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- ItemPatterning and control of the nanostructure in plasma thin films with acoustic waves: mechanical vs. electrical polarization effects(Cambridge : RSC Publ., 2021) García-Valenzuela, Aurelio; Fakhfouri, Armaghan; Oliva-Ramírez, Manuel; Rico-Gavira, Victor; Rojas, Teresa Cristina; Alvarez, Rafael; Menzel, Siegfried B.; Palmero, Alberto; Winkler, Andreas; González-Elipe, Agustín R.Nanostructuration and 2D patterning of thin films are common strategies to fabricate biomimetic surfaces and components for microfluidic, microelectronic or photonic applications. This work presents the fundamentals of a surface nanotechnology procedure for laterally tailoring the nanostructure and crystalline structure of thin films that are plasma deposited onto acoustically excited piezoelectric substrates. Using magnetron sputtering as plasma technique and TiO2 as case example, it is demonstrated that the deposited films depict a sub-millimetre 2D pattern that, characterized by large lateral differences in nanostructure, density (up to 50%), thickness, and physical properties between porous and dense zones, reproduces the wave features distribution of the generated acoustic waves (AW). Simulation modelling of the AW propagation and deposition experiments carried out without plasma and under alternative experimental conditions reveal that patterning is not driven by the collision of ad-species with mechanically excited lattice atoms of the substrate, but emerges from their interaction with plasma sheath ions locally accelerated by the AW-induced electrical polarization field developed at the substrate surface and growing film. The possibilities of the AW activation as a general approach for the tailored control of nanostructure, pattern size, and properties of thin films are demonstrated through the systematic variation of deposition conditions and the adjustment of AW operating parameters.
- ItemStudy of TiAl thin films on piezoelectric CTGS substrates as an alternative metallization system for high-temperature SAW devices(Rio de Janeiro : Elsevier, 2021) Seifert, Marietta; Lattner, Eric; Menzel, Siegfried B.; Oswald, Steffen; Gemming, ThomasTi/Al multilayer films with a total thickness of 200 nm were deposited on the high-temperature (HT) stable piezoelectric Ca3TaGa3Si2O14 (CTGS) as well as on thermally oxidized Si (SiO2/Si) reference substrates. The Ti–Al films were characterized regarding their suitability as an alternative metallization for electrodes in HT surface acoustic wave devices. These films provide the advantage of significantly lower costs and in addition also a significantly lower density as compared to Pt, which allows a greater flexibility in device design. To realize a thermal stability of the films, AlNO cover as well as barrier layers at the interface to the substrate were applied. The samples were annealed for 10 h at up to 800 °C in high vacuum (HV) and at 600 °C in air and analyzed regarding the γ-TiAl phase formation, film morphology, and possible degradation. The Ti/Al films were prepared either by magnetron sputtering or by e-beam evaporation and the different behavior arising from the different deposition method was analyzed and discussed. For the evaporated Ti/Al films, AlNO barriers with a lower O content were used to evaluate the influence of the composition of the AlNO on the HT stability. The sputter-deposited Ti/Al films showed an improved γ-TiAl phase formation and HT stability (on SiO2/Si up to 800 °C in HV and 600 °C in air, on CTGS with a slight oxidation after annealing at 800 °C in HV) as compared to the evaporated samples, which were only stable up to 600 °C in HV and in air.