Growth of crystalline thin films of picene on semimetallic Bi(111) surface

We report the scanning tunneling microscopy/spectroscopy (STM/STS) studies on structural and electronic properties of picene films grown on the semimetallic Bi(111) substrate held at different temperatures. Under room-temperature deposition, the picene molecules form a crystalline (001) monolayer with the standing-up orientation, indicating the weak molecule-substrate interaction. When deposited on the Bi(111) substrate held at 150 K, picene molecules form a bulk-like (211̄ monolayer with building blocks of picene trimers. High-resolution STM images reveal that each trimer consists of two tilted molecules and one side-on molecule. Further reducing the deposition temperature to 90 K leads to the formation of nanostripe arrays, in which the side-on molecules adopt the π-π stacking. STS measurements demonstrate that the crystalline (001) monolayer of picene exhibits a larger gap compared with picene crystals, which can be attributed to the decoupling of the upright standing molecules from the semimetallic Bi(111) substrate.