Structure of clean and H-saturated epitaxial two-dimensional Er silicide on Si(111) studied by SEXAFS

Abstract 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 T 4 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 A, 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 A, respectively. These results clearly indicate that H adsorption induces a remarkable switch of the Si top layer buckling from B-type (clean ErSi 2 ) to A-type orientation. In addition, a strong outward relaxation of the Si top bilayer atoms with respect to their positions in clean ErSi 2 is observed upon H dosing.