The electrode potential-dependent formation of oxygen species on copper in noncomplexing aqueous media, encompassing oxide phase films and adsorbed oxygen/hydroxide, are explored at different pH values by means of surface-enhanced Raman spectroscopy (SERS). This technique provides a monolayer-sensitive in- situ vibrational probe, which can follow potential-dependent surface speciation on voltammetric or longer time scales. In alkaline NaClO4 electrolytes (pH 13), the cyclic voltammetric peaks associated with copper oxide phase-film formation and removal are correlated quantitatively with simultaneously acquired SER spectral sequences. The latter indicate the sequential formation of Cu2O and then mixed Cu2O/Cu(OH)2 layers, diagnosed by the appearance of metal−oxygen lattice vibrations at 625/525 and 460 cm-1, respectively. The potential-dependent speciation is in concordance with the Pourbaix diagram, certifying the “bulk-phase” nature of the films. The Raman band intensity−film thickness correlation (the ...