Plasmonic metamaterials: enabling new routes for localized surface chemistry.

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Metamaterials are artificial structures composed of periodical nano- or micro-scale building blocks generally composed of layered conductors, semiconductors and dielectric barriers. In metallic metamaterials, local electronic resonances, known as plasmon resonances, are localized in the vicinity of the nanostructures. These resonances are highly tunable and can be exploited for a variety of applications including narrow-band optical filters, photovoltaic elements, and ultrasensitive analytical devices. The long-term objective of this proposed research program is to develop new metamaterials that we will exploit for spatially controlled plasmon-mediated chemical reactions and integration with transition metal dichalcogenides (TMDs). The overarching goal lies in understanding the fundamental interactions of plasmon modes with other molecules or materials under specific irradiation conditions. We will develop new 2D metastructures with specific shapes and geometries. Structures with linear or chiral anisotropies will be created and optimized to respond under linearly or circularly polarized light in both the visible and the infrared spectral ranges. Plasmonic platforms with multiple resonances spanning from the visible to the infrared range will be made and characterized using our nanophotonic infrastructure in conjunction with the mid-infrared beamline at the Canadian light source. Plasmon-mediated reactions will be investigated using these structures. Hot carriers, either electrons or holes, generated through the excitation of plasmons will be used to investigate reactions such as functionalization of diazonium salts on metal surfaces or alkyne-azide cycloadditions. The synergistic role of the hot carriers and probable thermal effects will be investigated under temperature-controlled conditions and under distinct irradiance of the excitation light source. Multichemical patterning using plasmon-mediated chemistry will be conducted on fractal structures. Such structures exhibit multiple plasmon resonances that can each be selectively excited with specific wavelengths and polarizations, thus enabling precise spatial control of chemical functionalization. We will combine the excitonic properties of TMDs with surface plasmon resonances from our metastructures. We anticipate that such hybrid plasmon-exciton materials will exhibit enhanced optical and conduction properties. Using tip-enhanced spectroscopy, we expect to measure enhanced luminescence and second harmonic generation. The combination of chiral plasmonic structures with resonances that match the excitonic wavelength should yield enhanced emission of circularly polarized light. In addition to the fundamental knowledge provided by this program, the new hybrid properties and spatially controlled molecular patterning enabled by plasmon will be exploited for the conception of the next generation of photonic devices with performance and flexibility well beyond the state of the art.