Influence of N2 ratio in Hydrogen/Nitrogen Plasma on Titanium dioxide/Aluminum doped Zinc Oxide Bilayer Films Applied for Multifunctional Energy-saving Glass

This study reports titanium oxide/aluminum-doped zinc oxide films on glass for multifunctional energy-saving glass. This multifunctional energy-saving glass includes both low emissivity (low-e) and self-cleaning features. According to Hagen–Rubens relation, the emissivity of the material is accompanied by a decrease in electricity resistivity. In addition, the hydrogen plasma treatment contributes to decrease of electrical resistivity of aluminum-doped zinc oxide. However, certain amount of nitrogen can be mixed with hydrogen in plasma annealing to avoid annealing energy absorbed a lot by hydrogen during annealing process due to high thermal conductivity of hydrogen. Hydrogen/Nitrogen $(\mathrm{H}_{2}/ \mathrm{N}_{2})$ plasma treatment at different Hydrogen/Nitrogen ratio can reduce the electrical resistivity. The titanium dioxide/aluminum-doped zinc oxide (TiO $_{2} /$AZO) films were deposited on glass substrates using in-line sputtering. After, the TiO $_{2} /$AZO films were following plasma annealed at different $\mathrm{H}_{2}/ \mathrm{N}_{2}$ ratio: 100/0, 100/100 and 100/150 (sccm/sccm) respectively. Structure, optical transmittance, and electrical properties of as deposited and plasma annealed films were measured. X-ray diffractometer spectra shows the TiO $_{2} /$AZO films of zinc oxide crystal plane at (002). Experiment results indicates $\mathrm{H}_{2}/ \mathrm{N}_{2}$ gas flow ratio in plasma annealing of TiO $_{2} /$AZO films indeed influences the structure and electrical properties of TiO $_{2} /$AZO films. The $\mathrm{H}_{2}/ \mathrm{N}_{2}$ plasma ratio at 100/100 corresponds to lesser electrical resistivity and emissivity of TiO $_{2} /$AZO films among all samples. The electrical properties of the TiO $_{2} /$AZO films were achieved by applying $\mathrm{H}_{2}/ \mathrm{N}_{2}$ plasma ratio of 100/100, where the films electrical resistivity decreased from $2.54 \times 10 ^{-3}($ as-deposited sample) to $1.25 \times 10 ^{-3} \Omega -$cm. Decrease of electric resistivity of aluminum-doped zinc oxide may result from oxygen removal in zinc oxide in Hydrogen/Nitrogen plasma treatment. The emissivity of as-deposited was 0.48. The emissivity of $\mathrm{H}_{2}/ \mathrm{N}_{2} \quad =100 /0$, 100/100 and 100/150 sccm plasma treatment samples were 0.31, 0.28 and 0.30 respectively. The average transmittance in visible wavelength $(380 \sim 780$ nm) of all plasma treatment TiO $_{2} /$AZO films is over than 70%. Hydrophilic is defined as a surface with a water contact angle lower than 90°. The self-cleaning features improves when lowering their water contact angle. The hydrophilicity of TiO $_{2} /$AZO films were analyzed by contact angle meter. The contact angle of as-deposited sample (TiO $_{2} /$AZO) after ultraviolet radiation was 72°. The contact angle of all plasma treatment TiO $_{2} /$AZO films after ultraviolet radiation was about than 50°. Improve of photocatalytic property for $\mathrm{H}_{2}/ \mathrm{N}_{2}$ plasma treatment could be ascribed to 1. surface modification; 2. oxygen vacancies and Ti $^{3+}$. In addition, we produce single TiO2 films on glass substrates, and its were following plasma treatment. We found that the hydrophilicity of plasma treatment TiO $_{2} /$AZO films changes slow compared to that of plasma treatment TiO2 at different time. The combination of two materials forms the TiO $_{2} /$AZO films was stable hydrophilicity than that of single films The good hydrophilic property observed from low contact angle. This means the prepared TiO $_{2} /$AZO samples can apply to selfcleaning glass. The optimum $\mathrm{H}_{2}/ \mathrm{N}_{2}$ ratio in plasma treatment was 100/100, and applied in energy-saving glass.