Method for determining the signal linearity in single and multidetector counting systems in X-ray photoelectron spectroscopy

Both predictable and unpredictable non-linearities occur in the electron co unting systems which provide the intensity scales of different X-ray photoe lectron spectrometers. The predictable effects are inherent in good system design and may be accurately corrected as they are both stable and repeatab le. Unpredictable effects occur due to inadequate design, deterioration in service or poor setting-up procedures. We have therefore, devised a method to measure this non-linearity in X-ray photoelectron spectroscopy (XPS). A widescan (survey) spectrum is recorded from a copper or stainless steel sam ple at both high and low X-ray source emission currents. The ratio of these spectra, at each emission energy, allows non-linearities to be easily meas ured. We show results for one example of a predictable system exhibiting on ly dead time effects which can be corrected to give 1% accuracy up to 5 Mc/ s. We also show results for an unpredictable multichannel detector system w here the non-linearity exceeds 5% at counting rates below 20 kc/s and reach es 50% at 500 kc/s. Crown Copyright (C) 1999 Published by Elsevier Science B.V.