Doctoral Defense in Physics - Swetha Suresh Babu

Doctoral candidate:
Swetha Suresh Babu

Title of thesis:
High power impulse magnetron sputtering of tungsten and zirconium: An ionization region model study

Opponents:
Dr. Tomáš Kozák, University of West Bohemia, Department of Physics and NTIS - European Centre of Excellence
Dr. Claudia Lazzaroni, Associate Professor, Université Sorbonne Paris Nord, France

Advisor:
Dr. Jón Tómas Guðmundsson, professor at the Faculty of Science, University of Iceland.

Other members of the doctoral committee:
Dr. Daniel Lundin, professor at Plasma and Surface Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden.
Dr. Snorri Þorgeir Ingvarsson, professor at the Faculty of Science, University of Iceland.

Chair of Ceremony:
Dr. Birgir Hrafnkelsson, Professor and Head of the Faculty of Physical Sciences, University of Iceland

Abstract:
The plasma dynamics of high power impulse magnetron sputtering (HiPIMS) discharges with a tungsten and zirconium targets are studied by applying the ionization region model (IRM). The IRM effectively captures the temporal variations of the species densities as well as the electron energy, providing insights into key discharge parameters such as ionization and back-attraction probabilities and the working gas rarefaction processes. When operating with tungsten target, the discharge current at the cathode target surface is composed of both argon and tungsten ions and the argon ions precede the tungsten ions. The investigations reveal that for tungsten target, an initial peak in the discharge current waveform is primarily due to argon ion bombardment, transitioning to dominance by tungsten ions as the discharge progresses. The model illustrates how tungsten ions increasingly contribute to the discharge current at higher cathode voltages, effectively leading to higher discharge current densities, highlighting changes in ionization and back-attraction probabilities correlating with voltage increases. In case of zirconium target, roughly 2/3 of the discharge current at the cathode target surface is carried by Ar⁺ ions while only about 1/3 is carried by Zr⁺ ions. Using the IRM, the substantial effect of electron impact ionization in promoting working gas rarefaction is observed, a critical factor in these discharges, especially pronounced at lower pressures and higher current densities. For HiPIMS discharges with both tungsten and zirconium targets, there are significant contributions from both argon ions and metal ions. This indicates that with both tungsten and zirconium targets the discharges operate on combination of working gas and self-sputter recycling.

About the doctoral candidate:
Swetha was born in India and pursued an Integrated Master’s degree in Physics from the Central University of Tamil Nadu (CUTN) in 2018, followed by a Master of Philosophy in Physics from Madras Christian College (MCC), India, in 2019. Her research during both master’s programs focused on improving bone implants by coating titanium alloys with bone cement and characterizing them to enhance their compatibility and performance. She gained valuable research experience through internship at the Physical Research Laboratory (PRL) in Ahmedabad - Indian Space Research Organisation (ISRO). She began her Ph.D. studies at the University of Iceland in February 2020, where she has contributed to the scientific community by publishing four peer-reviewed papers. Swetha has also delivered lectures and presented posters at international conferences.