Use Of Plasmons Research Articles

Polarized and Evanescent Guided Wave Surface-Enhanced Raman Spectroscopy of Ligand Interactions on a Plasmonic Nanoparticle Optical Chemical Bench.

This study examined applications of polarized evanescent guided wave surface-enhanced Raman spectroscopy to determine the binding and orientation of small molecules and ligand-modified nanoparticles, and the relevance of this technique to lab-on-a-chip, surface plasmon polariton and other types of field enhancement techniques relevant to Raman biosensing. A simplified tutorial on guided-wave Raman spectroscopy is provided that introduces the notion of plasmonic nanoparticle field enhancements to magnify the otherwise weak TE- and TM-polarized evanescent fields for Raman scattering on a simple plasmonic nanoparticle slab waveguide substrate. The waveguide construct is called an optical chemical bench (OCB) to emphasize its adaptability to different kinds of surface chemistries that can be envisaged to prepare optical biosensors. The OCB forms a complete spectroscopy platform when integrated into a custom-built Raman spectrograph. Plasmonic enhancement of the evanescent field is achieved by attaching porous carpets of Au@Ag core shell nanoparticles to the surface of a multi-mode glass waveguide substrate. We calibrated the OCB by establishing the dependence of SER spectra of adsorbed 4-mercaptopyridine and 4-aminobenzoic acid on the TE/TM polarization state of the evanescent field. We contrasted the OCB construct with more elaborate photonic chip devices that also benefit from enhanced evanescent fields, but without the use of plasmonics. We assemble hierarchies of matter to show that the OCB can resolve the binding of Fe2+ ions from water at the nanoscale interface of the OCB by following the changes in the SER spectra of 4MPy as it coordinates the cation. A brief introduction to magnetoplasmonics sets the stage for a study that resolves the 4ABA ligand interface between guest magnetite nanoparticles adsorbed onto host plasmonic Au@Ag nanoparticles bound to the OCB. In some cases, the evanescent wave TM polarization was strongly attenuated, most likely due to damping by inertial charge carriers that favor optical loss for this polarization state in the presence of dense assemblies of plasmonic nanoparticles. The OCB offers an approach that provides vibrational and orientational information for (bio)sensing at interfaces that may supplement the information content of evanescent wave methods that rely on perturbations in the refractive index in the region of the evanescent wave.

Measuring dielectric and electro-optic responses of thin films using plasmonic devices.

This paper introduces a simple method for the measurement of the relative permittivity and the Pockels coefficient of electro-optic (EO) materials in a waveguide up to sub-THz frequencies. By miniaturizing the device and making use of plasmonics, the complexities of traditional methods are mitigated. This work elaborates the fabrication tolerance and simplicity of the method, and highlights its applicability to various materials, substrates and configurations. The method is showcased using drop-casted perovskite barium titanate (BaTiO3, BTO) nano-particle thin-films and it has previously been used to measure epitaxial thin film BTO. In this work we show the effective relative permittivity of drop casted BTO to be εeff ∼ 30 at 200 MHz, dropping to ∼ 18 at 67 GHz and similarly, the effective Pockels coefficient was found to be reff ∼ 16 at 350 MHz and ∼ 8 at 70 GHz. These values are a factor > 50 below the values found for thin film BTO. Yet, the fact that the method can be applied to such different samples and Pockels strengths gives testimony to its versatility and sensitivity.

Optical response of Au films for reproducible Si nano-structuring and its application for efficient micro-drop SERS with portable Raman system

Si nanostructuring by metal assisted chemical etching is highly sensitive to morphology of thin metal film, here we demonstrate use of plasmon driven optical or dielectric response of Au films for predicting nanopore or nanowire Si prior to etching, ensuring the process reproducibility. By controlling growth temperature, it is shown that same mass thickness of Au films can produce either nanopore, nanowire or hybrid (mix of the two) Si nanostructures, useful for various applications. Ag nanoparticles coated nanostructure Si is shown to be efficient surface enhanced Raman spectroscopy (SERS) substrate for dry state measurements with micro-Raman system. In contrast, by exploiting super-hydrophilicity and strong light coupling of nanostructure Si, a novel micro-drop SERS using portable Raman spectrometer is demonstrated as low-cost, reliable and easy field-deployable technique. With very low sample volume about 50 μL of as prepared Au nanoparticles and analyte, it is capable of producing SERS signal in samples containing 120 pg thiram, 240 pg Rh6G, 455 pg malachite green and 48 pg methylene blue. With advantages of micro-drop SERS, mainly high intensity signal with 3D dynamic hot-spots at high laser power, longer shelf-life colloidal gold, reusable substrates with no prior sample preparation, this method is envisaged to be an inexpensive technique for on-site trace detection applications and importantly quick generation of large experimental SERS data-set for machine learning (ML) driven studies. This is demonstrated by principal component analysis with ML classifier for 100% accurate prediction of trace dyes, pesticide and their binary mixtures.

Plasmonic Photocatalysis: Activating Chemical Bonds through Light and Plasmon

AbstractThe exceptionally large charge‐carrier density in photoexcited plasmonic nanoparticles (NPs) can be used for the making and breaking of high‐energy chemical bonds, which forms the basis of plasmonic photocatalysis. This review showcases the roadmap of important events and major bottlenecks in plasmonic photocatalysis, along with highlighting a few probable solutions for achieving the desired targets. The review starts with a discussion on various excitation and relaxation pathways, followed by the section on initial use of plasmons in enhancing the photocatalytic properties of semiconductor materials. Next, the sole use of plasmonic NPs in driving useful and industrially relevant chemical transformations is discussed. This is followed by a critical assessment of various challenges and opportunities in the area, along with a discussion on emerging experiments capable of overcoming these challenges. Decades of research have provided a clear understanding on charge generation and decay processes in plasmonic NPs. However, achieving an efficient separation and utilization of charge carriers is still a roadblock in realizing the full potential of plasmonic NPs in catalysis. In short, doing chemistry with plasmons is attractive; but it is high time to develop strategies that can quantitatively utilize the charge carriers for driving chemical transformations in a selective and efficient way.

Photon Upconversion for Photovoltaics and Photocatalysis: ACriticalReview.

Opportunities for enhancing solar energy harvesting using photon upconversion are reviewed. The increasing prominence of bifacial solar cells is an enabling factor for the implementation of upconversion, however, when the realistic constraints of current best-performing silicon devices are considered, many challenges remain before silicon photovoltaics operating under nonconcentrated sunlight can be enhanced via lanthanide-based upconversion. A photophysical model reveals that >1-2 orders of magnitude increase in the intermediate state lifetime, energy transfer rate, or generation rate would be needed before such solar upconversion could start to become efficient. Methods to increase the generation rate such as the use of cosensitizers to expand the absorption range and the use of plasmonics or photonic structures are reviewed. The opportunities and challenges for these approaches (or combinations thereof) to achieve efficient solar upconversion are discussed. The opportunity for enhancing the performance of technologies such as luminescent solar concentrators by combining upconversion together with micro-optics is also reviewed. Triplet-triplet annihilation-based upconversion is progressing steadily toward being relevant to lower-bandgap solar cells. Looking toward photocatalysis, photophysical modeling indicates that current blue-to-ultraviolet lanthanide upconversion systems are very inefficient. However, hope remains in this direction for organic upconversion enhancing the performance of visible-light-active photocatalysts.

Growth of faceted, monolayer-coated nanovoids in aluminium

Voids can cause structural and electrical failure in materials but also show promising properties for use in plasmonics and photonics. Key to understanding the mechanical, optoelectronic and thermal properties of voids is an accurate characterisation of their structure and evolution, in particular of their surfaces. Here we report the formation of voids, coated with a monolayer of tin, in two aluminium alloys. Amongst such voids, those with high aspect ratios (“tubular voids”) have been found to grow to hundreds of nanometres in length under certain heat treatment conditions. Using spectroscopy and atomic-resolution imaging in scanning transmission electron microscopy (STEM), we reveal that the voids are covered by a single-atomic-layer tin shell, which is continuous over the entire void surface and has the same atomic structure as the Al matrix. Tubular voids are invariably attached to Sn particles that have a specific orientation relationship with the Al matrix, whilst equiaxed voids are generally not attached to Sn particles exhibiting such an orientation relationship. The aspect ratios of tubular voids show a strong correlation with the coherence between the tin particle and the arrangement of the tin atoms in the void coating, along the growth directions of the tubular voids. These tubular voids could be considered as single-walled nanotubes that are embedded in the aluminium matrix and also as “anti-nanorods”. They are of great research interest because they are more likely to cause mechanical or electrical failure than equiaxed voids with the same volume. The coated voids are highly reproducible, controllable and free from contamination, and are therefore ideal for future studies of localized surface plasmon resonances (LSPRs).

Large plasmonic field enhancement on hydrogen-absorbing transition metals at lower frequencies: Implications for hydrogen storage, sensing, and nuclear fusion

The plasmonic enhancement of electromagnetic field energy density around planar surfaces of hydrogen-absorbing transition metals, Pd, Ti, and Ni, has been quantitatively investigated, to explore the use of plasmonics in the forthcoming hydrogen economy. We have observed that a large degree of energy focusing, with the enhancement factor over several hundreds, is available for these transition metals in the microwave region, even surpassing the enhancement for noble metals. This finding could potentially lead to technological progress in various hydrogen-related energy applications including hydrogen storage, sensing, and nuclear fusion.

(Invited) Plasmon-Driven Chemical Reactions

Plasmonic metal nanocrystals can interact strongly with light, efficiently converting light into heat and generating hot charge carriers. Both plasmonic photothermal conversion and hot carrier generation can accelerate chemical reactions. The use of plasmons to drive chemical reactions has recently become a new and active research field (Adv. Mater. 2014, 26, 5274). Plasmonic hot charge carriers can not only enhance the reaction yield and selectivity, but also introduce new reaction pathways. The lifetime of plasmonic hot charge carriers is on the femtosecond scale. Without immediate usage, they will rapidly relax, converting their energy into heat. We have employed two approaches to enable the use of plasmonic hot charge carriers. The first is the integration of Au or Ag nanoparticles with Pd or Pt nanoparticles. We have applied this approach to enhance Suzuki coupling reactions by localized plasmons (J. Am. Chem. Soc. 2013, 135, 5588; Adv. Funct. Mater. 2017, 27, 1700016). The second is the integration of plasmonic metals with semiconductors. A barrier is formed at the interface. The generated hot electrons and holes can quickly inject into the conduction or valence band and therefore get separated. The injected charge carriers can then drive chemical reactions. We have synthesized Au/TiO2 (Energy Environ. Sci. 2014, 7, 3431; J. Am. Chem. Soc. 2018, 140, 8497), Au/CeO2 (ACS Nano 2014, 8, 8152) and Au/BiOCl hybrid structures (J. Am. Chem. Soc. 2017, 139, 3513) as plasmonic photocatalysts to drive the photo-generation of reactive oxygen species, the selective oxidation of alcohols, and N2 photofixation. Specifically, oxygen vacancies have been introduced in the metal oxides to “work in-tandem” together with plasmonic hot charge carriers. For example, during the use of Au/BiOCl hybrid structures for the photocatalytic selective oxidation of benzyl alcohol, oxygen vacancies on BiOCl facilitate the trapping and transfer of plasmonic hot electrons to adsorbed O2, producing superoxide anion radicals, while plasmonic hot holes remaining on the Au surface mildly oxidize benzyl alcohol to corresponding carbon-centered radicals. The ring addition between these two radical species leads to the production of benzaldehyde along with an unexpected oxygen atom transfer from O2 to the product. In contrast, the oxygen atom in the product is usually from the benzyl alcohol reactant. In another example, Au nanoparticles are anchored on ultrathin TiO2 nanosheets with oxygen vacancies. The oxygen vacancies on the nanosheets chemisorb and activate N2 molecules, which are subsequently reduced to ammonia by hot electrons generated from plasmon excitation of the Au nanoparticles. The hybrid photocatalyst can accomplish photodriven N2 fixation in the “working-in-tandem” pathway at room temperature and atmospheric pressure. The apparent quantum efficiency of 0.82% at 550 nm for the conversion of incident photons to ammonia is higher than those reported so far. The oxygen vacancies play three roles. They act as the active sites for N2 molecules; they cause defect states within the bandgap for trapping plasmonic hot electrons and therefore lengthening their lifetime; and they function as a bridge between plasmonic hot electrons and the activated N2 molecules. This work offers a new approach for the rational design of efficient catalysts towards sustainable N2 fixation through a less energy-demanding photochemical process compared to the industrial Haber-Bosch process.

Gradient metal nanoislands as a unified surface enhanced Raman scattering and surface enhanced infrared absorption platform for analytics.

In the last few decades, the use of plasmonics in vibrational spectroscopy has expanded the scope of (bio)analytical investigations. Nevertheless, there is a demand for a combined platform that can be simultaneously efficient for Surface Enhanced Raman Scattering (SERS) and Surface Enhanced Infrared Absorption (SEIRA). Here, we present a solution on the basis of a plasmonic Ag nanoparticle layer with a thickness gradient. The optical resonance along the layer varies from the visible to the infrared range offering optimal and intermediate sites for SERS and SEIRA of the analyte molecule (mercaptobenzonitrile). Enhancement factors for the same mode were determined to be ca. 104 and 170 for SERS and SEIRA, respectively. We present a full optical and vibrational characterization and demonstrate further tunability. The platform resolves reproducibility and comparability issues by a combination of the two methods. It also offers individualized solutions for different investigation conditions, i.e. a choice between excitation wavelengths and resonant Raman molecules. The multiple applicabilities of the presented unifying substrate can contribute to the expansion of the vibrational spectroscopic field and to analytics.

Quantum plasmonic N00N state in a silver nanowire and its use for quantum sensing

The control of quantum states of light at the nanoscale has become possible in recent years with the use of plasmonics. Here, many types of nanophotonic devices and applications have been suggested that take advantage of quantum optical effects, despite the inherent presence of loss. A key example is quantum plasmonic sensing, which provides sensitivity beyond the classical limit using entangled N00N states and their generalizations in a compact system operating below the diffraction limit. In this work, we experimentally demonstrate the excitation and propagation of a two-plasmon entangled N00N state (N=2) in a silver nanowire, and assess the performance of our system for carrying out quantum sensing. Polarization entangled photon pairs are converted into plasmons in the silver nanowire, which propagate over a distance of 5 um and re-convert back into photons. A full analysis of the plasmonic system finds that the high-quality entanglement is preserved throughout. We measure the characteristic super-resolution phase oscillations of the entangled state via coincidence measurements. We also identify various sources of loss in our setup and show how they can be mitigated, in principle, in order to reach super-sensitivity that goes beyond the classical sensing limit. Our results show that polarization entanglement can be preserved in a plasmonic nanowire and that sensing with a quantum advantage is possible with moderate loss present.

Enhanced Photoluminescence from Organic Dyes Coupled to Periodic Array of Zirconium Nitride Nanoparticles

Noble metals, particularly gold, have been conventionally used for their suitable optical properties in the field of plasmonics. However, gold has a relatively low melting temperature, especially when nanosized, and the abundance of gold in the earth’s crust is low. These material-related limitations hinder the exploration of the use of plasmonics in several application areas. Transition metal nitrides are promising material alternatives because of their high mechanical and thermal stabilities, in addition to their acceptable plasmonic properties in the visible spectral region. Zirconium nitride (ZrN) is one such promising alternative owing to a higher carrier density than that of titanium nitride (TiN), which has been the most studied complementary material to gold. In this study, we have fabricated periodic arrays of ZrN nanoparticles and found that the ZrN array enhances the photoluminescence from an organic dye on the array; the photoluminescence intensity is increased by as much as 9.7× in the visibl...

Losses in plasmonics: from mitigating energy dissipation to embracing loss-enabled functionalities

Unlike conventional optics, plasmonics enables unrivalled concentration of optical energy well beyond the diffraction limit of light. However, a significant part of this energy is dissipated as heat. Plasmonic losses present a major hurdle in the development of plasmonic devices and circuits that can compete with other mature technologies. Until recently, they have largely kept the use of plasmonics to a few niche areas where loss is not a key factor, such as surface enhanced Raman scattering and biochemical sensing. Here, we discuss the origin of plasmonic losses and various approaches to either minimize or mitigate them based on understanding of fundamental processes underlying surface plasmon modes excitation and decay. Along with the ongoing effort to find and synthesize better plasmonic materials, optical designs that modify the optical powerflow through plasmonic nanostructures can help in reducing both radiative damping and dissipative losses of surface plasmons. Another strategy relies on the development of hybrid photonic-plasmonic devices by coupling plasmonic nanostructures to resonant optical elements. Hybrid integration not only helps to reduce dissipative losses and radiative damping of surface plasmons, but also makes possible passive radiative cooling of nano-devices. Finally, we review emerging applications of thermoplasmonics that leverage Ohmic losses to achieve new enhanced functionalities. The most successful commercialized example of a loss-enabled novel application of plasmonics is heat-assisted magnetic recording. Other promising technological directions include thermal emission manipulation, cancer therapy, nanofabrication, nano-manipulation, plasmon-enabled material spectroscopy and thermo-catalysis, and solar water treatment.

Plasmonic cell nanocoating: a new concept for rapid microbial screening.

Nanocoating of single microbial cells with gold nanostructures can confer optical, electrical, thermal, and mechanical properties to microorganisms, thus enabling new avenues for their control, study, application, and detection. Cell nanocoating is often performed using layer-by-layer (LbL) deposition. LbL is time-consuming and relies on nonspecific electrostatic interactions, which limit potential applications for microbial diagnostics. Here, we show that, by taking advantage of surface molecules densely present in the microbial outer layers, cell nanocoating with gold nanoparticles can be achieved within seconds using surface molecules, including disulfide- bond-containing (Dsbc) proteins and chitin. A simple activation of these markers and their subsequent interaction with gold nanoparticles allow specific microbial screening and quantification of bacteria and fungi within 5 and 30 min, respectively. The use of plasmonics and fluorescence as transduction methods offers a limit of detection below 35 cfumL-1 for E. coli bacteria and 1500 cfumL-1 for M. circinelloides fungi using a hand-held fluorescent reader. Graphical abstract A new concept for rapid microbial screening by targeting disulfide - bond-containing (Dsbc) proteins and chitin with reducing agents and gold nanoparticles.

Spermine induced reversible collapse of deoxyribonucleic acid-bridged nanoparticle-based assemblies

DNA-linked 2D and 3D nano-assemblies find use in a diverse set of applications, ranging from DNA-origami in drug delivery and medical imaging, to DNA-linked nanoparticle structures for use in plasmonics and (bio)sensing. However, once these structures have been fully assembled, few options are available to modulate structure geometry. Here, we investigated the use of the polycation spermine to induce DNA collapse in small oligonucleotide-linked (54 bp) gold nanoparticle structures by monitoring shifts in the localized surface plasmon resonance (LSPR) peak and by comparing the data with finite-difference time-domain (FDTD) simulations. Our data shows that low concentrations of spermine can be applied to induce large changes in DNA conformation, leading to a significant reduction in interparticle distance (from ∼25 to ∼3 nm) and enhanced plasmonic coupling. The DNA collapse is near-instantaneous and reversible, and its application at low and high DNA densities is demonstrated with surface plasmon resonance imaging (SPRi), showing the potential of spermine to dynamically modulate distances and geometry in DNA-based nano-assemblies.

Imaging the optical near field in plasmonic nanostructures.

Over the past five years, new developments in the field of plasmonics have emerged with the goal of finely tuning a variety of metallic nanostructures to enable a desired function. The use of plasmonics in spectroscopy is of course of great interest, due to large local enhancements in the optical near field confined in the vicinity of a metal nanostructure. For a given metal, such enhancements are dependent on the shape of the structure as well as the optical properties (wavelength, phase, polarization) of the impinging light, offering a large degree of control over the optical and spatial localization of the plasmon resonance. In this focal point, we highlight recent work that aims at revealing the spatial position of the localized plasmon resonances using a variety of optical and non-optical methods.

Plasmonic effects of au/ag bimetallic multispiked nanoparticles for photovoltaic applications.

In recent years, there has been considerable interest in the use of plasmons, that is, free electron oscillations in conductors, to boost the performance of both organic and inorganic thin film solar cells. This has been driven by the possibility of employing thin active layers in solar cells in order to reduce materials costs, and is enabled by significant advances in fabrication technology. The ability of surface plasmons in metallic nanostructures to guide and confine light in the nanometer scale has opened up new design possibilities for solar cell devices. Here, we report the synthesis and characterization of highly monodisperse, reasonably stable, multipode Au/Ag bimetallic nanostructures using an inorganic additive as a ligand for photovoltaic applications. A promising surface enhanced Raman scattering (SERS) effect has been observed for the synthesized bimetallic Au/Ag multispiked nanoparticles, which compare favorably well with their Au and Ag spherical nanoparticle counterparts. The synthesized plasmonic nanostructures were incorporated on the rear surface of an ultrathin planar c-silicon/organic polymer hybrid solar cell, and the overall effect on photovoltaic performance was investigated. A promising enhancement in solar cell performance parameters, including both the open circuit voltage (VOC) and short circuit current density (JSC), has been observed by employing the aforementioned bimetallic multispiked nanoparticles on the rear surface of solar cell devices. A power conversion efficiency (PCE) value as high as 7.70% has been measured in a hybrid device with Au/Ag multispiked nanoparticles on the rear surface of an ultrathin, crystalline silicon (c-Si) membrane (∼ 12 μm). This value compares well to the measured PCE value of 6.72% for a similar device without nanoparticles. The experimental observations support the hope for a sizable PCE increase, due to plasmon effects, in thin-film, c-Si solar cells in the near future.

Graphene-protected copper and silver plasmonics.

Plasmonics has established itself as a branch of physics which promises to revolutionize data processing, improve photovoltaics, and increase sensitivity of bio-detection. A widespread use of plasmonic devices is notably hindered by high losses and the absence of stable and inexpensive metal films suitable for plasmonic applications. To this end, there has been a continuous search for alternative plasmonic materials that are also compatible with complementary metal oxide semiconductor technology. Here we show that copper and silver protected by graphene are viable candidates. Copper films covered with one to a few graphene layers show excellent plasmonic characteristics. They can be used to fabricate plasmonic devices and survive for at least a year, even in wet and corroding conditions. As a proof of concept, we use the graphene-protected copper to demonstrate dielectric loaded plasmonic waveguides and test sensitivity of surface plasmon resonances. Our results are likely to initiate wide use of graphene-protected plasmonics.

Au nanoparticles on ultrathin MoS2sheets for plasmonic organic solar cells

A novel hole transport layer (HTL) composed of ultrathin two-dimensional, molybdenum disulfide (MoS2) sheets decorated with 20 nm gold nanoparticles (NPs) (MoS2@Au) was developed to make use of plasmonics for organic solar cells (OSCs).

Graphene for Terahertz Applications

The optoelectronic properties of graphene are being explored for possible use in plasmonics and metamaterials at terahertz frequencies.

Graphene versus metal plasmons

Although there is much debate regarding whether graphene is more suitable than metals for use in plasmonics, the useful operational frequency ranges of these materials are complementary. Nature Photonics spoke with Fengnian Xia about his team's recent work on graphene plasmonics.