Preparation of Orthorhombic WO3 Thin Films and Their Crystal Quality-Dependent Dye Photodegradation Ability

Che-Wei Chang,Yuan-Chang Liang

doi:10.3390/coatings9020090

Abstract

Direct current (DC) magnetron sputtering deposited WO3 films with different crystalline qualities were synthesized by postannealing at various temperatures. The in-situ DC sputtering deposited WO3 thin film at 375 °C exhibited an amorphous structure. The as-grown WO3 films were crystallized after annealing at temperatures of 400–600 °C in ambient air. Structural analyses revealed that the crystalline WO3 films have an orthorhombic structure. Moreover, the crystallite size of the WO3 film exhibited an explosive coarsening behavior at an annealing temperature above 600 °C. The density of oxygen vacancy of the WO3 films was substantially lowered through a high temperature annealing procedure. The optical bandgap values of the WO3 films are highly associated with the degree of crystalline quality. The annealing-induced variation of microstructures, crystallinity, and bandgap of the amorphous WO3 thin films explained the various photoactivated properties of the films in this study.

Highlights

Tungsten oxide (WO3 ), as a wide bandgap semiconductor, has been intensively investigated for various uses in scientific devices [1,2]
The WO3 thin films were Direct current (DC) sputtering deposited at 375 ◦ C; the as-grown films exhibited an amorphous structure because of large composition deviation from the stoichiometric value
The as-grown WO3 thin films were further conducted by thermal annealing procedures at

Summary

Introduction

Tungsten oxide (WO3 ), as a wide bandgap semiconductor, has been intensively investigated for various uses in scientific devices [1,2]. WO3 phase exists only in some WO3 nanostructures at room temperature, not frequently visible for other morphologies such as a thin-film structure. Most WO3 thin films synthesized through various methods are in a monoclinic structure; that is, the orthorhombic structure is limited in number. DC sputtering growth of monoclinic or amorphous WO3 thin films have been investigated for applications in gas-sensing, photocatalytic, and electrochromic devices, reports on the microstructure-dependent photodegradation properties of DC sputtering deposited orthorhombic WO3 photocatalysts toward organic dyes are still lacking. Synthesized amorphous WO3 thin films via DC sputtering under various oxygen pressures. The strategy to resolve this issue is to grow amorphous WO3 films under a low oxygen content atmosphere, and conduct various annealing procedures to obtain the stable orthorhombic WO3 phase. The results might be useful for designing orthorhombic WO3 thin-film photocatalysts with a desirable photodegradation ability toward organic dyes

Methods

Result and Discussions

Conclusions through the following equations

Findings

Conclusions