Thin film deposition based on microacoustic sol atomization (MASA)

Abstract

In this work, we demonstrate an innovative method for the deposition of functional thin films, based on microacoustic sol atomization (MASA) and subsequent gel condensation. This method offers several advantages over existing sol–gel deposition methods (e.g., ink-jet printing or dip coating), including a narrow droplet-size distribution with droplets in the low micrometer range, a miniaturizable aerosol source and the principle usability in roll-to-roll processes. The technique can be divided into three subsequent steps: In a first step, high-frequency surface acoustic waves atomize precursor solutions (sols) into an ultra-fine aerosol. In a second step, the aerosol condensates on the substrate surface, forming a gel, which in a third step can be pyrolyzed into a crystalline thin film. The new technique is demonstrated for the deposition of La2Zr2O7 buffer layers on biaxially textured Ni–5 %W tapes. Aerosols with median droplet diameters of 4 and 7.5 µm were produced from lanthanum/zirconium precursor solutions based on propionic acid or water, respectively. A continuous aerosol production was maintained for several minutes, allowing a droplet condensation on an area of about 1 cm × 5 cm. X-ray diffraction studies of the crystallized La2Zr2O7 films with a thickness of about 100 nm show a high crystalline quality with a strong (001) orientation. Additionally, our results indicate a significant influence of the fluid chemistry regarding the aerosol formation, as well as the droplet condensation and the thin film formation process, when the impinging droplets contain residual solvent. The deposition of functional thin films by microacoustic sol atomization (MASA) and subsequent condensation is demonstrated here for La2Zr2O7 buffer layers on biaxially textured Ni–5 %W tapes. Aerosols with median droplet diameters of 4 and 7.5 µm were produced via interaction of lanthanum/zirconium precursor solutions based on propionic acid or water, respectively, with high-power surface acoustic waves. A continuous aerosol production was maintained for several minutes, allowing a droplet condensation on an area of about 1 cm × 5 cm. X-ray diffraction studies of the crystallized La2Zr2O7 films with a thickness of about 100 nm show a high crystalline quality with a strong (001)-orientation.