Substrate effect on electrical conductance at a nanoasperity-graphene contact

Abstract

The use of graphene for applications such as micro- and nano-scale electronic devices often involves incorporating the two-dimensional material onto various substrates. However, the effects of the substrate's mechanical properties on electrical contact conductance are not fully understood. Here, we explore these effects by measuring the conductance between a nanoscale probe and a single layer of graphene with three different levels of substrate support: no substrate, i.e. free-standing graphene, an elastic substrate, and a rigid substrate. These three systems are studied using conductive atomic force microscopy experiments complemented by molecular dynamics simulations using the electrochemical dynamics with implicit degrees of freedom method. In both experiments and simulations, at a given normal force, current increases as: rigid substrate < elastic substrate < no substrate. We demonstrate that the substrate support influences graphene/tip contact conductance through substrate's elasticity, which determines contact size, as well as through variability of interatomic distances in the contact, which contributes to the interface resistivity.