In the past decade there has been a growing interest in one-dimensional (1D) nanostructures, such as nanowires, nanotubes and nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. One of the ways to obtain such architectures is a template-directed synthesis which is practically a straightforward route to 1D nanostructures. In this approach, the template simply serves as a scaffold, within (or around) which a different material is generated in situ and shaped into a nanostructure with its morphology complementary to that of the template. It is generally accepted that template-directed synthesis provides a simple, high-throughput, and cost-effective procedure that also allows the complex topology present on the surface of a template to be duplicated in a single step.
In the current work, utilization of the molecular bottle brushes as templates is proposed for the fabrication of conductive nanorods. Their non-spherical macromolecular geometries and lengths up to a few hundred nanometers allow the application of these structures in nanowire synthesis. The variety of molecular bottle brush architectures and their composition enables the adjustment of appropriate conditions for the preparation of conductive materials. Moreover, the ability of the brushes to assemble on a surface under certain conditions provides their usage as building blocks for the preparation of complex conductive networks. Here, the preparation, characterization, and applications of molecular bottle brushes are discussed. Two main goals were pursued.
First, to deepen the knowledge in the synthesis of molecular bottle brushes, and to investigate their behavior on the surface. Second, to explore the application of the brushes as templates or building blocks for the formation of conductive nanowires. For the purpose, new ways of molecular brush synthesis by using the “grafting to” approach had to be developed. It was found that the reaction of nucleophilic addition based on pentofluorophenol chemistry and a coupling “click chemistry” reaction can be used to fabricate molecular brushes. Both methods showed efficient results and demonstrated high reactivity of the backbone with the end groups of the side chains. The “click chemistry” approach, however, demonstrated better results considering higher thicknesses of the brushes and, therefore, higher grafting density of the side chains. The “grafting to” together with the “grafting from” methods are very powerful synthetic tools, which can be used in the fabrication of any desired molecular bottle brush architectures.
Additionally, complexation of oppositely charged bottle polymer brushes at a single-molecule level using AFM and CryoTEM was experimentally investigated. It was found that polyelectrolyte complexes have “scrambled-egg” morphology, where oppositely charged polymer chains are not oriented parallel to each other but cross each other.
Furthermore, molecular bottle brushes were used as templates for the preparation of conductive nanowires. Three approaches for their fabrication were tested. It was found that brushes could easily be covered with various conductive materials, for example conductive polymers or metals. It was showed that for very small, tiny objects as molecular bottle brushes, one can use FIB in order to build up electrodes at its ends. The electrodes could be sputtered with an accuracy of 500 nm and further be used in the determination of the conductivity. The molecular bottle brushes covered with palladium showed the resistance of 50 MΩ, which, regarding the size of the brush, corresponds to a conductivity of one single molecule being ~1 S*cm-1. The obtained conductivity data were in good correlation with the data found in literature.
We believe that the molecular bottle brushes have high potential applicability for the building of complex conductive networks. Future refinement of the synthetic methods, combined with improvements in structuring and positioning of objects at the nanoscale, could lead to their implementation in the construction of high-performance electronic devices.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:14-qucosa-164686 |
| Date | 16 April 2015 |
| Creators | Raguzin, Ivan |
| Contributors | Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Dr. habil. Leonid Ionov, Prof. Dr. Manfred Stamm, Prof. Dr. Rainer Jordan |
| Publisher | Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf |
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