1. 계산과학을 통한 나노재료의 이해 김상필 *, 안효신 †, 이승협 *, 이승철, 한승우 ‡, 이규환, 이광렬 한국과학기술연구원, 미래기술연구본부 * 한양대학교, 세라믹스 공학과 † 서울대학교, 재료공학부 ‡ 이화여자대학교, 물리학과 2004. 8. 19. 한국진공학회 할술발표회, 대구 EXCO International Symposium on Advanced Plasma Technology

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

3. KIST Supercom for NT-BT Storage Node 512 Computing Nodes Myrinet Public Network Head Node 3.07 TFlops

4. Contents Atomic Intermixing During Thin Multilayer Growth Role of Nitrogen in CNTs in the Field Electron Emission Third Element Addition Effect on the Residual Stress of Carbon Based Nanocomposite Films

5. 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

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

7. Co-Al System

8. 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

9. Deposition Behavior of Al on Co (001)

10. Deposition Behavior of Co on Al (001)

11. 1.4 ML 2.8 ML 4.2 ML N.R. Shivaparan, et al Surf. Sci. 476, 152 (2001) Co on Al (100)

12. Al on Co Co on Al Asymmetry in Interfacial Intermixing Deposition at 300K Initial kinetic energy 0.1eV

13. 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 the sufficient energy to overcome activation barrier?

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

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

17. Deposition Behavior on (001) Reaction Coordinate Co on Al (001)

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

19. Au on Pt (001) Pt on Au (001) M.I. Haftel et al., Phys. Rev. B 53, 8007 (1996).

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

21. Conclusions 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.

22. Contents Atomic Intermixing During Thin Multilayer Growth Role of Nitrogen in CNTs in the Field Electron Emission Third Element Addition Effect on the Residual Stress of Carbon Based Nanocomposite Films

23. Nitrogen incorporation significantly enhances the CNT growth resulting in vertically aligned CNTs. 16.7 vol. % C 2 H 2 in NH 3, CVD process Chemical Physics Letters, Vol. 372, 603(2003) Enhanced CNT Growth & Nitrogen

24. CNT is a strong candidate for field emission cathod materials 1. Structural advantage 2. Low turn-on voltage Field Emission from CNT What’s the role of incorporated nitrogen in the field emission?

25. Calculation Method Plane wave Ab initio tight binding calc. To obtain self-consistent potential and initial wave function Relaxation of the wave function Basis set is changed to plane wave to emit the electrons Time evolution Evaluation of transition rate by time dependent Schrödinger equation Localized basis Conversion of basis set 2 step calculation S. Han et al., PRB, Vol.66, 241402 (2002)

26. First-principles study of field emission of carbon nanotubes S. Han et al., PRB, Vol.66, 241402 (2002) Emission from Pure CNT

27. Cutoff radius 80, bias 0.7V/Å Band selection : E-E f = -1.5eV ~ 0.5V Emission from Pure CNT Emitted current(μA) Energy states (eV, E-E F ) A B C D

28. Localized states of CNT has a significant contribution of the field emission. A State B State D stateC state Localized states, Large emission current  * and  bonds: Extended states Emission from Pure CNT

29. Cutoff radius 80, bias 0.7V/Å Band selection : E-E f = -1.5eV ~ 0.5V Emission from N doped CNT Energy states (eV, E-E F ) Emitted current(μA) A B C D

30. Coupled states between localized and extended states contribute to the field emssion. B state A state C state D state π *+localized state Localized state π bond: Extended state Emission from N doped CNT

31. Nitrogen doped CNT Undoped CNT Emitted current(μA) Energy states (eV, E-E F ) Emitted current(μA) Energy states (eV, E-E F ) Enhanced Field Emssion by Nitrogen Incorporation Total current: 8.8  ATotal current: 13.2  A

32. Nitrogen Effect EFEF - N-doped CNT - Undoped CNT Localized state The nitrogen has lower on-site energy than that of carbon atom. T. Yoshioka et al, J. Phys. Soc. Jpn., Vol. 72, No.10, 2656-2664 (2003). The lower band energy makes it possible for more electrons to be filled in the localized states. Doped Nitrogen Position

33. Localized states of the electronic structure of CNT largely contribute to the field emission. Doped nitrogen enhances the emission by changing the electronic structure : mixed states of localized and extended states. Doped nitrogen lowers the energy level of the localized state, which makes electrons more localized to the tip of nanotube. Field Emission from N-doped CNT

34. Experimental Results Role of extrinsic atoms on the morphology and field-emission properties of carbon nanotubes L.H.Chan et al., APL., Vol.82, 4334(2003) N B

35. BORON DOPED NITROGEN DOPED Boron Doped CNT Doped Atom Position

36. Contents Atomic Intermixing During Thin Multilayer Growth Role of Nitrogen in CNTs in the Field Electron Emission Third Element Addition Effect on the Residual Stress of Carbon Based Nanocomposite Films

37. Syntheis and Residual Stress of WC-C Nanocomposite Films  Working gas: Ar, C 6 H 6 (total: 12sccm)  Base pressure : 2.0  10 -6 Torr  Deposition Pressure : 0.6 ~ 1  10 -4 Torr  Power density of target: 4.2~7.3 W/cm 2  RF Bias : - 200 V  Thickness: 350±50nm W n+, Ar H +, C m+ 1 2 3

38. (c) (d)(e)  -W 2 C (101) 2 nm2 nm 2 nm2 nm 2 nm2 nm 4 nm4 nm 4 nm4 nm 4 nm4 nm 4 nm4 nm 4 nm4 nm (e) 4 nm  -W 2 C (102)  -W 2 C (101) 4 nm (c)  -W 2 C (101) 4 nm (b) (a) 4 nm TEM Microstructures 4 nm (d)  -W 2 C (101)  -W 2 C (102)  Region 1 : W incorporation in a-C matrix  Region 2 : crystalline carbides begun emerging.  Region 3 : crystalline carbides phase presented. (a) 3.0, (b) 4.2, (c) 5.1, (d) 8.7, (d) 12.5 at.% 12 3

39. Syntheis and Residual Stress of WC-C Nanocomposite Films  Working gas: Ar, C 6 H 6 (total: 12sccm)  Base pressure : 2.0  10 -6 Torr  Deposition Pressure : 0.6 ~ 1  10 -4 Torr  Power density of target: 4.2~7.3 W/cm 2  RF Bias : - 200 V  Thickness: 350±50nm W n+, Ar H +, C m+ 1 2 3

40. Role of W in Residual Stress  Region 1 : W essentially act as the relaxation site of nearby carbon network, which is now proposed a generic origin in other W-DLC films.

41. Tetrahedral Amorphous Carbon Tetrahedral Amorphous Carbon (ta-C) Film –Non-hydrogenated amorphous carbon –High ratio of sp 3 hybridized carbon bonds (60-80%) –High hardness, density, and wear resistance –Smooth surface, chemical inertness, optical transparency RMS roughness = 0.95nm

42. Simulation Method Empirical Potential –Tersoff or Brenner Potential J. Tersoff, Phys. Rev. Lett., 61 (1988) 2879. D. Brenner, Phys. Rev. B 42 (1990) 9458. Diamond Substrate –Number of atoms : 608 –Temperature : 300K –Boundary condition : Y-Z axis Carbon Deposition –Number of deposited atoms : 500 atoms –Incident kinetic energy : 1 ~ 300 eV –Time step : 0.155 ~ 0.5 fs –Interval between carbon arrival : 1 ps –Full dynamics except fixed layer E = 75 eV

43. In case of 75 eV DepositionCoordination Strain Energy Min Max 4 3 2 5

44. Residual Compressive Stress J.-K. Shin et al, Appl. Phys. Lett., 27 (2001) 631-633.

45. Si Incorporated ta-C Films

46. Simulation Method Brenner force field for Carbon-Carbon bonding Tersoff force field for Carbon-Silicon and Silicon-Silicon bonding Diamond substrate : 6a 0 x 5a 0 x 6a 0 (1368 atoms) Deposition –Carbon atom : 75 eV –Si atom : 25 eV, 75 eV –Si concentration : 0.5 % ~ 5 % 53.5 A Fixed Layer

47. Residual Stress of ta-C:Si

48. Stress Reduction by Incorporated Si : Atoms in Calculated Area : Silicon atom : Carbon atom

49. Stress Reduction By Si Incorporation Si Atom Deposition

50. Role of Computational Modeling Provide physical intuition and insight in nano-scale materials phenomena. Provide virtual experimental tools where the physical experiment or analysis is impossible Allow fundamental theory (i.e. quantum mechanics) to be applied to a complex problem. Bridge the Gap between Fundamental Materials Science and Materials Engineering

51. Within five to ten years, there must be robust tools for quantitative understanding of structure and dynamics at the nanoscale, without which the scientific community will have missed many scientific opportunities as well as a broad range of nanotechnology applications.

52. IT Based Virtual Nano-Lab Researchers in the field of Nanotechnolgy Potential DB Virtual Reality User I/F Parallel Simul. Codes K*GRID Massive Computation

53. Acknowledgement Financial Support –KIST Creative Research Program –KIST Vision 21 Research Program –MOST Frontier Research Program “Center for Nanostructured Materials Technology” For more informations http://diamond.kist.re.kr/DLC http://diamond.kist.re.kr/SMS

55. 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

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

57. 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

58. 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

59. EAM Potential for Co-Cu system* CoCu Expt.Calc.Expt.Calc. a 0 ( Å )2.5072.5013.615 E coh (eV)4.3864.3663.5133.534 B (Gpa)180211.7140137 γ 100 (J/m 2 ) N/A2.7892.1661.987 γ 110 N/A3.0512.2372.166 γ 111 N/A2.5911.9531.903 γ 1000 2.7752.879N/A γ -1010 3.0353.042N/A γ 11-20 3.7913.350N/A * X. W. Zhou et al., Acta. Mater., 49, 4005 (2001).

60. 관찰이란 무엇인가 ? 어떤 현상을 오감을 통해 인지하는 것. – 五感 (Sensing) : Natural Phenomena (physics) – 認知 (Recognition) : Brain’s Job (human factor)

61. 눈으로 관찰하기

62. AFM/STM

63. Time Evolution of R i and v i Molecular Dynamic Simulation i Empirical Approach First Principle Approach Interatomic Potentials

64. Possible Nitrogen Effects Reduction in the strain energy of CNT Change in the Growth Kinetics

65. Computational Method Dmol 3 : ab-initio calculation based on DFT Known to be very accurate Strong in energy calculation – energetics Transition state calculation – growth kinetics

66. Radius(Å)  E(eV/atom) Cluster design ~10Å Bulk design Energy of flat graphite plate ~30Å Strain Energy Due to Curvature No Significance in Strain Energy Reduction

67. Calculation of Kinetics Energy Barrier Assumptions Flat graphitic plate represents large radius CNT Catalyst metals assist formation of carbon precursor and provide a diffusion path to the reaction front reactant product

68. The Growth of CNT Edge armchair zigzag

69. Reaction path Energy 176 meV tetragonpentagon hexagon Growth of Pure Carbon Zigzag Edge

70. Growth of Pure Carbon Armchair Edge Energy pentagon hexagon 160 meV 64 meV Reaction path

71. The Growth of CNT Edge armchair zigzag

72. 152meV 154meV Pure C Nitrogen incorporation tetragon pentagon hexagon Energy Reaction path 153 meV 176 meV Nitrogen Incorporation on Zigzag Edge 0meV a b c a,b 538meV c

73. Energy Nitrogen incorporation Pure C pentagon hexagon Reaction path 137meV 64meV 160meV Nitrogen Incorporation on Armchair Edge 160meV 137meV 303meV 5455meV

74. Growth with Incorporated Nitrogen 152meV87meV 179meV96meV Energy Nitrogen at top site Pure C pentagon hexagon Nitrogen at valley site 64meV 152meV 160meV 179meV 96meV 87meV Reaction path

75. Growth with Incorporated Nitrogen No barrier 333meV Energy Pure C Nitrogen in valley site tetragon pentagon hexagon Nitrogen in top site No barrier 176meV 333meV Reaction path No barrier

76. Growth with Incorporated Nitrogen No barrier Energy growth of C tetragon Pentagon hexagon growth near the nitrogen incorporated region. No barrier 176 meV No barrier

77. Electron Density

78. The Growth of CNT Edge armchair zigzag