Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session FT3: Graphene Synthesis; Plasma Light Generation |
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Chair: David Smith, General Electric Reserach Room: State D |
Tuesday, November 4, 2014 3:30PM - 3:45PM |
FT3.00001: Utilization of plasmas for graphene synthesis Michael Keidar, Alexey Shashurin Graphene is a one-atom-thick planar sheet of carbon atoms that are densely packed in a honeycomb crystal lattice. Graphene has tremendous range of potential applications ranging from high-speed transistors to electrochemical energy storage devices and biochemical sensors. Methods of graphene synthesis include mechanical exfoliation, epitaxial growth on SiC, CVD and colloidal suspensions. In this work the utilization of plasmas in synthesis process is considered. Types of carbonaceous structures produced by the anodic arc and regions of their synthesis were studied. Ultimate role of substrate temperature and transformations occurring with various carbonaceous structures generated in plasma discharge were considered. Synthesis of well-adhered graphene films on the various substrate materials with controllable flake thickness down to about 2 layers was demonstrated. Optimal synthesis conditions were analyzed. [Preview Abstract] |
Tuesday, November 4, 2014 3:45PM - 4:00PM |
FT3.00002: Functionalization of plasma synthesized advanced carbons Eva Kovacevic, Thibault Labbaye, Johannes Berndt, Thomas Strunskus, Elena Tatarova, Julio Henriques, Chantal Boulmer-Leborgne We report here about experiments concerning the plasma based functionalization of plasma produced carbon nanotubes and free-standing graphenes. The influence of nitrogen and ammonia plasma on the surface properties is investigated, involving the role of the surface temperature on the functionalization procedure. The effect of the plasma treatment on the different carbon materials is analyzed by means of contact angle measurements, near edge x-ray absorption fine spectroscopy (NEXAFS) and XPS. We will discuss the importance of the plasma characteristics for the formation of amino groups and nitrogen incorporation in the material. The important issues concern: the formation of dangling bonds, destructive effects of plasma-surface interactions and recovery of the surfaces. [Preview Abstract] |
Tuesday, November 4, 2014 4:00PM - 4:15PM |
FT3.00003: Controlled synthesis and electrocatalytic characteristics of Pt nanoparticles-supported nanographene synthesized by in-liquid plasma Hiroki Kondo, Tomoki Amano, Kenji Ishikawa, Makoto Sekine, Masaru Hori, Mineo Hiramatsu We investigated a high-speed synthesis of high-crystallinity nanographenes over 1 micro-gram/min using in-liquid plasma. In this study, nanographene materials with different crystallinity were synthesized using ethanol and 1-butanol. Pt nanoparticles were supported on their surfaces reducing 8 wt{\%}-H$_{2}$PtCl$_{6}$ in H$_{2}$O. G-band and D-band peaks in Raman spectra indicated nanographene materials. Nanographene materials synthesized using ethanol have higher crystallinity than those synthesized using 1-butanol. According to X-ray diffraction patterns, sizes of Pt nanoparticles are almost similar regardless of alcohol types. In cyclic voltammetry characteristics, peaks related to adsorption and desorption of hydrogen were clearly found in the both cases. The platinum effective areas were estimated to be 208.5 and 147.63 m$^{2}$/g for the cases using ethanol and 1-butanol, respectively. In addition, after potential cycling tests, nanographene materials synthesized using ethanol show almost no degradation, while those using 1-butanol show a drastic degradation. These results indicate that the higher-density Pt nanoparticles can be supported on the higher-crystallinity nanographene material and they show higher durability. [Preview Abstract] |
Tuesday, November 4, 2014 4:15PM - 4:30PM |
FT3.00004: Growth of graphene-based films using afterglow of inductively coupled plasma Mineo Hiramatsu, Masakazu Tomatsu, Hiroki Kondo, Masaru Hori Plasma-enhanced CVD (PECVD) employing methane/hydrogen gases has been used to grow diamond and carbon nanostructures. In the case of graphene growth using PECVD, excessive supply of carbon precursors and ion bombardment on the growing surface would cause secondary nuclei, resulting in small size of graphene grain and degradation in crystallinity. To overcome this issue, in this work, afterglow of inductively coupled plasma (ICP) was used for the growth of graphene. The CVD system is simple and consists of a reaction chamber and a remote radical source that uses an ICP in cylindrical geometry. Methane/hydrogen gases were fed through a quartz tube of 26 mm inner diameter and 20 cm in length. A five-turn rf (13.56 MHz) coil was mounted on the quartz tube. Substrates (Ni-coated Si and Cu foil) were located in the afterglow region of ICP. Growth experiments were carried out for 1-10 min at temperature of 700 C, rf power of 400 W, and total pressure of 100 mTorr. We have successfully fabricated graphene-based films, which was confirmed by the Raman spectrum and SEM image of deposit. We will discuss the planar graphene growth mechanism in terms of precursors and their surface reaction, in conjunction with the growth experiments using microwave plasma and ICP in planar geometry. [Preview Abstract] |
Tuesday, November 4, 2014 4:30PM - 4:45PM |
FT3.00005: Flickering of thoriated and lanthanized tungsten cathodes Thomas Hoebing, Patrick Hermanns, Andre Bergner, Cornelia Ruhrmann, Hannes Traxler, Ingmar Wesemann, Juergen Mentel, Peter Awakowicz Tungsten cathodes in HID-lamps are commonly doped with rare earth oxides to reduce the work function $\Phi$. A popular dopant ThO$_2$ decreases $\Phi$ from 4.55 eV to 3.0 eV and, therewith, reduces the cathode temperature. La$_2$O$_3$-cathodes seem to represent an alternative, since the reduction of $\Phi$ is comparable to that of thoriated cathodes. But a temporally unstable arc attachment can be observed at cathodes doped with La$_2$O$_3$. At thoriated cathodes, this flickering can also be detected, but less pronounced. It is attributed to a temporal increase of $\Phi$, induced by a transient shortage of La at the cathode tip. The arc attachment moves from the tip to colder areas of the cathode, where a high amount of La is present. Reasons for a temporal increase of $\Phi$ can be attributed to an insufficient transport of oxides from the interior of the cathode and an insufficient return of vaporized La by an ion current from the arc plasma to the cathode. Enrichments of La / Th compounds are formed on the cathode surface providing emitter material in case of a shortage at the tip. Cathode coverage and diffusion in the interior of the electrode, ThO$_2$- and La$_2$O$_3$-electrodes behave differently. Differences and their influence on the stability of the arc will be presented. [Preview Abstract] |
Tuesday, November 4, 2014 4:45PM - 5:00PM |
FT3.00006: Performance and aging effects of automotive HID-Lamps when replacing thorium in the electrodes Alexander Alexejev, Andre Bergner, Thomas Hoebing, Cornelia Ruhrmann, Peter Flesch, Juergen Mentel, Peter Awakowicz Tungsten electrodes in automotive HID-Lamps up to now are mostly doped with thoriumdioxide (ThO2). The doping decreases the work function $\Phi$ of tungsten from 4.55 eV to 3.0 eV, thus leading to a reduced electrode temperature, resulting in an increased lifetime of the lamp. However, usage of thorium is no longer recommendable, due to complicated trade relationships and transportation issues. An alternative filling or doping is being searched for, which should replace thoriumoxide without affecting the lamp performance. The fillings/dopants are usually rare earth iodides/oxides respectively. Rare earths have similar physical properties as thorium in terms of electronegativity and adsorption energy. Theoretically, several of them can replace thorium. The resulting lamp performance is, however, greatly affected even by minor changes in the filling/doping. The effect of each new component has therefore to be studied by an investigation of the electrode behaviour during lamp operation. The authors present different lamp configurations and their performances, being shown by optical observation and electrode temperature measurements, as well as the aging effects of the investigated lamps. [Preview Abstract] |
Tuesday, November 4, 2014 5:00PM - 5:15PM |
FT3.00007: Optically Pumped Lasing of Ar(4p$\to $4s) Excited in Linear Microplasma Arrays at Atmospheric Pressure Wilson Rawlins, Kristin Galbally-Kinney, Steven Davis, Alan Hoskinson, Jeffrey Hopwood The optically pumped rare-gas metastable laser is a chemically inert analogue to alkali laser systems. These devices require efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at elevated pressure. Linear arrays of microstrip resonators are well suited for this task. We have observed CW optical gain and lasing at 912 nm using linear micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure. Ar(4s) metastables are generated in flowing Ar/He mixtures by low-power, CW linear array microplasmas operating near 900 MHz and 1 atm. The metastables are optically excited to selected states in the Ar(4p) manifold by a tunable, CW Ti:S laser. Collisional energy transfer within the manifold produces a population inversion. The Ar(4s) concentration and the optical gain are probed by tunable diode laser spectroscopy. [Preview Abstract] |
Tuesday, November 4, 2014 5:15PM - 5:30PM |
FT3.00008: Plasma Formation During Operation of a Diode Pumped Alkali Laser (DPAL) in Cs Natalia Yu. Babaeva, Oleg Zatsarinny, Klaus Bartschat, Mark J. Kushner Diode pumped Alkali Lasers (DPALs) produce laser action on the resonant lines of alkali atoms. Diode lasers resonantly pump the $^{\mathrm{2}}$P$_{\mathrm{3/2}}$ state of the alkali atom which is collisionally relaxed to the $^{\mathrm{2}}$P$_{\mathrm{3/2}}$ state which then lases to the ground state $^{\mathrm{2}}$S$_{\mathrm{1/2}}$. The low optical quality of high power semiconductor diode lasers is converted into high optical quality laser radiation from the alkali vapor. The Cs DPAL system using Ar/Cs/C$_{\mathrm{2}}$H$_{\mathrm{6}}$ mixtures has shown promising results. (C$_{\mathrm{2}}$H$_{\mathrm{6}}$ is the collisional relaxant.) In other studies, resonant excitation of alkali vapor by low power lasers has been used to produce highly ionized channels, initiated through associative ionization and superelastic electron heating. The issue then arises if plasma formation occurs during DPAL by similar mechanisms which would be detrimental to laser performance. In this paper, we report on results from a computational study of a DPAL using Cs vapor. The global model addresses quasi-cw pumping of the Cs($^{\mathrm{2}}$P$_{\mathrm{3/2}})$ state by laser diodes, and includes a full accounting of the resulting electron kinetics. To enable this study, the B-spline R-matrix (BSR) with pseudostates method was employed to calculate electron impact cross sections for Cs. We found that for pump rates of many to 10 kW/cm$^{\mathrm{2}}$, plasma densities approaching 10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$ occur during laser oscillation with higher values in the absence of laser oscillation. [Preview Abstract] |
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