Molecular orbitals mapping

We have demonstrated that combining low energy electron diffraction with angle-resolved photoelectron spectroscopy is a very powerful method to elucidate the geometric and electronic structures of ordered molecular adsorbates. We applied this approach to the two different monolayer phases of PTCDA on Ag(110).
M. Wießner et al., Phys. Rev. B 86, 045417 (2012).

The properties of molecular films are determined by the geometric structure of the first layers near the interface. These are in contact with the substrate and feel the effect of the interfacial bonding, which particularly, for metal substrates, can be substantial. For the model system 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(110), the geometric structure of the first monolayer can be modified by preparation parameters. This leads to significant differences in the electronic structure of the first layer. We show that, by combining photoelectron momentum maps (PMM) with low-energy electron diffraction (LEED), we cannot only determine the electronic structure of the interfacial layer and the unit cell of the adsorbate superstructure, but also the arrangement of the molecules in the unit cell.  Moreover, in bilayer films, we can distinguish the first from the second layer and, thus, study the formation of the second layer and its influence on the buried interface.

Additionally, momentum patterns can give information about the electronic structure at the interface and the symmetry of molecular orbitals.

Figure caption: Experimental photoelectron momentum maps (PMM) determined for photoelectrons from the LUMO and HOMO regions for one ML PTCDA for the brick-wall and the herringbone phase on Ag(110).

Retrieve article

Electronic and geometric structure of the PTCDA/Ag(110) interface probed by angle-resolved photoemission; M. Wießner, D. Hauschild, A. Schöll, F. Reinert, V. Feyer, K. Winkler, B. Krömker; Phys. Rev. B 86, 045417 (2012); doi: 10.1103/PhysRevB.86.045417


Ultima modifica il Venerdì, 10 Gennaio 2014 10:40