Ehrlich–Schwoebel barrier
otherwise
Schwoebel barrier
(rus. барьер Эрлиха-Швобеля)
—
additional diffusion barrier, encountered by a surface atom, when crossing an atomic step.
Description
The effects of an atomic step on the diffusion of atoms on the surface can be represented by the diagram below (see Fig.) illustrating the potential relief pattern close to the step.
As you can see, an atom that collides with the step on the lower side may bond to the step, as the adsorption site on the lower terrace in close proximity to the step is characterised by a large number of nearest neighbours as compared with an atom on the terrace and, consequently, has higher binding energy. An atom that approaches the step on the top side meets a barrier that can be even greater than the diffusion barrier on the terrace Ediff. An additional barrier ΔEES, known as Ehrlich–Schwoebel barrier, is due to the fact that when crossing a step edge an atom passes through the area with a low number of nearest neighbours.
The concept of the Ehrlich–Schwoebel barrier is widely used in analysis of many morphological transformations on the surface. However, there is no reliable experimental measurement of its value. It appears that it does not exceed few tenths of an eV.
As you can see, an atom that collides with the step on the lower side may bond to the step, as the adsorption site on the lower terrace in close proximity to the step is characterised by a large number of nearest neighbours as compared with an atom on the terrace and, consequently, has higher binding energy. An atom that approaches the step on the top side meets a barrier that can be even greater than the diffusion barrier on the terrace Ediff. An additional barrier ΔEES, known as Ehrlich–Schwoebel barrier, is due to the fact that when crossing a step edge an atom passes through the area with a low number of nearest neighbours.
The concept of the Ehrlich–Schwoebel barrier is widely used in analysis of many morphological transformations on the surface. However, there is no reliable experimental measurement of its value. It appears that it does not exceed few tenths of an eV.
Illustrations
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A schematic image of potential surface topography near a stage. ΔEES is the Ehrlich-Schwoebel barrier that the atom on the surface (a dark circle) has to bridge in addition to the Ediff diffuse barrier on the terrace in order to cross the edge of stage and descend to the lower terrace. |
Author
- Saranin Alexander A.
Sources
- Schwoebel R. L. Step motion on crystal surfaces // J. Appl. Phys. 1966. V. 37, №10. P. 3682–3686.
- Ehrlich G., Hudda F.G. Atomic view of surface self-diffusion: Tungsten on tungsten // J. Chem. Phys. 1966. V. 44, №3. P. 1039–1049.