X-ray Photoelectron Spectroscopy (XPS)

XPS is a quantitative spectroscopic surface chemical analysis technique used to estimate empirical formulae [109,140–142]. XPS is also known as electron spectroscopy for chemical analysis (ESCA), [141].

XPS plays a unique role in giving access to qualitative, quantitative/semi-quantitative, and speciation information concerning the sensor surface [143]. XPS is performed under high vacuum conditions.

X-ray irradiation of the nanomaterial leads to the emission of electrons, and the measurement of the kinetic energy and the number of electrons escaping from the surface of the nanomaterials gives XPS spectra [109,140–142]. The binding energy can be calculated from kinetic energy. Specific groups of starburst macromolecules such as P=S, aromatic rings, C–O, and C=O can be identified and characterized by XPS [144].