Abstract
ZnO thin films were fabricated via magnetron sputtering on FTO substrates and subsequently modified by different intense pulsed ion beam (IPIB) irradiations (5-20 A/cm2) and 10 A/cm2 with different pulse numbers (1, 3, and 6 pulses). IPIB treatment induces transformation of uniform nanograins into coarser, agglomerated, partially fused structures, and with a non-monotonic evolution of surface roughness. Despite these surface modifications, the ZnO films retain their hexagonal wurtzite crystal structure and have negligible changes in optical bandgap (~3.2 eV) that reveals the preservation of the bulk electronic structure. Additionally, irradiation alters the surface composition and introduces defect states, as reflected by changes in XPS in Zn/O ratio and increased interfacial heterogeneity. At moderate irradiation conditions, partial surface smoothing and structural relaxation occur, whereas higher fluence (multiple pulses) leads to significant defect accumulation. As a result, after testing photoactivity irradiated samples have increased interfacial charge-transfer resistance and reduced photocurrent density. Overall, IPIB irradiation predominantly modifies surface properties, and excessive defect formation under high fluence conditions deteriorates charge transport and photoelectrochemical performance.