Nanomaterials 1 Nanoscopic Materials • Chemical methods to change physical and chemical properties – composition, substituents,…. • Size is another variable to change physical and chemical properties for constant chemical composition • Each physical property or fenomenon has a characteristic length • When particle size is comparable to the characteristic length, property start to depend on the size Nanomaterials 2 Nanoscopic Scales Nanomaterials 3 Nanoparticles 1 – 100 nm Traditional materials > 1 m Nanoscopic Materials 1 nm = 109 m 1 nm = 10 Å Nanomaterials 4 Size 1 – 100 nm Nanoscopic Materials EU definition (2011): A natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm. http://ec.europa.eu/environment/chemicals/nanotech/faq/definiti on_en.htm Nanomaterials 5 Nanoscale regime Size 1 – 100 nm (traditional materials > 1 m) Physical and chemical properties depend on the size !! Natural examples:  Human teeth, 1-2 nm fibrils of hydroxyapatite Ca5(PO4)3(OH) + collagen  Asbestos, opals, calcedon  Primitive meteorites, 5 nm C or SiC, early age of the Solar system Nanoscale objects have been around us, but only now we can observe them, manipulate and synthesize them. Nanoscopic Materials Nanomaterials 6 “Prey”, the latest novel by Michael Crichton, author of “Jurassic Park”. The horrible beasties threatening humanity in this new thriller are not giant dinosaurs, but swarms of minute “nanobots” that can invade and take control of human bodies. Last summer, a report issued by a Canadian environmental body called the action group on erosion, technology and concentration took a swipe at nanotechnology. It urged a ban on the manufacture of new nanomaterials until their environmental impact had been assessed. The group is better known for successfully campaigning against biotechnology, and especially against genetically modified crops. The research, led by a group at the National Aeronautics and Space Administration's Johnson Space Centre in Houston, has found in preliminary studies that inhaling vast amounts of nanotubes is dangerous. Since they are, in essence, a form of soot, this is not surprising. But as most applications embed nanotubes in other materials, they pose little risk in reality. Nanostructural Materials Nanomaterials 7 Room at the Bottom Nanomaterials 8 Nanoscale Writing Nanomaterials 9 STM Scanning Tunelling Microscopy Binning and Rohrer Nobel Prize 1986 Nanoscale Writing Nanomaterials 10 STM positioned Xe atoms on Ni crystal, 5 nm letters Nanomaterials 11 Properties of Nanoscopic Materials • Metallic behavior - a single atom cannot behave as a metal, nonmetal to metal transition : 100-1000 atoms • Magnetic behavior - Single domain particles, large coercive field • Depression of melting points in nanocrystals bulk Au mp 1064 C  10 nm Au 550 C • Negligible light scattering - new optics • Quantum size effects - information technology, storage media • High surface area - catalysts, adsorbents • Large interfacial area - new composites • Surface modifications - targeted drug delivery, medical and biological applications Nanomaterials 12 Nanoscopic Size The largest known bacterium Thiomargarita namibiensis - 100-750 microns Nanomaterials 13 The Nano-Family At least one dimension is between 1 - 100 nm 0-D structures (3-D confinement): • Quantum dots • Nanoparticles AFM 1 μm x 1 μm InAs on GaAs/InP Au nanoparticles CdTe nanoparticles Nanomaterials 14 Coherence Length, d XRD patterns of iron oxide nanocrystals of 4, 6, 8, 9, 10, 11, 12, 13, and 15 nm   cos k d  Scherrer equation k = 0.89,  = wavelength, β = full width at half-maximum of a standard (Si) Nanomaterials 15 The Nano-Family 1-D structures (2-D confinement): • Nanowires • Nanorods • Nanotubes • Nanofibers Nanomaterials 16 The Nano-Family 2-D structures (1-D confinement): • Thin films - CVD, ALD • Planar quantum wells • Superlattices • Graphene • SAM Nanoscopic Behavior of Materials Nanomaterials 17 • Surface Effects • Quantum Confinement Effects Differences between bulk and nanoscale materials Nanomaterials 18 Decreasing grain size = Increasing volume fraction of grain boundaries (50% for 3 nm particles) Surface Effects Ru particle diameter 2.9 nm Nanomaterials 19 Surface Effects Dispersion F = the fraction of atoms at the surface F is proportional to surface area divided by volume N = total number of atoms V ~ r3 ~ N n = number of atoms at the cube edge 33 2 11 Nrr r F  F Nanomaterials 20 Si . Surface Effects Properties of grain boundaries Lower coordination number of atoms Reduced atomic density (by 10 – 30 %) Broad spectrum of interatomic distances Experimental evidence  HREM  EXAFS, reduced number of nearest and next-nearest neighbors  Raman spectroscopy  Mössbauer spectroscopy, quadrupole splitting distribution broadened  Diffusivity enhanced by up to 20 orders of magnitude !!  Solute solubility in the boundary region Ag (fcc) and Fe (bcc) immiscible in (s) or (l), but do form solid solution as nanocrystalline alloy  EPR, nano-Si gives a sharp signal Nanomaterials 21 Surface Effects Atoms at surfaces - fewer neighbors than atoms in the bulk = lower coordination number - stronger and shorter bonds - unsatisfied bonds - surface atoms are less stabilized than bulk atoms The smaller a particle the larger the fraction of atoms at the surface, and the higher the average binding energy per atom The melting and other phase transition temperatures scale with surfaceto-volume ratio and with the inverse size Example: the melting point depression in nanocrystals 2.5 nm Au particles 930 K bulk Au 1336 K Nanomaterials 22 Surface Effects A = Atoms at surfaces (one layer) – fewer neighbors, lower coordination, unsatisfied (dangling) bonds B = Atoms close to surface (several layers) – deformation of coordination sphere, distorted bond distances and angles C = Bulk atoms, regular ordering – not present in particles below 2 nm Nanomaterials 23 Graphite shells Nanomaterials 24 Surface Effects Calculated mean coordination number as a function of inverse radius, represented by N1/3 for Mg clusters (triangles = icosahedra, squares = decahedra, diamonds = hcp Mean coordination number What value ? Nanomaterials 25 Surface Effects Atom binding (vaporization) energies lower in nanoparticles, fewer neighbors to keep atoms from escaping Plasticity of nanocrystalline ceramics Nanomaterials 26 Surface Effects Morphologies of bimetallic nanoparticles Surface Effects in Alloys Nanomaterials 27 Alloys: Core-shell Janus Random mixture Au-Pt 586 atoms Nanomaterials 28 ICP-OES: Ag 50.3 mol%, EDS: Ag 62.5 mol% ICP-OES: Ag 68.8 mol%, EDS: Ag 84.2 mol% Transition Electron Microscopy Energy Dispersive X-ray Spectroscopy Effects of Synthesis Nanomaterials 29 AgCu 413 Ag 393 Cu 569 Localized Surface Plasmon Resonance (LSPR) Nanomaterials 30 Localized Surface Plasmon Resonance (LSPR) Nanomaterials 31 Nanomaterials 32 Melting Point Depression Surface atoms in solids are bound by a lower number of shorter and stronger bonds Nanoparticles with a large fraction of surface atoms • Lowering of average cohesion energy • Increasing average amplitude of thermal • Increasing internal pressure Result = deprssion of melting point of nanoparticles. Nanomaterials 33 Melting Point and Enthalpy Depression Nanocalorimetry of Sn nanoparticles Tm bulk = 232 C Hm bulk = 58.9 J/g Nanomaterials 34 Melting Point and Enthalpy Depression Nanocalorimetry of Sn nanoparticles Nanomaterials 35 Melting Point Depression Homogeneous melting model Continuous Liquid Meling Melting particle is surrounded by liquid Triple point of coexisting solid and liquid nanoparticles of the same mass surrounded by vapor Thin melted layer of a constant thickness δ coexisting with solid core and vapor Liquid Skin Melting Nanomaterials 36 Melting Point Depression Sn – 4wt%Ag – 0.5wt%Cu Nano alloy particles bulk ∆ Homogeneous melting model: Tm(r) = mp of the cluster with radius r Tm bulk = mp of the bulk material  sg = the interfacial energies between the s and g phases  lg = the interfacial energies between the l and g phases s and l = solid and liquid phase densities M = molar mass Hm bulk = the bulk latent heat of melting Tm bulk = 218 C Nanomaterials 37 Gibbs–Thomson Equation rH V T TrT m sl l mol bulk m bulk mm    2)( Tm(r) = mp of the nanoparticle with radius r Tm bulk = mp of the bulk material Vmol l = the molar volume of the liquid = M/s solid?  sl = the interfacial tension between the s and l surface Hm bulk = the bulk molar enthalpy of melting, endothermic DSC In nanoparticles confined in pores bulk ~for Continuous Liquid Meling Nanomaterials 38 Phase Transitions Phase transitions = collective phenomena With a lower number of atoms in a cluster a phase transition is less well defined and broadened Small clusters behave more like molecules than as bulk matter bulk bulk First-Order Phase Transitions Nanomaterials 39 3 main consequences of a size decrease on caloric curve: * The transition is shifted, usually to a lower temperature (surface atoms are less coordinated and less bound than interior atoms) * The transition temp. is no longer sharp but becomes smooth and takes place over a finite range (fluctuations in TD quantities) * The latent heat is lower than in the bulk limit Nanomaterials 40 Surface Effects Reduction in particle size • Metal particles usually exhibit a lattice contraction • Oxide particles exhibit a lattice expansion YIG = Y3Fe5O12 Nanomaterials 41 Surface Effects Correlation between the unitcell volume (cubic) and the XRD particle size in -Fe2O3 nanoparticles The smaller the particle size the larger the unit cell volume. Nanomaterials 42 Surface Effects The inter-ionic bonding in nanoparticles has a directional character Ions in the outermost layer of unit cells possess unpaired electronic orbitals Associated electric dipole moments, aligned roughly parallel to each other point outwards from the surface The repulsive dipolar interactions increase in smaller particles reduced by allowing unit cell volume to increase Nanomaterials 43  Finite-size effects MO to Band transition Quantum Confinement Effects Physical and chemical properties depend on the size !! Quantum Size Effects Nanomaterials 44 Band gap dependency on the nanoparticle size Nanomaterials 45 Quantum Size Effects Metals Semiconductors Nanomaterials 46 Metal-to-Insulator Transition Nanomaterials 47 Band gap increases with decreasing size Metal-to-Insulator Transition Metallic behavior Single atom cannot behave as a metal nonmetal to metal transition 100-1000 atoms Magnetic behavior Single domain particles large coercive field Nanomaterials 48 Metal-to-Insulator Transition Variation of the shift, E, in the core-level binding energy (relative to the bulk metal value) of Pd with the nanoparticle diameter The increase in the core-level binding energy in small particles poor screening of the core charge the size-induced metal-nonmetal transition in nanocrystals Nanomaterials 49 Electrical Conductivity Particle size Bulk value Relativeconductivity Nanomaterials 50 Photoelectron spectra of Hg clusters of nuclearity n The 6p peak moves gradually towards the Fermi level the band gap shrinks with increase in cluster size 6s HOMO 6p LUMO Hg Valence electron configuration? Nanomaterials 51 a) Absorption spectra of CdSe nanocrystals (at 10 K) of various diameters b) Wavelength of the absorption threshold and band gap as a function of the particle diameter for various semiconductors. The energy gap in the bulk state in parenthesis Quantum Size Effects In Semiconductors Nanomaterials 52 Quantum Confinement Effects Fluorescence of CdSe–CdS core–shell nanoparticles with a diameter of 1.7 nm (blue) up to 6 nm (red) Smaller particles have a wider band gap Nanomaterials 53 Bohr Radii Quantum confinement - particles must be smaller than the Bohr radius of the electron-hole pair Nanomaterials 54 Quantum Confinement Effects Optical properties nc-TiO2 is transparent - applications? Blue shift in optical spectra of TiO2 nanoparticles Nanomaterials 55 NANO -particles, crystals, powders -films, patterned films -wires, rods, tubes -dots Nanostructured materials = nonequilibrium character good sinterability high catalytic activity difficult handling adsorption of gases and impurities poor compressibility PREPARATION METHODS Top-down: from bulk to nanoparticles Bottom-up: from atoms to nanoparticles Nanoscopic Materials Nanomaterials 56 Preparation Methods Top-down: from bulk to nanoparticles Bottom-up: from atoms to nanoparticles Nanomaterials 57 Bottom-up Synthesis: Atom Up Nanomaterials 58 NANOSTRUCTURAL MATERIALS  Atom Aggregation Method GEM – gas evaporation method  evaporation by heating – resistive, laser, plasma, electron beam, arc discharge  the vapor nucleates homogeneously owing to collisions with the cold gas atoms  condensation in an inert gas (He, Ar, 1kPa) on a cold finger, walls - metals, intermetallics, alloys, SiC, C60 in a reactive gas O2 TiO2, MgO, Al2O3, Cu2O N2, NH3 nitrides in an organic solvent matrix Bottom-up Synthesis Nanomaterials 59 NANOSTRUCTURAL MATERIALS SMAD – the solvated metal atom dispersion 1 – 2 g of a metal, 100 g of solvent, cooled with liquid N2 more polar solvent (more strongly ligating) gives smaller particles Ni powder: THF < toluene < pentane = hexane Carbide formation Ni(g) + pentane NixCyHz Ni3C 77 to 300 K 180 C, octane Bottom-up Synthesis Nanomaterials 60 NANOSTRUCTURAL MATERIALS  Thermal or Sonocative Decomposition of Precursors Fe(CO)5 nc-Fe + 5 CO sono [Co(en)3]WO4 nc-WC – 23% Co PhSi(OEt)3 + Si(OEt)4 + H2O gel -SiC (CH3SiHNH)n (l) Si3N4 + SiC laser M(BH4)4 (g) borides MB2+x (M = Ti, Zr, Hf) Si(OEt)4 + Ag+ or Cu2+ + H2O SiO2/Ag+ /Cu2+ SiO2/Ag/Cu Ar, 1500 C 300-400C H2, 550 C Bottom-up Synthesis Nanomaterials 61 NANOSTRUCTURAL MATERIALS  Reduction of Metal Ions Borohydride Reduction - Manhattan Project Aqueous, under Ar 2 Co2+ + 4 BH4 + 9 H2O Co2B + 12.5 H2 + 3 B(OH)3 Under air 4 Co2B + 3 O2 8 Co + 2 B2O3 Nonaqueous Co2+ + BH4 + diglyme Co + H2 + B2H6 TiCl4 + 2 NaBH4 TiB2 + 2 NaCl + 2 HCl + H2 MXn + n NR4[BEt3H] M + NR4X + n BEt3 + n/2 H2 M = group 6 to 11; n = 2,3; X = Cl, Br mixed-metal particles Bottom-up Synthesis Nanomaterials 62 NANOSTRUCTURAL MATERIALS Au colloidal particles HAuCl4 + NaBH4 in toluene/H2O system, TOABr as a phase transfer agent, Au particles in the toluene layer, their surface covered with Br, addition of RSH gives stable Au colloid Au fcc S S S S S S S S S S S S S Bottom-up Synthesis Nanomaterials 63 Bottom-up Synthesis SH Nanomaterials 64 Two-dimensional array of thiol-derivatised Au particles (mean diam 4.2 nm) Nanomaterials 65 TEM micrograph of hexagonal arrays of thiolized Pd nanocrystals: a) 2.5 nm, octane thiol b) 3.2 nm, octane thiol Nanomaterials 66 The d-l phase diagram for Pd nanocrystals thiolized with different alkane thiols. The mean diameter, d, obtained by TEM. The length of the thiol, l, estimated by assuming an all-trans conformation of the alkane chain. The thiol is indicated by the number of carbon atoms, Cn. The bright area in the middle encompasses systems which form close-paced organizations of nanocrystals. The surrounding darker area includes disordered or low-order arrangements of nanocrystals. The area enclosed by the dashed line is derived from calculations from the soft sphere model Nanomaterials 67 NANOSTRUCTURAL MATERIALS K + K+ Mg Mg in dry anaerobic diglyme, THF, ethers, xylene NiCl2 + 2 K  Ni + 2 KCl AlCl3 + 3 K  Al + 3 KCl Reduction by Glycols or Hydrazine “Organically solvated metals” Alkali Metal Reduction Nanomaterials 68 Alkalide Reduction 13 K+(15-crown-5)2Na + 6 FeCl3 + 2CBr4 THF 30 °C 2 Fe3C (nano) + 13 K(15-crown-5)2Cl0.43Br0.57 + 13 NaCl Anealed at 950 °C / 4 h Fe3C: 2 – 15 nm Nanomaterials 69 NANOSTRUCTURAL MATERIALS  Reactions in Porous Solids – Zeolites, Mesoporous materials Ion exchange in solution, reaction with a gaseous reagent inside the cavities M2+ + H2E ME M = Cd, Pb; E = S, Se Ship-in-the-Bottle Synthesis Ru3+ + Na-Y Ru(III)-Y Ru(III)-Y + 3 bpy Ru(bpy)3 2+ reduction of Ru(III) Conducting carbon wires Acrylonitrile introduced into MCM-41 (3 nm diam. channels) Radical polymerization Pyrolysis gives carbon filaments Bottom-up Synthesis Nanomaterials 70 NANOSTRUCTURAL MATERIALS  Gel or Polymer Matrices  Sol-Gel Method Aerogels, supercritical drying  Aerosol Spray Pyrolysis Aqueous solution, nebulization, droplet flow, solvent evaporation, chemical reaction, particle consolidation, up to 800 C 3Gd(NO3)3 + 5 Fe(NO3)3 Ga3Fe5O12 + 6 O2 + 24 NO2 MnCl2 + 2 FeCl3 + 4 H2O MnFe2O4 + 8 HCl Mn(NO3)2 + Fe(NO3)3 no go, why? Bottom-up Synthesis 2 MCln (g) + n H2  M0 + 2n HCl 850-900 C 3-11 nm Nanomaterials 71 NANOSTRUCTURAL MATERIALS  Inverse Micelles H2O + octane H2O H2O Cd2+ Se2- CdSe CdSe PhSeSiMe3 Bottom-up Synthesis Nanomaterials 72 Bottom-up Synthesis Nanomaterials 73 Bottom-up Synthesis 180 °C in octylamine 200 °C in dodecylamine Phase Control [NnBu4]2[Fe4S4(SPh)4] pyrrhotite Fe7S8 greigite Fe3S4 thiospinel, the sulfide analogue of magnetite Nanomaterials 74 Polymeric Nanoparticles from Rapid Expansion of Supercritical Fluid Solution Nanomaterials 75 Polymeric Nanoparticles from Rapid Expansion of Supercritical Fluid Solution Nanomaterials 76 Nanomaterials 77 Spinning Disc Processing (SDP) A rapidly rotating disc (300-3000 rpm) Ethanolic solutions of Zn(NO3)2 and NaOH, polyvinylpyrrolidone (PVP) as a capping agent Very thin films of fluid (1 to 200 m) on a surface Synthetic parameters = temperature, flow rate, disc speed, surface texture influence on the reaction kinetics and particle size Intense mixing, accelerates nucleation and growth, affords monodispersed ZnO nanoparticles with controlled particle size down to a size of 1.3 nm and polydispersities of 10% Nanomaterials 78 Electrospinning ThO2 from PVA/Th(NO3)4 Average diameter: 76 ± 25 nm Vapor-Liquid-Solid (VLS) Growth 79 (1) Metal catalyst nanoparticles - Au(s) Feed another element (Ge vapor, GeH4 or SiH4) at an elevated temperature (440-800 C/ultra-high- vacuum) Gaseous precursor feedstock is absorbed/dissolved in Au(s) till the solid solubility limit is reached (2) A liquid phase appears, melts to a droplet (3) The droplet becomes supersaturated with Ge When the solubility limit is reached (4), an excess material is precipitated out to form solid NWs beneath the droplet Eutectic 360 C Au (mp 1064 C) Si (mp 1410 C) Ge (mp 938 C) Vapor-Liquid-Solid (VLS) Growth 80 1 2 3 4 81 Vapor-Liquid-Solid (VLS) Growth Au Particles Au/Ge Eutectic Liquid Alloy Nucleation of NWs NW Growth 82 In-situ TEM images of the VLS process In-situ TEM images recorded during the process of nanowire growth: (a) Au nanoclusters in solid state at 500 °C (b) alloying initiated at 800 °C, at this stage Au exists mostly in solid state (c) liquid Au/Ge alloy (d) the nucleation of Ge nanocrystal on the alloy surface (e) Ge nanocrystal elongates with further Ge condensation (f) Ge forms a wire Nanomaterials 83 LaMer Mechanism Supersaturated solution Burst of nucleation Slow growth of particles without additional nucleation Separation of nucleation and growth Nanomaterials 84 Other Mechanisms Watzky-Finke mechanism Slow continuous nucleation - Fast autocatalytic surface growth Seed-mediated mechanism Au nanoclusters as seeds - Bi, Sn, In, Au, Fe, Fe3O4 Digestive rippening Surfactant exchange Nanomaterials 85 Thermal Decomposition of Precursors Fe(CO)5 oleic acid trioctylamine 350 o C, 1 h 350 o C, 1 h Fe Me3NO Fe2O3 6 nm Separation of nucleation and growth Fe(CO)5 thermal decomposition at 100 oC contributes to nucleation Fe(oleate) thermal decomposition at 350 oC contributes to growth OH O Surface Modification Nanomaterials 86 A nanoparticle of 5nm core diameter with different hydrophobic ligand molecules both drawn to scale. The particle is idealized as a smooth sphere. trioctylphosphine oxide (TOPO) triphenylphosphine (TPP) dodecanethiol (DDT) tetraoctylammonium bromide (TOAB) oleic acid (OA) Top-down Synthesis: Bulk Down Nanomaterials 87  Introduction of Crystal Defects (Dislocations, Grain Boundaries) • High-Energy Ball Milling - final size only down to 100 nm, contamination • Extrusion, Shear, Wear • High-Energy Irradiation • Detonative Treatment  Crystallization from Unstable States of Condensed Matter • Crystallization from Glasses • Precipitation from Supersaturated Solid or Liquid Solutions Nanomaterials 88 Top-down Synthesis: Bulk Down Lithographic Techniques electron beam and focused ion beam (FIB) lithography Nanomaterials 89 Top-down Synthesis: Bulk Down Lithographic Techniques electron beam and focused ion beam (FIB) lithography Nanomaterials 90 Nanocatalysis Polymers used as metal NP supports for catalysis Nanomaterials 91 Nanocatalysis Catalysis by nanoparticles encapsulated in PAMAM or PPI dendrimers Nanomaterials 92 Nanocatalysis Asymmetric heterogeneous catalysis on nanoparticles Nanomaterials 93 Hollow Nanoparticles formation of hollow spheres Nanomaterials 94 Applications Destruction of dangerous organic compounds (organophosphates - VX, chlorinated - PCB)