LAUSR

X‐ray photoelectron spectroscopy (XPS) is routinely employed to measure surface compositions. The standard approach to quantification treats the surface region as if it is homogeneous and applies sensitivity factors to measured peak intensities to calculate the ‘equivalent‐homogeneous composition’ of the sample expressed as a mole fraction, which is usually converted to atomic percent. In this insight note, we briefly summarise the main contributions to uncertainty in XPS composition measurements and provide expressions through which the uncertainty in the measured composition can be estimated and reported.