Yes / This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2 × 3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 μm for operation across 0.19-0.20 THz. The dimensions of the array were 20 × 13.5 × 0.125 mm3. Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits. / Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER, UE) under Grant RTI2018-095499-B-C31, in part by the Innovation Programme under Grant H2020-MSCA-ITN-2016 SECRET-722424, and in part by the U.K. Engineering and Physical Sciences Research Council (EPSRC) under Grant EP/E022936/1.

Detecting long wave infrared (LWIR) light at room temperature has posed a persistent challenge due to the low energy of photons. The pursuit of an affordable, high-performance LWIR camera capable of room temperature detection has spanned several decades. In the realm of contemporary LWIR detectors, they can be broadly classified into two categories: cooled and uncooled detectors. Cooled detectors, such as MCT detectors, excel in terms of high detectivity and fast response times. However, their reliance on cryogenic cooling significantly escalates their cost and restricts their practical applications. In contrast, uncooled detectors, exemplified by microbolometers, are capable of functioning at room temperature and come at a relatively lower cost. Nonetheless, they exhibit somewhat lower detectivity and slower response times. Within the scope of this work, I will showcase two innovative approaches aimed at advancing the next generation of LWIR detectors. These approaches are designed to offer high detectivity, swift response times, and room temperature operation. The first approach involves harnessing Dirac plasmon and the Seebeck effect in graphene to create a photo-thermoelectric detector. In addition, I will introduce the application of scanning near-field microscopy for revealing the plasmons generated in graphene, employing both imaging and spectroscopy techniques. The second approach entails the use of an oscillating circuit integrated with phase change materials and the modulation of frequency induced by infrared illumination to achieve LWIR detection. Finally, I will present the progress made in integrating graphene-based detectors in this work onto readout circuits to enable the development of dense pixel focal plane array.

The thesis aims to illustrate and highlight the potential of graphene-based fillers in reinforcing organic coatings deposited by cataphoresis. Thanks to particular surface modification processes of the graphene flakes, these have been properly distributed within the polymer matrix, providing the composite coating with remarkable protective performance. The optimization of the deposition process parameters, as well as the amount of filler, also allowed to improve the mechanical and conductivity properties of the cataphoretic matrix, suggesting the possibility of realizing multifunctional coatings. Finally, these ’smart’ coatings were made by combining two deposition techniques, creating two layers with distinct purposes, containing different types of graphene-based fillers. The cataphoretic primer provided the substrate with high corrosion protection, while the spray top coat possessed high properties of electrical conductivity and resistance to abrasion phenomena. Ultimately, graphene has proven to be an excellent resource as a reinforcing filler in multifunctional organic coatings.

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The application of membranes in liquid and gas separation is attractive because of their energy efficiency. Synthesis of membranes with well-defined nanostructure is necessary to achieve highly permeability and selectivity for separation processes. Recently, carbon nanomaterials such as graphene oxide nanoplatelets (GONPs) and carbon nanodots (CNDs) have emerged as an interesting class of nanomaterials due to their unique properties and tailorable functionalities. Incorporation of these nanomaterials in the membranes has been shown to improve membrane selectivity, mechanical robustness, and chemical stability. This dissertation elaborates on developing CNDs or GONPs embedded thin film composite (TFC) membranes using layer-by-layer (LbL) synthesis technique. Regarding the water desalination applications, GONPs were used to enhance the TFC membranes’ selectivity, chlorine resistant properties, and surface hydrophilicity. Incorporation of GONPs in the polyamide layer via LbL method resulted in an increase of surface hydrophilicity and salt rejection properties. Upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes (without GONPs). The LbL assembly was used to synthesize CNDs based TFC membranes for organic solvent nanofiltration (OSN) applications. Using the LbL framework, amineunctionalized CNDs were covalently crosslinked with trimesoyl chloride monomer to obtain nanoscale membranes. The synthesized membranes manifested high selectivity (up to 90%) when tested for dye molecules such as brilliant blue and disperse red in methanol. As the CNDs synthesized here are fluorescent under UV light, the resultant film is also fluorescent. This property can be harnessed for diagnostic purposes, such as tracking mechanical failure and fouling of the membranes. Based on the results, it can be concluded that the incorporation of carbon nanomaterials in the polymeric membranes has enhanced the hydrophilicity, mechanical stability, and chlorine resistant properties of the membranes. Overall, the LbL platform can be considered as a modular method in embedding nanoparticles in TFC membranes.

Heavy metals, oxyanions (NO3-, PO4-), pharmaceuticals, and dyes in aquatic environments are inevitable economic and health concerns. Ingestion of these contaminants, even in trace amounts, causes long and short-term serious threats to human health. Conventional pollutant mitigation strategies can be costly or ineffective. Due to high efficiency, simplicity, low price, adsorbent reuse, and pollutant (e.g., phosphates) recovery, adsorption has been widely used for wastewater purification. Many efficient, environmentally compatible, and cost-effective sorbents have been successfully applied in environmental remediation. Chapter I is about characterization of graphene-coated pinewood biochar hybrids and evaluation of their copper removal performances. Here, we synthesized three types of pinewood biochar-graphene composites consisting of three different graphene precursors and compared their aqueous Cu2+ removal performances against raw pinewood biochar. To the best of our knowledge, no previous work has characterized the copper decontamination by graphene-biochar hybrids. Chapter II is about thermally- and chemically-treated lignite adsorbents for phosphate remediation. We engineered a cost efficient lignite system with co-precipitated Ca2+/Mg2+ followed by pyrolysis at 600 ⁰C to remediate aqueous phosphates. Micro-sized surface deposited oxide/hydroxide/carbonate particles promoted phosphate uptake of Ca2+/Mg2+-modified-lignite by 31 and 72 times, compared to thermally treated lignite (w/o a chemical treatment) and the raw lignite, respectively. The exhausted adsorbent can act as a slow-release fertilizer, which is comparable with commercial phosphate fertilizers. Chapter III is about synthesis of activated lignite [A-L], Ca2+-modified lignite [Ca-L], and Fe3O4 nanoparticle-loaded activated lignite (Fe3O4-A-L) for phosphate remediation. Even though A-L has a very high surface area (2854 m2/g), it did not achieve much phosphate sorption. Ca-L phosphate uptake was highest due to the high concentrations of surface deposited CaCO3, CaO, and Ca(OH)2. A pH-independent (from pH 5 to 9) phosphate removal was reported by highly basic Ca-L. However, the Ca2+ leaching was highest at pH 5. Precipitation of Ca2+ phosphates/hydrophosphates is the major phosphate removal mechanism of Ca-L. Fe3O4 and Fe2O3 sites of Fe3O4-A-L enhanced phosphate adsorption capacity, 8-fold versus A-L (67.6 mg/g vs 8.0 mg/g at 25 ºC). Fe3O4-A-L remediated phosphates via inner-sphere surface complexation and precipitation.

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