AVS Historical Persons | Cedric Powell - 2007

Cedric Powell - 2007

Oral History Interview with Cedric Powell

Interviewed by Paul Holloway, October 17, 2007

HOLLOWAY: Good afternoon. My name is Paul Holloway. I'm a member of the AVS History Committee. Today is Wednesday, October 17, 2007. We're at the 54th International AVS Meeting in Seattle, Washington, and today I have the pleasure of interviewing Dr. Cedric Powell from the National Institute of Standards and Technology. Cedric is a long-time member of the AVS and he's been active in ASTM and some of the international standards activities that have been beneficial to the AVS, so we're very pleased to have you today for the interview Cedric. Thank you very much for agreeing.

POWELL: Thank you Paul.

HOLLOWAY: Again, perhaps you could give us a little bit about your university education and identify your strange accent.
: Okay. I grew up in Australia, specifically in Perth, Western Australia, where I received my bachelor of science degree and a PhD from the University of Western Australia. After completing the work for the latter degree, I went to a postdoc position in 1960 at Imperial College in London, United Kingdom, where I worked for Dennis Gabor, who later received the Nobel Prize in physics for his invention of holography. I worked there on a project to develop a high current, high power ion source intended for controlled thermonuclear reactions. Although this was never built, it was a very fruitful learning experience for me because I became much more familiar with a whole variety of surface phenomenon, ion surface interactions, and the various complications of moving beams of charged particles in complicated electric and magnetic fields.

HOLLOWAY: So, in 1962?

POWELL: I moved to Washington, D.C., to what was then the National Bureau of Standards. I was hired into the Electron Physics Section led then by Dr. Marton. He was replaced soon thereafter by Dr. John Simpson. My appointment was a very temporary one, as I was then expecting, after a year, to return to some position in Australia. That was my game plan at the time. (Holloway: Yeah.) But, my appointment was extended for a second year, a third year, and eventually was converted into a more permanent appointment and I stayed working at NBS, now the National Institute of Standards and Technology, NIST, until my retirement a year ago. I'm now continuing to work there on a part-time basis.

HOLLOWAY: Well, that's quite a long history at NIST and you have been very active. So, when you first arrived at NBS, did it have a surface physics group?

POWELL: No. As I said, I was in an electron physics group and my work at the time was mainly concerned with inelastic scattering of electrons of energies of roughly 8 keV to roughly 20 keV. This work was funded by the former Atomic Energy Commission, who were concerned with mechanisms of damage caused by ionizing radiation. (Holloway: Right.) And, so this was , I guess, an early theme in my work which later became valuable, what with some of the downsides of interactions of, in my case, electrons or other charged particles and x-rays with matter. The mid to late '60s was a time when surface science was becoming more significant. I guess I should have said earlier that my thesis work in Western Australia had been also concerned with inelastic scattering of electrons, typically about 1 to 2 keV by surfaces, and the identification of surface plasmons in particular. (Holloway: Right.) In the mid '60s, Russell Young (a colleague in the electron physics group) started an informal weekly meeting. It was called the Surface Science Lunch Bunch, [Laugh] and was an opportunity for me to begin interacting with other colleagues that included Ted Madey, John Yates, Alan Melmed, and a number of others over the years.

HOLLOWAY: Very powerful names.

POWELL: Yes. This was a big stimulation, a big learning experience for me. I think we all helped each other. So we became aware of new tools for surface science, new capabilities from the very beginning, and the promise of what could be done with these tools.


POWELL: In a reorganization of NBS in 1978, I became Chief of the newly-formed Surface Science Division. Prior to that, there were various colleagues doing surface science in different organizational parts of NBS. This reorganization brought together many of the colleagues actively involved in surface science, and it was a very exciting time.

HOLLOWAY: So, when did you first become involved with the AVS, and in what sort of roles?

POWELL: I'm not absolutely sure when I became a member, but I'm guessing it was probably around 1970. I do know that several years later I served on the Program Committee for the AVS Surface Science Division, and this was in the early '70s. Later, in the early '80s, I was active on the Program Committee for the Surface Science Division and became a member of the Executive Committee, and later a chair of the Surface Science Division. (Holloway: Yeah.) I think, to put this time period in a little bit of perspective, there was a huge growth of interest in surface science, (Holloway: Right.) and many colleagues active in this area were struggling in the early '70s to find a professional home. We had a situation where there were people who looked on themselves perhaps as physicists, chemists, or materials scientists, and who were looking primarily to the main professional societies. But, as it happened, these societies were organized in ways which didn't necessarily make it easy to accommodate new work in surface science, surface physics, or surface chemistry. The AVS was a leader in establishing a Surface Science Division. The history of this Division has been recounted by Peter Hobson and Al Czanderna, (Holloway: Right.) and so this was an early home for colleagues to present their work in surface science. I have to say that many of these people, or some of them, wondered whether or not this was appropriate because the AVS, although in existence for many years, was more known for its strength in vacuum science and vacuum technology (Holloway: Absolutely.) and it seemed incongruous, to put it mildly, to have a new activity, which later became a new Division, focused on surface science. So there was a reluctance of some colleagues to join the AVS. Nevertheless, the proof is in the history. Surface science continued to grow. This, in itself, created some additional pressures. In the early days of modern surface science, and continuing to the present, there was a strong emphasis on the properties of single-crystal surfaces. The new tools which had been developed, LEED in particular, initially allowed characterization of macroscopic single-crystal materials. Prior to that, field ion microscopy, field electron microscopy, and adsorption/desorption studies were the prime techniques. I guess I should also say that there was a lot of interest and activity in the Physical Electronics Conference (Holloway: Right.) where advances in surface science were reported annually. (Holloway: Right.) This was a prime source of intellectual stimulation in the field. But, as new tools were developed, particularly Auger electron spectroscopy and x-ray photo-electron spectroscopy (XPS), and as commercial instruments for these techniques became available in the late '60s, they were not only used to characterize single-crystal surfaces for applications in surface science, but there was a tremendous growth in applications (Holloway: Right.) involving surface characterizations of many types of materials (Holloway: Yes.) following a variety of processing conditions. (Holloway: Right.) For a number of years, results of work on more applied types of problems were presented at AVS meetings in the Surface Science Division program. But partly, because of overall growth, there was pressure on the program.

HOLLOWAY: On the number of papers that could be presented?



POWELL: There was also a certain degree of polarization in these two communities in that the people interested in the surface properties of single crystals thought that the more applied work was, dare I say it, of lesser quality than their own work, which, of course, was demeaning. But the former group of people did not realize the depth of intellectual thought that was needed for the design of experiments involving these complicated materials (Holloway: Right.) to get meaningful results on heterogeneous or complex surfaces which might have a variety of reactions and for which there might be a variety of processes that were operating. (Holloway: Right.) To be fair, I should also say that the more applied people, at that time, did not necessarily have an appreciation of the value of the concepts brought to them by the people doing experiments on single-crystal surfaces.

HOLLOWAY: Especially when their abstract had been rejected? [Laugh]

POWELL: Yes, you're right.

HOLLOWAY: So, there was also, in this same time period, activities other than at NBS through ASTM. Is that pertinent to this?

POWELL: Yes. I'd like to mention that ASTM formed Committee E-42 on Surface Analysis in 1976. It had come about through the efforts of a number of people a couple of years earlier. These people had been using the new surface analysis techniques and applying them to practical problems, and they realized that the techniques were more complicated than they had initially appreciated and that they needed guidance through the use of procedures which would help enable them get more reliable results. (Holloway: Right.) About this time, around 1975-76, a separate ASTM committee, D-32 on Catalysts, was formed and one of their first activities was to conduct a round robin involving Auger and XPS measurements on catalysts. (Holloway: Yeah.) This round robin was led by my NBS colleague Ted Madey, and involved other leaders in the field at the time, Charles Wagner and a Dr. Joshi. They found alarming spreads in reported energies and relative intensities from these catalyst materials, in both Auger and XPS. (Holloway: Right.) It was thought that these spreads were at least partly due to charging. Another round robin was organized with metal samples, and I led it with my NBS colleagues Nils Erickson and Ted Madey under the auspices of the ASTM E-42 Committee. At that time, I was the chair of the Auger subcommittee of E-42. The new round robin also showed considerable spreads in the energies and relative intensities of Auger and XPS peaks, but without the charging complications of the catalysts. These spreads showed that, although the precision of the measurements was excellent, the accuracy was poor. The round robin results formed the basis for my later activities at NBS/NIST. They also formed the basis for parallel activities of my colleague, Martin Seah, of the UK National Physical Laboratory (NPL).

HOLLOWAY: So, there was this confluence then of standardization work with ASTM E-42, activities and interests at NIST, and the Surface Science Division at AVS?


HOLLOWAY: Was there a resolution somehow of the pressures within the AVS Surface Science Division?

POWELL: During this period of time, from let's say '76 to the early '80s, there was a steady growth of what I would now call applied surface science. (Holloway: Right.) There were many AVS members presenting their work at AVS National Symposia and these presentations would typically be in the Surface Science Division sessions. As I mentioned earlier, this was a time of growth and there was pressure on the available slots. (Holloway: Right.) In approximately 1980, the AVS approved a scheme whereby ASTM E-42 would sponsor some sessions at the AVS meeting. So, for a number of years, I think probably four or five, this E-42 group would arrange sessions at the National Symposium. (Holloway: Right.) This was a convenient mechanism, like a band-aid in effect, for relieving the overcrowding in the Surface Science Division sessions, which were, of course limited in number, (Holloway: Right.) and it enabled the more applied work to be presented. I think it also enabled growth of the AVS with people who were interested in these topics, (Holloway: Uhm-hmm.) and for then, as well as continuing to the present time, the E-42 group met just prior to the AVS Symposium in the fall. In the spring, they used to meet in association with the Pittsburgh Conference. (Holloway: Right.) But, after several years, the incongruity of the ASTM E-42 group organizing sessions at the AVS Symposium became apparent. In reality, AVS members were part of the E-42 group, but the ASTM label in an AVS meeting program was thought to be inappropriate. So, I made a proposal in 1985 or 1986 to the AVS Board of Directors to form what later became the Applied Surface Science Division. (Holloway: Right.) The Board of Directors appointed a committee of four or five people, of which I was the chair, to study and report on possible options. I know Charlie Duke was on this committee, but I'm afraid I can't remember the other members. Our first recommendation was that the AVS create an Applied Surface Science Division. The Board agreed to do this, and I was appointed chair of the Division. This new Division then arranged its own sessions at later National Symposia of the Society.

HOLLOWAY: That seemed to work out and alleviated a lot of the pressures within the Society, and the Applied Surface Science Division and the Surface Science Division both remained very active and very successful.

POWELL: I think that's correct. Both Divisions have continued to grow and to prosper, and I think it's worked to the benefit of each, particularly in relieving the obvious overcrowding that occurred previously. An important side benefit of this change that has become more apparent with time is that the Applied Surface Science Division had a strong interest in the quantification of the different techniques that were used to probe surface properties. The initial interest was primarily in measurements of surface composition and sputter depth profiling. As a result, the interactions of charged particles and radiation with surfaces have been core elements of the Symposium programs arranged by the Applied Surface Science Division over the years.

HOLLOWAY: So that automatically led to improved quantification of the data and there were some topical conferences in that area that you were involved with I believe?

POWELL: That's correct. My colleague, Martin Seah at NPL, started organizing a UK conference on a two-year cycle on quantitative surface analysis in approximately 1982. It wasn't until 1986, however, that the opportunity came to organize a similar conference in the USA. This was stimulated, in part, by the IUVSTA Congress which was held in Baltimore in 1986, at which time the AVS Symposium was converted to a five day meeting. Previously it had been only a four-day program. At that time, the ASTM E-42 group had been meeting on the Monday prior to the Symposium. The ASTM group now needed to meet prior to that Monday, and I proposed a one-day topical conference at NBS on quantitative surface analysis. It was held on the Friday before the Baltimore meeting, and we held the E-42 meeting also in Gaithersburg on the Saturday following the topical conference. This topical conference was a big success, and we have then gone on to hold successive conferences in 1987 and continuing on a two-year cycle since then. I was the chair of the organizing committee for the first ten of these. Several years ago I asked other colleagues to take over, and these conferences are now organized by Dave Simons at NIST and Fred Stevie at North Carolina State University. All of the topical conferences after the first have been sponsored by the AVS Applied Surface Science Division, and this has been a big factor in their continuity and financial stability.

HOLLOWAY: The most recent of these topical conferences was held just prior to this year's AVS Symposium, here in the local area?

POWELL: That's correct. The twelfth conference in the series was held at Bellevue, Washington just prior to this year's AVS meeting. And again, it was very successful.

HOLLOWAY: That's quite a significant track record. You mentioned, in the process, IUVSTA in Baltimore. How does the IUVSTA become important in terms of the Applied Surface Science Division?

POWELL: IUVSTA had, by this time - this is the time of the 1986 Baltimore meeting - a Surface Science Division. The triennial IUVSTA Congresses are held on a three-year cycle. My first IUVSTA Congress was in 1977 in Vienna, and this was one of the first opportunities I had to meet and interact with various colleagues in surface science and later applied surface science. I probably met Martin Seah then but I cannot recall that for sure.

HOLLOWAY: It's like you've known him forever, huh? [Laugh]

POWELL: Well, almost forever, because we have very similar interests, and backgrounds, and had similar activities (Holloway: Yeah.) over the years. The IUVSTA Congresses were having growth pressures in their surface science sessions, similar to those in the AVS Symposia, and so their sessions were becoming more crowded. It was then natural to propose that IUVSTA also create an Applied Surface Science Division. This is what I did in 1986. My proposal was approved, and I became the founding chair of the IUVSTA Applied Surface Science Division in 1986, and continued in that role through 1992. I was also active on the IUVSTA Program Committee for the Applied Surface Science Division sessions at the IUVSTA congresses through 1995.

HOLLOWAY: So, the same type of conflict that we saw in the AVS was evident in the IUVSTA?

POWELL: Yes, exactly. The same sociology was evident and the same general growth in both surface science and applied surface science, and it was just mutually convenient to have separate sessions to accommodate this growth and it seemed to be a natural way of solving the problem. I recall that my proposal to create a new Applied Surface Science Division in IUVSTA was thought by some skeptics to be counterproductive; some people wondered whether other Divisions would wish to bifurcate similarly. But the historical result has been that only the original Surface Science has bifurcated with the formation of an Applied Surface Science Division. Instead growth in both AVS and IUVSTA has occurred through creation of additional Divisions that focused on new science and new technologies, such as nanometer science and technology and the like and magnetic materials. These new Divisions are in some ways derivative of surface science, but have become strong and separate in their own right.

HOLLOWAY: Right. Now, besides the Applied Surface Science Division activities that you've mentioned so far, there are also a series of workshops that IUVSTA have sponsored over the years. Would you like to say a word about these?

POWELL: Thank you. I think in the late 1980s IUVSTA decided to broaden its scientific activities by sponsoring a number of workshops. These were intended to bring together experts, a bit like Gordon Conferences in the U.S., to discuss some well-defined problems of emerging science in areas of interest to IUVSTA. It was thought that, with groups of fifty to eighty or so people, this would be a productive opportunity for IUVSTA. IUVSTA also provided some limited funds to sponsor these conferences. I organized one of the first of these IUVSTA workshops. This was held in 1990 at the University of York in the UK on "Surface and Interface Characterization with High Spatial Resolution". This is, of course, a topic which has continued to grow in importance with time. People are still concerned with analysis and characterization of materials, and surfaces in particular, on smaller and smaller length scales. There were other workshops in the mid and late '90s on Auger Electron Spectroscopy: From Physics to Data and on X-ray Photoelectron Spectroscopy: From Physics to Data in which I contributed as a member of the Program Committees. I was co-chair of two later workshops, one in 2002 on X-ray Photoelectron Spectroscopy: From Spectra to Results - Towards an Expert System and another in 2004 on Electron Scattering in Solids: From Fundamental Concepts to Practical Applications. I think that these workshops were very helpful in bringing together experts in the designated areas to stimulate thought and to expand horizons. The 2002 workshop was particularly noteworthy. Jim Castle, at the University of Surrey in the UK, had earlier proposed the notion of an expert system for XPS. This was intended as a set of rules embedded in software which would guide an inexperienced user as well as an expert in designing experiments and providing data, options, and suggestions for the analysis of measured data. I was aware of Jim's work and I was also interested in the same concept from earlier reading in other areas. Jim and I organized the 2002 workshop in St. Malo in France. This workshop was unusual in that, apart from the opening sessions, the program was unstructured. There were sixty or so experts from around the world. They were divided up into six groups of approximately ten each, and their instructions were to come up with recommendations for improved procedures in instrument and specimen characterization, experimental objectives, wide-scan interpretation, protocols for narrow scans, qualitative analysis, and quantitative analysis. By active discussion, we managed to come up with a series of detailed recommendations which, in effect, constitute a set of best practices in the field.

HOLLOWAY: So, this was all under the IUVSTA umbrella?

POWELL: That's right. Each of these six groups prepared a report which is available on the IUVSTA website (for the thirty-fourth workshop). A more condensed account was published in a paper co-authored by Jim Castle and myself in Surface and Interface Analysis in 2004.

HOLLOWAY: I see. Besides the IUVSTA and the ASTM activities, there were some other international activities towards standardization under the name of VAMAS and the ISO Organization. Can you tell us about that?

POWELL: VAMAS stands for the Versailles Project on Advanced Materials and Standards. This came about from a high-level meeting in 1982 that was held in Versailles, France with the presidents and prime ministers of the seven leading industrialized nations in the world (U.S., UK, Japan, Canada, France, Germany, and Italy) and the European economic community. They agreed at this meeting on some high-level collaborations on a variety of projects. These included high-speed trains (with magnetic levitation), some outer-space activities, possibly some bio activities, and one on advanced materials and standards. The latter, VAMAS, as it is now called, was set up at that time and I think that it is the only one of those high-level collaborations which is still in existence. It has just celebrated its twenty-fifth anniversary. They operate by identifying a number of "technical working areas." My colleague, Martin Seah at NPL and I proposed in 1984 that we set up one of these technical working areas on surface chemical analysis. This proposal was approved. I was the first chair and Martin was the first vice-chair. We switched roles in 1988 and again in 2000. This particular technical working area is, in fact, the most productive of all of the VAMAS TWAs, with some thirty-five completed projects. Many of these have been international round robins that have led to reference data, characterization of reference materials, and the validation of software. The round robins in particular were valuable in the same way as the early round robins of the ASTM E-42 committee in assessing the utility and reliability of improved procedures for instrument calibration and for data analysis.

HOLLOWAY: Well, running those round robins, I think, would be a challenge. I would think at times you would have some resistance from people, although there could be also some conflict as a result of that. Did you ever encounter any of that from the round robin exercises?

POWELL: Not really. Many people were eager to participate since they were concerned perhaps about the reliability of measurements by themselves or others and were concerned enough to participate in a project which might lead to an improvement. It was interesting for me when results started to come in, at least for the early E-42 round robin, to examine the similarities and differences in the results. It was also of interest to see the extent to which results from instruments from one manufacturer might be similar or different to those from another. This was a delicate area at NBS because we are not allowed to endorse or criticize instruments from particular manufacturers. We carefully coded each instrument type as Instrument A, Instrument B, etc. (Holloway: Right.) and did not publicly identify information that could reflect perhaps poorly or otherwise on any one manufacturer. (Holloway: Right.) What was interesting to me, in this first round robin, and in retrospect it's not surprising, was that the variability in results from one type of instrument could be very small or very large. I think that the magnitudes of the variabilities were largely due to the individual care taken in the measurements by a particular scientist or instrument operator. Although the round robin results might be viewed at first glance as giving insight on the relative merits of instruments from particular manufacturers, they could equally well be viewed as giving insight into the variability and skills of the individuals who operated and maintained them.

HOLLOWAY: As the mathematicians say, "It was a convolution of those two effects?" [Laugh]

POWELL: Exactly. And I had no way of distinguishing them.

HOLLOWAY: You alluded earlier to the variability of the intensities and energies in electron spectroscopy, for example. Has the standardization that has been achieved through ASTM E-42 and complementary activities through the AVS helped that situation?

POWELL: Yes. The E-42 group was very active as I said, starting in '76, in the development of a variety of recommended practices and guides. There are now over thirty of these that are available, and the history of the development of these standards was reviewed a few years ago by Al Czanderna in an article published in JVSTA. It's also important now to refer to the formation of an ISO Technical Committee on Surface Chemical Analysis. (Holloway: Yeah.) This is TC-201. The initiative for this came from Japan in approximately 1991, and the committee was established formally in 1992. I was asked by the Japanese secretariat to be the first chairman and served as chairman of this committee until 1998, after which I became chair of the subcommittee on Auger Electron Spectroscopy. The round robins that were started in the 1970s led to work at NBS to identify some of the factors which were responsible for the variability of reported energies and relative intensities in AES and XPS. There was parallel work by Martin Seah's group at the National Physical Laboratory in the UK to identify the factors responsible for the variabilitys and, in his case, to recommend certain energies for the calibration of Auger electron spectrometers and certain binding energies for the calibration of XPS spectrometers. It took about ten or so years for the basic measurement science to be completed. Along the way, Martin organized some further round robins that were conducted under the auspices of VAMAS. These were international round robins that helped to validate procedures for calibration of the energy and intensity scales. After the ISO committee was established, it became active in the development of documentary standards for the needed calibrations. I think I proposed a draft of an ASTM E-42 standard in the mid '90s that led to another round robin under E-42 sponsorship. This round robin helped to identify a couple of other factors that needed to be taken into account. The standard for calibrating the binding energy scales of XPS equipment was developed by ISO in approximately 2000, and a parallel E-42 document was prepared about the same time. The ISO committee later prepared two similar documents for calibration of the energy scales of Auger electron spectrometers.

HOLLOWAY: Those are all quite profound achievements and accomplishments for the committees, but I'd like to return to Cedric Powell. You started off with electrons interacting with solids and damage effects, etcetera. In terms of surface analysis, you have created a number of software packages that provide data for inelastic mean free paths and effective attenuation lengths for electron spectroscopies. Could you give us some indication as to the significance of those activities and data sets?

POWELL: Yes. I'd be glad to. Sometime in the early '80s, I was approached by Chuck Wagner, who was an early pioneer in XPS. He was then recently retired from the Shell Research Laboratories. He made pioneering studies of the so-called chemical shifts in XPS that are extremely valuable for identification of chemical state. He also introduced the concept of the Auger parameter, which was also very important for identification of chemical state, particularly for nonconducting samples where charging effects could make it difficult to measure binding energies reliably. He was a contributor to the XPS handbook produced by the Physical Electronics Company in the late '70s. (Holloway: Right.) Chuck approached NBS about creating an XPS database. Since I had known Chuck personally for many years, we discussed his proposal and rapidly agreed that this was desirable. We were able to persuade the NBS Office of Standard Reference to fund him and to create what became the NIST database on x-ray photoelectron spectroscopy. This was an early time for personal computers, and Chuck bought an Apple IIe computer soon after they were introduced. He and I had to agree on numerous details on how to proceed, what the structure of the data would be in the database, and how subscripts might be handled in the representation of XPS and Auger lines. (Holloway: Right.) After Chuck had assembled the first batch of data, in approximately 1985, a staff member at NBS developed the software for the database, in DOS. When the database was released, it was extremely popular, with sales over a number of years of over 500 copies. 

The XPS database project stimulated my interest in databases. Some years later, I was approached by Alex Jablonski (of the Institute of Physical Chemistry in Warsaw, Poland) whom I had met earlier at an international meeting. Alex had developed a database containing differential cross sections for elastic scattering of electrons by atoms. He had expertise in calculating these cross sections, and proposed that his database might become a NIST database. I saw the potential value of this database since I was aware that these cross sections were needed for a great variety of applications (e.g., plasma processes, electron-beam lithography in solids, and radiation dosimetry and therapy). There were then only a few tabulations of such data available for limited numbers of elements, electron energies, and scattering angles, but this new database covered all elements of the periodic table, all energies from 50 eV up to 20,000 eV in steps of 1 eV, and scattering angles in one degree steps. I foresaw that this would be an appropriate and very useful NIST database, and I was able to persuade other NIST colleagues to proceed. While the basic structure of the database was sound, many changes had to be made. For example, to make the database distinctive, Alex had arranged for it to start with a Polish folk tune. [Laugh] I decided this was not appropriate and perhaps not necessary. We also had to come up with a user's guide that was clear, and it was part of my job to help prepare that. (Holloway: Right.) I should also say that this database had been co-developed with Sven Tougaard of the University of Southern Denmark. NIST initially sold this database. 

Alex and I also became interested at that time in preparing a database of inelastic mean free paths. The inelastic mean free path is an important parameter for surface analysis by AES and XPS. Alex and I prepared a very detailed review and analysis of calculated data, values derived from experiments, and comparisons of the two. Alex wrote the software, and NIST released the database which also was initially sold. NIST later decided to make this database and the database with elastic-scattering cross sections available for free. Now, many hundreds of copies of these databases have been distributed just simply on user request. 

We then developed an effective attenuation length database for AES and XPS. The effective attenuation length is needed for film-thickness measurements and is needed to handle the complications due to elastic scattering. Alex and I, in separate scientific work, had been able to document these effects, and other groups were able to confirm them in experiments. While others had done some similar modeling, we wanted to prepare a software tool that people would find convenient to use and which would enable some fairly complicated equations to provide needed data for the average user. (Holloway: Uhm-hmm.) This database was based on data in the inelastic mean free path and elastic-scattering cross-section databases. (Holloway: Uhm-hmm.) 

More recently, NIST has issued a database in which AES and XPS spectra can be simulated for multi-layer thin-fim samples. This database was developed in cooperation with Wolfgang Werner of the Technical University of Vienna.We discussed the database design, and he agreed to prepare a database that would combine the needed physical data as well as the simulation software. This database was released about two years ago and has also been quite popular. Unfortunately, because of budget constraints, we have to sell it.

HOLLOWAY: Well, it sounds like quite a track record in databases and fundamental parameters for the electron spectroscopies. So, you're to be congratulated.

POWELL: Well, thank you very much. I think that they have had useful impacts by putting needed data into the hands of people who could use them. I should mention that we've been able to extend the database with elastic-scattering cross sections for electron energies up to 300 keV. This higher range is important for other applications, such as electron-probe microanalysis, analytical electron microscopy, and electron-beam lithography.

HOLLOWAY: We've covered quite a range of topics in the history. I wondered if there was anything else you'd like to add to the interview Cedric?

POWELL: I have greatly enjoyed my membership in the AVS and the opportunity to interact with a large variety of colleagues. The benefits to me have been incalculable. I mentioned earlier my involvement initially with the Surface Science Division and later the Applied Surface Science Division. I became a member, in the mid '80s, of the Scholarships and Awards Committee, and later a member of the Board of Directors. In the last few years, I've become a member of the Recommended Practices Committee. So, I feel I've come to know the Society better. I've obviously broadened my interactions and horizons by interacting with many people, particularly the users of surface-analytical techniques. These interactions have enriched and expanded my intellectual horizons. They've stimulated me to try to do things that would provide help where needed. Many users do not have the luxury of waiting for a solution tomorrow but need an answer today. They need guidance on how to use expensive instrument time more efficiently and more effectively to avoid common pitfalls; this is, in fact, a situation which continues to the present day. At the topical conference a few days ago, some of the attendees commented on the perceptions of their students. They were driven to solve problems, for example, in materials science. You, Paul, are a professor of materials science, (Holloway: Yeah.) and they look on the surface-analysis tools as simple "black boxes" that should provide an answer quickly. This is, of course, how it should be, but the students do not necessarily recognize the complications that can arise from heterogeneity of the samples, roughness, morphology, beam damage, and crystallographic effects which can modify considerably the observed intensities and which can lead to complications in interpretations of data. We had a workshop just last night, organized jointly by the Applied Surface Science Division and ASTM E-42, in which there were discussions of the problems and pitfalls in quantitative surface analyses and the extent to which multiple techniques can be useful. I think this workshop brought out, as well as the topical conference a few days ago, the value of information from multiple technique. These techniques may have different sampling depths. It is also important to mention that many modern advance materials are in the form of very thin films with nanometer dimensions. The distinction between surface, interface, and bulk properties then becomes less obvious. The distinction between what are considered surface or bulk analytical techniques is also not so obvious. With the continued development of advanced materials, particularly on the nanoscale and with the public concern on related environmental safety and health issues, there is a pressing need for improved characterization of of the physical and chemical properties of nano materials, nanoparticles, and nano-structured materials. These materials are often heterogeneous, and characterizations on the nanoscale may be needed. Such characterizations are very demanding for experts, for those in industry, and for students of the modern generation. It's important that new scientists coming into our field be educated and to be aware of the strengths and weaknesses of a variety of characterization tools so that they can use them effectively.

HOLLOWAY: Absolutely. I often tell my students that you can train a monkey to tune knobs on an instrument and do it properly, but it takes somebody with intelligence to actually understand when they're likely to have errors in their data and the pitfalls of collecting and analyzing and using those data.

POWELL: Yes. This is one of the things that I mentioned regarding the IUVSTA workshop for the development of an expert system for XPS. This was a lofty goal at the time, but I think it is happening now in an incremental or evolutionary way. The skills and expertise of experts can be embedded in software which, if carefully designed, can guide users to the more effective and efficient use of their techniques to everyone's betterment.

HOLLOWAY: Well said. Anything else?

POWELL: I think you've exhausted me. [Laughter]

HOLLOWAY: Well, let me thank you again, Cedric, for being willing to go through the interview and sharing your recollections with us today.

POWELL: Okay. Thank you Paul.


return to top