Electrical and mechanical effects in single-molecule junctions

Abstract

In single-molecule junctions, the behavior of a device is determined by the properties of an individual molecule. In this thesis we develop several models to describe both electrical and mechanical effects in such devices, which can be used to design molecules with a specific functionality. We show how the resistance of a molecule varies with its electrostatic environment, in particular due to capacitive interactions with neighboring molecules or metallic grains. A major challenge in the field of molecular electronics is making sure you are measuring the molecule you want to measure. Since molecules are generally flexible entities, they vibrate when current is flowing through them. The spectrum of these vibrations is unique to each species of molecules and we shown how it can be used as a 'molecular fingerprint' to identify single molecules. The electrical and mechanical effects described in this thesis come together in our design for an all-electric single-molecule motor. By applying an oscillating gate field, we can exert a force on a rotor containing a permanent electric dipole moment, and, under the right circumstances, drive it into a unidirectional motion. This rotation can be measured in real-time since the motion of the rotor changes the conductance of the molecule. We show that this approach provides full control over the speed and continuity of motion, thereby combining electrical and mechanical control at the molecular level.