2026-05-24T05:25:28Zhttps://keep.lib.asu.edu/oai/requestoai:keep.lib.asu.edu:node-1531982024-12-20T18:25:12Zoai_pmh:alloai_pmh:repo_items153198
https://hdl.handle.net/2286/R.I.27439
http://rightsstatements.org/vocab/InC/1.0/
All Rights Reserved
2014
x, 80 p. : col. ill
Masters Thesis
Academic theses
Text
eng
Vatan Meidanshahi, Reza
Mujica, Vladimiro
Chizmeshya, Andrew
Richert, Ranko
Arizona State University
Partial requirement for: M.S., Arizona State University, 2014
Includes bibliographical references (p. 67-80)
Field of study: Chemistry
We studied the relationship between the polarizability and the molecular conductance<br/><br/>that arises in the response of a molecule to an external electric field. To illustrate<br/><br/>the plausibility of the idea, we used Simmons' tunneling model, which describes image<br/><br/>charge and dielectric effects on electron transport through a barrier. In such a<br/><br/>model, the barrier height depends on the dielectric constant of the electrode-molecule-electrode junction, which in turn can be approximately expressed in terms of the<br/><br/>molecular polarizability via the classical Clausius-Mossotti relation. In addition to<br/><br/>using the tunneling model, the validity of the relationships between the molecular<br/><br/>polarizability and the molecular conductance was tested by comparing calculated<br/><br/>and experimentally measured conductance of different chemical structures ranging<br/><br/>from covalent bonded to non-covalent bonded systems. We found that either using<br/><br/>the tunneling model or the first-principle calculated quantities or experimental data,<br/><br/>the conductance decreases as the molecular polarizability increases. In contrast to<br/><br/>this strong correlation, our results showed that in some cases there was a weaker or<br/><br/>none correlation between the conductance and other molecular electronic properties<br/><br/>including HOMO-LUMO gap, chemical geometries, and interactions energies. All<br/><br/>these results together suggest that using the molecular polarizability as a molecular<br/><br/>descriptor for conductance can offer some advantages compared to using other<br/><br/>molecular electronic properties and can give additional insight about the electronic<br/><br/>transport property of a junction.<br/><br/>These results also show the validity of the physically intuitive picture that to a first<br/><br/>approximation a molecule in a junction behaves as a dielectric that is polarized in the<br/><br/>opposite sense of the applied bias, thereby creating an interfacial barrier that hampers<br/><br/>tunneling. The use of the polarizability as a descriptor of molecular conductance offers<br/><br/>signicant conceptual and practical advantages over a picture based in molecular<br/><br/>orbitals. Despite the simplicity of our model, it sheds light on a hitherto neglected<br/><br/>connection between molecular polarizability and conductance and paves the way for<br/><br/>further conceptual and theoretical developments.<br/><br/>The results of this work was sent to two publications. One of them was accepted<br/><br/>in the International Journal of Nanotechnology (IJNT) and the other is still under<br/><br/>review in the Journal of Physical Chemistry C.
Chemistry
Tunneling (Physics)
Polarizability (Electricity)--Mathematical models.
Polarizability (Electricity)
Charge exchange--Mathematical models.
Charge exchange
Molecular polarizability as a descriptor for molecular conductance