The measurement of the tip current noise as a method to characterize the exposed area of coated ESTM tips

A new method to characterize the uncoated area of electrochemical scanning tunneling microscopy (ESTM) tips based on the measurement of the rms tip current noise is presented. A clear relationship between this noise and the exposed area measured by means of different standard techniques is shown. A simple model based on the tip-electrolyte system allows adjustment of the relationship. The new technique is advantageous with respect to the standard methods because it is nondestructive and because it can be applied in situ during an ESTM experiment, allowing continuous monitoring of the tip coating state.