Bands alignment between organic layers of Alq3, Gaq3, Erq3 and graphene on 6H-SiC(0001)

This paper concerns physicochemical properties of three interfaces composed of organic layers of Alq3, Gaq3 or Erq3 vapor deposited on graphene/6H-SiC(0 0 0 1) surfaces. A graphene termination of 6H-SiC(0 0 0 1), about one monolayer thick, was produced in situ by thermal annealing of the substrate. The formation of the final interfaces and their characterization were also performed in situ under ultrahigh vacuum conditions. X-ray/UV photoelectron spectroscopies (XPS/UPS) were employed in this study. XPS results showed that the organic layers did not react chemically with the graphene/6H-SiC(0 0 0 1) surfaces at room temperature. In turn, UPS measurements showed that the adsorption of organic layers decreased the position of the vacuum level of the initial surface and one covered with the organic layers which initiated the surface dipoles. The vacuum level was lowered by 0.15 eV, 0.4 eV, and 0.9 eV for Alq3, Gaq3, Erq3 layers, respectively. The positions of highest occupied molecular orbitals (HOMOs) were also found. They were located at 1.55 eV, 1.75 eV, and 2.0 eV below the Fermi level, respectively, for Alq3, Gaq3, and Erq3 layers. The band energy diagrams for the three interfaces were constructed.

Automated summary

This paper investigates the physicochemical properties of organic layers of Alq3, Gaq3, or Erq3 vapor deposited on graphene/6H-SiC(0 0 0 1) surfaces. In situ thermal annealing was used to produce a one monolayer thick graphene termination of the substrate. The formation and characterization of the interfaces were performed under ultrahigh vacuum conditions. XPS/UPS were employed for characterization. XPS results show no chemical reaction between the organic layers and the graphene/6H-SiC(0 0 0 1) surfaces at room temperature. UPS measurements reveal a decrease in the vacuum level due to the adsorption of organic layers, resulting in the initiation of surface dipoles. The HOMO positions and band energy diagrams for the three interfaces were also determined.