Margherita Marsili Dipartimento di Fisica e Astronomia 'Galileo Galilei', Università di Padova Via Marzolo 8, 35131 , Padova , Italy
The realization of graphene, the two- dimensional (2D) sp2 -bonded form of carbon, and of its derivatives has led to a revolution in the fields of condensed-matter physics, basic science, and device technology [1,2]. The progress in the study of the outstanding properties of graphene and its derivatives has generated much interest for its silicon, germanium, or SiC counterparts, and for their hydrogenated versions.
For the accurate theoretical description of the electronic and optical properties of such systems we apply a three-step procedure: (i) the equilibrium atomic coordinates and the electronic ground state are obtained using DFT [5]; (ii) the quasiparticle (QP) bands are calculated within Hedin's GW approximation [6]; (iii) finally, we solve the Bethe-Salpeter equation (BSE) including the screened Coulomb interaction and the unscreened electron-hole exchange for all quasi particle bands to account for the excitonic effects in the optical spectra [7].
In this talk, results concerning optical and electronic properties of Si, Ge and SiC sheets, and their hydrogenated counterparts will be presented. Excitonic effects are found to be much more important in the hydrogenated Si and Ge sheets than in the corresponding 3D crystals and non-hydrogenated ones. In the SiC sheet, the ionic character of the C-Si bonds opens the zero gap at the K points present in the graphene and in the Si sheet. Hydrogenation further opens the gap with a minimum at BZ center. The corrugation of the SiC sheet after hydrogenation yields a dipole layer. It leads to significant differences for the electron escape or capture in dependence on the C- or Si-termination of the layer side. This effect makes functionalized SiC layers very interesting for electronic applications, e.g., as electron or hole filters.
[1] Katsnelson M. I., Mater. Today, 10, issue No. 1-2 (2007) 20.
[2] Fiori G. et al., Phys. Rev. B, 82 (2010) 153404.
[5] Giannozzi P. et al., J. Phys.: Condens. Matter, 21 (2009) 395502.
[6] Hedin L. and Lundquist B. J., in Solid State Physics,
edited by Ehrereich H., Seitz F. and Turnbull D.,
Vol. 23 (Academic Press, New York) 1969, p. 1.
[7] Onida G., Reining L. and Rubio A., Rev. Mod. Phys., 74 (2002) 601.