Microsoft PowerPoint - 나노 기술과 재료 -basic

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1 Nano Materials 김기범 서울대학교재료공학부 1

2 Contents Introduction Basics Synthesis of Nano Materials Fabrication of Nano Structure Nano Characterization Properties and Applications 2

3 Basics Crystal structure Surface Kinetics Surface chemistry Consolidation Quantum confinement 3

4 Basics- Crystal structure Crystalline vs. amorphous Crystalline SiO 2 Amorphous SiO 2 Crystalline Au Long range order Short range order Matrix Amorphous SiO 2 Crystalline Si 4 10nm

5 Basics- Crystal structure Definition of Crystal A crystal is an anisotropic, homogeneous body consisting of a three-dimensional periodic ordering of atoms, ions or molecules Definition of Lattice A lattice means a three-dimensional array of points coinciding with atom positions (the space arrangement of equivalent sites in a crystal ) Lattice Parameters 5

6 Basics- Crystal structure Crystal Structure Crystal structure = Lattice + Basis 6

7 Basics- Crystal structure Definition of Crystallographic direction Crystallographic direction is defined as a line between two points, or a vector. Note that the direction of [uvw] describes not only a line through the origin and the point uvw, but the infinite set of lines which are parallel to it. 7

8 Basics- Crystal structure Definition of Crystallographic plane The values ( h k l ) are called Miller indices, and they are defined as the smallest integral multiples of the reciprocals of the plane intercepts of axis. 8

9 Basics- Crystal structure Seven Crystal Systems 9

10 Basics- Crystal structure 14 Bravais Lattice 10

11 Basics- Crystal structure Close Packed Structure- FCC 11

12 Basics- Crystal structure Close Packed Structure- HCP 12

13 Diamond Basics- Crystal structure 1 2 tet. sites by cations 13 8 atoms/unit cell coordination #: 4:4 FCC with two atoms per lattice Si, Ge point, (0,0,0) and (,, ) two interwoven FCC lattices

14 Basics- Crystal structure Zinc Blende 1 2 tet. sites by cations 4 molecules/unit cell coordination #: 4:4 FCC with two different atoms 14 GaAs per lattice point, (0,0,0) (,, ) two interwoven FCC lattices

15 Wutzite Basics- Crystal structure 15

16 Carbon -diamond - graphite Basics- Crystal structure 16 covalent/van der Waals o 1.48/3.4 A 4 atoms/unit cell coordination #: 3

17 Basics- Crystal structure Carbon - graphene - fullerenes (C 60 ) - nanotube A.K.Geim, Nature Mater., 6, 183 (2007)

18 Basics- Crystal structure Carbon-Classification of carbon nanotubes - Single-wall CNT, double-wall CNT, multi-wall CNTs - Zigzag and armchair nanotubes, achiral nanotube SWCNT DWCNT Thin-MWCNT MWNCT

19 Basics- Crystal structure Carbon-Classification of carbon nanotubes - Zigzag and armchair nanotubes, achiral nanotube

20 Basics- Defects Point Defect - Vacancy - Interstitial - Impurities (Dopants) P. Ebert, Materials Today, 6, 36 (2003)

21 Basics- Defects ' oxygen vacancy: V +2e O

22 Basics- Defects

23 Basics- Defects Line Defect (dislocation) - edge - screw Dislocation line Burgers vector, b a)

24 Basics- Defects Line Defect (dislocation) -mixed Mixed Edge 24 Screw

25 Basics- Defects Line Defect (dislocation) - observation of dislocation high resolution transmission electron microscope image electron beam incident along an <011> zone of Si r b= 1 2 [011] 25

26 Basics- Defects Line Defect (dislocation) - lattice fringe image of dislocation narrow edge dislocation wide edge dislocation 26

$diffraction contrast transmitted$ $diffracted beam-dark field image$

27 Basics- Defects Line Defect (dislocation) - diffraction contrast transmitted beam-bright field image-dislocation-dark 27 diffracted beam-dark field image -dislocation-bright

28 28 Basics- Surface Surface Energy dg = -SdT + VdP + μ dn + γda G -2 γ = : surface energy [Jm ] A PT,, ni Estimation of surface energy Anisotropy FCC 1 2 γ {100} = 4ε = 2 2 a 1 γ = Nbερa Nb ρa i i i 2 : # of broken bonds, : surface atomic density 4ε 2 a a ε 5 ε γ { 111} = 2 3 γ 2 {110} = 2 a 2 a

29 Basics- Surface Anisotropy of Surface Energy 1 cm 2 1 cm 2 1 cm 2 (4x0.32x250)+(4x0.59x225) =851 erg 4x1x250=1000 erg 4x1x225=900 erg Equilibrium shape - total surface energy minimization 29 A.W. Adamson, Physical Chemistry of Surfaces (1982)

30 Basics- Surface Wulff plot - γ-plot- curved outer line γ = Ch i i - crystal shape- inner envelope NaCl Ag Ag Au 30 G. CaO, Nanostructures & (2004) Negative crystal UO 2 Y.-M Chiang, Physical Ceramics (1997)

31 Basics- Surface Surface Energy Surface Energy vs. size 31 Y.-M Chiang, Physical Ceramics (1997) G. CaO, Nanostructures & (2004)

32 Basics- Surface Curved Surface Δ PdV = γ da dv = r dr da = rdr π 8 π for sphere da 2γ Δ P = γ = dv r 1 1 Laplace equation Δ P = γ ( + ) r r 1 2 r, r: principal radii of curvature 32

33 Basics- Surface Curved Surface - pressure difference across a curved surface a change in solubility or vapor pressure - at constant T, P, n i, transfer one mole from plat to curved μ = μo + RT ln a = μo + RT ln c = μo + RT ln P Pr () 4 Δ μ = RT ln = γda = γ8 πrdr, Vm = πr Pr ( = ) 3 2γVm 1 Pr () = Pr ( = )exp[ ( )] RT r : Kelvin equation 3 33

34 Basics- Surface Solubility Vapor Pressure 34 G. CaO, Nanostructures & (2004)

35 Basics- Surface Melting Point - melting point particle size Transition Temperature T 2/3 ρ = Δ ρ 2T b s b Tm γs γl Hρsrs l Au PbTiO 3 35 Ph. Buffat, Phys. Rew., A13 (1976) 2287 K. Ishikawa, Phys. Rew., B37 (1976) 5852

36 Basics- Surface Melting Point of nano-wire - Ge nano-wire - Rayleigh instability 36 Y. Wu, Adv. Mater., 13 (2001) 520 D. Quere, Science, 249 (1990)1256.

37 Basics- Surface Melting Point & Lattice Parameter - CdS nanocrystal 37 A.N.Goldenstein, Science, 256 (1992)1425.

38 Basics- Surface Ostwald Ripening C r 2σVm 1 = Co(1 + ) RT r 38 J. B. Hannon, Phys. Rev. Lett., 79 (1997) 2506

39 Basics- Surface Capillary Rise 2 2cosθ Δ P = γ = γ = ρgh γ = r Rc Rρgh 2cosθ 0 < θ < 90 90< θ<180 θ 39

40 Basics- Surface Wetting & Spreading - contact angle γ SV =γ SL +γ LV cos θ θ: contact angle Young equation - wetting 40 nonwetting θ > 90 wetting θ < 90 spreading θ = 90 W. D. Kingery, Introduction to Ceramics (1976)

41 Basics- Surface Wetting - grain boundary 41 φ: dihedral angle W. D. Kingery, Introduction to Ceramics (1976)

Basics- Kinetics Homogeneous Nucleation - supersaturation (ΔGv) - surface spherical nuclei 4π r 2 γ Δ G = πr Δ G + 4πr γ 4 3 2 3 V critical radius r

42 Basics- Kinetics Homogeneous Nucleation - supersaturation (ΔGv) - surface spherical nuclei 4π r 2 γ Δ G = πr Δ G + 4πr γ V critical radius r * d( ΔG) * 2γ = 0 r = dr * ΔG r= r barrier height ΔG * V 42 π r ΔG V 16π r 3 * Δ G = 3 Δ GV W. D. Callister, Materials Science and Engineering

43 Basics- Kinetics Homogeneous Nucleation ex) supersaturated solution kt kt ΔGv = ln( C / Co) = ln(1 + σ ) Ω Ω σ = ( C C ) / C o o For nanoparticles - ΔG σ T v - γ 43 T>T>T>T E 1 2 3

44 Basics- Kinetics Nucleation Rate. N n v * ~ (# of stable nuclei) d (collision frequency) * ΔG Qd ~ K1exp( ) K2exp( ) kt kt 44 W. D. Callister, Materials Science and Engineering

45 Basics- Kinetics Mono-dispersed Particle - Lamar diagram How to achieve the uniformity in size? 1. High rate of nucleation 2. Quick down to the minimum concentration. prevent further nucleation 45 T. Sugimoto, Adv. Colloid Interface Sci., 28 (1987) 65

46 Basics- Kinetics Homogeneous Nucleation - subsequent growth 46 (1) diffusion controlled (2) interface controlled dr dt r r 2 2 = δr = = D( C = 2D( C k r D o t + r ( δr r o C 2 o ) S C = V ) r S ) V r k o m ( δr D m t + r o ) t + r 2 o 2 o (2-1) monolayer growth 1 1 dr 2 = kr m ; = kt dt m r ro δ r δ r 2 o = r 2 ro (2-2) multilayer growth dr = k ; r = k t+ r dt δr = δr p p o o

47 Basics- Kinetics Homogeneous Nucleation - for the uniformity in size diffusion controlled process is desired δr r (2-1) (2-2) r (or t) - how to achieve it extremely low concentration of growth species high viscosity, diffusion barrier, controlled supply of growth 47 species (1)

48 Basics- Kinetics Homogeneous Nucleation ex) ZnS diffusion of the HS- ion to the growing particle is the rate-limiting process 48 R.Williams et al., J. Colloid Interface Sci. 106, 388 (1985).

49 Basics- Kinetics Heterogeneous Nucleation 2 * * sin θ cosθ + 2 cosθ 2 heter = rhomo 3 r 2 3cosθ + cos Δ G =ΔG f( θ ) * * heter homo f ( θ ) = 2 3cosθ + cos 4 3 θ θ 49 W. D. Callister, Materials Science and Engineering

50 Basics- Surface chemistry Dispersion - a high solids homogeneous suspension with a well-defined rheological behavior Dispersion in liquid - wetting - interparticle interaction 50 R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

51 Basics- Surface chemistry Stabilization 51 R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

52 Basics- Surface chemistry Electrostatic Stabilization electrical repulsion van der waals attraction Electrical double layer - surface charge (Ψ o ) - stern potential (Ψ d ) specific adsorption of counter-ion - electrockinetic or ζ(zeta) potential at plane of shear (slipping plane) - double layer thickness (κ -1 ) 52 M i : molar concentration D.J.Shaw, Introduction to colloid and surface chemistry, 1992

53 Basics- Surface chemistry Van der Waals attraction induced dipole- induced dipole (London) ~ x -6 permanent dipole- induced dipole (Debye) ~ x -6 permanent dipole- permanent dipole (Keesom) ~ x -6 Attraction between two spheres Φ = A Ar 12S A: Hamaker constant 53 G. CaO, Nanostructures & (2004)

54 Basics- Surface chemistry Example- CdTe nanowire dipole-dipole interaction between nano-particles produce nanowires with self assembling modes intermediate stage nano-wire 54 Z. Tang, Science, 297 (2002)237

55 Basics- Surface chemistry DLVO theory Φ =Φ +Φ R A kinetic barrier primary minima secondary minima 55 P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

56 Basics- Surface chemistry DLVO theory - effect of Hamaker constant surface potential electrolyte conc M 10-2 M P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

57 Basics- Surface chemistry Steric Stabilization Steric stabilizer : amphipathic block or graft copolymer D. H. Napper, Polymeric Stabilization of Colloidal Dispersions (1983)

58 Basics- Stability of Nanoparticle Metal oxide nanoparticles in aqueous suspensions - kinetic stability- energy barrier (DLVO theory) - dispersion, aggregation, flocculation - thermodyamic stability- surface energy minimization - Ostwald ripening (dissolution-reprecipitation) * Is it possible to avoid the ripening of nanoparticles in suspension and to control their dimension by monitoring the precipitation conditions? ex) thermodynamically stable dispersed system- microemulsion answer) possible When the ph of precipitation is sufficiently far from the point of zero charge and the ionic strength sufficiently high, the ripening of nanoparticles is avoided. The stability condition, defined by a 'zero' interfacial tension, corresponds to the chemical and electrostatic saturation of the water-oxide interface. In such a condition, the density of charged surface groups reaches its maximum, the interfacial tension its minimum and further adsorption forces the surface area to expand and consequently, the size of nanoparticles to decrease. L. Vayssieres, Int. J. Nanotech. 2, 411 (2005)

59 Basics- Stability of Nanoparticle Microemulsion - clear, stable, isotropic liquid mixtures of oil, water, and surfactant, frequently in combination with a co-surfactant. - aqueous phase may contain salt(s) and/or other ingredients, and the oil may actually be a complex mixture of different hydrocarbons and olefins. - thermodynamically stable - interfacial tension is very low (10-2 ~10-3 mn/m) E. Ruckenstein, Chem. Phys. Lett. 57, 517 (1978) B.K. Paul, Current Science 80, 990 (2001)

60 Basics- Stability of Nanoparticle Metal oxide nanoparticles in aqueous suspensions point of zero interfacial tension γ decreases as ph increases unstable -ripening stable - no growth S.M.Ahmed, J. Phys. Chem. 73, 3546 (1969) L. Vayssieres, Int. J. Nanotech. 2, 411 (2005)

5Tm [K], in the temperature range where diffusional mass transport is appreciable resulting in a

61 Basics- Consolidation Consolidation (sintering) processes involved in the heat treatment of powder compacts at elevated temperatures, usually at T > 0.5Tm [K], in the temperature range where diffusional mass transport is appreciable resulting in a dense polycrystalline solid. - pore removal densification 61 MgO-doped Al 2 O 3 J. P. Schaffer et al, The Science and Design of Engineering Materials

62 Basics- Consolidation Solid state sintering final intermediate 62 initial

63 Basics- Consolidation Densification vs. Grain Growth 500μm TiO 2 & SiO 2 -doped Al 2 O 3 63 O. S. Kwon, Acta Mater., 50 (2002)

Introduction Capillarity( ) (flow ceased) Capillary effect ( ) surface and colloid science, coalescence process,

Introduction Capillarity( ) (flow ceased) Capillary effect ( ) surface and colloid science, coalescence process, Introduction Capillary forces in practical situation Capillary Model A Capillary Model system,