Evidence for Strain-Induced Local Conductance Modulations in Single-Layer Graphene on SiO2

TL;DR

This study demonstrates that strain in single-layer graphene on SiO2 causes local conductance modulations, altering its electronic spectra and linking mechanical deformation to electronic properties via phonon mode changes.

Contribution

It provides direct experimental evidence of strain-induced conductance changes in graphene and correlates these with phonon mode frequency shifts, advancing understanding of strain effects on 2D materials.

Findings

Strained graphene shows U-shaped conductance spectra unlike the V-shaped spectra of relaxed regions.

Strain maps correlate with local tunneling conductance variations.

Strain increases the out-of-plane phonon mode frequency, affecting charge tunneling.

Abstract

Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO2 substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs. bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene.