  The correct referencing of the binding energy (BE) 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, thus indicating that AdC aligns to the sample vacuum level (VL).
Here, results from a much larger sample set are presented including 360
specimens of thin-film samples comprising metals, nitrides, carbides, borides,
oxides, carbonitrides, and oxynitrides. Irrespective of the material system the
C 1s peak of AdC is found to follow changes in the sample work function fully
confirming previous results. Several observations exclude differential charging
as plausible explanation. All experimental evidence points instead to the VL
alignment at the AdC/sample interface as the source of shifts. 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.
