Self Diffusion in Silicon
What are the changes in configuration and energy as the silicon atom migrates into the neighboring vacant site?
adesh.zip
:Click HERE to Download a DEMO version of ADESHADESH works on PC-DOS. You will need the pkunzip.exe utility for this zipped file. ADESH works on MAC and UNIX workstations in a DOS window.
Answer
ADESH produced following results in a few minutes, on a PC with a Pentium (P5-133) micro-processor.
Figure 1
Green silicon atom migrates into a vacant neighboring site.
The calculations were performed with the MIGRATE utility
that accompanies the basic version of ADESH. It took about twenty
minutes of CPU time on a PC (P5 - 133).
Figure 1 shows the intermediate atomistic configurations
as the green silicon atom migrates.
At first, the neighbors
of the atom move with it. About halfway through,
the neighbors are no longer "visible" or attached to the
moving atom because they are out of the cutoff radius for
the potential function. New meighbors are formed.
Sometimes as many as seven.
Old neighbors, no longer 'connected' to the moving atom,
move away from it.
The movements of neighbors are
obvious. In the final, new position, the energy of the atom
is similar to the starting postion.
Green atom is migrating into a vacant site
marked with black circle.
Figure 2 Changes in the Configurational Energy During Migration of a Vacancy in Silicon
Figure 2 shows activation energy barrier for moving silicon atom into a neighboring vacant site.
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