Plasmon resonance absorption in sulfide-coated gold nanorods
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Gold nanorods 100 nm in diameter were grown within polycarbonate membranes as templates by the electrodeposition technique. A low-temperature sulfidation process was used to make gold sulfide nanoshells around the nanorods with a thickness of ∼7 nm. Optical absorption measurements were carried out on sulfide-coated gold nanorods obtained by dissolving the polycarbonate membrane. Several peaks were observed. These were analyzed on the basis of longitudinal and transverse modes of gold nanorods, the core–shell structure of gold–gold sulfide, and the presence of nanoparticles of gold. Theoretical analysis was carried out using a modified Mie scattering formalism. Satisfactory agreement between experimental results and theoretical fits were obtained.
I. INTRODUCTION
Surface plasmon resonance (SPR) in noble metal nanostructures has generated wide interest in recent years because of the unusual properties they exhibit and their potential applications in chemical/biological sensors,1–3 data storage,4 and optoelectronic devices.5–7 A number of researchers8–10 have studied the optical properties of nanostructured gold particles. The absorption characteristics have been analyzed by Mie scattering theory11 or the effective medium formalism.12 The optical properties of nonspherical nanostructures10,13 have also drawn quite a bit of researchers’ attention. A rather interesting aspect in this context is the spectroscopic investigation of metal nanowire with a coating of a semiconducting phase. Interest in these core–shell nanostructures originated from the expectation of a large nonlinear response due to the surface plasmon resonance.14,15 We had previously studied the shifts in plasmon resonance peak in metal-coremetal-oxide-shell spherical nanostructures grown within a silica gel matrix.16 We have been able to synthesize sulfide coated gold nanorods by a simple chemical method. Optical absorption characteristics of this material have been studied. The experimental data have been analyzed successfully using a modified Mie scattering formalism. The details are reported in this paper. II. EXPERIMENTAL
Gold nanorods were synthesized by electrodeposition. Figure 1 shows schematically the setup used for such a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0032 34
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 1, Jan 2006 Downloaded: 14 Mar 2015
growth. The electrolyte used was tetrachloroauric acid (HAuCl4·xH2O, supplied by Aldrich, Milwaukee, WI). A polycarbonate membrane (supplied by Whatman, Nuclepore, Clifton, NJ) of pore diameter 100 nm and membrane thickness 1 m was taken as the template, the oneside of which was painted by silver paste (supplied by Acheson Colloiden B.V. Holland, Scheemda, The Netherlands) to be used as cathode. A gold plate was used as the anode. For the growth of the gold nanorods 1.5 V was applied for 5 min. Aligned gold nanorods ∼100 nm were grown within polycarbonate template. The sample was used for the electrical measurement of
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