Structure of clean and H-saturated epitaxial two-dimensional Er silicide on Si(1 1 1) studied by SEXAFS

The atomic structure of H-saturated epitaxial two-dimensional (2D) Er silicide on Si(1 1 1) has been studied by means of surface-extended X-ray absorption fine structure. This structure consists of a single hexagonal erbium plane intercalated between the substrate and a bulk-like Si top bilayer, and oriented in the same way as the substrate double layers (A-type orientation). The Er atoms are positioned on T4 sites of the Si substrate. The interlayer spacings between the Er plane and the upper and lower Si top bilayer planes are 3.14 ± 0.03 and 2.24 ± 0.03 إ, respectively, and the interlayer spacings between the Er plane and the first and second Si substrate planes are 2.12 ± 0.03 and 2.95 ± 0.03 إ, respectively. These results clearly indicate that H adsorption induces a remarkable switch of the Si top layer buckling from B-type (clean ErSi2) to A-type orientation. In addition, a strong outward relaxation of the Si top bilayer atoms with respect to their positions in clean ErSi2 is observed upon H dosing.