Correlation between target surface and layer nucleation in the synthesis of Al–Cr–O coatings deposited by reactive cathodic arc evaporation

The deposition parameters of reactive cathodic arc are correlated with processes at the surface of the composite Al–Cr targets and the nucleation and phase formation of the synthesized Al–Cr–O layers. The oxygen pressure and the pulsed operation of the arc current influence the formation of intermetallic phases and solid solutions at the target surface. The nucleation of the ternary oxide coatings at the substrate site appears to be, to some extent, controllable by the intermetallics or solid solutions formed at the target surface. A specific nucleation process at the substrate site can therefore be induced by the free choice of target composition in combination with the oxygen pressure and a pulsed arc operation. It also allows the control over the oxide island growth at the target surface which occurs occasionally at higher oxygen pressure. This hypothesis is supported by the X-ray diffraction analysis of the layers as well as of the target surface, and the layer analysis by cross-sectional scanning electron microscopy and Rutherford backscattering spectroscopy.