Temperature and Strain Dependence of Transverse Electron Transport in Few Layer Graphene using Conductive Atomic Force Microscopy

While in-plane electron transport in few-layer graphene has been extensively studied over the past two decades, transport in the out-of-plane direction has received far less attention. In this work, the out-of-plane transport of few-layer graphene samples is investigated experimentally using conductive atomic force microscopy (C-AFM). Specifically, we vary the local strain by applying a force using the AFM probe, and separately we vary the temperature using a heated stage. In both cases, the conductive responses are measured. The AFM probe is extensively preconditioned, calibrated, and monitored both in situ and ex situ to minimize effects of contamination and ensure reproducibility. The measurements are compared against an interlayer electron tunneling theory that accounts for both strain and temperature effects. By independently controlling these two parameters, we investigate the influence of compressive strain and increased out-of-plane phonon amplitudes on electron tunneling, shedding light on why out-of-plane conductivity increases with temperature in graphitic materials