Microscopic correlation between chemical and electronic states in epitaxial graphene on SiC(000-1)

TL;DR

This study uses advanced spectromicroscopy techniques to analyze the microscopic correlation between chemical states and electronic properties in epitaxial graphene on SiC, revealing how thickness and interface chemistry influence electronic band structure.

Contribution

It provides detailed spatially-resolved insights into the chemical and electronic heterogeneity of epitaxial graphene on SiC, including Dirac point shifts and superlattice effects.

Findings

Graphene thickness varies across the surface and affects work function.

Multiple chemical states exist at the graphene/SiC interface, influencing charge transfer.

Dirac point position and band dispersion are sensitive to local structure and stacking.

Abstract

We present energy filtered electron emission spectromicroscopy with spatial and wave-vector resolution on few layer epitaxial graphene on SiC$(000-1) grown by furnace annealing. Low energy electron microscopy shows that more than 80% of the sample is covered by 2-3 graphene layers. C1s spectromicroscopy provides an independent measurement of the graphene thickness distribution map. The work function, measured by photoelectron emission microscopy (PEEM), varies across the surface from 4.34 to 4.50eV according to both the graphene thickness and the graphene-SiC interface chemical state. At least two SiC surface chemical states (i.e., two different SiC surface structures) are present at the graphene/SiC interface. Charge transfer occurs at each graphene/SiC interface. K-space PEEM gives 3D maps of the k_|| pi - pi* band dispersion in micron scale regions show that the Dirac point shifts as a function of graphene thickness. Novel Bragg diffraction of the Dirac cones via the superlattice formed by the commensurately rotated graphene sheets is observed. The experiments underline the importance of lateral and spectroscopic resolution on the scale of future electronic devices in order to precisely characterize the transport properties and band alignments.