Seminars Archive

Interface properties of graphene on metals and semiconductors: interplay between theory and experiments for an accurate characterization

Abstract
The outstanding electronic, optical, thermal and structural properties of graphene and its derivatives (nanotubes, nanoribbons) are widely recognized. The richness of such portfolio is increased by the possibility to functionalize graphene or to create interfaces with other materials. For example the deposition of graphene on metals opens the way to explore interesting properties of interface electronic states. These ones are intimately related to the nature of graphene-metal interaction that also affects the structural arrangement of the nano-sheet on the underneath substrate. While the behaviour of the Dirac cone in weakly and strongly interacting systems has been widely characterized, the unoccupied spectrum has been poorly explored. I will describe the achievement obtained through a joint experimental and theoretical characterization of the unoccupied states of different graphene-metal surfaces (G/Cu(111), G/Ir(111), G/Ni(111)).[1-3] In particular the results of non-linear and time-resolved photoemission experiments will be presented and supported by theoretical calculations, giving a detailed description of the interface and image states in these systems. Furthermore I will show how Thersoff-Hamman STM simulations have allowed an interpretation of STM and LEED measurements of graphene and hBN on Pt(110) and a complete characterization of their complex surface reconstruction and Moiré pattern. In the second part of the seminar I will briefly discuss the role of interface states in the improved performances of CNT/Si solar cells. Indeed by combining transient optical spectroscopy in the femtosecond timescale, I-V measurements and ab initio calculations we have recently demonstrated that trapping of electrons at the interface is the mechanism responsible of the increasing of efficiency in such solar cells.[4]

1) S. Pagliara, S. Tognolini, L. Bignardi, G. Galimberti, S. Achilli, M. I. Trioni, W. F. van Dorp, V. Ocelìk, P. Rudolf, and F. Parmigiani, Phys. Rev. B 91, 195440 (2015)
2) S. Tognolini, S. Achilli, L. Longetti, E. Fava, C. Mariani,  M. I. Trioni, S. Pagliara, Phys. Rev. Lett. 115, 046801 (2015)
3) S. Achilli, S. Ponzoni, S. Lisi, L. Longetti, C. Mariani, M. I. Trioni, S. Pagliara, submitted to New Journal of Physics
4) S. Ponzoni, S. Achilli, C. Pintossi, G. Drera, L. Sangaletti, P. Castrucci, M. De Crescenzi, S. Pagliara, accepted by ACS Applied Materials and Interfaces