X-RAY-ABSORPTION SPECTROSCOPY STUDY OF ATOMIC-STRUCTURE OF EPITAXIAL ERSI1.7(0001) ON SI(111)

The x-ray absorption near-edge spectra of the Si K edge were measured on ErSi1.7(0001), epitaxially grown on Si(111) at normal and glancing incidence angles of the light. The silicide films were prepared by coe vaporation under ultrahigh vacuum, characterized by low-energy electro n diffraction and photoemission and covered with a thin carbon protect ive layer before transferring to the synchrotron radiation facility. T he Si K edge showed a strong dependence on the polarization of the lig ht, denoting the different bonding characters of the p(x-y) and the p( z) Si final states. The experimental curves are compared to the ones c alculated by the extended-continuum method for different possible conf igurations of the Si atoms in the silicide: stoichiometric ErSi2; nons toichiometric ErSi1.7, where one out of six Si atoms of the hexagonal ring is missing; without and with relaxations of the Si and the Er ato ms due to the presence of ordered Si vacancies. The presence of these vacancies is immediately evidenced by comparison between experimental and calculated absorption curves. The best agreement is obtained when relaxations of Er and Si atomic positions around the vacancies are tak en into account. [S0163-1829(98)02407-2].