Abstract
Nowadays, multi-element cathodes are frequently employed to grow multi-element thin films and coatings using cathodic arc deposition processes. During cathode erosion, the cathode spot sequentially ignites on the cathode surface and imposes melting–solidification cycles that lead to material intermixing and the formation of a modified layer on the cathode surface. To allow us to study these surface modifications, a 10 μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode. This cathode was eroded by a dc steered arc discharge for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots. Furthermore, separated clusters of overlapping craters and a fully eroded surface caused by different stages of erosion were differentiated when scanning the erosion track in the lateral direction. Cross sections of single craters were prepared by focused ion beam techniques while metallographic methods were applied to obtain cross sections of overlapping craters and the modified layer. The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient (heat-affected zone) below the craters. The observations are discussed within the framework of established arc crater formation models.
Highlights
Cathodic arc deposition (CAD) is an industrial physical vapor deposition technique used to grow dense and well-adherent coatings
The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient below the craters
This was confirmed by the backscattered electron (BSE) image of the cathode cross section [Fig. 2(e)], which clearly demonstrated that the multilayer coating remained intact
Summary
Cathodic arc deposition (CAD) is an industrial physical vapor deposition technique used to grow dense and well-adherent coatings. For vacuum arcs of single-element cathodes, the so-called cohesive energy rule[3] was established as an empirical rule. It establishes a linear relationship between the cohesive energy of the cathode material and the arc burning voltage. Secondary relationships between cathode material properties and plasma parameters exist, e.g., a linear relationship of cohesive energy to mean ion charge states and ion kinetic energies.[8,10] Such relationships are of interest as the properties of the plasma have decisive influence on scitation.org/journal/jap the film growth conditions. Designing the cathode may allow us to control the film growth to some extent
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