Rufus Haynes Ritchie passed away peacefully on 28 July 2017. He was a corporate fellow at the Oak Ridge National Laboratory (ORNL) and a Ford Foundation Professor of Physics at the University of Tennessee, Knoxville. Among his many scientific contributions, the best known was the discovery of the collective oscillation of electrons at metal surfaces, known today as the surface plasmon. Ritchie, as he was called by many of his friends and even by his wife Dorothy, was the very definition of a gentleman and a scholar, and he was a mentor to hundreds of scientists during his long career.
Born in the coal-mining camp of Blue Diamond, Kentucky on 24 September 1924, Ritchie’s mother was a teacher and his father was a local coal mining executive. He originally studied electrical engineering and earned a bachelor’s degree from the University of Kentucky in 1947. During the Second World War he served in the Army Air Corps as a Second Lieutenant. During that period he attended military scientific education programs at Kenyon College, Yale Communications Cadet School, Harvard University, and the Michigan Institute of Technology. He joined the Health Physics Division of the Oak Ridge National Laboratory in 1949. With the exception of a few sabbaticals, at the Cavendish Laboratory of Cambridge University and in Denmark, he spent his entire scientific career there. In 1959 he received a PhD in physics, under the supervision of Richard D. Present, from the University of Tennessee at Knoxville. Several years later Ritchie took a joint faculty appointment there in the physics and astronomy department.
The health physics division of ORNL was specially created as a unit separate from the other scientific divisions in order to develop a body of staff specifically trained in radiation damage, both to materials and to living tissues. The early environment was one in which close collaboration between experimentalists and theorists was strongly encouraged, and such collaborations were to be a hallmark of Ritchie’s work throughout his career. In the early 1950s he was working with Robert Birkhoff on an investigation and analysis of experimental data on energy losses in the passage of charged particles through thin metal films. He became interested in the way energy losses were distributed when a fast electron passes through a thin metal foil and worked out the spectrum to describe how the metal should respond. Included in this work was the discovery of the surface-localized collective electronic oscillation, now known as the surface plasmon or surface plasmon polariton. This discovery was met with rather fierce resistance from those who doubted that the surface plasmon could exist, and initially Ritchie was hesitant to move forward with this work. However, encouraged by his colleagues and mentors at ORNL such as Birkhoff, Sam Hurst, and Jacob Neufeld as well as by David Pines, he published the prediction of surface plasmons in a 1957 paper in the Physical Review. Three years later a series of experiments at the National Bureau of Standards (now the National Institute of Standards and Technology) confirmed surface plasmon losses by electron scattering in reflection geometry. The full impact of Ritchie’s discovery became clear only years later with the advent of nanotechnology in the late 1990s. Specifically, the surface plasmon polariton can now be exploited to confine and manipulate light at the nanoscale, far below the diffraction limit of light, and provides large-field enhancements for biosensors, surface-enhanced Raman scattering, diode lasers, and numerous other physical effects. It can be firmly stated that his 1957 paper opened up the new fields of nanoplasmonics and nanophotonics to a variety of uses and that it has inspired many practical applications in opto-electronics, measurements of optical properties, photovoltaics, and solar energy conversion, as well as in biomedicine.
However, the surface plasmon was only the first of many seminal contributions. Ritchie is regarded as one of the founders of modern radiation dosimetry. He devised, for example, quantitative schemes in fast neutron dosimetry by the proportional counter method and by the threshold detector method. This work was essential for the creation of the Ichiban program to determine radiation exposure to the survivors of Hiroshima and Nagasaki. Ritchie was a world leader in the field of charged particles interacting with solids and surfaces. He developed a dielectric formalism for the response of a quantum plasma and studied electronic wakes, which are the spatial and temporal distributions of electronic fluctuations around fast ions moving in solids or near surfaces. He made major contributions to the Z3 (Barkas) effect in stopping power and to the theory of charge states in solids. He was responsible for developing the first nonperturbative theory of interaction of slow ions with matter, a subject highly relevant to the field of ion penetration in materials.
Among the many honors received during his career were the Distinguished Alumni Award of the Department of Physics and Astronomy of the University of Tennessee and the Jesse W. Beams Award of the Southeastern Section of the American Physical Society. He was a fellow of APS, and he received the Doctor Honoris Causa from the Universidad del Pais Vasco.
To his many scientific collaborators, Ritchie was an outstanding scientist who combined great physical intuition with stellar technical competence and mathematical ability. He could provide in a day or two a model and an elaborate calculation of an idea that had just arisen in previous discussions. He was able to adapt and improve it almost instantaneously after new sides or aspects of the problem were discovered. He was universally recognized as a great theoretical physicist, respected and admired by all. He had immense influence on everyone who ever worked with him.
Ritchie combined, to an unusual degree, a profound knowledge of the fundamentals and a deep sense of the history of scientific culture with a sympathetic and enthusiastic outlook towards new ideas. The seminal nature of this intellect, together with his open accessibility made him not only a superb condensed matter physicist, but also an excellent communicator and teacher, both in the classroom and outside it. But even more importantly, he was a warm person, a caring human being, full of love and concern about his family, friends, and coworkers. He will always be remembered by his finesse, gentle and immensely generous personality, and possessing an almost infinite kindness. His presence among us will be sorely missed.
