The quest for smaller and faster electronic devices requires new materials since silicon technology is reaching its limits. Particularly organic molecules are promising because of their capability to self assemble and their manifold electronic properties.

The electronic interactions between insulators - here ionic crystal layers - and organic molecules are generally weak due to the inert chemical property of the ionic shells. Thus there is a tendency for organic molecules to form disordered overlayers also including highly mobile phases. Only few systems which are known so far exhibit self-ordering on ultrathin insulators. Namely copper(II) octaethyl-porphyrin (CuOEP) on sodium chloride [1] and 3, 10-di(propyl)perylene (DPP) on CaF₂ / CaF / Si(111) [2].

We use Scanning Tunneling Microscopy (STM) to determine the geometric arrangement of the molecules on ultrathin insulators. With Ultraviolet Photoelectron Spectroscopy (UPS) and Near Edge X-ray Absorption Spectroscopy (NEXAFS) the occupied (UPS) and unoccupied (NEXAFS) density of electronic states can be mapped. From this data we intend to conclude on the interdependency of the molecular arrangement and the electronic structure of the adsorbate-substrate system.

STM images of NaCl deposited on a single crystalline Ag(111) surface. The individual monlolayers are visible in the survey image (left, 850 x 850 nm 2). The high resolution image (right, 15 x 15 nm2) shows the perfect ordering of the cloride ions indicating the crystallinity of the layer.

References
[1] L.Ramoino, M. von Arx, S. Schintke, A. Baratoff, H.-J.Güntherodt, T. A. Jung, Chem. Phys. Lett. 417, 22 (2006)
[2] H. Rauscher, T.A. Jung, J.-L. Lin, A. Kirakosian, F.J. Himpsel, U. Rohr, K. Müllen, Chem. Phys. Lett. 303, 363 (1999)

Contact
Kathrin Müller: kathrin.mueller psi.ch
Dr. T.A. Jung: thomas.jungpsi.ch

Academic partner
Prof. J. Osterwalder, Surface Physics, University Zürich

Financal support
PSI, NCCR Nanosciences, SNF