Electronic transport in molecular conductors with controlled charge density

 Dr. A. Morpurgo, Technical University Delft

In this talk I will discuss experimental investigations of the electronic transport properties of a number of different molecular conductors in which the carrier density is controlled externally by either electrostatic or chemical doping. 

In the first part I will focus on recent experiments performed on field effect transistors fabricated at the surface of single organic crystals. I will start by illustrating the technological progress that has made these investigations possible. I will then concentrate on the electrical behavior. Particularly noticeable are the high values of mobility achieved (up to 20 cm2/Vs in rubrene), its observed anisotropy and non-monotonic temperature dependence, and the small subtreshold slope. The results of the work performed so far indicate that field effect transistors fabricated on single crystals are suitable for the study of the intrinsic electronic properties of organic semiconductors.

In the second part of the talk I will concentrate on the transport properties of a large class of isostructural molecules –the metal phthalocyanines- that differ for only one single atom. This atom determines the basic electronic properties of the molecules, such as the shape of the molecular orbitals and the spin present in the molecular ground state. Transport is studied in thin films, in which a high density of charge carrier per molecules is introduced by means of doping with alkali-metals. This allows us to bring the film into a metallic state and to compare the behavior of the different molecules. Ongoing work is aiming at gaining control over the magnetic properties of the molecular systems, in which the magnetic interaction between the spin localized on different molecules is mediated by conduction electrons.