Observation of the Amorphous-to-Crystalline Surface Transition in Al-AlxOyUsing Slow Positrons

Abstract

The amorphous-to-crystalline surface transition of ${\mathrm{Al}}_x{\mathrm{O}}_y$ on the Al(111) surface is observed between 650 and 800 K with different ${\mathrm{O}}_2$ exposures by measuring the positronium (Ps) fraction produced by $e^{+}$ impinging on the surface. The data are interpreted in terms of vacancy-type defects in the film or at the metal-metal-oxide interface which as trapping sites for $e^{+}$ or Ps. As the ordering process proceeds to completion the trapping centers anneal out and the Ps fraction increases, showing an irreversible transition. This technique provides a new experimental method to study interfaces.