Ultra-thin graphene–polymer heterostructure membranes

C N Berger,A Vijayaraghavan,M Dirschka

doi:10.1039/c6nr06316k

C N Berger, A Vijayaraghavan + Show 1 more

Open Access

https://doi.org/10.1039/c6nr06316k

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Abstract

The fabrication of arrays of ultra-thin conductive membranes remains a major challenge in realising large-scale micro/nano-electromechanical systems (MEMS/NEMS), since processing-stress and stiction issues limit the precision and yield in assembling suspended structures. We present the fabrication and mechanical characterisation of a suspended graphene-polymer heterostructure membrane that aims to tackle the prevailing challenge of constructing high yield membranes with minimal compromise to the mechanical properties of graphene. The fabrication method enables suspended membrane structures that can be multiplexed over wafer-scales with 100% yield. We apply a micro-blister inflation technique to measure the in-plane elastic modulus of pure graphene and of heterostructure membranes with a thickness of 18 nm to 235 nm, which ranges from the 2-dimensional (2d) modulus of bare graphene at 173 ± 55 N m-1 to the bulk elastic modulus of the polymer (Parylene-C) as 3.6 ± 0.5 GPa as a function of film thickness. Different ratios of graphene to polymer thickness yield different deflection mechanisms and adhesion and delamination effects which are consistent with the transition from a membrane to a plate model. This system reveals the ability to precisely tune the mechanical properties of ultra-thin conductive membranes according to their applications.

Highlights

The stress–strain behaviour of single-layer graphene and graphene–polymer composites has been studied primarily using Raman spectroscopy.[13,14,15] By monitoring the G and 2D peak position and intensities as a function of applied force on a suspended graphene membrane, the strain and deflection of the membrane can be determined.[16,17] this technique provides indirect measurement of the stress–strain behaviour and probes only a specific area of the membrane, defined by the laser spot size.[18]
Transferred samples were inserted into a pressure chamber, pumped with N2 gas to the desired pressure and left for 24 hours in order for the N2 gas to diffuse into the micro-cavities, equilibrating the pressure across the membrane
On removal of the samples, membranes form a blister above the micro-cavity due to the imbalance in pressure between the lab atmosphere and the micro-cavity

Summary

Introduction

The stress–strain behaviour of single-layer graphene and graphene–polymer composites has been studied primarily using Raman spectroscopy.[13,14,15] By monitoring the G and 2D peak position and intensities as a function of applied force on a suspended graphene membrane, the strain and deflection of the membrane can be determined.[16,17] this technique provides indirect measurement of the stress–strain behaviour and probes only a specific area of the membrane, defined by the laser spot size.[18]. Micro-blister inflation, in which the deflection of a pressurised suspended membrane is monitored, has been used to study the interfacial and elastic properties of graphene as well as ultra-thin polymers.[18,19,20,21] An important aspect of the micro-blister inflation technique is that it removes complications due to contact mechanics that arise when large localised forces are applied, such as during nanoindentation.[19,22,23]

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