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Sample records for plasma cvd technique

  1. Plasma CVD of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Cruden, B.; Hash, D.; Meyyappan, M.; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    Carbon nanotubes(CNT) exhibit remarkable mechanical and unique electronic properties and thus have created excitement in the research community about their potential in electronics, computing, sensor and structural applications. Realization of these applications critically depends on the ability to control the properties(such as diameter, chirality) as well purity. We have investigated CNT growth using an inductively coupled plasma(ICP) process using hydrocarbon feedstock. The catalyst required for nanotube growth consists of thin sputtered layers of aluminum and iron(10 nm each) and aligned carbon nanotubes have been obtained. Optical emission diagnostics as well as a plasma modeling effort have been undertaken to understand growth mechanisms. This presentation will discuss growth characteristics under various pressure, power and feedgas compositions and our understanding from modeling and diagnostics.

  2. Investigation of the Millimeter-Wave Plasma Assisted CVD Reactor

    SciTech Connect

    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.

  3. Fabrication of graphene-based films using remote plasma CVD

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Mineo; Tsukada, Ryosuke; Kashima, Yohei; Naito, Masateru; Kondo, Hiroki; Hori, Masaru

    2012-10-01

    Plasma-enhanced CVD (PECVD) employing methane/hydrogen gases has been used to grow diamond, diamond-like carbon, and carbon nanotubes. In the case of microwave PECVD with methane/hydrogen system without catalyst nanoparticles at temperatures of 700--850 ^oC, where the substrate is exposed to the plasma, vertical nano-graphenes and carbon nanoflakes have been easily grown even on Cu substrate due to the ion bombardment and local electric field forces. In this work, we demonstrate the synthesis of planar few-layer graphene-based film using PECVD with remote plasma configuration. In the case using microwave plasma of cylindrical resonant cavity type, by simply installing grounded grid over the substrate plate for obtaining remote plasma configuration, we have successfully fabricated graphene-based films on Cu substrate, which was confirmed by the Raman spectrum and SEM image of deposit. Similar method will be applied to other plasmas such as low-pressure inductively coupled plasma, in order to verify the effectiveness of remote plasma configuration for the growth of planar graphene using PECVD technique. We will discuss the planar graphene growth mechanism in terms of precursors and their surface reaction.

  4. ECR Plasma CVD in Different Magnetic Field Configurations

    NASA Astrophysics Data System (ADS)

    Murata, Masayoshi; Uchida, Satoshi; Kishimoto, Kengo; Tanaka, Masayoshi; Komori, Akio; Kawai, Yoshinobu

    1992-05-01

    An electron cyclotron resonance (ECR) plasma is produced with a slotted Lisitano coil, and the axial distribution of the plasma parameters is measured in detail for different magnetic field configurations. It is found that the plasma density in uniform magnetic fields axially decreases more slowly than that in divergent magnetic fields. Furthermore, carbon films are formed by ECR plasma chemical vapor deposition (CVD), and the deposition rate obtained in the uniform magnetic fields is found to be larger than that obtained in the divergent magnetic fields.

  5. Toroidal plasma enhanced CVD of diamond films

    SciTech Connect

    Zvanya, John Cullen, Christopher Morris, Thomas Krchnavek, Robert R.; Holber, William Basnett, Andrew Basnett, Robert; Hettinger, Jeffrey

    2014-09-01

    An inductively coupled toroidal plasma source is used as an alternative to microwave plasmas for chemical vapor deposition of diamond films. The source, operating at a frequency of 400 kHz, synthesizes diamond films from a mixture of argon, methane, and hydrogen. The toroidal design has been adapted to create a highly efficient environment for diamond film deposition: high gas temperature and a short distance from the sample to the plasma core. Using a toroidal plasma geometry operating in the medium frequency band allows for efficient (≈90%) coupling of AC line power to the plasma and a scalable path to high-power and large-area operation. In test runs, the source generates a high flux of atomic hydrogen over a large area, which is favorable for diamond film growth. Using a deposition temperature of 900–1050 °C and a source to sample distance of 0.1–2.0 cm, diamond films are deposited onto silicon substrates. The results showed that the deposition rate of the diamond films could be controlled using the sample temperature and source to sample spacing. The results also show the films exhibit good-quality polycrystalline diamond as verified by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. The scanning electron microscopy and x-ray diffraction results show that the samples exhibit diamond (111) and diamond (022) crystallites. The Raman results show that the sp{sup 3} peak has a narrow spectral width (FWHM 12 ± 0.5 cm{sup −1}) and that negligible amounts of the sp{sup 2} band are present, indicating good-quality diamond films.

  6. ECR Plasma CVD Using a Slotted Lisitano Coil

    NASA Astrophysics Data System (ADS)

    Kawai, Yoshinobu; Komori, Akio; Ikeda, Hidehiko; Kishimoto, Kengo; Murata, Masayoshi; Uchida, Satoshi

    1990-11-01

    An ECR plasma is produced at relatively high pressures up to 25 mTorr with a slotted Lisitano coil 140 mm in diameter, and the radial distributions of plasma parameters are measured. It is found that the plasma is almost radially uniform even at pressures higher than 10 mTorr. Carbon films are formed on silicon wafers by introducing methane gas into the ECR plasma and the deposition rate is examined as a function of concentration of methane gas and substrate temperature. Furthermore, the physical properties of the films are analyzed by X-ray diffraction and Raman scattering. These results show that a slotted Lisitano coil is very useful for the ECR plasma CVD.

  7. Surface morphology and resistivity of aluminum oxide films prepared by plasma CVD combined with ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Nakai, H.; Shinohara, J.; Sassa, T.; Ikegami, Y.

    1997-01-01

    Plasma CVD combined with simultaneous ion beams has been developed in order to prepare ceramic insulating films which have strong force of adhesion and higher electric resistivity at high temperatures. Aluminum oxide (Al 2O 3) films were deposited on nickel based superalloy (Inconel 718) by thermal CVD, plasma CVD and ion beam assisted plasma CVD at the several substrate temperatures. The surface morphology of these films was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was confirmed that, by ion beam irradiation, the extent of crystallization was enhanced at lower substrate temperature and grain size became smaller. The electric resistivity was measured in the temperature range of RT to 800°C. The film, deposited by ion beam assisted plasma CVD at 800°C, had higher electric resistivity than the films by conventional CVD.

  8. Few layers isolated graphene domains grown on copper foils by microwave surface wave plasma CVD using camphor as a precursor

    NASA Astrophysics Data System (ADS)

    Ram Aryal, Hare; Adhikari, Sudip; Uchida, Hideo; Wakita, Koichi; Umeno, Masayoshi

    2016-03-01

    Few layers isolated graphene domains were grown by microwave surface wave plasma CVD technique using camphor at low temperature. Graphene nucleation centers were suppressed on pre-annealed copper foils by supplying low dissociation energy. Scanning electron microscopy study of time dependent growth reveals that graphene nucleation centers were preciously suppressed, which indicates the possibility of controlled growth of large area single crystal graphene domains by plasma processing. Raman spectroscopy revealed that the graphene domains are few layered which consist of relatively low defects.

  9. Photo-oxidation of Polymers Synthesized by Plasma and Initiated CVD

    DOE PAGESBeta

    Baxamusa, Salmaan H.; Suresh, Aravind; Ehrmann, Paul; Laurence, Ted; Hanania, Jiries; Hayes, Jeff; Harley, Stephen; Burkey, Daniel D.

    2015-11-09

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

  10. Photo-oxidation of Polymers Synthesized by Plasma and Initiated CVD

    SciTech Connect

    Baxamusa, Salmaan H.; Suresh, Aravind; Ehrmann, Paul; Laurence, Ted; Hanania, Jiries; Hayes, Jeff; Harley, Stephen; Burkey, Daniel D.

    2015-11-09

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

  11. Application of CVD diamonds as dosimeters of soft X-ray emission from plasma sources

    NASA Astrophysics Data System (ADS)

    Krása, J.; Juha, L.; Vorlíček, V.; Cejnarová, A.

    2004-05-01

    The thermoluminescent properties of polycrystalline chemical vapour deposition (CVD) diamond, as free-standing CVD cutting tool material, type CVDITE-CDM (De Beers Company), were studied with respect to its use in the dosimetry of soft X-ray emission from laser-produced plasma. The range of linearity for 5.9-keV radiation was measured to be only two orders of magnitude, ranging from a sensitivity threshold of ˜0.01 to ˜2 Gy. In this linearity range, the sensitivity of CVD diamonds is about 65 times lower than the sensitivity of TLD-100 dosimeters. The unpolished (grained) face of CVD diamonds shows ˜1.5-times higher thermoluminescence (TL) response after irradiation than the polished face, in the high-temperature range, but the polished face shows slightly higher TL response in the low-temperature range. A strong TL sensitivity to the blue portion of the visible light spectrum was measured. Simultaneous irradiation of TLD-100 dosimeters and CVD diamonds by soft X-rays emitted from a laser-produced plasma showed that CVDITE-CDM diamonds can be applied as detectors of intense soft X-ray radiation.

  12. Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor

    NASA Astrophysics Data System (ADS)

    Bülow, Tim; Gargouri, Hassan; Siebert, Mirko; Rudolph, Rolf; Johannes, Hans-Hermann; Kowalsky, Wolfgang

    2014-05-01

    A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80℃ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 -3 g m -2 d -1 at 60℃ and 90% relative humidity could be observed.

  13. Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor

    PubMed Central

    2014-01-01

    A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80℃ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 −3 gm−2d−1 at 60℃ and 90% relative humidity could be observed. PMID:24936155

  14. Microwave plasma CVD of NANO structured tin/carbon composites

    DOEpatents

    Marcinek, Marek; Kostecki, Robert

    2012-07-17

    A method for forming a graphitic tin-carbon composite at low temperatures is described. The method involves using microwave radiation to produce a neutral gas plasma in a reactor cell. At least one organo tin precursor material in the reactor cell forms a tin-carbon film on a supporting substrate disposed in the cell under influence of the plasma. The three dimensional carbon matrix material with embedded tin nanoparticles can be used as an electrode in lithium-ion batteries.

  15. Field emission from carbon nanotubes produced using microwave plasma assisted CVD

    SciTech Connect

    Zhang, Q.; Yoon, S.F.; Ahn, J.; Gan, B.; Rusli; Yu, M.B.; Cheah, L.K.; Shi, X.

    2000-01-30

    Electron field emission from carbon nanotubes prepared using microwave plasma assisted CVD has been investigated. The nanotubes, ranging from 50 to 120 nm in diameter and a few tens of microns in length, were formed under methane and hydrogen plasma at 720 C with the aid of iron-oxide particles. The morphology and growth direction of the nanotubes are found to be strongly influenced by the flow ratio of methane to hydrogen. However, the electron field emission from these massive nanotubes show similar characteristics, i.e., high emission current at low electric fields.

  16. Effects of Time Parameter in Pulse Plasma CVD on Narrow-Chirality Distributed growth of Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Kato, Toshiaki; Kaneko, Toshiro

    2015-09-01

    Single-walled carbon nanotubes (SWNTs) are promising materials in industry application, since they have many brilliant characteristics However, since the electronic and optical properties of SWNTs strongly depend on chirality, the selective synthesis of SWNTs with desired chiralities is one of the major challenges in nanotubes science and applications. In this study, time-controlled pulse plasma CVD has been developed aiming for the mass production of narrow chirality distributed SWNTs. Through the comparison of continuous plasma CVD and pulse plasma CVD, it is found that the amount of SWNTs can be increased in keeping with the initial narrow chirality distribution by repeating pulse plasma CVD. The effects of pulse time parameter, plasma off time, on the chirality distribution of SWNTs are also investigated. The chirality distribution becomes narrow with an increase in the plasma off time up to 60 sec, then it becomes broad with an increase in the off time. These indicate, adjustment of plasma time parameter in pulse plasma CVD can improve the uniformity of chirality distribution, resulting in the mass production of very narrow chirality distributed SWNTs. This work was supported by a Grant-in-Aid for JSPS Fellows Grant Number 15J01481.

  17. A thermocouple-based remote temperature controller of an electrically floated sample to study plasma CVD growth of carbon nanotube

    NASA Astrophysics Data System (ADS)

    Miura, Takuya; Xie, Wei; Yanase, Takashi; Nagahama, Taro; Shimada, Toshihiro

    2015-09-01

    Plasma chemical vapor deposition (CVD) is now gathering attention from a novel viewpoint, because it is easy to combine plasma processes and electrochemistry by applying a bias voltage to the sample. In order to explore electrochemistry during the plasma CVD, the temperature of the sample must be controlled precisely. In traditional equipment, the sample temperature is measured by a radiation thermometer. Since emissivity of the sample surface changes in the course of the CVD growth, it is difficult to measure the exact temperature using the radiation thermometer. In this work, we developed new equipment to control the temperature of electrically floated samples by thermocouple with Wi-Fi transmission. The growth of the CNT was investigated using our plasma CVD equipment. We examined the temperature accuracy and stability controlled by the thermocouple with monitoring the radiation thermometer. We noticed that the thermocouple readings were stable, whereas the readings of the radiation thermometer changes significantly (20 °C) during plasma CVD. This result clearly shows that the sample temperature should be measured with direct connection. On the result of CVD experiment, different structures of carbon including CNT were obtained by changing the bias voltages.

  18. Microwave engineering of plasma-assisted CVD reactors for diamond deposition

    NASA Astrophysics Data System (ADS)

    Silva, F.; Hassouni, K.; Bonnin, X.; Gicquel, A.

    2009-09-01

    The unique properties of CVD diamond make it a compelling choice for high power electronics. In order to achieve industrial use of CVD diamond, one must simultaneously obtain an excellent control of the film purity, very low defect content and a sufficiently rapid growth rate. Currently, only microwave plasma-assisted chemical vapour deposition (MPACVD) processes making use of resonant cavity systems provide enough atomic hydrogen to satisfy these requirements. We show in this paper that the use of high microwave power density (MWPD) plasmas is necessary to promote atomic hydrogen concentrations that are high enough to ensure the deposition of high purity diamond films at large growth rates. Moreover, the deposition of homogeneous films on large surfaces calls for the production of plasma with appropriate shapes and large volumes. The production of such plasmas needs generating a fairly high electric field over extended regions and requires a careful design of the MW coupling system, especially the cavity. As far as MW coupling efficiency is concerned, the presence of a plasma load represents a mismatching perturbation to the cavity. This perturbation is especially important at high MWPD where the reflected fraction of the input power may be quite high. This mismatch can lead to a pronounced heating of the reactor walls. It must therefore be taken into account from the very beginning of the reactor design. This requires the implementation of plasma modelling tools coupled to detailed electromagnetic simulations. This is discussed in section 3. We also briefly discuss the operating principles of the main commercial plasma reactors before introducing the reactor design methodology we have developed. Modelling results for a new generation of reactors developed at LIMHP, working at very high power density, will be presented. Lastly, we show that scaling up this type of reactor to lower frequencies (915 MHz) can result in high density plasmas allowing for fast and

  19. Microwave engineering of plasma-assisted CVD reactors for diamond deposition.

    PubMed

    Silva, F; Hassouni, K; Bonnin, X; Gicquel, A

    2009-09-01

    The unique properties of CVD diamond make it a compelling choice for high power electronics. In order to achieve industrial use of CVD diamond, one must simultaneously obtain an excellent control of the film purity, very low defect content and a sufficiently rapid growth rate. Currently, only microwave plasma-assisted chemical vapour deposition (MPACVD) processes making use of resonant cavity systems provide enough atomic hydrogen to satisfy these requirements. We show in this paper that the use of high microwave power density (MWPD) plasmas is necessary to promote atomic hydrogen concentrations that are high enough to ensure the deposition of high purity diamond films at large growth rates. Moreover, the deposition of homogeneous films on large surfaces calls for the production of plasma with appropriate shapes and large volumes. The production of such plasmas needs generating a fairly high electric field over extended regions and requires a careful design of the MW coupling system, especially the cavity. As far as MW coupling efficiency is concerned, the presence of a plasma load represents a mismatching perturbation to the cavity. This perturbation is especially important at high MWPD where the reflected fraction of the input power may be quite high. This mismatch can lead to a pronounced heating of the reactor walls. It must therefore be taken into account from the very beginning of the reactor design. This requires the implementation of plasma modelling tools coupled to detailed electromagnetic simulations. This is discussed in section 3. We also briefly discuss the operating principles of the main commercial plasma reactors before introducing the reactor design methodology we have developed. Modelling results for a new generation of reactors developed at LIMHP, working at very high power density, will be presented. Lastly, we show that scaling up this type of reactor to lower frequencies (915 MHz) can result in high density plasmas allowing for fast and

  20. A comparative study of remote plasma sources for environmentally-friendly CVD chambers cleaning

    SciTech Connect

    Raoux, S.; Lai, K.C.; Nguyen, H.; Sarfaty, M.; Li, S.T.; Davidow, J.; Huang, T.F.

    1999-07-01

    CVD chamber cleaning is the main source of perfluorocompound (PFC) emission from semiconductor fabrication plants. Over the past years, several attempts have been made to optimize chamber cleaning efficiency and reduce its environmental impact. A new cleaning technology has been introduced that improves the overall tool productivity while virtually eliminating PFC emission concerns. A remote high-density plasma source dissociates NF{sub 3} molecules, and the reactive byproducts are injected in the CVD chamber to etch the deposition residues. Due to near-complete utilization of the source gas, the technology provides reduced clean time, and the MMTCE (Million Metric Ton Carbon Equivalent) of the process can be reduced by two orders of magnitude, compared to classical in-situ RF plasma cleans. In this study, the authors compare the characteristics of a microwave-driven and a magnetically-enhanced indicatively coupled NF{sub 3} discharge. Optical Emission Spectroscopy. Quadrupole Mass Spectroscopy, Fourier Transform Infra Red and etch rate measurements were used to characterize the different sources and assess the environmental impact of the clean processes. A comparative analysis of the two types of plasma sources is made with respect to implementation of this cleaning technology in an industrial environment.

  1. Simultaneous synthesis of nanodiamonds and graphene via plasma enhanced chemical vapor deposition (MW PE-CVD) on copper.

    PubMed

    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

  2. Nucleation control and selective growth of diamond particles formed with plasma CVD

    NASA Astrophysics Data System (ADS)

    Ma, Jing Sheng; Kawarada, Hiroshi; Suzuki, Jun-Ichi; Yokota, Yoshihiro; Yonehara, Takao

    1990-01-01

    To obtain polycrystals with large and uniform grain size, diamond particles have been selectively formed on a SiO2 dot-patterned Si substrate using plasma-assisted CVD. After pretreatment by abrasive powders to increase diamond nucleation densities on both Si and SiO2, an Ar beam is used to irradiate obliquely the pretreated surface. As a result, diamond can no longer nucleate on Si; it nucleates only on one edge of the SiO2 dots and grows over the Si substrate to about 10 microns. Well defined polycrystals having equal grain sizes have been obtained. The role of the Ar beam irradiation on Si and on SiO2 is also discussed.

  3. Synthesis, characterization and cathodoluminescence of nanostructured SnO2 using microwave plasma enhanced CVD

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Yuan; Chen, Tzu-Wang; Lin, Chun-Chun; Hsieh, Wei-Jen; Chang, Ku-Ling; Shih, Han C.

    2007-05-01

    Nanostructured tin oxides have been synthesized in the form of nano-pins using SnCl2 · 2H2O as precursors in a short period of 2.5 min by microwave plasma enhanced CVD. The resulting nano-pins have square cross sections of 50-60 nm at the pin head, 10-20 nm at the pin proper and less than 5 nm at the pin tail; the full length of the pin is about several micrometres. The optical properties measured by cathodoluminescence show strong indigo emission at 404 and 460 nm. The nucleation and growth are dominated by a self-catalytic vapour-liquid-solid mechanism, which has been studied in this work.

  4. Low pressure plasma diagnostics by cars and other techniques

    SciTech Connect

    Hata, N. )

    1989-01-01

    Within the past several years, intensive research activities relating amorphous-silicon technology have stimulated plasma-chemical-vapor-deposition (plasma-CVD) diagnostics by laser-spectroscopic techniques. Among them, coherent anti-Stokes Raman spectroscopy (CARS) has attracted much attention because of its great success in combustion diagnostics, and has been employed for low-pressure-plasma studies. Gas-phase species such as SiH{sub 4}, H{sub 2}, Si{sub 2}H{sub 6}, SiH{sub 2}, and GeH{sub 4} have been detected, time dependences of their concentration and spatial profiles of their concentration and rotational temperature have been determined, and the gas-phase mechanisms have been discussed. This talk will employ those results as examples, and discuss (1) the potential of CARS for gas-phase analysis in CVD (including (i) what species are monitored, (ii) what information is obtained, and (iii) what are the advantages and limitations), and (2) some other diagnostic techniques that provide additional information for better understandings of CVD mechanisms.

  5. Plasma-assisted CVD of fluorinated, hydrogenated amorphous silicon. Final report

    SciTech Connect

    Coleman, J.H.; Hammes, J.P.; Wiesmann, H.J.

    1981-01-01

    During the past year, three novel large-area (100 cm/sup 2/) a-Si:H solar cells were developed with the following configurations: inverted NIP/SS cells with an improved red response; inverted a-Si:H/a-B:H heterojunction cells with high V/sub oc/; and NIP/metal cells with a CVD P-layer grown pyrolytically from silane and diborane. Initial experiments were performed using disilane as the deposition gas for the intrinsic layer in both NIP/SS and PIN/SS structures. Coatings of In/sub 2/O/sub 3/, using a technique developed by Dr. Ovadyahu, were applied to NIP/SS cells in order to evaluate its potential as a conductive coating in practical amorphous silicon solar cells.

  6. The effect of nitrogen incorporation in DLC films deposited by ECR Microwave Plasma CVD

    NASA Astrophysics Data System (ADS)

    Seker, Z.; Ozdamar, H.; Esen, M.; Esen, R.; Kavak, H.

    2014-09-01

    Diamond like carbon (DLC) and nitrogenated diamond like carbon (DLC:N) films have been deposited by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MP CVD) on Si (1 1 0), steel and glass substrates, using CH4 and N2 as plasma source. The effect of nitrogen doping on the optical, electrical, structural and mechanical properties of films was investigated. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy results showed that sp2 bonded carbon phases increased while the sp3 bonded carbon phases decreased by nitrogen doping. Microhardness measurements showed a decrease in hardness (from 75 to 69 GPa) according to nitrogen incorporation. Average transmittance of all the films was over 90% and band gap energy (Eg) of the films decreased due to increasing nitrogen flow rate. The film morphology was studied using the atomic force microscopy (AFM). Electrical properties were characterized by Hall measurement. Undoped DLC was p-type with a conductivity of 9.81 × 10-6 (Ω cm)-1. DLC films became n-type by nitrogen doping. The best conductivity value for the nitrogen doped DLC films was found 2.77 × 10-5 (Ω cm)-1. PL spectra of DLC and DLC:N films showed three peaks at 405 nm (3.06 eV), 533 nm (2.32 eV) and 671 nm (1.84 eV).

  7. Diagnostic techniques for thermal plasmas

    SciTech Connect

    Fincke, J.R.; Snyder, S.C.; Swank, W.D.; Haggard, D.C.; Reynolds, L.D.

    1994-12-31

    The plasma diagnostic techniques discussed are Rayleigh and coherent Thomson scattering, Coherent-Anti-Stokes-Raman Spectroscopy (CARS) and enthalpy probes. The quantities measured are heavy species and electron temperature, ionized fraction, plasma composition, and velocity. Examples of results from both subsonic and supersonic jets are presented and limitations discussed.

  8. Chemical composition and selected mechanical properties of Al-Zn alloy modified in plasma conditions by RF CVD

    NASA Astrophysics Data System (ADS)

    Kyzioł, Karol; Kluska, Stanisława; Januś, Marta; Środa, Marcin; Jastrzębski, Witold; Kaczmarek, Łukasz

    2014-08-01

    The paper reports results of the study of surface composition and selected functional properties of 7075 (Al-Zn) alloys modified in Ar, N2, SiH4 and CH4 atmosphere at reduced pressure. RF CVD (Radio Frequency Chemical Vapour Deposition) technique was used in the study. The type or weight percentage of carbon in each modification varied in the resultant SiN:H and SiCN:H coatings. Alloy samples were treated with Ar+ plasma etching and N+ ion implantation at reduced pressure. The tests proved the values of selected mechanical properties (hardness ca. 10.5 GPa, Young modulus ca. 95 GPa) and adhesion (delamination force ca. 11.5 mN) to be higher in the case of SiCN:H anti-wear coating (deposited in SiH4:CH4:N2 = 1:1:2 gas mixture) than the values of the respective parameters obtained in the remaining modifications. Further, carbon doped coatings (SiCN:H) exhibited significantly improved hardness (by about 50 to 70%) and nearly threefold increase in delamination force in comparison with SiCN:H coatings.

  9. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    NASA Technical Reports Server (NTRS)

    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.

  10. System for the growth of bulk SiC crystals by modified CVD techniques

    NASA Technical Reports Server (NTRS)

    Steckl, Andrew J.

    1994-01-01

    The goal of this program was the development of a SiC CVD growth of films thick enough to be useful as pseudo-substrates. The cold-walled CVD system was designed, assembled, and tested. Extrapolating from preliminary evaluation of SiC films grown in the system at relatively low temperatures indicates that the growth rate at the final temperatures will be high enough to make our approach practical. Modifications of the system to allow high temperature growth and cleaner growth conditions are in progress. This program was jointly funded by Wright Laboratory, Materials Directorate and NASA LeRC and monitored by NASA.

  11. High efficiency light-induced dielectrophoresis biochip prepared using CVD techniques.

    PubMed

    Wu, Hung-Wei; Huang, Yao-Sheng; Lee, Hsin-Ying; Tsai, Wu-Han; Chen, Kuan-Yu; Jian, Li-Yi

    2016-10-01

    This article describes a high-efficiency light-induced dielectrophoresis biochip containing a thin film prepared through inductively coupled plasma chemical vapor deposition (ICPCVD). The biochip comprises two ITO glass substrates and a photoconductive amorphous silicon thin film. The biochip can effectively sort particular particles (or cells) by projecting visible light onto the surface of the silicon thin film. The sorting efficiency of biochips is highly associated with the quality of the deposited amorphous silicon thin films; therefore, the choice of deposition technique is extremely critical. However, no study has examined this problem. Hence, the current study thoroughly compared the efficiency of the biochip when films produced through plasma-enhanced chemical vapor deposition and ICPCVD are used. PMID:27530346

  12. CVD graphene growth and transfer techniques for the fabrication of micromechanical resonators

    NASA Astrophysics Data System (ADS)

    Losowyj, Daniel; Storch, Isaac; McCune, Thomas; McEuen, Paul

    2013-03-01

    Graphene's superlative mechanical strength, electrical mobility, low mass, and large surface area make it a prime candidate for use in micromechanical resonators, which have potential applications in mass and force sensing, radio frequency signal processing, and optomechanics. Our resonators use graphene grown by chemical vapor deposition (CVD) and have excellent mechanical performance, but their electrical performance is comparatively worse than that of exfoliated graphene devices. We attribute these limitations to contamination from copper oxidation during the growth and solvents used in the transfer process. To remedy this, we have performed CVD growths on copper foils with long anneal times, confirming with Raman spectroscopy and SEM that the graphene is single layer and high quality. We have also found that graphene suspended on a substrate can survive high temperature air annealing, provided that the temperature ramp is gradual. Improving the electrical performance of these novel devices will facilitate their use in a variety of new experiments and applications.

  13. Epitaxial and polycrystalline GaAs solar cells using OM-CVD techniques

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Shin, B. K.; Stirn, R. J.

    1980-01-01

    GaAs epitaxial films were grown by chemical vapor deposition using organo-metallic sources (OM-CVD) on single crystal and polycrystalline bulk GaAs, as well as on bulk polycrystalline and recrystallized thin-film Ge substrates. Details of Antireflecting Metal-Oxide-Semiconductor (AMOS) solar cells fabricated on GaAs films grown on bulk polycrystalline Ge and recrystallized Ge thin-film substrates will be discussed, as well as preliminary photovoltaic results obtained for n(+)/p homojunction structures.

  14. Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD).

    PubMed

    Böke, Frederik; Giner, Ignacio; Keller, Adrian; Grundmeier, Guido; Fischer, Horst

    2016-07-20

    Densely sintered aluminum oxide (α-Al2O3) is chemically and biologically inert. To improve the interaction with biomolecules and cells, its surface has to be modified prior to use in biomedical applications. In this study, we compared two deposition techniques for adhesion promoting SiOx films to facilitate the coupling of stable organosilane monolayers on monolithic α-alumina; physical vapor deposition (PVD) by thermal evaporation and plasma enhanced chemical vapor deposition (PE-CVD). We also investigated the influence of etching on the formation of silanol surface groups using hydrogen peroxide and sulfuric acid solutions. The film characteristics, that is, surface morphology and surface chemistry, as well as the film stability and its adhesion properties under accelerated aging conditions were characterized by means of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and tensile strength tests. Differences in surface functionalization were investigated via two model organosilanes as well as the cell-cytotoxicity and viability on murine fibroblasts and human mesenchymal stromal cells (hMSC). We found that both SiOx interfaces did not affect the cell viability of both cell types. No significant differences between both films with regard to their interfacial tensile strength were detected, although failure mode analyses revealed a higher interfacial stability of the PE-CVD films compared to the PVD films. Twenty-eight day exposure to simulated body fluid (SBF) at 37 °C revealed a partial delamination of the thermally deposited PVD films whereas the PE-CVD films stayed largely intact. SiOx layers deposited by both PVD and PE-CVD may thus serve as viable adhesion-promoters for subsequent organosilane coupling agent binding to α-alumina. However, PE-CVD appears to be favorable for long-term direct film exposure to aqueous

  15. Microwave plasma CVD-grown graphene-CNT hybrids for enhanced electron field emission applications

    NASA Astrophysics Data System (ADS)

    Kaushik, Vishakha; Shukla, A. K.; Vankar, V. D.

    2014-12-01

    The growth and electron emission characteristics were investigated from a hybrid structure of multiwalled carbon nanotubes (MWCNTs) and multilayer layer graphene (MLG) deposited on silicon substrate coated with iron catalyst and an interlayer of aluminium. The hybrid structures were synthesized in a two-step process by microwave plasma-enhanced chemical vapour deposition technique. The formation of MWCNTs takes place by absorption and precipitation of carbon radicals into the catalyst particles. Thereafter, ample carbon forms MLG on tip of the MWCNTs resulting in a MLG-MWCNTs hybrid nanostructure. MLG was observed to grow branching out of the tips and sidewalls of the MWCNTs and is expected to attach by Van der Walls bonds. Transmission electron microscopy and micro-Raman spectroscopy confirmed the crystalline nature of the hybrid structures. Electron emission studies were carried out using a diode-type field emission setup. The enhancement factor was found to be ~3,500 for bare MWCNTs, ~4,070 to ~5,000 for hybrid structures and ~6,500 for N-doped MLG-MWCNTs hybrid structures. Modification in the defects structure and enhancement of emission sites are suggested to be responsible for the increase of the field emission characteristics.

  16. Fabrication of Ultrasensitive Field-Effect Transistor DNA Biosensors by a Directional Transfer Technique Based on CVD-Grown Graphene.

    PubMed

    Zheng, Chao; Huang, Le; Zhang, Hong; Sun, Zhongyue; Zhang, Zhiyong; Zhang, Guo-Jun

    2015-08-12

    Most graphene field-effect transistor (G-FET) biosensors are fabricated through a routine process, in which graphene is transferred onto a Si/SiO2 substrate and then devices are subsequently produced by micromanufacture processes. However, such a fabrication approach can introduce contamination onto the graphene surface during the lithographic process, resulting in interference for the subsequent biosensing. In this work, we have developed a novel directional transfer technique to fabricate G-FET biosensors based on chemical-vapor-deposition- (CVD-) grown single-layer graphene (SLG) and applied this biosensor for the sensitive detection of DNA. A FET device with six individual array sensors was first fabricated, and SLG obtained by the CVD-growth method was transferred onto the sensor surface in a directional manner. Afterward, peptide nucleic acid (PNA) was covalently immobilized on the graphene surface, and DNA detection was realized by applying specific target DNA to the PNA-functionalized G-FET biosensor. The developed G-FET biosensor was able to detect target DNA at concentrations as low as 10 fM, which is 1 order of magnitude lower than those reported in a previous work. In addition, the biosensor was capable of distinguishing the complementary DNA from one-base-mismatched DNA and noncomplementary DNA. The directional transfer technique for the fabrication of G-FET biosensors is simple, and the as-constructed G-FET DNA biosensor shows ultrasensitivity and high specificity, indicating its potential application in disease diagnostics as a point-of-care tool. PMID:26203889

  17. Depot de composes inorganiques du Si par plasma CVD sur substrats polymeriques: Caracterisation structurale et fonctionnelle

    NASA Astrophysics Data System (ADS)

    da Silva Sobrinho, Argemiro Soares

    Structural and functional characterization studies of plasma-enhanced chemically vapor deposited (PECVD) silicon compounds (SiO2 and Si3N4, hereafter "SiN") on 13 mum polyethylene terephthalate (PET) substrates have been carried out. Barrier coatings were deposited in a dual-frequency (microwave/radio frequency) pilot-scale PECVD reactor for continuously-moving flexible webs up to 30 cm in width. The volatile silicon compounds used for SiO2 deposition were HMDSO (C6 H18Si2O) and SiH4, while the latter served to deposit SiN. Coating thicknesses, d, in the range 8 nm ≤ d ≤ 200 nm, were measured using a variety of techniques. The "interphase" region between the deposited layers (eg. PECVD SiO2 or SiN) and the PET substrate has been investigated and compared to PVD (electron beam evaporated) SiO2. Composition profiles determined by electron microprobe analysis (EMA), TOF-ERD, and XPS all show an extended interphase region more than 50 nm in width, while that of the PVD SiO2 is narrower. We have also examined ultra-thin (about 10 and 27 nm) SiO2 and SiN PECVD layers on 50 nm spin-coated PET substrates by non-destructive infrared (IR) techniques. The IR spectra also confirm that the thin PECVD deposits comprise an organosilicon phase with Si-CHx bonds. Oxygen transmission (OTR) and water vapor transmission (WVTR) measurements were carried out with MOCON "Oxtran" and "Permatran-W" instruments, respectively. We typically found OTR values of about 0.5 scc/m 2-day and WVTR about 0.3 g/m2-day, for barrier thicknesses exceeding a "critical" value (dc, about 8nm for SiN, and 15nm for SiO2), but the minimum permeation values depend upon the concentration of defect sites in the coating (partly related to substrate microroughness). In order to confirm this correlation, we have developed a technique to characterize the types, origins and number densities of coating defects. We found an excellent correlation between measured OTR values and the number densities and size

  18. Ion composition measurement techniques for space plasmas

    NASA Technical Reports Server (NTRS)

    Gloeckler, George

    1990-01-01

    Plasmas found in space range from the solar wind with a typical temperature of 100,000-1,000,000 K, about 400 km/s bulk flow speed, and high ionization (charge states) of ions, to the hot, slowly moving plasmas in the outer magnetospheres of the giant planets, to the cold, corotating plasmas in inner magnetospheres. Space plasma instruments and techniques are reviewed, with an emphasis on hot plasma composition measurements. Starting with Faraday Cup detectors some 30 years ago, plasma instruments have evolved to the present time-of-flight systems with excellent mass resolution and three-dimensional viewing capabilities.

  19. Analysis of the Response of CVD Diamond Detectors for UV and sX-Ray Plasma Diagnostics Installed at JET

    NASA Astrophysics Data System (ADS)

    Caiffi, B.; Coffey, I.; Pillon, M.; Osipenko, M.; Prestopino, G.; Ripani, M.; Taiuti, M.; Verona, C.; Verona-Rinati, G.

    Diamond detectors are very promising candidates for plasma diagnostics in a harsh environment. In fact, they have several proprieties which make them suitable for magnetic fusion devices: radiation hardness, high thermal conductivity, high resistivity, high carrier mobility and a large bandgap (5.5 eV). The latter makes them insensitive to visible radiation and allows low noise measurements without any cooling. In 2008 two CVD (Chemical Vapour Deposition) single crystal diamond (SCD) detectors were installed at the JET tokamak as extreme UV and soft X-Ray diagnostics [1]. In this work the neutron background in these detectors was measured shielding the UV and soft X-Ray radiation by closing a local vacuum valve. The UV detector was found to be insensitive to the neutron flux, while the soft X Ray detector signal exhibited spikes during the highest neutron rate pulse (neutron rate 1016n/s, which corresponds to a flux of φn ˜105n/cm2s in the detector location). These spikes were found to be due to the (n,p) reaction within the plastic filter in front of the soft X-Ray detector. The UV SCD was also used to perform time of flight (ToF) measurements in laser ablation experiments. ToFs were found to be an order of magnitude higher than expected if only the drift velocity is considered. This discrepancy could be due to a delay between the arrival time of the impurities in the plasma and their emission in an energy range which SCD is sensitive to (Eph >5.5 eV). The delay is found to be comparable with the expected ionization times for edge plasma conditions.

  20. Plasma-enhanced CVD preparation of isotopes of group IV and VI elements

    NASA Astrophysics Data System (ADS)

    Sennikov, P. G.; Kornev, R. A.

    2016-03-01

    The plasma-chemical reduction was studied experimentally of molybdenum, sulfur and germanium fluorides with different isotopic composition by hydrogen in plasmas sustained by inductively coupled (IC) and capacitively-coupled (CC) RF discharges. The emission spectra of plasmas recorded under different experimental conditions are discussed. Reaction mechanisms are proposed. In the case of 98MoF6 reduction in CCP, the combined radical-atomic mechanism including intermediate MoF3 resulting in bulk and powder 98Mo formation was established. In the emission spectrum of the 32SF6 + H2 system in ICP at 0.2 Torr, only lines assigned to SiF2, SiF and F2 * originating from the decomposition of 32SF6 and a fast reaction of its products with the reactor's quartz walls were observed. Due to this etching process, the yield of 32S was moderate. Increasing the pressure in the reactor above 1 Torr resulted in an increase of the 32S yield. The mechanism of 72GeF4 reduction depends on the pressure and plasma type. At 0.25 Torr in ICP, a 72Ge deposit was formed via the 72GeF radical; however, at 3.5 Torr in CCP, the mechanism changed to a molecular one. Results of the study of the structure and the isotopic and chemical purity of isotope samples obtained are briefly presented.

  1. Plasma-enhanced CVD silicon nitride antireflection coatings for solar cells

    NASA Technical Reports Server (NTRS)

    Johnson, C. C.; Wydeven, T.; Donohoe, K.

    1983-01-01

    Multilayer plasma-enhanced chemical vapor deposition (PECVD) silicon nitride antireflection coatings were deposited on space quality silicon solar cells. Preliminary experiments indicated that multilayer coatings decreased the total reflectance of polished silicon from 35 percent to less than 3 percent over the spectral range 0.4-1.0 micron. The solar cell energy conversion efficiency was increased from an average of 8.84 percent to an average of 12.63 percent.

  2. Dendrimer-templated Fe nanoparticles for the growth of single-wall carbon nanotubes by plasma-enhanced CVD.

    PubMed

    Amama, Placidus B; Maschmann, Matthew R; Fisher, Timothy S; Sands, Timothy D

    2006-06-01

    A fourth-generation (G4) poly(amidoamine) (PAMAM) dendrimer (G4-NH2) has been used as a template to deliver nearly monodispersed catalyst nanoparticles to SiO2/Si, Ti/Si, sapphire, and porous anodic alumina (PAA) substrates. Fe2O3 nanoparticles obtained after calcination of the immobilized Fe3+/G4-NH2 composite served as catalytic "seeds" for the growth of single-wall carbon nanotubes (SWNTs) by microwave plasma-enhanced CVD (PECVD). To surmount the difficulty associated with SWNT growth via PECVD, reaction conditions that promote the stabilization of Fe nanoparticles, resulting in enhanced SWNT selectivity and quality, have been identified. In particular, in situ annealing of Fe catalyst in an N2 atmosphere was found to improve SWNT selectivity and quality. H2 prereduction at 900 degrees C for 5 min was also found to enhance SWNT selectivity and quality for SiO2/Si supported catalyst, albeit of lower quality for sapphire supported catalyst. The application of positive dc bias voltage (+200 V) during SWNT growth was shown to be very effective in removing amorphous carbon impurities while enhancing graphitization, SWNT selectivity, and vertical alignment. The results of this study should promote the use of exposed Fe nanoparticles supported on different substrates for the growth of high-quality SWNTs by PECVD. PMID:16771309

  3. Raman Spectroscopy of a-C:H Films Deposited Using Ar + H2 + C7H8 Plasma CVD

    NASA Astrophysics Data System (ADS)

    Dong, Xiao; Koga, Kazunori; Yamashita, Daisuke; Seo, Hyunwoong; Itagaki, Naho; Shiratani, Masaharu; Setsuhara, Yuichi; Sekine, Makoto; Hori, Masaru

    2015-09-01

    We investigated the effects of ion energy on Raman spectra of a-C:H films prepared by Ar + H2 + C7H8 plasma CVD. Raman spectra were measured with a laser Raman spectrometer (JASCO NRS-3100). Both the D-peak position and G-peak position shift toward higher wavenumbers as ion energy increases. The intensity ratio of the D-peak and G-peak, ID/IG increases with increasing the ion energy, indicating that the amount of ring-like sp2 clusters increases. The H content in a-C:H derived from photoluminescence (PL) background decreases with increasing the ion energy. The full width at half maximum of the G-peak, FWHMG related to the C-C sp3 content and H content increases with increasing the ion energy to 100 eV, whereas it decreases with increasing further the ion energy to 105 eV. The variation of FWHMG is consistent with that of mass density. There results indicate that the structure of a-C:H films transforms from polymer-like carbon to diamond-like one with increasing the ion energy above the threshold value of ~ 100 eV.

  4. Plasma-assisted CVD of fluorinated, hydrogenated amorphous silicon. Final technical report, September 15, 1979-September 15, 1980

    SciTech Connect

    Coleman, J. H.; Hammes, J. P.; Wiesmann, H. J.

    1980-01-01

    During the past year, approximately 300 large-area (400 cm/sup 2/) PIN hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated and tested. a-Si:H PIN cells which were plasma deposited at 200/sup 0/ to 350/sup 0/ were found to have high internal currents (13mA/cm/sup 2/), whereas those which were deposited by CVD at 500/sup 0/ to 650/sup 0/C had low internal currents. When corrected for optical losses in the top electrode, the internal quantum efficiency vs wavelength for the PIN cells indicated a peak value above 80% at about 525nm, which decreased monotonically to zero at about 725 nm. When the published values of RCA and EXXON were corrected similarly for optical loss, nearly identical values of internal quantum efficiencies were found. Calculations based on a model proposed by Cody et al of EXXON indicated that the depletion width was less than 0.4 microns for all PIN cells, thereby limiting junction efficiency in the red portion of the solar spectrum since the 1/e photon range exceeds this value. A novel inverted NIP cell was tested and found to have its maximum quantum response shifted to 625 nm. Also, an amorphous boron (a-B) layer deposited on a-Si:H to form a PIN heterojunction improved blue response and Voc. A combination of the red-responsive cells and the a-B heterojunction cells could raise efficiency to 8%.

  5. Tuning Effect of N2 on Atmospheric-Pressure Cold Plasma CVD of TiO2 Photocatalytic Films

    NASA Astrophysics Data System (ADS)

    Di, Lanbo; Li, Xiaosong; Zhao, Tianliang; Chang, Dalei; Liu, Qianqian; Zhu, Aimin

    2013-01-01

    To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TiCl4 should be greater than the stoichiometric ratio (pO2/pTiCl4 > 1). However, this may lead to the formation of powder instead of film on the substrate when using volume dielectric barrier discharge (volume-DBD) at atmospheric pressure. In this study, by adding N2 into the working gas Ar, TiO2 photocatalytic films were successfully fabricated in the presence of excess O2 (pO2/pTiCl4 = 2.6) by using a wire-to-plate atmospheric-pressure volume-DBD. The tuning effect of N2 on the deposition of TiO2 film was studied in detail. The results showed that by increasing the N2 content, the deposition rate and particle size of the TiO2 film were reduced, and its photocatalytic activity was enhanced. The tuning mechanism of N2 is further discussed.

  6. Characteristics of indium oxide plasma filters deposited by atmospheric pressure CVD

    SciTech Connect

    Langlois, E.; Murthy, S.D.; Bhat, I.; Gutmann, R.; Brown, E.; Dziendziel, R.; Freeman, M.; Choudhury, N.

    1995-07-01

    Thin films of undoped and tin-doped In{sub 2}O{sub 3} are being investigated for use as plasma filters in spectral control applications for thermal photovoltaic cells. These films are required to exhibit high reflectance at wavelengths longer than the plasma wavelength {lambda}{sub p}, high transmittance at wavelengths shorter than {lambda}{sub p} and low absorption throughout the spectrum. Both types of films were grown via atmospheric pressure chemical vapor deposition (APCVD) on Si (100) and fused silica substrates using trimethylindium (TMI), tetraethyltin (TET), and oxygen as the precursors. Fourier Transform InfraRed (FTIR) spectroscopy was used to measure the filter transmittance and reflectance between 1.8--20 {micro}m. Nominal conditions used during the growth of undoped In{sub 2}O{sub 3} were a substrate temperature of 450 C and partial pressures of 1.4 {times} 10{sup {minus}4} atm. and 1 {times} 10{sup {minus}3} atm. for TMI and O{sub 2} respectively. The O{sub 2}/TMI partial pressure ratio and substrate temperature were systematically varied to control the filter characteristics. The plasma wavelength {lambda}{sub p} was found to be a sensitive function of these parameters. Post-growth annealing of the films was done in inert as well as air ambient at elevated temperatures, but was found to have no beneficial effect. Tin-doped In{sub 2}O{sub 3} was grown under similar conditions as above, with a typical TET partial pressure of 4 {times} 10{sup {minus}6} atm. Here also, the material properties and consequently the optical response were found to be strongly dependent on growth conditions such as O{sub 2} and TET partial pressures. Both undoped and tin-doped In{sub 2}O{sub 3} grown on fused silica exhibited enhanced transmittance due to the close matching of refractive indices of In{sub 2}O{sub 3} and silica. X-ray diffractometer measurements indicated that all these films were polycrystalline and highly textured towards the (111) direction. The best

  7. Temperature dependent growth of GaN nanowires using CVD technique

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Kumar, Vikram; Singh, R.

    2016-05-01

    Growth of GaN nanowires have been carried out on sapphire substrates with Au as a catalyst using chemical vapour deposition technique. GaN nanowires growth have been studied with the experimental parameter as growth temperature. Diameter of grown GaN nanowires are in the range of 50 nm to 100 nm while the nanowire length depends on growth temperature. Morphology of the GaN nanowires have been studied by scanning electron microscopy. Crystalline nature has been observed by XRD patterns. Optical properties of grown GaN nanowires have been investigated by photoluminescence spectra.

  8. The Formation of Nanocrystalline Diamond Coating on WC Deposited by Microwave Assisted Plasma CVD

    NASA Astrophysics Data System (ADS)

    Toff, M. R. M.; Hamzah, E.; Purniawan, A.

    2010-03-01

    Diamond is one form of carbon structure. The extreme hardness and high chemical resistant of diamond coatings determined that many works on this area relate to coated materials for tribological applications in biomedicine, as mechanical seals or cutting tools for hard machining operations. In the work, nanocrystalline diamond (NCD) coated tungsten carbide (WC) have been deposited by microwave assisted plasma chemical vapor deposition (MAPCVD) from CH4/H2 mixtures. Morphology of NCD was investigated by using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The quality of NCD is defined as ratio between diamond and non diamond and also full width at half maximum (FWHM) was determined using Raman spectra. The result found that the NCD structure can be deposited on WC surface using CH4/H2 gas mixture with grain size ˜20 nm to 100 nm. Increase %CH4 concentration due to increase the nucleation of NCD whereas decrease the quality of diamond. Based on Raman spectra, the quality of NCD is in the range ˜98.82-99.01% and 99.56-99.75% for NCD and microcrystalline (MCD), respectively. In addition, FWHM of NCD is high than MCD in the range of 8.664-62.24 cm-1 and 4.24-5.05 cm-1 for NCD and MCD respectively that indicate the crystallineity of NCD is smaller than MCD.

  9. Plasma techniques for reprocessing nuclear wastes

    SciTech Connect

    Siciliano, E.R.; Lucoff, D.M.; Omberg, R.P.; Walter, A.E.

    1993-06-01

    A newly emerging plasma-based system, currently under development for material dissociation and mass separation applications in the area of high-level radioactive waste treatment, may have possible applications as a central processing unit for spent nuclear fuel reprocessing. Because this system has no moving parts and obtains separations by electromagnetic techniques, it offers a distinct advantage over chemically based separation techniques, in that the total waste volume does not increase. The basic concepts underlying the operation of this plasma-based system are discussed, along with the demonstrated and expected capabilities of this system. Possible fuel reprocessing configurations using this plasma-based technology are also mentioned.

  10. Brachiocephalic Vein Stenting and Body-Floss Technique as a Treatment of CVD in Dialysis-Dependent Patient – Case Report and Literature Review

    PubMed Central

    Krycińska, Róża; Trznadel, Agata; Kuchalska, Paulina; Lis, Michał; Dołęga-Kozierowski, Bartosz; Dyś, Krzysztof; Drelichowski, Stanisław; Witkiewicz, Wojciech

    2015-01-01

    Summary Background Given the increasing number of elderly hemodialysis-dependent patients with concomitant chronic diseases the successful creation and maintenance of reliable vascular access become a real challenge. In current literature central vein disease (CVD) is defined as at least 50% narrowing up to total occlusion of central veins of the thorax including superior vena cava (SVC), brachiocephalic (BCV), subclavian (SCV) and internal jugular vein (IJV). The incidence of CVD has been reported to be as high as 23% in the total dialysis population and 41% in those with access related complains. Case Report 61-year-old man has been admitted to the local radiology department with symptoms of the superior vena cava syndrome. The venography revealed occlusion of the right brachiocephalic vein. Due to Tortuosity and lack of stamp of right subclavian vein contributed to the decision to perform recanalization by “body floss” technique. In a further step we have performed PTA of obstructed vein segment using 7×40 mm balloon. Due to the presence of residual stenosis it was decided to implant two self – expanding stents 10×40 mm. After the procedure the patient was discharged in good condition and transferred to dialysis center. Conclusions Main objective was the salvage of a functioning arteriovenous fistula. Performed endovascular intervention is a safe and effective approach to correct CVD for a short term. To ensure long lasting effects the patient will require enhanced follow-up and inevitable reinterventions. For that matter, prevention of CVD remains critical. PMID:26000070

  11. Plasma diagnostic techniques using particle beam probes

    SciTech Connect

    Jennings, W C

    1980-07-01

    A brief overview is given of particle beam probing. The fundamental concepts common to all techniques are discussed as well as the design considerations for choosing a particular diagnostic technique. The capabilities of existing and proposed techniques, and the present status of the techniques in major magnetic confinement geometries is also presented. Techniques which involve the injection of a beam of neutral particles into the plasma are then considered. The techniques of beam attenuation, beam scattering, and active charge exchange using a beam of light particles such as hydrogen or helium are first presented. Optical measurements of the Zeeman splitting of the radiation from a neutral lithium beam is then discussed, including a new proposal for significantly improving this technique through the addition of a dye laser. Two techniques involving the injection of heavy neutral particles are then presented, and the section concludes with two proposed techniques for measuring the properties of the alpha particles produced from actual fusion reactions. The diagnostic techniques which are based upon the injection of a beam of charged particles into the plasma are next described. The advantages and limitations of these techniques in comparison with the neutral techniques are discussed, followed by a description of specific techniques.

  12. Comparative Study of Solid-Phase Crystallization of Amorphous Silicon Deposited by Hot-Wire CVD, Plasma-Enhanced CVD, and Electron-Beam Evaporation

    SciTech Connect

    Stradins, P.; Kunz, O.; Young, D. L.; Yan, Y.; Jones, K. M.; Xu, Y.; Reedy, R. C.; Branz, H. M.; Aberle, A. G.; Wang, Q.

    2007-01-01

    Solid-phase crystallization (SPC) rates are compared in amorphous silicon films prepared by three different methods: hot-wire chemical vapor deposition (HWCVD), plasma-enhanced chemical vapor deposition (PECVD), and electron-beam physical vapor deposition (e-beam). Random SPC proceeds approximately 5 and 13 times slower in PECVD and e-beam films, respectively, as compared to HWCVD films. Doping accelerates random SPC in e-beam films but has little effect on the SPC rate of HWCVD films. In contrast, the crystalline growth front in solid-phase epitaxy experiments propagates at similar speed in HWCVD, PECVD, and e-beam amorphous Si films. This strongly suggests that the observed large differences in random SPC rates originate from different nucleation rates in these materials while the grain growth rates are relatively similar. The larger grain sizes observed for films that exhibit slower random SPC support this suggestion.

  13. Plasma mass filtering techniques: applications and requirements

    NASA Astrophysics Data System (ADS)

    Gueroult, Renaud; Fisch, Nathaniel J.

    2013-10-01

    Plasma mass filters differ from conventional chemical filtering techniques in that elements are dissociated, and can therefore be processed without regard to chemical form. In addition, plasma filters can be in principle operated at larger velocities compared to their gaseous and/or liquid counterparts, so that larger throughputs are possible. On the other hand, one has to pay the price of ionization, which sets a lower limit for the processing cost. Plasma mass filtering techniques are consequently foreseen as a promising solution for separation processes which are simultaneously chemically challenging and of high added value. Such separation processes can be, for example, found within the context of nuclear waste remediation, or nuclear spent fuel reprocessing. However, although plasma separation techniques appear globally attractive for these distinct needs, the plasma parameters required to fulfill a particular separation process are expected to depend strongly on the process's attributes (volume, composition, mass difference), which may vary significantly. Such operating parameters' variations are shown to be well accommodated by a particular configuration, called the Magnetic Centrifugal Mass Filter. Work supported by US DOE under contract Nos DE-AC02-09CH11466 and DE-FG02-06ER54851.

  14. Plasma filtering techniques for nuclear waste remediation

    DOE PAGESBeta

    Gueroult, Renaud; Hobbs, David T.; Fisch, Nathaniel J.

    2015-04-24

    The economical viability of nuclear waste cleanup e orts could, in some cases, be put at risk due to the difficulties faced in handling unknown and complex feedstocks. Plasma filtering, which operates on dissociated elements, offers advantages over chemical techniques for the processing of such wastes. In this context, the economic feasibility of plasma mass filtering for nuclear waste pretreatment before ultimate disposal is analyzed. Results indicate similar costs for chemical and plasma solid-waste pretreatment per unit mass of waste, but suggest significant savings potential as a result of a superior waste mass minimization. This performance improvement is observed overmore » a large range of waste chemical compositions, representative of legacy waste's heterogeneity. Although smaller, additional savings arise from the absence of a secondary liquid waste stream, as typically produced by chemical techniques.« less

  15. Plasma filtering techniques for nuclear waste remediation

    SciTech Connect

    Gueroult, Renaud; Hobbs, David T.; Fisch, Nathaniel J.

    2015-04-24

    The economical viability of nuclear waste cleanup e orts could, in some cases, be put at risk due to the difficulties faced in handling unknown and complex feedstocks. Plasma filtering, which operates on dissociated elements, offers advantages over chemical techniques for the processing of such wastes. In this context, the economic feasibility of plasma mass filtering for nuclear waste pretreatment before ultimate disposal is analyzed. Results indicate similar costs for chemical and plasma solid-waste pretreatment per unit mass of waste, but suggest significant savings potential as a result of a superior waste mass minimization. This performance improvement is observed over a large range of waste chemical compositions, representative of legacy waste's heterogeneity. Although smaller, additional savings arise from the absence of a secondary liquid waste stream, as typically produced by chemical techniques.

  16. Visualization techniques in plasma numerical simulations

    NASA Astrophysics Data System (ADS)

    Kulhánek, P.; Smetana, M.

    2004-03-01

    Numerical simulations of plasma processes usually yield a huge amount of raw numerical data. Information about electric and magnetic fields and particle positions and velocities can be typically obtained. There are two major ways of elaborating these data. First of them is called plasma diagnostics. We can calculate average values, variances, correlations of variables, etc. These results may be directly comparable with experiments and serve as the typical quantitative output of plasma simulations. The second possibility is the plasma visualization. The results are qualitative only, but serve as vivid display of phenomena in the plasma followed-up. An experience with visualizing electric and magnetic fields via Line Integral Convolution method is described in the first part of the paper. The LIC method serves for visualization of vector fields in two dimensional section of the three dimensional plasma. The field values can be known only in grid points of three-dimensional grid. The second part of the paper is devoted to the visualization techniques of the charged particle motion. The colour tint can be used for particle’s temperature representation. The motion can be visualized by a trace fading away with the distance from the particle. In this manner the impressive animations of the particle motion can be achieved.

  17. Diagnostics of nonlocal plasmas: advanced techniques

    NASA Astrophysics Data System (ADS)

    Mustafaev, Alexander; Grabovskiy, Artiom; Strakhova, Anastasiya; Soukhomlinov, Vladimir

    2014-10-01

    This talk generalizes our recent results, obtained in different directions of plasma diagnostics. First-method of flat single-sided probe, based on expansion of the electron velocity distribution function (EVDF) in series of Legendre polynomials. It will be demonstrated, that flat probe, oriented under different angles with respect to the discharge axis, allow to determine full EVDF in nonlocal plasmas. It is also shown, that cylindrical probe is unable to determine full EVDF. We propose the solution of this problem by combined using the kinetic Boltzmann equation and experimental probe data. Second-magnetic diagnostics. This method is implemented in knudsen diode with surface ionization of atoms (KDSI) and based on measurements of the magnetic characteristics of the KDSI in presence of transverse magnetic field. Using magnetic diagnostics we can investigate the wide range of plasma processes: from scattering cross-sections of electrons to plasma-surface interactions. Third-noncontact diagnostics method for direct measurements of EVDF in remote plasma objects by combination of the flat single-sided probe technique and magnetic polarization Hanley method.

  18. Bond dissociation mechanism of ethanol during carbon nanotube synthesis via alcohol catalytic CVD technique: Ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Oguri, Tomoya; Shimamura, Kohei; Shibuta, Yasushi; Shimojo, Fuyuki; Yamaguchi, Shu

    2014-03-01

    supergrowth CVD technique) [26]. Recently, several experimental studies have been carried out in an attempt to understand these complicated dissociation processes. For example, Tomie et al. [27] performed in situ mass spectroscopic analysis during CNT synthesis by the ACCVD technique and revealed that ethylene molecules are formed by the dissociation of ethanol, which means that C-O bonds in the ethanol molecules are dissociated during CNT synthesis. Moreover, Xiang et al. [28] employed isotopically labeled ethanol (i.e., 12CH3-13CH2-OH, 13CH3-12CH2-OH, and so forth) to trace the carbon atoms during CNT synthesis and revealed that the carbon further away from the hydroxyl group in the ethanol is preferentially incorporated into the SNWT structure, which was confirmed from the different G band peaks of the Raman spectra. This experimental finding shows that the C-C bonds in ethanol molecules are dissociated during CNT synthesis. Although many experimental studies [29-32] have revealed part of the dissociation process during CNT growth, it is not yet well understood how the initial dissociation of carbon source molecules affects the subsequent formation process of CNTs.In parallel with the many experimental studies, there has been numerous computational works focusing on the formation process of CNTs. However, most of these studies [9-16] did not take the dissociation of carbon source molecules into account and examined the cap formation process starting from isolated carbon atoms. This is mainly due to the fact that a low-impact interatomic potential appropriately describing the dissociation of carbon source molecules has not been established for classical molecular dynamics (MD) simulation. Meanwhile, several classical MD simulations using the ReaxFF potential [33], which describes chemical reactions with a reasonable degree of accuracy but has a high computational cost, have demonstrated the dissociation of hydrocarbons on a nickel cluster [34] and a flat metal surface [35

  19. Next Generation Plasma Impedance Probe Instrumentation Technique

    NASA Astrophysics Data System (ADS)

    Carlson, C. G.; Swenson, C. M.; Fish, C.

    2003-12-01

    Four Utah State University Plasma Impedance Probes (PIP) were part of NASA's Sequential Rocket Study of Descending Layers in the E-Region (E-Winds). The payloads were launched at 11:19 pm, 1:41 am, 2:50 am and 3:07 am on June 30 and July 1, 2003 from Wallops Island, Virginia into the nighttime D and E-regions. The PIP is a suite of instruments for observing relative and absolute electron densities, magnetic field strength, and electron-neutral collision frequency. The suite consists of a Plasma Frequency Probe, a Swept Impedance Probe, a Q probe, an experimental Ion Impedance probe, and a DC Langmuir probe. The first four instrument diagnostics are based on the impedance characteristics of an antenna immersed in plasma. Resonance effects at low frequencies (1-100 kHz) where ion dynamics become important were observed by the Ion Impedance Probe. This data set may lead to the first mid-latitude measurements of ion-neutral collision frequency and full conductivity measurements of the ionosphere. Preliminary analysis of flight data shows a considerable amount of sensitivity in all of the instruments that should allow for absolute electron density measurement in the 1 to 10 per cc range and comparable accuracy in electron neutral collision frequency. This paper presents the instrumentation techniques, calibrations and initial results for this flight.

  20. Functional metal oxide coatings by molecule-based thermal and plasma chemical vapor deposition techniques.

    PubMed

    Mathur, S; Ruegamer, T; Donia, N; Shen, H

    2008-05-01

    Deposition of thin films through vaccum processes plays an important role in industrial processing of decorative and functional coatings. Many metal oxides have been prepared as thin films using different techniques, however obtaining compositionally uniform phases with a control over grain size and distribution remains an enduring challenge. The difficulties are largely related to complex compositions of functional oxide materials, which makes a control over kinetics of nucleation and growth processes rather difficult to control thus resulting in non-uniform material and inhomogeneous grain size distribution. Application of tailor-made molecular precursors in low pressure or plasma-enhanced chemical vapor deposition (CVD) techniques offers a viable solution for overcoming thermodynamic impediments involved in thin film growth. In this paper molecule-based CVD of functional coatings is demonstrated for iron oxide (Fe2O3, Fe3O4), vanadium oxide (V2O5, VO2) and hafnium oxide (HfO2) phases followed by the characterization of their microstructural, compositional and functional properties which support the advantages of chemical design in simplifying deposition processes and optimizing functional behavior. PMID:18572690

  1. Low temperature plasma enhanced CVD epitaxial growth of silicon on GaAs: a new paradigm for III-V/Si integration

    NASA Astrophysics Data System (ADS)

    Cariou, Romain; Chen, Wanghua; Maurice, Jean-Luc; Yu, Jingwen; Patriarche, Gilles; Mauguin, Olivia; Largeau, Ludovic; Decobert, Jean; Roca I Cabarrocas, Pere

    2016-05-01

    The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs.

  2. Low temperature plasma enhanced CVD epitaxial growth of silicon on GaAs: a new paradigm for III-V/Si integration.

    PubMed

    Cariou, Romain; Chen, Wanghua; Maurice, Jean-Luc; Yu, Jingwen; Patriarche, Gilles; Mauguin, Olivia; Largeau, Ludovic; Decobert, Jean; Roca I Cabarrocas, Pere

    2016-01-01

    The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs. PMID:27166163

  3. Low temperature plasma enhanced CVD epitaxial growth of silicon on GaAs: a new paradigm for III-V/Si integration

    PubMed Central

    Cariou, Romain; Chen, Wanghua; Maurice, Jean-Luc; Yu, Jingwen; Patriarche, Gilles; Mauguin, Olivia; Largeau, Ludovic; Decobert, Jean; Roca i Cabarrocas, Pere

    2016-01-01

    The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs. PMID:27166163

  4. Comparative evaluation of CVD diamond technologies

    SciTech Connect

    Anthony, T.R.

    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.

  5. New novel cleaning technique for extending mean time between mechanical cleans in a Genus tungsten CVD reactor

    SciTech Connect

    Lujan, R.D.; Fleming, J.G.; Baird, J.L.; Gentry, M.S.

    1994-12-31

    During the chemical vapor deposition of blanket tungsten from the reduction of tungsten hexafluoride (WF{sub 6}), metallic parts within the reaction chamber accumulate metallic tungsten, tungsten oxyfluorides, and other related tungsten species. The usual method for removal of the chamber deposits is to open the chamber and perform a labor intensive mechanical clean, which involves the use of hydrogen peroxide (H{sub 2}O{sub 2}) and deionized (DI) water, or an in-situ fluorine-base plasma clean. The authors have investigated the use of repetitive in-situ nitrogen trifluoride (NF{sub 3}) plasma cleans during the course of operating a Genuse 8721 tungsten chemical vapor deposition reactor. The Genuse reactor has been retrofitted with self-ratchetting linear slides, which allow the wafer clamps to be extended into the NF{sub 3} plasma. They have extended the mean time between failures (MTBF) due to the use of 10 minute plasma clean every 75--100 wafers. Deposition for this process is 8,000 angstroms per wafer, using 6 deposition sites. The total tungsten deposition for a 0.5 micron tungsten plug is 4 microns, per a 25 wafer lot. Instead of a total removal of the accumulated tungsten from the chamber hardware, a partial etchback of the deposition from the wafer clamps and wafer chucks was performed. With this, sources for particles and backside deposition were eliminated. They see an increase in wafer-to-wafer uniformity, lot-to-lot repeatability, and particle reduction due to the use of frequent plasma clean. Recovery time after a plasma clean is excellent and no detrimental effects from hydrogen fluoride ``poisoning`` were seen.

  6. Hot-Wire CVD Amorphous Si Materials for Solar Cell Application

    SciTech Connect

    Wang, Q.

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films and their application to solar cells fabricated using the hot-wire chemical vapor deposition (HWCVD) or (CAT)-CVD will be reviewed. This review will focus on the comparison to the standard plasma enhance (PE) CVD in the terms of deposition technique, film properties, and solar cell performance. The advantages of using HWCVD for a-Si:H solar cell research as well as the criteria for industry's adaptation of this technique for mass production will be addressed.

  7. Interlayer utilization (including metal borides) for subsequent deposition of NSD films via microwave plasma CVD on 316 and 440C stainless steels

    NASA Astrophysics Data System (ADS)

    Ballinger, Jared

    . Surface boriding was implemented using the novel method of microwave plasma CVD with a mixture of hydrogen and diborane gases. On 440C bearings, dual phase boride layers of Fe2B and FeB were formed which supported adhered nanostructured diamond films. Continuity of the films was not seamless with limited regions remaining uncoated potentially corresponding to delamination of the film as evidenced by the presence of tubular structures presumably composed of sp2 bonded carbon. Surface boriding of 316 stainless steel discs was conducted at various powers and pressures to achieve temperatures ranging from 550-800 °C. The substrate boriding temperature was found to substantially influence the resultant interlayer by altering the metal boride(s) present. The lowest temperatures produced an interlayer where CrB was the single detected phase, higher temperatures yielded the presence of only Fe2B, and a combination of the two phases resulted from an intermediate boriding temperature. Compared with the more common, commercialized boriding methods, this a profound result given the problems posed by the FeB phase in addition to other advantages offered by CVD processes and microwave generated plasmas in general. Indentation testing of the boride layers revealed excellent adhesion strength for all borided interlayers, and above all, no evidence of cracking was observed for a sole Fe2B phase. As with boriding of 440C bearings, subsequent diamond deposition was achieved on these interlayers with substantially improved adhesion strength relative to diamond coated TiN interlayers. Both XRD and Raman spectroscopy confirmed a nanostructured diamond film with interfacial chromium carbides responsible for enhanced adhesion strength. Interlayers consisting solely of Fe2B have displayed an ability to support fully continuous nanostructured diamond films, yet additional study is required for consistent reproduction. This is in good agreement with initial work on pack borided high alloy steels

  8. Enhancing the mechanical properties of single-crystal CVD diamond.

    PubMed

    Liang, Qi; Yan, Chih-Shiue; Meng, Yufei; Lai, Joseph; Krasnicki, Szczesny; Mao, Ho-Kwang; Hemley, Russell J

    2009-09-01

    Approaches for enhancing the strength and toughness of single-crystal diamond produced by chemical vapor deposition (CVD) at high growth rates are described. CVD processes used to grow single-crystal diamond in high density plasmas were modified to incorporate boron and nitrogen. Semi-quantitative studies of mechanical properties were carried out using Vickers indentation techniques. The introduction of boron in single-crystal CVD diamond can significantly enhance the fracture toughness of this material without sacrificing its high hardness (∼78 GPa). Growth conditions were varied to investigate its effect on boron incorporation and optical properties by means of photoluminescence, infrared, and ultraviolet-visible absorption spectroscopy. Boron can be readily incorporated into single-crystal diamond by the methods used, but with nitrogen addition, the incorporation of boron was hindered. The spectroscopic measurements indicate that nitrogen and boron coexist in the diamond structure, which helps explain the origin of the enhanced fracture toughness of this material. Further, low pressure/high temperature annealing can enhance the intrinsic hardness of single-crystal CVD diamond by a factor of two without appreciable loss in fracture toughness. This doping and post-growth treatment of diamond may lead to new technological applications that require enhanced mechanical properties of diamond. PMID:21832321

  9. Self-organized formation of hierarchically-ordered structures in laser-activated plasma CVD of sp3-bonded BN films

    NASA Astrophysics Data System (ADS)

    Komatsu, Shojiro; Shiratani, Masaharu

    2014-01-01

    The hierarchical pattern formation with three stages, that is, (1) film-thickness topography, (2) fractal or concentric-ring pattern, and (3) cone morphology at micron or sub-micrometer order, was found here for the first time in the BN films prepared by plasma CVD assisted with pulsed excimer laser irradiation at 193 nm. The detailed topography consisting of unevenness in the film-thickness was obtained owing to the two-dimensional X-ray diffraction (2D-XRD) mapping method using a collimated X-ray of 0.1 mm in the diameter, where very high sensitivity was realized by selecting the X-ray from the substrate material, that was exponentially attenuated through the absorption from the film material according to Beer’s law. The important roles of the etching reactions in this process were experimentally verified here for the first time due to the 2D-mapping method. The formation mechanism of the hierarchical patterns was discussed.

  10. Photodetectors on the basis of Ge/Si(001) heterostructures grown by the hot-wire CVD technique

    SciTech Connect

    Shengurov, V. G. Chalkov, V. Yu.; Denisov, S. A.; Alyabina, N. A.; Guseinov, D. V.; Trushin, V. N.; Gorshkov, A. P.; Volkova, N. S.; Ivanova, M. M.; Kruglov, A. V.; Filatov, D. O.

    2015-10-15

    The fabrication of photodetectors for the wavelength range of communications λ = 1.3–1.55 µm on the basis of Ge/Si(001) heterostructures with thick (∼0.5 µm) Ge layers grown by the hot-wire technique at reduced growth temperatures (350°C) is reported. The single-crystal Ga layers are distinguished by a low density of threading dislocations (∼10{sup 5} cm{sup –2}). The photodetectors exhibit a rather high quantum efficiency (∼0.05 at λ = 1.5 µm and 300 K) at moderate reverse saturation current densities (∼10{sup –2} A cm{sup –2}). Thus, it is shown that the hot-wire technique offers promise for the formation of integrated photodetectors for the wavelength range of communications, especially in the case of limitations on the conditions of heat treatments.

  11. Low-temperature-deposited insulating films of silicon nitride by reactive sputtering and plasma-enhanced CVD: Comparison of characteristics

    NASA Astrophysics Data System (ADS)

    Sato, Masaru; Takeyama, Mayumi B.; Nakata, Yoshihiro; Kobayashi, Yasushi; Nakamura, Tomoji; Noya, Atsushi

    2016-04-01

    The characteristics of SiN x films deposited by reactive sputtering and plasma-enhanced chemical vapor deposition (PECVD) are examined to obtain high-density films at low deposition temperatures. PECVD SiN x films deposited at 200 °C show low densities of 2.14-2.20 g/cm3 regardless of their composition, while their refractive index varies depending on their composition. PECVD requires the substrate temperature to obtain high-density films, because a possible cause of low-density films is the amount of Si-H bond, rather than that of N-H bond, in the films originating from hydrogen incorporated by the insufficient decomposition of SiH4 molecules at low temperatures. The sputtered SiN x films with high density are obtained at a temperature lower than 200 °C and considered a promising candidate for insulating films at low process temperatures.

  12. Direct synthesis and characterization of optically transparent conformal zinc oxide nanocrystalline thin films by rapid thermal plasma CVD

    PubMed Central

    2011-01-01

    We report a rapid, self-catalyzed, solid precursor-based thermal plasma chemical vapor deposition process for depositing a conformal, nonporous, and optically transparent nanocrystalline ZnO thin film at 130 Torr (0.17 atm). Pure solid zinc is inductively heated and melted, followed by ionization by thermal induction argon/oxygen plasma to produce conformal, nonporous nanocrystalline ZnO films at a growth rate of up to 50 nm/min on amorphous and crystalline substrates including Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), gold, titanium, and polyimide. X-ray diffraction indicates the grains of as-deposited ZnO to be highly textured, with the fastest growth occurring along the c-axis. The individual grains are observed to be faceted by (103) planes which are the slowest growth planes. ZnO nanocrystalline films of nominal thicknesses of 200 nm are deposited at substrate temperatures of 330°C and 160°C on metal/ceramic substrates and polymer substrates, respectively. In addition, 20-nm- and 200-nm-thick films are also deposited on quartz substrates for optical characterization. At optical spectra above 375 nm, the measured optical transmittance of a 200-nm-thick ZnO film is greater than 80%, while that of a 20-nm-thick film is close to 100%. For a 200-nm-thick ZnO film with an average grain size of 100 nm, a four-point probe measurement shows electrical conductivity of up to 910 S/m. Annealing of 200-nm-thick ZnO films in 300 sccm pure argon at temperatures ranging from 750°C to 950°C (at homologous temperatures between 0.46 and 0.54) alters the textures and morphologies of the thin film. Based on scanning electron microscope images, higher annealing temperatures appear to restructure the ZnO nanocrystalline films to form nanorods of ZnO due to a combination of grain boundary diffusion and bulk diffusion. PACS: films and coatings, 81.15.-z; nanocrystalline materials, 81.07.Bc; II-VI semiconductors, 81.05.Dz. PMID:22040295

  13. Effects of annealing in silicon nitride film deposited by inductively coupled plasma CVD on GaN

    NASA Astrophysics Data System (ADS)

    Liu, Xiu-juan; Wang, Ni-li; Zhang, Yan; Li, Xiang-yang

    2014-11-01

    Silicon nitride (SiNx) films on GaN were deposited, using the inductively coupled plasma chemical vapor deposition (ICPCVD) method with different radio-frequency chuck power (RF power). After deposition, all the films were annealed at 750° in N2, and some pins and bubbles were observed on the surface of some films, but this phenomenon was not observed on the films which were deposited with RF power=0W, as well as films deposited by a two-step-deposition method, which was consisted of setting RF power=0W at the beginning, and setting RF power=2W after that. To study the mechanism of origin of these pins and bubbles, Atomic force microscopy(AFM) was performed to study surface morphology and measure the height of the pins and bubbles, it was found that the height of bubbles was about 300nm, and the depth of pins was about 300nm, which were almost the same as the film thickness. It was showed that the pins and bubbles were originated from gas escaping from the inner films after high-temperature annealing. X-ray photoelectron spectra(XPS) was used to characterize the chemical composition of the films before and after annealing, independently. It was found that, on GaN-SiNx interface and SiNx film surface, the N element content decreased a lot after annealing, but N content remained almost the same in those films with RF power=0W. which indicated that reducing of N content was closely related with those pins and bubbles. RF power increased the plasma energy and caused GaN surface damage. The ion bombardment broke some N-Si bonds and N-Ga bonds, as a result some N reactants didn't perform as Si-N bond, but performed in other bonds such as N-H bonds or N-N bonds, and a high-temperature annealing process would cause NH3 or N2 escape from the film. The pins were voids which resulted from the film broken by the gas, and the bubbles came from bulge resulted from gas escape.

  14. Effect of plasma CVD operating temperature on nanomechanical properties of TiC nanostructured coating investigated by atomic force microscopy

    SciTech Connect

    Shanaghi, Ali; Rouhaghdam, Ali Reza Sabour; Ahangarani, Shahrokh; Chu, Paul K.

    2012-09-15

    Highlights: ► The TiC{sub x} nanostructure coatings have been deposited by PACVD method. ► Dominant mechanism of growth structure at 490 °C is island-layer type. ► TiC{sub x} nanostructure coating applied at 490 °C, exhibits lowest friction coefficient. ► Young's moduli are 289.9, 400 and 187.6 GPa for 470, 490 and 510 °C, respectively. ► This higher elastic modulus and higher hardness of nanocoating obtain at 490 °C. -- Abstract: The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H{sub 11} hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperatures are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.

  15. Comparative analyses of plasma probe diagnostics techniques

    SciTech Connect

    Godyak, V. A.; Alexandrovich, B. M.

    2015-12-21

    The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.

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

    SciTech Connect

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

    2011-10-04

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

  17. Synthesis of beta-SiC/SiO2 core-sheath nanowires by CVD technique using Ni as catalyst.

    PubMed

    Panda, S K; Sengupta, J; Jacob, C

    2010-05-01

    Cubic silicon carbide (beta-SiC)/SiO2 nanowires with uniform and knotted-core structures have been synthesized on nickel-coated Si(111) substrates at 1150 degrees C by using hexamethyldisilane (HMDS) as the source material in a hot wall atmospheric pressure chemical vapor deposition (APCVD) system. The nanowires consist of a single crystalline beta-SiC core wrapped with an amorphous SiO2 shell. The as-prepared SiC nanowires and the deposited Ni films were characterized by field emission scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, infrared spectroscopy and atomic force microscopy. The results show that the nanowires are random in direction and have diameter ranges from 25 nm to 70 nm. The core of the nanowires has a cubic zinc blend structure and a high density of planar defects is often found. The twin plane defects are suspected to be the main reason for the formation of the knotted-core SiC nanowires. A possible growth mechanism based on vapor-liquid-solid (VLS) by base growth technique is proposed. PMID:20358897

  18. Plasma filtering techniques for nuclear waste remediation.

    PubMed

    Gueroult, Renaud; Hobbs, David T; Fisch, Nathaniel J

    2015-10-30

    Nuclear waste cleanup is challenged by the handling of feed stocks that are both unknown and complex. Plasma filtering, operating on dissociated elements, offers advantages over chemical methods in processing such wastes. The costs incurred by plasma mass filtering for nuclear waste pretreatment, before ultimate disposal, are similar to those for chemical pretreatment. However, significant savings might be achieved in minimizing the waste mass. This advantage may be realized over a large range of chemical waste compositions, thereby addressing the heterogeneity of legacy nuclear waste. PMID:25956646

  19. Plasma filtering techniques for nuclear waste remediation

    DOE PAGESBeta

    Gueroult, Renaud; Hobbs, David T.; Fisch, Nathaniel J.

    2015-04-24

    Nuclear waste cleanup is challenged by the handling of feed stocks that are both unknown and complex. Plasma filtering, operating on dissociated elements, offers advantages over chemical methods in processing such wastes. The costs incurred by plasma mass filtering for nuclear waste pretreatment, before ultimate disposal, are similar to those for chemical pretreatment. However, significant savings might be achieved in minimizing the waste mass. As a result, this advantage may be realized over a large range of chemical waste compositions, thereby addressing the heterogeneity of legacy nuclear waste.

  20. Effect of incorporation of deuterium on vacancy-type defects of a-C:H films prepared by plasma CVD

    NASA Astrophysics Data System (ADS)

    Ozeki, K.; Sekiba, D.; Uedono, A.; Hirakuri, K. K.; Masuzawa, T.

    2015-03-01

    Amorphous deuterated carbon (a-C:D) films were prepared using plasma-enhanced chemical vapor deposition (PECVD) from CH4/CD4 and CH4/D2 source gases. For CH4/CD4, the gas flow ratio of CD4/(CD4 + CH4) was varied from 0 to 100%. For CH4/D2, the additional partial gas pressure of D2 was increased from 1 to 7 Pa as the flow rate increased, and the partial gas pressure and the flow rate of CH4 were maintained at 10 Pa and 10 sccm, respectively. The concentrations of hydrogen (H) and deuterium (D) relative to carbon (C) in the films and the film densities were determined by elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). Positron annihilation spectroscopy (PAS) was performed to measure the vacancy-type defect of the film. The S value obtained from PAS measurement correlates to the vacancy-type defect in the film. The film hardness was also measured using a nanoindenter. For CH4/CD4, the D concentration in the film increased when the CD4/(CH4 + CD4) gas ratio increased, whereas the concentration of H decreased. For CH4/D2, the D concentration in the film increased with increasing D2 partial pressure, whereas the concentration of H decreased. From the PAS results, the S value increased with increasing CD4/(CH4 + CD4) gas ratio for CH4/CD4, whereas the S value did not change with any D2 partial pressure for CH4/D2. The hardness and the mass density of the films decreased when the CD4/(CH4 + CD4) gas ratio increased for CH4/CD4, whereas the hardness and the density did not change with any D2 partial pressure for CH4/D2. A correlation among the S value, the film hardness and the film density was observed, and the S value, the film hardness and the film density did not correlate to the D concentration in the film. These findings suggest that information about the vacancy-type defect of the hydrogenated amorphous carbon films is crucial for evaluation of their mechanical properties and density.

  1. A comparative study of electrical probe techniques for plasma diagnostics

    NASA Technical Reports Server (NTRS)

    Szuszczewicz, E. P.

    1972-01-01

    Techniques for using electrical probes for plasma diagnostics are reviewed. Specific consideration is given to the simple Langmuir probe, the symmetric double probe of Johnson and Malter, the variable-area probe of Fetz and Oeschsner, and a floating probe technique. The advantages and disadvantages of each technique are discussed.

  2. Plasma Sheet Velocity Measurement Techniques for the Pulsed Plasma Thruster SIMP-LEX

    NASA Technical Reports Server (NTRS)

    Nawaz, Anuscheh; Lau, Matthew

    2011-01-01

    The velocity of the first plasma sheet was determined between the electrodes of a pulsed plasma thruster using three measurement techniques: time of flight probe, high speed camera and magnetic field probe. Further, for time of flight probe and magnetic field probe, it was possible to determine the velocity distribution along the electrodes, as the plasma sheet is accelerated. The results from all three techniques are shown, and are compared for one thruster geometry.

  3. Positron plasma control techniques for the production of cold antihydrogen

    SciTech Connect

    Funakoshi, R.; Hayano, R. S.; Amoretti, M.; Macri, M.; Testera, G.; Variola, A.; Bonomi, G.; Bowe, P. D.; Hangst, J. S.; Madsen, N.; Canali, C.; Carraro, C.; Lagomarsino, V.; Manuzio, G.; Cesar, C. L.; Charlton, M.; Joergensen, L. V.; Mitchard, D.; Werf, D. P. van der; Doser, M.

    2007-07-15

    An observation of a clear dependence of antihydrogen production on positron plasma shapes is reported. For this purpose a plasma control method has been developed combining the plasma rotating-wall technique with a mode diagnostic system. With the help of real-time and nondestructive observations, the rotating-wall parameters have been optimized. The positron plasma can be manipulated into a wide range of shapes (aspect ratio 6.5{<=}{alpha} < or approx. 80) and densities (1.5x10{sup 8}{<=}n < or approx. 7x10{sup 9} cm{sup -3}) within a short duration (25 s) compatible with the ATHENA antihydrogen production cycle.

  4. Plasma Technology as a New Preservation Technique

    NASA Astrophysics Data System (ADS)

    Rincón, R.; Calzada, M. D.

    The preliminary results of using the surface wave discharge at the atmospheric pressure on groups of lentils and sherry Fino wine samples are presented. In this research, the capability of active species and UV radiation from the plasma, has been assessed on preservation of food. Besides, the generation and emission of both excited molecules in a metastable state N2}(B3Π {g-> A3}Σ u{+) and the de-excitation of species NO(A2}Σ {+) producing UV radiation have been also studied.

  5. The surface modification of clay particles by RF plasma technique

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Keol

    In this study, the surface coatings of ball clay, organoclay and exfoliated clay prepared by sol-gel process were done by RF plasma polymerization to improve the surface activity of the clay filler. Characterization of the above plasma-treated clays has been carried out by various techniques. The effects of plasma-treated clays as substitute of carbon black in styrene-butadiene rubber (SBR) and ethylene-propylene-diene monomer (EPDM) on the curing and mechanical properties were investigated. After plasma treatment, the tensile properties of organo and exfoliated clay were not unsatisfactory to that of carbon black filler system. Moreover, only 10 phr filler loading of plasma-treated organoclay in EPDM vulcanizates showed better results than 40 phr filler loading of carbon black in EPDM vulcanizates. The main objective of this study was to verify the applicability of the plasma technique for modifying clay surfaces for their use in the tire manufacturing industry. Another purpose was to reveal the advantage of the plasma technique used to obtain modified-clay and improved properties that those materials can display.

  6. Diagnostic techniques in thermal plasma processing (Part II). Volume 2

    SciTech Connect

    Boulos, M.; Fauchais, P.; Pfender, E.

    1986-02-01

    Techniques for diagnostics for thermal plasmas are discussed. These include both optical techniques and in-flight measurements of particulate matter. In the core of the plasma, collisional excitation of the various chemical species is so strong that the population of the corresponding quantum levels becomes high enough for net emission from the plasma. In that case, the classical methods of emission spectroscopy may be applied. But in the regions where the temperatures are below 4000/sup 0/K (these regions are of primary importance for plasma processing), the emission from the plasma is no longer sufficient for emission spectroscopy. In this situation, the population of excited levels must be increased by the absorption of the light from an external source. Such sources, as for example pulsed tunable dye lasers, are now commercially available. The use of such new devices leads to various techniques such as laser induced fluorescence (LIF) or Coherent Anti Stockes Raman Spectroscopy (CARS) that can be used for analyzing plasmas. Particle velocity measurements can be achieved by photography and laser Doppler anemometry. Particle flux measurements are typically achieved by collecting particles on a substrate. Particle size measurements are based on intensity of scattered light. (WRF)

  7. CVD diamond as an optical material for adverse environments

    NASA Astrophysics Data System (ADS)

    Snail, Keith A.

    A status report is presented on the obstacles and current research related to using CVD diamond as an optical material. Problems discussed include properties of CVD carbon deposits, including structure, thermal conductivity and oxidation resistance, which are relevant to the optical uses of diamond; absorption coefficient measurements on CVD diamond in the visible and IR; and a review of various aspects of the synthesis of CVD diamond, including the growth of transparent and translucent diamond, efforts to grow diamond at low substrate temperatures, and approches to reducing the optical scatter of as grown polycrystalline diamond films and windows. Particular attention is given to techniques for reducing optical scatter which involve modifying materials morphologies during the growth process by controlling nucleation density, renucleaton frequency, and/or the orientation of crystal faces at film surfaces; techniques for postdeposition polishing of the surface of CVD diamond films and windows; and optical applications for CVD diamond.

  8. CVD diamond as an optical material for adverse environments

    NASA Astrophysics Data System (ADS)

    Snail, Keith A.

    1991-01-01

    A status report is presented on the obstacles and current research related to using CVD diamond as an optical material. Problems discussed include properties of CVD carbon deposits, including structure, thermal conductivity and oxidation resistance, which are relevant to the optical uses of diamond; absorption coefficient measurements on CVD diamond in the visible and IR; and a review of various aspects of the synthesis of CVD diamond, including the growth of transparent and translucent diamond, efforts to grow diamond at low substrate temperatures, and approches to reducing the optical scatter of as grown polycrystalline diamond films and windows. Particular attention is given to techniques for reducing optical scatter which involve modifying materials morphologies during the growth process by controlling nucleation density, renucleaton frequency, and/or the orientation of crystal faces at film surfaces; techniques for postdeposition polishing of the surface of CVD diamond films and windows; and optical applications for CVD diamond.

  9. Adaptive Techniques for Plasma and Fluid Simulation

    NASA Astrophysics Data System (ADS)

    Hewett, Dennis

    2000-10-01

    Particle simulation methods enjoy freedom from traditional difficulties in ALE--advection and mesh tangling. Particle methods suffer from interrelated problems of high noise, high CPU requirements, and often inadequate resolution where it is needed most. Recently, new methods (GaPH, JCP 1996) have been developed that aggressively fragment the particle representation to probe for emerging features, and aggressively merge, for economy, if such features fail to materialize. A new particle model, KEYDRO capitalizes on these strengths while fixing known deficiencies in previous attempts. Similarly, in a model called aETHER, "adaptive node" techniques have now been applied to Lorentz gauge Maxwell's equations using analogous concepts to identify and concentrate on emerging features. Most recently, these concepts have been applied to a modified set of EM field equations wherein the Poisson equation has been replaced by the zero-electron-mass momentum equation. A discussion of these concepts will be presented with emphasis on the collisional, quasi-neutral, but fully electromagnetic regimes where they will be applied. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

  10. Polymerization and surface modification by low pressure plasma technique

    NASA Astrophysics Data System (ADS)

    Tsafack, M.-J.; Hochart, F.; Levalois-Grützmacher, J.

    2004-06-01

    A durable water repellent, stain resistant or flame retardant character can be conferred to polyacrylonitrile (PAN) textiles by using the plasma induced graft polymerization technique. The monomers used are perfluoroalkylacrylate, (meth)acrylate phosphates, and phosphonates which are well known to be effective for the waterproofing and the fireproofing of polymeric substrates, respectively.

  11. Enhanced surface functionality via plasma modification and plasma deposition techniques to create more biologically relevant materials

    NASA Astrophysics Data System (ADS)

    Shearer, Jeffrey C.

    Functionalizing nanoparticles and other unusually shaped substrates to create more biologically relevant materials has become central to a wide range of research programs. One of the primary challenges in this field is creating highly functionalized surfaces without modifying the underlying bulk material. Traditional wet chemistry techniques utilize thin film depositions to functionalize nanomaterials with oxygen and nitrogen containing functional groups, such as --OH and --NHx. These functional groups can serve to create surfaces that are amenable to cell adhesion or can act as reactive groups for further attachment of larger structures, such as macromolecules or antiviral agents. Additional layers, such as SiO2, are often added between the nanomaterial and the functionalized coating to act as a barrier films, adhesion layers, and to increase overall hydrophilicity. However, some wet chemistry techniques can damage the bulk material during processing. This dissertation examines the use of plasma processing as an alternative method for producing these highly functionalized surfaces on nanoparticles and polymeric scaffolds through the use of plasma modification and plasma enhanced chemical vapor deposition techniques. Specifically, this dissertation will focus on (1) plasma deposition of SiO2 barrier films on nanoparticle substrates; (2) surface functionalization of amine and alcohol groups through (a) plasma co-polymerization and (b) plasma modification; and (3) the design and construction of plasma hardware to facilitate plasma processing of nanoparticles and polymeric scaffolds. The body of work presented herein first examines the fabrication of composite nanoparticles by plasma processing. SiOxC y and hexylamine films were coated onto TiO2 nanoparticles to demonstrate enhanced water dispersion properties. Continuous wave and pulsed allyl alcohol plasmas were used to produce highly functionalized Fe2 O3 supported nanoparticles. Specifically, film composition was

  12. Designed CVD growth of graphene via process engineering.

    PubMed

    Yan, Kai; Fu, Lei; Peng, Hailin; Liu, Zhongfan

    2013-10-15

    able to further enhance the control to such a segregation technique, especially for the thickness of graphene. By designing a cosegregation process of carbon atoms with other elements, such as nitrogen, doped graphene could be synthesized directly with a tunable doping profile. Copper with negligible carbon solubility provides another platform for process engineering, where both carbon dissolution and segregation steps are negligible in the CVD process. Carbon atoms decomposed from precursors diffuse on the surface and build up the thermodynamically stable honeycomb lattice. As a result, graphene growth on copper is self-limited, and formation of multilayer graphene is generally prohibited. Being able to control this process better, as well as the high quality produced, makes copper-based growth the dominating synthesis procedure in the graphene community. We designed a two-temperature zone system to spatially separate the catalytic decomposition step of carbon precursors and the surface graphitization step for breaking this self-limited growth feature, giving high-quality Bernal stacked bilayer graphene via van der Waals epitaxy. We performed the so-called wrinkle engineering by growing graphene on nanostructured copper foil together with a structure-preserved surface transfer. In such a way, we controlled the wrinkling or folding on graphene and further fabricated graphene nanoribbon arrays by self-masked plasma etching. Moreover, by designing a two-step patching growth process on copper, we succeeded in synthesizing the mosaic graphene, a patchwork of intrinsic and nitrogen-doped graphene connected by single crystalline graphene p-n junctions. By following a general concept of process engineering, our work on the designed CVD growth of graphene and its 2D hybrids provides a unique insight of this research field. It enables the precise growth control of graphene together with the in-depth understanding of CVD growth process, which would further stimulate the pace of

  13. Dynamics of blood plasma by spectropolarimetry and biochemical techniques

    NASA Astrophysics Data System (ADS)

    Voloshynska, Katerina; Ilashchuka, Tetjana; Prydij, Olexander; Gruia, Maria

    2014-08-01

    The aim of the study was to establish objective parameters of the field of laser and incoherent radiation of different spectral ranges (UV, visible, IR) as a non-invasive optical method of interaction with different samples of biological tissues and fluids of patients to determine the dynamics of metabolic syndrome and choosing the best personal treatment. As diagnostic methods have been used ultraviolet spectrometry samples of blood plasma in the liquid state, infrared spectroscopy middle range (2,5 - 25 microns) dry residue of plasma polarization and laser diagnostic technique of thin histological sections of biological tissues.

  14. Nutrition and CVD risk

    Technology Transfer Automated Retrieval System (TEKTRAN)

    There is a wide range of dietary approaches purported to decrease the risk of developing cardiovascular disease (CVD). Some were first identified early in the 20th century whereas others have been recognized more recently. Some have stood the test of time and others have not. None are without contro...

  15. Solution based CVD of main group materials.

    PubMed

    Knapp, Caroline E; Carmalt, Claire J

    2016-02-21

    This critical review focuses on the solution based chemical vapour deposition (CVD) of main group materials with particular emphasis on their current and potential applications. Deposition of thin films of main group materials, such as metal oxides, sulfides and arsenides, have been researched owing to the array of applications which utilise them including solar cells, transparent conducting oxides (TCOs) and window coatings. Solution based CVD processes, such as aerosol-assisted (AA)CVD have been developed due to their scalability and to overcome the requirement of suitably volatile precursors as the technique relies on the solubility rather than volatility of precursors which vastly extends the range of potentially applicable compounds. An introduction into the applications and precursor requirements of main group materials will be presented first followed by a detailed discussion of their deposition reviewed according to this application. The challenges and prospects for further enabling research in terms of emerging main group materials will be discussed. PMID:26446057

  16. Diagnostic techniques for measuring suprathermal electron dynamics in plasmas (invited)

    SciTech Connect

    Coda, S.

    2008-10-15

    Plasmas, both in the laboratory and in space, are often not in thermodynamic equilibrium, and the plasma electron distribution function is accordingly non-Maxwellian. Suprathermal electron tails can be generated by external drives, such as rf waves and electric fields, or internal ones, such as instabilities and magnetic reconnection. The variety and importance of the phenomena in which suprathermal electrons play a significant role explains an enduring interest in diagnostic techniques to investigate their properties and dynamics. X-ray bremsstrahlung emission has been studied in hot magnetized plasmas for well over two decades, flanked progressively by electron-cyclotron emission in geometries favoring the high-energy end of the distribution function (high-field-side, vertical, oblique emission), by electron-cyclotron absorption, by spectroscopic techniques, and at lower temperatures, by Langmuir probes and electrostatic analyzers. Continuous progress in detector technology and in measurement and analysis techniques, increasingly sophisticated layouts (multichannel and tomographic systems, imaging geometries), and highly controlled suprathermal generation methods (e.g., perturbative rf modulation) have all been brought to bear in recent years on an increasingly detailed, although far from complete, understanding of suprathermal electron dynamics.

  17. Recent Advances in High-Growth Rate Single-Crystal CVD Diamond

    SciTech Connect

    Liang, Q.; Yan, C; Meng, Y; Lai, J; Krasnicki, S; Mao, H; Hemley, R

    2009-01-01

    There have been important advances in microwave plasma chemical vapor deposition (MPCVD) of large single-crystal CVD diamond at high growth rates and applications of this diamond. The types of gas chemistry and growth conditions, including microwave power, pressure, and substrate surface temperatures, have been varied to optimize diamond quality and growth rates. The diamond has been characterized by a variety of spectroscopic and diffraction techniques. We have grown single-crystal CVD diamond over ten carats and above 1 cm in thickness at growth rates of 50-100 {micro}m/h. Colorless and near colorless single crystals up to two carats have been produced by further optimizing the process. The nominal Vickers fracture toughness of this high-growth rate diamond can be tuned to exceed 20 MPa m{sup 1/2} in comparison to 5-10 MPa m{sup 1/2} for conventional natural and CVD diamond. Post-growth high-pressure/high-temperature (HPHT) and low-pressure/high-temperature (LPHT) annealing have been carried out to alter the optical, mechanical, and electronic properties. Most recently, single-crystal CVD diamond has been successfully annealed by LPHT methods without graphitization up to 2200 C and < 300 Torr for periods of time ranging from a fraction of minute to a few hours. Significant changes observed in UV, visible, infrared, and photoluminescence spectra are attributed to changes in various vacancy centers and extended defects.

  18. A technique to reduce plasma armature formation voltage

    SciTech Connect

    Jamison, K.A. ); Littrell, D.M. )

    1991-01-01

    The initiation of a plasma armature by foil vaporization in a railgun is often accompanied by a large, fast, voltage transient appearing on both the breech and muzzle of the gun. For a railgun driven by an inductor/opening switch power supply, this voltage transient becomes a concern during current commutation from the switch to the railgun. To lessen the requirements on the opening switch, techniques must be found to reduce the armature formation voltage. This paper presents the experimental results from railgun firings at AFATL's Electromagnetic Launcher Basic Research Facility (Site A-15, Eglin Air Force Base, Florida) using different shapes of initiation foils. These foils have been designed to vaporize into a plasma armature with reduced transient voltages. A design criteria was developed to ensure that all portions of the foil vaporize at slightly different times.

  19. A technique to reduce plasma armature formation voltage

    NASA Astrophysics Data System (ADS)

    Jamison, Keith A.; Littrell, Donald M.

    1991-01-01

    Experimental results from railgun firings using different shapes of initiation foils are presented. These foils have been designed to vaporize into a plasma armature with reduced transient voltages. A design criteria was developed to ensure that all portions of the foil vaporize at slightly different times. Using this approach, a factor of three reduction in the voltage transient during plasma armature initiation has been observed. The impact of the armature voltage transient is discussed, along with a description of design techniques, test conditions, and experimental findings. To quantify the results, a model of current commutation which includes transient armature voltage data was developed. However, the results of the reduced transient voltage spike do not show shorter commutation time.

  20. CVD diamond layers for electrochemistry

    NASA Astrophysics Data System (ADS)

    Kowalska, M.; Fabisiak, K.; Wrzyszczyński, A.; Banaszak, A.; Szybowicz, M.; Paprocki, K.; Bała, W.; Bylicki, F.

    2014-09-01

    Diamond electrodes of different morphologies and qualities were manufactured by hot filament chemical deposition (HF CVD) techniques by changing the parameters of diamond growth process. The estimation of diamond quality and identification of different carbon phases was performed by Raman spectroscopy measurements. The effect of diamond quality and amorphous carbon phase content on the electrochemical response of an obtained diamond electrode in 0.5 M H2SO4 as supporting electrolyte was investigated by cyclic voltammetry with [Fe(CN)6]4-/3- as a redox probe. The kinetic parameters such as catalytic reaction rate constant k0 and electron transfer coefficient α were determined. The obtained results show that the analytical performance of undoped diamond electrodes can be implemented just by the change of diamond layers quality.

  1. Nano powders, components and coatings by plasma technique

    DOEpatents

    McKechnie, Timothy N.; Antony, Leo V. M.; O'Dell, Scott; Power, Chris; Tabor, Terry

    2009-11-10

    Ultra fine and nanometer powders and a method of producing same are provided, preferably refractory metal and ceramic nanopowders. When certain precursors are injected into the plasma flame in a reactor chamber, the materials are heated, melted and vaporized and the chemical reaction is induced in the vapor phase. The vapor phase is quenched rapidly to solid phase to yield the ultra pure, ultra fine and nano product. With this technique, powders have been made 20 nanometers in size in a system capable of a bulk production rate of more than 10 lbs/hr. The process is particularly applicable to tungsten, molybdenum, rhenium, tungsten carbide, molybdenum carbide and other related materials.

  2. Nano powders, components and coatings by plasma technique

    NASA Technical Reports Server (NTRS)

    McKechnie, Timothy N. (Inventor); Antony, Leo V. M. (Inventor); O'Dell, Scott (Inventor); Power, Chris (Inventor); Tabor, Terry (Inventor)

    2009-01-01

    Ultra fine and nanometer powders and a method of producing same are provided, preferably refractory metal and ceramic nanopowders. When certain precursors are injected into the plasma flame in a reactor chamber, the materials are heated, melted and vaporized and the chemical reaction is induced in the vapor phase. The vapor phase is quenched rapidly to solid phase to yield the ultra pure, ultra fine and nano product. With this technique, powders have been made 20 nanometers in size in a system capable of a bulk production rate of more than 10 lbs/hr. The process is particularly applicable to tungsten, molybdenum, rhenium, tungsten carbide, molybdenum carbide and other related materials.

  3. CVD amorphous silicon solar cells

    SciTech Connect

    Hegedus, S.S.; Baron, B.N.; Rocheleau, R.E.

    1984-05-01

    Development of all-CVD TCO/p-i-n/metal/substrate a-Si devices made by CVD from disilane is reported. The reactor and conditions for depositing device quality CVD a-Si at growth rates up to 10 A/sec are described. Conductivity, optical properties and density of states of CVD i layers are described. Photovoltaic device characteristics of all - CVD and hybrid (CVD/GD) pin and nip devices are compared. Efficiencies up to 4% were achieved. An analysis of collection efficiency indicates a hole ..mu../tau/ of 1 - 4 X 10/sup -9/ cm/sup 2//V. Cell performance is consistent with a series connected double junction model.

  4. Plasma deposition and surface modification techniques for wear resistance

    NASA Technical Reports Server (NTRS)

    Spalvins, T.

    1982-01-01

    The ion-assisted or plasma coating technology is discussed as it applies to the deposition of hard, wear resistant refractory compound films. Of the many sputtering and ion plating modes and configurations the reactive magnetron sputtering and the reactive triode ion plating techniques are the preferred ones to deposit wear resistant coatings for tribological applications. Both of these techniques incorporate additional means to enhance the ionization efficiency and chemical reaction to precision tailor desirable tribological characteristics. Interrelationships between film formation, structure, and ribological properties are strictly controlled by the deposition parameters and the substrate condition. The enhanced ionization contributes to the excellent adherence and coherence, reduced internal stresses and improved structural growth to form dense, cohesive, equiaxed grain structure for improved wear resistance and control.

  5. Homocysteine, B-vitamins and CVD.

    PubMed

    McNulty, Helene; Pentieva, Kristina; Hoey, Leane; Ward, Mary

    2008-05-01

    There is considerable interest in plasma homocysteine (tHcy) as a CVD risk factor. Although the secondary prevention trials published to date have been inconclusive in confirming a benefit of tHcy-lowering treatment with B-vitamins on CVD events generally, such studies are widely recognised to have been insufficiently powered to detect a significant effect for the predicted magnitude of association between tHcy and heart disease risk, and therefore cannot be interpreted as evidence that no relationship exists. In fact, a recent meta-analysis of clinical trials has confirmed that folic acid supplementation reduces the risk of stroke, particularly in individuals without a history of stroke. Evidence supporting a causal relationship between elevated tHcy and heart disease also comes from genetic studies. The most important genetic determinant of tHcy in the general population is the common C677T variant in methylenetetrahydrofolate reductase (MTHFR) that results in higher tHcy. Individuals with the homozygous mutant (TT) genotype have a significantly higher (14-21%) risk of heart disease. Plasma tHcy is very responsive to intervention with the B-vitamins required for its metabolism, in particular folic acid, and to a lesser extent vitamins B12 and B6. Thus, although primarily aimed at reducing neural-tube defects, folic acid fortification may have an important role in the primary prevention of CVD via tHcy lowering. Besides folate, riboflavin is required as a cofactor for MTHFR and enhanced riboflavin status results in a marked lowering in tHcy specifically in individuals with the TT genotype, presumably by neutralising the variant form of the enzyme. About 10% of the UK and Irish populations have the TT genotype. In the present paper the potential role of folate and related B-vitamins in the primary prevention of CVD and the implications for nutrition policy are explored. PMID:18412997

  6. Simplex-in-cell technique for collisionless plasma simulations

    NASA Astrophysics Data System (ADS)

    Kates-Harbeck, Julian; Totorica, Samuel; Zrake, Jonathan; Abel, Tom

    2016-01-01

    We extend the simplex-in-cell (SIC) technique recently introduced in the context of collisionless dark matter fluids [1,2] to the case of collisionless plasmas. The six-dimensional phase space distribution function f (x , v) is represented by an ensemble of three-dimensional manifolds, which we refer to as sheets. The electric potential field is obtained by solving the Poisson equation on a uniform mesh, where the charge density is evaluated by a spatial projection of the phase space sheets. The SIC representation of phase space density facilitates robust, high accuracy numerical evolution of the Vlasov-Poisson system using significantly fewer tracer particles than comparable particle-in-cell (PIC) approaches by reducing the numerical shot-noise associated with the latter. We introduce the SIC formulation and describe its implementation in a new code, which we validate using standard test problems including plasma oscillations, Landau damping, and two stream instabilities in one dimension. Merits of the new scheme are shown to include higher accuracy and faster convergence rates in the number of particles. We finally motivate and outline the efficient application of SIC to higher dimensional problems.

  7. Nuts and CVD.

    PubMed

    Ros, Emilio

    2015-04-01

    Nuts are nutrient-dense foods with complex matrices rich in unsaturated fatty acids and other bioactive compounds, such as l-arginine, fibre, healthful minerals, vitamin E, phytosterols and polyphenols. By virtue of their unique composition, nuts are likely to beneficially affect cardiovascular health. Epidemiological studies have associated nut consumption with a reduced incidence of CHD in both sexes and of diabetes in women, but not in men. Feeding trials have clearly demonstrated that consumption of all kinds of nuts has a cholesterol-lowering effect, even in the context of healthy diets. There is increasing evidence that nut consumption has a beneficial effect on oxidative stress, inflammation and vascular reactivity. Blood pressure, visceral adiposity and the metabolic syndrome also appear to be positively influenced by nut consumption. Contrary to expectations, epidemiological studies and clinical trials suggest that regular nut consumption is not associated with undue weight gain. Recently, the PREvención con DIeta MEDiterránea randomised clinical trial of long-term nutrition intervention in subjects at high cardiovascular risk provided first-class evidence that regular nut consumption is associated with a 50 % reduction in incident diabetes and, more importantly, a 30 % reduction in CVD. Of note, incident stroke was reduced by nearly 50 % in participants allocated to a Mediterranean diet enriched with a daily serving of mixed nuts (15 g walnuts, 7.5 g almonds and 7.5 g hazelnuts). Thus, it is clear that frequent nut consumption has a beneficial effect on CVD risk that is likely to be mediated by salutary effects on intermediate risk factors. PMID:26148914

  8. Picosecond photoconductivity of natural and CVD diamonds

    NASA Astrophysics Data System (ADS)

    Garnov, Serge V.; Pimenov, Sergej M.; Ralchenko, Victor G.; Klimentov, Sergei M.; Konov, Vitali I.; Korotoushenko, K. G.; Obraztsova, E. D.; Plotnikova, S. P.; Sagatelyan, D. M.; Holly, Sandor

    1995-07-01

    Photoexcitation and recombination of nonequilibrium charge carriers in both natural gemstone diamonds and CVD (chemical vapor deposition) polycrystalline diamond films in UV spectrum regions have been investigated. Transient picosecond photoconductivity technique applied permitted to conduct measurements with the time resolution better than 200 picoseconds and to register a charge carrier concentration value as low as 1020 - 1013 cm-3. The dependencies of photocurrent amplitude as a function of incident laser radiation intensity in the range from 103 to 1010 W/cm2 have been obtained. Charge carrier lifetimes had been measured and charge carrier drift mobility were estimated. It is shown that the electronic properties of high quality thick CVD diamond films are comparable to those of the most perfect natural type IIa crystals. Investigation of Raman and luminescence spectra of diamonds have been performed along with scanning electron microscopy studies to characterize bulk and surface structure of tested specimens.

  9. CVD-Enabled Graphene Manufacture and Technology.

    PubMed

    Hofmann, Stephan; Braeuninger-Weimer, Philipp; Weatherup, Robert S

    2015-07-16

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

  10. CVD-Enabled Graphene Manufacture and Technology

    PubMed Central

    2015-01-01

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

  11. Atmospheric pressure plasma-initiated chemical vapor deposition (AP-PiCVD) of poly(diethylallylphosphate) coating: a char-forming protective coating for cellulosic textile.

    PubMed

    Hilt, Florian; Boscher, Nicolas D; Duday, David; Desbenoit, Nicolas; Levalois-Grützmacher, Joëlle; Choquet, Patrick

    2014-01-01

    An innovative atmospheric pressure chemical vapor deposition method toward the deposition of polymeric layers has been developed. This latter involves the use of a nanopulsed plasma discharge to initiate the free-radical polymerization of an allyl monomer containing phosphorus (diethylallylphosphate, DEAP) at atmospheric pressure. The polymeric structure of the film is evidence by mass spectrometry. The method, highly suitable for the treatment of natural biopolymer substrate, has been carried out on cotton textile to perform the deposition of an efficient and conformal protective coating. PMID:25362895

  12. C(1) metabolism and CVD outcomes in older adults.

    PubMed

    McNulty, Helene; Strain, J J; Pentieva, Kristina; Ward, Mary

    2012-05-01

    CVD is the most common cause of death in people over 65 years. This review considers the latest evidence for a potential protective effect of C(1) donors (folate and the metabolically related B-vitamins) in CVD. Such an effect may or may not be mediated via the role of these nutrients in maintaining plasma homocysteine concentrations within a desirable range. Despite predictions from epidemiological studies that lowering plasma homocysteine would reduce cardiovascular risk, several secondary prevention trials in at-risk patients published since 2004 have failed to demonstrate a benefit of homocysteine-lowering therapy with B-vitamins on CVD events generally. All these trials were performed in CVD patients with advanced disease; thus current evidence suggests that intervention with high-dose folic acid is of no benefit in preventing another event, at least in the case of heart disease. The evidence at this time, however, is stronger for stroke, with meta-analyses of randomised trials showing that folic acid reduces the risk of stroke, particularly in people with no history of stroke. Genetic studies provide convincing evidence to support a causal relationship between sub-optimal B-vitamin status and CVD. People homozygous for the common C677T variant in the gene encoding the folate-metabolising enzyme, methylenetetrahydrofolate reductase (MTHFR), typically have a 14-21% higher risk of CVD. Apart from folate, riboflavin is required as a co-factor for MTHFR. New evidence shows that riboflavin intervention results in marked lowering of blood pressure, specifically in patients with the MTHFR 677TT genotype. This novel gene-nutrient interaction may provide insights as to the mechanism that links C(1) metabolism with CVD outcomes. PMID:22152927

  13. Effect of active screen plasma nitriding pretreatment on wear behavior of TiN coating deposited by PACVD technique

    NASA Astrophysics Data System (ADS)

    Raoufi, M.; Mirdamadi, Sh.; Mahboubi, F.; Ahangarani, Sh.; Mahdipoor, M. S.; Elmkhah, H.

    2012-08-01

    Titanium based alloys are used extensively for improving wear properties of different parts due to their high hardness contents. Titanium nitride (TiN) is among these coatings which can be deposited on surface using various techniques such as CVD, PVD and PACVD. Their weak interface with substrate is one major drawback which can increase the total wear in spite of favorite wear behavior of TiN. Disc shaped samples from AISI H13 (DIN 1.2344) steel were prepared in this study. Single TiN coating was deposited on some of them while others have experienced a TiN deposition by active screen plasma nitriding (ASPN). Hardness at the surface and depth of samples was measured through Vickers micro hardness test which revealed 1810 Hv hardness as the maximum values for a dual-layered ASPN-TiN. Pin-on-disc wear test was done in order to study the wear mechanism. In this regard, the wear behavior of samples was investigated against pins from 100Cr6 (Din 1.3505) bearing steel and tungsten carbide-cobalt (WC-Co) steel. It was evidenced that the dual-layer ASPN-TiN coating has shown the least weight loss with the best wearing behavior because of its high hardness values, stable interface and acceptable resistance against peeling during wearing period.

  14. Growth process of hydrogenated amorphous carbon films synthesized by atmospheric pressure plasma enhanced CVD using nitrogen and helium as a dilution gas

    NASA Astrophysics Data System (ADS)

    Mori, Takanori; Sakurai, Takachika; Sato, Taiki; Shirakura, Akira; Suzuki, Tetsuya

    2016-04-01

    Hydrogenated amorphous carbon films with various thicknesses were synthesized by dielectric barrier discharge-based plasma deposition under atmospheric pressure diluted with nitrogen (N2) and helium (He) at various pulse frequencies. The C2H2/N2 film showed cauliflower-like-particles that grew bigger with the increase in film’s thickness. At 5 kHz, the film with a thickness of 2.7 µm and smooth surface was synthesized. On the other hand, the films synthesized from C2H2/He had a smooth surface and was densely packed with domed particles. The domed particles extended with the increase in the film thickness, enabling it to grow successfully to 37 µm with a smooth surface.

  15. Comparative Analysis of Techniques to Purify Plasma Membrane Proteins

    PubMed Central

    Weekes, Michael P.; Antrobus, Robin; Lill, Jennie R.; Duncan, Lidia M.; Hör, Simon; Lehner, Paul J.

    2010-01-01

    The aim of this project was to identify the best method for the enrichment of plasma membrane (PM) proteins for proteomics experiments. Following tryptic digestion and extended liquid chromatography-tandem mass spectrometry acquisitions, data were processed using MaxQuant and Gene Ontology (GO) terms used to determine protein subcellular localization. The following techniques were examined for the total number and percentage purity of PM proteins identified: (a) whole cell lysate (total number, 84–112; percentage purity, 9–13%); (b) crude membrane preparation (104–111; 17–20%); (c) biotinylation of surface proteins with N-hydroxysulfosuccinimydyl-S,S-biotin and streptavidin pulldown (78–115; 27–31%); (d) biotinylation of surface glycoproteins with biocytin hydrazide and streptavidin pulldown (41–54; 59–85%); or (e) biotinylation of surface glycoproteins with amino-oxy-biotin (which labels the sialylated fraction of PM glycoproteins) and streptavidin pulldown (120; 65%). A two- to threefold increase in the overall number of proteins identified was achieved by using stop and go extraction tip (StageTip)-based anion exchange (SAX) fractionation. Combining technique (e) with SAX fractionation increased the number of proteins identified to 281 (54%). Analysis of GO terms describing these proteins identified a large subset of proteins integral to the membrane with no subcellular assignment. These are likely to be of PM location and bring the total PM protein identifications to 364 (68%). This study suggests that selective biotinylation of the cell surface using amino-oxy-biotin in combination with SAX fractionation is a useful method for identification of sialylated PM proteins. PMID:20808639

  16. Synthesis of graphene by cobalt-catalyzed decomposition of methane in plasma-enhanced CVD: Optimization of experimental parameters with Taguchi method

    NASA Astrophysics Data System (ADS)

    Mehedi, H.-A.; Baudrillart, B.; Alloyeau, D.; Mouhoub, O.; Ricolleau, C.; Pham, V. D.; Chacon, C.; Gicquel, A.; Lagoute, J.; Farhat, S.

    2016-08-01

    This article describes the significant roles of process parameters in the deposition of graphene films via cobalt-catalyzed decomposition of methane diluted in hydrogen using plasma-enhanced chemical vapor deposition (PECVD). The influence of growth temperature (700-850 °C), molar concentration of methane (2%-20%), growth time (30-90 s), and microwave power (300-400 W) on graphene thickness and defect density is investigated using Taguchi method which enables reaching the optimal parameter settings by performing reduced number of experiments. Growth temperature is found to be the most influential parameter in minimizing the number of graphene layers, whereas microwave power has the second largest effect on crystalline quality and minor role on thickness of graphene films. The structural properties of PECVD graphene obtained with optimized synthesis conditions are investigated with Raman spectroscopy and corroborated with atomic-scale characterization performed by high-resolution transmission electron microscopy and scanning tunneling microscopy, which reveals formation of continuous film consisting of 2-7 high quality graphene layers.

  17. The iterative Monte Carlo technique for collisionless plasma flow to a surface

    SciTech Connect

    Pitcher, C.S.

    1993-03-01

    A new technique for modelling the boundary plasma of magnetic fusion devices is described. The technique represents a natural extension of existing Monte Carlo codes, which are presently constrained to have the plasma background specified by either measurements or predictions from plasma fluid codes. The new approach, the Iterative Monte Carlo (IMC) technique, self-consistently determines the ambipolar electric field in the plasma by feeding back into the simulation the evolving plasma density using the Boltzmann relation. The IMC technique is applied, for demonstrative purposes, to the problem of collisionless one-dimensional plasma flow to a surface. Such a problem has previously been solved exactly using kinetic approaches in the published literature using two different particle source functions. Good agreement between the IMC results and the exact solutions is obtained.

  18. Schottky barrier solar cells of weakly hydrogenated CVD amorphous silicon

    NASA Astrophysics Data System (ADS)

    Nakashita, T.; Hirose, M.; Osaka, Y.

    1981-01-01

    Electronic properties of CVD a-Si were remarkably improved by hydrogen plasma annealing. As a result, the Schottky-barrier solar cells without an antireflection coating have provided a conversion efficiency of 2.7% at 100 mW/sq cm, and no Staebler-Wronski effect has been observed in the hydrogenated CVD a-Si cell. It is also found that the fill factor is dependent on incident light intensity, because of changes in its series and parallel resistances by light illumination.

  19. Ion beam figuring of CVD silicon carbide mirrors

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

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

  20. Structure and spectroscopic analysis of the graphene monolayer film directly grown on the quartz substrate via the HF-CVD technique

    NASA Astrophysics Data System (ADS)

    Mahmoud, Waleed E.; Al-Hazmi, Farag S.; Al-Ghamdi, A. A.; Shokr, F. S.; Beall, Gary W.; Bronstein, Lyudmila M.

    2016-08-01

    Direct growth of a monolayer graphene film on a quartz substrate by a hot filament chemical vapor deposition technique is reported. The monolayer graphene film prepared was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The optical properties were studied by spectroscopic elliposmetry. The experimental data were fitted by the Forouhi-Bloomer model to estimate the extinction coefficient and the refractive index of the monolayer graphene film. The refractive index spectrum in the visible region was studied based on the harmonic oscillator model. The lattice dielectric constant, real and imaginary dielectric constants and the ratio of the charge carrier number to the effective mass were determined. The surface and volume energy loss parameters were also found and showed that the value of the surface energy loss is greater than the volume energy loss. The determination of these optical constants will open new avenue for novel applications of graphene films in the field of wave plates, light modulators, ultrahigh-frequency signal processing and LCDs.

  1. Arc Plasma Synthesis of Nanostructured Materials: Techniques and Innovations

    SciTech Connect

    Das, A. K.; Bhoraskar, S. V.; Kakati, M.; Karmakar, Soumen

    2008-10-23

    Arc plasma aided synthesis of nanostructured materials has the potential of producing complex nano phase structures in bulk quantities. Successful implementation of this potential capability to industrial scale nano generation needs establishment of a plasma parameter control regime in terms of plasma gas, flow pattern, pressure, local temperature and the plasma fields to obtain the desired nano phase structures. However, there is a need to design innovative in situ experiments for generation of an extensive database and subsequently to correlate plasma parameters to the size, shape and phase of the generated nanostructures. The present paper reviews the various approaches utilized in the field of arc plasma nanosynthesis in general and in the authors' laboratories in particular. Simple plasma diagnostics and monitoring schemes have been used in conjunction with nano materials characterization tools to explore the possibility of controlling the size, shape, yield and phase composition of the arc generated nanostructures through plasma control. Case studies related to synthesis of AlN, Al2O3, TiO2, ZrO2, ZnO), magnetic (e.g. {gamma}-Fe2O3, Fe3O4) and single elemental materials (e.g. carbon nanotubes) are presented.

  2. Spectroscopic Techniques for the Characterisation of Spectrochemical Plasma Sources

    NASA Astrophysics Data System (ADS)

    Jonkers, J.; de Regt, J. M.; van der Sijde, B.; van der Mullen, J. A. M.

    In spectrochemistry, various plasma sources are used for the analysis of samples. The simplest way to characterise these plasma sources is to determine the absolute intensities of several atomic lines of the main plasma gas (argon or helium). From these measurements absolute population densities of excited states can be deduced and, via a so-called Boltzmann plot, the electron temperature Te and density ne. This method works quite well as long as the plasma is relatively close to equilibrium. The reason why spectrochemical plasmas can show strong deviations from equilibrium will be discussed. An other limitation of emission spectroscopy is the lack of accurate transition probabilities for transitions from highly excited states. For argon 15 of these probabilities have been determined with an uncertainty of ±25%.

  3. Modeling for CVD of Solid Oxide Electrolyte

    SciTech Connect

    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

  4. Argan oil improves surrogate markers of CVD in humans.

    PubMed

    Sour, Souad; Belarbi, Meriem; Khaldi, Darine; Benmansour, Nassima; Sari, Nassima; Nani, Abdelhafid; Chemat, Farid; Visioli, Francesco

    2012-06-01

    Limited - though increasing - evidence suggests that argan oil might be endowed with potential healthful properties, mostly in the areas of CVD and prostate cancer. We sought to comprehensively determine the effects of argan oil supplementation on the plasma lipid profile and antioxidant status of a group of healthy Algerian subjects, compared with matched controls. A total of twenty healthy subjects consumed 15 g/d of argan oil - with toasted bread - for breakfast, during 4 weeks (intervention group), whereas twenty matched controls followed their habitual diet, but did not consume argan oil. The study lasted 30 d. At the end of the study, argan oil-supplemented subjects exhibited higher plasma vitamin E concentrations, lower total and LDL-cholesterol, lower TAG and improved plasma and cellular antioxidant profile, when compared with controls. In conclusion, we showed that Algerian argan oil is able to positively modulate some surrogate markers of CVD, through mechanisms which warrant further investigation. PMID:22082585

  5. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  6. Atomistic modelling of CVD synthesis of carbon nanotubes and graphene

    NASA Astrophysics Data System (ADS)

    Elliott, James A.; Shibuta, Yasushi; Amara, Hakim; Bichara, Christophe; Neyts, Erik C.

    2013-07-01

    We discuss the synthesis of carbon nanotubes (CNTs) and graphene by catalytic chemical vapour deposition (CCVD) and plasma-enhanced CVD (PECVD), summarising the state-of-the-art understanding of mechanisms controlling their growth rate, chiral angle, number of layers (walls), diameter, length and quality (defects), before presenting a new model for 2D nucleation of a graphene sheet from amorphous carbon on a nickel surface. Although many groups have modelled this process using a variety of techniques, we ask whether there are any complementary ideas emerging from the different proposed growth mechanisms, and whether different modelling techniques can give the same answers for a given mechanism. Subsequently, by comparing the results of tight-binding, semi-empirical molecular orbital theory and reactive bond order force field calculations, we demonstrate that graphene on crystalline Ni(111) is thermodynamically stable with respect to the corresponding amorphous metal and carbon structures. Finally, we show in principle how a complementary heterogeneous nucleation step may play a key role in the transformation from amorphous carbon to graphene on the metal surface. We conclude that achieving the conditions under which this complementary crystallisation process can occur may be a promising method to gain better control over the growth processes of both graphene from flat metal surfaces and CNTs from catalyst nanoparticles.

  7. Atomistic modelling of CVD synthesis of carbon nanotubes and graphene.

    PubMed

    Elliott, James A; Shibuta, Yasushi; Amara, Hakim; Bichara, Christophe; Neyts, Erik C

    2013-08-01

    We discuss the synthesis of carbon nanotubes (CNTs) and graphene by catalytic chemical vapour deposition (CCVD) and plasma-enhanced CVD (PECVD), summarising the state-of-the-art understanding of mechanisms controlling their growth rate, chiral angle, number of layers (walls), diameter, length and quality (defects), before presenting a new model for 2D nucleation of a graphene sheet from amorphous carbon on a nickel surface. Although many groups have modelled this process using a variety of techniques, we ask whether there are any complementary ideas emerging from the different proposed growth mechanisms, and whether different modelling techniques can give the same answers for a given mechanism. Subsequently, by comparing the results of tight-binding, semi-empirical molecular orbital theory and reactive bond order force field calculations, we demonstrate that graphene on crystalline Ni(111) is thermodynamically stable with respect to the corresponding amorphous metal and carbon structures. Finally, we show in principle how a complementary heterogeneous nucleation step may play a key role in the transformation from amorphous carbon to graphene on the metal surface. We conclude that achieving the conditions under which this complementary crystallisation process can occur may be a promising method to gain better control over the growth processes of both graphene from flat metal surfaces and CNTs from catalyst nanoparticles. PMID:23774798

  8. Synthesis of Carbon Nanotubes Array by CVD

    NASA Technical Reports Server (NTRS)

    Zhu, S.; Su, C.; Cochrane, J. C.; Lehoczky, S. L.; Muntele, I.; Ila, D.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Since the properties of multi-wall carbon nanotubes (MWCNT) are superior in many devices such as electronics and sensors, many efforts have been involved in synthesizing particular structural or dimensional MWCNT. Uniform aligned MWCNT array is one of the prototype structures for devices such as filed emission device and microelectromechanical systems in which a large length to diameter ratio may also be required. Most aligned MWCNT recently synthesized by plasma enhanced chemical vapor deposition (CVD) have cone shaped structures. This presentation will illustrate aligned MWCNT array synthesized on silicon substrates using thermal CVD that could produce MWCNT with uniform diameter. An array of nickel particles was used as catalyst for MWCNT growth. A thin Ti or Au buffer layer was coated on the substrate prior to depositing nickel particles. Because the MWCNT size depends on the catalyst particle size, the nickel particle size annealed at various temperatures was investigated. MWCNT were grown on the substrate in the temperature range of 700 C - 1000 C and the pressure range of 1 to 300 torr. Methane and hydrogen gases with methane content of 1 - 10 % were used for the MWCNT synthesis. Morphology, length and diameter of MWCNT were determined by scanning electron microscopy and Raman spectroscopy. The detailed results of synthesis and characterizations will be discussed in the presentation.

  9. CVD boron on calcium chromate powder

    SciTech Connect

    Coonen, R.M.

    1984-09-01

    This study was an experimental effort to improve the compositional homogeneity of a pyrotechnic mixture of boron and calcium chromate (CaCrO/sub 4/). Boron was deposited onto calcium chromate powders at 350/sup 0/C from a diborane and hydrogen gas mixture at a pressure of 40 torr by Chemical Vapor Deposition (CVD). The B:CaCrO/sub 4/ ratio of the coated powders was analyzed by inductively-coupled plasma spectroscopy and the distribution of the two phases was observed by electron microprobe analysis. The pyrotechnic activity was determined by differential thermal analysis. In addition to varying the composition of the mixture, an attempt was made to vary the boron distribution by coating both sized and unsized CaCrO/sub 4/ powders. Boron was deposited for 2 h onto sized CaCrO/sub 4/ powder, which resulted in a higher weight percentage of boron in comparison to the unsized powder. CVD coated CaCrO/sub 4/ powders began their pyrotechnic activity at an auto ignition temperature that was lower than the auto ignition temperature observed for mechanically blended mixtures. The coating of sized CaCrO/sub 4/ powder improved the uniformity of boron deposition of CaCrO/sub 4/, but it also decreased the pyrotechnic activity.

  10. CVD diamond - fundamental phenomena

    SciTech Connect

    Yarbrough, W.A.

    1993-01-01

    This compilation of figures and diagrams addresses the basic physical processes involved in the chemical vapor deposition of diamond. Different methods of deposition are illustrated. For each method, observations are made of the prominent advantages and disadvantages of the technique. Chemical mechanisms of nucleation are introduced.

  11. Investigation of plasma diagnostics using a dual frequency harmonic technique

    SciTech Connect

    Kim, Dong-Hwan; Kim, Young-Do; Cho, Sung-Won; Kim, Yu-Sin; Chung, Chin-Wook

    2014-09-07

    Plasma diagnostic methods using harmonic currents analysis of electrostatic probes were experimentally investigated to understand the differences in their measurement of the plasma parameters. When dual frequency voltage (ω{sub 1},ω{sub 2}) was applied to a probe, various harmonic currents (ω{sub 1}, 2ω{sub 1},ω{sub 2}, 2ω{sub 2},ω{sub 2}±ω{sub 1},ω{sub 2}±2ω{sub 1}) were generated due to the non-linearity of the probe sheath. The electron temperature can be obtained from the ratio of the two harmonics of the probe currents. According to the combinations of the two harmonics, the sensitivities in the measurement of the electron temperature differed, and this results in a difference of the electron temperature. From experiments and simulation, it is shown that this difference is caused by the systematic and random noise.

  12. Advanced modeling techniques in application to plasma pulse treatment

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. F.; Pashchenko, F. F.

    2016-06-01

    Different approaches considered for simulation of plasma pulse treatment process. The assumption of a significant non-linearity of processes in the treatment of oil wells has been confirmed. Method of functional transformations and fuzzy logic methods suggested for construction of a mathematical model. It is shown, that models, based on fuzzy logic are able to provide a satisfactory accuracy of simulation and prediction of non-linear processes observed.

  13. Power Efficient Plasma Technique for Rapid Water Sterilization

    NASA Astrophysics Data System (ADS)

    Hershcovitch, Ady

    2015-11-01

    Water especially good quality drinking water is a dwindling resource for significant segments of the world population. The BBC quoted this article (http://www.ft.com/cms/s/2/8e42bdc8-0838-11e4-9afc-00144feab7de.html) for a claim that water shortage is a bigger problem than climate change. One option for increasing the water supply is to recycle waste and polluted water by inexpensive, environmentally friendly methods. First steps involve filtrations while the last step is water disinfection. Presently disinfection is done chemically and/or UV radiation. Some chemicals cannot be used in large quantity due to residual toxicity, while UV disinfection systems consume a great deal electricity. Plasmas in water are very attractive for water sterilization due to UV radiation, ozone, etc. generation inside the water volume. Commercially available devices like NK-03 Blue Ballast System are used aboard ships for water purification. But, presently utilized plasmas: glow, pulsed arcs are not power efficient. Vortex stabilized plasmas, which are power efficient, can even degrade medications (antibiotics) advancing the state-of-the-art by orders of magnitude, especially when combined with electron beams. Disinfection scheme will be presented. Work supported by Contract No. DE-AC02-98CH1-886 with the US DOE.

  14. Electron diffraction studies on CVD grown bi-layered graphene

    NASA Astrophysics Data System (ADS)

    Lingam, Kiran; Karakaya, Mehmet; Podila, Ramakrishna; Quin, Haijun; Rao, Apparao; Dept. of Physics and Astronomy, Clemson University, Clemson, SC USA 29634. Team; Advanced Materials Research Laboratories, Clemson University, Anderson, SC USA 29625 Collaboration

    2013-03-01

    Graphene has generated enormous interest in the scientific community due to its peculiar properties like electron mobility, thermal conductivity etc. Several recent reports on exfoliated graphene emphasized the role of layer stacking on the electronic and optical properties of graphene in case of bi-layered and few layered graphene and several synthesis techniques like chemical vapor deposition (CVD) on Copper foils are employed to prepare graphene for applications at a large scale. However, a correlated study pertinent to the stacking order in CVD grown graphene is still unclear. In this work, using a combination of Raman spectroscopy and selected area electron diffraction analysis we analyzed the preferred misorientation angles in a CVD grown bi-layered graphene and also the role of Cu crystal facets on the graphene stacking order will be presented.

  15. Plasma-based ambient mass spectrometry techniques: The current status and future prospective.

    PubMed

    Ding, Xuelu; Duan, Yixiang

    2015-01-01

    Plasma-based ambient mass spectrometry is emerging as a frontier technology for direct analysis of sample that employs low-energy plasma as the ionization reagent. The versatile sources of ambient mass spectrometry (MS) can be classified according to the plasma formation approaches; namely, corona discharge, glow discharge, dielectric barrier discharge, and microwave-induced discharge. These techniques allow pretreatment-free detection of samples, ranging from biological materials (e.g., flies, bacteria, plants, tissues, peptides, metabolites, and lipids) to pharmaceuticals, food-stuffs, polymers, chemical warfare reagents, and daily-use chemicals. In most cases, plasma-based ambient MS performs well as a qualitative tool and as an analyzer for semi-quantitation. Herein, we provide an overview of the key concepts, mechanisms, and applications of plasma-based ambient MS techniques, and discuss the challenges and outlook. PMID:24338668

  16. Characterisation of CVD diamond detectors used for fast neutron flux monitoring

    NASA Astrophysics Data System (ADS)

    Foulon, F.; Bergonzo, P.; Amosov, V. N.; Kaschuck, Yu.; Frunze, V.; Tromson, D.; Brambilla, A.

    2002-01-01

    Natural diamond detectors (NDD) have been successfully used for fast neutron spectrometry on various fusion installations in plasma diagnostics. These detectors can work at high temperature, are radiation hard and exhibit a high energy resolution. However, the use of NDD is limited by the availability of IIa type diamonds exhibiting high electronic properties. With the recent advance in the growth of high quality chemically vapour deposited (CVD) diamond at LETI, CVD diamond appears to be a very promising material for plasma diagnostics. We present here for the first time results of the use of CVD diamond detectors for fast neutron flux monitoring on a neutron generator. The characteristics of CVD diamond detectors are compared with that of high quality NDD made by TRINITI. Pulse height spectra have been measured with CVD detectors and NDD under both 5.5 MeV alpha particles and 14.1 MeV neutrons. The quality of CVD diamond enables the recording of structured spectra allowing the distinction between the different neutron reactions on carbon. The efficiency of CVD diamond monitors and their actual limitations are analysed and discussed.

  17. Application of rf-thruster technique for fusion plasma heating

    NASA Astrophysics Data System (ADS)

    Freisinger, J.; Loeb, H. W.

    On the basis of RF ion thruster devices, a family of RF injector generators (RIGs) for the heating of fusion plasmas up to the temperature of thermonuclear burn has been developed. Hydrogen ion beams of 10-40 amps can be accelerated by means of the RIGs to 30 kV, so that ion beam densities of more than 250 mA/sq cm are achievable at uniform profiles within only 1 deg of divergence angle. The use of electrodeless quartz ionizers yields a very high atomic ion fraction, low admixture of impurities, long lifetime, high reliability, simple mechanical elements, and easy control.

  18. Electronic properties of CVD diamond

    NASA Astrophysics Data System (ADS)

    Nebel, C. E.

    2003-03-01

    The electronic properties of chemical vapour deposited (CVD) diamond are reviewed based on data measured by transient and spectrally resolved photoconductivity experiments, photo-thermal deflection spectroscopy (PDS) and electron paramagnetic resonance (EPR) where substitutional nitrogen (P1-centre) and carbon defects (H1-centre) are detected. The results show that nominally undoped high quality polycrystalline CVD diamond is a n-type semiconductor due to the presence of substitutional nitrogen. The sub-band-gap optical absorption is governed by amorphous graphite present at grain boundaries. Spectrally resolved photoconductivity experiments measured in the same regime are partially dominated by diamond bulk properties which are comparable to single crystalline Ib and IIa diamond and partially by grain boundaries. Mobilities and drift length of carriers are discussed and compared to properties of single crystalline diamond.

  19. Study of the plasma surface interactions by the "spinning wall" technique

    NASA Astrophysics Data System (ADS)

    Guha, Joydeep

    For the past few decades plasma etching has emerged as a dominant processing step in integrated-circuit (IC) device manufacturing. Due to the presence of reactive radicals and ions, plasmas are rich in chemistry and are widely used to etch sub-micron size features with complete fidelity. Radicals such as Cl, F, O etc. are the active species in the plasma that reacts with the material in the presence of ions forming volatile products, which leads to material removal. However, in these low pressure plasmas the radicals are lost to the reactor walls, which affect their number densities in the plasma. An important parameter to quantify radical loss at the surface is the recombination coefficient, gamma, defined as the probability per collision with the surface that an impinging radical will recombine. The surface in contact with the plasma interacts with the radicals, neutrals, ions, electrons, photons etc., which makes the measurement of kinetic parameter like the atom recombination probability a real challenge. A new technique has been developed to study the plasma-surface interactions in-situ. In this technique a cylindrical substrate is rapidly rotated between the plasma and differentially pumped diagnostic chambers, allowing portions of the surface to be periodically exposed to the plasma and then analyzed by desorption mass spectrometry and Auger electron spectroscopy. The time elapsed between the plasma exposure and subsequent analysis is controlled by varying the rotation frequency of the substrate. Using this technique Langmuir-Hinshelwood atom recombination probabilities have been measured in O2, Cl2, O2/Cl 2, Cl2/Ar and O2/Ar plasmas. A variety of diagnostic techniques have been used to analyze the plasmas. The gas temperature ( Tg) was measured by adding a trace amount of N2 (5%) to the plasma and measuring the emission of the N2 second positive system C 3piu, nu' → B 3pig, nu'' in the ultraviolet region. The electron densities (ne) were measured using a

  20. The extended growth of graphene oxide flakes using ethanol CVD

    NASA Astrophysics Data System (ADS)

    Huang, Jingfeng; Larisika, Melanie; Fam, W. H. Derrick; He, Qiyuan; Nimmo, Myra A.; Nowak, Christoph; Tok, I. Y. Alfred

    2013-03-01

    We report the extended growth of Graphene Oxide (GO) flakes using atmospheric pressure ethanol Chemical Vapor Deposition (CVD). GO was used to catalyze the deposition of carbon on a substrate in the ethanol CVD with Ar and H2 as carrier gases. Raman, SEM, XPS and AFM characterized the growth to be a reduced GO (RGO) of <5 layers. This newly grown RGO possesses lower defect density with larger and increased distribution of sp2 domains than chemically reduced RGO. Furthermore this method without optimization reduces the relative standard deviation of electrical conductivity between chips, from 80.5% to 16.5%, enabling RGO to be used in practical electronic devices.We report the extended growth of Graphene Oxide (GO) flakes using atmospheric pressure ethanol Chemical Vapor Deposition (CVD). GO was used to catalyze the deposition of carbon on a substrate in the ethanol CVD with Ar and H2 as carrier gases. Raman, SEM, XPS and AFM characterized the growth to be a reduced GO (RGO) of <5 layers. This newly grown RGO possesses lower defect density with larger and increased distribution of sp2 domains than chemically reduced RGO. Furthermore this method without optimization reduces the relative standard deviation of electrical conductivity between chips, from 80.5% to 16.5%, enabling RGO to be used in practical electronic devices. Electronic supplementary information (ESI) available: The ethanol CVD setup, TEM of CVD treated RGO, graphite 2D Raman spectra, GO synthesis, transfer and reduction methods and details of characterization techniques are described in the document. See DOI: 10.1039/c3nr33704a

  1. Comparison of ionospheric plasma drifts obtained by different techniques

    NASA Astrophysics Data System (ADS)

    Kouba, Daniel; Arikan, Feza; Arikan, Orhan; Toker, Cenk; Mosna, Zbysek; Gok, Gokhan; Rejfek, Lubos; Ari, Gizem

    2016-07-01

    Ionospheric observatory in Pruhonice (Czech Republic, 50N, 14.9E) provides regular ionospheric sounding using Digisonde DPS-4D. The paper is focused on F-region vertical drift data. Vertical component of the drift velocity vector can be estimated by several methods. Digisonde DPS-4D allows sounding in drift mode with direct output represented by drift velocity vector. The Digisonde located in Pruhonice provides direct drift measurement routinely once per 15 minutes. However, also other different techniques can be found in the literature, for example the indirect estimation based on the temporal evolution of measured ionospheric characteristics is often used for calculation of the vertical drift component. The vertical velocity is thus estimated according to the change of characteristics scaled from the classical quarter-hour ionograms. In present paper direct drift measurement is compared with technique based on measuring of the virtual height at fixed frequency from the F-layer trace on ionogram, technique based on variation of h`F and hmF. This comparison shows possibility of using different methods for calculating vertical drift velocity and their relationship to the direct measurement used by Digisonde. This study is supported by the Joint TUBITAK 114E092 and AS CR 14/001 projects.

  2. Plasma diagnostic techniques in thermal-barrier tandem-mirror fusion experiments

    SciTech Connect

    Silver, E.H.; Clauser, J.F.; Carter, M.R.; Failor, B.H.; Foote, J.H.; Hornady, R.S.; James, R.A.; Lasnier, C.J.; Perkins, D.E.

    1986-08-29

    We review two classes of plasma diagnostic techniques used in thermal-barrier tandem-mirror fusion experiments. The emphasis of the first class is to study mirror-trapped electrons at the thermal-barrier location. The focus of the second class is to measure the spatial and temporal behavior of the plasma space potential at various axial locations. The design and operation of the instruments in these two categories are discussed and data that are representative of their performance is presented.

  3. ECR plasma cleaning: an in-situ processing technique for RF cavities

    SciTech Connect

    Wu, G.; Moeller, W-D.; Antoine, C.; Jiang, H.; Pechenezhskiy, I.; Cooley, L.; Khabiboulline, T.; Terechkine, Y.; Edwards, H.; Koeth, T.; Romanenko, A.; /Cornell U., Phys. Dept. /Jefferson Lab

    2008-01-01

    A condition for Electron Cyclotron Resonance (ECR) can be established inside a fully assembled RF cavity without the need for removing high-power couplers. As such, plasma generated by this process can be used as a final cleaning step, or as an alternative cleaning step in place of other techniques. Tests showed filtered dry air plasma can successfully remove sulfur particles on niobium surface while the surface oxygen content remains intact.

  4. Comparison of Plasma Density Measurements in ICP Discharges Using Langmuir Probe, Plasma Oscillation Probe and Interferometry Techniques

    NASA Astrophysics Data System (ADS)

    Evans, John; Zawalski, Wade; Chen, Francis

    2000-10-01

    A comparison study of the application of various probe theories, including the so-called orbital motion limited (OML) and ABR theories, in the interpretation of Langmuir probe I-V characteristics is performed. Experimental data for the comparison is obtained in an inductively coupled plasma (ICP) source over a wide range of parameters of interest to the plasma processing community. Measurements of Ni from the Hiden Electrostatic Plasma Probe (ESP) characteristics and software are compared to ``known" values of Ne obtained via microwave interferometry and the plasma oscillation probe (POP) technique, in regimes including those where the probe theories yield different results. Excellent agreement is obtained between the interferometry and POP methods at low Po, whereas POP starts to fail at Po>5 mTorr, as expected. Langmuir probe results using OML theory yield reasonable agreement for Ne<2x1011cm-3, but fail at higher Ne. Closely spaced multiple peaks in the spectra of the POP are observed in some cases at higher RF input powers, possibly due to RF modulation of the source plasma density, leading to experimental uncertainty in Ne values thus obtained. Other considerations for the applicability of the POP method will also be discussed.

  5. NATO Advanced Research Workshop on Non-Thermal Plasma Techniques for Pollution Control

    NASA Astrophysics Data System (ADS)

    1992-09-01

    Acid rain, global warming, ozone depletion, and smog are preeminent environmental problems facing the world today. Non-thermal plasma techniques offer an innovative approach to the cost-effective solution of these problems. Many potential applications of non-thermal plasmas to air pollution control have already been demonstrated. On 21-25 Sept. 1992, leading experts from academia, government laboratories, and industry met at Cambridge University, England to discuss laboratory studies and industrial implementation of non-thermal plasmas for the abatement of hazardous gaseous wastes. Papers presented at the workshop are included.

  6. A penalization technique to model plasma facing components in a tokamak with temperature variations

    NASA Astrophysics Data System (ADS)

    Paredes, A.; Bufferand, H.; Ciraolo, G.; Schwander, F.; Serre, E.; Ghendrih, P.; Tamain, P.

    2014-10-01

    To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modeling of particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma-wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.

  7. A comparison of emissive probe techniques for electric potential measurements in a complex plasma

    SciTech Connect

    Sheehan, J. P.; Hershkowitz, N.; Raitses, Y.; Kaganovich, I.; Fisch, N. J.

    2011-07-15

    The major emissive probe techniques are compared to better understand the floating potential of an electron emitting surface in a plasma. An overview of the separation point technique, floating point technique, and inflection point in the limit of zero emission technique is given, addressing how each method works as well as the theoretical basis and limitations of each. It is shown that while the floating point method is the most popular, it is expected to yield a value {approx}1.5T{sub e}/e below the plasma potential due to a virtual cathode forming around the probe. The theoretical predictions were checked with experiments performed in a 2 kW annular Hall thruster plasma (n{sub e} {approx} 10{sup 9}-10{sup 10} cm{sup -3}and T{sub e} {approx} 10-50 eV). The authors find that the floating point method gives a value around 2T{sub e}/e below the inflection point method, which is shown to be a more accurate emissive probe technique than other techniques used in this work for measurements of the plasma potential.

  8. Localized CVD growth of oriented and individual carbon nanotubes from nanoscaled dots prepared by lithographic sequences

    NASA Astrophysics Data System (ADS)

    Vigolo, B.; Cojocaru, C. S.; Faerber, J.; Arabski, J.; Gangloff, L.; Legagneux, P.; Lezec, H.; LeNormand, F.

    2008-04-01

    Using a combination of top-down lithographic techniques, isolated, individual and oriented multi-wall carbon nanotubes (MWNTs) were grown on nickel or iron nanoscaled dots. In the first step of the process, micron-sized catalytic metallic dots (either iron or nickel) were prepared using UV lithography. MWNTs were then synthesized from these catalysts using a direct current plasma-assistance and hot-filament-enhanced chemical vapor deposition (CVD) reactor. Samples were characterized by means of scanning electron microscopy. It turns out that the splitting up of the micron-sized dot is favored in the iron case and that the surface diffusion of the metal is enhanced using ammonia in the gaseous mixture during the CVD process. The results are discussed giving arguments for the understanding of the MWNT growth mechanism. In a second step, a focused ion beam (FIB) procedure is carried out in order to reduce the initial dot size down to submicronic scale and subsequently to grow one single MWNT per dot. It is found that nickel is most appropriate to control the size of the dot. Dots of size 200 nm ± 40 nm are then required to grow individual MWNTs.

  9. Ionospheric Plasma Drift Analysis Technique Based On Ray Tracing

    NASA Astrophysics Data System (ADS)

    Ari, Gizem; Toker, Cenk

    2016-07-01

    Ionospheric drift measurements provide important information about the variability in the ionosphere, which can be used to quantify ionospheric disturbances caused by natural phenomena such as solar, geomagnetic, gravitational and seismic activities. One of the prominent ways for drift measurement depends on instrumentation based measurements, e.g. using an ionosonde. The drift estimation of an ionosonde depends on measuring the Doppler shift on the received signal, where the main cause of Doppler shift is the change in the length of the propagation path of the signal between the transmitter and the receiver. Unfortunately, ionosondes are expensive devices and their installation and maintenance require special care. Furthermore, the ionosonde network over the world or even Europe is not dense enough to obtain a global or continental drift map. In order to overcome the difficulties related to an ionosonde, we propose a technique to perform ionospheric drift estimation based on ray tracing. First, a two dimensional TEC map is constructed by using the IONOLAB-MAP tool which spatially interpolates the VTEC estimates obtained from the EUREF CORS network. Next, a three dimensional electron density profile is generated by inputting the TEC estimates to the IRI-2015 model. Eventually, a close-to-real situation electron density profile is obtained in which ray tracing can be performed. These profiles can be constructed periodically with a period of as low as 30 seconds. By processing two consequent snapshots together and calculating the propagation paths, we estimate the drift measurements over any coordinate of concern. We test our technique by comparing the results to the drift measurements taken at the DPS ionosonde at Pruhonice, Czech Republic. This study is supported by TUBITAK 115E915 and Joint TUBITAK 114E092 and AS CR14/001 projects.

  10. Study on the low leakage current of an MIS structure fabricated by ICP-CVD

    NASA Astrophysics Data System (ADS)

    Tsai, S.-Y.; Lu, Y.-M.; Hon, M.-H.

    2008-03-01

    As the dimensions of electric devices continue to shrink, it is becoming increasingly important to understand how to obtain good quality gate oxide film materials wilth higher carrier mobility, lower leakage current and greater reliability. All of them have become major concerns in the fabrication of thin film oxide transistors. A novel film deposition method called Inductively Coupled Plasma-Chemical Vapor Deposition (ICP-CVD) has received attraction in the semiconductor industry, because it can be capable of generating high density plasmas at extremely low temperature, resulting in less ion bombardment of the material surface. In this work, we present the results of crystallized silicon dioxide films deposited by inductively coupled plasma chemical vapor deposition technique at an extremely low temperature of 90°C. The value of the refractive index of the crystallized ICP-CVD SiO2 film depends on the r.f. power of the ICP system, and approximates to be 1.46. This value is comparable to that of SiO2 films prepared by thermal oxidation. As the r.f. power of ICP applied more than 1250 Watts, still only the (111) diffraction peak is observed by XRD, which implies a very strong preferred orientation or single crystal structure. Too low or too high r.f. power both produces amorphous SiO2 films. From the I-V curve, the MIS device with a SiO2 dielectric film has a lower leakage current density of 6.8×10-8A/cm2 at 1V as the film prepared at 1750 watts. The highest breakdown field in this study is 15.8 MV/cm. From the FTIR analysis, it was found that more hydrogen atoms incorporate into films and form Si-OH bonds as the r.f. power increases. The existence of Si-OH bonds leads to a poor reliability of the MIS device.

  11. Using a Filtration Technique to Isolate Platelet Free Plasma for Assaying Pyrophosphate

    PubMed Central

    TOLOUIAN, RAMIN; CONNERY, SEAN M.; O’NEILL, W. CHARLES; GUPTA, AJAY

    2015-01-01

    SUMMARY Background Vascular calcification (VC) is a strong prognostic marker of mortality from cardiovascular disease. Extracellular inorganic pyrophosphate (PPi) is a critical inhibitor of vascular calcification and it has been reported that hemodialysis patients have reduced plasma PPi levels, suggesting that altered PPi metabolism could contribute to VC in hemodialysis patients. Platelets are rich in PPi and release of PPi from platelets during storage or processing of plasma can lead to falsely elevated plasma PPi levels. To prepare plasma samples that are suitable for measuring PPi levels, ultracentrifugation has been used to remove platelets. Consequently, plasma PPi measurements have been limited to research laboratories since the majority of clinical laboratories do not have access to an ultracentrifuge. The purpose of the present study was to test the validity of an improved method of preparing platelet free plasma that uses filtration with a 300,000 Dalton molecular weight cut-off filter to exclude platelets, while minimizing their release of PPi. Methods In 20 maintenance hemodialysis patients, PPi levels were measured in plasma samples prepared by the conventional technique of low-speed centrifugation to remove red and white blood cells versus a novel filtration technique. Results Plasma prepared by filtration had significantly lower platelet counts (0 vs. 3 – 7 103/μL) and PPi levels (1.39 ± 0.30 μM vs. 2.74 ± 1.19 μM; mean ± SD, p < 0.01). Conclusions The filtration method appears effective in excluding platelets without causing trauma to platelets and can be used by clinical laboratories to prepare platelet-depleted plasma for PPi measurement. PMID:23289181

  12. A penalization technique to model plasma facing components in a tokamak with temperature variations

    SciTech Connect

    Paredes, A.; Bufferand, H.; Ciraolo, G.; Schwander, F.; Serre, E.; Ghendrih, P.; Tamain, P.

    2014-10-01

    To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modeling of particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.

  13. An inexpensive technique for the time resolved laser induced plasma spectroscopy

    NASA Astrophysics Data System (ADS)

    Ahmed, Rizwan; Ahmed, Nasar; Iqbal, J.; Aslam Baig, M.

    2016-08-01

    We present an efficient and inexpensive method for calculating the time resolved emission spectrum from the time integrated spectrum by monitoring the time evolution of neutral and singly ionized species in the laser produced plasma. To validate our assertion of extracting time resolved information from the time integrated spectrum, the time evolution data of the Cu II line at 481.29 nm and the molecular bands of AlO in the wavelength region (450-550 nm) have been studied. The plasma parameters were also estimated from the time resolved and time integrated spectra. A comparison of the results clearly reveals that the time resolved information about the plasma parameters can be extracted from the spectra registered with a time integrated spectrograph. Our proposed method will make the laser induced plasma spectroscopy robust and a low cost technique which is attractive for industry and environmental monitoring.

  14. Large-scale quantification of CVD graphene surface coverage

    NASA Astrophysics Data System (ADS)

    Ambrosi, Adriano; Bonanni, Alessandra; Sofer, Zdeněk; Pumera, Martin

    2013-02-01

    The extraordinary properties demonstrated for graphene and graphene-related materials can be fully exploited when a large-scale fabrication procedure is made available. Chemical vapor deposition (CVD) of graphene on Cu and Ni substrates is one of the most promising procedures to synthesize large-area and good quality graphene films. Parallel to the fabrication process, a large-scale quality monitoring technique is equally crucial. We demonstrate here a rapid and simple methodology that is able to probe the effectiveness of the growth process over a large substrate area for both Ni and Cu substrates. This method is based on inherent electrochemical signals generated by the underlying metal catalysts when fractures or discontinuities of the graphene film are present. The method can be applied immediately after the CVD growth process without the need for any graphene transfer step and represents a powerful quality monitoring technique for the assessment of large-scale fabrication of graphene by the CVD process.The extraordinary properties demonstrated for graphene and graphene-related materials can be fully exploited when a large-scale fabrication procedure is made available. Chemical vapor deposition (CVD) of graphene on Cu and Ni substrates is one of the most promising procedures to synthesize large-area and good quality graphene films. Parallel to the fabrication process, a large-scale quality monitoring technique is equally crucial. We demonstrate here a rapid and simple methodology that is able to probe the effectiveness of the growth process over a large substrate area for both Ni and Cu substrates. This method is based on inherent electrochemical signals generated by the underlying metal catalysts when fractures or discontinuities of the graphene film are present. The method can be applied immediately after the CVD growth process without the need for any graphene transfer step and represents a powerful quality monitoring technique for the assessment of large

  15. Diamond film by hot filament CVD method

    NASA Technical Reports Server (NTRS)

    Hirose, Y.

    1988-01-01

    Diamond synthesis by the hot filament CVD method is discussed. A hot filament decomposes gas mixtures and oxygen containing organic compounds such as alcohols. which are carbon sources. The resulting thin films, growth mechanisms, and characteristics and problems associated with the hot filament CVD method are analyzed and evaluated.

  16. Electronic properties of CVD and synthetic diamond

    NASA Astrophysics Data System (ADS)

    Nebel, C. E.; Müautnz, J.; Stutzmann, M.; Zachai, R.; Güautttler, H.

    1997-04-01

    Transport and contact properties of synthetic IIb- and intrinsic chemical vapor deposition (CVD) -diamond films are discussed. The samples have been investigated by time-of-flight and transient photoconductivity experiments using Cr/Au contacts. A hole depletion layer at the Cr/Au-IIb-diamond interface and an electron depletion layer at the Cr/Au-CVD-diamond interface is detected. The data indicate that our normally undoped CVD-diamond films are n-type semiconductors. In IIb diamond the mobilities of electrons and holes have been measured, while in CVD diamond no carrier transit can be detected due to the short Schubweg less than or equal to 1 μm. Two trap levels located approximately 190 meV below the conduction band and 670 meV above the valence band are deduced. Electron spin resonance experiments demonstrate that these CVD films are highly defective, containing about 1018 cm-3 carbon related defects (g=2.0029).

  17. FTIR monitoring of industrial scale CVD processes

    NASA Astrophysics Data System (ADS)

    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.

  18. Laser velocimetry measurements in non-isothermal CVD systems

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Researchers at the NASA Langley Research Center are applying laser velocimetry (LV) techniques to characterize the fluid dynamics of non-isothermal flows inside fused silica chambers designed for chemical vapor deposition (CVD). Experimental issues involved in the application of LV techniques to this task include thermophoretic effects on the LV seed particles, seeding the hazardous gases, index of refraction gradients in the flow field and surrounding media, optical access, relatively low flow velocities, and analysis and presentation of sparse data. An overview of the practical difficulties these issues represent to the use of laser velocimetry instrumentation for CVD applications is given. A fundamental limitation on the application of LV techniques in non-isothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias results from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a research CVD reactor are presented which indicate that current models for the interaction of forces such as Stokes drag, inertia, gravity, and thermophoresis are not adequate to predict thermophoretic effects on particle-based velocimetry measurements in arbitrary flow configurations.

  19. A deconvolution technique for B-dot signals from a plasma-driven electromagnetic launcher

    NASA Astrophysics Data System (ADS)

    Bouvier, Brigitte U.

    1989-06-01

    A novel technique is being developed to quantify the current distribution in the plasma armature of an electromagnetic launcher (EML). The technique relies on data from B-dot probes inserted above the barrel of an EML. The current distribution is found by taking the fast Fourier transform of the integral of the B-dot signal and deconvolving it with a geometry-dependent weight function. The result allows calculation of the total plasma length and total current magnitude. The author describes the signal-analysis technique, discusses results obtained from theoretical B-dot signals, and suggests possible sources of error which may be encountered when deconvolving experimental B-dot signals.

  20. Beams, brightness, and background: Using active spectroscopy techniques for precision measurements in fusion plasma research

    SciTech Connect

    Thomas, Dan M.

    2012-05-15

    The use of an injected neutral beam-either a dedicated diagnostic beam or the main heating beams-to localize and enhance plasma spectroscopic measurements can be exploited for a number of key physics issues in magnetic confinement fusion research, yielding detailed profile information on thermal and fast ion parameters, the radial electric field, plasma current density, and turbulent transport. The ability to make these measurements has played a significant role in much of our recent progress in the scientific understanding of fusion plasmas. The measurements can utilize emission from excited state transitions either from plasma ions or from the beam atoms themselves. The primary requirement is that the beam 'probe' interacts with the plasma in a known fashion. Advantages of active spectroscopy include high spatial resolution due to the enhanced localization of the emission and the use of appropriate imaging optics, background rejection through the appropriate modulation and timing of the beam and emission collection/detection system, and the ability of the beam to populate emitter states that are either nonexistent or too dim to utilize effectively in the case of standard or passive spectroscopy. In addition, some active techniques offer the diagnostician unique information because of the specific quantum physics responsible for the emission. This paper will describe the general principles behind a successful active spectroscopic measurement, emphasize specific techniques that facilitate the measurements and include several successful examples of their implementation, briefly touching on some of the more important physics results. It concludes with a few remarks about the relevance and requirements of active spectroscopic techniques for future burning plasma experiments.

  1. Techniques of Electrode Fabrication

    NASA Astrophysics Data System (ADS)

    Guo, Liang; Li, Xinyong; Chen, Guohua

    Electrochemical applications using many kinds of electrode materials as an advanced oxidation/reduction technique have been a focus of research by a number of groups during the last two decades. The electrochemical approach has been adopted successfully to develop various environmental applications, mainly including water and wastewater treatment, aqueous system monitoring, and solid surface analysis. In this chapter, a number of methods for the fabrication of film-structured electrode materials were selectively reviewed. Firstly, the thermal decomposition method is briefly described, followed by introducing chemical vapor deposition (CVD) strategy. Especially, much attention was focused on introducing the methods to produce diamond novel film electrode owing to its unique physical and chemical properties. The principle and influence factors of hot filament CVD and plasma enhanced CVD preparation were interpreted by refereeing recent reports. Finally, recent developments that address electro-oxidation/reduction issues and novel electrodes such as nano-electrode and boron-doped diamond electrode (BDD) are presented in the overview.

  2. Algorithm for polarimetry data inversion, consistent with other measuring techniques in tokamak plasma

    NASA Astrophysics Data System (ADS)

    Kravtsov, Yu. A.; Chrzanowski, J.; Mazon, D.

    2011-06-01

    New procedure for plasma polarimetry data inversion is suggested, which fits two parameter knowledge-based plasma model to the measured parameters (azimuthal and ellipticity angles) of the polarization ellipse. The knowledge-based model is supposed to use the magnetic field and electron density profiles, obtained from magnetic measurements and LIDAR data on the Thomson scattering. In distinction to traditional polarimetry, polarization evolution along the ray is determined on the basis of angular variables technique (AVT). The paper contains a few examples of numerical solutions of these equations, which are applicable in conditions, when Faraday and Cotton-Mouton effects are simultaneously strong.

  3. Experimental, theoretical and computational study of frequency upshift of electromagnetic radiation using plasma techniques

    SciTech Connect

    Joshi, C.

    1992-09-01

    This is a second year progress report on Experimental, Theoretical and Computational Study of Frequency Upshift of Electromagnetic Radiation Using Plasma Techniques.'' The highlights are: (I) Ionization fronts have been shown to frequency upshift e.m. radiation by greater than a factor 5. In the experiments, 33 GHz microwave radiation is upshifted to more than 175 GHz using a relativistically propagating ionization front created by a laser beam. (II) A Letter describing the results has been published in Physical Review Letters and an invited'' paper has been submitted to IEEE Trans. in Plasma Science.

  4. Development of a novel plasma scanning technique for high-quality anodic bonding

    NASA Astrophysics Data System (ADS)

    Wu, Jim-Wei; Yang, Chii-Rong; Huang, Che-Yi

    2016-04-01

    Anodic bonding is a type of nonintermediate wafer bonding technique that has been widely used in microelectromechanical systems for sealing devices or assembling microstructures. However, the conventional anodic bonding method has a limitation. The specimens being bonded must typically be in contact with the anode and cathode electrodes during the bonding process. In general, the initial bonding position corresponds to the contact area of the two electrodes; subsequently, the bonded region gradually extends to cover the entire target region. Nevertheless, the traditional diffuse bonding method provides limited bonding efficiency in industrial applications. Therefore, this paper proposes a novel plasma bonding technique for 2D scanning anodic bonding. In this technique, the plasma is positioned to simultaneously heat and bond specimens. We conducted an experiment that entailed bonding 4-inch silicon/glass wafers by using N2 plasma. The results revealed that an almost bubble-free bonded interface and an average bonding strength exceeding 37 MPa were achieved for a bonding time of 15 min 53 s, bonding voltage of 2 kV, noncontact distance (between the cathode electrode and the bonding specimens) of 3 mm, variable raster scan path, scan speed of 3 mm s-1, and continuous scan steps of 2.5 mm in the x- and y-axes. A comprehensive series of experiments were performed to validate the bonding performance of the proposed technique.

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

    DOEpatents

    Hemley, Russell J.; Mao, Ho-kwang; Yan, Chih-shiue

    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.

  6. Rolling-contact fatigue and wear of CVD-SiC with residual surface compression

    SciTech Connect

    Chao, L.Y.; Lakshminarayanan, R.; Shetty, D.K.; Cutler, R.A.

    1995-09-01

    The rolling-contact fatigue life and wear of CVD-SiC coatings with surface compression were studied using a three-ball-on-rod rolling-contact fatigue (RCF) tester. Two levels of surface compression in the coatings, approximately 190 {micro}m thick, were introduced by using substrates of a liquid-phase sintered SiC and a SiC-30 vol% TiC to obtain desired thermal-expansion mismatches with the CVD-SiC. Residual surface compressions of 250 and 680 MPa were measured in the CVD-SiC coatings on SiC and SiC-30 vol% TiC substrates, respectively, by a strain-gage technique. In the RCF test, the fatigue life of the CVD-SiC coating with the moderate surface compression was limited by severe wear by a brittle fracture mechanism at a Hertzian contact stress of 5.5 GPa. The CVD-SiC coating on the SiC-30 vol% TiC composite, on the other hand, did not show measurable wear. A majority of the tests (11 out of 16) were suspended at 100 h or stopped due to failure of the steel balls. Five tests stopped due to spalling of the CVD-SiC coating at weak interfaces 10 to 15 {micro}m below the contact surface. Examination of the microstructure of the CVD-SiC coating in cross sections revealed that the weak interfaces that led to the spalling were related to discontinuous growth of the CVD-SiC in the form of nodules or growth regions. Elimination of these defective structures is likely to enhance the tribological performance of surface-toughened CVD-SiC.

  7. Large-scale quantification of CVD graphene surface coverage.

    PubMed

    Ambrosi, Adriano; Bonanni, Alessandra; Sofer, Zdeněk; Pumera, Martin

    2013-03-21

    The extraordinary properties demonstrated for graphene and graphene-related materials can be fully exploited when a large-scale fabrication procedure is made available. Chemical vapor deposition (CVD) of graphene on Cu and Ni substrates is one of the most promising procedures to synthesize large-area and good quality graphene films. Parallel to the fabrication process, a large-scale quality monitoring technique is equally crucial. We demonstrate here a rapid and simple methodology that is able to probe the effectiveness of the growth process over a large substrate area for both Ni and Cu substrates. This method is based on inherent electrochemical signals generated by the underlying metal catalysts when fractures or discontinuities of the graphene film are present. The method can be applied immediately after the CVD growth process without the need for any graphene transfer step and represents a powerful quality monitoring technique for the assessment of large-scale fabrication of graphene by the CVD process. PMID:23396554

  8. CVD silicon carbide mirrors for EUV applications

    NASA Astrophysics Data System (ADS)

    Keski-Kuha, Ritva A.; Osantowski, John F.; Leviton, Douglas B.; Saha, Timo T.; Wright, Geraldine A.; Boucarut, Rene A.; Fleetwood, Charles M.; Madison, Timothy J.

    1995-10-01

    Advances in optical coating and materials technology have made possible the development of instruments with substantially improved efficiency in the extreme ultraviolet (EUV). For example, the development of chemical vapor deposited (CVD) SiC mirrors provides an opportunity to extend the range of normal incidence instruments down to 60 nm. CVD-SiC is a highly polishable material yielding low scatter surfaces. High UV reflectivity and desirable mechanical and thermal properties make CVD-SiC an attractive mirror and/or coating material for EUV applications. The EUV performance of SiC mirrors as well as some strengths and problem areas are discussed.

  9. Status of Plasma Physics Techniques for the Deposition of Tribological Coatings

    NASA Technical Reports Server (NTRS)

    Spalvins, T.

    1984-01-01

    The plasma physics deposition techniques of sputtering and ion-plating are reviewed. Their characteristics and potentials are discussed in terms of synthesis or deposition of tribological coatings. Since the glow discharge or plasma generated in the conventional sputtering and ion-plating techniques has a low ionization efficiency, rapid advances have been made in equipment design to further increase the ionization efficiency. The enhanced ionization favorably affects the nucleation and growth sequence of the coating. This leads to improved adherence and coherence, higher density, favorable morphological growth, and reduced internal stresses in the coatings. As a result, desirable coating characteristics can be precision tailored. Tribological coating characteristics of sputtered solid film lubricants such as MoS2, ion-plated soft gold and lead metallic films, and sputtered and ion-plated wear-resistant refractory compound films such as nitrides and carbides are discussed.

  10. Underwater plasma-MIG arc welding: Shielding technique and pressure reduction by a centrifugal pump

    SciTech Connect

    Creutz, M.; Mewes, D.; Bartzsch, J.; Draugelates, U.

    1995-12-31

    In comparison to hyperbaric underwater welding in diving chambers, wet welding techniques promise higher flexibility and lower costs. One technique for creating a local dry and pressure reduced welding zone is the use of a centrifugal pump. Results of experimental investigations in combination with a plasma-MIG arc welding system are presented in this paper. Special importance is attached to the local pressure reduction in view of the fact that low pressure, i.e. a high pressure difference between surrounding water and dry welding area, is a good condition for welding but is difficult to be obtained with other shielding systems than pressure chambers. Plasma-MIG welding has been done under water with a good result on the weld quality. Values of the hardness of the joint and the appearance of the weld structure are nearly comparable to atmospheric welds.

  11. High-speed sterilization technique using dielectric barrier discharge plasmas in atmospheric humid air

    NASA Astrophysics Data System (ADS)

    Miyamae, M.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

    2010-11-01

    The inactivation of Bacillus atrophaeus spores by a dielectric barrier discharge (DBD) plasma produced by an ac voltage application of 1 kHz in atmospheric humid air was investigated in order to develop low-temperature, low-cost and high-speed plasma sterilization technique. The biological indicators covered with a Tyvek sheet were set just outside the DBD plasma region, where the air temperature and humidity as a discharge gas were precisely controlled by an environmental test chamber. The results show that the inactivation of Bacillus atrophaeus spores was found to be dependent strongly on the humidity, and was completed within 15 min at a relative humidity of 90 % and a temperature of 30 C. The treatment time for sterilization is shorter than those of conventional sterilization methods using ethylene oxide gas and dry heat treatment. It is considered that reactive species such as hydroxyl radicals that are effective for the inactivation of Bacillus atrophaeus spores could be produced by the DBD plasma in the humid air. Repetitive micro-pulsed discharge plasmas in the humid air will be applied for the sterilization experiment to enhance the sterilization efficiency.

  12. In situ technique for measurement and control of transistor characteristics during remote plasma etching

    NASA Astrophysics Data System (ADS)

    Lishan, David; Hu, Evelyn

    1991-09-01

    In situ electrical monitoring has been carried out in a remote plasma etching system allowing accurate control of device electrical parameters. We have used this technique to gate recess-etch two different high electron mobility transistor structures while recording device source-drain I-V characteristics throughout the etching. Current versus etching time data and time elapsed I-V curves are presented.

  13. Saturation of CVD Diamond Detectors

    SciTech Connect

    Lucile S. Dauffy; Richard A. Lerche; Greg J. Schmid; Jeffrey A. Koch; Christopher Silbernagel

    2005-01-01

    A 5 x 0.25 mm Chemical Vapor Deposited (CVD) diamond detector, with a voltage bias of + 250V, was excited by a 400 nm laser (3.1 eV photons) in order to study the saturation of the wafer and its surrounding electronics. In a first experiment, the laser beam energy was increased from a few tens of a pJ to about 100 µJ, and the signal from the diamond was recorded until full saturation of the detection system was achieved. Clear saturation of the detection system was observed at about 40 V, which corresponds with the expected saturation at 10% of the applied bias (250V). The results indicate that the interaction mechanism of the 3.1 eV photons in the diamond (Ebandgap = 5.45 eV) is not a multi-photon process but is linked to the impurities and defects of the crystal. In a second experiment, the detector was irradiated by a saturating first laser pulse and then by a delayed laser pulse of equal or smaller amplitude with delays of 5, 10, and 20 ns. The results suggest that the diamond and associated electronics recover within 10 to 20 ns after a strong saturating pulse.

  14. Studies on non-oxide coating on carbon fibers using plasma enhanced chemical vapor deposition technique

    NASA Astrophysics Data System (ADS)

    Patel, R. H.; Sharma, S.; Prajapati, K. K.; Vyas, M. M.; Batra, N. M.

    2016-05-01

    A new way of improving the oxidative behavior of carbon fibers coated with SiC through Plasma Enhanced Chemical Vapor Deposition technique. The complete study includes coating of SiC on glass slab and Stainless steel specimen as a starting test subjects but the major focus was to increase the oxidation temperature of carbon fibers by PECVD technique. This method uses relatively lower substrate temperature and guarantees better stoichiometry than other coating methods and hence the substrate shows higher resistance towards mechanical and thermal stresses along with increase in oxidation temperature.

  15. Multiwalled carbon nanotube CVD synthesis, modification, and composite applications

    NASA Astrophysics Data System (ADS)

    Qian, Dali

    Well-aligned carbon multiwall nanotube (MWNT) arrays have been continuously synthesized by a floating catalytic chemical vapor deposition (CVD) method involving the pyrolysis of xylene-ferrocene mixtures. The CVD parameters have been studied to selectively synthesize nanotubes with required dimensions. A mixed tip-root growth model has been proposed for the floating catalytic CVD synthesis. Coarsening of the catalyst particle at the root end promoted MWNT wall coarsening (addition of new concentric graphene shells), while the smaller catalyst particle at the tip contributed to MWNT elongation. A two-step process in which ferrocene was fed for only five minutes to nucleate the DTs was developed to understand if a continuous supply of catalyst was necessary for continued growth. The results show that the ferrocene was only necessary for initial nucleation. To simplify the CVD process further, another two-step synthesis method was developed in which the ferrocene was pre-decomposed so that the nanotube nucleation could be isolated from the growth, enabling quantification of growth mechanisms and kinetics. Mass spectra and hydrocarbon analyses of the CVD reactor tail gas were performed to understand the pyrolysis chemistry. Well-aligned N-doped and Ru-doped MWNT arrays have been produced by pyrolysis of pyridine ferrocene mixtures and xylene-ferrocene-ruthenocene mixtures, respectively. Various material characterization techniques were used to measure the dopant distributions and correlate the catalyst phase with the novel nanotube structures. High-temperature annealing has been shown to be a viable means to remove both the catalyst particles and certain microstructural defects within the CVD-derived DTs. The phase transformation of catalyst during annealing has also been studied. Homogeneous distribution of MWNTs in polystyrene matrices was achieved by an ultrasonic assisted solution-evaporation method. Addition of only 1 wt % DTs to polystyrene increased the polymer

  16. Development of CVD mullite coatings for Si-based ceramics

    NASA Astrophysics Data System (ADS)

    Auger, Michael Lawrence

    1999-09-01

    To raise fuel efficiencies, the next generation of engines and fuel systems must be lighter and operate at higher temperatures. Ceramic-based materials, which are considerably lighter than metals and can withstand working temperatures of up to 1400sp°C, have been targeted to replace traditional metal-based components. The materials used in combustion environments must also be capable of withstanding erosion and corrosion caused by combustion gases, particulates, and deposit-forming corrodants. With these demanding criteria, silicon-based ceramics are the leading candidate materials for high temperature engine and heat exchanger structural components. However, these materials are limited in gaseous environments and in the presence of molten salts since they form liquid silicates on exposed surfaces at temperatures as low as 800sp°C. Protective coatings that can withstand higher operating temperatures and corrosive atmospheres must be developed for silicon-based ceramics. Mullite (3Alsb2Osb3{*}2SiOsb2) was targeted as a potential coating material due to its unique ability to resist corrosion, retain its strength, resist creep, and avoid thermal shock failure at elevated temperatures. Several attempts to deposit mullite coatings by various processing methods have met with limited success and usually resulted in coatings that have had pores, cracks, poor adherence, and required thermal post-treatments. To overcome these deficiencies, the direct formation of chemically vapor deposited (CVD) mullite coatings has been developed. CVD is a high temperature atomistic deposition technique that results in dense, adherent crystalline coatings. The object of this dissertation was to further the understanding of the CVD mullite deposition process and resultant coating. The kinetics of CVD mullite deposition were investigated as a function of the following process parameters: temperature, pressure, and the deposition reactor system. An empirical kinetic model was developed

  17. Fracture Characteristics of Monolayer CVD-Graphene

    PubMed Central

    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. 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. PMID:24657996

  18. Measurement of temperature and electrons density distribution of atmospheric arc plasma by moiré deflectometry technique

    NASA Astrophysics Data System (ADS)

    Salimi Meidanshahi, Fatemeh; Madanipour, Khosro; Shokri, Babak

    2013-04-01

    In the present paper, the refractive index, electron density and temperature distribution of atmospheric arc plasmas are measured by moiré deflectometry. The deflection angle of rays passing through the plasma is obtained by moiré fringe analysis. Then by using inverse Abel transform integral for this axisymmetric plasma, the refractive index distribution is obtained in different points of plasma and environment. Considering the relation between plasma temperature and refractive index, the spatial temperature distribution of the arc plasma is evaluated. Also, in contrast to conventional models to obtain electron number density, in which the refractive index of plasmas is approximately assumed equal to the electron refractive index, a model is used for accurate and absolute measurement of the electron density profile. This technique is especially suitable for measuring axially symmetric plasma parameters.

  19. Chiral electron transport in CVD bilayer graphene

    NASA Astrophysics Data System (ADS)

    Lee, Kyunghoon; Eo, Yun Suk; Kurdak, Cagliyan; Zhong, Zhaohui

    2014-03-01

    Charge carriers in bilayer graphene have a parabolic energy spectrum. Due to this band structure they are massive quasiparticles having a finite density of state at zero energy like other non-relativistic charge carriers in conventional two dimensional materials. However, they are massive Dirac fermions which have a chiral nature similar to the case of massless Dirac fermions in single layer graphene. Coupling of pseudospin and motion of charge carrier via chirality can result in dramatic consequence for transport in bipolar regime like Klein tunneling, Fabry-Perot interference, collimation of charge carrier, Veslago lens, etc. However, little attention has been paid to chiral dependent electron transport in bilayer graphene. Here we study these properties by probing phase coherent transport behavior in CVD bilayer graphene devices with sub-200nm channel length. Complex Fabry-Perot interference patterns are observed in resonant cavities defined by local gating. By applying Fourier analysis technique, we successfully analyze and identify the origin of each individual interference pattern in bipolar and monopolar regime. Our initial results also hint at the observation of cloaking of electronic states against chiral electrons in bilayer graphene.

  20. Transfer of CVD-grown monolayer graphene onto arbitrary substrates.

    PubMed

    Suk, Ji Won; Kitt, Alexander; Magnuson, Carl W; Hao, Yufeng; Ahmed, Samir; An, Jinho; Swan, Anna K; Goldberg, Bennett B; Ruoff, Rodney S

    2011-09-27

    Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside. The dry transfer technique utilizes a polydimethylsiloxane frame that attaches to the poly(methyl methacrylate) spun over the graphene film, and the monolayer graphene was transferred onto shallow depressions with 300 nm depth. The improved wet transfer onto perforated substrates with 2.7 μm diameter holes yields 98% coverage of holes covered with continuous films, allowing the ready use of Raman spectroscopy and transmission electron microscopy to study the intrinsic properties of CVD-grown monolayer graphene. Additionally, monolayer graphene transferred onto flat substrates has fewer cracks and tears, as well as lower sheet resistance than previous transfer techniques. Monolayer graphene films transferred onto glass had a sheet resistance of ∼980 Ω/sq and a transmittance of 97.6%. These transfer techniques open up possibilities for the fabrication of various graphene devices with unique configurations and enhanced performance. PMID:21894965

  1. CVD diamond for nuclear detection applications

    NASA Astrophysics Data System (ADS)

    Bergonzo, P.; Brambilla, A.; Tromson, D.; Mer, C.; Guizard, B.; Marshall, R. D.; Foulon, F.

    2002-01-01

    Chemically vapour deposited (CVD) diamond is a remarkable material for the fabrication of radiation detectors. In fact, there exist several applications where other standard semiconductor detectors do not fulfil the specific requirements imposed by corrosive, hot and/or high radiation dose environments. The improvement of the electronic properties of CVD diamond has been under intensive investigations and led to the development of a few applications that are addressing specific industrial needs. Here, we report on CVD diamond-based detector developments and we describe how this material, even though of a polycrystalline nature, is readily of great interest for applications in the nuclear industry as well as for physics experiments. Improvements in the material synthesis as well as on device fabrication especially concern the synthesis of films that do not exhibit space charge build up effects which are often encountered in CVD diamond materials and that are highly detrimental for detection devices. On a pre-industrial basis, CVD diamond detectors have been fabricated for nuclear industry applications in hostile environments. Such devices can operate in harsh environments and overcome limitations encountered with the standard semiconductor materials. Of these, this paper presents devices for the monitoring of the alpha activity in corrosive nuclear waste solutions, such as those encountered in nuclear fuel assembly reprocessing facilities, as well as diamond-based thermal neutron detectors exhibiting a high neutron to gamma selectivity. All these demonstrate the effectiveness of a demanding industrial need that relies on the remarkable resilience of CVD diamond.

  2. Study of carboxylic functionalization of polypropylene surface using the underwater plasma technique

    NASA Astrophysics Data System (ADS)

    Joshi, R. S.; Friedrich, J. F.; Wagner, M. H.

    2009-08-01

    Non-equilibrium solution plasma treatment of polymer surfaces in water offers the possibility of more dense and selective polymer surface functionalization in comparison to the well-known and frequently used low-pressure oxygen plasma. Functional groups are introduced when the polymer surface contacts the plasma moderated solution especially water solutions. The emission of ions, electrons, energy-rich neutrals and complexes, produced by the ion avalanche are limited by quenching, with the aid of the ambient water phase. The UV-radiation produced in plasma formation also helps to moderate the reaction solution further by producing additional excited, ionized/dissociated molecules. Thus, monotype functional groups equipped polymer surfaces, preferably OH groups, originating from the dissociated water molecules, could be produced more selectively. An interesting feature of the technique is its flexibility to use a wide variety of additives in the water phase. Another way to modify polymer surfaces is the deposition of plasma polymers carrying functional groups as carboxylic groups used in this work. Acetic acid, acrylic acid, maleic and itaconic acid were used as additive monomers. Acetic acid is not a chemically polymerizing monomer but it could polymerize by monomer/molecular fragmentation and recombination to a cross linked layer. The other monomers form preferably water-soluble polymers on a chemical way. Only the fragmented fraction of these monomers could form an insoluble coating by cross linking to substrate. The XPS analysis was used to track the alterations in -O-CO- bond percentage on the PP surface. To identify the -COOH groups on substrate surface unambiguously, which have survived the plasma polymerization process, the derivatization with trifluoroethanol was performed.

  3. CVD silicon carbide characterization. Final report, August 1992-October 1993

    SciTech Connect

    Graves, G.A.; Iden, D.

    1994-08-01

    Chemically vapor deposited (CVD) silicon carbide is a candidate material for high quality ground and space-based mirror substrates and high quality reflective optics. Statistically valid material property data has not been available, however, to make durability and lifetime predictions for such optics. The primary purpose of this study was to determine the Weibull and slow crack growth parameters for CVD silicon carbide. Specimens were cut from various locations in a 25 mm thick, 50 cm diameter piece of SiC to analyze bulk material property homogeneity. Flexural strength was measured using a four-point bend technique. In addition to mechanical testing for strength, hardness, and fracture toughness, the material crystallography and microstructure were studied. Thermal expansion, thermal diffusivity, specific heat, optical absorption, and infrared reflectivity measurements were also conducted. Raman spectroscopy was used to check for any residual stress. Test results show this CVD silicon carbide is a high-purity, homogeneous, fine-grained substrate material with very good mechanical, optical, and thermal properties.

  4. PREFACE: IX International Conference on Modern Techniques of Plasma Diagnostics and their Application

    NASA Astrophysics Data System (ADS)

    Savjolov, A. S.; Dodulad, E. I.

    2016-01-01

    The IX Conference on ''Modern Techniques of Plasma Diagnosis and their Application'' was held on 5 - 7 November, 2014 at National Research Nuclear University MEPhI (NRNU MEPhI). The goal of the conference was an exchange of information on both high-temperature and low-temperature plasma diagnostics as well as deliberation and analysis of various diagnostic techniques and their applicability in science, industry, ecology, medicine and other fields. The Conference also provided young scientists from scientific centres and universities engaged in plasma diagnostics with an opportunity to attend the lectures given by the leading specialists in this field as well as present their own results and findings. The first workshop titled ''Modern problems of plasma diagnostics and their application for control of chemicals and the environment'' took place at Moscow Engineering and Physics Institute (MEPhI) in June 1998 with the support of the Section on Diagnostics of the Council of Russian Academic of Science on Plasma Physics and since then these forums have been held at MEPhI every two years. In 2008 the workshop was assigned a conference status. More than 150 specialists on plasma diagnostics and students took part in the last conference. They represented leading Russian scientific centres (such as Troitsk Institute of Innovative and Thermonuclear Research, National Research Centre ''Kurchatov Institute'', Russian Federal Nuclear Centre - All-Russian Scientific Research Institute of Experimental Physics and others) and universities from Belarus, Ukraine, Germany, USA, Belgium and Sweden. About 30 reports were made by young researchers, students and post-graduate students. All presentations during the conference were broadcasted online over the internet with viewers in Moscow, Prague, St. Petersburgh and other cities. The Conference was held within the framework of the Centre of Plasma, Laser Research and Technology supported by MEPhI Academic Excellence Project (Russian

  5. Crystallographic anisotropy of growth and etch rates of CVD diamond

    SciTech Connect

    Wolfer, M; Biener, J; El-dasher, B S; Biener, M M; Hamza, A V; Kriele, A; Wild, C

    2008-08-05

    The investigation of orientation dependent crystal growth and etch processes can provide deep insights into the underlying mechanisms and thus helps to validate theoretical models. Here, we report on homoepitaxial diamond growth and oxygen etch experiments on polished, polycrystalline CVD diamond wafers by use of electron backscatter diffraction (EBSD) and white-light interferometry (WLI). Atomic force microscopy (AFM) was applied to provide additional atomic scale surface morphology information. The main advantage of using polycrystalline diamond substrates with almost random grain orientation is that it allows determining the orientation dependent growth (etch) rate for different orientations within one experiment. Specifically, we studied the effect of methane concentration on the diamond growth rate, using a microwave plasma CVD process. At 1 % methane concentration a maximum of the growth rate near <100> and a minimum near <111> is detected. Increasing the methane concentration up to 5 % shifts the maximum towards <110> while the minimum stays at <111>. Etch rate measurements in a microwave powered oxygen plasma reveal a pronounced maximum at <111>. We also made a first attempt to interpret our experimental data in terms of local micro-faceting of high-indexed planes.

  6. Electroluminescent and photosensitive films prepared by DTC-CVD method

    NASA Astrophysics Data System (ADS)

    Zavyalova, Ludmila V.; Svechnikov, George S.

    1997-08-01

    The original chemical vapor deposition (CVD) method used in fabrication A2B6 films, photodetectors and electro- luminescent emitters based on these films have been reported. The basic idea behind this method is thermal decomposition of dithiocarbamates (DTC). The proposed method does not require expensive materials and vacuum equipment. Moreover, the DTC-CVD method differs from the known CVD methods in source material delivery method, a low deposition temperature and a non-sealed reactor geometry. Both CdS and CdS1-xSex were obtained at temperature of 240- 280 degrees C and were activated directly in the grown process by Cu and In, or by annealing in mixture CdS: Cu, Cl. Photodetectors with absorption maxima at 500-750 nm have dark conductivity (sigma) D EQ 10-9 divided by 10-8 (Omega) -1 cm-1 and photoconductivity (sigma) ph equals 10-2 divided by 10-1 (Omega) -1 cm-1 at 200 lux. CdS films with thickness of 6 divided by 12 micrometers have been used as sandwich-type photoconductor detectors. Electroluminescence ZnS:Mn films prepared by DTC-CVD method at the substrate temperature of 200 DIV 300 degrees C without additional annealing have high luminance and luminous efficiency. Deposition at a law temperature makes it possible to use flexible polymer films or low cost glasses as substrates. Because the technique is rather simple and can be applied to obtain all types of thin film electroluminescence structure layers, we expect a low price of light sources based on these films.

  7. Z-pinch diagnostics, plasma and liner instabilities and new x-ray techniques

    SciTech Connect

    Oona, H.; Anderson, B.; Benage, J.

    1996-09-01

    Pulse power experiments of the last several decades have contributed greatly to the understanding of high temperature and high density plasmas and, more recently, to the study of hydrodynamic effects in thick imploding cylinders. Common to all these experiments is the application of a large current pulse to a cylindrically symmetric load, with the resulting Lorenz force compressing the load to produce hydrodynamic motion and/or high temperature, high density plasma. In Los Alamos, Pulsed power experiments are carried out at two facilities. Experiments at low current (from several million to ten million Amperes) are conducted on the Pegasus II capacitor bank. Experiments with higher currents (10`s to 100`s MA range) are performed in Ancho Canyon with the explosively driven Procyon and MAGO magnetic flux compression generator systems. In this paper, the authors present a survey of diagnostic capabilities and results from several sets of experiments. First, they discuss the initiation and growth of instabilities in plasmas generated from the implosion of hollow z-pinches in the pegasus and Procyon experiments. Next they discuss spectroscopic data from the plasmas produced by the MAGO system. They also show time resolved imaging data from thick ({approximately} .4 mm) liner implosions. Finally, the authors discuss improvements to x-ray and visible light imaging and spectrographic diagnostic techniques. The emphasis of this paper is not so much a detailed discussion of the experiments, but a presentation of imaging and spectroscopic results and the implications of these observations to the experiments.

  8. Sex specific differences in the predictive value of cholesterol homeostasis markers and 10-Year CVD event rate in Framingham Offspring Study participants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Available data are inconsistent on factors influencing plasma cholesterol homeostasis marker concentrations and their value in predicting subsequent cardiovascular disease (CVD) events. To address this issue the relationship between markers of cholesterol absorption (campesterol, sitosterol, cholest...

  9. Two approaches to plasma polarimetry: Angular variables technique and Stokes vector formalism

    NASA Astrophysics Data System (ADS)

    Bieg, Bohdan; Chrzanowski, Janusz; Kravtsov, Yury A.; Murari, Andrea; Orsitto, Francesco

    2013-08-01

    The modern plasma polarimetry is based on Stokes vector formalism (SVF) suggested and developed in depth by Segre (see Ref. [1] and cited there references). Segre's equations describe evolution of the Stokes vector along the ray in the weakly inhomogeneous and weakly anisotropic plasma. Alternative approach - angular variables technique (AVT) - suggested by Czyż et al. [2] in distinction to SVF deals with angular parameters of the polarization ellipse. Equations for angular parameters drastically differ from the SVF equations; however, AVT and SVF equations happen to be equivalent to each other. This paper proves equivalence of the SVF and AVT and in the sometime reveals some practical distinctions between two approaches. Although all the results of SVF can be obtained in frame of the AVT and vice versa, in specific problems one of the methods can be more convenient. Generally, AVT may serve as a valuable compliment to traditional SVF, providing sometimes more simple an less laborious solution of polarimetric problems.

  10. CVD 908, CVD 908-htrA, and CVD 909 live oral typhoid vaccines: a logical progression.

    PubMed

    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. PMID:17582563

  11. High T(sub c) superconductors fabricated by plasma aerosol mist deposition technique

    NASA Technical Reports Server (NTRS)

    Wang, X. W.; Vuong, K. D.; Leone, A.; Shen, C. Q.; Williams, J.; Coy, M.

    1995-01-01

    We report new results on high T(sub c) superconductors fabricated by a plasma aerosol mist deposition technique, in atmospheric environment. Materials fabricated are YBaCuO, BiPbSrCaCuO, BaCaCuO precursor films for TlBaCaCuO, and other buffers such as YSZ. Depending on processing conditions, sizes of crystallites and/or particles are between dozens of nano-meters and several micrometers. Superconductive properties and other material characteristics can also be tailored.

  12. Thermal plasma processing of materials

    SciTech Connect

    Pfender, E.; Heberlein, J.

    1992-02-01

    Emphasis has been on plasma synthesis of fine powders, plasma Chemical Vapor Deposition (CVD), on related diagnostics, and on modeling work. Since plasma synthesis as well as plasma CVD make frequent use of plasma jets, the beginning has been devoted of plasma jets and behavior of particulates injected into such plasma jets. Although most of the construction of the Triple-Torch Plasma Reactor (TTPR) has already been done, modifications have been made in particular modifications required for plasma CVD of diamond. A new reactor designed for Counter-Flow Liquid Injection Plasma Synthesis (CFLIPS) proved to be an excellent tool for synthesis of fine powders as well as for plasma CVD. An attempt was made to model flow and temperature fields in this reactor. Substantial efforts were made to single out those parameters which govern particle size, size distribution, and powder quality in our plasma synthesis experiments. This knowledge is crucial for controlling the process and for meaningful diagnostics and modeling work. Plasma CVD of diamond films using both reactors has been very successful and we have been approached by a number of companies interested in using this technology for coating of tools.

  13. A facile process for soak-and-peel delamination of CVD graphene from substrates using water

    PubMed Central

    Gupta, Priti; Dongare, Pratiksha D.; Grover, Sameer; Dubey, Sudipta; Mamgain, Hitesh; Bhattacharya, Arnab; Deshmukh, Mandar M.

    2014-01-01

    We demonstrate a simple technique to transfer chemical vapour deposited (CVD) graphene from copper and platinum substrates using a soak-and-peel delamination technique utilizing only hot deionized water. The lack of chemical etchants results in cleaner CVD graphene films minimizing unintentional doping, as confirmed by Raman and electrical measurements. The process allows the reuse of substrates and hence can enable the use of oriented substrates for growth of higher quality graphene, and is an inherently inexpensive and scalable process for large-area production. PMID:24457558

  14. A facile process for soak-and-peel delamination of CVD graphene from substrates using water

    NASA Astrophysics Data System (ADS)

    Gupta, Priti; Dongare, Pratiksha D.; Grover, Sameer; Dubey, Sudipta; Mamgain, Hitesh; Bhattacharya, Arnab; Deshmukh, Mandar M.

    2014-01-01

    We demonstrate a simple technique to transfer chemical vapour deposited (CVD) graphene from copper and platinum substrates using a soak-and-peel delamination technique utilizing only hot deionized water. The lack of chemical etchants results in cleaner CVD graphene films minimizing unintentional doping, as confirmed by Raman and electrical measurements. The process allows the reuse of substrates and hence can enable the use of oriented substrates for growth of higher quality graphene, and is an inherently inexpensive and scalable process for large-area production.

  15. The Deflection Plate Analyzer: A Technique for Space Plasma Measurements Under Highly Disturbed Conditions

    NASA Technical Reports Server (NTRS)

    Wright, Kenneth H., Jr.; Dutton, Ken; Martinez, Nelson; Smith, Dennis; Stone, Nobie H.

    2004-01-01

    A technique has been developed to measure the characteristics of space plasmas under highly disturbed conditions; e.g., non-Maxwellian plasmas with strong drifting populations and plasmas contaminated by spacecraft outgassing. The present method is an extension of the capabilities of the Differential Ion Flux Probe (DIFP) to include a mass measurement that does not include either high voltage or contamination sensitive devices such as channeltron electron multipliers or microchannel plates. This reduces the complexity and expense of instrument fabrication, testing, and integration of flight hardware as compared to classical mass analyzers. The new instrument design is called the Deflection Plate Analyzer (DPA) and can deconvolve multiple ion streams and analyze each stream for ion flux intensity (density), velocity (including direction of motion), mass, and temperature (or energy distribution). The basic functionality of the DPA is discussed. The performance characteristics of a flight instrument as built for an electrodynamic tether mission, the Propulsive Small Expendable Deployer System (ProSEDS), and the instrument s role in measuring key experimental conditions are also discussed.

  16. Development of a Technique for Measuring Local Electric Field Turbulence in a Tokamak Plasma

    NASA Astrophysics Data System (ADS)

    Thompson, D. S.; Fonck, R. J.; Burke, M. G.; McKee, G. R.; Lewicki, B. T.; Winz, G. R.

    2013-10-01

    Accessible methods for measuring Ẽ (R , t) in large-scale magnetic confinement experiments are highly desired for validation studies of plasma turbulence models. A new technique based on neutral beam emission spectroscopy is being developed to address this need. Rapid fluctuations in the separation of spectral components of the motionally induced Stark spectrum can reflect fluctuations in the intrinsic electric field of the plasma. Polarization spectroscopy via high resolution, high-throughput spectrometers that compensate for field-of-view broadening is being developed to isolate and measure these fluctuations. Cross-power correlation analysis between the linewidth fluctuations and plasma density fluctuations will be employed to extract the expected small signals. Electric field fluctuations at mid-minor-radius, normalized to an estimated MSE field, are expected to be on the order of Ẽ /EMSE ~ 1 ×10-3 in the PEGASUS Toroidal Experiment and are comparable to those expected in NSTX and in DIII-D. Work supported by US DOE Grant DE-FG02-89ER53296.

  17. Removal Dynamics of Nitric Oxide (NO) Pollutant Gas by Pulse-Discharged Plasma Technique

    PubMed Central

    Zhang, Lianshui; Wang, Xiaojun; Lai, Weidong; Cheng, Xueliang; Zhao, Kuifang

    2014-01-01

    Nonthermal plasma technique has drawn extensive attentions for removal of air pollutants such as NOx and SO2. The NO removal mechanism in pulse discharged plasma is discussed in this paper. Emission spectra diagnosis indicates that the higher the discharge voltage is, the more the NO are removed and transformed into O, N, N2, NO2, and so forth. Plasma electron temperature Te is ranged from 6400 K at 2.4 kV discharge voltage to 9500 K at 4.8 kV. After establishing a zero-dimensional chemical reaction kinetic model, the major reaction paths are clarified as the electron collision dissociation of NO into N and O during discharge and followed by single substitution of N on NO to form N2 during and after discharge, compared with the small fraction of NO2 formed by oxidizing NO. The reaction directions can be adjusted by N2 additive, and the optimal N2/NO mixing ratio is 2 : 1. Such a ratio not only compensates the disadvantage of electron competitive consumption by the mixed N2, but also heightens the total NO removal extent through accelerating the NO oxidization process. PMID:24737985

  18. The Deflection Plate Analyzer: A Technique for Space Plasma Measurements Under Highly Disturbed Conditions

    NASA Technical Reports Server (NTRS)

    Wright, Kenneth H., Jr.; Dutton, Ken; Martinez, Nelson; Smith, Dennis; Stone, Nobie H.

    2003-01-01

    A technique has been developed to measure the characteristics of space plasmas under highly disturbed conditions; e.g., non-Maxwellian plasmas with strong drifting populations and plasmas contaminated by spacecraft outgassing. The present method is an extension of the capabilities of the Differential Ion Flux Probe (DIFP) to include a mass measurement that does not include either high voltage or contamination sensitive devices such as channeltron electron multipliers or microchannel plates. This reduces the complexity and expense of instrument fabrication, testing, and integration of flight hardware as compared to classical mass analyzers. The new instrument design is called the Deflection Plate Analyzer (DPA) and can deconvolve multiple ion streams and analyze each stream for ion flux intensity (density), velocity (including direction of motion), mass, and temperature (or energy distribution). The basic functionality of the DPA is discussed. The performance characteristics of a flight instrument as built for an electrodynamic tether mission, the Propulsive Small Expendable Deployer System (ProSEDS), and the instrument s role in measuring key experimental conditions are also discussed.

  19. A computationally assisted spectroscopic technique to measure secondary electron emission coefficients in radio frequency plasmas

    NASA Astrophysics Data System (ADS)

    Daksha, M.; Berger, B.; Schuengel, E.; Korolov, I.; Derzsi, A.; Koepke, M.; Donkó, Z.; Schulze, J.

    2016-06-01

    A computationally assisted spectroscopic technique to measure secondary electron emission coefficients (γ-CAST) in capacitively-coupled radio-frequency plasmas is proposed. This non-intrusive, sensitive diagnostic is based on a combination of phase resolved optical emission spectroscopy and particle-based kinetic simulations. In such plasmas (under most conditions in electropositive gases) the spatio-temporally resolved electron-impact excitation/ionization rate features two distinct maxima adjacent to each electrode at different times within each RF period. While one maximum is the consequence of the energy gain of electrons due to sheath expansion, the second maximum is produced by secondary electrons accelerated towards the plasma bulk by the sheath electric field at the time of maximum voltage drop across the adjacent sheath. Due to these different excitation/ionization mechanisms, the ratio of the intensities of these maxima is very sensitive to the secondary electron emission coefficient γ. This sensitvity, in turn, allows γ to be determined by comparing experimental excitation profiles and simulation data obtained with various γ-coefficients. The diagnostic, tested here in a geometrically symmetric argon discharge, yields an effective secondary electron emission coefficient of γ =0.066+/- 0.01 for stainless steel electrodes.

  20. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  1. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  2. Synthesis of Nanosized Titanium Oxide and Nitride Through Vacuum Arc Plasma Expansion Technique

    NASA Astrophysics Data System (ADS)

    Lepeshev, A. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.; Shaihadinov, A. A.

    2016-12-01

    Physical vapor deposition techniques such vacuum arc plasma deposition — which are very commonly used in thin film technology — appear to hold much promise for the synthesis of nanocrystalline thin films as well as nanoparticles. Monodisperse and spherical titanium oxide (TiO2) and nitride nanoparticles were produced at room temperature as a cluster beam in the gas phase using a cluster-deposition source. Using the basic principles of the gas condensation method, this study has developed vacuum arc nanoparticle synthesis system. We demonstrate that major process deposition parameter is the pressure in the plasma chamber. This is the major advantage of these techniques over thermal evaporation. Our method affords TiN powders with high specific surface areas exceeding 200m2g-1. TEM micrograph of TiO2 nanoparticles prepared at an oxygen pressure of 60Pa show an average particle size of 6nm. TiO2 nanoparticles prepared at an oxygen pressure of 70Pa were observed to not have a reduced average particle size.

  3. Surface Modification of Graphene Oxides by Plasma Techniques and Their Application for Environmental Pollution Cleanup.

    PubMed

    Wang, Xiangxue; Fan, Qiaohui; Chen, Zhongshan; Wang, Qi; Li, Jiaxing; Hobiny, Aatef; Alsaedi, Ahmed; Wang, Xiangke

    2016-02-01

    Graphene oxides (GOs) have come under intense multidisciplinary study because of their unique physicochemical properties and possible applications. The large amount of oxygen-containing functional groups on GOs leads to a high sorption capacity for the removal of various kinds of organic and inorganic pollutants from aqueous solutions in environmental pollution cleanup. However, the lack of selectivity results in difficulty in the selective removal of target pollutants from aqueous solutions in the presence of other coexisting pollutants. Herein, the surface grafting of GOs with special oxygen-containing functional groups using low-temperature plasma techniques and the application of the surface-modified GOs for the efficient removal of organic and inorganic pollutants in environmental pollution are reviewed. This paper gives an account of our research on the application of GO-based nanomaterials in environmental pollution cleanup, including: (1) the synthesis and surface grafting of functional groups on GOs, summarizing various types of low-temperature plasma techniques for the synthesis of graphene/GOs; and (2) the application of graphene/GOs and their composites for the efficient removal of organic and inorganic pollutants from aqueous solutions, including the interaction mechanism according to recently published results. PMID:26915704

  4. Ni-catalysed carbon nanotubes and nanofibers assemblies grown on TiN/Si(1 0 0) substrates using hot-filaments combined with d.c. plasma CVD

    NASA Astrophysics Data System (ADS)

    Fleaca, Claudiu Teodor; Le Normand, François

    2014-02-01

    Different carbon nanotubes or nanofibers (CNTs or CNFs) assemblies were obtained using Ni catalyst deposited by Pulsed Laser Deposition (PLD) on TiN/Si(1 0 0) substrate from a H2/C2H2 mixture using plasma emerging from triode configured electrodes with two pairs of intercalated incandescent filaments at 1 kPa and 700 °C. In the presence of a relative intense plasma (54 W power), a dense CNT carpet was grown. The TEM images revealed the presence of elongated yet contorted 10-15 nm diameter CNTs with encapsulated Ni particles at their tips. Using a low plasma power (8 W) in similar conditions and from the same catalyst, a different morphology resulted: few self-sustained long fibrils (diameter around 1 μm) which are curved under the action of their own weight containing compacted CNTs/CNFs and (only in the confined zones near the lateral edges) 50-200 nm thick filaments presenting buds-like structures and Y-shape junctions.

  5. Flow field velocity measurements for non-isothermal systems. [of chemically reactive flow inside fused silica CVD reactor vessels

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Experimental techniques which can be potentially utilized to measure the gas velocity fields in nonisothermal CVD systems both in ground-based and space-based investigations are considered. The advantages and disadvantages of a three-component laser velocimetry (LV) system that was adapted specifically for quantitative determination of the mixed convective flows in a chamber for crystal growth and film formation by CVD are discussed. Data from a horizontal research CVD reactor indicate that current models for the effects of thermophoretic force are not adequate to predict the thermophoretic bias in arbitrary flow configurations. It is concluded that LV techniques are capable of characterizing the fluid dynamics of a CVD reactor at typical growth temperatures. Thermal effects are shown to dominate and stabilize the fluid dynamics of the reactor. Heating of the susceptor increases the gas velocities parallel to the face of a slanted susceptor by up to a factor of five.

  6. Thin CVD Coating Protects Titanium Aluminide Alloys

    NASA Technical Reports Server (NTRS)

    Clark, Ronald; Wallace, Terryl; Cunnington, George; Robinson, John

    1994-01-01

    Feasibility of using very thin CVD coatings to provide both protection against oxidation and surfaces of low catalytic activity for thin metallic heat-shield materials demonstrated. Use of aluminum in compositions increases emittances of coatings and reduces transport of oxygen through coatings to substrates. Coatings light in weight and applied to foil-gauge materials with minimum weight penalties.

  7. Local determination of ionospheric plasma convection from coherent scatter radar data using the SECS technique

    NASA Astrophysics Data System (ADS)

    Amm, O.; Grocott, A.; Lester, M.; Yeoman, T. K.

    2010-03-01

    A new technique for merging line-of-sight (LOS) data of the ionospheric plasma convection velocity, as obtained from coherent scatter radars, into a full velocity vector field on a sphere is presented. This technique is based on the expansion into Spherical Elementary Current Systems (SECS) which have been successfully applied to many other problems in ionosphere-magnetosphere physics. Despite their name mentioning currents for historical reasons, SECS can be used as basis functions for any continuously differentiable vector field on a sphere. In contrast to the traditional modeling of the radar data with spherical harmonics over the whole auroral zone, the new technique does not require any “a priori” model input but relies solely on the measured data, nor does it need any explicit boundary conditions to be specified. The new technique is designed to be applied locally to areas where sufficient radar backscatter exists. The analysis area that satisfies this condition may have any shape and is not limited to, e.g., spherical caps. A test with synthetic data shows that the method performs excellently (less than 5% relative error) if 25% or more of the optimal coverage of input data are actually available as backscatter data, with respect to the scale on which the results for the velocity vector field are desired to be obtained. Still if only 10% of the optimal coverage of input data are available, the technique performs fairly well with a relative error of ˜12%. A second test with real LOS input data from the SuperDARN radars shows that on such a local area with sufficient backscatter, our new technique is able to reproduce mesoscale details of the LOS data significantly better than the current standard analysis based on the technique of Ruohoniemi and Baker (1998) which processes the radar data on the whole auroral zone. While the new technique is presented here for the application with LOS radar data, it can be applied for merging any kind of vector component

  8. CVD-produced boron filaments

    NASA Technical Reports Server (NTRS)

    Wawner, F. E.; Debolt, H. E.; Suplinskas, R. D.

    1980-01-01

    A technique for producing boron filaments with an average tensile strength of 6.89 GPa has been developed which involves longitudinal splitting of the filament and core (substrate) removal by etching. Splitting is accomplished by a pinch wheel device which continuously splits filaments in lengths of 3.0 m by applying a force to the side of the filament to create a crack which is then propagated along the axis by a gentle sliding action. To facilitate the splitting, a single 10 mil tungsten substrate is used instead of the usual 0.5 mil substrate. A solution of hot 30% hydrogen peroxide is used to remove the core without attacking the boron. An alternative technique is to alter the residual stress by heavily etching the filament. Average strengths in the 4.83-5.52 GPa range have been obtained by etching an 8 mil filament to 4 mil.

  9. Measurement of xenon plasma properties in an ion thruster using laser Thomson scattering technique

    SciTech Connect

    Yamamoto, N.; Tomita, K.; Sugita, K.; Kurita, T.; Nakashima, H.; Uchino, K.

    2012-07-15

    This paper reports on the development of a method for measuring xenon plasma properties using the laser Thomson scattering technique, for application to ion engine system design. The thresholds of photo-ionization of xenon plasma were investigated and the number density of metastable atoms, which are photo-ionized by a probe laser, was measured using laser absorption spectroscopy, for several conditions. The measured threshold energy of the probe laser using a plano-convex lens with a focal length of 200 mm was 150 mJ for a xenon mass flow rate of 20 {mu}g/s and incident microwave power of 6 W; the probe laser energy was therefore set as 80 mJ. Electron number density was found to be (6.2 {+-} 0.4) Multiplication-Sign 10{sup 17} m{sup -3} and electron temperature was found to be 2.2 {+-} 0.4 eV at a xenon mass flow rate of 20 {mu}g/s and incident microwave power of 6 W. The threshold of the probe laser intensity against photo-ionization in a miniature xenon ion thruster is almost constant for various mass flow rates, since the ratio of population of the metastable atoms to the electron number density is little changed.

  10. Measurement of xenon plasma properties in an ion thruster using laser Thomson scattering technique.

    PubMed

    Yamamoto, N; Tomita, K; Sugita, K; Kurita, T; Nakashima, H; Uchino, K

    2012-07-01

    This paper reports on the development of a method for measuring xenon plasma properties using the laser Thomson scattering technique, for application to ion engine system design. The thresholds of photo-ionization of xenon plasma were investigated and the number density of metastable atoms, which are photo-ionized by a probe laser, was measured using laser absorption spectroscopy, for several conditions. The measured threshold energy of the probe laser using a plano-convex lens with a focal length of 200 mm was 150 mJ for a xenon mass flow rate of 20 μg/s and incident microwave power of 6 W; the probe laser energy was therefore set as 80 mJ. Electron number density was found to be (6.2 ± 0.4) × 10(17) m(-3) and electron temperature was found to be 2.2 ± 0.4 eV at a xenon mass flow rate of 20 μg/s and incident microwave power of 6 W. The threshold of the probe laser intensity against photo-ionization in a miniature xenon ion thruster is almost constant for various mass flow rates, since the ratio of population of the metastable atoms to the electron number density is little changed. PMID:22852670

  11. The use of laser-induced plasma spectroscopy technique for the characterization of boiler tubes

    NASA Astrophysics Data System (ADS)

    Nicolas, G.; Mateo, M. P.; Yañez, A.

    2007-12-01

    The present work focuses on the characterization of boiler tube walls using laser-induced plasma spectroscopy technique with visual inspection by optical and scanning electron microscopy of the cross-sections of these tubes. In a watertube boiler, water runs through tubes that are surrounded by a heating source. As a result, the water is heated to very high temperatures, causing accumulation of deposits on the inside surfaces of the tubes. These deposits play an important role in the efficiency of the boiler tube because they produce a reduction of the boiler heat rate and an increase in the number of tube failures. The objectives are to determine the thickness and arrangement of deposits located on the highest heat area of the boiler and compare them with tube parts where the heat flux is lower. The major deposits found were copper and magnetite. These deposits come mainly from the boiler feedwater and from the reaction between iron and water, and they do not form on the tube walls at a uniform rate over time. Their amount depends on the areas where they are collected. A Nd:YAG laser operating at 355 nm has been used to perform laser-induced plasma spectra and depth profiles of the deposits.

  12. Non-thermal plasma as preparative technique to evaluate olive oil adulteration.

    PubMed

    Van Durme, Jim; Vandamme, Jeroen

    2016-10-01

    In recent years adulteration of pure extra virgin olive oil (EVOO) with other types of vegetable oils has become an important issue. In this study, non-thermal plasma (NTP) is investigated as an innovative preparative analytical technique enabling classification of adulterated olive oil from an ascertained authentic batch of olive oil in a more sensitive manner. Non-thermal plasma discharges are a source of highly oxidative species such as singlet oxygen, and atomic oxygen. It was assumed that NTP-induced oxidation triggers unique lipid oxidation mechanisms depending on the specific composition of the oil matrix and minor constituents. In this work EVOO samples were adulterated with sunflower oil (1-3%) and submitted to NTP treatment. Results showed that while untreated samples could not be classified from the authentic olive oil reference, NTP treatments of 60min (Ar/O2 0.1%) on the oil batches resulted in the formation of a unique set of secondary volatile lipid oxidation products enabling classification of adulterated oil samples. PMID:27132839

  13. CVD Diamond Detector Stability Issues for Operation at the National Ignition Facility

    SciTech Connect

    Schmid, G J; Koch, J A; Moran, M J; Lerche, R A; Izumi, N; Phillips, T W; Glebov, V Y; Sangster, T C; Stoeckl, C

    2003-08-22

    Synthetic diamond crystals produced by the Chemical Vapor Deposition (CVD) technique can serve as fast, radiation hard, neutron sensors for the National Ignition Facility (NIF). Here we explore the stability issues, such as charge trapping and high-flux saturation, that will be relevant to operation at the NIF.

  14. Novel 3D Tissue Engineered Bone Model, Biomimetic Nanomaterials, and Cold Atmospheric Plasma Technique for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Wang, Mian

    This thesis research is consist of four chapters, including biomimetic three-dimensional tissue engineered nanostructured bone model for breast cancer bone metastasis study (Chapter one), cold atmospheric plasma for selectively ablating metastatic breast cancer (Chapter two), design of biomimetic and bioactive cold plasma modified nanostructured scaffolds for enhanced osteogenic differentiation of bone marrow derived mesenchymal stem cells (Chapter three), and enhanced osteoblast and mesenchymal stem cell functions on titanium with hydrothermally treated nanocrystalline hydroxyapatite/magnetically treated carbon nanotubes for orthopedic applications (Chapter four). All the thesis research is focused on nanomaterials and the use of cold plasma technique for various biomedical applications.

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

    SciTech Connect

    Koynov, S.; Grebner, S.; Schwarz, R.; Vassilev, L.; Sieber, I.; Schmidt, M.; Fuhs, W.

    1997-07-01

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

  16. The MDF technique for the analysis of tokamak edge plasma fluctuations

    NASA Astrophysics Data System (ADS)

    Lafouti, M.; Ghoranneviss, M.; Meshkani, S.; Elahi, A. Salar; Elahi

    2014-02-01

    Tokamak edge plasma was analyzed by applying the multifractal detrend fluctuation analysis (MF-DFA) technique. This method has found wide application in the analysis of correlations and characterization of scaling behavior of the time-series data in physiology, finance, and natural sciences. The time evolution of the ion saturation current (Is ), the floating potential fluctuation (Vf ), the poloidal electric field (Ep ), and the radial particle flux (Γ r ) has been measured by using a set of Langmuir probes consisting of four tips on the probe head. The generalized Hurst exponents (h(q)), local fluctuation function (Fq(s)), the Rényi exponents (τ(q)) as well as the multifractal spectrum f(α h ) have been calculated by applying the MF-DFA method to Is , Vf , and the magnetohydrodynamic (MHD) fluctuation signal. Furthermore, we perform the shuffling and the phase randomization techniques to detect the sources of multifractality. The nonlinearity shape of τ(q) reveals a multifractal behavior of the time-series data. The results show that in the presence of biasing, Is , Vf , Ep , and Γ r reduce about 25%, 90%, 70%, and 50%, respectively, compared with the situation with no biasing. Also, they reduce about 15%, 90%, 35%, and 25%, respectively, after resonant helical magnetic field (RHF) application. In the presence of biasing or RHF, the amplitude of the power spectrum of Is , Vf , Γ r , and MHD activity reduce remarkably in all the ranges of frequency, while their h(q) increase. The values of h(q) have been restricted between 0.6 and 0.68. These results are evidence of the existence of long-range correlations in the plasma edge turbulence. They also show the self-similar nature of the plasma edge fluctuations. Biasing or RHF reduces the amount of Fq(s). The multifractal spectrum width of Is , Vf , and MHD fluctuation amplitude reduce about 60%, 70%, and 42%, respectively, by applying biasing. In the presence of RHF, their width reduces about 60%, 85%, and 75

  17. Effect of dry oxidation on the energy gap and chemical composition of CVD graphene on nickel

    NASA Astrophysics Data System (ADS)

    Aria, Adrianus I.; Gani, Adi W.; Gharib, Morteza

    2014-02-01

    The findings presented herein show that the electronic properties of CVD graphene on nickel can be altered from metallic to semiconducting by introducing oxygen adsorbates via UV/ozone or oxygen plasma treatment. These properties can be partially recovered by removing the oxygen adsorbates via vacuum annealing treatment. The effect of oxidation is studied by scanning tunneling microscopy/spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS). As probed by STM/STS, an energy gap opening of 0.11-0.15 eV is obtainable as the oxygen/carbon atomic ratio reaches 13-16%. The corresponding XPS spectra show a significant monotonic increase in the concentration of oxygenated functional groups due to the oxidation treatments. This study demonstrates that the opening of energy gap in CVD graphene can be reasonably controlled by a combination of UV/ozone or oxygen plasma treatment and vacuum annealing treatment.

  18. Synthesis of Few-Layer Graphene Using DC PE-CVD

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Hyuk; Castro, Edward Joseph D.; Hwang, Yong Gyoo; Lee, Choong Hun

    2011-12-01

    Few layer graphene (FLG) had been successfully grown on polycrystalline Ni films or foils on a large scale using DC Plasma Enhanced Chemical Vapor Deposition (DC PE-CVD) as a result of the Raman spectra drawn out of the sample. The size of graphene films is dependent on the area of the Ni film as well as the DC PE-CVD chamber size. Synthesis time has an effect on the quality of graphene produced. However, further analysis and experiments must be pursued to further identify the optimum settings and conditions of producing better quality graphene. Applied plasma voltage on the other hand, had an influence on the minimization of defects in the graphene grown. It has also presented a method of producing a free standing PMMA/graphene membrane on a FeCl3(aq) solution which could then be transferred to a desired substrate.

  19. Hydrogen and hydrogen-related defects in CVD diamond

    SciTech Connect

    Rutledge, K.M.M.

    1998-12-31

    Hydrogen is a detrimental impurity in many chemical vapor deposited (CVD) materials, particularly those involved in electronic or optical applications. For example, active hydrogen defects have been observed in materials such as silicon, Si, gallium arsenide, GaAs, and diamond, C, thin films. Hydrogen and its related defects can be identified, quantified, and observed using magnetic resonance techniques. These techniques allow a unique quantitative, non-destructive view of hydrogen in the solid-state. Nuclear magnetic resonance (NMR) is used to study hydrogenated defects directly, while electron paramagnetic resonance (EPR) is used to observe hydrogen associated with paramagnetic defects. These observations can enhance understanding of the effects of hydrogen incorporation on the properties of such materials.

  20. Leakage current measurements of a pixelated polycrystalline CVD diamond detector

    NASA Astrophysics Data System (ADS)

    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 pixelated detector arrays. The anode and cathode contacts are realised by depositing gold to produce ohmic contacts. Measurements of I-V characteristics were performed to study the material uniformity. The bias voltage is stepped from -1000V to 1000V to investigate the variation of leakage current from pixel to pixel. Bulk leakage current is measured to be less than 1nA.

  1. The validation of the Z-Scan technique for the determination of plasma glucose

    NASA Astrophysics Data System (ADS)

    Alves, Sarah I.; Silva, Elaine A. O.; Costa, Simone S.; Sonego, Denise R. N.; Hallack, Maira L.; Coppini, Ornela L.; Rowies, Fernanda; Azzalis, Ligia A.; Junqueira, Virginia B. C.; Pereira, Edimar C.; Rocha, Katya C.; Fonseca, Fernando L. A.

    2013-11-01

    Glucose is the main energy source for the human body. The concentration of blood glucose is regulated by several hormones including both antagonists: insulin and glucagon. The quantification of glucose in the blood is used for diagnosing metabolic disorders of carbohydrates, such as diabetes, idiopathic hypoglycemia and pancreatic diseases. Currently, the methodology used for this determination is the enzymatic colorimetric with spectrophotometric. This study aimed to validate the use of measurements of nonlinear optical properties of plasma glucose via the Z-Scan technique. For this we used samples of calibrator patterns that simulate commercial samples of patients (ELITech ©). Besides calibrators, serum glucose levels within acceptable reference values (normal control serum - Brazilian Society of Clinical Pathology and Laboratory Medicine) and also overestimated (pathological control serum - Brazilian Society of Clinical Pathology and Laboratory Medicine) were used in the methodology proposal. Calibrator dilutions were performed and determined by the Z-Scan technique for the preparation of calibration curve. In conclusion, Z-Scan method can be used to determinate glucose levels in biological samples with enzymatic colorimetric reaction and also to apply the same quality control parameters used in biochemistry clinical.

  2. Vitamin D and risk of CVD: a review of the evidence.

    PubMed

    Fry, Catherine M; Sanders, Thomas A B

    2015-08-01

    This review summarises evidence for an association between vitamin D status and CVD and the mechanisms involved. Vitamin D3 is predominantly provided by the action of UVB from sunlight on skin. Average UK diets supply 2-3 μg/d vitamin D but diets containing at least one portion of oily fish per week supply about 7 μg/d. Pharmacological doses of vitamin D2 (bolus injection of 7500 μg or intakes >50 μg/d) result in a smaller increase in plasma 25(OH)D than those of D3 but physiological doses 5-25 μg/d seem equivalent. Plasma 25(OH)D concentrations are also influenced by clothing, obesity and skin pigmentation. Up to 40 % of the population have plasma 25(OH)D concentrations <25 nmol/l in the winter compared with <10 % in the summer. The relative risk of CVD death is 1·41 (95 % CI 1·18, 1·68) greater in the lowest quintile of plasma 25(OH)D according to meta-analysis of prospective cohort studies. Acute deficiency may inhibit insulin secretion and promote inflammation thus increasing the risk of plaque rupture and arterial thrombosis. Chronic insufficiency may increase arterial stiffness. There is no evidence to support claims of reduced CVD from existing trials with bone-related health outcomes where vitamin D was usually co-administered with calcium. Although several trials with cardiovascular endpoints are in progress, these are using pharmacological doses. In view of the potential toxicity of pharmacological doses, there remains a need for long-term trials of physiological doses of D2 and D3 with CVD incidence as the primary outcome. PMID:25697289

  3. Scrolling of Suspended CVD Graphene Sheets

    NASA Astrophysics Data System (ADS)

    Martynov, Oleg; Yeom, Sinchul; Bockrath, Marc; UC: Riverside Team

    Carbon Nanoscrolls, one dimensional spiral forms of graphitic carbon, have attracted recent interest due to their novel proposed properties. Although various production methods and studies of carbon nanoscrolls have been performed, low yield and poor controllability of their synthesis have slowed progress in this field. Suspended graphene membranes and carbon nanotubes have been predicted as promising systems for the formation of graphene scrolls. We have suspended chemical vapor deposition (CVD)-grown graphene over large holes in a Si/SiO2 substrate to make suspended membranes upon which nanotubes are placed. Initial experiments have been performed showing that tears or cuts of the suspended sheet can initiate scrolling. Our latest progress towards carbon nanotube initiated formation of graphene scrolls and suspended CVD graphene scrolling, along with measurements of these novel structures will be presented.

  4. Enhanced nonlinear iterative techniques applied to a non-equilibrium plasma flow

    SciTech Connect

    Knoll, D.A.; McHugh, P.R.

    1996-12-31

    We study the application of enhanced nonlinear iterative methods to the steady-state solution of a system of two-dimensional convection-diffusion-reaction partial differential equations that describe the partially-ionized plasma flow in the boundary layer of a tokamak fusion reactor. This system of equations is characterized by multiple time and spatial scales, and contains highly anisotropic transport coefficients due to a strong imposed magnetic field. We use Newton`s method to linearize the nonlinear system of equations resulting from an implicit, finite volume discretization of the governing partial differential equations, on a staggered Cartesian mesh. The resulting linear systems are neither symmetric nor positive definite, and are poorly conditioned. Preconditioned Krylov iterative techniques are employed to solve these linear systems. We investigate both a modified and a matrix-free Newton-Krylov implementation, with the goal of reducing CPU cost associated with the numerical formation of the Jacobian. A combination of a damped iteration, one-way multigrid and a pseudo-transient continuation technique are used to enhance global nonlinear convergence and CPU efficiency. GMRES is employed as the Krylov method with Incomplete Lower-Upper(ILU) factorization preconditioning. The goal is to construct a combination of nonlinear and linear iterative techniques for this complex physical problem that optimizes trade-offs between robustness, CPU time, memory requirements, and code complexity. It is shown that a one-way multigrid implementation provides significant CPU savings for fine grid calculations. Performance comparisons of the modified Newton-Krylov and matrix-free Newton-Krylov algorithms will be presented.

  5. Reuse of healing abutments: an in vitro model of plasma cleaning and common sterilization techniques.

    PubMed

    Vezeau, P J; Keller, J C; Wightman, J P

    2000-01-01

    The reuse of transgingival healing abutments has been advocated by several implant manufacturers, but cleaning and sterilization procedures to yield clean and optimal surfaces have yet to be developed. The objective of this in vitro project was to investigate various cleaning and sterilization regimens for the removal of biological debris to support reattachment of subgingival connective tissue. Simulated clinical healing abutment surfaces were exposed to culture medium with serum for 1 hour to simulate biological exposure. Simulated healing abutment surfaces not contaminated by serum were used to represent the "as-is" healing abutment surface without prior in vivo use. The discs were cleaned with detergent before sterilization by ultraviolet light (UV) or steam autoclaving (AC) both with and without 1- and 5-minute plasma cleaning (PC). A series of surface analytical techniques (XPS, AES, and surface contact angles) and in vitro analysis of cell attachment and spreading using gingival fibroblasts were performed. After exposure to the simulated biological conditions, clinical cleaning followed by UV resulted in contaminated surfaces and relatively high levels of cell attachment. PC before UV treatment enhanced surface energetics but did not affect cell attachment and spreading. AC increased surface wetting angles; which were decreased somewhat by previous PC. Cell attachment was significantly reduced by AC. Although some increase in cell attachment after longer plasma cleaning was noted in the AC group, no difference in cell spreading was seen in any AC group. Cell spreading seemed to be less for all AC groups compared with all UV, as-is, and control groups. Although certain cleaning (PC) and sterilization (UV) procedures can be effective for cleaning transgingival healing abutments, those using AC are questionable due to their propensity for organic and inorganic contamination and unfavorable surface alteration. PMID:11307410

  6. Insights in the plasma-assisted growth of carbon nanotubes through atomic scale simulations: effect of electric field.

    PubMed

    Neyts, Erik C; van Duin, Adri C T; Bogaerts, Annemie

    2012-01-18

    Carbon nanotubes (CNTs) are nowadays routinely grown in a thermal CVD setup. State-of-the-art plasma-enhanced CVD (PECVD) growth, however, offers advantages over thermal CVD. A lower growth temperature and the growth of aligned freestanding single-walled CNTs (SWNTs) makes the technique very attractive. The atomic scale growth mechanisms of PECVD CNT growth, however, remain currently entirely unexplored. In this contribution, we employed molecular dynamics simulations to focus on the effect of applying an electric field on the SWNT growth process, as one of the effects coming into play in PECVD. Using sufficiently strong fields results in (a) alignment of the growing SWNTs, (b) a better ordering of the carbon network, and (c) a higher growth rate relative to thermal growth rate. We suggest that these effects are due to the small charge transfer occurring in the Ni/C system. These simulations constitute the first study of PECVD growth of SWNTs on the atomic level. PMID:22126536

  7. Mutual relation among lattice distortion, Hall effect property and band edge cathodoluminescence of heavily-boron-doped microwave-plasma CVD diamond films homoepitaxially grown on vicinal (001) high-pressure/high-temperature-synthesized Ib substrates

    NASA Astrophysics Data System (ADS)

    Mori, Reona; Maida, Osamu; Ito, Toshimichi

    2015-04-01

    We have investigated properties of heavily-B-doped diamond (HBD) films homoepitaxially grown with boron-to-carbon (B/C) mole ratios ranging from 1000 to 5000 ppm in the source gas mainly by using X-Ray diffraction (XRD), cathodoluminescence (CL), and Hall effect measurements. Each HBD layer was deposited on a vicinal (001) substrate of high-pressure/high-temperature synthesized Ib-type diamond with 5° misorientation angle by means of high-power-density microwave-plasma chemical-vapor-deposition method with a source gas composed of 4% CH4 in H2 and H2-diluted B(CH3)3. XRD data indicated that the lattice constant of the B-doped layer slightly decreased for the B/C ratios≤3000 ppm while slightly increasing for that of 5000 ppm, suggesting that for the latter HBD sample a part of the incorporated B atoms behaved differently from the remaining other B atoms. By contrast the Hall data indicated that all the HBD samples had a degenerate feature only at temperatures well below room temperature (RT), above which a semiconducting feature was evident, and that the density of the degenerate holes steeply increased from 1.3×1019 to 1.2×1021 cm-3 with increases in the incorporated B density, [B], from 1.2×1020 to 5.9×1020 cm-3. This drastic change in the hole density strongly suggested the presence of a [B]-dependent impurity band. Their evident near-band-edge CL spectra taken at RT and 85 K demonstrated that radiative transition features in the HBD layers considerably varied for the B/C ratios studied. The CL peaks were consistently assigned by assuming both the presence of an impurity band and a slight bandgap shrinkage. These observed features are discussed in relation to the energy separation between the low-mobility impurity band assumed and the valence band in the high-quality HBD layer which are not merged in energy.

  8. Raman spectroscopic investigation of polycrystalline structures of CVD-grown graphene by isotope labeling

    NASA Astrophysics Data System (ADS)

    Wang, Shengnan; Suzuki, Satoru; Hibino, Hiroki

    2014-10-01

    Topological defects, such as point defects, dislocations and grain boundaries, have a dramatic influence on the chemical and physical properties of large-scale graphene grown by chemical vapor deposition (CVD) method. Here we demonstrate the Raman visualization of polycrystalline structures in an isotopically modified CVD graphene. By means of the reversible reaction of methane on a copper catalyst, the etching of 12C-lattice and surface deposition of 13C-atoms occur in CVD graphene by sequentially introducing hydrogen and isotopic methane after standard growth of graphene with full monolayer coverage. Spatial Raman spectroscopic mapping on labeled graphene reveals pronounced network-like 13C-rich regions, which are further identified to exist along the grain boundaries of graphene by low-energy electron microscopy. The structural defects inside the graphene grains are also targeted in the isotope labeling process. Our work opens a new way to investigate multiple grain structures in CVD graphene with a simple spectroscopic technique.Topological defects, such as point defects, dislocations and grain boundaries, have a dramatic influence on the chemical and physical properties of large-scale graphene grown by chemical vapor deposition (CVD) method. Here we demonstrate the Raman visualization of polycrystalline structures in an isotopically modified CVD graphene. By means of the reversible reaction of methane on a copper catalyst, the etching of 12C-lattice and surface deposition of 13C-atoms occur in CVD graphene by sequentially introducing hydrogen and isotopic methane after standard growth of graphene with full monolayer coverage. Spatial Raman spectroscopic mapping on labeled graphene reveals pronounced network-like 13C-rich regions, which are further identified to exist along the grain boundaries of graphene by low-energy electron microscopy. The structural defects inside the graphene grains are also targeted in the isotope labeling process. Our work opens a new

  9. Novel plasma immersion ion implantation and deposition hardware and technique based on high power pulsed magnetron discharge

    SciTech Connect

    Wu Zhongzhen; Tian Xiubo; Shi Jingwei; Wang Zeming; Gong Chunzhi; Yang Shiqin; Chu, Paul K.

    2011-03-15

    A novel plasma immersion ion implantation technique based on high power pulsed magnetron sputtering (HPPMS) discharge that can produce a high density metal plasma is described. The metal plasma is clean and does not suffer from contamination from macroparticles, and the process can be readily scaled up for industrial production. The hardware, working principle, and operation modes are described. A matching circuit is developed to modulate the high-voltage and HPPMS pulses to enable operation under different modes such as simultaneous implantation and deposition, pure implantation, and selective implantation. To demonstrate the efficacy of the system and technique, CrN films with a smooth and dense surface without macroparticles were produced. An excellent adhesion with a critical load of 59.9 N is achieved for the pure implantation mode.

  10. Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

    DOE PAGESBeta

    Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Lau, Y. Y.; Gilgenbach, R. M.

    2015-11-19

    In this study, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ~600 kA with ~200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. As amore » result, this technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.« less

  11. Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

    NASA Astrophysics Data System (ADS)

    Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Lau, Y. Y.; Gilgenbach, R. M.

    2015-11-01

    In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ˜600 kA with ˜200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.

  12. Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents.

    PubMed

    Yager-Elorriaga, D A; Steiner, A M; Patel, S G; Jordan, N M; Lau, Y Y; Gilgenbach, R M

    2015-11-01

    In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ∼600 kA with ∼200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines. PMID:26628134

  13. Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

    SciTech Connect

    Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Lau, Y. Y.; Gilgenbach, R. M.

    2015-11-19

    In this study, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ~600 kA with ~200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. As a result, this technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.

  14. Tomography of homogenized laser-induced plasma by Radon transform technique

    NASA Astrophysics Data System (ADS)

    Eschlböck-Fuchs, S.; Demidov, A.; Gornushkin, I. B.; Schmid, T.; Rössler, R.; Huber, N.; Panne, U.; Pedarnig, J. D.

    2016-09-01

    Tomography of a laser-induced plasma in air is performed by inverse Radon transform of angle-resolved plasma images. Plasmas were induced by single laser pulses (SP), double pulses (DP) in collinear geometry, and by a combination of single laser pulses with pulsed arc discharges (SP-AD). Images of plasmas on metallurgical steel slags were taken at delay times suitable for calibration-free laser-induced breakdown spectroscopy (CF-LIBS). Delays ranged from few microseconds for SP and DP up to tens of microseconds for SP-AD excitation. The white-light and the spectrally resolved emissivity ε(x,y,z) was reconstructed for the three plasma excitation schemes. The electron number density Ne(x,y,z) and plasma temperature Te(x,y,z) were determined from Mg and Mn emission lines in reconstructed spectra employing the Saha-Boltzmann plot method. The SP plasma revealed strongly inhomogeneous emissivity and plasma temperature. Re-excitation of plasma by a second laser pulse (DP) and by an arc discharge (SP-AD) homogenized the plasma and reduced the spatial variation of ε and Te. The homogenization of a plasma is a promising approach to increase the accuracy of calibration-free LIBS analysis of complex materials.

  15. Comparison of Fabrication Techniques for Micro-Scale Spark Gap Plasma Switches

    NASA Astrophysics Data System (ADS)

    Burnette, Matthew; Staack, David

    2014-10-01

    Microplasma spark gaps with 2D geometries were fabricated by two techniques on alumina, first using photolithography and metal sputtering with thicknesses of hundreds of nanometers, and second using thermal-spray several microns thick, but with lower feature resolution. Several high temperature metals were tested as electrode material for the microplamsa device, including tungsten and chromium; however the chromium samples were not robust enough, eroding away too quickly for extensive testing. Scanning electron microscope (SEM) images were taken before and after testing to determine the wear on the samples. The sputtered tungsten thin films and thermal-spray deposited nickel films on alumina were compared after testing in 1 atm of helium running for one hour at a current of 1 mA. Slight wear and discoloration were noted on the anodes, yet significant erosion occurred on the cathodes; no wear was noted on the alumina. The thermally-sprayed nickel sample had the least wear, while the thin tungsten sample had the most wear. Discoloration was also seen on the nearby floating-voltage electrodes despite not being a part of the circuit, most likely due to heating. As the electrodes eroded, the plasma attachment point moved unpredictably. This work was supported in part by the Department of Defense Army Research Office under Grant W911NF1210007.

  16. A novel technique for the numerical simulation of hot collision-free plasma; Vlasov hybrid simulation

    SciTech Connect

    Nunn, D. )

    1993-09-01

    This paper reports a simple novel technique for the numerical simulation of hot collision-free plasmas. The method is termed Vlasov hybrid simulation (VHS). A time varying phase space simulation box and grid are defined, and the phase fluid within the box is filled with simulation particles. The distribution function F (or [sigma]F) is defined on the phase trajectory of each particle. At each timestep F (or [sigma]F) is interpolated from the simulation particles onto the phase space grid. Particles are followed continuously until exiting from the phase box and are not constantly recreated at phase space grid points. The algorithm is very efficient, stable, and has low noise levels. Distribution function fine structure is tolerated and the formalism does not require diffusion of the distribution function. The VHS method is particularly valuable when the flux of phase fluid across the phase box boundary is significant. In this case VHS codes have a dynamic population of particles-giving great efficiency gains over PIC codes with fixed particle populations. The VHS method has been applied to the numerical simulation of triggered VLF emissions in the magnetosphere and gives results in close agreement with observations. 27 refs., 13 figs., 1 tab.

  17. Coupled Electro-Thermo-Mechanical Finite Element Modeling of the Spark Plasma Sintering Technique

    NASA Astrophysics Data System (ADS)

    Schwertz, Maxime; Katz, Aurélien; Sorrel, Emmanuel; Lemonnier, Sébastien; Barraud, Elodie; Carradò, Adele; d'Astorg, Sophie; Leriche, Anne; Nardin, Michel; Vallat, Marie-France; Kosior, Francis

    2016-04-01

    This paper deals with the development of a novel and predictive finite element method (FEM) model coupling electrical, thermal, and mechanical time-dependent contributions for simulating the behavior of a powdery material submitted to a spark plasma sintering (SPS) treatment by using COMSOL Multiphysics® software. The original approach of this work lies in the use of the modified Cam-Clay model to solve the mechanical phenomenon occurring during a SPS sintering treatment. As the powder properties and behaviors are different from the final sintered material and display a nonlinear dependence as a function of temperature and pressure, the model includes the description of the sample densification. In this way, numerical and experimental results obtained on conductive model material (aluminum) such as temperature, stress distributions, and shrinkage, were directly compared. This FEM model demonstrated the ability to predict the powder behavior during temperature-controlled experiments precisely, as they are typically performed in the SPS technique. This approach exhibits a remarkable level of interest because it takes into account the nature of the material and also the specific characteristics of the powder studied.

  18. On the OES line-ratio technique in argon and argon-containing plasmas

    NASA Astrophysics Data System (ADS)

    Siepa, Sarah; Danko, Stephan; Tsankov, Tsanko V.; Mussenbrock, Thomas; Czarnetzki, Uwe

    2014-11-01

    Optical emission spectroscopy is used to investigate capacitively coupled argon and argon-hydrogen-silane plasmas. The argon collisional-radiative model (CRM) used to extract the electron density and temperature from the spectra is presented. The electron energy distribution function, which is an input parameter to the model, is discussed in detail. Its strong variation with pressure is found to significantly influence the results for the (effective) temperature. For the analysis of the spectra the common line-ratio technique is applied. Special attention is paid to the choice of lines and a pair of line-ratios for optimum accuracy is suggested. For the argon gas mixture at high partial pressure of the admixed molecular gases the CRM reduces to a corona-like model, extended by a quenching term. The line-ratio method is found to fail under these conditions due to the strong depopulation of the argon 1s states. As a consequence, individual line intensities have to be used and an absolute calibration is required. An easy calibration method, which relies on the results obtained by the line-ratio method in pure argon, is proposed and applied.

  19. Nutrigenetics, plasma lipids, and cardiovascular risk

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cardiovascular disease (CVD) results from complex interactions between genetic and environmental factors. The evidence supports that gene-environment interactions modulate plasma lipid concentrations and potentially CVD risk. Several genes (eg, apolipoprotein A-I and A-IV, apolipoprotein E, and he...

  20. Dimensionless Numbers Expressed in Terms of Common CVD Process Parameters

    NASA Technical Reports Server (NTRS)

    Kuczmarski, Maria A.

    1999-01-01

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

  1. Interfaces in nano-/microcrystalline multigrade CVD diamond coatings.

    PubMed

    Almeida, Flávia A; Salgueiredo, Ermelinda; Oliveira, Filipe J; Silva, Rui F; Baptista, Daniel L; Peripolli, Suzana B; Achete, Carlos A

    2013-11-27

    The interfaces of multilayered CVD diamond films grown by the hot-filament technique were characterized with high detail using HRTEM, STEM-EDX, and EELS. The results show that at the transition from micro- (MCD) to nanocrystalline diamond (NCD), a thin precursor graphitic film is formed, irrespectively of the NCD gas chemistry used (with or without argon). On the contrary, the transition of the NCD to MCD grade is free of carbon structures other than diamond, the result of a higher substrate temperature and more abundant atomic H in the gas chemistry. At those transitions WC nanoparticles could be found due to contamination from the filament, being also present at the first interface of the MCD layer with the silicon nitride substrate. PMID:24164667

  2. A controlled atmosphere tube furnace was designed for thermal CVD

    NASA Astrophysics Data System (ADS)

    Rashid, M.; Bhatti, J. A.; Hussain, F.; Imran, M.; Khawaja, I. U.; Chaudhary, K. A.; Ahmad, S. A.

    2013-06-01

    High quality materials were used for the fabrication of hi-tech tube furnace. The furnace was especially suitable for thermal Chemical Vapor Deposition (CVD). High density alumina tube was used for the fabrication of furnace. The tube furnace was found to have three different temperature zones with maximum temperature at central zone was found to be 650°C. The flexible heating tape with capacity of 760°C was wrapped on the tube. To minimize the heat losses, asbestos and glass wool were used on heating tape. The temperature of the tube furnace was controlled by a digital temperature controller had accuracy of ±1°C. Methanol was taken as the representative of hydrocarbon sources, to give thin film of carbon. The a-C: H structure was investigated by conventional techniques using optical microscopy, FT-IR and SEM.

  3. Guiding of high intensity ultrashort laser pulses in plasma channels produced with the dual laser pulse ignitor-heater technique

    SciTech Connect

    Volfbeyn, P.; Leemans, W.P.

    1998-07-01

    The authors present results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme is proposed and experimentally tested in hydrogen and nitrogen. It makes use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a > 5 {times} 10{sup 17} W/cm{sup 2}, 75 fs laser pulse.

  4. RMF concept: a rotating-magnetic-field technique for driving steady plasma currents in compact toroid devices

    SciTech Connect

    McKenna, K.F.

    1980-09-01

    The generation and/or sustaining of a Compact Toroid (CT) configuration using the RMF technique is a relatively new and unknown concept. In this report the basic principles, historical development, and current theoretical understanding of this concept are reviewed. Significant experimental and theoretical results, potential problem areas, and recommendations for the direction of future work are discussed. An illustrative analysis of the application of the RMF technique to a CT reactor is presented. The results of a recent experiment, the Rotamak, in which a Spheromak-like CT plasma was produced using the RMF technique, are presented.

  5. Role of sulodexide in the treatment of CVD.

    PubMed

    Andreozzi, G M

    2014-06-01

    Treatment of vascular diseases should be based on established pathophysiological concepts, and this also applies to chronic venous disease (CVD). On the basis of the latest research in this field, this paper summarizes the most advanced pathophysiological knowledge regarding the hemodynamics of the large veins and of the microcirculation, the endothelial function and inflammation, and the use of sulodexide in the treatment of CVD. The emerging theories on the pathophysiology of CVD consider inflammation, endothelial glycocalyx dysfunction, and the consequent changes in the extracellular matrix to play key roles in the development of CVD, and support a renewed interest in the research and application of sulodexide. As part of active approach to the treatment of CVD including edema and trophic venous alterations, sulodexide could help to alleviate progressive signs and symptoms of disease in any clinical CEAP class of CVD, from C1 to C6. PMID:24936534

  6. New technique in plasma polarimetry: Evolution equations for angular parameters ‘amplitude ratio-phase difference’ of polarization ellipse

    NASA Astrophysics Data System (ADS)

    Kravtsov, Yury A.; Chrzanowski, Janusz; Bieg, Bohdan

    2012-02-01

    New technique is suggested in plasma polarimetry: Differential equations for angular parameters of polarization ellipse, characterizing the amplitude ratio and the phase difference between orthogonal components of the wave field. Equations for angular variables ‘amplitude ratio-phase difference’ are derived, which allow direct calculation of the parameters of polarization ellipse, omitting solutions for the Stokes vector. The simplest analytical solutions are presented for the pure Faraday and the pure Cotton-Mouton effects. Behavior of angular parameters in the homogeneous and inhomogeneous plasmas is illustrated by numerical modeling in conditions when the Faraday and Cotton-Mouton effects are large enough and comparable in strength.

  7. Techniques for the remote sensing of space plasma in the heliosphere via energetic neutral atoms - A review

    NASA Technical Reports Server (NTRS)

    Hsieh, K. C.; Curtis, C. C.; Fan, C. Y.; Gruntman, M. A.

    1992-01-01

    A survey is conducted for state-of-the-art techniques for detecting energetic neutral atoms (ENAs) in the 100-300 keV range, in regions from the heliospheric boundary to the auroral zones where the solar wind plays a crucial role. While ENA spectrometry allows sampling of the mass and energy distributions of a distant plasma, ENA imaging gives a global view of the structures and dynamics of an extended plasma. The ENA instrument designs discussed share many components which exhibit excellent flight performance as elements in charged-particle analyzers for space missions.

  8. Observation of twinning in diamond CVD films

    NASA Astrophysics Data System (ADS)

    Marciniak, W.; Fabisiak, K.; Orzeszko, S.; Rozploch, F.

    1992-10-01

    Diamond particles prepared by dc-glow-discharge enhanced HF-CVD hybrid method, from a mixture of acetone vapor and hydrogen gas have been examined by TEM, RHEED and dark field method of observation. Results suggest the presence of twinned diamond particles, which can be reconstructed by a sequence of twinning operations. Contrary to the 'stick model' of the lattice, very common five-fold symmetry of diamond microcrystals may be obtained by applying a number of edge dislocations rather than the continuous deformation of many tetrahedral C-C bonds.

  9. Study of atmospheric pressure weakly ionized plasma as surface compatibilization technique for improved plastic composites loaded with cellulose based fillers

    NASA Astrophysics Data System (ADS)

    Lekobou, William Pimakouon

    Atmospheric pressure plasmas have gained considerable interest from researchers recently for their unique prospective of engineering surfaces with plasma without the need of vacuum systems. They offer the advantage of low energy consumption, minimal capital cost and their simplicity as compared to conventional low pressure plasmas make them easy to upscale from laboratory to industry size. The present dissertation summarizes results of our attempt at applying atmospheric pressure weakly ionized plasma (APWIP) to the engineering of plastic composites filled with cellulose based substrates. An APWIP reactor was designed and built based on a multipoint-to-grounded ring and screen configurations. The carrier gas was argon and acetylene serves as the precursor molecule. The APWIP reactors showed capability of depositing plasma polymerized coating rich in carbon on substrates positioned within the electrode gap as well as downstream of the plasma discharge into the afterglow region. Our findings show that films grow by forming islands which for prolonged deposition time grow into thin films showing nodules, aggregates of nodules and microspheres. They also show chemical structure similar to films deposited from hydrocarbons with other conventional plasma techniques. The plasma polymerized deposits were used on substrates to modify their surface properties. Results show the surface of wood veneer and wood flour can be finely tuned from hydrophilic to hydrophobic. It was achieved by altering the topography of the surfaces along with their chemical composition. The wettability of wood veneer was investigated with contact angle measurements on capacitive drops and the capillary effect was utilized to assess surface properties of wood flour exposed to the discharges.

  10. Chrome and Zinc Contaminants Removal from Silicon (100) Surfaces by Remote Plasma Cleaning Techniques

    NASA Astrophysics Data System (ADS)

    Lee, Seungwook; Lee, Jaegab; Lee, Chongmu

    2001-06-01

    Removal of Cr and Zn impurities on Si surfaces using remote plasma H2 was investigated. Si surfaces were contaminated intentionally with low-purity acetone. To determine the optimum process conditions, remote plasma H2 cleaning was conducted for various rf powers and plasma exposure times. After remote plasma H2 cleaning, Si surfaces were analyzed by total X-ray reflection fluorescence (TXRF), surface photovoltage (SPV) and atomic force microscopy (AFM). The concentrations of Cr and Zn impurities were reduced by more than a factor of 2 and the minority carrier lifetime increased. Also the root-mean-square (RMS) roughness decreased by more than 30% after the remote plasma H2 cleaning. TXRF analysis results show that remote plasma H2 cleaning is effective in eliminating Cr and Zn impurities from the Si surface only if it is performed under optimum process conditions. AFM analysis results also show that remote plasma H2 cleaning causes no damage to the Si surface. Cr and Zn impurities on the Si substrate are considered to be contaminated as forms of hydroxides, silioxides and oxides on chemical oxides formed during intentional chemical contamination. The removal mechanism of Cr and Zn impurities using remote plasma H2 treatments is proposed for the lift-off during the removal of underlying chemical oxides.