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We propose and numerically investigate a smart, optically transparent digital metasurface reflective in the mmWave range, based on CVD graphene programmable elements. For both TM and TE polarizations, we detail the optimization of the unit cells, designed to exhibit two distinct states that correspond to those of binary encoding. The whole metasurface encoding can be customized to provide different electromagnetic functions, such as wide-band beam splitting at a controlled angle and reduction of the Radar Cross Section. Optically transparent metasurfaces could be integrated and exploited in windows and transparent surfaces in future Beyond-5G and 6G ecosystems. [ABSTRACT FROM AUTHOR]

Graphene is a material with exceptional optical, electrical and physicochemical properties that can be combined with dielectric waveguides. To date, several optical devices based on graphene have been modeled and fabricated operating in the near-infrared range and showing excellent performance and broad application prospects. This paper covers the main aspects of the optical behaviour of graphene and its exploitation as electrodes in several device configurations. The work compares the reported optical devices focusing on the wavelength tuning, showing how it can vary from a few hundred up to a few thousand picometers in the wavelength range of interest. This work could help and lead the design of tunable optical devices with integrated graphene layers that operate in the NIR. [ABSTRACT FROM AUTHOR]

In this study, we present a two-dimensional dielectric grating which allows achieving high absorption in a monolayer graphene at visible and near-infrared frequencies. Dielectric gratings create guided-mode resonances that are exploited to effectively couple light with the graphene layer. The proposed structure was numerically analyzed through a rigorous coupled-wave analysis method. Effects of geometrical parameters and response to the oblique incidence of the plane wave were studied. Numerical results reveal that light absorption in the proposed structure is almost insensitive to the angle of the impinging source over a considerable wide angular range of 20°. This may lead to the development of easy to fabricate and experimentally viable graphene-based absorbers in the future. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and experimentally demonstrate that few-layer Chemical Vapour Deposition graphene can be employed for the fabrication of fully optical transparent antennas for microwave applications. We show that planar graphene-based antennas, having a size of tens of square centimeters, can achieve relatively high gain over a wide operating bandwidth (>3.5 GHz) simultaneously covering the GPS, WiFi, Bluetooth, and 5G bands. The measured 3D radiation patterns show dipole-, quadruple-, and hexapole-behavior. These findings open up routes for the realization of innovative devices where “invisible and hidden” antennas could be integrated in smart windows or photovoltaic systems, fostering configurations for camouflage, and communications systems. Furthermore, the possibility to handle different radiation patterns could allow the engineering of complex systems such as antenna arrays devoted to beam-steering, beam-forming, and healthcare applications. Finally, combining graphene transparency and flexibility could also pave the way for the realization of wearable devices, demanding invisibility, which operate on the surface of the human body or can be integrated in transparent devices (for example, in contact lenses) reducing their invasiveness. [ABSTRACT FROM AUTHOR]

In this work, we detail the integration of monolayer graphene electrodes in Silicon Nitride waveguides to achieve wavelength tuning. The numerical results show that wavelength shifts of a few hundred to several thousand picometers shift can be obtained depending on the configuration. These results will help guide the design of graphene-based tunable optical devices operating in the near infrared range. [ABSTRACT FROM AUTHOR]

In this paper, we report on the engineering and the realization of optically transparent graphene-based microwave devices using Chemical Vapour Deposition (CVD) graphene whose sheet resistance may be tailored down to values below 30 Ω/sq. In particular, we show that the process was successfully used to realize and characterize a simple, optically transparent graphene-based wire-grid polarizer at microwave frequencies (X band). The availability of graphene operating in a quasi-metallic region may allow the integration of graphene layers in several microwave components, thus leading to the realization of fully transparent (and flexible) microwave devices. [ABSTRACT FROM AUTHOR]

Chemical doping is an effective way to increase the conductivity of graphene. Despite the efforts made by many to achieve p-doping, mainly on CVD graphene, by using a variety of oxidant agents, there is still space to evaluate and optimize methodologies to further reduce the sheet resistance while maintaining high optical transparency. In this study, we developed "new" routes to dope graphene heavily using thionyl chloride that is known to act as chlorinating agent. It was found that, in addition to the nucleophilic reactions replacing oxygen with chlorine, the thermal (T ≥ 120 °C) and pyridine-catalytic activations of the SOCl 2 chemistry result in more p-doping functionalities in the graphene basal plane. A sheet resistance value of 18 Ω/□ was obtained for a 6-layer stacked graphene films with an optical transmittance of 85% at 550 nm. Furthermore, the possibility offered by the plasma oxidation of graphene in a controlled way, allows to introduce in the graphene basal plane the right amount of epoxy and hydroxyl defects so as to maximize the dopant functionalization and, hence, the carrier density, without affecting significantly the carrier mobility. This route allowed to reach a minimum sheet resistance value of 120 Ω/□ for a single layer graphene with 97.5% optical transparency. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • "Heavy" graphene doping by combining SOCl 2 and Au NPs doping methodologies. • New insights into the chemistry of graphene doping by Au NPs activated by SOCl 2. • Rs value of 35 Ω/□ for a 2L graphene while maintaining a transparency of 95%. • Graphene Rs/T performances meet the technical target required by TLC applications. The three values of transparency, conductivity and flexibility make graphene a valid alternative to replace traditional electrode materials such as indium tin oxide in electrical and optical devices. In recent years, research efforts have been addressed to investigate doping methodologies for reducing further the sheet resistance while maintaining high transparency. In this contribution, we explore the possibility to integrate both the covalent and non-covalent doping in order to increase the carrier charge density without affecting their mobility significantly. We present a new graphene doping methodology that combines the effect of SOCl 2 covalent p-doping with a synergic p-doping effect of cationic gold nanoparticles activated by the same SOCl 2 chemistry. We demonstrate that this original co-doping strategy can provide CVD graphene multilayers with record sheet resistance Rs performances, which meet the technical target required by several industrial applications. [ABSTRACT FROM AUTHOR]