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Maya N. Nair - Synchrotron SOLEIL

Modification of Electronic Properties of Graphene by Functionalization, Nanostructuration and Growth

Graphene is an ideal candidate for future high-speed nanoelectronics. However, the lack of band gap is a major drawback. Several methods have already proposed to modify the band structure of graphene[1, 2]. Here I will present three different ways to modify the electronic properties of graphene, i.e. functionalization by atomic intercalation, nanostructuration and the appropriate tuning of the growth conditions.

I will first show the functionalization of epitaxial graphene with gold intercalation. After gold intercalation between the monolayer and the buffer layer of epitaxial graphene, we have observed two different stable structures. One structure consists of an irregular distribution of gold clusters (diluted phase) and another consisting of a continuous Au monolayer (film phase). We have studied precisely the diluted phase by STM and ARPES. We observe that the clusters modify the graphene band structure around the van Hove singularities by a strong extension without any significative charge transfer. They also preserve the linear dispersion of graphene quasi particles while increasing their Fermi velocity [3].

Secondly, I will describe the modification of the electronic properties of graphene by nanostructuration. Graphene nanoribbons grown on the sidewall facet of SiC substrate exhibit a bandgap of 0.5eV. The structural origin of this bandgap was studied by STM and STEM measurements and DFT calculations [4]. We have concluded that the bandgap is due to electronic confinement in nanometer size miniribbons.

Finally, I will demonstrate that the precursor growth state of graphene, the buffer layer, is indeed a semiconducting graphene layer under adequate growth conditions. We have recently shown that on SiC(0001) substrate, a well ordered buffer layer exhibits a bandgap of more than 0.5eV [5], twice the previous value in epitaxial graphene samples [6].We have identified an electronic periodicity in agreement with the STM observations. We believe that this electronic periodicity can be at the origin of the band gap opening [7].

References :

[1]. R. Balog, B. Jørgensen, L. Nilsson, M. Andersen, E. Rienks, M. Bianchi, M. Fanetti, E. Laegsgaard, A. Baraldi, S. Lizzit, Z. Sljivancanin, F. Besenbacher, B. Hammer, T.G. Pedersen, P. Hofmann, and L. Hornekaer, Nat. Mater. 9, 315 (2010)

[2]. E. Bekyarova, S. Sarkar, S. Niyogi, M.E. Itkis, and R.C. Haddon, J. Phys. D. Appl. Phys. 45, 154009 (2012).
[3]. M.N. Nair, M. Cranney, F. Vonau, D. Aubel, P. Le Fèvre, A. Tejeda, F. Bertran, A. Taleb-Ibrahimi and L. Simon, Phys. Rev. B. 85, 245421 (2012).

[4]. I. Palacio, A. Celis, M. N. Nair, A. Gloter, A. Zobelli, M. Sicot, D. Malterre, M.S. Nevius, W. A. de Heer, C. Berger, E.H. Conrad, A. Taleb-Ibrahimi and A. Tejeda, Nano Lett. 15,182 (2015)

[5]. M.S. Nevius, M. Conrad, F. Wang, A. Celis, M.N. Nair, A. Taleb-Ibrahimi, A. Tejeda, and E.H. Conrad, Phys. Rev. Lett. 115 136802, (2015)

[6]. S.Y. Zhou, G.-H. Gweon, a V Fedorov, P.N. First, W. A de Heer, D.-H. Lee, F. Guinea, A. H. Castro Neto, and A. Lanzara, Nat. Mater. 6, 770 (2007)

[7]. M. N. Nair, A. Celis, A. Zobelli, A. Gloter, E. H. Conrad, C. Berger, W. A. de Heer, A. Taleb-Ibrahimi, and A. Tejeda (in preparation)


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