Plasmonic Au Nanoparticles Research Articles

Optical Response of CVD-Grown ML-WS2 Flakes on an Ultra-Dense Au NP Plasmonic Array

The combination of metallic nanostructures with two-dimensional transition metal dichalcogenides is an efficient way to make the optical properties of the latter more appealing for opto-electronic applications. In this work, we investigate the optical properties of monolayer WS2 flakes grown by chemical vapour deposition and transferred onto a densely-packed array of plasmonic Au nanoparticles (NPs). The optical response was measured as a function of the thickness of a dielectric spacer intercalated between the two materials and of the system temperature, in the 75–350 K range. We show that a weak interaction is established between WS2 and Au NPs, leading to temperature- and spacer-thickness-dependent coupling between the localized surface plasmon resonance of Au NPs and the WS2 exciton. We suggest that the closely-packed morphology of the plasmonic array promotes a high confinement of the electromagnetic field in regions inaccessible by the WS2 deposited on top. This allows the achievement of direct contact between WS2 and Au while preserving a strong connotation of the properties of the two materials also in the hybrid system.

Surface-Enhanced Raman Spectroscopy Substrates: Plasmonic Metals to Graphene.

Surface-enhanced Raman spectroscopy (SERS), a marvel that uses surfaces to enhance conventional Raman signals, is proposed for a myriad of applications, such as diagnosis of diseases, pollutants, and many more. The substrates determine the SERS enhancement, and plasmonic metallic nanoparticles such as Au, Ag, and Cu have dominated the field. However, the last decades have failed to translate SERS prototypes into real-life applications. Irreproducibility on the SERS signal that stems from the roughened SERS substrates is the main causative factor for this observation. To mitigate irreproducibility several two-dimensional (2-D) substrates have been sought for use as possible alternatives. Application of 2-D graphene substrates in Raman renders graphene-enhanced Raman spectroscopy (GERS). This account used density functional theory (DFT) substantiated with experimental Raman to compare the enhancement capabilities of plasmonic Au nanoparticles (SERS), graphene substrate (GERS), and coupling of the two SERS and GERS substrates. The DFT also enabled the study of the SERS and GERS systems molecular orbital to gain insight into their mechanisms. The amalgamation of the SERS and GERS occurrence, i.e., graphene doped with plasmonic metallic substrates showed a pronounced enhancement and matched the Au-driven enhancement emanating from both electromagnetic and charge transfer SERS and GERS mechanisms.

2D Wavelength‐Polarization Dispersive Microspectroscope Based on a Hybrid Plasmonic Helical Nanostructure

AbstractMicrospectrometer features remarkable portability and integration and is prospected to provide quick detection tools to daily life and revolutionize research techniques. Due to the extremely finite footprint, microspectrometer can hardly analyze the polarization feature by placing a polarizer in the optical path as conventional spectrometers. Here, a novel 2D wavelength‐polarization dispersive microspectroscope based on a carbon nanocoil with plasmonic Au nanoparticles (Au/CNC) as a dispersive component is demonstrated. The unique 2D dispersion properties of Au/CNC are examined by microspectroscopic and Fourier spatial microscopic exploration. Au/CNC disperses light as wavelength to bands of different diffraction orders like a grating along the coil axis. The wavelength of the incident light can be obtained from the location of the signal lines in a relatively large visible‐near‐infrared wavelength range. Perpendicular to the coil axis, incident light is dispersed as polarization with bright and dark areas. Therefore, the left‐ and right‐circularly polarized light can be distinguished, and polarization orientation of linearly polarized light can be obtained. This effect provides a powerful microspectrometer that simultaneously analyzes wavelength and polarization features. Moreover, this potent tool can further evolve new revolutionary techniques via integration with other systems.

Surface-enhanced Raman scattering (SERS) active substrate from gold nanoparticle-coated porous silicon for sensitive detection of horseradish peroxidase enzyme

The sensitive detection of horseradish peroxidase (HRP) enzyme using a gold nanoparticle/porous silicon (AuNPs/PSi) active substrate via surface-enhanced Raman scattering (SERS) is demonstrated. Electrochemical porosification via galvanostatic anodization in hydrofluoric acid (HF) mixed with ethanol was used to fabricate mesopore-size PSi layers onto a p-type Si (100) wafer. The AuNPs were reduced onto the meso-PSi surface through a spontaneous galvanic displacement reaction by dipping the substrates in a simple plating bath. The structural features and morphology of the designed frameworks were elucidated by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The SERS performance of the AuNPs/PSi substrate was firstly examined and evaluated using crystal violet dye as the target analyte, where it exhibited enhanced SERS response. Moreover, the active substrate displayed an extremely sensitive and reproducible SERS response toward the HRP enzyme as a reactive analyte. The active substrate exhibited excellent detectable performance with a very low concentration of 10−8 M HRP and an enhancement factor (EF) of approximately 4.8 × 105. The analytical enhancement of Raman signals in response to Au plasmonic nanoparticles signifies the combination of the charge-transfer mechanism and electromagnetic amplification because of the formed density of hotspot regions. Therefore, the current newly fabricated AuNPs/PSi substrates have optimistic prospects in biophysical, biochemical, and biomedical applications as highly active SERS substrates.

Remarkably enhanced photocatalytic performance of Au/AgNbO3 heterostructures by coupling piezotronic with plasmonic effects

Both localized surface plasmon resonance (SPR) effect in noble metal nanostructures and piezotronic effect in piezoelectric semiconductors have been proven to be effective in improving photocatalytic performance. In this work, we report a novel heterostructured piezo-photocatalyst by decorating plasmonic Au nanoparticles (AuNPs) on piezoelectric AgNbO3 nanocubes. The optimized Au/AgNbO3 nanocomposites exhibit significantly enhanced photocatalytic activities toward hydrogen evolution reaction from water (392 μmol g−1 h−1) and degradation of organic pollutants (first-order rate constant of 0.054 min−1 for RhB) assisted by ultrasonic mechanical vibration (110 W, 40 kHz), which are about 2.2- and 5.7-times that of under only light irradiation, respectively. The considerably promoted photocatalytic activity can be attributed to a synergetic coupling of SPR and piezotronic effect, by which energetic hot electrons generated on the plasmonic AuNPs can be effective extracted onto AgNbO3 driven by mechanical vibration induced piezo-potential near the heterojunction. This work undoubtedly demonstrates that the integration of SPR and piezotronic effects holds great promise to improve the photocatalytic efficiencies.

Synergistic enhancement of photocatalytic CO2 reduction by plasmonic Au nanoparticles on TiO2 decorated N-graphene heterostructure catalyst for high selectivity methane production

Energy-efficient photocatalytic CO2 reduction (PCO2R) into sustainable solar fuels is a highly enticing challenge for simultaneous settling of energy and environmental issues. Herein, we illustrate the synthesis and photocatalytic performance of a judiciously designed plasmonic Au nanoparticles photodeposited on TiO2-decorated N-doped graphene (ANGT-x) heterostructure catalyst showing remarkably enhanced CO2 reduction activity with high selectivity for methane production. Compared to typical binary Au-TiO2 photocatalyst, the ANGT2 exhibited almost 60 times higher electron consumption rate (Relectron) value ~ 742.39 µmol g−1h−1 for the reduced products, which, to the best of our knowledge is the highest PCO2R rate ever reported under comparable conditions. The superior performance of ANGT2 catalyst is attributed to the synergistic contributions from improved light absorbance, enhanced CO2 uptake together with improved charge transfer kinetics and efficient suppression of photogenerated (e-h) recombination rate bestowed by seamless interfacial contact between Au NPs and N-graphene-TiO2 components.

Coupled Molecular Emitters in Superstructures Interact with Plasmonic Nanoparticles

Using hyperspectral measurements, J‐aggregate nanorods of porphyrin molecules embedded in plasmonic Au nanoparticles arrays are studied. Measurements of J‐aggregate nanorods that cross onto a plasmonic array exhibit a shift in their absorption peak, and display weak coupling properties only for the embedded part. Furthermore, a significant thickness‐dependent redshift in the plasmonic resonance for the J‐aggregate clusters is observed. Such redshift is also dependent on the ratio of J‐aggregate in the plasmonic dipole interaction area, reaching values of up to 120 meV for ≈40% coverage. In addition, for large clusters of J‐aggregates, the plasmonic spectrum shows coupling behavior between the systems indicated by a small Rabi splitting. The findings are validated by a quasi‐static model based on the change of the dielectric environment around the embedded nanoparticles. Using the model, the fraction of embedding J‐aggregates in the plasmonic interaction area is correlated with the change in plasmonic resonance peak. These results offer insight into the coupled nature of molecular emitters in supramolecular structures and their interaction with plasmonic nanoparticles and can lead to new types of sensitive optical detectors based on these interactions.

Simultaneous visible and ultraviolet photoresponse improvement of MoS2/ZnO heterostructure photodetector via direct resonant coupling of Au nanoparticles localized surface plasmon resonance

Localized surface plasmon resonance (LSPR) as a unique property of metal nanoparticles (NPs) has been widely applied to enhance the performance of optoelectronic devices. However, limited by the specific resonance frequency of plasmonic NPs, the LSPR of NPs can only improve the photoresponse performance of photodetectors at specific wavelength. In this work, a simple strategy is proposed to simultaneously improve the performance of the p-MoS2/n-ZnO heterostructure photodetector in visible and ultraviolet (UV) light regions by modifying Au NPs. The Ilight/Idark ratio of the photodetector is considerably increased after the functionalization with plasmonic Au NPs under visible and UV light illumination due to the direct resonant coupling of LSPR. In particular, the photocurrent of the photodetector increases 14.8 times after Au NPs modification under 532 nm illumination, giving rise to an obvious increase in responsivity, external quantum efficiency and specific detectivity. Moreover, the modification of Au NPs facilitates the rapid separation of electrons and holes due to the generation of surface depletion regions located at Au/MoS2 and Au/ZnO interfaces. Consequently, the photoresponse speed is also drastically improved after Au NPs decoration in both visible and ultraviolet light regions. The strategy of direct resonant coupling of Au NPs LSPR with two photosensitive materials proposed in this work will provide a new avenue for optimizing the performance of optoelectronic devices.

Plasmonic Au-decorated hierarchical p-NiO/n-ZnO heterostructure arrays for enhanced photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is one of most effective ways for converting solar energy into chemical energy. Single-component semiconductor structures as photoanodes always suffer from poor ability to capture photons and serious recombination of electron-hole pairs, which pose inferior photocurrent performance. In order to increase the photocurrent density, here, a hierarchical heterostructure of p-NiO/n-ZnO decorated with Au nanoparticles (NPs) was designed and prepared as photoanodes. Specifically, a n-ZnO nanorods@nanodisks (NRs@NDs) constructure was completely coated with a thin p-NiO layer to construct a miniature p-n junction arrays, and plasmonic Au NPs were attached on the surface of the thin p-NiO layer. Benefiting from such p-n heterostructure, p-NiO/n-ZnO NRs@NDs heterojunction arrays exhibited excellent rectifying behaviour for their I–V and semi-log I–V curves. Moreover, the photoanode of p-NiO/n-ZnO NRs@NDs had a lower emission intensity than that of n-ZnO NRs@NDs, which indicated the effective inhibition of electron-hole pairs recombination. More importantly, the photocurrent density of Au/p-NiO/n-ZnO NRs@NDs was measured to be as high as 1.78 mA cm −2 , outperforming that of pure n-ZnO NRs@NDs (0.61 mA cm −2 ). This method provides a green, and highly efficient photoanode for the PEC water splitting. • A micro p-NiO/n-ZnO NRs@NDs heterostructure decorated with plasmonic Au NPs was prepared. • p-NiO/n-ZnO NRs@NDs heterojunction arrays exhibited excellent rectifying behaviour. • The synergetic effect of inner electric field of p-n junctions and plasmonic Au effectively inhibit charge recombination. • The photocurrent density increased by approximately 2.9-fold compared to that of pure n-ZnO NRs@NDs.

Enhancing CO2 photoreduction over ZIF-based reticular materials by morphology control of Au plasmonic nanoparticles

Plasmonic-based reticular materials are promising photocatalysts for CO2 reduction due to their efficient charge separation, band structure and crystalline properties.

In Situ Raman Probing of Hot‐Electron Transfer at Gold–Graphene Interfaces with Atomic Layer Accuracy

AbstractPlasmonic metals under photoexcitation can generate energetic hot electrons to directly induce chemical reactions. However, the capability and fundamental insights of the transportation of these hot electrons at plasmonic metal‐2D material interfaces remain unclear. Herein, hot‐electron transfer at Au‐graphene interfaces has been in situ studied using surface‐enhanced Raman spectroscopy (SERS) with atomic layer accuracy. Combining in situ SERS studies with density functional theory calculations, it is proved that hot electrons can be injected from plasmonic Au nanoparticles to graphene and directly penetrate graphene to trigger photocatalytic reactions. With increasing graphene layers, the transportation of hot electrons decays rapidly and would be completely blocked after five layers of graphene. Moreover, the transfer of hot electrons can be modulated by applying an external electric field, and the hot‐electron transfer efficiency under electrochemical conditions is improved by over three times in the presence of a monolayer of graphene.

In Situ Raman Probing of Hot-Electron Transfer at Gold-Graphene Interfaces with Atomic Layer Accuracy.

Plasmonic metals under photoexcitation can generate energetic hot electrons to directly induce chemical reactions. However, the capability and fundamental insights of the transportation of these hot electrons at plasmonic metal-2D material interfaces remain unclear. Herein, hot-electron transfer at Au-graphene interfaces has been in situ studied using surface-enhanced Raman spectroscopy (SERS) with atomic layer accuracy. Combining in situ SERS studies with density functional theory calculations, it is proved that hot electrons can be injected from plasmonic Au nanoparticles to graphene and directly penetrate graphene to trigger photocatalytic reactions. With increasing graphene layers, the transportation of hot electrons decays rapidly and would be completely blocked after five layers of graphene. Moreover, the transfer of hot electrons can be modulated by applying an external electric field, and the hot-electron transfer efficiency under electrochemical conditions is improved by over three times in the presence of a monolayer of graphene.

Bimetal-modified g-C3N4 photocatalyst for promoting hydrogen production coupled with selective oxidation of biomass derivative

The solar-driven coproduction of hydrogen (H2) fuel and value-added chemicals from biomass derivatives represents a promising strategy to address the energy and environment issues. Herein, the Ni-Au bimetal modified g-C3N4 photocatalyst was synthesized by a step-by-step photodeposition method and used to promote the photocatalytic coproduction of H2 and furfural from furfural-alcohol aqueous solution. In the designed Ni-Au/g-C3N4 photocatalyst, g-C3N4 was the main light-harvesting material for generating electron-hole pairs which were separated efficiently by metal/g-C3N4 interface, plasmonic Au nanoparticles further increased the light utilization efficiency, and Ni acted as both electron trap and the active sites for H2 evolution. Beneficial from the synergy of three components, the Ni-Au/g-C3N4 photocatalyst exhibited 3-folds activity of Au/CN sample toward photocatalytic coproduction of H2 and furfural. Both photoluminescence spectroscopy and photoelectrochemical measurements demonstrated the more efficient separation and transfer of photogenerated charge carriers in Ni-Au/g-C3N4 photocatalyst. In situ electron spin resonance revealed the generations of hydroxyl radical and carbon center radical in the photocatalytic reaction. Based on the systematic characterizations, a photocatalytic mechanism was proposed and discussed. This work provides a rational construction of photocatalysts for coproduction of H2 and value-added chemicals from biomass derivatives as well as explores the synergistic effect of bimetallic cocatalyst on enhancing the photocatalysis.

Dual plasmonic Au and TiN cocatalysts to boost photocatalytic hydrogen evolution

Employing a suitable cocatalyst is very important to improve photocatalytic H2 evolution activity. Herein, two plasmonic cocatalysts, Au nanoparticles and TiN nanoparticles were in-situ coupled over the g-C3N4 nanotube to form a ternary 0D/0D/1D Au/TiN/g-C3N4 composite via a successive thermal polycondensation and chemical reduction method. The g-C3N4 nanotube acted as a support for the growth of Au and TiN nanoparticles, leading to intimate contact between g-C3N4 nanotube with Au nanoparticles and TiN nanoparticles. As a result, multiple interfaces and dual-junctions of Au/g-C3N4 Schottky-junction and TiN/g-C3N4 ohmic-junction were constructed, which helped to promote the charged carriers’ separation and enhanced the photocatalytic performance. Furthermore, loading plasmonic cocatalysts of Au nanoparticles and TiN nanoparticles can enhance the light absorption capacity. Consequently, the Au/TiN/g-C3N4 composite exhibited significantly enhanced photocatalytic H2 evolution activity (596 μmol g−1 h−1) compared to g-C3N4 or binary composites of Au/g-C3N4 and TiN/g-C3N4. This work highlights the significant role of cocatalysts in photocatalysis.

Distinguishing Plasmonic Photoinduced Electron Transfer and Photothermal Enhancement Mechanisms for Photoelectrocatalytic Ethanol Oxidation on Au Nanoparticle-Decorated Photoelectrodes

Plasmonic Au nanoparticle photoelectrodes were fabricated and characterized with ultrafast transient absorption (TA) and photomodulated cyclic voltammetry (CV) to determine whether the plasmonic ph...

Au-Cu2-xTe Plasmonic Heteronanostructure Photoelectrocatalysts.

Semiconductor nanocrystals coupled with plasmonic Au nanoparticles have been widely studied as photoelectrocatalysts for solar water splitting. Among these, heterostructures of copper chalcogenides with Au remained a unique category for their dual plasmon character. However, while sulfides and selenides of copper have been extensively reported, heterostructures of copper tellurides with Au have not been explored. Herein, the plasmonic semiconductor Cu2-xTe disks grown on Au nanoparticles (disk-on-dot) were explored as efficient photoelectrocatalysts for hydrogen evolution reactions (HER). This has been successfully designed by growing Cu2-xTe disks on presynthesized Au nanoparticles under optimized reaction conditions. The resulting heterostructured nanocrystals acted as efficient photoelectrocatalysts for the H2 evolution reaction with a low Tafel slope and less cathodic overpotential in the presence of light. Details of their synthesis, characterization, optical properties, and electrocatalytic activities are studied and reported in this letter.

Selective and efficient aerobic oxidation of benzyl alcohols using plasmonic Au-TiO2: Influence of phase transformation on photocatalytic activity

Chemical processes using heterogeneous photocatalytic systems are widely used for the synthesis of valuable fine chemicals. To improve these chemical processes both environmental and energy aspects must be kept in mind for favorable reaction conditions, such as optimum temperature and atmospheric pressure. In this study, plasmonic Au nanoparticles (Au NP) dispersed over TiO2 photocatalyst with different phases of TiO2 (amorphous, anatase and rutile) have been synthesized by using a facile sol–gel method followed by calcination for the photocatalytic oxidation of benzyl alcohol (BnOH) to benzaldehyde (BzH) under visible light irradiation at ambient conditions. The best photocatalyst exhibits high surface area and excellent catalytic conversion efficiency (96%) for the oxidation of BnOH to BzH in less reaction time using a green solvent, acetonitrile at room temperature. The detailed optimization of reaction parameters was performed for alcohol conversion. In addition the corresponding green metrics parameters were also calculated. The photocatalyst also shows excellent stability and reusability for multiple cycles. This work suggests that the Au-TiO2 catalyst provides a novel green and sustainable approach for the selective and efficient aerobic oxidation of BnOH to BzH under visible light irradiation. Furthermore, the impact of different phases of TiO2 on the photocatalytic activity has also been discussed.

Bare laser-synthesized plasmonic Au and TiN nanoparticles as functional additives to polymer nanofiber platforms for tissue engineering applications

Exhibiting strong optical absorption in the visible – near-infrared, plasmonic nanomaterials can be used as transducers in optical biosensing, contrast agents in bioimaging and synthesizers of photothermal therapy. Such functionalities promise their employment as functional elements in tissue engineering platforms, but such applications typically require ultraclean nanomaterials to minimize toxicity problems, which is not easy using conventional chemical synthesis routes. We recently demonstrated the possibility of fabricating ultraclean bare (ligand-free) plasmonic Au and TiN nanoparticles by ultrashort laser ablation in liquid ambient. Exempt of any toxic contaminants and exhibiting a series of imaging and therapeutic functionalities, these nanomaterials present promising objects for various biomedical applications. Here, we review our recent progress in the co-electrospinning of laser-synthesized Au and TiN nanoparticles with polymers to form functionalized matrices for tissue engineering.

Comparison of pharmacokinetics and biodistribution of laser-synthesized plasmonic Au and TiN nanoparticles

Plasmonic nanostructures offer wide range of diagnostic and therapeutic functionalities for biomedical applications. Gold nanoparticles (Au NPs) present one of the most explored nanomaterial in this field, while titanium nitride nanoparticles (TiN NPs) is a new promising nanomaterial with superior plasmonic properties for biomedicine. However conventional chemical techniques for the synthesis of these nanomaterials cannot always match stringent requirements for toxicity levels and surface conditioning. Laser-synthesized Au and TiN NPs offer exceptional purity (no contamination by by-products or ligands) and unusual surface chemistry. Therefore, these NPs present a viable alternative to chemically synthesized counterparts. This work presents comparative analysis of pharmacokinetics and biodistribution of laser-synthesized 20 nm Au and TiN NPs under intravenous administration in mice model. Our data show that Au NPs and bare TiN NPs are rapidly eliminated from the blood circulation and accumulate preferentially in liver and spleen, while coating of TiN NPs by hydrophilic polymer polyethylene glycol (PEG) significantly prolongates blood circulation time and improves delivery of the NPs to tumor. We finally discuss potential applications of laser synthesized Au NPs in SERS, SEIRA and electrocatalysis, while TiN nanoparticles are considered as promising agents for photothermal therapy and photoacoustic imaging.

First principle and experimental investigations of monodispersed Au plasmonic nanoparticles on TiO2

Plasmonic nanostructures play an important part in improving the light absorption of semiconductors that are feasible for photovoltaic and other optical devices. In this context, we have synthesized TiO2 thin films with monodispersed Au nanoparticles. These metallic nanoparticles act as plasmonic structures over the smooth semiconductor surface thereby enhancing their properties. X-ray diffraction was done to confirm the formation of the rutile phase while electron microscope images reveal the presence of Au nanoparticles over the entire surface of TiO2 film. Electronic properties were performed to determine a direct bandgap of 2.8 eV which was reduced significantly to 0.3 eV. Thermoelectric calculations were performed to explore the various temeperature dependent physical properties. Optical properties were also enhanced as high values of optical absorption and refractive index were obtained for TiO2 thin film with monodispersed Au nanoparticles.