Thesis (MTech. degree in Chemistry)--Tshwane University of Technology, 2010. / Discusses an accurate and sensitive method for the determination of trace levels of mercury in environmental air samples may be established using cost effective technologies.

published_or_final_version / Chemistry / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 184-188).

Thesis (Master of Science)--Miami University, Dept. of Physics, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], ???, ??? p. : ill. Includes bibliographical references (p. Xx-Xx).

Desde o desenvolvimento de técnicas para controlar o movimento atômico usando a força de pressão de radiação, muitas aplicações tem sido sugeridas e implementadas. Entre estas, o aprisionamento atômico e o desenvolvimento de estruturas espaciais com átomos frios merece atenção especial devido à sua potencial aplicação em depósitos superficiais como litografia. Realizamos, neste trabalho, um estudo sobre feixes atômicos e sua desaceleração e compressão espacial. Realizamos também estudos numéricos sobre a formação de estruturas em anéis em feixes atômicos, verificando ser factível, e estudando também a compressão destas estruturas espaciais, com vistas a possíveis aplicações em nanolitografia atômica. / From the very beginning of the development of atomic motion control techniques using the radiation pressure force, a variety of applications have been suggested and implemented. Of all these, atomic trapping techniques and the development of spatial structures using cold atoms deserves special attention due to its potential application to surface deposition such as lithography. In the present work, we perform a study on atomic beams and their deceleration and spatial compression. We also perform numerical studies and present experimental observation of the realization of spatial ring structures in atomic beams, verifying its factibility, and we study the compression of such ring-shaped structures with application in atomic nanolithography as the ultimate goal.

An atmospheric pressure radio frequency capacitively coupled plasma (CCP) has been developed and characterized for applications in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and gas chromatography (GC). The CCP torch was initially designed as an atom reservoir for carrying out elemental analysis using atomic absorption. Functionally, the device consists of two parts, the CCP discharge tube and the tantalum strip electrothermal vaporization sample introduction system. The torch design provides for very effective energy transfer from the power supply to the plasma by capacitive coupling. Therefore, the plasma can be generated at atmospheric pressure with a flexible geometry. The plasma can be operated at very low rf input powers (30-600 W) enabling optimal conditions for atom resonance line absorption measurements. Absorption by the analyte takes place within the plasma discharge which is characterized by a long path length (20 cm) and low support gas flow rate (0.2 L/Min). Both of these characteristics ensure a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of 3.5-40 pg. A preliminary measurement gave a Fe I excitation temperature of approximately 4000 K for the discharge. At this temperature, potential chemical interferences are likely to be minimal. Chemical interferences for Fe, Al, As, Ca, Co, Cd, Li, Mo and Sr were negligible in the determination of silver. Chloride interference, which is prevalent in GF-AAS, was not found. The amount of Ag found in a SMR#1643b (NIST) water sample was 9.5 ± 0.5 ng/g which fell in the certified range of 9.8 ± 0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added to the SRM and recoveries were found to be in a range from 105 % to 96.2 %. The RSD obtained for 7 replicates of 270 pg silver was 4.6 %. The results for the CCP AES are even more promising. The interferences of thirteen elements are negligible in the determination of silver. The chloride interference was not found. The detection limits for Ag, Cd, Li, Sb and B are 0.7, 0.7, 2, 80 and 400 pg respectively. The amount of silver found in a SRM#1643b (NIST) water sample was 9.3 ± 0.5 ng/g which also fell in the certified range of 9.8 ±0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added into the SRM#1643b (NIST) samples; the recoveries were found to range from 97 % to 104 %. The RSD obtained for 7 analyses of 270 pg silver were 1.5 % for CCP-AES. It was also found that the signal to noise ratios (S/N) are higher in the AES mode than those in the AAS mode in the same CCP atomizer. In order to exploit advantages inherent in both GF-AAS and I CP-AES, an atmospheric pressure capacitively coupled plasma sustained inside a graphite furnace was developed. This source combines the high efficiency of atomization in furnaces and the high efficiency of the excitation in atmospheric pressure plasmas. In general, plasma sources are able to effectively excite high-lying excited states for most metals and non-metals and can also ionize vaporized elements. Therefore the possibility exists of using non-resonance lines to avoid the effects of self-absorption at high analyte concentrations. Ion lines may also be used in cases where they provide better sensitivity or freedom from spectral interferences. This source also offers the ability to independently optimize vaporization and excitation. However, the most important aspect of this new source is that it can be used for simultaneous, multielement determinations of small sized samples in a graphite furnace atomizer, a design which has been proven to be effective over many years of use. Preliminary quantitative characteristics of this new atmospheric pressure plasma emission source have been studied. The detection limit for Ag of 0.3 pg is lower than the value of 0.4 pg reported for GF-AAS. Variants of the CCP, including a gas chromatography (GC) detector, combinations of laser ablation - CCP, rf sputtering - CCP direct solid analysis, and its application as an intense spectral lamp have been developed and are reported in this dissertation. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Spectroscopic investigations have been carried out on hollow cathode discharges adapted from laser technology for use as a spectroscopic light source and the argon inductively coupled plasma (ICP) as an excitation source for nonmetal emission. High and low voltage aluminum and copper hollow cathode discharges were studied as a source of ionic and resonant atomic metal emission. The high voltage versions achieve strongly positive current-voltage behavior through utilization of the obstructed discharge phenomenon. The current-pressure-intensity-voltage relationships for low and high voltage copper hollow cathode discharges were studied with the inert gases He, Ne, Ar, Kr, and Xe. The intensity for copper resonant atomic emission with the fill gases Ar, Kr, and Xe improved relative to neon in the high voltage lamp when compared to the low voltage lamp. Absorption measurements through the cathode bore show the ground state atom density to increase with the atomic weight of the fill gas at any given level of intensity, at the fill gas pressure yielding highest resonant atomic copper emission. The estimated ion/atom intensity ratio is increased with fill gases which have metastable or ionization energies greater than the excitation energy of the ion transition. A copper hollow cathode lamp incorporating a short positive column discharge in front of the cathode opening was investigated for its lineshape as measured spectroscopically and by its atomic absorption sensitivity. Incorporation of this positive column allowed higher intensities to be obtained at the same line quality as a commercial hollow cathode lamp. An enlarged cathode volume also improves the lineshape at a given intensity. Inductively coupled plasma spectra for the elements C, O, N, Cl, P, S, and Br were obtained in the vacuum ultraviolet utilizing a vacuum polychromator and SWR film. The detection limit for injected O₂ and N₂ detected electronically by the VUV emissions is 1.3 and 0.9 micrograms respectively with this system. A VUV filter photometer was utilized for oxygen and phosphorus analysis. The detection limit for injected oxygen was 1 microgram with this photometer; the detection limit for phosphorus as inorganic phosphate in aqueous solution is 10⁻³ M. The bandpass of the photometer limits its selectivity.

Light actinides and copper systems were studied using resonant soft X-ray spectroscopy. An instrumental and experimental setup for soft X-ray spectroscopy meeting the requirements of a closed source for radioactivity was developed and described in detail. The setup was used for studies of single-crystal PuO2 oxidation. The existence of higher oxidation state than Pu(IV) in some surface areas of the single crystal were found from O 1s X-ray absorption measurements. Furthermore, from comparison with first principles calculations it was indicated that plutonium oxide with Pu fraction in a higher oxidation state than Pu(IV) consists of inequivalent sites with Pu(IV)O2 and Pu(V)O2 rather than a system where the Pu oxidation state is constantly fluctuating between Pu(IV) an Pu(V). It was shown that a combination of resonant O Kα X-ray emission and O 1s X-ray absorption spectroscopies can be used to study electron correlation effects in light-actinide dioxides. The electronic structure of copper systems was studied using resonant inelastic soft X-ray scattering and absorption spectroscopy. It was found that X-ray absorption can be used to monitor changes in the oxidation state but as differences between systems with the same oxidation state are in many cases small, speciation is uncertain. Therefore, a method utilizing resonant inelastic X-ray scattering as fingerprint to characterize complex copper systems was developed. The data recorded at certain excitation energies revealed unambiguous spectral fingerprints for different divalent copper systems. These specific spectral fingerprints were then used to study copper films exposed to different solutions. In particular, it was shown that resonant inelastic X-ray scattering can be used in situ to distinguish between CuO and Cu(OH)2, which is difficult with other techniques.