NANO LETTERS
Metallic Photonic Crystals Based on Solution-Processible Gold Nanoparticles
2006 Vol. 6, No. 4 651-655
Xinping Zhang,* Baoquan Sun, and Richard H. Friend CaVendish Laboratory, UniVersity of Cambridge, J J Thomson AVenue, CB3 0HE Cambridge, U.K.
Hongcang Guo, Dietmar Nau, and Harald Giessen Institute of Applied Physics, UniVersity of Bonn, Wegelerstrasse 8, 53115 Bonn, Germany Received November 30, 2005; Revised Manuscript Received January 16, 2006
ABSTRACT We demonstrate the fabrication of metallic photonic crystals, in the form of a periodic array of gold nanowires on a waveguide, by spincoating a colloidal gold suspension onto a photoresist mask and subsequent annealing. The photoresist mask with a period below 500 nm is manufactured by interference lithography on an indium tin oxide (ITO) glass substrate, where the ITO layer has a thickness around 210 nm and acts as the waveguide. The width of the nanowires can be controlled from 100 to 300 nm by changing the duty cycle of the mask. During evaporation of solvent, the gold nanoparticles are drawn to the grooves of the grating with apparently complete dewetting off the photoresist for channels less than 2 µm in width, which therefore form nanowires after the annealing process. Strong coupling between the waveguide mode and the plasmon resonance of the nanowires, which is dependent on the polarization and incidence angle of the light wave, is demonstrated by optical extinction measurements. Continuity of the nanowires is confirmed by conductivity properties. Simplicity, high processing speed, and low cost are the main advantages of this method, which may have a plethora of applications in telecommunication, all-optical switching, sensors, and semiconductor devices.
Periodical arrangements of metallic nanoparticles1,2 or nanowires3 are generally referred to as metallic photonic crystals. Such structures are important because of their special physical properties based on collective electronic oscillation excited by the incident electromagnetic field, namely, the particle plasmon resonance.1-5 A number of potential applications in selective spectral absorption, all-optical switching,6 distributed feedback,7,8 and biosensors,9 have been proposed. WaVeguided metallic photonic crystals exhibit unique optical properties due to their strong coupling between the waveguide mode and the particle plasmon resonance.1-3 Different methods have been demonstrated to fabricate metallic nanostructures. Electron beam lithography (EBL) with subsequent evaporation and lift-off is commonly used to produce one- or two-dimensional photonic crystal structures. However, a small dynamic range of fabrication area (
