Surface plasmon polariton waveguides with subwavelength confinement

Surface plasmon polaritons（SPPs） are evanescent waves propagating along metal-dielectric interfaces, which provide an effective way to realize optical wave guiding with subwavelength confinement. Metallic nanostructures supporting SPPs,that is, plasmonic waveguides, are considered as required components to construct nanophotonic devices and circuits with a high degree of miniaturization and integration. In this paper, various types of plasmonic waveguides operating in the visible, infrared, and terahertz regions are reviewed, and the status of the research on their fundamentals, fabrications,and applications is provided as well. First, we discuss the mechanisms of SPPs beyond the diffraction limit, and their launching methods. Then, the characteristics of SPPs on various plasmonic waveguides are reviewed, including top-down and bottom-up fabricated types. Considering applications, certain prototypes of plasmonic devices and circuits constructed by plasmonic waveguides for bio/chemo sensing, router, and light modulation are demonstrated. Finally, a summary and future outlook of plasmonic waveguides are given.

Viologens-based redox mediators with tunable HOMO–LUMO energy gap for highly effective hydrogen peroxide electrosynthesis

In comparison with the developing nano-carbon catalysts,some small organic molecules are also emerging as catalysts with typical features,however,their working mechanism is still unclear.Here,we synthesized a series of viologen-based heterogeneous catalysts with the same molecular skeleton but different substituent groups through anion exchange engineering.These viologen-based molecules were used as a model catalyst to investigate the underlying structure–function relationship for small molecules-based H_(2)O_(2) electrosynthesis.Differing from the commonly reported carbon-based electrocatalysts,viologens can produce H_(2)O_(2) in a synergistic manner,which means that viologens can not only directly catalyze oxygen reduction but also serve as a redox mediator.We found that the ring current and H_(2)O_(2) selectivity of viologens deliver an increasing trend with the increase of the alkyl chain length of alkyl-substituted viologens and further increase when using benzyl as the substituent group.As a result,a benzyl-substituted viologen(BV)delivers the best electrocatalytic performance among the samples,including the highest H_(2)O_(2) selectivity of 96.9%at 0.6 V and the largest ring current density of about 13.6 mA·mmol-1.Furthermore,density functional theory(DFT)calculations disclose that the carbon atoms bonded with positively charged N are the active sites and the small highest occupied molecular orbital(HOMO)–lowest unoccupied molecular orbital(LUMO)energy gap of BV is beneficial to the synergistic mechanism for H_(2)O_(2) production.This work sheds new insight into the efficient H_(2)O_(2) production in a synergistic manner for small molecules-based electrocatalysts.