVD of SiN X for III-V device passivation

NASA Astrophysics Data System (ADS)

Lee, J. W.; MacKenzie, K.; Johnson, D.; Shul, R. J.; Pearton, S. J.; Ren, F.

1998-06-01

Electron Cyclotron Resonance SiH 4/N 2 and SiH 4/NH 3 discharges have been employed for deposition of SiN X over a range of temperatures (25-120°C), source powers (200-700 W), pressures (15-40 mTorr), SiH 4 percentages (20-50%) and additional Ar flow rates (0-30 sccm). Deposition rates were in the range 100-700 Å min -1, with refractive indices of 1.7-2.3. The SiH 4/N 2 chemistry allowed a wider process window for tailoring the stress in the SiN X films, with chuck temperature, ECR source power, chamber pressure, SiH 4 composition and Ar addition all producing a transition from compressive to tensile stress, or vice-versa.

Optical fiber characteristics and standards; Proceedings of the Meeting, Cannes, France, November 25-27, 1985

NASA Technical Reports Server (NTRS)

Bouillie, Remy (Editor)

1986-01-01

Papers are presented on outside vapor deposition, the plasma activated CVD process for large scale production of telecommunication fibers, axial lateral plasma deposition technology from plastic clad silica, coatings for optical fibers, primary coating characterization, and radiation-induced time dependent attenuation in a fiber. Topics discussed include fibers with high tensile strength, the characteristics and specifications of airborne fiber optic components, the baseband frequency response of multimode fibers, and fibers for local and broadband networks. Consideration is given to industrial measurements for single mode and multimode fibers, the characterization of source power distribution in a multimode fiber by a splice offset technique, the measurement of chromatic dispersion in a single mode optical, and the effect of temperature on the refracted near-field optical fiber profiling technique.

Niobium-germanium superconducting tapes for high-field magnet applications

NASA Technical Reports Server (NTRS)

Braginski, A. I.; Roland, G. W.; Daniel, M. R.; Woolam, J. A.

1977-01-01

A process of fabricating superconducting Nb3Ge tapes by chemical vapor deposition (CVD) has been developed and tapes up to 10 meters long fabricated. The typical properties achieved were: critical temperature T sub c = 20 K, upper critical field H sub c2 = 29 tesla at 4.2 K, and J sub c = 3 to 4 x 10 to the 8th power A m(-2) at 4.2 K, 18 tesla. The relative depression of T sub c and H sub c2 compared with the best thin film samples sputtered on sapphire was due to the presence of Nb5Ge3 second-phase particles used as flux pinning centers and to strains induced by thermal mixmatch with Hastelloy B tape substrates. A peculiar field dependence of flux pinning force that was observed in both CVD and sputtered Nb3Ge indicated a premature pin-breaking mechanism or a phase inhomogeneity. Directions of further optimization work were defined.

Effects of gas flow rate on the etch characteristics of a low- k sicoh film with an amorphous carbon mask in dual-frequency CF4/C4F8/Ar capacitively-coupled plasmas

NASA Astrophysics Data System (ADS)

Kwon, Bong-Soo; Lee, Hea-Lim; Lee, Nae-Eung; Kim, Chang-Young; Choi, Chi Kyu

2013-01-01

Highly selective nanoscale etching of a low-dielectric constant (low- k) organosilicate (SiCOH) layer using a mask pattern of chemical-vapor-deposited (CVD) amorphous carbon layer (ACL) was carried out in CF4/C4F8/Ar dual-frequency superimposed capacitively-coupled plasmas. The etching characteristics of the SiCOH layers, such as the etch rate, etch selectivity, critical dimension (CD), and line edge roughness (LER) during the plasma etching, were investigated by varying the C4F8 flow rate. The C4F8 gas flow rate primarily was found to control the degree of polymerization and to cause variations in the selectivity, CD and LER of the patterned SiCOH layer. Process windows for ultra-high etch selectivity of the SiCOH layer to the CVD ACL are formed due to the disproportionate degrees of polymerization on the SiCOH and the ACL surfaces.

New CVD-based method for the growth of high-quality crystalline zinc oxide layers

NASA Astrophysics Data System (ADS)

Huber, Florian; Madel, Manfred; Reiser, Anton; Bauer, Sebastian; Thonke, Klaus

2016-07-01

High-quality zinc oxide (ZnO) layers were grown using a new chemical vapour deposition (CVD)-based low-cost growth method. The process is characterized by total simplicity, high growth rates, and cheap, less hazardous precursors. To produce elementary zinc vapour, methane (CH4) is used to reduce a ZnO powder. By re-oxidizing the zinc with pure oxygen, highly crystalline ZnO layers were grown on gallium nitride (GaN) layers and on sapphire substrates with an aluminum nitride (AlN) nucleation layer. Using simple CH4 as precursor has the big advantage of good controllability and the avoidance of highly toxic gases like nitrogen oxides. In photoluminescence (PL) measurements the samples show a strong near-band-edge emission and a sharp line width at 5 K. The good crystal quality has been confirmed in high resolution X-ray diffraction (HRXRD) measurements. This new growth method has great potential for industrial large-scale production of high-quality single crystal ZnO layers.

Synthesis Methods of Carbon Nanotubes and Related Materials

PubMed Central

Szabó, Andrea; Perri, Caterina; Csató, Anita; Giordano, Girolamo; Vuono, Danilo; Nagy, János B.

2010-01-01

The challenge on carbon nanotubes is still the subject of many research groups. While in the first years the focus was on the new synthesis methods, new carbon sources and support materials, recently, the application possibilities are the principal arguments of the studies. The three main synthesis methods discussed in this review are the arc discharge, the laser ablation and the chemical vapour deposition (CVD) with a special regard to the latter one. In the early stage of the nanotube production the first two methods were utilized mainly for the production of SWNTs while the third one produced mainly MWNTs. The principle of CVD is the decomposition of various hydrocarbons over transition metal supported catalyst. Single-walled (SWNT), multi-walled (MWNT) and coiled carbon nanotubes are produced. In some case, interesting carbonaceous materials are formed during the synthesis process, such as bamboo-like tubes, onions, horn-like structures. In this paper, we refer to the progresses made in the field of the synthesis techniques of carbon nanotubes in the last decade.

Thermoelectric properties of CVD grown large area graphene

NASA Astrophysics Data System (ADS)

Sherehiy, Andriy; Jayasinghe, Ruwantha; Stallard, Robert; Sumanasekera, Gamini; Sidorov, Anton; Benjamin, Daniel; Jiang, Zhigang; Yu, Qingkai; Wu, Wei; Bao, Jiming; Liu, Zhihong; Pei, Steven; Chen, Yong

2010-03-01

The thermoelectric power (TEP) of CVD (Chemical Vapor Deposition) grown large area graphene transferred onto a Si/SiO2 substrate was measured by simply attaching two miniature thermocouples and a resistive heater. Availability of such large area graphene facilitates straight forward TEP measurement without the use of any microfabrication processes. All investigated graphene samples showed a positive TEP ˜ + 30 μV/K in ambient conditions and saturated at a negative value as low as ˜ -75 μV/K after vacuum-annealing at 500 K in a vacuum of ˜10-7 Torr. The observed p-type behavior under ambient conditions is attributed to the oxygen doping, while the n-type behavior under degassed conditions is due to electron doping from SiO2 surface states. It was observed that the sign of the TEP switched from negative to positive for the degassed graphene when exposed to acceptor gases. Conversely, the TEP of vacuum-annealed graphene exposed to the donor gases became even more negative than the TEP of vacuum-annealed sample.

Synthesis, characterization and oxidation of metallic cobalt (Co) thin film into semiconducting cobalt oxide (Co3O4)thin film using microwave plasma CVD

NASA Astrophysics Data System (ADS)

Rahman Ansari, Akhalakur; Hussain, Shahir; Imran, Mohd; Abdel-wahab, M. Sh; Alshahrie, Ahmed

2018-06-01

The pure cobalt thin film was deposited on the glass substrate by using DC magnetron sputtering and then exposed to microwave assist oxygen plasma generated in microwave plasma CVD. The oxidation process of Co thin film into Co3O4 thin films with different microwave power and temperature were studied. The influences of microwave power, temperature and irradiation time were investigated on the morphology and particle size of oxide thin films. The crystal structure, chemical conformation, morphologies and optical properties of oxidized Co thin films (Co3O4) were studied by using x-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Raman Spectroscopy and UV–vis Spectroscopy. The data of these films showed complete oxidation pure metallic cobalt (Co) into cobalt oxide (Co3O4). The optical properties were studied for calculating the direct band gaps which ranges from 1.35 to 1.8 eV.

Fabrication of nanostructured metal oxide films with supercritical carbon dioxide: Processing and applications

NASA Astrophysics Data System (ADS)

You, Eunyoung

Nanostructured metal oxide films have many applications in catalysis, microelectronics, microfluidics, photovoltaics and other fields. Since the performance of a device depends greatly on the structure of the material, the development of methodologies that enable prescriptive control of morphology are of great interest. The focus of this work is to control the structure and properties of the nanostructured metal oxide films using novel synthetic schemes in supercritical fluids and to use those films as key building components in alternative energy applications. A supercritical fluid is a substance at a temperature and pressure above its critical point. It typically exhibits gas-like transport properties and liquid-like densities. Supercritical fluid deposition (SFD) utilizes these properties of supercritical CO2 (scCO2) to deposit chemically pure metal, oxides and alloys of metal films. SFD is a chemical vapor deposition (CVD)-like process in the sense that it uses similar metal organic precursors and deposits films at elevated temperatures. Instead of vaporizing or subliming the precursors, they are dissolved in supercritical fluids. SFD has typically shown to exhibit higher precursor concentrations, lower deposition temperatures, conformal deposition of films on high aspect ratio features as compared to CVD. In2 O3, ZnO and SnO2 are attractive materials because they are used in transparent conductors. SFD of these materials were studied and In2 O3 deposition kinetics using tris(2,2,6,6-tetramethyl-3,5-heptanedionato) In (III) as precursor were determined. Growth rate dependence on the deposition temperature and the precursor concentrations were studied and the physicochemical and optical properties of In2 O3 films were characterized. Metal oxide nanochannels that can potentially be used for microfluidics have been fabricated by sequentially performing nanoimprint lithography (NIL) and SFD. NIL was used to pattern photoresist grating on substrates and SFD of TiO2 was performed thereafter. Subsequent calcination of the samples at high temperature of 400 °C revealed TiO2 nanochannels. H2-assisted-codeposition of Pt and cerium oxide using SFD was performed on porous carbon substrates for their use as anodes for direct methanol fuel cells. X-ray photoelectron analysis revealed that Pt was deposited as a pure metal and Ce was deposited as an oxide. Electrochemical analysis of a full cell revealed that an anode prepared with SFD exhibited better performance than that prepared with conventional brush-painting method. The second process that was developed is a direct spray-on technique to rapidly deposit crystalline nanoscale dendritic TiO2 onto a solid surface. This technique employs atomization of precursor solutions in supercritical fluids combined with the plasma thermal spraying. A solution of metal oxide precursor in scCO2 was expanded across a nozzle into the plasma jet where it is converted to metal oxide. We have investigated TiO2 as our model system using titanium tetra isopropoxide (Ttip) as a precursor. The film structure depends on key process variables including precursor concentration, precursor solution flow rate and plasma gun to substrate distance. The high surface area of the deposited films is attractive for applications in photovoltaics and we have fabricated dye-sensitized solar cells using these films.

Scattering of low-energetic atoms and molecules from a boron-doped CVD diamond surface

NASA Astrophysics Data System (ADS)

Allenbach, M.; Neuland, M. B.; Riedo, A.; Wurz, P.

2018-01-01

For the detection of low energetic neutral atoms for the remote sensing of space plasmas, charge state conversion surfaces are used to ionize the neutrals for their subsequent measurement. We investigated a boron-doped Chemical Vapor Deposition (CVD) diamond sample for its suitability to serve as a conversion surface on future space missions, such as NASA's Interstellar Mapping and Acceleration Probe. For H and O atoms incident on conversion surface with energies ranging from 195 to 1000 eV and impact angles from 6° to 15° we measured the angular scattering distributions and the ionization yields. Atomic force microscope and laser ablation ionization mass spectrometry analyses were applied to further characterize the sample. Based on a figure-of-merit, which included the ionization yield and angular scatter distribution, the B-doped CVD surface was compared to other, previously characterized conversion surfaces, including e.g. an undoped CVD diamond with a metallized backside. For particle energies below 390 eV the performance of the B-doped CVD conversion surfaces is comparable to surfaces studied before. For higher energies the figure-of-merit indicates a superior performance. From our studies we conclude that the B-doped CVD diamond sample is well suited for its application on future space missions.

Raman studied of undoped amorphous carbon thin film deposited by bias assisted-CVD

NASA Astrophysics Data System (ADS)

Ishak, A.; Fadzilah, A. N.; Dayana, K.; Saurdi, I.; Malek, M. F.; Nurbaya, Z.; Shafura, A. K.; Rusop, M.

2018-05-01

The undoped amorphous carbon thin film carbon was deposited at 200°C-350°C by bias assisted-CVD using palm oil as a precursor material. The effect of different substrate deposition temperatures on structural and electrical properties of undoped doped amorphous carbon film was discussed. The structural of undoped amorphous carbon films were correlated with Raman analysis through the evolution of D and G bands, Fourier spectra, and conductivity measurement. The spectral evolution observed showed the increase of upward shift of D and G peaks as substrate deposition temperatures increased. The spectral evolution observed at different substrate deposition temperatures show progressive formation of crystallites. It was predicted that small number of hydrogen is terminated with carbon at surface of thin film as shown by FTIR spectra since palm oil has high number of hydrogen (C67H127O8). These structural changes were further correlated with conductivity and the results obtained are discussed and compared. The conductivity is found in the range of 10-8 Scm-1. The increase of conductivity is correlated by the change of structural properties as correlated with characteristic parameters of Raman spectra including the position of G peak, full width at half maximum of G peak, and ID/IG and FTIR result.

Nitrogen and silicon defect incorporation during homoepitaxial CVD diamond growth on (111) surfaces

DOE PAGES

Moore, Samuel L.; Vohra, Yogesh K.

2015-01-01

Chemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectronmore » Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. As a result, altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.« less

Investigation of Lithium-Air Battery Discharge Product Formed on Carbon Nanotube and Nanofiber Electrodes

NASA Astrophysics Data System (ADS)

Mitchell, Robert Revell, III

Carbon nanotubes have been actively investigated for integration in a wide variety of applications since their discovery over 20 years ago. Their myriad desirable material properties including exceptional mechanical strength, high thermal conductivities, large surface-to-volume ratios, and considerable electrical conductivities, which are attributable to a quantum mechanical ability to conduct electrons ballistically, have continued to motivate interest in this material system. While a variety of synthesis techniques exist, carbon nanotubes and nanofibers are most often conveniently synthesized using chemical vapor deposition (CVD), which involves their catalyzed growth from transition metal nanoparticles. Vertically-aligned nanotube and nanofiber carpets produced using CVD have been utilized in a variety of applications including those related to energy storage. Li-air (Li-O2) batteries have received much interest recently because of their very high theoretical energy densities (3200 Wh/kgLi2O2 ). which make them ideal candidates for energy storage devices for future fully-electric vehicles. During operation of a Li-air battery O2 is reduced on the surface a porous air cathode, reacting with Li-ions to form lithium peroxide (Li-O2). Unlike the intercalation reactions of Li-ion batteries, discharge in a Li-air cell is analogous to an electrodeposition process involving the nucleation and growth of the depositing species on a foreign substrate. Carbon nanofiber electrodes were synthesized on porous substrates using a chemical vapor deposition process and then assembled into Li-O2 cells. The large surface to volume ratio and low density of carbon nanofiber electrodes were found to yield a very high gravimetric energy density in Li-O 2 cells, approaching 75% of the theoretical energy density for Li 2O2. Further, the carbon nanofiber electrodes were found to be excellent platforms for conducting ex situ electron microscopy investigations of the deposition Li2O2 phase, which was found to have unique disc and toroid morphologies. Subsequent studies were conducted using freestanding carpets of multi-walled CNT arrays, which were synthesized using a modified CVD process. The freestanding CNT arrays were used as a platform for studying the morphological evolution of Li2O2 discharge product as a function of rate and electrode capacity. SEM imaging investigations found that the Li2O 2 particles underwent a shape evolution from discs to toroids as their size increased. TEM imaging and diffraction studies showed that the microscale Li2O2 particles are composed of stacks of thin Li 2O2 crystallites and that splaying of the stacked crystallite array drives the observed disc to toroid transition. Modeling was performed to gain insights into the nucleation and growth processes involved during discharge in Li-O2 cells. The modeling study suggests that poor electronic conductivity of the depositing phase limits the rate capability obtainable in Li-O2 cells. Modeling can provide substantial insights into paths toward electrode optimization. Understanding the size and shape evolution of Li2O2 particles and engineering improved electrode architectures is critical to efficiently filling the electrode void volume during discharge thereby improving the volumetric energy density of Li-O2 batteries. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

C_7F_16/He rf plasma CVD of a-C:F films

NASA Astrophysics Data System (ADS)

Hokoi, Kohji; Akazawa, Masamichi; Sugawara, Hirotake; Sakai, Yosuke

2000-10-01

Fluorinated carbon is one of the most promissing materials with low dielectric constant ɛr and high dielectric strength V_b. We have deposited a-C:F films by rf (13.56 MHz) plasma enhanced CVD method using the following liquid materials; C_7F_16, (C_3F_7)_3N/(C_4F_9)_3N and C_8F_18/C_8F_16O.(C. P. Lungu et al.), Jpn. J. Appl. Phys. 38, L1544--6 (1999) The films showed ɛr values in a range of 1.9--3.0 and V_b>2 MV/cm. In this work, we added He (3 Pa) to C_7F_16 (60 Pa) plasmas, expecting that He atoms in the metastable excited state (He*, 19.8 eV) would promote C_7F_16 decomposition in gas phase or activation of the film surface during deposition. The films with the thickness up to 2300 nm were deposited on unheated Si substrate with an rf power of 100 W. The deposition rate derived from the film thickness measurement by SEM and ellipsometry was about 230 nm/min. This value is roughly two times as large as that of the films deposited by C_7F_16 (60 Pa) plasmas without He. We discuss the mechanism that leads to such a significant increase in the deposition rate.

Prediction of the properties of PVD/CVD coatings with the use of FEM analysis

NASA Astrophysics Data System (ADS)

Śliwa, Agata; Mikuła, Jarosław; Gołombek, Klaudiusz; Tański, Tomasz; Kwaśny, Waldemar; Bonek, Mirosław; Brytan, Zbigniew

2016-12-01

The aim of this paper is to present the results of the prediction of the properties of PVD/CVD coatings with the use of finite element method (FEM) analysis. The possibility of employing the FEM in the evaluation of stress distribution in multilayer Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N, Ti/(Ti,Si)N/(Ti,Si)N, and Ti/DLC/DLC coatings by taking into account their deposition conditions on magnesium alloys has been discussed in the paper. The difference in internal stresses in the zone between the coating and the substrate is caused by, first of all, the difference between the mechanical and thermal properties of the substrate and the coating, and also by the structural changes that occur in these materials during the fabrication process, especially during the cooling process following PVD and CVD treatment. The experimental values of stresses were determined based on X-ray diffraction patterns that correspond to the modelled values, which in turn can be used to confirm the correctness of the accepted mathematical model for testing the problem. An FEM model was established for the purpose of building a computer simulation of the internal stresses in the coatings. The accuracy of the FEM model was verified by comparing the results of the computer simulation of the stresses with experimental results. A computer simulation of the stresses was carried out in the ANSYS environment using the FEM method. Structure observations, chemical composition measurements, and mechanical property characterisations of the investigated materials has been carried out to give a background for the discussion of the results that were recorded during the modelling process.

Effect of trichloroethylene enhancement on deposition rate of low-temperature silicon oxide films by silicone oil and ozone

NASA Astrophysics Data System (ADS)

Horita, Susumu; Jain, Puneet

2017-08-01

A low-temperature silcon oxide film was deposited at 160 to 220 °C using an atmospheric pressure CVD system with silicone oil vapor and ozone gases. It was found that the deposition rate is markedly increased by adding trichloroethylene (TCE) vapor, which is generated by bubbling TCE solution with N2 gas flow. The increase is more than 3 times that observed without TCE, and any contamination due to TCE is hardly observed in the deposited Si oxide films from Fourier transform infrared spectra.

MgO buffer layers on rolled nickel or copper as superconductor substrates

DOEpatents

Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

2001-01-01

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

Method for making MgO buffer layers on rolled nickel or copper as superconductor substrates

DOEpatents

Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

2002-01-01

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

Fabrication and investigation of the optoelectrical properties of MoS2/CdS heterojunction solar cells

PubMed Central

2014-01-01

Molybdenum disulfide (MoS2)/cadmium sulfide (CdS) heterojunction solar cells were successfully synthesized via chemical bath deposition (CBD) and chemical vapor deposition (CVD). The as-grown CdS film on a fluorine tin oxide (FTO) substrate deposited by CBD is continuous and compact. The MoS2 film deposited by CVD is homogeneous and continuous, with a uniform color and a thickness of approximately 10 nm. The optical absorption range of the MoS2/CdS heterojunction covers the visible and near-infrared spectral regions of 350 to 800 nm, which is beneficial for the improvement of solar cell efficiency. Moreover, the MoS2/CdS solar cell exhibits good current-voltage (I-V) characteristics and pronounced photovoltaic behavior, with an open-circuit voltage of 0.66 V and a short-circuit current density of 0.227 × 10-6 A/cm2, comparable to the results obtained from other MoS2-based solar cells. This research is critical to investigate more efficient and stable solar cells based on graphene-like materials in the future. PMID:25593552

CVD-grown horizontally aligned single-walled carbon nanotubes: synthesis routes and growth mechanisms.

PubMed

Ibrahim, Imad; Bachmatiuk, Alicja; Warner, Jamie H; Büchner, Bernd; Cuniberti, Gianaurelio; Rümmeli, Mark H

2012-07-09

Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Raman Enhancement and Photo-Bleaching of Organic Dyes in the Presence of Chemical Vapor Deposition-Grown Graphene.

PubMed

Weng, Jiaxin; Zhao, Shichao; Li, Zhiting; Ricardo, Karen B; Zhou, Feng; Kim, Hyojeong; Liu, Haitao

2017-10-19

Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that graphene enhances the Raman signal of a wide range of dyes. The photo-bleaching of the dyes was reduced when the dyes were in contact with graphene. In contrast, monolayer hexagonal boron nitride (h-BN) was much less effective in reducing the photo-bleaching rate of the dyes. We attribute the suppression of photo-bleaching to the energy or electron transfer from dye to graphene. The results highlight the potential of CVD graphene as a substrate for protecting and enhancing Raman response of organic dyes.

What Drives Metal-Surface Step Bunching in Graphene Chemical Vapor Deposition?

NASA Astrophysics Data System (ADS)

Yi, Ding; Luo, Da; Wang, Zhu-Jun; Dong, Jichen; Zhang, Xu; Willinger, Marc-Georg; Ruoff, Rodney S.; Ding, Feng

2018-06-01

Compressive strain relaxation of a chemical vapor deposition (CVD) grown graphene overlayer has been considered to be the main driving force behind metal surface step bunching (SB) in CVD graphene growth. Here, by combining theoretical studies with experimental observations, we prove that the SB can occur even in the absence of a compressive strain, is enabled by the rapid diffusion of metal adatoms beneath the graphene and is driven by the release of the bending energy of the graphene overlayer in the vicinity of steps. Based on this new understanding, we explain a number of experimental observations such as the temperature dependence of SB, and how SB depends on the thickness of the graphene film. This study also shows that SB is a general phenomenon that can occur in all substrates covered by films of two-dimensional (2D) materials.

Field Emission and Nanostructure of Carbon Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merkulov, V.I.; Lowndes, D.H.; Baylor, L.R.

1999-11-29

The results of field emission measurements of various forms of carbon films are reported. It is shown that the films nanostructure is a crucial factor determining the field emission properties. In particular, smooth, pulsed-laser deposited amorphous carbon films with both high and low sp3 contents are poor field emitters. This is similar to the results obtained for smooth nanocrystalline, sp2-bonded carbon films. In contrast, carbon films prepared by hot-filament chemical vapor deposition (HE-CVD) exhibit very good field emission properties, including low emission turn-on fields, high emission site density, and excellent durability. HF-CVD carbon films were found to be predominantly sp2-bonded.more » However, surface morphology studies show that these films are thoroughly nanostructured, which is believed to be responsible for their promising field emission properties.« less

Passivation of InGaAs(001)-(2 × 4) by Self-Limiting Chemical Vapor Deposition of a Silicon Hydride Control Layer.

PubMed

Edmonds, Mary; Kent, Tyler; Chagarov, Evgueni; Sardashti, Kasra; Droopad, Ravi; Chang, Mei; Kachian, Jessica; Park, Jun Hong; Kummel, Andrew

2015-07-08

A saturated Si-Hx seed layer for gate oxide or contact conductor ALD has been deposited via two separate self-limiting and saturating CVD processes on InGaAs(001)-(2 × 4) at substrate temperatures of 250 and 350 °C. For the first self-limiting process, a single silicon precursor, Si3H8, was dosed at a substrate temperature of 250 °C, and XPS results show the deposited silicon hydride layer saturated at about 4 monolayers of silicon coverage with hydrogen termination. STS results show the surface Fermi level remains unpinned following the deposition of the saturated silicon hydride layer, indicating the InGaAs surface dangling bonds are electrically passivated by Si-Hx. For the second self-limiting process, Si2Cl6 was dosed at a substrate temperature of 350 °C, and XPS results show the deposited silicon chloride layer saturated at about 2.5 monolayers of silicon coverage with chlorine termination. Atomic hydrogen produced by a thermal gas cracker was subsequently dosed at 350 °C to remove the Si-Cl termination by replacing with Si-H termination as confirmed by XPS, and STS results confirm the saturated Si-Hx bilayer leaves the InGaAs(001)-(2 × 4) surface Fermi level unpinned. Density function theory modeling of silicon hydride surface passivation shows an Si-Hx monolayer can remove all the dangling bonds and leave a charge balanced surface on InGaAs.

The Dependence of CNT Aerogel Synthesis on Sulfur-driven Catalyst Nucleation Processes and a Critical Catalyst Particle Mass Concentration.

PubMed

Hoecker, Christian; Smail, Fiona; Pick, Martin; Weller, Lee; Boies, Adam M

2017-11-06

The floating catalyst chemical vapor deposition (FC-CVD) process permits macro-scale assembly of nanoscale materials, enabling continuous production of carbon nanotube (CNT) aerogels. Despite the intensive research in the field, fundamental uncertainties remain regarding how catalyst particle dynamics within the system influence the CNT aerogel formation, thus limiting effective scale-up. While aerogel formation in FC-CVD reactors requires a catalyst (typically iron, Fe) and a promotor (typically sulfur, S), their synergistic roles are not fully understood. This paper presents a paradigm shift in the understanding of the role of S in the process with new experimental studies identifying that S lowers the nucleation barrier of the catalyst nanoparticles. Furthermore, CNT aerogel formation requires a critical threshold of Fe x C y  > 160 mg/m 3 , but is surprisingly independent of the initial catalyst diameter or number concentration. The robustness of the critical catalyst mass concentration principle is proved further by producing CNTs using alternative catalyst systems; Fe nanoparticles from a plasma spark generator and cobaltocene and nickelocene precursors. This finding provides evidence that low-cost and high throughput CNT aerogel routes may be achieved by decoupled and enhanced catalyst production and control, opening up new possibilities for large-scale CNT synthesis.

Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method

NASA Astrophysics Data System (ADS)

Ghaemi, Ferial; Abdullah, Luqman Chuah; Tahir, Paridah Md; Yunus, Robiah

2016-11-01

In this study, different types of graphene, including single-, few-, and multi-layer graphene, were grown on a stainless steel (SS) mesh coated with Cu catalyst by using the chemical vapor deposition (CVD) method. Even though the SS mesh consisted of different types of metals, such as Fe, Ni, and Cr, which can also be used as catalysts, the reason for coating Cu catalyst on the SS surface had been related to the nature of the Cu, which promotes the growth of graphene with high quality and quantity at low temperature and time. The reaction temperature and run time, as the most important parameters of the CVD method, were varied, and thus led to the synthesis of different layers of graphene. Moreover, the presence of single-, few-, and multi-layer graphene was confirmed by employing two techniques, namely transmission electron microscopy (TEM) and Raman spectroscopy. On top of that, electron dispersive X-ray (EDX) was further applied to establish the influence of the CVD parameters on the growth of graphene.

Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method.

PubMed

Ghaemi, Ferial; Abdullah, Luqman Chuah; Tahir, Paridah Md; Yunus, Robiah

2016-12-01

In this study, different types of graphene, including single-, few-, and multi-layer graphene, were grown on a stainless steel (SS) mesh coated with Cu catalyst by using the chemical vapor deposition (CVD) method. Even though the SS mesh consisted of different types of metals, such as Fe, Ni, and Cr, which can also be used as catalysts, the reason for coating Cu catalyst on the SS surface had been related to the nature of the Cu, which promotes the growth of graphene with high quality and quantity at low temperature and time. The reaction temperature and run time, as the most important parameters of the CVD method, were varied, and thus led to the synthesis of different layers of graphene. Moreover, the presence of single-, few-, and multi-layer graphene was confirmed by employing two techniques, namely transmission electron microscopy (TEM) and Raman spectroscopy. On top of that, electron dispersive X-ray (EDX) was further applied to establish the influence of the CVD parameters on the growth of graphene.

Is Beta-Amyloid Accumulation a Cause or Consequence of Alzheimer’s Disease?

PubMed Central

Wang, Shaoxun; Mims, Paige N.; Roman, Richard J.; Fan, Fan

2017-01-01

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is characterized by the pathological hallmarks of extracellular beta-amyloid (Aβ) plaques and intraneuronal tau-containing neurofibrillary tangles in the brain. Intraneuronal accumulation of Aβ also plays a role to accelerate AD progression by promoting neurodegeneration. Additionally, AD is associated with the development of amyloid angiopathy (CAA), in which Aβ builds up on the walls of the cerebral arteries, which augments the development of cerebral vascular disease (CVD). Conversely, CVD promotes Aβ deposition and the development of AD by affecting the balance of Aβ production and clearance. However, it remains to be determined whether the accumulation of Aβ is a cause or consequence of AD. The interaction between AD and CVD is a topic of considerable current interest. Here, we discuss the role of CVD in Aβ accumulation and the development of AD to provide a new point of view that combination therapies that address the accompanying cerebral microvascular disease may potentiate the efficacy of emerging treatment for AD. PMID:28815226

Ballistic Josephson junctions based on CVD graphene

NASA Astrophysics Data System (ADS)

Li, Tianyi; Gallop, John; Hao, Ling; Romans, Edward

2018-04-01

Josephson junctions with graphene as the weak link between superconductors have been intensely studied in recent years, with respect to both fundamental physics and potential applications. However, most of the previous work was based on mechanically exfoliated graphene, which is not compatible with wafer-scale production. To overcome this limitation, we have used graphene grown by chemical vapour deposition (CVD) as the weak link of Josephson junctions. We demonstrate that very short, wide CVD-graphene-based Josephson junctions with Nb electrodes can work without any undesirable hysteresis in their electrical characteristics from 1.5 K down to a base temperature of 320 mK, and their gate-tuneable critical current shows an ideal Fraunhofer-like interference pattern in a perpendicular magnetic field. Furthermore, for our shortest junctions (50 nm in length), we find that the normal state resistance oscillates with the gate voltage, consistent with the junctions being in the ballistic regime, a feature not previously observed in CVD-graphene-based Josephson junctions.

Low-temperature synthesis of 2D MoS2 on a plastic substrate for a flexible gas sensor.

PubMed

Zhao, Yuxi; Song, Jeong-Gyu; Ryu, Gyeong Hee; Ko, Kyung Yong; Woo, Whang Je; Kim, Youngjun; Kim, Donghyun; Lim, Jun Hyung; Lee, Sunhee; Lee, Zonghoon; Park, Jusang; Kim, Hyungjun

2018-05-08

The efficient synthesis of two-dimensional molybdenum disulfide (2D MoS2) at low temperatures is essential for use in flexible devices. In this study, 2D MoS2 was grown directly at a low temperature of 200 °C on both hard (SiO2) and soft substrates (polyimide (PI)) using chemical vapor deposition (CVD) with Mo(CO)6 and H2S. We investigated the effect of the growth temperature and Mo concentration on the layered growth by Raman spectroscopy and microscopy. 2D MoS2 was grown by using low Mo concentration at a low temperature. Through optical microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, photoluminescence, and transmission electron microscopy measurements, MoS2 produced by low-temperature CVD was determined to possess a layered structure with good uniformity, stoichiometry, and a controllable number of layers. Furthermore, we demonstrated the realization of a 2D MoS2-based flexible gas sensor on a PI substrate without any transfer processes, with competitive sensor performance and mechanical durability at room temperature. This fabrication process has potential for burgeoning flexible and wearable nanotechnology applications.

Diameter and Geometry Control of Vertically Aligned SWNTs through Catalyst Manipulation

NASA Astrophysics Data System (ADS)

Xiang, Rong; Einarsson, Erik; Okawa, Jun; Murakami, Yoichi; Maruyama, Shigeo

2009-03-01

We present our recent progress on manipulating our liquid-based catalyst loading process, which possesses greater potential than conventional deposition in terms of cost and scalability, to control the diameter and morphology of single-walled carbon nanotubes (SWNTs). We demonstrate that the diameter of aligned SWNTs synthesized by alcohol catalytic CVD can be tailored over a wide range by modifying the catalyst recipe. SWNT arrays with an average diameter as small as 1.2 nm were obtained by this method. Additionally, owing to the alignment of the array, the continuous change of the SWNT diameter during a single CVD process can be clearly observed and quantitatively characterized. We have also developed a versatile wet chemistry method to localize the growth of SWNTs to desired regions via surface modification. By functionalizing the silicon surface using a classic self-assembled monolayer, the catalyst can be selectively dip-coated onto hydrophilic areas of the substrate. This technique was successful in producing both random and aligned SWNTs with various patterns. The precise control of the diameter and morphology of SWNTs, achieved by simple and scalable liquid-based surface chemistry, could greatly facilitate the application of SWNTs as the building blocks of future nano-devices.

Atomic mechanism for the growth of wafer-scale single-crystal graphene: theoretical perspective and scanning tunneling microscopy investigations

NASA Astrophysics Data System (ADS)

Niu, Tianchao; Zhang, Jialin; Chen, Wei

2017-12-01

Chemical vapor deposition (CVD) is the most promising approach for producing low-cost, high-quality, and large area graphene. Revealing the graphene growth mechanism at the atomic-scale is of great importance for realizing single crystal graphene (SCG) over wafer scale. Density functional theoretical (DFT) calculations are playing an increasingly important role in revealing the structure of the most stable carbon species, understanding the evolution processes, and disclosing the active sites. Scanning tunneling microscopy (STM) is a powerful surface characterization tool to illustrate the real space distribution and atomic structures of growth intermediates during the CVD process. Combining them together can provide valuable information to improve the atomically controlled growth of SCG. Starting from a basic concept of the substrate effect on realizing SCG, this review covers the progress made in theoretical investigations on various carbon species during graphene growth on different transition metal substrates, in the STM study of the structural intermediates on transition metal surfaces, and in synthesizing graphene nanoribbons with atomic-precise width and edge structure, ending with a perspective on the future development of 2D materials beyond graphene.

Synthesizing Diamond from Liquid Feedstock

NASA Technical Reports Server (NTRS)

Tzeng, Yonhua

2005-01-01

A relatively economical method of chemical vapor deposition (CVD) has been developed for synthesizing diamond crystals and films. Unlike prior CVD methods for synthesizing diamond, this method does not require precisely proportioned flows of compressed gas feedstocks or the use of electrical discharges to decompose the feedstocks to obtain free radicals needed for deposition chemical reactions. Instead, the feedstocks used in this method are mixtures of common organic liquids that can be prepared in advance, and decomposition of feedstock vapors is effected simply by heating. The feedstock used in this method is a solution comprising between 90 and 99 weight percent of methanol and the balance of one or more other oxyhydrocarbons that could include ethanol, isopropanol, and/or acetone. This mixture of compounds is chosen so that dissociation of molecules results in the desired proportions of carbon-containing radicals (principally, CH3) and of OH, H, and O radicals. Undesirably, the CVD temperature and pressure conditions thermodynamically favor the growth of graphite over the growth of diamond. The H radicals are desirable because they help to stabilize the growing surface of diamond by shifting the thermodynamic balance toward favoring the growth of diamond. The OH and O radicals are desirable because they preferentially etch graphite and other non-diamond carbon, thereby helping to ensure the net deposition of pure diamond. The non-methanol compounds are included in the solution because (1) methanol contains equal numbers of C and O atoms; (2) an excess of C over O is needed to obtain net deposition of diamond; and (3) the non-methanol molecules contain multiple carbon atoms for each oxygen atom and thus supply the needed excess carbon A typical apparatus used in this method includes a reservoir containing the feedstock liquid and a partially evacuated stainless-steel reaction chamber. The reservoir is connected to the chamber via tubing and a needle valve or other suitable flow controller. When the liquid enters the low-pressure environment inside the chamber, it evaporates to form a vapor mixture of the same chemical composition. In addition to the inlet for the feedstock liquid, the chamber is fitted with an outlet connected to a vacuum pump (not shown) through a throttle valve (also not shown) that is automatically controlled to keep the pressure at or near the required value throughout the deposition process. Inside the chamber, a spiral filament made of tungsten, tantalum, graphite, or other high-melting-temperature material is electrically heated to a temperature >2,000 C high enough to cause dissociation of vapor molecules into the aforementioned radicals. A deposition substrate typically, a diamond-polished silicon wafer about 2.5 cm square is positioned about 2 cm away from the filament. The exact location of the substrate is chosen so that the substrate becomes heated by the filament to a deposition temperature in the approximate range of 800 to 1,000 C.

Gas-to-particle conversion in the particle precipitation-aided chemical vapor deposition process II. Synthesis of the perovskite oxide yttrium chromite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dieten, V.E.J. van; Dekker, J.P.; Hurkmans, E.J.

1993-11-01

In the particle precipitation-aided chemical vapor deposition process, an aerosol is formed in the gas phase at elevated temperatures. The particles are deposited on a cooled substrate. Coherent layers with a controlled porosity can be obtained by a simultaneous heterogeneous reaction, which interconnects the deposited particles. The synthesis of submicrometer powder of the perovskite oxide yttrium chromite (YCrO[sub 3]) by gas to particle conversion, which is the first step of the PP-CVD process, has been investigated, and preliminary results are shown. The powders have been synthesized using yttrium trichloride vapor (YCl[sub 3]), chromium trichloride vapor (CrCl[sub 3]), and steam andmore » oxygen as reactants. The influence of the input molar ratio of the elements on the composition and characteristics of the powders has been investigated. Phase composition has been determined by X-ray diffraction (XRD). The powders have been characterized by transmission electron microscopy (TEM) and sedimentation field flow fractionation (SF[sup 3]). At a reaction temperature of 1283 K the powders consist of the chromium sesquioxide (Cr[sub 2]O[sub 3]), or a mixture of Cr[sub 2]O[sub 3] and YCrO[sub 3]. At stoichiometeric input amounts of metal chlorides and steam the formation of YCrO[sub 3] seems to be favored. 19 refs., 6 figs., 3 tabs.« less

Direct growth of nanocrystalline hexagonal boron nitride films on dielectric substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tay, Roland Yingjie; Temasek Laboratories@NTU, 50 Nanyang Avenue, Singapore, Singapore 639798; Tsang, Siu Hon

Atomically thin hexagonal-boron nitride (h-BN) films are primarily synthesized through chemical vapor deposition (CVD) on various catalytic transition metal substrates. In this work, a single-step metal-catalyst-free approach to obtain few- to multi-layer nanocrystalline h-BN (NCBN) directly on amorphous SiO{sub 2}/Si and quartz substrates is demonstrated. The as-grown thin films are continuous and smooth with no observable pinholes or wrinkles across the entire deposited substrate as inspected using optical and atomic force microscopy. The starting layers of NCBN orient itself parallel to the substrate, initiating the growth of the textured thin film. Formation of NCBN is due to the random andmore » uncontrolled nucleation of h-BN on the dielectric substrate surface with no epitaxial relation, unlike on metal surfaces. The crystallite size is ∼25 nm as determined by Raman spectroscopy. Transmission electron microscopy shows that the NCBN formed sheets of multi-stacked layers with controllable thickness from ∼2 to 25 nm. The absence of transfer process in this technique avoids any additional degradation, such as wrinkles, tears or folding and residues on the film which are detrimental to device performance. This work provides a wider perspective of CVD-grown h-BN and presents a viable route towards large-scale manufacturing of h-BN substrates and for coating applications.« less

Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye.

PubMed

Xiao, Gaofei; Zeng, HongYan; Xu, Sheng; Chen, ChaoRong; Zhao, Quan; Liu, XiaoJun

2017-10-01

TiO 2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating MgAl hydrotalcite (Ti-MgAl-LDH) was prepared by chemical vapor deposition (CVD) method. Response surface method (RSM) was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N 2 flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti-MgAl-LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process. According to the results from X-ray diffraction, scanning electron microscopy, Brunner-Emmet-Teller and Barrett-Joyner-Hallender, thermogravimetric and differential thermal analysis, UV-vis diffuse reflectance spectra analyses, the Ti species (TiO 2 or/and Ti 4+ ) were successfully coated on the MgAl-LDH matrix. The Ti species on the surface of the Ti-MgAl-LDH lead to a higher photocatalytic performance than commercial TiO 2 -P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating MgAl-LDH material with good photocatalytic performances. Copyright © 2017. Published by Elsevier B.V.

Properties, synthesis, and growth mechanisms of carbon nanotubes with special focus on thermal chemical vapor deposition.

PubMed

Nessim, Gilbert D

2010-08-01

Carbon nanotubes (CNTs) have been extensively investigated in the last decade because their superior properties could benefit many applications. However, CNTs have not yet made a major leap into industry, especially for electronic devices, because of fabrication challenges. This review provides an overview of state-of-the-art of CNT synthesis techniques and illustrates their major technical difficulties. It also charts possible in situ analyses and new reactor designs that might enable commercialization. After a brief description of the CNT properties and of the various techniques used to synthesize substrate-free CNTs, the bulk of this review analyzes chemical vapor deposition (CVD). This technique receives special attention since it allows CNTs to be grown in predefined locations, provides a certain degree of control of the types of CNTs grown, and may have the highest chance to succeed commercially. Understanding the primary growth mechanisms at play during CVD is critical for controlling the properties of the CNTs grown and remains the major hurdle to overcome. Various factors that influence CNT growth receive a special focus: choice of catalyst and substrate materials, source gases, and process parameters. This review illustrates important considerations for in situ characterization and new reactor designs that may enable researchers to better understand the physical growth mechanisms and to optimize the synthesis of CNTs, thus contributing to make carbon nanotubes a manufacturing reality.

Recent Results with CVD Diamond Trackers

NASA Astrophysics Data System (ADS)

Adam, W.; Bauer, C.; Berdermann, E.; Bergonzo, P.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K. K.; Gheeraert, E.; Grigoriev, E.; Hallewell, G.; Hall-Wilton, R.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Karl, C.; Kass, R.; Knöpfle, K. T.; Krammer, M.; Logiudice, A.; Lu, R.; Manfredi, P. F.; Manfredotti, C.; Marshall, R. D.; Meier, D.; Mishina, M.; Oh, A.; Pan, L. S.; Palmieri, V. G.; Pernicka, M.; Peitz, A.; Pirollo, S.; Polesello, P.; Pretzl, K.; Procario, M.; Re, V.; Riester, J. L.; Roe, S.; Roff, D.; Rudge, A.; Runolfsson, O.; Russ, J.; Schnetzer, S.; Sciortino, S.; Speziali, V.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R. J.; Tesarek, R.; Trawick, M.; Trischuk, W.; Vittone, E.; Walsh, A. M.; Wedenig, R.; Weilhammer, P.; White, C.; Ziock, H.; Zoeller, M.; RD42 Collaboration

1999-08-01

We present recent results on the use of Chemical Vapor Deposition (CVD) diamond microstrip detectors for charged particle tracking. A series of detectors was fabricated using 1 x 1 cm 2 diamonds. Good signal-to-noise ratios were observed using both slow and fast readout electronics. For slow readout electronics, 2 μs shaping time, the most probable signal-to-noise ratio was 50 to 1. For fast readout electronics, 25 ns peaking time, the most probable signal-to-noise ratio was 7 to 1. Using the first 2 x 4 cm 2 diamond from a production CVD reactor with slow readout electronics, the most probable signal-to-noise ratio was 23 to 1. The spatial resolution achieved for the detectors was consistent with the digital resolution expected from the detector pitch.

Deposition of amorphous carbon thin films by aerosol-assisted CVD method

NASA Astrophysics Data System (ADS)

Fadzilah, A. N.; Dayana, K.; Rusop, M.

2018-05-01

This paper reports on the deposition of amorphous carbon (a-C) by Aerosol-assisted Chemical Vapor Deposition (AACVD) using natural source of camphor oil as the precursor material. 4 samples were deposited at 4 different deposition flow rate from 15 sccm to 20 sccm, with 5 sccm interval for each sample. The analysis includes the electrical, optical and structural analysis of the data. The a-C structure which came from the manipulation of synthesis parameter was characterized by the solar simulator system, UV-VIS-NIR, Raman spectroscope and AFM. The properties of a-C are highly dependent on the deposition techniques and deposition parameters; hence the influences of gas flow rate were studied.

Corrosion resistance of monolayer hexagonal boron nitride on copper

PubMed Central

Mahvash, F.; Eissa, S.; Bordjiba, T.; Tavares, A. C.; Szkopek, T.; Siaj, M.

2017-01-01

Hexagonal boron nitride (hBN) is a layered material with high thermal and chemical stability ideal for ultrathin corrosion resistant coatings. Here, we report the corrosion resistance of Cu with hBN grown by chemical vapor deposition (CVD). Cyclic voltammetry measurements reveal that hBN layers inhibit Cu corrosion and oxygen reduction. We find that CVD grown hBN reduces the Cu corrosion rate by one order of magnitude compared to bare Cu, suggesting that this ultrathin layer can be employed as an atomically thin corrosion-inhibition coating. PMID:28191822

Ballistic Transport Exceeding 28 μm in CVD Grown Graphene.

PubMed

Banszerus, Luca; Schmitz, Michael; Engels, Stephan; Goldsche, Matthias; Watanabe, Kenji; Taniguchi, Takashi; Beschoten, Bernd; Stampfer, Christoph

2016-02-10

We report on ballistic transport over more than 28 μm in graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride. The structures are fabricated by an advanced dry van-der-Waals transfer method and exhibit carrier mobilities of up to three million cm(2)/(Vs). The ballistic nature of charge transport is probed by measuring the bend resistance in cross- and square-shaped devices. Temperature-dependent measurements furthermore prove that ballistic transport is maintained exceeding 1 μm up to 200 K.

Fluorescence and Raman Spectroscopy of Doped Nanodiamonds

NASA Astrophysics Data System (ADS)

Kudryavtsev, O. S.; Khomich, A. A.; Sedov, V. S.; Ekimov, E. A.; Vlasov, I. I.

2018-05-01

Raman and fluorescence spectroscopic techniques were used to study doped nanodiamonds synthesized at high pressure and high temperature (HPHT technique) and by chemical vapor deposition from the gas phase (CVD technique). For the CVD diamonds, a hundred-fold increase in fluorescence intensity of the silicon-vacancy centers normalized to the volume of the probe material was observed with an increase in synthesized diamond particle diameter from 150 to 300 nm. Graphitization temperature upon heating in the air significantly lower than for detonation nanodiamonds was found for the boron-doped HPHT nanodiamonds.

Effect of Atomic Hydrogen on Preparation of Highly Moisture-Resistive SiNx Films at Low Substrate Temperatures

NASA Astrophysics Data System (ADS)

Heya, Akira; Niki, Toshikazu; Takano, Masahiro; Yonezawa, Yasuto; Minamikawa, Toshiharu; Muroi, Susumu; Minami, Shigehira; Izumi, Akira; Masuda, Atsushi; Umemoto, Hironobu; Matsumura, Hideki

2004-12-01

Highly moisture-resistive SiNx films on a Si substrate are obtained at substrate temperatures of 80°C by catalytic chemical vapor deposition (Cat-CVD) using a source gas with H2. Atomic hydrogen effected the selective etching of a weak-bond regions and an increase in atomic density induced by the energy of the surface reaction. It is concluded that Cat-CVD using H2 is a promising candidate for the fabrication of highly moisture-resistive SiNx films at low temperatures.

Experimental characterization and modeling for the growth rate of oxide coatings from liquid solutions of metalorganic precursors by ultrasonic pulsed injection in a cold-wall low-pressure reactor

NASA Astrophysics Data System (ADS)

Krumdieck, Susan Pran

Several years ago, a method for depositing ceramic coatings called the Pulsed-MOCVD system was developed by the Raj group at Cornell University in association with Dr. Harvey Berger and Sono-Tek Corporation. The process was used to produce epitaxial thin films of TiO2 on sapphire substrates under conditions of low pressure, relatively high temperature, and very low growth rate. The system came to CU-Boulder when Professor Raj moved here in 1997. It is quite a simple technique and has several advantages over typical CVD systems. The purpose of this dissertation is two-fold; (1) understand the chemical processes, thermodynamics, and kinetics of the Pulsed-MOCVD technique, and (2) determine the possible applications by studying the film structure and morphology over the entire range of deposition conditions. Polycrystalline coatings of ceramic materials were deposited on nickel in the low-pressure, cold-wall reactor from metalorganic precursors, titanium isopropoxide, and a mixture of zirconium isopropoxide and yttria isopropoxide. The process utilized pulsed liquid injection of a dilute precursor solution with atomization by ultrasonic nozzle. Thin films (less than 1mum) with fine-grained microstructure and thick coatings (up to 1mum) with columnar-microstructure were deposited on heated metal substrates by thermal decomposition of a single liquid precursor. The influence of each of the primary deposition parameters, substrate temperature, total flow rate, and precursor concentration on growth rate, conversion efficiency and morphology were investigated. The operating conditions were determined for kinetic, mass transfer, and evaporation process control regimes. Kinetic controlled deposition was found to produce equiaxed morphology while mass transfer controlled deposition produced columnar morphology. A kinetic model of the deposition process was developed and compared to data for deposition of TiO2 from Ti(OC3H7) 4 precursor. The results demonstrate that growth rate and morphology over the range of process operating conditions would make the Pulsed-MOCVD system suitable for application of thermal barrier coatings, electrical insulating layers, corrosion protection coatings, and the electrolyte layers in solid oxide fuel cells.

A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

PubMed

Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

2011-09-01

In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

Synthesis of Multi-Walled Carbon Nanotubes from Plastic Waste Using a Stainless-Steel CVD Reactor as Catalyst.

PubMed

Tripathi, Pranav K; Durbach, Shane; Coville, Neil J

2017-09-22

The disposal of non-biodegradable plastic waste without further upgrading/downgrading is not environmentally acceptable and many methods to overcome the problem have been proposed. Herein we indicate a simple method to make high-value nanomaterials from plastic waste as a partial solution to the environmental problem. Laboratory-based waste centrifuge tubes made of polypropylene were chosen as a carbon source to show the process principle. In the process, multi-walled carbon nanotubes (MWCNTs) were synthesized from plastic waste in a two-stage stainless steel 316 (SS 316) metal tube that acted as both reactor vessel and catalyst. The steel reactor contains Fe (and Ni, and various alloys), which act as the catalyst for the carbon conversion process. The reaction and products were studied using electron probe microanalysis, thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy and scanning electron microscopy. Optimization studies to determine the effect of different parameters on the process showed that the highest yield and most graphitized MWCNTs were formed at 900 °C under the reaction conditions used (yield 42%; Raman I D / I G ratio = 0.48). The high quality and high yield of the MWCNTs that were produced in a flow reactor from plastic waste using a two stage SS 316 chemical vapor deposition (CVD) furnace did not require the use of an added catalyst.

Synthesis of Multi-Walled Carbon Nanotubes from Plastic Waste Using a Stainless-Steel CVD Reactor as Catalyst

PubMed Central

Durbach, Shane

2017-01-01

The disposal of non-biodegradable plastic waste without further upgrading/downgrading is not environmentally acceptable and many methods to overcome the problem have been proposed. Herein we indicate a simple method to make high-value nanomaterials from plastic waste as a partial solution to the environmental problem. Laboratory-based waste centrifuge tubes made of polypropylene were chosen as a carbon source to show the process principle. In the process, multi-walled carbon nanotubes (MWCNTs) were synthesized from plastic waste in a two-stage stainless steel 316 (SS 316) metal tube that acted as both reactor vessel and catalyst. The steel reactor contains Fe (and Ni, and various alloys), which act as the catalyst for the carbon conversion process. The reaction and products were studied using electron probe microanalysis, thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy and scanning electron microscopy. Optimization studies to determine the effect of different parameters on the process showed that the highest yield and most graphitized MWCNTs were formed at 900 °C under the reaction conditions used (yield 42%; Raman ID/IG ratio = 0.48). The high quality and high yield of the MWCNTs that were produced in a flow reactor from plastic waste using a two stage SS 316 chemical vapor deposition (CVD) furnace did not require the use of an added catalyst. PMID:28937596

Chemical Vapor Synthesis of Niobium Aluminides

DTIC Science & Technology

1992-01-01

69 4.2.2 Deposition on Singly Supported Niobium Substrates ............ . . . ..... 72 4.3 DEPOSITION OF NbxSiy FROM H2, NbC15 , AND SICl4 ...direct CVD of NbxSiy from the hydrogen reduction of SiCl4 and NbCl5 is described by the overall reaction: xNbCl5 + ySiCl4 + (5x + 4y)/2 H2 - NbxSiy

Annealed CVD molybdenum thin film surface

DOEpatents

Carver, Gary E.; Seraphin, Bernhard O.

1984-01-01

Molybdenum thin films deposited by pyrolytic decomposition of Mo(CO).sub.6 attain, after anneal in a reducing atmosphere at temperatures greater than 700.degree. C., infrared reflectance values greater than reflectance of supersmooth bulk molybdenum. Black molybdenum films deposited under oxidizing conditions and annealed, when covered with an anti-reflecting coating, approach the ideal solar collector characteristic of visible light absorber and infrared energy reflector.

Development of hot-pressed and chemical-vapor-deposited zinc sulfide and zinc selenide in the United States for optical windows

NASA Astrophysics Data System (ADS)

Harris, Daniel C.

2007-04-01

By the mid 1950s, there was a need for infrared-transmitting materials with improved optical and mechanical characteristics for military and commercial instruments. The newly invented "heat-seeking" missile also required a more durable infrared-transmitting dome. Some properties of ZnS were known from studies of natural minerals. More properties of pure ZnS and ZnSe were measured with single crystals grown in Air Force and industrial laboratories in the 1950s. In 1956, a team led by William Parsons at the Eastman Kodak Hawk-Eye Works in Rochester, New York began to apply the technique of hot pressing to make infrared-transmitting ceramics from powders. This work led to commercial production of six materials, including ZnS (IRTRAN® 2) and ZnSe (IRTRAN® 4) in the 1960s. Because the hot pressed materials could not be made in very large sizes and suffered from undesirable optical losses, the Air Force began to look for alternative manufacturing methods around 1970. Almost immediately, highly successful materials were produced by chemical vapor deposition under Air Force sponsorship by a team led by James Pappis at the Raytheon Research Division in Waltham, Massachusetts. Chemical-vapor-deposited materials replaced hot pressed materials in most applications within a few years. From a stream of Air Force contracts in the 1970s and early 1980s, Raytheon produced two different grades of ZnS for windows and domes, one grade of ZnSe for high-energy CO II laser windows, and a composite ZnS/ZnSe window for aircraft sensor pods. In 1980, a competitor called CVD, Inc., was formed by Robert Donadio, who came from the Raytheon Research Division. CVD began with a license from Raytheon, but soon sued Raytheon, arguing that the license violated the Sherman Antitrust Act. Raytheon countersued for breach of employment contracts and misappropriation of trade secrets. In 1984, a jury ruled in favor of CVD, which went on to build a lucrative business in ZnSe and ZnS. CVD was eventually purchased, first by Morton, and later by Rohm & Haas. II-VI, Inc. was formed in 1971 by Carl J. Johnson and James E. Hawkey to produce CdTe optics for industrial CO II lasers. When Raytheon introduced ZnSe into the market in 1974, it was obvious that ZnSe was superior to CdTe, so II-VI purchased ZnSe from Raytheon to produce optical components. The supply of ZnSe was never stable enough for II-VI, which therefore began its own effort to deposit ZnSe in 1975. In 1980, II-VI became an investor in and customer of CVD, Inc., buying a substantial portion of the ZnSe that could be supplied by both Raytheon and CVD. Still pressed to meet customer demand, II-VI built its first ZnSe production furnace in the period 1983-1986. A second furnace came on line in 1988 and two more were operational by 1990. Finally attaining excess capacity, II-VI became a supplier of ZnS as well as ZnSe. In 1990, Raytheon exited the ZnS and ZnSe business, leaving it mainly to CVD and II-VI.

Isotropic plasma etching of Ge Si and SiN x films

DOE PAGES

Henry, Michael David; Douglas, Erica Ann

2016-08-31

This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF 3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiN x are described with etch rate reductions achieved by adjusting plasma chemistry with O 2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiN x etch rates while retarding Ge etching.

Optically Transparent Microwave Polarizer Based On Quasi-Metallic Graphene.

PubMed

Grande, Marco; Bianco, Giuseppe Valerio; Vincenti, Maria Antonietta; de Ceglia, Domenico; Capezzuto, Pio; Scalora, Michael; D'Orazio, Antonella; Bruno, Giovanni

2015-11-25

In this paper, we report on the engineering and the realization of optically transparent graphene-based microwave devices using Chemical Vapour Deposition (CVD) graphene whose sheet resistance may be tailored down to values below 30 Ω/sq. In particular, we show that the process was successfully used to realize and characterize a simple, optically transparent graphene-based wire-grid polarizer at microwave frequencies (X band). The availability of graphene operating in a quasi-metallic region may allow the integration of graphene layers in several microwave components, thus leading to the realization of fully transparent (and flexible) microwave devices.

Optically Transparent Microwave Polarizer Based On Quasi-Metallic Graphene

PubMed Central

Grande, Marco; Bianco, Giuseppe Valerio; Vincenti, Maria Antonietta; de Ceglia, Domenico; Capezzuto, Pio; Scalora, Michael; D’Orazio, Antonella; Bruno, Giovanni

2015-01-01

In this paper, we report on the engineering and the realization of optically transparent graphene-based microwave devices using Chemical Vapour Deposition (CVD) graphene whose sheet resistance may be tailored down to values below 30 Ω/sq. In particular, we show that the process was successfully used to realize and characterize a simple, optically transparent graphene-based wire-grid polarizer at microwave frequencies (X band). The availability of graphene operating in a quasi-metallic region may allow the integration of graphene layers in several microwave components, thus leading to the realization of fully transparent (and flexible) microwave devices. PMID:26603112

Synthesis of ZrO 2 thin films by atomic layer deposition: growth kinetics, structural and electrical properties

NASA Astrophysics Data System (ADS)

Cassir, Michel; Goubin, Fabrice; Bernay, Cécile; Vernoux, Philippe; Lincot, Daniel

2002-06-01

Ultra thin films of ZrO 2 were synthesized on soda lime glass and SnO 2-coated glass, using ZrCl 4 and H 2O precursors by atomic layer deposition (ALD), a sequential CVD technique allowing the formation of dense and homogeneous films. The effect of temperature on the film growth kinetics shows a first temperature window for ALD processing between 280 and 350 °C and a second regime or "pseudo-window" between 380 and 400 °C, with a growth speed of about one monolayer per cycle. The structure and morphology of films of less than 1 μm were characterized by XRD and SEM. From 275 °C, the ZrO 2 film is crystallized in a tetragonal form while a mixture of tetragonal and monoclinic phases appears at 375 °C. Impedance spectroscopy measurements confirmed the electrical properties of ZrO 2 and the very low porosity of the deposited layer.

Controlled growth of MoS2 nanopetals on the silicon nanowire array using the chemical vapor deposition method

NASA Astrophysics Data System (ADS)

Chen, Shang-Min; Lin, Yow-Jon

2018-01-01

In order to get a physical/chemical insight into the formation of nanoscale semiconductor heterojunctions, MoS2 flakes are deposited on the silicon nanowire (SiNW) array by chemical vapor deposition (CVD). In this study, H2O2 treatment provides a favorable place where the formation of Sisbnd O bonds on the SiNW surfaces that play important roles (i.e., the nucleation centers, catalyst control centers or ;seeds;) can dominate the growth of MoS2 on the SiNWs. Using this configuration, the effect of a change in the S/MoO3 mass ratio (MS/MMoO3) on the surface morphology of MoS2 is studied. It is shown that an increase in the value of MS/MMoO3 leads to the increased nucleation rate, increasing the size of MoS2 nanopetals. This study provides valuable scientific information for directly CVD-grown edge-oriented MoS2/SiNWs heterojunctions for various nanoscale applications, including hydrogen evolution reaction and electronic and optoelectronic devices.

Cryochemical and CVD processing of shperical carbide fuels for propulsion reactors

NASA Astrophysics Data System (ADS)

Blair, H. Thomas; Carroll, David W.; Matthews, R. Bruce

1991-01-01

Many of the nuclear propulsion reactor concepts proposed for a manned mission to Mars use a coated spherical particle fuel form similar to that used in the Rover and NERVA propulsion reactors. The formation of uranium dicarbide microspheres using a cryochemical process and the coating of the UC2 spheres with zirconium carbide using chemical vapor deposition are being developed at Los Alamos National Laboratory. The cryochemical process is described with a discussion of the variables affecting the sphere formation and carbothermic reduction to produce UC2 spheres from UO2. Emphasis is placed on minimizing the wastes produced by the process. The ability to coat particles with ZrC was recaptured, and improvements in the process and equipment were developed. Volatile organometallic precursors were investigated as alternatives to the original ZrCl4 precursor.

Control of nanoparticle size and amount by using the mesh grid and applying DC-bias to the substrate in silane ICP-CVD process

NASA Astrophysics Data System (ADS)

Yoo, Seung-Wan; Hwang, Nong-Moon; You, Shin-Jae; Kim, Jung-Hyung; Seong, Dae-Jin

2017-11-01

The effect of applying a bias to the substrate on the size and amount of charged crystalline silicon nanoparticles deposited on the substrate was investigated in the inductively coupled plasma chemical vapor deposition process. By inserting the grounded grid with meshes above the substrate, the region just above the substrate was separated from the plasma. Thereby, crystalline Si nanoparticles formed by the gas-phase reaction in the plasma could be deposited directly on the substrate, successfully avoiding the formation of a film. Moreover, the size and the amount of deposited nanoparticles could be changed by applying direct current bias to the substrate. When the grid of 1 × 1-mm-sized mesh was used, the nanoparticle flux was increased as the negative substrate bias increased from 0 to - 50 V. On the other hand, when a positive bias was applied to the substrate, Si nanoparticles were not deposited at all. Regardless of substrate bias voltages, the most frequently observed nanoparticles synthesized with the grid of 1 × 1-mm-sized mesh had the size range of 10-12 nm in common. When the square mesh grid of 2-mm size was used, as the substrate bias was increased from - 50 to 50 V, the size of the nanoparticles observed most frequently increased from the range of 8-10 to 40-45 nm but the amount that was deposited on the substrate decreased.

Understanding the Mechanism of SiC Plasma-Enhanced Chemical Vapor Deposition (PECVD) and Developing Routes toward SiC Atomic Layer Deposition (ALD) with Density Functional Theory.

PubMed

Filatova, Ekaterina A; Hausmann, Dennis; Elliott, Simon D

2018-05-02

Understanding the mechanism of SiC chemical vapor deposition (CVD) is an important step in investigating the routes toward future atomic layer deposition (ALD) of SiC. The energetics of various silicon and carbon precursors reacting with bare and H-terminated 3C-SiC (011) are analyzed using ab initio density functional theory (DFT). Bare SiC is found to be reactive to silicon and carbon precursors, while H-terminated SiC is found to be not reactive with these precursors at 0 K. Furthermore, the reaction pathways of silane plasma fragments SiH 3 and SiH 2 are calculated along with the energetics for the methane plasma fragments CH 3 and CH 2 . SiH 3 and SiH 2 fragments follow different mechanisms toward Si growth, of which the SiH 3 mechanism is found to be more thermodynamically favorable. Moreover, both of the fragments were found to show selectivity toward the Si-H bond and not C-H bond of the surface. On the basis of this, a selective Si deposition process is suggested for silicon versus carbon-doped silicon oxide surfaces.

Buffer layers on metal surfaces having biaxial texture as superconductor substrates

DOEpatents

Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

2000-01-01

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /Ni, (RE=Rare Earth), RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /CeO.sub.2 /Ni, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /CeO.sub.2 /Cu, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

Characterization, shaping, and joining of SiC/superalloy sheet for exhaust system components

NASA Technical Reports Server (NTRS)

Cornie, J. A.

1977-01-01

Hafnium carbide was shown to be virtually inert when in contact with silicon carbide and Waspaloy for at least 200 hr at 1093 C (2000 F). Extensive interaction was noted with other superalloys such as HA-188. A continuous CVD HfC deposition process was developed for deposition of up to 8 microns on .14 mm (.0056 in.) SiC tungsten core filament at rates as high as .6 m/min. The rate can be increased by increasing the length of the reactor and the output of the power supply used in resistive heating of the filament substrate. The strength of HfC coated filament varies with thickness in a Griffith-like manner. This strength reduction was greater for HfC coatings than for tungsten coatings, presumably because of the greater ductility of tungsten.

Diamond Nucleation Using Polyethene

NASA Technical Reports Server (NTRS)

Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

2013-01-01

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Diamond nucleation using polyethene

DOEpatents

Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

2013-07-23

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

The CVD ZrB2 as a selective solar absorber

NASA Astrophysics Data System (ADS)

Randich, E.; Allred, D. D.

Coatings of ZrB2 and TiB2 for photothermal solar absorber applications were prepared using chemical vapor deposition (CVD) techniques. Oxidation tests suggest a maximum temperature limit for air exposure of 600 K for TiB2 and 800 K for Z4B2. Both materials exhibit innate spectral selectivity with emittance at 375 K ranging from 0.06 to 0.09 and solar absorptance for ZrB2 ranging from 0.67 to 0.77 and solar absorptance for TiB2 ranging from 0.46 to 0.58. ZrB2 has better solar selectivity and more desirable oxidation behavior than TiB2. A 0.071 micrometer antireflection coating of Si3N4 deposited on the ZrB2 coating leads to an increase in absorptance from 0.77 to 0.93, while the emittance remains unchanged.

EDC-mediated DNA attachment to nanocrystalline CVD diamond films.

PubMed

Christiaens, P; Vermeeren, V; Wenmackers, S; Daenen, M; Haenen, K; Nesládek, M; vandeVen, M; Ameloot, M; Michiels, L; Wagner, P

2006-08-15

Chemical vapour deposited (CVD) diamond is a very promising material for biosensor fabrication owing both to its chemical inertness and the ability to make it electrical semiconducting that allows for connection with integrated circuits. For biosensor construction, a biochemical method to immobilize nucleic acids to a diamond surface has been developed. Nanocrystalline diamond is grown using microwave plasma-enhanced chemical vapour deposition (MPECVD). After hydrogenation of the surface, 10-undecenoic acid, an omega-unsaturated fatty acid, is tethered by 254 nm photochemical attachment. This is followed by 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide (EDC)-mediated attachment of amino (NH(2))-modified dsDNA. The functionality of the covalently bound dsDNA molecules is confirmed by fluorescence measurements, PCR and gel electrophoresis during 35 denaturation and rehybridisation steps. The linking method after the fatty acid attachment can easily be applied to other biomolecules like antibodies and enzymes.

Graphitized hollow carbon spheres and yolk-structured carbon spheres fabricated by metal-catalyst-free chemical vapor deposition

DOE PAGES

Li, Xufan; Chi, Miaofang; Mahurin, Shannon Mark; ...

2016-01-18

Hard-sphere-templating method has been widely used to synthesize hollow carbon spheres (HCSs), in which the spheres were firstly coated with a carbon precursor, followed by carbonization and core removal. The obtained HCSs are generally amorphous or weakly graphitized (with the help of graphitization catalysts). In this work, we report on the fabrication of graphitized HCSs and yolk–shell Au@HCS nanostructures using a modified templating method, in which smooth, uniform graphene layers were grown on SiO 2 spheres or Au@SiO 2 nanoparticles via metal-catalyst-free chemical vapor deposition (CVD) of methane. Furthermore, our work not only provides a new method to fabricate high-quality,more » graphitized HCSs but also demonstrates a reliable approach to grow quality graphene on oxide surfaces using CVD without the presence of metal catalysts.« less

Surface Design and Engineering Toward Wear-Resistant, Self-Lubricating Diamond Films and Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1999-01-01

The tribological properties of chemical-vapor-deposited (CVD) diamond films vary with the environment, possessing a Jekyll-and-Hyde character. CVD diamond has low coefficient of friction and high wear resistance in air but high coefficient of friction and low wear resistance in vacuum. Improving the tribological functionality of materials (such as achieving low friction and good wear resistance) was an aim of this investigation. Three studies on the surface design, surface engineering, and tribology of CVD diamond have shown that its friction and wear are significantly reduced in ultrahigh vacuum. The main criteria for judging whether diamond films are an effective wear-resistant, self-lubricating material were coefficient of friction and wear rate, which must be less than 0.1 and on the order of 10(exp 6) cu mm/N(dot)m, respectively. In the first study the presence of a thin film (less than 1 micron thick) of amorphous, nondiamond carbon (hydrogenated carbon, also called diamondlike carbon or DLC) on CVD diamond greatly decreased the coefficient of friction and the wear rate. Therefore, a thin DLC film on CVD diamond can be an effective wear-resistant, lubricating coating in ultrahigh vacuum. In the second study the presence of an amorphous, nondiamond carbon surface layer formed on CVD diamond by ion implantation significantly reduced the coefficient of friction and the wear rate in ultrahigh vacuum. Therefore, such surface layers are acceptable for effective self-lubricating, wear-resistant applications of CVD diamond. In the third study CVD diamond in contact with cubic boron nitride exhibited low coefficient of friction in ultra high vacuum. Therefore, this materials combination can provide an effective self-lubricating, wear-resistant couple in ultrahigh vacuum.

Microcontact printing of monodiamond nanoparticles: an effective route to patterned diamond structure fabrication.

PubMed

Zhuang, Hao; Song, Bo; Staedler, Thorsten; Jiang, Xin

2011-10-04

By combining microcontact printing with a nanodiamond seeding technique, a precise micrometer-sized chemical vapor deposition (CVD) diamond pattern have been obtained. On the basis of the guidance of basic theoretical calculations, monodisperse detonation nanodiamonds (DNDs) were chosen as an "ink" material and oxidized poly(dimethylsiloxane) (PDMS) was selected to serve as a stamp because it features a higher interaction energy with the DNDs compared to that of the original PDMS. The adsorption kinetics shows an approximately exponential law with a maximum surface DND density of 3.4 × 10(10) cm(-2) after 20 min. To achieve a high transfer ratio of DNDs from the PDMS stamp to a silicon surface, a thin layer of poly(methyl methacrylate) (PMMA) was spin coated onto the substrates. A microwave plasma chemical vapor deposition system was used to synthesize the CVD diamond on the seeded substrate areas. Precise diamond patterns with a low expansion ratio (3.6%) were successfully prepared after 1.5 h of deposition. Further increases in the deposition time typically lead to a high expansion rate (∼0.8 μm/h). The general pattern shape, however, did not show any significant change. Compared with conventional diamond pattern deposition methods, the technique described here offers the advantages of being simple, inexpensive, damage-free, and highly compatible, rendering it attractive for a broad variety of industrial applications. © 2011 American Chemical Society

Process for manufacturing hollow fused-silica insulator cylinder

DOEpatents

Sampayan, Stephen E.; Krogh, Michael L.; Davis, Steven C.; Decker, Derek E.; Rosenblum, Ben Z.; Sanders, David M.; Elizondo-Decanini, Juan M.

2001-01-01

A method for building hollow insulator cylinders that can have each end closed off with a high voltage electrode to contain a vacuum. A series of fused-silica round flat plates are fabricated with a large central hole and equal inside and outside diameters. The thickness of each is related to the electron orbit diameter of electrons that escape the material surface, loop, and return back. Electrons in such electron orbits can support avalanche mechanisms that result in surface flashover. For example, the thickness of each of the fused-silica round flat plates is about 0.5 millimeter. In general, the thinner the better. Metal, such as gold, is deposited onto each top and bottom surface of the fused-silica round flat plates using chemical vapor deposition (CVD). Eutectic metals can also be used with one alloy constituent on the top and the other on the bottom. The CVD, or a separate diffusion step, can be used to defuse the deposited metal deep into each fused-silica round flat plate. The conductive layer may also be applied by ion implantation or gas diffusion into the surface. The resulting structure may then be fused together into an insulator stack. The coated plates are aligned and then stacked, head-to-toe. Such stack is heated and pressed together enough to cause the metal interfaces to fuse, e.g., by welding, brazing or eutectic bonding. Such fusing is preferably complete enough to maintain a vacuum within the inner core of the assembled structure. A hollow cylinder structure results that can be used as a core liner in a dielectric wall accelerator and as a vacuum envelope for a vacuum tube device where the voltage gradients exceed 150 kV/cm.

Epitaxial regrowth of silicon for the fabrication of radial junction nanowire solar cells

NASA Astrophysics Data System (ADS)

Kendrick, Chito E.; Eichfeld, Sarah M.; Ke, Yue; Weng, Xiaojun; Wang, Xin; Mayer, Theresa S.; Redwing, Joan M.

2010-08-01

Radial p-n silicon nanowire (SiNW) solar cells are of interest as a potential pathway to increase the efficiency of crystalline silicon photovoltaics by reducing the junction length and surface reflectivity. Our studies have focused on the use of vapor-liquid-solid (VLS) growth in combination with chemical vapor deposition (CVD) processing for the fabrication of radial p-n junction SiNW array solar cells. High aspect ratio p-type SiNW arrays were initially grown on gold-coated (111) Si substrates by CVD using SiCl4 as the source gas and B2H6 as the p-type dopant source. The epitaxial re-growth of n-type Si shell layers on the Si nanowires was then investigated using SiH4 as the source gas and PH3 as the dopant. Highly conformal coatings were achieved on nanowires up to 25 μm in length. The microstructure of the Si shell layer changed from polycrystalline to single crystal as the deposition temperature was raised from 650oC to 950oC. Electrical test structures were fabricated by aligning released SiNWs onto pre-patterned substrates via fieldassisted assembly followed by selective removal of the n-type shell layer and contact deposition. Current-voltage measurements of the radial p-n SiNWs diodes fabricated with re-grown Si shell layers at 950°C demonstrate rectifying behavior with an ideality factor of 1.93. Under illumination from an AM1.5g spectrum and efficiency for this single SiNW radial p-n junction was determined to be 1.8%, total wire diameter was 985 nm.

A systematic study of atmospheric pressure chemical vapor deposition growth of large-area monolayer graphene.

PubMed

Liu, Lixin; Zhou, Hailong; Cheng, Rui; Chen, Yu; Lin, Yung-Chen; Qu, Yongquan; Bai, Jingwei; Ivanov, Ivan A; Liu, Gang; Huang, Yu; Duan, Xiangfeng

2012-01-28

Graphene has attracted considerable interest as a potential material for future electronics. Although mechanical peel is known to produce high quality graphene flakes, practical applications require continuous graphene layers over a large area. The catalyst-assisted chemical vapor deposition (CVD) is a promising synthetic method to deliver wafer-sized graphene. Here we present a systematic study on the nucleation and growth of crystallized graphene domains in an atmospheric pressure chemical vapor deposition (APCVD) process. Parametric studies show that the mean size of the graphene domains increases with increasing growth temperature and CH 4 partial pressure, while the density of domains decreases with increasing growth temperature and is independent of the CH 4 partial pressure. Our studies show that nucleation of graphene domains on copper substrate is highly dependent on the initial annealing temperature. A two-step synthetic process with higher initial annealing temperature but lower growth temperature is developed to reduce domain density and achieve high quality full-surface coverage of monolayer graphene films. Electrical transport measurements demonstrate that the resulting graphene exhibits a high carrier mobility of up to 3000 cm 2 V -1 s -1 at room temperature.

Controllable growth of shaped graphene domains by atmospheric pressure chemical vapour deposition

NASA Astrophysics Data System (ADS)

Fan, Lili; Li, Zhen; Li, Xiao; Wang, Kunlin; Zhong, Minlin; Wei, Jinquan; Wu, Dehai; Zhu, Hongwei

2011-12-01

Graphene domains in different shapes have been grown on copper substrates via atmospheric pressure chemical vapour deposition by controlling the growth process parameters. Under stabilized conditions, graphene domains tend to be six-fold symmetric hexagons under low flow rate methane with some domains in an irregular hexagonal shape. After further varying the growth duration, methane flow rate, and temperature, graphene domains have developed shapes from hexagon to shovel and dendrite. Two connecting modes, through overlap and merging of adjacent graphene domains, are proposed.Graphene domains in different shapes have been grown on copper substrates via atmospheric pressure chemical vapour deposition by controlling the growth process parameters. Under stabilized conditions, graphene domains tend to be six-fold symmetric hexagons under low flow rate methane with some domains in an irregular hexagonal shape. After further varying the growth duration, methane flow rate, and temperature, graphene domains have developed shapes from hexagon to shovel and dendrite. Two connecting modes, through overlap and merging of adjacent graphene domains, are proposed. Electronic supplementary information (ESI) available: Schematics of CVD setups for graphene growth, Raman spectra and SEM images. See DOI: 10.1039/c1nr11480h

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.

Strain Gauges Based on CVD Graphene Layers and Exfoliated Graphene Nanoplatelets with Enhanced Reproducibility and Scalability for Large Quantities

PubMed Central

Yokaribas, Volkan; Schneider, Daniel S.; Friebertshäuser, Philipp; Lemme, Max C.; Fritzen, Claus-Peter

2017-01-01

The two-dimensional material graphene promises a broad variety of sensing activities. Based on its low weight and high versatility, the sensor density can significantly be increased on a structure, which can improve reliability and reduce fluctuation in damage detection strategies such as structural health monitoring (SHM). Moreover; it initializes the basis of structure–sensor fusion towards self-sensing structures. Strain gauges are extensively used sensors in scientific and industrial applications. In this work, sensing in small strain fields (from −0.1% up to 0.1%) with regard to structural dynamics of a mechanical structure is presented with sensitivities comparable to bulk materials by measuring the inherent piezoresistive effect of graphene grown by chemical vapor deposition (CVD) with a very high aspect ratio of approximately 4.86 × 108. It is demonstrated that the increasing number of graphene layers with CVD graphene plays a key role in reproducible strain gauge application since defects of individual layers may become less important in the current path. This may lead to a more stable response and, thus, resulting in a lower scattering.. Further results demonstrate the piezoresistive effect in a network consisting of liquid exfoliated graphene nanoplatelets (GNP), which result in even higher strain sensitivity and reproducibility. A model-assisted approach provides the main parameters to find an optimum of sensitivity and reproducibility of GNP films. The fabricated GNP strain gauges show a minimal deviation in PRE effect with a GF of approximately 5.6 and predict a linear electromechanical behaviour up to 1% strain. Spray deposition is used to develop a low-cost and scalable manufacturing process for GNP strain gauges. In this context, the challenge of reproducible and reliable manufacturing and operating must be overcome. The developed sensors exhibit strain gauges by considering the significant importance of reproducible sensor performances and open the path for graphene strain gauges for potential usages in science and industry. PMID:29258260

Large Area CVD MoS2 RF transistors with GHz performance

NASA Astrophysics Data System (ADS)

Nagavalli Yogeesh, Maruthi; Sanne, Atresh; Park, Saungeun; Akinwade, Deji; Banerjee, Sanjay

Molybdenum disulfide (MoS2) is a 2D semiconductor in the family of transition metal dichalcogenides (TMDs). Its single layer direct bandgap of 1.8 eV allows for high ION/IOFF metal-oxide semiconducting field-effect transistors (FETs). More relevant for radio frequency (RF) wireless applications, theoretical studies predict MoS2 to have saturation velocities, vsat >3×106 cm/s. Facilitated by cm-scale CVD MoS2, here we design and fabricate both top-gated and embedded gate short channel MoS2 RF transistors, and provide a systematic comparison of channel length scaling, extrinsic doping from oxygen-deficient dielectrics, and a gate-first gate-last process flow. The intrinsic fT (fmax) obtained from the embedded gate transistors shows 3X (2X) improvement over top-gated CVD MoS2 RF FETs, and the largest high-field saturation velocity, vsat = 1.88 ×106 cm/s, in MoS2 reported so far. The gate-first approach, offers enhancement mode operation, ION/IOFF ratio of 10, 8< and the highest reported transconductance (gm) of 70 μS/ μm. By manipulating the interfacial oxygen vacancies in atomic layer deposited (ALD) HfO2-x we are able to achieve 2X current density over stoichiometric Al2O3. We demonstrate a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Desalination by Membrane Distillation using Electrospun Polyamide Fiber Membranes with Surface Fluorination by Chemical Vapor Deposition.

PubMed

Guo, Fei; Servi, Amelia; Liu, Andong; Gleason, Karen K; Rutledge, Gregory C

2015-04-22

Fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were fabricated by electrospinning and rendered hydrophobic by applying a conformal coating of poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) using initiated chemical vapor deposition (iCVD). A set of iCVD-treated electrospun PA6(3)T fiber membranes with fiber diameters ranging from 0.25 to 1.8 μm were tested for desalination using the air gap membrane distillation configuration. Permeate fluxes of 2-11 kg/m2/h were observed for temperature differentials of 20-45 °C between the feed stream and condenser plate, with rejections in excess of 99.98%. The liquid entry pressure was observed to increase dramatically, from 15 to 373 kPa with reduction in fiber diameter. Contrary to expectation, for a given feed temperature the permeate flux was observed to increase for membranes of decreasing fiber diameter. The results for permeate flux and salt rejection show that it is possible to construct membranes for membrane distillation even from intrinsically hydrophilic materials after surface modification by iCVD and that the fiber diameter is shown to play an important role on the membrane distillation performance in terms of permeate flux, salt rejection, and liquid entry pressure.

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature

PubMed Central

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-01-01

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures. PMID:28772520

Effects of Thickness and Amount of Carbon Nanofiber Coated Carbon Fiber on Improving the Mechanical Properties of Nanocomposites

PubMed Central

Ghaemi, Ferial; Ahmadian, Ali; Yunus, Robiah; Ismail, Fudziah; Rahmanian, Saeed

2016-01-01

In the current study, carbon nanofibers (CNFs) were grown on a carbon fiber (CF) surface by using the chemical vapor deposition method (CVD) and the influences of some parameters of the CVD method on improving the mechanical properties of a polypropylene (PP) composite were investigated. To obtain an optimum surface area, thickness, and yield of the CNFs, the parameters of the chemical vapor deposition (CVD) method, such as catalyst concentration, reaction temperature, reaction time, and hydrocarbon flow rate, were optimized. It was observed that the optimal surface area, thickness, and yield of the CNFs caused more adhesion of the fibers with the PP matrix, which enhanced the composite properties. Besides this, the effectiveness of reinforcement of fillers was fitted with a mathematical model obtaining good agreement between the experimental result and the theoretical prediction. By applying scanning electronic microscope (SEM), transmission electron microscope (TEM), and Raman spectroscopy, the surface morphology and structural information of the resultant CF-CNF were analyzed. Additionally, SEM images and a mechanical test of the composite with a proper layer of CNFs on the CF revealed not only a compactness effect but also the thickness and surface area roles of the CNF layers in improving the mechanical properties of the composites. PMID:28344263

Acetylene-sourced CVD-synthesised catalytically active graphene for electrochemical biosensing.

PubMed

Osikoya, Adeniyi Olugbenga; Parlak, Onur; Murugan, N Arul; Dikio, Ezekiel Dixon; Moloto, Harry; Uzun, Lokman; Turner, Anthony Pf; Tiwari, Ashutosh

2017-03-15

In this study, we have demonstrated the use of chemical vapour deposition (CVD) grown-graphene to develop a highly-ordered graphene-enzyme electrode for electrochemical biosensing. The graphene sheets were deposited on 1.00mm thick copper sheet at 850°C using acetylene (C 2 H 2 ) as carbon source in an argon (Ar) and nitrogen (N 2 ) atmosphere. An anionic surfactant was used to increase wettability and hydrophilicity of graphene; thereby facilitating the assembly of biomolecules on the electrode surface. Meanwhile, the theoretical calculations confirmed the successful modification of hydrophobic nature of graphene through the anionic surface assembly, which allowed high-ordered immobilisation of glucose oxidase (GOx) on the graphene. The electrochemical sensing activities of the graphene-electrode was explored as a model for bioelectrocatalysis. The bioelectrode exhibited a linear response to glucose concentration ranging from 0.2 to 9.8mM, with sensitivity of 0.087µA/µM/cm 2 and a detection limit of 0.12µM (S/N=3). This work sets the stage for the use of acetylene-sourced CVD-grown graphene as a fundamental building block in the fabrication of electrochemical biosensors and other bioelectronic devices. Copyright © 2016 Elsevier B.V. All rights reserved.

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature.

PubMed

Miyake, Shojiro; Suzuki, Shota; Miyake, Masatoshi

2017-02-10

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures.

The CRDS method application for study of the gas-phase processes in the hot CVD diamond thin film.

NASA Astrophysics Data System (ADS)

Buzaianumakarov, Vladimir; Hidalgo, Arturo; Morell, Gerardo; Weiner, Brad; Buzaianu, Madalina

2006-03-01

For detailed analysis of problem related to the hot CVD carbon-containing nano-material growing, we have to detect different intermediate species forming during the growing process as well as investigate dependences of concentrations of these species on different experimental parameters (concentrations of the CJH4, H2S stable chemical compounds and distance from the filament system to the substrate surface). In the present study, the HS and CS radicals were detected using the Cavity Ring Down Spectroscopic (CRDS) method in the hot CVD diamond thin film for the CH4(0.4 %) + H2 mixture doped by H2S (400 ppm). The absolute absorption density spectra of the HS and CS radicals were obtained as a function of different experimental parameters. This study proofs that the HS and CS radicals are an intermediate, which forms during the hot filament CVD process. The kinetics approach was developed for detailed analysis of the experimental data obtained. The kinetics scheme includes homogenous and heterogenous processes as well as processes of the chemical species transport in the CVD chamber.

Development of graphene process control by industrial optical spectroscopy setup

NASA Astrophysics Data System (ADS)

Fursenko, O.; Lukosius, M.; Lupina, G.; Bauer, J.; Villringer, C.; Mai, A.

2017-06-01

The successful integration of graphene into microelectronic devices depends strongly on the availability of fast and nondestructive characterization methods of graphene grown by CVD on large diameter production wafers [1-3] which are in the interest of the semiconductor industry. Here, a high-throughput optical metrology method for measuring the thickness and uniformity of large-area graphene sheets is demonstrated. The method is based on the combination of spectroscopic ellipsometry and normal incidence reflectometry in UV-Vis wavelength range (200-800 nm) with small light spots ( 30 μm2) realized in wafer optical metrology tool. In the first step graphene layers were transferred on a SiO2/Si substrate in order to determine the optical constants of graphene by the combination of multi-angle ellipsometry and reflectometry. Then these data were used for the development of a process control recipe of CVD graphene on 200 mm Ge(100)/Si(100) wafers. The graphene layer quality was additionally monitored by Raman spectroscopy. Atomic force microscopy measurements were performed for micro topography evaluation. In consequence, a robust recipe for unambiguous thickness monitoring of all components of a multilayer film stack, including graphene, surface residuals or interface layer underneath graphene and surface roughness is developed. Optical monitoring of graphene thickness uniformity over a wafer has shown an excellent long term stability (s=0.004 nm) regardless of the growth of interfacial GeO2 and surface roughness. The sensitivity of the optical identification of graphene during microelectronic processing was evaluated. This optical metrology technique with combined data collection exhibit a fast and highly precise method allowing one an unambiguous detection of graphene after transferring as well as after the CVD deposition process on a Ge(100)/Si(100) wafer. This approach is well suited for industrial applications due to its repeatability and flexibility.

Pyrolytic Carbon Coatings on Aligned Carbon Nanotube Assemblies and Fabrication of Advanced Carbon Nanotube/Carbon Composites

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh

Chemical vapor deposition (CVD) is a technique used to create a pyrolytic carbon (PyC) matrix around fibrous preforms in carbon/carbon (C/C) composites. Due to difficulties in producing three-dimensional carbon nanotube (CNT) assemblies, use of nanotubes in CVD fabricated CNT/C composites is limited. This dissertation describes efforts to: 1) Study the microstructure of PyC deposited on CNTs in order to understand the effect of microstructure and morphology of carbon coatings on graphitization behavior of CNT/PyC composites. This understanding helped to suggest a new approach for controlled radial growth of CNTs. 2) Evaluate the properties of CNT/PyC structures as a novel form of CNT assemblies with resilient, anisotropic and tunable properties. PyC was deposited on aligned sheets of nanotubes, drawn from spinnable CNT arras, using CVD of acetylene gas. At longer deposition times, the microstructure of PyC changed from laminar turbostratic carbon to a disordered carbon. For samples with short PyC deposition times (up to 30 minutes), deposited carbon layer rearranged during graphitization treatment and resulted in a crystalline structure where the coating and original tube walls could not be easily differentiated. In contrast, in samples with longer carbon deposition durations, carbon layers close to the surface of the coating remained disordered even after graphitization thermal treatment. Understanding the effect of PyC microstructure transition on graphitization behavior of CNT/PyC composites was used to develop a new method for controlled radial growth of CNTs. Carbon coated aligned CNT sheets were graphitized after each short (20 minutes) carbon deposition cycle. This prevented development of disorder carbon during subsequent PyC deposition cycles. Using cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. This resulted into radial growth of CNTs, from 40 to 100 nm. Infiltration of PyC into stacked layered sheets of aligned CNTs produced resilient foam-like materials that exhibited complete recovery from 90% compressive strain. PyC coated the junctions between nanotubes and also increased their surface roughness. These changes were assumed to be responsible for the resiliency of the, once inelastic, assembly of nanotubes. While nanotubes' alignment resulted in anisotropic properties of the foams, variation in PyC infiltration duration was used to tune the foams' properties. Further investigation into properties of these foams showed promising results for their application as pressure/strain sensor and selective liquid absorbers for oil spill clean ups. Finally, CNT foams were used as novel substrates for growth of secondary nanotube assemblies. In order to achieve that, foams were first coated with alumina buffer layers using atomic layer deposition (ALD) method. New nanotubes were further grown inside the foams by CVD of acetylene over iron nano-particles. Super low density and highly porous structure of the foams allowed for diffusion of catalyst along with growth gasses into their bulk, which resulted in growth of secondary nanotubes throughout the thickness of the foams. The thickness of the alumina buffer layer was shown to influence CNT nucleation density and growth uniformity across the thickness of the foams. Compressive mechanical testing of the foams showed an order of magnitude increase in compression strength after secondary CNT growth.