Plasmon logic gates designed by modal engineering of 2-dimensional crystalline metal cavities

Abstract : The main objective of this PhD work is to design, fabricate and characterize plasmonic devices based on highly crystalline metallic cavities for the two-dimensional information transfer and logic gate operations. First, we thoroughly characterize the optical response of ultra-thin gold colloidal cavities of sub-micronic size (400 to 900 nm) by dark- field spectroscopy (Fig. 1a). The dispersion of the high order plasmonic resonances of the cavities is measured and compared with a good agreement to simulations obtained with a numerical based on the Green Dyadic Method (GDM). We further extend our experiments to systematically tune the spectral responses of these colloidal nanoprisms in vicinity of metallic thin film substrates. A comprehensive study of these sub-micronic size cavity in bowtie antenna configuration is performed. We show a polarization-dependent field enhancement and a nanoscale field confinement at specific locations in these bowtie antennas. We systematically study the effects that could potentially affect the plasmonic resonances by non-linear photon luminescence microscopy, which has proved to be an efficient tool to observe the surface plasmon local density of states (SPLDOS). Inparticular, we show that an effective spatially and spectrally tuning of the high order plasmonic resonances can be achieved by the modification of the substrate (dielectric or metallic), by the controlled insertion of a defect inside a cavity or by the weak electromagnetic coupling between two adjacent cavities. The rational tailoring of the spatial distribution of the 2D confined resonances was applied to the design of devices with tunable plasmon transmittance between two connected cavities. The specific geometries are produced by focused ion milling crystalline gold platelets. The devices are characterized by non-linear luminescence mapping in confocal and leakage radiation microscopy techniques. The latter offers a unique way to observe propagating SPP signal over a 2D plasmonic cavity. We demonstrate the polarization-dependent mode-mediated transmittance for devices withadequate symmetry. The results are faithfully reproduced with our simulation tool based on Green dyadic method. Finally, we extend our approach to the design and fabrication of a reconfigurable logic gate device with multiple inputs and outputs. We demonstrate that 10 out of the possible 12 2-input 1-output logic gates can be implemented on the same structure by choosing the two input and the one output points. We also demonstrate reconfiguration of the device by changing polarization of the incident beam, set of input locations and threshold of the non-linear luminescence readout signal.
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Upkar Kumar. Plasmon logic gates designed by modal engineering of 2-dimensional crystalline metal cavities. Micro and nanotechnologies/Microelectronics. Université Paul Sabatier - Toulouse III, 2017. English. ⟨NNT : 2017TOU30170⟩. ⟨tel-01963241⟩

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