SCATTERING IN ELECTRON SPECTROMETERS, DIAGNOSIS AND AVOIDANCE .1. CONCENTRIC HEMISPHERICAL ANALYZERS

The unwanted scattering of electrons in electron spectrometers leads t o a loss of sensitivity, distortion of the spectral background and pro blems in calibrating spectrometer intensity/energy transmission functi ons. Here we develop three methods to analyse the extent of the contri bution and how to reduce it to an insignificant level. The three diagn ostic methods involve either the measurement of the region of the M4,5 VV Auger electron peaks from Ag in AES, or the reflection of an electr on beam from a biased sample, or the 3p1/2 photoelectron peak from Ag irradiated with Mg Kalpha x-rays. In this work analyses are made for c oncentric hemispherical analysers. In Part II, cylindrical mirror anal ysers are studied. It appears that in our spectrometers, a modified VG Scientific Escalab II with either the original analyser or a 210 anal yser, the major scattering contributions arise from high-energy electr ons that strike the outer hemisphere giving rise to a spectrum of seco ndary electrons. These cause the scattered electron contribution to va ry approximately as E(p)-2.43, where E(p) is the pass energy, to incre ase approximately in proportion to the spectrometer input slit area fo r AES studies, to fall approximately inversely with an increase in the lens magnification from 1 to 3 and, in the constant DELTAE mode, to i ncrease with the analysed electron energy. Thus, for each lens magnifi cation, there exists a range of slits and pass energies for which the scattering may be maintained at < 1 %. In the constant DELTAE mode, pa ss energies of greater-than-or-equal-to 50 eV are generally safe, wher eas in the constant DELTAE/E mode, retardation ratios of less-than-or- equal-to 4 are required.