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