Search

[Display omitted] • A facile, large-area, and cost-effective method to fabricate gap-controlled and highly ordered Ag NP arrays has been demonstrated. • The gap-controlled and highly ordered Ag NP arrays can be employed as both efficient plasmonic photocatalysts and stable SERS platforms. • The apparent activation energy of the photocatalytic reaction of 4NBT conversion to DMAB is significantly reduced as the gap decreases, owing to the high-intensity hot spots that facilitate the reaction. Plasmon-enhanced photocatalysis has attracted considerable attention due to its low energy consumption and high energy throughput. Surface-enhanced Raman scattering (SERS) is a highly sensitive and label-free nondestructive tool to investigate plasmon-driven photocatalytic reactions. Herein, we present a facile method to fabricate gap-controlled Ag nanoparticle (NP) arrays with uniform and high-density distribution of hot spots, which can be employed as both efficient plasmonic photocatalysts and stable SERS platforms. The plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4NBT), which transforms it into p, p′-dimercaptoazobenzene (DMAB), is detected by using an in situ SERS technique at the excited wavelength of 785 nm. According to the temperature and laser power density dependent photocatalytic reaction rates observed on the Ag NP arrays, we quantitatively determined that the reductive coupling of 4NBT is more likely to occur as the gap decreases. The finite-difference time-domain (FDTD) simulation results demonstrate that the plasmonic hot spots are significantly enhanced with a decrease in gap, which in turn reduces activation energy. The gap-controlled Ag NP arrays are efficient for both promotion and detection of plasmon-driven catalytic reactions, and may pave a pathway for implementing efficient plasmonic photocatalytic platforms. [ABSTRACT FROM AUTHOR]

Abstract: Well-ordered silver nano arrays, prepared using anodic aluminum oxide (AAO) template by laser molecular beam epitaxy (L-MBE) method, were adhered to the work electrode using conductive adhesive to be a Surface-enhanced Raman scattering (SERS) substrate. Variable SERS signals of paranitrobenzoic acid (PNA) on the electrode modified with silver nano arrays were recorded with electric potential ranging from 0.1 to −0.5V. The SERS spectra of PNA using DFT-B3PW91 with lanl2dz based on two models were calculated. It indicate that the adsorption orientation of probe molecules on the silver nano arrays with potential change of the electrode. [Copyright &y& Elsevier]

Abstract: The highly ordered anodic aluminum oxide (AAO) template was fabricated using aluminum anodizing in electrolytes with two-step method, which apertures were about 50–80nm. The nickel nanowires with about 40–70nm in diameter was prepared on the AAO template by laser-MBE (molecular beam epitaxy). And high quality Raman spectra of SudanII were obtained on the glass covered with the nickel nanowires. On the nickel nanowires there are both surface enhanced Raman scattering (SERS) and tip enhanced Raman scattering (TERS). The new observations not only enlarge the range of SERS applications, but also imply a possible new enhancement mechanism. Otherwise the Raman and SERS frequencies of SudanII molecule were calculated using, respectively, DFT and B3PW91. [Copyright &y& Elsevier]

The controllable catalytic reaction plays a pivotal role in heterogeneous catalysis. Surface-enhanced Raman scattering (SERS) and tip enhanced Raman spectroscopy (TERS) are considered promising techniques for the study of catalytic reactions due to the highly localized sensitivity of SERS and the nanoscale spatial resolution of TERS. Herein, Ag/Au composite films were employed as catalyst for in situ monitoring of the catalytic reaction of 4‑nitrobenzenethiol (4NBT) to p, p′‑dimercaptoazobenzene (DMAB). The catalytic reaction of 4NBT adsorbed on Au film can be manipulated at the nanoscale using TERS by controlling the height between the tip-apex and the sample surface in Ag tip-Au substrate geometry. According to finite difference time domain (FDTD) simulations, the 'hot electron' induced by the localized surface plasmon is sufficient for promoting the catalytic reaction. These findings provide a novel way for controllable graph drawing of molecules at the nanoscale level. Unlabelled Image • A dual-function substrate with both surface-enhanced Raman scattering (SERS) and catalytic activity was proposed. • The proposed Ag tip-Au substrate system was more efficient for controlling catalytic reaction at the nanoscale. • 'Hot electron' induced by the localized surface plasmon is sufficient for promoting the catalytic reaction. [ABSTRACT FROM AUTHOR]

Abstract: A sandwich structured substrate was designed for quantitative molecular detection using surface enhanced Raman scattering (SERS), in which the probe molecule was sandwiched between silver nanoparticles (SNPs) and silver nanoarrays. The SNPs was prepared using Lee–Meisel method, and the silver nanoarrays was fabricated on porous anodic aluminum oxide (AAO) using electrodepositing method. The SERS studies show that the sandwich structured substrate exhibits good stability and reproducibility, and the detection sensitivity of Rhodamine 6G (R6G) and Melamine can respectively reach up to 10−19 M and 10−9 M, which is improved greatly as compared to other SERS substrates. The improved SERS sensitivity is closely associated with the stronger electromagnetic field enhancement, which stems from localized surface plasmon (LSP) coupling between the two silver nanostructures. Furthermore, the SERS intensity increased almost linearly as the mother concentration increased, which indicates that such a sandwich structure may be used as a good SERS substrate for quantitative analysis. [Copyright &y& Elsevier]

Tip-enhanced Raman scattering (TERS) is a promising analytical approach for some two-dimensional materials and offers the possibility to correlate imaging and chemical data. Tip-enhanced Raman spectra of graphene are discussed in some details, including substrate, gap between tip-apex and sample surface as well as Ag-nanowire. The TERS spectra give special emphasis to the possibility of TERS tip to induce a large number of defects only while got the tip attached to sample surface. Then the dependence of the TERS spectra of graphene and gap between the probe tip and sample surface was studied, and distribution features of electromagnetic (EM) field around tip were also simulated by finite-difference time-domain (FDTD). The Raman signal enhancement of graphene was further discussed with respect to experimental data. Furthermore, the Ag-nanowire as a nano-antenna could significantly enhance the weak Raman signal of D-band of monolayer graphene is shown, and the TERS spectra of graphene with regard to different regions of Ag-nanowires (endpoints, body) were obtained toward investigating into the distribution of electromagnetic field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlled writing of information at the micro/nano scale. • Information or characters are successfully read by SERS technology. • The photocatalytic properties of the 4NBT were systematically investigated. • The plasma distribution propertiese were analysed by FDTD simulations. • High quality gold nanoporous arrays were prepared on the AAO template. The plasma exciton induced photocatalytic reaction has considerable potential in terms of controllability and selectivity. In this paper, with the advantage of Raman fingerprinting, the localized photocatalytic reaction driven by surface plasmons is realized by the writing and reading process of encrypted information at the micro/nano scale. A layer of probe molecules (4-nitrobenzenethiol, 4-NBT) was assembled on a gold nanoporous array grown on porous anodic aluminium oxide (AAO) membranes. The focused Raman spot is manipulated in a two-dimensional micro/nano manipulation technique to control the movement of the spot at an excitation wavelength of 633 nm. Probe molecules within the spot trajectory will undergo a photocatalytic reaction to produce p,p'-dimercaptoazobenzene (DMAB) molecules, thereby writing the specific information required. The use of Raman mapping to image the characteristic peaks of formed DMAB under excitation light with a longer wavelength of 785 nm enables the readout of 2D micro/nano cryptograms. Combined with finite-difference time-domain (FDTD) simulations, it was found that the presence of a large number of regularly arranged hot spots on the surface of the array is the key to achieving the efficient photocatalytic reaction. This study enables real-time, lossless recording/reading of encrypted information with the aid of 2D Raman technology. This would be a very interesting research area with broad application in confidential information storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • The gold micro-nano arrays can be served as the substrate for photocatalytic reaction research. • Gold arrays structure with a diameter of 500 nm has a more efficient photocatalytic reaction. • Combining simulation to explain the mechanism of plasma-driven photocatalysis. Plasma-driven photocatalytic reactions have great research value in the fields of energy utilization, environmental pollution treatment and micro-nano information encryption. In most cases, the substrates used to study photocatalytic reactions are dispersed and disordered, which leads to poor signal reproducibility and makes it difficult to realize applications in the field of quantitative analysis. In this paper, two different sizes of polystyrene (PS) microspheres were used as templates to prepare gold microsphere arrays (Au MA) with homogeneous particle size and regular arrangement. The p-Aminothiophenol (PATP) was selected as the probe molecule to systematically investigate the photocatalytic reaction on Au MA, and the dependence of the photocatalytic reaction on the particle size of the spheres was discussed. It was found that the smaller size of Au MA has higher catalytic activity. In addition, using conventional gold films as a comparison, no significant photocatalytic reaction was found under the same experimental conditions. The reason is the existence of strong surface plasma "hot spots" in the interstices of the particles on the surface of the Au MA, which promotes the reaction. The above experimental results are of theoretical and practical significance for the in-depth study of the photocatalytic effect of micro-nano array catalytic substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Characteristics of the electronically excited state of pyrimidine–Ag20 is calculated. [•] SERRS of pyrimidine were obtained on Ag electrode with increase of the cathode potentials. [•] Different incident wavelength regions are dominated via CHEM and EM mechanisms of SERRS. [•] The trend of absorption spectrum of S-complex is similar to that of SERRS spectrum. [Copyright &y& Elsevier]

[Display omitted] • Realization of photocatalytic and reverse photocatalytic reactions of PATP with laser irradiation. • The catalytic reaction efficiency of gold nanostars is higher than that of gold nanospheres. • The branching structure of gold nanostars not only enhances Raman scattering, but also has stronger catalytic activity. Surface plasmon resonance (SPR) generated in gold nanoparticles can induce the conversion of p-Aminothiophenol (PATP) molecules into p,p'-dimercaptoazobenzene (DMAB) molecules by coupling reaction under the action of excitation light. Molecular detection of samples by surface enhanced Raman spectroscopy (SERS) techniques allows the study of their plasma-driven photocatalytic reaction processes. In this study, we used gold nanostars (GNS) as the substrate to study its catalytic performance and sensitivity. On this basis, catalytic substrates of gold nanospheres (GNPs) were prepared for comparison. The catalytic reactions of PATP molecules on each of the above two substrates were systematically investigated under 633 nm laser irradiation. The reduction process was subsequently observed by introducing NaBH 4 solution. The results show that photocatalytic reactions can be achieved on both substrates under laser excitation at the same wavelength. However, the catalytic and reduction reaction rates on GNSs as a substrate are much faster than those of GNPs. This phenomenon may be due to the abundant nano-branched microstructures on the surface of GNSs, which will generate more and stronger local surface plasma hot spots under the irradiation of excitation light. In order to test the above hypothesis, the surface electromagnetic field distribution of two nanostructures was numerically simulated using the finite-difference time domain (FDTD) method. It is found that the star-like nanostructures not only have the same inter-particle hot spot system as the spherical nanostructures, but also have a large number of high-intensity single-particle hot spot systems arising from the abundance of branched nanostructures on their own surfaces. Compared with the spherical nanostructures, they are characterized by a dual hot spot system, which accelerates the photocatalytic reaction rate. The above experiments are of some reference significance for the in-depth study of multi-branched nanostructures and surface plasma distribution properties and their applications. [ABSTRACT FROM AUTHOR]

• Graphene were used as catalytic surfaces for photocatalysis studies. • The catalytic of graphene improved with the decrease in the number of layers. • The SERS effect of graphene improved with the decrease in the number of layers. Graphene has been extensive studied in the field of photocatalysis. Herein, single-crystal and polycrystalline graphenes are prepared by mechanical exfoliation and chemical vapor deposition (CVD), respectively. The photocatalytic properties of polycrystalline graphene are carefully assessed by using 4-nitrobenzenethiol (4-NBT), as a probe molecule, under incident 532 nm laser beam. Similarly, the photocatalytic properties of single-crystal graphene are also investigated with 4-aminothiophenol (PATP) under incident 633 nm laser radiation. In order to solve the problem of uneven distribution of probe molecules on graphene, the internal standard method is adopted by using 2-naphthalenethiol (2-NT), as the internal standard molecule. The experimental findings indicate that PATP can be catalyzed onto the surface of single-crystal graphene under the irradiation of 633 nm laser beam and its catalytic properties significantly increase with decreasing the number of graphene layers. In addition, when single-crystal graphene is used as the Surface-enhanced Raman scattering (SERS) enhancement substrate, the SERS enhancement was also increased with the decrease of the number of layers. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) is a promising technique to investigate the plasmon-driven catalytic reaction, in which the Raman signal originates from the electromagnetic (EM)enhancement mechanism and the chemical enhancement (CE) mechanism. Here, we designed and synthesized a novel SERS substrate based on SiO 2 wrapped Ag nanoparticles (Ag@SiO 2 core-shell nanoparticles substrate, Ag@SiO 2 CSNS). Meanwhile, the SERS substrate based on Ag nanoparticles (Ag NS) also was prepared for comparison. Then, plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4-NBT) to p,p′-dimercaptoazobenzene (DMAB) were systematically investigated on Ag and Ag@SiO 2 , respectively. The result revealed that, the Fermi level of Ag@SiO 2 CSNS is lower than Ag NS, and the catalytic reaction greatly hindered by the Ag@SiO 2 CSNS under the same excitation laser wavelength. With the same condition excitation laser, Raman signal enhancement effects are different when applying Ag NS and Ag@SiO 2 CSNS, which could be attributed to that the inert SiO 2 shell eliminates CE mechanism of the Raman signal. These results provide a simple strategy to figure out the mechanism of the catalytic reaction based on Surface-enhanced Raman scattering. Unlabelled Image • Ag@SiO 2 core-shell nanoparticles substrate was prepared for the investigation of SERS and catalytic reaction. • The surface-enhanced Raman scattering enhanced mechanism of Ag@SiO 2 substrates can be distinguished effectively. • The Fermi level of Ag@SiO 2 is lower than that of Ag nanoparticles so that catalytic is not available on Ag@SiO 2 substrate. [ABSTRACT FROM AUTHOR]