Projectile mass dependent nano patterning and optical band gap tailoring of muscovite mica

Abstract

We report surface pattern formation and simultaneous optical band gap reduction of multi-elemental muscovite mica due to differential sputtering of constituent elements and defect creation by various energetic ion bombardments. 14 keV Ar+, O2+, NO+, N2+, and C+ ions bombardment exhibits projectile mass dependent ripple like surface structure formation, and band gap alteration. It is observed that the lightest C+ ion is less effective, while the heaviest Ar+ ion is most suitable for well-defined ripple pattern formation as well as band gap reduction. Investigation of mica surface by X-ray Photoelectron Spectroscopy (XPS) shows projectile dependent depletion of different elements, specifically, potassium (K) atoms, which link the aluminosilicate layers, and also reside on the top of the surface. A remarkable sputter erosion of K atoms by Ar+ ion is observed due to similar mass of Ar and K. The optical band gap, estimated from the UV-VIS-IR data, shrinks from 3.6 eV (virgin) to 1.8 eV (Ar + ion bombarded) in case of indirect transition. Urbach energy is also estimated from the optical absorption data and is correlated with the ion induced damage to explain the defect mediated change of the band gap.