SiO2/Si interface probed with a variable-energy positron beam

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Abstract
The annihilation characteristics of a monoenergetic beam of positrons, after implantation in Si with a 350‐nm overlayer of SiO2, were measured as a function of mean implantation depth. Positrons implanted overlapping the SiO2/Si interface were observed to decay from a state with properties distinctively different from the state in bulk Si and the thermally grown SiO2, i.e., a positron interface state. The momentum distribution of the annihilating positron‐electron pair, as observed in the Doppler broadening of the annihilation line, is much broader for this state than for either bulk Si or SiO2, in contrast to previously observed localized positron states in solids and at surfaces which show a narrower distribution.