Room-temperature single-electron tunnelling in surfactant stabilised iron oxide nanoparticles

Iron oxide nanoparticles have been synthesised by the reduction of FeCl3·6H2O and FeCl2·4H2O (mass ratio 2:1) in propan-2-ol. The particles were stabilised by the addition of lauric acid and the resultant particles could be readily dispersed in chloroform. Room-temperature single-electron tunnelling through these iron oxide particles has been achieved (to our knowledge) for the first time, using an STM tip–particle–substrate double junction. Characterisation of the particles by XPS and FTIR show that they are Fe2O3, or possibly Fe3O4 with an outer layer of Fe2O3, coated with a carboxylic acid monolayer. The particle diameter given by TEM is of the order of 5.0±0.9 nm. From the Coulomb staircase behaviour observed in the I–V curves, we estimate a nanoparticle capacitance of 6.7×10−19 F which is in agreement with that expected for particles of this size.