ELECTRONIC-STRUCTURE OF EPITAXIAL YB SILICIDE

The formation of epitaxially ordered Yb silicide has been investigated by use of low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), electron-energy-loss spectroscopy (EELS), and soft-x-ray photoemission spectroscopy (SXPS), and the epitaxial phases formed have been characterized by k-resolved uv photoemission spectroscopy (UPS) and inverse-photoemission spectroscopy (IPES). Thus, filled and empty electronic states as well as excitations between them have been assessed for various Yb silicide phases. The epitaxial Yb silicides have been prepared in two ways: by solid-state epitaxy of room-temperature-deposited Yb films on Si(111) via annealing, and by evaporation of Yb onto heated Si(111) substrates. The latter preparation method gave better ordering at lower temperatures. The phase diagram of the Yb-Si(111) interface has been established by AES and LEED, and from the 4f emission characteristics of the various surfaces in SXPS, a YbSi2-x phase is associated with the epitaxial (2X2) silicide. A structure model for this Yb silicide is suggested with a pure Si surface with ordered vacancies as the terminating layer. k-resolved UPS and IPES spectra are presented that demonstrate the order in the epitaxial silicide phase via complex dispersing features. A consistent interpretation of EELS results is based on the combined density-of-states results of UPS and IPES. Moreover, the EELS measurements add information on the morphology of the silicide phase via the plasmon behavior, which suggests an island-growth mechanism of the epitaxial silicide.