Study of intense pulsed ion beam irradiation effect on magnetron sputtered ZnO thin films

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.