Ma. Vasilev et al., COMPENSATING FOR BACKGROUND OF SECONDARY ELECTRONS IN ELECTRON-SPECTROSCOPY, Instruments and experimental techniques, 38(1), 1995, pp. 119-120
The background slope in records of electron spectra due to true second
ary electrons can be eliminated by adding harmonic signals at frequenc
ies omega and 2 omega. Then a superposition of the first and second de
rivatives of the signal is detected at 2 omega, and the background slo
pe can be eliminated by selecting the amplitudes and phases of the mod
ulation signals.