Spontaneous Emission Enhancement of Fluorophore by Plasmonic Nanoantenna

Optical nanoantennas are very efficient for manipulating and controlling light. These nanoantennas support plasmonic oscillations and enhance the local field. This enhancement can be used in different applications. In this thesis, I have designed and fabricated metallic (plasmonic) nanodisks (NDs) array to enhance the emission of fluorescence dye molecules. For emission enhancement, a fluorescence dye (LDS750) with an emission band (emission peak 650 nm) close to plasmon resonance of plasmonic nanoantenna is selected. Localized surface plasmon resonance of NDs depends on the size, shape as well as dielectric properties of the materials. The plasmonic nanodisks are designed to observe their interaction with LDS750 dye in the range of 600-700 nm wavelength. The proper geometry of the nanodisks is designed to achieve plasmon resonance, which spectrally overlaps with the emission spectrum of LDS750. Diameter and period of the nanodisk array have been varied to find out the best spectral overlap. The effect of these parameters on the optical response has been investigated numerically and experimentally. Simulations are performed using the Finite-Difference Time-Domain (FDTD) method. The fabrication process of NDs is done by using electron beam lithography, electron beam evaporation process followed by development and lift-off. Investigated plasmonic NDs arrays are made of gold (Au) with periods of 360 nm, 400 nm and 440 nm while diameter range is in between 105-195 nm for each period. LDS750 fluorescence dye molecules are mixed with Ploymethyl methacrylate 2% solution in anisole (PMMA A2) as dielectric host medium. A layer of PMMA and LDS750 mix is added on top of the NDs to investigate the emission enhancement of LDS750. The numerical and experimental study of the NDs and LDS750 hybrid system, provide how the parameters of the plasmonic nanodisks such as diameter, period and substrate, play significant roles in the enhancement of the emission of LDS750 dye. The time-resolved fluorescence spectroscopy results and Fluorescence Lifetime Imaging (FLIM) results are strong evidence of emission enhancement of LDS750 dye in the presence of NDs. The interaction between the enhanced localize electric field of NDs and LDS750 modified the spontaneous emission by increasing the rate of LDS750 excitation. Consequently, the decay rate change of LDS750 due to the Purcell enhancement. The achieved results from this research would guide the design and fabricate plasmon hybrid system for practical applications

Spontaneous Emission Enhancement of Fluorophore by Plasmonic Nanoantenna

Optical nanoantennas are very efficient for manipulating and controlling light. These nanoantennas support plasmonic oscillations and enhance the local field. This enhancement can be used in different applications. In this thesis, I have designed and fabricated metallic (plasmonic) nanodisks (NDs) array to enhance the emission of fluorescence dye molecules. For emission enhancement, a fluorescence dye (LDS750) with an emission band (emission peak 650 nm) close to plasmon resonance of plasmonic nanoantenna is selected. Localized surface plasmon resonance of NDs depends on the size, shape as well as dielectric properties of the materials. The plasmonic nanodisks are designed to observe their interaction with LDS750 dye in the range of 600-700 nm wavelength. The proper geometry of the nanodisks is designed to achieve plasmon resonance, which spectrally overlaps with the emission spectrum of LDS750. Diameter and period of the nanodisk array have been varied to find out the best spectral overlap. The effect of these parameters on the optical response has been investigated numerically and experimentally. Simulations are performed using the Finite-Difference Time-Domain (FDTD) method. The fabrication process of NDs is done by using electron beam lithography, electron beam evaporation process followed by development and lift-off. Investigated plasmonic NDs arrays are made of gold (Au) with periods of 360 nm, 400 nm and 440 nm while diameter range is in between 105-195 nm for each period. LDS750 fluorescence dye molecules are mixed with Ploymethyl methacrylate 2% solution in anisole (PMMA A2) as dielectric host medium. A layer of PMMA and LDS750 mix is added on top of the NDs to investigate the emission enhancement of LDS750. The numerical and experimental study of the NDs and LDS750 hybrid system, provide how the parameters of the plasmonic nanodisks such as diameter, period and substrate, play significant roles in the enhancement of the emission of LDS750 dye. The time-resolved fluorescence spectroscopy results and Fluorescence Lifetime Imaging (FLIM) results are strong evidence of emission enhancement of LDS750 dye in the presence of NDs. The interaction between the enhanced localize electric field of NDs and LDS750 modified the spontaneous emission by increasing the rate of LDS750 excitation. Consequently, the decay rate change of LDS750 due to the Purcell enhancement. The achieved results from this research would guide the design and fabricate plasmon hybrid system for practical applications

Plasmon-modulated photoluminescence enhancement in hybrid plasmonic nano-antennas

In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. Our lithographically defined plasmonic nanodisks with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the coupled dye molecules. We show that the enhancement of the spontaneous emission rate arises from the superposition of three principal phenomena: (i) metal enhanced fluorescence, (ii) metal enhanced excitation and (iii) plasmon-modulated photoluminescence of the photoexcited nanostructures. Overall, the observed enhanced emission is attributed to the bi-directional near-field coupling of the fluorescent dye molecules to the localized plasmonic field of nano-antennas. We identify the role of exciton-plasmon coupling in the recombination rate of the sp-band electrons with d-band holes, resulting in the generation of particle plasmons. According to our comprehensive experimental analyses, the mismatch between the enhanced emission and the emission spectrum of the uncoupled dye molecules is attributed to the plasmon-modulated photoluminescence of the photoexcited hybrid plasmonic system.publishedVersionPeer reviewe

Controlling the plasmon resonance via epsilon-near-zero multilayer metamaterials

Localized plasmon resonance of a metal nanoantenna is determined by its size, shape and environment. Here, we diminish the size dependence by using multilayer metamaterials as epsilon-near-zero (ENZ) substrates. By means of the vanishing index of the substrate, we show that the spectral position of the plasmonic resonance becomes less sensitive to the characteristics of the plasmonic nanostructure and is controlled mostly by the substrate, and hence, it is pinned at a fixed narrow spectral range near the ENZ wavelength. Moreover, this plasmon wavelength can be adjusted by tuning the ENZ region of the substrate, for the same size nanodisk (ND) array. We also show that the difference in the phase of the scattered field by different size NDs at a certain distance is reduced when the substrate is changed to ENZ metamaterial. This provides effective control of the phase contribution of each nanostructure. Our results could be utilized to manipulate the resonance for advanced metasurfaces and plasmonic applications, especially when precise control of the plasmon resonance is required in flat optics designs. In addition, the pinning wavelength can be tuned optically, electrically and thermally by introducing active layers inside the hyperbolic metamaterial

Controlling the plasmon resonance via epsilon-near-zero multilayer metamaterials

Localized plasmon resonance of a metal nanoantenna is determined by its size, shape and environment. Here, we diminish the size dependence by using multilayer metamaterials as epsilon-near-zero (ENZ) substrates. By means of the vanishing index of the substrate, we show that the spectral position of the plasmonic resonance becomes less sensitive to the characteristics of the plasmonic nanostructure and is controlled mostly by the substrate, and hence, it is pinned at a fixed narrow spectral range near the ENZ wavelength. Moreover, this plasmon wavelength can be adjusted by tuning the ENZ region of the substrate, for the same size nanodisk (ND) array. We also show that the difference in the phase of the scattered field by different size NDs at a certain distance is reduced when the substrate is changed to ENZ metamaterial. This provides effective control of the phase contribution of each nanostructure. Our results could be utilized to manipulate the resonance for advanced metasurfaces and plasmonic applications, especially when precise control of the plasmon resonance is required in flat optics designs. In addition, the pinning wavelength can be tuned optically, electrically and thermally by introducing active layers inside the hyperbolic metamaterial.publishedVersionPeer reviewe