Shape elongation of embedded Zn nanoparticles induced by swift heavy ion irradiation. A SAXS study

Zinc nanoparticles (NPs) of ∝10 nm in diameter were irradiated with 200 MeV Xe¹⁴⁺ ions with various fluences ranging from 2 x 10¹¹ to 4 x 10¹⁴ ions/cm². The shape elongation of the NPs and the mean inter-particle (IP) distance were evaluated by small angle X-ray scattering (SAXS) in the transmission configuration using synchrotron X-ray of 18 keV. The azimuth angle dependence of SAXS signal, which was isotropic for unirradiated state, changed to anisotropic exceeding the fluence of 1 x 10¹³ ions/cm². It indicated that the NPs collectively deformed from spheres to spheroids. The signal due to the ion tracks was observed at all the fluences where the measurements were carried out, i.e., between 2 x 10¹¹ and 4 x 10¹⁴ ions/cm² except the unirradiated state. This observation is consistent with the erasing and overwriting mechanism for the core-shell tracks instead of the simple black-painting model. The IP distance perpendicular to the SHI beam increased with the fluence, indicating that dynamical dissolution and agglomeration of NPs proceed with the fluence in addition to the elongation. Swift heavy ion (SHI) irradiation induces not only the shape elongation of nanoparticles (NPs) but an increase of the inter-particle distance perpendicular to the SHI beam, i.e., dissolution of smaller NPs and agglomeration to larger ones. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)