Fabrication of α-W and β-W Films By Using CsF–CsCl–WO₃ Molten Salt: Effect of Oxygen Contents in W Films

Electrodeposition of W films in CsF–CsCl eutectic melts was investigated after adding 2.0 mol% of WO 3 at 773–973 K. The oxygen content in W films electrodeposited at various temperatures was analyzed using inert gas fusion and non-dispersive infrared spectroscopy (NDIR). Oxygen contents in the W films gradually decreased from 6.65 at% to 0.24 at% as the bath temperature increased from 773 K to 923 K along with the crystal phase change from β -W to α -W, confirmed by X-ray diffractometry (XRD). Then, vacuum annealing treatment was performed for the electrodeposited β -W films. The crystal phase was transformed to pure α -W after annealing at 973 K for 3 h and the oxygen content in W films decreased from 1.82 at% to 0.38 at%. Finally, based on the above findings, we provide a promising two-step method for preparing mirror-like and dense α -W films.