We present a comprehensive study of structural and electronic properties of the adsorbate system H 2 -phthalocyanine (H 2 Pc) on Ag(111). A comparison with copper-phthalocyanine (CuPc) on Ag(111) allows us to elucidate the impact of the central metal atom in the molecule on the adsorbate-substrate interaction. This metal atom is one fundamental parameter which can be changed in order to modify the properties of phthalocyanine molecules, and therefore its influence on the adsorption behavior is highly relevant. From high-resolution electron diffraction, we obtained a phase diagram for submonolayer coverages which turns out to be similar to that of CuPc/Ag(111). The most striking difference is a higher stability of a commensurate phase, indicating a stronger and more adsorption site-specific bonding of the H 2 Pc molecules. Furthermore, ultraviolet photoelectron spectroscopy and x-ray standing waves prove chemisorptive interaction between molecules and substrate and a significant bending of the molecules with the nitrogen atoms approaching the surface. We conclude that the attractive interaction of metal-phthalocyanine molecules with Ag (111) is mainly mediated by the aromatic body of the molecule (the tetraazaporphyrin ring in particular) rather than by the central metallic atom which (in the case of CuPc) already shows Pauli repulsion.

We have studied the surface phonon modes of the reconstructed Si(111)-(7×7) surface by polarized Raman spectroscopy. Six surface vibration modes are observed in the frequency range between 62.5 and 420.0 cm −1 . The mode frequencies agree very well with reported calculation results. This enables their attribution to calculated eigenmodes, whose elongation patterns are dominated by specific atomic sites: the two most characteristic novel fingerprints of the (7×7) reconstruction are sharp Raman peaks from localized adatom vibrations, located at 250.9 cm −1 , and collective vibrations of the adatoms and first-and second-layer atoms, located at 420.0 cm −1 . While the sharp localized adatom vibration peak is a substantial refinement of an earlier broad spectral structure from electron energy-loss spectroscopy, no spectroscopic features were reported before in the collective-vibration frequency region. Furthermore, we observe in-plane wagging vibrations in the range from 110 to 140 cm −1 , and finally the backfolded acoustic Rayleigh wave at 62.5 cm −1 , which coincides with helium atom scattering data. Moreover, the Raman peak intensities of the surface phonons show a mode-specific dependence on the polarization directions of incident and scattered light. From this polarization dependence the relevant symmetry components in the Raman scattering process (A 1 and/or E symmetry) are deduced for each mode.