Growth and Structural Properties of Pb Islands on Epitaxial Graphene on Ru(0001)

Structural properties of Pb islands grown on graphene/Ru(0001) at various deposition temperatures (T D) and annealing temperatures (T A) are investigated by a low-temperature scanning tunneling microscope. Single-layer Pb islands with a 2 × 2 reconstruction are only formed at T D of 80 K and disappear with post-annealing to room temperature (RT). It is revealed that a morphological transition of the Pb islands takes place, from irregular shapes to a hexagonal equilibrium shape, with increasing T D or T A to RT. Moreover, Pb islands grown at T D of RT are larger than those grown at a T D of 80 K and annealed to RT. All Pb islands with a T A or T D of RT are (111)-faceted with thicknesses of even-numbered atomic layers and exhibit a weak interaction between Pb and graphene.