Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 33: Oxides and Insulators: Epitaxy and Growth
O 33.2: Vortrag
Dienstag, 27. März 2007, 16:00–16:15, H41
Oxidation on the nanoscale - the tungsten-water reaction in high electric fields — •Carsten Nowak1, Guido Schmitz2, Reiner Kirchheim1, and Christian Oberdorfer2 — 1Institut für Materialphysik, Universität Göttingen, D-37077 Göttingen — 2Institut für Materialphysik, Universität Münster, D-48149 Münster
The oxidation of nanoscale needle-shaped tungsten tips in water vapor at room temperature is strongly depending on the electric field around the nanotip. Above a critical field strength of the order of 109 V/m the natural oxidation process is extended by a field-induced oxidation reaction. Investigation of the oxidation kinetics reveals that the oxidation reaction virtually terminates after some seconds. The morphology of the formed oxide layer shows a distinct pressure dependence in the range of 10−4 to 101 mbar H2O, with a characteristic size of the formed oxide layer of up to some 100 nm. Using pulsed laser atom probe tomography, the stoichiometry of the formed oxide is determined to be WO3.
Calculation of the electric field distribution around the tip with the finite element method allows conclusions about the field-influence on oxide growth and the appearance of different morphologies in dependence of the water pressure. Special attention will be paid to the aspect of charge compensation, and it will be discussed to which degree the enhanced oxidation reaction under the influence of the electric field is material independent.