Scanning Tunneling Microscopy and Density Functional Theory Study on Zinc(II)-Phthalocyanine Tetrasulfonic Acid on Bilayer Epitaxial Graphene on Silicon Carbide(0001)

Abstract

Zinc(II)-phthalocyanine tetrasulfonic acid (Zn-PcS) molecules physisorbed on bilayer epitaxial graphene on silicon carbide (SiC(0001)) were studied by using scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). Two different methods were used to deposit Zn-PcS molecules and regardless of the method being used, the surface coverage stayed very low indicating the weakness of surface-molecule interaction. STS measurements revealed that derivative of tunneling current with respect to voltage (dI/dV) measured on Zn-PcS molecules did not exhibit the characteristic dip observed on dI/dV curves of pristine bilayer epitaxial graphene. DFT calculations show that the energy of the lowest unoccupied molecular orbital (LUMO) of the Zn-PcS molecule is below the Dirac point of graphene which enhances local density of states (LDOS). We attribute the disappearance of the dip in the dI/dV curves measured on the Zn-PcS/bilayer system to the LUMO of Zn-PcS. Charge density calculations along Zn-PcS/graphene interface reveal that there is a small charge transfer from graphene to the molecule. Calculated adsorption energy (3.13 eV) of the molecule is notably low and is consistent with the observed low surface coverage at room temperature.

π-Orbital mediated charge transfer channels in a monolayer Gr–NiPc heterointerface unveiled by soft X-ray electron spectroscopies and DFT calculations

“…Furthermore, due to its insulating nature, SiC is particularly suitable for all those applications that require to restrict the current flow to the graphene or the molecular layers. Moreover, the Gr-SiC system has been recently studied as a substrate for the growth and adsorption of metal phthalocyanine complexes, focusing on the STM analysis of the adsorption geometry and temporary charging, 19,[33][34][35][36][37] with interesting perspectives as hybrid architectures for molecular spin qubits. 38,39 In this work, we managed to build and characterize a novel heterointerface between a monolayer of Gr transferred onto SiC and a physisorbed single layer of NiPc that was obtained by thermal evaporation in ultra-high vacuum conditions.…”

“…Furthermore, due to its insulating nature, SiC is particularly suitable for all those applications that require to restrict the current flow to the graphene or the molecular layers. Moreover, the Gr–SiC system has been recently studied as a substrate for the growth and adsorption of metal phthalocyanine complexes, focusing on the STM analysis of the adsorption geometry and temporary charging, 19,33–37 with interesting perspectives as hybrid architectures for molecular spin qubits. 38,39…”