Probability of absorption/implantation of low-energy ions in O-covered vanadium

Energy dependence of the absorption/implantation probability, αab, of H 2 + ions in vanadium covered by an oxygen monolayer was studied in the range 0.5–300 eV by plasma-membrane techniques. In contrast to what one would expect in the case of a clean surface, αab was found: (1) to be appreciably smaller than 1 (αab ≈ 0.2) at the lowest energies, and (2) to monotonically increase with ion energy, with a particularly steep rise in the range 0.5 to ∼7 eV – just where αab is expected to sharply decrease at a clean surface.