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Charge Transport in Molecular Junctions Beyond Tunneling Open Access


Other title
molecular electeronics
donor- acceptor bilayer
diazonium derived layers
charge transport mechanism
molecular rectifier
click chemistry
multistep tunneling
thick junctions
Type of item
Degree grantor
University of Alberta
Author or creator
Bayat, Akhtar
Supervisor and department
McCreery, Richard (Chemistry)
Examining committee member and department
Kraatz, Bernhard (Chemistry)
Gibbs-Davis, Julianne (Chemistry)
McCreery, Richard (Chemistry)
Veinot, Jonathan (Chemistry)
Mar, Arthur (Chemistry)
Department of Chemistry

Date accepted
Graduation date
2017-06:Spring 2017
Doctor of Philosophy
Degree level
Electrical behavior of thin layers of molecules sandwiched vertically between two carbon contacts is the subject of this thesis. The main focus was put on the effect of molecular structural variations on charge transport through the molecular layers. The charge transport mechanism was deduced by analyzing the dependence of current on voltage, thickness of the molecular layer and temperature. The effect of compositional asymmetry was investigated in bilayers made from two different molecules. Multilayers made from only one type of molecule by reduction of diazonium ions are compositionally symmetric and were found to exhibit symmetric current-voltage characteristics. Bilayers made from two different molecules also showed symmetric current-voltage behavior when the second layer of the bilayer was only a monolayer, attached via azide-alkyne click chemistry to a multilayer of ethynylbenzene, and the total thickness of the bilayer was less than 5 nm. The charge transport properties of thin bilayers were found to be consistent with tunneling charge transport mechanism. Bilayers consisting of multilayers of two different molecules were rectifiers, given the total thickness of the bilayer was more than 10 nm and the bilayer was composed of a multilayer of an electron acceptor molecule such as naphthalene diimide together with a multilayer of an electron donor molecule such as fluorene in a vertical stack. Reversing the order of the two multilayers in the bilayer resulted in reverse rectification direction, confirming the molecular origin of this rectification behavior. The rectification persisted even at low temperatures of liquid helium. Charge transport in thick molecular junctions was studies further in a series of phenylthiophene derivative molecular junctions with thickness of 2-16 nm. A multistep tunneling charge transport was suggested to be operative in these thick carbon-based molecular junctions.
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
Citation for previous publication
S. Y. Sayed, A. Bayat, M. Kondratenko, Y. Leroux, P. Hapiot, and R. L. McCreery; “Bilayer Molecular Electronics: All-Carbon Electronic Junctions Containing Molecular Bilayers Made with “Click” Chemistry” Journal of the American Chemical Society 2013, 135, 12972-12975.A. Bayat, J. C. Lacroix and R. L. McCreery; “Control of Electronic Symmetry and Rectification through Energy Level Variations in Bilayer Molecular Junctions” Journal of the American Chemical Society 2016, 138, 12287-12296.

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