The Phase Evolution and Photocatalytic Properties of a Ti-TiO2 Bilayer Thin Film Prepared Using Thermal Oxidation

Ying-Chieh Lee,Yaw-Teng Tseng,Ping-Yuan Lee,Chen-Tien Chiu,Endrika Widyastuti,Tzu-Che Lin,Fu-Yang Xu

doi:10.3390/coatings11070808

Abstract

Ti-TiO2 bilayer thin films were successfully prepared onto a glass substrate using magnetron sputtering with different TiO2 bottom layer conditions. These represent a lack of (as-deposited) and full oxygen content (annealed). Single-layer Ti was additionally used as a control. The influence of oxygen diffusion phenomena of the bottom layer of TiO2 to the upper layer of Ti thin films at different oxidation temperatures on structural, optical, and photocatalytic performance was investigated. X-ray diffraction (XRD) results confirmed that the crystalline phases coexisting on thin-film samples oxidized at 450 °C were TiO, TiO1.4, (bilayer, as-deposited TiO2), anatase (bilayer, annealed TiO2), and rutile (single and bilayer). This finding showed that the film’s phase structure evolution is significantly affected by oxygen diffusion from the bottom layer. Further increasing the thermal oxidation temperature caused a notable decline in the amorphous zone in bilayer thin films based on TEM analysis. Bilayer thin films lead to higher degradation of methylene blue under UV light radiation (63%) than single-layer films (45%) oxidized at 450 °C. High photocatalytic activity performance was found in the bilayer annealed TiO2-Ti thin-film sample. This study demonstrates that the bilayer modification strategy promotes the oxygen-induced bottom layer of TiO2 bilayer thin films.

Highlights

Semiconductor-based photocatalytic reactions have been fascinating as a promising technology that relies on the interaction between light and solid semiconductor particles.Titanium dioxide (TiO2 ) has been acknowledged as the most crucial photocatalyst that strongly resists chemical and photo-corrosion, is non-toxic, and has thermal stability [1].Several methods have been introduced to synthesize TiO2 thin films, such as the sol-gel method [2], the combustion method [3], the chemical vapor deposition (CVD) method [4], and the sputtering method [5]
When the temperature was set at 450 ◦ C, we found that only the TiO2 rutile phase was detected in sample 1
Hexagonal TiO and TiO1.04 phases appeared. This is because the titanium dioxide bottom layer does not provide sufficient oxygen for the pure titanium film upper layer during thermal oxidation

Summary

Introduction

Semiconductor-based photocatalytic reactions have been fascinating as a promising technology that relies on the interaction between light and solid semiconductor particles.Titanium dioxide (TiO2 ) has been acknowledged as the most crucial photocatalyst that strongly resists chemical and photo-corrosion, is non-toxic, and has thermal stability [1].Several methods have been introduced to synthesize TiO2 thin films, such as the sol-gel method [2], the combustion method [3], the chemical vapor deposition (CVD) method [4], and the sputtering method [5]. The magnetron sputtering technique was approved for providing solid substrate adhesion and a large area with uniform thickness [6,7]. The high-power impulse magnetron sputtering (HiPIMS) technique has demonstrated significant potential in material processing. This technique enables accessing high-density plasmas with excessive quantities of ionized species, high-energy transfer functions, and low duty cycles than direct current magnetron sputtering (DC-MS) [5,8,9]. The DC-MS technique generates coatings with a higher deposition rate than the HiPIMS technology. The combined HiPIMS and DC-MS method has been suggested to increase deposition rates and improve physical, chemical, and functional properties [14,15,16]

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Results

Conclusion