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ABSTRACT: SERS active surfaces were prepared by depositing silver films using Tollen's reaction on to barium titanate beads. The SERS activity of the resulting surfaces was probed using two thiols (benzene thiol and 1,2-benzene dithiol) and rhodamine 6G. The intensity of the SERS signal for the three analytes was investigated as a function of silver deposition time. The results indicate that the SERS intensity increased with increasing thickness of the silver film until a maximum signal intensity was achieved; additional silver deposition resulted in a decrease in the SERS intensity for all of the studied molecules. SEM measurement of the Ag coated barium titanate beads, as a function of silver deposition time, indicate that maximum SERS intensity corresponded with the formation of atomic scale islands of silver nanoparticles. Complete silver coverage of the beads resulted in a decreased SERS signal and the most intense SERS signals were observed at deposition times of 30 min for the thiols and 20 min for rhodamine 6G.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 08/2011; 79(3):456-61. · 2.10 Impact Factor
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ABSTRACT: We employed a simple and effective electroless (EL) plating approach to produce silver nanoparticles (NPs) on bare silicon, on dielectric ZnO nanowires (NWs) and on Si NWs, respectively. The surface stability of the homogeneous Ag NPs formed on the ZnO NW surfaces was investigated by surface enhanced Raman spectroscopy (SERS), which show that the attachment of thiol to the Ag surface can slow down the oxidation process, and the SERS signal remains strong for more than ten days. To further examine the Ag NP oxidation process in air, the oxygen content in the silicon nanowire core/Ag sheath composites was monitored by the energy dispersive x-ray (EDX) method. The amount of oxygen in the system increases with time, indicating the silver NPs were continuously oxidized, and it is not clear if saturation is reached in this time period. To investigate the influence of the Ag NPs size distribution on the oxidation process, the oxygen amount in the NPs formed by EL deposition and e-beam (EB) evaporation on a bare silicon surface was compared. Results indicate a faster oxidation process in the EL formed Ag NPs than those produced by EB evaporation. We attribute this observation to the small diameter of the EL produced silver particles, which results in a higher surface energy.
Nanotechnology 05/2010; 21(21):215706. · 3.98 Impact Factor
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ABSTRACT: We have developed dielectric core/metal sheath nanowire (NW) composites for surface-enhanced Raman scattering (SERS), in which an electroless (EL) Ag plating approach was employed. The NW surface was uniformly covered with a high density of 3D silver islands, having a diameter in the 20-30 nm range and spaced less than approximately 10 nm apart. In comparison with the silver deposition via e-beam evaporation, the EL coating approach has the advantage of full metal coverage of the NWs. This approach also provides a fast and simple way to completely cover any nanostructures with Ag, including nanowires, regardless of the orientation or shape. SERS measurements were performed using benzene thiol and the SERS signal strength of the EL-coated NW composites was significantly greater than expected, since the surface plasmon resonance (SPR) of 20 nm Ag nanospheres is weak and in the UV, while our measurements were performed using a 514.5 nm laser line. However, we have modeled this system using our electric field calculations and the results indicate that the strong SERS signal is due to plasmonic coupling of neighboring closely spaced islands, as well as an enhanced substrate effect. In addition, the nanowire core serves as a template for the formation of these small, closely spaced Ag islands, resulting in the strong SERS signal.
Nanotechnology 02/2010; 21(8):85705. · 3.98 Impact Factor
