Scanning tunneling microscopy evidence of a special bonding of Cu adatoms on Si(111)-root 3 x root 3-Ag surface - Direct observation of surface-stateelectron migration

STM observations provide direct evidence that the S-1 surface states around the Cu adatoms on the root 3 x root 3-Ag substrate are donated by excess e lectrons from Cu adatoms, resulting in metallic surface bonds of Cu adatoms on the root 3 x root 3-Ag surface. These donated electrons can easily migr ate along the SI surface states together with the Cu adatoms: this can be e xplained by the delocalized character of the S-1 surface state and the Coul omb attraction between the donated electrons and the adatoms. (C) 2000 Else vier Science B.V. All lights reserved.