STS investigations to describe corrosion procedures on thin CrN layers

摘要

To represent the corrosion characteristics of thin hard material layers, CrN layers, which wre magnetron sputtered, have been exposed to solutions with chloride or sulfate ions. The alterations of the layer surfaces were examined. Static immersion tests were carried out ex-situ in 1 mol L~(-1) NaCl or 1 mol L~(-1) Na_2SO_4 solution over a period of 14 months. For in-situmeasureents, the layers were inserted into the electrochemical cell of an EC STM as the working electrode. The sample potential was altered cyclically. At the same time, voltammograms were taken and the topography alteration was observed. Alterations in the surface strcture were documented as hybrid information resulting from changes in topography and the chemical consistency or the thickness of the oxide layers. These modifications were demonstrated with scanning tunnelling spectroscopy before and after the treatment with solutions. Several chemical phses (initial state and oxide layers) were distinguished with raster tunnelling spectroscopy (measurements I(V) and I(z)). The evaluation of the I(z) spectroscopy showed that the tip was in mechanical contact with the sample if an oxide layer of greater thickness has existed. Exemplary XPS investigations demonstrated corrosive alterations of the CrN layers due to oxidation. Asymmetry and peak locations suggest that in addition to Cr_2O_3 and CrN a complex mixture of different chromium oxides such as Cr_2O_3 and Cr(OH)_x exists.