)Hewlett-Packard Labs, Quantum Sciences, 1501 Page Mill Rd, Palo Alto, CA 94304, USA
)Transport in conjugated organic molecular films produced by either self-assembly (SAM) or Langmuir-Blodgett method are of most interest for applications as possible microelectronics components (diodes and switches). In short molecules the transport is mainly due to resonant tunneling through extended molecular states. It is shown that the current through molecular films strongly depends on the orientation of the molecules in the film with respect to electrodes [1,2]. This is a consequence of a strong directional character of p orbitals that determine the conductance through the conjugated molecules. Gating of the molecule is studied for various attachments to the electrodes. The results may be relevant to recent experiments on conformational dependence of current through certain SAMs (switching) and field effect on SAM. In short molecules, where the molecular quantum dot (conjugated fragment like phenyl ring, etc.) is insulated from the electrodes by asymmetric saturated groups (e.g. aliphatic) the current rectification can be in excess of 100 [3]. Switching of the current can be achieved in bistable molecular conductors with a field-switchable dipole group [4]. Current hysteresis can also be achieved in tunneling through molecular quantum dot with attractive electron-electron correlations, which should occur without retardation [5]. The results will be discussed together with current experimental situation.
