| AVS 65th International Symposium & Exhibition | |
| Advanced Surface Engineering Division | Monday Sessions |
| Session SE-MoA |
| Session: | New Challenges and Opportunities in Surface Engineering |
| Presenter: | Grzegorz Greczynski, Linköping University, Sweden |
| Authors: | G. Greczynski, Linköping University, Sweden S. Mraz, RWTH Aachen University M. Hans, RWTH Aachen University J. Lu, Linköping University, Sweden L. Hultman, Linköping University, Sweden J.M. Schneider, RWTH Aachen University, Germany |
| Correspondent: | Click to Email |
Alloying with Al is a common strategy to improve thermal and chemical stability of transition metal nitride (TMN) coatings deposited by magnetron sputtering. The solubility of Al in rock-salt-structure TMNs is, however, limited which presents a great challenge to increase Al concentration substantially, while avoiding precipitation of thermodynamically-favored wurtzite-AlN phase (w-AlN), which is detrimental to mechanical properties.
We present a novel thin film deposition method, which allows for unprecedented control over the phase formation in metastable TMN layers. The technique relies on hybrid high power impulse/dc-magnetron co-sputtering (HIPIMS/DCMS) of elemental targets in Ar/N2 gas mixture with precise synchronization of the substrate bias pulse to the Al+-populated portion of the HIPIMS discharge which is superimposed onto a continuous TM neutral flux supplied from a DCMS-operated target. This results in a separation of film-forming species in time and energy domains and enables us to overcome the limitations of the conventional processing where phase formation is to large extent determined by the high adatom mobility and gas-ion-induced mixing, both taking place at the very surface, which drive the system towards thermodynamic equilibrium.
To demonstrate versatility of this technique we grow three series of high-Al-content films, namely Ti0.28Al0.72N, V0.26Al0.74N, and Zr0.48Al0.52N, all as a function of the amplitude of the synchronized bias pulse, which corresponds to varying the incident energy of Al+ ions EA1+. For all materials systems, the crystalline phase content is a very sensitive function of EA1+ and can be tuned from completely hexagonal in the limit of low EA1+ values (≲ 60 eV) to pure cubic obtained with EA1+ ≳ 250 eV. A complete transition from hexagonal w-AlN to supersaturated cubic NaCl structure is a consequence of the fact that the subplantation depth of Al+ metal-ions increases with increasing EA1+, as supported by Monte Carlo TRIDYN simulations. This innovative synthesis methodology enables unprecedented control over the phase formation and, hence, film properties and opens novel scientific avenues.