Effects of inclination angle applied to a polyethylene terephalate substrate before the coating of Al-doped ZnO on film quality and mechanical and optical properties

A flat plate in the deposition stage is designed to be tilted flexibly with an angle such that an inclination angle is formed between the ion beam and the direction normal to a polyethylene terephthalate (PET) substrate. Five kinds of PET/aluminum-doped zinc oxide specimen, with 0°, 15°, 30°, 45°, and 60° inclination angles, respectively, were prepared to examine the effect of inclination angle on the mechanical, electrical, and optical properties and morphology of coating films. Using the peaks of the ZnO (002) and ZnO (103) planes in X-ray diffraction analyses, the relative intensity ratios for these two crystallines are defined and used to evaluate the parameters of composite grain size ((g)Composite) and residual stress ((σ)Composite). The experimental results indicate that (σ)Composite increases but (g)Composite mostly decreases with increasing inclination angle. A nearly linear relationship is found between (g)Composite and the d-spacing parameter ((d)Composite). They both decrease with increasing inclination angle. The intensities of ZnO (002) and ZnO (103) planes significantly influence the mean transmittance, absorption, and reflection in the wavelength range of 801–2500 nm (near-infrared). An increase in the relative peak intensity of ZnO (002) increases the mean transmittance and thus lowers the mean absorption and reflectance. The average transmittance decreases and the average reflection increases in the wavelength range of 300–2500 nm with increasing inclination angle. Increasing the composite grain size decreases the average reflection. The ZnO film thickness is proportional to the mean surface roughness of the film.