EELS peak intensity dependence on primary electron energy for the Si(111)7×7 and Si(111)-Cr surface structures

Abstract

The intensity of elastic and bulk plasma loss peaks and also the energy position of the bulk plasma loss peak in the electron energy loss spectra of the Si(111)7×7, Si(111)1×1-Cr and ( 3 × 3 )R30-Cr surface structures were studied as a function of the primary electron energy, E o, in the 200–3000 eV range. It was found that the intensity of elastic and bulk plasma loss peaks had oscillations with periods of 120–140 and 750–900 eV. These oscillations can be caused by the effects of electron diffraction from lattice planes and variation of the electron backscattering coefficient with depth, respectively. During formation of the Si(111)1×1-Cr and α( 3 × 3 )R30-Cr structures the oscillations with periods 120–140 eV were partly retained, showing the existence of an Si(111) lattice framework in subsurface region of the substrate. However, under formation of the Cr-rich phase with β( 3 × 3 )R30-Cr structure they disappeared, showing reconstruction of the Si(111) lattice in the subsurface region. The evolution with E o of the intensity of elastic and bulk loss peaks is correlated with the change in composition and thickness of the different structures of the Si(111)-Cr surface layer. It has been estimated that the thickness of the Cr-rich phase with β( 3 × 3 )R30-Cr structure is between 8 and 15 Å.