High-Resolution Photoemission Study of Different NTCDA Monolayers on Ag(111):  Bonding and Screening Influences on the Line Shapes

Abstract

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 1s 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.

Nanoscale Assembly of Paramagnetic Organic Radicals on Au(111) Single Crystals

“…It is also worth noting that three contributions to the main peak can be identified because of the signals from the CÀC, the CÀH, and CH 3 species (Figure 1, bottom). This assignment indicates a more efficient screening of the core hole in the internal ring C À C bonds, in agreement with previous work, [32][33][34] and may be attributed to cooperation in the screening of two adjacent rings, that is, improved charge delocalization along this channel. [34] O 1s and N 1s core-level spectra can be used to ascertain if the paramagnetic function of this pyrene derivative is intact because the unpaired electron is delocalized over the two equivalent NO groups.…”

“…[32,33] Each chemically inequivalent carbon site should, in principle, yield a different contribution to the spectrum. However, small differences in binding energy, the limits imposed by linewidths, and by the resolution of our experiment would make their identification by curve fitting largely speculative.…”

“…Both N 1s and O 1s spectra were fitted to a unique Voigt profile characterized by a constant Lorentzian width of 0.10 eV and a Gaussian width of 1.00 eV, in agreement with the intrinsic lifetime and inhomogeneous broadening found in the literature for core-hole states in organic molecules. [32,33] This indicates that the paramagnetic function of this pyrene derivative is intact and the degradation to iminonitroxide or to the diimmino derivatives [35] upon deposition (see Table S1 in the Supporting Information) can thus be excluded. The presence of an imino group as a degradation product would imply the presence of an XPS line at lower binding energy because breaking the nitrogen-oxygen bond hinders the electronwithdrawing action of the oxygen atoms, decreasing the binding energy [36] of the photoelectrons emitted from the N 1s core levels.…”

Adsorption geometry and interface states: Relaxed and compressed phases of NTCDA/Ag(111)

“…This finding is also in accordance with a marked chemical shift in XPS binding energies [37] and the partial filling of the former LUMO of adsorbed NTCDA [18]. According to NIXSW findings for C 1s and O 1s core levels the planar molecular structure of NTCDA becomes warped when adsorbed on Ag(111).…”

Threshold Photoelectron Spectrum of Isolated NTCDA

“…Most investigations so far focused on the chemistry and physics of thin films deposited on surfaces. In a number of experiments NTCDA was deposited on a Ag(1,1,1) surface and investigated by X-ray absorption and photoemission [4][5][6][7]. Thin films on a Au substrate were also studied by photoelectron spectroscopy and an IE of 8 eV was reported [8].…”