Binding energy referencing in X-ray photoelectron spectroscopy: Expanded data set confirms that adventitious carbon aligns to the sample vacuum level

The correct referencing of the binding energy scale is essential for the accuracy of chemical analysis by X-ray photoelectron spectroscopy. The C 1s C-C/C-H peak from adventitious carbon (AdC), most commonly used for that purpose, was previously shown to shift by several eVs following changes in the sample work function phi SA , thus indicating that AdC aligns to the sample vacuum level (VL). Here, results from a much larger sample set including 360 specimens comprising metals, nitrides, carbides, borides, oxides, carbonitrides, and oxynitrides are presented. Irrespective of the material system the C 1s peak of AdC is found to follow changes in phi SA fully confirming previous results. Several observations exclude differential charging as plausible explanation for the C 1s peak shifts. All experimental evidence points instead to the VL alignment at the AdC/sample interface as the main reason. Should the C 1s peak of AdC be used for spectra referencing the measurement of sample work function is necessary, irrespective of whether samples are measured grounded or insulated from the spectrometer.