| Detailed control of electrical current through a single molecule plays an important role in the development of molecular electronic devices. Precise modeling of charge transfer through molecular junctions calls for combining the theory of quantum transport with ab initio electronic structure calculations. In this thesis, first-principles simulations of Scanning Tunneling Microscopy and Spectroscopy have been used to characterize organic molecules on semiconductor surfaces. Theories behind these quantum theoretical treatments have been presented and several applications have been discussed and compared with experiments. Cases studied in this work include various types of organic molecules on silicon surfaces with different crystal faces. Successful explanation of experimental measurements and extraction of novel information indicate that simulations provide a powerful tool for molecular identifications. Additionally, some novel experiments have been proposed to enhance the contrast among different adsorbates. |
