Assembled Films of Sn-Doped In2O3 Plasmonic Nanoparticles on High-Permittivity Substrates for Thermal Shielding

This study presents the infrared (IR) plasmonic responses of assembled films consisting of Sn-doped In 2 O 3 nanoparticles (ITO-NP films) placed on different substrates. The reflectance properties of the NP films are found to depend on substrate permittivity that affects the types of solar thermal-shielding. Increasing the substrate permittivity provides high reflectance in the IR range resulting from the plasmon modes and the interference effect in the NP films, as demonstrated through changes in the optical properties by tuning substrate permittivity. In particular, the plasmon modes played an important role in enhancing reflectance in the near-IR range. Induced image charges in the substrates produced field interactions with the plasmon modes in the NP films that are formed along the in-plane and out-of-plane directions, a consideration further verified by the strong image charges induced by metallic substrates consisting of ITO films. On the other hand, the interference effects contributed to the reflectance in the mid-IR range, which was also dependent on substrate permittivity. These results suggest that the plasmon modes and optical interference of the NP films can be modulated by tuning the permittivity of the substrate, thereby contributing to the development of reflective-type solar-thermal shielding in the IR range. This study not only contributes to an understanding of the plasmon modes and the interference effect of the NP films interacting with the substrates but also assists in the growth and development of IR applications based on transparent oxide semiconductor NPs.