Experiments relative to the desorption of negative ions during low-energy electron impact on surfaces

Abstract

During collisions of low-energy electrons on adsorbed layers, resonant processes may induce intense negative ion desorptions. For such investigations an electrostatic mirror configuration was used to freely decelerate an electron beam just as it reached the investigated surface. The same optical system ensured a very efficient collection for the negative desorbed ions before carrying out their mass and energy analysis. The desorption of H − ions from water vapour over-layers adsorbed on (100) and (111) aluminium crystals was reported here. Additional intensity measurements were performed. They provided useful information relative to the surface work function of the sample and to the variation of both secondary electron emission and electron backscattering during very low-energy electron collisions.