Abstract
Plasmonic black surfaces formed by two-dimensional arrays of ultra-sharp convex metal grooves, in which the incident radiation is converted into gap surface plasmon polaritons (GSPPs) and subsequently absorbed (via adiabatic nanofocusing), are fabricated and investigated experimentally for gold, nickel, and palladium, using scanning electron microscopy, optical microscopy, and reflection spectroscopy for their characterization. Absolute reflectivity spectra obtained for all fabricated arrays demonstrate very efficient and broadband absorption of unpolarized light exceeding the level of 95%, averaged over the investigated wavelength range of 400–985 nm. The highest averaged absorption level (~97%) is achieved with 250-nm-period arrays in palladium that also has the highest melting temperature (~1552°C), promising thereby potential applications for broadband absorption, e.g., within thermophotovoltaics. For one-dimensional arrays, GSPPs are excited only with the electric field polarized perpendicular to the groove orientation, resulting in 94–96% absorption of the appropriately polarized light for the arrays in nickel and palladium while featuring practically flat surface reflectivity spectra for the orthogonal polarization. The largest ratio (~10.7) between averaged reflectivities for orthogonal polarizations is achieved with the groove arrays in palladium, pointing thereby towards applications as broadband and low-dispersion linear polarizers operating in reflection, e.g., within ultra-fast optics.
Highlights
Correspondence and requests for materials should be addressed to Plasmonic black metals via radiation absorption by two-dimensional arrays of ultra-sharp convex grooves
Plasmonic black surfaces formed by two-dimensional arrays of ultra-sharp convex metal grooves, in which the incident radiation is converted into gap surface plasmon polaritons (GSPPs) and subsequently absorbed, are fabricated and investigated experimentally for gold, nickel, and palladium, using scanning electron microscopy, optical microscopy, and reflection spectroscopy for their characterization
The 1D plasmonic black gold p-polarized reflectivity exhibit some oscillations [Fig. 1(d), Supplementary Fig. S1], which has been related to combined interference effects of mutual phase differences in the remaining reflectivity from groove bottoms, caused by nm-variations in the groove depth, and non-ideal surface geometry of the array[17]
Summary
Correspondence and requests for materials should be addressed to Plasmonic black metals via radiation absorption by two-dimensional arrays of ultra-sharp convex grooves. Plasmonic black surfaces formed by two-dimensional arrays of ultra-sharp convex metal grooves, in which the incident radiation is converted into gap surface plasmon polaritons (GSPPs) and subsequently absorbed (via adiabatic nanofocusing), are fabricated and investigated experimentally for gold, nickel, and palladium, using scanning electron microscopy, optical microscopy, and reflection spectroscopy for their characterization. Composite materials with selective absorption and thermal emission properties have been suggested, including for example ordered arrays of gold-cross resonators placed on a dielectric spacer layer above a planar gold surface[4], ordered arrays of metal elements combining two nano-scale split-rings[5], arrays of ultra-thin silver resonant absorbers[6], or random arrays of colloidal metal geometries or nanoantennas[7] Tapered nanostructures, such as plasmonic V-grooves, involve strong SPP confinement to the groove bottom, for example, used when guiding SPPs along individual grooves[8]. Application perspectives for these configurations along with the material selection are discussed
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