Top Layer Engineering of FTO Thin Films via Low-Energy Ar-Ion Beam for Multi-Property Modulation

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Chinese explanation / 中文解读

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Original abstract

Abstract Low-energy ion-beam irradiation has emerged as a powerful route for tuning of the physicochemical properties of materials, due to its controllable defect modulation capabilities at various depth. This article shows how the structural, optical, chemical, and electronic properties of fluorine-doped tin oxide (FTO) thin films are interconnected when defects and vacancies are created in the topmost surface layer using low-energy (1 keV) Ar-ion irradiation at normal incidence (fluence: 6 × 10¹⁷ ions cm⁻²), followed by thermal annealing in vacuum and oxygen atmospheres. The ion beam induced amorphization and subsequent recovery of crystallinity indicates nominal alteration of lattice strain without significant alteration of rms roughness. The Ar-ion irradiation modifies the oxidation state of Sn, accompanied by residual argon incorporation while the thermal annealing leads to removal of fluorine as well as restoration of oxidation state of Sn. Intriguingly, the irradiation–annealing sequence yields enhanced absorption in the 200–550 nm range without any modulation in the bandgap. Additionally, the thermal annealing promotes the generation of additional free electrons, leading to a substantial enhancement in carrier concentration and an improvement in charge-carrier mobility. These effects are associated and correlated with modified effective mass, plasma frequency, electron density, and optical porosity, as quantified using Sellmeier’s analysis and Bruggeman effective medium approximation. Interestingly, the observed modification of the density of states in the vicinity of the conduction band unequivocally signifies the enhanced conductive character of the surface. The tuned electronic and transport properties highlight the potential of ion-engineered FTO films for resistive memory device applications.

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