Intergranular effects on the local electronic properties of the passive film on nickel

The electronic properties of the granular and intergranular sites of passive films grown on Ni(1 1 1) single-crystal surfaces in alkaline solution have been studied with scanning tunnelling spectroscopy. The results show no effect of the grain boundaries on the intrinsic semiconductive properties of the single layer hydroxide passive film. In contrast the local properties of the duplex oxide/hydroxide passive film are changed from nearly intrinsic on the grains to p-type at the grain boundaries. The implications of these local modifications of the electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed.

► Scanning tunneling spectroscopy applied to characterise passive films grown on nickel.
► Surface electronic properties of granular and intergranular sites differentiated.
► Hydroxide passive layer is a relatively large gap intrinsic semiconductor.
► Direct tunneling through the passive film shut off by thickness increase.
► Semiconductive properties of the duplex passive film modified at grain boundaries.