Self-Organized In-Depth Gradients in Highly Ti-Doped ZnO Films: Thermal Versus MW Plasma Annealing

Highly Ti-doped ZnO films have been produced by a spin-casting sol-gel process. The spin-casted films show high in plane homogeneity and optical quality. However, when inspected in depth, the surface composition is Ti rich. We show that two possible annealing processes can be considered depending on the properties to exploit. To promote in-depth homogenization, thermal annealing processes have been applied. Meanwhile, the gradients can be exacerbated, thanks to a non-negligible surface sputtering, by applying microwave (MW) plasma treatments with Ar discharges at different pressures. The microstructural properties of the differently processed films have been obtained prior to a study by grazing incidence X-ray fluorescence (GI-XRF) spectroscopy, which reveals the in-depth composition trends induced by the two alternative annealing procedures. The final wetting, electrical and optical properties of the films are described in accordance with the Ti distribution pattern revealed by GI-XRF. The study underlines for the first time how MW plasma annealing processes can be used to exacerbate self-induced atomic gradients in sol-gel films with potential implications in catalytic and biomedical applications.

Effect of Nitrogen Flow in Hydrogen/Nitrogen Plasma Annealing on Aluminum-Doped Zinc Oxide/Tin-Doped Indium Oxide Bilayer Films Applied in Low Emissivity Glass

Low emissivity glass (low-e glass), which is often used in energy-saving buildings, has high thermal resistance and visible light transmission. Heavily doped wide band gap semiconductors like aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) have these properties, especially after certain treatment. In our experiments, in-line sputtered AZO and ITO bilayer (AZO/ITO) films on glass substrates were prepared first. The deposition of AZO/ITO films was following by annealing in hydrogen/nitrogen (H2/N2) plasma with different N2 flows. The structure and optical and electrical properties of AZO/ITO films were surveyed. Experiment results indicated that N2 flow in H2/N2 plasma annealing of AZO/ITO films slightly modified the structure and electrical properties of AZO/ITO films. The X-ray diffraction peak corresponding to zinc oxide (002) crystal plane slightly shifted to a higher angle and its full width at half maximum decreased as the N2 flow increased. The electrical resistivity and the emissivity reduced for the plasma annealed AZO/ITO films when the N2 flow was raised. The optimum H2/N2 gas flow was 100/100 for plasma annealed AZO/ITO films in this work for low emissivity application. The emissivity and average visible transmittance for H2/N2 = 100/100 plasma annealed AZO/ITO were 0.07 and 80%, respectively, lying in the range of commercially used low emissivity glass.

The Effects of Thermal and Atmospheric Pressure Radio Frequency Plasma Annealing in the Crystallization of TiO2 Thin Films

Amorphous TiO2 thin films were respectively annealed by 13.56 MHz radio frequency (RF) atmospheric pressure plasma at discharge powers of 40, 60, 80 W and thermal treatment at its corresponding substrate temperature (Ts). Ts was estimated through three measurement methods (thermocouple, Newton’s law of cooling and OH optical emission spectra simulation) and showed identically close results of 196, 264 and 322 °C, respectively. Comparing with thermal annealing, this RF atmospheric pressure plasma annealing process has obvious effects in improving crystallization of the amorphous films, based on the XRD and Raman analysis of the film. Amorphous TiO2 film can be changed to anatase film at about 264 °C of Ts for 30 min plasma treatment, while it almost remains amorphous after 322 °C thermal treatment for the same time.