Abstract
I was certainly surprised, and felt extremely honored, when Salvador Miret-Artés suggested that he would like to organize this festschrift. Before that day I never anticipated that such an honor would come to me. I would like to thank Salvador for the large amount of time and work he has expended in organizing this special issue, the Editors of Journal of Physics: Condensed Matter for making it possible, and also the contributing authors for their efforts.
My family home was outside of Petersburg, Virginia in Dinwiddie County in an area that was, during my youth, largely occupied by small farms. This is a region rich in American history and our earliest ancestors on both sides of the family settled in this area, beginning in the decade after the first Virginia settlement in Jamestown. My father was an engineer and my mother was a former school teacher, and their parents were small business owners.
From earliest memories I recall being interested in finding out how things worked and especially learning about the wonders of nature. These interests were fostered by my parents who encouraged such investigations during long walks, visits to friends and relatives, and trips to museums. However, my earliest memory of wanting to become a scientist is associated with a Christmas gift of a chemistry set when I was about ten years old. I was absolutely fascinated by the amazing results that could be achieved with simple chemical reactions and realized then that I wanted to do something in life that would be associated with science.
The gift of that small chemistry set developed over the next few years into a serious interest in chemistry, and throughout my junior high-school years I spent nearly all the money I earned doing odd jobs for neighbors on small laboratory equipment and chemical supplies, eventually taking over our old abandoned chicken house and turning it into a small chemistry lab. I remember being somewhat frustrated at the limits, mainly financial, that kept the scale of my chemical experiments to simple things such as growing crystals of all available salts, making interesting colors and dyes, and a whole variety of pyrotechnics. The fireworks and small explosives were largely carried out without the knowledge of my parents, and it was surely fortunate that my lab was well away from the house because fires nearly got out of hand a couple of times.
Interest in becoming a chemist continued into my high-school years until I took a traditional course in elementary physics. This course was a little out of the ordinary because it was taught by the industrial shop teacher, Mr John M Leete, a man who had an interest in science but very little scientific training or knowledge. He had been given this course because there was nobody else available to teach it, and the way he chose to handle his assignment was to gather the eight or so students around a circular table and spend each hour of class time reading a book together and trying to understand it. This turned out to be an interesting and effective way to learn, with Mr Leete probably learning just as much as the students. The experience of this course made quite an impression, not only because of the fascination of the subject matter, but also because of what it demonstrated about the process of teaching and learning. It was at this time that I realized that physics was the science that I wanted to pursue.
I finished high-school at the beginning of 1961, and after working in a local tobacco factory for a short period I enrolled as an undergraduate at the University of Richmond, a college with a very beautiful campus on the outskirts of Richmond and relatively close to home in Petersburg. Another advantage of living in Richmond was that I could continue playing in the Richmond Symphony Orchestra, eventually becoming its principal bassoonist. Music was an interest that developed in high school, which was when I first became a member of the Richmond Symphony, and later in college I earned a modest income playing there as well as in the Norfolk Symphony and several other ensembles. After four years in Richmond and graduating with a degree in physics and mathematics I enrolled as a graduate student in the Physics Department of the University of Virginia. At Virginia I went to work with the well-known Professor Nicholas Cabrera who was then also the department Chair. After a little more than a year, Cabrera took a temporary leave of absence to take a position in Mexico, but this temporary departure later became permanent when he answered a call to return to Spain to establish and lead the Department of Physics at the new Universidad Autonoma de Madrid. Before leaving Virginia, however, Cabrera hired a new Assistant Professor who had already made quite a name for himself, and this was Vittorio Celli. Celli and I immediately hit it off and I continued my studies with him. He is the person to whom I owe the greatest debt as a teacher and mentor who instilled the highest standards of scientific research.
We began work on some problems in superconductivity and surface magnetism which I found very interesting, but one day we had a meeting with Professor Sam Fisher of the Department of Aeronautical Engineering at Virginia that totally changed the direction of our research. Sam and his graduate students had carried out a series of experiments on the scattering of high-quality jet beams of helium atoms off of clean, cleaved lithium fluoride surfaces under high-vacuum conditions. Essentially, Sam was repeating experiments originally performed by Otto Stern and coworkers in Frankfurt and Hamburg in the late 1920s, but he had not realized the fact that he was seeing diffraction patterns. We immediately recognized that he was measuring diffraction, and not long thereafter we recognized that his measurements should be sufficiently precise to measure energy transfers due to single quantum excitations of vibrations at the surface. Both Vittorio and I quickly dropped the research that we had been doing and started to think about developing theories that could exploit the possibilities of gaining information about the microscopic structure and dynamics of surfaces using, as a tool, the methods of atom scattering. With Cabrera and Frank Goodman, who was Guest Professor in the Aeronautical Engineering Department, we developed these ideas into theories that have turned out to be useful for describing both diffraction and single-phonon inelastic scattering in atom-surface collisions. This experience of developing theoretical explanations for that interesting new data of Fisher's group left me with a great appreciation for experimental physics and is probably the reason that a large part of my work ever since has been oriented toward trying to develop theoretical methods to aid in explaining experimental results. A major change in life, and one very much for the better, occurred during my graduate school years, and this was marriage to Lucy Schenkman. We met through our mutual interest in music when I was an undergraduate in Richmond. Our marriage has been a very rewarding experience. We are extremely proud of our two children, who have now gone on into their marriages and careers, and have given us four wonderful grandchildren.
After receiving my PhD in 1969 I took a position as Assistant Professor of Physics at Clemson University and have remained there ever since. During those early years at Clemson our teaching loads were rather high, but there was still time to carry out a research program and mentor graduate students. Clemson had established a generous sabbatical program and in 1977 I took my first sabbatical at the Centre d'Études Nucléaires de Saclay (now Le Centre CEA de Saclay), working with Jean Lapujoulade and Georges Armand. Armand by that time was doing work in various areas of the theory of surface physics and Lapujoulade was leader of a group that had built one of the earliest pieces of apparatus for scattering jet beams of helium atoms from surfaces under clean high-vacuum conditions. This sabbatical was the beginning of a very fruitful and extremely pleasant collaboration working on a large variety of problems on the structure and dynamics of metal surfaces as elucidated by helium atom scattering, a collaboration that lasted until the retirements of Armand and Lapujoulade in the early 1990s. Nearly every summer and two additional sabbaticals in 1984 and 1992 were spent in this very stimulating research atmosphere located in the scientific complex on the southern edge of Paris. This period included collaborations and interactions with many of the colleagues, visitors and students at Saclay including C S Jayanthi, Abdelkader Kara, Luc Barbier, Hans-Joachim Ernst, Francoise Fabre and Bernard Salanon.
Directly after this first sabbatical I spent a summer under the auspices of an Oak Ridge Associated Universities grant working with Rufus Ritchie in what was then the Health Sciences Division of the Oak Ridge National Laboratory (ORNL). Ritchie was a senior scientist at ORNL as well as a professor at the Physics Department of the University of Tennessee at nearby Knoxville. This one summer at ORNL also developed into a long and productive, as well as extremely pleasant, scientific collaboration with Ritchie that lasted into the 1990s. During the academic years at Clemson I was able to take off to ORNL for week-long periods several times a year. Our work involved calculating energy transfers in the interactions of electrons and other charged particles with surfaces, problems involving interactions of atomic and charged particles with surface plasmons and theories for developing interaction potentials between particles or between particles and surfaces. This work also had the great advantage of developing interactions and scientific collaborations with many others at ORNL, including Thomas Ferrell and Bruce Warmack.
One of the advantages of being a scientist is the opportunity to travel and meet colleagues and people from all over the world. Sometimes the importance of the social aspects of science is not recognized, but they play an important role both in the satisfaction of being a scientist and also in shaping the problems and research topics that a given scientist works on, and sometimes in unexpected ways. As an example, these first visits to Paris and Oak Ridge brought me into contact with many scientists, several of which I would eventually collaborate with throughout my career. Among these were Salvador Miret-Artés and Pedro Echenique.
In the early 1980s, during one of my summer visits to Saclay, it was Jean Lapujoulade who brought me a preprint of a manuscript by Salvador Miret-Artés, and asked me to look at it to see if it made any sense. Indeed, the ideas in that paper did make sense. In fact, Miret-Artés had pointed out a very special type of resonance effect that should be readily observable in He atom scattering from corrugated surfaces, an effect that was obvious when one thought about it a little, but that nobody up to then had ever noticed. This paper eventually led to a visit by Miret-Artés to Saclay where we met, and over the years this meeting developed into a friendship and a long and valuable collaboration that continues to this day.
My collaboration with Pedro Echenique was initiated through contact with Rufus Ritchie. From the beginning Ritchie would often mention the name of this very energetic and brilliant Basque with whom he worked while he was on sabbatical at the University of Cambridge in England and with whom he had a continuing collaboration. Furthermore, several of the problems the two of us worked on were ones that Ritchie had also discussed with Echenique. The collaboration between Echenique and Ritchie continued to be prolific, and within a few years of that initial ORNL visit I was also collaborating with Echenique, and that collaboration continues.
Beginning the summer of 1985 I began a collaboration with Professor J Peter Toennies of the Max-Planck-Institut für Strömungsforschung in Göttingen, Germany (now the Max-Planck-Institut für Dynamik und Selbstorganization). Toennies was already, at that time, a major figure in the areas of physics and chemistry that use molecular and atomic beams. This was just a few years after he, with graduate student Bruce Doak, had succeeded in the first measurements of surface specific phonons using He atom scattering and, in particular, had obtained complete dispersion relations for Rayleigh modes. This was precisely the type of experiment that Celli, Cabrera and I had suggested over a decade earlier, so our research interests were an excellent match. Our work that summer with graduate student Christof Wöll and postdoc Angela Lahee developed experimental and theoretical methods for measuring the presence of isolated atomic or molecular adsorbates on surfaces. This initial visit led to a long and productive period of research on many aspects of He atom scattering from surfaces, and almost every summer from then through 1997 was spent in the very pleasant and historic city of Göttingen, which still has visible roman ruins and many old German buildings dating from the 1500s. This period was marked by interactions and collaborations with many of the graduate students, postdocs and visitors to the Toennies lab. Many of these collaborations continue to some extent even today, and include work with Andrew Graham, John Ellis, Frank Hofmann, Massimo Bertino, Robert Grisenti, Alexi Glebov, Wieland Schöllkopf, Walter Silvestri and Horst-Günter Rubahn. It was also during this period that I developed a long friendship and scientific collaboration with Jim Skofronick and Sanford Safron of the Department of Physics at Florida State University. Both were frequent visitors to the Toennies laboratory, and our collaboration extended far beyond our overlapping stays there. Among the fondest memories of visits to Göttingen are the many long walks and bicycle rides taken with these colleagues and many others through the streets of Göttingen and the surrounding countryside of Niedersachsen.
The long series of visits to Göttingen were interrupted by three summers beginning in 1988 at the Institut für Grenzflachenforschung and Vakuumphysik at the Forschungszentrum Jülich in Germany working with George Comsa and his group. I had met Comsa in the late 1970s at a scientific meeting in France and we had continued our scientific correspondence ever since, which eventually led to the invitation to visit his lab for an extended stay. Among the very large range of surface-related experiments being carried out in the Comsa group were machines, operated by Bene Poelsema and Rudolf David and the then graduate students Klaus Kern and Peter Zeppenfeld, devoted to He atom scattering from metal and adsorbate-covered surfaces. Once again, it was a great privilege to carry out scientific research in such a stimulating environment.
In 1998, with a three-month summer visit, I began a collaboration with Professor Karl-Heinz Rieder at the Institut für Experimentalphysik of the Freie Universität Berlin in Germany. Rieder was a pioneer in the field of surface scattering experiments using helium and other rare gas atomic beams as projectiles and after he moved to the Freie Universität from the IBM Zürich laboratories he continued this work as well as becoming a world leader in the field of single molecule manipulation on surfaces using scanning tunneling microscopy (STM). This collaboration resulted in visits to Berlin every summer through 2006 during which we collaborated on several projects involving both atom-surface scattering and STM. The work during this period included interesting collaborative work with many members of the Rieder group including Ludwig Bartels, Daniel Farías, Gerhard Meyer and Saw Hla. It was a great experience to be able to pursue science in such favorable surroundings, and to have, in addition, all the cultural advantages of the city of Berlin with its concerts, opera and museums.
Although I have been fortunate to be able to take my family to live in many beautiful and interesting places such as Göttingen, Jülich and Berlin, it has always been Paris and France that we remembered with the greatest fondness, probably because it was the first of our travel ventures and because our children were very young when we first went and they did a large part of their growing up there. So it was a real pleasure to have the opportunity to return to Paris for an extended summer visit in 2007, this time not at Saclay, but at the Université de Paris-Sud in its Laboratoire des Collisions Atomiques et Moléculaires (LCAM). Several times in the preceding years I had discussed and corresponded with Hocine Khemliche of that laboratory about their experiments on the scattering of ions and neutral atoms and molecules from surfaces. They had just published a paper that had attracted considerable attention on the diffraction of very fast atoms from the corrugated surface of lithium fluoride, and our discussions eventually led to an invitation to come and work with him and his colleague, Philippe Roncin. It was a real pleasure for my wife and I to return to the Paris area and to re-experience some of the things that we had done there two decades earlier, to observe the changes in culture and lifestyles that had occurred since, and to experience a whole new set of adventures.
The following summer of 2008 I was Guest Professor at the Donostia International Physics Center in San Sebastian, Spain. This institute was created and is directed by Pedro Echenique and it was a great honor to be able to work in that environment and enjoy the company and discussions with all the prominent scientists there, the many guests as well as the permanent staff.
In the spring and summer of 2009 I was Guest Professor in the Institut für Experimentalphysik of the Technische Universität Graz in Austria, the institute directed by Professor Wolfgang Ernst. The story of how this particular collaboration developed is interesting because it illustrates again how important personal contacts and social interactions are in the progress of science. In 2007 I was contacted by Bodil Holst, then of the TU-Graz and now at the Technical University of Bergen in Norway, about the possibility of having one of her very bright graduate students visit Clemson for a few months as a part of his work in analyzing some He atom scattering data that they had taken on silica glass surfaces. A decade earlier Holst had been a postdoctoral research associate at the Toennies laboratory in Göttingen during several of the summers I was also there and, although we never worked directly together at that time, we had many interesting discussions about science and other subjects. The student, Wolfram Steurer, arrived in Clemson in the middle of the fall semester with his belongings in a bag that was smaller than the guitar he carried strapped over his back. He immediately created for himself a place in our department, and by the time he left three months later we had developed some rudimentary ideas of how to analyze the data he had, and we also suspected that this data might reveal some new aspects of the dynamics of glass surfaces that had not been realized before. Wolfram delved into this problem with a vengeance, and shortly afterwards we began a series of papers involving Holst, Ernst and Steurer and the Graz graduate students, Andreas Apfolter and Mattias Koch, as well as Elin Søndergård of the French CNRS laboratory located at the St Gobain Corporation's research facilities in Paris. It was this initial contact with Holst a decade earlier that eventually led to a productive period of research on glass surfaces, something that I would have never predicted beforehand, but a collaboration that shows every sign of continuing into the future to produce new and interesting results.
So, this brings the history of my career in science nearly to the present. In 2008 I decided, after several years of contemplation, to retire from official service at Clemson and become an emeritus faculty member. However, I am still actively continuing research, retain an office in the department, keep regular contact with my university peers, and remain active in promoting and mentoring the careers of some of my colleagues. Above all, however, I remain active in many of the collaborations that I have developed over the years, some of which are described here. As this brief story should indicate, I have enjoyed a very rich life in science, and much of this enjoyment is due to the people I have been associated with. One could not have asked for a finer group of friends, colleagues, students and collaborators, and I fully anticipate that my association with them and my contributions to science will continue into the foreseeable future.