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 (RuO2ns) were fabricated via electrostatic self-assembly of unilamellar RuO2ns crystallites derived by total exfoliation of an ion-exchangeable layered ruthenate. Ultrathin films with submonolayer to monolayer RuO2ns coverage and multilayered RuO2ns 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 RuO2ns crystallite were successfully measured by means of scanning probe microscopy. The sheet resistance of an isolated single RuO2ns 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.