Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session WF2: Plasma-Surface Interactions |
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Chair: Svetozar Popovic, Old Dominion University Room: Duquesne |
Friday, November 10, 2017 10:00AM - 10:15AM |
WF2.00001: ABSTRACT WITHDRAWN |
Friday, November 10, 2017 10:15AM - 10:30AM |
WF2.00002: In Situ Measurement of Electron Emission Yields from Plasma-Exposed Surfaces Mark Sobolewski Accurate plasma simulations require knowledge of the flux or yield of electrons emitted from plasma-exposed surfaces. Yields can be measured in beam studies, but it is usually impractical to produce a beam of each possible energetic particle that could be produced by the plasma. In contrast, in-situ measurements, performed during plasma exposure, may provide useful values or bounds for effective or total electron emission yields, summed over all or some subset of the energetic particles present in a given plasma. Here, measurements were performed in an inductively coupled plasma system equipped with variable-frequency rf bias. An insulating cap is placed on the rf-biased electrode to minimize edge effects. The rf voltage and current across the sheath adjacent to the rf-biased electrode are measured and analyzed by detailed, numerical sheath models, which allow the current of emitted electrons to be distinguished from other mechanisms of current flow. The observed dependence on voltage and rf phase allows some discrimination between emission induced by energetic positive ions and that induced by photons and metastables. The technique is validated by comparing results from argon discharges with beam studies and then is applied to plasma etching discharges in fluorocarbon gases. [Preview Abstract] |
Friday, November 10, 2017 10:30AM - 10:45AM |
WF2.00003: Surface Erosion of MAX Phase Micro-Trenches using a Plasma Jet from an Electrothermal Plasma Source Jonathan Coburn, T. E. Gebhart, Chad Parish, Ezekiel Unterberg, Donald Hillis, Mohamed Bourham Erosion characteristics of plasma-facing component (PFC) materials must be evaluated under extreme edge localized mode (ELM) and hard disruption conditions. Investigation of material alternatives to tungsten is essential, allowing for solutions suitable for operating magnetic fusion reactor environments. Novel MAX phase ceramics were exposed to an electrothermal (ET) plasma source operated at Oak Ridge National Laboratory. A technique was developed using a dual FIB/SEM to carve micrometer-scale trenches into the surface of polished MAX samples. FIB ruler markings were etched in \textasciitilde 1$\mu $m increments on a trench wall shadowed from plasma exposure. These samples were exposed to a lexan ET plasma stream in a He environment, at a specified impact angle, with IR camera and visible spectrometer diagnostics. Current pulses of 8kA over 160$\mu $s yielded heat fluxes of a few GW/m$^{\mathrm{2}}$ on the sample surface. Post-experiment SEM analysis indicated that this heat flux was enough for surface melting and boiling, but not enough to achieve a fully sublimating erosion regime. FIB ruler markings indicate \textasciitilde 1$\mu $m of erosion depth in melted/vaporized areas. Results encourage higher heat flux ET exposures for future studies of MAX phases, SiC, and other novel materials using this micro-trenching technique. [Preview Abstract] |
Friday, November 10, 2017 10:45AM - 11:00AM |
WF2.00004: Plasma-Surface Interactions at Atmospheric Pressure: Polystyrene Etching and Surface Modification by a Plasma Jet Pingshan Luan, V. S. Santosh K. Kondeti, Andrew Knoll, Peter Bruggeman, Gottlieb Oehrlein In this work we studied the interaction of a well-characterized radio frequency (RF) atmospheric pressure plasma jet (APPJ) with polystyrene (PS) as a model polymer. A number of plasma processing parameters, such as treatment distance and angle, feed and environment gas compositions, were investigated by evaluating both polymer thickness and surface chemical composition change after treatment. The effect of different plasma species on polymer surface was compared. We found that for both Ar/O$_{\mathrm{2}}$ and Ar/H$_{\mathrm{2}}$O plasma the etch rate of PS decayed exponentially with treatment distance, whereas surface oxidation increased to a maximum and then decreased. Both the exponential decay constant and oxidation maximum varied with gas composition due to changes in the gas phase species. A surface reaction model based on Langmuir adsorption can explain the observed difference in trends. The reaction rate between incident atomic O or OH radical flux and etched C flux was estimated. Besides, the apparent activation energy (E$_{\mathrm{a}})$ of etching reactions was measured by varying substrate temperature. [Preview Abstract] |
Friday, November 10, 2017 11:00AM - 11:15AM |
WF2.00005: Surface ripple formation during plasma etching of silicon Kouichi Ono, Nobuya Nakazaki, Hirotaka Tsuda, Yoshinori Takao, Koji Eriguchi Atomic- or nanometer-scale roughness on feature surfaces has become an important issue to be resolved in the fabrication of nanoscale devices. Control of the surface roughening during plasma etching might be possible, given a deeper understanding of plasma-surface interactions concerned with it. We have investigated the surface morphology evolution in response to ion incidence angle onto substrate surfaces during silicon etching in chlorine-based plasmas, through Monte Carlo simulations and experiments using sheath control plates. The simulations showed randomly roughened surfaces at normal incidence, while ripple structures at off-normal angles of incidence, traveling laterally across the surface in the direction of ion incidence. Correspondingly, the experiments demonstrated sawtooth-like ripples whose crests/troughs are elongated perpendicularly to the direction of ion incidence at intermediate off-normal angles, while small ripples or slit-like grooves whose crests/toughs are parallel to the direction of ion incidence at high off-normal angles, as predicted by simulations. These results are discussed in terms of the effects of ion reflection from feature surfaces and those of geometrical shadowing of the feature. [Preview Abstract] |
Friday, November 10, 2017 11:15AM - 11:30AM |
WF2.00006: Comparison of Polymer Etching Mechanisms by Cold Atmospheric Plasma (CAP) Sources Under Well-Defined Conditions Andrew Knoll, Pingshan Luan, Adam Pranda, Gottlieb Oehrlein Cold atmospheric plasma sources are important sources of reactive chemical species that can used to deactivate bacteria and biomolecules or modify surfaces under mild conditions, leading to use in numerous applications. We examine varying substrate temperature on polymer etching using an atmospheric pressure plasma jet (APPJ) and a surface microdischarge (SMD) source. The APPJ shows high etch rates but mild surface modification whereas the SMD shows no etching at room temperature but significant surface modification. An Arrhenius equation is used to fit the temperature dependence of etch rate and yields apparent activation energies. APPJ treatment activation energy increases as a function of distance from 0.2 eV up to 0.5 eV. The activation energy of the SMD source is significantly higher than the APPJ at 0.8-0.9 eV and overall causes less etching. The directionality of etching is investigated using patterned samples. APPJ etching has anisotropy which becomes more isotropic with increasing treatment distance where the SMD has only isotropic etching. APPJ induced etching of these polymers must include other reactive species than neutral species alone, potentially line-of-sight charged particles, that enhance the rate of chemical etching. SMD etching is consistent with neutral chemical etching only, highlighting key differences between these two sources. The authors gratefully acknowledge financial support by US Department of Energy (DE-SC0001939) and National Science Foundation (PHY-1415353). [Preview Abstract] |
Friday, November 10, 2017 11:30AM - 11:45AM |
WF2.00007: Deuterium uptake by Sn films on a W substrate Oluseyi Fasoranti, Bruce Koel Sn is under consideration as a liquid-metal plasma-facing component for high power load applications in the divertor region of fusion reactors due to potential abilities for self-recovery and heat-flux management. Improved fundamental understanding of deuterium-Sn interactions that occur in Sn films on W substrates will be useful for further evaluating the compatibility of this system with fusion reactors. We report on surface science experiments under UHV conditions exploring the thermal stability and deuterium uptake by Sn films on polycrystalline W substrates using surface diagnostic tools such as AES, XPS, LEIS, and TPD. Our results show that multilayer Sn films start to evaporate near 1170 K, but the Sn monolayer on W is not fully removed until 1800 K. Clustering or diffusion of Sn films was observed above 310 K. Deuterium uptake on Sn films at 310-750 K from irradiation using 700 eV D2$+$ ions showed lower uptake on liquid Sn films compared to solid Sn. Oxidation of solid and liquid Sn films by O2 was studied using XPS, with more extensive oxidation at higher temperature. TPD shows Sn loss from SnO2 films at below the Sn multilayer desorption temperature. Irradiation of these oxidized Sn films by 700 eV D2$+$ caused reduction of the film to metallic Sn. [Preview Abstract] |
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