Electronic and Geometric Corrugation of Periodically Rippled, Self-nanostructured Graphene Epitaxially Grown on Ru(0001)

TL;DR

This study reveals that the ripples in epitaxial graphene on Ru(0001) are primarily electronic in origin, with structural corrugation being much smaller than previously thought, leading to a nanostructured electronic landscape.

Contribution

The paper provides detailed measurements distinguishing structural and electronic corrugation in graphene on Ru(0001), showing electronic effects dominate the observed ripples.

Findings

Structural corrugation is much smaller than predicted or previously reported.

Electronic corrugation is strong enough to invert STM contrast.

Graphene exhibits a nanostructured landscape of electron and hole pockets.

Abstract

Graphene epitaxially grown on Ru(0001) displays a remarkably ordered pattern of hills and valleys in Scanning Tunneling Microscopy (STM) images. To which extent the observed "ripples" are structural or electronic in origin have been much disputed recently. A combination of ultrahigh resolution STM images and Helium Atom diffraction data shows that i) the graphene lattice is rotated with respect to the lattice of Ru and ii) the structural corrugation as determined from He diffraction is substantially smaller (0.015 nm) than predicted (0.15 nm) or reported from X-Ray Diffraction or Low Energy Electron Diffraction. The electronic corrugation, on the contrary, is strong enough to invert the contrast between hills and valleys above +2.6 V as new, spatially localized electronic states enter the energy window of the STM. The large electronic corrugation results in a nanostructured periodic landscape of electron and holes pockets.