TY - BOOK
T1 - Molecular Monolayer Junctions
T2 - Chemistry, conductance and configuration
AU - Downey, Elisabeth Ffion
PY - 2018
Y1 - 2018
N2 - The work presented in this thesis aims to understanding some of the factors affecting the performance of monolayer-based molecular junctions. The topics covered range from structural characterization of monolayers, to how chemical modification of the molecule affects the monolayer, to the electrical properties of large area junctions. In this work, self-assembled monolayers (SAMs) were used to fabricate the molecular layer for large area junctions. The structural and binding properties of the SAMs – comprised of molecules with various chemical modifications – were assessed electrochemically and via XPS. Characterization included deduction of monolayer stabilities, densities and side-chain interactions. It was shown that using dithiocarbamate (DTC) as a binding group increases the stability of monolayers with respect to thiol-bound counterparts. Further to this, side-group contributions were seen to affect the density of monolayers; bulky side-groups increased the average single-molecule area due to steric and electrostatic repulsion/attraction and resulted in less homogeneous monolayers.Electronic analysis of the different SAMs was carried out via conducting probe atomic force microscopy (CP-AFM) and in large area solid-state devices, with reduced graphene oxide (rGO) as the top contact. SAMs with DTC binding groups produced junctions with lower conductance than thiol-bound junctions, attributed to an increase in contact resistance and weaker electrode coupling. It was also shown that side-group functionalization can be used to ‘tune’ the conductance of molecular wires as well as produce a molecular switch via redox functionality. The same trends were observed in both CP-AFM and large area device junctions. A comparison of different experimental set-ups showed the importance of junction configuration on the measured electronic properties. It was deduced that the current-limiting factor the large area device was the electrical contact area between rGO and the molecules – consistent with other large area devices reported in literature. To obtain better, more consistent data about the electrical properties of large area junctions, two new junction configurations were presented, both based on modified CP-AFM set ups. Finally, future work with the aim to demonstra te the thermoelectric effect in monolayer junctions was proposed, which has thus far not been reported for permanent solid-state devices. Transition voltage spectroscopy (TVS) was employed to deduce suitable molecules for such experiments, and once again emphasise the importance of junction configuration.
AB - The work presented in this thesis aims to understanding some of the factors affecting the performance of monolayer-based molecular junctions. The topics covered range from structural characterization of monolayers, to how chemical modification of the molecule affects the monolayer, to the electrical properties of large area junctions. In this work, self-assembled monolayers (SAMs) were used to fabricate the molecular layer for large area junctions. The structural and binding properties of the SAMs – comprised of molecules with various chemical modifications – were assessed electrochemically and via XPS. Characterization included deduction of monolayer stabilities, densities and side-chain interactions. It was shown that using dithiocarbamate (DTC) as a binding group increases the stability of monolayers with respect to thiol-bound counterparts. Further to this, side-group contributions were seen to affect the density of monolayers; bulky side-groups increased the average single-molecule area due to steric and electrostatic repulsion/attraction and resulted in less homogeneous monolayers.Electronic analysis of the different SAMs was carried out via conducting probe atomic force microscopy (CP-AFM) and in large area solid-state devices, with reduced graphene oxide (rGO) as the top contact. SAMs with DTC binding groups produced junctions with lower conductance than thiol-bound junctions, attributed to an increase in contact resistance and weaker electrode coupling. It was also shown that side-group functionalization can be used to ‘tune’ the conductance of molecular wires as well as produce a molecular switch via redox functionality. The same trends were observed in both CP-AFM and large area device junctions. A comparison of different experimental set-ups showed the importance of junction configuration on the measured electronic properties. It was deduced that the current-limiting factor the large area device was the electrical contact area between rGO and the molecules – consistent with other large area devices reported in literature. To obtain better, more consistent data about the electrical properties of large area junctions, two new junction configurations were presented, both based on modified CP-AFM set ups. Finally, future work with the aim to demonstra te the thermoelectric effect in monolayer junctions was proposed, which has thus far not been reported for permanent solid-state devices. Transition voltage spectroscopy (TVS) was employed to deduce suitable molecules for such experiments, and once again emphasise the importance of junction configuration.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01012010744&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Molecular Monolayer Junctions
PB - Department of Chemistry, Faculty of Science, University of Copenhagen
ER -