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Title: New development on graphene contacted single molecular junctions
Author: Zhang, Q.
ISNI:       0000 0000 6360 3678
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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Molecular electronics holds great promise to realize the ultimate miniaturization of electronic devices and the investigation of charge transport properties through molecules tethered between pairs of electrode contacts is one of the most active areas of contemporary molecular electronics. To date, metallic materials have been widely used as the electrodes to construct molecular junctions, where desired characteristics are outstanding stability, conductivity, and fabricability. However, there is an increasing realization that new single molecule electrical junction functionality can be achieved through the use of non-metallic electrodes. Fundamental studies suggest that carbon based materials have the potential to be valuable alternative electrode materials for molecular electronics in the next generation of nanostructured devices. In light of the discussion above, we symmetrically investigate the possibility of constructing non-metallic molecular junctions and the corresponding charge transport properties through such junctions by replacing the common gold electrodes with graphene electrodes. We have measured the electrical conductance of a molecular junction based on alkanedithiol/alkanediamine chains sandwiched between a gold and a graphene electrode and compared the effects of anchoring groups in graphene based junctions. We also studied the technical effects of molecule-electrode contacts by comparing methods for capturing and measuring the electrical properties of single molecules in gold−graphene contact gaps. The decay obtained by STM based I(s) and CP-AFM BJ techniques, which is much lower than the one obtained for symmetric gold junctions, is related to the weak coupling at the molecule−graphene interface and the electronic structure of graphene. This asymmetric coupling induces higher conductance for alkanediamine chains than that in the same hybrid metal−graphene molecular junction using thiol anchoring groups. Moreover, we introduce an efficient data sorting algorithm and demonstrate its capacity on real experimental data sets. As a consequence, we suggest that novel 2D materials could sever as promising electrodes to construct nonsymmetric junctions and the use of appropriate anchoring groups/techniques may lead to a much lower decay constant and more conductive molecular junctions at longer lengths.
Supervisor: Yang, Li ; Nichols, Richard ; Zhao, Cezhou Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral