Synchrotron Radiation X‑ray Photoelectron Spectroscopy as a Tool To Resolve the Dimensions of Spherical Core/Shell Nanoparticles

In this work we demonstrate the potential of synchrotron X-ray photoelectron spectroscopy (XPS) to provide quantitative information on the intrinsic dimensions of core–shell nanoparticles. The methodology is based on the simulation of depth profiling curves, using simplified quantitative models earlier proposed in the literature. Three model systems consisting of X@Fe2O3 (with X = Au, Pt, and Rh) metal–iron oxide core–shell nanoparticles, formed via oxidation of size-selected 5 nm bimetallic FeX nanoparticles inside the spectrometer, were measured in situ by near ambient pressure XPS. We show that when the shell layer is composed of a unique component, the experimental depth profiling curve can be simulated by the quantitative calculations and reveal the core and the shell thickness of the nanoparticles. On the contrary, a significant offset between the experimental and the theoretical depth profiling curves implies intermixing between the core and the shell layers. In this case the theoretical model has been modified to represent the more complex particle morphology. Transmission electron microscopy results are in good agreement with the XPS findings, confirming the validity of the model to predict the nanoparticle dimensions.