Transition from Metallic to Semiconducting Behavior in Oxygen Plasma-treated Single-layer Graphene
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Transition from Metallic to Semiconducting Behavior in Oxygen Plasma-treated Singlelayer Graphene Amirhasan Nourbakhsh1,2, Mirco Cantoro1,3,*, Tom Vosch4, Geoffrey Pourtois1, Johan Hofkens4, Marc M. Heyns1,5, Bert F. Sels1,2, and Stefan De Gendt1,4 1
imec, Kapeldreef 75, B-3001 Leuven, Belgium
2
Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium 3
Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200d, B-3001 Leuven, Belgium 4
Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200f, B-3001 Leuven, Belgium 5
Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium *Electronic mail: [email protected] ABSTRACT We investigate the structural, optical and electrical properties of single-layer graphene exposed to oxygen plasma treatment. We find that the pristine semimetallic behavior of graphene disappears upon plasma treatment, in favour of the opening of a bandgap and the featuring of semiconducting properties. The metal-to-semiconductor transition observed appears to be dependent on the plasma treatment time. The semiconducting behavior is also confirmed by photoluminescence measurements. The opening of a bandgap in graphene is explained in terms of graphene surface functionalization with oxygen atoms, bonded as epoxy groups. Ab initio calculations of the density of states show more details about the oxygen–graphene interaction and its effects on the graphene optoelectronic properties, predicting no states near the Fermi level at increasing epoxy group density. The structural changes are also monitored by Raman spectroscopy, showing the progressive evolution of the sp2 character of pristine graphene to sp3, due to the lattice decoration with out-of-plane epoxy groups. INTRODUCTION Graphene is a 2-D, atomically-thin film of in-plane, sp2-bonded carbon atoms arranged into a honeycomb lattice. Graphene exhibits a variety of intriguing phenomena all deriving from the unique details of its electronic band structure [1]. Its electronic transport properties have been found to be largely superior to those of materials traditionally employed in microelectronics. Therefore, graphene is one of the most promising candidates for applications in CMOS and postCMOS [2]. Single-layer graphene (SLG) is a gapless semimetal. For some of the applications of graphene in electronics and optoelectronics, particularly in logic and switching, a bandgap is required. A number of approaches could be pursued to induce the opening of a bandgap in graphene. When SLG is tailored in few nm-wide ribbons, a quantum confinement-induced bandgap appears [3]. A radically different approach resides in the breaking of the SLG lattice
symmetry, with the aid of specific atomic or molecular functionalization; this can cause the opening of a finite bandgap at its charge neutrality level. In turn, this can render graphene a building block for electronic a
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