The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed...

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We study plasmonic lattice modes in two dimensional arrays of large metallic nanodisks in strongly inhomogeneous environments with controlled dielectric asymmetries. This is done within the two limits of positive (air/substrate) and negative (Si/substrate) asymmetries. In the former, the nanodisks are exposed to air, while in the latter, they are fully embedded in a dielectric material with a refractive index much higher than that of the glass substrate (Si). Our results show that in the air/substrate limit, the arrays can mainly support two distinct visible and infrared peaks associated with the optical coupling of multipolar plasmonic resonances of nanodisks in air and substrate (normal modes). As the nanodisks are gradually embedded in Si, i.e., going from the positive to negative asymmetry limit, the visible peak undergoes more than 200 nm red shift without significant mode degradation. Our results show that as this transition happens, a third peak (anomalous mode) becomes dominant. The amplitude and wavelength of this peak increase quadratically with the thickness of the Si layer, indicating formation of a unique collective mode. We study the impact of this mode on the emission semiconductor quantum dots, demonstrating they become much brighter as the result of the long-reach plasmonic fields of the nanodisks when the arrays are in this mode.

We study the application of plasmonic lattice modes of arrays of closely packed large metallic nanodisks for chemical and biological sensors with ultrahigh sensitivity and refractive index dynamic range. Our results show that by changing the refractive index of the environment the narrow spectral features associated with these collective modes can be shifted by about 250 nm, going from visible (∼650 nm) to infrared (∼900 nm) range without any mode degradation. We attribute this shift to the refractive-index enhancement of the superstrate collective modes of these arrays. This index enhancement allows the arrays to preserve their mode integrity within this range. We show that, because of this feature and the ultra-long range fields of these modes, such structures can offer a unique platform for biosensors based on dielectric-coated metallic nanoparticle arrays. In such structures, the dielectric layers are used to tune the collective modes of the arrays, protect them against environmental degradation, and to prepare bio-functionalized surfaces for certain biological targets. We demonstrate that such a platform allows us to set the operation wavelength of these sensors within the visible-infrared spectral range with sensitivity more than 520 nm/refractive index unit and a figure of merit of about 17.

We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.