Controlled Deposition of Nanostructured Hierarchical TiO₂ Thin Films by Low Pressure Supersonic Plasma Jets

Plasma-assisted supersonic jet deposition (PA-SJD) is a precise technique for the fabrication of thin films with a desired nanostructured morphology. In this work, we used quadrupole mass spectrometry of the neutral species in the jet and the extensive characterization of TiO₂ films to improve our understanding of the relationship between jet chemistry and film properties. To do this, an organo-metallic precursor (titanium tetra-isopropoxide or TTIP) was first dissociated using a reactive argon-oxygen plasma in a vacuum chamber and then delivered into a second, lower pressure chamber through a nozzle. The pressure difference between the two chambers generated a supersonic jet carrying nanoparticles of TiO₂ in the second chamber, and these were deposited onto the surface of a substrate located few centimeters away from the nozzle. The nucleation/aggregation of the jet nanoparticles could be accurately tuned by a suitable choice of control parameters in order to produce the required structures. We demonstrate that high-quality films of up to several µm in thickness and covering a surface area of few cm² can be effectively produced using this PA-SJD technique.