We theoretically propose and numerically demonstrate a tunable ultra-broadband anisotropic absorber, which consists of a multi-layer BP/dielectric structure stacking on a gold mirror. The simulated results show that the proposed absorber can achieve nearly perfect absorption efficiency over the wavelength range from 16 to 28 μm. Meanwhile, benefiting from the unique and versatile characteristics of BP materials, the absorption efficiency and absorption bandwidth can be actively controlled by either carrier doping or the geometrical parameters. These results may have great potential applications in designing anisotropic meta-devices with tunable spectral and polarization selectivity in the infrared and terahertz regimes.
In this work, the authors fabricated Cu2O porous nanostructured films (PNFs) on glass slide substrates by the newly developed positive bias deposition approach in a balanced magnetron sputtering (MS) system. It was found that the surface morphology, crystal structure and optical property of the as-deposited products were greatly dependent on the applied positive substrate bias. In particular, when the substrate was biased at +50 V and +150 V, both of the as-prepared Cu2O PNFs exhibited a unique triangular pyramids-like structure with obvious edges and corners and little gluing, a preferred orientation of (111) and a blue shift of energy band gap at 2.35 eV. Quantitative calculation results indicated that the traditional bombardment effects of electrons and sputtering argon ions were both negligible during the bias deposition in the balanced MS system. Instead, a new model of tip charging effect was further proposed to account for the controllable formation of PNFs by the balanced bias sputtering deposition.
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