Deformation of colloidal silica particles using MeV Si ion irradiation

Spherical submicrometer-sized silica particles were prepared by the Stِber process, from a reaction mixture containing tetraethoxysilane, ammonia and ethanol, and deposited onto silicon wafers. While the properties of these SiO2 particles depend on their size, size distribution and shape, monodisperse spherical particles were obtained with a narrow size distribution. The samples were then irradiated at room temperature with Si ions at two energies (4 MeV and 6 MeV) and fluences up to 5 × 1015 Si/cm2, at an angle of 45° with respect to the sample surface. The size, size distribution and shape of the silica particles were determined using scanning electron and atomic force microscopes. By means of the Si ion irradiation, the as-prepared spherical silica particles can be turned into ellipsoidal particles, as a result of an increase of the particle dimensions perpendicular to the ion beam and a decrease in the direction parallel to the ion beam. This effect increases with the ion energy and fluence, and depends on the electronic energy loss processes to which the impinging ions are subjected. Our results also suggest that the particle deformation is more important in the case of larger as-prepared silica colloids.