Synthesis of sodium tungsten oxide nano-thick plates

In this letter a simple procedure to synthesize sodium tungsten oxide nano-thick plates from WO 3 films has been reported. WO 3 films were grown by pulsed-laser deposition method and then heat treated at temperatures up to 560 °C and times up to 120 min. Slide glass was used as both substrate and sodium source simultaneously. XRD analysis revealed presence of an amorphous structure for as-deposited WO 3 films. On the other hand, XRD showed formation of a monoclinic WO 3 structure with annealing in lower temperatures and a triclinic Na 0.5 WO 3.25 structure with annealing at higher temperatures. Intensity of the triclinic phase peaks enhanced drastically by rising annealing temperature and time. SEM results depicted presence of Na 0.5 WO 3.25 nano-thick plates with thickness of about 160 nm and width of about 3 μm. Finally, XPS analysis revealed that heat treatment temperature does not affect tungsten valence state.