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Molecular Dynamics Study of Ballistic Rearrangement of Surface Atoms During Ion Bombardment on Pd(001) Surface. Sang-Pil Kim and Kwang-Ryeol Lee Computational Science Center Korea Institute of Science and Technology, Seoul, Korea [email protected] (S.-P. Kim), [email protected] (K.-R. Lee). - PowerPoint PPT Presentation
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Molecular Dynamics Study of Ballistic Molecular Dynamics Study of Ballistic Rearrangement of Surface Atoms During Rearrangement of Surface Atoms During
Ion Bombardment on Pd(001) SurfaceIon Bombardment on Pd(001) Surface
Sang-Pil Kim and Kwang-Ryeol Lee
Computational Science CenterKorea Institute of Science and Technology, Seoul, Korea
[email protected] (S.-P. Kim), [email protected] (K.-R. Lee)
Ion Bombardment (Sputtering)Ion Bombardment (Sputtering)
Deposition Film coating
Ion bombardmentIon bombardment Surface treatmentSurface treatment
Science, 285, 1551 (1999).
- Most works utilized sputtering as deposition tool are focused on the reaction phenomena between recoiled ions from the target and substrate atoms to deposit.
- Since a possibility to manufacture the nano patterns on the surface was introduced, it has taken an enormous attention to researchers.
- Such a peculiar process resulted in enhancing the possibility for designing nano sized patterning by cheap and simple method.
ApplicationsApplicationsChaudhari et al., NATURE 411, 56 (2001)
Ordered adsorption of large molecules
Facsko et al., SCIENCE, 285, 1551 (1999)
Optoelectronic devices
Azzaroni et al., APL 82, 457 (2003)
Molding templates
De
po
sit
ion
Sp
utt
eri
ng
Moroni et al., PRL 91, 167207 (2003)
Manipulating magnetism
Catalytically active surface
Manipulating film texture
Theoretical ApproachTheoretical ApproachSigmund theorySigmund theory
• Agreement: ripple formation/ orientation• Disagreement: in-plane ordering, wavelength
coarsening• Toward improvement
Nonlinear terms considered New terms included to the equation (ex. shadowing effect, surface anisotropy…)
* P. Sigmund, Phys. Rev. 184, 383 (1969).
• Incident energy spreading: Gaussian
Local correction to the uniform flux due to non-flat geometry
• Normal erosion velocity at O
• Considering the surface diffusion to reduce surface area Bradley-Harper (BH) theory
Fundamentally based on the
“Negative Deposition” concept
10keV Ar on Au(001)10keV Ar on Au(001)
*Total simulation time: 41 ps
32.64×32.64×20.4 nm3 Au substrate (1.28 mil. atoms)
Initial 2.5 ps 9.5 ps
15 ps 22 ps Final
RelativeHeight
Simulation movie http://diamond.kist.re.kr/CSC
Sputtering Process Erosion + Rearrangement
Rearrangement EffectRearrangement Effect
10 keV Ar ion impacts on Au(001)
crater with rimrecurving atoms
recurving cluster
Rearrangement atoms
Research StrategyResearch StrategyTo understand formation mechanism of surface patterning during ion bombardments
Direct observation of atomic scale behaviorDirect observation of atomic scale behavior
Quantitative analysis
Molecular Dynamics (MD) Simulation- Massive MD- EAM+ZBL interatomic potential
- MD statistics (1,000 individual calculations)- Auto-correlation function
Computational ProcedureComputational Procedure
Pd(001)
0.5, 1.0, 2.0 keV
0, 30, 45, 60, 75°
Materials
Polar Angle (θ)
Incident Energy
45° ([110] direction)
ArIon
Azimuthal Angle (Φ)
ZBLAr
LJ potential
Pd
EAM + ZBL
Inter-atomic potential
-Substrate temperature: 300K-LAMMPS code (http://lammps.sandia.gov)
Simulation geometry on Pd(001) surface
Simulation Conditions
Sputtering vs. Rearrangement YieldSputtering vs. Rearrangement Yield
Yrearrangement >> Ysputtering
Various for the incident angle
Ratio = 2.8±0.5
Yields Ratio
Rearrangement DistributionRearrangement Distribution
Pd
X: impact point
0.5keV Ar[100]
[110]Beam dir.
- Symmetric but anisotropic distribution could be obtained at normal incidence.
- In the case of 30° and 45°, rearrangement atoms were accumulated in front of the impact point along the beam direction.
- In the case of more than 60°, the atoms moved beside the beam direction.
Surface Structure EvolutionSurface Structure Evolution15.56×15.56 nm2, 4,200 (17.34 ions/nm2) Ar bombardments
Atomic Configuration 2D Auto-correlation function
- To confirm the rearrangement effect on the formation of surface patterns, many Ar atoms were bombarded on the Pd(001).
- The correlation image is a little distorted diamond shape along <100> and <010> direction.
Initial surface height
ComparisonComparison0.5 keV Ar on Pd(001) with normal direction
Experimental Result*4,200 Bombarding Result Rearrangement Distribution
2D auto-correlation function
*T.C. Kim et al., PRL 92, 246104 (2004).
- 2D auto-correlation function after 4,200 bombarding is in consistent with an experimental result.
- 4 fold anisotropic surface pattern results from the accumulation of the rearranged atoms of anisotropic lateral distribution.
• MD simulation shows that ballistic rearrangement of the surface atom by ion bombardment plays an important role in the surface structure evolution.
• Present simulation of Ar ion bombardment on Pd(001) surface demonstrates the formation of 4 fold symmetric patterns which is in good agreement with the previous experimental observation.
• Existing kinetic models which are based on the negative deposition concept should be revised to consider this effects.
ConclusionConclusion