Anisotropic deformation of colloidal particles under 4 MeV Cu ions irradiation

Anisotropic deformation of colloidal particles was investigated under ion irradiation with 4 MeV Cu ions. In this study, 0.5 μm-diameter colloidal silica particles, 0.5 μm-diameter Au-silica core-shell particles, and 15 nm-diameter Au colloids embedding in a planar Si/SiO2 matrix were irradiated with 4 MeV Cu ions at room temperature and normal incidence. In colloidal silica particles, ion beam irradiation causes dramatic anisotropic deformation; silica expands perpendicular to the beam and contracts parallel, whereas Au cores elongate. Au colloids in a planar SiO2 matrix were anisotropically transformed from spherical colloids to elongated nanorods by irradiating them with 4 MeV Cu ions. The degree of anisotropy varied with ion flux. Upon irradiating the embedded Au colloids, dark-field light scattering experiments revealed a distinct color shift to yellow, which indicates a shift in surface plasmon resonance. A surface plasmon resonance measurement reveals the plasmon resonance bands are split along the arrays of Au colloids. Our measurements have revealed resonance shifts that extend into the near-infrared spectrum by as much as 50 nm.