Time-of-flight analysis of direct atomic recoils produced by pulsed ${\mathrm{Ar}}^{+}$-ion irradiation of a polycrystalline magnesium surface enables the identification of hydrogen, as well as other surface atoms. The data demonstrate the direct detection of surface hydrogen and the first direct observation of oxygen-induced surface segregation of hydrogen in a metal at room temperature.

• Received 14 June 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1676