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Free keywords:
alumina; scanning tunnelling microscopy; defect states; scanning tunnelling spectroscopy; energy gap; insulating thin films
Abstract:
The electronic properties of one-dimensional defects in ultrathin Al2O3 films have been investigated by low-temperature STM and STS. Whereas line defects between two oxide domains show almost no topographic contrast in low bias images, they appear with a distinct corrugation at higher positive sample bias. Conductance spectroscopy and imaging reveal three unoccupied states at +2.5, +3.0, and +4.5 V localized along the domain boundaries. The defect-induced states are responsible for the observed contrast variation and originate most likely from a nonstoichiometric oxide composition at the interface between two Al2O3 domains.
