Core Level Spectra of Organic Molecules Adsorbed on Graphene.

Abhilash Ravikumar,Guido Fratesi,Gian Brivio

doi:10.3390/ma11040518

Abhilash Ravikumar, Guido Fratesi + Show 1 more

Open Access

https://doi.org/10.3390/ma11040518

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Journal: Materials	Publication Date: Mar 29, 2018
Citations: 2	License type: CC BY 4.0

Affiliation: University of Milano-Bicocca, University of Milan

Abstract

We perform first principle calculations based on density functional theory to investigate the effect of the adsorption of core-excited organic molecules on graphene. We simulate Near Edge X-ray absorption Fine Structure (NEXAFS) and X-ray Photoemission Spectroscopy (XPS) at the N and C edges for two moieties: pyridine and the pyridine radical on graphene, which exemplify two different adsorption characters. The modifications of molecular and graphene energy levels due to their interplay with the core-level excitation are discussed. We find that upon physisorption of pyridine, the binding energies of graphene close to the adsorption site reduce mildly, and the NEXAFS spectra of the molecule and graphene resemble those of gas phase pyridine and pristine graphene, respectively. However, the chemisorption of the pyridine radical is found to significantly alter these core excited spectra. The C 1s binding energy of the C atom of graphene participating in chemisorption increases by ∼1 eV, and the C atoms of graphene alternate to the adsorption site show a reduction in the binding energy. Analogously, these C atoms also show strong modifications in the NEXAFS spectra. The NEXAFS spectrum of the chemisorbed molecule is also modified as a result of hybridization with and screening by graphene. We eventually explore the electronic properties and magnetism of the system as a core-level excitation is adiabatically switched on.

Highlights

Advances in 2D physics were stimulated with the discovery of graphene in 2004 [1]
Several doping methodologies have been proposed to overcome this limitation of graphene such as: electrostatic doping due to interaction with a substrate [16,17], hetero-atom substitutional doping by B or N atoms [18,19,20,21] or by covalent functionalization of organic molecules on graphene [22,23,24,25,26]
We have studied the effect of adsorption of core excited organic molecules on graphene by analyzing the core level shifts and the Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra

Summary

Introduction

Advances in 2D physics were stimulated with the discovery of graphene in 2004 [1]. Graphene is a two-dimensional allotrope of sp hybridized carbon with a honeycomb lattice structure presenting several interesting properties and has been studied extensively in the recent past [2,3,4,5,6]. Graphene shows a linear dispersion of band structure with the valence and conduction bands intersecting at the K and K 0 points of the first Brillouin zone corresponding to the Fermi level [3] This results in several interesting properties such as ballistic transport [1,7,8], the anomalous integral and the half integral quantum Hall effect [9,10] and high charge mobility due to relativistic Dirac fermions [10]. The effect of molecular adsorption is found to play a key role in determining the electronic and magnetic properties of graphene systems.

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