For the first time, latent tracks induced by swift Kr ions have been directly observed in mica. These tracks are imaged by atomic-force microscopy as hollows which are associated with softer areas in the mica surface. The track core is formed by disordered mica. The mean diameter of the observed hollows increases with the electronic stopping power of the ions. The track shape along the ion path is deduced from the analysis of both the number of the tracks per unit area and their diameter distribution. These observations are the first images of nanometric changes of elastic properties.

• Received 29 April 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1582