Near-infrared optics of nanoparticles embedded silica thin films.

This work investigates experimentally the near-infrared optical properties of SiO2 thin film embedded with tungsten (W) nanoparticles at varying volume fractions. The samples are prepared by using the technique of magnetron sputtering. The formation and distribution of W nanoparticles are characterized using transmission electron microscopy, and the volume fraction of W nanoparticles is validated by Auger electron spectroscopy. Near- and mid-infrared diffuse reflectance measurements are conducted using Fourier transform infrared spectroscopy. The samples exhibit wavelength selective optical response in the near-infrared region and are suitable for applications involving selective thermal emitters/absorbers. Measured reflectance data is utilized to estimate the effective dielectric function of the nano-composites. Calculated reflectance spectra in different samples are compared to the measured spectra using the experimentally measured dielectric function of these samples in the near-infrared region. Reflectance spectra after thermal annealing at different temperature are compared to show how the thermal treatment affects the optical properties of samples. Optimized structures are proposed for thermal emitters and absorbers with different volume fractions of W nanoparticles.