Influence of Sn on the optical anisotropy of single-domain Si(001)

We apply reflectance anisotropy spectroscopy (RAS) and low-energy electron diffraction (LEED) to the study of Sn deposited on a single-domain vicinal Si(001) sample. Large variations in RAS are recorded when up to 5 monolayers (ML) of Sn is deposited on the Si substrate at room temperature. We observe (2 x 2) and (1 x 1) LEED patterns for the 0.5-ML and 1.0-ML Sn covered surfaces, respectively. The (1 x 1) LEED pattern exists beyond this coverage and up to 5.0-ML deposition. Even though a(1 x 1) LEED pattern is observed upon deposition of 1.5 ML. surprisingly, a significant optical anisotropy is observed. After annealing to 570 degreesC for 2 min, we observe a progression of LEED pattern changes from c(4 x 4)-->(6 x 2)-->(8 x 4) --> (5 x 1) with increased Sn coverage up to 1.5 ML. Similar RAS line shapes are obtained for all reconstructions produced through annealing with the exception of the (5 x 1). For the (5 x 1) phase, a significant anisotropy appears in the region of 1.8 eV. Similarities in the RAS line, shape for both the (5 x 1) phase and that obtained after deposition of 1.5 ML of Sn at room temperature may indicate a RAS sensitivity to Sn dimer orientation within the uppermost layer.