We study control of optical coupling of plasmon resonances in metallic nanoantenna arrays using ultrathin layers of silicon. This technique allows one to establish and tune plasmonic lattice modes of such arrays, demonstrating a controlled transformation from the localized surface plasmon resonances of individual nanoantennas to their optimized collective lattice modes. Depending on the polarization and incident angle of light, our results support two different types of the silicon-induced plasmonic lattice resonances. For s-polarization these resonances follow the Rayleigh anomaly, while for p-polarization an increase in the incident angle makes the lattice resonances significantly narrower and slightly blueshifted.

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 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 biological sensing using the hybridization phase of localized surface plasmon resonances (LSPRs) with diffraction modes (photonic lattice modes) in arrays of gold nanoantennas. We map the degree of the hybridization process using an embedding dielectric material (Si), identifying the critical thicknesses wherein the optical responses of the arrays are mainly governed by pure LSPRs (insignificant hybridization), Fano-type coupling of LSPRs with diffraction orders (hybridization state), and their intermediate state (hybridization phase). The results show that hybridization phase can occur with slight change in the refractive index (RI), leading to sudden reduction of the linewidth of the main spectral feature of the arrays by about one order of magnitude while it is shifted nearly 140 nm. These processes, which offer significant improvement in RI sensitivity and figure of merit, are utilized to detect monolayers of biological molecules and streptavidin-conjugated semiconductor quantum dots with sensitivities far higher than pure LSPRs. We further explore how these sensors can be used based on the uncoupled LSPRs by changing the polarization of the incident light.

We study the impact of structural features of Si/Al oxide junctions on metal-oxide plasmonic metafilms formed via placing such junctions in close vicinity of an Au/Si Schottky barrier. The emission intensity and dynamics of colloidal semiconductor quantum dots deposited on such metafilms are investigated, while the surface morphology and structural compositions of the Si/Al oxide junction are controlled. The results show the conditions wherein the Si/Al oxide junction can reshape the impact of plasmonic effects, allowing it to increase the lifetimes of excitons. Under these conditions, the plasmonic metafilms can quarantine excitons against the fluctuating trap environments of the quantum dots, offering super-plasmonic emission enhancement that includes enhancement of the spontaneous emission decay rate combined with the suppression of Auger decay.

We use localized surface plasmon resonances in metallic nanoantennas to suppress defect environment of colloidal quantum dots and to enhance and polarize their spontaneous emission. For this we study the interaction of such quantum dots with functional metal-oxide plasmonic metastructures consisting of an Au/Si Schottky junction in close vicinity of a Si/Al oxide charge barrier. We show that optically excited quantum dots can couple with such metastructures via their electric dipole fields, offering super-plasmonic processes that include the impact of hot electron generation and fixed negative charges at the Si/Al oxide junction. For metallic nanoantennas with small aspect ratios our results show that these metastructures can reduce the defect-induced nonradiative decay rates of quantum dots such that their lifetime can become significantly longer than those in the absence of such nanoantennas. For metallic nanoantennas with larger aspect ratios these structures lead to ultrahigh enhancement of exciton-plasmon coupling, making the spontaneous emission of quantum dots strongly polarized while increasing their emission intensities by about 50 times. These results show by keeping excitons in the cores of quantum dots, the metastructures suppress migration of photo-excited electrons to surface defects and, therefore, reduce Auger recombination. Coherent dynamics associated with the quantum dot-induced exciton-plasmon coupling is theoretically investigated.

We show that under certain conditions the plasmonic field of a hybrid system consisting of a metallic nanoparticle and a semiconductor quantum dot can be converted into ultrashort stationary pulses with temporal widths as short as 300 ps. This happens as this system interacts with an infrared and visible laser fields, both with time-independent amplitudes. These fields generate quantum coherence via simultaneous interband and intersubband transitions of the quantum dot, forcing the polarization dephasing rate of the quantum dot to become negative during the plasmon pulses. This makes the amplitudes of such pulses time-independent (undamped), indicating total suppression of quantum decoherence of the quantum dot. These results suggest that hybrid quantum dot-metallic nanoparticle systems can act as undamped coherent-plasmonic oscillators.

We demonstrate tunable polarization-dependent infrared plasmonic lattice modes in the range of 1 to 1.7 μm in arrays of large gold nanodisks with a rectangle lattice structure. We show that when these arrays are exposed to air, their main mode appears around 1 μm. Under this condition, addition of chemicals leads to significant wavelength shifts in this mode, offering a refractive index sensitivity of about 795 nm/RIU (refractive index unit). Our results show that this process is accompanied by excitation of a sharp peak associated with an infrared lattice mode at about 1.62 μm, suggesting an abrupt refractive-index switching of the collective modes of the arrays. By depositing ultrathin layers of Si, we show that the wavelength of the 1 μm mode can be shifted, covering the whole telecom band ranges. We demonstrate that this can lead to tunable narrow- and wide-band polarization switching of the collective modes of the arrays within this range with a high extinction ratio.