No description available.

No description available.

Thesis (doctoral)--University of Turku.

In this thesis two studies of reactive metal adsorption upon a low index single crystal silicon dioxide surface are presented in addition to a study of sulphur adsorption upon a low index single crystal nickel surface. Chromium growth upon the a-quartz Si02(0001) (J84xJ84) Rll 0 surface is studied at three coverages, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±0.33 ML, using surface extended x-ray absorption fine structure (SEXAFS). SEXAFS measurements, from the chromium K-edge, recorded at both grazing and normal incidence show that chromium growth proceeds via the formation of mesoscopic particles with a body centred cubic (b.c.c.) like structure having an average nearest neighbour Cr-Cr distance of 2.36±O.03 A. This represents a contraction of 5.6 % from the bulk b.c.c. lattice spacing of 2.49 A. There is no evidence of a surface reaction between chromium and the surface oxygen. SEXAFS was used to study titanium reactional growth on a-quartz (0001) (J84xJ84) Rll 0 and (lx1). Three nominal coverages were studied, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±O.33 ML. Both normal and grazing incidence SEXAFS data were recorded and show the formation of a spatially extensive region in which an interfacial reaction has occurred between surface oxygen and adsorbate titanium atoms. Coupled with this is the formation of subnanometre titanium clusters. The metal oxide has nearest neighbour Ti-O distances close to those of both the anatase and rutile forms of titania with the metallic titanium clusters having a Ti-Ti distance within experimental error that of bulk hexagonal close packed (h.c.p.) titanium, 2.89 A. A re-examination of the surface geometry of Ni(1l0)c(2x2)S using SEXAFS has been performed. Data out to an electron wavevector of 9 A-I are analysed with a new code to assess the influence of multiple scattering. The first shell S-Ni distance is determined to be 2.20±O.02 A with the next nearest neighbour distance being 2.29±O.02 A, giving a top-layer Ni expansion of 14±3% relative to the bulk. The influence of multiple scattering does not significantly alter these values from earlier studies.

No description available.

This study employed a commercial code FLUENT to simulate a chemical vapor deposition process in a rectangular chamber for deposition of a silicon dioxide layer on a rectangular substrate. We focus on the deposition rate and heat transfer coefficient (Nu number) on the substrate surface. We discuss the effects of the size of inlet region, the distance from inlet to substrate, the size of outlet region, the Reynolds number, the temperature of substrate, the ratio of the inlet flow rates of the two reaction gases on the deposition rate. The results show that the four corners at the substrate has the lowest deposition rate no matter how the variables are changed. Near the four corners there exist a region with high deposition rate. The deposition rate is more uniform when inlet is larger or equal to the substrate, and when the distance between the inlet and the substrate is small. The larger the size of the outlet region, the larger the uniform deposition rate region present on the central part of the substrate. The deposition rate increases with increasing Re number. However the uniformity remains similarly. The deposition rate also increases with increasing the substrate temperature. A study of the inlet flow rate ratio of TEOS and indicates that TEOS flow rate governs the process. A proper flow rate ratio gives a better deposition rate.

This study employed a commercial code to simulate a chemical vapor deposition process in a rectangular chamber for deposition of a silicon dioxide layer on a rectangular substrate. We focus on the deposition rate on the substrate surface. We discuss the effects of the Reynolds number, the distance from inlet to substrate, the size of inlet region, the temperature of the inlet region, and the temperature of substrate. The results show that as the temperature increase, the deposition rate on the substrate grows highly. This effect will decrease if the temperature is above the specific range. Besides, it is easily deposited unequally on the edge and corner region of the substrate. However, the central region on the substrate is still uniform. We could get bigger uniform area to adjust the proper conditions.

Thesis (M.S.P.H.)--University of Michigan, 1942.

Thesis (M.S.P.H.)--University of Michigan, 1942.

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