Titanium dioxide (TiO2) displays photocatalytic behavior under near-ultraviolet (UV) illumination. In another scientific field, it is well understood that the excitation of localized plasmon polaritons on the surface of silver (Ag) nanoparticles (NPs) causes a tremendous increase of the near-field amplitude at well-defined wavelengths in the near UV. The exact resonance wavelength depends on the shape and the dielectric environment of the NPs. We expected that the photocatalytic behavior of TiO2 would be greatly boosted if it gets assisted by the enhanced near-field amplitudes of localized surface plasmon (LSP). Here we show that this is true indeed. We named this new phenomenon "plasmonic photocatalysis". The key to enable plasmonic photocatalysis is to deposit TiO2 on a NP comprising an Ag core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. The most appropriate diameter for Ag NPs and thickness for the SiO2 shell giving rise to LSP in the near UV were estimated from Mie scattering theory. Upon implementing a device that took these design considerations into account, the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst, monitored by decomposition of methylene blue, was enhanced by a factor of 7. The enhancement of the photocatalytic activity increases with a decreased thickness of the SiO2 shell. The plasmonic photocatalysis will be of use as a high performance photocatalyst in nearly all current applications but will be of particular importance for applications in locations of minimal light exposure.

Abstract:The subwavelength mode volumes of plasmonic filters are well matched to the small size of state-of-the-art active pixels in CMOS image sensor arrays used in portable electronic devices. Typical plasmonic filters exhibit broad (> 100 nm) transmission bandwidths suitable for RBG or CMYK color filtering. Dramatically reducing the peak width of filter transmission spectra would allow for the realization of CMOS image sensors with multi-and hyperspectral imaging capabilities. We find that the design of 5 layer metalinsulator-metal-insulator-metal structures gives rise to multi-mode interference phenomena that suppress spurious transmission features and give rise to single transmission bands as narrow as 17 nm. The transmission peaks of these multilayer slot-mode plasmonic filters (MSPFs) can be systematically varied throughout the visible and near infrared spectrum, leading to a filter that is CMOS integrable, since the same basic MSPF structure can operate over a large range of wavelengths. We find that MSPF filter designs that can achieve a bandwidth less than 30 nm across the visible and demonstrate experimental prototypes with a FWHM of 70 nm, and we describe how experimental structure can be made to approach the limits suggested by the model.

The NO intercalation properties of substituted double-layered cuprates, La2-x Ba x SrCu2O6, have been studied by means of XRD, ED, HREM, and FT-IR. The NO absorbability was strongly influenced not only by the amount of Ba substitution but also by the pretreatment with saturated water vapor at 60 °C. The Ba substitution leads to √2a × √2a and 3a × 3a superstructures, which are associated with the ordering of Ba and oxygen vacancies, respectively. The sample with the superstructure showed rapid NO uptake at 250 °C only after water vapor treatment. The XRD measurement demonstrates a two-stage lattice expansion along the c axis after reactions with water vapor and subsequently with NO. The parallel HREM study suggests that the expanded structure is due to the insertion of H2O and NO species into interlayers between bottom planes of CuO5 pyramids. Aging the sample in water vapor leads to the formation of interlayer hydroxyl groups, which are effective in promoting NO intercalation by expanding the interlayer spacing between the CuO5 sheets.

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The substituted double-layered cuprate, Lal.5Bao.5SrCu206, characterized b y the 3a x 3a superstructure, incorporates large quantities of gaseous nitric monoxide via intercalation.