Probing the Electrical Properties of Overlapped Graphene Grain Boundaries by Raman spectroscopy

TL;DR

This study uses Raman spectroscopy to analyze overlapped grain boundaries in CVD-grown polycrystalline graphene, revealing their impact on electrical properties and potential for improved conductivity in large-area graphene.

Contribution

It provides detailed characterization of overlapped grain boundaries, showing their inhomogeneous doping and electrical effects, which was previously not well understood.

Findings

Overlapped boundaries contain AB stacked bilayers.

Raman spectra show G band splitting depending on overlap width.

Charge carriers cause inhomogeneous doping, lowering Fermi level by 0.3-0.4 eV.

Abstract

The effect of grain boundaries and wrinkles on the electrical properties of polycrystalline graphene is pronounced. Here we investigate the stitching between grains of polycrystalline graphene, specifically, overlapping of layers at the boundaries, grown by chemical vapor deposition (CVD) and subsequently doped by the oxidized Cu substrate. We analyze overlapped regions between 60 and 220 nm wide via Raman spectroscopy, and find that some of these overlapped boundaries contain AB stacked bilayers. The Raman spectra from the overlapped grain boundaries are distinctly different from bilayer graphene and exhibit splitting of the G band peak. The degree of splitting, peak widths, as well as peak intensities depend on the width of the overlap. We attribute these features to inhomogeneous doping by charge carriers (holes) across the overlapped regions via the oxidized Cu substrate. As a result, the Fermi level at the overlapped grain boundaries lies between 0.3 and 0.4 eV below the charge neutrality point. Our results suggest an enhancement of electrical conductivity across overlapped grain boundaries, similar to previously observed measurements(1). The dependence of charge distribution on the width of overlapping of grain boundaries may have strong implications for the growth of large-area graphene with enhanced conductivity.