No description available.

No description available.

No description available.

No description available.

This thesis describes theoretical studies of composites formed on the encapsulation of one dimensional (lD) crystals within single walled carbon nanotubes (SWNT), chemical interactions between nanotubes/C60 and porphyrins/molecular species of titanium and neutral and anionic T]6, T]6-bis (tricarbonylchromium) Flu and Flu* _complexes. The principal aims of this research were to (i) calculate the structures of 1D crystals within SWNTs, (ii) identify chemical interactions between nanotubes and their guests, (iii) probe any changes in structure of the guest species on intercalation and (iv) make comparison with experimental data. Density Functional Theory (DFT) calculations were performed using the SIESTA code, which permits calculations to be performed on larger systems containing thousands of atoms. DFT calculations were used both to propose and to test possible structural models for crystals inside SWNTs. The calculated structures were then compared with experimental images and proposed model structures. The results presented herein demonstrate the successful application of this methodology in the analysis of HgTe@SWNT, Pb!z@SWNT, Sb2Se3@SWNT and CuI@SWNT. Electronic band structures and density of states were calculated for most systems. This thesis commences with an introduction to single walled carbon nanotubes which includes structures, properties and applications of nanotubes. In addition, experimental and theoretical studies of both pristine nanotubes and filled SWNT composites are discussed. Chapter 2 then describes the computational chemistry including Density Functional Theory (DFT) and the DFT codes that were used throughout this thesis. Also, some test calculations are reported to compare the performance of a new DFf code SIESTA with another well known DFf code, ADF. The results presented herein can be divided into three parts. Firstly, composites formed on the encapsulation of inorganic nano-crystals in SWNTs (Chapters 3, 4, 5 and 6), secondly porphyrins and molecular species of Ti interacting bucky balls (Chapters 7 and 8) and finally, electronic structures of fluorenyl complexes of chromium. Chapter 3 describes calculations on HgTe@SWNT. The structure of HgTe, grown inside SWNTs, has been well characterised by HRTEM and a model structure corresponding to experiment has been established. In our study, different ID HgTe structures including the model derived from experimental data were optimised. The calculated structure was in excellent agreement with a previous calculation. Three different diameters of nanotubes based on the experimental report were selected to encapsulate the HgTe structure. For the larger diameter of tubes, the calculated structure is excellent agreement with the experiment. The structure, binding energy, charge transfer and density of states (DOS) confirm that the interaction between SWNT and HgTe is small. Chapter 4 describes the results of calculations on lead diiodide crystals inside SWNTs. A model structure deduced from the HRTEM was inserted into a SWNT. The calculated structure is good agreement with the predicted structure by the experimentalists. This study further concludes that the interaction between and nanocrystal is small and the smaller diameter tube may introduce the structural change anticipated by the experimentalists. The main aim of chapter 5 was to propose a model for Sb2Se3 crystals in SWNTs. The results of DFf calculations gave good agreement with transmission electron microscopic studies. This study reveals that more precise values can be obtained with exothermic binding energy when it is encapsulated within larger diameter tubes.

No description available.

Porous materials are highly valued for a wide variety of scientific and technological applications and organic molecular crystals offer an alternative to established inorganic materials. In this thesis, the porosity of tris-N-phenylureido steroidal crystals IS characterised and the versatility of the steroidal crystal system is demonstrated. Material properties can often be adjusted by mixing components in varying proportions to form alloys, but this phenomenon is rarely demonstrated for organic molecules. In organic crystals, molecules pack into an array which has symmetry and dimensions specific to the compound. Thus, in general, molecules cannot be substituted for molecules of a different compound. The studies presented here demonstrate that organic alloys are possible if the crystal structure possesses voids which are able to accommodate significant p0l1ions of the new molecules. A variety of multi-component steroidal crystals have been created with diverse and complex channel interiors. These have been characterised by optical microscopy, single X-ray crystallography, IH NMR and mass spectrometry. Finally, molecular machines which perform mechanical work on a molecular level are of great interest within the scientific community. The operational range of molecular motion is often too restricted to create macroscopic phenomena, but by confining the molecular machines to small spaces such as nanopores, molecular movement on the nanometre level can be sufficient to dominate the physical and chemical behaviour of guest molecules. In this thesis, the prospect of creating a new type of molecular machine assembly to propel molecules unidirectionally along crystal channels has been investigated. Crystal engineering has been used to design porous steroidal crystals with azobenzene moieties, capable of photoinduced isomerisation, protruding into the crystal channels. The resulting crystals have been analysed by optical microscopy and solid-state UV-vis spectroscopy, and the distribution of guest molecules within the crystals has been investigated by Raman and IR microspectroscopy and fluorescence microscopy.

No description available.

This thesis has developed a method for generating single crystals of the mineral port- landite. These crystals were formed on a silicon wafer substrate by drying a filtered solution of calcium hydroxide under nitrogen, using a specially developed glass cell. The resulting precipitate was confirmed to be calcium hydroxide using a combination of Raman spec- troscopy, SAED and XRD. The specimens were characterised using SEM, TEM and FIB and were seen to be hexagonal and prismatic with an aspect ratio 1:2. Additional facets, of the (1011) index, were also seen. In addition, nucleation sites were generated by rapidly drying the calcium hydroxide solution on a heated silicon wafer substrate. The resulting sites produced partially orientated growth of subsequent depositions of portlandite, with the (0001) facets parallel to the substrate. Forced carbonation - in pure CO2 with 97% relative humidity - of these portlandite crystals yielded a solid state reaction, without the necessity of excess water to act as a solvent. Evidence of an hydrated and amorphous form of calcium carbonate was seen, with an increase in volume of approximately 4.3 times in the first hour of carbonation. This was characterised using SEM, TEM and SAED and confirmed to be calcium carbonate using Raman, with a characteristic peak of shift between 1081cm-1 and 1085cm-1. The presence of calcite in the reaction products was also confirmed using XRD. Using the same drying cell, a filtered calcium hydroxide solution was applied to the exterior and interior surfaces of three varieties of brick. Additional fine, acicular features were seen and conglomerations of which were cross-sectioned using the focussed ion beam, showing a thickness of approximately O.lp,m. Additional high surface area, floret-type precipitate features were characterised on the surface of brick substrates, following calcium- hydroxide deposition. This was achieved using SEM, and additionally using EDX. Such features were seen to consist primarily of calcium.

The Landau theory of phase transitions is used to model aspects of the behaviour of the minerals anorthoclase and nepheline. In both these minerals, there are multiple phase transitions, with separate time and temperature dependencies. The concepts of order parameter coupling and gradient energies are shown to give useful quantitative descriptions of these minerals. The displacive phase transition in anorthoclase is studied by X-Ray powder diffraction. The temperature dependence of the order parameter is shown to depend on the composition and the degree of noncovergent Al, Si ordering. These dependencies correspond with a simple Landau potential, where both the composition <I>x</I> and the degree of ordering <I>Q</I><SUB>t</SUB> couple to the square of the displacive order parameter <I>Q</I>. At low temperatures, quantum mechanical saturation of order parameters occurs. The extent of saturation is characterised by a temperature <I>θ</I><SUB>s</SUB>, which is a function of the high frequency phonons in the structure. When a saturated phase transition is coupled with a classical effect, anomalous behaviour is expected in the phase diagrams. These anomalies are investigated for anorthoclases in the composition range Ab<SUB>7</SUB>Or<SUB>30</SUB> to Ab<SUB>55</SUB>Or<SUB>45</SUB>. An analogous model is applicable to ferroelectric materials at low temperatures, such as KH<SUB>2</SUB>PO<SUB>4</SUB> and SrTiO<SUB>3</SUB>. The role of local structural distortions in feldspar is analysed, where twin domains and solute atoms are used to distort the bulk structure. The wall thickness of a twin boundary is measured at various temperatures using single crystal X-ray diffraction. The thickness is 25 Å at room temperature, and increases on heating towards <I>T<SUB>c</SUB></I>. This is consistent with the Ginzburg-Landau model of fluctuations in the order parameter. The range of distortions due to solute atoms is found to be similar, as determined from anomalies in the temperature - composition phase diagram of anorthoclase.