Photoconductivity studies of nanoparticle arrays

1. Photoconductivity studies of nanoparticle arrays and development of linker molecules for efficient inter-particle coupling Dawn A. Bonnell, University of Pennsylvania, DMR 0425780 Figure 2. (a) Fluorescence image of single nanoparticles and small clusters of particles, (b) schematic diagram of the substrate used, (c) TEM image of the substrate with deposited nanorods, also showing gold markers in black. Figure 1. TEM image of a 230 nm x 600 nm electrode gap containing a thin film of 6 by 31 nm TOPO-capped CdSe nanorods drop-cast from solution. To investigate inter-particle coupling with aliphatic ligands, Researchers at the Nanoscale Science and Engineering Center (NSEC) at the University of Pennsylvania have studied the fluorescence from single semiconductor particles and nanoparticle clusters (from 1 to ~ 50 000 particles). Combined transmission-electron, atomic-force and fluorescence spectroscopy allowed direct determination of the number of particles present in a single fluorescent source. We showed that single particles and clusters of two and three nanoparticles show statistically indistinguishable fluorescence, while approx. five or more particles can be distinguished by their longer on-times. Electrical transport in the dark and under Illumination was studied in arrays of elongated CdSe nanocrystals (nanorods) as a function of nanorods’ aspect ratio, surface chemistry and temperature. Temperature dependence of the conductivity follows an activated hopping process at temperatures above 200K with activation energies of a few hundred meVs that increase with increasing aspect ratio. The observed dark and photocurrent properties of these artificial solids are best described by trap-dominated transport.