Effects of dielectric screening on the optical properties of metallic nanoshells E. Prodan a , P. Nordlander a,b, * , N.J. Halas b,c a Dept. Physics and Astronomy, M.S. 61, Rice University, P.O. Box 1892, Houston, TX 77251, USA b Dept. Elec. and Comp. Engineering, M.S. 366, Rice University, Houston, TX 77251, USA c Dept. Chemistry, M.S. 60, Rice University, Houston, TX 77251, USA Received 10 September 2002; in final form 4 November 2002 Abstract The time dependent density functional method for the calculation of optical properties of metallic nanoshells is extended to include the combined influence of a dielectric core and a dielectric embedding medium. The coupling between the polarization charges at the inner and outer surfaces of the shell is found to strongly influence the position of the plasmon resonances. The method is applied to gold nanoshells with gold sulfide cores in water for two different diameters, and the energies of the calculated plasmon resonances are found to be in good agreement with experimental measurements. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction The metallic nanoshell, a nanoparticle consist- ing of a thin gold or silver shell surrounding a dielectric core, displays unique and structurally tunable optical properties [1–4]. The energies of the plasmon resonances of these nanoparticles depend on the ratio of the thickness of the metallic shell with respect to the overall diameter of the particle [5]. By controlling the thickness of the metallic shell, the plasmon frequencies can be systematically placed at arbitrary wavelengths be- tween the mid infrared and the UV part of the optical spectrum [6]. The tunability of the plasmon resonances in metallic nanoshells has made these particles attractive in various applications such as resonant photo-oxidation inhibitors [7], optical triggers for opto-mechanical materials [8] and drug delivery implants [9]. Classical Mie scattering provides a convenient approach for the description of the optical prop- erties of nanoshells but requires the frequency dependent dielectric function of the nanoparticle as a critical input. While dielectric functions for many bulk solids are known, it is not clear how appropriate a bulk dielectric function would be for a particle of nanoscale dimensions. In view of the considerable scientific interest in metallic nano- shells, it is clearly of interest to develop a more fundamental description of their electronic and optical properties. Chemical Physics Letters 368 (2003) 94–101 www.elsevier.com/locate/cplett * Corresponding author. Fax: +713-348-4150. E-mail address: nordland@rice.edu (P. Nordlander). 0009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0009-2614(02)01828-6