Abstract
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.
Highlights
Based on sub-wavelength-thick thin films embedded with nanoparticles, Mie-metamaterials enjoy the benefit of easy fabrication and the prospect of applications in wavelength selective thermal emitter/absorber [8,26,27]
The SiO2 thin films with different volume fractions of W nanoparticles can be considered as three novel materials that are on top of an opaque W layer, and its dielectric function can be extracted from measured reflectance spectra
The near-infrared optical properties are exploited for W nanoparticles embedded SiO2 thin film at different volume fractions, which are manufactured by the technique of magnetron sputtering and display optically selective properties
Summary
The artificial thermal metamaterials which have selective high emissivity at narrowband or broadband wavelength range show promising potentials in the advanced engineering applications, such as thermophotovoltaics (TPVs), infrared thermal sensing [1,2,3,4,5,6,7,8], thermal diodes [9,10,11,12], radiation cooling [13,14,15,16], thermal rectification [17,18,19, 43], biosensors, and chemical sensors [20,21]. 2. Samples preparation We use the technique of magnetron sputtering to prepare our samples with various volume fractions of W nanoparticles embedded in SiO2 thin films. To analyze the depth dependent atomic concentrations and the volume fractions of W nanoparticles, we use Auger electron spectroscopy (AES) in combination with sputter etching, which is performed inside the Perkin-Elmer Multi-Technique Surface Analysis System 5500. When samples are measured within the near-infrared range, the FTIR spectrometer uses a halogen source as the incident light and the diffuse integrated golden sphere is equipped with an Indium Gallium Arsenide (InGaAs) detector which is highly accurate in the wavelength region of 0.9 μm to 2.6 μm. When samples are measured within the mid-infrared range, a ceramic source is employed and Mercury Cadmium Telluride (MCT) detector with sufficient accuracy in the range 2.5 μm to 15 μm is used together with the diffuse integrated golden sphere. Each set of reflectance measurement consist of a background scan and five measurements taken at different locations on a sample surface
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