Mater. Res. Soc. Symp. Proc. Vol. 1 © 2012 Materials Research Society DOI: 10.1557/opl.2012.361 Combined AFM-SEM testing for mechanical property determination of graphene oxide paper Congwei Wang 1 and Asa H. Barber 1 1 Department of Materials, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, U.K. ABSTRACT A novel technique combining both atomic force microscopy (AFM) and scanning electron microscopy (SEM) is used to test the mechanical properties of densely-packed graphene oxide (GO) paper. Individual beams of GO paper with variable widths were prepared using focussed ion beam (FIB) microscopy and tensile tested to failure using the AFM while observing with SEM. A variation in the tensile strength of the GO paper beams up to 64.8 MPa was recorded in the vacuum testing condition. An increase in breaking stress of GO paper with decreasing sample width was determined and proposed as being due to fewer defects present in GO beams of smaller width. INTRODUCTION Graphene-based materials have attracted significant interest since monolayer graphene was first isolated in 2004 [1] due to their extraordinary electronic, mechanical, magnetic, thermal and other physical and chemical properties [2]. The examination of graphene properties has required several approaches to fabricate or isolate single layer graphene sheets. Micro-mechanical exfoliation [3] has been shown as effective in producing the highest quality pristine graphene sheets, which is ideal for most fundamental physical studies. Other methods rely on epitaxial growth of graphene using chemical vapour deposition (CVD) [4] for the fabrication of large area monolayer graphene. Chemical methods are perhaps the most scalable method for producing relatively large amounts of graphene from colloidal suspensions [5] and allow potentially further chemical functionalization of graphene for a range of applications. Chemical solution based graphene originates from the oxidation of natural graphite and produces a hydrophilic intermediary, graphite oxide, which has a layered structure (AB stacking) and can be further exfoliated into graphene oxide (GO) by additional mechanical energy [5, 6]. Graphene oxide typically preserves the carbon basal plane structure of the parent graphite, while decorating the material with other functional groups, such as hydroxyl, carboxyl and carbonyl groups along the basal plane and edges. These functionalized GO materials can be solution processed and easily assembled into macroscopic materials under orientated filtration to give the graphene oxide paper. Functional groups typically incorporating oxygen are particularly effective at chemically linking GO sheets stacked together within the paper, allowing effective stress transfer between the sheets to improve the overall mechanical properties of the paper. The elastic modulus of GO paper has been previously measured as between 6-42 GPa, with a breaking strength of 30-120 MPa [6, 7]. While these mechanical properties are considerably lower than the expected inherent properties of the graphene basal plane, GO papers outperform many other foil-like materials, including bucky paper and exfoliated vermiculite [8]. These superior modulus and breaking strengths for GO paper compared to other paper-like materials is 407