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Title:Binding and diffusion of a silicon adatom on silicon (001) surface: An atomic scale simulation
Author(s):Wang, Jun
Doctoral Committee Chair(s):Rockett, Angus A.
Department / Program:Materials Science and Engineering
Discipline:Materials Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Physics, Condensed Matter
Engineering, Materials Science
Abstract:The properties of a silicon adatom on Si(001) surface and around three single-layer steps, namely type A (S$\rm\sb A$), bonded type B (S$\rm\sb B$) and nonbonded type B (S$\rm\sb{B\sp\prime}$), on Si(001) have been studied, using a modified empirical and first-principle methods. The results presented in this thesis, providing the atomistic scale details of the adatom-surface interactions, represent an improved understanding to the growth of a technologically important material and surface, Si(001). These results indicate that single-layer steps on Si(001) do not serve as good sinks for the lone adatoms. The presence of the step on the surface may affect the growth behavior of the surface by changing the nucleation rate of the surface dimers and diffusivity of the adatoms. It is shown that there is a moderate additional energy barrier (0.2 $\pm$ 0.1 eV) to cross the S$\rm\sb A$ step. The dimer-top lattice site on the lower terrace adjacent to the step edge is stabilized (by 0.15 $\pm$ 0.1 eV) with respect to the flat surface result although the most stable binding sites near the step are unaffected. This behavior can be understood based on the disruption of dimer tilt near the step. The results suggest that adatoms are more likely to stop on lattice sites at the S$\rm\sb A$ step edge than on lattice sites on the open surface. This may affect the relative dimer formation rate near the step with respect to the behavior on the flat surface even in the absence of a clear change in binding energy. The effect of the S$\rm\sb A$ step terrace edge on adatom behavior is very short ranged and weak. This is consistent with the relatively small strain field and lack of change in dangling bond density associated with the step edge. The growth of the S$\rm\sb A$ step is proposed to be limited by nucleation of new dimer rows along the step edge. The results suggest that the S$\rm\sb{B\sp\prime}$ step should accumulate adatoms rapidly both from above and below. The energy barrier to cross the S$\rm\sb{B\sp\prime}$ step is $\sim$0.2 eV greater than for diffusion on the flat surface. The binding sites along the S$\rm\sb{B\sp\prime}$ step edge are similar to those on the flat surface but are paired and connected by a low-energy diffusion pathway that may facilitate formation of dimers along the step edge. The S$\rm\sb B$ step attracts adatoms ${\sim}0.5\pm0.2$ eV more strongly than any other site on the surface. However, these sites are relatively inaccessible due to surrounding high energy barriers. Based on the results, the upper side of the S$\rm\sb B$ step should be repulsive to adatoms. The diffusion barrier for adatoms approaching the step rises and the binding sites become less favorable there. Hence, growth of the S$\rm\sb B$ step is probably much slower than the S$\rm\sb{B\sp\prime}$ step, which explains its observed predominance on Si(001) surfaces. It is proposed that growths of both B type steps are flux limited and hence are highly temperature dependent.
Issue Date:1995
Rights Information:Copyright 1995 Wang, Jun
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9543761
OCLC Identifier:(UMI)AAI9543761

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