Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session VF1: Nanoparticles |
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Chair: Koichi Sasaki, Hokkaido University Room: Salon D |
Friday, November 10, 2017 8:00AM - 8:15AM |
VF1.00001: Effect of the electrostatic interaction in the coagulation of nanoparticles in argon-silane plasma simulations Benjamin Santos, Fran\c{c}ois Vidal, Laura Cacot, Claude Boucher It is known that nanoparticles in low-temperature plasmas are mostly charged negatively. Recently Mamunuru et al.~\footnote{Plasma Chem Plasma Process 37, 701–715 (2017).}, pointed out the existence of positively charged and neutral nanoparticles. This possibility promotes the coagulation because of the Coulomb interaction enhancement between particles of opposite charge. Moreover, Ravi et al.~\footnote{Phys. Rev. E 79, 26408 (2009).} studied the coagulation enhancement between neutral and charged nanoparticles, which is due to the image potential. In this work, we extended the study on the effects of the electrostatic interaction between nanoparticles on particle growth in an argon-silane low-temperature plasma. For this purpose, we developed a computer simulation based on the general dust-plasma self-consistent model established by the Girshick's group~\footnote{Plasma Chem Plasma Process 34, 1–15 (2013) and references therein.}, but we use a more rigorous approach, which includes polarization induction for calculating the electrostatic force between dielectric particles. It is shown that the coagulation is enhanced in neutral-charged particles encounters but in a lesser way than the previous study~\textsuperscript{2}. Detailed results will be discussed during presentation. [Preview Abstract] |
Friday, November 10, 2017 8:15AM - 8:30AM |
VF1.00002: Effect of Vaporization on Aerosol Dynamics in Low Temperature Dusty Plasmas Necip Uner, Elijah Thimsen Low temperature dusty plasmas (LTDP) are known to display a wide range of emergent phenomena due to the complex interactions between particles and the plasma. Some of the unique properties of dusty plasmas, such as suppressed coagulation and particle heating, have been successfully utilized for synthesizing monodisperse nanoparticles of various materials with high crystallinity. The general conception of nanoparticle growth involves nucleation due to the rapid conversion of gaseous precursors, which is followed by surface growth. Coagulation is effectively suppressed if the particle concentration is lower than the ion density, due to electrostatic interactions between negatively charged nanoparticles. The absence of reports on the synthesis of metal particles suggests that there may be additional dynamics occurring in LTDP. By sending premade aerosols into a radio frequency argon plasma, we demonstrate that metal particles can vaporize in the LTDP, despite the low gas temperature. Due to the nonequilibrium vaporization process unique to LTDP, a monodispersed aerosol was found to emerge from a polydispersed aerosol. A theoretical model for the evolution of the size distribution will be presented along with experimental results for several materials. [Preview Abstract] |
Friday, November 10, 2017 8:30AM - 8:45AM |
VF1.00003: Investigation of Wear-resistant Enhancement of Polyurethane Composite Film with Plasma-treated Carbon-nanotubes Daisuke Ogawa, Kazuki Michiya, Hideo Uchida, Keiji Nakamura Our former results showed that the plasma-treated CNTs enhanced the wear-resistance of polyurethane (PU) by means of making a CNT composite film. In particular, a treatment with the plasma made from a gas mixture of nitrogen and carbon dioxide was the most effective to enhance the wear-resistance. We have not understood the mechanism of the enhancement yet, but speculating two possibilities for the enhancement. The first possibility is due to a physical effect, in which the plasma treatment somehow enhances more uniform and more mono-sized distribution of CNTs in a PU film. The second possibility is due to a chemical effect. According to the discharge condition, nitrogen, carbon and oxygen species in the plasma can create isocyanate groups (R-NCO) on the CNTs. In fact, isocyanate groups can harden PU through chemical reactions. In order to find the main cause of the enhancement, we first observed the film with an optical microscope. However, the observation showed that the distribution of CNTs treated with the plasma was almost the same as that of other CNTs. On the other hand, the other investigation with acridine yellow, which is an indicator of the isocyanate groups through fluorescence, showed more isocyanate groups on the CNTs treated with the plasma. [Preview Abstract] |
Friday, November 10, 2017 8:45AM - 9:00AM |
VF1.00004: Self-consistent numerical simulation of carbon transport in the arc discharge for carbon nanotube synthesis Alexander Khrabry, Andrei Khodak, Kentaro Hara, Valerian Nemchinsky, Igor Kaganovich In carbon nanotube synthesis in the arc, graphite anode ablates providing carbon material into the arc core. Most of the carbon material deposits onto a surface of cathode, whereas some part of it escapes from the inter-electrode gap, cools down and serves as a feedstock for growth of nanoparticles. Carbon atoms associate into carbon dimers, trimmers, etc. with the dimers being the main precursor for growth of carbon nanotubes. Ablation rate is very sensitive to such arc parameters as arc current and gap width. Numerical simulations of carbon arc were performed using self-consistent model which couples effects of fluid flow, carbon transport, current flow, and heat transfer in both plasma and electrodes. Plasma model accounts for non-equilibrium conditions in the arc including effects of space-charge sheaths and solves separate transport equations for ion and neutral species. The arc model was implemented into general-purpose CFD-code ANSYS CFX, which was highly customized for this purpose. Very good agreement between simulation results and experimental data [1] on ablation/deposition rates and density profile of carbon dimers were obtained. [1] V. Vekselman et.al., Plasma Sources Sci. Technol. (2017) [Preview Abstract] |
Friday, November 10, 2017 9:00AM - 9:15AM |
VF1.00005: On the Structure Control of Vertical Nanographene Network Mineo Hiramatsu, Hitoshi Nozaki, Takuya Suzuki, Keigo Takeda, Hiroki Kondo, Masaru Hori Carbon nanowalls (CNWs) are few-layer graphenes, standing vertically on a substrate to form a self-supported network of wall structures. The maze-like architecture of CNWs would be useful as a platform for electrochemical and bio-sensing, and energy conversion, due to the large surface area of conductive carbon and the wide capability of surface modification including decoration with metal nanoparticles. CNWs can be fabricated using PCVD. The balance between carbon precursors and etching radicals would affect the morphology, crystallinity and growth rate of CNWs. For example, H content in the plasma increased, crystallinity improved and interspaces between adjacent nanowalls increased, while the growth rate of CNWs decreased. From a practical point of view, control of CNW structures including spacing between adjacent nanowalls and crystallinity is significantly important, and their nucleation control should be crucial, since the basic structure would be determined by the nucleation. We carried out CNW growth using PCVD employing CH4/H2/Ar mixture with emphasis on the structure control of CNWs. In this work, we report the effects of ion bombardment and catalytic metals on the nucleation of vertical nanographenes to realize active control of interspace between adjacent walls. [Preview Abstract] |
Friday, November 10, 2017 9:15AM - 9:30AM |
VF1.00006: Nanoparticle formation from HMDSO in an atmospheric pressure plasma jet Roger Wallimann, Gina Oberbossel, Denis Butscher, Philipp Rudolf von Rohr Nanoparticles are admixed to fine powders to enhance their flowability. In industry, this is mostly done in time consuming batch processes. As an alternative which could be used in a continuous process, the silica nanoparticle formation in plasma was investigated. For nanoparticle formation, HMDSO, argon and oxygen were used in an atmospheric pressure plasma jet powered by a sinusoidal high voltage generator. Oxygen levels, gas flow and frequency were varied to find optimal particle production conditions. The particles were collected using an electrostatic precipitator. HMDSO dissociation and conversion was determined by weight measurements of the precipitator tube. Particles were analyzed using FTIR and SEM to attain their composition and size, respectively. Conversion rates were in the range of 3 to 10{\%}. Below a frequency of 70 kHz, only film formation occurs since most of the nuclei are lost on the channel walls. Optimal oxygen levels for maximum yield was shown to be 2.5{\%}, below and above, dissociation was limited by power input and plasma quenching, respectively. Particle size was in the range of 30-60 nm and increased slightly with decreased volume flow. The composition of the films and particles were silica-like with a low amount of carbon. [Preview Abstract] |
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