X-ray photoelectron spectroscopy (XPS or ESCA) has been employed to investigate the changes in the surface chemistry of polymers produced by their exposure to plasmas and ion beams and the chemistry of thin polymeric films produced by the ion beam irradiation of films of condensed organic material. Modification by hydrogen plasmas of fluoropolymers is shown to result in extensive defluorination and hydrogenation of the surface regions of the polymer to a depth of ~20Å. In the initial stages of the reaction ESCA analysis reveals the presence of a smooth reaction gradient within the ESCA sampling depth. The modification is accompanied by extensive crosslinking of the polymer surface. A model is also proposed to account for these observations. In order to try and gain an insight into the contributions of the various components of a plasma with polymer surfaces the interaction of low energy (l-5keV) argon ions with fluoropolymer and polymers containing cajbon hydrogen and oxygen were studied. The reaction leads to the depletion of the surface region in the most electronegative components of the polymer. The modification, irrespective of the beam energy used, is homogeneous within the ESCA sampling depth using Mg(_ka1,2) radiation. The polymers all lead to the formation of a highly crosslinked, unsaturated carbonaceous surface layer on bombardment. This defunctionalisation is marked in the ESCA spectra by modifications in the lineshape of the C(_1s) photoionisation peak, the asymmetry of which has been found to, in a qualitative sense at least, reflect the presence of unsaturation in the systems. The exposure of condensed films of hexafluorobonzene to relatively low doses of argon ions has been shown to result in the formation of a thin film of an involatile polymeric residue. The product bears a striking resemblance in its chemistry to that of plasma polymerised films of hexafluorobenzene. Apart from the potential ability of such films, e.g. as dielectric films in microelectronics fabrication, they also illustrate the link between the interactions of ion beams with organic materials and plasmolysis of such materials. The thermal stability of films produced by the ion beam induced polymerisation and plasma polymerisation of hexafluorobenzene is also investigated.

Inductively coupled plasma - mass spectrometry is widely accepted as the leading technique for trace element analysis. It suffers however, from a range of interferences both spectral and non - spectral which limit the range of analytes and substrates which may be successfully analyzed. This study has investigated the use of mixed gas plasmas as a means of reducing or removing these interference effects. In addition the use of mixed gas plasmas for sensitivity enhancement has been assessed using both wet and dry sample introduction systems. Simplex optimization procedures have been used throughout. The addition of nitrogen to all three argon gas flows of the ICP was evaluated, and the instrumental operating conditions were optimized to allow for the maximum removal of the ArCl+ interference on As and Se. The addition of nitrogen to the nebulizer gas was particularly effective in the removal of the ArCl+. The use of nitrogen addition also facilitated the determination of arsenic in samples where it was previously found to be impossible. The addition of methane was also applied to all three gas flows of the ICP, however, in this case only the addition to the nebulizer gas was successful in removing interferences. These included ArO+, ClO+ and CeO+ in addition to ArCl+ . Detection limits, recoveries and CRM analysis were all improved by the use of methane addition when compared to nitrogen addition or standard argon plasmas. Hydrogen addition was applied solely to the nebulizer gas and found to significantly increase the magnitude of the interferences from argon based polyatomic ions, whilst reducing those from metal oxides. The addition of hydrogen was useful in reducing MO+ interferences, but the removal of other interferences proved unsuccessful. The addition of ethene to the nebulizer gas has been used to remove many of the polyatomic interferences encountered in ICP-MS, including those based on Na, S and P. Ethene addition was as effective as, and usually better than, the addition of both methane and nitrogen. Detection limits, recoveries, calibrations and CRM analysis were all improved by its use. The use of ethene addition has lead to improvement in the determination of As, Cu, Fe, Gd, Ni, Se, and V in the presence of the relevant interference precursors. Most importantly it has been shown that a whole range of interferences can be reduced simultaneously with the addition of ethene. The plasma operating parameters and ion optics settings of a commercial ICP-MS instrument were optimized to yield maximum SBRs for elements across the mass range. It was shown that simple manual tuning of the instrument did not effect the SBRs, when compared to the simplex optimized conditions. Finally it was shown that the addition of molecular gases to the ICP, did not result in any significant improvements in sensitivity, when compared to the all argon system. Finally it has been shown that the addition of a relatively small amount of hydrogen to the nebulizer gas can lead to an enhancement in the signal obtained using laser ablation sampling. This enhancement was greatest for low mass elements and had no effect on the heavy mass element signal.

A low pressure-inductively coupled plasma (LP-ICP) ion source has been investigated for the production of atomic and molecular ions for mass spectrometry (MS). A dedicated LPICP- MS was constructed, by modifying a Hewlett Packard mass selective detector, to detect ions from the LP-ICP. The ion sampling interface and ion optics were designed using established theory and the use of a computer simulation program. Perfluorotributylamine was continuously introduced into the LP-ICP, via a molecular leak, and the ion sampling interface, plasma forward power, and plasma gas flow rates, were optimised. When the LP-ICP ion source was sustained at 6W with a gas flow of 6 ml min'* helium, and iodobenzene and dibromobenzene, introduced via GC, only atomic signals for iodine and bromine were observed. Detection limits were 4 and 76 pg for iodobenzene and dibromobenzene respectively. The addition of nitrogen to a LP helium ICP increased the molecular signal for chlorobenzene, resulting in a detection limit of 2 pg. However, the addition of nitrogen did not aid the production of molecular ions of iodobenzene and dibromobenzene. When 0.07 ml min' of isobuiane was added to the LP-ICP mass spectra similar to those obtained by an electron impact source were observed. However, on the addition of more isobutane only the molecular ions (M*) for chlorobenzene, iodobenzene and dibromobenzene were observed. The detection limits for the instrument operating in the molecular mode were 100, 140 and 229 pg for chlorobenzene, iodobenzene and dibromobenzene respectively. Langmuir probe measurements were used to asses the effect of plasma forward power and gas flow rate on the local plasma potential, ion number density, electron temperature and electron number density within the LP-ICP. The local plasma potential varied from +50 V to -20 V depending on the plasma conditions used. The ion and electron number densities increased with increasing plasma power, with ion number densities of approximately 10^ cm' ^ and electron number densities of approximately at 10* cm ^ The effect of extra plasma gas had a less distinct affect on the plasma excited species. A plasma sustained at 6 W, 7 ml min'' helium and 1.8 ml min'* isobutane was used to provide both quantitative and qualitative information of tetraethyllead in the standard reference friel (NBS SRM 1637 II), with .the determined value of 13.06 ± 0.91 being in good agreement with the certified value of 12.9 ± 0.07 expressed as total lead.

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The work detailed in this thesis concerns polymers synthesised by R.F. inductively coupled plasmas excited in fluorine containing monomer vapours. The structure and bonding in a series of polymers prepared from per-fluoroaromatic monomers by plasma polymerization was investigated by ESCA. The composition and structural features of these films were compared and contrasted with each other and with plasma polymers derived from the same parent compounds with lower degrees of fluorination. Critical emission spectra, ~260-600nm, from these plasmas were recorded and a correlation made between certain species fluorescing in the gas phase and functional groups within the polymer. An association hcis also been made between the peaks at ~280 and ~510nm in the optical emission spectrum. Difluorocarbene is responsible for the peak at ~280nm but the peak at 510nm has an unknown origin. The effect of copolymerizing a fluoroaronatic compound with a second component on polymer composition has been examined, where the comonomer has ranged from an inert gas to an organic hydrocarbon analogue. Copolymerizaticn resulted in a stabilisation of the rearrangement mechanisms normally associated with the plasma polymerization of a perfluoroaromatic compound; CF=CF(_n) and CF(_2) groups were greatly reduced in intensity in the ccpolymer. The binding energy of the CF-CF(_n) peak indicated that the component peak was, in fact, due to CF-CF(_aromatic) i.e. copolymerization had also resulted in a greater retention of the aromatic nature of the parent fluorocotpound. Polymers were also prepared by irradiating the monomer vapour with wavelengths >130nm. Perfluorobenzene could not be polymerized with UV irradiation of wavelengths greater than 200nm, but could however be polymerized with wavelengths below 200nm. This produced a polymer whose composition, as determined by ESCA, was very similar to the composition of plasma polymers derived from the same monomer indicating that the mechanisms involved in both polymerizations are similar. Vibrationally excited ground state perfluorobenzene is thought to be involved in the reaction pathway.

In this Thesis the processes of electron emission from cathode electrodes are studied theoretically, and the applicability of these mechanisms to the non refractory cathodes that can be used to sustain thermal arcs was examined. Apparatus that was used to generate and manipulate thermal arcs along rail electrodes is described in this thesis. Techniques for driving arcs over polished sample electrodes with magnetic or aerodynamic forces are outlined. Scanning electron microscopy was used to study emission site formation on highly polished electrodes with a natural 2.5 nm oxide layer. Theoretical maximum electron current densities that can be extracted by the arc were calculated and these were used, in conjunction with information from the experimental work, to make estimates of the lifetime of emission spots that are seen on the cathode electrodes of thermal arc devices. The lifetime was found to be dependent on the arc velocity over a range of velocity values from 3 to 80 ms(^-1). The lifetime measured ranged from 2.4 µs to 0.024 µs. Experiments on arcs driven at a constant velocity using a combination of aerodynamic and magnetic forces showed that the formation of emission spots was independent of die applied external magnetic field. The presence of artificially grown copper (11) oxide layers, 50 nm and 100 nm thick, were found to influence the lifetime. The effect of the oxide layer was predicted using a simple model accounting for the change of resistance that such an oxide layer would be expected to cause. Additional experiments showed that the resistance of the arc was independent of the oxide layer thickness, as predicted by the model.

No description available.