This PDF file contains the front matter associated with SPIE Proceedings Volume 11082, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Plasmon-induced hot electron transfer has attracted much attention as a novel strategy for the solar energy conversions. However, the solar energy conversion efficiency is limited by the insufficient absorption on monolayer of metallic nanoparticles. To solve this problem, in the present study, we apply the principle of strong coupling to plasmonic water splitting induced by the plasmon-excited electron transferring into wide-bandgap semiconductor on a Au nanoparticle (Au-NP)/TiO2 thin-film/Au-film (ATA) photoanode. Strong coupling between the Fabry-Pérot nanocavity mode of the TiO2 thin-film/Au-film and the localized surface plasmon mode of the Au-NPs is induced when their resonant frequencies overlap. To increase the coupling strength in this strong coupling regime, a key feature is partially inlaying of Au-NPs into the TiO2 nanocavity by several nanometers. Under a three-electrode system measurement with a saturated calomel electrode (SCE) as a reference electrode, a Pt wire as a counter electrode and an electrolyte of KOH (0.1 mol/dm3), we demonstrated that the action spectrum of incident photon to current conversion efficiency (IPCE) exhibited two bands, which almost corresponds to the absorption spectrum of ATA. The IPCE of ATA is extraordinarily enhanced as compared to that of Au-NPs/TiO2 photoanode. Most importantly, under the strong coupling regime, the internal quantum efficiency (IQE) of the photocurrent generation is also enhanced at the strong coupling wavelengths. The increase in IQE implies the possibility of increasing the generation of hot electrons due to the strong coupling. The plasmon-induced water splitting using a two-electrode system is also discussed.

Plasmonics has been studied and used for various optoelectronic applications include efficient light-emitting diodes (LEDs) [1]. Next important challenge is to develop device applications and to extend into wide wavelength regions [2]. Here, I present the new nanostructures and methods to tune the plasmonic resonances for wide wavelength range including deep UV. Recently, we observed unusual localized surface plasmon (LSP) resonance spectra that have a narrow bandwidth and high intensity by fabricating multilayered Ag nanoparticle sheet structures [3]. The peaks of the extinction spectra were clearly split into two peaks on metal substrates, while this phenomenon was not observed on a transparent substrate. This optical phenomenon should be due to the mode splitting effect by the strong coupling. The strong dipole oscillator located near the metal interface can interact with the mirror image of the dipole oscillator, which has the opposite phase. This presents a powerful and useful technique to tune the strong mode coupling effect without any lithographic structures. Quite recently, we also found the similar peak splitting and sharpened of the LSP spectra for random metal nano-hemispheres, fabricated by thermal annealing of metal thin layers, on metal substrates through thin SiO2 spacer layer. We call such structure nano-hemispheres on mirror (NHoM). The LSP spectra of Ag NHoM became much larger and sharper, and also tunable in UV to visible wavelength region by the spacer thickness of the structure. In order to extend this technique into deep UV region, we fabricated NHoM structures by using aluminum which has the LSP resonance in ultra-deep UV regions. We obtained very strong and sharp resonance peak due to the mode splitting effect by the strong coupling at 156 nm by the by the electromagnetic simulations. As far as we know, this is the LSP spectrum which has the shortest peak wavelength in ultra-deep-UV region. The similar LSP spectra in deep UV region were obtained by experiments and found to be well tunable by the thickness of the SiO2 spacers. I believe that our approaches using tunable plasmonics including Deep-UV region will bring high efficient plasmonic LEDs with practical use level and will develop future optic and photonic technologies for smart societies. [1] K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, A. Scherer, Nat. Mater. 3, 601 (2004). [2] K. Okamotoa, M. Funatob, Y. Kawakamib, K. Tamada, J. Photochem. Photobiol. C, 32, 58 (2017). [3] K. Okamoto, D. Tanaka, R. Degawa, X. Li, P. Wang, S. Ryuzaki, and K. Tamada, Sci. Rep. 6, 36165 (2016).

Light cone has been known for long time, where the frequency is linearly proportional to the inverse of wave length as the consequence of the absence of interaction between light and vacuum. In this talk, I will discuss that novel light cone can be created in a metamaterial with silicon spheres residing on sites of face-center-cubic (fcc) lattice. Intriguingly the linear frequency dispersion is realized over a loop in k space, which yields a nodal-line (NL) semimetal, one of the topological states attracting significant interest recently. Exploiting the topological property of NL, one can slow light significantly, which is yearned for important applications, including telecommunication, optic storage, information processing based on light, aperture radar and so on. We show that the symmetries of fcc lattice work harmonically to support the topological NL, rendering the mechanism applicable for many other systems, such as electrons and phonons.

Electron energy loss spectroscopy (EELS) studies in a scanning transmission electron microscope (STEM) have recently provided a new level of understanding for the operation of plasmonic cavity structures. One key feature of the technique is its ability to create very high spatial resolution maps of the local density of optical states (LDOS) in such cavities. In this presentation, I will discuss EELS studies of several active nanometallic cavity structures. Both electrical and nanomechanical control of plasmonic cavities will be illustrated.

Broad-area semiconductor lasers are widely used in high-power applications including material processing, large-scale display and laser surgery as well as pump sources for solid-state and fiber lasers. A serious problem of such lasers are their instabilities which cause spatio-temporal and spectral fluctuations of output beams. Such instabilities are rooted in the nonlinear interactions of multiple lasing modes and the gain medium. Much effort has been invested in stabilizing the broad-area semiconductor lasers by minimizing the number of lasing modes, but with limited success. We propose and demonstrate a different approach for stabilization via complex interference in wave-chaotic or disordered cavities that maintains multi-mode operation. Instead of suppressing the filaments via external signals, we disrupt the coherent nonlinear processes that lead to their formation by using cavities with complex spatial structure to create many propagating waves with random phases. The complex interference of these waves prevents the formation of self-organized structures such as filaments that are prone to modulational instabilities. We demonstrate the generality and robustness of this approach through experiments and numerical simulations with two different systems, (i) two-dimensional (2D) microcavities featuring chaotic ray dynamics and (ii) one-dimensional (1D) cavities with random fluctuations of the refractive index. The chaotic ray dynamics and the structural disorder are responsible for the creation of multi-wave interference effects, respectively. Our approach can suppress spatiotemporal instabilities in broad-area semiconductor lasers without while keeping multimode operation. It is applicable to other types of lasers such as solid-state lasers and fiber lasers.

Optical properties of a plasmonic metasurface made of a monolayer of gold nanoparticles in close proximity to an aluminum thin film were studied numerically and experimentally. Extinction spectra of the plasmonic metasurface were studied as functions of the thickness of a dielectric spacer between the monolayer of gold nanoparticles and the aluminum film in the visible wavelength range. The goal was to study the excitation of a collective surface plasmon resonance (SPR) mode and a gap plasmon mode as well as their dependence on the spacer thickness, nanoparticles spacing and their size. By using finite-difference-time-domain (FDTD) calculations we find that the SPR extinction peak first red-shifts and then splits into two peaks. The first extinction peak is associated with the collective SPR mode of the monolayer and it shifts to shorter wavelengths as the spacer layer decreases. As the spacer layer decreases from 35 nm to 7.5 nm, the second peak gradually appears in the extinction spectra of the metasurface. We assign the second peak to the gap mode. The gap mode first appears at around 620 nm or greater and it shifts to larger wavelength for larger nanoparticle spacing and size. The FDTD simulations are confirmed by an examination of the dispersion curves of a similar multilayer system. The computational results match the experimental results and confirm the excitation of the two modes.

In this work, surface plasmons (SPs) on germanium (Ge) thin film that are excited by cyclotron-motion electron bunch are investigated by finite-difference time-domain simulation. The excited SPs propagate along the electron’s circular orbital. (The electron energy is 30 keV. With the magnitude of external magnetic field being 3 T, the Larmor radius and cyclotron frequency are 200 um and 4.93E11 rad/s, respectively. The optical property of Ge is described by Drude model with the high-frequency dielectric constant, plasma frequency and collision frequency to be set as 16.55, 2.1627E13 and 2.746E11, respectively. And the frequency of SPs is 3 THz.) The dispersion relations of the SPs are obtained by simulation. When adding periodic Ge gratings on the Ge thin film along the electron’s circular orbital, the SPs-manipulated Smith-Purcell radiation (SPR) will emit with the frequency of electron excited SPs. Furthermore, the emitted radiation carries optical angular momentum (OAM) due to the propagation of SPs along the circular orbital. The simulated phase distributions of emitted radiations show spiral patterns, which demonstrates they have different topological charges.

Strong coupling between quantum emitters and cavities is of particular interest because of the potential application in quantum devices such as quantum gates and single photon sources. The quantum gate based on the strong coupling between a single atom and a cavity has been realized. The atoms based systems require precise control of the atoms which are difficult to be integrated and scaled up on a single chip. For the solid state system, strong coupling between a photonic crystal cavity and a single quantum dot has been demonstrated at cryogenic temperature. Recently, the plasmonic nanocavity provides a platform for strong coupling at the ambient temperature due to its extremely small mode volume. However, to precisely position a single emitter into a high field region of a plasmonic nanocavity is still challenging. In this work, a few fluorophores are embedded into a plasmonic nanocavity through the oligonucleotides. A plasmonic nanocavity consists of a functionalized nanoparticle and a metal film. Among 45 fluorophore-embedded nanocavities we measured, 20% of them show clear mode splitting. On the contrary, for the controls, none of the nanocavities shows mode splitting. We believe that some of the molecules have been strongly coupled to the plasmonic nanocavity. The EM simulation shows the mode volume is extremely small, which means only a few molecules can be located in the high field region. With the improvement of the molecule design, the deterministic strong coupling can be realized based on this configuration for quantum devices.

Hybrid nanoplasmonics is a recent and promising branch of research, that attempts to control the energy transfer between nano-emitters and surface plasmons. Colloidal quantum dots are good emitters due to their unique set of optical properties. In our work, quantum dots were excited in close proximity to a silver nanowire and the quantum dot emission was transferred into guided propagating nanowire surface plasmons (SPs) that were scattered at the nanowire end. Compared with metallic nanoparticles, silver nanowires enable the propagation of SPs in a well-defined direction along the nanowire axis, allowing for long-distance energy transfer between the nano-emitter and a specific nanowire point of interest. The challenge related to this promising hybrid system is to control the position of quantum dots on the nanowire. Our approach of nano-emitters positioning is based on two-photon photopolymerization of a photosensitive material containing quantum dots. This approach allows one to use light for positioning the quantum dots on the plasmonic nanosystem in a controlled manner. We report on a new controlled hybrid plasmonic nanoemitter based on coupling between quantum dots and propagating surface plasmons that are supported by silver nanowires, considered as surface plasmons resonators and observed through their scattering at the nanowire ends. A parametric study of the distance between the quantum dots and the nanowire extremity shows that precise control of the position of the launching sites enables control of light intensity at the wire end, through surface plasmon propagation length. This new approach is promising to produce efficient acceptor-donor hybrid nano-systems.

The strong interest in solar energy motivates the scientific community to improve the energy conversion efficiency of solar panels (SPs). Indeed, the implementation of plasmonic nanoparticles (NPs) in SPs can enhance the absorption coefficient due to the well-known localized surface plasmons resonances (LSPR) and then increase SP efficiency. However, the silicon-based SPs do not absorb the solar radiation above 1000 nm wavelengths. One of the solutions is to use an enhancement of up-conversion photoluminescence (PL) coupled with a plasmonic NP [1]. Shortly, a fluorophore absorbing several photons simultaneously in the IR exhibits emission in the range of the silicon absorption band and this process can be enhanced by plasmonics. Recently, it has been shown that 170 nm-diameter single gold nanocylinders (GNCs) have multi-resonant characteristics [2]. In this work, we report on the simultaneous excitation and emission enhancements of quantum dots up-conversion PL (two-photon photoluminescence (TPPL)) assisted by dipolar and quadrupolar modes of a single GNC. Indeed, the use of radial and linear polarizations allows us to obtain singly or doubly enhanced TPPL respectively. We show that double resonantly enhanced up-conversion can be higher by 4-7 times than single resonant up-conversion. References [1] J.G. Smith, J.A. Faucheaux, P. K. Jain, "Plasmon resonances for solar energy harvesting: A mechanistic outlook," Nano Today, 10, 67-80 (2015). [2] A. Movsesyan, A.-L. Baudrion, P.-M. Adam, "Revealing the hidden modes of a gold nanocylinder, " Journal of Phys. Chem. C, 122(41), 23651-23658 (2018).

Research in nanophotonic materials and design is yielding advances that are opening conceptually new paths to the realization of metasurfaces consisting of tunable nanoantenna arrays. These tunable metasurfaces can enable dynamic, active control of all of the key constitutive properties of light – amplitude, phase, wavevector and polarization – opening new applications such as phased-array optical beam steering, reconfigurable flat optics, visible light modulation for communication and thermal radiation management.

The optical response of epsilon-near-zero (ENZ) materials has been a topic of significant interest in the last few years as the electromagnetic field inside media with near-zero permittivity has been shown to exhibit unique optical properties, including strong electromagnetic wave confinement, non-reciprocal magneto-optical effects, and abnormal nonlinearity. These ultrathin ENZ materials are promising for the enhancement of quantum emission for optical sensing and enhanced absorption/emittivity for energy harvesting. This talk will review our recent development on a gate-tunable conducting oxide epsilon-near-zero meta-structures. I will present our recent development on the use of gate-tunable materials, transparent conducting oxides, to demonstrate an electrically tunable ultrathin ENZ perfect absorber enabled by the excitation of ENZ mode. In addition, I will present the active control of emissive properties of quantum emitters and enhanced optical nonlinearity in hybrid ENZ-plasmonic heterostructures.

Topological photonics offers remarkable solutions to robust light propagation and coupling. Two challenges can be identified: (1) making topological structures reconfigurable, and (2) shrinking them to nanoscale. I will discuss a platform that addresses both challenges: a valley plasmonic crystal for graphene surface plasmons. We demonstrate that a designer metagate, placed within a few nanometers of graphene, can be used to impose a periodic Fermi energy landscape on graphene. For specific metagate geometries and bias voltages, the combined metagategraphene structure is shown to produce complete propagation band gaps for the plasmons, and to impart them with nontrivial valley-linked topological properties. Sharply curved domain walls between differently patterned metagates are shown to guide highly localized plasmons without any reflections owing to suppressed intervalley scattering.

The development of laser miniaturizing is never stop; several kinds of approaches such as microdisk lasers and nanowire lasers, have been exploited to scale down the sizes of cavity by using surface plasmons in replacement of photonic resonance in the laser cavity. Graphene is a membrane with thickness of only one atom and the carrier mobility can be as high as about 15000 cm² /Vꞏs. Until now graphene has been widely used for many optoelectronics applications, for example, ultrafast photodetector, modulator, biosensor, transparent electrode and so on. As far as plasmonic laser is concerned, since the insulator layer on the metal structure is required to be very thin, it seems to be feasible to add a single-layered graphene in between the nanowire and metal while preserving the capability of forming surface plasmon polariton (SPP). Besides, we would like to take advantage of good electrical property of graphene to make a plasmonic nanolaser which can be modulated by externally applied current. By adding graphene on the insulator can form a versatile platform, called graphene-insulator-metal (GIM) structure, that can modulate the plasmonic wave characteristics. In this study, we successfully fabricated and demonstrated the SPP nanolaser on GIM structure. The lasing threshold of ZnO nanowire on aluminum with graphene was lower than that without graphene. It was attributed to the changes of plasmon frequency of metal resulting from the induced electrons or holes by graphene.

We take advantage of the recent advances in terahertz-nano technology to study quantum scale light-matter interaction. Terahertz waves can be squeezed down to extreme aspect ratio nanogaps which are composed of metal-insulator-metal barriers. Noble metals such as gold or silver can serve as good conductors at this terahertz frequencies, and the electric field intensity inside the metallic nanogaps can be orders of magnitudes larger than the incident one. Cross sections of molecules can be hugely enhanced and the probing depth decrease dramatically. As the gap size decreases down to the nanometer regime, quantum mechanical effects such as electron tunneling across the nanogaps are almost inevitable, rendering different dielectric constants to the gap material than that without tunneling. These efforts originated from the nearly perfect transmission through terahertz slot antennas with tens of microns of feature sizes, together with its nanometer-sized counterparts. In this work, we will discuss our recent results of extreme terahertz phenomena on plasmonic nanoantenna structures. On the one hand, we demonstrate ultrafast control of tunneling currents using macroscopic loops of terahertz antenna. Light-field induced surface currents projects upon the barrier loops fabricated on a metallic film, spatiotemporally changing the local electric potentials. The total tunneling currents flowing through the loops are critically affected by the symmetry of the loop, enabling ultrafast full-wave rectification of electromagnetic waves in sub-picosecond scale. On the other hand, we demonstrate our terahertz nanoresonator can support nearly up to 70 % absorption of incident terahertz radiation by direct Ohmic loss in metal at this long wavelength limit, breaking the good conductor approximation which is generally considered in terahertz frequency.

Light incident on nanoscale metal-insulator-metal (MIM) plasmonic gratings generates surface plasmon polaritons (SPPs) which resonate and propagate within the grating structure. The SPP resonant wavelength can be altered by introducing a gradient in the width of the MIM grooves. Specifically, a symmetrically graded grating with a narrow central groove leads to a gradient in the effective refractive index such that the index increases in the direction of the central groove. This index gradient guides non-localized SPP waves towards the grating center. This waveguiding of SPPs along with localized SPP modes within the narrow central grooves give rise to multi-wavelength electric field enhancement at the grating center. SPP coupling across the grooves leads to an increase in electromagnetic field strength with decreasing groove width. However, standard nanofabrication techniques limit the minimum width of the grooves to approximately 50nm, preventing maximum field enhancement. Herein we report on the development of a novel nanoplasmonic graded grating with a 10 nm central groove flanked by increasingly wider grooves on either side, which are fabricated using thin film RF magnetron sputter deposition technique. These structures are studied using COMSOL Multiphysics modelling in which we vary the groove width, groove separation and groove depth, and thus demonstrate localization of broadband incident light. Raman spectroscopy and fluorescence microscopy are used to demonstrate field enhancement at several visible wavelengths.

All practical plasmonic metals suffer from inherent ohmic losses that naturally increase the temperature of resonantly excited plasmonic components. For instance, the operation temperature of plasmonic near-field transducers in heat assisted magnetic recording (HAMR) is estimated to be close to 300 - 500 0C. It is therefore imperative to understand the influence of temperature on the evolution of optical properties of thin metals films to perform systematic and rational design of practical high temperature nanophotonic components in a wide variety of research areas, including HAMR, photothermal therapy, thermophotovoltaics, and near field radiative heat transfer. In this talk, we will present the experimentally probed temperature induced deviations to the optical response of important plasmonic metals: gold, silver and titanium nitride up to 900 0C, and outline the dominant microscopic physical mechanisms governing the optical response. Using extensive numerical calculations, we demonstrate the importance of incorporating the temperature induced deviations into numerical models for accurate multiphysics modeling of practical high temperature nanophotonic applications - transducers for HAMR, broadband emitters for thermophotovoltaics and high temperature sensors.

We experimentally investigated the oscillation of the water vapor microbubble generated in degassed water using thermoplasmonic effect. A CW laser was focused on a gold nanoisland film to realize localized thermoplasmonic heating of the degassed water and subsequent generation of a water vapor microbubble. The generated bubble was found to be oscillating at 0.5{1 MHz although the laser power was constant. When the laser spot size, namely, the heating spot size, was fixed to 2.7 μm, the bubble diameter and the oscillation frequency was almost independent on the laser power. On the other hand, the bubble size significantly increased as the laser spot size increases from 2.8 to 3.7 μm. Besides, the oscillation frequency decreased as the bubble size increased, which was the same order of magnitude as the bubble resonance frequency. These results suggest that the behavior of the water vapor microbubble is highly dependent on the outmost region of the laser spot, to which the bubble contacts periodically.

We report the plasmonic photoelectric conversion phenomenon acquired by plasmons of metal nanostructures. The photoelectric conversion device consists of plasmonic atoms and a thin film of thermoelectric material. We detected electric current flowing the thermoelectric material when plasmons of the nanostructure are excited. This photoelectric conversion is attributed to the plasmonic local heat induced by plasmons. The plasmonic local heat propagated to the surrounding thermoelectric film, resulting in a thermal gradient which generate electric currents via Seebeck effect. In addition, we observed that the plasmonic nanohole arrays without thermoelectric materials also exhibit photoelectric conversion. Its photoelectric conversion efficiency was 0.0015%. In this paper, we discussed the wavelength dependencies and conversion efficiencies of the plasmonic photoelectric conversion. Moreover, we calculated the theoretical thermal degrees of the plasmonic local heat in order to discuss the plasmonic local heat propagation and dissipation.

Plasmonic nanostructures, with their unique ability to localize electromagnetic fields into nanoscale volumes to create the so-called hot spots, have been widely studied for the enhancement of nonlinear conversion. Various nonlinear optical processes such second-harmonic generation (SHG), third-harmonic generation, or four-wave mixing have been observed in different designed configurations. The SHG process is known to be forbidden in centrosymmetric nanostructures. Thanks to the broken centro-symmetry at the metal surface as well as to the high degree of the asymmetric spatial variation of the inducing electromagnetic fields, strong SHG in noble metals is experimentally observed via properly design. In this work, we studied the SHG of vertical and planar split ring resonator (SRR) arrays. Via a unique nanofabrication technique, we are able to accurately control the alignment of nano-structures on top of each other and experimentally realize vertical split ring resonators (VSRRs). As VSRRs allow the coupling of both the incident electric and magnetic field to the excitation of magnetic dipole resonance, the induced strong fields confined within two vertical prongs are beneficial for the SHG enhancement. In addition, a better field confinement is achieved for vertical configurations since the localized fields in the planar SRR gaps are inevitably leaked to the underlying substrate. The nonlinear optical measurements showed a 2.6-fold enhancement of SHG nonlinearity for VSRR metasurface compared to their planar counterparts. Through the analysis of multipole decomposition, we found that except for electric dipole, the dominant mode for VSRRs is electric quadrupolar resonance, while that for planar SRRs is magnetic dipole. This work paves the way in increasing the nonlinear transition quantum efficiency and provides a new insight in designing novel nonlinear sources.

Polarization is one of the most important properties of light, which is also a typical dimension for light field manipulation. With specially designed meta-atoms and tailorable phase distribution, metasurfaces have been employed to achieve arbitrary polarization state in linear regime. Moreover, metasurface is also a platform for various nonlinear light generation, which can be used to realize an integrated polarized light source combined with its powerful capability of polarization manipulation. Here, we demonstrate a nonlinear plasmonic metasurface that is able to simultaneously realize nonlinear light generation and polarization manipulation. Split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) rotated by 90 degrees are selected to generate orthogonal polarizations of second harmonic (SH) components under the same linear polarized fundamental wave (FW), respectively. Phase difference and amplitude ratio between SH components can be tailored by adjusting the arm length of SRRs and CSRRs. By introducing spatial offset between adjacent basic supercells, we can achieve phase difference between two orthogonal components and thus realize polarization control of output SH emission and beam splitting at the same time. Two separated SH beams with orthogonal circular polarizations are achieved from a linearly polarized FW, and illuminated by circularly polarized FW, the same nonlinear plasmonic metasurface can generate linearly polarized SH, which can be viewed as a SH quarter-wave plate. Furthermore, arbitrary elliptical polarized SH can also be obtained from properly designed nonlinear metasurfaces. Our design provides a new approach for miniaturized light source for special polarization requirement, which may have potential applications in integrated optics.

We present second harmonic generations (SHG) of NLO polymers grown on Ag thin films at surface plasmon polariton (SPP) resonances. The Ag film itself exhibits surface nonlinear susceptibility and it is enhanced at the SP resonances. Our experimental results demonstrated that growing the NLO polymer layers on the Ag films was useful for further amplifying the conversion efficiencies of the SP-enhanced SHG. There was optimal polymer thickness for the SHG conversions, and approximately 40-fold maximum amplification was gained. The dependency of the SHG conversions on the polymer thickness was explained in terms of the bulk nonlinearities and the multiple reflections inside the polymer layer.

The optical responses of metal nanoparticles are associated with their localized surface-plasmon resonances. Such resonances give rise to strong local fields near the particles, which are particularly advantageous for nonlinear interactions. Here, we present an overview of our results on second-harmonic generation (SHG) from metasurfaces consisting of metal nanoparticles and discuss factors that affect its efficiency. Our metasurfaces consist mainly of ordered arrays of nanoparticles. L or T shaped particle appear non-centrosymmetric also at normal incidence, a requirement for SHG. The quality of the particles is crucial for homogeneous plasmon resonances and high overall SHG efficiency. Beyond this, subtle details of sample structure strongly influence the response. Furthermore, the response from SHG-active non-centrosymmetric particles can be enhanced by SHG-passive centrosymmetric particles. Both effects arise from lattice interactions between the members of the array. By extending these concepts further, we have shown the importance of surface lattice resonances for SHG efficiency, allowing the response to be enhanced even for reduced particle density. The nonlinear responses are assumed to depend mainly on the resonance at the fundamental wavelength. However, this is not sufficient as such, because the details of the local-field distributions, which are closely associated with particle geometry, are also crucial. We have also extended our work to random metal nanoisland films, where a dielectric overlayer shifts the plasmon resonance away from the resonance at the SHG wavelength. Rather surprisingly, the SHG response is enhanced because of strongly enhanced local fields at the fundamental wavelength as the dielectric loading is increased.

Plasmonics that utilizes the interaction of light with charged particles, such as electrons in metals, has been an area of interest for decades. As the dimensions of the plasmonic device have been shrunk into the nanoscale, the quantum confinement effects need to be considered within such small devices. Here, we choose the ultra-thin metallic film to study the quantum confinement effect on the nonlinear properties. Due to the quantum confinement, fruitful intersubband transitions (ISBT) exist in this metallic quantum well (MQW). The dipole transition elements associated to these ISBT are on the order of enanometer, which is much larger than those of the traditional nonlinear crystals. Therefore, giant third-order nonlinearity has been achieved in the 3 nm Au quantum well. The χ(3) reaches up to (0.49 + 2.0i) × 10-15 m2V-2, which is almost four-order of magnitude higher than the case of the bulk film. Furthermore, by using epitaxial-growth method of the TiN/Al2O3 heterostructures, coupled MQW (cMQW) has been utilized to support the large second-order susceptibility up to 1500 pm/V. With such ultrahigh nonlinearities and atomic-flat quality of the TiN MQW, TiN/Al2O3 heterostructures based hyperbolic metamaterials has been implemented for the applications of the pulse limiter. In addition, when combined with the nano-photonic waveguides, such as photonic crystals, on-chip super-continuum light sources and/or frequency comb can be realized. Last but not least, due to the ultrafast response of both χ(2) and χ(3), tunable metasurface and/or on-chip optical modulators with exceptional performance are on the horizon. Implementing the MQW opens a new regime for engineering extraordinary optical nonlinearities and novel applications.

The development of plasmonic metasurface-based optical structures requires alternative, high-performance plasmonic materials, in replacement of commonly used noble metals. Ideally, plasmonic materials should have the properties of low-cost, low-loss, high chemical, mechanical, and thermal stabilities, biocompatibility, spectral tunability, as well as integrability with existing semiconductor technologies. Recently, we have developed epitaxial growth techniques for forming smooth, single-crystalline aluminum and titanium nitride films on transparent sapphire substrates using nitrogen-plasma-assisted molecular-beam epitaxy. In comparison to silver and gold, aluminum- and titanium-nitride-based plasmonics have better stabilities and spectral responses in the ultraviolet and visible spectral regions, making them particular suitable for ultraviolet surface-enhanced surface Raman spectroscopy (UV-SERS), optical energy harvesting, and metamaterial-based linear and nonlinear optics. In this talk, I will present our recent experimental results in these areas. References: (1) C.-Y. Wang, H.-Y. Chen, L. Sun, W.-L. Chen, Y.-M. Chang, H. Ahn, X. Li, S. Gwo, Nat. Commun. 2015, 6, 7734. (2) S. Gwo, H.-Y. Chen, M.-H. Lin, L. Sun, X. Li, Chem. Soc. Rev. 2016, 45, 5672–5716. (3) F. Cheng, P.-H. Su, J. Choi, S. Gwo, X. Li, C.-K. Shih, ACS Nano 2016, 10, 9852–9860. (4) C.-W. Cheng, Y.-J. Liao, C.-Y. Liu, B.-H. Wu, S. S. Raja, C.-Y. Wang, X. Li, C.-K. Shih, L.-J. Chen, S. Gwo, ACS Photonics, 2018, 5, 2624–2630. (5) W.-P. Guo, R. Mishra, C.-W. Cheng, B.-H. Wu, L.-J. Chen, M.-T. Lin, S. Gwo, 2019, manuscript in preparation.

Conventional precision nanofabrication method, such as electron-beam lithography or focused-ion beam milling, can be used to fabrication of two-dimensional (2D) nanostructures. These 2D nanostructures, which are now referred as “metasurfaces”, have shown interesting optical properties and are intensely studied by researchers around the world in recent years. There are several phenomena, however, only exist in a 3D nanostructures. It is highly desirable to be able to overcome the obstacles to fabricate 3D nanostructures, which will possible open new applications for Plasmonics. In this study, nanofabrication of various 3D nanostructures using a method combining Nanospherical-Lens Lithography and Hole Mask Lithograph will be demonstrated. The fabricated nanostructures would cover large-area and fabricated with high-throughput. The fabricated nanostructures can be made from various materials that can be evaporated. Nanostructures made from plasmonic metal, including Au, Ag and Al can be used for plasmonic applications. We will present several 3D nanostructures that can be fabricated using the proposed method. Several applications that take advantage of the fabricated nanostructures will also be introduced.

The chiral interaction between transverse optical spin and circularly polarized emitters provides a novel way to manipulate spin information at the nanoscale. Here, we demonstrate the valley (spin)-dependent directional emission of transition metal chalcogenides (TMDs) into plasmonic eigenstates of a silver nanowire. Due to the spin-path locking of the plasmonic eigenstates, the emission from the two different valleys of TMDs material will couple to the guided modes propagating in opposite directions. The high valley polarization of TMDs and high density of the transverse optical spin of the plasmonic wire together offer a novel platform for a chiral network even at room temperature without any magnetic fields. S.-H. Gong, F. Alpeggiani, B. Sciacca, E.C. Garnett and L. Kuipers, Nanoscale chiral valley-photon interface through optical spin-orbit coupling, Science 359, 443-447 (2018)

We present a novel plasmonic sensor configuration that allows the discrimination of chiral molecules. The sensor consists of handed gold nanostructures of gammadion shape, distributed in a racemic (50/50 mixture) matrix with C4 symmetry. Its optical response enhances the interaction with molecules thus circular dichroism can be measured in the visible range. The bare sensors exhibit a flat CD signal, providing background-free CD measurements for molecular detection. We have used a chiral molecular model based on L-, D-, and the racemic mixture of phenylalanine, which allows us to evaluate the opposite chiral effects while having a reference system. Additionally, we have used molecular thermal evaporation technique to deposit a dense molecular layer on top of the sensors in a controllable and reproducible way. Our results show the discrimination of phenylalanine enantiomers through positive or negative peaks while the racemic mixture shows a flat signal. In addition, we present preliminary results that show that this approach is also suitable for microfluidics systems with a much lower density of chiral molecules.

Gene expression monitoring within whole plants is critical for many applications ranging from plant biology to biofuel development. Herein, we report a unique multimodal method for in vivo imaging and biosensing of nucleic acid biotargets, specifically microRNA, within whole plant leaves by integrating three complementary techniques: surface-enhanced Raman scattering (SERS), X-ray fluorescence (XRF), and plasmonics-enhanced two-photon luminescence (TPL). The method described utilizes plasmonic nanostar-based inverse molecular sentinel (iMS) nanoprobes, which not only provide large Raman signal enhancement upon target binding, but also allow for localization and quantification by XRF and plasmonics-enhanced TPL. This report lays the foundation for the use of plasmonic nanoprobes for in vivo functional imaging of nucleic acid biotargets in whole plants.

Here we report on the interplay between the magnetic, optical and magneto-optical properties of magnetoplasmonic crystals (MPC) based on the 1D diffraction gratings. A wide range of the characteristic parameters is examined to be effective for magnetic field sensor application. The gratings with periods of 320 nm and 740 nm with corresponding profile heights of 20 nm and 100 nm were used. Using ion-beam sputtering the diffraction gratings were covered by combination of following functional layers: noble metal - silver or gold with thicknesses of 50 or 100 nm; ferromagnetic metal - iron, silver, permalloy with thicknesses of 5, 20, 50, 100 nm; passivation layer of silica nitride with thicknesses of 20, 30 or 40 nm. The details of fabrication and characterization of magnetoplasmonic crystals will be discussed. We show how the 1D MPC can operate as highly sensitive and local sensor of DC magnetic field by utilizing the magneto-modulation sensor technique combined with the magneto-optical probes. As a result, the design of sensor prototype was optimized and the achieved sensitivity was found to be up to 10 μOe at a local area of 1 mm2. The main contribution to effect of MPC design on sensor parameters is geometry-driven magnetic properties formed during fabrication and depended on characteristic parameters of MPC. The developed sensor has sensitivity suitable for in biomedical applications and can be further improved by optimizing the sensing element and the sensor’s setup overall design.

Our recent exploration of pulsed molecular optomechanics in plasmonic nanocavities shows unexpected and unusual nonlinear effects. Extreme plasmonic nanocavities are created by placing spherical Au nanoparticles above a gold planar mirror, forming Nanoparticle-on-Mirror (NPoM) constructs. Depositing a self-assembled molecular layer under the Au nanoparticles ensures placement of these molecules inside the high-field mode. We perform power-dependent ps SERS measurements with on- and off- resonant pump conditions for several molecular systems including biphenyl-4-thiol (BPT) and p-terphenyl thiol (TPDT). Key results are the reversible nonlinear saturation of emission from the anharmonicity of this optomechanical molecular system. Our earlier work showed the superlinear antiStokes emission [1], and more recently superlinear Stokes emission is also observed [2], arising from the driven vibrational dynamics. In our new data we identify several new power-dependent dynamics. One is the irreversible reconfiguration of the molecular and atomic-scale Au morphologies, which in the ultrasmall volume nanocavities here is inevitable. We correlate these effects with the instantaneous effective temperature of the molecules and compare this to that of the electrons in the surrounding NPoM structure. The second new effect is a reversible saturation which comes from the anharmonicity of the vibrations, and again is only seen in such tightly coupled nanocavities. These experiments reveal the complexity of molecular-light interactions in extreme nano-optics and open up new ways to treat molecules as optomechanical systems that can be used in device configurations. [1] Single-molecule optomechanics in picocavities, Science 354, 726 (2016) [2] Pulsed molecular optomechanics in plasmonic nanocavities, PRX 8, 011016 (2018)

In this work, we have designed and fabricated an array of plasmonic nano-ellipse that interacts with different types of QEs in the visible range of wavelength. The proper geometry of our design provides such absorption-reflection properties which spectrally overlap with the emission spectrum of the QE. Alongside such spectral overlap, a thin layer of the dielectric layer between the plasmonic structures and a gain medium provides the possibility of spatial overlap. The interaction between the strong subwavelength localized field at the edges of the gold nano-ellipses and QEs, enhances Purcell factor towards the modification of the fluorescence and decay time of QEs. This approach allows enhanced emission from different emitters embedded in hybrid quantum systems. In this work, we study the energy transfer between the fluorescent dye molecules and CdSe/ZnS hydrophobic QDs with the array of plasmonic nano-ellipses.

While availability of nanoscale fabrication tools has uncovered a rich area of physical phenomena with applications including sensing, energy, and imaging - scalable nanomanufacturing techniques allowing for technological impact still remain elusive. Self-assembly of nanoarchitectured systems, with control on atomic and molecular length scales, not only hold promise for device fabrication but offer new functionality for probing and interacting with molecular systems. For example, understanding hierarchical driving forces in assembly of nanospheres from colloid enables arranging 2D ‘metamolecule’ building blocks where the geometry of resultant oligomers, gap spacing, and dielectric environment provide additional degrees of freedom for tuning electromagnetic response. I will present metasurface geometries exhibiting magnetic fields at optical frequency and billon-fold electric field enhancements in nanogaps. The reproducibility offered by controlling nanogap spacing with chemical crosslinkers allows for acquisition of large data sets needed for machine learning analysis. Our group has recently demonstrated that plasmonic nanoantennas enhance surface enhanced Raman scattering (SERS) signals sufficiently for continuously monitoring metabolites produced by bacteria. Multivariate statistical analysis of SERS data from nanogaps incorporated in microfluidic devices shows bacterial metabolite concentration can be quantified across five orders of magnitude and detected in supernatant from Pseudomonas aeruginosa cultures as early as three hours after innoculation. Bacteria exposed to a bactericidal antibiotic were differentially less susceptible after 10 h of growth, indicating that these devices may be useful for early intervention of bacterial infections. Analysis with artificial neural networks pushes quantification down to the femtomolar regime offering the promise of quantification down to the single molecule limit. We will also show results demonstrating the ability to discriminate antibiotic resistance to rifampicin and susceptibility to carbenicillin in Psuedomonas Aeruginosa through SERS analysis of metabolites in cellular lysate. Discrimination accuracies greater than 99% are achieved using big data machine learning techniques like convolutional neural networks. Yet these techniques require large quantities of labeled data, which is extraordinarily expensive to acquire for medical diagnostics due to the need for experts to culture and analyse bacterial samples. Thus we have also introduced few shot and semi-supervised machine learning techniques in the analysis of SERS spectra to greatly reduce the amount of labeled data. We have demonstrated an increase in one shot classification of over 10% through the use of a semi-supervised variational autoencoder and a spike timing plasticity dependent model designed for few shot learning. These results demonstrate that SERS is a fast, accurate, and facile method for identification of pathogenic states by analysis of unknown metabolites. The ability of clinicians to quickly determine the susceptibility of an infection to antibiotic therapy is critical to limit the spread of antibiotic resistant bacterial strains.

In fluorescence microscopy, the upright microscope mounting a Xe lamp, fluorescent filter units including Cy5, GFP, and that composed of Cy3-excitation filter (λ = 535 ± 25 nm), Cy5-dichroic mirror (cutoff wavelength: 660 nm), Cy5-emission filter (λ = 700 ± 30 nm), and imaging cameras, was used. In cell imaging, two-color sensitive images of breast cancer cells were observed with a Bull’s eye-plasmonic chip with 480 nm-pitch. The fluorescence intensity in the Bull’s eye type was larger than those in the line & space pattern and hole array pattern under the microscope. On the plasmonic chip, EpCAM and EGFR in breast cancer cells were detected by 7-fold brighter fluorescence compared with those on the glass slide. In VSD imaging, action potential corresponding to spiking changes of membrane potential of neurons was observed with VSD. Rat hippocampal neurons were cultured in plasmonic-chips and glass-bottomed dishes and neurons were labeled with di-4 ANEPPDHQ. The frame rate for fluorescence images was 1ms, and the action potential was directly measured. Spikes of VSD signals were frequently detected on the plasmonic chip compared with glass-bottomed dish.

The optical properties in visible – near infrared range of Pd nano-hole arrays (PNA) and Pd thin films under hydrogen absorption – desorption processes have been investigated. The PNA samples show plasmonic resonances with about three times more transmission than that of the Pd thin film samples with a similar thickness. Remarkably, due to the plasmonic effect the PNA samples exhibit two times larger transmission change, normalized to the Pd cover area, under the hydrogen absorption/desorption processes at the Wood’s anomaly positions. The PNA sample can be used as a hydrogen sensor that has a better signal-to-noise ratio than the one based on the corresponding Pd thin film. The experimental results are confirmed by the finite-difference time domain (FDTD) calculations.

Tunable quality factors (Q-factor) in topological photonics devices have gathered great attention in recent years. The devices with high-refractive-index (HRI) dielectric metasurfaces or non-symmetric nano-photonics devices have demonstrated the concept of bound states in the continuum, which allow the ultra-sharp resonance and extreme large Q-factor. By controlling the structures, the quality factor of resonance would be tunable. Ker-Ker effects, coupled mode theories, and symetric proteced semi bound states in the continuum will be presentated. The effect could be applied in advance design in narrow-band filters, sensors, photodetectors, etc.

Nanogap optical antennas enable enhancement of light-matter interactions owing to their great field enhancement. Interesting properties have been studied over recent years, such as high-order harmonics generation, electrically driven absorption, optical rectification and nonlinear tunnelling effect. However, as the gap size is shrunk down to the nanometer scale, losses dramatically increase and coupling efficiency of antenna with free-space decreases. This work reports conditions of perfect coupling, also called critical coupling, between a periodic array of nanogap metal-insulator-metal (MIM) antennas and free-space. We demonstrate that critical coupling is still achievable, even for the thinnest gaps.

Metal nanostructures can favorably change the properties of fluorescent molecules, increasing quantum yield, excitation and emission rates in a process known as plasmon enhanced fluorescence (PEF). Interactions between the nanostructures and fluorescent molecules can be described by three PEF mechanisms; near-field enhancement (NFE), resonance energy transfer (RET) and radiative decay engineering (RDE). The effect of these mechanisms on fluorescence is distance dependent, with enhancement occurring for distances greater the ~5nm and quenching of the signal when the fluorescent molecule is in close proximity to the nanostructure. This work focusses on the near-field enhancements associated with a gold nanorod array surface to determine a suitable setup for PEF applications. Using a finite element method (FEM) model, various nanorod array setups were simulated and the resonance and maximum field enhancements, E/E0 determined for each. Field enhancements occurred at different wavelengths than resonance as the enhancement was dominated by the existence of hot-spots. The maximum field enhancement of 7.88 occurred for an array of nanorods with 50nm diameter, 150nm height and center-to-center spacing of 60nm. The enhancement was due to hot-spots within the narrow gaps between nanorods, therefore this setup was not experimentally as fluorescent molecules would be unable to fit into the gaps. Nanorods with 50nm diameter and 100nm height in an array with 100nm periodicity provided an alternative setup, with maximum field enhancement of 6.37 due to a hot-spot at the top of the nanorod. Analysis showed that the field enhancement decreased rapidly with distance from the surface, but remained sufficiently strong for PEF applications.

Here the engineering of anisotropic plasmonic metasurfaces in the form of nanostripes or nanostripe dimers is demonstrated by a novel self-organization technique. Subwavelength quasi-1D glass templates are fabricated over large (cm2) area by ion beam induced wrinkling, enabling the maskless confinement of out-of-plane tilted gold nanostripe arrays supporting localized plasmon resonances easily tunable from the Visible to the Near-Infrared spectrum. A multi-step variant of the method allows to achieve plasmon hybridization in Au-silica-Au nanostrip dimer arrays with excitation of plasmonic electric dipole and magnetic dipole mode featuring strong subradiant near-field enhancement. The selforganized method enables to tune the hybridized plasmonic mode in the Visible and Near-Infrared spectrum opening the possibility to exploit these templates in highly sensitive biosensing and/or nonlinear optical spectroscopies.

Atomically terminated plasmonic tips effectively focus light on the Å scale, opening the atomistic limit in optical microscopy. Seeing an atom, a single chemical bond, imaging the vibrational normal modes inside one molecule, and seeing sound and imaging with atomically confined phonons are among the recent observations made in our laboratory, under the rubric of tip-enhanced Raman spectromicroscopy (TER-sm). I will use these examples to highlight the unusual properties of pico-plasmonics and develop optics in the atomistic near-field in terms of confined charge, field, light, and photon. There is much to be seen and manipulated on the Å-scale.

The propagation of the surface plasmon-polariton (SPP) waves guided by an interface of a metal and a reciprocal, uniaxially chiral, bianisotropic material were studied. The wavenumbers and the spatial profiles of the SPP waves were computed when the waves were guided by the interface perpendicular to the direction of the chirality. When the chirality parameter was negligible, the SPP waves were p polarized. When the chirality parameter was large, the SPP waves were neither p nor s polarized. The solutions of the dispersion equation were found only when the chirality parameter was complex and the real part was smaller than a threshold value.

In this paper, we theoretically design a nanostructure combined bowtie nanoantenna with V-structured hole, which offers a way to increase the ability of the nanostructure to enhance the optical near field. This nanostructure is designed to both limit the incident light in the nanoscale and produce large near-field enhancement. In addition, we study the effect of the geometric parameters of the bowtie nanoantenna with V-structured hole on the enhancement. Such structure will be beneficial to the focusing and collimating capabilities of integrated lens antennas.

We present a theoretical and experimental study of a nanostructured guided-mode resonant (GMR) spectral filter operating in the long-wave infrared (LWIR) wavelength range. The component is made of III-V semiconductors: heavily n-doped InAsSb for the grating and GaSb for the waveguide of the GMR resonator. Angular and temperature dependencies are also presented with the relative experimental setups.

In this paper, a composite grating with nanogaps was designed to realize local field enhancement. The composite grating consists of a short and a long rod each period, which is seperated by a nanogap with two alternating metal width. And a small rectangle is dug in the middle of long rods. The simulation result shows that the local field can be greatly enhanced. This is because that the plasmonics resonance couple between each metal section occurs. And this nanostructure can be used in improving local field enhancement.

Aiming to develop realistic high-resolution photo images for visual anti-counterfeit media, in this study, we fabricated the world’s smallest level of 8K photo with color pixel composed of metal-insulator-metal (MIM) disk-based structure. In addition, we devised a method of preprocessing photo data in order to express realistic images with structural color pixels.

A structure consists of a rectangular ring and a rectangular strip based on metal-insulator-metal (MIM) waveguide is proposed. When the rectangular strip is added in the suitable position, the plasmonic-induced transparency (PIT) effect will occur compared with the original single rectangular ring structure. The transmittance and resonance frequency can be changed via variation length and width of the rectangular strip. The structure is simulated by finite element method (FEM).

In this paper, we propose a tunable dual-band metamaterial absorber with wide-angle characteristics. The absorber is composed of a cross-shaped graphene layer and a layer of gold separated by a dielectric spacer. The simulated results show that there are two near-perfect absorption peaks in infrared band. Also, the peak wavelengths of absorber can be adjusted by changing the Fermi energy of the graphene and geometric parameters. In addition, the absorber can maintain a high absorption at a wide range of incident angles for both TE and TM waves. Such a device could be used as tunable sensors, filters, detector or other graphene-based photonic devices.

The infrared sensing market has experienced increased attention in recent years, due in large part to a widening of the application space from defense and research to commercial and consumer avenues. The uncooled market has been dominated by microbolometers, yet a recent resurgence of polycrystalline PbSe photoconductors could be the key to infrared photon detectors operating at room temperature. Typically, PbSe detectors are operated at 230 K, and can achieve sensitivity similar to its cryogenically cooled counterparts. In an effort to develop truly uncooled photon detectors, we have investigated surface plasmon resonant (SPR) structures for MWIR sensitivity enhancement of PbSe photoconductors. Au disc-shaped nanostructures were modeled to determine the required dimensions for a targeted resonance region between 3.5 μm to 4 μm. Finite element modeling (FEM) was then used to determine the effect of square disc arrays on the absorption of PbSe thin films. Modeled results suggest up to a three-fold increase in PbSe absorption in films with embedded structures. Square disc arrays made up of 500 nm and 1000 nm discs were patterned, fabricated, and embedded into sensitized polycrystalline PbSe thin films. FTIR spectra were collected to validate the model and determine the viability of SPR structures in a polycrystalline thin films. Based on FEM results, numerical models were constructed to predict photoconductor performance. Herein, we present the design, modeling, fabrication, and measured spectra of Au disc arrays embedded in PbSe films, as well as MWIR photoconductor performance predictions suggesting increased operating temperature with the utilization of SPR structures.

The work on Au-Ge nanoparticles (Nps) carried out so far by us has been successfully applied to devices like Bilayer, Trilayer, Hepta-layer Quantum dot infrared photodetectors (QDIP). An improved photonic response is achieved for the devices in terms of responsivity, photocurrent, responsivity, absorption and scattering. The dedicated standard recipe to get Nano-particles of different materials (Metals, Semiconductor) on distinguished substrate are revealed. It has been observed that the processes are repeated multiple time at the condition where desirable plasmonic condition does not match. Here the process has been optimized with multiple repeated annealing of Gold (Au) and Gold-Germanium (Au₈₈Ge₁₂) that shows the consistent pattern of reflectance where each anneal modifies the refractive index in same order with variable thickness of annealed film. This technique dilutes the constraints of fresh sample preparation whenever the nanoparticle response is dull, then the induced variation in size and volume of particle along with tuned distribution will become suitable.

In this article a novel design of arrow shaped nanoantenna has been reported. The analysis of the proposed arrow shaped nanoantenna made up of four arrow shaped arms has been performed. Further, its electric field enhancement has been calculated through finite element method (FEM) using COMSOL Multiphysics. The designed nanoantenna exhibits extremely sharp resonance in the narrow range. Owing to its pointed design, the arrow shaped nanoantenna exhibits high field confinement.

Particulate matters (PMs), which are condensed from air pollutants, pose severe health threats in many industrialized countries. Various chemical analyses of the particulate matters are crucial to specify their air pollutant sources and reduce PMs. Here, we report a chemical analysis technique for the PMs based on Surface Enhanced Raman Spectroscopy (SERS). Distinctive Raman spectroscopic signals are detected from PMs whose surface are dispersed with gold nanoparticle aggregates. By exploiting the molecular specific sensitivity of SERS, we distinguish between the PMs according to their sources. To be specific, artificially generated PM materials as a reference are successfully distinguished from soil dusts collected from on-site. This work would pave a way towards identifying the PMs according to their sources and developing an on-site chemical analysis of PMs.

We propose a narrowband plasmonic absorber based on 3D fractal geometries. The geometric parameters of the proposed structure were optimized to exhibit strong absorption (above 90% for normal incidence) for transverse magnetic polarization in the region of electromagnetic spectrum used in optical communications (1.0 - 2.0 μm). The proposed structure demonstrated that the resonant peaks can be tunned with the geometric parameters of the structure. We also analyzed the dependence of thickness and effects of fractal rotation to analyze fabrication tolerance.

A few different sodium borate glasses were made with various combinations of dopants ions, Sm³⁺, Dy³⁺, Tb³⁺ and Ag⁺. Absorption, and fluorescence spectral data of these samples were recorded. Chromaticity diagrams were plotted to measure color coordinates and color temperature. Samples were subjected to heat treatments above the glass transition temperature, to induce silver nanoparticles. Heat treated samples revealed a large enhancement in luminescence under 405 nm diode laser excitation and a relatively weaker enhancement under 375 nm laser excitation, which indicates the influence of plasmonic effect.

Plasmonic bowtie nanoantennas, which are metastructures that manipulate light and generate an intense localized electric field, demonstrate potential for surface enhanced Raman spectroscopy (SERS) signaling. Nanoantenna-based SERS can be employed to amplify molecular fingerprints, which is important for biomolecular and chemical reaction sensing. Nanoantenna electric field (or hot spot) optimization occurs when the plasmonic resonant wavelength of the structure closely matches the wavelength of the incident light. Depending on the excitation wavelength, the fabrication procedures can have tighter constraints. In this work, we fabricated several device arrays following nanoantenna design optimization for operation at 532nm wavelength. Fabrication steps utilized electron beam lithography (EBL) and nanopatterning tools, development, physical vapor deposition (PVD) by electron beam evaporation deposition (EBED), and resist removal by lift off. The polymer resist employed consist of a bilayer of polymethyl methacrylate (PMMA) in anisole (495k M.W. and 950k M.W.) sourced from MicroChem, Corp. The developer used (also sourced from MicroChem, Corp) was methyl isobutyl ketone: isopropyl alcohol (MIBK:IPA) in a 1:3 ratio. The influence of the developer step on the shape and quality of nanoantenna arrays was studied as the bowtie nanoantennas merged together or lost their defined shape. This study explored a specific bowtie nanoantenna design of 90-nm side lengths and 50-nm gap size, and 532-nm by 1.5 μm separation from its nearest neighbor. These nanoantennas were patterned in 10x5 and 10x25 grids with varying developer exposure times (10-100 seconds). Results reveal that the final device footprint has clear and defined shapes at as well as merged, undefined shapes across at 10-second window (40s-50s). At the upper end of the window, a greater than 40% increase in nanoantenna surface area is consistently observed.

Molecular analysis has revolutionized many applications, including bio-safety, bio-engineering and biofuel research; however, there are limited practical tools for in situ detection during field work. New technology is needed to translate molecular advances from laboratory settings into the practical realm. The unique characteristics of plasmonic nanosensors have made them ideal candidates for field-ready sensing applications. Herein, we discuss the development of a fiber-based plasmonic sensor capable of direct detection (i.e., no washing steps required) of miRNA targets, which are detected by immerging the sensor in the sample solution. This sensor is composed of an optical fiber that is decorated with plasmonic nanoprobes based on silver-coated gold nanostars to detect target nucleic acids using the surface-enhanced Raman scattering sensing mechanism of nanoprobes referred to as inverse molecular sentinels. The fiber sensors were tested in extracts from leaves of plants that were induced to have different miRNA expression levels. The results indicate that the fiber sensors developed have the potential to be a powerful tool for field analysis.

In this work the sensitivity of graphene and sulfide coated biosensors is analyzed in details by an efficient frequency domain finite element method. The proposed sensors are designed by introducing a thin film sulfide coating over a bimetallic surface plasmon resonance biosensor composed by gold and silver. The sensitivity of the proposed sensors can be highly enhanced by introducing the top thin layers. The influence of several sulfide composites in combination with the graphene layer is tuned and optimized by adjusting their optical and geometrical parameters.

In recent decades the advancement in the field of plasmonics has been crucial for the development of applications such as chemical detection, photothermal cancer therapy, and memory elements. In this work we present theoretical and experimental results focusing on the characterization of gold nanorods (AuNRs) coated with polyelectrolytes.These AuNRs constitute ideal nanoparticle-biomolecular hybrid system for study of photothermal heating effects. To start we synthesized AuNRs using a seed-mediated growth procedure. This synthesis employs a surfactant system using hexadecyltrimethylammonium bromide (CTAB) for stability with the addition of silver ions for improved formation. Once synthesized the nanorods were coated with polyelectrolytes sodium poly (acrylic acid) (PAA), poly (allylamine hydrochloride) (PAH), and poly (sodium-4-styrenesulfonate) (PSS) by a layer-by-layer absorption technique. Making use of the positive surface charge of CTAB-coated AuNRs, in this technique electrostatic absorption of an anionic polyelectrolyte and a cationic polyelectrolyte through charge reversal is enabled. The coated nanorods are characterized by UV-vis spectroscopy and electron microscopy to control the effectiveness of each polyelectrolyte on coating the nanorods. In addition to characterizing these AuNRs experimentally we also calculate their optical properties (far-field and near-field) via electrodynamics simulations, using the finite-difference time-domain method.