Abstract
High-resolution electron energy-loss spectroscopy was applied to determine phonon dispersions of cleaved AlSb(110), GaP(110), GaSb(110), and InAs(110) surfaces. Besides the acoustic surface waves and the optical Fuchs-Kliewer modes additional flat phonon bands were detected in all materials. The experimental results agree very well with recent ab initio calculations of surface phonon dispersion curves. For GaP(110), several phonon modes are observed within the fundamental gap between acoustic and optical bulk phonon bands. In AlSb(110) a gap mode is detected very close to the bulk optical band edge whereas the GaSb gap is free of surface-localized states. The measurements confirm theoretical predictions that significant gap modes exist at these surfaces if the anion mass is smaller than the cation mass. For the acoustic and the Fuchs-Kliewer modes chemical trends are demonstrated. The differences of the excitation energies in the materials considered depend only on the anion and cation masses as well as the nearest-neighbor distances.
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