Many of the highlights in the surface science field in the last years have arisen from the study of organic molecules adsorbed upon, but physically decoupled from, metallic substrates. When adsorbed on bare surfaces like Cu, the strong interaction between the two can have a number of different effects on the chemistry, functionality and assembly of the adsorbates. These effects can be reduced or even prevented by incorporating an ultra-thin insulating film between the molecule and the metal, enabling the retention of the desired molecular properties. Previous studies have almost exclusively used films of inorganic material, such as alkali halides and metal oxides. In this work, an all-organic alternative approach has been developed, which should allow a greater degree of control over the nature of the decoupling film and its corresponding interactions. To demonstrate the potential impact of the molecule-substrate interaction on the formation of molecular nanostructures, the adsorption and assembly of a prototypical molecular tecton, terephthalic acid (TPA), has been explored on Cu(110) and Cu(111). On Cu(110), the TPA is deprotonated and goes on to form a range of metal-organic or all-organic monolayer films. The exact structure obtained is determined by the total molecular coverage, which is rationalised by consideration of the TPA adsorption energies and the molecular density in each phase. On Cu(111), TPA adsorbs intact, and assembles into a brickwork-like structure characterised by both uncharacteristically short and elongated hydrogen bonds. This unusual assembly is the result of the oft-cited, but in general poorly understood, ‘interplay of intermolecular and molecule-substrate interactions’. In a bid to understand the observed supramolecular assembly of TPA on Cu(111), a simple algorithm has been developed that is capable of predicting both its quantitative and qualitative aspects. Moreover, this analytical model can be readily expanded to more complex assemblies, such as those using more complex molecules and surfaces. In addition, the formation of Cu- and Fe-terephthalate complexes has been explored. Oxalic acid (OA) monolayers have been investigated as prototype organic decoupling layers for the Cu(110) and Cu(111) surfaces. This molecule was chosen as, in previous work, it had been reported to adsorb in an upright orientation and assemble into a densely packed monolayer on Cu(110). In this work, a flat-lying, low density film has been obtained on Cu(110), which later proved to be incapable of supporting molecular ‘overlayers’unless it was cooled to low temperature prior to the deposition of molecular overlayers. In contrast, a densely-packed, upright monolayer was obtained on Cu(111). This decoupling layers was effective even at room temperature, and moreover appears to plays a significant role in determining the assembly of the overlayer species. These studies indicate the potential of vertically standing organic films as both decoupling layers and also as a tool with which to directly modify and control the assembly of organic nanostructures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:618968 |
| Date | January 2014 |
| Creators | White, Thomas W. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/62963/ |
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