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Sang-Pil Kim and Kwang-Ryeol Lee Computational Science Center

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 spkim@kist.re.kr (S.-P. Kim), krlee@kist.re.kr (K.-R. Lee).

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Sang-Pil Kim and Kwang-Ryeol Lee Computational Science Center

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  1. Molecular Dynamics Study of Ballistic Rearrangement of Surface Atoms During Ion Bombardment on Pd(001) Surface Sang-Pil Kimand Kwang-Ryeol Lee Computational Science Center Korea Institute of Science and Technology, Seoul, Korea spkim@kist.re.kr (S.-P. Kim), krlee@kist.re.kr (K.-R. Lee)

  2. Ion bombardment  Surface treatment Ion Bombardment (Sputtering) Deposition  Film coating 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.

  3. Catalytically active surface Manipulating film texture Applications Facsko et al., SCIENCE, 285, 1551 (1999) Chaudhari et al., NATURE 411, 56 (2001) Ordered adsorption of large molecules Optoelectronic devices Molding templates Manipulating magnetism Deposition Sputtering Azzaroni et al., APL 82, 457 (2003) Moroni et al., PRL 91, 167207 (2003)

  4. Theoretical Approach Sigmund theory • Incident energy spreading:Gaussian • Normal erosion velocity at O Local correction to the uniform flux due to non-flat geometry • Considering the surface diffusion to reduce surface area Bradley-Harper (BH) 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…) Fundamentally based on the “Negative Deposition” concept * P. Sigmund, Phys. Rev. 184, 383 (1969).

  5. 10keV Ar on Au(001) 32.64×32.64×20.4 nm3Au substrate (1.28 mil. atoms) Initial 2.5 ps 9.5 ps Relative Height 15 ps 22 ps Final Simulation movie  http://diamond.kist.re.kr/CSC *Total simulation time: 41 ps

  6. recurving cluster recurving atoms crater with rim Rearrangement Effect Sputtering Process  Erosion + Rearrangement Rearrangement atoms 10 keV Ar ion impacts on Au(001)

  7. Research Strategy To understand formation mechanism of surface patterning during ion bombardments • Direct observation of atomic scale behavior • Molecular Dynamics (MD) Simulation • Massive MD • EAM+ZBL interatomic potential • Quantitative analysis • MD statistics (1,000 individual calculations) • Auto-correlation function

  8. EAM + ZBL LJ potential Inter-atomic potential Ar Pd ZBL Ion Ar Materials Pd(001) Incident Energy 0.5, 1.0, 2.0 keV Polar Angle (θ) 0, 30, 45, 60, 75° Azimuthal Angle (Φ) 45° ([110] direction) Computational Procedure • Substrate temperature: 300K • LAMMPS code (http://lammps.sandia.gov) Simulation geometry on Pd(001) surface Simulation Conditions

  9. Sputtering vs. Rearrangement Yield Yields Ratio • Yrearrangement >> Ysputtering • Various for the incident angle • Ratio = 2.8±0.5

  10. Beam dir. [110] [100] Rearrangement Distribution Pd 0.5keV Ar X: impact point • 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.

  11. Surface Structure Evolution 15.56×15.56 nm2, 4,200 (17.34 ions/nm2) Ar bombardments Initial surface height 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.

  12. Comparison 0.5 keV Ar on Pd(001) with normal direction 2D auto-correlation function 4,200 Bombarding Result Experimental Result* Rearrangement Distribution • 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. *T.C. Kim et al., PRL 92, 246104 (2004).

  13. Conclusion • 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.

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