Electronic States of Fullerenes Adsorbed on Si(111)7×7 Surface

Abstract

Electronic states are calculated by the DV-Xα-LCAO method for two model clusters C 60 Si 101 H 60 and C 70 Si 101 H 60 of the C 60 /Si(111) and C 70 /Si(111) surfaces where fullerene molecules reside on the center of the unfaulted half of the 7×7 unit cell. Due to the electron transfer from the Si substrate, the molecules have ionicities, C 60 -3.35 and C 70 -2.63 . For C 60 molecule, occupied (unoccupied) orbitals near the Fermi level have high charge density around double bonds between two hexagons (around single bonds on pentagons). For C 70 molecule, both occupied and unoccupied orbitals have high charge density around single bonds. The charge density of an individual occupied (unoccupied) orbital has a shape like a trigonal doughnut (clover leaves) over C 60 molecule, and it is high in three (four) regions over C 70 molecule which is nearly C s (D 2 ) symmetry. These should be compared with the scanning tunneling microscopy images.