Electron transport through porphyrin molecular junctions
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Authors
Zhou, Qi
Issue Date
2016-12
Type
Electronic thesis
Thesis
Thesis
Language
ENG
Keywords
Physics
Alternative Title
Abstract
The first factor studied, that is, the metal ion center in the porphyrin molecule, show that the conductance for iron (III) porphyrin (protected) is 3.74 ×10-5 G0, and the conductance for the free base porphyrin (protected) is 4.73×10-5 G0, where is the quantized unit of electrical conductance. Through our collaborative efforts, first principles calculations carried out by our collaborators for the molecular levels of an isolated molecule (without electrodes) show that the energy levels of an iron (III) porphyrin molecule are slightly shifted compared to that of the free base porphyrin. For the free base porphyrin, the highest occupied molecular orbital (HOMO) level (-4.952 eV) lies between the chemical potentials of the substrate (-4.7 eV) and the STM tip (-5.1 eV). This level serves as a channel for electron transport. For the iron (III) porphyrin, the HOMO is at -5.306 eV, which is not in between the chemical potentials of the substrate. Therefore, a significantly smaller conductance is expected for the iron (III) porphyrin compared to the conductance of a free base porphyrin, because of the lack of the electron transport channel. However, the conductance measured from G-S experi-ments is comparable, i.e. 3.74 ×10-5 G0 for iron (III) porphyrin and 4.73×10-5 G0 for free base porphyrin. This suggests that the molecular energy level broadening and shifting occurs for porphyrin molecules when coupled with the metal electrodes, and this level broadening and shifting may significantly affect the electron transport through molecular junctions.
Description
December 2016
School of Science
School of Science
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY