@article{icenhour_lindsay_permann_martineau_green_shannon_2024, title={The MOOSE electromagnetics module}, volume={25}, ISSN={["2352-7110"]}, DOI={10.1016/j.softx.2023.101621}, abstractNote={The Multiphysics Object-Oriented Simulation Environment (MOOSE) electromagnetics module has been developed to increase MOOSE physics module capabilities, enabling standalone and coupled computational electromagnetics within the MOOSE multiphysics ecosystem. The module is actively being utilized in the areas of plasma physics and advanced manufacturing, and it currently provides initial demonstrated capability in multi-dimensional, complex-valued electromagnetic wave propagation, electrostatic contact, reflection and transmission, and electromagnetic eigenvalue problems. Two-dimensional wave propagation and one-dimensional wave reflection and transmission are showcased as examples in this work. The modularity, parallelism, and plug-in infrastructure for custom future development is inherited from MOOSE itself, and the module can be used with both MOOSE-based and external codes, giving great flexibility.}, journal={SOFTWAREX}, author={Icenhour, Casey T. and Lindsay, Alexander D. and Permann, Cody J. and Martineau, Richard C. and Green, David L. and Shannon, Steven C.}, year={2024}, month={Feb} }
 @article{shutayfi_raj_eapen_shannon_2023, title={Design, Modeling, and Analysis of a Compact-External Electromagnetic Pumping System for Pool-Type Liquid Metal-Cooled Fast Reactors}, volume={193}, ISSN={["1873-2100"]}, url={https://doi.org/10.1016/j.anucene.2023.109997}, DOI={10.1016/j.anucene.2023.109997}, abstractNote={Current pool-type Liquid Metal-Cooled Fast Reactors (LMCFRs), either under development or operational, immerse main reactor components in the primary coolant, (i.e. sodium), that includes heat exchangers, shielding structures, and pumping systems. Proposed main pumping systems, for some reactors that are under development, use electromagnetic pumps (EMPs) for primary coolant circulation. Annular linear induction pumps (ALIPs) are the preferred type since they are known for their advantages over mechanical centrifugal pumps (MCPs) when used to circulate liquid metals. This is due to ALIPs’ absence of moving parts such as shafts and impellers, seals and bearings, auxiliary lubrication systems, and simplicity of flow and pressure control mechanism. The immersion of reactor components in the primary sodium in the reactor vessel minimizes the likelihood of radioactive coolant leakage and loss of coolant accidents. However, since there is only one access point to reactor components, the immersion of ALIPs prevents additional potential advantages. Online pump inspection and replacement, reduction of negative effects on pump components due to the high temperature and radiation environment, an additional heat removal mechanism for self-cooled ALIPs, and simple decommissioning procedures are some possible advantages. This paper discusses a study conducted to investigate the possibility of using large EMPs, ALIP type, that are located outside the reactor vessel and connected in parallel, instead of in vessel sodium immersed ones for pool-type LMCFRs. The large, outside-vessel EMP idea is tested on a liquid metal-cooled test reactor design using an experimentally validated multiphysics finite element analysis tool. Specifically, the steady state reactor’s primary circuit cooling and pressure requirements are used to design two, in-vessel ALIPs and then two outside-vessel ALIPs. The two pumping systems are compared in terms of their geometries, performance characteristics, and impact on overall reactor design. It is found that the outside-vessel EMP design provides the same performance requirements and offers additional advantages compared to the in-vessel pump with only minimal reactor vessel modification and a slight drop in efficiency.}, journal={ANNALS OF NUCLEAR ENERGY}, author={Shutayfi, Mohammed and Raj, Anant and Eapen, Jacob and Shannon, Steven}, year={2023}, month={Dec} }
 @article{shutayfi_raj_eapen_shannon_2023, title={Design, Modeling, and Analysis of a Compact-External Electromagnetic Pumping System for Pool-Type Liquid Metal-Cooled Fast Reactors}, volume={193}, ISSN={["1873-2100"]}, DOI={10.1016/j.anucene.2023.109997r}, journal={ANNALS OF NUCLEAR ENERGY}, author={Shutayfi, Mohammed and Raj, Anant and Eapen, Jacob and Shannon, Steven}, year={2023}, month={Dec} }
 @article{morsell_bhatt_dechant_shannon_2023, title={Effect of dielectric target properties on plasma surface ionization wave propagation}, volume={56}, ISSN={["1361-6463"]}, url={https://doi.org/10.1088/1361-6463/acbfc9}, DOI={10.1088/1361-6463/acbfc9}, abstractNote={Abstract}, number={14}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Morsell, Joshua and Bhatt, Naman and Dechant, Corey and Shannon, Steven}, year={2023}, month={Apr} }
 @article{xiao_brandon_morsell_nam_bae_lee_shannon_2023, title={Effect of focus ring with external circuit on cathode edge sheath dynamics in a capacitively coupled plasma}, volume={41}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0002496}, DOI={10.1116/6.0002496}, abstractNote={Capacitively coupled plasmas are widely used in semiconductor processes. The control of plasma to obtain uniform deposition and etching is an open problem, particularly within a few millimeters of the substrate edge. Complex material stacks commonly referred to as focus rings are placed at the wafer edge to provide uniform processes across the entire substrate but have limitations with regard to process window and eventual material erosion. One approach is to combine a focus ring with a tunable external circuit ground path termination to extend the plasma uniformity to the wafer edge over a wider process space. The external circuit coupling focus ring to the ground influences the ion energy profile and the ion angular profile by changing the impedance between the focus ring and the ground and allows wafer edge tuning over a wide range of operating parameters. In this work, it is found that the adjustable external circuit can control the partitioning of bias and RF voltages between the RF powered and passively coupled plasma facing surfaces. The focus ring with an external circuit assembly can also control the spatial distribution of plasma density and, therefore, improve the sheath edge profile. These results point to possible source designs for engineering the distribution of power dissipation and the electric field of the wafer edge in industrial plasma reactors.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Xiao, Yuhua and Brandon, Joel and Morsell, Joshua and Nam, Sang Ki and Bae, KiHo and Lee, Jang-Yeob and Shannon, Steven}, year={2023}, month={May} }
 @article{morsell_trosan_stapelmann_shannon_2023, title={Plasma surface ionization wave interactions with single channels}, volume={32}, ISSN={["1361-6595"]}, url={https://doi.org/10.1088/1361-6595/acf9c9}, DOI={10.1088/1361-6595/acf9c9}, abstractNote={Abstract}, number={9}, journal={PLASMA SOURCES SCIENCE & TECHNOLOGY}, author={Morsell, Joshua and Trosan, Duncan and Stapelmann, Katharina and Shannon, Steven}, year={2023}, month={Sep} }
 @article{dechant_icenhour_keniley_gall_lindsay_curreli_shannon_2023, title={Verification and validation of the open-source plasma fluid code: Zapdos*,**}, volume={291}, ISSN={["1879-2944"]}, DOI={10.1016/j.cpc.2023.108837}, abstractNote={Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. This paper outlines Zapdos verification, benchmarking, and validation efforts for 1D and 2D RF capacitively-coupled plasma discharge models for mid-range pressures (0.1 - 1 Torr). The verification process involved using the method of manufactured solutions to assess Zapdos spatial and temporal error convergence. L2 errors ranged from 10−2 to 10−4, while the convergence's slope were in agreement with the predicted slopes for the tested variable and time integration orders. The benchmarking process involved comparisons to previously results from the validated finite element code, LSODI [1], [2], [3]. These works included 1D and 2D simulations for a range of plasma parameters (densities, temperatures, voltage, etc.). For the 1D cases, Zapdos and LSODI results were in very good agreement. In the 2D cases, variable behaviors matched, with slight discrepancies in peak values. The validation process involved comparisons to experimental works including electron density measurements by microwave interferometry [4] and metastable density measurements by planar laser-induced fluorescence imaging [5]. Results shown reasonable agreement at higher pressure, with results starting to diverge at low pressures. Probable causes for this diverges are the limitation of the fluid assumption for plasmas at low pressure, or the need for more robust boundary conditions. Overall, Zapdos shown reasonable results for the verification, benchmarking, and validation efforts, and Zapdos can be downloaded at https://github.com/shannon-lab/zapdos. Program Title: Zapdos CPC Library link to program files: https://doi.org/10.17632/j76jr9m66p.1 Developer's repository link: https://github.com/shannon-lab/zapdos Licensing provisions: LGPL-2.1 Programming language: C++, Python Supplementary material: shannon-lab.github.io/zapdos Nature of problem: For the plasma computational community, multiphysics packages are needed for the highly couple physics seen in plasma problems (e.g. chemistry, fluid flow, heat transfer, electromagnetic, etc.). One limiting factor for these types of computational research is the high cost to purchase the licenses needed for established multiphysics packages, such as COMSOL. An additional problem that can arise is the limited ability to add new physics to these existing frameworks, in such a way that new physics can be easily coupled to current models. For any new software that wants to tackle these problems, the question of verification and validation for these codes needs to be addressed. Solution method: Zapdos is an open-source finite element plasma fluid solver based on the MOOSE multiphysics framework. MOOSE (Multiphysics Object Oriented Simulation Environment) solves highly nonlinear, tightly coupled sets of partial differential equations (PDEs) and houses multiple physics applications that can be easily coupled together. Zapdos, along with the MOOSE ecosystem, is all free, open-source, and completing customizable with no black box components. Zapdos has gone through verification and validation for applications common in the plasma computational community. Additional comments including restrictions and unusual features: Zapdos, along with MOOSE and other MOOSE applications, require an Unix based operating system.}, journal={COMPUTER PHYSICS COMMUNICATIONS}, author={DeChant, Corey and Icenhour, Casey and Keniley, Shane and Gall, Grayson and Lindsay, Alexander and Curreli, Davide and Shannon, Steven}, year={2023}, month={Oct} }
 @article{dechant_icenhour_keniley_lindsay_gall_hizon_curreli_shannon_2023, title={Verification methods for drift-diffusion reaction models for plasma simulations}, volume={32}, ISSN={["1361-6595"]}, url={https://doi.org/10.1088/1361-6595/acce65}, DOI={10.1088/1361-6595/acce65}, abstractNote={Abstract}, number={4}, journal={PLASMA SOURCES SCIENCE & TECHNOLOGY}, author={DeChant, Corey and Icenhour, Casey and Keniley, Shane and Lindsay, Alexander and Gall, Grayson and Hizon, Kimberly Clein and Curreli, Davide and Shannon, Steven}, year={2023}, month={Apr} }
 @article{du_kruger_nam_lee_yoo_eapen_kushner_shannon_2022, title={Comparison of glancing-angle scatterings on different materials in a high aspect ratio plasma etching process using molecular dynamics simulation}, volume={40}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0002008}, DOI={10.1116/6.0002008}, abstractNote={In plasma etching for microelectronics fabrication, one of the objectives is to produce a high aspect ratio (HAR) via and trench structures. A principal contributor to the HAR feature shape is the manner in which energetic ions interact with sidewalls inside the feature. The scattering angle and energy loss of ions reflecting from sidewalls determine the sidewall slope and can lead to defects such as microtrenching and bowing. Understanding how ions interact with sidewalls can improve our control of the critical dimensions of HAR features. Ions accelerated in the plasma sheath arrive in the feature with energies as large as a few keV and initially strike the sidewalls at glancing angles. These scattering events extend to the photolithographic mask. Scattering from the mask at glancing angles can produce ions incident into the underlying feature with a broader angular distribution, leading to less desirable feature properties. In this work, results are discussed from Molecular Dynamics (MD) simulations of glancing-angle scattering of argon ions from three materials common to HAR etch: polystyrene (as a photoresist surrogate), amorphous carbon (a hard mask material), and SiO2 (a common insulating material used in microelectronics devices). Results from simulations reveal a transition from specular scattering to diffuse scattering as the angle of the incident ion decreases (90° being glancing incidence) and incident energy increases. Scattering from polystyrene is more diffuse compared to amorphous carbon and SiO2 for identical incident ion conditions.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Du, Yao and Kruger, Florian and Nam, Sang Ki and Lee, Hoki and Yoo, Suyoung and Eapen, Jacob and Kushner, Mark J. and Shannon, Steven}, year={2022}, month={Sep} }
 @article{peterson_xiao_ford_kraus_shannon_2021, title={Electron temperature measurements with a hairpin resonator probe in a pulsed low pressure capacitively coupled plasma}, volume={5}, url={https://doi.org/10.1088/1361-6595/ac02b2}, DOI={10.1088/1361-6595/ac02b2}, abstractNote={Electron temperature is measured from time resolved hairpin resonator probe measurements in a pulsed capacitively coupled argon plasma at 400 mTorr. Effective collision frequency is related to the electron energy distribution via the effective conductivity and closes a system of equations that allow electron temperature to be determined. Results generally show good agreement with expected behavior and unfiltered time-resolved optical emission measurements.}, journal={Plasma Sources Science and Technology}, publisher={IOP Publishing}, author={Peterson, D and Xiao, Y and Ford, K and Kraus, P and Shannon, S}, year={2021}, month={Jun} }
 @article{xiao_du_smith_nam_lee_lee_shannon_2021, title={Focus ring geometry influence on wafer edge voltage distribution for plasma processes}, url={https://doi.org/10.1116/6.0000981}, DOI={10.1116/6.0000981}, abstractNote={Capacitively coupled wafer-bearing cathodes are widely used in etching and deposition processes. Uniform electric field and plasma density across the wafer surface are necessary for process control all the way to the edge of the wafer. Terminating structures at the wafer edge such as focus rings are used to improve uniformity and minimize costly edge exclusion. The focus ring can be viewed as an arbitrary impedance element at the wafer edge that balances the sheath voltage above it and the region above the wafer, minimizing field variation at the wafer edge. To validate this assumption, a one-dimension circuit model with focus rings was developed. The simulations were compared to experimental results measured using hairpin probe, VI probe, and a retarding field energy analyzer (Impedans RFEA). It was found that the focus ring coupling acts as a voltage divider only in high voltage cases, and the sheath voltage drop over the focus ring will increase in low voltage cases and does not rigorously follow the voltage divider model typically used.}, journal={Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films}, author={Xiao, Yuhua and Du, Yao and Smith, Carl and Nam, Sang Ki and Lee, Hoki and Lee, Jang-Yeob and Shannon, Steven}, year={2021}, month={Jul} }
 @article{smith_nam_bae_lee_shannon_2021, title={Modulating power delivery in a pulsed ICP discharge via the incorporation of negative feedback mechanisms}, volume={130}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0060240}, DOI={10.1063/5.0060240}, abstractNote={Inductively coupled plasmas driven by pulsed RF power have been used by the semiconductor industry for decades as they offer numerous advantages compared to continuous mode discharges. Current state-of-the-art global models characterize the plasma under conditions where power delivery is user defined and typically constant. This work details the development of an integrated global plasma-circuit model, which couples a transient plasma model with a broader circuit model that captures the behavior of the power delivery system. The transient response of electron density ne and the magnitude of the delivered and reflected power is captured for the duration of a pulse event. The plasma model incorporates negative feedback mechanisms that enhance the magnitude of reflected power in the early ON-cycle. These feedback mechanisms include a skin depth-dependent derivation of plasma impedance and a generalized electron energy distribution function. These mechanisms decrease the rate of power delivery and dnedt in the early power on cycle. Data taken in the global plasma-circuit model was benchmarked to hairpin probe measurements that were taken on the NC state’s inductively coupled argon oxygen system. Experimental data were taken using a working gas of high purity argon at pressures ranging from 2.67 to 6.67 Pa, and center point electron densities were measured in the range of 109–1010cm−3.}, number={16}, journal={JOURNAL OF APPLIED PHYSICS}, author={Smith, Carl L. and Nam, Sang Ki and Bae, Kiho and Lee, Jang-Yeob and Shannon, Steven}, year={2021}, month={Oct} }
 @article{qu_lanham_shannon_nam_kushner_2020, title={Erratum: Power Matching to Pulsed Inductively Coupled Plasmas [J. Appl. Phys. 127, 133302 (2020)]}, url={https://doi.org/10.1063/5.0023888}, DOI={10.1063/5.0023888}, abstractNote={First Page}, journal={Journal of Applied Physics}, author={Qu, Chenhui and Lanham, Steven J. and Shannon, Steven C. and Nam, Sang Ki and Kushner, Mark J.}, year={2020}, month={Aug} }
 @article{qu_lanham_shannon_nam_kushner_2020, title={Power matching to pulsed inductively coupled plasmas}, url={https://doi.org/10.1063/5.0002522}, DOI={10.1063/5.0002522}, abstractNote={Matching of power delivery to nonlinear loads in plasma processing is a continuing challenge. Plasma reactors used in microelectronics fabrication are increasingly multi-frequency and/or pulsed, producing a non-linear and, in many cases, non-steady state electrical termination that can complicate efficient power coupling to the plasma. This is particularly the case for pulsed inductively coupled plasmas where the impedance of the plasma can significantly change during the start-up-transient and undergo an E–H (capacitive-to-inductive) transition. In this paper, we discuss the results from a computational investigation of the dynamics of power matching to pulsed inductively coupled plasmas (Ar/Cl2 mixtures of tens of mTorr pressure) using fixed component impedance matching networks and their consequences on plasma properties. In this investigation, we used set-point matching where the components of the matching network provide a best-case impedance match (relative to the characteristic impedance of the power supply) at a chosen time during the pulsed cycle. Matching impedance early during the pulse enables power to feed the E-mode, thereby emphasizing capacitive coupling and large excursions in the plasma potential. This early power coupling enables a more rapid ramp-up in plasma density while being mismatched during the H-mode later in the pulse. The early match also produces more energetic ion bombardment of surfaces. Matching late in the pulse diminishes power dissipated in the E-mode at the cost of also reducing the rate of increase in plasma density.}, journal={Journal of Applied Physics}, author={Qu, Chenhui and Lanham, Steven J. and Shannon, Steven C. and Nam, Sang Ki and Kushner, Mark J.}, year={2020}, month={Apr} }
 @article{peterson_ford_brandon_shannon_koh_chua_bera_tian_rauf_kraus_2020, title={Radiofrequency phase resolved electron density measurements with the hairpin resonator probe}, volume={53}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/ab6944}, abstractNote={A floating hairpin resonator probe is used to measure electron density within the radiofrequency cycle of a parallel plate capacitively coupled plasma at steady state. A time resolution capable of detecting electron density oscillations within the radiofrequency cycle is demonstrated. Electron density oscillations are observed at the drive frequency over a range of operating conditions including 10–250 mTorr (1.3–33 Pa) in argon driven at 13.56 or 27.12 MHz. Localized electron density oscillation amplitudes show moderate agreement with literature and fluid simulations near the powered electrode and disagreement in the plasma bulk. The technique is useful for studying electron heating mechanisms in radiofrequency discharges due to its high time resolution.}, number={14}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Peterson, D. J. and Ford, K. and Brandon, J. and Shannon, S. C. and Koh, T. and Chua, T. C. and Bera, K. and Tian, W. and Rauf, S. and Kraus, P. A.}, year={2020}, month={Apr} }
 @article{list_ma_arora_donnelly_shannon_2019, title={Complex transients in power modulated inductively-coupled chlorine plasmas}, volume={28}, ISSN={1361-6595}, url={http://dx.doi.org/10.1088/1361-6595/ab000c}, DOI={10.1088/1361-6595/ab000c}, abstractNote={Time-dependent studies of power-modulated chlorine inductively-coupled plasmas are presented. Power at 13.56 MHz applied to the plasma was modulated between high and low power states. Time-resolved optical emission, power delivery, and Langmuir probe measurements revealed at least two conditions upon switching from high to low power: a ‘normal’ mode in which electron temperature (Te) remains constant, while electron and ion number densities (ne and n+) and optical emission spectroscopic (OES) intensities smoothly drop to a level roughly equal to the fractional drop in power, and an ‘abnormal’ mode in which ne, n+ and OES intensities plummet before the plasma re-ignites and these values rise to levels more commensurate with the drop in power. Whether the plasma operates in the normal or abnormal mode is sensitive to impedance matching conditions and is also a function of pressure and pulsing parameters. This ignition delays in the abnormal mode can be qualitatively understood in terms of a power balance model commonly used to explain instability-induced, self-modulation in highly electronegative plasmas, caused by the slower time response of negative ions compared with electrons. The study indicates that power modulation for added control in processes such as plasma etching will require careful measurement and possibly control of power with microsecond resolution.}, number={2}, journal={Plasma Sources Science and Technology}, publisher={IOP Publishing}, author={List, Tyler and Ma, Tianyu and Arora, Priyanka and Donnelly, Vincent M and Shannon, Steven}, year={2019}, month={Feb}, pages={025005} }
 @article{zafar_martin_shannon_2019, title={Doppler-free, Stark broadened profiles at low plasma densities in helium}, volume={230}, ISSN={0022-4073}, url={http://dx.doi.org/10.1016/j.jqsrt.2019.03.020}, DOI={10.1016/j.jqsrt.2019.03.020}, abstractNote={This work utilizes Doppler-free saturation spectroscopy to measure Doppler-free, Stark broadened spectral profiles for the π-polarization of the HeI 21P → 61D transition in a low density (ne=7×1010−2×1012 cm−3) helium plasma. The measurements were performed in an electron-cyclotron resonance discharge at 23 mTorr with electron density being diagnosed using a combination of Langmuir probe and microwave interferometry techniques. The Doppler-free profiles were observed to be nearly symmetric at ne < 1011 cm−3 but markedly asymmetric above this transition point. Electron density is extracted from the spectral data via fitting to a spectral model based on quasi-static Stark broadening. The fit results are compared to ne measurements obtained using a combination of Langmuir probe and microwave interferometry techniques. The fit and measured ne are shown to agree within 20% on average. Finally, the quasi-static model is shown to be valid in the low-density regime for 21P → 61D helium transition.}, journal={Journal of Quantitative Spectroscopy and Radiative Transfer}, publisher={Elsevier BV}, author={Zafar, Abdullah and Martin, Elijah and Shannon, Steve}, year={2019}, month={Jun}, pages={48–55} }
 @book{icenhour_lindsay_martineau_shannon_2019, title={Electromagnetics Simulations with Vector-valued Finite Elements in MOOSE}, number={INL/CON-18-52320-Rev000}, journal={Idaho National Laboratory Report}, author={Icenhour, C.T. and Lindsay, A.D. and Martineau, R.C. and Shannon, S}, year={2019} }
 @article{ford_peterson_brandon_nam_walker_shannon_2019, title={Measurement of localized plasma perturbation with hairpin resonator probes}, volume={26}, ISSN={1070-664X 1089-7674}, url={http://dx.doi.org/10.1063/1.5065509}, DOI={10.1063/1.5065509}, abstractNote={In situ plasma diagnostics present the classical problem of the scientific measurement: how does one accurately measure a system without also perturbing it? The uncertainty in the degree of perturbation then reflects an inherent uncertainty in the diagnostic results. Microwave probes are no exception. This work discusses an experimental methodology for quantifying the local perturbation in hairpin resonator probe measurements. By pulsing the delivered power to a plasma, an electron density hairpin spike (HS) is readily detected at generator shutoff. The phenomenon is understood to arise from an apparent density rise as the plasma sheath collapses, thus raising the spatially averaged density measured between the hairpin tines. Other explanations for the density rise are eliminated, and the utility of the HS is presented. Under the conditions investigated, the HS provides an experimental comparison to a previous sheath correction factor developed by Sands et al.}, number={1}, journal={Physics of Plasmas}, publisher={AIP Publishing}, author={Ford, Kristopher and Peterson, David J. and Brandon, Joel and Nam, Sang Ki and Walker, Dustin and Shannon, Steven C.}, year={2019}, month={Jan}, pages={013510} }
 @article{coumou_smith_peterson_shannon_2019, title={Time-Resolved Electron Density Measurement Characterization of E–H-Modes for Inductively Coupled Plasma Instabilities}, volume={47}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2019.2909476}, DOI={10.1109/TPS.2019.2909476}, abstractNote={Inductively coupled plasma sources driven by RF power at low-pressure regimes are well adopted for high-volume manufacturing of semiconductor devices. One vexing challenge to the utility of these plasma processing reactors is the existence of the E–H-mode transition. Industry notably avoids the process region associated with this transition, where plasma instabilities and bimodal power coupling prohibit reliable RF power delivery. One plasma instability detailed in this paper is associated with a hysteresis in coupled RF power (current) varying for the E-mode, or weakly capacitive coupling to the plasma, in comparison to the stronger current coupling in the H-mode, where inductive coupling is preferentially dominant. As a result, approximately two orders of magnitude of electron density is relinquished in this transition region from serving industrial manufacturing processes. We characterize the plasma parameter variation through the E-mode to H-mode with a time-resolved measurement of the electron density. Electronegative chemistries are incorporated into our experimental setup. The experimental scheme serves to evaluate RF power delivery and ameliorate its coupling through the transition region. We seek to extend this paper to adopt more efficient power coupling for toroidal plasma sources.}, number={5}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Coumou, David J. and Smith, Shaun T. and Peterson, David J. and Shannon, Steven C.}, year={2019}, month={May}, pages={2102–2109} }
 @article{zafar_martin_shannon_2018, title={High resolution magnetic field measurements in hydrogen and helium plasmas using active laser spectroscopy}, volume={89}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.5039334}, DOI={10.1063/1.5039334}, abstractNote={Passive spectroscopic measurements of Zeeman splitting have been used reliably to measure magnetic fields in plasmas for decades. However, a requirement is that the field magnitude must be sufficiently strong to be resolved over Doppler and instrument broadening (typically >10 000 G). A diagnostic for measuring magnetic fields spectroscopically well below this limit (>20 G) with high sensitivity has been developed at the Oak Ridge National Laboratory. The diagnostic relies on measuring a high resolution spectral profile using Doppler-free saturation spectroscopy (DFSS) and then fitting the spectrum to a quantum mechanical model. DFSS is an active, laser based technique that greatly reduces the influence of Doppler broadening and eliminates instrument broadening. To date, the diagnostic has been successfully employed to measure the magnetic field in magnetized (550-900 G), low-temperature (5-10 eV), low-density (1010–1012 cm−3), hydrogen and helium plasmas in the 5-200 mTorr pressure range using a low power (25 mW) diode laser. Implementing an approximate crossover resonance model, the measurements are shown to be accurate within 5 G for helium and 83 G for hydrogen. The accuracy in hydrogen can be improved to 39 G if the crossover resonances are neglected. A more robust crossover model can decrease this error to <1 G.}, number={10}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Zafar, Abdullah and Martin, Elijah and Shannon, Steve}, year={2018}, month={Oct}, pages={10D126} }
 @article{poulose_goeckner_shannon_coumou_overzet_2017, title={Driving frequency fluctuations in pulsed capacitively coupled plasmas}, volume={71}, ISSN={1434-6060 1434-6079}, url={http://dx.doi.org/10.1140/epjd/e2017-80096-7}, DOI={10.1140/epjd/e2017-80096-7}, number={9}, journal={The European Physical Journal D}, publisher={Springer Nature}, author={Poulose, John and Goeckner, Matthew and Shannon, Steven and Coumou, David and Overzet, Lawrence}, year={2017}, month={Sep} }
 @article{peterson_kraus_chua_larson_shannon_2017, title={Electron neutral collision frequency measurement with the hairpin resonator probe}, volume={26}, ISSN={1361-6595}, url={http://dx.doi.org/10.1088/1361-6595/aa80fa}, DOI={10.1088/1361-6595/aa80fa}, abstractNote={Electron neutral collision frequency is measured using both grounded and floating hairpin resonator probes in a 27 MHz parallel plate capacitively coupled plasma. Operating conditions are 0.1–2 Torr (13.3–267 Pa) in Ar, He, and Ar–He gas mixtures. The method treats the hairpin probe as a two wire transmission line immersed in a dielectric medium. Measurements are obtained using a pressure and sheath correction process by sweeping over assumed collision frequencies in order to obtain the measured collision frequency. Results are compared to hybrid plasma equipment module simulations and show good agreement.}, number={9}, journal={Plasma Sources Science and Technology}, publisher={IOP Publishing}, author={Peterson, David J and Kraus, Philip and Chua, Thai Cheng and Larson, Lynda and Shannon, Steven C}, year={2017}, month={Aug}, pages={095002} }
 @article{talley_shannon_chen_verboncoeur_2017, title={IEDF distortion and resolution considerations for RFEA operation at high voltages}, volume={26}, ISSN={1361-6595}, url={http://dx.doi.org/10.1088/1361-6595/aa9465}, DOI={10.1088/1361-6595/aa9465}, abstractNote={Retarding field energy analyzers (RFEA) have been used extensively to measure the ion flux energy distribution function of plasmas. For consistency, the ion flux energy distribution function is referred to as the ion energy distribution function (IEDf) even though it more accurately represents the one-dimensional ion velocity distribution function. In the past, these devices have operated at voltages less than 1 kV. Higher operating voltages (>2 kV) are currently desired. For an RFEA to operate at these voltages, design changes are necessary that impact the energy resolution and cause space charge build-up. To investigate the effect the design changes have for a high voltage RFEA, electromagnetic simulations and particle-in-cell (PIC) simulations were used to analyze the electric field between the grids, the potential drop in the grid holes, and space charge build-up between the grids. Non-unique optimized dimensions for the RFEA increased the electric field uniformity. The optimization minimizes the electric field from distorting the IV curve or adversely affecting the energy resolution. It was found that a larger grid gap distance and smaller grid hole diameter decreases the potential drop in the grid holes improving energy resolution. IV curves from the PIC simulation were used to obtain space charge distorted IEDfs. The point at which space charge distorts the IV curve is dependent on the grid gap distance and incoming flux. Space charge build-up was found to only affect low energy ions which manifested by cutting off the low energy portion of the IEDf. To fix space charge distortions, the flux into the probe can be limited or it may be possible to account for the distortion when calculating the IEDf.}, number={12}, journal={Plasma Sources Science and Technology}, publisher={IOP Publishing}, author={Talley, M L and Shannon, S and Chen, L and Verboncoeur, J P}, year={2017}, month={Nov}, pages={125001} }
 @book{mededovic thagard_sankaran_kushner_shannon_2017, title={Science challenges in low-temperature plasma science and engineering: Enabling a future based on electricity through non-equalibrium plasma chemistry}, institution={National Science Foundation}, author={Mededovic Thagard, S. and Sankaran, M. and Kushner, M.J and Shannon, S.}, year={2017} }
 @article{tangpatjaroen_grierson_shannon_jakes_szlufarska_2017, title={Size Dependence of Nanoscale Wear of Silicon Carbide}, volume={9}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/acsami.6b13283}, DOI={10.1021/acsami.6b13283}, abstractNote={Nanoscale, single-asperity wear of single-crystal silicon carbide (sc-SiC) and nanocrystalline silicon carbide (nc-SiC) is investigated using single-crystal diamond nanoindenter tips and nanocrystalline diamond atomic force microscopy (AFM) tips under dry conditions, and the wear behavior is compared to that of single-crystal silicon with both thin and thick native oxide layers. We discovered a transition in the relative wear resistance of the SiC samples compared to that of Si as a function of contact size. With larger nanoindenter tips (tip radius ≈ 370 nm), the wear resistances of both sc-SiC and nc-SiC are higher than that of Si. This result is expected from the Archard's equation because SiC is harder than Si. However, with the smaller AFM tips (tip radius ≈ 20 nm), the wear resistances of sc-SiC and nc-SiC are lower than that of Si, despite the fact that the contact pressures are comparable to those applied with the nanoindenter tips, and the plastic zones are well-developed in both sets of wear experiments. We attribute the decrease in the relative wear resistance of SiC compared to that of Si to a transition from a wear regime dominated by the materials' resistance to plastic deformation (i.e., hardness) to a regime dominated by the materials' resistance to interfacial shear. This conclusion is supported by our AFM studies of wearless friction, which reveal that the interfacial shear strength of SiC is higher than that of Si. The contributions of surface roughness and surface chemistry to differences in interfacial shear strength are also discussed.}, number={2}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Tangpatjaroen, Chaiyapat and Grierson, David and Shannon, Steve and Jakes, Joseph E. and Szlufarska, Izabela}, year={2017}, month={Jan}, pages={1929–1940} }
 @article{zafar_martin_shannon_isler_caughman_2016, title={A temporally and spatially resolved electron density diagnostic method for the edge plasma based on Stark broadening}, volume={87}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.4955484}, DOI={10.1063/1.4955484}, abstractNote={An electron density diagnostic (≥1010 cm−3) capable of high temporal (ms) and spatial (mm) resolution is currently under development at Oak Ridge National Laboratory. The diagnostic is based on measuring the Stark broadened, Doppler-free spectral line profile of the n = 6–2 hydrogen Balmer series transition. The profile is then fit to a fully quantum mechanical model including the appropriate electric and magnetic field operators. The quasi-static approach used to calculate the Doppler-free spectral line profile is outlined here and the results from the model are presented for H-δ spectra for electron densities of 1010–1013 cm−3. The profile shows complex behavior due to the interaction between the magnetic substates of the atom.}, number={11}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Zafar, A. and Martin, E. H. and Shannon, S. C. and Isler, R. C. and Caughman, J. B. O.}, year={2016}, month={Jul}, pages={11E505} }
 @article{li_zhang_qiao_yu_peterson_zafar_kumar_curtarolo_hunte_shannon_et al._2016, title={All The Catalytic Active Sites of MoS2 for Hydrogen Evolution}, volume={138}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.6b05940}, DOI={10.1021/jacs.6b05940}, abstractNote={MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s-1 (65-75 mV/dec), 3.2 s-1 (65-85 mV/dec), and 0.1 s-1 (120-160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7-10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies.}, number={51}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Li, Guoqing and Zhang, Du and Qiao, Qiao and Yu, Yifei and Peterson, David and Zafar, Abdullah and Kumar, Raj and Curtarolo, Stefano and Hunte, Frank and Shannon, Steve and et al.}, year={2016}, month={Dec}, pages={16632–16638} }
 @article{imada_ishimaru_xue_zhang_shannon_weber_2016, title={Amorphization resistance of nano-engineered SiC under heavy ion irradiation}, volume={478}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2016.06.031}, DOI={10.1016/j.jnucmat.2016.06.031}, abstractNote={Silicon carbide (SiC) with a high-density of planar defects (hereafter, ‘nano-engineered SiC’) and epitaxially-grown single-crystalline 3C-SiC were simultaneously irradiated with Au ions at room temperature, in order to compare their relative resistance to radiation-induced amorphization. It was found that the local threshold dose for amorphization is comparable for both samples under 2 MeV Au ion irradiation; whereas, nano-engineered SiC exhibits slightly greater radiation tolerance than single crystalline SiC under 10 MeV Au irradiation. Under 10 MeV Au ion irradiation, the dose for amorphization increased by about a factor of two in both nano-engineered and single crystal SiC due to the local increase in electronic energy loss that enhanced dynamic recovery.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Imada, Kenta and Ishimaru, Manabu and Xue, Haizhou and Zhang, Yanwen and Shannon, Steven C. and Weber, William J.}, year={2016}, month={Sep}, pages={310–314} }
 @article{chen_zhang_wang_crespillo_fontana_graham_duscher_shannon_weber_2016, title={Dose dependence of helium bubble formation in nano-engineered SiC at 700 °C}, volume={472}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2016.01.029}, DOI={10.1016/j.jnucmat.2016.01.029}, abstractNote={Knowledge of radiation-induced helium bubble nucleation and growth in SiC is essential for applications in fusion and fission environments. Here we report the evolution of microstructure in nano-engineered (NE) 3C SiC, pre-implanted with helium, under heavy ion irradiation at 700 °C up to doses of 30 displacements per atom (dpa). Elastic recoil detection analysis confirms that the as-implanted helium depth profile does not change under irradiation to 30 dpa at 700 °C. While the helium bubble size distribution becomes narrower with increasing dose, the average size of bubbles remains unchanged and the density of bubbles increases somewhat with dose. These results are consistent with a long helium bubble incubation process under continued irradiation at 700 °C up to 30 dpa, similar to that reported under dual and triple beam irradiation at much higher temperatures. The formation of bubbles at this low temperature is enhanced by the nano-layered stacking fault structure in the NE SiC, which enhances point defect mobility parallel to the stacking faults. This stacking fault structure is stable at 700 °C up to 30 dpa and suppresses the formation of dislocation loops normally observed under these irradiation conditions.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Chen, C.-H. and Zhang, Y. and Wang, Y. and Crespillo, M.L. and Fontana, C.L. and Graham, J.T. and Duscher, G. and Shannon, S.C. and Weber, W.J.}, year={2016}, month={Apr}, pages={153–160} }
 @article{lindsay_graves_shannon_2016, title={Fully coupled simulation of the plasma liquid interface and interfacial coefficient effects}, volume={49}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/49/23/235204}, DOI={10.1088/0022-3727/49/23/235204}, abstractNote={There is a growing interest in the study of coupled plasma-liquid systems because of their applications to biomedicine, biological and chemical disinfection, agriculture, and other areas. Optimizing these applications requires a fundamental understanding of the coupling between phases. Though much progress has been made in this regard, there is still more to be done. One area that requires more research is the transport of electrons across the plasma-liquid interface. Some pioneering works (Rumbach et al 2015 Nat. Commun. 6, Rumbach et al 2015 J. Phys. D: Appl. Phys. 48 424001) have begun revealing the near-surface liquid characteristics of electrons. However, there has been little work to determine the near-surface gas phase electron characteristics. Without an understanding of the near-surface gas dynamics, modellers are left to make assumptions about the interfacial conditions. For instance it is commonly assumed that the surface loss or sticking coefficient of gas-phase electrons at the interface is equal to 1. In this work we explore the consequences of this assumption and introduce a couple of ways to think about the electron interfacial condition. In one set of simulations we impose a kinetic condition with varying surface loss coefficient on the gas phase interfacial electrons. In a second set of simulations we introduce a Henry’s law like condition at the interface in which the gas-phase electron concentration is assumed to be in thermodynamic equilibrium with the liquid-phase electron concentration. It is shown that for a range of electron Henry coefficients spanning a range of known hydrophilic specie Henry coefficients, the gas phase electron density in the anode can vary by orders of magnitude. Varying reflection of electrons by the interface also has consequences for the electron energy profile; increasing reflection may lead to increasing thermalization of electrons depending on choices about the electron energy boundary condition. This variation in anode electron density and energy as a function of the interface characteristics could also lead to significant variation in near-surface gas chemistries when such reactions are included in the model; this could very well in turn affect the reactive species impinging on the liquid surface. We draw the conclusion that in order to make more confident model predictions about plasma-liquid systems, finer scale simulations and/or new experimental techniques must be used to elucidate the near-surface gas phase electron dynamics.}, number={23}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Lindsay, Alexander D and Graves, David B and Shannon, Steven C}, year={2016}, month={May}, pages={235204} }
 @book{shannon_eapen_maria_weber_2016, title={Novel Engineered Refractory Materials for Advanced Reactor Applications}, url={http://dx.doi.org/10.2172/1246903}, DOI={10.2172/1246903}, abstractNote={This report summarizes the results of DOE-NEUP grant 10-853. The project spanned 48 months (36 months under the original grant plus a 12 month no cost extension). The overarching goal of this work was to fabricate and characterize refractory materials engineered at the atomic scale with emphasis on their tolerance to accumulated radiation damage. With an emphasis on nano-scale structure, this work included atomic scale simulation to study the underlying mechanisms for modified radiation tolerance at these atomic scales.}, institution={Office of Scientific and Technical Information  (OSTI)}, author={Shannon, Steven and Eapen, Jacob and Maria, Jon-Paul and Weber, William}, year={2016}, month={Mar} }
 @article{imada_ishimaru_sato_xue_zhang_shannon_weber_2015, title={Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance}, volume={465}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2015.06.036}, DOI={10.1016/j.jnucmat.2015.06.036}, abstractNote={Nano-engineered 3C–SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Imada, Kenta and Ishimaru, Manabu and Sato, Kazuhisa and Xue, Haizhou and Zhang, Yanwen and Shannon, Steven and Weber, William J.}, year={2015}, month={Oct}, pages={433–437} }
 @article{zhang_zafar_coumou_shannon_kushner_2015, title={Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas}, volume={117}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4922631}, DOI={10.1063/1.4922631}, abstractNote={Control of ion energy distributions (IEDs) onto the surface of wafers is an ongoing challenge in microelectronics fabrication. The use of capacitively coupled plasmas (CCPs) using multiple radio frequency (rf) power sources provides many opportunities to customize IEDs. In dual-frequency CCPs using a fundamental frequency and its second harmonic, varying the relative voltages, powers, and phases between the fundamental and second harmonic biases have demonstrated potential as control mechanisms for the shape of the IEDs. In this paper, we report on computational and experimental investigations of IED control in dual-frequency and triple-frequency CCPs where the phase between the fundamental and second harmonic frequency voltage waveform is used as a control variable. The operating conditions were 5–40 mTorr (0.67–5.33 Pa) in Ar and Ar/CF4/O2 gas mixtures. By changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects was significant and not only shifted the dc self-bias but also affected plasma uniformity. When changing phases of higher harmonics, the energies and widths of the IEDs could be controlled. With the addition of a 3rd high-frequency source, the plasma density increased and uniformity improved. Computed results for IEDs were compared with experimental results using an ion energy analyzer in systems using rf phase locked power supplies.}, number={23}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Zhang, Yiting and Zafar, Abdullah and Coumou, David J. and Shannon, Steven C. and Kushner, Mark J.}, year={2015}, month={Jun}, pages={233302} }
 @article{martin_goniche_klepper_hillairet_isler_bottereau_colas_ekedahl_panayotis_pegourie_et al._2015, title={Electric field determination in the plasma-antenna boundary of a lower-hybrid wave launcher in Tore Supra through dynamic Stark-effect spectroscopy}, volume={57}, ISSN={0741-3335 1361-6587}, url={http://dx.doi.org/10.1088/0741-3335/57/6/065011}, DOI={10.1088/0741-3335/57/6/065011}, abstractNote={Interaction of radio-frequency (RF) waves with the plasma in the near-field of a high-power wave launcher is now seen to be an important topic, both in understanding the channeling of these waves through the plasma boundary and in avoiding power losses in the edge. In a recent Letter, a direct non-intrusive measurement of a near antenna RF electric field in the range of lower hybrid (LH) frequencies (ELH) was announced (2013 Phys. Rev. Lett. 110 215005). This measurement was achieved through the fitting of Balmer series deuterium spectral lines utilizing a time dependent (dynamic) Stark effect model. In this article, the analysis of the spectral data is discussed in detail and applied to a larger range of measurements and the accuracy and limitations of the experimental technique are investigated. It was found through an analysis of numerous Tore Supra discharges that good quantitative agreement exists between the measured and full-wave modeled ELH when the launched power exceeds 0.5 MW. For low power the measurement becomes inaccurate utilizing the implemented passive spectroscopic technique because the spectral noise overwhelms the effect of the RF electric field on the line profile. Additionally, effects of the ponderomotive force are suspected at sufficiently high power.}, number={6}, journal={Plasma Physics and Controlled Fusion}, publisher={IOP Publishing}, author={Martin, E H and Goniche, M and Klepper, C C and Hillairet, J and Isler, R C and Bottereau, C and Colas, L and Ekedahl, A and Panayotis, S and Pegourie, B and et al.}, year={2015}, month={Apr}, pages={065011} }
 @article{lindsay_anderson_slikboer_shannon_graves_2015, title={Momentum, heat, and neutral mass transport in convective atmospheric pressure plasma-liquid systems and implications for aqueous targets}, volume={48}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/48/42/424007}, DOI={10.1088/0022-3727/48/42/424007}, abstractNote={There is a growing interest in the study of plasma-liquid interactions with application to biomedicine, chemical disinfection, agriculture, and other fields. This work models the momentum, heat, and neutral species mass transfer between gas and aqueous phases in the context of a streamer discharge; the qualitative conclusions are generally applicable to plasma-liquid systems. The problem domain is discretized using the finite element method. The most interesting and relevant model result for application purposes is the steep gradients in reactive species at the interface. At the center of where the reactive gas stream impinges on the water surface, the aqueous concentrations of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively within 50 μ ?>m of the interface. Recognizing the limited penetration of reactive plasma species into the aqueous phase is critical to discussions about the therapeutic mechanisms for direct plasma treatment of biological solutions. Other interesting results from this study include the presence of a 10 K temperature drop in the gas boundary layer adjacent to the interface that arises from convective cooling. Though the temperature magnitudes may vary among atmospheric discharge types (different amounts of plasma-gas heating), this relative difference between gas and liquid bulk temperatures is expected to be present for any system in which convection is significant. Accounting for the resulting difference between gas and liquid bulk temperatures has a significant impact on reaction kinetics; factor of two changes in terminal aqueous species concentrations like H2O2, NO2− ?>, and NO3− ?> are observed in this study if the effect of evaporative cooling is not included.}, number={42}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Lindsay, Alexander and Anderson, Carly and Slikboer, Elmar and Shannon, Steven and Graves, David}, year={2015}, month={Sep}, pages={424007} }
 @book{kushner_adamovich_aydil_baalrud_barnat_graves_donnelly_economou_eden_gekelman_et al._2014, title={A low temperature plasma science program: Discovery science for societal benefit}, journal={FESAC Strategic Planning Panel}, author={Kushner, M.J and Adamovich, Igor and Aydil, Eray and Baalrud, Scott D. and Barnat, Edward and Graves, David B. and Donnelly, Vincent and Economou, Demetre J. and Eden, J. Gary and Gekelman, Walter and et al.}, year={2014} }
 @article{zhang_varga_ishimaru_edmondson_xue_liu_moll_namavar_hardiman_shannon_et al._2014, title={Competing effects of electronic and nuclear energy loss on microstructural evolution in ionic-covalent materials}, volume={327}, ISSN={0168-583X}, url={http://dx.doi.org/10.1016/j.nimb.2013.10.095}, DOI={10.1016/j.nimb.2013.10.095}, abstractNote={Ever increasing energy needs have raised the demands for advanced fuels and cladding materials that withstand the extreme radiation environments with improved accident tolerance over a long period of time. Ceria (CeO2) is a well known ionic conductor that is isostructural with urania and plutonia-based nuclear fuels. In the context of nuclear fuels, immobilization and transmutation of actinides, CeO2 is a model system for radiation effect studies. Covalent silicon carbide (SiC) is a candidate for use as structural material in fusion, cladding material for fission reactors, and an inert matrix for the transmutation of plutonium and other radioactive actinides. Understanding microstructural change of these ionic-covalent materials to irradiation is important for advanced nuclear energy systems. While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic energy loss may, however, produce additional damage or anneal pre-existing defects. At intermediate transit energies where electronic and nuclear energy losses are both significant, synergistic, additive or competitive processes may evolve that affect the dynamic response of materials to irradiation. The response of crystalline and nanostructured CeO2 and SiC to ion irradiation are studied under different nuclear and electronic stopping powers to describe some general material response in this transit energy regime. Although fast radiation-induced grain growth in CeO2 is evident with no phase transformation, different fluence and dose dependence on the growth rate is observed under Si and Au irradiations. While grain shrinkage and amorphization are observed in the nano-engineered 3C SiC with a high-density of stacking faults embedded in nanosize columnar grains, significantly enhanced radiation resistance is attributed to stacking faults that promote efficient point defect annihilation. Moreover, competing effects of electronic and nuclear energy loss on the damage accumulation and annihilation are observed in crystalline 4H-SiC. Systematic experiments and simulation effort are needed to understand the competitive or synergistic effects.}, journal={Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms}, publisher={Elsevier BV}, author={Zhang, Y. and Varga, T. and Ishimaru, M. and Edmondson, P.D. and Xue, H. and Liu, P. and Moll, S. and Namavar, F. and Hardiman, C. and Shannon, S. and et al.}, year={2014}, month={May}, pages={33–43} }
 @article{jamison_zheng_shannon_allen_morgan_szlufarska_2014, title={Experimental and ab initio study of enhanced resistance to amorphization of nanocrystalline silicon carbide under electron irradiation}, volume={445}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2013.11.010}, DOI={10.1016/j.jnucmat.2013.11.010}, abstractNote={The crystalline-to-amorphous transition in nanocrystalline silicon carbide (ncSiC) has been studied using 1.25 MeV electron irradiation. When compared to literature values for single crystal silicon carbide under electron irradiation, an increase in the dose to amorphization (DTA) was observed, indicative of an increase in radiation resistance. Factors that contribute to this improvement are grain refinement, grain texture, and a high density of stacking faults (SFs) in this sample of ncSiC. To test the effect of SFs on the DTA, density functional theory simulations were conducted. It was found that SFs reduced the energy barriers for both Si interstitial migration and the rate-limiting defect recovery reaction, which may explain the increased DTA.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Jamison, Laura and Zheng, Ming-Jie and Shannon, Steve and Allen, Todd and Morgan, Dane and Szlufarska, Izabela}, year={2014}, month={Feb}, pages={181–189} }
 @article{lindsay_byrns_king_andhvarapou_fields_knappe_fonteno_shannon_2014, title={Fertilization of Radishes, Tomatoes, and Marigolds Using a Large-Volume Atmospheric Glow Discharge}, volume={34}, ISSN={0272-4324 1572-8986}, url={http://dx.doi.org/10.1007/s11090-014-9573-x}, DOI={10.1007/s11090-014-9573-x}, number={6}, journal={Plasma Chemistry and Plasma Processing}, publisher={Springer Science and Business Media LLC}, author={Lindsay, Alex and Byrns, Brandon and King, Wesley and Andhvarapou, Asish and Fields, Jeb and Knappe, Detlef and Fonteno, William and Shannon, Steven}, year={2014}, month={Aug}, pages={1271–1290} }
 @article{coumou_clark_kummerer_hopkins_sullivan_shannon_2014, title={Ion Energy Distribution Skew Control Using Phase-Locked Harmonic RF Bias Drive}, volume={42}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2014.2326600}, DOI={10.1109/tps.2014.2326600}, abstractNote={The energy distribution of ions accelerated through a radio frequency sheath and incident on a plasma-facing material significantly influences material interaction with the plasma and can impact manufacturing at the nanoscale. Ion energy distributions are controlled through appropriate mixing of drive frequencies, which has been shown to control distribution width. This paper presents a modification to multifrequency drive for ion energy control by exploiting a digital frequency and phase controller that enables modification of the higher order moments of the distribution, specifically, controlling the skew of the distribution. By modulating the sheath with two frequencies where one frequency is the harmonic of the other and controlling the relative phase of these two waveforms incident on the plasma-facing surface, skew control is achieved. A simple empirical model is presented to describe this method, as well as experimental validation of the model and demonstration of skew control in a parallel plate capacitively coupled reactor.}, number={7}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Coumou, David J. and Clark, David Hamilton and Kummerer, Theresa and Hopkins, Michael and Sullivan, Donal and Shannon, Steven}, year={2014}, month={Jul}, pages={1880–1893} }
 @article{chen_zhang_fu_wang_crespillo_liu_shannon_weber_2014, title={Irradiation-induced microstructural change in helium-implanted single crystal and nano-engineered SiC}, volume={453}, ISSN={0022-3115}, url={http://dx.doi.org/10.1016/j.jnucmat.2014.07.020}, DOI={10.1016/j.jnucmat.2014.07.020}, abstractNote={Microstructural evolution induced by helium implantation and subsequent heavy ion irradiation has been investigated in single crystal and nano-engineered (NE) 3C SiC. Implantation with 65 keV He+ ions was performed at 277 °C, and the helium depth distribution was determined by elastic recoil detection analysis (ERDA). Transmission electron microscopy (TEM) could not resolve the presence of bubbles in any of the helium-implanted single crystal SiC. However, helium platelets and small dislocation loops (∼50 nm in diameter) were observed in the single crystal sample with the highest implantation fluence after 1 h annealing at 700 °C. Following irradiation with 9 MeV Au3+ ions at 700 °C, no bubbles were observed in the helium-implanted single crystal SiC, regardless of helium fluence. For the helium-implanted NE SiC, subsequent irradiation with 9 MeV Au ions to a dose of 10 dpa at 700 °C resulted in the formation and growth of bubbles, and a bimodal helium bubble size distribution was observed at the highest helium concentration (8000 appm) in the NE SiC.}, number={1-3}, journal={Journal of Nuclear Materials}, publisher={Elsevier BV}, author={Chen, C.H. and Zhang, Y. and Fu, E. and Wang, Y. and Crespillo, M.L. and Liu, C. and Shannon, S. and Weber, W.J.}, year={2014}, month={Oct}, pages={280–286} }
 @article{klepper_martin_isler_colas_goniche_hillairet_panayotis_pegourié_jacquot_lotte_et al._2014, title={Probing the plasma near high power wave launchers in fusion devices for static and dynamic electric fields (invited)}, volume={85}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.4890247}, DOI={10.1063/1.4890247}, abstractNote={An exploratory study was carried out in the long-pulse tokamak Tore Supra, to determine if electric fields in the plasma around high-power, RF wave launchers could be measured with non-intrusive, passive, optical emission spectroscopy. The focus was in particular on the use of the external electric field Stark effect. The feasibility was found to be strongly dependent on the spatial extent of the electric fields and overlap between regions of strong (>∼1 kV/cm) electric fields and regions of plasma particle recycling and plasma-induced, spectral line emission. Most amenable to the measurement was the RF electric field in edge plasma, in front of a lower hybrid heating and current drive launcher. Electric field strengths and direction, derived from fitting the acquired spectra to a model including time-dependent Stark effect and the tokamak-range magnetic field Zeeman-effect, were found to be in good agreement with full-wave modeling of the observed launcher.}, number={11}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Klepper, C. C. and Martin, E. H. and Isler, R. C. and Colas, L. and Goniche, M. and Hillairet, J. and Panayotis, S. and Pegourié, B. and Jacquot, J. and Lotte, Ph. and et al.}, year={2014}, month={Nov}, pages={11E301} }
 @article{jamison_sridharan_shannon_szlufarska_2014, title={Temperature and irradiation species dependence of radiation response of nanocrystalline silicon carbide}, volume={29}, ISSN={0884-2914 2044-5326}, url={http://dx.doi.org/10.1557/jmr.2014.340}, DOI={10.1557/jmr.2014.340}, abstractNote={Abstract}, number={23}, journal={Journal of Materials Research}, publisher={Cambridge University Press (CUP)}, author={Jamison, Laura and Sridharan, Kumar and Shannon, Steve and Szlufarska, Izabela}, year={2014}, month={Dec}, pages={2871–2880} }
 @article{ishimaru_zhang_shannon_weber_2013, title={Origin of radiation tolerance in 3C-SiC with nanolayered planar defects}, volume={103}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4813593}, DOI={10.1063/1.4813593}, abstractNote={We have recently found that the radiation tolerance of SiC is highly enhanced by introducing nanolayers of stacking faults and twins [Y. Zhang et al., Phys. Chem. Chem. Phys. 14, 13429 (2012)]. To reveal the origin of this radiation resistance, we used in situ transmission electron microscopy to examine structural changes induced by electron beam irradiation in 3C-SiC containing nanolayers of (111) planar defects. We found that preferential amorphization, when it does occur, takes place at grain boundaries and at (1¯11) and (11¯1) planar defects. Radiation-induced point defects, such as interstitials and vacancies, migrate two-dimensionally between the (111) planar defects, which probably enhances the damage recovery.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Ishimaru, Manabu and Zhang, Yanwen and Shannon, Steven and Weber, William J.}, year={2013}, month={Jul}, pages={033104} }
 @misc{vineet_karl_a_j_c_a_d_2013, title={Substrate Cleaning Chamber And Cleaning And Conditioning Methods}, url={https://www.lens.org/184-581-960-252-75X}, number={US 8435379 B2}, author={Vineet, Mehta and Karl, Brown and A, Pipitone John and J, Hoffman Daniel and C, Shannon Steven and A, Miller Keith and D, Parkhe Vijay}, year={2013}, month={May} }
 @article{byrns_wooten_lindsay_shannon_2012, title={A VHF driven coaxial atmospheric air plasma: electrical and optical characterization}, volume={45}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/45/19/195204}, DOI={10.1088/0022-3727/45/19/195204}, abstractNote={Abstract}, number={19}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Byrns, Brandon and Wooten, Daniel and Lindsay, Alexander and Shannon, Steven}, year={2012}, month={Apr}, pages={195204} }
 @article{zhang_ishimaru_varga_oda_hardiman_xue_katoh_shannon_weber_2012, title={Nanoscale engineering of radiation tolerant silicon carbide}, volume={14}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/C2CP42342A}, DOI={10.1039/c2cp42342a}, abstractNote={Radiation tolerance is determined by how effectively the microstructure can remove point defects produced by irradiation. Engineered nanocrystalline SiC with a high-density of stacking faults (SFs) has significantly enhanced recombination of interstitials and vacancies, leading to self-healing of irradiation-induced defects. While single crystal SiC readily undergoes an irradiation-induced crystalline to amorphous transformation at room temperature, the nano-engineered SiC with a high-density of SFs exhibits more than an order of magnitude increase in radiation resistance. Molecular dynamics simulations of collision cascades show that the nano-layered SFs lead to enhanced mobility of interstitial Si atoms. The remarkable radiation resistance in the nano-engineered SiC is attributed to the high-density of SFs within nano-sized grain structures that significantly enhance point defect annihilation.}, number={38}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Zhang, Yanwen and Ishimaru, Manabu and Varga, Tamas and Oda, Takuji and Hardiman, Chris and Xue, Haizhou and Katoh, Yutai and Shannon, Steven and Weber, William J.}, year={2012}, pages={13429} }
 @inbook{shannon_2012, place={Boca Raton FL}, title={Plasma-Assisted Pattern Transfer at the Nanoscale}, booktitle={Nanofabrication Handbook}, publisher={CRC Press Taylor and Francis Group}, author={Shannon, S.}, editor={Cabrini, Stephano and Kawata, SatoshiEditors}, year={2012}, pages={111–126} }
 @article{saghir_shannon_2012, title={The impact of Langmuir probe geometries on electron current collection and the integral relation for obtaining electron energy distribution functions}, volume={21}, ISSN={0963-0252 1361-6595}, url={http://dx.doi.org/10.1088/0963-0252/21/2/025003}, DOI={10.1088/0963-0252/21/2/025003}, abstractNote={The Druyvesteyn relation for obtaining electron energy distribution functions (EEDFs) from Langmuir probes is derived based on a model that assumes spherical probe geometry and extends this formulation to arbitrary geometries including the more commonly used planar and cylindrical probes. In this paper, we revisit the formulation of the relationship between electron current, probe potential and EEDF for a cylindrical geometry that considers geometric differences between the spherical and cylindrical case and provides an identical integral relationship to that posed by Mott-Smith and Langmuir in 1926. Comparing the spherical and cylindrical integral relationships and EEDFs reconstructed from them, noticeable differences in EEDF shape are seen using the Druyvesteyn relation for cylindrical probes that becomes more pronounced for highly non-Maxwellian distributions. In order to minimize this geometry-induced distortion, a solution of the integral relation between EEDF and probe current may be needed in place of the more commonly used derivative formulation of Druyvesteyn.}, number={2}, journal={Plasma Sources Science and Technology}, publisher={IOP Publishing}, author={Saghir, Ahmed El and Shannon, Steven}, year={2012}, month={Mar}, pages={025003} }
 @misc{improving plasma process uniformity across a wafer by apportioning power among plural vhf sources_2011, url={https://www.lens.org/035-374-849-498-503}, number={US 7879731 B2}, year={2011}, month={Feb} }
 @article{el saghir_shannon_2011, title={Limitations of Regularization Methods for the Reconstruction of Electron Velocity Distribution Function}, volume={39}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2011.2125970}, DOI={10.1109/tps.2011.2125970}, abstractNote={The extraction of electron energy distribution functions (EEDFs) from Langmuir probe data is a discrete ill-posed problem. This problem rises due to the integral relationship between electron current and the probe voltage known as the Druyvesteyn relation. There have been a number of methods for the solution of this ill-posed problem ranging from data smoothing to a priori solution conditioning. Such methods include truncated singular value decomposition, truncated generalized singular value decomposition, and various regularization techniques. When these methods are extended to solve for similar integral relationships between electron current and electron distributions, complications arise due to their slightly different integral characteristics. For example, the electron velocity distribution function (EVDF) presents a similar ill-posed integral relationship. However, the EVDF integral presents an additional complication of rank deficiency that can` make accurate solutions of the inverse problem extremely challenging. In this paper, the ill-posed and rank deficiency problems of EEDF and EVDF reconstructions, respectively, are compared to highlight these challenges.}, number={4}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={El Saghir, A and Shannon, S}, year={2011}, month={Apr}, pages={1034–1037} }
 @misc{method of processing a workpiece in a plasma reactor with variable height ground return path to control plasma ion density uniformity_2011, url={https://www.lens.org/082-874-457-200-865}, number={US 7968469 B2}, year={2011}, month={Jun} }
 @misc{plasma process uniformity across a wafer by apportioning ground return path impedances among plural vhf sources_2011, url={https://www.lens.org/004-808-299-268-13X}, number={US 7884025 B2}, year={2011}, month={Feb} }
 @misc{plasma process uniformity across a wafer by controlling a variable frequency coupled to a harmonic resonator_2011, url={https://www.lens.org/145-961-377-173-552}, number={US 8080479 B2}, year={2011}, month={Dec} }
 @misc{plasma process uniformity across a wafer by controlling rf phase between opposing electrodes_2011, url={https://www.lens.org/003-021-090-469-410}, number={US 8076247 B2}, year={2011}, month={Dec} }
 @article{el saghir_shannon_2011, title={Reduction of EEDF Measurement Distortion in Regularized Solutions of the Druyvesteyn Relation}, volume={39}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2010.2090906}, DOI={10.1109/tps.2010.2090906}, abstractNote={Electron energy distribution function (EEDF) extraction from Langmuir probe data is an ill-posed problem due to the integral relationship between electron current and probe voltage. Both curve fitting of experimental data and reconstruction of the integral problem through methods, such as Tikhonov regularization, address this to some measure, with regularized solutions offering an advantage in overall EEDF accuracy over curve fitting. Although Tikhonov regularization provides a more accurate estimation of EEDF overall energy space, it typically also can distort the overall shape of the reconstructed distribution, particularly at high energies and energies below the distribution peak. This, combined with the relative ease of use that simple data smoothing algorithms provide, has limited the use of the more advanced reconstruction algorithms in EEDF analysis. In this paper, we will shed some light on these limitations and offer an alternative method to overcome these limitations.}, number={1}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={El Saghir, Ahmed and Shannon, Steven}, year={2011}, month={Jan}, pages={596–602} }
 @article{el saghir_kennedy_shannon_2010, title={Electron Energy Distribution Function Extraction Using Integrated Step Function Response and Regularization Methods}, volume={38}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2009.2036013}, DOI={10.1109/tps.2009.2036013}, abstractNote={Recently, electron energy distribution function (EEDF) extraction techniques have been evaluated using regularized solutions to the integral problem. These techniques do not assume any mathematical representation of the EEDF and solve the integral problem for any function that best represents the EEDF. Also, unlike the more widely used point-by-point extraction of the second-derivative relationship, the integrated relationship between electron current and the EEDF is used, instead of a relatively small fraction of the integrated data in the point-by-point method. In this paper, the electron current for an arbitrary distribution function is derived, assuming that the distribution is a sum of step functions representing such a function. This technique for EEDF extraction is validated by adding noise to numerically generated data and using a regularized least squares (RLS) method to calculate the original function by solving for the individual step function contribution to the total electron current. Comparisons are then made between the expected and the reconstructed solution to evaluate its accuracy with respect to EEDF reconstruction and integrated normalization of the electron density.}, number={2}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={El Saghir, A. and Kennedy, C. and Shannon, S.}, year={2010}, month={Feb}, pages={156–162} }
 @misc{c_2010, title={Method For Testing Plasma Reactor Multi-frequency Impedance Match Networks}, url={https://www.lens.org/078-180-755-189-413}, number={US 7812278 B2}, author={C, Shannon Steven}, year={2010}, month={Oct} }
 @misc{c_s_theodoros_j_g_s_alexander_jingbao_taeho_y_2010, title={Plasma Control Using Dual Cathode Frequency Mixing}, url={https://www.lens.org/089-103-194-978-761}, number={US 7838430 B2}, author={C, Shannon Steven and S, Grimard Dennis and Theodoros, Panagopoulos and J, Hoffman Daniel and G, Chafin Michael and S, Detrick Troy and Alexander, Paterson and Jingbao, Liu and Taeho, Shin and Y, Pu Bryan}, year={2010}, month={Nov} }
 @article{shannon_kinder_paterson_rauf_ventzek_2009, title={Guest Editorial Special Issue on Advances on Plasma Processing for Semiconductor Manufacturing}, volume={37}, ISSN={0093-3813 1939-9375}, url={http://dx.doi.org/10.1109/TPS.2009.2027934}, DOI={10.1109/TPS.2009.2027934}, abstractNote={The 12 papers in this special issue focus on surface interactions, plasma chemistry, and particle behavior near the surface.}, number={9}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Shannon, Steven and Kinder, Ron and Paterson, Alex and Rauf, Shahid and Ventzek, Peter L. G.}, year={2009}, month={Sep}, pages={1662–1664} }
 @misc{c_alexander_theodoros_p_s_j_2009, title={Plasma Generation And Control Using Dual Frequency Rf Signals}, url={https://www.lens.org/092-968-410-882-459}, number={US 7510665 B2}, author={C, Shannon Steven and Alexander, Paterson and Theodoros, Panagopoulos and P, Holland John and S, Grimard Dennis and J, Hoffman Daniel}, year={2009}, month={Mar} }
 @misc{gyoo_j_c_h_wonseok_kwang-soo_2008, title={Dual Bias Frequency Plasma Reactor With Feedback Control Of E.s.c. Voltage Using Wafer Voltage Measurement At The Bias Supply Output}, url={https://www.lens.org/062-461-753-606-236}, number={US 7359177 B2}, author={Gyoo, Yang Jang and J, Hoffman Daniel and C, Shannon Steven and H, Burns Douglas and Wonseok, Lee and Kwang-soo, Kim}, year={2008}, month={Apr} }
 @misc{gyoo_j_c_h_wonseok_kwang-soo_2008, title={Method Of Feedback Control Of Esc Voltage Using Wafer Voltage Measurement At The Bias Supply Output}, url={https://www.lens.org/061-721-158-934-878}, number={US 7375947 B2}, author={Gyoo, Yang Jang and J, Hoffman Daniel and C, Shannon Steven and H, Burns Douglas and Wonseok, Lee and Kwang-soo, Kim}, year={2008}, month={May} }
 @misc{c_alex_theodoros_p_dennis_yashushi_2008, title={Plasma Generation And Control Using A Dual Frequency Rf Source}, url={https://www.lens.org/073-265-216-590-516}, number={US 7431857 B2}, author={C, Shannon Steven and Alex, Paterson and Theodoros, Panagopoulos and P, Holland John and Dennis, Grimard and Yashushi, Takakura}, year={2008}, month={Oct} }
 @article{carter_hoffman_shannon_ryan_buchberger_2007, title={Global Modeling of Magnetized Capacitive Discharges}, volume={35}, ISSN={0093-3813}, url={http://dx.doi.org/10.1109/TPS.2007.906124}, DOI={10.1109/TPS.2007.906124}, abstractNote={Capacitive reactors for semiconductor processing must simultaneously balance many physical phenomena with engineering constraints to achieve the desired processing properties. Important phenomena include electromagnetic RF propagation, gas ionization, plasma heating, plasma transport, and nonlinear sheath effects. Constraints are driven by process uniformity, radical production, thermal control, and reactor-component lifetime. These phenomena and constraints are often modeled in isolation; however, in a real system, they can interact in ways that are not easily foreseen. It is highly desirable to have global models that can provide relatively quick feedback for the proposed modifications to these systems. While an approach based on fundamental physics models is highly desirable whenever possible, the system can quickly become too complicated for quick design evaluations. In this paper, we explore the interaction between several processes by combining fundamental physics models when reasonable, with simplified, heuristic, or even empirical models for processes that are difficult to model from first principles. The goal is to understand the interaction between these processes in a global system without becoming overly encumbered by details in the individual components of the model. We study the effects of static magnetic field on plasma transport and electromagnetic effects arising at high RF frequency. We also change the RF-coupled power and ionization efficiency in a simplified 2-D model geometry to contrast the various effects. We find that discharges with very high frequency and high plasma density can exhibit localized nulls in the RF fields caused by electromagnetic-propagation effects in the sheath region. We find that relatively low static magnetic fields can modify the radial-plasma density profiles. Good agreement is found between the radial-plasma profiles given by the model and those measured in an experiment where the currents in two concentric coils near the plasma are the only variables.}, number={5}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Carter, Mark D. and Hoffman, Dan and Shannon, Steve and Ryan, Philip M. and Buchberger, D.}, year={2007}, month={Oct}, pages={1413–1419} }
 @misc{c_s_theodoros_j_g_s_alexander_jingbao_taeho_y_2007, title={Plasma Control Using Dual Cathode Frequency Mixing}, url={https://www.lens.org/198-151-282-809-229}, number={US 2007/0000611 A1}, author={C, Shannon Steven and S, Grimard Dennis and Theodoros, Panagopoulos and J, Hoffman Daniel and G, Chafin Michael and S, Detrick Troy and Alexander, Paterson and Jingbao, Liu and Taeho, Shin and Y, Pu Bryan}, year={2007}, month={Jan} }
 @misc{c_alex_theodoros_p_dennis_yashushi_2007, title={Plasma Generation And Control Using A Dual Frequency Rf Source}, url={https://www.lens.org/001-723-961-714-703}, number={US 2007/0006971 A1}, author={C, Shannon Steven and Alex, Paterson and Theodoros, Panagopoulos and P, Holland John and Dennis, Grimard and Yashushi, Takakura}, year={2007}, month={Jan} }
 @misc{c_alexander_theodoros_p_s_j_2006, title={Plasma Generation And Control Using Dual Frequency Rf Signals}, url={https://www.lens.org/093-426-771-044-119}, number={US 2006/0266735 A1}, author={C, Shannon Steven and Alexander, Paterson and Theodoros, Panagopoulos and P, Holland John and S, Grimard Dennis and J, Hoffman Daniel}, year={2006}, month={Nov} }
 @article{bera_hoffman_shannon_delgadino_ye_2005, title={Frequency optimization for capacitively coupled plasma source}, volume={33}, ISSN={0093-3813}, url={http://dx.doi.org/10.1109/TPS.2005.845934}, DOI={10.1109/TPS.2005.845934}, abstractNote={Design of an all-in-one (main etch, PR ash and clean) dielectric etch chamber requires independent control of plasma generation from ion energy. Plasma simulation has been performed for a capacitively coupled discharge to study frequency effect on electron density, power deposition, and dissociation fraction. Simulation results demonstrate that plasma production efficiency enhances with increase in frequency while energy of the bombarding ions diminishes. A very high frequency source has been developed to generate high density plasma while radio frequency bias has been used to control ion energy. As illustrated, the etch rate for a dual damascene trench etch process increases, while damage due to ion bombardment is reduced. The dissociation fraction is well behaved to provide necessary corner protection. High-frequency source was used to achieve better performance for dual damascene trench etch process.}, number={2}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Bera, K. and Hoffman, D. and Shannon, S. and Delgadino, G. and Ye, Yan}, year={2005}, month={Apr}, pages={382–383} }
 @misc{c_s_theodoros_j_g_s_alexander_jingbao_taeho_y_2005, title={Plasma Control Using Dual Cathode Frequency Mixing}, url={https://www.lens.org/145-542-565-144-947}, number={US 2005/0090118 A1}, author={C, Shannon Steven and S, Grimard Dennis and Theodoros, Panagopoulos and J, Hoffman Daniel and G, Chafin Michael and S, Detrick Troy and Alexander, Paterson and Jingbao, Liu and Taeho, Shin and Y, Pu Bryan}, year={2005}, month={Apr} }
 @misc{c_alex_theodoros_p_dennis_yashushi_2005, title={Plasma Generation And Control Using A Dual Frequency Rf Source}, url={https://www.lens.org/118-952-420-673-621}, number={US 2005/0034816 A1}, author={C, Shannon Steven and Alex, Paterson and Theodoros, Panagopoulos and P, Holland John and Dennis, Grimard and Yashushi, Takakura}, year={2005}, month={Feb} }
 @article{shannon_hoffman_yang_paterson_holland_2005, title={The impact of frequency mixing on sheath properties: Ion energy distribution and Vdc∕Vrf interaction}, volume={97}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1905798}, DOI={10.1063/1.1905798}, abstractNote={A dual frequency rf sheath is analyzed using a simple rf sheath model to study the interaction between the two driving rf currents and their effect on sheath parameters. A symmetric rf discharge with defined electron density and dc sheath potential is modeled using a sharp boundary sheath approximation. Three results of this study are reported: (1) reproduction of trends in ion energy distribution functions predicted and measured in previous studies, (2) a frequency-mixing-dependent relationship between the dc sheath potential and applied rf potential, and (3) an additional asymmetry in the ion energy distribution function generated by the intermodulation components resulting from the nonlinear sheath.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Shannon, Steven and Hoffman, Daniel and Yang, Jang-Gyoo and Paterson, Alex and Holland, John}, year={2005}, month={May}, pages={103304} }
 @article{holloway_shannon_sepke_brake_2001, title={A reconstruction algorithm for a spatially resolved plasma optical emission spectroscopy sensor}, volume={68}, ISSN={0022-4073}, url={http://dx.doi.org/10.1016/S0022-4073(00)00017-0}, DOI={10.1016/S0022-4073(00)00017-0}, abstractNote={The reconstruction algorithm used for a new spatially resolved plasma optical emission spectroscopy sensor is described. The sensor has a wedge shaped field of view which is rotated horizontally across the plasma. The resulting signal as a function of angle defines an ill-posed linear problem that must be solved to determine the emissivity as a function of radius in the plasma. This problem is solved by modified Tikhonov regularization using a finite difference regularizer which discourages rapid variation in the reconstructed emission. The optimal regularization parameter is determined by minimizing the product of the norm of the residual and the norm of this regularizer. The robustness of the algorithm against noise introduced into idealized data is demonstrated, both for a standard Abel inversion problem and for test data based on the sensor model. The algorithm is used to reconstruct emitted power density profiles and to perform actinometry in a Lam TCP 9400 plasma processing tool; these reconstructions show qualitatively correct behaviors.}, number={1}, journal={Journal of Quantitative Spectroscopy and Radiative Transfer}, publisher={Elsevier BV}, author={Holloway, James Paul and Shannon, Steve and Sepke, Scott M. and Brake, M.L.}, year={2001}, month={Jan}, pages={101–115} }
 @article{collard_shannon_holloway_brake_2000, title={Optical emission reference data for the GEC reference cell}, volume={28}, ISSN={0093-3813}, url={http://dx.doi.org/10.1109/27.902246}, DOI={10.1109/27.902246}, abstractNote={A complete set of optical emission data for the gaseous electronic conference reference cell (GEC) is presented for discharges at 75, 100, 150, and 200 V peak-to-peak and at pressures of 100, 250, 500, and 1000 mtorr. When the GEC project was initiated, these were the setpoints that were to be examined. This paper provides a set of data that can be used as a comparison for other diagnostics. The emission is compared to metastable data obtained from laser-induced fluorescence in helium and argon and computer generated data of the argon metastable data. There is good agreement between these three sets of data and the profiles found in this paper, which can be used as a consistency check for the capacitively coupled GEC reference cell. The data presented were collected with an automated scanning sensor, which gathers wedges of optical emission (Ar I 750.4 nm), at ten vertical heights parallel to the bottom electrode surface. The digitized data was converted to emissivity data as a function of radius using a Tikhonov regularization method.}, number={6}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Collard, C. and Shannon, S. and Holloway, J.P. and Brake, M.L.}, year={2000}, pages={2187–2193} }
 @article{shannon_holloway_brake_1999, title={Spatially resolved fluorine actinometry}, volume={17}, ISSN={0734-2101 1520-8559}, url={http://dx.doi.org/10.1116/1.581933}, DOI={10.1116/1.581933}, abstractNote={A method has been developed to obtain spatially resolved optical emission spectra. This method is used in a diagnostic known as actinometry, where the relative concentration of fluorine can be obtained by examining the ratio of two spectral lines having similar excitation thresholds and excitation cross sections. Generally, the etch rate of silicon is correlated to the concentration of fluorine. In this modified actinometry method, radial emissivity profiles of the discharge are obtained 1 cm above the wafer surface by using a rotating stage to capture small wedges of light from the etching discharge, and analyzing these wedges using a regularized reconstruction algorithm. The relative fluorine concentration is obtained by comparing the ratio of a fluorine (703.75 nm) to argon (750.39 nm) emission line. The atomic fluorine radial profiles correlate to hard masked silicon etch radial profiles processed in a Lam TCP 9400 SE inductively coupled plasma processing tool using an SF6/Ar chemistry. Fluorine loading on the radial fluorine concentration profile over the wafer surface was investigated and found to affect the radial actinometry profile.}, number={5}, journal={Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films}, publisher={American Vacuum Society}, author={Shannon, Steven and Holloway, James Paul and Brake, M. L.}, year={1999}, month={Sep}, pages={2703–2708} }
 @article{shannon_holloway_flippo_brake_1997, title={A spatially resolved optical emission sensor for plasma etch monitoring}, volume={71}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.119938}, DOI={10.1063/1.119938}, abstractNote={A spatially resolved optical emission spectroscopy sensor has been developed, and the resulting reconstructed radial emission profiles from an ArI and ArII line compare well with Ar sputter etch uniformity profiles. The new sensor collects light from a wedge shaped field of view, and is rotated around a single collection point in order to observe the entire plasma through a relatively small viewpoint.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Shannon, Steven and Holloway, James Paul and Flippo, Kirk and Brake, M. L.}, year={1997}, month={Sep}, pages={1467–1468} }
 @phdthesis{shannon, title={A Glow Discharge Tomography Sensor for Monitoring Etch Uniformity}, author={Shannon, S.} }
 @phdthesis{shannon, title={Spatially resolved analysis of plasma etch discharges using a novel optical emission spectroscopy sensor}, author={Shannon, S.} }