Imaging Individual Chemical Bonds and Tuning Single-Molecule Charge States at Surfaces
In an effort to make advances in electronics through ever smaller devices, the field of molecular electronics has emerged as a natural step in achieving ultimate miniaturization of devices down to the size of single molecules. Progress in molecular electronics is intimately linked to understanding these devices at the atomic and molecular length scales at which they operate. As a move in this direction we have performed local probe studies in which we have nondestructively imaged the products of chemical reactions within molecular electronics elements. We have also imaged and tuned the orbitals and charge states of individual molecular electronics elements on surfaces. This dissertation, after introducing the field of nanoelectronics and the local probe techniques used in the study, reports on imaging of chemical structures of on-surface synthesized molecules and conductive polymers with individual-chemical-bond resolution and their relationship to the electronic structure. Depending on the specific molecules and surfaces used, the on-surface synthesized molecular structures formed single molecule products (monomers), chemically reacted intermediates, or conductive polymers exhibiting extended electronic structure along their backbone. This dissertation additionally demonstrates orbital gating of molecules on a back-gated graphene device. The energy alignment of molecular orbitals on graphene was tuned using an electrostatic back-gate, which resulted in molecules switching between neutral and negatively charged states. This control of charge states of single molecules on surfaces and identification of on-surface synthesized reaction products with sub-molecular resolution contributes to our understanding of molecular electronics elements at their natural length scales.