For an oxide whose presence in a film can be signed by measuring the gap, the semi-conduction type (chromine n and p, fig.1), but also the lateral distribution (hematite (Fe,Cr)2O3, fig.2 ), or again the adherence level (TiO2 rutile, fig.3) are all information that delivers technology and helps us to better understand the mechanisms conditioning the durability of in-service alloys.
fig.1: photocurrent vs. potential curves of chromia Cr2O3 fthermally grown on pure chromium, underlining the n-type (resp. p-type) SC of the internal (resp. external) part of the scale.
fig.2: photocurent images at 2.41 eV et 2.73 eV of an oxide film thermally grown on a ferrtic steel, underlining the spatial distribution of haematite Fe2O3 and of the rhomboedric solid solution (Fe,Cr)2O3.
This kind of information allows to better understand le development of catastrophic oxidation of steels, linked with the formation of iron oxides instead of a passive chromia layer Cr2O3.
fig.3: Interface Cohesion Image (ICI) and Structural Qualitu Image (SQI) obtained from photocurrent recorded at differents applied potetials on a thermal oxide thin film of TiO2 rutile, underlining heterogeneities of dechohesion and growth stresses.
These heterogeneities are linked to the presence of pores, cavities, micro disbondings which can lead to the oxide film spallation and consequantly to the rapid degradation of the material.