Dr. Jeremy Grace, Principal Engineer at Semrock, Inc., talks about his research and describes some fun times in the lab.
Hope this interview gives the followers of The Science and Engineering Cafe the chance to get to know Jeremy and his work.
Please note that Dr. Grace’s tutorial “Practical Aspects of Plasma Modification of Polymer Materials and Plasma Web Treatment” is available online on the Society of Vacuum Coaters website via this link:
Also, this course is available through the on location education program. For more information please visit:
What made you choose plasma as your field of study?
Aside from an undergraduate physics laboratory experiment involving Langmuir probes in a glow discharge tube, my first working experience with plasmas was in sputter-deposited high Tc superconducting thin films for a post doctoral position. Later, when I started work at Kodak, the group I joined had recently become involved in glow-discharge treatment of polymer surfaces. After developing practical tests to quantify the effects of the treatments, my colleagues and I conducted pilot-scale plasma modification experiments and delivered plasma treatment processes to the production environment. I then turned my attention to learning more about the glow discharge plasma sources. It was not so much that I chose plasmas as a field of study, rather that I decided I needed to know more about plasmas in order to continue to develop polymer treatment technology for Kodak.
What message would you like to send to the followers of “The Science and Engineering Café”?
Among Ralph Waldo Emerson’s famous quotes are, “Do not go where the path may lead, go instead where there is no path and leave a trail,” and, “Life is a journey, not a destination.” I think it is important to consider these words and absorb their meaning and relevance to scientific and technological journeys, as well as other journeys we may take in life. I can recall several examples of the consequences of focusing on the destination and not the journey, and the lost opportunities that resulted. In those cases, not only was opportunity lost, but also the destination was never reached. I can also recall examples of the benefits and the growth that resulted from a group of people embracing the journey and following promising paths to real success, even though the destination had to change. In such chases, there is not only the realization that the original goals are not going to be met, but also there is the recognition that other successes have occurred, and those successes are enabling for the achievement of somewhat different goals. These different goals are perhaps even more important or more significant than the original goals. Based on my experiences, the message I would emphasize is that one should be wary of excessive focus on goals, particularly if the goals are not subject to reevaluation in light of what new information is available. Sometimes you may learn or discover things that all but prove that the goals are unachievable, irrelevant, or insignificant; if that knowledge leads to important and meaningful results elsewhere, then the failure to achieve the original goal can be quite a success. If you focus excessively on the destination and do not pay attention during the journey, you may find yourself in a place where, to quote Gertrude Stein, “There is no there there.”
Describe your favorite plasma experiment.
My favorite plasma experiment was one where I varied the driving frequency from 40 kHz to 13.56 MHz in a capacitively coupled discharge and compared the treatment effects on samples placed in different locations. The motivation for the experiment came from my interest in constructing a dual frequency capacitively coupled plasma source for web treatment. I had heard Professor M. R. Wertheimer discuss Microwave/RF dual frequency plasma sources, where the microwaves provide efficient ionization and produce high plasma densities, while the radiofrequency (RF) electrodes produce sheath fields that accelerate ions to substrates placed on the RF electrodes. One of the benefits of the dual frequency approach is that ion density and bombardment energy can be controlled quasi-independently. I later learned that a similar concept had driven the development of an RF/mid-frequency (MF) dual plasma source for PECVD – the Novellus Concept 1, which had a shower head electrode driven at 13.56 MHz introducing PECVD working gas into a gap above a substrate platen, which was driven by an MF power supply operating at 10’s of kHz . In the hopes of being able to control ion densities and ion energies quasi-independently, I set out to construct a dual frequency plasma treater with two sets of capacitively coupled electrodes – one driven at 13.56 MHz, and the other driven at 40 kHz. As I was setting up the system and testing the RF and MF sources, alone and in combination, I collaborated with a surface scientist, Louis Gerenser, to characterize the effects of the dual frequency plasma source on polyester web material. From the initial experiments, it became clear that the effects of the MF capacitively coupled plasma were noticeably different from those of the RF capacitively coupled plasma. Furthermore, it seemed that the MF plasma alone provided treatment effects that could not be readily achieved with the RF plasma. As the MF plasma was supposed to provide the substrate bias, the samples were processed in proximity to the MF electrodes. In order to find out in more detail what aspects of the treatment configuration were providing the unusual results, I set up a single electrode pair and ran experiments with samples located on both treatment electrodes and located above the treatment electrodes and treated at floating potential. We had a few different power supplies and were able to set up to treat at 40 kHz, 450 kHz, and 13.56 MHz. Preliminary work established treatment times and powers required to produce similar surface chemical effects on samples treated at floating potential a few cm away from the treatment electrodes. By carrying out a series of treatments at these different driving frequencies, we were able to observe that the apparent benefits for generating the desired surface chemistry diminished with increasing driving frequency, and they diminished when the samples were treated at floating potential (a few cm from the electrodes) instead of in the cathode sheath near the treatment electrodes. Even though plasma density and ion energies were not independently controlled when treating samples in the cathode sheath of the MF plasma, the results were not only interesting, but also useful, and they led to the development of the “high efficiency” plasma treater and associated patents for its use in treating polyester webs, polyolefin webs, and paper webs.
Who should attend the “Plasma Modification of Polymer Materials and Plasma Web Treatment” at the Society of Vacuum Coaters conference?
Short answer: Graduate students, staff scientists, technicians, technologists, and technical managers who work in the area or have interest in the area of surface modification of polymers by plasmas. Long answer: Plasma treatments are used in the web coating and roll conversion industries to tailor polymer surfaces while preserving their bulk properties. The short course is intended for engineers, scientists, and technicians who would like to gain a better understanding of the influence of plasma process factors on treatment performance, as well as the practical issues related to process robustness, process speed, and ease of scale-up. While much of the short course deals with treatment of polymer webs, the key concepts presented are applicable to polymer surfaces in general and plasma treatment of materials in general.