Deformation, alignment and anisotropic optical properties of gold nanoparticles embedded in silica

Gold/silica composite films with single and multilayer structures were fabricated by simultaneous gold sputtering and plasma-enhanced chemical vapor deposition of SiO2. Heating during or after deposition was performed to control particle size. Samples were irradiated, at liquid nitrogen temperature, using 15 MeV Cu3+ ions or 27.5 MeV In7+ ions. Microstructural analysis by transmission electron microscopy revealed that spherical or nearly spherical gold nanoparticles were transformed during the irradiation into prolate ellipsoids whose long axis is along the ion beam direction. The optical absorption band attributed to surface plasmon resonance of gold particles was located at 520 nm for single layer films and at 602 nm for multilayer structures. After ion irradiation, this band splits into two polarization-dependent bands whose positions strongly depend on the size, aspect ratio and alignment of the nanorods.