Chameleons have a diagnostic thermal protection that enables them to live under various conditions. Our developed special radiative control therefore is inspired by the chameleon thermal protection ability by imitating its two superposed layers as two pigment particles in one coating layer. One particle imitates a chameleon superficial surface for color control (visible light), and another particle imitates a deep surface to reflect solar irradiation, especially in the near-infrared region. Optical modeling allows us to optimally design the particle size and volume fraction. Experimental evaluation shows that the desired spectral reflectance, i.e., low in the VIS region and high in NIR region, can be achieved. Comparison between the measured and calculated reflectances shows that control of the particle size and dispersion/aggregation of particle cloud is important in improving the thermal-protection performance of the coating. Using our developed coating, the interior temperature decreases and the cooling load is reduced while keeping the dark tone of the object.

Recently, solar thermal conversion technology, wherein solar energy is directly converted into thermal energy, has attracted significant attention as it ensures sustainable and modern clean energy generation for a progressive society. A direct-absorption solar collector that uses plasmonic nanofluids is useful for collecting solar energy. Thus, improving the solar absorption performance of plasmonic nanoparticles can further reduce the fabrication cost. We conceptualized multilayer sputtered (metal–insulator–magnetic) plasmonic nanoparticles that exhibit a broadband absorption spectrum and are easy to mass-produce. Particles with a metal–insulator–magnetic structure have not been developed in the past. To clarify the physics of the optical properties of the particles, electromagnetic field analysis was performed using COMSOL Multiphysics. Electromagnetic field analysis of the stacked plasmonic nanoparticles showed that the absorption efficiency depended on particle size and film thickness; the absorption peak increased significantly for an increasing particle size with a long shift, indicating the broadening of the absorption spectrum. In addition, the absorption spectrum could be controlled by changing the number of metal layers and the structure of the plasmonic nanoparticles. To quantitatively evaluate the spectral absorption efficiency, the total sunlight absorption efficiency (TSA) was defined as an evaluation parameter. TSA showed that the solar absorption performance of two-layer plasmonic nanoparticles was approximately 2.4 times that of homogeneous nanoparticles of the same size. Thus, the present study demonstrates the usefulness of bilayer plasmonic nanoparticles.

This study explores the mechanisms underlying nonthermal instabilities in non-metallic materials exposed to femtosecond laser irradiation. By employing ab initio molecular dynamics (AIMD) simulations and phonon calculations within the harmonic approximation, we investigated the behaviors of SiO2, SiC, Al2O3, and GaN under highly excited electronic states. The AIMD simulations revealed material-specific electronic temperature thresholds beyond which rapid atomic acceleration occurs. The analysis of atomic rearrangement energies associated with nonthermal acceleration revealed a common mechanism across all materials: electron delocalization accompanied by an increase in inter-nuclear Coulomb repulsion. Phonon calculations using harmonic approximation confirmed that elevated electronic temperatures destabilize the crystal lattice. As the electron temperature increases, phonon modes progressively shift to imaginary frequencies, indicating lattice instability. Notably, bending-dominant and optical modes are particularly prone to softening into imaginary modes, thus playing a critical role in structural destabilization. Furthermore, the increase in kinetic energy during nonthermal melting becomes more pronounced as the number of imaginary phonon modes increases, highlighting their critical role in facilitating structural collapse.