Investigation on chemical instability and optical absorption of ion bombarded Si surfaces

Ion beam induced nano ripple formation has gained enormous interest for its potential applications in different fields like DNA origami, magnetic anisotropy, anti-reflection coating, tuning hydrophobicity etc. The ripple pattern formation on solid surface is explained as an instability generation due to sputtering of surface atoms, mass redistribution, and chemical instability owing to preferential sputtering. In the present framework, we have investigated how the variation of chemical phase formation by NO⁺, N₂⁺ and O₂⁺ion bombardment alters the chemical instability, which influencesthe ripple pattern formation on surface.In case of NO⁺ ion bombardment, silicon oxide and nitride (which later turned into oxynitride in presence of ripple)are simultaneously formed, whereas in case of N₂⁺ or O₂⁺ bombardment, either silicon nitride or silicon oxide is formed. Hence, the instability generation due to sputtering of both elemental silicon and its two compounds (oxide and nitride) causes additional instability generation in case of NO⁺ than N₂⁺ or O₂⁺, resulting in early ripple formation.The sputtering yield of pure Si and its compounds in each cases are calculated using SRIM freeware. Surface chemical nature, detected using X-ray photo electron spectroscopy, confirms the formation ofsilicon nitride and silicon oxide respectively in case of nitrogen and oxygen bombardment, whereas the NO⁺ bombardment causes the formation of silicon oxide with silicon oxynitride. The optical absorption of such structurally and chemically modified surfaces, examined by UV-VIS spectroscopy, reveals more absorbance of UV-VIS spectra (200-800 nm) for N²⁺ bombarded and NO⁺ bombarded surfaces than virgin and O²⁺ bombarded Si surfaces. Hence, N₂ and NO⁺ bombarded Si surfaces are more suitable for anti-reflective coating surface.