Adsorption of Sn on cleaved Si(111) surfaces

Abstract

The initial steps of ultrahigh vacuum deposition of Sn on clean cleaved Si(111) surfaces kept at room temperature were studied using low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and photoemission yield spectroscopy (PYS). AES shows the formation of a seemingly uniform Sn overlayer up to 2 ML followed by the growth of metallic islands. During the adsorption stage, up to 2 ML, the initial 2 × 1 reconstructed surface is first replaced by a √3 × √3 R30° pattern in the 13ML range and then by a 1 × 1 diagram beyond 0.5 ML. Size and valency effects are observed in the very first interaction process up to 13ML. The electronic properties deduced from PYS reveal a monotonous decrease of the ionization energy up to 1 ML, a slight displacement of the Fermi level position towards the top of the valence band at that coverage, and the replacement of the double-structured dangling bond peak of Si(111) 2 × 1 by an apparently unique peak of Sn-induced dangling bond states. A remarkable situation occurs at 1 ML coverage with a very well ordered overlayer and the possible opening of a gap in the induced surface states.