| The organic materials are envisioned to be used as building blocks for designing of functional devices to broaden and partially replace the current-used silicon-based devices infuture. Due to easily processing and environmental friendly properties of organic materials, molecular electronics show a great promise to overcome some difficulties encountered in current-used silicon-based technology, for example, further miniaturization, mechanically folding, self-regeneration, self-repairing, to name a few. At current stage, this field is still in its infancy, and many challenges still remain. In particular, the experimental ability to address these materials at atomic level is strongly required in order to thoroughly understand their intrinsic properties. This thesis is dedicated to the electronic characterization of single molecules, conjugated polymers, and molecular nanostructures at sub-nanometer resolution by utilizing low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS). Within this thesis, I focused on a few representative molecular systems and measured their structural and electronic properties. The results are divided into three parts, which are (1) characterization of the single-molecular super-exchange coupling, capacitance, conductance and metal contact at sub-nanometer resolution, (2) fabrication of poly-p-phenylene oligomers utilizing on-surface Ullmann coupling reaction, and systematic characterization of their electronic properties including band structure, localized excitations and dopant states at sub-nanometer resolution, and (3) fabrication of different molecular nanostructures by using supramolecular self-assembly method and STM manipulation strategy, and investigation of their electronic structure in real space as well as in reciprocal space. Owing to the high resolution of LT-STM and STS to probe both geometric and electronic properties at the atomic level, several pertinent problems regarding the electronic structure of organic materials have been solved. This fundamental study might be important for putting organic materials into practical use as future electronic components. (Abstract shortened by UMI.). |
