On the effect of Edge vs bulk effects in Graphene Nanoribbons

TL;DR

This paper investigates how edge and bulk effects influence the electrical properties of graphene nanoribbons, combining computational modeling and experimental SGM to understand size-dependent shifts in charge neutrality point.

Contribution

It demonstrates that the CNP shift is due to electric field effects at edges rather than doping differences, providing new insights into size-dependent electronic behavior of GNRs.

Findings

CNP shifts towards lower values with decreasing GNR width due to electric field effects

No significant difference between edge and bulk regions in GNRs from SGM data

CNP sign change is unlikely caused by doping, but possibly by band structure variations

Abstract

Recent works have shown how the electrical properties of graphene nanoribbons (GNRs) show a size-dependence in terms of resistivity, charge neutrality point (CNP) and band structure once their widths drop below approximately 50 nm. It has been observed that the CNP switches sign below a certain GNR width, and in this article, we explore this via computational modelling of the electric field and the conductance of GNRs in the presence of an AFM tip. We show that CNP is expected to shift towards lower values as GNR width reduces as a result of the significantly enhanced electric field around edges, but that a change in sign is not expected. We also show experimentally via high-resolution Scanning Gate Microscopy (SGM) that there does not appear to be any significant difference between the edges and the bulk of a GNR, indicating that the switch in CNP is not due to differential doping, and may instead be due to variations in the band structure as a function of size.