1. Atomic Scale Computational Simulation for Nano-materials and Devices: A New Research Tool for Nanotechnology Kwang-Ryeol Lee Future Technology Research Division, KIST, Seoul, Korea 2 nd International Symposium on Bio- and Nano-Electronics in Sendai, Dec. 9-10, 2006

2. Today’s Talk Introduction to computational simulation Role of atomic scale simulation in nano- materials and devices research Case Study : Asymmetry in atomic scale intermixing during deposition of thin metallic multilayers

3. Research method to investigate a complex system based on the reasonable principles of a simple system. What is Computational Simulation? 10keV Ar on Au 75eV C on diamond

4. Empirical Approach First Principle Approach Interatomic Potentials Molecular Dynamics Simulation Time evolution of R i and v i i

5. Fundamental Models - First Principle Calculation - Ab initio MD Atomic Level Simulation - Monte Carlo Approach - Classical MD Engineering Design ns fs ss ms ps min Time Length Scale 1A10A100A 1m1m 1mm Continuum Models - FEM/FDM - Monte Carlo Approach - Phase Field Theory Hierarchy of Computer Simulation

6. Computation & Simulation in Atomic Scale Ab initio Calculation Molecular Dynamic Simulation

7. Nanomaterials

8. ~ nm Characteristics of Nanotechnology Continuum media hypothesis is not allowed. –Band Theory –Diffusion and Mechanics

9. 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 Size Dependent Properties

10. Scale Down Issues 1~2nm ~0.1  m <10 nm Kinetics based on continuum media hypothesis is not sufficient.

11. 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 Chracteristics of Nanotechnology

12. GMR Spin Valve Major materials issue is the interfacial structure in atomic scale Major materials issue is the interfacial structure in atomic scale

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

14. Insufficient Experimental Tools

15. Synthesis & Manipulation Analysis & Characterization Analysis & Characterization Modeling & Simulation Modeling & Simulation Methodology of Conventional R&D

16. Synthesis & Manipulation Analysis & Characterization Analysis & Characterization Modeling & Simulation Modeling & Simulation Methodology of Nanotechnology

17. Computation & Simulation in Atomic Scale Ab initio Calculation Molecular Dynamic Simulation 1nm = 1,000 atoms 10nm= 1,000,000 atoms 100nm=1,000,000,000 atoms

18. Cluster Supercomputer & Visualization Beowulf Cluster @ CALTECH

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

20. Thin Film Growth Model (conventional)

21. Adatom (normal incident  0.1 eV) 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 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 300K Initial Temperature 300K Constant Temperature Fixed Atom Position Calculation Methods 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. Deposition in Co-Al System Co on Al (001) Al on Co (001)

23. 3ML Al on Co(001) 3ML Co on Al(001) Asymmetry in Interfacial Intermixing

24.  CoAl compound layer of B2 structure was formed spontaneously. Radial Distribution Function of Interface

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

26. 3ML Al on Co(001) 3ML Co on Al(001) Asymmetry in Interfacial Intermixing Deposition at 300K Initial kinetic energy 0.1eV

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

28. Adatom (normal incident  0.1 eV) 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 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 300K Initial Temperature 300K Constant Temperature Fixed Atom Position Calculation Methods 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).

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

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

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

33. New Chinese Proverb? 百聞不如一見 百見不如一習

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

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

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

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

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

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

40. How thick is the nonmagnetic (B2) interlayer? 5Å5Å 7Å7Å 10Å 30Å Si substrate Co (variable thickness) Al (840Å) Capping layer (50Å)

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

42. Summary Al on Co Co on Al Asymmetry in interfacial intermixing was observed in both MD simulation and experiment.

43. Acknowledgement Financial Support –Core Capability Enhancement Program of KIST (V00910, E19190) Collaborators –KIST Mr. Sang-Pil Kim Dr. Seung-Cheol Lee –Hanyang University Prof. Yong-Jae Chung –Yonsei University Prof. Chungnam Whang Dr. Jae Young Park Ms. Hyunmi Hwang

44. Computational Materials Simulation Lab. http://diamond.kist.re.kr/SMS