Showing papers on "Plasmon published in 2015"

Mid-infrared plasmonic biosensing with graphene

Abstract: Infrared spectroscopy is the technique of choice for chemical identification of biomolecules through their vibrational fingerprints. However, infrared light interacts poorly with nanometric-size molecules. We exploit the unique electro-optical properties of graphene to demonstrate a high-sensitivity tunable plasmonic biosensor for chemically specific label-free detection of protein monolayers. The plasmon resonance of nanostructured graphene is dynamically tuned to selectively probe the protein at different frequencies and extract its complex refractive index. Additionally, the extreme spatial light confinement in graphene—up to two orders of magnitude higher than in metals—produces an unprecedentedly high overlap with nanometric biomolecules, enabling superior sensitivity in the detection of their refractive index and vibrational fingerprints. The combination of tunable spectral selectivity and enhanced sensitivity of graphene opens exciting prospects for biosensing.

Efficient hot-electron transfer by a plasmon-induced interfacial charge-transfer transition

Abstract: Plasmon-induced hot-electron transfer from metal nanostructures is a potential new paradigm for solar energy conversion; however, the reported efficiencies of devices based on this concept are often low because of the loss of hot electrons via ultrafast electron-electron scattering. We propose a pathway, called the plasmon-induced interfacial charge-transfer transition (PICTT), that enables the decay of a plasmon by directly exciting an electron from the metal to a strongly coupled acceptor. We demonstrated this concept in cadmium selenide nanorods with gold tips, in which the gold plasmon was strongly damped by cadmium selenide through interfacial electron transfer. The quantum efficiency of the PICTT process was high (>24%), independent of excitation photon energy over a ~1-electron volt range, and dependent on the excitation polarization.

Highly confined low-loss plasmons in graphene–boron nitride heterostructures

Abstract: Graphene plasmons were predicted to possess simultaneous ultrastrong field confinement and very low damping, enabling new classes of devices for deep-subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light–matter interactions and nano-optoelectronic switches. Although all of these great prospects require low damping, thus far strong plasmon damping has been observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this Article we exploit near-field microscopy to image propagating plasmons in high-quality graphene encapsulated between two films of hexagonal ​boron nitride (h-BN). We determine the dispersion and plasmon damping in real space. We find unprecedentedly low plasmon damping combined with strong field confinement and confirm the high uniformity of this plasmonic medium. The main damping channels are attributed to intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key to the development of graphene nanophotonic and nano-optoelectronic devices.

Plasmonic Films Can Easily Be Better: Rules and Recipes

Abstract: High-quality materials are critical for advances in plasmonics, especially as researchers now investigate quantum effects at the limit of single surface plasmons or exploit ultraviolet- or CMOS-compatible metals such as aluminum or copper. Unfortunately, due to inexperience with deposition methods, many plasmonics researchers deposit metals under the wrong conditions, severely limiting performance unnecessarily. This is then compounded as others follow their published procedures. In this perspective, we describe simple rules collected from the surface-science literature that allow high-quality plasmonic films of aluminum, copper, gold, and silver to be easily deposited with commonly available equipment (a thermal evaporator). Recipes are also provided so that films with optimal optical properties can be routinely obtained.

Plasmon-enhanced optical sensors: a review

Abstract: Surface plasmon resonance (SPR) has found extensive applications in chemi-sensors and biosensors. Plasmons play different roles in different types of optical sensors. SPR transduces a signal in a colorimetric sensor through shifts in the spectral position and intensity in response to external stimuli. SPR can also concentrate the incident electromagnetic field in a nanostructure, modulating fluorescence emission and enabling plasmon-enhanced fluorescence to be used for ultrasensitive detection. Furthermore, plasmons have been extensively used for amplifying a Raman signal in a surface-enhanced Raman scattering sensor. This paper presents a review of recent research progress in plasmon-enhanced optical sensing, giving emphasis on the physical basis of plasmon-enhanced sensors and how these principles guide the design of sensors. In particular, this paper discusses the design strategies for nanomaterials and nanostructures to plasmonically enhance optical sensing signals, also highlighting the applications of plasmon-enhanced optical sensors in healthcare, homeland security, food safety and environmental monitoring.

Plasmon-induced resonance energy transfer for solar energy conversion

Abstract: In Forster resonance energy transfer (FRET), energy non-radiatively transfers from a blue-shifted emitter to a red-shifted absorber by dipole–dipole coupling. This study shows that plasmonics enables the opposite transfer direction, transferring the plasmonic energy towards the short-wavelength direction to induce charge separation in a semiconductor. Plasmon-induced resonance energy transfer (PIRET) differs from FRET because of the lack of a Stoke's shift, non-local absorption effects and a strong dependence on the plasmon's dephasing rate and dipole moment. PIRET non-radiatively transfers energy through an insulating spacer layer, which prevents interfacial charge recombination losses and dephasing of the plasmon from hot-electron transfer. The distance dependence of dipole–dipole coupling is mapped out for a range of detuning across the plasmon resonance. PIRET can efficiently harvest visible and near-infrared sunlight with energy below the semiconductor band edge to help overcome the constraints of band-edge energetics for single semiconductors in photoelectrochemical cells, photocatalysts and photovoltaics. Plasmon-induced resonance energy transfer is revealed and explored for solar energy harvesting from visible and near-infrared light.

Review of plasmonic fiber optic biochemical sensors: improving the limit of detection.

Abstract: This paper presents a brief overview of the technologies used to implement surface plasmon resonance (SPR) effects into fiber-optic sensors for chemical and biochemical applications and a survey of results reported over the last ten years. The performance indicators that are relevant for such systems, such as refractometric sensitivity, operating wavelength, and figure of merit (FOM), are discussed and listed in table form. A list of experimental results with reported limits of detection (LOD) for proteins, toxins, viruses, DNA, bacteria, glucose, and various chemicals is also provided for the same time period. Configurations discussed include fiber-optic analogues of the Kretschmann–Raether prism SPR platforms, made from geometry-modified multimode and single-mode optical fibers (unclad, side-polished, tapered, and U-shaped), long period fiber gratings (LPFG), tilted fiber Bragg gratings (TFBG), and specialty fibers (plastic or polymer, microstructured, and photonic crystal fibers). Configurations involving the excitation of surface plasmon polaritons (SPP) on continuous thin metal layers as well as those involving localized SPR (LSPR) phenomena in nanoparticle metal coatings of gold, silver, and other metals at visible and near-infrared wavelengths are described and compared quantitatively.

Plasmonic Copper Sulfide Nanocrystals Exhibiting Near-Infrared Photothermal and Photodynamic Therapeutic Effects

Abstract: Recently, plasmonic copper sulfide (Cu2–xS) nanocrystals (NCs) have attracted much attention as materials for photothermal therapy (PTT). Previous reports have correlated photoinduced cell death to the photothermal heat mechanism of these NCs, and no evidence of their photodynamic properties has been reported yet. Herein we have prepared physiologically stable near-infrared (NIR) plasmonic copper sulfide NCs and analyzed their photothermal and photodynamic properties, including therapeutic potential in cultured melanoma cells and a murine melanoma model. Interestingly, we observe that, besides a high PTT efficacy, these copper sulfide NCs additionally possess intrinsic NIR induced photodynamic activity, whereupon they generate high levels of reactive oxygen species. Furthermore, in vitro and in vivo acute toxic responses of copper sulfide NCs were also elicited. This study highlights a mechanism of NIR light induced cancer therapy, which could pave the way toward more effective nanotherapeutics.

Realizing Strong Light-Matter Interactions between Single-Nanoparticle Plasmons and Molecular Excitons at Ambient Conditions.

Abstract: Realizing strong light-matter interactions between individual two-level systems and resonating cavities in atomic and solid state systems opens up possibilities to study optical nonlinearities on a single-photon level, which can be useful for future quantum information processing networks. However, these efforts have been hampered by unfavorable experimental conditions, such as cryogenic temperatures and ultrahigh vacuum, required to study such systems and phenomena. Although several attempts to realize strong light-matter interactions at room temperature using plasmon resonances have been made, successful realizations on the single-nanoparticle level are still lacking. Here, we demonstrate the strong coupling between plasmons confined within a single silver nanoprism and excitons in molecular J aggregates at ambient conditions. Our findings show that deep subwavelength mode volumes V together with quality factors Q that are reasonably high for plasmonic nanostructures result in a strong-coupling figure of merit-Q/root V as high as similar to 6 x 10(3) mu m(-3/2), a value comparable to state-of-the-art photonic crystal and microring resonator cavities. This suggests that plasmonic nanocavities, and specifically silver nanoprisms, can be used for room temperature quantum optics.

Localized Surface Plasmon Resonance Biosensing: Current Challenges and Approaches

Abstract: Localized surface plasmon resonance (LSPR) has emerged as a leader among label-free biosensing techniques in that it offers sensitive, robust, and facile detection. Traditional LSPR-based biosensing utilizes the sensitivity of the plasmon frequency to changes in local index of refraction at the nanoparticle surface. Although surface plasmon resonance technologies are now widely used to measure biomolecular interactions, several challenges remain. In this article, we have categorized these challenges into four categories: improving sensitivity and limit of detection, selectivity in complex biological solutions, sensitive detection of membrane-associated species, and the adaptation of sensing elements for point-of-care diagnostic devices. The first section of this article will involve a conceptual discussion of surface plasmon resonance and the factors affecting changes in optical signal detected. The following sections will discuss applications of LSPR biosensing with an emphasis on recent advances and approaches to overcome the four limitations mentioned above. First, improvements in limit of detection through various amplification strategies will be highlighted. The second section will involve advances to improve selectivity in complex media through self-assembled monolayers, “plasmon ruler” devices involving plasmonic coupling, and shape complementarity on the nanoparticle surface. The following section will describe various LSPR platforms designed for the sensitive detection of membrane-associated species. Finally, recent advances towards multiplexed and microfluidic LSPR-based devices for inexpensive, rapid, point-of-care diagnostics will be discussed.

Real-time tunable lasing from plasmonic nanocavity arrays

Abstract: Plasmon lasers can support ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. However, most plasmon-based nanolasers rely on solid gain materials (inorganic semiconducting nanowire or organic dye in a solid matrix) that preclude the possibility of dynamic tuning. Here we report an approach to achieve real-time, tunable lattice plasmon lasing based on arrays of gold nanoparticles and liquid gain materials. Optically pumped arrays of gold nanoparticles surrounded by liquid dye molecules exhibit lasing emission that can be tuned as a function of the dielectric environment. Wavelength-dependent time-resolved experiments show distinct lifetime characteristics below and above the lasing threshold. By integrating gold nanoparticle arrays within microfluidic channels and flowing in liquid gain materials with different refractive indices, we achieve dynamic tuning of the plasmon lasing wavelength. Tunable lattice plasmon lasers offer prospects to enhance and detect weak physical and chemical processes on the nanoscale in real time.

Theory and computation of hot carriers generated by surface plasmon polaritons in noble metals

Abstract: Hot carriers (HC) generated by surface plasmon polaritons (SPPs) in noble metals are promising for application in optoelectronics, plasmonics and renewable energy. However, existing models fail to explain key quantitative details of SPP-to-HC conversion experiments. Here we develop a quantum mechanical framework and apply first-principles calculations to study the energy distribution and scattering processes of HCs generated by SPPs in Au and Ag. We find that the relative positions of the s and d bands of noble metals regulate the energy distribution and mean free path of the HCs, and that the electron–phonon interaction controls HC energy loss and transport. Our results prescribe optimal conditions for HC generation and extraction, and invalidate previously employed free-electron-like models. Our work combines density functional theory, GW and electron–phonon calculations to provide microscopic insight into HC generation and ultrafast dynamics in noble metals.

Multifunctional Au-ZnO Plasmonic Nanostructures for Enhanced UV Photodetector and Room Temperature NO Sensing Devices

Abstract: In this study we report the enhancement of UV photodetection and wavelength tunable light induced NO gas sensing at room temperature using Au-ZnO nanocomposites synthesized by a simple photochemical process Plasmonic Au-ZnO nanostructures with a size less than the incident wavelength have been found to exhibit a localized surface plasmon resonance (LSPR) that leads to a strong absorption, scattering and local field enhancement The photoresponse of Au-ZnO nanocomposite can be effectively enhanced by 80 times at 335 nm over control ZnO We also demonstrated Au-ZnO nanocomposite's application to wavelength tunable gas sensor operating at room temperature The sensing response of Au-ZnO nancomposite is enhanced both in UV and visible region, as compared to control ZnO The sensitivity is observed to be higher in the visible region due to the LSPR effect of Au NPs The selectivity is found to be higher for NO gas over CO and some other volatile organic compounds (VOCs), with a minimum detection limit of 01 ppb for Au-ZnO sensor at 335 nm

Distinguishing between plasmon-induced and photoexcited carriers in a device geometry

Abstract: The use of surface plasmons, charge density oscillations of conduction electrons of metallic nanostructures, to boost the efficiency of light-harvesting devices through increased light-matter interactions could drastically alter how sunlight is converted into electricity or fuels. These excitations can decay directly into energetic electron-hole pairs, useful for photocurrent generation or photocatalysis. However, the mechanisms behind plasmonic carrier generation remain poorly understood. Here we use nanowire-based hot-carrier devices on a wide-bandgap semiconductor to show that plasmonic carrier generation is proportional to internal field-intensity enhancement and occurs independently of bulk absorption. We also show that plasmon-induced hot electrons have higher energies than carriers generated by direct excitation and that reducing the barrier height allows for the collection of carriers from plasmons and direct photoexcitation. Our results provide a route to increasing the efficiency of plasmonic hot-carrier devices, which could lead to more efficient devices for converting sunlight into usable energy.

Holographic optical metasurfaces: a review of current progress

Abstract: In this article, we review recent developments in the field of surface electromagnetic wave holography. The holography principle is used as a tool to solve an inverse engineering problem consisting of designing novel plasmonic interfaces to excite either surface waves or free-space beams with any desirable field distributions. Leveraging on the new nanotechnologies to carve subwavelength features within the large diffracting apertures of conventional holograms, it is now possible to create binary holographic interfaces to shape both amplitude phase and polarization of light. The ability of the new generation of ultrathin and compact holographic optical devices to fully address light properties could find widespread applications in photonics.

Bright visible light emission from graphene

Abstract: Electrically biased suspended graphene devices show an intense electroluminescence in the visible range with a tunable emission spectrum. Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics1,2. In particular, the strong light–matter interaction in graphene3 has allowed for the development of state-of-the-art photodetectors4,5, optical modulators6 and plasmonic devices7. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range8,9. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced10. Hot electrons (∼2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency8,9. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

Hyperbolic Plasmons and Topological Transitions Over Uniaxial Metasurfaces

Abstract: We explore the unusual electromagnetic response of ultrathin anisotropic $\ensuremath{\sigma}$-near-zero uniaxial metasurfaces, demonstrating extreme topological transitions---from closed elliptical to open hyperbolic---for surface plasmon propagation, associated with a dramatic tailoring of the local density of states. The proposed metasurfaces may be implemented using nanostructured graphene monolayers and open unprecedented venues for extreme light confinement and unusual propagation and guidance, combined with large tunability via electric bias.

Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field.

Abstract: Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave-particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

Plasmon-Enhanced Formic Acid Dehydrogenation Using Anisotropic Pd–Au Nanorods Studied at the Single-Particle Level

Abstract: Plasmonic bimetal nanostructures can be used to drive the conventional catalytic reactions efficiently at low temperature with the utilization of solar energy. This work developed Pd-modified Au nanorods, which work as the light absorber and the catalytically active site simultaneously, and exhibit efficient plasmon-enhanced catalytic formic acid dehydrogenation even when below room temperature (5 °C). Plasmon-induced interface interaction and photoreaction dynamics of individual nanorods were investigated by single-particle photoluminescence measurement, and a complete quenching phenomenon at the LSPR region was observed for the first time. More importantly, the spatial distribution of the SPR-induced enhancement, analyzed by the finite difference time domain (FDTD) simulation, shows that only tip-coated Pd can be affected for the occurrence of plasmon resonance energy transfer. This finding provides a route to decrease the amount of Pd species by the selective deposition only at the field-enhanced sites.

Anomalous ultrafast dynamics of hot plasmonic electrons in nanostructures with hot spots

Abstract: The interaction of light and matter in metallic nanosystems is mediated by the collective oscillation of surface electrons, called plasmons. After excitation, plasmons are absorbed by the metal electrons through inter- and intraband transitions, creating a highly non-thermal distribution of electrons. The electron population then decays through electron-electron interactions, creating a hot electron distribution within a few hundred femtoseconds, followed by a further relaxation via electron-phonon scattering on the timescale of a few picoseconds. In the spectral domain, hot plasmonic electrons induce changes to the plasmonic resonance of the nanostructure by modifying the dielectric constant of the metal. Here, we report on the observation of anomalously strong changes to the ultrafast temporal and spectral responses of these excited hot plasmonic electrons in hybrid metal/oxide nanostructures as a result of varying the geometry and composition of the nanostructure and the excitation wavelength. In particular, we show a large ultrafast, pulsewidth-limited contribution to the excited electron decay signal in hybrid nanostructures containing hot spots. The intensity of this contribution correlates with the efficiency of the generation of highly excited surface electrons. Using theoretical models, we attribute this effect to the generation of hot plasmonic electrons from hot spots. We then develop general principles to enhance the generation of energetic electrons through specifically designed plasmonic nanostructures that could be used in applications where hot electron generation is beneficial, such as in solar photocatalysis, photodetectors and nonlinear devices.

Optical Properties and Plasmonic Performance of Titanium Nitride

Abstract: Titanium nitride (TiN) is one of the most well-established engineering materials nowadays. TiN can overcome most of the drawbacks of palsmonic metals due to its high electron conductivity and mobility, high melting point and due to the compatibility of its growth with Complementary Metal Oxide Semiconductor (CMOS) technology. In this work, we review the dielectric function spectra of TiN and we evaluate the plasmonic performance of TiN by calculating (i) the Surface Plasmon Polariton (SPP) dispersion relations and (ii) the Localized Surface Plasmon Resonance (LSPR) band of TiN nanoparticles, and we demonstrate a significant plasmonic performance of TiN.

Tunable Light–Matter Interaction and the Role of Hyperbolicity in Graphene–hBN System

Abstract: Hexagonal boron nitride (hBN) is a natural hyperbolic material, which can also accommodate highly dispersive surface phonon-polariton modes. In this paper, we examine theoretically the mid-infrared optical properties of graphene–hBN heterostructures derived from their coupled plasmon–phonon modes. We find that the graphene plasmon couples differently with the phonons of the two Reststrahlen bands, owing to their different hyperbolicity. This also leads to distinctively different interaction between an external quantum emitter and the plasmon–phonon modes in the two bands, leading to substantial modification of its spectrum. The coupling to graphene plasmons allows for additional gate tunability in the Purcell factor and narrow dips in its emission spectra.

Design and Modeling of Spoof Surface Plasmon Modes-Based Microwave Slow-Wave Transmission Line

Abstract: This paper presents a theoretical model and validates experimentally the microwave slow-wave transmission line (SW-TL) based on spoof surface plasmon (SSP) modes Equivalent circuit models are first presented for characterizing the SSP structures and developed to serve as an insightful guideline to design the SW-TL at a given cutoff frequency and Bloch impedance A mode converter connecting a conventional microstrip transmission line to the SW-TL is necessarily proposed to ensure that the quasi-TEM modes of the microstrip line are gradually transformed to the operating TM modes of the SW-TL The presented schematic of SW-TL paves a promising avenue for the unprecedented interconnector footprint miniaturization of integrated circuits, and the enhanced electromagnetic compatibility, for example, in multilayered monolithic microwave integrated circuits

Fano Resonance and Spectrally Modified Photoluminescence Enhancement in Monolayer MoS2 Integrated with Plasmonic Nanoantenna Array

Abstract: The manipulation of light-matter interactions in two-dimensional atomically thin crystals is critical for obtaining new optoelectronic functionalities in these strongly confined materials. Here, by integrating chemically grown monolayers of MoS2 with a silver-bowtie nanoantenna array supporting narrow surface-lattice plasmonic resonances, a unique two-dimensional optical system has been achieved. The enhanced exciton-plasmon coupling enables profound changes in the emission and excitation processes leading to spectrally tunable, large photoluminescence enhancement as well as surface-enhanced Raman scattering at room temperature. Furthermore, due to the decreased damping of MoS2 excitons interacting with the plasmonic resonances of the bowtie array at low temperatures stronger exciton-plasmon coupling is achieved resulting in a Fano line shape in the reflection spectrum. The Fano line shape, which is due to the interference between the pathways involving the excitation of the exciton and plasmon, can be tuned by altering the coupling strengths between the two systems via changing the design of the bowties lattice. The ability to manipulate the optical properties of two-dimensional systems with tunable plasmonic resonators offers a new platform for the design of novel optical devices with precisely tailored responses.

Nanoscale temperature mapping in operating microelectronic devices

Abstract: Modern microelectronic devices have nanoscale features that dissipate power nonuniformly, but fundamental physical limits frustrate efforts to detect the resulting temperature gradients. Contact thermometers disturb the temperature of a small system, while radiation thermometers struggle to beat the diffraction limit. Exploiting the same physics as Fahrenheit's glass-bulb thermometer, we mapped the thermal expansion of Joule-heated, 80-nanometer-thick aluminum wires by precisely measuring changes in density. With a scanning transmission electron microscope and electron energy loss spectroscopy, we quantified the local density via the energy of aluminum's bulk plasmon. Rescaling density to temperature yields maps with a statistical precision of 3 kelvin/hertz(-1/2), an accuracy of 10%, and nanometer-scale resolution. Many common metals and semiconductors have sufficiently sharp plasmon resonances to serve as their own thermometers.

Photonic Crystal Fiber-Based Surface Plasmon Resonance Sensor with Selective Analyte Channels and Graphene-Silver Deposited Core

Abstract: We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber’s properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU−1) with resolution as high as 2.4 × 10−5 RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46–1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor’s footprint.

Surface plasmon resonance sensor based on D-shaped microstructured optical fiber with hollow core.

Abstract: To solve the phase matching and analyte filling problems in the microstructured optical fiber (MOF)-based surface plasmon resonance (SPR) sensors, we present the D-shaped hollow core MOF-based SPR sensor. The air hole in the fiber core can lower the refractive index of a Gaussian-like core mode to match with that of a plasmon mode. The analyte is deposited directly onto the D-shaped flat surface instead of filling the fiber holes. We numerically investigate the effect of the air hole in the core on the SPR sensing performance, and identify the sensor sensitivity on wavelength, amplitude and phase. This work allows us to determine the feasibility of using the D-shaped hollow-core MOFs to develop a high-sensitivity, real-time and distributed SPR sensor.

Distinguishing adjacent molecules on a surface using plasmon-enhanced Raman scattering

Abstract: Different adjacent molecules adsorbed on a surface can be distinguished by their Raman modes using a plasmon-enhanced Raman scattering technique with a spatial resolution below 1 nm.

Leveraging Nanocavity Harmonics for Control of Optical Processes in 2D Semiconductors

Abstract: Optical cavities with multiple tunable resonances have the potential to provide unique electromagnetic environments at two or more distinct wavelengthscritical for control of optical processes such as nonlinear generation, entangled photon generation, or photoluminescence (PL) enhancement. Here, we show a plasmonic nanocavity based on a nanopatch antenna design that has two tunable resonant modes in the visible spectrum separated by 350 nm and with line widths of ∼60 nm. The importance of utilizing two resonances simultaneously is demonstrated by integrating monolayer MoS2 ,a two-dimensional semiconductor, into the colloidally synthesized nanocavities. We observe a 2000-fold enhancement in the PL intensity of MoS2which has intrinsically low absorption and small quantum yieldat room temperature, enabled by the combination of tailored absorption enhancement at the first harmonic and PL quantum-yield enhancement at the fundamental resonance.

Plasmon enhancement of luminescence upconversion

Abstract: Frequency conversion has always been an important topic in optics. Nonlinear optics has traditionally focused on frequency conversion based on nonlinear susceptibility but with the recent development of upconversion nanomaterials, luminescence upconversion has begun to receive renewed attention. While upconversion nanomaterials open doors to a wide range of new opportunities, they remain too inefficient for most applications. Incorporating plasmonic nanostructures provides a promising pathway to highly efficient upconversion. Naturally, a plethora of theoretical and experimental studies have been published in recent years, reporting enhancements up to several hundred. It is however difficult to make meaningful comparisons since the plasmonic fields are highly sensitive to the local geometry and excitation condition. Also, many luminescence upconversion processes involve multiple steps via different physical mechanisms and the overall output is often determined by a delicate interplay among them. This review is aimed at offering a comprehensive framework for plasmon enhanced luminescence upconversion. We first present quantum electrodynamics descriptions for all the processes involved in luminescence upconversion, which include absorption, emission, energy transfer and nonradiative transitions. We then present a bird's eye view of published works on plasmon enhanced upconversion, followed by more detailed discussion on comparable classes of nanostructures, the effects of spacer layers and local heating, and the dynamics of the plasmon enhanced upconversion process. Plasmon enhanced upconversion is a challenging and exciting field from the fundamental scientific perspective and also from technological standpoints. It offers an excellent system to study how optical processes are affected by the local photonic environment. This type of research is particularly timely as the plasmonics is placing heavier emphasis on nonlinearity. At the same time, efficient upconversion could make a significant impact on many applications including solar energy conversion and biomedical imaging. The marriage of luminescent materials research with nanophotonics currently being initiated with plasmon enhanced upconversion research explores a new frontier in photonics that could potentially spawn many exciting new fields.