Pit Growth in NiFe Thin Films

Pit growth was studied in 80Ni‐20Fe sputtered thin films by analysis of images of the growing pits. The pit current density was found to increase with pit growth potential until reaching a limiting value. The limiting current density increased with decreasing film thickness. The mass‐transfer resistance to the active pit wall exceeds by an order of magnitude that predicted from a simple radial‐diffusion model. It is suggested that the undercut, remnant passive film collapses over the pit wall causing a constriction. A voltage component calculation matches the data rather well and indicates that pit growth below the limiting current density is limited by a combination of ohmic, concentration, and surface activation considerations.