Solution-Processable Carbon Nanotube Molecular Junctions
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Nanotechnology is the manipulation of matter at the supramolecular, molecular and atomic scale. As a result, nanotechnology is included in various fields of science including surface science, organic chemistry, molecular biology, semiconductor physics, microfabrication and molecular engineering. One of the ambitions for nanotechnology is to develop electrical devices where the active component is a single molecule or nanomoiety. In order to fabricate such devices, it is of paramount importance to develop strategies beyond the current top-down lithographic approaches typically employed in the semiconductor industry. In this regard, the ability to control the assembly of single-molecules and individual nanomoieties directly in solution can allow for the development of solution-processable approaches in nanotechnology, towards the fabrication of single-molecule devices. In this thesis, it will be discussed how molecular junctions with functional single molecules are fabricated in aqueous solutions employing single-walled carbon nanotubes as potential nanoelectrodes. Furthermore, it will be demonstrated how the assembly of molecular junctions can facilitate other functions and the construction of both nanostructures and microstructures. To begin, relevant work will be discussed that has been done in this field to date and outline clear ambitions of the study presented here. Subsequently, the key characterisation techniques that underpin all the results in this study will be described. In this work, it will be reported how metallic carbon nanotubes can act as nanoelectrodes in molecular junction assemblies and how conductive measurements of individual molecules are performed. Therefore, for the first time, the molecular junction conductance of a series of oligophenyls were successfully measured, which were formed via a solution-based assembly method. Measured molecular conductance values of the series of oligophenyls resulted in a β value of 0.5 Å−1. Furthermore, it will be described how the approach outlined previously can be extended to the synthesis of tri-amine molecular linkers as well as the formation of three-terminal junctions as the foundation of carbon nanotube-based single-molecule electronic devices. This research resulted in an increase in the formation of Y-shape molecular junctions by ~25%. Next, this report will outline the formation of molecular junctions in two-dimensional structures, which can allow for the development of electrical devices into networks. Utilising modified DNA sequences, “click” chemistry can lead to nanotube network with dimensions ranging into the micrometre scale. Building on this work, it will be further report on the change in physical properties when these two-dimensional superstructures are embedded into polymeric thin films. Finally, conclusions of the research will be drawn and it will be discussed how the findings obtained in this work can contribute to the development of novel single-molecule electronic devices.
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