Plasmon-Mediated Scattering of Light by Ion Eroded Ag(110) Surfaces

Abstract

Enhanced scattering of laser light from polished and ion bombarded Ag(110) surfaces is reported. Ar+ ions with energy 500 eV were directed against the sample at angles of incidence between 30° and 45°. The ion current was about 4–6 μA. The experiments were made with a diode pumped solid-state green laser that emitted at 532 nm, with a continuous wave power output around 5 mW. In a controlled series of experiments a sudden increase in scattered intensity could be observed at a fluence of about 2 × 1017 ions/cm2. The scatterograms showed radially oriented intensity streaks, superimposed on a diffuse and isotropic background intensity. No correlations with low-index crystallographic directions were found. The surface structure was studied by means of optical interferometry and atomic force microscopy. The scattered light was found to be dominated by the contribution from shallow surface indentations and scratches remaining from the polishing process. It is demonstrated that the sputtering creates a surface topography with correlation length of a few μm. A mechanism based on surface plasmons is proposed to be responsible for the observed increase in scattered intensity.