CU(110) - DISORDER OR ENHANCED ANHARMONICITY - A COMPUTER-SIMULATION STUDY OF SURFACE-DEFECTS AND DYNAMICS

By using molecular dynamics and an effective n-body potential adapted to copper, we show the dynamical behavior of (110) surfaces to be greatly affected by the large concentration of defects present at high temperatures. Above T = 1000 K, surface anharmonicity is increased by point defects as do the vibrational amplitudes of atoms pertaining to surface layers. Accounting for thermal attenuation observed in diffraction experiments requires both. thermal disorder and surface anharmonicity to be considered. Surface relaxations are found to decrease on increasing the temperature, in qualitative agreement with recent experiments. At the highest temperature we studied, T = 1233 K, thermally generated adatoms become fully delocalized along the close-packed rows [110BAR], a feature characterizing the early stages of anisotropic surface melting.