Prototypical single-molecule transistors with supramolecular gates:: varying dipole orientation

Recently, we presented a prototypical three-terminal device, in which the current through a hybrid-molecular diode, whose current voltage characteristic is determined by a single molecule in the junction of a scanning tunneling microscope, is modified by nanometer-sized charge transfer complexes covalently linked to the molecule in the gap [Phys. Rev. Lett. 92 (2004) 188303]. Since the complexes are formed by electron acceptors covalently bound to the molecule in the gap, and electron donors coming from the ambient fluid, this set-up represents a chemical-field-effect transistor based on a single molecule with a nanometer-sized gate. The gating effect was explained by an interface dipole model. Here, we present first tests of this model addressing the orientation of the electrical dipoles. By using amino- and carboxylic acid functionalized molecules in the hybrid-molecular diode we study the effect of dipoles being perpendicular, instead of parallel, to the transistor channel direction and find agreement with the model. (C) 2004 Elsevier B.V. All rights reserved.