An XPEEM study of structural cation distribution in swelling clays. I. Synthetic trioctahedral smectites

X-PEEM images and XPS were collected on isolated layers of three synthetic swelling clays, one hectorite and two saponites with various charge, recording the Si(2p), Al(2p) and Mg(2p) core level spectra from the clay sheets. Spectra were fitted to determine the different components of the core levels. Due to their large full width at half maximum, Si XPS spectra were fitted using two to three doublets. It appears that, for a given clay mineral, Si, Al and Mg binding energies (BE) were constant, for all the observed layers. However, variations of the Si BE were observed depending on the nature of the mineral investigated. The various components obtained from the fit of Si spectra could be assigned to different substitution rates; binding energy shifting to lower values with substitution increase in the layer. Furthermore, variations in Si BE according to charge location were assigned to the influence of exchangeable cation.