HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY STUDIES OF AL ADSORPTION ON SI(111)

We have studied the high-resolution electron-energy-loss spectra at zero momentum transfer (q = 0) for the (square-root 3 X square-root 3)R 30-degrees, (square-root 7 X square-root 7)R 19.1-degrees, and 7 X 7 structures formed when Al is deposited on Si(111)-(7 X 7) and annealed. For the square-root 3 X square-root 3 structure, we found loss peaks at 32.3 and 69.2 meV that agree very well with calculated energies, as well as several other loss peaks of uncertain origin. We have tentatively identified phonon energies for the square-root 7 X square-root 7 structure, and demonstrated that for some sample preparations there may be a remnant of the (7 X 7)-Al structure present for surfaces showing the square-root 7 X square-root 7 and even the square-root 3 X square-root 3 reconstructions in low-energy electron diffraction.