MeV ion beam deformation of colloidal silica particles

Abstract

Spherical sub-micrometer-sized silica particles were prepared by the Stöber process, from a reaction mixture containing tetraethoxysilane, ammonia and ethanol, and deposited into silicon wafers. The samples were then irradiated at room temperature with 4MeV Si, Ti, Pt or Au ions at a fluence of 4×1015ions/cm2, under an angle of 49° with respect to the sample surface. The size, size distribution and shape of the silica particles were determined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). After the irradiation the spherical silica particles can be turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and a decrease in the direction parallel to the ion beam. This effect increases with the ion fluence and depends on the electronic stopping power of the impinging ion. For the series of 4MeV ions we used in this work a relative transverse diameter change of 17% per 1keV/nm was obtained and it seems that no threshold for the electronic energy loss exists.