Extreme Electrical Resistivity Modulation in Suboxidized Ag Thin Films

The electrical conductivity of Ag layers deteriorates considerably upon oxidation, typically resulting in undesirable increases in resistivity. Although stoichiometric Ag oxides have been extensively studied, the structural, chemical, and electrical characteristics of substoichiometric Ag oxide states remain poorly understood. This gap persists largely because of the conventional assumption that thermally activated oxidation of Ag inevitably leads to the formation of stable stoichiometric oxides, most notably Ag2O. In this study, we present experimental and computational evidence for the emergence of metastable substoichiometric Ag oxide states, represented by locally O-enriched domains with Ag12O4 and Ag12O5-like configurations, embedded within predominantly metallic Ag layers during postgrowth annealing at mild temperatures. These substoichiometric oxidation states arise transiently under nonequilibrium conditions and profoundly modify electron transport. Even small fractions of such suboxide-like states, dispersed within a metallic Ag matrix, act as exceptionally strong electron-scattering centers, driving the resistivity to near-dielectric levels with only modest thermal input. As a result, the electrical resistivity increases by up to 8 orders of magnitude at annealing temperatures as low as 390 K, while these suboxide states undergo spontaneous reduction and recovery of metallic conductivity upon annealing above 510 K. By systematically excluding the formation of stoichiometric Ag2O through thermodynamic considerations and structural and chemical analyses, this work establishes that the observed electrical anomalies originate from substoichiometric oxidation states rather than bulk oxide phase formation. This study offers insights into oxidation-driven electrical resistivity modulation in noble-metal systems.