Near‐edge electron energy loss fine structure: Core excitation of chemisorbed molecules in the laboratory

Abstract

Reflection near‐edge electron energy‐loss fine structure (NEELFS) has been used to study C 1s and N 1s core excitation spectra of pyridine chemisorbed on Ag(100) and Ag(111) surfaces at submonolayer and monolayer coverages. The N 1s spectra of pyridine on both Ag surfaces show dramatic changes with exposures between 1 and 5 L, which correspond to coverages in the submonolayer region. The spectral changes track a shift in the average orientation of the pyridine molecules from a small to a large tilt angle relative to the surface. The NEELFS spectra of pyridine on Ag(111) were found to be similar to the corresponding near edge x‐ray absorption fine structure (NEXAFS) spectra. These results demonstrate that NEELFS spectra recorded by small‐angle reflection electron‐energy‐loss (EELS) are sensitive to molecular orientation. With improved large‐angle performance, the angular dependence of NEELFS should allow experimental determination of molecular orientation in a manner analogous to polarization‐dependent NEXAFS.