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Molecular Dynamic Simulation of Atomic Scale Intermixing in Co-Al Thin Multi layer

Molecular Dynamic Simulation of Atomic Scale Intermixing in Co-Al Thin Multi layer. Sang-Pil Kim * , Seung-Cheol Lee and Kwang-Ryeol Lee Future Technology Research Division Korea Institute of Science and Technology, Seoul, Korea krlee@kist.re.kr http://diamond.kist.re.kr/DLC

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Molecular Dynamic Simulation of Atomic Scale Intermixing in Co-Al Thin Multi layer

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  1. Molecular Dynamic Simulation of Atomic Scale Intermixing in Co-Al Thin Multilayer Sang-Pil Kim*, Seung-Cheol Lee and Kwang-Ryeol Lee Future Technology Research Division Korea Institute of Science and Technology, Seoul, Korea krlee@kist.re.krhttp://diamond.kist.re.kr/DLC * also at Ceramics Engineering Division, Hanyang University 2004. 12. 5. CISAS 2003, Changwon National University

  2. Scientific Computation & Simulationin (sub) Atomic Scale First Principle Calculation Molecular Dynamic Simulation

  3. Nanoscience and Nanomaterials

  4. ~ nm ~ nm ~ nm Characteristics of Nanomaterials • Continuum media hypothesis is not allowed. • Diffusion & Mechanics • Band Theory

  5. Energy Q-Size Particles N=2,000 Atomic Orbitals N=1 Molecules N=2 Clusters N=10 Semiconductor N>>2,000 Vacuum Smaller Size Conduction Band hn hn CdSe Nanoparticles Valence Band Case I : Size Dependent Properties Han et al, Nature Biotech., 19, 631 (2001).

  6. Chracteristics of Nanotechnology • Continuum media hypothesis is not allowed. • Large fraction of the atom lies at the surface or interface. • Abnormal Wetting • Abnormal Melting of Nano Particles • Chemical Instabilities

  7. Case III : GMR Spin Valve Major Materials Issue is the interfacial structure and chemical diffusion in atomic scale

  8. Nanoscience or Nanotechnology • To develop new materials of devices of novel properties by understanding a phenomenon in the scale of atoms or molecules and manipulating them in an appropriate manner. Needs Atomic Scale Understandings on the Structure, the Kinetics and the Properties

  9. Insufficient Experimental Tools

  10. Scientific Computation & Simulationin (sub) Atomic Scale First Principle Calculation Molecular Dynamic Simulation

  11. KIST 1024 CPU Cluster System Top 22nd supercomputer in the world

  12. The Present Work • We employed the molecular dynamic simulation to understand the atomic scale phenomena during thin film process in spintronic devices. . • We focused on the interfacial intermixing behavior in atomic scale. • New device utilize the electron spin to differentiate electrical carriers into two different types according to their spin projection onto a given quantization axis, ½. • By transferring a magnetic information from one part of the device to another by using nanoscale magnetic elements. • J.F.Gregg et al., J. Phys. D: Appl. Phys. 35(2002) R121

  13. Performance of spintronics devices are largely depends on theInterface Structuresof the Metal/Metal or Metal/Insulator Controlling & Understanding The atomic behavior at the interface are fundamental to improve the performance of the nano-devices!

  14. [001] z y x [010] [100] Adatom (0.1eV, normal incident) 300K Initial Temperature Substrate 300K Constant Temperature Fixed Atom Position Program : XMD 2.5.30 x,y-axis : Periodic Boundary Condition z-axis : Open Surface Atom flux : 5ps/atom MD calc. step : 0.5fs

  15. i Time Evolution of Ri and vi MD Simulation Interatomic Potentials Lennard-Jones: Inert Gas Embedded Atom Method: Metals Many Body Potential: Si, C

  16. FCC - Al HCP - Co EAM Potential for Co and Al * A. Voter et al. MRS Symp.Proc. , 175 (1987) ** R. Pasianot et al , PRB 45 12704 (1992)

  17. EAM Potential for Co–Al CoAl B2 * Intermetallic Compound , Vol 1, 885 (1994) ** C. Vailhe et al. J. Mater. Res., 12 No. 10 2559 (1997) *** R.A. Johnson, PRB 39 12554 (1989)

  18. CoAl: B2 Phase Diagram of Co-Al

  19. Deposition Behavior of Al on Co (001)

  20. Deposition Behavior ofCo on Al (001)

  21. CoAl: B2 Al on Co Co on Al

  22. Deposition Behavior on (111) Al on Co Co on Al TOP VIEW

  23. Co on Al (100)

  24. Co on Al (100) 1.4 ML 2.8 ML 4.2 ML N.R. Shivaparan, et al Surf. Sci. 476, 152 (2001)

  25. CoAl Structural Analysis • CoAl compound layer was formed spontaneously.

  26. Co Structural Analysis

  27. Energy Barrier for Co Penetration (3) (1) (2) (1) (3) (2) Reaction Coordinate • Activation barrier is larger than the incident kinetic energy (0.1eV) of Co. • How can the deposited Co atom get that sufficient energy to overcome the activation barrier?

  28. 1 3.5eV 2 3 4 Acceleration of Deposited Co Near Al Substrate Co Hollow site Al (1) (4) (2) (3)

  29. Deposition Behavior on (001) Co on Al Al on Co

  30. Al on Co (001) Contour of Acceleration Co on Al (001)

  31. Reaction Coordinate Depostion Behavior on (001) Co on Al (001)

  32. Deposition Behavior on (001) Al on Co (001)

  33. Deposition Behavior on (001) Al on Al (001) Al on Al (100)

  34. Conclusions • Conventional thin film growth model assumes negligible intermixing between the adatom and the substrate atom. • In nano-scale processes, the model need to be extended to consider the atomic intermixing at the interface. Conventional Thin Film Growth Model Calculations of the acceleration of adatom and the activation barrier for the intermixing can provide a criteria for the atomic intermixing.

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