Optical absorption spectrum of gold atoms deposited on SiO ₂ from cavity ringdown spectroscopy

The optical properties of gold atoms supported on amorphous silica (α-SiO2) were studied experimentally and theoretically in the visible range. Samples were prepared in situ by depositing Au atoms at low coverages (5×1012cm-2) in UHV, and the optical absorption spectra were recorded by cavity ringdown spectroscopy. The atomic absorption bands can be attributed to gold atoms trapped at Si-O• and Szi-O- defect sites. The absence of optical transitions typical for Au2 shows that the atoms are efficiently anchored at these defect sites, preventing diffusion and aggregation. Furthermore, these experimental results reveal that it is now possible to study optical properties of well-defined nanostructures at surface coverages as low as 5×1011cm-2.