@article{myers_ranieri_smirnova_hewitt_peterson_quesada_lenker_stapelmann_2021, title={Measuring plasma-generated center dot OH and O atoms in liquid using EPR spectroscopy and the non-selectivity of the HTA assay}, volume={54}, ISSN={["1361-6463"]}, url={https://doi.org/10.1088/1361-6463/abd9a6}, DOI={10.1088/1361-6463/abd9a6}, abstractNote={Abstract Plasma-generated hydroxyl radicals ( · OH) and oxygen atoms (O) produced by the COST reference plasma jet, a micro-scaled atmospheric pressure plasma jet, were investigated using a variety of experimental techniques. Several gas admixtures were studied to distinguish the contributions of the two reactive oxygen species. Large discrepancies between inferred aqueous · OH densities were noted when using a 2-hydroxyterephthalic acid (HTA) fluorescence assay and electron paramagnetic resonance (EPR) measurements with the spin trap 5,5-dimethyl-1-pyrroline N -oxide—especially when oxygen was present in the feed gas. A series of follow-up experiments including optical emission spectroscopy, H 2 O 2 quantification, and EPR measurements of atomic oxygen using the spin trap 2,2,6,6-tetramethylpiperidine, revealed that the inconsistencies between the measured aqueous · OH were likely due to the propensity of atomic oxygen to hydroxylate TA in a manner indistinguishable from · OH. This renders the HTA assay non-selective when both · OH radicals and atomic oxygen are present, which we report for all three gas admixtures in our experiments. Additionally, considerable degradation of both HTA and the spin adducts measured using EPR spectroscopy was apparent, meaning actual radical densities in the plasma-treated liquid may be considerably higher than implied. Degradation rates compared favorably to previously measured gas phase densities of atomic oxygen in the predecessor of the COST jet and reported degradation of other chemical probes. These results show the prolific role of atomic oxygen in plasma-induced liquid chemistry and caution against diagnostic techniques that are unable to account for it.}, number={14}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, publisher={IOP Publishing}, author={Myers, B. and Ranieri, P. and Smirnova, T. and Hewitt, P. and Peterson, D. and Quesada, M. Herrera and Lenker, E. and Stapelmann, K.}, year={2021}, 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}, 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{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{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{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} }