Mehdi Keshavarz Hedayati

Design of a Perfect Black Absorber at Visible Frequencies Using Plasmonic Metamaterials

The design and fabrication of a plasmonic black absorber with almost 100% absorbance spanning a broad range of frequencies from ultraviolet (UV) to the near infrared (NIR) is demonstrated. The perfect plasmonic absorber is achieved by a combination of a metal film with suitable metal/dielectric nanocomposites. Our fabrication technique is simple, versatile, cost-effective, and compatible with current industrial methods for solar absorber production.

Review of Plasmonic Nanocomposite Metamaterial Absorber

Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface _lasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.

Green chemistry and nanofabrication in a levitated Leidenfrost drop

Green nanotechnology focuses on the development of new and sustainable methods of creating nanoparticles, their localized assembly and integration into useful systems and devices in a cost-effective, simple and eco-friendly manner. Here we present our experimental findings on the use of the Leidenfrost drop as an overheated and charged green chemical reactor. Employing a droplet of aqueous solution on hot substrates, this method is capable of fabricating nanoparticles, creating nanoscale coatings on complex objects and designing porous metal in suspension and foam form, all in a levitated Leidenfrost drop. As examples of the potential applications of the Leidenfrost drop, fabrication of nanoporous black gold as a plasmonic wideband superabsorber, and synthesis of superhydrophilic and thermal resistive metal–polymer hybrid foams are demonstrated. We believe that the presented nanofabrication method may be a promising strategy towards the sustainable production of functional nanomaterials.

Plasmonic tunable metamaterial absorber as ultraviolet protection film

Plasmonic metamaterials designed for optical frequency have to be shrunk down to few 10th of nanometer which turns their manufacturing cumbersome. Here, we shift the performance of metamaterial down to ultraviolet (UV) by using ultrathin nanocomposite as a tunable plasmonic metamaterial fabricated with tandem co-deposition. It provides the possibility to realize a plasmonic metamaterial absorber for UV frequency with marginal angle sensitivity. Its resonance frequency and intensity can be adjusted by changing thickness and filling factor of the composite. Presented approach for tunable metamaterials for high frequency could pave the way for their application for thermo-photovoltaic, stealth technology, and UV-protective coating.

An omnidirectional transparent conducting-metal-based plasmonic nanocomposite.

A transparent conducting metal (TCM) composed of a stack of a gold film and silver/polymer nanocomposite fabricated by sputtering onto a glass substrate is presented. The plasmonic metamaterial shows an omnidirectional optical transmission up to 80 in the visible spectrum, which is comparable to that of ITO, and the electrical conductivity is one order of magnitude higher than that of ITO.

Effective Optical Properties of Plasmonic Nanocomposites

Plasmonic nanocomposites find many applications, such as nanometric coatings in emerging fields, such as optotronics, photovoltaics or integrated optics. To make use of their ability to affect light propagation in an unprecedented manner, plasmonic nanocomposites should consist of densely packed metallic nanoparticles. This causes a major challenge for their theoretical description, since the reliable assignment of effective optical properties with established effective medium theories is no longer possible. Established theories, e.g., the Maxwell-Garnett formalism, are only applicable for strongly diluted nanocomposites. This effective description, however, is a prerequisite to consider plasmonic nanocomposites in the design of optical devices. Here, we mitigate this problem and use full wave optical simulations to assign effective properties to plasmonic nanocomposites with filling fractions close to the percolation threshold. We show that these effective properties can be used to properly predict the optical action of functional devices that contain nanocomposites in their design. With this contribution we pave the way to consider plasmonic nanocomposites comparably to ordinary materials in the design of optical elements.

Photoresponsive Transparent Conductive Metal with a Photobleaching Nose

Smart materials that respond to a stimulus or their environment to produce a dynamic and reversible change in critical properties are in focus of actual research. [ 1 ] Among several stimuli, photochromism is receiving increasing attention because of its potential applications in molecular switching, lenses, and data storage among others. [ 2 ] In general, photochromic molecules can turn any composite into a smart material provided the host matrix is soft enough (e.g., a polymer) to let the molecule rotate upon illumination. The unique properties of these molecules can be even more benefi cial implemented into the devices whose optical properties are the matter of interest (e.g., optoelctronic devices) and to make them smart. In this regard, transparent conductors (TCs) can be a proper matter since their optical properties are crucial. Traditionally, indium tin oxide (ITO) has been widely implemented as a standard TC in different kinds of optoelectronic devices. However having phototunable optical transparency along with high electrical conductivity would be potentially applicable for novel smart optoelectronic sensors. During the course of last decades great efforts have been made to develop new kind of TCs to replace ITO. [ 3–5 ] In this regard, different materials and composites have been proposed and studied, including conductive polymers, [ 6 ]

Review of Metasurface Plasmonic Structural Color

The environmental concerns in the current century is not only limited to the polluting effect of the fossil fuel consumption but also the recycling challenges of waste turns to be a substantial challenges of the industry. Recycling of colored discarded materials is very difficult because of the problems in relation to the dissociation of diverse chemical compounds present in the colorant agents. Single or double component materials which could create various colors by geometrical changes can be a great solution to the mentioned limitations. Metasurfaces’ and metamaterials’ structural color therefore draws attention as they enable generation of vivid colors only by geometrical arrangement of metals which not only ease the recycling but at the same time enhance the mechanical stability of the colors. In this review, the progress in the field of plasmonic metasurface- and metamaterial-based structural colors is reviewed.

Broadband Anti-Reflective Coating Based on Plasmonic Nanocomposite

We report on the fabrication, the characterization, and the optical simulation of a gold–silica nanocomposite and present its integration into a broadband anti-reflective coating (ARC) for a silicon substrate. The two-layer ARC consists of a nanocomposite (randomly distributed gold cluster in a silica matrix) and a pure silica film. We capitalize on the large refractive index of the composite to impose an abrupt phase change at the interface of the coating to diminish the light reflection from the substrate through the ultrathin nanocoating. The average reflectivity of the silicon can be reduced by such a coating to less than 0.1% in the entire visible spectrum. We experimentally and numerically prove that percolated nanocomposites with an overall thickness of 20 nm can provide anti-reflectivity up to near infrared (NIR). The ARC bandwidth can be shifted more than 500 nm and broadened to cover even the NIR wavelength by changing the volume filling fraction of the gold clusters. The angular sensitivity of thin ultrathin antireflective coating is negligible up to 60°. The present ARC could find applications in thermo-photovoltaics and bolometers.