We report scanning tunneling microscopy (STM) results that reveal localized features on the exposed surface of amorphous aluminum oxide that are regularly present but which cannot be uniquely identified with STM as electronic defects or surface adsorbents. With the simultaneous use of ballistic electron emission microscopy (BEEM) we can examine the electronic transport properties of these local features and determine that they are caused by the presence of adsorbates. By examining the local density of states of these adsorbates through scanning tunneling spectroscopy and BEEM we have identified them as chemisorbed ${\mathrm{O}}_2^{-}.$

• Received 29 March 2002

DOI:https://doi.org/10.1103/PhysRevB.65.201403