that differ strongly from those of the constituent materials. Due to this remarkable flexibility, thin-film nanocomposites belong per se to the class of metasurfaces, whose fields of applications are constantly growing in key technological areas, including communications, energy, catalysis, and medicine. In the field of nanophotonics, the use of metasurfaces formed by planar arrangements of metallic and dielectric nanostructures has enabled the control of light at subwavelength scales, allowing light manipulation and processing in ways that are impossible to achieve with natural materials. [1][2][3][4] In particular, plasmonic metasurfaces based on nanostructured noble metals, either embedded in a dielectric film or deposited on top of a substrate, have shown extraordinary capabilities to strongly absorb, scatter, or confine incident light. More recently, nanostructures formed by high-index dielectric materials (mainly semiconductors such as Si and Ge) have gained momentum due to the particularities of their resulting electric and magnetic Mie resonances and have opened the field of the so-called Mie-resonant metaphotonics (also termed as Mie-tronics). [3,5,6] A relevant outcome of the improved understanding of these resonant phenomena has been acknowledged that there are alternative materials to the noble metals or conventional semiconductors that show plasmonic and Mie resonances, and, furthermore, that are better suited to address some specific nanophotonics applications. Among them are materials that offer plasmonic response in the ultraviolet, can withstand resonances at high temperature, or can be activated upon external excitation. [7][8][9][10] Bismuth (Bi) is one of such alternative materials and stands out due to its particular electronic structure, and optical and thermoelectronic properties. [11][12][13][14] Only very recently it has been shown that its electronic band structure displays giant interband electronic transitions in the mid-infrared, which, in turn, endows the dielectric function ε with a unique property that enables Bi-based nanostructures to show a dual behavior, enabling both plasmonic-like resonances in the ultraviolet and visible regions of the spectrum, and high-refractive-index Mie resonances in the near-and mid-infrared regions of the spectrum. [15,16] So far, metasurfaces based on Bi nanostructures have found applications in integrated photonic devices as perfect Random metasurfaces based on disordered phase-change nanostructures with broadband ultraviolet-visible plasmonic properties are fantastic platforms for the development of active photonic components due to their versatility. Here optical ON-OFF switching upon nanosecond laser irradiation of Bi-based random metasurfaces is demonstrated profiting from the solid-liquid phase transition of the Bi nanostructures. The fast switching time is revealed by using single-pulse real-time reflectivity measurements with sub-nanosecond temporal resolution. A sudden reflectivity decrease is observed upon laser excitation, triggered by hea...
Direct Laser Interference Patterning (DLIP) is a versatile technique that enables the fabrication of periodic micro‐ to nanometric scale structures over large areas in a variety of materials. The periodically modulated excitation pattern can be exploited to trigger a range of complex processes, including heating, melting, ablation, and matter reorganization.In this work, a novel strategy is developed to combine deep‐ultraviolet (UV) DLIP (λ = 193 nm, τ = 23 ns) and real‐time optical reflectivity and diffraction techniques to unravel the formation dynamics of grating structures with periods down to Λ = 740 nm. Applied to crystalline Ge wafers, single‐pulse topography modulation profiles with amplitudes up to 85 nm can be imprinted. Moreover, the dynamics of the melting and solidification processes, as well as the surface topography deformation, can be followed in real‐time. Combined with a model, changes in topography over time with ns resolution can be obtained. The results unambiguously reveal that the formation process of the 3D structures can only be understood when taking both Marangoni convection and thermocapillary waves into account. The technique presented here has the potential to unravel the formation dynamics of a wide range of periodic structures in other materials.
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