Plasmonic Nanowire Research Articles

Plasmon-Driven Highly Selective CO2 Photoreduction to C2H4 on Ionic Liquid-Mediated Copper Nanowires.

Selective CO2 photoreduction to value-added multi-carbon (C2+) feedstocks, such as C2H4, holds great promise in direct solar-to-chemical conversion for a carbon-neutral future. Nevertheless, the performance is largely inhibited by the high energy barrier of C-C coupling process, thereby leading to C2+ products with low selectivity. Here we report that through facile surface immobilization of a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) ionic liquid, plasmonic Cu nanowires could enable highly selective CO2 photoreduction to C2H4 product. At an optimal condition, the resultant plasmonic photocatalyst exhibits C2H4 production with selectivity up to 96.7 % under 450 nm monochromatic light irradiation, greatly surpassing its pristine Cu counterpart. Combined in situ spectroscopies and computational calculations unravel that the addition of EMIM-BF4 ionic liquid modulates the local electronic structure of Cu, resulting in its enhanced adsorption strength of *CO intermediate and significantly reduced energy barrier of C-C coupling process. This work paves new path for Cu surface plasmons in selective artificial photosynthesis to targeted products.

Plasmon‐Driven Highly Selective CO2 Photoreduction to C2H4 on Ionic Liquid‐Mediated Copper Nanowires

AbstractSelective CO2 photoreduction to value‐added multi‐carbon (C2+) feedstocks, such as C2H4, holds great promise in direct solar‐to‐chemical conversion for a carbon‐neutral future. Nevertheless, the performance is largely inhibited by the high energy barrier of C−C coupling process, thereby leading to C2+ products with low selectivity. Here we report that through facile surface immobilization of a 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIM‐BF4) ionic liquid, plasmonic Cu nanowires could enable highly selective CO2 photoreduction to C2H4 product. At an optimal condition, the resultant plasmonic photocatalyst exhibits C2H4 production with selectivity up to 96.7 % under 450 nm monochromatic light irradiation, greatly surpassing its pristine Cu counterpart. Combined in situ spectroscopies and computational calculations unravel that the addition of EMIM‐BF4 ionic liquid modulates the local electronic structure of Cu, resulting in its enhanced adsorption strength of *CO intermediate and significantly reduced energy barrier of C−C coupling process. This work paves new path for Cu surface plasmons in selective artificial photosynthesis to targeted products.

Optical Characterization of Size‐ and Substrate‐Dependent Performance of Ultraviolet Hybrid Plasmonic Nanowire Lasers

AbstractNanowire‐based plasmonic lasers are now established as nano‐sources of coherent radiation, appearing as suitable candidates for integration into next‐generation nanophotonic circuitry. However, compared to their photonic counterparts, their relatively high losses and large lasing thresholds still pose a burdening constraint on their scalability. In this study, the lasing characteristics of zinc oxide (ZnO) nanowires on silver (Ag) and aluminum (Al) substrates, operating as optically‐pumped short‐wavelength plasmonic nanolasers, are systematically investigated in combination with the size‐dependent performance of the hybrid cavity. A nanomanipulation‐assisted single nanowire optical characterization combined with high‐throughput photoluminescence spectroscopy enabled the correlation of the lasing characteristics to the metal substrate and the nanowire diameter. The results evidence that the coupling between excitons and surface plasmons is closely tied to the relationship between substrate dispersive behavior and cavity diameter. Such coupling dictates the degree to which the lasing character, be it more plasmonic‐ or photonic‐like, can define the stimulated emission features and, as a result, the device performance.

Computational study of optical force on a dielectric and a plasmonic nanowire

In this paper, the optical force exerted on a dielectric and a plasmonic nanowire with a circular cross-section of sub-micrometer radius anw is numerically calculated using the Muller boundary integral equations and the Minkowski electromagnetic stress tensor. A Complex Point Source (CPS) of micrometer lateral size b is used as the incident light in the visible spectral range. Computations show that the optical force acting on the dielectric nanowire is always smaller than that on the plasmonic one under the same conditions which originates from the excitation of surface plasmon waves. Calculations also reveal that the optical force in both nanowires has an oscillatory dependence on λ but there are sharp peaks for the dielectric nanowire due to the excitation of whispering gallery modes. In the plasmonic wire, however, the force angle is positive for all of the studied wavelengths but for the dielectric wire it is negative. This means that, the optical force in the plasmonic nanowire is mainly scattering-dominated but for dielectric one it is gradient-dominated.

Polarization‐directed nanophotonic routers based on two‐dimensional inorganic molecular crystals

AbstractPhotonic and plasmonic hybrid nanostructures are the key solution for integrated nanophotonic circuits with ultracompact size but relative low loss. However, the poor tunability and modulability of conventional waveguides makes them cumbersome for optical multiplexing. Here we make use of two‐dimensional molecular crystal, α‐Sb2O3 as a dielectric waveguide via total internal reflection, which shows polarization‐sensitive modulation of the propagating beams due to its large polarization mode dispersion. Both experiments and simulations are performed to verify such concept. These Sb2O3 nanoflakes can be coupled with plasmonic nanowires to form nanophotonic beam splitters and routers which can be easily modulated by changing the polarization of the incidence. It thus provides a robust, exploitable and tunable platform for on‐chip nanophotonics.image

Deep Learning Enabled SERS Identification of Gaseous Molecules on Flexible Plasmonic MOF Nanowire Films.

Through the capture of a target molecule at the metal surface with a highly confined electromagnetic field induced by surface plasmon, surface enhanced Raman spectroscopy (SERS) emerges as a spectral analysis technology with high sensitivity. However, accurate SERS identification of a gaseous molecule with low density and high velocity is still a challenge due to its difficulty in capture. In this work, a flexible paper-based plasmonic metal-organic framework (MOF) film consisting of Ag nanowires@ZIF-8 (AgNWs@ZIF-8) is fabricated for SERS detection of gaseous molecules. Benefiting from its micronanopores generated by the nanowire network and ZIF-8 shell, the effective capture of the gaseous molecule is achieved, and its SERS spectrum is obtained in this paper-based flexible plasmonic MOF nanowire film. With optimal structure parameters, spectra of gaseous 4-aminothiophenol, 4-mercaptophenol, and dithiohydroquinone demonstrate that this film has good SERS performance, which could maintain obvious Raman signals within 30 days during reproducible detection. To realize SERS identification of gaseous molecules, deep learning is performed based on the SERS spectra of the mixed gaseous analyte obtained in this flexible porous film. The results point out that an artificial neural network algorithm could identify gaseous aldehydes (gaseous biomarker of colorectal cancer) in simulated exhaled breath with high accuracy at 93.7%. The integration of the flexible paper-based film sensors with deep learning offers a promising new approach for noninvasive colorectal cancer screening. Our work explores SERS applications in gaseous analyte detection and has broad potential in clinical medicine, food safety, environmental monitoring, etc.

Non-noble plasmonic nanowires enhanced flexible random lasers

We conducted an investigation on a flexible random laser (RL) device featuring non-noble plasmonic enhancement and scattering. The RL device was created by integrating copper nanowires (Cu NWs) and laser dyes (rhodamine 6G, R6G) into an acrylamide (AM) hydrogel matrix. The substantial overlap between the plasmonic resonance of Cu NWs and the emission of R6G effectively mitigates the requirements for lasing generation. Furthermore, the robust scattering induced by the three-dimensional distribution of Cu NWs contributes to a reduction in the laser threshold. Notably, the unique properties of the AM hydrogel ensure that the laser device exhibits excellent tensile recovery performance. The RL device is capable of maintaining stable lasing performance even after 100 % tensile deformation. This flexible laser device offers the advantages of a straightforward fabrication process, low cost, and robust lasing characteristics, thus paving the way for their advanced application in the future.

Self-Organized Plasmonic Nanowire Arrays Coated with Ultrathin TiO2 Films for Photoelectrochemical Energy Storage

Self-Organized Plasmonic Nanowire Arrays Coated with Ultrathin TiO₂ Films for Photoelectrochemical Energy Storage

Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion.

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light-matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.

Superplastic Nanomolding of Aluminum Waveguides for Subwavelength Light Routing, Splitting, and Encryption.

Plasmonic nanowires (NWs) due to their polarization-dependent optics and enhanced light-matter interactions have presented vibrant capabilities in functional nanophotonic devices. However, current demonstrations have largely been based on chemically synthesized Ag NWs, which are extremely unstable and poorly functional. Here we show single-crystalline Al NWs can be fabricated by a superplastic nanomolding (SPNM) technique on a centimeter scale, which are earth-abundant and highly stable. They present robust properties of multimode waveguiding with long-term stability, high efficiency of beam splitting in response to the polarization, and durable thermal optical modulation, which can be readily applied as nanophotonic routers, splitters, and information encryptors. Moreover, this SNPM technique is extendable to other metals, which are highly exploitable for functional nanophotonic devices and integrated optical chips.

Synthesis of plasmonic W18O49 interconnected nanowire frameworks with strong photo-enhanced hydrogen evolution reaction activity

The synthesis of high-order tungsten oxide nanowire frameworks (NWFs) is achieved using an unordinary stable molecular precursor formed by mixing tungsten hexachloride with methanol. The solvothermally obtained NWFs are well characterized with diffraction, microscopy, and nitrogen adsorption techniques. Time-resolved absorption spectroscopy and proton activity measurements reveal the stability of tungsten precursors in methanol. In butanol, the precursor decomposes rapidly into solid hydrated tungsten oxide and leads to the formation of freestanding nanowires (FNWs) after the solvothermal treatment. The NWFs show a blue shift in their characteristic plasmonic absorption wavelength when compared with FNWs. Such phenomenon is attributed to the high population of connecting nodes, which are postulated to be the plasmonic hot spots where the light-induced electromagnetic fields are amplified. The photo-deposition of palladium nanoparticles was hence selectively formed on these connecting nodes on the NWFs while showing no apparent selectivity on the FNWs. Furthermore, when applied as an electrode catalyst for the hydrogen evolution reaction, the NWFs demonstrated a much stronger photo-induced enhancement compared with the FNWs. The photo-induced effects demonstrate the advantage of plasmonic field enhancement through connected nanowires which can be obtained through a facile synthesis process.

Modulation of Cathodoluminescence by Surface Plasmons in Silver Nanowires (Small 33/2023)

Modulation of Cathodoluminescence by Surface Plasmons in Silver Nanowires (Small 33/2023)

SERS Endoscopy for Monitoring Intracellular Drug Dynamics.

Understanding the dynamics and distribution of medicinal drugs in living cells is essential for the design and discovery of treatments. The tools available for revealing this information are, however, extremely limited. Here, we report the application of surface-enhanced Raman scattering (SERS) endoscopy, using plasmonic nanowires as SERS probes, to monitor the intracellular fate and dynamics of a common chemo-drug, doxorubicin, in A549 cancer cells. The unique spatio-temporal resolution of this technique reveals unprecedented information on the mode of action of doxorubicin: its localization in the nucleus, its complexation with medium components, and its intercalation with DNA as a function of time. Notably, we were able to discriminate these factors for the direct administration of doxorubicin or the use of a doxorubicin delivery system. The results reported here show that SERS endoscopy may have an important future role in medicinal chemistry for studying the dynamics and mechanism of action of drugs in cells.

Selective Detection of Intracellular Drug Metabolism by Metal‐Organic Framework‐Coated Plasmonic Nanowire

AbstractUnveiling intracellular drug metabolism is crucial for improving drug development, which requires real‐time detection with molecular selectivity in the intracellular environment. Surface‐enhanced Raman scattering (SERS) with metal nanoparticles enables the detection of molecules in living cells, but after entering the cells, most nanoparticles are captured into vesicles, limiting the SERS detection inside these compartments. Moreover, the identification of the target signal in the complex intracellular environment is challenging due to Raman fingerprints from endogenous material interfering with the drug signal. To overcome these issues, here the coating of a silver nanowire with zeolitic imidazolate framework‐8 (ZIF‐8) as a novel endoscopic probe with molecular selectivity to investigate the location and metabolism in cells of a common anticancer drug, irinotecan, is reported. Irinotecan in cells is metabolized by carboxylesterase to form SN‐38, which inhibits topoisomerase I and DNA synthesis. Thanks to the molecular selectivity of ZIF‐8, the endoscopic probe selectively adsorbs and detects SERS signal of SN‐38 over irinotecan. This selectivity enables monitoring of the conversion of irinotecan into SN‐38 and following its intracellular location over time. This work clearly shows the potential of metal‐organic framework‐coated nanowire endoscopy to specifically track drug molecules and explore their metabolism in cells.

MoS2 nanosheets decorated plasmonic silicon nanowires as SERS substrates for ultra-sensitive multiple analyte detection

We report the fabrication of hybrid SERS-active substrates for ultra-sensitive detection of diverse analyte molecules such as explosives, dyes, and bio-proteins. Vertically aligned (12-µm long, 250-nm diameter) Si nanowires (SiNWs) were prepared by a facile silver-assisted electroless (SAE) etching process. Ag and Au nanoparticles (NPs) were initially decorated on SiNWs using a simple immersion bath method. A hybrid SERS substrate was designed by encapsulating the 2D material (MoS2) on bi-metallic (Ag-Au nanoparticles) functionalized SiNWs. The synergetic effect from MoS2 nano-sheets and bi-metallic NPs produced superior detection of analytes down to ultra-trace levels. The versatility of hybrid substrate was tested extensively by detecting (i) malachite green (MG), (ii) melamine, (iii) naphthalene, (iv) bovine serum albumin (BSA), (v) adenine, (vi) L-Cysteine, (vii) Escherichia coli (E. coli), and (viii) tetryl (an explosive) molecules. We have observed excellent signal reproducibility with very low RSD values (3–5%). The analytic enhancement factors were estimated to be 3.6 × 108 for MG, 1.2 × 107 for melamine, and 6.4 × 105 for BSA, respectively. The estimated ‘limits of detection’ (LOD) for MG, melamine, naphthalene, adenine, and BSA were 216 pM, 42 nM, 78 nM, 5 nM, 7 nM, respectively. Furthermore, the durability of the substrate was studied extensively by evaluating the signal strength of 100 µM melamine for a prolonged duration in an ambient atmosphere. These established novel, robust, versatile, and potentially practical SERS-active hybrid substrates facilitate easy molecular detection in the field in conjunction with a portable or hand-held Raman spectrometer.

Modulation of Cathodoluminescence by Surface Plasmons in Silver Nanowires.

The waveguide modes in chemically-grown silver nanowires on silicon nitride substrates are observed using spectrally- and spatially-resolved cathodoluminescence (CL) excited by high-energy electrons in a scanning electron microscope. The presence of a long-range, travelling surface plasmon mode modulates the coupling efficiency of the incident electron energy into the nanowires, which is observed as oscillations in the measured CL with the point of excitation by the focused electron beam. The experimental data are modeled using the theory of surface plasmon polariton modes in cylindrical metal waveguides, enabling the complex mode wavenumbers and excitation strength of the long-range surface plasmon mode to be extracted. The experiments yield insight into the energy transfer mechanisms between fast electrons and coherent oscillations in surface charge density in metal nanowires and the relative amplitudes of the radiative processes excited in the wire by theelectron.

Plasmonic Molybdenum Dioxide Ultrathin Nanowire Bundles for Highly Sensitive, Stable, and Reproducible Surface-Enhanced Raman Spectroscopy

In surface-enhanced Raman spectroscopy (SERS) detection, it is important to improve the sensitivity, stability, and reproducibility of semiconductor surface-enhanced Raman scattering (SERS) substrates. Here, a simple chemical method was used to synthesize molybdenum dioxide ultrathin nanowire bundles. The ultrathin nanowire bundles of molybdenum dioxide demonstrate distinct and robust surface plasmon resonance (SPR) effects within the visible light range. As a low-cost SERS substrate, the plasmonic molybdenum dioxide nanowire beams exhibit a Raman enhancement factor of 2.9 × 107 and a minimum detection limit of 1.0 × 10–11 mol L–1 for Rhodamine 6G. In addition, these SERS substrates based on molybdenum dioxide ultrathin nanowires exhibit good chemical stability and can resist corrosion by strong acids and bases over time. The molybdenum dioxide ultrathin nanowire bundles have a high potential to become an ideal metal-oxide-based SERS substrate material.

Promising Photoluminescence Enhancement of Tris(8-hydroxyquinoline)aluminum by Simultaneous Localized and Propagating Surface Plasmons of Ag Nanostructures

The continuous performance optimization of tris(8-hydroxyquinoline)aluminum (Alq3) materials is of great significance during the commercialization process of organic light-emitting diodes (OLEDs). In incorporating Ag nanostructures into Alq3, the photophysical properties are greatly improved by the plasmon–exciton coupling effect. Localized surface plasmons (LSPs) in Ag nanoparticles (NPs) efficiently increased the absorption ability. The coexistence of LSPs and propagating surface plasmons (PSPs) in Ag nanowires (NWs) leads to a PL enhancement of 5.3-fold and a full-width at half maximum (FWHM) narrowed by 10 nm. Temperature-dependent PL measurements exhibit that the plasmonic density of states (DOS) increases with decreasing temperature below 40 °C, and the thermal exchange can be accelerated by the introduction of Ag nanostructures. Effective suppression of the thermal accumulation effect is further proved by excitation intensity (EI)-dependent PL measurements. We also found that Ag nanostructures could mainly change the y coordinates in International Commission on Illumination (CIE), leading to a higher brightness. The 5372 K color temperature of an Ag NWs-embedded composite is suitable for daylight-type fluorescent OLEDs. The results would pave an effective way for further optimizing the optical performance of light-emitting materials in OLEDs.

Nanowire dimer optical antenna brightens the surface defects of silicon.

Plasmonic hot spots located between metallic dimer nanostructures have been utilized comprehensively to achieve efficient light emission. However, different from the enhancement occurred in the plasmonic hot spot, the investigation of light emission off the hot spot on submicron scale remains challenge. In this work, we have constructed a plasmonic nanowire dimer (NWD) system to brighten the light emission of the surface defects of silicon off the hot spot on the submicron scale. The NWD can trap light through plasmonic gap, then, the excited emitter on the submicron scale can radiate light efficiently by coupling with the dipole gap plasmonic mode. Furthermore, the coupling of dipole plasmonic mode with the emitters can be tuned by changing the gap size, and then photoluminescence emission was drastically enhanced up to 126 folds. Theoretical simulations reveal the photoluminescence enhancement arises from the combination of the NWD's high radiation efficiency, Purcell enhancement, efficient redirection of the emitted photoluminescence and the excitation enhancement. In this study, the photoluminescence signal can be effectively enhanced by placing nano-antenna patch on the detected low-quantum-efficiency emitters, which may open up a pathway toward controlling plasmonic gap mode enhanced light emission off the hot spot on submicron scale.

Theoretical Investigations on the Plasmon-Mediated Dissociation of Small Molecules in the Presence of Silver Atomic Wires.

Plasmonic nanoparticles can promote bond activation in adsorbed molecules under relatively benign conditions via excitation of the nanoparticle's plasmon resonance. As the plasmon resonance often falls within the visible light region, plasmonic nanomaterials are a promising class of catalysts. However, the exact mechanisms through which plasmonic nanoparticles activate the bonds of nearby molecules are still unclear. Herein, we evaluate Ag8-X2 (X = N, H) model systems via real-time time-dependent density functional theory (RT-TDDFT), linear response time-dependent density functional theory (LR-TDDFT), and Ehrenfest dynamics in order to better understand the bond activation processes of N2 and H2 facilitated by the presence of the atomic silver wire under excitation at the plasmon resonance energies. We find that dissociation is possible for both small molecules at high electric field strength. Activation of each adsorbate is symmetry- and electric field-dependent, and H2 activates at lower electric field strengths than N2. This work serves as a step toward understanding the complex time-dependent electron and electron-nuclear dynamics between plasmonic nanowires and adsorbed small molecules.