High resolution electron energy loss spectroscopy on the LaF 3/Si(111) heterostructure

Abstract

Epitaxial layers of lanthanum trifluoride (LaF 3) were deposited under ultrahigh vacuum (UHV) conditions onto a clean silicon (111)-(7 × 7) substrate. The (Fuchs-Kliewer) surface phonon polariton spectra of the LaF 3 films were measured by high resolution electron energy loss spectroscopy (HREELS) on layers up to a thickness of $ ̃ 80 Å. They are discussed in comparison with calculated loss spectra using a dielectric theory approach and infrared reflectivity data of the LaF 3 phonon spectrum known from literature. For monolayer coverage an additional loss near 40 meV is observed; its intensity variation with layer thickness suggests an interpretation in terms of an interface phonon or localized molecular vibration.