Swift heavy ion irradiated thin films of bismuth vanadate for oxygen evolution reaction: Impact of defect engineering and opening of ion tracks

Abstract

Swift heavy ion (SHI) irradiation using 150 MeV Xe ions (fluence: 5 × 109 –5 × 1011 ions cm-2) was employed for defect engineering in hydrothermally synthesized BiVO4 (BVO) thin films in order to investigate their impact on photoelectrochemical (PEC) performance toward the oxygen evolution reaction (OER). SHI treatment induces residual stress and amorphization, along with the formation of bismuth-rich hillocks above oxygen-deficient ion tracks. At high fluence (5×1011 ions cm-2), excessive defect accumulation and ion track overlap result in irreversible degradation of PEC activity. In contrast, lower fluences (5 × 109 and 1 × 1010 ions cm-2) generate a moderate defect density that initially traps charge carriers but show photocurrent density improvements of 58.6% and 25.2% with time, respectively. Post-PEC analysis reveals that latent ion tracks are transformed into nanoscale holes up to 30 nm in diameter and 200 nm in depth. The sample irradiated at 1 × 1010 ions cm⁻² exhibits particularly well-defined holes, indicating an optimal balance between defect formation and mechanical stress. A comprehensive set of structural, electronic, and morphological analyses was employed to correlate defect evolution with PEC behaviour. The obtained results demonstrate the potential of SHI irradiation as a precise tool for nanoscale morpho-structural engineering. The controlled formation of nanoscale holes enables the integration of cocatalysts or plasmonic structures, offering a promising route to enhance PEC efficiency and broaden the material’s applicability in energy-related technologies.