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Sample records for hot-wire cvd growth

  1. Growth of boron doped hydrogenated nanocrystalline cubic silicon carbide (3C-SiC) films by Hot Wire-CVD

    Energy Technology Data Exchange (ETDEWEB)

    Pawbake, Amit [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Mayabadi, Azam; Waykar, Ravindra; Kulkarni, Rupali; Jadhavar, Ashok [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Waman, Vaishali [Modern College of Arts, Science and Commerce, Shivajinagar, Pune 411 005 (India); Parmar, Jayesh [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Bhattacharyya, Somnath [Department of Metallurgical and Materials Engineering, IIT Madras, Chennai 600 036 (India); Ma, Yuan‐Ron [Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan (China); Devan, Rupesh; Pathan, Habib [Department of Physics, Savitribai Phule Pune University, Pune 411007 (India); Jadkar, Sandesh, E-mail: sandesh@physics.unipune.ac.in [Department of Physics, Savitribai Phule Pune University, Pune 411007 (India)

    2016-04-15

    Highlights: • Boron doped nc-3C-SiC films prepared by HW-CVD using SiH{sub 4}/CH{sub 4}/B{sub 2}H{sub 6}. • 3C-Si-C films have preferred orientation in (1 1 1) direction. • Introduction of boron into SiC matrix retard the crystallanity in the film structure. • Film large number of SiC nanocrystallites embedded in the a-Si matrix. • Band gap values, E{sub Tauc} and E{sub 04} (E{sub 04} > E{sub Tauc}) decreases with increase in B{sub 2}H{sub 6} flow rate. - Abstract: Boron doped nanocrystalline cubic silicon carbide (3C-SiC) films have been prepared by HW-CVD using silane (SiH{sub 4})/methane (CH{sub 4})/diborane (B{sub 2}H{sub 6}) gas mixture. The influence of boron doping on structural, optical, morphological and electrical properties have been investigated. The formation of 3C-SiC films have been confirmed by low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy and high resolution-transmission electron microscopy (HR-TEM) analysis whereas effective boron doping in nc-3C-SiC have been confirmed by conductivity, charge carrier activation energy, and Hall measurements. Raman spectroscopy and HR-TEM analysis revealed that introduction of boron into the SiC matrix retards the crystallanity in the film structure. The field emission scanning electron microscopy (FE-SEM) and non contact atomic force microscopy (NC-AFM) results signify that 3C-SiC film contain well resolved, large number of silicon carbide (SiC) nanocrystallites embedded in the a-Si matrix having rms surface roughness ∼1.64 nm. Hydrogen content in doped films are found smaller than that of un-doped films. Optical band gap values, E{sub Tauc} and E{sub 04} decreases with increase in B{sub 2}H{sub 6} flow rate.

  2. Degradation of a tantalum filament during the hot-wire CVD of silicon nitride thin films

    Energy Technology Data Exchange (ETDEWEB)

    Oliphant, C.J. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); National Metrology Institute of South Africa, Private Bag X34, Lynwood Ridge, Pretoria 0040 (South Africa); Arendse, C.J., E-mail: cjarendse@uwc.ac.za [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); Muller, T.F.G. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); Jordaan, W.A. [National Metrology Institute of South Africa, Private Bag X34, Lynwood Ridge, Pretoria 0040 (South Africa); Knoesen, D. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa)

    2015-01-30

    Electron backscatter diffraction revealed that during the hot-wire deposition of silicon nitride, a tantalum filament partially transformed to some of its nitrides and silicides. The deposition of an encapsulating silicon nitride layer occurred at the cooler filament ends. Time-of-flight secondary ion mass spectroscopy disclosed the presence of hydrogen, nitrogen and silicon containing ions within the aged filament bulk. Hardness measurements revealed that the recrystallized tantalum core experienced significant hardening, whereas the silicides and nitrides were harder but more brittle. Crack growth, porosity and the different thermal expansion amongst the various phases are all enhanced at the hotter centre regions, which resulted in failure at these areas. - Highlights: • Tantalum filament degrades and fails during hot-wire CVD of silicon nitride thin films. • An encapsulating silicon nitride layer is deposited at the cooler ends. • Electron backscatter diffraction reveals Ta-silicides and -nitrides with a Ta core. • Filament failure occurs at hot centre regions due to different mechanical properties of Ta, its silicides and nitrides.

  3. The Influence of the Hot Wire Temperature on the Crystallization of μc-Si:H Films Prepared by Hot Wire-Assisted-ECR-CVD

    OpenAIRE

    Li, Ying; Li, Zhi Zhong; Chen, Guang hua; Kumeda, Minoru

    2007-01-01

    We have constructed a hot-wire-assisted ECR-CVD system to prepare a-Si:H and μc-Si:H films. The effect of hot wire (HW) temperature on crystallization of a-Si:H films is studied in the films prepared by this system. At low HW temperature, about 20 at.% hydrogen is included in the film. With increasing the HW temperature, the contents of the total hydrogen, SiH2 and SiH decrease, and the microcrystalline phase appears. It is found from the area of the TO peak of the Raman scattering spectra th...

  4. Untersuchungen zur Hot-wire CVD auf kristallinem Silizium und deren Anwendung in Solarzellen

    OpenAIRE

    Seitz, Holger

    2000-01-01

    In den letzten Jahren konnte ein beachtlicher Fortschritt bei der Entwicklung kostengünstiger, hoch effektiver Si-Solarzellen mit kristalliner Basis und einem Emitter aus amorphem Silizium (a-Si:H) beobachtet werden. Für die Herstellung dieser Emitter wird zur Zeit ausschliesslich die plasmaunterstützte chemische Gasphasenabscheidung (PECVD)verwendet, die jedoch aufgrund ihrer Hochfrequenztechnik sehr aufwendig ist. Die Hot-wire CVD, das heisst die Abscheidung durch Zersetzung eines Gases an ...

  5. Hot wire CVD deposition of nanocrystalline silicon solar cells on rough substrates

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hongbo B.T., E-mail: h.li@uu.n [Utrecht University, Faculty of Science, Debye Institute for Nanomaterials Science, P.O. Box 80000, 3508 TA Utrecht (Netherlands); Werf, Karine H.M. van der; Rath, Jatin K.; Schropp, Ruud E.I. [Utrecht University, Faculty of Science, Debye Institute for Nanomaterials Science, P.O. Box 80000, 3508 TA Utrecht (Netherlands)

    2009-04-30

    In silicon thin film solar cell technology, frequently rough or textured substrates are used to scatter the light and enhance its absorption. The important issue of the influence of substrate roughness on silicon nanocrystal growth has been investigated through a series of nc-Si:H single junction p-i-n solar cells containing i-layers deposited with Hot-wire CVD. It is shown that silicon grown on the surface of an unoptimized rough substrate contains structural defects, which deteriorate solar cell performance. By introducing parameter v, voids/substrate area ratio, we could define a criterion for the morphology of light trapping substrates for thin film silicon solar cells: a preferred substrate should have a v value of less than around 1 x 10{sup -6}, correlated to a substrate surface rms value of lower than around 50 nm. Our Ag/ZnO substrates with rms roughness less than this value typically do not contain microvalleys with opening angles smaller than {approx} 110{sup o}, resulting in solar cells with improved output performance. We suggest a void-formation model based on selective etching of strained Si-Si atoms due to the collision of growing silicon film surface near the valleys of the substrate.

  6. Properties of Boron-dopedμc-Ge:H Films Deposited by Hot-wire CVD

    Institute of Scientific and Technical Information of China (English)

    HUANG Haibin; SHEN Honglie; WU Tianru; LU Linfeng; TANG Zhengxia; SHEN Jiancang

    2015-01-01

    Boron-doped hydrogenated microcrystalline Germanium (μc-Ge:H)fi lms were deposited by hot-wire CVD. H2 diluted GeH4 and B2H6 were used as precursors and the substrate temperature was kept at 300ć. The properties of the samples were analyzed by XRD, Raman spectroscopy, Fourier transform infrared spectrometer and Hall Effect measurement with Van der Pauw method. It is found that thefi lms are partially crystallized, with crystalline fractions larger than 45% and grain sizes smaller than 50 nm. The B-doping can enhance the crystallization but reduce the grain sizes, and also enhance the preferential growth of Ge (220). The conductivity of thefi lms increases and tends to be saturated with increasingdiborane-to-germane ratio . All the Hall mobilities of the samples are larger than 3.8 cm2·V-1·s-1. A high conductivity of 41.3Ω-1ίcm-1 is gained at=6.7%.

  7. Novel Gas Barrier SiOC Coating to PET Bottles through a Hot Wire CVD Method

    Directory of Open Access Journals (Sweden)

    Masaki Nakaya

    2016-01-01

    Full Text Available In an attempt to enhance the gas barrier enhancement of plastic containers such as poly(ethylene terephthalate bottles, a novel method was found using a hot wire CVD technique, where tantalum wire is heated and exposed to a gas flow of vinyl silane. The resultant SiOC thin film was confirmed to characteristically contain Si-Si bonds in its surface and demonstrate a remarkably and highly practical decrease of the permeation of various gas through poly(ethylene terephthalate bottles.

  8. Development of laser-fired contacts for amorphous silicon layers obtained by Hot-Wire CVD

    Energy Technology Data Exchange (ETDEWEB)

    Munoz, D. [XaRMAE-Universitat de Barcelona, Departament de Fisica Aplicada i Optica, Diagonal 647, Barcelona 08028 (Spain)], E-mail: delfina@eel.upc.edu; Voz, C.; Blanque, S. [Universitat Politecnica de Catalunya, Grup de Recerca en Micro i Nanotecnologies, Jordi Girona 1-3, Barcelona 08034 (Spain); Ibarz, D.; Bertomeu, J. [XaRMAE-Universitat de Barcelona, Departament de Fisica Aplicada i Optica, Diagonal 647, Barcelona 08028 (Spain); Alcubilla, R. [Universitat Politecnica de Catalunya, Grup de Recerca en Micro i Nanotecnologies, Jordi Girona 1-3, Barcelona 08034 (Spain)

    2009-03-15

    In this work we study aluminium laser-fired contacts for intrinsic amorphous silicon layers deposited by Hot-Wire CVD. This structure could be used as an alternative low temperature back contact for rear passivated heterojunction solar cells. An infrared Nd:YAG laser (1064 nm) has been used to locally fire the aluminium through the thin amorphous silicon layers. Under optimized laser firing parameters, very low specific contact resistances ({rho}{sub c} {approx} 10 m{omega} cm{sup 2}) have been obtained on 2.8 {omega} cm p-type c-Si wafers. This investigation focuses on maintaining the passivation quality of the interface without an excessive increase in the series resistance of the device.

  9. Synthesis of nanometal oxides and nanometals using hot-wire and thermal CVD

    Energy Technology Data Exchange (ETDEWEB)

    Mitra, S. [Department of Physics and Engineering Physics, University of Tulsa, Tulsa, OK 74104 (United States)], E-mail: saibal-mitra@utulsa.edu; Sridharan, K.; Unnam, J. [Department of Chemical Engineering, University of Tulsa, Tulsa, OK 74104 (United States); Ghosh, K. [Department of Physics, Astronomy, and Materials Science, Missouri State University, MO65897 (United States)

    2008-01-15

    We report the synthesis of nano-oxides of molybdenum, tungsten, and zinc. Molybdenum oxide (MoO{sub 3}) and tungsten oxide (WO{sub x}) were produced by hot-wire CVD with molybdenum and tungsten filaments, respectively while zinc oxide (ZnO) was produced by thermal CVD. When high purity molybdenum wire was oxidized at ambient system atmosphere, nanorods and nanostraws of MoO{sub 3} with length ranging from {approx} 20-80 nm and diameters ranging from {approx} 5-15 nm were produced. Also, the oxidation of the tungsten filament led to the deposition of tungsten oxide nanorods (10-25 nm diameter and 75-90 nm long) and nanospheres with diameters of {approx} 60 nm. Each oxide was reduced to its metallic form by annealing in a hydrogen environment to produce metallic nanoparticles. Nanorods and nanoribbons of ZnO with diameters ranging from 20-65 nm and lengths up to 2 {mu}m were also produced.

  10. Preparation of hydrogenated microcrystalline silicon films with hot-wire-assisted MWECR-CVD system

    Institute of Scientific and Technical Information of China (English)

    He Bin; Chen Guang-Hua; Zhu Xiu-Hong; Zhang Wen-Li; Ding Yi; Ma Zhan-Jie; Gao Zhi-Hua; Song Xue-Mei; Deng Jin-Xiang

    2006-01-01

    Intrinsic hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared by hot-wire-assisted microwave electron-cyclotron-resonance chemical vapour deposition (Hw-MwECR-CVD) under different deposition conditions.Fourier-transform infrared spectra and Raman spectra were measured.Optical band gap WaS determined by Tauc plots,and experiments of photo-induced degradation were performed.It was observed that hydrogen dilution plays a more essential role than substrate temperature in microcrystalline transformation at low temperatures. Crystalline volume fraction and mean grain size in the films increase with the dilution ratio (R=H2/(H2+SiH4)).With the rise of crystallinity in the films,the optical band gap tends to become narrower while the hydrogen content and photo-induced degradation decrease dramatically.The samples,were identified as μc-Si:H films,by calculating the optical band gap.It is considered that hydrogen dilution has an effect on reducing the crystallization activation energy of the material,which promotes the heterogeneous solid-state phase transition characterized by the Johnson-Mehl-Avrami (JMA) equation.The films with the needed structure can be prepared by balancing deposition and crystaUization through controlling process parameters.

  11. Deposition of device quality silicon nitride with ultra high deposition rate (> 7 nm/s) using hot-wire CVD

    NARCIS (Netherlands)

    Verlaan, V.; Houweling, Z.S.; van der Werf, C.H.M.; Romijn, I.G.; Schropp, R.E.I.; Goldbach, H.D.

    2008-01-01

    The application of hot-wire (HW) CVD deposited silicon nitride (SiNx) as passivating anti-reflection coating on multicrystalline silicon (mc-Si) solar cells is investigated. The highest efficiency reached is 15.7% for SiNx layers with an N/Si ratio of 1.20 and a high mass density of 2.9 g/cm3. These

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

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Mengdi, E-mail: M.Yang@utwente.nl; Aarnink, Antonius A. I.; Kovalgin, Alexey Y.; Gravesteijn, Dirk J.; Wolters, Rob A. M.; Schmitz, Jurriaan [MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands)

    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 molecular 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.

  13. Low temperature back-surface-field contacts deposited by hot-wire CVD for heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Munoz, D. [Universitat Politecnica de Catalunya, Grup de Recerca en Micro i Nanotecnologies, Jordi Girona 1-3, Barcelona 08034 (Spain)], E-mail: delfina@eel.upc.edu; Voz, C.; Martin, I.; Orpella, A.; Alcubilla, R. [Universitat Politecnica de Catalunya, Grup de Recerca en Micro i Nanotecnologies, Jordi Girona 1-3, Barcelona 08034 (Spain); Villar, F.; Bertomeu, J.; Andreu, J. [CeRMAE-Universitat de Barcelona, Departament de Fisica Aplicada i Optica, Diagonal 647, Barcelona 08028 (Spain); Roca-i-Cabarrocas, P. [LPICM-Ecole Polytechnique, CNRS 91128 Palaiseau (France)

    2008-08-30

    The growing interest in using thinner wafers (< 200 {mu}m) requires the development of low temperature passivation strategies for the back contact of heterojunction solar cells. In this work, we investigate low temperature deposited back contacts based on boron-doped amorphous silicon films obtained by Hot-Wire CVD. The influence of the deposition parameters and the use of an intrinsic buffer layer have been considered. The microstructure of the deposited thin films has been comprehensively studied by Spectroscopic Ellipsometry in the UV-visible range. The effective recombination velocity at the back surface has been measured by the Quasi-Steady-State Photoconductance technique. Complete double-side heterojunction solar cells (1 cm{sup 2}) have been fabricated and characterized by External Quantum Efficiency and current-voltage measurements. Total-area conversion efficiencies up to 14.5% were achieved in a fully low temperature process (< 200 deg. C)

  14. Growth process conditions of tungsten oxide thin films using hot-wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Houweling, Z. Silvester, E-mail: Z.S.Houweling@uu.nl [Nanophotonics - Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University, Princetonlaan 4, 3584 CB Utrecht (Netherlands); Geus, John W. [Electron Microscopy, Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands); Jong, Michiel de; Harks, Peter-Paul R.M.L.; Werf, Karine H.M. van der; Schropp, Ruud E.I. [Nanophotonics - Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University, Princetonlaan 4, 3584 CB Utrecht (Netherlands)

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer Process parameters to control hot-wire CVD of WO{sub 3-x} are categorized. Black-Right-Pointing-Pointer Growth time, oxygen partial pressure, filament and substrate temperature are varied. Black-Right-Pointing-Pointer Chemical and crystal structure, optical bandgap and morphology are determined. Black-Right-Pointing-Pointer Oxygen partial pressure determines the deposition rate up to as high as 36 {mu}m min{sup -1}. Black-Right-Pointing-Pointer Nanostructures, viz. wires, crystallites and closed crystallite films, are controllably deposited. - Abstract: We report the growth conditions of nanostructured tungsten oxide (WO{sub 3-x}) thin films using hot-wire chemical vapor deposition (HWCVD). Two tungsten filaments were resistively heated to various temperatures and exposed to an air flow at various subatmospheric pressures. The oxygen partial pressure was varied from 6.0 Multiplication-Sign 10{sup -6} to 1.0 mbar and the current through the filaments was varied from 4.0 to 9.0 A, which constitutes a filament temperature of 1390-2340 Degree-Sign C in vacuum. It is observed that the deposition rate of the films is predominantly determined by the oxygen partial pressure; it changes from about 1 to about 36,000 nm min{sup -1} in the investigated range. Regardless of the oxygen partial pressure and filament temperature used, thin films with a nanogranular morphology are obtained, provided that the depositions last for 30 min or shorter. The films consist either of amorphous or partially crystallized WO{sub 3-x} with high averaged transparencies of over 70% and an indirect optical band gap of 3.3 {+-} 0.1 eV. A prolonged deposition time entails an extended exposure of the films to thermal radiation from the filaments, which causes crystallization to monoclinic WO{sub 3} with diffraction maxima due to the (0 0 2), (2 0 0) and (0 2 0) crystallographic planes, furthermore the nanograins sinter and the films exhibit a cone

  15. Growth Process Conditions of Tungsten Oxide Thin Films Using Hot-Wire Chemical Vapor Deposition

    NARCIS (Netherlands)

    Houweling, Z.S.; Geus, J.W.; de Jong, M.; Harks, P.P.R.M.L.; van der Werf, C.H.M.; Schropp, R.E.I.

    2011-01-01

    We report the growth conditions of nanostructured tungsten oxide (WO3−x) thin films using hot-wire chemical vapor deposition (HWCVD). Two tungsten filaments were resistively heated to various temperatures and exposed to an air flow at various subatmospheric pressures. The oxygen partial pressure was

  16. Microcrystalline silicon from very high frequency plasma deposition and hot-wire CVD for ``micromorph`` tandem solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Brummack, H.; Brueggemann, R.; Wanka, H.N.; Hierzenberger, A.; Schubert, M.B. [Univ. Stuttgart (Germany). Inst. fuer Physikalische Elektronik

    1997-12-31

    The authors have grown microcrystalline silicon from a glow discharge at very high frequencies of 55 MHz and 170 MHz with high hydrogen dilution, and also, at more than 10 times higher growth rates, similar films by hot-wire chemical vapor deposition. Both kinds of materials have extensively been characterized and compared in terms of structural, optical and electronic properties, which greatly improve by deposition in a multi- instead of a single-chamber system. Incorporation of these different materials into pin solar cells results in open circuit voltages of about 400 mV as long as the doped layers are microcrystalline and rise to more than 870 mV if amorphous p- and n-layers are used. Quantum efficiencies and fill factors are still poor but leave room for further improvement, as clearly demonstrated by a remarkable reverse bias quantum efficiency gain.

  17. Flexible a-Si:H/nc-Si:H tandem thin film silicon solar cells on plastic substrates with i-layers made by hot-wire CVD

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hongbo; Werf, C.H.M. van der; Rath, J.K. [Utrecht University, Faculty of Science, SID - Physics of Devices, Utrecht (Netherlands); Borreman, A. [Helianthos b.v., Arnhem (Netherlands); Schropp, Ruud E.I.

    2008-08-15

    In this letter we report the result of an a-Si:H/nc-Si:H tandem thin film silicon solar mini-module fabricated on plastic foil containing intrinsic silicon layers made by hot-wire CVD (efficiency 7.4%, monolithically series-connected, aperture area 25 cm{sup 2}). We used the Helianthos cell transfer process. The cells were first deposited on a temporary aluminum foil carrier, which allows the use of the optimal processing temperatures, and then transferred to a plastic foil. This letter reports the characteristics of the flexible solar cells obtained in this manner, and compares the results with those obtained on reference glass substrates. The research focus for implementation of the hot-wire CVD technique for the roll-to-roll process is also discussed. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. EBSD analysis of tungsten-filament carburization during the hot-wire CVD of multi-walled carbon nanotubes.

    Science.gov (United States)

    Oliphant, Clive J; Arendse, Christopher J; Camagu, Sigqibo T; Swart, Hendrik

    2014-02-01

    Filament condition during hot-wire chemical vapor deposition conditions of multi-walled carbon nanotubes is a major concern for a stable deposition process. We report on the novel application of electron backscatter diffraction to characterize the carburization of tungsten filaments. During the synthesis, the W-filaments transform to W2C and WC. W-carbide growth followed a parabolic behavior corresponding to the diffusion of C as the rate-determining step. The grain size of W, W2C, and WC increases with longer exposure time and increasing filament temperature. The grain size of the recrystallizing W-core and W2C phase grows from the perimeter inwardly and this phenomenon is enhanced at filament temperatures in excess of 1,400°C. Cracks appear at filament temperatures >1,600°C, accompanied by a reduction in the filament operational lifetime. The increase of the W2C and recrystallized W-core grain size from the perimeter inwardly is ascribed to a thermal gradient within the filament, which in turn influences the hardness measurements and crack formation.

  19. Carbon Nanotubes Deposited by Hot Wire Plasma CVD and water assisted CVD for Energetic and Environmental Applications

    OpenAIRE

    2014-01-01

    Nanoscience and Nanotechnology have experienced a tremendous growth in few years. Nanotechnologies are the design, characterization, production and application of structures, devices and systems by controlling shape and size at nanometer scale. Carbon exists in several forms, depending on how the carbon atoms are arranged, their properties vary. One of the carbon forms is carbon nanotubes, which are capped at each end by half of a fullerene, and have aroused great interest in the research com...

  20. On the development of single and multijunction solar cells with hot-wire CVD deposited active layers

    NARCIS (Netherlands)

    Li, H. B. T.; Franken, R.H.; Stolk, R.L.; Schuttauf, J.A.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2008-01-01

    We present an overview of the scientific challenges and achievements during the development of thin film silicon based single and multijunction solar cells with hot-wire chemical vapor deposition (HWCVD) of the active silicon layers. The highlights discussed include the development of Ag/ZnO coating

  1. Preparation of microcrystalline single junction and amorphous-microcrystalline tandem silicon solar cells entirely by hot-wire CVD

    Energy Technology Data Exchange (ETDEWEB)

    Kupich, M.; Grunsky, D.; Kumar, P.; Schroeder, B. [University of Kaiserslautern (Germany). Department of Physics

    2004-01-25

    The hot-wire chemical vapour deposition (HWCVD) has been used to prepare highly conducting p- and n-doped microcrystalline silicon thin layers as well as highly photoconducting, low defect density intrinsic microcrystalline silicon films. These films were incorporated in all-HWCVD, all-microcrystalline nip and pin solar cells, achieving conversion efficiencies of {eta}=5.4% and 4.5%, respectively. At present, only the nip-structures are found to be stable against light-induced degradation. Furthermore, microcrystalline nip and pin structures have been successfully incorporated as bottom cells in all-hot-wire amorphous-microcrystalline nipnip- and pinpin-tandem solar cells for the first time. So far, the highest conversion efficiencies of the 'micromorph' tandem structures are {eta}=5.7% for pinpin-solar cells and 7.0% for nipnip solar cells. (author)

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

    Science.gov (United States)

    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.

  3. Silicon nitride at high growth rate using hot wire chemical vapor deposition

    NARCIS (Netherlands)

    Verlaan, V.

    2008-01-01

    Amorphous silicon nitride (SiNx) is a widely studied alloy with many commercial applications. This thesis describes the application of SiNx deposited at high deposition rate using hot wire chemical vapor deposition (HWCVD) for solar cells and thin film transistors (TFTs). The deposition process of H

  4. Silicon nitride at high growth rate using hot wire chemical vapor deposition

    NARCIS (Netherlands)

    Verlaan, V.

    2008-01-01

    Amorphous silicon nitride (SiNx) is a widely studied alloy with many commercial applications. This thesis describes the application of SiNx deposited at high deposition rate using hot wire chemical vapor deposition (HWCVD) for solar cells and thin film transistors (TFTs). The deposition process of H

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-02-04

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

  6. Dual catalytic purpose of the tungsten filament during the synthesis of single-helix carbon microcoils by hot-wire CVD.

    Science.gov (United States)

    Oliphant, C J; Arendse, C J; Malgas, G F; Motaung, D E; Muller, T F G; Knoesen, D

    2009-10-01

    We report on the deposition of crystalline single-helix carbon microcoils, in the as-deposited state, by the hot-wire chemical vapor deposition process without any special preparation of nano-sized transition metal catalysts and subsequent post-deposition annealing. Tungsten, originating from the heated tungsten filament, is identified as the catalyst material responsible for the growth of the microcoils. High-resolution transmission spectroscopy, combined with Raman spectroscopy, confirm that the as-deposited microcoils are crystalline, which is induced by the high deposition temperature in the vicinity of the heated filament. These results suggest a simplified, less tedious deposition process for the growth of carbon microcoils, once the process has been optimized.

  7. Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

    Directory of Open Access Journals (Sweden)

    Muller TFG

    2009-01-01

    Full Text Available Abstract We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap.

  8. Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD.

    Science.gov (United States)

    Arendse, C J; Malgas, G F; Muller, T F G; Knoesen, D; Oliphant, C J; Motaung, D E; Halindintwali, S; Mwakikunga, B W

    2009-01-21

    We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200-700 degrees C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as identical withSi-H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures >/=400 degrees C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap.

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

    NARCIS (Netherlands)

    Yang, Mengdi; Aarnink, Antonius A.I.; Kovalgin, Alexeij Y.; Gravesteijn, Dirk J; Wolters, Robertus A.M.; Schmitz, Jurriaan

    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 (H2), which reacted with WF6 at the substrate to deposit W. The

  10. Hot Wire CVD for thin film triple junction cells and for ultrafast deposition of the SiN passivation layer on polycrystalline Si solar cells

    NARCIS (Netherlands)

    Schropp, R.E.I.; Franken, R.H.; Goldbach, H.D.; Houweling, Z.S.; Li, H. B. T.; Rath, J.K.; Schuttauf, J.A.; Stolk, R.L.; Verlaan, V.; van der Werf, C.H.M.

    2008-01-01

    We present recent progress on hot-wire deposited thin film solar cells and applications of silicon nitride. The cell efficiency reached for μc-Si:H n–i–p solar cells on textured Ag/ZnO presently is 8.5%, in line with the state-of-the-art level for μc-Si:H n–i–p's for any method of deposition. Such c

  11. Effect of hydrogen on low temperature epitaxial growth of polycrystalline silicon by hot wire chemical vapor deposition

    Science.gov (United States)

    Yong, Cao; Hailong, Zhang; Fengzhen, Liu; Meifang, Zhu; Gangqiang, Dong

    2015-02-01

    Polycrystalline silicon (poly-Si) films were prepared by hot-wire chemical vapor deposition (HWCVD) at a low substrate temperature of 525 °C. The influence of hydrogen on the epitaxial growth of ploy-Si films was investigated. Raman spectra show that the poly-Si films are fully crystallized at 525 °C with a different hydrogen dilution ratio (50%-91.7%). X-ray diffraction, grazing incidence X-ray diffraction and SEM images show that the poly-Si thin films present (100) preferred orientation on (100) c-Si substrate in the high hydrogen dilution condition. The P-type poly-Si film prepared with a hydrogen dilution ratio of 91.7% shows a hall mobility of 8.78 cm2/(V·s) with a carrier concentration of 1.3 × 1020 cm-3, which indicates that the epitaxial poly-Si film prepared by HWCVD has the possibility to be used in photovoltaic and TFT devices.

  12. Impact of microcrystalline silicon carbide growth using hot-wire chemical vapor deposition on crystalline silicon surface passivation

    Energy Technology Data Exchange (ETDEWEB)

    Pomaska, M., E-mail: m.pomaksa@fz-juelich.de [Forschungszentrum Jülich, IEK5-Photovoltaics, Wilhelm-Johnen-Strasse, 52425 Jülich (Germany); Beyer, W. [Helmholtz-Zentrum Berlin für Materialien und Energie, Silicon Photovoltaics, Kekuléstrasse 5, 12489 Berlin (Germany); Neumann, E. [Forschungszentrum Jülich, PGI-8-PT, Wilhelm-Johnen-Strasse, 52425 Jülich (Germany); Finger, F.; Ding, K. [Forschungszentrum Jülich, IEK5-Photovoltaics, Wilhelm-Johnen-Strasse, 52425 Jülich (Germany)

    2015-11-30

    Highly crystalline microcrystalline silicon carbide (μc-SiC:H) with excellent optoelectronic material properties is a promising candidate as highly transparent doped layer in silicon heterojunction (SHJ) solar cells. These high quality materials are usually produced using hot wire chemical vapor deposition under aggressive growth conditions giving rise to the removal of the underlying passivation layer and thus the deterioration of the crystalline silicon (c-Si) surface passivation. In this work, we introduced the n-type μc-SiC:H/n-type μc-SiO{sub x}:H/intrinsic a-SiO{sub x}:H stack as a front layer configuration for p-type SHJ solar cells with the μc-SiO{sub x}:H layer acting as an etch-resistant layer against the reactive deposition conditions during the μc-SiC:H growth. We observed that the unfavorable expansion of micro-voids at the c-Si interface due to the in-diffusion of hydrogen atoms through the layer stack might be responsible for the deterioration of surface passivation. Excellent lifetime values were achieved under deposition conditions which are needed to grow high quality μc-SiC:H layers for SHJ solar cells. - Highlights: • High surface passivation quality was preserved after μc-SiC:H deposition. • μc-SiC:H/μc-SiO{sub x}:H/a-SiO{sub x}:H stack a promising front layer configuration • Void expansion at a-SiO{sub x}:H/c-Si interface for deteriorated surface passivation • μc-SiC:H provides a high transparency and electrical conductivity.

  13. Deposition of silicon nitride thin films by hot-wire CVD at 100 {sup o}C and 250 {sup o}C

    Energy Technology Data Exchange (ETDEWEB)

    Alpuim, P., E-mail: palpuim@fisica.uminho.p [Departamento de Fisica, Universidade do Minho, 4800-058 Guimaraes (Portugal); Goncalves, L.M. [Departamento de Electronica Industrial, Universidade do Minho, 4800-058 Guimaraes (Portugal); Marins, E.S. [Departamento de Fisica, Universidade do Minho, 4800-058 Guimaraes (Portugal); Viseu, T.M.R. [Departamento de Fisica, Universidade do Minho, 4710-057 Braga (Portugal); Ferdov, S. [Departamento de Fisica, Universidade do Minho, 4800-058 Guimaraes (Portugal); Bouree, J.E. [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, 91128 Palaiseau (France)

    2009-04-30

    Silicon nitride thin films for use as passivation layers in solar cells and organic electronics or as gate dielectrics in thin-film transistors were deposited by the Hot-wire chemical vapor deposition technique at a high deposition rate (1-3 A/s) and at low substrate temperature. Films were deposited using NH{sub 3}/SiH{sub 4} flow rate ratios between 1 and 70 and substrate temperatures of 100 {sup o}C and 250 {sup o}C. For NH{sub 3}/SiH{sub 4} ratios between 40 and 70, highly transparent (T {approx} 90%), dense films (2.56-2.74 g/cm{sup 3}) with good dielectric properties and refractive index between 1.93 and 2.08 were deposited on glass substrates. Etch rates in BHF of 2.7 A/s and < 0.5 A/s were obtained for films deposited at 100 {sup o}C and 250 {sup o}C, respectively. Films deposited at both substrate temperatures showed electrical conductivity {approx} 10{sup -14} {Omega}{sup -1} cm{sup -1} and breakdown fields > 10 MV cm{sup -1}.

  14. Effect of argon ion energy on the performance of silicon nitride multilayer permeation barriers grown by hot-wire CVD on polymers

    Energy Technology Data Exchange (ETDEWEB)

    Alpuim, P. [Centro de Física, Universidade do Minho, 4710-057 Braga (Portugal); INL, International Iberian Nanotechnology Laboratory, 4715-330 Braga (Portugal); Majee, S. [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Cerqueira, M.F. [INL, International Iberian Nanotechnology Laboratory, 4715-330 Braga (Portugal); Tondelier, D. [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Geffroy, B. [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Laboratoire d' Innovation de Chimie des Surfaces et des Nanomatériaux, IRAMIS/NIMBE, CNRS UMR 3685, CEA Saclay, 91191 Gif-sur-Yvette (France); Bonnassieux, Y. [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Bourée, J.E., E-mail: jean-eric.bouree@polytechnique.edu [Laboratoire de Physique des Interfaces et des Couches Minces, CNRS UMR 7647, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France)

    2015-11-30

    Permeation barriers for organic electronic devices on polymer flexible substrates were realized by combining stacked silicon nitride (SiN{sub x}) single layers (50 nm thick) deposited by hot-wire chemical vapor deposition process at low-temperature (~ 100°°C) with a specific argon plasma treatment between two successive layers. Several plasma parameters (RF power density, pressure, treatment duration) as well as the number of single layers have been explored in order to improve the quality of permeation barriers deposited on polyethylene terephthalate. In this work, maximum ion energy was highlighted as the crucial parameter making it possible to minimize water vapor transmission rate (WVTR), as determined by the electrical calcium test method, all the other parameters being kept fixed. Thus fixing the plasma treatment duration at 8 min for a stack of two SiN{sub x} single layers, a minimum WVTR of 5 × 10{sup −4} g/(m{sup 2} day), measured at room temperature, was found for a maximum ion energy of ~ 30 eV. This minimum WVTR value was reduced to 7 × 10{sup −5} g/(m{sup 2} day) for a stack of five SiN{sub x} single layers. The reduction in the permeability is interpreted as due to the rearrangement of atoms at the interfaces when average transferred ion energy to target atoms exceeds threshold displacement energy. - Highlights: • Αn original way to achieve permeation barriers on polymer substrates is developed. • It combines SiN{sub x} multilayers grown by HWCVD with an intermediate Ar plasma treatment. • A minimum of water vapor transmission rate is found related to maximum Ar ion energy. • This minimum is due to atomic rearrangement in SiN{sub x} interfaces under the impact of ions. • The average Ar ion energy must exceed atomic threshold displacement energy for Si.

  15. Synthesis of γ-WO{sub 3} thin films by hot wire-CVD and investigation of its humidity sensing properties

    Energy Technology Data Exchange (ETDEWEB)

    Jadkar, Vijaya; Waykar, Ravindra; Jadhavar, Ashok [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Pawbake, Amit [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Physical and Material Chemistry Division, National Chemical Laboratory, Pune 411 008 (India); Date, Abhijit [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Plenty Road, Bundoora, Melbourne VIC 3083 (Australia); Late, Dattatray [Physical and Material Chemistry Division, National Chemical Laboratory, Pune 411 008 (India); Pathan, Habib; Gosavi, Suresh; Jadkar, Sandesh [Department of Physics, Savitribai Phule Pune University, Pune 411 007 (India)

    2017-05-15

    In this study, monoclinic tungsten oxide (γ-WO{sub 3}) have been grown in a single step using HW-CVD method by resistively heating W filaments in a constant O{sub 2} pressure. The formation of γ-WO{sub 3} was confirmed using low angle-XRD and Raman spectroscopy analysis. Low angle-XRD analysis revealed that as-deposited WO{sub 3} film are highly crystalline and the crystallites have preferred orientation along the (002) direction. HRTEM analysis and SAED pattern also show the highly crystalline nature of WO{sub 3} with d spacing of ∝ 0.38 nm, having an orientation along the (002) direction. Surface topography investigated by SEM analysis shows the formation of a uniform and homogeneous cauliflower like morphology throughout the substrate surface without flaws and cracks. A humidity sensing device incorporating WO{sub 3} is also fabricated, which shows a maximum humidity sensitivity factor of ∝ 3954% along with a response time of ∝14 s and a recovery time of ∝25 s. The obtained results demonstrate that it is possible to synthesize WO{sub 3} in a single step by HW-CVD method and to fabricate a humidity sensor by using it. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Dual catalytic purpose of the tungsten filament during the synthesis of single-helix carbon microcoils by hot-wire CVD

    CSIR Research Space (South Africa)

    Oliphant, CJ

    2009-10-01

    Full Text Available post-deposition annealing. Tungsten, originating from the heated tungsten filament, is identified as the catalyst material responsible for the growth of the microcoils. High-resolution transmission spectroscopy, combined with Raman spectroscopy, confirm...

  17. The influence of charge effect on the growth of hydrogenated amorphous silicon by the hot-wire chemical vapor deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Q.; Nelson, B.P.; Iwaniczko, E.; Mahan, A.H.; Crandall, R.S.; Benner, J. [National Renewable Energy Lab., Golden, CO (United States)

    1998-09-01

    The authors observe at lower substrate temperatures that the scatter in the dark conductivity on hydrogenated amorphous silicon (a-Si:H) films grown on insulating substrates (e.g., Corning 7059 glass) by the hot-wire chemical vapor deposition technique (HWCVD) can be five orders of magnitude or more. This is especially true at deposition temperatures below 350 C. However, when the authors grow the same materials on substrates with a conductive grid, virtually all of their films have acceptable dark conductivity (< 5 {times} 10{sup {minus}10} S/cm) at all deposition temperatures below 425 C. This is in contrast to only about 20% of the materials grown in this same temperature range on insulating substrates having an acceptable dark conductivity. The authors estimated an average energy of 5 eV electrons reaching the growing surface in vacuum, and did additional experiments to see the influence of both the electron flux and the energy of the electrons on the film growth. Although these effects do not seem to be important for growing a-Si:H by HWCVD on conductive substrates, they help better understand the important parameters for a-Si:H growth, and thus, to optimize these parameters in other applications of HWCVD technology.

  18. Hot wire chemical vapor deposition: recent progress, present state of the art and competitive opportunities

    NARCIS (Netherlands)

    Schropp, R.E.I.

    2009-01-01

    Hot Wire CVD (also called Catalytic CVD or initiated CVD) is an elegant low pressure deposition technique for the deposition of functional films, both inorganic and organic, based on the decomposition of precursor sources at a heated metallic surface. The conformal deposition of thin films on rigid

  19. Further Studies Of Hot-Wire Anemometry

    Science.gov (United States)

    Mckenzie, Robert; Logan, Pamela; Bershader, Daniel

    1990-01-01

    Report discusses factors affecting readings of hot-wire anemometer in turbulent supersonic boundary layer. Represents extension of work described in "Hot-Wire Anemometry Versus Laser-Induced Fluorescence" (ARC-11802). Presents theoretical analysis of responses of hot-wire probe to changes in flow; also compares measurements by hot-wire probe with measurements of same flows by laser-induced fluorescence (LIF).

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

    Energy Technology Data Exchange (ETDEWEB)

    Abrutis, Adulfas, E-mail: adulfas.abrutis@chf.vu.lt; Silimavicus, Laimis; Kubilius, Virgaudas; Murauskas, Tomas; Saltyte, Zita; Kuprenaite, Sabina; Plausinaitiene, Valentina [Faculty of Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius (Lithuania)

    2014-03-15

    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 were 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.

  1. Subminiature Hot-Wire Probes

    Science.gov (United States)

    Westphal, R. V.; Lemos, F. R.; Ligrani, P. M.

    1989-01-01

    Class of improved subminiature hot-wire flow-measuring probes developed. Smaller sizes yield improved resolution in measurements of practical aerodynamic flows. Probe made in one-wire, two-perpendicular-wire, and three-perpendicular-wire version for measurement of one, two, or all three components of flow. Oriented and positioned on micromanipulator stage and viewed under microscope during fabrication. Tested by taking measurements in constant-pressure turbulent boundary layer. New probes give improved measurements of turbulence quantities near surfaces and anisotropies of flows strongly influence relative errors caused by phenomena related to spatial resolution.

  2. Hot-wire anemometer for spirography.

    Science.gov (United States)

    Plakk, P; Liik, P; Kingisepp, P H

    1998-01-01

    The use of a constant temperature hot-wire anemometer flow sensor for spirography is reported. The construction, operating principles and calibration procedure of the apparatus are described, and temperature compensation method is discussed. Frequency response is studied. It is shown that this hot-wire flow transducer satisfies common demands with respect to accuracy, response time and temperature variations.

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

    Science.gov (United States)

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

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

  4. Frequency Responses Of Hot-Wire Anemometers

    Science.gov (United States)

    Watmuff, Jonathan H.

    1992-01-01

    Report describes theoretical study of frequency response of constant-temperature hot-wire anemometer, with view toward increasing frequency response while maintaining stable operation in supersonic flow. Effects of various circuit parameters discussed.

  5. Ultrafast deposition of silicon nitride and semiconductor silicon thin films by Hot Wire Chemical Vapor Deposition

    NARCIS (Netherlands)

    Schropp, R.E.I.; van der Werf, C.H.M.; Verlaan, V.; Rath, J.K.; Li, H. B. T.

    2009-01-01

    The technology of Hot Wire Chemical Vapor Deposition (HWCVD) or Catalytic Chemical Vapor Deposition (Cat-CVD) has made great progress during the last couple of years. This review discusses examples of significant progress. Specifically, silicon nitride deposition by HWCVD (HW-SiNx) is highlighted, a

  6. Optimization of process parameters in a large-area hot-wire CVD reactor for the deposition of amorphous silicon (a-Si:H) for solar cell application with highly uniform material quality

    Energy Technology Data Exchange (ETDEWEB)

    Pflueger, A.; Mukherjee, C.; Schroeder, B. [Department of Physics, Center of Materials Science, University of Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern (Germany)

    2002-07-01

    Scale-up of a-Si:H-based thin film applications such as solar cells, entirely or partly prepared by hot-wire chemical vapor deposition (HWCVD), requires research on the deposition process in a large-area HWCVD system. The influence of gas supply and filament geometry on thickness uniformity has already been reported, but their influence on material quality is systematically studied for the first time. The optimization of deposition parameters for obtaining best material quality in our large-area HWCVD system resulted in an optimum filament temperature, T{sub fil}{approx}1600C, pressure, p=8mTorr and silane flow, F(SiH{sub 4})=100sccm, keeping the substrate temperature at T{sub S}=200C. A special gas supply (gas shower with tiny holes of uniform size) and a filament grid, consisting of six filaments with an interfilament distance, d{sub fil}=4cm were used. The optimum filament-to-substrate distance was found to be d{sub fil-S}=8.4cm. While studying the influence of different d{sub fil} and gas supply configurations on the material quality, the above-mentioned setup and parameters yield best results for both uniformity and material quality. With the setup mentioned, we could achieve device quality a-Si:H films with a thickness uniformity of {+-}2.5% on a circular area of 20cm in diameter. The material, grown at a deposition rate of r{sub d}{approx}4A/s, was characterized on nine positions of the 30cmx30cm substrate area, and revealed reasonable uniformity of the opto-electronic properties, e.g photosensitivity, {sigma}{sub Ph}/{sigma}{sub D}=(2.46{+-}0.7)x10{sup 5}, microstructure factor, R=0.17{+-}0.05, defect densities, N{sub d(PDS)}=(2.06{+-}0.6)x10{sup 17}cm{sup -3} and N{sub d(CPM)}=(2.05{+-}0.5)x10{sup 16}cm{sup -3} (film properties are given as mean values and standard deviations). Finally, we fabricated pin solar cells, with the i-layer deposited on small-area p-substrates distributed over an area of 20cmx20cm in this large-area deposition system, and

  7. Angular response of hot wire probes

    Science.gov (United States)

    di Mare, L.; Jelly, T. O.; Day, I. J.

    2017-03-01

    A new equation for the convective heat loss from the sensor of a hot-wire probe is derived which accounts for both the potential and the viscous parts of the flow past the prongs. The convective heat loss from the sensor is related to the far-field velocity by an expression containing a term representing the potential flow around the prongs, and a term representing their viscous effect. This latter term is absent in the response equations available in the literature but is essential in representing some features of the observed response of miniature hot-wire probes. The response equation contains only four parameters but it can reproduce, with great accuracy, the behaviour of commonly used single-wire probes. The response equation simplifies the calibration the angular response of rotated slanted hot-wire probes: only standard King’s law parameters and a Reynolds-dependent drag coefficient need to be determined.

  8. Hot-wire anemometry in transonic flow

    Science.gov (United States)

    Horstman, C. C.; Rose, W. C.

    1977-01-01

    The use of hot-wire anemometry for obtaining fluctuating data in transonic flows has been evaluated. From hot-wire heat loss correlations based on previous transonic data, the sensitivity coefficients for velocity, density, and total temperature fluctuations have been calculated for a wide range of test conditions and sensor parameters. For sensor Reynolds number greater than 20 and high sensor overheat ratios, the velocity sensitivity remains independent of Mach number and equal to the density sensitivity. These conditions were verified by comparisons of predicted sensitivities with those from recent direct calibrations in transonic flows. Based on these results, techniques are presented to obtain meaningful measurements of fluctuating velocity, density, and Reynolds shear stress using hot-wire and hot-film anemometers. Example of these measurements are presented for two transonic boundary layers.

  9. Hot wire anemometry in transonic flow

    Science.gov (United States)

    Horstman, C. C.; Rose, W. C.

    1975-01-01

    The use of hot-wire anemometry for obtaining fluctuating data in transonic flows has been evaluated. From hot-wire heat loss correlations based on previous transonic data, the sensitivity coefficients for velocity, density, and total temperature fluctuations have been calculated for a wide range of test conditions and sensor parameters. For sensor Reynolds numbers greater than 20 and high sensor overheat ratios, the velocity sensitivity remains independent of Mach number and equal to the density sensitivity. These conclusions were verified by comparisons of predicted sensitivities with those from recent direct calibrations in transonic flows. Based on these results, techniques are presented to obtain meaningful measurements of fluctuating velocity, density, and Reynolds shear stress using hot-wire and hot-film anemometers. Examples of these measurements are presented for two transonic boundary layers.

  10. Hetero- and homogeneous three-dimensional hierarchical tungsten oxide nanostructures by hot-wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Houweling, Z.S., E-mail: Silvester.Houweling@asml.com [Utrecht University, Debye Institute for Nanomaterials Science, Nanophotonics—Physics of Devices, Princetonlaan 4, 3584 CB Utrecht (Netherlands); Harks, P.-P.R.M.L.; Kuang, Y.; Werf, C.H.M. van der [Utrecht University, Debye Institute for Nanomaterials Science, Nanophotonics—Physics of Devices, Princetonlaan 4, 3584 CB Utrecht (Netherlands); Geus, J.W. [Utrecht University, Inorganic Chemistry and Catalysis, Padualaan 8, 3584 CH Utrecht (Netherlands); Schropp, R.E.I. [Utrecht University, Debye Institute for Nanomaterials Science, Nanophotonics—Physics of Devices, Princetonlaan 4, 3584 CB Utrecht (Netherlands)

    2015-01-30

    We present the synthesis of three-dimensional tungsten oxide (WO{sub 3−x}) nanostructures, called nanocacti, using hot-wire chemical vapor deposition. The growth of the nanocacti is controlled through a succession of oxidation, reduction and re-oxidation processes. By using only a resistively heated W filament, a flow of ambient air and hydrogen at subatmospheric pressure, and a substrate heated to about 700 °C, branched nanostructures are deposited. We report three varieties of simple synthesis approaches to obtain hierarchical homo- and heterogeneous nanocacti. Furthermore, by using catalyst nanoparticles site-selection for the growth is demonstrated. The atomic, morphological and crystallographic compositions of the nanocacti are determined using a combination of electron microscopy techniques, energy-dispersive X-ray spectroscopy and electron diffraction. - Highlights: • Continuous upscalable hot-wire CVD of 3D hierarchical nanocacti • Controllable deposition of homo- and heterogeneous WO{sub 3−x}/WO{sub 3−y} nanocacti • Introduction of three synthesis routes comprising oxidation, reduction and re-oxidation processes • Growth of periodic arrays of hetero- and homogeneous hierarchical 3D nanocacti.

  11. Accuracy Of Hot-Wire Anemometry In Supersonic Turbulence

    Science.gov (United States)

    Logan, Pamela; Mckenzie, Robert L.; Bershader, Daniel

    1989-01-01

    Sensitivity of hot-wire probe compared to laser-induced-florescence measurements. Report discusses factors affecting readings of hot-wire anemometer in turbulent supersonic boundary layer. Presents theoretical analysis of responses of hot-wire probe to changes in flow; also compares measurements by hot-wire probe with measurements of same flows by laser-induced fluorescence (LIF). Because LIF provides spatially and temporally resolved data on temperature, density, and pressure, provides independent means to determine responses of hot-wire anemometers to these quantities.

  12. A Comparison between Thin-Film Transistors Deposited by Hot-Wire Chemical Vapor Deposition and PECVD

    Directory of Open Access Journals (Sweden)

    Meysam Zarchi

    2015-03-01

    Full Text Available The effect of new growth techniques on the mobility and stability of amorphous silicon (a-Si:H thin film transistors (TFTs has been studied. It was suggested that the key parameter controlling the field-effect mobility and stability is the intrinsic stress in the a-Si:H layer. Amorphous and microcrystalline silicon films were deposited by radiofrequency plasma enhanced chemical vapor deposition (RF-PECVD and hot-wire chemical vapor deposition (HW-CVD at 100 ºC and 25 ºC. Structural properties of these films were measured by Raman Spectroscopy. Electronic properties were measured by dark conductivity, σd, and photoconductivity, σph. For amorphous silicon films deposited by RF-PECVD on PET, photosensitivity's of >105 were obtained at both 100 º C and 25 ºC. For amorphous silicon films deposited by HW-CVD, a photosensitivity of > 105 was obtained at 100 ºC. Microcrystalline silicon films deposited by HW-CVD at 95% hydrogen dilution show σph~ 10-4 Ω-1cm-1, while maintaining a photosensitivity of ~102 at both 100 ºC and 25 ºC. Microcrystalline silicon films with a large crystalline fraction (> 50% can be deposited by HW-CVD all the way down to room temperature.

  13. Hot-Wire Chemical Vapor Deposition of Few-Layer Graphene on Copper Substrates

    Science.gov (United States)

    Soler, Víctor-Manuel Freire; Badia-Canal, Jordi; Roca, Carles Corbella; Miralles, Esther Pascual; Serra, Enric Bertran; Bella, José-Luís Andújar

    2013-01-01

    Chemical vapor deposition (CVD) of graphene on copper is an efficient technology for producing high-quality graphene for large areas. The objective of this work is to deposit graphene/few-layer graphene (FLG) using different types of copper substrate by a new hot-wire CVD process. We carried out the processes at temperatures below 1000 °C with acetylene (C2H2) as a precursor gas. After a general characterization of the samples, the results mostly indicate the formation of FLG on copper samples by this method. Nevertheless, the presence of pure, crystalline, and sufficiently flat surfaces is needed for depositing high-quality graphene layers.

  14. Contribution to advanced hot wire wind sensing

    OpenAIRE

    Kowalski, Lukasz

    2016-01-01

    La consulta íntegra de la tesi, inclos l'article no comunicat públicament per drets d'autor, es pot realitzar prèvia petició a l'Arxiu de la UPC The thermal anemometry is a method which allows to estimate wind magnitude be the mean of measuring heat transfer to the ambient in a forced convection process. For Earth's atmosphere condition, this method is typically applied to the hot wires made of temperature dependent electrical conductor, typically platinum or tungsten, which working with o...

  15. High-angle tilt boundary graphene domain recrystallized from mobile hot-wire-assisted chemical vapor deposition system.

    Science.gov (United States)

    Lee, Jinsup; Baek, Jinwook; Ryu, Gyeong Hee; Lee, Mi Jin; Oh, Seran; Hong, Seul Ki; Kim, Bo-Hyun; Lee, Seok-Hee; Cho, Byung Jin; Lee, Zonghoon; Jeon, Seokwoo

    2014-08-13

    Crystallization of materials has attracted research interest for a long time, and its mechanisms in three-dimensional materials have been well studied. However, crystallization of two-dimensional (2D) materials is yet to be challenged. Clarifying the dynamics underlying growth of 2D materials will provide the insight for the potential route to synthesize large and highly crystallized 2D domains with low defects. Here, we present the growth dynamics and recrystallization of 2D material graphene under a mobile hot-wire assisted chemical vapor deposition (MHW-CVD) system. Under local but sequential heating by MHW-CVD system, the initial nucleation of nanocrystalline graphenes, which was not extended into the growth stage due to the insufficient thermal energy, took a recrystallization and converted into a grand single crystal domain. During this process, the stitching-like healing of graphene was also observed. The local but sequential endowing thermal energy to nanocrystalline graphenes enabled us to simultaneously reveal the recrystallization and healing dynamics in graphene growth, which suggests an alternative route to synthesize a highly crystalline and large domain size graphene. Also, this recrystallization and healing of 2D nanocrystalline graphenes offers an interesting insight on the growth mechanism of 2D materials.

  16. Using hot wire and initiated chemical vapor deposition for gas barrier thin film encapsulation

    Energy Technology Data Exchange (ETDEWEB)

    Spee, D.A., E-mail: diederickspee@gmail.com; Rath, J.K.; Schropp, R.E.I.

    2015-01-30

    Hot wire CVD (HWCVD) and initiated CVD (iCVD) are very well suited deposition techniques for the fabrication of transparent thin film gas barriers. Single inorganic or organic layers, however, face challenges, which are hard to overcome: unavoidable defects and low intrinsic barrier function. We demonstrate that by combining inorganic HWCVD films and organic iCVD films, a water vapor transmission rate a low as 5 ∗ 10{sup −6} g/m{sup 2}/day at 60 °C and 90% RH for a simple pinhole free three layer structure is obtained even with non-optimized individual layers. Given the 100 °C deposition temperature, the layer stacks can be deposited on any sensitive electronic device.

  17. Hot-wire anemometry in hypersonic helium flow

    Science.gov (United States)

    Wagner, R. D.; Weinstein, L. M.

    1974-01-01

    Hot-wire anemometry techniques are described that have been developed and used for hypersonic-helium-flow studies. The short run time available dictated certain innovations in applying conventional hot-wire techniques. Some examples are given to show the application of the techniques used. Modifications to conventional equipment are described, including probe modifications and probe heating controls.

  18. New hot wire anemometer with alternate current and synchronic detection

    Science.gov (United States)

    Stoian, Monica; Rachek, Adil; Chirtoc, Mihai

    2009-01-01

    The feasibility of hot wire anemometer in to a new measurement configuration is demonstrated in this work and we validate our results by a numerical model. We have created an anemometer probe with hot wire using a new scheme, in alternate current and synchronic detection (3ω method). We use this instrument to register the velocity magnitude in boundary layer for a forced convection flow. The probe and its alimentation also the measuring support and bridge Wheatstone, have been created by us. The physical parameter was recorded is an exchange heat quantity between hot wire and fluid flow. In steady state, experimental data verify the numerical results with an average error of 3%.

  19. A dual-amplifier hot-wire anemometer

    Science.gov (United States)

    Sadeh, W. Z.; Finn, C. L.

    1979-01-01

    The conceptual design of a dual-amplifier constant-temperature hot-wire anemometer is described. This hot-wire anemometer consists of three basic independent modules: a Wheatstone bridge in which the hot wire is one of its arms, an error-correction amplifier, and a voltage-controlled current source. The last two modules constitute the feedback network of this hot-wire anemometer. Thus the output voltage across the wire is a true function of the instantaneous changes in the wire resistance induced by the cooling effect of the flow. The dual-amplifier is capable of reaching relatively high frequency response through adequate selection of its active elements. Suitable gain of the error-correction amplifier and proper choice of the transfer function of the current source has yielded a frequency bandwidth up to 200 kHz.

  20. Crystal growth of CVD diamond and some of its peculiarities

    CERN Document Server

    Piekarczyk, W

    1999-01-01

    Experiments demonstrate that CVD diamond can form in gas environments that are carbon undersaturated with respect to diamond. This fact is, among others, the most serious violation of principles of chemical thermodynamics. In this $9 paper it is shown that none of the principles is broken when CVD diamond formation is considered not a physical process consisting in growth of crystals but a chemical process consisting in accretion of macro-molecules of polycyclic $9 saturated hydrocarbons belonging to the family of organic compounds the smallest representatives of which are adamantane, diamantane, triamantane and so forth. Since the polymantane macro-molecules are in every respect identical with $9 diamond single crystals with hydrogen-terminated surfaces, the accretion of polymantane macro- molecules is a process completely equivalent to the growth of diamond crystals. However, the accretion of macro-molecules must be $9 described in a way different from that used to describe the growth of crystals because so...

  1. Unraveling the complex chemistry using dimethylsilane as a precursor gas in hot wire chemical vapor deposition.

    Science.gov (United States)

    Toukabri, Rim; Shi, Yujun

    2014-05-07

    The gas-phase reaction chemistry when using dimethylsilane (DMS) as a source gas in a hot-wire chemical vapor deposition (CVD) process has been studied in this work. The complex chemistry is unraveled by using a soft 10.5 eV single photon ionization technique coupled with time-of-flight mass spectrometry in combination with the isotope labelling and chemical trapping methods. It has been demonstrated that both free-radical reactions and those involving silylene/silene intermediates are important. The reaction chemistry is characterized by the formation of 1,1,2,2-tetramethyldisilane (TMDS) from dimethylsilylene insertion into the Si-H bond of DMS, trimethylsilane (TriMS) from free-radical recombination, and 1,3-dimethyl-1,3-disilacyclobutane (DMDSCB) from the self dimerization of either dimethylsilylene or 1-methylsilene. At low filament temperatures and short reaction time, silylene chemistry dominates. The free-radical reactions become more important with increasing temperature and time. The same three products have been detected when using tantalum and tungsten filaments, indicating that changing the filament material from Ta to W does not affect much the gas-phase reaction chemistry when using DMS as a source gas in a hot-wire CVD reactor.

  2. CVD growth and processing of graphene for electronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Shishir; Rezvani, Ehsan; Nolan, Hugo; Duesberg, Georg S. [School of Chemistry, Trinity College Dublin, Dublin 2 (Ireland); Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2 (Ireland); McEvoy, Niall; Kim, Hye-Young; Lee, Kangho; Peltekis, Nikos; Weidlich, Anne; Daly, Ronan [Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2 (Ireland)

    2011-11-15

    The remarkable properties of graphene have potential for numerous applications; however, their exploitation depends on its reliable production. The chemical vapour deposition (CVD) growth of graphene on metal surfaces has become one of the most promising strategies for the production of high quality graphene in a scaleable manner. Here, we discuss graphene growth on nickel (Ni) and copper (Cu) directly from both gaseous hydrocarbons and solid carbon precursors. Further, we discuss in detail the transfer of graphene films to insulating substrates, by direct and polymer supported transfer methods. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. A Hot-wire Circuit with Very Small Time Lag

    Science.gov (United States)

    Weske, John R

    1943-01-01

    A circuit for a hot-wire anemometer for the measurement of fluctuating flow is presented in the present report. The principal elements of the circuit are a Wheatstone bridge, one branch of which is the hot wire; and an electronic amplifier and a current regulator for the brief current which in combination maintain the bridge balance constant. Hence the hot wire is kept at practically constant resistance and temperature, and the time lag caused by thermal inertia of the wire is thereby reduced. Through the addition of a nonlinear amplifying stage the reading of the instrument has been rendered proportional to the velocity. A discussion of certain characteristics of the circuit and the results of related calibrating tests are given.

  4. A review of hot wire anemometry in transonic flows

    Science.gov (United States)

    Stainback, P. C.

    1985-01-01

    The present paper provides a review of hot wire anemometry for compressible flows, giving particular attention to the transonic flow problem. It is pointed out that the first and most important definitive work in hot wire anemometry for compressible flows was reported by Kovasznay (1953). The existence of three independent fluctuating modes in compressible flows for small perturbations was found, taking into account the vorticity mode, the entropy mode, and the sound-wave mode. A review of Kovasznays' method for supersonic flows is also presented, and advances reported by Markovin (1956) are examined. Attention is given to experiments conducted by Horstman and Rose (1977), a general solution to the hot wire problem at transonic conditions sought by Stainback et al. (1983), and some apparent problems.

  5. A crossed hot-wire technique for complex turbulent flows

    Science.gov (United States)

    Cutler, A. D.; Bradshaw, P.

    1991-01-01

    This paper describes a crossed hot-wire technique for the measurement of all components of mean velocity, Reynolds stresses, and triple products in a complex turbulent flow. The accuracy of various assumptions usually implicit in the use of crossed hot-wire anemometers is examined. It is shown that significant errors can result in flow with gradients in mean velocity or Reynolds stress, but that a first-order correction for these errors can be made using available data. It is also shown how corrections can be made for high turbulence levels using available data.

  6. Effect of rotation on a rotating hot-wire sensor

    Science.gov (United States)

    Hah, C.; Lakshminarayana, B.

    1978-01-01

    An investigation was conducted to discern the effects of centrifugal and Coriolis forces on a rotating hot-wire. The probe was calibrated in a wind tunnel as well as in a rotating mode. The effect of rotation was found to be negligibly small. A small change in cold resistance (1.5%) was observed in the rotating wire. The rotation seems to have a negligible effect on the fluid mechanics, heat transfer and material characteristics of the wire. This is a significant conclusion in view of the potential application of the hot-wire probe in a rotating passage (such as turbomachinery).

  7. Model for predicting thermal conductivity using transient hot wire method

    Science.gov (United States)

    Kumar, Sublania Harish; Singh K., J.; Somani A., K.

    2016-05-01

    The use of the hot wire method for estimating the thermal conductivity measurement has recently known a significant increase. However, this method is theoretically not applicable to materials. Thermal conductivity values are necessary whenever a heat transfer problem is to be evaluated.

  8. Constant temperature hot wire anemometry data reduction procedure

    Science.gov (United States)

    Klopfer, G. H.

    1974-01-01

    The theory and data reduction procedure for constant temperature hot wire anemometry are presented. The procedure is valid for all Mach and Prandtl numbers, but limited to Reynolds numbers based on wire diameter between 0.1 and 300. The fluids are limited to gases which approximate ideal gas behavior. Losses due to radiation, free convection and conduction are included.

  9. Cooling method prolongs life of hot-wire transducer

    Science.gov (United States)

    Baldwin, L. V.; Sandborn, V. A.

    1964-01-01

    To cool a hot-wire transducer, the two ends of the wire are supported on thermally and electrically conductive rods, surrounded by a fluid cooling medium. By keeping the supporting rods at a substantially constant temperature, the probe is prevented from overheating.

  10. Constant-Operating-Resistance Hot-Wire Probe

    Science.gov (United States)

    Stainback, P. C.

    1985-01-01

    Effects of lead-wire-resistance changes with temperature nullified. Constant-operating-resistance hot-wire probe uses two sets of leads. Exposed to identical conditions, comparison of resistance gives change in sensing element itself. Data taken in more convenient manner, with advantage of not having to constantly check for possible changes in lead resistance and consequently readjust potentiometer.

  11. CVD-graphene growth on different polycrystalline transition metals

    Directory of Open Access Journals (Sweden)

    M. P. Lavin-Lopez

    2017-01-01

    Full Text Available The chemical vapor deposition (CVD graphene growth on two polycrystalline transition metals (Ni and Cu was investigated in detail using Raman spectroscopy and optical microscopy as a way to synthesize graphene of the highest quality (i.e. uniform growth of monolayer graphene, which is considered a key issue for electronic devices. Key CVD process parameters (reaction temperature, CH4/H2flow rate ratio, total flow of gases (CH4+H2, reaction time were optimized for both metals in order to obtain the highest graphene uniformity and quality. The conclusions previously reported in literature about the performance of low and high carbon solubility metals in the synthesis of graphene and their associated reaction mechanisms, i.e. surface depositionand precipitation on cooling, respectively, was not corroborated by the results obtained in this work. Under the optimal reaction conditions, a large percentage of monolayer graphene was obtained over the Ni foil since the carbon saturation was not complete, allowing carbon atoms to be stored in the bulk metal, which could diffuse forming high quality monolayer graphene at the surface. However, under the optimal reaction conditions, the formation of a non-uniform mixture of few layers and multilayer graphene on the Cu foil was related to the presence of an excess of active carbon atoms on the Cu surface.

  12. Hot-wire calibration in subsonic/transonic flow regimes

    Science.gov (United States)

    Nagabushana, K. A.; Ash, Robert L.

    1995-01-01

    A different approach for calibrating hot-wires, which simplifies the calibration procedure and reduces the tunnel run-time by an order of magnitude was sought. In general, it is accepted that the directly measurable quantities in any flow are velocity, density, and total temperature. Very few facilities have the capability of varying the total temperature over an adequate range. However, if the overheat temperature parameter, a(sub w), is used to calibrate the hot-wire then the directly measurable quantity, voltage, will be a function of the flow variables and the overheat parameter i.e., E = f(u,p,a(sub w), T(sub w)) where a(sub w) will contain the needed total temperature information. In this report, various methods of evaluating sensitivities with different dependent and independent variables to calibrate a 3-Wire hot-wire probe using a constant temperature anemometer (CTA) in subsonic/transonic flow regimes is presented. The advantage of using a(sub w) as the independent variable instead of total temperature, t(sub o), or overheat temperature parameter, tau, is that while running a calibration test it is not necessary to know the recovery factor, the coefficients in a wire resistance to temperature relationship for a given probe. It was deduced that the method employing the relationship E = f (u,p,a(sub w)) should result in the most accurate calibration of hot wire probes. Any other method would require additional measurements. Also this method will allow calibration and determination of accurate temperature fluctuation information even in atmospheric wind tunnels where there is no ability to obtain any temperature sensitivity information at present. This technique greatly simplifies the calibration process for hot-wires, provides the required calibration information needed in obtaining temperature fluctuations, and reduces both the tunnel run-time and the test matrix required to calibrate hotwires. Some of the results using the above techniques are presented

  13. Hot wire chemical vapor deposition chemistry in the gas phase and on the catalyst surface with organosilicon compounds.

    Science.gov (United States)

    Shi, Yujun

    2015-02-17

    CONSPECTUS: Hot wire chemical vapor deposition (HWCVD), also referred to as catalytic CVD (Cat-CVD), has been used to produce Si-containing thin films, nanomaterials, and functional polymer coatings that have found wide applications in microelectronic and photovoltaic devices, in automobiles, and in biotechnology. The success of HWCVD is largely due to its various advantages, including high deposition rate, low substrate temperatures, lack of plasma-induced damage, and large-area uniformity. Film growth in HWCVD is induced by reactive species generated from primary decomposition on the metal wire or from secondary reactions in the gas phase. In order to achieve a rational and efficient optimization of the process, it is essential to identify the reactive species and to understand the chemical kinetics that govern the production of these precursor species for film growth. In this Account, we report recent progress in unraveling the complex gas-phase reaction chemistry in the HWCVD growth of silicon carbide thin films using organosilicon compounds as single-source precursors. We have demonstrated that laser ionization mass spectrometry is a powerful diagnostic tool for studying the gas-phase reaction chemistry when combined with the methods of isotope labeling and chemical trapping. The four methyl-substituted silane molecules, belonging to open-chain alkylsilanes, dissociatively adsorb on W and Ta filaments to produce methyl radical and H2 molecule. Under the typical deposition pressures, with increasing number of methyl substitution, the dominant chemistry occurring in the gas phase switches from silylene/silene reactions to free-radical short chain reactions. This change in dominant reaction intermediates from silylene/silene to methyl radicals explains the observation from thin film deposition that silicon carbide films become more C-rich with a decreasing number of Si-H bonds in the four precursor molecules. In the case of cyclic monosilacyclobutanes, we have

  14. Hot wire/film behavior in low-temperature gases

    Science.gov (United States)

    Kwack, E. Y.; Shakkottai, P.; Luchik, T. S.; Aaron, K. M.; Fabris, G.; Back, L. H.

    1992-01-01

    Commercially available hot wires/films were used to measure the velocities of evaporated hydrogen or helium gas during cryogenic mixing experiments. Hot wires were found to be too delicate to use in this harsh environment. Hot films were rugged enough to use at cryogenic temperatures even though they failed after a number of thermal cycles. Since the hot films have small aspect ratios, 13.4 and 20, they are quite sensitive to the thermal loading, Tw/Tg, even with a correction for the conduction end loss. In general, although the increase of the Nusselt number with Reynolds number at low temperatures was similar to that at room temperature, there was also a pronounced variation with Tw/Tg over the large range of 1.2 to 12 investigated.

  15. Algorithm to optimize transient hot-wire thermal property measurement.

    Science.gov (United States)

    Bran-Anleu, Gabriela; Lavine, Adrienne S; Wirz, Richard E; Kavehpour, H Pirouz

    2014-04-01

    The transient hot-wire method has been widely used to measure the thermal conductivity of fluids. The ideal working equation is based on the solution of the transient heat conduction equation for an infinite linear heat source assuming no natural convection or thermal end effects. In practice, the assumptions inherent in the model are only valid for a portion of the measurement time. In this study, an algorithm was developed to automatically select the proper data range from a transient hot-wire experiment. Numerical simulations of the experiment were used in order to validate the algorithm. The experimental results show that the developed algorithm can be used to improve the accuracy of thermal conductivity measurements.

  16. Algorithm to optimize transient hot-wire thermal property measurement

    Science.gov (United States)

    Bran-Anleu, Gabriela; Lavine, Adrienne S.; Wirz, Richard E.; Kavehpour, H. Pirouz

    2014-04-01

    The transient hot-wire method has been widely used to measure the thermal conductivity of fluids. The ideal working equation is based on the solution of the transient heat conduction equation for an infinite linear heat source assuming no natural convection or thermal end effects. In practice, the assumptions inherent in the model are only valid for a portion of the measurement time. In this study, an algorithm was developed to automatically select the proper data range from a transient hot-wire experiment. Numerical simulations of the experiment were used in order to validate the algorithm. The experimental results show that the developed algorithm can be used to improve the accuracy of thermal conductivity measurements.

  17. Hot-wire amperometric monitoring of flowing streams.

    Science.gov (United States)

    Wang, J; Jasinski, M; Flechsig, G U; Grundler, P; Tian, B

    2000-01-10

    This paper describes the design of a hot-wire electrochemical flow detector, and the advantages accrued from the effects of locally increased temperature, mainly thermally induced convection, upon the amperometric monitoring of flowing streams. A new hydrodynamic modulation voltammetric approach is presented, in which the solution flow rate remains constant while the temperature of the working electrode is modulated. Factors influencing the response, including the flow rate, temperature pulse, or applied potential, have been investigated. The hot-wire operation results also in a significant enhancement of the flow injection amperometric response. The minimal flow rate dependence observed with the heated electrode should benefit the on-line monitoring of streams with fluctuated natural convection, as well as various in-situ remote sensing applications.

  18. Transient Free Convection Development in Hot-Wire Experiments

    Science.gov (United States)

    Giaretto, Valter

    The transient behavior of free convection along the vertical wire of a hot-wire apparatus has been experimentally investigated at room temperature and ambient pressure, using water and propylene glycol. The development of free convection has been studied using an ad hoc apparatus, in order to obtain the best agreement between the vertical direction and the wire. The measurements were corrected for radiation influences, and the effects induced by free convection were detected at the wire-fluid interface. The convection outcomes have been correlated to fluid properties and test conditions. A suitable time scale has been introduced, which is defined by the modified Fourier and a proper definition of the local Grashof number. The obtained correlation has been applied to data found in the literature. The possibility of describing the free convection development at the wire-fluid interface could enable the fluid properties related to momentum diffusion to be investigated by the hot-wire technique.

  19. Turbulence measurements in shock induced flow using hot wire anemometry

    Science.gov (United States)

    Hartung, Lin C.; Duffy, Robert E.; Trolier, James W.

    1988-01-01

    Heat transfer measurements over various geometric shapes have been made by immersing models in shock-induced flows. The heat transfer to a body is strongly dependent on the turbulence level of the stream. The interpretation of such heat transfer measurements requires a knowledge of the turbulence intensity. Turbulence intensity measurements, using hot-wire anemometry, have been successfully carried out in shock-induced flows. The experimental procedures for making such measurements and the techniques required are discussed.

  20. Nonlinear theory of a hot-wire anemometer

    Science.gov (United States)

    Betchov, R

    1952-01-01

    A theoretical analysis is presented for the hot-wire anemometer to determine the differences in resistance characteristics as given by King's equation for an infinite wire length and those given by the additional considerations of (a) a finite length of wire with heat loss through its ends and (b) heat loss due to a nonlinear function of the temperature difference between the wire and the air.

  1. Distributed flow sensing using optical hot -wire grid.

    Science.gov (United States)

    Chen, Tong; Wang, Qingqing; Zhang, Botao; Chen, Rongzhang; Chen, Kevin P

    2012-04-09

    An optical hot-wire flow sensing grid is presented using a single piece of self-heated optical fiber to perform distributed flow measurement. The flow-induced temperature loss profiles along the fiber are interrogated by the in-fiber Rayleigh backscattering, and spatially resolved in millimeter resolution using optical frequency domain reflectometry (OFDR). The flow rate, position, and flow direction are retrieved simultaneously. Both electrical and optical on-fiber heating were demonstrated to suit different flow sensing applications.

  2. Calibration of Direct Velocimetry Using Hot Wire Anemometry

    Science.gov (United States)

    Holland, Michael L.; DeSilva, Upul P.; Johnson, Joseph A., III

    1997-01-01

    We studied the functionality of the IFA300 Hot Wire Anemometry system and its feasibility for the calibration of Direct Estimator Velocimetry (DEV) using Laser Induced Florescence (LIF). The experimental setup consisted of a single-wire hot wire probe measuring one component of velocity, the anemometry computational hardware and software, an HP oscilloscope, and a table fan to produce a simple flow with fluctuations. Measurements were taken at several points in the stream wise and transverse directions in the flow and various parameters recorded such as mean velocities temperature, turbulence intensities, skewness coefficients and flatness coefficients. The IFA300 software also allowed us to perform statistical manipulations such as spectrum analysis on velocities samples and correlation. Utilization of data files, also produced by the anemometry software, and post analysis were performed to produce graphical representations of turbulent intensity versus probe position and a flow field velocity profile. We concluded that the IFA300 Hot Wire Anemometry system is a reliable and functional method for calibration of DEV using LIF. Our future intentions are to set up a test chamber such that both velocity measurement techniques can be applied simultaneously, thus the calibration.

  3. Industrialization of Hot Wire Chemical Vapor Deposition for thin film applications

    Energy Technology Data Exchange (ETDEWEB)

    Schropp, R.E.I., E-mail: r.e.i.schropp@tue.nl

    2015-11-30

    The consequences of implementing a Hot Wire Chemical Vapor Deposition (HWCVD) chamber into an existing in-line or roll-to-roll reactor are described. The hardware and operation of the HWCVD production reactor is compared to that of existing roll-to-roll reactors based on Plasma Enhanced Chemical Vapor Deposition. The most important consequences are the technical consequences and the economic consequences, which are both discussed. The technical consequences are adaptations needed to the hardware and to the processing sequences due to the different interaction of the HWCVD process with the substrate and already deposited layers. The economic consequences are the reduced investments in radio frequency (RF) supplies and RF components. This is partially offset by investments that have to be made in higher capacity pumping systems. The most mature applications of HWCVD are moisture barrier coatings for thin film flexible devices such as Organic Light Emitting Diodes and Organic Photovoltaics, and passivation layers for multicrystalline Si solar cells, high mobility field effect transistors, and silicon heterojunction cells (also known as heterojunction cells with intrinsic thin film layers). Another example is the use of Si in thin film photovoltaics. The cost perspective per unit of thin film photovoltaic product using HWCVD is estimated at 0.07 €/Wp for the Si thin film component. - Highlights: • Review of consequences of implementing Hot Wire CVD into a manufacturing plant • Aspects of scaling up to large area and continuous manufacturing are discussed • Economic advantage of introducing a HWCVD process in a production system is estimated • Using HWCVD, the cost for the Si layers in photovoltaic products is 0.08 €/Wp.

  4. Statistical calibration via Gaussianization in hot-wire anemometry

    Science.gov (United States)

    Gluzman, Igal; Cohen, Jacob; Oshman, Yaakov

    2017-03-01

    A statistical method is introduced, that is based on Gaussianization to estimate the nonlinear calibration curve of a hot-wire probe, relating the input flow velocity to the output (measured) voltage. The method uses as input a measured sequence of voltage samples, corresponding to different unknown flow velocities in the desired operational range, and only two measured voltages along with their known (calibrated) flow velocities. The method relies on the conditions that (1) the velocity signal is Gaussian distributed (or has another known distribution), and (2) the measured signal covers the desired velocity range over which the sensor is to be calibrated. The novel calibration method is validated against standard calibration methods using data acquired by hot-wire probes in wind-tunnel experiments. In these experiments, a hot-wire probe is placed at a certain region downstream of a cube-shaped body in a freestream of air flow, properly selected, so that the central limit theorem, when applied to the random velocity increments composing the instantaneous velocity in the wake, roughly holds, and renders the measured signal nearly Gaussian distributed. The statistical distribution of the velocity field in the wake is validated by mapping the first four statistical moments of the measured signals in different regions of the wake and comparing them with corresponding moments of the Gaussian distribution. The experimental data are used to evaluate the sensitivity of the method to the distribution of the measured signal, and the method is demonstrated to possess some robustness with respect to deviations from the Gaussian distribution.

  5. A Physically Based Correction for Hot Wires in Wall Proximity

    Science.gov (United States)

    Durst, F.; Zanoun, E.-S.; Gad-El-Hak, M.

    2003-11-01

    It is common practice to calibrate hot wires in a freestream of constant and known velocity. When wires of this kind are utilized for near-wall measurements, the additional heat losses to the wall and other factors that have not been accounted for in the calibration have the potential for introducing significant errors. It is, therefore, highly desirable to find a generally applicable correction to thermal-probe measurements near walls. Following on our presentation at a previous meeting (Bul. Am. Phys. Soc. 45, no. 9, p. 141, 2000), we present herein a physically based correction for hot wires in wall proximity. As a standard, a laser Doppler velocimeter is used to provide accurate near-wall measurements of the mean velocity profile. Here the error due to the finite measuring volume of the laser is proportional to the curvature of the velocity profile, and hence is negligible in the linear and quasi-linear regions of that profile. For the flow around a hot wire near highly and moderately conducting walls, we show that the Grashof number is at least one order of magnitude less than the cube of the Reynolds number, and thus that diffusion not convection dominates the heat transfer to the wall. The universal correction curve we derive takes into account the effect of wire diameter, overheat ratio, wall thermal conductivity, wall distance, and wall thickness. In the experiments we conducted with a horizontal flat plate centrally mounted in a wind tunnel, perceptible heat loss was observed due to the shear flow on the other side of the working surface. The resulting error is caused by the change of the thermal boundary condition, and helps explain the wide scatter observed between channel flow and boundary layer experiments, particularly when using walls of poorly conducting materials.

  6. The static response of a bowed inclined hot wire

    Science.gov (United States)

    Smits, A. J.

    1984-01-01

    The directional sensitivity of a bowed, inclined hot wire is investigated using a simple model for the convective heat transfer. The static response is analyzed for subsonic and supersonic flows. It is shown that the effects of both end conduction and wire bowing are greater in supersonic flow. Regardless of the Mach number, however, these two phenomena have distinctly different effects; end conduction appears to be responsible for reducing the nonlinearity of the response, whereas bowing increases the directional sensitivity. Comparison with the available data suggests that the analysis is useful for interpreting the experimental results.

  7. Hot-wire anemometry for superfluid turbulent coflows

    OpenAIRE

    Durì, Davide; Baudet, Christophe; Moro, Jean-Paul; Roche, Philippe-Emmanuel; Diribarne, Pantxo

    2015-01-01

    International audience; We report the first evidence of an enhancement of the heat transfer from a heated wire to an external turbulent coflow of superfluid helium. We used a standard Pt-Rh hot-wire anemometer and overheat it up to 21 K in a pressurized liquid helium turbulent round jet at temperatures between 1.9 K and 2.12 K. The null-velocity response of the sensor can be satisfactorily modeled by the counterflow mechanism, while the extra cooling produced by the forced convection is found...

  8. [How reliable is a hot-wire anemometer?].

    Science.gov (United States)

    von Rechenberg, H; Konder, H; Höser, K; Lennartz, H

    1985-08-01

    To examine the advantage of hot-wire anemometer for clinical use, we have checked two types of this tools with respect to reliability and validity. It was found that electronic suppression of noise caused a distortion of the measurements. Furthermore changes of transducers were also responsible for deviations from true values. We require of the manufacturer to indicate the threshold of perception and the coefficient of variation for repeated measurements with several transducers. We recommend a simple rule which permits an estimation of the limits of reliable measurements for clinical use depending on the threshold of the equipment and on the parameters of ventilation.

  9. Kinetic study on hot-wire-assisted atomic layer deposition of nickel thin films

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Guangjie, E-mail: ygjhzh@dpe.mm.t.u-tokyo.ac.jp; Shimizu, Hideharu; Momose, Takeshi; Shimogaki, Yukihiro [Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2014-01-15

    High-purity Ni films were deposited using hot-wire-assisted atomic layer deposition (HW-ALD) at deposition temperatures of 175, 250, and 350 °C. Negligible amount of nitrogen or carbon contamination was detected, even though the authors used NH{sub 2} radical as the reducing agent and nickelocene as the precursor. NH{sub 2} radicals were generated by the thermal decomposition of NH{sub 3} with the assist of HW and used to reduce the adsorbed metal growth precursors. To understand and improve the deposition process, the kinetics of HW-ALD were analyzed using a Langmuir-type model. Unlike remote-plasma-enhanced atomic layer deposition, HW-ALD does not lead to plasma-induced damage. This is a significant advantage, because the authors can supply sufficient NH{sub 2} radicals to deposit high-purity metallic films by adjusting the distance between the hot wire and the substrate. NH{sub 2} radicals have a short lifetime, and it was important to use a short distance between the radical generation site and substrate. Furthermore, the impurity content of the nickel films was independent of the deposition temperature, which is evidence of the temperature-independent nature of the NH{sub 2} radical flux and the reactivity of the NH{sub 2} radicals.

  10. Methods of Measurement of High Air Velocities by the Hot-wire Method

    Science.gov (United States)

    Weske, John R.

    1943-01-01

    Investigations of strengths of hot wires at high velocities were conducted with platinum, nickel, and tungsten at approximately 200 Degrees Celcius hot-wire temperature. The results appear to disqualify platinum for velocities approaching the sonic range; whereas nickel withstands sound velocity, and tungsten may be used for supersonic velocities under standard atmospheric conditions. Hot wires must be supported by rigid prolongs at high velocities to avoid wire breakage. Resting current measurements for constant temperature show agreement with King's relation.

  11. Measurements of thermal conductivity and thermal diffusivity of hen egg-white lysozyme crystals using a short hot wire method

    Science.gov (United States)

    Fujiwara, Seiji; Maki, Syou; Tanaka, Seiichi; Maekawa, Ryunosuke; Masuda, Tomoki; Hagiwara, Masayuki

    2017-07-01

    Thermal conductivity and thermal diffusivity of hen egg-white lysozyme (HEWL) crystals were examined by using the transient short hot wire method. This method is based on the conventional hot wire method, but improved by using a wire that is much shorter than conventional ones. The magneto-Archimedes levitation technique was utilized to attach the HEWL crystals onto the wire. Owing to the upward magnetic force, the HEWL crystals were deposited at the air-liquid interface of the protein buffer solution where the short hot wire was preliminarily fixed. In situ observation clarified that the wire was completely buried into the HEWL crystals. By means of these techniques, the measurement of thermal conductivity and thermal diffusivity of HEWL crystals was realized for the first time. Gadolinium chloride (a paramagnetic subject) was used as a precipitant agent of crystallization. Crystal growth was carried out over 20 h at 17.2 °C. The applied magnetic field was 4 T. Measurements were conducted during the crystal growth at two different times. The thermal conductivity and diffusivity of the HEWL crystals were determined to be 0.410 W/(m.K) and 3.77×10-8 m2/s at 14 h after, and 0.438 W/(m.K) and 5.18×10-8 m2/s at 20 h after, respectively. We emphasize that this method is versatile and applicable for other protein crystals.

  12. Hot-wire ignition of AN-based emulsions

    Energy Technology Data Exchange (ETDEWEB)

    Turcotte, Richard; Goldthorp, Sandra; Badeen, Christopher M. [Canadian Explosives Research Laboratory, Natural Resources Canada, Ottawa, Ontario, K1A 0G1 (Canada); Chan, Sek Kwan [Orica Canada Inc., Brownsburg-Chatham, Quebec (Canada)

    2008-12-15

    Emulsions based on ammonium nitrate (AN) and water locally ignited by a heat source do not undergo sustained combustion when the pressure is lower than some threshold value usually called the Minimum Burning Pressure (MBP). This concept is now being used by some manufacturers as a basis of safety. However, before a technique to reliably measure MBP values can be designed, one must have a better understanding of the ignition mechanism. Clearly, this is required to avoid under ignitions which could lead to the erroneous interpretation of failures to ignite as failures to propagate. In the present work, facilities to prepare and characterize emulsions were implemented at the Canadian Explosives Research Laboratory. A calibrated hot-wire ignition system operated in a high-pressure vessel was also built. The system was used to study the ignition characteristics of five emulsion formulations as a function of pressure and ignition source current. It was found that these mixtures exhibit complicated pre-ignition stages and that the appearance of endotherms when the pressure is lowered below some threshold value correlates with the MBP. Thermal conductivity measurements using this hot-wire system are also reported. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

  13. Development of subminiature multi-sensor hot-wire probes

    Science.gov (United States)

    Westphal, Russell V.; Ligrani, Phillip M.; Lemos, Fred R.

    1988-01-01

    Limitations on the spatial resolution of multisensor hot wire probes have precluded accurate measurements of Reynolds stresses very near solid surfaces in wind tunnels and in many practical aerodynamic flows. The fabrication, calibration and qualification testing of very small single horizontal and X-array hot-wire probes which are intended to be used near solid boundaries in turbulent flows where length scales are particularly small, is described. Details of the sensor fabrication procedure are reported, along with information needed to successfully operate the probes. As compared with conventional probes, manufacture of the subminiature probes is more complex, requiring special equipment and careful handling. The subminiature probes tested were more fragile and shorter lived than conventional probes; they obeyed the same calibration laws but with slightly larger experimental uncertainty. In spite of these disadvantages, measurements of mean statistical quantities and spectra demonstrate the ability of the subminiature sensors to provide the measurements in the near wall region of turbulent boundary layers that are more accurate than conventional sized probes.

  14. A bidirectional respiratory flowmeter using the hot-wire principle.

    Science.gov (United States)

    Yoshiya, I; Nakajima, T; Nagai, I; Jitsukawa, S

    1975-02-01

    We have devised a bidirectional respiratory flowmeter using the hot-wire principle. The flow-direction sensor consists of a pair of tungsten wires strung parallel to the platinum hot-wire one on each side of the platinum wire. When the gas stream passes through the transducer, the upstream wire is cooled and the downstream wire is heated by the gas stream producing a temperature difference between the two tungsten wires. The difference in resistance thus produced between them is detected and amplified by a differential amplifier whose output serves as a triggering signal of flow inversion. The switching times of the flow inversion of the present instrument are 3 ms during panting and 10 ms during quiet breathing, when the distances from the platinum wire to the tungsten wires are 1.6 mm. Artifacts produced by the delay in switching are practically negligible. The flowmeter can be adapted for many kinds of respiratory flow measurement, except under the condition when inflammable gases are used.

  15. Preparation of high-quality hydrogenated amorphous silicon film with a new microwave electron cyclotron resonance chemical vapour deposition system assisted with hot wire

    Institute of Scientific and Technical Information of China (English)

    Zhu Xiu-Hong; Chen Guang-Hua; Yin Sheng-Yi; Rong Yan-Dong; Zhang Wen-Li; Hu Yue-Hui

    2005-01-01

    The preparation of high-quality hydrogenated amorphous silicon (a-Si:H) film with a new microwave electron cyclotron resonance-chemical vapour deposition (MWECR-CVD) system assisted with hot wire is presented. In this system the hot wire plays an important role in perfecting the microstructure as well as improving the stability and the optoelectronic properties of the a-Si:H film. The experimental results indicate that in the microstructure of the a-Si:H film, the concentration of dihydride is decreased and a trace of microcrystalline occurs, which is useful to improve its stability, and that in the optoelectronic properties of the a-Si:H film, the deposition rate reaches above 2.0nm/s and the photosensitivity increases up to 4.71× 105.

  16. Hot-wire measurements with automatic compensation of ambient temperature changes

    Directory of Open Access Journals (Sweden)

    Miheev Nikolay I.

    2015-01-01

    Full Text Available A single sensor hot-wire device with automatic temperature compensation for velocity measurements is developed. Experience in measuring the velocity and temperature in a flow with variable temperature using self-made hot-wire equipment and probes is discussed. Results of the corresponding methodical experiments are presented.

  17. Hot-wire measurements with automatic compensation of ambient temperature changes

    OpenAIRE

    Miheev Nikolay I.; Molochnikov Valeriy M.; Kratirov Dmitriy V.; Hayrnasov Konstantin R.; Zanko Philipp S.

    2015-01-01

    A single sensor hot-wire device with automatic temperature compensation for velocity measurements is developed. Experience in measuring the velocity and temperature in a flow with variable temperature using self-made hot-wire equipment and probes is discussed. Results of the corresponding methodical experiments are presented.

  18. Carbon nanotube electrodes for hot-wire electrochemistry.

    Science.gov (United States)

    Gründler, Peter; Frank, Otakar; Kavan, Ladislav; Dunsch, Lothar

    2009-02-23

    The use and preparation of single-walled carbon nanotubes (SWCNTs) at thin metallic wire electrodes for hot-wire electrochemical studies is described. The nanotubes were deposited on metal substrates such as gold by electrophoresis from a dispersion containing sodium dodecyl sulphate as an anionic surfactant. The formation of a layer of pure SWCNTs is achieved by thermal treatment at 350 degrees C. When heated in situ by a strong ac current, the electrodes can be used for electrochemical studies of nanotubes at increased temperatures. The state and functionality of the electrodes were characterized by Raman spectroscopy, scanning electron microscopy, and cyclic voltammetry with both anionic and cationic redox systems (dopamine, ferrocene carboxylic acid). First time experiments at the heated SWCNT electrodes demonstrated an excellent suitability of these as-prepared electrodes for thermoelectrochemical studies.

  19. Hot-wire anemometry for superfluid turbulent coflows.

    Science.gov (United States)

    Durì, Davide; Baudet, Christophe; Moro, Jean-Paul; Roche, Philippe-Emmanuel; Diribarne, Pantxo

    2015-02-01

    We report the first evidence of an enhancement of the heat transfer from a heated wire to an external turbulent coflow of superfluid helium. We used a standard Pt-Rh hot-wire anemometer and overheat it up to 21 K in a pressurized liquid helium turbulent round jet at temperatures between 1.9 K and 2.12 K. The null-velocity response of the sensor can be satisfactorily modeled by the counterflow mechanism, while the extra cooling produced by the forced convection is found to scale similarly as the corresponding extra cooling in classical fluids. We propose a preliminary analysis of the response of the sensor and show that-contrary to a common assumption-such sensor can be used to probe local velocity in turbulent superfluid helium.

  20. Hot-wire polysilicon waveguides with low deposition temperature.

    Science.gov (United States)

    Masaud, Taha M Ben; Tarazona, Antulio; Jaberansary, Ehsan; Chen, Xia; Reed, Graham T; Mashanovich, Goran Z; Chong, H M H

    2013-10-15

    We fabricated and measured the optical loss of polysilicon waveguides deposited using hot-wire chemical vapor deposition at a temperature of 240°C. A polysilicon film 220 nm thick was deposited on top of a 2000 nm thick plasma-enhanced chemical vapor deposition silicon dioxide layer. The crystalline volume fraction of the polysilicon film was measured by Raman spectroscopy to be 91%. The optical propagation losses of 400, 500, and 600 nm waveguides were measured to be 16.9, 15.9, and 13.5 dB/cm, respectively, for transverse electric mode at the wavelength of 1550 nm. Scattering loss is expected to be the major contributor to the propagation loss.

  1. Computerized hot-wire anemometry--principles of calculation.

    Science.gov (United States)

    Hald, A; Stigsby, B

    1980-04-01

    Principles of calculation of respiratory parameters based on a hot-wire anemometer with special reference to computer monitoring were evaluated. Flow-rate, gas-pressure, and flow-direction signals were recorded simultaneously on magnetic tape. Subsequent quantitative analyses were performed on a general purpose digital minicomputer. An analysis epoch of 256 s was selected from the 3 channels. After identification of one cycle baseline values of flow-rate and pressure were determined. Different time-lags in one respiratory cycle (inspiratory time, pause time and expiratory time) could be determined. Inspiratory and expiratory volumes were obtained by integration. Peak of the thoracic cage and the lungs were calculated using the above mentioned parameters. Finally, the respiratory frequency was calculated.

  2. Hot-wire anemometry for superfluid turbulent coflows

    Science.gov (United States)

    Durı, Davide; Baudet, Christophe; Moro, Jean-Paul; Roche, Philippe-Emmanuel; Diribarne, Pantxo

    2015-02-01

    We report the first evidence of an enhancement of the heat transfer from a heated wire to an external turbulent coflow of superfluid helium. We used a standard Pt-Rh hot-wire anemometer and overheat it up to 21 K in a pressurized liquid helium turbulent round jet at temperatures between 1.9 K and 2.12 K. The null-velocity response of the sensor can be satisfactorily modeled by the counterflow mechanism, while the extra cooling produced by the forced convection is found to scale similarly as the corresponding extra cooling in classical fluids. We propose a preliminary analysis of the response of the sensor and show that—contrary to a common assumption—such sensor can be used to probe local velocity in turbulent superfluid helium.

  3. Hot-Wire Method for Kinematic Viscosity Estimation

    Science.gov (United States)

    Giaretto, Valter

    2010-03-01

    This paper explores the characterization of thermal and momentum diffusion properties of condensed phase biological fluids. The widely used transient hot-wire technique for determination of thermal diffusion properties is proposed here to investigate also the apparent kinematic viscosity of fluids with the apparatus commonly adopted for thermal conductivity and/or thermal diffusivity determination. The undesired onset of convection in the determination of thermal diffusion properties is in this case the useful effect measured at the wire-fluid interface. From a theoretical point of view, the onset of convection time at a given vertical position along the wire has been related to the Prandtl number, and the reliability of the kinematic viscosity has been studied and preliminarily tested in the case of water.

  4. Micromachined hot-wire thermal conductivity probe for biomedical applications.

    Science.gov (United States)

    Yi, Ming; Panchawagh, Hrishikesh V; Podhajsky, Ronald J; Mahajan, Roop L

    2009-10-01

    This paper presents the design, fabrication, numerical simulation, and experimental validation of a micromachined probe that measures thermal conductivity of biological tissues. The probe consists of a pair of resistive line heating elements and resistance temperature detector sensors, which were fabricated by using planar photolithography on a glass substrate. The numerical analysis revealed that the thermal conductivity and diffusivity can be determined by the temperature response induced by the uniform heat flux in the heating elements. After calibrating the probe using a material (agar gel) of known thermal conductivity, the probe was deployed to calculate the thermal conductivity of Crisco. The measured value is in agreement with that determined by the macro-hot-wire probe method to within 3%. Finally, the micro thermal probe was used to investigate the change of thermal conductivity of pig liver before and after RF ablation treatment. The results show an increase in thermal conductivity of liver after the RF ablation.

  5. On near-wall hot-wire measurements

    Science.gov (United States)

    Khoo, B. C.; Chew, Y. T.; Teo, C. J.

    A specially constructed hot-wire probe was used to obtain very near-wall velocity measurements in both a fully developed turbulent channel flow and flat plate boundary layer flow. The near-wall hot-wire probe, having been calibrated in a specially constructed laminar flow calibration rig, was used to measure the mean streamwise velocity profile, distributions of streamwise and spanwise intensities of turbulence and turbulence kinetic energy k in the viscous sublayer and beyond; these distributions compare very favorably with available DNS results obtained for channel flow. While low Reynolds number effects were clearly evident for the channel flow, these effects are much less distinct for the boundary layer flow. By assuming the dissipating range of eddy sizes to be statistically isotropic and the validity of Taylor's hypothesis, the dissipation rate ɛiso in the very near-wall viscous sublayer region and beyond was determined for both the channel and boundary layer flows. It was found that if the convective velocity Uc in Taylor's hypothesis was assumed to be equal to the mean velocity Uat the point of measurement, the value of (ɛ+iso)1 thus obtained agrees well with that of (ɛ+)DNS for y+>=80 for channel flow; this suggests the validity of assuming Uc=Uand local isotropy for large values of y+. However, if Uc was assumed to be 10.6uτ, the value of (ɛ+iso)2 thus obtained was found to compare reasonably well with the distribution of (ɛ+iso)DNS for y+<=15.

  6. Nanoscale Hot-Wire Probes for Boundary-Layer Flows

    Science.gov (United States)

    Tedjojuwono, Ken T.; Herring, Gregory C.

    2003-01-01

    Hot-wire probes having dimensions of the order of nanometers have been proposed for measuring temperatures (and possibly velocities) in boundary-layer flows at spatial resolutions much finer and distances from walls much smaller than have been possible heretofore. The achievable resolutions and minimum distances are expected to be of the order of tens of nanometers much less than a typical mean free path of a molecule and much less than the thickness of a typical flow boundary layer in air at standard temperature and pressure. An additional benefit of the small scale of these probes is that they would perturb the measured flows less than do larger probes. The hot-wire components of the probes would likely be made from semiconducting carbon nanotubes or ropes of such nanotubes. According to one design concept, a probe would comprise a single nanotube or rope of nanotubes laid out on the surface of an insulating substrate between two metallic wires. According to another design concept, a nanotube or rope of nanotubes would be electrically connected and held a short distance away from the substrate surface by stringing it between two metal electrodes. According to a third concept, a semiconducting nanotube or rope of nanotubes would be strung between the tips of two protruding electrodes made of fully conducting nanotubes or ropes of nanotubes. The figure depicts an array of such probes that could be used to gather data at several distances from a wall. It will be necessary to develop techniques for fabricating the probes. It will also be necessary to determine whether the probes will be strong enough to withstand the aerodynamic forces and impacts of micron-sized particles entrained in typical flows of interest.

  7. Non-classical crystallization of silicon thin films during hot wire chemical vapor deposition

    Science.gov (United States)

    Jung, Jae-Soo; Lee, Sang-Hoon; Kim, Da-Seul; Kim, Kun-Su; Park, Soon-Won; Hwang, Nong-Moon

    2017-01-01

    The deposition behavior of silicon films by hot wire chemical vapor deposition (HWCVD) was approached by non-classical crystallization, where the building block of deposition is a nanoparticle generated in the gas phase of the reactor. The puzzling phenomenon of the formation of an amorphous incubation layer on glass could be explained by the liquid-like property of small charged nanoparticles (CNPs), which are generated in the initial stage of the HWCVD process. Using the liquid-like property of small CNPs, homo-epitaxial growth as thick as 150 nm could be successfully grown on a silicon wafer at 600 °C under the processing condition where CNPs as small as possible could be supplied steadily by a cyclic process which periodically resets the process. The size of CNPs turned out to be an important parameter in the microstructure evolution of thin films.

  8. Influence of process pressure on β-SiC growth by CVD

    Science.gov (United States)

    Andreev, A. A.; Sultanov, A. O.; Gusev, A. S.; Kargin, N. I.; Pavlova, E. P.

    2014-10-01

    3C-SiC films grown on Si (100) substrates by CVD method using silane-propane- hydrogen system were analyzed for crystallinity at various process pressures. The deposition experiments were carried out in a shower-head type cold-wall CVD reactor. The influence of growth conditions on a structural modification of experimental samples was studied by X-ray diffraction (XRD) measurements, Fourier transform infrared spectroscopy (FTIR) and spectroscopic ellipsometry (SE).

  9. Ultratough CVD single crystal diamond and three dimensional growth thereof

    Science.gov (United States)

    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.

  10. High growth rate of a-SiC:H films using ethane carbon source by HW-CVD method

    Indian Academy of Sciences (India)

    Mahesh M Kamble; Vaishali S Waman; Sanjay S Ghosh; Azam Mayabadi; Vasant G Sathe; T Shripathi; Habib M Pathan; Sandesh R Jadkar

    2013-12-01

    Hydrogenated amorphous silicon carbide (a-SiC:H) thin films were prepared using pure silane (SiH4) and ethane (C2H6), a novel carbon source, without hydrogen dilution using hot wire chemical vapour deposition (HW-CVD) method at low substrate temperature (200 °C) and at reasonably higher deposition rate (19.5 Å/s < d < 35.2 Å/s). Formation of a-SiC:H films has been confirmed from FTIR, Raman and XPS analysis. Influence of deposition pressure on compositional, structural, optical and electrical properties has been investigated. FTIR spectroscopy analysis revealed that there is decrease in C–H and Si–H bond densities while, Si–C bond density increases with increase in deposition pressure. Total hydrogen content drops from 22.6 to 14.4 at.% when deposition pressure is increased. Raman spectra show increase in structural disorder with increase in deposition pressure. It also confirms the formation of nearly stoichiometric a-SiC:H films. Bandgap calculated using both Tauc’s formulation and absorption at 104 cm-1 shows decreasing trend with increase in deposition pressure. Decrease in refractive index and increase in Urbach energy suggests increase in structural disorder and microvoid density in the films. Finally, it has been concluded that C2H6 can be used as an effective carbon source in HW-CVD method to prepare stoichiometric a-SiC:H films.

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

    Science.gov (United States)

    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.

  12. Investigation of Constant Temperature Hot-wire System Response using Laser Pulse

    Science.gov (United States)

    Jaffa, Nicholas; Morris, Scott; Cameron, Joshua

    2016-11-01

    Constant temperature hot-wire systems use a Wheatstone bridge and feedback amplifier circuit to maintain a constant average temperature across the wire yielding frequency responses of order 100 kHz. This high frequency response allows hot-wires to be used extensively for aerodynamic measurements in high speed flows and uncertainty at these high frequencies can be difficult to diagnose. The standard frequency response check for constant temperature hot-wires uses an electronic pulse across the circuit to check the electronic feedback circuit response time, but does not account for the impact of the heat transfer along the wire. In order to investigate the frequency response of the entire constant temperature hot-wire system, including the heat transfer along the wire, a novel method was developed using a pulsed PIV laser focused to illuminate only the hot-wire. The laser pulse duration was effectively an instantaneous change in wire surface temperature through radiation. A hot-wire was placed in a uniform open calibration jet for a range of flow conditions. The response of the entire hot-wire system was observed across a range of conditions including changes in flow, wire temperature, and thermal boundary conditions and compared with the electronic pulse test.

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

    Science.gov (United States)

    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.

  14. A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids

    OpenAIRE

    Perkins, R. A.; Roder, H. M.; Nieto de Castro, C. A.

    1991-01-01

    A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously use...

  15. Application of the hot-wire anemometer to respiratory measurements in small animal.

    Science.gov (United States)

    Godal, A; Belenky, D A; Standaert, T A; Woodrum, D E; Grimsrud, L; Hodson, W A

    1976-02-01

    A hot-wire anemometer was evaluated to determine its suitability for measurement of small tidal volumes. Used with a constant background flow of gas, the output of the hot-wire anemometer was linear and independent of respiratory frequency, temperature, and humidity. The change in output with CO2 concentration was negligible within the physiologic range. The use of a background flow eliminates the need for one-way valves, minimizes dead space, and maintains the flow velocity past the hot wire within its range of linear response.

  16. Hot wire deposited hydrogenated amorphous silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mahan, A.H.; Iwaniczko, E.; Nelson, B.P.; Reedy, R.C. Jr.; Crandall, R.S. [National Renewable Energy Lab., Golden, CO (United States)

    1996-05-01

    This paper details the results of a study in which low H content, high deposition rate hot wire (HW) deposited amorphous silicon (a-Si:H) has been incorporated into a substrate solar cell. The authors find that the treatment of the top surface of the HW i layer while it is being cooled from its high deposition temperature is crucial to device performance. They present data concerning these surface treatments, and correlate these treatments with Schottky device performance. The authors also present first generation HW n-i-p solar cell efficiency data, where a glow discharge (GD) {mu}c-Si(p) layer was added to complete the partial devices. No light trapping layer was used to increase the device Jsc. Their preliminary investigations have yielded efficiencies of up to 6.8% for a cell with a 4000 {Angstrom} thick HW i-layer, which degrade less than 10% after a 900 hour light soak. The authors suggest avenues for further improvement of their devices.

  17. Hot-wire vs laser, is there a difference?

    Science.gov (United States)

    Munger, A. C.; Beckman, T. M.; Kramer, D. P.

    When a design for an ordnance device utilizing new technology begins to take shape, all of the various design elements are approached individually and then ultimately tested as a single system. This approach allows the various elements to float within an overall design envelope. The embracing of laser technology for the ignition system of various ordnance designs should ideally take this path. The reality for many of us is that the total system will not be completely re-engineered. The laser ignition system will need to be integrated into existing systems. This will require innovative electrical to laser interfaces and also require that the physical output of the new device duplicate that of the replaced electrical devices. This seems like a given when the technology is examined; after all, both hot-wire technology and laser technology provide energy to effect ignition of the energetic material and should have no influence on the burning characteristics. This statement appears to be the 'truth' but when asked to produce any evidence to support the contention, we at Mound had none. This paper will report on some experiments that were conducted to begin building the data base that supports this hypothesis.

  18. "Hot-wire" microfluidic flowmeter based on a microfiber coupler.

    Science.gov (United States)

    Yan, Shao-Cheng; Liu, Zeng-Yong; Li, Cheng; Ge, Shi-Jun; Xu, Fei; Lu, Yan-Qing

    2016-12-15

    Using an optical microfiber coupler (MC), we present a microfluidic platform for strong direct or indirect light-liquid interaction by wrapping a MC around a functionalized capillary. The light propagating in the MC and the liquid flowing in the capillary can be combined and divorced smoothly, keeping a long-distance interaction without the conflict of input and output coupling. Using this approach, we experimentally demonstrate a "hot-wire" microfluidic flowmeter based on a gold-integrated helical MC device. The microfluid inside the glass channel takes away the heat, then cools the MC and shifts the resonant wavelength. Due to the long-distance interaction and high temperature sensitivity, the proposed microfluidic flowmeter shows an ultrahigh flow rate sensitivity of 2.183 nm/(μl/s) at a flow rate of 1 μl/s. The minimum detectable change of the flow rate is around 9 nl/s at 1 μl/s.

  19. Synthesis of wo3 nanogranular thin films by hot-wire CVD

    NARCIS (Netherlands)

    Houweling, Z.S.; Geus, J.W.; Schropp, R.E.I.

    2010-01-01

    By resistively heating tungsten filaments in a constant air flow under a reduced pressure, nanogranular amorphous WO3 thin films are deposited on glassy carbon substrates. The substrate surface temperature is monitored by a thermocouple. For deposition times of 15 min and longer, the films show crys

  20. Thin Film Organic / Inorganic Multilayer Gas Barriers by Hot-Wire and Initiated CVD

    NARCIS (Netherlands)

    Spee, D.A.

    2013-01-01

    A very attractive property for many optoelectronic devices, such as solar cells and organic light emitting diodes (OLEDs), is light weight and mechanical flexibility. This will open new technological opportunities, such as thin flexible lighting, lightweight conformable solar cells, and rollable dis

  1. Towards a general growth model for graphene CVD on transition metal catalysts

    Science.gov (United States)

    Cabrero-Vilatela, Andrea; Weatherup, Robert S.; Braeuninger-Weimer, Philipp; Caneva, Sabina; Hofmann, Stephan

    2016-01-01

    The chemical vapour deposition (CVD) of graphene on three polycrystalline transition metal catalysts, Co, Ni and Cu, is systematically compared and a first-order growth model is proposed which can serve as a reference to optimize graphene growth on any elemental or alloy catalyst system. Simple thermodynamic considerations of carbon solubility are insufficient to capture even basic growth behaviour on these most commonly used catalyst materials, and it is shown that kinetic aspects such as carbon permeation have to be taken into account. Key CVD process parameters are discussed in this context and the results are anticipated to be highly useful for the design of future strategies for integrated graphene manufacture.The chemical vapour deposition (CVD) of graphene on three polycrystalline transition metal catalysts, Co, Ni and Cu, is systematically compared and a first-order growth model is proposed which can serve as a reference to optimize graphene growth on any elemental or alloy catalyst system. Simple thermodynamic considerations of carbon solubility are insufficient to capture even basic growth behaviour on these most commonly used catalyst materials, and it is shown that kinetic aspects such as carbon permeation have to be taken into account. Key CVD process parameters are discussed in this context and the results are anticipated to be highly useful for the design of future strategies for integrated graphene manufacture. Electronic supplementary information (ESI) available: Fig. S1. See DOI: 10.1039/c5nr06873h

  2. The use of hot-wire anemometry in transonic periodic flow

    Science.gov (United States)

    Bodapati, S.; Lee, C.-S.

    1984-01-01

    The unsteady wake profiles of an airfoil with an oscillating flap were measured in the NASA Ames 11 x 11-foot transonic wind tunnel. Laser Doppler Velocimetry (LDV) and holography techniques were used in limited region where optical accessability is available. X-hot-film wire was used to measure the wake profiles in the complete region to obtain magnitude and direction of the flow. A thorough calibration was carried out to determine the sensitivity coefficients of the hot-wire in three different tunnels at transonic speeds. A calculation procedure is established to resolve the hot-wire signals at transonic speeds and applied in the measurements of steady and periodic wake profiles. The effect of flow incidence on the hot-wire signals is evaluated and incorporated in the analyses. Typical hot-wire results are compared with the results of LDV, holography and pitot-static tube embedded with Kulite transducers.

  3. Hot wire and spark pyrolysis as simple new routes to silicon nanoparticle synthesis

    CSIR Research Space (South Africa)

    Scriba, MR

    2012-11-01

    Full Text Available gases, silane and diborane or silane and phosphine were used. While hot wire pyrolysis always results in multifaceted particles, those produced by spark pyrolysis are spherical. Electrical resistance measurements of compressed powders showed that boron...

  4. Hot-wire based phase resolved measurement techniques for turbomachinery flows

    Science.gov (United States)

    Jaffa, Nicholas; Morris, Scott; Cameron, Joshua

    2013-11-01

    Resolving the details of turbomachinery rotor flows from the stationary reference frame is difficult due to the high sensor frequency response required. Hot-wires have the necessary frequency response but are sensitive to both total temperature and velocity. In high-speed turbomachinery flows, the large blade-to-blade total temperature gradients prevent traditional hot-wire methods from being used to measure velocity directly. In order to decouple the effects from the temperature variation, a single constant temperature hot-wire was operated at different overheats at the exit of a high-speed transonic axial compressor rotor. The multiple overheat method was used to decouple the phase locked averages of total temperature and velocity magnitude from the phase locked average hot-wire voltages for different overheats. The phase locked average total temperature and velocity magnitude fields show flow features relative to the rotor including blade wakes, boundary layers, and tip clearance flows.

  5. A calibration technique to correct sensor drift issues in hot-wire anemometry

    Science.gov (United States)

    Talluru, K. M.; Kulandaivelu, V.; Hutchins, N.; Marusic, I.

    2014-10-01

    Accurate calibration is imperative to obtain reliable flow measurements using hot-wire anemometry. Calibration errors owing to temperature drift, wire degradation, changes in ambient conditions etc can lead to substantial uncertainties in hot-wire measurements. A new calibration procedure is implemented here to account for most forms of drift that are typically encountered during high quality flow measurements using hot-wires. The method involves obtaining single point recalibrations of the hot-wire (in the free-stream) at regular intervals during the course of an actual experiment, and using these during post-processing to correct for any drift encountered. Unlike many other existing schemes, this proposed calibration correction method is not solely restricted to correcting temperature drift.

  6. Optimization of Single-Sensor Two-State Hot-Wire Anemometer Transmission Bandwidth.

    Science.gov (United States)

    Ligęza, Paweł

    2008-10-28

    Hot-wire anemometric measurements of non-isothermal flows require the use of thermal compensation or correction circuitry. One possible solution is a two-state hot-wire anemometer that uses the cyclically changing heating level of a single sensor. The area in which flow velocity and fluid temperature can be measured is limited by the dimensions of the sensor's active element. The system is designed to measure flows characterized by high velocity and temperature gradients, although its transmission bandwidth is very limited. In this study, we propose a method to optimize the two-state hot-wire anemometer transmission bandwidth. The method is based on the use of a specialized constanttemperature system together with variable dynamic parameters. It is also based on a suitable measurement cycle paradigm. Analysis of the method was undertaken using model testing. Our results reveal a possible significant broadening of the two-state hot-wire anemometer's transmission bandwidth.

  7. Improved method of analyzing hot-wire measurements in supersonic turbulence

    Science.gov (United States)

    Logan, Pamela

    1989-01-01

    The present analysis method for hot-wire data in supersonic turbulence takes sound field effects into account and yields greater accuracy in its treatment of flow variable fluctuations than existing methods despite requiring only a moderately accurate estimate of static pressure fluctuations. The method demonstrates the way in which neglecting pressure fluctuations will affect hot-wire data analysis, as well as indicating the probable direction the errors will take.

  8. Thermal Conductivity of Saturated Liquid Toluene by Use of Anodized Tantalum Hot Wires at High Temperatures

    OpenAIRE

    Perkins, R. A.; Ramires, M. L. V.; Nieto de Castro, C. A.

    2000-01-01

    Absolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temper...

  9. Use of the Hot Wire Anemometry for Velocity and Temperature Measurements in a Turbomachine

    OpenAIRE

    Blidi, Sami; Miton, Hubert

    1995-01-01

    The hot film anemometry in a highly heterogeneous unsteady flow is a quite complex measurement technique. The velocity is determined from the heat flux measurement. The part of the signal related to velocity must be kept apart from one related to temperature and to pressure of flow. After a brief return to the principle of hot wire anemometry and the different heat transfer models between hot wire and flow, an experimentally established heat flux expression is presented. This study was achiev...

  10. Application of Hot-wire Method for Measuring Thermal Conductivity of Fine Ceramics

    Directory of Open Access Journals (Sweden)

    Shangxi WANG

    2016-11-01

    Full Text Available Ceramic substrate is preferred in high density packaging due to its high electrical resistivity and moderate expansion coefficient. The thermal conductivity is a key parameter for packaging substrates. There are two common methods to measure the thermal conductivity, which are the hot-wire method and the laser-flash method. Usually, the thermal conductivities of porcelain is low and meet the measurement range of hot-wire method, and the measured value by hot-wire method has little difference with that by laser-flash method. In recent years, with the requirement of high-powered LED lighting, some kinds of ceramic substrates with good thermal conductivity have been developed and their thermal conductivity always measured by the means of laser flash method, which needs expensive instrument. In this paper, in order to detect the thermal conductivity of fine ceramic with convenience and low cost, the feasibility of replacing the laser flash method with hot wire method to measure thermal conductivity of ceramic composites was studied. The experiment results showed that the thermal conductivity value of fine ceramics measured by the hot-wire method is severely lower than that by the laser-flash method. However, there is a positive relationship between them. It is possible to measure the thermal conductivity of fine ceramic workpiece instantly by hot-wire method via a correction formula.DOI: http://dx.doi.org/10.5755/j01.ms.22.4.12543

  11. Hot-wire accuracy in supersonic turbulence from comparisons with laser-induced fluorescence

    Science.gov (United States)

    Logan, Pamela; Bershader, Daniel; Mckenzie, Robert L.

    1988-01-01

    A hot-wire anemometer and a new, nonintrusive, laser-induced fluorescence (LIF) technique are used to survey a turbulent boundary layer in a supersonic channel flow at Mach no. 2.06. The purpose is to test the accuracy of using the hot wire to measure the fluctuation amplitudes of static temperature and density in a compressible turbulent flow by comparing the results with independent and direct LIF measurements. Several methods of hot-wire calibration and analysis are applied. With each method, the hot-wire response can be related primarily to fluctuations of mass flux and total temperature, from which fluctuations of static temperature and density are calculated. However, these calculations are shown to be valid only if the fluctuations in static pressure are negligible. The acquisition and the analysis of the hot-wire data are often simplified further by neglecting the effects of fluctuations in total temperature. Comparisons of the fluctuation amplitudes of temperature and density obtained by hot-wire and LIF measurements demonstrate that such assumptions might not always be warranted, even in apparently simple flows.

  12. Metal oxide growth, spin precession measurements and Raman spectroscopy of CVD graphene

    Science.gov (United States)

    Matsubayashi, Akitomo

    The focus of this dissertation is to explore the possibility of wafer scale graphene-based spintronics. Graphene is a single atomic layer of sp 2 bonded carbon atoms that has attracted much attention as a new type of electronic material due to its high carrier mobilities, superior mechanical properties and extremely high thermal conductivity. In addition, it has become an attractive material for use in spintronic devices owing to its long electron spin relaxation time at room temperature. This arises in part from its low spin-orbit coupling and negligible nuclear hyperfine interaction. In order to realize wafer scale graphene spintronics, utilization of CVD grown graphene is crytical due to its scalability. In this thesis, a unique fabrication method of the metal oxide layers on CVD graphene is presented. This is motivated by theoretical work showing that an ultra thin metal oxide film used as a tunnel barrier improves the spin injection efficiency. Introducing a titanium seed layer prior to the aluminum oxide growth showed improved surface and film uniformity and resulted in a completely oxidized film. Utilizing this unique metal oxide film growth process, lateral spin valve devices using CVD graphene as a channel are successfully fabricated. Hanle spin precession measurements are demonstrated on these CVD graphene spin devices. A non-local Hanle voltage model based upon the diffusive spin transport in a solid is utilized to find the spin diffusion length and spin relaxation time of CVD graphene. The measured spin relaxation times in CVD graphene were compatible with the values found in the literature. However, they are an order of magnitude shorter than the theoretical values expected in graphene. To investigate possible origins of this order of magnitude shorter spin relaxation time in graphene, crystal and electrical modifications in CVD graphene are studied throughout the entire device fabrication process. Raman spectroscopy is utilized to track CVD graphene

  13. Competition of silene/silylene chemistry with free radical chain reactions using 1-methylsilacyclobutane in the hot-wire chemical vapor deposition process.

    Science.gov (United States)

    Badran, I; Forster, T D; Roesler, R; Shi, Y J

    2012-10-18

    The gas-phase reaction chemistry of using 1-methylsilacyclobutane (MSCB) in the hot-wire chemical vapor deposition (CVD) process has been investigated by studying the decomposition of MSCB on a heated tungsten filament and subsequent gas-phase reactions in a reactor. Three pathways exist to decompose MSCB on the filament to form ethene/methylsilene, propene/methylsilylene, and methyl radicals. The activation energies for forming propene and methyl radical, respectively, are determined to be 68.7 ± 1.3 and 46.7 ± 2.5 kJ·mol(-1), which demonstrates the catalytic nature of the decomposition. The secondary gas-phase reactions in the hot-wire CVD reactor are characterized by the competition between a free radical chain reaction and the cycloaddition of silene reactive species produced either from the primary decomposition of MSCB on the filament or the isomerization of silylene species. At lower filament temperatures of 1000-1100 °C and short reaction time (t ≤ 15 min), the free radical chain reaction is equally important as the silene chemistry. With increasing filament temperature and reaction time, silene chemistry predominates.

  14. Modelling and operation of sub-miniature constant temperature hot-wire anemometry

    Science.gov (United States)

    Samie, M.; Watmuff, J. H.; Van Buren, T.; Hutchins, N.; Marusic, I.; Hultmark, M.; Smits, A. J.

    2016-12-01

    High-Reynolds number flows are very common in technological applications and in nature, and hot-wire anemometry is the preferred method for measuring the time-series of fluctuating velocity in such flows. However, measurement of very high-Reynolds number flows requires hot-wires with higher temporal and spatial resolution than is available with conventional probes. Much effort has therefore been devoted to decreasing the size of the hot-wire probes and this has led to associated challenges with operation. It is this latter operation problem which is the focus of this paper. To this end, an existing theoretical model of constant-temperature hot-wire anemometers (Perry 1982 Hot-Wire Anemometry (New York: Oxford University Press), Watmuff 1995 Exp. Therm. Fluid Sci. 11 117-34) is applied, and its accuracy is tested for the first time by comparison to measurements using an in-house constant temperature anemometer (CTA) for both conventional 5~μ m-diameter wires and sub-miniature hot-wires. With the aid of this model, we propose modifications to the CTA design and demonstrate successful operation of the CTA with the Princeton nano-scale thermal anemometry probe (NSTAP) (Bailey et al 2010 J. Fluid Mech. 663 160-79). It is also shown that the transfer function obtained from the model can be utilized to estimate the true frequency response and cut-off frequency of a hot-wire-CTA system to the velocity fluctuations, which is essential in accurate measurements of energy spectrum and higher order statistics of turbulent flows.

  15. Low temperature CVD growth of ultrathin carbon films

    Directory of Open Access Journals (Sweden)

    Chao Yang

    2016-05-01

    Full Text Available We demonstrate the low temperature, large area growth of ultrathin carbon films by chemical vapor deposition under atmospheric pressure on various substrates. In particularly, uniform and continuous carbon films with the thickness of 2-5 nm were successfully grown at a temperature as low as 500 oC on copper foils, as well as glass substrates coated with a 100 nm thick copper layer. The characterizations revealed that the low-temperature-grown carbon films consist on few short, curved graphene layers and thin amorphous carbon films. Particularly, the low-temperature grown samples exhibited over 90% transmittance at a wavelength range of 400-750 nm and comparable sheet resistance in contrast with the 1000oC-grown one. This low-temperature growth method may offer a facile way to directly prepare visible ultrathin carbon films on various substrate surfaces that are compatible with temperatures (500-600oC used in several device processing technologies.

  16. Uncertainties in hot-wire measurements of compressible turbulent flows implied by comparisons with laser-induced fluorescence

    Science.gov (United States)

    Mckenzie, R. L.; Logan, P.

    1986-01-01

    A hot-wire anemometer and a new nonintrusive laser-induced fluorescence (LIF) technique are used to survey a Mach 2 turbulent boundary layer. The hot-wire anemometer's ability to accurately measure mass flux, temperature, and density fluctuations in a compressible flow is examined by comparing its results with those obtained using LIF. Several methods of hot-wire calibration are used, and the uncertainties in their measurements of various fluctuating flow parameters are determined. The results show that although a hot-wire operated at high overheat can measure mass flux fluctuations, temperature and density fluctuations are not determined accurately from such measurements. However, a hot-wire operated at multiple overheats can be used to measure static and total temperature fluctuations. The presence of pressure fluctuations and their correlation with density can prevent the use of hot-wire data to determine density fluctuations.

  17. Improved Control Of cheese Manufacture Through continuous Vat Monitoring Of Coagulation Parameters Using The Hot Wire Method

    OpenAIRE

    LeFevre, Michael John

    1995-01-01

    The hot wire method, with pH and temperature sensors, was evaluated to determine its usefulness and application for cheese production automation. Coagulation of milk substrate was measured with the hot wire instrument and by four other methods: Formagraph, Brookfield®, vixcometer, Omnispec™ bioactivity monitor, and Sommer and Matsen rolling bottle method. The hot wire, using the time at maximum slope, detected coagulation before methods that measure resistance to shear, and after methods that...

  18. Mass flow-rate control unit to calibrate hot-wire sensors

    Energy Technology Data Exchange (ETDEWEB)

    Durst, F.; Uensal, B. [FMP Technology GmbH, Erlangen (Germany); Haddad, K. [FMP Technology GmbH, Erlangen (Germany); Friedrich-Alexander-Universitaet Erlangen-Nuernberg, LSTM-Erlangen, Institute of Fluid Mechanics, Erlangen (Germany); Al-Salaymeh, A.; Eid, Shadi [University of Jordan, Mechanical Engineering Department, Faculty of Engineering and Technology, Amman (Jordan)

    2008-02-15

    Hot-wire anemometry is a measuring technique that is widely employed in fluid mechanics research to study the velocity fields of gas flows. It is general practice to calibrate hot-wire sensors against velocity. Calibrations are usually carried out under atmospheric pressure conditions and these suggest that the wire is sensitive to the instantaneous local volume flow rate. It is pointed out, however, that hot wires are sensitive to the instantaneous local mass flow rate and, of course, also to the gas heat conductivity. To calibrate hot wires with respect to mass flow rates per unit area, i.e., with respect to ({rho}U), requires special calibration test rigs. Such a device is described and its application is summarized within the ({rho}U) range 0.1-25 kg/m{sup 2} s. Calibrations are shown to yield the same hot-wire response curves for density variations in the range 1-7 kg/m{sup 3}. The application of the calibrated wires to measure pulsating mass flows is demonstrated, and suggestions are made for carrying out extensive calibrations to yield the ({rho}U) wire response as a basis for advanced fluid mechanics research on ({rho}U) data in density-varying flows. (orig.)

  19. On hot-wire diagnostics in Rayleigh-Taylor mixing layers

    Energy Technology Data Exchange (ETDEWEB)

    Kraft, Wayne N. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Banerjee, Arindam [Missouri University of Science and Technology, Department of Mechanical and Aerospace Engineering, Rolla, MO (United States); Andrews, Malcolm J. [Texas A and M University, Department of Mechanical Engineering, College Station, TX (United States); Los Alamos National Laboratory, NM (United States)

    2009-07-15

    Two hot-wire flow diagnostics have been developed to measure a variety of turbulence statistics in the buoyancy driven, air-helium Rayleigh-Taylor mixing layer. The first diagnostic uses a multi-position, multi-overheat (MPMO) single wire technique that is based on evaluating the wire response function to variations in density, velocity and orientation, and gives time-averaged statistics inside the mixing layer. The second diagnostic utilizes the concept of temperature as a fluid marker, and employs a simultaneous three-wire/cold-wire anemometry technique (S3WCA) to measure instantaneous statistics. Both of these diagnostics have been validated in a low Atwood number (A{sub t}{<=} 0.04), small density difference regime, that allowed validation of the diagnostics with similar experiments done in a hot-water/cold-water water channel facility. Good agreement is found for the measured growth parameters for the mixing layer, velocity fluctuation anisotropy, velocity fluctuation p.d.f behavior, and measurements of molecular mixing. We describe in detail the MPMO and S3WCA diagnostics, and the validation measurements in the low Atwood number regime (A{sub t}{<=} 0.04). We also outline the advantages of each technique for measurement of turbulence statistics in fluid mixtures with large density differences. (orig.)

  20. Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer-Free Device Fabrication.

    Science.gov (United States)

    Wang, Huaping; Yu, Gui

    2016-07-01

    Graphene is the most broadly discussed and studied two-dimensional material because of its preeminent physical, mechanical, optical, and thermal properties. Until now, metal-catalyzed chemical vapor deposition (CVD) has been widely employed for the scalable production of high-quality graphene. However, in order to incorporate the graphene into electronic devices, a transfer process from metal substrates to targeted substrates is inevitable. This process usually results in contamination, wrinkling, and breakage of graphene samples - undesirable in graphene-based technology and not compatible with industrial production. Therefore, direct graphene growth on desired semiconductor and dielectric substrates is considered as an effective alternative. Over the past years, there have been intensive investigations to realize direct graphene growth using CVD methods without the catalytic role of metals. Owing to the low catalytic activity of non-metal substrates for carbon precursor decomposition and graphene growth, several strategies have been designed to facilitate and engineer graphene fabrication on semiconductors and insulators. Here, those developed strategies for direct CVD graphene growth on semiconductors and dielectrics for transfer-free fabrication of electronic devices are reviewed. By employing these methods, various graphene-related structures can be directly prepared on desired substrates and exhibit excellent performance, providing versatile routes for varied graphene-based materials fabrication.

  1. Cold-walled UHV/CVD batch reactor for the growth of Si1_x/Gex layers

    DEFF Research Database (Denmark)

    Thomsen, Erik Vilain; Christensen, Carsten; Andersen, C.R.;

    1997-01-01

    A novel cold-walled, lamp-heated, ultrahigh vacuum chemical vapor deposition (UHV/CVD) batch system for the growth of SiGe layers is presented. This system combines the batch capability of the standard UHV/CVD furnace with the temperature processing available in rapid thermal processing (Rm) equi...

  2. NUMERICAL SIMULATION OF THE GROWTH OF NANOPARTICLES IN A FLAME CVD PROCESS

    Institute of Scientific and Technical Information of China (English)

    Lixi Wang; Si Chen; Hongyong Xie

    2004-01-01

    The growth of titania nanoparticles in a flame CVD process has been simulated by computational fluid dynamics, based on the change rate of particle number density due to their collisions calculated from an integral collision kernel. The assumptions made on constant particle volume density nv (nd3), constant density of particle surface area ns (nd2), and constant entity nd2.5 in coagulation process have been examined. Comparisons have been made on particle size distribution between measurement results and predictions from present model of particle growth and Kruis model of particle dynamics for titania nanoparticles synthesized by the flame CVD process. Effects of operational parameters such as O2 mole fraction and particle number density on mean particle size and size distribution have been discussed.

  3. O método de fio quente: técnica em paralelo e técnica de superfície The hot wire method: the hot wire parallel technique and the hot wire surface technique

    Directory of Open Access Journals (Sweden)

    W. N. dos Santos

    2002-06-01

    Full Text Available A condutividade térmica é uma das propriedades físicas mais importantes de um material. A sua determinação experimental apresenta algumas dificuldades e requer alta precisão na determinação dos fatores necessários para o seu cálculo. O método de medida de condutividade térmica para materiais refratários mais usado hoje em todo o mundo, tanto nos centros de pesquisa, quanto nos laboratórios industriais, é o Método do Fio Quente, onde a condutividade térmica é calculada a partir do transiente de temperatura gerado por uma fonte de calor ideal, infinitamente longa e fina num meio material infinito. Neste trabalho são comparados os resultados obtidos utilizando-se duas técnicas diferentes para a detecção do transiente térmico: numa delas, a temperatura é medida na superfície do fio quente, (técnica de fio quente de superfície, e na outra, a temperatura é medida a uma certa distância do fio quente (técnica de fio quente paralelo. Os resultados experimentais mostram uma grande vantagem da técnica de fio quente de superfície em relação a técnica de fio quente paralelo para materiais com condutividade térmica superior a 10 W/mK. O intervalo de tempo considerado no cálculo é bem maior que aquele que seria utilizado na técnica de fio quente paralelo, obtendo-se assim resultados mais precisos e confiáveis.Thermal conductivity is one of the most important physical properties of a material. However, its experimental evaluation may presents some specific troubles, and high precision in the determination of the factors involved in its calculation is required. Specifically for refractory materials, the experimental technique employed worldwide for thermal conductivity calculations is the hot wire technique, in which the thermal conductivity is calculated starting from the temperature transient generated by an ideal, infinitely thin and long heat source embedded in an infinite surrounding material. In this work comparisons

  4. dc-ac hot-wire procedure for determining thermophysical properties under pressure

    Science.gov (United States)

    Nilsson, O.; Sandberg, O.; Bäckström, G.

    1986-09-01

    The paper describes a new hot-wire method for simultaneous determination of thermal conductivity and heat capacity per unit volume of electrically insulating liquids and solids under pressure. The method uses dc heating of the hot wire, whereas the temperature increase is recorded by an ac bridge circuit. The temperature data obtained are analyzed using the exact solution instead of the commonly used long time approximation. The procedure was tested on a number of alcohols and water and the accuracy was found to be 1.5%. New data on glycerol up to 1.5 GPa are presented. The appearance of an automagnetoresistance effect when Ni is employed as hot-wire probe is discussed.

  5. A hot-wire method for high-intensity turbulent flows

    Science.gov (United States)

    Mueller, U. R.

    1983-01-01

    A measuring technique for determing instantaneous, three-dimensional velocity vectors in highly turbulent flows by means of a 4-sensor hot-wire probe is described. As is well known, the hot-wire signal received in reversing flows cannot uniquely be interpreted. This difficulty is circumvented by tracking the thermal wake of a heated wire. Whenever the approximate flow direction is indicated by a temperature-sensitive wake detector, all components of the instantaneous velocity vector are evaluated by means of a digital data reduction method. Uniqueness of the solution derived from the triple-hot-wire response equations is examined. A first application of the proposed measuring technique in the recirculating flow downstream of a backward-facing step is described.

  6. Vorticity Measurements Using a 6-Sensor Hot-Wire Probe in a Tangentially-Fired Furnace

    Institute of Scientific and Technical Information of China (English)

    何伯述; 刁永发; 许晋源; 陈昌和

    2003-01-01

    Vorticity, which represents the rotation of a fluid element, is an important characteristic of turbulence. Various methods have been used to measure vorticity. A hot-wire/hot-film anemometer (HWA) was used here to measure the vorticity in turbulent flows. The velocity components and their partial derivatives were simultaneously measured with a new 6-sensor hot-wire (HW) probe assuming ideal yaw and pitch factors with Jorgensen's expression and Taylor's hypothesis to analyze the data. The accurate 6-sensor hot-wire probe results for the velocity field were used to determine the velocity gradients and, therefore, the vorticity vector field. The data was measured in an isothermal model of a tangentially fired furnace. The experimental results in the tangentially fired furnace agree with numerical results.

  7. Measurement of gas flow velocity: anemometer with a vibrating hot wire.

    Science.gov (United States)

    Kiełbasa, Jan

    2010-01-01

    I propose a new method to measure velocity of a gas flow, which utilizes the time derivative of the voltage observed on a vibrating hot-wire sensor. The wire vibrates with an amplitude a and a frequency f, and is kept perpendicular to the gas flow direction in the plane containing the flow velocity vector v(g). When the parameters of vibrations are tuned, the number of zeros per vibration period of the hot-wire voltage function changes. I demonstrate that at the point of change, the unknown gas velocity is directly expressed by the parameters of vibrations v(g)=2pifa. Therefore, the velocity can be measured without any prior calibration of the hot-wire speed-voltage curve and the method can be used for gases of slowly changing temperature or composition.

  8. Distributed hot-wire anemometry based on Brillouin optical time-domain analysis.

    Science.gov (United States)

    Wylie, Michael T V; Brown, Anthony W; Colpitts, Bruce G

    2012-07-02

    A distributed hot-wire anemometer based on Brillouin optical time-domain analysis is presented. The anemometer is created by passing a current through a stainless steel tube fibre bundle and monitoring Brillouin frequency changes in the presence of airflow. A wind tunnel is used to provide laminar airflow while the device response is calibrated against theoretical models. The sensitivity equation for this anemometer is derived and discussed. Airspeeds from 0 m/s to 10 m/s are examined, and the results show that a Brillouin scattering based distributed hot-wire anemometer is feasible.

  9. Basic ideas and concepts in hot wire anemometry: an experimental approach for introductory physics students

    Science.gov (United States)

    El Abed, Mohamed

    2016-01-01

    The purpose of hot wire anemometry is to measure the speed of an air stream. The classical method is based on the measure of the value of a temperature dependant resistor inserted in a Wheatstone bridge (Lomas 1986 Fundamentals of Hot Wire Anemometry (Cambridge: Cambridge University Press)). In this paper we exhibit the physics behind this method and show that by using a wire whose resistance does not vary on the field of temperature explored (from 20 °C to 200 °C), it is however possible to make accurate measurements. Finally, limitations of the method are discussed.

  10. Hot-wire anemometry for in-flight measurement of aircraft wake vortices

    Science.gov (United States)

    Jacobsen, R. A.

    1977-01-01

    A development program has demonstrated that hot-wire anemometry can be used successfully on an aircraft in flight to make measurements of wake vortices produced by another aircraft. The probe, whose wires were made of platinum/rhodium, 10 microns in diameter, provides unambiguous results for inflow angles less than about 35 deg. off the probe axis. The high frequency response capability of the hot-wire system allows detailed measurement of the flow structure, and the study of aircraft hazards associated with wake turbulence.

  11. Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System

    OpenAIRE

    Roder, Hans M.; Perkins, Richard A.; Laesecke, Arno; Nieto de Castro, Carlos A.

    2000-01-01

    A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relat...

  12. Optimization of Single-Sensor Two-State Hot-Wire Anemometer Transmission Bandwidth

    OpenAIRE

    Paweł Ligęza

    2008-01-01

    Hot-wire anemometric measurements of non-isothermal flows require the use of thermal compensation or correction circuitry. One possible solution is a two-state hot-wire anemometer that uses the cyclically changing heating level of a single sensor. The area in which flow velocity and fluid temperature can be measured is limited by the dimensions of the sensor’s active element. The system is designed to measure flows characterized by high velocity and temperature gradients, although its tr...

  13. Characterization of particles in the Langley 0.3 meter transonic cryogenic tunnel using hot wire anemometry

    Science.gov (United States)

    Singh, J. J.; Marple, C. G.; Davis, W. T.

    1982-01-01

    Hot wire anemometry was used to identify the nature of particles reportedly observed during free stream velocity measurements in the Langley 0.3-meter transonic cryogenic tunnel using a Laser Doppler Velocimeter. Since the heat-transfer process from the hot wire depends on the thermal conductivity and sticking capability of the particles, it was anticipated that the hot wire anemometer response would be affected differently upon impaction by liquid droplets and solid aerosols in the test gas stream. Based on the measured time response of the hot-wire anemometer in the cryogenic tunnel operated in the 0.3-0.8 Mach number range, it is concluded that the particles impacting the hot wire are liquid in nature rather than solid aerosols. It is further surmised that the liquid aerosols are unevaporated liquid nitrogen droplets used for cooling the tunnel test gas.

  14. A thermo-electro-mechanical simulation model for hot wire cutting of EPS foam

    DEFF Research Database (Denmark)

    Petkov, Kiril; Hattel, Jesper Henri

    2016-01-01

    A one-dimensional thermo-electro-mechanical mathematical model describing the effects taking place within a Ni-Cr20% wire used in a hot-wire cutting process for free forming and rapid prototyping of expanded polystyrene (EPS) is investigated and simulated. The model implements and solves three semi...

  15. Rethinking the participatory web : A history of HotWired's 'new publishing paradigm,' 1994-1997

    NARCIS (Netherlands)

    Stevenson, Michael

    2014-01-01

    This article critically interrogates key assumptions in popular web discourse by revisiting an early example of web “participation.” Against the claim that Web 2.0 technologies ushered in a new paradigm of participatory media, I turn to the history of HotWired, Wired magazine’s ambitious web-only pu

  16. Electrically active, doped monocrystalline silicon nanoparticles produced by hot wire thermal catalytic pyrolysis

    CSIR Research Space (South Africa)

    Scriba, MR

    2011-05-01

    Full Text Available Doped silicon nanoparticles have successfully been produced by hot wire thermal catalytic pyrolysis at 40 mbar and a filament temperature of 1800 °C, using a mixture of silane and diborane or phosphine. All particles are monocrystalline with shapes...

  17. Composition and crystallinity of silicon nanoparticles synthesised by hot wire thermal catalytic pyrolysis at different pressures

    CSIR Research Space (South Africa)

    Scriba, MR

    2009-04-01

    Full Text Available The effect of pressure on the structure and composition of silicon nanoparticles synthesized by hot wire thermal catalytic pyrolysis (HW-TCP) of pure silane has been investigated. Light brown powders were produced at silane pressures of 10 and 50...

  18. The calibration of (multi-)hot-wire probes. 2. Velocity-calibration

    NARCIS (Netherlands)

    Dijk, van A.; Nieuwstadt, F.T.M.

    2004-01-01

    We review a set of velocity calibration methods for one popular configuration of a four-hot-wire probe with the aim of finding a method of estimating with 10% accuracy (based on full scale) the mean flow vector, the rms of the turbulent velocity component and the associated linearized anisotropy inv

  19. A Hot-Wire Method Based Thermal Conductivity Measurement Apparatus for Teaching Purposes

    Science.gov (United States)

    Alvarado, S.; Marin, E.; Juarez, A. G.; Calderon, A.; Ivanov, R.

    2012-01-01

    The implementation of an automated system based on the hot-wire technique is described for the measurement of the thermal conductivity of liquids using equipment easily available in modern physics laboratories at high schools and universities (basically a precision current source and a voltage meter, a data acquisition card, a personal computer…

  20. All hot wire chemical vapor deposition low substrate temperature transparent thin film moisture barrier

    NARCIS (Netherlands)

    Spee, D.A.; Schipper, M.R.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2013-01-01

    We deposited a silicon nitride/polymer hybrid multilayer moisture barrier for flexible electronics in a hot wire chemical vapor deposition process, entirely below 100 °C. We were able to reach a water vapor transmission rate (WVTR) as low as 5×10−6 g/m2/day at a temperature of 60 °C and a relative h

  1. Optimization of Single-Sensor Two-State Hot-Wire Anemometer Transmission Bandwidth

    Directory of Open Access Journals (Sweden)

    Paweł Ligęza

    2008-10-01

    Full Text Available Hot-wire anemometric measurements of non-isothermal flows require the use of thermal compensation or correction circuitry. One possible solution is a two-state hot-wire anemometer that uses the cyclically changing heating level of a single sensor. The area in which flow velocity and fluid temperature can be measured is limited by the dimensions of the sensor’s active element. The system is designed to measure flows characterized by high velocity and temperature gradients, although its transmission bandwidth is very limited. In this study, we propose a method to optimize the two-state hot-wire anemometer transmission bandwidth. The method is based on the use of a specialized constanttemperature system together with variable dynamic parameters. It is also based on a suitable measurement cycle paradigm. Analysis of the method was undertaken using model testing. Our results reveal a possible significant broadening of the two-state hot-wire anemometer's transmission bandwidth.

  2. Thermal Conductivity of Saturated Liquid Toluene by Use of Anodized Tantalum Hot Wires at High Temperatures.

    Science.gov (United States)

    Perkins, R A; Ramires, M L; Nieto de Castro, C A

    2000-01-01

    Absolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temperature was monitored throughout the measurements to study the stability of the wire calibration. The relative expanded uncertainty of the resulting data at the level of 2 standard deviations (coverage factor k = 2) is 0.5 % up to 480 K and 1.5 % between 480 K and 550 K, and is limited by drift in the wire calibration at temperatures above 450 K. Significant thermal-radiation effects are observed at the highest temperatures. The radiation-corrected results agree well with data from transient hot-wire measurements with bare platinum hot wires as well as with data derived from thermal diffusivities obtained using light-scattering techniques.

  3. The calibration of (multi-) hot-wire probes. 1. Temperature calibration

    NARCIS (Netherlands)

    Dijk, van A.; Nieuwstadt, F.T.M.

    2004-01-01

    We study the performance of the classical relation for the correction for ambient temperature drift of the signal of a hot-wire anemometer and the influence of practical assumptions. It is shown that most methods to estimate the operational temperature via the temperature/resistance coefficient lead

  4. A High-Temperature Transient Hot-Wire Thermal Conductivity Apparatus for Fluids.

    Science.gov (United States)

    Perkins, R A; Roder, H M; Nieto de Castro, C A

    1991-01-01

    A new apparatus for measuring both the thermal conductivity and thermal diffusivity of fluids at temperatures from 220 to 775 K at pressures to 70 MPa is described. The instrument is based on the step-power-forced transient hot-wire technique. Two hot wires are arranged in different arms of a Wheatstone bridge such that the response of the shorter compensating wire is subtracted from the response of the primary wire. Both hot wires are 12.7 µm diameter platinum wire and are simultaneously used as electrical heat sources and as resistance thermometers. A microcomputer controls bridge nulling, applies the power pulse, monitors the bridge response, and stores the results. Performance of the instrument was verified with measurements on liquid toluene as well as argon and nitrogen gas. In particular, new data for the thermal conductivity of liquid toluene near the saturation line, between 298 and 550 K, are presented. These new data can be used to illustrate the importance of radiative heat transfer in transient hot-wire measurements. Thermal conductivity data for liquid toluene, which are corrected for radiation, are reported. The precision of the thermal conductivity data is ± 0.3% and the accuracy is about ±1%. The accuracy of the thermal diffusivity data is about ± 5%. From the measured thermal conductivity and thermal diffusivity, we can calculate the specific heat, Cp , of the fluid, provided that the density is measured, or available through an equation of state.

  5. Tandem solar cells deposited using hot-wire chemical vapor deposition

    NARCIS (Netherlands)

    Veen, M.K. van

    2003-01-01

    In this thesis, the application of the hot-wire chemical vapor deposition (HWCVD) technique for the deposition of silicon thin films is described. The HWCVD technique is based on the dissociation of silicon-containing gasses at the catalytic surface of a hot filament. Advantages of this technique ar

  6. The influence of temperature fluctuations on hot-wire measurements in wall-bounded turbulence

    Science.gov (United States)

    Örlü, Ramis; Malizia, Fabio; Cimarelli, Andrea; Schlatter, Philipp; Talamelli, Alessandro

    2014-07-01

    There are no measurement techniques for turbulent flows capable of reaching the versatility of hot-wire probes and their frequency response. Nevertheless, the issue of their spatial resolution is still a matter of debate when it comes to high Reynolds number near-wall turbulence. Another, so far unattended, issue is the effect of temperature fluctuations—as they are, e.g. encountered in non-isothermal flows—on the low and higher-order moments in wall-bounded turbulent flows obtained through hot-wire anemometry. The present investigation is dedicated to document, understand, and ultimately correct these effects. For this purpose, the response of a hot-wire is simulated through the use of velocity and temperature data from a turbulent channel flow generated by means of direct numerical simulations. Results show that ignoring the effect of temperature fluctuations, caused by temperature gradients along the wall-normal direction, introduces—despite a local mean temperature compensation of the velocity reading—significant errors. The results serve as a note of caution for hot-wire measurements in wall-bounded turbulence, and also where temperature gradients are more prevalent, such as heat transfer measurements or high Mach number flows. A simple correction scheme involving only mean temperature quantities (besides the streamwise velocity information) is finally proposed that leads to a substantial bias error reduction.

  7. Optoelectronic properties of hot-wire silicon layers deposited at 100 °C

    NARCIS (Netherlands)

    Brinza, M.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2008-01-01

    Hot-wire chemical vapor deposition is employed for the deposition of amorphous and microcrystalline silicon layers at substrate temperature kept below 100 °C with the aid of active cooling of the substrate holder. The hydrogen dilution is varied in order to investigate films at the amorphous-to-micr

  8. Modeling and characterization of the sensitivity of a hot-wire particle velocity sensor

    NARCIS (Netherlands)

    Honschoten, van J.W.; Yntema, D.R.; Wiegerink, R.J.; Elwenspoek, M.

    2008-01-01

    The sensitivity of an innovative acoustic sensor composed of four hot-wires is analyzed. An analytical model is presented that describes both the air flow and the temperature distribution in and around the probe. The presence of the chip surface in the vicinity of the wires influences the acoustic f

  9. Eddy-correlation measurements above a maize crop using a simple cruciform hot-wire anemometer

    NARCIS (Netherlands)

    Bottemanne, F.A.

    1979-01-01

    For measurements of the vertical transport of heat and momentum in the turbulent and slightly unstable boundary layer above a maize crop eddy-correlation techniques were applied. In addition to a vertical Gill-propellor anemometer and a Gill-propellor bivane, a cruciform hot-wire probe, mounted on a

  10. Hot wire chemical vapor deposition: limits and opportunities of protecting the tungsten catalyzer from silicide with a cavity

    Energy Technology Data Exchange (ETDEWEB)

    Frigeri, P.A. [Dept. de Fisica Aplicada i Optica, Universitat de Barcelona, Barcelona-08028 (Spain); Nos, O., E-mail: oriol_nos@ub.ed [Dept. de Fisica Aplicada i Optica, Universitat de Barcelona, Barcelona-08028 (Spain); Ecotecnia (ALSTOM Group) (Spain); Bengoechea, S.; Frevert, C.; Asensi, J.M.; Bertomeu, J. [Dept. de Fisica Aplicada i Optica, Universitat de Barcelona, Barcelona-08028 (Spain)

    2009-04-30

    Hot Wire Chemical Vapor Deposition (HW-CVD) is one of the most promising techniques for depositing the intrinsic microcrystalline silicon layer for the production of micro-morph solar cells. However, the silicide formation at the colder ends of the tungsten wire drastically reduces the lifetime of the catalyzer, thus limiting its industrial exploitation. A simple but interesting strategy to decrease the silicide formation is to hide the electrical contacts of the catalyzer in a long narrow cavity which reduces the probability of the silane molecules to reach the colder ends of the wire. In this paper, the working mechanism of the cavity is elucidated. Measurements of the thickness profile of the silicon deposited in the internal walls of the cavity have been compared with those predicted using a simple diffusion model based on the assumption of Knudsen flow. A lifetime study of the protected and unprotected wires has been carried out. The different mechanisms which determine the deterioration of the catalyzer have been identified and discussed.

  11. Facet-dependent study of efficient growth of graphene on copper by ethanol-CVD

    Indian Academy of Sciences (India)

    Anil Kumar Singh; Anjan Kumar Gupta

    2015-12-01

    The growth of graphene by chemical vapour deposition (CVD) on copper is the most promising scalable method for high-quality graphene. The use of ethanol, an economic and safe precursor, for the fast growth of graphene on copper by a home-built CVD set-up was analysed. Full coverage of uniform single-layer graphene with high crystalline quality was found on $\\langle100\\rangle$ textured Cu foils in just 30 s. The nucleation density of graphene islands was found to be independent of facets but the island shape showed facet dependence. Diamond-like islands were observed on Cu(100) facets while random shaped islands were seen on other facets. The last observation is discussed in terms of a competition between graphene-island growth and its relaxation rate on different facets. On Cu(100) slower island growth as compared to its relaxation leads to equilibrium shapes as opposed to other facets. Further, an observed evolution in graphene contrast in electron micrographs with time on different facets was discussed in terms of oxygen diffusion between graphene and Cu.

  12. CVD growth and characterization of 3C-SiC thin films

    Indian Academy of Sciences (India)

    A Gupta; D Paramanik; S Varma; C Jacob

    2004-10-01

    Cubic silicon carbide (3C-SiC) thin films were grown on (100) and (111) Si substrates by CVD technique using hexamethyldisilane (HMDS) as the source material in a resistance heated furnace. HMDS was used as the single source for both Si and C though propane was available for the preliminary carbonization. For selective epitaxial growth, patterned Si (100) substrates were used. The effect of different growth parameters such as substrate orientation, growth temperature, precursor concentration, etc on growth was examined to improve the film quality. The surface morphology, microstructure and crystallinity of grown films were studied using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS).

  13. Growth mechanisms and defects in boronated CVD diamond as identified by scanning tunneling microscopy

    Science.gov (United States)

    Kreutz, T. J.; Clausing, R. E.; Heatherly, L., Jr.; Warmack, R. J.; Thundat, T.; Feigerle, C. S.; Wandelt, K.

    1995-05-01

    Boron-doped CVD-diamond films were grown in a simple hot filament reactor. A set of samples grown using various methane-in-hydrogen concentrations has been examined by scanning tunneling microscopy in air. On the diamond (111) crystal faces monoatomic steps could be observed giving evidence for layer growth. At low CH4 concentrations the layers form triangular growth spirals. Screw dislocations in the middle of the spirals serve as continuous sources of steps for the layer growth producing (111) faces of high crystal perfection. At higher methane concentrations the crystal perfection declines and the (111) crystal faces exhibit a mosaic structure. The size of the subgrains in the mosaic pattern decreases with increasing CH4 concentration. Nucleation of new layers takes place at the subgrain boundaries. The topography of (001) crystal faces did not significantly change with the methane-in-hydrogen concentration and did not allow the determination of the underlying growth mechanism.

  14. Effect of a Balanced Concentration of Hydrogen on Graphene CVD Growth

    Directory of Open Access Journals (Sweden)

    S. Chaitoglou

    2016-01-01

    Full Text Available The extraordinary properties of graphene make it one of the most interesting materials for future applications. Chemical vapor deposition (CVD is the synthetic method that permits obtaining large areas of monolayer graphene. To achieve this, it is important to find the appropriate conditions for each experimental system. In our CVD reactor working at low pressure, important factors appear to be the pretreatment of the copper substrate, considering both its cleaning and its annealing before the growing process. The carbon precursor/hydrogen flow ratio and its modification during the growth are significant in order to obtain large area graphene crystals with few defects. In this work, we have focused on the study of the methane and the hydrogen flows to control the production of single layer graphene (SLG and its growth time. In particular, we observe that hydrogen concentration increases during a usual growing process (keeping stable the methane/hydrogen flow ratio resulting in etched domains. In order to balance this increase, a modification of the hydrogen flow results in the growth of smooth hexagonal SLG domains. This is a result of the etching effect that hydrogen performs on the growing graphene. It is essential, therefore, to study the moderated presence of hydrogen.

  15. Influence of tungsten on the carbon nanotubes growth by CVD process

    Energy Technology Data Exchange (ETDEWEB)

    Escobar, Mariano [Instituto de Fisicoquimica de Materiales, Ambiente y Energia, CONICET-UBA, Pabellon II, Ciudad Universitaria (1428) Bs As (Argentina); LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina)], E-mail: mescobar@qi.fcen.uba.ar; Rubiolo, Gerardo H. [LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina); Unidad de Actividad Materiales, CNEA, Av. Gral. Paz 1499, San Martin (1650), Bs As (Argentina); Moreno, M. Sergio [Centro Atomico Bariloche, (8400) S.C. de Bariloche, Rio Negro (Argentina); Goyanes, Silvia [LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina); Candal, Roberto [Instituto de Fisicoquimica de Materiales, Ambiente y Energia, CONICET-UBA, Pabellon II, Ciudad Universitaria (1428) Bs As (Argentina)

    2009-06-24

    The effect of tungsten (W) on the growth of multi-walled carbon nanotubes (MWNTs) using the chemical vapour deposition (CVD) process over a metal Fe-W catalyst incorporated into a silica matrix is reported. A W molar content in Fe/SiO{sub 2} up to 10% was studied. The incorporation of only 2% of W substantially modifies the crystalline phases and the crystalline degree of the catalyst during the MWNTs synthesis. This fact seems to have a strong influence on the type and yield of the carbonaceous species obtained by the CVD of acetylene, at 600 deg. C and 180 Torr, over each catalyst. Tungsten interacts with iron within the matrix, diminishing the catalytic activity of the metal nanoparticles, and both, carbon nanotubes and carbon nanofibers, are obtained when tungsten is present. The results obtained support the hypothesis of a base growth model for carbon nanotubes indicating a strong interaction between silica matrix and Fe/W nanoparticles, independently of the content of W.

  16. Measurements of mass flux and concentration in supersonic air/helium mixing by hot-wire anemometry

    OpenAIRE

    KONDO, Akira; Sakaue, Shoji; Arai, Takakage; 近藤 暁; 坂上 昇史; 新井 隆景

    2008-01-01

    In the present study we made efforts to realize a measurement method of mass flux and concentration in supersonic air/helium flow in order to clarify the mixing process. The measuring equipment, which was used for measuring the fluctuations of mass flux and concentration, is consisted of a double-hot-wire probe and CVA (Constant Voltage Anemometer) circuit with 500 kHz bandwidth. The distance between two wires of double-hot-wire probe was 0.16 mm. By using the same material as the hot wire, t...

  17. Study of Flow Deformation around Wind-Vane Mounted Three-Dimensional Hot-Wire Probes

    DEFF Research Database (Denmark)

    Rømer Rasmussen, K.; Larsen, Søren Ejling; Jørgensen, F. E.

    1981-01-01

    Open wind tunnel tests on several different sensor systems consisting of triaxial hot-wire probes mounted on wind vanes (DISA and Riso vanes) have shown that flow deformation around the hot-wire sensor introduces errors in the measured velocity components. Though changes in the horizontal...... components proved to be negligible, flow deformation resulted in an overestimation of the vertical component from 1.1 to 1.5, depending on the direction of the vertical component. Turbulence and mean value data were adjusted by use of a linear correction derived from the wind tunnel tests. Wind vane...... construction must strike a compromise between minor flow disturbance and sufficient probe support. The final version of the DISA vane resulted in an acceptable vertical correction of about 10%....

  18. Study of Flow Deformation around Wind-Vane Mounted Three-Dimensional Hot-Wire Probes

    DEFF Research Database (Denmark)

    Rømer Rasmussen, K.; Larsen, Søren Ejling; Jørgensen, F. E.

    1981-01-01

    Open wind tunnel tests on several different sensor systems consisting of triaxial hot-wire probes mounted on wind vanes (DISA and Riso vanes) have shown that flow deformation around the hot-wire sensor introduces errors in the measured velocity components. Though changes in the horizontal...... components proved to be negligible, flow deformation resulted in an overestimation of the vertical component from 1.1 to 1.5, depending on the direction of the vertical component. Turbulence and mean value data were adjusted by use of a linear correction derived from the wind tunnel tests. Wind vane...... construction must strike a compromise between minor flow disturbance and sufficient probe support. The final version of the DISA vane resulted in an acceptable vertical correction of about 10%....

  19. High Reynolds Number Effects on Multi-Hole Probes and Hot Wire Anemometers

    Science.gov (United States)

    Ramachandran, N.; Smith, A.; Gerry, G.; Kauffman, W.

    1995-01-01

    The paper reports on the results from an experimental investigation of the response of multi-hole and hot wire probes at high flow Reynolds numbers (Re approx. 10(exp 6)). The limited results available in literature for 5-hole probes are restricted to Re approx. 10(exp 4). The experiment aims to investigate the probe response (in terms of dimensionless pressure ratios, characterizing pitch, and yaw angles and the total and static pressures) at high Re values and to gauge their effect on the calculated velocity vector. Hot wire calibrations were also undertaken with a parametric variation of the flow pressure, velocity and temperature. Different correction and calibration schemes are sought to be tested against the acquired data set. The data is in the analysis stage at the present time. The test provided good benchmark quality data that can be used to test future calibration and testing methods.

  20. Development of absolute hot-wire anemometry by the 3omega method.

    Science.gov (United States)

    Heyd, Rodolphe; Hadaoui, Abdallah; Fliyou, Mohamed; Koumina, Abdelaziz; El Hassani Ameziane, Lahcen; Outzourhit, Abdelkader; Saboungi, Marie-Louise

    2010-04-01

    We have developed hot-wire anemometry applying the 3omega method. The approach is based on the same heat transfer process as traditional anemometry, but substituting the constant current by a sinusoidal current and using synchronous detection to measure the conductive-convective exchange coefficient and the gas flow rate. Our theoretical model is tested with air flow at 300 K under atmospheric pressure: The experimental results are in agreement with the numerical simulation, justifying the technical choices in the 3omega method and the approximations made. The effectiveness of the 3omega method for measuring the flow rate and the conductive-convective exchange coefficient between the hot wire and flowing gas is discussed.

  1. Absolute Steady-State Thermal Conductivity Measurements by Use of a Transient Hot-Wire System.

    Science.gov (United States)

    Roder, H M; Perkins, R A; Laesecke, A; Nieto de Castro, C A

    2000-01-01

    A transient hot-wire apparatus was used to measure the thermal conductivity of argon with both steady-state and transient methods. The effects of wire diameter, eccentricity of the wire in the cavity, axial conduction, and natural convection were accounted for in the analysis of the steady-state measurements. Based on measurements on argon, the relative uncertainty at the 95 % level of confidence of the new steady-state measurements is 2 % at low densities. Using the same hot wires, the relative uncertainty of the transient measurements is 1 % at the 95 % level of confidence. This is the first report of thermal conductivity measurements made by two different methods in the same apparatus. The steady-state method is shown to complement normal transient measurements at low densities, particularly for fluids where the thermophysical properties at low densities are not known with high accuracy.

  2. Spatial resolution correction for hot-wire anemometry in wall turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Chin, C.; Hutchins, N.; Ooi, A.; Marusic, I. [University of Melbourne, Department of Mechanical Engineering, Melbourne, VIC (Australia)

    2011-05-15

    We investigate spatial resolution issues in hot-wire anemometry measurements of turbulence intensity and energy spectra. Single normal hot-wire measurements are simulated by means of filtering direct numerical simulation (DNS) of turbulent channel flow at Re{sub {tau}} = 934. Through analysis of the two-dimensional energy spectra from the DNS, the attenuation of the small-scale energy levels is documented, especially in the near-wall region. The missing energy displays anisotropic characteristics, and an attempt is made to model this using an empirical equation, thus providing a correction scheme for all wall normal locations. The empirical model is assessed using experimental boundary layer data and shown to effectively correct both the streamwise one-dimensional energy spectra and turbulence intensity at a Reynolds number significantly above that of the DNS. (orig.)

  3. Development of absolute hot-wire anemometry by the 3ω method

    Science.gov (United States)

    Heyd, Rodolphe; Hadaoui, Abdallah; Fliyou, Mohamed; Koumina, Abdelaziz; Ameziane, Lahcen El Hassani; Outzourhit, Abdelkader; Saboungi, Marie-Louise

    2010-04-01

    We have developed hot-wire anemometry applying the 3ω method. The approach is based on the same heat transfer process as traditional anemometry, but substituting the constant current by a sinusoidal current and using synchronous detection to measure the conductive-convective exchange coefficient and the gas flow rate. Our theoretical model is tested with air flow at 300 K under atmospheric pressure: The experimental results are in agreement with the numerical simulation, justifying the technical choices in the 3ω method and the approximations made. The effectiveness of the 3ω method for measuring the flow rate and the conductive-convective exchange coefficient between the hot wire and flowing gas is discussed.

  4. Thermal conductivity measurements using hot-wires at small Peclet number

    Science.gov (United States)

    Arwatz, Gilad; Fan, Yuyang; Hultmark, Marcus

    2015-11-01

    The feasibility of using hot-wires to measure gas thermal conductivity is investigated. When the local Peclet number of a hot-wire is small (Pewire becomes less sensitive to velocity. This phenomenon can be utilized to measure the thermal conductivity of the gas. To investigate the viability of the principle of operation, a lumped capacitance model is proposed, capturing the effects of both convection and conduction on heat transfer from the wire. By investigating the sensitivity of the model to velocity, temperature and conduction, it is shown that as wire dimension decreases, the sensor becomes less sensitive to both velocity and temperature and more sensitive to conduction. The model also captures the effect of varying wire dimension as well as overheat ratio.

  5. Hot-wire probe used for measurement of one dimensional flow with bidirection

    Science.gov (United States)

    Tu, Chengxu

    2010-08-01

    In order to solve the difficulties of the measurement of one-dimensional and bi-direction flow by a hot-wire probe, a test method and the model experiment are presented in this paper. Based on the exiting hot-wire sensor, another same sensor is added. The two sensors are installed in parallel whose distance is 6 times their diameters, and they are separately connected to the controller. If the flow goes around two circular cylinders in tandem with the low Reynolds number, an obvious velocity drop between free-stream and gap flow can be found. Consequently, the velocity detected by the upstream sensor is higher than that by the downstream one. Because the relatively fixed position of the pair of sensors has been determined beforehand, the direction of the one-dimensional flow can be deduced from the plus and minus of velocity drop detected by the two sensors.

  6. A comparison of calibration techniques for hot-wires operated in subsonic compressible slip flows

    Science.gov (United States)

    Jones, Gregory S.; Stainback, P. C.; Nagabushana, K. A.

    1992-01-01

    This paper focuses on the correlation of constant temperature anemometer voltages to velocity, density, and total temperature in the transonic slip flow regime. Three different calibration schemes were evaluated. The ultimate use of these hot-wire calibrations is to obtain fluctuations in the flow variables. Without the appropriate mean flow sensitivities of the heated wire, the measurements of these fluctuations cannot be accurately determined.

  7. Hybrid approach to data reduction for multi-sensor hot wires

    Science.gov (United States)

    Hooper, C. L.; Westphal, R. V.

    1991-01-01

    A hybrid approach to implementing the calibration equations for a multisensor hot-wire probe is discussed. The approach combines some of the speed of a look-up approach with the moderate storage requirements of direct calculation based on functional fitting. Particular attention is given to timing and storage comparisons for an X-wire probe. The method depends on the oft-employed concept of an effective cooling velocity which is a function only of the bridge output voltage.

  8. Measuring two-dimensional components of a flow velocity vector using a hot-wire probe.

    Science.gov (United States)

    Kiełbasa, Jan

    2007-08-01

    The article presents a single-hot-wire probe adapted to detect the direction of flow velocity. The modification consists of the introduction of a third support which allows to measure voltage at the central point of the wire. The sign of voltage difference DeltaU between both parts of the wire is the measure of the direction of flow velocity in a system of coordinates associated with the probe.

  9. Gravitationally defined velocities for a low speed hot-wire calibration

    Science.gov (United States)

    Haw, R. C.; Ali, S. K.; Foss, J. F.

    1987-01-01

    A technique to provide the reference velocity for a low speed hot-wire calibration is described. A pivoted arm falls under the action of gravity and the resulting velocity field can be used to define the transfer function coefficients in a modified Collis and Williams (1959) relationship. In nominal agreement with a published result, a deviation from this relationship for a film Reynolds number such that Re exp n of less than about 0.24 is observed.

  10. Hot-wire anemometry for turbulence measurements in helium-air mixtures

    Science.gov (United States)

    Libby, P. A.; Larue, J. C.

    1979-01-01

    The use of extended hot-wire anemometry involving an interfering probe is shown to permit measurements of variable density turbulence such as arises in the mixing of helium and air. The methods of calibration and data reduction leading to time series in one or more velocity components, in the mass fraction of helium, and in the mixture density are described. Typical results in various flows to which the technique has been applied are discussed.

  11. Optimization of experimental conditions of hot wire method in thermal conductivity measurements

    OpenAIRE

    Ma, Luyao

    2012-01-01

    This work studied the hot wire method in measuring thermal conductivity at room temperature. The purpose is to find the optimized experimental conditions to minimize natural convection in liquid for this method, which will be taken as reference for high temperature thermal conductivity measurement of slag. Combining room temperature experiments and simulation with COMSOL Multiphysics 4.2a, the study on different experimental parameters which may influence the accuracy of the measured thermal ...

  12. Experimental determination of the onset of turbulence on inclined plates using hot wire velocity measurements

    OpenAIRE

    Rodríguez Sevillano, Angel; Pérez Grande, María Isabel; Meseguer Ruiz, José

    2010-01-01

    The problem of determination of the turbulence onset in natural convection on heated inclined plates in an air environment has been experimentally revisited. The transition has been detected by using hot wire velocity measurements. The onset of turbulence has been considered to take place where velocity fluctuations (measured through turbulence intensity) start to grow. Experiments have shown that the distance to the plate edge where the onset begins depends both on the plate inclinatio...

  13. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing

    Science.gov (United States)

    Lundström, H.

    2015-08-01

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  14. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing.

    Science.gov (United States)

    Lundström, H

    2015-08-01

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  15. Note: Improving long-term stability of hot-wire anemometer sensors by means of annealing

    Energy Technology Data Exchange (ETDEWEB)

    Lundström, H., E-mail: hans.lundstrom@hig.se [Department of Building, Energy and Environmental Engineering, University of Gävle, SE-801 76 Gävle (Sweden)

    2015-08-15

    Annealing procedures for hot-wire sensors of platinum and platinum-plated tungsten have been investigated experimentally. It was discovered that the two investigated sensor metals behave quite differently during the annealing process, but for both types annealing may improve long-term stability considerably. Measured drift of sensors both without and with prior annealing is presented. Suggestions for suitable annealing temperatures and times are given.

  16. Hot-Wire Calibration at Low Velocities: Revisiting the Vortex Shedding Method

    OpenAIRE

    Sattarzadeh, Sohrab S.; Athanasia Kalpakli; Ramis Örlü

    2013-01-01

    The necessity to calibrate hot-wire probes against a known velocity causes problems at low velocities, due to the inherent inaccuracy of pressure transducers at low differential pressures. The vortex shedding calibration method is in this respect a recommended technique to obtain calibration data at low velocities, due to its simplicity and accuracy. However, it has mainly been applied in a low and narrow Reynolds number range known as the laminar vortex shedding regime. Here, on the other ha...

  17. Introducing a nano-scale crossed hot-wire for high Reynolds number measurements

    Science.gov (United States)

    Fan, Yuyang; Fu, Matthew; Hultmark, Marcus

    2016-11-01

    Hot-wire anemometry is commonly used for high Reynolds number flow measurements, mainly because of its continuous signal and high bandwidth. However, measuring two components of velocity in high Reynolds number wall-bounded flows has proven to be quite challenging with conventional crossed hot-wires, especially close to the wall, due to insufficient resolution and obstruction from the probe. The Nano-Scale Thermal Anemometry Probe (NSTAP) is a miniature hot-wire that drastically increased the spatial and temporal resolutions for single-component measurements by using a nano-scale platinum wire. Applying a novel combining method and reconfiguration of the NSTAP design, we created a sensor (x-NSTAP) that is capable of two-component velocity measurements with a sensing volume of approximately 50 × 50 × 50 μ m, providing spatial and temporal resolutions similar to the single component NSTAP. The x-NSTAP is deployed in the Superpipe facility for accurate measurements of the Reynolds stresses at very high Reynolds numbers. Supported under NSF Grant CBET-1510100 (program manager Dimitrios Papavassiliou).

  18. Novel method and experimental validation of statistical calibration via Gaussianization in hot-wire anemometry

    Science.gov (United States)

    Gluzman, Igal; Cohen, Jacob; Oshman, Yaakov

    2016-11-01

    We introduce a statistical method based on Gaussianization to estimate the nonlinear calibration curve of a hot-wire probe, that relates the input flow velocity to the output (measured) voltage. The method uses as input a measured sequence of voltage samples, corresponding to different unknown flow velocities in the desired operational range, and only two measured voltages along with their known (calibrated) flow velocities. The novel method is validated against standard calibration methods using data acquired by hot-wire probes using wind-tunnel experiments. We demonstrate our new calibration technique by placing the hot-wire probe at certain region downstream of a cube-shaped body in a free stream of air flow. For testing our calibration method we rely on flow statistics that exist, among others, in a certain region of a turbulent wake formed downstream of the cube-shaped body. The specific properties are: first, the velocity signal in the wake should be as close to Gaussian as possible. Second, the signal should cover the desired velocity range that should be calibrated. The appropriate region to place our probe is determined via computation of the first four statistical moments of the measured signals in different regions of the wake.

  19. Improvements of a nano-scale crossed hot-wire for high Reynolds number measurements

    Science.gov (United States)

    Fan, Yuyang; Hultmark, Marcus

    2015-11-01

    Hot-wire anemometry, despite its limited spatial and temporal resolution, is still the preferred tool for high Reynolds number flow measurements, mainly due to the continuous signal. To address the resolution issues, the Nano-Scale Thermal Anemometry Probe (NSTAP) was developed at Princeton University. The NSTAP has a sensing volume more than one order of magnitude smaller than conventional hot-wires, and it has displayed superior performance. However, the NSTAP can only measure a single component of the velocity. Using a novel combining method, a probe that enables two-component velocity measurements has been created (the x-NSTAP). The measurement volume is approximately 50 × 50 × 50 μ m, more than one order of magnitude smaller in all directions compared to conventional crossed hot-wires. The x-NSTAP has been further improved to allow more accurate measurements with the help of flow visualization using a scaled model but matching Reynolds number. Results from turbulent flow measurements with the new x-NSTAP are also presented. Supported under NSF grant CBET-1510100 (program manager Dimitrios Papavassiliou).

  20. Apparatus to study the onset of free convection about vertical and inclined hot wires

    Science.gov (United States)

    Giaretto, Valter; Miraldi, Elio; Torchio, Marco F.

    2007-07-01

    This article describes a methodology and an apparatus used to evaluate the onset time of free convection in hot-wire experiments. The evaluation of the onset time is useful to obtain a measurement interval that is suitable to estimate the thermal properties of a fluid. If a pure conduction regime is present, the hot-wire temperature increment versus time is a straight line in a semilog plot, whereas the convection effect induces a deviation from this trend. An algorithm based on the F test is proposed to evaluate the onset time of free convection. The experimental facility has the particular feature of allowing an easy change of the hot-wire inclination angle up to 118.3mrad. The wire is kept in a tilted position by a permanent horseshoe magnet, and the tilting angle from the vertical is measured by a theodolite. Some testing results using water are discussed for vertical and inclined wires. A good agreement between the experimental onset times and the theoretical ones is found in the case of a vertical wire.

  1. Apparatus to study the onset of free convection about vertical and inclined hot wires.

    Science.gov (United States)

    Giaretto, Valter; Miraldi, Elio; Torchio, Marco F

    2007-07-01

    This article describes a methodology and an apparatus used to evaluate the onset time of free convection in hot-wire experiments. The evaluation of the onset time is useful to obtain a measurement interval that is suitable to estimate the thermal properties of a fluid. If a pure conduction regime is present, the hot-wire temperature increment versus time is a straight line in a semilog plot, whereas the convection effect induces a deviation from this trend. An algorithm based on the F test is proposed to evaluate the onset time of free convection. The experimental facility has the particular feature of allowing an easy change of the hot-wire inclination angle up to 118.3 mrad. The wire is kept in a tilted position by a permanent horseshoe magnet, and the tilting angle from the vertical is measured by a theodolite. Some testing results using water are discussed for vertical and inclined wires. A good agreement between the experimental onset times and the theoretical ones is found in the case of a vertical wire.

  2. Real-time monitoring of the laser hot-wire welding process

    Science.gov (United States)

    Liu, Wei; Liu, Shuang; Ma, Junjie; Kovacevic, Radovan

    2014-04-01

    The laser hot-wire welding process was investigated in this work. The dynamics of the molten pool during welding was visualized by using a high-speed charge-coupled device (CCD) camera assisted by a green laser as an illumination source. It was found that the molten pool is formed by the irradiation of the laser beam on the filler wire. The effect of the hot-wire voltage on the stability of the welding process was monitored by using a spectrometer that captured the emission spectrum of the laser-induced plasma plume. The spectroscopic study showed that when the hot-wire voltage is above 9 V a great deal of spatters occur, resulting in the instability of the plasma plume and the welding process. The effect of spatters on the plasma plume was shown by the identified spectral lines of the element Mn I. The correlation between the Fe I electron temperature and the weld-bead shape was studied. It was noted that the electron temperature of the plasma plume can be used to real-time monitor the variation of the weld-bead features and the formation of the weld defects.

  3. Investigation on Characterizing Heated Pulsating Flows with Hot Wire Anemometers - A Hands-On Approach

    Directory of Open Access Journals (Sweden)

    Marius Alexandru PANAIT

    2014-06-01

    Full Text Available The pulsating heated flows are traditionally a difficult subject to treat with conventional hot wire or film methods. Special factors that complicate matters are flow reversal and non linear flow effects of vortices and wire probe wake disturbances on the heat transfer to the hot film or wire sensor in heated pulsating flows. The presence of these strongly nonlinear and unknown terms leads to great difficulties in calibration of hot film probes in this particular regime. The paper analyses the current state of matters in the field and reports a series of solutions that have been practically tested in a case of a high speed pulsated heated flow. Normally such measurements are made in a non-contact fashion using a LDV system or various visualization techniques but there have been recent attempts to use a constant temperature hot wire anemometer system (CTA.To obtain meaningful calibration for hot wire films in hot pulsating flows, a comparison system on other principles (LDV was used, as well as a specially designed nozzle to replace the calibrator unit that could not be operated with heated fluid due to structural integrity reasons. The method as described below works well for the expected speed range that could be generated using the special nozzle.

  4. Characteristics of a hot-wire microsensor for time-dependent wall shear stress measurements

    Energy Technology Data Exchange (ETDEWEB)

    Loefdahl, L.; Chernoray, V. [Thermo and Fluid Dynamics, Chalmers University of Technology, 41296, Goeteborg (Sweden); Haasl, S.; Stemme, G. [Department of Signals, Sensors and Systems, Microsystem Technology, Royal Institute of Technology, 10044, Stockholm (Sweden); Sen, M. [Department of Aerospace and Mechanical Engineering, University of Notre Dame, 46556, Notre Dame, IN (United States)

    2003-09-01

    Hot-wire microsensors for the purpose of measuring the instantaneous velocity gradient close to a wall were designed and their characteristics were evaluated. The sensors were made using MEMS (microelectromechanical systems) technology, which permits the fabrication of various microgeometrical configurations with high precision and good repeatability. The design is based on estimates of the heat rates from the sensor wire to the air, through the supports, and to the wall. Several hot-wire configurations were fabricated with wires positioned in the range 50-250 {mu}m from the wall. Requirements for the design and details of the fabrication methodology are outlined. The hot-wire microsensors were calibrated and tested in a flat-plate boundary layer with and without pressure gradients and were found to have good steady-state characteristics. In addition, the developed sensors were used for preliminary studies of transitional phenomena and turbulence, and the sensors were found to have a good time-dependent response as well. (orig.)

  5. Thermal MEMS flow meter for gaseous working fluids on the basis of the hot-wire thermoanemometric sensor

    Science.gov (United States)

    Tsivinskaya, T. A.; Avaeva, L. G.; Grigoriev, P. V.; Mileshin, S. A.

    2016-10-01

    This paper describes the main principles of constructing innovative MEMS flow meters for gaseous working fluids. MEMS flow meter contains hot-wire thermoanemometrisc sensor which response to the temperature change caused by convective working fluid heat transfer from a hot-wire. The advantages of using hot-wire thermoanemometric sensors were analyzed. The main emphasis of this work is on speed, construction simplicity and small size of the sensor. The new approach to the solution of a problem of sensor output signal relation with the working fluid temperature is presented. This approach is based on adding an extra temperature sensor and a special scheme for thermal compensation to the hot-wire sensor. The temperature scale between temperature sensors (thermistors) corresponds to the flow speed and the flow rate.

  6. A generic strategy for co-presentation of heparin-binding growth factors based on CVD polymerization.

    Science.gov (United States)

    Deng, Xiaopei; Lahann, Joerg

    2012-09-14

    A multifunctional copolymer with both aldehyde and alkyne groups is synthesized by chemical vapor deposition (CVD) for orthogonal co-immobilization of biomolecules. Surface analytical methods including FTIR and XPS are used to confirm the surface modification. Heparin-binding growth factors [basic fibroblast growth factor (bFGF) in this study] can be immobilized through interaction with heparin, which was covalently attached to the CVD surface through an aldehyde-hydrazide reaction. In parallel, an alkyne-azide reaction is used to orthogonally co-immobilize an adhesion peptide as the second biomolecule.

  7. Measurements of the Thermal Conductivity and Thermal Diffusivity of Polymer Melts with the Short-Hot-Wire Method

    OpenAIRE

    Wicaksono, Hendro; Zhang, Xing; Fujii, Motoo

    2001-01-01

    In this paper, the thermal conductivity and thermal diffusivity of four kinds of polymer melts were measured by using the transient short-hot-wire method. This method was developed from the hot-wire technique and is based on two-dimensional numerical solutions of unsteady heat conduction from a wire with the same length-to-diameter ratio and boundary conditions as those in the actual experiments. The present method is particularly suitable for measurements of molten polymers where natural con...

  8. Effect of substrate roughness on growth of diamond by hot filament CVD

    Indian Academy of Sciences (India)

    Awadesh K Mallik; S R Binu; L N Satapathy; Chandrabhas Narayana; Md Motin Seikh; S A Shivashankar; S K Biswas

    2010-06-01

    Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 m to 0.91 m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of 3 to non-3 content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640°C without any additional substrate heating. The coatings grown at adverse conditions for 3 deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable 3 condition gives clear faceted grains.

  9. CVD growth of graphene under exfoliated hexagonal boron nitride for vertical hybrid structures

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Min [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Center for Human Interface Nanotechnology (HINT) (Korea, Republic of); Jang, Sung Kyu [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Song, Young Jae [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Department of Physics, Sungkyunkwan University (SKKU), Suwon 440-746 (Korea, Republic of); Lee, Sungjoo, E-mail: leesj@skku.edu [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Center for Human Interface Nanotechnology (HINT) (Korea, Republic of); College of Information and Communication Engineering, Sungkyunkwan University (SKKU), Suwon 440-746 (Korea, Republic of)

    2015-01-15

    Graphical abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO2, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems. - Abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO{sub 2}, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems.

  10. The features of CNT growth on catalyst-content amorphous alloy layer by CVD-method

    Science.gov (United States)

    Dubkov, S.; Bulyarskii, S.; Pavlov, A.; Trifonov, A.; Kitsyuk, E.; Mierczynski, P.; Maniecki, T.; Ciesielski, R.; Gavrilov, S.; Gromov, D.

    2016-12-01

    This work is devoted to the CVD-synthesis of arrays of carbon nanotubes (CNTs) on Co-Zr-N-(O), Ni-Nb-N-(O), Co- Ta-N-(O) catalytic alloy films from gas mixture of C2H2+NH3+Ar at a substrate temperature of about 550°C.Heating of the amorphous alloy causes its crystallization and squeezing of the catalytic metal onto the surface. As a result, small catalyst particles are formed on the surface. The CNT growth takes place after wards on these particles. It should be noted that the growth of CNT arrays on these alloys is insensitive to the thickness of alloy film, which makes this approach technically attractive. In particular, the possibility of local CNT growth at the ends of the Co-Ta-N-(O) film and three-level CNT growth at the end of more complex structure SiO2/Ni-Nb-N-O/SiO2/Ni-Nb-N-O/SiO2/Ni-Nb-N-O/SiO2 is demonstrated.

  11. Design and Development of an Acoustic Levitation System for Use in CVD Growth of Carbon Nanotubes

    Science.gov (United States)

    Qasem, Amal ali

    The most widely used methods for growth of carbon nanotubes (CNTs) arc discharge, laser ablation, and chemical vapor deposition (CVD). Some of these methods have difficulties, such as controlling the quality and straightness of the nanotube in the synthesis of CNTs from substrates. Also, the enhanced plasma chemical vapor deposition method with the catalyst on a substrate produces straighter, larger diameter nanotubes by the tip growth method, but they are short. The difficulty in the floating catalyst method is that the nanotubes stay in the growth furnace for short times limiting growth to about one mm length; this method also leaves many catalyst impurities. One factor that limits CNT growth in these methods is the difficulty of getting enough carbon atoms to the growth catalyst to grow long nanotubes. The motivation of this work is that longer, higher quality nanotubes could be grown by increasing growth time and by increasing carbon atom movement to catalyst. The goal of this project is to use acoustic levitation to assist chemical vapor deposition growth by trapping and vibrating the growing CNTs for better properties. Our levitation system consists of a piezoelectric transducer attached to an aluminum horn and quartz rod extending into the growth furnace. The most important elements of our methods to achieve the acoustic levitation are as follows. 1. Using COMSOL Multi-physic Simulation software to determine the length of quartz rod needed to excite standing waves for levitation in the tube furnace. 2. Determining the resonance frequency of different transducers and horns. 3. Using ultrasound measurement to determine the time of flight, velocity of sound and sound wavelength of different horns. 4. Making Aluminum horns with the appropriate lengths. 5. Using ultrasound measurement to determine the changing of quartz rod velocity of sound and length in the furnace. 6. Mounting the transducer to booster horn and aluminum cylindrical horn above a reflector to

  12. Low-temperature growth of multi-walled carbon nanotubes by thermal CVD

    Energy Technology Data Exchange (ETDEWEB)

    Halonen, Niina; Leino, Anne-Riikka; Maeklin, Jani; Kukkola, Jarmo; Toth, Geza [Microelectronics and Materials Physics Laboratories, University of Oulu (Finland); Sapi, Andras; Nagy, Laszlo; Puskas, Robert; Kukovecz, Akos; Konya, Zoltan [Department of Applied and Environmental Chemistry, University of Szeged (Hungary); Wu, Ming-Chung; Liao, Hsueh-Chung; Su, Wei-Fang [Department of Materials Science and Engineering, National Taiwan University, Taipei (China); Shchukarev, Andrey; Mikkola, Jyri-Pekka [Department of Chemistry, Institute of Technical Chemistry, Chemical-Biological Center, Umeaa University (Sweden); Kordas, Krisztian [Microelectronics and Materials Physics Laboratories, University of Oulu (Finland); Department of Chemistry, Institute of Technical Chemistry, Chemical-Biological Center, Umeaa University (Sweden)

    2011-11-15

    Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene:methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi- as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. New CVD-based method for the growth of high-quality crystalline zinc oxide layers

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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).

  15. Simultaneous measurements of three velocity components by a flying hot-wire method using an x-array hot-wire probe. 2nd Report. Calibration technique and its application to a flow field downstream of a vortex generator; X gata nessen probe wo mochiita flying hot wire ho ni yoru sokudo no sanhoko seibun no doji keisoku. 2. Nessen sensor no kosei hoho to uzu hasseiki karyu no keisokurei

    Energy Technology Data Exchange (ETDEWEB)

    Shiino, T. [Nissan Motor Co. Ltd., Tokyo (Japan); Yamamoto, K.; Shizawa, T.; Honami, S. [Science University of Tokyo, Tokyo (Japan). Faculty of Engineering

    1995-12-25

    This paper proposes a calibration technique for a flying hot-wire method that uses with an X-array hot-wire probe. The flying hot-wire system moves the hot-wire probe in the span wise Z-direction of the flow field. The calibration of yaw and pitch angle sensitivities of the probe is of utmost importance to this system. After careful calibration, the system is applied to a three-dimensional flow to obtain three components of the mean velocity and six components of the Reynolds stress. The mean velocities and the Reynolds shear stresses downstream of a pair of vortex generators embedded in a two-dimensional boundary layer show the same profiles as those obtained with an ordinary X-array hot-wire probe. In one traverse, the flying hot-wire system can measure 60 points of six components of the Reynolds stress with good accuracy. 6 refs., 15 figs.

  16. Evaluation of a hot-wire hair removal device compared to razor shaving.

    Science.gov (United States)

    Biesman, Brian S

    2013-07-01

    We describe a blinded, controlled, prospective clinical study of a hot-wire device promoted for hair removal and the reduction or delay of hair regrowth (no!no!, Radiancy, Inc., Orangeburg, NY) compared to a shaving control. Twenty-two subjects were treated by trained clinical staff with the hot-wire device according to its Instructions for Use on the lower leg two times per week for 8 weeks. An adjacent site was shaved with a razor blade on the same schedule to provide a control. Subjects were followed for 3 months after the last treatment to study the durability of the results. Standardized high-resolution photographs were made at baseline, once a week during treatment, and monthly during the post-treatment follow-up period. Micro-tattoos were used to ensure treatments and photographs were reliably made in the same anatomical location from visit to visit. Both active and control sites were shaved prior to baseline and allowed to regrow for a fixed period of time before first treatment to provide a consistent and well-defined baseline hair condition. Quantitative hair counts were made by a third party from the photographs and standard statistical analysis was performed to look for differences between the active and control sites. Visual assessments and quantitative analysis was also performed on the photographs to see if there were any differences in hair thickness (diameter) and hair color between the active and control sites. The results show that shaving and the hot-wire device are indistinguishable in short-term or long-term effect, based on both visual assessment of the photographs and statistical analysis of the hair counts. The control (shaving) had a mean baseline hair count of 79.4, which remained stable (74.8-84.3) during the 8 week-treatment phase and climbed substantially after stopping treatment to 98.8, 100.1, and 104.6 at 1, 2, and 3 months post-treatment, respectively. The active (hot-wire device) had a mean baseline hair count of 86.0 which

  17. A strategy to eliminate all nonlinear effects in constant-voltage hot-wire anemometry.

    Science.gov (United States)

    Berson, Arganthaël; Blanc-Benon, Philippe; Comte-Bellot, Geneviève

    2009-04-01

    A constant-voltage anemometer is subject to nonlinear effects when the operating hot wire is exposed to large velocity fluctuations in the incident flow. This results in the generation of undesirable higher harmonics, just as in the two classic systems, constant-current and constant-temperature anemometers, for which no attempts are normally made to correct the nonlinearities. The present investigation shows that these undesirable higher harmonics can be suppressed in the case of a constant-voltage anemometer. A new approach to process experimental data is proposed. It is based on three explicit equations established and solved with all terms included, i.e., without linearization. These are (1) the first-order differential equation that describes the electronic circuit of a constant-voltage anemometer-this equation permits to deduce the instantaneous resistance of the hot wire from the output voltage of the anemometer; (2) the first-order differential equation that expresses the thermal lag behavior of the hot wire when used in a constant-voltage mode-this equation permits to restore the instantaneous resistance that an ideal wire would have without thermal inertia in the same flow conditions; and (3) the algebraic relation that expresses the heat-transfer law of an ideal wire, according to King's law, a look-up table, or a polynomial fit-this relation permits to deduce the instantaneous flow velocity from the instantaneous resistance of the ideal wire. The proposed method is easily implemented on a personal computer and permits odd turbulence moments, such as skewness factors, to be obtained satisfactorily.

  18. A strategy to eliminate all nonlinear effects in constant-voltage hot-wire anemometry

    Science.gov (United States)

    Berson, Arganthaël; Blanc-Benon, Philippe; Comte-Bellot, Geneviève

    2009-04-01

    A constant-voltage anemometer is subject to nonlinear effects when the operating hot wire is exposed to large velocity fluctuations in the incident flow. This results in the generation of undesirable higher harmonics, just as in the two classic systems, constant-current and constant-temperature anemometers, for which no attempts are normally made to correct the nonlinearities. The present investigation shows that these undesirable higher harmonics can be suppressed in the case of a constant-voltage anemometer. A new approach to process experimental data is proposed. It is based on three explicit equations established and solved with all terms included, i.e., without linearization. These are (1) the first-order differential equation that describes the electronic circuit of a constant-voltage anemometer—this equation permits to deduce the instantaneous resistance of the hot wire from the output voltage of the anemometer; (2) the first-order differential equation that expresses the thermal lag behavior of the hot wire when used in a constant-voltage mode—this equation permits to restore the instantaneous resistance that an ideal wire would have without thermal inertia in the same flow conditions; and (3) the algebraic relation that expresses the heat-transfer law of an ideal wire, according to King's law, a look-up table, or a polynomial fit—this relation permits to deduce the instantaneous flow velocity from the instantaneous resistance of the ideal wire. The proposed method is easily implemented on a personal computer and permits odd turbulence moments, such as skewness factors, to be obtained satisfactorily.

  19. Basic study on hot-wire flow meter in forced flow of liquid hydrogen

    Science.gov (United States)

    Oura, Y.; Shirai, Y.; Shiotsu, M.; Murakami, K.; Tatsumoto, H.; Naruo, Y.; Nonaka, S.; Kobayashi, H.; Inatani, Y.; Narita, N.

    2014-01-01

    Liquid hydrogen (LH2) is a key issue in a carbon-free energy infrastructure at the energy storage and transportation stage. The typical features of LH2 are low viscosity, large latent heat and small density, compared with other general liquids. It is necessary to measure a mass flow of liquid hydrogen with a simple and compact method, especially in a two phase separate flow condition. We have proposed applying a hot-wire type flow meter, which is usually used a for gas flow meter, to LH2 flow due to the quite low viscosity and density. A test model of a compact LH2 hot-wire flow meter to measure local flow velocities near and around an inside perimeter of a horizontal tube by resistance thermometry was designed and made. The model flow meter consists of two thin heater wires made of manganin fixed in a 10 mm-diameter and 40 mm-length tube flow path made of GFRP. Each rigid heater wire was set twisted by 90 degrees from the inlet to the outlet along the inner wall. In other words, the wires were aslant with regard to the LH2 stream line. The heated wire was cooled by flowing LH2, and the flow velocity was obtained by means of the difference of the cooling characteristic in response to the flow velocity. In this report, we show results on the basic experiments with the model LH2 hot-wire flow meter. First, the heat transfer characteristics of the two heater wires for several LH2 flow velocities were measured. Second, the heating current was controlled to keep the wire temperature constant for various flow velocities. The relations between the flow velocity and the heating current were measured. The feasibility of the proposed model was confirmed.

  20. 热丝TIG焊方法最新研究进展%Research on Development of Hot-wire TIG Welding Process

    Institute of Scientific and Technical Information of China (English)

    赵福海; 华学明; 叶欣; 吴毅雄

    2011-01-01

    综述了各类热丝TIG焊方法的特点及其技术与工艺难点,并着重阐述了近些年来研究较多的脉冲加热热丝TIG焊、窄间隙热丝TIG焊、超高速热丝TIG焊的研究进展.%The characteristics of hot-wire welding process and the principles and technical difficulties of many kinds of hot-wire welding process were briefly introduced. The research progress of several advanced hot- wire welding processes in recent years, including pulse-heated hot-wire TIG welding process, narrow gap hot-wire TIG welding process and ultra-high-speed hot-wire welding process was introduced.

  1. Use of hot-wire anemometry for turbulence measurements in shock induced flows

    Science.gov (United States)

    Hartung, L. C.; Duffy, R. E.; Troller, J. W.

    1986-01-01

    A research program is currently being conducted with the aim to investigate the operating environment of future gas turbines. The present paper provides a description of the experimental methods which have been employed in performing turbulence intensity measurements in shock-induced flows. In a discussion of the instrumentation, attention is given to the employed low pressure shock tube, the hot-wire probe, the anemometer, the test facility, the experimental setup, the Kistler pressure transducer, and silicon piezoresistive gages. Aspects of instrumentation calibration are considered along with data corrections, experimental data, and data processing.

  2. Hot-Wire Calibration at Low Velocities: Revisiting the Vortex Shedding Method

    Directory of Open Access Journals (Sweden)

    Sohrab S. Sattarzadeh

    2013-01-01

    Full Text Available The necessity to calibrate hot-wire probes against a known velocity causes problems at low velocities, due to the inherent inaccuracy of pressure transducers at low differential pressures. The vortex shedding calibration method is in this respect a recommended technique to obtain calibration data at low velocities, due to its simplicity and accuracy. However, it has mainly been applied in a low and narrow Reynolds number range known as the laminar vortex shedding regime. Here, on the other hand, we propose to utilize the irregular vortex shedding regime and show where the probe needs to be placed with respect to the cylinder in order to obtain unambiguous calibration data.

  3. Heat transfer monitoring by means of the hot wire technique and finite element analysis software.

    Science.gov (United States)

    Hernández Wong, J; Suarez, V; Guarachi, J; Calderón, A; Rojas-Trigos, J B; Juárez, A G; Marín, E

    2014-01-01

    It is reported the study of the radial heat transfer in a homogeneous and isotropic substance with a heat linear source in its axial axis. For this purpose, the hot wire characterization technique has been used, in order to obtain the temperature distribution as a function of radial distance from the axial axis and time exposure. Also, the solution of the transient heat transport equation for this problem was obtained under appropriate boundary conditions, by means of finite element technique. A comparison between experimental, conventional theoretical model and numerical simulated results is done to demonstrate the utility of the finite element analysis simulation methodology in the investigation of the thermal response of substances.

  4. Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise

    Science.gov (United States)

    Fontana, Richard Remo

    1988-01-01

    This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.

  5. Fabrication and testing of subminiature multi-sensor hot-wire probes

    Science.gov (United States)

    Ligrani, P. M.; Westphal, R. V.; Lemos, F. R.

    1989-01-01

    A method for the fabrication of hot-wire sensors measuring 0.6 micron in diameter and 200 microns in length is described. This method allows accurate control of sensing-element orientation, thus making it possible to produce multisensor probes. Test results obtained with a miniature sensor fabricated by this method, for the outer region of a turbulent boundary layer developing in a zero presure gradient were compared to measurements from a conventional-sized probe made in the same flow, demonstrating that, because of their improved spatial resolution, subminiature sensors can provide more accurate measurements in boundary layers than do the conventional probes.

  6. Calibration of Hot Wire Anemometers. (Latest Citations from the Aerospace Database)

    Science.gov (United States)

    1996-01-01

    The bibliography contains citations concerning calibration methods and measurement correction schemes for hot wire anemometers. Coverage includes static and dynamic calibration of sensors having single, multiple, cross, and ring wire configurations. Correction methods to account for yaw angle, low-velocity flow, microgravity, wall proximity, and highly fluctuating turbulence, velocity, or temperature are covered. Correction methods are also referenced for installations having multiple sensors. Hot film and laser anemometers, and the use of anemometers in specific industrial and aerospace applications are extensively covered in separate biblographies. (Contains 50-250 citations and includes a subject term index and title list.)

  7. Flow gradient corrections on hot-wire measurements using an X-wire probe

    Science.gov (United States)

    Gooden, J. H. M.; van Lent, M.

    A method has been developed to correct hot-wire measurements by means of a single X-wire probe for the effect of gradients normal to the plane of the wires in the mean flow velocities as well as in the turbulence intensities. Dataprocessing is performed in an iterative way, using the results of measurements with different probe rolling angles, to determine the gradient corrections along the traverse from the previous loop. The method has been applied to measurements in the wake above the trailing edge flap of a wing and it is shown that substantial improvements in the results have been achieved.

  8. Constant-temperature hot-wire anemometer practice in supersonic flows. I - The normal wire

    Science.gov (United States)

    Smits, A. J.; Hayakawa, K.; Muck, K. C.

    1983-01-01

    The performance of a constant-temperature normal hot-wire in a supersonic flow is critically examined. It is shown that this instrument is inherently unsuitable for measuring turbulent temperature correlations because of the highly nonlinear response to temperature fluctuations, particularly at low overheat ratios. The instrument is therefore limited to measurements of mean and fluctuating mass-flow rates. Suitable calibration procedures, as well as the limits on spatial and temporal resolution are discussed, and corrections for mean stagnation temperature changes are suggested.

  9. Constant-temperature hot-wire anemometer practice in supersonic flows. II - The inclined wire

    Science.gov (United States)

    Smits, A. J.; Muck, K. C.

    1983-01-01

    The performance of a constant-temperature inclined hot-wire in a supersonic flow is critically examined. It is shown that calibration techniques applicable to subsonic flow, such as the cosine cooling law cannot be used when the flow is supersonic. Calibration and measurement procedures appropriate to supersonic flow are suggested, together with the possible limits on their validity. Experimental results for different wires indicate that the sensitivities do not seem to depend on flow direction according to any simple correlation. When the sensitivity exhibits a strong dependence on flow direction, the wire should be discarded to avoid errors due to nonlinear effects.

  10. Dynamic characteristics of a simple constant-temperature hot-wire anemometer.

    Science.gov (United States)

    Lu, S S

    1979-06-01

    A simple constant-temperatue hot-wire anemometer has been analyzed and tested in a shock tube and by electronic tests. In the derivation of the governing equations, the finite open-loop gain of an operational amplifier is considered. The measured values of the natural frequency and the damping coefficient for the anemometer system are in satisfactory agreement with the theory. For short probe cables, the frequency response is found to be limited by the finite open-loop gain of the amplifier.

  11. Kalibrasi Single-Normal Hot-Wire Probe Sigmond Cohn Alloy 851 untuk Aliran Jet Terpulsasi

    OpenAIRE

    Hariyo Priambudi Setyo Pratomo; Klaus Bremhorst

    2006-01-01

    Calibration of a Sigmond Cohn alloy 851 single normal hot-wire probe was performed with a stationary calibration method with a range of nozzle exit velocity from 2 up to 80 m/s. The calibration aims to determine the best calibration response equation associated with the accuracy of curve fit. The curve fit accuracy test shows that the extended power-law equation provides a better curve fit than the simple power-law equation. A look-up table method used can improve the accuracy of curve fit of...

  12. Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

    Science.gov (United States)

    Kim, Chan-Soo; Youn, Woong-Kyu; Lee, Dong-Kwon; Seol, Kwang-Soo; Hwang, Nong-Moon

    2009-07-01

    The nanocrystalline alpha silicon nitride (α-Si 3N 4) was deposited on a silicon substrate by hot-wire chemical vapor deposition at the substrate temperature of 700 °C under 4 and 40 Torr at the wire temperatures of 1430 and 1730 °C, with a gas mixture of SiH 4 and NH 3. The size and density of crystalline nanoparticles on the substrate increased with increasing wire temperature. With increasing reactor pressure, the crystallinity of α-Si 3N 4 nanoparticles increased, but the deposition rate decreased.

  13. Atomic scale KMC simulation of {100} oriented CVD diamond film growth under low substrate temperature—Part Ⅰ Simulation of CVD diamond film growth under Joe-Badgwell-Hauge model

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The growth of {100} oriented CVD (Chemical Vapor Deposition)diamond film under Joe-Badgwell-Hauge (J-B-H) model is simulated at atomic scale by using revised KMC (Kinetic Monte Carlo) method. The results show that: (1) under Joe's model, the growth mechanism from single carbon species is suitable for the growth of {100} oriented CVD diamond film in low temperature; (2) the deposition rate and surface roughness () under Joe's model are influenced intensively by temperature ()and not evident bymass fraction of atom chlorine; (3)the surface roughness increases with the deposition rate, i.e. the film quality becomes worse with elevated temperature, in agreement with Grujicic's prediction; (4) the simulation results cannot make sure the role of single carbon insertion.

  14. Atomic scale KMC simulation of {100} oriented CVD diamond film growth under low substrate temperature—Part I simulation of CVD diamond film growth under Joe—Badgwell—Hauge model

    Institute of Scientific and Technical Information of China (English)

    Xizhong; YuZhang; 等

    2002-01-01

    The growth of {100} oriented CVD( Chemical Vapor Deposition) diamond film under Joe-Badgwell-Hauge(J-B-H) model is simulated at atomic scale by using revised KMC(Kinetic Monte Carlo)method.The results show that:(1) under Joe's model,the growth mechanism from single carbon species is suitable for the growth of {100} oriented CVD diamond film in low temperature;(2) the deposition rate and surface roughness(Rq) under Joe's model are influenced intensively by temperature(Ts) and not evident bymass fraction Wc1 of atom chlorine;(3) the surface roughness increases with the deposition rate.i.e.the film quality becomes worse with elevated temperature,in agreement with Grujicic's prediction;(4) the simulation results cannot make sure the role of single carbon insertion.

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    Tomohiro Iwasaki

    2016-06-01

    Full Text Available Abstract 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.

  17. Thermal Conductivity of Amorphous and Nanocrystalline Silicon Films Prepared by Hot-Wire Chemical-Vapor Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Nemeth, William M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jugdersuren, B. [Sotera Defense Solutions, Inc.; Kearney, B. T. [Naval Research Laboratory; Queen, D. R. [Naval Research Laboratory; Metcalf, T. H. [Naval Research Laboratory; Culbertson, J. C. [Naval Research Laboratory; Chervin, C. N. [Naval Research Laboratory; Stroud, R. M. [Naval Research Laboratory; Wang, Q. [Formerly NREL; Liu, Xiao [Naval Research Laboratory

    2017-07-31

    We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  18. Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Jugdersuren, B.; Kearney, B. T.; Queen, D. R.; Metcalf, T. H.; Culbertson, J. C.; Chervin, C. N.; Stroud, R. M.; Nemeth, W.; Wang, Q.; Liu, Xiao

    2017-07-01

    We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  19. Thin film solar cells with Si nanocrystallites embedded in amorphous intrinsic layers by hot-wire chemical vapor deposition.

    Science.gov (United States)

    Park, Seungil; Parida, Bhaskar; Kim, Keunjoo

    2013-05-01

    We investigated the thin film growths of hydrogenated silicon by hot-wire chemical vapor deposition with different flow rates of SiH4 and H2 mixture ambient and fabricated thin film solar cells by implementing the intrinsic layers to SiC/Si heterojunction p-i-n structures. The film samples showed the different infrared absorption spectra of 2,000 and 2,100 cm(-1), which are corresponding to the chemical bonds of SiH and SiH2, respectively. The a-Si:H sample with the relatively high silane concentration provides the absorption peak of SiH bond, but the microc-Si:H sample with the relatively low silane concentration provides the absorption peak of SiH2 bond as well as SiH bond. Furthermore, the microc-Si:H sample showed the Raman spectral shift of 520 cm(-1) for crystalline phase Si bonds as well as the 480 cm(-1) for the amorphous phase Si bonds. These bonding structures are very consistent with the further analysis of the long-wavelength photoconduction tail and the formation of nanocrystalline Si structures. The microc-Si:H thin film solar cell has the photovoltaic behavior of open circuit voltage similar to crystalline silicon thin film solar cell, indicating that microc-Si:H thin film with the mixed phase of amorphous and nanocrystalline structures show the carrier transportation through the channel of nanocrystallites.

  20. Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

    Science.gov (United States)

    Jugdersuren, B.; Kearney, B. T.; Queen, D. R.; Metcalf, T. H.; Culbertson, J. C.; Chervin, C. N.; Stroud, R. M.; Nemeth, W.; Wang, Q.; Liu, Xiao

    2017-07-01

    We report 3 ω thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 ∘C . They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60 % crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  1. Formation of isolated carbon nanofibers with hot-wire CVD using nanosphere lithography as catalyst patterning technique

    NARCIS (Netherlands)

    Houweling, Z.S.; Verlaan, V.; ten Grotenhuis, G.T.; Schropp, R.E.I.

    2008-01-01

    Recently the site-density control of carbon nanotubes (CNTs) has attracted much attention as this has become critical for its many applications. To obtain an ordered array of catalyst nanoparticles with good monodispersity nanosphere lithography (NSL) is used. These nanoparticles are tested as catal

  2. Thermally induced nano-structural and optical changes of nc-Si:H deposited by hot-wire CVD

    CSIR Research Space (South Africa)

    Arendse, CJ

    2009-04-01

    Full Text Available , R. Swanepoel, B.A. Julies, C. Arendse, T. Muller, C.C.Theron, A. Gordijn, P.C.P. Bronsveld, J.K. Rath, R.E.I. Schropp, Thin Solid Films 515, 8040 (2007) [10] S.K. Kim, K.C. Park, J. Jang, J. Appl. Phys. 77, 5115 (1995) [11] H. Li, R.H. Franken, R...

  3. EBSD analysis of tungsten-filament carburization during the hot-wire CVD of multi-walled carbon nanotubes

    CSIR Research Space (South Africa)

    Oliphant, CJ

    2014-02-01

    Full Text Available -scale synthesis of multi-walled carbon nanotubes ~MWCNTs! using HWCVD ~Dillon et al., 2003!. Despite the efforts to reduce filament aging, the fila- ment alloying process is still being investigated. Previous studies have focused primarily on linking microscopy, X... pyrometer. At Received August 23, 2013; accepted November 26, 2013 *Corresponding author. E-mail: coliphant@nmisa.org Microsc. Microanal. Page 1 of 10 doi:10.1017/S1431927613014001 MicroscopyAND Microanalysis © MICROSCOPY SOCIETY OF AMERICA 2013 each...

  4. Formation of isolated carbon nanofibers with hot-wire CVD using nanosphere lithography as catalyst patterning technique

    NARCIS (Netherlands)

    Houweling, Z.S.; Verlaan, V.; ten Grotenhuis, G.T.; Schropp, R.E.I.

    2008-01-01

    Recently the site-density control of carbon nanotubes (CNTs) has attracted much attention as this has become critical for its many applications. To obtain an ordered array of catalyst nanoparticles with good monodispersity nanosphere lithography (NSL) is used. These nanoparticles are tested as catal

  5. Microfluidic flowmeter based on micro "hot-wire" sandwiched Fabry-Perot interferometer.

    Science.gov (United States)

    Li, Ying; Yan, Guofeng; Zhang, Liang; He, Sailing

    2015-04-06

    We present a compact microfluidic flowmeter based on Fabry-Perot interferometer (FPI). The FPI was composed by a pair of fiber Bragg grating reflectors and a micro Co(2+)-doped optical fiber cavity, acting as a "hot-wire" sensor. Microfluidic channels made from commercial silica capillaries were integrated with the FPIs on a chip to realize flow-rate sensing system. By utilizing a tunable pump laser with wavelength of 1480 nm, the proposed flowmeter was experimentally demonstrated. The flow rate of the liquid sample is determined by the induced resonance wavelength shift of the FPI. The effect of the pump power, microfluidic channel scale and temperature on the performance of our flowmeter was investigated. The dynamic response was also measured under different flow-rate conditions. The experimental results achieve a sensitivity of 70 pm/(μL/s), a dynamic range up to 1.1 μL/s and response time in the level of seconds, with a spatial resolution ~200 μm. Such good performance renders the sensor a promising supplementary component in microfluidic biochemical sensing system. Furthermore, simulation modal was built up to analyze the heat distribution of the "hot-wire" cavity and optimize the FPI structure as well.

  6. Further elucidation of nanofluid thermal conductivity measurement using a transient hot-wire method apparatus

    Science.gov (United States)

    Yoo, Donghoon; Lee, Joohyun; Lee, Byeongchan; Kwon, Suyong; Koo, Junemo

    2017-08-01

    The Transient Hot-Wire Method (THWM) was developed to measure the absolute thermal conductivity of gases, liquids, melts, and solids with low uncertainty. The majority of nanofluid researchers used THWM to measure the thermal conductivity of test fluids. Several reasons have been suggested for the discrepancies in these types of measurements, including nanofluid generation, nanofluid stability, and measurement challenges. The details of the transient hot-wire method such as the test cell size, the temperature coefficient of resistance (TCR) and the sampling number are further investigated to improve the accuracy and consistency of the measurements of different researchers. It was observed that smaller test apparatuses were better because they can delay the onset of natural convection. TCR values of a coated platinum wire were measured and statistically analyzed to reduce the uncertainty in thermal conductivity measurements. For validation, ethylene glycol (EG) and water thermal conductivity were measured and analyzed in the temperature range between 280 and 310 K. Furthermore, a detailed statistical analysis was conducted for such measurements, and the results confirmed the minimum number of samples required to achieve the desired resolution and precision of the measurements. It is further proposed that researchers fully report the information related to their measurements to validate the measurements and to avoid future inconsistent nanofluid data.

  7. Thermal conductivity measurement in clay dominant consolidated material by Transient Hot-Wire method.

    Science.gov (United States)

    Garnier, J. P.; Gallier, J.; Mercx, B.; Dudoignon, P.; Milcent, D.

    2010-06-01

    The transient hot-wire (THW) technique is widely used for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffusivity with the same hot wire. This technique was also tried to determine thermal properties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by the THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick). The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1) in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation state on the wire temperature (Δt) measurements and (2) in the compacted clay-geomaterial at different moisture states. The Δt / ln(t) diagrams allow the calculation of two thermal conductivities. The first one, measured in the short time acquisition (thermal conductivity of the material.

  8. Thermal conductivity measurement in clay dominant consolidated material by Transient Hot-Wire method.

    Directory of Open Access Journals (Sweden)

    Milcent D.

    2010-06-01

    Full Text Available The transient hot-wire (THW technique is widely used for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffusivity with the same hot wire. This technique was also tried to determine thermal properties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by the THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick. The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1 in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation state on the wire temperature (Δt measurements and (2 in the compacted clay-geomaterial at different moisture states. The Δt / ln(t diagrams allow the calculation of two thermal conductivities. The first one, measured in the short time acquisition (< 1s, characterizes the microtexture of the material and its hydrated state. The second one, measured for longer time acquisitions, characterizes the mean thermal conductivity of the material.

  9. Hot-Film and Hot-Wire Anemometry for a Boundary Layer Active Flow Control Test

    Science.gov (United States)

    Lenahan, Keven C.; Schatzman, David M.; Wilson, Jacob Samuel

    2013-01-01

    Unsteady active flow control (AFC) has been used experimentally for many years to minimize bluff-body drag. This technology could significantly improve performance of rotorcraft by cleaning up flow separation. It is important, then, that new actuator technologies be studied for application to future vehicles. A boundary layer wind tunnel was constructed with a 1ft-x-3ft test section and unsteady measurement instrumentation to study how AFC manipulates the boundary layer to overcome adverse pressure gradients and flow separation. This unsteady flow control research requires unsteady measurement methods. In order to measure the boundary layer characteristics, both hot-wire and hot-film Constant Temperature Anemometry is used. A hot-wire probe is mounted in the flow to measure velocity while a hot-film array lays on the test surface to measure skin friction. Hot-film sensors are connected to an anemometer, a Wheatstone bridge circuit with an output that corresponds to the dynamic flow response. From this output, the time varying flow field, turbulence, and flow reversal can be characterized. Tuning the anemometers requires a fan test on the hot-film sensors to adjust each output. This is a delicate process as several variables drastically affect the data, including control resistance, signal input, trim, and gain settings.

  10. Extrapolation of Calibration Curve of Hot-wire Spirometer Using a Novel Neural Network Based Approach.

    Science.gov (United States)

    Ardekani, Mohammad Ali; Nafisi, Vahid Reza; Farhani, Foad

    2012-10-01

    Hot-wire spirometer is a kind of constant temperature anemometer (CTA). The working principle of CTA, used for the measurement of fluid velocity and flow turbulence, is based on convective heat transfer from a hot-wire sensor to a fluid being measured. The calibration curve of a CTA is nonlinear and cannot be easily extrapolated beyond its calibration range. Therefore, a method for extrapolation of CTA calibration curve will be of great practical application. In this paper, a novel approach based on the conventional neural network and self-organizing map (SOM) method has been proposed to extrapolate CTA calibration curve for measurement of velocity in the range 0.7-30 m/seconds. Results show that, using this approach for the extrapolation of the CTA calibration curve beyond its upper limit, the standard deviation is about -0.5%, which is acceptable in most cases. Moreover, this approach for the extrapolation of the CTA calibration curve below its lower limit produces standard deviation of about 4.5%, which is acceptable in spirometry applications. Finally, the standard deviation on the whole measurement range (0.7-30 m/s) is about 1.5%.

  11. Hot wire anemometer measurements in the unheated air flow tests of the SRB nozzle-to-case joint

    Science.gov (United States)

    Ramachandran, N.

    1988-01-01

    Hot-Wire Anemometer measurements made in the Solid Rocket Booster (SRB) nozzle-to-case joint are discussed. The study was undertaken to glean additional information on the circumferential flow induced in the SRB nozzle joint and the effect of this flow on the insulation bonding flaws. The tests were conducted on a full-scale, 2-D representation of a 65-in long segment of the SRB nozzle joint, with unheated air as the working fluid. Both the flight Mach number and Reynolds number were matched simultaneously and different pressure gradients imposed along the joint face were investigated. Hot-wire anemometers were used to obtain velocity data for different joint gaps and debond configurations. The procedure adopted for hot-wire calibration and use is outlined and the results from the tests summarized.

  12. Recovery of rectified signals from hot-wire/film anemometers due to flow reversal in oscillating flows.

    Science.gov (United States)

    Yang, Yingchen; Jones, Douglas L; Liu, Chang

    2010-01-01

    Hot-wire/film anemometers have been broadly used in experimental studies in fluid mechanics, acoustics, and ocean engineering. Yet, it is well known that hot-wire/film anemometers rectify the signal outputs due to the lack of sensitivity to flow direction. This main drawback, in turn, makes them less useful for diverse fluctuating flow measurements. To solve this issue, a rectification recovery method has been developed based on reconstruction of the Fourier series expansion in conjunction with signal-squaring approach. This signal recovery method was experimentally examined and proven to be successful for both conventional and microfabricated hot-wire/film anemometers. The method was further applied to dipole field measurements, with data from recovered signals perfectly matching the analytical model of the dipole field.

  13. Calibration, Data Acquisition, and Post Analysis of Turbulent Fluid Flow in a Calibration Jet Using Hot-wire Anemometry

    Science.gov (United States)

    Moreno, Michelle

    2004-01-01

    The Turbine Branch concentrates on the following areas: Computational Fluid Dynamics (CFD), and implementing experimental procedures to obtain physical modeling data. Hot-wire Anemometry is a valuable tool for obtaining physical modeling data. Hot-wire Anemometry is likely to remain the principal research tool for most turbulent air/gas flow studies. The Hot-wire anemometer consists of a fine wire heated by electric current. When placed in a fluid stream, the hot-wire loses heat to the fluid by forced convection. In forced convection, energy transfer is due to molecular motion imposed by an extraneous force moving fluid parcels. When the hot-wire is in "equilibrium", the rate of heat input to the wire is equal to the rate of heat loss at the wire ends. The equality between heat input and heat loss is the basis for King s equation, which relates the electrical parameters of the hot-wire to the flow parameters of the fluid. Hot-wire anemometry is based on convective heat transfer from a heated wire element placed in a fluid flow. Any change in the fluid flow condition that affects the heat transfer from the heated element will be detected virtually instantaneously by a constant-temperature Hot-wire anemometry system. The system implemented for this research is the IFA 300. The system is a fully-integrated, thermal anemometer-based system that measures mean and fluctuating velocity components in air, water, and other fluids. It also measures turbulence and makes localized temperature measurements. A constant-temperature anemometer is a bridge and amplifier circuit that controls a tiny wire at constant temperature. As a fluid flow passes over the heated sensor, the amplifier senses the bridge off-balance and adjusts the voltage to the top of the bridge, keeping the bridge in balance. The voltage on top of the bridge can then be related to the velocity of the flow. The bridge voltage is sensitive to temperature as well as velocity and so the built-in thermocouple

  14. A Study on Process Characteristics and Performance of Hot Wire Gas Tungsten Arc Welding Process for High Temperature Materials

    OpenAIRE

    Padmanaban MR,Anantha; Neelakandan, Baskar; Kandasamy,Devakumaran

    2016-01-01

    Hot wire gas tungsten arc welding (HW-GTAW) process is the one where the filler wire is pre-heated close to its melting point before it is fed in to the arc. The effect of HW-GTAW parameters such as welding current, hot wire current and the wire feed rate during welding of super ASS 304H stainless steel tubes were evaluated in terms of heat input, voltage-current (V-I) characteristics and weld bead characteristics such as bead weight and geometry. The results obtained indicate that for a cons...

  15. Applying hot-wire anemometry to directly measure the water balance in a proton exchange membrane fuel cell for a pre-humidified hydrogen stream

    DEFF Research Database (Denmark)

    Berning, Torsten; Shakhshir, Saher Al

    2016-01-01

    In a recent publication it has been shown how the water balance in a proton exchange membrane fuel cell can be determined employing hot wire anemometry. The hot wire sensor has to be placed into the anode outlet pipe of the operating fuel cell, and the voltage signal E that is read from the senso...

  16. Landing Gear Components Noise Study - PIV and Hot-Wire Measurements

    Science.gov (United States)

    Hutcheson, Florence V.; Burley, Casey L.; Stead, Daniel J.; Becker, Lawrence E.; Price, Jennifer L.

    2010-01-01

    PIV and hot-wire measurements of the wake flow from rods and bars are presented. The test models include rods of different diameters and cross sections and a rod juxtaposed to a plate. The latter is representative of the latch door that is attached to an aircraft landing gear when the gear is deployed, while the single and multiple rod configurations tested are representative of some of the various struts and cables configuration present on an aircraft landing gear. The test set up is described and the flow measurements are presented. The effect of model surface treatment and freestream turbulence on the spanwise coherence of the vortex shedding is studied for several rod and bar configurations.

  17. Onset temperatures in hot wire Ignition of AN-Based emulsions

    Energy Technology Data Exchange (ETDEWEB)

    Chan, Sek Kwan [Orica Mining Services, Quebec (Canada); Turcotte, Richard [Canadian Explosive Research Laboratory, Ottawa (Canada)

    2009-02-15

    Hot wire ignition experiments were carried out recently at the Canadian Explosives Research Laboratory on a few emulsion formulations. The data indicate that there is a pressure-dependent onset temperature beyond which the wire temperature increases at an accelerated rate. In order to explain this observation and to detect this temperature more consistently, particularly at low pressures, the data are reanalysed by comparing the experimental wire temperature with that predicted from theory for the heating of an inert material. For this purpose, an analytical theory from the literature is reviewed and the numerical solution developed in this report is described. The latter can deal with more general solutions with variable thermal properties and chemical reactions in the condensed medium surrounding the wire. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  18. Direct drag and hot-wire measurements on thin-element riblet arrays

    Science.gov (United States)

    Wilkinson, S. P.; Lazos, B. S.

    1987-01-01

    An experimental study of stream wise, near-wall, thin-element riblet arrays under a turbulent boundary layer has been conducted in low-speed air. Hot-wire data show that a single, isolated thin-element riblet causes formation of counter-rotating vortex-pairs with a spanwise wavelength of 130 viscous lengths. Abrupt shifts in turbulence intensity magnitude and peak location are observed for streamwise riblet arrays as spanwise riblet spacing is varied. Direct drag measurements show net drag reduction (up to 8.5 percent) over a wide range of riblet spacings along with behavior at discrete non-dimensional spacings indicative of vortex activity. Overall, the data suggest that more than one drag reduction mechanism may be involved.

  19. Process improvement in laser hot wire cladding for martensitic stainless steel based on the Taguchi method

    Science.gov (United States)

    Huang, Zilin; Wang, Gang; Wei, Shaopeng; Li, Changhong; Rong, Yiming

    2016-09-01

    Laser hot wire cladding, with the prominent features of low heat input, high energy efficiency, and high precision, is widely used for remanufacturing metal parts. The cladding process, however, needs to be improved by using a quantitative method. In this work, volumetric defect ratio was proposed as the criterion to describe the integrity of forming quality for cladding layers. Laser deposition experiments with FV520B, one of martensitic stainless steels, were designed by using the Taguchi method. Four process variables, namely, laser power ( P), scanning speed ( V s), wire feed rate ( V f), and wire current ( I), were optimized based on the analysis of signal-to-noise (S/N) ratio. Metallurgic observation of cladding layer was conducted to compare the forming quality and to validate the analysis method. A stable and continuous process with the optimum parameter combination produced uniform microstructure with minimal defects and cracks, which resulted in a good metallurgical bonding interface.

  20. Measuring on-line compliance in ventilated infants using hot wire anemometry.

    Science.gov (United States)

    Baboolal, R; Kirpalani, H

    1990-10-01

    We investigated the validity of using tidal volume (VT) as measured by the neonatal volume monitor (NVM) to derive respiratory compliance. The NVM is a noninvasive device that measures VT by hot wire anemometry. The quotient of VT and the inflation pressure amplitude from the mechanical ventilator provided a measure of respiratory compliance. This was validated against the single breath occlusion technique in 15 infants (birth weight 0.9 to 4.4 kg). To ensure fully passive expiration, only paralyzed or sedated patients were studied. Only 12 of the 15 infants were analyzed because of limitations in the single breath technique. In three infants the flow-volume curves obtained were alinear, indicating inhomogeneity. In the 12 infants with acceptable single breath data, agreement between the two methods was excellent. Using the expired volume, r2 was .99. We conclude that the NVM can be used to obtain valid estimates of respiratory compliance on-line in intubated infants.

  1. Hot Wire Anemometer Turbulence Measurements in the wind Tunnel of LM Wind Power

    DEFF Research Database (Denmark)

    Fischer, Andreas

    Flow measurements were carried out in the wind tunnel of LM Wind Power A/S with a Dantec Streamline CTA system to characterize the flow turbulence. Besides the free tunnel flow with empty test section we also investigated the tunnel flow when two grids with different mesh size were introduced...... downstream of the nozzle contraction. We used two different hot wire probes: a dual sensor miniature wire probe (Dantec 55P61) and a triple sensor fiber film probe (Dantec 55R91). The turbulence intensity measured with the dual sensor probe in the empty tunnel section was significantly lower than the one...... measured with the triple sensor probe. The turbulence intensity as well as the mean flow velocity downstream of the grids were not homogeneous in space. The grid with the finer mesh size created higher turbulence intensity. For both grids we found a functional form of the power spectral density...

  2. Calibration and Measurement in Turbulence Research by the Hot-Wire Method

    Science.gov (United States)

    Kovasznay, Kaszlo

    1947-01-01

    The problem of turbulence in aerodynamics is at present being attacked both theoretically and experimentally. In view of the fact however that purely theoretical considerations have not thus far led to satisfactory results the experimental treatment of the problem is of great importance. Among the different measuring procedures the hot wire methods are so far recognized as the most suitable for investigating the turbulence structure. The several disadvantages of these methods however, in particular those arising from the temperature lag of the wire can greatly impair the measurements and may easily render questionable the entire value of the experiment. The name turbulence is applied to that flow condition in which at any point of the stream the magnitude and direction of the velocity fluctuate arbitrarily about a well definable mean value. This fluctuation imparts a certain whirling characteristic to the flow.

  3. Measurement of the Thermal-Conductivity Coefficient of Nanofluids by the Hot-Wire Method

    Science.gov (United States)

    Minakov, A. V.; Rudyak, V. Ya.; Guzei, D. V.; Pryazhnikov, M. I.; Lobasov, A. S.

    2015-01-01

    In this work, the authors present results of adaptation and testing of the hot-wire method for determination for the thermal-conductivity coefficient of nanofluids. A mathematical model of heat transfer with allowance for free convection has been constructed to elucidate the parameters of an experimental setup and the range of its applicability. The experimental procedure has been tested on measurements of the thermal conductivities of water and ethylene glycol. The thermal-conductivity coefficient of a nanofluid has been measured at room temperature. The nanofluid under study was prepared on the basis of ethylene glycol and alumina nanoparticles. The concentrations of the nanoparticles ranged from 0.5% to 2% by volume. Good agreement has been obtained between the measured values of the thermal-conductivity coefficient and the data of other authors.

  4. Computational aspects of hot-wire identification of thermal conductivity and diffusivity under high temperature

    Science.gov (United States)

    Vala, Jiří; Jarošová, Petra

    2016-07-01

    Development of advanced materials resistant to high temperature, needed namely for the design of heat storage for low-energy and passive buildings, requires simple, inexpensive and reliable methods of identification of their temperature-sensitive thermal conductivity and diffusivity, covering both well-advised experimental setting and implementation of robust and effective computational algorithms. Special geometrical configurations offer a possibility of quasi-analytical evaluation of temperature development for direct problems, whereas inverse problems of simultaneous evaluation of thermal conductivity and diffusivity must be handled carefully, using some least-squares (minimum variance) arguments. This paper demonstrates the proper mathematical and computational approach to such model problem, thanks to the radial symmetry of hot-wire measurements, including its numerical implementation.

  5. Real-time monitoring of laser hot-wire cladding of Inconel 625

    Science.gov (United States)

    Liu, Shuang; Liu, Wei; Harooni, Masoud; Ma, Junjie; Kovacevic, Radovan

    2014-10-01

    Laser hot-wire cladding (LHWC), characterized by resistance heating of the wire, largely increases the productivity and saves the laser energy. However, the main issue of applying this method is the occurrence of arcing which causes spatters and affects the stability of the process. In this study, an optical spectrometer was used for real-time monitoring of the LHWC process. The corresponding plasma intensity was analyzed under various operating conditions. The electron temperature of the plasma was calculated for elements of nickel and chromium that mainly comprised the plasma plume. There was a correlation between the electron temperature and the stability of the process. The characteristics of the resulted clad were also investigated by measuring the dilution, hardness and microstructure.

  6. A Thermal Analysis of a Hot-Wire Probe for Icing Applications

    Science.gov (United States)

    Struk, Peter M.; Rigby, David L.; Venkataraman, Krishna

    2014-01-01

    This paper presents a steady-state thermal model of a hot-wire instrument applicable to atmospheric measurement of water content in clouds. In this application, the power required to maintain the wire at a given temperature is used to deduce the water content of the cloud. The model considers electrical resistive heating, axial conduction, convection to the flow, radiation to the surroundings, as well as energy loss due to the heating, melting, and evaporation of impinging liquid and or ice. All of these parameters can be varied axially along the wire. The model further introduces a parameter called the evaporation potential which locally gauges the maximum fraction of incoming water that evaporates. The primary outputs of the model are the steady-state power required to maintain a spatially-average constant temperature as well as the variation of that temperature and other parameters along the wire. The model is used to understand the sensitivity of the hot-wire performance to various flow and boundary conditions including a detailed comparison of dry air and wet (i.e. cloud-on) conditions. The steady-state power values are compared to experimental results from a Science Engineering Associates (SEA) Multi-Element probe, a commonly used water-content measurement instrument. The model results show good agreement with experiment for both dry and cloud-on conditions with liquid water content. For ice, the experimental measurements under read the actual water content due to incomplete evaporation and splashing. Model results, which account for incomplete evaporation, are still higher than experimental results where the discrepancy is attributed to splashing mass-loss which is not accounted in the model.

  7. Kinetics of low pressure CVD growth of SiO2 on InP and Si

    Science.gov (United States)

    Iyer, R.; Lile, D. L.

    1988-01-01

    The kinetics of low pressure CVD growth of SiO2 from SiH4 and O2 has been investigated for the case of an indirect (remote) plasma process. Homogeneous (gas phase) and heterogeneous operating ranges have been experimentally identified. The process was shown to be consistent within the heterogeneous surface-reaction dominated range of operation. A kinetic rate equation is given for growth at 14 W RF power input and 400 mtorr total pressure on both InP and Si substrates. The process exhibits an activation energy of 8.4 + or - 0.6 kcal/mol.

  8. Extension of the lifetime of tantalum filaments in the hot-wire (Cat) 3 Chemical Vapor Deposition process

    CSIR Research Space (South Africa)

    Knoesen, D

    2008-01-01

    Full Text Available One of the prime components of a hot-wire (Cat) Chemical Vapor Deposition system is the filament used to pyro-catalytically crack the gases like silane. Burnt out tantalum filaments were studied to determine the possible improvement of lifetime...

  9. Investigation of thermal and hot-wire chemical vapor deposition copper thin films on TiN substrates using CupraSelect as precursor.

    Science.gov (United States)

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    Copper films were deposited on oxidized Si substrates covered with TiN using a novel chemical vapor deposition reactor in which reactions were assisted by a heated tungsten filament (hot-wire CVD, HWCVD). Liquid at room temperature hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) was directly injected into the reactor with the aid of a direct-liquid injection (DLI) system using N2 as carrier gas. The deposition rates of HWCVD Cu films obtained on TiN covered substrates were found to increase with filament temperature (65 and 170 degrees C were tested). The resistivities of HWCVD Cu films were found to be higher than for thermally grown films due to the possible presence of impurities into the Cu films from the incomplete dissociation of the precursor and W impurities caused by the presence of the filament. For HWCVD films grown at a filament temperature of 170 degrees C, smaller grains are formed than at 65 degrees C as shown from the taken SEM micrographs. XRD diffractograms taken on Cu films deposited on TiN could not reveal the presence of W compounds originating from the filament because the relative peak was masked by the TiN [112] peak.

  10. Surface morphology, growth rate and quality of diamond films synthesized in hot filament CVD system under various methane concentrations

    Science.gov (United States)

    Ali, M.; Ürgen, M.

    2011-08-01

    Hot filament chemical vapor deposition (CVD) technique has been used to deposit diamond films on silicon substrate. In the present study, diamond films were grown at various vol.% CH 4 in H 2 from 0.5% to 3.5%, at substrate temperature and pressure of 850 °C and 80 torr, respectively. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were employed to analyze the properties of deposited films. The formation of methyl radicals as a function of vol.% CH 4 not only changes film morphology but also increase film growth rate. At low, intermediate and high vol.% CH 4, cluster, faceted cubes and pyramidal features growth, were dominant. By increasing vol.% CH 4 from 0.5% to 3.5%, as the growth rate improved from ˜0.25 μm/h to ˜2.0 μm/h. Raman studies features revealed high purity diamond films at intermediate range of vol.% CH 4 and grain density increased by increasing CH 4 concentration. The present study represents experimentally surface morphology, growth rate and quality of diamond films grown in hot filament CVD system at various CH 4 concentrations.

  11. Atomic scale KMC simulation of {100} oriented CVD diamond film growth under low substrate temperature-Part II Simulation of CVD diamond film growth in C-H system and in Cl-containing systems

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The growth of {100}-oriented CVD diamond film under two modifications of J-B-H model at low substrate temperatures was simulated by using a revised KMC method at atomic scale. The results were compared both in Cl-containing systems and in C-H system as follows: (1) Substrate temperature can produce an important effect both on film deposition rate and on surface roughness; (2) Aomic Cl takes an active role for the growth of diamond film at low temperatures; (3) {100}-oriented diamond film cannot deposit under single carbon insertion mechanism, which disagrees with the predictions before; (4) The explanation of the exact role of atomic Cl is not provided in the simulation results.

  12. Room Temperature Growth of Hydrogenated Amorphous Silicon Films by Dielectric Barrier Discharge Enhanced CVD

    Institute of Scientific and Technical Information of China (English)

    GUO Yu; ZHANG Xiwen; HAN Gaorong

    2007-01-01

    Hydrogenated amorphous silicon (a-Si:H) films were deposited on Si (100) and glass substrates by dielectric barrier discharge enhanced chemical vapour deposition (DBD-CVD)in (SiH4+H2) atmosphere at room temperature.Results of the thickness measurement,SEM (scanning electron microscope),Raman,and FTIR (Fourier transform infrared spectroscopy) show that with the increase in the applied peak voltage,the deposition rate and network order of the films increase,and the hydrogen bonding configurations mainly in di-hydrogen (Si-H2) and poly hydrogen (SiH2)n are introduced into the films.The UV-visible transmission spectra show that with the decrease in Sill4/ (SiH4+H2) the thin films'band gap shifts from 1.92 eV to 2.17 eV.These experimental results are in agreement with the theoretic analysis of the DBD discharge.The deposition of a-Si:H films by the DBD-CVD method as reported here for the first time is attractive because it allows fast deposition of a-Si:H films on large-area low-melting-point substrates and requires only a low cost of production without additional heating or pumping equipment.

  13. Velocity derivative skewness in isotropic turbulence and its measurement with hot wires

    Energy Technology Data Exchange (ETDEWEB)

    Burattini, Paolo [Universite Libre de Bruxelles, Physique Statistique et des Plasmas, Brussels (Belgium); University of Newcastle, Discipline of Mechanical Engineering, Newcastle, NSW (Australia); Lavoie, Philippe [Imperial College London, Department of Aeronautics, London (United Kingdom); Antonia, Robert A. [University of Newcastle, Discipline of Mechanical Engineering, Newcastle, NSW (Australia)

    2008-09-15

    We investigate the effect of the hot wire resolution on the measurement of the velocity derivative skewness in homogeneous isotropic turbulence. Single- and cross-wire configurations (with different lengths and separations of the wires, and temporal sampling resolution) are considered. Predictions of the attenuation on the basis of a model for the energy spectrum are compared to experimental and numerical data in grid and box turbulence, respectively. It is shown that the model-based correction is accurate for the single wire but not for the cross-wire. In the latter case, the effect of the separation between the wires is opposite to that found in the experiments and simulations. Moreover, the attenuation predicted by the numerical data is in good agreement with that observed in the experiment. For both probe configurations, the sampling resolution has a sizeable attenuation effect, but, for the X-probe, the impact of the separation between the wires is more important. In both cases, the length of the wires has only a minor effect, in the non-dimensional range of wire length investigated. Finally, the present experimental data support the conclusion that the skewness is constant with the Reynolds number, in agreement with Kolmogorov's 41 theory. (orig.)

  14. Onset temperatures in hot wire ignition of AN-based emulsions

    Energy Technology Data Exchange (ETDEWEB)

    Chan, S.K. [Orica Canada Inc., Brownsburg-Chatham, PQ (Canada); Turcotte, R. [Natural Resources Canada, Ottawa, ON (Canada). Canadian Explosives Research Laboratory

    2009-02-15

    The minimum burning pressure (MBP) for commercial ammonium nitrate (AN)-based explosives is widely used as a hazard assessment method. In this study, hot wire ignition experiments were conducted on 5 different AN emulsion formulations at 3 different ignition currents and initial pressures above and below the MBP of each respective formula. Results from the study were then used to model heat transfer and vaporization, dissociation, and decomposition rates. An energy balance model was used to predict the onset temperature at which the wire temperature deviated from the inert heating curve. The study showed that wire temperature cannot be used to predict the ignition point of the AN-based explosive. It was concluded that comprehensive models for chemical reactions and heat feedback from the high temperature end of the reaction zone in the combustion front are needed in addition to phase change energy models in order to accurately predict onset temperatures prior to the ignition of AN-based emulsions. 16 refs., 10 figs.

  15. HOT WIRE MEASUREMENT OF TURBULENT BOUNDARY LAYER ON A FILM COOLING PLATE WITH DIFFUSION HOLES

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This study experimentally investigated the film cooling flowfield of a single row of diffusion holes, from which the secondary air flow was injected into a turbulent boundary layer with zero pressure gradient on a flat plate. Circular-shaped holes were also tested as a basis for comparison. All the holes were inclined downstream at 35° with respect to the surface and the lateral spacing between the holes was 3 diameters of the hole. The mainstream velocity was maintained at 17 m/s and the Reynolds number based on the injection hole diameter was almost 11000. The density ratio of the jet to mainstream was 1.0, and the jet-to-mainstream velocity ratios M were 0.5 and 1.5. Normal-type and X-type hot wire anemometries were used to measure the streamwise mean velocity and its components, the normal and shear turbulent Reynolds stress components at the locations from the backward edge of the injection hole to 25 diameters downstream.

  16. Formation quality optimization of laser hot wire cladding for repairing martensite precipitation hardening stainless steel

    Science.gov (United States)

    Wen, Peng; Feng, Zhenhua; Zheng, Shiqing

    2015-01-01

    Laser cladding is an advantaged repairing technology due to its low heat input and high flexibility. With preheating wire by resistance heat, laser hot wire cladding shows better process stability and higher deposition efficiency compared to laser cold wire/powder cladding. Multi-pass layer were cladded on the surface of martensite precipitation hardening stainless steel FV520B by fiber laser with ER410NiMo wire. Wire feed rate and preheat current were optimized to obtain stable wire transfer, which guaranteed good formation quality of single pass cladding. Response surface methodology (RSM) was used to optimize processing parameters and predict formation quality of multi-pass cladding. Laser power P, scanning speed Vs, wire feed rate Vf and overlap ratio η were selected as the input variables, while flatness ratio, dilution and incomplete fusion value as the responses. Optimal clad layer with flat surface, low dilution and no incomplete fusion was obtained by appropriately reducing Vf, and increasing P, Vs and η. No defect like pore or crack was found. The tensile strength and impact toughness of the clad layer is respectively 96% and 86% of those of the substrate. The clad layer showed nonuniform microstructure and was divided into quenched areas with coarse lath martensite and tempered areas with tempered martensite due to different thermal cycles in adjacent areas. The tempered areas showed similar hardness to the substrate.

  17. A high-performance constant-temperature hot-wire anemometer

    Science.gov (United States)

    Watmuff, Jonathan H.

    1994-08-01

    A high-performance constant-temperature hot-wire anemometer has been designed based on a system theory analysis that can be extended to arbitrary order. A motivating factor behind the design was to achieve the highest possible frequency response while ensuring overall system stability. Based on these considerations, the design of the circuit and the selection of components is discussed in depth. Basic operating instructions are included in an operator's guide. The analysis is used to identify operating modes, observed in all anemometers, that are misleading in the sense that the operator can be deceived by interpreting an erroneous frequency response. Unlike other anemometers, this instrument provides front panel access to all the circuit parameters which affect system stability and frequency response. Instructions are given on how to identify and avoid these rather subtle and undesirable operating modes by appropriate adjustment of the controls. Details, such as fabrication drawings and a parts list, are provided to enable others to construct the instrument.

  18. Short hot wire technique for measuring thermal conductivity and thermal diffusivity of various materials

    Science.gov (United States)

    Xie, Huaqing; Gu, Hua; Fujii, Motoo; Zhang, Xing

    2006-01-01

    A transient short hot wire technique (SHWT) is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of various materials such as liquids, gases or powders. A metal wire with (or without) insulation coating serves both as a heating unit and as an electrical resistance thermometer and the wire is calibrated using water and toluene with known thermophysical properties. This SHWT includes correlation of the experimental data with numerically simulated values based on a two-dimensional heat-conduction model. For the measurements with proportional relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are obtained from the slope and the intercept of the measured temperature rise and those of calculated non-dimensional temperature rise by including the heat flux and the properties of the wire. For the measurements with nonlinear relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are extracted from a curve fitting method by using the downhill simplex method to match the experimental data and the numerical values. This technique is applied here using air as a testing sample. The effect of natural convection is investigated and the accuracy of this measurement is estimated to be 2% for thermal conductivity and 7% for thermal diffusivity.

  19. Response of the Nevzorov hot wire probe in Arctic clouds dominated by very large droplet sizes

    Directory of Open Access Journals (Sweden)

    A. Schwarzenboeck

    2009-05-01

    Full Text Available During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC and total condensed water content (TWC in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.

  20. Hydrogenated Nanocrystalline Silicon Thin Films Prepared by Hot-Wire Method with Varied Process Pressure

    Directory of Open Access Journals (Sweden)

    V. S. Waman

    2011-01-01

    Full Text Available Hydrogenated nanocrystalline silicon films were prepared by hot-wire method at low substrate temperature (200∘C without hydrogen dilution of silane (SiH4. A variety of techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD, Fourier transform infrared (FTIR spectroscopy, atomic force microscopy (AFM, and UV-visible (UV-Vis spectroscopy, were used to characterize these films for structural and optical properties. Films are grown at reasonably high deposition rates (>15 Å/s, which are very much appreciated for the fabrication of cost effective devices. Different crystalline fractions (from 2.5% to 63% and crystallite size (3.6–6.0 nm can be achieved by controlling the process pressure. It is observed that with increase in process pressure, the hydrogen bonding in the films shifts from Si–H to Si–H2 and (Si–H2n complexes. The band gaps of the films are found in the range 1.83–2.11 eV, whereas the hydrogen content remains <9 at.% over the entire range of process pressure studied. The ease of depositing films with tunable band gap is useful for fabrication of tandem solar cells. A correlation between structural and optical properties has been found and discussed in detail.

  1. Hot-wire substoichiometric tungsten oxide films deposited in hydrogen environment with n-type conductivity

    Science.gov (United States)

    Kostis, I.; Michalas, L.; Vasilopoulou, M.; Konofaos, N.; Papaioannou, G.; Iliadis, A. A.; Kennou, S.; Giannakopoulos, K.; Papadimitropoulos, G.; Davazoglou, D.

    2012-11-01

    Substoichiometric tungsten oxide nanostructured films were synthesized by a hot-wire deposition technique in hydrogen-rich environment and characterized for their structural and electrical properties. A semiconducting behaviour was identified, allowing n-type conductivity even at room temperature which is an important result since it is well known that fully stoichiometric tungsten trioxide is nearly an insulator. Current-voltage characteristics for various temperatures were measured for tungsten oxide/Si heterostructures and analysed using proper modelling. As a result, the conduction mechanism inside the films was identified and found to be of a dual nature, with variable range hopping being dominant at near room temperatures. The saturation current was found to be thermally activated and the activation energy was calculated at 0.40 eV and the grain boundaries barrier at 150 meV. From Hall measurements it was also revealed that the dominant carriers are electrons and a carrier concentration of about 1014 cm-3 was estimated.

  2. An economical dual hot-wire liquid water flux probe design

    Science.gov (United States)

    LeBoeuf, Richard L.; de Dios Rivera, Juan; de la Jara, Emilio

    2015-01-01

    The velocity, liquid water content (LWC) and their product, the liquid water flux (LWF), are of interest for research in environmental sciences, fog collection, and free-space communications. This paper provides a design for an economical dual hot-wire LWF probe, which enables the ground-based measurement of velocity, LWC and LWF. The design accounts for the droplet deposition efficiency, prong conduction, saturation and sensitivity. The operating mode and probe configurations are described. Two 125 μm diameter, 5 cm long platinum wires having 2 and 50 °C wire to air temperature offsets would yield measurement uncertainties of about 6% for velocity and from 8 to 22% for the LWC and from 2 to 17% for the LWF given velocities in the range 2 to 8 m/s and LWC in the range 0.2 to 0.8 g/m3. The lower uncertainties correspond to higher LWF, which is of particular interest in fog collection projects. The recurring costs of the instrument's mechanical and electrical components would be about US 150 per unit. Therefore, the design presented herein is a viable option for large-scale sensor networks.

  3. Removal of SU-8 resists using hydrogen radicals generated by tungsten hot-wire catalyzer

    Science.gov (United States)

    Kono, Akihiko; Arai, Yu; Goto, Yousuke; Horibe, Hideo

    2012-03-01

    We investigated removal of chemically amplified negative-tone i-line resist SU-8 using hydrogen radicals, which was generated by the catalytic decomposition of H2/N2 mixed gas (H2:N2 = 10:90vol.%) using tungsten hot-wire catalyzer. SU-8 with exposure dose from 7 (Dg100×0.5) to 280mJ/cm2 (Dg100×20) were removed by hydrogen radicals without a residual layer. When the distance between the catalyzer and the substrate was 100mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 50°C, removal rate of SU-8 was 0.17μm/min independent of exposure dose to the SU-8. Finally, we obtained high removal rate for SU-8 (exposure dose = 14mJ/cm2 (Dg100)) of approximately 4μm/min when the distance between the catalyzer and the substrate was 20mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 165°C.

  4. A high-performance constant-temperature hot-wire anemometer

    Science.gov (United States)

    Watmuff, Jonathan H.

    1994-01-01

    A high-performance constant-temperature hot-wire anemometer has been designed based on a system theory analysis that can be extended to arbitrary order. A motivating factor behind the design was to achieve the highest possible frequency response while ensuring overall system stability. Based on these considerations, the design of the circuit and the selection of components is discussed in depth. Basic operating instructions are included in an operator's guide. The analysis is used to identify operating modes, observed in all anemometers, that are misleading in the sense that the operator can be deceived by interpreting an erroneous frequency response. Unlike other anemometers, this instrument provides front panel access to all the circuit parameters which affect system stability and frequency response. Instructions are given on how to identify and avoid these rather subtle and undesirable operating modes by appropriate adjustment of the controls. Details, such as fabrication drawings and a parts list, are provided to enable others to construct the instrument.

  5. Fiber optic hot-wire flowmeter based on a metallic coated hybrid long period grating/fiber Bragg grating structure.

    Science.gov (United States)

    Caldas, Paulo; Jorge, Pedro A S; Rego, Gaspar; Frazão, Orlando; Santos, José Luís; Ferreira, Luís Alberto; Araújo, Francisco

    2011-06-10

    In this work an all-optical hot-wire flowmeter based on a silver coated fiber combining a long period grating and a fiber Bragg grating (FBG) structure is proposed. Light from a pump laser at 1480  nm propagating down the fiber is coupled by the long period grating into the fiber cladding and is absorbed by the silver coating deposited on the fiber surface over the Bragg grating structure. This absorption acts like a hot wire raising the fiber temperature locally, which is effectively detected by the FBG resonance shift. The temperature increase depends on the flow speed of the surrounding air, which has the effect of cooling the fiber. It is demonstrated that the Bragg wavelength shift can be related to the flow speed. A flow speed resolution of 0.08  m/s is achieved using this new configuration.

  6. Air flow transmitter based on hot wire%热线式空气流量变送器

    Institute of Scientific and Technical Information of China (English)

    宋彦峥; 亢春梅; 等

    2001-01-01

    设计并研制一种热线式空气流量变送器,其准确度达到±1% ,并具有极好的响应速度。%A kind of hot-wire style air flow transmitter has been designed and manufactured.Its accuracy is±1%,and has excellent respond speed.

  7. Variable temperature hot wire anemometry applied to the joint analysis of the velocity and temperature fluctuations in a mixing layer

    OpenAIRE

    Ndoye, M.; Delville, J.; Dorignac, E.; Arroyo, G.

    2011-01-01

    International audience; Our study provides a detailed description of the thermal mixing process in an anisothermal mixing layer. Velocity and temperature are simultaneously measured at the same point by using a new hot wire anemometer. This anemometer implements the multiple overheat principle, associated with a non linear Levenberg-Marquardt signal processing. These simultaneous measurements allowed an analysis based on conditional Probability Density Functions (PDFs), joint PDFs and a quadr...

  8. The dependence of Nusselt number on Reynolds number for a hot-wire sensor in supercritical CO2 flow

    Science.gov (United States)

    Vukoslavcevic, Petar; Wallace, James

    2005-11-01

    An analysis of the heat transfer mechanism around a hot-wire sensor in superctitical CO2 flow has been performed, and the dependence of the Nusselt number (Nu) on the Reynolds number (Re) has been determined. A special, closed flow loop, capable of inducing variable speed flow at different pressures and temperatures in the ranges of 0.15-2 m/s, 15-70^oC and 1-100 bar, has been used to create a supercritical CO2 flow around a hot-wire sensor operated in the constant temperature mode. The Nu and Re numbers were determined based on the known heat convected from the sensor, the flow speed and the sensor temperature and dimensions. The experiment was performed along a line of constant 80 bar pressure in the temperature range of 25-65^oC. It was found that, at a given pressure and temperature, the relation Nu=F(Re) has the classical form Nu=M+NRe^n, with the parameters M and N being functions of pressure and temperature. The dependence of these parameters on temperature was analyzed, and the most convenient reference temperature was chosen. In contrast to the operation of hot-wires in air and water, the dependence of the parameters M and N on the Prandtl number can result in nonunique solutions.

  9. Improvement of the Crystallinity of Silicon Films Deposited by Hot-Wire Chemical Vapor Deposition with Negative Substrate Bias

    Science.gov (United States)

    Zhang, Lei; Shen, Honglie; You, Jiayi

    2013-08-01

    We have investigated the effect of negative substrate bias on microcrystalline silicon films deposited on glass and stainless steel by hot-wire chemical vapor deposition (HWCVD) to gain insight into the effect of negative substrate bias on crystallization. Structural characterization of the silicon films was performed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. It was found that the crystallinity of the films is obviously improved by applying the substrate bias, especially for films on stainless steel. At hot-wire temperature of 1800°C and negative substrate bias of -800 V, grain size as large as 200 nm was obtained on stainless-steel substrate with crystalline fraction 9% higher than that of films deposited on glass and 15% higher than that of films deposited without substrate bias. It is deduced that the improvement of the crystallinity is mainly related to the accelerated electrons emitted from the hot wires. The differences in this improvement between different substrates are caused by the different electrical potential of the substrates. A solar cell fabricated by HWCVD with -800 V substrate bias is demonstrated, showing an obviously higher conversion efficiency than that without substrate bias.

  10. A novel data reduction technique for single slanted hot-wire measurements used to study incompressible compressor tip leakage flows

    Science.gov (United States)

    Berdanier, Reid A.; Key, Nicole L.

    2016-03-01

    The single slanted hot-wire technique has been used extensively as a method for measuring three velocity components in turbomachinery applications. The cross-flow orientation of probes with respect to the mean flow in rotating machinery results in detrimental prong interference effects when using multi-wire probes. As a result, the single slanted hot-wire technique is often preferred. Typical data reduction techniques solve a set of nonlinear equations determined by curve fits to calibration data. A new method is proposed which utilizes a look-up table method applied to a simulated triple-wire sensor with application to turbomachinery environments having subsonic, incompressible flows. Specific discussion regarding corrections for temperature and density changes present in a multistage compressor application is included, and additional consideration is given to the experimental error which accompanies each data reduction process. Hot-wire data collected from a three-stage research compressor with two rotor tip clearances are used to compare the look-up table technique with the traditional nonlinear equation method. The look-up table approach yields velocity errors of less than 5 % for test conditions deviating by more than 20 °C from calibration conditions (on par with the nonlinear solver method), while requiring less than 10 % of the computational processing time.

  11. Structural evolution of a Ta-filament during hot-wire chemical vapour deposition of Silicon investigated by electron backscatter diffraction

    CSIR Research Space (South Africa)

    Oliphant, CJ

    2012-03-01

    Full Text Available In this study we investigate the structural changes of a burnt-out tantalum filament that was operated at typical hydrogenated nanocrystalline silicon synthesis conditions in our hot-wire chemical vapour deposition chamber. Scanning electron...

  12. Growth of one-dimensional Si/SiGe heterostructures by thermal CVD

    Energy Technology Data Exchange (ETDEWEB)

    Mouchet, Celine; Latu-Romain, Laurence; Rouviere, Emmanuelle; Celle, Caroline; Simonato, Jean-Pierre [CEA, LITEN, DTNM, LCH, 38054 Grenoble (France); Cayron, Cyril [CEA, LITEN, DTH, Grenoble Electron Microscopy at Minatec, 38054 Grenoble (France)], E-mail: jean-pierre.simonato@cea.fr

    2008-08-20

    The first results on a simple new process for the direct fabrication of one-dimensional superlattices using common CVD chambers are presented. The experiments were carried out in a 200 mm industrial Centura reactor (Applied Materials). Low dimensionality and superlattices allow a significant increase in the figure of merit of thermoelectrics by controlling the transport of phonons and electrons. The monocrystalline nanowires produced according to this process are both one-dimensional and present heterostructures, with very thin layers (40 nm) of Si and SiGe. Concentrations up to 30 at.% Ge were obtained in the SiGe parts. Complementary techniques including transmission electronic microscopy (TEM), selected area electron diffraction (SAED), energy dispersive x-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM) in bright field and high angle annular dark field (HAADF STEM), and energy-filtered transmission electron microscopy (EF-TEM) were used to characterize the nanoheterostructures.

  13. Influence of bowl shaped substrate holder on growth of polymeric DLC film in a microwave plasma CVD reactor

    Indian Academy of Sciences (India)

    Sambita Sahoo; S K Pradhan; Venkateswarlu Bhavanasi; Swati S Pradhan; S N Sarangi; P K Barhai

    2012-12-01

    The properties of diamond like carbon (DLC) films grown in modified microwave plasma CVD reactor is presented in this paper. By using bowl shaped steel substrate holder in a MW plasma CVD reactor (without ECR), films have been grown at relatively high pressure (20Torr) and at low temperature (without heating). The input microwave power was about 300W. Earlier, under the same growth conditions, no deposition was achieved when flat molybdenum/steel substrate holders were used. In this study, two different designs of bowl shaped steel substrate holder at different bias have been experimented. Raman spectra confirm the DLC characteristics of the films. FTIR results indicate that the carbon is bonded in the 3 form with hydrogen, and this characteristic is more pronounced when smaller holder is used. UV-visible spectra show high visible transmittance (∼85%) for films grown in both the holders. The nanoindentation hardness of the films have a wide range, about 4–16GPa. Field emission scanning electron microscope (FESEM) images reveal that the films have featureless and smooth surface morphology. These films are polymeric in nature with moderately high hardness, which may be useful as anti-scratch and anti-corrosive coatings.

  14. Airflow Measurement of the Car HVAC Unit Using Hot-wire Anemometry

    Directory of Open Access Journals (Sweden)

    Fojtlín Miloš

    2016-01-01

    Full Text Available Thermal environment in a vehicular cabin significantly influence drivers’ fatigue and passengers’ thermal comfort. This environment is traditionally managed by HVAC cabin system that distributes air and modifies its properties. In order to simulate cabin thermal behaviour, amount of the air led through car vents must be determined. The aim of this study was to develop methodology to measure airflow from the vents, and consequently calculate corresponding air distribution coefficients. Three climatic cases were selected to match European winter, summer, and spring / fall conditions. Experiments were conducted on a test vehicle in a climatic chamber. The car HVAC system was set to automatic control mode, and the measurements were executed after the system stabilisation—each case was independently measured three times. To be able to evaluate precision of the method, the airflow was determined at the system inlet (HVAC suction and outlet (each vent, and the total airflow values were compared. The airflow was calculated by determining a mean value of the air velocity multiplied by an area of inlet / outlet cross-section. Hot-wire anemometry was involved to measure the air velocity. Regarding the summer case, total airflow entering the cabin was around 57 l s-1 with 60 % of the air entering the cabin through dashboard vents; no air was supplied to the feet compartment. The remaining cases had the same total airflow of around 42 l s-1, and the air distribution was focused mainly on feet and windows. The inlet and outlet airflow values show a good match with a maximum mass differential of 8.3 %.

  15. Airflow Measurement of the Car HVAC Unit Using Hot-wire Anemometry

    Science.gov (United States)

    Fojtlín, Miloš; Planka, Michal; Fišer, Jan; Pokorný, Jan; Jícha, Miroslav

    2016-03-01

    Thermal environment in a vehicular cabin significantly influence drivers' fatigue and passengers' thermal comfort. This environment is traditionally managed by HVAC cabin system that distributes air and modifies its properties. In order to simulate cabin thermal behaviour, amount of the air led through car vents must be determined. The aim of this study was to develop methodology to measure airflow from the vents, and consequently calculate corresponding air distribution coefficients. Three climatic cases were selected to match European winter, summer, and spring / fall conditions. Experiments were conducted on a test vehicle in a climatic chamber. The car HVAC system was set to automatic control mode, and the measurements were executed after the system stabilisation—each case was independently measured three times. To be able to evaluate precision of the method, the airflow was determined at the system inlet (HVAC suction) and outlet (each vent), and the total airflow values were compared. The airflow was calculated by determining a mean value of the air velocity multiplied by an area of inlet / outlet cross-section. Hot-wire anemometry was involved to measure the air velocity. Regarding the summer case, total airflow entering the cabin was around 57 l s-1 with 60 % of the air entering the cabin through dashboard vents; no air was supplied to the feet compartment. The remaining cases had the same total airflow of around 42 l s-1, and the air distribution was focused mainly on feet and windows. The inlet and outlet airflow values show a good match with a maximum mass differential of 8.3 %.

  16. A hot-wire method based thermal conductivity measurement apparatus for teaching purposes

    Science.gov (United States)

    Alvarado, S.; Marín, E.; Juárez, A. G.; Calderón, A.; Ivanov, R.

    2012-07-01

    The implementation of an automated system based on the hot-wire technique is described for the measurement of the thermal conductivity of liquids using equipment easily available in modern physics laboratories at high schools and universities (basically a precision current source and a voltage meter, a data acquisition card, a personal computer and a high purity platinum wire). The wire, which is immersed in the investigated sample, is heated by passing a constant electrical current through it, and its temperature evolution, ΔT, is measured as a function of time, t, for several values of the current. A straightforward methodology is then used for data processing in order to obtain the liquid thermal conductivity. The start point is the well known linear relationship between ΔT and ln(t) predicted for long heating times by a model based on a solution of the heat conduction equation for an infinite lineal heat source embedded in an infinite medium into which heat is conducted without convective and radiative heat losses. A criterion is used to verify that the selected linear region is the one that matches the conditions imposed by the theoretical model. As a consequence the method involves least-squares fits in linear, semi-logarithmic (semi-log) and log-log graphs, so that it becomes attractive not only to teach about heat transfer and thermal properties measurement techniques, but also as a good exercise for students of undergraduate courses of physics and engineering learning about these kinds of mathematical functional relationships between variables. The functionality of the experiment was demonstrated by measuring the thermal conductivity in samples of liquids with well known thermal properties.

  17. ROBUST hot wire probe efficiency for total water content measurements in glaciated conditions

    Science.gov (United States)

    Leroy, Delphine; Lilie, Lyle; Weber, Marc; Schwarzenboeck, Alfons; Strapp, J. Walter

    2017-04-01

    During the two High Altitude Ice Crystals (HAIC, Dezitter et al. 2013)/High Ice Water Content (HIWC, Strapp et al., 2016a) international flight campaigns that investigated deep convection in the tropics, the French Falcon 20 research aircraft was equipped with two different devices measuring the Total Water Content (TWC): - the IKP-2 (Isokinetic Probe, Davison et al. 2008, 2016), - and the hot wire ROBUST probe (Strapp et al. 2008; Grandin et al. 2014). The IKP-2 probe is an evaporator that has been specifically designed to measure high ice water content (Strapp et al. 2016b) with a collection efficiency near unity. It has undergone extensive performance assessment in liquid and glaciated conditions in several wind tunnels. The Robust probe was initially developed by Science Engineering Associates to estimate high ice water content in a high speed wind tunnel, in harsh conditions where other hot-wires had been observed to suffer failures. It was known at the outset that, like other hot-wire TWC probes, it would measure only a quasi-constant fraction of the true ice water content. Early wind tunnel and flight experience with the ROBUST probe revealed that this fraction was the order of 40% for ice crystals. During the HAIC/HIWC campaigns (Leroy et al. 2016, 2017), supercooled liquid water conditions were documented according to a detailed analysis of a Rosemount Ice detector (RICE) and a Cloud Droplet Probe (CDP) measurements, and were found to be rare. Thus, the HAIC/HIWC dataset represents a unique opportunity to study in more detail the ROBUST efficiency in glaciated conditions, using the IKP-2 values as a comparative reference. Comparison of IKP-2 and ROBUST measurements will show that the ROBUST behavior differs between low (below 1.5 g/m3) and high (above 2 g/m3) ice content conditions and is also sensitive to temperature. The sensitivity of the ROBUST collection efficiency to ice particles size could also be explored as optical imaging probes were part of the

  18. Highly conducting phosphorous doped Nc-Si:H thin films deposited at high deposition rate by hot-wire chemical vapor deposition method.

    Science.gov (United States)

    Waman, V S; Kamble, M M; Ghosh, S S; Mayabadi, Azam; Sathe, V G; Amalnekar, D P; Pathan, H M; Jadkar, S R

    2012-11-01

    In this paper, we report the synthesis of highly conducting phosphorous doped hydrogenated nanocrystalline silicon (nc-Si:H) films at substantially low substrate temperature (200 degrees C) by hot-wire chemical vapor deposition (HW-CVD) method using pure silane (SiH4) and phosphine (PH3) gas mixture without hydrogen dilution. Structural, optical and electrical properties of these films were investigated as a function of PH3 gas-phase ratio. The characterization of these films by low-angle X-ray diffraction, Raman spectroscopy and atomic force microscopy revealed that, the incorporation of phosphorous in nc-Si:H induces an amorphization in the nc-Si:H film structure. Fourier transform infrared spectroscopy analysis indicates that hydrogen predominately incorporated in phosphorous doped n-type nc-Si:H films mainly in di-hydrogen species (Si-H2) and poly-hydrogen (Si-H2)n bonded species signifying that the films become porous, and micro-void rich. We have observed high band gap (1.97-2.37 eV) in the films, though the hydrogen content is low (< 1.4 at.%) over the entire range of PH3 gas-phase ratio studied. Under the optimum deposition conditions, phosphorous doped nc-Si:H films with high dark conductivity (sigma Dark -5.3 S/cm), low charge-carrier activation energy (E(act) - 132 meV) and high band gap (- 2.01 eV), low hydrogen content (- 0.74 at.%) were obtained at high deposition rate (12.9 angstroms/s).

  19. Structure and wettability property of the growth and nucleation surfaces of thermally treated freestanding CVD diamond films

    Science.gov (United States)

    Pei, Xiaoqiang; Cheng, Shaoheng; Ma, Yibo; Wu, Danfeng; Liu, Junsong; Wang, Qiliang; Yang, Yizhou; Li, Hongdong

    2015-08-01

    This paper reports the surface features and wettability properties of the (1 0 0)-textured freestanding chemical vapor deposited (CVD) diamond films after thermal exposure in air at high temperature. Thermal oxidation at proper conditions eliminates selectively nanodiamonds and non-diamond carbons in the films. The growth side of the films contains (1 0 0)-oriented micrometer-sized columns, while its nucleation side is formed of nano-sized tips. The examined wettability properties of the as-treated diamond films reveal a hydrophilicity and superhydrophilicity on the growth surface and nucleation surface, respectively, which is determined by oxygen termination and geometry structure of the surface. When the surface termination is hydrogenated, the wettability of nucleation side converted from superhydrophilicity to high hydrophobicity, while the hydrophilicity of the growth side does not change significantly. The findings open a possibility for realizing freestanding diamond films having not only novel surface structures but also multifunction applications, especially proposed on the selected growth side or nucleation side in one product.

  20. The dynamic response of a hot-wire anemometer: IV. Sine-wave voltage perturbation testing for near-wall hot-wire/film probes and the presence of low-high frequency response characteristics

    Science.gov (United States)

    Teo, C. J.; Khoo, B. C.; Teo, C. J.; Chew, Y. T.

    2001-01-01

    Experiments were performed using the electronic sine-wave voltage-perturbation test to systematically study the frequency responses of near-wall hot-wire probes subjected in turn to varying magnitudes of convective velocity and different effects of wall influence. In addition, quartz-substrate hot-film gauges with various thicknesses of quartz coating were also investigated. Results of the high cut-off frequency obtained using the sine-wave test (fsine) were found to be in fair agreement with those obtained using the square-wave test (fS) both for hot-wire and for hot-film sensors. The sine-wave test response curve exhibited a distinct bulging effect for the hot-film gauges. For the hot-wire sensors, a much weaker bulging effect was also observed. In contrast to fS and fsine, the low frequency response characteristic corresponding to the location of the bulging effect (fbulge) compared much more favourably with the dynamic frequency response (fD) obtained by Khoo et al and Chew et al using a known near-wall fluctuating flow field. Freymuth's theory for non-cylindrical hot-film sensors incorporating the Bellhouse-Schultz model was applied to predict the responses of the hot-film wall gauges when they were subjected to electronic sine-wave testing and dynamic perturbation testing under different parametric conditions. Although it is one-dimensional in nature, the model is capable of predicting most of the trends observed in the present study and previous works by Khoo et al (1998a) and Chew et al (1998a).

  1. Epitaxial Growth of beta-Silicon Carbide (SiC) on a Compliant Substrate via Chemical Vapor Deposition (CVD)

    Science.gov (United States)

    Mitchell, Sharanda L.

    1996-01-01

    Many lattice defects have been attributed to the lattice mismatch and the difference in the thermal coefficient of expansion between SiC and silicon (Si). Stacking faults, twins and antiphase boundaries are some of the lattice defects found in these SiC films. These defects may be a partial cause of the disappointing performance reported for the prototype devices fabricated from beta-SiC films. The objective of this research is to relieve some of the thermal stress due to lattice mismatch when SiC is epitaxially grown on Si. The compliant substrate is a silicon membrane 2-4 microns thick. The CVD process includes the buffer layer which is grown at 1360 C followed by a very thin epitaxial growth of SiC. Then the temperature is raised to 1500 C for the subsequent growth of SiC. Since silicon melts at 1415 C, the SiC will be grown on molten Silicon which is absorbed by a porous graphite susceptor eliminating the SiC/Si interface. We suspect that this buffer layer will yield less stressed material to help in the epitaxial growth of SiC.

  2. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    Science.gov (United States)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2-SiH4-C2H4-HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  3. Necessary Conditions for Accurate, Transient Hot-Wire Measurements of the Apparent Thermal Conductivity of Nanofluids are Seldom Satisfied

    Science.gov (United States)

    Antoniadis, Konstantinos D.; Tertsinidou, Georgia J.; Assael, Marc J.; Wakeham, William A.

    2016-08-01

    The paper considers the conditions that are necessary to secure accurate measurement of the apparent thermal conductivity of two-phase systems comprising nanoscale particles of one material suspended in a fluid phase of a different material. It is shown that instruments operating according to the transient hot-wire technique can, indeed, produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the exact geometry of the hot wire. Furthermore, it is shown that an approximate analytic solution can be employed with equal success, over the time range of 0.1 s to 1 s, provided that (a) two wires are employed, so that end effects are canceled, (b) each wire is very thin, less than 30 \\upmu m diameter, so that the line source model and the corresponding corrections are valid, (c) low values of the temperature rise, less than 4 K, are employed in order to minimize the effect of convection on the heat transfer in the time of measurement of 1 s, and (d) insulated wires are employed for measurements in electrically conducting or polar liquids to avoid current leakage or other electrical distortions. According to these criteria, a transient hot-wire instrument has been designed, constructed, and employed for the measurement of the enhancement of the thermal conductivity of water when TiO2 or multi-wall carbon nanotubes (MWCNT) are added. These new results, together with a critical evaluation of other measurements, demonstrate the importance of proper implementation of the technique.

  4. Coherent structure in the turbulent wake behind a circular cylinder 3. Flow visualization and hot wire measurements

    Science.gov (United States)

    Yamane, Ryuichiro; Oshima, Shuzo; Okubo, Masaaki; Kotani, Juzo

    1988-07-01

    In the previous papers the authors have reported that the two-dimensional Kármán vortices behind a circular cylinder are deformed until they form chains of spoon-shaped vortex couples whose spanwise scale is about 8 d, which is a new type of coherent structure. In this report experimental evidence of this structure is presented. Formation process of the structure and the turbulence in it were investigated for the wake behind a circular cylinder with Re = 2100 and 4200 by means of the flow visualization technique, simultaneous hot wire measurements, spanwise correlation measurements, construction of instantaneous velocity field by the conditional sampling method, etc.

  5. Some influences of approximate values for velocity, density and total temperature sensitivities on hot wire anemometer results

    Science.gov (United States)

    Stainback, P. C.

    1986-01-01

    There is a renewed interest in hot wire anemometry at transonic speeds. Recent results were published which indicate that at transonic speeds a heated wire is sensitive only to mass flow and total temperature, results similar to those obtained for supersonic flows. Other results were obtained to show that the sensitivity is a function of velocity, density, and total temperature, results in agreement with many of those obtained in the 1950s. An analysis of anemometry results was made to evaluate possible errors when various assumptions were made concerning the sensitivity of a heated wire to fluid flow variables.

  6. Selective growth of diamond by hot filament CVD using patterned carbon film as mask

    Institute of Scientific and Technical Information of China (English)

    HE Zhoutong; YANG Shumin; LI Qintao; ZHU Dezhang; GONG Jinlong

    2008-01-01

    Selected-area deposition (SAD) of diamond films was achieved on silicon substrates with carbon film mask by hot filament chemical vapor deposition. Needle tip scraped lines were used to grow diamond films. Scanning electron microscope (SEM) investigation demonstrates that highly selective and sharp edged diamond films were produced. The results also demonstrate that the proper substrate temperature is very important for diamond selective growth in this deposition process. Since the enhancement of diamond growth was not observed on the needle tip scraped area of Si wafer with diamond powder scratching, the selective growth was considered to be closely correlated to silicon carbide formed during carbon film deposition and the residual carbon in the scraped area.

  7. A comprehensive investigation on CVD growth thermokinetics of h-BN white graphene

    Science.gov (United States)

    Song, Xiufeng; Li, Qiguang; Ji, Jianping; Yan, Zhong; Gu, Yu; Huo, Chengxue; Zou, Yousheng; Zhi, Chunyi; Zeng, Haibo

    2016-09-01

    As an isomorph of graphene, monolayer hexagonal boron nitride (h-BN), so-called white graphene, has been in the spotlight of two-dimensional materials due to its outstanding properties. However, the growth of large and uniform white graphene monocrystalline with low density of defects is still a great challenge. Here, we present a comprehensive investigation on the growth thermokinetics of white graphene monocrystalline domains via atmospheric pressure chemical vapor deposition with the solid ammonia borane as precursors, which will be more suitable for future industrial production due to the handy process and precursor. The single domain size, coverage on substrate, and thickness of white graphene were taken as targeted parameters of products. And then, their dependences on the flow rate of carrier gas, heating temperature of ammonia borane, growth temperature and time were studied in details. Finally, after optimizing the above conditions, both white graphene monocrystalline domains as large as 80 μm2 and polycrystalline ultrathin film with coverage ratio of 95%-100% can be achieved facilely without using vacuum technique. Such white graphene products would be of great significance for the tunnel barrier for the tunneling transistor and the dielectric layers for nanocapacitor with the graphene based heterostructures.

  8. Effect of CVD Process Temperature on Activation Energy and Structural Growth of MWCNTs

    Science.gov (United States)

    Shukrullah, S.; Mohamed, N. M.; Shaharun, M. S.; Saheed, M. S. M.; Irshad, M. I.

    2016-03-01

    This study investigated the effect of process temperature and activation energy on chemical vapor deposition growth of multi-walled carbon nanotubes (MWCNTs). A vertically fluidized bed reactor was used to grow MWCNTs by catalytic decomposition of ethylene over Fe2O3/Al2O3 at the cost of very low activation energy of 19.516 kJ/mole. FESEM, TEM, and Raman spectroscopy were used to characterize the growth parameters of MWCNTs in the temperature range of 873.15 K to 1273.15 K (600 °C to 1000 °C). SAED patterns were taken to investigate the crystallinity of the grown structures. The experimental results revealed that MWCNTs grown at the optimum process temperature of 1073.15 K (800 °C) exhibited hexagonal crystal structures, narrow diameter distribution and shorter inter-layer spacing. However, the inner and outer walls of most of MWCNTs grown at the temperatures above and below the optimum were non-uniform and defective. The higher process temperatures promoted the agglomeration of the catalyst particles and decomposition of the carbon precursor, which in return increased the tube diameter, surface defects and amorphous carbon content in the product. The intensity ratio plots also predicted low crystallinity in MWCNTs grown at unoptimized process temperatures. The highest I G/ I D ratio of 1.43 was determined at 1073.15 K (800 °C), which reflects high pct yield, purity and crystalline growth of MWCNTs.

  9. A hot-wire probe for thermal measurements of nanowires and nanotubes inside a transmission electron microscope.

    Science.gov (United States)

    Dames, C; Chen, S; Harris, C T; Huang, J Y; Ren, Z F; Dresselhaus, M S; Chen, G

    2007-10-01

    A hot wire probe has been developed for use inside a transmission electron microscope to measure the thermal resistance of individual nanowires, nanotubes, and their contacts. No microfabrication is involved. The probe is made from a platinum Wollaston wire and is pretensioned to minimize the effects of thermal expansion, intrinsic thermal vibrations, and Lorentz forces. An in situ nanomanipulator is used to select a particular nanowire or nanotube for measurement, and contacts are made with liquid metal droplets or by electron-beam induced deposition. Detailed thermal analysis shows that for best sensitivity, the thermal resistance of the hot-wire probe should be four times that of the sample, but a mismatch of more than two orders of magnitude may be acceptable. Data analysis using the ratio of two ac signals reduces the experimental uncertainty. The range of detectable sample thermal resistances spans from approximately 10(3) to 10(9) KW. The probe can also be adapted for measurements of the electrical conductance and Seebeck coefficient of the same sample. The probe was used to study a multiwalled carbon nanotube with liquid Ga contacts. The measured thermal resistance of 3.3 x 10(7) KW had a noise level of approximately +/-3% and was repeatable to within +/-10% upon breaking and re-making the contact.

  10. High removal rate of cross-linked SU-8 resist using hydrogen radicals generated by tungsten hot-wire catalyzer

    Energy Technology Data Exchange (ETDEWEB)

    Kono, Akihiko, E-mail: a.kono@neptune.kanazawa-it.ac.jp [Kanazawa Institute of Technology, 7-1 Ougigaoka, Nonoichi, Ishikawa 921-8501 (Japan); Arai, Yu; Maruoka, Takeshi; Yamamoto, Masashi; Goto, Yousuke; Takahashi, Seiji; Nishiyama, Takashi [Kanazawa Institute of Technology, 7-1 Ougigaoka, Nonoichi, Ishikawa 921-8501 (Japan); Horibe, Hideo [Osaka City University, Sugimoto, Sumiyoshiku, Osaka 558-8585 (Japan)

    2014-07-01

    This paper discusses the removal of chemically amplified negative-tone i-line resist SU-8 using hydrogen radicals generated by the catalytic decomposition of H{sub 2} molecules in H{sub 2}/N{sub 2} mixed gas (H{sub 2}:N{sub 2} = 10:90 vol.%) using a tungsten hot-wire catalyzer. SU-8 resists with exposure doses from 7 to 280 mJ/cm{sup 2} were removed by hydrogen radicals, although the SU-8 removal rate was independent of the exposure dose. The SU-8 removal rate increased with both substrate and catalyzer temperature, in addition to a decrease in the distance between the catalyzer and substrate. A high removal rate for cross-linked SU-8 with an exposure dose of 14 mJ/cm{sup 2} of approximately 4 μm/min was achieved with a catalyzer to substrate distance of 20 mm, and catalyzer and initial substrate temperatures of 2400 and 165 °C, respectively. - Highlights: • Chemically amplified negative-tone i-line resist SU-8 removed by hydrogen radicals • Hydrogen radicals generated by catalytic H{sub 2} decomposition using hot-wire catalyzer • The cross-linked SU-8 resist was removed at a rate of approximately 4 μm/min.

  11. Numerical and experimental determination of the minimum and maximum measuring times for the hot wire parallel technique

    Directory of Open Access Journals (Sweden)

    Santos W. N. dos

    2003-01-01

    Full Text Available The hot wire technique is considered to be an effective and accurate means of determining the thermal conductivity of ceramic materials. However, specifically for materials of high thermal diffusivity, the appropriate time interval to be considered in calculations is a decisive factor for getting accurate and consistent results. In this work, a numerical simulation model is proposed with the aim of determining the minimum and maximum measuring time for the hot wire parallel technique. The temperature profile generated by this model is in excellent agreement with that one experimentally obtained by this technique, where thermal conductivity, thermal diffusivity and specific heat are simultaneously determined from the same experimental temperature transient. Eighteen different specimens of refractory materials and polymers, with thermal diffusivities ranging from 1x10-7 to 70x10-7 m²/s, in shape of rectangular parallelepipeds, and with different dimensions were employed in the experimental programme. An empirical equation relating minimum and maximum measuring times and the thermal diffusivity of the sample is also obtained.

  12. Growth and Characterization of Silicon Carbide (SiC) Nanowires by Chemical Vapor Deposition (CVD) for Electronic Device Applications

    Science.gov (United States)

    Moore, Karina

    In recent years nanowires have gained a generous amount of interest because of the possible application of nanowires within electronic devices. A nanowire is a one dimensional semiconductor nanostructure with a diameter less than 100 nm. Nanowires have the potential to be a replacement for the present day complimentary metal oxide semiconductor (CMOS) technology; it is believed by 2020, a 5--6 nm gate length within field effect transistors (FET) would be realized and cease further miniaturization of electronic devices. SiC processes several unique chemical and physical properties that make it an attractive alternative to Si as a semiconductor material. Silicon carbide's properties make it a perfect candidate for applications such as high temperature sensors, x-ray emitters and high radiation sensors. The main objective of this thesis is to successfully grow silicon carbide nanowires on silicon substrates with the assistance of a metal catalyst, by the process of chemical vapor deposition (CVD). The contributions made by the work carried out in this thesis are broad. This is the first study that has carried out a comprehensive investigation into a wide range of metal catalyst for the growth of SiC nanowires by the process of chemical vapor deposition. The study proved that the surface tension interactions between the silicon substrate and the metal catalyst are the controlling factor in the determination of the diameter of the nanowires grown. This study also proved that the silicon substrate orientation has no impact on the growth of the nanowires, similar growth patterns occurred on both Si and Si substrates. The nanowires grown were characterized by a variety of different methods including scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and raman spectroscopy. The effect of temperature, growth temperature, growth time and the catalyst type used are investigated to determine the most suitable conditions necessary for SiC nanowire

  13. Comparison of three velocity measurement systems - A laser transit anemometer (LTA), an on axis laser Doppler anemometer (LDA) and a constant temperature hot-wire anemometer (CTA)

    Science.gov (United States)

    Bennett, M. J.; Mawlood, S. N.; Al-Daini, A. J.; Girgis, N. S.

    Three flow-velocity measurement systems, an on-axis LDA, an LTA, and a constant temperature hot-wire anemometer (CTA), are described and compared by applying them to the measurement of velocity in a high-pressure closed-circuit wind tunnel and to the velocity profiles of a free jet. A system operating on the LTA principle, the Polytec L2F, was used to produce the probability density functions for the two flow situations and to calibrate the hot-wire CTA system, and the hot-wire calibration curve at normal pressure and temperature was used to develop a semiempirical model for the evaluation of velocity at elevated pressures and temperatures. An experimental arrangement in which LTA and LDA measuring systems may be used simultaneously with no separation of the respective measuring volumes in any axis is described, and the methods which may be used to counteract the inaccuracies of such an arrangement are discussed.

  14. Growth and characterization of nanodiamond layers prepared using the plasma-enhanced linear antennas microwave CVD system

    Energy Technology Data Exchange (ETDEWEB)

    Fendrych, Frantisek; Taylor, Andrew; Peksa, Ladislav; Kratochvilova, Irena; Kluiber, Zdenek; Fekete, Ladislav [Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i, Na Slovance 2, CZ-18221 Prague 8 (Czech Republic); Vlcek, Jan [Department of Physics and Measurement, Institute of Chemical Technology Prague, Technicka 5, CZ-16628 Prague 6 (Czech Republic); Rezacova, Vladimira; Petrak, Vaclav [Faculty of Biomedical Engineering, Czech Technical University, Sitna 3105, CZ-27201 Kladno 2 (Czech Republic); Liehr, Michael [Leybold Optics Dresden GmbH, Zur Wetterwarte 50, D-01109 Dresden (Germany); Nesladek, Milos, E-mail: fendrych@fzu.c [IMOMEC division, IMEC, Institute for Materials Research, University Hasselt, Wetenschapspark 1, B-3590 Diepenbeek (Belgium)

    2010-09-22

    Industrial applications of plasma-enhanced chemical vapour deposition (CVD) diamond grown on large area substrates, 3D shapes, at low substrate temperatures and on standard engineering substrate materials require novel plasma concepts. Based on the pioneering work of the group at AIST in Japan, the high-density coaxial delivery type of plasmas has been explored (Tsugawa et al 2006 New Diamond Front. Carbon Technol. 16 337-46). However, an important challenge is to obtain commercially interesting growth rates at very low substrate temperatures. In this work we introduce the concept of novel linear antenna sources, designed at Leybold Optics Dresden, using high-frequency pulsed MW discharge with a high plasma density. This type of pulse discharges leads to the preparation of nanocrystalline diamond (NCD) thin films, compared with ultra-NCD thin films prepared in (Tsugawa et al 2006 New Diamond Front. Carbon Technol. 16 337-46). We present optical emission spectroscopy data for the CH{sub 4}-CO{sub 2}-H{sub 2} gas chemistry and we discuss the basic properties of the NCD films grown.

  15. The over-step coalescence of carbon atoms on copper surface in the CVD growth of graphene: density functional calculations

    Directory of Open Access Journals (Sweden)

    Yingfeng Li

    2013-05-01

    Full Text Available The ways in which carbon atoms coalesce over the steps on copper (111 surface are ascertained by density functional theory (DFT calculations in the context of chemical vapor deposition (CVD growth of graphene. Two strategies, (1 by putting carbon atoms on and under the steps separately and (2 by importing additional carbon atoms between the ones separated by the steps, have been attempted to investigate if an over-step coalescence of carbon atoms could take place. Based on analyses about the optimized configurations and adsorption energies of carbon atoms nearby the steps, as well as the energy evolution curve of the system throughout the geometry optimizations process, we determined the main way in which graphene grows over the steps continuously: the carbon atoms, adsorbed additionally on the locations between the already existing ones which are separated by the steps, link them (these carbon atoms separated by the steps together. The direct over-step coalescence of the carbon atoms separated by the steps is very difficult, although the energy barrier preventing their coalescence can be weakened by importing carbon atoms on and under the steps gradually. Our results imply potential applications in directing the fabrication of graphene with particular structure by controlling the surface topography of copper substrate.

  16. Mathematical Model of Quasi-state Temperature Distribution of Hot-Wire during Hot-Wire TIG Welding Process%热丝TIG焊热丝准稳态温度场的解析模型

    Institute of Scientific and Technical Information of China (English)

    赵福海; 华学明; 叶欣舢; 吴毅雄

    2012-01-01

    Based on the law of the conservation of energy and Fouriers law, the mathematical models re-spectively considering the effect of resistance heat and the heat transferred through the weld pool on the hot-wire temperature distribution were developed. And then based on the superposition principle the math- ematical model of quasi-state temperature distribution of ,hot-wire heated by resistance energy was devel- oped. The accuracy of the mathematical model was validated by comparing the result of calculating from the mathematical model with the experimental result from the literature. The impact of current density, wire feeding speed, wire extension on temperature distribution of hot-wire was elaborately discussed. The results show that the mathematical model has high accuracy to effectively analyze the process of wire heat-ed by resistance energy. The larger the current density or wire extension is, the higher the temperature in different positions on the wire extension is, however, the bigger the wire feeding speed is, the higher the pre-heating temperature is. In some certain cases, the matching relations among current density, wire feeding speed and wire extension can be concluded.%基于能量守恒和傅里叶定律,建立了电阻加热和熔池传热对热丝温度分布影响的数学模型;基于叠加原理建立了电阻加热热丝钨极惰性气体(TIG)焊热丝准稳态温度分布的数学解析模型,并验证了其计算结果;讨论了热丝电流密度、送丝速度以及焊丝干伸长等因素对焊丝温度分布的影响规律.结果表明:该数学模型具有很高的精确性,可用于热丝加热过程的分析.焊丝电流密度越大,焊丝各位置温度越高;送丝速度越大,焊丝各点的温度越低;焊丝干伸长越大,焊丝端部的预热温度越高.得到了一定条件下焊丝电流密度、送丝速度和焊丝干伸长三者之间的数值匹配关系.

  17. Structure characterization and strain relief analysis in CVD growth of boron phosphide on silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Li, Guoliang [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Abbott, Julia K.C.; Brasfield, John D. [Department of Chemistry, The University of Tennessee, Knoxville, TN 37996 (United States); Liu, Peizhi [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Dale, Alexis [Department of Chemistry, The University of Tennessee, Knoxville, TN 37996 (United States); Duscher, Gerd [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Rack, Philip D. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Feigerle, Charles S., E-mail: cfeigerl@tennessee.edu [Department of Chemistry, The University of Tennessee, Knoxville, TN 37996 (United States)

    2015-02-01

    Highlights: • Crystalline boron phosphide was grown on vicinal 4H (0 0 0 1)-SiC surfaces. • The microstructure evolution of defects generated at the interface was characterized by transmission electron microscopy. • The evolution of lattice distortion and strain are determined. - Abstract: Boron phosphide (BP) is a material of interest for development of a high-efficiency solid-state thermal neutron detector. For a thick film-based device, microstructure evolution is key to the engineering of material synthesis. Here, we report epitaxial BP films grown on silicon carbide with vicinal steps and provide a detailed analysis of the microstructure evolution and strain relief. The BP film is epitaxial in the near-interface region but deviates from epitaxial growth as the film develops. Defects such as coherent and incoherent twin boundaries, dislocation loops, stacking faults concentrate in the near-interface region and segment this region into small domains. The formation of defects in this region do not fully release the strain originated from the lattice mismatch. Large grains emerge above the near-interface region and grain boundaries become the main defects in the upper part of the BP film.

  18. Study of Mg Powder as Catalyst Carrier for the Carbon Nanotube Growth by CVD

    Directory of Open Access Journals (Sweden)

    Jianli Kang

    2011-01-01

    Full Text Available The possibility of using magnesium powder as catalyst carrier for carbon nanotube growth by chemical vapor deposition, which may pave a new way to in situ fabricate CNT/Mg composites with high CNT dispersion, was investigated for the first time. The fabrication process of the catalyst supported on Mg powder involves the preparation of colloid by a deposition-precipitation method, followed by calcination and reduction. The results show that the interaction between catalyst and support plays an important role for the catalytic property of the catalyst. Ni alloyed with Mg shows no activity for the decomposition of methane. The introduction of Y in Ni/Mg catalyst can promote the reaction temperature between Ni and Mg and thus enhance the activity of the catalyst. A large amount of carbon nanotubes (CNTs with an average diameter of 20 nm was obtained using Ni/Y/Mg catalyst at 450∘C, while only a few short CNTs were obtained using Ni/Mg catalyst due to the low activity of the catalyst at lower temperature.

  19. A method of measuring the three-dimensional mean flow and turbulence quantities inside a rotating turbo-machinery passage. [by hot-wire anemometer

    Science.gov (United States)

    Gorton, C. A.; Lakshminarayana, B.

    1975-01-01

    A method of measuring the three-dimensional components of mean velocity and turbulence quantities within a rotating turbomachinery passage is developed through the use of hot wire anemometry techniques. Equations are derived which, when solved simultaneously and in conjunction with the data obtained from the hot wire anemometer measurements, will provide values for the radial, axial and tangential components of mean velocity, turbulence intensity and turbulence stress within the rotating turbomachinery passage. A three-bladed rocket pump inducer model, operating in air, was used in the experimentation. The method is very accurate and provides very useful information on the characteristics of the flow inside rotor passages hitherto unexplored.

  20. Applying hot-wire anemometry to directly measure the water balance in a proton exchange membrane fuel cell - Part 2: Experimental

    DEFF Research Database (Denmark)

    Al Shakhshir, Saher; Andreasen, Søren Juhl; Berning, Torsten

    2016-01-01

    can be directly converted into the fuel cell water balance. In this work an ex-situ experimental investigation is performed to examine the effect of the wire diameter and the outlet pipe diameter on the voltage signal. For a laboratory fuel cell where the mass flow rate the anode outlet is small......In order to better understand and more accurately measure the water balance in a proton exchange membrane fuel cell, our group has recently proposed to apply hot wire anemometry in the fuel cell's anode outlet. It was theoretically shown that the electrical signal obtained from the hot wire sensor...

  1. Joint tests at INL and CEA of a transient hot wire needle probe for in-pile thermal conductivity measurement

    Energy Technology Data Exchange (ETDEWEB)

    Daw, J.E.; Knudson, D.L. [Idaho National Laboratory, Idaho Falls, ID 83415, (United States); Villard, J.F.; Liothin, J.; Destouches, C. [CEA, DEN, DER, Instrumentation Sensors and Dosimetry Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France); Rempe, J.L. [Rempe and Associates, LLC, Idaho Falls, ID, 83404 (United States); Matheron, P. [CEA, DEN, DEC, Uranium Fuels Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France); Lambert, T. [CEA, DEN, DEC, Innovative Fuel Design and Irradiation Laboratory, Cadarache, F-13108 St Paul-Lez-Durance, (France)

    2015-07-01

    Thermal conductivity is a key property that must be known for proper design, testing, and deployment of new fuels and structural materials in nuclear reactors. Thermal conductivity is highly dependent on the physical structure, chemical composition, and the state of the material. Typically, thermal conductivity changes that occur during irradiation are currently measured out-of-pile using a 'cook and look' approach. But repeatedly removing samples from a test reactor to make measurements is expensive, has the potential to disturb phenomena of interest, and only provides understanding of the sample's end state when each measurement is made. There are also limited thermo-physical property data available for advanced fuels; and such data are needed for simulation codes, the development of next generation reactors, and advanced fuels for existing nuclear plants. Being able to quickly characterize fuel thermal conductivity during irradiation can improve the fidelity of data, reduce costs of post-irradiation examinations, increase understanding of how fuels behave under irradiation, and confirm or improve existing thermal conductivity measurement techniques. This paper discusses efforts to develop and evaluate an innovative in-pile thermal conductivity sensor based on the transient hot wire thermal conductivity method (THWM), using a single needle probe (NP) containing a line heat source and thermocouple embedded in the fuel. The sensor that has been designed and manufactured by the Idaho National Laboratory (INL) includes a unique combination of materials, geometry, and fabrication techniques that make the hot wire method suitable for in-pile applications. In particular, efforts were made to minimize the influence of the sensor and maximize fuel hot-wire heating. The probe has a thermocouple-like construction with high temperature resistant materials that remain ductile while resisting transmutation and materials interactions. THWM-NP prototypes were

  2. Fabrication of nc-Si/c-Si solar cells using hot-wire chemical vapor deposition and laser annealing

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Bing-Rui; Wuu, Dong-Sing; Mao, Hsin-Yuan [Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227 (China); Wan, Meng-Shen; Huang, Wei-Hao; Horng, Ray-Hua [Institute of Precision Engineering, National Chung Hsing University, Taichung 40227 (China)

    2009-06-15

    In this paper, we present the performance of Si heterojunction solar cells prepared by hot-wire chemical vapor deposition and laser annealing. Under high hydrogen-dilution-ratio conditions, the crystallinity of the phosphorous-doped emitter layers was greatly improved due to hydrogen-induced crystallization. The grain boundary defects of the nano-crystalline emitter layer were further promoted using a laser (355 nm) crystallization technique. It was found that both the short-circuit current density and fill factor of the Si heterojunction solar cells were mainly dependent on the energy density of the laser beam. An efficiency of 14.2% is achieved for the n-nc-Si/p-c-Si heterojunction solar cell under a laser irradiation density of 382 mW/cm{sup 2}. (author)

  3. Structural and optical studies on hot wire chemical vapour deposited hydrogenated silicon films at low substrate temperature

    Energy Technology Data Exchange (ETDEWEB)

    Gogoi, Purabi; Agarwal, Pratima [Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam (India)

    2009-02-15

    Thin films of hydrogenated silicon are deposited by hot wire chemical vapour deposition technique, as an alternative of plasma enhanced chemical vapour deposition technique. By varying the hydrogen and silane flow rate, we deposited the films ranging from pure amorphous to nanocrystallite-embedded amorphous in nature. In this paper we report extensively studied structural and optical properties of these films. It is observed that the rms bond angle deviation decreases with increase in hydrogen flow rate, which is an indication of improved order in the films. We discuss this under the light of breaking of weak Si-Si bonds and subsequent formation of strong Si-Si bonds and coverage of the growing surface by atomic hydrogen. (author)

  4. Characteristics of a micro-mechanical thermal flow sensor based on a two hot wires principle with constant temperature operation in a small channel

    Science.gov (United States)

    Lange, P.; Weiss, M.; Warnat, S.

    2014-12-01

    A thermal mass flow sensor with high dynamic flow range in silicon bulk micromachining membrane technology is presented. The response behavior of this sensor based on a two hot wire principle is described. This sensor configuration uses two hot wires mounted closely spaced one behind the other within a thin membrane, kept at the same temperature. The power to compensate cooling of and the interaction between the two hot wires are used to calculate mass flows and directionality of flows of gaseous and liquid fluids in a small channel. The response shows both anemometric and calorimetric behavior, depending on fluid, channel height and flow range. The hot wires are heated relative to temperature sensors located also on an isolated membrane on the same chip. Choosing an appropriate evaluation procedure an independence of the signal from the ambient temperature is achieved. This configuration will be discussed in view of the published results of single heater flow sensors, being of calorimetric or anemometric type. A calculation method for the determination of linear and power law range of the response is given.

  5. Low Temperature Silicon Nitride by Hot Wire Chemical Vapour Deposition for the Use in Impermeable Thin Film Encapsulation on Flexible Substrates

    NARCIS (Netherlands)

    Spee, D.A.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2011-01-01

    High quality non porous silicon nitride layers were deposited by hot wire chemical vapour deposition at substrate temperatures lower than 110 C. The layer properties were investigated using FTIR, reflection/transmission measurements and 1:6 buffered HF etching rate. A Si–H peak position of 2180 cm−1

  6. Single and multijunction silicon based thin film solar cells on a flexible substrate with absorber layers made by hot-wire CVD

    NARCIS (Netherlands)

    Li, Hongbo

    2007-01-01

    With the worldwide growing concern about reliable energy supply and the environmental problems of fossil and nuclear energy production, the need for clean and sustainable energy sources is evident. Solar energy conversion, such as in photovoltaic systems, can play a major role in the urgently needed

  7. Metallic Tungsten Nanostructures and Highly Nanostructured Thin Films by Deposition of Tungsten Oxide and Subsequent Reduction in a Single Hot-Wire CVD Process

    NARCIS (Netherlands)

    Harks, P.P.R.M.L.; Houweling, Z.S.; de Jong, M.M.; Kuang, Y; Geus, J.W.; Schropp, R.E.I.

    2012-01-01

    The synthesis of metallic tungsten nanostructures and highly nanostructured thin films is presented. Crystalline tungsten oxide nanostructures are deposited on glassy carbon substrates kept at 700 100 8C by oxidizing resistively heated tungsten filaments in an air flow under subatmospheric pressures

  8. rf excited optical emission spectrum of radicals generated during hot wire chemical vapour deposition for the preparation of microcrystalline silicon thin film%射频激发热丝化学气相沉积制备硅薄膜过程中光发射谱的研究

    Institute of Scientific and Technical Information of China (English)

    李天微; 刘丰珍; 朱美芳

    2011-01-01

    To study the radicals behavior in the hot wire chemical vapour deposition (HWCVD) process for the preparation of microcrystalline Si (μc-Si: H) thin film, a weak radio frequency (rf) power was introduced to excite the radicals generated in HWCVD chamber. The spectrum of fi-excited HWCVD (rf-HWCVD) was obtained by subtracting the emission of hot wires from the spectrum measured by OES. The influence of the rf power on the rf-HWCVD spectrum can be neglected as the rf power density was less than 0. 1 W/cm2. Under the same deposition parameters, the emission spectra for rf-HWCVD and plasma enhanced CVD (PECVD) processes are different. Under the low deposition pressure ( 7.5 Pa), the intensities of Sill * and Hα vary with the hot wire temperature reversely, which is characteristic of HWCVD with high gas dissociation rate and high concentration of atomic H. The ratio of intensity of Hα to Sill * in the emission spectrum of rf-HWCVD varying with deposition pressure is consistent with the crystalline fraction of μc-Si: H film. The results indicate that the optical emission spectroscopy measurement is a suitable method for the investigation of the HWCVD process excited by a weak rf-power.%采用射频(rf)激发,在热丝化学气相沉积(HWCVD)制备微晶硅薄膜的过程中产生发光基元,测量了rf激发HWCVD(rf-HWCVD)的光发射谱,比较了相同工艺条件下rf-HWCVD和等离子体增强CVD(PECVD)的光发射谱,分析了rf功率、热丝温度和沉积气压对rf-HWCVD光发射谱的影响.结果表明,在射频功率<0.1W/cm1时,rf-HWCVD发射光谱反映了HWCVD高的气体分解效率和高浓度原子氢的特点,能够解释气压变化与微晶硅薄膜微结构的关系,是研究HWCVD气相过程的有效方法之一.

  9. Expired tidal volumes measured by hot-wire anemometer during high-frequency oscillation in preterm infants.

    Science.gov (United States)

    Zimová-Herknerová, Magdalena; Plavka, Richard

    2006-05-01

    We sought to determine the normocapnic values of expiratory tidal volume measured by hot-wire anemometer, and to evaluate how often expiratory tidal volume exceeds estimated anatomical dead space during high-frequency oscillatory ventilation (HFOV) in preterm infants. We also sought to determine the relationship between expiratory tidal volume and other respiratory parameters. The neonatal respiration monitor SLE 2100 VPM, a hot-wire anemometer, was used to measure expired tidal volume (V(T,E)) in patients ventilated by the Sensormedics 3,100A during routine clinical use of HFOV. Two hundred and fourteen simultaneous measurements of PaCO(2), V(T,E), fraction of inspired oxygen (FiO(2)), continuous distending pressure (CDP), frequency, and amplitude were obtained from 28 patients. The median birth weight was 852 g (range, 435-3,450 g), and median gestational age was 27.2 weeks (range, 23.3-41.0 weeks). One hundred and eighteen (55%) normocapnic measurements, 42 (20%) hypocapnic measurements, and 54 (25%) hypercapnic measurements were recorded in which the median V(T,E) was 1.67 ml/kg (95% confidence interval (CI), 1.55-1.79), 1.94 ml/kg (95% CI, 1.74-2.14), and 1.54 ml/kg (95% CI, 1.42-1.66), respectively. The measured V(T,E) exceeded 2.0 ml/kg in 30 instances of normocapnic V(T,E) (14%) and 54 of all V(T,E) (25%), and 3 ml/kg only in 7 (3%) and 11 (5%) instances of normocapnic and all V(T,E). There was a significant difference in median normocapnic V(T,E) obtained when FiO(2) was between 0.21-0.35, compared to values obtained when FiO(2) was 0.36-1.0 (1.61 ml/kg (95% CI, 1.52-1.70) vs. 2.06 ml/kg (95% CI, 1.93-2.19), P 47 should predict hypercapnia in 81% of cases. In conclusion, expired tidal volume measurement by heated double-wire anemometer sensor is feasible, provides useful real-time information about tidal volume changes, and may improve the clinical management of HFOV.

  10. Welding Technology Research of TIG Arc Hot Wire to Copper and Steel%TIG电弧热丝对铜、钢堆焊的工艺研究

    Institute of Scientific and Technical Information of China (English)

    柳燕; 姜华; 韩家强; 赵广军; 王晰

    2012-01-01

    针对某产品铜带焊接工艺,提出了一种电弧热丝方式应用于TIG堆焊铜、钢工艺的研究。电弧热丝可有效预热低电阻率的焊接材料,如铜;传统的电阻热丝只能加热具有高电阻率的焊接材料,如钢。采用电弧热丝系统,热丝电流小于50A时即可有效预热焊丝,与电阻热丝电流400A相当。在相同焊接电流下,能够大大提高焊接熔敷速度;在相同送丝速度下,降低焊接电流,大大降低焊接设备功率。同时证明2种热丝加热方式对钢基体、铜合金的影响相同,特别是对堆焊层铜合金中泛铁量的影响相当。%A kind of arc hot wire method is put forward to TIG welding copper and steel technology research for copper welding process of a product.Arc hot wire can effectively preheat welding materials with low resistivity,such as copper;while the traditional resistance hot wire can heat welding materials with high resistivity only,such as steel.Using arc hot wire system,wire can be preheated effectively when hot wire current is less than 50 A which is equivalent to resistance hot wire current 400 A.Under the same welding current,the weld speed can be greatly improved;in the same wire feed speed,the welding current can be reduced,which can greatly reduce the welding equipment power.At the same time that two kinds of heating methods have the same effect on steel matrix and copper alloy,especially the effect on the extensive iron content of copper alloy in surfacing layer.

  11. Simplified Transient Hot-Wire Method for Effective Thermal Conductivity Measurement in Geo Materials: Microstructure and Saturation Effect

    Directory of Open Access Journals (Sweden)

    B. Merckx

    2012-01-01

    Full Text Available The thermal conductivity measurement by a simplified transient hot-wire technique is applied to geomaterials in order to show the relationships which can exist between effective thermal conductivity, texture, and moisture of the materials. After a validation of the used “one hot-wire” technique in water, toluene, and glass-bead assemblages, the investigations were performed (1 in glass-bead assemblages of different diameters in dried, water, and acetone-saturated states in order to observe the role of grain sizes and saturation on the effective thermal conductivity, (2 in a compacted earth brick at different moisture states, and (3 in a lime-hemp concrete during 110 days following its manufacture. The lime-hemp concrete allows the measurements during the setting, desiccation and carbonation steps. The recorded Δ/ln( diagrams allow the calculation of one effective thermal conductivity in the continuous and homogeneous fluids and two effective thermal conductivities in the heterogeneous solids. The first one measured in the short time acquisitions (<1 s mainly depends on the contact between the wire and grains and thus microtexture and hydrated state of the material. The second one, measured for longer time acquisitions, characterizes the mean effective thermal conductivity of the material.

  12. The Laser Welding with Hot Wire of 316LN Thick Plate Applied on ITER Correction Coil Case

    CERN Document Server

    Fang, Chao; Wu, Weiyue; Wei, Jing; Zhang, Shuquan; Li, Hongwei; Dolgetta, N; Libeyre, P; Cormany, C; Sgobba, S

    2014-01-01

    ITER correction coil (CC) cases have characteristics of small cross section, large dimensions, and complex structure. The cases are made of heavy thick (20 mm), high strength and high toughness austenitic stainless steel 316LN. The multi-pass laser welding with hot wire technology is used for the case closure welding, due to its low heat input and deformation. In order to evaluate the reliability of this welding technology, 20 mm welding samples with the same groove structure and welding depth as the cases were welded. High purity argon was used as the shielding gas to prevent oxidation because of the narrowness and depth of the weld. In this paper investigation of, microstructure characteristics and mechanical properties of welded joints using optimized welding parameters are presented. The results show that the base metal, fusion metal, and heat affected zone (HAZ) are all have fully austenitic microstructure, and that the grain size of fusion metal was finer than that of the base metal. The welding resulte...

  13. Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

    Science.gov (United States)

    Chaudhari, Pradip; Singh, Arvind; Topkar, Anita; Dusane, Rajiv

    2015-04-01

    In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and 10B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2 μm and 0.5 μm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

  14. Role of oxygen and nitrogen in n-type microcrystalline silicon carbide grown by hot wire chemical vapor deposition

    Science.gov (United States)

    Pomaska, Manuel; Mock, Jan; Köhler, Florian; Zastrow, Uwe; Perani, Martina; Astakhov, Oleksandr; Cavalcoli, Daniela; Carius, Reinhard; Finger, Friedhelm; Ding, Kaining

    2016-12-01

    N-type microcrystalline silicon carbide (μc-SiC:H(n)) deposited by hot wire chemical vapor deposition provides advantageous opto-electronic properties for window layer material in silicon-based thin-film solar cells and silicon heterojunction solar cells. So far, it is known that the dark conductivity (σd) increases with the increase in the crystallinity of μc-SiC:H(n)films. However, due to the fact that no active doping source is used, the mechanism of electrical transport in these films is still under debate. It is suggested that unintentional doping by atmospheric oxygen (O) or nitrogen (N) contamination plays an important role in the electrical transport. To investigate the impact of O and N, we incorporated O and N in μc-SiC:H(n) films and compared the influence on the microstructural, electronic, and optical properties. We discovered that, in addition to increasing the crystallinity, it is also possible to increase the σd by several orders of magnitude by increasing the O-concentration or the N-concentration in the films. Combining a high concentration of O and N, along with a high crystallinity in the film, we optimized the σd to a maximum of 5 S/cm.

  15. Measurement of the thermal conductivity of carbon nanotube--tissue phantom composites with the hot wire probe method.

    Science.gov (United States)

    Sarkar, Saugata; Zimmermann, Kristen; Leng, Weinan; Vikesland, Peter; Zhang, Jianfei; Dorn, Harry; Diller, Thomas; Rylander, Christopher; Rylander, Marissa Nichole

    2011-06-01

    Developing combinatorial treatments involving laser irradiation and nanoparticles require an understanding of the effect of nanoparticle inclusion on tissue thermal properties, such as thermal conductivity. This information will permit a more accurate prediction of temperature distribution and tumor response following therapy, as well as provide additional information to aid in the selection of the appropriate type and concentration of nanoparticles. This study measured the thermal conductivity of tissue representative phantoms containing varying types and concentrations of carbon nanotubes (CNTs). Multi-walled carbon nanotubes (MWNTs, length of 900-1200 nm and diameter of 40-60 nm), single-walled carbon nanotubes (SWNTs, length of 900-1200 nm and diameter hot wire probe method. Increasing CNT concentration from 0 to 1.0 mg/mL caused the thermal conductivity of phantoms containing SWNTs, SWNHs, and MWNTs to increase by 24, 30, and 66%, respectively. For identical CNT concentrations, phantoms containing MWNTs possessed the highest thermal conductivity.

  16. Near-wall hot-wire measurements . Part II: Turbulence time scale, convective velocity and spectra in the viscous sublayer

    Science.gov (United States)

    Khoo, B. C.; Chew, Y. T.; Teo, C. J.

    This work continues the studies of Khoo et al. (Exp. Fluids 29: 448-460, 2001), where experiments were performed in turbulent-channel and flat-plate boundary-layer flows using near-wall hot-wire probes. The probability density function (pdf) of the wall-shear stress and streamwise velocity fluctuations in the viscous sublayer, buffer region and beyond were compared and analyzed. The convective velocity Uc of the streamwise velocity fluctuations in the very near-wall region was obtained using a two-point correlation technique. It was found that in the viscous sublayer, Uc is approximately constant at 13uτ and 15uτ, respectively, for the channel and boundary-layer flows. Spectra data for the viscous sublayer are presented for the first time, and the normalized spectral plots for different flow conditions collapse at high frequencies or wavenumbers, thus indicating the possible presence of small-scale universality at different Reynolds numbers. The integral time scale corresponding to the streamwise velocity fluctuations in the viscous sublayer is also presented.

  17. A Novel Portable Absolute Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids

    Science.gov (United States)

    Assael, Marc J.; Antoniadis, Konstantinos D.; Metaxa, Ifigeneia N.; Mylona, Sofia K.; Assael, John-Alexander M.; Wu, Jiangtao; Hu, Miaomiao

    2015-11-01

    A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2 { W}{\\cdot }m^{-1}{\\cdot }{K}^{-1} to 4 { W}{\\cdot }m^{-1}{\\cdot }{K}^{-1} is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to × 120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.

  18. Nanostructured Hydrogenated Silicon Films by Hot-Wire Chemical Vapor Deposition: the Influence of Substrate Temperature on Material Properties

    Directory of Open Access Journals (Sweden)

    V.S. Waman

    2011-01-01

    Full Text Available Thin films of hydrogenated nanocrystalline silicon are prepared at reasonably higher deposition rates (9-13 Å/s by indigenously fabricated hot-wire chemical vapor deposition system at various substrate temperatures (Ts. In this paper we report extensively studied structural, optical and electrical properties of these films by Fourier transform infrared (FTIR spectroscopy, low angle X-ray diffraction (low angle XRD, micro-Raman spectroscopy and UV-Visible spectroscopy. The low angle XRD and micro-Raman spectroscopy analysis indicate amorphous-to-nanocrystalline transition occurred at Ts = 300 °C. It is observed that volume fraction of crystallites and its size increases with increase in Ts. The low angle XRD study also shows nc-Si:H films with well-identified lattice planes of (111 orientation. In addition, it is observed from the FTIR spectroscopy that the hydrogen is incorporated in the film mainly in Si-H2 and (Si-H2n complexes. The nc-Si:H films with low hydrogen content (< 4 at. % and wide band gap (1.83-1.89 eV and low refractive index (< 3 is useful for various device applications.

  19. Response of the Nevzorov hot wire probe in clouds dominated by droplet conditions in the drizzle size range

    Directory of Open Access Journals (Sweden)

    A. Schwarzenboeck

    2009-12-01

    Full Text Available During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC and total condensed water content (TWC in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.

  20. Evaluation of performance of multi-sensors hot-wire probes using Neural-Networks in-situ calibration

    Science.gov (United States)

    Liberzon, Dan; Kit, Eliezer

    2015-11-01

    Neural Networks (NN) based in-situ calibration of hot-wire anemometers was recently successfully implemented in field measurements. Although proving feasibility of field measurements using this, relatively new, calibration method the acquired field data also revealed some significant ambiguities in use of combined two- or three-sensor probes. A clearly better behavior of the probe comprised of four sensors (a pair of X shaped probes) has motivated the presented here work, aimed to investigate the NN based procedure performance dependence on the number of wires in the probe. Hypothesizing that the main reason for performance differences is in the fact that a 3-wire probe lacks any special features to withstand the noise in the signal due to temperature fluctuations and sensors' contamination, series of wind tunnel experiments with grid generated turbulence were designed and performed. Performance of a various multi-sensor probes' geometries was examined using the NN based method, while standard calibration data sets were also obtained prior to each set of measurements serving as a reference and as alternative training sets for the NN. The obtained results clearly indicated an advantage in using a symmetrical geometry, and especially using the four-sensor probe to obtain a reasonable description of the 3D velocity field. This is argued to be a result of redundant information on one or several velocity components present in four-sensor probes and serving as an efficient tool for noise reduction.

  1. Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhari, Pradip, E-mail: pradipcha@gmail.com [Semiconductor Thin Films and Plasma Processing Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai – 400076 (India); Singh, Arvind, E-mail: arvindsingh1884@gmail.com [Electronics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085 (India); Topkar, Anita, E-mail: anita.topkar@gmail.com [Electronics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085 (India); Dusane, Rajiv, E-mail: rodusane@iitb.ac.in [Semiconductor Thin Films and Plasma Processing Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai – 400076 (India)

    2015-04-11

    In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and {sup 10}B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2 µm and 0.5 µm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

  2. Low temperature deposition of polycrystalline silicon thin films on a flexible polymer substrate by hot wire chemical vapor deposition

    Science.gov (United States)

    Lee, Sang-hoon; Jung, Jae-soo; Lee, Sung-soo; Lee, Sung-bo; Hwang, Nong-moon

    2016-11-01

    For the applications such as flexible displays and solar cells, the direct deposition of crystalline silicon films on a flexible polymer substrate has been a great issue. Here, we investigated the direct deposition of polycrystalline silicon films on a polyimide film at the substrate temperature of 200 °C. The low temperature deposition of crystalline silicon on a flexible substrate has been successfully made based on two ideas. One is that the Si-Cl-H system has a retrograde solubility of silicon in the gas phase near the substrate temperature. The other is the new concept of non-classical crystallization, where films grow by the building block of nanoparticles formed in the gas phase during hot-wire chemical vapor deposition (HWCVD). The total amount of precipitation of silicon nanoparticles decreased with increasing HCl concentration. By adding HCl, the amount and the size of silicon nanoparticles were reduced remarkably, which is related with the low temperature deposition of silicon films of highly crystalline fraction with a very thin amorphous incubation layer. The dark conductivity of the intrinsic film prepared at the flow rate ratio of RHCl=[HCl]/[SiH4]=3.61 was 1.84×10-6 Scm-1 at room temperature. The Hall mobility of the n-type silicon film prepared at RHCl=3.61 was 5.72 cm2 V-1s-1. These electrical properties of silicon films are high enough and could be used in flexible electric devices.

  3. Experimental comparison of two hot-wire techniques for resolution of turbulent mass flux and local stagnation temperature in supersonic flow

    Science.gov (United States)

    Walker, D. A.; Ng, W. F.; Walker, M. D.

    1988-01-01

    The performance of two constant-temperature normal hot-wire techniques in a supersonic flow is examined. The first technique uses a single-wire and rapid scanning of multiple overheat ratios. Time averages of the signals at all overheats are used to separate the mean and rms mass flux, stagnation temperature and their cross-correlation. The second technique uses a dual-wire probe with each wire operating at different overheat ratios, giving instantaneous mass flux and stagnation temperature. Preliminary results indicate that the separation distance (0.18 mm) between the two hot wires in the dual-wire probe does not introduce significant error. However, the rms mass flux inferred from the dual-wire technique is a factor of two higher than that from the single-wire technique.

  4. On the use of hot-wire anemometry in pulsating flows. A comment on 'A critical review on advanced velocity measurement techniques in pulsating flows'

    OpenAIRE

    Berson, Arganthaël; Blanc-Benon, Philippe; Comte-Bellot, Geneviève

    2010-01-01

    International audience; In their recent topical review, Nabavi and Siddiqui (Meas. Sci. Technol. 2010 21 042002) recommended the use of hot-wire anemometry for velocity measurements in pulsating flows, especially at high frequency. This recommendation is misleading. The procedures invoked by these authors are valid only for small-amplitude fluctuations, which are of little interest for pulsating flows. When large-amplitude velocity changes occur without flow reversal, new procedures for the c...

  5. The synthesis of CVD single crystal graphene growth on copper substrate%铜基板上 CVD 法生长单晶石墨烯及研究现状

    Institute of Scientific and Technical Information of China (English)

    吴涛; 蒋业华; 张晓伟

    2015-01-01

    石墨烯是一种以S P2键结合的二维碳的同素异形体,其独一无二的优异性能,使得其在过去几十年里受到了石墨烯研究工作者的极大兴趣。但石墨烯不同于自然界的石墨,并且受限于小尺寸和低产率。化学气相沉积法(CVD )的出现解决了这些问题,并逐渐发展为一种规模生产大面积、大尺寸、多应用石墨烯的重要方法。但化学气相沉积法生长石墨烯是多晶石墨烯并且由于晶界会产生降解性能。因此,石墨烯生长研究的下一个关键问题是如何让大晶粒单晶石墨烯生长。本文主要叙述了4种代表性预处理铜基板来生长毫米级单层石墨烯的方法:电化学抛光后高温退火、盒状铜箔基板、融化再结晶成新的铜基板、让铜基板富氧。以及现在发展的石墨烯晶粒的特殊空间结构,这些特殊晶粒包括雪花、六瓣鲜花、金字塔和六角形的石墨烯洋葱圈形状。综述了利用不同预处理铜基板的工艺得到毫米级单晶石墨烯的方法。尽管CVD生长单晶石墨烯已经有了空前的进步,但仍然有潜在的挑战,例如,晶元尺寸单晶石墨烯的生长和器件的制作,以及对石墨烯生长机制和生长动力学的进一步了解。%As a two‐dimensional (2D) sp2‐bonded carbon allotrope ,graphene has attracted enormous interest o‐ver the past decade due to its unique properties .In the initial research ,graphene was isolated from natural graphite ,and limited to small sizes and low yields .Recently developed chemical vapor deposition (CVD) tech‐niques have emerged as an important method for the scalable production of large‐size and high‐quality graphene for various applications .However ,CVD‐derived graphene is polycrystalline and demonstrates degraded proper‐ties induced by grain boundaries .Thus ,the next critical step of graphene growth relies on the synthesis of large graphene single crystals .We

  6. Relationship of roughness of building stones on the effective thermal conductivity determined by transient hot-wire method

    Science.gov (United States)

    Benoit, Merckx; Jean-Didier, Mertz; Patrick, Dudoignon; David, Giovannacci; Jean-Philippe, Garnier

    2013-04-01

    Alteration of inorganic materials in monuments is mainly related to relative humidity change in the porous network. Characterization of water content is a complex issue, specially in case of non-intrusive measurement. An innovative method is developed to quantify the water content using a direct calculation of the thermal conductivity. In order to validate the non-intrusive application to heritage stone, a control of the influence of the rock-sensor interface is required. The study was carried out on five sedimentary french rocks : three limestones (lithographic, oolithic and micritic), a sandstone of Fontainebleau and the so-called Tuffeau limestone. The textural properties are characterized by optical and electronical microscopy, X-ray diffraction, and mercury intrusion porosimetry. The transient hot-wire method is useful to obtain a quick value of effective conductivity of material. Initially used in liquids and gas, It's now more and more used for solid materials. The calculation of one effective thermal conductivity is formulated by the slope of recorded DT/ln(t) diagrams. In case of continuous and homogeneous media, only one slope can be measured. For heterogeneous solids a typical curve present two slopes : the first one measured in the short time acquisitions (arithmetic average roughness (Sa) is ranged between 44 µm and 1 µm, respectively for the coarse-grained limestone (Bretigny) and the finest one (Migné). According to the relative error of the apparatus (10%), the conductivity value is constant, independently of the surface polishing state. Thus, this evolution confirms that the method could be used on many stony materials as they are present in the built cultural heritage.

  7. Hot-wire chemical vapor deposition of WO{sub 3−x} thin films of various oxygen contents

    Energy Technology Data Exchange (ETDEWEB)

    Houweling, Z. Silvester, E-mail: Silvester.Houweling@asml.com [Section Nanophotonics – Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University, Princetonlaan 4, 3584 CC Utrecht (Netherlands); Geus, John W. [Inorganic Chemistry and Catalysis, Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands); Schropp, Ruud E.I. [Section Nanophotonics – Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University, Princetonlaan 4, 3584 CC Utrecht (Netherlands)

    2013-06-15

    We present the synthesis of tungsten oxide (WO{sub 3−x}) thin films consisting of layers of varying oxygen content. Configurations of layered thin films comprised of W, W/WO{sub 3−x}, WO{sub 3}/W and WO{sub 3}/W/WO{sub 3−x} are obtained in a single continuous hot-wire chemical vapor deposition process using only ambient air and hydrogen. The air oxidizes resistively heated tungsten filaments and produces the tungsten oxide species, which deposit on a substrate and are subsequently reduced by the hydrogen. The reduction of tungsten oxides to oxides of lower oxygen content (suboxides) depends on the local water vapor pressure and temperature. In this work, the substrate temperature is either below 250 °C or is kept at 750 °C. A number of films are synthesized using a combined air/hydrogen flow at various total process pressures. Rutherford backscattering spectrometry is employed to measure the number of tungsten and oxygen atoms deposited, revealing the average atomic compositions and the oxygen profiles of the films. High-resolution scanning electron microscopy is performed to measure the physical thicknesses and display the internal morphologies of the films. The chemical structure and crystallinity are investigated with Raman spectroscopy and X-ray diffraction, respectively. - Highlights: • Synthesis of tungsten oxide thin films of controllable oxygen content. • Partial reduction of WO{sub 3−x} thin films during deposition. • Deposition of layered films with configurations of W, W/WO{sub 3−x}, WO{sub 3}/W/WO{sub 3−x}. • Synthesis of WO{sub 3−x} films with atomic oxygen-to-tungsten ratios between 0.3 and 3.

  8. Design, Modeling, Fabrication, and Evaluation of Thermoelectric Generators with Hot-Wire Chemical Vapor Deposited Polysilicon as Thermoelement Material

    Science.gov (United States)

    de Leon, Maria Theresa; Tarazona, Antulio; Chong, Harold; Kraft, Michael

    2014-11-01

    This paper presents the design, modeling, fabrication, and evaluation of thermoelectric generators (TEGs) with p-type polysilicon deposited by hot-wire chemical vapor deposition (HWCVD) as thermoelement material. A thermal model is developed based on energy balance and heat transfer equations using lumped thermal conductances. Several test structures were fabricated to allow characterization of the boron-doped polysilicon material deposited by HWCVD. The film was found to be electrically active without any post-deposition annealing. Based on the tests performed on the test structures, it is determined that the Seebeck coefficient, thermal conductivity, and electrical resistivity of the HWCVD polysilicon are 113 μV/K, 126 W/mK, and 3.58 × 10-5 Ω m, respectively. Results from laser tests performed on the fabricated TEG are in good agreement with the thermal model. The temperature values derived from the thermal model are within 2.8% of the measured temperature values. For a 1-W laser input, an open-circuit voltage and output power of 247 mV and 347 nW, respectively, were generated. This translates to a temperature difference of 63°C across the thermoelements. This paper demonstrates that HWCVD, which is a cost-effective way of producing solar cells, can also be applied in the production of TEGs. By establishing that HWCVD polysilicon can be an effective thermoelectric material, further work on developing photovoltaic-thermoelectric (PV-TE) hybrid microsystems that are cost-effective and better performing can be explored.

  9. Direct growth of doping-density-controlled hexagonal graphene on SiO2 substrate by rapid-heating plasma CVD.

    Science.gov (United States)

    Kato, Toshiaki; Hatakeyama, Rikizo

    2012-10-23

    A transfer-free method for growing carrier-density-controlled graphene directly on a SiO(2) substrate has been realized for the first time by rapid-heating plasma chemical vapor deposition (RH-PCVD). Using this method, high-quality single-layer graphene sheets with a hexagonal domain can be selectively grown between a Ni film and a SiO(2) substrate. Systematic investigations reveal that the relatively thin Ni layer, rapid heating, and plasma CVD are critical to the success of this unique method of graphene growth. By applying this technique, an easy and scalable graphene-based field effect transistor (FET) fabrication is also demonstrated. The electrical transport type of the graphene-based FET can be precisely tuned by adjusting the NH(3) gas concentration during the RH-PCVD process.

  10. A step-by-step experiment of 3C-SiC hetero-epitaxial growth on 4H-SiC by CVD

    Science.gov (United States)

    Xin, Bin; Jia, Ren-Xu; Hu, Ji-Chao; Tsai, Cheng-Ying; Lin, Hao-Hsiung; Zhang, Yu-Ming

    2015-12-01

    To investigate the growth mechanism of hetero-epitaxial SiC, a step-by-step experiment of 3C-SiC epitaxial layers grown on 4H-SiC on-axis substrates by the CVD method are reported in this paper. Four step experiments with four one-quarter 4H-SiC wafers were performed. Optical microscopy and atomic force microscopy (AFM) were used to characterize the morphology of the epitaxial layers. It was previously found that the main factor affecting the epilayer morphology was double-positioning boundary (DPB) defects, which normally were in high density with shallow grooves. However, a protrusive regular "hill" morphology with a much lower density was shown in our experiment in high-temperature growth conditions. The anisotropic migration of adatoms is regarded as forming the morphology of DPB defects, and a new "DPB defects assist epitaxy" growth mode has been proposed based on the Frank-van der Merwe growth mode. Raman spectroscopy and X-ray diffraction were used to examine the polytypes and the quality of the epitaxial layers.

  11. Growth kinetics of nc-Si:H deposited at 200 °C by hot-wire chemical vapour deposition

    CSIR Research Space (South Africa)

    Oliphant, CJ

    2011-05-01

    Full Text Available . Vallat-Sauvain, N. Wyrsch, U. Kroll, C. Droz, U. Graf, Sol. Energy Mater. Sol. Cells 78 (2003) 469. 3. C.J. Arendse, G.F. Malgas, T.F.G. Muller, D. Knoesen, C.J. Oliphant, D.E. Motaung, S. Halindintwali, B.W. Mwakikunga, Nanoscale Res. Lett. 4 (2009...

  12. Synthesis of nanocrystalline silicon thin films using the increase of the deposition pressure in the hot-wire chemical vapour deposition technique

    Directory of Open Access Journals (Sweden)

    J.K. Rath

    2010-01-01

    Full Text Available Nanostructured thin silicon-based films have been deposited using the hot-wire chemical vapour deposition (HWCVD technique at the University of the Western Cape. A variety of techniques including optical and infrared spectroscopy, Raman scattering spectroscopy, X-rays diffraction (XRD and transmission electron microscopy (TEM have been used for characterisation of the films. The electrical measurements show that the films have good values of photoresponse, and the photocurrent remains stable after several hours of light soaking. This contribution will discuss the characteristics of the hydrogenated nanocrystalline silicon thin films deposited using increased process chamber pressure at a fixed hydrogen dilution ratio in monosilane gas.

  13. A study of the turbulent wake of an airfoil in an air stream with a 90° curvature using hot-wire anemometry and large eddy simulation

    OpenAIRE

    Farsimadan, Ehsaan

    2008-01-01

    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University. The broad aim of the work presented in this thesis is to investigate the wake of an airfoil under the combined effects of streamwise curvature and pressure gradient. This was accomplished by an experimental investigation using hot-wire anemometry and large eddy simulation (LES). The wake was generated by placing a NACA 0012 airfoil in a uniform stream of air, which is then subjected to an abr...

  14. Carbide-forming groups IVB-VIB metals: a new territory in the periodic table for CVD growth of graphene.

    Science.gov (United States)

    Zou, Zhiyu; Fu, Lei; Song, Xiuju; Zhang, Yanfeng; Liu, Zhongfan

    2014-07-09

    Early transition metals, especially groups IVB-VIB metals, can form stable carbides, which are known to exhibit excellent "noble-metal-like" catalytic activities. We demonstrate herein the applications of groups IVB-VIB metals in graphene growth using atmospheric pressure chemical vapor deposition technique. Similar to the extensively studied Cu, Ni, and noble metals, these transition-metal foils facilitate the catalytic growth of single- to few-layer graphene. The most attractive advantage over the existing catalysts is their perfect control of layer thickness and uniformity with highly flexible experimental conditions by in situ converting the dissolved carbons into stable carbides to fully suppress the upward segregation/precipitation effect. The growth performance of graphene on these transition metals can be well explained by the periodic physicochemical properties of elements. Our work has disclosed a new territory of catalysts in the periodic table for graphene growth and is expected to trigger more interest in graphene research.

  15. 衬底对 CVD生长石墨烯的影响研究%SUBSTR ATES FOR CVD GROWTH OF GRAPHENE RESEARCH

    Institute of Scientific and Technical Information of China (English)

    张玮; 满卫东; 涂昕; 林晓棋

    2013-01-01

    石墨烯有独特的结构和优异的性能,在电子、信息、能源、材料和生物医药等领域都有着广阔的应用前景。为了更好的应用这种新型材料,如何大规模可控合成高质量石墨烯是一个必须克服的困难。相比与机械剥离法、化学氧化还原法和碳化硅表面外延生长法,化学气相沉积法( CVD)因其可以生长大面积高质量连续石墨烯膜而倍受关注。基于石墨烯的生长机理,从衬底材料的角度,综述了近几年衬底对CVD生长石墨烯的影响的研究进展。展望了衬底选择的发展新趋势。%Graphene has a unique structure and excellent properties.It has broad application prospects in electronics, infor-mation, energy, materials and biomedicine and other fields.For a better application of this new material, how large quality-controlled synthesis of grapheme is a necessary overcome difficulties.Compared with the mechanical exfoliation, chemical ox-idation-reduction and epitaxial growth on SiC, chemical vapor deposition ( CVD) method has been receiving significant atten-tion because of it can grow high-quality large-area grapheme films.Based on the growth mechanism of grapheme , the recent substrates for CVD growth of grapheme research from the perspective of the substrate material is reviewed.Finally, the devel-opment of new trends in substrate selection are prospected.

  16. Study of porogen removal by atomic hydrogen generated by hot wire chemical vapor deposition for the fabrication of advanced low-k thin films

    Energy Technology Data Exchange (ETDEWEB)

    Godavarthi, S., E-mail: srinivas@cinvestav.mx [Program of Nanoscience and Nanotechnology, Cinvestav-IPN (Mexico); Universidad Nacional Autonoma de Mexico, Instituto de Ciencias Fisicas, Av. Universidad, Cuernavaca, Morelos (Mexico); Wang, C.; Verdonck, P. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Matsumoto, Y.; Koudriavtsev, I. [Program of Nanoscience and Nanotechnology, Cinvestav-IPN (Mexico); SEES, Electrical Engineering Department, Cinvestav-IPN (Mexico); Dutt, A. [SEES, Electrical Engineering Department, Cinvestav-IPN (Mexico); Tielens, H.; Baklanov, M.R. [imec, Kapeldreef 75, 3001 Leuven (Belgium)

    2015-01-30

    In order to obtain low-k dielectric films, a subtractive technique, which removes sacrificial porogens from a hydrogenated silicon oxycarbide (SiOC:H) film, has been used successfully by different groups in the past. In this paper, we report on the porogen removal from porogenated SiOC:H films, using a hot wire chemical vapor deposition (HWCVD) equipment. Molecular hydrogen is dissociated into atomic hydrogen by the hot wires and these atoms may successfully remove the hydrocarbon groups from the porogenated SiOC:H films. The temperature of the HWCVD filaments proved to be a determining factor. By Fourier transform infrared spectroscopy, X-ray reflectivity (XRR), secondary ion mass spectrometry (SIMS), ellipsometric porosimetry and capacitance-voltage analyses, it was possible to determine that for temperatures higher than 1700 °C, efficient porogen removal occurred. For temperatures higher than 1800 °C, the presence of OH groups was detected. The dielectric constant was the lowest, 2.28, for the samples processed at a filament temperature of 1800 °C, although porosity measurements showed higher porosity for the films deposited at the higher temperatures. XRR and SIMS analyses indicated densification and Tungsten (W) incorporation at the top few nanometers of the films.

  17. Influence of growth conditions on microstructure and defects in diamond coatings grown by microwave plasma enhanced CVD

    Indian Academy of Sciences (India)

    Kalyan Sundar Pal; Sandip Bysakh; Awadesh Kumar Mallik; Nandadulal Dandapat; Someswar Datta; Bichitra K Guha

    2015-06-01

    Diamond coatings were grown on SiO2/Si substrate under various process conditions by microwave plasma chemical vapour deposition (MPCVD) using CH4/H2 gas mixture. In this paper, we present a microstructural study to elucidate on the growth mechanism and evolution of defects, viz., strain, dislocations, stacking faults, twins and non-diamond impurities in diamond coatings grown under different process conditions. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the diamond coatings. It has been shown that our new approach of prolonged substrate pre-treatment under hydrogen plasma yielded a new growth sequence that the SiO2 layer on the Si substrate was first reduced to yield Si layer of ∼150 nm thickness before diamond was allowed to grow under CH4–H2 plasma, created subsequently. It has also been shown that Si and O as impurity from the substrate hinders the initial diamond growth to yield non-diamond phases. It is being suggested that the crystal defects like twins, stacking faults, dislocations in the diamond grains and dislocations in the intermediate Si layer are generated due to the development of non-uniform stresses during diamond growth at high temperature.

  18. Substrate patterning with NiOx nanoparticles and hot-wire chemical vapour deposition of WO3x and carbon nanostructures

    Science.gov (United States)

    Houweling, Z. S.

    2011-10-01

    The first part of the thesis treats the formation of nickel catalyst nanoparticles. First, a patterning technique using colloids is employed to create ordered distributions of monodisperse nanoparticles. Second, nickel films are thermally dewetted, which produces mobile species that self-arrange in non-ordered distributions of polydisperse particles. Third, the mobility of the nickel species is successfully reduced by the addition of air during the dewetting and the use of a special anchoring layer. Thus, non-ordered distributions of self-arranged monodisperse nickel oxide nanoparticles (82±10 nm x 16±2 nm) are made. Studies on nickel thickness, dewetting time and dewetting temperature are conducted. With these particle templates, graphitic carbon nanotubes are synthesised using catalytic hot-wire chemical vapour deposition (HWCVD), demonstrating the high-temperature processability of the nanoparticles. The second part of this thesis treats the non-catalytic HWCVD of tungsten oxides (WO3-x). Resistively heated tungsten filaments exposed to an air flow at subatmospheric pressures, produce tungsten oxide vapour species, which are collected on substrates and are subsequently characterised. First, a complete study on the process conditions is conducted, whereby the effects of filament radiation, filament temperature, process gas pressure and substrate temperature, are investigated. The thus controlled growth of nanogranular smooth amorphous and crystalline WO3-x thin films is presented for the first time. Partially crystalline smooth hydrous WO3-x thin films consisting of 20 nm grains can be deposited at very high rates. The synthesis of ultrafine powders with particle sizes of about 7 nm and very high specific surface areas of 121.7±0.4 m2·g-1 at ultrahigh deposition rates of 36 µm·min-1, is presented. Using substrate heating to 600°C or more, while using air pressures of 3·10-5 mbar to 0.1 mbar, leads to pronounced crystal structures, from nanowires, to

  19. Molecular dynamics simulation of graphene growth at initial stage on Ni(100) facet for low flux C energy by CVD

    Energy Technology Data Exchange (ETDEWEB)

    Syuhada, Ibnu, E-mail: ibnu-syuhada-p3@yahoo.com; Rosikhin, Ahmad, E-mail: aulia-fikri-h@yahoo.co.id; Fikri, Aulia, E-mail: a.rosikhin86@yahoo.co.id; Noor, Fatimah A., E-mail: fatimah@fi.itb.ac.id; Winata, Toto, E-mail: toto@fi.itb.ac.id [Departement of Physics, Institute of Technology Bandung, Tamansari 64 Street, East Java (Indonesia)

    2016-02-08

    In this study, atomic simulation for graphene growth on Ni (100) at initial stage via chemical vapor deposition method has been developed. The C-C atoms interaction was performed by Terasoff potential mean while Ni-Ni interaction was specified by EAM (Embedded Atom Modified). On the other hand, we used very simple interatomic potential to describe Ni-C interaction during deposition process. From this simulation, it shows that the formation of graphene is not occurs through a combined deposition mechanism on Ni substrate but via C segregation. It means, Ni-C amorphous is source for graphene growth when cooling down of Ni substrate. This result is appropriate with experiments, tight binding and quantum mechanics simulation.

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

    Science.gov (United States)

    2013-01-01

    a,b , Paul N. Barnes c , Chakrapani V. Varanasi e , Jack Burke d , Bang -Hung Tsao d , and Sharmila M. Mukhopadhyay b a. Air Force Research...catalysts play a big role in the structure and properties of the resulting CNTs. The three different techniques compared here have two different approaches...catalysts at the interface suggests the silica nanolayer keeps them anchored and prevents them from migrating during CNT growth. Figure 5: Cross

  1. Fracture Characteristics of Monolayer CVD-Graphene

    OpenAIRE

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-01-01

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. ...

  2. Film Growth Rates and Activation Energies for Core-Shell Nanoparticles Derived from a CVD Based Aerosol Process

    Directory of Open Access Journals (Sweden)

    Frederik Weis

    2015-03-01

    Full Text Available Silica core-shell nanoparticles of about 60–120 nm with a closed outer layer of bismuth or molybdenum oxide of 1–10 nm were synthesized by an integrated chemical vapor synthesis/chemical vapor deposition process at atmospheric pressure. Film growth rates and activation energies were derived from transmission electron microscopy (TEM images for a deposition process based on molybdenum hexacarbonyl and triphenyl bismuth as respective coating precursors. Respective activation energies of 123 ± 10 and 155 ± 10 kJ/mol are in good agreement with the literature and support a deposition mechanism based on surface-induced removal of the precursor ligands. Clean substrate surfaces are thus prerequisite for conformal coatings. Integrated aerosol processes are solvent-free and intrinsically clean. In contrast, commercial silica substrate particles were found to suffer from organic residues which hinder shell formation, and require an additional calcination step to clean the surface prior to coating. Dual layer core-shell structures with molybdenum oxide on bismuth oxide were synthesized with two coating reactors in series and showed similar film growth rates.

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

    Science.gov (United States)

    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.

  4. Atomic-Level Investigation of CHx and C2Hx Adsorption on β-SiC (111 Surface for CVD Diamond Growth from DFT Calculations

    Directory of Open Access Journals (Sweden)

    Naichao Chen

    2011-01-01

    Full Text Available The focus of this paper is on the adsorption of unsaturated hydrocarbon molecules on β-SiC (111 surfaces during diamond film growth. The CHx and C2Hx molecules have been investigated to obtain a specific insight into absorbing diamond processes on the atomic scale. Structural and electronic properties of CHx and C2Hx adsorption on the Si- and C-terminated surfaces have been studied by first-principles calculations based on density functional theory (DFT. From the calculated energetics and geometries, we find that C2Hx adsorption on the Si-terminated surfaces has six possible surface reconstructions. For the C-terminated surface, there exist eight possible surface reconstructions. Five surface reconstructions, including CH2 adsorption on the Si- and C-terminated surface, CH–CH2 and CH=CH2 adsorption on the C-terminated surface, and C2H5 adsorption on the Si-terminated surface, have the largest hydrogen adsorption energies and more stability of surface reconstructions. Calculations demonstrate that the Si-terminated surface is energetically more favorable for fabricating CVD diamond coatings than the C-terminated surface.

  5. Hydrogenated Silicon Carbide Thin Films Prepared with High Deposition Rate by Hot Wire Chemical Vapor Deposition Method

    Directory of Open Access Journals (Sweden)

    M. M. Kamble

    2014-01-01

    Full Text Available Structural, optical, and electrical properties of hydrogenated silicon carbide (SiC:H films, deposited from silane (SiH4 and methane (CH4 gas mixture by HW-CVD method, were investigated. Film properties are carefully and systematically studied as function of deposition pressure which is varied between 200 mTorr and 500 mTorr. The deposition rate is found to be reasonably high (9.4 nm/s CVD method to prepare stoichiometric SiC:H films.

  6. Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method.

    Science.gov (United States)

    Wang, Ying; Yang, Zaixing; Wu, Xiaofeng; Han, Ning; Liu, Hanyu; Wang, Shuobo; Li, Jun; Tse, WaiMan; Yip, SenPo; Chen, Yunfa; Ho, Johnny C

    2016-12-01

    Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact.

  7. Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method

    Science.gov (United States)

    Wang, Ying; Yang, Zaixing; Wu, Xiaofeng; Han, Ning; Liu, Hanyu; Wang, Shuobo; Li, Jun; Tse, WaiMan; Yip, SenPo; Chen, Yunfa; Ho, Johnny C.

    2016-04-01

    Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact.

  8. Fracture Characteristics of Monolayer CVD-Graphene

    Science.gov (United States)

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-03-01

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. The fracture toughness, describing the ability of a material containing inherent flaws to resist catastrophic failure, of the CVD-graphene has turned out to be exceptionally high, as compared to other carbon based 3D materials. These results imply that the CVD-graphene could be an ideal candidate as a structural material notwithstanding environmental susceptibility. In addition, the measurements reported here suggest that specific non-continuum fracture behaviors occurring in 2D monoatomic structures can be macroscopically well visualized and characterized.

  9. Note: effect of the tilting angle of the wire on the onset of natural convection in the transient hot wire method.

    Science.gov (United States)

    Lee, Seung-Hyun; Jang, Seok Pil

    2012-07-01

    In this paper, numerical and experimental investigations are systematically performed to identify the effect of the tilting angle of the wire on the onset of natural convection in the transient hot wire method (THWM), a widely accepted technique for measuring the thermal conductivity of various media, especially nanofluids. To validate our numerical simulation code, the numerical results are compared with theoretical solutions as well as with experimental results. Based on the results, we show that the onset time of natural convection in THWM decreases rapidly with the increase of the wire's tilting angle from vertical position. Also, we systematically show the effect of the wire's tilting angle on the linear region, which is a suitable measurement interval, and on the measurement error of THWM.

  10. Carburization of tungsten filaments in a hot-wire chemical vapor deposition process using 1,1,3,3-tetramethyl-1,3-disilacyclobutane.

    Science.gov (United States)

    Tong, L; Shi, Y J

    2009-09-01

    The alloying of tungsten filament when using 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB) in a hot-wire chemical vapor deposition reactor was systematically studied by scanning electron microscopy, Auger electron spectroscopy, analysis of the power consumed by the filament, and in situ mass spectrometric measurements of the gas-phase species produced in the process. Only carburization of the W filament was observed. The carburization is mainly caused by the interaction of methyl radicals with the filament. Graphite as well as both WC and W2C alloys can form on the filament surface, depending on the filament temperatures and source gas pressures. Both WC and graphite are converted to W2C with the diffusion of C into the filament. It is shown that filament carburization affects the consumption rate of the source gas and the intensities of gas-phase reaction products. Gas-phase reactions dominate at T or = 1800 degrees C.

  11. Low temperature silicon nitride by hot wire chemical vapour deposition for the use in impermeable thin film encapsulation on flexible substrates.

    Science.gov (United States)

    Spee, D A; van der Werf, C H M; Rath, J K; Schropp, R E I

    2011-09-01

    High quality non porous silicon nitride layers were deposited by hot wire chemical vapour deposition at substrate temperatures lower than 110 degrees C. The layer properties were investigated using FTIR, reflection/transmission measurements and 1:6 buffered HF etching rate. A Si-H peak position of 2180 cm(-1) in the Fourier transform infrared absorption spectrum indicates a N/Si ratio around 1.2. Together with a refractive index of 1.97 at a wavelength of 632 nm and an extinction coefficient of 0.002 at 400 nm, this suggests that a transparent high density silicon nitride material has been made below 110 degrees C, which is compatible with polymer films and is expected to have a high impermeability. To confirm the compatibility with polymer films a silicon nitride layer was deposited on poly(glycidyl methacrylate) made by initiated chemical vapour deposition, resulting in a highly transparent double layer.

  12. Turbulence measurements in a transonic boundary layer and free-shear flow using laser velocimetry and hot-wire anemometry techniques

    Science.gov (United States)

    Johnson, D. A.; Rose, W. C.

    1976-01-01

    Quantitative measurements of the turbulence fluctuations in velocity and mass flux have been obtained in Mach 0.6 and 0.8 turbulent boundary layer and free-shear layer flows by laser velocimetry and hot-wire anemometry techniques. To evaluate the effects of compressibility, these transonic data are compared to available incompressible and supersonic results. Based on some simplifying assumptions, estimates of the rms density fluctuations are made for which error bounds are given. In addition to these fluctuation data, the compressible mean velocity data obtained with the laser velocimeter are presented and compared to pitot tube results. The investigation was conducted in the Ames 6- by 6-Foot Supersonic Wind Tunnel at free-stream Mach numbers of 0.6 and 0.8 for a unit Reynolds number of about 10,000,000 per meter.

  13. Apparatus for Comparing Thermal Conductivity of Nanofluids and Base Fluid Using Simultaneously Measured Resistance Variation Signals from Two Hot Wire Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Shin Pyo [Kyonggi University, Suwon (Korea, Republic of)

    2015-01-15

    Exact comparisons of the thermal conductivities of the base fluid and a nanofluid are very important in the early stages of nanofluid development. A simple procedure of measuring the thermal conductivity of the two fluids by the transient hot wire method and numerically dividing these values is used for this purpose. However, because the experiments are not performed simultaneously and the physical properties of the measurement system are sometimes not properly known, large errors are incurred during the evaluation process. This article proposes a new apparatus for thermal conductivity comparison where the working principle is mainly based on relative measurement rather than absolute measurement. The measuring circuit and data processing steps are explained in detail; a validation test was performed using the well-known glycerine and engine oil.

  14. Gas doping ratio effects on p-type hydrogenated nanocrystalline silicon thin films grown by hot-wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Luo, P.Q. [Solar Energy Institute, Department of Physics, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China)], E-mail: robt@sjtu.edu.cn; Zhou, Z.B. [Solar Energy Institute, Department of Physics, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China)], E-mail: zbzhou@sjtu.edu.cn; Chan, K.Y. [Thin Film Laboratory, Faculty of Engineering, Multimedia University, Jalan Multimedia, Cyberjaya 63100, Selangor (Malaysia); Tang, D.Y.; Cui, R.Q.; Dou, X.M. [Solar Energy Institute, Department of Physics, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China)

    2008-12-30

    Hydrogenated nanocrystalline silicon (nc-Si:H) grown by hot-wire chemical vapor deposition (HWCVD) has recently drawn significant attention in the area of thin-film large area optoelectronics due to possibility of high deposition rate. We report on the effects of diborane (B{sub 2}H{sub 6}) doping ratio on the microstructural and optoelectrical properties of the p-type nc-Si:H thin films grown by HWCVD at low substrate temperature of 200 deg. C and with high hydrogen dilution ratio of 98.8%. An attempt has been made to elucidate the boron doping mechanism of the p-type nc-Si:H thin films deposited by HWCVD and the correlation between the B{sub 2}H{sub 6} doping ratio, crystalline volume fraction, optical band gap and dark conductivity.

  15. Note: Effect of the tilting angle of the wire on the onset of natural convection in the transient hot wire method

    Science.gov (United States)

    Lee, Seung-Hyun; Jang, Seok Pil

    2012-07-01

    In this paper, numerical and experimental investigations are systematically performed to identify the effect of the tilting angle of the wire on the onset of natural convection in the transient hot wire method (THWM), a widely accepted technique for measuring the thermal conductivity of various media, especially nanofluids. To validate our numerical simulation code, the numerical results are compared with theoretical solutions as well as with experimental results. Based on the results, we show that the onset time of natural convection in THWM decreases rapidly with the increase of the wire's tilting angle from vertical position. Also, we systematically show the effect of the wire's tilting angle on the linear region, which is a suitable measurement interval, and on the measurement error of THWM.

  16. Annealing effects on capacitance-voltage characteristics of a-Si/SiN(x) multilayer prepared using hot-wire chemical vapour deposition.

    Science.gov (United States)

    Panchal, A K; Rai, D K; Solanki, C S

    2011-04-01

    Post-deposition annealing of a-Si/SiN(x) multilayer films at different temperature shows varying shift in high frequency (1 MHz) capacitance-voltage (HFCV) characteristics. Various a-Si/SiN(x) multilayer films were deposited using hot wire chemical vapor deposition (HWCVD) and annealed in the temperature range of 800 to 900 degrees C to precipitate Si quantum dots (Si-QD) in a-Si layers. HFCV measurements of the as-deposited and annealed films in metal-insulator-semiconductor (MIS) structures show hysterisis in C-V curves. The hysteresis in the as-deposited films and annealed films is attributed to charge trapping in Si-dangling bonds in a-Si layer and in Si-QD respectively. The charge trapping density in Si-QD increases with temperature while the interface defects density (D(it)) remains constant.

  17. An Oscillating Boundary Temperature Method for the Determination of Transient Thermal Conductivity and Internal Heat Generation with a Comparison to a Transient Hot-Wire Method

    Science.gov (United States)

    Chirdon, William M.; Patil, Abhijeet P.

    2011-10-01

    An oscillating boundary temperature (OBT) method is proposed to simultaneously determine transient thermal properties including thermal conductivity, thermal diffusivity, internal heat generation, and volumetric heat capacity for exothermic solids and semi-solids over a narrow, controlled temperature range by using internal temperature measurements of the thermal wave. A comparison of this method and a transient hot-wire (THW) method is conducted in the presence of heat generation using physical properties which change over time. The advantages and disadvantages of both methods are discussed. The OBT method is potentially useful for the analysis of exothermic solid or semi-solid materials such as hydrating (freshly mixed) cement and concrete, polymers and composites undergoing polymerization reactions, and biological tissues.

  18. Measurements of Thermal Conductivity and Thermal Diffusivity of Hen Egg-White Lysozyme Crystals and Its Solution Using the Transient Short Hot Wire Method

    Science.gov (United States)

    Fujiwara, Seiji; Maki, Syou; Maekawa, Ryunosuke; Tanaka, Seiichi; Hagiwara, Masayuki

    2017-08-01

    Protein crystals are an essentially important biological sample to advance the analysis of X-ray structure, but their thermophysical properties, especially thermal conductivity and thermal diffusivity, have not been studied sufficiently. This current situation can be attributed to various kinds of technical problems; e.g., the fragility of protein crystals and the difficulty of nucleation control. Ideally speaking, protein crystallization should be carried out under a " containerless condition" to eliminate any mechanical distortion of the crystals from the walls. To realize the condition, we have developed an original crystallization method by means of the magneto-Archimedes effect. In this paper, a transient short hot wire method was combined with the technique of magneto-Archimedes effect to realize simultaneous measurement of thermal conductivity and thermal diffusivity of hen egg-white lysozyme (HEWL) crystals. As the results, thermal conductivity and thermal diffusivity of HEWL crystals were found to be 0.410-0.438 \\hbox {W}\\cdot \\hbox {m}^{-1}\\cdot \\hbox {K}^{-1} and 3.77-5.18× 10^{-8} \\hbox {m}2\\cdot \\hbox {s}^{-1}, respectively. We clarified by the crystallizing process of HEWL that the crystals were magnetically levitated at the air-liquid interface and the short hot wire was completely buried into them as the crystals grew. We also measured the HEWL solution by the same methods. The thermal conductivity of the solution had almost the same value as that of water and had little dependency on the concentration of HEWL, but the thermal diffusivity was unclear.

  19. Numerical-experimental analyses by Hot-Wire method of an alumina cylinder for future studies on thermal conductivity of the fusion breeder materials

    Science.gov (United States)

    Lo Frano, R.; Moscardini, M.; Aquaro, D.

    2014-11-01

    The determination of the thermal conductivity of breeder materials is one of the main goal in order to find the best candidate material for the fusion reactor technology. Experimental tests have been and will be carried out with a dedicated experimental devices, built at the Department of Civil and Industrial Engineering of the University of Pisa. The methodological approach used in doing that is characterized by two main phases strictly interrelated each other: the first one focused on the experimental evaluation of thermal conductivity of a ceramic material, by means of hot wire method, to be subsequently used in the second phase, based on the test rig method, to determine the thermal conductivity of pebble bed material. To the purpose, two different experimental devices have been designed and built. This paper deals with the first phase of the methodology. In this framework, the equipment set up and built to perform Hot wire tests, the ceramic material (a cylinder of alumina), the experimental procedure and the measured results obtained varying the temperature, are presented and discussed. The experimental campaign has been lead from 50°C up to 400°C. The thermal conductivity of the ceramic material at different bulk temperatures has been obtained in stationary conditions (detected on the basis of the temperature values measured during the experiment). Numerical analyses have been also performed by means of FEM code Ansys©. The numerical results were in quite good agreement with the experimental one, confirming also the reliability of code in reproducing heat transfer phenomena.

  20. Ultra-thin SiN{sub x} in superlattice via nitridation of a-Si in-situ hot wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Rai, Dharmendra Kumar; Solanki, Chetan Singh; Balasubramaniam, K.R., E-mail: bala.kavaipatti@gmail.com

    2014-08-28

    The fabrication of ultra-thin SiN{sub x} (< 2 nm) is a necessary step in third generation photovoltaics, memory, or light-emitting diode applications. Using the low temperature, cheap, scaleable synthesis technique of hot-wire chemical vapor deposition (HWCVD) for this purpose poses many challenges. Here, an approach of fabricating ultra thin SiN{sub x} of thickness ∼ 1.9 nm in a superlattice (SL) structure via nitridation of a-Si layers in-situ HWCVD at 250 °C is reported. Quantum well SL and quantum dot (QD) SL films are realized, wherein SiN{sub x} layers are formed by nitriding a-Si. Both these films investigated by Raman spectroscopy and high resolution transmission electron microscopy, reveal the formation of ultra-thin SiN{sub x} in a SL structure with a-Si, accompanied by sharp interfaces. In addition, annealing of the SL structures, results in QDs of crystalline Si in the a-Si layers, maintaining the SiN{sub x} layer as well as the sharp interface between the SiN{sub x} and a-Si layers of the as-deposited SL structure. - Highlights: • Ultra thin SiN{sub x} is fabricated by hot wire chemical vapor deposition. • SiN{sub x} layer of thickness ∼ 1.9 nm is formed via nitridation of a-Si layer at 250 °C. • Ultra thin SiN{sub x} layers are realized in superlattice films of quantum wells and quantum dots.

  1. Development of scientific and technological basis for the fabrication of thin film solar cells on the basis of a-Si:H and {mu}c-Si:H using the 'hot-wire' deposition technique. Final report; Entwicklung wissenschaftlicher und technischer Grundlagen fuer die Herstellung von Duennschichtsolarzellen auf der Basis des a-Si:H und {mu}c-Si:H mit der 'Hot-Wire'-Depositionstechnik. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, B.

    2002-01-22

    Two new deposition systems were realized enabling the entire and respectively, large area deposition of a-Si:H based solar cells using the so called 'hot-wire' (HW) CVD. The deposition conditions for appropriate n- and p-doped a-Si:H and {mu}c-Si:H layers have been developed. For the first time in the world a-Si:H based pin solar cells were entirely deposited by the HWCVD method. A maximum initial conversion efficiency of {eta}{sub initial}=8.9% was obtained. After the development of a suitable p/n-tunnel/recombination junction pin-pin tandem structures with a-Si:H absorbers could be entirely fabricated by the HWCVD for the first time in the world, too. A conversion efficiency of {eta}=7% was measured for the tandem cell, after some structural degradation took place. In general, the stability of the HWCVD solar cells is not satisfactory, what could be attributed to a structural instability of the HWCVD-p-layers. For the first time we have deposited nip solar cells on stainless steel substrates entirely by HWCVD ({eta}{sub initial}>6%). The incorporation of {mu}c-Si:H absorber layers by HWCVD or ECWR-PECVD into pin solar cells was not successfull until now. Large area deposition of a-Si:H films has been performed in a simple vacuum vessel. Under consideration of appropriate filament and gas supply geometry as well as simulation calculations a good electronic quality and a film thickness uniformity of {delta}d={+-}2.5% of the material was obtained. i-layers for small area solar cells on an area of 20 x 20 cm{sup 2} have been deposited which could be completed to solar cells with very uniform conversion efficiencies of {eta}{sub initial} = 6,1{+-}0.2%. This result represents a proof of concept for the large area deposition of a-Si:H based solar cells using the HWCVD. Also for the first time the HWCVD was used for the deposition of emitter layers on c-Si-wafers to realize hetero solar cells. Hetero solar cells with amorphous, microcrystalline and epitaxial n

  2. A new calibration method of constant temperature hot wire anemometer%恒温热线风速仪的一种新型校准方法

    Institute of Scientific and Technical Information of China (English)

    姚惠元; 刘国政; 孙楠; 董军

    2013-01-01

    恒温热线风速仪作为一种风洞流场测量元件,在湍流脉动测速任务中发挥了重要作用。对热线风速仪的校准工作进行了研究,将B样条与递推最小二乘相结合,提出了一种新型校准方法。该方法选取具有低阶光滑特性的B样条函数进行逆向建模,并采用递推最小二乘的方法估计控制参数,有效地提高了校准精度和实时性。通过对实际风洞实验的数据分析,验证了提出的该校正方法的有效性,并表明其具有样本点少、校正精度高、简单实用等显著优点。%As a flow field measuring elements for wind tunnel,the constant temperature hot wire anemometer plays an im-portant role in the measurement of turbulent fluctuation task. The calibration of the hot wire anemometer is studied. Using the B-spline and recursive least squares as a combination,a new calibration method is proposed,which chooses B-spline function with low order smooth characteristics for reverse modeling,and estimates the control parameters using the method of recursive least squares. The method effectively improved the calibration accuracy and real-time. Through the analysis of wind tunnel experimen-tal data,the effectiveness of the correction method is validated. The experiment shows that it has the advantages of fewer sample points,higher correction accuracy,simple and useful.

  3. Developing the Beijing CVD

    Institute of Scientific and Technical Information of China (English)

    LU JINGXIAN

    2006-01-01

    @@ Slowly but surely, the high-end villa property in Beijing is gaining new momentum. Limited amounts of new properties, rising prices and increasing demand will be the trend in the villa market in 2006, real estate experts predict. Among them, the exclusive Central Villa District(CVD), a top-tier villa area along the Wenyu River in northeast Beijing, has emerged as a hot spot of the market.

  4. Nanocrystalline Si/SiO{sub 2} core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, Y., E-mail: ymatsumo@cinvestav.mx; Dutt, A. [SEES, Electrical Engineering Department, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Cinvestav-IPN, Mexico, D.F. 07360 (Mexico); Santana-Rodríguez, G. [Institute of Material Research, Universidad Nacional Autónoma de México, Coyoacán 04510 (Mexico); Santoyo-Salazar, J. [Department of Physics, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Cinvestav-IPN, Mexico, D.F. 07360 (Mexico); Aceves-Mijares, M. [Departament of Electronics, Instituto Nacional de Astrofísica Óptica y Electrónica, Tonantzintla, Puebla 72000 (Mexico)

    2015-04-27

    We report the fabrication of a stable Si/SiO{sub 2} core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiO{sub x} matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

  5. Effect of Si-H bond on the gas-phase chemistry of trimethylsilane in the hot wire chemical vapor deposition process.

    Science.gov (United States)

    Shi, Y J; Li, X M; Toukabri, R; Tong, L

    2011-09-22

    The effect of the Si-H bond on the gas-phase reaction chemistry of trimethylsilane in the hot-wire chemical vapor deposition (HWCVD) process has been studied by examining its decomposition on a hot tungsten filament and the secondary gas-phase reactions in a reactor using a soft laser ionization source coupled with mass spectrometry. Trimethylsilane decomposes on the hot filament via Si-H and Si-CH(3) bond cleavages. A short-chain mechanism is found to dominate in the secondary reactions in the reactor. It has been shown that the hydrogen abstractions of both Si-H and C-H occur simultaneously, with the abstraction of Si-H being favored. Tetramethylsilane and hexamethyldisilane are the two major products formed from the radical recombination reactions in the termination steps. Three methyl-substituted disilacyclobutane molecules, i.e., 1,3-dimethyl-1,3-disilacyclobutane, 1,1,3-trimethyl-1,3-disilacyclobutane, and 1,1,3,3-tetramethyl-1,3-disilacyclobutane are also produced in reactor from the cycloaddition reactions of methyl-substituted silene species. Compared to tetramethylsilane and hexamethyldisilane, a common feature with trimethylsilane is that the short-chain mechanism still dominates. However, a more active involvement of the reactive silene intermediates has been found with trimethylsilane.

  6. N-type crystalline silicon films free of amorphous silicon deposited on glass by HCl addition using hot wire chemical vapour deposition.

    Science.gov (United States)

    Chung, Yung-Bin; Park, Hyung-Ki; Lee, Sang-Hoon; Song, Jean-Ho; Hwang, Nong-Moon

    2011-09-01

    Since n-type crystalline silicon films have the electric property much better than those of hydrogenated amorphous and microcrystalline silicon films, they can enhance the performance of advanced electronic devices such as solar cells and thin film transistors (TFTs). Since the formation of amorphous silicon is unavoidable in the low temperature deposition of microcrystalline silicon on a glass substrate at temperatures less than 550 degrees C in the plasma-enhanced chemical vapour deposition and hot wire chemical vapour deposition (HWCVD), crystalline silicon films have not been deposited directly on a glass substrate but fabricated by the post treatment of amorphous silicon films. In this work, by adding the HCl gas, amorphous silicon-free n-type crystalline silicon films could be deposited directly on a glass substrate by HWCVD. The resistivity of the n-type crystalline silicon film for the flow rate ratio of [HCl]/[SiH4] = 7.5 and [PH3]/[SiH4] = 0.042 was 5.31 x 10(-4) ohms cm, which is comparable to the resistivity 1.23 x 10(-3) ohms cm of films prepared by thermal annealing of amorphous silicon films. The absence of amorphous silicon in the film could be confirmed by high resolution transmission electron microscopy.

  7. Design of Robot Wire Feed System for Hot Wire TIG Welding%热丝TIG焊机器人送丝系统设计

    Institute of Scientific and Technical Information of China (English)

    杨芙; 曲治瑾; 柏久阳; 张文明

    2012-01-01

    The wire feed system is the important part of TIG (Tungsten Inert Gas) welding robot. However, the traditional wire feed system is almost electrical control, besides, positioning accuracy is low and cannot realize the digital control. In order to meet the application of the TIG welding robot, a hot wire TIG welding robot of wire feed system based on PIC(Peripheral Interface Controller) was designed. The regulation of wire feed speed at 2 m/min-4 m/min was achieved and free communication system was realized by host computer.%送丝系统是TIG焊机器人系统的重要组成部分.传统送丝系统多采用电气控制,定位精度低且难以实现数字化控制.为了配合TIG焊机器人的应用,本文设计了一款基于PIC单片机的热丝TIG焊机器人送丝系统.实现了送丝速度在0.4~4 m/min范围可调,同时实现了送丝控制系统与机器人的自由通讯并能接受机器人的管理.

  8. Reliability of thermal conductivity measurement of liquids by using transient hot-wire, photon-correlation spectroscopy and the laser flash method

    Science.gov (United States)

    Kwon, Suyong; Lee, Joohyun; Kim, Dae Ho

    2016-05-01

    Measuring the thermal conductivity of liquids is important, but not easy, because of the complexity of and the natural convection in liquids, and reliable thermal conductivity measurements in liquids under various sample conditions is essential for data accuracy. We have introduced and developed a validation chain for measuring the thermal conductivity of liquids by using three different experimental methods: the transient hot-wire (THW), the photon correlation spectroscopy (PCS) and the laser flash (LF) methods in the temperature range from -30 to 90 °C. We checked the performance of the validation chain developed in this study by measuring the thermal conductivity of liquid toluene. We found good agreement between the thermal conductivity data obtained by using the THW, PCS and LF methods. To demonstrate the use of this validation chain for measurements of thermophysical properties in liquids, we also showed its use in measuring the specific heat of a volatile liquid, toluene which can be extracted from thermal conductivity, thermal diffusivity, and density measurements without any effects of volatilization.

  9. 恒温热线式气体流量传感器的研究%Study of Constant Temperature Hot-wire Gas-flow Transducer

    Institute of Scientific and Technical Information of China (English)

    沈永滨; 李庆军; 修爱军

    2000-01-01

    通过理论分析对金属丝在强迫热交换下,建立了测量气体流量数学模型;设计了温度补偿电路,通过实验数据对其性能作出了评价,使恒温热线式气体流量传感器具有灵敏度高、响应速度快、测量范围宽等特点.此测量方法可广泛应用于各种可燃气体流量的测量.%The mathematical model of Hot-wire gas-flow transducer is built up through theoretical analysis on the metal-wire under forced heat exchanging; and the temperaturecompensating circuit is designed and evaluated by experimental data, so that the transducer gets the features of high-sensitivity, quick-responding, wide-measuring range and so on. This kind of mesuring-methiod can be widely used in the flow-measuring of various flammable gases.

  10. Nanocrystalline Si/SiO2 core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

    Science.gov (United States)

    Matsumoto, Y.; Dutt, A.; Santana-Rodríguez, G.; Santoyo-Salazar, J.; Aceves-Mijares, M.

    2015-04-01

    We report the fabrication of a stable Si/SiO2 core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiOx matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

  11. Effect of the initial structure on the electrical property of crystalline silicon films deposited on glass by hot-wire chemical vapor deposition.

    Science.gov (United States)

    Chung, Yung-Bin; Lee, Sang-Hoon; Bae, Sung-Hwan; Park, Hyung-Ki; Jung, Jae-Soo; Hwang, Nong-Moon

    2012-07-01

    Crystalline silicon films on an inexpensive glass substrate are currently prepared by depositing an amorphous silicon film and then crystallizing it by excimer laser annealing, rapid thermal annealing, or metal-induced crystallization because crystalline silicon films cannot be directly deposited on glass at a low temperature. It was recently shown that by adding HCI gas in the hot-wire chemical vapor deposition (HWCVD) process, the crystalline silicon film can be directly deposited on a glass substrate without additional annealing. The electrical properties of silicon films prepared using a gas mixture of SiH4 and HCl in the HWCVD process could be further improved by controlling the initial structure, which was achieved by adjusting the delay time in deposition. The size of the silicon particles in the initial structure increased with increasing delay time, which increased the mobility and decreased the resistivity of the deposited films. The 0 and 5 min delay times produced the silicon particle sizes of approximately 10 and approximately 28 nm, respectively, in the initial microstructure, which produced the final films, after deposition for 300 sec, of resistivities of 0.32 and 0.13 Omega-cm, mobilities of 1.06 and 1.48 cm2 V(-1) S(-1), and relative densities of 0.87 and 0.92, respectively.

  12. Mechanical and piezoresistive properties of thin silicon films deposited by plasma-enhanced chemical vapor deposition and hot-wire chemical vapor deposition at low substrate temperatures

    Science.gov (United States)

    Gaspar, J.; Gualdino, A.; Lemke, B.; Paul, O.; Chu, V.; Conde, J. P.

    2012-07-01

    This paper reports on the mechanical and piezoresistance characterization of hydrogenated amorphous and nanocrystalline silicon thin films deposited by hot-wire chemical vapor deposition (HWCVD) and radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using substrate temperatures between 100 and 250 °C. The microtensile technique is used to determine film properties such as Young's modulus, fracture strength and Weibull parameters, and linear and quadratic piezoresistance coefficients obtained at large applied stresses. The 95%-confidence interval for the elastic constant of the films characterized, 85.9 ± 0.3 GPa, does not depend significantly on the deposition method or on film structure. In contrast, mean fracture strength values range between 256 ± 8 MPa and 600 ± 32 MPa: nanocrystalline layers are slightly stronger than their amorphous counterparts and a pronounced increase in strength is observed for films deposited using HWCVD when compared to those grown by PECVD. Extracted Weibull moduli are below 10. In terms of piezoresistance, n-doped radio-frequency nanocrystalline silicon films deposited at 250 °C present longitudinal piezoresistive coefficients as large as -(2.57 ± 0.03) × 10-10 Pa-1 with marginally nonlinear response. Such values approach those of crystalline silicon and of polysilicon layers deposited at much higher temperatures.

  13. Hot-wire chemical vapor deposition prepared aluminum doped p-type microcrystalline silicon carbide window layers for thin film silicon solar cells

    Science.gov (United States)

    Chen, Tao; Köhler, Florian; Heidt, Anna; Carius, Reinhard; Finger, Friedhelm

    2014-01-01

    Al-doped p-type microcrystalline silicon carbide (µc-SiC:H) thin films were deposited by hot-wire chemical vapor deposition at substrate temperatures below 400 °C. Monomethylsilane (MMS) highly diluted in hydrogen was used as the SiC source in favor of SiC deposition in a stoichiometric form. Aluminum (Al) introduced from trimethylaluminum (TMAl) was used as the p-type dopant. The material property of Al-doped p-type µc-SiC:H thin films deposited with different deposition pressure and filament temperature was investigated in this work. Such µc-SiC:H material is of mainly cubic (3C) SiC polytype. For certain conditions, like high deposition pressure and high filament temperature, additional hexagonal phase and/or stacking faults can be observed. P-type µc-SiC:H thin films with optical band gap E04 ranging from 2.0 to 2.8 eV and dark conductivity ranging from 10-5 to 0.1 S/cm can be prepared. Such transparent and conductive p-type µc-SiC:H thin films were applied in thin film silicon solar cells as the window layer, resulting in an improved quantum efficiency at wavelengths below 480 nm.

  14. 固体单相催化剂CVD法制备成束或分散MWCNT%Solid Single Phase Catalyst for Growth of Bundled or Dispersed MWCNT by CVD

    Institute of Scientific and Technical Information of China (English)

    徐军明; 张孝彬; 李昱; 陶新永; 陈飞; 杨晓芳

    2003-01-01

    Fe-Mo-Mg-O catalyst prepared by combustion method has great efficiency to grow carbon nanotubes with CVD method. Through investigation of TEM, it is found that bundles of multi-wall carbon nanotubos (MWCNT) can be got when the catalyst is directly used to synthesize the product in CH4/H2 afinosphere; however, the dispersed carbon nanotubes are obtained while the catalyst is reduced firstly in the H2 before the synthesis. The morphology and structure of the catalysts before and after reduced are analyzed by TEM and XRD. The growth mechanism is suggeested for the formation off these two kinds of carbon nanotubes.

  15. Review and Analysis of Hot-wire/film Anemometry for Hypersonic Airflow Measurement%高超声速热线/热膜风速仪研究综述及分析

    Institute of Scientific and Technical Information of China (English)

    韦青燕; 张天宏

    2012-01-01

    In terms of the requirements for hot - wire/film anemometry in hypersonic airflow measurement, the recent research and development of hot - wire/film anemometry are summarized. The key problems and technical features are discussed for hypersonic hot-wire/film anemometry based on probe manufacture, control circuit design and probe calibration. The effects on thermal testing system are analyzed form hot-wire/film material, geometry and control-circuit mode, and several calibration methods are compared. Finally, some approaches have been proposed as reference to the research of hypersonic anemometry in China.%针对高超声速流场测量对热线/热膜风速仪的需求,对近年来国内外热线/热膜风速仪研制现状进行了归纳.重点从探头制备、控制电路设计及探头校准三个方面,阐述了热线/热膜测试系统应用于高超声速流场测量必须解决的关键问题及各种方案的特点;分析了探头材料、构型及控制电路模式对高超声速流场中热线/热膜测试系统性能的影响,并对热线/热膜探头校准的几种方法进行了对比,总结出可供发展我国自主知识产权高超声速热线/热膜技术的意见.

  16. Hot-wire air flow meter for gasoline fuel-injection system. Calculation of air mass in cylinder during transient condition; Gasoline funsha system yo no netsusenshiki kuki ryuryokei. Kato untenji no cylinder juten kukiryo no keisan

    Energy Technology Data Exchange (ETDEWEB)

    Oyama, Y. [Hitachi Car Engineering, Ltd., Tokyo (Japan); Nishimura, Y.; Osuga, M.; Yamauchi, T. [Hitachi, Ltd., Tokyo (Japan)

    1997-10-01

    Air flow characteristics of hot-wire air flow meters for gasoline fuel-injection systems with supercharging and exhaust gas recycle during transient conditions were investigated to analyze a simple method for calculating air mass in cylinder. It was clarified that the air mass in cylinder could be calculated by compensating for the change of air mass in intake system by using aerodynamic models of intake system. 3 refs., 6 figs., 1 tab.

  17. GCMS and FTIR studies of by-product inhibited growth and the rate-limiting step in TEOS-based SiO{sub 2} CVD

    Energy Technology Data Exchange (ETDEWEB)

    Bartram, M.E.; Moffat, H.K. [Sandia National Labs., Albuquerque, NM (United States). Chemical Processing Science Dept.

    1995-04-01

    To improve process reliability and deposition methods, it is essential to identify the rate-limiting step in TEOS-based SiO{sub 2} CVD and its dependence on process conditions. For this purpose, experiments designed to evaluate by-product inhibition effects and to identify the rate-limiting step in TEOS decomposition have been carried out in a research reactor using GCMS and FTIR. By repetitively sampling a series of reactions in which TEOS was first mixed with ethylene, ethanol, and water in the gas-phase, GCMS was used to show clearly that these reaction by-products do not inhibit the heterogeneous reaction step on SiO{sub 2} at 1,000K. FTIR was used to determine that ethoxy groups from TEOS dissociative chemisorption have a significant lifetime on the SiO{sub 2} surface at CVD temperatures and have an activation energy for decomposition of 16kcal/mol{+-}4kcal/mol. This is much higher than the activation energy of 6 kcal/mol reported for the initial chemisorption step and is near the 22 kcal/mol reported for the overall activation energy for SiO{sub 2} deposition in a cold-wall reactor. These results suggest that, whether or not surface ethoxy groups inhibit TEOS reactions, their decomposition may be directly related to the rate-limiting step in SiO{sub 2} deposition.

  18. Decomposition of hexamethyldisilane on a hot tungsten filament and gas-phase reactions in a hot-wire chemical vapor deposition reactor.

    Science.gov (United States)

    Shi, Yujun; Li, Xinmao; Tong, Ling; Toukabri, Rim; Eustergerling, Brett

    2008-05-14

    To study the effect of an Si-Si bond on gas-phase reaction chemistry in the hot-wire chemical vapor deposition (HWCVD) process with a single source alkylsilane molecule, soft ionization with a vacuum ultraviolet wavelength of 118 nm was used with time-of-flight mass spectrometry to examine the products from the primary decomposition of hexamethyldisilane (HMDS) on a heated tungsten (W) filament and from secondary gas-phase reactions in a HWCVD reactor. It is found that both Si-Si and Si-C bonds break when HMDS decomposes on the W filament. The dominance of the breakage of Si-Si over Si-C bond has been demonstrated. In the reactor, the abstraction of methyl and H atom, respectively, from the abundant HMDS molecules by the dominant primary trimethylsilyl radicals produces tetramethylsilane (TMS) and trimethylsilane (TriMS). Along with TMS and TriMS, various other alkyl-substituted silanes (m/z = 160, 204, 262) and silyl-substituted alkanes (m/z = 218, 276, 290) are also formed from radical combination reactions. With HMDS, an increasing number of Si-Si bonds are found in the gas-phase reaction products aside from the Si-C bond which has been shown to be the major bond connection in the products when TMS is used in the same reactor. Three methyl-substituted 1,3-disilacyclobutane species (m/z = 116, 130, 144) are present in the reactor with HMDS, suggesting a more active involvement from the reactive silene intermediates.

  19. The application and optimization of induction hot wire systerm of aluminum alloy%铝合金感应热丝系统应用及优化

    Institute of Scientific and Technical Information of China (English)

    黄学斌

    2014-01-01

    Ultrasonic and high frequency induction hot wire systems of aluminum alloy were developed in this study. By using a high frequency induction heating power with 1.1 MHz frequency instead of the ultrasonic heating power, the 1.2 mm aluminum welding wire could be heated to a satisfactory temperature. Besides, both the aluminum welding wire with the diameter of 1.6 mm and 1.2 mm could be heated steadly and effectively at 0~2 m/min wire feeding rate. Furthermore, the differences of wire temperature-induction heating current relationships between the two heating systems were compared and discussed.%构建了铝合金超音频及高频感应热丝系统,实现了铝合金感应热丝系统的稳定应用。通过采用最高振荡频率为1.1 MHz的高频感应电源,解决了超音频感应热丝系统无法有效加热直径为1.2 mm铝合金焊丝的问题,实现了1.6 mm和1.2 mm不同直径铝合金焊丝在0~2 m/min的送丝速度内的有效稳定加热。对比了超音频及高频感应热丝系统不同直径焊丝温度随感应电流的变化曲线,并对相关现象进行了解释和分析。

  20. Improvement of μc-Si:H n–i–p cell efficiency with an i-layer made by hot-wire CVD by reverse H2-profiling

    NARCIS (Netherlands)

    Li, H. B. T.; Franken, R.H.; Stolk, R.L.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2008-01-01

    The technique of maintaining a proper crystalline ratio in microcrystalline silicon (μc-Si:H) layers along the thickness direction by decreasing the H2 dilution ratio during deposition (H2 profiling) was introduced by several laboratories while optimizing either n–i–p or p–i–n μc-Si:H cells made by

  1. Improvement of μc-Si:H n–i–p cell efficiency with an i-layer made by hot-wire CVD by reverse H2-profiling

    NARCIS (Netherlands)

    Li, H. B. T.; Franken, R.H.; Stolk, R.L.; van der Werf, C.H.M.; Rath, J.K.; Schropp, R.E.I.

    2008-01-01

    The technique of maintaining a proper crystalline ratio in microcrystalline silicon (μc-Si:H) layers along the thickness direction by decreasing the H2 dilution ratio during deposition (H2 profiling) was introduced by several laboratories while optimizing either n–i–p or p–i–n μc-Si:H cells made by

  2. The In situ growth of Nanostructures on Surfaces (INS) endstation of the ESRF BM32 beamline: a combined UHV-CVD and MBE reactor for in situ X-ray scattering investigations of growing nanoparticles and semiconductor nanowires.

    Science.gov (United States)

    Cantelli, V; Geaymond, O; Ulrich, O; Zhou, T; Blanc, N; Renaud, G

    2015-05-01

    This paper presents the upgraded `In situ growth of Nanoscructures on Surfaces' (INS) endstation of the InterFace beamline IF-BM32 at the European Synchrotron Radiation Facility (ESRF). This instrument, originally designed to investigate the structure of clean surfaces/interfaces/thin-films by surface X-ray diffraction, has been further developed to investigate the formation and evolution of nanostructures by combining small- and wide-angle X-ray scattering methodologies, i.e. grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXD). It consists of a UHV chamber mounted on a z-axis type goniometer, equipped with residual gas analysis, reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) to complete the X-ray scattering investigations. The chamber has been developed so as up to eight sources of molecular beam epitaxy (MBE) can be simultaneously mounted to elaborate the nanostructures. A chemical vapor deposition (CVD) set-up has been added to expand the range of growing possibilities, in particular to investigate in situ the growth of semiconductor nanowires. This setup is presented in some detail, as well as the first in situ X-ray scattering measurements during the growth of silicon nanowires.

  3. Nanomorph Silicon Thin Films Prepared by Using an HW-MWECR CVD System

    Institute of Scientific and Technical Information of China (English)

    HU Yue-Hui; MA Zhan-Jie; ZHOU Huai-En; ZHU Xiu-Hong; CHEN Guang-Hua; ZHOU Jian-Er; RONG Yan-Dong; LI Ying; SONG Xue-Mei; ZHANG Wen-Li; DING Yi; GAO Zhuo

    2005-01-01

    @@ We have prepared hydrogenated nano-amorph silicon (na-Si:H) films by using a hot-wire-assisted microwave electron-cyclotron-resonance (HW-MWECR) chemical vapour deposition (CVD) system. The films are deposited in two steps: in the first 9min, a hydrogenated amorphous silicon layer is deposited by using hydrogen-diluted silane with a concentration of SiH4/(SiH4+H2) = 20%, and then a nanocrystalline silicon (nc-Si) layer is deposited by using various highly hydrogen-diluted silane. The Raman TO-like mode peak of the films was found in the range 497-508 cm-1. When the silane concentration used for preparation of the nc-Si layer is 14.3%, the film has a large crystalline volume fraction of 65.4%, a wide optical band gap of 1.89eV and a low hydrogen content of 9.5at.%. Moreover, the na-Si:H films rather than nc-Si possess high photosensitivity of about 15.

  4. Study of low-defect and strain-relaxed GeSn growth via reduced pressure CVD in H2 and N2 carrier gas

    Science.gov (United States)

    Margetis, J.; Mosleh, A.; Al-Kabi, S.; Ghetmiri, S. A.; Du, W.; Dou, W.; Benamara, M.; Li, B.; Mortazavi, M.; Naseem, H. A.; Yu, S.-Q.; Tolle, J.

    2017-04-01

    High quality, thick (up to 1.1 μm), strain relaxed GeSn alloys were grown on Ge-buffered Si (1 0 0) in an ASM Epsilon® chemical vapor deposition system using SnCl4 and low-cost commercial GeH4 precursors. The significance of surface chemistry in regards to growth rate and Sn-incorporation is discussed by comparing growth kinetics data in H2 and N2 carrier gas. The role of carrier gas is also explored in the suppression of Sn surface segregation and evolution of layer composition and strain profiles via secondary ion mass spectrometry and X-ray diffraction. Transmission electron microscopy revealed the spontaneous compositional splitting and formation of a thin intermediate layer in which dislocations are pinned. This intermediate layer enables the growth of a thick, strain relaxed, and defect-free epitaxial layer on its top. Last, we present photoluminescence results which indicate that both N2 and H2 growth methods produce optoelectronic device quality material.

  5. Dispersive growth and laser-induced rippling of large-area singlelayer MoS2 nanosheets by CVD on c-plane sapphire substrate

    Science.gov (United States)

    Liu, Hongfei; Chi, Dongzhi

    2015-06-01

    Vapor-phase growth of large-area two-dimensional (2D) MoS2 nanosheets via reactions of sulfur with MoO3 precursors vaporized and transferred from powder sources onto a target substrate has been rapidly progressing. Recent studies revealed that the growth yield of high quality singlelayer (SL) MoS2 is essentially controlled by quite a few parameters including the temperature, the pressure, the amount/weight of loaded source precursors, and the cleanup of old precursors. Here, we report a dispersive growth method where a shadow mask is encapsulated on the substrate to ‘indirectly’ supply the source precursors onto the laterally advancing growth front at elevated temperatures. With this method, we have grown large-area (up to millimeters) SL-MoS2 nanosheets with a collective in-plane orientation on c-plane sapphire substrates. Regular ripples (~1 nm in height and ~50 nm in period) have been induced by laser scanning into the SL-MoS2 nanosheets. The MoS2 ripples easily initiate at the grain boundaries and extend along the atomic steps of the substrate. Such laser-induced ripple structures can be fundamental materials for studying their effects, which have been predicted to be significant but hitherto not evidenced, on the electronic, mechanical, and transport properties of SL-MoS2.

  6. CVD growth of (001) and (111)3C-SiC epilayers and their interface reactivity with pradeodymium oxide dielectric layers

    Energy Technology Data Exchange (ETDEWEB)

    Sohal, R.

    2006-07-24

    In this work, growth and characterisation of 3C-SiC thin films, investigation of oxidation of thus prepared layers and Pr-silicate and AlON based interface with SiC have been studied. Chemical vapor deposition of 3C-SiC thin films on Si(001) and Si(111) substrates has been investigated. Prior to the actual SiC growth, preparation of initial buffer layers of SiC was done. Using such a buffer layer, epitaxial growth of 3C-SiC has been achieved on Si(111) and Si(001) substrates. The temperature of 1100 C and 1150 C has been determined to be the optimal temperature for 3C-SiC growth on Si (111) and Si(001) substrates respectively. The oxidation studies on SiC revealed that a slow oxidation process at moderate temperatures in steps was useful in reducing and suppressing the g-C at the SiO{sub 2}/SiC interface. Clean, graphite-free SiO{sub 2} has been successfully grown on 3C-SiC by silicon evaporation and UHV anneal. For the application of high-k Pr{sub 2}O{sub 3} on silicon carbide, plausible interlayer, Pr-Silicate and AlON, have been investigated. Praseodymium silicate has been prepared successfully completely consuming the SiO2 and simultaneously suppressing the graphitic carbon formation. A comparatively more stable interlayer using AlON has been achieved. This interlayer mainly consists of stable phases of AlN along with some amount of Pr-aluminates and CN. Such layers act as a reaction barrier between Pr{sub 2}O{sub 3} and SiC, and simultaneously provide higher band offsets. (orig.)

  7. Optimisation of surface treatments of TiO{sub 2}:Nb transparent conductive coatings by a post-hot-wire annealing in a reducing H{sub 2} atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Castro, M.V.; Rebouta, L.; Alpuim, P.; Cerqueira, M.F.; Benelmekki, M.; Garcia, C.B. [Centre of Physics, University of Minho, 4710-057 Braga (Portugal); Alves, E.; Barradas, N.P. [Ion Beam Laboratory (ITN), EN 10, 2686-953 Sacavém (Portugal); Xuriguera, E. [Dept. Ciència dels Materials, Universitat de Barcelona, Barcelona (Spain); Tavares, C.J., E-mail: ctavares@fisica.uminho.pt [Centre of Physics, University of Minho, 4710-057 Braga (Portugal)

    2014-01-01

    Transparent and electrically conductive niobium-doped TiO{sub 2} thin films have been deposited on glass surfaces by d.c.-pulsed reactive magnetron sputtering from a composite Ti:Nb target, using oxygen as reactive gas. A rapid 1 min annealing at 500 °C in an atomic hydrogen rich atmosphere, obtained by flowing H{sub 2} on a Ta filament resistively heated to 1750 °C in vacuum (hot-wire), proved to be very efficient in enhancing the electrical properties of these ∼ 100 nm thick TiO{sub 2}:Nb thin films. Dark conductivity (σ{sub d}) and its activation energy were measured as a function of (inverse) temperature and the value of σ{sub d} at room temperature was used to assess the effect of the H{sub 2} annealing on the transport properties. A 5-order of magnitude increase in electrical conductivity was observed for optimised treatment conditions at a hydrogen pressure of 10 Pa. A maximum value of σ{sub d} in the range of ∼ 1.4 × 10{sup 3} S/cm was attained for optimised conditions, where a level of ∼ 6 at.% of H doping was measured close to the film surface. X-ray photoelectron spectroscopy, elastic recoil detection analysis, Rutherford backscattering and Raman spectroscopies were used to access information of composition and film structure for the explanation of the strong enhancement of the film's electrical conductivity and band-gap widening to 3.45 eV following hot-wire treatments. These thin films can be used as transparent conductive oxide contact layers for photovoltaic applications. - Highlights: • Transparent electrically conductive Nb-doped TiO{sub 2} thin films deposited on glass. • Post-H-treatments by a hot-wire process introduce hydrogen in the thin films. • 5-Order increase in electrical conductivity was found for post-H-treatment.

  8. An important atomic process in the CVD growth of graphene: Sinking and up-floating of carbon atom on copper surface

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yingfeng [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing, 102206 (China); Li, Meicheng, E-mail: mcli@ncepu.edu.cn [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing, 102206 (China); Su Zhou Institute, North China Electric Power University, Suzhou, 215123 (China); Gu, TianSheng [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing, 102206 (China); Bai, Fan [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001 (China); Yu, Yue; Trevor, Mwenya [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing, 102206 (China); Yu, Yangxin [Department of Chemical Engineering, Tsinghua University, Beijing, 100084 (China)

    2013-11-01

    By density functional theory (DFT) calculations, the early stages of the growth of graphene on copper (1 1 1) surface are investigated. At the very first time of graphene growth, the carbon atom sinks into subsurface. As more carbon atoms are adsorbed nearby the site, the sunken carbon atom will spontaneously form a dimer with one of the newly adsorbed carbon atoms, and the formed dimer will up-float on the top of the surface. We emphasize the role of the co-operative relaxation of the co-adsorbed carbon atoms in facilitating the sinking and up-floating of carbon atoms. In detail: when two carbon atoms are co-adsorbed, their co-operative relaxation will result in different carbon–copper interactions for the co-adsorbed carbon atoms. This difference facilitates the sinking of a single carbon atom into the subsurface. As a third carbon atom is co-adsorbed nearby, it draws the sunken carbon atom on top of the surface, forming a dimer. Co-operative relaxations of the surface involving all adsorbed carbon atoms and their copper neighbors facilitate these sinking and up-floating processes. This investigation is helpful for the deeper understanding of graphene synthesis and the choosing of optimal carbon sources or process.

  9. Growth of single-walled carbon nanotubes on a Co-Mo-MgO supported catalyst by the CVD of methane in a fixed bed reactor: Model setting and parameter estimation

    Science.gov (United States)

    Izadi, Nosrat; Rashidi, Ali Morad; Horri, Bahman Amini; Mosoudi, Mohamad Reza; Bozorgzadeh, Hamid Reza; Zeraatkar, Ahmad

    2011-06-01

    In this work methane was decomposed to hydrogen and carbon to determine its kinetic behavior during reaction over a Co-Mo-MgO supported catalyst using the CVD (Chemical Vapor Deposition) technique. Decomposition of methane molecules was performed in a continuous fixed bed reactor to obtain data to simulate methane decomposition in a gas phase heterogeneous media. The products and reactants of reaction were analyzed by molecular sieve column followed by GC-analysis of the fractions to determine the amount of product converted or reactant consumed. The synthesis of single-walled carbon nanotubes was performed at atmospheric pressure, different temperatures and reactant concentrations. The experimental data analyzed to suggest the formula for calculation of the initial specific reaction rate of the carbon nanotubes synthesis, were fitted by several mathematical models derived from different mechanisms based on Longmuir-hinshelwood expression. The suggested mechanism according to dissociation adsorption of methane seems to explain the catalytic performance in the range of operating conditions studied. The apparent activation energy for the growth of SWNTs was estimated according to Arrhenius equation. The as grown SWNTs products were characterized by SEM, TEM and Raman spectroscopy after purification. The catalyst deactivation was found to be dependent on the time, reaction temperature and partial pressure of methane and indicated that the reaction of deactivation can be modeled by a simple apparent second order of reaction.

  10. Synthesis of CVD-graphene on rapidly heated copper foils.

    Science.gov (United States)

    Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Hwangbo, Yun; Yoon, Jong-Hyuk; Lee, Eun-Kyu; Ryu, Jaechul; Lee, Hak-Joo; Cho, Seungmin; Lee, Seung-Mo

    2014-05-07

    Most chemical vapor deposition (CVD) systems used for graphene growth mainly employ convection and radiation heat transfer between the heating source and the metal catalyst in order to reach the activation temperature of the reaction, which in general leads to a long synthesis time and poor energy efficiency. Here, we report a highly time- and energy-efficient CVD setup, in which the metal catalyst (Cu) is designed to be physically contacted with a heating source to give quick heat transfer by conduction. The induced conduction heating enabled the usual effects of the pretreatment and annealing of Cu (i.e., annihilation of surface defects, impurities and contaminants) to be achieved in a significantly shorter time compared to conventional CVD. Notably, the rapid heating was observed to lead to larger grains of Cu with high uniformity as compared to the Cu annealed by conventional CVD, which are believed to be beneficial for the growth of high quality graphene. Through this CVD setup, bundles of high quality (∼252 Ω per square) and large area (over 16 inch) graphenes were able to be readily synthesized in 40 min in a significantly efficient way. When considering ease of scalability, high energy effectiveness and considerable productivity, our method is expected to be welcomed by industrialists.

  11. Growth and characterization of single-crystal CVD diamond for radiation detection applications; Synthese et caracterisation de diamants monocristallins pour applications de detecteur de rayonnements

    Energy Technology Data Exchange (ETDEWEB)

    Tranchant, N

    2008-01-15

    This work aimed at the study of the synthesis of single crystal diamond using the Microwave enhanced Chemical Vapour Deposition technique (MPCVD). The work enabled the development and optimisation of the growth conditions, from the study of the crystalline quality, of the material purity, and of its electronic properties. The assessment of the transport properties was the most determinant: the use of the time of flight (TOF) technique has enabled the measurement of the carrier mobilities and of their kinetic properties as a function of the temperature. When coupled with collected charge efficiency measurements, the work led to remarkable carrier mobility values obtained in the synthesised crystals (3000 cm{sup 2}.V-1.s{sup -1}). Prepared samples were mounted as detection devices and used successfully in real conditions for the monitoring of ultra-fast pulses, as well as for neutron fluency monitoring, and for medical dosimeters for radiotherapy applications. (author)

  12. Nickel Base Alloy Cladding by Double Hot Wire TIG Welding Procedure on Tubesheet of Steam Generator%核电蒸汽发生器管板镍基合金双热丝钨极氩弧焊堆焊技术

    Institute of Scientific and Technical Information of China (English)

    罗成

    2012-01-01

    介绍了蒸汽发生器管板镍基合金堆焊新工艺——双热丝钨极氩弧焊,从热丝钨极氩弧焊的基本原理、堆焊材料的选择和堆焊工艺参数等方面作了基本论述.就双热丝钨极氩弧堆焊的使用,简述了堆焊工艺试验、工艺评定、预评定和产品应用的过程,说明镍基合金双热丝钨极氩弧焊在蒸发器管板上堆焊应用是成功的.%It is introduced that nickel - base alloy double hot wire TIG cladding procedure on tubesheet of steam generator. Those aspects are discussed basically from principle of double hot wire TIG cladding, choosing of cladding consumables and cladding parameters etc. Cladding test, procedure qualification, prequalification and product application for nickel base alloy double hot wire TIG cladding are described briefly. It is successful that application of nickel base alloy double hot wire TIG cladding procedure on tubesheet of steam generators.

  13. Catalytic CVD of SWCNTs at Low Temperatures and SWCNT Devices

    Science.gov (United States)

    Seidel, Robert; Liebau, Maik; Unger, Eugen; Graham, Andrew P.; Duesberg, Georg S.; Kreupl, Franz; Hoenlein, Wolfgang; Pompe, Wolfgang

    2004-09-01

    New results on the planar growth of single-walled carbon nanotubes (SWCNTs) by catalytic chemical vapor deposition (CVD) at low temperatures will be reported. Optimizing catalyst, catalyst support, and growth parameters yields SWCNTs at temperatures as low as 600 °C. Growth at such low temperatures largely affects the diameter distribution since coalescence of the catalyst is suppressed. A phenomenological growth model will be suggested for CVD growth at low temperatures. The model takes into account surface diffusion and is an alternative to the bulk diffusion based vapor-liquid-solid (VLS) model. Furthermore, carbon nanotubes field effect transistors based on substrate grown SWCNTs will be presented. In these devices good contact resistances could be achieved by electroless metal deposition or metal evaporation of the contacts.

  14. High collection efficiency CVD diamond alpha detectors

    Energy Technology Data Exchange (ETDEWEB)

    Bergonzo, P.; Foulon, F.; Marshall, R.D.; Jany, C.; Brambilla, A. [CEA/Saclay, Gif-sur-Yvette (France); McKeag, R.D.; Jackman, R.B. [University College London (United Kingdom). Electronic and Electrical Engineering Dept.

    1998-06-01

    Advances in Chemical Vapor Deposited (CVD) diamond have enabled the routine use of this material for sensor device fabrication, allowing exploitation of its unique combination of physical properties (low temperature susceptibility (> 500 C), high resistance to radiation damage (> 100 Mrad) and to corrosive media). A consequence of CVD diamond growth on silicon is the formation of polycrystalline films which has a profound influence on the physical and electronic properties with respect to those measured on monocrystalline diamond. The authors report the optimization of physical and geometrical device parameters for radiation detection in the counting mode. Sandwich and co-planar electrode geometries are tested and their performances evaluated with regard to the nature of the field profile and drift distances inherent in such devices. The carrier drift length before trapping was measured under alpha particles and values as high as 40% of the overall film thickness are reported. Further, by optimizing the device geometry, they show that a gain in collection efficiency, defined as the induced charge divided by the deposited charge within the material, can be achieved even though lower bias values are used.

  15. Researches on Thermal Conductivity Measurement of Insulating Material by Improved Parallel Hot-wire Method%用改进的平行热线法测量绝热材料导热系数的研究

    Institute of Scientific and Technical Information of China (English)

    张桃; 朱春玲; 蔡玉飞; 张涛; 史素青

    2015-01-01

    基于平行热线法的测量原理,在加热电路中串联一个限流电阻,使加热过程中由于热线温升引起电阻增大造成的功率变化减小至0.6%,提高测量精度;采用铂电阻温度传感器代替传统的热电偶实现温度测量,用于低温下的温度测量,扩大导热系数测量范围。采用这种测量方法,搭建绝热材料导热系数的测量平台,测量硬质聚氨酯泡沫塑料的导热系数,与国家玻璃纤维产品质量监督检验中心的鉴定结果对比,其相对误差在5%以内,验证了改进的平行热线法的正确性。%Based on the measuring principle of parallel hot wire method,a current limiting resistor is cascaded in the heating circuit to reduce the power variation to 0.6%,which is caused by resistance increases due to the hotline temperature rise in heating process,with the measurement accuracy improved.Platinum resistance temperature sensor is used to replace the tra-ditional thermocouple to achieve temperature measurement,which can be used in low temperature and expand the scope of the thermal conductivity measurement.Ameasuring platform of insulation material's thermal conductivity is built,with the thermal conductivity of rigid polyurethane foam measured.Compared with the identification results of National Glass Fiber Product Quality Supervision and Inspection Center,the relative error is less than 5%,so the correctness of the improved par-allel hot wire method is verified.

  16. Origin, state of the art and some prospects of the diamond CVD

    CERN Document Server

    Spitsyn, B V; Alexenko, A E

    2000-01-01

    A short review on the diamond CVD origin, together with its state of the art and some prospects was given. New hybrid methods of the diamond CVD permit to gain 1.2 to 6 times of growth rate in comparison with ordinary diamond CVD's. Recent results on n-type diamond film synthesis through phosphorus doping in the course of the CVD process are briefly discussed. In comparison with high-pressure diamond synthesis, the CVD processes open new facets of the diamond as ultimate crystal for science and technology evolution. It was stressed that, mainly on the basis of new CVDs of diamond, the properties of natural diamond are not only reproduced, but can be surpassed. As examples, mechanical (fracture resistance), physical (thermal conductivity), and chemical (oxidation stability) properties are mentioned. Some present issues in the field are considered.

  17. Measurement of thermal conductivity of gas hydrate with transient hot-wire method%瞬态热线法测定瓦斯水合物导热系数

    Institute of Scientific and Technical Information of China (English)

    陈文胜; 潘长虹

    2013-01-01

    为研究瓦斯水合物的热量传递机理,基于瞬态热线法原理,建立一套实验设备对瓦斯水合物及纯甲烷水合物的导热系数进行了测试.结果表明,实验所选瓦斯气体生成水合物的导热系数与甲烷水合物导热系数均随温度的升高而升高.该研究从瓦斯水合物的热物性因素方面论证了对煤矿抽采瓦斯进行水合固化分离后以NGH(水合物储运)形式进行储运的可行性.%This paper is an effort to study the heat transfer mechanism of gas hydrate by developing an experiment apparatus based on the principle of transient hot-wire method in order to measure thermal conductivity of methane hydrate and gas hydrate.The results show an increase in the thermal conductivity of the selected gas hydrate formation and methane hydrate due to the increasing temperature.From the aspects of thermal factors of gas hydrate,the study verifies the feasibility of gas storage and transportation in the form of NGH (natural gas hydrate) following the hydration solidification and separation of coal mine gas.

  18. Carbon nanostructures from Fe-C nanocomposites by activated CVD methods

    Energy Technology Data Exchange (ETDEWEB)

    Fleaca, Claudiu; Morjan, Ion; Alexandrescu, Rodica; Dumitrache, Florian; Soare, Iuliana; Gavrila-Florescu, Lavinia [Laser Photochemistry Laboratory, NILPRP, Bucharest (Romania); Le Normand, Francois; Faerber, Jaques [Groupe Surfaces and Interfaces, IPCMS, UMR 7504 CNRS, Strasbourg (France)

    2010-04-15

    Iron-based core-shell nanoparticles can present interesting catalytic properties for the growth of carbon nanostructures. We report the synthesis of various carbon nanostructures using activated chemical vapour deposition methods. These structures were analysed by Scanning Electron Microscopy (SEM) and Raman spectroscopy. Laser pyrolysis technique was used for synthesis of less than 10 nm diameter Fe-C core-shell catalyst nanoparticles. Acetone suspensions of Fe-C nanoparticles were drop-casted or spin coated onto Si(100) substrates. The consequence of hydrogen selective etching of these nanocomposites at 550 C, followed by a treatment with a mixture of H{sub 2} and C{sub 2}H{sub 2} at 700 C (both in the presence of hot filaments) was the growth of corrugated ribbons and decorated or distorted carbon nanotubes/nanofibers. Round agglomerate nanoparticles and long and very thin nanotubes were observed on the substrates edges (protected from direct etching). By adding in similar conditions a glow discharge plasma to hot filaments, the resulted deposits contain oriented nanotubes. Due to the implication of the electric field, the presence of both plasma and hot wires seems to significantly change the specific growth conditions of carbon nanostructures towards those resulted when only incandescent filaments were used (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Leakage current measurements of a pixelated polycrystalline CVD diamond detector

    OpenAIRE

    Zain, R.M.; Maneuski, D.; O'Shea, V.; Bates, R.; Blue, A.; Cunnigham, L.; Stehl, C.; Berderman, E.; Rahim, R. A.

    2013-01-01

    Diamond has several desirable features when used as a material for radiation detection. With the invention of synthetic growth techniques, it has become feasible to look at developing diamond radiation detectors with reasonable surface areas. Polycrystalline diamond has been grown using a chemical vapour deposition (CVD) technique by the University of Augsburg and detector structures fabricated at the James Watt Nanofabrication Centre (JWNC) in the University of Glasgow in order to produce pi...

  20. Application of Crystal Growth Theory in Graphene CVD Nucleation and Growth%经典晶体生长理论在石墨烯CVD成核和连续生长中的应用

    Institute of Scientific and Technical Information of China (English)

    王璐; 高峻峰; 丁峰

    2014-01-01

    石墨烯由于具有奇异的电子性质而成为多个学科研究的热门材料,其在各个领域的潜在应用也逐渐被实现.而石墨烯工业化应用的前提之一是大面积高质量石墨烯的合成.在合成石墨烯的众多方法中,过渡金属表面化学气象沉积法(CVD)作为制备大面积高质量石墨烯的主要方法而被深入研究和广泛使用.作为二维晶体的石墨烯,其生长过程应该遵循经典的晶体生长理论,因此本文从经典的晶体生长理论出发,结合密度泛函理论(DFT)对石墨烯CVD生长过程的具体计算,来介绍石墨烯的微观生长机制.主要从三个方面系统地介绍了石墨烯的CVD生长机理:(1)石墨烯在金属催化剂表面的成核过程,包括二维碳团簇在金属平台和台阶附近的成核过程和成核速率,并据此提出石墨烯在成核生长过程中的种子生长法.(2)经典的Wulff构造理论在石墨烯CVD生长中的应用,通过研究不同石墨烯边界结构在金属表面的稳定性和边界能来获得不同催化剂金属表面石墨烯晶粒的平衡态形状或能量最低结构.(3)动力学Wulff构造理论在石墨烯生长中的应用,通过研究金属原子钝化石墨烯边的稳定结构和不同边界的生长过程来研究石墨烯的生长动力学.金属原了钝化的扶手型(armchair,AC)石墨烯边界的存在大大地降低了碳原子加入到边界形成六元环所需要克服的势垒,导致了AC石墨烯边界的生长速度较快最后消失,而留下生长较慢的锯齿型(zigzag,ZZ)石墨烯边界.以上在原子尺度上对石墨烯CVD生长过程中成核和连续生长过程的微观机制研究对实验上生长大面积高质量的石墨烯材料提供了有价值的理论参考.

  1. FTIR monitoring of industrial scale CVD processes

    Science.gov (United States)

    Hopfe, V.; Mosebach, H.; Meyer, M.; Sheel, D.; Grählert, W.; Throl, O.; Dresler, B.

    1998-06-01

    The goal is to improve chemical vapour deposition (CVD) and infiltration (CVI) process control by a multipurpose, knowledge based feedback system. For monitoring the CVD/CVI process in-situ FTIR spectroscopic data has been identified as input information. In the presentation, three commonly used, and distinctly different, types of industrial CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch process for manufacturing carbon fibre reinforced SiC composites for high temperature applications, (ii) a continuously driven CVD thermal process for coating float glass for energy protection, and (iii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibers. The feasibility of the concept with FTIR in-situ monitoring as a core technology has been demonstrated. FTIR monitoring sensibly reflects process conditions.

  2. Non-classical crystallization of thin films and nanostructures in CVD and PVD processes

    CERN Document Server

    Hwang, Nong Moon

    2016-01-01

    This book provides a comprehensive introduction to a recently-developed approach to the growth mechanism of thin films and nanostructures via chemical vapour deposition (CVD). Starting from the underlying principles of the low pressure synthesis of diamond films, it is shown that diamond growth occurs not by individual atoms but by charged nanoparticles. This newly-discovered growth mechanism turns out to be general to many CVD and some physical vapor deposition (PVD) processes. This non-classical crystallization is a new paradigm of crystal growth, with active research taking place on growth in solution, especially in biomineralization processes. Established understanding of the growth of thin films and nanostructures is based around processes involving individual atoms or molecules. According to the author’s research over the last two decades, however, the generation of charged gas phase nuclei is shown to be the rule rather than the exception in the CVD process, and charged gas phase nuclei are actively ...

  3. Rare earth-doped alumina thin films deposited by liquid source CVD processes

    Energy Technology Data Exchange (ETDEWEB)

    Deschanvres, J.L.; Meffre, W.; Joubert, J.C.; Senateur, J.P. [Ecole Nat. Superieure de Phys. de Grenoble, St. Martin d`Heres (France). Lab. des Materiaux et du Genie Phys.; Robaut, F. [Consortium des Moyens Technologiques Communs, Institut National Polytechnique de Grenoble, BP 75, 38402 St Martin d`Heres (France); Broquin, J.E.; Rimet, R. [Laboratoire d`Electromagnetisme, Microondes et Optoelectronique, CNRS-Ecole Nationale Superieure d`Electronique et Radioelectricite de Grenoble, BP 257, 38016 Grenoble, Cedex (France)

    1998-07-24

    Two types of liquid-source CVD processes are proposed for the growth of rare earth-doped alumina thin films suitable as amplifying media for integrated optic applications. Amorphous, transparent, pure and erbium- or neodymium-doped alumina films were deposited between 573 and 833 K by atmospheric pressure aerosol CVD. The rare earth doping concentration increases by decreasing the deposition temperature. The refractive index of the alumina films increases as a function of the deposition temperature from 1.53 at 573 K to 1.61 at 813 K. Neodymium-doped films were also obtained at low pressure by liquid source injection CVD. (orig.) 7 refs.

  4. EFFECTS OF OPERATING CONDITIONS ON THE DEPOSITION OF GaAs IN A VERTICAL CVD REACTOR

    OpenAIRE

    JAE-SANG BAEK; JIN-HYO BOO; YOUN-JEA KIM

    2008-01-01

    A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide (GaAs) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The ...

  5. Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH4-NH3 gas mixtures.

    Science.gov (United States)

    Eustergerling, Brett; Hèden, Martin; Shi, Yujun

    2007-11-01

    The application of a laser-induced electron impact (LIEI) ionization source in studying the gas-phase chemistry of the SiH(4)/NH(3) hot-wire chemical vapor deposition (HWCVD) system has been investigated. The LIEI source is achieved by directing an unfocused laser beam containing both 118 nm (10.5 eV) vacuum ultraviolet (VUV) and 355 nm UV radiations to the repeller plate in a time-of-flight mass spectrometer. Comparison of the LIEI source with the conventional 118 nm VUV single-photon ionization (SPI) method has demonstrated that the intensities of the chemical species with ionization potentials (IP) above 10.5 eV, e.g., H(2), N(2) and He, have been significantly enhanced with the incorporation of the LIEI source. It is found that the SPI source due to the 118 nm VUV light coexists in the LIEI source. This allows simultaneous observations of parent ions with enhanced intensity from VUV SPI and their "fingerprint" fragmentation ions from LIEI. It is, therefore, an effective tool to diagnose the gas-phase chemical species involved with both NH(3) and SiH(4) in the HWCVD reactor. In using the LIEI source to SiH(4), NH(3) and their mixtures, it has been shown that the NH(3) decomposition is suppressed with the addition of SiH(4) molecules. Examination of the NH(3) decomposition percentage and the time to reach the N(2) and H(2) steady-state intensities for various NH(3)/SiH(4) mixtures suggests that the extent of the suppression is enhanced with more SiH(4) content in the mixture. With increasing filament temperatures, the negative effect of SiH(4) becomes less important.

  6. 热线法测试隔热耐火材料高温导热系数的实验研究%Experimental Research on High Temperature Thermal Conductivity of Insulating Refractory with Hot-Wire Method

    Institute of Scientific and Technical Information of China (English)

    雒彩云; 陶冶; 杨莉萍; 徐子君; 钟秋

    2014-01-01

    在简述了不同导热系数测试方法的基础上,提出了用非稳态热线法测试隔热耐火材料高温导热系数的方法,并针对目前国内高温导热系数的热线法测试装置比较空缺的情况,对现有热线法导热仪进行升级改造,同时,采用FLUENT软件对测量区温场进行模拟计算。改造后的仪器,测试温度范围从最高500℃提高到1000℃,测量时间缩短了近1/2。经过标样测试与数据比对,该装置具有较好的准确度和重复性,达到了预期目标,可应用于科研及工程材料测试。%Based on the analysis of different thermal conductivity test methods, the unsteady hot-wire test method was utilized to test high temperature thermal conductivity of insulating refractory. In view of the domestic vacancy of high temperature thermal conductivity tester, the reconstruction of existing tester was conducted. FLUENT is used for simulation temperature of measuring field. After reconstruction, the highest test temperature was increased from 500 ℃ to 1000 ℃, test time was reduced by half at least. The test results for standard samples show that the established device has good accuracy and repeatability, the device will achieve the desired target, improve the test efficiency, and can be applied to scientific research and engineering materials test.

  7. CVD of pure copper films from amidinate precursor

    OpenAIRE

    2009-01-01

    Copper(I) amidinate [Cu(i-Pr-Me-AMD)]2 was investigated to produce copper films in conventional low pressure chemical vapor deposition (CVD) using hydrogen as reducing gas-reagent. Copper films were deposited on steel, silicon, and SiO2/Si substrates in the temperature range 200–350°C at a total pressure of 1333 Pa. The growth rate on steel follows the surface reaction between atomic hydrogen and the entire precursor molecule up to 240°C. A significant increase of the growth rate at tempera...

  8. High-rate diamond deposition by microwave plasma CVD

    Science.gov (United States)

    Li, Xianglin

    In this dissertation, the growth of CVD (Chemical Vapor Deposition) diamond thin films is studied both theoretically and experimentally. The goal of this research is to deposit high quality HOD (Highly Oriented Diamond) films with a growth rate greater than 1 mum/hr. For the (100)-oriented HOD films, the growth rate achieved by the traditional process is only 0.3 mum/hr while the theoretical limit is ˜0.45 mum/hr. This research increases the growth rate up to 5.3 mum/hr (with a theoretical limit of ˜7 mum/hr) while preserving the crystal quality. This work builds a connection between the theoretical study of the CVD process and the experimental research. The study is extended from the growth of regular polycrystalline diamond to highly oriented diamond (HOD) films. For the increase of the growth rate of regular polycrystalline diamond thin films, a scaling growth model developed by Goodwin is introduced in details to assist in the understanding of the MPCVD (Microwave Plasma CVD) process. Within the Goodwin's scaling model, there are only four important sub-processes for the growth of diamond: surface modification, adsorption, desorption, and incorporation. The factors determining the diamond growth rate and film quality are discussed following the description of the experimental setup and process parameters. Growth rate and crystal quality models are reviewed to predict and understand the experimental results. It is shown that the growth rate of diamond can be increased with methane input concentration and the amount of atomic hydrogen (by changing the total pressure). It is crucial to provide enough atomic hydrogen to conserve crystal quality of the deposited diamond film. The experimental results demonstrate that for a fixed methane concentration, there is a minimum pressure for growth of good diamond. Similarly, for a fixed total pressure, there is a maximum methane concentration for growth of good diamond, and this maximum methane concentration increases

  9. Effect of current stress during thermal CVD of multilayer graphene on cobalt catalytic layer

    Science.gov (United States)

    Ueno, Kazuyoshi; Ichikawa, Hiroyasu; Uchida, Takaki

    2016-04-01

    To improve the crystallinity of multilayer graphene (MLG) by CVD at a low temperature, the effect of current stress during thermal CVD on a cobalt (Co) catalytic layer was investigated. The crystallinity of MLG obtained by CVD with current was higher than that without current at the same temperature. This indicates that current has effects besides the Joule heating effect. The current effects on the Co catalytic layer and the MLG growth reaction were investigated, and it was found that current had small effects on the grain size and crystal structure of the Co catalyst and large effects on the MLG growth reaction such as large grain growth and a low activation energy of 0.49 eV, which is close to the value reported for carbon surface diffusion on Co. It is considered that the enhancement of MLG growth reaction by current leads to the improved crystallinity of MLG at a relatively low temperature.

  10. Investigation of the Millimeter-Wave Plasma Assisted CVD Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Vikharev, A; Gorbachev, A; Kozlov, A; Litvak, A; Bykov, Y; Caplan, M

    2005-07-21

    A polycrystalline diamond grown by the chemical vapor deposition (CVD) technique is recognized as a unique material for high power electronic devices owing to unrivaled combination of properties such as ultra-low microwave absorption, high thermal conductivity, high mechanical strength and chemical stability. Microwave vacuum windows for modern high power sources and transmission lines operating at the megawatt power level require high quality diamond disks with a diameter of several centimeters and a thickness of a few millimeters. The microwave plasma-assisted CVD technique exploited today to produce such disks has low deposition rate, which limits the availability of large size diamond disk windows. High-electron-density plasma generated by the millimeter-wave power was suggested for enhanced-growth-rate CVD. In this paper a general description of the 30 GHz gyrotron-based facility is presented. The output radiation of the gyrotron is converted into four wave-beams. Free localized plasma in the shape of a disk with diameter much larger than the wavelength of the radiation is formed in the intersection area of the wave-beams. The results of investigation of the plasma parameters, as well as the first results of diamond film deposition are presented. The prospects for commercially producing vacuum window diamond disks for high power microwave devices at much lower costs and processing times than currently available are outlined.

  11. Hot-wire synthesis of Si nanoparticles

    CSIR Research Space (South Africa)

    Scriba, MR

    2008-01-01

    Full Text Available , laser ablation or etching, and bottom-up synthesis such as colloidal chemistry and gas phase pyrolysis. The chemical processes in the latter are generally equivalent to those in the chemical vapour deposition of compact films. In the case of silicon... the deposition unit for thin films [3], leads us to believe that thermal catalytic pyrolysis, based on established HWCVD techniques, is a viable process for Si nanoparticle (powder) synthesis. The objective of this research is to produce Si nanoparticles...

  12. Reusable Hot-Wire Cable Cutter

    Science.gov (United States)

    Pauken, Michael T.; Steinkraus, Joel M.

    2010-01-01

    During the early development stage of balloon deployment systems for missions, nichrome wire cable cutters were often used in place of pyro-actuated cutters. Typically, a nichrome wire is wrapped around a bundle of polymer cables with a low melting point and connected to a relay-actuated electric circuit. The heat from the nichrome reduces the strength of the cable bundle, which quickly breaks under a mechanical load and can thus be used as a release mechanism for a deployment system. However, the use of hand-made heated nichrome wire for cutters is not very reliable. Often, the wrapped nichrome wire does not cut through the cable because it either pulls away from its power source or does not stay in contact with the cable being cut. Because nichrome is not readily soldered to copper wire, unreliable mechanical crimps are often made to connect the nichrome to an electric circuit. A self-contained device that is reusable and reliable was developed to sever cables for device release or deployment. The nichrome wire in this new device is housed within an enclosure to prevent it from being damaged by handling. The electric power leads are internally connected within the unit to the nichrome wire using a screw terminal connection. A bayonet plug, a quick and secure method of connecting the cutter to the power source, is used to connect the cutter to the power leads similar to those used in pyro-cutter devices. A small ceramic tube [0.25-in. wide 0.5-in. long (.6.4-mm wide 13-mm long)] houses a spiraled nichrome wire that is heated when a cable release action is required. The wire is formed into a spiral coil by wrapping it around a mandrel. It is then laid inside the ceramic tube so that it fits closely to the inner surface of the tube. The ceramic tube provides some thermal and electrical insulation so that most of the heat generated by the wire is directed toward the cable bundle in the center of the spiral. The ceramic tube is cemented into an aluminum block, which holds it in position. The leads of the nichrome wire are attached to screw terminals that connect them to power leads. A bayonet plug mounted at the bottom of the rectangular block connects the power leads to a relay circuit. A thin aluminum shell encloses the entire structure, leaving access points to attach to the bayonet plug and to feed a cable into the cylinder. The access holes for the deployment cable are a smaller diameter than the nichrome coil to prevent the cable from coming in direct contact with the nichrome when loaded. It uses the same general method of severing a cable with a heated wire as was used previously, but implements it in such a way that it is more reliable and less prone to failure. It creates a mechanism to create repeatability that was nonexistent in the previous method.

  13. Phenomena at hot-wire electrodes.

    Science.gov (United States)

    Gründler, P

    2000-06-01

    An overview is given describing phenomena at heated microelectrodes where matter and heat energy are simultaneously emitted into the solution. With controlled electric heating, virtual "quiescent" periods as well as ones with constant streaming conditions are found that depend on the heating time. A close look at a permanently heated wire reveals a well defined structure with stationary concentration, temperature and flow rate profiles. The observed phenomena can be utilised for analytical measurements, e.g. with the novel method "Temperature Pulse Voltammetry" (TPV).

  14. Novel chemical cleaning of textured crystalline silicon for realizing surface recombination velocity <0.2 cm/s using passivation catalytic CVD SiN x /amorphous silicon stacked layers

    Science.gov (United States)

    Thanh Nguyen, Cong; Koyama, Koichi; Higashimine, Koichi; Terashima, Shigeki; Okamoto, Chikao; Sugiyama, Shuichiro; Ohdaira, Keisuke; Matsumura, Hideki

    2017-05-01

    In this study, the development of a novel chemical cleaning method suitable for textured surfaces of crystalline silicon (c-Si) used for solar cells is demonstrated. To remove contaminants from such textured structures, chemicals have to penetrate into their complicated fine structures. Thus, the viscosity, reaction activity, and surface tension of the chemicals are adjusted by increasing the reaction temperature or introducing a surfactant. Actually, the use of concentrated (conc.) sulfuric acid (H2SO4) of 140 °C and the introduction of methanol (CH3OH) to other chemicals contribute to the improvement of the cleaning ability in textured structures. The present cleaning method in conjunction with plasma-damage-less catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD passivation with silicon-nitride (SiN x )/amorphous silicon (a-Si) stacked layers, also contributes to the decrease in the surface recombination velocity (SRV) of c-Si. The maximum estimated SRV (SRVmax), evaluated under the assumed absence of recombination in bulk c-Si, is less than 1.1 cm/s for textured surfaces, and the real SRV, evaluated by changing the c-Si substrate thickness, is less than 0.2 cm/s.

  15. CVD 908, CVD 908-htrA, and CVD 909 live oral typhoid vaccines: a logical progression.

    Science.gov (United States)

    Tacket, Carol O; Levine, Myron M

    2007-07-15

    Typhoid fever remains an important public health problem in many parts of the world. Despite the availability of oral Ty21a (Vivotif; Berna Biotech) and parenteral Vi polysaccharide vaccine (Typhim Vi; Aventis Pasteur), improved typhoid fever vaccines have been sought. These include a series of vaccine candidates developed at the Center for Vaccine Development, University of Maryland, based on attenuation of Salmonella enterica serovar Typhi by deletions in the aroC, aroD, and htrA genes. These vaccine candidates, designated "CVD 908," "CVD 908-htrA," and "CVD 909," have been developed and tested in volunteers with variable success. This review summarizes the clinical data that directed the logical progression of this vaccine development strategy.

  16. Chromized Layers Produced on Steel Surface by Means of CVD

    Institute of Scientific and Technical Information of China (English)

    KASPRZYCKA Ewa; BOGDA(N)SKI Bogdan; JEZIORSKI Leopold; JASI(N)SKI J(o)zef; TORBUS Roman

    2004-01-01

    Chemical vapour deposition of chromium on the surface of carbon steel has been investigated using a novel CVD method that combines the low cost of pack cementation method with advantages of vacuum technique. The processes have been performed in chromium chlorides atmosphere at a low pressure range from 1 to 800 hPa, the treatment temperature 800 to 950℃. Studies of the layers thickness, the phase composition, Cr, C and Fe depth profiles in diffusion zone have been conducted. The effect of the vacuum level during the process and the process parameters such as time and temperature on layer diffusion growth on the carbon steel surface has been investigated.

  17. Knowledge of risk factors for diabetes or cardiovascular disease (CVD) is poor among individuals with risk factors for CVD.

    Science.gov (United States)

    Kilkenny, Monique F; Dunstan, Libby; Busingye, Doreen; Purvis, Tara; Reyneke, Megan; Orgill, Mary; Cadilhac, Dominique A

    2017-01-01

    There is limited evidence on whether having pre-existing cardiovascular disease (CVD) or risk factors for CVD such as diabetes, ensures greater knowledge of risk factors important for motivating preventative behaviours. Our objective was to compare knowledge among the Australian public participating in a health check program and their risk status. Data from the Stroke Foundation 'Know your numbers' program were used. Staff in community pharmacies provided opportunistic health checks (measurement of blood pressure and diabetes risk assessment) among their customers. Participants were categorised: 1) CVD ± risk of CVD: history of stroke, heart disease or kidney disease, and may have risk factors; 2) risk of CVD only: reported having high blood pressure, high cholesterol, diabetes or atrial fibrillation; and 3) CVD risk free (no CVD or risk of CVD). Multivariable logistic regression analyses were performed including adjustment for age and sex. Among 4,647 participants, 12% had CVD (55% male, 85% aged 55+ years), 47% were at risk of CVD (40% male, 72% 55+ years) and 41% were CVD risk free (33% male, 27% 55+ years). Participants with CVD (OR: 0.66; 95% CI: 0.55, 0.80) or risk factors for CVD (OR: 0.65; 95% CI: 0.57, 0.73) had poorer knowledge of the risk factors for diabetes/CVD compared to those who were CVD risk free. After adjustment, only participants with risk factors for CVD (OR: 0.80; 95% CI: 0.69, 0.93) had poorer knowledge. Older participants (55+ years) and men had poorer knowledge of diabetes/CVD risk factors and complications of diabetes. Participants with poorer knowledge of risk factors were older, more often male or were at risk of developing CVD compared with those who were CVD risk free. Health education in these high risk groups should be a priority, as diabetes and CVD are increasing in prevalence throughout the world.

  18. The Charge Collection Properties of CVD Diamond

    CERN Document Server

    Behnke, T; Oh, A; Steuerer, J; Wagner, A; Zeuner, W; Behnke, Ties; Hüntemeyer, Petra; Oh, Alexander; Steuerer, Johannes; Wagner, Albrecht; Zeuner, Wolfram

    1998-01-01

    The charge collection properties of CVD diamond have been investigated with ionising radiation. In this study two CVD diamond samples, prepared with electrical contacts have been used as solid state ionisation chambers. The diamonds have been studied with beta particles and 10 keV photons, providing a homogeneous ionisation density and with protons and alpha particles which are absorbed in a thin surface layer. For the latter case a strong decrease of the signal as function of time is observed, which is attributed to polarisation effects inside the diamond. Spatially resolved measurements with protons show a large variation of the charge collection efficiency, whereas for photons and minimum ionising particles the response is much more uniform and in the order of 18%. These results indicate that the applicability of CVD diamond as a position sensitive particle detector depends on the ionisation type and appears to be promising for homogeneous ionisation densities as provided by relativistic charged particles.

  19. Substrate Strengthening of CVD Coated Steels

    Institute of Scientific and Technical Information of China (English)

    O.Kessler; M.Heidkamp; F.Hoffmann; P.Mayr

    2004-01-01

    Properties of components and tools can be improved by the combination of coating and heat treatment processes due to the addition of single process advantages and due to the utilization of process interactions. Several low and high alloyed, structural and tool steels (AISI 4140, 52100, H13, A2, D2, etc.) have been treated by CVD-TiN-coating plus laser beam hardening respectively carburizing plus CVD-TiN-coating. Homogeneous, dense TiN-coatings with high hardness,high compressive residual stresses and good adhesion were supported by high strength substrate surfaces. Especially CVD plus laser beam hardening offers the possibility to reduce distortion due to the small heated surface volume.

  20. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    Science.gov (United States)

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

    1981-01-01

    A new approach has been initiated at JPL to fabricate thin-film, high efficiency GaAs solar cells on low-cost, single-crystal Si substrates having a thin CVD interlayer of Ge to minimize the lattice and thermal expansion mismatch. For initial experiments, n(+)/p GaAs cells were grown by OM-CVD on single-crystal GaAs and Ge wafers. Details of the growths and performance results will be presented. Subsequently, a combined epitaxial structure of OM-CVD GaAs on a strongly adherent Ge interlayer on (100) Si was grown. This is the first report of the successful growth of this composite structure. Low module costs projected by JPL SAMICS methodology calculations and the potential for 400-600W/kg space solar arrays will be discussed.

  1. CVD diamond pixel detectors for LHC experiments

    Energy Technology Data Exchange (ETDEWEB)

    Wedenig, R.; 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.; Eijk, B. van; 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.; Knoepfle, 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.; Wagner, A.; Walsh, A.M.; Weilhammer, P.; White, C.; Zeuner, W.; Ziock, H.; Zoeller, M.; Blanquart, L.; Breugnion, P.; Charles, E.; Ciocio, A.; Clemens, J.C.; Dao, K.; Einsweiler, K.; Fasching, D.; Fischer, P.; Joshi, A.; Keil, M.; Klasen, V.; Kleinfelder, S.; Laugier, D.; Meuser, S.; Milgrome, O.; Mouthuy, T.; Richardson, J.; Sinervo, P.; Treis, J.; Wermes, N

    1999-08-01

    This paper reviews the development of CVD diamond pixel detectors. The preparation of the diamond pixel sensors for bump-bonding to the pixel readout electronics for the LHC and the results from beam tests carried out at CERN are described.

  2. Método de fio quente na determinação das propriedades térmicas de polímeros Hot wire technique in the determination of thermal properties of polymers

    Directory of Open Access Journals (Sweden)

    Wilson N. dos Santos

    2004-12-01

    Full Text Available A técnica de fio quente paralelo normalizada para a determinação da condutividade térmica de materiais cerâmicos foi empregada na determinação das propriedades térmicas de polímeros. As amostras foram preparadas em forma de paralelepípedos retangulares, com dimensões de (230x80x30mm. Neste trabalho, a condutividade térmica e o calor específico foram simultaneamente determinados a partir do mesmo transiente térmico experimental e a difusividade térmica foi calculada a partir dessas duas propriedades. Cinco diferentes polímeros com diferentes estruturas a temperatura ambiente foram selecionados neste trabalho. Os cálculos foram feitos utilizando-se um método de ajuste por regressão não linear, de tal maneira que todos os pontos experimentais obtidos são considerados nos cálculos dessas propriedades térmicas. O equipamento utilizado neste trabalho é totalmente automatizado. A reprodutibilidade dos resultados foi muito boa com respeito à condutividade térmica, obtendo-se um desvio máximo de apenas 0,5% entre os valores máximo e mínimo para todas as amostras ensaiadas, mesmo introduzindo propositadamente alguns defeitos no arranjo experimental, em relação ao modelo teórico. Todavia, pequenos desvios do modelo teórico podem causar drásticas influências nos valores de calor específico, obtendo-se desvios de até 32% em relação ao arranjo experimental correto. Os resultados experimentais foram então comparados com aqueles encontrados na literatura. As discrepâncias observadas entre alguns desses valores podem estar associadas ao grau de cristalinidade ou à história térmica da amostra, ficando assim mostrada a aplicabilidade desta técnica na determinação das propriedades térmicas de polímeros.The hot wire parallel technique standardized for determining thermal conductivity of ceramic materials was employed in the determination of thermal properties of polymers. Samples were prepared in shape of rectangular

  3. Scalable ZnO nanotube arrays grown on CVD-graphene films

    Directory of Open Access Journals (Sweden)

    J. B. Park

    2016-10-01

    Full Text Available We report the growth of wafer-scale arrays of individually position-controlled and vertically aligned ZnO nanotube arrays on graphene deposited by chemical vapor deposition (CVD-graphene. Introducing two-dimensional layered materials such as graphene as a growth buffer has recently been suggested for growing nanomaterials on traditionally incompatible substrates. However, their growth has been restricted to small areas or had limited controllability. Here, we study the distinct growth behavior of ZnO on CVD-graphene that makes the selective area growth of individual nanostructures on its surface difficult, and propose a set of methods to overcome this. The resulting nanotube arrays, as examined by scanning electron microscopy and transmission electron microscopy, exhibited uniform morphologies and high structural quality over a large area and could be prepared on a broad variety of substrates, including amorphous, metallic, or flexible substrates.

  4. Lipids, atherosclerosis and CVD risk: is CRP an innocent bystander?

    DEFF Research Database (Denmark)

    Nordestgaard, B G; Zacho, J

    2009-01-01

    exclude that genetically elevated CRP cause CVD. CONCLUSION: These data suggest that elevated CRP per se does not cause CVD; however, inflammation per se possibly contributes to CVD. Elevated CRP levels more likely is a marker for the extent of atherosclerosis or for the inflammatory activity...

  5. Deposition and Coating Properties on CVD Tungsten

    Institute of Scientific and Technical Information of China (English)

    DU Ji-hong; LI Zheng-xiang; LIU Gao-jian; ZHOU Hui-Huang; CHUN liang

    2004-01-01

    Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.

  6. Epitaxial nucleation of CVD bilayer graphene on copper.

    Science.gov (United States)

    Song, Yenan; Zhuang, Jianing; Song, Meng; Yin, Shaoqian; Cheng, Yu; Zhang, Xuewei; Wang, Miao; Xiang, Rong; Xia, Yang; Maruyama, Shigeo; Zhao, Pei; Ding, Feng; Wang, Hongtao

    2016-12-08

    Bilayer graphene (BLG) has emerged as a promising candidate for next-generation electronic applications, especially when it exists in the Bernal-stacked form, but its large-scale production remains a challenge. Here we present an experimental and first-principles calculation study of the epitaxial chemical vapor deposition (CVD) nucleation process for Bernal-stacked BLG growth on Cu using ethanol as a precursor. Results show that a carefully adjusted flow rate of ethanol can yield a uniform BLG film with a surface coverage of nearly 90% and a Bernal-stacking ratio of nearly 100% on ordinary flat Cu substrates, and its epitaxial nucleation of the second layer is mainly due to the active CH3 radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this nucleation mechanism will help clarify the formation of BLG by the epitaxial CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.

  7. Investigation of multilayer domains in large-scale CVD monolayer graphene by optical imaging

    Science.gov (United States)

    Yu, Yuanfang; Li, Zhenzhen; Wang, Wenhui; Guo, Xitao; Jiang, Jie; Nan, Haiyan; Ni, Zhenhua

    2017-03-01

    CVD graphene is a promising candidate for optoelectronic applications due to its high quality and high yield. However, multi-layer domains could inevitably form at the nucleation centers during the growth. Here, we propose an optical imaging technique to precisely identify the multilayer domains and also the ratio of their coverage in large-scale CVD monolayer graphene. We have also shown that the stacking disorder in twisted bilayer graphene as well as the impurities on the graphene surface could be distinguished by optical imaging. Finally, we investigated the effects of bilayer domains on the optical and electrical properties of CVD graphene, and found that the carrier mobility of CVD graphene is seriously limited by scattering from bilayer domains. Our results could be useful for guiding future optoelectronic applications of large-scale CVD graphene. Project supported by the National Natural Science Foundation of China (Nos. 61422503, 61376104), the Open Research Funds of Key Laboratory of MEMS of Ministry of Education (SEU, China), and the Fundamental Research Funds for the Central Universities.

  8. Strain Release Induced Novel Fluorescence Variation in CVD-Grown Monolayer WS2 Crystals.

    Science.gov (United States)

    Feng, Shanghuai; Yang, Ruilong; Jia, Zhiyan; Xiang, Jianyong; Wen, Fusheng; Mu, Congpu; Nie, Anmin; Zhao, Zhisheng; Xu, Bo; Tao, Chenggang; Tian, Yongjun; Liu, Zhongyuan

    2017-10-04

    Tensile strain is intrinsic to monolayer crystals of transition metal disulfides such as Mo(W)S2 grown on oxidized silicon substrates by chemical vapor deposition (CVD) owing to the much larger thermal expansion coefficient of Mo(W)S2 than that of silica. Here we report fascinating fluorescent variation in intensity with aging time in CVD-grown triangular monolayer WS2 crystals on SiO2 (300 nm)/Si substrates and formation of interesting concentric triangular fluorescence patterns in monolayer crystals of large size. The novel fluorescence aging behavior is recognized to be induced by the partial release of intrinsic tensile strain after CVD growth and the induced localized variations or gradients of strain in the monolayer crystals. The results demonstrate that strain has a dramatic impact on the fluorescence and photoluminescence of monolayer WS2 crystals and thus could potentially be utilized to tune electronic and optoelectronic properties of monolayer transition metal disulfides.

  9. Estudo do Processo TIG Hot-Wire com Material de Adição AISI-316L Analisando o Efeito do Sopro Magnético do Arco sobre a Diluição do Cordão de Solda

    Directory of Open Access Journals (Sweden)

    Erick Alejandro González Olivares

    Full Text Available Resumo: O processo TIG com adição de arame quente (HotWire é considerado um processo altamente produtivo em comparação ao processo TIG convencional com arame frio (ColdWire, sendo possível alcançar grandes taxas de deposição e baixas porcentagens de diluição, características essas que permitem ao processo ser uma ótima alternativa para aplicações de revestimentos. Existem variadas opções em configurações de circuitos elétricos para aquecer o arame de adição no processo TIG Hot-Wire, entre elas podemos destacar a utilização da corrente contínua pulsada e a corrente alternada. No presente trabalho foi utilizada a corrente contínua constante e foram estudadas duas configurações do circuito elétrico para aquecer o material de adição, as quais em teoria provocam diferentes comportamentos no arco voltaico e, portanto, nas propriedades geométricas do cordão de solda. Uma primeira análise realizada sobre o arco voltaico demonstra que se forma um sopro mágnetico constante ao se aquecer o arame com corrente contínua constante. Segundo os ensaios realizados, a direção do sopro magnético depende da polaridade da corrente para aquecer o arame. Uma análise macrográfica dos cordões de solda obtidos demonstraram que os melhores resultados foram para os ensaios feitos com Hot-Wire, conseguindo diluições de até um 2% aproximadamente para uma velocidade de arame de 7,5 m/min, 1 kW de potência de aquecimento do arame e usando uma velocidade de soldagem de 30 cm/min.

  10. Effect of Hot-wire NG-TIG Process on Mechanical Properties of Welded Joints for T91/P91 Steel%T91/P91窄间隙热丝TIG焊接工艺对接头力学性能的影响

    Institute of Scientific and Technical Information of China (English)

    沈学峰; 杨成龙; 杨仁杰; 唐新华; 芦凤桂

    2012-01-01

    通过对T91/P91窄间隙热丝TIG焊试验,对比研究了焊接接头各区包括焊缝、热影响区、母材的显微组织,以及各项力学性能比如常温拉伸、高温拉伸、硬度及冲击性能,从而探究窄间隙热丝TIG焊对T91/P91钢焊接性的影响.试验结果表明,焊接接头组织均匀,主要为回火马氏体;抗拉强度达到了母材水平甚至比母材更强;焊缝区域硬度分布比较均匀,硬度值高于热影响区和母材;焊缝的冲击韧性也与母材相当.研究结果表明,窄间隙热丝TIG焊可以改进T91/P91焊接接头的焊接质量,焊接接头各项力学性能均满足使用需求,从而获得了较高质量的焊接接头.%In order to study the weld properties of narrow gap hot-wire TIG (NG-TIG) welding on T91/P91, the microstructure and mechanical properties of welded joint and HAZ as well as base metal were studied respectively (including room temperature tensile, high temperature tensile, hardness and impact properties), which can give an access to explore the effect of narrow gap hot-wire NG-TIG welding. The results show that homogeneous microstructure and good mechanical properties such as higher tensile strength, hardness of the welded joint is higher than base metal and equivalent impact energy, which indicate that the qualitiy of the T91/P91 welded joint were improved by hot-wire NG-TIG, which can meet the requirements of industrial standards.

  11. Synthesis of carbon nanotubes by plasma-enhanced CVD process: gas phase study of synthesis conditions

    OpenAIRE

    Guláš, Michal; Cojocaru, Costel Sorin; Fleaca, Claudiu; Farhat, Samir; Veis, Pavel; Le Normand, Francois

    2008-01-01

    International audience; To support experimental investigations, a model based on ChemkinTM software was used to simulate gas phase and surface chemistry during plasma-enhanced catalytic CVD of carbon nanotubes. According to these calculations, gas phase composition, etching process and growth rates are calculated. The role of several carbon species, hydrocarbon molecules and ions in the growth mechanism of carbon nanotubes is presented in this study. Study of different conditions of gas phase ...

  12. Synthesis of carbon nanbotubes by plasma-enhanced CVD process: gas phase study of synthesis conditions

    Science.gov (United States)

    Guláš, M.; Cojocaru, C. S.; Fleaca, C. T.; Farhat, S.; Veis, P.; Le Normand, F.

    2008-09-01

    To support experimental investigations, a model based on Chemkin^TM software was used to simulate gas phase and surface chemistry during plasma-enhanced catalytic CVD of carbon nanotubes. According to these calculations, gas phase composition, etching process and growth rates are calculated. The role of several carbon species, hydrocarbon molecules and ions in the growth mechanism of carbon nanotubes is presented in this study. Study of different conditions of gas phase activation sources and pressure is performed.

  13. CVD Lu(2)O(3):Eu coatings For Advanced Scintillators.

    Science.gov (United States)

    Topping, Stephen G; Sarin, V K

    2009-03-01

    Currently Lu(2)O(3):Eu(3+) scintillators can only be fabricated via hot-pressing and pixelization, which is commercially not viable, thus restricting their use. Chemical vapor deposition is being developed as an alternative manufacturing process. Columnar coatings of Lu(2)O(3):Eu(3+) have been achieved using the halide-CO(2)-H(2) system, clearly signifying feasibility of the CVD process. Characterization of the coatings using high resolution scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis have been used as an aid to optimize process parameters and attain highly oriented and engineered coating structures. These results have clearly demonstrated that this process can be successfully used to tailor sub-micron columnar growth of Lu(2)O(3):Eu(3+), with the potential of ultra high resolution x-ray imaging.

  14. a-SiNx:H 薄膜的热丝化学气相沉积及微结构研究%Research of hot wire chemical vapor deposition and micro-structure of a-SiNx:H thin film

    Institute of Scientific and Technical Information of China (English)

    张娜; 周炳卿; 张林睿; 路晓翠

    2016-01-01

    In order to study the effect of hot wire temperature on the properties of a-SiNx:H thin films, by using hot wire chemical vapor deposition method and using SiH 4 , NH3 , H2 as reaction gas source , a-SiNx:H films were deposited by changing the temperature of hot wire .Film luminescent properties , microstructure and bonding characteristics were gotten and analyzed in detail by means of measurement methods such as ultraviolet-visible optical absorption spectroscopy , Fourier transform infrared transmission spectroscopy , and photoluminescence spectrum .The results show that , when wire temperature is at 1645℃, H content reaches greatest , N content is extremely small , film has high refractive index and a large degree of order .When the wire temperature is at 1713℃, H content decreases , N content reaches extremes .And then, with the increase of hot wire temperature, N content decreases and internal defect intensity increases .The results show that the best value of hot filament temperature is between 1596℃ to 1680℃ and the refractive index of film is 2.0.The film, with full nitrogen and hydrogen contents and stable structure and characteristics , is suit to choose as silicon-based solar cell antireflection film .%为了研究热丝温度对a-SiNx:H薄膜性能的影响,采用热丝化学气相沉积法,以SiH4,NH3,H2为反应气源,改变热丝温度沉积薄膜。通过紫外-可见光吸收谱、傅里叶红外透射光谱、光致发光光谱等测试手段对薄膜发光特性、微观结构及键合情况进行表征与分析。从测试情况可知,当热丝温度为1645℃时,H含量最大,N含量最小,同时其折射率最高,薄膜材料的有序度增大;当热丝温度为1713℃时,H含量减少,N含量达到最大,且随着热丝温度增大,薄膜中N含量又开始下降,内部缺陷态密度增加。结果表明,热丝法制备a-SiNx :H薄膜的热丝温度最佳值在1596℃~1680℃之间,此

  15. Modeling for CVD of Solid Oxide Electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Starr, T.L.

    2002-09-18

    Because of its low thermal conductivity, high thermal expansion and high oxygen ion conductivity yttria-stabilized zirconia (YSZ) is the material of choice for high temperature electrolyte applications. Current coating fabrication methods have their drawbacks, however. Air plasma spray (APS) is a relatively low-cost process and is suitable for large and relatively complex shapes. it is difficult to produce uniform, relatively thin coatings with this process, however, and the coatings do not exhibit the columnar microstructure that is needed for reliable, long-term performance. The electron-beam physical vapor deposition (EB-PVD) process does produce the desirable microstructure, however, the capital cost of these systems is very high and the line-of-sight nature of the process limits coating uniformity and the ability to coat large and complex shapes. The chemical vapor deposition (CVD) process also produces the desirable columnar microstructure and--under proper conditions--can produce uniform coatings over complex shapes. CVD has been used for many materials but is relatively undeveloped for oxides, in general, and for zirconia, in particular. The overall goal of this project--a joint effort of the University of Louisville and Oak Ridge National Laboratory (ORNL)--is to develop the YSZ CVD process for high temperature electrolyte applications. This report describes the modeling effort at the University of Louisville, which supports the experimental work at ORNL. Early work on CVD of zirconia and yttria used metal chlorides, which react with water vapor to form solid oxide. Because of this rapid gas-phase reaction the water generally is formed in-situ using the reverse water-gas-shift reaction or a microwave plasma. Even with these arrangements gas-phase nucleation and powder formation are problems when using these precursors. Recent efforts on CVD of zirconia and YSZ have focused on use of metal-organic precursors (MOCVD). These are more stable in the gas

  16. Mo-C Multilayered CVD Coatings

    Directory of Open Access Journals (Sweden)

    A. Sagalovych

    2013-12-01

    Full Text Available Production processes of multi-layered Mo-C coatings by the method of chemical vapor deposition (CVD with the use of organometallic compounds were developed. Coatings are applied on technical purpose steel DIN 1.2379 (H12F1 and DIN 1.7709 (25H2MF (ÉI10 heat-treated ball with the high class of surface roughness (> 10. The average deposition rate was 50 μm / h. The optimal conditions of deposition coatings for different technological schemas were defined. Metallographic investigations of the obtained coatings were carried out. Tribological studies of the friction and wear characteristics of sliding friction in conditions of boundary lubrication of Ï-S multilayered CVD coatings shows, that coatings have low friction coefficients (0075-0095 at loads up to 2.0 kN, showed high resistance to wear and are effective in increasing the stability of the pair for precision friction pairs of hydraulical units.

  17. Comparative evaluation of CVD diamond technologies

    Energy Technology Data Exchange (ETDEWEB)

    Anthony, T.R. [General Electric Corporate Research & Development Center, Schenectady, NY (United States)

    1993-01-01

    Chemical vapor deposition (CVD) of diamonds occurs from hydrogen-hydrocarbon gas mixtures in the presence of atomic hydrogen at subatmospheric pressures. Most CVD methods are based on different means of generating and transporting atomic hydrogen in a particular system. Evaluation of these different techniques involves their capital costs, material costs, energy costs, labor costs and the type and quality of diamond that they produce. Currently, there is no universal agreement on which is the best technique and technique selection has been largely driven by the professional background of the user as well as the particular application of interest. This article discusses the criteria for evaluating a process for low-pressure deposition of diamond. Next, a brief history of low-pressure diamond synthesis is reviewed. Several specific processes are addressed, including the hot filament process, hot filament electron-assisted chemical vapor deposition, and plasma generation of atomic hydrogen by glow discharge, microwave discharge, low pressure radio frequency discharge, high pressure DC discharge, high pressure microwave discharge jets, high pressure RF discharge, and high and low pressure flames. Other types of diamond deposition methods are also evaluated. 101 refs., 15 figs.

  18. TSC response of irradiated CVD diamond films

    CERN Document Server

    Borchi, E; Bucciolini, M; Guasti, A; Mazzocchi, S; Pirollo, S; Sciortino, S

    1999-01-01

    CVD diamond films have been irradiated with electrons, sup 6 sup 0 Co photons and protons in order to study the dose response to exposure to different particles and energies and to investigate linearity with dose. The Thermally Stimulated Current (TSC) has been studied as a function of the dose delivered to polymethilmetacrilate (PMMA) in the range from 1 to 12 Gy with 20 MeV electrons from a linear accelerator. The TSC spectrum has revealed the presence of two components with peak temperatures of about 470 and 520 K, corresponding to levels lying in the diamond band gap with activation energies of the order of 0.7 - 1 eV. After the subtraction of the exponential background the charge emitted during the heating scan has been evaluated and has been found to depend linearly on the dose. The thermally emitted charge of the CVD diamond films has also been studied using different particles. The samples have been irradiated with the same PMMA dose of about 2 Gy with 6 and 20 MeV electrons from a Linac, sup 6 sup 0 ...

  19. Cold Vacuum Drying (CVD) Set Point Determination

    Energy Technology Data Exchange (ETDEWEB)

    PHILIPP, B.L.

    2000-01-12

    This document provides the calculations used to determine the error of safety class signals used for the CVD process These errors are used with the Parameter limits to arrive at the initial set point. The Safety Class Instrumentation and Control (SCIC) system provides active detection and response to process anomalies that, if unmitigated would result in a safety event. Specifically actuation of the SCIC system includes two portions. The portion which isolates the MCO and initiates the safety-class helium (SCHe) purge, and the portion which detects and stops excessive heat input to the MCO on high tempered water MCO inlet temperature. For the MCO isolation and purge the SCIC receives signals from MCO pressure (both positive pressure and vacuum) helium flow rate, bay high temperature switches, seismic trips and time under vacuum trips.

  20. CVD diamond sensors for charged particle detection

    CERN Document Server

    Krammer, Manfred; Berdermann, E; Bergonzo, P; Bertuccio, G; Bogani, F; Borchi, E; Brambilla, A; Bruzzi, Mara; Colledani, C; Conway, J; D'Angelo, P; Dabrowski, W; Delpierre, P A; Dencuville, A; Dulinski, W; van Eijk, B; Fallou, A; Fizzotti, F; Foulon, F; Friedl, M; Gan, K K; Gheeraert, E; Hallewell, G D; Han, S; Hartjes, F G; Hrubec, Josef; Husson, D; Kagan, H; Kania, D R; Kaplon, J; Kass, R; Koeth, T W; Lo Giudice, A; Lü, R; MacLynne, L; Manfredotti, C; Meier, D; Mishina, M; Moroni, L; Oh, A; Pan, L S; Pernicka, Manfred; Peitz, A; Perera, L P; 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, Peter; Wetstein, M; White, C; Zeuner, W; Zöller, M

    2001-01-01

    CVD diamond material was used to build position-sensitive detectors for single-charged particles to be employed in high-intensity physics experiments. To obtain position information, metal contacts shaped as strips or pixels are applied to the detector surface for one- or two- dimensional coordinate measurement. Strip detectors 2*4 cm/sup 2/ in size with a strip distance of 50 mu m were tested. Pixel detectors of various pixel sizes were bump bonded to electronics chips and investigated. A key issue for the use of these sensors in high intensity experiments is the radiation hardness. Several irradiation experiments were carried out with pions, protons and neutrons exceeding a fluence of 10/sup 15/ particles/cm/sup 2/. The paper presents an overview of the results obtained with strip and pixel detectors in high-energy test beams and summarises the irradiation studies. (8 refs).

  1. Premature menopause linked to CVD and osteoporosis.

    Science.gov (United States)

    Park, Claire; Overton, Caroline

    2010-03-01

    Premature menopause affects 1% of women under the age of 40, the usual age of the menopause is 51. Most women will present with irregular periods or no periods at all with or without climacteric symptoms. Around 10% of women present with primary amenorrhoea. A careful history and examination are required. It is important to ask specifically about previous chemotherapy or radiotherapy and to look for signs of androgen excess e.g. polycystic ovarian syndrome, adrenal problems e.g. galactorrhoea and thyroid goitres. Once pregnancy has been excluded, a progestagen challenge test can be performed in primary care. Norethisterone 5 mg tds po for ten days or alternatively medroxyprogesterone acetate 10 mg daily for ten days is prescribed. A withdrawal bleed within a few days of stopping the norethisterone indicates the presence of oestrogen and bleeding more than a few drops is considered a positive withdrawal bleed. The absence of a bleed indicates low levels of oestrogen, putting the woman at risk of CVD and osteoporosis. FSH levels above 30 IU/l are an indicator that the ovaries are failing and the menopause is approaching or has occurred. It should be remembered that FSH levels fluctuate during the month and from one month to the next, so a minimum of two measurements should be made at least four to six weeks apart. The presence of a bleed should not exclude premature menopause as part of the differential diagnosis as there can be varying and unpredictable ovarian function remaining. The progestagen challenge test should not be used alone, but in conjunction with FSH, LH and oestradiol. There is no treatment for premature menopause. Women desiring pregnancy should be referred to a fertility clinic and discussion of egg donation. Women not wishing to become pregnant should be prescribed HRT until the age of 50 to control symptoms of oestrogen deficiency and reduce the risks of osteoporosis and CVD.

  2. A 3D tomographic EBSD analysis of a CVD diamond thin film

    Directory of Open Access Journals (Sweden)

    Tao Liu, Dierk Raabe and Stefan Zaefferer

    2008-01-01

    Full Text Available We have studied the nucleation and growth processes in a chemical vapor deposition (CVD diamond film using a tomographic electron backscattering diffraction method (3D EBSD. The approach is based on the combination of a focused ion beam (FIB unit for serial sectioning in conjunction with high-resolution EBSD. Individual diamond grains were investigated in 3-dimensions particularly with regard to the role of twinning.

  3. Rare genetic variants associated with early onset CVD

    NARCIS (Netherlands)

    Maiwald, S.

    2015-01-01

    Cardiovascular disease (CVD) is the major cause of morbidity and mortality in Western societies. CVD is mainly triggered by atherosclerosis. A combination of lipid accumulation, inflammation at the vessel wall and thrombotic reactions are underlying its pathobiology. Despite improvements in the ther

  4. Prevention: Reducing the risk of CVD in patients with periodontitis.

    Science.gov (United States)

    Genco, Robert J; Van Dyke, Thomas E

    2010-09-01

    The association between periodontitis and other chronic diseases, such as cardiovascular disease (CVD) and type 2 diabetes mellitus, could be related to systemic inflammation initiated by a local inflammatory challenge. Oliveira et al. have added lack of oral hygiene, and its link with systemic inflammation, to the spectrum of risk factors for CVD.

  5. Heat transfer model of an iCVD reactor

    NARCIS (Netherlands)

    Bakker, R.; Verlaan, V.; Verkerk, A.D.; van der Werf, C.H.M.; van Dijk, L.; Rudolph, H.; Rath, J.K.; Schropp, R.E.I.

    2009-01-01

    Contrary to conventional HWCVD, the power consumption in the iCVD process is dominated by heat conduction rather than radiation. This is due to the fact that while the typical wire temperature for HWCVD is about 1750–2200 °C, for iCVD the temperature is only 250–500 °C. Typical deposition pressures

  6. Purification of carbon nanotubes grown by thermal CVD

    Science.gov (United States)

    Porro, S.; Musso, S.; Vinante, M.; Vanzetti, L.; Anderle, M.; Trotta, F.; Tagliaferro, A.

    2007-03-01

    We show the results of a set of purifications on carbon nanotubes (CNT) by acid and basic treatments. CNTs were obtained by thermal decomposition of camphor at 850 °C in a CVD growth system, by means of a growth process catalyzed by iron clusters originating from the addition of ferrocene in the precursors mixture. The purification procedures involved HNO 3, H 2SO 4, HSO 3Cl and NaOH for different process temperatures. As-grown CNTs showed a consistent presence of metal catalyst (about 6 wt%), evidenced by TGA. The purification treatments led to a certain amount of opening of the CNT tips, with a consequent loss of metal catalyst encapsulated in tips. This is also confirmed by BET analysis, which showed an increase of the surface area density of CNT after the purification. FT-IR and XPS revealed the presence of carboxylic groups on the CNT surface chemically modified by the harsh environment of the purification process. Among the various treatments that have been tested, the 1:3 solution of nitric and sulphuric acid was the most effective in modifying the CNT surface and inducing the formation of functional groups.

  7. Mechanics-driven patterning of CVD graphene for roll-based manufacturing process

    Science.gov (United States)

    Kim, Sang-Min; Jang, Bongkyun; Jo, Kyungmin; Kim, Donghyuk; Lee, Jihye; Kim, Kyung-Shik; Lee, Seung-Mo; Lee, Hak-Joo; Han, Seung Min; Kim, Jae-Hyun

    2017-06-01

    Graphene is considered as a promising material for flexible and transparent electrodes due to its outstanding electrical, optical, and mechanical properties. Efforts to mass-produce graphene electrodes led to the development of roll-to-roll chemical vapor deposition (CVD) graphene growth and transfer, and the only remaining obstacle to the mass-production of CVD graphene electrodes is a cost-effective patterning technique that is compatible with the roll-to-roll manufacturing. Herein, we propose a mechanics-driven technique for patterning graphene synthesized on copper foil (commonly used in roll-to-roll manufacturing). The copper foil is exposed to high temperature for a prolonged period during the CVD growth of graphene, and thus can result in recrystallization and grain growth of the copper foil and thereby reducing to the yield strength. This softening behavior of the copper was carefully controlled to allow simple stamp patterning of the graphene. The strength of the underlying substrate was controlled for the accuracy of the residual patterns. The proposed stamp patterning technique is mask-less and photoresist-free, and can be performed at room temperature without high-energy sources such as lasers or plasma. To demonstrate the capability of this process to produce a continuous electrode, a transparent in-plane supercapacitor was fabricated using the proposed patterning technique.

  8. Measurement of Thermal Conductivity of Magnetic Fluids under External Uniform Magnetic Field Using Transient Hot-wire Method%磁性液体在均匀磁场中的瞬态双热线导热系数的测试

    Institute of Scientific and Technical Information of China (English)

    顾邦明; 王正良; 张立桥; 陈善飞

    2011-01-01

    Polymeric a-olefin based magnetic fluids sealed in two glass tubes were placed in external magnetic field. To eliminate the end effect and the natural convection induced by magnetic field force and gravity force, the transient hot wire (THW) instrument was developed for accurate measurements of the thermal conductivity of magnetic fluids. The hot wire apparatus was calibrated utilizing distilled water and anhydrous alcohol as reference fluids, which showed that the experimental system has a high accuracy. Effects of the direction of external magnetic field to the magnetic fluids with different volume fraction of suspended magnetic particles were measured. Results indicated that: when the direction of external magnetic field was parallel to the heat flow (the temperature gradient) , the thermal conductivity of the magnetic fluid increased greatly. The conductivity increased almost linearly with the strength of the magnetic field, the higher the particle concentration, the more increment was. On the other hand, when the magnetic field was perpendicular to the heat flow, little change in the thermal conductivity was found.%将封有聚a-烯烃合成油基磁性液体的两玻璃管放置于磁场中,为消除磁场力、重力所引起的磁性液体自然对流的影响,消除端部效应,研制了磁性液体在均匀磁场中瞬态双热线导热系数的实验测量系统,经与蒸馏水、乙醇标准样品的导热系数测量比较,实验装置有较高的测量精度.实验测量了不同方向的均匀磁场对不同体积浓度的磁性液体导热系数的影响.结果显示,当磁场方向与热通量方向一致时,磁场显著强化磁性液体的导热系数,其导热系数随磁场强度的增加而近似线性增加,且体积浓度越大增加量越大;当磁场方向与热通量方向垂直时,磁性液体的导热系数随磁场强度的变化不明显.

  9. Effect of mixture ratios and nitrogen carrier gas flow rates on the morphology of carbon nanotube structures grown by CVD

    CSIR Research Space (South Africa)

    Malgas, GF

    2008-02-01

    Full Text Available This paper reports on the growth of carbon nanotubes (CNTs) by thermal Chemical Vapour Deposition (CVD) and investigates the effects of nitrogen carrier gas flow rates and mixture ratios on the morphology of CNTs on a silicon substrate by vaporizing...

  10. CVD carbon powders modified by ball milling

    Directory of Open Access Journals (Sweden)

    Kazmierczak Tomasz

    2015-09-01

    Full Text Available Carbon powders produced using a plasma assisted chemical vapor deposition (CVD methods are an interesting subject of research. One of the most interesting methods of synthesizing these powders is using radio frequency plasma. This method, originally used in deposition of carbon films containing different sp2/sp3 ratios, also makes possible to produce carbon structures in the form of powder. Results of research related to the mechanical modification of these powders have been presented. The powders were modified using a planetary ball mill with varying parameters, such as milling speed, time, ball/powder mass ratio and additional liquids. Changes in morphology and particle sizes were measured using scanning electron microscopy and dynamic light scattering. Phase composition was analyzed using Raman spectroscopy. The influence of individual parameters on the modification outcome was estimated using statistical method. The research proved that the size of obtained powders is mostly influenced by the milling speed and the amount of balls. Powders tend to form conglomerates sized up to hundreds of micrometers. Additionally, it is possible to obtain nanopowders with the size around 100 nm. Furthermore, application of additional liquid, i.e. water in the process reduces the graphitization of the powder, which takes place during dry milling.

  11. Raman modes in transferred bilayer CVD graphene

    Directory of Open Access Journals (Sweden)

    Niilisk Ahti

    2015-01-01

    Full Text Available A systematic experimental Raman spectroscopic study of twisted bilayer graphene (tBLG domains localized inside wide-area single layer graphene (SLG produced by low-pressure CVD on Cu foil and transferred onto SiO2/Si substrate has been performed. According to the Raman characterization the tBLG domains had a great variety of twisting angles θ between the bottom and top graphene layers (6° < θ < 25°. The twisting angle θ was estimated from the spectral position of the rotating R and R' modes in the Raman spectrum.Under G band resonance conditions the breathing mode ZO' with a frequency of 95- 97 cm−1 was detected, and a breathing mode ZO was found in the spectra between 804 cm−1 and 836 cm−1, its position depending on the twisting angle θ. An almost linear relationship was found between the frequencies ωZO and ωR. Also a few other spectral peculiarities were found, e.g. a high-energy excitation of the G band resonance, the 2G overtone appearing at 3170-3180 cm−1 by the G band resonance, revealing a linear dispersion of 80 cm−1/eV of the 2D band in tBLG

  12. An assessment of radiotherapy dosimeters based on CVD grown diamond

    CERN Document Server

    Ramkumar, S; Conway, J; Whitehead, A J; Sussman, R S; Hill, G; Walker, S

    2001-01-01

    Diamond is potentially a very suitable material for use as a dosimeter for radiotherapy. Its radiation hardness, the near tissue equivalence and chemical inertness are some of the characteristics of diamond, which make it well suited for its application as a dosimeter. Recent advances in the synthesis of diamond by chemical vapour deposition (CVD) technology have resulted in the improvement in the quality of material and increased its suitability for radiotherapy applications. We report in this paper, the response of prototype dosimeters based on two different types (CVD1 and CVD2) of CVD diamond to X-rays. The diamond devices were assessed for sensitivity, dependence of response on dose and dose rate, and compared with a Scanditronix silicon photon diode and a PTW natural diamond dosimeter. The diamond devices of CVD1 type showed an initial increase in response with dose, which saturates after approx 6 Gy. The diamond devices of CVD2 type had a response at low fields (1162.8 V/cm), the CVD2-type devices show...

  13. Simultaneous synthesis of nanodiamonds and graphene via plasma enhanced chemical vapor deposition (MW PE-CVD) on copper.

    Science.gov (United States)

    Gottlieb, Steven; Wöhrl, Nicolas; Schulz, Stephan; Buck, Volker

    2016-01-01

    The simultaneous growth of both nanodiamonds and graphene on copper samples is described for the first time. A PE-CVD process is used to synthesize graphene layers and nanodiamond clusters from a hydrogen/methane gas mixture as it is typically done successfully in thermal CVD processes for graphene synthesis. However, the standard thermal CVD process is not without problems since the deposition of graphene is affected by the evaporation of a notable amount of copper caused by the slow temperature increase typical for thermal CVD resulting in a long process time. In sharp contrast, the synthesis of graphene by PE-CVD can circumvent this problem by substantially shortening the process time at holding out the prospect of a lower substrate temperature. The reduced thermal load and the possibility to industrially scale-up the PE-CVD process makes it a very attractive alternative to the thermal CVD process with respect to the graphene production in the future. Nanodiamonds are synthesized in PE-CVD reactors for a long time because these processes offer a high degree of control over the film's nanostructure and simultaneously providing a significant high deposition rate. To model the co-deposition process, the three relevant macroscopic parameters (pressure, gas mixture and microwave power) are correlated with three relevant process properties (plasma ball size, substrate temperature and C2/Hα-ratio) and the influence on the quality of the deposited carbon allotropes is investigated. For the evaluation of the graphene as well as the nanodiamond quality, Raman spectroscopy used whereas the plasma properties are measured by optical methods. It is found that the diamond nucleation can be influenced by the C2/Hα-ratio in the plasma, while the graphene quality remains mostly unchanged by this parameter. Moreover it is derived from the experimental data that the direct plasma contact with the copper surface is beneficial for the nucleation of the diamond while the growth and

  14. Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method.

    Science.gov (United States)

    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.

  15. Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method

    Science.gov (United States)

    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.

  16. Systematic study of pre-irradiation effects in high efficiency CVD diamond nuclear particle detectors

    CERN Document Server

    Marinelli, M; Milani, E; Paoletti, A; Pillon, M; Tucciarone, A; Verona-Rinati, G

    2002-01-01

    Many outstanding properties of diamond can, in principle, lead to the development of radiation detectors with interesting capabilities. In particular, diamond-based nuclear particle detectors are good candidates to replace silicon-based detectors in several fields, e.g. in high-flux applications such as next generation particle-accelerator experiments or beam monitoring. However, the high concentration of defects (grain boundaries, impurities) in synthetic diamond films can strongly limit the detector's performance. A significant increase in the efficiency of CVD diamond detectors is achieved by means of pre-irradiation (pumping) with beta particles. We report here on a systematic study of the effects of pumping in high-quality microwave CVD diamond films. The efficiency (eta) and charge collection distance (CCD) of nuclear particle detectors based on these films depend on the methane content in the growth gas mixture and on the film thickness. Both efficiency and CCD behave in a markedly different way in the...

  17. Electronic properties and strain sensitivity of CVD-grown graphene with acetylene

    Science.gov (United States)

    Yang, Meng; Sasaki, Shinichirou; Ohnishi, Masato; Suzuki, Ken; Miura, Hideo

    2016-04-01

    Although many studies have shown that large-area monolayer graphene can be formed by chemical vapor deposition (CVD) using methane gas, the growth of monolayer graphene using highly reactive acetylene gas remains a big challenge. In this study, we synthesized a uniform monolayer graphene film by low-pressure CVD (LPCVD) with acetylene gas. On the base of Raman spectroscopy measurements, it was found that up to 95% of the as-grown graphene is monolayer. The electronic properties and strain sensitivity of the LPCVD-grown graphene with acetylene were also evaluated by testing the fabricated field-effect transistors (FETs) and strain sensors. The derived carrier mobility and gauge factor are 862-1150 cm2/(V·s) and 3.4, respectively, revealing the potential for high-speed FETs and strain sensor applications. We also investigated the relationship between the electronic properties and the graphene domain size.

  18. Influence of surface morphology and microstructure on performance of CVD tungsten coating under fusion transient thermal loads

    Science.gov (United States)

    Lian, Youyun; Liu, Xiang; Wang, Jianbao; Feng, Fan; Lv, Yanwei; Song, Jiupeng; Chen, Jiming

    2016-12-01

    Thick tungsten coatings have been deposited by chemical vapor deposition (CVD) at a rapid growth rate. A series of tungsten coatings with different thickness and surface morphology were prepared. The surface morphology, microstructure and preferred orientation of the CVD tungsten coatings were investigated. Thermal shock analyses were performed by using an electron beam facility to study the influence of the surface morphology and the microstructure on the thermal shock resistance of the CVD tungsten coatings. Repetitive (100 pulses) ELMs-like thermal shock loads were applied at various temperatures between room temperature and 600 °C with pulse duration of 1 ms and an absorbed power density of up to 1 GW/m2. The results of the tests demonstrated that the specific surface morphology and columnar crystal structure of the CVD tungsten have significant influence on the surface cracking threshold and crack propagation of the materials. The CVD tungsten coatings with a polished surface show superior thermal shock resistance as compared with that of the as-deposited coatings with a rough surface.

  19. CVD Diamond Sensors In Detectors For High Energy Physics

    CERN Document Server

    AUTHOR|(INSPIRE)INSPIRE-00334150; Trischuk, William

    At the end of the next decade an upgrade of the Large Hadron Collider (LHC) to High Luminosity LHC (HL-LHC) is planned which requires the development of new radiation tolerant sensor technology. Diamond is an interesting material for use as a particle detector in high radiation environments. The large band gap ($5.47\\,\\text{eV}$) and the large displacement energy suggest that diamond is a radiation tolerant detector material. In this Thesis the capability of Chemical Vapor Deposition (CVD) diamond as such a sensor technology is investigated. The radiation damage constant for $800\\,\\text{MeV}$ protons is measured using single crystalline CVD (scCVD) and polycrystalline CVD (pCVD) diamonds irradiated to particle fluences up to $12 \\times 10^{15}\\,\\text{p/cm}^2$. In addition the signal response of a pCVD diamond detector after an irradiation to $12 \\times 10^{15}\\,\\text{p/cm}^2$ is investigated to determine if such a detector can be operated efficiently in the expected HL-LHC environment. By using electrodes em...

  20. Optimization of CVD parameters for long ZnO NWs grown on ITO/glass substrate

    Indian Academy of Sciences (India)

    ABDULQADER D FAISAL

    2016-12-01

    The optimization of chemical vapour deposition (CVD) parameters for long and vertically aligned (VA) ZnO nanowires (NWs) were investigated. Typical ZnO NWs as a single crystal grown on indium tin oxide (ITO)-coated glass substrate were successfully synthesized. First, the conducted side of ITO–glass substrate was coated with zinc acetate dihydrate to form seed layer of ZnO nanocrystals. Double zone tube furnace connected to vacuum pump was used for ZnO growth process. Zn metal powder was positioned at the first zone at temperature 900$^{\\circ}$C. The ITO–glass substrate with pre-coated seed layer was then located in the second zone of tube furnace at growth temperature of 550$^{\\circ}$C. The growth of ZnO NWs was controlled under constant concentration of seed layer, while other parameters such as argon and oxygen flow rates, substrate position, time and oxygen flow rate were varied.The VA ZnO NWs were finally characterized by scanning electron microscopy, X-ray diffractometer and high-resolution transmission electron microscope equipped with energy-dispersive X-ray spectroscopy. The results showthat long and VA ZnO NWs were single crystalline with hexagonal wurtzite structure. The ultimate length and average diameter of ZnO NWs were 10 $\\mu$m and 50–100 nm, respectively. These were achieved under optimized CVD growth parameters. The mechanism of vertical growth model of ZnO NWs is also discussed.

  1. Fabrication of Fe nanowires on yittrium-stabilized zirconia single crystal substrates by thermal CVD methods

    Energy Technology Data Exchange (ETDEWEB)

    Kawahito, A. [Graduate School of Chemical Science and Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628 (Japan); Yanase, T. [Frontier Chemistry Center, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628 (Japan); Endo, T.; Nagahama, T.; Shimada, T., E-mail: shimadat@eng.hokudai.ac.jp [Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628 (Japan)

    2015-05-07

    Magnetic nanowires (NWs) are promising as material for use in spintronics and as the precursor of permanent magnets because they have unique properties due to their high aspect ratio. The growth of magnetic Fe whiskers was reported in the 1960s, but the diameter was not on a nanoscale level and the growth mechanism was not fully elucidated. In the present paper, we report the almost vertical growth of Fe NWs on a single crystal yttrium-stabilized zirconia (Y{sub 0.15}Zr{sub 0.85}O{sub 2}) by a thermal CVD method. The NWs show a characteristic taper part on the bottom growing from a trigonal pyramidal nucleus. The taper angle and length can be controlled by changing the growth condition in two steps, which will lead to obtaining uniformly distributed thin Fe NWs for applications.

  2. Fabrication of Fe nanowires on yittrium-stabilized zirconia single crystal substrates by thermal CVD methods

    Science.gov (United States)

    Kawahito, A.; Yanase, T.; Endo, T.; Nagahama, T.; Shimada, T.

    2015-05-01

    Magnetic nanowires (NWs) are promising as material for use in spintronics and as the precursor of permanent magnets because they have unique properties due to their high aspect ratio. The growth of magnetic Fe whiskers was reported in the 1960s, but the diameter was not on a nanoscale level and the growth mechanism was not fully elucidated. In the present paper, we report the almost vertical growth of Fe NWs on a single crystal yttrium-stabilized zirconia (Y0.15Zr0.85O2) by a thermal CVD method. The NWs show a characteristic taper part on the bottom growing from a trigonal pyramidal nucleus. The taper angle and length can be controlled by changing the growth condition in two steps, which will lead to obtaining uniformly distributed thin Fe NWs for applications.

  3. Aplicação da técnica de fio quente na determinação das propriedades térmicas de polímeros fundidos Hot wire technique in the determination of thermal properties of melt polymers

    Directory of Open Access Journals (Sweden)

    Wilson N. dos Santos

    2005-11-01

    properties of a material that are needed for heat transfer calculations. Reliable thermal properties values are essential for polymers, both in steady and non-steady state situations. Nowadays, several different techniques for the determination of the thermal diffusivity and thermal conductivity may be found in the literature. In this work, the hot wire parallel technique is employed in the experimental determination of the thermal properties of polymers. Three semi-crystalline polymers (HDPE, LDPE and PP, and two amorphous polymers (PS and HIPS were selected for this work. Samples are prepared through the extrusion process starting from the powder or pellets of the solid polymer. A special mould of stainless steel in the shape of a rectangular parallelepiped provided with ceramic insulators between the hot wire, thermocouple and the mould is employed to store the melt extruded polymer whose thermal properties will be measured. Measurements are carried out from room temperature up to approximately 50 ºC above the melting point. Experimental results obtained are checked against data found in literature and those ones furnished by the manufacturers. A critical analysis of this method shows the advantages and disadvantages of this technique when compared with the laser flash technique.

  4. Role of Reaction and Factors of Carbon Nanotubes Growth in Chemical Vapour Decomposition Process Using Methane—A Highlight

    Directory of Open Access Journals (Sweden)

    Sivakumar VM

    2010-01-01

    This paper reviewed the synthesis of CNT by CVD especially focusing on methane CVD. Various parameters influencing the reaction and CNT growth were also discussed. A detailed review was made over the different types of CVD process, influence of metal, supports, metal-support interaction, effect of promoters, and reaction parameters role in CNTs growth.

  5. Present limitations of CVD diamond detectors for IMRT applications

    Energy Technology Data Exchange (ETDEWEB)

    De Angelis, C. [Dipartimento di Tecnologie e Salute, Istituto Superiore di Sanita and INFN, Viale regina Elena 299, 00161 Rome (Italy)], E-mail: cinzia.deangelis@iss.it; Casati, M. [Dipartimento di Fisiopatologia dell' Universita and INFN, Florence (Italy); Bruzzi, M. [Dipartimento di Energetica dell' Universita and INFN, Florence (Italy); Onori, S. [Dipartimento di Tecnologie e Salute, Istituto Superiore di Sanita and INFN, Viale regina Elena 299, 00161 Rome (Italy); Bucciolini, M. [Dipartimento di Fisiopatologia dell' Universita and INFN, Florence (Italy)

    2007-12-11

    The aim of the work was to test the suitability of chemical vapor deposited (CVD) diamond detectors for dosimetry in IMRT fields. We used in-house CVD detectors prepared with state-of-the-art polycrystalline diamond films (Element Six Ltd., UK). The parameters considered were time stability, dynamic response, dose-rate dependence and energy dependence. Output factors and TPR were measured in conventional photon fields and dose measurements were performed in IMRT fields using the step-and-shoot technique. Results prove that CVD diamond detectors are suitable for dosimetry in conventional treatments, but they still do not fit the IMRT dosimetry requirements, mainly because of their slow dynamic response. In particular, the slow dynamics affects linearity at low Monitor Units and renders it impossible to follow the sharp transients of IMRT fields. Time stability and dose-rate dependence as well must be improved to reduce their influence on dose assessment.

  6. Investigation on the priming effect of a CVD diamond microdosimeter

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    CVD diamond microdosimeter is an ideal substitute of common Si.GaAs detector for extremely strong radiation experimental environment due to its high band gap energy, fast charge collection, low dielectric constant and hardness. In order to improve its character, a CVD diamond microdosimeter was irradiated by a proton dose of 46 Gy, and a lateral micro-ion beam induced charge (IBIC) technique was utilized to characterize it in low beam current (~fA). It was clearly shown that charge collection efficiency and energy resolution were greatly improved after proton irradiation of that dose. Moreover, the homogeneities of both its counting performance and collection efficiency were enhanced. Proton irradiation of 46 Gy has been proved to be an effective way to prime a CVD diamond.

  7. Investigation on the priming effect of a CVD diamond microdosimeter

    CERN Document Server

    Lu Rong Rong; Jiang Da; Li Xiao Lin; Zhu Jie Qing

    2002-01-01

    CVD diamond microdosimeter is an ideal substitute of common Si, GaAs detector for extremely strong radiation experimental environmental due to its high band gap energy, fast charge collection, low dielectric constant and hardness. In order to improve its character, a CVD diamond microdosimeter was irradiated by a proton dose of 46 Gy, and a lateral micro-ion beam induced charge (IBIC) technique was utilized to characterize it in low beam current (approx fA). It was clearly shown that charge collection efficiency and energy resolution were greatly improved after proton irradiation of that dose. Moreover, the homogeneities of both its counting performance and collection efficiency were enhanced. Proton irradiation of 46 Gy has been proved to be an effective way to prime a CVD diamond

  8. CVD Method for Carbon Nanotubes Preparation Based on Orthogonal Experiment Using C3H6

    Institute of Scientific and Technical Information of China (English)

    SU Xunwen; JIANG Fang

    2015-01-01

    Carbon nanotubes (CNTs) have potential applications in many fields, chemical vapor deposition (CVD) is an effective method for CNTs preparation. By CVD, the catalytic pyrolysis temperature, pyrolysis time and the size of the raw gas lfow have a great inlfuence on yield rate of CNTs and their form. In this paper, the orthogonal experiment analysis method is used for studying the inlfuence factors of yield rate of CNTs. Research results show that, in the suitable temperature range of preparing CNTs, there is relatively more CNTs with excellent morphology, otherwise, if the temperature is too low, the growth of CNTs will not be sufifcient; if the temperature is too high, then CNTs will be generated with excessive defects; with longer growth time of suitable pyrolysis of CNTs, higher yield of CNTs will be obtained; CNTs morphology with reaction time is not proportional; too low or too high raw gas lfow rate is not conducive to the growth of CNTs. We have found the optimum conditions for the CNTs preparation: pyrolysis temperature 680℃, pyrolysis time 35 min, propylene lfow rate of 180 mL/min. The results have a reference value for the preparation of CNTS and their composites.

  9. Carbon Nanotubes by CVD and Applications

    Science.gov (United States)

    Cassell, Alan; Delzeit, Lance; Nguyen, Cattien; Stevens, Ramsey; Han, Jie; Meyyappan, M.; Arnold, James O. (Technical Monitor)

    2001-01-01

    Carbon nanotube (CNT) exhibits extraordinary mechanical and unique electronic properties and offers significant potential for structural, sensor, and nanoelectronics applications. An overview of CNT, growth methods, properties and applications is provided. Single-wall, and multi-wall CNTs have been grown by chemical vapor deposition. Catalyst development and optimization has been accomplished using combinatorial optimization methods. CNT has also been grown from the tips of silicon cantilevers for use in atomic force microscopy.

  10. CVD polymers fabrication of organic surfaces and devices

    CERN Document Server

    Gleason, Karen K

    2015-01-01

    The method of CVD (chemical vapor deposition) is a versatile technique to fabricate high-quality thin films and structured surfaces in the nanometer regime from the vapor phase. Already widely used for the deposition of inorganic materials in the semiconductor industry, CVD has become the method of choice in many applications to process polymers as well. This highly scalable technique allows for synthesizing high-purity, defect-free films and for systematically tuning their chemical, mechanical and physical properties. In addition, vapor phase processing is critical for the deposition of insol

  11. Engineered CVD Diamond Coatings for Machining and Tribological Applications

    Science.gov (United States)

    Dumpala, Ravikumar; Chandran, Maneesh; Ramachandra Rao, M. S.

    2015-07-01

    Diamond is an allotropes of carbon and is unique because of its extreme hardness (~100 GPa), low friction coefficient (fracture toughness can be tuned by controlling the grain size of the coatings from a few microns to a few nanometers. In this review, characteristics and performance of the CVD diamond coatings deposited on cemented tungsten carbide (WC-Co) substrates were discussed with an emphasis on WC-Co grade selection, substrate pretreatment, nanocrystallinity and microcrystallinity of the coating, mechanical and tribological characteristics, coating architecture, and interfacial adhesion integrity. Engineered coating substrate architecture is essential for CVD diamond coatings to perform well under harsh and highly abrasive machining and tribological conditions.

  12. Physics and applications of CVD diamond

    CERN Document Server

    Koizumi, Satoshi; Nesladek, Milos

    2008-01-01

    Here, leading scientists report on why and how diamond can be optimized for applications in bioelectronic and electronics. They cover such topics as growth techniques, new and conventional doping mechanisms, superconductivity in diamond, and excitonic properties, while application aspects include quantum electronics at room temperature, biosensors as well as diamond nanocantilevers and SAWs.Written in a review style to make the topic accessible for a wider community of scientists working in interdisciplinary fields with backgrounds in physics, chemistry, biology and engineering, this is e

  13. Control growth of silicon nanocolumns' epitaxy on silicon nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Chong, Su Kong, E-mail: sukong1985@yahoo.com.my [University of Malaya, Low Dimensional Materials Research Centre, Department of Physics (Malaysia); Dee, Chang Fu [Universiti Kebangsaan Malaysia (UKM), Institute of Microengineering and Nanoelectronics (IMEN) (Malaysia); Yahya, Noorhana [Universiti Teknologi PETRONAS, Faculty of Science and Information Technology (Malaysia); Rahman, Saadah Abdul [University of Malaya, Low Dimensional Materials Research Centre, Department of Physics (Malaysia)

    2013-04-15

    The epitaxial growth of Si nanocolumns on Si nanowires was studied using hot-wire chemical vapor deposition. A single-crystalline and surface oxide-free Si nanowire core (core radius {approx}21 {+-} 5 nm) induced by indium crystal seed was used as a substance for the vapor phase epitaxial growth. The growth process is initiated by sidewall facets, which then nucleate upon certain thickness to form Si islands and further grow to form nanocolumns. The Si nanocolumns with diameter of 10-20 nm and aspect ratio up to 10 can be epitaxially grown on the surface of nanowires. The results showed that the radial growth rate of the Si nanocolumns remains constant with the increase of deposition time. Meanwhile, the radial growth rates are controllable by manipulating the hydrogen to silane gas flow rate ratio. The optical antireflection properties of the Si nanocolumns' decorated SiNW arrays are discussed in the text.

  14. Surface analysis of CVD diamond exposed to fusion plasma

    NARCIS (Netherlands)

    Porro, S.; De Temmerman, G.; MacLaren, D. A.; Lisgo, S.; Rudakov, D. L.; Westerhout, J.; Wiora, M.; John, P.; Villalpando, I.; Wilson, J. I. B.

    2010-01-01

    Microcrystalline undoped and heavily boron-doped polycrystalline diamond layers have been deposited on various substrates by hot filament CVD and exposed to hydrogen plasma in a linear plasma reactor (Pilot-PSI, The Netherlands) that simulates the high flux and high density plasma conditions of toka

  15. Atmospheric pressure CVD of SNO2 and ZNO:AL

    NARCIS (Netherlands)

    Deelen, J. van; Kniknie, B.J.; Steijvers, H.L.A.H.; Mannie, G.; Thune, P.; Illiberi, A.

    2012-01-01

    Atmospheric pressure CVD (APCVD) is a highly cost effective method of depositing transparent conductive oxides (TCOs). In this work, insights in alcohol addition in the widely applied SnO2 process are discussed, including high resolution TEM images. Furthermore, the APCVD process of ZnO:Al was demon

  16. Hot wire anemometry. Citations from the NTIS data base

    Science.gov (United States)

    Habercom, G. E., Jr.

    1980-08-01

    Citations include principles; calibrating; circuit diagrams; flow measurement; hypersonic, supersonic, transonic, and subsonic characteristics; boundary layer studies; turbulence; jet, pipe, and tunnel flow; mathematical models; wind tunnel model tests, airport structure simulation; mass transfer and flow stability; probe modifications; flow about geometric forms; flow patterns; and related topics. This updated bibliography contains 249 citations, 28 of which are new entries to the previous edition.

  17. Thermal stability of hot-wire deposited amorphous silicon

    CSIR Research Space (South Africa)

    Arendse, CJ

    2006-04-01

    Full Text Available of vacancy clustering at 400 -C, caused by the alignment of unterminated Si dangling-bonds that consequently results in an increase in the defect size, concentration or both. Raman scattering shows evidence that no crystallization is induced at 400 -C...

  18. Hot-Wire Probe for Compressible Subsonic Flow

    Science.gov (United States)

    Stainback, P. C.; Johnson, C. B.; Basnett, C. B.

    1985-01-01

    Probe measures velocity, density, and total temperature fluctuations. Three-wire probe used with each wire operating at different overheat ratio. Technique extendable into transonic and low supersonic flow regimes without difficulty except for those problems usually associated with lengthy calibration and possible wire breaking.

  19. Hot-wire chemical vapour deposition of carbon nanotubes

    CSIR Research Space (South Africa)

    Cummings, FR

    2006-07-01

    Full Text Available and thermal conductivity, which have led to them being identified as possible components in a variety of applications such as reinforced composites, nano-scale electronic, electrochemical and power devices. Techniques used to synthesize CNTs include laser...

  20. Hot-wire assisted ALD: from idea to realization

    NARCIS (Netherlands)

    Kovalgin, Alexey

    2016-01-01

    Atomic Layer Deposition (ALD) was conventionally developed as a purely thermal process to deposit two-element films such as oxides and nitrides. ALD of single-element films (metals and semiconductors), with a few exceptions, is still a difficult task. Plasma-enhanced ALD (PEALD) can enable depositio