CROSSED-FIELD (TROCHOIDAL) ELECTRON MONOCHROMATORS AND THEIR OPTIMIZATION

In electron spectroscopy a wide variety of methods using the dispersiv e properties of both magnetic and electric fields are applied to analy se the energies of charged particles moving in a longitudinal magnetic field [1, 2]. Retarding potential analysers where a uniform magnetic field is used, however, possess a disadvantage: an integral characteri stic (retarding curve) must be differentiated in order to determine th e energy spectrum. In analysers with a non-uniform magnetic field (whi ch is increased or decreased in the retarding region), electrons are a nalysed by both the longitudinal and total components of electron velo city [3]. The method of using a Wien filter with nonuniform transverse fields, immersed in a weak longitudinal magnetic field, has also been reported [4). A complicated system of magnetic field formation of the se analysers is coupled with restrictions on the magnetic field altera tion rate [5]. Trochoidal electron monochromators (TEMS) have a favour able advantage-principle simplicity-enabling low-energy electron beams to be obtained. Since being created [6], the TEM has been used in a s eries of studies of electron scattering by atoms and molecules [7-9] a nd solid surfaces [10, 11]. The monochromator theory has been consider ed in detail in the literature [12,13] where the principal parameters of the TEM were calculated. Here we consider the influence of transver se potential drop at the entrance slit and suggest the minimization of beam distortion at the exit by means of the proper choice of non-unif orm transverse electric field parameters.