Jeremy Grace Interview

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:

http://www.svc.org/Education/Webinars.cfm#W314

Also, this course is available through the on location education program. For more information please visit:

 

  Enjoy the interview!

 

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.

 

Figure 4 from a US patent (US 6,399,159) entitled “High Efficiency Treatment of Polyolefins” The bottom figure is from one of the patents that resulted from the bench-top experiment described in the interview. A successful pilot-scale version of the “high-efficiency” treater, shown schematically in the figure, was built and used to carry out treatments for a variety of projects. Thanks go to my colleague, Michael Heinsler, who took on the project to build the device and dealt with all the real-world issues, including the vacuum-compatible, electrified, cooled drum to serve as the cathode.

Figure 4 from a US patent (US 6,399,159) entitled “High Efficiency Treatment of Polyolefins”.
This patent resulted from the bench-top experiment described in the interview. A successful pilot-scale version of the “high-efficiency” treater, shown schematically in the figure, was built and used to carry out treatments for a variety of projects. Thanks go to my colleague, Michael Heinsler, who took on the project to build the device and dealt with all the real-world issues, including the vacuum-compatible, electrified, cooled drum to serve as the cathode.

The figure shows how the chemical nature of the incorporated nitrogen from plasma treatment of a polyester varies from amine-like to amide-like as the driving frequency increases or as the sample is placed away from the treatment electrodes at floating potential, rather than treated in the cathode sheath (similar results are obtained for PET or PEN). The shift in the N 1s distribution to amine-like functionalities is accompanied by an increase in surface nitrogen (the amount of incorporated nitrogen is higher — it is distributed more deeply into the treated surface — and the amount of surface oxygen is reduced — oxygen is lost in the treatment process).

The figure shows how the chemical nature of the incorporated nitrogen from plasma treatment of a polyester varies from amine-like to amide-like as the driving frequency increases or as the sample is placed away from the treatment electrodes at floating potential, rather than treated in the cathode sheath (similar results are obtained for PET or PEN). The shift in the N 1s distribution to amine-like functionalities is accompanied by an increase in surface nitrogen (the amount of incorporated nitrogen is higher — it is distributed more deeply into the treated surface — and the amount of surface oxygen is reduced — oxygen is lost in the treatment process).

 

  7 comments for “Jeremy Grace Interview

  1. Phil Belcyk
    September 15, 2015 at 1:36 pm

    Great interview!

  2. Jeremy Grace
    September 15, 2015 at 2:24 pm

    Thank you Phil!

  3. Eric Liu
    September 16, 2015 at 9:00 pm

    Dr. Grace,

    Corona treatments have been used for the treatment of polymers since the 60s, but the technology did not take off. Do you happen to know why? Thank you.

    • Jeremy Grace
      September 17, 2015 at 8:41 pm

      I believe the “corona” treatments you mention are dielectric barrier discharge treatments. They are commonly called “corona discharge treatments” (CDT) even though that description is not accurate.

      The short answer to your question is that CDT is still used in many industrial processes, but it has not proven universally effective as a plasma treatment technology. While running CDT processes in room air is relatively economical, the treatment chemistry is dominated by the oxygen in the air, and, therefore, the range of treatment chemistry available by CDT is rather limited. Not every treatment need can be met by standard CDT treatment chemistry. I present a longer answer with some more detail below.

      CDT processes generally are carried out in air at standard pressure. Even in cases where effort is made to control the gas environment, the sample surface will bring a boundary layer of air with it as it enters the treatment zone. Furthermore, the standard CDT plasma tends to be spatially non-uniform — streamers of electrons produce the activated species and the streamers tend to extinguish and reform near the same locations. Because the plasma chemistry tends to be dominated by the excited oxygen species in these discharges, and because the treatment effects can be spatially non-uniform, CDT is not universally effective. There are many cases where it can be used successfully, but there are also many cases where alternative plasma treatment technologies (vacuum glow discharge, for example) produce better results.

      In order to achieve electrical break-down at atmospheric pressure, the treatment gaps in CDT are generally very small (millimeter scale, roughly speaking). If both discharge electrodes are bare metal, the initial discharge will progress to an arc-discharge. To prevent arcs from forming, dielectric barriers are introduced on either or both electrodes, or the electrode system can be used only when a dielectric substrate (such as a polymer web) covers one of the electrodes. With the dielectric barrier, as the streamers form and electrons travel to the dielectric surface, the surface charges up and effectively extinguishes the streamer, thus preventing the streamer from developing into an arc. For large electrodes (to treat wide rolls of material, for example) it is important to prevent arc formation. By contrast, there are treatment technologies that produce controlled arcs and use effluent from the arc discharges to treat localized regions of a substrate. These arc sources can be made in an array to treat wide objects, such as a roll of material transported beneath the discharge array.

      As plasma treatment technology has developed, the attractive features of the low-pressure glow-discharges (in particular, control over chemistry and a more uniform treatment process), along with the desire to avoid working at low pressures (to eliminate pump-down times and the need for vacuum equipment) motivated researchers to develop atmospheric pressure glow discharges. Several different approaches have been used to produce stable glow-like discharge with more uniform distribution of reactive species in atmospheric pressure plasmas, including displacing the room air with helium and adding the desired process gas in small amounts to the helium background. Atmospheric pressure glow discharge treatment processes are still attracting interest today.

      Ultimately the process complexity and cost, in addition to the ability to achieve the desired treatment result, are key determinants in putting a treatment technology into industrial use. Because the treatment needs vary so widely from one industrial application to another, and because the effective budget for treatment processes differs so widely from one type of product to another it is unlikely that any single treatment technology will dominate the market.

    • Jeremy Grace
      September 21, 2015 at 9:50 pm

      Eric, in re-reading my reply, I noticed that I omitted the greeting… that answer to your question should have begun, “Eric, thanks for your question….” Apologies for that unintentional omission.

  4. Tom Juliano
    September 21, 2015 at 1:05 pm

    Jeremy – brilliant words and insights on goals and journeys! Lots of truth nuggets in there!

    • Jeremy Grace
      September 21, 2015 at 9:53 pm

      Tom,
      Thanks for the kind words. I am glad you found nuggets in the thoughts I shared about goals and journeys.

Comments are closed.

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