High-energy ion treatments of amorphous As40Se60 thin films for optical applic ations

The treatment of 100 MeV Ag swift-heavy ion (SHI) irradiation with five different fluences (3×10¹⁰, 1×10¹¹, 3×10¹¹, 1×10¹², and 3×10¹² ions/cm²) was used to design optical and structural properties of amorphous (a-) As₄₀Se₆₀ chalcogenide thin films. Swanepoel method was applied on transmission measurements to determine the changes in optical bandgap, Tauc parameter and linear optical parameters, i.e., linear optical absorption, extinction coefficient and linear refractive index. Dispersion of the material was determined by Wemple–DiDomenico relation. Changes in nonlinear optical parameters of third-order optical susceptibility and nonlinear refractive index were determined using semi-empirical relations. Changes in surface morphology of the films were investigated using SEM observation, which indicated that fluence 3×10¹² ions/cm² was upper threshold limit for these films for ion treatment. It is observed that optical bandgap reduces from 1.76 eV to 1.64 eV, and nonlinear refractive index increases from 1.31×10⁻¹⁰ esu] to 1.74×10⁻¹⁰ esu]. Linear refractive index initially increases from 2.80 to 3.52 (for fluence 3×10¹⁰ ions/cm²) and then keeps decreasing. The observed changes in optical properties upon irradiation were explained in terms of structural rearrangements by Raman measurement. The study was compiled with the previous literature to propose SHI as an effective optical engineering technique to achieve desired changes according to the need of optical/photonic applications.