Optical and electrochromic properties of amorphous and crystalline tungsten oxide films

A detailed systematic study of the tungsten oxide thin films has been carried out using colored WO₃ films after they were annealed at progressively increasing temperatures ranging from 350 to 450°C in oxygen environments. The structural properties of the films were characterized using x-ray diffraction (XRD) and Raman spectroscopy. The amorphous WO₃ films remain as an amorphous phase up to 385 °C and begin to crystallize at 390°C and then are completely crystallized at 450°C. Absorption peaks of the films are found to shift to a higher energy side with increasing annealing temperature up to 385°C and then shift abruptly to a lower energy as the films begin to crystallize at 390°C.