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Inspired by the proposal that single molecules will be functional elements of future nanoelectronic devices, there exists considerable interest in understanding charge transport in individual molecules. To study charge transport in single-molecule junctions, we exploit the STM microscope’s Blinking approach. It is a “current vs. time” molecular capturing procedure, able to electrically detect spontaneous individual molecular junctions under a constant sub-nm precise interelectrode distance. Here, we will present a novel plasmon-supported methodology (PBJ), based on Blinking to increase the timescale of the junctions. The (stabilising) force of the nearfield gradient is exploited to provide additional endurance to junctions, increasing the detected lifetime from hundreds of milliseconds to the order of seconds. Also, we will present our advances exploiting PBJ under electrochemical control, trapping redox metalloproteins resonant to the localized surface plasmon excitation wavelength.

OLEDs consisting of Au-NPs sandwiched between anode and hole injection layer, and close to an active layer inside PEDOT:PSS is fabricated by Ultrasonic Spray Coating (USSC). Optimized surface coverage of Au-NPs on ITO facilitates efficient charge injection and an optimized position of the Au-NPs away from the active layer accelerates the radiative recombination. Obtained results indicate that USSC could effortlessly tune the surface coverage and the vertical position of the Au-NPs to enhance the OLED’s efficacy. This paves the way for the fabrication of large area, high efficient OLEDs with USSC.

In this work we propose the use of self-assembled CdZnO nanoparticles as a route to improve power absorption in midinfrared GaAs-based quantum well infrared photodetectors (QWIPs). We experimentally demonstrate low temperature growth of CdZnO nanoparticles on GaAs and characterize their plasmonic response in the mid-IR. Computational analysis of the plasmonic resonances coupled to intersubband transitions in GaAs quantum wells show that intersubband absorption at normal incidence, forbidden by quantum selection rules, can be obtained. Gains in the quantum well power absorption as high as 5.5 are also reported.

In this work, we explore a new bottom-up approach based on plasmon-assisted hydrothermal synthesis (PAHS) to achieve localized growth of zinc oxide (ZnO) in hybrid nanophotonic devices. By engineering gold nanogap antennas, we achieve efficient control over the localization and enhancement of both the electric field and the generated heat. A nanobutterfly antenna is designed to achieve both polarization-dependent heat localization and localized electric field enhancement. A few-nm-thick ZnO layer is grown at the targeted location of the nanogap antenna thanks to selective plasmonic heating. We also numerically study the back-action induced by the material synthesis on the heat generated by the antenna and show how PAHS can be used as a self-limited growth method. The PAHS method opens new perspectives for the design and fabrication of hybrid nanophotonic devices.

We investigate hybrid dielectric-metallic transmission color filters for cost-effective, narrow linewidth filters that are fully CMOS compatible. Through the interference of the resonance phenomena in a metallic hole array with a magnetic dipole resonance in a dielectric nanopillar, a narrow linewidth transmission window is opened. An additional metal cover on top of the pillar further suppresses transmission at longer wavelengths due to a localized surface plasmon polariton. FDTD simulations predict a transmission of over 50% and a linewidth of down to 25 nm for the green filter. The out-of-band suppression is lower compared to previously reported metal-insulator-metal filters.

Owing to their tunable electromagnetic properties, subwavelength structures such as metamaterials have enabled novel applications across fields of engineering. In particular, metal-insulator-metal (MIM) plasmonic metamaterials have demonstrated efficient light energy absorption based on localized surface plasmon resonances. Due to these properties, MIM plasmonic resonance structures present its potential applications for photon absorption or emission at elevated temperatures, such as thermophotovoltaics. However, majority of reported MIM plasmonic structures are built with materials with a lower melting point such as gold or silver. Therefore, there are needs to explore how refractory materials affect the resonance properties of MIM plasmonic structures for high-temperature applications. In this work, we numerically report MIM plasmonic metamaterials built with highly refractory materials. Based on finite-difference timedomain (FDTD) simulation results, light absorption of these metamaterials peaks as high as 99.9% at the wavelength of 8.3 μm. This strong, selective absorption is attributed to the localized surface plasmon resonance. The results of this study suggest that the applications of MIM plasmonic devices may be extended for higher-temperature environments.

We have studied how the light-matter colocalization effect, which is the overlap effect between target and electric field distribution, affects the sensitivity of nanogap-based surface plasmon resonance (SPR) sensors. The SPR characteristics of the nanogap structure were calculated using a rigorous coupled-wave analysis program with DNA immobilization and hybridization cases. The colocalized shift (COS) and its relative value, relative optical signature (ROS), were defined to explain the capability change according to the gap size (g) along with the momentum matching condition of the nanogap. The maximum sensitivity, defined as the COS value compared to the changed refractive index, was 514.8 deg / (μm * RIU), which appeared at a relatively large interval (g = 17nm). When increasing the nanogap size, the ROS and reflectance also increased. However, the trend reversed, and the decrease in ROS reached a negative range at a 9 nm gap or more. This ROS is due to damping in the multiple localized surface plasmon polariton mode, and the strong field confinement inside the nanogap induces a negative shift. The zero-shift, the most avoidable when designing an SPR sensor, and near-field distribution with plasmon mode, is observed across different gap size and period pairs. The effect of colocalization inside the nanogap, as identified through various metrics, promises a highly sensitive detection potential for biological applications.

Localized surface plasmon resonances (LSPR) in plasmonic nanostructures have shown high sensitivities for optical sensing and spectroscopy applications. Individual plasmonic nanoresonators are capable of detecting analytes in ultrasmall volumes. Light being diffraction limited results in weak coupling efficiency (approximately 1% extinction in free space) to the nanoresonator. Improving the signal to noise ratio (SNR) at the output requires a dark field microscope which makes the sensing system bulky. Light interaction with nanoantenna can be improved by using dielectric waveguides for interrogation. Besides this, compact and completely integrated on-chip biosensors can be realized with easier interrogation and multiplexed detection capabilities. Waveguide interrogated plasmonic nanoresonators have been investigated in the past for spectral shift based refractive index (RI) sensing modality. Such sensors require bulky spectrometers for obtaining the output spectrum. In contrast to it, intensity shift based RI sensors require photodetectors which are compact and easily integrable on chip. We propose a small footprint phase shifted Bragg grating (PSBG) waveguide made of silicon nitride loaded with a gold nanoresonator. Numerical investigation of the structure's optical response and its potential for intensity shift based refractometric sensing has been done in the visible wavelength range. The grating possesses a Fabry Perot cavity with a high Q-factor (1008) thus increasing the photon lifetime and interaction of light with the nanoantenna. Intensity shift based RI sensing results show sensitivity of 394%/RIU for PSBG excited nanoantenna compared to 57%/RIU observed in strip waveguide loaded with nanoantenna. Besides this, light coupling efficiency to plasmonic nanoresonator is 35% on excitation with PSBG waveguide in comparison to 12% observed in strip waveguide based excitation scheme. Strategies for further improvement in coupling efficiency are also reported.

We demonstrated gold nanodimer arrays could improve the signal-to-noise ratio (SNR) of fluorescence correlation spectroscopy (FCS). In this research, we explore the feasibility of plasmon-enhanced FCS for biomolecular study using a nanodimer array whose gap size was 18 nm. Fluorescence nanobead with a diameter of 40 nm was first examined to verify if gold nanodimer arrays can enhance SNR of fluorescence and scattering intensities. We emphasize that plasmon-enhanced FCS can improve the precision for analyzing the dynamics of the particle by combining scattering characteristics of nanodimer arrays to surface plasmon resonance imaging technique. We have also observed the fluorescence enhancement and plasmon scattering in the movement of lysosome in HEK293 cells. It was found that we could measure diffusion properties such as diffusion coefficients and anomalous exponents with a low standard deviation.

We present a model for exciton-plasmon coupling based on energy exchange mechanism between quantum emitters (QE) and localized surface plasmons in metal-dielectric structures. Plasmonic correlations between QEs give rise to a collective state exchanging its energy cooperatively with a resonant plasmon mode. By defining carefully the plasmon mode volume for a QE ensemble, we obtain a relation between the QE-plasmon coupling and the cooperative energy transfer rate that is expressed in terms of local fields. For a single QE near a sharp metal tip, we find analytically the enhancement factor for the QE-plasmon coupling relative to the QE coupling to a cavity mode. For QEs distributed in an extended region enclosing a plasmonic structure, we find that the ensemble QE-plasmon coupling saturates to a universal value independent on system size and shape, consistent with the experiment.

Highly localized electric field induced by the excitation of the localized surface plasmon provides huge gradient of the field intensity in nano-scale. Such gradient results in exotic perturbation for molecules at electrified interfaces with plasmonically-active metal nanostructures. In this study, plasmon-induced hydrogen evolution reactions have been successfully induced by the combination of the plasmonic metal nanostructures on the p-type GaP semiconductor electrode. Through various photoelectrochemical measurements, it was found that the present system showed the relatively higher efficiency under the neutral condition compared with the acidic and the basic conditions. In addition, the unique molecular process has been observed by using the isotopic water molecules. By the examination of the isotopic effect, the effect of the field localization on the reaction was discussed.

III-V GaSb based strained layer superlattice (SLS) can provide broadband detection from 3 to 15 microns and beyond. However, the longer wavelength material has smaller external quantum efficiency (EQE) because of the smaller absorption coefficient and carrier diffusion length. The usual approach of using thicker material for higher EQE is not viable because of the limited carrier collection. In this work, we adopt a metasurface on top of a thin detector material to increase its absorption without increasing the thickness, thereby increasing EQE. The metasurface consists of an array of rings. These rings excite different optical responses in different wavelength regimes, thus yielding a broad detection spectrum. In the MWIR regime, they diffract light collectively, and in the LWIR and VLWIR regimes, they focus light as Fresnel lenses and excite localized surface plasmon polaritons (SPPs). Through these different optical interactions, the incident radiation is redirected and trapped in the detector volume. When the trapped light interferes constructively, the optical intensity builds up to a large value, leading to a large absorption in a thin material. A properly designed metastructure is thus able to achieve a large EQE in a broad spectrum. The thin absorbing layer also allows several of them stacking together to form a multi-color detector. Narrowband detection can be obtained in each color using circular posts instead of rings. By exploiting different optical field profiles under different optical responses, a voltage-switchable detection scheme can be implemented to detect four discrete wavelengths ranging from MWIR to VLWIR. The broad and narrow band designs thus show the flexibility of metastructures. To compare the present metastructure approach with the more conventional approaches using microlenses and Fresnel lenses that can also reduce dark current while maintaining a sizable QE, we optimize the respective structures and compare the merits under different approaches.

Controlling and manipulating light-matter interaction phenomena at the nanoscale leads to a variety of fascinating effects that are currently the focus of an intense research from both a fundamental and technological perspectives. In this talk, I will summarize the most recent advances on the fabrication and performance features of coherent light sources operating at the nanoscale, which are attained by the interaction of localized surface plasmons with optical gain nonlinear dielectric media [1]. The optical gain is provided by functional ferroelectric platforms, either by stimulated emission [2] or by nonlinear frequency conversion processes [3]. The mechanisms responsible for the intensification of the radiation–matter interaction processes are discussed in each case.

Metasurfaces consisting of periodically arranged plasmonic nanoparticles could become a promising platform for optical filtering and nonlinear experiments. However, due to the high absorption loss of noble metals e.g. gold, the localized surface plasmon resonances (LSPR) of individual nanoparticles exhibit very low quality factors (Q ~ order of 10), which is not suitable for practical usage. Here, we experimentally demonstrate a plasmonic metasurface with ultra-high-Q (above 1000) surface lattice resonances (SLRs) around the optical telecommunication wavelength of 1550 nm by optimizing the LSPR of rectangular gold nanoparticles and the overall array size.

In this contribution we report on a low cost plasmonic electrode for light-sensing applications. The electrode combines a conducting nonstoichiometric indium oxide (InOx) layer with an ultrathin (~5 nm) discontinuous Au layer. The InOx and Au layers were deposited on glass substrates by plasma enhanced reactive thermal evaporation and thermal evaporation, respectively. Several device configurations with one or two Au layer(s) sandwiched between InOx layers were fabricated and characterized. The morphological and structural properties of both Au and InOx layers were analyzed using AFM and XRD techniques. In particular, the effect of thermal annealing (673 K, 15 min) on the surface morphology of Au layers grown on bare glass and InOx-coated substrate was investigated. It has been also found that the oxide film grown above an underlying nanostructured Au layer is amorphous, while a reference InOx film on glass is nanocrystalline with a smooth surface. The electrical properties of InOx grown on the Au surface are worsened due to Au-induced structural disorder. The observed difference in transmission spectra of the glass/InOx/Au and glass/Au/InOx structures indicates the difference in the morphology of the metal layer. Thus, the optical and morphological properties of the InOx electrode can be varied in a wide range by incorporating several Au layers.

Surface enhanced Raman spectroscopy (SERS) is a powerful molecular analytical tool that allows for highly sensitive chemical detection of low concentration analytes through the amplification of electromagnetic (EM) fields generated by the excitation of localized surface plasmons. SERS performance such as enhancement factor (EF), reproducibility and repeatability is highly related to distribution profile of Au nanoparticles on SERS substrates. The uniformity distribution of Au nanoparticles usually results in good SERS performance. We introduce a new SERS substrate that produces improved performance through surface modification of silicon wafers. For this purpose, hydrophilic silicon wafers are prepared and then their surfaces are coated with tannic acid (TA) by thermal treatment. TA is used as a surface modifier with low cost and high adhesion to synthesize uniform and dense Au nanoparticles. The direct synthesis of Au nanoparticles is carried out through the successive ionic layer absorption and reaction (SILAR) method. 2- naphthalenethiol (2-NAT) dye was utilized to confirm the SERS performance of the as-fabricated substrate. The SERS performance was optimized by controlling the thickness of the Au nanoparticle layer synthesized by repeating the SILAR cycle. We expect the proposed SERS substrate to exhibit good reproducibility and repeatability due to the high uniformity distribution of Au nanoparticles.

In this paper, we propose a broadband nanoantenna for solar energy harvesting, whose elements compose of dual triangles, a hexagonal pillar and a ring column. The optical characteristics are analyzed numerically by the three dimensional finite-difference time-domain (FDTD) method. It is found that the average absorptivity of the nanostructure is 84.53% in the visible and near-infrared waveband raning from 400-1800nm. In addition, the prefect light absorbing capability is independent of the incident light polarization state, and it can keep up an average absorptivity of 86% for an incident angle as large as ±60°. We attribute the better absorption property of the nanoantenna to Fabry-Perot resonance, lighting-rod effects and the localized surface plasmon resonance enhancement.

Electroluminescence based on inelastic tunnelling has been investigated for many years in scanning tunnelling microscopy (STM) and plasmonic antenna platforms. Here, we report an electrically excited nanosource with a bowtieshaped tunnel junction that has achieved an output power. The tunnel junction in our experiments is formed via an electromigration (EM) process. The benefits of our new structural design include higher tunnel currents, ultra-strong electrical field enhancement and a higher Purcell factor. By varying the geometric parameters of the plasmonic antenna, the energies of these LSP modes can be tuned for different confinement lengths.

The precise understanding of the spatiotemporal characteristics of ultrafast surface plasmons is a prerequisite for applications of plasmonics. Here, we report on the investigation of near-field imaging and dynamics of propagating and localized surface plasmons (PSPs and LSPs) using photoemission electron microscopy (PEEM) of the trench on the silver film and gold bowtie nanostructure. The actual propagation direction of PSPs is directly obtained by reading PEEM images via the non-collinear exciting method by the trench. The results have demonstrated that the trench structure is potential as a 2D plasmonic dispersion element. Moreover, we experimentally obtain different LSPs dephasing times in the tips of the bowtie nanostructure by interferometric time-resolved PEEM. Experimental result reveals the dynamics of the LSP field initially oscillate at the laser field frequency and finally develop into its eigenfrequency after experiencing a few periods of frequency fluctuation.

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).

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-Perot 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.

Localized surface plasmon resonances can increase the quantum efficiency of photon emitters through both absorption and spontaneous emission enhancement effects. Despite extensive studies, experimental results that clearly distinguish the two plasmonic enhancement effects are rarely available. Here, we present clear spectral signatures of the plasmonic enhancement effects on the absorption (excitation) and spontaneous emission (Purcell factor) by analyzing the temperature dependent photoluminescence (PL) properties of InGaAs/GaAs single quantum well (QW) coupled to colloidal gold nanorods (AuNRs) at different GaAs capping layer thickness (d). We find that when the emitting InGaAs layer is close to the AuNRs (d = 5 nm), the plasmonic enhancement effect on the QW PL is dominated by the Purcell factor that significantly increases the external quantum efficiency of the QW that otherwise barely emits. When d is increased to 10 nm, the temperature dependence of the PL enhancement factor (F) reflects absorption enhancement in the capping layer followed by carrier diffusion and capture by the well. First F increases with temperature and then decreases following the temperature dependence of the carrier diffusion coefficient in GaAs. By factoring out the contribution of the captured carriers to F, it is shown that carrier transfer to the well reaches saturation with increasing incident laser power. In addition to providing insight into the plasmonic enhancement mechanism, the results presented in this work suggest that colloidal plasmonic nanoparticles can be used as simple probes for understanding carrier transport phenomena in arbitrary semiconductor heterostructures.

There has recently been an extensive amount of work in the field of nanoplasmonics, where plasmonic phenomena occurring on a variety of nanostructrues present an alternative approach to surface plasmon resonance (SPR) biosensing. The architectures of these nanostructures are often complex, where localized regions of high plasmonic activity (sensitive to RI changes) are interdispersed among regions of little to no plasmonic activity (with no RI sensitivity). To date, the bulk of work on nanoplasmonic sensors has focused on the optimization of a nanostructure in terms of its optical characteristics, in terms of either its sensitivity to RI changes or likewise, in its figure of merit (FOM). In contrast, there has been very little discussion on the role of analyte transport in nanoplasmonic sensing. It is known that the selective immobilization of bioreceptors only to the sensitive regions can lead to significant increases in sensing performance: a result that is solely tied to increases in analyte transport. Hence, when selectively functionalized and operated under diffusion-limited conditions, the rate of analyte transport becomes strongly dependent on the nanoplasmonic architecture. Using numerical results, we have previously shown that this rate is dependent on two factors (i) the fill fraction of the sensitive regions, and (ii) the difference in size between individual localized sensitive regions and the overall size of the sensing surface. Despite the lack of discussion, the role of analyte transport remains paramount for the design of a nanoplasmonic structure. For example, changes to a nanostructure that result in an increase in RI sensitivity might induce a decrease in the rate of analyte capture, resulting in a sensor with an overall reduction in performance. In this talk we will demonstrate the ties between optical performance and the rate of analyte transport. We will present experimental data taken from a variety of plasmonic nanostructures, including variation of both their base photonic element (nanorods, nanodisks, and wires) as well as their packing density. We will show that, despite the large differences in optical characteristics, the characteristics of analyte transport follow relatively simple scaling trends. We will show that these experimental data have very good match to analytical predictions. In addition, we will discuss how the kinetics between analyte and bioreceptor will affect the optimal design of a nanostructure: sparse arrays of photonic elements have dominant performance for systems having strong kinetics, whereas for systems with poor kinetics, dense arrays of photonic elements have better performance.

Metamaterials, or synthetic materials that have engineered material parameters, have been utilized to demonstrate extraordinary usefulness in the control of electromagnetic waves. In this paper, a novel metalens design in the near infrared band from 1.5μm to 3μm is presented. It consists of a Fresnel zone plate (FZP)-type metasurface which is called a plasmonic waveguide coupler (PWC), situated on a slab of type I hyperbolic metamaterial (HMM) that lies on a silicon substrate which has a silver nanodipole embedded within it. The PWC is made out of rings of Indium Tin Oxide (ITO) and the type I HMM is constructed using a periodic stack of ITO and silicon layers that, through effective medium theory (EMT), act as a slab of type I HMM. Together the PWC and the HMM slab serve to focus incoming radiation onto a focal point marked by the location of the silver (Ag) nanodipole. The Ag nanodipole allows for high subwavelength confinement of optical modes because the in-focal point component of the electromagnetic field vector couples to the plasmonic resonance of the dipole. The maximum achieved resolution is up to 0.01667 λ at an operating wavelength of 1.53 μm and electric field intensity enhancement of 106 is achieved. The enhancement in field is related to the principal localized surface plasmon resonances (LSPRs) around the resonator’s edges on the interface between the Ag nanodipole and the substrate.

Advanced functional infrared (IR) photodetectors with wavelength selectivity are promising for a wide range of applications, such as multicolor imaging, gas analysis and biomedical analysis. Graphene is considered to be a promising material for novel IR detectors. However, the absorption of graphene is constant at approximately 2.3% and rather small. We have developed multispectral high-performance graphene IR photodetectors using metal-insulator-metal (MIM) or single-layer (SL) plasmonic metasurfaces (PMs). MIM- or SL-PMs induce localized surface plasmons on their surfaces and enhance absorption at the wavelength, which can be controlled by their surface patterns, such as the period or the gaps between micropatches. The absorption of graphene with PMs was theoretically investigated for various structural parameters. The absorption wavelength can be controlled based on plasmonic resonance by varying the surface geometry of the PMs. Graphene-based IR photodetectors with SL-PMs were fabricated by the chemical vapor deposition of graphene and then transferred onto the PMs. Wavelength-selective enhancement of the optical absorption and detection by graphene could be achieved due to the effect of the PMs. The results obtained here are expected to contribute to the realization of multispectral graphene infrared image sensors.

The structural and optical properties of amorphous silicon (a-Si) and Ag-dispersed amorphous silicon (a-Si:Ag) thin films irradiated by femtosecond (fs) laser at various energy densities are investigated comparatively in this article. It is found that at a lower energy density of 100 mg/cm2 , the film microstructure evolves from a completely amorphous phase to an intermediate one containing both amorphous and polycrystalline silicon. During laser irradiation, the formation of nanocrystals in a-Si films begins at lower energy density, but the existing Ag nanoparticles inhibits somehow the crystallization of a-Si in a-Si:Ag films at the same energy density. As the energy density is increased to a moderate value of 200 mj/cm2 , the surface of a-Si:Ag films featuring a vertically aligned pillar-shaped structure is emerging. Both the crystallinity and the root mean square of surface roughness exhibit a monotonic increase with the increase of energy density. The Ag nanoparticles are dispersed uniformly in a silicon matrix, resulting in a resonant light absorption due to so-called localized surface plasmon. The localized surface plasmon resonance (LSPR) wavelengthes of the irradiated aSi:Ag films are increased significantly from 600 nm to about 820 nm, and the bandwidth of the measured absorptance is enhanced in the range of 600~1600 nm. The nanocrystallization mechanism, the formation of pillar-shaped structures and the light absorption enhancement are explained regarding the high electron density and the plasma-surface interactions.

In recent years, many quantum lights-based applications were suggested, ranging from encrypted communication and precision metrology to fluorescent biomolecules detection and advanced spectroscopy schemes. Such applications mostly rely on entanglement, the property of correlations between particles which cannot be explained by classical mechanisms, to overcome classical light limitations. Some of these applications, e.g. nonlinear spectroscopy, require the use of entangled-photon-pair interaction (EPPI) with the matter. However, such entangled pairs, generated through spontaneous parametric down-conversion (SPDC), are scarce, and multi-photon interaction with matter is usually very weak and barely detectable. Therefore, an enhancement of this interaction is needed. In our research, we investigate a novel way to achieve such enhanced EPPI using metallic nanoparticles (MNPs), which are known for their exceptional capability of light-matter coupling at their localized surface plasmon resonance (LSPR). We present a novel way of theoretically estimating the rate of EPPI with MNPs, based on a simple method of classical light second-harmonic generation (SHG) measurements. The theory is supported with experimental results, obtained for a solution of silver NPs (SNPs). These results show an estimated six orders-of-magnitude EPPI enhancement, relative to the best organic molecules, and indicate that the use of SNPs can be advantageous for realization of advanced quantum light applications.

In-situ sensing in high temperature and chemically reactive environments – i.e., within solid oxide fuel cells or power plant boiler systems – is inherently challenging due to the rapid degradation of most traditional sensor materials within this regime. Although optical fiber based sensors provide clear advantages in this context, progress in this area of application has hinged on the development of (a) optical fiber materials and (b) thin film materials with strong optical response to gas environment, both of which must resist degradation under such conditions. Conducting metal oxide thin films have been examined in the literature as a candidate to solve the latter problem, due to a free-carrier governed optical response in the NIR (1-2 μm), that can be strongly dependent upon gas environment. In this work, we present the impact of incorporating gold nanoparticles in one such metal oxide, lanthanum-doped strontium titanite (LSTO), on the gas sensing response, both in the NIR and UV-VIS range. Via optical transmission measurements performed at high temperature (up to 800 C), the intertwined free-carrier response of the film and the localized surface plasmon response of the nanoparticles are examined in the presence of hydrogen of varying concentration. Measurements are presented for films coated both on planar substrates and on optical fibers.

Atoms are extremely accurate resonators. This property serves to build up precise sensors for time keeping, accelerometer and many others. However, their accuracy depend on their environment. For example, at the vicinity of a surface (metallic or dielectric) the atomic resonances are shifted by the Casimir-Polder interaction. The spatial dependency of this interaction (1/z3, in the non retarded regime) can be a crucial limitation for the development of compact sensors at the micrometer size scale. To address this issue, we explore the tunability property of the Casimir- Polder interaction with resonant surface plasmon modes. These latter are generated using nano-structured metallic layers. We found that the atomic resonance shift can be almost suppressed and the Purcell factor enhanced. More recently, we investigate quadrupole atomic transitions in surface plasmon. Those transitions are extremely weak in vacuum (~1 Hz) but can be enhanced if the spatial variation of the electromagnetic field become stronger as expected with localized surface plasmons. In this context, we will present our results, obtained with a cesium vapor, and discuss the potential application of creating new excitation channels in atomic spectrum.

Near filed optical lithography has been a promising alternative to photolithography for its high resolution, low cost and high throughput. Bowtie aperture, one type of nanoscale ridge aperture, is widely used in near filed optical lithography. However, the bowtie structure milled by focused ion beam (FIB) usually suffers from non-vertical sidewall with taper and rounded corner due to Gaussian ion beam profile and redeposition effects. Here, we report a novel method to fabricate bowtie aperture with sub-15 nm gap, producing highly confined electric near-field by localized surface plasmon (LSP) excitation and nanofocusing of the closely tapered gap. Utilizing a passive flexure stage for contact control, we present our recent lithography results with a record 20 nm resolution (FWHM).

The tunable localized surface plasmons in novel antenna of Au nanosphere dimer coated by graphene is studied theoretically. We demonstrate the electronic tuning of graphene based Au nanosphere antenna via modifying the Femi level of graphene for realizing active tunable localized surface plasmons. It is found that localized electronic field shows an evident increasing, as the graphene layers increase. The resuts are explained as the more evidently enhanced resonance of localized surface plasmons for multilayer graphene than monolayer graphene nanoantenna when the incident light matches to the resonance wavelength of the Au-graphene hybrid system. In addition, it is revealed there is observable blue-shift for the resonance wavelength when the graphene layers get increased. The study provides basic understanding for tuning graphene based on Au nanosphere antenna for a wide range of applications such as single-molecule fluorescence, SERS and photothermal therapy.

The focusing spot beyond diffraction limit is critical to plasmonic direct-writing lithography. To improve the speed and precision of plasmonic direct-writing lithography, we design a new periodically repeated circular hole/elliptical ring plasmonic structure named as split-focusing structure used for producing two focusing spots under the incidence of linearly polarized plane wave at 633nm wavelength. It consists of SiO2 substrate and coated silver film with holes and slits of different shapes. By designing appropriate structure parameters to excite localized surface plasmon resonance, two split subwavelength spots are produced on the focal plane. Finite-difference time-domain (FDTD) method is used for numerical simulation. The simulation result indicates that the focal length of structure is 36nm and the full width at half maximum (FWHM) of single spot is 50nm. Both split spots can be used for direct writing so the speed of photoetching will be raised. The dual spots are both in circular shape, which is beneficial to improve the pattern precision. The influence of structure parameters on focusing performance is also analyzed to guide the practical fabrication of structure. The split-focusing structure designed in this paper also owns application values in data storage and non-contact sensing.

Localized surface plasmon based on coupled metallic nanoaggregates has been extensively studied in enhancing light scattering and optical force, which depends on the geometry/symmetry of plasmonic oligomers and the refractive index of surrounding medium. As the interparticle gap distance between nanoparticles becomes smaller than several nanometers, quantum effects can change the plasmon coupling in classical predictions. However, most of the research on plasmonic scattering and optical force has been done based on local calculations even for the gap below ~3 nm, in which the nonlocal screening plays a vital role. Here, we theoretically investigate the nonlocal effect on the evolution of plasmon resonance modes in strongly coupled nanoparticle dimer antennas with the gap down to 1 nm. Then, the refractive index sensing and optical force in this nonlocal system is evaluated and compared with the results in classical calculations. We find that in the nonlocal regime, both refractive index sensibility factor and optical force are actually smaller than their classical counterparts mainly due to the saturation of both plasmon-shifts and near-field enhancement. These results would be beneficial for the understanding of interaction between light and nonlocal plasmonic nanostructures and the development of plasmonic devices such as nanoantennas, nanosensors, and photonic manipulation.

In this report, we introduce our proposed nanophotonic structures for highly efficient optical manipulation, including utilizing photonic crystal waveguides, nanocavities, and metallic structures with localized surface plasmon resonances. Owing to their waveguide-accessible configurations and highly concentrated optical modes with large field gradients beyond the diffraction limit, highly efficient optical trapping can be realized in sub-wavelength scale.

In this paper, a pair of hollow bow-tie nanoantenna with a feed gap has been designed using gold in the visible frequency range. This nanoantenna exhibits a strong field enhancement in the feed gap region at the resonance wavelength due to the localized surface plasmon. The absorption cross-section of this nanoantenna has been compared with the solid bowtie nanoantenna and it has been observed that the absorption cross section in hollow bowtie nanoantenna is less as compared to solid bowtie nanoantenna. This is because of the less volume availability for light absorption in the hollow bowtie nanoantenna. So, the main reason of using a hollow bowtie over a solid bowtie is the reduced absorption cross-section. Further, properties of hollow bowtie nanoantenna have been enhanced by geometric optimization using COMSOL Multiphysics software.

Localized surface plasmons have been reported for periodic 2D monolayer black phosphorene (BP) nanoribbons in the infrared region. The anisotropic nature of BP causes different plasmonic effects depending on their orientation over select dielectric substrates, leading to tunability and promising future applications in imaging and other detectors. Computational models are used to demonstrate that by tuning the localized plasmonic resonance, as well as the orientation of the BP nanoribbon, it is possible to obtain desired coupled resonance modes and enhanced absorption capabilities. The modes obtained from the absorption spectra span the infrared range and extend our understanding of BP plasmons.

We develop a theory for spontaneous decay of a quantum emitter (QE) situated near metal-dielectric structure supporting localized surface plasmons. If plasmon resonance is tuned close to the QE emission frequency, the emission is enhanced due to energy transfer from QE to localized plasmon mode followed by photon emission by plasmonic antenna. The emission rate is determined by intimate interplay between the plasmon coupling to radiation field and the Ohmic losses in metal. Here we develop plasmon Green function approach that includes plasmon’s interaction with radiation to obtain explicit expressions for radiative decay rate and optical polarizability of a localized plasmon mode in arbitrary plasmonic nanostructure. Within this approach, we provide consistent definition of plasmon mode volume by relating it to plasmon mode density, which characterizes the plasmon field confinement, and recover the standard cavity form of the Purcell factor, but now for plasmonic systems. We show that, for QE placed at ”hot spot” near sharp tip of a small metal nanostructure, the plasmon mode volume scales with the metal volume while being very sensitive to the proximity to the tip. Finally, we derive the enhancement factor for radiated power spectrum for any nanoplasmonic system and relate it to the Purcell factor for spontaneous decay rate. We illustrate our results by numerical example of a QE situated near gold nanorod tip.

Typical excitations in metal nanostructures are localized surface plasmon resonances (LSPR) and propagating surface plasmon polaritons (SPPs) at metal-dielectric interfaces. If the metal film is prepared with holes or periodic corrugation, then diffracted light can be coupled to both LSPR and SPPs. Controlled engineering of the geometric parameters like height and periodicity of corrugation affect the strength and spectral position of LSPR, changing the metal film thickness changes the height of the extraordinary transmission (EOT) peak, and light-SPP coupling can be changed by altering the dimensionality and refractive index contrast in the attached photonic layer. In this study, we report for plasmonic interference coupling (PIC) where the plasmonic electromagnetic (EM) enhancement is critically dependent to the optical interference in the metal-insulator-metal (MIM) structure. The basic structure consists of the top metal with nanopores as a plasmonic layer and the bottom metal as an optical mirror. By controlling the thickness of the dielectric insulator at the middle, the optical interference patterns (i.e. constructive or deconstructive interference) were alternated at the top nanopore layer, thus resulting in great effects on surface-enhanced Raman scattering (SERS) responses. Therefore, we could clearly understand that such a MIM structure should be well designed by considering PIC characteristics to effectively utilize a plasmonic EM enhancement. We used nonporous anodic aluminum oxide (AAO) and titanium dioxide templates for accomplishing such a PIC structure. Furthermore, low-cost aluminum was applied to create non-uniform nanopore AAO and compared their optical properties with those of uniform AAO-based PIC structures (i.e. high-cost template). Finally, we could confirm scalable cost-effective PIC structures. Our results might provide the suitable design way for the applications of enhanced EM on plasmonic-integrated devices.

Metal nanoparticles demonstrate unique optical properties that are mostly due to localized surface plasmon resonances (LSPRs). In addition, when nanoparticles are arranged in arrays (metasurfaces), their responses can be modified by the presence of the neighboring particles. As a result, sharp spectral features can be observed. Such features, called surface lattice resonances (SLRs), are related to the appearance of diffraction orders in the optical response. Both types of resonances can lead to local-field enhancement and thereby boost nonlinear optical effects. For the particular case of second-harmonic generation (SHG) the sample needs to be also non-centrosymmetric. This condition is fulfilled when, for example, V-shaped nanoparticles are used in the array. Increasing the number of particles typically increases the optical density, which should increase the nonlinear response with the square of the particle density. This approach, however, has its limitations because, when the particles are too close to each other, the quality of the LSPRs decreases leading to an effect opposite to the desired. Here, we will show the counterintuitive effect that the nonlinear response can be enhanced by reducing the number of particles in the array. In order to verify our idea, we use two arrays of V-shaped gold nanoparticles fabricated on a glass substrate by electron-beam lithography and lift-off methods. The particles are distributed in 500 x 500 nm2 square arrays in two configurations: i) all lattice points are filled with particles (V1) or ii) every other particle in the lattice is removed in a way that the remaining particles form a rotated (by 45°) square array with a pitch of 707 nm (V2). Both samples have two eigenpolarizations: one along the symmetry axis (y) of the V shape and other in the perpendicular direction (x). In the SHG experiments, the incident beam from an optical parametric oscillator was incident on the sample. Polarizers and a half-wave plate were used to control the polarization of the fundamental (1000 – 1300 nm) and second-harmonic beams. The SHG signal was collected by a photon counting system. The sample V2, that has reduced (by a factor of 2) density of particles in the array, shows the expected decrease in the strength of the resonance peak (1151 nm) and a slight redshift of the resonance wavelength with respect to the sample V1 (1081 nm). In order to achieve fair comparison of the nonlinear signals, we tuned the incident wavelength to the position of approximately equal losses for both samples (1135 nm). The sample V2 is found to have, by a factor of 7, stronger response than sample V1. Such enhancement in the nonlinearity is related to the improvement in the quality of the resonance for sample V2, for which the width of the resonance is reduced by ~30% compared to V1. This is due to SLRs that are present for sample V2. Our results are in good agreement with calculations by using an approach based on the discrete-dipole approximation.

A dynamic all-optically controlled surface plasmon polartions (SPP) novel high-performance multi-function optical microscope, combining optical microscopic imaging, bio-sensing and surface enhanced Raman Scattering (SERS) in a single microscopic system, is presented in this talk. This new configuration uses phase shift of SPP standing wave generated from sub-wavelength slit arrays embedded in a thin metal film to achieve super-resolution wide-field microscopic imaging; phase sensitive surface plasmon resonance (pSPR) bio-sensing technology based on differential phase measurement between radially polarized (RP) and azimuthally polarized (AP) beams to obtain an ultra-high sensitivity and a wide dynamic range simultaneously; the coupling between the localized surface plasmon (LSP) of metallic nano-particles and SPP virtual probe with longitudinal electric field to significantly improve the sensitivity of SERS system. With the integration of these three technologies in a single microscopic configuration, the system can achieve wide-field super-resolved imaging of biological specimens, ultra-high sensitivity for molecule detection and real-time monitoring for reaction process of biological samples simultaneously, fulfilling the requirement of multi-parameter multi-function real-time in-situ measurement of biological samples. The new microscopic scheme has great importance in real-time dynamic study on nano-scale biological living cells as well as accurate near field mapping.

Upconverting nanophosphors (UCNPs) absorb two or more photons at 980nm and emit a higher energy photon in the visible range. UCNPs provide distinct advantages as biological imaging agents in that they have no autofluorescence, don’t photobleach, are capable of deep tissue imaging, exhibit no blinking, and are physically robust. Through surface modifications with an amphiphilic polymer, we can not only functionalize UCNPs for targeted imaging, but also tether them to plasmonic nanoparticles such as gold nanorods (AuNRs) for enhanced upconversion and multifunctionality. We developed a process to construct UCNP-AuNR nanoclusters using polyethylene glycol. The UCNP-AuNR nanocluster is further modified with an anti-epidermal growth factor receptor (aEGFR), allowing specific binding to bladder cancer cells that highly express epidermal growth factor receptor. Once the nanoclusters bind to the cell membrane we can (1) perform targeted and high contrast imaging of the bladder cancer cells and (2) utilize localized surface plasmon of AuNRs to selectively kill the cells in situ upon detection by UCNP fluorescence. Successful conjugation and integrity of the UCNP-AuNR nanoclusters were confirmed via electron microscopy. Then, through a combination of brighftield, confocal upconversion fluorescence, and infrared darkfield microscopy we demonstrate selective binding and high-contrast upconversion imaging of the bladder cancer cells. Finally, through a series of in vitro studies, we demonstrate two different methods of cell killing. First, with a continuous wave laser, we demonstrate effective thermal ablation of cells. Second, with a femtosecond pulse laser, we demonstrate optoporation of the cell membrane that allows increased uptake of drugs.

Hot-electron (HE) transfer process in hybrid metal nanoparticle capped layered two-dimensional dichalcogenides (TMDs) can result in the modification of dielectric constant as well as doping of the semiconductor. Hot-carrier transfer process due to optical excitation is an attractive mechanism for enhancing the efficiency of photodetectors or photovoltaic devices. However, HE driven processes are usually non-radiative in nature and are not usually utilized in light emitting system. In this work, it has been demonstrated that by using the optical excitation resonant to plasmons in the hybrid structure, hot electrons are transferred from metal to semiconductor that causes the formation hybridized exciton-plasmon state that eventually gives rise to the enhanced photoluminescence (PL) emission. The localized surface plasmon (LSP) induced off-resonant to the emitted photons has also been utilized to enhance the PL emission. TMDs such as single monolayer Molybdenum Disulfide (MoS2) material has high exciton binding energy, which can facilitate strong exciton-plasmon interaction. The light emitted from MoS2 structure is weak due to intervalley scattering in indirect-gap multilayer structures or due to relatively low absorption of direct-bandgap monolayer structure. Hybrid Ag-MoS2 plasmonic structures were realized by nucleating silver film of optimum thickness into islands by nucleation on chemical vapor deposition (CVD) grown monoloyer MoS2 structure. The LSP energy of the system is centered at 2.33 eV, with the two exciton absorption peaks at 1.85 and 2.0 eV. The carrier dynamics studied by ultrafast time-resolved spectroscopy reveals HE mediated hybridization of exciton within 700 fs. The emisson energy at 1.83 eV can be tuned by the input power due to HE transfer from Ag to MoS2. A three-fold enhancement in the PL intensity has also been observed.

Localized surface plasmons (LSP) can be excited in metal nanoparticles (NP) by UV, visible or NIR light and are described as coherent oscillation of conduction electrons. Taking advantage of the tunable optical properties of NPs, we propose the realization of a plasmonic structure, based on the LSP interaction of NP with an embedding matrix of amorphous silicon. This study is directed to define the characteristics of NP and substrate necessary to the development of a LSP proteomics sensor that, once provided immobilized antibodies on its surface, will screen the concentration of selected antigens through the determination of LSPR spectra and peaks of light absorption. Metals of interest for NP composition are: Aluminium and Gold. Recent advances in nanoparticle production techniques allow almost full control over shapes and size, permitting full control over their optical and plasmonic properties and, above all, over their responsive spectra. Analytical solution is only possible for simple NP geometries, therefore our analysis, is realized recurring to computer simulation using the Discrete Dipole Approximation method (DDA). In this work we use the free software DDSCAT to study the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, shape, aspect-ratio and metal type. Experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.

Light-matter interactions in two dimensional (2D) materials have given new momentum to nano optoelectronics since the observation of localized surface plasmons interacting with the excitons. Graphene, a typical metallic 2D crystal with high optical absorbance, can provide surface plasmon effects to proximate molecules as nanostructured metals do. The spontaneous emission rate can be enhanced by the coupling of plasmonic modes with the emission frequencies of organic molecules. However, most experimental and theoretical studies report graphene plasmonics in the terahertz to mid-infrared range. Here, we demonstrate the optical transition and significant amplification of singlet emission from phosphoric molecule on a graphene substrate, with simultaneous enhancement of triplet emission in the visible regime. The spectroscopic investigations ascribe these phenomena to the coupling of graphene plasmonic modes with molecular transient dipole. The modulation of emission channel and quantum efficiency is achieved by specifically controlling the organic molecular surface density on graphene. The single layer graphene is the most efficient substrate for plasmon coupling, however, remarkable strong PL intensity is achieved by forming multi-stacks of the organic molecule-graphene hybrid layer. This work suggests a novel route for the manipulation of organic molecular emissions using graphene plasmonics, and can be applied in developing photonic devices with high quantum efficiency.

Strontium Barium Niobate (SBN) has been known for its highest electro optic coefficient amongst the known photorefractive materials. SBN thin films were prepared using Pulsed Laser Deposition (PLD) technique on the conducting LSCO coated Si Substrate and its tetragonal tungsten bronze structure was confirmed using X-ray diffraction technique. Surface Plasmon Resonance (SPR) technique has been effectively used by exploiting the SBN thin film in Otto configuration using prism coupling technique. The SPR reflectance curves for prism/air-gap/gold/SBN/LSCO/Si system were obtained by varying the applied electric field from 0 to 150kV/cm. A continuous increase in minimum reflectance of SPR curves with increase in the electric field across the SBN thin film has been obtained indicating variation in optical properties of SBN thin film on application of electric field. This increase in reflectance was attributed to the change in propagation constant of wave vector due to the change of optical properties of the film under consideration. The resonance condition changes hence the SPR minimum reflectance angle and position changes.

Compared to the highly sensitive silicon based affordable visible light detectors, infrared photodetectors require significant improvement. Localized surface plasmon resonances of metal nanoparticles can be utilized for increasing the absorption efficiency of semiconductors suited for detection of infrared radiation. In this work, plasmonic gold nanorods (AuNRs) are used to enhance generation of charge carriers and photon emission by InAs/InGaAs/GaAs quantum dots-in-a-well semiconductor heterostructures. Comparison of measured and calculated scattering spectra reveals that the AuNRs on GaAs exhibit red to green colors depending on their proximity to the GaAs surface. On the other hand, theoretical and experimental near-field optical characterization show that the electric field is tightly localized at the AuNR-GaAs interfacial regions, creating a convenient platform for investigating localized carrier generation and diffusion by monitoring the emission of InAs QDs. The carrier generation and photon emission enhancement is studied as a function of the GaAs thickness (distance) and temperature. Analysis of the QD emission enhancement as a function of distance reveals a Forster radius of 3.85 ± 0.15 nm, a near-field decay length of 4.8 ± 0.1 nm and an effective carrier diffusion length of 64.0 ± 3.0 nm. These distance parameters indicate two emission enhancement mechanisms: plasmon enhanced carrier generation inside the GaAs layer and diffusion to the InAs QDs, and direct near-field excitation of the InAs/InGaAs quantum well. The emission enhancement increases with temperature, confirming the importance of charge carrier diffusion from the GaAs to the InAs QDs, where recombination and photon emission takes place.

Tunable UV devices can enable enhanced functionalities such as multiplexed sensing, wavelength-tunable light emission and so on. Interestingly, in the UV range, graphene shows a tunable optical absorption due to pi-plasmon resonance. In this work we study the UV transmission through monolayer graphene films transferred on top of aluminum hole-arrays. Transmittance though the hole-array was measured before and after graphene transfer. Interaction of graphene pi-plasmons with surface plasmon resonances leads to strong wavelength shifts, i.e. the surface plasmon resonance at the top-interface red-shifts when graphene is added. Furthermore, it is observed that maximum shift occurs in the 280 to 310 nm wavelength range. This is attributed to an enhanced graphene optical conductivity owed to pi-plasmons.