XPS: binding energy calibration of electron spectrometers 4?assessment of effects for different x-ray sources, analyser resolutions, angles of emission and overall uncertainties
✍ Scribed by Seah, M. P.; Gilmore, I. S.; Spencer, S. J.
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 638 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0142-2421
No coin nor oath required. For personal study only.
✦ Synopsis
A detailed analysis is made of the binding energy calibration of X-ray photoelectron spectrometers when using monochromated Al Ka x-rays or unmonochromated Al or Mg Ka x-rays. The binding energies of the peaks for Cu Ag and Au as well as for the Ni Fermi edge, are measured at high resolution using monochro-2p 3¿2 , 3d 5¿2 4f 7¿2 , mated Al Ka x-rays. The apparent binding energy shifts of the peaks are then calculated for this source, and also for the Al and Mg unmonochromated x-ray sources, using full synthetic Ka x-ray structures, as a function of Gaussian spectrometer energy resolutions in the range 0.2-1.5 eV. For all three x-ray sources, the relative binding energies for the Cu and Au peaks are contained within »0.015 eV but the e †ects for Ag are 2p 3¿2 4f 7¿2 3d 5¿2 stronger and the containment range 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 56Ä for all the peak separations to be restricted to the above range of »0.026 eV. Other instrumental e †ects may give rise to additional larger or smaller e †ects. Non-optimized 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% conÐdence varies across the binding energy range. Example calculations show that seven repeats of both the Cu and Au binding energies may be used to deÐne the peak repeatability and that one or two measurements 2p 3¿2 4f 7¿2 can then be made for each calibration peak to deÐne the calibration. The precise number of measurements to be used depends on the peak energy repeatability and the required conÐdence limits for the calibration. In practical situations, however, it is likely that the greatest uncertainty in the binding energy scale arises from the drift in the electronics between calibrations.