Near-Infrared Plasmonic Characteristics of Sputter-Deposited Nanocomposite Coatings formed by Indium Tin Oxide Nanoparticles in a SiO ₂ Matrix

High Resolution Image Download MS PowerPoint Slide This study explores the fabrication of nanocomposite coatings combining a gas aggregation cluster source (GAS) with reactive sputtering to embed plasmonic Indium Tin Oxide (ITO) nanoparticles (NPs) into a SiO 2 matrix. ITO NPs absorb in the infrared while remaining transparent in the visible range, enabling applications across a broad spectral window. By adjusting the relative deposition rates of SiO 2 and ITO NPs, we achieve coatings with varied filling factors. These structures exhibit localized surface plasmon resonance peaks between 2.2 and 2.5 μm. The resulting microstructure, shaped by self-shadowing during ballistic deposition, leads to persistent porosity─even at low ITO loadings (5 vol %). Spectroscopic ellipsometry and cross-sectional analysis reveal void fractions up to 30 vol %, resulting in an effective refractive index as low as 1.2. Postdeposition annealing in N 2 at 350 °C for 65 min enhances plasmonic response, shifting and amplifying the infrared absorption peak. This modulation in the short-wave infrared (SWIR) region is visualized using hyperspectral imaging. The study underscores the importance of deposition dynamics in shaping microstructure and optical behavior, highlighting challenges in producing dense nanocomposites with tailored infrared optical properties.