Fabrication and characterization of electrochromic nanocrystalline WO₃/Si (111) thin films for infrared emittance modulation applications

Abstract

Tungsten oxide thin films with different stoichiometry have been deposited on Si (111) wafers by pulsed laser deposition (PLD) technique under different conditions. The structural properties and infrared emissivity of WO3 thin films were analysed using a scanning accessory of a transmission electron microscope (STEM), x-ray diffraction (XRD), Raman spectra (RS) and Fourier transform infrared (FT-IR) spectra. Thin films deposited at 200 °C on Si showed an amorphous structure, while those annealed in air at 300 and 400 °C showed nanocrystalline and porous triclinic structures. These porous and nanocrystalline structures could be used to improve electrochromic colour efficiency and responsing, recovery properties. However, samples deposited at 200 °C and annealed at 240 °C for 0.5 h in oxygen showed a triclinic structure with average 10 nm crystallites. Nanocrystalline WO3 thin films on Si (111) synthesized by this technique might find applications in infrared emittance modulation systems.

Structural, optical and morphological studies on laser ablated nanostructured WO3 thin films

“…These observations are consistent with findings in the X-ray diffraction patterns of the films. The broad feature at around 960 cm À1 observed for films deposited at 673 K can be assigned to W 6+ O stretching mode of terminal oxygen atoms present on the surface of the cluster and microvoid structures in the film [27,28]. Some authors attributes this feature at 960 cm À1 to W O stretching modes at grain boundaries which become observable when the grain size is in the nanometer range [29,30].…”

Effect of thermal annealing on the phase evolution of silver tungstate in Ag/WO 3 films

“…Frey et al [22] observed Raman bands at wavenumbers 781 and 315 cm À1 corresponding to WO 2 phase which is obtained by reducing WO 3 . Fang et al [23] observed two broad band envelopes around 952 and 790 cm À1 for the as-deposited tungsten oxide film prepared by pulsed laser deposition technique.…”

Orientationally textured thin films of WOxdeposited by pulsed laser deposition

“…Pulsed laser deposition (PLD) is known to be an important method for the deposition of oxide materials [5], but there have been relatively fewer investigations of its utility in the deposition of WO 3 and substoichiometric WO x Following deposition using PLD from a WO 3 target using 308 nm radiation the microstructure and subsequent electrical properties of WO 3 thin films have been investigated [6,7], in particular the influence of substrate temperature and oxygen pressure. The films were deposited onto ITO coated glass and Si(111) substrates.…”

“…Pressure also influenced microstructure: at lower pressures the films were found to be amorphous, but for O 2 pressures between 15 and 20 Pa they became polycrystalline. In the second study [7] WO 3 was deposited onto Si(111) at 200°C and postdeposition annealing was used which again converted the films from amorphous into polycrystalline.…”