INTERNAL SCATTERING OF ELECTRONS IN A HEMISPHERICAL SPECTROMETER

Seah and Smith have reported a method of measuring the peak-to-background ratio below the silver LMM Auger peak as a function of the pass energy of a hemispherical electron spectrometer. They used this measurement to reveal the extent of a contribution to the observed spectrum due to secondary electrons generated at the outer hemisphere near to its exit plane. This scattering is caused by electrons whose kinetic energies are just above those passing round the central trajectories of the spectrometer. The work reported here extends this method to a range of kinetic energies and reveals a varying contribution of the internal scattering to the shape of the measured spectrum across the energy span 50-2500 eV. This has an important effect upon attempts to measure the true shape of the background of a spectrum and the manner in which it depends, for example, upon the atomic number of the sample. Calibration methods are presented for the evaluation of the internal scattering of the spectrometer with the objective of finding ways to remove it from the measured spectrum. With the aid of electron optical modelling, the origin of the internal scattering is attributed both to electrons with energies just above those passed by the spectrometer that strike the outer hemisphere and to very energetic electrons leaving the sample and striking surfaces inside the transfer lens between the sample and the hemispheres. These methods are applied to a number of spectra of pure elements to demonstrate the efficacy of the procedure.