Domains of doping in graphene on polycrystalline gold: first-principles and scanning tunneling spectroscopy studies

TL;DR

This study combines first-principles calculations and scanning tunneling spectroscopy to explore how the gold substrate's surface structure influences doping in graphene, revealing potential for electronic property engineering.

Contribution

The paper provides new insights into how substrate surface variations affect graphene doping, combining DFT simulations with experimental STS data.

Findings

Doping levels vary with substrate surface structure and atomic arrangements.

STS reveals energetic heterogeneity with regions of zero and p-type doping.

DFT results align with experimental observations, showing surface structure impacts doping.

Abstract

We have studied the graphene/gold interface by means of density functional theory (DFT) and scanning tunneling spectroscopy (STS). Weak interaction between graphene and the underlying gold surface leaves unperturbed Dirac cones in the band-structure, but they can be shifted with respect to the Fermi level of the whole system, which results in effective doping of graphene. DFT calculations revealed that the interface is extremely sensitive to the adsorption distance and to the structure of metal's surface, in particular strong variation in doping can be attributed to the specific rearrangements of substrate's atoms, such as the change in the crystallographic orientation, relaxation or other modifications of the surface. On the other hand, STS experiments have shown the presence of energetic heterogeneity in terms of the changes in the local density of states (LDOS) measured at different places on the sample. Randomly repeated regions of zero-doping and p-type doping have been identified from parabolic shape characteristics and from well defined Dirac points, respectively. The doping domains of graphene on gold seem to be related to the presence of various types of the surface structure across the sample. DFT simulations for graphene interacting with Au have shown large differences in doping induced by considered structures of substrate, in agreement with experimental findings. All these results demonstrate the possibility of engineering the electronic properties of graphene, especially tuning the doping across one flake which can be useful for applications of graphene in electronic devices.