Optical Properties of One-Dimensional Metal Nanostructures
- PDF / 203,172 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 100 Downloads / 250 Views
M3.8.1
Optical Properties of One-Dimensional Metal Nanostructures Encai Hao , Shengli Zou, and George C. Scha tz Department of Chemistry and Institute for Nanotechnology Northwestern University 2145 Sheridan Road Evanston, Illinois 60208, U.S.A.
ABSTRACT We present a theoretical study of the optical properties of one-dimensional (1-D) metal nanostructures including nanorods and nanotubes. Although the optical properties of gold nanotubes are similar to that of gold nanorods, both the longitudinal and transverse plasmon resonances of gold nanotubes show much larger red-shifting and narrower. The E-field calculations indicate that the 1-D gold nanostructures, particularly gold nanotubes have great potential for applications to SERS. INTRODUCTION There is a great deal of interest in the nanoscience field in characterizing noble metal structures having dimensions in 1-100 nm range, as such structures which are intermediate in size between isolated molecules (atoms) and the bulk phase can have properties which are quite different from either limit. In addition, some of the synthetic methods provide capabilities for varying structure over a broad range, thereby providing the possibility of adapting the structures to new applications. During the last 10 years, great progress has been achieved in controlling particle sizes, and recently particle shapes. Since 1997, nanorods and nanowires,[1-3] following by triangular nanoprisms,[4,5] nanodisks,[6] and even multipod nanostructures[7] have been added to the family of nanoparticles. This generation of nanoparticles is not only structurally anisotropic, but importantly they exhibit intrinsic shape-dependent optical properties.[2-4, 6-8] For example, the fluorescence yield of gold nanorods can be a million times stronger than that of the gold nanospheres.[3] These examples demonstrate that the shape effect can be as important as the size effect for nanoscale materials. In addition, these structures lead to optical and electrical properties that make them desirable for emerging applications involving bio-labels, photovoltaic behavior, chemical sensing, and surface enhanced Raman scattering (SERS). To understand these intriguing optical features, a number of theoretical approaches have been developed,[8-10] including the discrete dipole approximation (DDA), finite difference time domain method (FDTD), the multiple multipole method, and the modified long wavelength approximation (MLWA). Among them, the DDA is a particularly useful technique for describing isolated nanoparticles with arbitrary shape and a complex surrounding environment (solvent, substrate, other nearby particles).[9] In the DDA, the object of interest is represented as a cubic array of N polarizable elements. The response of this array to an applied electromagnetic field is then described by self-consistently determining the induced dipole moment in each element. This information can be used to determine far-field properties like extinction efficiencies. Another use
M3.8.2
of DDA is to calculate the electromag
Data Loading...
