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David M. A. Mackenzie: Qualitative analysis of scanning gate microscopy on epitaxial graphene

posted 6 Aug 2019, 08:57 by info admin   [ updated 6 Aug 2019, 08:57 ]
David M. A. Mackenzie, Vishal Panchal, Héctor Corte-León, Dirch H. Petersen, and Olga Kazakova 
Department of Electronics and Nanoengineering, Aalto University, FI-00076 Aalto, Finland 

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 current densities [1]. 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(0001) and were covered by 1LG/2LG with area ratio of 85:15%, respectively (Fig 1a). Local electric-field sensitivity maps of the devices were obtained in a bend measurement geometry (Fig 1b) using electrical SGM with a conductive tip (Fig 1c). We observe that the voltage measured upon gating 2LG islands was inverted (Fig 1d) relative to anticipated reference maps on 1LG (Fig 1e). Finite element modelling (FEM) of the current densities and voltage showed good qualitative agreement with the SGM maps when the effect of the gate was reversed for 2LG (Fig 1 f-g). We expand on tip-only FEM results, as shown in Fig 1f [1], by modelling both the tip and cantilever using a distributed-charge perturbation (Fig 1g) to achieve greater qualitative agreement between experimental results and simulations. The model can be used to predict mixed 1LG/2LG response to electric field.

1. Mackenzie et. al., 2D Materials, 6, 025023, 2019

David Mackenzie is a research fellow in the Nanoscience and Advanced Materials group based at the Department of Electronics and Nanoengineering, Aalto University, Finland. Research interests include fabricating devices based on two-dimensional materials, accuracy of electrical measurements, gas sensing measurements, finite element simulations, and Raman spectroscopy.