The deposition of ultrathin films from liquid-phase is still a rare protocol, even with the breakthroughs by Keszler and colleagues. Our team at the Naval Research Laboratory* has demonstrated that ruthenium dioxide (RuO2) can be deposited from commercially available precursors as a disordered, nanoscopic, ultrathin film on a variety of substrates using a scalable, atom-efficient, low-temperature, liquid-phase, self-limiting synthetic protocol (*C.N. Chervin, I.R. Pala, M.D. Donakowski, P.A. DeSario, J.J. Pietron, J.W. Long, J.C. Owrutsky, J.S. Melinger, M.S. Osofsky, R.M. Stroud, T.H. Brintlinger, C.M. Krowne, F.J. Rachford, K.M. Bussmann, K.M. Charipar, A. Khachatrian, P. Cunningham, B. Jugdersuren, X. Liu). The resulting RuO2 nanoskins are broadband transparent over an uncommonly large range for an oxide (UV to microwave) with an electrical conductivity that can be tuned over three orders of magnitude by calcining without ripening the particles comprising the film. The frequency dependence of the complex conductivity, obtained by broadband terahertz time-domain spectroscopy shows strong localization effects in RuO2 nanoskins, whereas sputtered RuO2 films exhibit a more conventional Drude-type (i.e., metallic) response. Temperature-dependent magneto-transport measurements (1.75K&lt;T&lt;300K and 0&lt;B&lt;8T) reveal a metal–insulator transition for the disordered form of RuO2 and an overall conductivity-temperature formalism that fits two-dimensional transport. Freestanding 10-nm-thick RuO2 films allow us to extract electron micrographic and selected area electron diffraction data confirming the predominant role of disorder in this form of RuO2, a structural assignment also seen by thin-film pair distribution function analysis. Our characterization of this metallic oxide in its disordered, nanoscopic form using optical, structural, thermal, microscopic, mechanical, electrochemical, and chemical state measurements has led us to categorize it as a member of a rare n–µ quadrant of electronic materials: one that exhibits a high concentration of electronic carriers (n) of low mobility (µ). These atypical physical characteristics of disordered, ultrathin RuO2 may correlate with its remarkable energy-storage and electrocatalytic properties and guide us to the design of newly functional materials once expressed in disordered, nanoscopically connected forms.

Solution-Deposition of disordered RuO2 nanoskins: An example from the fourth quadrant of electronic materials

253rd National Meeting (2017)

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