Colloidal nanocrystals air bridge fabricated by direct lithography

We report on the direct lithographic fabrication of a polymeric air bridge embedding semiconductor colloidal nanocrystals (NCs). Two ensembles of NCs emitting at 637 nm and 550 nm, respectively, were dispersed into different matrices of SU-8 negative photoresist. The first matrix was deposited on a Si substrate and localized by photolithography thus obtaining an array of red-emitting stripes with micrometer resolution. The second matrix was then deposited on the first layer of stripes and analogously localized in order to obtain a second array perpendicular to the lower one. Suspended emitting structures in the micrometer range were therefore obtained, as confirmed by scanning electron microscopy (SEM) and spatially resolved photolummescence (PL) measurements on the fabricated sample. The developed and applied method allows the fabrication of three-dimensional active structures by means of several realigned lithographic steps. This opens the way to the fabrication of extremely efficient photonic devices whose optical properties, such as spectral filtering, directionality and emission efficiency, can be finely tuned through a 3D photonic crystal (PC) technology. (c) 2007 Elsevier B.V. All rights reserved.