STEM and EELS study of the Graphene/Bi 2 Se 3 Interface D.M. Kepaptsoglou 1 , D. Gilks 2 , L. Lari 2,3 , Q.M. Ramasse 1 , P. Galindo 4 , M. Weinert 5 , L. Li 5 , G. Nicotra 6 and V.K. Lazarov 2 1 SuperSTEM Laboratory, STFC Daresbury Campus, Warrington, WA4 4AD, UK 2 Department of Physics, University of York, Heslington, York, YO10 5DD, UK, 3 York JEOL Nanocentre, University of York, Heslington, York, YO10 5BR, UK 4 Department of Computer Science and Engineering, Universidad de Cádiz, 11510 Puerto Real, Spain 5 University of Wisconsin Milwaukee, Milwaukee, 53211,WI, USA 6 Institute for microelectronics and microsystems, CNR Catania, 95121 Catania CT, Sicilia, Italy Bi 2 Se 3 is a 3D topological insulator (TI) that has attracted a lot of research interest due to its exotic properties [1], associated with topologically-protected helical two-dimensional surface states and one- dimensional bulk states associated with line defects such as dislocations. Recent theoretical studies [2] have shown that when graphene is placed near Bi 2 Se 3 the strong spin orbit interaction due to proximity effects will open the band gap in graphene for 0.2 eV. Therefore TI/graphene heterostructures are promising platform for developing electronic and spintronic graphene based devices. It has been recently shown that when Bi 2 Se 3 is grown either on epitaxial graphene or free-standing graphene flakes [1,2], a rich grain structure develops due to the spiral nature of the film growth. The grain boundaries and growth-induced screw dislocations in this system provide grounds for interesting new physics that can be accessed by a combination of scanning tunneling microscopy and transmission electron microscopy techniques such as STEM-HAADF and EELS. In this work we investigate the nature of the graphene/Bi 2 Se 3 interface in order to understand the complex epitaxy between the film and substrate as this ultimately determines the structure and functional properties of the graphene/Bi 2 Se 3 interface topological states. The Bi 2 Se 3 films were grown on epitaxial graphene/SiC(0001) and free- standing graphene (Figure 1a) by chemical vapor deposition. The structure and electronic structure of the Bi 2 Se 3 /epitaxial graphene/SiC(0001) interface were studied in cross-section by state-of-the-art aberration-corrected STEM and atomically-resolved EELS. HAADF imaging (Figure 1) confirmed the presence of an epitaxial carbon layer at the Bi 2 Se 3 /epitaxial graphene/SiC(0001) interface. Combined imaging and atomically-resolved EELS maps confirm that both the Bi 2 Se 3 /carbon and carbon/SiC(0001) interfaces are atomically sharp with a Se termination of the Bi 2 Se 3 layer. Analysis of the C K fine structure across the interface stack confirms that the observed interface carbon layer is in fact epitaxial graphene, indicating that the bonding between the Se atomic plane and the epitaxial graphene has a Van der Waals nature. This weak bonding is further corroborated by strain analysis of the HAADF images, showing the absence of strain at the Bi 2 Se 3 /epitaxial graphene/SiC(0001) interface. Such weak bonding would be the key factor for the multiple epitaxial relations which leads to both low- and high-angle boundaries observed in Bi 2 Se 3 thin films when grown on graphene substrate [3,4]. References: [1] Y Ando, J. Phys. Soc. Jpn 82 (2003), p.102001 [2] L. Kou et al., Nano Lett. 13 (2012), p. 6251 Paper No. 0575 1151 doi:10.1017/S1431927615006546 © Microscopy Society of America 2015 Microsc. Microanal. 21 (Suppl 3), 2015 https://doi.org/10.1017/S1431927615006546 Downloaded from https://www.cambridge.org/core. IP address: 3.235.21.12, on 02 Jun 2020 at 13:37:17, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.