Ion Beam Deposition
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B.R. Appleton, R.A. Zuhr, T.S. Noggle, N. Herbots, S.J. Pennycook, and G.D. Alton
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Introduction Ion beam processing of materials has a tradition at Oak Ridge National Laboratory that is as old as the laboratory itself. Consequently, w h e n we began looking for a competitive way to participate in the excitement and new physics beginning to emerge from the fabrication and study of artificially structured materials, it was natural to look for a growth technique that inc o r p o r a t e d ion b e a m p r o c e s s i n g . O u r division, the Solid State Division, has a variety of ion implantation and ion beam analysis accelerators which are integrated with pulsed-laser sources into ultrahigh vacuum (UHV) surface analysis and processing chambers. These facilities allow us to do ion beam and laser processing of materials in UHV at temperatures from liquid helium to several hundred degrees centigrade and to study these alterations in situ by a variety of ion beam (ion scattering, ion channeling, nuclear reactions, etc.) and surface analysis (low energy electron diffraction, Auger, etc.) techniques. Since isotope separation has been done continually at ORNL for almost 45 years, 1 the idea and advantages for altering this technique to do materials fabrication in UHV were immediately obvious. In the following article we will briefly review the history of the ion beam deposition (IBD) concept, describe our preliminary apparatus, and point out the inherent advantages of IBD for fabricating and studying artificially structured materials. Recent results obtained by IBD will be presented. Isotope Separation The concept which forms the basis for ion beam deposition dates back to the early days of the development of isotope separation t e c h n i q u e s . 2 , 3 T h e s e m a s s s p e c trometry principles w e r e utilized in a massive fashion at ORNL starting in 1943 to separate large quantities of uranium-235 from the more abundant isotope uranium238 as part of the Manhattan Project. 1 After World War II, Eugene Wigner convinced the government that electromagnetic isotope separation was an important technique to p r e s e r v e for future scientific needs. As a consequence, scaled-down versions of the original isotope separation facilities at ORNL have operated continuously to provide samples to researchers all over the world for s t u d i e s in nuclear physics, chemistry, biology, the earth sciences, and medicine. During peak production the isotope separation facilities at ORNL had 1100 large separating units in operation and employed about 25,000 people. 1 Many of the ion source and separa-
tion techniques developed at ORNL form the basis of present day high-current ion implantation technology. Isotope separation has been used continuously in laboratories all over the world since the late 1940s. It comprised a field of study all its own in addition to providing research samples for many other disciplines. Even though the literature of isotope separation is too vast to review here, it should be recognized that it was
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