1 / 22

Pattern Formation via BLAG

Pattern Formation via BLAG. Mike Parks & Saad Khairallah. Outline. Simulate laboratory experiments If successfully simulated, proceed to new computer experiments. Phase 1: Deposition. Gold particles incoming onto the surface from a heat source. The particles will not move much at T=20K.

maura
Download Presentation

Pattern Formation via BLAG

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Pattern Formation via BLAG Mike Parks & Saad Khairallah

  2. Outline • Simulate laboratory experiments • If successfully simulated, proceed to new computer experiments.

  3. Phase 1: Deposition Gold particles incoming onto the surface from a heat source The particles will not move much at T=20K Xenon Substrate T=20K

  4. Phase 2: Desorbtion Xenon particles desorbing Gold particles walk randomly With a sticking probability of one they form clusters when colliding Thin xenon film acts as timer Substrate T>20K

  5. Final State: Clusters Final Equilibrium State: clusters on substrate (abrupt interface) Substrate T>>20K

  6. Control Parameters • Parameters for Cluster Creation: • The thickness of the xenon layer acts as a timer • Sticking probability coefficient ~1 (DLCA) • Surface coverage • External potential (???) • No need to satisfy thermodynamics constraints: • surface free energy and the three growth modes

  7. Results to simulate… • Weighted cluster size grows as S~t2 • Density decays as N~t-2. • Fractal dimension according to DLCA size ~ (average radius)^Dimension.

  8. - - - - + + + + …our contribution: • Charge the particles • Apply electric field perturbation Uniform E

  9. Simulation • Start with uncharged particles interacting on a square lattice with Lennard-Jones potentials. • When two atoms become adjacent, they bond to form a cluster. • Update simulation time as t = (# Atoms Moved)/(# Atoms), i.e. diffusion does not depend on time. • Simple metropolis algorithm No KMC: • We are not describing the dynamics on the surface. • Pattern formation via BLAG does not depend on time explicitly.

  10. Implementation Issues: • Need to efficiently determine when to merge clusters • Use bounding boxes on clusters and check for adjacent atoms only when boxes overlap • Linked-cell method implemented for L-J potentials

  11. The SIMULATIONS Performed • Uncharged particles: mimic experiment • Charged particles: uniformly distributed • Charged particles with uniform electric field: weak and strong

  12. Results (Uncharged) Initial Configuration Final Configuration

  13. Power Law Dependence(uncharged) Experiment: 1.9 +/- 0.3 Simulation: 2.00 +/- 0.03 Agreement!

  14. Fractal Dimension(uncharged) Agreement!

  15. Modification : Add Charge • Add a positive or negative charge of magnitude 1.6e-19 Coulombs to all atoms, such that the net charge is zero. • Distribute the charged particles uniformly over the lattice. • Clusters that form as to have no net charge interact only with L-J potential.

  16. Results (Charged Particles) Final Configuration

  17. Fractal Dimension(charged plus charged with e-field) Fractal: New results. We see same dimension as with no charging.

  18. Power law : Size~t2

  19. Interpretation… The effect of charging subsides according to coverage: • Fast decay if high coverage: particles neutralize each other quickly • Slow decay if low coverage: particles neutralize each other slowly

  20. Interpretation… • When charging effect subsides fast, L-J takes over giving close results to exp. • When charging effect subsides slow, Coulomb potential acts longer altering results from exp.. • So what does the electric field do?

  21. Electric Field Effect… • The electric field accelerates the process of particles neutralizing each other making the charge effect decay fast. • We expect L-J to dominate on the long run • Hence results closer to experiment

  22. Future work… • The model, DLCA based on sticking probability coefficient ~1: so change that number allowing for non-sticking collisions. • Have a metallic substrate to alter the potential with an image potential • Apply varying electric field • More complicated: 3D clusters.

More Related