Spherical silica colloids with a diameter of 1.0 µm, made by wet chemical synthesis, were irradiated with 2-16 MeV Au ions at fluences ranging from 2×1014 to11×1014 cm2. The irradiation induces an anisotropic plastic deformation turning the spherical colloids into ellipsoidal oblates. After 16 MeV Au irradiation to a fluence of 11×1014cm2 a size-aspect 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 crystalline Al2O3 and Ag particles. The data provide strong support for the thermal spike model of anisotropic deformation.

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Journal Nucl. Instrum. Methods Phys. Res. B
van Dillen, T, Snoeks, E, Fukarek, W, van Kats, C.M, Velikov, K.P, van Blaaderen, A, & Polman, A. (2001). Anisotropic deformation of colloidal particles under MeV ion irradation. Nucl. Instrum. Methods Phys. Res. B, 175-177, 350–356.