ANHARMONICITY BUT ABSENCE OF SURFACE MELTING ON AL(001)

Medium-energy ion-scattering measurements and Monte Carlo simulations have been used to study the Al(001) surface as a function of temperatu re. Surface melting does not occur and the surface stays well ordered up to the bulk melting point T-m=933.52 K. The combination of the effe ctive-medium potential, used to simulate the interacting Al atoms, and ion-scattering calculations on the simulated Al(001) surface, reprodu ces the ion-scattering intensities very well. The Monte Carlo simulati ons show that the surface relaxations and the vibration amplitudes bot h display strongly anharmonic behavior which extends several layers in to the crystal and increases with increasing temperature.