Diffusion and Evaporation of Nitrogen on Tungsten (100)
Coulman, Donald James
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https://hdl.handle.net/2142/77309
Description
Title
Diffusion and Evaporation of Nitrogen on Tungsten (100)
Author(s)
Coulman, Donald James
Issue Date
1984
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Surface diffusion and evaporation from a layer of nitrogen chemisorbed on the (100) plane of tungsten has been examined using Auger spectroscopy. The initial localized deposit required for diffusion measurements in a concentration gradient is created by a highly collimated molecular beam. The sample, under computer control, is moved across an electron beam, and the Auger spectra are recorded automatically at different points on the surface. Nitrogen diffusion over the (100) tungsten surface was found to be concentration independent, taking place over a barrier of 28 kcal/mole with a prefactor D(,0) of 3.0 x 10('-2)cm('-2)/sec. At the temperatures 900 < T < 1050 K necessary to observe spreading on the order of 50-100 (mu)m in the concentration profile evaporation was found to be a competing process. Therefore, the desorption kinetics of (beta) chemisorbed nitrogen on W(100) was studied by a combination of Auger spectroscopy and flash desorption. The activation energy for desorption was found to be 82 kcal/mole with a prefactor of 0.01 molecules/(cm('2)sec). A comparison with the diffusion of nitrogen on the W(110) surface is made, showing for the first time the effect of surface structure on the diffusion of a chemisorbed gas on a solid surface.
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