Electronic Transport Properties of Ruthenium and Ruthenium Dioxide Thin Films

Resistivities (ρ) and Hall coefficients (RH) of polycrystalline Ru and RuO2 thin films were measured from 293 to 600 K in vacuum, O2, and CO. Differing nanostructures and textures were sputtered at normal, confocal, and glancing incidences to 20 - 300 nm thickness. For Ru in planar or nanorod morphologies, defects have negligible effect on RH, which is similar to RH in bulk metal. Models of effective thickness are derived for the nanorod morphology. For Ru and RuO2 films, decreases in ρ on first heating are caused by defect annealing; subsequent heating shows metallic behavior. Changes from n-type to p-type conduction in RuO2 are correlated to grain structures and film strains. For certain RuO2 films, oxygen loss in high vacuum is demonstrated and a RH phase diagram is constructed to reflect the switch in dominant carriers from electrons to holes. Exposure of some RuO2 films to pure CO is shown to cause an irreversible increase in ρ. Resistivity hysteresis loops after multiple heat cycles with switching from O2 to CO are posited to be consistent with catalysis on Ru rather than RuO2 surfaces. It is shown that switching the gas environment from O2 to CO can change dominant carriers. The physical instability, breakup, and reduction of RuO2 films to Ru metal upon CO exposure is demonstrated