Surface analysis using a new toroidal electrostatic analyzer in medium energy ion scattering

A new toroidal electrostatic analyzer (ESA) in medium energy ion scattering has been designed and fabricated for structural analysis of surfaces. The present analyzer has a wide interelectrode distance of 16 mm and thus covers a broad energy range of 10 % of the pass energy at a constant applied voltage. In order to get a good energy resolution, we employed a photon-counting image acquisition system (PIAS: Hamamatsu Photonics) with an excellent spatial resolution of 40-50 mu m, which was combined with a three-stage microchannel plate. We calculated the electric fields of the toroidal ESA including the fringing field by a finite element method and then performed Monte Carlo simulation of deflection trajectories of ions. Thus the optimum conditions of the geometry and size of the entrance and exit slits were determined. Our toroidal analyzer resolved three surface peaks from the Si isotopes(Si-28, Si-29 and Si-30) clearly in the aligned spectra from H-terminated Si(001) and Si(111) and the energy resolution (Delta E/E) was estimated to be about 1 x 10(-3). We describe the notable features of the new toroidal analyzer and show direct detection of H on Si(001) and Si(111) as a typical application.