Adsorption configurations of pentacene on Ge(100) and its temperature dependence

Abstract

We have studied the adsorption of pentacene on Ge(100) using scanning tunneling microscopy (STM). Four different distinct features labeled A, B-1, B-2 and C were found in the STM images taken at room temperature. In the A configuration, the pentacene molecules adsorb parallel to the Ge dimer rows and are lying on top of the dimer row. In the B-1 and B-2 configurations, the pentacene molecules adsorb perpendicular to the Ge dimer row directions. Among them, the B-1 configuration is divided symmetrically into two parts and the B-2 configuration is divided into three unequal parts. In the C configuration, the pentacene molecules adsorb parallel to the Ge dimer rows and are located in between two Ge dimer rows. The C configuration was converted into a more stable A configuration during scanning by STM tip. The diffusion of pentacene in the A configuration is observed at room temperature. With annealing the pentacene adsorbed surface to 350℃, it is found that the A and C configurations are converted into the B-2 configuration, however, the B-1 configuration is retained. We conclude that the B configuration is thermodynamically most stable.