Plasmonic Heat Shielding in the Infrared Range Using Oxide Semiconductor Nanoparticles Based on Sn-Doped In2O3: Effect of Size and Interparticle Gap

We present in this work advanced results concerning heat shielding based on assembled sheets of In2O3:Sn nanoparticles (ITO-NP sheets) in terms of particle size and interparticle gap. We demonstrate that the oxide semiconductor nanoparticles are crucial to achieve required optical properties relevant to energy-saving applications. In the infrared (IR) range, strong electric-field (E-field) interactions between NPs are formed locally at narrow interparticle gaps. Changes in thickness and particle size greatly increase the magnitude and peak separation of the resonant reflectance, which widely covers the IR range. As a consequence, the size-dependent plasmonic properties contribute to high heat-shielding efficiency. As confirmed by electrodynamic simulations, plasmonic coupling results in these spectral changes due to three-dimensional E-field interactions along the in-plane and out-of-plane directions. Moreover, the resonant reflectance is tuned by mechanical stretchable strains, indicating one of the important factors for determining the resonant reflectance in addition to the control of particle size. From another perspective, the interparticle gap markedly affects the mechanism of electron transport in the NP sheets. The high electromagnetic transmission in the microwave range was due to the low electrical conductance caused by the spatial confinement of free carriers into the NPs. These results promoted development of flexible heat shielding in which optical and electromagnetic control is feasible for a wide range of wavelengths from ultraviolet to microwaves. Control of particle size and interparticle gap revealed important aspects that should be considered in structural design when fabricating heat-shielding materials.