Distance dependence of the Surface Enhanced Raman Scattering effect observed in amorphous TiO 2 on nanostructured gold Eric Nardou, Dominique Vouagner, Anne-Marie Jurdyc, Alice Berthelot, Anne Pillonnet, Virginie Sablonière, Bernard Champagnon ⇑ Université de Lyon, Université Lyon 1, CNRS, UMR 5620, Laboratoire de Physico-Chimie des Matériaux Luminescents, F-69622 Villeurbanne Cedex, France article info Article history: Available online 8 April 2011 Keywords: Surface Enhanced Raman Scattering Surface Plasmon Resonance Glasses Gold Amorphous film TiO 2 abstract Plasmon resonance of gold nanoparticles is responsible of the electromagnetic (EM) Surface Enhanced Raman Scattering (SERS) effect. Interaction of an amorphous matrix with a SERS substrate was studied. Thin films with different thickness of amorphous TiO 2 coated on a Klarite Ò substrate show a 100 times enhancement of the Raman signal. Distance dependence of the SERS interaction was shown to be less than 60 nm. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Plasmon resonance of noble metals’ nanoparticles in glasses is nowadays a very active subject [1]. It is also known from the ancient time as a way to produce beautiful colored glasses. This is well illustrated by the Lycurgus cup of the 4th century AD kept in the British Museum. This cup appears green in reflected light whereas it appears red by transmission. Made from gold nanopar- ticles embedded in the glassy matrix, it is called ruby glass due to its bright ruby color. This color is due to the Surface Plasmon Resonance (SPR) absorption corresponding to the resonance between the electromagnetic wave frequency and that of the collective excitation of conduction electrons in gold. Gold plasmon resonance lies in the visible range of the electromagnetic spectrum, near 530 nm for spherical particles, and gives rise to the bright ruby color of the Baccarat or Saint Louis glasses. The polarisability a i for an ellipsoidal nanoparticle, character- ized by semi-axis a, b, c and the depolarization factor A i , depends on the nanoparticle shape and dielectric constants of the matrix e m and of the gold nanoparticle e(k)(Fig. 1). a i ¼ 4pabc 3  eðkÞ e m e m þ A i ½eðkÞ e m  Electro-Static Approximation (ESA) can be used to describe the plasmon enhancement of the electric field [2]. The electric potential V near a metallic nanoparticle at a distance r is propor- tional to: V ðr; HÞ¼ E 0 ðr  gR 3 =r 2 Þ cos H where E 0 is the incident electric field parallel to the z axis, R the spherical nanoparticle’s radius and g the enhancement factor at the wavelength k defined by: g ¼ðeðkÞ e m Þ=ðeðkÞþ 2 e m Þ The normal E n and tangential E t fields are then. E 2 t / 2E 2 0 ð1  gÞ 2 and E 2 n / E 2 0 ð1 þ 2gÞ 2 In the case of a gold nanoparticle the dielectric constant of the metal has a large negative real component and a small imaginary component so that the condition eðkÞ¼2 e m is fulfilled for a wavelength in the visible g ? 1. Near a nanoparticle the electric field is greatly enhanced in resonant conditions. The Raman scattered intensity I, taking into account the excita- tion electric field E 2 and the scattered field E 0 2 , is proportional to the fourth power of the electric field. Hence for example the zz polarized mode is given by: I zz / E 2 n   E 02 n   / E 4 0 ð1 þ 2gÞ 2 ð1 þ 2g 0 Þ 2 g 0 being the enhancement factor at the wavelength k 0 of the scat- tered phonons. In resonant conditions the Raman scattering is greatly en- hanced: it is responsible of the electromagnetic Surface Enhanced Raman Scattering (SERS) effect. It is worth to notice that the SERS 0925-3467/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2011.03.024 ⇑ Corresponding author. Address: Laboratoire de Physico-Chimie des Matériaux Luminescents, 12 rue Ada Byron, 69622 Villeurbanne Cedex, France. Tel.: +33 472448334. E-mail address: bernard.champagnon@univ-lyon1.fr (B. Champagnon). Optical Materials 33 (2011) 1907–1910 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat