Defect engineering and opening of the ion tracks in the swift heavy ion irradiated thin films of bismuth vanadate: Impact on oxygen evolution reaction for solar water splitting

Abstract

Swift heavy ion (SHI) irradiation using 150 MeV Xe ions (5×109 to 5×1011 ions cm-2) was applied to engineer defects in hydrothermally synthesized BiVO4 (BVO) thin films and analyze its impact on photoelectrochemical (PEC) performance toward the oxygen evolution reaction (OER). Exposure to SHI induces residual stress and amorphization, accompanied by bismuthrich hillocks forming above oxygen-depleted ion tracks. At high fluence (5 × 1011 ions cm-2), excessive defect accumulation and overlapping tracks lead to irreversible PEC degradation. In contrast, lower fluences (5×109 and 1010 ions cm-2) generate moderate defects that initially trap charge carriers but subsequently enhance performance, resulting in photocurrent density increase of 58.6 and 25.2 %, respectively. Post-PEC analysis reveals that latent ion tracks evolve into nanoscale holes, with diameters up to 30 nm and depths up to 200 nm. Notably, the 1010 ions cm-2 sample exhibits well-defined holes, suggesting an optimal defect–stress balance that facilitates localized restructuring. This study provides new insights into SHI-induced modifications in BVO and demonstrates the potential of ion beam irradiation for nanoscale morphostructural engineering. The controlled formation of nanoscale holes opens opportunities for incorporating cocatalysts or plasmonic structures to further enhance PEC activity.