Kris's Research Notes

December 17, 2010

Droplet Experiments — Movies

Filed under: GaAs Simulations — Kris Reyes @ 8:24 pm

Here are the movies for all droplet experiments I have done:


December 16, 2010

Droplet Size Experiments — Deposited Gallium Histogram

Filed under: GaAs Simulations — Kris Reyes @ 5:25 pm

This is a follow-up to this post.

In that post, I described how the experiment was run. I deposited 4 monolayers of Gallium, then annealed for 30 seconds. To deposit 4 monolayers of Gallium, I specified that Gallium should be deposited for 4 \times \frac{1}{r_{\downarrow Ga}} seconds, since r_{\downarrow Ga} is flux with units monolayers/second. As a result, the experiments will not deposit 4 monolayers exactly. This could be a problem. (more…)

December 10, 2010

Droplet Size Experiments — Part 6. Low Temperature and Arrhenius Plots

Filed under: GaAs Simulations — Kris Reyes @ 2:38 am

This is a follow up to this post. Here we repeat the droplet size experiments, but include lower temperatures. We also consider different intra-droplet bonding energies and present Arrhenius plots of droplet size with respect to inverse temperature. (more…)

December 8, 2010

KMC Code Description

Filed under: GaAs Simulations — Kris Reyes @ 1:40 am

This note briefly explains how I get the KMC code up and running. To run the simulation, we must generate 6 files, which we describe below.

  1. Energy file — contains pairwise bonding energy between extended species, desorption potentials and diffusion coefficients;
  2. Profile file — the atom configuration used to initialize the simulation;
  3. Graph file — the underlying lattice (more generally, graph) the atoms occupy;
  4. Species file — how an extended species of an atom is determined from its local neighborhood;
  5. Legal Neighborhoods file — lookup tables that specify whether an event is legal for a given local neighborhood;
  6. Trial File — points to the other files as well as specifying the remaining parameters of the simulation. (more…)

December 2, 2010

Droplet Size Experiments — Part 5. Sample Profiles

Filed under: GaAs Simulations — Kris Reyes @ 6:14 pm

Here are sample profiles for each trial described in this post. For each (T, r_{\downarrow Ga}) pair, we ran 16 trials. Here are sample final height profiles (truncated to 256 atoms) for each pair. Each plot has the actual height profile and the smoothed profile used in calculating both the autocorrelation function and droplet histograms. The plots are ordered by Temperature in rows and by Ga Flux in columns. (more…)

Droplet Size Experiments — Part 4. Droplet Size Histograms

Filed under: GaAs Simulations — Kris Reyes @ 6:07 pm

Here are histograms of droplet width, height and mass described in this post. Each row correspond to a fixed (T, r_{\downarrow Ga}) pair ordered first by temperature, then by flux. The columns correspond to width, height and mass, respectively. (more…)

Droplet Size Experiments — Part 3. Autocorrelations

Filed under: GaAs Simulations — Kris Reyes @ 5:53 pm

Here are the autocorrelation functions described in this post. The rows correspond to temperature, increasing from 450K to 600K. The columns correspond to increasing Ga flux, from 0.1 monolayers/sec to 0.4 monolayers/sec. In each plot, we also indicate the average droplet size as calculated with histograms (red) and autocorrelation (green). (more…)

Droplet Size Experiments – Part 2

Filed under: GaAs Simulations — Kris Reyes @ 7:59 am

This is a follow-up to this post.

Previously, we had observed that the droplet widths we had previously obtained were wrong because we did not have enough droplets to meaningfully calculate such statistics. So I repeated the experiments on a lattice of width 8192 atoms. (more…)