Optical properties of the 127° cylindrical energy analyzer used in LEIS experiments

Abstract

The optical properties of the 127° cylindrical energy analyzer used in low energy ion scattering (LEIS) experiments are studied by means of SIMION 3D version 6.0 program. The dependence of the acceptance solid angle Ω on the target plane coordinates ( x, y) and the relative particle energy ε completely describes the optical properties of an analyzer. The Ω(x,y,ε) function is calculated from the computed trajectories of ions emitted from different points of the target plane. The influence of spherical aberrations to the error in the energy measurement is determined experimentally. The experimental results agree very well with the results obtained using the numerical simulations as well as, with the results obtained by means of the second order analytical approach. The optical properties are analyzed for different electrode potential configurations i.e. for different deflection voltage modes defined according to the potentials of the inner and the outer electrode. The applied deflection voltage mode does not change Ω(x,y,ε) significantly. However, there is an important influence of the deflection voltage mode to the analyzer constant due to the acceleration of ions traversing along the optical axis of the analyzer. The knowledge of Ω(x,y,ε) can be used to determine the dependence of the energy spectra on the optical properties of the analyzer as well as, on the primary beam profile. This is of particular interest in the analysis of LEIS spectra, because deviation of spectra caused by the optics of the analyzer can be a source of significant errors in quantitative surface composition analysis.