High-resolution photoemission study of different NTCDA monolayers on Ag(111):: Bonding and screening influences on the line shapes

We present high-resolution C 1s and O 1s photoemission results of different NTCDA monolayer states adsorbed on a Ag(111) substrate (NTCDA = 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride). The comparison of mono- and multilayer data clearly proves the chemisorptive character of the bonding of this planar aromatic molecule to the metal substrate. The rich fine structures of the monolayer spectra exhibit large differences for the three distinct monolayer states observed, leading to the conclusion of significant differences in their bonding. The fine structures are interpreted in detail on the basis of a thorough peak-fit analysis which allows a consistent assignment of the various photoemission main and satellite lines. As a result, the binding energies of the Is levels of all C and O atoms and the relative intensities of the most significant satellite lines are extracted, the latter providing important information on the bonding and the dynamic screening process.