erlands, uses the channeling of medium-energy charged particles and the blocking of the backscattered ions to determine atomic structures at surfaces or interfaces. The research group at FOM has published important papers reporting the use of this technique for both basic research on surface melting and more practical investigations of atomic arrangements at silicon-silicide interfaces. It took 8 years after the first paper from FOM was published before a publication based on this technique appeared from a U.S. laboratory. The second and third double-alignment ion scattering instruments in the United States have just come on-line at IBM and AT&T Bell Laboratories. The scientists at FOM have worked closely with High Voltage Engineering Europa B.V., a European company that is now selling these systems.

High-Resolution Electron Loss Spectroscopy

In high-resolution electron loss spectroscopy (ELS), monoenergetic electrons are inelastically scattered from a surface and subsequently energy-analyzed. The characteristic losses seen in the scattered beam measure the vibrational modes of molecules adsorbed on the surface or the phonon modes of the clean surface. The basic concepts of this experiment as well as the instrumentation were developed to study molecules in the gas phase. The first application of this technique to surfaces was presented by F.Propst and W.Piper (University of Illinois) in 1967, but the real development of the instrumentation and the procedure into a useful technique for surface science was accomplished by H.Ibach (West Germany) and S.Andersson (Sweden). One of the most demanding applications of this instrument is the measurement of surface phonon dispersion on clean or adsorbate-covered surfaces. Ibach’s group reported the first phonon dispersion curve in 1982, and it was 4 years before a phonon curve was measured in the United States (by L.Kesmodel at Indiana University). The instrument development at the Kernforschungsanlage in West Germany by Ibach’s group was transferred to Leybold-Heraeus, where a commercial ELS system was built and marketed. Until a few years ago it was the only ELS system that could be purchased. At present, two U.S. companies are marketing ELS instruments.

Angle-Resolved Photoemission Using Synchrotron Radiation

Angle-resolved photoemission has become the primary tool for measuring electronic properties both within the bulk and on the surfaces of solids. U.S. scientists led in the development of this technique. In 1977, an analyzer was built by scientists at the National Bureau of Standards (NBS) and the University of Pennsylvania using electron optics developed at NBS for studying gas-phase systems. In 1979 IBM introduced a new two-dimensional display system, and in 1982 a high-resolution instrument with variable momentum



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