Scattering of neutral hydrogen at energies less than 1 keV from tungsten and diamondlike carbon surfaces

Neutral atom to negative ion conversion efficiencies were studied for polished tungsten and diamondlike carbon surfaces using a beam of incident hydrogen atoms. Neutral atoms at energies below 1 keV were scattered from the surfaces using incident angles between 6° and 20° measured from the surface plane. The angular and energy distributions of negative ions backscattering from the surfaces were measured and used to calculate the fraction of the incident beam that was converted to negative ions. The highest number and the lowest overall energy loss of backscattered ions were both observed near the specular reflection angle of the incident beam for the two surface materials studied. The total conversion efficiency was calculated to be near 2% for the tungsten and diamondlike carbon surfaces. Measurements taken while the surfaces were heated show a significant reduction in conversion efficiency, which is credited to the removal of adsorbates from the top layers of the surfaces.