Alpha and deuteron irradiation effects on silica nanoparticles

We present an experimental investigation focused on the effects of alpha and deuteron irradiation on different silica nanoparticles. The study has been devoted also to characterize the induced point defects and the eventual structural modifications to evaluate the effects of the different irradiation source in comparison with the bulk materials. After irradiation up to about 10^16 ions cm^-2, we performed electron paramagnetic resonance (EPR), photoluminescence (PL), infrared (IR) absorption, Raman, and atomic force microscopy (AFM) measurements. We found that the two types of irradiation qualitatively induce comparable effects. Furthermore, irradiation generates the socalled twofold coordinated Si and the H(I) point defects, originating from the reaction of the former with hydrogen atoms. The occurrence of these defects is a not trivial and interesting finding due to its connection to irradiationinduced oxygen deficiency, not yet evidenced by other irradiation of silica nanoparticles. We also detected the E'Si paramagnetic centers and found that their lineshape at the highest fluence, independently from the nanoparticles size and irradiation source, is different from the one observed in the bulk. Furthermore, the integral of the E0Si signal does not depend significantly on the nanoparticles size differing from previous irradiation with b-ray of the same nanoparticles. AFM images indicate the absence of significant radiation induced sintering between the nanoparticles in the plan orthogonal to the irradiation direction suggesting the absence of morphological changes, whereas IR measurements suggest the occurrence of some structural modifications in all the nanoparticles, which consist in the decrease of the peak value of the Si–O–Si angle distribution. Finally, irradiation effects are induced not uniformly along the irradiation direction, as supported also by micro- Raman investigation of an irradiated bulk silica material and simulations of ions penetration profiles. These results suggest the occurrence of some irradiation effects due to light ion bombardment specific of nanoparticles.