Tailoring Tungsten Oxide Layers for Cold Field Emission Cathodes: Anodization and Thermal Oxidation Approaches

This study explores the optimization of tungsten oxide layers formed via thermal oxidation and anodization for cold field emission applications. Surface modifications can enhance tungsten emitters by improving the emission stability and reducing ion-induced damage. Polycrystalline tungsten samples were treated using two oxidation methods: thermal oxidation (at 550–750 °C, 10³–10⁴ Pa) and anodization (in 0.33 mol/L H₃PO₄ at 5–35 V). Lower temperatures and pressures (550 °C, 10³ Pa) produced smoother (R_a ∼ 23 nm) and uniform oxide layers (∼240 nm thick), improving the high-voltage stability (7.5–8.5 kV). Anodized layers, while less stable at high voltages, exhibited enhanced emission at lower operational voltages (∼5.5–7 kV). Field emission microscopy confirmed that thermally oxidized layers perform better under high electrostatic fields, whereas anodized layers offer a rapid response and lower threshold voltages. These findings demonstrate that both oxidation techniques are scalable and tunable for optimizing cold field emitters, with tailored properties suited to specific applications in electron microscopy and related technologies.