Evaluation of physical chemistry on-line modules

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Slocum, Laura E.
Towns, Marcy H.
Issue Date
Thesis (M.S.)
Department of Chemistry
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We have modeled in one-dimension two-dimensional (2-D) quantum wire structures: the notched electron stub tuner (NEST) and the double-notched electron stub tuner (D-NEST). The models consisted of square barriers representing the notches and square wells representing the stubs. We have calculated the transmission coefficient as a function of electron energy and/or device geometries to study electron transport through these quantum wire models. The transfer matrix method was used to calculate the transmission coefficient by utilizing a program written with Mathematica. The program and technique were verified using one-dimensional systems from the literature.We studied the principle of wave interference in the NEST model in the form of intersection points of several curves of the transmission coefficient versus barrier/well separation plotted with no offset. The creation of standing waves, in certain regions of the NEST model, by the interference of incident and reflected waves, gives rise to these intersection points. We have identified features in the conductance curves of the NEST and the transmission coefficient curves of the NEST model (the intersection points) that are very similar and may be explained by the same principle of wave interference.We have studied double-barrier resonant tunneling (DBRT) to assist in our study of the D-NEST model. The resonances in DBRT are attributed to the creation of standing waves between the two barriers for the tunneling and non-tunneling regimes. We attempted to prove the existence of these standing waves by studying the probability density in the D-NEST model. The well of the D-NEST model was scanned down the length of the double-barrier well region to investigate its effect on the transmission coefficient for this purpose. A small square barrier, used as a probe, was also used to study the probability density in the same way as the well was used. Initial scans of the probe above a simple square barrier gave us insight into the possibility of using it to scan for the probability density in the well region. The "over-the-barrier" resonances (attributed to standing waves) were studied in this case.We have developed knowledge of the transmission properties of these models that may aid in the understanding of the electron transport through the 2-D devices. We believe that to "fine tune" the conductance output of the D-NEST device, the second notch should be placed at a location that permits the creation of standing waves, for a specific electron energy value, between the two notches of the device. The "fine tuning" of the conductance output into a square-wave pattern could improve the devices performance as a potential switching mechanism.