Adsorption behavior of triphenylene on Ru(0001) investigated by scanning tunneling microscopy

As a representative of small aromatic molecules, triphenylene (TP) has markedly high carrier mobility and is an ideal precursor for building graphene nanostructures. We mainly investigated the adsorption behavior of TP molecules on Ru(0001) by using scanning tunneling microscopy (STM). In submonolayer regime, TP molecules are randomly dispersed on Ru(0001) and the TP overlayer can be thoroughly dehydrogenated and converted into graphene islands at 700 K. Due to weak interaction between TP molecules and graphene, the grooves formed among graphene islands have confinement effect on TP molecules. TP adopts a flat-lying adsorption mode and has two adsorption configurations with the 3-fold molecular axis aligned almost parallel or antiparallel to the [1 (1) over bar 00] direction of the substrate. At TP coverages of 0.6 monolayer (ML) and 0.8 ML, the orientational distributions of the two adsorption configurations are equal. At about 1.0 ML, we find the coexistence of locally ordered and disordered phases. The ordered phase includes two sets of different superstructures with the symmetries of (root 19 x root 19)R23.41 degrees and p (4 x 4), respectively. The adsorption behavior of TP on Ru(0001) can be attributed to the delicate balance between molecule-substrate and molecule-molecule interactions.