The composition and morphology of fluorinated anodic oxide (FAO) films grown on InAs (1 1 1) A in alkaline aqueous (pH 11.5) and acid waterless (pH 1.5) electrolytes are studied by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) in order to reveal the passivation mechanism of fluorine on the FAO/InAs(1 1 1) A interface. The formation of the highest oxidation form of As+5 and passivation of defects in the FAO layers during the fluorination process explain the reduction of the density of surface states and unpinning of the Fermi level on the fluorinated AO/InAs(1 1 1) A interface. (C) 2010 Elsevier B. V. All rights reserved.