resumo
Anodic titania films were prepared on titanium by novel powerful pulsed discharge technique which confers extremely high rates of the film growth. Electrochemical impedance spectroscopy (EIS) has been used as a main method to study the structure and semiconductive properties of the anodic oxide films grown in sulphuric acid electrolyte. The EIS results are supported with microscopic observations and photoelectrochemical measurements. For comparison, the properties of the anodic films prepared by the conventional galvanostatic anodisation in the same electrolyte were also examined. For modeling of the impedance spectra, different equivalent circuits taking into account the effects of space charge region and film structure were proposed. Thinner anodic films (d approximate to 25 nm) prepared by both methods demonstrate a similar behaviour characteristic of amorphous barrier-type oxide, whereas a very significant difference in the properties of the films produced by the two different approaches was revealed for thicker films (d = 70-120 nm). The discharge-prepared films in this range of thickness are composed by one compact layer with a relatively low concentration of ionised donors (N-d = (1-3) x 10(18) cm(-3)) estimated from Mott-Schottky plots, whilst the conventional galvanostatic method leads to the development of two-layer films consisting of an inner compact layer and a nanoporous outer one. The latter samples exhibit a significantly reduced photocurrent response at short wavelengths and an essentially higher concentration of ionised donors as compared with the films obtained by the pulsed discharge method. (C) 2012 Elsevier Ltd. All rights reserved.
palavras-chave
PHASE ELEMENT BEHAVIOR; OXIDE-FILMS; PASSIVE FILMS; GROWTH-RATE; ELECTROCHEMICAL CHARACTERIZATION; PHOTOELECTROCHEMICAL BEHAVIOR; SEMICONDUCTING-FILMS; EIS CHARACTERIZATION; TITANIUM ELECTRODES; CORROSION BEHAVIOR
categoria
Electrochemistry
autores
Poznyak, SK; Lisenkov, AD; Ferreira, MGS; Kulak, AI; Zheludkevich, ML
nossos autores
Aleksey Lisenkov
Investigador Júnior
Mário Guerreiro Silva Ferreira
Professor(a) Jubilado(a)
Mikhail Zheludkevich
Investigador Principal Convidadoagradecimentos
Financial support of FCT project PTDC/CTM/72223/2006 is gratefully acknowledged.