ATOMIC-STRUCTURE OF SI(100) SURFACES

The structure of a clean Si(100) and a Ni-contaminated Si(100) was inv estigated using scanning tunneling microscopy. The clean Si(100) shows the 2 x 1 reconstruction with a surface dimer vacancy density less th an 2%. The major defects on the clean surface are a single dimer vacan cy and the C defect. A small amount of Ni on the surface drastically c hanges the surface structure and produces 2 x n reconstructions. The f ormation of vacancy clusters is favored. A rebonded S-B step is prefer red on the clean Si(100) while a nonrebonded S-B step with a split-off dimer is mainly observed on the Ni-contaminated Si(100) and in the vi cinity of dimer vacancies of the lower terrace on the clean Si(100).