Highly sensitive hydrogen detection by medium energy Ne⁺ impact

Hydrogen atoms on solid surfaces were measured directly by elastic recoil detection analysis (ERDA) using medium energy (100-150 keV) Ne⁺ ions with an excellent sensitivity of (∼ 1 × 10¹² H/cm²) without any absorber foils and time-of-flight techniques. An electrostatic toroidal analyzer acquired H⁺ ions with energy around 11 keV recoiled from Si(111)-1 × 1-H surfaces. The H⁺ fraction strongly depends upon emerging angle and takes a value more than 50% at the angle below 70° and a saturated value of 17% at the angle above 80° with respect to surface normal. We detected H atoms on the reduced TiO₂(110) exposed to water molecules at room temperature (2 L) and estimated the absolute amount of H to be ∼ 2.0 × 10¹⁴ H/cm² corresponding to ∼ 38% (∼ 0.38 ML) of the bridging oxygen atoms.