Tuning the Optical Properties of WO3 Films Exhibiting a Zigzag Columnar Microstructure

Tungsten oxide WO3 thin films are deposited by DC reactive magnetron sputtering. The Reactive Gas Pulsing Process (RGPP) associated with the GLancing Angle Deposition method (GLAD) are implemented to produce zigzag columnar structures. The oxygen injection time (t(ON) time) and the pulsing period are kept constant. Three tilt angles alpha are used: 75, 80, and 85 degrees and the number of zigzags N is progressively changed from N = 0.5, 1, 2, 4, 8 to 16. For each film, refractive index, extinction coefficient, and absorption coefficient are calculated from optical transmission spectra of the films measured in the visible region from wavelength values only. Absorption and extinction coefficients monotonously drop as the number of zigzags increases. Refractive indices are the lowest for the most grazing tilt angle alpha = 85 degrees. The highest refractive index is nevertheless obtained for a number of zigzags close to four. This optimized optical property is directly correlated to changes of the microstructure, especially a porous architecture, which is favored for high tilt angles, and tunable as a function of the number of zigzags.

Automated summary

Tungsten oxide WO3 thin films are deposited using DC reactive magnetron sputtering, and a unique zigzag columnar structure is achieved through the Reactive Gas Pulsing Process (RGPP) and Glancing Angle Deposition method (GLAD). Optical properties such as refractive index, extinction coefficient, and absorption coefficient are tuned by adjusting the number of zigzags in the structure, with absorption and extinction coefficients decreasing as the number of zigzags increases. The lowest refractive index is observed at the highest tilt angle of 85 degrees, while the highest refractive index is obtained at a zigzag number close to four, indicating a correlation between microstructure changes and optimized optical properties.