Temperature Dependence of Electrical Resistance in Films of Gold Nanoparticles Linked by Organic Molecules

The electrical resistances of films of gold nanoparticles linked by hexanedithiol and octanedithiol molecules were measured as a function of temperature from 4 up to 375 K. The electrical resistance of these films goes through a minimum at a temperature T *. The change of resistance with temperature is semiconductor-like below T * and metal-like above T *. We argue that this behavior of the electrical resistance might not be the signature of a Mott−Hubbard metal-to-insulator transition but instead the signature of thermally activated electron conduction with a temperature-dependent electron tunneling where the tunneling gap between nanoparticles increases when the films expand thermally. Measuring the electrical resistances of different films revealed how T * relates to the size of the nanoparticles and to the expansion coefficients of the substrates on which the films were deposited. Simple model calculations agree well with the experimental data. Water/ice trapped within nanopores in the films leads to a hysteretic resistance versus temperature behavior between 220 and 300K.