2026-09-20T08:09:24Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/21598 2023-07-10 col_2142_5131 col_2142_11615 com_2142_5130 com_2142_9130 com_2142_8903

10000-01-01 1996 Seebauer, Edmund G. Allen, Clark Eldon 2011-05-07T13:13:26Z 2011-05-07T13:13:26Z Surface diffusion is of fundamental importance in a variety of industrial kinetic processes, including surface reactions, crystal growth and sintering. However, surface diffusion parameters are rarely used to model industrial processes, resulting from three deficiencies in the literature. First, of the significant amount of work done in the laboratory, only a fraction has been conducted under real industrial temperatures. Second, no sufficient predictive models existed previously to estimate surface diffusion parameters. Third, for chemical reactions at surfaces, no simple method existed to determine whether a reaction might be diffusion-limited. This work attacks these deficiencies from experimental, theoretical and computational points of view. Experimentally, mass transfer diffusion of antimony and indium on Si(111) was studied under real industrial temperatures using the newly developed technique second harmonic microscopy (SHM). Activation energies and pre-exponential factors for the two systems are presented in terms of a mass transfer diffusion mechanism. Also discussed are recent improvements to the SHM technique, including signal-enhancing (factor of 2500) and resolution-enhancing (factor of 2) procedures. Second, a new physical picture and empirical model have been developed to predict diffusivities of adsorbates on metallic, semiconducting and insulating substrates for both the intrinsic and mass transfer diffusion regimes. The empirical model is based upon the most comprehensive review in the literature, compiled expressly for this purpose. Theoretical considerations are employed in order to approximate from first principles the energies and entropies associated with the different diffusion mechanisms. The new physical picture for mass transfer diffusion was verified computationally by the molecular dynamics study of Ge/Si(111) in conjunction with experiments conducted concurrently and independently in this laboratory. Finally, both theoretical and computational methods were employed to develop a potential laboratory experiment to allow one to determine whether a recombinative surface reaction is diffusion-limited. Monte Carlo simulations, in conjunction with a finite difference approach to Fick's Law, prove that diffusion-limited desorption leads to an average radial distribution of adsorbate about any reference atom which is history dependent not only on time, but also on the initial concentration. Thus, for a particular coverage, one should measure different reaction rates dependent only upon the initial coverage. Made available in DSpace on 2011-05-07T13:13:26Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9712187.pdf: 12562455 bytes, checksum: 972c42e08594133bc293438f589e386b (MD5) Previous issue date: 1996 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:51:52Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:23:51-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only 9780591197280 AAI9712187 (UMI)AAI9712187 http://hdl.handle.net/2142/21598 eng Copyright 1996 Allen, Clark Eldon Chemistry, Physical Engineering, Chemical Physics, Atomic New understandings of surface diffusion text Chemical and Biomolecular Engineering Chemical Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.