ELECTRONIC STATES OF C60 AND C70 MOLECULES 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 at the center of the unfaulted half of the 7×7 unit cell. For the C 60 molecule, occupied (unocupied) orbitals near the Fermi level have high charge density around double bonds between two hexagons (around single bonds on pentagons). For the 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 the C 60 molecule, and it is high in three (four) regions over the C 70 molecule which is nearly C s(D2) symmetry. These should be compared with the scanning tunneling microscopy images.