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Introduction Method Results Summary
Surface Modification through Sulfur CompoundDeposition
Connor Glosser
University of Florida
Florida Society for Materials SimulationAugust 4, 2011
Introduction Method Results Summary
Outline
1 IntroductionIon Beam Deposition
2 MethodComputational DetailsSimulation
3 ResultsBondingSputtering
4 Summary
Introduction Method Results Summary
Ion Beam Deposition
Plasma Processing
Treating a surface with a plasma to alter chemical orphysical properties
AdhesionCleaning/SterilizationEtching
Introduction Method Results Summary
Ion Beam Deposition
What do we do?
Molecular Dynamics (MD) simulation24000+ atomsREBO potential (short range)Lennard-Jones potential (long range)Bottom-up approach
Polystyrene (PS) substrate placed in a simulated ion beam
Introduction Method Results Summary
Ion Beam Deposition
What do we look for?
Sputtering products from depositionsBonds formed with incident particlesDepth profile of incident particles(Ideally) crosslinking in substrate polymers
Introduction Method Results Summary
Computational Details
How do we do it?
Integrator: Velocity-verlet predictor-correctorLangevin thermostat; mimics heat dissipation of largersystemsBeam deposited along z-axis; x and y axes have periodicboundariesClassical potential assumes no electronic effects (charge,excitation)
Introduction Method Results Summary
Computational Details
Integrator
Verlet Algorithm
Forwards & backwards Taylor expansion of F = mx
r(t + ∆t) = r(t) + ∆t · v(t) +∆t2 · a(t)
2+ . . . (1)
r(t − ∆t) = r(t) − ∆t · v(t) +∆t2 · a(t)
2− . . . (2)
Velocity-Verlet is similar; uses average acceleration over the ∆ttime interval
Introduction Method Results Summary
Computational Details
REBO
REBO Potential
Eij =∑i,j>i
VR(rij)− bijVA
(rij)
Reactive Empirical Bond-Order potentialImprovement on standard Lennard-Jones potential; allowsfor covalent (single, double, triple) carbon bondingVr and Va govern repulsion and attraction, respectively; bijdetermines bonding
Introduction Method Results Summary
Computational Details
Thermostat
Thermostat system to maintain an average temperatureMimics heat dissipation in larger systemsLangevin Thermostat: adds “wind resistance”
Introduction Method Results Summary
Simulation
Procedure
1 Equilibrate substrate & incident particles2 Check relaxation time after 1 deposition3 Run several depositions4 Re-equilibrate system.5 Clear sputtered species from beam trajectory
Introduction Method Results Summary
Bonding
Snapshots
(a) Sulfur-Carbon (b) Sulfur-Hydrogen (c) Atomic Sulfur
Figure: Comparison of three substrates after 48ps
Introduction Method Results Summary
Bonding
Color-Coded
(a) Sulfur-Carbon (b) Sulfur-Hydrogen (c) Atomic Sulfur
Figure: Red: bonded to substrate, Blue: NonbondingPurple: Beam-bonding, Yellow (not shown): Noninteracting
Introduction Method Results Summary
Sputtering
Atomic Sulfur
0 50 100 150
0
20
40
60
80
100
Mass HuL
Freq
uenc
y
Introduction Method Results Summary
Sputtering
Sulfur-Hydrogen
0 20 40 60 80
0
5
10
15
20
25
Mass HuL
Freq
uenc
y
Introduction Method Results Summary
Sputtering
Sulfur-Carbon
0 20 40 60
0
2
4
6
8
10
12
Mass HuL
Freq
uenc
y
Introduction Method Results Summary
Summary
In conclusion...
REBO potentials effectively model large hydrocarbonsystemsPreliminary results confirm prior findings that faster-movingions have greater effectsAll three ions sputter predictable species
Future Work
Statistical comparison of current dataSimulation of multiple beam energiesExtension to more compounds
Appendix
Acknowledgements
Thank you!
Funding provided by the NSF REU programSpecial thanks for Dr. Susan Sinnott, Leah Hill, and TravisKemper at the University of Florida for project advisementand supervision