The influence of annealing atmosphere on the formation and characteristics of microvoid WO3–Sb films

WO3–Sb thin films with and without Sb doping were prepared by the sol–gel spin-coating method. The surface morphology, crystal structure, and binding energy of the WO3–Sb films were investigated before and after annealing under O2 or N2 atmospheres. After spin-coating, Sb2O3 precipitates on the surface of the as-deposited amorphous WO3 films with different Sb/W molar ratios. After annealing in O2 or N2 ambients, the precipitates start to disappear and then microvoids appear on the surface of the crystalline WO3 films with 5% and 10% molar ratios of Sb. WO3–Sb thin films present the monoclinic phase after annealing at 700 °C in N2, whereas films show the tetragonal phase after annealing at the same temperature in O2. In addition, Sb segregation occurs on the surface of the WO3 films with Sb additives after annealing at 700 °C in N2 ambient. This study discusses the connection among the Sb additive of the WO3–Sb films and how they are influenced by the Sb/W molar ratios and the annealing atmospheres of WO3–Sb films.

► Some white precipitates (Sb2O3) revealed on the surface of the WO3–Sb films.
► The precipitates disappear and then the microvoids form after annealing at 500 °C.
► The O2-annealed effects can assist the phase transformation.
► Surface segregation of Sb occurs in the WO3–Sb films after annealing in N2.