Article

An effective surface-enhanced Raman scattering template based on a Ag nanocluster-ZnO nanowire array

Department of Chemistry, National University of Singapore, Singapore.
Nanotechnology (Impact Factor: 3.82). 05/2009; 20(17):175705. DOI: 10.1088/0957-4484/20/17/175705
Source: PubMed

ABSTRACT

An effective surface-enhanced Raman scattering (SERS) template based on a 3D hybrid Ag nanocluster (NC)-decorated ZnO nanowire array was fabricated through a simple process of depositing Ag NCs on ZnO nanowire arrays. The effects of particle size and excitation energy on the Raman scattering in these hybrid systems have been investigated using rhodamine 6G as a standard analyte. The results indicate that the hybrid nanosystem with 150 nm Ag NCs produces a larger SERS enhancement factor of 3.2 x 10(8), which is much higher than that of 10 nm Ag NCs (6.0 x 10(6)) under 532 nm excitation energy. The hybrid nanowire arrays were further applied to obtain SERS spectra of the two-photon absorption (TPA) chromophore T7. Finite-difference time-domain simulations reveal the presence of an enhanced field associated with inter-wire plasmon coupling of the 150 nm Ag NCs on adjacent ZnO nanowires; such a field was absent in the case of the 10 nm Ag NC-coated ZnO nanowire. Such hybrid nanosystems could be used as SERS substrates more effectively than assembled Ag NC film due to the enhanced light-scattering local field and the inter-wire plasmon-enhanced electromagnetic field.

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    • "When the Ag-ZnO nanostructures are exposed to visible light, charge carriers are formed in the noble metal by the absorption of visible light, and are directly injected from the optically excited plasmonic-metal nanostructures into the semiconductor [24,25]. This unique property, in addition to its optical and electrical characteristics , makes Ag-ZnO nanostructures a potential candidate for photocatalysis and special applications that require antibacterial properties [26] [27], surface-enhanced Raman scattering [28] [29], and gas-sensing abilities [30] [31]. "
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    ABSTRACT: In this study, the synthesis of silver-zinc oxide (Ag-ZnO) nanostructures with a plant-extract-mediated hydrothermal method was investigated. The eco-friendly plant extract Azadirachta indica (Neem) was used as a reducing agent. The X-ray diffraction patterns showed the formation of face-centered cubic (fcc) Ag nanoparticles (NPs) and a wurtzite ZnO structure. An optical study of these nanostructures revealed two absorption edges: one at 393 nm corresponding to ZnO and the other at approximately 440 nm corresponding to Ag. A morphology study showed that hierarchical ZnO nanostructures were decorated with 10–50-nm-diameter Ag NPs. The formation and growth mechanism were also examined. A photoelectrochemical study was performed to investigate the electronic interactions between the ZnO and Ag NPs in the photoanode upon exposure to light. The Ag NPs act as electron acceptors, inhibiting electron–hole recombination. The photocatalytic activity of the Ag-ZnO nanostructures was examined by observing the degradation of aqueous methylene blue (MB) dye under natural sunlight. The apparent rate constant determined for the photocatalytic degradation of MB by the Ag-ZnO nano-structures was 5.9668 × 10 −2 min −1 , which was faster than that of the untreated ZnO nanostructures (2.527 × 10 −2 min −1). This plant-extract-mediated synthetic route could also be applied to the synthesis of other Ag-semiconductor oxide nanostructures.
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    • "The SERS technique has been a powerful tool to record molecular vibration spectra and for chemical analysis since Fleishmann's group first found the SERS phenomenon on a silver electrode in 1974 (Fleischmann et al. 1974). The SERS technique can enhance the Raman scattering intensity of molecules adsorbed on noble metal surfaces by more than ten orders of magnitude and allow surface-enhanced Raman spectroscopy detection sensitivity to reach the single-molecule level (Jeanmaire and Van Duyne 1977; Albrecht and Creighton 1977; You et al. 2010; Wang et al. 2010; Camargo et al. 2009; Fang et al. 2009; Deng et al. 2009). Surface-enhanced fluorescence is the effect that the fluorescence emission intensity of molecular fluorescence near metal surfaces significantly increases compared with molecular fluorescence in the free state (Emmanuel and Samuel 2008; Lu et al. 2007; Lakowicz 2001; Lakowicz 2004a, b). "
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    ABSTRACT: Silver nanomaterials are often used as surface enhancement substrates even though silver is easily oxidized in air. In this paper, we investigate the influence of natural oxidation on the surface enhancement effect of silver nanoparticle (AgNP) films. The AgNP films were prepared by the vacuum thermal evaporation method, and the AgNP size range was 10-100 nm. Changes in the AgNP film thickness, surface morphology, particle size, and roughness with oxidation time were continuously measured with atomic force microscopy for 2 weeks. A detailed analysis of these parameters is presented. In addition, we used Rhodamine 6G to examine the surface enhancement effect of the AgNP films with different oxidation times. The results showed that the intensity of both the Raman and fluorescence signals increased and approximately periodically oscillated with increasing oxidation time. Here, we qualitatively discuss the mechanism of the influence of natural oxidation on the surface enhancement effect of silver nanostructures, which could provide a feasible way to improve the surface enhancement performance of silver nanomaterial substrates.
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    ABSTRACT: Structural and magnetic properties of Ni nanowires (NWs) electrochemically deposited into pores of porous silicon (PS) template under the stationary galvanostatic regime have been investigated. Samples have been studied in detail by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and magnetic measurements. SEM analysis revealed the formation of PS/Ni nanocomposite at the initial stages of Ni deposition with the characteristic dimensions of Ni nanoparticles varying in the range 40 - 60 nm. After 60 min of deposition Ni continuous nanowires of 10 μm length have been formed. XRD analysis confirmed polycrystalline structure of Ni in the PS template with the preferential orientation along <111> axis. Also some amount of Ni2Si silicide was formed, which diffraction peak at 2Θ ≈ 33° was especially pronounced for the small deposition times. The possiblemechanism of nickel silicide formation during the electrochemical process has been discussed. It has been supposed that the presence of amorphous silicon on the pore walls facilitates the diffusion of Ni inside silicon matrix with subsequent nickel silicide formation without heating. The idea has been confirmed by the fact that on crystalline silicon the formation of nickel silicide was not observed. The magnetic properties have been investigated by studying the temperature dependence (77 -700 K) of the specific magnetization σ. The measured σ values were lower with respect to that of bulk Ni. The effect has been explained by the influence of uncontrolled formation of nickel silicide, which causes, after heating, larger irreversibility of σ(T) curves for samples with less deposition time. The obtained σ(T) dependencies allowed us to determine the Curie temperature, TC, which for small deposition times of Ni was lower (575 K) with respect to the bulk Ni (630 K). This is caused by the influence of dimensional effects on TC value. The performed ferromagnetic resonance measurements for arrays of Ni NWs in PS templates with different porosities P allowed obtaining the crossover of magnetic anisotropy type from "easy axis" for P< 0.7 to "easy plane" for P>0.7. This crossover is induced by the growth of dipole-dipole interaction between closely packed Ni NWs with P growth. The magnetization M versus magnetic field H measurements performed for samples with P = 0.7 revealed the dominant role of the shape anisotropy of Ni NWs. It was confirmed both by the analysis of the squareness of the M(H) hysteresis loops and anisotropy field obtained within the random anisotropy model for the magnetic field oriented either parallel or perpendicular to the NW axis.
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