Toward an increased reliability of chemical bonding assignment in insulating samples by x-ray photoelectron spectroscopy

Abstract

X-ray photoelectron spectroscopy (XPS) spectra from solid samples are conventionally referenced to the spectrometer Fermi level (FL). While, in the case of metallic samples, alignment of the sample and the spectrometer FLs can be directly verified from the measured Fermi edge position, thus allowing to assess the surface electrical potential, this is not a workable option for insulators. When applied, it generates a large spread in reported binding energy values that often exceed involved chemical shifts. By depositing insulating amorphous alumina thin films on a variety of conducting substrates with different work functions, we show not only that FL referencing fails but also that the Al 2 O 3 energy levels align instead to the vacuum level, as postulated in the early days of XPS. Based on these model experiments that can be repeated for all sorts of thin-film insulators, a solution to the binding energy reference problem is proposed for reliable assessment of chemical bonding.

Hierarchical FAU Zeolites Boosting the Hydrocracking of Polyolefin Waste into Liquid Fuels

“…Therefore, these crystalline nanoflakes on the Y–H zeolite, formed through a hydrothermal dissolution and recrystallization process, are probably X zeolite that shares the same FAU topology as the parent Y zeolite but with a much lower Si/Al ratio close to 1 (Table S1). , However, the nanoflakes formed on the surface of Y-L may contain Al 2 O 3 , as the surface Si/Al ratio is lower than 1 and the binding energy of Al shifts to a lower position (74.6 eV, compared to 75.0 eV in the original Y zeolite) . These results indicate the beneficial effect of adding CTAB that promotes the formation of X zeolite nanoflakes (FAU type) in the synthesis of the Y–H zeolite.…”