Chirality And Orientational Transition Of Pentacene On Bi(111)

In this thesis,utilizing UHV-STM and molecular beam epitaxy (MBE), we have studied the preparation methods of high quality of semi-metallic Bi film as well as the growth modes of pentacene. By depositing 20 monolayer(ML) of Bi atoms onto the Si(111)-7×7 surface at room temperature with subsequent annealing at～120K, a highly ordered Bi surface has been obtained. The molecular arrangement and chirality of the self-assembly of pentacene on Bi(111) were investigated. Upon adsorption on Bi(111), this achiral molecule spontaneously forms two types of chiral pinwheel clusters with opposite chirality. Within the clusters, each pentacene molecule is aligned in the symmetric axis of Bi(111), resulting the formation of six molecular rows. In each row, the adjacent pentacene molecule is shifted along the long molecular axis. When the molecule number exceeding four, the shifting directions is reversed, lead to the formation of bent flabellum. The formation mechanism is attributed to the competition betweenπ-πinteraction and the net attractive interaction among the pentacene molecules.We also shows that the single pentacene molecule exhibits a flat-lying orientation. With coverage increasing, pentacene molecules form various clusters with side-on orientation, and finally form crystalline monolayer with standing-up geometry. These different molecular orientations can be understood by the competition between the molecule-molecule interaction and molecule-substrate interaction.