Hyperfine interaction study of the decoration of the internal wall of nanosized voids by impurity probes

We observe the trapping of implanted radioactive Co-57 atoms at empty nano-cavities formed in (111) Si by the desorption of He from bubbles. The absorption of 14.4 keV gamma-rays roughly monitors the displacement of the activity, while anodic stripping and counting the remaining 122 keV gamma-ray intensity is employed to obtain an accurate depth profile and to isolate the wanted fraction of the sample. Mossbauer spectroscopy shows that only damage and/or CoSi2-nuclei related sites are present in samples implanted at 300 and 400 degrees C. In a sample implanted with Co at RT at the same side as the cavity-generating He atoms, the Mossbauer spectra reveal two new quadrupole split components after 30 min annealing at 700 degrees C. We present arguments for the tentative identification of these to a cavity edge site (79%, strong bonding) and to a cavity plane site (21%, weak bonding).