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With the miniaturisation of silicon based technology approaching its fundamental physical limit, molecular electronic components are considered an alternative route to prolong the lifetime of integrated circuit technology. In order to realise this technology, the fundamental physical and electronic properties of such nanoscopic materials and devices must be fully understood. This thesis reports the successful formation and characterisation of a series of novel molecular wires on both planar and nanoparticulate surfaces, from which two papers have been published. Formation of these wires was achieved using the reproducible chemical self- assembly method often utilised in bottom-up molecular electronics. After the initial chemisorption of a functional headgroup to a suitable substrate , subsequent layers were chemically reacted by means of an imine bond formation. This allowed multilayer donor-a- bridge-acceptor systems of up to ea. 10.4 nm in length to be constructed. Not only does this method allow the formation of reasonably complex systems, it also enables functionality to be incorporated into the wire. The assembly characteristics of various wires have been characterised using Quartz Crystal Microbalance and X-ray Photoelectron Spectroscopy, and in the case of those on Ti02 nanoparticles, with Infrared Spectroscopy. Furthermore, an investigation into the factors affecting the formation of upright, homogeneous mono layers was carried out on a set of related compounds, revealing the importance of molecule-molecule and molecule-substrate interactions. Multiple molecular wires were also characterised with respect to their electrical properties which show symmetrical or asymmetrical current-voltage curves. This was done using Scanning Tunnelling Spectroscopy to obtain current-voltage characteristics, as well as the so called current jump method to measure single molecule current or that of small clusters of molecules. The effect of increasing molecular length and steric hindrance on molecular current rectification was examined, as well as the effect of increasing length on single molecule conductance.

The ionic liquid, l-Ethyl-3-methylimidazolium bis- (trifluoromethylsulfonyl)-imide (EMITFSI) was studied as an electrolyte for rechargeable lithium batteries. This work focused on two main topics: cathodic stability and lithium ion transport. The ionic liquid was synthesised and purified until Br < 40 ,vtppm, H20 < 2 ppm. Effects of water on the cathodic stability limit were studied using a platinum microdisc electrode and a :gold microdisc electrode array. The response of the cathodic current on the water concentration suggests catalytic decomposition of EMr with moisture. The cathodic potential limit shifted negative with addition of lithium salt, especially on a nickel microelectrode, so that deposition and stripping current for lithium was observed. This is attributed to the formation of a solid electrolyte interface (SEI). Evidence for the formation of a SEI was also found from cyclic voltammograms and impedance spectra for lithium metal electrodes as well as open circuit cell potentials. Addition of LiTFSI to EMITFSI resulted in a decrease in the conductivity (e.g., from 10.5 to 5.6 mS cm-l for 0.47 mol dm-3 ) and the lithium ion diffusion coefficient was found to be 1.2 x 10-7 cm2 S·l for 0.47 mol dm-3 added Li salt. The transference number for .lithium ions) in LiTFSI / EMITFSI was found to be proportional to the concentration of the lithium salt. The measured value of 0.04 for 0.47 mol dm-3 is significantly higher than that of LiBF4 / EMIBF4 at the same concentration and temperature. This may be explained with two factors; the differences in size and dissociation level ofthe anions. The charge / discharge rate performance· of LiFeP04 carbon composite electrodes with various thicknesses in different concentrations of LiTFSI I EMITFSI electrolytes was studied using 3-electrode cells. At fast charge or discharge rates, discharge capacities were approximately inversely proportional to C-rate, suggesting that the capacities were controlled by lithium ion diffusion in the pores of the composite electrode. Differences in rate perfonnance were found between charge and discharge and for different concentrations of lithium salt in the ionic liquid. Two models are proposed to explain above phenomena; a transmission circuit to represent electrolyte resistance, and a salt depletion model simplified by the assumption of a compact discharge front. An optimised cell was designed and constructed according to the above fmdings, using a 14 LiFeP04 positive electrode, mol dm-3 LiTFSI / EMITFSI and a lithium negative electrode. The cell gave a discharge capacity of more than 100 mAh g-l over 850 cycles.

This work describes the development of a nanostructured palladium microelectrode for use in scanning electrochemical microscopy. Once loaded with hydrogen to form the coexistent ? + ? phase palladium hydride the potential of the nanostructured microsensor depends not on the H/Pd ratio, but on the activity of the protons in the solution. This thesis is focussed on extending the lifetime of the microsensor such that it can be successfully utilised in scanning electrochemical experiments. The controlled potential method of loading the palladium film is investigated by application of a novel analytical technique. A measurement of the amount of hydrogen stripped from within the palladium lattice provides useful information on the efficiency of the controlled potential method of loading and on the amount of palladium remaining on the underlying disc. It has been shown that repeated use of the microsensor can lead to degradation of the palladium film. A controlled current approach to loading the potential is introduced and many loading parameters are investigated including the loading current, loading time and solution pH. Also investigated are the film properties including film thickness, film freshness and the presence of the nanostructure. It is shown that controlled current loading can provide the required H/Pd ratio from first loading, even in a plain palladium film. The use of the palladium microsensor in scanning electrochemical microscopy experiments is introduced. The microsensor is shown to be responsive to the changes in pH surrounding a platinum substrate undergoing cyclic voltammetry in a solution of 0.5 M Na2SO4. Well defined peaks which coincide with adsorption, evolution and consequent desorption of hydrogen on the Pt disc are seen in the potential, and pH measured by the tip. This shows that it is possible to use this nanostructured palladium hydride microsensor in scanning electrochemical microscopy experiments.

No description available.

No description available.

No description available.

No description available.

This thesis reports on the development of novel screen-printed electrodes for use as energy-storage (supercapacitor) devices. The thesis covers four primary topics; the first considers the basic fundamentals of electrochemistry, which are essential for understanding and furthering the development of energy-storage devices. Section two reports on the electrode materials, highlighting the important contribution of each material towards the electrochemical mechanisms involved at their surfaces. Furthermore, a novel, yet simplistic methodology for characterising various carbon nanomaterials (in terms of their edge and basal content) without recourse to expensive laboratory equipment is presented. Section three describes the processes involved in screen printing but moreover, illustrates how the modification of the electrode with nanomaterials can transform a seemingly redundant electrode into a highly desirable and sometimes ideal option targeted towards the application of energy-storage. The development of true screenprinted supercapacitors utilising transition metal nanomaterials, shows proof of concept for the future advancement of screen-printed electrodes as thin, highly flexible energy-storage devices. The final section highlights some of the limitations found in electrical impedance spectroscopy that are often overlooked. Lastly, a simple methodology is described that has been found to offer improved accuracy in the galvanostatic (charge/discharge) measurement of capacitance.