Near-field photocurrent nanoscopy on bare and encapsulated graphene

TL;DR

This paper introduces a nanoscale opto-electronic technique combining infrared nanoscopy with electrical read-out to map local properties of graphene, revealing nanoscale variations and effects of edges and grain boundaries in both bare and encapsulated forms.

Contribution

The study presents a novel, non-invasive method for high-resolution mapping of optical and electronic properties in graphene devices, applicable to various device architectures.

Findings

Nanoscale variations in carrier density and thermoelectric properties are revealed.

Strong charge build-up near edges in encapsulated graphene/h-BN devices.

The technique enables detailed characterization without special device modifications.

Abstract

Opto-electronic devices utilizing graphene have already demonstrated unique capabilities, which are much more difficult to realize with conventional technologies. However, the requirements in terms of material quality and uniformity are very demanding. A major roadblock towards high-performance devices are the nanoscale variations of graphene properties, which strongly impact the macroscopic device behaviour. Here, we present and apply opto-electronic nanoscopy to measure locally both the optical and electronic properties of graphene devices. This is achieved by combining scanning near-field infrared nanoscopy with electrical device read-out, allowing infrared photocurrent mapping at length scales of tens of nanometers. We apply this technique to study the impact of edges and grain boundaries on spatial carrier density profiles and local thermoelectric properties. Moreover, we show that the technique can also be applied to encapsulated graphene/hexagonal boron nitride (h-BN) devices, where we observe strong charge build-up near the edges, and also address a device solution to this problem. The technique enables nanoscale characterization for a broad range of common graphene devices without the need of special device architectures or invasive graphene treatment.