ILTPC Newsletter 29

Images to Excite and Inspire!

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LTP Perspectives: Policy, Opportunities, Challenges

Choose Your Research Problems Carefully

The scientific advances of the field of low temperature plasma science can be quickly translated to society benefiting applications. This translational nature of LTP science is something that we should take pride in but also comes with a great responsibility.

The majority of the research performed by the international LTP community in universities, national laboratories and to some extent in industry is funded by governments. Government funding comes from fellow citizens who pay taxes. In this sense, your next-door neighbor is funding your research.

Given the finite resources of governments, decisions on funding priorities need to be made. A former president of the United States, Dwight D. Eisenhower, addressing the American Society of Newspaper Editors in 1953 said: “The cost of one modern heavy bomber is this; a modern brick school in more than thirty cities. It is two electric power plants, each serving a town of 60,000 population…We pay for a single fighter with a half-million bushels of wheat.” President Eisenhower was speaking in military terms but the same applies to funding of LTP science. Instead of funding our research, governments could have spent the money on improving healthcare, building new transportation systems, reducing pollution or on foreign aid to relieve hunger and suffering in the developing world. But that was not the decision – our research was funded instead.

Why were those decisions made? Why was our research funded? Certainly, part of the logic for these decisions is based on governments needing to educate the next generation of scientists and engineers. While the primary motivation is indeed investments in the future, these decisions go beyond work force development. Governments believe that our research will, in the long run, do more to improve healthcare and relieve hunger than directly spending that money now on those goals. Indeed, science has fulfilled that promise with, for example, vaccines and synthetic fertilizer that are believed to have saved the lives of a billion people. While many government agencies fund mission driven research that directly targets technological innovation, they also fund basic research not directly linked to future technologies. This basic research has shown to be responsible for major, often serendipitous, discoveries that benefit our society. Investigations in fundamental science enable diverse creativity, a corner stone of science and is equally important as mission driven research. However, that does not relieve the fundamental researcher from choosing problems that have relevance to society.

There is a very large opportunity cost that is borne by society, by governments and by your next-door neighbor, to fund our research. LTP has in large part met the expectation that our research, funded by our next-door-neighbors, has indeed provided value in countless areas ranging from enabling the semi-conductor revolution to water disinfection and space propulsion. We have a collective responsibility to continue to do so by choosing our research challenges and research questions carefully to ensure they benefit society.

Prof. Mark J. Kushner University of Michigan, USA mjkush@umich.edu Prof. Peter J. Bruggeman University of Minnesota, USA pbruggem@umn.edu

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Leaders of the LTP Community: Career Profiles

Professor Gottlieb Oehrlein – A Scientist and Mentor for All Seasons

As one of the top low temperature plasma scientists in the world, Professor Gottlieb Oehrlein has made key contributions in deepening our understanding of plasma-surface interactions. Gottlieb Oehrlein is a Professor in the Department of Materials Science and Engineering and the Institute for Research in Electronics and Applied Physics (IREAP) at the University of Maryland, College Park, USA. He received his Vordiplom in physics from Würzburg University (Germany) in 1976, and M.S. and Ph.D. degrees in physics from the State University of New York at Albany in 1978 and 1981, respectively. He further received the SUNY Chancellor’s Distinguished Dissertation Award for his PhD research on defects in solid state materials. Upon graduation, he joined IBM as a Research Staff Member at the IBM T. J. Watson Research Center in Yorktown Heights, NY.

While at IBM, he leveraged his graduate school work on defectivity in semiconductors by applying it to the new field of low temperature plasmas, most notably employing surface analysis techniques such as x-ray photoelectron spectroscopy and ellipsometry. Focusing on the plasma surface interactions that occur when exposing the materials to novel plasma chemistry, he helped determine the role of gas chemistry admixtures such as O₂ and H₂ to CF₄, CHF₃ and CF₄/H₂ on the etching of SiO₂, Si and other materials in capacitively coupled plasmas. His work identified the near-surface damage and presence of reaction layers such as SiC, and CF_x, which are now instrumental in enabling selective patterning.

From 1993-2000, he returned to his Alma Mater in Albany, as a Professor of Physics, where Eric (a co-author of this profile) had the pleasure of meeting him and becoming a member of his research group. While working in his lab, the focus of Prof. Oehrlein’s research turned to the characterization of inductively coupled plasmas and the detailed understanding of the mechanisms behind the evolution of the fluorocarbon reaction layer during dielectric etching. His graduate students had many discussions over lunch debating the fluorocarbon film formation and its role as a function of ion energy. One theory was that it was an inhibiting layer to which its thickness governed the selectivity between various dielectric films, while the other theory was that it was a source of fluorine which could enable unique etch enhancements. Ultimately, the research proved that the fluorocarbon film was both an inhibiting layer and a source of fluorine.

In 2000, Prof. Oehrlein relocated to the University of Maryland and shifted his research focus to the mechanistic understanding of plasma-surface interactions behind dielectric etch selectivity to photoresist materials, as 193 nm resists became prevalent in the industry. Here, Sebastian and Bobby (co-authors of this profile) joined the lab as graduate students. The group’s research was key to understanding the role of polymeric structure and sidegroups, such as methyl adamantyl methacrylate, in determining etch rate selectivity as a function of ion energy and plasma chemistry. The highly competitive and inspiring environment that brought about many a discovery is fondly remembered while the group collaborated with a world-class team including Professors David Graves, Grant Willson and Ray Phaneuf to investigate plasma interactions with polymers and photoresists.

Beginning in 2010, IBM had awarded Prof. Oehrlein with an IBM Faculty Award and we all had the opportunity to collaborate again on the experimental validation of Atomic Layer Etching (ALE). In this seminal work, Prof. Oehrlein and his group were able to validate prior models of fluorination profiles, thin film formation and resulting selectivities, and demonstrate the ability to achieve self-limited cyclical etching of SiO₂ using fluorocarbon gas chemistries. Somehow the thread of this work that started over 20 years ago in Albany continued to be improved upon in College Park from graduate student to graduate student and ultimately resulted in a graduate student generational meeting at the most fitting place: an ALE house during AVS 2022 in Pittsburgh, PA.

Prof. Oehrlein has coauthored more than 300 publications with ~12,000 citations and H index of 60. He is a Fellow of AVS (1998), International Union of Pure and Applied Chemistry (2000), and International Plasma Chemistry Society (2017). He received the Electronics Division Award of the Electrochemical Society (1992), the IBM Faculty Award in 2002 and 2010, the Plasma Prize of the Plasma Science and Technology Division of AVS (2005), the DPS Nishizawa Award (2019) and the AVS John A. Thornton Memorial Award (2019). In March 2023, Prof. Oehrlein will receive the Plasma Material Science Hall of Fame Award in Nagoya.

Overall, Prof. Oehrlein is best known for his work understanding plasma surface interactions. His research methods continue to lead to groundbreaking insights in his current work on plasma material interactions using atmospheric pressure plasma sources for modification of organic materials, biomolecules, foods, control of microorganisms, and catalysts to produce renewable fuels.

Dr. Eric A. Joseph, Dr. Sebastian Engelmann and Dr. Robert (Bobby) Bruce IBM T. J. Watson Research Center, USA ejoseph@us.ibm.com, suengelm@us.ibm.com, rlbruce@us.ibm.com

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General Interest Announcements

2nd US Low Temperature Plasma Summer School, June 26-30 2023

The 2nd United States Low Temperature Plasma Summer School (USLTPSS) will be held June 26-30, 2023 on the campus of the University of Michigan, Ann Arbor, MI, USA. The USLTPSS is intended to provide an opportunity for graduate students and researchers new to the low temperature (LTP) field to be immersed in the fundamentals and applications of LTPs for one week and to learn from leading researchers in their field. The lecturers and topics for the 2nd USLTPSS are listed on the USLTPSS webpage. There will also be hands-on session in diagnostics and modeling, posters sessions and special topic mini-workshops.

As part of the registration fee, accommodations will be provided for students and post-doctoral scholars in university dormitories. Breakfast, lunch and several dinners will be provided. For attendees not staying in university housing, lunch and several dinners will be provided.

Attendance at the USLTPSS is limited. To apply to attend the USLTPSS, please fill out this application.

Applications received by March 15 will receive full consideration. The application portal will be closed on April 1, 2023.

Contacts: Prof. Peter J. Bruggeman University of Minnesota, USA pbruggem@umn.edu Prof. Mark J. Kushner University of Michigan, USA mjkush@umich.edu

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Meetings and Online Seminars

20^th International Conference on Plasma Physics and Applications, Iași, Romania, 14-16 June 2023

We cordially invite you to the 20^th International Conference on Plasma Physics and Applications (CPPA), on 14-16 June 2023, fully in person. The conference venue is Alexandru Ioan Cuza University of Iași, Romania.

The International Conference on Plasma Physics and Applications is organized by the Alexandru Ioan Cuza University of Iași (UAIC) and the National Institute for Laser, Plasma and Radiation Physics, Bucharest (INFLPR), every two years, alternatively in Bucharest and Iasi. The Conference is focused on advances in plasma fundamentals and applications and provides a forum for discussion and scientific collaborations for Romanian and international plasma community.

CPPA welcomes any contribution on plasma physics, from fundamentals to applications. The contributions will be assigned to one of the four major topics:

• T1. Processes in plasma, modelling and simulation
• T2. Gas discharge physics, plasma sources and diagnostics, space, dusty and laser plasmas
• T3. Plasma material processing and fusion technology
• T4. Plasma applications in environment, biology, medicine and agriculture

Please check the webpage for the international scientific committee, the local organizing committee and practical information.

Contacts: Prof. Lucel Sirghi, Dr. Bogdana Mitu Conference Chairs Assoc. Prof. Ionut Topala, Dr. Monica Magureanu Scientific Secretaries Alexandru Ioan Cuza University of Iași, Romania cppa2023@uaic.ro

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Community Initiatives and Special Issues

Please submit your announcement for Community Initiatives and Special Issues to iltpc-central@umich.edu.

Research Highlights and Breakthroughs

Describing Local and Non-local Electron Heating by the Fokker-Planck Equation

Local Ohmic and non-local (stochastic, collisionless) heating in plasmas is revisited in a recent paper, by applying the Fokker-Planck equation in combination with the Langevin equation for the derivation of the heating operator. The paper provides on the one hand a review of the present knowledge on the basis of the Boltzmann equation, while on the other hand new research results are introduced. This includes, in particular, the use of the Fokker-Planck equation for describing the electron-field interaction, a generalized plasma dispersion function (for arbitrary distribution functions, considering a velocity dependent elastic collision frequency), and a concept for integrating the heating operator in a local Boltzmann solver. The latter concept allows calculating the global distribution function in the non-local regime at low pressures. The general concept is investigated in detail for the case of inductively coupled radio-frequency plasmas (ICPs). Particular emphasis is on using a self-consistent electric field profile. Finally, yet importantly, the role of elastic collisions in converting energy gained in the field into heat, characterized by irreversibility, is investigated. The paper is written in a tutorial style and all concepts are derived from first principles. It should serve as an introduction to the field for advanced students as well as a reference for experienced researchers.

Contacts: Prof. Uwe Czarnetzki Ruhr University Bochum, Germany uwe.czarnetzki@rub.de Prof. Luís Lemos Alves Universidade de Lisboa, Portugal llalves@tecnico.ulisboa.pt

Source: Reviews of Modern Plasma Physics 6, 31 (2022). https://doi.org/10.1007/s41614-022-00086-0

Acquired Non-Thermal Plasma Resistance Mediates a Shift Towards Aerobic Glycolysis and Ferroptotic Cell Death in Melanoma

Over time, cancer patients undergoing treatment often develop resistance to therapy. This acquired therapy resistance represents a major obstacle as it leads to poor patient outcomes. Therefore, the potential for cancerous cells to acquire resistance should be investigated, especially for novel, developing treatments like non-thermal plasma (NTP).

In this study, we developed, for the first time, an NTP-resistant cell line (A375-NTP-R) from a previously sensitive melanoma cell line (A375) to investigate NTP sensitivity and resistance pathways. After 12 consecutive weeks of repeat NTP exposure and re-culturing, the cell line became nearly 10 times more resistant to NTP compared to the parent cell line of the same age. RNA sequencing analysis showed several altered metabolic and cell death pathways. Further metabolic evaluation showed that the NTP-resistant cells demonstrated a shift from cellular respiration to aerobic glycolysis. Cell death analysis revealed that NTP-resistant cells were more vulnerable to lipid peroxidation and ferroptosis, while NTP-sensitive cells were more prone to apoptosis.

Altogether, we uncovered fundamental insights and new hypotheses into NTP sensitivity and resistance. We also established a valuable new method for studying these mechanisms, which can be applied to other cell lines/cancer types. We hope these insights could provide the first steps towards identifying potential treatment biomarkers for NTP therapy.

Contact: Dr. Abraham Lin abraham.lin@uantwerpen.be Prof. Annemie Bogaerts annemie.bogaerts@uantwerpen.be University of Antwerp, Belgium

Source: Drug Resistance Updates 67, 100914 (2023). https://doi.org/10.1016/j.drup.2022.100914

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New Resources

Please submit your announcement for New Resources to iltpc-central@umich.edu.

Career Opportunities

Other career opportunities

Collaborative Opportunities

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Disclaimer

The content of this Newsletter comes from the contributions of members of the ILTPC. The Newsletter editors are attempting to provide as inclusive a newsletter as possible by publishing contributions from all members of the ILTPC. However, they do reserve the right to not publish contributions that they deem as not being appropriate. The Newsletter editors may do some light editing of the original submissions to maintain a consistent tone and style. The editors expect that submitting contributors have permission to share images. Inclusion of items in the Newsletter should not be interpreted as an endorsement by the editors nor as an advertisement for commercial purposes. The content of this newsletter should also not be interpreted as an endorsement by our sponsors – the US National Science Foundation, the US Department of Energy and the University of Michigan.

Editors: Prof. Peter J. Bruggeman University of Minnesota, USA pbruggem@umn.edu Prof. Mark J. Kushner University of Michigan, USA mjkush@umich.edu