# 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 $\gamma_{BB}$.

### $\gamma_{AB} = 1.10 eV$

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.