Kris's Research Notes

May 30, 2011

Basic Mixtures

Filed under: GaAs Simulations — Kris Reyes @ 3:09 pm

In this post, we consider a two species system where a droplet of species B sits on a substrate of species A. The atoms occupy positions on the same lattice as our GaAs system. Atoms move by hopping — exchanging with an adjacent vacuum position. There are no atom-atom exchanges. We have three types of bonds which occur in the system: \gamma_{AA}, \gamma_{BB}, \gamma_{AB}. These are bonds between two A atoms, two B atoms and an A and B atom, respectively.

We fix the temperature at T = 900K and allow the system to anneal for 1000 seconds. We vary the bond energies:

\displaystyle \gamma_{AA}, \gamma_{BB} \gamma_{AB} = \left\{ 0.9, 1.0, 1.10\right\} eV.

Here are the results of the simulation. The plots are organized into three groups of nine. Each group corresponds to a fixed $\gamma_{AB}$. Each row is a fixed \gamma_{AA}, increasing from 0.9 to 1.10. Similarly, each column fixes \gamma_{BB}.

\gamma_{AB} = 0.90 eV

\gamma_{AB} = 1.0 eV

\gamma_{AB} = 1.10 eV

Consider the \gamma_{AB} =1.10, \gamma_{AA} = \gamma_{BB} = 0.9 case. Here are movies for the system over 10, 20, 1000 and 5000 seconds.

10 seconds

20 seconds

1000 seconds

5000 seconds

We note that most of the A-B mixing occurs within the first 20 seconds. It seems that the system comes to an equilibrium by 1000 seconds — by then there is no more A-B mixing, just A atoms diffusing on the surface.

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