The voltage-dependent manipulation of few-layer graphene with a scanning tunneling microscopy tip

Strain and deformation alter the electronic properties of graphene, offering the possibility to control its transport behavior. The tip of a scanning tunneling microscope is an ideal tool to mechanically perturb the system locally while simultaneously measuring the electronic response. Here we stretch few- and multi-layer graphene membranes supported on SiO2 substrates and suspended over voids. An automated approach-retraction method stably traces the graphene deflection hysteresis curve hundreds of times across four samples, measuring the voltage-dependent stretching, from which we extract the hysteresis width. Using a force-balance model, we are able to reproduce the voltage-dependent hysteretic graphene extension behavior. We directly observe a voltage-dependent interplay where electrostatic forces dominate at high voltage and van der Waals forces at low voltage. The relative contribution of each force is dependent on the graphene and tunneling resistance, giving rise to different observed voltage-dependent behavior between samples. Understanding the voltage dependence of these forces impacts scanning probe measurement of 2D materials and informs oscillating graphene device design where similar forces act from the side walls of cavities, leading towards strain engineering of layered 2D systems. (C) 2020 Elsevier Ltd. All rights reserved.