High Elemental Selectivity To Sn Submonolayers Embedded In Al Using Positron Annihilation Spectroscopy

In the present work, we demonstrate that metal layers in the submonolayer range embedded in a matrix are revealed with unprecedented sensitivity by coincident Doppler-broadening spectroscopy of the positron annihilation using a monoenergetic positron beam. The measured electron momentum distribution specific for Sn is clearly observable in Al/Sn/Al-layered samples even at a Sn area density of as low as 7.3 x 10(-2) mu g/cm(2) below 200 nm Al. An explanation for the high elemental selectivity for the thin Sn layers is set forward in terms of efficient positron trapping due to the changing positron affinity at the Al/Sn-interface and quantum-dot-like positron states in Sn nanoparticles.