Local structure of NH2 on Si(100)-(2x1) and its effect on the asymmetry of the Si surface dimers

A scanned-energy mode photoelectron diffraction study of the Si(100)-(2 x 1) surface with adsorbed NH2 provides quantitative determination of key structural parameters previously only predicted from theoretical calculations. In particular, the N atoms occupy off-atop sites at a dimerized surface Si atom with N-Si bond lengths of 1.73 +/- 0.08 Angstrom and bond angle relative to the surface normal of 21 degrees +/- 4 degrees. The adsorption greatly reduces the Si dimer asymmetry relative to that of the clean surface