Anisotropic deformation of colloidal particles under MeV ion irradiation

Abstract

Spherical silica colloids with a diameter of 1.0 um made by wet chemical synthesis, were irradiated with 2-16 MeV Au ions at fluences ranging from 2*10^(14) to 11*10^(14) cm^(-2). The irradiation induces an anisotropic plastic deformation turning the sperical colloids into ellipsional oblates. After 16 MeV Au irradiation to a fluence of 11*10^(14) cm^(-2) a size-asapect ratio of 4.7 is achieved. The size polydispersity (~3%) remains unaffected by the irradiation. The transverse diameter increases with the electronic energy loss above a threshold value of ~0.6 keV/nm. Non-ellipsoidal colloids are observed in the case that the projected ion range is smaller than the colloid diameter. The deformation effect is also observed for micro-crystalline ZnS and amorphous TiO2 colloids, as well as ZnS/SiO2 core/shell particles. No deformation is observed for crystaline Al2O3 and Ag particles. The data provide strong support for the thermalspike model of anisotropic deformation.