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H. Riedl, S. Kagerer, L. Zauner, T. Wojcik, S. Kolozsvári, J Capek, T Kozák, P Zeman, P.H. Mayrhofer:
"Influence of transition metal dopants on the reactive HiPIMS deposition of γ-Al2O3 thin films";
Talk: PLATHINIUM (Plasma Thin film International Union Meeting), Antibes; 2019-09-13 - 2019-09-17.

The outstanding oxidation resistance, thermo-mechanical stability, and chemical inertness of alumina attracts particular attention in academia and industry. Especially, in the field of hard protective coatings there are many research activities [1] focusing on the synthesis of the different polymorphs α- and γ-Al2O3 (corundum and cubic), respectively. To overcome the thermodynamic barrier stabilizing these structure types, extremely high deposition temperatures are crucial during film growth (either in CVD or PVD). Apart from this fact, the formation of isolating Al2O3 layers on the target surface may lead to massive arc events, and hence destabilizes PVD based deposition process [2,3].
Therefore, alternative concepts involving PVD based synthesis at low temperatures are extremely interesting. Within this study, we investigated in detail the influence of small amounts of tungsten on the process stability and phase formation of DC as well as high power impulse magnetron sputtered (Al1-xWx)2O3 thin films in reactive gas atmospheres (Ar/O2 mixtures). Through the introduction of high amplitude impulses at relatively low duty cycles, the amount of ionized species, either for the target-near gas or sputtered target-atoms, can be increased drastically. To gain an in-depth understanding on the influence of small amounts of tungsten compared to pure Al targets but also on different HiPIMS parameters (e.g. frequency, pulse length, power density, or synchronized bias signals), the ionization of e.g. Al+, Al++ or O2+ was investigated by ion mass spectroscopy methodically. In addition, the obtained coating structures were analyzed with respect to phase formation and morphology applying X-ray diffraction combined with electron imaging techniques (SEM and HR-TEM).

Keywords: R-HiPIMS deposition, Alumina; Transition metals; Polymorph Structures;

[1] K. Bobzin, N. Bagcivan, P. Immich, M. Ewering, Thermal Investigation of Al2O3 Thin Films for Application in Cutting Operations, Adv. Eng. Mater. 11 (2009) 590-594.
[2] T. Kohara, H. Tamagaki, Y. Ikari, H. Fujii, Deposition of α-Al2O3 hard coatings by reactive magnetron sputtering, Surf. Coat. Technol. 185 (2004) 166-171.
[3] O. Zywitzki, G. Hoetzsch, Influence of coating parameters on the structure and properties of Al2O3 layers reactively deposited by means of pulsed magnetron sputtering, Surf. Coat. Technol. 86-87 (1996) 640-647.