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Measurement of the intrinsic properties of processing plasmas is critically important in understanding discharges so that the optimum conditions can be achieved. Several different diagnostic methods have been developed and tested. A planar probe has been used to measure the ion flux and electron temperature in both inductively coupled and capacitively coupled plasma systems, at various pressures and applied powers, using the assumption that the electron energy distribution is a Maxwellian.</p> Frequency modulation spectroscopy (FMS) has been used to detect species in a plasma. It has been shown to be very effective, giving a significantly increased S/N ratio compared to both single pass absorption and low frequency mechanical modulation techniques. It has been used to measure excited argon atom concentrations, in both capacitively and inductively produced plasmas. The argon atom 4s[3/2]₁ level concentration was found to be between 2 x 10⁸ and 1 x 10¹¹ atom/cm³ and to generally increase with increasing applied power and to decrease with increasing total pressure. The temperature of the atoms was also measured and was found to be approximately 323 ± 17 K. A simple compact laser source at 308 nm has been produced from a frequency doubled cooled commercial diode laser. This has been used to detect the OH radical, by absorption, within the afterglow of a microwave discharge, produced either directly or chemically. Simple kinetic models have provided explanations of the variations in OH concentration with discharge conditions. A novel method, cavity laser induced fluorescence (CLIP), that combines the advantages of both laser induced fluorescence (LIF) and cavity ring down spectroscopy CRDS, has been shown to increase the sensitivity of a diagnostic system compared to absorption. This method could be used to follow concentration variations of a reaction in a single laser shot. Although such variation can be observed using LIF, it requires a calibration and a many laser shot experiment with a signal recorded at each time point. Whilst CRDS allows temporal information about the absolute concentrations of the species observed to be obtained, it is not as sensitive as LIF. By combining the two in CLIP, it may be possible to retain the sensitivity of LIF with the advantage of CRDS so that absolute and time varying concentrations can be obtained in a single pulsed laser shot. LIF and CRDS signals have been observed using the A ²?_u ? X ²S_g⁺ transition of the N₂⁺ ion. The lifetime of the A ²?_u state in the discharge was found to be sufficiently long for a time of flight experiment to be contemplated (an ion with a velocity of 10 kms^-1 on average would travel 5 mm before radiating). Although the preliminary tests for the time of flight experiment have shown that this method is not feasible with a pulsed laser, the basic cavity locking procedures required for an analogous continuous wave experiment have been successfully demonstrated. A frequency doubled diode laser source has been constructed and tested, with the eventual aim of detecting N₂⁺ via the B ²S_u ? X ²S_g⁺ electronic transition. This has been found to be insufficiently intense to be used for a proposed two dimensional velocity mapping experiment, but several strategies to improve its performance are suggested.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph. D.)--University of California, San Diego, and San Diego State University, 2004. / Vita. Includes bibliographical references (leaves 215-217).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xv, 145 p.; also includes graphics (some col.) Includes bibliographical references (p. 138-145). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D. in Mechanical Engineering)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

The surface-specific analytical technique of X-ray photoelectron spectroscopy (XPS) is described, and was used to study various geochemical materials and organic compounds. Variation of surface pyrite density with coal particle size (53-250/µm) in a typical Canadian coal (Minto) provided some interesting data- it is very likely that as coal is crushed, one eventually reaches a particle size where the surface pyrite/carbon ratio maximizes. It is this parameter that is examined here, and correlations were found between (i) surface pyrite concentration,(ii) surface pyrite/sulfate ratio, and (iii) oxidized and non-oxidized sulfur with particle size. This is information which should find useful application in coal cleaning technology. For non-oxidized coal, we find the area of exposed pyrite on the coal surface is approximately inversely proportional to coal particle radius. However, for oxidized coal the appearance of curves depends on the oxidation times, but there is a particle size which exhibits maximum surface pyrite relative to 1/radius, corresponding to the intercept point of the two linear segments (low and higher values of 1/R) for the non-oxidized coal (fig. 3.9), and which is evidently that we will call the "characteristic" size of constituent pyrite. XPS 2p₃/₂ sulfur peaks from major sulfur constituents other than sulfate in sediment recovered from Mahoney Lake (south-central British Columbia, Canada) show a surprisingly periodic variation in sulfur 2p₃/₂ binding energy (BE), and hence molecular structure, with sediment age. The pattern ceases at a core depth of about 3.2 meters, where a major deposit of fine sandy sediment occurs just below ash deposition (2.6m) from a major eruption of Mount Mazama, Oregon, approximately 6500 year ago, which led to the formation of Crater Lake. Sedimental sulfur exists mainly as sulfate; however, there is a pronounced increase in amount of the lower BE sulfur species relative to sulfate toward lower depths. The "reduced" species also shows a trend towards slightly higher oxidation level at lower depths. We are able to suggest the probable chemical forms in which the sulfur species exist, which is of interest to biologists working on sulfur transformation studies in lakes. BE' s for nitrogen Is and sulfur 2p₃/₂ in the metal chelates of dibenzyldithiocarbamic acid M(DBDTC)n for n=2, M=Cu(II) and Zn(II), and for n=3, M=Bi(III), have been measured. The nature of the spectral peaks and core BE's indicates that the nitrogen atom in the DBDTC is not intramolecularly bound with the metal as had been previously suggested. The relatively high BE's for the nitrogen Is orbitals indicate planar geometry for the coordinated ligands, and the form [formula omitted] to reasonably represent their structure, which agrees with previous infrared studies. / Science, Faculty of / Chemistry, Department of / Graduate

In 2005, our group first reported a two-pulse multi-element analysis technique that was both sensitive and minimally destructive. The first laser pulse ablated a thin layer of the sample over a hundred m spot; the second laser pulse at 193 nm induced multi-analytes in the desorbed plume to fluoresce. Since then, this technique of laser-excited atomic fluorescence (LEAF) of ablated plumes, or PLEAF for short, had been applied to the analysis of aqueous lead colloids and metals. Sub ng/g and tens of atto-mole detection limits were demonstrated. The non-selective photoexcitation in PLEAF was believed to be due to smeared energy levels of species in dense plumes. Smearing was especially severe for highly excited states such as those reached by 193 nm excitation. As the plumes subsequently expanded, the electronic structure of the plume species evolved adiabatically from a dense gas to that of an isolated atom with the electrons still in the excited states. Signature fluorescence from multi-analytes was therefore possible. The suggested mechanism implied that ArF laser-induced PLEAF should be applicable to any sample matrix and any analyte as long as the species were imbedded in dense plumes and whose excited states could be reached by 193 nm photoexcitation. We therefore investigated the universality of PLEAF in this study by extending the analysis to ceramics, polymers, and their composites. We showed that these matrices could be successfully sampled and emissions from practically all analyte elements were observed. The detection sensitivity was orders of magnitude better than alternative laser spectrochemical probes such as laser-induced breakdown spectroscopy (LIBS). Under minimally destructive conditions, emissions from Al, Ca, Co, Cr, Cu, Fe, In, Mg, Mn, Na, Pb, Sn, and Si were observed. We also applied the technique to four practical problems: The analysis of dried paint for trace lead when g/g detection limits were achieved; the analysis of valuable potteries when two look-alike specimens were differentiated based on practically non-destructive single-shot analysis; the elemental analysis of ink when lines written with different pens could be discriminated yet without discernable sample destruction even under the microscope; and the analysis of electrode-plastic interfaces when the detection sensitivity was comparable to SIMS. In some of these applications, we found that the fluorescence intensity varied with the fluence and the timing of the ArF laser pulse in ways suggestive of particulates in the plume. Because nearly all analyte elements were excited in PLEAF, multi-analyte spectra were generated even in single-shot analysis. We showed that the rich spectral information contents could be fully exploited by chemometric techniques such as principal component analysis, SIMCA and K-means clustering. In sum, the combination of PLEAF and chemometrics paved way for ultra-sensitive and minimally destructive multi-element analysis of complex samples. The analysis was all-optical and therefore could be done in air with no restriction on sample size. No sample preparation was needed. The analysis was fast, with a turn-around time of minutes. At the end, the sample was not visibly damaged even when examined under the microscope. If the ablation could be congruent, 3-dimensional chemical profiling at tens to hundreds of m lateral resolution and tens of nm depth resolution would be possible.

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