Electronic properties of the Sm–Pd(111) and Sm–graphene–Pd(111) interfaces

The Sm–Pd(111) and Sm-graphene-Pd(111) interfaces have been investigated by X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS), and Low energy electron diffraction (LEED). For Sm–Pd(111) a mixed interface was observed as Sm was deposited on the Pd substrate at ambient temperature. Monolayer (ML) graphene was grown on Pd(111) by exposure to ethylene at elevated temperatures. Subsequently, near monolayer coverage of Sm was deposited at room temperature. Only trivalent Sm atoms were observed in the Sm/Pd(111) system. Divalent Sm atoms were observed in the Sm/graphene/Pd(111) system for sub-monolayer Sm coverage; however, the Sm atoms became trivalent upon annealing above 450 K. Sm atoms migrate to the C-Pd interface predominantly through boundaries between graphene domains of different planar orientations to form a mixed Sm–Pd interface. A monotonic decrease in the sample work function of about 2 eV was observed with increasing Sm coverage for the Sm coverages under investigation. • Mixed Sm–Pd interfaces were observed as Sm was deposited on Pd(111) at room temperature. • Up to 64% divalent Sm atoms were observed as sub-monolayer Sm was deposited on one monolayer graphene on Pd(111). • After annealing to 450 K only trivalent Sm atoms were observed. • The work function was found to decrease by about 2 eV after depositing one monolayer Sm on both interfaces. • The observed matching of work functions between the graphene layer and the substrate may have bearing on use in electronic devices.