Surface Enhanced Raman Effect Research Articles

Surface-enhanced Raman effect on MoS2–WS2 composite structures

Surface-enhanced Raman effect on MoS2–WS2 composite structures

Spatiotemporal imaging and manipulation of surface plasmons

Abstract Surface plasmon polaritons (SPPs) are travelling surface waves that have shown promise for applications in nanophotonics as they provide a direct route toward photon-mediated electrical signal generation – a central paradigm for speeding up and scaling down photonic elements. SPP waves have also generated fundamental interest due to their high-field strength and sub-wavelength confinement, properties that have enabled the surface-enhanced Raman effect. Over the last decade, photoemission electron microscopy (PEEM) has emerged as a pioneering technique for imaging surface electric fields through ultrashort laser pulse mediated electron emission and has therefore become an indispensable tool for characterizing plasmonic phenomena at interfaces in a variety of materials. PEEM offers nanometer spatial resolution and femtosecond temporal resolution, allowing SPPs to be prepared, monitored, and manipulated on the nanometer-femtosecond scale. Through a brief review of recent reports, we aim to introduce PEEM-based SPP imaging and manipulation modalities and highlight their utility in the context of emerging nanoscale and quantum materials science advancements.

Tungsten Nitride with a Two-Dimensional Multilayer Structure for Boosting the Surface-Enhanced Raman Effect.

The development of high-performance surface-enhanced Raman scattering (SERS) substrates is an urgent and important task. Here, tungsten nitride (WN) with a two-dimensional (2D) multilayer structure has been successfully prepared through a nitriding WO2.90 precursor. In addition to the highly active "hot spots" formed on the surface of the WN sheets, a large number of gaps between the nanosheets also exhibit a strong local surface plasmon resonance effect, which greatly improves the SERS activity. Evaluated as the SERS substrate, the WN with a 2D multilayer structure exhibits good SERS characteristics and good homogeneity and stability, even after strong acid, strong alkali, or long-term light treatment. Significantly, typical environmental contaminants such as dichlorophenol and butylated hydroxyanisole also exhibit strong Raman enhancement signals. This research provides a new method for designing inexpensive, high-activity, and universal SERS substrates.

Editorial

Editorial

Martin Fleischmann. 29 March 1927—3 August 2012

Martin Fleischmann was an electrochemist whose work revolutionized the subject. He was a consummate mathematician and inspired inventor of new experimental methods. His work led to the development of several important techniques in the field: ground-breaking studies of electrocrystallization stemming from the development of high-speed potentiostats; the discovery of the surface-enhanced Raman effect; the development of microelectrodes; the study of stochastic effects as a means to derive basic information about electrochemical reactions; and the systematic development of concepts of electrochemical engineering. But for many, his name is indelibly associated with the ‘cold fusion’ episode that took place at the end of his career in the late 1980s. Regarded by some as a blemish on Fleischmann's highly distinguished life in science, cold fusion continues even today to excite debate and controversy. Nevertheless, he is remembered with esteem and affection by his many colleagues and leaves a powerful legacy in his discipline.

Solution Processed Photodetectors with PVK-WS2 Nanotube/Nanofullerene Organic-Inorganic Hybrid Films.

Organic-inorganic hybrid photodetectors have attracted increased interest due to their exceptional properties, such as flexibility, transparency, and low cost for many promising applications. Low-dimensional tungsten disulfide (WS2) nanostructures have outstanding electrical and optical properties, making them ideal candidates for ultrasensitive photodetector devices. In this paper, photodetectors were fabricated with hybrid thin films containing two different WS2 nanomaterials, one-dimensional (1D) WS2 nanotubes (WS2-NTs) and a zero-dimensional (0D) WS2 nanofullerene (WS2-FLs) hybrid with poly(N-vinyl carbazole) (PVK). The electrical responses of the devices under visible-light illuminations were studied. The photodetector devices with 0D WS2-FLs/PVK hybrid thin films have relatively higher sensitivity and stable voltage responses to visible light. Besides, the hybrid film shows a strong surface-enhanced Raman effect (SERS). These materials and new strategies enable the creation of a new class of processed photodetectors for practical applications.

Sb2Se3 nanorods in the confined space of TiO2 nanotube arrays facilitating photoelectrochemical hydrogen evolution

Antimony selenide (Sb2Se3) is a very handy light-absorbing material in photochemical devices based on TiO2 nanotube arrays (TNT), but it has some problems with anisotropy and agglomeration. Large particles of antimony selenide instead impede photon transport and are susceptible to photocorrosion instability, making it crucial to develop a strategy for the directional growth of rod-shaped Sb2Se3 arrays. Herein, we successfully achieved the deposition of Sb2Se3 inside the tube of TNT by pulsed electrodeposition strategy to obtain the oriented Sb2Se3 nanorod arrays for efficient photoelectron transport. The conductive atomic force microscopy indicates the enhanced electron transfer performance. The UV spectral conclusion shows that the deposition of rod-shaped Sb2Se3 enhances the UV–vis diffuse absorption of TiO2, meanwhile, TNT acts as a shell to protect antimony selenide and effectively prevents its photocorrosion phenomenon. Therefore, the photocurrent density of TNT/Sb2Se3 NRs is 6.79 times as that of bare TNT. The Pt/TNT/Sb2Se3 NRs electrode exhibits a photocurrent density of 2.6 mA cm−2 (−0.2 V RHE) and considerable hydrogen evolution performance. In addition, the Surface-Enhanced Raman effect (SERS) originated from this Sb2Se3 array, is first observed, which is expected to reduce the cost of SERS technology.

Effect of Gold Nanospheres and Nanodots on the Performance of PEDOT:PSS Solar Cells.

Gold nanospheres were synthesized using a modified Turkevich method (d = 14±4 nm, λmax = 531 nm), while gold nanodots made of spheres (5±2 nm) and non-spherical nanodots (aspect ratio of 1.7±0.4) were synthesized using a modified seed mediated method. The spherical gold nanodots exhibited a transverse excitation mode at 525 nm while the non-spherical gold nanodots showed an additional longitudinal excitation mode observed in the UV-vis spectrum at 794 nm. The gold nanodots also exhibited a surface enhanced Raman effect which significantly influenced the electronic properties of the photovoltaic device. The incorporation of Au nanospheres in a PEDOT:PSS hole transport layer increased the photovoltaic device efficiency by 51%. This was attributed to a decrease in the series resistance which improved the hole transport pathways in the PEDOT:PSS and enhanced the current density of the photovoltaic device. In contrast, incorporation of spherical and non-spherical gold nanodots into the PEDOT:PSS hole transport layer resulted in a decrease in current density and a consequent decrease in efficiency. This can be attributed to the electron-hole recombination and accumulation of space charges by the non-spherical gold nanodots in PEDOT:PSS resulting in an increased series resistance and leakage currents and hence a reduced device performance. Thus, the morphological, structural and opto-electrical properties of the gold nanospheres and nanodots influenced the device performance of the PEDOT:PSS solar cells.

Surface enhanced Raman effect of Ag/TiO2 thin films with arbitrarily cut, flexible and reusable performance

In this work, the controllable Ag/TiO2 SERS composites were successfully synthesized based on Ti foils with hydro-thermal treatment method. Flexible Ag/TiO2 SERS substrates could be pasted onto the surface of object with arbitrary shape to detect organic pollutants. Using R6G as probe molecule, Ag/TiO2 nonabelts could detect SERS signal up to 10−7 M. TiO2 can be used not only as the template of SERS substrate, but also as photo-catalytic material, which played a decisive role in photo-catalytic activity. The result of cycling experiment for the as-prepared SERS substrates indicated that it maintained good detection performance after 10 cycles.

Surface enhanced Raman effect on CVD growth of WS2 film

Chemical vapor deposition (CVD) method was used to grow large area and layer controllable WS2 film. Our results show that the as grown WS2 film is an excellent substrate for surface enhanced Raman scattering (SERS). The Raman enhancement effect depends crucially on the layer number of WS2 film: monolayer WS2 offers the strongest Raman signal, and the Raman enhancement effect gradually decreases with the increase in the layer number of WS2. Further analysis indicates that this transition originates from the charge transfer yield between the R6G molecules and the underlying WS2 substrate.

The fabrication, characterization of honeycomb-type porous Ag/N-TiO2 nanomaterial and its application in SERS study

ABSTRACTCombined template method with sol-gel method to make the mixed solution including polystyrene microsphere emulsion, TiO2 sol and NH3·H2O aging at room temperature. Annealing at 500 centigrade for 2 hours on mesoporous TiO2 nano material doped with nitrogen. Wrapped Ag nanoparticles on the surface of mesoporous TiO2 nano material through redox reaction. The morphology and optical porosities were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), BET tester and Surface enhanced Raman scattering (SERS). The results showed this material has excellent surface enhanced Raman effect, optical absorption effect and also has a great specific surface area.

Au monolayer film coating with graphene oxide for surface enhanced Raman effect

A self-terminated electrochemical atomic layer deposition process is developed to fabricate Au monolayer (ML) film layer-by-layer. It is found that the under potential deposited hydrogen (Hupd) provides perfect termination after each ML deposition and the further ML growth can be replicated after a surface activation using a positive potential to remove the Hupd layer. Voltammetric measurements, deposition current analysis, and EQCM show clear characteristics of UPD hydrogen surface termination and the ML deposition. Both XRR and HREED confirm the Au ML film formation. Moreover, the Au ML film appears to be effective for surface enhanced Raman effect of GO on the Au ML film.

Spectroscopic Observation of Reversible Surface Reconstruction of Copper Electrodes under CO2 Reduction

The ability of copper to catalyze the electrochemical reduction of CO2 has been shown to greatly depend on its nanoscale surface morphology. While previous studies found evidence of irreversible changes of copper nanoparticle and thin film electrodes following electrolysis, we present here the first observation of the reversible reconstruction of electrocatalytic copper surfaces induced by the adsorbed CO intermediate. Using attenuated total internal reflection infrared and surface-enhanced Raman spectroscopies, the reversible formation of nanoscale metal clusters on the electrode is revealed by the appearance of a new C≡O absorption band characteristic of CO bound to undercoordinated copper atoms and by the strong enhancement of the surface-enhanced Raman effect. Our study shows that the morphology of the catalytic copper surface is not static but dynamically adapts with changing reaction conditions.

Research Progress of the Metal-based Photonic Crystals

Metal-based photonic crystals (PCs), which provide a unique optic-electric properties based on its intrinsic char- acteristic, is of great significance for the applications in the field of new energy system, such as solar cells, water electrolysis, light emitting diode (LED), etc. This article reviews the research progress of the metal-based PC, including the fabrication method, property investigation and the relative applications. Metal-based PCs are generally fabricated from the building blocks of metal, metal oxide or their composites materials. The fabrication method refers to the bottom up and top down ap- proach. Bottom up approach covers the self-assembly of the metal nanoparticles directly or infiltrating the nanoparticles into the opal template and the subsequent removal of the template toward the metal-based inverse opals. Top down approach re- fers to the lithography and deposition. The lithography approach includes laser lithography, reaction ion etching, etc. And the deposition method covers physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc. Furthermore, the metal-based PCs demonstrate many excellent properties based on the combination of the light manipulation property of PCs and the intrinsic property of the metal materials. For example, the materials showed surface-enhanced Raman effect, which can provide special optic signal and demonstrate the application in high-sensitive detecting of organic molecules. The com- bination of Plasmon effect of metal particles and photonic stopband of the PCs can improve the emission intensity, which is significant for the application in high efficient detecting of special material. Otherwise, the stopband of metal-based PCs is beneficial for the improvement of the optic adsorbent property and photoluminescence property. Furthermore, the combina- tion of metal materials and its suitable stopband can amplify its optic-electronic property, sensing property and the op- tic-catalytic behavior. Finally, the potential applications of metal-based PCs on the new energy system is put forward. Typi- cally, it was used as optic-electric materials in solar cell, water electrolysis, and high efficient LED. This review will provide an important insight for the new energy development and potential utilization.

A novel Au-Pt@PPy(polypyrrole) coral-like structure: Facile synthesis, high SERS effect, and good electro catalytic activity

The Au–Pt@PPy(polypyrrole) with a novel three-dimensional structure was synthesized by a facile one-pot reaction. Raman spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–vis spectroscopy (UV–vis), and cyclic voltammograms (CV) were employed to characterize the complex. TEM and SEM results indicated that the products had novel three-dimensional (3D) multi-branch structures, which were controllable by simply adjusting the ratios of HAuCl4 to H2PtCl6 added. Raman characterization proved that the products had significant surface-enhanced Raman effect with the aid of long-range effect of the enhanced electromagnetic (EM) field and roughness in nanometer-scale. CV results showed that the Au–Pt@PPy with coral-like structure had high catalytic efficiency for methanol oxidation.

Gold nanoparticle substrates for recyclable surface-enhanced Raman detection of Rhodamine 6G and Sudan I

Excellent and recyclable surface-enhanced Raman scattering substrates were fabricated via a one-step route: reducing gold ions to Au nanoparticles with silicon–hydrogen bond and assembling them in-situ on the Si wafer. Gold nanoparticles with the average size of 22nm were epitaxially grown and uniformly assembled. The substrate exhibited excellent surface-enhanced Raman effect in the low concentration detection (1×10−10M) of Rhodamine 6G with relative standard deviation of <20%, and sustained stable enhancement efficiency in the recycle usage. The substrates were also employed to detect Sudan I dye with distinguished sensitivity and uniformity. More significantly, these substrates kept Au nanoparticles from growing larger during the Raman detection, compared with the conventional substrates, indicating it was a meaningful possibility for the practical applications.

Plasmonic dimer antennas for surface enhanced Raman scattering

Electron beam induced deposition (EBID) has recently been developed into a method to directly write optically active three-dimensional nanostructures. For this purpose a metal–organic precursor gas (here dimethyl-gold(III)-acetylacetonate) is introduced into the vacuum chamber of a scanning electron microscope where it is cracked by the focused electron beam. Upon cracking the aforementioned precursor gas, 3D deposits are realized, consisting of gold nanocrystals embedded in a carbonaceous matrix. The carbon content in the deposits hinders direct plasmonic applications. However, it is possible to activate the deposited nanostructures for plasmonics by coating the EBID structures with a continuous silver layer of a few nanometers thickness. Within this silver layer collective motions of the free electron gas can be excited. In this way, EBID structures with their intriguing precision at the nanoscale have been arranged in arrays of free-standing dimer antenna structures with nanometer sized gaps between the antennas that face each other with an angle of 90°. These dimer antenna ensembles can constitute a reproducibly manufacturable substrate for exploiting the surface enhanced Raman effect (SERS). The achieved SERS enhancement factors are of the order of 104 for the incident laser light polarized along the dimer axes. To prove the signal enhancement in a Raman experiment we used the dye methyl violet as a robust test molecule. In future applications the thickness of such a silver layer on the dimer antennas can easily be varied for tuning the plasmonic resonances of the SERS substrate to match the resonance structure of the analytes to be detected.

Fast one-step silicon–hydrogen bond assembly of silver nanoparticles as excellent surface-enhanced Raman scattering substrates

A one-step method was reported to directly fabricate efficient surface-enhanced Raman scattering substrates based on the silicon–hydrogen bond assembly of Ag nanoparticles on a Si wafer, exhibiting an excellent surface-enhanced Raman effect in the low concentration detection (1 × 10−12 M) of Rhodamine 6G and Sudan I with relative standard deviation (RSD) of <20%.

Surface-enhanced Raman effect in ultra-thin CuPc films employing periodic silver nanostructures

In order to investigate the interaction of organic molecules with metals by means of Raman spectroscopy, special substrates were designed which combine interference and surface-enhancement mechanisms. Triangular shaped silver nanostructures with an angle bisector and a height of about 80 nm were prepared by nanosphere lithography on silicon substrates with a 100-nm oxide layer. Utilizing these substrates the dependence of the Raman signal intensity on the thickness of copper phthalocyanine (CuPc) was studied in the range from few percentages of a monolayer coverage up to 80 nm using an in situ setup. At an excitation in resonance with the plasmons of the nanostructures (2.6 eV) an increase of the signal was observed during film growth. Contrary to that, excitation at 1.92 eV in resonance with the CuPc absorption band leads to a strongly enhanced Raman signal for submonolayer coverage which hardly changes with the CuPc film thickness in the ultra-low coverage regime.

Contributions to the early development of surface-enhanced Raman spectroscopy

It is now more than 30 years since the discovery of the surface-enhanced Raman effect. For much of that time a strong and at times dominant interest has been the investigation of the underlying physics of the phenomenon, stimulated in part by the enormous magnitude of the enhancement effect, but it