Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session FT2: Modeling and Simulation: Plasma SourcesLive
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Chair: Alex Likhanskii, Applied Materials |
Tuesday, October 6, 2020 8:00AM - 8:15AM Live |
FT2.00001: High frequency sheath modulation and higher harmonic generation in a low pressure very high frequency capacitively coupled plasma excited by sawtooth waveform Nishant Sirse, Sarveshwar Sharma, Miles Turner A particle-in-cell (PIC) simulation study is performed to investigate the discharge asymmetry, higher harmonic generations and electron heating mechanism in a low pressure very high frequency capacitively coupled plasma (CCP) excited by a saw-tooth like current waveform. Two current densities, 50 A/m$^{\mathrm{2}}$ and 100 A/m$^{\mathrm{2}}$ are chosen for a constant gas pressure of 5 mTorr in argon plasma. The driving frequency is varied from 13.56 MHz to 54.24 MHz. At a lower driving frequency, high frequency modulations on the instantaneous sheath edge position at the grounded electrode are observed. These high frequency oscillations create multiple ionization beam like structures near to the sheath edge that drives the plasma density in the discharge and responsible for discharge/ionization asymmetry at lower driving frequency. Conversely, the electrode voltage shows higher harmonics generation at higher driving frequencies and corresponding electric field transients are observed into the bulk plasma. At lower driving frequency, the electron heating is maximum near to the sheath edge followed by electron cooling within plasma bulk, however, alternate heating and cooling i.e. burst like structures are obtained at higher driving frequencies. These results suggest that electron heating in these discharges will not be described accurately by simple analytical models. [Preview Abstract] |
Tuesday, October 6, 2020 8:15AM - 8:30AM Live |
FT2.00002: Particle-in-Cell/Monte Carlo Simulation of RF Hollow Cathode Discharge Kallol Bera, Shahid Rauf Radio-frequency (RF) hollow cathode discharges (HCD) are used as plasma source for material processing in the semiconductor industry. Hollow cathode systems typically consist of an array of small hollow cylindrical holes on the cathode. Under certain conditions, the plasma in the hollow cavities can become more intense due to hollow cathode effect (HCE). In this study, we investigate RF hollow cathode discharge using Particle-in-Cell/Monte Carlo simulation. In this model, using charge density of particles, Poisson equation is solved for electric potential that yields electric field. Using this electric field, all charged particles' velocities are updated and the particles are moved. The leap-frog scheme is used for integrating the equations of motion. Based on probability arrays, particle collisions with each other and with neutrals are considered. Thereafter, particle density, hence charge density is determined. Statistics of these collisions are used to determine how electron energy is dissipated in the plasma. We have explored the effect of gas pressure and RF voltage on plasma density in the RF HCD using this model. At higher pressure, plasma penetrates inside the hole, leading to HCE enhancement. We compare the simulation results with experimental data in RF HCD. [Preview Abstract] |
Tuesday, October 6, 2020 8:30AM - 8:45AM Live |
FT2.00003: 2D Particle in cell simulations of simultaneous positive and negative streamer propagation of a twin surface dielectric barrier discharge Ryan T. Nguyen-Smith, Quan-Zhi Zhang, Peter Awakowicz, Julian Schulze In this work, the propagation mechanisms of plasma streamers are studied on a twin surface dielectric barrier discharge (SDBD) in air under atmospheric pressure using 2D particle in cell simulations. The physical SDBD has two exposed and symmetric electrodes separated by a single dielectric barrier allowing for positive and negative streamers to ignite simultaneously. In order to determine the interactivity of the two streamers, the propagation behavior for the positive and negative streamers are investigated both independently and simultaneously under identical constant voltage conditions. Furthermore, a heavy focus of an alternating voltage waveform is also considered, thereby investigating the large dynamics of the streamers under alternating voltage polarities. It is shown that the simultaneous ignition of both streamers as well as the alternating voltage leads to discharge enhancement and increased surface coverage. It is also shown that additional streamer branches covering the metallic electrode may occur. The enhanced discharge and surface coverage may be beneficial in many SDBD applications including but not limited to flow control, air purification, plasma enhanced catalysis, and removal of volatile organic compounds from exhaust gasses. [Preview Abstract] |
Tuesday, October 6, 2020 8:45AM - 9:00AM Live |
FT2.00004: Spatially-resolving Discharge Parameters in Microwave Plasmas for CO$_2$ Conversion from Atomic Oxygen Emission Pedro Viegas, Floran Peeters, Bram Wolf, Alex van de Steeg, Luca Vialetto, Pieter-Willem Groen, Waldo Bongers, Gerard van Rooij, Richard van de Sanden, Paola Diomede At DIFFER, microwave (MW) plasma reactors are used to efficiently convert CO$_2$ into carbon-neutral fuels and chemicals. The optimal conditions for these reactors have shown a strong correlation with pressure and discharge contraction dynamics and have been obtained in contracted plasma conditions. Characterization of the plasma parameters in these highly heterogeneous discharges often relies on estimations of the electron density and power density profiles. However, these profiles are determined from the experimentally measured radiative emission of atomic oxygen, under an unverified assumption of proportionality. In this work, a collisional-radiative model of O atom in CO$_2$ MW plasmas is used to complement the experiments and assess the validity of this assumption. The simulations relate the radiative emission of O atom with electron density, power density, and other discharge parameters, resolving their spatial profiles. The electron density is shown to have a broader profile than initially assumed, with implications on discharge contraction, which depends on ionisation and recombination rates. As a result of the combined experimental and numerical study, the contraction of the CO$_2$ MW discharge is explained through its relationship with charged particle kinetics. [Preview Abstract] |
Tuesday, October 6, 2020 9:00AM - 9:15AM Live |
FT2.00005: Analysis of spectra of the pMRP using a spectral kinetic model Michael Friedrichs, Junbo Gong, Ralf Peter Brinkmann, Jens Oberrath The planar multipole resonance probe (pMRP) is a diagnostic-tool based on the concept of active plasma resonance spectroscopy (APRS), which excites the plasma in the GHz range and records the response to detect resonances. Due to its planar design the pMRP is especially suited to monitor plasma processes without perturbing them. To determine plasma parameter from measured resonance, a model for the relation between plasma and resonance parameter is required. To allow for simultaneous measurement of electron density and temperature a kinetic model is necessary to determine a relationship between the electron temperature and the half width of the resonance peak. In this work a spectral kinetic approach in cylindrical coordinates- a particle simulation where the fields are calculated in the Fourier space by means of Bessel's functions - for the pMRP will be presented to analyze the influence of kinetic effects on the half-width. [Preview Abstract] |
Tuesday, October 6, 2020 9:15AM - 9:30AM Live |
FT2.00006: Quantum Efficiency of Photoelectron Emission from Metal Surfaces with Laser Wavelengths from UV to NIR Yang Zhou, Yi Luo, Peng Zhang Laser-induced electron emission is important to free electron lasers, ultrafast electron microscopes, X-ray sources, and novel plasma sources. Here, we calculate the quantum efficiency (QE), defined as the number of emitted electrons per incident photon, for laser wavelengths from UV to NIR, using a recent quantum model based on the exact solution of time-dependent Schrödinger equation [1-3]. The dominant electron emission mechanism varies from multiphoton emission to strong field tunneling, depending on the laser intensity. For relatively low laser intensity $I$, QE \textasciitilde $I^{\mathrm{n-1}}$ for $n-$photon absorption processes. Increasing laser intensity can increase QE significantly beyond the $I^{\mathrm{n-1}}$ scaling, due to the non-equilibrium heating produced by the intense sub-picosecond laser pulse and the strong field tunneling. Adding a dc field shifts the dominant $n-$photon processes to smaller value of $n$, because of the combined effects of the narrowing and lowering of the potential barrier by the dc field [2,3]. [1] P. Zhang and Y. Y. Lau, Sci. Rep., 6, 19894 (2016). [2] Y. Luo, and P. Zhang, Phys. Rev. B, 98, 165442 (2018); Phys. Rev. Applied, 12, 044056 (2019). [3] Y. Zhou, and P. Zhang, J. Appl. Phys., 127, 164903 (2020). [Preview Abstract] |
Tuesday, October 6, 2020 9:30AM - 9:45AM Live |
FT2.00007: Particle-in-cell simulation of dual frequency capacitively coupled plasma with pulsed DC biasing at low pressure Peng Tian, Jason Kenney, Shahid Rauf Pulsed capacitively coupled plasma (CCP) is being widely used in industry over the last decade due to its capability to control ion energy and fluxes, particularly in etching processes such as high aspect ratio (HAR) etching or atomic layer etching. Among those, radio-frequency (RF) pulsing is one of the most common schemes that's being used and studied extensively, in which a pulse-enveloped sinusoidal wave is used as power source. Direct current (DC) pulsing is an attractive option for biasing due to reduced electron heating and better control over ion energy. In this study, a 1D particle-in-cell (PIC) plasma model is used to study the kinetics of a RF Ar plasma at 1 -- 10's mTorr, with pulsed DC bias at 100's kHz pulsing frequency and a very high frequency RF source. Results for IED and bulk plasma characteristics will be discussed over a range of pressures, duty cycles, and pulsing frequencies. [Preview Abstract] |
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