STM ON CRACKS IN BRITTLE MATERIALS

For a better understanding of local materials faults such as dislocations, grain boundaries and cracks, the stress and strain fields must be known near the defect cores where continuum theories predict singular behavior. Scanning tunnelling microscopy allows the examination of these defects in detail. Because of the limited positioning possibilities of conventional STM's these defects can only be examined when they are very numerous. Therefore, a STM was developed which allows the exact positioning of the measuring system and macroscopic as well as high-resolution surface scanning. Special problems like convolution effects (between STM tip and the surface) and preparation problems are discussed, and examples are given. First measurements on such rough surfaces as fracture surfaces, and on macroscopic defects, e.g. cracks, are presented.