A graphene surface force balance.

Jude Britton,Samuel W Coles,Antal Koós,Christian D Van Engers,Adrian T Murdock,Nicole Grobert,Nico E A Cousens,Susan Perkin,Vitaliy Babenko

doi:10.1021/la5028493

Jude Britton, Samuel W Coles + Show 7 more

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https://doi.org/10.1021/la5028493

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Abstract

We report a method for transferring graphene, grown by chemical vapor deposition, which produces ultraflat graphene surfaces (root-mean-square roughness of 0.19 nm) free from polymer residues over macroscopic areas (>1 cm2). The critical step in preparing such surfaces involves the use of an intermediate mica template, which itself is atomically smooth. We demonstrate the compatibility of these model surfaces with the surface force balance, opening up the possibility of measuring normal and lateral forces, including friction and adhesion, between two graphene sheets either in contact or across a liquid medium. The conductivity of the graphene surfaces allows forces to be measured while controlling the surface potential. This new apparatus, the graphene surface force balance, is expected to be of importance to the future understanding of graphene in applications from lubrication to electrochemical energy storage systems.

Highlights

Graphene is likely to play a key role in a broad range of electronic, electrochemical, and structural applications
As a final step in this work, we demonstrate that the resulting graphene surfaces are sufficiently smooth to allow for force measurements in a surface force balance (SFB), by presenting a proof-of-principle measurement
A new double-transfer procedure has been demonstrated for preparation of ultraflat graphene surfaces over macroscopic areas

Summary

Introduction

Graphene is likely to play a key role in a broad range of electronic, electrochemical, and structural applications. Because the study of these systems continues to focus on the nanoscale, understanding the interaction of graphene with ultrathin films, molecular assemblies, and even individual molecules becomes increasingly important.[1−4] To reliably investigate such structures with techniques, such as atomic force microscopy and scanning tunneling microscopy, smooth substrates, devoid of contamination and large features, are required.[5] surface force measurements, which require smooth surfaces over macroscopic areas, are constrained by these requirements.[6] Graphene can be prepared directly from graphite, either mechanically[7] or via chemical exfoliation;[8] the characteristics of the graphene flakes produced are largely uncontrollable, and the mean flake size is limited to only a few micrometers. Difficulties arise in transferring graphene from the growth substrate to the target material, with polymer contamination of the graphene surface common when using current transfer methods.[10−15] graphene is generally wrinkled because of a difference in thermal expansion coefficients of graphene and the growth substrate upon cooling after synthesis.[16,17]

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