Study of Argon Flow Effects on Transmittance in Multilayer Thin Films for Aviation Lighting

Lighting devices installed on airfields and runways are regulated in terms of the color, intensity, and angle of the light they emit according to their function. This study aims to improve the performance of thin films used in taxiway lights, which require high transmission efficiency in the wavelength range of 510-550 nm.<br/>First, the multilayer thin films were designed using the Essential Macleod program, combining SiO₂ and Nb₂O₅ materials. The composition and thickness of each layer were optimized to achieve over 95% of transmittance in the 510-550 nm wavelength range. The designed multilayer thin films were deposited using an RF sputtering method under different argon flow rate (50 sccm, 75 sccm, 100 sccm). X-ray Diffraction (XRD) analysis confirmed that all thin films under the three conditions exhibited amorphous characteristics. Elemental compositions were verified through Energy Dispersive X-ray Fluorescence (EDXRF) analysis. The L and K characteristic lines of the Nb and Si multilayer thin films were characterized at high and low photon energy range. The relative concentration of the Nb were compared using count per second (CPS) under different argon conditions. The surface and uniformity of the deposited layers were evaluated using Scanning Electron Microscopy (SEM). The total thickness of the multilayer thin films is about 5.5μm based on cross section images. X-ray Photoelectron Spectroscopy (XPS) analysis presented that the Nb₂O₅ phase was predominant under the 50 sccm of argon flow rate. However, the presence of the NbO₂ phase was revealed under the 100 sccm of argon flow, indicating reduction of Nb oxides from Nb₂O₅ to NbO₂. The transmittance measurements of the fabricated multilayer thin films showed the highest transmittance of 95.3% under the 50 sccm of argon flow. Overall results indicated that the NbO₂ phase in multilayer thin films may contribute to the reduction in transmittance. Current results in this study suggest the potential for significantly improving the efficiency of taxiway lights.