Cadmium telluride as a potential conversion surface

Abstract

In instruments for low energetic neutral atom imaging of space plasmas, a charge state conversion surface (CS) is used to convert neutral atoms into ions for detection. We investigated a cadmium telluride (CdTe) coated sample as a novel material candidate regarding its suitability to be used as a CS. We measured the efficiency of converting H and O atoms into negative ions by surface scattering, as well as their angular scattering distribution, for energies from 195 eV to 1 keV at 8° incidence angle. Also, the energy distribution of scattered particles was recorded for incident O2+ ions, which confirms that molecules are mainly scattered as single atoms. The mean energy loss per atom was about 45%. The negative ion yield from scattering off CdTe was up to 13% for O and about 2% for H, which is comparable to other CS coatings in use. CdTe shows a nearly circular angular scattering cone of width comparable to established CS materials. We conclude that CdTe is a viable CS coating material for ENA instruments in space applications.