Conductivity of ruthenate nanosheets prepared via electrostatic self-assembly: characterization of isolated single nanosheet crystallite to mono- and multilayer electrodes.

Ultrathin films composed of ruthenate nanosheets (RuO(2)ns) were fabricated via electrostatic self-assembly of unilamellar RuO(2)ns crystallites derived by total exfoliation of an ion-exchangeable layered ruthenate. Ultrathin films with submonolayer to monolayer RuO(2)ns coverage and multilayered RuO(2)ns thin films were prepared by controlled electrostatic self-assembly and layer-by-layer deposition using a cationic copolymer as the counterion. Electrical properties of a single RuO(2)ns crystallite were successfully measured by means of scanning probe microscopy. The sheet resistance of an isolated single RuO(2)ns crystallite was 12 kΩ sq(-1). Self-assembled submonolayer films behaved as a continuous conducting film for coverage above 70%, which was discussed based on a two-dimensional percolation model. Low sheet resistance was attained for multilayered films with values less than 1 kΩ sq(-1). Interestingly, the grain boundary resistance between nanosheets seems to contribute only slightly to the sheet resistance of self-assembled films.