The incorporation of molecules as low-cost and stable structures in electronic circuits is a promising strategy to miniaturize electronic components. Although single-molecule electronics is still at an early phase, the investigation of charge transport through single molecules is fundamentally important to understand the relevant scientific concepts and technological applications. In this dissertation, we measured and modulated the charge transport perpendicular to the plane of small benzene

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... ivatives. In contrast to the conventional strategy to link molecules to electrodes via anchoring groups, we used the electrode potential to control the geometry of molecules and to form the junctions through π-system-metal electrode interactions. Using a combination of electrochemical STM (EC-STM) imaging and STM-BJ methods, the measurement of charge transport through single, flat oriented tetrafluoroterephthalic acid (TFTPA) molecules on an electrified Au (111) electrode showed that, at potentials below the potential of zero-charge (pzc) of Au(111), the molecules lie flat on the electrode and form highly ordered structures. The conductance of TFTPA, along the axis perpendicular to the benzene plane, is 0.24 ± 0.04 G0, consistent with reports for other molecules oriented flat in the junction. The configuration dependent conductivity has been confirmed by first-principles non-equilibrium Green's function computation performed by Professor John Perdew and Dr. Haowei Peng at Temple University. Hence, the electrochemical surface potential can be employed to control the orientation of molecules to access a new charge transport measurement axis. Building on our previous results (Chapter 3), we studied charge transport through two fundamentally important molecules, tetracyanoquinodimethane (TCNQ) and tetrafluorotetracyanoquinodimethane (F4TCNQ) to determine the effect of molecule-electrode binding while maintaining the same core molecular structure. The findings show that on the negatively charged Au(111), the flat-oriented TCNQ [...]