Static and Time-Resolved Terahertz Measurements of Photoconductivity in Solution-Deposited Ruthenium Dioxide Nanofilms

Thin-film ruthenium dioxide (RuO₂) is a promising alternative material as a conductive electrode in electronic applications because its rutile crystalline form is metallic and highly conductive. Herein, a solution-deposition multilayer technique is employed to fabricate ca. 70 ± 20 nm thick films (nanoskins), and terahertz spectroscopy is used to determine their photoconductive properties. Upon calcining at temperatures ranging from 373 to 773 K, nanoskins undergo a transformation from insulating (localized charge transport) behavior to metallic behavior. Terahertz time-domain spectroscopy (THz-TDS) indicates that nanoskins attain maximum static conductivity when calcined at 673 K (σ = 1030 ± 330 S·cm^–1). Picosecond time-resolved terahertz spectroscopy using 400 and 800 nm excitation reveals a transition to metallic behavior when calcined at 523 K. For calcine temperatures less than 523 K, the conductivity increases following photoexcitation (Δ<i>E</i> < 0) while higher calcine temperatures yield films composed of crystalline, rutile RuO₂ and the conductivity decreases (Δ<i>E</i> > 0) following photoexcitation