SPR based refractive index modulation of nanostructured SiO2 films grown using GLAD assisted RF sputtering technique

Abstract

Low refractive index materials have always gained attention for avoiding optical losses in numerous devices like Light emitting diodes (LEDs), Distributed Bragg Reflectors (DBRs) etc. Glancing angle deposition (GLAD) has proven to be an effective method for depositing porous nanostructures with low refractive index. SiO2 has the lowest refractive index in comparison to most of the materials present in nature and is therefore utilized extensively in the fabrication of optical devices with minimum optical losses. The present work focuses on the SiO2 nanostructured thin films grown using glancing angle (GLAD) configuration in RF Sputtering technique under varying deposition conditions (glancing angle and pressure) at fixed thickness. The deposited porous SiO2 nanostructured layers have well-defined nanorods of feature size smaller than 100 nm. The refractive index corresponding to all the deposited SiO2 nanostructured films came out to be smaller than the corresponding value (1.49) mentioned in the literature for bulk SiO2. The refractive index has been observed to vary in a wide range (1.05 to 1.40). Characterization of the deposited SiO2 nanostructured films was carried out using Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive X-Ray (EDS) analysis, and Atomic Force Microscopy (AFM) to assess the qualitative properties of the deposited nanostructured SiO2 films. Surface Plasmon Resonance (SPR) and Ellipsometry studies are performed to determine the refractive index value of the deposited nanostructured SiO2 thin films. A refractive index value as low as ∼ 1.05 at a wavelength of 633 nm is achieved for SiO2 nanostructured thin film deposited at 30 mTorr deposition pressure and 80° glancing angle.