Π-Orbital Mediated Charge Transfer Channels in Functionalized Graphene

Functionalization makes graphene (Gr)-based materials extremely appealing for several applications, such as photonics, optoelectronics, and sensing, [1,2] provided that clear information on the charge transfer mechanisms at the interface can be obtained. Indeed, in the case of layered materials or two-dimensional semiconductors, the operation of electronic devices cannot be separated from the control of the generation and flow of charge carriers at the surface or through the junction that is present at the interface between two layers.<br/>Organic molecules are often chosen to functionalize Gr since they can form covalent bonds with the carbon atoms of the lattice after chemical [3] or electrochemical [4] treatments, but also can be deposited on the surface through physisorption, as done in this work with the formation of a single-molecule thick layer of Nickel Phthalocyanine (NiPc) on a monolayer Gr substrate. Moreover, the selection of aromatic scaffolds allows the formation of π-stacked layers, whose electronic properties are possibly altered by the π-orbitals interactions, even when there is no formation of chemical bonds.<br/>Indeed, in this presentation, I will deal with the characterization of the interlayer electron transfer channels in a NiPc-Gr heterointerface, probed by the employment of both experimental techniques (Resonant Photoelectron and X-Ray Absorption Spectroscopies) and DFT calculations. The discussion will bring evidence that the relaxation pathway, which occurs in the femtosecond timescale, involves only π-symmetry orbitals, that are opportunely oriented in a π-stacked flat layer. This allows the transfer of electrons from the molecules, selectively excited thanks to the synchrotron radiation’s photon energy tunability, to the p-doped Gr layer, unveiling the potential of this particular nanoarchitecture for the application in electronic devices.<br/><br/><b>References</b><br/>[1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, and A. A. Firsov, <i>Two-Dimensional Gas of Massless Dirac Fermions in Graphene</i>, Nature <b>438</b>, 197 (2005).<br/>[2] F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, and K. S. Novoselov, <i>Detection of Individual Gas Molecules Adsorbed on Graphene</i>, Nat. Mater. <b>6</b>, 652 (2007).<br/>[3] S. Freddi, M. C. R. Gonzalez, P. Carro, L. Sangaletti, and S. De Feyter, <i>Chemical Defect-Driven Response on Graphene-Based Chemiresistors for Sub-ppm Ammonia Detection</i>, Angew. Chemie Int. Ed. <b>61</b>, e2022001 (2022).<br/>[4] G. Ambrosio, A. Brown, L. Daukiya, G. Drera, G. Di Santo, L. Petaccia, S. De Feyter, L. Sangaletti, and S. Pagliara, <i>Impact of Covalent Functionalization by Diazonium Chemistry on the Electronic Properties of Graphene on SiC</i>, Nanoscale <b>12</b>, 9032 (2020).