Scattering in electron spectrometers, diagnosis and avoidance. I. Concentric hemispherical analysers

Abstract

AbstractThe unwanted scattering of electrons in electron spectrometers leads to a loss of sensitivity, distortion of the spectral background and problems in calibrating spectrometer intensity/energy transmission functions. Here we develop three methods to analyse the extent of the contribution and how to reduce it to an insignificant level. The three diagnostic methods involve either the measurement of the region of the M4,5VV Auger electron peaks from Ag in AES, or the reflection of an electron beam from a biased sample, or the 3p1/2 photoelectron peak from Ag irradiated with Mg Kα x‐rays. In this work analyses are made for concentric hemispherical analysers. In Part II, cylindrical mirror analysers are studied. It appears that in our spectrometers, a modified VG scientific Escalab II with either the original analyser or a 210 analyser, the major scattering contributions arise from high‐energy electrons that strike the outer hemisphere giving rise to a spectrum of secondary electrons. These cause the scattered electron contribution to vary approximately as E, where Ep is the pass energy, to increae approximately in proportion to the spectrometer input slit area for AES studies, to fall approximately inversely with an increase in the lens magnification from 1 to 3 and, in the constant ΔE mode, to increase with the analysed electron energy. Thus, for each lens magnification, there exists a range of slits and pass energies for which the scattering may be maintained at <1%. In the constant ΔE mode, pass energies of ≥50 eV are generally safe, whereas in the constant ΔE/E mode, retardation ratios of ≤4 are required.