ITO films were deposited onto non-treated PET using a radio frequency magnetron sputtering system and low-power oxygen plasma-treated PET. Argon (49.7 sccm) was used as the inert gas in the chamber, and oxygen (0.3 sccm) was also used in the chamber. The base pressure of the deposition chamber was around 10-6 Torr, and the working process pressure was around 10-2 Torr. ITO films with a thickness of 50 nm were deposited at room temperature. The oxygen plasma-treated PET surfaces were bombarded by a low-power oxygen gas. The oxygen plasma power, incident angle, and exposure time were 30 to 100 W, 70°, and 5 s, respectively.
X-ray diffraction [XRD] measurements of the SiOx film were performed using an X-ray diffractometer (X'Pert Pro, Philips, PANalytical B.V., Almelo, The Netherlands) equipped with monochromic CuKα radiation (λ = 1.054056 Å) operated at 40 kV and 30 mA. The diffraction pattern was measured at room temperature in normal θ-2θ scanning mode over angles ranging from 10° to 90° with a step of 0.05°, and measurements were performed at a rate of 0.2 s/step.
We also characterized the film's surface morphology using atomic force microscopy [AFM] in the tapping mode (Multimode AFM Nanoscope IIIa, Digital Instruments, Inc., Tonowanda, NY, USA). An ultra-lever cantilever with a spring constant of 26 N/m and a resonance frequency of 268 kHz was used for scanning. Optical transmittance measurements were carried out with an UV-Vis NIR spectrometer.
The wetting properties of the surfaces were determined by the static contact angle method. The contact angles were measured by increasing and then decreasing the volume of a drop of liquid (distilled water) deposited on the sample surface. Recorded images were digitized and analyzed with a software routine that evaluated the tangent at the point of contact between the drop and the surface (i.e., the contact angle).
Measurements to determine the resistivity of the thin films were performed using a four-point probe test. Rectangular sections (3 × 1 cm2) were cut from the substrate. The surfaces of the sections were cleaned thoroughly before the resistivity measurements were made. The four-point probe was placed in contact with the surface of the film, and a fixed current of 10 mA was applied across the outer two probes. The voltage drop across the two inner probes was measured.