Synthesis and transport properties of ZnO nanorods and nanoparticles assemblies

We report here on the elaboration and transport properties of assemblies of ZnO nanoparticles and nanorods synthesized by organometallic chemistry. Two different methods have been used to prepare the samples. The first one consists in the deposition of the nano-objects on the substrate ( drop-casting method) whereas the second one consists in the direct synthesis of the nano-objects on the substrate ( in situ method). All the samples were highly resistive in the dark. Conductivity of as-grown nanorods was light-sensitive whereas the one of as-grown nanoparticles was not. Annealing the nanoparticles at 200. C increases their dark resistance and strongly decreases their resistance under light. We analyse the transient photoconductivity when the light is abruptly switched on and off. The increase of the current when the light is switched on is fast and follows a simple exponential function. Decrease of the current when the light is switched off is slower and can be described by a stretched exponential function for short times and by a power law at longer times. Our various experiments are discussed in the light of other experiments on ZnO nanorods and CdSe nanoparticles, and to available models describing transport in assemblies of semiconductor nanoparticles.