The properties of colloidal silica particles depend on their size and shape, which in turn determine the different roles they can play as electronic substrates, electrical and thermal insulators, photonic bandgap crystals, masks for lithographic nanopatterning, etc, in technologically expected nanodevices. Ion irradiation induces damage and structural changes in solids due to energy losses of multi-MeV heavy ions via ionization events and atomic collisions occurring in the near-surface region of the irradiated sample. Spherical silica particles were prepared using the Stober process, and deposited onto silicon wafers. The samples were then irradiated at room temperature with MeV Si ions and after the irradiation the spherical silica particles turned into oblate particles, as a result of the increase of the particle dimension perpendicular to the ion beam and the decrease in the parallel direction. The objective of the present work is to study not only the deformation of spherical SiO₂ particles, but also the structural and mechanical changes induced by the ion irradiation. The size, size distribution and shape of the silica particles were determined by scanning electron microscopy. Photoacoustics measurements were performed in order to study the structural characteristics and anisotropies of the samples, these structural differences can be initially deduced from the phonon vibration spectra. The photoacoustic measurements are carried out using a pulsed laser to excite the samples and piezoelectric sensors to detect the vibration signals. Our results revealed significant structural differences between the spherical and the deformed silica particles. Also, indentation studies were performed in order to characterize the mechanical properties of the particles. 

Juan-Carlos Cheang-Wong*, Instituto de Física, Universidad Nacional Autónoma de México, Mexico
Ulises Morales, Instituto de Física, Universidad Nacional Autónoma de México, Mexico
Rosalba Castañeda-Guzmán, CCADET, Universidad Nacional Autónoma de México, Mexico

*presenting author