Tunable Absorption of Light via Localized Plasmon Resonances on a Metal Surface with Interspaced Ultra-thin Metal Gratings

Abstract

We studied optical reflection properties of complex metal (Ag) surfaces with close-interspaced ultra-thin metal gratings. Prominent reflection minima were observed corresponding to enhanced absorption of light. Our analysis convinced us that the period-dependent mode is ascribed to Bloch-wave-like resonances of surface plasmon waves at the overall effective metal surfaces, and the ridge-widthdependent mode to Fabry-Pérot-like resonances of localized surface plasmon waves in micro-/nanocavities defined by regions of the grating ridges. The latter resonance mode is shown highly tunable with variation of the grating ridge width. Such structures may be applied in spectrum resolvable photovoltaic devices, bio-sensing, and studying optical properties of cavity-coupled molecules or functional nanomaterials.

Tunable broadband plasmonic perfect absorber at visible frequency

“…However, so far most of the applied techniques (e.g. perforated metallic films [2], grating structured systems [3] and metamaterials [4][5][6] ) are either costly or has low fabrication tolerance and their absorption resonance is narrow-band which limits their utility for energy harvesting. Recently, we show experimentally for the first time fabrication of a broadband perfect plasmonic absorber in a stack of gold and gold-SiO 2 nanocomposite showing nearly 100% absorbance at visible frequencies [7][8].…”

Fabrication of broadband omnidirectional non-reflective gold surfaces by electrodeposition

“…Gradient refractive index coatings or multilayer coatings of materials with appropriate refractive indices allow a more broadband antireflection. [3][4][5][6] An alternative method to produce anti-reflecting surfaces consists of focusing on their topography: by mixing the substrate material with air on a sub-wavelength scale, it is possible to obtain coatings with a refractive index which varies with their thickness. Nanoporous films exhibiting anti-reflection properties have been thus fabricated by several methods, such as the demixing of a binary polymer blend 7 or by wet or dry etching.…”

Optical Transmission Through Multilayered Ultra-Thin Metal Gratings

“…Recently, the study of optical interaction with ultra-thin metal gratings (one-or two-dimensional) has drawn the interest of researchers in the field of plasmonics [1][2][3][4][5][6][7][8][9][10][11][12]. Due to excitation of bound surface plasmons (SP) in the ultra-thin metal layer of gratings [13][14][15], some anomalous optical properties arise.…”

“…Thus, bound SPs can play a deterministic role on the optical properties of metal structures with ultra-thin meal films. Relevant optical structures have been investigated for applications in sensing [8,9], photodetecting [10], and optical absorbing [11,12].…”

“…The substrate, sandwiched dielectrics and metal are assumed to be silica (ε s =2.16), polymer (ε 2 =2.56), and silver (ε 1 , as defined in Ref. [12]); the top cover is air (ε 0 =1). Figure 1b shows transmission spectra of the multilayer gratings with up to 5 layers for normal incidence of TMpolarized light, in which the grating period p=400 nm, ridge width w=300 nm (or slit width s=100 nm), metal thickness t 1 =20 nm, and sandwiched dielectric thickness t 2 =120 nm for all.…”