Qualitative analysis of scanning gate microscopy on epitaxial graphene

David M A Mackenzie,Dirch H Petersen,Vishal Panchal,Olga Kazakova,Héctor Corte-León

doi:10.1088/2053-1583/ab0572

David M A Mackenzie, Dirch H Petersen + Show 3 more

Open Access

https://doi.org/10.1088/2053-1583/ab0572

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Abstract

We present scanning gate microscopy (SGM) studies of graphene Hall-cross devices where bi-layer graphene (2LG) regions show unexpected signal inversion relative to single-layer graphene (1LG), an observation reproduced via finite element modelling of the current densities. This is attributed to gate-induced charge carrier redistribution between the two layers in 2LG. Hall cross devices were fabricated from epitaxial graphene 6H–SiC(0 0 0 1) and were covered by 1LG/2LG with the area ratio of 85:15%, respectively. Local electric-field sensitivity maps of the devices were obtained in two different measurement geometries using electrical SGM with a conductive tip, where it was observed that the voltage of 2LG islands was inverted relative to anticipated reference maps. Finite element modelling of the current densities and voltage response showed good qualitative agreement with the SGM maps when the effect of the gate was reversed for 2LG. The behaviour is attributed to gate-induced charge carrier redistribution between the two layers in 2LG. The model can be used generally as a tool to predict mixed 1LG/2LG response to electric field. Moreover, regions near the corners of the device show the highest sensitivity when the local electric field was applied to the scanning probe microscopy tip. These regions are capable of detecting highly local electric fields down to 110 kV cm−1.

Highlights

Over a decade on, graphene remains a hot topic amongst other 2D-materials, with significant amount of research devoted towards bandgap engineering
We present scanning gate microscopy (SGM) studies of graphene Hall-cross devices where bi-layer graphene (2LG) regions show unexpected signal inversion relative to single-layer graphene (1LG), an observation reproduced via finite element modelling of the current densities
Each possible mixed-layer device has distinct island size and distribution, which leads to a different combination of the negative and positive components of the overall measured signal.When considering the response of mixed-layer graphene devices to local electric fields in non-symmetrical measurement geometries (such as figure 2(b) and in [15]), it is important to consider the localised gating effect of the tip as well as the topographically-dependent effects of the relative 2LG island size, distribution, and cantilever gating. These effects can be minimised by choosing a symmetrical measurement geometry, and are qualitatively predictable using Finite-element simulations (FES)

Summary

Introduction

Graphene remains a hot topic amongst other 2D-materials, with significant amount of research devoted towards bandgap engineering. Applications that require a large number of devices to behave precisely can benefit greatly from large-scale uniformity of number of the graphene layers. Due to the additional interlayer interactions and electric field screening in 2LG [15, 16], their exact shape, size and location have been shown to greatly alter the performance of devices in applications such as resistance metrology [17,18,19] and environmental sensors [20,21,22,23]

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