Scattering of light at micro- and nanostructures of triangular shape

Abstract

The development of new photonic and plasmonic devices rely on the new pioneering techniques of micro- and nanofabrication, combining both standard lithography techniques and self-assembly. The combination of colloidal crystals, projection patterning and soft-lithography are examples of fabrication techniques which allow to obtain complex structures of sizes smaller than the wavelength of visible light. In many cases, the structures fabricated by this way are not possible to obtain using standard lithography techniques, like electron-beam, UV-VIS lithography and focused ion beam (FIB). We have used two-dimensional colloidal crystals as templates to fabricate arrays of isolated metallic particles of triangular shape on surfaces and two-dimensional gratings. Either dielectric or metallic structures can be obtained. In the later case the coupling between light and the locally confined surface plasmon-polaritons leads to resonances, field enhancements and other related phenomena. The scattering properties of the particles and gratings have been investigated experimentally, using a confocal, a near- field optical microscope and a spectrometer, and theoretically, using FDTD methods. We show that triangular particles of noble metals are highly sensitive to the relative direction of incidence of light and its polarization. On the other hand, the light scattered in the direction perpendicular to the plane of the particles reveals strong spectral dependency. This dependency can be exploited to fabricate photonics devices sensitive to the direction of incidence of light.