The gate-controllable complex conductivity of graphene offers unprecedented opportunities for reconfigurable plasmonics at terahertz and mid-infrared frequencies. However, the requirement of a gating electrode close to graphene and the single 'control knob' that this approach offers limits the practical implementation and performance of these devices. Here we report on graphene stacks composed of two or more graphene monolayers separated by electrically thin dielectrics and present a simple and rigorous theoretical framework for their characterization. In a first implementation, two graphene layers gate each other, thereby behaving as a controllable single equivalent layer but without any additional gating structure. Second, we show that adding an additional gate allows independent control of the complex conductivity of each layer within the stack and provides enhanced control on the stack equivalent complex conductivity. These results are very promising for the development of THz and mid-infrared plasmonic devices with enhanced performance and reconfiguration capabilities.

Isolators, or optical diodes, are devices enabling unidirectional light propagation by using non-reciprocal optical materials, namely materials able to break Lorentz reciprocity. The realization of isolators at terahertz frequencies is a very important open challenge made difficult by the intrinsically lossy propagation of terahertz radiation in current non-reciprocal materials. Here we report the design, fabrication and measurement of a terahertz non-reciprocal isolator for circularly polarized waves based on magnetostatically biased monolayer graphene, operating in reflection. The device exploits the non-reciprocal optical conductivity of graphene and, in spite of its simple design, it exhibits almost 20 dB of isolation and only 7.5 dB of insertion loss at 2.9 THz. Operation with linearly polarized light can be achieved using quarter-wave plates as polarization converters. These results demonstrate the superiority of graphene with respect to currently used terahertz non-reciprocal materials and pave the way to a novel class of optimal non-reciprocal devices.

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The experimentally-observed stable, electrically-conducting interface formed between hydrophobin protein HFBII and silicon provides a model system for the Bio/ICT interfaces required for bionanoelectronics. The present work used molecular dynamics (MD) computer simulations to investigate the atom-scale details of the assembly and structure of the HFBII/silicon interface, using models on the order of 40,000 atoms to compute energy profiles for the full protein interacting with a bare Si(111) substrate in aqueous solution. Five nanoseconds of free, equilibrated dynamics were performed for six models with initial protein:silicon separations ranging from 1.2 to 0.2 nanometers in steps of 0.2 nm. Three of the models formed extensive protein:silicon van der Waals's interfacial contacts. The model with 0.2 nm starting separation serves as an illustrative example of the dynamic interface created, whereby hydrophobic patch residues cycle between flat and more protruding patch conformations that favor respectively close inter-patch and close patch-surface contacts, with protein:surface separations cycling between 0.2 and 0.4 nm over the 5 ns of dynamics. Analysis of residue-based binding energies at the interface reveal three leucines Leu19, Leu21 and Leu63, together with isoleucine Ile22 and alanine Ala61, as the primary drivers towards adhesion on bare silicon, providing the atom-scale details of HFBII’s hydrophobic patch which in turn provides leads for the engineering of more tightly-coupled interfaces.

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