XPS - BINDING-ENERGY CALIBRATION OF ELECTRON SPECTROMETERS 4 - ASSESSMENT OF EFFECTS FOR DIFFERENT X-RAY SOURCES, ANALYZER RESOLUTIONS, ANGLES OF EMISSION AND OVERALL UNCERTAINTIES

A detailed analysis is made of the binding energy calibration of X-ray photoelectron spectrometers when using monochromated Al K alpha x-ray s or unmonochromated Al or Mg K alpha x-rays. The binding energies of the peaks for Cu 2p(3/2), Ag 3d(5/2) and Au 4f(7/2), as well as for th e Ni Fermi edge, are measured at high resolution using monochromated A l K alpha x-rays. The apparent binding energy shifts of the peaks are then calculated for this source, and also for the Al and Mg unmonochro mated x-ray sources, using full synthetic K alpha x-ray structures, as a function of Gaussian spectrometer energy resolutions in the range 0 .21.5 eV. For all three x-ray sources, the relative binding energies f or the Cu 2p(3/2) and Au 4f(7/2) peaks are contained within +/-0.015 e V but the effects for Ag 3d(5/2) are stronger and the containment rang e must be increased to +/-0.026 eV, Further data and calculations are provided for surface core-level shifts and here it is found necessary to restrict emission angles to 56 degrees for an the peak separations to be restricted to the above range of +/-0.026 eV. Other instrumental effects may give rise to additional larger or smaller effects. Non-op timized settings for monochromators can show further shifts of up to /-0.2 eV. The uncertainties associated with the above calibration are then analyzed to show how the uncertainty at 95% confidence varies acr oss the binding energy range. Example calculations show that seven rep eats of both the Cu 2p(3/2) and Au 4f(7/2) binding energies may be use d to define the peak repeatability and that one or two measurements ca n then be made for each calibration peak to define the calibration. Th e precise number of measurements to be used depends on the peak energy repeatability and the required confidence limits for the calibration. In practical situations, however, it is likely that the greatest unce rtainty in the binding energy scale arises from the drift in the elect ronics between calibrations. (C) 1998 John Wiley & Sons, Ltd.