Photoemission electron microscopy of oxide fracture at slip steps on metals

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Abstract
The surface deformation of metals and the concomitant mechanical behavior of the surface oxide film may be observed simultaneously by photoemission microscopy. This is illustrated by photoemission micrographs of steel and aluminum plastically deformed in either tension or compression. During tensile deformation of both metals the ’’natural’’ thin surface oxide is ruptured by the emerging slip steps. This reveals the bare metal surface of the step itself, which appears on the micrographs as a line of enhanced photoemission (exoelectrons). On the other hand, compressive deformation of ?4% rarely enhances the photoemission, the majority of the slip lines exhibiting only topographical contrast. This difference is related to the geometry of the slip steps as well as to the behavior of the surface oxide. In compression the oxide on aluminum does not fracture at the slip steps, and no exoelectron emission is observed. The oxide on steel clearly does fracture, but few slip steps emit exoelectrons because they are difficult to illuminate.