A new method for the investigation of the inhibition efficiency against corrosion by organic films adsorbed on metals based on the measurement of Z-approach curves by AC-SECM is proposed. Preliminary measurements conducted on four copper-inhibitor systems exposed to aqueous solutions support that a characteristic frequency can be defined, which corresponds to the frequency of the AC potential signal applied to the SECM tip for which a transition between negative- and positive-feedback behaviours is observed in the approach curves. From the shift of this characteristic frequency towards higher values, the enhancement of the corrosion protection efficiency of the inhibitor system can be established. Furthermore, the effects of inhibitor nature, concentration, and pre-treatment duration for the formation of the surface films, can be readily investigated
