Impact of local stacking on the graphene-impurity interaction: theory and experiments

TL;DR

This study combines experimental STM/STS and theoretical models to analyze how local stacking configurations affect the interaction between graphene and impurities on SiC substrates, revealing how impurity states vary with local environment.

Contribution

It provides a combined experimental and theoretical analysis of local stacking effects on graphene-impurity interactions using STM/STS, Anderson model, and DFT calculations.

Findings

Adatom resonance width is smaller at the center of a graphene hexagon.

Impurity state shifts toward the Dirac point depending on local stacking.

Experimental results agree with Anderson model predictions.

Abstract

We investigate the graphene-impurity interaction problem by combining experimental - scanning tunneling microscopy (STM) and spectroscopy (STS) - and theoretical - Anderson impurity model and density functional theory (DFT) calculations - techniques. We use graphene on the SiC(000-1)(2x2)_C reconstruction as a model system. The SiC substrate reconstruction is based on silicon adatoms. Graphene mainly interacts with the dangling bonds of these adatoms which act as impurities. Graphene grown on SiC(000-1)(2x2)_C shows domains with various orientations relative to the substrate so that very different local graphene/Si adatom stacking configurations can be probed on a given grain. The position and width of the adatom (impurity) state can be analyzed by STM/STS and related to its local environment owing to the high bias electronic transparency of graphene. The experimental results are compared to Anderson's model predictions and complemented by DFT calculations for some specific local environments. We conclude that the adatom resonance shows a smaller width and a larger shift toward the Dirac point for an adatom at the center of a graphene hexagon than for an adatom just on top of a C graphene atom.