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OO13.07 - What is the Effect of Functionalization on the Electronic Structure of Graphene? 
April 24, 2014   9:45am - 10:00am

The chemical functionalization of graphene is of wide interest; it gives promise of tailoring its physical properties, chemical reactivity and interfacial characteristics when combined into three-dimensional materials. In addition, monolayer sheets can readily be obtained in large quantities through the oxidation and exfoliation of graphite to graphene oxide, making it an attractive route to the production of chemically modified graphene for low cost applications[1]. Significant questions remain over the structure and properties of these chemically modified graphenes. In particular, it is critical to consider changes to the electronic structure - the linear dispersion in the band structure of graphene around the ‘Dirac’ point is one of its defining features. Such studies require a more controlled system of modification than wet chemical oxidation and functionalization of graphite.We will introduce the controlled oxygen and nitrogen functionalization of graphene in ultra-high vacuum, allowing systematic study of the effect of functionalization. Starting with the model system of graphene grown by chemical vapour deposition on copper [2,3], we will show how angle-resolved photoemission spectroscopy (ARPES) can reveal the changes in electronic structure induced by functionalization. Complementary insight into the chemical changes is given by X-ray photoemission spectroscopy, whilst Raman spectroscopy and low-voltage aberration-corrected transmission electron microscopy reveal the structural changes. Combined, the results show that low levels (few %) of functionalization can either disrupt the graphene lattice with irreversible disorder (here for nitrogen), or result in reversible functionalization with no damage to the carbon lattice (here for oxygen), indicating that detailed understanding of the functionalization process is required. Surprisingly, in both cases, even this low level of functionalization is sufficient to destroy graphene’s band structure such that it is no longer a semi-metal but rather an electronically disordered material. These results have important implications for the properties and application of chemically modified graphene, and for the control of its surface chemistry.[1] Park, S. & Ruoff, R. S. Chemical methods for the production of graphenes. Nature Nanotechnology 4, 217-224 (2009).[2] Wilson, N. R. et al. Weak mismatch epitaxy and structural feedback in graphene growth on copper foil. Nano Research 6, 99-112 (2013). [3] Marsden, A. J. et al. Is graphene on copper doped? Physica status solidi - Rapid Research Letters 7, 643-646 (2013).

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