Plasmonic Near‐Complete Optical Absorption and Its Applications

Abstract

absorption of light. It is, however, possible to engineer artificial materials that are extremely thin and can absorb nearly 100% of the incident light. The most common approach to achieving near perfect absorption (NPA) of light consists of "blocking" the possibility of transmission by, for example, using a reflective surface. Under these circumstances, the amount of light absorbed is controlled by the reflectance of the material, since, in these cases, the absorption is given by A = 1 − | r | 2 . Clearly, high absorption can be obtained when there is vanishing reflectance (r = 0), which takes place under conditions of optical impedance matching. [4] In the following section, we discuss physical interpretations and mechanisms that have been employed for achieving near complete absorption of light using metallic nanostructures, including metasurfaces, as the absorptive element. This is followed by an overview of the applications of near-perfect absorption in fields such as chemical sensing, optoelectronics and photocatalysis. This review ends with an outlook. We note that near-perfect absorption can be achieved with a wide range of materials, for which excellent review papers have been previously published. [5][6][7] The Physics of Perfect Absorption Thin Film Perfect Absorbers: InterferenceAs an introduction, we first review simple thin film approaches to NPA since these play a fundamental role in understanding the underlying physics. Optical thin-film coatings are essential in optical systems today and the simplest example of a thin-film absorber consists of a stack of an optically thin metal film, a thin dielectric film and a highly reflective metallic film. Thin film coatings are widely used as anti-and high-reflection coatings, beamsplitters, and wavelength filters on lenses, windows, displays, [8] and absorbers for efficiency enhancements in photovoltaic cells, [9] as well light emitting diodes (LED) and photodetectors. [10] Their characteristics, design, and fabrication have been studied for over a century and are well-known. [4] In the next section, we will further discuss thin film absorbers where one layer is textured on the nanoscale, but thin-film systems are particularly useful as optical absorbers exhibiting distinct advantages over nanostructured optical metasurfaces. While textured surfaces require an additional level of processing, potentially requiring complex, top-down nanofabrication techniques, [11][12][13] Near-complete absorption of light has the potential to underpin advances in photodetection, advanced chemistry, coloration of materials, and energy. This review paper reports recent progress on the development of metasurfaces and thin film structures that produce strong absorption bands in the visible and longer wavelength regions of the electromagnetic spectrum, due in part to the excitation of plasmonic resonances. Proof-of-concept demonstrations are discussed for applications of these in chemical sensing, the generation of structural color, the creation of optoelectronic devices, and p...

Self‐Assembled, 10 nm‐Tailored, Near Infrared Plasmonic Metasurface Acting as Broadband Omnidirectional Polarizing Mirror

“…Indeed, even in most recent literature, although nanostructuration and randomness have been considered to achieve strong interference in a broad spectral range, this was done without considering or harnessing anisotropy effects. [ 18,24,25,30,57,58 ] Therefore, thanks to its unique structure and optical properties, the metasurface design presented in this work is, to our knowledge, the only one among the reported self‐assembled reflective metasurfaces [ 3,12–14,18,19,24,25,29,30,57,58 ] that enables a broadband omnidirectional polarizing mirror functionality in the near infrared, as discussed in Section S9 in the Supporting Information. Furthermore, to our knowledge, the best metasurface design presented in this work (orange curves in Figure 3d) takes advantage over the best‐performing state‐of‐the‐art lithographic reflective metasurfaces, not only because of its much larger achievable area but also because it enables a superior performance as broadband omnidirectional polarizing mirror.…”

“…[1] Accordingly, they have enabled flat and subwavelength-thin optical components such as lenses, beam steerers, perfect absorbers, coatings with structural colors, polarization controllers or mirrors, opening the way to photonic devices with new functionalities and a smaller footprint. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] To present optimal optical functionalities, the structure of plasmonic metasurfaces needs to be tailored at a scale much smaller than their operation wavelength. Therefore, for operation in the ultraviolet, visible and near infrared regions, such tailoring needs to be achieved at the scale of few nanometers.…”

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3D Silver Dendrites for Single‐molecule Imaging by Surface‐enhanced Raman Spectroscopy

“…To move towards new frontiers in molecular sensing, optical spectroscopies and nanotechnology have been combined. [1][2][3] SERS-spectroscopy is a successful example of such a combination that not only reveal the presence or absence of a target molecule in an analyzing media, [4,5] but also recognize its fingerprint and shows sensitivity down to the single molecule level. [6] An abnormal increase of a Raman signal from analyte molecules is observed when they are adsorbed on or located in a close vicinity to SERS-active substrates.…”

“…In recent decades, sensing technologies have become so powerful that today diverse sensors pervade our daily lives giving a raise to tightening our requirements to their accuracy, precision, and analysis speed, which are especially critical for the molecular detection in medicine and pharmaceutics, forensics and security, environmental monitoring and other areas of human life. To move towards new frontiers in molecular sensing, optical spectroscopies and nanotechnology have been combined [1–3] . SERS‐spectroscopy is a successful example of such a combination that not only reveal the presence or absence of a target molecule in an analyzing media, [4,5] but also recognize its fingerprint and shows sensitivity down to the single molecule level [6] …”