Alignment and FLIM imaging of Ag nanowires with CdTe quantum dots

Summary form only given. One-dimensional nanostructures are desirable in modern technology for their potential applications as the smallest possible carriers for electrons or plasmonic signals. The ability to direct the signal from source to destination could have major implications in the fields of nanoelectronics and photonics. However, one of the major challenges facing the application of these 1D nanostructures is in their alignment. These structures are often grown in solution and so are randomly oriented, requiring an alignment procedure during deposition to a substrate. Silver nanowires were synthesised according to the polyol procedure adopted by Sun et. al. The reaction was carried out under a constant temperature of 160degC for 60 minutes and TEM images of the resulting wires revealed dimensions of ~100 nm diameter and up to 14 mum length. Part of the resulting solution was centrifuged a number of times and the solvent was changed from ethylene glycol to ethanol, resulting in excess particles being removed and the wire dispersion containing a mix more uniform in wire dimensions. Several methods for the alignment of the nanowires were investigated. One method involved the evaporation rate of the solvent itself, with ethanol showing a radial alignment of nanowires upon evaporation of a droplet at room temperature. Using channels etched into the surface of the glass substrates, alignment effects were examined regarding capillary flow, with suggestions that a controlled approach may prove a potential technique. One further effect regards the application of an electric field across a solution of the nanowires. A combined approach involving each of these methods could also prove beneficial. Absorption spectroscopy was also carried out on the samples and the lifetime emission of CdTe quantum dots was examined in close proximity to the nanowires using confocal microscopy in tandem with fluorescence lifetime imaging microscopy (FLIM). Results of this FLIM analysis - showed two distinct lifetime bands, with a shorter lifetime band being enhanced and a longer lifetime band being quenched. These two lifetime bands can be attributed to intrinsic recombination of carriers in the quantum dot core and to mediated effects due to the presence of surface states respectively.