Organic semiconducting materials and organic-inorganic hybrid systems provide large potential for novel applications in electronic and opto-electronic devices. To realize and optimise these applications a detailed knowledge of the electronic structure as well as its dependence on the interaction and geometrical structure as interfaces is mandatory.

In case of the interaction of organic molecules with metal substrates new states appear, which depending on their character may as well help or hinder the transport of charge through a contact interface. In this talk I will demonstrate the potential of angular resolved UPS (ARUPS) in analysing the spatial distribution of molecular orbitals. This approach allows a direct identification of the hybridisation of molecular states with substrate density of states, which leads to the formation of new, common metal-molecule hybrid states [1].
Moreover, I will report on an unconventional order phenomenon observed for a molecular overlayer. This so called inverse melting leads to the formation of a disordered liquid or gaseous phase upon temperature decrease [2]. I will show, that this reversible second order phase transition can be explained by the delicate balance of vertical and lateral forces present in case of a 2D adsorbate system.

[1] J. Ziroff, F. Forster, A. Schöll, P. Puschnig, and F. Reinert, Hybridization of Organic Molecular Orbitals with Substrate States at Interfaces: PTCDA on Silver. Physical Review Letters 104(23), (2010).

[2] A. Schöll, L. Kilian, Y. Zou, J. Ziroff, S. Hame, F. Reinert, E. Umbach, and R.H. Fink, An unusual phase transition in two dimensions: inverse melting of a metal-organic interface. Science 329,303, (2010).

Host:  Bob Bartynski