Near-field scanning optical microscopy of colloidal CdSe nanowires

We have developed a nono-optical technique using diffraction limited far-field fluorescence monitoring of near-field scanning optical microscopy (NSOM) experiments. The technique was combined with time resolved (TR) spectroscopy and was used to study the emission properties of single colloidal CdSe nanowires (NWs) with spatial resolution similar to 100 nm. The use of this novel technique reveals a critical role of organic suspensions in optical experiments with single colloidal nanostructures. We observed that organic suspensions form a viscous shell which acts as a nano lens providing efficient coupling of excited and emitted photons to the NW. We demonstrate that physical distortion of the shell produced by the near-field probe effects the emission dynamics of single NWs. Temperature dependent measurements show that the emission decay of a colloidal NW is dominated by size-dominated by size-dependent non-radiative recombination.