Charge transport through single molecules in two- and three-terminal mechanical break junctions

During the past decades the downscaling of integrated circuits has been governed by Moore's law, which predicts device dimensions on the order of 10 nm in 2020. Fundamental research in molecular electronics explores the possibility of fabricating such nanoscale devices from single molecules, which offer the prospects of chemical tunability and self-assembly. The experiments that are reported in this Thesis are based on lithographically fabricated mechanically controllable break junctions (MCBJs). These devices enable the formation and tuning of two nanometer-spaced gold electrodes for the electrical characterization of a single molecule. The first part of this Thesis addresses the goal of stable anchoring in single-molecule junctions. An experimental protocol for the trapping of single molecules is established and used to study the influence of established chemical anchoring groups on the electronic properties of single-molecule junctions in vacuum. We then present a new fullerene-based end group that allows for the formation of stable junctions with robust electronic coupling. The second part of this Thesis covers the integration of two-terminal MCBJs with a third electrode (a gate), the potential of which can shift the electronic levels on the molecule. Two types of electrically and mechanically tunable devices are presented and characterized in detail. A nanoscale island in the Coulomb blockade regime serves as a first experimental test system, in which the mechanical and electrical tuning of charge transport is demonstrated.Kavli Institute of Nanoscience DelftApplied Science