pattern formation via blag
Download
Skip this Video
Download Presentation
Pattern Formation via BLAG

Loading in 2 Seconds...

play fullscreen
1 / 22

Pattern Formation via BLAG - PowerPoint PPT Presentation


  • 94 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Pattern Formation via BLAG' - maura


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
pattern formation via blag

Pattern Formation via BLAG

Mike Parks & Saad Khairallah

outline
Outline
  • Simulate laboratory experiments
  • If successfully simulated, proceed to new computer experiments.
phase 1 deposition
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

phase 2 desorbtion
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

final state clusters
Final State: Clusters

Final Equilibrium State:

clusters on substrate

(abrupt interface)

Substrate

T>>20K

control parameters
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
results to simulate
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.
our contribution
-

-

-

-

+

+

+

+

…our contribution:
  • Charge the particles
  • Apply electric field perturbation

Uniform E

simulation
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.
implementation issues
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
the simulations performed
The SIMULATIONS Performed
  • Uncharged particles: mimic experiment
  • Charged particles: uniformly distributed
  • Charged particles with uniform electric field: weak and strong
results uncharged
Results (Uncharged)

Initial Configuration

Final Configuration

power law dependence uncharged
Power Law Dependence(uncharged)

Experiment:

1.9 +/- 0.3

Simulation:

2.00 +/- 0.03

Agreement!

modification add charge
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.
results charged particles
Results (Charged Particles)

Final Configuration

fractal dimension charged plus charged with e field
Fractal Dimension(charged plus charged with e-field)

Fractal:

New results. We see same dimension as with no charging.

interpretation
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

interpretation1
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?
electric field effect
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
future work
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.
ad