Electronic and Vibronic Properties of Single Molecules in Molecule/Graphene Nanoribbon/Au(111) Heterostructures

Semiconducting graphene nano-ribbon possesses a band gap and thus they have the capability to act as a buffer that effectively decouples molecules of interest electronically from the substrate [1]. Here we investigate the structural, electronic, and vibronic properties of individual para-sexiphenyl (6P) molecules separated from a gold surface by graphene nano-ribbons in vertically and laterally stacked heterostructures by using a custom-built low temperature ultrahigh vacuum scanning tunneling microscope. dI/dV tunneling spectroscopy is used to measure the electronic structures of 6P molecules in the molecule/graphene nanoribbon/Au(111) heterostructures. For the vertically stacked heterostructures the energy gap and the molecular orbital locations are found to be much closer to the gas phase values as compared to the molecules directly adsorbed on Au(111) surface and in lateral heterostructures. Moreover, the d2I/dV2 vibrational spectroscopy of 6P reveals a strong vibrational mode associated with the c=c on ring stretching of the molecules.

[1] Y. Li et al. Anomolous Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure. Nat. Commun. 8, 946 (2017).