Nanopositioning of colloidal nanocrystal emitters by means of photolithography and e-beam lithography

We propose a new technique for the localization of colloidal nanocrystals (NCs) by directly exposing a polymer/NCs blend to a lithographic process. Our approach relies on the dispersion of CdSe/ZnS core/shell NCs into a layer of photo- or electro-sensitive resist, which is subsequently patterned by means of photolithography or electron beam lithography (EBL), respectively. We have characterized the behaviour of both positive (polymethil-methacrylate, PMMA) and negative (SU-8 epoxy resin) resists as polymeric hosts for colloidal nanoemitters. The morphological and optical analysis of the processed samples showed the successful localization of the colloidal NCs. This technique enables the fabrication of two or three dimensional active photonic crystals devices or distributed feed-back lasers based on colloidal nanocrystal emitters with sub-micron resolution, without recurring to etching processes. Moreover, by decreasing the concentration of nanocrystals in the blend and by isolating very small regions of the layer, realization of single NC/photon emitters can be enabled. As a further advantage, the possibility to re-align subsequent lithographic steps enables the localization of different colloidal nanoemitters with micron- and nanometer resolution, thus merging red, green and blue emission on the same substrate.