Anisotropy of Co nanoparticles induced by swift heavy ions -: art. no. 220101

Spherical metallic nanoparticles have been formed in SiO2 layers by 160-keV implantation of Co ions at a fluence of 10(17) ions cm(-2). The implanted samples were next irradiated with 200-MeV I-127 at fluences ranging from 10(11) to 10(14) ions cm(-2) at room temperature. Modifications of nanoparticle size and shape were observed by transmission-electron microscopy and have been characterized by magnetic measurements at 295 and 5 K. For I-127 fluences below 10(12) ions cm(-2), the nanoparticles grow in size but remain spherical. For higher fluences an anisotropic growth occurs, with elongation and the preferential easy axis seen along the incident-beam direction. The nanoparticle's growth and deformations are attributed to thermal spike effects.