Sodium As A Plasmonic Material:Fabrication,Properties And Applications

Low-loss plasmonic materials have been highly pursued for decades because of the fundamental importance and promising advantages to versatile applications,such as optoelectronic devices,photo-detection and sub-diffraction imaging.Perfectly featured by the free-electron-gas model,sodium has long been regarded as the excellent plasmonic material,but has seldom been explored because of the high chemical reactivity.Here,we present a sodium-based plasmonic platform with low optical loss enabled by a straightforward spin-coating process.At the same time,we adopt a unique porous structure of three-dimensional TiO2/Au nanoparticles to experimentally explore the potential mechanisms of rhodamine B(RhB)based photocatalytic degradation.The main research contents are as follows1.By combining the ultra-smooth quartz substrate with the self-built advantages of annealing and self-cleaning treatments,the prepared sodium film(contacted with the substrate)exhibits an extremely low optical loss and high reflectance of>100%relative to the standard silver mirror,which shows good agreement with theoretical analysis and numerical simulations.As a direct demonstration,we measured the propagation length of the surface plasmon polaritons with the sodium based nanostructures,which overpasses 100 ?m for 1180 nm excitation.The excellent plasmonic performance combined with the highly scalable fabrication process makes sodium metal a promising candidate as a low-loss plasmonic material beyond conventional noble metals.2.The non-noble metal sodium,featured by low optical loss has been employed for reflective plasmonic color filters.By rational designing the structural parameters as well as fine controlling the sequential physical etching with ion beam,the periodic sodium nanopattens have been realized,exhibiting appealing reflective structural colors with minimal measured reflectance?15%and half width bandwidth?20 nm.The full-wave numerical simulations reveal that,the sharp optical mode beneficial for the narrowband structural color filtration can be ascribed to the hybridized cavity surface plasmons.To demonstrate a landscape of full structural colors,we experimentally fabricated series of sodium nanodisk patterns with gradient manipulation of the period and rod diameter.The measured angle-resolved reflectance spectra shows that the color filter is not only narrowband but also angular insensitive in the visible range.Our sodium based reflective plasmonic color filters may provide alternative routes to imaging,displays and sensing applications.3.We adopt a unique porous structure of three-dimensional TiO2/Au nanoparticles to experimentally explore the potential mechanisms of rhodamine B(RhB)based photocatalytic degradation.The highly efficient absorbance measured across the entire ultraviolet and infrared regions shows the broadband light harvesting capability and photocatalytic activity,in which the direct bandgap transition,plasmon sensitization as well as the plasmonic photothermal effect can be beneficial for the photocatalytic reaction.The RhB photocatalytic degradation experiments were conducted systematically under solar irradiance with finely chosen optical filters.The plasmon assisted photocatalytic rate of our TiO2/Au structure can be enhanced by>30%as compared to the referenced TiO2 structure(equivalent to 2-4 times promotion with respect to the same quantity of the active material TiO2).Our experimental results may provide a clear understanding for the wavelength-dependent plasmon enhanced photocatalytic processes.