Evaluating the Internal Structure of Core-Shell Nanoparticles Using X-ray Photoelectron Intensities and Simulated Spectra

The functionality of a new version of the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) (Werner, W. S. M.; et al. U.S. Department of Commerce/NIST: Gaithersburg, Maryland, 2014) has been extended by implementing a new geometry engine. The engine enables users to simulate Auger-electron spectra and X-ray photoelectron spectra for different predefined morphologies (planar, islands, spheres, multilayer core-shell particles). We compared shell thicknesses of core-shell nanoparticles derived from core-shell XPS peak intensities using Shards method, which allows one to estimate shell thicknesses of core-shell nanoparticles, and a series of SESSA simulations for a wide range of nanoparticle dimensions. We obtained very good agreement of the shell thicknesses for cases where elastic scattering within the shell can be neglected, a result that is in accordance with the underlying assumptions of the Shard model. If elastic-scattering effects are important, there can be thickness uncertainties of up to 25%. Experimental spectra of functionalized gold nanoparticles obtained by Techane et al. were analyzed with SESSA 2.0 both with respect to the relevant peak intensities as well as the spectral shape. Good agreement between experiment and theory was found for both cases. These results show that the single-sphere model for core-shell nanoparticles is valid when just using peak intensities, but more detailed modeling is needed to describe the inelastic background.