Combination of Nanoholes with Metal Nanoparticles–Fabrication and Characterization of Novel Plasmonic Nanostructures Andrea Csa ´ki & Andrea Steinbru ¨ ck & Siegmund Schro ¨ ter & Wolfgang Fritzsche Received: 6 October 2005 / Accepted: 2 May 2006 / Published online: 1 July 2006 # Springer Science+Business Media, Inc. 2006 Abstract Small metal nanostructures, especially gold and silver nanoparticles, are known for their interesting optical properties caused by plasmonic effects. Molec- ular plasmonics, a combination of these optically active nanostructures with the molecular world, opens new possibilities for bioanalytics and (bio-) nanophotonics. Isotropic or anisotropic, homogeneous or heteroge- neous metal nanoparticles provide a platform for dif- ferent, highly defined functional units with interesting optical properties such as plasmon waveguides or mo- lecular beacons. Nanohole arrays in metal layers are another promising component for nanophotonics. New photonic materials were realized from combinations of single metal nanoparticles with individual nanoholes in metals. Atomic force microscopic imaging was used to determine the particle location as well as the lateral dimensions and the topography of the resulting struc- tures. Besides ultramicroscopic characterization of the nanoarrangements, such as nanoparticles positioned in nanoholes, far-field optical methods were also applied to investigate their optical properties. Key words Surface plasmons . Plasmon excitation . Plasmonics . Metal nanoparticles . Core-shell particles . Nanohole . Optical characterization . Ultramicroscopic characterization Introduction Plasmons in metal nanostructures Metal structures provide interesting effects by collec- tive oscillations of their conduction electrons, called plasmons. One can differentiate between volume, sur- face, and particle plasmons. Surface plasmons, or more precisely, surface plasmon polaritons (SPP), can be ex- cited at the interface between a metal and a dielectric medium by coupling of the electron density oscillation with an incident electromagnetic wave. Under specific conditions, this interaction results in a longitudinal wave propagating along the surface. Subwavelength noble metal particles exhibit optical properties distinct from that of bulk material [1–4]. Incident electromag- netic waves induce plasmons in subwavelength par- ticles (r << l, where r is the particle radius). The electromagnetic waves penetrate particles of subwave- length dimension, e.g., 30 nm for silver particles [5], and polarize the conducting electrons (induced dipole) resulting in collective oscillations. The quanta of this coherent oscillation are the so-called particle plasmons (also known as Mie or localized surface plasmons). The particle plasmons induce the strong color of colloid solutions (plasmon bands) and the defined colors of single nanoparticles. The extinction (sum of absorption and scattering efficiencies) and the reso- nance energy, and therefore also the color appearances, Plasmonics (2006) 1: 147–155 DOI 10.1007/s11468-006-9012-9 A. Csa ´ki : A. Steinbru ¨ ck : W. Fritzsche Microsystems, IPHT, PO Box 100 239, 07702 Jena, Germany S. Schro ¨ ter Division Optics, IPHT, PO Box 100 239, 07702 Jena, Germany A. Csa ´ ki (*) Microsystems, IPHT, A.-Einstein-Str. 9, 07745 Jena, Germany e-mail: csaki@ipht-jena.de