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.