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Atomic Scale Understanding of the Surface Intermixing during Thin Metal Film Growth

Atomic Scale Understanding of the Surface Intermixing during Thin Metal Film Growth. 김상필 1,2 , 이승철 1 , 정용재 2 , 이규환 1 , 이광렬 1 1 한국과학기술연구원 , 계산과학센터 2 한양대학교 , 재료공학부. 진공학회 , 표면 및 계면과학 심포지움 2007. 2. 7. Devices with Thin Multilayers. 1~2nm. GMR Spin Valve. Major materials issue is the

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Atomic Scale Understanding of the Surface Intermixing during Thin Metal Film Growth

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  1. Atomic Scale Understanding of the Surface Intermixing during Thin Metal Film Growth 김상필1,2, 이승철1, 정용재2, 이규환1, 이광렬1 1한국과학기술연구원, 계산과학센터 2한양대학교, 재료공학부 진공학회, 표면 및 계면과학 심포지움 2007. 2. 7.

  2. Devices with Thin Multilayers 1~2nm GMR Spin Valve Major materials issue is the interfacial structurein atomic scale

  3. Smaller Size CdSe Nanoparticles Nanoscience or Nanotechnology • To develop new materials or devices of novel properties by understanding a phenomenon in the scale of atoms or molecules and manipulating them in an appropriate manner.

  4. Smaller Size CdSe Nanoparticles Nanoscience or Nanotechnology • To develop new materials or devices of novel properties by understanding a phenomenon in the scale of atoms or molecules and manipulating them in an appropriate manner.

  5. Nanoscience or Nanotechnology needs atomic scale understandings of structure, kinetics and properties.

  6. Interatomic Potentials • Empirical Approach • First Principle Approach i Time evolution of Ri and vi Molecular Dynamics Simulation

  7. Devices with Thin Multilayers 1~2nm GMR Spin Valve Major materials issue is the interfacial structurein atomic scale

  8. Thin Film Growth Model (conventional)

  9. Calculation Methods Adatom (normal incident  0.1 eV) 300K Initial Temperature 300K Constant Temperature Fixed Atom Position • Co-Al EAM potential* • x,y-axis : Periodic Boundary Condition • z-axis : Open Surface • Deposition rate:1.306 × 10-1 nm/nsec • MD calc. step : 0.1fs R. Pasianot et al, Phys. Rev. B45, 12704 (1992). A. F. Voter et al , MRS Proc. 82, 175 (1987). C. Vailhe et al, J. Mater. Res. 12, 2559 (1997).

  10. Deposition in Co-Al System Co on Al (001) Al on Co (001)

  11. Asymmetric Interface Formation

  12. Radial Distribution Function of Interface • CoAl compound layer of B2 structure was formed spontaneously.

  13. Atomic deposition behavior Co on Al(111) Al on Co(111)/(0001)

  14. 3ML Al on Co(001) 3ML Co on Al(001) Asymmetry in Interfacial Intermixing

  15. Asymmetry in Au-Pt Au on Pt (001) Pt on Au (001)

  16. Deposited Atom of 5.0 eV Co on Cu (100) Cu on Co (100)

  17. 3ML Al on Co(001) 3ML Co on Al(001) Asymmetry in Interfacial Intermixing • Deposition at 300K • Initial kinetic energy 0.1eV

  18. Interface Energy Argument

  19. Snapshots of Co penetration

  20. (1) (2) (3) (4) Activation Barrier for Intermixing Reaction Coordinate

  21. Calculation Methods Adatom (normal incident  0.1 eV) 300K Initial Temperature 300K Constant Temperature Fixed Atom Position • Co-Al EAM potential* • x,y-axis : Periodic Boundary Condition • z-axis : Open Surface • Deposition rate:1.306 × 10-1 nm/nsec • MD calc. step : 0.1fs R. Pasianot et al, Phys. Rev. B45, 12704 (1992). A. F. Voter et al , MRS Proc. 82, 175 (1987). C. Vailhe et al, J. Mater. Res. 12, 2559 (1997).

  22. (1) 3.5eV (2) Co (3) (4) Al (1) (2) (3) (4) Acceleration of Adatoms near Surface

  23. J. R. Manson et al, Phys. Rev. B29, 1084 (1984). R. Wang et al., Phys. Rev. B51, 1957 (1995). F. Montalenti et al., Phys. Rev. B64, 0814011 (2001). Local accleration of deposited atoms As the atom approaches the surface, its kinetic energy increases significantly due to its attraction to the surface. The initial kinetic energy is negligible compared to the gain due to the acceleration.

  24. (1) 3.5eV (2) Co (3) (4) Al (1) (2) (3) (4) Acceleration of Adatoms near Surface

  25. Co on Al (001) Al on Co (001) Contour of Acceleration on (001) Surface

  26. Co Al (1) (2) (3) (4) Kinetic Criteria for Intermixing Activation Barrier for Mixing Local Acceleration (1) 3.5eV (2) (3) (4) Reaction Coordinate

  27. Intermixing : Al on Co (001)

  28. Deposition in Co-Al System Co on Al (001) Al on Co (001)

  29. 百聞不如一見 百見不如一知

  30. Co on Al Al on Co Asymmetry of Surface Reaction Do you have experimental evidence?

  31. (bond direction) a o a a a c1 c2 c2 Da a o o Da o a c1 A a B intensity d (angle) Ion Scattering Spectroscopy CoAxial Impact Collision Ion Scattering Spectroscopy (CAICISS) • Energy range of ~ keV → penetration depth : < 10 Å

  32. Polar Scan in [1100] on Co (0001) Surface ¯

  33. In [1100] direction OnTop site(s) Bridge fcc hcp Al atom(s) 1.8 ± 0.05 Å Ah1’, Af1’ 1st Co layer Ah1,,Af1 Ah2’, Af2’ Ah2 2nd Co layer Polar scan of Al added Co (0001) DFT calculation results

  34. Al on Co (0001) Surface

  35. Al(001) [100] 1st A11 2nd A121 A123 A122 3rd A132 A130 4.05 Å 4th 4.05 Å Polar Scan in [100] on Al (001) Surface A121 (31.7°) A121 (58.3°) A132 (32.7°) A11 (12.9°) A122 (11.52°) A122 (26.4°) A132 (20.4°) A130 (79.1°)

  36. [100] 1st A11 Al 2nd Co 3rd A130 A131 C232 C230 C231 4.05 Å 4th 2.867 Å Polar Scan of Co added Al (001)

  37. Spin-Up B2 - CoAl HCP - Co Spin-Down Magnetic Properties of Co-Al system FCC - Al Spin resolved DOS

  38. Magnetic properties of Co-Al Thin Layer MOKE (Magneto-Optic Kerr effects) Cu Capping layer (50Å) Cu Capping layer (50Å) Cu Capping layer (50Å) Co (30Å) Al (30Å) Co (30Å) Co (30Å) Cu buffer layer (1500Å) Al (840Å) Cu buffer layer (1500Å) Si substrate Si substrate Si substrate

  39. Capping layer (50Å) Al (30Å) Co (30Å) Cu buffer layer (1500Å) Co Si substrate Al Capping layer (50Å) Co (30Å) Al (840Å) Si substrate Effect of Coating Sequence Capping layer (50Å) Co (30Å) Cu buffer layer (1500Å) Si substrate Al

  40. Capping layer (50Å) Co (30Å, 5Å) Cu buffer layer (1500Å) Si substrate Co Thickness Effect

  41. Capping layer (50Å) Al (30Å) Co (30Å) Cu buffer layer (1500Å) Co Si substrate Al Capping layer (50Å) Co (30Å) Al (840Å) Si substrate Effect of Coating Sequence Capping layer (50Å) Co (30Å) Cu buffer layer (1500Å) Si substrate Al

  42. Capping layer (50Å) Co (variable thickness) 5Å 7Å Al (840Å) Si substrate 30Å 10Å How thick is the nonmagnetic (B2) interlayer?

  43. Thickness of B2 Layer : 3ML 3ML ~ 10Å

  44. Conclusion Co on Al Al on Co Asymmetry in interfacial intermixing was observed in both MD simulation and experiment, which is governed by a kinetic criteria

  45. Acknowledgement • Financial Support • Core Capability Enhancement Program of KIST(V00910, E19190) • CAICISS and MOKE Measurement • Prof. Chungnam Whang • Dr. Jae Young Park • Ms. Hyunmi Hwang

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