Terahertz Hybrid Graphene–Metal Reflectarrays
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Graphene, which is a planar or 2D allotrope of carbon, is actually the buildingblock of graphite. Graphene has potential applications in many fields, such as highfrequencyfield-effect transistors, flexible electronics, touch panels, optoelectronicdevices, energy storage devices, and wearable technology. Despite such promise,most of the graphene-based applications to date are limited to either theoreticalwork or laboratory research. This is due to the many challenges related tofabrication of graphene-based devices.Continuous graphene is a necessity for many electrical and optical applications.These applications, however, are built upon substrates that are not suitablefor graphene growth. As a result, graphene must be transferred from its growthsubstrate (usually Cu foil) to a different substrate (such as a silicon wafer). Transfertechniques often introduce defects in graphene, such as wrinkles, cracks, and voidsor holes. To address this problem, we developed a wet graphene transfer method inwhich we add a copolymer to poly(methyl methacrylate) (PMMA) prior to transfer.Unlike previously reported wet methods, we show that adding a copolymer layeratop a PMMA layer before transfer improves graphene continuity by virtuallyeliminating cracks and holes. The result, as determined by quantitative imageanalysis, is 99.8% continuous graphene over a 1 cm × 1 cm area.In addition to its many unique electronic properties, graphene can sustainTHz-frequency plasmons at room temperature. In an attempt to exploit this property for THz communication, we have demonstrated a hybrid graphene–metalreflectarray structure. In this reflectarray, the active elements are metal andgraphene reduces the reflected power by destroying the confinement. Lastly,we investigate all-graphene plasmonic antenna arrays, and propose an array ofsuspended graphene regions to realize plasmonic resonant cavities.