Hydrogen interaction with oxidized Si(111) probed with positrons

A variable-energy positron beam was utilized to study the interface action of hydrogen with Si(111) covered by an ultrahigh-vacuum thermally grown oxide of 2–3 nm thickness. It was observed that positrons implanted at shallow depth (<100 nm) after diffusion are trapped either at the interface between the oxide and the Si or in the oxide. The positron-annihilation characteristics of these trapped positrons are found to be very sensitive to hydrogen exposure. The momentum distribution of the annihilating positron–electron pair, as observed in the Doppler broadening of the annihilation line, broadens considerably after exposure to hydrogen. The effect recovers after annealing at [Formula: see text], suggesting a hydrogen binding at the interface of ~3 ± 0.3 eV.