Controlled shape modification of embedded Au nanoparticles by 3Â MeV Au2+-ion irradiation

Shape modification of embedded Au nanoparticles by 3 MeV Au2+-ion irradiation has been studied by cross-sectional transmission electron microscopy (XTEM). The ion irradiation on spherical Au nanoparticles shallowly-embedded in SiO2 caused a well-controlled transformation of shape to ellipsoidal. Satellite nanoparticles of smaller sizes were found to nucleate around the ellipsoids. Rapid growth of the ellipsoidal nanoparticles was observed as the applied fluence increased from 3 × 1015 to 7 × 1015 ions cm−2. The XTEM study also revealed the crystallinity of the ellipsoids formed by MeV ion irradiation. Reduction in the surface plasmon resonance (SPR) peak intensity in the optical absorption spectrum indicates partial dissolution of the spherical nanoparticles by ion irradiation. We have thus obtained a unique near-surface structure of ellipsoidal nanoparticles. The results are discussed in terms of effects of ion energy deposition and inverse Ostwald ripening.