Introduction to Nanotechnology and Nanomaterials Chapter 2-3: Basic Science for Nanotechnology ;kl;kl;l;klklkl; 1 Nanomaterials

1. Crystal structure (General) 2. Surface Energy (Thermodynamics) Contents 1. Crystal structure (General) 2. Surface Energy (Thermodynamics) 3. Kinetics (Nucleation and Growth, Phase Transformation) 4. Surface Passivation and Consolidation 5. Electronic and Optical Properties of Nanostructure 2 Nanomaterials

Phase transformation deals with Vapor phase to solid phase – film growth Solution phase to solid phase – colloidal process Solid phase transformation Need thermodynamic driving force for phase transformation.

Derivation of Fick’s 1 st and 2nd equation:

Homogeneous Nucleation - supersaturation (DGv) - surface Basics- Kinetics Homogeneous Nucleation - supersaturation (DGv) - surface spherical nuclei 5 Nanomaterials W. D. Callister, Materials Science and Engineering

Homogeneous Nucleation ex) supersaturated solution For nanoparticles Basics- Kinetics Homogeneous Nucleation ex) supersaturated solution For nanoparticles 6 Nanomaterials

Basics- Kinetics q Nucleation Rate Nanomaterials 7 Nanomaterials W. D. Callister, Materials Science and Engineering

q Nucleation Rate in Liquid Basics- Kinetics q Nucleation Rate in Liquid The rate of nucleation per unit volume and per unit time, RN, is proportional to N: number of growth species n: #of atoms/unit area c: #of atoms/unit volume 1 2 a y 8 Nanomaterials

Basics- Kinetics Phase Transformation in Liquid: Stokes law: From the Stokes-Einstein Relation, Stokes law: Einstein relation: Now, if we assume that a=r=l, the diameter of the growth species

Mono-dispersed Particle - Lamar diagram Basics- Kinetics How to achieve the uniformity in size? High rate of nucleation Quick down to the minimum concentration.  prevent further nucleation Mono-dispersed Particle - Lamar diagram 10 Nanomaterials T. Sugimoto, Adv. Colloid Interface Sci., 28 (1987) 65

Homogeneous Nucleation - subsequent growth (1) diffusion controlled Basics- Kinetics Homogeneous Nucleation - subsequent growth (1) diffusion controlled Nanomaterials

Homogeneous Nucleation Basics- Kinetics Homogeneous Nucleation Flux by diffusion, d r x Jd Since, 12 Nanomaterials

Homogeneous Nucleation (2) interface controlled Basics- Kinetics Homogeneous Nucleation (2) interface controlled The growth proceeds layer by layer; the growth species are incorporated into one layer and proceeds to another layer The surface process is so fast that second layer growth proceeds before the first layer growth is complete 13 Nanomaterials

Homogeneous Nucleation - for the uniformity in size Basics- Kinetics Homogeneous Nucleation - for the uniformity in size  diffusion controlled process is desired - how to achieve it  extremely low concentration of growth species high viscosity, diffusion barrier, controlled supply of growth species (2-1) (2-2) (1) 14 Nanomaterials Nanomaterials

Homogeneous Nucleation ex) ZnS Basics- Kinetics Homogeneous Nucleation ex) ZnS diffusion of the HS- ion to the growing particle is the rate-limiting process 15 Nanomaterials Nanomaterials R.Williams et al., J. Colloid Interface Sci. 106, 388 (1985).

q Heterogeneous Nucleation Basics- Kinetics q Heterogeneous Nucleation 16 Nanomaterials Nanomaterials W. D. Callister, Materials Science and Engineering

- wetting - interparticle interaction Basics- Kinetics q Dispersion - a highly homogeneous suspension of solids with a well-defined rheological behavior q Dispersion in liquid - wetting - interparticle interaction 17 Nanomaterials R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

Basics- Surface chemistry q Stabilization 18 Nanomaterials R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

Basics- Surface chemistry Electrostatic Stabilization Surface charge density: Preferential adsorption of ions Dissociation of surface charged species Isomorphic substitution of ions Accumulation and depletion of electrons Physical adsorption of charged species onto the surface (1.6x10-19 joule/eV)(6x1023/mol) 19 Nanomaterials

Basics- Surface chemistry The concentration of charge determining ions corresponding to a neutral or zero charged surface is defined as a point-of-zero charge (p.z.c). At pH>p.z.c – the oxide surface is negatively charged due to the hydroxyl groups, OH- At pH<p.z.c – the oxide surface is positively charged due to hydrogen ions, H+ The surface charge density or surface potential, E in volt, is now simply related to the pH and the Nernst equation. 20 Nanomaterials

Basics- Surface chemistry Electric Potential at the Proximity of Solid Surface The distributions of both ions are mainly controlled by a combination of (a) Coulombic force or electrostatic force (b) entropic force or dispersion (c) Brownian motion Formation of double layer: (a) Stern layer: electric potential drops linearly through the tightly bound layer of solvent and counter ions (b) Gouy layer (diffuse double layer): beyond the Helmholtz plane until the counter ions reach the average concentration in the solution (c) z(zeta) potential: potential at plane of shear (slipping plane) 21 Nanomaterials

Basics- Surface chemistry In the Gouy layer, the counter ions diffuse freely and the electric potential does not reduce linearly. Double layer thickness is typically of about 10 nm. An electrostatic repulsion between two equally sized spherical particles of radius r, and separated by s 22 Nanomaterials D.J.Shaw, Introduction to colloid and surface chemistry, 1992

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 23 Nanomaterials G. CaO, Nanostructures & Nanomaterials (2004)

Basics- Surface chemistry Example- CdTe nanowire dipole-dipole interaction between nano-particles produce nano-wires with self assembling modes intermediate stage nano-wire 24 Nanomaterials Z. Tang, Science, 297 (2002)237

Basics- Surface chemistry DLVO theory (Derjaguin, Landau, Verwey, Overbeek) primary minima secondary kinetic barrier 25 Nanomaterials http://www.zeta-meter.com/ P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

Basics- Surface chemistry DLVO theory - effect of Hamaker constant surface potential electrolyte conc. 10-2 M 10-3 M Larger – smaller thickness of double layer- more attraction Larger – more attraction Larger – more repulsion P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

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

Basics- Surface chemistry The advantages of using surfactant in colloid chemistry: Vacuum process Wet-chemical process

Basics- Surface chemistry

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 MgO-doped Al2O3 30 Nanomaterials J. P. Schaffer et al, The Science and Design of Engineering Materials

Basics- Consolidation Solid state sintering final intermediate initial 31 Nanomaterials

Basics- Consolidation Densification vs. Grain Growth 500mm TiO2 & SiO2-doped Al2O3 32 Nanomaterials O. S. Kwon, Acta Mater., 50 (2002) 4865-4872