Supramolecular network formation from solution-based deposition techniques

The spontaneous formation of supramolecular assemblies has been viewed as a potential route to the creation of functional nano-scale architectures for a number applications in electronics. In this thesis a number of assemblies formed from molecular constituents deposited from the solution phase have been studied. The structures formed by two carboxylic acid derivatives on the highly oriented pyrolytic graphite (HOPG) surface from nonanoic acid solutions are presented. Quaterphenyl-tetracarboxylic acid (QPTC) molecules are observed to form a supramolecular network where all the constituents lay parallel to one another on the surface. The network is stabilised by four carboxylic acid dimer bonds per molecule in addition to admolecule-substrate interactions. Terphenyl-tetracarboxylic acid (TPTC) molecules form a much more complex structure with individuals orientating themselves in one of three directions to form a network with hexagonal symmetry but no translational order. To characterise such an unusual supramolecular morphology we introduce a rhombus tiling representation of the network where each molecule is schematically replaced with a lozenge rhombus producing a tiling. Such tilings have been studied previously in the literature and utilising this we are able to determine that the morphology is stabilised by entropic contributions to the free energy. In addition to this we present the tip-induced manipulation of the TPTC supramolecular network. The manipulation is performed by imaging the structure within a specific voltage bias range resulting the TPTC molecules reordering into a close packed structure. Returning the voltage to that conventional used for imaging causes the network to relax back into the open structure although with a different morphology. We then discuss the changes induced in these supramolecular networks when additional molecular species are introduced to the system. First, coronene and perylene are separately codeposited with QPTC resulting in the formation of a hexagonally ordered network with coronene or perylene located at the vertices of six QPTC molecules. This new structure is observed to form even when QPTC is deposited first. Second, the adsorption of coronene into the porous TPTC network is presented. When the TPTC network forms before the introduction of coronene we note little effect on the network morphology. However, when the molecules are mixed in the solution phase and deposited simultaneously we observe the non-uniform adsorption of coronene into the TPTC structure. At higher coronene concentrations we note the network forms with a different morphology shifted towards a more ordered state suggesting that when the molecules are deposited sequentially the system is kinetically trapped in the originally formed structure. We then present a series of studies of molecular adsorption on the Au (111) surface. First, hexaazatrinaphthylene (HATNA) molecules are observed to form stable supramolecular structures when deposited from ethanol solutions. A core hydrogen bonding junction is identified. The network switches between two domain orientations and we identify a linear defect where the two domains meet. Second, we report the adsorption of Tri( 4-bromophenyl) benzene (TBPB) on the Au (111) surface. TBPB forms three different structures at room temperature. When samples are heated during the deposition stage we observe the covalent coupling of pairs of molecules to form dimers. This reaction is confirmed by ToFSIMS experiments. The substrate is confirmed to play a significant role in the coupling process as subsequent experiments on HOPG failed to yield dimer formation. Finally we demonstrate the potential of a UHV-prepared sample by templating the adsorption of adamantanethiols. Finally, we demonstrate the adsorption of a solubilised derivative of perylene tetracarboxylic dianhydride (PTCDA). PTCDA molecules have poor solubility in most solvents commonly used for liquid deposition. The addition of alkane chains attached to the sides of the perylene core promotes the solubility of the molecule in these solvents whilst leaving the anhydride functionality intact. Deposition is performed from 1-phenyloctance solutions on HOPG. The molecules form an ordered structure characterised by a single molecule unit cell. The results presented in this thesis show that the understanding of supramolecular networks has progressed to the point where changes in the morphology can be induced via a variety of processes

Supramolecular network formation from solution-based deposition techniques

The spontaneous formation of supramolecular assemblies has been viewed as a potential route to the creation of functional nano-scale architectures for a number applications in electronics. In this thesis a number of assemblies formed from molecular constituents deposited from the solution phase have been studied. The structures formed by two carboxylic acid derivatives on the highly oriented pyrolytic graphite (HOPG) surface from nonanoic acid solutions are presented. Quaterphenyl-tetracarboxylic acid (QPTC) molecules are observed to form a supramolecular network where all the constituents lay parallel to one another on the surface. The network is stabilised by four carboxylic acid dimer bonds per molecule in addition to admolecule-substrate interactions. Terphenyl-tetracarboxylic acid (TPTC) molecules form a much more complex structure with individuals orientating themselves in one of three directions to form a network with hexagonal symmetry but no translational order. To characterise such an unusual supramolecular morphology we introduce a rhombus tiling representation of the network where each molecule is schematically replaced with a lozenge rhombus producing a tiling. Such tilings have been studied previously in the literature and utilising this we are able to determine that the morphology is stabilised by entropic contributions to the free energy. In addition to this we present the tip-induced manipulation of the TPTC supramolecular network. The manipulation is performed by imaging the structure within a specific voltage bias range resulting the TPTC molecules reordering into a close packed structure. Returning the voltage to that conventional used for imaging causes the network to relax back into the open structure although with a different morphology. We then discuss the changes induced in these supramolecular networks when additional molecular species are introduced to the system. First, coronene and perylene are separately codeposited with QPTC resulting in the formation of a hexagonally ordered network with coronene or perylene located at the vertices of six QPTC molecules. This new structure is observed to form even when QPTC is deposited first. Second, the adsorption of coronene into the porous TPTC network is presented. When the TPTC network forms before the introduction of coronene we note little effect on the network morphology. However, when the molecules are mixed in the solution phase and deposited simultaneously we observe the non-uniform adsorption of coronene into the TPTC structure. At higher coronene concentrations we note the network forms with a different morphology shifted towards a more ordered state suggesting that when the molecules are deposited sequentially the system is kinetically trapped in the originally formed structure. We then present a series of studies of molecular adsorption on the Au (111) surface. First, hexaazatrinaphthylene (HATNA) molecules are observed to form stable supramolecular structures when deposited from ethanol solutions. A core hydrogen bonding junction is identified. The network switches between two domain orientations and we identify a linear defect where the two domains meet. Second, we report the adsorption of Tri( 4-bromophenyl) benzene (TBPB) on the Au (111) surface. TBPB forms three different structures at room temperature. When samples are heated during the deposition stage we observe the covalent coupling of pairs of molecules to form dimers. This reaction is confirmed by ToFSIMS experiments. The substrate is confirmed to play a significant role in the coupling process as subsequent experiments on HOPG failed to yield dimer formation. Finally we demonstrate the potential of a UHV-prepared sample by templating the adsorption of adamantanethiols. Finally, we demonstrate the adsorption of a solubilised derivative of perylene tetracarboxylic dianhydride (PTCDA). PTCDA molecules have poor solubility in most solvents commonly used for liquid deposition. The addition of alkane chains attached to the sides of the perylene core promotes the solubility of the molecule in these solvents whilst leaving the anhydride functionality intact. Deposition is performed from 1-phenyloctance solutions on HOPG. The molecules form an ordered structure characterised by a single molecule unit cell. The results presented in this thesis show that the understanding of supramolecular networks has progressed to the point where changes in the morphology can be induced via a variety of processes

Image processing techniques for the detection and characterisation of features and defects in railway tracks

This thesis describes the research that led to the development of a machine vision system in collaboration with TATA, UK and Sheffield Supertram. This was part of a European initiative for Predictive Maintenance employing non-intrusive inspection and data analysis known as PM’n’Idea. The hardware and software design, construction, and evaluation of a prototype for predictive maintenance are presented. The prototype was tested on Sheffield and Warsaw’s tram systems. The prototype has been designed with due account of a specified set of environmental constraints such as a high level of vibrations and space restrictions of the target trams. Special computer vision techniques have been specifically developed to be used with the prototype. Various image processing techniques and algorithms have been evaluated for the purpose of detection and characterisation of a series of rail abnormalities and faults. The system described in this thesis makes use of a number of standard and modified image processing techniques, not only to alleviate the requirements for manual inspections, but also to allow continuous monitoring and tracking of any defects or abnormalities in a rail track. Currently, detecting defects in their earlier stages can only be achieved by using close visual inspection i.e. line walking. Extensive testing and evaluation of the performance of the prototype inspection system at Sheffield Supertram indicated that the system was able to detect abnormalities with a resolution down to 0.1 mm. Evidence of the classification rates for the standard and modified algorithms that are implemented in the system are presented in this thesis. The algorithms developed show an average success rate of 88.9% in detecting surface bound abnormalities

Efficient pre-segmentation filtering in MRCP

Magnetic Resonance Cholangiopancreatography (MRCP) is an evolving MRI technique designed for the imaging of the biliary tree, a system of narrow ducts that collect bile, produced within the liver, store it in the gall bladder, and deliver it into the small intestine as needed. Current MRCP protocols, used to diagnose problems in this ductal system, generate cluttered and noisy, low resolution, non-isometric volume data, often with significant intensity non-uniformities. This combination of undesirable characteristics presents particular challenges for the application of automated image analysis techniques. This thesis examines the development, characterisation, and testing of novel and efficient pre-segmentation filtering procedures designed to achieve increased robustness and precision in the subsequent segmentation and analysis of the biliary tree from MRCP data. A focused set of image preprocessing algorithms has been developed so as to facilitate the operation of non-complex segmentation and computer assisted diagnosis (CAD) procedures. Most notable in this regard are a number of novel techniques designed to address the key areas of this image processing task. These techniques consist of: • a new histogram preserving approach to inter-image and intervolume intensity non-uniformity correction, • a highly versatile adaptive smoothing filter, implemented as an oriented, scaled and shaped ellipsoid filter mask, • the downhill filter, an efficient new algorithm for morphological reconstruction by dilation, and • a novel approach to the reconstruction of fine branching structures in noisy volume data. Through this combination of flexible and efficient preprocessing algorithms, an effective route towards robust MRCP segmentation and analysis, and routine CAD in the assessment of the biliary tree from MRCP is presented

Automated segmentation and characterisation of white matter hyperintensities

Neuroimaging has enabled the observation of damage to the white matter that occurs frequently in elderly population and is depicted as hyperintensities in specific magnetic resonance images. Since the pathophysiology underlying the existence of these signal abnormalities and the association with clinical risk factors and outcome is still investigated, a robust and accurate quantification and characterisation of these observations is necessary. In this thesis, I developed a data-driven split and merge model selection framework that results in the joint modelling of normal appearing and outlier observations in a hierarchical Gaussian mixture model. The resulting model can then be used to segment white matter hyperintensities (WMH) in a post-processing step. The validity of the method in terms of robustness to data quality, acquisition protocol and preprocessing and its comparison to the state of the art is evaluated in both simulated and clinical settings. To further characterise the lesions, a subject-specific coordinate frame that divides the WM region according to the relative distance between the ventricular surface and the cortical sheet and to the lobar location is introduced. This coordinate frame is used for the comparison of lesion distributions in a population of twin pairs and for the prediction and standardisation of visual rating scales. Lastly the cross-sectional method is extended into a longitudinal framework, in which a Gaussian Mixture model built on an average image is used to constrain the representation of the individual time points. The method is validated through a purpose-build longitudinal lesion simulator and applied to the investigation of the relationship between APOE genetic status and lesion load progression

Using a water treatment residual and compost co-amendment as a sustainable soil improvement technology to enhance flood holding capacity

The recycling of clean wastes, such as those from the treatment of drinking water, has gained importance on the environmental agenda due to rising costs of landfill disposal and movement towards a ‘zero’ waste economy. More than one third of the globe’s soils are degraded and as such policies towards determining soil health parameters and reversing destruction of the globe’s most valuable non-renewable source are at the forefront of environmental debate. This thesis questions the opportunity for water treatment residual (WTR) to be used as a beneficial material for the co-amendment of soil with compost to improve the soil’s flood holding capacity (Kerr et al., 2016), which includes functions such as the water holding capacity, hydraulic conductivity, soil structure and shear strength. Currently, water treatment residual is typically sent to landfill for disposal, but this research shows that the reuse of WTR as a co-amendment is able to improve the flood holding capacity of soils. This research crosses the boundary between geotechnical and geoenvironmental and provides a holistic approach to quantifying a soil from both perspectives. Iron based water treatment residual from Northumbrian Water Ltd was used in both laboratory and field trials to establish the effect of single WTR and a compost and WTR co-amendment on the water holding capacity (the gravimetric water content, volumetric water content, volume change of samples i.e. swelling and shrinkage), and the effect of amendment on the erosional resistance, hydraulic conductivity and shear strength compared to a control soil. A series of four trials were conducted to develop and establish a novel method to determine the water holding capacity, supplemented by standard geotechnical methods to determine the flood holding capacity. The use of x-ray computed tomography has provided accompanying information on the morphology of dried WTR and changes in the internal characteristics of amended soil between a dry and wet state. The amendment application rate ranges from 10 – 50%. Experiments have shown that the single amendment of WTR, compared to a control soil, yields significant increases in the hydraulic conductivity (by up to a factor of 28), increases the shear strength of soils at low testing pressure (25 kPa) by 129%, increases the maximum gravimetric water content by up to 13.7%, and improves swelling by up to 12% (but only at the highest amendment rate, 30%), increases the maximum void ratio when saturated by 11%, and reduces shrinkage by maintaining porosity by 14%. However the application of WTR as a single amendment has implications for the chemical health of the soil as it is highly effective at immobilising phosphorous as and such cannot not effectively be used as a soil amendment. The single application of compost yielded significant improvement in the water holding capacity (improving gravimetric water content by up to 34.7%, increasing the sample volume by up to 83.3%, and increased the void ratio by 8.2%), however this application reduces the hydraulic conductivity by up to 84.5% and the shear strength by 3% compared to the control soil. Co-amendment using compost and WTR (in two forms, air dried 80% solids and wet at 20% solids, as produced from water treatment works) improved the flood holding capacity of soils by retaining the structural improvements of amendment using WTR and the water holding capacity improvements of compost. Compared to the control soil, for co-amended soils the gravimetric water content was improved by up to 25%, the volume increased by up to 51.7%, experienced 13% less shrinkage and an 11.5% increase in maximum void ratio. The hydraulic conductivity was also improved by up to 475%, and shear strength was increased at both low and high testing pressures by to 53.8%. Taking into account these effects of co-amendment on essential soil functions that determines a soil’s flood holding capacity (maximum gravimetric water content, volume change, resistance against shrinkage, void ratio (porosity), hydraulic conductivity and shear strength), the economical and environmental sustainability issues, the co-amendment of soil using compost and WTR may provide a solution to both recycling clean waste product and improving the quality of soil

Super-resolution of 3-dimensional scenes

Super-resolution is an image enhancement method that increases the resolution of images and video. Previously this technique could only be applied to 2D scenes. The super-resolution algorithm developed in this thesis creates high-resolution views of 3-dimensional scenes, using low-resolution images captured from varying, unknown positions

X-ray imaging of failure and degradation mechanisms of lithium-ion batteries

Lithium-ion batteries are becoming increasingly energy and power dense, and are required to operate in demanding applications and under challenging conditions. Both safety and performance of lithium-ion batteries need to be improved to meet the needs of the current demand, and are inextricably linked to their microstructure and mechanical design. However, there is little understanding of the complex, multi-length scale, structural dynamics that occur inside cells during operation and failure. From the evolving particle microstructure during operation to the rapid breakdown of active materials during failure, the plethora of dynamic phenomena is not well understood. In this thesis, both ex-situ and operando X-ray imaging, and computed tomography, in combination with image-based modelling and quantification are used to characterise battery materials and components in 3D. Degradation mechanisms are investigated across multiple length-scales, from the electrode particle to the full cell architecture, and direct comparisons between materials in their fresh and failed states are made. Rapid structural evolution that occurs during operation and failure is captured using high-speed synchrotron X-ray imaging, and quantified by correlating sequential tomograms. Consistent degradation mechanisms that occur over fractions of a second are identified and are shown to contribute significantly towards uncontrolled and catastrophic failure, and previously unexplored interplay between the mechanical design of cells and their safety and performance is described. The experiments reported here assess the thermal and mechanical responses of cells to extreme operating and environmental conditions. The interaction between the dynamic architecture of active materials and the mechanical designs of commercial cells are revealed, highlighting the importance of the engineering design of commercial lithium-ion batteries and their efficacy to mitigate failure. These insights are expected to influence the future design of safer and more reliable lithium-ion batteries