On the use of the micromarker technique for studying the growth mechanism of thin oxide films

The high temperature behavior of microscopic markers, deposited on to pure and ceria-coated nickel, was tested. The markers, having a form of 20-nm-thick palladium bumps with a fractional surface coverage of 0.05 and 30-nm thick gold bumps with a surface coverage of 0.25, apparently interfered with the oxide growth, increasing the oxidation rate on their surface at 973 K over one order of magnitude. As detected by a combination of Auger electron spectroscopy and Rutherford backscattering spectrometry, for ceria modified nickel, the markers’ depth-position coincided with the ceria particles dispersed in the vicinity of the oxide–gas interface. For pure nickel oxide films, the markers were easily incorporated into the growing oxide during very early stages of oxidation and were difficult to detect at the oxide–metal interface. It is proposed that the catalytic behavior of the markers was caused by their fragmentation into a large number of islands, leading to the refinement of the oxide grains, which in turn accelerated the substrate oxidation rate. Some precautions necessary in conducting the marker experiments are defined.