Gas Sensing with Bare and Graphene-covered Optical Nano-Antenna Structures

Carbon Nanostructure Embedded Novel Sensor Implementation for Detection of Aromatic Volatile Organic Compounds: An Organized Review

For field-like environmental gas monitoring and noninvasive illness diagnostics, effective sensing materials with exceptional sensing capabilities of sensitive, quick detection of volatile organic compounds (VOCs) are required. Carbon-based nanomaterials (CNMs), like CNTs, graphene, carbon dots (Cdots), and others, have recently drawn a lot of interest for their future application as an elevated-performance sensor for the detection of VOCs. CNMs have a greater potential for developing selective sensors that target VOCs due to their tunable chemical and surface properties. Additionally, the mechanical versatility of CNMs enables the development of novel gas sensors and places them ahead of other sensing materials for wearable applications. An overview of the latest advancements in the study of CNM-based sensors is given in this comprehensive organized review.

Smart optical cross dipole nanoantenna with multibeam pattern

In this paper, an optical smart multibeam cross dipole nano-antenna has been proposed by combining the absorption characteristic of graphene and applying different arrangements of directors. By introducing a cross dipole nano-antenna with two V-shaped coupled elements, the maximum directivity of 8.79 dBi has been obtained for unidirectional radiation pattern. Also, by applying various arrangements of circular sectors as director, different types of radiation pattern such as bi- and quad-directional have been attained with directivities of 8.63 and 8.42 dBi, respectively, at the wavelength of 1550 nm. The maximum absorption power of graphene can be tuned by choosing an appropriate chemical potential. Therefore, the radiation beam of the proposed multibeam cross dipole nano-antenna has been controlled dynamically by applying a monolayer graphene. By choosing a suitable chemical potential of graphene for each arm of the suggested cross dipole nano-antenna without the director, the unidirectional radiation pattern shifts ± 13° at the wavelength of 1550 nm. Also, for the multibeam nano-antenna with different arrangements of directors, the bi- and quad-directional radiation patterns have been smartly modified to uni- and bi-directional ones with the directivities of 10.1 and 9.54 dBi, respectively. It is because of the graphene performance as an absorptive or transparent element for different chemical potentials. This feature helps us to create a multipath wireless link with the capability to control the accessibility of each receiver.

A Review on the Development of Tunable Graphene Nanoantennas for Terahertz Optoelectronic and Plasmonic Applications

Exceptional advancement has been made in the development of graphene optical nanoantennas. They are incorporated with optoelectronic devices for plasmonics application and have been an active research area across the globe. The interest in graphene plasmonic devices is driven by the different applications they have empowered, such as ultrafast nanodevices, photodetection, energy harvesting, biosensing, biomedical imaging and high-speed terahertz communications. In this article, the aim is to provide a detailed review of the essential explanation behind graphene nanoantennas experimental proofs for the developments of graphene-based plasmonics antennas, achieving enhanced light-matter interaction by exploiting graphene material conductivity and optical properties. First, the fundamental graphene nanoantennas and their tunable resonant behavior over THz frequencies are summarized. Furthermore, incorporating graphene-metal hybrid antennas with optoelectronic devices can prompt the acknowledgment of multi-platforms for photonics. More interestingly, various technical methods are critically studied for frequency tuning and active modulation of optical characteristics, through in situ modulations by applying an external electric field. Second, the various methods for radiation beam scanning and beam reconfigurability are discussed through reflectarray and leaky-wave graphene antennas. In particular, numerous graphene antenna photodetectors and graphene rectennas for energy harvesting are studied by giving a critical evaluation of antenna performances, enhanced photodetection, energy conversion efficiency and the significant problems that remain to be addressed. Finally, the potential developments in the synthesis of graphene material and technological methods involved in the fabrication of graphene-metal nanoantennas are discussed.

Ultra-deep sub-wavelength mode confinement in nano-scale graphene resonator-coupled waveguides

Graphene is capable of supporting very slow waves due to sustaining surface plasmon polaritons (SPPs) at THz frequencies, whereas the metal counterpart can support such modes only at optical frequencies. In this paper, a graphene-based resonator-coupled waveguide supporting transverse-magnetic-polarized SPP modes is rigorously studied, which is capable of providing ultra-deep sub-wavelength mode confinement at the working frequency of 40 THz. First, graphene is described both electronically and electromagnetically, as in these regards, graphene's quantum capacitance plays an important role, which is calculated via its DC characteristic. Since we aim to excite extremely slow waves in graphene waveguides, namely, SPP modes, it is necessary to contemplate a non-local conductivity model to characterize graphene. Furthermore, SPP modes create strong fields at the vicinity of a graphene strip in addition to high mode confinement, accentuating the importance of including nonlinear phenomena in characterizing the wave vector of SPP (WVP) modes. Furthermore, the WVP associated with a graphene waveguide is perturbed when placing another waveguide next to it. In this work, these phenomena are explored in detail to design a graphene-based resonator-coupled waveguide, which is superior to a single graphene-based waveguide in terms of confining propagating waves. Here, a comprehensive methodology is established for assessing miniaturized graphene devices, in which nonlinear, coupling, and spatial dispersion phenomena significantly affect their characteristics.

Miniaturized nanohole array based plasmonic sensor for the detection of acetone and ethanol with insights into the kinetics of adsorptive plasmonic sensing

The present work demonstrates development of a miniaturized plasmonic platform comprised of a Au nanohole array (NHA) on a Si/Si3N4 substrate. Plasmonic responses of the NHA platform, which is coated with Cu-benzenetricarboxylate metal organic framework (MOF), are found to be promising even towards 500 nmol mol-1 (ppb) of acetone or ethanol vapors at room temperature. The sensing characteristics are further investigated by varying the operating temperature (296 K to 318 K) of the sensor and the concentrations of vapors (500 nmol mol-1 to 320 μmol mol-1). The plasmonic responses for the sensors are correlated with the adsorption of vapors on the MOF surface and modeled in accordance to Langmuir-type adsorption. Kinetic parameters are estimated for the adsorption of fixed concentrations of acetone and ethanol vapors within the studied operating temperature range. The linear variation of characteristic response time constants with the operating temperature provides Arrhenius activation energies for the adsorption of acetone and ethanol vapors. The comparatively lower activation energy estimated for the adsorption of ethanol results in faster and more sensitive response of the sensor towards that analyte. The plasmonic sensor for the detection of nmol mol-1 level acetone and ethanol vapors at room temperature along with the kinetic correlation on plasmonic response with the adsorption of the analytes described herein offer new insights to existing reports on surface modification and plasmonic detection.

Vapour sensing properties of graphene-covered gold nanoparticles

We investigated the vapour sensing properties of different graphene-gold hybrid nanostructures. We observed the shifts in the optical spectra near the local surface plasmon resonance of the gold nanoparticles by changing the concentration and nature of the analytes (ethanol, 2-propanol, and toluene). The smaller, dome-like gold nanoparticles proved to be more sensitive to these vapours compared to slightly larger, flat nanoparticles. We investigated how the optical response of the gold nanoparticles can be tuned with a corrugated graphene overlayer. We showed that the presence of graphene increased the sensitivity to ethanol and 2-propanol, while it decreased it towards toluene exposure (at concentrations ≥ 30%). The slope changes observed on the optical response curves were discussed in the framework of capillary condensation. These results can have potential impact on the development of new sensors based on graphene-gold hybrids.

Nanostructured Dielectric Fractals on Resonant Plasmonic Metasurfaces for Selective and Sensitive Optical Sensing of Volatile Compounds

Advances in the understanding and fabrication of plasmonic nanostructures have led to a plethora of unprecedented optoelectronic and optochemical applications. Plasmon resonance has found widespread use in efficient optical transducers of refractive index changes in liquids. However, it has proven challenging to translate these achievements to the selective detection of gases, which typically adsorb non-specifically and induce refractive index changes below the detection limit. Here, it's shown that integration of tailored fractals of dielectric TiO₂ nanoparticles on a plasmonic metasurface strongly enhances the interaction between the plasmonic field and volatile organic molecules and provides a means for their selective detection. Notably, this superior optical response is due to the enhancement of the interaction between the dielectric fractals and the plasmonic metasurface for thickness of up to 1.8 μm, much higher than the evanescent plasmonic near-field (≈30 nm) . Optimal dielectric-plasmonic structures allow measurements of changes in the refractive index of the gas mixture down to <8 × 10^-6 at room temperature and selective identification of three exemplary volatile organic compounds. These findings provide a basis for the development of a novel family of dielectric-plasmonic materials with application extending from light harvesting and photocatalysts to contactless sensors for noninvasive medical diagnostics.