Correlated electron transport across atomic and molecular tunnel junctions

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dc.contributor.advisor Greer, James C. en McDermott, Shane 2018-10-09T08:52:34Z 2018-10-09T08:52:34Z 2018 2018
dc.identifier.citation McDermott, S. 2018. Correlated electron transport across atomic and molecular tunnel junctions. PhD Thesis, University College Cork. en
dc.identifier.endpage 197 en
dc.description.abstract As transistors continue to miniaturise the importance of describing electronics on an atomic scale increases. A molecular junction consists of a molecule connected to to metal electrodes via linker molecules and may be thought of as the prototype system for electronics on a few nanometre length scale. For charge transport calculations such systems are usually treated with a single particle approximation such as NEGF+DFT non-equilibrium Green’s function plus density functional theory. Typical single particle treatments are incomplete due to approximations made in the treatment of the electronic structure leading to discrepancies between theory and experiment by orders of magnitude, believed to be due to electron correlation. A solution to this is an accurate many body treatment of charge transport explicitly accounting for electron correlation. In this thesis the comparison of many body method MECS (Many Electron Correlated Scattering) to experiment and single particle methods, in particular the (NEGF+DFT) is performed. Comparison with single particle methods is established for alkane-based and silane-based molecular junctions utilising both thiol and amine linker molecules. In addition, components of the method such as electrostatic behaviour and screening, electronegativity, sensitivity to boundary conditions, and the level of treatment of electron correlation are tested. Comparisons with single particle methods yield agreement for systems with a lower degree of electron correlation such as alkane-based molecular junctions, with a larger disagreement between single particle and MECS methods for the moderately correlated silane-based junctions. A complex band structure analysis was performed on silane and alkane junctions with an emphasis on the dependence with respect to the linker molecules was undertaken to further investigate energy level alignment and demonstrate how alignment is affected by end groups. Electrostatic calculations have been used to investigate and quantify the effects of the screening effect on point contact and molecular junction voltages focussing on the screening length into the metal contacts was performed. This allows for more accurate estimates of the applied voltage across the junctions. The application of single particle open system boundary conditions through the use of the Wigner function is shown to be robust with respect to electrode dimensions and geometry, and is demonstrated to have little impact on the current for molecular junctions. Electronegativity calculations consist of a hexatriene-di-thiol model system with variable treatment of the electron correlation in comparison with conventional electronic structure treatments and demonstrate that correcting ionisation potentials and electron affinities with electron correlation leads to increasing the overlap to the exact one-electron reduced density matrix thereby improving theoretical predictions of electron currents on the nanoscale. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2018, Shane McDermott. en
dc.rights.uri en
dc.subject Electron transport en
dc.subject Molecular junctions en
dc.title Correlated electron transport across atomic and molecular tunnel junctions en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD en
dc.internal.availability Full text available en Not applicable en
dc.description.version Accepted Version
dc.contributor.funder Science Foundation Ireland en
dc.description.status Not peer reviewed en Physics en
dc.check.type No Embargo Required
dc.check.reason Not applicable en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.embargoformat Embargo not applicable (If you have not submitted an e-thesis or do not want to request an embargo) en
dc.internal.conferring Summer 2018 en
dc.internal.ricu Tyndall National Institute en
dc.relation.project info:eu-repo/grantAgreement/NSF/Directorate for Mathematical & Physical Sciences::Division of Materials Research/0353831/US/NSF-Europe: Photonics, Plasmonics and Molecule-Based Nanomaterials: Preparation, Design, Properties Optimization and Device Aspects/ en
dc.relation.project info:eu-repo/grantAgreement/SFI/SFI Principal Investigator Programme (PI)/06/IN.1/I857/IE/Semiconductor and Molecular Wire Simulation for Technology Design/ en

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