Semiconducting properties of surface oxide films

The Kelvin probe technique directly provides information about the work function of the surface oxide, which can be interpreted also as electrode potential, providing useful information about reactivity of surfaces and interfaces. An important topic in this context are novel Zinc-Aluminium-Magnesium alloys (ZAMs) where in earlier works the native oxide layer was shown to play a crucial role in the delamination behaviour (see e.g. [1]).

An important finding was that at the cut edge or at defects down to the steel, the beneficial effect of magnesium at least at the initial stages of exposure is mainly due to enhancing the effect of the zinc cations, which were found to replace reactive Fe2+ sites in the iron oxide layer and thus significantly decrease the oxygen reduction rate [2].

Further it was investigated how different pretreatments, such as alkaline and acidic cleaning, change the semiconducting properties of alumina as well as ionic mobility. A strong correlation between OH fraction and Fermi level position in the oxide was found [3-6].

1.
Hausbrand, R.; Stratmann, M.; Rohwerder, M.: The physical meaning of electrode potentials at metal surfaces and polymer/metal interfaces: Consequences for delamination. Journal of the Electrochemical Society 155 (7), pp. C369 - C379 (2008)
2.
Krieg, R.; Rohwerder, M.; Evers, S.; Schuhmacher, B.; Schauer-Pass, J.: Cathodic self-healing at cut-edges: The effect of Zn2+ and Mg2+ ions. Corrosion Science 65, pp. 119 - 127 (2012)
3.
Özkanat, Ö.; Salgin, B.; Rohwerder, M.; Mol, J. M. C.; De Wit, H. J. H. W.; Terryn, H. A.: Scanning Kelvin probe study of (Oxyhydr)oxide surface of aluminum alloy. The Journal of Physical Chemistry C 116 (2), pp. 1805 - 1811 (2012)
4.
Özkanat, Ö.; Salgin, B.; Rohwerder, M.; Mol, J. M. C.; De Wit, H. J. H. W.; Terryn, H. A.: Erratum: Scanning Kelvin probe study of (oxyhydr)oxide surface of aluminum alloy (The Journal of Physical Chemistry C (2012) 116:2 (1805-1811) DOI: 10.1021/jp205585u). Journal of Physical Chemistry C 116 (10), p. 6505 - 6505 (2012)
5.
Salgin, B.; Özkanat, Ö.; Mol, J. M. C.; Terryn, H. A.; Rohwerder, M.: Role of surface oxide properties on the aluminum/epoxy interfacial bonding. The Journal of Physical Chemistry C 117 (9), pp. 4480 - 4487 (2013)
6.
Salgin, B.; Hamou, F. R.; Rohwerder, M.: Monitoring surface ion mobility on aluminum oxide: Effect of chemical pretreatments. Electrochimica Acta 110, pp. 526 - 533 (2013)
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