Scanning tunnelling microscopy of tetracene on Si(100)-2 x 1

Scanning tunnelling microscopy (STM) has been used to follow the adsorption of tetracene molecules on the Si(100)-2 x 1 surface. Two distinct types of adsorption are indicated by filled state images but three types may be distinguished in empty state images. Molecules aligned both along and perpendicular to the silicon dimer rows can be observed. The calculated charge densities associated with occupied and unoccupied orbitals near the Fermi level are compared with the STM images. Possible bonding arrangements and their correlation with the STM images are postulated.