Detection of H ⁺ recoiled from Si(1 1 1)-1 × 1-H by medium energy Ne ⁺ impact

We detected the H ⁺ ions recoiled from Si(1 1 1)-1 × 1-H by medium energy 80-150 keV Ne ⁺ impacts. The H ⁺ fraction is dependent on emerging angle and emerging energy. With decreasing the emerging angle scaled from the surface normal the H ⁺ fraction increases and reaches a saturation below ∼70° and almost 100% for emerging energy above 13 keV. In contrast, the charge state is not equilibrated even at ∼85°. Such strong dependence on emerging angle is due to the location of H bound by Si atoms on top of the surface. The sensitivity to H on the surfaces is estimated to be better than 5 × 10 ¹² atoms/cm ² at a small emerging angle (θ _out < ∼75°), where the H ⁺ fraction reaches ∼100%. The unexpectedly large energy spread for the recoiled H ⁺ spectra is attributed to the Doppler broadening caused by the zero-point energy of the vibrating H-Si system and additionally to small energy transfers among the three bodies of Ne ⁺ and H-Si, although the assumption of binary collision between Ne ⁺ and H is approximately valid. This H detection technique can be widely applied to analysis of chemical reactions including adsorption and desorption mediated by water and hydroxyl on various kinds of metal-oxide surfaces.