Optical band gap tailoring of muscovite mica via monolayer modification by ultra-low energy ion beam sputtering

In this paper, we report the band gap tailoring of naturally available muscovite mica by ultra-low energy (300 eV) Ar⁺ ion sputtering at normal ion incidence. The muscovite mica is an insulating material (wide band gap ~ 6 eV) having various potential applications from biological substrate deposition to electronic device fabrication. The first monolayer of mica is modified by ultra-low energy ion beam, which leads to the reduction of optical band gap. The ion dose is varied to study the optical band gap information. It is observed that the band gap decreases significantly with increasing ion doses. By varying ion doses, the indirect band gap could be tailored from 2 eV to 1.1 eV, which indicates the semiconducting nature of mica surface. The optical responses of pristine and modified mica are studied by UV–Visible Spectrophotometry and the band gap is calculated from Tauc's plot. The band gap narrowing is supported by the band gap estimation of modified mica from Conductive Atomic Force Microscopy (C-AFM) analysis. The X-ray photoelectron spectroscopy (XPS) study shows that ion bombardment sputters most of the K atoms and other elements in mica along with Carbon adsorption, which leads to change the density of states of mica, resulting in the tailoring of band gap. The surface morphology study of ion modified mica surfaces, investigated by Atomic Force Microscopy (AFM), shows the formation of random rough surface, which transform to irregular pillar like structure at longer time of ion irradiation.