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 FT1: Plasma Surface Interactions |
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Chair: Kenji Ishikawa, Nagoya University Room: State EF |
Tuesday, November 4, 2014 3:30PM - 4:00PM |
FT1.00001: Smart material-based radiation sources Invited Speaker: Scott Kovaleski From sensors to power harvesters, the unique properties of smart materials have been exploited in numerous ways to enable new applications and reduce the size of many useful devices. Smart materials are defined as materials whose properties can be changed in a controlled and often reversible fashion by use of external stimuli, such as electric and magnetic fields, temperature, or humidity. Smart materials have been used to make acceleration sensors that are ubiquitous in mobile phones, to make highly accurate frequency standards, to make unprecedentedly small actuators and motors, to seal and reduce friction of rotating shafts, and to generate power by conversion of either kinetic or thermal energy to electrical energy. The number of useful devices enabled by smart materials is large and continues to grow. Smart materials can also be used to generate plasmas and accelerate particles at small scales. The materials discussed in this talk are from non-centrosymmetric crystalline classes including piezoelectric, pyroelectric, and ferroelectric materials, which produce large electric fields in response to external stimuli such as applied electric fields or thermal energy. First, the use of ferroelectric, pyroelectric and piezoelectric materials for plasma generation and particle acceleration will be reviewed. The talk will then focus on the use of piezoelectric materials at the University of Missouri to construct plasma sources and electrostatic accelerators for applications including space propulsion, x-ray imaging, and neutron production. The basic concepts of piezoelectric transformers, which are analogous to conventional magnetic transformers, will be discussed, along with results from experiments over the last decade to produce micro-thrusters for space propulsion and particle accelerators for x-ray and neutron production. [Preview Abstract] |
Tuesday, November 4, 2014 4:00PM - 4:15PM |
FT1.00002: Simulation of the Vapor Shield Effect on Plasma Facing Materials under Tokomak-Like Disruption Conditions Nouf Almousa, Mohamed Bourham Hard disruptions are expected in large tokomaks, where plasma-facing components (PFCs) receive radiant high heat fluxes resulting in surface melting and evaporation. The boundary layer at the ablating/melting surfaces absorbs a fraction of the heat flux and a vapor shield effect protects the PFCs from further erosion. The energy transmission factor through the vapor shield $f_{vs}$ is modeled in a 1-D, time dependent code to calculate the erosion under disruption-like conditions of 55 GW/m$^{2}$ over 150 $\mu$s. The $f_{vs}$ value was found to be strongly dependent on materials properties, plasma pressure, and density, but weakly dependent on the plasma internal and kinetic energies. Calculations of $f_{vs}$ at each time step and mesh point are used to predict the ablated mass. The code predictions are used to estimate the erosion rate and erosion thickness for varies PFMs. It has been found that high-Z PFMs suffer higher ablation rate as compared to low-Z PFMs. However, the erosion in units of material thickness indicates that the erosion thickness of the highest Z PFMs (tungsten) is less than that of the lowest Z PFMs (beryllium). Detailed comparisons of the erosion behavior and properties of PFMs are presented. [Preview Abstract] |
Tuesday, November 4, 2014 4:15PM - 4:30PM |
FT1.00003: Ion induced electron emission from semiconductors: The effect of conduction band electrons and surface electric fields David Urrabazo, Matthew Goeckner, Lawrence Overzet A few recent publications point to the possibility of controlling the ion induced electron emission (IIEE) yield from semiconductor surfaces in real time through controlling the numbers of electrons in the semiconductor's conduction band (ne,CB). Of course, ion bombardment induced electron emission also occurs in the plasma processing of semiconductors, and should cause differences between processing n- and p-type wafers if it truly depends upon ne,CB. Hagstrum's Auger neutralization theory for semiconductors assumes that the IIEE yield should NOT depend upon ne,CB, and as a result most models make the assumption that the IIEE yield is independent of ne,CB (and the position of the Fermi level as well as temperature). To our knowledge, no one has investigated this assumption! Therefore, we have experimentally and theoretically investigated it by using and extending Hagstrum's theory as well as by measuring the IIEE yield from semiconductor samples versus doping density and type. In addition, we have begun both theoretical and experimental investigations into the effects of a surface E-field on IIEE for semiconductors. We will introduce a device we have designed, modeled, and begun fabricating for measuring the IIEE yield while independently controlling the ion flux and E-field. [Preview Abstract] |
Tuesday, November 4, 2014 4:30PM - 4:45PM |
FT1.00004: A Comparative Study of Polymer and Biomolecule Surface Modifications by an Atmospheric Pressure Plasma Jet and Surface Microdischarge in Controlled Environments Elliot Bartis, Andrew Knoll, Pingshan Luan, Connor Hart, Joonil Seog, Gottlieb Oehrlein, David Graves, Walter Lempert In this work, polymer- and lipopolysaccharide-coated Si substrates were exposed to a surface microdischarge (SMD) and an atmospheric pressure plasma jet (APPJ) in controlled ambients. We seek to understand how plasma-ambient interactions impact biodeactivation and surface modifications by regulating the ambient gas chemistry and the proximity of the plasma to the ambient. A key difference between the SMD and APPJ is that the APPJ needs an Ar feed gas and the SMD does not. By adding small N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ admixtures to Ar, we find that the O$_{\mathrm{2}}$ admixture in the APPJ is a key factor for both deactivation and surface modification. After plasma treatments, we detected a new chemical species on a variety of surfaces that was identified as NO$_{\mathrm{3}}$. We find that NO$_{\mathrm{3}}$ forms even with no N$_{\mathrm{2}}$ in the feed gas, demonstrating that this species forms due to interactions with ambient N$_{\mathrm{2}}$. Despite a very different discharge mechanism, the SMD modifies surfaces similarly to the APPJ, including NO$_{\mathrm{3}}$ formation. The SMD generates large O$_{\mathrm{3}}$ concentrations, which do not correlate with NO$_{\mathrm{3}}$, suggesting that O$_{\mathrm{3}}$ alone is not involved in the NO$_{\mathrm{3}}$ formation mechanism. The authors gratefully acknowledge financial support by the US Department of Energy (DE-SC0005105 and DE-SC0001939) and National Science Foundation (PHY-1004256). [Preview Abstract] |
Tuesday, November 4, 2014 4:45PM - 5:00PM |
FT1.00005: ABSTRACT HAS BEEN MOVED TO MR2.00004 |
Tuesday, November 4, 2014 5:00PM - 5:15PM |
FT1.00006: Effect of Cryogenic Cooling for Gallium Nitride Film Placed in Argon Plasma Daisuke Ogawa, Yoshitaka Nakano, Keiji Nakamura There is no doubt for a gallium nitride (GaN) film to have plasma-induced damage (PID) when exposed in a plasma discharge. Our technique to make in-situ monitoring on a GaN film exposed in argon plasma is valuable toward to reveal the evolution of the damage. We evaluated the PID with photoluminescence (PL) that is excited with a ultra-violet light source. Our preliminary result showed that the PL intensity at the blue luminescence band (BL: 400 -- 480 nm) increased while the intensity at yellow luminescence (YL: 480 -- 700 nm) decreased as the plasma exposure time increased. Chen et al. previously found that PL spectrum changes due to both PID and substrate temperature. However, BL intensity is independent from the substrate temperature, while BL intensity is dependent on the degree of PID. In this experiment, we performed the plasma exposure to a GaN film under the situation when the substrate temperature was cooled with liquid nitrogen. The substrate temperature is set at -110 degC and exposed plasma in 15 minutes. In this condition, our BL stayed almost constant. This is an indication that we might be able to avoid the damage in the wavelength shorter than 480 nm. We will show more details from this results and further progresses in this presentation. [Preview Abstract] |
Tuesday, November 4, 2014 5:15PM - 5:30PM |
FT1.00007: Study of the effect of pressure on thermionic emission current John Haase, David Go Thermionic emission is the process in which heating a cathode allows electrons to gain sufficient energy to overcome the material's work function and be ejected into vacuum. By collecting the emitted electrons at a lower temperature anode and passing them through a load, the thermal energy is directly converted into electrical energy in a process called thermionic energy conversion (TEC). Operating a plasma in the interstitial gap between the cathode and anode produces positive space charge to offset the negative electrons and can improve TEC performance. However, this necessarily requires that the TEC device operates at pressures higher than vacuum. The introduction of a gas between the electrodes of a TEC device can either attenuate, due to elastic collisions, or increase, due to ionization, the current, and this is a strong function of the driving potential from the cathode to anode. In this work, the collected current from thermionic emission in noble gases is examined over a range of pressures and potentials, both experimentally and using kinetic particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Initial theoretical, simulation, and experimental results show that for electrons with energies below the ionization energy the current $i$ scales with pressure $p$ as $i\propto p^{-n}$, where $\frac{1}{2}\le n\le 1$. [Preview Abstract] |
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