Inelastic diffraction in coadsorbed periodic structures

We show For the first time that, with two coadsorbed periodic structures it is possible to observe in a diffraction condition unique to one structure a relative enhancement of the vibrational losses characteristic of the spec ies contained in the respective periodic structure. A recently developed SP A-LEED instrument equipped with an electron monochromator and analyser was used to distinguish true elastic diffraction from inelastic diffraction in the vibrational losses of coadsorbed (2 x 3)N/Cu(110) and the alpha-phase b enzoate ((4)(3)(-1)(5)) structure on Cu(110). Vibrational enhancements by f actors of 4-20 were found in energy loss spectra and momentum-resolved spot profiles. Inelastic spot profiles are qualitatively consistent with a kine matic description of the energy-momentum conservation induced broadening fr om both loss-before-diffraction (L-D) and diffraction-before-loss (D-L) eve nts. (C) 1998 Elsevier Science B.V. All rights reserved.