Optical and electronic properties of Ag nanodots on Si(111)

Reflectance anisotropy spectroscopy (RAS) has been used, together with scanning tunnelling spectroscopy (STS), to investigate the optical and electronic properties of nanodots formed by depositing Ag on the Si(111)-3 x 1- Ag surface. One-dimensional (1D) arrays of nanodots were grown on a single- domain (3 x 1)-Ag surface and the anisotropic optical response in the 0.5-5eV range measured by RAS. Aligned, elongated Ag islands were also grown on this surface to compare their properties with those of the nanodots. STS of the Ag islands showed distinct metallic behaviour, whereas the nanodots revealed a bandgap of similar to 0.6 eV, indicating that the surface of the dots has a non-metallic character, similar to that of the Si(111)-3 x 1-Ag surface. RAS also showed substantial differences between the structures, with a large infrared anisotropy for the metallic Ag islands consistent with anisotropic Drude-like intraband transitions, whereas the nanodots gave a negligible response in this spectral region. The RAS results in the infrared spectral region are consistent with the difference in the metallic character of the nanodots and islands, as determined by STS.