Combining Small-Angle X-ray Scattering with Photoelectron Spectroscopy to Increase the Accuracy of Silica Shell Thickness Measurements on Inorganic Nanocrystals

X-ray photoelectron spectroscopy (XPS) is widely used to measure the surface chemistry of nanomaterials, yet it can also provide structural information. The thickness of surface passivation shells can be determined with XPS and hard X-ray photoelectron spectroscopy (HAXPES), but accuracy depends upon knowledge of the density of core and shell materials. This property is typically sourced from literature data on bulk materials, which may not be correct for nanomaterials. We representatively refine shell thickness XPS and HAXPES measurements for silica shells on iron oxide and lanthanide nanoparticles, exploiting electron densities experimentally derived by small-angle X-ray scattering (SAXS) measurements of the core–shell nanoparticles in liquid mixtures with different densities. This results in improved agreement between XPS results and transmission electron microscopy (TEM) and SAXS shell thickness measurements. Thereby, HAXPES provided results in closer agreement with TEM and SAXS than XPS, likely due to a lower sensitivity to coating thickness variations.