Core level binding energies of functionalized and defective graphene

Abstract

SummaryX-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn–Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone–Thrower–Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.

Bottom-up approach for the low-cost synthesis of graphene-alumina nanosheet interfaces using bimetallic alloys

“…Based on DFT calculations performed on both Highly Oriented Pyrolitic Graphite 30 and Gr (ref. 31), the presence of this kind of defects in a concentration 41% would clearly show up in our high-resolution core level spectra in the form of lower BE components.…”

On the relation between chemical composition and optical properties of detonation nanodiamonds

“…3(b)). This component is attributed to the 5-membered carbon ring defects present in the graphitic shell of the DNDs [39,40].…”

Calculation of the graphene C1score level binding energy

“…These issues may be partly addressed by explicitly including an extra electron charge within the conduction band of the material, resulting in a so-called "screened core-hole". However, using a PAW dataset or a pseudopotential does not allow the other core electron(s) to arXiv:1411.3874v2 [cond-mat.mes-hall] 11 Dec 2014 relax, which may limit the accuracy of the absolute binding energies 20 . Although a rigid shift can be applied to align the calculated values with experiment, this assumes that the effect of core-hole relaxation is of identical magnitude for every atom of interest -which can be a priori uncertain for atoms of different elements.…”

“…In the ∆KS total energy differences method 20,38 , the core level binding energy is the total energy difference between a first core ionized state and the ground state in a spin-polarized calculation. To make the unit cell charge-neutral, a compensating electron charge is introduced into the conduction band.…”