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• We demonstrate that the Tamm structure achieves dual-band, high Q-factor perfect absorption within the mid-infrared range. • Tamm phonon polaritons (TPhPs) are effectively excited at hBN/α-MoO 3 interfaces with a photonic crystal, enhancing light absorption. • Due to α-MoO 3 's in-plane anisotropy, TPhPs excited in the 12–18 μm range exhibit excellent polarization-dependent absorption. • Introducing this dual-band perfect absorber offers a streamlined method to develop versatile and dynamic optical devices. Phonon polaritons (PhPs) in two-dimensional van der Waals crystals, such as hexagonal boron nitride (hBN) and α-phase molybdenum trioxide (α-MoO 3), exhibit remarkable spatial confinement and extremely low optical losses, offering possibilities for the development of novel micro and nanophotonic devices at mid-infrared wavelengths. Here, we demonstrate the potential of the proposed Tamm structure to achieve dual-band high quality-factor perfect absorption within the mid-infrared range. This structure utilizes upper and lower spacer layers to isolate the anisotropic materials hBN and α-MoO 3 from one-dimensional photonic crystals, where the Tamm phonon polaritons (TPhPs) are respectively excited at the interfaces, facilitating strong coupling with incident light and leading to significant dual-band perfect absorption phenomena. The results demonstrate that due to polariton resonances, the absorption peaks exhibit extremely narrow absorption bandwidths, with the maximum quality-factor reaching up to 297. In addition, tunable resonant wavelengths and polarization-dependent absorption properties are also demonstrated in the proposed Tamm structure. This study provides an alternative and straightforward approach for constructing dynamic and multifunctional optical devices such as optical modulators, tunable multi-band filters and biosensors. [ABSTRACT FROM AUTHOR]

Epitaxial heterostructures are of particular interest owing to their fascinating properties for wide applications in energy, environment and electronic devices. The understanding of epitaxial growth in solution phase, however, remains a fundamental challenge to realize the rational synthesis of heterostructures. Here we report that anatase TiO 2 can epitaxially grow on the selective polar surface of single-crystal and single-domain ferroelectric PbTiO 3 nanoplates. The interplay of ferroelectric polar surface and corresponding ion adsorptions on them has been revealed experimentally and theoretically to determine the epitaxial growth mode, giving rising to zero-dimensional (0D)/two-dimensional (2D) and 2D/2D heterostructures. A combination of experimental and theoretical calculations indicate that the resulting heterostructures adopt a polarization-dependent photocatalytic performance under visible light irradiation, including hole-based photodegradation and electron-based hydrogen evolution reaction (HER) of water splitting. Such findings allow investigation of the potential of ferroelectric polarization towards tuning epitaxial growth and functionality of heterostructures. [ABSTRACT FROM AUTHOR]

A transmission metasurface with polarizationtransforming functionalities is presented. The unit cell is characterized by broad band, low profile and low loss. Due to the asymmetric structure, the proposed metasurface shows different responses to different linear-polarized incidences. For a particular linear-polarized incidence, the polarization direction of transmitted waves will be rotated by 90° in 3.72-8.28 GHz with high polarization conversion ratio (PCR). However, for the orthogonal-polarized ones, the incidence will be reflected totally and the polarization remains. The operating mechanism of the proposed metasurface is analyzed both by theoretical investigations and numerical simulations. Measured results of the fabricated samples are in good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]