SCATTERING IN ELECTRON SPECTROMETERS, DIAGNOSIS AND AVOIDANCE .2. CYLINDRICAL MIRROR ANALYZERS

An analysis is made of the effects leading to an unwanted scattered ba ckground of electrons in cylindrical mirror analysers (CMAs). This wor k complements that given in Part I on concentric hemispherical analyse rs. It is shown that scattering from the middle region of the inner su rface of the mirror electrode is significant but that the amount of sc attering reaching the detector may be reduced by reducing the area of the output slit or by adding a deflection post filter to the optics as occurs in some commercial instruments. Internal scattering causes a h igher background so that peak-to-background ratios are attenuated and transmission function calibrations involve a systematic error. Evidenc e for this error is a step in the calibration curves for I(E)/En(E) es tablished earlier. The steps appearing in the curves for Cu and Ag ref erence samples give a direct measure of the scattering intensity. Cali bration plots are established for this purpose. Results from previous interlaboratory comparisons are analysed showing that in commercial CM As with large-area energy selection slits the scattering may reach 35% of the copper true background at 950 eV, complicating the subsequent use of the data. Concentric hemispherical analysers and some commercia l CMAs show very low scattering. In some CMAs the analogue detection s ystems cause a similar enhanced background in addition to scattering, boosting the above figure of 35% to 100%.