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.kr http://diamond.kist.re.kr/DLC * also at Ceramics Engineering Division, Hanyang University 2004. 12. 5. CISAS 2003, Changwon National University

2. Scientific Computation & Simulation in (sub) Atomic Scale First Principle CalculationMolecular Dynamic Simulation

3. Nanoscience and Nanomaterials

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

5. Case I : Size Dependent Properties Atomic Orbitals N=1 Molecules N=2 Clusters N=10 Q-Size Particles N=2,000 Semiconductor N>>2,000 h Energy h Conduction Band Valence Band Vacuum CdSe Nanoparticles Smaller Size 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 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 Needs Atomic Scale Understandings on the Structure, the Kinetics and the Properties

9. Insufficient Experimental Tools

10. Scientific Computation & Simulation in (sub) Atomic Scale First Principle CalculationMolecular Dynamic Simulation

11. KIST 1024 CPU Cluster System Top 22 nd supercomputer in the world Top 22 nd 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 the Interface Structures of the Metal/Metal or Metal/Insulator Controlling & Understanding The atomic behavior at the interface are fundamental to improve the performance of the nano-devices! Controlling & Understanding The atomic behavior at the interface are fundamental to improve the performance of the nano-devices!

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

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

16. FCC - Al HCP - Co PropertyAl*Co** Expt.Calc.Expt.Calc. A 0 ( Å ) 4.054.0492.5072.512 E coh (eV)3.363.394.394.29 B (GPa)7979.4180185 * A. Voter et al. MRS Symp.Proc., 175 (1987) ** R. Pasianot et al, PRB 45 12704 (1992) EAM Potential for Co and Al

17. EAM Potential for Co – Al * 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) PropertyCoAl(B2) Expt.*Calc. **Calc. *** A 0 ( Å ) 2.862.8672.994 E coh (eV) 4.454.4684.083 B (GPa) 162178169 CoAl B2

18. Phase Diagram of Co-Al CoAl: B2

19. Deposition Behavior of Al on Co (001)

20. Deposition Behavior of Co on Al (001)

21. CoAl: B2 Al on Co Co on Al

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

23. Deposition Behavior on (001) Al on AlCo on Co

24. Al on Al (100)

25. Co on Al (100) 6144 substrate atoms (16x16x6)a 0 (512 atoms/ML) Deposition Energy : 0.1eV

26. Co on Al (100)

27. 1.4 ML 2.8 ML 4.2 ML N.R. Shivaparan, et al Surf. Sci. 476, 152 (2001) Co on Al (100)

28. Structural Analysis CoAl  CoAl compound layer was formed spontaneously.

29. Co Structural Analysis

30. Energy Barrier for Co Penetration (1) (2) (3) (1)(2) (3) 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?

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

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

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

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

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

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

38. 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.

39. (1) (2) (3) (1) (2) (3) Reaction Coordinate Energy Barrier for Intermixing Reaction Coordinate (1) (2) (3)

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

41. Co Deposition on Al (001) Co on Al (001)

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

43. Co on Co (0001) 1344 substrate atoms(168atoms/ML) After 10ML (1680atoms) in 5 eV Co-substrate a  misfit! c b c b c a  misfit! c b c b a b a b a b a Remove misfits

44. Figures from Scientific American, June 2002 Spintronic Nanodevices 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

45. Case II : Scale Down Issues 2~4nm 0.13  m 10 nm Kinetics based on continuum media hypothesis is not sufficient.

46. Methodology of Nano-R&D Synthesis & Manipulation Modeling & Simulation Modeling & Simulation Analysis & Characterization Analysis & Characterization

47. Conventional Thin Film Growth Model Conventional thin film growth model simply assumes that intermixing between the adatom and the substrate is negligible.