Tailoring mechanically-tunable strain fields in graphene

TL;DR

This paper demonstrates a purely mechanical method to induce and control tunable strain fields in suspended graphene using silicon micro-machined actuators, enabling advanced strain engineering without substrate interference.

Contribution

It introduces a mechanical approach with micro-machined actuators for controllable strain application in graphene, avoiding electrical coupling and substrate disturbances.

Findings

Achieved tunable strain gradients up to 1.4%/μm

Demonstrated multiple axis straining capabilities

Identified edge defects as mechanical failure points

Abstract

There are a number of theoretical proposals based on strain engineering of graphene and other two-dimensional materials, however purely mechanical control of strain fields in these systems has remained a major challenge. The two approaches mostly used so far either couple the electrical and mechanical properties of the system simultaneously or introduce some unwanted disturbances due to the substrate. Here, we report on silicon micro-machined comb-drive actuators to controllably and reproducibly induce strain in a suspended graphene sheet, in an entirely mechanical way. We use spatially resolved confocal Raman spectroscopy to quantify the induced strain, and we show that different strain fields can be obtained by engineering the clamping geometry, including tunable strain gradients of up to 1.4 %/$\mu$m. Our approach also allows for multiple axis straining and is equally applicable to other two-dimensional materials, opening the door to an investigating their mechanical and electromechanical properties. Our measurements also clearly identify defects at the edges of a graphene sheet as being weak spots responsible for its mechanical failure.