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S. Kagerer, L. Zauner, T. Wojcik, S. Koloszvári, T Kozák, J Capek, P Zeman, H. Riedl, P.H. Mayrhofer:
"Reactive HiPIMS deposition of Al-oxide thin films using W-alloyed Al targets";
Surface & Coatings Technology, 422 (2021), 127467; 1 - 10.

The outstanding oxidation resistance, thermo-mechanical stability, and chemical inertness of alumina, but also the synthesis of phase pure polymorphs attract particular attention in academia and industry. Especially, the difficulties regarding the synthesis of α- or γ-structured Al2O3 by physical vapor deposition techniques are still strong limitations. Within this study, we investigated in detail the influence of 2 at.% tungsten in the Al-target on the process stability and phase formation during reactive DC magnetron sputtering as well as high power impulse magnetron sputtering (HiPIMS) of Al2O3-based coatings. The small addition of W to the Al target allows to increase the oxygen partial pressure by more than 200% while maintaining a stable deposition process. Ion mass spectroscopy measurements yield a promising high fraction of 16O+ and 32O2+, when operating the W-containing target in the metal-to-poisoned transition mode. A significant increase of 16O+ is further provided by the target surface oxide in poisoned mode. Detailed time-of-flight ion mass spectroscopy investigations during one HiPIMS pulse show a clear temporal separation of the individual ions arriving at the substrate plane during the pulse on-time, allowing for controlled ion attraction by synchronizing the bias pulse to the discharge impulse. Equal amounts of 27Al+ and 32O2+ can be attracted using a bias on-time between 400 μs and 900 μs in the "off-time" (after glow) leading to a dense and nano-crystalline coating. Detailed electron microscopy investigations show the presence of metallic phase fractions for higher duty cycles (7.5%). Decreasing the duty cycle to 3.75% leads to amorphous coatings when operating the Al-target at the highest oxygen partial pressure in metallic mode.

r-HiPIMS deposition; Alumina; Target Poisoning; Polymorph Structures

http://dx.doi.org/10.1016/j.surfcoat.2021.127467

https://publik.tuwien.ac.at/files/publik_298104.pdf