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Comparisons of Analytical Approaches for Determining Shell Thicknesses of Core–Shell Nanoparticles by X‑ray Photoelectron Spectroscopy
journal contribution
posted on 2018-01-25, 00:00 authored by C. J. Powell, W. S. M. Werner, H. Kalbe, A. G. Shard, D. G. CastnerWe
assessed two approaches for determining shell thicknesses of
core–shell nanoparticles (NPs) by X-ray photoelectron spectroscopy
(XPS). These assessments were based on simulations of photoelectron
peak intensities for Au-core/C-shell, C-core/Au-shell, Cu-core/Al-shell,
and Al-core/Cu-shell NPs with a wide range of core diameters and shell
thicknesses. First, we demonstrated the validity of an empirical equation
developed by Shard for determinations of shell thicknesses. Values
of shell thicknesses from the Shard equation typically agreed with
actual shell thicknesses to better than 10%. Second, we investigated
the magnitudes of elastic-scattering effects on photoelectron peak
intensities by performing a similar series of simulations with elastic
scattering switched off in our simulation software. Our ratios of
the C-shell 1s intensity to the Au-core 4f7/2 intensity
with elastic scattering switched off were qualitatively similar to
those obtained by Torelli et al. from a model that neglected elastic
scattering. With elastic scattering switched on, the C 1s/Au 4f7/2 intensity ratios generally changed by less than 10%, thereby
justifying the neglect of elastic scattering in XPS models that are
applied to organic ligands on Au-core NPs. Nevertheless, elastic-scattering
effects on peak-intensity ratios were generally much stronger for
C-core/Au-shell, Al-core/Cu-shell, and Cu-core/Al-shell NPs, and there
were second-order dependences on core diameter and shell thickness.