Ambipolar thermoelectric power of chemically-exfoliated RuO₂ nanosheets

The electrical conductivity and Seebeck coefficient of RuO₂ nanosheets are enhanced by metal nanoparticle doping using Ag-acetate solutions. In this study, RuO₂ monolayer and bilayer nanosheets exfoliated from layered alkali metal ruthenates are transferred to Si substrates for device fabrication, and the temperature dependence of their conductivity and Seebeck coefficients is investigated. For pristine RuO₂ nanosheets, the sign of the Seebeck coefficient changes with temperature from 350-450 K. This indicates that the dominant type of charge carrier is dependent on the temperature, and the RuO₂ nanosheets show ambipolar carrier transport behavior. By contrast, the sign of the Seebeck coefficient for Ag nanoparticle-doped RuO₂ nanosheets does not change with temperature, indicating that the extra charge carriers from metal nanoparticles promote n-type semiconductor behavior.