@article{morsell_dechant_gall_trosan_lietz_stapelmann_shannon_2024, title={Estimation of mean electron energy in helium surface ionization waves on dielectric substrates}, volume={57}, ISSN={["1361-6463"]}, url={https://doi.org/10.1088/1361-6463/ad5451}, DOI={10.1088/1361-6463/ad5451}, abstractNote={Abstract The determination of basic plasma parameters in atmospheric pressure discharges is critical to advancing their use in applications. Atmospheric pressure plasma jets have found use in the fields of medicine, agriculture, material modification and others. Atmospheric pressure plasma jets often generate plasma surface ionization waves (SIW) which interact with and propagate over surfaces. Electrical diagnostics are challenging in SIW due to high collision frequencies and small scale of the plasma discharge. This work employs a passive optical emission line ratio technique to estimate the mean electron energy in SIW over planar dielectric substrates. The method uses an intensity ratio of two helium triplet lines: He( 3 3 S ) at 706.5 nm and He( 3 3 D ) at 587.56 nm. A collisional-radiative model is used to correlate line ratio to mean electron energy and determine dependencies on electron density and He/air gas mixture. Mean electron energies ranging from 3–8 eV are determined in He/air mixtures and are found to remain constant as the surface wave propagates radially. This work provides a 2D, time-resolved, mean electron energy diagnostic for surface ionization wave propagation and validation of numerical modeling in atmospheric pressure systems with spatially varying He/air gas mixtures. The model in question is designed for use with any He line ratio in the n = 3 excitation level.}, number={39}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Morsell, Joshua and Dechant, Corey and Gall, Grayson and Trosan, Duncan and Lietz, Amanda M. and Stapelmann, Katharina and Shannon, Steven}, year={2024}, month={Oct} }
@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
Surface ionization waves (SIWs) propagating along dielectric covered, grounded surfaces have been studied for various dielectric bulk and surface conditions; a dependence on the propagation velocity with respect to dielectric electrical thickness and near surface permittivity profiles are observed. SIWs generated by an atmospheric pressure plasma source are imaged interacting with planar dielectric surface. Surface wave velocity is obtained by tracking emission intensity as a function of time. Target dielectric thickness is varied from
d
=
0.15
−
10
mm and dielectric constant is varied from
ϵ
r
=
6.21
−
9.4
. The propagation of SIWs can be generally predicted by relating their velocity to the RC time constant of the circuit generated between the plasma and the dielectric surface, but it is found that this approximation breaks down for dielectric substrates of sufficient thickness and wave velocity becomes constant. The results show that wave velocity is stable and predictable for target thicknesses beyond a certain point determined by the permittivity of the target material. It is also shown that SIW propagation is strongly driven by the dielectric material near to the surface of the target in addition to the bulk material. The possible mechanisms driving these thickness dependent behaviors is discussed.}, 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
The study of plasma surface ionization waves (SIWs) in recent years has primarily focused on planar surfaces and periodic two dimensional structures. In application, substrates are likely to have non-planar morphology such as cracks, pores, and steps. Additionally, targets for the applications of medicine or catalysis may have targets with heterogeneous composition. This classification of targets are brought under the umbrella of complex interfaces. In this work, plasma SIWs were incident on a complex target consisting of a single channel cut into glass slides. The SIW velocities for the in-channel portion of the wave and radially propagating portion of the wave were tracked. It was found that surface wave velocities are not significantly affected by channel geometry, but primarily increase with pulse energy. A third propagation direction for the SIW is characterized in the azimuthal direction relative to the radial portion of the wave. Channel geometry is found to greatly effect the area treated by the plasma but not the propagation velocity of the surface wave. Surface wave morphology and the impact on application is also discussed. A simple model was introduced to understand the mechanisms behind SIW escape from a channel. It was found that the ratio of pulse energy to a geometry dependent minimum energy can predict the escape angle of a SIW from single channels.}, number={9}, journal={PLASMA SOURCES SCIENCE & TECHNOLOGY}, author={Morsell, Joshua and Trosan, Duncan and Stapelmann, Katharina and Shannon, Steven}, year={2023}, month={Sep} }