High-resolution grid-less retarding potential analyser and its application for sputter negative ion source

Abstract

An advanced, grid-less, retarding field analyzer (RFA) operating in energy distribution and absolute energy determination modes was developed Two different experimental geometries were used in order to verify the SIMION calculated resolution of the RFA. In energy distribution operation mode, an acceptable resolution of RFA σR of a few eV was achieved by selecting the appropriate geometry responsible for the topography of the retarding field. The device was used to measure the absolute energies and energy distributions of negative ions: H−, Fe−, Ni− and Cu− sputtered from solid cathode surfaces by a 4.2–4.5 keV Cs+ beam employing a modified Source of Negative Ions by Caesium Sputtering (SNICS). All spectra were similar to that of sputtered neutrals with a FWHM of <10 eV and a high energy tail. Depending on the value of surface binding energy, ESBE, the energy of negative beams surpassed or fell behind eU cath by a fraction of eV. After considering ESBE and the work functions of emitting and retarding surfaces, the preliminary conclusion was that the negative ions under investigation were created near the cathode surface.